| Summary: | 碩士 === 國立高雄應用科技大學 === 模具工程系碩士班 === 92 === This study provides numerical simulations and analyses of the flow field in an imprinting process of laser-assisted direct imprint technology. To this end, we have developed a computer program code based on the SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) algorithm. The program is capable of solving the velocity and pressure distributions of fluid in a region constituted of several connected rectangular blocks. The boundary conditions of each block may be assigned independently and the use of non-uniform grid spacing is allowable. With the quasi-stationary assumption this program may be employed to simulate transient flow fields with moving boundaries. In order to verify the validity of this program, a problem involving flow in a piston-cylinder device is proposed. Cyclic simple-harmonic motion of the piston causes the flow in the cylinder. For this problem, a numerical method using the coordinate-transformation technique is available. When the maximum velocity of the piston is set to be 0.125m/s, comparison between the results obtained from the two methods shows that the average errors of velocity components are within, respectively, 2.52×10-4m/s and 4.7×10-4m/s at any point in the first half period.
When analyzing the flow field of imprinting process by using this program, we assume that the free surface is flat for all time and the moving velocity of the free surface is specified via the overall mass conservation. The contents under investigation in this study include comparison of flow fields with non-slip condition or zero-shear-stress condition at the solid-liquid interfaces, the delay of imprinting time caused by the fluid''s pressure acting on the mould, the effect of molten depth of the silicon substrate, and the velocity field after the mould had reached the bottom position. It is found that the resisting force acting on the mould due to fluid''s pressure is less than 0.5% of the initial push force exerted on the mould. That means the flowing of liquid silicon has little influence on the imprinting time. The maximum pressure difference and the maximum velocity are higher in the cases of non-slip condition at solid-liquid interface and for shallower molten depth. The impact of upward liquid and the downward mould at the end of the stroke will cause an abrupt change in pressure distribution and this will induce a significant circulating flow, which may then affect the solidification of liquid silicon.
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