Injection molding principle and general processing characteristics

Author: MULAN – Plastic Molding Manufacturer

Injection molding is to inject plastic melt into a closed mold cavity at high speed under high pressure, and obtain a plastic product that is completely consistent with the shape of the mold cavity after cooling and shaping. Injection molding must meet two necessary conditions: the plastic must be injected into the injection mold cavity in a molten state, and the injected plastic melt must have sufficient pressure and flow velocity to completely fill the mold cavity, so injection molding must have Basic functions such as plastic plasticization, melt injection molding and packing molding. Plasticization: During the plasticization process of injection molding, the solid plastic is conveyed by the rotating screw, continuously moves forward along the direction of the screw groove, and heats up after heating, compaction, shearing and kneading of the screw thread. It is converted into a viscous fluid plastic melt with uniform density, viscosity and composition and stable distribution.

Injection molding process: The plasticized plastic melt is stored in the storage area of ​​the barrel, and the screw moves axially during injection molding. Under the action of the screw injection pressure, the plastic melt flows through the barrel installed at a certain rate. The nozzle in the front section, the mold gating system, etc. are injected into the cavity of the mold. Cooling and shaping process: the plastic melt injected into the mold cavity injection mold overcomes various flow resistances and fills the cavity, and the plastic melt filled with the cavity is subjected to huge pressure from the cavity, which drives the flow of the plastic melt Returning to the trend of the barrel, the plastic melt shrinks due to the cooling effect of the cavity. At this time, the injection screw continuously provides pressure to keep the plastic melt filling the cavity without backflow, and properly replenishes the plastic melt into the cavity to fill the shrinkage space in the cavity until the plastic melt gradually cools and solidifies into a product.

Details determine success or failure has become the standard pursued by every industry. Nowadays, the precision of products is getting higher and higher, and the quality requirements are getting stricter. This requires strict control of every link of the product in the production process. , strict supervision, especially the injection molding products industry. Injection molded parts processing products have penetrated into every industry, and the continuous improvement of plastic performance has made many parts that must be made of metal before can be completely replaced by plastic parts. However, due to the natural fluidity of plastics, the size is not easy to control, making the manufacturing process of injection molded parts more difficult than other industries, especially in the details, if you don't pay attention, injection molding processing is prone to pores, color difference, and flashing If the phenomenon is serious, the product will be scrapped directly. These common problems in the injection molding process directly test whether the injection molding engineer can control the details of the injection molding processed products in place.

The characteristics of ordinary injection molding processing are: the dimensional accuracy of the injection molded parts is not high, generally it can be assembled as the standard, and the appearance requirements of the injection molded parts are relatively high, and the second processing (such as oil injection) may be used if necessary. To improve the appearance of defects. Ordinary injection molding does not require a particularly precise injection molding machine, nor does it require specially designated materials. Commonly used thermoplastics can be used for production, so ordinary injection molding processes are widely used in the modern plastics industry. Injection molding If the wall thickness of the injection molded part is uneven, the product will deform or shrink. To solve this problem, it is best to advise the customer to modify the product. If the product cannot be changed, it can only be reversed at the transition between thick and thin. Angle or R angle to transition, this will reduce the stress problem of the plastic when it flows. If the stress is reduced, the product will not be easily deformed. Of course, the thick and thin parts should not exceed 60%, otherwise it must be thinned or increased. thick.