Abstract:
The invention relates to a welding method involving the use of a non-fusing electrode ( 12 ) according to which the electrode ( 12 ) is provided with power from a power source once the arc ( 11 ) between the electrode ( 12 ) and the workpieces ( 13, 14 ) to be joined has been ignited. The invention also relates to a tack welding method. The aim of the invention is to improve the quality of the weld seam in the starting phase of the welding process. To this end, the invention provides that before the actual welding process, a start program ( 22 ) is performed without the introduction of a filler material during which the electrode ( 12 ) is supplied with pulsed power in the form of current or voltage pulses over a presettable length of time ( 23 ) whereby causing the liquid molten bath to oscillate or vibrate, and that after the execution of the start program ( 22 ), the actual welding process is carried out during which the electrode ( 12 ) is preferably supplied with constant power.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   Applicants claim priority under 35 U.S.C. §119 of Austrian Application No. A553/2002 filed Apr. 10, 2002. Applicants also claim priority under 35 U.S.C. §365 of PCT/AT03/00076 filed Mar. 18, 2003. The international application under PCT article 21(2) was not published in English. 
   BACKGROUND OF THE INVENTION 
   The invention relates to a welding method using a non-consumable electrode, in which the electrode is supplied with energy from a power source after the ignition of an electric arc between the electrode and the workpieces to be joined. 
   Furthermore, the invention relates to a tack welding method using a non-consumable electrode and without introduction of any additional material, in which the electrode is supplied with energy from a power source after the ignition of an electric arc between the electrode and the workpieces to be joined. 
   Various welding methods have already been known, in which the electrode is supplied with energy from a power source after the ignition of an electric arc between the electrode and the workpieces to be joined, thus causing the workpieces to fuse together. For the ignition of the electric arc, different ignition processes and, in particular, contact ignition or HF ignition may be employed. 
   SUMMARY OF THE INVENTION 
   The invention is based on the object of providing a welding method using a non-consumable electrode, and a tack welding method using a non-consumable electrode and without introduction of any additional material, by which the quality of the weld is improved in the start phase of the welding process. 
   This object of the invention is achieved in that, prior to the welding process proper, i.e., after the ignition of the electric arc, a start program is performed without introduction of an additional material, by which the electrode is supplied with pulsed energy in the form of current or voltage pulses over a presettable period of time, thus causing the liquid melt bath to oscillate or vibrate, and that the welding process proper is carried out after termination of the start program. 
   In the welding process proper, the electrode is preferably supplied with constant power. 
   Furthermore, the object of the invention is also achieved by a tack welding method as mentioned above, wherein, prior to the welding process proper, a start program is performed, by which the electrode is supplied with pulsed energy in the form of current or voltage pulses over a presettable period of time, thus causing the liquid melt bath to oscillate or vibrate, and that the welding process proper is carried out after termination of the start program by supplying the electrode with constant power. 
   By carrying out said special start program and, in particular, a socalled tacking process, it is ensured that the melt bath produced will be set in vibration and the flowing together of the melt baths of the two workpieces will be facilitated by the vibration of the melt bath. This is of particular relevance to the extent that no additional material in the form of a welding wire is introduced into the melt bath, but the weld seam is merely formed by the fused material, thus rendering impossible any filling up of the weld seam with an additional material. In such welding methods without introduction of any additional material weld holes are, thus, prevented from forming at the beginning of the welding process and it is feasible from the very beginning of the welding process to form a constant weld without any weld holes. If an electric arc is ignited in conventional prior-art welding methods, the fused material of the workpieces will, in fact, be pressed apart by the energy introduced and will solidify. In doing so, a weld hole may form, or the weld may have a smaller weld thickness in its central region, at the beginning of the welding process. This is actually avoided by the start program, by which the melt bath is set in vibration due to the introduction of pulsed energy, as the melt bath is not permanently subjected to constant power introduction. 
   Furthermore, very short welds can be produced on account of the start program, since a complete formation of the weld seam is obtained from the very beginning of the welding process, i.e., immediately upon ignition of the electric arc, thus enabling the length of the weld seam to be kept very short. This is of particular advantage if aluminum is used as the material of the workpieces to be welded, since no distortion of the material due to slighter heating in the event of short welds will occur. 
   By the solution according to the invention considerable enlargement of the bridging of the clearance between the workpieces to be welded is also reached, because the oscillating melt baths forming of the workpieces ensure an enhanced flowing together of the workpieces. 
   The introduction of energy during the start program can be controlled in a manner that the mean value of the pulsed energy corresponds with the amplitude of the welding current set for the subsequent constant-energy welding process proper. The start program may, thus, be readily adapted to the subsequent welding process proper. 
   The parameters of the start program and, in particular, the pulse parameters like pulse height, pulse width, pulse frequency, pulse break and, possibly, curve shape are advantageously freely settable at the power source. 
   It is also feasible that the parameters of the start program, by a control and/or evaluation device provided in the welding apparatus or in the power source, are automatically fixed or varied as a function of the parameters of the welding process proper. 
   In this respect, it is, for instance, possible that the parameters of the start program are automatically fixed or varied as a function of the amplitude of the welding current used for the welding process proper. 
   It is also feasible that the parameters of the start program are automatically fixed or varied as a function of the material thickness and/or material of the workpieces to be welded or further parameters of the welding process proper. 
   Finally, also several start programs having different parameters or curve shapes can be defined and stored, and said defined and stored start programs are used and/or varied by the control and/or evaluation device to select the parameters for the start program. 
   The start program, during which the electrode is supplied with pulsed energy over a presettable period of time, can also be carried out for a presettable period of time after the ignition of the electric arc. 
   During said presettable period of time after the ignition of the electric arc, the electrode is preferably supplied with constant power. 
   If the electrode, during the presettable period of time after the ignition of the electric arc, is supplied with constant power different from that supplied during the welding process proper, it will be ensured that the electric arc will be stabilized during the period between the ignition of the electric arc and the beginning of the start program, prior to the initiation of the start program and, after this, the welding process proper. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention will be described in more detail by way of exemplary embodiments. 
       FIG. 1  is a schematic illustration of a welding apparatus; 
       FIG. 2  in a simplified, schematic illustration represents the time course of the welding current during an embodiment of a welding process; 
       FIG. 3  in a simplified, schematic illustration represents a further time diagram of the welding current during another welding process. 
   

