A major Tier 1 automotive supplier was achieving a very good level of quality in its manufacturing process welding nuts to a metal seat frame. The experiment provided optimal values for each factor and showed, surprisingly, that quality improves as the tip pressure is reduced. The welding operation in question involves attaching four nuts to the lower seat support in the front bucket seat of an automobile. Bolts are then used to fasten the nuts to guide rails that allow the occupant to adjust the seat. In the welding station operation, the lower seat-support-pan fixture rotates counterclockwise to align the seat frame with four projection nut welding machines. The factors in the welding operation include the following: Tip force - the pressure level with which the electrodes contact the metal is controlled by an air pressure regulator; Weld current - current amperage levels are controlled by a transformer and weld timer controller; Squeeze time - the amount of time the electrodes make contact before the current is passed through; Hold time - the amount of time the upper electrode makes contact with the nut while the current is passing through; Cool time - the amount of time the electrode makes contact while the weld is in the cool-down period. The response for the experiment is the torque at which each nut weld fails as measured with a peak-reading torque wrench. 'DOE offers the opportunity to move manufacturing operations to a higher level by scientifically mapping the application space. While human intuition is usually only capable of grasping first-order effects, DOE also considers second-order and multiple factor interaction effects. Design-Ease greatly simplifies the use of DOE by automating the process of designing experiments and analyzing the results' said the project leader for this study. The weld current, weld time, tip force, and interaction between squeeze time and weld time were identified as significant factors. Hold time was not a significant factor. The model 'predicted vs. actual' showed some correlation but not strong enough for reliable predictions. The predicted torque measurements will then be the same as the preceding settings. If it is necessary to increase the tip force to 52.5 lb/in2, the weld current will need to be increased to 12,500 A for a weld time of approximately 11 cycles to duplicate the torque levels of the previous two examples. Based on the study predictions, the company made a running change to reduce the welding tip force to the recommended levels, this change quickly eliminated the small number of defects that were experienced in the past, and the company is currently running with essentially zero defects.


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    Title :

    Study yields zero weld defects in auto seat frames


    Published in:

    Welding Journal, New York ; 87 , 10 ; 36-38


    Publication date :

    2008


    Size :

    3 Seiten, 3 Bilder, 1 Tabelle



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English




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