One part, three zones that each need a different tool
A turbine blade splits cleanly into three inspection zones once you actually look at what each one requires. The aerofoil is a freeform curved surface that needs full-field 3D scanning. The root attachment is a set of discrete, precisely engineered features that needs CMM probing. The internal cooling passages are sealed inside the blade with no external access at all, and only CT scanning can see them. Treat all three the same way with a single method and you’ll either miss deviation across the aerofoil, waste time over-probing the root, or never actually check the internal channels at all.
The aerofoil: why a 3D scanner beats a CMM here
The aerofoil’s twisted, tapered profile is a continuous surface, not a set of discrete features. A CMM measures by touching individual points, and on a shape like this, deciding where those points go is close to guesswork, a probe can easily miss the exact spot where the blade has drifted out of tolerance simply because nobody thought to place a point there. A 3D scanner solves this by capturing the entire surface at once rather than sampling locations one at a time.
ATOS Q is the 3D scanner to reach for on a new-build blade under controlled conditions, a stationary blue light system built for the accuracy a first-article or batch inspection needs. GOM Scan1 is the portable version of the same capability, useful when the blade’s still mounted in a disk assembly or being checked in a maintenance bay rather than brought to a dedicated inspection cell. Either way, the output is a full-field scan compared against nominal CAD and rendered as a colour deviation map, so a twist across the span or a localised bulge shows up visually rather than depending on a probe happening to land in the right place.
The root attachment: why a CMM is actually the right call here
This is the opposite case from the aerofoil, and worth stating plainly so it doesn’t read as a contradiction. The root or fir-tree attachment, where the blade locks into the turbine disk, is made up of discrete serrated features with defined edges and flat faces, the same kind of geometry a CMM handles efficiently and accurately. It also carries the highest mechanical load on the entire part, which is why its GD&T tolerances run tighter than almost anything else on the blade. A CMM probes each serration face and calculates position and profile against the correct datum structure, which matters enormously here, an attachment that measures fine in isolation but references the wrong datum plane can still pass inspection while carrying a fit problem that only shows up once it’s under load in the engine.
So the rule is simple. Freeform surface, scan it. Discrete engineered features, probe it. The aerofoil and the root aren’t the same kind of geometry, which is why they need different tools rather than one machine forced to do both jobs.
The internal channels: the zone nothing else can reach
Cooling channels run through the blade core to keep it from melting at turbine inlet temperature, and they have no external opening large enough to inspect, let alone probe. Industrial CT X-ray metrology, METROTOM, captures the complete internal geometry non-destructively, channel diameter, the wall thickness separating the channel from the outer aerofoil surface, and any blockage or casting defect sitting inside a passage that would otherwise stay invisible until the blade failed in service. The same wall thickness principles that apply to a cast housing apply here too, except the margin on a turbine blade’s internal wall is often the difference between a blade that survives its design life and one that doesn’t.
Thermal barrier coating thickness gets checked in the same CT pass on a coated blade, since the coating sits as a distinct layer over the substrate and its own thickness variation needs verifying separately from the metal geometry underneath it.
Worn blades need a different starting point entirely
A blade pulled out of an MRO cycle often has no usable drawing behind it, especially on older engine platforms where documentation has gone missing or the part’s been through enough repair cycles that its as-built geometry no longer matches anything on file. That’s reverse engineering work rather than standard inspection against a known print, scanning and CT together to capture the blade’s actual current geometry, then rebuilding a usable CAD model that separates genuine design intent from the wear it’s picked up over years of service.
Bring the blade in, new-build or worn
Tell us which zone is actually giving you trouble and we’ll match the method to it. Global TechSolutions runs ATOS Q and GOM Scan1 for the aerofoil scanning, CMM for the root attachment, and METROTOM for the internal channels, as the ZEISS Partner Metrology Centre in Singapore. For the broader picture on how metrology fits into aerospace manufacturing and MRO, our aerospace metrology page covers that wider ground.
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