Additive Surface Graining in Prototype Tooling for Injection Molding

Surface properties of injection molded parts have a strong effect on the visual and haptic perception of the parts by customers. Especially for injection molded automotive interior parts, grained surfaces can often be found. In conventional tooling, graining requires separate process steps. This makes the realization of grained injection molded prototype parts very complex. By additive manufacturing of injection molds in prototype tooling, it is possible to print micro structures into the mold surface in one printing operation. An injection mold with four different graining structures varying in depth and distance was designed and additively manufactured. The specification regarding the surface graining was analyzed by means of roughness measurements of the CAD model, injection mold and injection molded parts. Results show the feasibility of highly controllable additive surface graining.