POM milling – tips and tricks from K&B

1. fields of application of our technical plastics

Our engineering plastics, such as polyoxymethylene (POM), are characterised by their special properties with regard to thermal, electrical conductivity and mechanical usability in contact with a milling cutter. Our “Engineering Plastics” also contribute to countless areas of application due to their impact strength. Our plastic products are particularly in demand for technical applications, in equipment construction or also for the processing of precise components. Polyoxymethylene is used as a material, e.g. after machining in contact with our CNC milling machines, for the manufacture of housings, rollers, seals and many other products. For us, efficient machining with our CNC milling machines and an attractive price/performance ratio are the most important factors.
Industries and application areas that benefit from the final use of our products are listed below:

  • Sliding applications of all kinds
  • Effective design solutions with snap-on fasteners
  • Components for electrical insulation
  • Products for a water contact application
  • Parts with high-gloss surfaces and scratch resistance
  • Several products for the fields of pharmaceutical technology, medical technology, food technology and drinking water technology

2. properties and characteristics of POM plastic

The polymerization of formaldehyde contributes to the formation of polyoxymethylene. The material is one of the most durable engineering plastics. In addition to high wear resistance, the low frictional resistance of the material ensures that our POM plastic has excellent sliding properties and can also be sterilised. In addition, the corresponding blanks of our plastic turning shop have a high elasticity and behave water-repellent. Our plastic products are also extremely robust to the extent that they can easily absorb vibration and minor impacts. The material is excellently suited for machining the POM plates with our CNC milling machines. The corresponding plastic products are also used in the food industry and mechanical engineering, since polyoxymethylene, due to its good resistance to chemicals, is suitable for contact with organic solvents and is also food-compatible. The dimensional stability as well as the simple machinability of the plastics by means of CNC milling cutters makes the material suitable for milling. The plastic, also known as “acetal”, is perfected by the plastics turning shop K&B with our CNC milling cutters into tailor-made blanks and semi-finished products.
In the following we have listed the most important properties of POM plastic in a table:

  • high strength and toughness of the material
  • high impact strength
  • high resistance to wear and tear
  • excellent gliding properties
  • easy machinability by CNC milling
  • good creep resistance
  • enormous dimensional stability
  • hydrophobic

3. POM-C vs. POM-H

Due to its different sliding properties, polyoxymethylene is basically divided into two types of plastic. Acetal homopolymer (POM-H) is characterized by slightly higher density and strength. The alternative plastic acetal copolymer (POM-C), on the other hand, offers better abrasion resistance and impact strength, as well as higher resistance to chemicals and a lower melting point. In addition to these conventional grades of polyoxymethylene, we also offer the following subtypes of POM-C plastic:

  • POM-C Food Grade
  • POM-C KTW / W270 (drinking water approval)
  • POM-C + 25% glass fibre

4. polyoxymethylene in comparison with alternative plastics

Compared to alternative plastics, polyoxymethylene is versatile due to its properties and has now largely replaced PA6 as a material. In many applications, POM can be used much better because, for example, the water absorption of our POM blanks is lower than that of PA6 plastic and, in addition, they are much more efficiently suited for machining by CNC milling.

5 Our recommendations for milling and clamping engineering plastics

Compared to metal materials, plastics have a lower thermal conductivity and a lower modulus of elasticity. Especially when machining POM-plates we recommend to be careful, because improper milling can lead to too high temperatures and the material expands due to heat. The heat released during CNC milling can also contribute to stresses within the semi-finished products. With regard to the general tension, we pay particular attention to the fact that we never work with a blunt milling machine, since such carelessness can result in deformations of the workpiece. These can then be seen in the form of dimensional deviations that lie outside the tolerance range.
For these reasons, the K&B plastics turning shop recommends that you take material-related guidelines into account when machining or CNC milling plastics in order to achieve perfect work results.
First of all, it is advisable to use tempered semi-finished products for milling technical plastics such as polyoxymethylene and to aim for the highest possible cutting speeds. In order to prevent the chips from being drawn in by the milling cutters used, a properly functioning removal of the chips should be ensured. In addition to the advantages of sharply ground cutting edges of the milling cutters, the importance of which has already been mentioned, we recommend that the chips be removed evenly on all sides when milling in order to avoid distortion within the blanks. In addition, clamping impressions should always be kept as low as possible, as otherwise impressions of the clamping tools in the plastic can be the consequence. In order to be able to carry out “clean” machining with the milling machine, the plastic plate should be sufficiently supported due to the tendency towards low material stiffness and should rest on the machine table with the full surface if possible. When milling technical plastics, it is important to ensure that the CNC milling machines run with as little vibration as possible so that high-quality blanks can be produced.

The production of dimensionally accurate parts, which require high cutting volumes or uneven chip removal, is a somewhat more complicated task. Cut-to-size parts should be pre-machined to a residual dimension in order to temper them afterwards. In addition, we recommend one-day intermediate storage in order to reduce the heat and residual stresses generated by the milling cutter. The plastic blank can then be finally machined.

Are you interested in tailor-made blanks that meet your individual application requirements? Do not hesitate to contact us! We would be pleased to deal with your request and make you a non-binding offer!