Investigation and Characterization of Wear-Resistant Coatings Applied to Steel Injection Molds by Thermal-Spray

The purpose of this study was to explore the potential of thermal-spray processes in applying wear-resistant coatings on injection molding inserts. High velocity oxy fuel (HVOF) and cold-spray (CS) processes were respectively used in applying Nickel-based and Cobalt-based alloys on tempered steel substrate. This article discusses the improvements in hardness and wear resistance through coating by replacing the heat treatment. Changes in the main deposition parameters (powder characteristics, stand off distance, powder feed rate, traverse speed and gas temperature) were investigated. Material properties such as hardness and roughness were characterized. The surface requirements were achieved through finishing and polishing operations. To verify the actual molding capabilities, real parts were produced using a glass-fibre reinforced polymer. To evaluate the wear behaviour of the surface in operating conditions a mold with four cavities was used. The mold was configured to allow the comparison between coated and heat-treated inserts. Surface topography was characterized in defined key-zones after each scheduled stop of the molding process. Experimental results showed that steel mold inserts coated by thermal spray and then polished can be a valid alternative to heat-treated steel for most applications.