DE102006050297B4 - Pulsed arc process - Google Patents

Abstract

Inert gas arc welding method for carrying out a welding process in which material of a welding wire used as a melting electrode is transferred to a welding bath, with a process cycle that comprises a basic phase and a pulse phase in which an arc burns and the welding wire is positively polarized, the material of the welding wire is transferred to the weld pool in a short circuit phase and the resolution of the short circuit is at least supported by stopping or withdrawing the welding wire from the workpiece, and after the short circuit is resolved an arc is ignited again and the welding wire is reversed again to move it towards the workpiece, whereby to a short circuit, a first polarity change is carried out, in which the welding wire is negatively polarized, and after the polarity change an arc ignites with a negatively polarized welding wire, and after a light has expired arc phase with a negatively polarized welding wire, a second polarity change is carried out within the process cycle, in which the welding wire is positively polarized, with a third process phase after the pulse phase ...

Description

The invention relates to an inert gas arc welding method according to the preamble of claim 1.

The invention further relates to an inert gas arc welding apparatus for carrying out such a welding process.

Shielding arc welding processes include both MIG (metal inert gas) and MAG (metal active gas) welding processes. A welding process is for example in the international publication WO 00/64620 A1 described teaching the use of a short arc with cyclically reversed wire feed, wherein welding with low heat input is realized in the workpiece. In this case, the end of the welding electrode formed as a melting electrode is melted in a DC arc and the wire is moved in the direction of the workpiece until the liquid end contacts the molten bath and causes a short circuit. After reaching the short circuit, the forward movement of the wire is stopped and possibly retracted so that the wire is moved away from the workpiece. Such backward movement can assist the transition of the molten volume (drops) from the wire to the molten pool. An essential advantage of such a method, in addition to the low heat input, is a substantially spatter-free drop transition into the molten bath.

However, such a known welding method has the disadvantage that the heat input into the workpiece must be substantially increased if more volume is to be melted off in order to increase the welding speed. Depending on the welding task, however, the acceptable heat input into the workpiece is limited by the workpiece used, for example in the case of thin metal sheets, so that the known welding method is disadvantageous despite certain advantages in certain applications.

The publication US 2006/0207983 A1 relates to a welding process comprising a series of welding cycles including a short-circuit phase using two welding electrodes, each cycle comprising an arc and a short-circuit phase, and wherein one or both electrode currents are reversed in one phase of the welding cycle to melt before a short-circuit phase of a subsequent welding cycle Transfer metal from the second electrode to the first electrode. The article "Solutions to Problems of Tiny Spatter and Arc Interruption in AC Pulsed MIG Arc Welding" deals with the investigation of the occurrence of welding spatters and arc interruptions in pulsed AC arc welding of aluminum alloys and stainless steel.

The generic publication AT 501489 A1 relates to an inert gas arc welding process for performing a welding process in which material of a welding wire used as a consumable electrode is transferred into a weld pool, with a process cycle comprising a ground phase and a pulse phase in which an arc is burning and the welding wire is positively poled, Material of the welding wire is transferred in a short-circuit phase in the molten bath and the dissolution of the short circuit by stopping or retracting the welding wire from the workpiece is at least supported and after the resolution of the short circuit, an arc ignites again and the welding wire is reversed again to move it towards the workpiece , For a short circuit, a first polarity change is carried out within the process cycle, in which the welding wire is negatively poled, whereby after the polarity change an arc with negatively poled welding wire ignites and after a phase of arc with negatively poled welding wire a second polarity change is carried out within the process cycle which the welding wire is positively poled again. Furthermore, after the pulse phase, a third process phase with reduced energy input into the welding wire compared to the pulse phase is performed.

The invention has for its object to improve a conventional gas-shielded arc welding process to the extent that even thinnest sheets are processed and beyond the emergence of weld spatter is even better avoided.

This object is achieved in a surprisingly simple manner with a method according to claim 1 and with a protective gas arc welding apparatus according to claim 16.

