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Development of a Direct Laser Joining of hybrid Plastic-Metal components for industrial applications

Final Report Summary - PMJOIN (Development of a Direct Laser Joining of hybrid Plastic-Metal components for industrial applications)

Executive Summary:
The automotive industry is continuously looking for reducing energy consumption by using lightweight structures. In this search for weight savings, the introduction of plastic/composite parts instead of metal ones is researched extensively. But, as metals cannot be excluded as the fundamental material in many applications, many (future) products are being forecast to contain several types of materials. To date, the joining of plastics to metals takes place by methods such as adhesive bonding, mechanical joining, or overmoulding, which all involve a large number of assembly operations and/or design constraints.
The PMjoin project aimed to overcome some of the disadvantages of these more conventional techniques and concerned the development of a new innovative joining concept using a direct non-contact laser joining process, without the need for additional (filler) materials, liquid/ solid adhesive bonds or assembly elements, but offering a robust physical and mechanical bond between plastic and metal and ensuring the integrity of the structure.
The laser-based (PMjoin) joint offers higher process flexibility compared to mechanical joints especially through the use of flexible beam guiding systems. Compared to adhesive bonding solutions, it can be much faster with high joint resistance and same flexibility, but without contaminant or deterioration risks.
Another important aim of this project fits with a general requirement for technical components, which is to achieve flexible automatic joining prototypes for dissimilar plastic-metal material combinations with short cycle times and a broad field of applications.
The PMjoin consortium comprised three large companies FAURECIA, Peugeot Citroën SA and VALEO, all end users from the automotive sector, LASEA as laser source integrator in industrial applications and ANDALTEC as high-tech SME supporting innovation in the plastic field. The consortium was complemented with FRAUNHOFER ILT, IK4-TEKNIKER and ARMINES, research Centers of excellence in laser, manufacturing and material characterisation topics.

Project Context and Objectives:
Nowadays, environmental and resource concerns together with customers’ demand of high functionality, have imposed strict requirements on industrial products. This would translate directly into higher manufacturing costs and reduced competitiveness, against the low labour cost of emerging countries, unless innovative design and production methodologies are used.
In the search for lightweight structures to slow down energy consumption, the transportation industry is increasingly interested in partially substituting steel with lighter materials. This fact is causing a large inclusion of non-metallic materials such as plastics (plain polymers, copolymers or reinforced polymers (composites)) in this industrial field, since they are 2.7 or 7.8 times lighter than aluminium or steel respectively. The evolution of material sharing between 2011 and 2020 presented by PSA Peugeot Citroën for vehicles confirms this reality, as is shown in Figure 1. However, metals cannot be excluded as fundamental base material from many applications. Thus, most (future) engineering structures or products will be made of several types of materials, with the advantages and functionalities of each one exploited to the full.
Metals are normally used to achieve high mechanical properties, such as high strength-toughness ratio, or to take advantage of certain physical properties, such as high thermal or electrical conductivity and high heat resistance. Meanwhile, plastic materials are principally used for their low weight, high corrosion resistance, insulation, excellent formability and greater design flexibility. When now using a combination of plastics and metals as construction materials, consideration must be given to how to join these dissimilar materials. This kind of joining in fact presents significantly different challenges from those associated with similar materials joining, due to the differences in chemical, mechanical and thermal properties of the materials in question.
Nowadays, the joining together of plastic and metallic materials uses different methods than those used for similar material joining. Most of these techniques however, involve a large number of fabrication steps. The methods currently robust enough for use in industry are:
-Adhesive bonding: A simple and flexible but non-environmentally friendly process that consists in introducing a chemical adhesive at the plastic-metal interface. These "glued" joints require extensive preparation, long curing times and they can suffer from deterioration by external influences and low mechanical resistance.
-Mechanical joining: There are a variety of mechanical joining processes, such as bolting, screwing, etc. All these processes require additional assembly elements, such as bolts, screws or rivets. Although these assembly methods produce joints with good mechanical performance, there are limitations in terms of poor flexibility in joint design (shape and position must be previously chosen) and low productivity rate.
-Mould-in joining (or over-moulding): A common technique where the metal part is introduced into the melted polymer during the plastic injection moulding operation. The main drawback is the hybrid part geometry restriction, which is given by the mould.
To overcome the aforementioned disadvantages, the direct thermal joining of plastic and metal may present a potential solution. It will lead on the one hand to the development of new, high-class products with completely new properties (scope), and on the other, the shortening of the process chain will lead to a more economical and faster production of existing and new products (scale) (see Figure 2).
The PMjoin project primarily aims to develop an innovative joining concept for Plastic and Metal (PM) materials using a direct non-contact laser joining process, without the need for additional (filler) materials, liquid/solid adhesive bonds or assembly elements, which offers a robust physical and mechanical bonding, and ensures the integrity of the structure.
The PMjoin laser joint offers higher process flexibility compared to mechanical joints, especially through the use of flexible beam guiding systems, by means of a fibre optic, scanning mirrors, etc. where the only limitation is the accessibility to the joining zone. Compared to adhesive solutions, the new direct laser joining technique is much faster with high joint mechanical performance and the same flexibility but without contaminant risks. Furthermore, in comparison to other fusion welding techniques, the precise control of the laser energy in the focal spot enables a good localised material processing, with minimum heat affected area, resulting in very small and accurately positioned joint seams on the overall part.
This new direct laser approach had not been developed for industrial use so far, and processes tested for joining plastic-metal combinations did not yet exist for commercial structures or components at the onset of the project.
Thus, another important aim of this project fitted with a general requirement for technical components, which is to achieve flexible automatic joining prototypes for dissimilar plastic-metal materials with short cycle times and a broad field of applications.
The PMjoin project concept is based on the application of laser sources with two main objectives:
1) to modify the surface of the metal (structuring) to prepare it for the joining of the plastic and
2) to obtain the laser joining between both materials based on a plastic melting, without phase transformation into the metal structure created.
In technical terms, the joining properties are governed mainly by:
▪ the kind of plastic (or composite); opaque or transparent
▪ the kind of metal
▪ the structuring on the metal and
▪ the laser irradiation conditions
In this project, consideration was given to the fact that plastics have low thermal conductivity (that means that heat remains concentrated in the laser-material interaction zone) and their optical properties depend on molecular composition, crystalline nature, the colour of the base material and pigments and on the wavelength of the incident laser radiation. In general terms, the basic plastic materials usually show over a 85% transmissivity when they are irradiated with near-infrared lasers such as Nd:YAG or Yb-fibre laser with a typical wavelength of 1.06μm, or Direct Diode lasers, with wavelengths between 808 and 980 nm. On the other hand, metals offer always laser-absorbing abilities, though with wide differences among them. Thus, at the irradiation area, the laser energy is transformed into heat because of the absorption of it at the metal interface, and by means of heat conduction, the plastic is subsequently heated and melted.
If plastics are optically “transparent” to the laser wavelength, the laser beam is focused on the metal surface, as it is transmitted through the plastic material (Figure 3 a). On the contrary, if plastics are optically “opaque” to the laser (in other words, absorb the laser wavelength), the laser beam has to be focused on the external surface of the metal component (Figure 3 b) and the heat conduction through the metal resulting in the plastic melting at the interface. Of course, this second approach consumes more laser power due to the extra energy needed to heat the metal sheet and by conduction to melt the polymer surface.
In both cases, an external pressure (force) with a defined holding time is applied during the thermal joining process to improve the thermal conduction between the parts and to push the molten plastic into the surface structures of the metal part. The joining is produced only at the boundary between the metal and the plastic, in a clean manner, getting a physical interconnection due to the molten polymer and a mechanical connection due to the inclusion of the melt material into the metal that results from interlocking with the surfaces microstructure. For many application, it is also important that the top surface of the plastic or metal is not damaged by the laser radiation.
To achieve a feasible Polymer-Metal laser joining in industrial terms, several technical aims had to be met:
- Modification of the metal surface to anchor the plastic material. This involved the study of the influence of different structuring strategies and patterns that allow the flow of the molten polymer into the metal.
- Selection of best suited laser sources for structuring and joining. This covered different kinds of pulsed or continuous laser sources with appropriate wavelengths and laser parameters depending on the materials to be joined, different laser beam shapes (spot, line,...) intensity distributions (Gaussian, Flat-Top,...) etc.
- Evaluation of the thermal and optical properties of the different material couples: transmittance, absorbance, thermal conductivity, decomposition or melting temperature, etc.
- Development of the best optical beam path. Design of suitable optical elements based on diffractive lenses or scanning optics to attain different beam shapes or heating geometries according to materials and applications requirements.
- Validation of efficient clamping or holding fixtures to carry out the proper joining.
- Definition of the initial design of the parts around the joining zone to achieve the required high-strength union.
- Online monitoring of the joining process in order to clarify the joining mechanisms and to detect possible defects.
- Union characterization. The existence of tight physical and mechanical bonding (that means an anchor effect) was demonstrated through high shear/or pull strengths and the evaluation of defects.
- Horizontal supporting activities based on advanced simulation methodologies that contribute to obtain the basic knowledge of the physical phenomena involved in the joint process, reducing the number of experimental essays and predicting the best processes conditions as well as the joint performance.
A summary of the technical advances and innovations accomplished within the PMjoin project, are shown in Figure 4.
Only through the integration of all this knowledge into a novel, monitored and automated laser joining technique for joining of hybrid polymer-metal material combinations, can the real industrial needs be satisfied. Thus, the final aim of the PMjoin project was to develop different plastic-metal joining strategies, through direct laser joining technologies using different beam qualities and scenarios, to obtain functional plastic-metal components
In the frame of this project, the study was limited to specific applications related to the automotive industry focused on the material and process characteristics with two main goals;
- to reduce the weight of the component introducing polymers where appropriate according to the requirements;
- to achieve design requests, which currently are difficult to or not obtained with the use of an extra adhesive product, mechanical joining or mould-in techniques, and that are easier to manufacture through the reduction in the number of pieces and manufacturing steps.
The chosen applications were in the field of automotive lighting, seating and door panels.

