Downward gas-metal-arc welding process
BACKGROUND OF INVENTION 
     This invention relates to gas-metal-arc welding process by which a vertically downward weld deposit bead can be produced. The process involves continuously feeding a consumable or meltable electrode wire towards the weld deposit, utilizing a shielding gas flowing around the end of the electrode and the arc gap, to produce a plasma field in the gap. This process, by controlling and appropriately positioning the plasma field and causing a globular free-flight transfer for depositing metal from the wire upon the weld pool or deposit, permits welding downwardly, i.e. moving the welding wire downwardly, without run-off of the molten metal due to gravity. 
     In prior, generally vertically arranged weld beads, the procedure for applying the weld involved depositing the metal in an upward direction. That is, weld material has been applied upon the substrate and molten material applied upon the &#34;shelf&#34; or upper end of the weld bead so that the bead is gradually built upwardly. The prior system is relatively slow and presents quality and penetration problems. Thus, this invention is an improvement to the prior upward welding system for forming generally upright or vertical welds. 
     The general process involved, that is, the utilization of a shielding gas comprising a four-gas mixture, with a consumable wire electrode and the production of a hot plasma field within which the weld metal transfer occurs, is disclosed in my prior U.S. Pat. No. 4,463,243, issued July 31, 1984, for a &#34;Welding System.&#34; Said process is additionally and further described in my subsequent U.S. Pat. No. 4,572,942, issued Feb. 25, 1986, for a &#34;Gas-Metal-Arc Welding Process.&#34; In addition, the process may utilize a welding gun, such as disclosed in my prior U.S. Pat. No. 4,464,560, granted Aug. 7, 1984, for an &#34;Arc Welding Gun With Gas Diffuser and External Cooling Conduit&#34; to John G. Church and Emerson G. Malone. Further, a suitable welding gun and this kind of process is further disclosed in U.S. Pat. No. 4,529,863, issued July 16, 1985, for a &#34;Gas-Metal-Arc Welding Method&#34; to John-Claude Lebel. 
     The process disclosed in these prior patents produced a high rate of deposition of weld material which rapidly forms high-quality weld beads. The rate of metal deposition, the speed of formation of the bead and the quality of the bead all are substantially improved as compared with earlier welding processes. However, my U.S. patent application, Ser. No. 190,309, filed May 4, 1988, for a &#34;High Rate Deposition Gas-Metal-Arc Welding Process&#34; discloses a generally similar process but achieving substantially higher rates of speed for forming weld beads. 
     In this present application, I have discovered a process for producing, at relatively high deposition rates, weld beads in a downward direction, that is, by moving the welding wire, with the welding gun, downwardly, as compared to the prior processes utilized for forming verticaltype welds, namely, upwardly. This present, downward procedure produces high-quality welds with better penetration and much greater speeds of formation than that previously achievable through the conventional upwardly formed beads. 
     SUMMARY OF INVENTION 
     This invention contemplates a process for forming weld beads downwardly, that is, depositing the bead metal along a downward path for producing &#34;vertical&#34; or upright weld beads. The process includes the utilization of a consumable wire electrode which is arranged roughly horizontal relative to the weld substrate and which is surrounded by a flowing four-gas mixture directed around the electrode and towards the substrate. Sufficient electrical voltage and amperage is applied to the electrode to produce a hot plasma field in the arc gap between the end of the electrode and the substrate. This plasma field is generally conical in shape and is arranged coaxially, at all times, to the axis of the electrode wire. 
     Metal is transferred from the electrode to the substrate by means of globular, free-flight transfer wherein the globules of metal move along the axis of the conical plasma field, coaxially with the electrode wire. Meanwhile, the base of the conical field is positioned, by suitably adjusting the voltage and the length of the arc gap, to be coextensive, transversely, with the width of the forming bead. Thus, the globules are precisely directed along the axis of the plasma and upon reaching the substrate are uniformly spread out or distributed thereon and adhere to the substrate. 
     The welding gun within which the wire electrode is melted, is advanced in an axial direction at a rate sufficient to provide the metal needed to compensate for the melt-off of the globules. In addition, the welding gun is moved downwardly along a path which is in alignment with the central axis of the bead and equidistant from the opposite edges of the bead. Thus, the length of the arc gap is maintained, the continuous flow of the globules is maintained at a consistent rate, and the base of the conical plasma field remains coextensive with the width of the bead. This results in a high-speed deposition of metal, wherein the metal adheres and there is no run-off due to gravity. The resulting bead is of a generally higher quality than that achievable in the prior upward welding. In addition, a better penetration pattern and depth is achieved through this improved method. 
