J.A. Arsecularatne

Prediction of chip flow direction and cutting forces in oblique machining with nose radius tools

A method is described for calculating the chip flow direction in terms of the tool cutting edge geometry and the cutting conditions, namely feed and depth of cut. By defining an equivalent cutting edge based on the chip flow direction it is then shown how cutting forces can be predicted given the work materials flow stress and thermal properties. A comparison between experimental results obtained from bar turning tests and predicted values for a wide range of tool geometries and cutting conditions shows good agreement.

On tool-chip interface stress distributions, ploughing force and size effect in machining

This paper starts with a comprehensive review of techniques used to determine tool-chip interface stress distributions and reported results. Methods used to determine the so-called ploughing force are described. Finally, machining theory is used to investigate the ploughing force and size effect and to analyse a set of split tool test results obtained from the literature.

Calculation of optimum cutting conditions for turning operations using a machining theory

A method is described for calculating the optimum cutting conditions in turning for objective criteria such as minimum cost or maximum production rate. The method uses a variable flow stress machining theory to predict cutting forces, stresses, etc. which are then used to check process constraints such as machine power, tool plastic deformation and built-up edge formation. A modified form of Taylor tool life equation where the constants are determined using the machining theory has been employed in predicting tool life for the optimisation procedure. The obtained results indicate that the described method is capable of selecting the appropriate cutting conditions.

On the wear mechanism of human dental enamel.

The mechanisms and controlling factors in human enamel wear are not fully understood yet. To address this problem, we have used focused ion beam (FIB) milling and field emission scanning electron microscopy (FESEM) to investigate the processes taking place below the wear surface of enamel specimens from in vitro wear tests. These reveal the generation of subsurface cracks during wear of enamel. An analysis of published qualitative and quantitative experimental wear results for enamel as well as for ceramics shows the similarities of the wear processes taking place under similar contact conditions, despite the differences that exist between these two materials. It is shown that, for the considered conditions, fracture under elastic contact is responsible for enamel wear.

Ceramic-like wear behaviour of human dental enamel

This paper reports a transmission electron microscopy (TEM) analysis of subsurfaces of enamel specimens following in vitro reciprocating wear tests with an enamel cusp sliding on a flat enamel specimen under hydrated conditions. The obtained results show that crack formation occurred in the wear scar subsurface. The path followed by these cracks seems to be dictated either by the histological structure of enamel or by the contact stress field. Moreover, the analysis of a set of enamel wear results obtained from the literature and application of fracture-based models, originally developed for ceramics, correlate well, confirming the similar wear processes taking place in these materials. This analysis also reveals a marked influence of coefficient of friction on the enamel wear rate: for a higher coefficient of friction value, enamel wear can be severe even under forces generated during normal operation of teeth.

Prediction of tool life in oblique machining with nose radius tools

A method is described for predicting tool life from cutting temperatures calculated from machining theory. The method is applied to oblique nose radius tools. A comparison is made between predicted and experimental results for two plain carbon steel work materials and a range of tool geometries and cutting conditions.

Carbon Nanotube Reinforced Ceramic Composites and their Performance

Carbon nanotubes are considered as excellent reinforcements for improving the properties of ceramic composites. This paper reviews the reported techniques for the preparation of various ceramic coated CNTs, CNT-ceramic composites, CNT-ceramic composite coatings, etc. It is noted that a wide range of techniques have been used to fabricate these composites. Their characterisation has revealed that considerable improvements in electrical/thermal properties can be achieved, but only a few studies have demonstrated significant improvements in macro-scale mechanical properties of ceramics such as fracture toughness.

The oxley modeling approach, its applications and future directions

Abstract The Oxley machining theory which allows for the high strain-rate/high temperature flow stress and thermal properties of the work material is described. It is shown how the theory that was originally developed for the orthogonal process and later extended to oblique machining, can be used to predict cutting forces, temperatures and subsequently built-up edge formation conditions, tool life and cutting edge deformation conditions. It is also shown how the theory can be applied to obtain predictions in machining with restricted contact tools and in intermittent cutting processes, and to obtain work material properties using machining test results. Finally, some consideration is given to the future directions of machining research at UNSW. The Oxley Model can be used for predicting the performance parameters for different machining processes by taking into account the fundamentals of the chip formation process.

Nose radius oblique tool: Cutting force and built-up edge prediction

A semi-empirical machining theory is described for predicting cutting forces and temperatures for oblique nose radius tools from cutting conditions and a knowledge of work material flow stress and thermal properties. By defining an equivalent cutting edge based on the chip flow direction, predictions are made for different cutting conditions and tool geometries (nose radii and rake angles in particular). It is shown how the cutting conditions giving a built-up edge can be determined from the predicted temperatures. For finishing conditions a comparison between predicted and experimental results is made and this shows good agreement.

Assessment of constitutive equations used in machining

Machining of metals is characterised by plastic deformation occurring at high strains, strain-rates and temperatures. In the few predictive machining theories reported in literature, two types of constitutive equations, the power-law relation and Johnson-Cook equation, have mainly been used for describing the materials plastic behaviour. This paper aims at assessing the above constitutive equations in terms of their ability to describe the material behaviour for a wide range of strain-rates and temperatures encountered in machining. The focus is on the plain carbon steel and copper work materials. Using the above constitutive equations, flow stress results were determined for conditions encountered in machining and then compared with experimental results obtained from literature which are compatible with the rate equations applicable to the microscopic deformation mechanisms under considered conditions. It was concluded that considerable improvements are required for the aforementioned constitutive equations for accurate prediction of the work material behaviour under machining conditions and that further development is needed for more reliable and accurate constitutive equations.