FR2474367A1 - METHOD FOR REGULATING THE WELDING CURRENT IN THE CASE OF RESISTOR WELDING, IN PARTICULAR POINT WELDING, AND DEVICE FOR CARRYING OUT SAID PROCESS - Google Patents

Abstract

THE SUBJECT OF THE INVENTION IS A PROCESS FOR REGULATING THE WELDING CURRENT BY THE SUCCESSFUL INCREASE OF THE WELDING CURRENT. THE INCREASE OF THE WELDING CURRENT 6 IS STOPPED WHEN THE WELDING CORD RESISTOR 7 MOVEMENT REACHES THE VALUE OF ITS LOCAL MAXIMUM, OR APPROACHES 10 OF THIS MAXIMUM, SO THAT THE WELD IS ACHIEVED AT THE VALUE OF THE WELDING CURRENT THAT IS REACHED WHEN THE CURRENT IS STOPPED. APPLICATION IN PARTICULAR TO THE AUTOMATIC CONTROL OF THE RESISTANCE POINT WELDING PROCESS.

Description

The present invention relates to a method for regulating the flow of

  welding in the case of resistance welding, in particular spot welding, and

  a device for implementing this method.

  In the practice of resistance welding, in particular spot welding, a high and uniform weld bond quality must be ensured even during a particular variation of the technological conditions of the welding process and affecting the quality of the welded connections. Current practice is satisfied to a large extent with the fixed

  transformer and phase regulation of the

  at the beginning of the welding process, which must now be

  approximately the same current during welding.

  This possibility does not take into account fluctuations in

  the voltage of the mains, the wear of the electrodes of

  modification of the surface state of the sheet

  and other variations affecting the welding current.

  In these circumstances, the case may occur that the

  welding force decreases so that a high-quality weld

  mediocre or even no welding is performed.

  In addition, there are known devices compensating a voltage drop of the sector. In any case, their

  application does not solve the falls in the current of

  Drovoked by other influences.

  Similar devices are known

  regulating the constant value of the welding current, respectively other quantities, such as for example the tension of the weld bead or the power delivered thereto. The disadvantage of such solutions is that they do not adhere to the varying conditions of weld bond formation, as affected by the welded elements themselves,

  the geometry of the connection by welding, the state of

  and electrodes and which require adjustment when changing the thicknesses to be welded, the material, the

  number of welding layers, surface treatment.

  There are also known devices that

  parent of one of the energy variables of the cord of

  duration, voltage, power consumption, etc ... to previously set limit values and correct the conditions for the next weld when a value

  measurement is found outside the range of

  mites fixed during the realization of the weld seam.

  The disadvantage is that the regulatory intervention does not

  no weld bead on which the variation was found, but the next for which the conditions can be modified in the meantime. In addition, the adjustment of this system is very complicated. The optimal values of the adjustment are obtained in particular empirically

court each technological case.

  Also known is a device which uses the abrupt increase of the welding current, another

  increase of this current being stopped when the

  the thermal expansion of the weld bead given by its derivative with respect to time reaches the previously set value and the welding is carried out at the current value reached. The disadvantage of this method, otherwise perfect, is that it requires the measurement of a mechanical quantity, namely the thermal expansion of the weld bead. This causes problems in some welding machines. In addition, a sensor, which

  converts the mechanical quantity, that is, the dilat-

  in one electrical signal is required.

  The present invention remedies in a large

  measure to the disadvantages of the aforementioned solutions. The pro-

  In the case of resistance probing, in particular spot welding, the present invention relies on the abrupt increase of the welding current, so that this increase is halted when the resistance of the weld bead reaches the value of its local maximum, or approaches this maximum, so that the weld is performed at the value of the welding current reached at the time of the increase of the current. The method of regulating the welding current according to the invention is implemented thanks to the device

  according to the invention, whose source of resistance

  the weld seam is connected by a diverter

  and a comparator with the input of the reference quantity

  the signal input of a flip-flop. The exit of

  the flip-flop is connected to the blocking input of the genera-

  sawtooth which is connected by the electronic control of the Darameters of the welding process to the welding process setting input. The kind of

  the order of tripping of the sawtooth,

  electronic control of the parameters of the welding process, is connected to the zero adjustment input of the flip-flop, to the start input of the sawtooth generator and simultaneously, via the delay circuit, to the input for delay adjustment, at the entrance

  pulse generator of the flip-flop.

