The Electric Vehicle revOLUTION enabled by advanced materials highly hybridized into lightweight components for easy integration and dismantling providing a reduced life cycle cost logic
Fredrik Bajers Vej 5
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Lone Varn Johannsen (Ms.)
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Grant agreement ID: 314744
1 November 2012
31 October 2016
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€ 8 933 842
Advanced lightweight materials for lighter, more environment-friendly electric cars in cities
TRANSPORT AND MOBILITY
CLIMATE CHANGE AND ENVIRONMENT
Grant agreement ID: 314744
1 November 2012
31 October 2016
€ 13 438 488,67
€ 8 933 842
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Final Report Summary - EVOLUTION (The Electric Vehicle revOLUTION enabled by advanced materials highly hybridized into lightweight components for easy integration and dismantling providing a reduced life cycle cost logic)
Global trends toward CO2 reduction and resource efficiency have significantly increased the importance of lightweight materials over the last years: the European Commission has set severe targets for average new car CO2 emissions of 95 g/km by 2020, and the forecast for 2030 is to reduce the emissions down to 75 g/km.
Weight reduction directly decreases the energy consumption and then the CO2 emissions, enabling as a consequence the downsizing of powertrain and braking system and providing additional weight saving. This matter is particularly interesting for electrified powertrains, whose diffusion is crucial to reduce the CO2 emissions: weight saving allows to increase range with the existing battery or to maintain range with a smaller battery.
Currently, the traction battery cost and the range of autonomy are among the most limiting factors to Full Electric Vehicles (FEVs) market penetration; due to the fact that their cost is directly related to battery size, being fixed the rate €/kWh and the range, the light-weighting design becomes a balance between weight and cost. Hence, the key of success for CO2 reduction relies on the conception of a FEV body archetype characterized by extreme lightweight countermeasures as a combination of specific metallic alloys and high performance composites for structural parts, balancing the cost due to light-weighting with the downsizing of the traction battery.
This is a big challenge for the automotive industry: similar to the aerospace one, where composites are largely used. Automotive has unique limiting factors including surface finish and impact performance requirements, manufacturing cycle time, joining manufacturing infrastructure and production volumes.
The Body in White (BiW) is the heaviest vehicle element, representing about 40% of the total vehicle weight, thus it is the most appropriate area of implementation of lightweight measures.
The above represents the environment of the EVolution project. Funded by the EC FP7 Programme and based on Pininfarina Nido FEV concept, fully in aluminium, the project demonstrated that it is possible to consistently reduce the vehicle weight, maintaining the structural performances, through the wide use of new materials and process technologies by developing a multi-material BiW.
In particular, the development and manufacturing were focused on five specific subsystems named demonstrators: the underbody, the structural node, the front crossmember, the side door and the mechanical subframe. Structures engineering, materials, and process technologies were considered as design variables in a design for purpose environment, driven by virtual analysis, in order to propose solutions feasible and optimized for the specific performances and the requested target weight: 50% of reduction respect to the equivalent steel solution for each demonstrator.
Nido BiW, fully in aluminium, was redesigned to be a media to integrate the demonstrators, following the approach to lightweight everywhere, reinforcing only where it is necessary, while accomplishing structural performances, crashworthiness included.
Furthermore, a set of new functionalized composite materials tailored for the specific automotive applications was developed and up-scaled during the project.
The industrial viability and the sustainability were successfully assessed both from a technical point of view, by means of scalability study of the considered materials and technologies and physical tests, and from a cost and TAKT time perspective, for medium-high production volumes (30,000 units/year).
Project Context and Objectives:
The purpose of the EVolution project was to demonstrate the sustainable and industrial viable production of a Full Electric Vehicle (FEV) of 600 kg weight, taking as starting point the FEV concept Nido.
To gain this final target several intermediate objectives were pursued, substantially related to:
• Engineering of an optimized lightweight FEV Body in White (BIW) archetype with high crash performances, capable of integrating subsystems hybridised with lightweight materials and containing an innovative level of technology. In particular the hybridization was to be applied on five representative components of the vehicle, named demonstrators (designed, manufactured and tested), whose weight was requested to be 50% lighter with respect to the equivalent steel solution:
1. Front Crossmember (crash cross beam and crash box)
2. Suspension mechanical sub-frame
3. Under body
4. Structural node
5. Side door
• Innovative lightweight materials development characterized by:
1. hierarchical structures featuring micro- and nano scale reinforcements and additives and macro scale structures such as sandwich and multi-layered/functionally graded structures to address materials properties at all length scales;
2. highly recyclability obtainable by a deep hybridization of diverse materials in which separation between the materials nano-, micro- and macro- is removed;
3. enhanced structural and non-structural properties (such as thermal, conductivity and flame retardant) using a minimum of functional additives;
4. properties tailored to minimize the material types (metals and polymers) employed in individual components and structures.
• New processing routes development, based on existing proven technologies to enable the commercial production of the new materials and their integration into components.
• Novel technique development for the monitoring of the ‘health’ of joints between materials and within hybridized components.
• Bonding and de-bonding technologies development in order to achieve 100% recoverability and zero waste for material integration and end-of-life dismantling of hybrid components.
The abovementioned target implied a definition of intermediate and/or more specific objectives, detailed here below.
The requested final Full Vehicle and demonstrators weight targets needed the identification of a reference weight range for the BiW. This activity was possible through the analysis of the Bill Of Materials (BOM) of the baseline concept Nido. As the Nido concept development was stopped after a few months, some data were not available, so a certain amount of assumption was made to estimate the weight of some parts.
Assuming a Full Vehicle weight of 600 kg and evaluating for each area (apart from the BiW) a reasonable weight reduction range considering new market and technologies trends, the body structure weight was evaluated for difference. Propaedeutic to this activity, a detailed analysis of traction battery weight considering the same autonomy range and the emergent cells technologies was performed, identifying a promising solution lightweighted with about 70 kg compared to the Nido.
Considering all these results together, the BiW target range evaluated was 100 ÷ 115 kg, corresponding to an average weight reduction of about 35% of Nido BiW, fully in aluminium.
Advanced and specifically tailored thermoplastic composite materials were considered in EVolution project: while thermosets contain polymeric chains that cross-link together during the heating-cooling phase (curing process) to form an irreversible chemical bond, thermoplastic chains do not cross-link. As no chemical bonding takes place, when thermoplastics are heated the material softens and can be reshaped. This characteristic allows thermoplastics to be remoulded and recycled.
As for metallic material, aluminium was selected.
In some specific case the materials development was tailored for a specific enabled technology.
Below, the specific target for each material family selected is reported in more details.
Thermoplastic Composite materials
1. Polymer Composites (micro scale reinforcement) objectives
• PLA polymer composites made with advanced glass fibres, vegetable fibres and nanofiller development: increase of mechanical properties of 60% reflecting the same value in weight reduction; level of bio-resources in the compound at least of the 70%.
• Hybrid PA based multi-functional composites, long-fibre PA based composite by in situ polymerization and by compression/injection development: by means of the proposed technologies 50% higher moduli were expected to be obtained. This increase in the modulus can imply a weight reduction of 15%. Moreover, these technologies for PA were expected to eliminate the existing size limitation.
2. Polymer Matrix Nanocomposites (nano scale reinforcement) objectives
• Polymer nano composites (PNC) PP matrix and nanofillers: to develop PNC with: enhanced creep resistance (more than 75% improvement to virgin PP) and enhanced impact resistance (200% increase to virgin PP) without ruining the other mechanical properties.
About 30% of weight reduction respect to FP7 NANOTOUGH project combining rubber, PP and nanofillers with both short and long glass fibres.
3. Polymeric Foams and Sandwich Structures objectives
• Polymeric foams pristine and nano-reinforced foams based on thermoplastics (PP composites, nanocomposites) and polyurethane development: referring to state-of-the-art foams, to improve the compressive and tensile properties of the reinforced foam by 10–15% compared to the pure foam produced from the same base polymer and to eliminate the thermal expansion coefficient mismatch between foam and the bulk polymer for building sandwich structures. To increase the natural origin renewable raw material in end products by up to 35–40%.
• Low density PP and PU foams for sandwich structural core development: referring to state-of-the-art PVC foams, to double the mechanical properties at a 50% reduced density.
1. Aluminium Shaping and Forming objectives
• Aluminium casting Alloy A356: reference values for Aluminium cast A356 properties: 9.5% elongation and 140 MPa Yield Strength; to reach 14.5% elongation and 120 MPa YS by T6 heat treatment; to optimize the heat treatment stages (solubilisation and quenching) to achieve 17% elongation and 240 MPa YS.
2. Aluminium Foam and Sandwiches structure objectives
• Improvement of foaming process allowing a homogeneous nucleation
• RF active hot-melt nanostructured-adhesives and relative assembling/disassembling technology: reduction of cycle time of adhesive bonding of 30% in the case of plastic joints and of 20% in the case of metal joints; plastic joint enhancement of mechanical properties of 15%.
• Structural joining of similar and dissimilar materials – all combinations of PP, PA, PLA, Al: 15% improvement of the mechanical performance of protocolled joints.
• In-situ Joint Health non-destructive monitoring: to inspect a component from his manufacturing to end of life, its whole life time; to develop a method and a monitoring system to allow the inspection during the manufacturing process up to the repair shop; to provide information on defects under the surface of materials. Inspection time shorter than 1 minute per full large component.
Considering the European market, the BiW was dimensioned in order to achieve the structural reference values, in order to be ready for obtaining good biomechanical values through an appropriate development of the restraint system and interior trim (out of scope of EVolution project) during ECE R94 Front Crash 56 kph 40% ODB and ECE R95 Side Crash 50 kph. The structural reference values considered were carried out from the experience of the industrial members of the Consortium.
As for the global and local static performances, the state-of-the-art of A-segment cars was considered as reference.
The multi-material architecture was requested to be conceived in order to be suitable in particular for mass production; a units/year volume of 30,000 was identified as the most appropriate for the scope. A check for low production volumes (1,000 units/year) was performed to have a comparison with the baseline Nido.
The relative TAKT time is intended as the average time between the start of production of one unit and the start of production of the next unit, when these production starts are set to match the rate of customer demand. Assuming production volumes of 30,000 cars per year and 220 working days per year, this would mean that 136 parts would need to be manufactured per day. More specifically, considering a standard inefficiency around 15%, 2 shifts and 7.5 hours per shift, the TAKT time for 30,000 cars per year is 5.7 minutes, meaning that the proposed technologies must have a TAKT time below or equal to 5.7 minutes to be affordable.
Today there is a general consensus among the automotive industry that the increment of cost due to lightweighting is acceptable if below 6 €, considering a production of 50,000 cars/year (value close to 30,000); even if for EVolution a cost reference was not set, it was decided to face with this value (6 €/kg-saved), because it is essential to provide an industrial viability analysis:
cost-per-kg-saved = (EVo part cost – Ref. part cost) / (weight of Ref. part – weight of EVo part)
The EVolution Consortium cooperated according to the design for purposes holistic approach to define the new BiW. This methodology equally treated materials, design alternatives and processes as design variables during the concept definition phase. Lightweighting and part count reduction, which were two pillars to redesign Nido concept, were influenced by selected materials and enabled technologies to manufacture parts; these two latest items were related also to the affordability target and were connected with each other. The assembly method selection was cross related with materials (and then lightweighting) and part count reduction. The concept definition was interrelated with all these topics, and guided by CAE analysis through all its development; the CAE analysis was in particular bonded with materials modelling methodologies, to improve models level of confidence. The LCA surveyed materials, technologies and joining methods singularly and mutually related. The testing activity integrated/confirmed the forecast performed during the concept definition phase.
This holistic approach merged together the industrial activities with the research ones, allowing all partners to cooperate toward a common target composed by many facets associated to each specialty. Specific technical reviews monitored the work progressing and the results in accordance with project targets and planning.
The macroscopic objective, mainly related to industrial purposes, was the lightweighted BiW, focused in particular on the five demonstrators; according to the identified weight and structural target, the most appropriate elements hybridisation was defined through an applied research activity working on the materials definition, tailoring them for the specific performances of each part and the peculiar technologies proposed. The material up-scaling was a task representing the link between industry and research, implementing the lab scale definition to the industry needs, without significantly degrade the materials properties through the selected processes. Similarly, the manufacturing phase proved the new materials suitability for the selected technologies, evidencing the areas of improvement necessary to achieve the passage from prototype stage to industrial application, whilst the testing activities plan on specimens, demonstrators and subsystems confirmed the overall job, providing unique information about new materials behaviour, the effect of manufacturing process and their applicability on real automotive components.
