A model for bonding mechanisms in indirect laser powder bed fusion of nylon/alumina blends

Ceramics with intricate geometries can be produced by indirect laser powder bed fusion (LPBF) where a polymer is added to bind the ceramic particles together during laser heating. We use observations from video images captured under realistic LPBF processing conditions of nylon/alumina blends to propose a mechanistic model based on permeation. We then use the model to predict the operating conditions required to achieve particle bonding during indirect LPBF. The physical basis for the model is that particle bonding occurs when molten nylon binder permeates through the porous alumina shell that surrounds the nylon particles and forms solid bridges when the nylon solidifies. The model predictions are tested by building parts using a wide range of laser powers and scan speeds to determine experimentally if particle bonding has occurred. The results show that a permeation-based model is an accurate descriptor of binding mechanisms in indirect LPBF of mixed nylon/alumina powders.