What is a CMM? Everything you need to know about coordinate measuring machines and their types. (2022)

What is a CMM machine?

What is a CMM? Everything you need to know about coordinate measuring machines and their types. (1)

A coordinate measuring machine, also known as a CMM, is a piece of equipment that measures the geometries of physical objects. CMMs using a probing system to detect discreet points on the surfaces of objects.

The very first CMM made its appearance in the early 60s. Originally developed by Ferranti Company in Scotland in the 50s, this 2-axis CMM used a 3D tracing device with a simple digital readout that displayed XYZ positions. Ferranti used its CMM to measure precision components for their military products. Three-axis models were developed in the later 60s.

CMMs are most often used to test a part or assemble to determine whether or not it respects the original design intent. CMMs are integrated within quality assurance or quality control workflows to check the dimensions of manufactured components to prevent or resolve quality issues.

(Video) Basics of CMM Coordinate Measuring Machine | 3D Measurement

The advantages of using CMMs over manual inspections or checks performed with conventional metrology instruments, such as micrometers and height gauges, are: accuracy, speed and the reduction of human error.

There are several different types of CMMs. Typically, CMMs are categorized based on their structures. Each structure has its pros and cons. Let’s take a look at different CMM types in more detail.

What are the different CMM types?

What is a CMM? Everything you need to know about coordinate measuring machines and their types. (2)

Bridge CMM

Bridge CMMs feature a probing system that moves along three axes: X, Y and Z; these axes are orthogonal to each other in a Cartesian coordinate system. Each axis has a sensor that monitors the probe’s position (in micrometres) as it moves along an object and detects points on the object’s surface. These points form what is called a point cloud, which “illustrates” the surface area users are interested in inspecting. Bridge CMMs can be divided into two CMM sub-types: moveable-table and moveable-bridge CMMs.

(Video) All about CMM | Application, Uses, Features, Parts, Types of Coordinate Measuring Machine

The pros of bridge CMMs

  • One of the most accurate types of CMMs
  • Ideal to measure machined parts with high tolerances
  • Perfect for small- to medium-sized components
  • Enabled for multi-sensor measurements, such as probing and scanning

The cons of bridge CMMs

  • Can be expensive
  • Have a fixed measurement volume
  • Lack of portability; you need to bring the part to the system or use machinery to move them around
  • Sensitive to vibrations and must be used in a metrology lab
  • Require rigid setups for each inspected part
  • Complex to operate and needs skilled workers to program the device

Gantry CMM

Gantry CMMs are somewhat like bridge CMMs; however, they are usually much larger. Because they are designed to eliminate the need to lift a part onto a table and offer similar accuracy levels as bridge CMMs, Gantry CMMs are regularly used for very heavy or large parts. Gantry CMMs must be mounted on a solid foundation, directly on the floor.

The pros of gantry CMMs

  • Highly accurate
  • Large measurement volume, which facilitates inspections of large/heavy parts
  • Easier to load and unload components than a bridge CMM

The cons of gantry CMMs

  • Can be expensive
  • Have a fixed measurement volume
  • Lack of portability; you need to bring the part to the system or carry out significant assembly/disassembly to move the CMM
  • Takes up a lot of floor space
  • Sensitive to vibrations and must be used in a metrology lab
  • Require rigid setups for each inspected part
  • Complex to operate and needs skilled workers to program the device

Cantilever CMM

A cantilever CMM differs from a bridge CMMS as the measuring head is only attached to one side of a rigid base. Cantilever CMMs provide open access to inspection technicians on all three sides for ease of operation

The pros of cantilever CMMs

  • Highly accurate
  • Suitable for smaller parts
  • Access to three sides makes it easier to manually or automatically load and unload components

The cons of cantilever CMMs

  • Can be expensive
  • Have a fixed measurement volume
  • Lack of portability; you need to bring the part to the system
  • Sensitive to vibrations and must be used in a metrology lab
  • Require rigid setups for each inspected part
  • Complex to operate and needs skilled workers to program the device

Horizontal Arm CMM

Horizontal arm CMMs, as their name implies, have horizontally mounted probes as opposed to vertically mounted probes like other CMMs. They are designed to measure long and thin objects that could not be inspected with vertical CMMs, like sheet metal. Horizontal arm CMMs are also often used to inspect geometries that are difficult to reach. There are two types of horizontal arm CMMs: plate-mounted and runway-mounted.

