Arc starting process for long stick out submerged arc welding

Abstract

To provide an arc starting process for long stick-out submerged arc welding.SOLUTION: The disclosed technology relates generally to welding technology, and more particularly to an electrode assembly for arc welding, such as submerged arc welding. In one aspect, a welding system includes a welding power source and an electrode assembly operatively coupled to the welding power source and an electrode. The welding power source is configured to apply a direct current electrode negative (DCEN) to the electrode using the electrode assembly to establish an arc between the electrode and the workpiece, and to apply a direct current electrode positive (DCEP) or an alternating current (AC) to the electrode after the arc is established.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Incorporation by reference to priority applications All applications for which a foreign or domestic priority claim is identified in an Application Data Sheet filed with this application are hereby incorporated by reference pursuant to Title 37, Code of Federal Regulations, Section 1.57 (37 CFR 1.57).

[0002] This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 63 / 681,731, entitled "ARC-START PROCESSES FOR LONG STICK OUT SUBMERGED ARC WELDING," filed August 9, 2024. The above application is incorporated herein by reference in its entirety.

[0003] The disclosed technology relates generally to welding technology, and more particularly to methods for operating arc welding equipment, such as submerged arc welding (SAW) equipment. [Background technology]

[0004] Various welding techniques utilize a welding wire that serves as a source of metal. For example, in metal arc welding, an electric arc is created when a voltage is applied between a consumable welding electrode wire, which serves as one electrode and is advanced toward the workpiece, and the workpiece, which serves as the other electrode. The arc melts the tip of the metal wire, thereby creating droplets of molten metal wire that deposit on the workpiece to form a weld or weld bead.

[0005] The technical and economic demands on welding technologies continue to become more complex. For example, there is an ever-increasing need for higher bead quality, both in appearance and mechanical properties, including high yield strength, ductility, and fracture toughness. At the same time, higher bead quality is often required while maintaining economic feasibility. Some welding technologies attempt to address these conflicting demands through improvements in consumable materials, for example, through improvements in the physical design and / or composition of the electrode wire.

[0006] Submerged arc welding (SAW) can provide a very economical solution for some applications. The high deposition rates achieved with the submerged arc are a major factor in the economies realized with this process. Summary of the Invention [Means for solving the problem]

[0007] In one aspect, a welding system includes a welding power source and a welding tool operably coupled to the welding power source and the electrode, the welding power source configured to apply a direct current electrode negative (DCEN) to the electrode using an electrode assembly to establish an arc between the electrode and a workpiece, and to apply a direct current electrode positive (DCEP) or alternating current (AC) to the electrode after the arc is established.

[0008] In another aspect, a method of operating a welding system is provided that includes applying a direct current electrode negative (DCEN) to an electrode to establish an arc between the electrode and a workpiece, and applying a direct current electrode positive (DCEP) or alternating current (AC) to the electrode after the arc is established. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a schematic of a submerged arc welding (SAW) system in accordance with an embodiment of the present technology; [Figure 2] FIG. 1 illustrates a conventional electrode assembly for a SAW system. [Figure 3A] FIG. 1 illustrates a conventional electrode assembly for a SAW system over a workpiece having a groove. [Figure 3B] FIG. 1 illustrates a long stick-out (LSO) electrode assembly for a SAW system over a workpiece having a groove. [Figure 4] 1 is a flow diagram of a method of operating a welding system in which a direct current electrode positive (DCEP) is applied to an electrode to begin a weld. [Figure 5] FIG. 5 shows graphs of voltage, current, and wire feed speed of the welding system during the method shown in FIG. 4. [Figure 6A] 5A-5C show LSO electrodes at various times during the process shown in FIG. 4. [Figure 6B] 5A-5C show LSO electrodes at various times during the process shown in FIG. 4. [Figure 6C] 5A-5C show LSO electrodes at various times during the process shown in FIG. 4. [Figure 6D] 5A-5C show LSO electrodes at various times during the process shown in FIG. 4. [Figure 6E] 5A-5C show LSO electrodes at various times during the process shown in FIG. 4. [Figure 6F] 5A-5C show LSO electrodes at various times during the process shown in FIG. 4. [Figure 6G] 5A-5C show LSO electrodes at various times during the process shown in FIG. 4. [Figure 7] 1 is a flow chart illustrating a method of operating a welding system in which a direct current electrode negative (DCEN) is applied to an electrode to initiate welding, according to some embodiments. [Figure 8] FIG. 8 shows graphs of voltage, current, and wire feed speed of the welding system during the method shown in FIG. 7. [Figure 9A] 8A-8D show the LSO electrode at various times during the process shown in FIG. 7. [Figure 9B] 8A-8D show the LSO electrode at various times during the process shown in FIG. 7. [Figure 9C] 8A-8D show the LSO electrode at various times during the process shown in FIG. 7. [Figure 9D] 8A-8D show the LSO electrode at various times during the process shown in FIG. 7. [Figure 9E] 8A-8D show the LSO electrode at various times during the process shown in FIG. 7. [Figure 9F] 8A-8D show the LSO electrode at various times during the process shown in FIG. 7. [Figure 9G] 8A-8D show the LSO electrode at various times during the process shown in FIG. 7. [Figure 10] 1 is a flow chart illustrating a method of operating a welding system in which a DCEN biased asymmetric alternating current (AC) is applied to an electrode initiated weld, according to some embodiments. [Figure 11] 11A and 11B show graphs of voltage and current of the welding system during the method shown in FIG. 10. DETAILED DESCRIPTION OF THE INVENTION

[0010] In processes using consumable electrodes, an electrode or wire melts to provide additional metal to bridge the gap and form a weld joint joining two metal workpieces. Welding processes using consumable electrodes include shielded arc welding (SMAW), gas metal arc welding (GMAW), or metal inert gas (MIG) welding, flux cored arc welding (FCAW), metal cored arc welding (MCAW), and submerged arc welding (SAW).

[0011] Submerged Arc Welding FIG. 1 schematically illustrates a submerged arc welding (SAW) system 100 for depositing filler or weld metal on a workpiece 102. The system 100 includes an electrode 104 having a tip 106, a contact tip 110 coupled to the electrode 104, and a power source 108 electrically coupled to the contact tip 110 and the workpiece 102. Although not shown, the system 100 also includes one or more processors or controllers communicatively coupled to the power source 108 and a non-transitory computer-readable storage medium. The non-transitory computer-readable storage medium stores instructions that, when executed by the one or more processors or controllers, cause the one or more processors to perform various welding methods disclosed herein. The system 100 also includes a flux delivery system 112 configured to dispense flux 114 onto the workpiece 102 during the SAW process. The electrode 104 generally includes a metal or alloy, and the flux includes a granular fusible material. During the SAW process, heat is obtained from an arc 116 between the electrode 104 and the workpiece 102. The arc is shielded by a blanket of flux 114 placed above the joining area in front of the arc 116. Filler metal is obtained primarily from the electrode 104 and is continuously supplied through the blanket of flux 114 to the arc 116 and to a pool 122 of molten flux. Additional filler metal can be obtained by adding cold or hot wire to the weld pool 122 or from metal powder contained in the flux 114. Thus, unlike other flux processes, SAW uses two consumables (electrode 104 and flux 114), and these two consumables can be supplied separately.

[0012] A distinguishing feature of SAW is the flux 114, which covers the weld area and prevents arc radiation, sparks, spatter, and smoke emissions. The flux 114 enables high deposition rates and high-quality weld deposit characteristics. In addition to shielding the arc 116 from view, the flux 114 provides slag 118, which protects the weld metal 120 as it cools, deoxidizing and refining it, insulating the weld and slowing its cooling rate, and aiding in the formation of the weld contour.

