Empirical Design Rules for Binder Jetting Additive Manufacturing

Abstract

Metal binder jetting additive manufacturing (BJAM) is an additive manufacturing (AM) process that builds parts from a feedstock metal powder material by spreading a layer of powder, then depositing liquid binder over the desired cross-sectional area to bind the powder together. Once completed, the part is cured and depowdered, resulting in a green part with the desired form but lacking functional material properties. Heat treatment, typically in the form of sintering, is required to impart the desired properties to the material by pyrolyzing the binder and densifying the part.

During each of these steps is the challenge of creating or maintaining a dimensionally accurate part that adheres to the intended geometry of the part that was designed. Each step has interactions between process parameters, material properties, and geometric feature characteristics that determine the degree of accuracy of the finished part. Benchmarking and understanding the physical phenomena of each of these steps is a field of active research with many domains to be covered. In particular, there is a lack of information on the dimensional accuracy of the printed green parts prior to post-processing and how to design parts to achieve a desired accuracy.

The goal of this work is to develop a set of design rules that can be applied when designing for binder jetting additive manufacturing with stainless steel (SS316L). This was done by printing artifacts with geometric primitives at different scales and orientations to determine which features can be printed successfully. Six types of features were included in the design of these to examine minimum feature dimensions and clearances. The artifacts were analysed with the help of a custom developed automated computer vision approach to quantify the degree of dimensional accuracy. These results are compiled into a practical set of design rules for designers that express printability and dimensional error as a function of feature type, nominal dimension, thickness, and orientation. Future work is proposed to expand the formalization of design rules for binder jetting additive manufacturing and to apply this workflow to other processes.