Abstract:
A welding torch is provided that includes a motorized arrangement for advancing continuous electrode wires during welding. The torch has a pair of rollers that contact the electrode wire to force it through the torch during welding. A force adjustment selector is provided in the torch handle that allows the operator to alter the force or pressure applied to the electrode wire. Markings on the handle, or stops provided between the selector and the handle allow for easy adjustment and verification of the proper pressure or force applied for specific types of electrode wires.

Description:
BACKGROUND 
     The present invention relates generally to welding systems, and more particularly to a technique for advancing a wire electrode in a welding gun. 
     A wide range of welding techniques have been developed and are presently in use. Arc welding is a prominent and important class of welding in which an electric arc is established between a welding electrode and a work piece. The arc generally results from electrical power supplied to the electrode from a welding power supply. The power supply channels welding current to a welding gun or torch in which the electrode is placed. The gun is coupled to a cable that extends back to the power supply. The work piece is typically grounded, or at a polarity opposite that of the electrode. As the electrode is approached closely to or contacts the work piece, and arc is established that produces heat needed for melting either the work piece or the electrode or both. 
     One type of arc welding is generally referred to as metal inert gas (MIG) welding. In MIG welding, a continuous wire electrode is fed from a spool to the welding gun and from a tip of the welding gun to the location where the arc is established. The electrode is charged, such that the arc is established between the advancing wire electrode and the work piece. In many applications, an inert gas is also channeled to the welding gun tip to surround the weld and protect the weld both while the weld joint is molten and during solidification of the weld. Other wire electrode welding techniques do not use such gasses, but may rely upon a flux core within the wire electrode. 
     In welding applications employing wire electrodes, a challenge consists in driving the electrode toward the welding gun tip in a controlled and predictable manner. Current technologies for driving wire electrodes include driving one or more rollers that capture the continuous wire electrode therebetween, and drive the electrode towards the tip. The rollers are often positioned in the welding gun or handle itself, and a small drive motor powers a drive roller to advance the electrode, which is sandwiched between the moving rollers. 
     One difficulty in such arrangements is the need to provide the proper force or pressure on the electrode positioned between the rollers. Different sizes and types of wire electrode are available, and these typically require different roll pressures. For example, hand-held motorized welding torches may be used to feed relatively soft aluminum wire electrode (e.g., 4000 series), and also relatively harder aluminum wire electrodes (e.g., 5000 series) in a single handle arrangement. The softer electrodes require less roll pressure than the harder electrodes. If the roll pressure is too low, the wire electrode may seize in the contact tip of the torch. Excessive roll pressure, on the other hand, may cause the wire to be bent or wavy as it exits the contact tip. This waviness may complicate the welding operation by providing a relatively unpredictable location in which the electrode will contact the work piece. Electrode roll pressure is particularly problematic in pulsed MIG welding, where the harder aluminum wire electrode with an excessively low roll pressure will tend to withdraw an arc into the tip, and excessively high pressures will cause the electrode to drive through the point where the arc is concentrated, bending the wire. 
     Current approaches to adjustment of the roll pressure for motorized hand-held continuous electrodes basically rely upon trial and error in the adjustment process. The operator typically has little or no feedback from the device as to the level of pressure being applied on the electrode. Consequently, improper roll pressure in such applications is a continuing problem. 
     There is a need, therefore, for an improved technique for controlling roll pressure for advancement for continuous wire electrodes for welding applications. There is a particular need for a technique that provides user feedback and facilitates the adjustment operation when the nature of the electrode demands such adjustment. 
     BRIEF DESCRIPTION 
     The invention provides a novel arrangement for adjusting roll pressure in such applications designed to respond to these needs. The invention may be implemented in a range of welding settings, and is particularly well-suited to all continuous wire electrode applications, such as MIG welding. The invention is also particularly well-suited to arrangements in which a hand-held motorized welding torch allows for adjustment of roll pressure for continuous feed of wire electrodes. The electrodes may be flux cored electrodes or electrodes used with shielding gasses or other shielding media. 
     In accordance with certain aspects of the invention, a system for adjusting drive pressure on a continuous wire welding electrode is provided. The system includes a pair of rollers configured to capture the electrode wire therebetween. The rollers may be positioned in a motorized assembly within a welding torch. A pressure adjustment assembly is coupled to one of the rollers and configured to permit operator adjustment of a force urging the coupled roller towards the other roller. An operator indicator provides feedback to a welding operator of which of a plurality of preset force settings for the pressure adjustment assembly is currently set. 
