FR2514682A1 - Resistance spot welding of steel sheets coated with zinc - where each welding electrode is sepd. from sheet by brass strip forming copper:zinc alloy on weld - Google Patents

Abstract

Welding is achieved by at least two electrodes, which are connected to one or more sec. windings of a transformer, of which the prim. winding is fed with AC. A foil or strip made of an alloy of Cu and a metal compatible with the coating on the steel sheets is inserted between each electrode and the sheets. The foil or strip pref. contains 60-65% Cu and 35-40% Zn, i.e. a brass. The pref. spot welding machine contains two electrodes driven by jacks towards or away from the sheets to be welded. A cassette contg. a spool (a) on which a brass strip is wound is used for the stepwise feeding of the strip between one electrode and the sheet; the strip then travels back to the cassette and is wound onto a second spool (b). A second cassette is used in the same manner for the other electrode. The process is used for steel sheet coated with Zn by electroplatg. or by dipping in molten Zn, eliminating the need for frequent cleaning of the electrodes.

Description

The present invention relates to resistance resistance spot welding of coated steel sheets, ie of electro-galvanized or galvanized sheets, for example;
It is known that in the automobile industry, in particular for forming the base of vehicles, coated steel sheets are used which constitute protection against corrosion. These sheets are assembled by spot resistance welding, which causes destruction of the coating at the weld points, so that protection against corrosion is ultimately ineffective.

 In addition, spot welding, by resistance of such sheets presents many difficulties, in particular the coating adheres to the electrodes and fouls them so that they must be cleaned constantly.

 The applicant, in its application No. 81 18 007 of SEPTEMBER 24, 1981, proposed a method making it possible to remedy the various drawbacks mentioned above, said method consisting in inserting between each electrode and the corresponding surface of the steel sheet coated with weld a strip of copper alloy and a metal compatible with the coating of the sheets to be welded.

Thanks to such a method, an alloyed copper film is added to the welding point which constitutes good protection against corrosion and the duration of use of the electrodes is extended, the energy consumption remaining equal.
The present invention relates to a device for implementing the above method, a simple device, inexpensive and very easily adaptable to welders of different types.

 The device according to the invention is intended to equip resistance resistance spot welding machines of coated steel sheets, said welding machines comprising several welding electrodes electrically connected to one or more secondary windings of a transformer whose winding primary is intended to be connected to an alternating current source, and is characterized in that it comprises means for supporting a roll of a strip of a strip of copper alloy comprising a material compatible with the coating of welding plates, means for guiding the strip of strip to insert it between the sheets to be welded and the corresponding electrode, and means for controlling the movement of the strip after each welding has been carried out.

 Thanks to this arrangement, a very simple assembly is produced which adapts to all types of resistance, spot welders and which allows a high welding rate.

 So that no welding point can be carried out without the strip having been inserted between the electrode and the sheet, the device comprises feeler means for checking the length of the roll of the strap strip, said feeler means being inserted on a signaling circuit.

 According to another characteristic, the device comprises means for receiving the strip of strip for winding the part of said strip remaining after the welding points have been made and means for controlling the winding of said part of the strip. after each weld has been completed.

 According to a particular constructive characteristic, the device comprises a housing provided with an axis for receiving a roll of the strip of strip, a second motor axis intended to support a roller for receiving the part of the strip remaining after the completion of the points of welding, said second motor axis being integral with a ratchet wheel with which cooperates a pawl carried by a movable lever against the action of a return spring and a single-acting pneumatic cylinder whose free end of the rod of the piston is arranged to push the lever against the action of the return spring when the cylinder is pressurized.

 So that the length of the strip of tape moved after each welding point is always regular, the device includes means for modifying the value of the angular displacement of the motor axis as a function of the thickness of the portion of tape remaining after the production of the weld points wound on the receiving roller.

 According to a constructive characteristic, the feeler means comprise a finger intended to cooperate with the roller of the strip of strip, said finger being carried by an assembly sliding diametrically relative to the axis of said roller and connected to elastic means tending to apply said finger against said roller, said assembly comprising a movable stop to limit the return stroke of the lever as a function of the thickness of the roll of the strip of strip.

 In order to facilitate the use of the device according to the invention and to easily replace the strip of strip, the roll of the strip of strip and the roller for receiving the part of the strip of strip remaining after the welding spots have been produced, are housed in a cassette, the housing being provided with elastic means for fixing the cassette.

 Preferably, the device comprises manual means for controlling the rotation of the ratchet wheel. So we can when replacing the tape, check the operation and tighten it.

 Finally, according to a last characteristic, the means for guiding the strip of strip consist of C-shaped sections of insulating material fixed to the housing by elastic clips.

