EFFECTS OF PRINTING CONDITIONS ON PROPERTIES OF POLYCARBONATE SAMPLES MADE BY FUSED FILAMENT FABRICATION PROCESS By Yishu Yan A thesis submitted to The Johns Hopkins University in conformity with the requirements for the degree of Master of Science in Engineering Baltimore, Maryland May, 2019 © Yishu Yan 2019 All rights reserved Abstract Fused filament fabrication (FFF) is one of the most popular 3D printing processes. However, the quality control of FFF remains as a challenge, resulting in wide variations of geometries and inferior mechanical properties compared to those made by traditional manufacturing methods. Multiple factors can influence the geometry and mechanical properties of parts fabricated by FFF, including model design, printing parameters, and environmental conditions. The quality control of FFF remains as a big challenge. To investigate these issues, we have fabricated and characterized samples made of amorphous homopolymer polycarbonates under controlled printing parameters and environmental conditions. Then, we have characterized three dimensional geometries and mechanical properties by x-ray micro-computed tomography (micro-CT) and tensile tests. Our studies show that large geometry and bonding strength variations appear from different printing parameters. Our infrared thermography showed that heating bed still resulted in over 3 ℃/mm temperature gradient within samples which led to warping while increasing the environmental temperature could mitigate this problem. In addition, micro-CT data showed that high environmental humidity would ii ABSTRACT induce significant porosity of the polycarbonate samples. We envision that the findings from our study will contribute to providing guidelines of selecting printing conditions for FFF printer users and manufactures. Primary Reader: Prof. Sung Hoon Kang Secondary Reader: Prof. Thao (Vicky) Nguyen iii Acknowledgements I would like to acknowledge the support of the National Science Foundation (DMREF-1628974) and the start-up fund from the Whiting School of Engineering at Johns Hopkins University. I give my most sincere gratitude to my research advisor Professor Sung Hoon Kang, for his patient guidance, valuable suggestions and enthusiastic encouragement of my research work. I gratefully acknowledge Mr. Lichen Fang who has been both a great mentor and important partner throughout this project. Also, I would like to express my great appreciation to Professor Thao (Vicky) Nguyen for her great help in this project and for being my thesis reader. I would like to thank Professor Kevin J. Hemker for his priceless insight and Mr. Ojaswi Agarwal for his help in lots of aspects. I would also like to acknowledge Professor Stavros Gaitanaros for allowing us to use his lab/facilities, and Ms. Sirui Bi, Mr. Emilio Bachtiar and Dr. Jonathan Seppala for help with experiment and helpful advice. A special gratitude goes to all the Kang Lab members for always being there to iv ACKNOWLEDGEMENTS support me during the whole research process. Without their help and inspiration, this project wouldn’t be realized to me. It’s a fortune for me to spend two inestimable years at Johns Hopkins University. I appreciate all the difficulties I have encountered, all the feelings I have gained, and all the people I have met here. I wish all of my colleagues and mentors the best in the future. v Dedication This thesis is dedicated to my beloved parents, Mrs. Hong Wang and Prof. Zongxin Yan. Your affection, love and encouragement make what I become today. I will always be your pride. vi Contents Abstract ii Acknowledgements iv List of Tables xi List of Figures xii 1 Introduction 1 1.1 3D printing ...................................................................................................... 1 1.1.1 3D printing introduction ........................................................................ 1 1.1.2 Fused filament fabrication ..................................................................... 2 1.1.3 Other 3D printing methods .................................................................... 4 1.1.4 3D printing materials ............................................................................. 5 1.2 Key problems .................................................................................................. 7 1.2.1 3D geometrical evaluation ..................................................................... 7 1.2.2 Warping and delamination ..................................................................... 8 vii CONTENTS 1.2.3 Environmental conditions .................................................................... 10 1.3 Approaches .................................................................................................... 11 1.2.1 Micro-CT evaluation ............................................................................ 11 1.2.2 Mitigate warping .................................................................................. 12 1.2.3 Expected outcome ................................................................................ 13 1.4 Outline of thesis ............................................................................................ 15 2 Sample preparation 16 2.1 System set up ................................................................................................. 16 2.1.1 Material .............................................................................................. 16 2.1.2 Enclosure............................................................................................ 17 2.1.3 Environmental conditions control system .......................................... 18 2.2 Printing conditions ........................................................................................ 21 2.3 Conclusion of the Chapter ............................................................................. 22 3 Evaluation methods 23 3.1 Micro-CT evaluation ..................................................................................... 23 3.1.1 Micro-CT calibration ........................................................................... 23 3.1.2 3D geometric information .................................................................... 24 viii CONTENTS 3.1.3 Circular fitting ...................................................................................... 26 3.2 Mechanical test .............................................................................................. 27 3.2.1 Specimens preparation ......................................................................... 27 3.2.2 Tensile test ........................................................................................... 29 3.3 Conclusion of the Chapter ............................................................................. 30 4 Result 1: Printing parameters 31 4.1 Layer thickness .............................................................................................. 31 4.1.1 Geometrical properties ......................................................................... 31 4.1.2 Mechanical properties .......................................................................... 33 4.2 Nozzle temperature ....................................................................................... 35 4.2.1 Infrared thermography ......................................................................... 35 4.2.2 Geometrical properties ......................................................................... 37 4.2.3 Mechanical properties .......................................................................... 40 4.3 Nozzle movement speed ................................................................................ 41 4.3.1 Geometrical properties ......................................................................... 41 4.3.2 Mechanical properties .......................................................................... 43 4.4 Conclusion of the Chapter ............................................................................. 44 5 Result 2: Environmental conditions 46 ix CONTENTS 5.1 Environmental temperature ........................................................................... 46 5.1.1 Surface performance ............................................................................ 46 5.1.2 Warping................................................................................................ 47 5.2 Environmental humidity ................................................................................ 50 5.3 Conclusion of the Chapter ............................................................................. 51 6 Conclusion and future work 52 6.1 Conclusion ..................................................................................................... 52 6.2 Prospective work ........................................................................................... 53 Bibliography 55 Vita 64 x List of Tables 1 Average heating time to reach certain temperature 19 2 Relative humidity change with time after turning on lab compressed air 28 3 Temperature of print head area 37 xi List of Figures 1.1 Principle of fused filament fabrication process 4 1.2 Micro-CT image of internal defects inside of FFF parts 8 1.3 Schematic image of warping effect 9 1.4 Principle components of a microcomputed tomography scanner 12 2.1 System set up of a FFF printer 17 2.2 Fan heater and temperature controller 18 2.3 Relative humidity change with time after turning on lab compressed air 20 2.4 Schematic image of nozzle temperature, layer thickness, and nozzle