Patent Application
20100243614
The present disclosure relates to a method of repairing holes in a work piece. More particularly, the present disclosure relates to an improved method of repairing holes in a work piece using conductive heat resistance welding.
An undesirable defect or hole located in a metallic work piece may be repaired by welding. Welding is a known process for joining materials by causing coalescence. For example, a damaged work piece and adjacent filler material are heated to form a molten pool in the area of the defect. The molten pool is then cooled to solidification thereby forming a weldment.
It is known to fill a defect or hole in the work piece with a consumable filler plug and sandwich the work piece between sacrificial donor plates to create a stack. The stack is further sandwiched between one or more layers of electrode backing plates, which are then brought into contact with welding electrodes. An electrical current is passed between the electrodes, thereby resistively heating the electrode backing plates and conductively heating the sacrificial donor plates, work piece, and consumable filler plug. The donor plates, work piece, and filler plug coalesce into a liquid pool within the hole, which is then cooled to form a weldment.
A method of repairing a hole in a work piece includes placing a plug within the hole of the work piece and covering opposing top and bottom open end portions of the hole, as well as a portion of adjacent work piece, with a top donor sheet and a bottom donor sheet, respectively. A portion of the top donor sheet that is located above the hole is covered with at least one top electrode backing plate and a portion of the bottom donor sheet that is located beneath the hole is covered with at least one bottom electrode backing plate. The top electrode backing plate is contacted with a top electrode and the bottom electrode backing plate is contacted with a bottom electrode. Electrical current is transmitted between the top electrode and the bottom electrode to resistively heat the top and the bottom electrode backing plates and conductively heat a portion of the top and the bottom donor sheets, the plug, and the work piece to form a molten mixture that at least partially fills the hole. The top donor sheet and the bottom donor sheet are constrained with constraint plates that force the donor sheets against the work piece to contain the molten mixture within the hole.
Another method of repairing a hole in a work piece includes preparing a stack that includes at least one top electrode backing plate, a top donor sheet, a work piece having a hole therein and a plug located within the hole, a bottom donor sheet, and at least one bottom electrode backing plate. The electrode backing plates and donor sheets all lie above or beneath the hole in the work piece. The top and the bottom donor sheets are constrained against the work piece. The top and the bottom electrode backing plates are contacted with electrodes. The stack is heated by electrical current to melt the top and the bottom donor sheets, the plug, and the work piece thereby forming a weldment.
A welding stack for performing repairs includes a work piece having a top surface, a bottom surface, and a hole extending from the top surface to the bottom surface. A plug is located within the hole. A top donor plate is in contact with the top surface of the work piece and a bottom donor plate is in contact with the bottom surface of the work piece, so that the hole is sandwiched between the top donor plate and the bottom donor plate. At least one top constraint plate is in contact with the top donor plate and at least one bottom constraint plate is in contact with the bottom donor plate. The constraint plates force the donor plates against the work piece to facilitate preventing expulsion of molten material from the hole during conductive heat resistance welding.
To form prior art welding stack 22, work piece 10 having hole 16 is sandwiched between donor sheets 26A, 26B, electrode backing plates 28A, 28B, and electrodes 30A, 30B. Plug 24 is substantially cylindrical and smaller than hole 16 so that plug 24 fits inside of hole 16. Plug 24 is consumed by the welding process and is formed of the same material as work piece 10. A top end of hole 16, as well as top side 12 of work piece 10 adjacent hole 16, are covered by top donor sheet 26A. Similarly, a bottom end of hole 16, as well as bottom side 14 of work piece 10 adjacent hole 16, are covered by bottom donor sheet 26B. Donor sheets 26A, 26B are consumable by the welding process and are formed of the same material as work piece 10. Although donor sheets 26A, 26B are shown singularly, there can be additional layers of donor sheets in succession. A top side of top donor sheet 26A is covered by top electrode backing plate 28A and a bottom side of bottom donor sheet 26B is covered by bottom electrode backing plate 28B. Thus, electrode backing plates 28A, 28B sandwich donor sheets 26A, 26B that sandwich work piece 10 to create stack 22. Electrode backing plates 28A, 28B include substantially circular plates and are located in vertical alignment or centrally above and beneath hole 16. Electrode backing plates 28A, 28B, can be formed of steel or any other material having a higher melting temperature than the melting temperature of donor sheets 26A, 26B. Although electrode backing plates 28A, 28B are shown singularly, there can be additional layers of electrode backing plates in succession. A top side of top electrode backing plate 28A is in contact with top electrode 30A and a bottom side of bottom electrode backing plate 28B is in contact with bottom electrode 30B. Molten pool is located in a center of welding stack 22 and encompasses the area of hole 16 as well as a potion of work piece 10, and donor sheets 26A, 26B.
