Coordinate Measuring Machine - CMM [Types, Principle & Advantages]
Traditionally, using hand tools or an optical comparator, measurements were visually taken in the industry. These instruments, however, take considerable time and have minimal precision.
On the other hand, using the coordinate processing technology for metrology, a coordinate measuring machine (CMM) analyses the height, width, and depth of the component.
Moreover, such a device can calculate the objective automatically, track the recorded values, and extract measurements from GD&T. Coordinate measuring machines are one of the important mainstays for product verification.
Every day, it is used to classify fast designs and manufacturing modules that have complicated geometries with close tolerances. So, let first start to know what is Coordinate Measuring Machines.
Coordinate Measuring Machine(CMM):
A Coordinate Measurement Machine (CMM) is either a contact model using touch probes, a measurement spherical object, or a non-contact model using other means, such as cameras and lasers. Some models intended for the automobile industry can also calculate limits greater than 30 feet (10 m ) in height.
The location of the probes may be controlled manually or, by means of a computer, automatically (CNC). In a three-dimensional Cartesian coordinate system ( i.e., with X Y Z axes), CMMs usually define the location of a probe with respect to its distance from a reference sphere.
In addition to moving the probe along the X, Y, and Z axes, certain devices often permit the probe angle to be controlled to allow areas that otherwise would be difficult to be measured.
Using a touch trigger probe, scanning, or vision probe tip, a classic, bridge-style coordinate measuring machine (CMM) precisely calculates the geometry of an object along the X, Y, and Z-axis to take a sequence of precise points on the surface of the products.
Coordinate measurement machines can be manufactured from a wide range of materials, but because of its stiffness to weight ratio and enabling the building materials to be thermally dynamic, a mixture of granite and aluminium has been commonly embraced by the industry.
In consumer software metrology, variations in atmospheric temperatures and hence extension or constriction of the materials of the system are tracked and adjusted for.
In order to ensure that specific consistency specifications are met and adhered to, and the high accuracy is achieved, the most common application of a CMM is to measure the performance of the manufacturing product against the specifications given.
Contact us to know more about the application of these measuring machines in manufacturing industries.
Why CMM is needed?
The coordinate measuring machines are very important in the industry for metrology nowadays. Conventional means of the handheld inspection being used in metrology have their drawbacks and depend heavily on the ability of the workers to examine the products.
Components that are poorly fabricated will go unnoticed and be delivered to your client. Furthermore, as production design gets more refined, components are rendered more intricate, which means that certain attributes can only be precisely calibrated with a Coordinate measurement machine.
This is where CMM inspection technology delivers precise, repeatable results in a fraction of the time, all the while satisfying increasing-consumer expectations, with the need to accelerate and optimize examination procedures in metrology.
The bottom line-a CMM will save time and money for your business and will increase your manufacturing process to compete for more lucrative jobs. There are various case studies available online that show the measurement accuracy of CMMs.
Moreover, these case studies also explain the use of CMMs for various product measurements in different industries.
Types of CMM:
Coordinate measurement machines are available in four major types: bridge, cantilever, gantry, and horizontal arm. Dependent on the machine samples, each one offers specific benefits.
The bridge type is the most common example of a CMM machine. According to Wikipedia, in a three-dimensional Cartesian coordinate system, the traditional 3D "bridge" CMM machine makes probe travel along three axes, X, Y, and Z, which are orthogonal to each other.
Each axis has a sensor that tracks, generally with micrometer precision, the probe heads on that axis. When the probe touches (or otherwise senses a specific spot) on the target, the computer scans the three position sensors, thereby measuring the spot of one point on the object's surface area.
This approach is repeated if required, rotating the probe each time, to create a "point cloud" that defines the points of interest on the surface.
A precision granite plate with two legs carrying the X-axis carriage is the backbone of most bridge machines.
In the 1970s, Ferranti's original design in Scotland was the cantilever CMM machines, and nowadays they are made in limited numbers, typically as hard-bearing equipment for the shop floor.
Usually used to calculate comparatively tiny components, they offer free access on three sides to the user. On the side of a rigid framework containing the Y-axis, the X-axis measurement beam is connected.
Owing to intrinsic rigidity, this reduces the size of the X beam, making the unit suitable for smaller products only. The cantilever machine excels as a shop floor CMMs, so it relates itself well to automated loading or unloading.
Gantry Coordinate measurement machines are used primarily for very heavy and bulky components that need a bridge machine to be extremely precise.
Many gantry devices are actually fixed to the floor and do also have a significant base. The manufacturer specifies this specification and should not be overlooked.
Smaller gantry devices, typically 1.5 to 2 meters in height, have four vertical columns carrying broad Y-axis beams. The carriage of the X-axis travels between the two assisted Y-axis beams.
