GB1568826A

GB1568826A - Method and apparatus for vacuum induction bonding

Info

Publication number: GB1568826A
Application number: GB4769776A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1975-11-24
Filing date: 1976-11-16
Publication date: 1980-06-04
Also published as: FR2332095B1; JPS5275640A; FR2332095A1; IT1064829B; DE2652877A1; JPS5953156B2

Description

(54) IMPROVEMENTS IN METHOD AND APPARATUS FOR VACUUM INDUCTION BONDING (71) We, GENERAL ELECTRIC COMPANY, a corporation organized and existing under the laws of the State of New York, United States of America, residing at 1, River Road, Schenectady, 12305, State of New York, United States of America do hereby declare the invention, for which we pray that a patent may be granted to us, and the metbod by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the joining of a jgurality of members to form an article and ma particularly, to the vacuum induction bonding d such In the operation d a gas turbine engine, particularly of the axialAlow type, it is desirable to minimize leakage of gases between adjacent stages of the compressor and of the tune portion. Because of the hier tem- perature operation of the turbine, control of such leakage can be more difficult because of the more limited scope of materials available and because of the wear or damage to tip portions of airfoils which are in dose proximity to, or in relative rubbing relationship with, an opposing member. For example, this can occur in the case of turbine blades in relative rotation with a turbine shroud.

After a period of time in such strenuous operating conditions, turbine blades can ex habit tip craking or abrasion conditions which, prior to the present invention, were considered to be unrepairabie. Replacement of the relatively costly blade was then required.

It is a principal object of the present invention to provide an improved method and apparatus for vacuum induction bonding astable to the joining of a plurality of members, such as a new tip cap portion to an existing airfoil or blade member.

According to one aspect of the invention there is prided a method of induction bonding wherein a plurality of members are held by holding means within an induction heating coil disposed within a hollow chamber, the members being in juxtaposition at a joint so as to define an article, - fluid is evacuated from the chamber and force is applied to press the juxtaposed members together by means induding a piston slidable within an opening in a wall of the chamber and having one portion exposed to atmosphere and another portion exposed directly to the interior of the chamber, so that the piston operates through the opening as a direct function of atmospheric pressure acting on said one portion of the piston and as a direct function of vacuum within the chamber acting on said other portion of the piston.

According to another aspect, the present invention provides apparatus for vacuum indiction bonding of a plurality of members in juxtaposition at a joint to define an article, the apparatus including a hollow chamber defined by walls, and having an outlet allowing evacuation of fluid from the chamber; force transmitting means to force the juxtapositioned members together; an induction heating means including an induction heating coil adapted to apply heat at the joint; and hiding means to hold the article in alignment with the force transmitting means and within the induction heating means, the force transmitting means including a piston which is disposed within an opening in a wall of the chamber and movable in fluid sealing relationship with and reciprocally though the opening, one portion af the piston being exposed directly to the atmosphere and another portion of the piston being exposed directly to the chamber, the piston being free to operate through the opening as a direct function of atmospheric pressure operating on said one portion of the piston and as a direct function of vacuum within the chamber operating on said another portion of the piston.

The invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a diagrammatic representation of a turbine blade with a replacement tip cap in spaced apart relationship at the tip; Figure 2 is a partially sectional, diagrammatic presentation of an embodiment of the apparatus of the present invention with a turbine blade and blade tip positioned as the workpiece; Figure 3 is a view of the induction heating means within the vacuum chamber and taken along lines 3-3 of Figure 2; Figure 4 is a partially sectional, fragmentary view of another embodiment of the apparatus associated with the present invention; and Figure 5 is a fragmentary, partially sectional view of another form of the single-point type contact or loading means associated with a preferred forml of the present invention.

Although the present invention can be practiced with a variety of articles, its application to turbomachinery rotor blades, particularly those found in the turbine section, have been seen to provide significant benefit.

Because of the requirement for a close tolerance between the tip of such a rotor blade and, for example, a circumscribing shroud, coupled with the modern requirement for cooling of the tip from within the blade, there has resulted a design of a rotor blade which is expensive to manufacture. Therefore, it is highly desirable to be able to repair such a blade rather than to replace it in the event of damage. The present invention, in one form, is directed to the repair of such an article. Although in the following description the bonding together of two members is described, it will be appreciated that the apparatus provided by the invention may be used, in suitable cases, to bond together more than two members.

