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Closed mold tooling is a method of producing composite parts using matched molds that fully enclose the laminate while resin is injected or drawn in under vacuum, rather than laid up in an open mold. This approach improves dimensional control, surface finish, and repeatability compared to traditional open molding, making it ideal for higher-volume and higher-quality production.
Closed mold tooling typically delivers better part consistency, higher fiber volume, lower emissions, and cleaner shop conditions than open molding. It also reduces labor, improves cycle times, and produces both cosmetic and structural surfaces that are closer to final spec right out of the mold.
Closed mold tooling can be engineered for Resin Transfer Molding (RTM), Light RTM (LRTM), Silicone RTM (SRTM), Vacuum Infusion (VARTM), Reusable Vacuum Bags (RSB), and “light” High Pressure RTM (HP‑RTM) applications. Each process has unique flow, pressure, and vacuum requirements, so the tool is designed around your resin system, part geometry, and production volume.
Closed mold tools are commonly built from tool-grade composites, aluminum, and different grades of steel, chosen based on temperature, pressure, and production life requirements. Steel tooling is preferred for high-volume, long-life production, while composite or aluminum tooling can be a cost-effective option for prototypes or lower volumes.
Closed mold tooling is capable of delivering high-gloss, Class A cosmetic surfaces on the mold side, provided the tool surface is properly prepared and maintained. Because the surface is formed against a rigid mold face under controlled pressure, parts generally come out with minimal post-finishing requirements.
Initial tooling cost is usually higher than simple open molds because of matched surfaces, seals, and internal hardware, but the overall cost per part is often lower at scale. Savings come from reduced labor, faster cycles, lower scrap rates, and better material utilization over the life of the tool.