Development of Innovative Gas- Assisted Foam Injection Molding
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Development of Innovative Gas- Assisted Foam Injection Molding Technology By Peter Ungyeong Jung A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Department of Mechanical and Industrial Engineering University of Toronto © Copyright by Peter Ungyeong Jung 2013 Development of Innovative Gas-Assisted Foam Injection Molding Technology Peter Ungyeong Jung Degree of Doctor of Philosophy, 2013 Department of Mechanical and Industrial Engineering University of Toronto ABSTRACT Injection molding technology is utilized for a wide range of applications from mobile phone covers to bumper fascia of automotive vehicles. Foam injection molding (FIM) is a branched manufacturing process of conventional injection molding, but it was designed to take advantage of existing foaming technology, including material cost saving and weight reduction, and to provide additional benefits such as improvement in dimensional stability, faster cycle time, and so on. Gas-assisted injection molding (GAIM) is another supplemental technology of injection molding and offers several advantages as well. This thesis study takes the next step and develops innovative gas-assisted foam injection molding (GAFIM) technology, which is the result of a synergistic combination of two existing manufacturing technologies, FIM and GAIM, in order to produce a unique thermoplastic foam structure with proficient acoustic properties. The foam structure manufactured by GAFIM consists of a solid skin layer, a foam layer, and a hollow core; and its 6.4-mm thick sample outperformed the conventional 22-mm thick polyurethane foam in terms of the acoustic absorption coefficient. With respect to ii foaming technology, GAFIM was able to achieve a highly uniform foam morphology by completely decoupling the filling and foaming phases. Moreover, the additional shear and extensional energies from GAFIM promoted a more cell nucleation-dominant foaming behavior, which resulted in higher cell density and smaller cell sizes with both CO2 and N2 as physical blowing agents. Lastly, it provided more direct control of the degree of foaming because the pressure drop and pressure drop rate was controlled by a single parameter, that being the gas injection pressure. In summary, innovative, gas-assisted foam injection molding technology offers not only a new strategy to produce acoustically functioning thermoplastic foam products, but also technological advantages over the conventional foam injection molding process. Gas-assisted foam injection molding can become the bedrock for more innovative future applications. iii ACKNOWLEDGEMENT First of all, I would like to thank God the Father for presenting this opportunity to me six years ago and giving me courage to accept this challenging task. I truly believe that He walked this long journey with me and I could not have finished it without His love, guidance, and blessings. I cannot say enough how grateful I am for my supervisor, Prof. Chul B. Park, for his excellent guidance and the valuable life lessons that I learned from him. He has been very supportive and patient throughout my program and presented numerous opportunities for me to mature as a researcher and a person. I also would like to thank Prof. Hani E. Naguib for being my Ph.D. thesis committee member and always encouraging me as one of his own students. I am also very appreciative to Prof. Chandra for his time and effort as my Ph.D. thesis committee member and his very valuable technical advice. I am grateful for Prof. Ashgriz and Prof. Turng for becoming my exam committee members in such a short notice and for their valuable feedback. I am indebted to my colleagues at the Microcellular Plastics Manufacturing Lab for sharing my ups and downs on daily basis, which is not an easy task. I sincerely thank my previous and current colleagues, Dr. Anson Wong, Reza Nofar, Kamlesh Majithiya, Nemat Hossieny, Hassan Mahmood, Dr. Amir Ameli, Davoud Jahani, Dr. Saleh Amani, Konstantin Kovalski, Medhi Saniei, Dr. Jing Wang, Dr. Sunny Leung, Dr. Mohamed Hassan, Dr. Yanting Guo, Lun Howe Mark, Mo Xu, Ali Rizvi, Alireza Naeini, Vahid Shaayegan, Weidan Ding, Anna Zhao, Sai Wang, Dr. Reza Bazegari, Dr. Adhikary Kamal. I am also grateful to the many undergraduate students who have assisted me in iv my research throughout the years, especially, Hyunwoo Lee, Taewon Park, and Chenkun Li. There are two of my colleagues with whom I have shared a lot of struggles and frustrations; together, we were able to overcome obstacles, and they have supported me incredibly throughout the years. Thus, my special thanks go to Raymond Chu and Dr. Changwei Zhu. I was very fortunate to get to know so many hyungs and establish valuable friendships