I. Overview

With the continuous improvement of high-speed, high-precision, high-reliability, high-rigidity, low-noise performance of CNC machine tools, people have more and strict requirements on various performance indexes of their key functional components, the ball screw pair, among which the balls The friction torque of the lead screw pair is one of the important performance indicators. The smoothness and smoothness of the ball screw pair are the direct manifestation of the friction characteristics of the ball screw pair. Whether the ball screw pair operation is stable depends mainly on the variation of the pre-tightening torque of the ball screw pair, and the smoothness of the ball chain movement in the ball screw pair is different at different rotation speeds. The smoothness of the ball screw pair not only affects the positioning accuracy of the machine tool, but also directly affects the transmission efficiency, noise, temperature rise, stiffness, and service life of the ball screw pair. Therefore, the characteristics of the frictional torque of the ball screw are studied in depth, and the cause of the friction torque fluctuation of the screw is found. It is of practical significance to improve the quality of the ball screw by-product and meet the development of high-end CNC machine tools in China.

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Second, the factors affecting the frictional torque of the ball screw

1. Mechanism of frictional torque generated by ball screw

The ball screw pair is composed of a screw, a nut, an inverter and a ball. It converts the rotary motion into a linear motion or converts the torque into an axial reciprocating force with high precision, high rigidity and high. Life, high reliability, high efficiency and so on. The ball screw pair uses the ball as the power transmission medium between the screw and the nut, and the ball rolls to make the lead screw and the nut move relative to each other, but the ball in the screw nut performs a large part in addition to the rolling motion. In the sliding motion, in addition to the micro-slip occurring in the contact portion of the ball screw, macroscopic sliding caused by external forcing conditions mainly occurs. Balls running between the screw and nut threads perform a completely indefinite movement like a tennis ball in a rain gutter. The mutual squeezing and pushing between the balls causes the balls to slide from time to time, without the ball cage. The friction between the balls is considerable due to the extremely high radial pressure.

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Third, the ball screw pair friction torque measurement method

(1) Starting the friction torque In order to start the rotation of the ball screw pair, a large torque is required, which is called the starting friction torque. It is equivalent to 2 to 2.5 times the dynamic friction torque. Once the ball screw pair is operated, the torque is rapidly reduced.

Dynamic friction torque When the ball screw is moved, the dynamic friction torque caused by the preloading load and the friction torque generated by the ball circulation will be generated. The dynamic friction torque can also be based on the pre-tightening force required by the user. Under the condition that the actual contact angle β is equal to 45o, the theoretical friction torque value is obtained according to the calculation formula.

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Fourth, the conclusion

Due to the rapid development of mechatronics technology, users have higher and higher requirements for the performance of ball screw. Therefore, as a specialized enterprise, we make full use of our own advantages, and actively use the advanced equipment of the rolling function component performance laboratory to conduct multi-variety and high-volume product testing. Based on the test results, we carry out basic theoretical research and explore the comprehensive performance improvement of rolling functional components. Methodology, establish and improve the theoretical system of new product development and product quality improvement. Develop core technologies with independent intellectual property rights, and explore efficient, precise, practical and reliable manufacturing methods, equipment technology and testing methods for rolling functional components. As always, we will continue to carry out trials, improvements, retests and re-improvements of ball screw by-products, strive to improve the comprehensive performance of products, shorten the gap with advanced foreign products, and contribute to the development of rolling functional components in China.

For details, please refer to the "Mechanical Worker Cold Processing CIMT2007 Special Issue" or download the PDF file.

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