VOCABULARY TERMS: BLANKED, BLANKING

Blanked, Blanking The process of cutting out blanks, from metal strips of proper thickness (gauge) prior to striking into coins, medals or other items. The manufacture of blanks is the first step of many metalworking processes by cutting blanks from previous rolled strip stock. The goal of blanking is to provide the correct metal composition in a form suitable for the required press with the blank in the proper shape, weight, diameter and thickness. To these five requirements is often added three others, particularly for coining presses, the proper preparation of the edge, by upsetting; coin blanks are also annealed (to soften them for striking) and metal cleaned (to rid all surface adherents).

Blanking is accomplished with blanking dies in a press (most any kind of metalworking press). It is called cutting-out in England, and the blanking press that accomplishes this a cutting-out press. Americans called it simply cutting – particularly with a single blank – until 1896, when multiple blanking was introduced and the term "blanking" was thereafter applied to all blank production.

History of Blanking. Globular lumps of metal were first used as blanks for the earliest coins. Later, the metal was hammered into thin, flat sheets and cut to approximate shape by hand shears (providing struck pieces with very irregular edges). Attempts were made of casting blanks to be later struck (cast blanks). However, it was Leonardo da Vinci, and later goldsmiths, who developed a rolling mill to create flat plates from which blanks could be cut. Da Vinci also made a drawing of a crude blanking punch (see illustration). It is doubtful it was ever used, as the blanks had to be ejected through a opening in the punch.

Da Vinci also drew plans for a blanking press based upon the concept of a drop hammer. A manual wheel pulled a weight on a cord to the top of the press; when released it dropped on a spring blanker. The blanking dies cut out the circular blank from metal strip. The spring caused the blanking die to retract separating it from the metal strip (stripper). There is no record that da Vinci's press was ever built (or would have worked in the 16th century). However, in the 20th century the International Business Machine Company financed the construction of a full scale model from da Vinci's drawings. (This model is now in the Smithsonian Institution, Washington).

Leonardo da Vinci envisaged several important blanking technologies: using strip stock, employing a blanking die and stripping the skeleton strip from the blanker. (Da Vinci's drawing also indicated a duality in his concept – blanking was done on one side, embossing on the other with a blanking press coupled to a striking press. In theory, he reasoned correctly, a blank had to be created before a piece could be struck. Perhaps he intended that with a single impact from the drop hammer, that a piece could be struck and a blank for the next striking be formed at the same time.)

Before, and long after da Vinci's time, coin blanks were cut out with shears from hammered flat plates. They were then trimmed to approximate circular shape by grouping together a handful in a stack and filing their edges. This repetitious work was all done by hand. It was only then they could be struck by moneyers.

As a substitute, or when round blanks could not be made, coins were often struck on square or lozenge-shaped blanks, called klippe. These were easy to cut with shears. If even this could not be done, blanks were cut in a closely circular shape, resulting in mis-shaped coins. At Spanish-American mints with no blanking equipment (Mexico City, 1535-1732, Lima and Potosi until 1767) the coins struck from these oddly shaped blanks and are called cob money.

The first blanking press for making coin blanks was developed by Max Schwab in Augsburg, Germany in 1550. He developed the blanking press – along with a rolling mill – to accompany the screw press he had improved upon. He tried, unsuccessfully, to sell these to the Vienna Mint, but it was the French ambassador who learned of his innovations and ordered these for the Paris Mint.

A mintworker from the Lyons mint, Aubin Olivier, was instructed to go to Augsburg, learn the operation of these machines and transport them to Paris. He arrived at the Paris Mint 31 January 1551 with a rolling mill, draw plates, a blanking press and one of Schwab's improved screw presses. Placed in use immediately, blanking was done from stock drawn and rolled on Schwab's equipment. Quantity blanking was in production there by Antoine Brulier for coins struck in early 1552.

The first known supplier of blanks to coinage mints was Avesta, a Swedish mint near a large copper mine ("copper mountain") in central Sweden. In 1672 Avesta supplied copper blanks to the Royal Mint London for the regal copper coinage of Charles II.

