TRANSIENT HEAT ANALYSIS OF A PHOTO ACTIVATED ADHESIVE WORKHOLDING (PAAW ...

160 Pages·2013·3.41 MB·English

The Pennsylvania State University
The Graduate School
Department of Industrial and Manufacturing Engineering

TRANSIENT HEAT ANALYSIS OF A PHOTO ACTIVATED ADHESIVE
WORKHOLDING (PAAW) JOINT DURING LASER DE-BONDING PROCESS

A Thesis in
Industrial Engineering
by
Mahesh Mantena

© 2013 Mahesh Mantena

Submitted in Partial Fulfillment
of the Requirements
for the degree of

Master of Science

August 2013
The thesis of Mahesh Mantena was reviewed and approved* by the following

Edward C. De Meter
Professor of Harold & Inge Marcus Department of Industrial and Manufacturing
Engineering
Thesis Advisor

Christopher Saldana
The Harold and Inge Marcus Career Assistant Professor

Paul C. Griffin
Peter and Angela Dal Pezzo Department Head Chair
Head of the Harold & Inge Marcus Department of Industrial & Manufacturing
Engineering

*Signatures are on file in the Graduate School

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ABSTRACT

Photo-Activated Adhesive Workholding (PAAW) is a technology used to fixture
“difficult-to-hold” workpieces for manufacturing and inspection. Using this technology,
a workpiece is adhered to grippers within the fixture using a photo-curable adhesive.
After processing, the workpiece is de-bonded from the grippers by either forcing it off
with an external tool or by rotating the grippers within the fixture.
In either case, de-bonding leads to external stresses on the workpiece that are
directly correlated to adhesive strength. The adhesives used for PAAW applications are
very strong and tough at room temperature. As a consequence, de-bonding stresses can
be an issue for applications in which the workpiece is compliant or comprised of a
material that is either weak or brittle. For these applications, the adhesive must be
weakened substantially prior to de-bonding.
One method of doing this is to use adhesive that is impregnated with particles of
carbon black. Prior to de-bonding, the adhesive joint is exposed to pulsed, Nd:YAG laser
radiation. The heat transfer degrades the adhesive and results in permanent loss of
strength. The problem is that the physical mechanisms by which this occurs are not
understood.
The goal of this thesis was to gain a scientific understanding of the physical
mechanisms that enable the laser degradation process. The specific objectives of this
thesis were:
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 To develop models to quantify the laser radiation absorbed within an adhesive
joint as a function of carbon black concentration, adhesive joint thickness, and
incipient laser radiation irradiance
 To characterize adhesive decomposition as a function of temperature
 To characterize the release of heat during adhesive decomposition and to
determine whether it is a significant factor during laser degradation
 To determine if heat transfer from a carbon black particle is sufficient to cause a
localized zone of adhesive degradation.
 To characterize temperatures within the adhesive matrix and to determine whether
they are sufficiently high to result in one or more modes of adhesive
decomposition

To study the thermal degradation characteristics of the polymer adhesive, a
simultaneous Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis
(TGA) was performed using TA instruments equipment. The behavior of the polymer
adhesive was studied as it decomposes for a pure adhesive sample and a 0.1% carbon
black impregnated polymer sample. The heats of reaction were calculated for both the
samples. The results showed that the urethane oligomers started to decompose at around
220˚C. The polymer adhesive completely decomposed at 420˚C.
From the experimental results, it was observed that the strength of the Light
Activated Adhesive Gripper joint varies with respect to various parameters such as pulse
width, frequency, amount of carbon black, etc. A heat absorption analysis was carried out
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and the presumed heat absorption of the carbon black particles and the polymer adhesive
was calculated. The presumed heat absorption values were found out to be much higher
than the heats of reaction as the polymer decomposed during the DSC-TGA analysis. It
was also observed that the absorption coefficient increased substantially in the presence
of carbon black. It was assumed that the increase in absorption in the presence of carbon
black was used to generate heat in the joint. A closed form classical point source heat
generation model was used to check for the possible rise in temperature in the LAAG
joint in the presence of carbon black. It is well known that carbon black is a good
absorber of energy. It was initially assumed that the carbon black alone was absorbing the
radiation from the laser. The temperatures developed due to absorption of laser radiation
by carbon black alone were well below the required temperature of 220˚C to cause any
damage. Hence, it was concluded that in order to damage the joint, the entire matrix has
to absorb the radiation from the laser.
A Finite Element Analysis was performed to account for various shortcomings of
the classical heat generation model. It was assumed that the entire LAAG joint was
absorbing the energy from the laser. A transient heat study was performed for a specific
set of laser parameters and joint composition as a function of varying levels of laser pulse
frequency (75Hz, 100Hz, 120Hz, and 200Hz). The results showed that for high
frequencies, the baseline temperature in the LAAG joint increased dramatically and was
observed to be well beyond 220˚C. These results further validated that the entire matrix
had to absorb energy for the joint to fail as a result of heat generation.
Looking at the results from the Finite Element Analysis (FEA) in Solidworks and
the DSC-TGA results of the polymer adhesive, this report gives convincing evidence that
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the joint is being damaged due to the breakage of the polyurethane oligomers as the
baseline temperature in the entire system increases due to the short pulses of the laser. It
was concluded that the polymer adhesive begins to disintegrate due to decomposition of
the major constituent as the baseline temperature in the system crosses the minimum
threshold of about 220˚C.
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TABLE OF CONTENTS
List of Figures..................................................................................................................... ix
Acknowledgements ............................................................................................................. xiii