Electrical current is transmitted through an approximate center of welding stack 22 by electrodes 30A, 20B. Electrode backing plates 28A, 28B are resistively heated by electrodes 30A, 30B and donor sheets 26A, 26B are conductively heated by electrode backing plates 28A, 28B. The conductive heating of donor sheets 26A, 26B also conductively heat plug 24 and work piece 10 adjacent hole 16 so that donor sheets 26A, 26B, plug 24, and work piece 10 form molten pool 32 in the area of hole 16. When current to electrodes 30A, 30B is turned off or electrodes 30A, 30B are withdrawn from stack 22, molten pool 32 cools and solidifies into a weldment.
Located within, and scattered throughout weldment 34, are voids 36. Most materials, including aluminum and aluminum alloys, shrink during solidification causing cracking, porosity, or voids 36 in weldment 34. Voids are highly undesirable as they reduce the strength and other mechanical properties of both weldment 34 and the overall work piece 10. The area of work piece 10 surrounding weldment 34 is deformed or “sucked in”. Furthermore, donor plates 26 are deformed and curving away from weldment 34. The deformation of work piece 10, weldment 34, and/or donor plates 26 is undesirable as it indicates the presence of unsatisfactory weldment 34. Expulsed material 38 was part of molten pool 32 that escaped upwardly and outwardly from hole 16 during the welding process and hardened to a bottom surface or a top surface of top donor sheet 26A and/or top electrode backing plate 28A. Expulsed material 38 is undesirable as it is a sign of a non-uniform weld. Expulsed material 38 often reduces the volume of molten pool 32 leaving voids 36 within hole 16 thereby creating a satisfactory weldment 34. There is a need to improve the quality and consistency of weldments 34 formed using prior art stack 22 with conductive heat resistance welding.
Constraint plates 44A, 44B provide mechanical restraint to donor sheets 26A, 26B, respectively, by forcing donor sheets 26A, 26B centrally toward work piece 10. By constraining donor sheets 26 toward work piece 10, hydrostatic pressure within hole 16 is maintained and molten pool 32 is not expulsed during the welding process. While electrode backing plates 28A, 28B provide some force to donor sheets 26A, 26B located in substantial vertical alignment directly above hole 16, constraint plates 44A, 44B provide substantial force to donor sheets 26A, 26B peripherally or at a location spaced laterally or horizontally away from hole 16. In the depicted embodiments, a space or recess for electrode backing plates 28A, 28B and electrodes 30A, 30B is cut out of constraint plates 44A, 44B. Constraint plates 44A, 44B facilitate preventing cracks and/or deformation of donor sheets 26A, 26B during welding. By keeping donor sheets 26A, 26B stiff and pressed against work piece 10, molten pool 32 has no path to escape hole 16 and therefore, the resulting weldment is substantially free of voids.
As described above, constraint plates 48A, 48B provide mechanical restraint to donor sheets 26A, 26B by forcing donor sheets 26A, 26B toward work piece 10. The functionality of constraint plates 48A, 48B is similar to constraint plates 44A, 44B. By keeping donor sheets 26A, 26B pressed against work piece 10, molten pool 32 has no path to escape hole 16 and therefore, the resulting weldment is substantially free of voids. After conductive heat resistance welding is applied to welding stack 40 or 46, any unconsumed portion of donor sheets 26A, 26B, electrode backing plates 28A, 28B, electrodes 30A, 30B, constraint plates 44A, 44B, 48A, 48B are removed from work piece 10. If any excess, extraneous, or undesirable material remains attached to work piece 10 after welding, it can be removed so that the mechanical properties of the repaired work piece 10 similar to the mechanical properties of original work piece.
Vertical, horizontal, above, beneath, top and bottom have been used through the specification to help define relative directions. Although the present disclosure has been described with reference to exemplary embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosure.
