Overview
olyoxymethylene (POM) grade M90 (Copolymer) combines excellent mechanical strength, low friction, and superior chemical resistance compared to Homopolymer grades. These characteristics make it suitable for gears, bearings, and critical automotive components. Its inherent high crystallinity drives volumetric shrinkage of 1.8–2.5%, while precise thermal control is required during processing to maintain dimensional stability and prevent material property shifts. This guide integrates injection molding, process control, quality assurance, and additive manufacturing to minimize defects and achieve tolerances of ±0.05 mm.
Injection Molding: Parameter Control
Autodesk Moldflow simulations predict shrinkage within ±0.1%, enabling pre-tooling adjustments. The processing window is carefully defined to utilize the co-polymer's stability while ensuring optimal flow for high-precision parts.
| Parameter | Range | Effect |
|---|---|---|
| Melt Temperature | 200–225°C | >230°C initiates chain scission and formaldehyde release |
| Mold Temperature | 80–120°C | 10°C increase reduces warpage by 20–30% (3D scanning) |
| Injection Pressure | 80–120 MPa | Prevents flash while ensuring cavity fill |
| Packing Pressure | 60–80% of injection | Compensates shrinkage |
| Cooling Time | 10–20 s | Avoids sink marks |
Injection Molding
For features <0.5 mm, specific controls are mandatory:
- Plunger volume: <1 cm³
- Mold surface: Ra <0.1 μm
- Vent depth: 0.005–0.01 mm
Variothermal molding (150°C injection → rapid cooling) reduces residual stress by ~40%, extending fatigue life.
Process Stability and Quality Control
Beyond parameter optimization, material stability forms the foundation for defect-free production.
Pre-Treatment (Drying)
POM M90 absorbs moisture rapidly. Dry to <0.02% using:
- Dehumidifying dryer at 80°C for 3–4 h
- Verify via Karl Fischer titration for critical parts
Undried resin causes splay and voids.
Thermal Management
While stable up to 225°C, prolonged residence time (e.g., 5 min) or high shear stress can cause MFI drift and degradation. Mitigate with:
- Nitrogen barrel purging
- 0.1–0.5% hindered phenol stabilizers
- Formaldehyde <10 ppm (real-time sensor)
Use screws with L/D ≥20:1 and compression ratio ≤2.0:1 to minimize shear.
Mold Design & Annealing
- Oversize cavities by +1.9–2.2%
- Maintain wall thickness 1–3 mm
- Integrate conformal cooling (±2°C uniformity)
- Use fan gates to limit weld line strength loss (<30%)
Post-molding: Anneal at 140°C for 30 min; birefringence confirms stress relief.
In-Process Monitoring
- In-line rheometry tracks MFI drift
- SPC controls critical dimensions
- AOI detects surface defects (<1% reject rate)
Additive Manufacturing (AM)
While injection molding dominates volume production, additive methods enable rapid iteration.
Fused Deposition Modeling (FDM)
- Blend with 10–20% polyolefin for adhesion
- Nozzle: 210–230°C | Bed: >100°C (enclosed)
- Speed: <30 mm/s | Layer: 0.1–0.2 mm
- Density: >95% of molded parts
Avoid dark color masterbatches (>0.5% carbon black reduces stability).
Selective Laser Sintering (SLS)
- Tensile strength: ~50 MPa (~80% of molded)
- Suits complex internal channels
Case Study:
FDM prototypes validated snap-fits in 48 h vs. 6 weeks for tooling.
Energy use: 3–5× injection molding per part.
Sustainability & Material Recovery
Regrind ≤20% retains >90% properties. Closed-loop systems recover >90% scrap. Track thermal history via MFI testing.
Conclusion
POM M90 demands integrated control: drying, thermal management, mold design, and monitoring. Injection molding delivers precision at scale; additive manufacturing accelerates design validation. Future developments include AI process optimization and bio-based POM variants.For a deeper dive into M90’s flow behavior, alkali resistance, and grade selection for thin-wall parts, see our companion guide: POM M90: High-Flow, Alkali-Resistant Precision Engineering Plastic.
