WO1995032833A1

WO1995032833A1 - Method for friction welding a shaft to a disk and assembly formed thereby

Info

Publication number: WO1995032833A1
Application number: PCT/US1995/006638
Authority: WO
Inventors: Herman Arthur Nied; Marshall Gordon Jones; Mark Gilbert Benz
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1994-05-31
Filing date: 1995-05-25
Publication date: 1995-12-07
Anticipated expiration: 1996-11-30
Also published as: DE19580739T1

Abstract

A rotation frictional welding method joins a tapered wedge (30) at one end (33) of a shaft (26) within a tapered aperture (32) in the plane of a disk (28). This method produces an overhung disk shaft assembly (24) with a shaft (26) having a tapered wedge (30) at one end (33) which is positioned in an welded within a tapered aperture (32) in a disk (28).

Description

METHOD FOR FRICTION WELDING A

SHAFT TO A DISK AND ASSEMB Y

FORMED THEREBY

Technical Field

The present invention relates to rotational friction welding joining of a shaft to a disk and, more particularly, to such a joining method and an overhung disk shaft assembly having particular application to x-ray tube anode manufacturing.

Rarkσround Art.

Currently, several joining methods exist for attaching either a solid or hollow shaft to a disk. These methods include mechanical attachment, fusion welding, brazing, diffusion bonding, and friction welding, all of which are well known in the industry. Unfortunately, these existing methods have various drawbacks. For example, mechanical attachment by screw threads and nuts is difficult, costly, and prone to the loosening of the fasteners during application, especially for high temperature applications. Fusion welding, although an inexpensive and high production approach for attaching a shaft to a disk produces residual stresses and a heat affect zone that can generate regions of failure during application. Furthermore, it is difficult to control the penetration of the fusion zone.

One method for avoiding the inherent problems associated with mechanical, fusion, brazing, or diffusion processes is a joining method such as rotational friction welding. Inertia friction weld joining is particularly appealing for axisymmetric components and will generate a highly localized joint without melting at the weld interface.

Rotational friction welding using either inertia or continuous direct drive friction welding produces a narrow heat affected zone due to the nature of friction welding. This region usually requires heat treatment in order that the weld joint have bulk metal mechanical properties. Inertia friction butt welds produced by directly welding a thick hollow or solid shaft to a disk are commonly used in fabrication. However, the welding of a solid shaft has inherent problems and is not recommended as a practice for load carrying disk-rotor assemblies at elevated temperature.

Rotor assemblies having a disk and shaft can be fabricated using friction welding with different pre-weld joint designs. A common method for joining a shaft directly to a disk is by friction welding, such as a direct butt weld. The problem with this type of weld is that most of the deformation occurs only at the end of the shaft with little metal displacement locally on the disk face. Good welds are difficult to produce due to the lack of material displacement and poor temperature distribution since the disk acts as a heat sink.

One known method for improving friction welding process is to directly butt weld the shaft to a boss on the disk. Unfortunately, such friction welds have the inherent problem that material close to the center line generates weld defects at the joint interface due to lack of heat generated and material displacement. The center of the shaft is essentially a stagnation point due to zero angular velocity at that location and does not produce substantial metal flow locally even though there is a high contact stress at that location. For solid butt welds, the material flow for such a weld is radially outward, thereby producing a flash on the exterior.

A further improved butt weld eliminating center line defects is produced by using a thick walled tube joint design. For example, the disk can have a hole through the boss and a thick hollow tube can be friction welded at some axial location. Even though this offers an improvement over the solid butt- welds described above, the weld produced is still susceptible to fatigue failure due to cyclic bending stresses generated in the shaft by rotational loads such as unbalance.

It would be desirable then to have a friction welding method to directly attach either a solid or a hollow shaft within the plane of a disk to produce an overhung disk shaft assembly which is suitable for high temperature applications.

Summary of the Invention

The present invention is a method for placing the weld joint within the plane of the disk to produce an integral overhung disk shaft assembly having greater structural integrity at elevated temperatures. The joining method of the present invention reduces the probability of generating weldline defects and, thereby, increases fatigue life and reliability. In accordance with one aspect of the present invention, a rotational friction weld method joins either a solid or a hollow shaft to a disk using a tapered wedge joint which will produce an angular weld directly within the plane of the disk at a location that would not be subjected to high stress fields.

In a preferred embodiment of the present invention, the rotational friction weld method securely attaches either solid or hollow shafts to a target disk for manufacturing overhung disk shaft assemblies useful in x-ray tube anodes . This provides a joining method that increases the strength and stability of the rotor or overhung assembly when subjected to elevated temperatures in x-ray tubes.

