WO2007101669A1

WO2007101669A1 - Sequential parallel welding with computer-controlled switching devices

Info

Publication number: WO2007101669A1
Application number: PCT/EP2007/001947
Authority: WO
Inventors: Thomas Hansel
Original assignee: Gm Global Technology Operations, Inc.
Priority date: 2006-03-07
Filing date: 2007-03-07
Publication date: 2007-09-13
Also published as: DE102006010467A1

Abstract

A welding apparatus (1) for the spot welding of a plurality of sheet metal sections (16, 17) using a current supplied by a power source (2) has a plurality of welding guns (7, 8, 9) which each have a first electrode (10) and a second electrode (11). The first electrode (10) can be connected to a first pole (3) of the power source (2) and the second electrode (11) can be connected to a second pole (4) of the power source (2). To connect the first electrode (10) to the first pole (3), a switching device (5) is provided for each first electrode (10), wherein one switching device (5) connects the first electrode (10) assigned to it to the power source (2), while the other switching devices (5) do not connect the first electrodes (10) respectively assigned to them to the power source (2).

Description

Sequential parallel welding with computer-controlled

switching devices

Description

The invention relates to a welding device for spot welding of a plurality of sheet metal sections lying on top of one another with an electric current.

Such welding devices are known as welding tongs in the prior art, which are attached to the extreme end of a welding robot arm. The welding gun has a first jaw and a second jaw that can be operated by the robot. For spot welding, a laminated core is clamped between the first jaws and the second jaws and then a high welding current is sent through the first jaw and the second jaws. The welding current heats the laminated core in the area between the first jaw and the second jaw, the sheet material becomes liquid and connects to a spot weld. After the welding robot has completed a welding point, the first and the second jaws are opened and the welding robot moves them to the next welding point where the procedure is as above.

JP 3-230871 shows a capacitance spot welding machine having three welding electrodes. An AC voltage source is available via a plurality of control and switching devices, three capacitors and three transformers connectable to the three electrodes.

JP 3060875 shows a spot welding device with two welding guns, which are actuated by a pneumatic cylinder. The two welding guns are each connected via parallel-connected transformers to a common voltage source.

DE 674 769 and DE 765 468 show large and unwieldy welding devices that do not lead to satisfactory welds when used in motor vehicle construction.

In the devices known in the prior art is a disadvantage that welds are very time consuming. Moreover, the devices known from JP 3060875 and JP 3-230871 are disadvantageous in that they have a complicated structure and do not provide reliable welding results.

The invention is therefore based on the task of providing a welding system that is simple in construction and with which fast and reliable welding can be carried out.

This object is achieved according to the invention by the subject matter of the independent claims. Advantageous developments emerge from the respective dependent claims.

The invention in this respect includes a welding device for spot welding of a plurality of sheet metal sections which is powered by a voltage source and which is equipped with two or more welding guns, each having a first electrode or a second electrode, the first electrode having a first pole of the voltage source is connected and the second electrode is connected to a second pole of the voltage source and for connecting the first electrode to the first pole, a switching device is provided, which is connected to a central control unit, which selectively actuates the switching device, wherein the switching device, the control device so actuates that exactly one switching device connects the first electrode associated with the voltage source, while the other switching device or the other switching devices does not connect or connect the first electrodes associated with each other with the voltage source. In this case, the idle times between the welds, the duration of welds and / or the welding voltages or welding currents can be varied with the control unit according to the invention.

According to a further idea underlying the invention, a single voltage source or current source is used for a plurality of welding tongs or welding electrodes, wherein the current distribution to the various electrodes is effected by switches which are controlled by a central computer. This is done so that essentially always only one pair of electrodes is supplied with power. In this case, a commercial electric welding machine is used as a power source.

In a very simple embodiment, two or more welding guns are provided, each having a first electrode and a second electrode. In this case, the term "welding tongs ^w is to be understood more generally here, since the first electrode and the second electrode do not have to be able to be pivoted against one another like tongs. Rather, it is also possible to drive these linearly against each other when a laminated core brought between the electrodes to be welded. The first electrode is connectable to a first fol of the voltage source and the second electrode is connectable to the second pole of the voltage source. The invention is characterized by simplicity in that the first electrode and the second electrode of each welding gun each with the same

Voltage source are connectable. However, the invention is not limited to the provision of a single voltage source for the entire welding device. It is also possible to provide a plurality of voltage sources, provided that at least the electrodes of two welding tongs according to the principles of the invention are operated on a single voltage source.

In a very simple exemplary embodiment, in each case the first electrode can be connected to the first pole, specifically via a switching device. In this case, the switching devices for the connection of the first electrodes to the first pole of the voltage source can also be combined, as is the case with a mechanical switch. This then has a center contact, which can be selectively brought via a movement with the terminal contacts for the first electrode in combination. In this case, the switching device according to the invention is formed in each case by the connection contact for the first electrodes. The second electrodes may all be connected in parallel with the second pole of the voltage source. In a particularly advantageous embodiment, a switching device is also provided for each of these, so that selectively a respective first electrode and a second electrode of a welding tongs can be connected to the poles of the common voltage source.

