Research On The ’Trap’ Effect Of Semi-Fixed Abrasive Plate For Precision Machining With High Efficiency

Abrasive machining is the primary method of precision or ultra-precision processing technology. Semi-fixed abrasive machining technique is proposed to reduce or eliminate the surface defects caused by large abrasive grains and improve the efficiency of precision or ultra-precision processing.The mechanisms of typical abrasive machining methods are reviewed, and semi-fixed abrasive machining technique is defined as a class of processing method, such as grinding with low hardness wheel, lapping/polishing with proper material pad, or magnetic field assisted machining with proper magnetic strength. The relationships of ’trap’ effect and semi-fixed, chip storage, embedded grain are analyzed, and the result shows the ’trap’ effect is determined by the mechanical property of machining tool.The mechanisms of material removal of advanced ceramics in three different domains, brittle mode, ductile mode, and elastic mode, are reviewed, based on which, the preliminary theory of designing semi-fixed abrasive plate (SFAP) is proposed. The bonding agent, manufacture and measurement of ordinary grinding wheel are summarized, water and one kind of resin named SSB are adopted as the bonding agent of SFAP. The results of machining and measurement tests show the SFAP with SSB have better ’trap’ effect and higher strength, and which is focused on by this work. The evaluation parameters of SFAP include hardness, compression and resilience rate, shear strength, and microstructure.The model of discrete element for one kind of SFAP is proposed under the assumptions of circle abrasive grains and normal distribution of grain size. The constitutive relation between grains is defined by contact-stiffness model, slip model and parallel-bond model, and corresponding parameters are obtained through experiments of compression ratio and indentation with 90μm indenter.The ’trap’ effect of the SFAP is simulated with the discrete element model, adopting dimensionless load and relative trap time as evaluating parameters. The effects of manufacture parameters of SFAP, processing parameters, size and shape of large grain are discussed. The manufacture parameters of SFAP include porosity, hardness of grains, average grain size, friction coefficient of grain, and bonding strength. The processing parameters include load, rotating speed of SFAP and friction coefficient of workpiece.Semi-fixed abrasive machining experiments on damage-free single crystal silicon are performed to verify the ’trap’ effect, using surface roughness Ra as evaluating parameter. The effect of size and concentration of large grain, hardness of SFAP, processing load are discussed. The experimental results and the simulation results are compared and analyzed. The ’trap’ decreases with the increase of SFAP hardness or large grain size, because it is more difficult to embed in the SFAP for large grain when the SFAP is harder or the size of that grain is larger, on which the simulation results are consistent with those of experiments. The ’trap’ effect decrease with the increase of processing load, because the normal load acted by single abrasive grain or large grain on the workpiece is increased, while dimensionless load is adopted as evaluating parameter of ’trap’ effect in simulation, the absolute value of large grain or abrasive grain acted on workpiece is neglected. The rotating speed of SFAP has little influence on ’trap’ effect, for the variation of the rotating speed does not change the load of large grain or abrasive grain acted on the workpiece. While the frequency of single grain passing through the workpiece surface during unit time increases with the increase of rotating speed of SFAP, leading to an increase of surface roughness. The concentration of large grain has little influence on the ’trap’ effect, however, there exists one threshold of the number of large grains to be accommodated by SFAP, when the number of large grains is no more than the threshold, all large grains embed into SFAP; otherwise, a part of large grains can not embed into SFAP and bear the processing load, leading to an increase of surface defects.Semi-fixed abrasive machining experiments are carried on single crystal silicon, stainless steel, and copper, to verify the characters of high efficiency and precision of the SFAP manufactured in this work. The effects of processing load, rotating speed of SFAP, processing time on the surface roughness and material removal rate of workpiece are discussed.