Shot size

Where it comes up

• Plastic injection moldingMolten thermoplastic injected into a steel or aluminum mold. Lowest piece price for plastic parts at 5,000+ a year.
• Zinc and aluminum die castingMolten zinc or aluminum injected into steel dies at high pressure. Thin walls and net shape at 2,500+ parts a year.

Related terms

Short shot

A short shot is an injection molded part that is incomplete because plastic froze before filling the whole cavity. Causes include low shot size or pressure, blocked vents, thin walls, and long flow lengths. Molders often run short shots on purpose during mold trials to study fill.

Tonnage

Tonnage is the force a press can apply, rated in tons, and the force a job requires. Stamping tonnage is estimated from cut length, material thickness, and shear strength. In molding and die casting, clamp tonnage must exceed cavity pressure times projected area to keep the tool closed.

Cold runner

A cold runner is an unheated channel system in an injection mold that carries molten plastic from the sprue to the gates. The runner solidifies with each shot and is ejected with the parts, then scrapped or reground. Cold runner molds cost less than hot runner molds but waste more material.