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7/30/2019 Adaptive Thesis
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A Thesis on
DEVELOPMENT OF SIMULATION FOR
AN ADAPTIVE CONTROL
MACHINING SYSTEM
ABSTRACT
In any machining process the economic objective is to
maximize the metal removal rate by the highest possible feed rate
under the constraint of tool breakage. An NC Program merely
guides and controls a Machining process. It cannot respond and
react to variations in machining conditions during the operation.
This results in many unfavorable situations like greater lead times,
tool damage, extreme caution in work handling etc. during
machining. Machining force regulation and tool wear are
challenging problems since the force and temperature rise varies
significantly under normal operating conditions. In order to
overcome above mentioned problems, the concept of ADAPTIVE
CONTROL MACHINING was introduced. The purpose of
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introducing this concept is to control and optimize the variable
cutting parameters. The main aim of Adaptive Control Machining
(ACM) is:
1. Improve the process productivity
2. Reduce the operational costs
3. Reduce the machining lead times
Adaptive Control system (AC) maximises material
removal rates and minimises cycle times by optimising the cutting
feed rate based on a controlled spindle load. The applications of
ACM are not only limited to NC machining but such systems are
designed to compensate for environment changes perceived,
monitored, altered or reset according to the situation In the current
project undertaken, we have elucidated and applied the Adaptive
Control principles to TURNING. As a part of this work, we have
conducted experiments on a LATHE machine. The specimens
selected for this experiment are specially designed so that the
required sources of variability are included. In accordance to the
results obtained, the application of Adaptive control principles to
TURNING is aptly justified. As part of this work, a simulation is
developed for turning process based on adaptively controlled
experimental data.
TABLE OF CONTENTS
CHAPTER I: INTRODUCTION 5
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1.1 Basics of adaptive control 5
1.2 Structure of adaptive control 8
1.3 Classification of Adaptive control system 9
1.4 Sources of variability 11
1.5 Need for adaptive control 13
1.6 Applications of adaptive control 13
CHAPTER II: LITERATURE REVIEW
2.1 Introduction 14
2.2 Brief discussion 15
2.3 Cutting constraints 17
2.4 Proportionality gain constant for EN8 18
2.5 Proportionality gain constant for EN24 21
2.6 Summary 24
CHAPTER III: PROBLEM DEFINITION
3.1 Generation of experimental data 25
3.1.1 Simulation 26
3.2 Experimental setup 27
3.3 Sensing equipment in experimental work 28
3.4 Dynamometers and thermocouples 29
3.5 Material selection 30
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CHAPTER IV: ILLUSTRATION OF THE PROPOSED
METHODOLOGY
4.1 Theoretical relations 32
4.2 Experimental procedure 35
CHAPTER V: RESULTS AND DISCUSSIONS
5.1 Graphical representation 62
5.2 Inferential data 65
CHAPTER VI:
CONCLUSIONS & SCOPE FOR FUTURE STUDY 71
APPENDIX: About the simulation software 73
REFERENCES & BIBLIOGRAPHY 76
CHAPTER I:
INTRODUCTION TO ADAPTIVE CONTROL MACHINING
(ACM)
1.1 INTRODUCTION
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While CNC technology coupled with CAD/CAM has long
helped to introduce flexibility in batch production, there still
remains some major inefficiency inherent in most machining
processes. Present day CNC technology relies on the programmers'
input of appropriate cutting parameters - even when sophisticated
software systems are used to generate NC programs. The fact is
that NC programming is based on predetermined and unchanged
conditions. The control mechanisms of CNC machines are limited
to geometry and kinematics. As such, they follow pre-programmed
and constant speed and feed rates during each cutting segment.
Consequently, they do not have the flexibility required for adapting
to the dynamic changes that occur during cutting. This inflexibility
would be acceptable if cutting conditions were uniform during
machining.
In practice, however, cutting conditions tend to
continuously vary for many of the following reasons:
Uneven work piece surface.
Gradual tool wear.
Material hardness varies within each work piece.
Work piece dimensions vary from piece to piece.
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Temperature variations in material during cutting.
The fixture's stability may be affected during cutting.
NC programs may contain errors.Advances in CAD/CAM technology have caused machinists to
focus most of their attention to "defining the required geometry"
and ignore the need to consider the rest of the previously
mentioned conditions. However, with all of the those deviations in
mind, NC programmers have no alternative but to be conservative
in determining cutting parameters - resulting in safer but more
inefficient cutting processes.