[0013] During the SAW process, the heat of the arc 116 melts a portion of the flux 114 along with the tip 106 of the electrode 104, forming a weld pool 122 as shown in FIG. 1. The tip 106 of the electrode 104 and the weld area are constantly surrounded and shielded by the molten flux 114, which itself is covered with a layer of unmelted flux 114. The electrode 104 is held spaced apart just above the workpiece 102, and an arc 116 is ignited between the electrode 104 and the workpiece 102. As the electrode 104 advances along the joint, the lighter molten flux 114 rises above the molten metal in the weld pool 122 as a slag 118. The molten metal in the weld pool 122, which has a higher melting point (freezing point), solidifies, while the slag 118 above it remains molten. The slag 118 then solidifies above the newly solidified weld metal 120, protecting it from contamination while it heats up and reacts with oxygen and nitrogen in the atmosphere. After cooling and removing the unmelted flux 114 for reuse, the solidified slag 118 can be easily removed from the weld.

[0014] A power supply 108 generates the voltage and current for the system 100, which are applied to the workpiece 102 and the electrode 104. The current is applied to the electrode via a contact tip 110. High currents can be used in submerged arc welding, which can generate very high heat. Because the current is applied to the electrode 104 just above the tip 106 of the electrode 104, relatively high amperages can be used with small diameter electrodes. This allows for very high current densities to be achieved with a relatively small electrode cross-sectional area. Electrodes as small as 64 inches can carry currents of 600 amperes or more, providing densities on the order of 100,000 amperes per square inch, which is 6 to 10 times the current density carried by a rod electrode.

[0015] High current densities result in much higher melting rates for a given electrode diameter than with stick electrode welding, which is affected by the electrode material, flux 114, current type, polarity, and the length of the wire beyond the electrical contact point at the gun or head.

[0016] Submerged arc welding can be performed with either direct current (DC) or alternating current (AC) power. DC current provides better control of bead shape, penetration, and welding speed and is relatively easy to initiate. Bead shape is usually best with a DC electrode positive (DCEP or reverse polarity), which also provides maximum penetration. The highest deposition rate and lowest penetration can be achieved with a DC electrode negative (DCEN or positive polarity). AC current minimizes arc blow and provides penetration between DCEP and DCEN.

[0017] The insulating blanket of flux 114 above the arc 116 prevents heat from escaping quickly and concentrates it in the weld zone. Not only are the electrode 104 and the base metal of the workpiece 102 melted rapidly, but the melting penetrates deep into the base metal. Deep penetration allows for the use of a small weld groove, thus minimizing the amount of filler metal per foot of joint and enabling high welding speeds. Furthermore, high welding speeds minimize the total heat input into the assembly, thus minimizing thermal distortion problems. Submerged arc welding allows even relatively thick joints to be welded in a single pass.

[0018] The weld formed under the protective layer of flux 114 has good ductility and impact resistance, and a uniform bead appearance. Mechanical properties at least equivalent to those of the base metal are consistently obtained. In single-pass welding, a large amount of base material is melted relative to the amount of filler metal used. Therefore, in such welding, the base metal can have a significant effect on the chemical and mechanical properties of the weld. For this reason, it may not be necessary to use an electrode with the same composition as the base metal for welding many low-alloy steels. However, the chemical composition and properties of multi-pass welds are less influenced by the base metal and depend more on the electrode composition, flux activity, and welding conditions.

[0019] By adjusting the current, voltage, and travel speed, the operator has close control of penetration to provide any depth, from a deep, narrow bead with high crown reinforcement to a wide, nearly flat bead with shallow penetration. A bead with deep penetration may contain as much as 70% molten base metal, while a shallow bead may contain only as little as 10% base metal. In some cases, the deep penetration characteristics of submerged arc welding can be used to eliminate or reduce the cost of edge preparation.

[0020] Fluxes serve several functions in submerged arc welding. These functions include covering the molten weld metal to protect it from the atmosphere and acting as a slag that purifies the molten deposit by removing oxides and other non-metallic inclusions. Metal additions to the flux increase the alloy content of the deposit and deoxidize it.

[0021] Based on the manufacturing method of the flux, there are four types of flux: fused, bonded, agglomerated, and mechanically mixed.

[0022] Fluxes are also distinguished as basic, acidic, and neutral. Basic fluxes contain metal oxides that dissociate easily, while acidic fluxes contain oxides that dissociate only slightly. Neutral fluxes neither add nor subtract from the composition of the weld deposit. Fluxes with a CaO or MnO to SiO2 ratio greater than 1 are considered basic, those close to 1 are considered neutral, and those less than 1 are acidic.

[0023] With the proper selection of equipment, submerged arc welding is widely applicable to industrial welding requirements. It can be used on all types of joints, welding the full range of carbon and low-alloy steels, from 16-gauge sheet to the thickest plate. It is also applicable to some high-alloy, heat-treated, and stainless steels, and is the preferred process for rebuilding and hardening. Any degree of mechanization can be used, from handheld, semi-automatic guns to boom- or truck-transported, fixture-held multiple welding heads.

[0024] The high quality of submerged arc welding, its high deposition rate, deep penetration, the process's amenability to full mechanization, and its comfort characteristics (no glare, sparks, spatter, smoke, or excessive heat radiation) make it the preferred process in steel fabrication. Submerged arc welding is used extensively in ship and barge construction, rail car manufacturing, pipe fabrication, and the fabrication of structural beams, girders, and columns where long welds are required. Automated submerged arc equipment is also an important feature of welding areas in factories that produce mass-produced assemblies joined with repetitive short welds.

[0025] Factors other than deposition rate also influence lower welding costs. Continuous electrode feed from coils in the 60 lb to 1000 lb weight range contributes to high utilization rates. Costs are reduced when the deep penetration characteristics of the process eliminate or reduce joint preparation. After the weld is made, protective fluxes eliminate spatter, minimizing cleanup costs.

[0026] When submerged arc welding equipment is used properly, the weld bead is smooth and uniform, so polishing or machining is rarely required. The rapid heat input of the process minimizes distortion, reducing the cost of straightening the finished assembly, especially if a carefully planned welding sequence is followed. In fact, submerged arc welding often allows for pre-machining of parts, further contributing to manufacturing cost savings.

[0027] Because of these and other advantages offered by SAW, there is a desire and need for further improvements in various aspects of SAW, including higher productivity and weld quality. For example, because one of the technical advantages of SAW is derived from preheating the consumable electrode, there is a desire and need for further improvements in preheating configurations through improved electrode assembly designs.

[0028] Long stick-out electrode assembly for submerged arc welding FIG. 2 shows an electrode assembly 200 positioned above a workpiece 202, defining an electrical stick-out. The electrode assembly 200 includes a head portion 224 configured to receive an electrode 204. The head portion 224 includes a contact tip 210, an electrode guide tube 226, and an insulating guide 228. The contact tip 210 is radially disposed around the electrode 204 and configured to transfer electrical current from a power source (e.g., power source 108 shown in FIG. 1) to the electrode 204. The electrode 204 includes a tip portion 206 configured to extend beyond the head portion 224. The portion of the electrode 204 extending between the tip portion 206 and the end of the head portion 224 is referred to as the visible stick-out 232, while the portion of the electrode 204 extending between the tip portion 206 and the contact tip 210 is referred to as the electrical stick-out or electrical electrode extension 230. Unless otherwise stated, "stick-out length" as used herein refers to the length of the electrical stick-out 230, which is the parameter that primarily affects the electrical response of the electrode assembly 200. During operation of the electrode assembly 200, the tip portion 206 is positioned adjacent to the workpiece 202, and the distance between the contact tip 210 and the workpiece 202 is referred to as the contact tip-to-work distance (CTWD) 234.

