DE102008017172B4 - Device for joining with a short-circuiting MSG process - Google Patents

Abstract

Device for short-circuited joining with a MSG process with continuous wire feed and melting electrode, characterized in that control means are provided which, depending on a measurement of a cyclically varying in a short-circuited MSG process physical variable (U, I), the conclusions of a Start short circuit (K, K, K) and / or a short-circuit end (A, A, A), initiate a polarity change without additional control of the wire feed to the electrode, wherein the control means are adapted to a positive polarity when a short circuit occurs to lay the electrode, and wherein the control means are adapted to apply a negative polarity to the electrode after the end of a short circuit.

Description

State of the art

Metal arc welding and brazing (MSG welding and brazing or summarized MSG joining) have long been used as a technique for welding and brazing two or more joining partners as well as for applying welding consumables and brazing alloys. For this purpose, a filler material in the form of a cored wire, solid wire or in strip form is melted in an arc generated by an electrical energy source in a protective gas atmosphere. In this case, the arc burns between the base material and the melting-off tracking wire, which represents the electrode.

Depending on the filler material used and the inert gas used, one speaks of metal inert gas welding and soldering (MIG welding, MIG brazing) or of metal active welding and brazing (MAG welding, MAG brazing). In summary, these methods are referred to as MSG processes.

Depending on process parameters, different distinguishing features and procedures arise.

There are short arc, transition arc, spray arc, long arc, rotation arc and pulsed arc.

Short-circuited arc processes can be generated which have two different phases, the so-called arc burning phase and the short-circuit phase. In the arc burning phase, the electrode, a filler material is melted and touched due to a growing drop volume at the melting filler material and the other wire feed the workpiece. It comes to a short circuit. In this short-circuit phase, the drop is further constricted by an increasing short-circuit current and also drawn off into the molten bath due to the surface tension. Through a by the separation of the drop from the still fixed wire resulting gap ignites the arc again.

Characteristic of this process is a change between an arc-burning phase and a short-circuit phase of each of the phases resulting in the process through the process. The drop transition described above in the short arc process takes place exclusively in the short-circuit phase. In other types of arc occur more or less large shares of the material transition in the arc burning phase.

So far, short-circuiting MSG processes are mainly operated with direct current. The electrode is positive and the workpiece is negatively polarized. However, there are also embodiments to realize a short arc process with alternating polarity. The polarity changes are specified by a frequency from the outside.

Short-circuited MSG processes that are performed with a purely negatively polarized electrode are known only for flux cored wires. Solid wires create an unstable process that is not suitable for all joining tasks.

The process with a positively polarized electrode leads, according to observation, more heat into the workpiece (molten bath) than the process with negatively polarized electrode and can melt off smaller amounts of filler material. For a constant droplet detachment can be achieved at a positively polarized electrode.

From the AT 501 489 A1 is a welding process with pronounced wire feed control known. A welding current control is in the EP 1 658 919 A2 disclosed. Here a reignition takes place during a polarity change. A welding process with two electrodes is in the US 2006/0207983 A1 described.

Purpose and advantages of the invention

The invention has for its object to improve a short-circuiting MSG process with consumable electrode.

This object is solved by the features of claim 1.

In the dependent claims advantageous and expedient developments of the invention are given.

The invention is based on a device for joining with a short-circuiting MSG process with continuous wire feed and consumable electrode. The essence of the invention resides in the provision of control means which initiate a polarity change at the electrode as a function of detection of a cyclically varying physical variable in the case of a short-circuited MSG process, which allows conclusions to be drawn on shorting and / or shorting. This combines the advantages of a plus-pole electrode for regular droplet detachment and the advantages of a negatively poled electrode for higher deposition rate on a colder workpiece, without additional control beyond the automatic internal control of the arc process itself use. An additional control of the wire feed to the electrode does not take place. A polarity change is only determined by a cyclically varying physical quantity, which only has to be detected.

Thus, a separate control of the arc length as in a process with imposed frequency is not necessary.

The arc process can, so to speak, follow its "natural conditions" essentially freely, except for the changing polarity.

1. A. Charakteristik der Spannungskennlinie der Energiequelle zum Fügen mit dem MSG-Prozess
2. B. Verhalten der Übergangswiderstände zwischen der Drahtelektrode und dem Werkstück sowie dem Kontaktrohr und der Elektrode
3. C. Veränderungen in der Legierung der Drahtelektrode und/oder des Werkstücks
4. D. Veränderungen in der Oberflächenbeschaffenheit der Bauteile und der Drahtelektrode.
5. E. Änderungen des Abstands eines Kontaktrohres zum Werkstück
6. F. Änderungen in der Schweiß- bzw. Lötgeschwindigkeit
7. G. Änderungen der Schutzgaszusammensetzung
8. H. Änderungen der Umgebungsfaktoren wie Temperatur, Feuchtigkeit, Luftbewegungen etc.

