A Comprehensive Guide to CMM Technology
CMMs, or coordinate measuring machines, measure the precise physical dimensions of an object. The object is placed on a stage where the CMM’s probe collects three-dimensional data points to plot and reconstruct the object in digital software. CMMs can be manually controlled or programmed with direct computer control (DCC) for automated data collection.
Coordinate measuring machines are excellent tools for product quality inspection applications in manufacturing facilities. However, CMMs require significant initial investments, so it is essential that companies consult with an expert before reaching the purchasing stage. These experienced industry professionals can also help integrate the CMM into a facility’s existing system.
At AIMS Metrology, we offer expert consulting services, complete turnkey solutions, calibration, training, programming, and retrofitting services for CMMs.
Table of Contents
- What is a CMM Used For?
- How Do CMMs Work?
- Our Five Axis Technology
- Capabilities of CMMs
- How to Calibrate a CMM
- Considerations of CMMs
- Types of CMMs
- Probe Types of CMMs
- Hard Bearing, Linear Motor and Air Bearing
- Benefits and Applications of CMM Technology
- CMM Technology and AIMS metrology
What Is a CMM Used For?
CMMs are most commonly used for inspections. These machines measure the dimensions of an object along the X, Y, and Z planes and compare the gathered data against the set standards for the part design, alerting an operator about any detected defects.
How Do CMMs Work?
CMMs are complex machines with four main parts:
- A stage or a slab where operators place the object
- A probe—attached to a stylus—that measures the distance between it and the nearest surface
- A gantry or bridge system that moves the probe along the XYZ axes
- Software to assimilate and analyze the collected data points
Once a CMM’s probe collects the data points for a physical object, the information is analyzed by the software to digitally recreate the object or measure it against the ideal data set.
Our Five Axis Technology
Opposed to traditional 3-axis measuring technology, our 5-axis technology measures much faster due to the extended measurement ranges provided by the additional axises. The 5 axis system provides improved accuracy and repeatability allowing a reduction in inspection time, faster calibration, less material handling and more cost saving advantages.
Capabilities of CMMs
CMMs have numerous capabilities used to recreate 3D representations of objects for a wide variety of applications, including:
- Batch inspection and creation of reports for manufactured goods
- Digitization of 3D objects
- Dimensional measurement
- In-depth mapping
- Inspection and calibration of equipment
- Measurement system analysis (MSA)
- Testing for part or product defects
How to Calibrate a CMM
CMMs perform and collect a variety of measurements, such as:
However, to provide precise and accurate measurements, they need to be regularly inspected and calibrated for each measurement type. While calibration may include physical adjustments to the hardware, it primarily focuses on adjusting the software to ensure tighter, more precise results.
Manufacturers and installation service providers calibrate CMMs according to the procedures established in the ISO 10360 series. The calibration procedure may involve modifying the software against a standardized target object—i.e., an artifact. During this process, the CMM is tasked with measuring a standard artifact such as a ball and cone or swift-check gauge. The CMM must accurately measure the object within set tolerances, while the technician adjusts for inaccuracies until the CMM is operating properly.
Technicians can also calibrate the machines with a laser interferometer for more rigorous applications. This process allows for a more precise recalibration, but takes more time and requires an experienced technician.
Considerations of CMMs
Before investing in a CMM, industry professionals should consider what type of machine and probe would be most optimal for their application.
Types of CMMs
There are four distinct types of CMMs, each of which is characterized by how the probe is mounted and, consequently, how it moves around the object during the measuring process.
The four types of CMMs are:
- Bridge CMMs
The most popular type of CMM, bridge CMMs feature a simple, three-axis structure. They are available in two varieties: moving bridge and fixed, or unmoving, bridge. These machines are low cost and ideal for smaller parts because the part has to be lifted onto an elevated stage.
- Cantilever CMMs
Much like bridge CMMs, cantilever CMMs are mostly used for small parts. However, they can have automatic loading and unloading processes, making them ideal for shop floors. Operators can access the part on three sides of the CMM, which offers greater access than bridge CMMs. However, the X-axis beam is rigid, which establishes part size restrictions.
