Nowadays, quality inspection is one of the most important tasks of companies that manufacture products for industry. It guarantees that the products meet the customers' requirements and fulfill their purpose 100%.
What is industrial CT metrology? Industrial computed tomography enables the non-destructive testing of components and assemblies. It enables the measurement and material analysis of parts for quality verification.
In industrial CT metrology, components are scanned with a high-power X-ray beam and a high number of X-ray images are produced. These offer the possibility of creating CAD models with which the components can be compared with 3D data. Differences that are outside the defined tolerances can thus be identified reliably and accurately.
In modern quality testing, components are tested for various requirements in order to guarantee their function. Quality testing is particularly critical for safety-relevant components. They must be inspected closely, as production errors can have fatal consequences.
In most cases, the quality requirements of the components are precisely prescribed by customers. The quality department must then decide how the customer's requirements can be monitored, guaranteed and documented. For many components, it is sufficient to perform optical or mechanical measurements in order to be able to guarantee the dimensional accuracy of the components.
However, if the quality requirements are very high, normal measuring techniques can quickly reach their limits. This is particularly the case when safety-relevant components are involved, on whose function human lives depend. This can be the case in the automotive industry, the aviation industry and the aerospace industry, among others. It is then in the interest of the companies to use measuring techniques that guarantee 100% dimensional accuracy and the corresponding material requirements. Here, traditional measuring techniques quickly reach their natural limits.
Mechanical measuring techniques include measuring methods such as the caliper gauge and measuring gauges. The micrometer and measuring systems with mechanical scanning are also referred to as mechanical measuring devices. They can be used in quality inspection to monitor the dimensional accuracy of components.
Which mechanical measuring techniques are used depends on the customer's requirements. The decisive factor is the tolerance specified for the components. While calipers can only be used to check tolerances of +- 0.1 mm, modern multi-sensor measuring devices can be used to take digital measurements, some of which can detect tolerances of several hundredths of a millimeter.
Material tests and dimensions inside the components cannot be checked with mechanical measuring instruments!
Optical measuring devices use optical sensors or laser beams to measure components. Unlike mechanical measuring devices, they can detect tolerances of less than 1 µm. In contrast to mechanical measuring devices, the measurements are made without contact to the component being measured. The advantage of optical measuring instruments is primarily their accuracy. Since the components do not have to be scanned by a sensor for measurement, measurement inaccuracies are also eliminated.
Industrial computed tomography is used as a measurement technique when conventional measurement techniques do not provide the required accuracy, or components and assemblies are too complicated. These can be, for example, dimensional data of assemblies whose components must be checked individually, but which cannot be disassembled for the measurements. By means of computed tomography, industrial metrology also offers the possibility of checking material inclusions that can lead to qualitative problems in the component.
Industrial computed tomography is now an established procedure in the
quality assurance, with which production and processes can be reliably monitored. In addition, industrial CT measurement technology offers the possibility of digitally recording components and complete assemblies. In contrast to tactile measurement techniques, which quickly reach their limits, industrial CT measurement technology can capture complex component structures and filigree component geometries and enables digital assessment.
The 3D volume models created with industrial CT measurement technology can be evaluated for their component properties, which includes both the outer skin and the internal structures. It also offers the possibility of finding defects, such as air pockets, porous areas, cracks or void, which represent qualitative problems. Even fiber runs can be made visible with industrial computed tomography.
Another advantage of computed tomography is the inspection of complete assemblies, which can be used to check the accuracy of fit of the individual components. An assessment of the assembly condition can be made without requiring disassembly of the assemblies.
The non-destructive measurement of components using industrial CT metrology allows complex 3D volume models to be created, which can be used to produce plans for reproduction. Since it is also possible to perform wall thickness analyses inside components and assemblies with computed tomography, exact plans can be produced for reproduction.
Another advantage of industrial CT metrology is the ability to directly compare two or more components. This makes it possible to detect differences that may occur during industrial production. For example, products manufactured at the beginning of a batch, in the middle of a production batch and at the end of production can be compared. In this way, tolerances in production that can lead to qualitative problems can be identified.
In industrial CT measurement technology, a distinction must be made between different methods:
In two-dimensional industrial CT metrology systems, the object to be measured is not rotated. These systems can measure parts in a single beam path. This measurement technique is best suited for inspecting damaged areas inside the components and for recording two-dimensional dimensional data.
In three-dimensional CT measurement technology, the component to be measured is rotated, thus enabling the creation of complex 3D models. In the measurement process, the objects to be measured are recorded layer by layer. Data models are created that consist of many different points. They can be converted into 3D models with which an accurate quality check can be carried out.
To create 3D models, computers with high computing power and a lot of storage space are required. Three-dimensional CT measuring systems are more expensive than two-dimensional CT measuring systems due to their more complex technology and higher requirements.
The Helix CT measuring technique is based on the three-dimensional CT measuring technique. However, the component to be measured is also displaced in the longitudinal axis. The X-ray image is built up helically (helix). The Helix CT measuring technique is particularly suitable for longer components that cannot be measured with the other measuring methods.
Systems for industrial CT metrology can also be differentiated based on their size. The size requirements are determined by the dimension of the components to be measured and the required measuring accuracy.
Macro CT measuring systems are manufactured for large components and assemblies. They can X-ray objects of several meters edge length. Since the measuring accuracy suffers from this, these systems are mostly used in the quality inspection of complete assemblies. This makes it possible to determine whether all components in the assemblies have been correctly installed. High-resolution measurement of individual components is not possible with macro CT measurement technology in most cases.
Micro CT measuring systems are developed for components with a maximum edge length of up to 10 cm. The resolution of these systems is in the micrometer range and is suitable for the precise quality assessment of components. These systems are especially often used for the inspection of composite materials. They can identify cracks, inclusions, burrs and void that lead to qualitative problems.
Sub-micro CT systems play only a small role in industrial CT metrology. They are used for the measurement of very small components and offer a resolution of up to 500 μm. They are mostly used for quality control of electronic components or for the measurement of organic objects.
Computed tomography provides important information for the quality control of components that cannot be generated with other measuring techniques. For most companies, however, it is not worthwhile to acquire industrial CT measuring equipment because its use is limited for industrial production and the equipment is very expensive.
Service providers such as Q-Tech offer the possibility of measuring components and assemblies with industrial CT measurement technology and incorporating the results into quality monitoring. This allows the quality of the corresponding components to be guaranteed or appropriate production changes to be initiated.