System and method of friction welding a workpiece

1. A method of friction welding a workpiece comprising:

positioning a curl forming die proximate first and second parts that are disposed along an axis, the curl forming die including a first die portion and a second die portion that is disposed opposite the first die portion, wherein the first die portion has a first opening that receives the first part, the second die portion has a second opening that receives the second part, and the first and second die portions cooperate to define a cavity; and

friction welding the first part to the second part such that a first curl is generated proximate the first part and a second curl is generated proximate the second part, wherein the first curl and the second curl are formed by the curl forming die during friction welding, the cavity receives the first part, the second part, the first curl, and the second curl, and the cavity is disposed further from the axis than the first opening and the second opening.

2. The method of claim 1 wherein the curl forming die extends continuously around the first part, the second part, the first curl, and the second curl.

3. The method of claim 1 wherein the first part is friction welded to the second part by rotating at least one of the first part and the second part about the axis.

4. The method of claim 3 wherein positioning the curl forming die includes moving the curl forming die from an initial position to a forming position in which the curl forming die extends around the first part and the second part before friction welding the first part to the second part.

5. The method of claim 4 further comprising moving the curl forming die from the forming position to the initial position after friction welding the first part to the second part.

6. The method of claim 3 wherein the curl forming die forms the first curl and the second curl into a plurality of splines that extend substantially parallel to the axis.

7. A method of friction welding a workpiece comprising:

positioning a curl forming die proximate a first part and a second part; and

friction welding the first part to the second part such that a first curl is generated proximate the first part and a second curl is generated proximate the second part, wherein the first curl and the second curl are formed by the curl forming die during friction welding into a thread that extends around the workpiece and the curl forming die is rotated about an axis to unthread the curl forming die from the thread after friction welding the first part to the second part.

8. The method of claim 1 wherein the curl forming die forms the first curl and the second curl into a thread that extends around the workpiece.

9. The method of claim 1 wherein the first die portion is spaced apart from the first part and the second part before the first curl and the second curl are generated.

10. The method of claim 1 wherein the second die portion is spaced apart from the first part and the second part before the first curl and the second curl are generated.

11. A method of friction welding a workpiece comprising:

providing a first part that has a first hole and a second part;

positioning a first curl forming die proximate the first part and the second part;

positioning a second curl forming die inside at least one of the first part and the second part; and

friction welding the first part to the second part such that a first external curl and a first internal curl are generated from the first part and a second external curl is generated from the second part, wherein the first external curl and the second external curl are formed by the first curl forming die and the first internal curl is formed by the second curl forming die.

12. The method of claim 11 wherein the second curl forming die is inserted into the first hole and is disposed proximate an end surface of the second part that is disposed adjacent to the first part before the first part is friction welded to the second part.

13. The method of claim 12 wherein the second curl forming die is a rod that is spaced apart from the first part before friction welding the first part to the second part.

14. The method of claim 11 wherein the second part defines a second hole, wherein the second curl forming die is inserted into the first hole and the second hole before friction welding the first part to the second part.

15. The method of claim 14 wherein a second internal curl is generated from the second part when the first part is friction welded to the second part, wherein the first internal curl and the second internal curl are formed by the second curl forming die.

16. The method of claim 15 wherein the second curl forming die is spaced apart from the first part and the second part before the first part is friction welded to the second part.

17. The method of claim 1 further comprising a second curl forming die that is disposed inside the first part and that forces an internal curl from the first part against the first part.

18. The method of claim 17 wherein the second curl forming die is disposed inside the second part and forces an internal curl from the second part against the second part.