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Introduction to Precision Casting Processes
2021-09-22
First, after pressure holding, the die must be opened to remove the precision cast part; therefore, the time interval from the end of injection to the opening of the die is referred to as the mold-opening time. Opening the die within an adequate time allows the precision casting to attain a sufficient level of strength while still in the die. If the mold-opening time is inconsistent with the ejection time, the part will deform or crack. Conversely, if the mold-opening time is too short, the casting will be ejected while its strength is still relatively low, which can also lead to deformation.
Second, during the die-casting process, liquid metal enters the die cavity and completely fills it. The time required for this filling is referred to by precision casting plants as the fill time. The fill time depends on the size and complexity of the casting; for relatively simple castings, the fill time is typically quite short.
Third, the holding time depends on the material and wall thickness of the precision casting. For castings with a high melting point, a wide solidification temperature range, and thick walls, the holding time should be longer; for those with a narrow solidification range and thin walls, the holding time should be shorter. During the pressure-holding phase, precision casting manufacturers must also carefully control the duration. Insufficient holding time can easily lead to shrinkage porosity defects in the casting. However, excessively long pressure-holding time does not significantly improve the quality; on the contrary, it can make it difficult to shear off the flash and sprue from the vertical die-casting machine. Therefore, precise control of the pressure-holding time is a critical factor.
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