RU1797539C - Method of arc power welding by modulated current - Google Patents

Abstract

Usage: for arc mechanized welding with modulated current mainly in shielding gases. SUMMARY OF THE INVENTION: the welding voltage in a pause is increased from Wick to UPC 0.8 0.8Ueo, where IW is the voltage at the end of the pulse, Un is the voltage at the end of the pause, Uco is the specified voltage of the natural arc break with a stationary floating electrode. In this case, the duration of the pause is maintained according to the expression OZZgKf, where Gkf is the duration of cooling of the slag layer on the surface of the weld bead to the temperature at which the slag conducts electrical conductivity. 4 ill.

Description

The invention relates to techniques for mechanized arc welding with modulated current, mainly in shielding gases, and can be used in mechanical engineering, shipbuilding, construction, etc.

A known method of welding with stepwise movement of the head, reduced in a pause synchronously with a decrease in the feed rate of the electrode. In this case, the welding voltage in the pause is also reduced. In the process pulse, these parameters increase accordingly. The disadvantage of this method is the low quality of the resulting seams, because the weld pool is characterized by increased depth and a small width. These phenomena occur due to a lack of power in the pause of the welding process.

The purpose of the invention is to increase process stability and improve weld formation during welding in shielding gases. The goal is achieved by increasing the pause voltage from LW to LW 0.8Ueo, where LW is the welding voltage at the end of the pulse, IW is the voltage at the end of the pause, Ueo is the specified voltage of the natural arc break with a stationary floating electrode. In this case, the pause duration is equal to the sum of the durations of the transition period of the increase in the welding voltage from IRC to UPC 0.8Ueo and the specified duration of burning of the stationary arc at the welding voltage equal to less than 0.33 gff, where tff is the duration of cooling of the slag layer on the surface of the weld bead to temperature at which the slag loses its electrical conductivity.

The difference of the proposed method lies in the variation of the welding voltage in a pause (below the lower one adopted in the known invention) and in the time interval of a pause (less than the lower limit accepted in the known invention). The method allows welding with modulated current with periodically varying within a wide range the feed rate of the melt K P

ABOUT

with s o

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an electrode without arc breaks during the entire welding cycle.

There are two welding options for the proposed method. According to the first variant, the duration of burning of a stationary arc at a welding voltage of IPK is equal to zero. In this case, the duration of the pause is strictly limited by the duration of the transition period of the increase in the welding voltage of UHK to UHK (synchronous with a decrease in the feed rate of the floating electrode). Here, the feed rate of the floating electrode can be reduced to zero. In the second option, the duration of burning of a stationary arc is more than zero - its value is supported depending on technological goals. In both cases, the arc is not interrupted.

In FIG. 1 shows the values of the welding current voltage in accordance with the position of the current-voltage characteristics of the current-voltage characteristic of the current source and the current-voltage characteristics of the VR-welding head at various intermediate stages of the transition from pulse to pause during welding according to the known invention; figure 2 is the same when welding according to the invention; Fig. 3 is a sequence diagram of the flow rate of the floating electrode Vs, the welding voltage U and the welding current during welding according to the known invention; figure 4 is the same when welding according to the invention.

As follows from FIG. 1, when welding according to the known invention, the parameters in the pulse correspond to the point Au with the coordinates: 1I and Un. At this point, the curves of the current-voltage characteristics of the I – V characteristic power supply and the current-voltage characteristics of the welding head Uen intersect. This means that the CBapKVi mode parameters in pulse 1I and UH are achieved by setting the feed speed of the floating electrode (the corresponding current-voltage characteristic of the welding head is indicated by the same symbol) and the open circuit voltage of the MXI power source, which corresponds to the current-voltage characteristic of the power source I – V characteristic (in this case, it is adopted sloping, which is determined by the electrical circuit of the source. Other current-voltage characteristics of the source are possible). After the pause signal has occurred, the electrode feed rate decreases, which is shown in Scheme 1 by a series of current-voltage curves of the welding head of Vet, Vea, etc. to Vei. Each value of the sequentially reduced feed rate of the floating electrode corresponds to the same

increased welding voltage Ui, U2, etc. up to Un, Un can be equal to Oe0 (indicated by a dashed line in Fig. 1) or be 0.9Ue0. When welding according to the known

of the invention, the feed rate of the floating electrode can be reduced below Vei down to zero and kept at zero until the arc breaks at a voltage of Ue0. Further

0 pause may continue for (0.0330, 9) gcf, Open circuit voltage source. power supply during the transition from pulse to

the pause sequentially increases from

Uhh through the values Uxxi, Uxx2. to value 5. nor llxxn corresponding to Ue0. Re-excitation of the arc during welding according to the known invention in the case of using welding flux as a protective medium is not difficult and occurs as

0 is described above.

