SU1637969A1 - Arc welding rectifier with combination output parameters - Google Patents

Abstract

The invention relates to mechanical engineering and is intended for electric arc welding with a consumable electrode at a constant current. The purpose of the invention is to increase the productivity and quality of welding. The rectifier contains a power transformer, a thyristor rectifier, current and arc voltage sensors, a control algorithm setting unit, a comparison unit, a comparator, a logic unit, and a control generation unit. The control system forms a steeply dipping section of the characteristic in the range of operating modes of welding. With an increase in the current and a decrease in the voltage on the arc by 15 .. 20% below the set operating value, a transition to a gently dipping, hard or increasing portion of the external characteristic is made. This reduces splashing and improves weld formation by feeding the arc from a welding rectifier with a combined external characteristic. 3 il. Yo

Description

The invention relates to mechanical engineering and is intended for electric arc welding by a direct current melting electrode.

The purpose of the invention is to increase the productivity and quality of welding.

Figure 1 shows the functional scheme of the welding rectifier; Figure 2 shows the external current-voltage characteristics of the welding rectifier; FIG. 3 shows the output characteristics of the voltage and current sensors during the welding process.

A welding rectifier for arc welding with combined external characteristics contains a power transformer 1 connected to the thyristor unit 2. A voltage sensor 3 connected to the outputs of the thyristor unit 2, a choke 4 connected to one output

thyristor unit 2, current sensor 5 connected to another output of thyristor unit 2, outputs of current sensor 5 and voltage sensor 3 are connected to the inverting input of control voltage generating unit 6, the other input of which is connected to welding task setting unit 7, unit 6 output forming the control voltage through the control pulse shaping unit 8 is connected to the input of the thyristor unit 2. In addition, the welding rectifier contains the control algorithm generation unit 9 performed on the operational amplifier according to the scheme asshtabnogo adder, a comparator 10, an operational amplifier configured, assembled to increase the interference immunity and stable switching of the regenerator circuit 11 and the first 00 VTOO

h |

yoo yu

a swarm 12 transistor switches assembled on field-effect transistors, a source follower 13, a resistor 14, a storage capacitor 15, a comparison unit 16 made on an operational amplifier, an adjustable resistor 17 and a diode 18, a divider 19, a variable resistor 20 and a equalizer 21. In this case the control algorithm generation unit 9 is connected to the output of the voltage-stabilizer divider 19 and through a variable resistor 20 to the output of the current sensor 5, the output of the control algorithm generation unit 9 is connected to the non-inverting input of the comparison unit 16 and an inverting input of the comparator 10, to the non-inverting input of which a negative signal Udn is received from the output of voltage sensor 3. The output of the comparator 10 is connected via a parallel-connected diode and resistor to the inputs (gates) of the first 11 and second 12 transistor switches, the drain of the first transistor switch 11 is connected to the output of the control algorithm generation unit 9 9, and its source is connected to the source repeater 13, the transistor drain key 12 through a resistor 14, and its source through a storage capacitor 15 is connected to the input (gate) of the source follower 13, the output of which is connected to the inverting input of the comparator unit 16, the output of the comparator unit 16 through regulation the first resistor 17 and a diode 18 is connected to the master circuit voltage Uz welding mode and the non-inverting input of the voltage control 6.

Figure 2 shows a family of combined external characteristics of a welding rectifier with a steeply dipping 22 and gently dipping (hard) 23 areas and an algorithm for the welding mode VCB OSV), calculated by the equation

VCB A + R3ICB, (1)

where VCB is arc voltage; ICB - welding current;

A is the coefficient depending on the diameter of the electrode wire;

R3 - equivalent resistance of the welding circuit.

The intersection point of the VCB BAS) and one of the external characteristics of the rectifier in its steeply dipping section gives the operating point B, which determines the operating parameters of the welding process (current Sv and voltage DCB). The voltage Una of the fracture point B from the steeply dipping part of the external characteristic to the gently dipping (the voltage of the hard part is taken 15-20% less than the operating voltage Un (0.8-0.85) VCB.

The locus of fracture points from one area of external characteristics to another lies on fracture line 25, described by the equation

Vn KJcB + Vno; (2)

where Vn is the stress point of the external characteristic;

KP - the angular coefficient;

Vno - constant constituting the fracture tension;

Equation (2) is used as an algorithm for controlling the welding process when operating on a combined external characteristic of a rectifier.