No matter how optimized NC programs may be, they
cannot take into account these dynamic variations encountered
during cutting. At best, long NC programs may be created with
different feed rates for each segment. However, these programs
still cannot modify cutting parameters in real time in order to adapt
to unexpected conditions that may occur during cutting.
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Adaptive control systems ensure automatic optimization ofthe machining process to reduce cycle times, increase tool
utilization and prevent tool breakage, thus lowering machining
costs and increasing machine capacity. These adaptive control
systems are applicable on CNC milling, turning and drilling
applications. Typical applications include rough milling when the
material and work piece surface hardness vary, die and mold
manufacturing, blade manufacturing and helical milling on turning
centers. Machining cycle times are typically reduced by 10 to 40
percent, depending upon the application. Feed rate optimization
algorithms use geometry and force models to calculate
Feed rates for each tool move, based on a reference peak
force. The adaptive controller adjusts the feed rate during
machining to maintain the reference peak force. It is the
combination of these methods that yields accurate force control,
unobtainable with either method by itself.
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Adaptive control alone is inadequate to handle significant
transient cut conditions because of the slow system response time.
Design parameters for the adaptive controllers are selected using
an experimentally validated machining process model.
Experimental results demonstrate the ability of the integrated
system to effectively regulate peak forces for cutting conditions
commonly encountered in end milling operations. The focus of this
research is peak force regulation in 3-axis machining through the
use of optimized feed rates and adaptive force control. Our current
feed rate optimization program is effective in force regulation but
it is subject to inaccuracies caused by errors in the force prediction
model. These inaccuracies can result in high peak forces during
machining, leading to unacceptable dimensional errors or surface
finish. On the other hand, if the peak forces are too low, the
machining efficiency is reduced. An on-line adaptive controller is
proposed to compensate for these inaccuracies, providing accurate
regulation of the reference peak force. Force control algorithms
have been developed and evaluated by numerous researchers.
1.2 STRUCTURE OF ADAPTIVE CONTROL
SYSTEM:
For a machining operation, the term adaptive control
denotes a control system that measures certain output process
variables and uses these to control speed and feed.
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In short, if there are any deviations in the properties and
behavior of work materials and tools, adaptive control system
converts a lifeless machine into a self-thinking and self acting
machine. During the past decade the part programmer has to
mention the operating parameters like feed, speed, depth of cut
basing on his knowledge and experience. Moreover, increasing
complexities in work pieces material, tool material and cutting
conditions have made optimized selection of spindle speed and
feed rate practically impossible.
In order to overcome such problems, adaptive control
systems are used for controlling and optimizing variable cutting
parameters.
1.3: CLASSIFICATION OF ADAPTIVE CONTROL
SYSTEM
Adaptive control employs automatic on-line adjustment of
the parameters for optimizing the performance of machining
systems. Adaptive controllers are of three types
Adaptive control with Constraint (ACC) Adaptive control with Optimization (ACO) Combination of (1) & (2)
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1.3.1Adaptive control with optimization:
In this form AC, an index of performance is specified for
the system. This performance index should be a measure of overall
process performance such as production rate or cost per volume of
metal removed. The objective of this AC is to optimize the index
of performance by manipulating speed or feed in the operation.
1.3.2Adaptive control with constraint:
It regulates cutting parameters to maintain a resultant
parameter such as cutting force, spindle power or tool tip
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temperature which allows power capacity of machine to be fully
utilized.
1.4 SOURCES OF VARIABILITIES:
The flexibility of any system depends upon the hindrances
which affect its performance. Similarly, there are some variables
which affect a machining process. In this section, we shall consider
various sources of variations in a machining process. They are
summarized below along with probable solutions to them.
Uneven work piece surface. Gradual tool wear. Material hardnessvaries within each work piece. Work piece dimensions vary from piece to piece. Temperature variations in material during cutting. The fixture's stability may be affected during cutting. NC programs may contain errors. Spindle deflection
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1.5 NEED FOR ADAPTIVE CONTROL SYSTEM:
Increasing complexities in cutting conditions have made
optimized selection of spindle speed and feed rate practically
impossible. To ensure the quality of machined products. To reduce
the machining costs and increase the machining efficiency. To
satisfy optimal machining criteria, some form of on line control
system is required by which performance is monitored and the
machine conditions are adjusted according to the results obtained.
In order to overcome above mentioned problems, the concept of
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ADAPTIVE CONTROL MACHINING was introduced. In automatic
adaptive control, a set of sensors continuously measures
performance and a computer combines these inputs with assumed
weighting factors and adjusts the m/c to approach optimum
performance after each set of inputs.
