DE3301039A1 - Method and control arrangement for resistance welding - Google Patents

Abstract

The method and the control arrangement for controlling the electrical work during resistance welding of, preferably, chain links using a welding process which operates with a constant frequency make it possible to supply a precisely defined quantity of energy at a specific time to a welding point, as a result of which uniform and reproducible welded connections are implemented which ensures an increased welding reliability. The object of the invention is to supply a defined quantity of energy corresponding to a desired value to a welding point during each mains half cycle. This is done by switching on the energy supply to the welding point, subject to a preset phase-gating angle, during each mains half cycle which causes the welding, and, once a work integral corresponding to a desired value for the relevant mains half cycle has been reached, being switched off within the same mains half cycle. Turn-off thyristors are preferably used for controlling the electrical work. <IMAGE>

Description

Method and control arrangement for resistance

welding The invention relates to a method and a control arrangement to control the electrical work during Wideratanda welding ton preferably Xette links in welding processes that work with a constant number of periods, resulting in uniform Welding processes as well as reproducible welded joints and increased welding reliability be achieved.

There are several known methods and control arrangements designed to to compensate electrical disturbances during resistance welding. The steadily increased Quality requirements for the welded connections place ever closer tolerances the welding parameters ahead, which in turn makes disturbance compensation more important wins and ever better regulation and control procedures are used.

Other procedures are based on different principles, some more or less disadvantageous.

Compensation circuits for mains voltage fluctuations are known, where the phase angle of the white voltage depends on the mains voltage is controlled. A lower line voltage has one smaller phase length; a larger mains voltage a larger phase angle to the pole. Since here no machine-related disturbance variables are taken into account, the supplied one moves Welding energy in a relatively large tolerance range.

Controls with a closed action sequence 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 process from this the resistance or, through integration over time, the welding energy. One of these measured or determined variables represents the actual value and is displayed with compare setpoint values obtained by test welds. If the Actual values from the setpoints are controlled by changing the phase control angle the alternating mains voltage.

Although disturbance variables are detected in this method, the adjustment However, the phase intersection angle can be used at the earliest during the following Grid half-period. Such control methods are in DE-OS 2346561 and the DE-OS 2526870 described, you are in welding processes with a low number of welding periods disadvantageous if during each net half cycle of the welding point a certain Amount of energy to be supplied.

Furthermore, methods are known, according to which the weld in a Welding time that cannot be adhered to exactly and usually lasts for several periods a certain electrical work is supplied. Such methods are in the DE-OS 1690558 and DE-OS 1765801 described. The implementation of these procedures takes place in such a way that the work performed on a welding station is determined and by Achievement of a overall work want the supply of further electrical ones Energy is switched off without having to adhere to the exact welding voltage and the welding time must be observed. The disadvantage here is that the welding machines and the welding process allow a tolerance of the welding time in a certain range must, which can not always be realized, and that the shutdown of the energy supply can only take place when the mains AC voltage crosses zero, which means that ton is present from the outset there is a tolerance range for the sole energy.

A method for more precise energy metering is described in DE-OS 2322748 described. Here, after reaching the welding zone, the total energy to be supplied the supply of further energy until the zero passage of the one which is just causing the weld Period drastically reduced by adding a second secondary winding to the welding transformer is short-circuited by means of a thyristor. This method allows one more precise energy supply to the welding point than the previously mentioned method, however is from the second secondary winding until the zero crossing of the mains alternating voltage a large part of the electrical energy is converted into waste heat. This procedure is on a corresponding welding transformer tied with two secondary windings, which means that it cannot be used on tor-hand welding machines.

With the procedures outlined, it is not or only approximately possible, to supply an exact amount of energy to a welding point in a certain time.

Since there is a demand for ever higher welding quality, it is necessary to dose the energy supply to the welding point quantitatively and precisely in terms of time can.

The aim of the invention is to provide a method and a control arrangement to control the electrical work in resistance welding with which to create it is possible to have uniform and reproducible welded joints as well to realize increased welding reliability compared to known methods.

The invention is based on the object of a method and a control arrangement to control the electrical work in resistance welding to create the it enable the welding point to have a setpoint value during each network half-cycle corresponding, defined amount of energy to supply what previously known solutions did not finish exactly because the technical prerequisites were lacking.

