INFLUENCES OF PROCESS PARAMETERS ON THE MECHANICAL PROPERTIES OF HYBRID SHEET METAL-FRP-COMPOSITES MANUFACTURED BY PREPREG PRESS TECHNOLOGY

The aim of lightweight design is to reduce the mass of a product or structure while keeping the material properties on a constant level. With this approach it is possible to decrease the energy consumption and emissions of vehicles, for example. For a few years in the field of automotive lightweight design a trend towards tailored and/or multi-material respectively hybrid structures is obvious. Tailored components can be realised by the use of high-strength metal alloys like 22MnB5 and modern process technologies like partial press hardening or partial inductive hardening. Multi-material structures characterise a combination of two or more materials on a component level. A well-known example is the so called "Erlanger Beam". Here, a sheet metal hat structure is combined with a polymer ribbing to improve the mechanical properties while the weight decreases up to 30 %. In contrast to multi-material systems hybrid materials or structures are defined as a combination of different materials on a material level. That means, i. e. sheet metal and fibre reinforced plastics (FRP) are extensively joined together usually by adhesive bonding. The prepreg press technology is one approach to manufacture hybrid structures. Hybrid components include a lightweight potential up to 50 % compared to sheet metal structures corresponding to boundary conditions like the load situation or geometrical constraints. Current research work at the Chair for Automotive Lightweight Construction at the University of Paderborn concentrates on the investigation of hybrid materials and their processing. In particular, new manufacturing processes like the prepreg press technology are developed in order to enhance the attractiveness and availability of hybrid components for automotive mass production. This includes, for example, trimming process chains, reducing cycle times and thus a reduction of process steps and costs. In addition, various combinations of hybrid materials are examined based on material and component tests. This paper will show basic technological investigations in the field of prepreg press technology. In this process the prepreg is directly pressed onto a formed sheet metal structure and pre-cured for about 90 to 120 s. The post-curing is realised in an anyway downstream cataphoretic dip painting process. The bonding is realised by the use of the epoxy resin as an adhesive. With expected cycle times of less than five minutes the developed approach for manufacturing locally reinforced components is one possibility to solve the challenges of high-volume manufacturing in the field of CFRP. In the available paper the optimisation of process parameters (pressure, time, and temperature) will be discussed. The focus is to identify influences i. e. on the mechanical properties, e. g. (bending) strength or adhesion properties. The results are adequate process windows for the prepreg press technology regarding varying boundary conditions or different aims (costs vs. properties/quality).