Polyoxymethylene (POM)

Polyoxymethylene (POM) - assemblean

Materials

Processing techniques for POM

Injection molding

POM is an excellent injection-moldable engineering thermoplastic and is used in particular for the series production of precision components such as gears, plain bearings, housings, and valves. Both POM-H (homopolymer) and POM-C (copolymer) are suitable for injection molding, although POM-C has higher thermal stability against hydrolysis, making it easier to process. The recommended cylinder temperatures are approx. 190–210°C, depending on the type and manufacturer's specifications, this can also be up to 230°C. The mold temperature should be between 60–100°C, with higher mold temperatures promoting improved surface quality and dimensional accuracy. The injection pressure is typically between 800 and 1200 bar. After injection molding, the parts should be cooled in a controlled manner to minimize stress and warping. POM can also be injection molded with glass fibers or PTFE additives to optimize stiffness, abrasion resistance, or sliding properties depending on the application.

Extrusion

POM can be processed using extrusion, particularly for the production of rods, sheets, profiles, and film strips for machining blanks. The extrusion of POM requires precise process control in order to achieve a homogeneous melt and the required crystallinity. The cylinder temperature profiles range between 170–200°C, with moderate shear preferred to avoid thermal decomposition. The mold temperatures are typically between 80–120°C. The extruded semi-finished products are characterized by high strength, rigidity, and excellent dimensional stability and are ideal for further machining. Due to their low water absorption, the dimensional stability of the extruded products is maintained even under changing climatic conditions.

Machining

Since POM is extremely easy to machine, machining (turning, milling, drilling) is a widely used manufacturing method, especially for prototypes or small series with tight tolerances. Machining can be carried out with standard HSS or carbide tools. Coolants are usually not essential, but can be used to optimize surface quality and heat dissipation. Due to its low tendency to form burrs and good chip breaking properties, POM is ideal for precision parts such as gears, sliding elements, and valve components. However, when machining POM, the springback effects (dimensional change after machining) should be taken into account, which is why post-tempering is often recommended to reduce stress.

Materials

Comparison of the mechanical and chemical properties of POM-C, POM-H, and POM with 25% GF

Polyoxymethylene (POM) is available as a homopolymer (POM-H), copolymer (POM-C), and in glass fiber-reinforced form, and differs in its mechanical and chemical properties. POM-H is characterized by high stiffness and strength, while POM-C offers slightly lower stiffness but better chemical resistance and higher elongation at break. The melting point of POM-H is around 175°C, while that of POM-C is around 165°C. Both types absorb very little moisture, ensuring good dimensional stability even in humid environments.

Glass fiber reinforced POM has significantly higher stiffness and tensile strength, making it attractive for components subject to high loads. However, it is more brittle and has significantly lower elongation at break. The coefficient of sliding friction is slightly higher than that of unreinforced POM, which should be taken into account in sliding applications. In terms of chemical resistance, POM-H and POM-C are highly resistant to many chemicals, while the glass fiber reinforced variant is slightly less resistant but more mechanically resilient.

POM-C is particularly advantageous in processing, as it is easier to injection mold and offers greater dimensional stability. POM-H offers better mechanical properties, but requires more precise processing. Glass fiber-reinforced POM is more demanding to process, but is used when high rigidity and strength are required, for example in heavily loaded gears or precision parts.

Characteristic	POM-H (homopolymer)	POM-C (copolymer)	POM with 25% GF
Density [g/cm³]	1.41	1.39	1.50
Tensile strength [MPa]	65–75	60–70	95–110
E-Modulus [MPa]	2800–3200	2500–2900	6000–8000
Elongation at break [%]	20–40	30–60	2–4
Melting point [°C]	175	165	approx. 170
Water absorption (23°C, sat.) [%]	0.8	0.4	0.3
Coefficient of sliding friction (dry)	0.2–0.35	0.2–0.35	0.3–0.4
Chemical resistance	Very good	Very good	Good
Processability (injection molding)	Good	Very good	Medium

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Polyoxymethylene (POM)

Structure and composition of POM

Main advantages of POM

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Precision and versatility

High dimensional stability

moisture resistance

Good surface quality

Processing techniques for POM

Injection molding

Extrusion

Machining

Areas of application for POM

Automotive industry

Consumer goods

Industry and mechanical engineering

Comparison of the mechanical and chemical properties of POM-C, POM-H, and POM with 25% GF

All technical advantages at a glance

High strength

High abrasion resistance

Excellent dimensional stability

High chemical resistance

Thermal stability

Good sliding and dry-running properties

High machinability

Cost-effective with high precision

Suitable manufacturing processes

Injection moulding

Vacuum casting

CNC

Further materials

ABS

Polyamide

Stainless steel