  The advantage of the process according to the invention is that it makes it possible to compensate for disturbing influences.

  occasional and external, for example the short-

  Parallel circuit of the current through the adjacent weld

  or by the fortuitous contact of the elements to be welded, which

  would otherwise lead to a reduction in the

  through the welding point and thus to the training

  poor connections. Furthermore, the method according to the invention allows to adanter the welding current to the

  situations resulting from the intentions of the manufacturer,

  for example to the different thicknesses of the sheet to be welded and to the different number of welding layers,

  which are modified during the welding operation. The work

  technologists to adjust the conditions

  welding is thus facilitated. The disoositive according to

  vertion adarte itself according to a predetermined setting the survey curve to changing technological conditions. An advantage of the method and the device according to

  the invention lies in the fact that the correction of the

  welding process starts at the beginning of this process of

  in the changing conditions

a correction was found.

  The device according to the invention does not require

  no particular transducer or transducer and is

  not only to fixed installations but also to

to the Soudaze clamps.

  An exemplary embodiment of the invention is

  reoresented in the accompanying drawings.

  Figure 1 shows the resistance pattern

  typical of the weld seam and the increase in dia-

  meter of the weld point in the case of a con-

both of the welding current.

  Figure 2 represents a comparison of

  the resistance of the weld seam and the

  crissemert in diameter of the weld point in the case

  a sudden increase in the welding current.

  Figure 3 illustrates the Drincipe of Function

  the embodiment of the invention and the manner in which the signal for stopping the current increase is equal to the resistance curve of the weld seam,

to derive, respectively.

  3r, FIG. 4 shows an exemplary embodiment of the invention according to the invention. In the case of the constant adjustment of the welding current, the typical resistance curve R of the cord of FIG.

  weld is represented on curve 1. The curve 2

  to be conert the diameter D of the weld point increases

  likewise. It is visible that near the

  as tmaxt at which the resistance R of the weld bead reaches its local maximum, the weld point, whose diameter D increases in time t during the welding operation, begins to form. In case we leave the welding current I

  grow abruptly during the weld, curve 3, the

  lure of resistance R, curve 4, will reach its maximum Rmax again after a few moments. At this maximum corresponds approximately the beginning of the formation of the weld spot, but its diameter D, curve 5,

  is growing rapidly with the rising value of

  The stiffness of the increase in the diameter of

  meter D is significantly higher than in the case of the constant adjustment of the welding current I, only the energy saturation of the weld bead and the projection of molten metal appear with time

out of the weld point.

  It has been determined experimentally that the higher the welding current I grows, the sooner the maximum resistance Rmax is reached.

  R of the weld seam and earlier begins the increase

the welding point.

  It has furthermore been found that the maximum Rmax is reached later in the case of a modification

  external conditions such as, for example,

  the thickness or increase in the number of sheets to be welded or the increase, caused by their wear, in the diameter of the electrodes, that is to say in the case of higher values of the welding current I.

  When from the values concerned, which correspond to

  lie when Rmax is reached in time tmax, is

  the quotient I / De, we thus obtain the intensity of the welding process, through which it is known that it represents the invariant of the process of welding.

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  welding for one type of material, where De is the electrode diameter This quotient is constant for thicknesses

  and a different number of the sheets to be welded, for

  Few electrode diameters under otherwise constant conditions. We draw only the time tmax, in

  which is reached the maximum of the resistance of the cor-

  weld, represents the invariant of the welding process, yes means that the value corresponding to the energy requirements of the welding connection in

  course, the welding current I1 is reached.

