Nylon

Nylon — polyamide, PA — is the workhorse engineering thermoplastic for moving parts. The family covers PA6 with melting point 220 °C, PA66 at 260 °C, and PA12 at 178 °C, with unfilled tensile strength of 75–85 MPa and glass-filled grades reaching 180 MPa. Density sits between 1.04 and 1.45 g/cc depending on filler.

What makes nylon special is its low coefficient of friction (0.2–0.4 against steel), self-lubricating behaviour and fatigue resistance. Gears, bushings, conveyor wheels, automotive intake manifolds, fuel-line connectors, sporting goods and 3D-printed functional prototypes all rely on PA chemistry. Nymax, Zytel, Vestamid, Akulon and Ultramid are the resin families you will encounter most in industrial work.

The catch is moisture. PA6 absorbs up to 3.5 % water at saturation and grows roughly 0.6 % per 1 % moisture; PA66 absorbs around 2.5 %, PA12 only 1.5 %. That single property dictates which grade lives in which environment, and ignoring it is the most common reason nylon parts fail in the field.

Resin pricing in 2026 runs USD 3.20–4.50 per kg for unfilled PA6, USD 4.50–6.00 for PA66, and USD 9–14 per kg for PA12 powders used in MJF and SLS. Glass fibre adds 10–25 % depending on loading.

Nylon replaces metal where lubrication, weight and cost matter more than absolute stiffness. A glass-filled PA66 intake manifold weighs 50 % less than the cast aluminium it replaced and dampens noise enough to skip an extra acoustic shield. Bushings made from PA6 with internal MoS₂ run for years against a hardened steel shaft without grease.

Glass-fibre reinforcement transforms the property set. PA66-GF30 (30 % glass) raises tensile from 80 MPa to 180 MPa, modulus from 2.8 GPa to 9.5 GPa, and heat-deflection temperature from 75 °C to 250 °C at 1.8 MPa load. That is metal-replacement territory in everything except creep performance under sustained load above 80 °C.

On the additive side, MJF and SLS have made PA12 the default for end-use 3D-printed parts: isotropic Z-strength within 80 % of XY (versus 30–50 % for FDM), surface finish that beats most printed plastics, and per-part costs of USD 60–280 for a 100 × 100 × 50 mm functional housing. That economic window was simply not available in 2018.

Reference part: a 90 × 60 × 30 mm geared bracket with a 12 mm shaft bore and four mounting bosses. Quantities reflect typical Orinovate batch sizes from prototype through production.

Picking the right amide chemistry is half the design battle. Use PA6 where toughness and surface finish matter more than heat; PA66 where heat and stiffness lead; PA12 anywhere humidity is unpredictable or part dimensions are non-negotiable.

Nylon is process-friendly in injection moulding and the powder-bed 3D processes; less so in CNC where heat from cutting can absorb humidity mid-cycle and warp blanks. Match the process to the volume and tolerance band you actually need.

The mapping below is what Orinovate quotes most often. Each row reflects an actual job from 2025–2026, with the grade and process that survived qualification.

Wall thickness for injection-moulded PA sits at 1.0–3.5 mm. Below 1.0 mm you risk short shots in glass-filled grades; above 3.5 mm you trap voids in the thick zone because the skin freezes before the core. Maintain ±10 % wall uniformity and use 3:1 transitions on thickness changes.

Plan for shrinkage that varies with fibre orientation. Unfilled PA6 shrinks 1.5–2.0 % isotropically; PA66-GF30 shrinks 0.4 % along flow but 1.2 % across flow. Long thin parts will warp toward the gate side unless you balance gate count or design ribbing that controls warpage. For 3D-printed PA12, design Z-axis features expecting +0.3 % growth from cake heat soak.

For wear duty, target a surface roughness Ra < 0.8 μm on the moving face and a hardness differential where the steel shaft sits at HRC 55+ and the PA bushing at Rockwell M85. Keep PV (pressure × velocity) below 0.35 MPa·m/s for unlubricated PA6 and 0.7 MPa·m/s for PA6-MoS₂.

