Structural Analysis Explanation of Injection Molding Machine

The injection molding machine is mainly divided into an injection part and a locking part in terms of mechanical structure. The function of the injection part is to melt plastic and inject it into the mold cavity, while the function of the locking part is to control various actions such as mold opening and closing, ejecting products, etc.
1. Injection section
There are two main forms of injection: piston type and reciprocating screw type.
Nowadays, piston injection molding machines are very rare and will not be introduced here.
The reciprocating screw injection molding machine melts and mixes solid plastic particles (or powders) through the rotation of the screw in the heating cylinder, squeezing them into the front cavity of the cylinder. Then, the screw moves forward along the axial direction, injecting the plastic melt in the cavity into the mold cavity. During plasticization, plastic is pushed by the screw ribs and compacted in the screw groove, receiving heat transfer from the barrel wall. In addition, the friction between plastic and plastic, plastic and barrel, and the surface of the screw generates heat, gradually increasing the temperature to the melting temperature. The melted plastic is stirred and further mixed by Luoxuan, and enters the front of the barrel along the screw groove and pushes the screw back.
The components related to injection and plasticization mainly include screws, barrel, flow shuttle, check ring, nozzle, flange, feeding hopper, etc. The following will explain their roles and impacts in the plasticization process.
The screw is an important component of an injection molding machine. Its function is to transport, compact, melt, stir, and apply pressure to plastic. All of this is achieved through the rotation of the screw inside the barrel. When the screw rotates, plastic will generate friction and mutual movement on the inner wall of the barrel, the bottom surface of the screw groove, the advancing surface of the screw edge, and between plastic and plastic. The forward movement of plastic is the result of this combination of motion, and the heat generated by friction is also absorbed to increase the temperature of the plastic and melt it. The structure of the screw will directly affect the degree of these effects.
Ordinary injection molding screw structures can also be designed with components such as release screw, barrier screw, or split screw to improve plasticization quality.
The structure of the machine barrel is actually a circular tube with a cutting hole in the middle.
In the process of plastic plasticization, the power for its advancement and mixing comes from the relative rotation of the screw and barrel. According to the different forms of plastic in screw grooves, the screw is generally divided into three sections: solid conveying section (also known as feeding section), melting section (also known as compression section), and homogenization section (also known as metering section).
In textbooks related to plastic plasticization, the solid conveying section of plastics in the screw is regarded as a solid bed where plastic particles do not move with each other. Then, the ideal state of motion and friction between the solid bed and the barrel wall, the screw edge advancing surface, and the screw groove surface is calculated to determine the forward conveying speed of plastics. There are many differences between this and the actual situation, and it cannot be used as a basis to analyze the feeding situation of plastic particles with different shapes. If the plastic particles are not large, they will delaminate and roll when pulled forward by the inner wall of the barrel, and gradually be compacted to form a solid plug. When the diameter of the material particles is similar to the depth of the screw groove, their motion trajectory is basically a linear motion along the radial direction of the screw groove plus a linear motion at an angle. Due to the loose arrangement of plastic in the screw groove when the particles are large, the conveying speed is also slower. When the particles reach a certain size and enter the compression section with a diameter greater than the depth of the screw groove, the plastic will get stuck between the screw and the barrel. If the forward pulling force is not enough to overcome the force required to flatten the plastic particles, the plastic will get stuck in the screw groove and not advance forward.