WELDING ELECTRODES AND METHOD

Abstract: A welding electrode (1) having regions (2, 3) of reduced cross-sectional area at selected positions along the length of the electrode to assist in detaching droplets of weld metal during the welding process.

Description: TITLE: WELDING ELECTRODES AND METHOD A Field of the Invention: This invention relates to welding electrodes and to methods of manufacturing or preparing and using such 5 electrodes in electric arc welding operations. Background of the Invention: The transfer of molten weld metal within a welding arc is primarily influenced by the combined effects of gravity, surface tension and the magnetic pinch effect. 10 Developments in the field of Pulsed-Arc welding having attempted to achieve further control of weld metal transfer utilising an enhanced magnetic pinch effect. By this method, discrete pulses of elevated welding current are applied to the arc at electronically 15 controlled intervals, so timed as to aid the transfer of a given volume of molten weld metal per cycle.. In order to achieve a constant transferred volume, this process requires that the frequency of the welding current pulses be closely synchronised to the rate at which the 20 consumable wire is fed into the arc. In practice this can be difficult to achieve. The Sugar Industry crush their cane between geared rollers which lave a hardened, roughened surface, which ensures there is a constant feed of cane into the 25 crusher. This roughening of the rolled surface is achieved by depositing dobs of hardened weld metal onto the rollers. Unfortunately this surface does not last a full crushing season, so attempts are therefore made whilst the rollers are actually crushing cane to add more blobs of weld metal. Since the surface of the rollers is covered with treacle and the rollers are travelling at a surface speed of 16 metres per minute, and since the welding task must be performed in a semi-vertical position, the welding conditions are far from ideal. The existing methods result in irregular weld transfer, and low recovery rate of the welding consumable. Our early research efforts directed at a solution to this problem were based on the premise that if you wish to place a blob of metal on the surface of the roller, then a pulse mode of operation should be helpful. However, in pulsed arc welding a high current period is followed by a low current period, and since the low current period is at relatively low voltage, when this type of welding was tested in the adverse conditions outlined above, it was found that the arc was continually extinguished in the low current periods. Summary of the Invention and Objects: It is the object of the present invention to provide a modified welding electrode, and a method of forming same, by means of which the above problems may be substantially ameliorated. It should of course be appreciated that the modified welding electrode has applications far wider than the specific application described above, and the invention is by no means limited to that application. The invention therefore provides a welding electrode which is characterised by a series of reductions in cross-sectional area spaced at selected intervals along the length of the electrode. By forming regions of reduced cross-sectional area in the electrode, the electrode is effectively divided into discrete segments and the reduction in cross- sectional area ensure regular and controlled detachment of weld metal from the electrode. In this way, the volume of the transferred molten metal is governed by the consumable wire directly, and is independent of the rate of wire feed. This regulates and aids the stable transfer of a given volume of molten weld metal per cycle by means of a simple and easily achieved preparation of the welding consumable. The reduction in area is such that normal feeding of the consumable wire is not impaired and is typically achieved by a reduction in the original diameter of the wire of about 90 to 50%, say by the formation of one or more grooves or notches in the wire. In one specific embodiment of the invention, a flux cored "Hard Facing" type consumable wire with a nominal diameter of about 2.8 mm is formed with diametrically opposed deformations, such as notches, which reduces the diameter of the wire to about 2.5 mm. For this consumable, the welding conditions were optimised with a spacing of 10.47mm. The deposition rate achieved was in excess of 50% greater than previously obtained with plain electrode. The suitability for purpose of the welded surface, such as a cane crushing roller was also enhanced. The use of the modified consumable wire described above results in individual deposits of weld metal of substantially uniform volume with greatly increased weld metal deposition rate efficiency. Successful results have been achieved in the environment described above using an average arc voltage of about 35 volts, and an average arc current of about 400 amps. These parameters are the same as would be selected by a skilled welder for a flux cored "hard facing" electrode of 2.8 mm diameter. Thus, the use of the electrode embodying the invention is not dependent on the selection of special parameters, which depend on the material of the workpiece and the material