Abstract:
A method of magnetically welding an end fitting to a metal tube includes assembling a driver ring over an end of the tube and inserting a length of the end fitting into a bore of the tube. An overlap region of the tube, the driver ring and the cylinder are encompassed by an inductor assembly of a magnetic pulse welding apparatus and the tube is welded to the end fitting using the magnetic welding apparatus.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to welding, and more particularly to magnetic pulse welding of steel components of a propeller shaft of a vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002]     Vehicular driveshafts including, but not limited to, propeller shafts, transfer drive torque from one drivetrain component to another. For example, a driveshaft is commonly used to transfer drive torque from the output shafts of a transfer case to the differentials in the axle assemblies for driving the wheels of the motor vehicle. Driveshafts typically include a tube having angularly articulable joints disposed at either end. Exemplary joints include, but are not limited to, a universal joint (UJ) and a constant velocity joint (CVJ). The angularly articulable joints enable the driveshaft to accommodate changing relative angles between the drivetrain components while transferring drive torque therebetween.  
         [0003]     Traditionally, joints have been attached to the tube using common welding techniques, which result in imbalance in the driveshaft. As a result of this imbalance, the driveshafts must be balanced in order to inhibit noise and vibration that would otherwise be generated by the spinning driveshaft. The requisite balancing process increases the manufacturing cost and weight of the driveshaft.  
         [0004]     Alternative welding techniques, such as magnetic pulse welding (MPW), have been implemented to improve driveshaft balance during manufacture, thereby reducing the need for post-manufacture balancing. An exemplary MPW method is disclosed in U.S. Pat. No. 5,981,921, issued on Nov. 9, 1999 and entitled Method of Magnetic Pulse Welding an End Fitting to a Driveshaft Tube of a Vehicular Driveshaft. Although the welding method disclosed in U.S. Pat. No. 5,981,921 is acceptable for welding an aluminum tube to a steel joint, this method is unable to provide acceptable welds when welding components fabricated from a broader range of material types.  
       SUMMARY OF THE INVENTION  
       [0005]     Accordingly, the present invention provides a method of magnetically welding an end fitting to a metal tube. The method includes assembling a driver ring over an end of the tube and inserting a length of the end fitting into a bore of the tube. An overlap region of the tube, the driver ring and the cylinder are encompassed by an inductor assembly of a magnetic pulse welding apparatus and the tube is welded to the end fitting using the magnetic welding apparatus.  
         [0006]     In one feature, the method further includes concentrically aligning the end fitting and the tube to maintain a tolerance between the end fitting and the tube within a desired range.  
         [0007]     In another feature, the driver ring is press-fit over the end of the tube.  
         [0008]     In still another feature, the method further includes venting gases generated during welding through an open end of the tube.  
         [0009]     In yet another feature, the driver ring has a higher electrical conductivity than the tube.  
         [0010]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]      FIG. 1  is an illustration of an exemplary propeller shaft;  
         [0013]      FIG. 2  is a cross-sectional view of an end of the propeller shaft of  FIG. 1  illustrating welded components of the propeller shaft;  
         [0014]      FIG. 3  illustrates a fitting cycle for press-fitting a driver ring to an end of a propeller shaft tube of the propeller shaft;  
         [0015]      FIG. 4  illustrates a welding cycle for welding a yoke to the propeller shaft tube using a centering device;  
         [0016]      FIG. 5  illustrates a partial cross-sectional view of an assembly step of the exemplary propeller shaft; and  
         [0017]      FIG. 6  illustrates a partial cross-sectional view of an assembly step of the exemplary propeller shaft. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0019]     Referring now to  FIG. 1 , an exemplary propeller shaft  10  is illustrated. The propeller shaft  10  is of a type that is used to transfer drive torque from a transmission to a differential in a vehicle drivetrain. The propeller shaft  10  includes a tube  12 , a slip joint assembly  14  and a flange or bolt joint assembly  16 . It is appreciated that the propeller shaft  10  can include two slip joint assemblies  14  positioned at either end or two flange joint assemblies  16  at either end. It should also be noted that although the joint assemblies  14 , 16  are illustrated as universal joints, they are merely exemplary in nature. It is anticipated that other joint types, such as a constant velocity joint (CVJ), can substitute.  
         [0020]     Referring now to  FIG. 2 , the tube  12  is welded to the joint assemblies  14 , 16  using the magnetic pulse welding process of the present invention. Each joint assembly  14 , 16  includes a weld yoke  18  having a cylindrical land  20  extending therefrom. A bore or vent passage  22  extends through the land  20  to enable gases to escape during the welding process, as described in further detail below. The magnetic pulse welding process of the present invention collapses a driver ring  24  and the tube  12  on to the land  20  of the joint assembly  14 , 16 . The tube  12  and the land  20  are pressed together under such significant pressure that they are bonded or welded together. Because the collapsing force is so great, the land wall  26  must have a sufficient thickness to inhibit it from collapsing. The thickness of the land wall  26  is determined empirically on a case by case basis based on material properties and dimensions.  
         [0021]     Referring now to  FIGS. 3 through 4 , the magnetic welding process of the present invention will be described in detail. In order to enable a sufficiently strong bond between the components (i.e., tube  16  and weld yoke  18 ) the tolerance between the inner diameter (ID) of the tube  16  and the outer diameter (OD) of the land  20  is maintained within a desired range. The tolerance range is based on the material properties of both the land  20  and the tube  12  and is further determined based on the particular dimensions of the components. More specifically, the tolerance range is empirically determined for each component set (i.e., tube and weld yoke). Table 1 below, provides exemplary dimensions and a corresponding tolerance range for an exemplary application.  
