Effect of Primary Diamond Grain Size on Lapping Performance and Wear Process of Fixed Agglomerated Diamond Abrasive Pads

Fixed abrasive lapping, with the advantages of high material removal rate, excellent processed surface quality, and green environmental protection, is widely used in the lapping and polishing processing of semiconductor materials and optical glass, like SiC, GaN, sapphire, AlN, BK7 glass, fused silica glass, etc. For Fixed Abrasives (FA) Pads, as the lapping tools, its wear modes and wear process mechanism determine the stability of lapping process. Diamond grain sizes directly affect the lapping performance and wear behaviors. The work aims to investigate the effect of the primary diamond grain size on the wear mechanism of Fixed Agglomerated Diamond Abrasive (FADA) pads, and to improve the self-conditioning, lapping process stability and economic durability of the pads. The diamond grains with four sizes of 14 μm, 8 μm, 5 μm, 1 μm, were selected to prepare the agglomerated diamond (AD) abrasives by sintering method. The four types of AD abrasives were used to prepare the hydrophilic resin-based FADA pads on the platen vulcanizer. The lapping tests were carried out on the CP-4 polishing platform which acquired lapping forces and friction factors during lapping process and coordinates of workpiece in Z direction. BK7 glass was selected as the workpiece with the diameter of 76.2 mm and the thickness of 5 mm. The wear rates and lapping ratios of FADA pads were calculated, the morphologies of pads before and after lapping were observed by a scanning electron microscope, and the size distribution of debris was detected by BT-2800 Dynamic Image Particle Size Analysis System. The wear process (wear thickness of pads vs material removal thickness of BK7 glass) of FADA pads was analyzed. The experimental results indicated that the wear rate of FADA pads increased from 0.2 μm/min to 3.5 μm/min when the primary diamond grain size increased from 1 μm to 14 μm. From the morphologies of FADA pads before and after lapping, the surface of FADA pads after lapping still had sharp micro-cutting-edges when the diamond grain size was above 5 μm. The main wear mode was the fallen diamond grains off the surface of FADA pads according to the SEM of debris and its size distributions. However, for the diamond grain size below 1 μm of FADA pads, the clogged diamond grains and some scratches by debris were found on the surface of FADA pads. With the increasing diamond grain size, the values of tangential force Ft and friction factor f increased. During the whole lapping process, Ft and f more and more stable except under the condition of diamond grain size below 1 μm. The wear process of FADA pads consisted of three stages, namely initial rapid wear (I), stable wear (II), and severe wear (III). For the diamond grains above 5 μm, the wear process of three FADA pads gone through the stages of I and II. Under the same material removal thickness, the larger size the diamond grains were, the smaller the wear thickness of FADA pads was and the more stable the wear processes were. However, for diamond grains below 1 μm, the FADA pad wear process gone from I to III directly. Thus, with increase of the primary grain size, the self-conditioning ability of the FADA pads, material removal ability and lapping stability were improved. In summary, selecting the appropriate diamond grain sizes not only effectively improves the material removal rate and the stability of the lapping process, but also improves the self-conditioning and economic durability of the FADA pads. In addition, the time to enter the stable wear period is shortened. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.