and diameter of the electrode and the results desired. The modified wire may be used in applications. Other than surfacing, including the joining of metals, sheetmetal work, conditions of poor part alignment, and welding in outside environments. The invention also provides a method of arc welding comprising the step of feeding a welding electrode having a series of reductions in cross-sectional area spaced at selected intervals along the length of the electrode into the welding arc. The invention further provides a method of forming a welding electrode comprising the step of forming a series of reductions in cross-sectional area spaced at selected intervals along the length of the electrode. In one form of the invention, the reductions in cross-sectional area may be formed by means of driven notching rollers which form the reductions in cross- sectional area as the electrode is fed towards the welding arc. The notching rollers may perform the dual function of notching the electrode and driving it towards the welding arc. The electrode wire need only be transversely notched at diametrically opposed positions since any reduction in cross-sectional area of the required dimensions will have the effect of ensuring the detachment of the required volume of weld metal from the electrode. Brief Description of the Drawings: One preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a side elevation of an electrode wire in which a suitable deformation has been formed; Figure 2 is a schematic illustration of the sequence of events in a typical weld metal transfer cycle; Figure 3 is a schematic illustration in a modified metal weld transfer cycle; Figure 4 is a schematic illustration of an electrode wire notching roller arrangement, and Figure 5 is a perspective view of an alternative wire feeding and notching apparatus. Description of Preferred Embodiment: Referring firstly to Figure 1 of the drawings, an electrode wire 1 of about 2.8 mm in diameter is illustrated having transverse generally semi-circular notches 2 and 3 having a depth of about 1.5 mm at intervals of about 21.5 mm along the length of the electrode wire. It has been found that the formation of diametrically opposed notches 2,3 of the above depth is sufficient to ensure the predictable and controlled detachment of the required volume of weld metal from the electrode as the electrode is fed into an electric arc having the required welding parameters. As shown schematically in Figure 2 of the drawings, the electrode 1 is fed towards the arc A and as the melting of the electrode proceeds towards the notches 2,3, the reduced cross-sectional dimensions of the wire 1 at this point causes the magnetic pinch-effect which is present in the welding arc to be concentrated at this location to cause rupture of the weld metal at this position. Thus, the reduction in cross-sectional area in the electrode wire may be regarded as having a two-fold purpose: (a) to provide a region of reduced current-carrying capacity at which localised heating of the electrode will occur as a result of the increase in electrical resistance and the increase in current density, and (b) to provide a point of reduced surface tension between the tip of the electrode wire and the adjacent volume of weld metal in the arc. As will be evident from Figure 2 of the drawings, a molten droplet D of weld metal progressively forms on the end of the electrode wire as it is fed into the arc A, and as each region of reduced in cross-sectional dimensions enters the arc zone A, the wire 1 ruptures at that point leaving the droplet D free to transfer onto the workpiece W. The cycle is then repeated for each segment of electrode wire 1, and in the event that the electrode wire touches the workpiece resulting in the arc being extinguished, the region of reduced cross- sectional dimensions again provides a preferred site for the wire to rupture, so clearing the short circuit and facilitating re-establishment of the arc. Figure 3 illustrates another mode of arc transfer where, under the influence of the fluxing agents contained within the electrode wire or the composition of a shielding gas employed, the molten droplet D is repelled from the workpiece W. In these circumstances, the droplet D may remain attached to the end of the electrode wire 1 until such time that the weight of the droplet D exceeds the sum of the repelling arc force and the wire-to-droplet surface tension. In this instance, the invention again aids the regular detachment of droplets by the means described above. The notched regions 2, 3 of the electrode wire may be formed in the electrode wire during the manufacture of the wire, but it is presently preferred that the necessary notches be formed by the means feeding the electrode wire towards the arc. One such means is shown in Figure 3 of the drawings to comprise a pair of driven rollers R each having a peripheral semi-circular groove G having projections P machined in each groove G, as shown schematically in Figure 3. The notching rollers R may replace the wire feeding rollers in the welding apparatus being used to perform welding using the electrode modified in accordance with the invention. In an alternative combined wirefeeding and wirecrimping mechanism shown in Figure 