CMM (Coordinate Measuring Machine)
What is the Difference Between VMMs and CMMs?
Measurement is a necessity of the production process. It ensures uniformity, compliance, and that parts will fit into their larger components. Lacking adequate measurement protocols is a high expense that could even be life-threatening if products malfunction.
Still, if you work on any shop floor, you know that measurement is usually not a quick or easy task. It often requires tedious and repetitive work that only certain technicians are trained for. But there is hope for a better system with tools like KEYENCE’s CMMs and VMMs.
Although the acronyms sound similar, these measurement machines use completely different methods. In the following, we’ll discuss the differences between a CMM vs VMM, and when you should use each.
What is a VMM?
VMM stands for vision measuring machine or video measuring machine. A VMM tool uses optical components like a light, an imaging unit, and an image capture board.
Since VMMs use optics to collect measurement data, this is a non-contact measurement method. A part is placed on a stage, and the VMM machine analyzes it.
What is a CMM?
CMM stands for coordinate measuring machine. A CMM uses a probe to take coordinates and uses math to produce dimensional data and GD&T features. Some portable CMMs like KEYENCE’s XM Series don’t require a stage or specific shop area for measurement. Being portable allows for more free movement when measuring which is especially helpful for large or heavy parts.
Key Components Between CMMs vs VMMs
VMM
A VMM machine uses a small stage, usually less than 12x12 inches, for measuring parts, so VMMs work best with small or delicate parts.
The LM Series, KEYENCE’s version of a VMM, uses a telecentric lens and a magnified lens with 20-megapixel monochrome CMOS to gather images. This VMM can inspect up to 1000 parts and measure up to 5000 dimensions per part in just seconds. KEYENCE’s VMM tool then utilizes this measurement data to produce statistical reports and PASS/FAIL analyses in seconds.
CMM
CMM systems use contact probes, and portable ones can be moved around a shop floor, so they aren’t limited to parts that fit on a specific stage. The XM Series by KEYENCE can either have parts placed upon its stage, or be brought to the part on the shop floor for measurement. The XM Series CMM System is also able to follow the measuring probe with its camera head, allowing for measurement of parts up to 2 m.
In addition to dimensional data, CMMs also collect GD&T data like angularity, flatness, parallelism, and more. Because of this additional data, CMMs are also widely used for 3D part inspections. They produce data reports and PASS/FAIL analysis in real time so that the part being measured are ensured to meet quality assurance standards.
Comparative Analysis of Accuracy and Speed
CMM and VMMs are both superior options in the metrology world and are becoming more advanced all the time.
With that being said, there are slight differences between accuracy and speed which can help determine which would best would fit your needs.
Accuracy
For KEYENCE’s systems, the VMM has a better accuracy but smaller measurement area (under 1 ft), while the CMM is slightly less accurate, but can accommodate parts up to 6 ft.
However, there are situations where the VMM machine precision isn’t necessary, so its differing accuracy doesn’t always equal “better” for all parts. This expert VMM machine precision is only needed for parts with tight tolerances or parts that are very small such as medical or aerospace parts.
Speed
The VMM tool, the LM Series, is faster than the CMM because, by using automated vision technology, it can measure up to 600 parts at once, while the XM Series is limited to inspecting one part at a time.
Nonetheless, just like the accuracy difference between VMMs and CMMs, the speed difference isn’t always the most necessary. The LM is equipped for measuring 2D features on many small parts at once but can’t perform any 3D measurements and often can’t measure anything larger than a few inches. If you’re working with larger parts, or need 3D measurements, a CMM like the XM Series would be the better fit for you.
Precision in Action: Real-World Applications
Regardless of your industry, everyone strives for precision. But some industries, like the aerospace industry, need precision to a new level to prevent deadly malfunctions. That means that technicians have to bring their A-game for measurements, and sometimes that means compromising time. This is not the case when you use KEYENCE’s VMM or CMM systems.
Aerospace Industry: Gamma Aerospace, LLC
Gamma Aerospace, LLC manufactures large parts like stingers and struts, doors and access panels, seat tracks, and spars; it also manufactures small parts like brackets and fittings. Gamma Aerospace prides itself in taking the time for aerospace compliance so it can produce commercial airliners, helicopters, and military aircraft. But, the timing for their old metrology process was a huge downfall, so it needed a solution.
Gamma Aerospace integrated KEYENCE’s VMM and CMM and cut down their inspection time from hours to seconds while also improving precision by removing the possibility of human error. With the VMM for the small parts and CMM for the big parts, Gamma Aerospace changed its shop floor for the better.
Making the Decision Between CMM vs VMM
Deciding between a CMM or VMM machine requires you to consider your shop floor holistically. What are the sizes of the parts you measure? What level of accuracy and repeatability do you require? Do you work with a range of parts or usually the same?
Put simply, choosing a VMM is perfect for you if you measure large batches of small or fragile parts that need utmost accuracy. Alternatively, a CMM is more ideal if your parts are larger, require 3D inspection, and you’re looking for more versatility.
We know there is some gray area in making that decision, which is why we’re here to help. Contact us today to talk more about your measurement and inspection needs. Our expert team will help you make the right choice.
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