Efficient and economical new grinding tools and dressing tools promote the development of honing process
In order to further improve the accuracy of gears, surface quality, transmission quality, and reduce noise, the gears that have been cut (rolled, inserted, shaved) can be ground. Gear grinding includes profiling using a shaped grinding wheel as a grinding tool Method grinding, using double-cone grinding wheels, disc-shaped grinding wheels, worm grinding wheels, etc. as grinding tools to grind teeth and honing teeth with honing wheels. Generating gear grinding is mainly based on the principle of gear and rack meshing. The grinding wheel is equivalent to the teeth of an imaginary rack. During processing, the pitch circle of the gear is purely rolling along the pitch line of the imaginary rack.
The precision of the gear after the generative grinding is improved. Because the movement of the two is forced to be synchronized, the grinding wheel rotates once, according to the number of grinding wheel heads, the workpiece must turn several teeth (several pitch t=πm), so the cycle The knot accuracy is also high, and the cumulative error of the weekly knot is small. Gear grinding can correct problems such as improving the precision of front cutting gear processing, and heat treatment deformation reduces precision. For this reason, the grinding wheel used for tooth grinding by the generative method and profiling method must be precisely trimmed with a dresser on the grinder according to the requirements of the processed gear. The cost of the grinding wheel and the cost of multiple dressing are high, which is the disadvantage of the tooth grinding method. In addition, in the driving part of a car, in order to improve the meshing between the teeth, the gear teeth are often continuously trimmed into an offset drum shape along the tooth direction. It is difficult to grind this kind of tooth shape by the gear grinding method. This is another of them. One deficiency.
During gear honing, the honing wheel and the gear to be processed are like shaving gears. The honing wheel drives the gear to rotate at a certain speed. Relative sliding occurs between the meshing points of the tooth surface. Due to the abrasive particles on the surface of the honing wheel, the honing pressure and relative Under the action of sliding, a very thin layer of metal on the gear tooth surface is ground down, so that the gear can achieve higher precision and surface quality. There are three types of honing wheels: external tooth type, internal tooth type and worm type. Various types of hardened and non-hardened tooth profiles can be honed, and the internal tooth profile is more economical. During gear honing, the gear rotates with the wheel, and the machining allowance is small. It is a non-mandatory non-synchronous transmission, so the original pitch and cumulative error of the pitch is difficult to correct, but this kind of processing has high productivity and economical efficiency. Good, low cost, welcome to users, but can it make up for its low accuracy of the week? In addition, it is difficult to manufacture and trim inner honing gears with high precision. Can honing with high quality, high production efficiency and low cost be achieved? Based on this idea, Mitsubishi has developed corresponding products so that the precision of honing can reach or even exceed that of grinding. The principle and related products are introduced below.
In addition to the advantages of high efficiency and low cost in actual honing, the processed surface quality can also be higher than that of grinding teeth. Because the grinding marks left after grinding are in the tooth direction, honing is in the direction of the tooth shape and will Compression residual stress is formed, the fatigue strength is improved, the tooth surface of the processed gear is not easy to crack, the service life is prolonged, and the noise generated is also small. On the basis of these advantages, can there be ways to improve its shortcomings? Mitsubishi has developed the following two products, and the results are very good. Here are the following:
(1) Use TRG grinding tools to pre-process the gear before honing. The so-called TRG abrasive tool is a worm-shaped electrodeposited CBN abrasive abrasive tool. (Electrodeposition refers to the process of dissolving the salt or compound solution of the deposit and depositing it by electrochemical action. This process is carried out under certain electrolyte and operating conditions). It is different from general worm-shaped abrasive tools. It is not an integral grinding wheel. It uses the technology of manufacturing hobs to process a precision metal worm-shaped steel core, and then uses high-precision electrodeposition technology to deposit a very thin layer of super hard on its surface. CBN abrasive grains, the steel core itself has a very high precision, unlike ordinary abrasive tools, which must be produced on a special machine tool using complex and expensive dressing methods. Using it to grind gears can not only correct the pitch error of the gear, but also because of the use of energy High-speed continuous development of the grinding worm shape, precise tooth profile, no need to trim it specially. The above conditions and reasonable design make the repeat installation precision of TRG abrasive tools high, and the grinding quality is high and stable. It uses coarser No. 80 abrasive grains, and it has been verified that the quality of the processed surface is not lower than that of fine abrasive grains. Due to its stronger adhesion than fine abrasive grains, it has a longer life and high processing efficiency. (Picture 1 top).
