Airfoil Scanning Process Yields Parametric Model

Exact Metrology details the steps to a successful airfoil evaluation.

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Exact Metrology Inc. describes its Airfoil scanning procedures as having two parts: the scan process and the modeling process. The scanning process includes the setup of the scanner, the scan itself, the registration of the data accrued in the scan, and the validation of that data.

Exact Metrology receives airfoils that customers provide (although the scan can happen at the customer’s facility as well) for full documentation prior to scanning. Because of the reflective nature of the blades, a thin coating of Magnaflux spray is applied. The SKD-S2 spray is a second phase of the crack-checking processes. (Phase 1 is a die penetrant not typically needed.) When scanning the blade, Exact uses a fixture device that acts as an alignment constraint while holding the airfoil in place and enabling Exact technicians to capture data on the part without touching the part. The part is positioned on the rotating table or on a stationary marble top and scanned multiple times from multiple perspectives.

The targeting procedure uses an automated fitting of point clouds based on three positions on the part. The software then analyzes every point with overlap and runs a best fit algorithm to find the tightest and best alignment, resulting in a fully registered and organized point cloud.

The next step is to triangulate or mesh the points together. Points are “intelligently” removed from the network by algorithms in the software. Essentially, the points of redundancy are decimated and averaged. This mesh is further manipulated by reducing the points along flatter areas and retaining more triangles in areas of curvature and complexity.

In the surfacing process, a surface is basically draped over the mesh and smoothed to be reflective of the actual part. Once this task is completed and a complete watertight object is created, the model is ready to be exported in the client’s desired format. The final deliverable is a parametric model. Unlike a solid model, the parametric model possesses relationships of all dimensions within the CAD. 

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