Browsing by Author "Chen, Ren-Haw"

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A study on the optomechanical tolerance model for lens assembly
(2007-01-01)
Cheng, Chen-Chin
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Lin, Tsung-Yin
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Chen, Ren-Haw
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機械工程學系
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Department of Mechanical Engineering
Optomechanics is defined as the science or engineering of maintaining the proper shapes and positions of the functional elements in an optical system. At the optomechanical interface, manufacturing tolerances affect the shape and position of the surface in a lens system. Even very small variations will cause extra aberrations which degrade the optical performance of a lens system. The traditional approach to the optomechanical tolerance design is a top-down process. The optical designers typically designate the critical to quality parameters, such as tolerances of tilts, decenters, and locations of optical elements. A significant drawback of this top-down process is that the tolerances determined by optical designers do not take the real manufacturing and assembly process into consideration. As a result, some tolerances are too tight for the manufacturing, and the yield rate of the production is difficult to improve. The objective of this study is to develop a surface based optomechanical tolerance model that calculates the variation of the critical to quality parameters for a lens system. The distribution of these parameters can be treated as inputs to the optical design. Therefore, the optical performance will be predictable than the top-down approach, and the manufacturability of the optical system can be improved.
Experimental study of demolding properties on stereolithography tooling
(2007-08-01)
An, Chao-Chyun
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Chen, Ren-Haw
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機械工程學系
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Department of Mechanical Engineering
Direct tooling using stereolithography (SL) photopolymer has been developed as rapid tooling for short-run injection molds. However, the tool strength, thermal conductivity, and erosion resistance of SL mold are lower than that of the conventional metal mold. Previous study has showed that the tool life was limited under 200 shots and tool damage often occurs during part ejection. In this paper, experimental data from a demolding properties test are presented and discussed. The experiments were performed using various cooling time, hold pressure, and mold temperature. The experimental data were analyzed by measuring demolding force and surface roughness to evaluate tool life and failure mechanism in order to obtain a working range for the process parameters. The test result shows that the demolding force has close relation with cooling time and mold temperature.
Fine pitch "NCF-type Compliant-bumped COG"
(2007)
An, Chao-Chyun
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Chang, Shyh-Ming
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Chen, Ming-Yao
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Kao, Kuo-Shu
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Tsang, Jimmy
Non-Conductive-Film (NCF) type of Chip-on-Glass (COG) bonding method ensures the micro-order direct bonding between the IC electrode and glass substrate electrode. The binding force of the applied adhesive achieves electrical connections between the bumps on the IC chip and the electrodes on the glass substrate. The mathematical calculation results of bump stress and bump deformation are used to identify the environmental temperature range for the given COG bonding structure. Both of the calculation and experimental results demonstrate the feasibility of using the compliant bumps to achieve a high compressive stress, high bump deformation and low as well as stable connection resistance at various environmental temperatures. The 1,000 hrs 85 degrees C/85%RH reliability test result will be indicated.
Flow and Film-Forming Characteristics Analysis of Non-Newtonian Fluid Slot Coating
(2014-01-01)
Shu, Wei-Chu
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Wu, Tsai-Fang
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Chen, Ren-Haw
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Cheng, Kuei-Yuan
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Hsieh, Chih-Wei
The slot coating process in the production of polymer films has a wide range of applications. However, the process cannot be systemized. This study used the computational fluid dynamics software Polyflow to analyze the slot coating process and investigate the influence that the process parameters have on the characteristics of thin-film coating to reduce the time and cost consumed in the experimental methods. The rheological characteristics of the non-Newtonian fluid used in this study were first identified by conducting experiments, and then configured in the simulation software for fitting with mathematical models. In addition, the models of the slot coating process were constructed, and the Arbitrary Lagrangian-Eulerian (ALE) calculation methods were then used in the Polyflow software. The simulation results were then compared to the experimental results and the findings reported in relevant literature, to determine the influence that the process parameters have on the characteristics of thin-film coating. The simulation results were represented graphically in a coating window plot. The comparison results indicate that the viscosity-shear rate characteristic of the material in the shear rate range of optical film coating is an excellent fit for the Cross Law. When the coating speed is too high or the amount of fluid supply is insufficient, phenomena such as break lines, uneven thickness, and air entrainment can occur.
