CRP Technology’s Windform RS Heavy Duty is a selective laser sintering feedstock based on a glass-fibre-reinforced polyamide matrix. The powder is positioned for functional prototypes and short-series production components in motorsport, aerospace, and industrial automation where thick sections and mechanical load require a higher safety margin than general-purpose polyamide 12. Manufacturer-published data for the RS Heavy Duty platform list density 1.24 g/cm³ to ISO 1183-1, tensile strength 55.2 MPa, tensile modulus 3715 MPa, elongation at break 3.4% to ISO 527-2, flexural strength 82.7 MPa and flexural modulus 3654 MPa to ISO 178, notched Izod impact 32.6 J/m to ASTM D256, and heat deflection temperature 187.3°C at 1.82 MPa to ISO 75-2. The grade therefore occupies a stiffness band above unfilled polyamide 12 powders but below carbon-filled Windform SP and Windform XT 2.0. Its main technical role is to reduce the trade-off between elevated-temperature resistance and impact tolerance in laser-sintered glass-filled parts.

What Distinguishes the Heavy Duty Grade from Standard Windform RS and General-Purpose PA12?

The primary distinction is filler architecture. General-purpose polyamide 12 SLS powders for low-load visual prototypes typically exhibit tensile modulus below 2.0 GPa and heat deflection temperatures below 150°C at 1.82 MPa when tested to ISO 75-2. The glass-filled RS Heavy Duty raises the modulus above 3.6 GPa and the heat deflection temperature above 185°C. The shift is not free: elongation at break falls to approximately 3.4%, and notch sensitivity increases relative to unfilled nylon. Compared with the standard Windform RS formulation, the Heavy Duty designation is claimed by the manufacturer to target thicker cross-sections with reduced curl and improved dimensional stability, although published comparative data for Heavy Duty versus standard RS is limited. The glass reinforcement increases melt viscosity during sintering, which narrows the build window and requires a part bed temperature closer to the crystallization onset. On production equipment this is typically 8–15°C below the powder melting peak, as measured by differential scanning calorimetry. Operators therefore observe higher sensitivity to powder refresh rate and chamber temperature drift than with unfilled polyamide 12.

In production SLS systems using CO₂ lasers of 30–60 W and layer thickness of 0.12 mm, Windform RS Heavy Duty is processed with nitrogen inerting at oxygen levels below 1.5% by volume. The powder is supplied in sealed containers and is conditioned at 25–30°C and 30–40% relative humidity before charging. Moisture content above 0.12% by mass is not recommended because it reduces powder flowability and increases the incidence of impact-failed coupons. Refresh rates of 30–50% used powder to virgin powder are typical for glass-filled polyamide systems to maintain elongation at break above 3.0%. Lower refresh rates concentrate degraded polymer chains, causing a measurable drop in notched Izod impact and a rise in visible edge porosity. Build orientation is fixed by the anisotropic layer-bond strength of SLS: Z-oriented coupons tested to ISO 527-2 commonly retain 80–90% of the XY ultimate tensile strength. For components with hydraulic sealing faces, as-sintered surfaces of Ra 10–15 µm are not sufficient for elastomeric O-ring glands and require insert machining or sealing compound. Post-process heat treatment in a circulating oven at 150°C for 2 h can stabilise dimensions by relaxing internal stress gradients, but it may also increase surface oxidation if oxygen is not excluded.

Thermal and Mechanical Specification Matrix

Because the Heavy Duty designation is a load-oriented positioning within the RS series, the matrix reports the published RS-family data. Lot-specific certificates of analysis should be used for application allowables, and mechanical property data are generated on specimens conditioned to 23°C and 50% relative humidity according to ISO 291 unless otherwise specified.

Typical applications include motorsport ducting, intercooler end tanks, oil-cooler brackets, UAV gimbal supports, wind-tunnel test components, and assembly fixtures that cycle through paint-bake temperatures. In underhood service, the heat deflection temperature of 187.3°C at 1.82 MPa permits short-term thermal soak above 150°C, but continuous load at such temperatures requires creep testing because all semicrystalline polyamides lose matrix stiffness progressively before the HDT threshold. For structural brackets subjected to vibration, bolted-through load paths are preferred over threaded inserts because the notched Izod value of 32.6 J/m indicates lower crack-arrest capacity than unfilled nylon. Stainless-steel heat-set inserts with toothed flanks are used on samples when thread stripping torque exceeds 10 N·m. Dimensional control is influenced by layer orientation and part bed placement. Warpage on plates thicker than 10 mm can be held below 0.3% of the long axis when parts are orientated with the long axis parallel to the recoater travel and with a 0.2 mm shell offset applied to mating bores before shot peening. The grade is also used for soft-jaw tooling and robotic end-of-arm tools, where its density of 1.24 g/cm³ lowers moving mass relative to metal tooling while retaining enough compressive stiffness to resist deformation under clamping loads below 50 MPa.

When Carbon-Filled Windform SP Is Over-Specified for Medium-Stiffness Hardware

Carbon-filled Windform SP and Windform XT 2.0 are selected when the tensile modulus required by the assembly exceeds 8.0 GPa, as often occurs in thin-wall structural bracketry. The RS Heavy Duty grade is a lower-stiffness alternative. Its tensile modulus of 3.7 GPa reduces weight penalty versus carbon-filled systems only marginally, because density is higher than Windform SP by approximately 6%, but it avoids the electrically conductive nature of carbon-filled feedstock, which can accumulate in machine filter assemblies and complicate electrostatic discharge control. In addition, glass-filled RS Heavy Duty produces less tool wear in secondary CNC drilling and tapping than carbon-filled Windform SP, a relevant consideration for production runs exceeding 100 parts per batch where tool replacement intervals become part of cost-per-part. The thermal boundary is similar: both carbon-filled and glass-filled Windform grades are rated above 170°C HDT at 1.82 MPa, but carbon-filled grades may show anisotropic thermal expansion coefficients with differences between XY and Z approaching 25–35%, whereas glass-filled RS Heavy Duty is more orthotropic in-plane. This makes RS Heavy Duty preferable when parts must hold holes on multiple planes after thermal cycling.

The manufacturer supplies RoHS and REACH statements for the Windform RS Heavy Duty powder. The material is not designed for food-contact use under FDA 21 CFR 177 or for potable water contact without an approved barrier coating. If the end-use environment requires UL 94 V-0, Windform FR2 or Windform FR1 should be specified instead of RS Heavy Duty, because the standard glass-filled grade can burn and should not be installed adjacent to ignition sources. Chemical exposure to aliphatic hydrocarbons, common in motorsport, generally follows the behaviour of polyamide 12 in ISO 175-based immersion tests, but exposure to glycol-water coolants at temperatures above 90°C can reduce tensile strength through plasticisation; published data for this specific configuration is limited. For outdoor UV exposure, the glass-reinforced matrix requires a black UV-stable coating or painted surface because unprotected polyamide oxidation will embrittle thin walls. Steam autoclaving is not recommended for load-bearing parts because repeated steam exposure can reduce elongation at break by a process-dependent amount and can promote hydrolytic chain scission in the polyamide matrix.