School of Engineering
Department of Mechanical and Manufacturing Engineering
Creating a Digital Twin of a smart
cutting tool system
Parth Mahajan
17317419
April 2019
A dissertation submitted in partial fulfilment of the degree of
BAI (Mechanical and Manufacturing Engineering)
Parth Mahajan | 17317419
Declaration
I have read and I understand the plagiarism provisions in the General Regulations of the
University Calendar for the current year, found at http://www.tcd.ie/calendar.
I have also completed the Online Tutorial on avoiding plagiarism ‘Ready Steady Write’,
located at http://tcd‐ie.libguides.com/plagiarism/ready‐steady‐write.
Signed
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Abstract
The changing trends in the machining industry and the introduction of smart manufacturing
has increased market competitiveness. The demand for New Product Development, and
providing faster services demands the need for new solutions. The concept of industry 4.0
focusses on custom mass production and flexibility in production quantity. To cater to such
needs, the concept of Cyber Physical Systems along with Smart Manufacturing gives rise to
the idea of Digital Twin.
This research focuses on the creation of a Digital Twin for a CNC machining cutting tool. In
most machining processes, sensors are used to quantify the process. If a Digital Twin is
created of the system, the sensors will inform the Digital Twin and a much clearer picture of
the process can be obtained. In order to create a Digital Twin, a methodology has been
developed in project. It involves evaluating various designs and carrying out a sensitivity
analysis.
Three designs have been modelled and tested using FEA analysis in order to evaluate the
strain that occurs on them. The designs are rather fundamental and not complicated. The
material chosen for the cutting tool is structural steel or High-Speed Steel (HSS), with an
elastic modulus of 200,000 N/mm2. The cutting tool designs have been modelled as a
cantilever beam by adding a fixed support to the end that lies inside the tool post. The strain
has been evaluated at a location which has been constant but the length of the cutting tool
has been increased from 50mm to 80mm with an increment of 10mm each. A modification
in design 3 evaluates the impact on the cutting tool when some material is removed from
the cutting tool. This has been done in order to accommodate for a strain gauge that may be
installed in that location. The design 3 further evaluates the impact of increasing length for
various cutting forces. The cutting forces that occur are due to various factors such as feed
rate, cutting speed and depth of cut. These forces can be extremely high subject to these
parameters and hence a range of 500N to 3000N with an interval of 500N has been chosen.
The testing of these designs has been done analytically which has shown positive results.
Hence, a Digital Twin has been successfully created for a smart cutting tool system.
The trends observed show that the increase in the overhanging length or the length of the
cutting tool results in an increase in strain. The deformation also tends to increase with the
increasing cutting length and hence validates with the literature which talks about the
increasing deflection with the increase in cutting tool length. The physical testing of these
results is not in the scope of this project and can be done as an individual research project
and has been left for further research.
Keywords: Digital Twin/Smart Manufacturing/Smart cutting tool/ Cutting forces/ Strain/
Cantilever Beam/ Overhanging length
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Acknowledgements
I would sincerely like to express my gratitude to Dr. Garret O’ Donnell for his constant
guidance, support and feedback.
I would also like to thank my family and friends for their valuable support and
encouragement.
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Contents
Declaration ........................................................................................................................... i
Abstract ............................................................................................................................... ii
Acknowledgements ............................................................................................................ iii
Contents ............................................................................................................................. iv
Nomenclature .................................................................................................................... vi
1. Introduction .....................................................................................................................1
1.1
Cyber Physical Systems (CPS) ...............................................................................1
1.2
Digital Twin Concept ............................................................................................2
1.3
Research Context……………………………………………………………………………………………….3
1.3.1 Research Objective……………………………………………………………………………………….3
1.3.2 Overall Approach…………………………………………………………………………………………..4
2. Literature Review……………………………………………………………………………………………………….5
2.1
CNC Machining……………………………………………..……………………………………………………5
2.1.1
2.2
2.3
2.4
Turning Process…………………………………………………………………………………………6
Cutting Tool………………………………………………………………..……………………………………..7
2.2.1
Cutting tool material…………………………………………………………..……………………7
2.2.2
Tool Wear………………………………………………………………..………………………………8
2.2.3
Impact of forces on a cutting tool………………………….……………………………..….8
Modelling of a cutting tool……………………………………..…………………………………………9
2.3.1
Linear Elastic Beam Model for Tool Deflection……………………………………….10
2.3.2
Impact of longer tool length………………………………………..…………………………10
2.3.3
Use of ANSYS in Digital Twin..…………………………………………………………………11
Analytical Concept…………………………………………………………………………………………..12
3. Methodology……………………………………………………………………………………………………………15
3.1
Design Modelling……………………………………..…………………………………………………….15
3.2
Finite Element Analysis………………………………………..…………………………………………16
3.3
Analytical Model…………………………………………………………………………………………….17
3.4
Validation…………………………………….…………………………………………………………………18
4. Design Investigations………………………………………..……………………………………………………..19
4.1
Design 1………………………………………………………………………………………………………….19
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4.2
4.3
4.1.1
Constraints and forces………………………………………………………………………….19
4.1.2
Strain measurement for various lengths……………….…………………………..…20
4.1.3
Strain Vs increasing lengths for various forces.…………………………………….21
4.1.4
Deformation Vs increasing length ad deformation vs stick out distance 22
4.1.5
Analytical Validation………………………………..…………………………………………..24
4.1.6
Discussion on Design 1…………………………………………………………………………25
Design 2…………………………………………………………………………………………………………25
4.2.1
Constraints and forces………………………………………………….………………………25
4.2.2
Strain measurement for various lengths…….…………….………………………….26
4.2.3
Strain Vs increasing length for various forces…………….…………………………27
4.2.4
Analytical Validation………………………………………………….…………………………28
4.2.5
Discussion on design 2……………………………………………….…………………………28
Design 3……………………………………………………………………………………………………….29
4.3.1
Constraints and forces…………………………….……………………………………………29
4.3.2
Strain measurement for various lengths …….……………………………………….30
4.3.3
Strain Vs increasing lengths for various forces..……………………………………31
4.3.4
Deformation for various Cut out distances……….………………………………….32
4.3.5
Analytical Validation………………………………………….…………………………………32
4.3.6
Discussion on Design 3……………………………………….………………………………..33
5. Conclusion……………………………………………………………………………………………………………….34
References……………………………………………………………………………………………………………………36
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Nomenclature
CPS
Cyber Physical Systems
DT
Digital Twin
CNC
Computer Numeric Control
CNCMT
Computer Numeric Control Machine Tool
MES
Manufacturing Execution Systems
ERP
Enterprise Resource Planning
PLM
Product Lifecycle Management
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1 Introduction
Human needs are constantly changing with the technological advances as they develop
faster and faster. As they are entering the fourth industrial revolution, it is supported by the
concept of “Industry 4.0”. Figure 1.1 below shows the benefits of each revolution. The first
industrial revolution improved the quality of life, the second allowed mass production and
the third, flexible production. The manufacturing area needed to pass through these other
revolutions before finding a way to adapt its processes to human lives today. That is why
the fourth revolution is now getting the possibility of “flexible mass custom production and
flexibility in production quantity”. [1]
Figure 1.1 Progression of the Industrial Revolution over the past 2 centuries [1]
The fourth industrial revolution makes interaction with the virtual and the physical world
easier through the introduction of the Cyber Physical Systems (CPS).
