Analysis of Pressurized Cavity on Replication of Micro-Patterns with Injection Molding

학위논문 (박사)-- 서울대학교 대학원 : 기계항공공학부, 2016. 8. 이우일.First, we studied the effect of the cavity air pressure on the replication of micro-patterns in injection molding. When pressure is applied to the cavity air, the pressure at the flow front is increased and air surging in the mold channel occurs according to the injection rate and the cavity pressure. The pressure of the air trapped inside the micro-pattern is increased due to the decrease in volume in accordance with the progress of the pattern replication. The pressure gradient to the pattern direction with the cavity air pressure is larger than the case of non-pressurized. Therefore, the hesitation is reduced with the cavity air pressure resulting in the improvement of replication of the microscopic pattern. In this investigation, we carried out experiments for molds with a macroscopic pattern (ribs) and a microscopic pattern. In order to evaluate the quality of replication, we measured the filling heights of patterns with different ratio of the cavity air pressure to the injection pressure. The experimental results showed that the application of cavity pressure helps the replication of patterns both for macroscopic and microscopic scales. Second, numerical study was performed on the fluid flow with pressurized cavity air. The air flowing gap is modeled in order to implement the effect of the air surging. The pressure gradient through the micro-pattern was calculated when the flow front passes the micro-pattern. Numerical analysis was performed with respect to the various injection rates (0.24, 0.36, 0.48m/s) and a variety of mold inner pressure (0.1, 1, 4MPa). The height of the micro-pattern according to the injection speed and the cavity air pressure was analyzed for comparing the enhancement of replication.CHAPTER 1 INTRODUCTION 1 1.1 OVERVIEW 1 1.2 EFFECT OF THE CAVITY AIR PRESSURE 2 1.3 HESITATION EFFECT 5 1.4 OBJECTIVES OF THE RESEARCH 7 CHAPTER 2 MATERIAL AND PROCESS 9 2.1 MICRO INJECTION MOLDING 9 2.2 POLYMERS 12 2.2.1 Polypropylene(PP) 12 2.2.2 Polymethylmethacrylate(PMMA) 14 2.3 PROCESS FOR PRESSURIZING THE AIR 17 2.3.1 Injection molding machine 17 2.3.2 Pressurization machine 18 2.3.3 Mold sealing 21 2.4 MEASUREMENT OF PATTERN HEIGHT 25 CHAPTER 3 MECHANICAL TEST OF SPECIMENS WITH PRESSURIZED CAVITY AIR 27 3.1 COMPARE THE INNER AND SURFACE OF SPECIMEN 27 3.2 TENSILE STRENGTH TEST 31 CHAPTER 4 EXPERIMENTAL ANALYSIS ON REPLICATION OF MACRO- AND MICRO-FEATURES 35 4.1 CHANGES IN THE MACROSCOPIC FLOW FRONT 35 4.2 MEASUREMENT OF THE AIR SURGING 38 4.3 MACROSCOPIC RIB PATTERN 44 4.3.1 Dimension and configuration of pattern 44 4.3.2 Injection molding conditions for rib pattern 44 4.3.3 Results of rib pattern 45 4.4 MICROSCOPIC LINE PATTERNS 47 4.4.1 Direction of resin flow 47 4.4.2 Dimension and configuration of micro-patterns 48 4.4.3 Injection molding conditions for micro line patterns 49 4.4.4 Results of micro line patterns (parallel direction) 51 4.4.5 Results of micro line patterns (perpendicular direction) 54 4.5 MICROSCOPIC PRISM PATTERN 68 4.5.1 Direction of resin flow and injection conditions 68 4.5.2 Dimension and configuration of prism pattern 70 4.5.3 Results of prism pattern 72 CHAPTER 5 NUMERICAL ANALYSIS ON EFFECT OF PRESSURIZED CAVITY AIR 75 5.1 SOLUTION ALGORITHMS OF NUMERICAL SIMULATION 75 5.1.1 Governing equations 75 5.1.2 Solution algorithms of flow with moving free surfaces 80 5.1.3 Pressure-velocity coupling scheme 83 5.1.4 Rheological behavior of polymer melt 84 5.2 MODELING AND CONDITIONS FOR NUMERICAL ANALYSIS 86 5.2.1 Analysis domain 86 5.2.2 Boundary conditions 87 5.3 RESULTS OF NUMERICAL ANALYSIS 89 5.3.1 Air surging effect 90 5.3.2 Comparison of pressure gradient for direction of pattern filling 91 5.3.3 Rheological behavior near the micro-pattern 101 5.3.4 Improvement on replication of micro-pattern 103 SUMMARY AND CONCLUSIONS 106 REFERENCES 108 초록 111Docto