   DETAILED DESCRIPTION 
     FIG. 1  depicts a welding plant or welding apparatus  1  for various welding methods such as, e.g., WIG/TIG welding or electrode welding methods. It is, of course, possible to use the solution according to the invention with a power source or a welding current source. 
   The welding apparatus  1  comprises a welding current source  2  including an output part  3 , a control and/or evaluation device  4  and a switching member  5  associated with the output part  3  and the control and/or evaluation device  4 , respectively. The switching member  5  and the control and/or evaluation device  4 , respectively, are connected to a control valve  6  arranged in a supply line  7  for a gas  8 , particularly a protection gas such as, for instance, argon or helium or the like, provided between a gas reservoir  9  and a welding torch  10 . 
   The energy and, in particular current, for building up an electric arc  11  between an electrode  12  and the workpieces  13 ,  14  to be joined is supplied from the output part  3  of the welding power source  2  to the welding torch  10  and electrode  12  via a welding line  15 , wherein the workpieces  13 ,  14  to be welded are likewise connected with the welding apparatus  1  and, in particular, welding current source  2  via a further welding line  16  so as to enable an electric circuit to build up via the electric arc  11 . 
   In order to provide cooling to the welding torch  10 , the welding torch  10  is connectable with a fluid reservoir and, in particular, water reservoir  19  via a cooling circuit  17  with a flow control  18  interposed, whereby the cooling circuit  17  and, in particular, a fluid pump used for the fluid contained in the water reservoir  19  is started as the welding torch  10  is put into operation, thus effecting cooling of the welding torch  10 . 
   The welding apparatus  1  further comprises an input and/or output device  20 , via which the most different welding parameters or modes of operation of the welding apparatus  1  can be set. In doing so, the welding parameters set via the input and/or output device  20  are transmitted to the control and/or evaluation device  4 , which in turn will subsequently activate the individual components of the welding apparatus  1 . 
   It is, of course, possible to arrange all lines leading from the welding apparatus  1  to the welding torch  10  in a common hose package (not illustrated) and consequently connect said hose package with the welding torch  10  and the welding apparatus  1  via a central connection. 
   In  FIGS. 2 and 3 , time courses of the welding current for a welding method are schematically illustrated, the current I being plotted on the ordinate and the time t being plotted on the abscissa. It should be mentioned that the solution according to the invention is basically applicable to any welding technique known from the prior art and, in particular, alternating-current welding processes, a direct-current welding method, however, being described in the exemplary embodiment illustrated. 
   The exemplary embodiment described features a welding process in which no additional material, particularly no welding wire, is introduced into the welding process. The weld (not illustrated) is merely formed by the fused material of the workpieces  13 ,  14 . Such a welding process without any additional introduction of a consumable welding wire uses a non-consumable electrode  12 , from which the electric arc  11  is built up towards the workpieces  13 ,  14 . It is exactly the start phase of a welding process, i.e., after the ignition process for the electric arc  11 , which frequently involves problems during the formation of the weld, because the introduction of energy into the melt bath causes the latter to be pressed apart, which might lead to the formation of socalled weld holes, or very thin weld seams. This is actually avoided by the new method described below. 
   Welding processes of this type are, for instance, used in tack welding. The tack welding method is realized with a non-consumable electrode  12  and without introduction of any additional material, whereby two workpieces  13 ,  14 , particularly sheet metal plates, are welded together, preferably on their abutting surfaces or in an overlapping manner, while merely effecting a fusion of the workpieces  13 ,  14  via the electric arc  11 . In doing so, the electrode  12 , after the ignition of the electric arc  11 , is supplied during the welding process by the welding power source  1  with constant power and, in particular, direct current or direct voltage adjusted via the input and/or output device  20  prior to the welding process. The ignition of the electric arc  11  (schematically illustrated by an ignition pulse  21 ) may be effected in various known ways, i.e., for instance, through contact ignition or HF ignition, which will thus not be explained in more detail. It is merely indicated that, in accordance with the diagrams, HF ignition was effected in this exemplary embodiment, the ignition of the electric arc  11  by an ignition pulse  21  being apparent from the power curve. 
   At the onset of the welding process, i.e., after the ignition of the electric arc  11 , the solution according to the invention provides a start program  22 , particularly a tacking process, before the welding process proper, particularly a direct-current welding process, during which start program the electrode  12  is supplied with pulsed energy over a presettable period of time  23 . During the start program  22 , the electrode  12  is fed with current pulses  24  and/or voltage pulses. After termination of the start program  22 , i.e., upon expiration of the period  23 , the electrode  12  is supplied with constant power, particularly with a set current intensity  25 , as a function of the desired welding process proper. 
   Due to the pulsed energy supply during the start program  22 , it is ensured that the liquid melt bath is set in oscillation or vibration, thus preventing the melt bath from flowing apart during the start phase of the welding process. On account of the oscillating or pulsating melt bath of the workpieces  13 ,  14 , renewed flowing together of the melt bath is constantly achieved. It is, thus, ensured from the very beginning of the welding process that no welding holes will form and the weld seam will exhibit an accordingly large weld thickness. Thus, even very short welds as are desired in tack welding can be produced. 
   According to  FIG. 3 , it is also feasible to supply the electrode  12 , after the ignition of the electric arc  11 , with constant power and, in particular, a constant current intensity  27 , over a predetermined, presettable period of time  26 , whereupon the start program  22  is carried out upon expiration of the period  26 . After this, constant power feeding, i.e., the welding process proper at a selected current intensity  25 , is again realized. In doing so, the initial supply of the electric arc  11  with constant power, i.e., the current intensity  27  after the ignition of the electric arc  11  may differ from the supply with constant power for the welding process proper, i.e., the current intensity  25  after the start program  22 . Such an application offers the advantage that the initial supply of the electrode  12  with constant power, i.e., during the period  26 , causes the electric arc  11  to stabilize before the start program  22  and, after this, the welding process proper are started. 
   The introduction of energy during the start program  22  is preferably controlled in a manner that the mean value of the pulsed energy corresponds to the current intensity  25  for the subsequent welding process at constant power. The start program  22  can, thus, be adapted to the adjusted welding process proper. 
   At the welding current source  2 , the parameters of the start program  22  and, in particular, the pulse parameters like pulse height, pulse width, pulse frequency, pulse break and, possibly, curve shape are freely settable, particularly via the input and/or output device  20 . To this end, it is, for instance, feasible to arrange an operating element (not illustrated) at the input and/or output device  20 , via which operating element the start program  22  can be activated or invoked and, if desired, subsequently amended accordingly so as to enable the automatic running of the same with the desired parameters after the ignition of the electric arc  11 . 
   Examples of parameters for the start program  22  are: 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               Pulsed current amplitude: 
                3 A-220 A 
             