In this case, the protective gas arc welding method according to the invention has a process cycle, which in addition to a base phase and a pulse phase in which an arc burns and the welding wire is positively poled, also includes a short-circuit phase at which the droplet transition starts, with completion of the short-circuit phase, the droplet transition is complete completed. For a short circuit, a first polarity change is performed, in which the welding wire is negatively poled, wherein after the polarity change an arc ignites with negatively polarized electrode, and wherein after a Arc phase with negative poled welding wire a second polarity change is performed within the process cycle, in which the welding wire is positively poled again. The inventive method is characterized in that in the third process phase after a maximum time and before reaching the short circuit, a polarity change is performed, in which the welding wire is polarized from positive to negative. The fact that in the process of the invention in the third process phase with a reduced compared to the pulse phase energy input into the welding wire is used and after a predetermined maximum time and before reaching the short circuit, a reversal of the welding voltage, it is particularly ensured that in one of the third Process phase subsequent phase until reaching the short circuit no further energy input takes place. The welding process is compared to the known process even "colder", so that with the welding method according to the invention thinnest sheets can be welded, which is completely excluded by the powerless immersion of the liquid ball at the end of the welding wire in the weld pool that splashes are generated.

The described measure ensures that more material is melted within a process cycle by the negative polarity of the wire electrode in an arc phase, which can be transmitted for example after a polarity change followed by short circuit in the weld by means of a short arc with mechanically assisted shorting resolution. It has surprisingly been found that, despite the higher melting wire volume, the advantages of the generic arc welding method can be maintained in the welding method according to the invention. Due to the higher energy input into the negatively polarized welding wire, the arc output and thus the energy input into the workpiece can be kept reduced even in this phase of the process cycle. Ultimately, a spatter-free drop transition can be made possible with the inventive method even at higher wire speeds.

It should be noted that the protective gas arc welding method according to the invention comprises a process cycle comprising at least the process phases specified in claim 1. In addition, it may of course also have other phases, for example, several successive pulse phases running, each associated short-circuit phase for transmitting at least one drop into the weld pool, not in each case such a short circuit, a polarity change must be assigned. It is essential that at least once within the process cycle, a polarity change takes place, ignites an arc with negatively polarized electrode and then again a polarity reversal of the welding wire. It should also be pointed out that the term "second short circuit" does not exclude that a further short circuit is provided between the first short circuit and the second short circuit, the same applies to the term "second polarity change". In general, the process cycle according to the invention runs periodically, but it may also be that process cycle times of successive cycles vary depending on the process control. Essential process parameters which are controlled or regulated are the wire speed or direction, the welding voltage, the welding current and / or the arc length.

While the welding voltage typically designates the voltage between the wire electrode and the workpiece, the welding current indicates the current flowing from the electrode to the workpiece. However, it is also possible to take as welding voltage, the output voltage of the welding power source for the process according to the invention. In the first case, a more precise control or regulation of the welding process is possible.

The pulse phase usually differs from the basic phase in that it works with higher values, for example with a higher welding current or with a higher welding voltage.

In order to assist the drop transfer from the welding wire, preferably after the detection of the short circuit, the supply of the welding wire to the workpiece is stopped and / or the welding wire is withdrawn from the workpiece. To resume the welding process, the reversing of the welding wire is necessary.

Conveniently, this reversal can be started to move the welding wire in the direction of the workpiece after a predetermined period of time from the time of dissolution or the occurrence of the short circuit. This provides sufficient clearance between the welding wire and the workpiece so that a stable arc can be created before the welding wire is moved back toward the workpiece.

Similarly, it may also be expedient if after the dissolution of the short circuit, the reversing of the welding wire to move it in the direction of the workpiece is only started when the welding wire has reached a predetermined distance from the workpiece.

Another possibility is to reverse the wire toward the workpiece after the short circuit is released when a predetermined negative wire speed is reached. Negative means that the wire moves away from the workpiece.

The durations of certain phases of the process cycle only arise during the course of the phase, depending on the regulation or control of the welding process, inasmuch as consecutive process cycles can have different lengths of time. In order to avoid such uncertainties, it can be expediently provided that the process cycle duration of the individual process cycles is constant. This can be achieved, for example, by the duration of a controlled, d. H. predeterminable process phase is adapted to the duration of a controlled process phase, such that the entire process cycle duration, which is the sum of the duration of the individual process phases, can be kept constant. For example, the basic phase of the welding process, in which the welding wire is positively poled, can be adapted to the process phase in which the wire is reversed until a predetermined condition is reached.

In another advantageous embodiment, it can also be provided that at the beginning of the process cycle its duration is determined, but successive process cycles in the time period can differ from one another.

