An experimental investigation of selective laser melting for coating of WCCo powder on steel substrates

The performance of metal forming dies heavily depends on their surface characteristics including surface roughness and hardness. In forming complex part geometry, advanced die technologies are often used to control material flow such that wrinkling or fracture of workpiece can be prevented. This research investigate the use of selective laser melting (SLM) process to selectively coat WCCo on steel substrates to potentially improve metal forming die performance. Experiments were conducted to study the effects of volumetric energy density (VED) on the integrity and properties of the resulting surface. Instruments including microscopy, interferometry, spectroscopy, and hardness measurements were used to characterize the coated surfaces. The results show that coating defect such as cracks and spatters can be reduced with increased VED. The coating hardness, in general, decreases with increased VED. As stainless steel and H13 tool steel were used as the substrate, the study also identified that the thermal conductivity of the substrate material play a significant role in crack formation. It is also found that surface preparation, through machining, can affect the retention of the powder and lead to a higher surface hardness. Overall the hardness increase ranged from 200 % to 300 %. The conclusions of the present work can be used as a guide for developing high performance coating on sheet metal forming dies.