Manufacturing industry has been attempting to attain the required cutting performance in order to achieve high precision, fast productivity and lower maintenance costs. Vibrations generated during machining can be a serious problem degrading component quality, precision, tool service life, lathe performance and cutting rates. This paper is concerned with analysis of cutting process by using modal testing. Static and dynamic deformations of lathe collet chuck have a significant impact on cutting process stability, which affects workpiece quality and production output. Modal analysis was applied to develop a mathematical model of chucks dynamics, which consist of a number of mode shapes each with natural frequency and modal damping. Modal analysis and experimental measurements were performed on a collet chuck of CNC lathe installed in metal working company UAB “Stevila”

A. Senkus

E. Jotautiene

English

Journal of Vibroengineering

  VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. SEPTEMBER 2012. VOLUME 14, ISSUE 3. ISSN 1392-8716 
1227 
847. Investigation of vibro-acoustic properties of modern 
lathe collet chuck  
 
A. Senkus
1
, E. Jotautienė
2
 
Aleksandras Stulginskis University, Universiteto 10, LT-53361, Akademija, Kaunas District, Lithuania  
E-mail: 1Andrius.Senkus@stud.asu.lt, 2Egle.Jotautiene@asu.lt  
  
(Received 6 June 2012; accepted 4 September 2012) 
 
Abstract. Manufacturing industry has been attempting to attain the required cutting performance 
in order to achieve high precision, fast productivity and lower maintenance costs. Vibrations 
generated during machining can be a serious problem degrading component quality, precision, 
tool service life, lathe performance and cutting rates. This paper is concerned with analysis of 
cutting process by using modal testing. Static and dynamic deformations of lathe collet chuck 
have a significant impact on cutting process stability, which affects workpiece quality and 
production output. Modal analysis was applied to develop a mathematical model of chucks 
dynamics, which consist of a number of mode shapes each with natural frequency and modal 
damping. Modal analysis and experimental measurements were performed on a collet chuck of 
CNC lathe installed in metal working company UAB “Stevila”. 
 
Keywords: vibrations, modal analysis, natural frequencies.  
 
Introduction  
 
Machining operations in turning and milling are used in industrial manufacturing processes 
to obtain specific characteristics of workpiece such as part geometry, surface roughness, etc. The 
processes are based on removal of small amounts of metal from the workpiece by using a cutting 
tool. The cutting tool contacts the workpiece and the uncut chip over a very small area of several 
square millimeters. Temperature and pressure within the contact zone are relatively high 
(temperature is about 1200 oC and pressure is about 3000 N/mm2), which makes tool wear 
inevitable [1]. The parts are usually manufactured in 3-axis lathes that have high cutting speeds 
and tool cooling. A variation of indicated parameters caused by vibrations during machining 
operations of the lathe can be observed. These vibrations could lead to reduced productivity, 
since reduced cutting speeds have a negative effect on the workpiece surface by leaving 
vibration marks (waves) on the surface.  
Cutting forces create movements between the cutting tool and the workpiece, which can 
affect the cutting forces between the tool and the workpiece. Vibration marks left on the surface 
can affect the cutting forces in the following tool pass. This leads to the systems cutting force 
growth if the process is not naturally stable against the vibrations due to a large width cut and 
large cutting coefficients or flexible structure. Cutting forces also depend on tool geometry and 
material, workpiece material, feed-rate and cutting speed. If the cutting process is unstable, the 
amplitude of vibrations can start increasing exponentially until a value similar to chip thickness 
is reached. Tool vibration against the workpiece is called chatter, which can cause growth of 
cutting forces and lead to machine, cutting tool or workpiece damage [2]. The chatter system 
dynamics are modeled by delayed differential equations with constant or time varying periodic 
coefficients, which depend on the type of machining operation [2, 3]. 
It is well known that vibrations in cutting have a significant impact on machined surface 
roughness, manufactured part geometry, cutting tool and machines durability. High frequency 
noise emitted during machining can also cause environmental pollution and reduced 
productivity. Thus, the machine chatter has been a major issue when investigating cutting 
processes. However, this issue is not fully understood. It is difficult to construct an accurate 
mathematical dynamic model for analyzing vibrations in the cutting process.  
 
