Verification of Numerically Calculated Cooling Rates of Powder bed Additive Manufacturing

Abstract

In order to increase the powder bed production rates, the laser power and diameter are increased enabling faster scanning, thicker powder layers and wider hatches. These parameters however interact in a very complex manner: For example increasing the laser power may lead to significant evaporation of the molten metal. Increasing the scan speed may lead to reduced melting and lack of fusion of the powder particles. Combining higher scanning speeds with increased layer thickness enhances lack of fusion even more. Larger beam diameters reduce the energy density and hence impose limitations to scan speeds. Physics based modelling has the potential to shed light into how these competing phenomena interact and can accelerate fine tuning build parameters to achieve design goals. Models resolving the heat source powder interaction and describing the melt pool and solidification processes could not be formally validated using experimental data due to the extreme severity of the processing environment. In an effort to verify models describing melt pool behavior the results of two different algorithms are compared: Lattice Boltzmann and Finite Volume Computational Fluid Dynamics. Both codes were developed separately by two different and independent teams. A reference benchmark is defined with corresponding operation conditions. The physical assumptions are aligned as far as possible. The melt pool characteristics and the thermal cycles are compared.