The design of the helical internal gear ring is in principle the same as that of the helical external gear ring. Any basic rack form used for external helical gears can be applied to internal helical gears. However, there are several limitations to internal gear drives. Not only all those that apply to external gears, but there are also some others that are specific to internal gears. As with external gears, interference must be avoided to ensure effective tooth action.
1.Grinding helical internal gear rings
The processing principle of grinding helical internal gear rings: Internal gear grinding machines with multi-threaded grinding wheels, the grinding wheel that is ground during the processing of helical internal gear rings meshes with the workpiece in a motion-generating manner. In order to improve the grinding performance and grinding ratio, the grinding wheel spindle and the workpiece table rotate synchronously at high speed. A feature of the helical internal gear ring processing grinding machine is that the cross-axis angle between the grinding wheel and the workpiece axis is 20 to 35 degrees. This provides a higher sliding speed at the grinding contact point. Through high-speed grinding, gear accuracy (including pitch, profile and lead deviation) is improved, and tool life is also extended.
Unlike the case of grinding external gears, the grinding wheel for processing helical internal gear rings should be dressed at a higher frequency because its diameter is small and smaller than the workpiece diameter. This is not ideal in terms of cycle time and tool life. To address this problem, dressable ceramic CBN wheels are used in helical internal gear grinding machines – their life is longer than that of conventional ceramic wheels.
In addition, the use of high-speed spindles, combined with large cross-axis angles, allows grinding speeds of more than 20 m/s to be achieved. This results in longer tool life, shorter cycle times and lower tool costs. The main dresser gear of the helical internal gear grinding machine has the same geometry as the finished workpiece and its tooth flanks are electroplated with diamond. The dresser gear is automatically loaded and clamped to the workpiece fixture during the dressing cycle, similar to workpiece grinding.
2.Milling helical internal gears
In the machining of helical internal gears, the hobbing machines normally used for the production of spur gears cannot be used due to their shape. They are usually made with special milling machines (or gear shaping machines) for helical internal gears and gear shaping cutters. Recently, the efficiency of helical internal gear milling has been improved by a different process called milling.
Milling helical internal gears is similar to shaping or planing in terms of movement. However, the milling tool has multiple cutting edges arranged in sequence. Each cutting edge takes up material, creating the final shape continuously. If the milling tool has completely passed through the workpiece, the final shape has usually been achieved. Therefore, milling has a high cutting efficiency and is mainly used for helical internal gear rings.
Compared with gear shaping or gear shaping, the tooth geometry of the gear is directly generated by the involute shape of the milling tool cutting edge, rather than by the envelope of the cutting edge. Therefore, a broach can only produce one specific gear. For each number of teeth or module, a specific milling tool is required. Therefore, gear milling is mainly suitable for mass production.
The article mainly introduces the processing method of helical internal gear rings. Browsing the full text, you can understand that the design of internal helical gear teeth is in principle the same as that of external helical gears. Any basic rack form used for external helical gears can be applied to internal helical gears. However, there are several limitations to internal gear drives. Not only all those that apply to external gears, but also some others that are unique to internal gears. As with external gears, interference must be avoided to ensure effective tooth action.
