Investment Casting Patterns in Nickel-Base Superalloy Shell Processes

In investment casting foundries producing cobalt-chrome and nickel-base superalloy components for aero-engine hot-section parts, DSM Somos 7120 Epoxy Photopolymer functions as a consumable stereolithography pattern material within the lost-wax shell process. The resin is processed at 100% as-supplied single-component content without reactive diluent, filler, or accelerator addition; any introduction of talc or silica to the formulation is expressly avoided because post-burnout ash residue above 0.05 g per 100 g resin shifts shell inclusion probability beyond aerospace acceptance thresholds. Supplier liquid-state specifications for viscosity—typically in the range of 260–500 mPa·s at 30 °C—allow layer formation at 50–100 µm on 355 nm SLA systems without the addition of viscosity reducers. Compliance in this application is anchored to AS 9100D clause 8.5.1 for production control and to ASTM D638-14 tensile modulus data generated on green and postcured coupons, while final cast metal inspection is conducted under ISO 9001:2015 first-article requirements. The downstream production sequence begins with layer-wise photopolymerization at 50–100 µm slice thickness, followed by alcohol rinse, support removal, UV postcure in a 320–400 nm chamber at 60–120 kJ/m² cumulative exposure, and forced-air thermal postcure at 70–80 °C for 2–4 h to elevate monomer conversion and stabilize dimensions before ceramic shelling. Pattern geometry is hollowed with 1.5–3.0 mm wall thickness and internal lattice spacing to manage thermal expansion during autoclave or flash-fire dewax; heating ramp rates above 2–3 °C/min during burnout at 650–900 °C create internal pressure peaks that crack thin silica/zircon shells, particularly where wall thickness falls below 1.5 mm. Terminal finished products include equiaxed nickel-base superalloy turbine vanes, small structural brackets, and first-article castings produced from the lost pattern, with the 7120 pattern consumed in each casting tree.

Where aerodynamic test campaigns require high-fidelity contoured surfaces, the resin is employed for wind-tunnel model fabrication because its unfilled epoxy backbone yields a machinable surface after postcure without the high-temperature distortion associated with thermoplastic build materials. In this configuration, the formulation addition ratio remains 100 phr of DSM Somos 7120; no glass microsphere or milled carbon fiber is introduced into the aero-surface regions, because filler addition creates surface roughness signatures that corrupt boundary-layer transition measurements. Mechanical property qualification follows ASTM D638-14 for tensile modulus and ISO 527-2:2012 for strain at break, while dimensional conformity of contour sections is checked against ASME Y14.5-2018 feature control frames with local profile tolerance of ±0.15 mm. The production sequence begins with layer-wise photopolymerization at 50 µm slice thickness on a 355 nm SLA platform, followed by alcohol rinse, removal of supports from non-aerodynamic faces, UV postcure in a 320–400 nm chamber at 60–120 kJ/m² cumulative exposure, and thermal postcure in a forced-air oven at 70–80 °C for 2–4 h to stabilize tensile modulus and reduce residual unreacted cationic species. Sanding and filled-epoxy seam blending are constrained to non-wetted areas; surface roughness on forward surfaces is verified with ISO 4287 Ra and Rz parameters, and any localized filler repair on aero surfaces is rejected when Ra exceeds 0.8 µm. Terminal produced types include high-speed wind tunnel sting-mounted models, air data probe fairings, and static display aerodynamic test assets, each requiring post-test dimensional re-validation to detect thermal creep from tunnel heating.

What Causes Platinum-Cure Inhibition When Silicone Molds Are Built Around Epoxy Masters?

Platinum-catalysed room-temperature vulcanizing silicone tooling for low-volume polyurethane prototype production uses the 7120 build as the positive master because its low postcure surface porosity and dimensional stability permit direct silicone casting without grain-transfer defects. The epoxy master remains at 100% resin as supplied; no mold release agent is added to the formulation, but a thin solvent-based release film is applied between master and silicone. For the surrounding tool, addition-cure silicone is batch-mixed at a 10:1 base-to-catalyst weight ratio before vacuum degassing at −0.09 MPa absolute for 5–10 min to remove entrained air. Compliance for the tooling workflow is governed by ISO 9001:2015 clause 8.4.1 supplier control, and the final silicone mold is characterized using ASTM D2240-15 Shore A hardness and ASTM D412-16 tensile methods. Production sequence starts with the completed 7120 master postcured to full conversion; residual cationic species must be consumed or sealed because free photoacid can inhibit platinum cure at the interface, so a 60 °C postcure for 4 h followed by isopropyl wipe is standard before silicone pouring. After silicone mold cure at 25–35 °C for 16–24 h, the mold is stripped and used for polyurethane casting under vacuum. Terminal finished products include automotive interior switch bezels, gasket prototypes, and short-run consumer product housings requiring Shore A 40–60 silicone molds. Published data for inhibition thresholds in this specific epoxy/silicone pairing is limited; therefore the postcure and surface sealing protocol is treated as the primary de-risking step.