According to the proposed method (Fig. 2), in an impulse, the arc burns in the mode: current and (at the feed speed of the electrode VeH) and voltage UH, which is ensured by voltage no. 5 of the source UxxM. The mode in the pulse corresponds to the point AI. the intersection of the current-voltage curves of the VeH welding head and the Tskha power supply. Here and at subsequent stages of the transition to a pause mode, the process dynamics are the same as for welding according to the known invention: the electrode feed rate decreases sequentially through the values Vei, Ve2, ... Vei, and the voltage

5, the welding increases accordingly: UL lJ2 ... Ui By increasing the open circuit voltage of the power supply. The difference between the proposed welding method and the known one takes place at the stage of the end of the transition from the pulse mode to the pause mode: the transition process ends when the welding voltage Ui becomes 0.8Ue0 or less than this value, depending on the selected

5 preliminary limit value of the welding voltage in the pause Uпк- In fact, when welding according to the first embodiment of the proposed method, the pause is reduced to the duration of the transition period of the voltage increase by 0 from Cyc to Un and, unlike the prototype, there is no period when the arc breaks and the slag cools down to a temperature corresponding to the slag cooling interval - (0.033-0.9) tcf. Because the

5 when welding according to the proposed method, arc breakage is excluded, the welding process in a pause exists in the interval 0 t 0,033 Gkf. When welding according to the second embodiment of the proposed method, the pause duration exceeded

It lasts a transition period and can last as long as required by the technology (as a rule, until the specified weld width is reached), however, in this case too, the process exists in the time interval of 0 GP 0.033 gf. In contrast to the known invention, both variants of the proposed welding method do not allow arc breaking.

Fig. 3 shows a sequence diagram of the welding parameters according to the known invention, when the arc is broken, and the pause duration Гп is set to be longer than the duration of the transition period of the voltage increase hper from LW to UPC. The case where UPC Ueo has been adopted. At time ti, a signal is given to increase the feed rate ve of the floating electrode and decrease the welding voltage U. уе increases (Fig. 3a) from zero to ven (at time ta), and the welding voltage decreases to this moment from Umc to UWK (FIG. 3S). At the moment when the electrode touches the slag layer, a welding current arises, which increases like an avalanche, and at the moment of arc excitation, a current pulse with amplitude Q appears (Fig. 3c). After alignment of the feed and melting rates, the electrode flows

. stationary welding process with parameters 1) IR and 1H. On the current curve (Fig. 3c), a sawtooth curve corresponds to this process, the middle line of which is parallel to the z axis. At time t3, a signal is sent to decrease the feed rate of the floating electrode and increase the welding voltage U. The feed rate of the electrode decreases from yen to zero (moment m), and the Welding voltage increases to Ume. which in this case is equal to Ueo. At the moment of arc breaking, the voltage between the electrode and the workpiece becomes equal to the open circuit voltage of the source Uxxn. and welding current is zero. After a predetermined pause period at time ts, a signal is sent to increase the feed rate of the floating electrode and decrease the welding voltage. The cycle of modulation of the welding mode parameters is repeated.

 For the case of modulated current welding according to the invention in shielding gases, the current curves in FIG. 3c are shown with dashed lines. The modulation algorithm is saved as for submerged arc welding. In this case, the arc burning process is unstable. After the electrode is closed on the product, a current pulse of large amplitude A appears, as a result of which the electrode can melt explosively, like a fuse. After this, a repeated current pulse B and a short period of burning of the arc follow, followed by a natural break.

