What are the basics of mold design in injection molding processing?

Injection molding process is a common plastic manufacturing method, and its process flow is mainly: mold clamping, injection molding, pressure holding (pre-molding), cooling setting, mold opening, ejection, and mold clamping. Injection molding a cycle process, complete injection molding requires pre-molding, injection molding and cooling stereotypes in three stages. The following is a detailed introduction to the basics of mold design in injection molding processing.

First, injection molding process

1, pre-plastic stage

The screw starts to rotate, and then the plastic conveyed from the hopper is conveyed to the front part of the screw. The plastic is uniformly plasticized under the action of high temperature and shear force and gradually gathers at the front end of the barrel. As the melted plastic gathers, the pressure becomes more and more. Large, and finally overcome the screw back pressure to push the screw back gradually, when the plastic in front of the barrel reaches the required injection volume, the screw stops back and rotates, and the pre-molding phase ends.

2, injection stage

The screw moves forward under the effect of the injection cylinder, and the plastic stored in the front of the cartridge is pushed forward with multi-level speed and pressure, and injected into the closed mold cavity through the flow passage and the gate.

3, cooling and setting stage

The plastic is held in pressure in the mold cavity to prevent the plastic from flowing back until the plastic cures and the pressure in the cavity disappears. Cooling time is the largest proportion in a production cycle.

Second, the injection molding process parameters

1, injection pressure

Injection pressure is provided by the hydraulic system of the injection molding system. The pressure of the hydraulic cylinder is transmitted to the plastic solution through the screw of the injection molding machine. Under the pressure, the plastic solution enters the vertical flow path, the main flow path and the bypass flow path of the mold through the nozzle of the injection molding machine, and enters the mold cavity through the gate. This The process is the accommodation process or the filling process. The existence of pressure is to overcome the resistance during the flow of the solution, or conversely, the resistance existing in the flow needs to be offset by the pressure of the injection molding machine to ensure the smooth progress of the filling process.

2, injection time

Injection time refers to the time required for the plastic solution to fill the cavity, which does not include auxiliary times such as mold opening and closing. Although the injection time is very short, the impact on the forming cycle is small, but the adjustment of the injection time has a great effect on the gate, runner, and cavity pressure control. A reasonable injection time helps the ideal filling of the solution, and it is of great significance for improving the surface quality of the product and reducing the dimensional tolerance.

3, injection temperature

Injection molding temperature affects the important factors of injection pressure. Injection temperature must be controlled within a certain range. The temperature is too low, and the plasticity of the melt is poor, which affects the quality of the molded part and increases the difficulty of the process. The temperature is too high and the raw materials are easily decomposed. In the actual injection molding process, the injection temperature tends to be higher than the barrel temperature, and the high value is related to the injection rate and the properties of the material, up to 30°C. This is due to the high heat generated when the melt is sheared through the injection port.

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