CAE Study On The Effects Of The Wall Thickness Of The Lens On Automobile Lamp On The Weldline

Because of the complexity of the injection molding process, molding products easily produce various defects, which will seriously affect the quality of products and waste a lot of materials and energy. How to remove the defects and comprehensively improve the quality of products, are one of the important research topics in injection molding processing and die design and manufacture.The wall thickness of the plastic parts has an extremely important impact on molding defects, this is particularly for thin-wall plastic parts. By changing the partial wall thickness of the plastic part, the location of defects can be changed, and transferred to not crucial positions, and even defects can be inhibited, thereby the overall quality of injection molding products enhanced. However, at present, all of the people are not fully aware of the importance, which the formation of defects can be inhibited by changing the partial wall thickness of the plastic parts, and problems which are often resulted in by the wall thickness in the practical production. Although some studies have been reported, the research is not thorough enough, concrete and comprehensive. A lot of further research is still needed.The filling processes were analyzed with the software of MoldFlow for the lens on automobile lamp produced by Hella Tooling Changchun Co.Ltd. Through changing the wall thickness of the products, mold temperature and melt temperature, the reasons for weldline were investigated and important molding parameters were provided to clean the defect and other defects for practical production. The main conclusions of the present study are as follows:(1) The changing of the wall thickness had important effects on the length and location of weldline and molding parameters.a) When the concave die migrated to positive direction of X axis, the products produced the first weldline as the offset is 0.53mm. When the the offset increases, flow patterns weren't gradually becoming ideal, the number and the length of weldline was gradually increasing, the locations of weldline, as well as the final point of filling were gradually removed to gate position, and the quality of products was getting worse. When the offset increased from 0.82mm to 1.02mm, the racetrack would appear in the filling process, and it would be gradually becoming serious with the increase of the offset.b) When the concave die migrated to positive direction of Z axis or the wall thickness of Z1 surface reduced, the products produced the first weldline D or D1 as the offset or the reduction was 0.50mm or 0.40mm; and with the increase of the offset or the reduction, the length of the weldline D or D1 was gradually increasing. But, when the offset or reduction increased from 0.75mm to 0.8mm, the length of weldline D or D1 was shorter. And after the offset or reduction was more than 0.8mm, the length of weldline D or D1 would again increase and the products produced the second weldline E or E1.c) The effects of the wall thickness of X1 and X2 surfaces changed at the same time on the quality of the products were the greatest, the effects of the wall thickness of Z1 surfaces were smaller, and the effects of the wall thickness of Z2, Y1 and Y2 surfaces were the smallest.(2) Mold temperature had not very important effects on the length of weldline and molding parameters. When the offset was the same, the maximum injection pressure for the mold temperature of 66 0 C was bigger compared with the mold temperature of 90 0 C, the difference was within 5Mpa. The maximum bulk temperature and the maximum shear rate of the mold temperature of 66 0 C was bigger too, the difference of the maximum bulk temperature was about 2 0 C, and the difference of the maximum shear rate was about 4000×1/s. But the filling time for the mold temperature of 66 0 C was shortened, and the difference was about 0.25s.(3) Melt temperature had not very important effects on the weldline and molding parameters.a) The lower the melt temperature, the easier the products produced the weldline. When the concave die migrated to positive direction of X axis and the offset was 0.52mm, the products for the melt temperature of 280 0 C produced weldline; when the offset was 0.82mm, the products for the melt temperature of 320 0 C had not produced weldline, however at that time there were two weldlines on the products for the melt temperature of 280 0 C.b) The higher the melt temperature, the lower the maximum injection pressure and the higher the maximum bulk temperature.c) The lower the melt temperature, the bigger the effects of the melt temperature on the maximum shear rate. When the offset was the same, the maximum shear rate of the melt temperature of 300 0 Cwas bigger than the maximum shear rate of the melt temperature of 320 0 C, the difference was about 2000×1/s, however the maximum shear rate of the melt temperature of 280 0 Cwas bigger than the maximum shear rate of the melt temperature of 300 0 C, and the difference was at least 8000×1/s, and it would become increasing along with the increase of the offset.(4) It was founded that the effects of the offset or the reduction on the maximum wall shear stress were not big when the offset or the reduction was not big. When the offset or reduction reached a certain value and the melt temperature was not high in injection molding process, the maximum wall shear stress and the maximum injection pressure would increase fast along with the increase of the offset or the reduction, but when the melt temperature was higher, the maximum wall shear stress and the maximum injection pressure increased slowly.