3D Systems Figure 4™ TOUGH-GRY 15 Plastic is a gray, single-component photoreactive resin formulated for the Figure 4 Digital Light Printing platform. The grade designation carries a nominal tensile elongation at break of 15% measured under ASTM D638-14 after standard post-cure; this numerical suffix is the primary differentiating property against lower-elongation rigid gray resins. The material is supplied as a viscous liquid with lot-controlled viscosity and requires controlled ultraviolet post-cure to convert the photopolymer network to its final mechanical state. It is positioned for functional prototypes and low-volume production parts such as snap-fit enclosures, covers, brackets, and assembly fixtures. Its gray color provides uniform component appearance without secondary painting, but the cured photopolymer is not a direct thermomechanical equivalent of injection-molded polypropylene or ABS. Selection of TOUGH-GRY 15 should be based on process-specific test data rather than datasheet values alone.

How does the material compare with rigid gray and high-temperature Figure 4 resins?

Within the Figure 4 material portfolio, TOUGH-GRY 15 occupies an intermediate position between stiff lower-elongation rigid grades and high-heat resins. The nominal elongation at break of 15% under ASTM D638-14 allows more strain before fracture than rigid gray formulations; the material is therefore specified for snap-fit closures and clips. In contrast, Figure 4 High Temp 150 is selected when service temperature dominates, because its heat deflection temperature is higher than that of TOUGH-GRY 15. The gray color and moderate stiffness distinguish the grade from elastomeric materials, which exhibit high elongation but low load-bearing capacity. Exact numerical comparisons of tensile strength, tensile modulus, flexural strength, flexural modulus, and notched Izod impact require the manufacturer's current technical datasheets and lot certificates because post-cure equipment and build orientation shift values. The table below summarizes the primary selection logic.

The property that most consistently separates TOUGH-GRY 15 from rigid gray materials is not stiffness but failure mode; rigid gray parts tend to fail in a brittle manner, while TOUGH-GRY 15 exhibits ductile yielding under short-term tensile overload. This distinction is captured by tensile elongation at break, but it must be verified on parts with notches, layer boundaries, and surface roughness because photopolymerized parts are anisotropic. Layer-plane tensile properties can differ from vertical build-direction properties.

For design calculations, tensile specimens should be built in the same orientation as production parts and tested under ASTM D638-14 in the standard atmosphere of 23±2°C and 50±10% relative humidity. Flexural modulus is reported under ASTM D790-17; hardness is commonly measured under ASTM D2240-15. Notched Izod impact under ASTM D256-10 ranks impact tolerance, but notch preparation can introduce uncontrolled crack propagation in layered photopolymers. Heat deflection temperature under ASTM D648-16 is a short-term thermal ranking value, not a continuous use temperature. The cured material is crosslinked and does not have a melting point; long-term creep can occur below the reported HDT. Thickness-dependent cure effects mean thin sections may be more converted than thick sections because light penetration and oxygen inhibition vary through the part. Standardized coupon values should therefore be treated as upper-bound estimates for thick monolithic sections unless the post-cure dose is specifically adjusted.

Part orientation during printing controls the location of layer boundaries relative to applied stress. Tensile specimens built in the vertical direction generally exhibit lower tensile strength and elongation than those built in the plane of the build platform because interlayer adhesion is a strength-limiting interface. For snap-fit features, the beam should be oriented so that bending stress does not act perpendicular to the layer planes. Support contact points should be placed away from sealing surfaces and snap feet; support removal marks act as stress concentrators. The Figure 4 platform uses grayscale or exposure variation to improve feature accuracy at the edges of down-facing surfaces, but the exact behavior of TOUGH-GRY 15 at small feature sizes should be characterized with a dimensional capability study. For high-volume builds, dense nesting can influence local irradiance and dimensional repeatability; dense packing may require a higher post-cure dose or staggered printing.

Why post-cure dose is a production variable rather than a fixed setting

In Figure 4 processing, the green state contains residual unreacted monomer and photoinitiator. Ultraviolet post-cure drives additional conversion and crosslink density; the final elongation at break, tensile strength, and heat deflection temperature are therefore governed by the post-cure unit. A low-dose post-cure may leave residual monomer that reduces stiffness and chemical resistance, while excessive dose can increase brittleness and reduce the nominal 15% elongation. The post-cure chamber should be mapped with a calibrated UV radiometer, and the material-specific dose should be expressed in joules per square centimeter rather than exposure time alone. The UV source emission spectrum should overlap the residual photoinitiator absorption band; a spectral mismatch can result in incomplete conversion even at high total dose. Chamber load density affects shadowing and reflected irradiance; parts should be rotated or rearranged to avoid under-cured surfaces facing away from the lamps. The same consideration applies to clear or translucent fixtures used in the post-cure chamber, because they can alter local irradiance. Published datasheets generated with a specific post-cure routine may not be reproduced with the same dose on a different UV system, so production qualification should include a design of experiments that varies post-cure time and chamber loading.

