Patent Description:
Devices, systems, and methods consistent with the invention relate to material deposition with a dual wire configuration.

When welding, it is often desirable to increase the width of the weld bead or increase the length of the weld puddle during welding. There can be many different reasons for this desire, which are well known in the welding industry. For example, it may be desirable to elongate the weld puddle to keep the weld and filler metals molten for a longer period of time so as to reduce porosity. That is, if the weld puddle is molten for a longer period of time there is more time for harmful gases to escape the weld bead before the bead solidifies. Further, it may desirable to increase the width of a weld bead so as to cover wider weld gap or to increase a wire deposition rate. In both cases, it is common to use an increased electrode diameter. The increased diameter will result in both an elongated and widened weld puddle, even though it may be only desired to increase the width or the length of the weld puddle, but not both. However, this is not without its disadvantages. Specifically, because a larger electrode is employed more energy is needed in the welding arc to facilitate proper welding. This increase in energy causes an increase in heat input into the weld and will result in the use of more energy in the welding operation, because of the larger diameter of the electrode used. Further, it may create a weld bead profile or cross-section that is not ideal for certain mechanical applications. Rather than increasing the diameter of the electrode, it may be desirable to use at least two smaller electrodes simultaneously.

In order to improve welding, especially with respect to weld bed and/or weld puddle width and/or length features and their modifications, a welding or additive manufacturing contact tip according to claim <NUM> is described. Preferred embodiments are subject of the subclaims. The following summary presents a simplified summary in order to provide a basic understanding of some aspects of the devices, systems and/or methods discussed herein. This summary is not an extensive overview of the devices, systems and/or methods discussed herein. It is not intended to identify critical elements or to delineate the scope of such devices, systems and/or methods. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

In accordance with one aspect of the present disclosure, provided is a welding or additive manufacturing contact tip. The contact tip includes an electrically-conductive body extending from a proximal end of the body to a distal end of the body. The body forms a first bore terminating at a first exit orifice at a distal end face of the body, and a second bore terminating at a second exit orifice at the distal end face of the body. The first and second exit orifices are separated from each other by a distance configured to facilitate formation of a bridge droplet between a first wire electrode delivered through the first bore and a second wire electrode delivered through the second bore during a deposition operation.

In accordance with another aspect of the present disclosure, provided is a welding or additive manufacturing contact tip. The contact tip includes an electrically-conductive body extending from a proximal end of the body to a distal end of the body. The body forms a first bore through the body that extends from a first entrance orifice at the proximal end of the body to a first exit orifice at the distal end of the body, and a second bore through the body extending from a second entrance orifice at the proximal end of the body to a second exit orifice at the distal end of the body. The first and second exit orifices are separated from each other by a distance configured to facilitate formation of a bridge droplet between a first wire electrode delivered through the first bore and a second wire electrode delivered through the second bore during a deposition operation. The bridge droplet couples the first wire electrode to the second wire electrode prior to contacting a molten puddle created by the deposition operation.

In accordance with another aspect of the present disclosure, provided is a welding or additive manufacturing contact tip. The contact tip includes an electrically-conductive body extending from a proximal end of the body to a distal end of the body. The body forms a first channel terminating at a distal end face of the body, and a second channel terminating at the distal end face of the body. At the distal end face of the body, the first channel and the second channel are separated from each other by a distance configured to facilitate formation of a bridge droplet between a first wire electrode delivered through the first channel and a second wire electrode delivered through the second channel during a deposition operation. The bridge droplet couples the first wire electrode to the second wire electrode prior to contacting a molten puddle created by the deposition operation.

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:.

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.

As used herein, "at least one", "one or more", and "and/or" are open-ended expressions that are both conjunctive and disjunctive in operation. Any disjunctive word or phrase presenting two or more alternative terms, whether in the description of embodiments, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" should be understood to include the possibilities of "A" or "B" or "A and B.

While embodiments of the present invention discussed herein are discussed in the context of GMAW type welding, other embodiments of the invention are not limited thereto. For example, embodiments can be utilized in SAW and FCAW type welding operations, as well as other similar types of welding operations. Further, while the electrodes described herein are solid electrodes, again, embodiments of the present invention are not limited to the use of solid electrodes as cored electrodes (either flux or metal cored) can also be used without departing from the scope of the present invention. Further, embodiments of the present invention can also be used in manual, semi-automatic and robotic welding operations. Because such systems are well known, they will not be described in detail herein.

