Burner for a welding apparatus

Abstract

Burner for a welding apparatus having a non-melting electrode, a wire feed device for a welding wire and a power feed device for introducing an electric heating current into the welding wire that is supplied. The wire feed device can be activated in two directions of advance and an electric voltage applied by the power feed device to the welding wire can be regulated to ignite an igniting arc between the tip of the welding wire and the workpiece.

Claims

1. A welding method using a non-melting electrode and a welding wire as the filler material for igniting a primary arc between the non-melting electrode of a burner of a welding apparatus and a workpiece, the method comprising: establishing a short circuit between a tip of the welding wire and the workpiece; supplying the non-melting electrode with a welding current for maintaining the primary arc; adjusting an igniting current in the welding wire; lifting the welding wire away from the workpiece to ignite an igniting arc between the workpiece and the tip of the welding wire lifted from the workpiece; and igniting, via the igniting arc, the primary arc in a region ionized by the igniting arc between the non-melting electrode and the workpiece.

2. The welding method according to claim 1, further comprising applying a measuring voltage to the welding wire to detect the short circuit between the tip of the welding wire and the workpiece.

3. The welding method according to claim 1, further comprising preheating the welding wire with a heating current before adjusting the igniting current.

4. The welding method according to claim 1, wherein the lifting occurs with a reverse movement of the welding wire.

5. The welding method according to claim 1, wherein after ignition of the primary arc, the method further comprises supplying the welding wire in a pilger step feed movement.

6. The welding method according to claim 5, wherein a heating current supplied to the welding wire is activated and deactivated in coordination with the pilger step feed movement.

7. The welding method according to claim 5, further comprising regulating changes in parameters for advance times and/or retraction times and/or advance rates and/or heating current during the pilger step feed movement on a basis of a measurement of a start and stop of the short circuit between the tip of the welding wire and the workpiece.

Description

(1) The present invention is explained in greater detail below with reference to FIGS. 1 through 4, which show advantageous embodiments of the invention schematically and without restriction as examples.

(2) FIG. 1 shows a schematic overview of the elements of a welding apparatus with which the invention is implemented,

(3) FIG. 2 shows a schematic diagram of the ignition process carried out with the burner according to the invention,

(4) FIG. 3 shows a diagram of the current and voltage curves in ignition of the primary arc and

(5) FIG. 4 shows a diagram of the pilger step feed movement and the heating current thereby introduced into the welding wire.

(6) FIG. 1 shows the essential elements of welding apparatus for the description of the invention wherein the burner 1 and the electric unit 13 are generally represented as structurally separate units. The burner 1 has a non-melting electrode 2, usually made of tungsten, and a wire feed mechanism 3 for a welding wire 4. As shown by the arrows representing rotation, the wire feed mechanism 3 can convey the welding wire 4 in both directions, i.e., forward (in the direction of the tip 7 of the welding wire) and in reverse (in the opposite direction). The welding wire supply is usually unwound from a reel (not shown) in the usual way by the wire feed mechanism 3. Alternatively, the welding wire can be supplied in the form of a rod by hand. The welding wire advances from a welding wire feed 14 to the non-melting electrode, wherein an adequate distance is provided between the welding wire feed 14 and the workpiece to prevent the welding wire feed 14 from entering the region of a primary arc 11 between the non-melting electrode and a workpiece 8.

(7) To ensure a uniform and rapid melting of the tip 7 of the welding wire, the region of the welding wire 4 between the welding wire feed 14 and the tip 7 of the welding wire has a heating current I.sub.H flowing through it, preheating the welding wire by ohmic heating. The heating current I.sub.H is introduced into the welding wire 4 in the region of the welding wire feed 14 wherein the current flow is ensured only as long as there is a short circuit between the tip 7 of the welding wire and the workpiece 8 (either through direct contact or via the welding bath). As explained in greater detail below, an ignition current I.sub.Z can also be introduced into the welding wire 4 via the welding wire feed 14.

