Greyscale printing and characterization of the binder migration pattern during 3D sand mold printing

Abstract

Binder jetting is an additive manufacturing process in which a liquid binder is deposited onto a sand bed to fabricate components of a desired geometry. After deposition, the permeation and migration of the liquid binder in the porous sand bed has a critical impact on the final performance of the printed part. The purpose of this two-part study is to determine whether greyscale printing can be adapted for use in binder jetting. First, using Furan resin as the liquid binder and silica particles for the sand bed, we fabricated six sets of samples with different droplet volumes and measured the resulting migration patterns and quantified them based on deposited liquid saturation. The migration patterns are then correlated with the dimension error, strength, and formability of the printed samples. The results show that a larger liquid saturation produces better strength and formability with the tradeoff of a significant decrease in dimension error. Within this quantitative framework, the authors then demonstrate that gray-level printing—adjusting the droplet size of the liquid binder independently at each print head—can achieve the desired dimension error, strength, and formability at any specific location. Future applications may include the binder jetting of ceramic and metallic powders.