     One object of this invention is to provide a method which substantially increases the speed of formation, the quality of, and the penetration characteristics of a generally vertically arranged bead, that is, a welding bead which is generally upright. This object is achieved utilizing presently available equipment and presently available skilled welders so that the cost of the improved weld and speed of welding is not increased, but rather is decreased per unit because of the faster arc time for producing such welds. 
     A further object of this invention is to produce inexpensively a higher quality weld by a downward welding system. 
     Still a further object of this invention is to form a weld bead in one pass, with the bead being accurate and uniform in its shape and cross-section, with the weld being formed against the normal gravitational forces at a higher rate than that previously accomplished with upward type of welding. 
     These and other objects and advantages of this invention will become apparent upon reading the following description, of which the attached drawings form a part. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIG. 1 is an elevational, cross-sectional view, schematically showing the welding gun and the welding operation. 
     FIG. 2 is a perspective, schematic view showing the application of the weld bead in downward direction. 
     FIG. 3 is an enlarged, schematic, side view showing the application of the globules, by free flight, in downward movement of the welding rod. 
     FIG. 4 schematically shows the prior art method by which the bead is formed in a vertically upward direction, utilizing short-circuit transfer of molten metal from the tip of the welding wire electrode. 
     FIG. 5 is a schematic, plan view showing the application of a fillet weld to a pair of intersecting plates, utilizing the downward weld method. 
     FIG. 6 is a schematic, plan view showing the penetration achieved with the fillet type of weld. 
     FIG. 7 schematically illustrates a prior art weld, produced by welding upwardly, and showing a gap or fault which frequently occurs in such type of welding. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates, in cross-section, a consumable wire gas-metal-arc welding gun 10 of the type disclosed in my above-mentioned U.S. Pat. No. 4,464,560. This gun is utilized to weld with a wire electrode 11. The gun has a ceramic nozzle or sleeve 13 which surrounds a cylindrical diffuser 14 through which the wire is passed. 
     The diffuser includes an enlarged head 15 which closely fits within the nozzle. The nozzle is immovably attached to the head by means of a suitable set screw 16. The diffuser has a central bore 17 through which the wire electrode slides. In addition, its head 15 has an enlarged counterbore 18. 
     A tubular tip member 20 fits into the central bore 17 of the diffuser. This tip member has a central opening 21, which is slightly larger than the diameter of the wire electrode, so that the opening forms a guide through which the wire is fed. 
     A ring-like spacer 24 is inserted within the enlarged counterbore 18 of the diffuser head 15. This spacer ring has a number of radially outwardly extending fins 25. Thus, there are spaces around the outside of the ring and between the fins. These spaces communicate with angled passages 27 drilled in the head 15 of the diffuser. 
     A copper tube 30, having a threaded end 31, is attached to the diffuser head by means of threads 32 which form a threaded socket within the counterbore 18. A coolant tube 34 surrounds the copper tube and terminates in a loop 35 near the connection between the copper tube and the diffuser. Cooling water may be circulated through the coolant tube using a conventional pump and valve system, which are commercially available. 
     A sleeve 36 surrounds the copper tube and the coolant tube to provide a hand grip for the welder. This sleeve and additional external sleeves or grips are conventional. 
     The welding gun is arranged horizontally or aimed at a slight downward angle so that the tip 39 of the electrode is aimed toward the surface 40, i.e. weld deposit, pool or substrate, upon which the weld will be formed. Thus, an arc gap 41 is maintained between the tip 39 and the weld surface 40. 
     During operation of the welding apparatus, a globule 42 forms on the tip of the electrode. The connection between the forming globule and the end of the electrode gradually necks down until the globule is released. Then the released globules 43 transfer, by free flight, to the weld bead or deposit 44 into which it is absorbed. 
     In this system, a gas flow 46, comprising a four-gas mixture, flows through the copper tube 30 into the spaces between the fins 25 of the ring-like spacer 24. The flowing gas continues through the angled passages 27 in the diffuser head 15. Then, as illustrated by the dotted lines, the gas stream or flow angles against the interior surface of the nozzle 13 and then is reflected towards the central axis of the wire. Part of the gas flow is focused towards the intersection of the wire electrode axis and the weld surface 40, and part of the flow proceeds in a laminar-type flow towards the weld surface from which it is deflected. 