Turning now to the Figures, <FIG> depicts an exemplary embodiment of a welding system <NUM> in accordance with an exemplary embodiment of the present invention. The welding system <NUM> contains a welding power source <NUM> which is coupled to both a welding torch <NUM> (having a contact tip assembly - not shown) and a wire feeder <NUM>. The power source <NUM> can be any known type of welding power source capable of delivering the current and welding waveforms described herein, for example, pulse spray, STT and/or short arc type welding waveforms. Because the construction, design and operation of such power supplies are well known, they need not be described in detail herein. It is also noted that welding power can be supplied by more than one power supply at the same time - again the operation of such systems are known. The power source <NUM> can also include a controller <NUM> which is coupled to a user interface to allow a user to input control or welding parameters for the welding operation. The controller <NUM> can have a processor, CPU, memory etc. to be used to control the operation of the welding process as described herein. The torch <NUM>, which can be constructed similar to known manual, semi-automatic or robotic welding torches can be coupled to any known or used welding gun and can be of a straight or gooseneck type as described above. The wire feeder <NUM> draws the electrodes E1 and E2 from electrode sources <NUM> and <NUM>, respectively, which can be of any known type, such as reels, spools, containers or the like. The wire feeder <NUM> is of a known construction and employs feed rolls <NUM> to draw the electrodes E1 and E2 and push the electrodes to the torch <NUM>. In an exemplary embodiment of the present invention, the feed rolls <NUM> and wire feeder <NUM> are configured for a single electrode operation. Embodiments of the present invention, using a dual wire configuration, can be utilized with a wire feeder <NUM> and rollers <NUM> only designed for a single wire feeding operation. For example, rollers <NUM> can be configured for a single <NUM> inch diameter electrode, but will suitable drive two electrodes of a <NUM> inch diameter without modification to the wire feeder <NUM> or the rollers <NUM>. Alternatively, the wire feeder <NUM> can be designed to provide separate sets of rollers for feeding the electrodes E1/E2 respectively, or have rollers configured for feeding two or more electrodes simultaneously (e.g., via trapezoidal-shaped wire receiving grooves around the rollers that can accommodate two electrodes). In other embodiments, two separate wire feeders can also be used. As shown, the wire feeder(s) <NUM> is in communication with the power source <NUM> consistent with known configurations of welding operations.

Once driven by the rollers <NUM>, the electrodes E1 and E2 are passed through a liner <NUM> to deliver the electrodes E1 and E2 to the torch <NUM>. The liner <NUM> is appropriately sized to allow for the passage of the electrodes E1 and E2 to the torch <NUM>. For example, for two <NUM> inch diameter electrodes, a standard <NUM> inch diameter liner <NUM> (which is typically used for a single <NUM> inch diameter electrode) can be used with no modification.

Although the examples referenced above discuss the use of two electrodes having a same diameter, the present invention is not limited in this regard as embodiments can use electrodes of a different diameter. That is, embodiments of the present invention can use an electrode of a first, larger, diameter and an electrode of a second, smaller, diameter. In such an embodiment, it is possible to more conveniently weld two work pieces of different thicknesses. For example, the larger electrode can be oriented to the larger work piece while the smaller electrode can be oriented to the smaller work piece. Further, embodiments of the present invention can be used for many different types of welding operations including, but not limited to, metal inert gas, submerged arc, and flux-cored welding. Further, embodiments of the present invention can be used for automatic, robotic and semi-automatic welding operations. Additionally, embodiments of the present invention can be utilized with different electrode types. For example, it is contemplated that a cored electrode can be coupled with a non-cored electrode. Further, electrodes of differing compositions can be used to achieve the desired weld properties and composition of the final weld bead. Thus, embodiments of the present invention can be utilized in a broad spectrum of welding operations.

<FIG> depicts an exemplary contact tip assembly <NUM> of the present invention. The contact tip assembly <NUM> can be made from known contact tip materials and can be used in any known type of welding gun. As shown in this exemplary embodiment, the contact tip assembly has two separate channels <NUM> and <NUM> which run the length of the contact tip assembly <NUM>. During welding a first electrode E1 is passed through the first channel <NUM> and the second electrode E2 is passed through the second channel <NUM>. The channels <NUM>/<NUM> are typically sized appropriately for the diameter of wire that is to be passed there through. For example, if the electrodes are to have the same diameter the channels will have the same diameters. However, if different diameters are to be used then the channels should be sized appropriately so as to properly transfer current to the electrodes. Additionally, in the embodiment shown, the channels <NUM>/<NUM> are configured such that the electrodes E1/E2 exit the distal end face of the contact tip <NUM> in a parallel relationship. However, in other exemplary embodiments the channels can be configured such that the electrodes E1/E2 exit the distal end face of the contact tip such that an angle in the range of +/- <NUM>° exists between the centerlines of the respective electrodes. The angling can be determined based on the desired performance characteristics of the welding operation. It is further noted that in some exemplary embodiments the contact tip assembly can be a single integrated contact tip with a channels as shown, while in other embodiments the contact tip assembly can be comprised of two contact tip subassemblies located close to each other, where the current is directed to each of the contact tip subassemblies.

As shown in <FIG>, the respective electrodes E1/E2 are spaced by a distance S which is the distance between the closest edges of the electrodes. In exemplary embodiments of the present invention, this distance is in the range of <NUM> to <NUM> times the diameter of the larger of the two electrodes E1/E2, while in other exemplary embodiments the distance S is in the range of <NUM> to <NUM> times the largest diameter. For example, if each of the electrodes has a diameter of <NUM>, the distance S can be in the range of <NUM> to <NUM>. In other exemplary embodiments, the distance S is in the range of <NUM> to <NUM> times the diameter of one of the wire electrodes, such as the larger of the two electrodes. In manual or semi-automatic welding operations the distance S can be in the range of <NUM> to <NUM> times the largest electrode diameter, whereas in robotic welding operations the distance S can be in the same or another range, such as <NUM> to <NUM> times the largest electrode diameter. In exemplary embodiments, the distance S is in the range of <NUM> to <NUM>.

