Date of Award
Doctor of Philosophy (PhD)
Mechanical and Manufacturing Engineering
The objective of this thesis is to investigate the influence of thermal cycling on tool life in intermittent cuting processes. Particular emphasis is given to the peripheral milling process. In intermittent cutting processes, it has been established that the thermal cycling is the most significant factor which controls the type of failure and the life of cutting tools. The previous theoretical studies of the thermal cycling were based on strongly simplified models. The experimental studies were based on the measurement of the tool/chip interface temperature in the cutting period. Consequently, any implications for tool wear or breakage could only be indirectly estimated. In this work, the thermal cycling is studied by means of finite element computation of the transient temperatures and stresses in the tool wedge. The finite element formulation of the energy equations and the associated boundary conditions, which govern the heat transfer mechanism, is developed for the intermittent cutting processes. A two-dimensional tool/chip model is developed which reflects the interaction between the heat sources, and provides the capability of computing a complete temperature field. The computed temperature field is then used to determine the thermal stresses. The computation of a complete temperature field and the associated thermal stresses is necessary to explain experimentally determined characteristics of tool wear, cracking and breakage. The transient temperature field in both the chip and tool, and the corresponding thermal and mechanical stresses, are computed for the peripheral milling process with different cutting conditions. The theoretical results are correlated with experimental data. The experimental data are taken, mostly, from the tests of Barrow and Yellowley ⁽¹²⁾ and from similar tests conducted by the author. The experimental work concentrates on the flank wear of both high speed steel and sintered carbide milling cutter. It is found that the cutting time ratio has significant effect on tool life. The correlation shows that the number of thermal cycles is the most important parameter which affects the tool life in peripheral milling. The thesis starts with a statement of the problem and the scope of this work in Chapter 1. Chapter 2 provides a summary of the state of knowledge in the area of tool damage in intermittent cutting processes. The temperature problems in continuous and intermittent cutting process are discussed in Chapter 3. The mathematical modelling and the finite element formulation of the heat transfer problem are developed in Chapter 4. The modelling of the cutting process and the computation of the transient temperature distribution are presented in Chapter 5. Chapter 6 is devoted to the presentation and discussion of the computed thermal stresses. The important parameters which may affect the tool flank wear in milling are established and correlated to the experimental data in Chapter 7. Finally, Chapter 8 provides conclusions and recommendations for further research. Specifically, this thesis provides the following contributions: 1. The mathematical modelling and the finite element formulation of the transient heat transfer problem in intermittent cutting (Chapter 4). 2. Derivation of an automatic time step control algorithm for two-point recurrence schemes for the first order ordinary differential equations (Chapter 4). 3. Development of a two-dimensional tool/chip model for the cutting process (Chapter 5). 4. Implementation of a software system, based on he developed models, to compute the temperature and stress fields (Chapter 5 and 6). 5. The study of the influence of thermal cycling on tool flank wear in peripheral milling based on correlating the computed results with experimental data (Chapter 7).
Orady, Elsayed A., "The study of the effect of thermal cycling on the tool life in intermittent cutting processes using the finite element technique" (1982). Open Access Dissertations and Theses. Paper 3190.