The innovative technologies proposed by the EVolution consortium were basically:
• new hot forming techniques and improved casting methods for high strength aluminium alloys
• advanced injection and compression processes for tailored composite materials
The challenging task was to identify in details the new design opportunities offered by these technologies, translating them into an engineered new vehicle concept, whose performances were in line with the expectation also thanks to the wise definition/upgrading of the materials and their up-scaling and the most appropriate joining selection.
The technologies available made a sense if the large body parts were designed using intensively the opportunities offered: complex geometries, lower thickness, reduced part count number.
For this specific reason, the baseline Nido architecture, very similar to a space frame, was not suitable without consistent modifications, to extensively apply a design strategy allowed by these new manufacturing techniques.
In general, a Space Frame architecture presents simple-geometry panels welded or bonded/riveted to the frame itself.
It was clear that the EVolution technologies were not so aligned with the points above, so consequently the Space Frame philosophy was abandoned.
Hence the project looked to a central cell following the “monocoque” concept, in order to obtain the best trade-off between weight and performance, and to allow a robotized assembly scheme, orienting the study towards the medium production volumes, more than low volumes, considered just for comparison with the Nido.
The front end had a controlled folding in front crash and supports front suspension.
The rear end, semi structural, supported the rear suspension and carried on the specific exterior trims parts in order to allow different vehicle versions: city car, van or pick-up, emphasizing the modularity philosophy.
The Evolution project mantra was: “To lightweight everywhere, to reinforce where necessary”.
According to the project scope, the hybridisation of the body was done at demonstrator level only, but a subsequent theoretical study, described in a next paragraph of this section, was anyway performed, even if not requested, due to the high level of interest from an industrial point of view on the identified solutions.
The multi-material structure was studied in order to be assembled through new joining methods, excluding the spotwelds and leaving in certain limited area the MIG-welding. Thus the EVolution applied research was focused on structural adhesives suitable to bond aluminium with aluminium and aluminium with composite materials. This solution, coupled with self-piercing riveting (SPR) and/or mechanical fasteners, was able to sustain the performances requirements, reconceiving the strategy of interfaces design. This new methodology required different pre-treatments in the materials involved in the joints, with a potential risk of distortions. For this reasons the EVolution project studied also new equipment for distortion evaluation, in order to constitute the base of the assembly design methodologies for the next generation vehicles. Besides, a new set of radio-frequency activated hot melts adhesives for trim parts was conceived and up-scaled, constituting a new methodology for the joining of semi-structural plastic substrates, bringing important advantages in terms of dismantling at the end of life and energy saving.
The next paragraphs of this section describe in details the most significant results achieved by the EVolution project consortium; all the research and industrial information are produced in association with each demonstrator.
The five demonstrators
A great challenge successfully achieved in design the hybrid demonstrators was the appropriate simulation of the materials through the CAE analysis, especially to represent their behaviour in high-speed collision. This activity was possible thanks to a detailed experimental characterization at level of materials specimens, and a subsequent testing activity on real components as the demonstrators.
Nowadays, most of the research on the energy absorption of composite materials is of experimental type and mainly associated to the axial compression of tubular structures.
The validation of numerical codes for accurate simulations of complex composite structures subject to crash impacts is an important aspect of crashworthiness researches. Some studies can be found in literature, concerning aerospace and automotive structures, but they do not cover all the most used composite structure modelling. Moreover, it is rather difficult to obtain real data regarding impact tests or simulations of composite elements for cars due to the conﬁdentiality of information.
This state-of-the art underlines the great opportunity offered by the EVolution project, where composites physical demonstrators, representing real automotive components were tested, increasing the level of knowledge in the field of simulation of these new materials.
In fact unlike metals, the progressive energy absorption of composite structures is dominated by extensive micro-fracture instead of plastic deformation; in fact the composite structures absorb a high amount of energy by means of a complex combination of fracture mechanisms; the primary energy absorbing mechanisms in ﬁbre-reinforced plastics are ﬁbres cracking, matrix fracture, de-bonding of ﬁbres from the matrix and delamination of the layers making up the structure.
The very large stiffness of a ﬁbre device is such that its global elastic limit will not be exceeded almost up to the collapse itself. This serves to transmit the strength from the point of impact further into the structure so that higher loads can be absorbed without permanent damage.
Only when the load in the impact area surpasses the absolute strength of the laminate, failure in that area becomes total and the laminate starts to crumble progressively. In synthesis, the brittleness of composites ensures that they do not undergo the yield processes characteristic of ductile metals but, on the application of load, deform elastically up to the point of fracture.
A composite body thus disintegrates both structurally and microscopically during impact.
The load/deﬂection response for a composite structure shows a typical behaviour in which, after the initial peak load, the curve is much ﬂatter than the one characteristic of the plastically deforming metal structures. In the case of composite materials, the area under the curve, i.e. the amount of energy absorbed, is therefore much greater. This feature, combined with the lower density of the composites, makes it a far more efficient solution in terms of absorbed energy versus weight ratio, if well designed.
Keeping in account the above, the next sections describes in details the main results achieved by each EVolution project demonstrator.
The Front Crossmember
The current solutions in a front bumper beam component for mass market are basically made of metal, and only in few notable exceptions they are hybrid components.
In the EVolution project a full plastic-based structural front bumper beam was developed and prototyped, taking as a reference and improving the same component developed in a previous FP7 project, named Nanotough, designed using PP reinforced with NC and GF.
The Nanotough concept had a high toughness, but its stiffness did not fulfil the impact requirements, so basing on the AZT protocol and the ECE94 Full Front Crash simulations, different designs and raw materials were analysed to achieve the optimum performance/lightening ratio, bringing the demonstrator to the engineering sign-off concept definition.
The new beam design consisted of two components, front and rear beam shell members. The geometry of the front shell was adapted starting from the Nanotough design, keeping in account the characteristics of the several selected raw materials and the different manufacturing processes, while the rear shell was specific for EVolution. A core of specific rigid polyurethane (PUR) foam was inserted in selected beam sections to improve crash performances. For project purposes rigid PUR foams were developed from sustainable raw materials. The crash boxes, completely new, were characterized by a different strategy of energy absorption from previous project (structural PUR foam in place of internal ribs).
As for the above, target weight (50% weight saving over existing steel equivalent) was set referring to Nanotough steel baseline crossbeam, derived from a B-segment vehicle, and not from Nido state-of-the-art.
Starting from the background knowledge and the results obtained within the Nanotough project, a new polymer material composition as a combination of two key solutions from nanotechnology and advanced materials fields was proposed: the composition of the new polymeric material was specially tailored using the advanced material (PP with 30-50% GF) in which a special nanosilicate was added. The nanosilicate was evenly embedded into a thermoplastic elastomer matrix to obtain a smart masterbatch. The masterbach composition and the optimum ratio between components enable its use directly in a specific one step extrusion-injection process. Using the masterbatch, a 300% impact resistance increase compared to virgin PP, without substantially decreasing of stiffness and strength, was obtained due to a synergistically effect between the components. The solution was covered by a national patent application “Masterbatch for improving the impact strength of polypropylene with glass fibre and process for obtaining it” – OSIM registration number A 00247/06.04.2015 published in 28.10.2016-131445A2.
These impressive results were achieved also through a deep experimental and theoretical research to observe the influence of toughening of PP with SEBS on its mechanical response under impact tests, tensile tests with various strain rates, relaxation tests with various strains, and cyclic tests with a mixed deformation program and various maximum strains per cycle on neat polypropylene.
Constitutive equations were developed for the viscoelastoplastic response of PP/SEBS blends. A semi-crystalline polymer was treated as a viscoelastoplastic continuum consisting of a transient network of flexible chains (the amorphous phase) with crystalline inclusions. The viscoelastic response of the equivalent medium reflected rearrangement of temporary junctions in the network: separation of active chains from their junctions and attachment of dangling chains to the network. Each rearrangement event occurs at a random instant being driven by thermal fluctuations. Material constants in the stress-strain relations were determined by matching the experimental data. Correlations were established between changes in the viscoelastoplastic response of PP and evolution of its microstructure induced by the presence of an impact modifier.
Experimental investigation and constitutive modelling were performed of the mechanical behaviour of thermoplastic elastomers reinforced with carbon nanoparticles and polypropylene-clay nanocomposites under multi-step cyclic deformation with finite strains. The experimental analysis concentrates on multi-step cyclic tests with growing maximum elongation ratios and partial unloading (in each cycle of oscillations, tensile stress σ decreases to positive values σmin that change with number of cycles n).
Constitutive equations for the mechanical response of a polymer nanocomposite under an arbitrary three-dimensional deformation with finite strains are developed by means of the Clausius–Duhem inequality. To account for the time-dependent behaviour in creep and relaxation tests, the equivalent medium was treated as an ensemble of meso-domains with various activation energies for inelastic deformation (this distinguishes our approach from the conventional concepts in viscoelasticity of polymers that ascribe the time-dependent response to rearrangement of chains).
To reveal how the elastic behaviour of elastomers reinforced with nanoparticles is affected by swelling, constitutive modelling and numerical simulation have been performed of the mechanical response of nanocomposite hydrogels. Three different filler–network structures were investigated: (I) chemical gels where polymer chains are covalently cross-linked in the presence of non-interacting platelets (the platelets are not connected to the network); (II) physical gels in which polymerization of chains starts from surfaces of non-interacting platelets (chains are linked to the platelets by hydrogen and ionic bonds); and (III) physical gels with entangled chains linked to a secondary network of platelets.
Constitutive equations were developed for the elastic response of swollen elastomers and hydrogels under an arbitrary deformation with finite strains. An expression was derived for the free energy density of a polymer network based on the Flory concept of flexible chains with constrained junctions and solvent-dependent reference configuration. The importance of introduction of a reference configuration evolving under swelling was confirmed by the analysis of experimental data on nanocomposite hydrogels subjected to swelling and drying. Adjustable parameters in the stress–strain relations were found by fitting observations on swollen elastomers, chemical gels (linked by covalent bonds and sliding cross-links), and physical gels under uniaxial stretching, equi-biaxial tension, and pure shear.
One of the main goals of the applied research was to provide a deeper understanding of the relationships between processing conditions in twin screw extrusion and organoclay dispersion state. The main results in the EVolution project were to evidence that the Specific Mechanical Energy (SME) is not the only parameter controlling the dispersion and to determine specific intrinsic limits not to be exceeded such as the local temperature or the local stress to avoid organomodifier or polymer degradation. The knowledge of SME range where correlation between dispersion state and SME is valid and of its limits and the use of modelling in order to simulate the twin screw extrusion process (Ludovic© software) allowed to determine optimum conditions.
Nanotough study showed that there is a correlation with the dispersion state and specific mechanical energy. In EVolution we paid attention to direct mixing and to conditions limiting the dispersion. We investigated extreme conditions leading to high SME such as high screw speeds, extrusion at a lower barrel temperature and the use of a more viscous polypropylene grade.
First, an organoclay grade with an enhanced dispersion relatively to the grade used in the Nanotough project was selected and a model nanocomposite formulation (organoclay selected in polypropylene (PP) with PP grafted anhydride maleic) was defined for the extrusion trials. Extrusion trials were conducted on a new screw profile designed for the present purpose. A systematic study of extrusion conditions with high SME was performed, including dead stop experiments in order to investigate how the dispersion evolves along the screw profile. Extrusion conditions were systematically analysed using Ludovic© software to have access to local parameters along the screws. Collected samples were systematically studied in order to provide information on the dispersion state at different scales.
High screw speed trials highlighted the strong degradation of the polymer chains in such conditions due to large temperatures and stresses. When the SME is too high, it induces the polymer chain scission and thus a sharp decrease in polymer viscosity. Generally, a higher specific mechanical energy helps to improve the dispersion state. This is true unless the local temperature in the extruder is locally too high and induces a degradation of the organomodifier, leading to a decrease of the inter-lamellar distance and a more difficult exfoliation.
An optimization step of the dispersion of organoclay was performed by modelling the extrusion process. Ludovic© software was used to model different screw profiles and processing conditions (using the lab scale extruder specificities) and compare the resulting parameters. These parameters were compared to the parameters determined to limit the dispersion. These results can be used to determine optimized extrusion conditions for a given screw profile or specifications for the definition of twin screw extrusion profiles for dispersion purposes.
Based on the above, the up-scaling of this new material was investigated in order to establish the optimum processing parameters for masterbatch obtaining: two series of experiments on two twin screw extruders were done (Brabender and Leistritz), using three different temperatures profiles and two screw rotation speeds. The degree of dispersion of the silicate nanotube was evaluated by analysis of physical, thermal and dynamic mechanical properties.
