Abstract:
A system and method is provided for narrow groove joining of metals. The method includes feeding a wire to a weld joint formed by the metals to be joined and transmitting a welding current through a length of the wire. The method also includes creating a molten puddle in the weld joint with the welding current. The method further includes performing a low heat transfer process on the wire for a predetermined low heat duration to transfer a first portion of the wire to the molten puddle, and performing a high heat transfer process on the wire for a predetermined high heat duration to transfer a second portion of the wire to the molten puddle. The low heat transfer process creates the molten puddle at a root of the weld joint. The high heat transfer process creates an arc that climbs sidewalls of the weld joint and the molten puddle follows the arc up the sidewalls to a top of the weld joint.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Systems and Methods of the present invention relate to welding and joining of hard to weld metals, and more specifically to narrow-groove welding/joining of hard to weld metals. 
     2. Description of the Related Art 
     The joining/welding of weld joints of workpieces using a narrow groove technique can be difficult. For example,  FIG. 1A  illustrates a weld joint  10  that has a square groove with narrow spacing. Exemplary applications for such a joint is the welding/joining of hard to weld metals such as hard to weld steels, high carbon steels, etc. where minimum admixture is desirable but complete sidewall fusion is required. One example of a hard to weld joint is found in brake rotors, but of course, there are numerous other applications in which narrow-groove welding of hard to weld metals is desired. Conventional welding/joining methods can result in the weld  20  bridging the narrow gap resulting in a weak weld joint, as there is no penetration into the weld (see  FIG. 1B ). In addition, because the weld bead at the top of the weld is ground flush with the workpiece surface in many applications, complete fusion with the sidewalls is required for these narrow-groove applications. To minimize the bridging and achieve deeper penetration, higher heat input can be used to weld the joint, but this can result in excessive penetration of the joint edge and excessive admixture with the base material of the workpiece (see weld  20 ′ of  FIG. 1C ). Excessive mixing of the weld metal and the base metal is especially problematic when the base material is composed of high-carbon steel, e.g., such as that found in brake rotors, making the resulting weld bead crack sensitive. Accordingly, sufficient but not excessive sidewall bonding is desirable to achieve sufficient joint strength. 
     Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such approaches with embodiments of the present invention as set forth in the remainder of the present application with reference to the drawings. 
     BRIEF SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention include systems and methods for narrow groove joining of metals. These systems and methods allow the joining process to be “cold,” i.e., minimal admixture, but still achieve sufficient strength without weakening the finished weld. The method includes feeding a wire to a weld joint formed by the metals to be joined and transmitting a welding current through a length of the wire. The method also includes creating a molten puddle in the weld joint with the welding current. The method further includes performing a low heat transfer process on the wire for a predetermined low heat duration to transfer a first portion of the wire to the molten puddle, and performing a high heat transfer process on the wire for a predetermined high heat duration to transfer a second portion of the wire to the molten puddle. The low heat transfer process creates the molten puddle at a root of the weld joint. The high heat transfer process creates an arc that climbs sidewalls of the weld joint and the molten puddle follows the arc up the sidewalls to a top of the weld joint. 
     The system includes a wire feeder that feeds a wire to a weld joint formed by the metals to be joined. The system also includes a power supply that transmits a welding current through a length of the wire, and the welding current creates a molten puddle in the weld joint. The system further includes a controller that performs a low heat transfer process on the wire for a predetermined low heat duration to transfer a first portion of said wire to said molten puddle, and performs a high heat transfer process on the wire for a predetermined high heat duration to transfer a second portion of the wire to the molten puddle. The low heat transfer process creates the molten puddle at a root of the weld joint. The high heat transfer process creates an arc that climbs sidewalls of the weld joint and the molten puddle follows the arc up the sidewalls to a top of the weld joint. 
     These and other features of the claimed invention, as well as details of illustrated embodiments thereof, will be more fully understood from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects of the invention will be more apparent by describing in detail exemplary embodiments of the invention with reference to the accompanying drawings, in which: 
         FIG. 1A  illustrates a narrow-groove weld joint; 
         FIGS. 1B and 1C  illustrate problems with conventional methods of welding the narrow-groove weld joint of  FIG. 1A ; 
         FIG. 2  is a diagrammatical representation of an exemplary embodiment of a welding system that is consistent with the present invention; 
         FIGS. 3A-3E  illustrate the deposition of wire material in the weld joint of the system in  FIG. 2 ; 
         FIG. 4  illustrates an exemplary welding waveform that is consistent with the present invention; 
         FIG. 5  illustrates a block diagram of a program that can produce the exemplary waveform of  FIG. 4 ; and 
         FIG. 6  illustrates an exemplary controller that can be used in the system of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments of the invention will now be described below by reference to the attached Figures. The described exemplary embodiments are intended to assist the understanding of the invention, and are not intended to limit the scope of the invention in any way. Like reference numerals refer to like elements throughout. 