Accordingly, it is an object of the present invention to provide a rotational friction welding method of forming a shaft to a disk with application to x-ray tube anode assembly manufacturing. Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

Brief Description of the Drawings

Figs. 1 and 2 illustrate prior art arrangements of a welded shaft and disk;

Fig. 3 illustrates rotor components for welding a shaft to a disk in accordance with the present invention;

Fig. 4 illustrates an overhung disk shaft assembly having a solid shaft and a disk, in accordance with one embodiment of the present invention; and

Fig. 5 illustrates a finished machined friction welded overhung disk shaft assembly having a hollow shaft and a disk, in accordance with another embodiment of the present invention.

ngfailed Description of tιht»

Preferred Embodiments

The present invention relates to a friction welding method for providing a friction weld joint which directly attaches a shaft within the plane of a disk, suitable for high temperature applications. The welding process according to the present invention produces a weld that greatly reduces the susceptibility of welded components to defect generation. Since this weld also provides the strength and stability necessary for high speed rotor applications at elevated temperature to resist creep and fatigue failure, the weld procedure of the present invention is particularly suitable for application to x-ray tube anode assembly manufacturing. The friction weld joint is removed from areas susceptible to fatigue and placed into the plane of the disk.

Referring now to the drawings. Figs. 1 and 2 illustrate two prior art embodiments showing a shaft welded to a disk. The final machined component in each figure is indicated by dotted lines. Rotor assemblies having a disk and a shaft can be fabricated using friction welding with different pre-weld joint designs. For example. Fig. 1 shows one type of design for friction welding a solid shaft 10 directly to a disk 12. A weld interface 14 is shown in Fig. 1 as occurring at the intersection of the shaft and the disk, perpendicular to the shaft 10.

The problem with the type of weld illustrated in Fig. 1 is that most of the deformation occurs at the end 16 of the shaft in contact with the disk, with little metal displacement locally on the disk. Good welds are difficult to produce due to the lack of material displacement and poor temperature distribution since the disk 12 acts as a heat sink. A flash often forms at the end of the shaft 10 since most of the temperature rise occurs at end 16. The dead center intersection between the disk and the bar is a stagnation point since the relative angular velocity there is zero. Since the weld interface is perpendicular to the shaft, it is often subjected to high bending stresses.

Fig. 2 shows a prior art improvement over the weld of Fig. 1. Fig. 2 illustrates a prior art friction welding of a solid shaft 18 to a disk 20 using a butt weld. The local metal displacement for this type of weld is symmetric about weld interface 22. The weld interface 22 is perpendicular to the axis of rotation. For the type of weld illustrated in Fig. 2, at the dead center of rotation there is no radial displacement outward to form the flash similar to that which occurs with the weld of Fig. 1.

Referring now to Fig. 3, and in accordance with a preferred embodiment of the invention, there is illustrated rotor components for an overhung disk shaft assembly. The components, generally designated 24, include a shaft 26 and a disk 28. The shaft 26 may be any type of solid or hollow shaft. In accordance with this embodiment of the present invention, shaft 26 has a tapered wedge 30 at one end thereof. The disk 28 also has a tapered aperture 32. The tapered aperture is fabricated by conventional means, such as, boring within the plane of the disk and the tapered wedge is fabricated at end 33 of the shaft by conventional means, such as, turning on a lathe. The tapered aperture 32 mates with the wedge 30 of the shaft 26. As will be obvious to those skilled in the art, since Fig. 3 illustrates pre-weld components, there is adequate excess material that can be machined off during final machining of assembly 24 as illustrated in Fig. 4. The angle of the wedge 30 is equal to the angle of the aperture 32 machined in the disk 28, with respect to the center of rotation. Although the wedge of the shaft mates with the aperture of the disk to form a joint interface location, the wedge is not necessarily flush with the sides of the aperture in the disk.

The components of Fig. 3 are friction welded, which friction welding is preferably rotational inertia friction welding using an angle weld. As will be understood in the art, the welding process is accomplished by a welding machine suitable as necessary to provide mechanical energy input for the friction welding, which weld machine is well known in the art. In the rotational welding process, a large rotating inertia wheel attached to one component to be welded is brought into contact with the mating component while subjected to an axial load. The mechanical energy of rotation is dissipated at the interface of the contacting surfaces in the form of heat due to friction. The angular rotation decreases due to the resistive torque and comes to rest to terminate the process. The temperature generated at the weld interface is held below the melting point of the metal by proper selection of process parameters. The axial load forges the two components together.

In accordance with this embodiment of the present invention, shaft 26 has a pre-weld tapered wedge 30 at a first end. The disk 28 also has a pre- weld tapered aperture 32. The tapered aperture is fabricated within the plane of the disk and the tapered wedge is fabricated at end 33 of the shaft. The tapered aperture 32 mates with the tapered wedge 30 of the shaft 26. In order to practice the friction welding method of the present invention, both the wedge 30 and aperture 32 must be tapered. The tapered wedge is inserted into the tapered aperture of the disk to create a joint interface therebetween in the plane of the disk. The shaft is then friction welded to the disk to create a weld interface in an area of low fatigue in the plane of the disk. In a preferred embodiment of the method, we employ the step of rotational friction welding. The preferred rotational friction welding step is inertia welding.

