ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
Factors Influencing Cutting Forces in Turning
and Development of Software to Estimate
Cutting Forces in Turning
Dr R. R. Malagi, Rajesh. B. C
required to perform a machining operation. The feed motion
is defined as a motion that may be provided to the tool or
work piece by the machine tool which when added to the
primary motion, leads to repeated or continuous chip
removal and the creation of the machined surface with the
desired geometric characteristics. The cutting characteristics
of most turning applications are similar. For a given surface
only one cutting tool is used. This tool must overhang its
holder to some extent to enable the holder to clear the
rotating work piece. Once the cutting starts the tool and the
work piece are usually in contact until the surface is
completely generated. During this time, the cutting speed
and cut dimensions will be constant when a cylindrical
surface is being turned. In the case of facing operations, the
cutting speed is proportional to the work piece diameter, the
speed decreasing as the centre of the piece is approached.
Sometimes, a spindle speed changing mechanism is provided
to increase the rotating speed of the work piece as the tool
moves to the centre of the part. In general turning is
characterized by steady conditions of metal cutting. Except
at the beginning and the end of the cut the forces on the
cutting tool and tool tip temperature are essentially constant.
For the special case of facing, the varying cutting speed will
affect the tool tip temperature. Higher temperatures will be
encountered for larger diameter of the work piece. However
the cutting speed has only a small effect on cutting forces, the
forces acting on a facing tool may be expected to remain
almost constant during the cutting operation.
Abstract— Cutting is a process of extensive stresses and
plastic deformations. The high compressive and frictional
contact stresses on the tool face result in a substantial cutting
force F. Cutting forces are the background for the evaluation of
the necessary power in machining (choice of the electric motor).
They are also used for dimensioning of machine tool
components and the tool body. They influence the deformation
of the work piece machined, its dimensional accuracy, chip
formation and machining system stability. The direct approach
to study cutting forces in machining is very expensive and time
consuming, especially when a wide range of parameters is
included: tool geometry, materials, cutting conditions, etc. The
different approaches are Artificial Neural Network, Current
Sensor, Turning Dynamometer, Finite Element Method,
Mathematical Simulations and Softwares. Here an attempt is
made to give a brief review on various approaches for estimating
cutting forces and the effect of cutting parameters on cutting
forces in turning.
Index Terms— Cutting Forces, Cutting Parameters,
Dynamometer, Turning.
I. AN OVERVIEW OF THE TURNING
OPERATION
Turning is a metal cutting process used for generation of
cylindrical surfaces. Typically, the work piece is rotated on
the spindle and the tool is fed into it radically, axially or both
the ways simultaneously to give required surface. The term
turning, in general sense refers to generation of any
cylindrical surface with a single-point tool. More specifically
it is often applied just to the generation of external cylindrical
surfaces oriented primarily parallel to the work piece axis.
The generation of surfaces oriented primarily perpendicular
to the work piece axis is called facing. In turning the
direction of the feeding motion is predominantly axial with
respect to the machine spindle. In facing a radial feed is
dominant. Tapered contoured surfaces require both modes of
tool feed at the same time, often referred to as profiling . The
principle used in all machine tools is one of generating the
surface required by providing a suitable relative motion
between the work piece and the cutting tool. The primary
motion is the main motion provided by a machine tool to
cause a relative motion between the tool and the work piece
so that face of the tool approaches the work piece material.
Usually the primary motion absorbs most of the total power
II. CUTTING FORCES IN TURNING
The knowledge of cutting forces developing in the various
machining processes under given cutting factors is of great
importance, being a dominating criterion of material
machinability, to both: the designer-manufacturer of
machine tools, as well as to user. Furthermore, their
prediction helps in the analysis of optimisation problems in
machining economics, in adaptive control applications, in
the formulation of simulation models used in cutting
databases. In this regard, cutting forces being a substantial
dependent variable of the machining system has been
investigated by many researchers in various cutting processes
through formulation of appropriate models for their
estimation. These models are analytical, semi-empirical and
empirical relationships, which connect cutting factors to
37
ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
forces. The analytical models are based upon the theory of used to calculate the power P required to perform the machining
mechanics of cutting, orthogonal or oblique but they are operation,
P = VFC
(1)
complicated and mostly, they demand a-prior knowledge of
Thrust
force
F
:
this
force
is
in
direction
of
feed
motion
in
D
response magnitudes, as shear angle and friction angle.
