Patent Application
20130327755
The invention relates to a welding head in accordance with the generic part of claim 1 and to a method in accordance with the generic part of claims 18 and 19.
The use of such welding heads in so-called TIG welding apparatuses is known, for example, from the 1st edition, 2006, of “Wolfram-Intergasschweissen” of the DVS Verlag (Deutscher Verband für Schweissen and verwandte Verfahren e.V.). When welding with such welding apparatuses an arc is produced, starting from an electrode connected to a voltage source, which arc ends on the workpiece to be welded, that acts as an electrical mass. In such welding operations an additive substance can be supplied from the outside as required or the so-called melt bath alone can be produced from the material of the workpiece. The ignition of the arc can take place either by so-called contact ignition or by high-frequency ignition, whereby in the first instance a mechanical contact is briefly established between the electrode and in the second instance a high frequency is placed between the electrode and the workpiece.
When welding with such welding heads there is always the danger given the case that they are guided manually that upon an unintended mechanical contact during the welding operation a so-called alloying up of the electrode occurs, that is, that the electrode is welded unintentionally with the workpiece. This is particularly the case with inexperienced personnel and given a difficultly accessible welding connection on complex workpieces but absolutely also occurs occasionally in the case of an experienced hand.
After an alloying up the electrode must be separated from the workpiece again. During the separating procedure a piece of the electrode tip breaks off as a rule due to the material properties of tungsten and remains as a material inclusion connected to the workpiece. Such material inclusions require expensive grinding and similar subsequent improvement work or can even result in rejected material if the subsequent operations are too expensive or if they can no longer meet the mechanical requirements put on the workpiece.
In addition, in the case of workpieces consisting of expensive, corrosion-resistant alloys such material inclusions can be the starting point for corrosion phenomena. Furthermore, a subsequent grinding of the electrode into a reusable form becomes necessary.
This results in a high additional cost factor, on the one hand due to the enormous time loss on account of the subsequent working on the welding connection as well as on the electrode and on the other hand due to the material wear on the electrode and on grinding material or similar working material.
The previously described disadvantages can be prevented in a few hand-guided welding operations using a device for guiding and preventing an approach of the welding head to the workpiece to be worked. This is only worthwhile as a rule for reasons of cost if the same welding operations are concerned. Furthermore, the use of such devices is not always possible for reasons of space.
In order to mitigate somewhat the previously described disadvantages in particular in the case of rather high welding currents, the welding current is automatically reduced in the so-called TCS (TIG-Comfort Stop) welding when the electrode is approached to the workpiece. As a consequence, the damage to the electrode in the workpiece connected with an alloying up become somewhat less.
The invention therefore had the task of creating a welding head in accordance with the generic part of claim 1 and of indicating a method in accordance with the generic part of claims 18 and 19 in which an alloying up of the electrode on the workpiece can no longer occur even given a direct mechanical contacting, and furthermore the settling of drops of welding material on the electrode is largely prevented.
These two tasks are solved on the one hand by the characterizing features of claim 1 and on the other hand by the characterizing features of claims 18 and 19.
As a result of the movable support of the electrode and due to its movement made by the device (claim 1) almost no more wear occurs on the electrode even in the case of a contacting between the electrode and the workpiece. Furthermore, also no more inclusion of electrode material into the workpiece occurs. A subsequent grinding of the electrode after contact with the workpiece is therefore only necessary again at the earliest after multiple contacts.
As a result, considerable time and therefore also expense can be saved and more rapid progress make during hand-guided welding since a contacting of the electrode with the workpiece does not necessarily lead to an interruption of the work. Furthermore, even more complicated welding operations can be carried out by less-experienced persons, which can also save expenses.
The additional advantage results in comparison to stationary welding electrodes for the case that additional welding material is supplied for carrying out the welding procedure that the drop-like adhering of liquefied welding material on the welding material that constantly reoccurs occurs significantly less frequently with the welding electrode in accordance with the invention on account of its movement.
The frequently apparent deformation of the arc away from the desired cone-shaped and focused shape associated with such an adhesion, with the consequence of a more or less great deviation from the desired welding image, and, given correspondingly great drops, a defective welding connection or even an unsuccessful welding attempt is thus often avoided.
Consequently, the welding head in accordance with the invention can be advantageously used not only for the case that it is guided manually but rather it can also be advantageously used—for the case when welding material is being supplied—in such welding operations in which the welding head is, for example, controlled in a spatially precise manner by a robot. In this case there is as a rule no more danger of an unintended contacting of electrode and workpiece and there is still the advantage that as a result of the movement of the welding electrode in accordance with the invention an adhering of tear-shaped, liquefied welding material and the associated deterioration of the welding image clearly occurs less frequently.
The embodiment of the invention according to claim 2 has the advantage that there can be no danger of injury from welding heads placed again and again to the side during the welding operations. Furthermore, the device for moving the electrode can also have a longer service life since it is always put in operation only when actually required. Moreover, even a certain amount of energy can also be saved in this manner.
