The term parting line can be referred to the meaning "parting surface" which gives a better idea of the concept. Many design engineers face complexities in accepting the fact that the parting line is not merely a vector that may be randomly moved about on the design component.
However, parting line appears to be a faded vector upon the face of the designed component, when designed accurately. This faded vector signifies the two parting surfaces perfectly intersecting each other when the mold is closed. This draft must be placed on all the vertical faces away from the parting lines in the component. Hence, the broadest point on the component represents the "parting line".
Both the structural and functionality of the component are affected by design decisions of locating the parting line and the following application of draft to the plastic part. These choices should be made before hand when the part is sent to the mold maker to save production time. Following are the characteristics of a parting line:
- It divides the surface of the component into various separate regions and each region is generated with the help of an individual mold segment.
- Each parting line intersects with the projected boundary of the casting, when observed along the draw direction.
- Parting line exhibits an internal angle, the measure of which is always less than 180 degrees.
- Parting line also coincides with part of the bounding line of a parting surface.
- Parting line also exhibits flash along with it. Since a parting line is the place where two or more halves of the component meets. In some cases, the mold halves might not meet with enough accuracy or because injection pressure is high, material will creep into the space between the molds. This material is generally called molding flash or simply flashing.
The above characteristics of the parting line helps in identifying the parting line when it intersects with the projected boundary of the casting when observed along the draw direction.
To obtain the parting line, the corners of the castings are projected perpendicular to the plane along the parting direction. Also, the outermost boundary's perimeter is considered overlooking the innermost sections of the projected corners.
This is anticipated back to the casting and the relevant landing points are estimated. Then these landing points are coupled together in the same order to form parting line. Multiple substitutes of parting lines are required to be figured out in case of multiple landing points.
These alternatives of parting lines are able to generate flat, stepped or complex parting lines in reference to the shape of the components.
Besides the complexity involved in making the component, the various characteristics related to parting line design also greatly affect the tooling cost of the component. A non-planar parting line must be avoided. This implies a product design with a specific draw direction, taper the sections parallel, and to minimize undercuts to the draw direction to give natural draft.
If any critical surfaces exist, needs to be machined and designed underpinning the metal casting to avoid inclusions, which are also referred as higher machining allowance.