Precision and accuracy are vital in manufacturing, especially when making components or parts that make up the machines or equipment in a production process. The entire production could go to waste if the measurements are off by just a millimeter. Buyers will refuse to pay for products with wrong dimensions, and the manufacturer will have to restart production, spending double the resources, money and time to correct their errors.
To eliminate the risk of errors, manufacturers optimize technology instead of relying on instruments that depend on human bias and skill. A CMM or Coordinate Measuring Machine is perfect for this.
In this article, we will answer the question “what is a CMM machine,” and discuss its components, types, pros, cons and reasons for investing in one. If you are unfamiliar with how it works and want to learn more before buying or renting CMM equipment, this article is a good starting point.
What Is a CMM Machine?
A CMM machine is an advanced 3D measuring tool that runs on a sophisticated computer program and is operated by a trained technician. It measures dimensions on three axes: X, Y and Z (height, width and depth). Sophisticated, high-tech models can even perform five-axis CMM measuring, perfect for asymmetrical and irregularly-shaped objects.
CMM is best used in manufacturing high-precision cutting or molding products. The technology has vast applications. Hence, we have table-mounted CMMs that measure small items and giant machines that scan large, heavy workpieces that cannot be lifted off the floor.
Although the machine is often used to obtain an object’s physical measurements to inform the mass production process, it is also integrated into quality assurance workflows to ensure the dimensions of the components follow the original design intent and are consistent throughout the production process.
CMM machines are often categorized according to their structure. But before we discuss the different types of CMMs, let us first cover the components that make up this advanced measuring tool.
Components of a CMM Machine
A CMM primarily consists of these four parts:
- Mechanical Probe
- Granite Table or Surface Plate
- Controller
- Measuring Software
Each has a designated function and works together to obtain accurate results. Taking one out or if one isn’t functioning as well as the rest will result in errors.
Mechanical Probe
The probing system is the primary measuring component of a CMM. A probe interacts with the object and collects the data based on the coordinate system programmed in the CMM. It scans the object and converts the physical measurements into electric signals, feeding the data into the machine for analysis.
Probes come in different forms, shapes and sizes, the variation depending on the CMM type and the characteristics of the objects they measure.
Probers can be:
- Mechanical – This probe consists of a physical “arm” that moves over and around the object. Some touch the object, while others are non-contact and optical or proximity sensors to scan dimensions.
- Optical – Optical probes are non-contact and use sensors, lasers and cameras to measure objects.
Granite Table or Surface Plate
Objects must be stable to ensure accurate measurements on a CMM. In some cases, temperature and air pressure can even cause measurement discrepancies. This is why some CMMs are enclosed in highly controlled chambers to ensure accuracy.
The first iterations of CMM machines used granite because of its stability and high resistance to temperature and wear and tear. Today, manufacturers also use ceramic, steel and silicone carbide for the machine’s structure to help keep the Z-axis as secure and rigid as possible.
The surface plate may also come with various fixtures that help stabilize an object on the measuring table. These are customized attachments like magnets or clamps that hold things firmly in place without interfering with the probe.
Controller
The controller station houses the remote, joystick and other physical buttons for operating the CMM. It allows metrology company technicians to perform real-time recalibrations and overrides whenever necessary. Automation may be one of CMM’s best assets, but sometimes, technicians have to do things manually with the controller.
Measuring Software
The metrology software system that gets the machine working is vital for a CMM’s performance, speed and accuracy. The software collects, interprets, displays and stores data. It aids manufacturers in improving product design by presenting complex 3D forms as numerical and graphical data.
The software also powers the probes, providing commands, directions and sequences as it measures an object. Although the other parts are equally important, the software is crucial because it informs the next steps of production (i.e., whether to continue as is or make significant changes in the design or manufacturing process).
What Are the Different CMM Types?
CMMs are classified by type according to their distinguishing characteristics.
- Bridge CMM
The probe is the distinctive feature of the bridge CMM. It moves along the X, Y and Z axes and plots measurements against the Cartesian coordinate system. A sensor lies on each axis and records the probe’s location (in micrometers) when it detects a point on the surface. Collectively, these points are called the point cloud and become the machine’s basis for rendering a digital illustration of the object. The bridge CMM is one of the most accurate measuring devices for manufacturing.
- Gantry CMM
Gantry CMMs are bigger, more sophisticated versions of bridge CMMs. They are ideal for measuring large, heavy objects that are difficult to lift off the ground. Since the object stays on the floor, the machine must also be mounted directly on the foundation to ensure stability. Gantry measuring machines are highly accurate but aren’t portable and require a lot of floor space.
