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The flow analysis for the filling of injection molding is defined as the process that polymer melt is propelled into the mold cavity by pressure. The pressure forces the melt front to fill the mold cavity. Generally, the highest pressure is at the sprue. As the distance from the gate increases, the pressure decreases due to the friction loss of fluid flow. At the same time, the lowest pressure appears at the melt front advancement. The difference in pressure is the primary driving force that propels the molten thermoplastics. Normally, the filling process tends to flow towards the cavity areas with the minimum resistance. The regions of cavity where the molten polymer advances faster indicate that this area has a smaller resistive force against the flow. Similarly, a very slow advancement of melt front (indicated by denser melt front equipotential lines) represents an area that has a larger resistive force. This situation is shown in the figures below.



Flow behavior of the polymeric materials passes different thickness areas



The gating phenomena for different situations for the injection molding


To catch this behavior, the simulation is a wonderful way to help. This analysis is capable of solving the filling-related problems, such as short-shot (incomplete filling), weld line, air-trap, flow problems, burning surface defects, runner/flow balance, and gate design problems. Therefore, it can be used in the concept or product design phase. Besides, part or mold designers can shorten their design delivery time by testing the possible design in this computer simulation. In addition, the filling analysis can also be used to evaluate the processing properties of material and to serve as a reference of material selection. Process conditions and mesh sensitivity can also be evaluated by the flow analysis as well.