ANALYSIS OF METHODS FOR MEASURING UNEVENNESS OF FEED MOVEMENT OF METAL CUTTING MACHINES

Abstract

At very low feed rates in metal-cutting machines, the feed motion often becomes irregular and unstable. This irregularity is typically characterized by a sequence of periodic stops and sudden jerks, a phenomenon known in tribology and mechanical systems as the “stick-slip” effect. This effect arises due to the alternating sticking and sliding behavior between the contacting surfaces in motion, despite the fact that the machine's drive system is designed to maintain a consistent feed rate. As a consequence, the real feed velocity fluctuates around the intended value, leading to undesirable oscillations that significantly compromise both the dimensional accuracy and the surface finish of machined parts. The stick-slip effect becomes particularly problematic in high-precision machining operations, especially those involving microfeeds, where even minute deviations in the motion path can result in substantial quality issues or functional defects in the manufactured components.

Understanding and mitigating the stick-slip effect requires a detailed examination of both physical and mechanical factors contributing to motion instability. These include friction characteristics, system stiffness, drive dynamics, and the interaction between mechanical components at the microscopic level. Moreover, evaluating the effect quantitatively is essential for engineers and researchers working on improving feed mechanisms and control systems in precision machines.

This paper aims to provide a comprehensive analysis of the origins and behavior of irregular feed motion in low-speed cutting operations. It outlines key indicators and signatures of oscillatory feed dynamics and compares two primary methods for measuring these irregularities: indirect (based on control signals and position feedback) and direct (using displacement sensors or high-resolution encoders). The discussion includes an evaluation of the accuracy and limitations of each method, offering insights into their relative error characteristics and applicability in real-world machining environments.