847. INVESTIGATION OF VIBRO-ACOUSTIC PROPERTIES OF MODERN LATHE COLLET CHUCK. 
A. SENKUS, E. JOTAUTIENĖ 
 
 
 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. SEPTEMBER 2012. VOLUME 14, ISSUE 3. ISSN 1392-8716 
1228 
Vibrations are the main reason of machine chatter. This leads to destructive oscillating 
cutting forces, which generate vibration marks on the machined surface. Uneven cutting forces 
can reach values several times higher than those achieved by normal cutting process. This 
drastically shortens cutting tool and machines durability, may cause cutting tool failure and early 
lathe spindle bearing wear [4]. 
 
 
Fig. 1. Chatter in orthogonal cutting with block diagram [5] 
 
A simple cutting tool with one degree of freedom and a block diagram suggested by Eynian 
is shown in Fig. 1. It describes systems dynamics where τ is spindle lathe period and h0 is the 
intended chip thickness. The vibrations in cutting tool feed force direction y(t), called the inner 
modulation, decrease dynamic chip thickness h(t), where high vibration marks left from last pass 
y(t – τ), called outer modulation, increase dynamic chip thickness. Then [5]: 
 
)()()( 0 tytyhth −−+= τ   (1) 
 
When y(t) and y(t – τ) have a phase shift, the dynamic chip thickness will vary at vibration 
frequency and will induce a vibrating cutting force Fy(t), which could increase vibrations of the 
cutting tool. This phenomenon occurs only when the cutting depth, a, and cutting coefficient in 
cutting tool feed direction Ky are sufficiently large in comparison to tool supporting structure 
stiffness coefficient K and structural damping coefficient mKc 2/=ξ . The fluctuating energy 
of the structure is dissipated by damping [5].  
R. N. Arnold suggested that a decrease in cutting force due to cutting speed increase could 
lead to negative damping effect and can cause cutting process instability [6]. Later R. S. Hahn 
showed that this effect is not strong enough to act as the main reason for instabilities [7]. The 
regeneration of undulation was first discovered by Doi and Kato, where they have demonstrated 
that chip thickness regeneration causes uneven cutting forces [8]. 
Tlusty et al. [9] and Tobias et al. [10] suggested relationships for calculating stability limits 
while considering chip regeneration. Merrit showed the same model in a closed loop system 
[11].  
Modal analysis can be utilized for solving vibrations problems of machining operations. Here 
the mechanical system can be modeled as a set of vibration modes. Applying this analysis, 
 
847. INVESTIGATION OF VIBRO-ACOUSTIC PROPERTIES OF MODERN LATHE COLLET CHUCK. 
A. SENKUS, E. JOTAUTIENĖ 
 
 
 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. SEPTEMBER 2012. VOLUME 14, ISSUE 3. ISSN 1392-8716 
1229 
vibrations during the cutting process can be investigated. Experimental modal analysis has 
rapidly developed in the last decades. A finite element model (FEM) is also commonly applied 
to investigate the instability of machining process [4, 12, 13].  
The aim of the present investigation is to estimate the effect of the CNC lathe collet chuck on 
vibration amplitude and frequency characteristics. 
 
