With the development of the coordinate measuring machine(CMM) technology, CMM is more and more widely used. Because the structure and material of the CMM has a great influence on the accuracy, it becomes more and more highly required. Following are some common structural materials.
1. Cast iron
Cast iron is a kind of common used materials, mainly used for the base, sliding and rolling guide, columns, support, etc. It has the advantage of small deformation, good wear resistance, easy processing, low cost, linear expansion is most close to coefficient of parts (steel), It is the early used materials. In some measuring machine still mainly use cast iron materials. But it also has disadvantages: cast iron is susceptible to corrosion and abrasion resistance is lower than granite, its strength is not high.
Steel is mainly used for shell, support structure, and some measuring machine base also use steel. Generally adopts low carbon steel, and has to be heat treatment. The advantage of steel is good rigidity and strength. Its defect is easy to deformation, this is because the steel after processing, the residual stress inside the release lead to deformation.
Granite is lighter than steel, heavier than aluminum, it is the common used material. The main advantage of the granite is little deformation, good stability, no rust, easy to make graphic processing, flatness, easy to achieve higher platform than cast iron and suitable for the production of high precision guide. Now many of CMM adopts this material, the workbench, bridge frame, the shaft guide rail and Z axis, all made of granite. Granite can be used to make workbench, square, column, beam, guide, support, etc. Due to the small thermal expansion coefficient of granite, it is very suitable for cooperate with air-flotation guide rail.
Granite also exist some disadvantages: although it can made from the hollow structure by pasting, it is more complicated; Solid construction quality is big, not easy to process, especially the screw hole is difficult to process, cost much higher than cast iron; Granite material is crisp, easy to collapse when rough machining;
Ceramic is developed rapidly in recent years. It is the ceramic material after compacting sintering, regrinding. Its characteristic is porous, the quality is light (density is approximately 3g/cm3), high strength, easy processing, good abrasion resistance, no rust, suitable for Y axis and Z axis guide. Shortcomings of ceramic are high cost, technological requirements is higher, and manufacturing is complex.
5. Aluminum alloy
CMM mainly uses high-strength aluminum alloy. It is one of the fastest growing in recent years. Aluminum has the advantage of light weight, high strength, small deformation, heat conduction performance is good, and can carry out welding, suitable for measuring machine of many parts. Application of high strength aluminum alloy is the main trend of current.
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