The switching devices are connected to a central control unit, which selectively actuates the switching devices. The control unit actuates the switching devices so that exactly the first electrode associated with the voltage source, while the other switching devices do not connect their respective associated first electrode with the voltage source or expressly exclude these from the current flow.

The invention provides particularly reliable welded joints, because the invention avoids that secondary welding flows occur. This is understood to mean a welding current which flows from an electrode of a first welding tongs to an electrode of a second welding tongs, without this being desired. Such secondary welding currents reduce the electrical power generated at the spot weld, which is seen as the cause of unreliable welds. This is particularly well avoided, especially in the selective control of both the first electrodes and the second electrodes of the welding guns wired in accordance with the invention. But even then, if only one of the first electrodes is acted upon at a time with a welding current, results in a good welding result. Unlike in the case in which several first electrodes are supplied with welding current at the same time, in the procedure according to the invention no additional welding currents can be detected any more. This is attributed to the fact that it is very difficult to keep several parallel first electrodes simultaneously and always at the same voltage level. If this does not succeed, secondary welding currents are difficult to avoid due to the unpredictable small potential differences inside the laminated core.

The switching device can be designed as electrically or mechanically operable switch. In addition to a very simple mechanically operated switch, the as a connection contacts trained Schaiteinricntungen for the first electrode or for the second electrode of each welding gun provides, relays or thyristors can be provided. The control unit is advantageously designed as a computer or as a microcontroller, with the particularly flexible adjustments to predetermined mounting situations are possible.

The invention also relates to a welding robot with such a welding device, which is provided on the arm or at the fingertip. With such a welding robot, a welding device according to the invention can be moved in a particularly simple manner to a location provided for it, wherein the position and in particular the position and orientation of the individual spot welding points can be effected by conventional programming of the welding robot. If a welding robot in this way e.g. equipped with four welding guns, then there is a significant speed advantage over the previously known welding robots. The welding robot then need not approach each of the four spot welds individually, but it is sufficient to position the arm of the welding robot for all four welds once and then to supply with the invention successively the electrodes of his welding guns with welding current.

In a particularly advantageous embodiment, as many electrode pairs are mounted on a support or frame, as are necessary for welding a portion of a vehicle floor assembly or the entire vehicle floor assembly. After the rack is positioned on the vehicle floor assembly, the electrodes are brought together according to the procedure described above, and the welds are successively performed without loss of time by positioning individual welding guns. The invention is illustrated in the drawing using an exemplary embodiment.

FIG. 1 shows a schematic representation of a welding device according to the invention with three welding tongs,

FIG. 2 illustrates the flow of current through a welding tongs according to FIG. 1 at a first welding time,

FIG. 3 illustrates the welding current through others

Welding tongs from FIG. 1 at a second welding time,

FIG. 4 illustrates the welding current through a further welding tongs from FIG. 1 at a third welding time;

Figure 5 shows switching devices of another welding device according to the invention and

FIG. 6 shows the time profile of the welds according to FIGS. 2 to 4.

FIG. 1 shows a schematic representation of a welding device 1 according to the invention.

The welding device 1 has a DC voltage source 2 with a first pole 3 and with a second pole 4. Furthermore, a total of three switching devices 5 are provided, which are connected in parallel via a first supply line 6 to the first pole 3. In addition, a first welding gun 7, a second Welding tongs 8 and a third welding tongs 9 are provided, each having a first electrode 10 and a second electrode 11. Each first electrode 10 is connected via a short line piece 12, each with its associated switching device 5. The second electrodes 11 are connected to the second pole 4 via a second supply line 13. In this case, the second electrodes 11 are each connected in parallel.

A computer system 14 is connected via control lines 15 in each case to the switching devices 5 so that they can be selectively actuated. In this case, a connection between the first supply line 6 and the respective line piece 12 is produced in a selective operation.

Between the first pole 3 and the second pole 4, a laminated core is arranged consisting of a first metal sheet 16 made of sheet steel and a second metal sheet 17 made of sheet steel.

FIG. 2 illustrates the welding process in the region of the first welding tongs 7 at a time t = 0 sec. As can be clearly seen in this view, the computer system 14 via a control line 15, the first welding tongs 7 associated switching device 5 is operated so that selectively a current from the first pole 3 via the first lead 6 and the switching device 5 to the line piece 12 and first electrode 10 of the first welding gun 7 flows. From there, the welding current flows through the first metal sheet 16 and the second metal sheet 17 punctiform on the shortest path to the second electrode 11 - indicated by a small arrow - and via the second lead 13 back to the second pole 4. Thus, the material of the first metal sheet 16th and the second metal sheet 17 in the area between the first electrode 10 and the second electrode 11 in a punctiform manner. melted and welded on cooling. Thereafter, the switching device 5 of the first welding gun 7 is turned off.

