Papers by Author: David Lee Butler

Abstract: The surface of the grinding wheel and the conditions under which it is prepared has a profound influence upon the grinding performance as characterised by the grinding forces, power consumption, cutting zone temperature and component surface finish. Only by having a clear understanding of the wheel topography can the interaction of the grinding wheel surface with the workpiece be fully understood. Two dimensional measurements or profilometry, while being a relatively quick measurement to perform, suffers from information quality issues due to the subjectiveness of the profile location as well as questions regarding how representative a profile is of a three-dimensional real surface. While profilometric measurement has long been standardised in the form of various international standards, topographic standards have only recently been agreed upon and formalised as ISO 25178. In this paper a comprehensive approach to wheel topographic characterisation will be undertaken. Factors such as measurement strategy, filtering, active grain identification as well as the fidelity of surface replication will be considered. The paper will propose a recommended measurement strategy and surface parameter set deemed sufficient to provide a comprehensive understanding of the grinding wheel topography.

Abstract: A study was carried out to investigate effects of crystallographic structure on the machining performance with polycrystalline oxygen free copper (OFC) using a single crystalline diamond (SCD) micro-tool. The SCD micro-tool used in this study fabricated with a focused ion beam (FIB) has a cutting length of around 30 µm on the primary clearance face. It was found that a change in crystallographic orientation resulted in a variation in machining force, chip thickness and shear angle, leading to a change in machined surface integrity. When a micro-size tool traverses within a grain at a machining direction aligned with a particular crystallographic orientation, the work material in front of the machining tool is found to be severely deformed. If the orientation changes to a less favorable orientation, this may lead to a much reduced shear angle, a thicker chip, striation at the chip back, higher machining forces and a degraded machined surface. This study contributes to the understanding of the physics of micro scale mechanical machining (micro-machining).

Abstract: Surface measurement using three-dimensional stylus instruments is a relatively new technique that offers numerous advantages over more traditional profilometry methods. The information generated is, unlike profile measurement, less subjective and more statistical providing additional insight into the surface structure. One application of surface measurement that has encountered problems when using the profilometry method is that of grinding wheel characterisation. The wheel surface texture (topography) and the conditions under which it is generated have a profound effect upon the grinding performance as characterised by the grinding forces, power consumption, temperature, and surface integrity of components. A detailed knowledge of the nature of the topography of the grinding wheel would provide further insight into surface interactions between the wheel and workpiece as well as enabling improved control of the grinding process in general. In this paper four diamond grinding wheels of 91 and 181 micron grit size were subjected to differing dressing conditions to produce varying final wheel topographies. Three-dimensional surface measurement techniques were employed to quantitatively characterise the topographic change and provide an aerial estimation of the number of cutting grains. The results demonstrate that the techniques can distinguish between a worn and dressed wheel. In addition, the parametric values generated from the various surfaces can aid the user in determining when re-dressing is required.

Abstract: Recently, material removal utilising electrokinetic phenomenon was proposed as an alternative to create material removal at the nanometric level [1]. The concept of the introduced material removal process is to impinge particles contained in the slurry, under the influence of hydrodynamic and electrokinetic effects, onto the workpiece with a predetermined velocity to create material removal on the surface. The material removal process proved to be feasible where the material removal rate was reported to be in the range of a few hundred nm/hr with a surface roughness of a few nm (RMS). This paper aims to look into the effect of the electrochemical dissolution on the material removal process since high voltages are involved during the material removal process. During the experimental study, electrochemical dissolution was observed and it contributed a certain proportion of the material removal process. However, the main material removal mechanism still relies on the mechanical action of the abrasive particles on the surface of the workpiece to create material removal during the process.

Abstract: Abrasive flow machining (AFM) has become one of the more attractive finishing processes used in applications such as deburring, recast layer removal, radiusing as well as for polishing. Recently, there has been renewed interest in developing low cost/ low pressure modular AFM systems and media. The media which contains the abrasive particles is the key element in ensuring efficient material removal and a good surface finish. In this paper, the authors will present their work on the development and characterization of a new abrasive media formulation.

Abstract: With the demand for precise nanometric material removal with minimal defects, several non-contact ultraprecision machining techniques were developed over recent decades. The electrokinetic material removal technique [1] is one such method that allows material to be removed without any physical contact between the tool and the workpiece. In this work, the influence of the slurry mixture on the material removal rate for the electrokinetic material removal process is studied. During the process, it was observed experimentally that the mixture of the slurry affected the material removal rate. The parameters varied in the slurry mixture experiments were the size and concentration of the particles. Explanations for the behaviour of the material removal rate were also suggested during the study to further understand the electrokinetic material removal technique.