Project Results:
To achieve a successful Polymer-Metal laser-based joining technology in industrial terms, the following research activities were developed:

1. An experimental characterization of mechanical and physical properties of materials (metal and plastics) was carried out with two main aims. Firstly, to provide input into the simulation models. Secondly, to assure the quality and the suitability of the combined structuring and joining processes over test samples and prototype parts.
2. Concerning the modelling task, two different kinds of models were developed. On the one hand, a model able to predict optimum process parameters that yield the required polymer melting temperature and therefore to reduce the number of field tests. Additionally, a method to characterize the mechanical performance of the plastic-metal joint in correlation with the structuring parameters (e.g. structure density and microstructure geometry). The model of the behaviour allows an optimization of these parameters to maximize the performance of the joint in terms of strength in different load directions.
3. The influence of the micro-structuring parameters on the tensile-shear mechanical performance of the joint was studied for different material combination. Additionally, the optimal laser parameter window was obtained for the joining process and the different material combinations. Thus, the two possible laser joining methods were analysed (laser transmission and conductive joining) considering different laser irradiation strategies.
4. Once the process windows for the micro-structuring and joining processes were defined, the next step was focused on analysing the effect of monitoring and control of the laser power and material temperature during joining process. Also, the selected micro-structuring process window was analysed on prototype parts, which configuration was chosen based on the mechanical loads encountered in the real-life final application.
5. Demonstrator automotive lighting applications
6. Demonstrator automotive seating applications.
7. Demonstrator automotive structure applications- lateral reinforcement bar.
The main results achieved in the development of the listed work stages are described more in detail below.
1.- Material characterisation
The experimental characterization was focused on the optical, thermal and mechanical properties of both metal and plastic materials used by the end-users.
➢ The optical properties of materials were measured by UV/VIR/IS spectrophotometer resulting in the following characterisation: spectral total reflectance and transmittance for transparent polymers, spectral total reflectance for opaque materials, spectral absorbance inferred from the energy balance, evaluation of aforementioned magnitudes at available laser wavelengths.
➢ The following thermos-physical properties of materials were obtained via differential scanning calorimetry (DSC): glass transition point (s) for mainly amorphous polymers, melting point for polymer with higher degree of cristallinity, vicat softening point, degradation onset temperature and specific heats.
➢ The mechanical properties of both materials were measured by two Instron testing machines, obtaining the following mechanical properties: Young modulus, yield strength, maximum engineer strength, maximum true strength, and engineer strain at force maximum.

2.- Modelling
The main reason to develop models is the reduction in the number of field tests, because, by using numerical techniques, a considerable amount of parameters can be run in relatively short periods of time, in order to investigate their influence on the process.
Laser joining simulation models of dissimilar materials from different points of view: thermal, metal structuring and mechanical behaviour of the joint have been developed by the different labs. It allowed the prediction of laser joining parameters and mechanical response in future hybrid joining. Results from thermal, optical and mechanical materials characterization have fed the models.
Thermal simulation of the laser welding process of the metal-polymer parts
A finite element model was developed to simulate the temperature distribution during conduction (laser from metal side) and transmission (laser from polymer side) joining of polymer-metal parts. Knowing melting and degradation temperature of the polymers the simulations can be used to obtain processing windows for each specific material combination leading the experimental work. The following material combinations have been investigated:
• dual phase (DP1000, 1mm) steel and PA6+GF30 (4mm) (cond. joining),
• steel (20MnB5, 1mm) and PA6+GF30 (4mm) (cond. joining),
• Aluminum (A5182, 1mm) and PA66+GF30 (4mm) (cond. joining),
• stainless steel (X5 Cr Ni 18.10 1mm) and PC (1mm) (trans. joining).
The processing windows are given in terms of effective power density and effective interaction time. The power density is directly related to the laser power, while the interaction time is inverse to the feed rate. As an example the processing window for conduction joining of DP1000 and PA6+GF30 is shown in Figure 5.
With the information of the (simulated) processing windows the appropriate laser parameters (power, beam diameter, wavelength, etc.) and feed rate could be chosen for the joining process.
Structural mechanics simulations of the joint behaviour under stress
The mechanical behaviour of the joints for different micro-structuring conditions was simulated. This was done by simulating the response of a joined polymer-metal part under a load (force) using a FEM-solver of the structural mechanics equations. The geometry of a structure is parameterized by depth, width and under-cut formation. In the simulations the force is applied to one end of the polymer part, while the opposite end of the metal part is kept fix. For such a configuration the maximum stress occurring in the polymer is calculated giving the response to the load. The value of the maximum stress, calculated for specific join patterns, provided information about the joint's strength of the join. The following pattern items were varied: number of structures, distance between structures, structure geometry, thickness of the polymer part and mode of load application (simulation of tensile or peeling tests).
The simulations show that all items have an impact on the join strength to a certain extent. Besides of number and geometry of the structures, the distance between the structures and the thickness of the polymer evidence a relevant effect on the joint's mechanical performance.
This is documented in Figure 6, where a tensile test with a load of 1 kN is simulated and the maximum stress occurring in the polymer (PC) is calculated for polymer parts with 1 and 2 mm thickness.
The stress obtains a local minimum at a certain distance D meaning the strength of the join has a maximum there. Also the thickness of the polymer part has an influence on the strength.
For peeling tests the simulations showed a significant influence of the distribution of the structures on the maximum stress and, therefore, on the strength. As an example 10 structures (same structure as for tensile test) are distributed along 9 mm. The first (nearest to the force) and tenth structure remain at the same position, while the others vary. The variation is in such a way that the smallest distance occurs between first and second structure, the distance between the other structures is successively growing. So, if the first distance is very small, the last distance is very large.
The maximum tension is calculated for different distances between the first and second structure (Figure 7).
A non-equal distribution responds with less stress to the load than an equal distribution (dmin= 1000 µm) of the structures. The stress becomes smaller if the distance dmin gets smaller.
Structural mechanics simulations of the strain behaviour of a single structure
Two complementary studies have been performed to evaluate the effect of basic geometrical parameters of micro-structuring on plastic-metal joins in order to draw some useful conclusions about the most suitable groove geometry to get the best mechanical behaviour in plastic - metal joining. The plastic material considered in this study was PA – 30GF. The technical software used was ANSYS V14.5.7; ANSYS, Inc; PA, USA. These studies do not involve any experimental test to get a joining characterization.
The first study (study 1) was focused on evaluating the influence of angle α (defined between the horizontal axis and the wall surface of the groove (Figure 8a) on the joint's mechanical behaviour in terms of a tensile test. The values of angle α in the different geometrical models were: 0º, 5º, 10º, 15º, 20º, 25º, 30º, 35º, 40º and 45º.
As main conclusions we obtained the following:
- Angle α does not have a relevant impact on shear test values.
- The angle value (α) does not involve significant influence on joint's peeling properties.
- A deeper study in terms of friction influence would be useful in order to obtain a more reliable model.
- Experimental tests are required to correlate results obtained in this study with experimental data.
The study 2 performed a similar work but in this case the displacement was applied in “y” direction simulating a peeling test (Figure 8c) and an imposed movement of 0.16.
As it was expected the peeling forces increased when α angle was increased up to an asymptotic value (around α =60º). Friction coefficient and Friction Law could have a stronger impact than the assumed in this study. Therefore friction effect should be studied in deep. Experimental test need to be done to correlate these results (Figure 9)