After a first polarity change has been carried out within a process cycle, such that the welding wire is negatively poled, and after passing through an arc phase with negatively polarized electrode, a second polarity change takes place in which the welding wire is again positively poled. In this case, the second polarity change of the process cycle can be carried out without an associated short circuit between the welding wire and the workpiece being approached. Such a method is useful if an additional ignition aid can be used, which ensures that the arc ignites again after the second polarity change. Such an ignition aid can be, for example, that a large current change rate is used together with a high circular inductance, in particular the inductance of the welding choke. Another possibility is, for example, short-circuiting the output of the welding power source, again using the circular inductance to produce the necessary ignition voltage between the welding wire and the workpiece to ignite the arc with positively poled welding wire.

On the other hand, however, it may also be expedient if a short circuit is also assigned to the second polarity change of the process cycle, in which case, for example, even in a spatter-free manner, a drop transition from the tip of the welding wire into the weld pool is realized. The initiation of such a short circuit can be achieved, for example, by connecting an arc phase with a negatively poled welding wire to an arc phase in which the welding wire is negatively connected, within the given process parameters, in particular arc voltage, the arc current and / or the wire speed be set that within a predetermined maximum period of time usually a second short circuit between the welding wire and the molten bath is generated. Also in this case, the time duration until the short circuit is reached, as with the first short circuit, which is assigned to a first polarity change, is not precisely determined. As already described for the first polarity change, the polarity change can also be initiated at the second polarity change after a predetermined maximum time has elapsed, even if the short circuit has not yet been reached.

On the other hand, in another expedient method, the second polarity change can only be carried out despite reaching the short circuit when the further arc phase with negatively poled welding wire has lasted for at least a predetermined minimum period of time. In this process, the polarity change is delayed in response to the short circuit.

It should be noted that the further arc phase can be performed with negative poled welding parameters with the same welding parameters as the previous arc phase with negatively poled welding wire, so then ultimately the process cycle can have only a single arc phase with negatively poled welding wire, as indicated by start the short circuit and polarity reversal is terminated. On the other hand, according to the invention, however, the process cycle may also have further arc phases with a negative poled welding wire.

Preferably, following the arc phase, in which the welding wire is negatively poled, the second polarity change is performed, wherein process parameters such as welding current, welding voltage and / or wire speed can be adjusted so that after the second polarity change in a second short-circuit phase of the process cycle, the second short circuit between welding wire and workpiece is generated. It may be useful if with the second short circuit also liquid material of the welding wire is introduced into the weld pool, so that the wire speed can be further increased.

In a particular embodiment, it may be expedient if, before the end of the arc phase in which the welding wire is negatively poled, and before the second polarity change, the arc is extinguished, for example via the insertion of a dead time. The same applies to the first polarity change. In this respect, it may be advantageous if the arc is extinguished before the end of the arc phase, in which the welding wire is positively poled, and before the first polarity change described above

The retraction of the welding wire and the subsequent reversal of the wire may be as described above for the dissolution of the first short circuit. In particular, the welding wire can be pulled back to the second short circuit, in order to move it away from the workpiece, wherein after dissolution of the second short circuit, the welding wire is again reversed in order to move it in the direction of the workpiece. After dissolution of the second short circuit and after the second polarity change, an arc can then be ignited again, in which the welding wire is positively poled.

In order to avoid overloading of the welding source, it is preferably provided to regulate the short-circuit current in the short-circuit phases of the process cycle according to the invention, for example to a constant or a predetermined curve. By contrast, the arc phases, both positive and negative poled welding wires, can be controlled by controlling the welding current or voltage to a constant value or curve.

On the device side, the invention solves the above object with an inert gas arc welding device with a welding power source, a control device, a wire feed and retractor, and a welding torch, the controller after starting the welding process, a process cycle by controlling or regulating process parameters such as welding current , Welding voltage, wire feed or retraction, arc length and / or time interval lengths of process phases controls, wherein the process cycle has a basic phase and a pulse phase in which an arc is burning and the welding wire is positively poled, and wherein in a short-circuit phase after erasing the arc is a drop transition from the welding wire into the weld pool, the controller controls the wire feed and retractor after reaching the short circuit to stop the welding wire or to retract the welding wire from the We piece and subsequently for reversing, d. H. for moving the welding wire to the workpiece. The inert gas arc welding apparatus according to the invention comprises a means for generating a polarity change at the output of the power source to negatively polish the welding wire in the process cycle after a short circuit, after which an arc ignites with negatively poled welding wire, after its extinction another polarity change within the process cycle takes place in order to polish the welding wire again positive. In this case, the pole changing device is also controlled by the control device. Furthermore, after the pulse phase, a third process phase is carried out with reduced energy input into the welding wire compared to the pulse phase. The protective gas arc welding device according to the invention is characterized in that it is designed to carry out one of the above-described inert gas arc welding process, in which in the third process phase after a maximum time and before reaching the short circuit, a polarity change is performed in which the welding wire of positively poled to negative.

