The parting line of a die cast component represents where the two different sides of the mold come together. This line often (but not always) marks the border between the inside and outside of the part.

The location of the parting line indicates which side of the die is the cover and which is considered the ejector. A well placed parting line is important to the die casting process and has a significant effect on the quality of the part.

Value and Advantages

The parting line of a casting needs to be determined early in the design processes. When determining the location of the parting line the part designer and die cast engineer should work together to consider part functionality and die casting process. Often times it is useful to have most of the geometry in the ejector half; as this prevents the casting from sticking in the cover half.

The parting line is created where the two halves of the die meet. Gates, overflows, and vents will connect to the casting at the parting line. Also, flash will form at the parting line when the pressure from the injected metal tries to force the die halves apart. During the trimming process the gates, overflows, vents, and flash will need to be removed by the trim die. A well designed parting line will ease the trimming process.

When flash occurs it increases the thickness of the parting line; altering dimensions measured across the parting line. For critical dimension it is important to have measurements in only one die half to reduce dimensional tolerance.

The parting line can also effect the life of the die. Metal injected straight onto a surface will erode that surface faster. Positioning of the parting line to allow metal to flow more smoothly will improve die life and casting quality. Cosmetic surfaces are typically placed on the cover side of the casting.

To learn more about the role of parting lines, watch our video; if you have further questions about this or any other aspect of die cast design, contact us directly.