JPS5812108B2 - Method of welding in thermally ionized gas and welding torch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method of welding in a thermally ionized gas, in which a MIG-arc is maintained between a continuously supplied consumable electrode and a workpiece in a gas plasma, and the gas plasma is connected to a non-consumable plasma electrode. The present invention relates to a welding method such as that produced by a plasma arc maintained in a gas flow between a second electrode.

A process of this type, known as plasma MIG welding, is already known from British Patent No. 1,338,866.

According to this known method, the welding current is sent via the contact tube to the consumable electrode upstream of the nozzle, and the consumable electrode part at the level of the plasma electrode then conducts the current, so that an electromagnetic interaction occurs with the gas plasma. The current is generated between the consumable electrodes through which the current flows.

This interaction destabilizes the plasma arc.

This instability has two characteristics.

(a) The gas plasma contracts around the consumable electrode, so that the voltage across the plasma arc increases.

This is a detrimental effect because the low slope portion of the droop voltage characteristic of the plasma power source is generally used for plasma arcing, making continuous maintenance of the plasma arc less reliable.

(b) The contracted gas plasma climbs along the consumable electrode.

This creates an additional undesirable heat rise if the polarity of the consumable electrode is positive (relative to the workpiece) and begins to form a negative polarity (relative to the plasma electrode) on the consumable electrode, so that the plasma arc It will not be directed towards one piece, but rather towards a nearby consumable electrode.

The latter is a highly undesirable phenomenon, since it affects the welding process and usually disturbs the continuity of the welding process.

According to known methods, it is possible to maintain the stability of the plasma arc in the case of negative polarity, especially if the cathode formation on the consumable electrode is promoted by adding some oxygen or CO2 to the plasma gas. However, stability can only be obtained if the potentials of the contact tube and plasma electrode are given to each other within relatively narrow limits.

Complete or partial transfer of current from the plasma electrode to the consumable electrode instead of to the workpiece can easily occur, which is undesirable and usually disrupts the welding process.

This is because the plasma arc driven by the electromagnetic force may proceed further upwards between the plasma electrode and the contact tube, or even result in damage to these parts and leakage.

According to the known method, the current is sent to the consumable electrode via a contact tube, which tube is normally located outside the action range of the arc plasma and usually upstream of the end of the plasma electrode and above the nozzle.

The problem that arises in this case is that the extension of the consumable electrode, i.e. its current-carrying part between the contact tube and its free end, is relatively large;
If this exists, it can be harmful.

The object of the invention is to at least alleviate these drawbacks, to improve the plasma MIG welding process and to widen its range of applications.

This objective is achieved according to the invention by directing the welding current to the consumable electrode downstream of the plasma electrode.

It was surprising to find that the fact that the current supply to the consumable electrode takes place within the gas plasma itself has no negative effect on the welding process.

On the contrary, it is clear that benefits can be obtained both when the plasma electrode and the consumable electrode are of positive polarity as well as when they are of negative polarity.

When the process according to the invention is taken, the consumable electrode part at the level of the plasma electrode does not conduct electricity, and thus instability of the plasma arc due to magnetic interaction between the gas plasma and the consumable electrode is prevented.

As a result, the guides for the plasma electrode and the consumable electrode can be arranged closer to the nozzle and the extension, ie the electrically conductive part of the consumable electrode.

It is quite clear that there are other benefits when welding with negative polarity of the plasma electrode and the consumable electrode.

Even if a discharge occurs between the plasma electrode and the consumable electrode,
This discharge has no upward tendency.

On the contrary, this discharge rather moves in the direction of the workpiece.

A partial or complete discharge between the plasma electrode and the consumable electrode can occur in a stable state if the welding conditions are changed accidentally or intentionally, and the plasma arc between the plasma electrode and the workpiece cannot be maintained or maintained. becomes extremely difficult, while maintaining a discharge between the consumable electrode and the work piece.

This will occur, for example, if the working distance between the welding torch and the workpiece increases beyond a predetermined limit.

When the normal working distance is restored again, the plasma arc will again be naturally directed towards the workpiece.

