Parting line is a inevitable defect for the plastic injection molded part. It happened on the surface where the moving halve and the fixed halve meets and formed an edge like circle around the surface. When the mold is closed and the molten plastic gradually fills the cavity, high pressure inside the mold will push the molten flow occupy every space in the mold core and leave the circular mark around the parting surface.A number of considerations go into the placement of the parting line, with the goal of maintaining the overall integrity of the piece. Typically, as part of the finishing process, machinery will grind and smooth the parting line so it is no longer visible, if any extra material leaked into the space when the object was cast.
The product designer should fully communicated with the mold engineer to check the location of the parting line. For the mold designers, the parting surface should not be on the cosmetic side. Also, the precessing should be properly adjusted.
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