[0029] The electric stick-out 230 of the electrode 204 is preheated by Joule heating or resistance heating. If the electric electrode extension 230 is not long enough, the electrode 204 may not be sufficiently preheated. Increasing the length of the electric stick-out 230 increases the electrical resistance of the circuit, which further enhances heating and therefore increases the temperature of the tip 206 of the electrode 204, resulting in increased melting and deposition rates. Because the length of the filler wire extension affects the melting rate, the length of the electric stick-out 230 also controls the size of the weld bead. Furthermore, the electric electrode extension 230 affects the penetration due to its effect on the welding current. Increasing the length of the electric electrode extension 230 increases the preheating of the electrode 204 and the voltage drop across the electrode 204. A larger voltage drop can result in a more convex bead shape, which can be overcome by increasing the input voltage by 2 to 5 volts. The length of the electrical stickout 230 can be approximately 3-10 times the diameter of the electrode 204 (for a conventional SAW process) depending on the type of steel being welded.

[0030] FIG. 3A shows an electrode assembly 300A positioned above a workpiece 302 having a groove 303. In the illustrated configuration, the stick-out portion 330A of the electrode 304A extends a conventional distance (e.g., 3-12 times the diameter of the electrode) beyond the contact tip 310A. The electrode assembly 300A is positioned such that the head portion 324A is positioned above the groove 303 and the tip 306A of the electrode 304A is within the groove 303. More specifically, the head portion 324A is positioned such that the tip 306A is adjacent the bottom of the groove 303 without the head portion 324A contacting the workpiece 302. In the illustrated embodiment, the tip 306A is positioned within the groove such that the CTWD 334A is approximately 25 mm. Positioning tip 306A closer to the bottom of groove 303 allows for better and more consistent arc discharge between tip 306A and workpiece 302, resulting in more consistent deposition of filler metal into groove 303 and improved weld quality and efficiency.

[0031] To further improve submerged arc welding (SAW) technology, the long stick-out (LSO) or extended stick-out technology developed by Lincoln Electric Company can be employed. Long stick-out SAW refers to a SAW process in which the length of wire protruding from the electrode contact tip ("stick-out length") is increased compared to conventional SAW processes, e.g., greater than about 25 mm, thereby increasing the CTWD. As used herein, LSO refers to an electrode configuration in which the electrical stick-out exceeds about 10 times the diameter of the electrode 304A. A longer stick-out length allows for a longer electrode length to be preheated before melting at the electrode tip, thereby facilitating melting of the preheated electrode wire and increasing the electrode melting rate for a given current density. LSO SAW processes can achieve significant productivity improvements, achieving up to a 100% increase in submerged arc welding deposition rate compared to conventional SAW processes. LSO SAW processes can reduce or eliminate the problem of arc ignition failure by enabling full tuning of arc starting characteristics. LSO SAW may also provide improved control of energy input to the weld, lower heat input (less distortion), and a lower flux-to-wire ratio.

[0032] FIG. 3B shows an electrode assembly 300B positioned above a groove 303 in a workpiece 302. The electrode assembly 300B employs LSO technology, with the stick-out 330A extending beyond the contact tip 310A substantially greater than that shown in FIG. 3A, resulting in an electrical stick-out 330B protruding beyond the contact tip 310B. For example, in some embodiments, the stick-out 330B can have a length between 10 and 40 times the diameter of the electrode 304B. In some embodiments, the stick-out 330B can have a length greater than 40 times the diameter of the electrode 304B. The increased length of the stick-out portion 330B allows for a longer length of the electrode 304B to be preheated prior to melting at the electrode tip, thereby enabling increased melting and deposition rates, as described above.

[0033] Additionally, the increased stick-out length of an LSO SAW system allows it to easily fill grooves that conventional SAW systems could not fill, or could only fill using very precise placement and advanced operator skill. Specifically, while conventional SAW systems can be used for wide and / or short grooves, they typically cannot be easily used for deeper and / or narrower grooves because the size and shape of the head portion prevent the head portion from being positioned further into the deep / narrow groove without contacting and interacting with the workpiece. This causes the electrode tip to be too far away from the groove bottom, resulting in a weak arc between the electrode and the workpiece, a reduced filler metal deposition rate, and poor weld quality. Therefore, SAW systems with conventional stick-out lengths may have difficulty forming high-quality welds in deep and / or narrow grooves. In contrast, when the stick-out length of an LSO SAW system is increased to allow the electrode tip to be adjacent to the bottom of the narrow / deep groove, the reduced distance between the electrode tip and the groove bottom results in better arc discharge between the electrode and the workpiece. Thus, in addition to improving weld quality and deposition rate by allowing additional preheating of the electrode before arcing, the LSO SAW technique also allows for the deposition of filler metal in deeper and narrower grooves than conventional SAW techniques.

[0034] According to various embodiments, an LSO SAW electrode assembly allows for significantly higher deposition rates compared to conventional SAW electrode assemblies for the same current. During the welding process, current is transferred to the electrode by the contact tip at a specific amperage and voltage. As current flows through the electrode toward the electrode tip, the voltage drops and the electrode heats up. At the electrode tip, the current arcs toward the workpiece. With an LSO SAW assembly, the increased length of the electrode results in a higher percentage of the total voltage drop occurring within the electrode than with conventional SAW assemblies. In some embodiments, an LSO SAW assembly can be configured such that the voltage drop between the contact tip and the tip of the consumable electrode is at least 5%, at least 10%, at least 15%, or at least 20% (or a value within a range defined by any of these values) of the total voltage drop across the CTWD. In other embodiments, the electrode assembly is configured so that the voltage drop between the contact tip and the tip of the consumable electrode is at least 1 / 30 of the total voltage drop across the CTWD, 1 / 15 of the total voltage drop across the CTWD, 1 / 10 of the total voltage drop across the CTWD, 1 / 7 of the total voltage drop across the CTWD, 1 / 5 of the total voltage drop across the CTWD, or a value within a range defined by any of these values. For example, in a conventional SAW electrode assembly with a total voltage drop along the CTWD of 30 V, only about 1 V of that total voltage drop occurs within the consumable electrode, with the remainder (about 29 V) dropping across the arc length. In contrast, for an LSO SAW system with the same total voltage drop of 30 V, about 4 V of the voltage drop occurs across the CTWD, with the remainder (about 26 V) dropping across the arc length. The increased voltage drop through the longer electrode results in the electrode heating to a higher temperature than electrodes in conventional SAW configurations, resulting in increased deposition rates.

[0035] Experiments have shown that the deposition rate per current for an LSO SAW assembly can exceed 0.05 lb / hr / A, 0.06 lb / hr / A, 0.07 lb / hr / A, 0.08 lb / hr / A, or values ​​within a range defined by any of these values ​​during welding. Furthermore, experiments have shown that an LSO SAW assembly can achieve a given deposition rate with less current than a conventional SAW electrode assembly. For example, an LSO SAW assembly can achieve a deposition rate of greater than 35 lb / hr with currents less than about 900 A, 850 A, 800 A, 750 A, or 700 A, or currents within a range defined by any of these values ​​(e.g., currents between about 700 A and 750 A), while a conventional SAW electrode assembly requires a current of greater than about 900 A to achieve a similar deposition rate. Advantageously, Joule heating (I 2 Since R varies proportionally to the square of the current, the higher the current, the greater the improvement in deposition rate over conventional SAW electrodes, i.e., the relative improvement in deposition rate is expected to increase with increasing current.