 The invention will now be described in more detail with reference to a particular embodiment given by way of example only and shown in the accompanying drawings.

On these drawings
Fig. I is a schematic elevation view showing a device according to the invention,
Fig. 2 is a perspective view on a larger scale of a device according to the invention,
Fig. 3 is an elevational view on a larger scale of the device of FIG. I, the cover being assumed to be removed and the cassette being shown in phantom.

Fig. 4 is a sectional view along the line IV-IV of FIG. 3,
Fig. 5 is a sectional view along the line VV in FIG. 3,
Fig. 6 is a sectional view along line VI-VI of FIG. I,
Fig. 7 is a perspective view of a cassette, the cover being assumed to be removed, and
Fig. 8 is an elevational view similar to FIG. 3, the delivery roller being assumed to be empty.

 The device according to the invention is intended to equip a spot resistance welder of the type shown diagrammatically in FIG. I and comprising two mobile electrodes I and 2 connected to one or more secondary windings of a transformer, the primary winding of which is intended for be connected to an alternating current source.

 In this embodiment, we will assume that the two electrodes I and 2 are connected to cylinders 3 and 4 respectively to control their approximation in order to clamp coated steel sheets 5, to achieve weld points and their spacing to allow the sheets 5 to be removed and replaced with others to be welded.

 A device according to the invention is provided for each electrode I and 2, these being referenced in 6 and 6a. The devices 6 and 6a are identical and only the device 6 will be described here in detail.

 The device 6 comprises a box 7 closed by a cover 8 and in which is housed a cylinder 9 of a pneumatic cylinder comprising a socket 10 for connecting it to a source of compressed air. In the cylinder 9 is movable a piston against the action of a return spring 11, the piston rod being terminated by a thread 13 intended to receive a blind nut 12 with a lock nut 14, said blind nut constituting a head thrust for the lever 15. This lever 15 is integral with a ring 22 guided in a bearing at the bottom of the case 7 and crossed by an idler axis 16. the lever 15 comprises a pawl 17 cooperating with the teeth 18 of a wheel with ratchet, said lever 15 being extended by a lug 20 on which is hooked one of the ends of a tension spring 19, the other end of which is fixed to a stud 21 provided on the bottom of said housing 7.

 On the axis 16 is wedged a socket 23 integral with a pinion 24 which projects from the surface of the cover 8 through an opening 42, the ratchet wheel 18 being wedged on the socket 23.

 A bar 30 has in its central part a boss 29 which passes through an opening 31 of the cover 8 and which supports a feeler member 28.

 The bar 30 is integral with a plate 32 pierced with an elongated opening 33 through which extends a stud 25 integral with the bottom of the housing 7 and receiving on its threaded free end, a nut 33, a spring 35 being inserted between washers 36 to hold the plate 32 applied against a shoulder 37 of the stud.

 At its end opposite to that secured to the plate 32, the bar 30 is secured to a second plate 38 having two elongated openings 39 and 40 guided respectively on pins 26 and 27. These pins are threaded at their free end to receive nuts 42 and 43 respectively with interposition of the washers and springs to obtain an assembly identical to the assembly of the plate 32 so that the assembly can slide freely over a length corresponding to the length of the openings 33, 39 and 40.

 On the bottom of the housing 7, a stud 45 is provided on which one of the ends of a tension spring 46 is fixed, the other end of which is fixed to the bar 30.

 A switch 47 is provided in the housing 7 and is connected by a flexible conductive cable 48 to the electrical installation for controlling the welder so as to open the general circuit when its contact 49 is requested by the bar 30 (See FIG. 1 ).

 In the bottom of the housing 7 is pivoted an axis 50 which projects through an opening 51 of the cover 8 and which has at its free end a toothing identical to the toothing 24.

On the cover 8, ela tabs are provided.
ticks 53 for fixing a cassette 54 comprising, housed in a housing 58, a feed roller 55, a take-up roller 56 for a strip 59 of a copper alloy and of a material compatible with the coating of the sheets 5 to solder.

 The housing 58 includes pins 60 for guiding the strip 59, the latter passing through openings 61 of one of the side walls 62. In a wall 68 of the cup 58 an opening 64 is made for the passage of the feeler 28.

 The roller 55 has a grooved central circular hole 63 so that when the cassette 54 is put in place, the axis 50 engages to cooperate with the grooves of the hole 63 and that said roller 55 can rotate freely.

 The receiving roller 56 has a central hole 65 identical to the hole 63 and provided with grooves so that the pinion 24 when the cassette is put in place, is secured to said roller 56.

 On the bottom of the housing 58 are mounted retaining pawls 96 and 97 which cooperate with a toothing of a blank of the rollers 55 and 56 so that these can only rotate in the direction indicated by the arrows (see fig. 7).

