Patent GB-1186231-A (GB)
Title: Methods of and Apparatus for Determining the Acceptability of Percussive Welded Joints.
Inventor: PETERSON KARL ELMER
IPC: B23K9/22
Filed: 1967-05-03
Abstract: 1,186,231. Percussive welding. WESTERN ELECTRIC CO. Inc. 3 May, 1967 [6 May, 1966], No. 20425/67. Heading B3R. Percussive welded joints are rejected when the welding current waveform peaks at a value above or below a predetermined range of values during the shrinking of the arc, and also if current transients dip below an empirically determined amplitude for longer than a predetermined period. A percussive welding apparatus for welding a lead 10 to a stud 11, Fig. 1, comprises a spring-urged chuck 12, and a circuit including a battery 14, resistors 15, 17, and a capacitor 16. Optimum, or ideal voltage, current, and impedance, curves are plotted against welding time in Fig. 3, and the relative positions of lead 10 and stud 11 at these values are shown. Fig. 4 (not shown), comprises an ideal current waveform which peaks within an acceptable range of between 150 and 200 amperes. Fig. 5 (not shown), comprises the current waveform of an unsatisfactory weld, in which the waveform peaks above this range, and in addition there are current transients which dip below a predetermined amplitude, and remain there for longer than the predetermined period. A block diagram of an apparatus for carrying out the method, is shown in Fig. 6. Assuming a 100 ampere threshold for the welding current, a detector 20 is energized by the current, produces a signal, and triggers a pulse generator 21. A 50 millisecond pulse enables an OR gate 22 to operate for a 50 millisecond period, which is longer than the welding cycle. A pulse generator 24 is operated by detector 20 through a time delay 23, and the generator produces a one millisecond positive pulse window 19, Fig. 5 (not shown). Generator 24 simultaneously applies a one millisecond pulse 25 through a time delay 26 to enable an AND gate 27. Pulse 19 is applied to a comparator 29, along with a voltage signal, which follows the welding current input, and is supplied by an amplifier 30. If the waveform dips into window 19, comparator 29 produces a voltage signal which is integrated in an integrator 31. If the waveform does not remain continuously in window 19 for more than 200 micro seconds, the output of integrator 31 will not rise above zero volts, and a detector 32 will not be triggered. If, however, the time is 200 micro seconds or more, detector 32 is triggered and produces a signal which is gated through the enabled OR gate 22, and energizes a reject relay RY1, which operates means for indicating to the operator that the weld is unsatisfactory. Relay RY1 is also energized if the welding current peak is greater or less than the predetermined amplitude range, and this is determined after a time delay provided by a time delay circuit 26, by comparators 34, 35. If the peak is incorrect, AND gate 27 will receive a voltage signal from one of the comparators 34 or 35. This signal will remain on the input lead of gate 27 until pulse 25 enables the gate, approximately two milliseconds after the OR gate 22 is enabled by generator 21, and approximately 100 micro seconds after the trailing edge of window 19 is formed. If gate 22 is gated by a pulse from gate 27 it will energize reject relay RY1, so as to indicate that the weld is unsatisfactory. If the welding current waveform has a peak which falls in the acceptable amplitude range, and also does not dip into window 19 and remain therein for 200 micro seconds, OR gate 22 will not pass a signal, and after a predetermined period established by a time delay 38, an accept relay RY2 will be energized to indicate that the weld has passed both tests.