Modeling and analysis of chip evacuation forces for deep hole drilling processes

The demand for high aspect ratio holes produced using conventional microdrilling processes has recently increased for many industries, including ultra-precision, aerospace, and semiconductor industries. Because of the reduced hole size and increased aspect ratio, understanding chip formation and chip evacuation have become increasingly critical for achieving high quality holes. Without proper chip evacuation, the tool experiences high stress that leads to excessive tool wear and potentially catastrophic tool failure. To overcome the chip evacuation problem in deep hole drilling processes, peck drilling, in which the drill periodically engages with the workpiece, is often adopted at the expense of lower productivity. Hence, in order to improve process productivity and reduce cost, the mechanisms for chip evacuation processes in microdrilling holes with high aspect ratios must first be understood. In this research work, a comprehensive physics-based model that predicts chip evacuation force for near-macroscale (mesoscale) and microscale drilling is developed. A flute discretization approach is used for modeling and tracking the movement of chip particles at different cutting depths, followed by a kinetics analysis. An energy-based approach is used for estimating chip evacuation velocity and chip evacuation force. For microdrilling, the chip evacuation force model for mesoscale drilling is modified to accommodate the scaling effects (increased surface-to-volume ratio (SV ratio)) and size effects (direct chip removal from shearing and chip accumulation from ploughing) due to the non-negligible tool edge radii when compared to chipload. Specifically, the interparticle forces and energy caused by adhesion and air drag are included in the model. A friction model considering both adhesion and two-body deformation factors is developed via strain gradient theory and geometry deformation at the tool-chip contact region. In particular, we found that the friction coefficient changes with cutting parameters and chip thicknesses due to size effects in microdrilling. In fact, it is found that ploughing, caused by the size effects, thickens the chips and further affects the chip evacuation process. One of the unique features of these models is their capability to predict chip evacuation force at an arbitrary depth of cut without requiring experimental calibration which would lower productivity. Furthermore, our models are capable of adapting to new materials without necessitating expensive experiments. The chip evacuation force model is validated with microdrilling experiments and good agreement is found between the model predictions and experimental results. The chip evacuation force model is then extended for microdrilling with cutting fluids. The effects of chisel edge indentation and the friction changes due to lubrication are introduced for the chip thickness and friction models considering the same normal blade pressure for chip removal under both wet and dry conditions. Lubrication changes the interfacial shear stress, affecting both the friction as well as the total chisel indentation force by reducing the ratio of dry contact area. Modified chip thickness and friction coefficients are then used to develop a chip evacuation force model. Microdrilling experiments with S1001 cutting fluid are carried out and the predictions from both the chip thickness and chip evacuation force models closely align with the experimental data. The study of the chip evacuation processes is further extended for evaluating the effectiveness of the atomization-based cutting fluid (ACF) application in deep hole microdrilling processes, which requires significantly less cutting fluid than conventional flood cooling methods. ACF systems generate thin films of coolant with better impingement and penetration capability than conventional flood cooling methods. The effectiveness of ACF systems and the relationship between film thickness and aspect ratio (depth-per-diameter) is studied through a 3^2 factorial design of experiments. The results indicate that ACF application is a viable alternative to conventional dry and flood cooling methods, outperforming both by achieving a higher aspect ratio while requiring significantly less cutting fluid.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Lee, Chi-Ting

Contributors dc:contributor

• Kapoor, Shiv Gopal
• Kim, Harrison Hyung Min
• Shao, Chenhui
• Tawfick, Sameh H

• Manufacturing
• Drilling
• Acf
• Atomization
• Modeling
• Chip Evacuation
• Cutting Fluid
• Micro-drilling
• Chip Thickness

Statement dc:rights

• Copyright 2022 by Chi-Ting Lee. All rights reserved.

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/117560

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F117560