Acetal Plastic Machining

Your guide to Acetal Plastic Machining



Amongst the strongest and stiffest of all thermoplastics

Two general types of Acetal resins: Acetal Homopolymer and Acetal Copolymer

Both have very good machinability

Acetal, also known as POM, has excellent machinability. It is an engineering plastic known for being amongst the strongest and stiffest of all thermoplastics.

This guide will take you through the main attributes, common applications, notes for designers and suitable finishing and treatments, as well as UK stock sizes and property tables. Don't forget to bookmark the page so you can refer back later.

If you are interested in Acetal machined parts, please scroll to the bottom of the page for more information about our service and to request a quote.

Acetal Guide: Properties, Applications and Design Considerations


What is Acetal?
Acetal or POM (Polyoxymethylene) is an engineering plastic known for being amongst the strongest and stiffest of all thermoplastics.

There are two general types of Acetal resins available: Acetal Homopolymer and Acetal Copolymer.

Acetal homopolymer resins are made by the DuPont Company under the trade name Delrin®. Homopolymers are typically used in highly regulated industries.

Acetal copolymers are made by several companies. Slightly softer than Acetal homopolymers, the Acetal copolymers have a lower coefficient of friction.

You may also see Acetal referred to as:

  • Polyoxymethylene (POM)
  • POM-C (Acetal Copolymer)
  • POM-H (Acetal Homopolymer)
  • Ultraform® - Copolymer brand name
  • Celcon® - Copolymer brand name
  • Tecaform® - Copolymer brand name
  • Delrin® - Homopolymer trade name
  • Polyacetal
  • Polyformaldehyde

Unlike other engineering plastics that produce a long swarf thread when machined, Acetal chips in the machining process. It is therefore recommended to use very sharp cutting tools.

Industry Examples: 

Copolymer: Food & packaging | Medical & pharmaceutical | Automative | Electrical/Electronic | Agriculture

Homopolymers: Aerospace | Nuclear | Pharmaceutical

Typical Components & Applications: Electrical insulation | Medical applications | Food contact components (FDA compliant) | Gears | Bearings | Housings | Fasteners | Bushings | Handles | Seals | Valves | Tooling


Main Attributes:
Acetal Copolymer:
  • Absorbs very little moisture
  • High mechanical strength and rigidity
  • Improved dimensional stability over comparable homopolymer formulations due to the lower level of crystallinity
  • Low coefficient of friction
  • Good compressive strength
  • Good shock resistance
  • Better chemical resistance with high pH solutions
  • Lower centerline porosity than homopolymer in extruded shapes
  • Excellent machinability
Acetal Homopolymer:
  • Stiffer
  • Wide operating temperature range (-40°C to 120°C)
  • Higher flexural modulus at room temperature
  • Higher impact strengths at room temperatures and low temperatures
  • Tensile strength is approximately 10-15% higher than comparable copolymers
  • Slightly higher continuous use temperature than copolymer (95°C vs. 90°C)
  • Good compressive strength
  • Good shock resistance
  • Lower thermal expansion rate
  • Better wear resistance
  • Easy to machine

Note For Designers:

When machined, Acetal produces very few post machining burrs, meaning the process of de-burring can be avoided, saving precious time in manufacturing.

Acetal Copolymer has a slightly lower cost than Homopolymer (Delrin®).

Acetal Copolymers are available in a wide range of colours.

Some disadvantages of Acetal which are worth noting for material selection:

  • Flammable
  • Subject to UV degradation
  • Difficult to bond
  • Poor resistance to acids
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