1.1 Cyber Physical Systems
Cyber physical systems are systems that are integrations of computation, networking and
physical processes. Basically, embedded computers and networks monitor physical process
with feedback loops where physical processes affect computations. For example, highly
calibrated sensors in an area in a city could record the CO2 levels in the air, should that level
rise above a certain point, an alert will be sent, and an effort can be made to neutralize the
surplus CO2. This type of technology has economic and societal potential that is far greater
than originally thought while it was first being researched [2].
With the introduction of CPS, comes in the concept of smart manufacturing which makes
complex designs and real-time data sensing possible. This concept leads to time saving and
cost reduction, providing a method to interact within the virtual and physical world. Smart
manufacturing is an interdisciplinary technology integrating sensing and analysis of
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production information, representation of experience and knowledge as well as intelligent
decision-making based on these information, data, experience and knowledge [3,4].
The industrial processes need to extract the maximum potential from the simulations
performed [5], one of the most important being the accuracy of the simulation results. In
the manufacturing scenarios, the simulation of the machining processes provides
measurable benefits for the manufacturing industries, as a lot of resources and energy can
be saved and the workers safety can be increased if the machining processes are optimised.
In recent years, with the requirement of smart manufacturing mode, developed from the
CPS concept, the appearance of Digital Twin (DT) [6,7] technology provides an effective
resolution to integrate the physical world and the information world.
1.2 Digital Twin Concept
Digital twin is a combined ‘’multi-physics, multi-scale and probabilistic simulation
technique’’ which enables the mirroring of its physical twin. It adopts the best applicable
physical models, sensor updates etc. to achieve this [8]. The concept of the digital twin was
primarily introduced by John Vickers and Dr Michael Grieves in 2014 [9]. Since the
establishment of Digital twin, many experts have tried to introduce an explicit definition for
the term [10].
From Figure 1.2 below which shows a table, digital twin reflects two-way dynamic mapping
of physical objects and virtual models [11]. By building digital twin system that integrates
the manufacturing process, the innovation and efficiency from product design, production
planning to manufacturing implementation, can be effectively enhanced [12].
Figure 1.2 The understandings for Digital Twin from 8 famous companies
DT is a complete virtual prototype of an entire system, which can real-time reflect the all life
cycle of physical device or product. With DT, requirements of multiple engineering
disciplines are integrated and system level simulation and self-decision can be done based
on its real-time mapping data in the entire lifecycle. Computer Numeric Control Machine
Tool (CNCMT), which is the mother machine of industry [13] is an important equipment in
smart manufacturing.
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In order to better explain the concept of DT, figure 1.3 shows an example of how it can be
implemented in a manufacturing environment where Computer Numeric Control (CNC)
machines have been installed. For a DT driven product manufacturing example, figure 1.3
shows how a drive shaft which is a mechanical component for transmitting torque and
rotation, commonly applied in speed reducer can be manufactured using the integration of
real time data storage of the physical instrumentation and the virtual data that is preinstalled into the supply chain.
Figure 1.3 Drive Shaft Manufacturing based on Digital Twin [14]
The digital twin refers to the physical production factors (i.e., steel bars, CNC machine,
finished/semi-finished drive shaft, machine operator, shop floor environment), their
corresponding models (i.e., virtual production factors), and the digital twin data. Digital twin
data includes the physical data collected from sensors or numerical control systems installed
in the physical machining shop floor, the virtual data read from the virtual models as well as
the existing information systems (i.e. MES, ERP, PLM), and the data ties the two parts
together. [14]
1.3 Research context
In high end manufacturing processes such as machining of biomedical implants or
aeroengine components sensor systems can quantify the process. However, in many cases
the sensors can only quantify part of the process details. If a Digital Twin is created of the
system, the sensor data can inform the Digital Twin and then a more complete picture of the
process can be developed. This project will involve the FEA of tooling systems in order to
develop a digital twin of a smart cutting tool system.
1.3.1 Research Objective
The aim of this research is to create a Digital Twin of a smart cutting tool system.
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The specific objectives include:
•
•
•
Preparing a summary state of the art and literature review
Developing a methodology for designing the digital twin
Evaluating a number of digital twin designs and carrying out a sensitivity analysis
1.3.2 Overall approach
The project is based on the physical factors, that is the CNC machine data and the DT data
that is required for the cutting tool of a CNC machine. A basic cutting tool model of a 2-axis
CNC machine will be considered for the project, which can be replicated on ANSYS 18.0 so as
to evaluate the strain for different lengths that is experienced by the cutting tool due to the
cutting forces. The directional movement of the cutting tool with respect to the workpiece
can be seen in figure 1.4. The project focuses on the strain developed at a particular location
so as to make it feasible for the setup of sensors. The strain values have been observed for
increasing lengths of the cutting tool using a strain probe in ANSYS model.
(a) Component held by a chuck for the machine to attain zero point and (b) position of the
cutting tool with respect to the workpiece
Figure 1.4 Depiction of cutting tool directional movement with respect to the workpiece
The strain and deflection because of the increasing lengths for the cutting forces on the
cutting tool can be sensed by the strain gauges and dynamometers which will be connected
to the cutting tool for physical testing. But the application of strain gauge sensors and
physical validation of the simulation results have not been done as part of this project. The
validation is not in the scope of this project and can be carried out as future research using
the results and observations from this project.
