Process characterization of powder based laser metal deposition on thin substrates

Abstract

Powder-based laser metal deposition is a well-established generative manufacturing process in the field of tool and mould building to produce or repair components. Conventionally manufactured tools are often completely constructed of a high-alloyed, hardened-tempered, and expensive tool steel. An alternative way to manufacture tools and moulds is the combination of a cost-efficient, mild steel, and a functional coating. Such specific, locally adapted coating can be generated by laser metal deposition. The functional coating is just located in the area of the interaction zone of the tool. Consequently, costs and resources can be saved. Such coatings are created by positioning multiple individual weld tracks next to and on top of each other in an overlapping manner. It is therefore useful to characterize und optimize the individual weld track. Thermal processing methods, like a laser metal deposition, are always characterized by thermal distortion. The resistance against the thermal distortion of the work piece is decreasing with the reduction of the material thickness. Thus, there is a special process management for the laser based coating of thin-walled parts or tools with a small material thickness needed to reduce thermal distortion. The experimental approach in the present paper is to keep the energy and the mass per unit length constant by varying the laser power, the feed rate, and the powder mass flow. The typical seam parameters (such as width, height and depth, cross-sectional area, and angular distortion) are measured in order to characterize the cladding process, define process limits, and evaluate the process efficiency of an individual weld track. Ways to optimize dilution, angular distortion, and clad height are presented. After the characterization of individual weld tracks, optimized process parameters are deduced from the process window and used to create functional, two-dimensional coatings on thin substrates. Different scanning strategies are compared with each other to reduce processing time and thermal distortion.