FR2510447A1 - METHOD OF VERIFYING THE SATISFACTORY CHARACTER OF THE ARC WELDING CONDITIONS - Google Patents

Abstract

PROCEDURE FOR VERIFYING THE SATISFACTION OF STUD ARC WELDING CONDITIONS. BEFORE THE WELDING CURRENT DOMINATES THE PILOT ARC, CHECK THE VOLTAGE OF THE CURRENT IN THE INTERVAL BETWEEN STUD 5 AND PART 3 ON WHICH IT MUST BE WELDED. IF THE VOLTAGE IS ABOVE OR LOWER THAN PRE-ESTABLISHED MAXIMUM OR MINIMUM VALUES, THE WELDING CYCLE IS INTERRUPTED OR THE NEXT CYCLE MAY NOT BEGIN. A WARNING MAY BE ISSUED. THE REALIZATION OF DEFECTIVE WELDING IS THUS AVOIDED.

Description

The present invention relates to welding and, more particularly, to a

  method for checking that the conditions are satisfactory for the relief of elements, for example the stud welding, on metal parts by the method of arc welding controlled in position or guided.

  Experience has shown that in the welding of gou-

  Due to the controlled arc process, unsatisfactory welding results are sometimes obtained, which must be attributed to the contamination of the surfaces to be welded to one another. This problem is due in particular to the the presence of oil or grease residues on the workpiece, which in most cases includes sheet metal that has previously undergone a stretching process and for which purpose has been provided

  stretch lubrication oil The welding of the gou-

  jons by a controlled arc in position is used mainly on

  industrial production processes which operate to a large extent according to an automatic cycle It is inevitable that elements contaminated in this way reach the production line.

  not sufficiently penetrated and which, in most cases, does not

  It seems that at the end of the production line, imperfect welding can only be rectified at an excessively high price.

  The present invention is therefore aimed at detecting

  improperly prepared or improperly prepared in the area to be welded, the detection being performed at a sufficient stage

  early on a production line to avoid

  additional welding tasks or to interrupt the

  According to the invention, this problem is solved by comparing the average voltage of the pilot arc with a predetermined maximum value of the voltage, and causing the emission of a signal if the maximum voltage is reached.

authorized is exceeded.

  Surprisingly, a heavily contaminated surface, such as oil or grease, has almost no influence on the

  between the ends of the welding arc, although it is

  put that it is the welding arc that is responsible for the welding.

  On the other hand, the pilot arc is relatively sensitive to contaminations or to the fact that the surfaces have been inadequately prepared. In any case it has been established that insufficiently prepared surfaces cause an increase in the tension between the ends of the pilot arc, which

  is probably due to phenomena of evaporation or similar

  These phenomena influence the arc to such an extent

  that can be determined by conducting a verification

  without incurring a great expense.

  normal operating conditions, the prevailing

  between the ends of the pilot arc is about 20 to 25 V, whereas in the presence of contamination, it occurs

  voltages of approximately 30 to 40 V The normal operating voltage

  tion of the pilot arc therefore deviates very

  tension prevailing in the case of contamination.

  the pilot arc, particularly in the case of contamination

  tion, is a DC voltage subject to voltage peaks that follow each other closely and from which can be filtered, for example by an RC circuit, a mean voltage that can be measured and that can give rise to

  a signal Such a signal, which appears only when a signal

  is exceeded, is an indication, before the start of the welding arc, which is a warning that insufficient welding will occur, so that

  can then take preventive measures.

  Such a measure, which can be taken in response

  signal emitted as indicated above, consists of transmitting

  train the signal into an alarm to warn

  the operator of the imminence of a high quality weld

  In addition, it is possible to use the signal to stop the control unit of the work cycle and prevent further operation of the welding unit In this case, the control unit of the work cycle can to be stopped

  before the start of the welding arc, so that it does not occur

  no welding, or if there is not enough time for that, you can pocket the start of a subsequent work cycle.

  It can also happen that the voltage

  be the ends of the pilot arc falls below a range of

  their minimum and, in this case, one can also provoke

  the emission of a signal A fall below a voltage of

  nimal measured between the ends of the pilot arc can for example occur if a short circuit occurs, as a result

  any malfunction, in the interval between

  seen between the electrodes of the arc. Such a case risks, for example,

  ple to occur if the pilot arc leads to a fusion of the metal of the stud, or another element to be welded on the piece,

  so intense that a drop of molten metal forms a bridge.

  the proper welding of the welding arc would then be doubtful, and it is likely to result in a weld of inferior quality. Such a case can also be

  measuring the average voltage of the pilot arc and comparing

  at a pre-established value.

  A method for checking the conditions of stud welding according to the invention, and which illustrates this, will now be described, by way of illustration and in no way limiting, with reference to the appended figures in which: FIG. 1 is a diagram of FIG. a process circuit

  test system comprising, in the basic circuit, a

  a stud welding gun; and

  Figures 2 and 3 are diagrams showing different

  operating sequences within the scope of the

  verification method described by way of illustrative example.

