Near Net Shape Preforming of Thermoplastic Cut Pieces - an Alternative to Tape Laying?

Abstract

At DLR's Center for Lightweight Production Technology (ZLP) in Augsburg the potential of autonomous pre-forming by a robotic pick and place process for the fabrication of thermoplastic components was investigated. The focus was on curved, 3D near net shape preforms created from thermoplastic cut pieces prepared in a cutter with a "composite friendly" design minimizing the consolidation stress that mere 2D organic sheets endure, and also on the feasibility of a variable preform thickness by staggering as well as the usage of tailored cut pieces. The material is up to 400 mm wide and, for certain geometries or layups, has the potential to outperform other 3D-preforming technologies like thermoplastic fibre placement in terms of productivity. The cut pieces are fixed to each other by ultrasonic spot welding, yielding a stable preform for further processing. Instead of robot-teaching or offline programming, technology bricks for a flexible production were developed, including automated derivation of grip- and drop coordinates from CAD data, digital process and workflow description, com-puter vision-based gripping, autonomous cut piece transfer by means of collision free path planning and a multi-robot synchronization and execution layer. We give an overview of the developed technologies and achievements based upon several use cases from the field of thermoplastic aerospace composite part production.