Based on the length of the Y-axis, bigger gantry machines have six to eight columns or more. Situated on the X-axis carriage, the Z-axis may be as long as 4 meters, but typically it is between 1.2 and 2.0 meters deep.
The measuring range of gantry CMMs can vary from 1 x 2 x 1 m XYZ to 4 x 10 x 3 m XYZ, and it is possible to buy even bigger, particularly-built systems.
Horizontal arm CMMs were first developed by Steifelmayer in Germany. Horizontal arm systems were historically exclusively programming instruments and were manually controlled.
The machines were produced in the United States by companies like Bendix (now Sheffield) under the Portage brand. In order to weigh materials, Vernier scales were used and scribers were used as probes.
A horizontal arm coordinate measurement machine's configuration is somewhat distinct from the other three types in that it consists of a vertical column (X-axis) and a horizontal arm (Z) mounted on a saddle rising and falling the X-axis vertically.
So the thickness of a surface plate or a long beam is the Y-axis.
Of the four types of Coordinate measuring machines, (CMMs) listed, horizontal arm coordinates measuring machines are the least effective.
Nevertheless, they have some specified benefits: they can calculate large parts of the thin-walled / sheet-metal form placed in brackets reflecting the manufacturing location of the car body, such as doors, body sides, grills, dashboards, etc.
Precision is not the horizontal arm CMM's high point. Most devices work at volumetric tolerances of 30 μm and higher, but they are by far the most cost-effective approach for measurement of large parts requiring open tolerances.
The horizontal arm machine measuring range is from 2 x 2 x 1 m XYZ to 4 x 10 x 3 m XYZ.
Working Principle of CMMs:
Coordinate measuring machines (CMMs) refers to determine the 3D (x y and z) dimensions of objects with the help of probe contacts. The basic principle of CMM is putting the objects which need to be tested in the working range of the system.
It allows you to get the measurement of the object's coordinate either automatically (with the help of software) or with manual configuration. Thanks to software technology which helps in visualizing and analyzation of recorded data.
Then various mathematical calculation techniques are utilized for getting the shape, position tolerance, and other related features of the considered object.
Though advanced coordinate measurement machine provides various other features, however, the dimensional measurement is still the most fundamental application of CMMs.
Advantages of Coordinate Measuring Machines:
It is clear that a coordinate-measuring machine (CMM) plays a vital role in realms of measurements with high-speed ad quality assurance. CMMs are also widely utilized for various types of products within job shops in the united states. Here are some of the key advantages of the Coordinate measurement machines.
High Accuracy and precision
CMM can not only be utilized for precise measurement of length, width, height, and surface areas of the part but also a stylus calibration of CMM has the ability to accurately determine the flatness, cylindricity, roundness, and straightness within thousands of inch.
All the results are calculated from the same origin. This technique provides a high level of accuracy and reduces errors as compared to hand inspection in the manufacturing field with the help of scanning probes.
Though different parts of the machine such as a motor, probe, measuring Microscopes, etc. need to be replaced after a specific time frame (based on the working conditions) however, the machine itself has a long lifespan.
Coordinate measuring machines (CMMs) are universal measurement machines and need not be utilized for any other operation.
They can mark dimensions for any type of part surfaces like gears, cams, and round exteriors without any certain fixtures or gages.
Due to the light contact of prob most parts can be evaluated without being clamped to the rotary table or granite table.
Less Setup Time
Manual inspection of even a simple surface plate is a very time-consuming activity. The coordinate measuring machines widely utilized for the instantaneous alignment of a part in the united states. They can easily orient a part in a drawing direction according to the reference point.
The obtained data can directly be compared with the side drawing dimensions. Advanced technology produces a quick reference system according to the orientation defined by the operator.
Reduced Operator Command
Due to the computer numeric control, these machines automatically measure the smaller products with so much accuracy and easily operated with less expertise. This lessens the chances of measurement errors and enables us to scale different products with the same basic procedure in the quality lab.
The combination of all the above-mentioned advantages contributes to making the CMMs more productive as compared to the traditional investigation systems.
The integrated data handling system containing computational and analytical technology features allows the operators to recognize the productivity level.
Human error, caused by workers improperly using measurement tools, is a significant source of error in metrology. A coordinate measuring machine dramatically decreases the probability of errors and substantially improves the degree of precision.
Cantilever Coordinate measuring machines, in particular, are also the most precise but the least versatile. CMMs from Bridge and Gantry has good precision and are semi-flexible.
The CMMs of the Horizontal Arm gives the least precision but the most versatility in systems measuring.
However, the precision ratio is also much greater on all forms of coordinate measuring machines than it would be without one, making manufacturing far more cost-effective.
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