Introduction To Injection Mold Molding Technology
Jul 18, 2025
Injection molding technology is a manufacturing process that uses pressure, injection, cooling, and separation operations to shape molten plastic materials into specific forms of plastic products. The following provides a detailed introduction from aspects such as the process, mold design, and process parameters:
I. Injection Molding Process
1. Molding: The moving template of the injection machine drives the moving part of the mold to move towards the fixed part, causing the mold to close and forming a sealed cavity, preparing for the injection of the molten plastic.
2. Filling: The molten plastic is pressurized by the screw or plunger of the injection machine and injected into the mold cavity at a certain speed and pressure. Starting from the moment the mold closes, the injection molding process continues until the mold cavity is filled to approximately 95%.
3. Holding Pressure: After the mold cavity is filled with plastic, pressure is continuously applied to compress the melt and increase the plastic density to compensate for the plastic's shrinkage behavior. The holding pressure stage should continue until the gate solidifies and seals.
4. Cooling: Through the cooling system inside the mold, the plastic melt cools and solidifies in the mold cavity. The cooling time accounts for approximately 70% to 80% of the entire molding cycle. Inhomogeneous cooling can cause the plastic products to warp and deform.
5. Unmolding: The moving template of the injection machine drives the moving part of the mold to separate from the fixed part, leaving the molded plastic product on the moving part, preparing for demolding.
6. Demolding: Through demolding mechanisms such as push rods and ejection plates, the cooled and solidified plastic product is ejected or removed from the mold cavity, completing the entire injection molding cycle.
II. Key Points of Injection Mold Design
1. Cavity Layout: Based on the shape, size and production batch of the product, the number and arrangement of cavities should be reasonably designed to enhance production efficiency and the utilization rate of the mold.
2. Pouring System: This includes the main runner,分流 channels, and gate, and its design should ensure that the plastic melt can be uniformly and quickly filled into the mold cavity, while avoiding defects such as weld lines and bubbles.
3. Cooling System： A well-designed cooling system can shorten the molding cycle and improve the quality of the product. The layout of the cooling channels should be optimized according to the structure of the mold and the shape of the plastic product to ensure uniform cooling.
4. Demolding Mechanism： According to the structural characteristics of the product, an appropriate demolding method should be selected, such as top rod demolding or release plate demolding, to ensure that the product is not damaged during demolding.
III. Injection Molding Process Parameters
1. Injection Pressure: Provided by the hydraulic system of the injection molding system, it is used to overcome the resistance during the melt flow process and ensure the smooth filling process. The pressure at the nozzle of the injection machine is the highest, and it gradually decreases along the flow length.
2. Injection Time: It refers to the time required for the plastic melt to fill the cavity. Reasonable injection time is conducive to the ideal filling of the melt and is of great significance for improving the surface quality of the product and reducing dimensional tolerances.
3. Injection Temperature: An important factor affecting injection pressure. The barrel of the injection machine has 5 to 6 heating sections, and each type of raw material has its suitable processing temperature. If the temperature is too low, the melt plasticization is poor, and if the temperature is too high, the raw material is prone to decomposition.
IV. Post-Molding Processing
1. Finishing: Remove the burrs, spurs, gates, etc. on the product to make the surface smooth and the dimensions meet the requirements.
2. Inspection: Conduct size measurement, appearance inspection, performance testing, etc. on the product to ensure that the product meets the design requirements. For non-conforming products, timely analysis and handling should be carried out.
3. Post-processing: Depending on the needs of the product, some post-processing operations may also be required, such as assembly, painting, printing, etc., to increase the added value of the product.
