SU1320033A1 - Method of controlling resistance welding - Google Patents

Abstract

The invention relates to welding production, in particular to methods for controlling pressure welding processes, and can be used in resistance welding equipment for the manufacture of critical welded structures from light alloys of steels and non-ferrous metals. The invention makes it possible to improve the quality of the welded joint. The control parameter used is the voltage acting on the welding circuit of the machine, which makes it possible to calculate from the results of measurements of the electrical parameters of the welding circuit, in particular, the voltage U between the electrodes, which has a direct connection with the quality of the welding. This method of obtaining information does not require the use of unreliable in-use voltage measuring sensors, which simplifies the adjustment of the control and monitoring system, increases the accuracy of calculations and the quality of welding. 1 silt, 1 tab. CO ND O Oh with so

Description

The invention relates to welding production, in particular, to methods for controlling pressure welding processes and can be used in equipment for contact welding to manufacture critical Welded structures from light slags, steels and non-ferrous metals.

The aim of the invention is to improve the quality of the welded joint.

The drawing shows a block diagram of a device for controlling and monitoring resistance welding processes,

In modern welding industry, welding machines with control systems based on the use of rigid software control methods with automatic compensation5 when exposed to external disturbances, certain parameters of the set mode, welding are used to make critical welded structures. It is known to use mathematical models to predict the quality of welded joints. Deterministic models that reflect the physical essence of the welding process, build using differential equations of thermal conductivity and electrical potential, and also take into account the influence of unstabilizing factors that occur during the operation of welding equipment in industry,

Typically, the quality of a welded joint is estimated by the size of the welded core. The resulting prediction error of this parameter is determined by the calculation error due to the incomplete correspondence of the mathematical description of the model to the actual process, measurement errors of welding mode parameters and electric welding equipment, calculation errors.

When used as a control voltage parameter acting on the welding circuit, the resulting error is minimized.

Indeed, the voltage U. can be measured with an accuracy of up to the fifth digit. Modern current sensors, for example, using the Hall effect, provide measurement errors of about one percent. Most of the parameters needed to build a deterministic mode

calculated using U. and 1 (-C. according to exact mathematical formulas, for example, the resistance of the welded

-t--, inductive circuit R, ..,

ck

ck

the strength of the welding circuit L (.,

J

where T is the rise time of current i to the value 0.632 of its steady-state value, the voltage of the electrode is the electrode and, UcK-ici is ck LcK

d icK

 33 CK SC IC jj s

Resistance electrode - electrode

energy released in the zone

ck

welding - welding (thermal) Q

-se

to

 0.24 5 Ugj-ICK-dt and others.

An important parameter of the mathematical model is the ratio of the resistance of the welding machine to the resistance of the welded part,

, as it defines a sustainable-. 39

the welding process during the wear of the working surfaces of the electrodes and the change in the value of the welding pressure Pgg due to the manifestation of the effect of self-regulation of the welding process, i.e. automatic increase of the welding current by increasing the contact area of the electrodes with the product. However, for most welding machines, this effect appears to be bad

Zh

exactly since

more need-ee

my

This lack of welding machines can be corrected by the use of feedback control systems — however, such systems are unstable due to the instability of the equivalent z value of the machine’s welding circuit,

When used as a control parameter Ugj, this problem is solved, because instead of z, a welding circuit is used, the parameters of which depend only on its heating temperature, which is monitored and taken into account by changing the setpoint Up,,

The considered features of obtaining initial data for constructing a mathematical model provide it with high adaptability to the actual process,

As constructions for the implementation of the method, a machine for

spot welding DC type MTV-4802 and micro-computer type B7.

The installation consists of micro-EBM 1 with its control panel 2, the control panel 3 of the welding machine, the display 4 and the printing device 5.

The welding machine contains a controlled turning on angle of the thyristors on the contacts 6, a three-phase welding transformer 7, a power rectifier 8 with its internal resistance R 9, a welding circuit with resistance RCK 10, a component resistance RJJ 11, an inductance L 12, a current sensor 13, a sensor 14 force of electrodes, sensor 15 of temperature of the cooling water welding circuit and sensor 16 of the pedal.

For the operation of the system in a microcomputer, the following parameters are applied: a voltage proportional to the voltage of the network supplying the welding machine, the voltage setting of the welding circuit and „„, the voltage from the current sensor i

-.,, voltage from sensor

SL

expected voltage values

ck and

electrode - electrode

and and, - (are from technological

Uh j

tables or from experiment), the voltage from the sensors at the electrodes Fjj and the cooling water temperature, the data of the adjustment and load characteristics of the rectifier 8 along the steps of the welding transformer 7, the parameters of the required welding mode and their tolerances that are selected from the memory Computer or recruited from the remote control 1.

The microcomputer processes the entered data and records it in the program, including the initial angles d of the switching on of the thyristors of the power rectifier. The transformer stage is turned on manually. When the welding machine is first turned on, the microcomputer provides a program for calculating the parameters of the welding circuit. For this, the welding machine is switched on in the short-circuit mode of the electrodes.

