Patent Publication Number: US-2018050413-A1

Title: Systems and methods for changing electrodes in continuous welding processes

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/376,164, filed Aug. 17, 2016, the disclosure of which is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to systems and methods for continuous welding processes and in particular relates to systems and methods for changing electrodes in continuous welding processes. 
     BACKGROUND OF THE INVENTION 
     Gas tungsten arc welding (“GTAW”) is known to provide greater arc penetration than conventional welding methods and consequently provide for stronger, higher quality welds. GTAW is widely used in manufacturing, including in the cable and wire industry to butt weld longitudinal seams of metal tubes, cable armors, and outer shields. Heat generated between a tungsten electrode and a moving metal tube in a stationary welding system is used to butt weld open longitudinal seams of metal tubes. Inert shielding gas, such as argon and/or helium, is typically used to protect the weld area and the tungsten electrodes. 
     However, despite the inert gas shielding, heat produced during GTAW process causes tungsten electrodes to overheat and melt or otherwise deteriorate. Erosion or “burn-off” may deteriorate electrodes and require them to be replaced to ensure proper weld quantity. Electrode replacements are carried out after shutting down the welding system. This welding stoppage will disrupt the continuous welding of a metal tube and therefore limit the length of a metal tube that can be fabricated. Failure to replace deteriorated electrodes may lead to poor weld quality. Consequently, stoppages for electrode replacement may disrupt continuous welding processes and result in significant material wastage in some instances such as metal tube welding production. Maintaining a continuous welding process is especially necessary in welding long metal tubes to avoid product defects, material wastage and delays in production. 
     Therefore, there exists a need to provide a system and method to change electrodes for continuous welding processes. 
     BRIEF SUMMARY OF THE INVENTION 
     Disclosed herein are systems and methods for changing electrodes in continuous welding processes. 
     In a first aspect of the present invention, a welding system for a continuous welding operation is provided. The welding system may include a first welding assembly, a second welding assembly and a controller. The first welding assembly may have a first welding torch with a first electrode and may be connected to a first power source. The first welding assembly may be able to independently perform the continuous welding operation in a first mode. The second welding assembly may have a second welding torch with a second electrode and may be connected to a second power source. The second welding assembly may be able to independently perform the continuous welding operation in a second mode. The controller may be in communication with the first and second power sources. The controlled may be able to simultaneously control power to the first and power sources such that the welding assembly may perform a switchover from the first mode to the second mode without interrupting the continuous welding operation. The first electrode may be removed and replaced in the second mode without interrupting the second mode and the second electrode may be removed and replaced in the first mode without interrupting the first mode. 
     In accordance with the first aspect, the first and second electrodes may simultaneously perform the continuous welding operation during the switchover. The continuous welding operation may be a butt-welding operation to weld a longitudinal seam on a metal tube, the metal tube being moved with reference to the welding system. The first and second electrodes may be on opposite sides of the longitudinal seam. 
     Further in accordance with the first aspect, the controller may be a programmable logic controller. The programmable logic controller may reduce power to the first welding assembly and simultaneously increase power to the second welding assembly during the switchover. The rate of power reduction to the first welding assembly and rate of power increase to the second welding assembly may be linear. The welding assembly may include a human machine interface in communication with the programmable logic controller. The human machine interface may allow an operator to input control parameters for the switchover. The input control parameters may include any of a switchover time, weld speed, weld quality, power reduction, power acceleration and welders power ratio. The switchover may be manually initiated by an operator. 
     Still further in accordance with the first aspect, the welding system may include an electrode monitor to detect electrode deterioration. The welding system may include a weld quality monitor to detect weld quality. The weld quality monitor may initiate the switchover based on a predetermined weld quality requirement. The first and second torches may have removable caps for replacing electrodes. The welding system may include three or more welding assemblies in communication with the controller. The welding operation may be a gas tungsten arc welding procedure. 
     A second aspect of the present invention is a method for performing a continuous welding operation. A method in accordance with this aspect of the invention may include the steps of performing a welding operation in first mode with a first electrode, performing a switchover from the first mode to a second mode without disrupting the welding operation and replacing the first electrode in the second mode. The welding operation in the first mode may be performed with a first welding assembly having a first welding torch and the first electrode. The first welding assembly may be connected to a first power source. The welding operation in the second mode may be performed with the second welding assembly. The second welding assembly may have a second welding torch and a second electrode. The second welding assembly may be connected to a second power source. The switchover may be performed by a controller in communication with the first and second power sources. The switchover from the second mode to back to the first mode may be performed to maintain the continuous welding operation. 
     In accordance with the second aspect, the switchovers may be automatically initiated by sensors and the step of and replacing the electrodes may be automatically performed by mechanical actuators. 
