Asma Perveen

Analysis of surface and subsurface damage of micro-ground BK7 glass using on machine fabricated PCD micro-tool

This paper presents the research results of the morphology of subsurface damage (SSD) in BK7 glass ground with on-machine fabricated PCD micro tool. Grinding generated damages are assessed and characterised using bonding interface sectioning technique combined with field emission scanning electron microscopy (FESEM). Both the damage depth and surface roughness are found to be influenced by the depth of cut, feed rate and spindle speed. Two major type of grinding damage have been identified likely chipping damage and micro-cracking damage. Lateral, median and cone cracks are found to be existed in the sub-surface. These crack size varies from below to above 1 μm. The mechanism of damage nucleation and propagation are discussed also. Although the machined surface seems to show ductile mode behaviour even at higher material removal, analysis of subsurface damage shows that the material removal is a combined effect of grain dislodgement, micro-cracking and plastic deformation.

Characterisation and online monitoring of wear behaviour of on-machine fabricated PCD micro-tool while vertical micro-grinding of BK7 glass

This paper deals with the wear behaviour of polycrystalline diamond tool of 0.5 μm grain size during micro-grinding of BK7 glass. It was found that tool wear caused both diameter and length reduction and G ratio was found to be 940. Observation of tool surface gave clear indication of edge chipping and abrasion type of tool wear where grain was pulled out and micro-cracks and built up edge mechanism are responsible for wear mode. Tool wear progress can be divided into three stages. In the initial stage, tool suffers insignificant wear, then intermediate wear, and finally, severe worn out tool. Huge pitting on bottom surface, chipped side wall, longer centre line and double side wall lining are the major phenomena of severe tool wear. Moreover, the increasing tendency of normal cutting force is found to support the evidence of tool blunting but cannot clearly indicate the severity of wear. Monitoring of root mean square acoustic emission signal is found to give an indication of tool topographic condition, i.e., sharpness and bluntness of cutting edge. Moreover, this signal can also envisage minor and major tool chipping condition. Hence, monitoring the AE signal can be a plausible way of monitoring PCD tool condition.

Cutting Force Analysis of on-Machine Fabricated PCD Tool during Glass Micro-Grinding

Brittle and hard materials are problematic to mechanically micro machine due to damage resulting from material removal by brittle fracture, cutting force-induced tool deflection or breakage and tool wear. As a result, the forces arising from the cutting process are important parameter for material removal. This study was undertaken to investigate the effect of cutting conditions on cutting forces and the machined surface during the glass micro grinding using on-machine fabricated (Poly Crystalline Diamond) PCD tool. Experimental results showed that an increase in depth of cut and feed rate can result in increase of cutting forces and surface roughness as well. Among the forces in 3 axes, force along feed direction is found to be larger, which played a major role in material removal. Finally, it is observed that PCD tool exhibits promising behaviour to machine brittle material like BK-7 glass for producing micro molds and micro fluidic devices, since it has better wear resistance, experiences less cutting forces and generates smooth surfaces with Ra value of as low as 12.79 nm.

Effect of texturing on the friction characteristic of carbide and steel material by grinding process

In this paper, friction behavior of textured carbide and steel surface has been studied in order to investigate the effect of different patterns. Several simple textures have been fabricated using straight groove grinding wheel. By microstructuring, various spacing and height of the structure, we investigate the role of topography in terms of friction characteristic. The change of friction behavior has been tailored by grinding operation using straight grooved wheel and evaluated in terms of friction. Friction values were measured by Tribometer. Frictional properties of textured carbide and steel surfaces were assessed with the help of parallel steel slider with 2000g normal force under dry condition using four different sliding speeds. It is found from the experiment that except 30° and 90° angle patterns, rest of the patterns on carbide surfaces show friction reduction which is roughly from 0.15 to 0.13. On the other hand, similar textured patterns can reduce the COF from 0.17 to 0.13 in case of steel surface.

Modeling of Vertical Micro Grinding

Due to the small feed rate used in micro-machining, ploughing force needs to be considered in addition to the chip formation force. A new analytical model has been proposed to calculate cutting forces of micro-grinding process based on the process configuration, work piece material properties, and micro-grinding tool topography. The proposed approach allows the calculation of cutting force comprising both the chip formation force and ploughing forcec considering single grain interaction.

Fabrication of PCD Micro Tools Using Block EDM Method and Their Application to Different Microstructures in Brittle and Hard Materials

Fabrication of microelectrodes with different shape has become so important due to the high demand of industrial products not only with diversified shape but also of reduced dimension. However, to date, fabrication of different shapes in single setup is not possible and also need special indexing attachment. To solve this problem, in this study, a specially designed block containing three V slot of 60° 90° 120° has been designed and fabricated using wire cut machine to facilitate the fabrication of different shape micro-electrode. Then, with the help of block electro discharge machining method using this specially designed block, the feasibility of fabrication of microelectrodes with symmetrical and non-symmetrical section e.g. conical tool of angle 60° 90° 120°, rectangular, triangular, circular and semicircular tool from commercially available polycrystalline diamond rod has been investigated. As the size of electrode is of micron scale, multi-pass machining strategy has been taken to reduce the volumetric material removal, and thus to diminish the possible electrode breakage, which is especially significant. Finally, this strategy of using specially designed block has been found to be feasible for producing microelectrodes of various symmetrical and non-symmetrical sections down to few microns. In addition to this, the capabilities of these fabricated tools have been depicted by recommending few applications on both conductive and nonconductive material.Copyright