- Cantilever CMM
Unlike most CMM machines, the cantilever probe is attached to one side of the base. Technicians have free access to the object on three sides, making loading objects on the stable base easier.
- Optical CMM
A sophisticated take on the CMM, optical machines are portable, arm-free measuring devices that use high-tech optical sensors and triangulation methods to capture 3D scans and measurements. Although the accuracy of the optical CMM is a little lower, it is more affordable and can measure objects much faster than others.
The optical CMM would be great as a supplementary scanner. Optimize the other CMM machines for production stages where precision and accuracy are most critical, and use the optical CMM for post-production quality checks where its accuracy rate suffices.
- Horizontal Arm
As the name suggests, the probe for the horizontal arm CMM is mounted horizontally instead of vertically from the top, like most CMMs. It is ideal for measuring long objects, like metal poles and sheets. The horizontal arm probe is either plate-mounted or runway-mounted.
- Portable Measuring Arm
The most convenient and portable version of CMMs, the portable measuring arm allows technicians to measure objects on the production floor instead of bringing the specimens to the lab or measuring room. The articulated arm measures on six or seven axes with multiple sensors for probing and scanning. Lightweight, easy to operate and relatively inexpensive, the portable measuring arm is ideal when measuring objects that are still connected into assemblies.
How To Use a CMM Measuring Machine
There are prerequisites for using a CMM:
- Learn the alignment and coordinate system your machine uses.
- Learn the functions and operating controls of each component of the CMM machine.
The specific process of using a CMM depends on the type. For example, you can expect the procedure for a bridge CMM to differ from a portable measuring arm. But we can cover the essential points with these general steps:
- Identify the surfaces you need to measure based on the blueprint.
- Select, prepare and calibrate the probe.
- Ensure that the stylus and probe are clean (dust can affect the accuracy of the readings) and that the CMM is in the home position.
- Mount the object and use fixtures to keep it stable on the table, if necessary.
- Align the object and designate the Z-axis.
- Detect the points manually or automatically through sensors.
- Measure the object.
- Compare the measurements against the blueprint.
- Record the data and prepare the reports.
What Is CMM Programming?
CMM programming is the process of using a coordinate-measuring machine to measure three-dimensional objects. Designing the physical characteristics of a product that will be recreated or mass-produced using a CMM machine is also part of the programming process.
Technicians or operators in charge of a CMM machine are called CMM programmers. Their responsibilities include:
- Ensuring all of the machine’s components work properly
- Entering the correct code lines (measuring commands) into the machine
- Reading design blueprints and analyzing whether the prototype measures up
- Contributing to discussions about changing a product’s calibrations
Why Do I Need a CMM Machine?
A CMM plays a vital role in different manufacturing stages, like testing, assembly, molding and quality control. It has a simple purpose: to measure the dimensional accuracy of manufactured products. However, the data collected from CMM programming can improve all other manufacturing areas, from design development to quality assurance.
Benefits & Limitations of Coordinate Measuring Machine
Using a CMM instead of handheld inspection tools offers the following benefits:
- Precision and accuracy – You can take precise measurements down to micrometers.
- Speed – The machine can obtain various measurements in one pass.
- Versatility – CMMs, with their multiple features and functions, can be used for a wide range of applications.
- Data integrity – You can confidently use and trust the data because there’s little room for error.
Like any machinery, however, there are limitations to what you can do with CMMs:
- Some CMMs are too complex for just anyone to operate. Staff must undergo training and certification to ensure correct and appropriate applications.
- CMMs still need to be standardized. Switching from one manufacturer or software to another is still challenging.
- Errors are only eliminated in perfect conditions (i.e., the object is mounted on a stable base, and there are no environmental factors like fluctuating air pressure or dust that can cause discrepancies in readings.
- Applications are limited to the type of CMM you own. If you have a wide range of products to measure, you must buy or rent suitable types of CMM.
Find High-Performance CMM Machines at ATT Metrology Solutions
After learning the answer to the question “what is a CMM machine,” and more of its role in manufacturing, you may want to find out how your business can benefit from high-precision metrology equipment and where it fits in your current production process.
Our specialists at ATT Metrology Solutions will be happy to offer insights for your business’s improvement. We’ve been providing metrology solutions since 1988, applying our knowledge in robotics and large-scale metrology to meet our customers’ needs.
Contact us to request a quote or more information on our inspection services.
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