Injection molding principle and common processing characteristics
Publisher: Administrator Date：2020-07-31
Injection molding is to inject plastic melt into a closed mold cavity at high speed under high pressure, and after cooling and shaping, a plastic product that is completely consistent with the shape of the mold cavity is obtained.
Injection molding must meet two necessary molding 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 speed to completely fill the mold cavity, so injection molding must have Basic functions such as plasticization, melt injection and pressure holding molding.
Plasticization: In the plasticization process of injection molding, the solid plastic is conveyed by the rotating screw, and continuously moves forward in the direction of the screw groove. It is heated by heating, compacting, and shearing and mixing of screw threads. It is transformed into a viscous fluid plastic melt with uniform density, viscosity, composition and stable distribution.
Injection process: The plasticized plastic melt is stored in the storage area of the barrel, and the screw moves axially during injection. Under the action of the injection pressure of the screw, the plastic melt flows through the barrel at a certain rate. The nozzle of the front section, the mold pouring system, etc. are injected into the cavity of the mold.
Cooling and setting process: The plastic melt injected into the mold cavity of the injection mold overcomes various flow resistances and fills the mold cavity. The plastic melt filled with the mold cavity is subject to huge pressure from the mold cavity, which drives the flow of the plastic melt Going back to the barrel trend, the cooling effect of the mold cavity causes the plastic melt to cool down.
At this time, the injection screw continues to provide pressure to keep the plastic melt filling the cavity without backflow, and appropriately replenish the plastic melt in the mold cavity to fill the contraction space in the mold cavity until the plastic melt is gradually cooled and solidified 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 molding products have penetrated into every industry, and the continuous improvement of plastic performance has made many parts that had to be made of metal before can now be replaced by plastic parts.
However, due to the natural fluidity of plastics and the difficult size control, the manufacturing process of injection molded parts is more difficult than other industries, especially in the details. If you don’t pay attention to the details, the injection molding process is prone to pores, color aberrations, 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 controls the details of the injection molded product in place.
The characteristics of ordinary injection molding are:
The dimensional accuracy of injection molded parts is not high. Generally, it can be assembled as the standard. The appearance requirements of injection molded parts are relatively high. If necessary, a second processing (such as oil injection) may be used to improve appearance defects.
Ordinary injection molding does not require a particularly precise injection molding machine, nor does it require specially specified materials. Generally, commonly used thermoplastics can be used for production, so ordinary injection molding processes are widely used in the modern plastics industry.
In the injection molding process, if the wall thickness of the injection molded parts is uneven, it will cause the product to deform or shrink. To solve this problem, the first thing to suggest is that the customer modify the product. Of course, it is best. If the product cannot be modified, then the C can only be poured at the transition between thickness and thinness. Angle or R angle to transition, this will reduce the stress problem of the plastic when it flows, and reduce the stress, and the product will not be easily deformed. Of course, the thickness and thinness of the area cannot be more than 60%, otherwise it must be thinned or increased. thick.