[0036] In an LSO SAW system, the consumable electrode (e.g., electrode 304B) extends beyond the end of the head portion (e.g., head portion 324B), revealing the arc tip (e.g., tip 306B). As previously discussed, the portion of the electrode that extends beyond the contact tip portion is referred to as electrical stick-out. In some embodiments, electrical stick-out can be based on the diameter of the electrode. In some embodiments, the length of electrical stick-out can depend on the type of steel being welded, for example, whether the steel being welded is a low-alloy steel containing less than about 8% by weight of non-ferrous elements or a high-alloy steel containing more than about 8% by weight of non-ferrous elements. For example, in conventional SAW processes, when welding low-alloy and mild steels, the electrical stick-out length can be about 7-10 times the diameter of the electrode, while when welding high-alloy steels, the electrical stick-out length can be about 3-5 times the diameter of the electrode. In contrast, in LSO SAW processes according to various embodiments, the electrical stick-out distance (measured between the contact tip portion disposed at the end of the head portion and the arcing tip of the consumable electrode) can be at least 15 times the diameter of the electrode, such that the stick-out-to-diameter ratio for the LSO SAW process and system can be 15, about 20, about 25, about 30, about 35, about 40, about 45, about 50, about 55, about 60, greater than 60, or a value within a range defined by any of these values. In some embodiments, the electrode can have a diameter of 2.5 mm to 5.0 mm, and the electrical stick-out distance can be about 125 mm, about 130 mm, about 135 mm, about 140 mm, about 145 mm, about 150 mm, about 155 mm, about 160 mm, about 165 mm, or a value within a range defined by any of these values. For example, in at least one embodiment, the electrical stick-out length may be 155 mm and the electrode diameter may be 3.2 mm, which means the stick-out to diameter ratio is about 48. In another embodiment, the electrical stick-out length may be 125 mm and the electrode diameter may be 4.0 mm, which means the stick-out to diameter ratio is about 31.

[0037] While increased stick-out length can advantageously provide several benefits, such as higher deposition rates, various problems can arise when conventional electrode assemblies are used with stick-out lengths greater than 25 mm. For example, as the stick-out distance increases, the heated wire can move, becoming misaligned and wandering within the weld groove. This can be particularly problematic in welding deep, narrow grooves, which can be used to minimize the time and cost of joining thick sections, because the LSO welding electrode assembly may be too large to reach the bottom of the groove. To address this and other challenges, some electrode assemblies include a ceramic extension that acts as an insulating guide for the electrode. The extension provides, among other things, electrical and thermal insulation and mechanical rigidity to the heated electrode.

[0038] Arc Initiation Process One problem with LSO over SAW is that the arc initiation performance of LSO SAW systems is not comparable to that of SAW systems with standard stick-out.

[0039] Figure 4 is a flow chart illustrating a method 400 of operating a welding system including a conventional arc starting process, Figure 5 shows graphs of the voltage, current, and wire feed speed (WFS) of the system before, during, and after method 400, and Figures 6A-6G are images of an electrode 604 of system 600 above a workpiece 602 at various times during method 400. In some embodiments, system 600 may be an LSO SAW system generally similar to electrode assembly 300B shown and described above in connection with Figure 3B.

[0040] As shown in FIG. 6A , in step 402 of method 400, the welding process is initiated by immersing the tip 606 of the electrode 604 in the flux 614 and positioning the tip 606 over the workpiece 602 with no load applied between the electrode 604 and the workpiece 602. During this time, represented by period 501 in FIG. 5 , the voltage measured by the welding system is the open circuit voltage. In some embodiments, the open circuit voltage may be approximately 70 volts. However, because no load is applied between the electrode and the workpiece during period 501, typically no current flows between the electrode 604 and the workpiece 602. Furthermore, an arc has not yet been established, and therefore the WFS is 0 ipm.

[0041] In step 404, a direct current electrode positive (DCEP) load is applied to the electrode 604. As shown in FIG. 6B, applying DCEP to the electrode 604 creates an arc 616 between the electrode 604 and the workpiece 602, causing current to flow from the workpiece 602 to the electrode 604. During this time, represented by period 502 in FIG. 5, the voltage decreases from the open circuit voltage and the current spikes as current begins to flow. In some embodiments, the current fluctuates immediately after the arc 616 is established (e.g., during the first few hundred milliseconds of period 502), but may stabilize shortly after the arc 616 is established. For example, in some embodiments, the current may initially fluctuate between approximately 1200 A and 400 A, then stabilize at approximately 750 A after approximately 200 ms.

[0042] The system 600 is configured to continuously feed wire during the welding process, thereby ensuring that the electrode tip 606 remains an appropriate distance from the workpiece 602 during the welding process, maintaining the arc 616, and ensuring proper weld quality. In some embodiments, the system 600 is capable of detecting changes in voltage between the electrode 604 and the workpiece 602 and varying the WFS of the system 600 based on the change in voltage. The voltage between the electrode 604 and the workpiece 602 is correlated to the melting rate of the electrode 604; therefore, varying the WFS based on changes in voltage allows the system 600 to account for changes in melting rate. In some embodiments, the system 600 is configured to automatically increase the WFS upon detecting an increase in voltage to account for the corresponding increase in melting rate, thereby ensuring that the electrode tip 606 remains an appropriate distance from the workpiece 602 during the welding process and maintaining the arc 616.

[0043] Shortly after DCEP is applied and arc 616 is struck, system 600 detects the change in voltage and automatically increases the WFS to account for the increased distance between the unmelted portion of electrode 604 and workpiece 602 (due to tip 606 melting and breaking off). For example, in some embodiments, system 600 can increase the WFS to approximately 80 ipm. In some embodiments, the voltage between electrode 604 and workpiece 602 can be gradually increased during period 502, and system 600 can automatically increase the WFS during period 503 to account for the increased melting rate as a result of the increased voltage.

[0044] During time period 502, current flowing through electrode 604 heats (by resistive heating) the portion of electrode 604 between contact tip 610 and workpiece 602, and portion 636 of electrode 604 begins to glow red. As shown in FIG. 6B, glowing portion 636 is initially very small, extending only a short distance from tip 606. However, as the electrode continues to heat during time period 502, the length of glowing portion 636 increases. For example, as shown in FIG. 6C, glowing portion 636 may extend to just below the top of the flux 614 pile approximately halfway through time period 502, and may extend significantly above flux 614, approximately halfway toward contact tip 610, as shown in FIG. 6D, near the end of time period 502.

[0045] By the end of the period 502, the electrode 604 is sufficiently preheated that the system 600 increases the voltage between the electrode 604 and the workpiece 602 to maintain the arc 616. However, this large voltage increase further heats the electrode 604, increasing the melting rate and causing the WFS to increase to attempt to compensate for the increased melting rate. This feedback loop continues until a large portion of the electrode 604 melts and falls onto the workpiece 602, as shown in FIG. 6E. When this occurs, an arc flare 638 occurs. The arc flare 638 causes the current to fluctuate and the voltage to spike. This in turn causes the system, upon detecting the increased voltage, to gradually increase the WFS in an attempt to reduce the apparent gap between the electrode tip 606 and the workpiece. The high arc voltage, fluctuating current, and spike in WFS result in poor weld bead shape. In some embodiments, the arc flare 638 causes the voltage to spike to approximately 70 V and the WFS to spike above 200 ipm. In some embodiments, the system may automatically incrementally increase the WFS up to the system's maximum WFS upon detecting an increase in voltage due to an arc flare.