Methodology and research results 
 
Analytical modal analysis is based on defining the modal parameters from FEM. 
Experimental modal analysis was performed to determine selected modal parameters of 
components or the entire structure. 
In performing analytical modal analysis, a 3-D geometric model of lathe collet chuck was 
developed using AUTODESK Inventor software. This model provides a procedure in extracting 
the natural frequency response values. Observation of vibration modes of collet chuck in space 
provides a better capability to analyze the vibration model. The elements used in the FEM model 
meshing are quadratic tetrahedral elements. The boundary conditions of the supports to the base 
connection of the component and of all the other connecting surfaces are implemented in the 
final modal analysis and the natural frequencies of the structure are obtained. The calculated 
natural frequencies by the modal analysis of FEM are presented in Table 1. 
In classical modal analysis, the frequencies or impulse response functions are evaluated by 
measuring input forces and output responses of the structure. Commonly, this analysis is 
performed in frequency domain using a spectrum analyzer. The analyzer converts the analogue 
time domain signal into digital frequency domain from which the required parameters are 
computed digitally. 
In order to measure vibrations of the lathe components, PULSE software developed by 
Brüel&Kjær was used together with PULSE data acquisition module 3580, impact hammer 8206 
for creating known or controlled excitation and type 4370 piezoelectric charge accelerometers. 
Experimental modal analysis was performed in metal working company UAB “Stevila”. The 
collet chuck of CNC turning lathe CT 200 was used in this investigation (Fig. 2a). 
 
 
a) 
 
b) 
Fig. 2. a) CNC turning lathe CT 200 with measuring equipment: 1 – data acquisition module B&K Type 
3580; 2 – CNC turning lathe CT 200; 3 – PC with B&K PULSE software; 4 – collet chuck;                         
5 – accelerometer; b) 1 – location of accelerometer; 2 – direction of impact 
 
Natural frequencies and mode shapes were measured for static conditions using 
accelerometers and an impact hammer. The excited frequencies were recorded for static 
condition with no load. During the machining process, it is not easy to measure vibration 
 
847. INVESTIGATION OF VIBRO-ACOUSTIC PROPERTIES OF MODERN LATHE COLLET CHUCK. 
A. SENKUS, E. JOTAUTIENĖ 
 
 
 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. SEPTEMBER 2012. VOLUME 14, ISSUE 3. ISSN 1392-8716 
1230 
response and it is even more difficult to measure the dynamic cutting force. The force 
measurement was obtained by using the impulse response generated by the impact hammer and 
the impact force measured by the sensor located at the hammer tip. The accelerometer and 
impact force locations are shown in Fig. 2b.  
Time history of impulse force is illustrated in Fig. 3a. The acceleration time response of the 
lathe collet chuck to impact force input is given in Fig. 3b. It can be observed from Fig. 3b that 
the maximum value of acceleration is 324.84 m/s2. 
 
  
(a) (b) 
Fig. 3. Time history: (a) - excitation, (b) - response 
 
The auto spectrum of the excitation force is given in Fig. 4a and of the acceleration response 
in Fig. 4b. Normalizing the acceleration response to the excitation force, the frequency response 
function shown in Fig. 5 was obtained. Having the frequency response function, the modes, 
modal frequencies and modal damping of the collet chuck of CNC turning lathe can be obtained. 
 
  
(a) (b) 
Fig. 4. Auto spectrum: (a) – excitation, (b) – response 
 
Table 1 lists natural frequencies obtained from FEM modal analysis and experimental tests. 
The maximum relative error between the analytical and experimental results is in the range of 
0.001-4.981 %. These differences are relatively small and thus the analytical procedure used in 
this study should be adequate in determining the natural frequencies of the lathe collet chuck. 
 
847. INVESTIGATION OF VIBRO-ACOUSTIC PROPERTIES OF MODERN LATHE COLLET CHUCK. 
A. SENKUS, E. JOTAUTIENĖ 
 
 
 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. SEPTEMBER 2012. VOLUME 14, ISSUE 3. ISSN 1392-8716 
1231 
 
Fig. 5. Frequency response function (FFT) 
 
Table 1. Natural frequencies determined from measurements and simulations 
Mode Experimental, Hz Analytical, Hz Difference, % 
1 105.0 105.1 0.001 
2 166.0 163.0 1.807 
3 206.0 214.0 3.883 
4 256.3 246.0 4.003 
5 318.8 334.7 4.981 
6 696.3 704.7 1.208 
7 783.8 786.3 0.320 
8 833.8 845.6 1.415 
9 1101.0 1103.0 0.182 
10 1318.0 1327.0 0.683 
11 1530.0 1512.0 1.176 
12 1980.0 2005.0 1.263 
13 2632.0 2653.0 0.030 
14 3344.0 3345.0 0.030 
15 3660.0 3519.0 3.852 
 
