Research On The Structural Influences Of Warpage Of Injection Molded Parts

When the imbalance of internal stress of injection molding products exceeds its stiffness,warpage deformation will occur. Warpage deformation, as an important index of injectionmolding products, has received more and more concern and attention. At present, most of thedesign and manufacture of injection molding products belong to different apartments, andeven different companies. Therefore, for the warpage of product, the product designengineers do not much. If before the mold design, through optimizing the structure of theproducts to reduce or eliminate the warpage, we can reduce the number of repairing mold,testing mold, and shorten the production time. This article, focusing on the warpage ofinjection molding products, mainly studied the structural design of rib and wall thickness onthe influence law of warpage, and connecting with the actual products, verifies and modifiesthese rules. The main work of this paper is as follows:1、Based on the system study of the theory of the warpage of injection molding products,research the law that product structure how to influence the warpage. For the productstructure, through the following two points to reduce the warpage: set rib to improve therigidity of product; adjust the local wall thickness, in order to optimize the filling pattern,reduce the residual stress.2、Focusing on the warpage of injection molding products, research the rib how toinfluence the warpage.Effect of rib section on warpage By using the orthogonal experiment method, studiedthe effect of the shape parameter of rib on the warpage and the depth of sink mark. Byvariance analysis for the test results, obtained the optimum ratio, evaluated the shapeparameter of rib on the warpage and the depth of sink mark. Analysis results shows: In theparameters of rib section, bottom thickness and height are the main factors affecting thewarpage and sink mark, but the draft angle has little impact on the warpage and the shrinkagemark. To warp and shrinkage mark respectively, have been optimized combination. Whenproduct requires higher levels of warpage, select TF4H4A1. It means when we designed rib,the bottom thickness is set to0.7T (T is basic thickness of plastic parts, the same bellow), theheight is set to4T, the draft angle is set to0.25°, the warpage of plastic parts will be minimized. When product requires higher levels of sink mark, select TF1H1A4. It means whenwe designed rib, the bottom thickness is set to0.3T, the height is set to1T, the draft angle isset to1.50°, the depth of sink mark will be minimized.Effect of rib space on warpage The curve drawn by the analysis results show: As thedistance of rib increases, the warpage of plastic part increases gradually. When the space ofrib of more than5times the basic wall thickness, the curve is horizontal, it means that theincrease of space does not affect the warpage. Therefore, the smaller the distance, the smallerthe warpage, but it will add more material if the distance is too small. So, the distance of ribis best set in3~5times the basic wall thickness based on the actual needs.Effect of rib direction on warpage When the direction of the rib and the melt flowdirection are in the same, the rib likes a diversion effect, this can reduce the resistance offilling and is useful to the packing, all of the above can reduce the warpage. When thedirection of the rib is perpendicular with the melt flow direction, the rib likes a throttle, thisincrease the resistance of filling and is bad to the packing, this will cause the difference ofshrinkage in different area is bigger. When the direction of rib is radial, it can reduce theresistance of filling and the length of melt flow.Effect of rib layout on warpage For the same product in the same section of rib and thesame volume, study its effect on warpage when the layout of rib is triangle, square orhexagon. Analysis results show that, when the layout is square, the warpage of the product issmallest. The warpage of the sample is basically consistent with the analysis result. But somereferences showed hexagonal layout is best, this needs further validation.3、Focusing on the warpage of injection molding products, research the wall of thicknesshow to influence the warpage.The influence of the wall thickness to warpage Whether the material used is crystallineor amorphous plastic, within the scope of permission, the wall thickness of plastic part is thin,the smaller the part warp. If the material used is crystalline plastic, the amount of warpage ofthe plastic parts change little when the wall thickness in1.5mm~2.5mm and4.0mm~6.0mm;If the material used is amorphous plastic, the amount of warpage of the plastic parts changelittle when the wall thickness in1.4mm~3.0mm. Thus, the wall thickness of plastic partshould be preferred in the range. The influence on warpage of the transition form between different wall thicknessCommonly used methods of he transition form between different wall thickness are chamferand fillet. Simulation study found that, the angle of chamfer has little effect on the warpage,and when the transition form is fillet, the warpage is smallest and it is conducive to moldprocessing.Change the local wall thickness to reduce warpage In the process of melt filling，increase the local wall thickness on the formation of flow guiding device, reduce the localwall thickness on the formation of throttle. Simulation study found that, by adjusting the localwall thickness, to fill balance, the pressure and temperature distribution, the shrinkage tendsto be consistent, reduce the warpage.