Siemens Energy has developed a digital repair chain using ‘hybrid’ laser powder bed fusion that can add new features to gas turbine blades.
With it, cooling structures that prevent blade tip failure can be implemented in critical areas, meaning turbine blades can now be upgraded while being repaired.
Due to the coupling of high temperatures with high gas velocities during gas turbine operation, burn-off at the blade tip can occur, ultimately leading to gap formation and a measurable drop in the performance of the entire turbine. This process leads to a vicious circle. With greater gap formation, the temperature of the blade material increases due to the overflowing hot gas, which in turn leads to even faster material loss and further increases the gap between the blade tip and ring segment.
Using laser powder bed fusion (LPBF), structures with inner channels can be produced in high resolution on an existing component. This high resolution is important to incorporate the new cooling geometries with a very limited cross-section. With this new design, the critical areas can be cooled more effectively, thus preventing material loss.
The new digital repair chain will be used to both repair and upgrade damaged gas turbine blades. (Image: Siemens)
However, blades that have been in operation at high temperatures have individual shapes, making the LPBF repair more challenging. Therefore, a new CAD-CAM chain was developed by Siemens Energy that automatically adapts the shape of the LPBF tip to perfectly match each blade.
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By combining 3D blue laser scanning with an algorithm developed by the Siemens Energy team, a digital repair chain was established that can morph the geometry parametrically. The team also had to develop the LPBF process for an extremely oxidation-resistant material for the blade tip.
The first step of the new digtial chain is to perform a blue light scan of the damaged turbine blade, the data of which is then used to automatically morph the LPBF geometry to exactly fit the blade. (Image: Siemens)
According to Siemens Energy, the application of this technology to existing components is still a rather unexplored marginal area of 3D printing technology, known as hybrid LPBF repair (or HybridTech for short).
'The main difference between common R&D printing and hybrid is that we do not print an entire component on the plate, we are instead printing features on an already existing part,' explained Heiko Lammers, an AM advisory expert at Siemens Energy. 'This add-on slows down the tip degradation and ensures constant power output for our customers. We can therefore raise the value of the repaired component for both us and the customer to create a real win-win situation.'
The development of HybridTech is part of the research project 'Change in production technology' funded by the European Regional Development Fund.
The first blade sets have already been manufactured and a conversion of the standard repair procedure to the new process is now underway, according to Siemens Energy. The technology will be applied to other components in the future, with it being possible to upgrade completely new component designs using the new digital repair chain.