As conclusion, a quality masterbatch which disperses easily and uniformly in composites based on PP and GF was obtained on Leistritz twin screw extruder, at 220 rpm and 160 ±5 °C.
Concerning the costs, it was evidenced that the price of the nanofiller used in the masterbatch is 50-100 times lower than that of carbon nanotubes or carbon nanofibers to have the same effect on the mechanical properties at the same concentration. Moreover, the masterbatch and the hybrid material can be used for the fabrication of coloured parts, even in white.
A rigid Polyurethane (PU) foam based on recycled resources as a core material for cross-beam and crash boxes was developed in very broad range of densities 50-600 kg/m3. The PU foam formulation was based on aromatic polyester polyols obtained from recycled polyethylene terephthalate. In developed formulations sustainable raw material content reached up to 25 % of PU foam mass. The main innovation was related to the fact that by using sustainable polyols obtained from recycled PET waste it was possible to replace raw materials from petrochemical origin maintaining the same mechanical properties.
Because material was intended for impact absorption, usual mechanical strength data at quasi-static loads was not sufficient for further development of Finite Elements model for crossbeam deformation at impact. Thus mechanical properties at high strain rates were tested to select material with highest weight reduction.
A CEAST 9340 Drop Tower (Instron) equipment was modified to test compression of material instead of puncture impact. Normally this equipment is used to test materials according to ISO 6603-2 standard. PU foam cylinders were compressed at wide range of strain rates (quasi static testing: 0.002-0.5 s-1; high strain rate testing: 100-300 s-1). Obtained stress strain curves and other data were used in finite element modelling which identified two rigid PU foams densities as the optimal ones to fill core of crossbeam and crash boxes respectively.
Different foam feeding tests were carried out on Nanotough geometry, in order to define the filling strategy and the PP/PU adhesion.
Furthermore, thinking about a future design improvement, where a potential reduction of rigid PUR-foam could be necessary, a formulation to obtain material with apparent density of 34-47 kg/m3 was evaluated. Compression properties tests were done at quasi static loads, but considering the needs of high strain rate loads for CAE analysis, an empyreal model of stress strain behaviour at 180 s-1 was developed.
The different manufacturing tools were redesigned and modified, starting from the Nanotough ones, and other new tools were manufactured to prototype “extra parts” that the previous demonstrator had not.
The hybrid technology implemented in the front beam shell member mould was a method that combines in one step press moulding, employing continuous fibre reinforced thermoplastic (based on PP), and injection moulding, using long fibre reinforced thermoplastic (PPLGF50).
The feeding system of the fabrics was evolved from the Nanotough concept, using a system of spikes instead of a frame.
The injection strategy consisted of heating the organosheets using an infrared device before the mould closure. Different modifications were implemented through set of trials, taking into account also the design constraints of the existing Nanotough tool.
To minimize the tooling cost, taking into account that material volume was similar, both rear shell member and crashboxes were manufactured by one unique tool.
The reference technology was IMC (Injection Moulding Compounder), representing a combination of the continuous process of extrusion with the discontinuous operation of injection moulding; the parts were produced in a single stage production process. The IMC links a twin-screw compounding extruder, in this case with a specific profile for a proper dispersion of nano-reinforcements, to an injection process, hence it combines two process steps: the material compounding, which normally takes place at the raw material manufacturer, and the injection moulding process, which is usually done at the injection moulded premises. The moulding takes place in a twin platen clamp unit by means of sequential injection in order to have a proper distribution of the nano-reinforcements as well as the GF throughout the part.
The process parameters were defined by specific simulations and adjusted through several process trials.
A series of metallic inserts were introduced into all parts to improve joint strength of plastic parts and to avoid creep or stress relaxation.
Front and rear shell members were bonded together with a Polyurethane-based 2k adhesive, after a plasma treatment of the surfaces; subsequently the crossmember and the crashboxes were bolted together, obtaining the complete demonstrator.
Final weight reduction (more than 50% respect to the steel baseline), and crash test results underlined the potentiality of this solution in terms of raw materials, processes and performances.
As supplementary information, a comparison between the front crossmember of Nido, fully in aluminium, and of EVolution, fully in composite materials, was evaluated analysing in particular, the energy absorbed by these two subsystems during the ECE R94 56 kph 40% ODB front crash. As previously underlined, the internal energy absorption modalities are consistently different in these two subsystems: the engineering challenge was to design a non-metal structure lightweighted and more efficient in terms of impact energy absorption respect to a traditional solution.
From the CAE analyses results, it was evinced that at about 20 msec, immediately before the shotguns start to absorb the energy, the level of Joules absorbed by the EVolution demonstrator was about 30% higher than Nido’s.
This status means that the EVolution Front Crossmember was designed and optimized in order to be efficient into a specific range, as requested to a composite structure, and this target was achieved.
The competitive process TAKT time, below 1 min, and the lightweighting cost well under the reference value, proved the industrial viability of the proposed solution.
Further improvements of this already impressive result could be gained imagining removing the constraints associated to the previous project Nanotough heritage.
The Mechanical Subframe
Subframes are structural modules designed to carry specific automotive components as vehicle suspensions.
The Nido subframe solution, made in steel, consisted of three welded components (the main body, the stabilizer bar brackets and the brackets reinforcements). The EVolution target was to design and prototype a novel plastic based structural component 50% weight saving over existing steel equivalent.
The strategy of migration from metal to composite concept was mainly driven by:
• performance (static load cases of braking, bumping and cornering and fixing points dynamic stiffness);
• functional volume definition and constraints surfaces;
• geometry design for low rate cost/lightening composites, taking in account raw material and process;
• fatigue resistance capability of the raw material.
Two options were considered during the development: two composites shells mutually welded (1) and a solid component without hollows with variable thickness (2).
The first concept was characterized by a higher stiffness and lightweighting potential (containing the shell thickness with the usage of a core foam), but the tooling cost was very expensive.
The second solution had significantly lower tooling costs, but required a high-performance raw material to compensate the lower stiffness respect to the other alternative.
The main goal to obtain a composite thermoplastic material with high mechanical properties consists of achieving a good chemical anchorage between the fibres and the matrix.
In the specific case of the subframe, fatigue behaviour and strength were the main mechanical characteristics to be assured. The fatigue behaviour of any composite is influenced by the toughness of the resin. Polyamide (PA) was considered for the polymeric matrix due to its toughness and low cost. The reinforcement selected was Carbon Fibre (CF), superior to Glass Fibre (GF) in fatigue as well as specific strength. The CF actually available in the market are chemically designed to be compatible with epoxy resin, but not with thermoplastics as the APA6 (anionic polyamide). A large number of commercial fibres were tested, and some of them were thermally modified to improve their compatibility with the PA.
The material was developed in order to be tailored for an innovative manufacturing process, named CAPROCAST, previously patented by a partner belonging to the EVolution consortium (Fundacion Tecnalia Research & Innovation: EP2338665 A1/ US 9,290,622B2Process for polymerizing lactams in moulds; EP 2 743 061 B1/ CN 104086766A/ US2014/017268A1. Device for polymerizing lactams in moulds; WO2015/082728 A1/CN105793003. New device for polymerizing lactams in moulds), and promising for the automotive sector for its competitive costs and TAKT time.
In more details, CAPROlactam CASTing (CAPROCAST) is a reactive process of in-situ polymerization consisting of anionic Polyamide 6 (APA6) casting from its monomer, ε-caprolactam. It is a complex one-step process with a strict control of parameters that have influence during the polymerization and moulding; the low viscosity of the casting makes it easy to infiltrate the matrix in fabrics and textile preforms.
Basically, the CAPROCAST is an advanced Thermoplastic-Resin Transfer Moulding (TP-RTM) technology, enabling the obtaining of structural and complex 3D geometries, reinforced with fibres.
The mechanical properties of the composite material obtained through CAPROCAST technology could be compared with the current thermoplastic composite materials named organosheets.
The CAPROCAST process has some advantages over those of organosheets:
• only one moulding process from raw material to final parts (T-RTM process) vs. two processes of the organosheet (sheet obtaining and press-forming step);
• forming of complex 3-D geometries, with very depth shapes and complex angles, always keeping a perfect thickness control and a defined orientation of the fibres;
• design flexibility to obtain the mechanical requirements: the fibre lay-up and the thickness in each zone of the part can be customized, while the design with the organosheet is subjected to the commercially available materials.
The EVolution mechanical subframe design needed the above advantages. Its 160 mm-depth and its variable thickness, as well as the specific fibres orientation were hardly obtainable with a traditional press process. As for the above, the complex geometry of the EVolution Subframe cannot be manufactured through thermoforming with commercial organosheet semiproduct, but even considering feasible simpler geometries, the thermoforming process would be more energy consuming, and due to the high pressure level, the tool would be more expensive.
Similar costs and energy consideration can be made for HP-RTM process, whose advantage is to allow complex shapes as CAPROCAST, but unfortunately not recyclable and not weldable as the resin would be epoxy-based.
The subframe demonstrator was redesigned to fulfil mechanical requirements of the part and manufacturing feasibility either. Demoulding angles, textile fabric lay-up, layers overlapping and thickness transition were studied and defined. The raw material used consisted of different sheets of carbon fibre fabrics positioned as a lay-up; for its geometry, a preforming process was necessary, designing the overlaps and keep on the reinforcement continuity. The orientation of the fibres disposed in twelve layers was conceived to assure the mechanical properties.
A new tool was designed and produced for manufacturing the subframe by means of CAPROCAST technology.
Different feeding simulations were run to evaluate the filling times and the pressure distribution through the fibres and to set the location of the injection gates, while a set of thermal simulations were carried out to verify the correct heat-cooling strategy required by the production process.
After cutting the twelve textile reinforcement fabrics with the pattern previously defined, the preform was shaped on the male mould applying the vacuum. Then the tool was closed and clamped and the reactive system (caprolactam as well as catalyst and activator systems), was fed into the heated mould.
Once the fibres were completely wet, the polymerization of the reactive system to Polyamide 6 (APA6) occurred.
The polymerization process parameters were defined, taken into account that the polymerization itself takes place in a mould containing continuous fibre fabrics. Then, fibres selection, manufacturing of samples and mechanical characterization were performed.
Previously an up-scaling activity to demonstrate the viability of in situ APA6 carbon reinforced composites for subframe manufacturing was done; the APA6/CF material was tested in different demoulding temperatures to improve its mechanical properties and to reduce the moulding cycle, with a subsequent cheapening of the process.
To complete the activities performed during the concept definition, a durability test, representing an important field to be explored with this non-metallic new concept, was performed. According to the most common OEMs standards, the simplified fatigue spectra load (triaxial) was to be applied at the tire ground point, but this implied the presence of the whole front vehicle suspension. In the EVolution project the suspension was not available, so a specific test (a tensile fatigue test up to 10 kN totally) was designed to derive relevant results.
The component overtook 2,200,000 cycles without breakages, even if deformation of the bushing housings appeared after about 25,000 cycles; all the deformations occurred around the bushing housing, indicating a local lack of performances, but it is important to underline that in a high productivity environment, the bushing insertions would be automatized and would not damage the fabric. Moreover different bushings with collar could be used for a more even stress distribution and removal of friction with the lower arms.
A durability test was also performed on APA6/CF samples to complete the mechanical characterization obtaining some reference values about the material fatigue resistance. With respect to the common standards, a series of adaptations were performed to keep in account the novelty of the material, hence a 4-points bending test was performed on samples using a hydraulic machine working at 6 Hz equipped with a specific set of clamps developed for this test.
As preparatory activity to fatigue tests, some samples were submitted to quasi-static bending test to evaluate the ultimate flexural strength (UFS), as reference for the subsequent fatigue analysis. Due to the fact that the main interest was limited to the medium value of the fatigue strength, the Stair-case method was selected, reducing the number of required specimens.
The samples were submitted to 2,200,000 cycles; the first test was executed with an estimate mean value of the fatigue strength (54% of the UFS). Every time the sample broke before the planned number of cycles, the following one was tested with a lower load, otherwise with a higher one. The big dispersion of data corresponded to material characteristics dispersion. At the end, the fatigue limit evaluated was about the 71.7% of the UFS value.
The final release of the subframe demonstrator fulfilled the performances (static load and dynamic stiffness, durability) and the weight requirement (3.48 kg as final weight versus 6.8 kg as steel baseline weight). The TAKT time is below 5 min, including the polymerization time, with a lightweighting cost well below the reference value. Further cost saving could be obtained in the near future in terms of cost reduction of the CF, according to market expectations based on the on-going research activities.
