FI65933C - REFERENCE TO A FRAMEWORK FOR ENTRY IN TERMS AND CONDITIONS - Google Patents

Description

Between 65933 electrodes. This interaction may cause instability in the plasma arc. Namely, this instability may have two characteristics: a) shrinkage of the gas plasma around the consumable electrode, so that the voltage across the plasma arc increases. This is a detrimental phenomenon because a less steep portion of the descending voltage characteristic in the plasma power supply source for the plasma arc is generally used, and this makes the continuous maintenance of the plasma arc less reliable.

b) Climbing of the collapsed gas plasma along the consumable electrode, which in the case of relatively positive polarity of the consumable electrode (relative to the workpiece) generates excess and harmful heat and may cause and initiate the formation of a cathode (compared to a plasma electrode) on the consumable electrode so that the plasma arc does not point to the workpiece but instead to the nearest consumable electrode. The latter is a very detrimental phenomenon as it affects the welding process and usually interferes with the continuity of the process.

According to the known method, it has been possible to maintain the stability of the plasma arc in the case of negative polarity, especially if cathode formation on a consumable electrode is stimulated by adding some oxygen or carbon dioxide to the plasma gas, but stability is not achieved if the coupling tube and plasma electrode polarities are not relatively narrow. The complete or partial exchange of current from the plasma electrode to the consumable electrode instead of the workpiece easily occurs again, which is detrimental and usually leads to disturbances in the plasma arc, which is further upward between the plasma electrode and the coupling tube or even destroyed by electromagnetic forces. so that usually then leakage occurs.

According to a known method, where current is supplied to a consumable electrode via a connecting tube, this tube is generally located above the nozzle outside the area of action of the plasma arc and generally upstream of the end of the plasma electrode. In this case, there is a problem in that the extension of the wearable ¢ 5933 electrode, i.e. the current-carrying portion thereof, between the coupling tube and its free end is relatively large, which is a detrimental phenomenon in certain cases.

It is an object of the present invention to at least alleviate these disadvantages by improving the plasma MIG welding process and extending the scope of its applications.

The object of the present invention is realized according to the present invention by supplying a current for the MIG arc to a consumable electrode at a connection point located inside the gas plasma.

It has surprisingly been found that the fact that current is applied to a consumable electrode in the region of the gas plasma does not in itself have a detrimental effect on the welding process. Conversely, in the case of positive as well as negative polarity, the advantages achieved between the plasma electrode and the consumable electrode are obvious. When the supply according to the present invention is realized, the consumable electrode portion at the plasma electrode level is not current-carrying, so that the instability of the plasma arc due to the magnetic interaction between the gas plasma and the consumable electrode can be prevented. As a result, the plasma electrode, as well as the guide for the consumable electrode, can be arranged closer to the nozzle and the extension portion, i.e., the current-carrying portion of the consumable electrode, is made to decrease in length.

Another advantage is very obvious in the case of welding with a negative polarity between the plasma electrode and the consumable electrode. Even if a discharge occurs between the plasma electrode and the consumable electrode, this discharge does not tend to move upwards. On the contrary, this discharge shifts rather in the direction of the workpiece. A partial or complete discharge between the plasma electrode and the consumable electrode then occurs in a completely stable manner if the welding conditions change either accidentally or intentionally so that the plasma arc between the plasma electrode and the workpiece cannot be maintained or is maintained only with great difficulty. between the workpiece can then be maintained. This can happen, for example, if the working distance between the welding torch and the workpiece increases beyond certain limits. When the normal working distance is restored, the plasma arc re-ignites spontaneously towards the workpiece. This is a considerable advantage that is substantially relevant if the welding torch is held by hand. This is possible because the formation of the plasma arc anode on the consumable electrode or workpiece occurs very uniformly when using the method of the present invention, giving full advantage of this property, since the discharge between the plasma electrode and the consumable electrode is then stable. A significant advantage is the fact that the plasma arc cannot be extinguished during welding by a certain type of disturbance, as may occasionally occur with a previously known method. It has further been found that when the method of the present invention is utilized, it is no longer necessary to precisely adjust the consumable electrode and plasma electrode voltages relative to each other in order to prevent interference or to achieve a satisfactory welding process. The area in which a satisfactory transfer of material takes place is much larger. This is probably due to the shorter dimension length of the consumable electrode, so that the voltage gradient over the consumable electrode occurs only to a lesser extent.