Mechanical modelling of the joint at failure
The objective of modelling consisted in describing the mechanical behaviour of the joining weld. For that, Arcan-Mines test were performed considering certain groove geometry. Finite element calculations of the samples allowed to determine a modified Drucker Prager criterion describing first the plastic yield surface, and secondly the ultimate strength (breaking of the welded zone). This criterion function of I1, the trace of the stress tensor and J2 the Von Mises second invariant, is expressed as:
(J2)2 – βR02 + I1 (β-1) R0 = 0,
where β and R0 are specific constants depending on the tested material.
In term of application, the objective of this model was to be included in finite element calculations to design the industrial structures including welded zone which were proposed by the industrial partners of the project.
The first ARCAN-Mines test results were performed on specimens structured with a regular gap dcc=200 microns. We performed tests for four orientations, at 0°, 30º, 60º and 90°. The results are plotted in Figure 10. Usually the results of the tests oriented at 0° and 90°, give a good description of the criteria for all orientations.
Samples oriented at 30° and 60° are not broken in the join but outside close to anvils.
3.- Fundaments of micro-structuring and joining operations
The main goals of this task were:
▪ To study the feasibility to carry out both processes (micro-structuring and joining processes) for each material combination using the same laser source.
▪ To study the influence of structuring parameters on the mechanical performance of the joints.
▪ To study the influence of different laser sources on the micro-structure geometry and on the mechanical performance of the joints. To assess the influence of different irradiation methods for the joining operation on the joint's mechanical performance.
The following laser systems were used by the different partners:
Micro-structuring process: 200CW-Fiber Laser System and Nanosecond Fiber Laser System.
Joining process: 200CW-Fiber Laser System and 10kW High Power Diode Laser System.
Micro-structuring process: 1kW single mode fiber laser system.
Joining process: 3kW diode laser system
Joining process: 100W Fiber coupled diode laser system.

Micro-structuring process: 20W Femtosecond laser and 20W nanosecond pulsed fiber laser.
Joining process: 200W Fiber coupled diode laser system.
The joint configuration for the micro-structuring and subsequent joining process for each of the end-user applications was a lap-joint configuration (Figure 11). Different joining tests performed with different metal structuring patterns and strategies were analysed in terms of the joint's mechanical performance.

In the case of TEKNIKER the activity was focused on the following stages:
A) First stage: to study the possibility to carry out both operations (microstructuring and joining) with the same laser system (200W CW Fibre Laser System) and beam delivery optics to make easier and cheaper the whole process.
Table 1 shows that, in the cases of steel sheets having a thickness lower than 2 mm, it is possible to conduct the whole process with the same laser system (200W CW fibre laser system). However, for aluminium and cooper coated sheets high optical power levels are required during the joining process due to its high reflection percentage at the considered wavelength (requiring High Power Diode Laser). Likewise, with thicker steel samples 200W does not generate the enough energy to reach the metal-polymer interface. Furthermore, in the case of aluminium the micro-structuring process must be carried out by nanosecond pulsed laser system, allowing getting a successful micro-structuring on this sort of materials with ablation rates higher than other materials with pulsed wave.
Table 2 presents the failure force (Ffailure) achieved during the mechanical shear tests for the material combinations with possibility to carry out the whole process by the same laser system.