The further development according to claim 3 has the additional advantage that the person carrying out the welding operations does not have to pay attention to the cutting in of the device for moving the electrode. Furthermore, the construction of the electric/electronic switching elements of the welding head (not shown) is simplified since the start-up of the device and the starting of the gas flow can be controlled with the same cutting-in signal.
If the invention is developed further according to claim 4, the mobility of the electrode can be realized with relatively simple means.
Moreover, upon a rotation the stability of the arc is very largely ensured. In agreement therewith, traction tests on workpieces welded to each other showed that their tensile strength after they are welded with the welding head of the invention does not significantly differ from the tensile strength of compounds that were welded in accordance with the state of the art and therefore also fulfill their function. Furthermore, the adherence of tear-shaped, liquefied welding material on the welding electrode and the associated deterioration of the welding image are practically completely avoided in the case in which the welding material is applied from the outside, given the appropriate selection of the speed of rotation.
If the welding electrode is allowed to execute an oscillating motion, the transfer of the welding current onto the welding electrode becomes especially simple since on account of its limited movement course a fixed cable connection for transferring the welding current onto the electrode is still sufficient. Furthermore, as a result of the direct cable connection, power losses between voltage supply and electrode are avoided.
The embodiment of the invention according to claim 5 has the advantage that the electrode is supported with as little friction as possible, as a result of which on the one hand wear phenomena of the device are minimized and on the other hand as a consequence the power requirements for moving the electrode become as small as possible.
If the invention is developed further according to claim 6, a mechanical coupling between electrode and casing that can be constructively readily realized results, which coupling can also be readily loosened and reestablished in the case of an exchanging of the electrode. The advantage of the further development of the invention in accordance with claim 7 is that it represents a constructively simple structural form of the tightening device that can be economically produced. The transfer of the welding current onto the movable electrode according to claim 8 always offers a good contacting of the casing by the automatic readjusting of the carbon brush carried out by the spring until it is almost completely worn down. In addition, this embodiment has the advantage of a low electrical transitional resistance and low friction losses during its rotation.
The further development of the invention according to claim 9 has the advantage that such carbon brushes have a comparatively high conductivity so that sufficiently low transitional resistances are achieved even with carbon brushes that are built to be comparatively small.
If the invention is developed further invention according to claim 10, then an almost wear-free contacting of the electrode with its voltage supply results in addition to a very low transitional resistance.
If the invention is developed further according to claim 11, the advantage results that the rotation respectively oscillation is maintained, even given a mechanical contact between the workpiece and the electrode, against the associated, increasing forces of friction in that the direct current electromotor appropriately raises its power consumption up to its power limit
The advantage of the embodiment of the invention in accordance with claim 12 consists in that the drive shaft of the direct current electromotor and the shaft of the rotation of the casing can be arranged spatially as desired relative to one another, which makes possible fairly large constructive freedoms in the designing of the welding head.
Furthermore, this embodiment of the invention allows a relatively simple replacement of the casing when the latter has become worn out in the course of time due to the relatively large currents transferred to it by the carbon brush and due to the occurring friction. Furthermore, any desired translation can be selected by means of a gear connection and therefore an optimal adaptation to the particular selected direct current electromotor can be achieved.
If the invention is further developed according to claim 13 the advantage results that the welding head can be kept in a relatively slim construction form and therefore welding operations in a constricted environment can be more readily carried out. Furthermore, this embodiment constitutes an economical solution for the drive of the casing.
The further development according to claim 14 has an advantageous effect in particular on the service life of the carbon brush as well as of the direct current electromotor. It is not only ensured that the speed of the direct current electromotor is sufficiently high for preventing an alloying up even given a maximum welding current but the speed always follows the welding current again as far as possible downward.
If the invention is developed further according to claim 15 the advantage results that turbines can achieve relatively high drive performances with a relatively small installation size at the same time, as a result of which a relatively compact construction size of the welding head can be achieved. The fluid circulation, which is necessary in any case in most instances for cooling the welding head and is maintained by the welding apparatus also advantageously ensures (claim 16) the drive of the turbine. Since no additional electrical lines are required, the welding head of the invention can therefore also be retrofitted in a quite simple manner in welding apparatuses that were originally designed only for welding heads in accordance with the prior art.
In a retrofitting the welding head in accordance with the invention is simply connected as in the prior art to the inlet and the outlet of the fluid that start from the welding apparatus while the fluid is conducted to and from the turbine inside the welding head of the invention as needed.
The further development of the invention in accordance with claim 17 still has the advantage of a compact structural form of the welding head and is furthermore distinguished in that only a few other structural parts, that are also economical at the same time, are required in comparison to welding heads in accordance with the prior art.
The advantages of the method according to claim 18 concerns with which welding head described in the previous claims it is carried out.
The advantages of the method according to claim 19 correspond to those in the description of advantages for claims 1 and 4.
Starting from the cited advantages of the previously mentioned embodiments of the invention that are all based on the principle of the mobility of the electrode, a transfer of this principle to other welding methods is also offered, in particular to the manual arc welding and the so-called MSG (Metal Protection Gas) welding method (comparisons to both methods Wikipedia.org/welding).
