DE4322496C2 - Arrangement for CNC controlled resistance welding - Google Patents

Description

The invention relates to an arrangement for CNC controlled resistance welding according to the in Preamble of claim 1 specified type.

Basically, it is known to be a welding head NC or CNC controlled welding machine for spot, Hump, press, roll seam, roll point and the like Resistance welding in the direction of the Z axis using pneumatic actuator to move linearly, i.e. in Regarding the workpieces to be welded, preferably Sheets to be delivered while pressing on the Workpieces that are required for welding Generate welding power.

The position determination by means of a pneumatic actuator cylinder is usually done by determining the End position of the actuating cylinder or the end positions, if Multi-position cylinders can be used.

When using a single cylinder, the Infeed movement of the welding head onto the workpiece Welding electrode more or less hard on the work piece on. In addition, there is a longer pre-pressing time necessary before starting the welding process. Will the Prepress time reduced or even completely omitted, so at the time of reaching the final position of the position cylinder the welding current is switched on, so caused the impact force in the first milliseconds of the Welding process a significantly reduced Resistance, what with resistance welding at the beginning of the  Welding process leads to incorrect welding. At the Hump welding, for example, warms everyone Hump only slightly and is caused by the over Actuating cylinder generated welding force compressed, so that only undesirable at the welds so-called adhesive welds can be achieved.

Are multi-position cylinders for the delivery of the Welding head is used, so the on impact of the welding head on the welded part Workpiece reduced when the end position is reached and as a result of the preset delivery route lowers the welding electrode or welding tool is depressurized up to approx. 1 to 2 mm above the upper edge of the workpiece. This is followed by the welding power being constructed. During this process, the Electrode also on the workpiece and it must, to achieve good welding quality, a Prepress time of approx. 20 periods (when using 50 Hz Alternating current) = 0.4 sec duration before the actual welding process can be carried out can.

Such a method has a particularly disadvantageous effect in the case of roller seam welding over longer welding distances, since this usually requires the necessary welding power cannot be kept constant at all times.

A generic arrangement for the resistance welding is in the German utility model DE 89 10 447 U1 discloses. This resistance sweat arrangement is with a delivery device and a independent air cylinders. However, this welding arrangement is used only for projection welding. With this Arrangement is intended to apply a welding pressure to each welding hump and the welding head  is adjusted during the hump welding process. Here, both by means of the delivery device the welding pressure also by means of the compressed air cylinder generated.

However, this arrangement has the disadvantage that the Welding pressure cannot be set exactly and is also not easily reproducible.

A resistance welding assembly is also out of the DE 37 43 341 A1 known, in which the delivery device is designed as a spindle drive.

The invention has for its object a Arrangement according to the preamble of claim 1 specified type in such a way that a more precise adjustment and improved reproducibility of the welding pressure is made possible.

This task is characterized by the characteristics of claim 1 in connection with its Oberbe grip characteristics solved.

The delivery device is used exclusively for Infeed of the welding head and not for generation the welding pressure.

While positioning the welding head in Rich The direction of the X, Y and Z axes is thus that for the applied welding methods required preselectable Welding pressure built up pneumatically and independently of Infeed movements of the welding head in the direction of the Keep the Z axis for the duration of the welding process.

The arrangement according to the invention works with a extremely small air chamber for generating the sweat force. According to an advantageous development of the  Invention is the printing of the welding program by means of a proportional valve to the size of the Welding power automatically set. This is it possible to sweat in a program memory process control up to 99 different welding forces Preset settings.

As a result of that according to a further embodiment used servomotor-controlled spindle drive can the welding head in the vertical axis with maximum Speed of preferably 24 m per minute the workpiece will be delivered, taking precautionary measures is taken that at the end of the delivery movement Impact force goes to zero, because with the help of a such servo motor the last millimeter of Delivery route driven at minimum speed can be. When gently putting on the sweat Electrode on the workpiece is due to this with the pneumatic actuating cylinders adjusted there Compressed air fed in slightly compressed So the welding electrode is cushioned when put on. At the same time, the servo drive is braked and the infeed position locked electrically.