5 FIG. 3 shows the characteristics of the output signals of the current sensors 26 and voltage 27 during the welding process and the algorithms for controlling the welding process 28, which, taking into account the transmission coefficient of the Kdt current sensor and the voltage Kdn, has the form

Vn KpTsv + Vno, (3)

where Vn is the stress point of the external characteristic, equal to Vn КДП У; EV - welding current equal to Sv Kdt-1Sv;

5 Кр - the angular coefficient equal to Кп Кп КДн / Кдт;

Vno — constant component of fracture stress; equal to vno v0kah.

Dependence (3) is formed in block 9

0 forming a control algorithm performed on an operational amplifier included in the scale adder circuit. With the help of the divider 19 stabilized voltage is established

5 constant component of the fracture voltage Vno, variable resistor 20 - the value of the slope Kp.

The proposed welding rectifier allows welding with a melting electrode in a protective gas environment on a combined external characteristic, when in the range of operating modes the welding is carried out at its steeply dipping section, and with increasing current and lowering the arc voltage by 15-20% below the specified operating value, a transition is made to a gently dipping (hard) part of the external characteristic. This transition leads to a sharp increase in the welding current, which prevents process disruption, reduces splashing and improves the quality of the seam.

The formation of the form of the external characteristic of the rectifier is carried out by the action of current and voltage feedbacks.

When forming steeply dipping external characteristics, the reverse action

the current coupling of the current sensor 5 prevails over the action of the voltage feedback. Increasing the welding current St increases the negative signal of the current sensor 6. This signal is fed to the inverting input of the control voltage shaping unit 6, increasing the control voltage Vy at its output. The thyristor switching angle is increased and the voltage at the output of the rectifier decreases. In order to form a rigid part of the external characteristics, the feedback action on voltage must prevail over the action of current feedback. To do this, the current feedback is compensated by applying an additional compensating negative signal from the output of the comparison unit 16 to the non-inverting input of the control voltage shaping unit 6. In this case, when the voltage at the output of the rectifier decreases, a negative feedback signal is reduced by the load voltage / day, acting on the inverting input of the control voltage shaping unit 6. The voltage Vy at its output decreases. The switching angle of the thyristors a also decreases and the voltage at the output of the rectifier increases (maintains at a predetermined level).

The transition from a steeply dipping area of the external characteristic to a gently dipping (hard) area and vice versa is carried out automatically during the welding process according to the control algorithm (3) by compensating for the effects of current feedback.

At zero control voltage at the inputs (gates) of the transistor switches 11-12, the latter open and the signal Vn from the output of the control algorithm generation block 9 will flow both to the non-inverting input of the comparison block 16 and through the open transistor switch 11 and the source follower 13 to the inverting input of the unit 16 comparison. At the same time, at the output of the comparison unit 16, a zero signal (V 0) is obtained, which does not affect the control generation unit 6.

The positive potential at the inputs (gates) of the transistor switches 11-12 close the latter, as a result, the source repeater 13 will operate in the VPB signal memory mode on the capacitor 15 (break point B in FIG. 3), which is fed to the inverting input of the comparison unit 16. With increasing welding current, and hence the signal Vn,

arriving at the non-inverting input of block 16 of the comparison, at its output via Wits, the signal VK Vn - / PV, supplied through the variable resistor 17 and the diode 18 to the non-connecting 5 welding input of the welding current feedback unit 6 / dt. As a result, the signal Vy at the output of the control voltage shaping unit 6 will decrease, the angle will also decrease

10 turns on the thyristor rt and the voltage at the output of the rectifier, i.e. the slope of its external characteristic is reduced.

5 The speed of transistor switches is an order of magnitude higher than the speed of the thyristor opening control system, therefore the compensating signal VK from the moment of switching will increase from zero, and switching the arc power from the steeply-dipping part of the external characteristic to the steadily-changing (hard) area does not lead to a sudden change in direction straighteners and, consequently, to break

5 external characteristics.

The device works as follows.

Before starting the welding rectifier, the optimal welding algorithm (1), the control algorithm (2) and its optimal parameters, the required slope angles of the steeply-falling section (t gently-dipping (hard) section 2n of the external characteristic) are determined.

5 Variable resistors set the necessary parameters of the circuit: resistor 19 is the constant component of the fracture voltage equal to Vno Vo-Cdn; resistor 20 - angular

0 coefficient of the control algorithm (3), which is equal to Кп Кп Кдн / Кдт: corrector 21 with open transistor switches 11-12 - the angle of inclination of the steeply dipping section about the external characteristic; resistors 17 5 with closed transistor switches 11-12 angle of inclination gently dipping (hard) plot "l external characteristics.