     A third aspect of the present invention is a method of performing a switchover from a first electrode to a second electrode in a continuous welding operation. A method in accordance with this aspect of the invention may include the steps of providing a first welding assembly, providing a second welding assembly, providing a controller and inputting control parameters to the controller to perform a switchover from the first welding assembly to the second welding assembly without disrupting the continuous welding operation. The first welding assembly may have a first electrode capable of independently performing the welding operation. The second welding assembly may have a second electrode capable of independently performing the welding operation. The controller may be in communication with the first and second welding assemblies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the subject matter of the present invention and of the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings: 
         FIG. 1  is a schematic front view of a welding system according to a first embodiment of the present invention; 
         FIG. 2  is a schematic side view of the welding system of  FIG. 1 ; 
         FIG. 3  is a schematic side view of a welding system according to a second embodiment of the present invention; 
         FIG. 4A-4C  are schematic front views of the welding system of  FIG. 1  showing the sequential steps of a welder swap sequence according to another embodiment of the present invention; 
         FIG. 5  is a diagrammatic view of the welding system of  FIG. 1 ; 
         FIG. 6  is a diagrammatic view of a welder swap sequence; 
         FIG. 7  is a graph showing a power output during the welder swap sequence of  FIG. 6 ; 
         FIG. 8  is a diagrammatic view of input and output parameters of a programmable logic controller shown in  FIG. 6 ; and 
         FIG. 9  is a diagrammatic view of performing a welder swap sequence according to yet another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made to embodiments of the present invention illustrated in the accompanying drawings. Wherever possible, the same or like reference numbers will be used throughout the drawings to refer to the same or like features. It should be noted that the drawings are in simplified form and are not drawn to precise scale. Additionally, the term “a,” as used in the specification, means “at least one.” The terminology includes the words above specifically mentioned, derivatives thereof, and words of similar import. 
     Referring now to  FIG. 1 , there is shown a welding system  10  according to a first embodiment of the present invention. Welding system  10  includes a first welding assembly  100  and a second welding assembly  200 . The first welding assembly has a first electrode  102  attached to a first welding torch  104 . While a tungsten electrode is generally described herein, other electrodes may be used in conjunction with welding assembly  100 . A first actuator  106  connected to first welding torch  104  regulates torch positon with respect to a workpiece  30  through an arc length control (“ALC”) microprocessor (not shown). A removable cap  108  on first torch  104  can be unscrewed from the first welding torch to allow an operator to remove a deteriorated or spent electrode and reposition a fresh electrode in torch  104 . Welding assembly  100  includes a first power source  110  supplying power to first welding torch  104  through power line  112 . Power source  110  can be a constant current (“CC”), a constant voltage (“CV”), or a variable power source and can include both alternating and direct current systems. As shown herein, power source  100  provides direct current resulting in first electrode  102  being a negatively charged electrode (“DCEN”). A second line  114  from first power source  110  is connected to workpiece  30  to positively charge the workpiece as best shown in  FIG. 1 . A line  116  from power source  110  is used to ground welding assembly  100 . 
     Second welding assembly  200  is similar to first welding assembly  100 , and therefore like elements are referred to with similar numerals within the 200-series of numbers. For instance, second welding assembly includes second electrode  202  attached to second welding torch  204  which is regulated by second actuator  206 . A second separate power source  210  supplies power to second welding assembly  200 , and ensures that first and second welding assemblies can operate independently. Although the second welding assembly shown herein is similar to the first welding assembly, the second welding assembly may vary from the first welding assembly in other embodiments. 
     First and second power sources  116 ,  216  are connected by lines  118  and  218  to a PLC  12  respectively. As more fully explained below, PLC  12  can simultaneously control power supply to first and second welding assemblies to operate either the first or the second welding assembly, or to operate both assemblies simultaneously. A human machine interface (“HMI”)  14  allows an operator to input various settings and instructions to the PLC through input parameters  16 . 
