Plastic injection molding, also known as injection molding, is a molding method that combines injection and molding. The advantages of plastic injection molding are fast production speed, high efficiency, automated operation, and a variety of colors and shapes. The product size can range from simple to complex, with precise dimensions, and the product can be easily updated. Injection molding is suitable for mass production and complex shaping of products in the molding processing industry.
At a certain temperature, fully melted plastic material is stirred by a screw and injected into the mold cavity under high pressure. After cooling and solidification, the molded product is obtained. This method is suitable for batch production of complex shapes and is one of the important processing methods.
The injection time referred to here refers to the time required for the plastic melt to fill the mold cavity, excluding auxiliary time such as mold opening and closing. Although the injection time is short and has a small impact on the molding cycle, adjusting the injection time has a significant effect on controlling the pressure of the gate, runner, and mold cavity. Reasonable injection time helps the melt to fill evenly, and is extremely important for improving the surface quality of the product and reducing size tolerances.
The injection time of plastic injection molding should be much lower than the cooling time, about 1/10 to 1/15 of the cooling time, which can be used as a basis for predicting the total molding time of the plastic parts. When conducting mold flow analysis, the injection time in the analysis results is equal to the set injection time in the process conditions only when the melt is fully rotated and pushed into the mold cavity by the screw. If the screw pressure switch occurs before the mold cavity is full, the analysis result will be greater than the set process conditions.
The temperature of plastic injection molding is an important factor affecting injection pressure. The injection machine barrel has 5 to 6 heating sections, and each material has its suitable processing temperature (detailed processing temperature can be found in the data provided by the material supplier). The injection temperature must be controlled within a certain range.
If the temperature is too low, the melt will not plasticize well, which affects the quality of the molded parts and increases the difficulty of the process; if the temperature is too high, the material is easily decomposed. In the actual plastic injection molding process, the injection temperature is often higher than the barrel temperature, and the difference value is related to the injection rate and the material performance, which can reach up to 30°C. This is because the melt generates high heat due to shearing when passing through the nozzle. Two methods can be used to compensate for this difference in mold flow analysis. One is to measure the temperature of the melt when injected into the empty mold, and the other is to include the nozzle in the model when building the mold.