  Figure 1 schematically shows a pistol

  1 welding a support sleeve 2, which is placed manually

  to rest on a basic metal part,

  1 of the gun end 1 A stud holder 4 extends inside the sleeve 2 and carries at its front end a stud 5 for welding the stud holder 4 is retractable, in known manner, to the using a lifting electromagnet 6 in the gun 1 against the elasticity of a compression spring (not shown) When the electromagnet 6 for lifting is energized, the stud holder 4 and the stud 5 are drawn about 1.5 mm into the stud welding gun 1 (back stroke); when the electromagnet 6 is

  the stud holder 4 and the stud 5 are

  These operations and the structural elements they require are known from a number of electrical wires, necessary for use in normal operation of the gun 1, pass through the handle 7 of this pistol l The power supply circuit of the electromagnet 6 includes the wires and 11 From the handle also leaves a wire 13 which conducts the current for the two arcs, driver and welding In addition, the piece 3 is connected to an electric wire 14, so that a circuit-comprising the wire 13, the stud holder 4, is established,

  stud 5, part 3 and wire 14.

  The son 10, 11, 13 and 14 are connected to a control unit 8 of the work cycle, which is of a known type

  intended to be used in the case of guns welding guns.

  Unit 8 supplies at its terminals 16 and 17 the voltage

  designed to feed the lifting electro-magnet.

  The unit 8 delivers at its terminals 18 and 19 the voltage necessary to generate the pilot arc and the welding arc. The control unit 8 of the work cycle comprises a time control contact 9 and, when it is closed, actuates the lifting electromagnet 6 so as to move the stud holder 4 and the stud 5 away from the workpiece 3 to guide and stretch the bow

  pilot, which lasts for a period of time

  naked by the unit 8 The power supply circuit

  magnet 6 is also interrupted again by unit 8

  when it opens the contact 9 at almost the same time.

  that the welding arc is initiated so that with the

  weakening of the welding arc, the welding stud is plunged

  in the melt created on part 3, which leads to

its term the welding process.

  The operations just mentioned are

  will now be described in more detail with reference to the

  gures 2 and 3 Line a represents contact 9 which is

  the control unit 8 of control of the work cycle, for a period of time between t and t The closing of the control contact 9 at time t causes the supply of the lifting electro-magnet 6 -1, represented on the line b, the rear stroke being

  completed at time t 3 Stopping the power supply of the electro-

  6, as a result of the opening of the control contact 9, determined once again by the control unit 8 of the work cycle, occurs at time t and after a delay which -L 5 constitutes a characteristic of the electrical component, this

  is followed by the moment when the power supply to the electro-

  magnet 6 the process is completed with the stud 5 dive

  in the melt on the part 3 h at time t 6.

  With the withdrawal of the stud 5 of the part 3 immediately after the instant tl, the pilot arc is initiated between the stud 5 and the

  piece 3, at time t_ The measured tension between the extremes

  The pilot arc is illustrated on line c It has.

  in normal operation, the average level U1 which remains roughly until the moment, at which the voltage required for the welding arc is imposed on the pilot is then formed, under the effect of this tension, the voltage increase 50 in the gap still existing for the arc, and there is a short circuit with the dive of the stud 5 in the melt on the piece 3 at the moment k The current of the bow

  welding itself is shown at 51 on line d which shows

  be clear that at the moment t it occurs, in the curve

  downstream of the current 51 of the welding arc, a clear

  current draw due to short circuit and is followed by

the final weakening of the arc.

  Referring again to FIG. 1, it can be seen that for measuring the average voltage of the pilot arc, the terminals 18 and 19 are connected to an impedance transformer 24, the purpose of which is to ensure that the voltage who feeds him through the

  terminals 18 and 19 is transmitted to a value of regime,

  feeling the tension at the ends of the arc, at the

  22 and 23 and from there to a capacitor 27 by a gate 25 (shown in FIG. 1 in the simplified form of a control contact) and a resistor 26. The gate 25 is equipped with pilot wires 28, 29 connected to terminals 16 and 17 so

  to respond to the power supply of the electromagnet 6 lifting.

  The voltage supplied by the wires 28 and 29 therefore corresponds to

  line a of Figure 2, that is to say that during the

  the period between times t 1 and t 5, the door 25 is closed.

  (see line e of Figure 2), which allows the

  age of the voltage supplied by the impedance transformer 24.

  The voltage present at terminals 16 and 17 (line a of FIG.

  2) is also provided, by means of the specified

  28, 29, to a switch 30 acting as a multivariate

  monostable braking device which, from the closure of the contact 9, remains in the closed state indicated in the line f of FIG. 2

  from the moment t 1 to a moment t located soon after.

