Process requirements for injection molding


Injection molding is a specific cycle, and there are fi […]

Injection molding is a specific cycle, and there are five elements that affect injection molding: temperature, speed, pressure, position, and time. These five process elements determine the quality of injection molding. The quality problems often encountered in injection molding are mostly caused by abnormal quality caused by five points that are not well controlled.

Temperature is the primary factor in injection molding. Temperature can be divided into several key factors such as drying temperature, material temperature, and mold temperature. The drying temperature is the pre-drying of the plastic material to ensure its molding quality and the drying and wetness of the plastic within a certain range; the material temperature is the normal plasticization and smooth filling and molding of the plastic; the mold temperature is considered during the injection molding process. The important factors of injection mold temperature, appearance, molding cycle and other factors affect the cooling rate of the product in the mold cavity and the appearance quality of the product.

The second element speed: speed is divided into injection mold speed, molten material temperature, mold withdrawal speed, mold opening and closing speed, and ejector forward and mold withdrawal speed. The increase of injection speed affects the increase of mold pressure. Increasing the injection molding speed can increase the flow rate, the product quality is uniform, and the product quality is guaranteed. High-speed injection is suitable for long process products. The higher the speed, the higher the melt temperature, and the stronger the plasticizing ability. In order to reduce the specific capacity of the melt, reduce the internal pressure of the melt, and prevent its outflow, the opening and closing speed is an important condition to ensure the operation of the machine.

The third element is pressure: pressure is divided into injection pressure, holding pressure, back pressure, clamping pressure, mold base protection pressure, and ejection pressure. The injection pressure is used to ensure the pressure loss of the melt from the nozzle-runner-gate-cavity to ensure that the cavity is full; the holding pressure method is used to reduce the cracking or bending of the stick mold due to excessive injection pressure. ; The pressed method is used to prevent the mold from breaking due to foreign matter in the high-speed and high-pressure state; the top pressing method is used to prevent the product from being separated from the mold surface and damage the mold.

The fourth element is position: position can be divided into mold opening position, ejection modulus, measurement modulus, injection modulus, and buffer modulus. The opening position of the mold is to ensure that the demolding and taking parts can work normally; the top return stroke is to protect the ejection limit by the partial reset of the spring; the top return stroke is to ensure that there is enough plastic to fill the mold to ensure product quality; the top return stroke is to make the melt The specific capacity of the body in the metering chamber increases, and the internal pressure decreases, preventing the melt from flowing outward from the cavity; the top return stroke is to prevent the mechanical damage accident caused by the contact between the screw head and the nozzle.

The fifth element is time: time is divided into cooling time of plastic products, plastisol time, plastic drying time, plastic product cooling time, melting time, drying time, cycle time, and pressure holding time. The molded product needs a specific cycle; the injection time determines the size of the injection molded product; the pressure holding is to prevent the melt from flowing back; the effect of cooling shrinkage; the cooling time is to ensure the solidification of the plastic product and prevent the product from deforming; the injection time is to ensure The product is sufficient; the drying time is to ensure that the product will not become longer, and the quality will not be poor.