[0046] When the system increases the WFS to decrease the gap between the electrode 604 and the workpiece 602, it may overcompensate for the perceived gap between the electrode 604 and the workpiece 602 and increase the WFS too much. If this occurs, the unmelted tip 606 of the electrode 604 may not have enough time to preheat and melt before contacting the workpiece 602, potentially resulting in the still-solid electrode 604 impacting the workpiece 602. Thus, in some embodiments, the system 600 may overcompensate when detecting a voltage spike caused by an arc flare 638 and subsequently increasing the WFS, which may result in a hard short between the electrode 604 and the workpiece 602.

[0047] During period 504, when solid electrode 604 is shorted to workpiece 602, the voltage decreases and the current increases. For example, in some embodiments, the voltage decreases to about 47 V and the current increases to about 750 A. Meanwhile, the WFS is maintained at an increased rate for the duration of period 505. In some embodiments, system 600 monitors the voltage and maintains the WFS at a high rate while the voltage is above a threshold. After period 505, system 600 decreases the WFS.

[0048] During period 505, the voltage and WFS initially decrease, the current initially increases, and then all three stabilize. For example, in some embodiments, the voltage decreases to about 28 V and then stabilizes at about 35 V, the current increases to about 850 A and then stabilizes at about 750 A, and the WFS decreases to about 70 ipm and then stabilizes at about 100 ipm.

[0049] Fluctuating voltage and current after a short circuit can result in reduced weld quality. Furthermore, after an arc flare occurs, the electrode 604 may not be sufficiently heated for optimal welding for an extended period of time. As shown in FIG. 6F , the red-hot portion 636 of the electrode wire at the end of period 506 is not as long as in FIG. 6D , indicating that the electrode 604 is not as heated after the arc flare as it was before and during the arc flare. However, once the system reaches equilibrium (by the end of period 505), the electrode 604 continues to preheat during period 506, and eventually, as shown in FIG. 6G , the red-hot portion 636 becomes longer than in FIG. 6F and extends above the bed of flux 614, indicating that the electrode 604 is sufficiently preheated for optimal welding during period 508. Thus, when starting welding using method 400, it may take several seconds for the system 600 to reach a steady state for optimal welding. In some embodiments, the amount of time that elapses from when DCEP is first applied to begin the welding process (at the beginning of period 502) to when system 600 reaches a steady state (after period 505) can be between approximately 4 and 8 seconds. For example, in some embodiments, when starting a weld using a conventional DCEP process, it can take approximately 6 seconds for the system to reach an optimal welding steady state. Additionally, the force of the still-solid electrode 604 impacting the workpiece 602 after an arc flare can cause the electrode 604 to bend, and in embodiments where system 600 is an LSO SAW system, the bent electrode 604 can contact the ceramic extension, which can damage or break the ceramic extension.

[0050] Therefore, there is a desire and need for improved arc starting characteristics of welding systems.

[0051] To improve the arc initiation characteristics of a welding system, an arc can be established by first applying a direct current electrode negative (DCEN) to the electrode and then switching to DCEP. As described above in connection with FIGS. 4-6G, when the power supply is operating in DCEP mode, the electrode is connected to the positive terminal, the workpiece is connected to the negative terminal, and applied current flows from the workpiece to the electrode. On the other hand, when the system is operating in DCEN mode, the electrode is connected to the negative terminal, the workpiece is connected to the positive terminal, and current flows from the electrode to the workpiece. FIG. 7 is a flow chart illustrating a method 700 of operating a welding system including a DCEN arc initiation process, FIG. 8 is a graph of the voltage, current, and WFS of the welding system before, during, and after method 700, and FIGS. 9A-9G are images of an electrode 904 of system 900 above a workpiece 902 at various times during method 700. In some embodiments, system 900 can include one or more processors or controllers communicatively coupled to the welding power supply and a non-transitory computer-readable storage medium. A non-transitory computer-readable storage medium stores instructions that, when executed by one or more processors or controllers, cause the one or more processors to perform various welding methods, including method 700. In some embodiments, system 900 may be an LSO SAW system generally similar to electrode assembly 300B shown and described above in connection with FIG. 3B. In some embodiments, including the illustrated embodiment, system 900 is a single-arc system including a single electrode 904. However, in other embodiments, system 900 may be a multi-arc system including multiple electrodes 904 positioned adjacent to one another and each configured to generate an arc 916 during the welding process.

[0052] As shown in FIG. 9A , in step 702 of method 700, the welding process is initiated by immersing the tip of the electrode 904 in flux 914 and positioning the tip 906 over the workpiece 902 with no load applied between the electrode 904 and the workpiece 902. During this time, represented by period 801 in FIG. 8 , the voltage measured by the welding system is the open circuit voltage. In some embodiments, the open circuit voltage may be approximately 70 volts. However, because no load is applied between the electrode and the workpiece during period 801, typically no current flows between the electrode 904 and the workpiece 902. Furthermore, an arc has not yet been established, and therefore the WFS is 0 ipm.

[0053] In step 704, a direct current electrode negative (DCEN) is applied to the electrode 904. As shown in FIG. 9B, applying DCEN to the electrode 904 creates an arc 916 between the electrode 904 and the workpiece 902, causing current to flow from the electrode 904 to the workpiece 902. During this time, represented by period 802 in FIG. 8, the voltage is negative and, in some embodiments, may be between about −20 V and about −60 V. For example, in some embodiments, the voltage between the workpiece 902 and the electrode 904 when DCEN is applied may be about −20 V, about −30 V, about −40 V, about −50 V, about −60 V, between −30 and −50 V, between −40 and −60 V, or a value within a range defined by any of these values.

[0054] During period 802, the current may be negative and, in some embodiments, between about −100 A and about −1200 A. For example, in some embodiments, the current may be about −100 A, about −200 A, about −300 A, about −400 A, about −500 A, about −600 A, about −700 A, about −800 A, about −900 A, about −1000 A, about −1100 A, about −1200 A, or a value within a range defined by any of these values. In some embodiments, the current may fluctuate shortly after arc 916 is established (e.g., during the first few hundred milliseconds of period 802), but may stabilize shortly after arc 916 is established. For example, in some embodiments, the current may initially fluctuate between about −100 A and about −1200 A, but may stabilize at about −750 A after about 200 ms. In embodiments in which the system 900 is a multi-arc system having multiple electrodes 904, the multiple electrodes 904 can be coupled in parallel with each other so that the total current flowing between the electrodes 904 and the workpiece 902 is the sum of the currents for the individual electrodes 904.

[0055] The heat emitted by the arc 916 melts the surrounding metal (including the metal at the tip 906 and the workpiece metal near the arc 916). Once the tip 906 melts, it falls onto the workpiece 902 and mixes with the molten metal from the workpiece 902 to form a weld pool 922. Shortly after the arc 916 is struck and the tip 906 melts, the system 900 increases the WFS to account for the increased distance between the workpiece 902 and the electrode 904 (as the tip 906 melts and breaks off). In some embodiments, the WFS of the system during period 802 is between 75 and 200 ipm. For example, in some embodiments, the WFS of the system during period 802 can be approximately 110 ipm.

[0056] During period 802, current flowing through the electrode heats (by resistive heating) the portion of the electrode 904 between the contact tip 910 and the workpiece 902, and a portion 936 of the electrode 904 begins to glow red. As shown in Figure 9B, the glowing portion 936 is initially very small, extending only a short distance from the tip 906. However, as shown in Figure 9C, the glowing portion 936 can extend to just below the top of the flux 914 pile about halfway through period 802, and can extend significantly above the flux 914 by the end of period 802, as shown in Figure 9D.