             
                 
               Basic current amplitude: 
                3 A-220 A 
             
             
                 
               Pulse frequency: 
                40 Hz-200 Hz 
             
             
                 
               Pulse-duty factor: 
                4%-50% 
             
             
                 
               Period of time: 
                0 s-10 s 
             
             
                 
                 
             
           
        
       
     
   
   It is, of course, feasible to fix the parameters of the start program  22  independently of the control and/or evaluation device  4 , or automatically. In doing so, a suitable start program  22  can be established or computed by the control and/or evaluation device  4  on grounds of stored tables, algorithms or the like, which start program is preferably fixed as a function of the parameters adjusted for the welding process proper. In doing so, it is, for instance, possible that the parameters of the start program  22  are automatically fixed or varied by the control and/or evaluation device  4  provided in the welding apparatus  1 , as a function of the current intensity  25  for the welding process proper. This may be realized in various ways, for instance by reducing or increasing the current intensity  25  for the welding process by an amount or percentage change, or according to a defined algorithm. It is also feasible that the start program  22  is determined by the control and/or evaluation device  4  by inputting a material thickness or a material of the workpieces  13 ,  14  to be welded. 
   Furthermore, it is also feasible to store in the power source or welding apparatus  1  differently defined start programs  22  and, in particular, different start programs  22  having different parameters or curve shapes, which may be used or varied by the control and/or evaluation device  4  or selected by a user. 
   Finally, it should be noted that individual conditions or representations have been disproportionally illustrated in the previously described exemplary embodiments in order to enhance the understanding of the solution according to the invention. Moreover, individual states or representations of the previously described combinations of characteristic features of the individual exemplary embodiment in combination with other individual characteristic features from other exemplary embodiments may also constitute independent solutions according to the invention.