Mold Cavity Surface Research Articles

Simulation of a mold‐cooling process for gas‐assisted injection molded parts designed with a top rib on the gas channel

AbstractThe same CAE model used for the filling and packing stage in the gas‐assisted injection molding (GAIM) process simulation was also applied to simulate the cooling phase. This was made possible by using the line source method for modeling cooling channels. The cycle‐averaged and cyclic transient mold cavity surface temperature distribution within a steady cycle was calculated using the three‐dimensional modified boundary element technique similar to that used in conventional injection molding. The analysis results for GAIM plates of a semicircular gas channel design attached with a top rib are illustrated and discussed. It was found that the difference in cycle‐averaged mold wall temperatures may be as high as 10°C, and within a steady cycle, part temperatures may also vary by about 15°C. The conversion of the gas channel into equivalent circular pipe and further simplification into two‐node elements using the line source method not only affects the mold wall temperature calculation very slightly but also reduces the computer time by 93%. This indicates that it is feasible to achieve an integrated process simulation for GAIM under one CAE model, resulting in great computational efficiency for industrial application.

Integrated simulations of structural performance, molding process, and warpage for gas-assisted injection-molded parts. III. Simulation of cyclic, transient variations in mold wall temperatures

Whether it is feasible to perform an integrated simulation for structural analysis, process simulation, as well as warpage calculation based on a unified CAE model for gas-assisted injection molding (GAIM) is a great concern. In the present study, numerical algorithms based on the same CAE model used for process simulation regarding filling and packing stages were developed to simulate the cooling phase of GAIM considering the influence of the cooling system. The cycle-averaged mold cavity surface temperature distribution within a steady cycle is first calculated based on a steady-state approach to count for overall heat balance using three-dimensional modified boundary element technique. The part temperature distribution and profiles, as well as the associated transient heat flux on plastic-mold interface, are then computed by a finite difference method in a decoupled manner. Finally, the difference between cycle-averaged heat flux and transient heat flux is analyzed to obtain the cyclic, transient mold cavity surface temperatures. The analysis results for GAIM plates with semicircular gas channel design are illustrated and discussed. It was found that the difference in cycle-averaged mold wall temperatures may be as high as 10°C and within a steady cycle, part temperatures may also vary ∼ 15°C. The conversion of gas channel into equivalent circular pipe and further simplified to two-node elements using a line source approach not only affects the mold wall temperature calculation very slightly, but also reduces the computer time by 95%. This investigation indicates that it is feasible to achieve an integrated process simulation for GAIM under one CAE model, resulting in great computational efficiency for industrial application.

Automatic Design for Cooling Channels in Injection Molding under Steady-State Heat Conduction Analysis.

An arrangement of cooling channels in a mold should be designed properly to improve productivity and formability for a molded product in injection molding, because temperature distribution on the mold is dependent on the arrangement and has some influence on molded defects. The purpose of this study is to develop a methodology for automatically designing arrangement of cooling channels so as to obtain the suitable temperature distribution to reduce molded defects and to realize high productivity. A cooling channel is modeled by a set of autonomous elements which is arranged as a line and has performance for extracting heat in the mold. The arrangement of cooling channels are automatically obtained by autonomous action of these elements, according to information sent from sources which are located on the mold cavity surface and evaluate temperature on its location. For estimating the temperature distribution, a steady-state heat conduction is assumed for heattransfer in the mold and calculated by numerical analysis. Several numerical experiments have been conducted for estimating the proposed method, and the effectiveness and feasibility have beeit confirmed for automatic design of cooling channels.

Simulations of cyclic, transient variations of mold temperatures in the SMC compression molding process

AbstractThe dual reciprocity boundary element technique is used to simulate the cyclic SMC compression molding process, taking into account the heat transfer within the whole mold. The cyclic, transient variations in mold temperatures at different mold locations are illustrated through the analysis of a plate mold. The transient temperature fluctuation near the mold cavity surface is much larger than that away from it. It was also found that owing to the high heating fluid temperature (compared with the ambient air temperature), the heat transfer at the mold exterior surface shows a significant effect on the mold temperature distribution, especially when the mold is a small or medium size. The present method provides a complete and more accurate description of the mold temperature variation during the whole cycle history by including the mold as the analysis domain, meanwhile minimizing the computation time. Other analysis methods, including the constant mold wall temperature approach, the hybrid shape‐factor/finite element method, as well as the cycle‐averaged boundary element technique imposed with 1‐D transient analysis, basically overestimate mold wall temperatures and the associated charge conversion rate.

Simulation of the Cyclic Injection Mold-Cooling Process Using Dual Reciprocity Boundary Element Method

The cyclic, transient heat transfer within an injection mold is analyzed using iterative DRBEM/FDM based on transient heat conduction model in a decoupled sequence. It is found that the transient temperature fluctuation at mold cavity surface is much larger than that away from it. Simulated results from the present method are also compared with those calculated by a modified boundary element method based on a cycle-averaged approach and combined with a one-dimensional transient analysis

Simulations of cyclic transient mold cavity surface temperatures in injection mold-cooling process

In the present study, simulations of the injection mold-cooling process are developed by using a modified boundary element technique. The mold cavity surface temperature distributino is first calculated on a cycle-averaged basis. The temperature distribution and the temperature profile of the polymer melt and the corresponding transient heat flux on plastics-mold interface are then computed by finite difference method in a decoupled manner. Finally, the difference between cycle-averaged heat flux and transient heat flux is analyzed to obtain the cyclic transient mold cavity surface temperature. The analysis results for a box mold are illustrated and discussed.

