With the development of the automobile industry and the continuous improvement of gear transmission research and gear manufacturing technology, breakthroughs have been made in gear tooth modification technology. Through the modification of gear teeth, the accuracy of gears can be improved, thereby reducing the cost of gears. Reduce noise and vibration and extend the service life of gears.
1. Gear product parameters, modification requirements and processing process
1.1 Basic technical parameters and shape of gears
Module: m=3.5
Number of teeth: z=38 Pressure angle: α=20° Tooth width: B=22 Outer circle: D=Φ140.56
Inner hole: d=Φ750+0.03
Gear accuracy: 8GB10095-2001 Material: SAE8620
Heat treatment: S0.5～C59
1.2 Gear tooth modification requirements
Tooth profile crowning amount: 0.005～0.015
Tooth lead crowning amount: 0.010～0.022
Tooth tip relief: 0.3✕45°
1.3 Gear processing process
Forging→normalizing→rough turning→fine turning→gear hobbing→gear shaving→carburizing and quenching→inner hole grinding
2. Working principle of tooth shaving and the reasons for concave tooth profile
Teeth shaving has the advantages of low cost, high efficiency, and convenient modification.
The shaving process is a meshing process in which the shaving cutter and the gear to be shaved form a pair of helical gear pairs with misaligned axes. During the shaving process, the radial pressure between the two axes of the shaver and the gear to be shaved is constant. The unit area pressure on the meshing tooth surface is much larger than the unit area acting on the two pairs of meshing tooth surfaces, and the cutting force is also much bigger. The relative sliding speed near the shaving cutter and the gear pitch circle is the smallest, and the cutting force The deformation time and cutting force transmission time are longer, and more metal is cut off. This is the reason for the concavity of the shaving tooth profile (see Figure 1). The amount of concavity is about 0.01~0.03mm.
3. Teeth Shaving Modification
The tooth shape after shaving with a standard shaving cutter often produces a concavity of 0.01 to 0.03 mm near the pitch circle, which is the leading cause of gear noise. Special modification requirements for gear products: the tooth crown amount is 0.005~0.015mm, and the tooth crown amount is 0.010~0.022mm. At the same time, combined with its heat treatment deformation due to the large inner hole of the gear, the structure is similar to a ring gear. The heat treatment deforms significantly. According to experience, the tooth top will “collapse” after heat treatment, and both ends of the tooth surface will “hang down.” This will increase the tooth shape and tooth crowning shape after heat treatment. Therefore, the modification of the shaving teeth must also consider the heat treatment deformation. Through repeated trials, the tooth shape and tooth direction of the shaving teeth can be better modified.
3.1 Tooth Profile Modification
Shaving cutter modification is used to consciously concave the pitch circle part of the shaving cutter to make up for the concave defect in the tooth shape caused by the shaving process. We use the domestic Y7125 gear grinding machine to modify the shaving cutter and use the modification template (see Figure 2) to dress the grinding wheel so that the tooth shape of the shaving cutter after sharpening forms a concave shape, and the concave amount is controlled at about 0.015. Figure 3 shows the tooth profile curve after modification by the shaving cutter with diameter Φ240, number of teeth Z=73, module m=3.5, helix angle β=15°, and the tooth profile curve after heat treatment of the shaved workpiece. Judging from the tooth profile curve results after heat treatment. This shaving cutter modification method fully meets the tooth profile modification requirements of gears.
3.2 Gear Lead Modification
For the tooth modification of shaving teeth, the elastic deformation of the gear and the heat treatment deformation are mainly considered. The ideal tooth meshing length of a pair of gears is in contact with the entire length direction. In order to realize that the tooth width direction is loaded, the gear load-bearing capacity is improved. , usually, the teeth are shaved into crowning-shaped teeth, and the tooth crowning shape amount is generally domestic: when the tooth width is ≤30mm, the crowning shape amount does not exceed 0.015mm; when the tooth width is >30mm, the crowning shape amount should be appropriately increased according to the tooth width ratio, in view of the characteristics that the gear tooth crowning shape requirement is larger than that in China. We combine the characteristics of “hanging down” in the tooth width direction at both ends during the heat treatment process and control the tooth crowning shape between 0.010 and 0.015 during tooth shaving. This way, the tooth crowning amount after heat treatment will fully meet the requirements (0.010~0.022) on the drawing.
3.3 Modification of Radial Shaving Cutter
The radial shaving cutter is a gear cutter for finishing gears. The feed method of the radial shaving cutter is only radial feed movement, and it is more convenient to modify the tooth direction. It is easier to process crowning shaped teeth or tapered teeth. The tooth shape and tooth direction of the radial shaving cutter can be modified at the same time. We have also implemented this in the shaving process of gear products, which can fully meet the special modification requirements of the product.
4. Modification of tooth tip
In response to the requirements for tooth tip modification of gear products, we adopt the gear hobbing trimming method, that is, a flange is added to the design of the gear hob, so that when gear hobbing, the tooth top chamfering of 0.3×45° can be completed requirements. In short, through the modification of the shaving tooth profile and lead, combined with the heat treatment deformation, we have fully achieved the gear’s special modification requirements and satisfied customers’ needs.
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