analysis of the laser powder bed fusion additive manufacturing process through experimental ...

176 Pages·2016·8.3 MB·English

The Pennsylvania State University
The Graduate School
Department of Mechanical Engineering
ANALYSIS OF THE LASER POWDER BED FUSION ADDITIVE
MANUFACTURING PROCESS THROUGH EXPERIMENTAL
MEASUREMENT AND FINITE ELEMENT MODELING
A Dissertation in
Mechanical Engineering
by
Alexander Jay Dunbar
2016 Alexander Jay Dunbar
©
Submitted in Partial Fulfillment
of the Requirements
for the Degree of
Doctor of Philosophy
May 2016
ii
The dissertation of Alexander Jay Dunbar was reviewed and approved* by the following.
Pan Michaleris
Professor of Mechanical Engineering
Dissertation Adviser
Chair of Committee
Timothy W. Simpson
Professor of Mechanical and Industrial Engineering
Qian Wang
Professor of Mechanical Engineering
Allison Beese
Assistant Professor of Materials Science and Engineering
Karen Thole
Head of the Department of Mechanical and Nuclear Engineering
*Signatures are on file in the Graduate School.
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Abstract
The objective in this work is to provide rigourous experimental measurements
to aid in the development of laser powder bed fusion (LPBF) additive manufacturing
(AM). A specialized enclosed instrumented measurement system is designed to provide
in situ experimental measurements of temperature and distortion. Experiments include
comparisons of process parameters, materials and LPBF machines. In situ measurements
of distortion and temperature made throughout the build process highlight inter-layer
distortion effects previously undocumentedfor laser powderbedfusion. Results from these
experiments are also be implemented in the development and validation of finite element
models of the powder bed build process.
Experimental analysis is extended from small-scale to larger part-scale builds
where experimental post-build measurements are used in analysis of distortion profiles.
Experimental results provided from this study are utilized in the validation of a finite
element model capable of simulating production scale parts. The validated finite element
model is then implemented in the analysis of the part to provide information regarding the
distortion evolution process. A combination of experimental measurements and simulation
results are used to identify the mechanism that results in the measured distortion profile
for this geometry.
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Optimization of supportstructureprimarilyfocuses ontheminimization ofmaterial
use and scan time, but no information regarding failure criteria for support structure
is available. Tensile test samples of LPBF built support structure are designed, built,
and tested to provide measurements of mechanical properties of the support structure.
ExperimentaltestsshowthatLPBFbuiltsupportstructurehasonly30-40%oftheultimate
tensile strength of solid material built in the same machine. Experimental measurement
of LPBF built support structure provides clear failure criteria to be utilized in the future
design and implementation of support structure.
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Table of Contents
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii
Chapter 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Prior work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.1 Related Work in Welding . . . . . . . . . . . . . . . . . . . . . 2
1.1.2 Direct Deposition Additive Manufacturing . . . . . . . . . . . . 3
1.1.3 Laser Powder Bed Fusion Additive Manufacturing . . . . . . . 6
1.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.3 Objective in this Research . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Chapter 2. Measurement of Experimental In Situ Distortion and Temperature
Measurements During the Laser Powder Bed Fusion Additive
Manufacturing Process . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.2 Description of Experimental Procedure . . . . . . . . . . . . . . . . . . 21
vi
2.2.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.2 Measurement Equipment . . . . . . . . . . . . . . . . . . . . . 26
2.2.3 Processing Parameters . . . . . . . . . . . . . . . . . . . . . . . 28
2.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.5 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Chapter 3. Analysis of In Situ Measurements of Distortion and Temperature for the
Laser Powder Bed Fusion Additive Manufacturing Process . . . . . . . 40
3.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.3 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.3.1 Measurement Equipment . . . . . . . . . . . . . . . . . . . . . 46
3.3.2 Description of Experimental Cases . . . . . . . . . . . . . . . . 47
3.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.4.1 Comparison of Ti-6Al-4V and Inconel®718 Builds . . . . . . . 52
3.4.2 Comparison Between EOS M280 and Renishaw AM 250 Laser