Influences of Process Conditions on Stretching Characteristics of Crystalline Polymer Film
(2014-01-01)
Chen, Liang-Yu
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Su, Chung-Cheng
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Chen, Ren-Haw
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機械工程學系
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Department of Mechanical Engineering
Developing the interior structures of polymer films is essential for creating novel functions of such films. This study investigates the effects of extension parameters and processing procedures on the super-structure of a polypropylene (PP) film. An biaxial extension device is also designed and fabricated to analyze the effects of annealing, extension temperature, extension rate and other parameters on the super-structures of PP films. Based on super-structure analyses, the relationships between extension parameters and film structures are determined, and an extension process that involves a second time stretching procedure is suggested. Experimental results indicate that void structures can be generated by biaxial extension at the interface between the crystalline and amorphous regions in a film. The mechanical strength of the film is also affected by stretching and become highly oriented. Although a low extension temperature can increase the number of void structures generated at a low extension ratio, structure sizes are dispersed. Additionally, voids with uniform size can be obtained when the film is stretched at a high temperature; however, it needs a high extension ratio to promote the formation of void structures. As for annealing treatment, when the annealing temperature increased, the size and quantity of the spherulites that were formed in films by annealing also increased, but these films tend to have similar sizes and numbers of void structures. Based on the experimental results, this study also describes how parameters influence the void structures of a PP film created during the extension process. Analysis results further demonstrate how extension parameters and processing procedures can be adjusted to improve the fabrication of PP films.
On Flow Layer Uniformity in the Co-Extrusion of Polymer Multilayer Film
(2014-01-01)
Tzeng, Guo-Chiuan
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Chen, Ren-Haw
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機械工程學系
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Department of Mechanical Engineering
In the multilayer co-extrusion process, two or more materials are simultaneously brought together and layered in a single extrusion process. When co-extruding two polymers with different rheological properties, uniformity control of the flow layer at and downstream of the confluence is vital for the quality of multilayered film products. This work aimed to investigate the effects of viscosity and elasticity of the co-extruding polymers on the layer uniformity at the confluence. We conducted a PC/PMMA/PC three-layer film co-extrusion experiment to observe the flow of polymer melts at the confluence in the die. The thickness variation of each layer along the flow was recorded through a viewing window structured on the die wall using a camera. In addition, the flow and stress field analyses of PC/PMMA/PC co-extrusion were performed using POLYFLOW software. The research results demonstrated that oscillation of flow velocity in machine direction along the PC/PMMA interface accompanying a wavy distribution of layer thickness along the flow may occur due to the differences of viscosity and elasticity between the PC and PMMA. Although slipping may occur at the PC/PMMA interface, which reduces the shear stress between the PC and the PMMA layer boundaries, the shear stress distribution crossing the PC/PMMA interface is not continuous. The imbalance of the shear stresses along the adjacent PC and PMMA boundaries expands with the extrusion rate, which can cause the interface to distort. To avoid the occurrence of interfacial instability, the length of die channel downstream the confluence must be shortened as much as possible, and the extrusion rate must be lowered.
The experimental study on the defects occurrence of SL mold in injection molding
(2008-05-26)
An, Chao-Chyun
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Chen, Ren-Haw
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機械工程學系
;
Department of Mechanical Engineering
Past experience has shown that the defects occurrence in injection-molded parts of metal mold included weld line, flow mark and solid skin. In this study, a thin wall cavity is designed as flow path for plastic injection mold. The injection molding tests were performed by using metal mold and stereolithography (SL) mold to compare with the flow behavior and defects occurrence of flat parts. The experiments were performed with various process parameters to investigate the defects occurrence in the injection-molded parts. The experimental results showed that defects occurrence has close relation with injection speeds and mold temperatures. Flow marks of SL mold occur more easily when the mold temperature and the injection speed are low. Moreover, the injection-molded parts were examined whether the surface defects (flow mark and weld line) occurred and analyzed as the reference for the future SL mold design. (C) 2007 Elsevier B.V. All rights reserved.