Zhou, Yuchen
(2018)
On modelling and experimentation of planar grinding using abrasive pads with grits of defined geometries and distributions for enabling controlled surface texture.
PhD thesis, University of Nottingham.
Abstract
The surface of diamond grinding tool manufactured by current production method exhibits stochastic nature in terms of different grit size, irregular geometry, random crystallinegraphic orientation, non-uniform spacing, and varying protrusion heights. These topography characteristics has been found having various negative effects for the abrasive performance, especially in high-precision applications, causing less controllable surface topography, inefficient chip flow, high working temperature and cutting force.
The thesis covers the design and manufacture of laser generated novel abrasive pad with ordered abrasive grits from CVD polycrystalline diamond films, providing repeatable patterns and shapes for abrasive tool used in load controlled plane grinding process, which is regarded as engineered abrasive pad. Two major design parameters for engineered abrasive pad, including abrasive grit geometry and planar contact area between grits and workpiece surface, were investigated. An inverted test setup was developed to enable the evaluation for the performance of ordered abrasive pad under plane grinding operation. The analysis of material removal and surface topography was made and compared between conventional abrasive pad (randomly shaped grits) and two engineered abrasive pad (saw tooth and square frustum) to evaluate the influence of grit geometry on the grinding performance. Furthermore, a geometrical model was developed to simulate the surface roughness generated by engineered abrasive pad. Inverted tests were conducted allowing the validation of the model. Besides grit geometry, three abrasive pads (one conventional, two engineered) with different planar contact were also studied through inverted grinding test to evaluate the influence of planar contact area on grinding performance. An improvement of design for better material removal (31.5% in Chapter 7) was achieved by adjusting the planar contact area of engineered abrasive pad.
It was found that laser generated abrasive pad can provide not the only superior surface finish, but also introduce less damage to the workpiece surface. More efficient chip flow and very little tool wear leading to a longer tool life was also observed. In particular, the engineered grits with symmetric shape (square frustum) exhibits superior performance over conventional grits (randomly shaped) and asymmetric grits (saw tooth). A good agreement between simulation and experimental results was found for surface roughness prediction, therefore provide good initial results for numerically studying engineered abrasives under planetary abrasive machining processes. Moreover, the evaluation of planar contact area also shows laser generated abrasives can provide significant advantages in material removal when designed with comparable planar contact area as conventional abrasive pad under specific applications, particularly when the abrasive contact geometry is designed to provide clearance in the cutting directions. Combining the findings above, a preliminary benchmark methodology was proposed for design of engineered abrasive pad, which enables the future optimization of engineered abrasive tool.
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