Coordinate Measuring Machines are devices that perform geometric analysis. Manufacturers use CMMs for 3D measurements, tolerances, and quality inspection. For more than 50 years, CMMs have been a staple in several critical industries. The reason is quite simple. Factories strive to eliminate human error from their processes. Conventional metrological tools like calipers, height gauges, and micrometers are immensely susceptible to this. CMMs, however, mitigate personal mistakes in the manufacturing process. They save money, time, and raw materials.
What is a CMM Machine?
The primary purpose of a CMM is part measurement. It performs this with a physical or optical probing system. A CMM consists of a staging area, body, support beam, contact probe, stylus, and computer. The stylus is mounted on the probe arm. It is capable of orthogonal motion in three directions on the Cartesian plane. Different methods for each CMM achieve this motion. The tips of the stylus contain a touch trigger. The touch trigger records the coordinates of each point on the part body and sends this information to the computer. The computer generates a 3D CAD model using this “point cloud”. CMMs enable high-accuracy 3D measurements.
The Different Types of CMMs
Brücken-KMG
The Bridge CMM is one of the most extensively used CMMs in the industry. It is excellent for measuring small—to medium-sized parts. It consists of two supporting pillars and a cross-beam. The probe arm is attached to the cross-beam and provides vertical movement. The moving frame and arms comprise the other two axes of measurement.
Pros
The Bridge CMM, apart from being versatile, is also highly accurate. It is the ideal choice for machine parts with high tolerances. It comes in two variants: moving-bridge type and fixed-bridge type. It can suit several types of workshops. Bridge CMMs can achieve different tasks such as measuring, profiling, and scanning.
Cons
Cost is one of the limiting factors of bridge-type CMMs – they tend to be expensive. They are also limited in volume by their construction. Workers have to carry parts to the stage area for inspection, which is not always ideal. Finally, it requires skilled operators and is sensitive to environmental disturbances.
Gantry-KMG
A Gantry CMM has a cross-beam supported over two parallel frames on either side. The cross-beam travels freely up and down the beam. The probe arm attached to the cross-beam similarly travels sideways. Finally, like the bridge-type CMM, the probe displaces vertically to provide the final moving coordinate. Gantry CMMs are designed to analyze large machine parts and are often mounted directly on the shop floor.
Pros
Gantry CMMs are highly accurate and reliable options for measuring automobile parts. Their large staging volume ensures that most medium and large-sized parts are accommodated. Since Gantry CMMs are mounted on the floor, it is easier to load and unload heavier machine parts.
Cons
Like Bridge CMMs, Gantry CMMs are also quite expensive. However, since they are a specialized CMM type, they are worth the investment. If you invest in them, keep in mind that they are huge. Gantry CMMs take up a lot of the shop floor. Ultimately, since they are a fixed-type CMM, they are limited by their total volume.
Horizontalarm-KMG
Certain parts as automotive panels and plates are predominantly one-dimensional. They may be short but quite vast in length. These unconventional parts cannot be measured by Bridge or Gantry CMMs comfortably. Horizontal Arm CMMs consist of a side-mounted probe arm. Instead of traversing vertically, it travels horizontally. This way, it can measure objects with long profiles with ease. Plate-mounted and runway-mounted CMMs are the two types of devices in this category.
Pros
Horizontal Arm CMMs can measure objects with long profiles. They are simple to install and operate, and they are excellent for parts that require less tolerance. They are also space-saving and cost-effective.
Cons
They offer less accuracy than other types of CMMs. Due to their horizontal construction, they are predominantly limited to one dimension. Even though they are compact, they still require the part to be brought to them, so they do not have the benefit of portability.
Freischwinger-KMG
When the Ferranti company first designed CMMs in Scotland in the 1970s, they produced the Cantilever type. This CMM has a rigid base structure to which a horizontal beam is attached. The beam contains the probe arm and stylus. It differs from bridge-type CMM in that it only has one frame. It allows for open access on three sides of the machine. The Cantilever CMM provides high precision and is suitable for small to medium-sized objects.
Pros
Cantilever CMMs have high accuracy and a low probability of measurement errors. They are particularly efficient at measuring small parts like electronic components. As they are open on three sides, the operator can conveniently load and unload parts. Cantilever CMMs have excellent measurement speed. They are suitable for workshops that require rapid output.
Cons
Due to the rigid structure of the X-axis beam, Cantilever CMMs are limited by the size of the objects they can measure. Furthermore, they are not portable. They must be placed at a station in the workshop, with the operator bringing over parts to measure.
Tragbarer Messarm CMM
Excellent for on-the-spot measuring, Portable Arm CMMs have changed CMM operation on shop floors. They consist of an articulated arm probe with a stylus tip. The CMM can be transported to various stations in the workshop to measure parts. Portable measuring arms come with six to seven-axis systems, which allows the profiling of complex parts with ease. They can analyze objects in different stages of assembly, from individual parts to whole machines.
Pros
The lightest and maneuverable of CMMs, the portable measuring arm can change how dimensional analysis is performed in the shop. They are equipped with Leapfrog, multi-sensor, and scanning technologies. Portable arms are inexpensive and easy to operate.
Cons
Due to their portable nature, these types of CMMs have several concessions. They are not as accurate or precise as bridge-type CMMs, which means that they are not suitable for highly sensitive or small-part machinery.
Optisches KMG
Advancements in machine vision have enabled Optical CMMs to emerge as a game-changing measurement technique. Optical CMMs do not use physical probes but instead employ optical methodologies to measure objects. They perform dimensional analysis with laser triangulation, photogrammetry, and imaging systems. This makes Optical CMMs ideal for measuring delicate and deformable parts. Optical CMMs allow for in-line object inspection during assembly. They are indispensable for manufacturing and automation, forming the backbone of Industry 4.0.
Pros
Like measuring arm CMMs, Optical CMMs are mobile and lightweight. They sport quick acquisition times. They are versatile in operation, performing scanning, probing, and profiling with ease. They are cheap to procure and easy to set up. Being easy to operate, they can fit a large number of use cases. Optical CMMs are the best way to measure small and deformable machine parts.
Cons
Optical CMMs are less accurate than conventional CMMs, such as bridge-type or gantry. They require specific lighting to perform optimally. In addition, Optical CMMs can sometimes have difficulty measuring shiny and reflective surfaces. Similarly, Optical CMMs may not measure transparent materials accurately.
Choosing the Right CMM for Your Needs
CMMs have emerged as the leading measurement solution to reduce human-made errors during manufacturing. By improving quality control and dimensional measurements, CMMs enhance the factory’s production process. Over time, this leads to less raw material consumption, operational savings, and increased output.
When selecting a CMM, consider your particular application. While Cantilever CMMs are very accurate, they are not very versatile. The CMMs that see the most flexible use are Bridge and Gantry type CMMs.
The Horizontal Arm CMM is right for measuring long objects. Portable measuring arms and optical CMMs are the best for portable and modular operations. If you have more questions about selecting CMMs, reach out to us. We are looking forward to hearing about your measuring needs.