Molding Conditions of Injection Molding Machine (Part 2)

 1. Filling pressure


In injection molding conditions, filling pressure refers to the pressure to fill the resin into the mold, also known as primary pressure. The unit is MPa or kgf/cm2. That is the unit of pressure. There are also some injection molding machines that set the maximum injection pressure to 100%, and then adjust the injection molding conditions by changing the percentage. (Example: 35%)


If the filling pressure is too low, poor filling (underfill) will occur. If the filling pressure is too high, the parting surface may be momentarily opened by the pressure, and burrs may appear around the molded product. Sometimes poor release occurs.


2. Injection speed


Injection speed refers to the speed at which molten plastic fills the mold. The unit is mm/s.


When considering injection volume per unit of time, it may be stated as "injection rate", in which case the unit is cm3/s.


If the injection speed is too slow, filling defects may occur; if the injection speed is too fast, burrs and jet marks (unfavorable phenomenon of serpentine patterns on the surface of molded products) may appear.


3. Hold pressure


Pressure keeping means that after the entire cavity is filled with molten resin, before the gate is closed (referring to the gate solidification), the gate is pressurized with a constant pressure to prevent the resin from flowing back. The unit is MPa or kgf/cm2.


If the packing pressure is too low, the resin may flow back from the gate, causing the surface of the molded product to sink (dent) or shrink significantly, resulting in a smaller size.


If the packing pressure is too high, the product size may become too large, and burrs and poor release may occur.


In order to ensure that the packing is really effective, the holding time is very important. At the same time, it is also very important to fully understand that "the packing should not be closed before the gate is closed".


4. Injection time


The sum of filling time and holding time is usually called injection time. The dwell time can be adjusted by changing the injection time. The unit is s (second)

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