Session: 03-01-03: Annual Conference-Wide Symposium on Additive Manufacturing

Paper Number: 150540

150540 - Development of Pseudo-Binder-Jet-Printing Molding Technique for Rapid Materials and Process Screening 

Binder jet printing (BJP) is a versatile additive manufacturing (AM) platform, capable of producing complex geometries from a wide range of materials, including metals, ceramics, and polymers, without significant thermal distortion or residual stresses. However, developing new material systems and optimizing processing conditions can be expensive and time consuming, particularly when dealing with a variety of powder chemistries, sizes, and distributions, as well as different sintering aids and binders. Here, we propose a modified molding approach to produce comparable green parts that can be integrated into BJP’s unique process flow, which naturally decouples printing from consolidation, allowing for rapid screening of de-binding and sintering treatments on unique powder configurations, sintering aid concentrations, and binder chemistries without encumbering production printers. Additionally, most design of experiments (DOE) aimed at studying porosity, microstructure, or elemental distribution of BJP parts are conducted on simple geometries such as cubes, cylinders, dog-bones, or hourglasses, which can be cast from simple molds. Since this approach does not entail tedious steps associated with powder or binder changeover in BJP and enables the simultaneous generation of large quantities of test coupons with varying compositions, we believe that it can be used as an effective proxy for rapid materials and process screening. Although similar molding methods have been employed to test powder-binder compatibility, to our knowledge, little or no work has been reported that compares the material properties and microstructures of molded components to those produced by BJP. The aim of our study is to develop a molding technique that generates stainless steel 316L parts whose green/sintered densities and mechanical properties are similar to those produced by BJP and evaluate the viability of the proposed molding technique as a BJP process proxy.

To accomplish this goal, we mixed ExOne’s Aquafuse binder with spherical SS316L powder (average size 22.5 µm) and ethanol in various mass ratios. Boron nitride (BN) was added to the powder mix as a sintering aid, with the concentration varying from 0, 0.25, 0.5, to 0.75 wt% (BN-to-SS powder ratio). Ethanol was included in the slurry to increase flowability, as the binder phase alone made it too thick to be poured into a mold. Binder-to-ethanol ratios of 2:1, 4:3, and 1:1 were tested to determine the effect of slurry’s viscosity on the green and final part densities. An important aspect of mimicking the BJP process is the pressure exerted on the top powder layer during the raking process, which may improve the green part density. We leveraged two agitation devices (tapping and vibration) to control the sedimentation dynamics of powder and sintering aid particles during molding, facilitating the green part density and air bubble removal. The resulting relative density of the green parts from the proposed molding method varied from 69 to 76%, significantly higher than those of the BJP-derived green parts. These green parts were then subjected to burnout in a furnace at 460°C for 2 hours in air to remove the binder phase, followed by full sintering at temperatures ranging from 1150 to 1350°C for 2 to 12 hours in a vacuum environment. The densities and mechanical strengths of the sintered parts were measured to be 89~98% and 240~440 MPa, respectively, depending on the additive concentration and sintering temperature. These values are in reasonable agreement with those reported for BJP parts. We conclude that the proposed molding approach can be used as a rapid and cost-effective method to screen various process parameters relevant to BJP. 

Presenting Author: Tyler Bauder US Naval Research Laboratory

Presenting Author Biography: Dr. Bauder is a Post-Doc research engineer in Multifunctional Materials Branch at Naval Research Laboratory, where he has participated in multiple basic and applied research programs in the areas of materials testing, fracture and fatigue, additive manufacturing, and USMC vehicle programs. He completed his Ph.D. in Mechanical Engineering at Michigan State University in 2023. Technical focus areas include additive manufacturing of Ti-6Al-4V and steel alloys by Electron Beam Melting (EBM) and Binder Jet Printing (BJP), mechanical testing and characterization.

Authors:

Tyler Bauder US Naval Research Laboratory
Junghoon Yeom US Naval Research Laboratory
Kristina Chenevey US Naval Research Laboratory