This will involve major design parameters such as material shrinkage.
Therefore, the size of each part of the cavity can be determined only by grasping the shrinkage of the formed plastic in a specific manner.
Even if the selected die structure is correct but the parameters used are incorrect, it is impossible to produce qualified plastic parts. Plastic shrinkage and its influencing factors Thermoplastics are characterized by expansion after heating, shrinkage after cooling, and, of course, volume after compression. In the injection molding process, the molten plastic is injected into the mold cavity first.
After the filling is completed, the melt is cooled and solidified. When the plastic part is taken out from the mold, shrinkage occurs. This shrinkage is called forming shrinkage.
During the period of time from when the plastic part is taken out of the mold to the stability, there will still be slight changes in size. One change is to continue shrinking.
This shrinkage is called post-shrinkage. Another change is the swelling of some hygroscopic plastics due to moisture absorption. For example, when the moisture content of nylon 610 is 3%, the increase in size is 2%; and when the moisture content of glass fiber-reinforced nylon 66 is 40%, the increase in size is 0.3%.
However, the main role is the molding shrinkage. At present, the methods for determining the shrinkage (form shrinkage + post-shrinkage) of various plastics are generally recommended in the German national standard DIN16901. That is, the size of the mold cavity at 23°C±0.1°C is calculated by the difference between the corresponding plastic part size measured after being placed for 24 hours after molding at a temperature of 23°C and a relative humidity of 50±5%.