INVESTIGATIONS INTO TOOL-WEAR MONITORING
IN TURNING
BY
D. NAGESWARA RAO
Department of Mechanical Engineering
THESIS SUBMITTED
IN FULFILMENT OF THE REQUIREMENTS
OF THE DEGREE OF
DOCTOR OF PHILOSOPHY
to The
INDIAN INSTITUTE OF TECHNOLOGY, DELHI
INDIA
JANUARY, 1991
to my lovely son CHERRY
CERTIFICATE
This is to certify that the thesis entitled Investigations into Tool-wear Monitoring
in Turning which is being submitted by Mr.D.Nageswara Rao to the Indian Institute of
Technology, Delhi, for the award of the degree of Doctor of Philosophy in Mechanical
Engineering, is a record of bonafide research work carried out by him. He has worked
under our guidance and supervision and has fulfilled the requirements for the
submission of this thesis, which has attained the standard required for a Ph.D. degree
of this institute. The results presented in this thesis have not been submitted elsewhere
for the award of any degree or diploma.
LjL_Lz,
(U.R.K.Rao)
Professor
Mechanical Egg. Deptt.
liT, Delhi - 110 016.
.N.Rao)
Professor
Mechanical Egg. Deptt.
!IT, Delhi -110 016.
ACKNOWLEDGEMENTS
I wish to express my sincere gratitude to Prof.U.R.K.Rao and Prof.F.N.Rao for their
guidance and encouragement throughout this work.
1 record my thanks to the authority of Andhra University, Visakhapatnam, for having
sponsored me under Q1P. I sincerely thank my colleagues for sharing my work in the
department during this period. I also gratefully thank my senior colleague, Prof.D.Ganapathi
Rao for his concern about my work
/ acknowledge the help rendered to me at different stages of the experimental work
by Sri K.N.Madhu of Vibration Lab, Sri N.C.Sharma and Sri Jaya Parkash of Machine Tool Lab,
Sri Ramchander and Sri Srichand Sharma of NC Lab, Sri M.M.Verma, Sri Ramlal, Sri Azad Pal,
Sri Shivaram and Sri Har Dutta of Prod. Engg. Lab, Sri Kalia of Machine Shop, Sri Shiv Kumar
of Welding Lab, Sri Nagar and Sri Kirpal Singh of Metrology Lab, Sri Krishna Kumar of
Cybernetics Lab and many others.
I am much indebted to Mr.A.Rajendran, SSO, NC Lab, for his spontaneous help at all
times. I owe special thanks to coresearchers Mr.A.Mandal and Mr.J.K.Dutta who could spare
time for discussions.
I extend my thanks to Mr.A. Balachandran for typing this thesis and to Mr.N.D.R.Sharma
for taking the photographs presented in this thesis.
Finally, I take this opportunity to acknowledge the help and encouragement received
from many friends and well wishers which went a long way towards providing a favourable
atmosphere for work.
aNagesvvara Rao
ABSTRACT
The work in this thesis is concerned with investigations into the methods of online tool wear monitoring. The existing methods of tool wear monitoring are reviewed. The
review brings out that in-process tool-wear monitoring is attracting wide interest as The
present day manufacturing systems are tending towards greater automation.
Experiments are conducted to generate the data on cutting tool vibrations,
cutting forces, surface roughness, workplace dimensional changes and the types of chip
form. The relationships of the above parameters with the tool wear are examined. The
feasibility of using these relationships for on-line tool-wear monitoring is discussed and methodologies are proposed.
A mathematical model is formulated for predicting instantaneous tool wear
from the on-line cutting force data. The equation considers the effects of tool vibrations, MTN
compliances and workpiece dimensional changes. The predicted force values using the
model are compared with the measured values while conducting experiments on two lathes
under different cutting conditions,. The results reveal that it is feasible to use the proposed
model for on-line monitoring of tool wear. A methodology is presented to use the model for
instantaneous tool wear prediction.
The information from a single sensor may not help in predicting the tool wear
reliably. With this in view a multi-sensor approach is proposed. A methodology for the
intelligent assessment of the tool wear is presented involving the use of cutting forces, tool
vibrations, workpiece dimensional changes, surface roughness and chip formation as tool
wear indices in addition to the analytical predictions through the model developed in this
thesis.
CONTENTS
ACKNOWLEDGEMENTS
Page No.
