The CMM measurements are acquired by using a very sensitive touch-trigger or electronic probe to accurately measure a series of points along the X, Y, and X axes from the geometry of an object. These CMM measurements are required to qualify certain product parts in accordance with specifications.
What is CMM Measurement
A coordinate measuring machine, or CMM machine, is a device that is used to verify prototypes and production parts. The CMM measurements are acquired by using a very sensitive touch-trigger or electronic probe to accurately measure a series of points along the X, Y, and X axes from the geometry of an object. These CMM measurements are required to qualify certain product parts in accordance with specifications.
Why is a CMM Needed?
The traditional inspection methods were heavily reliant on the skill level of the person inspecting the parts or prototype. Along with the other limitations, the parts are sometimes manufactured incorrectly without being detected and are supplied to the customers. CMMs are made just to solve such problems. There are CMM manufacturers in Taiwan and they face the world to offer a variety of high-quality CMM solutions.
As parts are made more complex due to the increasingly intricate manufacturing design, a coordinate measuring machine is required to accurately measure the related features. With the need for more both speedy and accurate inspection processes, coordinate measuring machines will be able to make sure that parts are inspected effectively and efficiently within a given time frame, thereby yielding positive, repeatable results while meeting the demands of customers.
:: Read More: Taiwan CNC CMM Assures High-quality Production
Components of Coordinate Measuring Machine
The coordinate measuring machine is essentially comprised of several components: the probing system, controllers & software, and other accessories:
- The Probe: Rather than an optical or laser type probe, the probes used in a coordinate measuring machine have a spherical diameter. The spherical tips are generally made from ruby and zirconium, but can sometimes be made from other rigid materials that will not change size in the event of temperature fluctuations. Additionally, a needle-type probe with a sharp tip is sometimes used instead of the spherical type.
- Controllers and Software: Coordinate measuring machines are capable of data collection and reduction, achieved by a system typically consisting of application software, a desktop computer, and a machine controller. The software can either be developed by a third party or by an independent CMM maker.
- Granite Table: The surface of the coordinate measuring machine is often plated with stone material to yield highly accurate measurement. The Stone surface is less prone to scratches and deformation. Therefore, it has the benefit of a longer life span until it has to be replaced.
- Fixtures: The fixtures are an essential component in making sure that the coordinate measuring machine is coordinated as intended. The fixtures are able to make sure that the measured object does not move during a CMM operation because any slight bit of movement can lead to errors or inaccuracy. Therefore, it is common to see clamps, fixture plates, etc. being used to keep the measurement target in place.
- Air Compressors and Dyers: Due to the mechanical nature of a coordinate measuring machine, it is often equipped with an air compressor with a dryer. This is the most commonly found in the granite type or the standard bridge-type coordinate measuring machines.
How is the CMM Measurement Data Used
Every time the spherical probe touches the measurement object and is prompted to deflect, electrical signals are generated and are recorded in the computer. Any number of points can be collected and measured based on the requirements of the object.
The objective of collecting these points is so that the collective individual points can be used to validate the measurement of the actual parts against the CAD file data provided by the customer. This will ensure the quality of the data collected.
Also, the points are collected in a way that the shape of the part can be outlined (i.e., the point cloud). This is especially useful when the prototype of the measurement target is used as the foundation of the CAD program to produce more parts, which resembles the mechanism of a CNC machining.
Coordinate measuring machines are also ideal for measuring points inside the areas that can be difficult or impossible to reach with an optical system because the light tends to bounce around.
Advantages of CMM Measurement
Some of the benefits of CMMs include:
- Precise and Accurate: As mentioned previously, CMMs are able to yield highly accurate measurements as opposed to the old inspection methods. Aside from the fundamental parameters, CMMs are capable of measuring the flatness, roundness, straightness, and angularity of a part.
- Longevity: CMMs can generally last for many years, given that they are properly maintained. The robust materials that are used to construct the machine also optimize the lifespan of CMMs.
- Testing Random Parts: CMM measurement is a viable option for random sampling, as in pulling a random sample from a pool of arts. Theoretically speaking, if the sample you pulled (i.e., the representative sample) meets the tolerance specifications, the whole population should also pass the validation.
Limitations of CMM Measurement
Some of the limitations of CMM include:
- The probe must contact the part: Normally, this would not be an issue. But some parts have a very delicate and soft surface, the act of contacting them using the probe tip may damage the surface. Nevertheless, the CMM probe must physically contact the object when taking CMM measurement.
- No standardization: The software of CMMs is often uniquely designed to accommodate a particular type of machine, meaning that the control software is not interchangeable among different machines. This is especially important for operators who are in charge of managing and overseeing the machine as you need to know everything about the difference between the software programs.
- High volume testing: CMMs without a doubt excels at measuring high-cost, low volume parts, but with high volume operations, things could get quite troubling. Although CMMs will still be able to retain the same precision and accuracy, measuring a long run of parts may become expensive. For instance, using a CMM to measure hundreds and thousands of automotive parts may not be such a good idea.
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