The wire electrodes E1/E2 project from exit orifices on the end face of the contact tip <NUM>. The diameter of the exit orifices is slightly larger than the diameter of the wire electrodes E1/E2. For example, for a <NUM> inch wire, the diameter of the exit orifice could be <NUM> inches (<NUM>); for a <NUM> inch wire, the diameter of the exit orifice could be <NUM> inches (<NUM>); for a <NUM> inch wire, the diameter of the exit orifice could be <NUM> inches (<NUM>). The channels <NUM>, <NUM> and exit orifices are spaced appropriately to facilitate the formation of a single bridge droplet between the wire electrodes E1/E2 during a deposition operation. For exit orifices sized for electrodes having a diameter <NUM> inches and smaller, the distance between the exit orifices (inner circumference to inner circumference, similar to distance S) can be less than <NUM> to facilitate the formation of a bridge droplet. However, spacing of <NUM> or greater between the exit orifices may be possible, depending on the wire size, magnetic forces, orientation (e.g., angle) of the channels <NUM>, <NUM>, etc. In certain embodiments, the distance between the exit orifices is within the range of <NUM>% to <NUM>% of the diameter of one or both of the exit orifices, which can also correspond to the distance S between the wire electrodes being in the range of <NUM> to <NUM> times the diameter of the electrodes.

As explained further below, the distance S should be selected to ensure that a single bridge droplet is formed between the electrodes, before the droplet is transferred, while preventing the electrodes from contacting each other, other than through the bridge droplet.

<FIG> depicts an exemplary embodiment of the present invention, while showing in the interactions of the magnetic forces from the respective electrodes E1 and E2. As shown, due to the flow of current, a magnetic field is generated around the electrodes which tends to create a pinch force that draws the wires towards each other. This magnetic force tends to create a droplet bridge between the two electrodes, which will be discussed in more detail below.

<FIG> shows the droplet bridge that is created between the two electrodes. That is, as the current passing through each of the electrodes melts the ends of the electrodes the magnetic forces tend to draw the molten droplets towards each other until they connect with each other. The distance S is far enough such that the solid portions of the electrodes are not drawn to contact each other, but close enough that a droplet bridge is created before the molten droplet is transferred to the weld puddle created by the welding arc. The droplet is depicted in <FIG> where the droplet bridge creates a single large droplet that is transferred to the puddle during welding. As shown, the magnetic pinch force acting on the droplet bridge acts to pinch off the droplet similar to the use of pinch force in a single electrode welding operation.

Further, <FIG> depicts an exemplary representation of current flow in an embodiment of the present invention. As shown the welding current is divided so as to flow through each of the respective electrodes and passes to and through the bridge droplet as it is formed. The current then passes from the bridge droplet to the puddle and work piece. In exemplary embodiments where the electrodes are of the same diameter and type the current will be essentially divided evenly through the electrodes. In embodiments where the electrodes have different resistance values, for example due to different diameters and/or compositions/construction, the respective currents will be apportioned due to the relationship of V = I*R, as the welding current is applied to the contact tip similar to known methodologies and the contact tip provides the welding current to the respective electrodes via the contact between the electrodes and the channels of the contact tip. <FIG> depicts the magnetic forces within the bridge puddle that aid in creating the bridge droplet. As shown, the magnetic forces tend to pull the respective molten portions of the electrodes towards each other until they contact with each other.

<FIG> depicts an exemplary cross-section of a weld made with a single electrode welding operation. As shown, while the weld bead WB is of an appropriate width, the finger F of the weld bead WB, which penetrates into the work pieces W as shown, has a relatively narrow width. This can occur in single wire welding operations when higher deposit rates are used. That is, in such welding operations the finger F can become so narrow that it is not reliable to assume that the finger penetrated in the desired direction, and thus cannot be a reliable indicator of proper weld penetration. Further, as this narrow finger dives deeper this can lead to defects such as porosity trapped near the finger. Additionally, in such welding operations the useful sides of the weld bead are not as deeply penetrated as desired. Thus, in certain applications this mechanical bond is not as strong as desired. Additionally, in some welding applications, such as when welding horizontal fillet welds, the use of a single electrode made it difficult to achieve equal sized weld legs, at high deposition speeds, without the addition of too much heat to the welding operation. These issues are alleviated with embodiments of the present invention which can reduce the penetration of the finger and spread the finger making the side penetration of the weld wider. An example of this is shown in <FIG>, which shows a weld bead of an embodiment of the present invention. As shown in this embodiment, a similar, or improved weld bead leg symmetry and/or length can be achieved, as well as a wider weld bead at the weld depth within the weld joint. This improved weld bead geometry is achieved while using less overall heat input into the weld. Therefore, embodiments of the present invention can provide improved mechanical weld performance with lower amounts of heat input, and at improved deposition rates.