orthogonal cutting. The thrust force is used to calculate the power of
The semi-empirical expressions contain constants that are
feed motion. In three-dimensional oblique cutting, one more force
experimentally predicted and they can be classified as linear, component appears along the third axis. The thrust force F is
D
power and exponential functions. The most established further resolved into two more components, one in the direction of
cutting force relationship although old is that proposed by feed motion called feed force Ff, and the other perpendicular to it
Kienzle and Victor, also known as the specific cutting and to the cutting force FC called back force Fp, which is in the
resistance model. It will be considered in the following. Over direction of the cutting tool axis. [5]
the last years, empirical models for the machinability
parameters in various machining processes have been
developed using data mining techniques, such as statistical
design of experiments (Taguchi method, response surface
methodology), computational neural networks and genetic
algorithms. All these techniques are, more or less, ‗‘black
box‘‘ approaches but possess the advantage of providing the
impact of each individual factor and factor interactions, after
an appropriate design of the experiment. Especially, for the
Taguchi and response surface methodology, a minimum
amount of experimental trials is combined to a reliable global
examination of the variables interconnection, instead of
Fig.2: Force components in three dimensional oblique cutting
one-factor-at-a–time
experimental
approach
and
[5]
interpretation. Turning operations are widely used in
workshop practice for applications carried out in
III. FACTORS INFLUENCING ESTIMATION OF
conventional machine tools, as well as in NC and CNC
CUTTING FORCES
machine tools, machining centres and related manufacturing
systems. All three cutting force components are of interest The cutting forces in metal cutting depend upon several
because apart from the tangential (main) component that factors. The influence of each factor is discussed below in
gives the cutting power and its determination is apparently brief.
necessary, the radial and in-feed components control Work material- The cutting forces vary to a great extent
dimensional and form errors in case of work piece and tool depending upon the physical and mechanical properties of
deflections and tool wear. [4] In orthogonal cutting, the total the material. Tangential force can be determined by
cutting force F is conveniently resolved into two components multiplying the chip cross-section with the specific cutting
in the horizontal and vertical direction, which can be directly
resistance offered by the work material, which is found to be
measured using a force measuring device called a
decreasing with increasing chip thickness and increases with
dynamometer. If the force and force components are plotted
at the tool point instead of at their actual points of application increase in tensile strength and hardness of the material
along the shear plane and tool face, we obtain a convenient being cut.
Cutting speed- The tangential force Pz varies with increase
and compact diagram.
in cutting speed. It will be noted that the cutting forces first
increase with increase in cutting speed and on further
increase in speed reach a maximum value and start
decreasing and become fairly stabilized at higher speed
ranges. The initial rise in cutting force up to about 70 m/min
is due to the effect of built-up edge which does not occur at
high speeds. The cutting forces at high speeds beyond 70
m/min decreases because of high temperature involved
which tend to make the material plastic.
Feed- The tangential component of cutting force is greatly
Fig.1: Total Cutting Force F and Reaction Force F` In
Orthogonal Cutting [5]
influenced by the feed rate. It has been observed that cutting
The two force components act against the tool:
force changes linearly with feed at higher speeds, but at
Cutting force FC: this force is in the direction of primary motion.
slower speeds the change is exponential.
Cutting force constitutes about 70~80 % of the total force F and is
38
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Volume 2, Issue 1, July 2012
Depth of cut- The tangential component Pz increases in the and strain gauge locations has been determined to maximize
same proportion as the depth of cut, if the ratio of depth and sensitivity and to minimize cross-sensitivity. The developed
dynamometer is connected to a data acquisition system.
feed is more than four.
