POM (Delrin)

The Complete Guide to CNC Machining High-Density Polyethylene (HDPE)

Polyoxymethylene (POM), is widely utilized in CNC machining due to its excellent properties and versatility.

Derived from formaldehyde, POM belongs to the family of thermoplastic polymers and stands out for its high mechanical strength and rigidity. This material’s primary attribute is its high stiffness and hardness, making it ideal for applications requiring dimensional stability and mechanical precision. Additionally, POM exhibits outstanding resistance to wear and abrasion, rendering it suitable for environments where components undergo significant mechanical stress.

A defining feature of POM is its low coefficient of friction, enabling smooth, wear-resistant sliding between parts. This characteristic is highly advantageous in applications like gears, bushings, and bearings, where friction reduction is essential. POM also possesses low moisture absorption, enhancing its durability and performance in humid or variable environmental conditions.

In CNC machining, POM is valued for its ease of machinability, allowing it to be fabricated into complex parts with precision. Components like precision gears, structural fittings, and sliding parts can be easily produced from POM, making it a popular choice for applications that demand dimensional accuracy and wear resistance. Its combination of strength, stiffness, and low friction has made POM a staple material in various industries.

POM (Delrin) stands out in CNC machining for its impressive strength, low friction, and high dimensional stability, solidifying its reputation as a dependable material across numerous applications.

Subtypes

POM is the chemical abbreviation for polyoxymethylene plastic, a type of thermoplastic. POM can be further classified into two types:

POM-H (Homopolymer Acetal): Known for its higher strength and hardness, with Delrin being a common brand name.
POM-C (Copolymer Acetal): Offers greater chemical resistance and toughness, usually produced by other brands.

POM is a scientific term or chemical designation that encompasses all types of polyoxymethylene plastics.

Surface Finishes

When it comes to surface finishes, POM (Delrin) has unique characteristics that affect its treatment options. Due to its low surface energy, POM resists many traditional coatings, such as paints or powder coatings, which may not adhere effectively or provide a durable finish. This quality often limits the range of effective coating techniques for POM components.

Additionally, POM is challenging to bond with adhesives, making it difficult to attach to other materials. For joining POM with other parts, mechanical fastening methods such as screws or custom fittings are commonly used, as these maintain structural integrity without requiring adhesives.

POM is generally available in natural (white) and black colors, with limited availability in other colors. Because of its resistance to coatings, POM parts are typically left as-machined, with the surface finish resulting from CNC machining serving as the final finish. POM’s distinctive properties make it highly useful in CNC machining, though they also necessitate special consideration for surface finishing and joining techniques.

Design Tips

Consider wall thickness: POM (Delrin) is a rigid material, so wall thickness directly impacts the strength and stability of a part. While thinner walls can reduce weight, thicker walls add substantial rigidity, which is beneficial for applications requiring high strength. Balancing wall thickness based on the part’s intended function is essential to optimize both durability and weight.

Avoid sharp edges: POM is susceptible to stress concentration at sharp edges, which may lead to cracking over time. To improve durability and distribute stress, use rounded edges, radii, or fillets in the design.

Use gentle angles: Due to POM’s low coefficient of friction, sharp angles can lead to sliding or misalignment in certain applications. Gentle angles help reduce this risk, allowing smoother transitions between surfaces.

Consider support structures: Although POM is generally stable, long or thin parts may require additional support during CNC machining to maintain dimensional accuracy. Incorporate support structures in the design phase to prevent potential warping or bending.

Leave adequate tolerances: POM can undergo slight thermal expansion or contraction during machining. Incorporate tolerances in the design to account for these potential dimensional variations, particularly in applications requiring high precision.

Avoid undercuts: POM can be challenging to machine with complex shapes. Minimize undercuts in your design to avoid the need for intricate tooling and to simplify the machining process.

FAQ

Can you CNC POM?

Yes, POM (Delrin) can be CNC machined. POM is widely used in CNC machining due to its high stiffness, low friction, and excellent dimensional stability, which make it ideal for precision components and applications requiring tight tolerances.

When should you not use POM?

POM is not recommended for applications requiring exposure to high temperatures for prolonged periods, as it may deform or lose rigidity. Additionally, it may not be suitable for environments where strong acids or harsh chemicals are present, as they can degrade the material over time.

Is it hard to cut POM?

POM is generally easy to machine due to its rigidity and low friction properties, which allow smooth cutting and shaping. However, it can sometimes produce fine dust or chips during machining, so proper ventilation or extraction is recommended. Also, additional care may be needed for thin or long parts to prevent warping.

Why are POM prices so high?

POM prices can be influenced by various factors, including production costs, demand across industries like automotive, electronics, and consumer goods, and raw material availability. Economic conditions, energy prices, and international trade policies can also impact POM pricing, as with many engineering plastics.

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