Before starting welding with a potentiometer 7, the mode setting block is set

0 driving voltage Va. providing the necessary mode of welding.

In the initial state (at idle run of the welding rectifier), the negative potential VAH from the output of sensor 3, for example, arriving at the non-inverting input of comparator 10, is greater than the negative fracture voltage Vn. coming from the output of block 9 of forming the control algorithm to the inverting input of the comparator 10 (FIG. 3). At the same time at the output of the comparator 10 (FIG. 1) there is a negative voltage. As a result, the transistor switches 11-12 are open, and the signals / i Vn from the output of the control algorithm generation unit 9 will go both to the non-inverting input of the comparison unit 16 and through the open first transistor switch 11 and the source follower 13 to the inverting input of the comparison unit 16. At the same time, at its output, a zero signal V 0 is obtained, which does not affect the operation of the control voltage generating unit 6, the output of which is the control voltage Vy, which will correspond to the no-load voltage of the welding rectifier. Thus, in the initial state, at the output of the rectifier, the no-load voltage VXx is set, corresponding to the steeply dipping section of the external characteristic.

The process of exciting the arc begins with a short circuit of the electrode wire on the product. After initiating the arc and achieving the specified operating values of the VCB voltage and the current Ice, a stable arc is started. Since the arc is powered at the steeply dipping section of the external characteristic, the current fluctuations are not large, which significantly reduces splashing and improves the formation of the seam. By reducing the voltage on the arc to the magnitude of the voltage of the break point, when Vn VflH, a positive voltage is applied at the output of the comparator, which closes the transistor switches 11-12. As a result, the source follower 13 switches to the storage mode of the Vnu signal on the capacitor 15 (break point B1), which is fed to the inverting input of the comparison unit 16.

With a further increase in the welding current, and consequently, the signal Vn, coming to the non-inverting input of the comparison unit 16, a VK signal Vn-Vne appears at its output, coming through the variable resistor 17 and diode 18. to the non-inverting input of the voltage shaping unit 6 control 6, compensating for the effect of negative feedback on the welding current Udt. The voltage at the output of the rectifier is maintained at a predetermined level (the hard part of the external characteristic). Switching the arc power from the steeply dipping area of the external characteristic to the gently dipping area leads to an acceleration of the electrode wire melting, an increase in the arc length and the welding voltage value, when the value Udn Vn is reached at the output of the comparator 10

the voltage is negative and the welding rectifier switches to work with a steeply dipping section of the external characteristic.

Jump from a steep slope

external characteristics to the increasing area further increases the rate of increase of the welding current and expands the zone of the steady arc

0 In order to obtain the increasing portion of the external characteristic of the rectifier, when switching from a steeply dipping portion, it is necessary by resistor 17 to increase the compensating effect of the additional signal V "

5 up to a positive current feedback.

The proposed device has the ability to vary the steepness of the external characteristics of the welding rectifier.

0 without breaking it, to conduct the welding process at optimum conditions with increased process stability and expands the technological properties of thyristor welding rectifiers.

five

Claims (1)

Invention Formula An arc welder rectifier with combined external characteristics, containing a power transformer connected to a thyristor unit, to one output of which a choke is connected, and to another - a current sensor, a voltage sensor connected by its inputs to the outputs of the thyristor unit, current sensor outputs and voltages are connected to the inverting input of the control voltage shaping unit, the non-inverting input of which is connected to the welding mode setting unit, and the output through the control pulse shaping unit with of the connections to the input thyristor unit, and a source of stabilized voltage, characterized in that. in order to increase 5 of the productivity and quality of welding, it is equipped with a control algorithm generation unit, a stabilized voltage divider, a variable resistor, a comparator, the first and second field 0 transistors, a source follower, a storage capacitor, a comparison unit, a regulating resistor and a diode, while the input of the control algorithm generation unit is connected to the output 5 divider stabilized voltage and through a variable resistor - with the output of the current sensor; the output of the control algorithm generation unit is connected to the non-inverting input of the comparator and to the inverting input of the comparator, the non-inverting input of which is connected to the output of the voltage sensor, the output of the comparator is connected to the gates of the first and second field-effect transistors, the drain of the first field-effect transistor is connected to the output of the control algorithm generation unit, and the source to the source of the source transistor, the drain of the second field-effect transistor through a resistor, and its the source is connected via a storage capacitor to the input of the source follower, the output of which is connected to the inverting input of the comparison unit, the output of which is through an adjustable resistor and diode The g is connected to the input of the block forming the voltage. 1 2b 25 2 26 28 Puz.J