Polycarbonate injection molding requires disciplined drying, temperature, flow, cooling, and stress control because PC combines high toughness with demanding processing and limited chemical resistance. The correct settings depend on the exact grade, filler, color, part geometry, and resin supplier’s data sheet.
PC is often selected for impact resistance, dimensional stability, heat performance, or optical applications. It is not automatically the best choice for every clear or durable part; chemical exposure, UV, stress cracking, and surface requirements must be reviewed together.
Material preparation
- Confirm the exact PC grade, additive package, color, regrind limit, and approved processing window.
- Dry resin according to the supplier’s data sheet and record dryer temperature, dew point, time, and material exposure.
- Protect dried pellets from ambient moisture during transfer and keep the hopper and feed system clean.
- Use purge and residence-time controls to avoid contamination, yellowing, or degraded material.
Process and mold-design decisions
| Decision | PC-specific risk | Review focus |
|---|---|---|
| Wall thickness | Thick areas cool slowly and can retain stress or create sink | Uniform walls, cores, gradual transitions, and ribs |
| Gate and flow | High viscosity and restrictive gates increase shear and pressure | Gate size, location, flow length, weld lines, and fill profile |
| Mold temperature | Too-cold steel can freeze flow and increase residual stress | Cooling balance, mold temperature, and optical appearance |
| Draft and ejection | Stress during release can cause whitening or cracks | Draft, polish, ejector layout, and release direction |
Common PC molding problems
- Splay or bubbles: verify drying, handling, venting, and contamination.
- Cracks or crazing: check residual stress, sharp corners, ejection, inserts, and chemical exposure.
- Haze or flow marks: review resin condition, mold temperature, gate design, flow front, and surface finish.
- Warp or sink: review wall transitions, packing, cooling, fiber orientation if filled, and gate freeze.
Validation and RFQ checklist
- Provide the grade, color, optical or mechanical target, chemical environment, volume, and part model.
- Define critical dimensions, cosmetic zones, allowable weld lines, gate vestige, and stress-crack testing.
- Run a controlled trial with drying records, fill profile, pressure, mold temperature, cooling, weight, and inspection results.
- Approve the material and process window before changing grade or using regrind.
The engineering team can review PC material and DFM risks; the injection molding team and mold-making team can align gate, cooling, and ejection. Contact Cavity Mold with the PC grade and part files.
Technical references
Protolabs’ polycarbonate overview summarizes PC performance and application trade-offs. The ALBIS PC processing guide provides grade-specific handling and processing guidance.