With the delivery of the welding head is - as already mentioned - the pneu forming an integral component Matic actuators have also been adjusted, so that the welding force embodied by this at work piece also bears. At the end of the delivery movement the welding process can therefore begin immediately; a Prepress time before the start of the welding process is not more needed. Since the pneumatic actuator cylinder Proportional valve can be preset and the amount of Long-term pressure force via the proportional valve is held, especially when welding webs, in roll seam welding operation even over long sweats stretch a constant, high quality sweat  reproduce connection at every point of the weld decorable, so that such welded workpieces highest Meeting demands.

Another advantage of the arrangement according to the invention can be seen in that assigned to the Z axis neten, driven by an AC servo motor drove very fast infeed movements with infeed heights can be driven from up to 1 m, what with pneu matic multi-position cylinders not or only very is difficult to implement.

To create any curved seam lines between the welding tool and the Short stroke cylinder arranged a rotary drive.

The invention is based on one in the Drawing schematically illustrated execution example of an arrangement for delivering a Sweat  head in the Z-axis of a three-axis controlled CNC resistance welding machine described.

Show in detail

Fig. 1 is a view of an apparatus for Po sitionieren of a welding head of a CNC-controlled resistance welding machine in the direction of the Z-axis,

Fig. 2 is a circuit diagram for a welding pressure generating pneumatic cylinder assigned control arrangement, and

Fig. 3 is a plotted against the time axis tion diagram of the arrangement according to FIGS . 1 and 2.

A CNC-controlled Wi derstandsschweißmaschine not shown here has - as can be seen from Fig. 1 -, the machine frame 1 associated with vertical guide 2 , which carries a frame-fixed servo drive 3 and on which a support 4 in Z-Rich device arranged is. The support 4 carries a rotary drive 5 , the output of which is arranged coaxially aligned with the Z axis. The support 4 is further assigned 19 supporting the welding head 7 is an electrical feedthrough 6 and a one welding electrode. On the side facing away from the rotary drive 5 is a 5 rigidly connected to the housing of the rotary drive connected extremely short stroke double-acting trained, low Kammervolu men having Direction pneumatic cylinder 8 is arranged. The outwardly directed piston 9 of the pneumatic cylinder 8 is rigidly connected to an intermediate piece 10 . The intermediate piece 10 is guided on the one hand in the vertical guide 2 of the Z axis, and on the other hand forms the acquisition for a rigidly connected to the intermediate piece 10 ne spindle 11th Where the support 4 facing away from the end of the vertical guide 2, a bracket 12 is disposed opposite to the servo drive 3 on which a drivable through a belt 13 in Z-direction relative to the Ver tikalführung 2 held stationary about the Z-axis rotating bar mounted spindle nut 14 arranged which is in engagement with the spindle 11 . The intermediate piece 10 , the pneumatic cylinder 8 and the welding head 7 form a structural unit which is guided along the vertical guide 2 of the machine frame 1 and can be moved up and down via the spindle drive 11 in the direction of the Z axis.

The pneumatic cylinder 8 , as shown in FIG. 2, is constantly connected in its idle position via a control valve 15 to a compressed air source, not shown. If a new starting position is now to be approached, the CNC control of the welding machine (not shown here) that is not part of the invention passes a digitally coded welding pressure value via a line W to a proportional pressure valve P and switches a control valve 16 into its open position. At the same time, the servo drives, also not shown, of the axes X, Y and Z of the welding machine and of the rotary spindle drive 5 are controlled by the CNC control in a known manner in order to reach the new desired position. At the same time, the valve 15 is transferred into its blocking position and the valve 16 in its passage position. As a result, the compressed air is vented from the cylinder cylinder 17 above the line L1 and the control valve 15 . The control valve 16 is transferred from the CNC control to its open position and thus switches the pressure source via line L2 to the preset proportional valve P and the pressure source via line L3 to the lower cylinder chamber 18 , whereby the support 4 in Z- Direction rela tively to the moving in the Z direction via the spindle 11 moving intermediate piece 10 is moved.

From Fig. 3, the sequence of functions can be seen that the neces sary for the corresponding welding process welding pressure is built up during the start of the horizontal welding position, so that the Kurzhu bige pneumatic cylinder 8 before reaching the new welding position - in Fig. 3 the normalized time axis at position 1 - is already in its working position.

The functional sequences described above take place that is, simultaneously while positioning the sweat head in the direction of the X, Y and Z axes.

