3 Fundamentals of press design

526 Solid forming (Forging)
6.8.7 Minting and coin blanking lines
Rimming and edge lettering machines
Coin blanks are manufactured on high-speed blanking presses from an
indexed sheet metal strip (cf. Fig. 4.6.6 and 4.6.8). Depending on the
material characteristics and the condition of the die, a rough cut surface
and/or blanking burr are formed at the outside surface of the coin blank
(cf. Fig. 4.7.8). To achieve a high level of coin quality, the outside edge
of the coin blank must be smoothed. This is achieved by a radial upsetting
process in rimming and edge lettering machines.
When smoothing the edge, the coin blank is sized within extremely
narrow tolerance limits (+/– 0.02 mm). Reducing the diameter by 0.2 to
0.5 mm causes material to accumulate at the periphery of the coin
blank. Depending on the intended purpose, different upsetting shapes
can be selected (Fig. 6.8.17). The rimming or upsetting process helps to
accumulate the material necessary for forming the rim area of a coin.
Thus, this material does not have to be forced outwards from the center
of the coin blank. As a result, the coining process, conducted after upsetting,
requires less force. Reduction of the coining force leads in turn to
an increase in the service life of the coining dies.
Rimming machines are used for a diameter range from 14 to 50 mm
both with vertically and horizontally arranged upsetting shafts. In rimming
machines with a vertical upsetting shaft, the blanks are fed
towards the upset die, which comprises the upset ring and upset seg-
unprocessedblank shape R :highlyrounded shape P :slightlyrounded
s=blankedthickness
D>D
D D
Fig. 6.8.17 Upsetting shapes on coin blanks
t=upsetthickness
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
shape M :flatknurling shape S :flatknurling