B) Second stage: to study the influence of structuring parameters on the tensile-shear mechanical performance of the joint. The study was conducted on HC420 + PA-GF30. With this aim, several set of trials were conducted considering the effect of different variables: geometry (width and depth), structure density (defined as the ratio of structured area to the overall examined area), clamping pressure and reduction of structuring time.
The main conclusions corresponding to the study are summarized as follows:
- There is a direct correlation between breaking force and aspect ratio (depth/width) of microstructures. For microstructure patterns conducted by nanosecond pulses, the results revealed two different regimes depending on the number of scans considered: for Ntracks<10 the breaking forces showed a linear correlation, however for Ntracks>10 the breaking values tend to achieve a threshold.
- Concerning the effect of structure density: the breaking force of the interface rises with decreasing the distance between groove centres.
- The joint's mechanical performance is independent of the applied clamping pressure in the range 0.5-6 bar.
Concerning cycle time: Figure 12 shows the breaking force of HC420+PA-GF30 as a function of the ablation rate (time required to microstructure 1cm2) for different microstructure geometries produced by nanosecond laser and CW fibre laser. The higher breaking forces were achieved when longer ablation rates were considered. It is possible to see that different breaking forces are found for the same ablation rate by different microstructure parameters.
The optimization step was performed in two different ways:
- In the case of micro-structures generated by nanosecond pulses, the focusing lens used for previous textured patterns were replaced by a lens with shorter focal length. Based on this, it was possible to obtain the same microstructure pattern by a smaller number of tracks and thus, shorten the processing time.
- Based on the previous results a new set of trials was carried out considering higher structure density values and lower number of tracks.
The results (Figure 13) suggest that, in the case of microstructures generated by nanosecond pulses, for a certain ablation rate T, the time inverted in increasing structure density (dc-c↓) has higher beneficial effect on the failure force than the time inverted in increasing Ntracks. However this trend is not clearly evidenced in the case of microstructures generated by CW laser system.
C) Third stage. It was focused on the study of the influence of three different irradiation methods for the joining operation on the joint's mechanical performance: contour, simultaneous and TWIST joining (Figure 14). The study has been conducted again on HC420 + PAGF30.
The tensile shear results (Figure 15) evidence that, the failure mode for almost all the joined samples was interfacial failure. However, in the five cases of joining corresponding to contour HDPL and ns-structuring, the failure occurred within the polymer and the bond was still intact. Therefore, it does not provide information about the ultimate failure force of the joining. For the rest of results, the bar plot shows the same trend for both kind of microstructure patterns. In both cases, the strategies that provide better results in the frame of this study are contour joining by CW Fibre Laser System and TWIST joining with HPDL.
D) Fourth stage. The activity was focused on the optimization of the joint's mechanical performance for different metal-plastic combinations of the rest of the applications. The micro-structuring parameters for the needed pre-treatment along with the suitable parameters for the joining operation have been chosen based on the results obtained from the previous stages.
Table 3 shows an overview of the mechanical performance of the plastic-metal joints listed in Table 1. In the cases of applications 8 (XSG+PA66-GF) and 9 (P260+PA66-GF), the conductive joining process was carried out by different laser systems for micro-structuring and joining operations. In the case of XSG+PA66-GF the results in terms of tensile shear strength are quite similar; the main difference between them is related to the cycle times. For P260+PA66-GF combination the results reveal a meaningful improvement when the nanosecond laser and diode laser system are used for structuring and joining operation respectively. The joined samples Al5182+ PA66-GF (application 11) provided the most desirable results: the failure took place by polymer yield far away from the interface. The ultimate failure force (7400N) provides a measurement of the polymer properties. In the case of Faurecia material combination 7 (HC420+PAGF30) different tensile shear strength values are found depending on the laser systems used for structuring and joining process.
In the case of ILT the laser source used for microstructuring is a water cooled IPG 1000 W single-mode cw fibre laser. The laser beam is guided through an optical fibre. It is a laser source which has a very high beam quality. The beam source is portable and of simple automation, therefore, it can be integrated on different machines, machining centres, robots, etc. The laser radiation is deflected by a galvanometric scanner to achieve different structure orientations. The focusing optic has a focal length of 330 mm, having the resulting spot a radius of 20 µm.
For the microstructuring process the following parameters are varied:
• Scan speed v [m/s],
• Laser power P [W],
• Number of iterations N [#]
• Distance between adjacent structures dc-c [µm]
The scan speed is varied for each material between 7.5 10 and 12.5 m/s and for each setting the laser power is varied among 500-1000 W at a constant structure distance of 300 µm. The number of iterations is varied between 2, 3 and 4 iterations. The influence of the number of iterations on the characteristics of the structure geometry is exemplarily shown in Figure 16.
The main objective for the microstructuring process is to produce reproducible, open structures with an undercut geometry to enable a good interlocking between polymer and metal. Another objective is to consider economic issues like short process times to reduce costs for an industrial application. This means that higher scan speeds and lower number of iterations are preferred.
A set of trials was carried out studying the effect of scan speed, laser power, number of iterations for 2-4 and the distance between pattern centres. This analysis has been carried out for the different metal parts: Al5182, Al6016, DX53, FR4, P260, XSG and HC420LA.
Figure 17 shows the cross section for XSG metal samples for number of iterations N4. Best results were achieved with scan speed between 10 and 12m/s and 750 to 1000W laser power. The minimum structure distance was chosen for 150 µm (Figure 18). Similar trend was found for the remaining metal samples.
In the subsequent laser based joining process the plastic is bound to the metal. Therefore metal and polymer specimen are arranged in an overlap configuration and a joining force is applied. The laser system used for the joining process is a Laserline GmbH LDM 3000-100, 3000 W continuous wave diode laser, operating at 900-1070 nm wavelength. The laser beam is guided through an optical fibre into a zoom optics device (Laserline GmbH) with a focal length of 250 mm. The zoom optics allows forming the laser beam into a rectangular shape. The spot size can be varied flexibly between 5x5 mm² and 30x16 mm². In order to apply pressure and fix the sample-arrangement a pneumatic clamping device with a specimen-holding fixture is used. The specimens are irradiated through the clamping frame from the metal side. A cross-jet with pressured air prevents the optics from contamination with process emissions.
The investigated joining parameters were laser power (P, W) and pulse duration (t, ms).
The joining process in this study was carried out via simultaneous irradiation with a zoom optics. The spot size was adapted to the structured area of the metal. The process parameters were chosen via variation of laser power and irradiation time. The determination of the laser joining parameters is exemplarily shown for material P260. The samples were irradiated with two different laser powers (1270 and 1710 W) and three different irradiation times (1500, 2000 and 2500 ms). The resulting shear tensile strengths are depicted in a bar diagram (Figure 19a). The joining parameters were chosen by high strength of the connection with low standard deviation and no decomposition of the material in the joining process.
The highest shear tensile strengths were achieved with parameters PF6 and PF5. A cross section of PF6 shows a formation of bubbles and therefore a decomposition of the polymer matrix material (see Figure 19b, red marked spots). Thus these conditions cannot be viable for a durable connection. However, a cross-section of PF5 does not show this kind of decomposition (Figure 20), therefore this parameter setting was chosen for further joining tests.
The resulting shear tensile strengths of joining tests are as followed:
HC 420 LA PAGF30 SD 200 µm (L) 19.2 MPa
P260 PA66 woven SD 200 µm (C) 20.5 MPa
XSG PA66 woven SD 200 µm (C) 17.8 MPa
6016 PA66 woven SD 300 µm (L) 12.3 MPa
5182 PA66 woven SD 300 µm (L) 14.1 MPa
FR4 PC SD 200 µm (L) 17.2 MPa
DX53 PPt20 SD 300 µm (L) 16.4 MPa

