Dimensionless Enthalpy as Characteristic Factor for Process Control in Laser Powder Bed Fusion

In laser powder bed fusion (LPBF) melt pool morphology plays an important role in generating part quality and microstructural properties. Therefore, it is of interest to correlate the melt pool dimensions with processing parameters. To overcome the drawback of current energy input equations, like volume energy density, lacking the inclusion of material thermophysical properties, in this investigation dimensionless enthalpy is used as characteristic factor to predict melt pool dimensions of single scan lines. The relation between dimensionless enthalpy and melt pool morphology is investigated for a nickel base alloy and a maraging tool steel. It is shown that melt pool width can be predicted successfully for both materials, while for the prediction of melt pool depth dimensionless enthalpy alone is not sufficient. To account for a deviation in heat loss between the two materials the Fourier number was included in the enthalpy relation. Furthermore, the influence of scan direction and baseplate location on melt pool morphology was evaluated. While a significant dependence on scan direction could not be shown, melt pool depth is found to dependent on part location on the base plate. This dependence has been attributed to the combined effect of laser angle deviation and shielding gas flow.