     The arrangement may include a rotary adjustment mechanism, such as a screw that compresses a spring, the spring applying the desired force on an arm that supports one of the rollers. The feedback may be provided in the form of a mark or other indicia on the adjustment mechanism, along with marks on the torch handle that indicate either the force applied, or the electrode to which the force is matched, or some other indication of the current adjustment. The arrangement may further include one or more stops or detents that limit travel of the adjustment mechanism, further providing feedback to the operator and facilitating proper adjustment. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is perspective view of an exemplary welding torch for MIG welding incorporating aspects of the present invention; 
         FIG. 2  is a partially opened handle of the type shown in  FIG. 1  illustrating various parts of the roll pressure control arrangement of the invention; 
         FIG. 3  is a more detailed view of the components shown in  FIG. 2 ; and 
         FIG. 4  is an exploded view of the components shown in  FIG. 3 , illustrating a present embodiment for controlling electrode drive roll pressure. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings, and referring first to  FIG. 1 , a welding torch is illustrated and designated generally by reference numeral  10 . As will be appreciated by those skilled in the art, the torch, when placed in service, will be coupled to a source of welding power, as well as to other resources, such as a source of continuous wire electrode. The wire electrode and power source are typically provided in a welding base unit (not shown) which may be designed for drawing electrical power from the power grid or from a mobile power sources, such as an engine-driven generator (not shown). The welding resources, in the illustrated embodiment, may also typically include a source of inert gas which can be used to surround the electrode and weld during the welding operation. The illustrated welding torch is designed for MIG welding, such as with different sizes and grades of aluminum electrode wire. 
     The welding torch  10  shown in  FIG. 1  has a body or handle  12  that terminates in a neck  14  and tip  16 . In general, the welding resources, including the wire electrode, electrical power, and any shielding media will be delivered by a series of conduits  18  coupled to a rear end of the body  12  opposite the neck  14  and tip  16 . A welding cable (not shown) is typically coupled to the conduits and provides a flexible link to the welding base unit. As will be appreciated by those skilled in the art, electrical current is conducted through one of these conduits in which the wire electrode passes. The electrode passes through the body  12  of the torch and is captured between rollers  20  and  22  which apply a drive pressure to the electrode sufficient to draw the electrode from a remote spool (not shown), through the handle, and to force the electrode through the neck  14  and tip  16 . Within the tip  16 , a contact tip (not shown) will contact the electrode and apply the welding current to it prior to exiting the torch. Ultimately, the electrode, indicated by reference numeral  24  in  FIG. 1 , will exit the torch at the location of a desired weld joint. 
     As will be appreciated by those skilled in the art, to control the advancement of the welding electrode, and the application of electrical power to the electrode, and the flow of shielding media, where provided, the torch  10  is provided with a trigger  26 . The trigger, which is spring biased to an OFF position can be depressed to close an internal switch within the torch that activates the supply of welding resources. In particular, the switch (not shown) will energize a small electric motor that drives one or both of the rollers to advance the electrode toward the torch tip. In the illustrated embodiment, roller  20  is a drive roller, and includes a ridged or knurled outer surface that contacts the wire electrode. The other roller  22  is an idler in the present application. The rollers are urged into contact with the electrode as described in greater detail below. 
     In accordance with the present invention, and as illustrated in  FIG. 1 , the welding torch  10  includes a force or pressure adjustment selector  28  that can be manipulated to adjust the force or pressure applied between the rollers  20  and  22 , and thereby to the wire electrode. Stops may be provided for pre-selected forces or pressures, as described below. Indicators  30  are also provided in the body  12  of the torch that offer visual indications of the force or pressure setting between the rollers. Those skilled in the art will recognize that, in the illustrated arrangement of  FIG. 1 , an upper enclosure panel or door has been removed for exemplary purposes. That is, in use, the rollers  20  and  22  are typically covered by a panel that can be opened and closed, and maintained closed, so as to avoid damage to the internal components of the handle or to the advancing wire electrode. 
       FIG. 2  illustrates the same welding torch of  FIG. 1  but with a back panel or handle shell removed, and with the handle shell shown in  FIG. 1  rotated out to show both the components of the torch and the internal configuration of the torch handle. The handle shell  32  may, as in the illustrated embodiment, include internal features that facilitate adjustment of the drive roll pressure applied to the wire electrode. In the illustrated embodiment, the handle shell  32  is made of a hard moldable plastic material with features designed to permit access to the force adjustment selector  28 . These include an aperture  34  through which the selector  28  is accessed and may be rotated. An internal rib  36  serves to maintain alignment of the force adjustment selector  28  once the handle is assembled. Moreover, optional stops or abutments  38  are provided that serve to limit travel or rotation of the force adjustment selector  28  as described in greater detail below. 
