yes / The nature of the contact behaviour between a grinding wheel and a workpiece in the grinding process has a great effect on the grinding temperature and the occurrence of thermal induced damage on the ground workpiece. It is found that the measured contact length le in grinding is considerably longer than the geometric contact length lg and the contact length due to wheel-workpiece deflection lf. The orthogonal relationship among the contact lengths, i.e. lc2 = (Rrlf)2 + lg2, reveals how the grinding force and grinding depth of cut affect the overall contact length between a grinding wheel and a workpiece in grinding processes. To make the orthogonal contact length model easy to use, attempts on modification of the model are carried out in the present study, in which the input variable of the model, Fn’, is replaced by a well-established empirical formula and specific grinding power. By applying the modified model in this paper, an analysis on the contributions of the individual factors, i.e. the wheel/workpiece deformation and the grinding depth of cut, on the overall grinding contact length is conducted under a wide range of grinding applications, i.e. from precise/shallow grinding to deep/creep-feed grinding. Finally, using a case study, the criterion of using geometric contact length lg to represent the real contact length lc, in terms of convenience versus accuracy, is discussed.

<p>Unexplained acoustic emission spikes have been reported to occur at the workpiece entry and exit in interrupted machining operations, most notably during grinding. These AE spikes have yet to be fully explained in terms of their cause, or interpreted to yield useful information regarding the grinding process. This thesis research hence focuses on investigating this phenomenon. What started as a curiosity-driven project has resulted in an experimental technique to measure the actual contact length between the workpiece and the grinding wheel, as well as a technique for detecting grinding burn, which are of remarkable practical significance.</p> / Master of Applied Science (MASc)

High Speed Machining (HSM) is associated with higher cutting velocities and table feedrates and higher material removal rate, lower cutting forces in contrast to conventional machining. HSM can be undertaken dry or near dry and hence it is considered as environmentally friendly machining in relation to the use of cutting fluids. A key challenge in HSM is that, the thermal loads generated during the cutting process can be a major driver of thermally activated wear mechanism and hence affect machining performance. The ability of cutting tools to act as thermal barrier can be a highly desirable property for dry and HSM. Recently, research work has been conducted on laboratory based coated cutting tools to model and understand the fraction of heat that enters the cutting tool. These studies have shown the potential for TiN and TiAlN coated tools in reducing heat partition to the cutting tool when compared to uncoated tools. This PhD extended this work to modelling and characterising the heat partition for new generation commercial coated cutting tools considering tools from major insert manufactures. For this study commercial coated carbide tools were classified into two groups. In one group were coatings uniformly applied on both rake and flank faces of the insert (SERIES). The second group were tools that had different top coats for the rake and flank faces (Functionally Graded). This concept of functional grading is used to tailor the coating selection to the conditions that exist on a tool face. Moreover, the issue of restricted chip contact was modelled and clarified in terms of its impact on heat partition. This chip breaker design is of particular importance to inserts used for machining ductile materials. Thus the PhD has applied research methods to industrial cutting tools and helped elucidate the important aspects relating to the design, layout and selection of multilayer coatings. The heat partition was quantified by using a combined Finite Element (FE) and experimental approach. This methodology was applied by taking into consideration the appropriate friction phenomena during HSM i.e. sticking and sliding. A restricted contact length with groove profile geometry was considered for the application of heat load in the FE model. Orthogonal and external turning of AISI/SAE 4140 medium carbon alloy steel was conducted over a wide range of cutting speeds. An infrared thermal imaging camera was used to measure cutting temperatures. The results show that the layout of the coating can significantly affect the heat distribution into the cutting tool, specifically; the top coat can alter the friction conditions between the tool-chip contact. The distribution of heat (heat partition) into the cutting tool insert with the thickest layer of Al2O3 as a top coating is the lowest in the entire range of cutting speeds tested i.e. 10.5% at lower cutting speed and reduced to 3.4% at highest cutting speed. Investigations were also conducted to quantify the contribution of heat from the primary and secondary deformation zones using a combination of finite element modelling, analytical modelling and experimental data. The results deduced that the primary deformation zone heat source contributes 9.1% (on average) to the heat partition into the cutting tool. The contribution of the Thesis should be of interest to those who design, manufacture and coat cutting tools. It defines heat partition values for commercial coated carbide tools, assesses the requirements for multilayer design of thermally insulating cutting tools, the selection of coating top layer coats and the role of contact phenomenon on heat partition in dry and HSM of steels.

In this work, measurements and simulations were used to investigate the effects of grinding wheel topography on the geometric aspects of the grinding process. Since existing methods for measuring the grinding wheels were either not accurate enough or could only measure a small portion of a grinding wheel, a novel grinding wheel measurement system was developed. This system consists of a white light chromatic sensor, a custom designed positioning system and software. The resulting wheel scanning system was capable of measuring an entire grinding wheel with micron level accuracy. The system was used to investigate the effects of fine, medium and course dressing on grinding wheel surface topology and the resulting workpiece surface. New techniques were also developed to simulate metal removal in grinding. The simulation software consisted of a stochastic wheel model, dressing model and metal removal model. The resulting software could determine the uncut chip thickness, contact length for every cutting edge on a grinding wheel as well as the resulting surface roughness of the grinding wheel. The simulation was validated by comparing the wheel model used in the simulation to grinding wheel measurements and by comparing the simulated surface finish to the measured surface finish. There was excellent agreement between the predicted and experimentally measured surface topology of the workpiece. The results suggested that only 22 to 30% of the cutting edges exposed on the grinding wheel are active and that the average grinding chip is as much as 10 times thicker and 5 times shorter than would be produced by a grinding wheel with a regular arrangement of cutting edges as assumed by existing analytical approaches.