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2 Literature Review
With the changing landscape of technologies in this era of Industry 4.0, Simulation and
Digital Twin have become an asset, adding value to the process of New Product
Development. It not only speeds up the process, but even saves money that is spent on
gathering resources such as raw materials, performing machine setups etc. Ease in
innovation, acceleration in time for the product to reach the market, and product
maintenance evaluation are a few opportunities that this simulation driven approach offers.
These factors play an important role in the industrial environment and the creation of a
Digital Twin helps in assessing all the parameters through simulation.
2.1 CNC Machining
Computer Numerical Control or CNC refers to a method of removing material, or “shaping”,
a workpiece by using a set of coded commands to control the actions of a machine. CNC can
be used on a fixed or rotating workpiece where the drill bit moves in multiple dimensions
depending on the machine in use. [15] Features of a CNC machine includes:
•
•
•
•
•
The functions of the machine tool which are partly or fully taken over by a dedicated
computer (i.e. fully automated/computer controlled)
A micro or minicomputer, which is assigned to the machine tool. The movements of the
machine components, that are programmed and controlled by a set of coded
instructions in the form of numbers or letters
The program, that may be prepared by a programmer or obtained from drafting
software (e.g. AutoCAD)
The code can be modified and displayed on the machine, along with a simulated view of
the outcome
The availability of small computers with large memory capacities and program editing
capabilities that have popularised the use of CNC systems widely.
Figure 2.1 below shows the 2-axis CNC machine with the marked constituents of the
machine. The workpiece is held by the manual chuck and the cutting tool by a tool post.
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There are 2 different coordinate systems that are used by the tool for travelling in different
directions. The absolute system and the incremental system.
Absolute system: This system is consistently referenced to a fixed point in the drawing. This
point has the function of a co-ordinate zero point. It is defined in x and z. [15]
Incremental system: In this system, every measurement is considered from the previously
dimensioned position. It uses incremental dimensions that refer to the distance between
adjacent points. It is defined by u and w.
The Numeric Control (NC) code are written in a language called the G-code and M-code
using these coordinate systems. A CNC machine can carry out various machining processes
using a set of various cutting tools as per the required job, but the most common and widely
used is the turning process.
2.1.1 Turning Process
During the Turning process, a single point cutting tool is used to remove the material from
the rotating workpiece as can be seen in figure 2.2. The cutting tool is fed parallel to the axis
of rotation of the workpiece.
Figure 2.2 Turning process of material removal [16]
The feed rate or the speed at which the tool is fed into the workpiece varies as per the
material of the workpiece and the cutting tool itself. Two of the most commonly used
cutting tool used in turning can be seen in figure 2.3 below. One of them could be used for
the outer turning process and another for the process of boring or for internal turning of the
workpiece.
Figure 2.3 Turning process cutting tools
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2.2 Cutting Tool
A cutting tool is a sharp pointed tool that is used for the material removal process in CNC
machining. It can either have one edge or tip that could be used for cutting or various edges
that could be used for the process of removing material from the rotating workpiece.
Although all cutting tools serve one purpose, to cut through a material, there is a huge
difference between them. [17]
Normally, for a cutting tool to be effective, it has to:
•
•
•
•
•
•
be 30% to 50% harder than the material it will work on
be easily fabricated
have high thermal conductivity
have low coefficient of friction
be very resistance to wear
be chemically inert and stable
The cutting tool material plays a crucial role in determining the input parameters of speed at
which the workpiece rotates, feed rate, depth of cut etc. Figure 2.4 shows the anatomy of a
cutting tool.
Figure 2.4 Anatomy of a cutting tool [18]
2.2.1 Cutting Tool Material
•
•
•
•
•
High Speed Steel or Structural Steel: High Speed Steel is the most economical material to
use that can be manufactured into any type of tool needed. High Speed Steel works well
on all materials and can be coated to provide even better performance.
Cemented carbide: The most common material used in the industry today. It is offered in
several “grades” containing different proportions of tungsten carbide and binder (usually
cobalt). High resistance to abrasion.
Cermet: Another cemented material, based on titanium carbide (TiC). Binder is usually
nickel. It provides higher abrasion resistance compared to tungsten carbide at the
expense of some toughness. Extremely high resistance to abrasion.
Ceramics: Chemically inert and extremely resistant to heat, ceramics are usually
desirable in high speed applications, the only drawback being their high fragility. The
most common ceramic materials are based on alumina (aluminum oxide), silicon nitride
and silicon carbide.
Cubic boron nitrides (CBN): The second hardest substance. It offers extremely high
resistance to abrasion at the expense of much toughness. It is generally used in a
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•
machining process called "hard machining", which involves running the tool or the part
fast enough to melt it before it touches the edge, softening it considerably.
Polycrystalline diamonds: The hardest substance. Superior resistance to abrasion but
also high chemical affinity to iron which results in being unsuitable for steel machining. It
is used where abrasive materials would wear anything else. [18]
These materials have been created for usage with different kinds of workpiece materials as
per requirement. Of all these materials, HSS or structural steel is very easily accessible and is
a cheaper alternative with variations in respect to coating on the material.
2.2.2 Tool Wear
Tool wear is generally a gradual process due to regular operation. Tool wear can be
compared with the wear of the tip of an ordinary pencil. According to Australian standard,
the tool wear can be defined as the change of shape of the tool from its original shape,
during cutting, resulting from the gradual loss of tool material. [19]
Tool wear depends upon following parameters:
•
•
•
•
•
•
•
Tool and work piece material
Tool shape
Cutting Speed
Feed
Depth of cut
Cutting fluid used
Machine Tool characteristics etc.
The cutting tool parameters lead to the reason of why a Digital Twin is created. Through a
digital twin, the life of the cutting tool can be assessed, in the case of a New Product, the
input factors when fed into the Digital Twin, can tell whether the cutting tool will be
compatible with the new product or not. It would even tell the user the number of
workpieces it can machine at once and for what input parameters does one need to attain
that or vice versa. This minimizes the need to perform physical tests on the product, which
not only saves time, money and resources, but even enhances the potential at the
operational and servicing stage.
2.2.3 Impact of forces on a cutting tool
Past researches have shown the use of different Computer Aided Manufacturing (CAM)
software’s for the assessment of the parameters of cutting speed, feed rate for the
assessment of tool life. Due to the factors of feed rate, cutting speed and depth of cut, the
machining time and cutting force impact can be seen in figure 2.5 which shows the forces
and machining time plot where the forces can be seen going up to values of 2800 N.