 In the cover 8, an arcuate opening 66 is made, through which protrudes a stud 67 integral with the lever 15 so that the rotation of the wheel 18 and therefore that of the roller 56 can be manually controlled.

 On the cover 8 are provided two pairs of elastic tabs 70 and 71 intended to elastically respectively maintain C-shaped sections 72 and 73 of insulating plastic material, for example, these sections serving for guiding the strip 59 and being fixed in the vicinity of the electrode 2 by elastic clamps 75 (see fig. 6).

 In Figure 1 there is shown schematically the pneumatic circuit of the welder, this circuit comprising a distributor 80 connected by a conduit 81 to a source of compressed air. The jack 4 is a double-acting jack and the admission of compressed air on the side of the face of the piston provided with the rod is carried out by a conduit 84 inserted between the jack and the distributor 80. On the conduit 84 is connected a bypass 85 connected to the jack 3 for the admission of compressed air. in the latter, on the side of the piston face integral with the rod.

 A conduit 82 connects the piston 4 to the distributor for the admission of compressed air into the cylinder on the side of the free face of the piston and on this conduit is mounted a bypass 83 opening into the cylinder of the jack 3.

 As is usual when one end of the cylinders of the cylinders is at the intake, the other end is at the exhaust.

 On the distributor 80 there is provided a drawer for controlling by conduits 87 and 88 the admission of compressed air into the cylinders of the jacks 9 of the devices 6 and 6a so as to control the displacement of the rod 13 of the pistons to push the 15 corresponding levers. When the pistons are at the end of their travel, the drawer is moved and controls the venting of the jacks 9, so that by the action of the springs 11, the piston rods return to their original position.

 Schematically in Figure 1, there is shown the electric circuit for controlling the welder which comprises two conductors 90 and 91 connected to a line L1 and L2 with the interposition of a general switch 93. On the conductor 91 are inserted the switches 47 of devices 6 and 6a.

The operation is as follows
On each housing 7 of the devices 6 and 6a, a cassette 54 is put in place, the cassettes being held by the elastic tabs 53, and the pin 50, and the pinion 24 being engaged respectively in the holes 63 and 65 of the rollers 55 and 56.

 The strip 59 is fixed by its corresponding end to the roller 56 and it is unwound to be engaged in the guides 72 and 73 and pass in front of the corresponding electrode.

 By acting on the pin 67, the movement of the wheel 18 ^ is controlled so as to tension the strip 59.

 It will be noted that in order to put the cassette 54 in place, the bar 30 must be moved against the action of the spring 46, by acting on the boss 29 and thus move said bar away from the contact 49 of the switch 47, so that the circuit general electrical of the marine to be soldered is closed.

 The feeler member 28 crosses the opening 64 of the cassette 54 and abuts against the roller of the strip 59.

 When welding is ordered, the conduits 82 and 83 are at the intake, while the conduits 84 and 85 are in the open air. The electrodes and 2 are brought together to tighten the sheets 5 and the part of the strips. 59 inserted between said electrodes and the sheets.

 After the welding point has been made, the spacing of the electrodes 1 and 2 is controlled, the conduits 84 and 85 being at the intake while the conduits 82 and 83 are at the exhaust.

 When the electrodes 1 and 2 are separated by the conduits 87 and 88 of the compressed air is sent into the jacks 9 of the devices 6 and 6a.

The piston of the jack 9 moves against the action of the spring 11 and the thrust head 12 by bearing against the lever 15 makes it pivot in the direction of the arrow "f" against the action of the spring 19.

 The pawl 17 cooperating with the teeth of the ratchet wheel 18 drives the latter so that a certain length of strip 59 is wound on the roller 56.

 The conduits 87 and 88 are then vented by the distributor 80 and, under the action of the springs 11, the jacks 9 return to their initial position.

 The same process is reproduced with each welding and thus at the welding point is deposited a copper-coated alloy film itself protective, and it is avoided that part of the coating of the sheets adheres to the electrodes.

 It will be noted that the rod 13 of the piston of the jack 9 h each cycle moves by the same length and that the thickness of the supply roller of the strip 59 decreases, while the thickness of the take-up roller (roller 56) increases so that for a constant angular displacement of the lever 15, the length of strip 59 wound on the roller 56 when the thickness of the feed roller is large would be small whereas on the contrary, when the diameter of the take-up roller is large, the length of strip 59 wound on said roller 56 would be much more important. In order to avoid this drawback, and to obtain after each welding point a displacement of a constant length of the strip 59 independently of the respective diameters of the supply and take-up rolls, the device plans to reduce the angular displacement of the lever 15 as the diameter of the take-up roller increases.

 The free end of the plate 38 is arranged so as to constitute a stop 38a against which the lever 15 can come to bear.

