Integral versus differential design for high-volume manufacturing of composite structures

In order to decrease the weight of the automotive body structure and increase the energy efficiency of future cars, attention is now turning towards structural composites, mainly carbon fibre-reinforced plastics. Composites have several advantages such as their excellent weight-specific properties and the possibility to be manufactured in large integral designs for a reduced weight and potentially lower cost. However, carbon fibre composites are expensive and for a cost sensitive industry such as the automotive industry, the challenge lies in creating a favourable business case with a well-balanced trade-off between weight and cost. A method is proposed to visualise the cost and weight advantages of either pursuing an integral design or a differential design, i.e. dividing the structure into a greater number of parts that are later assembled. The method focuses on the impact on cost and weight and considers structures with different part sizes and geometrical complexities. It is shown that, depending on the manufacturing process and series volume, larger and more complex parts may become more cost effective when divided into several, later-joined sub-parts. However, for smaller and/or less complex shapes, an integral design solution is always the best choice.