In the first instance a movement of the rod electrode melting during the welding process would prevent an alloying up primarily before the welding process with the current source already being cut in, in particular during ignition and immediately after the welding process with the current source still cut in.
In the second instance an application of this principle for the mechanical reversal—that is, a movement of the so-called welding jet guiding the tracked welding wire around or along the axis of the welded wire—would prevent that in the case of an undesired so-called burning back of the welding wire to the welding jet the welding wire would not alloy up on the welding jet.
Five exemplary embodiments of the invention are described in the following using
in which
In the so-called V-butt joint shown in
A first embodiment of the welding head (1) in accordance with the invention according to the
A device (20) for rotating the electrode (2) comprises, among other things, a coupling (13) and a tightening device (14) that serve to establish a mechanically rigid connection of the shaft (11) of the direct current electromotor (10) to the electrode (2) via the casing (12). On the one hand the shaft (11) is permanently connected in a mechanically rigid manner via the coupling (13) to an end of the casing (12) and on the other hand the electrode is clamped in by the tightening device (14) at the other end of the casing (12).
The casing (12) itself is cylindrically constructed but has a greater cross section in its central area that contacts the carbon brush (17). Ball bearings are arranged on both sides of the greater cross section the outer rings (21, 22) of which bearings are fastened in the housing (9) and in whose inner rings (23, 24) the casing (12) is clamped.
In the simplest case the coupling (13) for the mechanically rigid connection between casing (12) and shaft (11) of the direct current electromotor (10) resting in the housing (9) can take place, for example, in that up to three threaded pins are screwed into the outer surface of the casing (12) that clamp the shaft (11) in in a centering manner in their cooperation.
The tightening device (14) for the mechanically rigid connection between the casing (12) and the otherwise freely rotating electrode (2) comprises a conical tightening insert (15) with four longitudinal slots and a precisely fitting bore for receiving the electrode (2). The outer surface of the tightening insert (15) is dimensioned in such a manner that it can be introduced sufficiently deep into the casing (12) but is then finally held centrally by the latter. Furthermore, the casing (12) has an outside thread that is not shown and onto which a tightening nut (16) can be screwed, as a result of which the electrode (2) is clamped sufficiently firmly in the tightening insert (15).
The electrode (2), that is firmly clamped in in this manner, rotates after the cutting in of the direct current electromotor (10) with its speed and the welding process can now begin without having to fear an undesired alloying up anymore. Care is to be taken that upon the selection of rather high welding currents the speed of the direct current electromotor (10) should also be raised in order to quite reliably prevent an alloying on even then.
It is ensured to a great extent by the direct current electromotor (10) that this necessary speed is maintained even if fluctuations of the friction in the ball bearings occur or the electrode (2) should grind on the workpiece (8).
The second embodiment of the invention shown in
This means that the entire device (20) rotates one third slower than the motor shaft (11) of the direct current electromotor (10), as a result of which the available torque on the electrode (2) is raised by a third.
In this manner it is ensured that the direct current electromotor (10) can largely maintain its speed to the extent possible in case the work piece (8) makes contact with the electrode (2) even at a higher contact pressure.
The third embodiment of the invention shown in
Of course, aside from water even another cooling agent, for example, with an even higher heat capacity can be used with which the turbine can then be driven in the same manner.
Moreover, in the case of welding heads not cooled by a fluid, cooling can be achieved by the protective gas (4) that is flowing out in any case. If the protective gas (4) is also conducted again over the turbine (26) the latter can also be driven by the flow of the protective gas (4).
Of course, a separate fluid circuit for gas current circuit can also be generated in the welding apparatus for driving the turbine (26) that serves exclusively for driving the turbine (26) and not simultaneously for also cooling the welding head (1). This could take place, for example, by connecting the work chamber (C) of the turbine (26) to a compressed air system.
Instead of the contacting with the carbon brush (17),the casing (12) can also, as shown in
In the embodiment shown in
As a result, the casing (12) is put in an oscillating movement during the rotation of the drive shaft (11), whose frequency is determined by the speed of the drive shaft (11) and whose amplitude is determined by the extent of the eccentric coupling.
The connection of the electrode (2) to its voltage supply takes place by a flexible line (36) whose end is permanently connected mechanically as well as electrically to the casing (12).
In all previously described embodiments the welding operation is initiated in a customary manner in that the welding head (1) is connected at first to its voltage source, that is not shown, and in the case of a hand-guided welding the person carrying out the welding operations manually initiates the supply of the gas flow (4) serving as protective gas. The direct current electromotor or the turbine (26) is automatically put in operation simultaneously with the supplying of protective gas (4). This ensures that the direct current electromotor (10) or the turbine (26) has reached its rated speed and the space between the electrode (2) and the work piece (8) is surrounded by protective gas before the actual welding operation begins. The same sequence in time of the supply of protective gas, the rotation of the electrode (2) on the one hand and the beginning of the welding operation on the other hand is also observed in welding operations controlled by robots.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 008 515.7 | Jan 2011 | DE | national |
| 10 2011 016 026.4 | Apr 2011 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE2012/000022 | 1/12/2012 | WO | 00 | 7/31/2013 |