<FIG> depicts a flow chart <NUM> of an exemplary welding operation of the present invention. This flow chart is intended to be exemplary and is not intended to be limiting. As shown, a welding current/output is provided by the welding power source <NUM> such that current is directed to the contact tip and electrodes consistent with known system constructions. Exemplary waveforms are discussed further below. During welding a bridge droplet is allowed to form <NUM> between the electrodes where the respective droplets from each electrode contact each other to create a bridge droplet. The bridge droplet is formed prior to contacting the weld puddle. During formation of the bridge droplet at least one of a duration or a droplet size is detected until such time as the droplet reaches a size to be transferred, and then the droplet is transferred to the puddle <NUM>. The process is repeated during the welding operation. To control the welding process the power source controller/control system can use either one of a bridge droplet current duration and/or a bridge droplet size detection to determine if the bridge droplet is of a size to be transferred. For example, in one embodiment a predetermined bridge current duration is used for a given welding operation such that a bridge current is maintained for that duration, after which droplet transfer is then initiated. In a further exemplary embodiment, the controller of the power source/supply can monitor the welding current and/or voltage and utilize a predetermined threshold (for example a voltage threshold) for a given welding operation. For example, in such embodiments, as the detected arc voltage (detected via a known type of arc voltage detection circuit) detects that the arc voltage has reached a bridge droplet threshold level the power supply initiates a droplet separation portion of the welding waveform. This will be discussed further below in some exemplary embodiments of welding waveforms that can be used with embodiments of the present invention.

<FIG> depicts an alternative exemplary embodiment of a contact tip <NUM> that can be used with embodiments of the present invention. As described previously, in some embodiments the electrodes can be directed to the torch via a single wire guide/liner. Of course, in other embodiments, separate wire guide/liners can be used. However, in those embodiments, where a single wire guide/liner is used the contact tip can be designed such that the electrodes are separated from each other within the contact tip. As shown in <FIG>, this exemplary contact tip <NUM> has a single entrance channel <NUM> with a single orifice at the upstream end of the contact tip <NUM>. Each of the electrodes enter the contact tip via this orifice and pass along the channel <NUM> until they reach a separation portion <NUM> of the contact tip, where the separation portion directs one electrode into a first exit channel <NUM> and a second electrode into the second exit channel <NUM>, so that the electrodes are directed to their discrete exit orifices <NUM> and <NUM>, respectively. Of course, the channels <NUM>, <NUM> and <NUM> should be sized appropriately for the size of electrodes to be used, and the separation portion <NUM> should be shaped so as to not scar or scratch the electrodes. As shown in <FIG>, the exit channels <NUM> and <NUM> are angled relative to each other, however, as shown in <FIG>, these channels can also be oriented parallel to each other.

Turning now to <FIG>, various exemplary waveforms that can be used with exemplary embodiments of the present invention are depicted. In general, in exemplary embodiments of the present invention, the current is increased to create the bridge droplet and build it for transfer. In exemplary embodiments, at transfer the bridge droplet has an average diameter which is similar to the distance S between the electrodes, which can be larger than the diameter of either of the electrodes. When the droplet is formed it is transferred via a high peak current, after which the current drops to a lower (e.g. background) level to remove the arc pressure acting on the wires. The bridging current then builds the bridge droplet without exerting too much pinch force to pinch off the developing droplet. In exemplary embodiments, this bridging current is at a level in the range of <NUM> to <NUM>% between the background current and the peak current. In other exemplary embodiments, the bridging current is in the range of <NUM> to <NUM>% between the background current and the peak current. For example, if the background current is <NUM> amps and the peak current is <NUM> amps, the bridging current is in the range of <NUM> to <NUM> amps (i.e., <NUM> to <NUM>% of the <NUM> amp difference). In some embodiments the bridging current can be maintained for a duration in the range of <NUM> to <NUM>, while in other exemplary embodiments the bridging current is maintained for a duration in the range of <NUM> to <NUM>. In exemplary embodiments the bridging current duration begins at the end of the background current state and includes the bridging current ramp up, where the ramp up can be in the range of <NUM> to <NUM> depending on the bridging current level and the ramp rate. With exemplary embodiments of the present invention, the pulse frequency of waveforms can be slowed down as compared to single wire processes to allow for droplet growth which can improve control and allow for higher deposition rates as compared to single wire operations.

