Modern industry is characterized by the precision with which components are manufactured. It has been assessed at a tenth of a micron and continues to grow continuously. In fact, the machine's stated accuracy has improved so much that it has become increasingly difficult to measure the actual deviation of manufactured parts. As a result, new control methods and metering equipment are constantly being developed and improved. One of the flexible, fast, and precise equipment units used to estimate the accuracy of a part is a coordinate measuring machine.
CMM applications
CMM is the most advanced modern means of automated and manual measurement, and it has found a variety of possible uses in the industry. Many different types of CMMs make this tool available on both large (gantry CMMs) and smallest (cantilever CMMs) machines. Multiple probe types (mechanical, optical, laser, or white light) ensure that you can even measure surfaces that must not be touched by the probe or any other object. The high degree of CMM automation allows it to be used both manually by machinists and to reduce labor by automating it for repetitive operations that involve high-volume production. How you use a CMM machine depends on what you want to achieve. Its level of flexibility and precision offers a lot of opportunities for manufacturers. You can use a CMM to redesign existing parts after machining or measuring them, or you can use it as part of an automated manufacturing chain. There are a number of options here, some of which are listed in the following paragraphs.
Things that must be done before using a CMM
CMMs use the most sophisticated instruments to make measurements. They can estimate failures in parts smaller than microns. However, in order for them to achieve the desired accuracy, the machinist must thoroughly prepare the equipment for the measurements. The degree of readiness depends on the precision of the part being measured. If we talk about the parts with the highest accuracy (parts with tolerances of IT6 or less), you will have to prepare the CMM and the area where you are going to make measurements. It must have a specific percentage of humidity and an optimal temperature, and it must be very clean, since with this precision even the slightest dust can affect the results of the operation. The CMM itself is usually calibrated using extremely precise metal balls. Its size and shape deviations are well known. The position of the sphere on the granite table is also known (usually there is a special fixture in the center of the table). The probe must touch multiple points of the sphere and determine its diameter and shape deviation. The measurements are then adjusted for their deviation and the spheres are measured again to ensure that the correct settings are saved.
CMM for complex surface measurements
The main purpose of a CMM is to measure complex surfaces. That's why CMMs can reach their full potential when they are used in turbine blades, aircraft wings, pump impellers, and other components with special surfaces. If you are making a large number of the same parts, and they are so precise that you have to check each and every single one, the automation of such jobs is also possible. However, in most cases, these parts are measured manually by a machinist. To measure complex surfaces, the machinist will manually move the probe along three axes using a remote control until the probe touches the part that the machinist needs. Then, after taking a large number of measurements, the points are analyzed and the contours of the part are connected as splines. The measurements are then compared to a 3D model of the part (including acceptable deviations) or some other data that shows the desired dimensions.
CMM for relational and formal deviations
Most high-quality parts are characterized not only by their dimensional errors, but also by the accuracy of their surface shape and their relative position to each other. These deviations are particularly important for rotating parts to reduce vibration and ensure smooth movement. CMM measurements of such deviations are not much different from those of complex surfaces. All formal and relational deviations have a base to compare them to. Therefore, in order to achieve the accuracy requirements, you must clamp the part to the base surface and measure the desired part. If we talk about the relationship between two surfaces, it is only necessary to design the fixture to clamp the first surface and measure the second surface.
CMM measurement of surface finish
The profilometer is the most common instrument for measuring surface finish. However, CMM machines can also measure the surface finish of parts because of their excellent accuracy. However, you will have to replace the probe with a special needle. The needle will then move along the surface and determine any type of microscopic unevenness that forms the surface finish.