In the case of positive polarity, the short span of the consumable electrode between the plasma electrode and the consumable electrode may be important, since this e.g. allows the workpiece to protrude beyond the large range in the wearable electrode. The change in MIG arc that occurs when the known method is used then occurs at a higher current intensity offset value in the welding current, thus allowing higher welding currents to be used below this offset current intensity value for the same amount of electrode material transferred as a result of reduced resistance heating Such stabilization of the plasma arc, which is accomplished with negative polarity, is not achievable with positive polarity, but it is often possible to choose a more favorable position of the plasma electrode compared to the plasma outlet because the smaller distance between the plasma electrode and the consumable electrode does not cause interference.

The invention also relates to a welding torch with which the method is carried out. The welding torch comprises a housing provided with a nozzle 5 65933, said welding torch further comprising a non-wearing plasma electrode, a wire guide in the housing for guiding the wearable electrode through the orifice of the nozzle and a connection for supplying plasma gas.

The welding torch is characterized by a coupling part having a coupling surface located downstream of the plasma electrode, at least a part of the coupling surface being substantially in line with the center line of the wire guide.

Any suitable part may be used for the coupling part, provided that it is suitably cooled so as to be able to withstand the combination of the heat generated by the current transition value and the heat transferred from the gas plasma.

In a preferred embodiment, the nozzle is adapted to act as a coupling part, the wire guide being arranged eccentrically with respect to the nozzle opening, the center line of the wire guide being substantially in line with the inner circumference of the nozzle opening. This nozzle is well suited for use as a coupling part as it is usually very well cooled. The plasma outlet of this embodiment may be circular or elliptical in shape.

It has been found that the asymmetrical arrangement of the wire guide relative to the nozzle does not affect the welding process. Apparently, an electromagnetic field outside the nozzle of the current-carrying part of the welding wire distributes the gas plasma symmetrically around this protruding part.

Another advantage of using the nozzle as a coupling part is that the supply of welding current to the coupling area of the nozzle is effected through the wall of the burner shell part. As a result, the supply of current to the welding wire causes nothing or only a weak magnetic field to act inside the shell part where the plasma electrode is located, so that the effect of current through the welding wire to the part of the plasma arc present in the torch is minimized.

Yet another embodiment of the present invention is characterized in that the nozzle is adapted to function as a non-wearing electrode, the coupling part being arranged downstream of the nozzle. As a result, the coupling part is located relatively close to the workpiece, so that the current-carrying part of the welding wire and its extent are extremely short.

65933

Embodiments of the present invention will now be described in detail with reference to the accompanying drawing, in which: Figure 1 shows an embodiment of the invention, and Figures 2-5 schematically show other embodiments of the apparatus.

Fig. 1 shows a welding apparatus 1 consisting of a welding torch 3 with a non-wearing plasma electrode 5 and a wire guide 15 arranged one on each side of the centerline T in the welding torch housing 21. The housing 21 consists of a nozzle 11 with plasma outlets 13 and a connection 23 for inert gas flow A. The shielding gas S can be supplied via the connections 27 in the shield 25. A plasma electrode 5 made of tungsten in the example in question is mounted on a copper holder 29, which is cooled by cooling water connections 31 and 33 and a cooling cell (not shown).

The nozzle 11 and the housing 21 are provided with a cooling slot (not shown) in a conventional manner. The electrode holder 29 is connected via a terminal 35 via an HF generator 7 to one of the two poles of the first said power supply source 9, the second pole being connected to the workpiece W. Through the terminal 37 the nozzle 11 is connected to one of the second poles of said power supply 19, the other pole is connected to the workpiece W. The holder 29 is insulated from the housing 21 by means of a snack 39 made of synthetic material. The displacement of the welding wire 17 in place is effected by means of rollers UI which are driven at an adjustable speed by means of a motor H3. The wire guide 15 is arranged relative to the nozzle 11 so that the center line Y of the wire guide is substantially aligned with a certain point on the inner circumferential line U5 of the nozzle 11, the nozzle defining the plasma outlet 13 so that the welding wire 17 contacts the nozzle's inner circumferential line U5. hitsauslan-all. Welding can be accomplished using either positive or negative polarity in the welding wire, nozzle, and plasma electrode as long as their polarity is the same.