Tool approach angle- The chip size is dependent upon the Cutting force signals were captured and transformed into
numerical form and processed using a data acquisition
approach angle. The tangential component Pz is more or less
system consisting of necessary hardware and software
0
0
constant within the range 90 to 55 and increases slightly for
running on MS-Windows based personal computer. The
approach angles less than 550. Axial component Pz is obtained results of machining tests performed at different
maximum for approach angle of 900 and decreases with cutting parameters showed that the dynamometer could be
decrease in approach angle. Radial component Py is used reliably to measure cutting forces. Morten
minimum for approach angle of 900 and increases with F.Villumsen, et al [6]. In their study they have used Finite
decrease in approach angle.
Element Method, A Lagrangian approach for prediction of
Side rake angle- All the three components of cutting forces cutting forces in metal cutting. The analysis which predicted
decreases as side rake angle changes from –ve value to +ve the best agreement between force output from analysis and
value ; the tangential component alone being predominant force output measured from experiments and at the same
for +ve side rake angles and other two being negligible. time, predicted a realistic chip formation was found. The
cutting force and thrust force were predicted and compared
However for higher –ve values, both Pz and Px are
with forces measured during experiments. The cutting force
considerable and thus result in vibrations. For negative side
Fx was overestimated by 104% and the thrust force Fz was
rake angle component Pz increases due to higher plastic over estimated by 60%. Y. Huang, S.Y. Liang [7] in this
deformation of chips and increased friction in the tool-chip approach they have used the effect of tool thermal property
interface. This type of variation is not so marked at higher for modelling of the cutting forces. But the proposed model
speeds as at lower speeds.
and finite element method (FEM) both predict lower thrust
Back rake angle- It controls the direction of chip flow either and tangential cutting forces and higher tool–chip interface
away from or towards the work piece depending upon temperature when the lower CBN content tool is used, but the
whether it is +ve or –ve. The vertical component Pz increases model predicts a temperature higher than that of the FEM.
slightly as the back rake angle increases from –ve value to Bandit Suksawat [8] described application of ANN for
classification chip form type and tangential cutting force
+ve value.
prediction is presented. The machining condition consisting
Flank wear- The tangential component Px as well as Pz and
of cutting speed, feed rate and cutting depth are determined
Py increase considerably with increase in flank wear.
as input parameters of BPNN input layer for classification
chip form and tangential cutting force in cast nylon turning
IV. LITERATURE REVIEW
operation with a single point high speed steel tool . From the
Metal cutting and forming have been traditionally the
results, it can conclude that ANN is effective for
most common manufacturing processes from the old ages.
classification chip form and cutting force prediction with
Machining processes have been here for a long time but
86.67% and 91.130% of accuracy, respectively. Xiaoli Li [9]
scientific researches on machining started only during 19th
in this paper proposes a new method to measure the cutting
century. Research has been done on several aspects of metal
forces in turning using inexpensive current sensors and the
cutting such as chip-formation, cutting mechanics, machined
cutting force model. First, the relationship between the
surface, tool wear-life etc. A considerable amount of
various factors, which affect the performance of the spindle
investigations has been directed towards the prediction and
and feed drive systems, and the models of the spindle and
measurement of cutting forces. That is because the cutting
feed drive systems are analysed. Then, some reliable and
forces generated during metal cutting have a direct influence
inexpensive Hall-effect current transducers are employed to
on the generation of heat, and thus tool wear, quality of
sense the current signals of the ac servomotor in a computer
machined surface and accuracy of the work piece. Due to the
numeric control (CNC) turning centre; the tangential ( Ft)
complex tool configurations/cutting conditions of metal
and axial (Fa) cutting forces in turning are estimated by
cutting operations and some unknown factors and stresses,
applying a Neuro–fuzzy technique. Finally, the normal
theoretical cutting force calculations failed to produce
cutting pressure (Kn) and effective friction coefficient (Kf)
accurate results. Therefore, experimental measurement of
are calculated through the cutting mechanical model, so the
the cutting forces became unavoidable. For this purpose,
axial cutting forces (Fr) can also be estimated based on the
many dynamometers have been developed Süleyman
model of cutting force. Experimental results demonstrate
Yaldıza*et al [1] In this study, a turning dynamometer that
that the method proposed can measure tangential, axial, and
can measure static and dynamic cutting forces by using strain
radial cutting forces with an error of less than 10%, 5% and
gauge and piezo-electric accelerometer respectively has been
25%, respectively.
designed and developed. The orientation of octagonal rings
39
ISSN: 2277-3754
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Volume 2, Issue 1, July 2012
V. DEVELOPMENT OF SOFTWARE
A. Introduction to Software Development
Software is being used on large scale basis by a number of
engineering professionals and firms for various applications.