  The process according to the invention operates from this

  way. The welding current I is allowed to grow abruptly

  According to curve 6. The appearance 7 of the resistance R of the weld bead is then measured and its derivative dR / dt also curve 8. At the instant tmax at which the speed R reaches the local maximum Rmax, the derivative dR / dt passes through the zero point. This state is detected and at

  from the signal obtained in this way, another

  Welding current I is stopped at the I1 value. The weld is then completed at the constant value

  welding current, curve 9. For technical reasons,

  In other embodiments of the electronic part, it is advantageous to detect the value of the derivative dR / dt

  sufficiently close to zero, so that the

  general from stopping the increase of the welding current I is indicated around the intervals t, before

  cue the maximum of the resistance Rmax is reached. Linen-

  time Lt may be comparable or less than

  half a period of the sector's 50 kz frequency, that is

  ie 0.01 s in the case of usual welding installations. The method according to the invention for regulating the welding current in the case of resistance welding, in particular spot welding, is implemented by means of the device according to the invention, whose source 11 of resistance of the weld bead is connected, Dar the diverter 12 and the comparator 13, to the input 19 of the reference variable to the signal input 20 of the flip-flop 14. The output of the flip-flop 14 is connected to the input block 23 of the sawtooth generator, which is connected by the electronic control 16

  parameters of the process of welding at the entrance of re-

  25 of the welding process 17. Exit 26 of

  the order of tripping of the sawtooth,

  16 of the parameters of the probing process being connected to the zero adjustment input 22 of

  latch 14, at the start input 24 of the gen-

  toothbrush 15 and simultaneously, by

  the delay circuit 18, at the input 27 for setting the delay, at the input 21 of the generator

pulses of the rocker 14.

  The action of the device according to the invention is based on the fact that the signal coming from the source 11 of the resistance curve of the weld bead is applied,

  In the diverter 12 whose output is connected to the

  13, at the input 19 of the reference variable.

  The comparator 13 determines the obtaining of the maximum resistance and delivers an order to the rocker 14 which changes state and stops the increase of the sawtooth by

  its output connected to the blocking input 23 of the genera-

  sawdust 15. The increase in the current of

  welding is thus blocked, which is determined by the

  rope of the exit of the sawtooth generator

  by the electronic control 16 of the parameters of the pro-

  welding process at the adjusting input 25 to the welding process 17. Output 26 of the tripping order

  of the saw tooth of the electronic control 16 of the

  the welding process is connected to the zero adjustment input 22 of the rocker 14 and to the start input 24 of the sawtooth generator 15, the rocker 14 changes state when the triggering of the sawtooth and thus unblocks the increase of the sojdage current. Simultaneously, the output 16 of the sawtooth engagement order is connected to the delay circuit 18 with the input 27 for the

  setting the delay, e the input 21 of the pulse generator

  of the weighbridge 14. The blocking is thus ensured

  during the first two to five weeks.

  The method and the device according to the invention

  can not be applied to the automatic control of

  resistance spot welding processes.

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Claims (2)

  1 - Process for regulating the flow of sulfur   in the case of resistance welding, in particular   spot welding bond, by sudden increase   welding current, characterized in that the   Welding current is stopped when the resistance curve of the weld seam reaches the value of its local maximum, or approaches this maximum, so   that the welding takes place at the value of the current of sou-   which is reached at the moment of cessation of current increase.   2 - Device for implementing the method   according to claim 1, characterized in that the source   this (11) of the resistance of the weld bead is connected, by the diverter (12) and the comparator (13),   with the input (19) of the reference variable to the   signal (20) of the flip-flop (14), the output of the flip-flop (14) being connected to the blocking input (23) of the sawtooth generator (15), which is connected by the electronic control ( 16) parameters of the   welding process at the adjusting inlet (25) of the   welding process (17), the output (26) of the order of de-   clipping of the sawtooth, the electronic control   (16) parameters of the welding process being   connected to the zero adjustment input (22) of the base   (14), at the start input (24) of the genera-   sawtooth (15) and at the same time, by   intermediate of the delay circuit (18), at the input (27) for setting the delay, at the input (21) of the generator pulses of the rocker (14).