(8) The electric unit 13 has a power feed device 5, a welding current source 12, a regulating device 9 and a measuring unit 10. The welding wire feed 14 is connected to the negative terminal of the power feed device 5 and is supplied with the heating current I.sub.H and/or the ignition current I.sub.Z by means of this terminal. The negative terminal of the welding current source 12 is connected to the non-melting electrode 2 and supplies it with the welding current I.sub.S required for maintaining the primary arc 11. In this case, the positive terminals of the power feed device 5 and the welding current source 9 are connected to the workpiece 8. Similarly the terminals can also be reversed. A measuring unit 10 measures the voltage applied to the welding wire feed 14, wherein a voltage drop characterizes a short circuit between the welding wire 4 and the workpiece 8, and a rise in current is characteristic of an interruption in the short circuit. Furthermore, the measuring unit 10 can also measure the voltage applied to the non-melting electrode, for example, to monitor the ignition and the integrity of the primary arc 11.

(9) A regulating unit 9 serves to control and coordinate the individual elements of the welding apparatus. The regulating unit 9 controls the power feed device 5 and the welding current source 12. In addition, the regulating unit 9 controls the drive of the wire feed device 3 and coordinates this with the power feed device 5 and with the welding current source 12. The regulating methods implemented by the regulating unit 9 are adequately well-known in the professional field and will be described in the present document only to the extent that they directly relate to the present invention. For reasons of simplicity, the components for supplying the inert gas to the non-melting electrode 2 have been omitted from the figures because those skilled in the art are familiar with these elements.

(10) In an alternative embodiment, the wire feed device 3 can also be arranged in the electric unit 13 and/or in the welding current source 12. A tube bundle, which is known from the prior art and in which all media are carried can be used as the connection to the burner.

(11) FIG. 2 is described in the following explanation with simultaneous reference back to FIG. 1, showing, consecutively, various states a) through f), which are to be run through for igniting the primary arc 11 according to the invention. State a) represents the situation immediately prior to ignition, wherein the distance m between the non-melting electrode 2 and the workpiece 8 is not sufficient to readily ignite a primary arc 11 with the voltage applied by the welding current source 12 to the non-melting electrode 2. Then a measuring voltage U.sub.M is applied to the welding wire 4 by means of the power feed device 5 described previously, and the wire feed mechanism 3 conveys the welding wire 4 in a fourth movement at the rate v.sub.1. As soon as the tip 7 of the welding wire touches the workpiece 8, the measuring unit 10 detects a sudden voltage drop, whereupon the wire feed device 3 is stopped and a short circuit is established between the welding wire 4 and the workpiece 8 as shown in state b). In this state b), an ignition current I.sub.Z is now fed into the welding wire by the power feed device 5 via the welding wire guide 14, and the welding wire 4 is moved backwards at a rate v.sub.2, whereupon an igniting arc 6 is formed when the tip 7 of the welding wire is lifted up from the workpiece 8 represented in state c). Before ignition of the igniting arc 6, the welding wire may optionally be preheated with a heating current.

(12) In alternative embodiments, the welding wire can also be raised by a movement guided transversely or obliquely to the axis of the welding wire or by a pivoting movement, for example, with the help of a device (not shown) with which the welding wire guide 14 can be pivoted or moved laterally. This would be advantageous in particular in applications in which the welding wire feed is in a shallow angle to the surface of the workpiece 8 and simply move the tip 7 of the welding wire backwards with the wire feed device 3 would not guide the igniting arc 6 close enough to the tip of the non-melting electrode 2.