Software helps in creating the database for manufacturing, to
increase the productivity of the designer, to improve the
quality of the design. A computer aided cutting force
estimating software has been developed for turning in this
work. The estimating software system is developed under
Fig. 3: Visual Basic 6.0 Programming Environment
Microsoft visual studio development environment.
The Visual Basic 6.0 consists of Integrated Development
B. Introduction to Visual Basic
Environment (IDE). IDE is the term commonly used in the
Visual Basic is an ideal programming language for
programming world to describe interface and environment
developing sophisticated professional applications for that we use to create our application. It is called integrated
Microsoft Windows. It makes use of Graphical User Interface because we can access virtually all the tools that we need
for creating robust and powerful applications. The Graphical from one screen called an interface.
User Interface (GUI) as the name suggests uses illustration of The Visual Basic IDE is made up of number of components
text, which enables users to interact with an application. This
 Menu bar
feature makes it easier to comprehend things in a quicker and
 Tool bar
easier way. Coding in GUI environment is quite a transition
 Project explorer
to traditional, linear programming methods where the user is
 Properties window
guided through a linear path of execution and is limited to a
 Form layout window
small set of operations. In a GUI environment, the number of
 Toolbox
options open to the user is much greater, allowing more
 Form designer
freedom to the user and developer. Features such as easier
 Object browser
compensation,
user-friendliness,
faster
application In visual basic 6.0 the IDE is in a Multiple Document
development and many other aspects such as ActiveX Interface (MDI) format. In this format, the windows
technology and internet features make Visual Basic an associated with the project will stay within a single container
interesting tool to work with. Visual Basic was developed known as the parent. Code and form-based windows will stay
from the BASIC programming language. In the 1970s within the main container form.
Microsoft started developing ROM based interpreted BASIC C. Methodology
for early microprocessor based computers. In 1982,
a) Creating Necessary Database
Microsoft QuickBasic revolutionized Basic and was
In this stage of software development the necessary
legitimized as a serious development language for MS-DOS machining data like unit power, correction coefficient for
environment. Later on Microsoft Corporation created the flank wear and correction factor for rake angle from CMTI
enhanced version of BASIC called Visual Basic for Machine Tool Design Hand book are made as tables in
Windows. Visual Basic 6.0 requires at least Microsoft Microsoft Access 2003 and stored as the database. These data
Windows 95/Windows NT 3.51,486 processor and a like unit power, correction coefficient for flank wear and
minimum of 16 MB RAM. Complete installations of the correction factor for rake angle are taken for the calculation
most powerful version of Visual Basic 6.0, the enterprise of power at the spindle in turn for the calculation of the
edition require more than 250 MB of hard disk space.
cutting force. The value of unit power is chosen depending on
the type of work material, hardness/tensile strength of work
Visual Basic 6.0 Programming Environment
Visual Basic is initiated by using Program Option → material and average chip thickness. The value of correction
Microsoft Visual Basic 6.0 → Visual Basic 6.0. Clicking the coefficient for flank wear is chosen depending on the flank
Visual Basic 6.0 icon, we can view a copyright screen wear, hardness of work material and average chip thickness.
enlisting the details of the license holder of the copy of Visual The value of correction factor for rake angle is taken
Basic 6.0. Then it opens a screen as shown in Fig.5.1 with the depending on rake angle of the tool.
interface elements such as Menu bar, Title bar, the new b) Formulas used for the calculations in the software
project dialog box. These elements permit the user to build
The formulas used in the developed application for the
different types of Visual Basic applications.
estimation of cutting force are taken from the CMTI Machine
Tool Design Hand book. Formulas used in the application
40
ISSN: 2277-3754
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International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
developed are given below with their abbreviations and the correction coefficient for flank wear and correction factor for
units.
