Development of a manufacturing process for mass production of thermoplastic, continuous fiber reinforced sandwich parts with a structured core

The sandwich construction with cover layers made of continuous fiber reinforced plastics and structured honeycomb core is the most efficient lightweight construction technology to realize components with minimal weight and maximum mechanical performance. Lengthy production times are still the limiting factor of this lightweight construction technology for cost sensitive markets with large production scales. To close this gap a novel multistage thermoforming process was developed for the processing of flat thermoplastic fiber reinforced sandwich panels into complex shaped sandwich parts in fully automatic manner.

The multistage thermoforming process consists of three main steps, heating of a flat sandwich panel via infrared radiation, robot-guided transfer of the panel into the cavity and thermoforming. The thermoforming step is also divided into three sub-process steps. These are the forming of the sandwich under preserving the characteristics of the core, stabilizing of the formed areas via vacuum gripping to the mold and closing of the sandwich by pressing the edge areas into a compact laminate. The shape of the formed sandwich shell and the transition geometry to the compact laminate can vary to the request of the required part design. To increase the freedom of form, it was also possible to demonstrate in a pilot process that the developed multistage thermoforming process can be combined with thermoplastic injection molding. Both processes together allow to produce complex and ready for use sandwich parts within cycle times of a minute with maximum system utilization.