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Streamlining high-quality plastics

Everything from the casing on your cell phone to the panels on your car is made of plastic that is manufactured using injection molding, by far the most common way of forming plastic products.

John Coulter, professor of mechanical engineering and mechanics, studies injection molding to help industries produce parts more efficiently. About 70 percent of the world’s plastic products, he says, are made using cold runner injection molding. More intricate parts, including many plastics for medical applications, are produced using hot runner injection molding, which reduces the amount of costly plastic that is wasted.

The “runner” is the channel through which molten plastic travels into a mold. In cold runner injection molding, the runner solidifies, slowing production, and must be recycled or discarded. Hot runner injection molding produces parts more rapidly, and the runner never solidifies.

“You can save money by eliminating runner scrap,” says Coulter, “and you can make more money by manufacturing parts more rapidly.

“Hot runner systems use more energy and pose maintenance challenges, but they can be cost-efficient with high-volume production of expensive, high-performance plastics.” Coulter’s research focuses on computer, medical, optical and electronics products that use high-performance plastics.

Because they are expensive polymers, companies want to use hot runner molding, but engineers must first solve the molecular degradation and other challenges posed by hot runner injection molding.

Coulter and his team study these materials as a function of time and position throughout the process. “For example, if a plastic stays hot too long, we look for the degraded spots, usually in the runner,” he says. “Through computer modeling, we reconfigure things until we obtain the desired results.”

The work is funded by the Research for Advanced Manufacturing in Pennsylvania, a partnership of Lehigh and Carnegie-Mellon Universities funded through the Pennsylvania Department of Community and Economic Development.

Coulter is collaborating with TE Connectivity, a leader in the connector products industry. The goal is to improve TE’s high-precision manufacturing process by switching from cold runner injection molding to a hybrid system that combines cold and hot runner processes.