Investigation on surface roughness of injection molded polypropylene parts with 3D optical metrology

Surface roughness is an important design specification for injection-molded plastic parts that are widely used in the consumer electronics, packaging, and automotive industry. Surface roughness serves both the appearance and functional requirements of injection moldings. It is not only influenced directly by the mold cavity surface, but also by injection molding parameters. However, there are few systematic studies on the effects of molding parameters on the surface roughness of molded parts. This study is to investigate the effects of molding parameters on the surface roughness of injection molded polypropylene parts. The molding parameters studied include cooling time, injection speed, holding pressure, and holding time. It turns out that the mold surface roughness plays the dominant role, while the molding parameters also exhibit a large influence on the surface roughness of molded parts. Among the parameters studied, the injection speed has the largest effect while the cooling time having the least effect on the surface roughness. This study implies that the surface roughness of molded parts can be cost effectively manipulated to a certain degree through controlling molding parameters, instead of modifying the surface furnish of mold cavity at a high cost.