Apart from some local design improvement at level of fixing points, necessary to industrialize the component, the use of continuous fibre thermoplastic composites based on APA6 in situ polymerization process instead of current metallic material solutions is indeed innovative and industrially viable: the EVolution subframe is the first component with high mechanical requirements manufactured with thermoplastic composites in the Automotive sector.
The Underbody demonstrator was the assembly of the firewall, the central floor with its reinforcements and the rear suspension cross-member, reengineered taking into account the constraints of the selected advanced forming technologies to exploit the weight reduction potential.
The approach followed was to merge in few new components as much parts as possible, optimizing each element for its function and reducing the thickness, respecting performance from one side and process constraints from the other. The final solution of this demonstrator was hybridized through high performance aluminium alloys and an advanced composite material component, with a noticeable variety of innovative manufacturing processes:
• gas forming, a plastic deformation process taking advantage from the higher elongation capabilities of the aluminium at high temperature;
• hot forming applied to multi-thickness raw aluminium sheet to obtain high strength and complex shapes parts with reduced spring-back effects, thanks to the hot working temperature range;
• CAPROCAST technology (the same technology proposed for the previously described mechanical subframe), applied to an underbody component selecting a specifically developed thermoplastic composite APA6-based reinforced with GF.
The obtained solution allowed the maximum potential in weight saving if compared to Nido underbody: proposed technologies enabled complex geometries with reduced thickness and a consistent part count reduction. As final result, the EVolution underbody weight was reduced by 47% compared to the Nido underbody, fully in aluminium, and the part count number was decreased with about 70% in comparison to the same baseline.
As extensively described in the “Impact” section of this document, the part count number reduction consistently affects the BiW assembly plant investment costs. An innovative element, today not present on the market, is represented by the firewall, which integrates in an unique component six Nido elements, wheel-arches included.
These impressive results were also due to an extensive applied research on the technologies simulation and up-scaling.
In more detail, as it was selected to manufacture two important underbody elements (the firewall and the central floor), a deep analysis of gas forming technology was done, to establish the best process parameters and to set a methodology to virtually simulate the process itself.
The gas forming consists of heating both the die and the aluminium sheet up to 500 °C and to subsequently inject nitrogen. The inert gas plays the role of the punch tool; it is injected from ad-hoc channels placed into a heating plate following a specific pressure curve, and the sheet is formed into its final shape, defined by a matrix tool.
An available mould of an existing bonnet, characterized by a simpler geometry, was selected for the abovementioned analysis with minor adjustments.
Different schemes of gas pressure increase were studied through several trials. The activity showed that the best pressure curve is a step curve, where periods of increasing pressure are followed by adjustment at constant pressure, whilst the minimum pressure required to obtain a proper forming is 23 bar.
Even if specific CAE tools already exist, a deeper knowledge of aluminium alloys at high temperature and an accurate calibration of the Pam-Stamp software parameters were required, in order to guarantee/validate the results of the EVolution prototypes produced via gas forming. The big challenge of the simulation of this process was the prediction of the final thickness distribution. The forming simulations were performed using the Pam-Stamp software: to properly describe the aluminium properties at high temperature, various aluminium alloys were characterized: AA5083, AA5182, AA5754, AA6016 and AA7020.
All the experimental forming tests were performed using AA5083 alloy, which was individuated as the best trade-off among performances, weldability and availability in small batches to manufacture the firewall and the central floor. The experimental values of thicknesses and geometry were compared with the values obtained through the virtual simulations. The good level of achieved correlation demonstrated that it is possible to use Pam-Stamp to evaluate the gas forming of aluminium sheets, hence the methodology was used for the EVolution firewall and central floor. The same conclusions can be applied on the other characterized alloys for future applications.
Thanks also to the virtual analysis output, the tooling design was optimized: in order to ensure process conditions as close as possible to the ideal isothermal forming process, both the lower plate and upper die were provided with a heating system, consisting of cartridge heaters and control thermocouples. Holes for air vent were also required to prevent air from being trapped between the sheet metal and the die during the forming process. Blocks from a special compression-resistant insulating material were used in the upper and lower part of the die to transfer forces from the ram and the bed of the press to the die.
Parts produced by hot forming are characterized by high strength, complex shapes and reduced springback effects. Shaping a metal at the hot working temperature range requires much less force and power than in cold working. Moreover at typical hot forming temperature, a metal also possesses far greater ductility than at its cold worked temperature. The much greater ductility allows for massive shape changes that would not be possible in cold worked parts. Rear suspension crossmember was designed and manufactured according to this process, as the front floor reinforcement. In particular, this element showed innovation contents also in terms of the use of a multi-thickness raw aluminium sheet to obtain a multi-thickness component, following the EVolution approach of “adding material where it is needed”, maximizing the ratio between performances and weight saving.
The CAPROCAST technology was applied to the floor rear reinforcement, selecting a specifically developed thermoplastic composite APA6-based reinforced with GF.
A series of tests on specimens were performed to identify the best demoulding temperature assuring the trade-off between material mechanical properties and reduced cycle time. Bulk modulus and tensile strength values were compared, concluding that the demoulding temperature increase does not affect in a relevant manner the modulus, and that the tensile strength reduction of 15%, still suitable for the application, carries on the important result of a cycle time reduction of 50%.
As the APA6/GF was applied to a component belonging to the BiW, one important goal was to verify the new material behaviour during the cataphoresis process (KTL).
The KTL process is composed by the following phases:
• Pre-treatment: some washing cycles at 60°C for few minutes followed by an anticorrosive treatment (phosphating) with lightly acid solution
• Deposition: cathodic electrodeposition in paint bath tank (300 volts at 30°C for 3 minutes)
• Oven: furnace up to 185°C for 20-30 minutes
The process takes place in a paint-shop, where also the subsequent phases of painting are performed but, for the new material, the KTL is the worst case for the chemical attack and the highest temperature applied.
Firstly, a pure thermal cycle on specimens was performed, positioning the samples into the oven at 190°C for selected time slots, measuring them through DSC and Fourier Transform Infrared Spectroscopy (FTIR) methodologies after each step. The first heating cycle at 190°C for 30 minutes creates small modifications to the material, while longer cycles do not generate consistent variations. A light oxidation was evidenced, whilst length and thickness variations measured were negligible. Based on these results it was concluded that the APA6/GF material is able to withstand a cataphoresis process, at least from the thermal point of view (the melting temperature of the material is above 200°C). Structural analysis (drop dart test) showed modifications of mechanical characteristics due to KTL, but they are limited and can be easily managed during the design phase.
A minor issue was the reaction of APA6/GF with phosphoric acids, because the plastic surface will become white, without modifying the mechanical properties: in order to have a proper adhesion of e-coating, a specific precursor is needed. For these reasons, it was concluded that the material is suitable for structural application not aesthetic.
Similar to what was done on the APA6/CF material, a durability test was also performed on APA6/GF samples to complete the mechanical characterization through the Stair-case method test, obtaining some reference values about the material fatigue resistance.
In a full vehicle the Underbody contributes to the overall static and dynamic stiffness of the body structure and plays an important role in the durability and in crashworthiness; these performances were evaluated through CAE analysis because in EVolution project it was out of scope to test the overall torsional stiffness of the whole BiW or place it on a 4-poster for a durability test. Hence, in order to correlate the CAE model and confirm the abovementioned performances, the most relevant mission to obtain the significant information about the demonstrator behaviour was identified in the rear part of the underbody, where the rear suspension is attached and the composite reinforcement is joined.
Through a series of tests on this subsystem CAE models were correlated, confirming the prevision with a deviation around 1%.
Extremely interesting is the contribution to the overall torsional stiffness provided by the rear reinforcement in APA6/GF developed material, corresponding to 20% of the whole result.
Concerning the cost analysis referred to 30,000 units/year, firstly a reference design was identified, being Nido suitable for the comparison to low volumes only (1,000 units/year).
With this purpose it was supposed to manufacture with traditional aluminium technologies (basically the cold stamping process) an underbody as close as possible to the EVolution one.
Of course this activity was a rough estimation, to be refined, if the case of true implementation, by a specific study, and the main conclusion was that such complex geometry is not replicable through a traditional cold stamping, evidencing that the standard solution presents higher costs per part and an overall higher weight, due to the necessary additional parts.
The EVolution project went far beyond the starting point of the Nido underbody, fully in aluminium, and made mostly by commercially extruded profiles. In particular:
• components integration allowed to compete in cost with the simpler extrusion based solution of the Nido
• the change of technology allowed optimization of shape and weight, very limited in the case of extrusion
Further cost reduction may arise from the usage of secondary aluminium alloys which are increasingly finding interest in the automotive world since combine recycling issues with cost efficiency.
In the current situation of a low automated process, where the oven was placed beside the press machine and manually loaded, the average TAKT time to produce an overall underbody was around 6 minutes, considering performing the gas forming operations in parallel and considering two shifts.
This TAKT time, even if in line with the 30,000 units/year scenario, can be optimized into a true industrial environment where a dedicated gas forming line, with oven and press machine, could be envisaged together with an automatic pre-heat of the aluminium sheets and the subsequent load in into the oven.
The Structural Node
The structural node demonstrator was the assembly of the front shotgun system (shotgun + front rail + reinforcement) with the relevant function to absorb the energy in the case of a frontal collision. More in detail, in the EVolution architecture it was the connection element between the central cell and the front end. A consistent pre-defined smart synergy with another demonstrator, the Front Crossmember, was crucial for an optimized crashworthiness.
The shot gun was designed to be manufactured through the innovative Aluminium Electromagnetic Pump Green Sand casting process (EPGS).
It is known that aluminium foundry is traditionally based in gravity pouring techniques, which have to be carried out very carefully to avoid that the molten metal experiences turbulences. Oxides are formed because of the great affinity that aluminium has to react with water vapour and with the oxygen present in the air.
The innovation introduced by EPGS process was an electromagnetic pump developed to achieve high mechanical properties in Al components with complex geometry, introducing molten aluminium inside sand mould in a counter-gravity way and with a controlled velocity. This meant no turbulence in filling stage, so no gas porosity defects in components. A challenging task was the development of the electromagnetic pump control system, to allow the metal to flow from the bias level to a determined height with a pre-specified flow rate. In order to achieve this goal, static and dynamic calibrations were performed to obtain basic relationships between electrical current and pressure over the melt. The electromagnetic device used to introduce molten aluminium inside the sand mould was able to reproduce the desired filing profiles calculated to obtain high requirement component with absence of defects. Ensuring repeatability in reproducing these filling profiles was one of the key points for a robust industrial scale process.
High production rates at industrial scale involve not only high flow rates, but also high flow temperatures and high filling times. All these parameters influence sand mould behaviour, and main characteristics like humidity or compactability for sand mould making need to be properly settled.
The mould consists of a mixture of silica sand and bentonite as binding agent. Sand forms a continuous loop, so a very important task was to check the equipment and its parameters for sand preparation in order to obtain similar properties in every mould, as moisture content, active clay content, loss on ignition, grains size distribution, compression strength, permeability and compactability, green shear and wet tensile test.
A specific aluminium alloy was optimized for the process and for this demonstrator. The aluminium alloy A356 was selected as the most adequate for this purpose. Several metallurgical treatments to modify the eutectic morphology and to refine grain size were applied, in order to obtain higher quality. All the procedure for metallurgical treatment, modification and refinement, as well as the methodologies to characterize their improvement on microstructure in a quantitative manner were performed during the EVolution framework. Besides, due to the fact the mechanical properties can be improved after a heat treatment, a consistent activity was done to evaluate dependency of each heat treatment stage on strength and elongation properties, and relations on final values of strength and elongation with parameter values on each stage. At the end it was possible to select the specific percentage of Strontium (Sr) for a required modified microstructure, the specific percentage of Titanium-Boron (Ti-B) for a required refined microstructure, and the associated procedures to have the additives active on the molten alloy, as well as the specific time and temperature values for solid solution and artificial ageing stages in a T6 heat treatment.
All these results were optimized in a lab-scale environment, therefore experimental activities in an industrial scale were carried out to obtain similar results with higher productivity rates.
A common practice in foundry industry is to use recycled material from their facilities to feed the melting furnace and combine it with raw materials from ingots. For these purposes, the impact of recycling scrap altered with Sr and Ti was experimentally evaluated, in order to calculate the percentage of each raw material that could be used without a detrimental effect in molten aluminium quality.