       FIG. 2  shows a schematic side view of welding system  10 . Welding assemblies  100 ,  200  are aligned and positioned over a moving workpiece  30 . Electrodes  102  and  202  are aligned on opposite sides of workpiece  30  as best shown in  FIG. 1 . As shown in  FIGS. 1 and 2 , both electrodes  102  and  202  are simultaneously energized in this mode. Electrons emitted from both electrodes travel across arc  34  creating thermal ionization of a shielding gas and melting workpiece  30  to produce a longitudinal weld  32 . Shielding gases, such as helium or argon, can be used to protect the weld site from oxidation and deterioration of the electrode. Line arrow  36  depicts the direction of workpiece  30  in reference to the stationary welding assemblies  100 ,  200 . Velocity of the workpiece  30  can be adjusted to control weld quality, weld strength and production output depending on the nature of the workpiece and production requirements. For example, velocity of the longitudinal metal cable workpiece  30  shown in  FIGS. 1 and 2  may be increased to reduce weld temperature at the weld zone or reduced to increase weld temperature at the weld zone. While a longitudinal metal cable workpiece  30  is shown in this embodiment, any other workpiece may be used in conjunction with welding system  10 . Although two welding assemblies with two electrodes are described in this embodiment, three or more electrodes may also be used to work in conjunction with the PLC and HMI according to other embodiments of the present invention. 
     Referring now to  FIG. 3 , there is shown a welding system  20  according to another embodiment of the present invention. Welding system  20  is similar to welding system  10  but includes a second set of welding assemblies  300  and  400 . Welding assemblies  300  and  400  are similar to welding assemblies  100  and  200 , and therefore like elements are referred to with similar numerals within the 300-series and 400-series of numbers respectively. For instance, welding assembly  300  includes third electrode  302  attached to third welding torch  304  which is actuated by second actuator  306 . Welding assemblies  300  and  400  may be connected to PLC  12  and HMI  14  in communication with welding assemblies  100  and  200 , or may be separately connected to a second PLC and a second HMI (not shown) to be operated independently from welding assemblies  100  and  200 . Welding assemblies  100  and  200  are in operation in  FIG. 3 , whereas welding assemblies  300  and  400  are on standby. Welding assemblies  300  and  400  can be used in conjunction with assemblies  100  and  200  to increase production speed, i.e., increased workpiece velocity, or used independently when assemblies  100  and  200  are placed on standby for maintenance. While two sets of welding assemblies are shown in this embodiment, other embodiments may have more than two sets of welding assemblies. Alternatively, single welding assemblies, i.e., with only one welding torch, may also be combined with dual welding assemblies. While independent PLC and HMI controls are described for each set of welding assemblies, PLC and HMI may serve more than one set of welding assemblies in other embodiments. It is to be understood that while a tungsten electrode is envisioned to be used with the welding systems described herein, electrodes made of different material may also be used. Various other accessories such as a closed water cooling system may also be used in conjunction with the welding systems of the current disclosure. 
       FIGS. 4A-4B  show schematic views of a welder swap sequence according to an embodiment of the present invention.  FIG. 4A  shows a first welding mode, wherein welding assembly  100  welds workpiece  30  and welding assembly  200  is in standby mode. PLC  12  ensures that only first power source  110  is energized in this mode. Power source  210  is placed in standby.  FIG. 4B  shows a second welding mode wherein welding assembly  100  and welding assembly  200  simultaneously weld workpiece  30 . In this second mode, welding arc  34  represents a combined arc production from welding assembly  100  and welding assembly  200 . Although two electrodes are energized in the second mode, weld  32  is similar to the first mode because PLC  12  ensures that total power supplied to both assemblies is equal to the power supplied to the welding assembly  100  in the first mode. As more fully explained below, PLC  12  ramps down power supply to welding assembly  100  while simultaneously ramping up power supply to welding assembly  200 .  FIG. 4C  shows a third mode wherein the PLC has fully energized welding assembly  200  and de-energized welding assembly  100 . Welding assembly  100  is now placed on standby with welding assembly  200  performing the welding operation. An operator may now unscrew cap  108  from torch  104  and replace electrode  102 . Welding assemblies  100  and  200 , and specifically the welding torches  104  and  204  are carefully positioned to allow an operator to replace a spent electrode from a welding assembly on standby without interrupting the energized opposite welding assembly. A second welder swap sequence can now be performed wherein welding assembly  100 , with the newly replaced electrode  102 , can replace welding assembly  200 . Thus, continuous welding of workpiece  30  can be performed using the welder swap sequence of welding system  10 . In other embodiments, a third or fourth welding assembly may be used in conjunction with the first and second welding assemblies to provide additional time between electrode swaps. For example, an operator may wait until a first, second and third electrode are deteriorated to replace these electrodes when the fourth electrode is in operation for a welding system having four welding assemblies. 
     Referring now to  FIG. 5 , there is shown a diagrammatic view of the welding system of  FIG. 1 . HMI  14  serves as a graphical user interface for an operator to input various control parameters to PLC  12 . The operator can also use HMI  14  to initiate the welder swap sequence. PLC  12  interfaces with first power source  110  and second power source  210 . Depending on the input parameters  16  received from HMI  14 , PLC  12  computes and regulates power supply to first and second power sources to, inter alia, perform the welder swap sequence. First welding assembly  100  and second welding assembly  200  are attached by connection lines  122  and  222  to first ALC  120  and second ALC  220  respectively as best shown in  FIG. 5 . ALCs  120  and  220  perform, inter alia, automatic setting of the starting arc gap and allow for higher weld travel speeds across workpiece  30 . 
