An Informational Brief on Polymer Machining
Delrin®, also commonly known as an acetal (polyoxymethylene) homopolymer, is an impact and wear resistant semi-crystalline thermoplastic popular for a broad range of machining applications. To list just a few of its impressive qualities, Delrin offers great stiffness, flexural modulus, and high tensile and impact strength.
How does AIP approach Delrin and its machining process? To start, we’ll explain the difference between machining Delrin, a thermoplastic, and machining thermosets.
Machining Thermoplastics vs Thermosets
We’ve already said that Delrin 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 Delrin, for example, melt in the 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 Delrin in particular? Acetal homopolymer is a semi–crystalline, engineering thermoplastic.
Properties & Grades of Machined Delrin
This strong, stiff and hard acetal homopolymer is easy to machine and exhibits dimensional stability and good creep resistance, among several other desirable qualities. Delrin is also known for its superior friction resistance, high tensile strength, and its fatigue, abrasion, solvent and moisture resistance.
The latter quality allows Delrin to significantly outperform other thermoplastics like Nylon in high moisture or submerged environments without losing high-performance in the process. In other words, Delrin can retain its low coefficient of friction and good wear properties in wet environments.
One of the main reasons for Delrin’s popularity is its sheer versatility. The above blend of unique qualities makes Delrin broadly applicable to various industries in the medical, aerospace and energy sectors. For example, you can machine Delrin for medical implants and instruments, or for industrial bearings, rollers, gears, and scraper blades. It is ideal for smaller applications at temperatures below 250 °F (121°C) and can have centerline porosity.
Some of the Delrin grades we regularly machine at AIP include:
PTFE (polytetrafluoroethylene) filled grades of Delrin is ideal where impact strength and wear capability are of the highest importance.
Acetals that are reinforced with glass have a much higher strength and greater heat resistance than other grades of Delrin.
There are FDA-compliant grades of Delrin available for use in medical and food-related applications.
It’s true that Delrin is an easy material to work with in terms of machining. It is a very stable material, which makes precise, tight tolerances easier to achieve for this thermoplastic.
While machining, keep in mind that Delrin is sensitive to heat at or above 250 °F (121°C).
Balance the material removal as best as you can to keep your dimensions stable.
We also suggest non-aromatic, air-based coolants to achieve optimum surface finishes and close tolerances. Coolants have the additional benefit of extending tool life as well.
Contamination is a serious concern when machining polymer components for technically demanding industries such as medical and life sciences. 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.
Delrin Machining Guide: Supportive Information
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