Flash. An irregularly shaped flange of excess metal squeezed out wherever possible in metalworking procedures like die striking. All dies will create flash if certain conditions exist – as an overweight or oversize blank – or if the pressure of the striking press is too great. This overabundance of metal must go somewhere and it finds the cracks between dies and collar – or if there is no collar, from between the dies themselves. Flash is not an anomaly of striking, but is inherent to any metal forming process. In coin manufacturing flash appears as a fin, wire edge or knife edge where it only forms at the rim/edge juncture because of the restraining collar. For medal manufacturing without a collar and open face dies it forms at the center of the edge of the medal (where it squeezes out between the dies).Flash from open face dies. All medallic items struck without a collar, that is, with open face dies, will always have some degree of flash, forming at the center line on the edge. It forms in the die gap, the space between the two dies beyond the edge. The mass of the blank that does not fill the cavities of the dies will cause metal to flow outward between these open face dies because there is nothing to restrain this metal flow.For multiple struck medals flash appears to "grow" on succeeding strikes. A typical 3-inch medal may have only a 1/16-inch flash after the first blow, 3/16th after the second, 1/4th after the fourth, and perhaps 5/16th inch after the final blow several strikes later. (A process set shows this evidence dramatically.)Less and less metal is being moved on subsequent strikes of these large medals. The final blows are to insure filling the lowest cavities in the dies, the high points in the struck piece. Therefore less and less metal will flow outward to widen the flash on final strikes.Flash from coining dies. This is comparable to a similar extruded metal fin formed when a collar is present (and struck with collar dies); such a fin is called a wire edge and occurs in the gap between the dies and the collar (the only place where excess metal may flow). This is decidedly a human error (from using an oversize planchet or continued striking with a worn collar). See fin.Flash in casting. Flash will occur at the parting line in casting; also should the mold have any fractures or cracks flash will form in these crevices. Flash is removed from cast ingots by a dressing with the use of files or wire brushes. For work pieces, as cast plaques or art medals, flash is removed by chasing prior to finishing, and is one reason for pieces known as cast and chased.Removing flash. Unless a few untrimmed specimens are set aside – as for process sets – flash normally exists only in the pressroom. After a medal is fully struck up it is taken to the next step of trimming. Here the flash is removed by turning on a lathe (for large round medals) or by trimming dies on a trip hammer press (for small or irregularly shaped medals). Turning on a lathe with the use of a form mold is the most practical method of removing flash from round medals. All flash has to be removed, and the edge made smooth, before any further work can be done, as edgelettering or finishing. See trimming.Obviously striking or coining with a collar – and the proper size blank and press impression – will strike a perfect piece without flash and such trimming is unnecessary.
excerpted with permission from
For Artists, Makers, Collectors and Curators
COMPILED AND WRITTEN BY D. WAYNE JOHNSON
Roger W. Burdette, Editor