US Mint studies planchet production alternatives
- Published: Mar 9, 2018, 6 AM
The U.S. Mint is contemplating what to do as 10 gas-powered rotary hearth annealing furnaces currently used at the Philadelphia and Denver Mints in planchet production reach the end of their useful service life.
The Mint is studying whether to replace the furnaces, or to outsource annealing operations while still retaining blanking production in-house, or whether to have all blanks produced by outside vendors.
During a technical presentation in February at the World Money Fair in Berlin, Richard Robidoux, division chief of engineering and new technology at the U.S. Mint and John C. Briggs from Fraunhofer USA’s Center for Manufacturing Innovations, jointly outlined research the Mint has pursued in streamlining blanking operations to make them more efficient and cost effective, including alternatives, like pushback blanking.
Pushback blanking allows punching of coinage blanks from already annealed materials, such as coinage strip; most blanks currently used for U.S. coins are punched from coinage strips, their edges are deburred, then the pieces are annealed in furnaces, and finally, a raised proto-rim is formed in an upset mill to create a planchet.
The U.S. Mint buys a combination of ready-to-use planchets and coinage strip. Currently, it contracts for ready to strike copper-plated zinc cent planchets from Jarden Zinc Products in Greenville, Tennessee. For copper-nickel 5-cent coins, copper-nickel clad dimes, quarter dollars and half dollars, and manganese-brass clad dollar coins, the Mint punches it own blanks from coiled coinage strip and finishes its own planchets. The current coinage strip vendors are Olin Brass in East Alton, Illinois, and PMX Industries in Cedar Rapids, Iowa.
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The Mint has been experimenting with several new production methods for blanks.
In 2014, the Mint researched laser cutting blanks, which, although found to be technically feasible, was deemed impractical in production of billions of coinage blanks.
In 2015, the Mint examined on a small scale the use of pushback blanking die technology. While pushback blanking, too, proved technically feasible, economic savings were not clearly defined, especially if the Mint were to choose instead to outsource blank production.
While investigating heat-treating technologies in 2016, it was determined that no more efficient method exists for annealing the blanks than a gas-powered rotary hearth. The furnaces currently in use are powered by natural gas.
In 2017, according to the technical report, an economically feasible pushback blanking operation was designed and demonstrated for quarter dollars, with 170 coinage strip coils processed and 50 million coins struck from the blanks produced.
Pushback blanking allows for direct blanking of annealed strip acquired from contractors. The blank would have a flat edge rather than a cupped edge.
The annealed strip is pressed between the blanking punch and a heavily spring-loaded pad. After punching, the blank is pushed back into the strip, the strip advances, keeping the blank flat, and the newly punched blank is knocked out later.
The Mint’s testing of the pushback technology, with Fraunhofer USA consultation, began with a single blanking die to determine parameters for blanking die construction. A 10-at-a-time-die configuration was established and used on narrow web scrap on test strikes for three denominations.
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Full-scale blanking execution was then tested using a 30-at-a-time-die configuration for high-volume production. Current blanking operations employ a 15-die configuration.
The Mint’s technical presentation indicated that the pushback blanks are better in appearance than blanks internally annealed currently at the Mint.
Coils of coinage strip weighing several tons each are moved and fed into the blanking presses using heavy, forklift-style machinery; handling coils that are already annealed to make the metal softer requires more care.
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