Year of Publication

2019

Degree Name

Master of Science in Manufacturing Systems Engineering (MSMSE)

Document Type

Master's Thesis

College

Engineering

Department

Mechanical Engineering

First Advisor

Dr. I. S. Jawahir

Abstract

Next generation defense and commercial applications for structural steels require new alloys that eliminate or reduce critical elements from their composition to lower cost and improve manufacturability, while maintaining or exceeding high strength and toughness requirements. A new alloy, denoted as AF9628, has recently been developed for this purpose and its manufacturing characteristics and the material response in component manufacturing must be fully understood.

In the present study, hardened AF9628 alloy was turned with a coated carbide cutting tool under fixed cutting speed, feed rate, and depth of cut parameters. This work focuses on chip-form and tool-wear analysis to understand, for the first time with AF9628, these fundamental aspects of the turning process and their relationship to productivity and part quality. Current industry standard practice of flood-cooled machining for AF9628 was used during machining experiments. Dry, minimum quantity lubrication (MQL), and cryogenic machining were investigated as alternative cooling and lubrication conditions.

High-speed imaging during AF9628 turning experiments provides a new insight into the chip formation process, while the use of optical microscopy and scanning white light interferometry allowed for further characterization of chip-form and tool-wear. Chip-form is favorable as short, arc-shaped chips with new tools under all of the tested cooling and lubrication conditions. As a result of rapid wear at the end of the tool-life in all of the experimental conditions, chip-form evolves to unfavorably long, snarled ribbon-like chips and the resultant cutting force increased by as much as 64% under flood-cooled conditions.

Tool-wear types that were observed during experiments include a combination of nose wear, built-up edge, plastic deformation, and groove wear on the rake face. Due to the fixed cutting parameters and cutting tool selected for this study, which were designed for flood-cooled machining in a prior study, undesirable failure of the cutting tools under dry, MQL, and cryogenic machining occurred. Future work requires experimentation across a wider processing space, and with different cutting tools, to thoroughly evaluate alternative cooling and lubrication techniques for machining AF9628.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2019.471

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