Electric heating – Metal heating – For bonding with pressure
Patent
1997-04-03
1999-11-02
Shaw, Clifford C.
Electric heating
Metal heating
For bonding with pressure
219 98, B23K 920
Patent
active
059775068
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an arc welding method for the connection of a component to a workpiece and to an apparatus for carrying out the method.
Such a method is known and is used for achieving a weld by means of an arc quickly and correctly. The components used are, for example, bolts or studs. In known methods, the arc voltage is set mechanically by means of the component lift. Specifically, the component lift is essentially proportional to the arc voltage. In this case, a value based on experience is set permanently. The arc voltage changes continuously during the welding process as a result of the surface characteristics of the parts to be welded and as a result of tolerances in the material production and in the contact pressure of the welding head used, which leads to quality fluctuations in the welds.
Patent Specification EP-B-0 241 249 describes a control circuit arrangement for the arc welding of components, a sequence controller determining the trigger moments of the rearward movement and of the forward movement of the welding arc, and a monitoring voltage being derived from a preweld current arc, which monitoring voltage is converted into a correction voltage and superimposed on a control voltage in order to control a changeover mode power supply unit which, using the control voltage corrected in this manner, adjusts its output current during the welding process to the resistance of the preweld current arc, said resistance being derived from the monitoring voltage. The trigger moments of the rearward movement and of the welding arc can also be corrected in the sequence controller with the aid of the monitoring voltage, which is derived from the preweld current arc. The magnitude of the output current and the welding time are thus adjusted for every welding process on the basis of the preweld current arc voltage. The component lift is adjusted by means of a cylindrical coil and a spring. Here too, the arc voltage can vary continuously during the welding process, as a result of the factors mentioned above, which leads to undesirable reductions in quality.
The known mechanical adjustment of the component lift and the insertion dimension for influencing the arc voltage allows these parameters to be corrected only once per weld. In addition, the mechanical adjustment of the component lift and the insertion dimension results in the risk of producing defective quality results because of incorrect adjustment. In practice, with the time pressure to which the operator is subject in each case, it is not always possible to avoid or to correct inaccuracies and deviations from the optimum settings. This results in corresponding reductions in quality, and scrap. In addition, the operation of the known welding devices is subject to correspondingly stringent requirements. Furthermore, as a result of the increasing quality requirements, it is desirable to ensure and, if necessary, to correct the quality directly in the production process itself.
The invention is based on the object of creating a method of the generic type which avoids the disadvantages indicated above, complies with present-day quality assurance demands, and can be carried out easily.
The stated object is achieved according to the invention in that a reference voltage profile is set for the arc voltage and the arc voltage is measured and compared with the current reference voltage repeatedly during the welding process in a control loop, as a controlled variable, a correction variable in each case being determined from the difference between the measured arc voltage and the current reference voltage, by means of which correction variable the component lift is in each case automatically corrected, as a manipulated variable. In consequence, the desired arc voltage is maintained precisely during the entire welding process, which ensures a significant improvement in the welding quality for different workpiece surface characteristics. In addition, time-consuming adjustments and corrections of the distance between the workpiece and the stud are no longe
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Emhart Inc.
Murphy Edward D.
Shaw Clifford C.
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