5, a shaft 10, rotated by a suitable geared motor (not shown), drives a gear 15 and adjustable throw crank 14 moulded on a rigid base plate 11. Gears 12 and 13 are in mesh with gear 15, respectively rotating cams 16 and 14, each fitted with ball bearing cam rollers 17. A reciprocating yoke 18, moves in direction A, between the guide rollers 19 mounted on base plate 11 when acted upon by the cam rollers 17 and moves in direction B by means of a return spring (not shown) . Crimping tools 22 and 27 are acted upon by the internal cam faces of yoke 18. Spring loaded feeding cams 20 are carried in a reciprocating manner by crank 16, in the forward stroke gripping the electrode wire 1, so advancing the wire 1 in the direction indicated. Stationary spring loaded gripping cams 21 allow the electrode wire 13 to advance in the forward direction, but grip the electrode wire to prevent backward motion of the wire during the return stroke of the feed cams 20. In a complete cycle of events the electrode wire 1 is carried forward by cams 20; at the end of the forward stroke the crimping tools 22 and 27 indent the wire, and during the return stroke the wire is held stationary by cams 21. It will be appreciated that the wire advances at a sinusoidal rate during the forward 180 degrees of rotation of the cam 24, while remaining stationary during the return 180 degrees of rotation. In this way, a dwell period is introduced into the wire feed and this may further assist in ensuring detachment of the molten droplet at the notched region 2, 3. The total length of forward wirefeed is adjustable over a range as set by the throw of the adjustable crank 24. It will be appreciated that the shape of the notch 2,3 formed in the electrode wire is not important to the invention and may be semi-circular, as shown in Figure 1, angular as shown in Figure 3, V-shaped or any other desired shape. The important feature is that a region of reduced cross-sectional area is formed in the electrode wire at spaced points along the length of the wire. Thus, similar results could be achieved by groove(s) cut in the surface of the electrode. While the spacing of the regions of reduced cross- sectional area are shown in the drawings as being uniform, there may be applications where it may be desirable to have different spacings along the length of the wire to achieve the transfer of different volumes of weld metal to the workpiece.

Claims: Claims: 1. A welding electrode characterised by a series of reductions in cross sectional area spaced at selected intervals along the length of the electrode. 2. The electrode of claim 1, wherein the reductions in cross-sectional area comprise one or more notches formed in the surface of the electrode to provide said series of reductions in cross-sectional area. 3. The electrode of claim 2, wherein said notches are formed at diametrically opposed positions of the electrode. 4. The electrode of claim 2 or 3, wherein said notches reduce the effective diameter of the electrode by an amount falling substantially within the range 5% to 20%. 5. The electrode of claim 4, wherein the diametric reduction falls substantially within the range 8% to 15%. 6. The electrode of claim 4 or 5, wherein the diametric reduction substantially falls within the range 9 to 12%. 7. A method of arc welding comprising establishing a welding arc and feeding a welding electrode according to any one of the preceding claims into said arc. 8. The method of claim 7, wherein said welding electrode is fed into the arc by a mechanism which also forms a series of reductions in cross sectional area spaced at selected intervals along the length of the electrode. 9. The method of claim 7 or 8, wherein said electrode is fed into the arc intermittently with a dwell period occuring as the portion of reduced cross section approaches said arc. 10. An apparatus for feeding and notching a welding electrode comprising means for advancing the electrode by a predetermined distance, means for causing transverse notching of the electrode, and means for advancing the electrode by a predetermined distance so that the electrode is transversely notched to produce a series of reductions in cross-sectional area spaced at selected intervals along the length of the electrode. 10. The apparatus of claim 9, comprising a pair of driven rollers having their peripheries adjacent each other or in contact, each roller having a groove in its periphery dimensioned to receive said electrode and spaced projections formed in each groove for transversely notching the electrode at diametrically opposed positions. 11. The apparatus of claim 9, wherein said means for feeding said electrode comprises a pair of gripping cams mounted on a reciprocating crank, said means for notching said electrode comprising a pair of opposed crimping tools mounted for crimping movement towards the electrode by a reciprocating cam means, and spring loaded gripping cams for allowing forward movement of the electrode whilst preventing reverse movement of the electrode.

Inventors: BROUGHAM WILLIAM KENNETH, CHEESMAN GARY LYN, BROUGHAM, WILLIAM, KENNETH, CHEESMAN, GARY, LYN
Applicants: WELDING IND LTD, WELDING INDUSTRIES LIMITED
Application year: 1991
Main classification: B23K35
IPC codes: B23K9, B23K35