Referring to the drawing, Figure 1 shows a turbine blade shown generally at 10 and including an airfoil body 12 and a tip cap 14. In the repair of such a turbine blade, a damaged blade tip can be removed, such as by machining, grinding, etc., and a separate, replacement tip cap 14 can be prepared for bonding with body or airfoil member 12.

The apparatus associated with the present invention, and in which such bonding can be accomplished, is shown in the partially sectional, diagrammatic view of Figure 2. In the embodiment of Figure 2, the apparatus includes a top wall 16, side walls 18, conveniently of glass or plastics material and a bottom wall 20. Together, these elements define a hollow chamber 22 in which the blade 10 is treated.

Top wall 16 includes an opening in which is disposed a force transmitting means such as piston 24 movable reciprocably through the opening. Fluid sealing means, such as "O" rings 26 are provided to maintain conditions within the chamber during movement of piston 24.

Mounted on bottom wall 20, or integral therewith, is a support 28 for holding the airfoil body. As shown in Figure 2, it is convenient to mount sidewalls 18 on the bottom wall 20, to be held initially by gravity and then by the vacuum produced within chamber 22. Fluid sealing means or "0" rings 30 are provided to avoid leakage between chamber 22 and the atmosphere outside the chamber.

Disposed within chamber 22 and positioned about the blade 10, in the area of the interface between airfoil body 12 and tip cap 14, is an induction heater shown generally at 32.

Such a heater shown in more detail in Figure 3, in this embodiment is a metal plate 34 such as of copper and to which are secured induction heating coils 36. The coils 36 are shaped to conform with the cross-sectional shape of the blade being repaired to provide uniform heat to the surfaces, particularly at their perimeters. Electrical leads 38 are connected with a low output, high frequency power supply (not shown). One example of such power supply has an output of about 5 KW and a frequency in the range of about 100-450 KHZ.

Also provided is a port 40 which is connected to a vacuum system capable of producing a vacuum of at least about 0.5 X 10-4 Torr for evacuating fluid such as air from the chamber. A variety of such systems are commercially available.

The form of the apparatus of the present invention shown in the drawing is adapted to treat a single article. Accordingly, the dimensions of the apparatus can be relatively small, with a relatively small associated vacuum system. In addition, because practice of the method associated with the present invention requires a relatively small pressure between the tip and the body the force transmitting piston 24 can be operated by atmospheric pressure when chamber 22 is evacuated. The pressure applied to the blade can be adjusted by adjusting the size of the piston on which the atmospheric pressure operates. For example, as shown in the embodiment of Figure 4, an insert 42 can be placed within the opening in top wall 16 and a smaller piston 24a can be used to apply a smaller amount of pressure to the blade. In this way, practice of the present invention does not require, and in its preferred form does not use, mechanical force generating means. If greater pressure is desired, piston 24 can be made of a heavier material or can be made hollow so that there can be added the desired amount of additional weight, for example steel shot, which together with the atmospheric pressure will apply the desired force to press members of the blade together.

It is preferred in the practice of the present invention to apply pressure uniformly to the interface between airfoil body 12 and tip cap 14 by use of a sphere 44 in Figures 2 and 4, or a pyramid or cone 46 in Figure 5. Such a loading is herein called a substantially single-point type loading and is intended to include within its definition an element which has a relatively small and preferably a point contact with force transmitting piston 24, and in the nature of a self-leveling element: it allows even mating at the interface between body 12 and tip cap 14. Through this arrangement, application of greater force to one portion of the interface, for example at the edges, is avoided. Although some forms of such a device are shown in the drawing, it will be appreciated by those skilled in the art that a variety of afiarrgements can be made to accomplish such a purpose.

Although an important feature of the present invention is the localized heating at the interface between members to be joined, it is also desirable to avoid transmission of such heat to other components of the apparatus.

Therefore, a thermal insulator, such as ceramic member or spacer 48, can be provided between tip cap 14 and other elements of the apparatus such as the sphere 44 or cone 46.

It now can be appreciated from the drawing and the above description that the apparatus of the present invention can be constructed relatively simply and economically. The chamber 22 can be made small and can be sized to fit the workpiece being treated in order to reduce the size of the vacuum. system required. For example, a relatively small vacuum system can evacuate the chamber to the specified range of at least about 0.5 X 104 Torr in about two minutes or less. In addiction, sidewall 18 is conveniently a glass or plastics material cylinder because the chamber itself is not heated. Similarly, other elements of the apparatus can be made from lightweight, relatively easy-towork materials such as aluminum or its alloys, the ceramic spacer 48 being included as a thermal insulator to inhibit conduction of heat away from workpiece. Also, as was mentioned before, atmospheric pressure can be used to operate on the force transmitting piston to apply, according to the size and weight of the piston, the pressure desired at the interface between members being joined.

