Micro-Injection Molding
Micro-Injection Molding refers to molding structure and the nanometer to micron level. (RDC 8/13/2009)
“Widely used mass-production methods of polymeric materials such as injection molding, however, require significant modification to adapt to micro molding application. One of the hurdles limiting the current technical capability in micro injection molding is that the molten polymer in a tiny cavity instantaneously freezes upon contacting the relatively cold cavity wall. The problem gets worse when micro features with higher aspect ratio are to be molded. The main objective of the proposed research is to develop a novel technology for successful micro injection molding with respect to lower cycle time, better replication and better mechanical and optical quality as compared to the existing technology. This objective will be accomplished by rapidly heating the mold surface so that the melt can fill the cavity isothermally and yet be processed within the normal injection molding cycle time. This isothermal filling not only facilitates complete filling of high-aspect-ratio micro features with lower melt temperature and slower filling rate than those currently used but is also expected to improve dimensional accuracy and mechanical and optical properties of micro-featured articles. Development of the integrated technology capable of replicating high-aspect-ratio micro features with lateral dimension less than 20 nm will push the current technical envelope of micro injection molding further into those areas that have so far predominated by etching- and lithography- based fabrications.”
(http://www.ecs.umass.edu/mie/labs/injection/research/micro/ 8/13/2009)
Recent Journal Articles
Microinjection molding of light-guided plates using LIGA-like fabricated stampers
(3456–3465)Journal of Applied Polymer Science 122 #5 (2011)
Huang and Ku of the National Kaohsiung First University of Science and Technology, Taiwan, studied the microinjection molding of light-guided plates (LGPs) using lithography, electroplating, and molding (LIGA)-like fabricated stampers. The 3.5-in. LGP has a thin wall (0.76 mm) and micron-sized features of truncated pyramidal prisms (70 μm wide and 38.3 μm deep, with a vertex angle of 70.5°) and v-grooves (9.8 μm deep). Stampers for LGP injection molding (IM) are fabricated precisely by combining the anisotropic wet etching of silicon-on-insulation wafers with electroforming. LGPs must have multiple quality characteristics, such as good replication effects on microfeatures and flatness of the plate. In this study, the Taguchi method and gray relational analysis are adopted to optimize the microinjection molding parameters. Experimental results demonstrate that mold temperature and holding pressure dominate the performance. Gray relational analysis and the Taguchi method can be used to determine the optimal process parameters for LGP molding. (RDC 9/6/2011)
Characterization of the microinjection molding process
(1214–1225)Polymer Engineering & Science 50 #6 (2010)
Using design of experiments studies for polyoxymethylene, high-density polyethylene,and polycarbonate materials, Chu et al show that injection speed was the most significant factor affecting plunger velocity and injection pressure during cavity filling, while the effects of mold and melt temperature varied with the material and machine settings. (RDC 11/6/2010)
Observation of instabilities in flow front during micro injection molding process
(1377–1381)Polymer Engineering & Science 50 #7 (2010)
Kim et al investigated filling characteristics during injection molding of a thinplate with micro-channels. For the smaller channels, an unstable filling flow developed, with continuous creation and merging of microballs looking like teeth on a gum. There is a critical channel width below which such instability takes place. (RDC 11/6/2010)
Review Articles
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Editor's Notes
As the literature is reviewed, and items of interest concerning this topic are found. These may be added in an abbreviated form with the reference. Readers and contributors are invited to add their own notes. Contributors may add them directly and other readers can simply send their notes to the editor, Roger Corneliussen at rcorneliussen@4spe.org. He may edit and add them to this page at his discretion.