- Gantry CMMs
Gantry CMMs are typically mounted directly to the floor and are suitable for handling large and heavy items. The measuring range can extend to 4m x 10m x 3m (XYZ), and customized gantry CMMs can be even greater. The advantage of this type of CMM is that objects are loaded onto the floor and measured without having to be elevated. However, integrating a gantry CMM into a facility requires a strong foundation that can handle the weight and operational strain.
- Horizontal Arm CMMs
Horizontal arm CMMs differs from the other three CMM types because their probes are attached to horizontal arms that affixed to vertical columns. They are available in two basic models: plate-mounted and two-runaway mounted.
While these machines are not as accurate as of the other types of CMMs (performing to 30 µm or larger tolerances), they are suitable for measuring thin components or difficult to reach objects, such as large, mounted components.
Probe Types of CMMs
While the arm design plays a large part in the CMM’s flexibility, the probe is the component responsible for detecting and recording the necessary data points.
Three of the most common types of probes used in CMMs are:
- Contact Probes
Contact probes, or touch probes, send out electrical impulses when they touch an object’s surface. The attached computer collects hundreds to thousands of data points based on the exact location of these pulses. These types of probes are available in touch trigger and analog scanning models.
- Non-Contact Probes
Non-contact probes collect data points by using a laser or machine vision to determine the distance between the probe and the object surface. These probes are faster but less accurate than contact probes and are suitable for measuring smaller, flexible, and more complex or precise parts.
- Multi-Sensor Probes
Multi-sensor probes use a combination of contact and non-contact measuring methods.
Hard Bearing, Linear Motor and Air Bearing
Bearing structure in general directly correlates with the accuracy and repeatabliliy of testing while all having specific pros and cons. Hard Bearing systems are designed to be more rugged and are often known for being able to take on higher loads than other types.
Linear Motor CMMs are designed with an updated linear motor system instead of conventional belts and pulleys. The use of a linear motor means that the LM needs virtually no maintenance, provides less downtime, and has a positioning accuracy in the submicron range. The LM line is also identified as smoother and faster than conventional air bearing systems.
Air-bearing supplied CMMs, are designed to float on air above its guide path. This non-friction system enables the CMM to achieve higher accuracy compared to other systems. Physical factors such as friction, wear, and contamination can cause roller bearing systems to be less accurate.
Benefits and Applications of CMMs
CMMs provide benefits to measurement applications across a wide range of industries.
Benefits of CMMs
Regardless of the machine and probe type employed, CMMs offer better measuring processes than other devices. Some of the benefits of using CMMs over other measurement instrumentation include:
- Greater accuracy. CMMs, especially automated models, ensure more accurate results by minimizing the risk of human error.
- A wider range of measurable objects. The variety of machines available enable CMMs to measure a wide range of parts, including fixed objects, large and heavy objects, and sensitive materials.
- More cost-effective. While CMMs are initially costly, they automate the inspection process, creating long-term savings by improving processing speed and reducing the frequency of part or product errors.
- Better measurement-time ratio. Automated CMMs collect data, analyze the results, and move the objects without the need for manual labor.
Applications and Industries Served by CMMs
CMMs are used for measuring and inspection operations throughout several industries. At AIM Metrology, we serve the following industries:
- Assembly and fabrication systems
- Automation systems
- Energy and green initiatives
- Military and defense
CMMs and AIMS Metrology
AIMS Metrology is an ISO/IEC 17025:2005 certified original equipment manufacturer (OEM) and expert in 5-Axis CMMs. Our product inventory includes a wide selection of CMMs, components, and accessories that are compatible with Renishaw parts and components.
Our expert team offers turnkey solutions from design to installation and calibration, as well as retrofitting, upgrading, and software training services.
Contact AIMS Metrology Today to Receive a Quote for the Right CMM
CMMs can facilitate your company’s object inspection and measurement operations, making them faster, safer, and more accurate. However, the large investment cost necessitates consulting with an expert to ensure that you select the optimal CMM type and probe equipment for your facility’s needs.
To learn more about our turnkey CMM solutions or to receive a product or service quote, contact us today.