       FIG. 2  depicts a welding system  100  in accordance with an exemplary embodiment of the present invention. The system  100  is a gas shielded metal arc welding (GMAW or MIG/MAG) system. However, other types of systems can be used with the present invention such as, e.g., metal core arc welding and flux cored arc welding. The system  100  includes a wire feeder  150  feeds a consumable electrode  140  (i.e., wire) to the weld joint  117  of workpieces  115 A,  115 B (see view A-A of  FIG. 2 ). A power supply  170  outputs a welding current to the wire  140  via contact tube  160 . The welding current creates an arc  110  that forms a molten puddle  145  (i.e., a weld puddle) in the weld joint  117 . A gas supply system  190  provides shielding gas to torch  120  to isolate the arc  110  from the atmosphere. The system  100  also includes a controller  180  that controls the power supply  170  such that a desired welding waveform is output. In addition, the controller  180  can also be configured to control the wire feeder  150  for the desired wire feed speed and/or other operations, e.g., operations related to arc initiation. Arc welding systems such as the GMAW system illustrated are known in the art. Thus, for brevity, detailed operation of the system  100  will not be discussed, except as necessary to explain the present invention. 
     In the system of  FIG. 2 , the weld joint  117  is a narrow-groove weld joint similar to that illustrated in  FIG. 1A . However, unlike conventional methods, the system in  FIG. 2  is controlled such that workpieces  115 A,  115 B will be joined with good bonding at the sidewalls and with minimum admixture of the base material. This is accomplished by joining the workpieces  115 A,  115 B using a combination of a low heat welding process (such as, e.g., short arc, surface tension transfer (STT), shorted retract welding, etc.) and a high heat welding process (such as, e.g., pulse spray transfer and wire feed speed modulation). The low heat process allows the arc  110  to “tighten up” and drop to the root of the weld joint  117  so as to prevent bridging of the gap as seen in conventional methods. The wider arc plume of the high heat process expands the puddle  145  to encompass the sides of the joint  117  and the arc  110  rides up the puddle  145  as the arc  110  deposits weld metal into the joint  117 . Thus, the high heat process ensures that there is sufficient admixture with the base metal to produce a good bond without weakening the weld due to excessive high-carbon steel admixing with the wire  140 . For clarity, the present invention will be described with reference to an exemplary embodiment using a short arc transfer process as the low heat input process and a pulse spray transfer process as the high heat input process. However, as stated above, the present invention is not limited to just these processes and the short arc transfer process can be substituted with other low heat input processes such as STT and CMT and the pulse spray transfer process can be substituted with other high heat input processes such as increasing or modulating the wire feed speed. 
     As illustrated in  FIG. 3A , the torch  120  travels in direction  111  along weld joint  117 . Power supply  170  (see  FIG. 2 ) is controlled such that its output is switched from a short arc transfer process to a pulse spray transfer process by, e.g., controller  180  or some other device. During the short arc transfer process, the arc  110  is tight and wire  140  will be pushed to the bottom of the weld joint  117 . At this time, the weld puddle  145  is small and there is little or no penetration into the base metal of workpieces  115 A,  115 B. After a predetermined time period, e.g., 50 ms to 1 second, the controller  180  will switch to the high heat input process and will control the power supply  170  such that the power supply  170  outputs a pulse spray transfer waveform. Of course, instead of being based on a predetermined time period, the switch from the short arc transfer process can be based on the number of short arc cycles, e.g., by counting the peak current periods. Once the power supply  170  outputs the pulse spray transfer waveform, the length and width of the arc  110  will quickly increase (see  FIG. 3B ). At this time, the weld puddle  145  is still at the bottom of the weld joint  117 , but the arc  110  is quickly growing towards the sidewalls of the weld joint  117 . As the arc width increases, the arc  110  will start to climb the sidewalls of the weld joint  117  and the puddle  145  will follow (see  FIG. 3C ). As the puddle  145  climbs the sidewalls, the heat of the puddle  145  will achieve the desired penetration into the sidewalls, i.e., some of each sidewall will melt and mix with the weld puddle  145 . This penetration will ensure that there is sufficient bonding between the sidewalls and the finished weld  146 . The low heat input phase of the present invention ensures that the arc  110  collapses sufficiently enough to allow the wire  140  to push it to the root of the of weld joint  117 . At the start of each high heat phase, a minimal puddle  145  is located at the root of the joint  117  and the expanding arc plasma will ride up the joint  117  for the duration of the high heat input phase. Accordingly, even if the sidewalls contain high-carbon steel or other alloys, the admixture between the weld metal and the base metal is not sufficient to appreciably weaken the finished weld  146 . Additionally, the heat input is minimal to reduce distortion. Further, the groove can be very narrow, as the weld process does not bridge the root of the joint  117 . 