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Figure 2.5 The effect of cutting parameters on cutting force and machining time [20]
All three cutting force components shown in Figure 2.6 are of interest because apart from
the tangential (main) component that gives the cutting power and its determination is
apparently necessary, the radial and in-feed components control dimensional and form
errors in case of work piece and tool deflections and tool wear. [21]
Figure 2.6 Force components in three-dimensional oblique cutting [22]
Cutting force, FC is in the direction of primary motion. Cutting force constitutes about
70~80% of the total force F and is used to calculate the power P required to perform the
machining operation. [22]
2.3 Modelling of a cutting tool
Although various in-process and post machining corrective measures are available at high
cost aiming at eliminating or minimizing effects of part distortion and tool deflection, the
ability to accurately predict and minimize tool deflections and part distortion via simulations
can significantly reduce manufacturing and assembly cost. Tool deflection and strain arises
from high dynamic cutting forces during machining processes. Dynamic cutting forces can be
predicted by physics-based machining models considering workpiece material properties,
CNC machining toolpath, part geometry, and cutting force computation models. Coupled
with tool compliance properties, a linear elastic tool deflection model can predict in-process
tool deflections along machining toolpath within the physics-based cutting force prediction
framework. [23]
A digital twin can account for ever increasing need for data accumulation and data
processing at all stages: those of design, development, testing, actual production,
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assessment and correction or adjustment of the process. To create a digital twin, data from
various sources are collected and analysed, such as physical dimensions, manufacturing
information, operational data and information flows from analytic software. This
information is combined into a virtual model. When designed appropriately, this model
results in a very accurate simulation of the actual physical assets and their modus operandi.
The ongoing flow of data facilitates analysis, which in turn results in a better production
outcome. [24]
2.3.1 Linear Elastic Beam Model for Tool Deflection
The linear elastic beam model for tool deflection prediction is developed within the physicsbased cutting force prediction framework. It includes two parts, modeling the tool as static
fixed-free end cantilever beam and mapping dynamic cutting force onto the tool to predict
tool deflections. Based on the assumption that majority of the tool deflection is due to the
overhang and gravity and inertia effects are not significant, the modeling for tool deflection
prediction follows linear elastic beam theory to reduce computational complexity while
preserving accuracy. The toolholder is modeled as a fixed end support holding the tool.
Similarly, the work holding and fixtures are also assumed to be rigid. [25]
There are cutting tools of various shapes and each tool is modeled using multiple beam
elements each with different moment of inertia due to varying geometry. A relatively simple
tool as shown in Figure 2.7 is modeled as a cantilever beam. [25]
Figure 2.7 Linear Elastic Model for tool deflection prediction [25]
2.3.2 Impact of longer tool length
The study done by G.M. Sayeed Ahmed, Hakeem Uddin Ahmed, and Syed Safi Uddin Samad,
on the effect of longer tool length on surface roughness and other parameters shows the
cutting tool overhang affects the surface quality, especially during the turning process.
Because the tool holder is subject to bending and buckling depend on effect point of the
cutting force (tangential force), cutting tool displaced. This situation has negative effects on
the surface quality as shown in figure 2.8.
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Figure 2.8 Tool holder undergoing deflection, δ due to the tangential force and Adjustable
Parameters in Turning Operations [26]
From their research it can be concluded that using a short tool length always provide good
surface roughness in a turning boring operation, no matter what cutting parameter or type
of boring bar used. It was observed that turning operation using a long tool length may set
excessive vibrations that decrease the surface quality. The variation of deflection with
respect to depth of cuts for different overhang distances can be seen in figure 2.9.
(a)
(b)
Figure 2.9 Variation of Deflection with respect to Depth of cut at tool overhangs of (a) 23
and (b) 33 mm [26]
In the measurements performed after the experiments were complete, it was observed that
the cutting tool deflection values increased as the tool overhang increased. [26]
2.3.3 Use of ANSYS in DT
A digital twin begins with a basic model that describes the asset. It provides
accurate operational pictures of assets right now. There is a significant business value in
identifying underutilized devices, so analyzing twin information can lead to optimal usage.
Simulations can be run on-site or in the cloud at scale - pushing models to the edge then
bringing insights they create back to the cloud. Complete integration requires connecting to
the customer’s PLM system, linking in CAD data and other valuable information recorded in
enterprise systems. A digital twin that centres on a common model and incorporates many
information sources enriches knowledge. [27]
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ANSYS software’s greatest value is in bringing together different aspects of simulation, so it
helps designers completely think through their designs. Because a simulation model
demonstrates how the assets should work, the twin approach shows exactly when operation
is amiss. Digital twins take simulation results out of the design studio and into real life to
provide immediate feedback on one asset or many. [27]
The ANSYS simulation results determine which area has the maximum or minimum strain or
even stress values in alignment with several input parameters. Evaluation of data for
optimum lengths to create a tool can easily be done using ANSYS. An example of how the
design model of a CNC turning single point cutting tool may look like in ANSYS can be seen in
Figure 2.10 below.
Figure 2.10 An example of a CNC single point cutting tool modelled in ANSYS
The above example shows how a designer can create an exact replica of the CNCMT and
later put in the constraints and loading to the components for simulation purposes. The
results can then be extracted and validated through physically performing various tests or
maybe simplify the design model and test it with the analytical model.
2.4 Analytical Concept
The DT data that has been derived from the ASYS model can be tested without the physical
testing by using the analytical model. The strain has been created on the cutting tool can be
validated using the analytical formula of strain. If a closer look is taken at the cutting tool, it
can be seen that a load is acting upon the edge or tip which is in contact with the workpiece.
It can be observed that when the cutting tool is attached with the tool holder, the back face
is fixed and constrained, hence not allowing any motion from that end. This eventually can
be modelled as the case of a cantilever beam.
A cantilever beam is a member with one end projecting beyond the point of support, free to
move in a vertical plane under the influence of vertical loads placed between the free end
and the support. A rectangular cantilever beam with a point load applied at its free end can
be seen in the Figure 2.11 below. The figure also shows that the bending moment for a
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cantilever beam is the maximum at the fixed end. The shear force value, however remains
constant throughout the beam.
