CRP Technology supplies Windform RL as a laser-sintering thermoplastic elastomer powder within the Windform product family. The material is positioned for flexible, non-filled selective laser sintering applications requiring rubber-like deformation and low Shore hardness. Published datasheet values list density at 0.97 g/cm³ under ISO 1183-1, Shore A hardness at 70–75 under ISO 868, tensile strength at break at 5.0 MPa under ISO 527-2, and elongation at break at 250% under ISO 527-2. These properties distinguish Windform RL from glass- and carbon-filled Windform grades, which are specified for rigid or semi-rigid functional prototypes. The low tensile modulus, typically reported near 8 MPa, places the material in a separate design space: it can accept repeated flexure without permanent failure, but it cannot substitute for PA12 in load-bearing brackets or structural housings. The powder is intended for use on commercial selective laser sintering systems with machine-specific parameter files supplied by CRP Technology.

Feedstock composition and published mechanical property envelope

The powder's published mechanical response places it in the low-modulus elastomer class. Tensile modulus is reported at 8 MPa under ISO 527-2, and flexural modulus at 12 MPa under ISO 178. These values are approximately two orders of magnitude below the 1,400–1,800 MPa flexural modulus range commonly cited for dry PA12 SLS feedstocks. Consequently, a wall thickness of 1.5 mm in Windform RL behaves as a flexible membrane, whereas the same geometry in PA12 is a rigid panel. Shore A hardness is measured under ISO 868; Shore D is not an appropriate scale for this feedstock because soft thermoplastic elastomer grades are not well differentiated by Shore D indentation. Tear strength near 20 kN/m under ISO 34-1 indicates that the material can tolerate rounded convolution roots, but sharp notches and parting-line defects remain crack-initiation sites. The published density under ISO 1183-1 is 0.97 g/cm³. Because the material is unfilled, sintered surfaces have a matte, elastomeric appearance rather than the fiber-marked surface of glass-filled SLS products.

The property comparison below uses representative published values. Batch release values may differ, and direct comparison is valid only when the same specimen geometry, orientation, and conditioning history are used.

What Build Chamber Conditions Are Required for Elastomeric SLS?

Across commercial SLS platforms, Windform RL is processed at a nominal layer thickness of 0.12 mm. The build chamber is maintained within a narrow thermal band below the powder's melting onset to keep unsintered powder free-flowing while fused layers remain sufficiently hot for interlayer adhesion. If the setpoint is too low, parts curl at free edges and show interlayer delamination; if too high, unsintered powder can form partially fused cake that is difficult to recycle. Machine-specific parameter files from CRP Technology are the normal starting point on CO₂ laser systems. Operators should not adjust laser power, scan count, or scan spacing independently without thermal validation, because the energy-density window for elastomeric SLS is tighter than that of filled PA12. A low-modulus material has less stiffness to resist curl during early layers, so thermal drift of ±2 °C from the qualified bed temperature can produce visible lift in flat unsupported regions.

On a typical 30 W CO₂ SLS system, the scan strategy for Windform RL uses lower effective energy density than glass-filled PA12 because the feedstock has no fiber reinforcement and is more susceptible to over-sintering. Process validation usually includes a raster scan pattern with broad overlap rather than high laser power; the target is a melt depth that penetrates one layer while avoiding vaporization at the surface. Because the material has a low modulus, local overheating can create a soft, under-cured area that later becomes a tear-initiation site. Published open parameter sets for Windform RL are limited; most machine builders rely on encrypted parameter files, so independent users should use trial builds with infrared surface temperature monitoring.

Powder aging is more consequential for Windform RL than for rigid polyamides. Repeated exposure of unsintered powder to bed temperature raises the fraction of thermally damaged particles, which reduces melt elongation and may increase the minimum wall thickness needed for watertight structures. Service bureaus typically monitor melt-flow response or powder-bed temperature behavior instead of relying on a fixed numerical refresh ratio. When the refreshed powder fraction is too high, the visual surface may appear smoother but tear resistance and low-temperature flexibility can fall; when too low, elongated parts may build with porosity. On EOS P-series and similar platforms, grounding and sieving procedures are the same as for PA12, but elastomer powders can retain more static charge during dry conditions, causing clumping in feed hoppers and uneven powder spreading.

Depowdering of convoluted thin-walled parts requires more time than rigid SLS parts because flexible walls can shield powder pockets. Compressed air from low-pressure nozzles should be used rather than hard mechanical picks to avoid surface scoring. After depowdering, glass-bead blasting is often applied to reduce open-pore surface roughness, but the resulting surface remains rougher than injection-molded TPE. The blasting operation should be controlled for time and air pressure because excessive impact can generate local heating and surface deformation in low-modulus elastomer walls.

Assessing Batch-to-Batch Variability and Incoming Powder Acceptance

For production runs, incoming powder should be subjected to a defined acceptance procedure because batch shifts in melt-flow behavior can alter sintered part elongation. The supplier's datasheet provides a baseline, but build-service operators typically verify powder flow, bulk density, and particle-size distribution before a new lot is introduced. A laser diffraction method such as ISO 13320 is used for particle-size distribution; anomalous fines content can increase powder-bed density and reduce part elongation. Apparent bulk density can be checked under ISO 3923-1. Melt-flow rate, where reported by the supplier, is not a substitute for sintered-coupon testing but can identify gross batch deviations. Quality control should also include a build of standardized tensile bars in XY and Z orientations at the start of each campaign. If z-axis elongation drops below the production requirement, the bed temperature, powder refresh ratio, or scan parameters should be reviewed before committing to full builds. This specificity matters because the combination of flexible powder and low-modulus parts can mask porosity in thick sections until flexible-wall fatigue testing reveals early cracking.