The research of LASEA was focused on the development of complex designs, taking advantage of the laser technology used. In a preliminary stage the objective in the task was based on the determination of the best ratio between micromachined and non-micromachined surfaces in order to reach the maximal resistance of the joining. These results were used later on the development of the mentioned complex designs.
In this task, LASEA also focused its research on the determination of the best design ensuring high tensile resistance for different kind of polymer/metal combinations. The study started by straight line design in order to observe the behaviour of a polymer/metal joining with a simple design of microstructures. After some joining tests performed with a 200W fibre guided laser, a selection of geometrical parameters was done. Once this choice was made, the designs were performed on all metallic plates and were sent to ANDALTEC to carry out the joining with their laser equipment.
LASEA continued its study with more complex designs firstly on X5CrNi stainless steel plates. A first selection of geometrical parameters was performed. After which, a set of 4 identical samples with the same microstructuration design and laser parameters was manufactured and sent to ANDALTEC for performing the joining and having a statistic study. After the identification of the most appropriate complex designs, LASEA performed the design on the other metal plates.
As shown in the Table 4, depending on the combination of polymer/metal joining the design inducing the highest resistance can vary but in general and for more reflective metals (Al for example) or the thin metal plates, the complex designs induce higher resistance. In this way, LASEA with ANDALTEC will patent the methodology followed for reaching complex designs and the designs inducing high tensile resistance.
The activity carried out by ANDALTEC consisted of an optimization of the joining parameters to achieve an efficient joining between metal and plastic. The laser used during this activity is a diode at 980 nm with a maximum output power of 105W. This laser is mounted on an ABB IRB1600 6 axis robot. The system has the possibility of applying pressure during operation thanks to a roller dispositive.
Different assays including both polymer-metal transmission and metal-polymer conductive joining processes were carried out in contour mode. The diameter of the spot was 3.8 mm and 2 welding lines were made in each joining test.
The joining parameters considered during optimization were: robot speed, pressure and power. Speed was maintained at 1 mm/s (the slowest value possible) and then the power was optimized within the range 20-100 Watts. Pressure was studied in the range 150-200 mbar. The joint's mechanical performance was assessed by tensile-shear test by a Universal testing machine Tinius Olsen.
A comprehensive study of the joint's mechanical performance was conducted based on the different structure design of Lasea.
The study was carried out for the different material combinations: DX53-PPt20, MnB5-PAGF30, MnB5-PPGF30, X5-PMMA, P260-PA66Woven, XSG-PA66Woven, DP600-PPGF30 DP1000-PPGF30 and AL-PC.
Table 4 summaries the highest values of ultimate shear strength reached for each material combination:
X5 – PMMA join was the unique case among those tested where plastic material broke before joining failure. It means joining between X5 and PMMA presents more resistance than PMMA itself. According to the results there is not a unique solution in terms of texturing. Depending on the application and plastic material involved there will be one specific texturing that will be more recommendable to carry out in order to optimize the PM join.
4.-Effect of monitoring on the join quality. Joining process on prototype parts
The first part of the task concerns the effect of optimizing the joints by process monitoring. Different approaches developed for monitoring and control of microstructuring and joining operations are herein summarized. Additionally, the results concerning the joint quality of representative joining configurations or prototype parts of the final application in the case of FAURECIA material combination were discussed.
Thermal monitoring
TEKNIKER carried out laser process control through infrared pyrometers and thermal camera in order to optimize the laser joining process. A close loop power-temperature control was introduced in order to maintain the temperature uniform along the laser joining seam tracks. Two devices were used: two colour pyrometer to maintain a uniform temperature on the irradiated material varying the laser power level during the joining process and an infrared thermal camera for monitoring the surface temperature map of the irradiated area.
The analysis was conducted on the material combination corresponding to the application 7 (HC420+PA-GF30): conductive joining. The joint's mechanical performance was assessed for two different joining conditions:
− Constant level power P=850W.
− T-P control considering a temperature set of 650ºC (data obtained from trials without T-P control).
Figure 21 illustrates the breaking force values of the polymer-metal join. The results do not suggest a significant improvement when the T-P control is considered. The results are not conclusive since the influence of the orientation of fibres prevails over the profit of the control and besides the length of the joining is very small.
Based on previous results, two set of additional trials were carried out:
- the study of the influence of the temperature-power control during the conductive joining process with longer joining areas (50x20mm2).
- the study of the influence of temperature-power control during laser transmission joining for the joining areas considered so far (10x20mm2).
But unfortunately in any case, the new results suggested a significant improvement when the T-P control is considered for the conditions studied at TEKNIKER.
ILT focused on the two following approaches for monitoring the joining process:
• Measuring the metal surface temperature for conductive joining process by infrared camera.
• Measuring temperature in interaction zone between polymer and metal by thermocouples.
To measure the surface temperature, the infrared Camera Optris PI160 is used. The camera has a wide temperature range from -20°C to 900°C. To measure the temperature in the interaction zone between polymer and metal a thermocouple is used. For the first thermocouple experiment the material combination: stainless steel (1.4301 1 mm) and PC (Makrolon®, 2 mm) was used. The metal was structured with the following parameters: laser power 750W, scan speed 10m/s, number of iterations 4, structure distance 300μm.
The whole joining area was irradiated simultaneously by an adaptable zoom optics. The parameters, laser power and irradiation time, were varied. The thermocouple was positioned in the middle of the structured area (Figure 22) measuring the maximum joining temperature in the joining zone. After joining, the specimens were tested by a tensile shear test and the breaking force determined.
The first joining parameters (510W, 1000ms irradiation time) provided a temperature in the joining zone of 129ºC. The tensile shear results (521±455N) led a low breaking force and high standard deviation. The second joining parameters (750 W, 1000 ms irradiation time) provided a joining temperature of 238ºC. The tensile shear results (1318±98N) led a better connection strength compared to the first joining parameters. This set up is quite easy to establish and the components are quite cheap. Because of this it is very suitable for industrial applications to find out good joining parameters for any material combination.
If the thermocouple is connected to a data logger, the temperature profile can be recorded. This set-up was tested for FAURECIA material combination (HC420LA + PAGF30). The thermocouple was positioned in the middle of the structured area, where the highest temperature was expected. The results showed that the temperature profile is a very important parameter to evaluate the gap bridging ability. By a longer period in which the melting temperature is exceeded, a bigger polymer volume is molten and can be used to bridge a gap.
On the other hand ANDALTEC used a Gentec-eo flash handheld probe (FLASH-500-55) in order to avoid differences between the real emitted and configured power. The goal was to control the proper melting of the polymer and also to avoid the plastic thermal degradation by using thermal sensor and Data Logger, temperature control system (label and heat sticks) to monitoring a range of temperature from 204°C to 260°C.
The heat sticks were used to monitor the degradation temperature of some selected polymers: 253°C, 399°C and 300°C for PPt20, PMMA and PC respectively.
Additionally, like ILT, Andaltec set thermal sensors between plastic and metal samples. The sensors collect the temperature values and send the information to a data logger in order to study the joining process. As one representative example, the results obtained during the joining between some DX53 metal plates with black PP 20% talc plastic samples are presented (Figure 23a).
Figure 23b discloses one example of the evolution of the temperature during a test. The maximum thermal value reached is 211.2 °C which is below the degradation temperature determined by Differential Scanning Calorimetry (DSC).
Joining process on Prototype parts
ILT manufactured and tested different specimens to find out the joint behaviour under different load orientation with the FAURECIA´s material combination (PA6-GF30 + HC420LA). The evaluation of these prototype parts is needed for the construction of the final demonstration parts. The different test specimens are shown in figure 24.
Several parameters were varied to find out the influence on the resulting bond strength within the microstructuring process: laser power, scan speed, number of iterations (N), distance between cavities (dc-c), structure orientation (lateral, parallel and crossed) and angle of incidence (θ). In summary the highest shear load was found for:
▪ Shear tension tests: N=4, θ=90º, dc-c=200μm
▪ Tensile tests: N=4, θ=45º, dc-c=200μm and linear, perpendicular orientation
▪ Peel and bending peel tests: they did no provided satisfying results. The maximum force under given experimental setup was not more than 400N. Thus, the peel forces should be avoided by the design.

TEKNIKER also manufactured and tested T prototype joined parts (Figure 25a), micro-structuring the metal with a different laser source emitting in the ns range in order to simulate the tensile or pull out force (Figure 25b) and to compare the results with those from ILT.
A comprehensive design of experiments was performed with the following micro-structure parameters (Figure 25c):
▪ Number of tracks: Ntracks=2, 4, directly related to the groove depth and width.
▪ Distance between groove centres: dc-c=200, 600µm.
▪ Alignment angle of the grooves θ=45º, 90º.
▪ Direction of structuring: longitudinal and transversal lines.
Concerning the joining process, contour strategy was considered using the CW Fibre Laser System and the following parameters: laser power 74W, joining speed 6mm/s, clamping pressure 3bar and spot diameter 1mm. The mechanical resistance of T-joints were checked by pull tests (Figure25b) considering two different polyamide thickness: 2.5 and 4mm.
The results revealed similar trends for the two polyamide thicknesses. In general terms, high values of standard deviation were found, ranging from 8% to 40%. It could be related to the small values of the contact areas. Furthermore, the following trends were identified:
▪ Clear influence of dc-c:
▪ There is no evidence of influence of structuring orientation (transversal or longitudinal) on the T-joints mechanical performance.
▪ An increase of the joint strength of about 27% was revealed for deeper grooves compared to shallower ones, keeping the remaining microstructure parameters constant.
▪ The influence of cavity angles θ, for a certain Ntracks, was negligible.
It can be concluded that the evolution of results with different lasers is quite similar, demonstrating the robustness of this kind of hybrid joining technology.

5.- Demonstrator: automotive lighting applications
This demonstrator, developed among VALEO, TEKNIKER, LASEA and ANDALTEC, consists of the assembly of the bulbholder of the rearlamp of the Renault Twingo. This rearlamp is a product manufactured by VALEO. The laser joining process is expected to be tested as alternative to the stamping + riveting process currently in use. Thus, the metal circuit of the bulbholder was joined to the plastic body by means of laser joining technology. The metal circuit is made of steel DX53 and the plastic of grey PP with 20% of talc.
Figure 27 a) and b) show a bulbholder with the riveted circuit (currently in use) and a bulbholder joined by laser respectively.
After removing the pins and texturing metal circuit both plastic and metal parts were totally ready to carry out the PMjoin process. The texturing was carried out by TEKNIKER and LASEA and the joining process mainly by ANDALTEC.
Texturing by TEKNIKER (T3):
A previous stage focused on selecting the optimum microstructuring parameters allowed to reach a balance between joint's mechanical performance and process time with continuous fibre laser system and following parameters: :
- Laser Power 200W
- Scanning speed v=7m/s.
- Distance between groove centres: 150 µm

Texturing by LASEA (T2):
LASEA textured the metal circuits by using a nanosecond pulsed fibre laser to generate a complex design:
- Laser Power 50W
- Pulse duration=100ns.