Birmingham metalworking factories, notably the Anglesey Copper Company, as early as 1787 were manufacturing blanks and tokens of fine quality. But it was Matthew Boulton who made tremendous improvements in blank manufacture at his Birmingham factories, and later in his Soho Mint, not only in cutting out perfect circles of correct gauge metal, but also in edge preparation. He did this with the aid of Jean-Pierre Droz, who he had hired away (1789) from the Paris Mint. By 1790 Boulton could blank uniform disks of proper metal in quantity with an upset edge for coining and striking coins, tokens or medals.

Back at the Paris Mint, Droz had left behind his inventive associate Philippe Gengembre. Gengembre was the mint's machinist with whom Droz had worked on a press feeder, one of the innovations that had attracted Boulton. Gengembre continued working to improve the mint's equipment and, by 1797, had succeeded in matching even Boulton's blanking technology.

Subcontracted blanking. Whenever a new mint is established, a steady supply of blanks is usually its greatest problem, solved by most early mint officials by securing blanks from outside sources. Early American mints purchased blanks from Boulton and other English manufacturers. Then the mint obtains its own equipment and expertise to manufacture its own blanks. Recently, the source of blanks has gone full circle; need for special blanks (clad or sandwich, plated, bimetal, or such) that private manufacturers outside of mints are again supplying blanks by contract, leaving mints to do only die preparation and striking.

For mints and medal makers, outside sources for blanks of precious metals are desirable since it precludes any need of salvaging scrap and reprocessing this (with potential scrap loss). Thus a small separate industry exists of supplying custom blanks of prescribed composition with exact diameter, thickness and other characteristics to order for mints and medal manufacturers.

Multiple blanking. It wasn't until the early 20th century that blanking dies of more than one punch were widely used in production blanking for coins. Dual punches were first used in England prior to 1888 (in the U.S. as early as 1896). The Tower Mint was blanking shillings two blanks at a time and as many as five copper coin blanks were cut out with each cycle of the blanking press. This was particularly useful for coins of small diameter (say, under one inch) where great quantities are in constant need to keep presses supplied.

The first person to develop multiple blanking is unknown. It probably originated in Germany; Cooper attributes this important coining development only to a German Dr. May. It was probably used in the metalworking field before it was adapted to coining and spread to all major mints nearly the same decade, before the turn of the 20th century.

Continued improvement in blanking now permits as many as 30 blanks to be created with each press cycle. This requires a wider strip of metal – with an elaborate blanking pattern – and very high quality steel to make the blanking die plate. Multiple blanking tends to reduce slightly the amount of scrap remaining after blanking, with far fewer malformed blanks, in a more efficient operation.

How blanks are made. Blanks are cut from strips that are made from ingots of correct composition;; rolling mills roll the strips to proper thickness (gauge and width (length of the strip is not that important). The strips are then fed into the blanking press. For short runs the strip may be fed by hand. For production blanking the strips are fed continuously for the length of the strip. After the blanks are punched, the leftover strip remains as skeleton scrap, destined to be melted and reprocessed into strips again. (From 30 to 35% remains as scrap in even the best blanking pattern.)

Blanking is accomplished on a blanking press with specially prepared blanking dies. Actually a "die set," blanking dies are formed of three basic parts: (1) a plate into which a hole is cut the exact shape and size of the intended blank, (2) a punch which fits into the opening in the plate, and (3) a stripper which removes the scrap from the punch. A separate punch holder is sometimes required to fasten small punches into the chuck of the blanking press (where changes to different diameters or shapes are required).

The plate and punch are made of hardened steel. The aperture in the plate has a slight flare – the hole widens slightly in the body of the plate – so the blank ejects easily. The plate and punch are positioned (setup) in the blanking press; its action can be described as follows: the punch forces the metal strip (of soft material, as bronze or silver) against the plate and pushes it through the aperture in the plate. This shears or cuts out the blank as the punch continues it's downward motion forcing the blank through the plate (to fall into a hopper or tote box below). As the punch withdraws the stripper forces the skeleton strip free of the punch.

Striations on the edge of the blank are the evidence the blanks have been sheared.

These shear marks are caused by tiny imperfect edge irregularities inside the aperture of the blanking plate. (See illustration.) When the blanking plate is freshly made, there are few striations. As it wears these tiny nicks may appear, and more striations appear on a well- worn blanking plate.

