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DTIC AD1005525: Development of In-Mold Assembly Methods for Producing Mesoscale Revolute Joints PDF

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ABSTRACT Title of Document: Development of In-Mold Assembly Methods for Producing Mesoscale Revolute Joints Arvind Ananthanarayanan, Doctor of Philosophy, 2009 Directed By: Professor Satyandra K.Gupta Department of Mechanical Engineering In-mold assembly is a promising process for producing articulated joints. It utilizes injection molding to automate assembly operations, which may otherwise require high labor times for production. Since injection molding is a high throughput process, in-mold assembly holds considerable promise in bulk production of assembled parts. However, current in-mold assembly methods cannot be used for manufacturing in- mold assembled products at the mesoscale. This is because the process changes considerably when the sizes of the molded parts are reduced. The premolded component in a mesoscale joint consists of miniature features. Hence, when a high temperature, high pressure polymer melt is injected on top of it, it is susceptible to plastic deformation. Due to presence of a mesoscale premolded component which is susceptible to deformation, traditional shrinkage models alone can not be used to characterize and control the clearances. This dissertation identifies and addresses issues pertaining to in-mold assembly of revolute joints at the mesoscale. First, this dissertation identifies defect modes which are unique to in-mold assembly at the mesoscale. Then it develops mold design templates which can be used for manufacturing in-mold assembled mesoscale revolute joints. Further, issues related to the deformation of the mesoscale premolded component are identified. Two novel mold design solutions to realize mesoscale in-mold assembled revolute joints are presented. The first involves use of mold inserts to constrain the premolded component to inhibit its deformation. The second involves use of a bi-directional flow of the polymer melt over the premolded component to balance the deforming forces experienced by it. Finally, methods to predict and control clearances that would be obtained in mesoscale in-mold assembled revolute joints are presented. To demonstrate the utility of the tools built as part of this research effort, a case study of a miniature robotic application built using mesoscale in-mold assembly methods is presented. This dissertation provides a new approach for manufacturing mesoscale assemblies which can lead to reduction in product cost and create several new product possibilities. Development of In-Mold Assembly Methods for Producing Mesoscale Revolute Joints By Arvind Ananthanarayanan Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2009 Advisory Committee: Professor Satyandra K. Gupta, Chairman/Advisor Associate Professor Hugh A. Bruck Professor Abhijit Dasgupta Associate Professor Srinivasa Raghavan Dr. Chandrasekhar Thamire © Copyright by Arvind Ananthanarayanan 2009 Acknowledgements First and foremost I would like to thank my parents for their constant support and inspiration. Without this every step of graduate school would have been impossible. I would also like to thank my grandparents for their love and affection. Professor Satyandra K. Gupta, my advisor and mentor has been a constant source of inspiration during my stay in graduate school. It would have been impossible to carry out this research effort if not for his motivation and patient mentoring. I would also like to thank Professor Hugh Bruck for giving me extremely valuable feedback about my research along every step of the way. He taught me to think critically and attack a problem with an unbiased approach. I would also like to thank my committee members Professor Abhijit Dasgupta, Professor Srinivasa Raghavan and Dr. Chandrasekhar Thamire for providing me with valuable insight on my research. This work was supported by the Army Research Office through MAV MURI Program (Grant No. ARMY W911NF0410176). I am thankful to the University of Maryland, the Mechanical Engineering Department for the opportunity and support. I would also like to thank my colleagues and friends in the Advanced Manufacturing lab – Alan, Arvind, Arun, Dan, Dominik, John and Wojciech who provided a very friendly and motivating work environment. Anita, Guru, Leicester, Patrick and Sergej helped me with the several experiments I had to conduct. My roommates, Anand and Ashis, provided for a friendly and peaceful environment at home throughout my stay in graduate school. I would also like to thank Aftab, Gaurav and Rishi who fueled some interesting research ideas during some of our passionate discussions at evening dinner parties. Special thanks must go out to Vivek, ii Chrisy and Prabha for providing me with company and making sure I never felt lonely away from home. Finally I would like to thank my cousins Archana and Aiswarya for their constant love and affection. They have never failed to motivate me during the many troubled times I have had during my stay at graduate school. iii Table of Contents Acknowledgements.......................................................................................................ii Table of Contents.........................................................................................................iv Index of Figures...........................................................................................................ix 1 Introduction...........................................................................................................1 1.1 Background....................................................................................................1 1.2 Motivation and Challenges............................................................................7 1.3 Dissertation Goals and Scope......................................................................10 2 Literature Review................................................................................................15 2.1 Advances in In-Mold Assembly..................................................................17 2.2 Prediction of Shrinkage in Injection Molding.............................................23 2.3 Mold Deformation during Injection Molding..............................................31 2.4 Fluid Structure Interaction for Non-Newtonian Flows................................36 2.5 Real-time Measurement of Injection Molding Process...............................42 2.6 Weld-lines in Injection Molded parts..........................................................49 2.7 Summary......................................................................................................60 3 Issues in In-Mold Assembly at the Mesoscale....................................................63 3.1 