Development of a Pneumatic Impact Micro-Injection Molding System
Date Issued
2005
Date
2005
Author(s)
Nian, Shih-Chih
DOI
zh-TW
Abstract
Abstract
In recent years, interest has been growing in fabrication of polymer-based Micro-Electro-Mechanical Systems (MEMS). Such products show great potential in optical and biological applications. Among polymer-based fabrication methods, micro-injection molding is versatile, precise, cost-effective, and highly productive.
Because micro-injection molding differs greatly from the traditional injection molding, a new design and construction is needed. A novel pneumatic impact micro-injection machine is constructed in this study. The molding characteristics including the filling patterns, processing effects, operation window, and micro-structure replication are investigated. The first part of this thesis presents the design concept, construction, process, and characteristics of the pneumatic impact micro-injection machine. The second part displays the flow visualization of filling a spiral cavity implemented with transparent window with aid of colored billets and high speed video camera during pneumatic impact micro-injection molding. The third part investigates the effects of processing conditions on the spiral flow using the pneumatic impact micro-injection molding machine. In the fourth part, test-sheet molds of different depths implemented with rapid mold heating/cooling system was constructed. The operation windows with various mold temperatures are defined for such impact micro-injection molding. The shrinkage and birefringence of molded parts are also studied. Finally, the molding of an optical component with feature of micro-lens array on surface was carried out. The effects of processing conditions on the quality of replication of microstructure are investigated and discussed.
The micro-injection molding machine can achieve an impact speed of 6500 mm/s. With the flow visualization facility observing the filling spiral cavity, the colored melt in the back soon take lead indicating that fountain flow is dominant. The flow length is deeper cavity is found longer, and the mold temperature significantly affects to the molding of thin part. The air pressure and hammer mass determines the impact energy and the filling process during impact micro-injection molding of spiral parts. From the molding of the test-sheets, it is found that thicker cavity and reasonably low mold temperature result in larger operation window. High mold temperature prevents short-shot, but causes serious shrinkage. From the molding of the optical components with micro-features, the micro lenses are found better replicated with high holding pressure, and are poorly replicated with high mold temperature and low holding pressure.
Subjects
衝擊射出
流動觀察
衝擊式微射出成型
射出成型
微射出成型
injection molding
micro-injection molding
impact type micro-injection molding
pneumatic impact micro-injection molding
flow visualization
Type
thesis