Molding flash
Flash, also known as flashing, is excess material attached to a molded
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....

, forged
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. Forging is often classified according to the temperature at which it is performed: '"cold," "warm," or "hot" forging. Forged parts can range in weight from less than a kilogram to 580 metric tons...

, or cast
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...

 product, which must usually be removed. This is typically caused by leakage of the material between the two surfaces of a mold (beginning along the parting line
Parting line
A parting line in moldmaking is the place where two or more parts of the mold meet. At times, either because the mold halves do not meet with enough precision or because injection pressure is high, material will creep into the space between the molds. This material is generally called molding...

) or between the base material and the mold (in the case of overmolding). Molding flash is seen when the optimized parameter on cull height is not calibrated. Proper design of mold parting surfaces can reduce or eliminate flash.

Molding flash can be caused from old or worn mold cavities that no longer fit tightly together. Other times, the complexity of the part requires so many mating pieces with such precise geometries that it is almost impossible to create a perfect fit on every impression. Most often, the type of material being molded, and its attendant viscosity in its liquid form, is the primary factor that leads to the creation of the unwanted mold flash.

The process of removing flash, known as deflashing, is commonly performed via cutting, breaking, grinding
Grinding (abrasive cutting)
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.A wide variety of machines are used for grinding:* Hand-cranked knife-sharpening stones * Handheld power tools such as angle grinders and die grinders...

, or tumbling. Some foundries use robot autogrinders to remove this unwanted material.

Witness mark

In plastic injection, a faint mark called witness mark (or witness line) will occur along the parting line. This is unavoidable and is usually accepted despite minor aesthetics issue. However, some part surfaces (e.g. when used for sealing) cannot tolerate witness mark, and thus either the mark must be removed post-molding or the mold
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....

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