The pros of horizontal arm CMMs

  • Long measurement volume (long and thin parts)
  • Good for parts requiring low tolerances
  • Does not require a significant foundation system
  • Quick and easy installation
  • Smaller footprint
  • Requires less ceiling height than other types of CMMs
  • Cost-effective

The cons of horizontal arm CMMs

  • Less accurate than other CMMs
  • Have a fixed measurement volume
  • Lack of portability; you need to bring the part to the system
  • Sensitive to vibrations and must be used in a metrology lab
  • Require rigid setups for each inspected part
  • Complex to operate and needs skilled workers to program the device

Portable measuring arm CMM

Portable measuring arm CMMs are coordinate measuring machines that can take measurements of parts right on shop floors, allowing for quick results and real-time analysis. As opposed to inspectors bringing components to a lab to be measured, technicians use an articulated arm, with either a six- or seven-axis system, to measure components wherever required; this is particularly useful to analyze parts while still integrated into their fixtures or assemblies. Portable measurement arms.

(Video) What is CMM? and types of Coordinate Measuring Machine

The pros of measuring arm CMMs

  • Portable and lightweight: you can bring the CMM to the part
  • Extendable measurement volume (leapfrog)
  • Enabled for multi-sensor measurements, such as probing and scanning
  • Relatively inexpensive
  • Easy to operate (no programming)

The cons of measuring arm CMMs

  • Less accurate than other types of CMMs
  • Sensitive to environmental vibrations
  • Requires rigid setups

Optical CMM

Optical CMMs are portable non-contact devices. These CMMs use an arm-free system with optical triangulation methods to scan and acquire 3D measurements of objects. Thanks to sophisticated image processing technology, optical CMMs are ultra-fast and guarantee metrology-grade accuracy. Optical CMM scanners are particularly conducive Industry 4.0 manufacturing.

While optical CMMs have a slightly lower level of accuracy, they are nevertheless accurate for a wide range of applications. In fact, optical CMMs are used in conjunction with traditional CMMs in order to free up production bottlenecks. Therefore, parts that require the critical level of accuracy are inspected with a conventional CMM. All other components can be assessed using a more cost-effective optical CMM, which provides satisfactory accuracy—but also portability, flexibility and speed.

The pros of optical CMMs

  • Portable and lightweight: you can bring the CMM to the part
  • Extendable measurement volume (leapfrog)
  • Enabled for multi-sensor measurements, such as probing and scanning
  • Very fast acquisition times
  • Relatively inexpensive
  • Easy to operate (no programming)
  • No rigid setups required

The cons of optical CMMs

  • Somewhat less accurate than conventional CMMs, depending upon the application

Why are we talking about CMM speed all the time?

What is a CMM? Everything you need to know about coordinate measuring machines and their types. (3)

Today’s manufacturers are under more pressure to increase throughput, offer just-in-time delivery schedules, and accelerate their time to market—all while significantly reducing costs to a minimum. When bottlenecks at the CMM occur, inspection procedures extend cycle times and ultimately increase non-value-added quality costs. CMM speed and efficiency is therefore critical.

(Video) Components of CMM Machine | Coordinate Measuring Machine

As previously mentioned, gridlocks at the CMM are often caused by the sheer volume of work that has to be carried out by a limited number of qualified metrologists. CMM programming times also significantly lengthen inspections as the CMM has to be configured for each type of component or sub-assembly to be assessed.