This is an essential advantage if the welding torch is hand held.

This is possible because the anodic formation of the plasma arc on the consumable electrode or workpiece is very smooth.

The full benefits in this regard can be obtained using the method of the present invention.

This is because the discharge between the plasma electrode and the consumable electrode becomes stable then.

The main advantage lies in the fact that the plasma arc does not become extinguished during welding due to certain disturbances, as sometimes occurs when using known methods.

Furthermore, it has been found that, using the method of the invention, it is no longer necessary to precisely adjust the potentials of the consumable electrode and the plasma electrode relative to each other in order to prevent disturbances or to obtain a satisfactory welding process.

The range over which satisfactory material transfer occurs is much larger.

This is likely due to the short extension of the consumable electrode, which results in a small voltage gradient across the consumable electrode.

When the polarity of the plasma electrode and the consumable electrode is positive, it is important that the consumable electrode extension is long, as this can result in greater penetration of the workpiece than if the consumable electrode extension were large. .

The rotation of the MIG-arc that occurs when using the known method occurs when the transfer current intensity of the welding current is high and as a result of the reduced resistance heating of the consumable electrode and the reduced heating of the gas plasma, the same Such stabilization of the plasma arc with a negative polarity, which allows the use of relatively high welding current intensities below this transition current intensity for the amount of deposited metal, is not achieved with a positive polarity.

However, it is often possible to choose a more suitable position of the plasma electrode relative to the plasma hole, since the distance between the plasma electrode and the consumable electrode is small so that no disturbances occur.

According to a preferred embodiment of the invention, the welding current is delivered to the consumable electrode via a contact area located in a thermally ionized gas atmosphere.

The "open" contact area exposed to the gas plasma has a better current carrying capacity than the closed contact area in the case of contact tubes or contact rings.

According to a preferred method in which the gas flow is guided through the plasma hole of the nozzle, the consumable electrode is brought into contact with the nozzle and the welding current is supplied to the consumable electrode via the nozzle.

The invention also relates to a welding torch for carrying out the above method.

The welding torch has a housing with a non-consumable plasma electrode, a wire guide and a connection for supplying plasma gas, the welding torch having a contact member having a contact surface arranged downstream of the plasma electrode, at least one of the contact surfaces. Some are characterized in that they are substantially aligned with the centerline of the wire guide.

Any contact member may be used provided that it is suitably cooled to withstand the heat build-up caused by current transfer and heat transfer from the gas plasma.

A preferred embodiment of the welding torch according to the invention comprises a nozzle with a plasma hole, said nozzle acting as a contact member;
It is characterized in that the wire guide is arranged eccentrically with respect to the plasma hole, and the center line of the wire guide is substantially aligned with a point on the periphery of the plasma hole.

The nozzle is very suitable for use as a contact member, since it is usually very well cooled.

The plasma in this embodiment is circular or oval.

It has been found that placing the wire guide symmetrically with respect to the nozzle has no effect on the welding process.

Apparently, the electromagnetic field of the current-carrying part of the welding wire outside the nozzle disperses the gas plasma symmetrically around its extension.

A further advantage of using a nozzle as the contact element is that the supply of welding current to the contact area on the nozzle takes place via the wall of the torch housing.

As a result, the current supply to the welding wire produces no or only a weak magnetic field inside the housing where the plasma electrode is located, so that the current passing through the welding wire does not affect the part of the plasma arc within the torch. The impact will be kept to a minimum.

Another embodiment of the welding torch according to the invention is characterized in that it comprises a nozzle with a plasma hole, said nozzle acting as a plasma electrode, and the contact member being arranged downstream of the nozzle.

As a result, the contact member is placed relatively close to the workpiece, so that the current-carrying part of the welding wire and therefore its extension becomes very short.

The invention also relates to an apparatus for carrying out the method of the invention,
The device is characterized by having a welding torch with a non-consumable plasma electrode, a wire guide, a plasma gas supply source, a power supply connecting the plasma electrode, and a second power source located downstream of the plasma electrode. A contact member having a contact surface connected to the supply source, at least a portion of the contact surface being at a point substantially aligned with the centerline of the wire guide.

