Requirements are constantly increasing in mechanical engineering in general and in machine tool construction in particular. Achieving maximum precision and performance values without increasing costs are constant challenges to being competitive. The machine bed is a decisive factor here. Therefore, more and more machine tool manufacturers are relying on granite. Due to its physical parameters, it offers clear advantages that cannot be achieved with steel or polymer concrete.
Granite is a so-called volcanic deep rock and has a very dense and homogeneous structure with an extremely low coefficient of expansion, low thermal conductivity and high vibration damping. Detailed information about these properties, which are advantageous for mechanical engineering, can be found here in this article.
Below you will discover why the common opinion that granite is mainly only suitable as machine foundation for high-end coordinate measuring machines is long outdated and why this natural material as a machine foundation is a very advantageous alternative to steel or cast iron even for high-precision machine tools.
Granite machine bed with ready-mounted roller guides for a gantry 5-axis milling machine from Heyligenstaedt.
High added value without additional costs with granite machine bed for machine tools
The increasing use of granite in mechanical engineering is not so much due to the massive increase in the price of steel. Rather, it is because the added value for the machine tool achieved with a machine bed made of granite is possible at very little or no extra cost. This is proven by cost comparisons of well-known machine tool manufacturers in Germany and Europe.
The considerable gain in thermodynamic stability, vibration damping and long-term precision made possible by granite cannot be achieved with a cast iron or steel bed, or only at relatively high cost. For example, thermal errors can account for up to 75% of the total error of a machine, with compensation often attempted for by software – with moderate success. Due to its low thermal conductivity, granite is the better foundation for long-term precision here.
With a tolerance of 1 μm, granite easily meets the flatness requirements according to DIN 876 for the degree of accuracy 00. With a value of 6 on the hardness scale 1 to 10, it is extremely hard, and with its specific weight of 2.8g/cm³ it almost reaches the value of aluminium. This also results in additional advantages such as higher feed rates, higher axis accelerations and an extension of the tool life, e.g. for cutting machine tools.
Thus, the change from a cast bed to a granite machine bed moves the machine tool in question into the high-end class in terms of precision and performance – at no extra cost. The commercial director is pleased about the higher contribution margins per machine sold. And the sales department proves with increasing sales successes that machine users can be convinced by the better arguments.
Better ecological footprint through granite in mechanical engineering
In contrast to materials such as steel or cast iron, natural stone does not have to be produced with a great deal of energy and using additives. Only relatively small amounts of energy are still required for quarrying and surface treatment. This results in a superior ecological footprint, which even at the end of a machine's life surpasses that of steel as a material. The granite bed can be the basis for a new machine or be used for completely different purposes, e.g. by shredding for road construction.
Nor are there any shortages of resources for granite. It is a deep rock formed from magma within the earth's crust. It has "matured" for millions of years and is available in very large quantities as a natural resource on almost all continents, including all of Europe and Germany.
Threaded inserts embedded in granite
Conclusion: The numerous demonstrable advantages of granite compared to steel or cast iron justify the increasing willingness of mechanical engineers to use this natural material as a foundation for high-precision, high-performance machine tools.