The invention will be described below by describing several embodiments with reference to the drawings, wherein

1 in a block diagram representation of a welder designed according to the invention,

2 the time course of the welding quantities welding current, welding voltage and wire speed for a first embodiment of an arc welding process,

3 the time history for the welding variables welding current, welding voltage, welding wire for a second embodiment of an arc welding method,

4 the time course for the welding quantities welding current, welding voltage and wire speed of a process cycle for a first embodiment of a welding method according to the invention,

5 the time course of the welding variables welding current, welding voltage and wire speed of a process cycle for a second embodiment of a welding method according to the invention and

6 the time course of welding variables welding current, welding voltage and Wire speed of a process cycle for a conventional welding process shows.

1 shows a block diagram of a welding machine 1 with which the protective gas arc welding process according to the invention can be carried out. The welding machine 1 includes one on a three-phase network 10 connected welding power source, a pole changing device 4 to reverse the polarity is connected downstream of the output. At the output of the pole changer is the welding voltage U _S , the welding current I _S is discharged. The welding power source 2 converts those from the net 10 provided energy in a regulated DC voltage or in a regulated DC. The polarity change device 4 and the welding power source 2 be from the controller 3 controlled. The latter also controls a wire feeder 5 which supplies the welding wire to the welding process. The device 5 includes a wire feed motor that conveys the wire from a wire supply, such as a wire spool. The control 3 causes the wire feed motor, this in a predetermined manner, for example, with a predetermined speed and / or acceleration in the direction of the burner 7 to promote. This ensures the contacting of the welding wire 11 with the welding voltage and has in the described embodiment, a second, not shown wire feed motor, with which the welding wire can be pulled away from the workpiece. This is ensured by a wire buffer 6 between burner and wire feeder 5 for picking up the wire when retracting the wire or when setting the negative wire speed. At the end of the burner, ie between the end of the welding wire 11 and the workpiece 9 An arc is formed 8th which is covered by a protective or active gas. The workpiece 9 is to close the welding circuit with the second pole of the pole changer 4 connected. Depending on the embodiment of the welding device this includes various, not shown measuring devices for detecting process parameters, such as welding voltage and welding current. In a particular embodiment, measuring devices are provided which detect the welding voltage and the welding current directly at the welding process between the wire electrode and the workpiece, so that a particularly precise control of the process cycle is possible. In this way, in particular the arc voltage can be detected.

Before looking at the use of the in 1 For the sake of clarity of illustration, a conventional method will first be described with reference to FIG. 3 for the purpose of carrying out the protective gas arc welding method according to the invention 6 described. 6 shows the time course of the three process parameters welding current I _S , welding voltage U _S and wire speed V _{D of} the welding wire over the period of about two process cycles. The pulsed arc is designed as a short arc and comprises one current pulse per process cycle. The process parameters are set in such a way that no droplet transition from the wire electrode into the molten bath takes place during the pulse, but only after the contact of the welding wire with the weld pool, so that the droplet transition is spatter-free. After reaching the short circuit, the welding wire is withdrawn and reversed again after the short circuit has been released, so that the wire is moved again in the direction of the workpiece. This in 6 shown short-arc method with mechanically assisted short circuit resolution has a very low heat input into the workpiece when the volume of melted wire per unit time is low.

In contrast, this now with reference to the 4 and 5 described inventive method to a similar low heat input into the workpiece, but far larger volumes per unit time can be melted.

2 shows in a similar manner as in the previous figure, the three process parameters welding current I _S , welding voltage U _{S ,} and wire speed V _D for another welding process.

Since the present invention does not relate to the ignition of the arc at the start of welding, it should be pointed out briefly that the ignition can be carried out, for example, with retraction of the wire after the first placing of the wire on the workpiece. Corresponding start parameters are set to meet the conditions at the beginning of the seam like a cold workpiece. The present invention relates to the arc process in a stable state after the startup phase.

