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ASSESSMENT OF ADDITIVE MANUFACTURING LIMITS FOR ECO-DESIGN OPTIMIZATION IN HEAT EXCHANGERS

Periodic Reporting for period 1 - AManECO (ASSESSMENT OF ADDITIVE MANUFACTURING LIMITS FOR ECO-DESIGN OPTIMIZATION IN HEAT EXCHANGERS)

Reporting period: 2019-10-01 to 2021-03-31

At a time when the aeronautical industry is investing about 70% of Research and Technology spending on making air transport increasingly environmentally-friendly, the next generation of engines will be giving off far more heat than their current counterparts. One of the challenges will be to optimize management of these rising heat levels, by drawing heat off from where it is generated, reusing as much as possible and dissipating the rest. AManECO project is aligned with the development of heat recovery solutions using very high-efficiency heat exchangers, with innovative designs and manufacturing methods such as metal additive manufacturing and experimental testing. These future generation of heat exchangers will supplement the actual HX designs, traditional manufactured for oil equipment products and will enable aircraft engines manufacturer´s, like SAFRAN, to strengthen its position as world leader in this type of complex parts.
AManECO aims to create a new design of HX after discovering the real limits of the metal AM and in particular laser powder bed fusion technology, in terms of thins geometries manufactured with INCO718 and AlSi7Mg0.6 alloys. In order to evaluate the maturity of the technology after finishing the project and a result, AManECO will propose a methodology able to create a HX design in accordance with ECO-Design TA in CS2.

AM has a great potential in terms of parts design and optimization in the field of aero-engines in particular advanced gear turbofans and high efficiency engines where an increased amount of energy has to be dissipated in cooling fluids. In this project the target are the heat exchangers and heat recovery systems optimization through the investigation of advanced AM techniques and tools. Unfortunately, a gap still exists between these structures optimized at computer scale and the industrial reality: the lack of fundamental knowledge of AM limits in terms of microstructures, surface quality, geometrical accuracy, thin features and associated performances may lead optimization tools to propose unrealistic structures at a real life level: high pressure losses due to roughness, mechanical failures due to wall thickness, the boundary limits of the process (i.e. the acceptable limits in terms of optimization potential with respect to final properties of the parts) have to be known in order to take them into account in the optimization software and, as a consequence, avoid time loss in the conception phase.

The work proposed in AManECO aims at optimizing the SLM manufacturing process of HX on several points:
- Allowing to assess the potential of SLM to design and build parts with radically new architecture, based on the knowledge to be developed and considering the Eco-design aspects.
- Allowing to optimize the conception phase of heat exchangers reducing this development time/cost/energy by assessing the limits of SLM technology, in terms of wall thickness, holes/gaps, overhang angle, thin layers, surface finish, etc., and include these limits in the design tools.
- Allowing an optimization of material used (AlSi7Mg0.6 and INCO718) for the same efficiency, by finding for instance the optimal wall thickness in heat exchangers or new shapes with improved heat transfer capacity.

Selective Laser Melting (SLM) is key for improved design and production process of aviation parts. Applied to heat exchangers (HX), it could dramatically improve global eco-efficiency through access to radically new designs and open horizons in terms of shape, weight, efficiency. Nevertheless, some questions need to be solved regarding capability of Additive Manufacturing (AM) to manufacture thin walls, small holes/gaps, low overhang angle, resulting surface roughness and mechanical strength. AManECO aims to enhance knowledge of metal AM and, specifically, the capability of SLM process to manufacture thin layers and wall thickness with adequate surface finish using AlSi7Mg0.6 and INCO 718 materials. In particular, to investigate aerothermal and mechanical performance of thin walls, to predict them in the design of AM-HX and consequently, be able to optimize the HX´s design process in an Eco-friendly way after knowing, the limits of the metal AM technology.

AManECO will enable to:
- Increase efficiency of HX up to 10%.
- Reduce the overall of HX manufacturing costs by 30%.
- Reduce material waste and scraps by 15 % per component.
- Reduce time-to market up to 1 month.
During the first periodic report different type of samples were designed with the aim to be characterized in different ways. Specifically, three type of samples were designed to be characterized in terms of surface properties, pressure resistance and gas tightness evaluation and equivalent stiffness assessment. All samples were manufactured in AlSi7Mg0.6 and INCO 718 materials in order to assess the minimum wall thickness achieved by SLM technology and the influence of this wall thickness on the samples properties. In addition, Finite Element Simulations were performed to predict the pressure resistance. These results were in line with the obtained experimental data.

A surface treatment was optimized for each material with the aim of reducing the roughness and improving the mechanical and aerothermal behaviour.

Thinner wall thicknesses than the current state of the art were achieved for AlSi7Mg0.6 and INCO 718 materials. These low wall thickness are able to withstand enough pressure proof for the aircraft application. In addition, the achieved equivalent yield strength and ultimate tensile strength are good enough for the application. Samples with higher wall thicknesses shows the better performance in terms of pressure proof and equivalent stiffness characterization. The surface treatments do not improve the mechanical behaviour of the samples, probably due to the reduction of samples’ wall thickness.

On the other hand, the design of a sample for aerothermal characterization is almost developed and the test bench prepared for this characterization.

The strategy for the final Eco-assessment was defined as well as questionnaires. In addition, LCI data collection was performed in all samples of both materials except for the samples intended for aerothermal characterization.
Lower wall thicknesses than those achieved in the current state of the art were achieved for SLM processing of AlSi7Mg0.6 and INCO 718 samples. This will allow to improve the efficiency of the final heat exchangers enabling a weight reduction.

Lighter and more compact heat exchangers will contribute to decrease the aircraft weight and increase the efficiency of thermal management systems. As a result, CO2 emissions will be reduced as well as fuel consumption. Thus, less GHG gasses will be emitted and fuel costs will be reduced. AMANECO is in line with EU policy aiming at reducing emissions from the aviation sector to address environmental aspects and societal needs.
E4 samples manufactured by SLM for equivalent stiffness characterization
E3 samples manufactured by SLM for gas tightness and pressure proof evaluation