Numerical Simulation Of Variable Mold Temperature Field During Injection Molding And Its Application

Variable mold temperature injection molding（VMTIM）is an innovative technology which controls the mold temperature field of injection processing,enlarges the range of application of injection molding.However,when the mold temperature rises,it will increase the cooling time,affect the molding cycle and reduce the production efficiency,so the quantitative analysis of its temperature field is of great significance.VMTIM achieves rapid cooling primarily through thermal convection and conduction of coolant.Rapid heating includes mold temperature machine with high temperature water/oil,electric heating rod,induction coil,alcohol lamp,tungsten lamp,gas pipeline,etc.They have differences in heat transfer mechanism,working conditions and heating efficiency.Heating efficiency,heating rate and temperature uniformity are the key parameters affecting production efficiency and product quality,and are the focus of variable mold temperature injection molding research.In this thesis,using heat transfer knowledge,combined with numerical and experimental methods,the influence of mold temperature on injection quality,the quantification of mold temperature machine,electric heating rod and induction coil temperature field,and the optimization of mold surface temperature field and related engineering applications were studied.The details are as follows.（1）The influence of mold temperature on injection molding quality of ABS,PC and POM was studied.For amorphous and crystalline injection-molded parts,roughness and glossiness were measured.The influence of mold temperature on melt viscosity,melt frozen layer and filling pressure was simulated.It shows that increasing the mold/cavity temperature reduced the melt viscosity and frozen layer thickness,improving the filling pattern.According to birefringence simulation of optical transparent material PC and crystallization simulation of POM,higher mold/cavity temperature had positive effects on optical properties and crystal size.The surface roughness and gloss of injection samples were measured at the temperature of50/70/90℃.It was found that the surface roughness decreased and surface gloss increased with the increase of mold temperature.（2）The mathematical model of three-dimension transient temperature field under different deterministic conditions（initial value and boundary condition）was discussed on the basis of reasonable simplification and assumption according to engineering background.The temperature field simulation of hot water heating,heating rod and induction heating were finished.The simulated results show that the heating rate rank was induction heating>heating rods heating>hot water heating.The uniformity of surface temperature distribution of mold/cavity was hot water heating>heating rod heating>induction heating.Therefore,combined with the simulation results and product characteristics,the heating rods with good heating efficiency and temperature uniformity was selected for optimization analysis and engineering application.（3）The optimization objective and optimization model of heating rod in complex cavity structure based on numerical results were established.The power of the heating rod was optimized by response surface analysis method based on the experimental results of Box-Behnken Design.The optimized power densities of five heating rods were calculated as H₁=0.18W/m m²、H₂=0.18W/m m²、H₃=0.20W/m m²、H₄=0.22W/m m²,respectively.The maximum temperature difference of the optimized mold surface was 4.47℃,and the uniformity of the optimized mold surface temperature was improved by 78.7%.The accuracy of the quadratic response surface equation was verified,and the error of the optimal value was 3.4%,which showed the effectiveness of the optimization method.（4）Engineering application of VMTIM to automobile parts and washing-machine panel injection molded parts was completed.According to injection molded parts features,heating rod and induction heating technologies were used respectively.To eliminate melt-lines and weld-lines caused by thickness difference and holes,optimization method,finite element analysis and mold flow simulation were used.The results of numerical simulation and experimental study show that higher mold temperature of VMTIM improved the filling pattern and surface quality of auto parts with inserts and multi-gated household electrical appliances with holes.According to the professional background and simulation results,improvement projects were put forward to expand the scope of application of mold change temperature technology,and completed the guidance of theory to production practice.