Figure 2.11 Cantilever Beam with a single point load W applied at the free end
A number of parameters can be evaluated analytically using the cantilever beam model of
the cutting tool. Specifically, for the calculation of strain. If it is a rectangular cross-sectional
bar, theoretically the strain can be calculated using,
∈=
𝐈=
𝐌∗𝐜
𝐈∗𝐄
𝐛∗𝐡𝟑
𝟏𝟐
(1)
(2)
Where:
∈ is the strain (mm/mm)
M is the moment (Force(N) * Length(mm))
c is the distance from the center of the beam to the point where the strain is being
measured (mm)
E is the modulus of elasticity (N/mm2)
I is the 2nd moment of area (mm4)
b is the width (mm)
h is the thickness (mm)
Another parameter that could be of interest for validation is the maximum deflection that
occurs on the beam at a particular length x. For the purpose of calculation of the maximum
deflection in the beam, the applicable formula is,
δ=
W∗ x3
3∗E∗I
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(3)
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Where:
δ
is the maximum deflection of the beam (mm)
W is the load that is being applied on it (N)
x
is the distance where the deformation needs to be evaluated (mm)
E
is the modulus of Elasticity (N/mm2)
I
is the 2nd moment of area (mm4)
For the case of a circular cross-section,
𝐈=
𝛑∗ 𝐑𝟒
𝟒
(4)
Where:
R is the radius of the circular cross-section
When the geometry is rather complex and it involves a rather arbitrary cross section, the
centroid tends to shift from the center axis for most cases. In this case, the second moment
of area with respect to the centroid, plus a term that includes the distances between the
two axes will be used.
This is called the parallel axis theorem and can be seen in figure 2.12 below.
(5)
Figure 2.12 Parallel axis theorem formula with an arbitrary cross section
Where:
Ix is the second moment of area for a complex geometry
Ix’ is the moment of area from the new axis
d is the location of the area from the centroidal axis and,
A is the area
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3 Methodology
To create a digital twin, it is very important that a fundamental model is chosen at once and
further constraints are applied for evaluation of various parameters. ANSYS is the chosen
software for the simulation of the model as it helps in assessing various parameters such as
strain, stresses, deformation etc. through the application of various constraints. Once, the
FEA analysis has been performed, the Digital Twin will then be informed about the various
conditions using sensors and a much clearer picture of the process can be drawn. Figure 3.1
shows the structure of the research project.
Digital Twin
-------------------------------------
-----------------------------------------------
FEA
Analytical Model
Experimental Validation
Figure 3.1 Procedural Flow Chart for the project work
3.1 Design Modelling
The design phase is when the physical model is replicated virtually for process optimisation.
The designing is done in ANSYS 18.0 design modeller using the static structural model as can
be seen in figure 3.2 below. This design is just an example of how a strain gauge may be set
up with a cap on top along with a tooling insert.
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Tooling Insert
Strain Gauge
Cutting Tool
Figure 3.2 Design model of a basic cutting tool with a strain gauge and tooling insert
The model of any cutting tool can be replicated using the correct design parameters. There
have been various design iterations that have been considered. All of those design iterations
can either be created on ANSYS design modeller or imported from a designing software such
as Solid Works. The design has been done modelled as a simplified bar of 25X25 mm like the
one used for turning process along with an iteration of a cylindrical bar with a 25 mm
diameter which can be modelled as a round boring bar for internal machining. These 2
iterations were created to begin with a simplistic model for obtaining strain. The strain
evaluation which is the main parameter has been assessed at a distance of 10mm from the
fixed end of the designs, i.e. the tool post, modelled as a cantilever beam. The final design
was created to accommodate the setup of a strain gauge inside the cutting tool, so as to
avoid hindrance with any operations and also to assess to impact of material removal from a
certain location in the cutting tool.
3.2 Finite Element Analysis
The FEA model is where the replicated physical model will be applied with the constraints
and forces for evaluation of the impact of various constraints. In order to obtain the best
results, a fine mesh with an appropriate mesh quality should be prepared so as to obtain the
best possible results and so that the results converge.
The aim is to receive maximum strain with a practical material like High Speed Steel (HSS).
The important thing to be kept in mind during the assessment of the FEA model is that only
the strain occurring on the cutting tool needs to be evaluated, so no strain should appear on
the tool post. The loads are then applied to the cutting tool for various iterations. Now, the
literature review shows that cutting forces can go up to a value of 3000 N as they depend on
the various factors such as feed rate, depth of cut and cutting speed.
In order to keep the model basic, a fixed support has been applied to the design model of all
the iterations so as to create a cantilever beam as can be seen in figure 3.3, which shows an
example of how the forces may be applied to the designs. This allows flexibility and ease in
the analysis of how these factors play a crucial role in the CNC cutting tool.
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Figure 3.3 FEA model with constraints and forces
The strain has been evaluated for various cutting tool lengths. This has been inspired from
the literature that shows how the increase in cutting tool length increases deflection in the
cutting tool. This increase in length assessment is important for the evaluation of the
suitable depth of cut or other parameters that may result in development of strain on the
cutting tool. This is an important simulation as it helps the DT in evaluating whether the
respective tool length is correct for the process or not.
3.3 Analytical Model
The analytical model is used for the validation of the results since the design has been
modelled as a cantilever beam. The physical testing would need various sensors and an
entire setup for that validation. For the purpose of calculation of strain for a rectangular
cross section, the second moment of area needs to be evaluated using equation 2. These
results will be used for equation 1 in the calculation of strain. The material that is used here
is High Speed Steel which has a modulus of elasticity value of 200,000 N/mm 2. The strain can
easily be calculated using these values at any location along the bar, that is c in equation 1.
The second moment of area obtained for the simple model of the cylindrical cutting tool can
be evaluated using equation 4. Later, the values will again be put into the equation 2 for
validation of the strain results at any point c. But the second moment of area for some
complex models are very different as the centroid would be shifted which would lead to a
change in second moment of area. The equations 5, that is the parallel axis theorem is used
to calculate the value of the second moment of area and hence the value of strain. Since,
the material composition is consistent throughout the young’s modulus value will remain
the same for the complex shapes. The moment however, since depends on the force applied
and the perpendicular distance from which the force has been applied, it will change with
the increasing length of the tool.
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The deformation values for various lengths can be evaluated using the equation 3.
3.4 Validation
The validation is the physical testing of the model using the strain gauges sensors and
dynamometers for sensing the real-time data of the cutting tool. The data received will then
be analysed and validated with the results of this experiment. If the design and FEA model
have been validated with the analytical model, it is predicted that it would validate with the
physical testing model too. The creation of the DT is part of this project, the validation
however is not in the scope as it will be done using the physical setup.