In fact, with regards to A356 alloy, Sr and Ti elements additions considered introduce changes in molten aluminium behaviour and during solidification, not only in microstructure. Intermetallic compounds are deposited at the bottom of the furnace and have to be removed when dross is taken away. Experimental tests were performed to determine which elements have to be removed and where they are located. Results confirmed that Sr oxides should be eliminated with dross cleaning and Ti intermetallic compounds should be removed with sludge cleaning.
The furnace in which the pump was placed was designed to enable the segregation of the entire oxides and impurities remaining in the melting process. During the holding time, metallurgical treatments were applied with the aim of maximizing the quality of the molten aluminium. Moulds were manufactured with a Disamatic® green sand moulding machine with a typical cycle time of 15 seconds. In conclusion, the EPGS process enables obtaining high performance components thanks to the advantage of a controlled counter gravity filling process, and with a highly competitive cycle time.
One of the characteristics of any sand mould process is the possibility to perform complex and hollow sections when a core is placed into the sand mould before the aluminium flows inside.
The innovation proposed in the EVolution project was to replace the sand core with a structural element, to form a multicomponent part after casting; in this case the front rail (made through extrusion process) was the core.
The shot gun component was designed to be a media to link parts obtained with different manufacturing technologies (extrusion and gas forming) and several aluminium alloys in one single component: the EVolution structural node demonstrator. Hence, shot gun and front rail were joined together during the casting process: extruded profiles were placed as inserts in sand moulds and during the filling process the molten aluminium covered them. Due to solidification shrinkage and the intermetallic surface, based on Zn and Al, specifically developed to improve the technological properties of the joining area created during the solidification, both of them produced a constraint that fixed extruded profiles with casting component.
The final weight of the structural node demonstrator was reduced by 25% compared to Nido equivalent system, and through this demonstrator, the EVolution project achieved an important weight reduction, coupled with excellent crash performances.
In fact the very first EVolution model, substantially equivalent to the baseline Nido, showed a critical behaviour in terms of deformation of the cabin compartment, and the inefficiency of the structural node, while current final EVolution model evidenced a central cell substantially undeformed (and, as described later, with a pulse in line with margin to the reference value). Of course this was due to a synergy with the Front Crossmember for the first 20 milliseconds of the phenomena and with the Underbody for the next ones, but for sure the Structural Node played the main role in such mission.
An economic analysis revealed that the EPGS green sand casting is two times cheaper compared to the traditional Low Pressure Die Casting (LPDC) process, whilst the TAKT time is below 5 min, demonstrating the industrial viability of the Structural Node demonstrator.
Further industrial opportunities can be evaluated beside the proposed technology. Alternative hybrid components, composed by casted parts over aluminium foams were analysed in the project framework, investigating the process parameters to achieve a successful joint, a component with a good behaviour, and all of this without damaging the foam and its structure.
Aluminium foams are a recent class of materials that have stimulated a great interest in several technological and domains because of their light weight structure and good physical, chemical and mechanical properties, as they combine the part of characteristics of a bulk metal with the structural advantage of foams. Specifically aluminium foams possess high specific stiffness and a good energy absorbing properties, so they offer a great potential for application in the Automotive Industry.
In the EVolution framework a set of novel foams based on aluminium and magnesium were customized for the needs of the automotive industry, with improved structures and properties. The successful implementation of metallic foams requires the development of design methods based on engineering constitutive laws.
Also the type and the amount of blowing agent required as well as the process parameters were optimized, through a very detailed analysis of the dependence of the peak expansion of the foam from the precursor density, and a new alternative process was developed: forging of aluminium foam sandwiches is a new technique that can lead to very cost effective parts and large series.
A major aim of the study was to provide a simple but reliable constitutive description of the behaviour of aluminium foams and its combination with a cast or extruded skin, in order to investigate the opportunity to apply this technology on the Structural Node demonstrator.
Several experimental test on specimen and corresponding correlated CAE models were analysed; in conclusion, it was demonstrated that for the filled cast specimens the percentage of behaviour improvement is not as high as the weight increase, which indicates that it would be more efficient to increase the thickness of the cast profile to attain that behaviour improvement compared to filling it with the foam. Regarding the extruded profiles, it was evidenced that they weigh more than the baseline, but the behaviour improvement exceeds this percentage, as the addition of the aluminium foam improves the bending performance. The same conclusion can be reached if the collapse load is normalized with the specimen mass and then compared.
This solution was not demonstrated in the demonstrator prototype, because the virtual analysis showed that the limited length of the front rail (185 mm) was not suitable to evidence the interesting improvement shown into stand-alone component by the foamed solution having the same weight of the not foamed one.
By the way, considering cars of different segments (C-D) it should be interesting to introduce this technology in the front rail. Other possible applications, considering different BiW architectures, could be found for example at the level of body side rockers.
The Side Door
The Door demonstrator is a complex subsystem which has a direct effect on the customer relevant overall vehicle performances.
The door is constrained on the central cell by the hinges and the latch system, leaning on the body side through a system of seals, whose work line is named P-P1 line.
As a door consistently concurs in occupant protection in the case of side (and front) collisions, it must be characterized by a global and local stiffness to provide an overall impression of robustness and to assure the proper functionality of the features and mechanism (latch, handles, hinges, door stopper, door catcher(s), window regulator, window scraper, exterior mirror, etc.). Furthermore, the door exterior panel has an aesthetic function, requiring a generation of an A-class surface.
The proposed EVolution door architecture consisted of two PP-based skins (inner and outer) including a structural aluminium frame. Compared to the Smart GmBh vehicle, which presented a similar concept, the novelties proposed into EVolution project were:
• a different technology respect to metal stamping or non-metallic materials injection moulding to produce the skins with low thicknesses and promising in terms of costs and TAKT time for automotive mass production;
• an optimized aluminium structure capable to comply to ECE R95 and the crush resistance to quasi-static cylinder intrusion based on FMVSS214 standard;
• the usage of an advanced composite material to manufacture the door skins.
The baseline to conceive this door was the one of the Nido concept, fully in aluminium. The EVolution door showed a weight reduced by about 3 kg, corresponding to a weight reduction around 30% compared to baseline, but with a compliance of main static and crash performances and assuring the main system functionalities.
The research activity performed on skins material was initially carried out starting from the formulation of Front Crossmember demonstrator material, but using a different type of PP and a Long Glass Fibre (LGF). The result was a material with increased stiffness and strength, similar impact resistance but tensile strain at break reduced of about 30%. Different attempts to increase this parameter were done, but each improvement showed a consistent decreasing of stiffness and strength. An optimized masterbatch in granular form was obtained, based on a block copolymer (SEBS), maleinized PP (MAPP), 30% of LGF and nanoclay (Halloysite).
The masterbatch was up-scaled in plates form, obtained through injection moulding, to be subsequently transformed into door interior and exterior skins via compression moulding process.
A detailed material characterization at each stage was performed. No significant degradation of mechanical properties was detected from lab scale to injected plates, but a consistent decreasing of performance was evidenced after compression moulding process. As main conclusion, the material was judged not suitable for up-scaling by compression moulding technology, being a material mainly optimized for injection moulding process.
Hence, the research activity was oriented on thermoplastic PP-based materials reinforced with natural fibres, to keep in account the high content of recyclability requested to the EVolution project solutions. A composite material from PP modified with SEBS, maleated PP and silane-treated hemp fibres percentage (30%) was developed: this composite material showed very good mechanical properties, well-balanced strength and stiffness, high ability to absorb and dissipate energy, good thermal stability. But from the analysis made, the result was that this composite is suited only for the injection moulding of small to medium auto parts, not for large parts like the door skins. The use of silane, maleated PP and SEBS to ensure good mechanical performance resulted as non-competitive from a rough analysis of the costs in the case of thin-walled large auto parts. Moreover no supplier for the treatment of hemp fibres on a large, industrial scale was found, so the material was abandoned for this specific application.
Keeping in account all the above, it was decided to focus the research on the best compression process technology to manufacture the door panels with a selected commercial material PP-based reinforced with natural fibres.
After an extensive benchmarking activity the Biotex Flax, a commercial thermoplastic commingled balanced 2x2 twill textile made from natural flax fibre and PP material, suitable for rapid processing and reduced weight, was selected for the application.
In order to evaluate the effect of the process on the mechanical process and to improve the level of predictability of the CAE models, a complete characterization of the material on samples obtained through compression moulding was performed, confirming its suitability for the identified manufacturing process family selected.
More in details, the manufacture of the door panels, since the inception of the EVolution project, was to utilise methods available on a heated press, a technology familiar to the automotive industry. Press moulding, along with other “out of autoclave” processes (Oven, Microwave, Induction etc) are being heavily investigated, within the composites industry, as an avenue to produce lower cost/lower TAKT time parts that have, traditionally, been too expensive for higher volume, low segment cars (e.g. A-C).
The identified manufacturing process to obtain the door demonstrator panel was the compression moulding: the advanced composite material preform is placed under pressure/temperature and formed through a hydraulic moulding press, featured with matched metal dies.
Given that the process does not involve an injection or transfer cycle, the tooling has less infrastructure requirements than tools designed for other moulding methods. Besides, cycle time is relatively low, so particularly interesting for the automotive industry.
With regards to the specific application case, PP processing is very sensitive to temperature and flax materials should be held at temperature for a short time as possible, to reduce any degradation of the fibres. Numerous trials were then conducted to optimise the processing conditions for the material, cycling from 70 º C to 190 º C and back down again, under applied pressure. The compression moulding process was very successful, but the concern was the processing time as it was approximately two hours per panel. This timescale (and associated cost) is certainly not appropriate for a mid-high volume car.
A deep investigation on potential alternative methods of processing the Biotex panels was done.
The stamp forming is very similar to the compression moulding technique that has been utilised to produce the panels except the fibrous material is consolidated into flat sheets prior to moulding. These sheets are then clamped in a frame, heated to 190 ºC in either an oven or Infra-Red heating bank, rapidly shuttled into the press and formed using tooling at ~50-60 ºC for approximately 60 seconds. The part can then be removed from the press and the next part, which will have been heated during the first part’s forming cycle, can be shuttled in for the forming step. This is a very rapid, continuous process. The heating cycle takes approximately 1-2 minutes and therefore gives an overall cycle time of approximately 3 minutes, well within the 5.7 minute TAKT time. Capital equipment required is a heated press and IR/Oven heating shuttle system.
Induction heating is, again, a very similar method to the compression moulding process but, in this instance, it is possible to place the non-consolidated materials into the tooling and raise the temperature to consolidate and form the part. The benefit with this method is that the induction heating coils can rapidly raise the tooling temperature within minutes, or possibly seconds, form the panels and then be rapidly cooled, using internal cooling channels, to allow part removal. As all heating/cooling is completed within the tooling alternative methods of pressure application could be used e.g. mechanical, hydraulic, pneumatic etc. reducing overall capital equipment costs. Processing times are slightly longer than stamp forming but still in the region of 4-5 minutes.
Apart from the TAKT time, in respect to the compression moulding, these methods would allow a cost reduction per part of about 30%.
All these technologies were compared in terms of costs with the injection moulding, a traditional process to manufacture such panels through advanced composites; a PP reinforced with GF was assumed as material to be used (in line with Smart GmbH solution).
In order to assure the same EVolution geometry, the preliminary analysis required as minimum thickness for both panels (inner and outer) the value of 2.8 mm.
Compared to the lower thickness defined and achieved in the EVolution door (outer panel: 2 mm; inner panel: 1.5 mm), this constraint implied a consistent weight increasing (>27%) respect to the technologies proposed into EVolution project. Besides, the injection moulding evidenced a superior cost per part (>30%) respect to stamp forming and induction heating, being comparable with compression moulding.
Thanks to the detailed experimental plan, including durability at different temperatures and hygrometry levels, flexural stiffness and crash performances, it was demonstrated that the EVolution door was lightweighted respect to a traditional solution (about 30% in comparison to an equivalent steel door) presenting the same structural behaviour and with a lightweighting cost in line with the reference value of 6 €/kg-saved.
It is remarkable to remind that these impressive results were obtained with a set of prototypical doors with a specific focus related to the panels, leaving the aluminium frame to be manufactured through “poor technologies”, as cut-and-fold, performance effective, but not competitive for medium-high volumes. Hence, further mass and cost saving could be obtained selecting another technology for the frame (e.g. among the ones of the underbody demonstrator).
It is important to notice that the technologies selected for the panels allow obtaining complex geometries; in particular, the inner panel, semi-structural, can replace the conventional trim panel of a standard door architecture, with additional savings.
