Doctoral Defense - Aaqib Ali

About the Event

The Department of Mechanical Engineering

Michigan State University

Ph.D. Dissertation Defense

Wednesday, April 30, 2025 at 11:00 AM EDT

Engineering Building Room 3405 and via Zoom

Contact Department or Advisor for Zoom Information

ABSTRACT

THE MECHANICS AND TRIBOLOGY IN MODULATION-ASSISTED MACHINING

By: Aaqib Ali

Advisor: Dr. Yang Guo

Machining difficult-to-cut alloys remains a significant challenge in modern manufacturing, affecting efficiency, cost, and product quality. These materials, known for their high strength, hardness, and toughness, generate elevated cutting forces and temperatures during machining. This leads to rapid tool wear, reduced machining productivity, and increased machining cost. Modulation-assisted machining (MAM) is a novel machining process which utilizes controlled tool oscillation in the tool feed direction to create periodic tool-work disengagement during the cutting process. These controlled cutting interruptions can help overcome the challenges in conventional continuous cutting operations by producing discrete chips and alleviating the constant thermomechanical stress at the tool-chip and tool-work contact, leading to reduced cutting temperature and tool wear.

This dissertation investigates the mechanics and tribology enabled by MAM. The study begins by analyzing the mechanics of MAM in orthogonal cutting configuration, including detailed characterization of the modulation system, modeling of cutting forces, direct observation of chip formation, and tool displacement using high-speed imaging across a range of modulation parameters. The effectiveness of MAM is then evaluated in turning operations across a wide range of difficult-to-cut alloys, including various cast irons, high-strength steel, hardened bearing steel, and stainless steel, as well as nickel-based and titanium-based superalloys. For each material, MAM performance is benchmarked against conventional turning in terms of tool wear.

A key contribution of this work is the experimental demonstration that MAM can drastically reduce tool wear by the extensive formation of protective oxide layers on the cutting tool . Unlike conventional machining, where such layers are rare or require specific material treatments, MAM enables consistent layer formation under a broad range of conditions. The effects of the work material, tool material, cutting conditions, and modulation parameters on the formation and characteristics of the protective oxide layers are also investigated.

It has been found that the oxide layers are composed of thermodynamically more favorable oxides including Al₂O₃, SiO₂, MnO (and MnS), and MgO that originate from the inclusions of the work material. Necessary conditions for the oxide layer formation are identified as: 1) negligible adhesion between the work material and the tool material, 2) occurrence of periodic tool-work disengagements during MAM, 3) sufficiently high cutting speed (or essentially high temperature), and 4) adequate hardness of the oxide. The mechanism of the oxide layer formation is proposed as the compaction and plastic deformation of oxide debris deposited onto the tool-work contact zone during repeated tool-work disengagement and engagement actions.  These findings reveal how MAM fundamentally alters the tribological conditions at the tool-work interface to reduce tool wear.

Overall, this study advances the understanding of wear reduction mechanisms in MAM and demonstrates its great potential to enhance the efficiency of machining difficult-to-cut alloys.

Persons with disabilities have the right to request and receive reasonable accommodation. Please call the Department of Mechanical Engineering at 355-5131 at least one day prior to the seminar; requests received after this date will be met when possible.