It meshes and rotates with the gear to be machined to generate and grind the teeth. (Figure 1 bottom) can improve the gear's tooth profile and tooth orientation accuracy, and can also improve the circumferential pitch and circumferential pitch accumulation accuracy. On the basis of this processing, the future honing can focus on its advantages, and further improve the tooth profile accuracy and the surface quality of the gear tooth surface.
(2) Develop high-efficiency diamond dressing tools that can grind special-shaped teeth. It is very difficult to manufacture and trim high-precision inner honing wheels. Mitsubishi also uses the above methods to first produce a precise steel gear that is the same as the gear to be machined (Figure 2), and then precisely deposit diamond grinding on the surface of the gear tooth. (Figure 3), use it as a dressing tool to make it mesh with the honing wheel to rotate, which can efficiently and conveniently dress the inner honing wheel and improve the accuracy of the honing wheel. This kind of dressing method is much simpler and faster than the previous ones. It is also the same as TRG abrasive tools. The abrasive grain size is also larger. The abrasive grain size is also larger. It can process the high-quality surface like fine abrasive grains. The combination) is strong, the processing efficiency is improved, and the service life is also prolonged (Figure 4).
This new type of dressing tool (abrasive tool) can dress 400-500 times and process 10,000 to 20,000 gears. If this layer of abrasive grains is worn out and can no longer be used, new abrasive grains can be electrodeposited again, which is very economical and convenient to continue to use. Moreover, its tooth profile can be pre-made so that the honing wheel can grind out the shape of the drum tooth. During the process of meshing and rolling of the honing gear, the tooth surface of the honing gear can be honed into a drum shape, thereby solving It is difficult to process special-shaped teeth.
The honing efficiency is high and the economy is good. The surface quality of the honing gear is high, but there are shortcomings. These shortcomings are made by the steel core of the precision-made worm-shaped abrasive and the precision-made dressing honing gear plus the precision electrodeposited super-hard abrasive CBN and PCD. The pre-processing and trimming tools have solved the above problems more satisfactorily, and can also produce drum-shaped teeth, which strongly promotes the more common use and development of the efficient, economical and simple gear honing process.
If the pre-processing of the CBN electric-shaped grinding wheel and diamond dressing gear honing developed by Mitsubishi Corporation is gear shaving and heat treatment, the honing method is difficult to repair these pre-processing errors and deformations. Use the grinding method Processing costs are high. At present, the TRG abrasive tool developed by Mitsubishi Corporation uses it as the pre-processing of gear honing not only to improve the accuracy of the gear, but also to reduce the processing cost. The so-called TRG abrasive tool (CBN electrodeposition worm-shaped grinding wheel) is made by electrodepositing CBN abrasive grains on a worm-shaped base metal. Due to the use of a worm shape that can be continuously developed and ground at high speed, it has a high pitch error correction ability, and due to the precision-made metal honing wheel substrate, precise electrodeposition technology, and reasonable design technology, this grinding tool High accuracy of tool installation. Using it as the pre-processing of gear honing ensures the gear honing and the precision improvement.
The grinding wheel for gear grinding must have a precise tooth profile. For this reason, a dresser (gear) with a precise tooth profile is first required to copy its precise tooth profile to the grinding wheel to accurately and efficiently grind a large number of gears. The dressing gear is to grind the tooth surface with a diamond grinding wheel to complete the dressing of the grinding wheel with a grinding tool that fixes diamond abrasive grains by electrodeposition on the steel gear shape base. The life of the dressing wheel varies according to the precision requirements of the gear being ground and the grinding conditions. Generally, a dressing wheel can do 400-500 dressings and can process 10,000-20000 gears. After dressing the grinding wheel, it is necessary to remove the old electrodeposited abrasive grains on its surface, and then deposit new abrasive grains before continuing to use.