Optics Design and Precision Manufacturing Technologies

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Authors: Wing Bun Lee, Yi Ping Chen, Suet To
Abstract: A strain gradient dependent crystal plasticity approach is adopted to model the size effect in the microforming process of sheet metal. To take into account the grain size effect in the simulation, the total slip resistance in each active system was assumed to be due to a mixed population of forest obstacles arising from both statistically stored and geometrically necessary dislocations. The non-local crystal plasticity has been established by directly incorporating the above slip resistance into the conventional rate-dependent crystal plasticity and implemented into the Abaqus/Standard FE platform by developing the user subroutine UMAT. The formulation has been recapitulated and followed by presentation of the numerical examples employing both the local and non-local formulation. The comparison of the counterpart simulation results reveals the grain size effect in the microforming process and demonstrates the availability of the code developed.
Authors: Kai Leung Yung, Hang Liu, Yan Xu, Hong Hu, Sui Man Ko, Matthew Kwan, Kon Sau Lau, Kam Fai Tam
Abstract: The precision control of the injection process in micro injection molding demands precise tracking of the moment that melt front passes through the nozzle so that accurate prediction of the amount of melt being injected into the mould can be achieved. The tracking accuracy, to large extent, depends on the processing of pressure signals followed by the identification of the critical moment that melt front reaches the nozzle. A new adaptive Kalman filter was introduced in this study to calculate and predict the amount of melt injected. The filter eliminated the delay error and was more robust than other filters. The adaptive Kalman filter switches between two Qs for steadystate and transient estimations, allowing resetting of the Kalman gain so that convergence is speeded up in calculations. Experimental and simulation results prove the effectiveness of the method proposed.
Authors: Chi Fai Cheung, Wing Bun Lee, Suet To, Ling Bao Kong
Abstract: One of the remarkable achievements of nanotechnology is the ability to achieve nanometric surface finishes in single-point diamond turning of high-precision components for complex optical surfaces. A better understanding of the surface generation mechanisms is of prime importance for the development for the prediction of the surface roughness. This paper presents a study of mechanisms of nano-surface generation in single-point diamond turning of various types of materials.
Authors: Ching Yuen Chan, Bang Kun Jin, Kai Leung Yung, Yan Xu
Abstract: A method of fabricating nanotemplate and nanowires by the anodization of bulk aluminum at room temperature is reported in this paper. Details of manufacturing processes as well as some in-depth discussions on the formation mechanism of nano pores with reference to the phenomena observed in experiments are presented. Effects of fabricating conditions such as the anodization time, temperature, current intensity, voltage and features of solutions, were studied in the experiments.
Authors: Sen Yeu Yang, Tzu Chien Huang, Po Hsun Huang, Tai Yu Ko
Abstract: This study reports the experimental investigation on the flow imbalance phenomena during filling symmetrical multi-cavity in injection molding of optic elements. There are two aspects in this study: First, the flow imbalance in the eight-cavity mold with normal H-type symmetric runners were observed and measured with aid of short-shot experiments. Second, the effects of three processing conditions including injection speed, melt temperature and mold temperature on flow imbalance were investigated. Flow imbalances are consistently observed and quantitatively measured. The results have shown that proper injection speed, high melt and high mold temperature can reduce the flow imbalance.

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