rake angle from database. There by calculates power at the
spindle and tangential cutting force. The calculated results
Cutting speed
in m/min
are stored in a table automatically. The user interface dialog
(2)
box consists of four buttons one for calculating when we click
3
on this button it calculates power at the spindle and
Metal removal rate
in cm /min
tangential cutting force. Show table after the calculation
(3)
when we click on the show table button it displays the results
Tool approach angle( x)= 900 – Side cutting edge angle
table showing input data and calculated cutting force. Clear
(4)
button when we click on this button it will clears all the data
from the user input dialog box making the user input box
Average chip thickness (as) = s sin (x) in mm
ready to input new data. End button when we click on this
(5)
button it closes the software.
d) Displaying estimated results
Power at the spindle (N) = U Kh Kr Q in kW
The calculated results are stored in a result table
(6)
automatically. The stored results can be displayed as shown
in fig 5.3. The stored results which can be easily exported to
Tangential cutting force (Pz)= 6120N/v in KN
Microsoft office Excel sheet from Microsoft Access result
(7)
table so that we can use the results to compare with
Where:
experimental results.
D= Diameter of work piece in mm
N= Spindle speed in rpm
S= Feed per revolution
t= Depth of cut in mm
U= Unit power in kW/cm3/min selected from the
database depending on work piece material, Hardness
of work material and average chip
thickness.
Kh=Correction factor for flank wear selected from
database depending on hardness of work material, average
chip thickness, and flank wear.
Kr = Correction factor for rake angle selected from
database depending on side rake angle of cutting tool.
c) Creating user interface dialog box
First considering all the parameters of metal cutting the
user interface dialog box is developed as shown in the fig.4,
Fig. 5: Results which can be displayed as shown
VI. EXPERIMENT AND DISCUSSION
To compare the estimated cutting forces and the actual
ones, cutting tests are done on the Kirloskar Lathe having
maximum power of 3.75 Kw, using Brazed Carbide cutting
tools and a Syscon cutting force Dynamometer. Work piece
used is of mild steel material of 25mm dia. Experimentation
is carried in a dry condition. Fig 6.1 Shows the Schematic
representation of experimental set up.
Fig. 4: User interface dialog box
In User interface dialog box the user has the facility input
the necessary data required for the estimation of cutting
force. By taking the input parameters software calculates
cutting speed, material removal rate, average chip thickness.
Then by using these data it will choose the unit power,
41
ISSN: 2277-3754
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International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
increases the section of the sheared chip increases because
the metal resists the rupture more and requires larger efforts
for chip removal. Hence the cutting force increases as the
feed rate increases.
B. Effect of Depth of Cut on Cutting Force
Cutting Conditions: Spindle Speed
= 415 rpm
Feed Rate
= 0.2 mm/rev
Work Material
= Mild steel
Rake Angle of tool = -50
Fig.6: Schematic Representation of Experimental Setup
Used
A. Effect of feed rate on cutting force
Cutting Conditions: Spindle Speed
Depth of cut
Work Material
Rake Angle of tool
Table 2: Estimated and Experimental Cutting Force Values at
Different Depth of Cuts
= 415 rpm
= 0.5 mm
= Mild steel
= +50
in
mm
Table.1: Estimated and Experimental Cutting Force Values at
Different Feed Rates
Estimated
Experimental
Feed
Resultant
Resultant
Rate in
Cutting
% Error
cutting Force
mm/rev
Force in
in Newton’s
Newton’s
0.2
488.38
413.33
15.36
0.3
578.27
619.98
6.73
0.37
683.85
764.64
10.56
0.45
818.21
928.98
11.92
Experimental
Estimated
Resultant
Resultant
cutting Force
Cutting Force
in Newton’s
in Newton’s
DOC
% Error
0.50
436.05
467.39
6.71
0.75
694.69
701.10
0.91
1.00
972.57
934.81
3.88
1.25
1316.16
1168.51
11.21
Fig. 8: Cutting Forces vs. Depth of Cut
Effect of Depth of cut on cutting force:
The results obtained (Fig.8) illustrates the evolution of
cutting forces according to the depth of cut. With the increase
in Depth of cut the chip thickness becomes significant whip
causes the growth of volume deformed and that requires
enormous cutting forces to cut the chip. Hence cutting force
increases as the Depth of cut increases.