According to the invention, the object is achieved in that within a The power supply to the welding point is switched on and after it has been reached of a certain degree of work within the same, corresponding to a target value Half-period is switched off, so that exactly the one for the welding in the respective Half-period necessary energy is supplied.

The amount of energy to be supplied can be used within a welding gate be variable from half-period to half-period.

The recording of the work integral that has flowed to the welding point U. I. dt takes place in a manner known per se by measuring the in the weld implemented service, which may be made up of the difference ton health service and Power loss is determined via shunts and their integration via the Time.

The work integral obtained in this way serves as a criterion for the shutdown the supply of further electrical energy.

According to the invention this is done in that, depending on the the respective network half-cycle of a welding process, the amount of energy to be supplied corresponding setpoint is provided. This setpoint is combined with the work integral of the relevant half-period. If the working integral reaches the size of the setpoint, the energy supply is switched off on the primary side of the Welding transformer by means of so-called disconnectable iyristors in the thyristor controller each triggered thyristor is extinguished.

The energy supply to the welding point is switched on within a mains half cycle can be switched off by igniting the polarized in the forward direction Thyristor of the thyristor controller, but at the latest at such a point in time that in the remaining part of the grid half-period, at least the dea Amount of energy of the welding point corresponding to the setpoint of the respective half-period can be fed.

The phase control angle can be adjusted taking into account a secured energy supply be variable for each half-cycle for a small amount of energy to be supplied a large phase cutting angle and vice versa, so that the power supply is switched off takes place after reaching the setpoint close to zero crossing of the mains voltage. Through this it is achieved that the welding transformer is less magnetic in a region Saturation is turned off.

The phase cutting angle and the target value of the incoming energy are determined by test welds.

The control arrangement can operate in an analog and / or digital manner.

The invention is illustrated using an exemplary embodiment.

FIG. 1 shows a control arrangement for implementing the method and FIG. 2 shows a correspondingly controlled welding current.

There is a welding current half-cycle counter 1, which for one The welding process counts the necessary number of ton periods and depends on the respective Half-cycle emits electrical signals, depending on which a setpoint generator 2 the setpoint of the energy to be supplied for the relevant half-period in Porm electrical signals to a trigger 3. Trigger 3 uses this, the setpoint corresponding electrical signals as a switching threshold for that of a measuring system 7 coming electrical signals corresponding to the work sintegrally. Achieved the working integral the size of the setpoint, the trigger 3 generates an electrical one Pulse with which the in a thyristor controller 5 corresponding to the respective half-wave In the forward direction polarized and ignited, disconnectable 9! hyristor is extinguished and thus the flow of energy from the network to a Sohweißtranstormator 6 interrupted is, An ignition stage 4 ensures the ignition of the IhY-ristorstellers 5 in each case forward polarized thyristor. The welding current half-cycle counter 1 generates electrical signals corresponding to the respective half-period, depending on their dependence the Zundstufe 4 specifies the phase control angle for the relevant half cycle.

The phase control angle may only be so large that one energy supply is guaranteed according to the target value, At the one in figure 2 it can be seen that for different amounts of energy to be supplied different phase control angles can be selected so that the welding current is switched off takes place near the zero crossing.

L e r s e i t e

Claims (5)

Method and control arrangement for resistance welding ton preferably chain links, with the work integral accruing to the welding point is determined in a known manner, characterized in that within Every half-cycle that causes the weld provides energy to the welding point switched on and after reaching a target value for the relevant network half-period corresponding work integral is switched off within the same network half-period will. 2. The method and control arrangement according to claim 1, characterized in that, to control the electrical work, chyristors which can preferably be switched off be used. 3. The method and control arrangement according to claim 1 and 2, characterized by the fact that the thyristors can be switched off, of which in the respective mains half-period The energy to be supplied to a weld depends on the phase angle which is large for small amounts of energy to be supplied and small for large amounts of energy to be supplied Amounts of energy. 4. The method and control arrangement according to claim 1-3, characterized in that the shutdown of the supply of further electrical energy by extinguishing the thyristors that can be switched off. 5. Control arrangement according to claim 1-4, characterized in that a welding continuous period counter (1), a setpoint generator (2) and an ignition stage (4) are connected downstream, the ignition stage (4) with a thyristor controller (5) and this is connected to a welding transformer (6) while the Setpoint generator (2) with a trigger (3) and this with the thyristor controller (5) Is connected and a measuring system (7) is connected upstream of the Triggr (3).