The selective laser sintering elastomer sold under the designation Windform TPU is a thermoplastic polyurethane powder formulated for polymer powder-bed fusion systems. Unlike polyamide-11 and polyamide-12 powders that dominate general SLS production, this grade is developed to deliver rubber-like elongation and low tensile modulus after laser consolidation. The powder is supplied as a free-flowing, near-white elastomer raw material with a bulk density of approximately 0.60 g/cm³; the sintered part density is reported in the range 1.03–1.10 g/cm³ when measured by displacement methods based on ISO 1183-1. Mechanical characterization is usually performed according to ASTM D412 or ISO 37, and the grade is typically associated with a Shore A hardness of 65–70, tensile strength from 5 MPa to 8 MPa, and elongation at break from 200% to 350%. These ranges are not deterministic specification limits; they shift with build orientation, powder-reuse fraction, and the laser scan strategy selected on the SLS machine. The material is intended for parts that require repeated bending, impact recovery, sealing compliance, or abrasion resistance without the stiff reinforcement found in carbon- or glass-filled Windform composites.

The tabulated values are drawn from public technical-data compilations and should be treated as engineering reference points rather than guaranteed acceptance criteria. For production, the current supplier technical data sheet, powder batch certificate, and ISO 9001-controlled measurements on the target SLS platform provide the binding values.

What separates Windform TPU from rigid laser-sintering grades?

The closest reference points in the Windform product portfolio are filled and unfilled polyamide-based powders. Rigid Windform grades such as Windform LX 3.0 and Windform XT 2.0 are measured with ISO 527-2 tensile-bar methods and show tensile moduli in the gigapascal range after glass or carbon reinforcement. Windform TPU, by contrast, is characterized with elastomer test methods such as ASTM D412, and its modulus is lower by two to three orders of magnitude. This difference is visible in part design: a clip or hinge made from Windform TPU accepts large recoverable deflection, whereas a glass-filled grade would fracture or require a live hinge. Compared with commodity unfilled polyamide-12 SLS powders, the TPU grade provides lower tensile strength and lower stiffness but much higher elongation and elastic recovery after strain; a PA-12 part may exhibit 10–30% elongation at break, while the TPU elastomer commonly exceeds 200%. The main trade-off is creep resistance: the TPU is not dimensionally stable under sustained load at elevated temperature, and it is not recommended as a load-bearing structural replacement for polyamide composites.

Within the broader SLS elastomer market, high-hardness TPU powders formulated for Shore A 85–90 are available. Windform TPU is positioned below that hardness band, which reduces spring force and sealing compression load but also lowers abrasion resistance relative to harder TPU chemistries. Users selecting between elastomer powders should test the specific compression force, recovery, and dynamic wear under the application duty cycle rather than relying on hardness alone.

In production, Windform TPU is used for convoluted bellows, dust boots, gaskets, protective covers, cable-management sleeves, and hand-held instrument grips. Because SLS does not require mold tooling, elastomer parts can be produced with internal return flanges, undercut sealing lips, and lattice padding that would require complex split molds or secondary bonding in liquid silicone or injection-molded rubber. A common production route involves building the part at 100–120 µm layer thickness, removing loose powder with compressed air, and then applying a light solvent or aqueous clean without aggressive alkaline detergent. The primary process benefit is geometric freedom; the main limitation is that sintered TPU surfaces have a characteristic granular texture and require tumbling or coating if low friction or smooth sealing contact is required.

Typical SLS machine settings for this material class involve a part-bed temperature close to the onset of the polyurethane melting endotherm, laser power density sufficient to fuse the current layer without bubbling, and a scan spacing that creates overlapping melt tracks. On 100 W-class CO₂ laser systems with 300–400 mm build dimensions, the part-bed temperature commonly falls in the 80–105 °C range, but the exact value depends on powder batch molecular weight, machine thermal calibration, and ambient humidity. Parts built in Z orientation usually show lower elongation at break than XY-oriented parts, and the difference can exceed 20% of the XY value in thin wall sections because interlayer fusion is less complete than in-plane fusion. These anisotropies require the designer to orient peel lips and flexure zones in the XY plane when possible.

