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Evaluating the Tool Point Dynamic Repeatability for High-Speed Machining Applications

Published

Author(s)

Kate Medicus, Tony L. Schmitz

Abstract

Recent technological advances in machine tool design and construction (most notably reliable high speed/power spindles and high velocity/acceleration drives), as well as cutting tool materials, have led to the increased popularity of high-speed machining (HSM). In HSM, the well-known lobing behavior of system stability is utilized to select cutting conditions for increased material removal rate. Specifically, stability lobe diagrams, which give a graphical increased material removal rate. Specifically, stability lobe diagrams, which give a graphical representation of stable/unstable cutting regions, are used to select optimal combinations of spindle speed (i.e., tooth passing frequencies that are a substantial integer fraction of the natural frequency associated with the most flexible system mode) and chip width. The determination of these diagrams, however, requires knowledge of the tool point frequency response function (FRF) and the specific cutting energy coefficients for the selected machining operation. Therefore, one important consideration for the successful shop floor implementation of HSM and the corresponding use of stability lobes is the dynamic repeatability of the tool point response. Variations in the tool point FRF between combinations of machines, holders, and tools (under ideally the same conditions) lead directly to deviations in stable cutting parameters and affect the reliability of the predicted stability lobe diagrams. In this work, we have investigated the dynamic repeatability of two separate tool clamping arrangements: a collet holder and the unique Schunk Tribos1 tool holding system. The Tribos holder offers clamping forces similar to typical shrink fit holders without the application of high temperatures during tool changes. Instead, the tool is inserted into the holder during elastic deformation of the holder body. The solid body is cylindrical with a nearly triangular hole in the unstressed state. For tool insertion, high radial forces are applied along the vertices of the triangle, producing a circular hole. When the external pressure is released, the tool is clamped along three contact lines. In both cases, an evaluation of the tool point dynamic repeatability was carried out under three conditions of increasing mechanical complexity. First, the baseline repeatability in the measurement procedure, impact testing using an instrumented hammer and accelerometer, was established. Second, the repeatability associated with tool changes (i.e., the tool/holder assembly was removed from the spindle and replaced) was determined. Third, the tool was removed from the holder, replaced, and the new repeatability evaluated. System variables that have been explored include collet torque and its influence on the tool point dynamic stiffness, as well as tool overhang length.
Proceedings Title
Proceedings of the 16th Annual Meeting of the American Society for Precision Engineering
Conference Dates
November 11-15, 2001
Conference Location
Arlington, VA
Conference Title
16th Annual Meeting of the American Society for Precision Engineering

Keywords

dynamic repeatability, high-speed machining

Citation

Medicus, K. and Schmitz, T. (2001), Evaluating the Tool Point Dynamic Repeatability for High-Speed Machining Applications, Proceedings of the 16th Annual Meeting of the American Society for Precision Engineering, Arlington, VA (Accessed April 13, 2024)
Created November 1, 2001, Updated February 19, 2017