Automating turbine blade repair using Polygonica

Posted by Richard Baxter | 2 Jul, 2025

Accurate registration and alignment of scan data is critical for worn-region modelling and repair in a variety of industries, particularly turbine blades, blisks and aerfoils. This can also include identification and machining of rest-material for CAM tool path generation.

This blog, demonstration and accompanying code example show how Polygonica can be used to automate accurate scan alignment to isolate regions for tool path planning.

A scanned model of a turbine blade with the end restored by adding additive material — A (simulated) scan of a worn turbine blade, which has first been cleaned using multi-axis milling and then restored using multi-axis additive repair. Material removal and material addition simulations were done using MachineWorks.

A closeup of a scanned model of a turbine blade with additive material added using a multi-axis path. — A (simulated) scan of a worn turbine blade, which has first been cleaned using multi-axis milling and then restored using multi-axis additive repair. Material removal and material addition simulations were done using MachineWorks.

Note that the models used and results created should be considered proof-of-concepts, intended to demonstrate how Polygonica's supported APIs can be used. In particular, no attention has been paid to creating additive paths that optimise welding properties such as isotropic strength.

Additive repair workflow

Although Polygonica has a full pipeline for creating good quality meshes from scan data, in many cases the scanners used in industries such as aerospace and energy will create a reasonable quality mesh directly from the hardware - so for this example we'll take that as our starting point.

The basic workflow for this demonstration involves:

automatic repair of the mesh created by the scanner
aligning the scan of the worn part with the original design part
computing smooth boundaries of the worn region on the design part
computing a milling toolpath to remove material in the worn region creating a smooth clean surface
computing an additive toolpath to add material to fill the volume of missing material
export the toolpaths to a MachineWorks demo to visualise the results

Two models of the same turbine bracket, one a scan and one a CAD part, in different coordinate spaces. — Left: A worn scan of a bracket part (grey) before alignment with the reference CAD part (brown). Right: After alignment using Polygonica. The boundary curves of the worn region are show. These were also computed using Polygonica.

The two parts have been aligned. The CAD part is transparent so the worn region on the scanned part can be clearly seen, as can the polycurve boundaries of the worn regions. — Left: A worn scan of a bracket part (grey) before alignment with the reference CAD part (brown). Right: After alignment using Polygonica. The boundary curves of the worn region are show. These were also computed using Polygonica.

The worn scan part with a polycurve around the scan boundary and a 3-axis milling toolpath to clean the worn region. — Left: The scan with a polycurve around the worn region boundary, and a 3-axis milling toolpath to clean the worn region, both created using Polygonica. The polycurve boundary can easily be converted to a parametric curve in a CAD engine or CAM system. Right: Showing 3-axis milling and additive repair paths created using Polygonica.

The worn scan part with both multi-axis milling and additive paths required to restore the part — Left: The scan with a polycurve around the worn region boundary, and a 3-axis milling toolpath to clean the worn region, both created using Polygonica. The polycurve boundary can easily be converted to a parametric curve in a CAD engine or CAM system. Right: Showing 3-axis milling and additive repair paths created using Polygonica.

Automatic mesh repair

It's rare for a mesh from any type of scanner to be completely manifold and free from artefacts. For some operations, such as registration and alignment, this may not matter too much, but for operations such as identifying regions and their boundaries, as well as creating 3D volumes and offsetting, results will be greatly improved if you are working with higher quality mesh data.

Polygonica's automatic mesh-healing has been described by users as 'magic' and forms the first step in many mesh-based workflows, additive repair being no different. Polygonica will automatically make the mesh watertight and manifold, as well as remove self-intersections and foldovers.

Feature-based alignment

Polygonica's alignment algorithms are feature-based. That is they attempt to identify specific features that are common to both the reference mesh and the mesh to be registered. These are then used as the basis for an initial global alignment. This approach has the advantage that accurate and performant registration can be achieved for parts that differ significantly in certain regions e.g. where the part has been significantly worn, or an in-process part where there are large areas that still need to be machined away.

Following the initial feature-based registration, an error-minimisation step occurs, which can optionally be controlled based on prioritisation of important regions of the part and also client-specified threshold values. The result is that very accurate alignment can be automatically achieved.

Two models of the same turbine blade, one a scan and one a CAD part, in differenct coordinate spaces. The scan shows some red polygons where there are self-intersections — Left: A worn scan of a turbine blade (grey) with self-intersections (red), which is in a different coordinate space to the reference CAD part (brown). Right: After healing and alignment using Polygonica we can clearly see the worn region.

The red polygons have been removed and the two parts have been aligned. The CAD part is transparent so the worn region on the scanned part can be clearly seen. — Left: A worn scan of a turbine blade (grey) with self-intersections (red), which is in a different coordinate space to the reference CAD part (brown). Right: After healing and alignment using Polygonica we can clearly see the worn region.

Computing smooth boundary curves

Polygonica has extensive functionality for working with both regions and curves lying on a mesh surface, and these are used to compute a smoothed boundary of the region to be repaired or machined on the original reference part.

The nearest distance between points on the two parts are compared based on a tolerance such that parts of the scanned mesh which lie further from the reference part than the tolerance are marked as worn regions. These regions can be filtered, with small gaps between regions being filled to join adjacent regions, and small islands being removed as these are most probably caused by noise from the scanner rather than actual wear on the part.

3D polycurves lying on the surface of the part are created from the boundaries of the regions. These curves are both smoothed and offset outwards across the surface to provide a clean boundary of the region in which repairs are needed.

Alternatively, the resulting polycurve create by Polygonica can easily be mapped to a parametric curve in a CAD engine so that it can be used to constrain path generation in an existing CAM system.

Creation of solid volumes

The boundary curve and surface region it contains are used as the basis to create solid volumes representing the space in which 'trimming' is required i.e. the worn surface is first tidied by CNC milling operations. A second volume is created representing the region in which material must be added to repair the part.

These operations make extensive use of Polygonica's advanced Boolean and offsetting algorithms, as well as other supporting functions such as hole-filling, advanced smoothing and surface remeshing.

Subtractive and additive path planning

Although Polygonica is not dedicated to subtractive path planning or CNC toolpath generation, it provides a number of very useful functions in this area for those working with polygon meshes.

For 2D operations Polygonica supports planar slicing and 2D profile operations such as Booleans and offset.

For multi-axis operations Polygonica supports fast 3D offsets, creation of intersection curves (non-planar slicing), constant distance offset of 3D curves across a surface and curve simplification to a tolerance.

The worn scan part with a polycurve around the scan boundary — Left: The worn scan with a polycurve around the scan boundary. This can easily be converted to spline or pcurve in a CAD engine or CAM system. Right: Multi-axis milling and additive repair paths created using Polygonica's 3D offset, intersection curve and curve offset.

The worn scan part with multi-axis milling and additive paths required to restore the part — Left: The worn scan with a polycurve around the scan boundary. This can easily be converted to spline or pcurve in a CAD engine or CAM system. Right: Multi-axis milling and additive repair paths created using Polygonica's 3D offset, intersection curve and curve offset.

Simulation of results in MachineWorks

MachineWorks is a different set of proprietary software libraries, also available from the developers of Polygonica. They are widely used in the CAM industry for fast simulation of both subtractive and additive CNC toolpaths.

For the purposes of demonstration we export the 3-axis and 5-axis paths created by Polygonica to see the results using the MachineWorks simulation engine.