Ancient Currency Immersed in Modern Engineering

Finally it’s lunchtime and you fancy a sandwich, you have a £5.00 budget so you find a deli and buy a sandwich for £2.45; we would all expect to get the correct amount of change back in the form of various denominations of coins, but not really think much more apart from putting the coins back into our pocket and enjoying our sandwich. Should we take the fact that we get to use this form of ancient currency for granted?

Coins have been around for thousands of years and have been used as a form of currency for just as long. The total number of coins in circulation in the UK alone is over 28,000 million pieces and the value of these coins is well over 4000 million British pounds sterling.

How are coins made? The design of each new coin is made from a plaster version several times bigger than the final coin will actually be. The plaster version is then scanned by a machine using a ruby-tipped scanner, this in turn feeds into a computer that produces a data file. The data file stores the all important intricate detail of each coin.

From this data file the EDM (Electrical discharge machining) machine cuts the metal, producing a die(metal mould) that the coins can be cast from. The dies that are produced are then placed in pairs into a striking machine and these are pressed onto a blank coins at such a pressure that they imprint and mould the coin, several hundred coins can be made a minute using this type of machine.

How long have EDM machines been around? The method of EDM can be traced as far back as 1770 when an English physicist first come across the effect of electrical discharges. But the first actual machine was not made until 1943 when two Russian scientists failed in task that they were working on, but subsequently come up with the first type of EDM machine.

To some in the industry EDM, is also known as spark erosion or wire erosion. It is a process using electrical current to cut complex shapes and designs out of a material. During the process an arc is formed between two electrodes, the first being the electrode tool and the second being the material also known as the workpiece electrode.

It is a very accurate method of cutting material and can cut hard component materials with ease that would not be very easily cut on other more traditional techniques. It is also a very accurate way of cutting complex shapes.

There are two forms of machine available and these are Wire EDM and Die Sink EDM. Wire type machines use a single strip of wire, which is made of brass, this wire is fed through the material in dielectric fluid of ionized water. Thicknesses of 300mm can be cut through using this technique.

Sinker type machines are where the electrode and material to be cut are placed in a liquid which is usually oil, these liquids are known as dielectric fluids a current is then fed to the parts and as the two get closer together(but do not ultimately touch) a spark is formed which jumps from one to the other cutting the material.

The most common use of these type of cutting machines are for mold making tools and the die industry, as used by the royal mint. The use of these machines is also rising in prototype engineering, in areas similar to aerospace and automobile.

So next time you need a component manufactured, think of EDM as it might be precisely what you require.

Post time: 03-24-2017