Session: 02-04-01: Session #1: Advanced Machining and Finishing Processes

Paper Number: 95037

95037 - Material Removal Characteristics of Longitudinal Turning of Green Ceramics 

Sintered powder ceramics are often used instead of metal parts for car engine valves and dental implants, because of their higher resistance to heat, corrosion, and wear. These ceramics are formed by mixing ceramic powder with polymer binders into a slurry and then either casting, extruding, or pressing them into a shape. They are then dried and fired. Various methods are used for shaping and post-processing the ceramics after firing. However, these techniques often suffer from high cost or low efficiency. An alternative is to machine the ceramics before firing, while they are in what is called the green state. This is much cheaper and has higher material removal rates than machining in the fired state.

However, green machining is not well understood, especially how the choice of process parameters during machining and the material aspects of the ceramic blank impact the machining forces and surface roughness generated. This paper examines the relationship between machining parameters and material composition on resultant forces and surface roughness in green turning of aluminum oxide rods. Turning experiments were performed with varied feed and cutting speed between high and low values. The rake angle of the cutting tool was also varied between zero and positive five degrees. Material factors of the green ceramic, including the type of cellulose binder used and the size of the ceramic particles were varied as well. Forces during turning were measured on a piezoelectric dynamometer and the surface roughness of the machined faces was measured with a white light interferometer. A design of experiments approach was used so that statistical analysis of the effects of the process and material parameters on force and roughness could be performed.

Results showed forces were higher at low feed, high cutting speed, positive five degree rake angle, and smaller particle size. Feed, rake angle, and particle size had the largest effects. Some of the second order interactions were statistically significant, but none were large. For surface roughness, the higher feed and zero degree rake angle resulted in greater roughness. Their interaction was also large and statistically significant, with feed having a greater effect on roughness with the zero degree rake tool.

The inverse correlation between feed and force contradicts other studies done with green ceramics, and may have occurred because lowering the feed caused a transition from cutting to ploughing, resulting in higher forces. It should be noted that ceramic powder debris instead of solid chips were produced during turning, indicating brittle cutting. Additionally, the higher force with the zero degree rake tool was surprising and likely occurred due to the tool cutting granules of binder and powder, while the five degree rake tool likely scooped granules out. It was expected that the zero degree tool would create a smoother surface because simulation studies of green machining had shown that more negative rake angles reduced crack formation on the surface. Microscope images of the machined surfaces didn’t show significant cracking, meaning this effect was likely not important for the aluminum oxide rods studied here.

Presenting Author: Jesse Castellana Georgia Institute of Technology

Presenting Author Biography: Jesse Castellana is graduate student pursuing a PhD in mechanical engineering at Georgia Institute of Technology. His research focuses on advanced manufacturing, specifically turning of green ceramic parts.

Authors:

Jesse Castellana Georgia Institute of Technology
Shreyes Melkote Georgia Institute of Technology