Nylon Injection Moulding: PA6 and PA66 Guide
Nylon (polyamide) is the default engineering thermoplastic for load-bearing, heat-exposed, and chemically challenged mechanical parts. PA6 and PA66 cover the bulk of applications; add 30% glass fibre and the material rivals cast aluminium brackets at a fraction of the weight. The trade-off is moisture absorption—Nylon takes water from the air and changes dimension as it does, which has to be designed for in any close-tolerance assembly.
Mechanical and Thermal Properties
Nylon is semi-crystalline. The table below shows dry-as-moulded (DAM) values. Once parts absorb moisture during service conditioning, impact resistance and toughness improve, but stiffness and tensile strength decrease slightly.
| Property | PA6 (unfilled) | PA66 (unfilled) | PA66-GF30 |
|---|---|---|---|
| Tensile strength (dry) | 70–85 MPa | 80–90 MPa | 170–195 MPa |
| Flexural modulus (dry) | 2,700–3,200 MPa | 3,000–3,500 MPa | 9,000–11,000 MPa |
| Elongation at break | 30–150% | 20–80% | 2–5% |
| Notched Izod impact | 5–7 kJ/m² | 4–6 kJ/m² | 9–12 kJ/m² |
| Heat deflection temp (1.8 MPa) | 55–65°C | 70–90°C | ~250°C |
| Continuous use temp | 85–100°C | 100–115°C | up to 150°C |
| Water absorption (24 h) | 1.3–1.6% | 1.0–1.3% | 0.7–1.0% |
| Mould shrinkage (unfilled) | 1.0–2.0% | 1.5–2.5% | 0.3–0.7% (flow dir.) |
The HDT jump on PA66-GF30—from ~90°C unfilled to approximately 250°C—is real and verified against multiple grade datasheets. It is the reason glass-filled Nylon dominates under-bonnet automotive applications.
Common Applications
Automotive: Intake manifolds, cooling system connectors, and engine covers. Nylon's resistance to engine oils, coolants, and elevated temperatures makes it ideal for under-the-hood use in both PA66 and PA66-GF30 grades.
Industrial Gear and Bearings: Bushings, cams, and small gears. The low friction coefficient allows smooth operation with minimal lubrication, though POM is often preferred where dimensional stability in humidity is critical.
Structural Brackets: Power tool housings and industrial clips. PA66-GF30 is routinely used as a lightweight alternative to cast aluminium in non-critical structural roles.
Electrical: Connectors and terminal blocks. Flame-retardant (UL 94 V-0) grades are available specifically for electrical-safety applications.
Processing and Design Guidelines
Nylon has a sharp melting point—above it the material flows like water, below it it solidifies quickly. That's great for filling thin walls, but it also means flash is a real risk if the tool parting line isn't held to close tolerances.
- Moisture Control: Dry for 4–8 hours before moulding. Moisture content above 0.2% produces splay and brittle parts. This is not a nice-to-have—it directly determines part quality.
- Wall Thickness: 1.5–3.5 mm. Thick sections in Nylon are prone to sink marks and internal voids; keep walls as uniform as possible.
- Shrinkage and Warp: Unfilled PA66 shrinks up to 2.5%. Glass filling is the most effective counter-measure for flat or structural parts. GF30 shrinkage in the flow direction is typically 0.3–0.7%, but cross-flow direction remains higher (0.7–1.2%), so anisotropic warp is possible if gating creates strongly directional flow.
- Draft Angles: Minimum 0.5° for unfilled grades. For glass-filled Nylon, use 1–2°—the fibres make the material more abrasive against the cavity wall and increase ejection resistance.
- Radii: Nylon is tough but notch-sensitive at sharp corners. Generous radii maximise fatigue life and impact resistance.
Material Grades
| Grade | Feature | Typical Use |
|---|---|---|
| PA6 Natural | Economical, easy flow | Cable ties, small clips |
| PA66 Natural | Heat and stiffness | Automotive connectors |
| PA66-GF30 | High rigidity and HDT | Engine brackets, tool bodies |
| PA66-GF50 | Extreme stiffness | Structural load-bearing |
| Flame-Retardant | UL94 V-0 | Circuit breakers, switches |
| PA12 | Low moisture absorption | Outdoor sensors, fuel lines |
For parts exposed to persistent moisture or submersion, PA12 absorbs far less water than PA6 or PA66 and maintains better dimensional stability—at higher material cost.
Advantages and Limitations
Why choose Nylon:
- High strength and stiffness, especially in glass-filled grades.
- Excellent fatigue resistance under repeated mechanical stress.
- Naturally resistant to oils, fuels, and many common industrial chemicals.
- Good for moving parts where some lubricity is needed.
What to watch for:
- Moisture uptake: Parts swell up to ~0.5% as they absorb moisture during conditioning. This must be accounted for in tight-tolerance assemblies.
- DAM vs conditioned properties: Tensile strength and stiffness are lower in conditioned parts than the DAM datasheet values—design to conditioned properties for structural applications.
- Chemical sensitivity: Strong acids and bases attack Nylon.
- Tool wear: Glass-filled grades will wear aluminium tooling; specify hardened steel for high-volume glass-filled runs.
Choosing Nylon vs Alternatives
- Nylon vs PP: Choose Nylon for load-bearing or elevated-temperature use. Choose PP for price, moisture resistance, or if the part needs a living hinge.
- Nylon vs POM: Choose Nylon for glass reinforcement, high impact, or extreme temperature requirements. Choose POM for the best dimensional stability in humid or wet conditions.
Sustainability
Nylon carries resin code 7. It has value in industrial recycling streams and is commonly reprocessed into fibre for the textile industry. Up to 20% regrind can typically be incorporated in non-structural parts. Bio-based polyamides made from castor oil are an option for sustainability-focused projects.
Nordmould provides tooling from €3,000 and low-volume production starting at 100 pieces. Send us your STEP file for a free DFM review—we'll verify wall thicknesses and advise on the right glass-fill percentage for your application.