In a preferred embodiment of the device of the invention, the torch has a nozzle with a plasma hole, the nozzle is connected to a second power supply, and the centerline of the wire guide is arranged at a point on the periphery of the plasma hole. are virtually aligned.

As a result of using a nozzle as a contact element, a separate contact device can be omitted.

The device according to the invention is suitable both for welding with a transferred plasma arc and also for welding with a non-transferred plasma arc.

A transferred plasma arc is maintained between the plasma electrode and the workpiece, which acts as a second electrode.

A non-transferred plasma arc is maintained between the plasma electrode and a second electrode other than the workpiece, such as a nozzle, an annular electrode or a separate rod electrode located upstream or downstream of the nozzle.

According to a further preferred embodiment of the device according to the invention, the two power supplies are connected in series, the nozzle being connected to the first power supply and the switch being connected to the second power supply.

With this device, the welding process can be started in a simple manner by first igniting a non-transferred plasma arc and, after ignition of the MIG arc, welding with the transferred plasma arc.

Another preferred embodiment provides a simple, inexpensive device in which the first power supply is constituted by a transformer and the nozzle is provided with an auxiliary electrode.

A further preferred embodiment of the invention is one in which the torch has a nozzle with a plasma hole, characterized in that the contact member is located downstream of the nozzle.

Welding with very short extensions of the welding wire is possible when a contact member is placed between the nozzle and the workpiece.

A further preferred embodiment provides a very compact and simple device in which the nozzle is connected to a first power supply and thus acts as a non-consumable plasma electrode.

A separate plasma electrode can thus be omitted.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The welding device 1 shown in FIG. 1 comprises a welding torch 3, which includes a non-consumable plasma electrode 5 and a welding torch housing 21.
It has wire guides 15, one on each side of the centerline T.

The housing 21 has a nozzle 11 with a plasma hole 13 and a connection 23 for supplying the inert gas stream A.

The shielding gas S can be supplied via a connection 27 in the shielding body 25.

In this embodiment, the plasma electrode 5 made of tungsten is mounted on a copper holder 29, which is cooled via cooling water connections 31 and 33 and a cooling duct (not shown).

The nozzle 11 and the housing 21 are provided with cooling ducts (not shown) in the usual manner.

The electrode holder 29 is connected to the connection terminal 35 via the HF-generator 7.
is used to connect to one of the two poles of the first power supply source 9, the other pole being connected to the workpiece W.

Using the connection terminal 37, the nozzle 11 is connected to the second power supply source 1.
9, and the other pole is connected to the workpiece W.

The holder 29 is insulated with respect to the housing 21 using an insert 39 of synthetic material.

The welding wire 17 to be welded is transported by means of rollers 41 driven at a controllable speed by a motor 43.

A wire guide 15 is arranged relative to the nozzle 11 such that the center line Y of the wire guide is substantially aligned with a point on the inner circumference of the nozzle 11 bounding the plasma hole 13 so that the welding wire 17 is directed to the welding current. It contacts the inner periphery of the nozzle, which acts as a contact member for sending the welding wire to the welding wire.

Welding can be performed with either positive or negative polarity of the welding wire, nozzle and plasma electrode as long as these polarities are the same.

The transferred plasma arc P is ignited by a high frequency discharge between the plasma electrode 5 and the workpiece W and is maintained by a power supply source 9.

Subsequently, the welding wire 17 can be fed after the MIG arc M has been ignited between the welding wire and the workpiece.

The welding wire is maintained at the appropriate potential by a power supply.

Positive polarity has advantages over negative polarity.

That is, the welding process is carried out smoothly in a high current range, for example 225 A or more.

The advantage of negative polarity over positive polarity is that the stability of the plasma is guaranteed as long as the discharge from the welding wire to the workpiece occurs.

Another advantage in certain cases is that the transfer of material disturbs the weld pool less and the roots of the combined arc on the weld pool are more regularly distributed, thus reducing the dispersion effect of the weld surface. .

