Warm Global Customers
With China Plastic Machinery
With China Plastic Machinery
Injection molding, also known as transfer molding, is a thermosetting plastic molding method developed on the basis of compression molding. It can form plastic parts with complex shapes, thin walls or large variations in wall thickness, and fine inserts.
During injection molding, thermoplastic raw materials (like compression molding, the plastic raw materials are powder or pre-pressed blanks) are loaded into the feeding chamber of the closed mold, and heated and plasticized in the feeding chamber; the molten plastic after plasticization enters the closed mold cavity through the pouring system at the bottom of the feeding chamber under the action of injection pressure; the plastic continues to be heated and pressurized in the mold cavity to solidify and form, and finally the mold is opened to take out the plastic part.
Compared with compression molding, injection molding has the following characteristics
(1) Short molding cycle and high production efficiency
Plastics are first heated and plasticized in the feeding chamber. During molding, plastics are pressed into the mold cavity through the pouring system at high speed. The plastics that are not completely plasticized come into contact with the high-temperature pouring system, causing the plastics to heat up quickly and evenly. At the same time, the molten material absorbs friction heat when passing through the narrow part of the pouring system, further increasing the temperature, which is conducive to the rapid hardening of the plastic parts in the mold cavity, thereby shortening the hardening time. The hardening time of injection molding is only one-third of that of compression molding.
(2) High dimensional accuracy and good surface quality of plastic parts
Because the plastics are heated evenly and cross-linked and hardened sufficiently, the mechanical properties of the plastic parts are improved, so that the strength, mechanical properties and electrical properties of the parts are improved. The dimensional accuracy of the height direction of the plastic parts is high, and the flash is very thin.
(3) It can form plastic parts with small inserts, deeper side holes and more complex parts
Since the plastic is pressed into the cavity in a molten state, the extrusion force on the slender core, inserts, etc. is smaller than that of the compression mold. The hole depth formed in the vertical direction of general compression molding is no more than 3 times its diameter, and the hole depth in the lateral direction is no more than 1.5 times its diameter, while injection molding can form through holes with a depth of no more than 10 times the diameter and blind holes with a depth of no more than 3 times the diameter.
(4) It consumes more raw materials
Due to the presence of condensate in the casting system, the plastic consumption is relatively high, which is particularly prominent for small plastic parts.
(5) The shrinkage rate of injection molding is greater than that of compression molding
The shrinkage rate of general phenolic plastics during compression molding is 0.8%, but the shrinkage rate during injection molding is 0.9%~1%, and the shrinkage rate is directional. This is caused by the directional flow of materials under pressure, which affects the precision of plastic parts, but has little effect on plastic parts filled with powder fillers.
(6) The structure of the injection mold is relatively complex and the process conditions are strict
During injection, the molten material enters the mold cavity through the pouring system for molding. Therefore, the structure of the injection mold is more complex than that of the compression mold, and the process conditions are stricter. In particular, the molding pressure is higher (much higher than the pressure during compression molding), and the operation is more troublesome and the manufacturing cost is also high. Therefore, injection molding is only used when compression molding cannot meet the requirements.
The injection molding process is basically similar to the compression molding process. The main difference between them is that the compression molding process is to add materials first and then close the mold, while the general structure injection mold requires closing the mold first and then adding materials during injection molding.
Injection molds, like compression molds, can also be divided into mobile injection molds and fixed injection molds according to how they are fixed on the press. However, the biggest feature of injection molds is that they have a separate feeding cavity. According to the structural characteristics of the feeding cavity, they can be divided into tank-type injection molds and plunger-type injection molds.
If you are interested in our company and machine, feel free to contact our sales engineer. We will contact you as soon as possible.