The welding process can now be carried out directly after the positioning process by switching on the welding current and carrying out the feed movement along the path to be welded. The welding force remains constant during the welding process itself. After reaching the weld end position - lying in Fig. 3 on the standardized time axis at point 3 - the welding current is switched off and the welding head is lifted by the servo drive 3 in the direction of the Z axis from the material to be welded. Then a new welding position can be approached by moving the X, Y and Z axes and the function sequence described above can be carried out again to produce one or more additional weld seams.

The welding pressure selected for the welding process used is applied pneumatically and, due to the small chamber volume of the pneumatic cylinder, can be kept constant over a long period of time, i.e. for the duration of the entire welding process, regardless of the feed movements of the welding head in the direction of the Z axis. The welding tool 19 of the welding head 7 is always gently on the material to be welded when approaching welding positions in the Z direction. Any impacts are cushioned by the pneumatic cylinder 8 .

After the desired welds have been carried out, the valve 16 is switched to its rest position and the lower cylinder chamber 18 is thereby vented. At the same time, the CNC control switches the valve 15 into its passage position, so that the upper cylinder chamber 17 is pressurized with compressed air from the compressed air source via the line L1 and so the welding head 7 from the welding position in the Z direction corresponding to the stroke Z ' of the pneumatic cylinder. Then, by moving the X, Y and Z axes, a removal position is approached in order to remove the finished weld metal and to be able to introduce new material to be welded into the welding machine.

When using vibration sensitive sweat electrodes as a welding tool it can be advantageous be a short after the positioning cycle Waiting cycle to precede the welding process to ensure safe to deliver that through the acceleration ver vibrations caused by the welding electrode have subsided.

By the inventive method and the through The proposed arrangement is the service life the welding rollers or tools significantly increase eats, which increases the cost of expensive welding tools leads to cost reduction. Also the Unit costs lower, since no pre-pressing times are necessary become manoeuvrable, and a greater throughput is possible , which means larger quantities in one unit of time are producible.  

The described configuration of the arrangement allows also previously unavailable delivery routes up to egg meters in the Z axis of welding machines of the ge named way to move quickly and at the same time one smooth delivery operation of the welding tools on and from the welding position.

The specific welding pressure for each welding process can be preset and during the welding process be kept constant over a long period of time. Hereby reproducible welding quality is achieved, so that quality inspection intervals can be reduced nen. At the same time, the operational reliability of the An increases order, because only with each new one to be welded Good at the beginning and at the end of the entire welding process a switching of the control valves is necessary.

The proportion of rework also decreases, which means that Rework costs are saved.

Finally, a wider variety of workpieces than previously produced on one system, whereby the space requirement within a production line decreases, and additional hall costs can be saved.

Claims (5)

1. Arrangement for CNC-controlled resistance welding with a feed device for feeding a welding head carrying a welding electrode in the Z direction, to which a pneumatic cylinder is assigned for setting the welding pressure, characterized in that the feed device ( 3 , 11 , 13 and 14 ) is in the respective setting position of the welding head ( 7 ) lockable in the Z-direction feed device ( 3 , 11 , 13 and 14 ), and that the pneumatic cylinder is a double-acting, short-stroke pneumatic cylinder ( 8 ), the pressure chambers ( 17 , 18 ) over One valve ( 15 , 16 ) each can be controlled in such a way that the preselectable welding pressure required for the welding process used is built up pneumatically during the positioning of the welding head ( 7 ) and independently of the feed movements of the welding head ( 7 ) in the direction of the Z axis for the duration of the Welding process is maintained. 2. Arrangement according to claim 1, characterized in that a control valve ( 16 ) is followed by a proportional valve (P), the setting of which is selectable for setting the welding pressure before. 3. Arrangement according to claims 1 or 2, characterized in that the lockable feed device ( 3 , 11 , 13 and 14 ), via a belt ( 13 ) and a spindle nut ( 14 ) by a servo drive ( 3 ) acted upon spindle drive ( 11 ) is. 4. Arrangement according to one of claims 1 to 3, characterized in that the pneumatic cylinder ( 8 ) and the welding head ( 7 ) along a vertical guide ( 2 ) of the machine frame ( 1 ) and form a structural unit which via the feed device ( 3 , 11 , 13 and 14 ) can be moved up and down. 5. Arrangement according to one of claims 1 to 4, characterized in that the welding head ( 7 ) via a rotary drive ( 5 ) is rotatably mounted about the Z axis.