Development of Conjugated In-mold Reaction Molding of Thermoset and Themoplastic Resins

Both thermosetting resins and thermoplastic resins have special desireable properties that are possessed by one, but not the other. This investigation involved a study of the development of conjugated molded parts that possess both sets of desireable characteristics as well as a study of the molds necessary for making these parts. A new molding technique has been developed in which rapid heating and coolling is performed by means of high-frequency induction heating. In this study, we report on studies using a modified technique in which the mold is heated and coolled at arbitrary times during the molding process in an ordinary injection machine combined with a high frequency generator. A high-frequency heating inductor is embedded in the mold. The molding process that was developed is as follows: (1) An uncured solution of Diallylphthalate (DAP) is sprayed onto the mold cavity surface. (2) After closing the sprayed mold, a thermoplastic is injected at ordinary resin injection temperatures (to investigate their conjugation with DAP). (3) The mold is heated by high-frequency induction heating, which cures the DAP. (4) The mold is cooled and the molded part released from the mold.The results that were obtauned are as follows: (1) The conditions for hardening the DAP were: mold temperature 140-150°C for 1-5mins. (2) The curing of the DAP: cured by heating after the conjugation. (3) Thermoplastics capable of conjugation with DAP: SAN and ABS resins.This method has led to the successful development of a new conjugated molding process, in which a thermoplastic resin (such as DAP) reacts and cures in the mold, while being conjugated with an injected thermoplastic resin (such as SAN or ABS).

Simulations of post-filling process considering the cooling effect of the mold cooling systems

Simulation of the post-filling process has been developed and performed to study the compressible polymer melt flow during the packing phase and the pressure development inside the mold cavity for the entire post-filling process. A mixed finite-element/finite-difference numerical scheme is implemented to solve the non-isothermal, compressible viscous flow equations. The transient, non-isothermal mold cavity surface temperatures which depend on the mold cooling channel arrangement and coolant flow conditions are also incorporated during simulation using hybrid finite-element/shape-factor method. It has been found that the difference in the pressure profile variation during the post-filling stage is quite distinguished for cases assuming constant mold wall temperature and cases with the consideration of the cooling effect of the cooling system configuration.

Experimental Results of Low Thermal Inertia Molding. I. Length of Filling

Abstract In injection molding, complete mold cavity filling is a design goal that has to be met 100% every time. Mold cavity filling is a complicated process which depends on many variables such as mold cavity surface temperature, injection pressure, injection speed, melt temperature, flow index of material being molded, etc. The aim of experimental investigation of the low thermal inertia molding (LTIM) [1] process is to demonstrate the feasibility of molding completely filled, thin parts at low injection pressure and injection speed without sacrificing part quality. The evaluation of the new molding concept consists of comparison of a conventionally molded thin rectangular part with an identical part molded by the LTIM process. The length of filling in the conventional cavity and in the LTIM cavity are compared at different injection pressures and injection speeds. The mold design, experimental procedure, and results of the molding are discussed in the following sections.

二軸回転球体研磨工具の幾可学的特性と鏡面仕上性能 金型自由曲面の自動仕上加工に関する研究 ＩＩ

It is necessary to develop the grinding and the polishing tools for finishing the free-form metal surface of a mold cavity automatically. In our previous paper, the dual-axis micro-grinding tool which can finish a cavity surface to a smooth surface of less than 2.5μmRmax has been reported. In this paper, a dual-axis polishing tool with a spherical elastic body which can finish the ground cavity surface to a mirror surface of less than 0.3μm Rmax was developed. This tool has the following properties: (1) The revolution ratio m of the polishing spindle to the main spindle influences both the cross loci and the cross angle of abrasive grains. (2) This tool which has a low polishing speed and reversal polishing motion like a hand work can automatically polish a mold cavity surface to a mirror surface of less than 0.3μm Rmax in every range of 0-90° inclination angle.

二軸回転マイクログラインディング工具の運動機構と仕上性能 金型自由曲面の自動仕上加工に関する研究 Ｉ

The purpose of this study is to develop a very useful grinding tool for finishing automatically the free-form metal surface of a mold cavity on the NC milling machine. A dual-axis microgrinding tool has been developed, in which a small disk grinding wheel having a part of the spherical body (diameter; 25 mm) can revolve on both the wheel and the spindle axes at the same time. This dual-axis micro-grinding tool has the following properties : (1) The tool can finish the free-form metal surface at high grinding speed and also at the almost same speed at every grinding point, namely the grinding speed is 1 130-1 140 m/min and only 0.7% of that is changed in all over the range of 0-90° inclination angle of mold cavity surface. (2) The small disk grinding wheel is rotated reversely every half revolution, so that the cross loci of abrasive grains are produced automatically on the surface. This reversal grinding motion has something in common with human operation for obtaining a mirror surface by hand work. (3) In grinding operation with CBN 120 metal bond wheel, the tool can finish a spherical cavity surface to a smooth surface of less than 2.5 μmRz.

Temperature Distribution in Molten Metal Flow Contacting with the Bare Surface of Cylindrical Mold Cavity

Temperature Distribution in Molten Metal Flow Contacting with the Bare Surface of Cylindrical Mold Cavity