Method for repairing a single crystal turbine blade

1. A method for repairing a single crystal turbine blade, which comprises an airfoil with a tip having a tip cover plate, tip cooling air holes and a tip crown, said method comprising:

a) removing the tip crown by manual grinding, thereby preserving the underlying tip cover plate;

b) preparing the tip cooling air holes by manual grinding;

c) closing said prepared tip cooling air holes by manual welding; and

d) building-up a new tip crown by a LMF (Laser Metal Forming) process

wherein between step (c) and (d) the tip is contour-grinded in preparation for the LMF welding process.

2. The method according to claim 1 , wherein the tip includes at least one letterbox, and that said at least one letterbox is prepared in step (b) by manual grinding and closed in step (c) by manual welding.

3. The method according to claim 1 , wherein the tip includes at least one damaged region which extends beyond the crown into the airfoil, and that said at least one damaged region is prepared in step (b) by manual grinding and closed in step (c) by manual welding.

4. The method according to claim 1 , further comprising a TIG (Tungsten Inert Gas) welding process is used for the manual welding in step (c).

5. The method according to claim 1 , wherein the LMF process uses an oscillating weld path for optimum weld quality and heat transport during the LMF process.

6. The method according to claim 1 , wherein after finishing the LMF process step (d) the tip area of the turbine blade is finally contoured by manual grinding.

7. The method according to claim 6 , wherein the final height of the tip is established by CNC machining.

8. The method according to claim 1 , wherein after finishing an outer contour of the turbine blade the blade is coated with a coating layer.

9. The method according to claim 8 , wherein after coating the blade, the closed tip cooling air holes are re-drilled.

10. The method according to claim 8 , wherein the turbine blade is provided with other cooling air holes outside of the tip, and that these other cooling air holes are re-opened after having been overcoated.

11. The method according to claim 9 , wherein after coating the blade, the closed tip cooling air holes are re-drilled by a laser.

12. A method for repairing a single crystal turbine blade, which comprises an airfoil with a tip having a tip cover plate, tip cooling air holes and a tip crown, said method comprising:

a) removing the tip crown by grinding, thereby preserving the underlying tip cover plate;

b) preparing the tip cooling air holes by grinding;

c) closing said prepared tip cooling air holes by welding; and

d) building-up a new tip crown by a LMF (Laser Metal Forming) process

wherein between step (c) and (d) the tip is contour-grinded in preparation for the LMF welding process.

13. The method according to claim 12 , wherein the tip includes at least one letterbox, and that said at least one letterbox is prepared in step (b) by grinding and closed in step (c) by welding.

14. The method according to claim 12 , wherein the tip includes at least one damaged region which extends beyond the crown into the airfoil, and that said at least one damaged region is prepared in step (b) by grinding and closed in step (c) by welding.

15. The method according to claim 12 , further comprising a TIG (Tungsten Inert Gas) welding process is used for the welding in step (c).

16. The method according to claim 12 , wherein the LMF process uses an oscillating weld path for optimum weld quality and heat transport during the LMF process.

17. The method according to claim 12 , wherein after finishing the LMF process step (d) the tip area of the turbine blade is finally contoured by grinding.

18. The method according to claim 17 , wherein the final height of the tip is established by CNC machining.

19. The method according to claim 12 , wherein after finishing an outer contour of the turbine blade the blade is coated with a coating layer.

20. The method according to claim 19 , wherein after coating the blade, the closed tip cooling air holes are re-drilled.