Laser joining process
This process was conducted by ANDALTEC with T2 and T3 conditions and to a lesser extent by TEKNIKER with only T3 condition. The main reason to conduct some joining trials at TEKNIKER was to analyze the feasibility to carried out the whole process (structuring and joining process) using a unique laser source.
Pins sinking test at ANDALTEC
The Pins sinking test defines the effort exerted on the pins of the circuit when the connector is assembled. The necessary force to sink the pins of the metal circuit in the plastic housing is tested by pushing all the pins at the same time. The minimum load capacity set by automotive manufacturers is 80N, considered as a minimum threshold load value to select the optimum microstructuring condition.
The results showed that only the texture T2 from TEKNIKER and the case of high power and small number of passes from LASEA fulfilled the requirements in terms of loading (>80N).
Figure28 shows a circuit textured by TEKNIKER. LASEA performed complex design on the metal part (but due to the desire of LASEA and ANDALTEC to protect the design, no image is showed here).
Based on the previous results, 50 metallic circuits were structured by the two set of microstructuring parameters by both LASEA and TEKNIKER and sent to ANDALTEC for the subsequent joining and validation operations
Validation plan
The validation plan was focused on elucidating by means of several tests the behaviour of the joined parts in those conditions that a bulbholder could suffer throughout its useful life.
Those tests carried out to validate the joining were selected based on end-users requirements. Specifically, the tests were chosen by studying thoroughly the VALEO standard validation plan for rear lamps. According to the bulbholder requirements and applications it was considered that the validation plan had to be based on the study of the following properties: mechanical strength, electrical behaviour, thermal resistance and physico-chemical properties. According to this, the tests which were included in the validation plan are listed below:
A. Pins sinking.
B. Resistance to fitting and removal.
C. Voltage drops.
D. Drop test resistance.
E. Resistance to heat with bulbs switched on.
F. Resistance to climatic cycling.
G. Behaviour in humid air.
H. Corrosion resistance.
All the tests of the validation plan for bulbholder demonstrator were carried out in ANDALTEC facilities.
The validation plan was developed with bulbholders and complete rear lamps (Figure 29). Some tests need to be done with the complete rear lamp because it reproduces real situations.
▪ All the bulbholders passed the tests. Therefore any shortcoming was found in terms of functionality preventing of dissuading the technology application in real parts.
▪ The Table 5 below shows a summary of the tests that have been carried out to develop the validation plan.

6.- Demonstrator: automotive seating applications
Design/ description of the demonstrator
The concept of the FAURECIA automotive backrest seat structure demonstrator is shown in Figure 30. Starting from an original steel backrest, the upper and lower cross-members, i.e. horizontal parts in Figure 30, are kept as they are, but the left and right steel side-members, i.e. the vertical parts in Figure 30 are replaced by composite side-members.
Performance evaluation of PMjoin process
FAURECIA carried out a detailed investigation into the process variables that influence the mechanical performance of the joint, i.e. tensile shear (following DIN EN 1465 for testing glued plastic parts), tensile pull (where there is no existing testing standard) and peel strength (DIN EN 28510 part 1 for testing glued plastic parts). The work was done in collaboration with TEKNIKER and ILT, where all samples were structured and joined.
In addition to the tensile shear tests done at room temperature, FAURECIA has also done additional climate chamber tests at -35˚C and +85 ˚C to determine the strength of the joints when using seats in different parts of the world. Likewise FAURECIA has done testing to determine the influence of humidity and a corrosive atmosphere on the mechanical performance of the PMjoin assembly. Finally the influence of the surface condition of the metal sample and the storage of the structured parts has also been analysed, showing a loss of mechanical strength of between 10 and 30% under the more aggressive conditions, meaning that safety factors are needed in the PMjoin design.
Manufacturing the demonstrators
For the structuring process, the same parameters were used for all joints by ILT. The parameters used are shown in the table below. The output power used was 750W.
For the structuring, only linear structures were used. In some areas of the backrest, this led to structures under an angle, as shown in Figure 31.
In total, twelve different joining areas were necessary for a complete backrest.
For the joining process, in a first step the recliners with mobile gusset sub-assemblies (which were welded beforehand at FAURECIA using conventional steel-steel laser welding) were joined with the composite side-members. The schematic setup of the parts inside jig is shown in Figure 32.
The contour welding process was applied and for each of the areas, the zoom optic was adjusted to focus 1000W of power into the maximum spot size available (30x16 mm²). The weld speed was adjusted for the mobile gusset to side-member joints, because of the thickness of the mobile gusset. To compensate the reduced heat conduction at the beginning of each joining step, the velocity of the laser radiation was also reduced for a few seconds.
In the last step of the manufacturing process, the PMjoin backrest was assembled to the steel cushion structure to get a complete seat structure for the validation (Figure 33).
In addition, a suspension mat, foam padding and seat covers were assembled, to ensure the correct positioning of the 95% dummy onto the seat for testing.
Seating validation tests
Two static tests and one dynamic test were performed. The static tests (Figure 34 and Figure 35) are to understand the behaviour of the seat in the event of a front and a rear crash. Both tests give a quantitative result, i.e. at what torque or at what force does the seat fail and how does a failure unfold? In contrast, the dynamic crash test shows what happens in real-life and gives a pass or fail report.
Static rear crash
Figure 34 below shows the set-up and a sequence of stills taken during the static rear test for one of the demonstrators tested.
The first of the tested structures failed in a-symmetrical way, with only the right gusset-to-side-member joint surviving the test. The left gusset was torn clean off the composite side-member. The latter was also the failure seen on both sides of the second backrest that was tested.
The torque recorded for the first tested backrest reached a maximum value of 1086Nm. The second one failed at a maximum torque of only 534Nm. Although the results do not match that of an all-steel structure, where the maximum torque recorded was close to 3000Nm, the behaviour shows promise. The premature failure was contributed to the variability of the conductive joining step of the PMjoin technique. If both sides of the structure were to perform in a similar way as the right hand side of the first tested structure, the maximum torque would have been higher. For that, a reliable closed-loop temperature-based feedback and a non-destructive test need to be developed.
Static front crash
Figure 35 below shows the set-up for the static front crash test.
The top cross-member in both cases broke clean off the rest of the backrest assembly. In addition to this, the joint at the lower (cross-member) back side also failed on both left and right hand side of the backrest, except for one side (RH) which was intact after the test of the second demonstrator. Closer inspection of the top cross-member joints shows how well the plastic had melted into the grooves. However, in some places there was also evidence of the plastic having been burnt, indicating overheating of the joint during the conductive joining step. Again, this shows the need for reliable closed-loop temperature-based feedback (and a non-destructive test for after the joining operation).
The maximum forces achieved for the two PMjoin demonstrators were 1.95 and 2.8kN compared with 4.05kN for an all-steel backrest. It is noteworthy that the all-steel structure performed exceptionally well, with the maximum force for a steel structure typically averaging around 3.2kN.
This means that for the static front crash test, one of the developed hybrid backrests achieved 89% of the steel version. Despite this very good result, the failure mode, i.e. the top cross-member breaking off clean, is unacceptable. This is, of course, related to stiffness of the composite side-members, as the steel equivalents absorb the pull load better as they bend. Further investigation into an improved design giving more flexibility during crash, is the recommended step here.
Dynamic rear crash
From the footage can be seen that the PMjoin backrest structure failed in the same a-symmetrical way as recorded for the rear static test of one of the tested PMjoin backrests. The tests show that the left gusset-to-side-member (front one) failed, whereas the right gusset-to-side-member (one at the far end from the camera) survived the crash.
Conclusions for the seating demonstrator
The results achieved confirm the technical feasibility of the PMjoin technique. Overall, the results are positive, but further work is needed to bring this technique onto the shop floor. In particular, the following further steps are to be considered:
▪ Redesign of the backrest to optimise the advantages offered by the PMjoin technique, thereby focussing in particular on:
o 2D joints: efficient clamping of a 3D joint during the conductive joining step will be challenging in a serial production environment.
o Avoiding peel loads: as confirmed by the coupon testing, the peel performance of the PMjoin technique remains low.
o Flexibility: the failure mode of the hybrid backrest is different from an all-steel structure and is determined by the rigid behaviour of the composite side-members; ways are to be explored to create a certain amount of flexing in the structure.
▪ The uncertainty of the conductive joining step was obvious from the testing of the seating demonstrator. The development of a reliable closed-loop temperature-based feedback is a recommended. In addition, a non-destructive test methodology needs to be developed to guarantee the joint quality.
7 Demonstrator: structure application-lateral reinforcement bar
The PSA demonstrator evaluates the hybrid joint between a metallic car door and a composite reinforcement bar. The demonstrator is a protection part in case of a lateral crash.
The main requirements for side impact beam are:
➢ lateral crash requirement
➢ painting process compatibility
➢ compatible with large scale production rates
➢ recyclability
The reinforcement bar consists of a biaxial orientated glass fabric sheet, which is embedded in a PA6.6 matrix. The thickness of the material is 1.5 mm. There are two joining areas on the metallic door. The metal material of the first areas A and B is P260 (Hinge side, thickness 1.76 mm), the second material for area C is XSG (Internal panel side, thickness 0.67 mm). The joining task is shown in Figure 36. Currently the reinforcement bar is joined with metallic inserts via spot welding. The influence of a more homogeneous power transmission enabled by the PMJoin approach on the joint performance has been investigated.
Furthermore for crash tests only a subset of the demonstrator was joined and validated. This subset consists of the reinforcement bar and the reinforcement hinge on the hinge side of the door.
The requirements for the joining areas were defined by PSA to compare the results with spot welding. For both joining zones on the hinge side (A and B), there is a required tensile shear force of 6710 N. For internal panel side (C), the required tensile shear force is 2*3900 N = 7800 N (for the two spot welds).
Microstructuring process
The laser source used for microstructuring is a water cooled IPG 1000 W single-mode cw fibre laser. The laser beam is guided through an optical fibre. For the considered materials (P260 and XSG) a comprehensive study was conducted considering different microstructuring parameters being finally selected the following two set of microstructuring options:
− Texturation A: P=750W, v=12.5m/s dc-c=300μm, N4, crossed.
− Texturation B: P=1000W, v=12.5m/s dc-c=300μm, N4, crossed.
The structured surfaces and the corresponding processing times are depicted in Figure 37.
Joining process
The laser system used for the joining process is a Laserline GmbH LDM 3000-100, 3000 W cw diode laser, operating at 900-1070 nm wavelength. The laser beam is guided through an optical fibre into a zoom optics device (Laserline GmbH) with a focal length of 250 mm. The selected joining parameters are showed in Figure 38.
The quantity of joined complete doors and subsets are summarized in Table 6.
Validation plan
The validation plan of PSA consists of three different types of tests:
➢ The first one is a lateral crash test, which was done with complete doors and the subsets with two different microstructuring parameters (named A and B) and two different joining areas (named big and small). For each set-up 3 doors and 3 subsets were be tested with only one exception.
➢ The second test is a door slamming durability test to validate the cyclically and long time performance of the joint. The door was opened and closed cyclically. The joint passes the test, if there is still a connection at the end. For this test, two doors were delivered to PSA. Slamming durability test was carried out on a vehicle: 100,000 cycles were realized and the holding of the assembling be observed every 5,000 cycles.
➢ The last test is a thermal differential dilatation test to simulate the painting shop crossing. One complete door is subjected to electrophoresis. The demonstrator is heated to a maximum temperature of 210°C during 30 minutes.
Crash test results
-Results of door sub-system crash test
To see any shifting of the reinforcement, a reference was marked.
For all doors, the reinforcement shifted in his position between the reinforcement and the door skin; proof of the joining rupture after the crash test (Figure 39).