65933

The arc P of the transferred plasma between the plasma electrode 5 and the workpiece W is ignited by a high-frequency discharge and is maintained by a power supply source 9. Subsequently, the weld dry wire 17 can be fed when the MIG arc M is ignited between the welding wire and the workpiece, the welding wire is kept at a suitable voltage by means of the power supply 19.

Positive polarity has the advantage over negative polarity in that the welding process is smoother in the high current range, e.g. above 225 A. The advantage of negative polarity over positive polarity is that the stability of the plasma is guaranteed as long as the electric discharge from the hit wire to the workpiece actually takes place. Another advantage in certain cases is that the transfer of material interferes less with the molten pool of material and that the combined arc of arc in the molten pool is more evenly distributed and thus has less of an interfering effect on the surface of this weld.

With respect to both polarities, welding with a non-displaced plasma arc between the plasma electrode 5 and the nozzle 11 is alternatively possible. For this purpose, it is sufficient to connect the power supply source 9 for the plasma arc through the switch terminal 47 to the nozzle 11 instead of connecting it to the workpiece W, so that said two power supply sources 9 and 19 are then connected in series with each other. It may be advantageous for the plasma arc to be completely independent of the workpiece. In the latter embodiment, using a non-transferable plasma arc between the plasma electrode and the nozzle, the simple inclusion of a switch 49 between the workpiece W and the second power supply source 19 provides substantial advantages for the MIG arc M. When the switch 49 is open, the plasma arc is ignited, which is not transferred to the workpiece W between the plasma electrode 5 and the nozzle 11. When the supply of the welding wire 17 begins, the switch 49 is closed to establish a connection between the workpiece, the power supply, the nozzle and the welding wire, so as to bring the welding wire to a suitable voltage relative to the workpiece. As a result, the plasma electrode is then also at a higher voltage compared to the workpiece. As a result, the plasma arc starting from the plasma electrode 5 moves from the nozzle 11 to the workpiece W and the discharge from the welding wire 17 to the workpiece 65 starts immediately. Then, when the wire feed stops and the switch 49 is opened, the plasma arc automatically returns to the non-transferable state between the plasma electrode 5 and the nozzle 11. In this case, the device is again ready to start the welding process again, so that it is no longer necessary to ignite the plasma by means of a high-frequency discharge.

As shown in Fig. 2, the non-displaced nozzle of the illustrated embodiment between the plasma electrode 5 and the nozzle 11, passing current through the connection switch terminal 47, can be replaced in a known manner by a second plasma electrode 51 in the housing 21, thereby maintaining a non-displaced plasma arc of the two plasma electrodes 5 and 51 between.

If both plasma electrodes 5 and 51 are made of tungsten, the power supply source 9 may consist of a transformer. If the third power supply source 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 electrode 5 and the workpiece W is guaranteed when the plasma arc is simultaneously present between the two plasma electrodes 5 and 51 and is not transferred to the workpiece. This is because if the plasma arc on the workpiece were extinguished by a disturbance during welding, it would be immediately re-ignited by the flow of thermally ionized gas provided by the plasma arc between the two plasma electrodes, which is independent of this workpiece.

Normally, welding is performed using direct current in the hit wire as well as in the plasma arc. The embodiment shown in broken lines in Fig. 1, consisting of two power supply sources 9 and 19 connected in series and a switch 49, can be made simpler and cheaper by replacing the rectifier from the first power supply source 9 with a cheaper transformer 57 (Fig. 3), then providing an auxiliary electrode 59 tungsten on the inner surface of the nozzle 11. By means of a short high-frequency discharge, an immovable AC-type arc is ignited between the plasma electrode 5 and the auxiliary electrode 59. Since there are two tungsten electrodes, the AC arc can be maintained by the transformer 57 without high-frequency discharge. The flow of argon gas fed to the shell 9 65933 is blown through the arc nozzle 11 onto the workpiece W. The device is then ready to be started by the plasma MIG process without subsequent high frequency discharge. For this purpose, the feeding of the welding wire 17 is started and when this wire touches the nozzle, the switch 49 is closed simultaneously. The welding wire 17 is then connected via a nozzle 11 to the positive pole of the DC supply source 19 and the negative pole is connected to the workpiece W. It is found that when the switch 49 is closed, a transferred plasma arc is formed between the electrode 5 and the workpiece W it can be maintained. After the DC discharge of the welding wire 17 is ignited, the cathode is permanently present on the workpiece W so that the discharge from the plasma electrode 5 to the workpiece W is always easily ignited within a positive period of time.