1.6 ADVANTAGES AND APPLICATIONS OF ADAPTIVE
CONTROL(AC) SYSTEMS:
Increase production ratesIncreased tool lifeGreater part protectionLess operator interventionEasier part programming
AC can deal with the following situations
Material and tool characteristic variations within their ownspecification
Variations of depth of cut(e.g., forgings and castings)Machinability variations within the work pieceVariations in machine tool behavior with time
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250 26.03 35 15 15 40.92 100 80 45260 30.44 36 16 15 42.15 109 80 45
270 36.21 38 16 12 42.94 118 80 45
280 38.32 36 16 13 41.48 125 80 45
290 40.33 34 15 12 39.05 123 80 45
300 43.33 34 14 12 38.67 126 80 45
Simulation for case 9:
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CHAPTER V
RESULTS AND DISSCUSIONS
In case of plain turning with ACC for EN8 it is observed that 39%
of machining time is saved, time taken to stabilize the force is
19.44 seconds and the optimum force utilized is 37 Kgf.
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In case of plain turning with ACC for EN24 it is observed that
32% of machining time is saved, time taken to stabilize the force is
26 seconds and the optimum force utilized is 41 Kgf. As compared
to EN8 optimum force utilization is more because of its higher
hardness number.
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In case of step turning with ACC for EN8 it is observed that 34%
of machining time is saved, time taken to stabilize the force is 24
seconds and the optimum force utilized is 38 Kgf.
In case of step turning with ACC for EN24 it is observed that 33%
of machining time is saved, time taken to stabilize the force is 30
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seconds and the optimum force utilized is 43 Kgf. In case of step
turning optimum force utilization is more and time saving is less
because of reduced feed rate to compensate increase in depth of
cut.
In case of plain turning with airgap for EN 8 it is observed that
42% of machining time is saved, time taken to stabilize the force
is 18 Sec and the optimum force utilized is 40Kgf.
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In case of plain turning with airgap for EN 24 it is observed that
40% of machining time is saved, time taken to stabilize the force is
19 seconds and the optimum force utilized is 40Kgf. In case of
plain turning with airgap percentage of time saving is more during
airgap tool moves at maximum feed rate.
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In case of plain turning with ACC for EN24 it is observed that
30% of machining time is saved, time taken to stabilize the force is
30 seconds and the optimum force utilized is 45Kgf. From this
graph we can understand that temperature rise is more during first
half and less during remaining half and it is proportional to 0.8
power of the feed.
In case of plain turning with airgap for EN24 it is observed that
45% of machining time is saved, time taken to stabilize the force is
35 seconds and the optimum force utilized is 46Kgf. In this case
temperature drop is more during airgap and temperature rise is less
compared to plain turning.
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In case of turning with fillet, airgap, taper turning for EN24 it is
observed that 30% of machining time is saved, time taken to
stabilize the force is 26 seconds and the optimum force utilized is
40Kgf. Machining time saved is less. During taper turning feed is
reduced continuously to compensate continuous increase in depth
of cut. From this we have observed that 30% of tool life is
increased due to constraints imposed on cutting force andtemperature rise. 40% of machining time is saved by applying
ACC principles to turning process.
CHAPTER VI
CONCLUSION & SCOPE FOR FUTURE STUDY
We conclude from the above that the results are improved
when we apply adaptive control principals in machining process.
Keeping in mind, the present day manufacturing scenario it is of
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prime importance that the manufacturing process we use, should
not lead to problems. This is kept under surveillance by the
introduction of adaptive control machining. The use of controller
is a must in adaptive control systems. However, taking into
account the immense expenditure incurred due to its installation,
we have carried out the same on a conventional machining system.
Fierce competition in international manufactured products
has resulted in rapid growth in the use of computer controlled
machine tools. Productivity gain during manufacturing and
particularly in machining With minimum modification in machine
control system, it maximizes use of existing controller hardware
Tests show that using ac system substantially 40% saving in
machining time are occurring with nominal expenditure on extra
hardware.
According to this work, it is obvious that the application of
adaptive control principles is fruitful. Simulation of turning
process for various conditions is very useful in understanding the
machining process.
SCOPE FOR FUTURE STUDY:
This work can be extended further. The methodology we
had proposed can be effectively applied to other machining
processes like milling, drilling, shaping etc.
