Milling stone and technical ceramics to millimetric accuracy

January 28, 2004

Brussels, Jan 2004

LITHO-PRO has developed a high-speed, precision milling process to finish brittle materials, rather than relying on skilled craftsmen. This cuts costs and increases efficiency in the stone and ceramics industry.

A large number of companies operate in the marble industry, mainly in quarrying, working and treatment. Converters buy large marble and granite blocks directly from quarries, cut them and deliver them to building companies. These blocks are then either automatically machined to standard sizes or finished manually to meet a customer's specific design.

Even though a machine can do all the hard coarse work and, using grinding techniques, a significant part of the fine work, the final touch has to be added by the craftsman. This is the main reason why designing stoneware is expensive and, so far, technology has been limited in what it can do in this final stage of the 'crafting' process.

The same limitations have limited the widespread use of ceramic components in high tech industry. While metal ceramics are being used increasingly in automotive, aerospace, military, medical and other applications, their fabrication costs are high and machinability poor – leading to subsurface damage.

High speed cutting approach

High-speed cutting (HSC) may now be the answer to both stone and technical ceramic finishing. HSC has long been used in the aircraft industry for milling aluminium. More recently, the technique has been applied increasingly for machining metal and hardened alloy steels. Now eight firms from six EU countries have been researching a high-speed dry milling technique that works with the traditional stone and ceramics process. It makes use of special computer-aided design and manufacturing (CAD/CAM) techniques with solid model patterning to mill marble, granite and technical ceramics.

" There has been good collaboration because the partners know each other well," says project coordinator, Dr Anthimos Georgiadis of Fachhochschule Nordostniedersachsen Automatisierungstechnik (FHNON) in Lüneburg, Germany.

The LITHO-PRO project has been experimenting with the new process for milling marble up to granite hardness and built two demonstrator units for different kinds of products – one accommodates pieces of up to 400x400x400 mm and the other up to 1200x600x450 mm. These new forms of milling tool are fast, five-axis machines that carry out complex cutting work with the help of an advanced three-dimensional (3D) control unit.

The demonstrators underwent experimental trials and field tests throughout 2003. They performed well milling natural stone – typically soft, medium and very hard marble – at high speed. "First trials on ceramics are now encouraging us to develop more dedicated tools, and at the end of the project, we think we'll have created a new generation of products," says Dr Georgiadis.

Project participants are developing an integrated environment capable of designing, pre- and end-manufacturing high-quality, complex natural stone and ceramics parts. Until now, this kind of 'advanced control' machinery has only been used in the metal treatment industry, so this is the first time the techniques have been adapted for stone and ceramics processing.

LITHO-PRO has also created a splitting process different to that used when cutting plastics or more brittle materials, where heat causes the materials to curl or chip. The stone and ceramic cutting process does not generate high temperatures; the emphasis when cutting natural stones rests more on how to split the crystals cleanly and how to remove the dust during the process.

Accuracy and advanced control

Netherlands partner Jabro Tools developed special 'demonstrator' tools out of submicron grain carbide, which has a strong and extremely sharp cutting edge for scything through marble stones at high speed. Its LithoCerm 1 five-axis milling centre – the small scale demonstrator, or SSD – offers a manufacturing accuracy for small parts of ±0.01 mm.

Cutting marble and ceramics under these conditions requires a tough machine that can operate at very high speeds with the minimum of vibration. The SSD therefore uses an IBAG (HF 100 AI 50) high-speed motor spindle, operating at up to 62 000 rev/min with a maximum power of 7.7 kW. An advanced 3D control unit has been adapted to the system. Siemens supplied the cell controller and drive units for both demonstrator units, and Artis the monitoring software. The project has also developed special numerical control software for the demonstrators not available on the market.

" Thanks to the CAD software and working from photos, CAD databases or data captured from existing forms via advanced scanning and digitising techniques, LithoCerm 1 sculpts with amazing precision and speed to create highly accurate, three-dimensional objects and large sculptural forms from marble, granite or ceramic," says Dr Georgiadis.

Broad range of applications

The LithoCerm 1 can be used for a broad range of production applications, which include customised pieces, such as statues and memorials stones, where attention to detail is very important. The new environment should also allow cutting of a novel generation of products for interiors, such as the lighting market, as well as for the traditional exterior building industry.

" It will also be able to craft high value ceramic products for the medical, electrical and electronics markets," adds Dr Georgiadis. "The stone and ceramic sectors are where Europe is strong, so applying modern technology to these areas will be highly fruitful."

DG Research
http://europa.eu.int/comm/dgs/research/i ndex_en.html
Item source: http://europa.eu.int/comm/research/indus trial_technologies/26-01-04_milling_ston e_en.html

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