Tear resistance and elastic recovery after repeated loading

Dynamic sealing and bellows applications load the material in repeated tension, compression, and shear. TPU elastomers exhibit stress softening and hysteresis in the first loading cycles; after cyclic conditioning, the force-stroke curve stabilizes and recovered energy improves. For quality control, tear strength is measured using ASTM D624 or ISO 34-1, and published Windform TPU-type materials typically fall between 25 kN/m and 40 kN/m. Compression set is evaluated with ISO 815-1 under controlled deflection and temperature; values for laser-sintered unfilled TPU are commonly reported in the 20–45% range after 24 h at 70 °C, but powder porosity and build orientation can shift this value substantially. For elastomer seals, users should specify compression set, stress-relaxation, and recovery after load removal, not only hardness and tensile properties, because a seal can pass hardness testing yet fail to maintain contact pressure after thermal ageing.

Windform TPU is not suited to continuous service above the softening region of the polyurethane hard segments. The exact upper service temperature should be derived from the application rather than a single heat-deflection value, because elastomer performance is load-dependent. For dynamic parts, the user should carry out fatigue testing under expected strain amplitude; there are no universal SLS fatigue curves that transfer directly from one powder lot to another. Chemical compatibility with fuels, brake fluids, and strong polar solvents should be tested; thermoplastic polyurethane can swell or hydrolyse in humid or acidic environments, especially at elevated temperature.

When powder refresh rate and moisture control shift batch-to-batch properties

Windform TPU is hygroscopic, and powder storage procedures have a direct effect on melt quality. The supplier’s handling guidance for TPU-class powders normally requires drying in a dry-air hopper or convection oven before use when powder has been exposed to ambient humidity above 60% RH. A typical drying condition for unfilled TPU powder is 70–80 °C for 8–12 h; higher temperatures may cause powder blocking or premature degradation. Moisture content should be kept below 0.08–0.10% by mass before feeding to the SLS system, because entrapped moisture can produce porosity, cratering, and inconsistent melt tracks. Recycled powder from breakout stations must be sieved to remove agglomerates and contamination, then blended with virgin material in a controlled ratio. The optimal refresh ratio is machine- and application-specific; if recycled powder fractions exceed the validated range, the part may show reduced elongation at break and lower tear strength due to molecular weight loss and oxidized surface species. Monitoring melt flow index or solution viscosity is less informative for TPU than for polyamides; instead, the supplier and experienced service bureaus track tensile elongation and tear strength against the used-powder fraction using lot-level test coupons.

The final surface of Windform TPU parts can be sealed by solvent smoothing, but mild process conditions are required because the elastomer can absorb solvent and become sticky. Painting, bonding, and flame-lamination must account for the low surface energy and flexible substrate. Mechanical fastening is usually preferred over adhesive bonding; when adhesive bonding is unavoidable, the joint area should be cleaned with isopropyl alcohol and tested for peel strength using ISO 11339 or ASTM D6862. Dimensional control follows SLS norms: the measured part dimensions should be checked against the build geometry using a coordinate measuring machine, because shrinkage compensation factors for TPU differ from those for polyamide powders. Typical shrinkage in the XY plane is lower than in the Z direction, and the exact values depend on the powder bed temperature, part wall thickness, and scan speed.

Clamped elastomer joints such as housing seals and vibration-isolation mounts subject the material to a fixed compressive deflection. Under constant strain, thermoplastic polyurethane exhibits stress relaxation, and the residual sealing force decreases over time. The rate of decay is temperature-dependent and can be measured with ISO 3384-1. In Windform TPU parts, as with most unfilled TPU elastomers, the stress remaining after 72 h at 23 °C under a fixed compression is generally lower than the initial sealing force; after elevated-temperature exposure the remaining stress may be lower still. This behavior means that a gasket designed only from room-temperature compression force can lose sealing contact after thermal cycling. Production drawings for safety-relevant sealing parts should define the minimum residual force after accelerated ageing rather than the initial assembly force. Published stress-relaxation data for laser-sintered Windform TPU specifically are limited; qualified suppliers often generate internal data with the actual part geometry and service medium.

Transferring a validated build from a laboratory-scale SLS machine to a production system requires more than scaling laser power. The part bed temperature stability, roller or recoater geometry, and inert gas flow in the build chamber influence the local cooling rate of the melt track. A process that produces acceptable elongation on a small machine may generate unacceptable interlayer porosity on a large machine if the build chamber has non-uniform temperature across the build area. For Windform TPU, large flat sections are especially sensitive to curl because the low elastic modulus does not resist thermal shrinkage stress. Production runs should include test coupons in the corners and center of the build, and the tensile strength, elongation at break, and Shore A hardness of those coupons should be recorded against build date, powder lot, and machine operating parameters. This lot-level data is necessary because no single property value is sufficient to predict the fatigue life of an elastomer part under end-use conditions.