As with the World Money Fair Technical Forum in 2021, the 18th event held earlier this year was also held virtually. This year it comprised 11 presentations over two days, hosted by Dieter Merkle of Schuler and Thomas Hogenkamp of Spaleck.
In this issue of Coin & Mint News™, we cover five of those presentations. In next month’s issue, we will follow up with the second half of the Technical Forum.
New Technologies for Manufacturing Complex-Shaped Coins
Aziya Ibrayeva of the Kazakhstan Mint described with new technologies developed to manufacture commemorative coins with complex shapes.
The first, ‘UNOVYS’, produced in 2021 for the National Bank of Kazakhstan, has a convex/concave configuration, making it difficult to obtain low relief engraving, the challenge being to guarantee its durability. The protruding relief on the coin was achieved using laser engraving.
On the reverse in the centre is a red square produced using colour pad printing, surrounded by a stylised composition consisting of engraved concentric circles and arcs. The difficulty was in positioning and applying the red image at the centre of the lowest point in the concave shape of the coin. This was achieved using a special tool with dynamic focusing, which increased production speed and quality.
The second commemorative coin – 550 Years of Finding the Miraculous Icon of Theotokos of Zhirovichy – was produced on behalf of the National Bank of Belarus. It features a relief image on the observe of a monastery with roof and walls highlighted with laser matting of different textures, giving volume and realism to the panorama of the monastery. The difficulty encountered was using the laser to create designs that distinguished the sunny and shaded side of the roof.
On the reverse is a relief copy of the icon made using selective chemical oxidation technology. The difficulty here was obtaining an exact reproduction of the icon. Several types of laser deposition technology were used to achieve the desired effect.
A third coin, the Kazakhstan Astana – Nur-Sultan, a composite featuring colour printing and rainbow interference technologies, was made in proof quality using sterling silver and an insert made of pure gold.
The correct positioning of the obverse and reverse dies and the different characteristics of the two metals during striking were major challenges, which were overcome by striking the gold insert separately.
Innovative New Surface Finishing, Forged by the Power of Light
Alexander Aminidis of ACSYS Lasertechnik presented the company’s new Femtosecond laser and PULSE FORGING™ technology.
The Femtosecond laser engraves in similar quality and speed as the established Picosecond laser systems. But, in addition, it can apply the new PULSE FORGING technology to make the surface smooth and shiny, as if polished. This technical development can be added to an existing Picosecond laser system.
Due to the extremely high repetition rate of the Femtosecond laser, ACSYS has developed a patented process, in conjunction with the University of Mittweida, that generates a shock wave through the plasma expansion with the femto pulses, which smooth the surface through kinetic energy. As well as the surface roughness being significantly improved, the shiny effect, similar to polishing, makes considerably more details visible.
Pulse forging is unique in that it is a cold process and, being very gentle to the surface, neither changes the hardness nor affects the material properties. There is also no change to the material’s stoichiometry and its corrosion protection properties are enhanced.
The single process only takes seconds to a few minutes and can be applied immediately after 3D engraving.
In addition to creating a smooth surface, decreasing surface roughness, and creating a silvered shiny effect similar to polishing, Pulse Forging makes it possible to polish areas which are very hard to reach for traditional technologies. It can also be used for a pre-polishing effect to make subsequent polishing easier and faster, as well as for selective polishing in chosen areas, and for new surface finishing effects.
Another innovation is an upgrade to the Laser Scan Head, which works with galvo engines and controls the position of the laser beam on the workpiece. The new Premium Performance version has significantly better dynamic and reverse movements, which decrease engraving time and increase productivity. It can be purchased new or can be retrofitted to all ACSYS ultrashort pulse systems built from 2016 onwards.
Optimising Milling and Polishing of Dies
This presentation was made by Ståle Lokken and Tor Olav Iversen of the Mint of Norway, and Dr Oliver Gossel of Röders TEC, manufacturers of high precision milling and grinding machines.
The Mint’s objective for this project was to improve the quality of working dies, avoid time-consuming manual retouching and shorten lead times. The Mint also wanted to cut the dies in hard material, again to increase efficiency.
The die cutting process still involves the cost and quality advantages of ball nose cutters, but an issue with standard ball nose cutters is the ‘chisel’ in the centre of the tool where the cutting speed is zero and so the cutting conditions are poor.
Röders TEC have circumvented this issue by inclining the workpiece 8-15° degrees depending on the contour of the die relative to it. The clamp holding the workpiece is designed to hold it at the desired angle and is programmed to move in sequence with the ball nose die. This new method has the advantage of both higher quality and reduced milling times.
