Life in Polymers: Machining Plastics and Why Compression Molding Beats Out Extrusion


Life in Polymers: Machining Plastics and Why Compression Molding Beats Out Extrusion

On the first episode of Life in Polymers, we’re breaking down the basics of machining plastics, and specifically the differences between extrusion and compression molding. Both are ways that machinable plastic shapes are manufactured, but each process is a different approach producing different results during certain machining operations. To provide insight, we’re joined by Jody Walker, Western Region Business Development Manager, and Paul Hanson, Eastern Region Business Development Manager of Westlake Plastics.

Professionals in the industry know: there are many challenges with machining plastics, most of which is felt by machinists that work primarily with metals. Not only is education on machining plastics sparse, but the techniques don’t translate.

“Machinists have spent most of their time on training on metal work. Metal work doesn’t translate to plastics. They are different materials,” Hanson said.

However, the industry has seen a strong trend in replacing metal with plastic. It’s lighter weight, more cost-effective, and for some industries, it’s even “stronger.”

“In industries where corrosion is an issue like the food processing industry, plastic actually works much better, as it can deal with water and other chemicals better than metal,” Walker said.

This trend means there is a demand for machined plastics. Extruding acetal into a sheet and rod has been the traditional way to get a stock shape that could be machined to create them, but it isn’t always effective.

“When a sheet of plastic is extruded, there are internal stresses created during the process. When a strip is cut from that extruded sheet, the part will curl. That’s a real problem for fabricators. Much of the time when these parts are installed, they won’t lay flat and can fail inspection,” Hanson said.

Hanson and Walker argue that compression molding is an alternative that more machinists need to consider. Though the process used to have barriers of high pricing, compression molding has become an accessible option for manufacturing plastic parts. Not only that, on average, compression molding plastic sheet provides much more reliable results during machining than extrusion. There is much less stress, and parts lay flat during machining and strips cut from compression molded sheet stay straight when made.

Listen to the podcast to learn more about Westlake’s own compression molded plastic, Pomalux, which Hanson and Walker say delivers a unique and superior product to machine.