(13) In FIG. 2, the igniting arc 6 is lengthened (state d) by moving the tip 7 of the welding wire back further until the distance n between the region ionized by the igniting arc 6 and the tip of the non-melting electrode 2 is so small that the primary arc 11 between the non-melting electrode 2 and the workpiece 8 is ignited merely because of a no-load voltage U.sub.S applied to the non-melting electrode 2, as represented in state e), while the igniting arc 6 is maintained at the same time. Ignition of the primary arc 11 can be detected by the measuring unit 10 based on the voltage drop associated with this, so that the regulating device 9 switches off the ignition current I.sub.Z when the primary arc 11 is burning under stable conditions, so that the igniting arc 6 is extinguished, as represented in state f). For welding, the welding wire 4 is then advanced at the rate of advance v.sub.3, which is standard in welding, to the workpiece 8 and into the region that is melted by the primary arc 11 and is resupplied, so that enough material is supplied for forming a welding bead.

(14) FIG. 3 shows the exemplary schematic curves of the following parameters during the ignition process described above: I.sub.wire current characteristic in the welding wire U.sub.wire voltage characteristic in the welding wire v.sub.D rate of advance of the welding wire U.sub.TIG voltage characteristic in the non-melting electrode I.sub.TIG current characteristic in the non-melting electrode

(15) At the start of the ignition process, which is labeled as i), a voltage U.sub.M is applied to the welding wire 4 and a voltage U.sub.E is applied to the non-melting electrode 2. Then, in the region labeled as ii), the welding wire is moved forward at the rate v.sub.1 until a short circuit is detected at point iii), based on the drop in voltage U.sub.wire, i.e., the tip 7 of the welding wire has come in contact with the workpiece 8. The forward movement of the welding wire 4 is stopped and a heating current I.sub.H is introduced into the welding wire to preheat it.

(16) For igniting the igniting arc, the current I.sub.wire is ramped up to an ignition current I.sub.Z in the welding wire 4 in the region iv), and the welding wire 4 is retracted via the wire feed device 3, so that the tip 7 of the welding wire is lifted up from the workpiece 8 and the igniting arc 6 is ignited. Ignition of the igniting arc 6 is thus recognizable by the associated rise in the voltage U.sub.wire in the welding wire. The welding wire is then moved backward further, while the igniting arc 6 is burning, until the primary arc 11 is ignited. This is recognizable due to the voltage drop thereby triggered in the voltage U.sub.TIG in the non-melting electrode 2 (this corresponds to the region v) in FIG. 3). The required igniting current I.sub.TIG for the primary arc 11 is thus also made available accordingly.

(17) Then the wire feed device 3 stops the welding wire 4 and the ignition current I.sub.Z is maintained in the welding wire until the primary arc 11 has reached a stable burning state. The primary arc 11 and the igniting arc 6 burn simultaneously in this region. Then at vi), the current in the welding wire 4 is turned off as soon as amperage required for the primary arc 11 has been reached, so that the igniting arc 6 goes out while the primary arc 11 continues to burn in a stable manner.

(18) The current I.sub.wire and/or the voltage U.sub.wire may also contain at least one pulse P.sub.i, P.sub.u for ignition of the igniting arc 6 in their curves. Therefore, in comparison with a constant curve, this achieves the result that the ignition takes place more rapidly due to the increased energy input.

(19) In addition, devices may also be provided to alter the angle of approach, the height, the position, etc. of the wire. This ensures that the igniting arc 6 will burn in the immediate vicinity of the non-melting electrode 2 and the segment for ignition of the primary arc 11 is ionized accordingly. For example, in an application in which the wire is supplied at a very shallow angle, the igniting arc 6 would also run with a very shallow curve and would therefore burn at a greater distance from the non-melting electrode 2. If the tip 7 of the welding wire is moved in the direction of the non-melting electrode 2 for the purpose of ignition, the igniting arc 6 is also brought closer to the non-melting electrode 2. For the subsequent welding operation, the tip 7 of the welding wire can be moved back from the altered position to the original position.

(20) The state at the end of the diagram in FIG. 3 corresponds essentially to the state f) in FIG. 2. For the example of an ignition method illustrated in FIG. 2, approximately 20 to 50 ms, for example, 30 ms, usually elapses between the start of the ignition process (point i) and stable burning of the primary arc 11 (point ix), where the respective value depends in particular on the distance between the tungsten electrode and the workpiece.