The in 2 The process shown has been divided into five time periods t ₁₁ to t ₁₅ . These designations are used below both to indicate the respective process phase as well as to indicate the duration of this process phase, since the respective meaning results immediately from the context.

In the basic phase t ₁₄ is regulated to a low current value, with arc burning with positively poled welding wire. It comes to the melting of the welding wire and the workpiece. At the end of the wire, a small ball of liquid metal forms. In the subsequent process phase t ₁₅ , a higher energy is introduced compared to the base phase t ₁₄ . In the pulse phase t ₁₅ is controlled to a constant value or a predetermined curve of the welding current or the welding voltage. At the same time, the power in the pulse is adjusted in such a way that the wire at the tip melts further, increasing the sphere of molten metal. At the same time, the short arc is adjusted so that the generated pinching force does not lead to detachment of the drop within the pulse phase t ₁₅ . Depending on the specific embodiment, different pulse edges can be set between the transition from the process phase t ₁₄ to the process phase t ₁₅ . At the end of the pulse process phase, a ball of liquid material has formed at the welding wire end.

Subsequent to the pulse process phase t ₁₅ , a further process phase t ₁₁ follows, in which, when the arc continues to burn, the energy input that is reduced in comparison to the pulse is further melted. For this third process _phase t ₁₁ , a minimum and a maximum time duration t _{11max is} defined. As a rule, the time interval in the process phase t _{11 is} determined by the occurrence of the short circuit. In this short circuit, ie at the end of this course, the melted drop at the end of the weld wire is transferred to the weld pool. If the arc voltage or the welding voltage falls below a certain threshold of, for example, 10 volts, the event is interpreted by the process control as a short circuit and the change takes place from the process phase t ₁₁ into the process phase t ₁₂ , which can be referred to as a short-circuit phase. However, should no short-circuit occur after expiration of a maximum time t _11max in the process _phase t ₁₁ , the control nevertheless _switches to the process _phase t ₁₂ .

In the process phases t ₁₄ and t ₁₅ , the wire speed is positive, causing the welding wire to the workpiece 9 emotional. The wire speed is set to a value corresponding to the desired deposition rate so that a stable welding process is established in conjunction with the other process parameters controlled by the controller.

With the beginning of the process phase t _12, the retraction of the wire begins as t, the course of the wire speed in the phase ₁₂ shows. The wire moves away from the workpiece, as indicated by the negative wire speed of the process phase t ₁₂ . Within the short-circuit phase is regulated to a constant short-circuit current.

After a certain time, the shorting bridge between the welding wire end, liquid metal and the workpiece opens 9 by pulling back the wire. In addition, with the start of the process phase t _12, the polarity of the output of the welding power source vice versa, as the curve for the welding voltage at the start of phase ₁₂ is t. The current direction thus changes as well. The tearing of the short-circuiting bridge forms an arc, a current flows in the negative direction. The current within the process phase t ₁₂ may be regulated to a low level to limit the power to a predetermined value after re-ignition and to prevent spatter.

After the process phase t ₁₂ , the phase t follows ₁₃ at which the arc with negative poled welding wire continues to burn and the current for a predetermined time t _{13 is} regulated to a certain current or voltage value. As a result of the negative polarity of the welding wire, considerably more wire is melted at the same electric power compared to the conditions in the basic phase t ₁₄ . After expiration of the time interval t ₁₃ , a second polarity change takes place by again reversing the polarity of the output voltage, whereby the process phase t ₁₄ starts. In the in 2 Example shown occurs at the second polarity change at the end of the process phase t ₁₃ no short circuit. The process parameters are therefore set so that no droplet is delivered to the weld pool at this time, which would otherwise be associated with splashing by the spacing of the weld wire from the weld pool.

On the process side, it is ensured that, after the second polarity change has been carried out, the arc starts again at the beginning of the already described basic phase t ₁₄ . For this purpose, it is possible, for example, to work with a sufficiently high welding current change rate which, in conjunction with the inductances in the welding circuit, in particular a welding choke, ensures that a high ignition voltage is available for igniting the arc.

