Parting line divides the part surface into separate regions each produced by a different mould segment. Parting line coincides with the projected boundary of the casting when viewed along the draw direction. The internal angle at the parting line is less than 180 degrees. Parting line coincides with part of the bounding line of a parting surface. Flash appears along the parting line.

Parting line identification: The first step in parting line design is to select an appropriate parting direction. One set of alternatives for the parting direction is provided by the centerlines of the minimal bounding box of the casting. Other alternatives are given by the direction of normal to large faces in the casting.

The criteria for selecting the most suitable parting direction include (in decreasing order):

Minimize undercuts (number and then volume of cores) Minimize the total draw distance (for both halves) Minimize draft allowance (volume increment).

An undercut feature is produced using a corresponding shaped core. This involves higher costs in terms of special materials, additional tooling and lower productivity. The number and volume of cores must be minimised by selecting an appropriate parting direction.

The parting line can be identified using its characteristic that it coincides with the projected boundary of the casting when viewed along the draw direction. The edges of the casting are first projected on to a plane perpendicular to the draw direction. The inner segments of the projected edges are ignored and the outermost perimeter (silhouette boundary) is determined. This is projected back to the casting and the corresponding landing points are determined. These points are connected in sequence to form the parting line. If multiple landing points occur (say, along edges parallel to the draw direction) then multiple alternatives of parting lines are available for selection. Depending on the shape of the component, the above method can generate flat, stepped or complex parting lines.