1、 Principle of multi-stage injection plastic flow:

1. The first injection of glue is carried out at a low speed. The nozzle is moved away from the cold material head and the second injection rate is increased to fill the mold cavity to shorten the time for the plastic to flow to the end of the gate, so as to maintain the minimum solidification of the filled plastic viscosity. However, it is difficult to control the correct pressure maintaining switching point for high-speed injection, so it is necessary to use multi-stage deceleration to effectively control and master the pressure maintaining switching point.

2. The action principle of segmented ejection:

Using electro-optic control to command the flow proportional valve in the oil pressure system, the injection speed at a certain point is instantly obtained to achieve segmented injection speed.

2、 The relationship between segmented ejection rate and pressure:

1. In the segmented injection molding process, regardless of how many changes occur during the filling process, the injection pressure is only one pressure, that is, one pressure, while in the pressure maintaining stage, regardless of how many stages of pressure maintaining, the speed can only be maintained at one pressure.

2. Segmented ejection instance:

(1) The same finished product can be formed using a smaller locking force, thereby extending the lifespan of the machine and mold;

(2) Mastering the correct pressure maintaining switching point during segmented deceleration can effectively ensure the stability of quality;

(3)When the molding plastic flow is too good, low-speed injection is adopted to prevent burrs, but the principle is not to allow the raw material to cool and solidify. After the molten resin passes through the flesh thickness, the injection rate is increased to quickly fill the mold cavity. Flow marks (which are the striped pattern of molten grease gradually appearing at the center of the gate) are caused by the boundary formed between the resin that initially flows into the mold cavity and the resin that flows in second.

(4) When the injection port (i.e. the gate) is formed with a thick thickness, if the injection speed is too fast, it will cause turbulence, and the cold material is prone to remain in the channel and form flow marks. Therefore, the cold material head should be pushed open by slowly and low-pressure injection to allow the plastic behind to enter smoothly.

(5)In injection molding engineering, the contact between the nozzle and the mold is caused by the cooling water of the mold cooling the mold at a lower temperature than the nozzle. Some of the heat is carried away by the mold, and the nozzle is prone to producing cold material heads. These cold material heads, when injected into the mold, will block at the gate and cause streaks or silver streaks. Exploring segmented injection can improve this defect.

(6) Precise and small parts, with fine gate sizes and extremely difficult gate balancing for most mold cavities. By opening the gate to the same size and using multi-stage injection technology, it can be overcome.

(7)The change in the switching position between the first low-speed injection and the second high-speed injection can correct the local displacement of the fusion line, such as moving the obvious parts on the appearance to less obvious positions (such as labeling).

(8)The phenomenon of concavity and poor fusion is opposite to each other during forming, and this method can be used to improve both; The injection rate of the sunken part of the product drops sharply, and the injection rate is quickly increased after filling the surface layer to the cold solidification stage. When filling the mold cavity, rapid injection of adhesive should be used to prevent poor fusion in the areas where fusion lines occur (generally, the surface sunken part of the formed product occurs at the thick part, which is caused by the volume shrinkage during the cooling and solidification of the molten resin).

(9)During the pressure maintaining process, segmented reduction can reduce the residual stress of the formed product.

(10)The forming conditions for thin and long flowing products require high pressure to be successfully completed, but high-speed and high-pressure injection can easily cause residual stress at the gate, which affects quality. Therefore, high-speed injection, medium speed filling, and low speed pressure maintaining are adopted to eliminate residual stress and prevent deformation of the finished product.

(11)Improvement in mold cooling: If the dynamic mold temperature is low and the fixed mold temperature is high, the formed product will not experience inward warping. If the dynamic mold temperature is high, the formed product may experience outward warping.

(12)Scorching (caused by the compression and combustion of gas inside the mold cavity) is most likely to occur at the parting line or fusion point, and the surface of the resin shows black carbonization marks. To ensure the smooth discharge of air and gas from the mold cavity, the injection rate must be reduced.