Another consistent activity in the frame of EVolution material research was performed in the use of non-conventional technologies to produce polypropylene based foams. These materials can find an application to create parts to locally absorb the impact energy in order to improve the occupants biomechanics. The first of these technologies is known as Improved Compression Molding Route (ICM) and it uses chemical blowing agents to produce low density non-crosslinked thermoplastic based foams within a wide density range. This technology was applied to the production of PP foams based on more or less complex formulations. The first type (Type #1) was based on a high melt strength polypropylene grade specially designed for foaming applications as it exhibited strain hardening, phenomena which is highly beneficial in the production of low density foams. Using formulation Type #1, it was possible to obtain foams with densities between 150 and 180 kg/m3 and presenting excellent mechanical properties due to their anisotropic cellular structure.
The formulation Type #2 included nanoclays and the same type of polymeric matrix as the Type #1. The presence of the nanoparticles induced a reduction of the strain hardening of the polymeric matrix and as a consequence it was possible to obtain products with a completely interconnected cellular structure, (100 % open cell content) but with excellent mechanical properties because the nanoparticles reinforced in an effective way the polymer comprising the cell walls of such open celled foams. When the open cell foams produced from formulation Type#2 were compared with foams with the same density and open cell content but based on formulation Type #1 (non-containing nanoparticles) a significant improved mechanical performance was observed for the foams based on the Type #2 formulation due to the presence of the nanoparticles.
Besides the previous two formulations, other two types of formulations were foamed using the ICM route. The results obtained for those two formulations allowed concluding that a proper combination of additives (formulation Type #3) permitted obtaining foamed materials with a significant weight reduction, (around 40%), excellent stiffness and with better impact resistance than the base polymeric matrix. Besides, the introduction of a polymeric matrix specially intended for foaming applications (formulation Type #4) allowed obtaining further improvements leading to the generation of lightweight materials with excellent mechanical performance.
The second technology used for the production of polypropylene based foams is known as Stages Molding, (STM). This technology is aimed at producing density reduced plastic parts and permits overcoming some of the drawbacks exhibited by current technologies (mainly injection moulding). STM permits producing large plastic parts, achieving high weight reductions, (up to 80%) and using high amount of fillers, (up to 80%). So-obtained parts present excellent surface quality and no internal stresses or sink marks since the driving force to fill the mould is the gas released by the chemical blowing agent used to generate the gaseous phase. In addition the possibility of generating skin-core structures widens the possibility of this technology. The mechanisms underlying the formation of the skin are of special interest because the mould is typically hot during the process contrarily as in other processes such as injection moulding where the mould is usually cold. Such mechanisms were investigated using X-ray radioscopy and it was found that they were based on a diffusion process from the molten polymer containing the gas phase to the mould coating. In addition, it was concluded that the skin thickness can be controlled by means of fine-tuning some of the foaming parameters such as foaming temperature of blowing agent concentration.
As a general conclusion it can be said that the two non-conventional technologies chosen to produce polypropylene based foams in the frame of EVolution project permitted widen the range of applications and the possibilities of foams based on a commodity polymer such as polypropylene either by adjusting the chemical composition of the material or by fine-tuning the foaming parameters in order to produce a foam with a density, cellular structure and mechanical performance optimum for its final application.
The “sixth demonstrator”: the door trim pocket
A preliminary screening about the properties of poly(lactic acid) (PLA)/poly carbonate (PC) blends performed before the beginning of the EVolution project allowed evidencing that the blending of PLA and PC in the presence of a catalytic system consisting in tetra-butyl ammonium tetra-phenyl borate (TBATPB) and triacetine was a promising strategy for improving the properties of PLA and making it able of being used in automotive applications. The process was patented (Copolymers based on polyester and aromatic polycarbonate US 20140128540 A1). However, the best formulations prepared thanks to this method were based on PC, which is a not biodegradable polymer.
Then the research in the framework of EVolution was focused into improving the ecological content of the material, by increasing the PLA content and replacing virgin PC with recycled PC. The use of recycled PC in a second series of trials and measurements resulted in materials with interesting tensile and impact properties having a PLA content increased up to 60%. Moreover, also a recycled PLA was employed, thus maximizing the ecological content of the developed materials.
On the basis of tensile and impact properties the most promising and more ecological formulations were selected, suitable to be validated in injection moulding applications and ready for scale-up trials.
In order to develop also bio-degradable composites, trials in the presence of cellulose fibres were carried out. The addition of fibres resulted in the increase in Elastic Modulus and decrease in elongation at break. The use of a catalyst based on TBATPB and triacetine improved the adhesion between fibres and matrix.
Hence the work activity allowed selecting peculiar formulations for beginning the scale-up part of the project on one side, but resulted also in a wide knowledge about the developed bio-based materials which can be particularly useful both for project success and for future scientific and technological innovation in the materials science field.
The preparation of several composites and considerations about availability and costs of the different materials, allowed preparing by industrial extrusion two different batches of extruded granules consisting in a blend of recycled PLA from thermoforming process and recycled injection mouldable PC and a composite of the same blend containing a certain percentages of chestnut fibres. The price of the catalyst impacts consistently on the price of the materials, and besides it was not possible to find it from industrial source, hence the products were up-scaled without the catalyst, taking into account to continue the research of it in order to improve the properties of the compounds. Three products were extruded in a co-rotating twin screw extruder F.lli Maris TM 30 MW (30 m diameter, ratio 40 L/D). The production process consisted of a pre-mix of all components of the formula and the following extrusion of the mix by dosing it in the main feeding.
Then the pellets were injected into an existing door pocket mould producing the sixth EVolution demonstrator.
The design of the BiW was performed in order to achieve the weight target of the integrated demonstrators and in the same time to assure its overall weight target.
The final BiW weight achieved was reduced by about 30% compared to the Nido concept (fully in aluminium), hence in target, whilst the three integrated demonstrator weights were all objective compliant, as analysed in the previous sections. It is noticeable to remark that many parts of the Nido which were designed in EVolution were missed or uncompleted and furthermore, the Nido crashworthiness was not completely satisfactory.
As requested, the Nido vehicle ergonomic was maintained, as well as the style features and the powertrain architecture, whilst the BiW archetype was changed from multifunctional rolling chassis + un-structural upper frame in central cell + semi-structural front end and modular rear end, as previously described.
All structural performances associated to BiW (and Full Vehicle) were achieved, crashworthiness included.
A theoretical industrial research was performed in order to individuate the peculiarities of the BiW assembly plant, keeping in account that:
• EVolution BiW was a multi-material structure,
• SPRs and structural adhesives were the main joining techniques selected,
• MIG-welding was limited in strictly selected area.
A plant to assembly a multi-material BiW could be reconfigured from an existing one or be totally new; in the case of reconfiguration, there would be a quote of investment to equip the existing robots, an amount of costs-per-year due to rivets and adhesives and a consistent operational costs-per year reduction due to the lower level of energy consumed thanks to the different joining method approach.
In the case of a brand new plant, the investments would surely be higher, but the degrees of freedom in lightweight the structure and the energy saving potential could be very relevant, contributing to the overall CO2 reduction.
In this context in fact, the BiW design strategy must aim to:
• extremely reduce the part count number of BiW elements
• smartly select the structural parts to be designed through composites materials in order to assemble them after the e-coating process, with the following advantages:
1. reduction of the e-coating vessels dimension (and then the amount of energy to activate the bath)
2. an optimal flow out from the BiW of the cataphoresis bath (e.g. assuming to redesign through composites the greatest part of the rear end, the typical “spoon effect” in retaining the bath would be eliminated, as the composite parts would be excluded from the e-coating).
• consider all the aesthetical exterior panels as designed and manufactured through composites materials, in order to:
1. perform a painting cycle at low temperatures (80°C vs. 140°C requested for the aluminium)
2. dimension specific painting ovens for these temperatures
3. drastically reduce the energy amount necessary for painting.
The assembly line reconfiguration aims to minimize the number of automatic assembly stations (robot) and to select the best joining process, to obtain, at the end, a downsized plant with a positive balance between investment, ownership and energy costs. The paint-shop optimization enables a high potential of energy saving and Global Warming Potential (GWP) reduction. A brilliant plants integration will allow further opportunity of energy and costs saving.
At a first glance, in order to be more compliant towards this idea, the EVolution current BiW can be improved imagining to apply the EVolution technologies also in other parts of the BiW, to achieve, together with the above, a further weight and part count reduction being fixed the structural performances.
Besides, supposing to remove the constraints associated to powertrain architecture, another optimization can be envisaged at the level of front end engineering.
In fact the lightweighting offers the interesting opportunity to downsize the electric powertrain and the battery, enabling the application of different electric powertrain architectures, which can free further ergonomics possibilities for the selected vehicle.
Replacing current powertrain architecture of Rear E-axle + Central battery with Front motors-in-wheel archetype, the rear floor shape can be modified in order to allow the ergonomics for 2 rear seats (city car version) or to improve the luggage compartment volume (Van and Pick-up versions).
The Front end structure can be designed as screwed to the central cell with the purpose to merge the completion of the BiW assembly and the placement of the front elements of the powertrain in a unique operation, further optimizing the plant costs and layout.
The innovative multi-material concept allows freeing other leverages aiming to downsize the paint-shop and its features (e-coating vessels, ovens) and to select environment-friendly painting method.
For example, excluding exterior aesthetical elements in aluminium replacing them with composites, it would not be necessary to paint aluminium parts not visible and already protected by e-coating with an impressive effect on costs, energy consumption and GWP. What demonstrated on the EVolution door exterior panel is promising to follow this strategy.
Life Cycle Assessment (LCA) methodology in accordance with the ISO 14040/44 was applied to evaluate the environmental impacts of the developed solutions, particularly focusing on the five demonstrators. The analysis followed a “cradle to grave” approach considering the entire product life cycle phases: production, use and end of life. For each case study, the functional unit was referred to one prototype considering the lightweight effects in terms of electric energy saving along a lifetime of 200,000 km in accordance with the 2009/33/EC Directive, taking in account:
• production (materials, energy, water, waste, emissions, etc.);
• use (weight of the component to estimate, through the fuel reduction value);
• end of life (evaluated only qualitatively focusing mainly on the joining technologies to understand the chances of dedicated dismantling for recycling/recovery).
It is interesting to highlight how the production phase showed a different contribution in terms of Global Warming Potential (GWP) compared to the use phase one. In fact, components made mainly of aluminium alloys or carbon fibres showed a production contribution higher than the use phase, while for example the crash crossbeam, which is made of plastic composites, showed an inverted behaviour. Another contribution to the CO2 reduction came from the side doors: natural fibres are CO2 neutral in the “cradle to grave” approach, differently from the traditional steel panels.
The LCA analysis compared the environmental impact of the EVolution vehicle with current production cars of similar dimensions showing that the applied multi-materials approach is able to reduce the CO2 footprint.
Mounting and dismantling are usually negligible within the End of Life Vehicle (ELV) analysis from the environmental impact point of view and, in particular, considering the main GWP indicator; nonetheless the mounting phase was considered having a strong impact on the assembly lay-out in the factory.
The five demonstrators were designed taking into account this aspect.
Globally, it was possible to assess that the mounting phase of the EVolution vehicle reduced the required labour compared to a traditional vehicle due to the consistent part count reduction.
Considering the dismantling phase, the differences between a traditional vehicle and the EVolution one were even smaller.
The dismantling phase can be seen in order of maintenance or of ELV.
Maintenance activity is strictly linked to the assembly techniques: some assembly techniques were easily reversible, while others were not. Referring to the assembly approach followed it was evident that the selected techniques were not new, but differently applied respect to a traditional BiW. This allows stating that the dismantling for maintenance did not require more time, energy or special equipment: it was not affected by the EVolution design.
Referring to one of the most common approaches to ELV, the vehicle is initially reclaimed from fluids and hazardous substances, then the dismantler separates the systems that can have an economic value as spare parts (like the moving parts). Moreover, in order to promote recycling, the dismantler removes also glass, catalysts, tyres and large plastic components (e.g. bumpers and fluid containers). After the dismantling step, the remaining parts are pressed basically for a logistic optimization and the wreck is treated by the shredder. Therefore, the materials (mainly ferrous and non-ferrous metals) are subsequently separated for recycling, while the automotive shredder residue (ASR), can be further treated though the post-shredding technologies or energy recovered. Anyway, such solutions are not completely developed in the different European Countries and so the ASR can still be disposed in landfill.
The whole vehicle could be dismantled and the separated materials sent to dedicated recycling centres, but this approach is often too expensive and so the previous one is usually preferred.
This approach can be indifferently applied to the EVolution solution: the only difference is the percentage of the different materials after the partition of the shredded parts.
The joining methods
As the EVolution developed solution was a multi-material BiW, a consistent activity was performed on the joining methods.