Conclusions  
 
A modal analysis method was adopted in the reported research work in order to analyze the 
cutting process of the CNC turning lathe CT 200. Modal analysis of lathe collet chuck was 
performed by means of finite elements method. The calculated natural frequencies could provide 
useful information in selecting the operating parameter values to avoid chatter in the cutting 
process that will extend service life of the cutting tools, the lathe and at the same time increase 
work productivity. The validity of theoretical predictions was conformed by comparisons with 
the results of experimental studies. The dependence of natural frequencies of mechanical links 
on geometric parameters and material properties has been demonstrated. The analysis presented 
can be used to optimize vibro-acoustic characteristics of lathe components with respect to the 
excitation forces. 
 
 
847. INVESTIGATION OF VIBRO-ACOUSTIC PROPERTIES OF MODERN LATHE COLLET CHUCK. 
A. SENKUS, E. JOTAUTIENĖ 
 
 
 VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. SEPTEMBER 2012. VOLUME 14, ISSUE 3. ISSN 1392-8716 
1232 
References 
 
[1] Rmili W., Ouahabi A., Serra R., Kiuos M. Tool wear monitoring in turning processes using 
vibratory analysis. International Journal of Acoustics and Vibrations, Vol. 14, 2009, p. 4 – 11. 
[2] Maia N. M. M., Silva J. M. M. E. Theoretical and Experimental Modal Analysis. New York: John 
Wiley & Sons, 1997, 299 p. 
[3] Petkevičius K., Volkovas V. Monitoring and identification of structural damages. Mechanika, 
Kaunas: Technologija, No. 17(3), 2011, p. 246 – 250. 
[4] Patwari A. U., Faris W. F., Nurul Amin A. K. M., Loh S. K. Dynamic modal analysis of vertical 
machining centre components. Advances in Acoustics and Vibration, Vol. 2009, 2009, p. 125 – 136. 
[5] Eynian M. Chatter Stability of Turning and Milling with Process Damping. Summary of the Doctoral 
Dissertation, University of British Columbia, Vancouver, 2010, 39 p.  
[6] Arnold R. N. The mechanism of tool vibration in the cutting of steel. Proceedings of Institution of 
Mechanical Engineers, Vol. 54, 1946, p. 261 – 284. 
[7] Hahn R. S. Metal cutting chatter and its elimination. Transactions of ASME, Journal of Engineering 
for Industry, Vol. 75, 1946, p. 1073 – 1080. 
[8] Doi S., Kato S. Chatter vibration of lathe tools. Transactions of ASME, 1956, p. 284 – 296. 
[9] Tlusty J., Polacek M. The stability of machine tool against self-excited vibrations in machining. 
International Research in Production Engineering, ASME, 1963, p. 465 – 474. 
[10] Tobias S. A., Fishwick W. Theory of regenerative machine tool chatter. The Engineer, Vol. 205, 
1958, p. 199 – 203. 
[11] Merritt H. E. Theory of self-excited machine-tool chatter. ASME Journal of Engineering for 
Industry, 1965, 87 p. 
[12] Rao S. S. The Finite Element Method in Engineering. NYC: Elsevier Inc., 2005, 663 p. 
[13] Cook R. D., Malkus D. S., Plesha M. E., Witt R. J. Concepts and Applicatons of Finite Element 
Analysis. NYC: John Wiley & Sons Inc., 2002, 719 p.  


Investigation of vibro-acoustic properties of modern lathe collet chuck

https://www.jvejournals.com/article/10678/pdf

Investigation of vibro-acoustic properties of modern lathe collet chuck

Abstract

Similar works

Full text

Available Versions

Journal of Vibroengineering