Preferably, a polarity change is performed on the electrode within a cycle. One cycle results from a total time of short-circuit phase and subsequent arc-burning phase. The cycle time is a function of the following factors:

1. A. Characteristic of the voltage characteristic of the energy source for joining with the MIG process
2. B. Behavior of the contact resistances between the wire electrode and the workpiece and the contact tube and the electrode
3. C. Changes in the alloy of the wire electrode and / or the workpiece
4. D. Changes in the surface finish of the components and the wire electrode.
5. E. Changes in the distance of a contact tube to the workpiece
6. F. Changes in welding or soldering speed
7. G. Changes in the protective gas composition
8. H. Changes in environmental factors such as temperature, humidity, air movements, etc.

Since all these factors are subject to changes, there are always different lengths of arc burning and short-circuit phases and thus different lengths of cycle times. The smaller the difference between the individual cycle durations, the smoother the process. Exactly the same cycle times can not be set accordingly.

In order to be able to use the different phase times and thus the inner regulation of the process, the Umpolzeitpunkte and the residence times in the individual polarities are inventively determined by characteristic features within a cycle. That is, at least one Umpolzeitpunkt depends on a recurring event within a cycle duration. The other Umpolzeitpunkt can take place after a determinable time or triggered by another recurrent event within the same cycle duration.

It is also conceivable that a polarity change is not made in each cycle.

According to the invention, the control means are designed to apply a positive polarity to the electrode when a short circuit occurs.

The polarity change can be made directly at the short-circuit detection or after a predetermined delay time.

In addition, after the end of a short circuit, the control means applies a negative polarity to the electrode, which can be initiated immediately at the detection time or after a predetermined delay time.

This approach is based on the finding that characteristic recurring features in a short-circuited MSG process are on the one hand the beginning of the short-circuit phase (corresponds to the end of the arc firing phase) and on the other hand the end of the short-circuit phase (corresponds to the beginning of the arc firing phase). Both events cause physical quantities of the arc process to change.

As a signal generator for a Umpolvorgang such a physical size can be measured. The consequences are Umpolvorgänge within a cycle, which have no fixed frequency, but process dependent are subject to the internal control of the arc process.

Preferably, the physical quantity to be measured is the arc voltage. An increase in voltage, a voltage drop or a voltage threshold value can be evaluated. From the voltage curve, the short-circuit time or the dissolution of the short circuit can be determined.

Also as a physical variable for the process of polarity reversal, the current profile can be detected. Here, too, a current gradient or the overshoot or undershoot of a current threshold value can be evaluated.

For the initiation of a polarity change, it is also possible to use a variable which derives from the current and / or the voltage. For example, a power threshold or a power gradient is determined and evaluated. Also conceivable is the evaluation of an impedance threshold or an impedance gradient.

In addition to these variables, an optical and / or acoustic effect of the short-circuiting MSG process can be evaluated for an initiation of a polarity change. This procedure makes use of the fact that, for example, when the short-circuit occurs, the arc extinguishes and, as a result, a brightness change occurs at the joint. In addition, the extinction and re-ignition of an arc can be recognized by its characteristic acoustics, which therefore also provides an indication of the interesting cycle changes in the short-circuited MSG process.

At least one Umpolzeitpunkt should be directed according to the invention for a recurring event. A subsequent polarity change can preferably also be carried out after a predetermined period of time after a polarity change of control means initiated by a physical variable.

Similarly, the device can also be used in energy sources for joining with a short-circuiting MSG process, which operate with an external control. Since in these also differently long arc burning and short circuit phases occur, the detection of a characteristic feature as a signal generator for a Umpolvorgang is necessary.

The device may already include an energy source for joining with the MSG process.

However, it is also conceivable that the device does not include an energy source, but is used in conjunction with a separate energy source. This makes it possible to connect the device of an existing energy source and thus to improve a conventional energy source as a retrofit circuit.

list of figures

Several embodiments of the invention are explained in more detail below with reference to the drawings, indicating further advantages and details.

• 1 einen erfindungsgemäßen Strom- und Spannungsverlauf zwischen einer Elektrode und einem Werkstück bei Einsatz einer erfindungsgemäßen Vorrichtung zum Fügen mit einem kurzschlussbehafteten MSG-Prozess und
• 2 in einem schematischen Schaltbild eine erfindungsgemäße Vorrichtung zum Fügen mit einem kurzschlussbehafteten MSG-Prozess.