Injection-moulded nylon takes texture well — VDI 30–36 is the sweet spot for hand-feel parts; deeper textures over VDI 42 risk the glass fibre showing through as a faint grain. For painted PA, plasma-treat or flame-treat the surface first because polyamide is low-energy and primers struggle to wet without it.

MJF and SLS PA12 ship out grey-white with a slightly granular surface (Ra ~ 7 μm). The standard finishing menu is dye-bath black for cosmetic uniformity, vapour smoothing for near-injection-moulded gloss, or media tumbling to soften edges. Watertight printed parts need infiltration: cyanoacrylate for small parts, two-part epoxy for larger volumes.

CNC nylon polishes nicely once you take humidity out of the equation: machine in a < 50 % RH room, then keep the finished part in a dry bag until assembly. Adhesion uses methyl-methacrylate (MMA) or polyurethane systems formulated for low-energy plastics; cyanoacrylate works on PA12 but is unreliable on PA6 unless the surface is plasma-activated.

A Tier-1 supplier replaced an aluminium-cast manifold with a vibration-welded PA66-GF35 assembly for a 2.0 L turbocharged engine. The plastic part dropped 1.6 kg per vehicle and reduced under-bonnet noise by 4 dBA at 3 000 rpm. Surface temperature peaked at 145 °C, well within the 250 °C HDT of the chosen Zytel 70G35.

Tooling came in at USD 320 000 across two halves with gas-assist channels, vibration-welded after moulding. Per-part cost at 250 k annual was USD 18.40, against USD 31.20 for the cast-aluminium incumbent. Burst pressure exceeded 4.5 bar, twice the boost target.

The programme launched in 38 weeks from kick-off, including six iterations of mould-flow optimisation to eliminate weld lines through the EGR boss. Three years later the line has produced 720 k units with a field-return rate below 14 ppm.

An industrial-inspection drone OEM moved from FDM PA-CF prototypes to MJF PA12 production for arm clamps, gimbal mounts and battery trays. Annual volume of 2 400 ship-sets did not justify injection-moulding tools, but consistency across 30+ part numbers did require a process upgrade.

Per-part cost across the 14 unique MJF parts averaged USD 88, with lead time of five working days from order to packed. Tensile testing showed 48 MPa XY and 41 MPa Z — within 85 % isotropy, comfortably above the 30 MPa design minimum. Total annual spend with Orinovate was USD 760 000, replacing what had been USD 1.4 M of FDM and small-run urethane casting.

The qualifying programme took nine weeks: three for first-article dimensional capability across all 14 parts, four for drop-test and vibration sign-off, two for field trial. Twelve months in, the OEM reports an 18 % weight saving versus the previous mixed-process build.

A North American snack-food plant replaced bronze bushings with cast-and-machined PA6 (Nylacast Nylube) on a 60 m conveyor that ran 22 hours a day. The original bronze parts needed grease re-lube every 14 days; the food-safety team wanted a dry solution.

We supplied 480 bushings of 28 mm bore × 35 mm OD × 22 mm length at USD 9.80 per part, machined from cast PA6 stock with internal solid lubricant. Lead time was 16 working days. Surface speed at the conveyor pulley measured 0.45 m/s, pressure 0.6 MPa — PV of 0.27 MPa·m/s, well inside the 0.35 limit for unlubricated PA6.

Eighteen months later the bushings showed 0.18 mm diametral wear against the original 0.35 mm allowance, projecting a 4-year service life. Lubrication labour was eliminated, saving an estimated USD 41 000 per year on a USD 14 800 retrofit cost.

Nylon rewards designers who pick the right amide for the right environment. PA6 for cost-driven indoor parts, PA66 when heat and stiffness matter, PA12 wherever moisture is unpredictable, PA46 and PPA when the application sits beyond 200 °C. Reinforce with glass when you need metal-replacement strength; leave it neat when you need toughness and surface quality.

Treat moisture as a first-class design variable: dry the resin before moulding, condition before measuring, and choose grades whose saturation behaviour matches the service environment. Do that, and nylon will deliver gears, housings and structural parts that match metal at half the weight and a third of the cost.