[0057] During time period 802, the electrode 904 continues to preheat at a constant rate as the system 900 continues to apply DCEN to the electrode 904. The voltage, current, and WFS are generally stable, which can result in a significantly improved bead shape for the weld produced during time period 802.

[0058] In step 706, DCEP is applied to the electrode 904. During this time, represented by period 803 in FIG. 8, the voltage and current are positive, and current flows from the workpiece 902 to the electrode 904. In some embodiments, during period 803, the voltage may be 20-60 V and the current may be 200-1000 A. For example, in some embodiments, the voltage may be approximately 40 V and the current may be approximately 650 A during period 903. The WFS may also remain relatively constant during period 903 and, in some embodiments, may be approximately the same as the WFS during period 802. For example, in some embodiments, the WFS may be 75-150 ipm during period 803. Additionally, the electrode 904 may be kept sufficiently preheated during period 803 for optimal welding. 9E-9G, the glowing portion 936 can extend consistently above the deposit of flux 914 throughout the entire period 803, and the length of the glowing portion 936 can remain relatively constant during this time. At this point, the welding system 900 is operating at a completely steady state, with the voltage, current, WFS, and temperature of the electrode 904 remaining constant.

[0059] In some embodiments, the system 900 is configured to switch from applying DCEN to applying DCEP when the electrode 904 is sufficiently preheated. However, it may be difficult for the system 900 to automatically determine whether the electrode 904 is sufficiently preheated. Thus, in some embodiments, the system 900 may be configured to switch from applying DCEN to applying DCEP to the electrode 904 after a predetermined amount of time. For example, in some embodiments, the system 900 is configured to apply DCEN for between 0.5 and 7 seconds, between 0.5 and 1 second, between 1 and 2 seconds, between 2 and 3 seconds, between 3 and 4 seconds, between 4 and 5 seconds, between 5 and 6 seconds, between 6 and 7 seconds, between 2 and 6 seconds, less than 5 seconds, less than 3 seconds, less than 2 seconds, or a value within a range determined by any of these values, and then switch to applying DCEP to the electrode 904. In some embodiments, the system 900 is configured to determine the stability of the arc 916 and switch to applying DCEP when it determines that the arc 916 is sufficiently stable. For example, in some embodiments, system 900 is configured to switch to applying DCEP when it determines that the voltage of arc 916 remains within a given percentage of a predetermined voltage for a given amount of time, e.g., remains within 20%, 15%, 10%, 5%, 2%, 1% of −50V, −45V, −40V, −35V, −30V, or a value within a range defined by any of these values, for between 0.5 and 4 seconds, between 0.5 and 1 second, between 1 and 2 seconds, between 2 and 3 seconds, between 3 and 4 seconds, or a value within a range defined by any of these values. In some embodiments, the amount of time that the system 900 applies DCEN before switching to applying DCEP may be determined empirically and may be based on the particular conditions and materials used during the welding process, such as the composition of the workpiece 902, electrode 904, and / or flux 914, the capabilities of the welding system 900, and / or the desired welding parameters (e.g., voltage, current, travel speed).In some embodiments, the amount of time that the system 900 applies DCEN before switching to applying DCEP may be pre-programmed into the system and / or may be set by an operator of the welding system 900.

[0060] As discussed above in connection with Figures 4-6G, when the system is operating in DCEP mode, current flows from the workpiece to the electrode. When this occurs, most of the heat generated by the arc is generated in the workpiece. For example, in some embodiments, when DCEP is applied, at least two-thirds of the arc heat is generated in the workpiece, with the remaining arc heat generated in the electrode. In contrast, when DCEN is applied to the electrode and workpiece, current flows from the electrode to the workpiece, and most of the heat generated by the arc is generated in the electrode, not the workpiece. For example, in some embodiments, when DCEN is applied, at least two-thirds of the arc heat is generated in the electrode, not the workpiece.

[0061] By initiating the welding process using DCEN and establishing an arc between the electrode and the workpiece, the voltage, current, WFS, and electrode temperature are more stable and less prone to fluctuation than when initiating the welding process using DCEP. This increased stability prevents arc flares and hard shorts between the welding electrode and the workpiece. Furthermore, the greater amount of heat generated at the electrode when DCEN is applied preheats the electrode at a faster and more consistent rate than when DCEP is applied, which prevents premature melting of the electrode wire and thus prevents the system from overcompensating and causing unmelted wire to strike the workpiece. Therefore, the increased stability also reduces the likelihood of the ceramic extension being damaged by contact with the electrode wire. Furthermore, initiating the welding process using DCEN may allow the welding electrode to be sufficiently preheated and reach a steady state more quickly than when DCEP is used to initiate the welding process. For example, as discussed above in connection with FIGS. 4-6G, when welding is initiated using DCEP, it may take approximately 4-8 seconds for the system 600 to reach a steady-state weld. In contrast, when a weld is initiated using DCEN, it can take the system approximately 2 seconds to reach a steady-state weld, which means that steady-state is reached approximately 2 to 4 times faster than when a weld is initiated using DCEP.

[0062] In some embodiments, the welding system can operate in a constant current (CC) mode, in which the system adjusts the voltage and WFS to maintain the current at a preset value. For example, in the illustrated embodiment, the welding system is operating in CC mode, with the current preset to −750 A during the arc starting process and 750 A during steady state mode, and the voltage and WFS vary to maintain those currents. However, in other embodiments, the welding system can operate in a constant voltage (CV) mode, in which the system adjusts the current to maintain the voltage (and WFS) at a preset value. In some embodiments, the system may be capable of switching between CC and CV modes. For example, in some embodiments, the system may be configured to operate in either CC or CV mode during the arc starting process and then switch to the other mode during the steady state process.

[0063] 4-6G, the system 600 applies DCEP to the electrode 604 after applying DCEN to initiate welding. However, in other embodiments, the system 600 can apply AC current to the electrode after applying DCEN to initiate welding.

[0064] Asymmetric AC welding start In the previously described embodiment, a direct current welding technique (DCEN) is used to initiate welding, followed by a second direct current welding technique (DCEP) during steady-state welding conditions. However, in other embodiments, an alternating current (AC) welding process can be used during weld start and steady-state welding. In AC welding, the welding power source periodically reverses the flow of current, causing the welding system to rapidly oscillate between DCEP and DCEN. In conventional AC welding processes, symmetrical AC is used for both weld start and steady-state welding. In symmetrical AC, the positive and negative portions of the AC waveform are mirror images of each other and balance each other so that the root mean square (RMS) voltage and length of both the positive and negative half cycles are identical. However, starting a weld using symmetrical AC can result in poor arc quality during the arc starting process due to insufficient preheating of the welding electrode. Therefore, an improved AC welding starting process that results in improved arc starting characteristics is desired.

[0065] To improve arc initiation characteristics during an AC welding initiation process, an arc can be established by first applying DCEN-biased asymmetric AC and then applying symmetric AC. Asymmetric AC refers to an AC waveform in which the positive and negative portions are not mirror images of each other, but rather have an imbalance between the positive and negative half-cycles due to differences in the RMS voltage and / or length of the positive and negative half-cycles. Thus, DCEN-biased asymmetric AC is asymmetric AC in which the RMS voltage and / or length of the negative half-cycle is greater than the RMS voltage and / or length of the positive half-cycle. FIG. 10 is a flow chart illustrating a method 1000 of operating a welding system including a DCEN-biased asymmetric AC arc initiation process, and FIG. 11 is a graph of the voltage and current of the welding system before, during, and after method 1000. In some embodiments, the welding system can include one or more processors or controllers communicatively coupled to a welding power source and a non-transitory computer-readable storage medium. The non-transitory computer-readable storage medium stores instructions that, when executed by one or more processors or controllers, cause the one or more processors to perform various welding methods, including method 1000.

