The Quality Control Of Injection Overmolding Car Exterior Corner Brace Based On CAE

As a molding technology of"in-mold assembly"or"in-mold welding", the injection overmolding has many advantages, such as reducing or canceling the second assembly, shortening the molding cycle and so on. The restrictions of injection equipment, mould technology and molding process make some limits to the popular application of injection overmolding. Therefore, it is very important to strengthen the relevant filed study and development.The exterior corner brace which consists of main body and sealing edge is usually located on the corner of posterior window for car. The typical quality problem in overmolding the part is larger warpage and poor interface bonding. At present, the traditional approach to solving the problem is debugging the mould structure or overmolding process parameters repeatedly so that the best way to control the quality is found, which will lead to the more production cost and energy waste inevitably. By CAE technology, one can not only predict the defects in overmolding exterior corner brace which are usually found by mould trial and error, but also can optimize the overmolding process parameters, improving the product quality and reduce production cost.On the basis of excluding the unreasonable structure technology design and the bad shot material match, by Moldflow, this paper focuses on studying the affects of gate location compositions and injection parameters on the overmolding part warpage and interfacial bonding.So, this paper first set four feasible gate location compositions to find the best through contrasting and analyzing the experiment results, then based on the best gate location composition studied the relationship between overmolding parameters, such as melt temperature, injection time holding pressure, cooling time and mold temperature, and the overmolding defects, such as part warpage and poor interfacial bonding. Finally, comprehensively considering overmolding quality, equipment tonnage and molding cycle, the paper selected the best process parameters composition. The results show that:1. The gate location composition has a greater influence on the overmolding part quality, of which different gate location on the sealing edge will affect the shear rate of post-injection melt and the pressure distribution in mould cavity, then affect the temperature and density distribution on the melt flow path. The uneven the temperature and density distribution will result in the uneven shrinkage of different regions on the sealing edge. When the residual stress induced by uneven shrinkage is more than the material Yield strength, the warpage on the sealing edge will happen. In addition, the uneven melt temperature distribution will also affect the heat transfer of the post-injection melt toward the interface between body and sealing edge, then affect the local melted layer depth and melting duration of the body sides, finally affect the interfacial bonding strength based on interfacial molecule diffusing each other.2. For each overmolding process parameter, there are different influences on the part warpage and interfacial bonding force.Within given process parameter values, the influence of body shot material (ASA) on the two quality index (part warpage and interfacial bonding force) is litter, the injection time of overmolding material (TPV) has a greater affect on the two indexes; the ASA holding pressure can more greatly affect the part height-direction warpage, but only has a medium degree influence on the interfacial bonding force; and the influence of TPV melt temperature on the interfacial bonding force is very significant, but the influence is opposite on the part warpage.3. An exterior corner brace of warpage reduction (total and height-direction) and interfacial bonding improvement can be gain under the following overmolding process conditions: ASA melt temperature 255℃, injection time 1.0s, holding pressure set as 70% of the Max injection pressure, cooling time 15s and TPV melt temperature 200℃, injection time 0.7s,holding press set as 70% of the Max injection pressure, cooling time 25s, mould temperature 70℃as well as.