Similarly, at the same time, the output of the welding power source can be short-circuited by a fast switch, whereby the current increases and then the switch can be opened again. In both cases, an ignition voltage is generated which is substantially higher than the idling voltage of the welding circuit. Thereafter, the process cycle described can start all over again.

In the described embodiment, it is provided that the total duration of the process cycles is constant, wherein the time intervals t ₁₁ and t _{14 are} variable and, accordingly, are coordinated with each other, the other process phase time intervals within one process cycle are predetermined. The following applies: t ₁₁ + t ₁₂ + t ₁₃ + t ₁₄ + t ₁₅ = constant.

In a further embodiment, the total process time is predetermined for each subsequent process cycle. Thus, depending on process parameters such as the pulse voltage, the process control can calculate a desired time duration of the process cycle and set it before the next cycle. Time intervals that were defined before the end of the process cycle can be set to other values in subsequent process cycles.

2 shows a method in which the speed of the welding wire for dissolution of the short circuit is reduced and changed to negative values. In an embodiment, not shown, it may also be provided that the welding wire is stopped without the wire being withdrawn. During the short circuit, the speed of the welding wire is then kept at zero.

3 shows for a further embodiment of a welding process, the time course of the process parameters welding current, welding voltage and wire speed, wherein the process to the in 2 shown at the expiration of the second polarity change. Again, in a basic phase t _38, a small ball of liquid metal is formed at the end of the welding wire which is amplified in the pulse phase t ₃₉ . Again, the pulse power is adjusted so that it does not come to the detachment of the drop. The pulse phase t ₃₉ in turn is followed by a third phase t ₃₁ , in which the welding wire is further melted and moved in the direction of the workpiece. The end of the process phase t ₃₁ is determined in the example by reaching the short circuit, at which time the process phase starts t ₃₃ , in which the droplet transition starts, the reversal of the wire starts and the first polarity change is performed. In the short-circuit phase t ₃₃ is again regulated to a predetermined short-circuit current. After a certain period of time, the short-circuit bridge between the wire end, liquid part and the workpiece opens again 9 by retracting the wire, the drop transition is terminated whereupon an arc forms with negatively poled welding wire. The current after the process phase t ₃₃ can be regulated to a low value in order to limit the power to a specific value after the re-ignition at the beginning of the process phase t ₃₄ , so that spatters are avoided.

This is followed in turn by a process phase, here t ₃₅ , in which work is carried out with an increased energy input compared with the preceding phase. The time t ₃₅ is predetermined for a single process cycle, but may vary from cycle to cycle. The fact that the welding wire is poled negatively from the phase t ₃₅ , there is a high energy input in the welding wire. Unlike the in 2 shown. By way of example, a short circuit is here associated with the second polarity change, which can be used in particular for the spatter-free discharge of a further drop to the molten bath. In addition, it can be dispensed with external Zündhilfen, since there is no danger that the arc does not ignite after the polarity change. At the end of the arc firing phase t ₃₅ with negatively poled welding wire, the polarity change is performed. It can be provided that between the phases t ₃₅ and t _36, a dead time is inserted to make sure that the arc is off. During this time, welding voltage and welding current would be zero.

After the pole change at the beginning of the process phase t ₃₆ , the open circuit voltage is applied. A welding current does not flow and the wire moves on the workpiece. Upon reaching the short circuit at the beginning of the process phase t ₃₇ , the welding voltage goes to the short-circuit value, being regulated to a low welding current, which may be constant or have a certain waveform. With the short circuit, the wire feed is reversed, causing the shorting bridge between liquid metal, wire, and workpiece to rupture at the beginning of the then basic phase t ₃₈ , thereby re-igniting an arc with positively poled welding wire. With the release of the short circuit, liquid material passes completely from the welding electrode into the weld pool.

Also at the in 3 In the example shown, it is provided that within a process cycle certain process phases each have a predetermined time interval length, which are set before the process cycle. In addition, the intervals of certain process phases are kept variable or on the one hand determined by the process itself, other intervals are then adapted to result in a constant period duration for successive process cycles. At the in 4 In particular, the intervals t ₃₄ , t ₃₅ and t _{39 may be} predetermined, while the time intervals t ₃₁ , t ₃₃ , t ₃₆ , t ₃₇ and t ₃₈ are kept variable.