In automotive engine test cells, underhood coolant and oil subsystem prototype housings impose conflicting demands: sufficient heat distortion resistance to survive dynamometer soak cycles and enough elongation to tolerate clamp loads at hose barbs. DSM Somos 7120 is used at 100% as-formulated single-component stock; rubber impact modifier addition is not recommended above 0.5 phr because the low crosslink density of the epoxy photopolymer already produces elongations above 10%, while dispersed rubber phases above this ratio reduce heat deflection temperature below the 55–65 °C range observed after standard ultraviolet and thermal postcure. Amine-based additive packages are also avoided in this vat-processing environment because they trigger premature dark gelation and layer-to-layer adhesion failures. The postcure cycle—UV at 320–400 nm for 60–120 kJ/m² then forced-air heating at 75 °C for 3 h—is required to raise HDT and reduce unreacted oxetane/epoxide monomer migration into circulating fluid. Immersion testing per ISO 175:2010 in reference coolant fluid at 80 °C for 168 h and tensile retention per ASTM D638-14 are used to qualify prototype housings; heat deflection is verified under ASTM D648-18 at 0.46 MPa after postcure. Downstream production involves SLA layering at 0.1 mm, support removal, postcure, thread insert installation, and dynamometer thermal cycling from −20 °C to 90 °C with no pressure loss. Terminal finished products include glycol coolant reservoir prototypes, diesel fuel filter bowl test units, and air intake duct mockups for assembly-tooling validation; field-scrapped patterns are rejected when surface whitening or microcracking exceeds 2% of wetted surface area.

When Electroless Metallization Must Adhere to Photopolymer Subrack Enclosures

Electromagnetic compatibility pre-compliance housings are produced from 7120 builds where the photopolymer serves as a dimensionally stable core for subsequent electroless copper/nickel metallization. Formulation addition ratio of the polymer core remains 100 parts by weight as-supplied; the metallization stack is not a resin additive but is deposited as a 3–5 µm copper layer followed by a 1–2 µm nickel cap. Surface preparation before plating uses chromic acid-free sodium hydroxide/phosphate etchant at 40–50 °C for 5 min to improve mechanical bonding. Compliance posture references RoHS Directive 2011/65/EU Annex II for restricted substances in the base resin, REACH Regulation 1907/2006 Article 33 for SVHC communication, and IEC 61000-4-3 for radiated immunity test configuration; adhesion of the metallic layer is tested per ASTM D3359-17 with a minimum classification of 3B. The downstream process is sequential: SLA build at 0.075 mm slices, alcohol rinse, UV postcure, thermal postcure at 70 °C for 2.5 h, mechanical sanding of support nibs, electroless copper and nickel plating, and final shielding effectiveness measurement using IEEE 299-2006 nested reverberation fixtures. Terminal finished types include 19-inch subrack front panels, handheld data collector housings, and shielded enclosure lids for pre-certification testing; metalized parts are limited to ambient service below 50 °C to avoid differential expansion fracture of the nickel cap.

Evaluating Long-Term Clamp Creep in Assembly Jigs and Inspection Nests

During multi-shift robotic welding campaigns, repeat-use assembly fixtures printed from 7120 are placed into robotic welding cells and CMM inspection stations where dimensional repeatability under moderate clamp loads outweighs prolonged wear resistance. The formulation addition ratio remains 100% resin; no talc or mineral filler is added because filler particles would reduce the precision of locating features and create anisotropic shrinkage on large flat sections. Compliance is maintained under ISO 9001:2015 clause 8.5.4 for preservation of production tooling, and mechanical benchmarking uses ASTM D638-14 tensile modulus and ASTM D648-18 HDT under 0.46 MPa after postcure. Production sequence includes SLA build at 0.1 mm slices, alcohol rinse, support removal, UV postcure at 60–120 kJ/m², thermal postcure at 75 °C for 4 h, installation of hardened steel bushings, and coordinate measurement against ASME Y14.5-2018 datums. Terminal products include drill jigs for sheet-metal prototyping, tack-welding locator nests, and CMM holding fixtures used at ambient temperatures below 40 °C; continuous clamp face stress is kept under 5 MPa to avoid creep-induced positional drift beyond ±0.1 mm during multi-shift operation.