Improved Methods for the Prediction of Chatter in Turning, Part 1: Determination of Structural Response Parameters

Abstract

The dynamics of the structure of a lathe at the cutting point are directly identified under normal machining operation using an improved version of a method originally proposed by Opitz and Weck. The improved method is based on the interrupted cutting of a specially designed, surface-modulated workpiece that provides a strong, broadband excitation. This interrupted cutting has been theoretically shown to permit the identification of the structure’s dynamics from input-output measurements, despite the intrinsic coupling of the structure with the cutting process during machining. All three components of the cutting force and the tool’s acceleration are measured simultaneously. It was found that the input force components were correlated, so that measurements from two distinct cutting configurations had to be used to obtain the elements of the structure’s transfer matrix. The modal parameters measured during the interrupted cutting tests were compared to the results of commonly used impact tests, which can only be applied when there is no cutting. This study showed that the damping of the machine tool’s structure increases during cutting by 20 to 40 percent of that measured by impact testing.

A semi-analytical model of non-linear vibrations in orthogonal cutting and experimental validation

“…The value of the damping coefficient K Ã Z 2:01 10 5 N m K2 s was estimated by extrapolating the value given by Wu for steel. An acceptable agreement between the model and the experimental results, see Fig. 14, was obtained by considering an increasing of the damping ratio xZ 0:0769 as it was been indicated in [34,35]. However, it is clear that further research have to be conducted in order to obtain a more acceptable model for ploughing mechanism when the internal damping of the structure is weak.…”

“…Many authors have indicated that the process damping, due to the ploughing mechanism, can induce a significant increase of the internal damping of the structure, Minis et al [34] and Shawky and Elbestawi [35]. For the experimental setup presented in Section 1, the internal damping of the structure is weak (ðxZ c=ð2 ffiffiffiffiffiffi km p ÞZ 0:00513Þ).…”

Modelling and experimental investigation of spindle and cutter dynamics for a high-precision machining center

“…In this paper, the machining process is considered from the perspective of complex interrelated dynamics of the machine tool mechanical structure and workpiece-cutting interactions. This approach was initially proposed by Merritt [14], Kegg [15], Minis et al [16][17][18] and Tlusty and Moriwaki [19], and was extended by Bordatchev and Orban [20] to deal with the dynamics of the machine tool spindle only. The concepts are expanded upon in this paper to include the dynamics of the cutting tool and thus create a more complete dynamic model of this important machine tool subsystem.…”

A method to identify the main mode of machine tool under operating conditions

“…The reason for this problem is that the cutting force which excites the machine tool is periodic and if it can fulfill the assumption of white noise excitation, this problem will not exist. To solve this problem, based on the research by Minis [8], we [9] presented a random cutting technique to produce white noise excitation by interrupted cutting of a specially designed workpiece, of which the surface is modulated with pseudorandomly distributed teeth and channels. With this random exciting technique, we propose a complete methodology for applying OMA in the case of heavy machine tool to estimate the dynamic modal parameters of the whole structure during machining.…”