 In FIG. 3, it has been assumed that the supply roller is full while the take-up roller is practically empty. At each movement of the rod 13 of the piston of the jack 9, the lever 15 will pivot in the active direction (direction of the arrow f) by an angle corresponding to the stroke of the piston.

 As the diameter of the strip 59 winding on the roller 56 increases, the diameter of the supply roller decreases and thus the feeler member 28 moves under the action of the spring 46, the pads 32 and 38 thanks at their elongated slots 33, 39 and 40 moving in the direction of the side of the housing 7 adjacent to the axis 16. Thus, the stop 38a is located on the return path of the lever 15.

 As the diameter of the take-up roller grows, the stop 38a stavançant, the active stroke of the lever 15 decreases. As can be seen in FIG. 8, as the stop 38a stops a return to the initial position of the lever 15 under the action of its spring 19, when the jack 9 is under pressure, part of the stroke of the pusher head 12 is carried out without touching lever 15.

 Such an arrangement is simple, safe and uncomplicated and ensures great regularity in the pitch of movement of the strip of strip 59.

 When the bard 59 has been completely debited and that, consequently, the roller 55 is empty, the bar 30 touches the contact 49, which opens the control circuit of the assembly so that the machine stops.

 A circuit could be provided to indicate that the supply roller is empty, or is almost empty, circuit controlled by the switch 47 and controlling an audible or visual signal.

 In the embodiment shown, it was assumed that the electrodes 1 and 2 were both movable vertically. the device according to the invention could also be adapted to welders of which only one electrode would be mobile. In this case, the movement of the strip of strip 59 would take place after the removal of the sheets when the welding point has been achieved.

 Of course, the invention is not limited to the embodiment which has just been described and which has been shown, it is possible to make numerous modifications of details without departing, for this, from the scope of the invention.

Claims (7)

CLAIMS 10 - Device adaptable to a resistance welding machine using coated steel sheet points, the ladi welding machine comprising several electrodes (I, 2)> welding electrically connected to one or more secondary windings of a transformer including the primary winding is intended to be connected to an alternating current source, characterized in that it comprises means (50) for supporting a roll (55) with a strip of a strip (59) of a binding of copper and a material compatible with the coating of the sheets to be welded (5), means (60, 72) for guiding the strip (59) of strip to insert the latter between the sheets to be welded (5) and the corresponding electrode (2), and cores to control the movement of the strip (59) after each weld has been made.  20 - Device according to claim?, Characterized in that it comprises feeler means (28) for checking the length of the roller (55) of the leaf strip (59), said feeler means (28) being inserted on an eyelash signaling bed.  30 - Device according to claim I, characterized in that it comprises means (56) for receiving the strip of strip (59) for winding the part of said strip remaining after the po S s of welding and means (I2-I5) for controlling the winding. t of said part of the strip after each weld has been carried out.  4 - Device according to claims # 'iions I and 3 characterized in that it comprises a housing (7 provided with an axis (50) for receiving a roll of the strip i strip (59) a second motor axis (24) intended to support n roller (56) for receiving the part of the strip remaining close to the production of the welding points, said second motor axl (24) being integral with a ratchet wheel (I8) with which a pawl (I7) cooperates ) carried by a movable lever (I5) against the action of a return spring (I9) and a single-acting pneumatic cylinder (9) whose free end (I2) of the piston rod (I3) is arranged so as to push the linier (I5) against the action of the return spring (19) when e jack (9) is pressurized.  50 - Device according to claim 4, characterized in that it comprises means (28,38) for modifying the value of the angular displacement of the motor axis (24) as a function of the thickness of the strip part remaining after the production of the weld points wound on the receiving roller (56).  60 - Device according to claims 2, 4 and 5, characterized in that the feeler means (28) comprise a finger intended to cooperate with the roll of the strip of strip (59) said finger being pcrté by a sliding assembly diametrically relative to to the axis of said roller (55) and connected to elastic means (46) tending to apply said finger (28) against said roller (55), said assembly comprising a movable stop (38a) to limit the return stroke of the lever (I5) as a function of the thickness of the roller (55) of the strip of strip (59).  70 - Device according to claim 4, characterized in that the roller (55) of the strip of strip (59) and the receiving roller (56) of the part of the strip of strip remaining after the completion of the welding points are housed in a cassette (54) the housing (7) being provided with elastic means (53) for fixing the cassette (54).  80 - Device according to claim 4, charac terized in that it comprises manual means (67) for controlling the rotation of the ratchet wheel (I8).  90 - Device according to claim I and claim 4, characterized in that the means for guiding the strip of strip are constituted by profiles in C (72,73) of insulating material fixed to the housing by elastic clips (7).