The method associated with the present invention is, in general, a vacuum induction heat bonding method for joining a plurality of members at prepared, cooperating surface portions. As such, it can include brazing, diffusion bonding, etc. Practice of the method, in the apparatus described above, includes first preparing cooperating surface portions of each member so that they mate one with the other that is, that they conform with one another across the joint gap between them.

For example, in the repair of a turbine blade of the type shown generally at 10 in Figure 1, a damaged tip is removed and a replacement tip cap 14 is prepared to have a shape and size which relates to the shape and size of the original tip of the blade, the tip cap including a tip cap bonding surface 15.

Similarly, the airfoil member is provided with an airfoil bonding surface 17. The bonding surfaces of body 12 and tip cap 14 are prepared, such as by machining, so that they match one another as nearly as practical and necessary for the joining method. Then the cooperating surfaces are cleaned, preferably by a high temperature vacuum heat treatment.

A bonding material, which can be in any of a variety of forms including foil, tape, sintered powder or powdered material, such as that described in U.S. Patent 3,759,692 -- Zelahy, patented September 18, 1973, the disclosure of which is incorporated herein by reference, can be, and generally is, interposed between the cooperating surfaces, although such materials as Ti and its alloys may be joinable without such material. Such a bonding material has been useful, for example with the Ni-base superalloys, in the practice of the diffusion bonding method with which one form of the present invention is generally related, as is described in U.S. Patent 3,632,319 -- Hoppin et al patented January 4, 1972, the disclosure of which is incorporated herein by reference.

The blade 10 is then held within vacuum chamber 22 in alignment with the force transmitting piston 24 and positioned within the induction heater 32 which includes heating coils 36 shaped to relate to the general crosssectional shape of the airfoil and tip cap bonding surfaces, as shown in Figure 3. As discussed above, ceramic insert 48 is then placed on tip cap 14 and a single-point type loading means is positioned on ceramic spacer 48 for contact with piston 24.

With the elements thus assembled, the Fluid, in this case air, in chamber 22 is evacuated to produce a vacuum of at least about 0.5 X 10-4 Torr, causing piston 24 to apply pressure through the single-point type loading means and ceramic spacer 48 uniformly to the tip cap 14 and across the interface to airfoil body 12. Then the induction heater including coil 36 is activated to generate the desired amount of heat for a time required to bond the members together, depending upon their metal or alloy of construction. As has been described in the abovereferenced patents, the disclosures of which have been incorporated herein by reference, only relatively small joint pressures are required, for example less than 500 psi and in some examples as little as 10 psi. Tem- peratures for the nickel-base superalloys generally are in the range of 2000-22500F (1090--1230"C), as measured by an infrared radiation sensor, although it will be appreciated by those skilled in the art that the present invention can be practiced in connection with a variety of materials at a variety of temperatures and pressures. One of the important features of the present invention is that it heats the interface between members being joined generally uniformly across a relatively narrow heat-affected zone, thus avoiding any detrimental effect on other material of the article.

In connection with the application of a tip cap such as 14 to an airfoil body 12, it has been recognized that heating of the relatively smaller and thinner tip cap 14 can cause an excess temperature at the joint. Therefore, a preferred form of the method associated with the present invention in connection with the joining of members one of which is larger Or heavier than the other, is that the portion of the induction coil be located such that the heavier or larger member be heated first in order to avoid such an excess temperature condition.

The present invention has been described in connection with a single chamber apparatus and with a single mode of operation. However, it will be appreciated by those skilled in the art that a plurality of chambers can be operated with a single vacuum, system or a single induction heating power source, or both, in order to provide a still more efficient pro duction type arrangement. In addition, it will be recognized that tip caps of a material different from that of the airfoil body can be applied according to the present invention as new manufacture as well as replacement in repair WHAT WE CLAIM IS: 1. Apparatus for vacuum induction bonding of a plurality of members in juxtaposition at a joint to define an article, the apparatus including a hollow chamber defined by walls and having an outlet allowing evacuation of fluid from the chamber; force transmitting means to force the juxtaportioned members together; an induction heating means including an induction heating coil adapted ta apply heat at the joint; and holding means to hold the article in alignment with the force transmitting means and within the induction heating means, the force transmitting means including a piston which is disposed within an opening in a wall of the chamber and movable in fluid sealing relationship with and recipn)- cally through the opening, one portion of the piston being exposed directly to the atmosphere and another portion of the piston being exposed directly to the chamber, the piston being free to operate through the opening as a direct function of atmospheric pressure operating on said one portion of the piston and as a direct function of vacuum within the chamber operating on said another portion of the piston.