As the punch forces the metal through the aperture in the plate, there is a tiny trail of metal debris on the edge of the blank. This burr is typical of all cutting and shaping in metalworking. Only one side has this burr and it is called the burr side. All burrs must be removed; blanks to be coined are deburred by upsetting. Blanks for striking with open face dies may be struck without removing the burrs first, as these will disappear during multiple striking and trimming.

Blanks are made of any size or shape with close tolerances. coin blanks must be exactly the weight of the intended coin; the upsetting does not remove any metal, but shapes the blank and makes it perfectly round. Then the blank can be fed into a coining press to be struck within collar dies. (Blanks before they are upset are called first process blank by collectors, a second process blank after they are upset.)

Blanks to be struck with open face dies may be made slightly larger than the intended diameter of the final piece; exact size blanks are not a requirement. These some- what oversize blanks, will have a part of their material – flash – removed after they are fully struck up after multiple striking.

Maximizing the number of blanks. During the sequence of blanking, irrespective whether the strip is hand fed under the blanker – or whether the strip is fed automatically –it is desirable to cut the blanks as closely together as possible. This is done to reduce cost by maximizing the number of blanks obtainable from the strip (and also reduce the amount left as skeleton scrap).

This blanking pattern is dramatically shown on the leftover strip and how successful the blanking press operator was to maximizing this number (for hand-fed blanking). The ingenuity of the press operator is even more dramatic for blanks that are irregularly shaped and hand fed: how to blank as many pieces as possible in the quickest time from the long strip of metal.

Cleaning blanks. In most metalworking operations, cleaning the workpieces is a step just prior to any metal forming, as in coining or striking. Removing oil or grease – and other surface debris – is required of this step of cleaning (see degreasing). Because blanks contain no detail yet, they can be severely cleaned by removing the top layer of metal. This removes all toning, tarnish and corrosion. The goal is to provide a surface which can be formed without any imperfections which the above surface contaminants may cause.

Blanks are cleaned by any of several methods: blanching, abrasive blasting, shot peening, acid dip (pickeling), heat treating, water hone (remeoving unwanted metal with a whetstone) . But the most popular in coin and medal production is barrel tumbling. Blanks are placed in a large drum along with sawdust, ball bearings, shot or other metal particles and the barrel is set to rotating.

The tumbling action causes all these objects to knock against each other. This removes toning, tarnish and corrosion by lightly removing the top surface. Afterwards the aggregate is removed and the blanks are separated (by screening). At this stage the blanks will have an activated surface, which, depending upon the environment, will start natural toning in from two days to six months.

Blanking anomalies. A broad spectrum of errors can occur in blanking. For the most part the most common is a clipped blank where the full circle of metal is not cut out as desired (the strip is not advanced far enough and the punch "clips" a part of a previous hole). double clip and multiple clip, as well as straight edge clip can also occur.

An incomplete punch shows the partial impression in metal that is later blanked and struck. A saddle strike is a modern error from the use of dual dies. Struck fragment is the aberrant use of a fragment of metal instead of a full blank. A very rare blanking anomaly is out-of-round blanks.

Too large a planchet is called a broad flan if this is noticed and the blank is reduced in size, it is a cut-down blank. An incorrectly chosen blank is wrong planchet. While a dumb blank contains gas pockets so it does not ring properly, it is a result of incorrect milling and rolling. [Other blanking errors occur, particularly in coining, see section 06.9 in the Study Guide Outline.]

Future of blanking. While new alloys, clad or sandwich metal compositions – bimetal and trimetal compositions – do not present blanking problems (if the composition can be rolled flat to a prescribed gauge), perhaps in the future we will see computer-controlled laser cutters that will provide blanks of any shape or size – particularly for unusual shape medals – to very close tolerances and maximize the number of blanks per given strip. Or, perhaps, blanks will be formed to any shape or size by high density molding. But for the present, as it has for the last 450 years, cutting out blanks of required size from strip metal stock remains the most satisfactory method of obtaining blanks for creating struck coins and medals.

References:
C43 {1966} Gilbert, blanking presses, #25, 27, pp 21.
C66 {1988} Cooper [ancient blanks] pp 10-12; [early blanking] 97-101; [modern] Chapter 17, 187-199.

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