     Once the puddle  145  reaches the top of the weld joint  117 , the puddle  145  can be expanded over the edges of the weld joint  117  in order to add some reinforcement to the weld (see  FIG. 3D ). Any excess weld metal can then be machined off at a later time. Like the low heat input duration, the duration of the high heat input process, e.g., the pulse spray transfer phase, can be based on a predetermined period of time or on a predetermined number of cycles, e.g., by counting the peak pulses, associated with the high heat input waveform. For example, the pulse spray transfer duration can be 50 ms to 2 seconds or 5 to 100 pulse cycles. At the end of the predetermined time period or upon reaching the predetermined count, the controller  180  switches from the pulse spray transfer process to the short arc transfer process. 
     As illustrated in  FIG. 3E , once the controller  180  switches to the short arc transfer process, the width of the arc  110  will decrease to its “short arc” size and the arc  110  will no longer want to bridge the gap of the weld joint  117 . The arc  110  then slips down the face of the weld bead toward the root of the weld joint  117 . As the arc  110  slips down, the “stick out” of wire  140  becomes longer, which increases the resistance of the wire  140 . The increased resistance of the wire  140  further decreases the heat input to the workpieces  115 A,  115 B during this phase. 
     As described above, exemplary embodiments of the present invention produce a “sewing machine” type action on the arc  110  as the torch  120  travels along the length of the weld joint  117 . In some embodiments, the travel speed can be above 15 ipm. In addition, depending on the diameter of the wire, the wire feed speeds can be above 400 ipm (e.g., for a 0.35 diameter wire). In some embodiments, the controller  180  (or some other device) can change the wire feed speed “on the fly” based on welding parameters such as arc voltage, current, etc. The duration of each process, i.e., the high heat input process and the low heat input process, is dependent on numerous parameters such as, e.g., wire feed speed, low heat cycle time, high heat cycle time, short arc length, pulse arc length, etc. 
     In addition, the composition of the wire may also affect the timing used in the system. For example, wire containing silicon bronze or aluminum bronze provides good characteristics for a process consistent with the present invention. Silicon bronze has a low melting temperature, which minimizes the penetration and admixture. Thus, in applications involving high-carbon steel base material, the weld puddle  145  will not pick up as much carbon and the finished weld will be less susceptible to cracking. In addition, silicon bronze has a relatively big difference between its short arc length and its pulse arc length and thus allows for a relatively wide heat input difference between the low heat process and the high heat process. These factors help the arc  110  to dive to the root of the weld joint  117  and up the sidewalls. Of course, the present invention is not limited to any particular wire composition and wires with other compositions can be used. For example, wire containing aluminum also shows similar behavior. 
