Manufacturing of Lightweight Parts by Sandwich Foam Injection Moulding using Recycled Thermoplastics

Reinforced, high-performance thermoplastics may have moduli of elasticity of up to 40 GPa, depending on the filler content. The filling materials can thereby consist of secondary raw materials such as recycled carbon fibers. By combining these highly stiff materials with unreinforced but material-compatible and foamable thermoplastics, excellent and complex lightweight sandwich structures can be realized in a one-shot process using the sandwich foam injection moulding technology. The core and top layers of these structures are usually made of two different components (2-C). The process is both reproducible and cost-efficient for high production volumes. The foaming process is carried out either by adding a chemical blowing agent or an inert gas at supercritical conditions. The resulting composite consists of a short-fiber reinforced high-modulus material in the outer layer and an unreinforced foamed material in the core. Due to the low requirements on performance, odour as well as surface properties, recyclates are particularly well suited for the use as core material. Three sources of recyclates are presented in the paper, which have been the scope of the specific studies: A) Polyolefin mixed fraction from household waste, B) PET (polyethylene terephthalate) waste flakes, and C) polyamide waste. Depending on the source mentioned, dedicated lightweight structures with specific properties may be produced—with applications in particular market segments. A suitable example in this context is the sandwich foam injection moulded functional support structure for the electro-mobility automotive industry with a design suitable for foam injection moulding. Moreover, a significantly higher specific stiffness was achieved with this semi-structural component compared to an existing reference structure.