In particular, potential joining technologies allowing the assembly of the new vehicle were identified, through an analysis and tuning of the existing technologies, whilst new methods were developed where the existing ones did not suit the required application.
More in detail, several research activities were conducted to:
1. define for demonstrators and BiW parts the best structural adhesives, primers and surface treatments to join:
• aluminium - aluminium
• aluminium - APA6/GF
• aluminium – Biotex
• aluminium - PP
2. to model the correspondent joining through a detailed experimental characterization, in order to model the adhesive performances at quasi-static and high strain rate
3. to identify and evaluate through virtual analysis the minimum number of riveting for joints tacking
4. to identify and model the structural foamed and monolithic aluminium joints
5. to define for the polymeric trims for mounting/dismantling activities a new set of radio-frequency activated hot-melts adhesives with quality verification.
To identify the best structural adhesives for multi-material interfaces, a detailed activity at level of body and demonstrators typical sections was performed. The interfaces were optimized/redesigned in order to allow the feasibility of the bonding and of the tacking into an industrial context.
In parallel, a test campaign on specimens of different substrates, representing the main interfaces of demonstrators and BiW, was performed to individuate the best structural adhesives and the primers/surface treatments to be applied. In the case of door demonstrator a specific primer was conceived.
The experimental results on bonded specimens were used to develop a methodology for adhesively bonded structures simulation to predict the joint strength. Followed approaches were based on continuum mechanics and damage mechanics.
According to the continuum mechanics approach the adhesive and adherents were modelled through continuum elements, assuming that the adhesive was perfectly bonded to the adherents. The assumption of a perfect bond means that the finite-element analysis takes no account of the adhesion properties of the interface.
The cohesive zone modelling (CZM) approach is a progressive damage evolution simulation methodology. It enables the complete adhesive structural response to be modelled in a single analysis up to the final point of failure without the need for additional post-processing of finite-element analysis results. It is a local approach, where damage is limited to zero volume lines and surfaces in two and three-dimensions, respectively. Thus, it is distinguished from continuum approaches, where damage is modelled over a finite region of the material.
In CZM models the fracture process includes a zone of discontinuity modelled by cohesive zones, thus using both strength and energy parameters to characterize the de-bonding process. In general, a cohesive law is described by two parts, a traction strengthening part and a traction softening part, either of which may be linear or non-linear.
Finite element analyses that include CZM techniques offer a powerful means to account for the largely nonlinear fracture behaviour of modern adhesively bonded joints, thanks to the opportunity to calibrate the CZM parameters by experimental data in order to accurately simulate the failure process.
The developed methodology was successfully applied and correlated with experimental test to the simulation of the rear underbody structure demonstrator to which adhesively bonding is extensively used.
The interaction of different combinations of aluminium casted and extruded beams with co-casted or extruded aluminium foams was analysed through specific tests (single shear lap, double shear lap, tensile test and peeling) on over-moulding joining to predict the mechanical behaviour of the joint between foam aluminium and casted/extruded aluminium component. Numerical models were tuned in order to predict specific mechanical behaviour of the joint between foam and aluminium (casted and extruded) component. Linear and nonlinear simulations have been performed using different joint modelling techniques, from simple kinematic joint to complex contact implementation.
The testing results of casted aluminium and foam aluminium specimens revealed that it is not necessary to introduce a geometrical interaction due to the fusion area between foam and casted. In case of casted and extruded specimens there is no cohesive area. In case of extruded profiles and foam aluminium it is necessary to add a glue agent in order to assure the position of both components.
In the area of semi-structural trims a new technique was developed, modifying a traditional polyolefinic hot-melt adhesive with ferromagnetic nanoparticles, in order to overcome the obstacle represented by the thermal insulation properties of polymers. In fact, using ferromagnetic fillers it was possible to warm up the adhesive from inside, through radiofrequency (RF) technique, bringing it to the melting temperature. Different tests were performed evaluating different kind of ferromagnetic particles, the induction frequency and power: as polymer are heat insulator, this technique cannot be applied as-is to join plastic parts: the RF system was upgraded by modifying internal hardware and by designing specific inductors to set the proper frequency for this specific application.
Tests performed on samples were scaled up designing and producing a system to apply the technology to an industrial component, the handle of a tailgate, big enough to be representative of the industrial production and not similar to samples, with medium dimensions to limit the cost of the equipment production but at the same time with reduced dimensions to allow a proper distribution of the adhesive even with manual equipment, and be made of material suitable for polyolefinic adhesive.
Three different adhesive mixtures were produced and tested mixing the hot-melt adhesive with various percentages of ferromagnetic nanoparticles, then the three components were analysed through shearography in order to assess the bonding quality and to evaluate the adhesive allowing the lower level of stress in the handle.
The comparison of cost, weight, cycle time and residual stress allowed selecting the best trade-off adhesive.
This technique was successfully evaluated also for the debonding process.
The application of this innovative adhesive constituted a new methodology for the joining of plastic substrates, bringing important advantages in terms of new manufacturing technologies, dismantling at the end of life and energy saving.
The Full Vehicle
As previously described, the overall EVolution objective was to demonstrate the sustainable production of a Full Electric Vehicle (FEV) of 600 kg weight, battery included.
During the project, this weight was checked several times performing an analysis of the Nido BOM. Each vehicle area was theoretically analysed in order to propose a credible weight reduction based on the future trends of research in the automotive field in order to achieve the 600 kg.
The EVolution final release had an overall weight corresponding to a +1% compared to the target. As for the nature of this analysis, the weight target was considered achieved.
The most consistent weight reductions were evaluated at the level of BiW (30%) and at the level of Traction Battery, where a potential weight reduction of 55% could be achieved with a battery type LiNiCoAlO2 without losing performance.
Based on these results, the overall full vehicle weight reduction from Nido to current EVolution was about 240 kg. From literature, a vehicle lightweighting of about 150 kg allows a traction battery downsizing closed to 3 kWh maintaining the same autonomy. Assuming energy-specific battery system costs of 500 €/kWh for the year 2015, the reduction in total battery system costs is about 1,500 €/car. Applying this rule of thumb to the EVolution weight reduction, with the same autonomy the downsizing would be close to 4.8 kWh, with a cost reduction of about 2,400 €/car.
In conclusion, weight saving will increase range with existing battery or maintain range with a smaller battery. By using smaller batteries, the required amount of power to charge them will be reduced and the associated CO2 emissions will also be decreased. Due to the fact that the EV cost is directly related to battery size, being fixed the rate €/kWh and the range, the lightweighting design will be a balance between weight and cost.
The overall project results, described in the previous sections, have an effect on the expected project impacts, linked to the project objectives deployed from the project idea, and then to the exploitable items.
After four years of activity, it was demonstrated that EVolution developed a lightweighted, multi-materials and modular Body in White concept highly recyclable, composed by a limited number of parts, considering as design development variables also the materials and the manufacturing technologies selection and the assembly strategy, to propose an innovative vehicle structure at affordable costs for medium production volumes, with reduced energy consumption and CO2 footprint.
It is clear that these overall results imply a consistent amount of industrial, scientific, economic and social/environmental impacts.
More in details, from an industrial point of view, the following items:
• complex shapes with reduced thickness feasibility
• consistent part count number reduction
• different strategy of parts assembly and painting
• high level of lightweighting
have an effect on the whole vehicle body architecture reconfiguration and a great potential impact in the assembly and painting plants architecture and then investment and ownership costs.
To have an idea, for a count part reduction of 40%, the corresponding reduction of junctions could be around 30% with a consequent saving of 10 robots, and an equivalent space saved of 90 m2, for 30,000 cars/year produced. Furthermore, in one year there will be an energy saving, considering that each spotweld requires 20 Wh (for aluminium) and each rivet requires 2.2 Wh. This amount can be quantified in about 7.9 €/car (considering an average cost of 0.15 €/Wh in Italy) and can partially compensate the higher cost of the rivets.
Moreover, the proposed joining methods, in principle replacing spotwelds with SPR and bonding, for dissimilar materials but also for Al-Al junctions, implies that fumes extraction installations and water recirculation circuit like those dedicated to the spot welding lines are not required. This will mean further assembly plant dimensions and layout reduction, energy saving and reduced cost of ownership.
As previously mentioned, the innovative multi-material concept allows freeing other leverages aiming to downsize the paint-shop and its features (e-coating vessels, ovens) and to select painting method environment-friendly. For example, excluding exterior aesthetical elements in aluminium replacing them in composites, it would not be necessary to paint aluminium parts not visible and already protected by e-coating. If it could be possible to avoid a separate stage of TopCoating of the composites aesthetical parts, the coating will have place only in the BiW paint-shop at lower temperatures (80°C instead of 140°C as required by aluminium). This would mean that it could be possible to eliminate one paint-shop, maintaining only the one of the BiW, with an impressive effect on costs, energy consumption and GWP. What was demonstrated on the EVolution door exterior panel is a promising strategy to follow.
Besides, some proposed technologies, if compared with the traditional ones, are less energy consuming, whilst some of the proposed new materials have a great bio-content, with a high CO2 reduction.
In general the LCA analysis evidenced that the applied multi-materials approach is able to reduce the CO2 footprint, comparing the EVolution solution with a traditional one.
It was demonstrated that the TAKT time of the new solution is in line with the one of a medium production (about 30,000 cars/year) and the cost increasing due to lightweighting is below the reference value of 6€/kg-saved recognized by the OEMs.
The consistent full vehicle lightweighting allows the powertrain (traditional or electric) downsizing, reducing vehicle costs. In particular for the Electric Vehicles (EVs) this effect is very important to reduce EVs cost, because of the High Voltage battery downsizing, enabling their market penetration.
From a social/environmental perspective, these results contribute to a diffusion of the multi-material vehicle structures and the composite materials not only for niche segments of market (Luxury or Sporty car), but also for the city cars for the mass and, thanks to the cost reduction of Traction Battery due to lightweighting and the potential strong reconfiguration of the assembly and painting plants, the philosophy of “Green Mobility” can become a reality for all, both in Europe and also in new emerging markets with high potential (e.g. China, India), with a consequent positive effect on global CO2 emission and the GWP reduction in all over the world. All OEMs worldwide will play a role in the global electrification of road transport, the success of which will be dependent on mastering the key enabling technologies, including the ones developed within the EVolution project perimeter.
Beside actual materials developed for the demonstrators, a great amount of scientific work was carried out, producing a consistent impact and exploitation/dissemination potential. In the European Charter for fundamental rights of the European Union it is stated that scientific research shall be free of constraints and freedom be respected. In a project like this involving university researchers and wanting to achieve specific targets it was important also to ensure sufficient academic freedom to develop general and fundamental knowledge that is publishable. This resulted in the development of necessary materials and models for the demonstrators, but also in a large number of peer reviewed scientific papers in web of science and presentations. These publications can be seen elsewhere in details but they fall into three main groups:
• Biomaterials. A focus of the project was sustainability of materials, and investigations were made on bio based polymers or blends. Poly(lactic acid) attracted special attention due to its availability and performance, however the impact properties are weak thus blends with polycarbonate or bio oils as plasticiser have been investigated, as well as reactive extrusion, stereo complexes to raise glass transition, influence of microstructure and processing.
• Mechanical modelling. Modelling was used for establishing material data like in the high deformation rate region and for life time predictions. Constitutive equations were made for example for ratcheting of PP, for nanofilled materials of various types, semi crystalline polymers for finite deformations, multiple step loading of PP and more. Some of these models and experiments formed the foundation for the numerical simulations of the demonstrator performance.
• Complex combined loads. Polymer products are used under the influence of complex loads in real life. Salts, pH, radiation (sunlight), chemicals (including moisture), thermal and mechanical loads. To develop a fundamental understanding, experiments were conducted on stimuli sensitive materials (like hydrogels) and general models were made.
To sum up, EVolution can truly contribute to the development of a European standard reference technology platform for electric vehicle part manufacturing, which contains architectures, models, methods, and tools for part development, verification, validation and testing.
Furthermore, the EVolution results are applicable also in the case of other typologies of vehicles with hybrid or internal combustion engine powertrains.
The project Exploitable Results (ERs) were identified during the project development; at the end of the activities, keeping in account the above, the potential ERs were 18, each one inter-related with the others. The Exploitation Strategy Seminars (ESSs) performed during the framework offered a concrete and useful opportunity to review the ERs list and the exploitation strategy both for the Consortium as a whole and for the single partner.
The EVolution consortium was composed by 24 partners coming from industry, research and academic world: this combination of competencies ensured a competitive advantage to the consortium in terms of exploitation potential.
