Helical gears is the abbreviation of “helical cylindrical gear”, that is, the cylindrical gear whose tooth line is cylindrical helix, which is used to transfer the motion between non intersecting and non parallel shafts. From the perspective of a single gear, it is the same as the helical gear used to transmit the movement between parallel shafts, except that the latter has a small helical angle (generally 7 ~ 15 degrees), and the helical angle of the meshing gear is the same and the direction of rotation is opposite, but the former has no such limitation.
Helical gear is the most common spiral bevel gear and hypoid gear. It has been widely used in many industrial fields, especially in the automotive industry. Helical gear is one of the main parts of mechanical transmission system. Its tooth surface structure is complex, and the structure and processing adjustment of gear cutting machine tool are the most complex. At the same time, machining tools, machine tool parameter setting, loading deformation and assembly error will cause the changes of meshing, bearing and vibration performance, which makes the quality control of helical gear in design and manufacturing extremely difficult.
1) The spiral direction can change the center distance and transmission ratio.
2) The steering can be changed by spiral rotation.
3) Wear fast.
4) Point contact.
5) Small axial force.
The structure of helical gear tooth surface is complex, and the control of its machining accuracy and meshing quality has always been a difficult problem in gear manufacturing technology. Helical gear is one of the main parts of mechanical transmission system. Its tooth surface accuracy and meshing quality are the key to ensure the comprehensive performance of mechanical products, such as efficiency, noise, transmission accuracy and service life. Due to the geometric characteristics, meshing process and the structure of the gear cutting machine tool of the helical gear, its trimming adjustment is the most complex. At the same time, the processing tool, machine tool parameter setting, loading deformation and assembly error will cause the changes of its meshing, bearing and vibration performance, which makes the quality control of the helical gear in the design and manufacture extremely difficult. Its special use and excellent meshing performance have very strict requirements on the geometric accuracy and meshing quality of the tooth surface. Therefore, improving the machining accuracy and meshing quality of the helical gear tooth surface has always been the object of extensive attention and research by experts and scholars all over the world, and has become the key technology and ultimate goal of gear manufacturing.
The processing technology of helical gear tooth surface is closely related to the development of forming theory and its processing machine tool. With the continuous improvement of machine tool manufacturing technology and forming theory, the processing quality of helical gear is also improving. Generally speaking, the development of helical gear processing machine tools and tooth surface processing technology are generally divided into two stages: traditional mechanical gear milling machine tools and their processing technology, modern CNC gear milling machine tools and their processing technology. The structure of the traditional mechanical gear milling machine tool is complex, and the transmission chain is long and extremely complex, which increases the transmission error, reduces the accuracy of the machine tool to a certain extent, resulting in poor quality stability of gear cutting. In addition, the processing and adjustment of the traditional mechanical gear milling machine tool is complex, especially when processing wheel blanks with small batch and different parameters, it is necessary to adjust the tool position, wheel position and various gear changing devices on the machine tool for many times, In this way, a better contact area can be obtained, and it has high requirements for operators and long processing cycle.
Gear hob is a helical gear with large helical angle and generally 1 ~ 3 thread heads. The teeth are very long and can divide multiple circles around the hob. When machining helical gears, with the hob feeding along the axial direction of the workpiece, the workpiece should also be attached with a rotation speed matching the helical angle of the helical gear.