<FIG> depicts an exemplary current waveform <NUM> for a pulsed spray welding type operation. As shown, the waveform <NUM> has a background current level <NUM>, which then transitions to a bridge current level <NUM>, during which the bridge droplet is grown to a size to be transferred. The bridge current level is less than a spray transition current level <NUM> at which the droplet starts its transfer to the puddle. At the conclusion of the bridge current <NUM> the current is raised to beyond the spray transition current level <NUM> to a peak current level <NUM>. The peak current level is then maintained for a peak duration to allow for the transfer of the droplet to be completed. After transfer the current is then lowered to the background level again, as the process is repeated. Thus, in these embodiments the transfer of the single droplet does not occur during the bridge current portion of the waveform. In such exemplary embodiments, the lower current level for the bridge current <NUM> allows a droplet to form without excessive pinching force to direct the droplet to the puddle. Because of the use of the bridge droplet, welding operations can be attained where the peak current <NUM> can be maintained for a longer duration at a higher level than using a single wire. For example, some embodiments can maintain the peak duration for at least <NUM>, and in the range of <NUM> to <NUM>, at a peak current level in the range of <NUM> to <NUM> amps, and a background current in the range of <NUM> to <NUM> amps. In such embodiments, a significantly improved deposition rate can be achieved. For example, some embodiments have achieved deposition rates in the range of <NUM> to 26lbs/hr, whereas similar single wire processes can only achieve a deposition rate in the range of <NUM> to <NUM> lbs/hr. For example, in one non-limiting embodiment a pair of twin wires having a diameter of <NUM>", using a peak current of <NUM> amps, a background current of <NUM> amps and a droplet bridge current of <NUM> amps can be deposited at a rate of 19lb/hr at a frequency of <NUM>. Such a deposition is at a frequency much less than conventional welding processes, and thus more stable.

<FIG> depicts another exemplary waveform <NUM> that can be used in a short arc type welding operation. Again, the waveform <NUM> has a background portion <NUM> prior to a short response portion <NUM> which is structured to clear a short between the droplet and the puddle. During the shorting response <NUM> the current is raised to clear the short and as the short is cleared the current is dropped to a bridge current level <NUM> during which the bridge droplet is formed. Again, the bridge current level <NUM> is less than the peak current level of the shorting response <NUM>. The bridge current level <NUM> is maintained for a bridge current duration that allows a bridge droplet to be formed and directed to the puddle. During transfer of the droplet current is then dropped to the background level, which allows the droplet to advance until a short occurs. When a short occurs the shorting response/bridge current waveform is repeated. It should be noted that in embodiments of the present invention it is the presence of the bridge droplet that makes the welding process more stable. That is, in traditional welding processes that use multiple wires there is no bridge droplet. In those processes when one wire shorts or makes contact with the puddle the arc voltage drops and the arc for the other electrode will go out. This does not occur with embodiments of the present invention, where the bridge droplet is common to each of the wires.

<FIG> depicts a further exemplary waveform <NUM>, which is a STT (surface tension transfer) type waveform. Because such waveforms are known, they will not be described in detail herein. To further explain an STT type waveform, its structure, use and implementation, <CIT>, is incorporated herein in its entirety. Again, this waveform has a background level <NUM>, and a first peak level <NUM> and a second peak level <NUM>, where the second peak level is reached after a short between the droplet and puddle is cleared. After the second peak current level <NUM>, the current is dropped to a bridge current level <NUM> where the bridge droplet is formed, after which the current is dropped to the background level <NUM> to allow the droplet to be advanced to the puddle, until it makes contact with the puddle. In other embodiments, an AC waveform can be used, for example an AC STT waveform, pulse waveform, etc. can be used.

As discussed above, the wire electrodes used in a multi-wire deposition operation (e.g., welding, additive manufacturing, hardfacing, etc.) can be spaced by a distance S that facilitates formation of a bridge droplet between the wire electrodes. The size of the bridge droplet is determined by the spacing between the wire electrodes and the spacing between the exit orifices in the contact tip. The size of the bridge droplet determines the width of the electric arc that exists during the deposition operation, and reducing the spacing between the exit orifices and wire electrodes narrows the arc width. Larger bridge droplets may be preferred for larger welds, and smaller bridge droplets preferred for smaller welds. Deposition rate is impacted by the arc width, and the deposition rate for small gauge wires can be increased by reducing the spacing between the exit orifices and wire electrodes (e.g., from approximately <NUM> to <NUM>).

The maximum spacing between the exit orifices and between the wire electrodes is reached when the magnetic forces developed by the current waveform (e.g., at the peak current level) still allow formation of the bridge droplet, and is exceeded when bridging is no longer possible. The minimum spacing is that which keeps the wires separated at the point of bridging. The magnetic forces tend to pull the wire electrodes together, and the wires are somewhat flexible. Thus, the minimum spacing between the exit orifices and between the wire electrodes will depend on the stiffness of the electrodes, which is impacted by parameters such as wire diameter, material of construction, etc..

<FIG> depicts an end portion of an exemplary welding torch in accordance with the present invention. Because the construction and operation of welding torches is generally known, the details of such construction and operation will not be discussed in detail herein. As shown, the torch includes a number of components and is used to deliver at least two wire electrodes and a shielding gas to a workpiece for a welding or additive manufacturing operation. The torch includes a diffuser <NUM> which aids in properly directing and distributing the shielding gas for a welding operation. Coupled to the downstream end of the diffuser <NUM> is a contact tip <NUM>, which is used to pass the welding current into the at least two wire electrodes which are passing though the contact tip simultaneously during welding. The contact tip <NUM> is configured to facilitate the formation of a bridge droplet between the wire electrodes that are delivered through bores or channels in the contact tip. The bridge droplet couples the first wire electrode to the second wire electrode prior to contacting a molten puddle created by the deposition operation, as discussed above.