Three different sized coin examples were engraved, and the polishing of the die face/relief was achieved using a Spaleck Die Finisher 33. High quality results were achieved by automatic polishing without any manual re-touching – allowing high quality coins to be produced directly from the dies.
Titanium Diboride – the New Universal Coin Die Coating for the PLATIT S-MPulse
Dr Juri Wehrs of Platit and Axel Nann and Robert Gall of Staatliche Münzen Baden-Württemberg gave a presentation on a new technology which is the result of a joint development between the two organisations – namely, the next generation of coin stamp PVD coatings for the Platit S-MPulse in-house PVD-hard coating system.
The Mint wanted a system which could produce high quality coatings for coin dies and edge lettering tools, and was easy to use. PLATIT could already meet these demands with its new S-MPulse machine.
However, the Mint also wanted one universal coin stamp coating for proof and circulation coin dies and all coin materials, that is environmentally and health friendly and 100% chromium-free.
At the time of this request, the new customised PLATIT S-MPulse PVD coating machine had recently been released. It offers high quality sputter coating, an easy-to-use technology, is environmentally friendly (no vapours, chemicals, or noise), safe for the operator, and a compact modular system that fits in any workshop. It fitted the Mint’s requirements!
Dies have mirror polished surfaces with roughness in the order of a few hundreds of nanometres. Within the same coin die engraved laser patterned areas that have roughness in a few tens of thousands of nanometres can be found – ie. more than three orders of magnitude difference in surface roughness. And with PVD coatings from the PLATIT S-MPulse, it is possible to perfectly replicate and copy every single detail of the coin die surface.
A coin die is also a tool which needs a clean surface to give a good performance. Coin dies can have residues on their surface and defects, and so should be cleaned before S-MPulse PVD coatings are applied. This can be achieved by careful polishing and efficient cleaning.
PLATIT Ceramicoin is the company’s new titanium diboride coating. It is a non-reactive process, and the coating consists of fully ceramic material. A coating thickness of approximately 1 µm is enough to cover and perfectly protect a coin die surface. The adhesion quality is very good – Rockwell Adhesion HF1 – so there is no delamination. It also has excellent scratch resistance and hardness (Nanohardness 25GPa).
The other advantages of Ceramicoin are no chromium, no chemical waste, no long-time contamination of the facility and no health risk, and because of the coating durability there is a significant increase in coin die life and a greatly reduced coin material build up.
A typical life cycle on the machine is four hours, which is very fast for PVD coating. The process starts with pumping and heating (65 mins), then plasma cleaning (37 mins), coating (38mins) and finally cooling/venting (35 to 65 mins). It can produce up to 40 coin dies per batch and 4-6 batches a day can yield up to 240 dies.
Quantum Leap for Coin Printing
Christian Schweikert from THIEME, manufacturers of graphic and industrial printing machines, introduced a high production, largely automated inkjet printing system for printing on coins and bars in multiple colours, which he described as a quantum leap for digital coin decoration.
The THIEME 505 D Mint is capable of production speeds of up to 600 coins per hour, allowing the decoration of large batches of coins in a short time using inkjet technology. It has two linear driven printing tables, with easy access to all parts on the machine including the printer, which is controlled by a Siemens system with a touch operator panel.
The machine can be operated as a stand-alone system with manual loading and unloading of the trays, or as a fully automated system with automatic loading from magazine trolleys, which can hold up to 45 trays.
To guarantee high resolution print, the printer uses CYMK with a ten-pass mode for each colour, with six passes for varnish and four for primer and white. The printer has 10 print heads and can achieve a resolution of 800 x 1500 dpi. In the standard configuration it is equipped with CMYK, white, primer and varnish. The inks are UV based and are cured directly after each printing pass.
To set up a new printing job, the embossing on the coin must be scanned in order to position the print in the correct position. The scanned coin is displayed on a screen and the operator moves the print image until it is in registration with the embossing. This only needs to be done once. The defined position will be stored on the printer.
After scanning, the operator loads all the coins into the recesses on the trays, which exactly match the coin’s size. No accurate positioning of the coins is required, but they are checked for height to avoid damaging the print heads. During printing the coins are kept in position by vacuum.
The first layer is a transparent primer to ensure a good bond between the colours and the metal. It can be followed by white or CMYK. The top and final coat is a transparent varnish to give high resistance against abrasion.
The printer was used to produce 1.25 million new €5 collector coins – the first of a nine-part series of collector coins for the German government to be issued between 2022 and 2024. This first coin, produced at the Staatliche Münzen Baden-Württemberg in Stuttgart, is called Insect Empire, the picture side showing wildlife with different insects and flowers. The initial production rate was 4,000 coins per 8-hour shift.