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When it comes to ruthless chase after quality control and the integrity of the product, manufacturers in various industries have a similar problem: how to find internal defects and anomalies, which are absolutely not perceived by other, non-destructive testing (NDT) techniques.
Human eye, ultrasonic probes, and even X-ray radiography often prove useless in the case of complicated geometries, microscopic variations in material, or deep internal architecture. It is here that the strength of high-tech technology, which is based on medical computed tomography (CT) will be an invaluable instrument in showing the invisible.
What is CT Scanning of Industry?
Industrial CT scanning is an effective non-destructive evaluation (NDE) method that employs X-rays to provide an entire three-dimensional (3D) volume of both internal and external structure of an object.
In contrast to the ordinary 2D X-ray radiography, where the result of a scan is a flat and superimposed shadow, CT scanning records several hundred 2D projection images at different angles as the part turns. These projections are then digitally manipulated to form a 3D model in the form of voxel models by the use of specialized computer software (called reconstruction), a mathematical procedure. The final model is represented by a voxel (a 3D pixel), which is an exact density value, and therefore an engineer can visually slice and inspect the part at any angle without physically destroying it.
It is this level of detail and this broad volumetric information that is the basic distinction that allows the Industrial CT Scanning to reveal defects that cannot be seen by the traditional methods.
The Limitations of Conventional Methods of NDT
In order to realize the metamorphic effect of such technology, it is useful to remember the shortcomings of traditional inspection methods:
- 2D X-ray Radiography: Although 2D X-rays are ideal in identifying large voids, porosity, or cracks, they are prone to superposition. Internal characteristics are projected to a plane, and it is not possible to know the precise depth or the spatial position of the defects, particularly in components where there are different wall thicknesses or complicated overlaps. Minor and tiny details may be totally obstructed by the material.
- Ultrasonic Testing (UT): UT is the type of testing performed with sound waves of high frequency to detect defects by measuring reflected energy. It works very well with the homogeneous materials, such as the welds and the thick metals. It, however, has problems with components that consist of composite materials, very porous, or components with extremely complicated shapes that diffract the sound wave (e.g., an extremely curved surface or an internal cavity). It is usually subjective to the talent of the inspector and the necessity of a coupling agent.
- Coordinate Measuring Machines (CMM) and Optical Scanners: They are excellent for external dimensional inspection and surface geometry. More importantly, they are not able to look inside a component, so they are not aware of internal defects such as shrinkage porosity, inclusions, and assembly problems.
Undercover: Flaws Exposed by Industrial CT
The volumetric data created by industrial CT scanning offers some major benefits of detecting defects and analyzing failures, and it is the only possible approach in some of the applications:
Elaborate Porosity and Void Analysis.
Porosity (little internal voids) and shrinkage are typical problems with materials that are produced by casting, additive manufacturing (3D printing), or injection molding. These weaknesses greatly reduce the mechanical performance, fatigue life and pressure integrity of a part.
The traditional X-ray may reveal a group of large pores, but CT scanning is able to:
- Measure the overall volume of void.
- Measure the size, shape and exact placement of each individual pore, to the level of microns.
- Divide porosity between critical stress points.
- Compliance with strict aerospace and automobile standards of maximum allowable pore size towards the surface.
Interior Fissures and Intrusions
Cracks in internal formation or small outside material inclusions are the primary causes of premature product failure. These defects can be separated by CT scanning:
- It is also capable of tracing the micro-cracks that are emanating out of an internal stress point, which could not be detected in the least by surface techniques such as dye penetrant or eddy current tests.
- It can easily locate and define foreign material inclusions (e.g., ceramic particles in a metal matrix or metal shards in a plastic part) by contrasting their density with the density of the surrounding material.
Complex Internal Assemblies Analysis
In sealed parts or multi-material, multi-assembly parts, CT scanning can give a virtual teardown:
- Electronics: Testing printed circuit board (PCB) solder joints, wire bonds and placement of components in an encased housing.
- Medical Devices: Checking the conformity and integrity of inner parts in implants or disposable surgical instruments.
- Complex Valves/Mechanisms: It is able to ensure that all internal springs, seals, and moving components are properly placed and free of debris at final assembly, which cannot be done using any other NDT technique.
Composites Fiber Orientation.
The orientation and consistency of the reinforcing fibers used in fiber-reinforced polymer (FRP) and other composite materials is very important in structural strength.
- Industrial CT scanning is able to scan the 3D orientation of the fibers across the part volume. Only the deviations in the alignment of fibers that can be seen and measured instantly weaken the material. This is a very essential check in quality control of aerospace composite components.
Other than Defect Detection: Metrology and Reverse Engineering
The use of such technology is much more than merely identifying defects. The 3D voxel data generated is also very precise in dimensional metrology and reverse engineering:
- Internal Metrology: CT scanners are the only technology that can do geometric dimensioning and tolerancing (GD&T) checks on internal features (e.g., the diameter of an internal cooling channel or the consistency of thickness of the wall) without machine tool intervention.
- Part-to-CAD Comparison: The scan data may be directly compared to the original CAD model to produce color deviation maps, and immediately identify where the as-manufactured part is varying with the design specification, both internally and externally. This is critical to first-article inspection (FAI).
The Future of Manufacturing Quality
Due to the growing complexity of products, with additive manufacturing, lightweight composite materials and reduced-size electronic devices, the need to have sophisticated tools to inspect them is increasing exponentially. Conventional NDT techniques, despite still being useful, are no longer capable of keeping up with the geometrical and material demands of current engineering.
Industrial CT scanning has become the gold standard in the 21st century and provides high-resolution, volumetric data as opposed to other non-destructive testing methods. It guarantees totally new standards of quality assurance, minimizes the threat of field failure, and pushes prices down by making it possible to apply adjustments to the processes in time using full internal structural data. Also read: 6 Important Things About Scanning Electron Microscopy (SEM)
Image source: elements.envato.com