It is known to those skilled in the art that it is not feasible to weld a straight shaft in a straight aperture in a disk.

However, in the method of our present invention, we produce an overhung disk shaft assembly which has a tapered wedge at one end of a shaft positioned in a tapered aperture of the disk thereby forming a joint interface therebetween. The shaft is welded to the disk at the joint interface in the plane of the disk. - ra ¬ in a preferred embodiment, the angle of the wedge 30 is equal to the angle of the aperture 32 machined in the disk 28, with respect to the center of rotation. Although the wedge of the shaft mates with the aperture of the disk to form a joint interface location, the wedge is not necessarily flush with the sides of the aperture in the disk.

Fig. 4 shows the components after welding in the form of an overhung disk shaft assembly, when the aperture 32 mates with the wedge 30, a weld interface 34 is created during the joining of the wedge 30 and the aperture 32. The weld interface is located along the initial taper of aperture 32 and has a larger weld surface area than that obtained in Figs. 1 and 2. This creates a rotor assembly 24 having greater structural integrity at elevated temperatures.

As can be seen in Fig. 4, the weld interface 34 is located in the plane of the disk 28, and is at a location which is not subjected to high stress fields. Consequently, the weld interface 34, in accordance with the present invention, is in an area of lower stress as compared to the weld interface in the butt welding of Fig. 1. There is relative material shear in the disk 28 and along the interface 34 angle during the welding process, flushing out surface oxides and contaminates into the flash. With the assembly of the present invention, any stagnation point where the material velocity is zero is eliminated. It is an advantage of the present invention that the weld interface is not perpendicular to bending moments applied to the assembly. A flash 36 is generated on both faces of the disk 28, which is removed during final machining. In Fig. 4, the axial force produced by the welding machine for providing the friction welding exerts a large contact stress normal to the weld interface, due to the wedging mechanism 30. Although the axial upset will make the shaft protrude the aperture 32 in the disk 28, by proper allowance for material in the joint the finished machined rotor assembly will be as illustrated by the dotted lines in Fig. 4.

Fig. 5 illustrates a final machined embodiment according to the invention, wherein an assembly 38 is comprised of a hollow shaft 40 welded to a disk 42. It should be noted that the present invention includes either a hollow shaft 40 or a solid shaft 26. That is, a wedge is fabricated at the end of the shaft 40 or 26 and a tapered aperture is fabricated in the disk 42 or 28, before the two components are friction welded together. Of course, as known in the art, the rate of energy dissipation for creating the weld will vary if the shaft is hollow as opposed to solid.

The material displacement along the taper of the weld interface will not provide any stagnation point or dead zone and will eliminate the source of defects associated with existing butt friction welding processes. In addition, the larger area of the weld provides greater strength.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that modifications and variations can be effected within the spirit and scope of the invention.

Claims

We claim :

1. A friction welding method for joining a shaft to a disk having a plane, the method comprising the steps of:

providing a disk with a tapered aperture in its plane;

providing a shaft with a tapered wedge at a first end; and

inserting the tapered wedge of the shaft into the tapered aperture of the disk during the friction welding to create a joint interface therebetween in the plane of the disk thereby welding the shaft to the disk at the joint interface to create a weld interface in an area of low fatigue in the plane of the disk.

2. A friction welding method as claimed in claim 1 wherein the step of welding further comprises the step of rotational friction welding.

3. A friction welding method as claimed in claim 2 wherein the step of welding further comprises the step of rotational inertia friction welding.

4. A friction welding method as claimed in claim 2 wherein the step of welding further comprises the step of continuous direct drive friction welding.

5. A friction welding method for joining a shaft to a disk having a plane, the method comprising the steps of: fabricating a tapered aperture in the plane of the disk;

fabricating a tapered wedge at a first end of a shaft; and

inserting the tapered wedge of the shaft into the tapered aperture of the disk during the friction welding to create a joint interface therebetween in the plane of the disk; thereby welding the shaft to the disk at the joint interface to create a weld interface in an area of low fatigue in the plane of the disk.

6. A friction welding method as claimed in claim 5 wherein the step of welding further comprises the step of rotational friction welding

7. A friction welding method as claimed in claim 6 wherein the step of welding further comprises the step of rotational inertia friction welding.

8. A friction welding method as claimed in claim 6 wherein the step of welding further comprises the step of continuous direct drive welding.

9. An overhung disk shaft assembly comprising:

a disk with a tapered aperture in its plane;

a shaft with a tapered wedge at a first end;

the tapered wedge of the shaft positioned in the tapered aperture of the disk thereby forming a joint interface therebetween and said shaft welded to said disk at the joint interface in the plane of the disk.

10. An overhung disk shaft assembly comprising:

a disk with a tapered aperture in its plane;

a shaft with a tapered wedge at a first end positioned in the tapered aperture of the disk thereby forming a joint interface therebetween; and

a high strength welded joint at the interface in the plane of the disk.