Research On The Effect Of3D Variable Cross-section Fan Gate On The Melt Flow Behavior

The thin-wall plastic part is widely applied to many fields including automobiles, instrumentation, home appliance and architectural decoration for its advantages such as saving materials, reducing the volume of products, lowering the cost. However, the melt filling process will become more difficult with the decreasing thickness of the plastic parts continuously, short shot, warpage, uneven thickness and other quality problems are appeared easily. Many of the quality problems are due to the uneven melt flow in the cavity. A kind design of3D variable cross-section gate was proposed, the melt flow could be adjusted to achieve balanced filling process and decrease the quality problems caused by uneven melt flow.Firstly, based on the principle of the Diverterless Supersonic Inlet(DSI), a design scheme for the fan gate with a kind of bump structure was proposed. Using Moldflow, the melt flow process through the fan gate with simplified bumps was numerically simulated. Under the same process conditions and the same bump height, the influences of the bumps with different geometric constructions on the melt filling process were analyzed. Comparing the results with the final molding quality, the geometric construction of the bump which was met the design requirements was selected.Secondly, after the cone bump was determined as needed geometric construction, the single factors analysis were made by Moldflow to research the effect of mold temperature, injection speed, melt temperature and other process parameters on the melt diversion, that is, the change of the melt front distance difference. Contrasting the molding quality of the bump fan gate with the common fan gate which has the same areas and width, the influence of the melt diversion on the flow front shape and the plastic part quality could be got. Comparing the volume shrinkages and warpage with different sizes parts, the effect of the melt diversion by the bump fan gate on the quality of the plastic parts was studied when the cavity size was increased.Thirdly, the bump fan gate inserts with different heights were designed and manufactured, injection molding experiments were done based on simulation. Under different process conditions and different bump heights, the weld lines and the melt diversion produced by the bump in the injection molding process were researched. Summarizing the influence of the process conditions and the bump height on the melt flow pattern, the extents of the bump height were determined eventually.Finally, the effects of bump fan gate on molding quality of the plastic parts with different size were tested. The experimental results show that using bump fan gate there is a great improvement on the molding quality of plastic parts when the width of the cavity is smaller. But to the plastic parts with a small length-width ratio, the melt diversion produced by the bump will reject the melt front reaching straight state.