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4 Design Investigations
In order to create the DT of a cutting tool system, 3 simple designs have been investigated as
part of the methodology through FEA. The impact of those forces acting on the cutting tool
have been assessed to measure strain across various lengths of the cutting tool. The impact
of deformation however, will be measured also the tool moves away from the tool post,
that is for the stick out distance or for the case of various locations of material removal.
4.1 Design 1
In order to create a DT of a smart cutting tool, the literature shows that a cutting tool can be
modelled as a cantilever beam. Because the approach used in this project is rather simplistic
than making a complex cutting tool, the first design is a 25X25 rectangular cross sectioned
bar made of structural steel with a length of 50mm as can be seen in Figure 4.1 below. The
design has been made in static structural system in Ansys 18 Design Modeler.
Figure 4.1 Design 1 of a 25X25 mm cross section bar with 50mm in length
4.1.1 Constraints and forces
In the modelling parameters, a fine mesh was created and then the design 1 has been
modelled as a cantilever beam using a fixed support and the forces have been applied to it
on the free end as can be seen in figure 4.2. The forces on the cutting tool depend on a lot
of parameters as can be seen in the literature review. Because of these factors, the value of
forces can be seen going up to significantly large values. The design undergoes a force range
of 500N to 3000N with an interval of 500N. A specific coordinate system has been defined
for the cutting tool 10mm away from the fixed end in order to measure the strain at that
point where the strain probe will help in otaining the value for the strain. The location of the
strain probe will not change with the increasing length of the cutting tool.
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Figure 4.2 Design constraints and forces applied on design 1
4.1.2 Strain Measurement for various lengths
The length of the cutting tool will be evaluated for four different cutting tool lengths as can
be seen in Figure 4.3 below. The strain however will be measured at a particular distance in
order to evaluate the variation due to the increase in length at a particular point in the
cutting tool.
(a)
(b)
(c)
(d)
Figure 4.3 Cutting tool lengths of (a) 50mm (b) 60mm (c) 70mm and (d) 80mm
The stick out distance or the distance that the cutting tool is away from the tool post plays
an important role in modelling the cutting tool and the creation of the DT. This is because
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firstly, it means the amount of the cutting tool that is left hanging from the tool post.
Secondly, it is important because in a smart cutting tool system, this would tell the DT
whether or not the cutting tool has been fixed at the required position using the obtained
sensor data. Figure 4.4 below shows various stick out distances for which the design 1 of
length 50mm has been tested. The tool holder length for this has been designed longer.
(a)
(b)
(c)
(d)
(e)
Figure 4.4 Design 1 with stick out distance of (a) 0mm (b) 10mm (c) 20mm (d) 30mm and
(e) 35mm
4.1.3 Strain Vs increasing length for various forces
The strain has been evaluated at a distance of 10 mm from the fixed end for the cutting tool
lengths seen in figure 4.3 above. The strain probe attached at that point evaluates the von mises strain value at that point as the von-mises strain considers the distortion theory and
gives a much clearer and reliable value. Figure 4.5 shows the strain probe setup for the case
of a 60mm length. The plot for the variation in increasing lengths can be seen in figure 4.6.
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Figure 4.5 The strain probe location on the cutting tool on the defined coordinate system
(a)
(b)
(c)
(d)
Figure 4.6 Strain Vs increasing length for a force of (a) 500 N (b) 1500 N (c) 2000 N and
(d) 3000 N
4.1.4 Deformation Vs Increasing length and Deformation Vs Stick out distance
When the total deformation was evaluated for the increasing distances, the FEA showed the
maximum deformation at the point of load, which can be seen in figure 4.7. It is observed
for a length of 50mm, when a load of 500N is applied on the design, it shows a gradual
decrease in the deformation as it moves away from the point of load, which was somewhat
expected from the design model.
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Figure 4.7 Deformation for a stick out distance of 0mm
For the case of 0mm stick out distance when the length is varied, it shows that the
deformation too increases, as can be seen in Figure 4.8 below for a load of 2500 N.
Figure 4.8 Deformation for a 2500 N load for increasing cutting tool length
The purpose of evaluating various stick out distances was to assess the deformation
occurring on the tool when the fixed location of the cutting tool moves at a particular
distance for a particular load. Hence, the deformation was plotted for various stick out
distances, for the force range used for strain and a few plots can be seen in figure 4.9 below.
(a)
(b)
Figure 4.9 Deformation at (a) 500 N and (b) 2000 N for various stick out distances
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4.1.5 Analytical Validation
Since the cutting tool has been modelled as a cantilever beam, the corresponding strain for
the forces can be tested too for increasing lengths. The equations 1 and 2 when used for the
design show that the analytical model verifies with the evaluated or observed values of
strain. The results mentioned in table 4.1 show the evaluation of strain for a 50mm length
that results in an error of 0.03 which is negligible. The plot has been created for the results
in figure 4.10. The values used for the evaluation however are 32250 mm4 for I and 200000
N/mm2. The values of strain however have been used for the maximum strain applied to the
tool edge in the case of a coarse mesh rather than a fine mesh, because the analytical strain
however does not consider the external parameters which are considered in a simulation.
Hence, for simplicity of calculations the result generated by a coarse mesh were used for the
analytical validation of a tool of 50mm.
Force Applied (N)
Observed Strain (mm/mm)
Analytical Strain (mm/mm)
500
0.000114765
0.000115
1000
0.000229531
0.000230
1500
0.000344296
0.000346
2000
0.000459062
0.000461
2500
0.000573827
0.000576
3000
0.000688593
0.000691
3500
0.000803358
0.000806
4000
0.000918124
0.000922
Table 4.1 Observed and Analytical maximum strain against various loads for a 50mm bar
Figure 4.10 Observed vs analytical maximum strain plot for a tool length of 50mm
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4.1.6 Discussion on Design 1
The idea of creating a simple design of cutting tool by choosing the 25X25mm cross section
bar and modelling it as a cantilever beam shows the similar properties as expected in the
literature review. Although, a few graphs have been shown but the same trend is followed
by all the loads as the length of the cutting tool is incremented. The strain increases
exponentially with the length. The increasing length increases the overhanging distance of
the beam which leads to the strain developed at a particular point increasing. The
deformation increases with the increasing length of the beam which is reviewed by the
literature and hence, verifies the results.