All the partners effectively contributed to exploitation during the overall project duration. The physical prototypes provided a tangible demonstration of the concept developed offering to industrial partners the opportunity to show the power of the innovations introduced to potential customers, and to academic institutions the occasion to diffuse the results of their research activities.
The general approach towards exploitation was that all partners were free to exploit secondary and tertiary markets based on their background Intellectual Property Right (IPR) and licensed foreground.
The overall strategy foresaw that:
• Universities and Research Organisations use the results in on-going consultancy for customers wishing to use EVolution technology via licensing agreements or disseminate results internally to groups that will enable further exploitation of the results for product development, new R&D initiatives or consultancy.
• SME partners lead the commercial introduction of the EVolution technologies into the European Market, with potential agreements with manufacturing and/or distribution third parties, able to provide the access required to achieve the ambitious forecasted market penetration (Competitive Impact). These agreements can generate further revenue for the core EVolution participants.
The commercial exploitation of the project is ensured: the majority of the industrial and research partners declared that they will continue to work on the themes of their interest with their own resources and also by looking for proper collaborative funding opportunities such as H2020 programs and other national/regional projects. Moreover, they have defined clear and effective plans for implementation for the near future. Some examples are listed here below.
Tecnalia (TEC) and FPK signed a specific commercial agreement to scale the CAPROCAST technology to a medium production volume, and a number of potential applications on existing components or for further feasibility studies are already under discussion with Centro Ricerche Fiat (CRF) and Innovazione Automotive e Metalmeccanica (IAM). Magneti Marelli Suspension division, a company of the Fiat Chrysler Automobile (FCA) Group, is also interest in the potentialities of this technology.
ICECHIM is discussing with a Romanian SME the possibility of licensing the knowledge about the masterbach of the Front Crossmember developed material, and is in contact with other customers for feasibility studies; in the future also an agreement with FPK could take place, being the product highly customized on FPK requests.
CIDAUT and Metalfoam (MET) will continue working on the theme of casted aluminium combined with foam which MET is primary interested in exploiting, while CIDAUT has several on-going contacts with existing and potential customers for the quotation of different parts/system to be manufactured with co-casting technology, not only hybrid Al-Al components but also for Steel-Al components.
The innovative forming technologies developed by IAM had already given birth to further R&D activities related to components or systems which can highly benefit from integration of parts and reinforcements/thickness reduction and zonal thickness optimization; many of these applications refer to the future model of the FCA light commercial vehicle (Ducato) which is produced in Abruzzo, the region where IAM and Susta (IAM third party) are located, putting the basis for a positive spill-over effect within the local economic context. Moreover Susta is currently in contact with many big automotive players to evaluate the application of the gas forming technologies to their products, while VE&D (another IAM third party), thanks to the knowledge gained within the project, is discussing with different customers the re-engineering of a number of components to make them lighter by applying the aluminium related technologies (combined with multi-thickness) and/or structural composite.
As the FCA Group company in charge of carrying on the research activities, CRF will develop knowledge and methodologies suitable for the hybrid BiW new car generation. The current FCA industrial plan foresees new sportier and lighter vehicle: considering the new safety requirements, the target can be achieved only developing hybrid BiW. At the end of the project CRF will train FCA’s designers about new BiW potentialities and design methodologies.
Finally, Pininfarina (PIN) will exploit the outcomes of the EVolution project offering to its customers a wider range of innovative design solutions and for future research activities not only on the market of FEV, but also in internal combustion engine concept. In particular, EVolution results will be proposed as potential solutions in on-going and new product development process of the Company. Moreover, since FEV and HEV market is expected to reach nearly the 19% of the total non ICEV market by 2020 and this will require a radical change of the concept of the vehicle, PIN will be ready to catch the new business opportunities which will arise from this changed supply chain in the automotive industry, in new market entrances and value creation among the production lines.
To ensure that all new knowledge and intellectual property generated by the EVolution project has been and will be managed correctly and adequately protected, the consortium developed an IPR strategy, combining exploitation and IP plan with a clear, reliable and robust policy in IP protection, including mechanisms for the policing and defence of the patents and other IPRs in case of any suspected infringement.
The ESSs greatly helped the consortium partners to analyse the possibility of IPR conflicts among partners contributing on a specific ER and to ponder on the need of setting specific partnership agreements for future exploitation of project results.
For the time being, ICECHIM filed a national patent application at OSIM Romania: Concentrat pentru imbunatatirea rezistentei la soc a polipropilenei cu fibra de sticla si procedeu de obtinere a acestuia (Masterbatch for improving of impact strength of polypropylene with glass fibre and process for obtaining it), Zina Vuluga, Cătălina-Gabriela Sânporean, Michaela Iorga, Denis Mihaela Panaitescu, Mihai-Cosmin Corobea, Dorel Florea, Stela Iancu şi Monica Duldner, patent application A 00247/06.04.2015.
FPK will consider a patent feasibility on the basis of the results of the demonstration for the frontal crossmember. In the same way, IAM and CIDAUT will consider the possibility of patenting their achievements related respectively to manufacturing technologies for lightweight components and advanced aluminium alloys, foams and sandwich structures.
Other partners are still considering the possibility of patenting their work (e.g. Latvian State Institute of Wood Chemistry (IWC), for their work on the PUR foams filled with nanoclays.
The work with the preparation of blends PLA/PC was protected by a previous patent owned by Pisa University (UNIPI), while the preparation of composites with cellulosic fibres is not yet protected, but for the time being there are not peculiar advancements and the process is not patentable. TECN has three active patent families related to the CAPROCAST process: two of them are related to the equipment, while the third one covers the process.
Collaboration agreements between FPK and TECN has been set to scale CAPROCAST technology to a medium volume automotive condition. Other collaborations between project partners may be considered for the future in case any interest may come out (e.g. Euromaster (EUMA) may be interested in exploiting the work of other partners so a transfer of knowledge may be needed or MET may be interested in setting specific agreements with CIDAUT to collaborate on common themes of interest).
Effective dissemination is a fundamental activity in any research process, since its success contributes decisively to the short and long term success of the project itself.
The scientific knowledge developed during the project has been and will be disseminated to the academic community by the projects academic partners (Universities and Research Organisations) and the commercial benefits of the developed technology has been and will be disseminated to end users and key decision makers by the industrial partners, who will use their existing links to the appropriate industrial, trade and professional organizations and associations.
A stakeholder analysis was preliminary performed to plan an effective dissemination, identifying the different individuals, groups, and organizations that are interested in the project and its results. Stakeholders were identified, listed and assessed in term of their interest in the project and importance for the dissemination.
Dissemination goals for each stakeholder group was identified; a peculiar group, the Advisory Board, composed by representatives of Industry and Academia, was periodically involved and informed about the EVolution project progress, to increase the dissemination channels to benefit about suggestion of further exploitation and dissemination opportunities.
Dissemination mechanisms/channels which used to pursue the identified targets are listed below:
• Project website
• Project meetings
• Pre-market stimulation – Technology Demonstration Event
• Clustering activities/Joint actions with other projects
• Scientific papers
• Publications in Trade Journals/Magazines (Industrial papers)
• Social Network
• Other media (TV, radio etc.)
Furthermore, dissemination material has been and will be prepared by the consortium partners for inclusion on the CORDIS FP7 and EUROPA websites, in particular for the NMP theme of the Cooperation Specific Programme, the EC web portal for the European Green Cars Initiative and the Directorate-General for Research and Innovation. Details of the EVolution project have been and will be made available for articles to be included in European electronic and paper publications such as research.
Up to now, it has been noticed that the number of visitors to the homepage of the EVolution project website, reflecting the general interest in the project, was equal to 19,510 total visits from the initiation of the homepage to the end of the project. Besides, the average number of visits per month has been surprisingly constant over the past three years.
Number of downloads of scientific papers related to the EVolution project has been monitored; for simplicity, it has been chosen to count the total number of citations to the leading scientist from universities and RTO’s participating in the project. In the period 2014-2016, those scientists have been cited 1,822 times according to Scopus.com. Papers by those scientist published in the same period were cited 199 times. The most cited paper in the publication list has been cited 13 times, so clearly the full impact of the publications has not been seen yet. Based on the studied trend, a total of 200 citations to the Evolution papers within the next few years is expected.
Moreover, the dissemination towards the academic and scientific community has also created a certain interest towards material research topics. In particular at Aalborg University (AAU), the green focus has attracted 6 international researchers from PhD to professor level working with topics like bio-based modification of nano-clay and bio polymers like PLA.
Measuring the impact of dissemination actions put in place by industrial partners it is not easy. Within the EVolution project there are 11 industrial partners, 7 of which are SMEs. Moreover, these organisations cover the entire automotive supply chain, from raw materials suppliers and processors and to component manufacturers and vehicle manufacturers with production facilities located within the EU. In particular, component manufacturers usually work in pair with the OEMs, so they do not have the full freedom to propose new solutions or new products if they are not, in some way, pulled by the OEM.
As first attempt, it has been decided to try to quantify the impact of dissemination of industrial partners in terms of:
• Consolidation of the business relationship with existing customers (and new business opportunities arisen)
• Contacts with new potential clients
• Contacts/request for further presentations/participation to events/lectures
thanks to the EVolution project.
In this regard, it is noteworthy to highlight the following:
• CIDAUT has been asked for two quotations from new customers and is discussing the introduction of the EVolution solutions (multi-material component manufacturing thanks to EPGS process and applicability of Al foams in components made of cast aluminium removing the sand cores and substituting them by ones in Al foam) in future projects with existing customers;
• Magneti Marelli-Suspension division, system manufacturer of the FCA Group, showed their interest in the opportunities offered by the CAPROCAST technology developed by TECN; CRF will take care of the transfer of knowledge to Magneti Marelli and to FCA designers to evaluate concrete opportunities of applicability of this technology;
• PIN has been invited to present the project in a plenary lecture at the 1st International Conference of Automotive Composites (ICAUTOC) held in Lisbon in September 2016 and then to submit a paper to be published on the International Journal of Automotive Composites (IJAC);
• TEC had the opportunities to expand their network thanks to the interaction with CRF and the IAM Consortium; contacts are on-going at the time of writing to evaluate the possibility of further collaborations. TECN has also been invited at the JEC World 2017 (Paris, March 2017) and will be the host for the Biannual Spanish Composite Workshop in June 2017.
• Susta was invited to present their work about gas forming technology to relevant automotive player, both existing and new potential customers. The work done within EVolution put also the basis for one regional project which deals with an integral aluminium side door; the project is just started and involves also CRF;
• The work with aluminium multi thickness and composite materials has created for VE&D new businesses opportunities and expanded the range to the customers we already knew. Crucial was the experience towards a structural multi-thickness aluminium alloy component as the front reinforcement firewall. The knowledge gained with the design of this material has allowed to expand to automotive customers (FCA and not only) towards the creation of light alloy structures with thickness variation (B-pillar, firewall, spars, mechanical stringers). Similarly, the activity related to the rear composite reinforcement allowed specializing VE&D knowledge towards the composite material, more and more dominant in the future industry. In this case VE&D is discussing with existing customers, the possibility to re-engineering some structural components or with semi-structural functions, in order to redesign not more in metal, but in a composite material in order to obtain weight reduction and, in some cases, stiffness increase.
• For many Research Organization (RO) partners the EVolution project turned to be an excellent reference for both R&D and commercial assignments for industry customers; in particular:
o the work about impact testing at high strain rates has brought to Danish Technological Institute (DTI) new customers within the defence and energy industry using fibre reinforced composites.
o the work done by ICECHIM attracted the interest of several organizations interested both in developing of new technologies based on results obtained within FP7-NMP projects and in possibility of transferring and licensing of these technologies. The “Renault Technologie Roumanie” Society has expressed interest in collaboration with ICECHIM to develop new technologies for improving the quality of Renault-Dacia parts and 2 Romanian SMEs were interested to take up the technology for masterbatch obtaining.
• KGR strengthened the collaboration with CRF and they will probably set some project proposals together with the Politecnico of Turin.
It is important to remark how the above list is meant to be as an illustrative, yet incomplete examle of the great impact the project had thanks to the dissemination actions put in place by all partners.
List of Websites:
Jesper de Claville Christiansen, Aalborg University
Phone: +45 9940 8970
Grant agreement ID: 314744
1 November 2012
31 October 2016
€ 13 438 488,67
€ 8 933 842
Deliverables not available
Grant agreement ID: 314744
1 November 2012
31 October 2016
€ 13 438 488,67
€ 8 933 842
Grant agreement ID: 314744
1 November 2012
31 October 2016
€ 13 438 488,67
€ 8 933 842