Local Laser Particle Fusion: Fusing of Hard Particles for the Reduction of High Contact Pressures in MMC Tool Surfaces

Abstract

Lubrication-free deep drawing with metal matrix composite (MMC) tool surfaces leads to scores and grooves due to particle penetration into the formed sheet metal, and results in high local contact pressure in the radius of the deep drawing tool. To improve on this, the ratio of contacting area to total area must locally be increased in high-load regions of the tool surface. Multi-stage laser melt injection (LMI) and local laser particle fusion (LLPF) were carried out to increase the hard particle content of the MMC tool surfaces. LLPF is a novel two-step LMI process whereby hard particles are locally fused together under additional powder feeding after a regular LMI. The resulting nugget was shown to grow in height and width with an increase in the pulse duration. The substrate temperature prior to the particle fusion had an influence on the defect-free nugget growth. Whilst the chemical composition of the fused tungsten carbide (FTC) nuggets was similar to FTC particles, their hardness was slightly reduced compared to literature values for tungsten carbide. For the first time, FTC nuggets could be successfully applied on MMC tool surfaces to realize an increased hard coating area.