     In the illustrated embodiment, the force adjustment selector  28  includes a button  40  that has a central opening or slot  42  for forcing rotation of the selector. That is, a tool, such as a screwdriver, can be inserted into the slot to rotate the selector, with access being provided via the aperture  34  in the handle shell as described above. 
     As best illustrated in  FIG. 3 , the button may also include an extension  44  that serves as a stop when abutments  38  are provided in the handle shell. That is, the button  40 , upon assembly of the handle, is positioned radially inward of the rib  36 , and can be rotated until the extension  44  contacts one of the abutments  38 . The abutments, thus, limit rotation of the selector. 
     As shown in  FIGS. 2 and 3 , the idler roller  22  is disposed on a pressure arm  46  that can be pivoted generally horizontally in the illustrated view. That is, arm  46  on which the idler roller  22  is held, can be pivoted toward the left in the figures, but is urged toward the right by spring pressure as described below. A lever or cam (not shown in the figures) may be provided for drawing the arm toward the left against the spring pressure to open a space between the rollers  20  and  22 , such as for initially inserting the wire electrode therebetween. The pivot point for arm  46  is slightly rear of the force adjustment selector  28  in the present embodiment. However, other arrangements may certainly be envisaged in which pressure is applied to the rollers through arms arranged differently, with pivot points differently positioned, as well as through other mechanical arrangements differing in style from that shown. The drive roller  20 , as noted above, has ridges, knurled or contoured surfaces that can be seen best in  FIG. 3 , while the idler roller has a groove  48  for receiving and directing the wire electrode between the rollers (the electrode not being shown in the figures for clarity). In certain arrangements, the drive roller may not be ridged, but may include a groove similar to the idler roller. 
     The same components are illustrated in  FIG. 4 , but with the basic components of the force adjustment selector  28  exploded to the left. In the present embodiment, the button  40  is provided with a position indicator  50 , such as a mark or groove. As will be appreciated by those skilled in the art, the position indicator  50  may be aligned with the settings  30  indicated in  FIG. 1  as the button is rotated by operator, providing a visual feedback of the position of the selector and thereby of the force or pressure setting corresponding to the rotational position of the indicator  50 . 
     The pressure arm  46  has an aperture or recess  52  formed therein, in which a compression spring  54 , or similar resilient force-creating member is positioned. A screw  56  extends through this spring and into aperture  52 , and is threaded into a mounting member  58  or support structure on which the pressure arm is pivoted. In the illustrated embodiment, the pressure arm is held on the mounting member  58  via a pivot pin  60  about which the arm can pivot during adjustment of the assembly. The compression spring  54  is thus captured between a bottom annular surface (not shown) of the recess  52  in the pressure arm and the head of the screw  56 . In a present embodiment, washers (not shown) are placed on either end of the spring to act as bearings, although the arrangement may be configured without these. Turning the screw  56  thereby compresses the spring  54  between the annular base of the pressure arm and the head of the screw. The degree of engagement of the screw with a corresponding threaded hole in the support structure on which the arm is mounted thereby determines the force or pressure exerted on the pressure arm, and thereby the force or pressure exerted between the rollers  20  and  22 . The button  40  has an inner surface that interfaces with ridges or other torque-conveying structures formed in the head of the screw  56 . Thus, rotation of the button  40  causes rotation of the screw  56 , and alters the pressure between the rollers  20  and  22  by altering the distance between the bottom of the head of screw  56  and the surface internal to the pressure arm against which the compression spring  54  bears. As will be appreciated by those skilled in the art, the change in this distance, in combination with the spring constant of the compression spring  54 , allows for various forces or pressures to be applied to the wire electrode when positioned between the rollers. 
     During assembly, prior to securing the handle shells on the welding torch, spring  54  is inserted into recess  52  of the pressure arm, and screw  56  is threaded into the threaded hole in the support member. The screw is then threaded into place to provide a desired preload to the compression spring  54  and thereby to the idler roll  22 . Once the desired preload is achieved the button  40  is placed over the head of the compression spring  56  with the indicator  50  appropriately oriented for the preload force. Thereafter, the handle shell may be installed. 
     Referring back to  FIG. 1 , then, the selector  28  can be rotated as described above to adjust the compression of the spring  54  as shown in  FIG. 4 , and thereby the force or pressure applied to the idler roller  22 . The settings  30  indicated by molded-in or added markings on the welding torch provide a guide and feedback for the welding operator for changing or setting the drive roll pressure, particularly useful when the type of electrode utilized is changed. In a present embodiment, for example, the settings  30  clearly indicate specific types of electrode wire, such as 4000 series aluminum wire electrode and 5000 series aluminum electrodes. More settings may, of course, be provided, as may settings for other types of wire electrodes. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.