adaptive thesis

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


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 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


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.

adaptive thesis

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