The deformation increases exponentially as the cutting tool moves away from the tool post
for a particular cutting tool length of 50mm. As the overhanging distance is increasing, the
tool deflects more, and this case too is reviewed from the literature review. The further
analytical testing done using the theoretical formula helps prove the case that the strain
values observed match with the analytical strain. This shows that a successful Digital Twin
has been created for Design 1.
4.2 Design 2
The process of turning can be performed using different tools, and one of it is a boring bar
used for internal machining. The boring bar can also be modeled as a cantilever beam of a
circular cross section with a point load acting on its free end. The circular cross section of
diameter 25mm has been used as the length is being incremented to assess the strain
developed on the tool for a range of forces acting on the tool. Figure 4.11 below shows the
design 2 for a length of 50mm. The material chosen for the design is structural steel.
Figure 4.11 Design 2 of a boring bar modeled as a cylindrical cantilever beam
4.2.1 Constraints and forces
The constraints and forces for this design cannot be applied on the entire edge. For this
design, a different approach has been used where a new coordinate system has been
defined with respect to the global coordinate system as can be seen in Figure 4.12. The
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defined coordinate system is then loaded with a point force acting downwards in the
negative y-axis whose magnitude is 500 N.
Figure 4.12 The constraints and forces acting on the cutting tool
The model is loaded with a range of forces from 500 N to 3000 N with an interval of 500 N.
4.2.2 Strain Measurement for various lengths
For this design, the strain will be assessed for the force range acting on it as the length
increases. The various lengths used for this design can be seen in Figure 4.13. A point load
has been applied to all the cases on the free end. Particular precaution has been taken to
make sure the strain only comes on the cutting tool and not the tool post because it is only
used for modelling, but the Digital Twin is being created only for the cutting tool.
(a)
(b)
(c)
(d)
Figure 4.13 Design 2 with a cutting tool length of (a) 50mm (b) 60mm (c) 70mm and
(d) 80mm
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4.2.3 Strain Vs increasing length for various forces
The Design has been evaluated for various lengths, but the strain is measured at a particular
location using a strain probe which is located at a distance of 10mm from the fixed end. The
strain observed by the probe for a cutting tool of length 60mm can be seen in figure 4.14
below. It shows that a new coordinate system has been defined in order to observe the
value of strain at the 10mm distance.
Figure 4.14 Location of the strain probe at a 10mm distance from the fixed end
For all the lengths evaluated, the location of the strain probe has been kept constant, that is
10mm away from the fixed end. The strain data observed by the probe for a particular load
has been plotted across the increasing lengths which can be seen in figure 4.15. The strain
used for plotting is the von-mises strain.
(a)
(b)
Figure 4.15 Strain measured against increasing length for a load of (a) 500 N and (b) 2000 N
When the deformation is observed for the increasing lengths, the plot for a load of 2000 N
can be seen in figure 4.16 below.
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Figure 4.16 Deformation for 2000 N for increasing cutting tool length
The deformation observed also has been evaluated for a range of 500N to 3000N and similar
curve has been observed for all loads.
4.2.4 Analytical Validation
The analytical validation for the design 1 had been done using the equations 1 and 2 and
similarly, the validation for the design 2 can be done using the equations 1 and 4. Since, the
design 1 showed that the results obtained were correct, it is predicted that the design 2 also
would be validated for all cases of varying stick out distances. The radius used is 12.5 mm
and the value of modulus of elasticity is 200000 N/mm2 since the material chosen for results
is structural steel.
4.2.6 Discussion on Design 2
The design was modelled in order to show the impact on a cutting tool strain for forces
acting on a tool such as a boring bar which is cylindrical in shape. The impact of various
forces was evaluated for increasing length of cutting tool due to cutting forces ranging from
500 N to 3000 N.
The strain was calculated at a constant distance of 10mm from the fixed end for various
lengths of the cutting tool. The results show that as the length of the cutting tool increases,
the strain at that point also increases. The results obtained for the deformation shows the
increase in tool deflection with the increase in tool length. This matches with the results
obtained in the literature review. The analytical testing formula are predicted to validate the
results for both the deformation and strain observed on the cutting tool.
Although, the plots are acceptable, the simulation results for this case can be refined by
changing the design, and adding additional cut into the material at the point of load, so as to
accommodate the tooling insert which rests on it. But since, the design is kept basic, a point
load is applied to it rather than removing material from the tool.
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4.3 Design 3
The design 3 analyses a more complexed case where some material is removed from the
cutting tool. The material removed from the cutting tool is of length 10mm. The assessment
parameter although still remain the same, i.e. the strain. The material removed is referred
to as cut out distance and it will also be assessed for incremented cutting tool length. The
purpose of the cut-out distance is that if in future for the testing, a strain gauge sensor is
attached to the cutting tool, then it could easily be fitted in that cut out distance. This design
will help generate results with the removed material, which would give much clearer results
for the strain values. The idea is still kept to be simplistic as before for creating the design
and hence the fundamental design is a rectangular bar with a 25X25mm cross section that is
50mm in length as can be seen in figure 4.17. The material chosen for the design is
structural steel. The 10mm cut out distance is at a 5 mm distance away from the fixed end.
Figure 4.17 Design 3 with a 10mm removed material 5mm away from the tool post
4.3.1 Constraints and forces
The design 3 has been modelled as a cantilever beam with the fixed end attached to the tool
post and the forces ranging from 500N to 3000N are applied at the free end of the cutting
tool. Figure 4.18 shows how the design has been constrained with the application of a fixed
support and the application of the cutting forces for a 60mm bar. The force has been applied
on the edge of the cutting tool for assessment of the impact of the force on the strain at the
location where the material is removed from.
Figure 4.18 Design 3 with the applied constraints and forces
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4.3.2 Strain measurement for various lengths
For this design, strain has been measured at the distance of 10mm from the fixed end which
lies in the region of the removed material. This is good because a sensor can be attached in
this area and the results can easily be validated for various lengths. Figure 4.19 shows the
various lengths for which the strain has been evaluated.
(a)
(b)
(c)
(d)
Figure 4.19 Design 3 with a length of (a) 50mm (b) 60mm (c) 70mm and (d) 80mm
Another factor that was of interest for this design was the impact of the movement of the
removed material from the point of load. The different cut out distances have been shown
in figure 4.20 for a fixed length of 50mm. This case has been designed to evaluate the
impact on deformation at 10mm away from the tool post due to the impact of material
removal at various locations. The cut-out distance here refers to the distance that the
removed material is away from the point of load.
