Method and apparatus for performing a magnetic pulse forming process
A magnetic pulse forming process is performed by an apparatus and a method that causes the plasticity of a workpiece to be preliminarily increased to facilitate deformation to the desired shape. Initially, a mandrel having a surface and an electrically conductive member are provided. The workpiece is oriented between the surface of the mandrel and the electrically conductive member, and a first electrical current is caused to flow through the workpiece and the electrically conductive member so as to increase the plasticity of the workpiece. Then, a second electrical current is caused to flow through the electrically conductive member and the workpiece so as to cause to cause the workpiece to be deformed into engagement with the surface of the mandrel.
This application claims the benefit of U.S. Provisional Application No. 60/639,247, filed Dec. 27, 2004, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTIONThis invention relates in general to magnetic pulse forming processes for deforming one or more metallic workpieces to a desired shape. In particular, this invention relates to an improved method and apparatus for performing such a magnetic pulse forming process wherein the plasticity of the workpiece to be deformed is preliminarily increased to facilitate deformation to the desired shape.
Magnetic pulse forming is a well known process that can be used to deform one or more metallic workpieces to a desired shape. Typically, a magnetic pulse forming process is performed by initially disposing a portion of a workpiece either about or within a mandrel having the desired shape. Then, an electromagnetic field is generated either within or about the workpiece. When this occurs, a large pressure is exerted on the workpiece, causing it to move toward the mandrel. If the electromagnetic field is generated about the exterior of the workpiece, then the workpiece is deformed inwardly into engagement with the mandrel. If, on the other hand, the electromagnetic field is generated within the interior of the workpiece, then the workpiece is deformed outwardly into engagement with the mandrel. Magnetic pulse forming can also be used to deform two metallic workpieces to a desired shape by initially disposing portions of first and second workpieces in an overlapping relationship and generating the electromagnetic field either within or about the overlapping portions of the first and second workpieces.
Magnetic pulse forming can be used, for example, to form male and female members of a typical sliding spline type of slip joint. Such male and female members typically have respective pluralities of splines formed thereon. The male member is generally cylindrical in shape and has a plurality of outwardly extending splines formed on the outer surface thereof. The male member may be formed integrally with or secured to an end of a conventional driveshaft assembly, for example. The female member, on the other hand, is generally hollow and cylindrical in shape and has a plurality of inwardly extending splines formed on the inner surface thereof. The female member may be formed integrally with or secured to a yoke that forms a portion of a conventional universal joint, for example. To assemble the slip joint, the male member is inserted within the female member such that the outwardly extending splines of the male member cooperate with the inwardly extending splines of the female member. As a result, the male and female members are connected together for concurrent rotational movement. However, the outwardly extending splines of the male member can slide axially relative to the inwardly extending splines of the female member to allow a limited amount of relative axial movement to occur therebetween.
The male and female members of such a sliding spline type of slip joint can be formed from hollow cylindrical workpieces that are deformed to have the male and females splines by means of magnetic pulse forming techniques. Typically, however, a relatively large amount of deformation is required in order to deform the workpieces to form such male and female splines. In this specific application, as well in a variety of other applications, such a relatively large amount of deformation can require a relatively large amount of energy to perform the magnetic pulse forming process. Additionally, such a relatively large amount of deformation may weaken or cause damage to the workpiece. Thus, it would be desirable to provide an improved method and apparatus for performing a magnetic pulse forming process wherein the plasticity of the workpiece to be deformed is preliminarily increased to facilitate deformation to the desired shape.
SUMMARY OF THE INVENTIONThis invention relates to an improved method and apparatus for performing a magnetic pulse forming process wherein the plasticity of the workpiece to be deformed is preliminarily increased to facilitate deformation to the desired shape. Initially, a mandrel having a surface and an electrically conductive member are provided. The workpiece is oriented between the surface of the mandrel and the electrically conductive member, and a first electrical current is caused to flow through the workpiece and the electrically conductive member so as to increase the plasticity of the workpiece. Then, a second electrical current is caused to flow through the electrically conductive member and the workpiece so as to cause to cause the workpiece to be deformed into engagement with the surface of the mandrel.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments, when read in light of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings, there is illustrated in
The first end 18 of the mandrel 16 is surrounded by the tubular workpiece 12 and is supported by a first electrically conductive insert 26 and an electrically conductive end member 28. The electrically conductive end member 28 is spaced from and electrically isolated from the outer member 14. The first insert 26 is preferably formed from a material that is a good electrical conductor, such as copper, for example. The second end 20 of the mandrel 16 is surrounded by a dielectric bushing 30. A bushing 32 surrounds the dielectric bushing 30 and abuts an inner wall of the tubular workpiece 12. The dielectric bushing 30 electrically insulates the bushing 32 from the mandrel 16 and prevents a short circuit from occurring with the tubular workpiece 12 during preheating, as will be explained in detail below. The dielectric bushing 32 also co-axially centers the mandrel 16 within the tubular workpiece 12. A second electrically conductive insert 34 is disposed between an outer wall of the tubular workpiece 12 and the outer electrically conductive member 14 to provide reliable and substantially uniform annular electrical contact between the outer electrically conductive member 14 and the tubular workpiece 12. The second insert 34 is also preferably formed from a material that is a good electrical conductor, such as copper, for example.
