What Is CMM and What Does It Do In CNC Machining?

Posted on Nov 26, 2020

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CNC cmm

The CNC CMM is a computer controlled coordinate measuring machine which is used primarily for testing the work pieces or the components that are produced.

 

What Is CNC CMM?

CMM stands for coordinate measuring machine. It is a machine used in the measurement of the physical geometrical characteristics of an object. A CMM can be either manually operated or controlled by computerized unit. CNC stands for computerized numerical control.

In CNC manufacturing, the machines used in metal working or other machining operations are controlled by automation system. The CNC CMM is computer controlled and used primarily in testing the work pieces or the components that are produced.

 

How Does CNC CMM Work?

The measurements done by a CNC CMM are defined by a probe attached to the third moving axis of this machine. The coordinate measuring machine can be a part of the CNC manufacturing operation to test the components. The test is to see whether or not the product has the features and properties as it is designed to be. The use of coordinate measuring machine in CNC guarantees the quality of the components or assembly as a result.

In a CMM test, the X, Y, and Z coordinates of the work piece will be precisely recorded. These are the essential references which will be further analyzed through regression algorithms for the construction of features. The regression algorithms refer to the analysis for estimating the relationships between a dependent variable and other independent variables.

To acquire the coordinates and collect the points for the analysis, a probe is placed in the machine. The positioning of the probe can be done manually or automatically by direct computer control (DCC). The computer controlled coordinate measuring machines can be programmed to measure identical parts in the manufacturing process repeatedly.

 

Basic Features of the CMM

The coordinate measuring machines can be made from multiple materials. The material that is most frequently used in making the CNC CMMs is a combination of granite and aluminum. Since this material has excellent stiffness yet still maintains a relatively light weight, it is suitable for industrial settings such as CNC manufacturing. The other feature of this aluminum alloy is that it is thermally dynamic. The expansion or contraction of the material can be monitored by the computerized control unit.

The probe, whether it is a scanning probe or vision probe, can be positioned by manual control or automatic control. The probe positioning of a CNC CMM is automatically controlled to which the positioning is defined by a 3-axis coordinate system. Besides the 3-axis movement, the turning angle of the probe can also be controlled in order to achieve the measurement for components that have more complex surfaces.

The primary goal of a CNC CMM is to test the accuracy of the parts or components that are machined against their original design to make sure the components have all the necessary qualities and their properties meet the requirements.

 

Why Is CMM Important?

The computer controlled coordinate measuring machines are important in inspecting the quality of the manufactured parts, especially in CNC machining or manufacturing. The reason why the machine needs to be computer controlled is that, the conventional handheld measuring approaches have their limitations. On top of that, the results of a manually conducted measurement depend on the skill of the personnel primarily. In other words, the accuracy of the measurement may vary.

The accuracy as well as precision is fundamentally crucial in a CNC working process. As a result, a measuring method that provides consistent accuracy is needed in this process. The CNC CMMs that are computer controlled are hence the best option for the job. In addition to the accuracy and precision, the speed is another key advantage of a CNC CMM.

With the automatically controlled coordinate measuring machine, the time it takes to complete a full loop of test is immensely reduced. Because the CNC CMMs can test the produced components repeatedly in high efficiency, both the quality of the parts and the lead time of the production can be improved. By using a CNC CMM, not only time but also quality of the production can be maintained.

 

Types of CMM

A coordinate measuring machine uses a probe to capture the geometric features of a part in 3 dimensions and put the collected information into analysis to test the result against the design. There are several types of CMMs and they are different by the way they are used in the inspection process.

The 3D bridge CMM allows the probe to move along the X, Y, and Z axis. The sensors for each axis monitor the position of the probe with high precision. The sensors enable the repeated measurement of an object’s surfaces to capture the details of the surfaces. The 3D bridge CMMs are considered a basic type of CMMs which have a simple structure and is easy to setup.

The cantilever CMM is used primarily for measuring smaller objects. The probe of a cantilever CMM is attached to only one side of the machine. This type of coordinate measuring machine can move quickly to inspect the parts. The key advantages of a cantilever CMM are the high level accuracy and low measurement uncertainty.

The horizontal arm CMM is useful in measuring objects with large or complex surfaces. The horizontal arm CMMs may be considered the least accurate CMMs, but they are quite applicable for measuring the components such as large metal sheets. Some horizontal arm CMMs have side mounted column which allows better accuracy and stability to the measurement.

 

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