                           TABLE 1                                   Dimension   Value (in)                           Land OD   2.35           Tube ID   2.609/2.639           Tolerance Range   0.005/0.015                      
 
 During the magnetic welding process, the tube  12  and weld yoke  18  are concentrically aligned along a common axis. Alignment of the components is tightly maintained to ensure that the tolerance between the land OD and the tube ID is maintained within the tolerance range at every point about the external circumference of the land  20  and the internal circumference of the tube  12 . By maintaining the tolerance range, the tube  12  is inhibited from moving (e.g., bouncing) relative to the weld yoke  18  during the assembly process. 
 
         [0022]     The magnetic welding process of the present invention further implements the annular band or driver ring  24  that is disposed about the OD of the tube  12 . The driver ring  24  is made from a highly conductive material including, but not limited to, annealed copper (Cu), a Cu alloy, aluminum (Al), an Al alloy and silver (Ag). The driver ring  24  has a significantly higher conductivity than the tube  12 . For example, in the case of a Cu driver ring  24  and a steel tube  12 , the driver ring  24  includes an exemplary conductivity of 6.0×10 7  (Ω-m) −1  and the tube  12  includes an exemplary conductivity of 0.6×10 7  (Ω-m) −1 . In this case, the driver ring  24  is approximately 10 times more conductive than the tube  12 . The driver ring  24  is preferably press-fit over the tube OD prior to assembling the weld yoke  18  onto the tube  12 . It is further anticipated that the driver ring  24  can be assembled onto the tube OD in other manners known in the art including, but not limited to, welding.  
         [0023]     The tube  12  and weld yoke  18  are welded together using an inductor assembly  30 . The inductor assembly  30  includes a first insulator ring  32 , a shaper ring  34 , a second insulator ring  36  and an inductor coil  38 . The first and second insulator rings  32 , 36  are formed from a dielectric material (e.g., Teflon®) and respectively provide electrical insulation between the tube  12  and the shaper  34  and between the shaper  34  and the inductor coil  38 . The shaper  34  focuses the electromagnetic energy generated by the inductor coil  38  over the driver ring  24 . The shaper  34  is preferably formed of a metal material including, but not limited to, copper alloy and is geometrically constructed to focus the magnetic field generated by the inductor coil  38  over the driver ring  24 , as discussed in further detail below.  
         [0024]     Stored energy from an energy storage device (e.g., a capacitor bank) is dumped into the inductor coil  38 , which transforms the electrical energy into magnetic energy to generate a magnetic field. The magnetic field generates eddy currents through the components. Because the shaper  34  focuses the electromagnetic energy, the eddy currents are particularly generated in the driver ring  24 . The eddy currents oppose the magnetic field generated by the inductor coil  38 , which produces a repulsive force that induces the driver ring  24  to collapse over the tube  12  and the land  20 . The collapsing force is so great and the driver ring  24 , the tube  12  and the land  20  are driven together at such a high rate of speed that the components are welded together.  
         [0025]     It should further be noted that the external circumference of the land can be straight and not include any features formed therein. More specifically, traditional magnetic pulse welding methods require features such as recesses to be formed in the land to provide sufficient retention of the joint to the tube after the welding process. Forming such features increases the manufacturing cost and complexity of the joint. Although the method of the present invention relieves the need for such features to be formed in the land, it is anticipated that the present method can be implemented with lands that include such features.  
         [0026]     Referring now to  FIGS. 5 and 6 , the assembly process of the exemplary propeller shaft  10  will be described in detail. A first driver ring  24 A is assembled onto a first end of the tube  12  and a second driver ring  24 B is assembled onto a second end of the tube  12 . The first joint assembly  14 , 16  is mounted in a fixture  40  that locates the first joint assembly to align a center axis of the first joint assembly  14 , 16  on a central axis A. The fixture  40  can include locating features (not shown) including, but not limited to, recesses and/or tabs that mate with corresponding recesses and/or tabs of the first joint assembly  14 , 16 . The first joint assembly  14 , 16  includes the vent passage  22 , described in detail above. The tube  12  is concentrically located on the central axis A by a fixture  42  and is assembled onto the weld yoke  18  of the first joint assembly  14 , 16 . More specifically, the land  20  is received into the tube  12 . The inductor assembly  30  encompasses the first joint assembly  14 , 16 , the driver ring  24  and the tube  12  and is energized to induce welding of the tube  12  and the first joint assembly  14 , 16  as described in detail above. Gases generated by the magnetic pulse welding process escape through the open second end of the tube  12 .  
         [0027]     The second joint assembly  14 , 16  is mounted in a fixture  42  that locates the second joint assembly  14 , 16  to align a center axis of the second joint assembly  14 , 16  on the central axis A. The fixture  42  can include locating features including, but not limited to, recesses and/or tabs that mate with corresponding recesses and/or tabs of the second joint assembly  14 , 16 . The partially assembled propeller shaft  10  (i.e., tube  12  and first joint assembly  14 , 16 ) is concentrically located on the central axis A by the fixture  42  and is assembled onto the weld yoke  18  of the second joint assembly  14 , 16 . More specifically, the land  20  is received into the tube  12 . The inductor assembly  30  encompasses the second joint assembly  14 , 16 , the driver ring  24 B and the tube  12  and is energized to induce welding of the tube  12  and the second joint assembly  14 , 16 , as described in detail above. Gases generated by the magnetic pulse welding process escape through the vent passage  22  of the first joint assembly  14 , 16 .  
         [0028]     The method of the present invention provides an improved weld for welding two components such as a tube to an end fitting (e.g., a joint). A significant improvement is achieved when welding a steel tube to a steel end fitting using the method of the present invention over traditional magnetic pulse welding methods. Further, the method of the present invention enables the end fitting to have a more simple design and to be less expensive by reducing the need for features to be formed in the external circumference of the land.  
         [0029]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.