Polycarbonate, Nylon & PEEK Injection Molding — Processing Parameters & Design Notes

By VNcontX Engineering  ·  June 3, 2026

Polycarbonate injection molding, nylon (PA6/PA66), and PEEK cover the upper tier of thermoplastic injection molding — resins specified when ABS cannot meet the heat, structural, or chemical requirement. This guide documents the processing window, failure modes, and design constraints for each resin, drawn from production runs at our facility in Ho Chi Minh City.

ABS is the default for a reason — it’s forgiving, cheap to dry, and tolerates a wide barrel window. But the moment a part needs optical clarity, continuous-use heat resistance, chemical exposure, or structural load under temperature, ABS stops being a material and starts being a compromise. The resins below are the correct alternatives, each with trade-offs that need to be understood before tooling is cut.

Polycarbonate (PC) Injection Molding

Polycarbonate is the resin engineers reach for when the part needs impact resistance that ABS can’t deliver, optical clarity, or a continuous-use temperature above 100 °C. It’s also one of the more unforgiving resins to process — moisture, gate geometry, and wall transitions all have outsized effects on the finished part.

Common Failure Modes in PC Parts

The majority of first-shot rejections in polycarbonate injection molding come from three sources:

• Splay / silver streaks — moisture in resin before molding. Fix: pre-dry at 120 °C min 4 hrs, check hopper temperature
• Cracking near gate — shear stress from undersized or pin-point gates. Fix: minimum gate diameter 1.0mm for wall ≥2mm; prefer edge or submarine gate
• Warpage on flat faces — asymmetric cooling from uneven wall thickness. Fix: maintain wall uniformity ±20%; increase mold temperature to 100 °C+
• Stress whitening — sharp corners under load. Fix: minimum corner radius R = 0.5× wall thickness on the drawing

Nylon Injection Molding — PA6 and PA66

Nylon is the structural workhorse of engineering plastics. PA66 runs at a higher melt temperature than PA6 and delivers better fatigue and heat resistance; PA6 has slightly better impact toughness and is cheaper per kg. For mechanical parts — gears, brackets, snap-fits, clips — both outperform ABS injection molding on tensile and flex modulus.

The critical characteristic of nylon that engineers underestimate: it is hygroscopic. PA6 can absorb up to 3.5% moisture at equilibrium. That moisture changes dimensional stability — parts that pass CMM inspection at molding can shift by 0.15–0.3mm in humid environments. If your application has tight running clearances, this must be accounted for in your tolerance stack.

Glass-Filled PA66 — What Changes

GF30 (30% glass fiber) is the most common structural upgrade. Tensile strength roughly doubles versus unfilled PA66 and heat deflection temperature rises to ~240 °C. The trade-off: the fiber orientation follows flow direction, creating anisotropic shrinkage. Parts with asymmetric ribs or off-center gates warp predictably along the fiber axis. Gate location becomes a structural decision, not just a flow decision.

We recommend requesting a Moldflow simulation report before cutting steel on GF30 parts with long flow lengths or thin rib geometry. This is available as part of our DFM review process.

PEEK Injection Molding

PEEK (polyetheretherketone) sits at the upper end of thermoplastic injection molding in terms of both performance and process difficulty. Continuous-use temperature to 260 °C, chemical resistance to virtually all organic solvents, excellent fatigue strength, and sterilization compatibility — PEEK is specified in aerospace, semiconductor, and medical-grade component applications where no lower-cost resin meets the spec.

The processing challenge: PEEK requires a barrel temperature of 360–400 °C, which is 80–120 °C above the processing window of PC or GF-PA66. Standard injection machines run to ~350 °C barrel max. PEEK requires a dedicated high-temperature press with reinforced screw and barrel — running PEEK on a standard machine degrades the resin and damages the equipment. We run PEEK on quoted projects with confirmed volume; contact us to discuss feasibility before submitting a drawing.

Mold steel selection for PEEK is not optional: P20 and soft aluminum tooling cannot withstand the combination of high injection pressure and mold temperature required. All PEEK tooling we produce uses H13 as a minimum. For prototype tooling runs in PEEK, semi-hardened H13 with careful gate sizing is the standard approach.

PC vs. Nylon vs. PEEK — Selection Guide

Most engineers arrive at resin selection by elimination rather than design: PEEK when PA66-GF30 fails the heat or chemical spec; PA66 when ABS fails the structural or wear spec; PC when ABS fails the impact or clarity spec. The table below maps common application requirements to the appropriate resin.

For parts that need both impact resistance and structural stiffness, a PC/ABS blend is often the more practical choice than either pure resin. We stock PC/ABS blends and can run them on the same tooling as standard PC — ask about material substitution during DFM review.

If your assembly uses a soft-touch grip or flexible seal layer, polypropylene injection molding and TPE/TPU injection molding are typically the substrate and overmold pairing — not PC or PEEK. PP runs at a lower barrel temperature (200–240 °C) and is substantially cheaper per kg; TPU overmolding on a PA66 substrate is one of the most common configurations we see for ergonomic handles and snap-fit enclosures.

If your part uses insert molding or overmolding, resin selection also affects bonding compatibility and differential shrinkage between the substrate and overmold layer — this needs to be flagged in the RFQ so we can advise on gate location and process sequencing.

Engineering Resin Molding from Vietnam — Cost Position

Section 301 tariffs apply a 25–145% import duty on Chinese-manufactured plastic parts entering the US. Vietnam-origin parts enter at 0% under current trade classification. For PC and PA66-GF30 components — which already carry a material cost premium over commodity resins — the tariff differential represents a significant total landed cost advantage.

EVFTA gives EU-bound shipments preferential tariff treatment. Cat Lai Port (25km from our facility) connects to West Coast US in 18–22 days by sea freight, or 2–3 days to LAX by air if your program timeline requires it.

Frequently Asked Questions