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Appendix
3Dimensional studio max (3Dsmax9):
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This is the product of AutoDesk developed in 1990.. This software
is ideal to create any object and to apply any textures to bring
reality to any object in 3D world. This software is very popular for
creating walk through, materials and virtual reality in space
simulations, tool design etc. It is extensively used in Architectural
engineering animation industries. In India; it is extensively used in
animation as well as in engineering industry.
Applications:
It can create any object in 3D world and can export any file format
especially for web (.JPG, .PNG, .AVI etc.). Video formats for
animation industry and simulation and can export dwf formats,
which can be viewed in any windows applications with
interactivity. It is so popular because it is very easy to understand
its views, textures and can render objects very quickly without
large usage of memory. It can bring about realistic effects in a
computer simulation when compared with other 3D soft wares like
Bryce 3D, Cinema 4D etc. The special effects in some popular
movies like The Independence Day in 1994, Crazy frog in
2005 etc. are created using this software. It is very ideal to create
3D environment and texturing in gaming industry as well.
Steps:
1. Create a cylinder in front view port and set its length to 300units.
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2. Take the copy of same cylinder and reduce its length to 20units and increase its radius to 5 units.
3. Take a box in top view and convert into editable mesh.Adjust its coordinates to bring it a tool shape. Now we have
a tool, chuck, and work piece.
4. Now animate the tool by setting auto key. Drag the slider to100
thframe. Translate the tool in y-direction up to 10
points.
5. In this way animate the tool in x-direction at requiredintervals in required positions.
6. In the same way animate the height of the work piece inaccordance with the tool at required intervals in required
positions.
7. Save the scene. Set the view render the complete animationup to required frames and convert it into a .AVI file which
can be played in any system.
Flash (MX):
Flash is a product of Macromedia which has its applications
developed for web (www) in 1993. Flash is popular software for
creating 2D animation, web animations, websites, presentations,
intros etc. The software is popular among 2D animations and game
designs. The flexibility in the tools enables the user for vector
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drawing in computers. The interactivity in action scripting made
flash the very popular subject in gaming industry. This is very
ideal for creating web graphics and animations. Because its a
vector-based programme, it requires less time to download when
compared with other GIF animations, which is very essential in
web. This is made flash a very popular subject for web animators
and web designers. It can readily import any file formats like
.JPEG, .PNG, .GIF, .AVI, .MOV, .MP3 etc. and can export file
formats required for web and video such as .JPG, .GIF, .PNG,
.AVI, .SWF, .EXE, .HTML, .SPLASH etc.
Steps:
1. Take a file of size 800*600.2. Go to file import and browse the simulation that we have
created using 3D Max earlier, which is in .AVI format.
3. Now create buttons from symbols to create interactivitywith simulation by using action scripting.
4. In flash, its very easy to add text and interact with theanimation. It can readily export any type of file format such
as .EXE, with interactivity, which is very essential.
REFERENCES / BIBLIOGRAPHY
1. Selection of machining parameters for constrainedmachining problem using evolutionary computation
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(International Journal of Advanced Manufacturing Technology-
2006)
2. Optimization of machining parameters for milling
operations using non-conventional methods.(Int.Journal of Adv
Manuf. Technology).
3. Design and implementation for maximum metal removal
rate control of a constant turning force system.(Int Journal of
Materials Processing Technology).
4. Adaptive turning force control with optimal robustness and
constrained feed rate.(Int. Journal of Machine Tools
Manufacture) .
5. Feed rate optimization for variant milling process based on
cutting force prediction (Int. Journal of Adv. Manufacturing
Technology.)
6. Model based machining force control(Int.Journal of
Dynamic Systems, Measurement And Control ASME)
7. Adaptive control constraint of machining processes(Int.
Journal of Advanced Manufacturing Technology)
8. Principals of automation and advanced manufacturing systems
by Dr. K.C. Jain and Sanjay Jain, Khanna Publishers.
9. Computer Aided Design and Manufacturing by Dr. Sadhu
Singh, Khanna Publishers.
10. Computer Aided Design and Manufacturing by Dr. SadhuSingh, Khanna Publishers.
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11. CAD / CAM by Mikell P. Groover and Emori W. Zimmers
Prentice Hall Publishers.
12. Material Science and Metallurgy by V. D. Kodgari Everest
Publishing House.
13. Automatic production systems and computer integrated
manufacturing by Mikell P. Groover, Prentice Hall Publishers.
14. Computers numerical control machining by Yorrem Koren.
15. CAD / CAM principles & applications, by P.N. Rao, TMH
publications.