Injection molding adds versatility to Vespel

Newark, DE —Design flexibility and Vespel haven't always gone hand in hand. In fact, the same physical properties that rendered this DuPont polyimide so resistant to wear, heat, and chemicals also made it difficult to manufacture in complex shapes—until now.

To make this "plastic of last resort" more versatile, DuPont has developed new polyimide materials suitable for injection molding. The company will use the materials to make "Vespel TP" custom molded parts in the U.S., Europe, and Asia. "Vespel TP offers all the geometric flexibility and tight tolerances of injection molding without sacrificing conventional Vespel's performance properties," says Pete Galeta, senior program manager at DuPont.

In the past, Vespel components have been produced in a proprietary direct-forming process that turns out parts cost effectively but imparts some geometric restrictions. Galeta explains that direct-forming favors parts with a uniform pressure distribution and simple linear surfaces. All but the simplest part features had to be machined, adding cost to the components. With the introduction of Vespel TP, the geometric drawbacks disappear. As examples of the possibilities for molded-in features, Galeta cites axial tabs on thrust washers, seal rings with molded in gaps, and scarf joints.

To support a wide variety of applications, DuPont will offer Vespel TP parts in several application-specific varieties, Galeta reports. One material formulation targets wear-intensive applications, such as thrust washers in automotive transmissions. Another formulation optimizes fuel resistance. Galeta expects it to be used in impellers and other fuel-pump components that can benefit from low "fuel-swell." "There's a lot of intricate geometry in the new common-rail fuel pump designs," he notes. Yet another formulation will optimize impact performance for dynamic parts such as compressor valves.

Vespel TP offers many of the same performance characteristics as traditional Vespel, so the choice between the two materials will likely be determined by volume and geometric requirements, Galeta says. At low production volumes—below 1,000 units for most components—traditional Vespel will continue to make the most sense even with secondary machining. In applications with higher volumes or with complex geometric requirements, Vespel TP will get the nod.