Abstract:
A method and apparatus for drawn arc welding includes the step of applying a magnetic field transversely to the arc to impel the arc along the welding gap. The invention permits tubular components to be welded using drawn arc welding, but is useful in welding nuts and other components having a continuous outer surface. The field may be varied to impel the arc between the inner and outer diameters of a tubular member being welded.

Description:
TECHNICAL FIELD 
     This invention relates to a method and apparatus for joining components by drawn arc welding. 
     BACKGROUND OF THE INVENTION 
     Drawn arc welding is widely used to join components in many industries, including the manufacture of automotive vehicles, components of automotive vehicles, and appliances, and is also used in the construction of ships. In drawn arc welding, the components to be welded are brought into contact with one another and each component is connected to the welding voltage supply so that a current is drawn through the components. One of the components is lifted away from the other component to define a gap (the size of the gap is typically of the order of millimeters or a fraction of a millimeter) while maintaining the current through the components. Accordingly, an arc is drawn through the gap and extends between the components, melting or softening a portion of them. The current is then turned off, and the components are allowed to move back into contact, where they are welded together by the molten metal. The parts may be pressed together to improve weld quality. Drawn arc welding requires relatively simple or “lean” equipment as compared to other welding processes. 
     However, drawn arc welding has heretofore been limited to welding relative small studs (typically 0.25 in. or less in diameter) and similar sized brackets. The welding of tubular brackets and large studs has not been possible, because it was not possible using prior art drawn arc welding techniques to assure a consistent weld around tubular members and large studs. In many applications, a consistent weld is critical, because welds that have voids or gaps are not sufficiently strong. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a magnetic field is generated by energizing electromagnetic coils to generate a magnetic field acting through said gap transversely with respect to the arc. Accordingly a resultant force is generated (as determined by the three finger rule well known to those skilled in the art) which impels the magnetic force along the gap. In the case of tubular brackets, the arc is impelled circumferentially around the bracket, so a consistent weld may be obtained around the circumference of the bracket. The field may be varied by known techniques, such as using additional coils placed appropriately or by physically moving the coils, to drive the arc between the inner and outer diameters of the component. Because of the impelled arc, brackets and nuts may be welded using the drawn arc welding technique that are significantly larger than is possible using prior art techniques, and tubular brackets may be welded using drawn arc techniques than could not be welded by drawn arc welding techniques known in the prior art. 
     It is important that the magnetic field be generated substantially transverse to the arc. It has already been proposed, for example, in U.S. Pat. No. 4,531,042, to generate a magnetic field acting parallel to the arc. However, this field will only contain the arc, and will not impel the arc relative to the components being welded. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view, partly in section, illustrating the manner in which electromagnetic coils are placed around the components to be welded; 
     FIG. 2 is a schematic illustration of the welding equipment used to effect welding and to provide electrical energy to the coils used when components are welded according to the present invention: 
     FIG. 3 is a view similar to FIG. 1, but illustrating an alternate embodiment of the present invention; 
     FIG. 4 is a top plan view of FIG.  3 : 
     FIGS. 5 and 6 are views similar to FIGS. 3 and 4 respectively, but illustrating still another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2 of the drawings, a tubular component or bracket generally indicated by the numeral  10  includes an outer circumferential surface  12 , an inner circumferential surface  14 , and a transversely extending end face  16  which connects the surfaces  12 , 14 . The end face  16  of the bracket  10  is to be welded to a component  18 , which in the case of FIG. 1 is a circular plate. According to the invention, an electromagnetic coil  20  is placed over the bracket  10  and a second electromagnetic coil  22  is placed around the component  18 . Electrical current is supplied to the coils by a coil power supply  24 . The contiguous ends of the coils  18 ,  20  are separated by a gap  26 . The coils are connected in series, such that the direction of current flow in one of the coils  20  or  22  is opposite to that in the other coil. Accordingly, the coils  20 ,  22  generate fields of opposite polarity, so that the resultant magnetic field acts radially with respect to the tubular component  10 . 
     Welding is effected by connecting welding electrodes  28 ,  30  of a conventional welding power supply  32  to the components  10  and  18  respectively. The welding electrodes  28 ,  30  are of opposite polarity, so that when the electrodes are energized, an electrical current will flow through the components  10  and  18  between the electrodes  28 ,  30 . However, prior to energization of the electrodes, the component  10  is installed in a stepper or linear motor  34  which is adapted to move the component  10  a small distance along its axis to establish a welding gap G between the components  10  and  18 . Instead of a stepper or linear motor, a solenoid and spring, and other similar devices may be used to move the component  10 . The gap G may be very small, and normally will not be more than a few millimeters or even a fraction of a millimeter. The stepper motor  34  is also controlled by the welding power supply  32 , which is set by the operator to establish a desired gap between the components and current level through the components according to procedures well known to those skilled in the art. If necessary, an inert shielding gas may be provided from mixer  33  in a manner well known to those skilled in the art. 
     When welding is to be effected, the component  10  is installed in the stepper motor  34  and the welding electrodes  28 ,  30  are fastened to the components  10  and  18 . The components  10  and  18  are then brought into contact with one another and the electrodes are energized to draw an electrical current through the components  10  and  18 . The stepper motor is then operated to withdraw the component  10  from the component  18  to establish the gap G and the coils  20 ,  22  are energized. Accordingly, an arc is drawn across the gap G. Coils  20 , 22  are then energized so that the resultant electromagnetic field impels the arc around the face  16 . The arc is maintained for a predetermined time and is then extinguished by turning off the current from the power supply. The stepper motor  34  is then operated to allow the component  10  to move into contact with the component  18 . Because of the impelling of the arc around the face  16 , a substantially uniform weld is achieved around the component  10 . Although the invention has been particularly described with respect to a tubular component, other components, such as nuts, may also be welded using the invention. It is necessary only that the component to be welded have a continuous surface to maintain continuity of the arc as it is being impelled. Additional coils may be provided which are offset radially from the gap G to vary the electromagnetic field so that the arc may be moved radially as well as circumferentially. 
     Referring now to the embodiment of FIGS. 3 and 4, elements the same as those in the embodiment of FIGS. 1 and 2 retain the same reference numeral. In FIGS. 3 and 4, the bracket  10  is welded to a component  36  which is a flat plate. Coils  38 ,  40  are offset radially from the tubular component  10  and circumscribe at least a portion of the component  10  and the edge surface  42  of the component  36 , and also circumscribes a sector of the gap G. The axes of the coils  38 ,  40  extend substantially parallel to the lower face  16  of the component  10 , and the coils are connected in series. Upon energization of the coils, a resultant magnetic field is generated which acts radially with respect to the component  10  and parallel to the gap G, thereby impelling the arc circumferentially about the gap G during welding of the components. Although two coils  38 ,  40  are disclosed, three or more coils may be used and would produce a more uniform field. Welding is effected in substantially the same way as disclosed above with respect to FIGS. 1 and 2. The placement of the coils in the embodiment of FIGS. 3 and 4 permits welding to larger plates such as the plate  36  than is possible using the coil placement illustrated in FIGS. 1 and 2. 
     Referring now to the embodiment of FIGS. 5-6, elements the same as those in the embodiments of FIGS. 1-4 retain the same reference numeral. FIGS. 5 and 6 are similar to FIGS. 3 and 4, except that the coils  38 , 40  are mounted on actuators  44 , 46  which oscillate the actuators between the dotted line positions in FIG.  6 . This movement of the coils  38 ,  40  varies the magnetic fields generated by the coils to impel the arc radially along the end face  16  between the outer surface  12  and the inner surface  14  as the arc is impelled circumferentially around the end face  16 .