Under the hood: Thermoplastics tackle tough jobs

Composites are established in vehicle interiors and also have gained traction in exterior and chassis components in the performance-car, pickup-truck and electric-vehicle segments. But they have been slow to make inroads into the engine compartment. Under the hood, heat from the internal-combustion engine and exposure to engine fluids (fuel, oil and coolant) already make it a tough environment. And it's getting tougher as increasingly strict emissions and fuel-economy requirements push the market toward smaller, turbocharged gasoline and diesel engines, many equipped with exhaust-gas recirculation systems. Underhood temperatures are on the rise because these harder-working engines run hotter, and available engine compartment space is scarce as cars get more compact and their deeply swept front ends make underhood cooling more difficult. Moreover, auto OEMs' extended new-car warranties put pressure on suppliers to use materials with longer service lives, yet they also are demanding reductions in component weight and cost.

The need for underhood components that perform better and longer at less weight and cost has opened a growth area for several families of fiber-reinforced, injection-moldable, high-temperature (semi)crystalline thermoplastics. The chemistry of these resins enables higher thermal and chemical performance and greater toughness than commodity thermoplastics.

Further, (semi)crystalline thermoplastics exhibit greater impact strength at lower weight, better aesthetics right out of the tool and melt reprocessability (facilitating welding and permitting recycling) —  all advantages vs. common thermosets.

In combination with the injection molding process, these materials overcome weight and design constraints and eliminate costly postproduction steps that are typical for aluminum, steel and thermoset composites, such as bulk molding compound (BMC), which are more difficult to form. The material/process combination facilitates unprecedented design freedom and parts integration. This enables quicker production of complex structures (the cycle times are fast, and smaller parts can be molded in multicavity tools) in a single step — with excellent repeatability and reproducibility (R&R). This makes the process ideal for mid- to high-volume vehicle builds, where production speed is a high priority and the initial higher cost of tooling can be justified. At these production volumes, manufacturing and part costs can be substantially less than those of cast or machined aluminum and steel. Several of the most exciting examples of composites in underhood applications are covered here.