A preheating current source 36 is electrically connected to the outer electrically conductive member 14 and to the electrically conductive end member 28. A switch 38 is provided to selectively interrupt the flow of electrical current from the preheating current source 36 to the outer electrically conductive member 14 and to the electrically conductive end member 28. The amplitude of the preheating current generated by the preheating current source 36 can be set as desired, but is preferably less than one hundred kiloamps. A pulse forming current source 40 is also electrically connected to the outer electrically conductive member 14 and to the electrically conductive end member 28. The amplitude of the pulse forming current generated by the pulse forming current source 40 can be set as desired, but is preferably at least five hundred kiloamps. It should be understood that larger or smaller current amplitudes could be used without departing from the scope and spirit of the invention. A switch 42 is provided to selectively interrupt the flow of electrical current from the pulse forming current source 40 to the outer electrically conductive member 14 and to the electrically conductive end member 28. The energy needed for producing a pulse forming current in the pulse forming current source 40 can be stored in one or more energy storing devices or capacitors 44, which can be charged by a high-voltage charging supply (not shown). Other energy storing devices, such as a motor/generator set or some other suitable pulse source, for example, can be used without departing from the scope and spirit of the invention.
In operation, it is desirable to provide a circumferentially uniform distribution of the pulse forming current with the outer electrically conductive member 14 and the electrically conductive end member 28, especially surrounding the first insert 26 and the second insert 34. Before beginning the forming cycle, the tubular workpiece 12 has a shape and position shown by dashed lines and depicted as A in
After the tubular workpiece 12 has reached the desired plasticity, the switch 38 of the preheating current source 36 is moved to the open position, and the switch 42 of the pulse forming current source 36 is moved to the closed position. The capacitors 44 are thus caused to discharge the stored energy through the electrically conductive end member 28, the first insert 26, the preheated tubular workpiece 12, the second insert 34, and the outer electrically conductive member 14. The arrows in
The method as described in
To militate against a supported portion of the inner tubular member 52 adjacent the second end 66 of the inner electrically conductive member 60 from being radially deformed, a dielectric bushing 70 can be disposed adjacent the supported portion of the inner tubular member 52 and be embedded into the external mandrel 54. A supported portion of the inner tubular member 52 adjacent the first end 60 of the inner electrically conductive member 58 is seated on a second dielectric bushing 72. The supported portion of the inner tubular member 52 adjacent the first end 60 of the inner electrically conductive member 58 is supported by a second electrically conductive end member 74 and a third insert 76, which contacts the external mandrel 54. In this embodiment, the first electrically conductive end member 62, the second electrically conductive end member 74, the inner tubular member 52, and the external mandrel 54 are concentrically disposed about longitudinal axis L. The second dielectric bushing 72 militates against radial deformation of the supported portion of the inner tubular member 52 adjacent the first end 60 of the inner electrically conductive member 58. The remainder of the structure and the forming process is the same as described above for
In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.
Claims
1. A method of deforming a workpiece comprising the steps of:
- (a) providing a mandrel having a surface;
- (b) providing an electrically conductive member;
- (c) orienting a workpiece between the surface of the mandrel and the electrically conductive member;
- (d) causing a first electrical current to flow through the workpiece and the electrically conductive member so as to increase the plasticity of the workpiece; and
- (e) causing a second electrical current to flow through the electrically conductive member and the workpiece so as to cause to cause the workpiece to be deformed into engagement with the surface of the mandrel.