4 shows the time course of the three specified welding parameters I _S , U _S and V _D for a variant of an arc welding method according to the invention. Again, about two process cycles are shown, with the process phases not described below analogous to those in 3 shown run. In particular, the second polarity change with associated short-circuit phase does not differ from that of 3 , After the pulse phase t ₄₉ , a process phase t ₄₁ follows, in which no short circuit occurs until the end. For this reason, after expiration of the maximum time t _41, a polarity change is performed in which the welding wire is polarized from positive to negative. The arc extinguishes, so that in the process phase t ₄₂ the open-circuit voltage with negative polarity is applied. Between the phases t ₄₁ and t ₄₂ , a dead time can be inserted to ensure that the arc is extinguished before the polarity change. The wire is moved further in the direction of the workpiece, so that at the end of the process phase t _42, a short circuit is generated. In this short-circuit phase t ₄₃ , the short-circuit current is kept at a predetermined value or course. After reaching the short circuit, the wire is decelerated and retracted, which is due to the negative wire speed in 4 is shown. With the dissolution of the short circuit, the drop is transferred from the wire into the weld pool. In the following process phase t ₄₄ , an arc starts when the short-circuiting bridge is torn open. The further course corresponds to that in 3 described method. Also in the arc welding method according to 4 the period duration is kept constant, with the time intervals of the process phases t ₄₁ , t ₄₄ , t ₄₅ , t ₄₈ and t _{49 being} predetermined and the other time intervals t ₄₂ , t ₄₃ , t ₄₆ and t ₄₇ resulting from the process be adjusted.

5 shows the time course of the specified welding parameters for a welding method according to the invention, similar to that in 4 is shown. The difference is in the second polarity change that occurs in the 5 is performed after reaching the short circuit, but not before reaching the short circuit as in the 4 shown method. The change from the process phase t ₅₅ to the process phase t ₅₇ takes place by the occurrence of the short circuit. With the occurrence of the short circuit, the polarity is changed, in which the welding wire is polarized from minus to plus. At the same time, the wire is withdrawn during the process phase t ₅₇ . With the rupture of the shorting bridge, the basic phase t _{58 is} changed and regulated to the basic current. The in the 4 and 5 The methods described can also merge into one another. If, for example, no short-circuit occurs during the process _phase t ₅₅ after a predetermined maximum time t _55max , the second polarity change, as in _FIG 4 shown, done. In the method according to 5 the cycle time of consecutive process cycles is constant. Before the start of the process cycle, the time intervals t ₅₁ , t ₅₅ , t ₅₈ and t ₅₉ are set to predetermined values, while the further time intervals of the process cycle t ₅₂ , t ₅₃ , t ₅₅ and t _{57 are} process-determined, such that the sum of the time intervals the process cycle gives a predetermined value.

According to the invention, the renewed reversing of the wire from negative to positive wire speed does not have to occur in response to the dissolution of the short circuit between wire, liquid metal and workpiece. Instead, as a trigger for reverting the wire movement from the negative direction to the positive direction, it is also possible to achieve a predetermined distance traveled by the wire, which lapses for a predetermined period of time or reaches a predetermined wire speed in the negative direction.

LIST OF REFERENCE NUMBERS

1

welding machine

2

welding source

3

control device

4

Polarity changing means

5

Wire feeder

6

wire buffer

7

burner

8th

Electric arc

9

workpiece

10

Phase power supply

11

welding wire

I _S

welding current

U _S

welding voltage

V _D

wire speed

T _ij

Process phase or duration of the process phase; i = 1..5; j = 1..9

Claims (16)