       FIG. 6  is a diagrammatic view of a welder swap sequence  40  according to another embodiment of the present invention. An operator can initiate swap sequence  42  through HMI  14 . Weld quality and/or electrode deterioration can be observed through a welding camera or other monitoring and visualization systems to determine swap sequence initiation  42 . Alternatively, an automatic monitoring system to automatically initiate swap sequence based on detecting predetermined weld quality and electrode deterioration thresholds may be used. In still other embodiments, a preset weld time or production rate may be used to automatically initiate weld swap sequence  42 . Once the welder swap sequence  42  has been initiated, PLC  12  computes and outputs  43  power acceleration and deceleration based on input parameters  16 . 
     Referring now to  FIG. 7 , there is shown a graph with power acceleration and deceleration for first welding assembly  100  and second welding assembly  200  before, during and after a welding swap sequence. Power acceleration and deceleration rates shown in  FIG. 7  are controlled by PLC output  43 . Prior to initiation of the welder swap sequence  42 , first welding assembly  100  is fully energized by first power source  110  through power line  112 , whereas, second welding assembly  200  is on standby. When welder swap sequence is initiated  42  at time  45 , power supply  112  to first welding assembly  100  is ramped down and power supply  212  to second welding assembly  200  is ramped up as best shown in  FIG. 7 . At time  46 , the welder swap sequence concludes by fully energizing second welding assembly  200  and de-energizing first welding assembly  100 . Although a linear power acceleration and deceleration is shown in this embodiment, non-linear power acceleration and deceleration rates may be used to execute the welder swap sequence. After first welding assembly  100  has been placed on standby at the end of the swap sequence, an operator may remove cap  108  from torch  104  and replace electrode  102 . 
       FIG. 8  is a diagrammatic view of input  16  and output parameters of PLC  12 . As more fully explained above, HMI  14  serves as a graphical user interface to accept input parameters  16  to control PLC output. Input parameters  14  can include swap time to determine the rate of power acceleration deceleration. For example, a longer swap time will allow for gradual power changes to accomplish the swap sequence, whereas a shorter swap time will require greater power modulation rates. Output power level can also determine PLC power output, wherein a larger output power level will generally require a longer swap time to accomplish the welder swap sequence. Similarly, other parameters such as rate of power acceleration and deceleration, power ratio, and weld speed can be input to PLC  12  to determine and control the welder swap sequence as desired. 
     Referring now to  FIG. 9 , there is shown a method for performing a welder swap sequence  50  using welding assembly  10  according to another embodiment of the present invention. Welder swap sequence  50  allows welding assembly  10  to perform a continuous welding operation without interruption. This is especially critical in continuous welding of long metal tubes because interrupting the welding operation to replace deteriorated electrodes may result in poor weld quality leading to material wastage. As best shown in  FIGS. 2 and 3 , a butt-welding operation on metal tube  30  with an open longitudinal seam must be continuously performed to achieve consistent weld quality to avoid discarding improperly welded tube material. The swap sequence can be manually initiated  52  by an operator through HMI  14  or by an automatic monitoring system as more fully described above. Once the swap sequence is initiated, PLC  14  controls power acceleration and deceleration  54  to welding assemblies  100  and  200  based upon predetermined input  16  transmitted from HMI  14 . Swap sequence concludes  56  by fulling energizing second welding assembly  200  and de-energizing welding assembly  100 . An operator can now replace  58  electrode  102  from standby welding assembly  100 . Alternatively, mechanical actuators may be used to replace electrode  102 . First welding assembly  100  is now ready to be used and can perform the welding procedure by initiating another swap sequence to replace second welding assembly  200 . The swap sequence between two or more welding systems may be repeated over and over again in this manner to allow for continuous welding. While manual intervention to identify/trigger welder swap and replace spent electrodes is generally described herein, other embodiments may be full automatic requiring no manual input once the input parameters and weld requirement have been input. 
     Furthermore, although the invention disclosed herein has been described with reference to particular features, it is to be understood that these features are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications, including changes in the sizes of the various features described herein, may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention. In this regard, the present invention encompasses numerous additional features in addition to those specific features set forth in the paragraphs above. Moreover, the foregoing disclosure should be taken by way of illustration rather than by way of limitation as the present invention is defined in the examples of the numbered paragraphs, which describe features in accordance with various embodiments of the invention.