     The gas flow, with the application of an appropriate electrical voltage and current to the wire electrode, generates a plasma field 47 within the arc gap. The plasma field includes a central, hot plasma zone 48 which is approximately conical in shape. 
     By appropriately adjusting the voltage and the length of the arc gap, the circular base of the hot plasma zone cone 48 may be positioned upon the weld surface so as to span the full width of the weld surface. That is, by centralizing the cone upon the central axis of the weld bead or the band of substrate upon which the bead is to be formed, the base of the cone can be transversely extended from side to side of the width of the band. Then, movement of the wire electrode towards the weld surface can be adjusted to maintain the length of the arc gap as the globules are melted off the weld tip. Simultaneously, the electrode is moved downwardly, in alignment with the central axis of the bead or the narrow band of the surface upon which the bead will be formed, equidistantly from the side edges of that band. Thus, the cone is stably controlled with respect to the axis of the wire, and the globules move along the axis of the wire. 
     The globules, upon reaching the weld pool, immediately spread out in all directions and adhere to the weld pool into which each globule is absorbed. This results in good adherence of the globules to the downwardly forming weld bead, notwithstanding the force of gravity which otherwise would tend to cause the molten globule to run down. 
     The operation of the downwardly moving weld electrode is schematically illustrated in FIG. 2. Thus, FIG. 2 illustrates a pair of intersecting plates 50 and 51 and the formation of a fillet weld 52 at the corner or intersection of the two plates. As can been schematically, the fillet weld deeply penetrates the plates at 53 to form a very rough T-shape cross-section which produces a better quality, stronger, crack-resistant weld. 
     FIG. 3 schematically illustrates the movement of the electrode downwardly, in the direction of the axis of the bead. The globule 42 on the tip of the electrode is released, and the travelling globules 43 freeflow, along the axis of the electrode and the plasma cone, to the weld surface. 
     FIG. 4 schematically illustrates the prior art weld method by which the weld is formed by moving the wire electrode upwardly. In this system, the plate 55 is used as a substrate upon which an upwardly formed weld bead 56 is applied. The electrode wire 11 forms a globule 42 upon its tip. However, this globule is transferred by a short circuit welding transfer, that is, by touching the globule to the weld pool at the shelf-like formation 57 on the upper end of the upwardly formed bead 56. 
     As illustrated in FIG. 6, the bead formed by the process of this application produces a sound, deep penetration. In contrast, the prior method for producing upwardly-formed beads has a tendency to be imperfect in places, including forming gaps 59, illustrated in exaggerated form in FIG. 7. 
     The wire electrode may vary in composition and diameter. As examples, electrodes, which are commercially available, may run in a diameter range of between about 0.016 to 0.062 inches. Preferable diameters are roughly in the range of between about 0.035 to 0.45 inches. The composition of the wire may be varied depending upon the nature of the welding and the results desired. Such compositions are known and commercially available. 
     Conventional feed mechanisms and systems for applying the desired electrical current and voltage are commercially available and known. Thus, the details of these are not included in this description. 
     It is desired, in performing the method of this application, to utilize a voltage which is roughly in the range of between about 20-40volts. A good, satisfactory voltage range is at about the middle point, that is, around 29-30 volts. The amperage may be set sufficiently high to produce a current density of about 400,000 amps per square inch of electrode wire cross-section. Preferably, the current density range is at a higher rate, such as around 500,000 amps per square inch and higher, depending upon circumstances, up to roughly 700,000 amps per square inch. 
     The length of the exposed portion of the electrode wire and the length of the arc may be varied, based upon trial and error for a particular welding purpose. By way of example, the &#34;stick-out,&#34; that is, the length of the wire between the end of the tubular tip 20 and the free end of the ceramic nozzle 13 may be in the range of about 5/16 inch. Then, the wire may continue outwardly of the end of the nozzle for about 1/2, with an approximate 1/2 inch arc gap. These dimensions, however, are illustrative and, as mentioned, will vary depending on circumstances. 
     The rate of deposit, utilizing the globular transfer system and the downwardly moving electrode wire, can be three to five times, more or less, than the rate of deposition of the vertical up welding method. By way of example, a deposition of 10-12 lbs. per hour may be achieved with the downward weld method of this application as contrasted with a deposition rate of approximately 3 lbs. per hour utilizing a corresponding vertically upward method of welding of the prior art. Notwithstanding the higher deposition rate, the molten globules readily adhere to the forming weld bead rather than run downwardly under the influence of gravity, as would be expected. 
     This invention may be further developed within the scope of the following claims.