A Comprehensive Guide to CMM TechnologyCMMs, 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.
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
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 CMMsCMMs 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 CMMCMMs perform and collect a variety of measurements, such as:
Considerations of CMMsBefore 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:
1 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.
2 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.
3 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.
4 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:
1 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.
2 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.
Hard Bearing, Linear Motor and Air Bearing
Benefits and Applications of CMMsCMMs provide benefits to measurement applications across a wide range of industries.
Benefits of CMMsRegardless 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 CMMsCMMs 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