Show it

• 1 a current and voltage profile according to the invention between an electrode and a workpiece when using a device according to the invention for joining with a short circuit MSG process and
• 2 in a schematic diagram of an inventive device for joining with a short-circuit subject MSG process.

Description of the embodiments

In 1 are the resulting current and voltage curves 1 . 2 between the electrode and the workpiece when using the device according to the invention for joining with a short-circuit subject MSG process.

In a solid line is the current waveform 1 and in dotted line the voltage curve 2 applied over time t.

In a short-circuit phase KS ₁ , a positive polarity is applied to an electrode. This polarity facilitates the detachment of a drop from the filler material. The residence time of this polarity is at least as long as it is necessary to dissolve the short circuit. However, it can be extended to change the heat input into the molten bath or into the workpiece. The dissolution of the short circuit at the time A ₁ is detected by the measurable change of a cyclically varying measured variable, for example, the rise of the arc voltage U over a predetermined voltage threshold. This process variable is used as a trigger signal to change the polarity W ₂ at the electrode. However, it is also possible to evaluate the current I.

The polarity change can be either immediate or, as in 1 shown, done with a predetermined delay time tv. After the polarity change W ₂ the electrode is negatively polarized. The negative polarity is then maintained until the beginning of the subsequent short-circuit phase KS ₂ . The beginning K _{2 of} the short-circuit phase is characterized by the measurable change of a cyclically varying process variable, eg the drop of the arc voltage U below a predetermined voltage threshold. This process variable can therefore be used as a trigger signal to a renewed polarity change W ₃ at the electrode to the original positive polarity. It starts a new cycle Z ₂ ,

If the re-occurring short circuit W ₃ occurs earlier than the delay time t _{v has} elapsed, takes place no polarity change to the negative polarity at the electrode.

Since, in this embodiment, arc welding and short-circuit phases of different process lengths occur in this embodiment, a compensation of the arc length takes place only by the automatic internal regulation. Thus, no separate regulation of the arc length is necessary.

The components required to recognize the characteristic recurrent events within one cycle or within several cycle times, as well as the components required to perform a polarity change, can either be integrated in one energy source or they can be designed as a separate device to provide one with one existing energy source with which it is possible to perform short-circuiting MSG joining processes.

In the latter variant, an extension of an existing energy source to another setting parameter, which makes it possible to vary the heat input into the molten bath or the workpiece by a polarity change except the already existing minimum parameters voltage level and associated wire feed speed.

The device may also be used in conjunction with an energy source for joining with a short-circuited MSG process that utilizes external regulation. Since different long cycle times also occur here, a characteristic feature must also be referred to for the polarity reversal processes.

In 2 is the schematic block diagram of a device according to the invention for short-circuiting joining with the MSG process shown.

It shows the connection of an energy source 1a for joining with the MSG process with a device 2a which is necessary for generating polarity changes. At a connection 5 a torch hose package is not shown connected and a return current cable 6 leads to a workpiece (not shown). Through lines 3 and 4 cyclically recurring physical quantities can be measured, that of the device 2a serve as a signal generator for change of polarity.

LIST OF REFERENCE NUMBERS

1

current profile

1a

energy

2

voltage curve

2a

contraption

3

management

4

management

5

connection

6

Rear power cable

Claims (9)

Device for short-circuited joining with a MSG process with continuous wire feed and melting electrode, characterized in that control means are provided which, depending on a measurement of a cyclically varying in a short-circuited MSG process physical variable (U, I), the conclusions of a Start short circuit (K ₁ , K ₂ , K ₃ ) and / or a short-circuit end (A ₁ , A ₂ , A ₃ ), initiate a polarity change without additional control of the wire feed to the electrode, wherein the control means are adapted to occur when a short circuit to put a positive polarity to the electrode, and wherein the control means are designed such that after the end of a short circuit to put a negative polarity to the electrode. Device after Claim 1 , characterized in that the physical variable to be measured is the current waveform (I). Device after Claim 1 , characterized in that the physical quantity to be measured is the voltage curve (U). Device after Claim 1 characterized in that the control means are adapted to use a size for the initiation of a polarity change, which derives from the current (I) and / or the voltage curve (U). Device after Claim 1 characterized in that the control means are adapted to evaluate for the initiation of a polarity change optical and / or acoustic effects of the process. Device according to one of the preceding claims, characterized in that the control means are designed, after a polarity change introduced by a physical quantity (I, U), to change the polarity again after a predetermined period of time has elapsed. Device according to one of the preceding claims, characterized in that the control means are adapted to make a polarity change only after a delay time (t _v ). Device according to one of the preceding claims, characterized in that the device already comprises an energy source for joining with the MSG process. Device according to one of the preceding claims, characterized in that the device is designed for connection to a separate energy source for joining with the MSG process.

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