Research summary of form grinding technology at China and abroad

With the development of mechanical industry, gear is developing towards the direction of high precision, high speed, low cost and low noise, which puts forward higher requirements for gear processing. The most commonly used processing method of gear is cutting. In addition, there are casting, die forging, hot rolling, cold rolling and other processing methods, but they are rarely used at present. According to different principles, cutting method can be divided into forming method and generating method. The forming method uses the milling cutter with the same shape of the cutting edge and the gear groove of the gear to cut one by one on the milling machine. The precision of the gear is poor and the production efficiency is low. The generating method uses the basic law of the tooth profile engagement to cut the tooth profile, and the processed tooth profile is the envelope line of the cutting edge’s movement track. As long as the tooth profile angle and the module are the same, the same tool can be used to cut in Processing, such as gear hobbing, gear shaping, gear grinding and so on, belongs to this method. At present, gear processing needs special equipment, such as gear shaper, gear hobber, gear grinder, etc. Gear grinding machine is a special equipment for gear grinding at present. Although it has achieved the requirements of high efficiency and precision, it is only used in mass production and has a single function. In order to improve the accuracy and machining efficiency of gear, forming grinding has gradually become one of the important methods of gear machining. There are many advantages of form grinding, such as high grinding accuracy, low roughness, good forming process stability, high production efficiency and so on. These advantages make form grinding more and more used in gear manufacturing. The key of complex profile grinding is the dressing of grinding wheel [2]. The common dressing methods of grinding wheel include grinding method, turning method, diamond roller dressing method, etc. At present, the new dressing method is CNC grinding wheel dressing method, which has the characteristics of high precision, high efficiency and flexible dressing.

Forming grinding is a kind of processing method that dressing the shape of the grinding wheel to match the shape of the workpiece. With the market demand for high precision, high efficiency and low cost production, forming grinding technology has developed rapidly. Forming grinding technology has experienced the following stages in the development process:

Reciprocating form grinding has been widely used. It is mainly suitable for the occasions with small grinding amount, simple workpiece surface and low precision requirements. In reciprocating form grinding, because there are many reciprocating space-time travel of the worktable, the machining efficiency is low, and the edge of the workpiece and the profile of the grinding wheel are easy to collide, so the retention is poor. It is easy to block and burn, and the rigidity of machine tool is low. It is easy to creep and vibrate. Because the processing efficiency, surface quality and economy of reciprocating form grinding are relatively low when processing new hard to process materials (such as cemented carbide, tool steel, etc.), in addition, it is no longer practical when processing engineering ceramics and nickel base alloy by general milling, turning and other processing methods at that time, so in 50 At the end of the s, a kind of grinding technology with high efficiency and economy, which can grind the blank directly, i.e. slow feed force grinding technology, appeared in the grinding field. Slow feed power grinding is a kind of form grinding with high grinding depth (up to 30mm), small feed (generally hundreds to dozens of times of ordinary grinding), high metal removal rate (100cm3 / min), high precision and good surface quality. However, this grinding method has many problems, such as large contact area between grinding wheel and workpiece, large heat output, easy burn of workpiece and so on. This method is suitable for medium metal removal and short grinding time. Continuous dressing form grinding, also known as CD form grinding, is an efficient grinding technology. The diamond roller and the grinding wheel are always in contact with each other during grinding and the grinding wheel is trimmed. The metal removal rate of this grinding method is 25 times of that of slow feed power grinding. The grinding wheel is not blocked during grinding, which can avoid burns, and it is always in a sharp state. The grinding force is small and stable, so it is suitable for processing with high precision and efficiency, large metal removal amount and many grinding surfaces. Because of continuous compensation, the radius of workpiece and grinding wheel will be reduced. At this time, CNC system is needed for control. CD forming mill is gradually developing to FMS automatic slow feed grinding system to adapt to automatic replacement of grinding wheel and workpiece, and meet the needs of multiple varieties and small batch production [6]. In addition, an efficient grinding technology developed in recent years is electroplated superhard grinding tools, especially electroplated CBN wheel high-speed forming grinding. Its grinding line speed, metal removal rate and grinding speed are very high, and the grinding accuracy and grinding speed continue to develop in a higher direction. The grinding wheel diameter of the powerful grinder manufactured by the German gubring automation company is 400mm, the linear speed can reach 209M / s, the power is 60kW, and the speed is 10000r / min [7]. In Japan, the problem of burn caused by strong grinding was studied and a new electroplated grinding wheel was invented. At the end of the 50’s, China began to study the high-speed grinding technology. For example, Northeast University, which has carried out a large number of experiments on high-speed grinding since the 90’s, independently developed an ultra-high-speed experimental grinder with a maximum speed of 250m / s [8]. At present, many foreign companies are continuing to study higher and faster grinding technology. The forming grinding technology is changing with each passing day. The research results will promote the forming grinding technology to a higher, more precise and faster direction.