       FIG. 4  illustrates an exemplary welding waveform  400  that is output from power supply  170  to the wire  140  via contact tube  160  (see  FIG. 2 ). The welding waveform  400  includes a low heat input period and a high heat input period. Specifically, the low heat input is provided by a short arc current waveform  410  and the high heat input is provided by a pulse spray current waveform  420 . The short arc waveform cycles from a background current I BS  ( 413 ) to a current value I PS . During the background current phase  413  the arc  110  is present, but no material from the wire  140  is transferred. When the wire  140  shorts to the weld puddle  145 , the current increases in value (see  411 ) until a droplet from wire  140  is transferred to the weld puddle  145  (see I PS ). The current value I PS  is approximate as the value may vary for each droplet that is transferred. Once the droplet is transferred, the current drops to the background current I BS . After the short arc transfer period, the welding current will follow the pulse spray current waveform pattern. As illustrated in  FIG. 4 , the current will ramp to a peak current value I PP  (see  421 ) and the peak current value I PP  will be held at that value for a predetermined time (see  422 ). The peak current value I PP  is set such that a droplet from wire  140  will transfer to the weld puddle  145  during the peak current hold time period. After holding the peak current value I PP  for the predetermined time period, the current ramps down to a background current value I BP  (see  423 ). The current is then held at the background current value I BP  for a predetermined time period (see  424 ) before the pulse spray transfer cycle begins again. Although there are many variations in the methods to control the low heat process and the high heat process, the short arc and pulse spray welding waveforms are known to those skilled in the art. Accordingly, they will not be further discussed in detail except as necessary to explain the present invention. 
     Based on a signal from the controller  180 , the power supply  170  (see  FIG. 2 ) outputs the short arc waveform  410  for a predetermined period of time t LH , e.g., 50 ms to 1 second. During this time the wire  140  is driven toward the root of the weld joint  117  as discussed above, and droplets from the wire  140  will transfer (see  412 ) to the weld puddle  145  as the short arc current waveform  410  cycles from the shorting period  411  to the arcing period  413 . The predetermined time period t LH  can be user settable or automatically determined (with an optional user “fine tune” adjustment) based on factors such weld joint dimensions, type of welding, wire feed speed, low heat cycle time, high heat cycle time, short arc length, pulse arc length, filler wire type, filler wire diameter, shielding gas type and flow rate, etc. Of course, instead of controlling the duration of the low heat input phase based on the predetermined time period t LH , the low heat input duration can be based on a predetermined number of short arc transfer cycles (count c LH ), e.g., by counting the number of shorting events. For example, count c LH  can be in a range from 5 to 100 shorting events. Similar to the predetermined time period t LH , the predetermined count c LH  can be user selectable or automatically determined (with an optional user “fine tune” adjustment) based on the factors discussed above. Of course, along with the predetermined time period t LH  and count c LH , other parameters of the waveform  410  such as the peak amplitude, peak ramp rate, background amplitude, frequency, etc. can be user adjusted and/or automatically determined based on the above discussed factors. 
     After the predetermined time period t LH  has elapsed (or count c LH  has been reached), the waveform  400  starts the pulse spray transfer process  420  for a duration based on a cycle count c HH , e.g., by counting the peak pulses. For example, c HH  can be in a range from 5 to 100 pulse cycles. Similar to the low heat input parameters, the predetermined high heat input count c HH  can be user settable or automatically determined (with an optional user “fine tune” adjustment) based on factors such weld joint dimensions, type of welding, wire feed speed, low heat cycle time, high heat cycle time, short arc length, pulse arc length, filler wire type, filler wire diameter, shielding gas type and flow rate, etc. Of course, instead of controlling the duration of the high heat input phase based on the predetermined count c HH , the high heat input duration can be based on a predetermined time period t HH , e.g., from 50 ms to 2 seconds. Similar to the predetermined high heat input count c HH , the predetermined time period t HH  can be user selectable or automatically determined (with an optional user “fine tune” adjustment) based on the factors discussed above. Of course, similar to the low heat input waveform  410 , along with the predetermined time period t HH  and count c HH , other parameters of waveform  420  such as the peak amplitude, peak ramp rate, peak duration, background amplitude, frequency, etc. can be user adjusted and/or automatically determined based on the above described factors. In the embodiment of  FIG. 4 , the welding waveforms  410  and  420  are DC. However, the present invention is not limited to DC waveforms and one or both of the low heat input process and high heat input process can be AC waveforms or the high heat process can be positive polarity and the low heat process negative polarity. 