Powder Bed Fusion Machines . . . . . . . . . . . . . . . . . . . 61
3.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.6 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
vii
Chapter 4. Experimental Validation of Finite Element Modeling for Laser Powder
Bed Fusion Deformation . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.3 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
4.3.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . 73
4.3.1.1 Description of Experimental Builds . . . . . . . . . . 74
4.3.1.2 Description of Measurement Equipment . . . . . . . . 78
4.3.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . 79
4.4 Powder Bed Fusion Simulation . . . . . . . . . . . . . . . . . . . . . . 85
4.4.1 Thermal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.4.2 Mechanical Analysis . . . . . . . . . . . . . . . . . . . . . . . . 86
4.4.3 Numerical implementation . . . . . . . . . . . . . . . . . . . . . 88
4.5 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.5.1 Model Comparison To Experimental Measurements . . . . . . . 92
4.5.2 Substrate Deformation . . . . . . . . . . . . . . . . . . . . . . . 97
4.5.3 Extension of Rotating Scan Pattern Case . . . . . . . . . . . . 102
4.5.4 Distortion Evolution in Time . . . . . . . . . . . . . . . . . . . 104
4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
4.7 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
viii
Chapter 5. ExperimentalMeasurementofMechanicalPropertiesofLaserPowderBed
Fusion Built Support Structure . . . . . . . . . . . . . . . . . . . . . . 113
5.1 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
5.3 Description of Experimental Procedure . . . . . . . . . . . . . . . . . . 116
5.3.1 Design of Experimental Test Pieces . . . . . . . . . . . . . . . . 116
5.3.2 Processing parameters . . . . . . . . . . . . . . . . . . . . . . . 121
5.3.3 Measurement Procedure . . . . . . . . . . . . . . . . . . . . . . 122
5.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
5.6 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Chapter 6. Conclusions And Future Work . . . . . . . . . . . . . . . . . . . . . . . 138
6.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
6.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
ix
List of Tables
2.1 Description of experimental cases . . . . . . . . . . . . . . . . . . . . . . . 30
2.2 Post-process measurements of the cases . . . . . . . . . . . . . . . . . . . 36
3.1 Description of experimental cases . . . . . . . . . . . . . . . . . . . . . . . 51
3.2 Post-process measurements for Case 1 (Ti-6Al-4V) and Case 2 (Inconel®
718) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.3 Post-process measurements for Case 3 (Ti-6Al-4V) and Case 4 (Inconel®
718) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.4 Post-process measurements of Case 1 (EOS M280) and Case 5 (Renishaw
AM250) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.1 Description of Experimental Cases . . . . . . . . . . . . . . . . . . . . . . 78
4.2 Case 1 (rotating scan pattern) peak distortion comparison by percent
deviation with experimental measurements . . . . . . . . . . . . . . . . . 82
4.3 Case 2 (constant scan pattern) peak distortion comparison by percent
deviation with experimental measurements . . . . . . . . . . . . . . . . . 83
4.4 Temperature dependent thermal properties of solid Inconel® 718 [1,2] . . 88
4.5 Temperature dependent mechanical properties of solid Inconel® 718 [3] . 89
4.6 As-used constant material properties and processing conditions . . . . . . 89
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4.7 Comparison of experimental measurements and simulation results for Case
1 (Rotating scan pattern). The error is averaged at each nodal location
in the FE model along the height of the part for each measurement
location(Figure 4.4). Measurements are normalized by the experimental
distortion measurement at each height . . . . . . . . . . . . . . . . . . . . 95
4.8 Comparison of experimental measurements and simulation results for Case
2 (Constant scan pattern). The error is averaged at each node in the
FE model along the height of the part for each measurement location
(Figure 4.4). Measurements are normalized by experimental distortion
measurement at each height . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.9 Comparison of experimental measurements and simulation results for Case
2 (Constant scan pattern) with and without a flexible substrate. The error
is averaged at each node in the FE model along the height of the part for
each measurement location (Figure 4.4). Measurements are normalized by
experimental distortion measurement at each height . . . . . . . . . . . . 102
5.1 Description of tensile samples . . . . . . . . . . . . . . . . . . . . . . . . . 121
5.2 Description of experimental cases (NA - Not Applicable) . . . . . . . . . . 122
5.3 Averaged Results for Tensile Tests . . . . . . . . . . . . . . . . . . . . . . 124