The Alfond Advanced Manufacturing Lab for Structural Thermoplastics at the University of Maine aims to increase the market presence of structural thermoplastic through development of innovative manufacturing processes to decrease cycle time, reduce waste and enhance repeatability and part quality. “It’s about making parts that are recyclable – just like aluminum and steel parts – but much, much lighter and highly engineered,” says David Erb, senior R&D program manager of the lab.
Five Key Trends
The evolution of thermoplastic materials and processes in the last decade has created more sophisticated non-structural parts for mass production, new advanced materials for high-performance applications and structural composites, and hybrid processes that utilize both. Here are five key developments in the ongoing evolution of thermoplastic composites.
1. Long Fiber Reinforced Thermoplastics
Most thermoplastic composite parts are made with noncontinuous fibers using injection molding. Short fibers (less than 1/8-inch) have been used in thermoplastic composites in the automotive sector for decades. More recently, long fiber reinforced thermoplastics (LFRTs) from 1/8-inch to one inch have entered the market. LFRTs are commonly available as pellets and used primarily in injection molding and compression molding.
Gordon says that long fibers enable more strength with less material. Aerospace manufacturers were early adopters of LFRT technology. LFRTs have begun to proliferate the automotive market not only for lightweighting advantages, but also because they are easy to process. “It’s a quick heat and cold cycle to mold something from LFRTs,” says Gordon. Long fiber injection molding also provides better creep impact and fatigue, says Morgan.
Direct long fiber thermoplastics (DLFTs) is a newer processing technique that provides long fibers without melting preformed pellets. In a three-step process, DLFT compounds a resin – typically polypropylene – with any additives, cuts continuous fiber rovings directly into the resin and then extrudes a portion of the reinforced material into a compression molding tool in the form of a dough-like charge or ‘bun.’ This allows control of the fiber length.
2. Continuous Fiber Reinforced Thermoplastics
Continuous fiber reinforced thermoplastics (CFRTs) are found in unidirectional tapes and used for woven sheets, filament winding and pultrusion. Ed Pilpel, senior technical advisor for PolyOne™ Advanced Composites, says that the introduction of CFRT prepreg materials has significantly improved the impact resistance of thermoplastic composites. This, in turn, has spurred new potential applications for materials such as Polystrand™ continuous fiber glass reinforced polypropylene in markets as varied as transportation, building and construction, and ballistic protection.