C. Effect of Cutting Speed on Cutting Force
Cutting Conditions: Feed Rate
= 0.2 mm/rev
Depth of cut
= 1 mm
Work Material
= Mild steel
Rake Angle of tool = -50
Fig. 7: Cutting Forces vs. Feed Rate
Effect of Feed rate on cutting force:
The results presented in Fig. 7 show the evolution of
cutting forces according to the feed rate. If the feed rate
42
ISSN: 2277-3754
ISO 9001:2008 Certified
International Journal of Engineering and Innovative Technology (IJEIT)
Volume 2, Issue 1, July 2012
Artificial Neural Network‖ International Conference on
Control, Automation and Systems 2010.
Table 3: Estimated and Experimental Cutting Force Values at
Different Cutting Speeds
Estimated
Experimental
Cutting
Resultant
Speed
%
Resultant
Cutting Force
in
Error
cutting Force
from software in
m/min
in Newton’s
Newton’s
20.53
866.63
934.81
31.56
852.73
934.79
8.78
47.90
997.12
934.80
6.25
76.03
1019.45
934.80
8.30
[3] G. Petropoulos1, I. Ntziantzias1, C. Anghel2, ―A predictive
model of cutting force in turning using taguchi and response
surface techniques‖ 1st International Conference on
Experiments/
Process
/
System/Modeling/Simulation/Optimization 1st IC-EpsMsO
Athens, 6-9 July, 2005.
[4] Morten F.Villumsen, Torben G Fauerholdt ―Prediction Of
Cutting Forces In Metal Cutting, Using The Finite Element
Method, A Lagrangian Approach‖ LS-DYNA An wender
forum , Bomberg 2008.
7.29
[5] Y. Huang, S.Y. Liang ―Cutting forces modeling considering
the effect of tool thermal property—application to CBN hard
turning‖ International Journal of Machine Tools &
Manufacture 43 (2003) 307–315.
[6] Bandit Suksawat ―Chip Form Classification and Main Cutting
Force Prediction of Cast Nylon in Turning Operation Using
Artificial Neural Network‖ International Conference on
Control, Automation and Systems 2010 Oct. 27-30,
[7] Xiaoli Li ―Development of Current Sensor for Cutting Force
Measurement in Turning‖ Journal of IEEE transactions on
instrumentation and measurement, vol. 54, no. 1, February
2005.
[8] Machine Tool Design Handbook‖ By CMTI, Bangalore Tata
McGraw-Hill Publishing Company ltd, New Delhi.
AUTHOR’S PROFILE
Dr. R. R. Malgi is currently working as Professor in Dept. of Mechanical
Engineering, Gogte Institute of Technology, Belgaum, and Karnataka. He has a
teaching experience of 15 years. 10 publications to his credit both at national
and international conferences and journals
Fig.9: Spindle Speed vs. Cutting force
Rajesh. B. C is currently studying M.Tech (Computer Integrated
Manufacturing) in Gogte Institute of Technology, Belgaum, and Karnataka.
Effect of Cutting speed on cutting forces: Fig 9 shows that
there is no much effect of cutting speed on cutting force. Still
increase in cutting speed generally leads to a reduction in
cutting forces. This is due to the rise in the temperature in the
cutting zone which makes the metal machined more plastic
and consequently the efforts necessary for machining
decreases.
VII. CONCLUSION
From the above results we can conclude that cutting force
increases as the feed rate and depth of cut increases. The
percentage of error is in the acceptable range hence the
developed application can be readily used for the estimation
of cutting forces and to know the effect of various cutting
parameters on cutting forces in turning.
REFERENCES
[1] Süleyman YALDIZ ―Development and Testing of a Cutting
Force Dynamometer for Milling‖ Journal of Polytechnic Vol: 8
No: 1 pp. 61-68, 2005.
[2] Bandit Suksawat ―Chip Form Classification and Main Cutting
Force Prediction of Cast Nylon in Turning Operation Using
43