Measuring technology for granite – accurate to the micron
Granite meets the requirements of modern measuring technology in mechanical engineering. Experience in the manufacture of measuring and test benches and coordinate measuring machines has shown that granite has distinct advantages over traditional materials. The reason is as follows.
The development of measurement technology in recent years and decades is still exciting today. In the beginning, simple measurement methods such as measuring boards, measuring benches, test benches, etc. were sufficient, but over time the requirements for product quality and process reliability became higher and higher. The measurement accuracy is determined by the basic geometry of the sheet used and the measurement uncertainty of the respective probe. However, measurement tasks are becoming more complex and dynamic, and the results must become more precise. This heralds the dawn of spatial coordinate metrology.
Accuracy means minimizing bias
A 3D coordinate measuring machine consists of a positioning system, a high-resolution measurement system, switching or measurement sensors, an evaluation system and measurement software. In order to achieve high measurement accuracy, the measurement deviation must be minimized.
Measurement error is the difference between the value displayed by the measuring instrument and the actual reference value of the geometric quantity (calibration standard). The length measurement error E0 of modern coordinate measuring machines (CMMs) is 0.3+L/1000µm (L is the measured length). The design of the measuring device, probe, measuring strategy, workpiece and user has a significant influence on the length measurement deviation. Mechanical design is the best and most sustainable influencing factor.
The application of granite in metrology is one of the important factors affecting the design of measuring machines. Granite is an excellent material for modern requirements because it fulfills four requirements that make the results more accurate:
1. High inherent stability
Granite is a volcanic rock composed of three main components: quartz, feldspar and mica, formed by the crystallization of rock melts in the crust.
After thousands of years of “aging”, granite has a uniform texture and no internal stress. For example, impalas are about 1.4 million years old.
Granite has great hardness: 6 on the Mohs scale and 10 on the hardness scale.
2. High temperature resistance
Compared to metallic materials, granite has a lower coefficient of expansion (approx. 5µm/m*K) and a lower absolute expansion rate (eg steel α = 12µm/m*K).
The low thermal conductivity of granite (3 W/m*K) ensures a slow response to temperature fluctuations compared to steel (42-50 W/m*K).
3. Very good vibration reduction effect
Due to the uniform structure, granite has no residual stress. This reduces vibration.
4. Three-coordinate guide rail with high precision
Granite, made of natural hard stone, is used as a measuring plate and can be machined very well with diamond tools, resulting in machine parts with high basic precision.
By manual grinding, the accuracy of the guide rails can be optimized to the micron level.
During grinding, load-dependent part deformations can be considered.
This results in a highly compressed surface, allowing the use of air bearing guides. Air bearing guides are highly accurate due to the high surface quality and the non-contact movement of the shaft.
in conclusion:
The inherent stability, temperature resistance, vibration damping and precision of the guide rail are the four major characteristics that make granite an ideal material for CMM. Granite is increasingly used in the manufacture of measuring and test benches, as well as on CMMs for measuring boards, measuring tables and measuring equipment. Granite is also used in other industries, such as machine tools, laser machines and systems, micromachining machines, printing machines, optical machines, assembly automation, semiconductor processing, etc., due to the increasing precision requirements for machines and machine components.
Post time: Jan-18-2022