A gas-shield arc welding process for performing a welding process in which material of a welding wire used as a consumable electrode is transferred into a weld pool having a process cycle comprising a ground phase and a pulse phase in which an arc is burning and the welding wire is positively poled, material of the welding wire in a short-circuit phase is transferred to the molten bath and the dissolution of the short circuit by stopping or retracting the welding wire from the workpiece is supported and after the dissolution of the short arc ignites again and the welding wire is reversed again to move it towards the workpiece, to a short polarity is performed a first polarity change in which the welding wire is negatively poled, and after the polarity change ignites an arc with negatively poled welding wire, and wherein after a Lich arc phase with negatively poled welding wire a second polarity change within the Process cycle is performed, in which the welding wire is positively poled, wherein after the pulse phase, a third process phase is performed with reduced compared to the pulse phase energy input into the welding wire, characterized in that in the third process phase (t41, t51) after a maximum time has elapsed ( t41) and before reaching the short circuit, a polarity change is performed, in which the welding wire is polarized from positive to negative. A method according to claim 1, characterized in that after the detection of the short circuit, the supply of the welding wire ( 11 ) to the workpiece ( 9 ) and / or the welding wire is withdrawn from the workpiece. Method according to one of claims 1 to 2, characterized in that s the reversal of the welding wire for movement of the same in the direction of the workpiece after a predetermined period of time from the time of dissolution or the occurrence of the short circuit is started. Method according to one of claims 1 to 3, characterized in that after the dissolution of the short circuit, the reversal of the welding wire ( 11 ) is started to move toward the workpiece when the welding wire has reached a predetermined distance from the workpiece or a predetermined negative speed. Method according to one of claims 1 to 4, characterized in that the process cycle duration is constant. Method according to one of claims 1 to 5, characterized in that the second polarity change of the process cycle without the setting of an associated short circuit between welding wire ( 11 ) and sweat bath is performed. Method according to one of claims 1 to 6, characterized in that after the arc phase (t44, t54), in which the welding wire is negatively poled, another arc phase (t45, t55) is carried out with negatively poled welding wire, within which predetermined process parameters, In particular, the arc voltage, the arc current and / or the wire speed are adjusted so that within a predetermined maximum time usually a second short circuit between welding wire ( 8th ) and workpiece ( 9 ) is produced. A method according to claim 7, characterized in that the second polarity change after a predetermined maximum period of time in the further arc phase (t45, t55) is performed with negatively poled welding wire, even if the short circuit in the other arc phase with negatively poled welding wire has not been reached , A method according to claim 7, characterized in that the second polarity change despite reaching the short circuit is only performed when the further arc phase (t45, t55) has continued with negatively poled welding wire at least a predetermined minimum period of time. Method according to one of claims 1 to 5, characterized in that following the arc phase (t44, t45, t54, t55), in which the welding wire is negatively poled, the second polarity change is performed, and wherein process parameters such as welding current, welding voltage and / or wire speed can be adjusted so that after the second polarity change in a second short-circuit phase (t47, t57) of the process cycle, the second short circuit between the welding wire and the workpiece is generated. A method according to claim any one of claims 7 to 10, characterized in that with the second short material of the welding wire is transferred into the molten bath. Method according to one of claims 1 to 11, characterized in that after elapse of an arc phase (t41, t45, t51) and before a polarity change, the arc is extinguished, if there is no short circuit. Method according to one of claims 7 to 12, characterized in that on the second short circuit, the welding wire is withdrawn to move it away from the workpiece, wherein after dissolution of the second short circuit, the welding wire is again reversed to move it towards the workpiece and wherein after dissolution of the second short circuit and after the second polarity change again an arc is ignited, in which the welding wire is positively poled. Method according to one of Claims 1 to 13, characterized in that the short circuit current is regulated in the short circuit phases (t43, t47, t53, t57) of the process cycle. Method according to one of claims 1 to 14, characterized in that in the basic phase (t48, t58), in the pulse phase (t49, t59) and in the third phase (t41, t51), either the welding current (I _S ) or the Welding voltage (U _S ) is regulated. A gas arc welding apparatus comprising a welding power source, a controller, a wire feed and retractor, and a welding torch, wherein the controller, after starting the welding process, performs a process cycle by controlling process parameters such as welding current, welding voltage, wire speed, arc length, and / or or process phase interval lengths, wherein the process cycle has a base phase and a pulse phase in which an arc is burning and the welding wire is positively poled, and wherein in a short circuit phase after extinguishing the arc, at least one drop detaches from and enters the welding wire Peat passes, the controller controls the wire feed and retracting device after reaching the short circuit to stop the welding wire or to retract the welding wire from the workpiece and after the release of the short circuit to move out of the welding wire to the workpiece, wherein a means for reversing the welding voltage is provided to negatively poling the welding wire in the process cycle after a short circuit, then ignites an arc with negatively poled welding wire, after its extinction another polarity change takes place within the process cycle to the Welding wire poles again positive, followed after the pulse phase, a third process phase with reduced compared to the pulse phase energy input into the welding wire, characterized in that in the third process phase (t41, t51) after a maximum time (t41, t51) and before Reaching the short circuit, a polarity change is performed, in which the welding wire is polarized from positive to negative.

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