How to choose the grinding fluid for different grinding processing methods?
August 07, 2021
In the metal grinding process, in order to obtain the ideal machining accuracy and surface quality, it is very important to choose the right grinding fluid. Different metal grinding processing methods produce different processing phenomena and different requirements for grinding fluids, so the grinding fluids used are more different.
Selection of water-based grinding fluid 1.1 Ordinary grinding Ordinary grinding is recommended to use ordinary emulsified grinding fluid with a dilution concentration of 2% to 5%, which is made of rust inhibitor, emulsifier and mineral oil. Ordinary grinding includes outer circle, inner circle, cone, surface grinding, etc. According to the difference of the grinding wheel particle size and the grinding amount, it can be divided into rough grinding and fine grinding. The rough grinding accuracy is not high, the processing dimension tolerance grade is IT8～IT7, and the surface roughness is 0.8～0.4 μm; the fine grinding can obtain higher processing accuracy and lower roughness, and the processing dimension tolerance grade is IT6～IT5. Grade, the surface roughness is 0.4～0.1μm. The linear speed of the grinding wheel in the grinding process is generally 30 to 35 m/s. During grinding, a large amount of fine metal chips and fine grinding particles threshed by the grinding wheel are produced, which are easy to stick to the surface of the grinding wheel and the workpiece, and damage the quality of the processed surface. Ordinary grinding processing requires cutting fluid to have good cleaning and cooling performance, as well as anti-rust and lubricating performance. 1.2 High-speed grinding Water-based grinding fluid is suitable for high-speed grinding. In metal grinding, the grinding with the grinding wheel speed exceeding 50 m/s is usually called high-speed grinding. The difference between high-speed grinding and ordinary grinding is that as the linear speed of the grinding wheel increases, the number of abrasive particles passing through the grinding area per unit time increases. Under the condition of a certain feed, the friction between the grinding wheel and the workpiece increases, making The heat generated per unit time also increases, and the grinding temperature rises significantly. According to the test, the grinding temperature (working average temperature) when the linear speed of the grinding wheel is 60 m/s is about 50%～70% higher than that of 30 m/s; the grinding temperature when the linear speed of the grinding wheel is 80 m/s is higher than 60m/s. At s, it is 15%-20% higher. As the temperature of the workpiece increases, the possibility of burns and cracks on the processed surface of the workpiece increases, and the processing size error increases. As the linear speed of the grinding wheel increases, the cutting thickness of the abrasive particles becomes thinner under a certain unit time of metal removal. Under high temperature and high contact pressure, the material to be ground adheres to the abrasive particles, and the chips will also be embedded in the pores of the grinding wheel. In this way, the pores on the surface of the grinding wheel are blocked and blunt, thereby reducing the grinding efficiency. Therefore, ordinary grinding fluids cannot be used during high-speed grinding. Instead, grinding fluids with good penetration performance, cooling performance, extreme pressure lubrication performance, anti-rust performance, settling performance and cleaning performance should be used to quickly remove the generated The waste scraps are washed clean and settled quickly to meet the requirements of the processing technology. In addition, due to high efficiency and large heat generation, high-speed grinding requires high requirements on the cooling performance and lubrication performance of the grinding fluid. The heat transfer effect of oil-based grinding fluid is poor, and the temperature of the grinding area is too high, which will cause the grinding fluid to produce smoke and cause environmental pollution in the work area. Moreover, due to insufficient cooling of the oil-based grinding fluid, it often causes the surface of the workpiece burn. Water-based grinding fluid has higher water content and better cooling effect than oil-based grinding fluid, so it becomes the reason for selection in high-speed grinding. 1.3 Power Grinding Strong grinding should choose water-based synthetic grinding fluid containing extreme pressure additives. Power grinding is also called power forming grinding. Generally, it is not necessary to perform rough machining of the workpiece before grinding. Instead, by increasing the grinding depth, the blank can directly grind the required dimensional accuracy, shape and position accuracy and surface processing quality of the workpiece. Grinding and forming at one time, the roughing and finishing are combined into one machine tool to complete, so as to achieve the purpose of shortening the production cycle and reducing the cost. Compared with general grinding, powerful grinding has a large cutting depth, grinding force and grinding heat, and more than 97% of the grinding power consumption is converted into heat energy. If the heat generated in the grinding process is not eliminated in time, the chips will melt to form weld beads, which will burn the machined surface and block the surface of the grinding wheel. Therefore, in order to ensure the grinding effect, the grinding wheel must be cleaned by high pressure and the workpiece must be forcedly cooled. . In the grinding process, the contact arc between the grinding wheel and the surface of the workpiece is longer, and the cleaning performance and cooling performance are higher than the lubrication performance and rust resistance. Cut force, reduce power consumption, and prevent burns. Sulfur-containing extreme pressure additives can also be used in combination with chlorine-containing extreme pressure additives to further improve the lubricating effect.
Selection of oil-based grinding fluid 2.1 Diamond wheel grinding Low-viscosity oil-based grinding fluid should be used for diamond grinding wheel grinding. Diamond grinding wheels have the characteristics of high hardness, high compressive strength, good wear resistance, and long service life. They are mainly used for grinding hard and brittle materials and metal materials such as cemented carbide, glass, ceramics, and semiconductor materials. Due to the high hardness of the workpiece, excessive heat generated during grinding will cause premature wear of the grinding wheel. Therefore, the grinding fluid should mainly have lubrication and cooling properties to keep the grinding wheel sharp. Diamond grinding wheel grinding uses a low-viscosity oil-based grinding fluid with good lubrication properties, which can quickly wash away debris and grinding wheel abrasive particles, and obtain better surface quality and machining accuracy of the processed parts. 2.2 Thread, gear and lead screw grinding Thread, gear and lead screw grinding should choose oil-based grinding fluid with low viscosity, high flash point, and extreme pressure additives. In metal cutting processing, the overall quenching of threads, gears and lead screws deforms greatly during heat treatment and grinding, and surface hardening treatment should be used as much as possible. In addition, the requirements for dimensional accuracy and surface processing quality are very high. Grinding is used after hardening to ensure that the processing dimensional accuracy and surface quality meet the process requirements. The lubrication performance of oil-based grinding fluid is better than that of water-based grinding fluid, which can prevent grinding wheel abrasive cutting edge friction loss and cutting adhesion, keep abrasive particles sharp, reduce grinding force, reduce grinding heat, and ensure a good guarantee Processing surface roughness; oil-based grinding fluid cooling rate is not as good as water-based grinding fluid, the workpiece produces less stress, and there are fewer surface grinding cracks on the workpiece; the extreme pressure additive added by the oil-based grinding fluid can react with the workpiece material and generate low resistance The lubricating film with shear strength can effectively improve the load capacity of the grinding fluid, reduce the wear of the cutting edge of the abrasive grain, reduce the friction between the abrasive grain and the workpiece during the grinding process, reduce the heat generated by the friction, and reduce the surface temperature of the workpiece , Reduce the residual stress of the workpiece. Because the grinding of threads, gears and leadscrews has high requirements on the forming surface of the grinding wheel, the machining dimensional accuracy is high, and the surface roughness is high, it is generally appropriate to use oil-based grinding fluids containing extreme pressure additives. At the same time, in order to obtain better cooling and cleaning properties and prevent the smoke from the grinding fluid, the oil-based grinding fluid should be added with the characteristics of low viscosity and high flash point.