ABSTRACT
LIST OF FIGURES
vi
LIST OF TABLES
NOMENCLATURE
xi
CHAPTER I INTRODUCTION
1.1WEAR MONITORING AND ITS IMPORTANCE
1
1.2 DIFFERENT METHODS SO FAR PROPOSED
3
1.3 PRESENT WORK
4
1.4 THESIS LAYOUT
5
CHAPTER II LITERATURE REVIEW
7
2.1 INTRODUCTION
7
2.2 DIRECT METHODS
7
2.2.1 Optical Techniques
8
2.2.2Electrical Resistance Technique
9
2.2.3Radioactive Technique
10
2.2.4Proximity Sensors
12
2.2.5Touch Trigger Probes
13
2.3 INDIRECT METHODS
15
2.3.1Cutting Temperature
15
2.3.2Cutting Forces and Torques
17
2.3.3Acoustic Emission
22
2.3.4Vibrations
29
2.3.5Surface Roughness of the Machined
Component
34
2.4 MACHINE TOOL CHATTER
35
38
2.5SUMMARY
CHAPTER III EXPERIMENTAL SET-UP AND PROCEDURE
39
3.1EXPERIMENTAL SET-UP
39
3.1.1Machine Tools
39
3.1.2Cutting Tool and Too!holder
42
3.1.2.1Cutting Tool
3.1.2.2Too'holder
3.1.3Vibration-Measurement
Instrumentation
3.1.3.1Accelerometer and Cable
3.1.3.2Charge Amplifier
3.1.3.3Instrument Tape Recorder
3.1.3.4Spectrum Analyser
3.1.3.5Data Memory System
3.1.4Instrumentation for Measuring
Cutting Forces
3.1.4.1Dynamometer
3.1.4.2Charge Amplifier
3.1.4.3Rectilinear Thermal Writing
Oscillograph
3.1.5Instrumentation for Measuring
Workpiece Diametral Charges
3.1.5.1Mercer Probe
3.1.5.2Mercer Gauge
3.1.5.3Oscillographic Recorder
3.1.6Surface Roughness Measurement
44
44
45
45
45
45
47
47
48
48
50
50
50
52
52
53
53
53
3.2THE EXPERIMENT
3.2.1Introduction
53
3.2.2Vibration Measurement
54
3.2.3Cutting Force Measurement
55
3.2.4Measurement of Changes in Workpiece
Dimensions
56
3.2.5Surface Roughness Measurement
56
3.2.6Chip Collection
57
iii
57
3.3SUMMARY
CHAPTER IV MATHEMATICAL MODEL FORMULATION
CHAPTER V
58
4.1
FORCE PREDICTION EQUATION
58
4.2
TOOL VIBRATION
62
4.2.1Vibration Equation
62
4.2.2Evaluation of Constants
64
4.3
CUTTING EDGE DEVIATION FROM WORKPIECE
DUE TO TOOL WEAR
67
4.4
MTW COMPLIANCE EQUATION
69
4.5
SYSTEM CONSTANT
72
4.6
FINAL EQUATION
74
4.7
REAL TIME APPLICATION OF THE EQUATION
77
RESULTS AND DISCUSSION
5.1
5.2
5.3
81
81
TOOL WEAR
5.1.1Tool Wear Pattern
81
5.1.2Tool Wear Progress With Machining
Time
83
83
TOOL VIBRATIONS
5.2.1Tool Vibration Spectra in the
Frequency Range of 0-5 kHz
83
5.2.2Vibration in Spectra in the
Frequency Range of 0-500 Hz
85
5.2.3Amplitudes in Narrow Frequency
Bands
90
5.2.4Comparison between Two Sets
of Spectra
94
5.2.5Summary on Tool Vibrations
94
CUTTING FORCE ANALYSIS
5.3.1Variation of Measured Cutting Force
Components with the Progress of
Tool Wear
iv
94
97
5.3.2Comparison of Calculated and Measured97
Radial Cutting Forces to Validate the
Proposed Mathematical Model.
5.3.2.1With 1 mm depth of cut
5.3.2.2With 0.3 mm depth of cut
5.3.2.3With 2 mm depth of cut
5.3.3Cutting Force Summary
101
101
105
105
5.4 SURFACE ROUGHNESS
107
5.5CHIP FORMATION
111
5.6 PROPOSED METHODOLOGY
113
5.6.1Proposed Methodology for Using
Vibration Amplitudes to Predict
Tool Wear On-line
113
5.6.2Tool Wear Data from Cutting Forces, 115
Tool Vibrations and the Workpiece
Dimensional Changes
5.6.3Inclusion of Surface Roughness and 117
Chip Formation Data.
5.6.4Processing of Data, Acquired
Simultaneously from All Sensors
and Decision Making
CHAPTER VI CONCLUSIONS
117
119
6.1 THE PRESENT WORK
119
6.2 SCOPE FOR FUTURE WORK
120
REFERENCES
122
APPENDIX I
SPECIFICATIONS OF THE INSTRUMENTS USED
128
APPENDIX II VIBRATION FREQUENCY OF THE TOOLHOLDER
134
APPENDIX III MANN-WHITNEY STATISTICAL TEST
135
CURRICULUM VITAE