Effect of gate size on melt flow resistance
The gate is the channel for the plastic melt to enter the mold cavity, and its size directly determines the flow resistance of the melt. A smaller gate size will produce a larger flow resistance, which will reduce the flow rate of the melt when filling the cavity and increase the pressure loss. For example, when precision injection molding small plastic products, if the gate size is too small, the melt may require a higher injection pressure to enter the cavity, which not only increases energy consumption, but may also cause the plastic to solidify prematurely at the gate, affecting the filling effect. On the contrary, although a larger gate size can reduce the flow resistance, it may cause the melt to flow too fast, resulting in injection, making the plastic unevenly distributed in the cavity, resulting in defects in the product, such as surface flow marks, internal stress concentration, etc.
Relationship between gate size and cavity filling order
The design of the gate size also affects the filling order of the cavity. A reasonable gate size enables the melt to evenly fill various parts of the cavity in a predetermined order. For products with complex shapes and multiple areas of different thickness or depth, the gate size needs to be determined according to the characteristics of these areas. For example, for thicker parts, the gate size can be appropriately increased to ensure sufficient melt flow to fill the area in a shorter time to prevent under-injection; for thinner parts, the gate size should be controlled to avoid too fast melt filling, resulting in trapped air or flash. By accurately designing the gate size, the melt can be smoothly advanced in the cavity, gradually flowing from the thick-walled area to the thin-walled area, and the filling sequence can be optimized, thereby improving the molding quality of the product.
The regulating role of gate size on filling balance
The gate size plays a key regulatory role in achieving plastic melt filling balance. In multi-cavity molds or single-cavity molds with multiple gates, differences in gate size will result in different filling speeds in different cavities or different parts of the same cavity. In order to achieve filling balance, the size of each gate needs to be finely adjusted. For example, by calculating the volume of each cavity or part, the length of the flow path, and the melt flow characteristics of the plastic, the appropriate gate size ratio is determined. If a cavity or part is always filled before other areas, the corresponding gate size can be appropriately reduced; on the contrary, if insufficient filling occurs, the gate size can be appropriately increased so that the melt in each area can be filled in the same time, reducing the product size deviation, warping deformation and other problems caused by unbalanced filling.
Comprehensive consideration and optimization method of gate size design
When designing the injection mold gate size, it is not only necessary to consider the filling balance, but also to comprehensively consider the characteristics of the plastic material, the shape and size requirements of the product, the structure of the mold, and the injection molding process parameters. First, the appropriate gate type should be selected according to the fluidity, viscosity and other characteristics of the plastic, and then the approximate position and number of the gate should be determined according to the quality requirements and appearance standards of the product. On this basis, the simulation software is used to simulate and analyze the melt filling process, predict the filling situation under different gate sizes, and repeatedly adjust and optimize according to the simulation results. At the same time, in the actual production process, it is also necessary to further fine-tune the gate size in combination with the trial mold situation to ensure that high-quality injection molded products are obtained under the premise of satisfying the filling balance, improve production efficiency and reduce production costs.