Threaded onto the outside of the diffuser <NUM> is an insulator <NUM>. The insulator <NUM> electrically isolates a nozzle <NUM> from the electrically live components within the torch. The nozzle <NUM> directs the shielding gas from the diffuser <NUM> to the distal end of the torch and the workpiece during welding.

Conventional contact tips have threads on an upstream or proximal end of the contact tip that thread into the diffuser. The contact tip and diffuser are connected by screwing the contact tip into the diffuser. Such a fastening system works well for welding with single wires. The welding wire can be threaded through the contact tip and the contact tip can be rotated around the wire multiple times and screwed into the diffuser. However, when welding with multiple welding wires simultaneously passing through the contact tip, such a fastening system would result in an undesirable twisting of the welding wires. For example, if two welding wires are passed through the contact tip, subsequently threading the contact tip onto the diffuser by multiple turns requiring greater than <NUM>° of rotation will result in the welding wires becoming twisted and unable to be fed through the contact tip.

The contact tip <NUM> in <FIG> is attached to the diffuser <NUM> by rotation of the contact tip through less than <NUM>°, such as <NUM>° (three-quarter turn), <NUM>° (one-half turn), <NUM>° (quarter turn), less than <NUM>°, etc. The rotation of the contact tip <NUM> necessary to attach the contact tip to the diffuser <NUM> can be any angle as desired that is preferably less than <NUM>° and results in the multiple wire electrodes passing through the contact tip not becoming unduly twisted during installation of the contact tip. If the welding wires are unduly twisted during installation of the contact tip, wire feeding problems will result and "bird nesting" of the welding wires can occur.

With reference to <FIG>, the contact tip <NUM> is attached to the diffuser <NUM> by a quarter turn, clockwise rotation of the contact tip within the diffuser. The contact tip <NUM> has a forward or downstream distal portion that has a tapered shape and includes flats <NUM> to accommodate gripping by a tool, such as pliers. The contact tip <NUM> has a rearward or upstream proximal portion <NUM> that is generally cylindrical, but includes a radially-projecting tab <NUM> that engages a slot <NUM> in an interior wall of the diffuser <NUM>, to securely connect the contact tip to the diffuser. The rearward portion <NUM> of the contact tip <NUM> is located within the diffuser <NUM> when the contact tip is installed onto the diffuser, and acts as a mounting shank for the contact tip. It can be seen that the diameter of the rearward portion <NUM> of the contact tip is smaller than the adjacent downstream portion, which results in a shoulder <NUM> projecting radially from the cylindrical rearward portion <NUM> of the contact tip. The shoulder <NUM> seats against the terminal end face of the diffuser <NUM> when the contact tip <NUM> is installed onto the diffuser.

The contact tip <NUM> can be made from known contact tip materials and can be used in any known type of welding gun. The contact tip can comprise an electrically-conductive body, such as copper, extending from its rearward, proximal end to its forward, distal end. As shown in this exemplary embodiment, the contact tip <NUM> has two separate wire channels or bores <NUM> and <NUM> which run the length of the contact tip. The channels <NUM>/<NUM> can extend between wire entrance orifices on the proximal end face of the mounting shank <NUM>, and wire exit orifices on the distal end face of the contact tip. During welding, a first wire electrode is delivered through the first channel <NUM> and a second wire electrode is delivered through the second channel <NUM>. The channels <NUM>/<NUM> are typically sized appropriately for the diameter of wire that is to be fed through the channel. For example, if the electrodes are to have the same diameter, then the channels will have the same diameters. However, if different wire sizes are to be used together, then the channels should be sized appropriately so as to properly transfer current to the differently-sized electrodes. Additionally, in the embodiment shown, the channels <NUM>/<NUM> are configured such that the electrodes exit the distal end face of the contact tip <NUM> in a parallel relationship. However, in other exemplary embodiments the channels can be configured so that the electrodes exit the distal end face of the contact tip such that an angle in the range of +/- <NUM>° exists between the centerlines of the respective electrodes. The angling can be determined based on the desired performance characteristics of the welding operation. The example contact tips discussed herein are shown having two electrode bores. However, it is to be appreciated that the contact tips could have bores for more than two electrodes, such as three or more bores.

