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Alternative structural material for precision machine components

Because machine tools and other high precision machines in the metrology field rely upon high stiffness, long term stability and excellent damping characteristics of the base material for their static and dynamic performance, designers are now looking for alternative materials for their structures to improve the performance of their machines and make them more cost-effective in their production.

This article will show comparisons of widely used and an alternative material for precision machine tool and measuring machine structures.

The most widely used material for these structures are cast iron, natural granite and welded steel fabrications. The materials have advantages and disadvantages. Steel fabricated structures are seldom used where high precision is required due to the lack of long-term stability and very poor damping properties. Good quality cast iron which is stress-relieved and annealed, will give the structure dimensional stability and can be cast into complex shapes, but needs an expensive machining process to form precision surfaces after casting.

Also the castings need to be painted to reduce corrosion of the structure. Good quality natural granite is becoming more and more difficult to find but has a higher damping capacity than cast iron. Again, as with cast iron, the machining of natural granite is labour intensive and expensive.

Structures in natural granite distort in the presence of water, coolant vapours and are excessively heavy due to the solidness of the structure. Precision granite castings, sometimes known as synthetic granite, epoxy granite or polymer concrete, overcome many of these disadvantages and possess most of the advantages of conventional materials, and in some cases even better them.

Precision granite castings are produced, by mixing granite aggregates, which are crushed, river-washed, kiln-dried and mixed with an epoxy resin system at ambient temperature (i.e. cold curing process).

The alternative material has an internal damping factor up to 10 times better than cast iron, up to 3 timer better than natural granite and up to 30 times better than steel fabricated structure (see end of document). It is more cost-effective, un-affected by water, coolants, oils, has excellent long-term stability, improved thermal stability, high torsional and dynamic stiffness, excellent noise absorption and it's low exothermic curing property aids to negligible internal stresses, co-efficient of expansion, which can be varied by changing the constituents, is usually aligned to cast iron. Threaded inserts, steel plates, coolant pipes, plastic pipes (for electrical wiring looms), hydraulic pipes etc. can be cast-in during the casting process.

To achieve an even higher degree of versatility, linear rails, ground slide-ways and motor mounts can be replicated or grouted-in to the ultimate accuracy, therefore eliminating the need for any post-cast machining. The surface finish of a precision granite casting is as good as the mould surface and in many instances the need for painting is not necessary.

Over the last decade a number of machine manufacturers have encompassed the use of this material in their machine structures. A great deal of know-how has been developed over the past decades to exploit these excellent properties.

Granitek Limited, is the Leicester based company who manufactures precision granite castings for a variety of industry sectors including machine tools, metrology, inspection, semi-conductor, pre-press, photo-imaging, laser-engraving, medical, dentistry and marine applications with customers on 3 continents.

For more information please call 0116 276 9800 or e-mail sales@granitek.co.uk

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Tel: +44 (0)116 2769800
email: info@granitek.co.uk

Mach 2004

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