This invention generally relates to gas metal arc welding (GMAW) and flux core arc welding (FCAW). In particular, the invention relates to wire feeding guns.
Wire feeding guns must perform several different functions in order for successful welding to occur. Those functions include directing the weld wire to the workpiece, conducting electric power to the weld wire, and shielding the welding arc from atmospheric air. In addition to the foregoing basic requirements, it is highly desirable that the weld wire be fed to the workpiece at an adjustable rate that suits the particular welding operation at hand. For maximum productivity, it is also necessary that the gun be very comfortable for the operator to maneuver as he directs the weld wire to the workpiece.
To satisfy the foregoing requirements, the wire feeding gun is connected by a long flexible cable to a wire feeder, which is wired to a welding machine. The wire feeder supplies the weld wire, electric power, cooling fluid, and shielding gas through the cable to the gun. In some instances, the cable may be as long as 50 feet.
In a typical wire feeding gun arrangement, there is a head tube on the end of the handle opposite the flexible cable. A diffuser is joined to the free end of the head tube. A contact tip is connected to the diffuser. The weld wire is guided by a liner, placed inside the head tube, that extends from the handle to the diffuser. From the diffuser, the weld wire passes through the contact tip, from which it emerges under the impetus of the feed mechanism.
In gas-shielded applications, it is vital that the gas adequately shield the welding arc from the ambient atmosphere. For that purpose, gas is supplied to the wire feeding gun from the wire feeder through the flexible cable. The gas is directed through the head tube to the interior of the diffuser. The gas flows from the diffuser to a nozzle that surrounds the contact tip. The gas then flows out the nozzle and surrounds the contact tip and the weld wire emerging from the contact tip. The gas thus shields the weld wire and the welding arc from the ambient atmosphere.
In known MIG welding guns of the type disclosed in U.S. Pat. No. 6,225,599, the nozzle assembly is insulated by a tubular insulator from an electrically hot conductor that conducts welding power from the gun handle to the diffuser. Accordingly, the diffuser is electrically hot. Another insulator is supported by the diffuser to separate the electrically hot conductor and diffuser from the electrically cold head tube exterior, locking nut, and nozzle. The contact tip can be connected to the diffuser by a nut, in which case, both the contact tip and nut are electrically hot. The contact tip transmits the welding electrical power from the diffuser and the conductor to the weld wire. The contact tip may be screwed into the diffuser.
In a known MIG welding gun, the welding electrical power is transmitted from the gun body to a brass fitting, which in turn transmits the welding electrical power to the aforementioned conductor. That brass fitting was designed with a frusto-conical surface that seats inside and against a frusto-conical surface formed in the distal end of the gun body. These engaging frusto-conical surfaces provide a self-centering of the brass fitting relative to the distal end of the gun body. The brass fitting is captured between a rotation nut and the distal end of the gun body, the latter having a threaded outer periphery that is threadably engaged by a threaded bore inside the rotation nut. The known rotation nut comprises a threaded brass nut encased in a shroud of molded nylon.
In this known MIG gun arrangement, current is carried from the gun body to the brass fitting across the aforementioned frusto-conical interface. This caused problems because the fit between the two frusto-conical surfaces was not always tight due to manufacturing tolerances and the current passing between them caused pitting and corrosion. Once pitting and corrosion started, the fit would deteriorate further, giving rise to a compounding problem. Furthermore, the brass fitting and gun body distal portion also had a non-frusto-conical interface where water was present, which could sometimes compound the problem if the head tube were mishandled. Corrosion at the frusto-conical interface could ultimately cause binding of the head tube assembly to the gun body.
There is a need for an improved mechanical interface between the head tube assembly and the welding gun body that will not be afflicted by pitting and corrosion, and that will not cause the binding of the head tube to the gun body.
The invention is directed to a welding gun in which a mechanical interface between the gun body and the head tube assembly is electrically insulated, and electric current is transferred through a rotation nut or other fastener that holds the head tube assembly and the gun body together.
One aspect of the invention is a welding gun comprising an electrically conductive gun body and a head tube assembly supported by the gun body, the head tube assembly comprising: an electrically conductive filling comprising an end that is engaged with the gun body; an electrically conductive tube comprising an end in contact with the fitting; a retaining device comprising an electrically conductive portion that is in contact with and coupled to the gun body and in contact with the fitting, the retaining device retaining the fitting in engagement with the gun body when the retaining device is coupled to the gun body; and an electrical insulator disposed between and in contact with respective portions of the fitting and the gun body.
Another aspect of the invention is a welding gun comprising an electrically conductive gun body and a head tube assembly supported by the gun body, the gun body comprising a threaded outer peripheral surface and a cavity defined in part by a frusto-conical inner peripheral surface, and the head tube assembly comprising: an electrically conductive fitting comprising an end that is received in the cavity of the gun body; an electrically conductive tube comprising an end supported by the fitting; a rotation nut comprising an electrically conductive portion that is in contact with the gun body and the fitting, the electrically conductive portion comprising a threaded inner peripheral surface that threadably engages the threaded outer peripheral surface of the gun body; and an electrical insulator disposed between and in contact with the fitting and the frusto-conical inner peripheral surface of the gun body. The rotation nut fastens the fitting to the gun body when the rotation nut is threadably engaged with the gun body.
A further aspect of the invention is a welding gun comprising: an electrically conductive gun body comprising a passageway, the passageway comprising a circular cylindrical inner peripheral surface and a frusto-conical inner peripheral surface; an electrically conductive fitting comprising a passageway, a collar and a circular cylindrical outer peripheral surface located inside the circular cylindrical inner peripheral surface of the gun body; an electrically conductive tube having one end supported in the passageway of the fitting and projecting forward of the fitting; an electrically insulative ring comprising a frusto-conical outer peripheral surface in contact with the frusto-conical inner peripheral surface of the gun body and a circular cylindrical inner peripheral surface in contact with the circular cylindrical outer peripheral surface of the fitting; and a retaining device comprising an electrically conductive portion that is in contact with and coupled to the gun body and in contact with the fitting. The retaining device retains the fitting in engagement with the gun body when the retaining device is coupled to the gun body.
Yet another aspect of the invention is a welding gun comprising: an electrically conductive gun body comprising a passageway; an assembly comprising a sequence of electrically conductive components connected in series to form a conductive path for electric current and a passageway for welding wire, one that retains the assembly in the inserted state when the rotation nut is threadably coupled to the gun body; and an electrically insulative ring installed between an electrically conductive portion of the gun body and an electrically conductive portion of the assembly. The ring comprises a frusto-conical outer peripheral surface.
A further aspect of the invention is a method of assembling a welding gun, comprising the following steps: sliding a ring of electrically insulative material onto an end portion of a head tube assembly until the ring is proximal to a first portion of the end portion of the head tube assembly having a maximum dimension greater than an inner diameter of the ring, the ring having a frusto-conical outer peripheral surface; inserting a second portion of the end portion of the head tube assembly into a cavity of a gun body until the frusto-conical outer peripheral surface of the electrically insulative ring engages a frusto-conical inner peripheral surface of the gun body cavity; and fastening the head tube assembly to the gun body
Other aspects of the invention are disclosed and claimed below.