The slot <NUM> in the interior wall of the diffuser <NUM> includes an axial portion <NUM> and a helical portion <NUM>. The axial portion <NUM> of the slot <NUM> extends to the downstream terminal end face of the diffuser <NUM>, against which the shoulder <NUM> of the contact tip <NUM> seats. After the welding electrodes are fed through the contact tip <NUM>, the radially-projecting tab <NUM> on the mounting shank <NUM> is inserted into the axial portion <NUM> of the <NUM> slot and the contact tip is pushed into the diffuser <NUM>. When the tab <NUM> reaches the helical portion <NUM> of the slot, the contact tip <NUM> is rotated to move the tab to the end of the helical portion. The helical portion <NUM> has a slight upstream pitch that draws the contact tip <NUM> inward as the contact tip is rotated, so that the shoulder <NUM> of the contact tip seats against the downstream terminal end face of the diffuser <NUM>. The tab <NUM> on the mounting shank <NUM> can have a tapered edge <NUM> that matches the pitch of the slot <NUM> in the diffuser <NUM>, to help ensure a tight connection between the two components. In the example embodiment shown, the helical portion <NUM> of the slot <NUM> allows for a quarter turn of the contact tip <NUM> to secure the contact tip to the diffuser <NUM>. However, it is to be appreciated that other rotational angles are possible (e.g., more or less than a quarter turn or <NUM>°). For example, the helical portion <NUM> of the slot can extend less than <NUM>° around the inner circumference of the interior chamber of the diffuser <NUM>.

<FIG> show an example embodiment of a contact tip <NUM> that includes a biasing mechanism to provide an axial force between the contact tip and the diffuser <NUM>. The illustrated biasing mechanism is a bias spring <NUM>, such as a wave washer. The bias spring <NUM> is compressed when the contact tip <NUM> is mounted to the diffuser <NUM>, to maintain an axial force between the contact tip and diffuser. The axial force helps to seat the radially-projecting tab <NUM> on the mounting shank <NUM> in the slot <NUM> in the diffuser <NUM>. In particular, the axial force can push the tapered surface of the tab <NUM> against the sidewall of the slot in the diffuser <NUM>, to help secure the contact tip in place and resist loosening (e.g., due to thermal cycling, mechanical impacts, etc.) The mounting shank <NUM> extends from the shoulder portion <NUM> of the contact tip <NUM>, and the bias spring <NUM> can be arranged annularly around the mounting shank, between the radially-projecting tab and the shoulder portion. The bias spring <NUM> can be captured on the mounting shank <NUM>, such that it cannot be removed without damaging the bias spring or contact tip. Various types of biasing mechanisms could be used to maintain an axial force between the contact tip <NUM> and diffuser <NUM>, such as lock washers or coil springs for example.

<FIG> illustrate a further embodiment of a contact tip <NUM> and diffuser <NUM> for multiwire welding or additive manufacturing. The contact tip <NUM> requires no rotation when installed onto the diffuser <NUM>, as will be described further below. The nozzle <NUM> and insulator portion <NUM> of the welding torch are substantially similar to the embodiment of <FIG>. Also, the contact tip <NUM> includes wire channels <NUM>/<NUM> and a shoulder <NUM> as discussed above.

The contact tip <NUM> and diffuser <NUM> are keyed so that there is only one possible installed orientation between the contact tip and diffuser. The interior surface <NUM> of the diffuser and the rearward portion <NUM> or mounting shank of the contact tip are shown as having corresponding flats that key the diffuser and contact tip. However, other keying mechanisms could be used, such as a slot and projection keying mechanism for example.

After the welding electrodes are passed through the contact tip <NUM>, the contact tip is inserted axially into the diffuser <NUM> without twisting or rotating the contact tip. The diffuser <NUM> is a collet style and clamps tightly against the rearward portion <NUM> of the contact tip, holding it in place by friction. The diffuser <NUM> can include a number slots <NUM>, <NUM>, <NUM> that allow the downstream end of the diffuser to expand slightly as the contact tip <NUM> is inserted into the diffuser. The expansion of the downstream end of the diffuser <NUM> results in a clamping force applied radially onto the rearward portion <NUM> of the contact tip. If desired, an additional clamping mechanism can be used to further secure the contact tip <NUM> within the diffuser <NUM>. For example, a set screw could fasten the contact tip to the diffuser, or a clamp could further compress the downstream end of the diffuser around the rearward portion of the contact tip. Such a clamp could be threaded onto the diffuser such that the clamping force applied to the downstream end of the diffuser is provided by the axial movement of the clamp as it is threaded onto the diffuser.

The use of embodiments described herein can provide significant improvements in stability, weld structure and performance over known welding operations. However, in addition to welding operations, embodiments can be used in additive manufacturing operations. In fact the system <NUM> described above can be used in additive manufacturing operations as in welding operations. In exemplary embodiments, improved deposition rates can be achieved in additive manufacturing operations. For example, when using an STT type waveform in a single wire additive process, using an <NUM>" wire can provide a deposition rate of about <NUM> lb/hr before becoming unstable. However, when using embodiments of the present invention and two <NUM>" wires a deposition rate of 7lbs/hr can be achieved in a stable transfer. Because additive manufacturing processes and systems are known, the details of which need not be described herein. In such processes a bridging current, such as that descried above, can be used in the additive manufacturing current waveform.

