Plastic Injection Molding
Injection molding is a common plastic manufacturing process that has been widely used in modern industry. The products produced using this type of product have many advantages, such as high precision, high quality, and excellent chemical and physical properties.
Injection Molding Process｜Plastic Product Production
The injection molding process is a method widely used in the production of plastic products. It injects molten plastic material into a mold of a specific shape, cools, and solidifies to form the desired product. This process is favored for its efficiency, cost-effectiveness, and ability to produce complex-shaped products.
The custom injection molding process is a common method for molding plastic products. It can be seen from the process flow that injection molding is a cyclic process. To complete injection molding, it needs to go through four major processes including pre-molding metering, injection filling, pressure maintaining and shrinking, and cooling and shaping process. Taking polyurethane injection molding as an example, the material needs to undergo a drying step before starting processing to avoid problems such as decreased physical properties and poor appearance during high-temperature processing.
1.Pre-molding Stage
The screw starts to rotate, and then the plastic transported from the hopper is transported to the front end of the screw. The plastic is plasticized evenly under the action of high temperature and shear force and gradually gathers at the front end of the barrel. As the molten plastic gathers, the pressure increases. Finally, the screw back pressure is overcome and the screw is gradually pushed back. When the plastic in the front of the barrel reaches the required injection volume, the screw stops retreating and rotating, and the pre-molding stage ends.
2.Injection Molding Stage
The screw moves forward under the action of the injection cylinder, pushing the plastic stored in the front of the barrel forward at multi-stage speed and pressure, and injects it into the closed mold cavity through the runner and gate.
3.Pressure Maintaining and Compressing Process
The injection pressure in the holding stage is called holding pressure. Under the action of this pressure, the melt in the mold cavity is fed due to cooling, and the product is compressed and densified. In this process, the holding pressure plays a dominant role.
The characteristics of the pressure holding stage are: the melt flows slowly under high pressure, the screw has a slight feeding displacement, and the product gradually shapes as the material cools and increases in density. During the pressure-holding stage, the melt flow rate is very small and does not play a leading role, but the pressure is the main factor affecting the process. During the pressure-holding stage, the pressure and specific volume in the mold are constantly changing.
4.Cooling and Shaping Stage
The plastic is pressure-maintained in the mold cavity to prevent the plastic from flowing back until the plastic solidifies and the pressure in the cavity disappears. Cooling and shaping time accounts for the largest proportion in a production cycle.
5.Mold Opening and De-molding
After the plastic is completely solidified, the mold is separated and the product is removed. This step requires ensuring that the product is intact and free of burrs and other defects.
6.Post-processing
Products may require post-processing, such as deburring, grinding, assembly, spraying, etc., to meet final usage requirements and aesthetic standards.
Key Elements of Injection Molding Process:
1.Mold Design: The design of the mold is crucial to the injection molding process, and it directly affects the quality and production efficiency of the product. Molds need to be precise, durable, and able to withstand high pressures and temperatures. Currently, most customers require custom injection molding.
2.Injection Molding Machine Selection: Select the appropriate injection molding machine based on the size, complexity, and production volume of the product. The specifications and capabilities of the injection molding machine directly affect the accuracy and efficiency of injection.
3.Plastic Materials: Choosing the right plastic material is critical to product quality. Different plastic materials have different melting points, flow properties, and shrinkage rates, all of which affect the performance of the final product.
4.Process Parameter Control: Parameters such as temperature, pressure, speed, and time during the injection molding process need to be precisely controlled to ensure the consistency and stability of product quality.
5.Quality Control: During the entire production process, quality inspections are required on products, including size, appearance, mechanical properties, etc., to ensure that the products meet design and quality standards.
Five Major Factors that Need to be Paid Attention to in the Injection Molding Process
1.Temperature: including baking material temperature, barrel temperature, mold temperature, and machine oil temperature
2.Pressure: including clamping pressure, mold opening pressure, injection pressure, holding pressure, seat in and seat out pressure, push in and push out pressure, back pressure, back pressure
3.Speed: including mold clamping speed, mold opening speed, injection speed, pressure holding speed, seat in and seat out speed, jacking in and out speed, rewinding speed
4.Time: injection time, holding time, baking time, molding cycle
5.Position: Injection-related position, mold opening-related position, mold closing-related position, reverse cable position
The continuous optimization and development of injection molding processes, such as using more advanced control systems, improving mold design, developing new plastic materials, etc., will help improve production efficiency, reduce costs, and produce higher-quality products. This process enables efficient production of everything from simple everyday items to complex industrial parts.
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