Conventional CMMs that are equipped with CMM probes are slow and not suitable for efficiently measuring complex shapes. Other CMMs, which have CMM sensors, tend to speed up inspection processes; however, they still need to be operated by experts.

Manufacturers are therefore increasingly looking for inspection technologies, like innovative optical CMMs, that can keep up with the breakneck pace required in demanding production environments and stringent quality assurance and quality control standards.

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Interested in taking advantage of both the accuracy and speed of cutting-edge optical CMM scanners? Looking to implement an optical CMM in your upcoming automated quality control projects?

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FAQs

What is CMM and its types? ›

There are four main types of coordinate measuring machine (CMMs): bridge, cantilever, gantry and horizontal arm. The one you choose will be determined by what you wish to use it for. All CMMs have three orthogonal axes, X, Y and Z which operate in a 3D coordinate system.

What is CMM machine? ›

What is a CMM machine? A coordinate measuring machine, also known as a CMM, is a piece of equipment that measures the geometries of physical objects. CMMs using a probing system to detect discreet points on the surfaces of objects.

What is CMM and why is it used? ›

Coordinate Measuring Machine (CMM) Parts

It is mainly used for three-dimensional measurement of dies such as automobile parts and various mechanical parts, three-dimensional objects such as prototypes, and measurement of differences from drawings.

How do you use a CMM Coordinate Measuring Machine? ›

Basics of CMM Coordinate Measuring Machine | GaugeHow.com - YouTube

What are the 5 levels of CMM? ›

The Capability Maturity Model (CMM) uses five software process levels of maturity to assess, further develop, and improve the software development processes of an entity.
...
The Five Maturity Levels of the Capability Maturity Model
  • Initial Level. ...
  • Repeatable Level. ...
  • Defined Level. ...
  • Managed Level. ...
  • Optimizing Level.
Feb 5, 2021

Where is CMM used? ›

A common use of CMMs is in manufacturing and assembly processes to test a part or assembly against the design intent. In such applications, point clouds are generated which are analysed via regression algorithms for the construction of features.

What are the basic elements of CMM? ›

CMMs are comprised of three main components: the machine itself, the measuring probe, and the control or computing system with appropriate measuring software. After placing a workpiece on the machine table, a probe is used to measure different points on it by mapping the x, y, z coordinates.

What is the accuracy of CMM? ›

Newest CMM realizes world-leading measurement accuracy of 0.28 μm.

How do you calculate CMM accuracy? ›

So, the formula U3 = 4 + 5L/1000 for volumetric accuracy means that the error for zero measured length is 4 µm, and for every additional meter of length measured it becomes 5 µm larger. The specification is commonly stated as U3 = 4 + 5L.

What is CMM testing? ›

CMMs are industrial inspection tools that measure the dimensional accuracy of manufactured goods. This is a crucial step to monitoring production quality to ensure large-sized parts meet design specifications for use in critical applications.

How many levels are in CMM? ›

The Capability Maturity Model (CMM) provides a framework for organising these evolutionary steps into five maturity levels that lay successive foundations for continuous process improvement.

What are the components of CMM? ›

CMMs are comprised of three main components: the machine itself, the measuring probe, and the control or computing system with appropriate measuring software. After placing a workpiece on the machine table, a probe is used to measure different points on it by mapping the x, y, z coordinates.

Videos

1. All About CMM | Introduction of Coordinate Measuring Machine
(GaugeHow)
2. Everything you need to know about CMM!
(Chamala Vaishnavi)
3. Types of CMM Prob | Coordinate Measuring Machine part-2
(BigCMM)
4. Online Course: Learn CMM(Coordinate Measuring Machine)
(BigCMM)
5. Coordinate Measuring Machine(CMM)-Metrology
(Ganesh C)
6. Chapter 18 Coordinate Measuring Machines
(Kay Rand Morgan)

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