Parting and Witness lines
The parting line is the witness line left on the parts that is where the sprue side (also called the A side) and the ejector side (also called the B side) of the molds meet. The customer should be made aware of the location of the parting and witness lines for MIM component design and function. Cosmetic and functional requirements may help guide parting and witness line locations. The parting and witness lines can be minimized by post sinter polishing operations.
Witness lines will be evident on the parts wherever there are moving or stationery pieces of steel (slides, ejector pins, core pins, inserted areas) that meet when the mold is closed for the molding process.
This picture shows parting line mismatch or flash. The mold can be adjusted to minimize this condition.