Nidec Machine Tool develops polish grinding method

9th February 2024

Harry Fowle

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Nidec Machine Tool has announced that it has developed 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.

While there are already high-accuracy polish-machining methods for external gears for mass-production, no such methods have been available for internal gears. After conducting research focused on this point, the Company has achieved positive results to secure the level of accuracy and production that conventional grinding, honing, or skiving methods could not.

Though the planetary gear mechanism boasts such merits as 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 affects 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 increase accordingly, the Company has realized this new machining method fast, and release it 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 it 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.