Application of cmm in cnc machining workshop
The characteristic of modern industry is the precision of manufacturing components. It has been evaluated as one tenth of a micron and continues to grow. In fact, the accuracy of machine tools declared by manufacturers has been improved so much that it is becoming more and more difficult to measure the actual deviation of manufactured parts. Therefore, new control methods and measuring equipment are constantly being developed and improved. One of the flexible, fast and accurate equipment units used to estimate part accuracy is CMM.
Application of CMM
CMM is the most advanced modern automatic and manual measurement means, and it has found many possible uses in the industry. Many different types of CMMs allow the tool to be used on large (gantry CMM) and minimal (cantilever CMM) machines. A variety of probe types (mechanical, optical, laser, or white light) ensure that you can even measure surfaces that the probe or any other object must not touch. The high level of CMM automation enables it to be used either manually by machinists or to reduce labor by automating it for repetitive operations involving mass production.
How you use the CMM machine depends on what you want to achieve. Its flexibility and level of accuracy provide many opportunities for manufacturers. You can use CMM to redesign existing parts after machining or measuring them, or you can use them as part of an automated manufacturing chain. There are many options, some of which are listed in the following paragraphs.
Things you must do before using CMM
CMMs use the most sophisticated instruments for measurement. They can estimate faults in parts smaller than micrometers. However, in order for them to achieve the desired accuracy, the machinist must thoroughly prepare the equipment for measurement. The degree of preparation depends on the accuracy of the component being tested. If we talk about the parts with the highest accuracy (parts with tolerance of IT6 or less), you will have to prepare the CMM and the area you will measure. It must have a specific percentage of humidity and optimum temperature, and it must be very clean, because even tiny dust can affect the operation result under this precision.
CMMs themselves are usually calibrated using extremely accurate metal balls. Its size and shape deviations are well known. The position of the sphere on the granite workbench is also known (usually there is a special fixture in the center of the workbench). The probe must contact multiple points of the sphere and determine its diameter and shape deviations. Then adjust the measurements according to their deviations and measure the sphere again to ensure that the correct settings are saved.
CMM for complex surface measurement
The main purpose of CMM is to measure complex surfaces. This is why CMM can fully realize its potential when they are used for turbine blades, aircraft wings, pump impellers and other components with special surfaces.
If you are making a large number of identical parts, and they are very accurate, you must check each part, then the automation of such operations is also possible. However, in most cases, these parts are measured manually by the machinist.
In order to measure complex surfaces, the machinist will use the remote control to manually move the probe along the three axes until the probe contacts the part the machinist needs. Then, after a large number of measurements, the points are analyzed and the contour of the part is connected into a spline. The measurement results are then compared with the 3D model of the part (including acceptable deviations) or some other data showing the required dimensions.
CMM for relationship and formal deviation
The characteristics of most high-quality parts lie not only in their size error, but also in the precision of their surface shape and the relative position between them. These deviations are particularly important for reducing vibration and ensuring smooth motion of rotating parts. CMM measurements of such deviations are not very different from measurements of complex surfaces. All form and relationship deviations have a base against which to compare. Therefore, in order to meet the accuracy requirements, you must clamp the part on the base plane and measure the required part. If we talk about the relationship between two surfaces, just design a fixture to clamp the first surface and measure the second surface.
