Definition of Acetal Copolymer (POM-C)
POM-C (Polyoxymethylene Copolymer), commonly known as Acetal Copolymer, is a high-performance engineering thermoplastic valued for its exceptional dimensional stability, low friction, wear resistance, and mechanical strength. It is widely machined on CNC mills and lathes for precision components. Common brand names include Celcon®, Hostaform®, and Duracon®.
Properties of CNC Machined Acetal Copolymer (POM-C)
| Property | Value |
|---|---|
| Mechanical Properties | |
| Ultimate tensile strength | 28 – 32 MPa |
| Yield strength | 26 – 31 MPa |
| Young’s modulus (modulus of elasticity) | 2.18 – 2.23 GPa |
| Elongation at break | 2 – 7 % |
| Thermal Properties | |
| Thermal expansion coefficient | 8.82 – 8.46 × 10-6/ºC |
| Common Applications | |
| Functional prototypes & production parts | Jigs & fixtures |
| Tools | |
Why Acetal Copolymer (POM-C) Matters in CNC Workshops
POM-C is the go-to acetal for CNC machining because its copolymer structure offers better thermal and chemical stability than the homopolymer (POM-H), reducing the risk of degradation during high-speed machining. Its low moisture absorption means parts hold tight tolerances even in humid environments, and its self-lubricating nature eliminates the need for external lubrication in moving assemblies.
Surface Finishes for Acetal Copolymer (POM-C)
As-Machined
The default finish from CNC machining plastic stock (Delrin, nylon, HDPE, ABS). Visible linear tool path scallop marks across machined surfaces with a matte plastic sheen. No secondary operation suitable for functional components, jigs, fixtures, and internal parts where cosmetic appearance is secondary to dimensional accuracy.
Flame Polished
Quick post-fabrication process that passes a controlled flame over acrylic (PMMA) cut edges, melting the surface micro-layer to produce a crystal-clear, glossy, transparent edge. Fast and cost-effective for acrylic sheet edges produces optical clarity on cut borders without the labor of hand polishing. Ideal for display cases, signage, and acrylic enclosures.
Vapor Polished
Post-fabrication chemical process that exposes transparent plastic parts (acrylic, PC, PETG) to solvent vapor, melting and smoothing the surface micro-layer to dramatically improve optical clarity and gloss. Removes machining lines and produces crystal-clear transparent parts — essential for prototype lenses, light guides, display windows, fluidic chambers, and medical components requiring optical transparency.
Painted
Post-fabrication spray painting in any custom color (matte, satin, gloss, metallic) followed by screen printing or pad printing for logos, labels, buttons, and graphics. Applied over a primed plastic surface for uniform color and adhesion. Allows custom fabricated plastic parts to match production aesthetics widely used for control panels, instrument faces, enclosures, and marketing/showcase components requiring exact brand color and graphic printing.
Sanded
Post-fabrication sanding with progressively finer grit sandpaper (typically 240–600 grit) produces a uniform low-gloss matte non-reflective surface. Hides machining marks, scratches, and surface inconsistencies while providing a soft tactile feel. Used for HDPE, UHMW, and nylon components where a durable, non-glare, fingerprint-resistant matte appearance is desired for industrial and functional parts.
Heat Formed
Thermoforming process that heats plastic sheet (acrylic, polycarbonate, ABS) to its glass transition temperature and bends it over a form tool to create precise angles and curved shapes. Produces clean, smooth bend radii with consistent surface finish no tool marks at the bend. Used for display stands, guards, enclosures, signage, and custom fabricated parts requiring 3D formed shapes from flat sheet stock.
