The process of automobile gear manufacturing typically involves several key steps: forging, rough machining, finishing, tooth cutting, shaving, heat treatment, grinding, and finally, boring the inner hole before storing the part. Among these, grinding the inner hole after heat treatment is one of the most critical operations, as it directly impacts the quality and lifespan of the gear. When grinding the inner hole of a helical gear (as shown in Figure 1), three rods of the same diameter are usually placed in a three-jaw chuck, aligned with the gear's teeth. The end face is then adjusted using a dial indicator to ensure proper alignment before clamping the gear with three jaws. This method is repeated for different parts by changing the pitch rods.
However, during daily production, our company has encountered issues where the radial circular runout of the ring gear does not meet the required specifications. These problematic parts mainly include thin-walled spur gears, helical gears, and helical gear weldments. For thin-walled spur gears, adjusting the clamping pressure can help reduce deformation. But when it comes to helical gears, the traditional method of using three round bars for clamping leads to several challenges.
Firstly, this approach is flawed because the helical gear’s geometry differs from that of a spur gear. The contact between the pitch rod and the gear is only at a single point, which doesn’t account for the helix angle. As a result, achieving consistent positioning becomes difficult. Secondly, each time the gear is clamped, the end face must be corrected, increasing processing time and reducing efficiency. Lastly, as the helix angle increases, the difficulty of machining also rises, making it impossible to process large-angle helical gears or weldments using this method.
To address these issues, we developed a new pitch clamp design tailored for helical gears. This fixture ensures that the distance from any point on the gear to the center remains consistent. By matching the tilt angle of the fixture to the helix angle of the gear, the machining principle is simplified, similar to that of a spur gear. This results in a straight-line contact, improving accuracy and stability.
In practice, the new pitch clamp features a multi-section design, allowing for better flexibility and increased contact area. This helps reduce errors caused by axial runout, heat treatment deformation, and inconsistent contact points. The assembly includes a wire-fixed roller that maintains the correct orientation, ensuring precise alignment during machining.
This improved fixture has been successfully applied in our workshop, significantly enhancing the quality and efficiency of helical gear machining. It is now being considered for broader applications, including helical gear weldments, marking a significant advancement in automotive gear manufacturing.
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