Granite as Foundation for High Accuracy Measurement Coordinate Measuring Machine
The use of granite in 3D coordinate metrology has already proven itself for many years. No other material fits with its´ natural properties as well as granite to the requirements of metrology. The requirements of measuring systems regarding temperature stability and durability are high. They have to be used in a production-related environment and be robust. Long-term downtimes caused by maintenance and repair would significantly impair production. For that reason, Many companies uses granite for all important components of measuring machines.
For many years now, manufacturers of coordinate measuring machines trust in the quality of granite. It is the ideal material for all components of industrial metrology which demand high precision. The following properties demonstrate the advantages of granite:
• High long-term stability – Thanks to the development process which lasts many thousand years, granite is free of internal material tensions and thus extremely durable.
• High temperature stability – Granite has a low thermal expansion coefficient. This describes the thermal expansion at the temperature changing and is only half that of steel and only a quarter of aluminium.
• Good damping properties – Granite has optimal damping properties and thus can keep vibrations to a minimum.
• Wear-free – Granite can be prepared that a nearly level, pore-free surface arises. This is the perfect base for air bearing guides and a technology which guarantees the wear-free operation of the measuring system.
Based on the above, the base plate, rails, beams and sleeve of the ZhongHui measuring machines are also made of granite. Because they are made of the same material a homogeneous thermal behaviour is provided.
Manual labour as predicate
So that the qualities of granite fully applies when operating a coordinate measuring machine, the processing of the granite components must be carried out with the highest precision. Accuracy, diligence and particularly experience are imperative for the ideal processing of the single components. ZhongHui carries out all processing steps itself. The final processing step is the hand lapping of the granite. The evenness of the lapped granite is checked minutely. shows the inspection of the granite with a digital inclinometer. The flatness of the surface can be determined sub-µm-precisely and be displayed as tilt model graphic. Only when the defined limit values are followed and the smooth, wear-free operation can be guaranteed, the granite component can be installed.
Measuring systems have to be robust
In today’s production processes the measuring objects have to be brought as fast and uncomplicated as possible to the measuring systems, irrespective of whether the measuring object is a large/heavy component or a small part. It is therefore of great importance that the measuring machine can be installed close to production. The usage of granite components supports this installation site as its uniform thermal behaviour shows clear benefits to the use of moulding, steel and aluminium. A 1 meter long aluminium component expands by 23 µm, when temperature changes by 1°C. A granite component with the same mass however expands itself for only 6 µm. For additional safety in the operational process bellow covers protect machine components from oil and dust.
Precision and durability
Reliability is a decisive criterion for metrological systems. The usage of granite in the machine construction guarantees that the measuring system is long-term stable and precise. As granite is a material which has to grow for thousands of years, it does not have any internal tensions and thus the long-term stability of the machine base and its geometry can be ensured. So granite is the foundation for high accuracy measurement.
Work begins typically with a 35 ton block of raw material which is sawn into workable sizes for either machine tables, or components such as X beams. These smaller blocks are then moved to other machines for finishing to their final sizes. Working with such massive pieces, while also trying to maintain high precision and quality, is a balance of brute force and a delicate touch that requires a level of skill and passion to master.
With a working volume that can handle up to 6 large machine bases, ZhongHui now has the capability for lights out production of granite, 24/7. Improvements like these allow reduced delivery times to the end customer, and also increase the flexibility of our production schedule to react faster to changing demands.
Should problems arise with a certain component, all other components which could be affected can be easily contained and verified for their quality, ensuring that no quality defects escape the facility. This may be something for granted in high volume production like Automotive and Aerospace, but it is unprecedented in the world of granite manufacturing.
Post time: Dec-29-2021