GB1259988A - Method and apparatus for detecting the expulsion of molten metal in resistance welding - Google Patents

Abstract

1,259,988. Welding by pressure. INSTITUT ELEKTROSVARKI IMENI E.O. PATONA. 21 Jan., 1969, No. 3295/69. Heading B3R. In resistance welding molten metal expulsion is detected by converting the energy of the shock wave caused by expulsion into an electric signal and registering the time of occurrence and magnitude of this signal to indicate the time of occurrence and magnitude of the expulsion. In an embodiment a transducer 1, Fig. 2, is secured to electrode 2, the transducer comprising a piezo-electric cell for converting the shock wave caused by expulsion into an electric signal. A discriminator 4 connected to the output of the transducer 2 separates and amplifies the signals from the transducer and supplies an indicator 5, e.g. an oscilloscope and a relay 6 which causes the operation of a light or sound-signalling device to indicate expulsion or of devices to reject and sort articles welded with or without expulsion. The discriminator 4 which receives an input from the welding transducer 7 to mark the beginning and end of the weld comprises a band-pass filter 8, Fig. 3, connected to the transducer 1 to separate and amplify signals in the range of 20-50 kc. per sec. and suppress signals outside this band. The transducer 7 is connected to a unit 11 which converts signals from the breaker into signals for triggering a gate generator 9 in the form of a Schmitt trigger, delay lines 12, 13 being provided between the unit 11 and the generator 9. The filter 8 and generator 9 are connected to an amplitude and time selector 10 which separates and amplifies those signals it receives simultaneously with the gating pulses, which exceed a preset level. To measure the parameters of several expulsions at one weld point a number of gate generators and selectors 10 are employed. In use in the course of welding the output of the transducer includes signals relating to the operation of auxiliary parts of the welding apparatus, low frequency signals caused by pressure changes due to heating and the high frequency shock signals. The filter 8 allows only those signals of 20- 50 kc. per sec. to pass to the selector 10 which also receives square-wave pulses corresponding to the time of welding current passage and the high-frequency shock pulse and a squarewave pulse arrive at the same time and the selector 10 emits a pulse indicating expulsion. This pulse is measured by indicator 5 and triggers relay 6.