Precision Fabrication and Development of Charging and Testing Methods of Fixed-Abrasive Lapping Plates
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Date
2003-07-12
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Abstract
The recording head industry is one of the dominant users of advanced ceramics such as alumina, silicon nitride, silicon carbide and AlTiC. The high hardness of these materials makes diamond the optimal abrasive for machining. One challenge when manufacturing recording heads for rigid disk drives is to generate surfaces that are both planar and smooth. Flatness tolerances are in the range of a few tens of nanometers to a few hundred nanometers per millimeter of length [1]. Roughness tolerances are in the range of a few nanometers to the subnanometer range [1]. Fixed-abrasive lapping, sometimes called nanogrinding, is a common method of machining used on ceramics. Fixed-abrasive lapping is generally a two-body abrasive process, with the abrasive grain fixed in the lapping plate that produces an extremely smooth surface due to the controlled depth of cut. The process of fabricating a quality fixed-abrasive lapping plate is a lengthy and sometimes demanding process. The goals of this research are to investigate the current fabrication process for improvements in surface texture quality, charging time and waste reduction of abrasive as well as the development of methods and equipment capable of estimating the lapping qualities of the plate during its fabrication process. The improvement of this process will reduce plate fabrication time and improve lapping performance. Current processes used to fabricate a plate can require 2 hours or more, and often the lapping quality of the plate is unknown until it is used. The research started by analyzing the current process used. The surface texture and charging quality were analyzed by quantifying characteristics such as surface roughness, kurtosis, bearing ratio and diamond concentration. The new process developed at the Precision Engineering Center changed the surface texture from scratches of random geometry to a continuous spiral groove cut by a diamond turning machine. This texture not only has better reproducibility than the random scratches, but the geometry of the individual features can be better controlled. The charging mechanism was also changed from a large charging ring that was half the diameter of the lapping plate to a small rolling cylinder. The cylinder creates higher pressures and the ability to follow the profile of the plate. These changes created a shorter charging time, higher charging quality and reduced abrasive waste during the charging process. A tribometer was developed to test the charging quality of the plate during the charging process. It took advantage of the changing friction coefficient on the surface of the plate with charging time. The mechanism constructed and tested did not perform as designed, but can be used as a prototype for future developments. The use of other equipment for charging verification utilizing friction or other aspects of the charging process is viable.
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Lapping, nanogrinding, polishing
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Degree
MS
Discipline
Mechanical Engineering
