Industrial CT scanning uses X-rays to look inside a casting or a battery for hidden cracks and holes, in the way a hospital scanner looks inside a body. CT stands for computed tomography. It finds faults that cannot be seen from outside and that a probe cannot reach.
The part sits on a turntable between an X-ray source and a detector. As the part turns through a full circle, the detector takes hundreds or thousands of X-ray pictures from different angles. Software then combines the pictures into a 3D model of the whole inside of the part. This step is called image reconstruction. Dense material shows differently from empty space, so a hole inside a metal casting shows as a dark spot.
For instance, a foundry makes aluminium castings for a car. A gas bubble inside the casting is a weak spot, but nothing can be seen from outside. The CT scanner takes about 1,500 pictures, builds the 3D model and finds a hole 0.3 mm wide. The software compares its size and position with the limit in the specification, and the casting is rejected.
A CT scan shows more than defects. The 3D model can be compared with the CAD design, so a plant can see how thick a wall is in a place that no probe can reach, or whether a channel inside a part is the right size. A scan takes from a few minutes to a few hours, depending on the size of the part and the detail needed. The machine sits in a shielded cabinet that keeps the X-rays inside, and in India the use of X-ray equipment is regulated by the Atomic Energy Regulatory Board (AERB).
The same method is used to check battery cells for folded layers inside. It is the same technique as in medical imaging equipment, but with a stronger X-ray beam and a part that turns, not a patient. The scan is slower and more costly than a probe on a coordinate measuring machine, so it is used for the parts where an inside fault is dangerous.