Process Development for Tip Repair of Complex Shaped Turbine Blades with IN718

摘要

One of the most common defects during the operation of turbine blades is wear of the blade tip, which can lead to scrap of the blades. Additive Manufacturing (AM) offers the possibility to avoid a cost-intensive replacement of the complete blade with repair processes via Laser Material Deposition (LMD, also known as Direct Energy Deposition, DED) processes. Due to the industrial relevance of the application, only limited information regarding the exact deposition strategy and the process parameters used for the LMD process is available. The blade geometry used in this study is characterized by the variation of the profile cross-sections over the height of the blade. In addition, the profiles are rotated around the center of their skeleton line, which is known as twist. Furthermore, the profiles are shifted along their tendon line towards the leading edge, which is referred to as the forward sweep. First, a suitable set of process parameters is determined with which pore- and crack-free basic probes with IN718 can be manufactured. In order to transfer these parameters to the turbine blade, various process strategies are investigated which take into account both the sensitive blade geometry and the kinematics of the production system used. These strategies include the adjustment of contour and hatch tracks, design of suitable fly-in and fly-out strategies, as well as measures for the production of the overhang. The shape accuracy after the process is assessed by comparing the repaired blade with its target geometry with optical measurements. In summary, the three-dimensional build-up strategy used enables a stable reproduction of the twist and forward sweep and achieves a sufficient oversize for machining. Thus, the developed process represents a basic solution for the near-net-shape repair of blade tip damage of complex blade geometries, which can be applied to other blade geometries.