Thermal characterization of direct metal deposition

The temperature distribution in the vicinity of the laser used in direct metal deposition (DMD) plays a critical role in determining the final microstructure and properties of the deposit and the heat-affected zone within the substrate. A system of deposition samples were studied consisting of AISI 1018 steel powder deposited onto an AISI 1018 steel substrate as a single pass or as overwritten multiple passes. The laser power and speed were varied to influence the heat input and the rate of cooling. The use of idealized one dimensional lines allowed for the solution of a quasi-steady state analytical temperature distribution. Numerical predictions were made using the commercial software SysWeld™ for single pass depositions. Peak temperatures and cooling rates were determined at selected locations experimentally using micro-hardness measurements which were supplemented by obtaining thermocouple data taken during deposition. The analytical model, numerical predictions, and experimental results are compared for single pass depositions to determine the extent to which existing commercial codes can accurately model the thermal environment for DMD.