Computed Tomography
Computed tomography (CT) is an X-ray-based, non-destructive 3D imaging method that reconstructs internal and external geometry from many 2D projections captured around a part, producing a volumetric model. In manufacturing, it enables dimensional verification, defect detection, assembly analysis, and reverse engineering of internal features inaccessible to tactile CMM or optical inspection.
On a shop floor, CT inspection typically begins with fixturing the component on a precision rotary table inside a shielded cabinet. The X-ray source and detector remain fixed as the part rotates through 360 degrees, capturing hundreds of 2D projections that reconstruction software turns into a single volumetric dataset. This volume can be sliced in any plane, making it possible to inspect coolant passages, undercuts, lattice structures, thin walls, and cast-in cavities that no probe or optical sensor can reach without destroying the part. Machinists use the resulting model to compare against CAD, measure wall thickness, map porosity, and confirm assembly alignment. For additive or hybrid manufacturing, the same scan supports wall-thickness analysis, pore mapping, and failure investigation before process parameters are released. CT does not replace the CMM for simple external dimensions, but it becomes the only practical way to verify internal geometry completely and non-destructively.
- Beam hardening distortion: Dense or mixed-material parts skew the reconstructed volume, creating phantom voids and dimensional drift when scan settings are not matched to thickness and alloy, leading to false rejects or missed defects.
- Resolution overreach: Coarse voxel sizes miss thin walls and small bores, yet users expect CMM-level certainty; if scan capability is not verified against feature tolerance, unstable measurements undermine quality decisions.
- Misuse on accessible features: CT is often applied to simple external dimensions that a CMM or optical system measures faster and more accurately, wasting cycle time and adding cost without improving confidence.
Is computed tomography a metrology tool or only a nondestructive inspection method?
Industrial CT is both. It performs nondestructive inspection and dimensional metrology, including CAD comparison and internal measurement of complex parts. The reconstructed volume enables quantitative wall-thickness analysis, porosity mapping, and feature verification, making it a full metrology solution when calibrated and validated for the measurement task.
When should CT be selected over a coordinate measuring machine (CMM) for machined components?
Choose CT when features are internal, inaccessible, or would require destructive sectioning to inspect. A single CT scan captures the entire internal and external volume. For straightforward external geometry, a CMM offers faster throughput and tighter uncertainty control, so CT is best reserved for hidden features that tactile probes cannot reach.
What data does CT produce that is useful in CNC and manufacturing workflows?
CT produces a voxel volume, point cloud, or reconstructed 3D dataset. That data can be compared directly to the CAD model, used to measure wall thickness, locate porosity, verify assembly alignment, and support reverse engineering or model-free manufacturing of parts with complex internal geometry.