Grinding wheel turning
Grinding wheel turning (also known as grinding wheel dressing) is a critical process in the grinding wheel’s operation. Specialized dressing tools (such as diamond pens and dressing rollers) are used to cut the grinding wheel surface, removing dull abrasive grains and clogged grinding chips, restoring the wheel’s sharpness and geometric accuracy to ensure grinding efficiency and quality. During the grinding process, the abrasive grains on the grinding wheel gradually wear and become blunt, forming a “passivation layer.” This increases grinding forces and temperatures, and can even cause workpiece burns (such as the appearance of a blue oxide film on 45 steel workpieces). Therefore, the quality of grinding wheel turning directly affects the grinding results. Improper dressing can result in uneven grinding wheel surfaces, increasing workpiece surface roughness (Ra values from 0.8μm to 3.2μm). Excessive dressing consumes excessive grinding wheel material, shortening its service life. Grinding wheel turning requires selecting appropriate dressing tools and parameters based on the grinding wheel type (such as alumina grinding wheel, silicon carbide grinding wheel), grit size (such as 46#, 80#) and grinding requirements (rough grinding, fine grinding).
The tool selection for abrasive turning must match the grinding wheel’s characteristics and dressing requirements. Diamond pens are the most commonly used dressing tools. They consist of natural diamonds (0.5-2 ct grit) or synthetic polycrystalline diamond (PCD) embedded in a toolholder and are suitable for dressing a wide range of grinding wheels. Natural diamond pens offer high sharpness and are suitable for fine dressing (surface roughness Ra ≤ 0.1 μm), but they are expensive. PCD pens offer excellent wear resistance and are relatively low cost, making them suitable for coarse dressing and high-volume production. Dressing rollers (such as diamond rollers) achieve dressing efficiency 5-10 times that of diamond pens through rolling contact with the grinding wheel. They are suitable for profile grinding (such as gear tooth grinding) and can achieve a dressing accuracy of 0.01 mm. Grinding wheel cutters (carbide blades) are also suitable for dressing coarse-grit grinding wheels (e.g., 36# and below), but they offer lower precision. When selecting dressing tools, consider the hardness of the grinding wheel: large-grain diamonds (1-2 ct) are suitable for dressing hard grinding wheels (such as WA80L), while small-grain diamonds (0.5 ct) are suitable for dressing soft grinding wheels (such as GC60K). An automotive parts manufacturer reduced dressing costs by 60% after replacing natural diamond pens with PCD dressing pens, while maintaining essentially the same dressing results.
The parameter settings for grinding wheel turning have a significant impact on dressing quality. Key parameters include the dressing speed ratio (the ratio of the dressing tool feed speed to the grinding wheel linear speed), dressing depth, feed rate, and dressing cycles. The dressing speed ratio is typically 0.001-0.01. A lower value (0.001-0.003) is used for fine dressing to achieve a smooth grinding wheel surface, while a higher value (0.005-0.01) is used for coarse dressing to improve dressing efficiency. The dressing depth (the amount of cut per time) is 0.001-0.01mm, with a fine dressing depth of ≤0.005mm and a coarse dressing depth of 0.005-0.01mm. A larger depth will cause chatter marks on the grinding wheel surface, while a smaller depth will prevent the passivation layer from being removed. The feed rate (the amount of feed per revolution of the dressing tool) is 0.1-0.5mm/r, with a fine dressing depth of ≤0.2mm/r and a coarse dressing depth of 0.3-0.5mm/r. The number of dressing cycles is determined by wheel wear, typically 2-4 times. The first dressing cycle removes most of the passivation layer, and subsequent dressing cycles refine the surface. For example, when dressing an 80# alumina grinding wheel for fine grinding, the parameters are: speed ratio 0.002, depth 0.003mm, feed rate 0.15mm/r, and 3 cycles. This can reduce the wheel surface roughness to Ra ≤ 0.05μm, and the workpiece Ra after grinding can reach 0.02μm.
The operating process and quality inspection of grinding wheel turning must be standardized. The position of the dressing tool must be adjusted before operation: the tip of the diamond pen must be 0.5-1mm lower than the center of the grinding wheel, with an inclination angle of 5°-10° to prevent the tip from being subjected to excessive impact force; the dressing roller must be parallel to the grinding wheel axis, with a parallelism error of ≤0.01mm/m. During dressing, the cooling system must be turned on, and cutting fluid must be used to flush the grinding chips generated by dressing to prevent clogging of the grinding wheel surface. The spark state must be observed during the dressing process: uniform and continuous sparks indicate normal dressing; sudden increases or decreases in spark size may indicate hard spots on the grinding wheel surface or wear of the dressing tool, and timely shutdown and inspection are required. The dressed grinding wheel must be tested for two indicators: geometric shape accuracy (such as flatness and roundness) is checked with a dial indicator, with an error of ≤0.01mm; sharpness is determined through trial grinding. If the grinding force is significantly reduced and there is no burning on the workpiece surface, the dressing is qualified. A bearing factory extended the service life of the grinding wheel by 30% and improved the grinding efficiency of bearing rings by 25% by standardizing the dressing process.
Different types of grinding wheels have different turning characteristics and considerations. Alumina (corundum) grinding wheels have a lower hardness and can be dressed with a greater depth and feed rate, making them suitable for coarse dressing. Silicon carbide grinding wheels are harder and more brittle, requiring a smaller depth and slower feed rate to avoid wheel chipping. Superhard grinding wheels (such as CBN and diamond wheels) require specialized diamond tools for dressing, with a dressing depth of ≤0.002mm and a speed ratio of 0.001-0.002. Advanced technologies such as electrolytic dressing are also required to ensure dressing accuracy. When dressing resin-bonded grinding wheels, the feed rate must be controlled to avoid excessive bond removal. For vitrified-bond grinding wheels, sufficient dressing cycles are required to remove the glassy layer on the surface. After dressing, the wheel should idle for 1-2 minutes to release surface stress and avoid vibration during use. After an aircraft engine factory adopted electrolytic dressing technology for CBN grinding wheels, the dressing time of the grinding wheels was shortened from 30 minutes to 5 minutes, and the surface roughness of the ground blade tenons was reduced from Ra0.4μm to Ra0.02μm, meeting the high-precision requirements.
