Abstract: Article discusses problems that easily occur in molding of plastic products in connector, uses MOLDFLOW software to simulate, compare original design and optimized design of a certain product, demonstrate feasibility of optimized scheme, thereby improving quality of injection products, shortening development cycle, and reducing production costs.

Development of high-density packaging and miniaturization in electronics industry requires designers to design small, thin-walled high-performance connectors, this requires higher quality plastic products for insulating and fixing contacts.
In order to improve quality of plastic products in connector, shorten processing cycle, quickly and efficiently occupy market, it is necessary to adopt advanced mold flow analysis technology. Before actual production, potential problems in product and mold design can be found, make improvements, so as to ensure that a qualified product can be produced after a trial.
Computer-aided engineering (CAE) technology has become the most effective way for these weak links in plastic product development, mold design and product processing. Compared with traditional mold design, CAE technology has great advantages in terms of improving productivity, ensuring product quality, reducing costs and reducing labor intensity. Using CAE (Moldflow) technology can simulate and analyze entire injection molding process on a computer before mold processing, accurately predict filling, holding pressure, cooling conditions of melt, as well as stress distribution, molecular and fiber orientation distribution in product, shrinkage and warping deformation of product, so that designer can find problem as soon as possible, modify part and mold design in time, instead of waiting for trial mold to repair mold. This is not only a breakthrough in traditional mold design methods, but also has great technical and economic significance for reducing or even avoiding mold repairs and scraps, improving product quality and reducing costs.

Quality problems that often occur during molding process of connector are: serious product warpage; some sockets have insufficient strength and are easy to crack. Here is an example to illustrate application of MOLDFLOW software in optimizing connector product and mold design.
Model of a certain type of connector is shown in Figure 1 below ( size is 47.3*8*7.3mm).
Selected material is: Solvay Advanced Polymers LCP Xydar G-930 BK (30% glass filled)

 

Figure 1 Connector model
Original design scheme and improved scheme are shown in Figure 2 and Figure 3.

 

For long plastic shells, if gate selection is unreasonable, plastic parts will be easily deformed after molding, will be scrapped in severe cases. In original design, gate was set on the side near edge. In improved scheme, gate is placed at the top, structure near side wall is modified to make wall thickness change more uniform. Figures 4 to 7 below compare warpage deformations in X and Z directions, which are decisive factors for product quality, in two design schemes.

 

 

 

Warpage refers to permanent plane error deformation caused by injection molding rather than loading. When internal stress caused by molding process is released, different shrinkage will occur and this phenomenon occurs. Different cooling rates will cause different shrinkage, because thicker part of part cools more slowly than thinner part, which will cause part to warp. The slower crystalline material in mold cools, the more fully polymer matrix crystallizes and the greater its shrinkage. Therefore, mold structure affects cooling rate, causing warpage. Structures with complex cores or sharp corners can cause molding cooling problems because they will retain heat, making crystallization of plastic in these areas slower and more complete, increasing local shrinkage.
Another reason for warpage is anisotropic characteristics of parts containing glass fibers, which cause different shrinkage. As mentioned earlier, shrinkage in flow direction will be hindered by a glass fiber, while transverse shrinkage is not affected, which is similar to pure resin. Fibers should be forced to line up along long side of part as much as possible to obtain a balanced and flat connector.
From comparison of above figures, it can be concluded that after adopting improved scheme, although amount of warping deformation in Z direction is slightly increased, amount of warping deformation in X direction is greatly reduced. These simulation analysis results provide a basis for us to adopt improvement plan.
In addition, pay attention to strength of connector hole. Figure 8 is a simulation diagram of weld pattern formed at connector hole. As pin density increases and wall thickness decreases, electrical insulation performance of connector matrix becomes more severe. Connector designer must pay attention to structural requirements of molded (blue letters removed) insulators. If cracks appear in press fit between insulating member and contact member, insulation performance of interconnection system will be destroyed, which is not allowed (blue letters are removed). You can change gate position, increase mold temperature and material temperature to eliminate or weaken welding line here. Fiberglass connector uses glass fiber to enhance rigidity and thermal performance of parts. At the same time, it will also cause anisotropy and possible deformation of designed parts. . Figure 9 is orientation map of glass fiber in improved scheme. In filling stage of injection molding process, glass fiber orientation on the surface of part is in flow direction, while at vortex center or mold center of part, orientation of glass fiber is more arbitrary, most of time perpendicular to flow direction. Because these fibers are more rigid than polymer matrix around them, mechanical properties in flow direction are significantly enhanced, while vertical direction is lower than expected.

 

Through MOLDFLOW software analysis, we can optimize gate position and structural design of connector before physical production and manufacturing, can view weld pattern of key parts and distribution of glass fiber in product, thereby improving quality of connector product and shortening product development cycle.