As conclusion:
➢ A good global behaviour of the door subsystem was observed
➢ The target was not achieved because no joining rupture are tolerated
➢ The joining broke but after the cracks of composite
-Results of partial sub-system crash test
All laser joining had a rupture with a disjoining of the composite with no more polymer in the texturing. The test showed a solicitation of the joining in tensile shear and tensile pure.
On the diagram (Figure 40), the different tests showed that the texturing B and the greater surface had the best result. The maximal strength of laser joining was definitely below the maximal strength of spot welding. An increase of the joining surface improved the mechanical behaviour of the laser joining. An extrapolation allows us to expect to achieve the target (spot welding).
-Slamming fatigue test results
The slamming fatigue was performed on two doors. The test finished without seeing any breaking on the joining area and no disjoining (Figure 41).
The laser based joining process is robust due to mechanical interlocking.
Good tensile shear strengths for both PSA material combinations were achieved in the case of
➢ P260 20.5 N/mm²
➢ XSG 17.8 N/mm²
Demonstrator mechanical behaviour
➢ Crash test
• The global mechanical behaviour of laser join should be good in coherence with join surface
• The maximal strength of the joins on the demonstrator are too low to valid the concept
➢ Slamming Fatigue test
• No disjoining observed during the slamming fatigue test
The mechanical behaviour of PSA demonstrator is not as good as needed, but a good perspective is expected with a adapted design to achieve the joining surface target.

