| Summary: | 碩士 === 國立臺灣大學 === 機械工程研究所 === 83 ===
Gas-assisted injection moulding for two-dimensional thin plate is approximated by a Hele-Shaw flow model through theoretical analysis and simplification. Modified SMAC and SOLA numerical methods are then employed to simulate numerically the flow field and pressure distribution. The effects on the interface movement, filling speed (or production rate), and blow-throungh phenomenon by changing the gas injection pressure and capillary number are investigated. Two flow situations are studied. One is for the gas-assisted injection moulding in a finite thin plate, the other is for the fingering phenomenon in a long, rectangular thin channel. The following conclusions are drawn from the numerical results.
(1) The filling speed of a gas-assisted injection moulding is faster than that of a conventional one. The deeper transmission of pressure in a gas-assisted injection moulding can prevent the sink mark; shrinkage, and warpage the product. Furthermore, enhancing the gas injection pressure can increase the` filling speed. However, the filling speed is reduced for a material with a larger capillary number.
(2) The fingering in a long, rectangular thin channel will finally branch out if the capillary number is small enough or he gas injection pressure is large enough. With the same capillary number, the branch-out phenomenon can happen earlier by increasing the gas injection pressure. However, since the filling speed is also increasing as the gas injection pressure is enhanced, the branch-out phenomenon may be. avoided before the injuection process is finished for a finite cavity.
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