Improvement of die-casting tools with duplex treatment

A comparative performance test of protected tools was made in die casting of driving wheels for automobiles with two types of cores in one casting plate. One set of cores was improved with plasma nitriding, while another one was improved with duplex treatment (plasma nitriding+deposition of 4-μm-thick PVD CrN coating). After 2700, 4150 and 7490 injections, surfaces on both types of tools were analysed using optical and scanning electron microscopes to identify damages of tool working surfaces. The most important damages were found to be strong erosion at the gate side, degradation of the CrN coating due to oxidation and the formation of sharp fractures through the coating due to thermal stresses. The performance tests, made under real manufacturing conditions, showed that wear of duplex treated tool is smaller than wear of the plasma nitrided tool.