Method for providing removable weld backing

1. A method for welding objects having limited backside access to a cavity behind a region to be welded, the method comprising:

inserting a fugitive backing material comprising a fusible material in an installation state into a first portion of the cavity proximate the region to be welded;

transforming the fugitive backing material to a rigid state;

forming a weld in the region so that a first portion of the fusible material facing the region becomes part of the formed weld; and

transforming a second portion of the fugitive backing material remaining unwelded to a removable state and removing the second portion from the cavity.

2. The method of claim 1 , wherein transforming the fugitive backing material to a rigid state comprises compacting the fugitive backing material.

3. The method of claim 1 , wherein transforming the fugitive backing material to a rigid state comprises curing the fugitive backing material.

4. The method of claim 1 , wherein transforming the fugitive backing material to a rigid state comprises hardening the fugitive backing material.

5. The method of claim 1 , wherein transforming the fugitive backing material to a rigid state comprises allowing gravity to hold the fugitive backing material in a desired position.

6. The method of claim 1 , further comprising preventing the fugitive backing material from extending into the region to be welded while inserting the fugitive backing material into the cavity.

7. The method of claim 1 , further comprising preventing the fugitive backing material from extending into the region to be welded while transforming the fugitive backing material to a rigid state.

8. The method of claim 1 , wherein the fusible material comprises one of the group consisting of a metal powder and a brazing compound.

9. The method of claim 1 , further comprising:

mixing particles of the fugitive backing material with a binder to form a paste;

inserting the paste in the cavity; and

allowing the paste to harden.

10. The method of claim 9 , wherein the binder comprises one of the group consisting of sodium silicate and hydrolyzed ethyl silicate.

11. The method of claim 1 , further comprising filling a second portion of the cavity with a second fugitive backing material.

12. The method of claim 1 , further comprising transforming the fugitive backing material to a comparatively more viscous state after inserting it into the cavity.

13. The method of claim 1 , further comprising transforming the second portion of the fugitive backing material to a comparatively less viscous state after welding.

14. The method of claim 13 , further comprising removing the second portion of the fugitive backing material from the cavity after transforming it into a comparatively less viscous state.

15. The method of claim 1 , wherein transforming the second portion of the fugitive backing material to a removable state comprises a process of chemical leaching.

16. The method of claim 1 , wherein transforming the second portion of the fugitive backing material to a removable state comprises a process of melting.

17. The method of claim 1 , wherein transforming the second portion of the fugitive backing material to a removable state comprises a process of sublimation.

18. The method of claim 1 , wherein transforming the second portion of the fugitive backing material to a removable state comprises a process of dissolving.

19. The method of claim 1 , wherein transforming the second portion of the fugitive backing material to a removable state comprises a process of releasing a force compacting the fugitive backing material.

20. The method of claim 1 , wherein transforming the second portion of the fugitive backing material to a removable state comprises a process of flushing the fugitive backing material out of the cavity.

21. The method of claim 1 , wherein transforming the second portion of the fugitive backing material to a removable state comprises a process of allowing gravity to act on the fugitive backing material.

22. A method for welding objects having limited backside access to a cavity behind a region to be welded, the method comprising:

placing a pre-formed weld backing in the cavity directly adjacent the region to be welded;

at least partially filling a portion of the cavity with a fugitive backing material to provide support for the pre-formed backing;

forming a weld in the region;

transforming the fugitive backing material to a removable state and removing the fugitive backing material from the cavity; and

removing the pre-formed weld backing from the cavity.

23. The method of claim 22 , further comprising transforming the fugitive backing material to a rigid state by one of the group consisting of compacting, curing, hardening, and allowing gravity to hold the fugitive backing material in a desired position after at least partially filling the portion of the cavity with the fugitive backing material.

24. The method of claim 22 , wherein the fugitive backing material is one of the group consisting of a metal powder, alumina, silica, quartz, and wax.

25. The method of claim 22 , wherein the fugitive backing material is removed by a process of dissolving.

26. The method of claim 22 , wherein The fugitive backing material is removed by a process of:

heating the fugitive backing material to a melting temperature; and

allowing the fugitive backing material to flow from an opening in the cavity.

27. The method of claim 22 , wherein the fugitive backing material is removed by a process of sublimation.

28. The method of claim 22 , wherein the fugitive backing material is removed by liquefying the fugitive backing material.