For both polarities, it is alternatively possible to weld between the plasma electrode 5 and the nozzle 11 using a non-transferred plasma arc.

For this purpose, the power supply 9 for the plasma arc is connected to the nozzle 1 instead of to the connection on the workpiece W using the connection terminal 47.
1, the two power supplies 9 and 19 being connected in series.

It is advantageous for the plasma arc to be completely independent of the workpiece.

In the latter embodiment, in which a non-transferred plasma arc is used to weld between the plasma electrode and the nozzle, the workpiece W and the MIG arc M are
It is substantially advantageous to provide a switch 49 between the second power supply 19 for use.

When the switch 49 is opened, the plasma arc that is not transferred to the workpiece W is ignited between the plasma electrode 5 and the nozzle 11.

Once feeding of welding wire 17 begins, switch 49 is closed to complete the workpiece-power supply-nozzle-welding wire connection and bring the welding wire to the appropriate potential with respect to the workpiece.

As a result, the plasma electrode is at a higher potential with respect to the workpiece.

As a result, the plasma arc starting from the plasma electrode 5 flies from the nozzle 11 to the workpiece W, and then the welding wire 1
7 to the work piece W starts immediately.

When the wire feed stops and the switch 49 is turned off, the plasma arc automatically returns from the plasma electrode 5 and nozzle 11 to its non-transitional form.

The device is then ready to restart the welding process, so that ignition of the plasma by means of a high-frequency discharge is no longer necessary.

As shown in FIG. 1, the nozzle of the above-described embodiment, which forms a non-transferred plasma arc between the plasma electrode 5 and the nozzle 11 via the connection terminal 47, is connected to the second plasma electrode in the housing 21 in a manner known per se. 51, in which case a non-transferred plasma arc would be formed between the two plasma electrodes 5 and 51.

If both plasma electrodes 5 and 51 are made of tungsten, the power supply 9 consists of a transformer.

If the third power supply 53 is connected to one of the two plasma electrodes and to the workpiece W via the switch 55, the stability of the plasma arc between the plasma electrode 5 and the workpiece W is This is ensured by the simultaneous presence of a plasma arc between the two plasma electrodes 5 and 51 in the housing 21 which is not transferred to the workpiece.

The reason for this is that if the plasma arc into the workpiece is extinguished due to turbulence during welding, it can be immediately ignited again by the thermally ionized gas flow created by the plasma arc between two plasma electrodes independent of the workpiece. will be done.

Welding is usually performed using direct current for welding wire and plasma arc.

The embodiment shown in FIG. 1 in dashed lines and consisting of two series-connected power supplies 9 and 19 and switch 49 is simple and inexpensive, and the first power supply 9 can be replaced by an inexpensive transformer 57 (FIG. 3).
It can be made by replacing with .

A tungsten auxiliary electrode 59 is then arranged inside the nozzle 11 .

A non-transferring alternating current arc is ignited between the plasma arc 5 and the auxiliary electrode 59 using a short high frequency discharge.

With two tungsten electrodes, an alternating current arc can be maintained by the transformer 57 without creating high frequency discharges.

The argon gas flow introduced into the housing 21 blows arc plasma through the nozzle 11 onto the workpiece W.

The device is now ready for the start of the plasma NIMIG welding process without high-frequency discharge.

For this purpose, the feeding of the welding wire 17 is started, this wire comes into contact with the nozzle, and the switch 49 is closed at the same time.

At that time, the welding wire 17 passes through the nozzle 11 and is connected to the DC power source 19.
, and its negative electrode is connected to the workpiece W.

When the switch 49 is closed, the transition plasma arc moves to the electrode 5.
It has been found that the discharge of the welding wire 17 is immediately ignited and maintained between the welding wire 17 and the workpiece W.

Once the DC discharge of the welding wire 17 occurs, the cathode will be permanently present on the workpiece W and the discharge from the plasma electrode 5 to the workpiece W will be firmly ignited during its positive period.

During the negative period of the plasma electrode 5, a plasma arc is constantly and constantly present between the plasma electrode and the nozzle.

It is surprising that the first ignition of the transferred plasma arc takes place so smoothly.