2. The method defined in claim 1 wherein said step (a) is performed by providing the mandrel having an outer surface, said step (b) is performed by providing the electrically conductive member having an inner surface, and said step (c) is performed by orienting the workpiece between the outer surface of the mandrel and the inner surface of the electrically conductive member.
3. The method defined in claim 1 wherein said step (a) is performed by providing the mandrel having an inner surface, said step (b) is performed by providing the electrically conductive member having an outer surface, and said step (c) is performed by orienting the workpiece between the inner surface of the mandrel and the outer surface of the electrically conductive member.
4. The method defined in claim 1 wherein said step (c) is performed by connecting a preheating current source so as to cause a first electrical current to flow through the workpiece and the electrically conductive member.
5. The method defined in claim 4 wherein said step (c) is performed by connecting the preheating current source through an electrically conductive end member and a first electrically conductive insert to a first portion of the workpiece and by connecting a second portion of the workpiece through a second electrically conductive insert to the preheating current source.
6. The method defined in claim 1 wherein said step (d) is performed by connecting a pulse current source so as to cause a first electrical current to flow through the workpiece and the electrically conductive member.
7. The method defined in claim 6 wherein said step (d) is performed by connecting the pulse current source through an electrically conductive end member and a first electrically conductive insert to a first portion of the workpiece and by connecting a second portion of the workpiece through a second electrically conductive insert to the pulse current source.
8. The method defined in claim 1 wherein said step (c) is performed by connecting a preheating current source so as to cause a first electrical current to flow through the workpiece and the electrically conductive member, and wherein said step (d) is performed by connecting a pulse current source so as to cause a first electrical current to flow through the workpiece and the electrically conductive member.
9. The method defined in claim 8 wherein said step (c) is performed by connecting the preheating current source through an electrically conductive end member and a first electrically conductive insert to a first portion of the workpiece and by connecting a second portion of the workpiece through a second electrically conductive insert to the preheating current source.
10. The method defined in claim 9 wherein said step (d) is performed by connecting the pulse current source through the electrically conductive end member and the first electrically conductive insert to the first portion of the workpiece and by connecting the second portion of the workpiece through the second electrically conductive insert to the pulse current source.
11. The method defined in claim 1 wherein said step (b) is performed by providing a magnetic field concentrator adjacent to the electrically conductive member, and wherein said step (c) is performed by orienting the workpiece between the surface of the mandrel and the magnetic field concentrator.
12. The method defined in claim 1 wherein said step (c) is performed by orienting first and second workpieces between the surface of the mandrel and the electrically conductive member, said step (d) is performed by causing a first electrical current to flow through the first and second workpieces and the electrically conductive member so as to increase the plasticity of the first and second workpieces, and said step (e) is performed by causing a second electrical current to flow through the electrically conductive member and the first and second workpieces so as to cause to cause the first and second workpieces to be deformed into engagement with the surface of the mandrel.
13. The method defined in claim 1 wherein said step (a) is performed by providing a mandrel having a surface and a recess, and wherein said step (e) is performed by causing the workpiece to be deformed into engagement with the surface and the recess of the mandrel.
14. An apparatus for deforming a workpiece comprising:
- a mandrel having a surface;
- an electrically conductive member positioned relative to said mandrel such that a workpiece can be oriented between said surface of said mandrel and said electrically conductive member;
- means for causing a first electrical current to flow through the workpiece and the electrically conductive member so as to increase the plasticity of the workpiece; and
- means for causing a second electrical current to flow through the electrically conductive member and the workpiece so as to cause to cause the workpiece to be deformed into engagement with the surface of the mandrel.
15. The apparatus defined in claim 14 wherein said means for causing a first electrical current to flow includes a preheating current source connected through an electrically conductive end member to a first electrically conductive insert that is adapted to engage the workpiece.
16. The apparatus defined in claim 14 wherein said means for causing a second electrical current to flow includes a pulse current source connected through an electrically conductive end member to a first electrically conductive insert that is adapted to engage the workpiece.
17. The apparatus defined in claim 14 wherein said means for causing a first electrical current to flow includes a preheating current source connected through an electrically conductive end member to a first electrically conductive insert that is adapted to engage the workpiece, and wherein said means for causing a second electrical current to flow includes a pulse current source connected through said electrically conductive end member to said first electrically conductive insert that is adapted to engage the workpiece.
Type: Application
Filed: Dec 19, 2005
Publication Date: Jul 20, 2006
Inventor: Boris Yablochnikov (Toledo, OH)
Application Number: 11/312,248
International Classification: B21J 5/04 (20060101);