1, plastic supply is insufficient, temperature is low, and injection quantity is insufficient.

2, the injection pressure is small, the injection time is short, and the holding time is short.

3. The injection speed is too fast or too slow.

4. The nozzle temperature is low, the blockage or the aperture is too small, and the temperature of the bucket is low.

Unstable size:

1. The molding conditions (temperature, pressure and time) are unstable and the molding cycle is inconsistent.

2. The injection molding machine has poor performance or uneven plasticization.

3. The electrical or hydraulic system of the machine is unstable.

There are bubbles:

1, the material temperature is too high and the heating time is too long.

2, the injection pressure is small.

3. The injection speed is too fast.

Pit or dent:

1, high material temperature, high mold temperature and short cooling time.

2. The injection pressure is low and the speed is slow.

3. Short injection and holding time.

4. Insufficient feeding, insufficient feeding and insufficient residual materials.

Extended data:

Injection molding process:

1, filling. The injection time is from the time when the mold is closed until the mold cavity is filled to about 95%. Theoretically, the shorter the filling time, the higher the molding efficiency; But in actual production, the molding time (or injection speed) is limited by many conditions.

2. Pressure maintaining stage. Continue to apply pressure to compact the melt and increase the density (densification) of the plastic to compensate for the shrinkage behavior of the plastic. In the process of holding pressure, the back pressure is high because the mold cavity is full of plastic. In the process of pressure-maintaining compaction, the screw of injection molding machine can only move forward slowly and slightly, and the flow speed of plastic is also slow, which is called pressure-maintaining flow.

In the pressure maintaining stage, the plastic is cooled and solidified by the mold wall, and the viscosity of the melt increases rapidly, so the resistance in the mold cavity is large. In the later stage of pressure holding, the density of materials continued to increase, and gradually formed plastic parts. The pressure holding stage will last until the gate is solidified and sealed, when the cavity pressure reaches the highest value.

3. Cooling stage. Because the molded plastic products can only be cooled and solidified to a certain rigidity, it can prevent the plastic products from being deformed by external force after demoulding. Because the cooling time accounts for about 70% ~ 80% of the whole molding cycle, a well-designed cooling system can greatly shorten the molding time, improve the injection productivity and reduce the cost.

Improper design of cooling system will prolong the molding time and increase the cost; Uneven cooling will further cause warpage and deformation of plastic products.

4, demoulding is the last link of an injection cycle. Although the product has been cold-solidified, demoulding still has a very important influence on the quality of the product. Improper demoulding method may lead to uneven stress during demoulding and product deformation during ejection.

There are two main demoulding methods: ejector pin demoulding and stripper plate demoulding. When designing the mold, we should choose the appropriate demoulding method according to the structural characteristics of the product to ensure the quality of the product.

The main problems and reasons in the database of China sci-tech periodicals-online reading-injection molding

Baidu encyclopedia-injection molding process