At a time t = 0.5 sec. the switching device 5 of the second welding gun 8 is turned on. This process is illustrated by a welding current arrow in FIG.

After turning off the welding current to the second welding gun 8, the welding current at a time t = 1.0 sec. on the third welding gun 9 is turned on, as illustrated by Figure 4. There is a Schweißstrompfeil drawn at the third welding gun 9, while the other two welding guns are not traversed by electricity.

FIG. 6 shows the time course of welds. At the times 0s, 0.6s, 1.2s and 1.7s, the welding current is switched on at each pair of electrodes and switched off again at times 0.5s, 1.1s, 1.6s and 2.1s. The idle times in between are very short compared to the welding times, they are only about 0.1s. The welding stresses of the last two welds are also smaller by 1 kV than the first two welds. With the computer system can thus be easily ensured an adaptation to different sheet thicknesses.

As can be seen particularly clearly in FIG. 5, the switching devices 5 can also be designed as switching contacts of a rotary switch, wherein the first supply line 6 can be selectively connected to each of the switching devices 5 via a movable switching bridge 18, similar to a distributor for spark plugs. The switching bridge 18 is arranged on an axis 19 of an electric motor 20, which can be acted upon by a control line 15 of the computer system 14. If the electric motor 20 is designed as a stepper motor o. Ä., Then can Welding parameters such as welding time and the times for switching on and off can be flexibly selected. Likewise, the computer system may vary the welding voltages or the welding currents.

The first welding gun 7, the second welding gun 8 and the third welding gun 9 are attached to the fingertip of a welding robot, not shown here. Once the welding robot has attached the welding guns to the laminated core, so that the first welding gun 7, the second welding gun and the third welding gun 9 are positioned at the designated welding points, they are pressed against each other via a hydraulic, not shown here. The clamped therebetween first metal sheet 16 and the second metal sheet 17 can not slip against each other. Thereafter, the computer system 14 via the control line 15, the electric motor 20 in motion, so that the axis 19 begins to rotate slowly. As a result, the connection contacts 5 of each line section 12 are successively connected to the first supply line 6, whereupon set the welding currents shown in Figures 2 to 4, when the switching bridge 18 is rotated.

In a further embodiment not shown here, the switching devices 5 in FIG. 1 are designed as actuatable relays. Thyristors are also conceivable in order to connect the welding current to the welding guns one after the other. Reference sign

1 welding device

2 voltage source

3 first pole

4 second pole

5 switching device

6 first supply line

7 first welding tongs

8 second welding tongs

9 third welding tongs

10 first electrode

11 second electrode

12 line piece

13 second supply line

14 computer system

15 control line

16 first metal sheet

17 second metal sheet

18 switching bridge

19 axis

20 electric motor

Claims

claims

Welding device (1) for punctiform welding of a plurality of sheet metal sections (16, 17) with a current supplied by a voltage source (2), wherein the

Welding apparatus (1) comprising the following features: two or more welding tongs (7, 8, 9) each having a first electrode (10) and a second electrode (11), - the first electrode (10) is connected to a first pole (3) connectable to the voltage source (2) and the second electrode (11) is connectable to a second pole (4) of the voltage source (2) for connecting the first electrode (10) to the first pole (3) for the first one Electrode (10) one each

Switching device (5) provided

- The switching devices (5) are connected to a central control unit (14) which selectively actuates the switching means (5), - the control unit (14) actuates the switching means (5) for welding so that exactly one switching device (5) hers associated first electrode (10) with the voltage source (2) connects, while the other switching device or the other switching devices (5) their respective first associated

Do not connect or connect electrodes (10) to the voltage source (2).

2. Welding device according to claim 1, characterized marked, that in each case a switching device is provided for connecting the second electrode to the second pole for the second electrode, wherein the control device actuates these switching devices so that exactly one switching input Direction associated with the first electrode and its associated second electrode to the voltage source, while the other switching device or the other switching means does not connect their respective associated first electrode and its associated second electrode with the voltage source.

3. Welding device according to claim 1 or claim 2, characterized in that for the respective welding gun (7, 8, 9) a mechanical actuator for

Compressing the first electrode (10) and the second electrode (11) are provided.-

4. Welding device according to one of the preceding claims, characterized in that the switching device (5) is designed as an electrically or mechanically operable switch, in particular as a relay or as a thyristor.

5. Welding device according to one of the preceding claims, characterized in that idle times between

Welds are short compared to the welding times.

6. Welding device according to one of the preceding claims, characterized in that welding stresses can be formed differently from one welding point to another welding point.

7. Welding device according to one of the preceding claims, characterized in that the control device is designed as a computer (14). Welding robot with a tail device according to one of the preceding figures, which is provided at the fingertip of the robot.