A STUDY ON THE INTEGRATED SIMULATIONS OF STRUCTURAL PERFORMANCE, MOLDING PROCESS AND WARPAGE FOR GAS-ASSISTED INJECTION MOLDED PARTS

• Main Authors: HU SHENG-YAN, 胡勝彥
• Other Authors: SHIA-CHUNG CHEN
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/78085409821165812330

博士 === 中原大學 === 機械工程研究所 === 86 === Gas-assisted injection molding process being an innovation molding process. However, the development of the CAE software for the structure performance and molding process analyses required for gas-assisted injection molded parts has met a challenge and an integrated analysis software can not be establishedup to now. The research goal of this study is to develop a unified CAE finite element model based on shell elements superimposed the beam elements representingthe gas channel, for the molding situation and the part design of gas-assisted injection molding. This method can not only extend the basic simulation scheme of the traditional injection molding process but also provide reasonable analysis results that do not to change the finite element mesh model for the entire molding process, warpage calculation and analysis of part structure performance. In the present study, both simulations and experiments are carried out in order to verify the distribution of gas penetrations. Numerical scheme based on a dual-filling-parameter technique is used to simulate the melt front and gas front advancements in primary gas penetration period. Simulation for the secondary gas penetration is developed using an isotropic melt-shrinkage modelcombined with the control-volume/FEM on a gapwise layer basis. Simulated results of both primary and secondary gas penetrations show reasonable agreement with the experimental observations. For the simulation of the cooling process, the cycle-averaged boundary method is applied combined the finite difference method in order to consider the cooling efficiency of the mold cooling system and solve the cycle-averaged mold wall temperature to be used as the initial and boundary conditions of filling/packing analysis. The line heat source approach, similar to the simplified the cooling channel into a linear rod element, was used. Then heat flux calculated from the thickness of skin layer was then used to obtain the cyclic, transient mold wall temperature variation via iterative way. After the simulations of filling and post-filling process, the variation and distribution of pressure, velocity and temperature are used to calculate theresidual stress. The residual stress is calculated by the linear thermo-viscoelastic model and used as the initial data of structural analysis considering the effect of part shrinkage and warpage. An analysis algorithm based on VRT/DKT elements superimposed with beam elements representing gas channels of various section geometry was develop to evaluate part bending behavior. An equivalent diameter was assigned to the beam element so that both the original gas channel and the circular beam have the same moment of inertia. The combinations of these three types of elements can simulate the sturctural performance of gas-assisted injection parts and it feasibility was also verified. In summary, the integrated analysis method for the gas-assisted injection parts can not only be extending the simulation scheme on traditional injection molding process which is based on the characteristic of 2 1/2-D analysis, but also be performed under a unified CAE finite element model based on the shell element superimposed by circular beam element. It has to assign different equivalent diameter for the analysis of structure, warpage and molding process. The geometry of hollowed-core distribution is the key factor for the precision of analysis. This investigation develops an integrated analysis method for the gas-assisted injection molding process and it is feasible to use the same CAE finite element model implemented for process simulation of gas-assisted injectionwhen performing part structural analysis as well as warpage calculation resulting in great computational efficiency for industrial application.