Five Elements of Injection Molding

2021-12-21

Injection pressure setting

The pressure is used to overcome the flow resistance and reflect the speed; the set value of the injection pressure is the limit value of the pressure in the filling stage. The actual pressure is shown on the display of the Injection Molding Machine "pressure curve".

Injection speed

Definition: Under a certain pressure, the speed at which the melt is injected from the nozzle into the mold.

effect:

1.The increase in injection speed will increase the filling pressure.

2.Increasing the injection speed can increase the flow length and make the product quality uniform.

3.High viscosity during high-speed injection, fast cooling, suitable for long-flow products.

4.Flow balance at low speed, product size is stable.

Setting principles:

1.Prevent mold expansion and avoid flash.

2.Prevent scorching due to excessive speed.

3.Under the premise of ensuring product quality, choose high-speed filling as much as possible to shorten the molding cycle. If the injection speed is too fast, it is easy to cause focal spots, flashes, internal bubbles or cause the melt injection to be too slow: flow marks, weld marks, and surface Rough, dull.

Injection time setting

Injection time:

Essentials: when the injection time just meets 95% of the state of the product; set the principle as small as possible to shorten the molding cycle

compress time:

The holding time is determined by weighing the product based on the condensation of the gate.

Holding pressure time is too long: overweight, whitening, strain, flashing, difficult demolding, too large size, too short holding time: insufficient weight, cavity inside the product, shrinkage, small size

Cooling time:

Reduce the cooling time until the following conditions are met;

When the finished product is ejected, there will be no whitening, straining, or cracking.

The size of the finished product will not become smaller as the cooling time is reduced

The actual temperature of the mold will not increase with the decrease of the cooling time

Injection molding machine temperature setting

Oil temperature:

For hydraulic presses, it is the thermal energy generated by the friction of the hydraulic oil in the continuous operation of the machine. It is controlled by cold water. Make sure that the oil temperature is around 45℃ when starting up. If the oil temperature is too high or too low, it will affect The transmission of pressure

Mold temperature:

Mold temperature will affect the fluidity and cooling rate of the melt. Because it affects the fluidity, it affects the appearance of the product (surface quality, burrs) and injection pressure; it affects the cooling rate, which affects the crystallinity of the product, which in turn affects the shrinkage rate and mechanical strength of the product. performance.

High mold temperature: good fluidity; high crystallinity; large shrinkage (thus resulting in smaller size); deformation; longer cooling time is required.

Low mold temperature: poor fluidity (resulting in flow lines, weld marks); low crystallinity; low shrinkage (resulting in larger size).

Previous: The advantages and differences of automatic and semi-automatic blow molding machines Next: What are the precautions for hot runner installation?