This is because cathode spots must be formed on the workpiece.

It is clear that the presence of the thermally ionized gas of the non-transitional plasma arc and the increase in potential at the plasma electrode during the positive phase, with the voltage of the DC power supply 19, is sufficient for this purpose.

Despite the fact that only half of the plasma stream flows to the workpiece and therefore the heat of the weld is less than in the case of a direct current plasma arc, the difference in welding results is only small.

When the four feeds of wire are completed and switch 49 is opened, the non-transitional alternating current plasma arc remains ready to be started again.

All of these circuits have been successfully used in welding tests using wire currents between 50A and 500A and plasma currents between 50A and 300A.

In the test, steel, stainless steel, copper, and aluminum welding wires with diameters of 1.6 to 0.9 mm were welded.

FIG. 4 shows an embodiment in which a separate contact member 61 connected to a second power supply 19 is placed between the nozzle 11 and the workpiece W.

The contact member has a contact surface 6 parallel to the center line Y of the wire guide 15.
Has 3.

The contact member is arranged such that the contact surface 63 is substantially aligned with the centerline Y.

The extension or welding wire 17, ie the current-carrying section between the contact element and the free end of the welding wire, is very short in this embodiment.

The contact member 61 should be suitably cooled and may be provided with cooling ducts (not shown) for this purpose.

The embodiment shown in FIG. 5 has a water-cooled copper holder 75 and a contact surface 73.
The contact member 71 is comprised of a tungsten portion 77 having a tungsten portion 77.

The nozzle 11 is contacted by a first power supply 9 and acts as a plasma electrode.

A separate plasma electrode within housing 21 is thus eliminated.

A high frequency generator is no longer needed in this embodiment.

This is because the plasma arc can optionally be ignited by a MIG arc that can be ignited by contacting the welding wire with the workpiece.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a practical embodiment of the present invention, Figures 2 to 5
The figures are schematic diagrams showing other embodiments of the apparatus for carrying out the method of the present invention, and identical parts are given the same reference numerals. 1... Welding device, 3... Welding torch,
5...Non-consumable plasma electrode, 9...First power supply source, 11...Nozzle, 13...
...Plasma hole, 15...Wire guide, 17.
... Welding wire, 19 ... Second power supply source, 21 ... Housing, 29 ... Holder, 37 ... Connection terminal, 39・・・・・・
Insert body, 41...Roller, 49, 55...
...Switch, 51...Second plasma electrode, 5
3... Third power supply source, 61... Contact member.

Claims (1)

[Claims] 1. A plasma arc is maintained in a gas flow between a non-consumable plasma electrode and a supplementary electrode, the gas plasma generated by the plasma arc is guided through a nozzle, and the consumable electrode is introduced into the gas plasma. and supplying the MIG arc current to the consumable electrode with a contact zone placed in the gas plasma in a method of welding in a thermally ionized gas that is continuously fed through a nozzle towards the workpiece and maintains the MIG arc between the consumable electrode and the workpiece. A welding method characterized by: 2. A method according to claim 1, characterized in that the consumable electrode is brought into contact with a nozzle and the MIG arc current is supplied to the consumable electrode through the nozzle. 3. In a welding torch comprising a housing with a nozzle with a hole, a non-consumable plasma electrode, a wire guide in the housing for guiding the consumable electrode through the nozzle hole, and a connection for supplying plasma gas, the plasma electrode Contact element 1 with contact surface 45.63.73 located downstream of 5
1.61.71, characterized in that at least a portion of said contact surface is substantially aligned with the centerline Y of the wire guide 15. 4. In the welding torch according to claim 3, the nozzle 11 is adapted to act as a contact member, the wire guide 15 is arranged centrally with respect to the nozzle hole 13, and the center line Y of the wire guide 15 is aligned with the nozzle hole. A welding torch characterized in that the welding torch is substantially aligned with the inner circumference 45 of 13. 5. Welding torch according to claim 3, characterized in that the nozzle 11 is adapted to act as a non-consumable electrode, and the contact member 71 is arranged downstream of the nozzle 11.