Electroforming for the manufacturing sector
Tony Hart explains the value of electroforming in manufacturing sectors.
In the world of metal manufacturing, electroforming frequently goes unrecognised – despite being used to make many products vital in modern society. This is understandable, since virtually all electroformed objects are manufacturing intermediates rather than end products. However, applications of electroforming, invented around 1840, have increased steadily during the last 100 years because of the accuracy that is achieved in dimensional reproduction and surface topography – essential for many high technology applications.
Electroforming is not a cheap process, so it is only used where its unique properties are vital in creating the end product. In fact, in most of its uses it is the only possible manufacturing method. The basic technology and equipment is simple and almost identical to that used for nickel electroplating.
Nickel is the metal used in the vast majority of electroforming applications. This is primarily due to its inherent properties – hardness, tensile strength, ductility and resistance to corrosion. Additionally, nickel deposition processes can be closely controlled to provide required deposit properties.
The ability to record and reproduce sound accurately is taken for granted in the 21st Century. This is particularly true of music, which, before the latter part of the 19th Century, could only be enjoyed in the form of a live performance. In the latter quarter of the century, however, sound recording technology was born. This involved cutting a groove into the surface of a metal cylinder. The topography of the groove was controlled by sound input being translated into vibration of cutting stylus. Reproduction took place using a phonograph where a needle follows the track on the cylinder transmitting vibrations mechanically to a primitive speaker.
By around 1910, however, the cylindrical roller was replaced by a flat disc, rotating in a horizontal plane. The information groove was still cut mechanically and sound was similarly reproduced by a needle, or later a diamond stylus, following the track on the disc.
The fundamental technology of sound reproduction on flat discs remained the same for more than 70 years. A helical information track was cut into a soft organic lacquer on a perfectly flat aluminium disc.
The original information track in the lacquer layer is soft but, in order to use industrial moulding processes to make the huge number of copies required by the market, a very hard mould material is essential.
This is where nickel electroforming fits in. The original image is coated with a very thin, 0.35µm, layer of silver. Nickel metal is deposited onto this conductive surface until a thick deposit has formed, which is separated from the origination to become a freestanding object – an electroform. The nickel deposit reproduces the information on the soft origination surface with absolute precision. The electroform is then used as a mould to produce huge numbers of replicas in materials, such as PVC. This process was the mainstay of the sound reproduction industry for decades and records remain popular among music fans today.
In the mid-1980s, a revolution took place with the introduction of the compact disc, involving, for the first time, digital technology. This required major development of the nickel electroforming process so that it could be used to manufacture CDs, where the precision required is far greater.
In the new technology, the helical information track is cut by a laser, producing around 30bln shallow depressions in a photosensitive organic film. These are typically 0.2µm deep, 0.4µm wide and 1.6µm long – the information being carried by variation of the length. All must be dimensionally perfect and in exactly the correct position on the disc surface.
With the advent of DVDs, even greater precision is vital as demonstrated by the image density shown on 36µm2 areas of modern CDs and Blu-ray discs.
Statistics referring to production quantities are as remarkable as those related to precision. During 2010, output in the European Union for all three types of disc was 4.3bln, combined with around 120 companies having optical disc replication facilities.
Manufacture of holograms
The technology for producing holographic images was invented by Hungarian-British physicist Dennis Gabor. However, the origination process is very expensive and original holographic images are created in a soft, fragile film, similar to disc production. For many years, this restricted production and use of holograms.
Fortunately, like disc originations, holographic images consist of shallow three-dimensional images and require similar dimensional precision. Consequently, nickel electroforming has been universally adopted as the only method by which holographic images can be mass-produced.
The most important commercial application of holography is for security systems, an essential feature of modern lifestyle. The overall market was estimated in 2007 to be in the region of US$5m. This includes production of banknotes, tax stamps, identity devices, finance cards and brand protection applications, preventing packaging counterfeiting.
Screen-printing has been used for many years to transfer decorative images to substrates such as fabrics. Due to the huge volumes of patterned materials required, at economic prices, by modern society, rotary screen-printing was developed.
A typical rotary printing screen consists of an electroformed nickel cylinder four metres long by 400mm diameter, with a wall thickness of 100µm. The screens are manufactured by electroforming billions of holes to be precisely in the cylinder walls with diameters from 0.08–0.6mm. The pattern in the screen is created by back-filling selected holes with resin allowing the printing ink to flow through the open holes.
In operation, a succession of screens is laid horizontally with the material to be printed running beneath them. As the screens rotate, the unfilled holes deliver ink onto the surface of the material being printed. Each screen delivers a different colour to print the final complex pattern.
Nickel electroforming is the only technology that can create seamless tubes with highly precise hole patterns and dimensions required by the printing process. It is the largest worldwide application of electroforming annually, consuming 2,000 tonnes of nickel and enabling an estimated one billion metres squared a year of decorative fabrics, wallpaper and carpets to be printed.
For thousands of years, grinding has been widely used in metalworking. Precision levels have, however, risen dramatically so that an accuracy of 0.005mm is required for applications in the aerospace and automotive industries. This has required a massive increase in the accuracy of grinding equipment, especially the technology by which grinding wheels are made.
Precision grinding wheels obviously lose dimensional accuracy and shape when in use. Consequently, a dressing tool is needed that is sufficiently hard and accurate to be used to restore the production wheels to their initial size and shape. Dressing tools, where diamonds are electroformed into a nickel matrix, are essential to achieve the required standards of precision, hardness and durability.
Nickel electroforming is a versatile process used in major industries where it is the only means of making vital artefact components, and remains a valuable part of our manufacturing industries.
Dr Tony Hart is Managing Director of Hart Materials Limited. A graduate of Aston University and a Chartered Chemist, he was awarded a higher doctorate by the Council for National Academic Awards for his achievements in industrial research and development over a period of 25 years