Papers by Author: D.J. Stephenson

Abstract: The residual stress on the ground surface of workpiece in high efficiency deep grinding (HEDG) has been investigated. It has been found that the mechanism in forming the ground surface residual stress in HEDG is much different to that in the conventional shallow cut grinding process. It is not a thermally dominant event as in most of the shallow cut grinding mode; it is instead driven by the combined effects of both the thermal and mechanical loadings. The compressive plastic deformation near the workpiece surface during grinding and the short contact time in the HEDG regime, makes it possible to generate compressive surface stresses even when the surface temperatures are above 700-800°C.

Abstract: Based on the concept of the interaction between a magnetic and electric field, a magnetic field was suppressed on the Electrochemical Machining (ECM) setup to improve the copying accuracy of ECM. Mathematical modeling and finite element modeling of the magnetic field was also developed using ANSYS to study the influence of permanent magnet design on the ECM process. The results indicate that by introducing the magnetic field the threshold of electrochemical reaction is decreased and the tracks of ions become complicated which makes the chemical reaction more extensive and more uniform in the inter-electrode gap. The distribution of magnetic field in the gap helps to improve the machining accuracy and the process efficiency, when the permanent magnet is at the end of the electrodes. Experiments have been carried out to validate the results of finite element analysis and the effect of a magnetic field on the ECM process is discussed.

Abstract: The purpose of this experimental research are investigation the growth behaviors of the oxide layer at different pre-dressing conditions in ELID pre-dressing, effects of voltage and duty ratio of the power supply, wheel speed on the oxide layer formation characteristics on the metal bond diamond wheel surface. The results indicated that the oxide layer thickness on the wheel surface increase with pre-dressing time. The oxide layer growth rate is faster in beginning period time of pre-dressing process then slow down. Both the thickness and growth rate of oxide layer increase with the increase of duty ratio and applied voltage. It takes longer time for oxide layer growth rate to reach to stable state in lower duty ratio condition than in higher duty ratio condition. There are no effects of wheel speed on oxide layer growth behaviors in the wheel speed range of 1000rpm to 4000 rpm.

Abstract: Optical surface finish below Ra 10nm can be achieved on a ‘Tetraform C’ grinder of ultra-high stiffness, when grinding a low alloy steel with or without the help of ELID (electrolytic in process dressing). Surface roughness generation modelling has been carried out to predict thepossible surface roughness values. Efforts have been made to transfer the process knowledge to different grinding mode using a rigid 5-axis Edgetek CNC grinder. The effects of material removal rate and grit size and also that of spark out passes on the surface roughness generated have been investigated.

Abstract: The current application of fluids in grinding processes is discussed, the issues related to the use of both mineral oil and water based fluids and the desire to move towards minimum quantity lubrication (MQL) or even dry grinding. The impact of fluid application strategy on workpiece quality is considered. In particular the importance of reliable thermal modelling and knowledge of the thermal partitioning of heat is essential if robust fluid application strategies are to be developed. Examples are given showing how an understanding of the thermal characteristics of the process can be used to develop different and successful fluid application strategies for various grinding regimes from creep feed through to high efficiency deep grinding (HEDG). The possibility of using solid lubricants is also discussed for particular grinding regimes.