As the plastic flows through different parts of the injection molding machine and mold, the pressure acting on the leading edge of the plastic will be lost due to resistance and friction and in addition, as the plastic contacts the mold wall, it begins to cool, increasing the amount of plastic Viscosity, which requires extra pressure to push the plastic forward.
The plastic cortex formed at the mold wall reduces the cross-sectional area of the plastic flow resulting in a pressure drop. There is a maximum limit on the pressure at which the injection molding machine can be used to push the screw at the set injection speed. The speed required to push the screw forward should never exceed the maximum achievable pressure.
For example, considering the maximum available hydraulic pressure for an injection molding machine is 2,200 psi and the required screw speed is 5 inches / second. To allow the screw to advance at 5 inches per second, if it requires 2400 psi, the machine will not provide The pressure so that the screw does not travel at 5 inches per second In this case, the process is under pressure.
Knowing the pressure loss on each part of the process development helps to determine the overall pressure loss and where a large pressure drop occurs.The mold can then be modified to reduce the pressure drop for a better duration It is important to ensure that the maximum pressure is not reached.
The first test mode process, from the above figure you can see the following points:
Plastic In order to reach the end of the filling, a total pressure of 2200 psi is required.
Plastic In order to reach the middle of the product it is almost necessary to achieve a total pressure of 2200 psi.
Based on the above two points, the process is subject to pressure limitations Plastic needs 1379-983 = 396 psi to reach the end of the tertiary splitter from the end of the secondary splitter Plastic needs 1897-1379 = 518 psi pressure to pass through the gate .
Therefore, the tertiary runner and gate appear to have a relatively large pressure drop, then both the tertiary runner and the gate should be enlarged, which will reduce the final pressure on the fill end to 1901 psi. Now the process is no longer pressure limited. Ensuring that sufficient injection pressure will help achieve consistent mold filling is one of the most important steps in the study of pressure drop during mold certification.
Finally, keep in mind the rule of thumb: The maximum injection pressure required should not exceed 80% of the maximum pressure the injection molding machine can obtain, above 80% and should be lower for thicker products that require higher packing pressure To avoid a sudden increase in pressure between different parts, the transition should be as smooth as possible.