(a)
(b)
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(c)
(d)
Figure 4.20 Design 3 with a cut-out distance of (a) 10mm (b) 15mm (c) 20mm and (d) 25mm
4.3.3 Strain Vs increasing length for various forces
The strain has to be evaluated for various lengths of design 3. The strain is measured at the
distance of 10mm from the fixed end, which puts the strain probe on the surface of the
removed material which can be seen in figure 4.21 for a tool length of 60mm.
Figure 4.21 Strain probe location for design 3
The strain measured for different lengths has been plotted for a range of 500 N to 3000 N.
The results obtained can be seen in figure 4.22 which shows the impact of a few loads on
the strain at the desired location.
(a)
(b)
Figure 4.22 Strain for increasing lengths at a cutting force of (a) 2000 N and (b) 3000 N
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The impact of deformation for this case has been evaluated and the plot can be seen in
figure 4.23 below for a load of 2500 N.
Figure 4.23 Deformation for various lengths at a force of 2500 N
4.3.4 Deformation for various cut out distance
The impact on the strain and deformation for the case of variations in the cut-out distances
has been evaluated for various loads at the free end. The strain and deformation have been
measured at the free end of the cutting tool which are the locations of the maximum values
for these two parameters. The plot can be seen in figure 4.24 below.
(a)
(b)
Figure 4.24 Deformation for a 50mm bar with the change in cut out distance for (a) 500 N
and (b)2000 N
4.3.5 Analytical Validation
This design is rather complex and according to the analytical formula mentioned in the
literature, this design would require the usage of the parallel axis theorem for calculation of
the second moment of area. This is because of the cut-out distance present at various
distances as tested due to which the centroid would shift from its place. This design is quite
similar to the design 1 with the only variation being the case of material removal from the
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design. Through the use of equations 1,2 and 5 the model can be tested analytically. Since,
the design 1 was validated for the various increasing lengths, it is predicted that this design
too can be validated analytically.
4.3.6 Discussion on design 3
This design was created keeping in mind the case that may arise where a sensor needs to be
fitted on the cutting tool. The idea of the removed material is also to evaluate the impact on
the strain for a cutting tool when the length of the tool increases. The strain has been
observed on the surface of the removed material at a distance of 10mm from the fixed end.
The location of strain observation has not been changed in relation to the cutting tool
length. The observed strain shows an increment in the strain value with the increase in its
length. The strain increases exponentially for the cutting tool length. This is the case for all
of the force range from 500 N to 3000 N. The increase in deformation with the increase in
length verifies with the literature which tells that the deflection increases with the increase
in cutting tool length.
For the case of the variation in the cut-out distance, it was seen that the deformation tends
to increase when the cut-out distance comes near the fixed end of the cutting tool. This is
because of the fact that according to the bending moment theory, the bending moment is
maximum at the fixed end of the cantilever beam. Hence, when some material is removed
from the area closer to the fixed end, the beam tends to deflect more and the same can be
observed from the result plots generated for deformation.
The results hence validate with the literature and can be said to be correct. Further
validation can be done through the physical testing of the design.
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5 Conclusion
The research investigated various designs for the evaluation of strain and observed a few
relations for the case of deformation which align with the literature review. The state of the
art shows how a cutting tool can be modelled as a cantilever beam, and the dependence of
deflection on the length of the cutting tool or overhanging length of the tool. The results
obtained for the impact of forces, can also be used to examine the impact of parameters on
which the cutting force depends, such as the cutting speed, depth of cut, or feed rate of the
cutting tool.
The design 1, which was a rectangular cross-sectioned bar of dimensions 25mmX25mm and
length 50mm were simulated for strain evaluation for a force range of 500N to 3000N. The
strain was measured at a location of 10mm of from the fixed end for increasing lengths of
the cutting tool from 50mm to 80mm. The cantilever modelled beam shows an increase in
the strain value as the length that is overhanging from the tool post increases. Similarly, the
deformation increases with the increase in cutting tool length. This result for beam
deflection verifies with the literature review which shows the impact of increasing over
hanged length leads to an increase in the deflection of the tool. The analytical testing
verifies the results for the strain generated from a coarse mesh. This is because the fine
mesh simulation usually converges and gives much more accurate results. However, for this
basic model, coarse mesh results can be used to verify for analytical testing. Hence, the
Digital Twin for design 1 has been created successfully.
The design 2 was modelled keeping in mind the turning tool used for internal machining
process. Hence, a 25mm circular cross section has been used for evaluation. The loading
however was different for this case, as a point load is applied to it to keep the model
simplistic. The strain again has been measured at fixed location of 10mm from the fixed end
of the cutting tool for different lengths. The results for the force range with the increasing
length of the cylindrical cantilever beam show a similar exponential increase for strain as
was observed in design 1. Hence, it can be said that the strain increases as the length of the
cutting tool increases. From the 2 evaluated designs, it is proven that longer the length of
the tool, the more strain is observed on it.
The design 3 however uses a different approach and is evaluated for a case of material
removal from the cutting tool. This may be used for future designing, where a strain gauge
may be fixed to the cutting tool of a certain length. The bar of 25mmX25mm cross-section
when has a 10mm material removed off it from a location of 5mm from the fixed end and
the strain is again evaluated at the same location as was done for the first 2 designs. The
strain shows a similar increase with the increasing length of the tool. If the material is
removed at various locations along the length it shows that closer the removed material is
to the edge of applied load, a lower deformation is observed on that edge. Hence, the
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deformation at the free end increases when the removed material reaches close to the area
of fixed end. This is due to the bending moment being maximum at that point.
Hence, a successful digital twin is created which tells the impact:
•
•
•
•
of increasing length on the strain of the cutting tool
material properties on the strain of a cutting tool
on deflection for an increase in length of a cutting tool
of cutting forces on the strain at a particular location of a cutting tool
Hence, the research agrees with the literature that a shorter length of cutting tool should be
used for the turning process. This would assist in resisting higher forces which would lead to
lesser tool wear and longer tool life. An area of interest could be evaluating the temperature
variations due to the increase in the length of the cutting tool. As, higher the temperature,
softer the workpiece, which would result in lesser cutting forces on the cutting tool, leading
to lesser tool wear. The increasing length of the tool leads to increasing vibrations which is
not suitable for precision machining. Although, for the measurement of the strain, a longer
tool length is required so that evident strain can be generated on the tool which can be
easily sensed by the sensors.
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