The sequence of parameters of the proposed method reflects figure 4. Here, at the time ti, a signal is received to increase the feedrate of the floating electrode in the pulse and decrease the welding voltage. Since the arc burns during a pause (in the mode: voltage UPK, current n), excitation of the arc is not required. Between the moments ti nt2, an increase in the feed rate of the floating electrode from uep to ven and a decrease in the welding voltage from Un to UHK occur (Fig. 4c). In this case, the welding current increases from n to 1I (Fig. 4c), in accordance with an increase in the electrode feed rate. Between the moments of t.2 and ts there is a stationary burning of the arc in the mode :;

The pulse duration rp is supported depending on the technological objectives: for example, if it is required to increase the penetration depth, mp increases, if it is necessary to increase the seam width with a small penetration depth, the reduction is reduced. At time 1c, a signal is sent to decrease the electrode feed rate and increase the welding voltage. This process occurs in the time interval between the moments t-z and t4. Figure 4 shows the case when in a pause the feed rate of the electrode is reduced to zero (this happens at time t4). Until time ts, the electrode is stationary (Fig. 4a), but the arc continues to burn, while the welding voltage increases from 11pc to Ucc 0.8Ue0. At time ts, when the welding voltage becomes equal to the set voltage upp. provide a signal to turn on the electrode supply and reduce the welding voltage. If an increase in the welding voltage greater than the set Un to Ueo is allowed (dashed line in Fig. 4c), an arc break can occur (Fig. 4c - the current decreases to zero). In this case, re-excitation of the arc is difficult: current pulses of amplitudes A and B arise (dashed curves in Fig. 4c), accompanied by an explosion of the floating electrode as a fusible conductor. Therefore, for process stability, the condition UHK 0.8Ueo must be observed.

The welding according to the second embodiment is carried out as follows: the feed speed of the ven electrode is set, which is adequate to the welding voltage Opt. while ven can be many times smaller than uye.

In order to implement the proposed welding method according to the first embodiment, it is necessary to include the UPK master, a sensor in the electric circuit of the welding machine

welding voltage, comparator and amplifier. The welding method of the second embodiment can be carried out on a welding machine prepared for welding according to the main invention.

PRI me R 1. Did you weld the butt joints in carbon dioxide according to the second embodiment of the proposed welding method. Welded metal plates were made of steel C3Cp 6 mm thick, the gap between the welded edges was 2 mm. We used an A-547U welding semiautomatic device complete with a modulation block of the design of the IES im. E.O.Patona (model), welding current source - rectifier VDU-506. We used welding wire Sv-08G2S with a diameter of 1.2 / mm. The welding mode is presented in table 1.

It was experimentally established that the voltage of the natural break in the pause is 42 V. Mode 1 is made according to the well-known invention, here Un 0.9Ueo. With such an increased voltage in the pause (38 V), the weld quality deteriorated due to increased spatter, porosity (due to weakened protection of the metal bath from the air) and several arc breaks resulting from random

0

5

0

5

deviations of the welding arc (the length of the arc increased).

When welding in mode 2, the arc burning process proceeded stably, pores were absent.

Since the arc was not interrupted in the pause, a slag layer on the surface of the roller did not form in the pause, so the duration can be infinitely long, and therefore the inequality 0.033 Gcf is true.

P erm 2. The design mode of welding by the proposed method according to the first embodiment is given (see table 2).

From the mode 2 adopted in Example 1, the calculation mode differs in that the length of the pause is equal to the duration of the transition period between the pulse and the pause / there is no stationary arc process in the pause. This option is somewhat more productive than the second option ..

Since the arc was not interrupted during the pause, a slag layer on the surface of the weld did not form, therefore, the length of the pause physically cannot be equal to any fraction of Gcf. It follows that in the first embodiment of the proposed welding method, the inequality 0 gn 0.033Tkf is true.

Claims (1)

The claims A method of mechanized arc welding with modulated current with a decrease in the welding voltage in a pause, with the exception of the fact that, in order to increase the stability of the process and improve the formation of the weld when welding in shielding gases, the welding voltage is increased from to Unit 0.8Ueo. where oik is the voltage at at the end of the pulse, pk is the voltage at the end of the pause, Ueo is the voltage of the natural arc break with a stationary melting electrode, while the pause duration is maintained within 0 t of 0.033 tff, where Gp. - pause time, hcf - the duration of the cooling of the slag layer on the surface of the weld bead to a temperature at which the slag loses its electrical conductivity. Table 1 and 1797539 10 table 2 Bk. 1 FIG. g.