2. The apparatus of claim 1, which includes a thermal insulating means for disposition between the force transmitting means and the article.

3. The apparatus of claim 1 or claim 2, in which the force transmitting means includes a substantially single-point type loading means to transmit force toward the article.

4. The apparatus of any of claims 1 to 3 in which the workpiece holding means includes a movable second wall portion at the base of the chamber in fluid sealing relationship with adjacent wall portions of the chamber.

5. Apparatus for vacuum induction bonding substantially as hereinbefore described with reference to and as illustrated in Figures 2 and 3 or Figures 4 or Figure 5 of the accompanying drawing.

6. A method of induction bonding wherein a plurality of members are held by holding means within an induction heating coil disposed within a hollow chamber, the members being in juxtaposition at a joint so as to de ffine an particle, fluid is evacuated from the chamber and force is applied to press the juxtaposed members together by means including a piston slidable within an opening in a wall of the chamber and having one portion exposed to atmosphere and another portion exposed directly to the interior of the chamber, so that the piston operates through the opening as a direct function of atmospheric pressure acting on said one portion of the piston and as a direct function of vacuum within the chamber acting on said other portion of the piston.

7. A method of induction bonding substantially as hereinbefore described with reference to the accompanying drawing.

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Claims

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avoiding any detrimental effect on other material of the article.

In connection with the application of a tip cap such as 14 to an airfoil body 12, it has been recognized that heating of the relatively smaller and thinner tip cap 14 can cause an excess temperature at the joint. Therefore, a preferred form of the method associated with the present invention in connection with the joining of members one of which is larger Or heavier than the other, is that the portion of the induction coil be located such that the heavier or larger member be heated first in order to avoid such an excess temperature condition.

The present invention has been described in connection with a single chamber apparatus and with a single mode of operation. However, it will be appreciated by those skilled in the art that a plurality of chambers can be operated with a single vacuum, system or a single induction heating power source, or both, in order to provide a still more efficient pro duction type arrangement. In addition, it will be recognized that tip caps of a material different from that of the airfoil body can be applied according to the present invention as new manufacture as well as replacement in repair WHAT WE CLAIM IS: 1. Apparatus for vacuum induction bonding of a plurality of members in juxtaposition at a joint to define an article, the apparatus including a hollow chamber defined by walls and having an outlet allowing evacuation of fluid from the chamber; force transmitting means to force the juxtaportioned members together; an induction heating means including an induction heating coil adapted ta apply heat at the joint; and holding means to hold the article in alignment with the force transmitting means and within the induction heating means, the force transmitting means including a piston which is disposed within an opening in a wall of the chamber and movable in fluid sealing relationship with and recipn)- cally through the opening, one portion of the piston being exposed directly to the atmosphere and another portion of the piston being exposed directly to the chamber, the piston being free to operate through the opening as a direct function of atmospheric pressure operating on said one portion of the piston and as a direct function of vacuum within the chamber operating on said another portion of the piston.
2. The apparatus of claim 1, which includes a thermal insulating means for disposition between the force transmitting means and the article.
3. The apparatus of claim 1 or claim 2, in which the force transmitting means includes a substantially single-point type loading means to transmit force toward the article.
4. The apparatus of any of claims 1 to 3 in which the workpiece holding means includes a movable second wall portion at the base of the chamber in fluid sealing relationship with adjacent wall portions of the chamber.
5. Apparatus for vacuum induction bonding substantially as hereinbefore described with reference to and as illustrated in Figures 2 and 3 or Figures 4 or Figure 5 of the accompanying drawing.
6. A method of induction bonding wherein a plurality of members are held by holding means within an induction heating coil disposed within a hollow chamber, the members being in juxtaposition at a joint so as to de ffine an particle, fluid is evacuated from the chamber and force is applied to press the juxtaposed members together by means including a piston slidable within an opening in a wall of the chamber and having one portion exposed to atmosphere and another portion exposed directly to the interior of the chamber, so that the piston operates through the opening as a direct function of atmospheric pressure acting on said one portion of the piston and as a direct function of vacuum within the chamber acting on said other portion of the piston.
7. A method of induction bonding substantially as hereinbefore described with reference to the accompanying drawing.