A coordinate measuring machine (or CMM) is a piece of equipment used to measure the actual dimensions of a physical object. It’s important to note that CMMs can either be manually controlled or fully automated with the aid of direct computer control (DCC).
How Does CMM Work?
Coordinate measuring machines consist of four major parts:
- Stage: This is where the operators place the object.
- Probe: Usually attached to the stylus, probes measure the distance to the nearest surface.
- Bridge system: It moves the probe along the XYZ axes.
- Software: CMM software assimilates and analyzes data collected from discrete points.
After the CMM’s probe collects the required data from the discrete points or the physical object, this information is analyzed using digital software. This process recreates the object or measures it against the provided ideal data set provided by the customer.
However, it’s imperative to note that each discrete point on the object is unique to the CMM’s coordinate system. Also, the CMM merges all the measured points to form a unique feature to which all the other features can be related.
What Is a CMM Used For?
A CMM is used to determine the coordinate points on the surface of an object. These coordinate points are later used to provide accurate measurements of any given object for testing, designing, profiling, reverse engineering, and assessing parts.
How to Calibrate a CMM
CMMs collect different measurements, ranging from distance, profile, and depth to angularity and dimensions.
However, if you’re looking to get precise and accurate measurements from a coordinate measuring machine, you’ll need to inspect and calibrate it for each measurement type. In some cases, calibrating a coordinate measuring machine might entail performing some physical adjustments to the hardware.
In other cases, calibrating a CMM entails software adjustments to ensure that you obtain tighter and more accurate results. Different manufacturers and installation services providers calibrate CMMs as per the procedures stipulated in the ISO 10360 series.
Also, in more rigorous applications, the operators can calibrate the CMMs using a laser interferometer.
What Are the Different Types of CMMs?
- Bridge – The most common type of CMM, bridge-style CMMs are further divided into moveable-table and moveable-bridge types. They provide technicians with stable anchors for the measuring apparatus. The bridge designs of CMMs are available as both portable units and as fixed machines, which makes them suitable for inspecting near or at the machining process. However, it’s important to note that bridge-style CMMs are limited to measuring small and mid-sized parts that can be lifted and placed on a table or a slab.
- Gantry – Gantry CMMs are used to measure large parts, such as automobiles, in which the floor is used as the datum. The design for gantry CMMs makes them suitable for measuring large and heavy machine parts, like gears, since there is no need to place an object on the table or slab. However, their big size means that they’re more expensive to purchase than other types of CMMs.
- Horizontal arm – Unlike other types of CMMs that mount their probes vertically, the horizontal arm-style CMMs mount all of theirs horizontally. This design makes horizontal arm CMMs suitable for measuring long and slender objects that vertical machines wouldn’t accommodate.
- Cantilever – Cantilever CMMs are usually supported at one point, making them less rigid than other styles. However, it is this type of design that makes cantilever-style CMMs only suitable for measuring small parts.
What Are the Different Probe Types of CMMs?
- Contact probes – These are probe types that send out electrical impulses every time they touch the surface of an object. The computer then uses the location of these impulses to collect the data points, which can number in the hundreds or the thousands.
- Non-contact probes – Unlike the contact probes, non-contact ones collect the required data using a machine vision or a laser to determine the distance between the object’s surface and the probe.
- Multi-sensor probes – These probe types of CMMs generally use a combination of contact and non-contact measuring techniques.
Benefits of CMM Technology
Several benefits come with CMM technology:
- CMMs provide greater accuracy since there is less risk of human error.
- This technology can measure a wide range of objects, from large to fixed to heavy ones. It can also be used to measure sensitive materials.
- This technology is cost-effective since it automates the entire inspection process.
- It provides a better measurement-to-time ratio since manual labor isn’t required.
Applications of CMM technology
Various industries use CMMs for inspection and measurement operations, including:
- Automobile
- Aerospace
- Energy and green initiatives
- Nuclear
- Military and defense
- Assembly and fabrication systems
- Automation systems
- Furniture
- Tool prototype
- Mechanical manufacturing
Conclusion
A CMM can help your company conduct measurements and inspections in a much faster, safer, and more accurate manner. However, due to its high initial cost, you must consult an expert to help you decide on the best CMM type and probe equipment that will perfectly suit your company’s operations.
