An Informational Brief on Polymer Machining

 

Did you know that PPS (or Polyphenylene sulfide) products offer the broadest resistance to chemicals of any high-performance thermoplastic? It’s no surprise that this makes them a popular choice for industrial applications such as wheel bushings, chemical pumps, and compound clamp rings for semiconductor wafers.

 

What goes into machining this thermoplastic, however, and how does it differ from metal machining, injection molding, or 3D printing?

 

With Machining PPS: A Plastics Guides, AIP provides you with a guide to this material and its machining process. First, let’s start with the basics: thermoplastics vs thermosets.

 

 

Machining Thermoplastics vs Thermosets

 

We’ve already said that PPS is a thermoplastic, but what does that mean exactly?

 

All polymers can more or less be divided into two categories: thermoplastics and thermosets. The main difference between them is how they react to heat. Thermoplastics like PPS, for example, melt in heat, while thermosets remain “set” once they’re formed. Understanding the technical distinction between these types of materials is essential to CNC machining them properly.

 

What type of thermoplastic is PPS in particular? It’s a semi-crystalline, high-performance thermoplastic that has an extremely stable molecular structure. The chemical resistance of PPS is often compared to PEEK  and fluoropolymers.

 

 

Properties & Grades of Machined PPS

 

There’s a lot to like about PPS’s material properties. As we mentioned before, PPS has exceptional chemical resistance that makes its bearing grades especially favorable for the chemical industry or caustic environments. In particular, its resistance to acids, alkalis, ketones, and hydrocarbons lend PPS stellar structural performance in harsh chemicals.

 

Additionally, PPS materials are inert to steam as well as strong bases, fuels and acids. Combine that with a low coefficient of thermal expansion and zero moisture absorption, and you get a material that is ideal for continuous use in corrosive or hostile environments. PPS has replaced stainless steel for a lot of industrial applications for this reason.

 

Most impressively, PPS will not dissolve at temperatures below approximately 200 °C, no matter what solvent is used. In fact, all grades of PPS share UL94 V-0 flammability ratings, without requiring flame retardant additives, resulting in an excellent material for aircraft where flame resistance is paramount.

 

Some grades of PPS that we regularly machine at AIP Precision Machining include Ryton®, Fortron®, TECHTRON®, TECTRON® HPV, TECATRON PVX and TECATRON CMP.

 

 

Machining PPS

 

Annealing PPS

The process of annealing and stress-relieving PPS reduces the likelihood of surface cracks and internal stresses occurring in the material. Post-machining annealing also helps to reduce stresses that could potentially contribute to premature failure. AIP’s special annealing process for PPS is designed to take the specific properties of PPS into account, and we advise anyone working with PPS to hire a manufacturer that understands its unique demands.

 

Machining PPS

PPS is a fantastic material for machining. Its low shrinkage and stable dimensional properties make it easy to machine to incredibly tight, precise tolerances. A unique characteristic of PPS is that when dropped, it sounds just like a piece of metal hitting the floor.

 

PPS, like many other thermoplastics, is notch sensitive, so take care to avoid sharp corners in design. We recommend carbide tipped cutting tools for working with PPS as they provide an ideal speed and surface finish.

 

We also suggest non-aromatic, water-soluble coolants, such as pressurized air and spray mists, to achieve optimum surface finishes and close tolerances. Coolants have the additional benefit of extending tool life as well. No known coolants attack nor degrade PPS.

 

Preventing Contamination

Contamination is a serious concern when machining polymer components for technically demanding industries such as aerospace. To ensure the highest level of sanitation down to the sub-molecular level, AIP Precision Machining designs, heat-treats, and machines only plastics, with any sub-manufactured metalwork processed outside our facility.

 

To learn more, read our article “Three Ways to Ensure Sterilization in Your Plastic Machined Medical Applications.”

 

 

PPS Machining Guide: Supportive Information

Chemical Resistant Materials Guide

Energy Sector Materials Guide

Aerospace Sector Materials Guide

 

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Company News: Retirement

After 40 years in various Quality Control roles—from inspection, regulatory affairs, management, and HSE—Dave Eckroth has retired. Having spent 22 of his 40 years at AIP, his “going-away” party felt like saying goodbye to a family member, not a coworker. We all wish him a safe, happy, healthy and very long retirement.

 

Dave has been instrumental in the regulatory aspects of AIP’s business, such as attaining our ISO certifications and keeping them up-to-date. He consistently raised the company’s Quality Health, Safety and Environment standards. As Dave has often said, “You can’t measure in quality.”

 

In Quality Control, Dave was the final gatekeeper to ensure customers received exactly what they ordered. He balanced efficiency with quality, and designed processes and procedures to avoid mistakes and mitigate risks. If a product needed to shift even a thousandth of an inch during inspection, Dave made sure it did.

 

We celebrated his retirement with a company luncheon. Though Dave could have picked any food, he chose good old-fashioned pizza. Many of us shared how much we’ve enjoyed working with him over the years, including our CEO, John MacDonald. Of Dave’s retirement, he said:

 

“Moments like this make me think that regardless of the many challenges we face, it is quite unique and special to have a dedicated group of people who have stuck together as a team for so many years.”

 

Dave thanked everyone and shared that AIP was the best place he’d ever worked. We sent Dave off with balloons and wish him all the best in retirement, where he plans to remodel his old Chevy truck.

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