with them throughout the years. They helped me to get through difficult times of my life, and shared their personal experiences and wisdoms with me. I would like to thank Dr. Kevin Y.H. Lee, Dr. Richard Eungkee Lee, Dr. Ryan S.G. Kim, Dr. Yongark Moon, Dr. Myungjae Lee, Dr. Kyungmin Lee, Dr. John W.S. Lee, Dr. Taekyun Lee, and Dr. Patrick Lee. I was also privileged to share special friendships with Esther Lee, Prof. Dongwoo Cho, Prof. Bosung Shin, Dr. Youngseok Kim, and Prof. Simon Park. Last, but definitely not the least, I would like to thank very special people in my life. I owe a big thank to Donna Lee for being a huge part of my life and inspiring me with her caring support, positive energy, and love. I cannot thank enough my beloved family, my dad, mom, and sister, Maria, for their unconditional love, endless support, having faith in me when I was doubting myself, encouraging me when I was struggling, and motivating me every day to try my best at everything I do to become a better person. I really am indebted to my mom, especially, for packing my lunch (and dinner sometimes) every weekday for the last six years, which have been fuel to my engine. I thank everyone else who helped me to get through this tall, challenging task. v TABLE OF CONTENTS ABSTRACT………………….. ........................................................................................ II ACKNOWLEDGEMENT .............................................................................................. IV TABLE OF CONTENTS ............................................................................................... VI LIST OF TABLES………….. ...................................................................................... XII LIST OF FIGURES………. ........................................................................................ XIII LIST OF SYMBOLS. .................................................................................................. XIX NOMENCLATURE………………………………………………………………….XXI CHAPTER 1 INTRODUCTION ................................................................................ 1 1.1 Thermoplastic Foams ............................................................................. 1 1.2 Open-Cell and Closed-Cell Foams ........................................................ 1 1.3 Thermoplastic Foam Processing ............................................................ 1 1.4 Injection Molding ................................................................................... 2 1.5 Foam Injection Molding ......................................................................... 4 1.6 Acoustic Thermoplastic Foams .............................................................. 5 vi 1.7 Research Motivation .............................................................................. 6 1.8 Thesis Objectives and Scope of Research .............................................. 7 1.9 Organization of Thesis ........................................................................... 8 CHAPTER 2 LITERATURE REVIEW AND THEORETICAL BACKGROUND …………………………..……………………………………….11 2.1 Thermoplastic Foam Processing ....................................................... 11 2.1.1 Fundamentals of Blowing Agents ........................................................ 11 2.1.2 Formation of Polymer/Gas Solution .................................................... 14 2.1.3 Theoretical Principles of Cell Nucleation and Growth Mechanisms ... 17 2.2 Manufacturing of Open-Celled Foam Structures ........................... 21 2.2.1 Open-Celled Structures with Foam Extrusion Technology ................. 21 2.2.2 Porous Structures by using Sacrificial Fillers ...................................... 22 2.3 Foam Injection Molding Technologies ............................................. 23 2.3.1 Conventional Foam Injection Molding and Microcellular Injection Molding Technologies ......................................................................... 23 2.3.2 Low Pressure and High Pressure Foam Injection Molding Technologies ………………………………………………………………………...25 2.3.3 Investigation of Foaming Behaviors in Foam Injection Molding Using Mold Pressure Profile ........................................................................... 27 2.3.4 Effect of Gas Counter Pressure on Foam Injection Molding Behavior 29 vii 2.4 Gas-Assisted Injection Molding ........................................................ 30 2.4.1 Conventional Gas-Assisted Injection Molding Technology ................ 30 2.4.2 Effect of Gas Channel .......................................................................... 32 2.4.3 Computer Simulation Analysis ............................................................ 33 2.4.4 Effect of GAIM on Polymer Crystalline Morphology ......................... 35 2.5 Acoustic Absorption and Insulation