Chapter 1 INTRODUCTION .............................................................................................. 1
1.1 Photo Activated Adhesive Workholding (PAAW) .................................................. 1
1.2 Problem Statement ................................................................................................. 8
1.3 Thesis Goals and Objectives .................................................................................. 10
1.4 Impact on Engineering Science .............................................................................. 10
1.5 Impact on Engineering Practice.............................................................................. 11
Chapter 2 BACKGROUND ................................................................................................ 12
2.1 Photocurable Adhesives ......................................................................................... 12
2.1.1 Photo-curing Polymerization Process ........................................................... 13
2.1.2 Dymax® 602 Rev-A..................................................................................... 14
2.1.3 Chemistry of Adhesives such as Dymax 602 Rev-A .................................... 15
2.2 Experimental Study of LAAG Technology: ........................................................... 16
2.2.1 Nd:YAG Laser Absorption Experiment ....................................................... 17
2.2.2 Pre/Post Exposure Tensile Test Experiment ................................................. 25
2.2.3 Conclusions................................................................................................. 33
Chapter 3 LITERATURE REVIEW .................................................................................... 35
3.1 Carbon Black & Nd-YAG Laser: ........................................................................... 35
3.2 Summary ............................................................................................................... 44
Chapter 4 RESEARCH METHODOLOGY......................................................................... 46
4.1 Goals and Objectives ............................................................................................. 46
4.2 Methodology ......................................................................................................... 47
4.2.1 Differential Scanning Calorimetry (DSC) and Thermogravimetric
Analysis (TGA) ............................................................................................ 48
4.2.2 Radiation Absorption – Heat Generation Analysis ....................................... 49
4.2.3 CB Particle Laser Absorption – Heat Transfer Analysis ............................... 50
4.2.4 FEA Based Heat Transfer Analysis of an Adhesive Joint during the
Absorption of a Complete Pulse Train .......................................................... 54
Chapter 5 POLYMER ADHESIVE CHARACTERIZATION ............................................. 56
5.1 Introduction ........................................................................................................... 56
5.1.1 Differential Scanning Calorimetry (DSC) .................................................... 56
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5.1.2 Thermo-gravimetric Analysis ...................................................................... 59
5.2 Simultaneous DSC-TGA Analysis ......................................................................... 61
5.3 Results................................................................................................................... 65
Chapter 6 RADIATION ABSOPRTION – HEAT GENERATION ANALYSIS .................. 71
6.1 Introduction ........................................................................................................... 71
6.2 Results Obtained from the Nd:YAG Laser Absorption Experiment ........................ 71
6.3 Laser Absorption calculations of the Adhesive joint ............................................... 73
6.3.1 Calculation Methodology ............................................................................ 75
6.3.2 Absorption Plot from absorption values obtained ......................................... 82
6.4 Critical Observations from the Laser Radiation Absorption Experiment ................. 84
Chapter 7 CLASSICAL HEAT TRANSFER ANALYSIS ................................................... 87
7.1 Classical Model Description .................................................................................. 87
7.2 Model Formulations and Solution Approach .......................................................... 90
7.2.1 Model Formulation ...................................................................................... 90
7.2.2 Model Analysis ........................................................................................... 93
7.3 Analysis Results .................................................................................................... 96
7.4 Conclusions ........................................................................................................... 100
Chapter 8 FEA BASED HEAT TRASNFER ANALYSIS ................................................... 102
8.1 Introduction ........................................................................................................... 102
8.2 Model Description ................................................................................................. 103
8.3 FEA Analysis ........................................................................................................ 108
8.4 Analysis Results .................................................................................................... 110
Chapter 9 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK ........... 120
9.1 Conclusions ........................................................................................................... 120
9.2 Recommendations for Future Work ....................................................................... 122
BIBLIOGRAPHY ............................................................................................................... 125
Appendix A- Nd:Yag Laser Absorption Experiment Data…………………………………...132
Appendix B- Laser Degradation Pulse Experiment Data…………………………………….135
Appendix C- Laser Degradation Carbon & Gap Analysis Data……………………………...137
Appendix D: Laser Degradation Power Analysis Data……………………………………….141
Appendix E- Relevant Thermal Data…………………………………………………………142
Appendix F- Code Used For Classic Thermal Analysis……………………………………...143
Appendix G- Simpsons Rule Java Code………………………………………………………145
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LIST OF FIGURES

