Inexpensive and resource-efficient lightweight construction is the challenge which is faced by a team of specialists from Ticona, the engineering polymers business of Celanese, from the Fraunhofer Institute for Chemical Technology (ICT) and the engineering company Edag. Their objective: the design and prototyping of a weight-optimised commercial vehicle storage compartment flap. The example chosen was a reinforcement frame using novel materials combined with the technology for the laying of thermoplastic tape which makes optimal use of the properties inherent in the material.
Polypropylene (PP) was used as the matrix material and unidirectional oriented glass fibres (UD-GF) for the reinforcing inlay in the form of what are known as UD-tapes. Sebastian Baumgärtner from the Fraunhofer ICT explains the procedure: “By processing the structure optimised in the 3D space at the 2D level, we were able to generate a flat inlay in the first process step using a tape laying machine; this flat inlay was consolidated thermally and can then be processed as a component-optimised semi-finished product”.
If components such as this reinforcing inlay have a frame-like structure, this step could have large material-saving potential. UD-tapes are only laid in the component sections in which they are required, thus reducing waste, depending on component geometry.
“In the downstream thermoplastic shaping process, the consolidated inlay is then heated in an infrared heater within the melting range of the matrix material and then shaped in a mould to form the structural component”, Manfred Reif, Application Development Engineer Composites at Ticona, explains the further process steps. “Water jet cutters then trim the fibre composite component and make the assembly and function holes. The steel outer skin is then joined to the composite structure by roll hemming in the final assembly”.
Positive conclusion: there was a considerable weight saving in the component demonstrated when compared to the steel construction currently used today. A solution was found that is also economical for small production runs thanks to lower tool costs. Savings can also be made by designing the component taking the loads into account. Material use is thus minimised, and further savings can be generated by using the comparatively inexpensive material combination PP-GF70.