Sphere forming mechanisms in vibration-assisted ball centreless grinding

• First studied sphere forming mechanism in vibration-assisted ball centreless grinding.
• Developed a 3D model for simulating vibration-assisted ball centreless grinding.
• Confirmed vibration-assisted ball centreless grinding has high accuracy & efficiency.
• Identified the rhythmical romation motion is critical for ball centreless grinding.

This paper aims to clarify the sphere forming mechanisms in vibration-assisted ball centreless grinding, a new technique for effectively processing balls using ultrasonic vibrations. Based on a comprehensive analysis of the ball rotation motion, geometrical arrangement and stiffness of the whole grinding system, a reliable mechanics model was successfully developed for predicting the sphere forming process. Relevant experiments conducted showed that the model had captured the mechanics and the major sphere forming mechanisms in ball centreless grinding. It was found that the ball whole surface can be well ground with a high accuracy, while efficiency is much enhanced compared with that in the traditional methods. The ball rotational speed which is controlled by the ultrasonic regulator has a great impact on final sphericity, and the speed controlled by the ultrasonic shoe dominates the whole processing time. To achieve a stable and high precision grinding, the ball needs to rotate rhythmically, and the wheel feed per step and the ball location angle should be controlled in a critical range.