Figure 1-1 Cross Sectional View of Photo Activated Adhesive Workholding (PAAW)
System ........................................................................................................................ 2
Figure 1-2 Photocurable Adhesive Deposited on to the Top of the Gripper Pin .................... 2
Figure 1-3. Locator Pins Used To Orient the Workpiece ...................................................... 3
Figure 1-4. Workpiece Properly Mounted onto Gripper Pins Using Locator Pins for
Accurate Orientation ................................................................................................... 3
Figure 1-5. High Intensity Spot Lamp with Light Guides and Light Guide Shrouds ............. 4
Figure 1-6. Ultraviolet Light from the Light Guides Polymerizing the Adhesive .................. 5
Figure 1-7. Residue Left on the Surface of the Gripper Pin Post-Processing......................... 6
Figure 1-8. Gripper Pin Surface Post-Grinding Process ....................................................... 7
Figure 1-9. Processed Workpiece Surface Post-Removal of the Hardened Adhesive ............ 7
Figure 2-1. Acrylate Monomer [12] ..................................................................................... 14
Figure 2-2. (Meth) acrylate group on both sides of R group [12] .......................................... 15
Figure 2-3. Reaction Sequence for Generalized Difunctional Hydroxy and Isocyanate
Reagents...................................................................................................................... 16
Figure 2-4.Experimental Setup (from left to right: Laser probe, LAAG joint, Lead plate,
Radiometer probe) ....................................................................................................... 19
Figure 2-5. Lead Plate protecting the Radiometer Probe during de-bonding level laser
radiation ...................................................................................................................... 20
Figure 2-6. Optical Transmission Efficiency of a LAAG Joint comprised of adhesive (0%
Carbon Black) with regard to Nd:YAG Laser Radiation as a Function of Varying
Gap Thickness and Prior Exposure to De-bonding Level Laser Radiation .................... 23
Figure 2-7. Optical Transmission Efficiency of a LAAG Joint comprised of adhesive
(0.05% Carbon Black) with regard to Nd:YAG Laser Radiation as a Function of
Varying Gap Thickness and Prior Exposure to De-bonding Level Laser Radiation ....... 24
Figure 2-8. Optical Transmission Efficiency of a LAAG Joint comprised of adhesive
(0.1% Carbon Black) with regard to Nd:YAG Laser Radiation as a Function of
Varying Gap Thickness and Prior Exposure to De-bonding Level Laser Radiation ....... 24
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Figure 2-9. Axial Load Strength of an Adhesive Joint (.1% Carbon Black, 0.003 in Gap
Thickness) as a Function of Varying Exposure to Pulsed Nd:YAG Laser Radiation
(Pulse Energy: 1.84 J, Pulse Frequency 100 Hz) .......................................................... 29
Figure 2-10. Axial Load Strength of an Adhesive Joint (.1% Carbon Black, 0.003 in Gap
Thickness) Subject to 36.8 J of Pulsed Nd:YAG Laser Radiation (Pulse Energy: 1.84
J) Delivered at Varying Average Power Corresponding to Varying Transmission
Frequencies ................................................................................................................. 30
Figure 2-11. Axial Load Strength of an Adhesive Joint (.1% Carbon Black, 76.2 µm Gap
Thickness) Subject to 36.8 J of Pulsed Nd:YAG Laser Radiation (Average Power ≈
185 W) Delivered at varying Combinations of Pulse Energy and Transmission
Frequency ................................................................................................................... 31
Figure 2-12. Axial Load Strength of an Adhesive Joint (.05% Carbon Black) before and
after Exposure to 75 J of Pulsed Nd:YAG Laser Radiation (Pulse: 2.5J,
Transmission Frequency: 80 Hz, Average Power = 200 W) ......................................... 32
Figure 2-13. Axial Load Strength of an Adhesive Joint (.1% Carbon Black) before and
after Exposure to 36.9 J of Pulsed Nd:YAG Laser Radiation (Pulse: 2.31J,
Transmission Frequency: 80 Hz, Average Power = 184.8 W) ....................................... 32
Figure 2-14. Formation of Voids and Occlusions for 0.1% CB at 203.2 µm ......................... 34
Figure 5-1. DSC curve showing the Theoretical Behavior of a Sample ................................ 58
Figure 5-2. TGA Curve of Copper Sulphate Pentahydrate................................................... 60
Figure 5-3. TA Instruments Simultaneous DSC/TGA SDT Q-600 ....................................... 61
Figure 5-4. Pure Adhesive Sample (left) and Carbon Black Adulterated Adhesive (.1%)
Sample (right) ............................................................................................................. 62
Figure 5-5. Alumina Crucibles (60μL) used as Reference pan (right), Sample pan
(darkened) and Extra pan (left) .................................................................................... 64
Figure 5-6. TGA Plot of Clear Unadulterated Polymer Sample ............................................ 66
Figure 5-7. DSC Plot of Clear Unadulterated Polymer Sample ............................................ 67
Figure 5-8.TGA curve of 0.1% Carbon Black Adulterated Polymer Sample ........................ 68
Figure 5-9. DSC curve of 0.1% Carbon Black Adulterated Polymer Sample ........................ 69
Figure 6-1. Optical Transmission Efficiency of a LAAG Joint comprised of adhesive (0%
Carbon Black) with regard to Nd:YAG Laser Radiation as a Function of Varying
Gap Thickness and Prior Exposure to De-bonding Level Laser Radiation .................... 72