Injection molding filling analysis
Injection filling analysis is a crucial step in the injection molding process, directly impacting part quality, production efficiency, and mold life. During injection molding, molten plastic is forced through the gating system into the mold cavity under pressure. The flow state, pressure distribution, and temperature changes during this process significantly impact the final product. Scientific and rational filling analysis can predict potential defects such as short shots, flash, and bubbles, enabling optimization during mold design and process parameter setting, reducing production costs and improving production yields.
When performing injection molding filling analysis, the first step is to clarify the structural characteristics and material properties of the plastic part. Different part shapes, such as complex cavity structures and the distribution of thin-walled or thick-walled areas, will cause the molten plastic to experience different resistance during flow. Parameters such as material fluidity, melt index, and viscosity determine the plastic’s ability to flow at specific temperatures and pressures. For example, engineering plastics with poor fluidity, such as polycarbonate, require higher injection pressures and temperatures during the filling process to ensure the melt can smoothly fill the entire cavity. For polyethylene with better fluidity, on the other hand, the pressure needs to be appropriately reduced to avoid problems such as flash.
The design of the mold’s gating system is a key factor influencing filling performance. The gating system includes main channels, branch channels, and gates, all of which have a direct impact on melt flow. A reasonable gate location should be set in a thick-walled area of the part or in a location that facilitates venting to ensure that the melt evenly fills the cavity and minimizes pressure loss along the flow path. The cross-sectional shape and size of the branch channels also need to be tailored to the part’s size and material properties. Generally, a circular cross-section offers less resistance, facilitating melt flow, while a rectangular or trapezoidal cross-section offers advantages in processing and venting.
The setting of process parameters plays a decisive role in the injection molding filling process. Parameters such as injection speed, injection pressure, holding pressure, melt temperature, and mold temperature influence each other and require coordinated optimization. Excessively fast injection speeds can cause turbulence in the melt within the mold cavity, entraining air and forming bubbles; while too slow an injection speed can cause the melt to cool too quickly during flow, resulting in short shots. Furthermore, mold temperature uniformity can affect the flow and cooling rate of the melt, which in turn affects the shrinkage and warpage of the plastic part. Filling analysis can simulate the melt flow state under different process parameter combinations and identify the optimal parameter settings.
With the development of computer technology, numerical simulation technology has been widely used in injection molding filling analysis. By establishing mathematical models and using finite element or finite volume methods to perform numerical calculations on the flow, heat transfer, and pressure distribution of the melt in the mold cavity, various phenomena during the filling process, such as the location of weld marks and the generation of bubbles, can be intuitively displayed. This not only reduces the number of mold trials and costs, but also improves the accuracy and efficiency of mold design and process parameter optimization. For example, in the mold design of complex plastic parts, numerical simulation can identify potential filling problems in advance and modify the gating system and cavity structure to ensure the quality of the plastic part and the stability of production.
