Investigation on failure analysis and optimization of WC–Co hard metals after long-term use in a bottle cap forming machine

Abstract

Failure analysis was performed on WC–Co hard metal molds after long-term use in a bottle cap forming machine. In addition, we simulated the optimal physical properties of the top and bottom molds for minimizing the wear caused by long-term use. To this end, we investigated the microstructure, wear, hardness, and transverse rupture strength (TRS) of the top and bottom molds with different WC particle sizes and WC/Co content ratios via simulations with Poisson's ratio and Young's modulus as inputs. The results show that a large stress distribution at the top and bottom molds did not signify a high maximum stress value; the stress distributions and maximum stress depended on the combination of materials used for the molds. It was concluded that WC–Co hard metal molds with similar physical properties would fracture readily or suffer wear due to the relatively high stress, where the optimal combination showed the lowest maximum stress (compared with the other combinations) at the top mold, with a larger stress distribution than that of the bottom mold. These findings are expected to be useful for optimizing applications where hard metal pieces come into contact, e.g. designing molds for bottle cap forming machines with longer lifetimes and fewer bottle cap defects.