DD203840A1 - PROCESS AND CONTROL ARRANGEMENT FOR RESISTANCE WELDING - Google Patents

Abstract

The method and the control arrangement for controlling the electrical work in the resistance welding of preferably chain links with a constant period Schweiszverfahren allow it to supply a Schweiszstelle in a certain time a precisely defined amount of energy, thereby gleichmaeszige and reproducible Schweiszverbindungen be realized, which ensures an increased Schweiszsicherheit. The essence of the invention lies in supplying a welding unit with a defined amount of energy corresponding to a nominal value during each half-cycle of the network. This is done by switching on the supply of energy to the welding point under specification of a phase-angle of incidence within each half-period causing the fuse, and switching it off within one and the same half-cycle after reaching a working integral corresponding to a nominal value for the respective half-cycle of the network. For controlling the electrical work preferably turn-off thyristors are used.

Description

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Method and control arrangement for resistance welding

Field of application of the invention:

The invention relates to a method and a control arrangement for controlling the electrical work in resistance welding of preferably chain links in the case of a constant period number welding process, whereby uniform welding processes and reproducible welds and increased welding safety can be achieved.

Characteristics of the known technical solutions : There are several known methods and control arrangements with the aim to compensate for electrical disturbances in resistance welding. The constantly increasing quality requirements for the welded joints presuppose ever closer toleration of the welding parameters, which in turn makes the disturbance variable compensation more important and ever better control and control methods are used. Previous methods are based on various principles, which are more or less ridiculous.

Compensation circuits are known for Fetzspannungsschwankungen, wherein the phase angle of the welding voltage is controlled in dependence on the Hetzspannung. A smaller IT voltage has one

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smaller. P.hasenanschnitt, a larger Hetz spännung result in a larger phase angle · Since no machine-related "disturbances are taken into account," the supplied welding energy moves in a relatively large tolerance range.

Controllers with a closed course of action work much more precisely. Different methods use different output variables as actual values. In general, the ".. welding current and / or the welding voltage" is measured and, depending on the method, the resistance or integration over time results in the welding energy. One of these measured or determined variables represents the actual value and is compared with reference values obtained by trial welding. In case of deviations of the actual values from the ·. Setpoints are controlled by a change in the phase angle of Uetzwechselspannung, .Zwar be at. However, the control over the phase angle can, however, earliest, during the following ITe tz-. half-period. Such control methods are described in DE-OS 2346561 and DE-OS 2526870. They are disadvantageous in welding processes with a low welding period number if a certain amount of energy is to be supplied to the welding point during each setting half-period.

Furthermore, methods are known according to which the welding point is supplied with a certain amount of electrical work in a welding time which is not to be observed, generally lasting several periods. Such methods are described in der.DE-OS 1690558 and DE-OS 1765801. The realization of these methods takes place in such a way that the work supplied to a welding point is determined and after reaching a

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  desired overall work, the supply of additional electrical energy is switched off, without the exact compliance of the welding voltage and the welding time. must be respected. The disadvantage here is that the welding machines and the welding process must allow a tolerance of the welding time in. A certain range, which can not always be realized, and that the shutdown of the power supply can be done only at Uulldurchgang the Ifetzwechsel voltage, wordurch. from the outset, there is a solar energy range of the welding energy,

A method for more accurate energy dosage. Is described in DE-OS 2322748. Here, after reaching the total energy to be supplied to the welding zone, the supply of further energy until the zero crossing of the period just causing the welding is drastically reduced by short-circuiting a second secondary winding of the welding transformer by means of a thyristor. Although this method allows a more accurate energy input to the weld than previously mentioned, much of the electrical energy is converted into waste heat from shorting the second secondary to the zero crossing of the AC mains voltage an application to

8.5 existing welding machines is not possible.

With the described method it is not or only approximately possible to supply a precise amount of energy to a weld in a certain time. Since the demand for ever higher weld quality exists, it is necessary to dose the energy supply to the weld quantitatively and in terms of time

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Aim of the invention;

The object of the invention is to provide a method and a control arrangement for controlling the electrical work in the case of continuous welding, with which it is possible to realize uniform and reproducible welded joints as well as increased welding safety compared to known methods.

