Mesoscale modelling and three-dimensional experimental validation of heat transfer in shallow beds of polyamide powders for laser powder bed fusion

A good understanding of temperature-dependent material properties and the associated process parameters is required to successfully model the heat transfer in laser powder bed fusion (LPBF). To quantify the temperature distribution along the depth and top surface, a stationary laser sintering experimental set-up equipped with two infrared cameras is constructed in this study. A shallow bed of polymeric powder is spread on infrared-transparent Zinc Selenide (ZnSe) glass, so that one of the thermal cameras can see the heat transfer along the depth from the bottom. Two carbon black powders of treated polyamide (PA12 CB of 60 mu m and PA6 CB of 80 mu m) are used. A 3D finite-element heat transfer model is developed considering conductive, convective, radiative heat transfer, and phase change. Temperature-dependent material properties, such as thermal conductivity, density, specific heat, and emissivity, are estimated and considered. The model's accuracy is validated by comparing the temperature data along XYZ directions with the experimental values. The PA6 CB powder exhibits higher laser absorption and thermal conductivity than PA12 CB. This finding is evident from the rapid heating of PA6 CB due to higher laser absorption and faster cooling rate due to higher thermal conductivity. The emissivity of the powder bed is nearly uniform with the temperature for both powders and drastically increases at the melt pool. This change in emissivity is captured in the model.