In order to prevent the smoldering of the working surfaces of the electrodes, the program provides for a reduction in the force of the electrodes, the turn-on time of the welding current and the voltage on the welding circuit in certain ratios to the operating mode. In the course of work, this program is periodically repeated in order to exclude measurement errors from heating the material of the welding circuit by way of

Tomato and., „. After

o

15

0

five

0

35

0 ego

changes in the installation (,. jiiu. of completing this operation, the microcomputer every time puts the program into operation and monitors the operation of the welding installation by outputting the necessary information to the display and printing, signals unavailable deviations in its operation and diagnoses their causes.

The main technical data of the welding machine is as follows. The power rectifier is six-phase, made of six D253-4000 diodes. The rectifier unit is located directly on the transformer. The welding circuit has a nominal reach and a solution of 500 and 150 mm, respectively. Resistance of the welding circuit at 29 C 33.5 Mk Ohm. The short-circuit currents of the transformer stages are 14 kA, 20 kA, 27 kA and 39 kA, respectively. Equivalent resistance across the transformer 92; 91, 99 and 85 Mk Ohm. The power of the machine when welding heat-resistant steel with a thickness of 2.5 + 2.5 mm at stage IV is 45 kVA. Short-term performance of 90 welds per minute.

Data on the welding of samples are given in the B table (bulk; ina, mm, 2.0+ + 2.0).

Welding is performed on standard samples when the following stabilizing factors affect the welding process: voltage variation in the supply network by +10 and -15%, change in welding force by + 20%, change in the radius of the electrodes by + 25%, shunting with setting the second points at a distance of 20 mm.

The welding process is controlled by the voltage on the welding circuit, which is set in accordance with the parameters of the welding material and experimental

ted

data. The specified value V is maintained by the feedback system on the deviation of the microcomputer of the machine with an accuracy of ± 1%. The quality of welded joints is determined by the magnitude of the breaking force.

The scatter of the results of mechanical shear tests, which characterize the stability of the welding process, is determined from a series of 10 samples for each combination of materials.

According to the existing standards, the strength variation should satisfy the condition

Rmskke RMIN

R

0.3,

Wed

where the maximum, minimum and average failure forces according to test results, 19 0.3.

Thus, the welding method on the voltage on the welded circuit ensures high quality of welded joints when exposed to the welding process destabilizing factors that occur during the operation of welding machines in production. conditions.

RJJ and Uj provide a welded joint with specified core dimensions.

The close relationship between these parameters is maintained for different metals and alloys under the influence of disturbing factors, such as voltage fluctuations in the network, compression force of the electrodes, change in their working fO surfaces, shunting from previously welded points.

Quality control of each weld point with a new welding method,

rather than selective, as is done. As an additional criterion for the welding process, the values of and, - and R-, are fixed by the end of the welding cycle.

33 y

The spread of these quantities is limited to the third digit.

The use of the method provides technological advantages in comparison with the known welding methods, therefore, it creates a significant technical and economic effect. Thus, the control of the welding process on the voltage on the secondary circuit and the control of its parameters stimulate the development of the effect of self-regulation of the process, stabilizes the welding process and contributes to the production of welded joints with specified strength characteristics.

As is known, the electrode-electrode resistance Tjj decreases during the welding process. This is associated with an increase in the contact area due to the heating of the metal and an increase in its plasticity.

The dynamics of this process are determined by the current density in the weld zone. With a constant current density equal to the set point, the melting point of the metal during the welding time will be achieved necessarily. Between density

25

, increases the safety margin of the welded structure, which allows reducing the number of welded points in the assembly or reducing their cross-section, which makes it possible to reduce the energy-capacity of the welding process, increase equipment productivity and reduce the cost of electrodes.

The reliability of the means of control when equipping a welding machine with manipulators for feeding and removing products during the welding process allows switching to deserted technology, which will provide an additional technical and economic effect.

The stability of the quality of welded joints makes it possible to reduce the amount of control due to the exclusion of mechanical tests of welded samples for shear. The elimination of this operation gives 35 great economic effect.

Claims (1)

Invention Formula A method of controlling and controlling the process of resistance welding, in which the process is controlled and controlled by a control parameter, characterized in that, in order to improve the quality of the welded joint current and voltage electrode - electron; there is a close connection as a control parameter. Thus, the voltage is used, in effect, the control during the welding process on the welding circuit of the machine. 33-6 RJJ and Uj provide a welded joint with specified core dimensions. The tight connection between these parameters is preserved for different metals and alloys when exposed to disturbing factors such as voltage fluctuations in the network, compression force of the electrodes, change of their working surfaces, shunting from previously welded points. Quality control of each weld point with a new welding method, rather than selective how it is done , increases the safety margin of the welded structure, which allows reducing the number of welded points in the assembly or reducing their cross section, which makes it possible to reduce the energy capacity of the welding process, increase equipment productivity and reduce the cost of electrodes. The reliability of the means of control when equipping a welding machine with manipulators for feeding and removing products during the welding process allows switching to deserted technology, which will provide an additional technical and economic effect. The stability of the quality of welded joints makes it possible to reduce the amount of control due to the exclusion of mechanical tests of welded samples for shear. The elimination of this operation gives a great economic effect. Invention Formula The method of controlling and controlling the process of resistance welding, in which the process is controlled and controlled by a control parameter, characterized in that, in order to improve the quality of the welded joint