As an efficient power transmission method, gear transmission is widely used in various industries. With the update of processing technology, soft tooth surface gears have been gradually eliminated and replaced by carburizing and quenching hard tooth surface gears. It achieves greater torque transmission in a smaller volume and greater torque transmission in the flexural strength and contact strength of the teeth.
What is a hard flank gear?
Hard tooth surface gears refer to gears with a hardness of HRC40 or more. Heat treatment, quenching or carburizing quenching are usually required. After heat treatment, the workpiece will be deformed due to heat treatment, and the accuracy of its preheating processing will generally be reduced by 1-2 grades. Therefore, it needs to be sorted out after heating. The most common machining method for this type of high-precision hard flank gear is hobbing, then carburizing and quenching, and finally grinding the flank. This process results in the same structure and carburizing layer across the entire tooth face. Depth, the final hardness of the tooth surface can reach HRC58-HRC62, and high tooth surface geometric accuracy and surface finish can be obtained.
The workpieces with smaller modules are machined with integral hobs, and the materials are generally coated high-speed steel or powder metallurgy. Due to the large size of the hob body and the high cost of large module gears, it is generally designed as a toothed hob. This type of disc cutter requires regular inspection of the wear of each blade and replacement of worn or chipped blades. Drop: For extra-large module gears (generally m>22), gear milling cutters are generally used for machining.
Gear grinding is the most efficient and reliable way to obtain high-precision tooth flanks to grind off hobbing allowances and their deformations. In order to make the force and meshing of the gear under load more reasonable, the gear will be corrected to a certain extent in the standard involute tooth shape and tooth direction. The CNC gear grinding machine grinds the tooth profile to the required geometric accuracy with preset parameters. By selecting the matching grinding wheel and dressing parameters, the final roughness requirements can be achieved by grinding. The general requirement in the industry is RA08. There are also some special applications, such as wind power gearboxes, which need to reach RA06 or even higher. Its processing methods are divided into developing grinding and forming grinding.
Generate a grinding method
The principle of machining is similar to that of gear hobbing. During the grinding process, the grinding process is very efficient because the grinding wheel and the teeth to be ground are continuously meshed, the tooth shape is gradually developed, and the grinding process is not interrupted. In actual machining, due to the limitation of the size of the grinding wheel, the development grinding is suitable for machining gears with small modulus (generally m<=12).
In the grinding process, grinding wheels made of alumina can be used. The grinding wheel is constantly updated during droplet movement to achieve the highest material removal efficiency; In the process of fine grinding, the knife is translated step by step, and the grinding wheel is ground at the same position to achieve stable tooth surface quality. For the mass production of a single variety of gears, high-precision CBN worm grinding wheels can also be used, which can greatly improve the grinding efficiency, but the cost is relatively high.
Expansion grinding places high demands on the precision and stability of the machine. At present, well-known machine tool companies include Reischauer in Switzerland, Liebherr in Germany, etc. The accuracy of machining gears can reach 4-5 or even higher.
Mohr Superhard can provide gear and worm grinding wheels, which can be matched with grinding machines: KAPP, HAAS, Monnierzahner, SAMP, GLEASON, Felsomat, etc.
Profile grinding method
The grinding wheel is trimmed into the same shape as the tooth shape by the diamond grinding wheel, and the teeth are ground one by one. This method of production is more flexible. When changing the gear model, simply trim the grinding wheel to the corresponding shape. The entire dressing and machining process is controlled by preset NC axes. The world's leading companies in the processing technology are Gleason, Heffler, etc., the machining accuracy of their copy grinding machines can reach 3 grades, and because the shape of the entire tooth surface is continuously ground by the copy grinding wheel, the roughness of the entire tooth surface can reach RA04-ra0.8。
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