Master of Engineering (Hons.)
Department of Mechanical Engineering
Howes, Stephen William, Process monitoring and control during spot welding of metallic coated steels, Master of Engineering (Hons.) thesis, Department of Mechanical Engineering, University of Wollongong, 1994. http://ro.uow.edu.au/theses/2524
Metallic coated steel sheet can be very aggressive towards copper alloy, resistance spot welding electrodes. These steels accelerate the electrode degradation process far in excess of that experienced when spot welding uncoated steels through an accumulation of the coating around the electrode tips, changing the geometry of the electrode and through an erosion process on the tip face in contact with the workpiece. The rate of electrode degradation is closely linked to the chemistry of the metallic coating and can be very severe, particularly when welding steels with coatings high in aluminium or when inappropriate welding conditions are used.
High volume welding industries employing these steels are n o w faced with the need to more frequently monitor weld quality and electrode condition in order to sustain structural integrity of their product. Being very time consuming, the traditional shop floor, destructive techniques for assessing weld quality, are no longer considered appropriate. This has provided the impetus for researchers to develop new, non-destructive techniques which are easily implemented and which remove operator judgement as to the condition of electrodes.
This work examines the feasibility of such a technique. The Adept (Advanced Grey Scale) Vision System has been assessed as to its ability to view and accurately measure the impression left by spot welding electrodes on the surface of a zinc-iron rich metallic coated steel during a simulated production run and to equate these measurements to weld nugget size and tensile shear strength.
The results of this work appear promising in that the vision system has identified electrode wear patterns and has successfully related these to both nugget size and tensile shear strength, these being paramount to engineers charged with design. The accuracy of the vision system has been thoroughly checked through the use of other techniques including carbon paper impression measurements of the degrading tips, profilometry on the impression left by the indenting electrode and ultrasonic and X-ray measurement of the weld prior to final destructive peel testing to measure actual weld nugget size. All techniques indicate trends that support the vision systems future capability as a new, non-destructive weld quality monitoring system.