Essence of the invention

The invention has for its object to provide a "method and a control arrangement for controlling the electrical work in resistance welding, which make it possible to supply the welding point / each power half-period, a setpoint corresponding, defined amount of energy, which does not esaktakt previously known solutions could because the technical requirements were missing *

According to the invention, the object is achieved in that 10 within a Setzhalbperiode the power is switched to • weld and turned off after reaching a certain, ein.-setpoint corresponding work integral within the same half-cycle, so that exactly the necessary for the welding in the jell 5-half period necessary Within a welding process, the amount of energy to be supplied can be variable from half-period to half-period.

The detection of the work integral ü · 1 · dt flowed into the weld takes place in a manner known per se by measuring the power converted in the weld, which is optionally determined from the difference between total power and power loss via shunts and their integration over time,

236823 2 .The work integral thus obtained serves as criterion for the switching off of the ^z ufuhr further electrical energy. According to the invention, this is achieved in that, depending on the respective network half-period of a welding operation, a nominal value corresponding to the amount of energy to be supplied is provided. This setpoint 'is compared with the working integral of the respective half-period. If the working integral reaches the size of the setpoint, the power supply is switched off on the primary side of the welding transformer by means of so-called turn-off thyristors, the thyristor ignited in the thyristor actuator is extinguished.

The switching on of the power supply to the weld takes place within a network half-period by igniting the respective forward biased turn-off thyristor Thyristorstellers, but at the latest at such a time that in the remaining part of the truncated network half period at least the setpoint of the respective half-period corresponding amount of energy Welding point can be supplied. The phase angle can be variable with respect to a secured power supply for each half-period variable for a small amount of energy to be supplied a large phase angle and vice versa, so that the shutdown of the power supply after reaching the setpoint near the Hulldurchgang the mains voltage. This ensures that the welding transformer is switched off in a region of low magnetic saturation.

The phase angle and the target value of the energy to be supplied are determined by trial welding.

The control arrangement can work analog and / or digital.

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Embodiment · · ·

The invention is illustrated by means of an embodiment.

FIG. 1 shows a control arrangement for implementing the JO method, and FIG. 2 shows a correspondingly controlled welding current. , , , There is a welding current half-cycle counter 1, which counts the number of half-periods necessary for a welding process and emits electrical signals corresponding to the respective half-period, in whose dependency a setpoint generator 2 supplies the desired value of the energy to be supplied for the relevant half-cycle Form of electrical signals to a trigger 3 are. The trigger 3 uses this, the setpoint corresponding.

ΙΌ electrical signals as switching threshold for coming from a measuring system 7, the Arbeitihtegral corresponding electrical signals. If the working integral reaches the size of the setpoint, the trigger 3 generates an electrical impulse with which the in

f5 a thyristor 5 according to the respective half-wave in the forward direction poled and ignited, turn-off thyristor is cleared and thus the energy flow from Fetz, is interrupted to a welding transformer 6. '

An ignition stage 4 ensures the ignition of the thyristor in the forward direction 5 each thyristor. The welding current half-wave counter 1 generates electrical signals corresponding to the respective half-cycle, in which the ignition stage determines the phase angle for the relevant half-cycle.

It can be seen from the welding current shown in FIG. 2 that different phase angle angles are selected for different amounts of energy to be supplied in such a way that the shutdown of the welding current takes place near the zero crossing.

Claims (5)

claims 1 · Method and control arrangement for resistance welding of preferably chain links, wherein the working point inflowing the welding point is determined in a manner known per se, characterized in that the energy supply to the welding point is switched on within each half-period causing the welding, and after reaching a target value for the relevant last half-period corresponding work integral. , is switched off within the same Uetzthalbperiode. ' 2 «method and control arrangement according to item 1, characterized in that for controlling the electrical work preferably turn-off thyristors are used. 3, method and control arrangement according to item 1 and 2, characterized in that the turn-off thyristors, of which in the respective Uetz-. given a half-period of a weld-dependent energy dependent phase angle, which is large for small 'amounts of energy to be supplied, ·· and small for large amounts of energy to be supplied. 4 · Method and control arrangement according to item 1-3, characterized in that the shutdown of Supply of additional electrical energy. Deletion of the turn-off thyristors is done. ~ 5. Control arrangement according to item 1-4 characterized in that a welding current half-period counter (1) a setpoint generator (2) and an ignition stage (4) are connected downstream, the ignition stage '(4) with a thyristor (5) and this with a welding transformer ( 6) is connected, while the setpoint generator (2) ~ with a "trigger" (3) "and this with the thyristor (5) is connected and" the trigger (3) is preceded by a measuring system (7). For this 1 sheet drawings