Nidec Machine Tool Corporation has announced that it has developed what it claims is the world’s first high-accuracy polishing (grinding) method to machine internal gears for mass production that are used for automobiles’ drive units and transmissions and for robots’ joints.

Although there are already high-accuracy polish-machining methods for external gears for mass-production, the company suggests that there are no such methods available for internal gears. As such, the company has achieved positive results to secure the level of accuracy and production that conventional grinding, honing or skiving methods could not.

Source: Nidec Machine ToolsSource: Nidec Machine Tools

While the planetary gear mechanism boasts high efficiency, high load capacity and compactness, gears used in the mechanism are required to be high quality, as even a slight distortion in the gears as the mechanism’s components impacts the durability and transmission efficiency, and may cause noise and vibration. As a growing number of products become electrified and automated, and as the needs for high precision gears subsequently increase, the company has realized this new machining method and released it to contribute to improving gears’ durability, transmission efficiency, and noise, vibration and harshness (NVH) performance.

This latest project identified and derived machining conditions based on Nidec Machine Tool’s processing machines and technologies. This project is part of the joint research with Germany’s RWTH Aachen University.

Processing machine: The company used ZI20A, the grinding machine that was previously developed for internal gears for mass production. This machine can process internal gears with high precision to the degree of productivity required for their mass production.

Selection of grinding stones for polishing: The company selected grinding stones, which are consumables, based on its assessment of their availability, economic efficiency and suitability for autonomous driving.

Specifying machining conditions: By targeting Ra0.1µm and Rz1.0µm or less (a general surface roughness index for polish machining), the company derived high-efficiency machining conditions that would maintain the post-polish gear accuracy of ISO levels 3 to 5, while preventing grinding burn.

For more on the technology, read the paper, “Application-oriented research on internal generating polishing.”

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