Study On ECD Dressing And Truing Of Diamond Grinding Wheel Tip And Its Micro Grinding Application

The micro-structure with controllable regular shape was manufactured on high performance material surfaces such as single crystal silicon carbide, silicon carbide reinforced aluminum(Si Cp-Al), ceramics and carbide alloy, which may produce new engineering application. However, the precision machining of those high performace materials with macroscopic size and microscopic structure depended on grinding machining of superhard diamond grinding wheel. In micro-grinding, tip of diamond grinding wheel was easy to wear. Thus, the metal bond was employed instead of resin bond. However, low efficiency of dressing and truing of metal-bonded diamond grinding wheel had been a bottleneck of industrialization. Therefore, the dry electro-contact discharge(ECD) dressing and truing method was proposed to true micro-tip of diamond grinding wheel. When micro grain distributed on wheel surface cut copper electrode, the impulse electric spark discharge occurred between rolled-up chip and metal bond of grinding wheel. The metal bond was removed gradually by impulse discharge so that high efficient dressing and truing was achieved. First, the impulse discharge removal mechanism, dressing and truing process of diamond grinding wheel micro tip were studied; Then, the micro-grinding performance of materials such as single crystal silicon carbide, Si Cp-Al and ceramics was investigated; Finally, The engineering applications of micro-structured surfaces were explored.(1) The dynamic experiment platform of dry impulse discharge removal was bulit. The on-line monitoring system of impuse discharge voltage and current waveforms was developed. The relationship model between characteristic parameters derived from impulse discharge current waveform and removal of metal bond in micron scale was also bulit. The research found that, for static and dynamic impulse discharge, the critical value(ratio of peak current to pulse duration) of spark discharge transformed into arc discharge was 0.059 and 0.038, respectively. In dressing and truing, the micro removal of metal bond can be predicted by characteristic impulse discharge parameters derived from dynamic impulse discharge waveform. The prediction error was 5.6% ~ 22.7%.(2) The micro-topographical removal model of diamond grain and metal bond was established. The relationship between discharge energy parameters, impulse discharge parameters and metal bond removal was investigated. The results show that the removal efficiency of diamond grains and metal bond was 0.013 mm3/min and 0.241 mm3/min, respectively. Compared with mechanical dressing, the dry ECD dressing can improve the dressing ratio and dressing efficiency about 34 times and 10 times, respectively. It may increase grain protrusion height about 12 μm. The dry mirror grinding of carbide alloy and die steel can be realized using coarse diamond grinding wheel. Their Ra can reached 0.089 μm and 0.022 μm, respectively.(3) For SD600, SD1200 and SD46 diamond grinding wheel, the dry ECD truing process of three diamond grinding wheels micro-tip with different grain sizes were developed. For ECD truing of SD600 and SD1200 diamond wheel micro-tip, the minimum tip radius was 33 μm and 15 μm, respectively. The minimum angle error was 1.1o and 2.4o, respectively. The micro-groove and micro-pyramid array structures with regular shape can be fabricated on carbide alloy and ceramic surfaces using trued micro-tip diamond grinding wheel.(4) Compared with mechanical grinding, the dry electrical discharge grinding of Si Cp-Al ceramic may reduce grinding force, grinding temperature and surface roughness about 41%, 1.3% and 25.6%, respectively. The wheel speed and feed speed had large influences on ground surface roughness, but depth of cut had little influence. The dry electrical discharge micro-grinding technology of carbide alloy was developed. It can effectively improve surface quality of micro-structured surface against mechanical grinding. The suitable impulse parameters were open-circuit voltage of 15 V, frequency of 5000 Hz, duty ratio of 50%.(5) The micro-groove structures curved surface of ceramic were fabricated by using trued SD600 micro-tip diamond grinding wheel. The depth error and tip angle error of micro-groove was 3 μm and 1.56o, respectively. The tip arc radius was 48 μm. The wind-driven experimental results indicate that micro-grooved structures may reduce air resistance by about 36% against smooth surface. Moreover, the micro electrical discharge forming machining of die steel, titanium alloy and Si Cp-Al surfaces with micro-array structure may be realized using electrode with micro array structure. The results show that the micro discharge removal efficiency of die steel was 17.5 times as much as titanium alloy. When average discharge current was 1.5 A, micro forming accuracy of Si Cp-Al was better.