Flash

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.
• ForgingClosed-die and open-die forgings in carbon, alloy, and stainless steel and aluminum, with grain flow for strength.
• Rubber extrusion and moldingSeals, gaskets, grommets, and profiles extruded or molded in EPDM, silicone, nitrile, neoprene, FKM, and TPE.

Related terms

Parting line

A parting line is the line on a molded or cast part where the two mold halves meet. It usually leaves a slight witness line and is where flash forms as the tool wears. Designers place it on an edge or noncosmetic surface and set draft away from it.

Trim die

A trim die is a press tool that shears flash, gates, runners, and overflows off a die casting or forging after it leaves the machine. Trim dies are a separate tooling line item, and complex parts can need more than one. Trimming leaves a slight witness line at the edge.

Closed-die forging

Closed-die forging is a forging process that presses or hammers heated metal between two shaped dies until it fills the die impression. It produces near-net parts with continuous grain flow and high fatigue strength, such as connecting rods, yokes, and wrench bodies. Excess metal escapes as flash and is trimmed.

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.