[0066] In step 1002 of the method, the welding process is initiated by immersing the tip of the electrode above the workpiece with no load applied between the electrode and the workpiece. During this time, represented by period 1101 in Figure 11, the voltage measured by the welding system is the open circuit voltage, but no current flows between the electrode and the workpiece because no load has yet been applied.

[0067] In step 1004, a DCEN biased asymmetric AC is applied to the electrode, which creates an arc between the electrode and the workpiece and allows current to flow between the electrode and the workpiece. During this time, represented by period 1102 in FIG. 11, the voltage and current oscillate between a negative half cycle 1104A and a positive half cycle 1104B. However, because the applied load is DCEN biased, the duration of the negative half cycle 1104A is longer than the duration of the positive half cycle 1104B. In some embodiments, the negative half cycle 1104A is two to four times longer than the positive half cycle 1104B. However, in other embodiments, the negative half cycle 1104A can be longer than the positive half cycle by a different amount. For example, in some embodiments, the negative half cycle is 1.5 to 10 times longer than the positive half cycle 1104B, 1.5 to 10 times longer than the positive half cycle 1104B, 5 to 10 times longer than the positive half cycle 1104B, 2 to 4 times longer than the positive half cycle 1104B, 4 to 6 times longer than the positive half cycle 1104B, 6 to 10 times longer than the positive half cycle 1104B, or a value within a range defined by any of these values. Because the negative half cycle 1104A is longer than the positive half cycle 1104B, the majority of each complete AC waveform is negative, and the system applies DCEN for the majority of the period 1102. For example, in some embodiments, the asymmetric AC is DCEN biased to 70 to 80% DCEN and 20 to 30% DCEP. However, in other embodiments, the DCEN-biased asymmetric AC may be biased by different amounts. For example, in some embodiments, the asymmetric AC is DCEN biased to a value within a range defined by 60-90% DCEN and 10-40% DCEP, 60-70% DCEN and 30-40% DCEP, 65-85% DCEN and 15-35% DCEP, or any of these ranges.

[0068] 11, the lengths of the negative and positive half cycles 1104A, 1104B are constant throughout the period 1102. However, in other embodiments, the lengths of one or both of the negative and positive half cycles 1104A, 1104B can vary during the period 1102.

[0069] In some embodiments, such as the embodiment shown in FIG. 11 , the DCEN biased asymmetric AC is configured such that the negative half cycle 1104A is longer than the positive half cycle 1104B, but the RMS voltages of the negative and positive half cycles 1104A, 1104B are the same (or within 10% of each other). However, in other embodiments, the RMS voltages of the negative and positive half cycles 1104A, 1104B may be different. For example, in some embodiments, the RMS voltage of the negative half cycle 1104A may be greater than the RMS voltage of the positive half cycle 1104B. In some embodiments, such as the embodiment shown in FIG. 11 , the RMS voltages of the negative and positive half cycles 1104A, 1104B may be constant throughout the period 1102. In other embodiments, the RMS voltage of one or both of the negative and positive half cycles may change during the period 1102.

[0070] In step 1106, symmetrical AC is applied to the electrodes. During this time, represented by period 1003 in FIG. 10 , the RMS voltage and length of the negative half cycle 1105A are approximately the same as the RMS voltage and length of the positive half cycle 1105B. In some embodiments, the RMS voltage of the symmetrical AC negative and positive half cycles 1105A, 1105B is the same as the RMS voltage of the DCEN-biased asymmetrical AC negative and positive half cycles 1104A, 1104B. In some embodiments, the length of the DCEN-biased asymmetrical AC negative half cycle 1104A is greater than the length of the symmetrical AC negative half cycle 1105A. In some embodiments, the length of the DCEN-biased asymmetrical AC positive half cycle 1104B is shorter than the length of the symmetrical AC positive half cycle 1105B.

[0071] In some embodiments, the system is configured to switch from applying DCEN-biased asymmetric AC to applying symmetric AC when the electrode is sufficiently preheated. However, it may be difficult for the system to automatically determine whether the electrode is sufficiently preheated. Therefore, in some embodiments, the system may be configured to switch from applying DCEN-biased asymmetric AC to applying symmetric AC after a predetermined amount of time. For example, in some embodiments, the system is configured to apply DCEN-biased asymmetric AC for 0.5 to 7 seconds, 0.5 to 1 second, 1 to 2 seconds, 2 to 3 seconds, 3 to 4 seconds, 4 to 5 seconds, 5 to 6 seconds, 6 to 7 seconds, 2 to 6 seconds, less than 5 seconds, less than 3 seconds, less than 2 seconds, or a value within a range determined by any of these values, and then switch to applying symmetric AC. In some embodiments, the system is configured to determine the stability of the arc between the electrode and the workpiece and switch to applying symmetric AC when it determines that the arc is sufficiently stable. In some embodiments, the amount of time that the system applies the DCEN biased asymmetric AC before switching to applying symmetric AC may be determined empirically and may be based on the particular conditions and materials used during the welding process, such as the composition of the workpiece, electrode, and / or flux, the capabilities of the welding system, and / or the desired welding parameters (e.g., voltage, current, travel speed). In some embodiments, the amount of time that the system applies the DCEN biased asymmetric AC before switching to applying symmetric AC may be pre-programmed into the system and / or set by the operator of the welding system.

[0072] Unless the context clearly dictates otherwise, throughout this specification and claims, words such as "comprises," "comprising," "includes," "including," and the like are to be interpreted in an inclusive sense, i.e., "including, but not limited to," rather than an exclusive or exhaustive sense. The word "coupled," as generally used herein, refers to two or more elements that are directly connected or connected via one or more intermediate elements. Similarly, the word "connected," as generally used herein, refers to two or more elements that are directly connected or may be connected via one or more intermediate elements. Furthermore, when used in this application, words such as "herein," "above," "below," and words of similar import refer to this application as a whole and not to any particular portions of this application. Where the context permits, words using the singular or plural in the above Detailed Description section may also include the plural or singular, respectively. The word "or" in reference to a list of two or more items encompasses all of the following interpretations of the word: any item in the list, all items in the list, and any combination of items in the list.

[0073] Additionally, conditional expressions used herein, such as "can," "could," "might," "may," "for example," "for example," "etc.", and the like, unless specifically stated otherwise or understood otherwise within the context in which they are used, are generally intended to indicate that some embodiments include certain features, elements, and / or conditions and other embodiments do not. Thus, such conditional expressions generally do not imply that features, elements, and / or conditions are in any way required by one or more embodiments, or that these features, elements, and / or conditions should be included or performed in any particular embodiment.