During the negative period, the plasma electrode 5 has a continuous arc of plasma between the plasma electrode and the nozzle. Surprisingly, the initial ignition of the transferred plasma arc can be so easily accomplished because a cathode point must be formed on the workpiece. The presence of thermally ionized gas in the arc of the untransferred plasma and the increase in voltage at the plasma electrode during the positive period relative to the voltage of the DC supply source 19 is apparently sufficient for this purpose. Despite the fact that only half of the plasma flow enters the workpiece, so that the heating of the weld is less than it is in the case of a direct current plasma arc, the difference in the welding result is only small. When the wire feed is completed and the switch 49 is opened, a non-displaced AC-type plasma arc is maintained, where start-up is again easily accomplished.

All of these circuits have been successfully used to perform welding experiments using wire currents between 50 A and 500 A and plasma currents between 50 A and 300 A. Welding wires made of steel, stainless steel, copper and aluminum, with diameters between 1.6 and 0.9 mm, were placed in the seam.

Fig. 4 shows an embodiment in which a separate coupling part 61 connected to the second power supply source 19 is arranged between the nozzle 11 and the workpiece W. The coupling part 10 65933 includes a coupling part 63 which is parallel to the center line Y of the wire guide 15, the coupling part being arranged so that the coupling surface 63 is substantially aligned with the center line Y. That is, the extension portion L9 of the welding wire 17, i.e., the current-carrying portion between the coupling part and the free end in the welding wire is extremely short in this embodiment. The coupling part 61 should be suitably cooled and may be provided with a cooling sol (not shown) for this purpose.

The embodiment shown in Fig. 5 consists of a coupling part 71 including a water-cooled copper holder 75 and a tungsten part 77 with coupling surfaces 73. The nozzle 11 is connected to the first said power supply source 9 and acts as a plasma electrode, a separate plasma electrode in the housing 21 can thus be omitted. Also, a high frequency generator is no longer necessary in this embodiment because the plasma arc can be spontaneously ignited by the α-arc of the MIG arc, which can be ignited by contacting the welding wire with the workpiece.

Claims (4)

11 65933 Patented suction cups A method for thermally ionizing gas welding, wherein the plasma arc is maintained in a gas flow between the non-wearing plasma electrode (5) and the second electrode and the gas plasma generated by the plasma arc is passed through a nozzle (11), the consumable electrode (17) being continuously fed to the gas plasma and the nozzle ) and wherein the MIG arc is maintained between the consumable electrode (17) and the workpiece (W), characterized in that the current for the MIG arc is supplied to the consumable electrode (17) at a connection point located inside the gas plasma. A welding torch for carrying out the method according to claim 1, comprising a housing (21) provided with a nozzle (11), said welding torch further comprising a non-wearing plasma electrode (5), a wire guide (15) in the housing for controlling the wearable electrode (17) through the opening and the connection (23) for the supply of plasma gas, characterized by a connection part (11, 61, 71) having a connection surface (45, 63, 73) located downstream of the plasma electrode (5), at least a part of the connection surface being substantially straight in line with the center line (Y) of the wire guide (15). Welding torch according to claim 2, characterized in that the nozzle (11) is adapted to act as a coupling part, the wire guide (15) being arranged eccentrically with respect to the nozzle opening (13), the wire guide (15) being substantially centerline (Y) in line with the inner circumference (45) of the nozzle opening (13). Welding torch according to Claim 2, characterized in that the nozzle (11) is adapted to act as a non-wearing electrode, the coupling part (71) being arranged downstream of the nozzle (11).