Processing on the Figure 4 platform uses a 405 nm LED projection system with a build layer thickness of 50 µm for production mode. Alternative layer heights may be available in the current software, but each layer setting changes cure depth, surface finish, and build time. Resin temperature should be maintained at 22–25°C before printing; cold resin increases viscosity, impairs coating and peeling behavior, and can generate delamination on large cross-sections. In uncontrolled production cells, a build-chamber temperature recorder or cabinet is used to detect temperature excursions. After printing, parts are washed in an ultrasonic bath containing ≥99% isopropyl alcohol or an approved alternative solvent for 5–10 min. Blind holes, snap-fit recesses, and internal channels require positive flushing or syringe rinsing because uncured resin trapped in these features can thermally polymerize during post-cure and produce surface defects. Residual solvent should be allowed to evaporate before post-cure. The resin tray film and projector window are production wear items; film clouding or projector contamination produces dimensional drift and soft layers. These failure modes are observed in multijob production cells and are addressed by scheduled replacement and first-article inspection.

Thermal limits and solvent contact boundaries

The cured photopolymer is crosslinked and does not exhibit a thermoplastic melting point. Short-term thermal performance is ranked by heat deflection temperature under 0.455 MPa per ASTM D648-16. Continuous load at temperatures approaching the HDT can produce creep, relaxation of press-fit joints, and loss of snap-fit retention force. The exact HDT value for a given lot is recorded on the manufacturer certificate and should be used for design rather than a generic datasheet number. Dry heat exposure may cause additional crosslinking and embrittlement over time; published aging data for this specific gray grade is limited. Solvent contact should be restricted to the cleaning solvent during post-processing. Strong ketones, aromatic hydrocarbons, chlorinated solvents, and alkaline solutions can attack the crosslinked network, especially on surfaces with residual stress or powder from support removal. Extended immersion in isopropyl alcohol beyond the recommended cleaning window is not advised because environmental stress cracking may initiate at surface flaws. The uncured resin should be kept away from water and humid air, as moisture can reduce cure conversion and create surface haze. Cured parts can be wiped with mild soap and water, but long-term hydrolytic aging data is limited.

Snap-fit enclosures, covers, and brackets are typical application contexts because the nominal 15% elongation at break under ASTM D638-14 gives a larger strain window than a rigid gray photopolymer. However, tensile elongation at break is not a direct predictor of snap-fit cycle life. Cantilever snap beams should be evaluated for root radius, deflection distance, insertion angle, and build orientation; support removal on the underside of a snap beam can leave rough surfaces that initiate fatigue cracks. Cyclic loading performance is not fully characterized in the published literature for this specific resin; part-level testing should record cycles to first crack, retention force loss, and permanent set. Snap-fit insertion force can be measured on a calibrated universal testing machine with displacement control, and retention force after cycling should be recorded. The material is not a drop-in replacement for injection-molded polypropylene living hinges because the crosslinked network cannot undergo the same cold-drawing mechanism. If a hinge is required, the hinge should be designed below the yield strain and post-cured in a constrained condition to avoid warpage. Under static overload, TOUGH-GRY 15 tends toward ductile yielding, but strain rate and notch severity strongly influence the observed failure mode.

When jigs and assembly fixtures require dimensionally stable gray parts

Assembly fixtures and jigs may be produced from TOUGH-GRY 15 when dimensional stability and moderate impact resistance are required at ambient temperature. The gray color reduces glare and allows part orientation marks to be read under shop-floor lighting. In these applications, the fixture should be post-cured to full conversion and inspected for flatness because large flat plates can distort during post-cure if the chamber irradiance is not uniform. Residual stress from the build process can relax over the first 24–48 h after post-cure; dimensional measurements should therefore be taken after a conditioning period. If the fixture will contact metal fasteners or abrasive surfaces, wear resistance should be tested; a standardized wear test such as ASTM G133 can be used to compare the photopolymer with machined acetal or glass-filled nylon. Holes for locating pins should be machined or reamed after printing when tight tolerances are required, because as-built hole roundness can vary with build orientation and support location. Production fluids such as cutting oils, hand lotions, and cleaning agents should also be included in compatibility screening when the fixture is used on an active assembly line.

Published data for fatigue, creep, and chemical compatibility for this specific gray photopolymer is limited. Engineering decisions should use internal process capability data and lot-specific certificates rather than generic property tables. The apparent ductility of bulk tensile bars may not transfer to thin-walled features with high surface-to-volume ratio; edge effects and oxygen inhibition during printing can create a less crosslinked interphase that alters local mechanical response. For critical applications, a validation build should be produced in the intended production orientation and post-cure equipment, then tested under the actual load state and environment. The absence of long-term field data for this specific formulation means that design margins should be larger than those used for well-characterized thermoplastics such as ABS or polycarbonate.

Material traceability and regulatory documentation should be assembled before production introduction. The supplier provides a lot certificate that records viscosity, color, and batch information; incoming inspection should verify the lot is within shelf life and has not been exposed to light. Mechanical test values are generated on standardized coupons and do not necessarily represent thin-walled production parts because layer boundaries, surface roughness, and residual stress are process-dependent. The material is accompanied by safety data sheet documentation; REACH and RoHS status is stated in the supplier declaration and should be verified against the current regulatory version. Published data for food-contact use under FDA 21 CFR 177 and biocompatibility under ISO 10993 is limited for this specific gray formulation; the grade is not marketed as a certified food-contact or medical material. Operators handling liquid resin should use nitrile gloves, safety glasses, and local exhaust ventilation. Any change in post-cure equipment, cleaning solvent, build orientation, or layer thickness should trigger a first-article inspection because the final mechanical properties are process-dependent and cannot be assumed from the datasheet.