SU1611642A1 - Method of controlling the welding current in resistance spot welding on single-phase machines - Google Patents

Abstract

The invention relates to mechanical engineering, namely to welding technology, and can be used in equipment for controlling welding. The purpose of the invention is to improve the quality of welded joints. First, reference welding is carried out in the absence of disturbing factors. At each time point is determined COSφ, a correction value N heating is performed according to the formula N = N _{e e} SOSφ / COSφ, where N _e - heating a predetermined value for the master part, determined in advance excluding disturbing factors

COSϕ _e , COSϕ are the power factors for the reference part and the actual process, respectively. This makes it possible to compensate for disturbing factors in the welding circuit. 4 il.

Description

This invention relates to the field of welding, in particular to AC contact welding machines.

The purpose of the invention is to improve the quality of welding by compensating for disturbing factors in the welding chain.

FIG. 1 shows the equivalent s.hema welding circuit in welding under reference conditions (in the absence of disturbances); in fig. 2 - the equivalent circuit of the welding circuit in welding with the introduction of magnetic masses in the welding circuit; in fig. 3 - equivalent circuit of the welding circuit with simultaneous change of the active resistance (shunting, electrode wear) and reactance (introduction of magnetic masses) of the circuit; in fig. 4 is a block diagram of a device implementing the proposed method.

The essence of the method is as follows.

The magnitude of the welding current is one of the most important parameters of the welding process. In this case, the welding current is understood as the effective value of the current flowing in the secondary circuit of the machine, which does not correspond to the current in the welding zone. The main task of the welding current control system is to change the turn-on angle of the thyristors so that the value of the welding current through the welding zone corresponds to the specified value of the heating value, which is defined as the ratio of the specified welding current to the full-phase current on a given load:

/ „

C5

Oi 4 GO

 and about

/

(one)

where 4 is the effective value of the welding

current;

Uc is the network voltage; Z - secondary impedance

contour;

K - transformation ratio. The current is stabilized by setting the thyristor switching angle in accordance with the formula

 fnift e

V

where boVi b - parameters of the regulating characteristic of the machine, determined by the magnitude of the angles on - t / .. 6,

--f, C2

To calculate the active resistances of a part and a shunt point, the formulas proposed by A. S. Gelman were used, and for calculating the inductance of a part made of J. magnetic material, the formula was written by KA Kochergin. For comparison, the values of currents obtained without compensation of disturbances are given.

The implementation of the proposed method is possible with the help of a device based on 10 micron computers, which stabilizes the welding current during mains voltage fluctuations with the measurement of cosff.

The basis of the device (Fig. 4) is a microcomputer 1, to the counting input of which through

......, iiv I4ll., J 1, DiXklirW i., l ij LS1 1 1 PGIGG OLID weight and 4CUC3

and the conductivity of the welding. | g key 2 generator 3 receives a pulse circuit. The time determined by unit 4 of the initial welding is performed at this measurement of the conduction angle of the thyristors, which opens the key 2 while the thyristors are in the wire condition. As a result, the counting output of the microcomputer in

conditions under which the required heating value is determined and fixed

NS i) system power factor at -.7 - .. MHI PUJDJVI's osclide

the reference load costp, then, when welding each 20 half-period, the number of impulses of parts arrives in perturbation conditions and sets the values proportional to the angle of conduction

thyristors. The analog input of the microcomputer of the conversion unit 5 is supplied with the voltage (2). proportional to the current sign f - - -vi j ij / iy uvy jiriy P ri n J Qf

heating rank based on the formula

.. but

network voltage.

The values of L / j and Safr in accordance with the scheme in FIG. 1 are defined as:

N - / s - / (U (,) H (w-, G

CO5f5

"WITH

J

(3)

we understand that

vr K + 4f4-V-)

Then, in reality, the required amount of heating is determined by formula (2). In the case of introducing magnetic masses into the cohort (Fig. 2), the magnitude of the effective current value will remain the specified - / 3.

In the case of a combined effect of shunting perturbations, electrode wear and deposited magnetic masses (Fig. 3), the fraction of the current flowing through the part (),

R-b ± Rg

+ / & + 7 & -wi Considering that Ky, by

for dependency (2)

 As an example, consider the cases of electrode wear, shunting and the effect of introducing reactivity into the contour during welding of 1 + 1 mild steel. The following parameters of perturbation were taken: for shunting, the shunt point is located at five diameters of the electrode; for electrode wear — the electrode is worn from 5 mm to 6 mm in diameter of the contact spot; for depositing magnetic masses - the size of sheets being welded is 0.4X0.4 m. The calculation results are shown in the table.

To calculate the active resistances of the part and the shunt point, the formulas proposed by A. S. Gelman were used, and to calculate the inductance of a part made of magnetic material, the formula was used by KA Kokorgin. For comparison, the values of currents obtained without compensation of disturbances are given.

The implementation of the proposed method is possible with the help of a device based on microelectronics, which stabilizes the welding current during mains voltage fluctuations with the measurement of cosff.

The basis of the device (Fig. 4) is a microcomputer 1, to the counting input of which through

 i., l ij LS1 1 1PGIG1 OLiD weights and 4CUC3

key 2 from generator 3 receives pulses during the time determined by block 4 and the second opens key 2 while the thyristors are in the conducting state. As a result, the counting output of the microcomputer in

 -.7 - .. MHI PUJDJVI's Osclid

 each half period receives the number of pulses proportional to the angle of conductance

thyristors. The analog input of the microcomputer of the conversion unit 5 is energized. proportional to the sign

network voltage.

The welding current is controlled by the counting output, which turns on the thyristor contactor 6 at the moment of time, determined by the required switching angle and counted from the moment of transition of the network sinusoid through zero. This moment is highlighted by the cei-sync block 7. From the remote control and display panel 8, microcomputers are inputted from the parameters of the welding process and the measured value |;: o.9f is displayed.

The device works as follows. When welding in reference conditions in the first period of the mains voltage, the angle of conduction of the thyristors, l, po, changes. which formula

C0. Ci ,.

determined by cosff. This value is fixed in the memory of the microcomputer to be indicated

on the remote control 8. In addition, this value can be simply entered from the remote control, if it was measured earlier. When welding under perturbation conditions, also in the first half-period of the mains voltage, the angle K is determined by which

According to the value of heating L / C given from the control panel, the heating value N is corrected by formula (2). Then, the welding current is controlled by varying the firing angle a.

55

Claims (1)

Invention Formula The method of controlling the welding current in single-phase resistance spot welding machines, consisting in determining the turning-on angle of the thyristors of the welding machine depending on the obtained value of the heating value L, taking into account its effective value of the welding current, the impedance of the welding circuit and the network voltage, characterized in that in order to improve the quality of welding by compensating disturbing factors in the welding chain, c. each time point is determined power factor coscp, and the value of the heating value is calculated by the formula , 2, coif where Л and со5ф, is the amount of heating and the power factor of the system, determined during welding in the absence of disturbing factors. FIG. 7 , FIG. 2  H Phage.5 2 at (Rig.4