How to Determine Parting Line ?
         The term "parting line" refers to the location at which the cavity insert, the core insert, and the plastic molding meet. Since the core and cavity insert meet at this location, any significant deflection of the cavity insert away from the core insert will result in a gap into which the plastic will flow and form a thin film of plastic known as "flash" . Imperfections in the core and gaps into which the plastic will flow.. Even with new and well-crafted molds, the location of the parting line usually results in a very slight "witness line" along its length..

        For this reason, the parting line should be located along a bottom edge of the part, or some other non-visual, non-functional edge. Consider the previous cup shown in Figure 4.1.
Placing the parting line very close to the lip as indicated by the dashed line in the left drawing of Figure 4.6 would result in a witness line and possible flash that might make the molded cup unusable, Alternatively, a better location for the parting line is at the bottom of the rim as indicated in Figure 4.2, corresponding to the parting line shown in the right drawing of Figure 4.6.
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