[0074] Although specific embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the present disclosure. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms, and various omissions, substitutions, and modifications of the forms of the methods and systems described herein may be made without departing from the spirit of the present disclosure. For example, while blocks are presented in a given arrangement, alternative embodiments may perform similar functions with different components and / or circuit topologies, and some blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each of these blocks may be implemented in a variety of different ways. Any suitable combination of elements and operations of the various embodiments described above may be combined to provide further embodiments. The various features and processes described above may be implemented independently of one another or combined in various ways. All possible combinations and subcombinations of features of the present disclosure are intended to be within the scope of the present disclosure. [Explanation of symbols]

[0075] 100 Submerged Arc Welding (SAW) System 102 workpieces 104 Electrode 106 Tip 108 Power supply 110 Contact tip 112 Flux Delivery System 114 Flux 116 Arc 118 Slag 120 Welding Metal 122 Welding Pool 200 Electrode Assembly 202 workpieces 204 Electrode 206 Tip part 210 Contact tip 224 Head part 226 Electrode Guide Tube 228 Insulation Guide 230 Electric Stick Out 232 Visible Stick Out 234 Contact tip-work distance (CTWD) 300A Electrode Assembly 300B Electrode Assembly 302 Workpiece 303 Groove 304A electrode 304B Electrode 306A Tip 306B Tip 310A Contact tip 310B Contact tip 324A head part 324B head part 330A Stick-out part 330B Stick-out part 501 period 502 period 503 period 504 period 505 period 506 period 508 period 600 System 602 workpiece 606 Electrode tip 610 Contact tip 614 Flux 616 Arc 636 parts 638 Arc Flare 801 period 802 period 803 period 900 Welding System 902 workpiece 903 period 904 Electrode 906 Tip 910 Contact tip 914 Flux 916 Arc 922 Welding Pool 936 parts 1003 period 1101 period 1102 period 1104A Half Cycle 1104B Half Cycle 1105A half cycle 1105B Half Cycle

Claims

1. a welding power source; an electrode assembly operably coupled to the welding power source and the electrode; A welding system comprising: the welding power source is configured to use the electrode assembly to apply a direct current electrode negative (DCEN) to the electrode to establish an arc between the electrode and a workpiece, and to apply a direct current electrode positive (DCEP) or an alternating current (AC) to the electrode after the arc is established; Welding system.

2. The welding system of claim 1 , wherein the electrode assembly comprises a contact tip, and the electrode assembly is configured to provide the DCEN to the electrode using the contact tip.

3. The welding system of claim 1 comprising a submerged arc welding (SAW) system.

4. The welding system of claim 3 , configured to provide a ratio of electrical stick-out distance to electrode diameter greater than 15 during welding.

5. The welding system of claim 1 , wherein the welding power source is configured to apply the DCEP to the electrode less than 5 seconds after applying the DCEN to the electrode.

6. The welding system of claim 1 , wherein the welding power supply is configured to apply the AC to the electrode less than 5 seconds after applying the DCEN to the electrode.

7. The welding system of claim 1 , wherein the DCEN has a voltage between about −20V and −60V and a current between about −100A and about −1200A.

8. 1. A method of operating a welding system, comprising: applying a direct current electrode negative (DCEN) to an electrode to establish an arc between the electrode and a workpiece; applying the DCEN to the electrodes, and then applying a direct current electrode positive (DCEP) or alternating current (AC) to the electrodes; A method comprising:

9. 9. The method of claim 8, wherein applying the DCEP or AC to the electrode comprises automatically applying the DCEP or AC to the electrode without receiving additional input from an operator of the welding system.

10. 9. The method of claim 8, wherein applying the DCEP or AC to the electrodes comprises applying the DCEP to the electrodes less than 5 seconds after applying the DCEN to the electrodes.

11. 11. The method of claim 10, wherein applying the DCEP or AC to the electrodes comprises applying the AC to the electrodes less than 5 seconds after applying the DCEN to the electrodes.

12. 9. The method of claim 8, wherein the ratio of electrical stick-out distance to the diameter of the electrode is greater than 15 while the DCEN is applied to the electrode.

13. 9. The method of claim 8, wherein the voltage of DCEN is between about -20V and -60V.

14. 9. The method of claim 8, wherein the current of the DCEN is between about −100 A and about −1200 A.

15. 1. A method of operating a welding system, comprising: applying a direct current electrode negative (DCEN) biased asymmetric alternating current (AC) to an electrode to establish an arc between the electrode and a workpiece; applying the DCEN biased asymmetric AC to the electrodes, and then applying a symmetric AC to the electrodes; A method comprising:

16. 16. The method of claim 15, wherein the DCEN biased asymmetric AC comprises at least one negative half cycle and at least one positive half cycle, the at least one negative half cycle being longer than the at least one positive half cycle.

17. 17. The method of claim 16, wherein a first root-mean-square (RMS) voltage of the at least one negative half-cycle is within 10% of a second RMS voltage of the at least one positive half-cycle.

18. 17. The method of claim 16, wherein the at least one negative half cycle includes a first negative half cycle and the symmetrical AC includes a second negative half cycle, the first negative half cycle being longer than the second negative half cycle.

19. 16. The method of claim 15, wherein applying the symmetric AC to the electrodes comprises applying the symmetric AC to the electrodes less than 5 seconds after applying the DCEN biased asymmetric AC to the electrodes.

20. 20. The method of claim 19, wherein applying the symmetric AC to the electrodes comprises applying the symmetric AC to the electrodes less than 3 seconds after applying the DCEN biased asymmetric AC to the electrodes.

21. 16. The method of claim 15, wherein the ratio of electrical stick-out distance to electrode diameter is greater than 15 while the DCEN biased asymmetric AC is applied to the electrodes.

22. 1. A non-transitory computer-readable storage medium storing instructions that, when executed by a system of one or more processors, cause the one or more processors to: applying a direct current electrode negative (DCEN) to an electrode of a welding system to establish an arc between the electrode and a workpiece; applying the DCEN to the electrodes, and then applying a direct current electrode positive (DCEP) or alternating current (AC) to the electrodes; A non-transitory computer-readable storage medium that causes

23. 23. The non-transitory computer-readable storage medium of claim 22, wherein the instructions, when executed by the system of one or more processors, cause the one or more processors to automatically apply the DCEP or AC to the electrode without receiving additional input from a welding system operator.

24. 23. The non-transitory computer-readable storage medium of claim 22, wherein the instructions, when executed by the system of one or more processors, cause the one or more processors to apply the DCEP to the electrode in less than five seconds after applying the DCEN to the electrode.

25. 23. The non-transitory computer-readable storage medium of claim 22, wherein the instructions, when executed by the system of one or more processors, cause the one or more processors to apply the AC to the electrodes in less than 5 seconds after applying the DCEN to the electrodes.

26. 1. A non-transitory computer-readable storage medium storing instructions that, when executed by a system of one or more processors, cause the one or more processors to: applying a direct current electrode negative (DCEN) biased asymmetric alternating current (AC) to an electrode of a welding system to establish an arc between the electrode and a workpiece; applying the DCEN biased asymmetric AC to the electrodes and then applying a symmetric AC to the electrodes; A non-transitory computer-readable storage medium that causes

27. 27. The non-transitory computer-readable storage medium of claim 26, wherein the instructions, when executed by the system of one or more processors, cause the one or more processors to automatically apply the symmetrical AC to the electrodes without receiving additional input from an operator of the welding system.

28. 27. The non-transitory computer-readable storage medium of claim 26, wherein the instructions, when executed by the system of one or more processors, cause the one or more processors to apply the symmetrical AC to the electrodes in less than 5 seconds after applying the DCEN-biased asymmetrical AC to the electrodes.

29. 27. The non-transitory computer-readable storage medium of claim 26, wherein the DCEN biased asymmetric AC includes at least one negative half cycle and at least one positive half cycle, the at least one negative half cycle being longer than the at least one positive half cycle.

30. 30. The non-transitory computer-readable storage medium of claim 29, wherein a first root-mean-square (RMS) voltage of the at least one negative half-cycle is within 10% of a second RMS voltage of the at least one positive half-cycle.

31. 30. The non-transitory computer-readable storage medium of claim 29, wherein the at least one negative half cycle includes a first negative half cycle and the symmetric AC includes a second negative half cycle, the first negative half cycle being longer than the second negative half cycle.

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