Stud joining method

Abstract

A welding apparatus for joining a weldable fastening element onto a workpiece by a welding process, wherein the welding apparatus comprises: an electric welding power source; a fastening element holding device for holding the fastening element during welding; a first drive device for moving the fastening element holding device along a first axis; a cleaning electrode holding device for holding a cleaning electrode along a second axis; and wherein the cleaning electrode is connectable to the electric welding power source. The fastening element holding device and the cleaning electrode holding device are mounted on a common tool carrier and the tool carrier is movable on a joining head by a tool carrier drive from a joining position to a cleaning position, and in the joining position the first axis defines a joining axis, and in the cleaning position the second axis is aligned with the joining axis.

What is claimed is: 
     
         1 . A method for joining a fastening element to a joining surface of a workpiece along a joining axis, the method for joining comprising the steps of:
 providing a joining apparatus comprising:
 a joining head; 
 a rotary drive; 
 a tool carrier mounted on the joining head and movable with the rotary drive from a cleaning position (R) to a joining position (S); 
 a fastening element holding device for holding the fastening element, the fastening element holding device mounted on the tool carrier at a first location and displaceable along a first axis by an axial drive device; 
 a cleaning electrode holding device holding a cleaning electrode, the cleaning electrode holding device mounted on the tool carrier at a second location and aligned along a second axis, and the cleaning electrode held by the cleaning electrode holding device is connectable to an electric power source; 
   cleaning the joining surface of the workpiece by the sub-steps of: moving the tool carrier with the rotary drive into the cleaning position (R) in which the second axis is aligned with the joining axis; locating the cleaning electrode above the joining surface of the workpiece; and then generating a cleaning arc between the cleaning electrode and the joining surface; and then   moving the tool carrier with the rotary drive into the joining position (S) in which the first axis is aligned with the joining axis;   bringing the fastening element and the workpiece together; and   joining the fastening element to the workpiece.   
     
     
         2 . A method for joining according to  claim 1 , wherein the cleaning arc is generated by the steps of:
 placing the cleaning electrode onto the workpiece;   supplying an electric cleaning current to the cleaning electrode; and   lifting the cleaning electrode off the workpiece.   
     
     
         3 . A method for joining according to  claim 1 , and further comprising the step of purging the cleaning electrode after the cleaning step. 
     
     
         4 . A method for joining according to  claim 1 , and further comprising the step of exchanging the cleaning electrode for a new cleaning electrode after the cleaning step. 
     
     
         5 . A method for joining according to  claim 1 , wherein the joining step includes drawing a welding arc having a first polarity, and the step of generating a cleaning arc is performed with a second polarity; and the first polarity is different from the second polarity. 
     
     
         6 . A method for joining according to  claim 1 , wherein the cleaning electrode is a weldable stud. 
     
     
         7 . A method for welding a stud to a joining surface of a workpiece along a joining axis, the method comprising the steps of:
 providing a welding apparatus comprising:
 an electric welding power source; 
 a fastening element holding device operable for holding the fastening element during the welding process; 
 a first drive device operable for moving the fastening element holding device along a first axis; 
 a cleaning electrode holding device for holding a cleaning electrode along a second axis different from the first axis; 
 wherein the fastening element holding device and the cleaning electrode holding device are mounted on a common tool carrier; 
 wherein the tool carrier and a tool carrier drive motor are mounted on a joining head, and the tool carrier drive motor is operable to move the tool carrier on and relative to the joining head from a joining position to a cleaning position, and in the joining position the first axis is aligned with the welding axis, and in the cleaning position the second axis is aligned with the welding axis; and 
 wherein the cleaning electrode held by the cleaning electrode holding device is connectable to the electric welding power source; and 
   placing the cleaning electrode above the joining surface of the workpiece;   generating a cleaning arc between the cleaning electrode and the joining surface of the workpiece;   cleaning the joining surface of the workpiece with the cleaning arc;   placing the welding stud above the joining surface of the workpiece;   generating a welding arc between the welding stud and the joining surface of the workpiece; and   bringing the stud and the workpiece together so that the stud is welded onto the workpiece.   
     
     
         8 . A method of welding according to  claim 7 , wherein the step of generating a cleaning arc includes the steps of:
 placing the cleaning electrode onto the workpiece;   switching on an electric cleaning current switched; and   lifting the cleaning electrode off the workpiece.   
     
     
         9 . A method of welding according to  claim 7 , and which after the cleaning step further comprises a step of purging the cleaning electrode. 
     
     
         10 . A method of welding according to  claim 7 , and which after the cleaning step further comprises a step of replacing the cleaning electrode. 
     
     
         11 . A method of welding according to  claim 7 , wherein the step of generating the cleaning arc is performed with a first polarity, and the step of generating the welding arc is performed with a second polarity, and the first polarity is different from the second polarity.