It is noted that exemplary embodiments are not limited to the usage of the waveforms discussed above and described herein, as other welding type waveforms can be used with embodiments of the present invention. For example, other embodiments can use variable polarity pulsed spray welding waveforms, AC waveforms, etc. without departing from the scope of the present invention. For example, in variable polarity embodiments the bridge portion of the welding waveform can be done in a negative polarity such that the bridge droplet is created while reducing the overall heat input into the weld puddle. For example, when using AC type waveforms, the waveforms can have a frequency of <NUM> to <NUM> of alternating negative and positive pulses to melt the two wires and form the bridge droplet between them. In further embodiments the frequency can be in the range of <NUM> to <NUM>.

As explained previously, embodiments of the present invention can be used with different types and combinations of consumables including flux cored consumables. In fact, embodiments of the present invention can provide a more stable welding operation when using flux cored electrodes. Specifically, the use of a bridging droplet can aid in stabilizing flux core droplets that can tend to be unstable in a single wire welding operation. Further, embodiments of the present invention allow for increased weld and arc stability at higher deposition rates. For example, in single wire welding operations, at high current and high deposition rates the transfer type for the droplets can change from streaming spray to a rotational spray, which appreciably reduces the stability of the welding operation. However, with exemplary embodiments of the present invention the bridge droplet stabilizes the droplets which significantly improves arc and weld stability at high deposition rates, such as those above 201b/hr.

Additionally, as indicated above the consumables can be of different types and/or compositions, which can optimize a given welding operation. That is, the use of two different, but compatible, consumables can be combined to create a desired weld joint. For example, compatible consumables include hardfacing wires, stainless wires, nickel alloys and steel wires of different composition can be combined. As one specific example a mild steel wire can be combined with an overalloyed wire to make a <NUM> stainless steel composition. This can be advantageous when a single consumable of the type desired does not have desirable weld properties. For example, some consumables for specialized welding provide the desired weld chemistry but are extremely difficult to use and have difficulty providing a satisfactory weld. However, embodiments of the present invention allow for the use of two consumables that are easier to weld with to be combined to create the desired weld chemistry. Embodiments of the present invention can be used to create an alloy/deposit chemistry that is not otherwise commercially available, or otherwise very expensive to manufacture. Thus, two different consumables can be used to obviate the need for an expensive or unavailable consumable. Further, embodiments can be used to create a diluted alloy. For example, a first welding wire could be a common inexpensive alloy and a second welding wire could be a specialty wire. The desired deposit would be the average of the two wires, mixed well in the formation of the bridged droplet, at the lower average cost of the two wires, over an expensive specialty wire. Further, in some applications, the desired deposit could be unavailable due to the lack of appropriate consumable chemistry, but could be reached by mixing two standard alloy wires, mixed within the bridged droplet and deposited as a single droplet. Further, in some applications, such as the application of wear resistance metals, the desired deposit may be combination of tungsten carbide particles from one wire and chrome carbide particles from another. Still in another application, a larger wire housing larger particles within is mixed with a smaller wire containing fewer particles or smaller particles, to deposit a mixture of the two wires. Here the expected contribution from each of the wires is proportional to the size of wire given the wire feed speeds are same. In yet another example, the wire feed speeds of the wires are different to allow the alloy produced to change based on the desired deposit but the mixing of the wires is still produced by the bridged droplet created between the wires.

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 scope of the invention as defined by the following claims.

Claim 1:
An additive manufacturing contact tip (<NUM>), comprising:
an electrically-conductive body extending from a proximal end of the body to a distal end of the body, the body forming:
a first channel (<NUM>, <NUM>) terminating at a distal end face of the body; and
a second channel (<NUM>, <NUM>) terminating at the distal end face of the body; wherein, at the distal end face of the body, the first channel (<NUM>, <NUM>) and the second channel (<NUM>, <NUM>) are separated from each other by a distance, wherein said distance provides a spacing (S) between the first wire electrode (E1, E2) and the second wire electrode (E1, E2) that is within a range of <NUM> to <NUM> times a diameter of the first and second wire electrodes (E1, E2), as measured between closest edges of the first and second wire electrodes (E1, E2), and being configured to facilitate formation of a bridge droplet between a first wire electrode (E1, E2) delivered through the first channel (<NUM>, <NUM>) and a second wire electrode (E1, E2) delivered through the second channel (<NUM>, <NUM>) during a deposition operation, wherein the current is passing through each of the electrodes (E1, E2), and wherein the bridge droplet couples the first wire electrode (E1, E2) to the second wire electrode (E1, E2) prior to contacting a molten puddle created by the deposition operation, wherein the body includes a mounting shank (<NUM>), and one or more entrance orifices, preferably the first entrance orifice and/or the second entrance orifice are located on the mounting shank (<NUM>), and the mounting shank (<NUM>) includes a radially-projecting tab (<NUM>), further comprising a bias spring located between the radially-projecting tab (<NUM>) and the distal end face of the body, or located between the radially-projecting tab (<NUM>) and the distal end of the body, and wherein the mounting shank (<NUM>) extends from a shoulder portion of the contact tip (<NUM>, <NUM>), and the bias spring is arranged annularly around the mounting shank (<NUM>) between the shoulder portion and the radially-projecting tab (<NUM>).