03/13/2025
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation defense by Michael Shone on "Powder Injection Molding (PIM): Feedstock Formulation And Their Effects On Rheological Properties, Feedstock."

Candidate Name: Michael Shone
Date: Thursday March 27, 2025
Time: 3 - 5 p.m.
Location: Anyone wishing to attend should contact the committee chair, Professor Margaret Sobkowicz-Kline, for the Zoom link.

Committee:
Advisor: Margaret Sobkowicz Kline, Professor, Plastics Engineering Department, UMass Lowell

Committee Members*
1. Carol Barry, Professor and Chair, Plastics Engineering Department, UMass Lowell
2. Stephen Driscoll, Professor, Plastics Engineering, UMass Lowell
3. Christopher Kuncho, Ph.D., Principal Materials Engineer, Raytheon Technologies

Abstract:
Powder injection molding (PIM) is a growing technology that uses multiphase systems, known as feedstocks, with conventional thermoplastic technology to form complex net shapes, with high volumes and tight tolerances, that subsequently are debound and sintered to make a final product. The powders that are used can consist of ceramics or metals, but to facilitate flow in the injection molding process, the powder must be suspended in a binder system that consists of wax, polymer or a combination of the two. Post processing is used to remove the binder system and densify the powder into a ceramic or metal part. To obtain suitable parts the solids loading levels of the feedstocks need to be high, typically greater than 40 % by volume.
This research explores the changes to physical properties, rheological properties, and injection molding behavior of a wax-based binder system with high solids loading level of silicon powder. Stearic acid is widely used in feedstock recipes, and the effort of this work is to expand upon past research to better understand feedstock formulation choices and their effect on the injection molding process. The effects are divided into the physical properties, rheological properties, and molding properties. The physical properties were assessed using a 3-point bend, thermal gravimetric analysis, differential scanning calorimetry, immersion density measurements, and thermal conductivity testing. The rheological properties were assessed by looking at viscosity curves via a flow ramp, characteristic yield stress and characteristic zero-shear viscosity via a large amplitude oscillatory strain (LAOS), and an exploratory thixotropic testing of the feedstock stability via repetitive frequency sweeps. The molding properties were assessed with an instrumented rectangular plaque mold and processing at different volumetric flow rates.
The main findings were that stearic acid is not always effective for reducing viscosity in powder injection molding feedstocks but shows evidence to work as a built-in mold release. From rheological standpoint, it enhances paraffin wax but negatively affects beeswax due to the expected interfering of beeswax's natural dispersant properties. The optimal carrier formulation for the feedstock was found to be a blend of beeswax and paraffin with a moderate loading level of stearic acid injected at a fast velocity, as this provided good flow, excellent surface quality, and reduced brittleness for handle-ability and ease of ejection.