Bevel gear is mainly used for transmission where two shafts intersect. The included angle between the two shafts is usually 90 °, which can also be less than 90 °. Bevel gears are generally processed on special machine tools such as bevel gear planer. In the absence of special machine tools for bevel gears, they can be processed on the milling machine with bevel gear milling cutter, which adopts forming cutter and indexing device to process on the milling machine. Due to the indexing error and tool installation error, generally only gears with 9 ~ 10 accuracy can be processed. In addition, in the process of machining, it needs to do multiple discontinuous gear division, and the productivity is also low. It is only used for gears with low machining accuracy in single piece small batch production and repair work.
1.Select bevel gear milling cutter. Because the diameters of the big end and the small end of the bevel gear are not equal, the base circle diameters of the big end and the small end are also not equal. The involute tooth profile of the big end is flat and the small end is curved. The tooth profile of bevel gear milled with forming milling cutter can not meet the small end if it wants to meet the large end. Therefore, when the bevel gear is processed with the bevel gear milling cutter on the milling machine, the tooth shape of the whole tooth can not be accurate, so the accuracy is low.
The bevel gear is designed according to the parameters of the big end. Therefore, the tooth profile curve of the bevel gear milling cutter should be manufactured according to the big end. In addition, because the slot at the small end of the bevel gear is narrow and the slot width at the small end of the standard bevel gear is 2 / 3 of that at the large end, the thickness of the bevel gear milling cutter should be manufactured according to the small end and should be slightly thinner than that at the small end. The bevel gear milling cutter is different from the ordinary cylindrical gear milling cutter. In order to prevent wrong selection, the “” mark is printed on the side of the bevel gear milling cutter.
Because the teeth of the bevel gear are on the conical surface, the tooth profile curve of the bevel gear milling cutter should be the same as that on the section perpendicular to the indexing conical surface. Bevel gear milling the first mock exam is also like cylindrical gear milling cutter, each modulus is divided into 8 cutter numbers according to the bending degree of the tooth profile curve. The difference is that it should be selected according to the number of equivalent teeth. The equivalent number of teeth shall be calculated first.
2.Clamping and adjustment of workpiece. Check the gear blank before clamping the workpiece, and check the gear blank angle and back cone angle with a universal protractor; Check the distance from the datum plane to the outer circle; Check the outer diameter of gear blank, etc.
Clamping of workpiece: according to different structural shapes, the common clamping method of bevel gear is to clamp the mandrel and nut. The Morse cone at the handle of the mandrel is matched with the conical hole of the main shaft of the dividing head, and is fastened on the dividing head with a tensioning screw. The workpiece is sleeved on the cylindrical part of the spindle, aligned with a dial indicator and pressed with a nut (see the figure below). For bevel gears with small diameter and large cone angle, or the bottom of small end groove is very close to the surface of inner hole, in order to avoid damaging the nut and even mandrel during tooth milling, micro cone mandrel with taper of 1:8000 ~ 1:1 000 can be used for clamping, which shall be determined according to the tolerance grade of aperture and other factors.
For workpieces with clamping parts such as large cone angle and diameter, steps at the end or large aperture, the three jaw self centering chuck on the dividing head can be directly used for clamping.
Alignment of workpiece during clamping. If the bevel gear is clamped with a special mandrel or spring chuck, alignment is generally not required. If the micro cone mandrel is used for clamping, it is generally not necessary to align. If necessary, the end face of the big end of the bevel gear can be checked and aligned. When clamping with chuck and clearance matched mandrel, it is necessary to align the radial circular runout of the large end and small end of the workpiece and the end circular runout of the large end.
Adjustment of indexing head. When the indexing head is installed on the worktable, it is necessary to make the spindle axis consistent with the feed direction, and then pull the indexing head spindle up to a cutting angle, which is equal to the root cone angle.
Adjustment of milling layer depth. After the workpiece and indexing head are adjusted, first adjust the split surface of the milling cutter to pass through the axis of the workpiece (tool alignment), then make the milling cutter contact and wipe the conical surface of the big end (based on the big end), exit the workpiece, raise the worktable to the full height of the big end tooth (2.2m), and then start milling the middle of the tooth groove. The workpiece with large modulus can be milled by several times in depth.
In order to prevent accidents caused by the sudden lifting of the indexing head spindle during cutting, it is best to mill from the big end to the small end.