Motivation....................................................................................................63 3.2 Defects Modes at the Mesoscale..................................................................63 3.2.1 Cavity Shape Change Methods...........................................................63 3.2.2 Molding Sequence for Mesoscale In-Mold Assembly........................65 3.2.3 Summary.............................................................................................71 3.3 Experimental Methods for Understanding Size Effects...............................73 iv 3.4 Generalized Framework for Modeling Interaction between Melt Flow and Premolded Component.................................................................................78 3.4.1 Definition of Deformation Problem for Premolded Components.......78 3.4.2 Mechanics-based Modeling of Plastic Deformation in Premolded Components........................................................................................79 3.5 Modeling Premolded Component Deformation...........................................83 3.5.1 Force on Premolded Component........................................................83 3.5.2 Non-linear Deformation of Premolded Component...........................86 3.6 Results and Discussion................................................................................87 3.7 Summary......................................................................................................94 4 Characterization and Control of Plastic Deformation in Mesoscale Premolded Components Using Single Gated Mold Design..........................................................96 4.1 Motivation....................................................................................................96 4.2 Development of a Novel Mold for Realizing Mesoscale Revolute Joints...98 4.3 Experimental Implementation of the Mechanics-Based Model for Controlling Plastic Deformation in Premolded Components....................102 4.3.1 Experimental Configuration..............................................................102 4.3.2 Development of a Predictive Model for Estimating Premolded Component Deformation..................................................................104 4.3.3 Comparison of Modeling Results with Experimental Data..............106 4.4 Results and Discussion..............................................................................108 4.5 Summary....................................................................................................112 v 5 Characterization and Control of Plastic Deformation in Mesoscale Premolded Components Using Multi Gated Mold Design.........................................................114 5.1 Motivation..................................................................................................114 5.2 Bi-directional Filling for In-mold Assembly.............................................115 5.3 Analysis of Weld-lines in In-Mold Assembled Mesoscale Revolute Joints 118 5.4 Experimental Setup....................................................................................121 5.5 Mechanics-based Model for Predicting the Plastic Deformation as a Function of Flow Front Progression..........................................................124 5.5.1 Overview of Approach......................................................................124 5.5.2 Force Modeling on Premolded Component......................................127 5.5.3 Computing Premolded Component Deformations............................128 5.5.4 Total Flow Front Progression...........................................................129 5.5.5 Iterative Computational Modeling for Obtaining Net Plastic Deformation......................................................................................130 5.6 Results and Discussion..............................................................................132 5.7 Summary....................................................................................................141 6 Characterization and Control of Pin Diameter..................................................143 6.1 Motivation..................................................................................................143 6.2 Clearances at the Mesoscale......................................................................144 6.3 Experimental Setup....................................................................................151 6.4 Results and Discussion..............................................................................156 6.5 Summary....................................................................................................166 vi 7 Design and Development of In-mold Assembled Miniature Robot.................168 7.1 Motivation..................................................................................................168 7.2 Challenges in Manufacturing Miniature Robots........................................168 7.3 Robot Redesign for In-Mold Assembly.....................................................170 7.4 Design of In-Mold Assembly Methods......................................................172 7.4.1 Selecting the Molding Sequence.......................................................173 7.4.2 Selection of the Mold Filling Strategy..............................................175 7.4.3 Selection of Design Parameters........................................................175 7.4.4 Mold Design......................................................................................178 7.5 Results and Discussion..............................................................................180 7.6 Summary....................................................................................................186 8 Conclusions.......................................................................................................188 8.1 Intellectual Contributions...........................................................................188 8.1.1 Identification of Defect Modes Specific to Mesoscale In-Mold Assembly...........................................................................................188 8.1.2 Development of Mold Design Solutions for Realizing In-Mold Assembly of Mesoscale Revolute Joints...........................................189 8.1.3 Characterization of Pin Diameter in In-Mold Assembled Mesoscale Revolute Joints..................................................................................191 8.2 Anticipated Benefits...................................................................................191 8.3 Future Directions.......................................................................................192 8.3.1 Development of Mold Design Templates to Manufacture Other Classes of Mesoscale Articulating Joints..........................................193 vii

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