Nidec Machine Tool Corp. a group company of Nidec Corp., has developed the world’s first high-accuracy polishing (grinding) method for machine internal gears for mass production. Specifically, these gears are intended for drive units and transmissions of automobiles and joints of robots.

High-accuracy polish-machining methods for external gears for mass production are already available. However, no such methods are yet available for internal gears. Thus, the company conducted a research focused on this point. Then, the positive results secured the level of accuracy and production that conventional grinding, honing, or skiving methods could not.

Mainly, planetary gear mechanism boasts such merits as high efficiency, high load capacity, and compactness. However, the gears used in the mechanism are required to be high quality. This is because even a slight distortion in the gears, as the mechanism’s components, affects the durability and transmission efficiency. Also, it may cause noise and vibration. As a growing number of products become electrified and automated, and as the needs for high-precision gears increase accordingly, the company has realized this new machining method fast. Accordingly, it released the new method to contribute to improving gears’ durability, transmission efficiency, and NVH (noise, vibration, and harshness) performance.

This latest R&D 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. For more details on the project, please see the attached paper.

Processing Machine

The company used ZI20A, the grinding machine that used its unique technology and was launched in 2009 for internal gears for mass production. This machine can process internal gears with high precision to the degree of productivity required for mass production.

Selection of Grinding Stones for Polishing

The company selected grinding stones, which are consumables, based on its preliminary 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 – 5, while preventing grinding burn.

With its world-leading gear-machining technology, Nidec Machine Tool provides machines, tools, and machining solutions to stay committed to contributing to solving social issues.