(21) After igniting of the primary arc 11, the welding process can be controlled in the traditional manner by the fact that the wire feed device 3 supplies the required amount of welding wire 4 into the welding bath, while the welding wire 4 is acted upon by a heating current I.sub.H for preheating it.

(22) The wire feed device 3 permits a rapid dynamic change between a forward movement and a reverse movement so that the ignition can be carried out fast enough. However, this feature may also be used advantageously during the welding process to have an advantageous influence on the quality of the weld. The method used for this purpose is explained in greater detail in conjunction with FIG. 4, where the welding wire 4 is supplied in a pilger step feed movement, such that the tip 7 of the welding wire emerges from the welding bath with each reverse movement and therefore stops the short circuit between the workpiece 8 and the welding wire 4.

(23) FIG. 4 shows this curve of heating current I.sub.H, rate of advance v.sub.D and short circuit KS in the form of a diagram. In the pilger step feed movement, the wire is alternately advanced at the rate v.sub.+ in a positive direction of advance and then is retracted in a negative direction of advance at a rate v.sub.. As shown in FIG. 4 the absolute value of the rate v.sub.+ is higher than the absolute value of the rate v.sub. so that the welding wire will have been conveyed further by a distance after each cycle of back-and-forth movement. The duration of the forward movement is also longer than the duration of the reverse movement, which reinforces the effect. The durations and rates are adjusted by the regulating device 9, so that the amount of filler material required to form the welding bead is always supplied.

(24) With each forward movement the tip of the welding wire dips into the melt bath, changes the direction of advance and then comes out of the melt bath again, so that the melt bath is thus induced to vibrate. This vibration, which always takes place in similar increments, ensures a very uniform and high-quality weld.

(25) With each forward movement, a short circuit is created when the tip 7 of the welding wire is immersed in the melt bath and the short circuit is stopped in retraction when the tip 7 of the welding wire emerges from the melt bath again. The short-circuit phases are characterized by the short-circuit signal KS in FIG. 4. Each time a short circuit is established and extinguished can be determined accurately by the measuring unit 10 on the basis of the associated changes in voltage. The short-circuit signal KS determined by the measuring unit 10 can be used to regulate the rate of advance to introduce a heating current I.sub.H, which is coordinated with the short-circuit phase, as can be seen in FIG. 4.

(26) As soon as the tip 7 of the welding wire penetrates into the welding bath and a short circuit is detected (at point I), the heating current I.sub.H is ramped up to a preset maximum value, wherein the welding wire is advanced at a constant rate of advance v.sub.+. After an advance time t.sub.1 (beginning at point II), the rate of advance is reduced continuously and then reverses until extinguishing of the short circuit (at point III) is detected. Then the reverse rate for a retraction time t.sub.2 (up to point IV) remains unchanged, whereupon this constant rate corresponds to the maximum retraction rate v.sub.. In parallel with the change in the rate of advance (i.e., between point II and point III), the heating current I.sub.H is ramped down in a regulated manner, so that when the short circuit is extinguished (point III), a very low heating current I.sub.H or none at all is flowing, so that no arc faults and/or no welding splashes are formed. At the same time, the regulating device 9 ensures that at least a measuring voltage is applied to the welding wire at all times, so that the changes in the short circuit can be detected at all times. After the retraction time t.sub.2 has elapsed, the rate of advance is again ramped down until the short-circuit signal is detected and the next cycle begins again (at point I). This method can be regulated by means of only a few parameters to be adjusted in that the maximum rates are each adjusted by establishing and/or extinguishing the short circuit.

LIST OF REFERENCE NUMERALS

(27) Burner (1) Non-melting electrode (2) Wire feed device (3) Welding wire (4) Power feed device (5) Igniting arc (6) Tip (7) of the welding wire Workpiece (8) Regulating device (9) Measuring unit (10) Primary arc (11) Welding current source (12) Electric unit (13) Welding wire guide (14)