Potential Impact:
General impact
Although the PMjoin technique was developed and demonstrated for automotive applications only, it can be applied to any industry investigating the advantages of plastic-metal hybrid components, such as for instance the electronics or aerospace industries.
The main impact of the present project is related to the introduction of lightweight components in the automotive sector directly affecting the Environmental sustainability of vehicles and reducing the resource consumption and waste generation, through the minimization of fuel consumption and its indirect emissions. This fact is aligned with the Regulation (EU) No 333/2014 of the European Parliament and of the Council of 11 March 2014 amending Regulation (EC) No 443/2009 to define the modalities for reaching the 2020 target to reduce CO2 emissions from new passenger cars. The project helps to the replacement of some steel parts by plastics or composites, besides the use of clean laser methods to join these plastic parts with remaining metal parts avoiding contaminant adhesives and associated volatile emission of traditional adhesive methods or assembly elements of traditional mechanical methods.
By the use of hybrid materials (plastic-metal) savings in weight of 40% and more could be achieved for some components. For instance, the introduction of the composite PA-66 + glass fabric 50%vol., allows the reduction of 40% in mass of the lateral reinforcement bar of the door (compared with steel).
In particular, the use of pure steel alloy materials can be reduced which facilitates the weight saving in automotive parts.
In this context, it must be mentioned that during the last years, the evolution of mass in European vehicles has risen gradually. The reason has been the integration of new products and devices in the passive safety, comfort, performance and equipment (ABS, air conditioning, etc.) and also increment of the vehicle size. However, the mass evolution in PSA vehicles, for instance, has shown a slight decrease since 2009, as shown in Figure 42, and the tendency is clearly to continue. Nowadays, the priority is to reduce the mass of each new vehicle and it is considered as an environmental imperative (according to the Corporate Average Fuel Economy CAFE 2020) to achieve reduction of (80-100) kg in mass immediately and 100 kg in the next 10 years. Thus, the replacement of certain steel parts of the vehicle by plastic composites goes in this line. In fact, Peugeot has reduced 100 kg in the model 208/207 and 140 kg in the new 308 reaching the challenge of CO2 emissions of less than 95 g/km by 2020. It is estimated that a reduction in mass of 110kg corresponds to a save of 5g of CO2. So the target in Peugeot is to have reached a reduction of 110 Kg in 2015 and a reduction of 220Kg in 2017/18.
PSA also asserts that there is a lot of room for composite materials by replacing steel especially in chassis suspension and body in white. For cost and technology reason, « 2020 » cars will be designed with a mix of steels, aluminiums and plastics / composites. This fact is pushing Tiers 1 like Faurecia and Valeo to move in the same direction.
This project will impact on a sustainable Road transport (represented by Faurecia, Valeo and PSA partners), one of the major sectors of European industry, manufacturing over a third of all passenger cars produced worldwide (750 millions cars). According to Eurostat, the transport industry directly employs more than 10 million people, accounting for 4.5% of total employment, and represents 4.6% of GDP (EU’s Gross Domestic Product). Manufacture of transport equipment provides an additional 1.7% GDP and 1.5% employment.
Another remarkable impact comes from the Economical sustainability of manufacturing, through the reduction in the number of manufacturing steps; mechanical interconnects and manufacturing operations by means of the development of more simple products.
New skills in the European workforce resulting also in indirect socio-economic benefits; the incorporation of this novel joining alternative in an industrial scenario entails the capture of new abilities by end-users. Dissemination tasks included in this project have transferred the acquired knowledge into several manufacturing sectors that can also benefit from this technology. Thus the impact will spread out the Manufacturing Sector. Manufacturing is still the driving force of the European economy. The manufacturing industry produces approximately 80 % of the EU’s exports – worth about €1.8 trillion in 2013. It involves around 2 million enterprises largely dominated by SMEs across the EU, employs about 30 million people directly (and another 40-60 million indirectly) contributing 15.1% of GDP.
There are 10 Project Results (Table 7) which have commercial/social significance in this automotive market and can be exploited as a stand-alone product, process, service, although some of them might need after the project further R&D, prototyping, engineering, validation etc... before they become commercially exploitable.
In the PMjoin project, four demonstrators were built using the knowledge gained through the project, all of which were related to the automotive sector.
Detailed Impact on developed demonstrators
- Demonstrator 1a for automotive lighting applications: Electric circuit board onto PP bulb holder
• Reduction of manufacturing costs because of the removal of manufacturing steps and scrap reduction
• Riveting involves 3 stations: heating, riveting + cutting and control where heating limits the production cycle to 70 s. With the new laser joining alternative this time is expected to shorten to 30s and the production rate to increase from 103 parts/h to 240 p/h giving cost savings about 57% per part that means 45000 €/year.
• New bulbholder designs will have less design constrains thanks to this new joining technology.
- Demonstrator 1b for automotive lighting applications: LED board on reflector
• Increased overall quality in terms of repetitively, tolerances, photometric properties and scrap.
• For example an annual production of Audi A6 consists of c.a. 40000 cars/year. The cost of each rear lamp is around 40€. If scrap could be reduced from 6% to 2% through the implementation of the expected PMjoin technology, this could save around 0.8 € per each rear lamp. Therefore the total saving per car ranges 1.6 € and for all cars 64000 €/year total saving costs can be obtained.
- Demonstrator 3 for laser PMjoin of automotive seating applications
At the moment, no plastic-to-metal backrest structures are in existence within Faurecia’s seating division. However, the results from the PMjoin project have shown the potential of the laser-based micro-structuring and (conductive) joining technique. The backrest structure was chosen as a demonstrator as it is a highly visible product within the company and its potential customers. It is still some time however, before a multi-material structure as the one represented by the seating demonstrator, will find its way into a high volume serial production. Nevertheless, there are a range of (less ‘visible’) subassemblies of the seat structure where the combination of steel with plastic/composite has a technical as well as a commercial advantage. For these subassemblies, the time to market is considerably shorter, and business cases will be prepared for these subassemblies o be manufactured using the PMjoin technology. Through a gradual introduction of the PMjoin technology for plastic-metal joining, it is estimated that the technique will contribute to a weight saving, compared with a current all-steel seat structure, of between 5 and 10% by 2020. For a more general acceptance in the automotive industry of composite as a replacement of steel components, the cost of the (manufacturing of the) composite alternative still has a long way to go.

Cost impacts
For Demonstrator 1 the operating cost for the PMjoin process is higher than those obtained for the current process. Nevertheless the laser joining is better in terms of tooling cost. For this application it can be concluded that is not recommended to use the new process under the given scenario.
In the case of Demonstrator 2, the current process is more cost-efficient than the PMjoin one. The main reason is the high equipment cost of the PMjoin approach. By increasing the number of units per year this could be minimized. In addition is worthy to mention that for this case the time cycle for PMjoin process is shorter than the current one.
The total operating cost for Demonstrator 3 (without labour) is close to 7 times higher than the current manufacturing cycle, taking into account only the operations that are different. The use of a multi-cavity tool for injection-moulding and a different heat source for the conductive joining (e.g. induction) should be considered to bring this cost down. Nonetheless, in the short term, the cost of a PMjoin based technology for serial production of hybrid backrests will remain much higher than the conventional manufacturing, so this will have to be offset against other advantages the hybrid backrest offers, such as weight saving or improved design flexibility (compared with steel side-members).
As an overall conclusion, the total operation cost is higher for the PMjoin process in comparison with the current joining technologies for the demonstrators developed in this project. Some additional efforts will be essential to facilitate the industrialization of the developed process. With the cost study, the PMjoin project has already identified some improvement areas, which can be summarized as follows:

• Redesign the new part specifically to suit this new joining technology. In this way, we could save material and achieve a significant reduction of the time cycle.
• Increasing the number of parts to be manufactured. In order to reduce the negative effect in the analysis of the high equipment amortization costs.
• The technology is only in the beginning and high improvement opportunities exist for reducing the manufacturing cost such as automation and tooling improvements.
• In the case of PSA and Faurecia, one of the main limitations is the investment in new equipment. This could be minimized by increasing the units/year rate.

Environmental impacts
In the case of Demonstrator 1, the environmental impact is quite similar between the current joining process of riveting and stamping and the PMjoin process but any of the parts have been adapted to the new process. Nevertheless the new laser plastic-metal joining process requires less mechanical effort than the current joining processes, so the plastic and metal parts are probably oversized. So a redesign of these two parts would improve the new PMjoin processes’ environmental impact.
In the case of Demonstrator 2, there is an impressive environmental impact reduction with the new PMjoin process (87% of decrease) in comparison to steel-steel spot welding where the cutting of the holes in the bar and the introduction of inserts widely worsen this factor. Moreover, the decrease takes place in all environmental aspects. The biggest impact reduction is obviously detected in the metal depletion, coming from removing the mild steel insert manufacturing step and energy consumption coming from the avoidance of the water jet cutting process. Other positive effects are relevant on: Climate Change affecting Human health and Ecosystems, Human toxicity, Particulate matter and fossil depletion.
In the case of Demonstrator 3, the total environmental impact of the new PMjoin process is almost similar to the environmental impact of the current process. But, it is observed that depending on the impact category, the environmental impact of each process is more favourable: while in the new PMjoin process the impacts in the fossil depletion or climate change (human health) are more important, the current process affects much more in the metal depletion category, human toxicity and particulate matter. Nevertheless the higher difference on environmental categories (taking into account both processes) is logically in the metal depletion. At this point, it is worth mentioning that the environmental impact of the joining steps in an isolated way decreases with the PMjoin process: in the current process, the impact reached a 3.83 % (‘welding’) and in the new PMjoin process the impact is 0.711% (‘Laser micro-texturing’ and ‘Laser joining’).Consequently, it can be concluded that the environmental impact of the new process is not lower because the manufacturing process of composite side-member causes a higher impact than the manufacturing process of steel side-members.

Explotation and Dissemination
The initial exploitation plan of the industrial end-users has been established during the project and can be found in the section B (confidential). Some internal agreements have been signed between the partners of the project for the exploitation of the results.
On the other hand the project has used ‘standard’ dissemination mechanisms, as flyers, press releases, presence in media, congresses and scientific publications. A complete list of dissemination and actions is presented later in this document.
This is an ongoing process beyond the end of the project. In fact, the validation of results has taken place during the last year in the project, so the preparation of papers and publications based on these results will take some time.
Furthermore the project has collaborated in different clustering activities proposed by the European Union:
• -Material modeling cluster providing information about thermal and mechanical simulation models of PMjoin
• -Joining dissimilar materials cluster during 2 workshops, sharing project results with the other 2 projects dealing with this issue and running in parallel in the same European Programme.
• -Engineering and Upscaling Cluster providing information required by the European Union to elaborate the roadmap

List of Websites:
More information is available in or can be requested by writing to the coordinator
The list of participants and their web pages links are available through the project website