Composite materials are increasingly used in high volume automotive applications, usually as a replacement for assemblies of multiple metallic parts such as stamped and spot-welded steel sheets. One of the motivations is to reduce tooling and assembly costs, in particular at lower production volumes. Other key driving forces are increased styling freedom, reduced system cost and weight reduction. With soaring fuel prices and environmental focus on CO2 emissions, reducing vehicle mass is presently a major concern for the automotive industry. Nearly all the composites used for high production volume automotive applications today are based on short or medium length random glass fibre technologies. However, there is a great interest in extending the range of materials and processes to advanced composites (continuous aligned fibre and high fibre volume fraction materials) as they would enable superior mass specific properties compared with metals, resulting in substantial weight savings. Advanced structural composites have, however, not seen widespread use in high volume automotive applications due to a series of inhibiting factors. These typically comprise higher cost and risk when compared with standard metal forming solutions. Novel composite technologies target some of the current drawbacks, but need to mature before being widely accepted in the high volume market. It is therefore necessary to not only evaluate and develop these technologies further, but also to propose practical tools to evaluate their performance and risk level, until they reach a state where their mechanical and economic performance clearly outweighs the risks associated with their implementation. The present work aims at developing a methodology to facilitate the evaluation of new composites manufacturing technologies, while at the same time decreasing the risks associated with implementation. A second objective is to identify suitable composite material and process technologies, which will offer competitive economic and performance gains. An evaluation methodology is thus proposed and validated with a practical case study based on the analysis of two novel structural composite processes for high volume automotive components. A spare wheel well was chosen as the demonstrator since it is a structural component and is assembled as a bolt-on part, making integration within the vehicle easier. Weight assumptions, which are used as performance criteria for all examined materials, have been obtained through extensive design and FEA studies for both strength and stiffness based criteria. Cost, discounted part price, investment and other figures of merit are used as economic performance criteria and have been established through novel technical cost evaluation techniques. The presented methodology manages uncertainties and evaluates performance, and is used as a basis for establishing relations between opportunities and risks. To achieve this, tools are introduced which support the evaluation methodology, notably: Risk based costing, including probabilistic distributions for input data to measure the quality of the results, Discounted technical economic modelling, including time value of money in the technical cost assessment to point out commercially focused effects of investments, discount rates and returns, Multi-objective optimisation, providing improved control with trade-off situations. For the case study, established as well as emerging processing technologies have been evaluated to serve as benchmarks for the study of two novel composite technologies. The analysis showed that the economic performance of currently used composite technologies is severely impeded by a high material cost in the final products and in some cases by long cycle times. It is also shown that the lower investment, when compared with metal stamping, can make such technologies favourable, especially for smaller series parts, despite the base material cost being higher. New technologies showed potential for improving the economic performance further; however, high discount rates due to risk impede commercialisation. Composites generally improved the weight performance compared with mild steel, especially for strength based designs. For the spare wheel well, the processing limitations, in particular the minimum achievable part thickness, were found to limit weight reduction substantially, giving unnecessary high properties. Thermoset materials showed more consistent weight reduction between low and high temperatures, followed by PA and then PP based composites. In conclusion, the technology assessment methodology presented here is intended for implementation in an industrial environment, where it will define common objectives facilitating better communication between engineering and management. This will in turn lead to an improvement in the efficient use of resources. In addition, it has been used to identify and develop supporting tools to aid assessment of technologies and to show techno-economic effects that are valuable in an industrial context. Finally, emerging composite technologies, where the base material constituents are combined together in a direct forming process, have been evaluated. The results have shown how the supply chain can be streamlined by avoiding for example, separate weaving and needling steps, improving the overall cost performance and providing the system supplier with improved leverage.
EPFL2008