Flexible parts produced from Windform RL are used for convoluted bellows, dust covers, cable glands, gaskets, protective covers, and soft-touch enclosures. Typical flexible wall thickness ranges from 1.0 mm to 2.5 mm, while mounting flanges are thickened to 3.0 mm or more to provide clamping compression. A common failure observed in production-like prototypes is delamination at the flange-to-wall transition when a sharp corner is used; a radius of at least 0.5 mm is recommended at the convolution root. Bellows are typically built with a corrugated profile rather than a nominally straight cylinder; the corrugations allow compression and extension without stretching the wall beyond its elastic limit. For a bellows designed with wall thickness 1.5 mm, the pitch, convolution angle, and root radius should be defined in CAD rather than transferred directly from a cast rubber drawing. SLS can produce a taper in wall thickness, but dimensions below 0.8 mm may be difficult to clean and can tear during depowdering.

Sealing applications require additional validation because tensile and tear values do not predict leakage or compression set under thermomechanical load. Compression set testing under ISO 815-1 should be performed on printed specimens at application temperature, not on injection-molded plaques. Published data for Windform RL in specific compression-set configurations is limited, so prototype validation is mandatory. Cyclic flex testing of bellows should use the actual stroke length and frequency; a standard tensile coupon test under ISO 527-2 is not a substitute for flex fatigue. For low-leakage dynamic seals, surface roughness and open porosity may require secondary sealing or coating because the as-sintered surface is not a homogeneous molded skin. For static gaskets, flange thickness should be at least 3.0 mm and the sealing land should be continuous to compensate for the as-sintered surface roughness.

When compression set, tear strength, and density differentiate elastomer powders

In comparative powder evaluations, Windform RL differs from SLS TPU powders primarily in density and hardness. The density of 0.97 g/cm³ under ISO 1183-1 is lower than the 1.06–1.10 g/cm³ density range of many commercial SLS TPU powders, giving Windform RL a mass reduction at equal volume. Shore A hardness of 70–75 under ISO 868 is below the Shore A 85–90 of many SLS TPU products; this increases compliance for low-pressure gaskets but reduces resistance to extrusion under high fluid pressure. Against PA12 SLS, the difference is not incremental: PA12 tensile strength near 48 MPa under ISO 527-2 and flexural modulus near 1,500 MPa under ISO 178 support structural components, while Windform RL tensile strength near 5.0 MPa limits its use to flexible or damping functions. The material also differs from glass- and carbon-filled Windform grades, which use fiber reinforcements to increase modulus and thermal distortion resistance. Because fiber-filled rigid grades and Windform RL are processed from separate powder beds, a single SLS build cannot produce a monolithic part with a rigid mounting bracket and flexible bellows; multi-material assemblies are produced as separate parts and joined mechanically or with adhesive.

Compared with cast polyurethane elastomers, Windform RL may show lower tear strength and higher compression set, but it eliminates the need for mold tooling and allows internal channels to be formed without cores. Compared with liquid silicone rubber, SLS Windform RL cannot match high-temperature stability or optical clarity, but it can produce hollow convoluted shapes without mold-parting lines. Published data for Windform RL as a direct replacement for silicone in high-temperature seals is limited, and substitution should be made only after prototype testing. The low hardness of Windform RL also means that thread-forming screws and press-fit inserts designed for PA12 may not achieve reliable clamp retention without a molded or insert-supported feature.

Because elastomeric SLS parts are often exposed to automotive, rail, or industrial sealing environments, chemical resistance and continuous service temperature should be confirmed before production. The standard datasheet does not list a full continuous-service temperature curve under ISO 2578 for every wall thickness; thermal aging at the upper application temperature should be validated on printed specimens. For contact with oils, greases, or cleaning agents, immersion testing should use the specific chemical, temperature, and strain condition. The powder should be stored in a dry area; if exposed to relative humidity above 60%, pre-drying at the supplier's specified time and temperature is recommended to prevent steam porosity in thick sections. The product is not a flame-retardant SLS feedstock; applications requiring UL 94 V-0, railway flammability, or other fire-safety classification require a dedicated FR-grade material rather than post-treatment of Windform RL. Users should verify REACH, RoHS, and any food-contact status from the current product SDS and technical datasheet because regulatory compliance can change with batch blending and region.

Post-process bonding of Windform RL to rigid SLS parts is usually performed with cyanoacrylate or structural polyurethane adhesives after surface activation. Because the material is a low-surface-energy elastomer, surface treatment is required to improve wetting. Atmospheric plasma or corona treatment can raise bond strength, but published data for this specific configuration is limited. Mechanical interlocking is preferred over adhesive bonding for structural joints because flexible deformation can peel a stiff adhesive layer. If a gasket is assembled into a rigid PA12 housing, closed-loop compression and limiting stops should be included to prevent excessive deformation that leads to extrusion and seal failure.