Milling method for straight bevel gears

Cylindrical bevel gears can be processed by ordinary milling machines. According to the number of times each tooth groove is cut, they can be divided into one-cut method, two-cut method and three-cut method. The basic principle is to cut the tooth groove by adjusting the relative position of the tool center with the center of the tooth groove, and then use the index plate to index the tooth groove, repeating the cutting process until all the tooth grooves are cut to complete the processing. Since this method belongs to the profiling method, the tooth shape of the tool also needs to be changed according to the number of teeth of the gear. For convenience of use, the tool is divided into several tool numbers. The commonly used spur bevel gear cutter is 8 pieces in a set, which is used to process spur bevel gears with the same module and the number of teeth ≥12. After selecting the tool number, milling machine and index head, the processing can be carried out. 1.1 Single-cut processing is the roughest. After the gear blank is mounted on the dividing head and clamped, adjust the lead angle of the gear so that its root cone is parallel to the cutting path of the tool. The tool cuts in from the small end and exits from the large end. If the module is large, it can be cut in several times in the tooth height direction until the tooth depth is reached. Then turn the dividing plate to separate the teeth and cut the next tooth groove. After repeated many times, the bevel gear processing is completed. Although this method has high processing efficiency and is easy to operate, its shortcomings are also most obvious. Due to the low precision of the gear and the lack of mutual adjustment of the position between the tool and the gear blank, the bevel gear has a completely constant tooth profile along the tooth length direction, which is significantly different from the theoretical state. If a spur gear cutter is used for processing, any portion along the tooth length direction will not match the theoretical tooth profile. If the spur gear cutter is adjusted according to the number of teeth at the big end, only the big end will match the theoretical tooth profile. The farther from the big end in the direction of the tooth length, the larger the tooth profile error. Therefore, although the single-cut method is effective in processing straight bevel gears, its accuracy is low. It is generally used in places where only the motion is transmitted and there is no requirement for the transmission accuracy and stability. The actual processing state is shown in Figure 2.

1.2 Double-knife processing

Compared with single-knife processing, the double-knife method adds the process of changing the relative position between the tool and the gear workpiece when processing one tooth groove. Each tooth groove is milled by two knives. The thickness center plane of the disc cutter moves a distance S relative to the axis of the gear workpiece. The gear workpiece is rotated by an angle A in the opposite direction from the moving direction to complete the second cut. In the third cut processing, the disk cutter moves in the opposite direction by 2S, and the gear workpiece also rotates by an angle of 2A in the opposite direction from the moving direction to complete the tooth groove processing. After repeated many times, the straight bevel gear processing is completed. Although the double-knife method is not as convenient as the single-knife method, its accuracy is much higher than that of the single-knife method, close to the teeth of the same height.

1.3 Three-cut method processing

In the absence of special equipment, the three-cut method is the most commonly used processing method. Each tooth groove is milled by 3 cuts. The first cut is used to roughly mill all the tooth grooves of the same width. The second cut is used to fine mill one side of the large end. The third cut is used to fine mill the other side of the large end. The dividing head is fixed to the table of the milling machine. After the first cut is completed, the table is moved by a distance S, and then the dividing head is used to slightly rotate the workpiece around its axis by an angle ω. The direction of the table offset is opposite to the rotation direction of the gear workpiece. After milling one side, slightly rotate the corner in the opposite direction and offset the table, and then process the other side. The offset and rotation angle are calculated according to the parameters of the gear being processed.