  -4 During the time period t 1 to t 4, the contact 32 of the switch 30 bypasses the capacitor 27 and ensures the complete discharge At time t 4, the contact 32 opens and the capacitor 27 can then be recharged by the

  voltage at the output terminals 22 and 23 of the trans-

  mateur 24, through the resistor 26 The resistance

  tance 26 and the capacitor 27 thus play the role of a cir-

  cooks RC (resistance-capacitor), which ensures the level-

  possible peaks of voltage in the interval between

  the ends of the arc, so that the charge of the condensa-

  27 represents the average voltage of the pilot arc, that is,

  ie the voltage U 2 illustrated on line E of FIG. 2

  (or the voltage U1 of line c).

  To ensure that the capacitor is fully

  charged before relying on the voltage U 2 as a measure

  verifying that the conditions are satisfactory for welding, the door 25 is closed by the control unit 8 of the duty cycle at time t 5, and a measurement of the voltage across the capacitor 27 is thus started using timer 33 just when the electromagnet

9 is no longer powered.

  the timer 33 is made operational by the

  The way in which it works is that it starts at the end of the

  operation of the control contact 9, i.e.

  as t 5, in order to release the output of a discriminator 34 from

  voltage for the duration of a pulse 42 produced by the

  33 (see line h in Figure 2). For this purpose, the

  Nuterie 33 is connected to the wires 28, 29 from the terminals 16, 17.

  To establish whether the voltage U 2 applied to the capacitor

  27 exceeds a maximum voltage U 3 (line i of FIG.

  re 2) or falls below a minimum voltage, a comparison

  35 is provided in the discriminator 34, to which

  known, the maximum voltage value U 3 and the minimum voltage value are applied at the same time as the

  are at terminals 47 and 48 If the voltage is higher (U 4) or

  lower than these values of the voltage, respectively, the

  applied to the exit point 49 of the discriminator 34

  unrelated 36 provided that the timer 33 is closed

  same time The closing period of timer 33 is de-

  ended by the aforementioned impulse 42 For reasons of time,

  it is not possible in the circuit, as described in

  Figure 2, than pocketing the subsequent cycles

  welding; the pulse corresponding to the welding arc de-

  I started can not be stopped By cons, the contact 36 has connected to the control unit 8 of the work cycle by k & - 38 son, cut a circuit without possibility to start another

  welding cycle Relay 36 is synchronized with a

  holding 36b, which must be manually adjusted again by means of a manual switch 60 The relay 36 can also be arranged to operate the device.

audible or visible greening.

  If it is desired to interrupt a welding cycle before the welding current is superimposed on the pilot arc, the measurement of the voltage across the capacitor 27 must be made before the instant t, that is to say before stopping

  the power supply of the electromagnet 6 of the Contraire-

  the mode, described above, of the operation of the

  33 with an impulse 42 when the judgment is stopped.

  supplying the electromagnet 6 at time t 5 it is possible, by inserting a bridge B, to arrange for the introduction of a timer 61 which closes at a predetermined instant Vz

  after feeding electromagnet 6 at time t, that is

  that is, a test pulse 43 is initiated immediately

  before time t (see line e in Figure 3).

  of, the pilot arc is near its end, and therefore the capacitor 27 is completely closed (see line f of Figure 3), so that at the moment of the pulse 43, the measurement of the voltage using the voltage discriminator 34 can

be performed reliably.

  The voltage, delivered at point 49 of the output of the

  34 Criminator of tension, is applied via

  of the timer 61, which is closed by the pulse 43, to a

  lais 37 at a stage early enough so that, if the value of the maximum tensile U 3 is exceeded (U 4), the beginning of the welding arc can still be avoided in this cycle by closing the

  contact 37a of relay 37 (connected by wires 39 to unit 8) -

  Relay 37 is arranged to stop the

  Only during a cycle of the control unit 8 of the work cycle With the inserted part placed above the bridge A, the relay 36 would also be powered as described above, which avoids an additional start of operation of the control unit 8 of the work cycle

  until the circuit has been reset by the opening

contact switch 60.

Claims (5)

  1 Method for checking that the conditions are satisfactory for welding studs or other elements   on a metal part by guided arc welding or   position, characterized in that the average voltage   existing at the ends of the interval between electro-   at the end of the duration of the pilot arc is compared with a maximum value established in advance and, if this value   is exceeded, a signal is generated.   Method according to claim 1, characterized in that the signal is forced to pocket the start of a new welding cycle until a manual switch has been operated. 3 Process according to claim 1, characterized   in that the signal causes the interruption of the cycle of   by pocketing the beginning of the welding arc.   Process according to any one of the claims   tions, characterized in that the signal sets a warning device.   Process according to any one of the claims   tions, characterized in that the signal is also   generated if the average voltage falls below a certain   their minimum established beforehand.