Material selection for injection molds of thick-walled PP-R parts: experimental comparison of conventional 316 l steel, CuBe alloy, and selective laser melting with conformal cooling on thermal performance, part quality, and financial viability

Abstract Injection molds with conformal cooling channels (CCC) produced by selective laser melting (SLM) can substantially reduce cycle time in thin-walled applications. Their comparative economic performance for thick-walled geometries has not been experimentally quantified. This study presents an experimental three-way comparison of mold concepts for injection molding a PP-R reduction-tee fitting with wall thickness up to 8.8 mm. The concepts are conventional 316 l stainless steel, copper-beryllium (CuBe) alloy by conventional machining, and 316 l with SLM-manufactured CCC incorporating honeycomb lattice-structure optimization (Materialise Magics). The evaluation combines two-stage finite element simulation (Moldflow), real-process trials with embedded pressure and temperature sensors, characterization of n = 15 parts collected per mold concept (subsamples of n = 5 for mass and n = 3 for tensile strength). A financial sensitivity analysis used real ERP cost data from a Brazilian hydraulic fittings manufacturer (2024 reference, R$/USD = 5.68). CuBe reduced the injection cycle by 18% and product cost by 12% at a 10% mold investment premium (USD 8,315 vs. USD 7,593), requiring 8-fold demand growth for 3-year payback. The SLM-CCC mold achieved 11% cycle reduction and 7% cost saving, but required 242% longer fabrication time, a 46% investment premium (USD 11,121), and 18-fold demand growth for equivalent payback. Differences in part weight and tensile strength across mold concepts were statistically significant (one-way ANOVA, p = 0.002 and p = 0.026, respectively). All three mold concepts produced parts meeting functional qualification for pressurized hot-water hydraulic systems. For the specific geometry and polymer tested, CuBe outperforms SLM-CCC across every economic metric, and the 18-fold demand threshold, not the thermal gain, is the decisive variable for evaluating SLM adoption.