Significance of defocussing distance in laser based directed energy deposition of steel powders: Effect on clad geometrical characteristics and process parameter maps.

Laser based directed energy deposition (L-DED) is an additive manufacturing process in which laser energy is used to fuse powder feedstock by melting while being deposited in a layer-by-layer manner, to produce three dimensional (3D) components. The quality of parts produced through this process depends on numerous process parameters. In the present work, the combined effects of defocussing distance, laser power and scanning speed on the geometrical characteristics of single line clads of AISI SS316L stainless steel and H13 tool steel powders produced through L-DED, was investigated. Theoretical analysis of the mutual interactions between laser, powder and substrate was used to explain the variations in clad geometry and deposition behaviour of the two steels. Process parameter maps were developed for the two steels and the influence of defocussing distance on optimal process parameter windows was evaluated. The work demonstrates that laser defocussing distance can be used as a simple but effective method to enhance the flexibility of the deposition process.