       FIG. 5  illustrates a block diagram of an exemplary control program  500  that can be used in embodiments of the present invention. The control program  500 , which can be implemented in controller  180  (or some other device), includes a low heat input program  502  and a high heat input program  504 . In exemplary embodiments of the present invention, the low heat input program  502  and the high heat input program  504  correspond to the short arc transfer welding waveform  410  and the pulse spray transfer welding waveform  420 , respectively. In step  510 , the program starts the short arc transfer phase. Based on, e.g., the arc voltage V (see  FIG. 1 ), the controller  180  determines when the wire  140  has shorted to puddle  145 . At this time, the program advances to step  520  where the shorting routine is started. The shorting routine is different based on the type of low heat input process, e.g., short arc, STT, CMT, etc. In our exemplary embodiment, the output current from the power supply  170  is raised during the time the wire  140  is shorted (see  FIG. 4  curve  411 ). Based on the arc voltage V, the controller  180  will determine when the droplet has transferred and the arc  110  has been reestablished. At this time, the program will go to step  510  where the output current from the power supply  170  will drop back to the background level I BS  (see  FIG. 4  curve  413 ) and wait for the wire  140  to once again short to the puddle  145 . During step  510 , the program will also check timer T (step  512 ) to see if has reached the predetermined time period t LH . If the timer T is less than time t LH , the program will go back to steps  510  and  520  where the short arc transfer process continues to be performed (step  514 ). If the timer T (step  512 ) is greater than or equal to the predetermined time t LH , the program will switch to the high heat input program  504  (step  516 ), which in this exemplary embodiment is a pulse spray transfer process. Of course, instead of timer T, step  512  can include a check of the number of short arc transfer cycles (count c LH ). 
     Once the pulse spray transfer process is initiated, the program will go to step  540  where the output current from the power supply  170  is ramped up to a peak current value I PP  (see  FIG. 4 , curve  421 ). The program will then advance to step  542  where the peak current value I PP  is held for a set time period so that a droplet from the wire  140  is transferred (see  FIG. 4 , curve  422 ). In step  422 , the peak counter C is incremented by one. After the set time period at the peak current I PP , the program advances to step  544  where the output current from the power supply  170  is ramped down to a background current I BP  (see  FIG. 4 , curve  423 ). The program then advances to step  546  where the background current I BP  is held for a set time period. After the set time period at the background current I BP , the program checks whether the value in counter C is greater than or equal to the predetermined count c HH  (step  550 ). If not, the pulse spray transfer process continues as the program goes back to step  540  (see step  552 ). If, at step  550 , the value in counter C is greater than count c HH , the controller  180  will switch back to the low heat input program  502  (step  554 ) and the short arc transfer process will be performed as described above. The low input/high input processes described above will continue until the welding operation is stopped. 
     In some exemplary embodiments, the controller  180  can be a parallel state-based controller with state tables that control various welding equipment, e.g., the power supply  170 , the wire feeder  150 , etc. For example, as illustrated in  FIG. 6 , the controller  180 ′ can include a weld state table  182  that is used to control the output of the power supply  170  and wire feeder state table  184  that controls wire feeder  150  to control the wire feed speed of the wire  140 . Of course, other state tables to control other equipment can also be included. Parallel state-based controllers are discussed in application Ser. Nos. 13/534,119 and 13/438,703, which are incorporated by reference herein in their entirety. Accordingly, parallel state-based controllers will not be further discussed in detail. In some exemplary embodiments, the weld state table  182  can define one or more welding processes that control the output of the power supply  170 . For example, the weld state table  182  can be programmed to perform the steps of the low heat input program  502  and the high heat input program  504  discussed above. Of course, the parallel state-based controller  180 ′ is not limited to the short arc transfer process and other low heat input processes can be programmed into the weld table  182  such as STT, shorted retract welding, etc. Similarly, the controller  180 ′ is not limited to the pulse spray transfer process and other high heat input processes can be used. 
     The exemplary embodiments discussed above combine a low heat input process with a narrowly focused arc (e.g., the short arc transfer process) with a high heat input process with a wide arc (e.g., the pulse spray transfer process). By combining these two processes, a “sewing machine” type action is created where the arc dives to the bottom of the joint during the low heat input process and then rises to the top of the joint during the high heat input process. The combination of these processes ensures that there is some admixture with the base metal to provide a strong bond but not so much as to weaken the finished weld. 
     The exemplary embodiments of the welding system, as shown in the Figures, depict the welding power supply, wire feeder system, and controller as separate components. However, this need not be the case as these components can be integrated into a single unit. Furthermore, the control hardware and software (for example a state table) can be found in any one of a welding power supply, system controller and/or a wire feeder. Embodiments of the present invention are not limited in this regard, and can have a modular construction as well, where the components of the system are provided in separate but combinable modules. 
     While the invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims.