Abstract:
A welding apparatus for welding a work piece is provided that has a weld gun with a nozzle body having an inner surface defining a cavity, and a distal opening forming a nozzle orifice. An electrode extends in the cavity and is configured to be positionable proximate the work piece. The weld gun is configured to provide a flow of shielding gas through the nozzle orifice. The welding apparatus is configured to position the nozzle orifice at a distance from the work piece sufficient to cause the inner surface to direct weld spatter to a weld pool on the work piece adjacent the nozzle. Additionally, the distance is such that laminar flow of the shielding gas is maintained under the predetermined gas flow rate.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a welding apparatus. 
       BACKGROUND OF THE INVENTION 
       [0002]    Robotic welding assemblies are commonly used to weld manufactured components, such as vehicle components. Gas metal arc welding, including metal inert gas (“MIG”) welding, is a high deposition rate process suitable for high production welding applications, such as assembly line processes. Wire is continuously fed from a spool, and a shielding gas is emitted around the area to be welded in order to keep ambient air away from the weld surface, as air tends to oxidize the weld, making the weld porous. A common problem with MIG welding is weld spatter, i.e., pieces of weld or weld material that break free from the wire or from the weld pool, wasting material and creating cleanup issues. 
       SUMMARY OF THE INVENTION 
       [0003]    A welding apparatus for welding a work piece is provided that has a welding gun with a nozzle body having an inner surface defining a cavity, and a distal opening forming a nozzle orifice. An electrode extends in the cavity and is configured to be positionable proximate the work piece. The weld gun is configured to provide a flow of shielding gas through the nozzle. The welding apparatus is configured to position the nozzle orifice at a distance from the work piece sufficient to cause the inner surface to direct weld spatter to a weld pool on the work piece adjacent the nozzle. Additionally, the distance is selected such that laminar flow of the shielding gas is maintained under the predetermined gas flow rate. A controller may be used to establish the position and maintain the laminar flow. The laminar flow helps reduce turbulence in the area of the weld pool, provide adequate protection of the weld pool from ambient air and reduces the tendency to blow the weld spatter away from the weld pool, and instead promotes the ability of the weld gun nozzle to direct the spatter into the weld pool, or toward the weld pool to be pulled therein via surface tension. This reduces waste of the weld material, e.g., reduces stray spatter, and promotes the ability of the shielding gas to minimize oxidation of the weld, to prevent poor porosity. Additionally, the relatively small distance reduces required flow rate of the shielding gas, minimizing energy costs. 
         [0004]    Various embodiments of the welding gun are provided, including, without limitation, an embodiment with a nozzle body having a concave inner surface to direct weld spatter, an embodiment with a threaded, removable extended nozzle portion, and various spring-loaded nozzle embodiments that allow the nozzle body to spring back to a position in which the nozzle orifice is at a desired distance from the work piece if temporarily displaced, such as when bumped by a work piece. 
         [0005]    The predetermined position may be electronically controlled, such as by a robotic welding apparatus that includes a base configured to support the work piece during welding, a welding gun defining a cavity surrounding an electrode and having a distal opening forming a nozzle orifice configured to be positionable proximate the work piece, with the weld gun being configured to provide a flow of shielding gas through the cavity and nozzle orifice. A controller is operatively connected to the welding gun and is operable to position the nozzle orifice, preferably not more than 3 millimeters from the work piece during the welding. 
         [0006]    A method of welding a work piece thus includes controlling a distance between the welding gun and the work piece when welding the work piece to permit weld spatter to deflect off of the welding gun nozzle into or toward a weld pool on the work piece, while also controlling a rate of shielding gas flow through the weld gun so that laminar flow of shielding gas from the weld gun is maintained. 
         [0007]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic illustration in partial cross-sectional side view of a first embodiment of a welding apparatus; 
           [0009]      FIG. 2  is a schematic illustration in partial cross-sectional side view of a second embodiment of a welding apparatus; 
           [0010]      FIG. 3  is a schematic illustration in partial cross-sectional side view of a third embodiment of a welding apparatus; and 
           [0011]      FIG. 4  is a schematic illustration in partial cross-sectional side view of a fourth embodiment of a welding apparatus. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,  FIG. 1  shows a robotic welding apparatus  10  that includes a welding gun  11  with a nozzle body  12 A,  12 B having a first nozzle body portion  12 A and a second nozzle body portion  12 B, each having threads, outer threads  50  and inner threads  52 , respectively, matable with one another. Nozzle body portion  12 B has a cavity  13  and a distal opening  14  forming a gas nozzle orifice  15 . The nozzle body portion  12 B has a concave inner surface  31 . In an alternative embodiment, the nozzle body portions  12 A,  12 B may be integrated as a single, unitary piece. In other alternative embodiments, the inner surface may be straight, rather than concave. An electrode wire, referred to herein as the electrode  29 , is shown in part. A remaining portion of the electrode  29  is spooled, and fed into the nozzle body  12 A,  12 B as the electrode is consumed during welding, as is known. A power supply  17  provides electrical power to the electrode  29 . 
         [0013]    The gun  11  is preferably a MIG-type welding gun, and is used to weld a work piece  16 . The welding gun  11  is mounted to a robotic assembly, represented by a robot arm  18 , that is electronically, hydraulically, pneumatically, or otherwise powered to move the welding gun  11  and thereby control the position of the gun  11  and nozzle orifice  15  relative to the work piece  16 . The work piece  16  is mounted on a base  20  during welding, and may be clamped or otherwise secured thereto. Position sensors  22  are secured to the base  20  and to the gun  11 . The position sensors  22  are operatively connected to an electronic controller  24 , which contains a processor with an algorithm configured to interpret position data retrieved from the sensors  22  and control the arm  18  to reposition the gun  11  as necessary in order to maintain a desired position of the gun  11  relative to the work piece  16 . The controller  24  also controls the power supply  17 . 
         [0014]    Specifically, the controller  24  is programmed to position the nozzle orifice  15  a distance D from a surface  26  of the work piece  16 . Alternatively, the distance D may be established from the surface of the base  20  facing the gun  11 . In either case, the distance D is selected to allow the nozzle orifice  15  to be sufficiently close enough to the work piece  16  so that weld spatter  28  (created by the electrode  29  or by the resulting arc  30  between the electrode  29  and work piece  16 ) that is initially ejected from a weld pool  32  will enter into the cavity  13  and deflect off of an inner surface  31  of the nozzle body portion  12 B, and back into the weld pool  32  situated below the nozzle orifice  15 . The spatter  28 , and other spatter referred to in the drawings, may deflect several times off of the inner surface  31  before deflecting back to the weld pool  32 . Typically, weld guns are spaced too far from a work piece  16  to enable redirection of weld spatter in this manner. This is partly due to shielding gas  34  flowing out of the opening. Shielding gas  34  is used to protect the electrode, arc and weld pool from ambient air, as air tends to oxidize the weld, leading to porosity that can weaken the weld. Additionally, the shielding gas provides a buffer to prevent drafts in the surroundings from affecting the arc and weld pool. A significant flow rate of shielding gas is typically required in order to accomplish these objectives. With a relatively high flow rate, a large gap is required between the work piece and the nozzle orifice in order to maintain laminar flow of the gas. 
         [0015]    The controller  24  controls the flow rate of shielding gas from a gas supply  36  in order to maintain laminar flow at the nozzle orifice  15 . Specifically, the controller  24  may control the position of a valve  38  to vary the flow rate of shielding gas. Thus, laminar flow is maintained while a predetermined distance D is also maintained. The distance D is determined based on a variety of factors, such as the expected size of the weld pool  32 , the size of nozzle orifice  15 , the material of both the work piece  16  and electrode  29 . 
         [0016]    In  FIG. 1 , the weld spatter  28  ejected from weld pool  32  hits the inner surface  31  of nozzle body portion  12 B at a position  28 A, is deflected off of inner surface  31  to a position  28 B in which it is used in the weld pool  32 . A separate weld spatter  28 D ejected from weld pool  32  is directed to position  28 E and then deflected to position  28 F, at which it is close enough to the weld pool  32  such that surface tension of the pool  32  will pull the spatter at position  28 F into the pool  32 . Accordingly, the apparatus  10  is configured so that weld spatter  28 ,  28 D is captured and redirected to be used for its intended purpose (forming a weld). It is noted that the nozzle body portion  12 B has a concave shape at the inner surface  31 , which helps in to focus and redirect the spatter toward the center of the cavity  13 , to enable its use in the weld pool  32 . 
         [0017]    Referring to  FIG. 2 , another embodiment of a robotic welding apparatus  110  is shown. The welding apparatus  110  has a weld gun  111  that has a nozzle body  112 A,  112 B formed from a first nozzle body portion  112 A and a second nozzle body portion  112 B. A coil spring  140  is positioned between an end of the first nozzle body portion  112 A and an annular shoulder  142  of the second nozzle body portion  112 B that protrudes inward in the cavity  113  formed by the nozzle body portions  112 A,  112 B. An outward-protruding annular lip  144  of the first nozzle body portion  112 A interferes with an inward protruding annular lip  146  of the second nozzle body portion  112 B to establish one extreme in relative axial positions of the nozzle body portions  112 A,  112 B. The second nozzle body portion  112 B is biased to the position shown, but is free to move axially relative to the first nozzle body portion  112 A (upward in the view of  FIG. 2 ), if the spring  140  is compressed, such as if the work piece  16  bumps the nozzle body portion  112 B. Without an external force, the spring  140  will return the second nozzle body portion  112 B to the position shown. The second nozzle body portion  112 B may be referred to as a nozzle extension and defines a distal opening  114  and a gas nozzle orifice  115  for laminar flow of the shielding gas  34 . Weld spatter  28 G and  28 H are shown in the process of being deflected by the inner surface  131  of the second nozzle body portion  112 B toward the weld pool  32 . 
         [0018]    Referring to  FIG. 3 , another embodiment of a robotic welding apparatus  210  is shown. The welding apparatus  210  has a weld gun  211  that has a nozzle body  212 A,  212 B formed from a first nozzle body portion  212 A and a second nozzle body portion  212 B. The first nozzle body portion  212 A has an outwardly-threaded portion  250 . The second nozzle body portion  212 B has an inwardly-threaded portion  252 , configured to be threaded onto the first nozzle body portion  212 B to define cavity  213  therewith. The second nozzle body portion  212 B may be referred to as a nozzle extension, and defines a distal opening  214  and a gas nozzle orifice  215  for laminar flow of the shielding gas  34 . Weld spatter  281  is shown in the process of being deflected by the inner surface  231  of the second nozzle body portion  212 B toward the weld pool  32 . The apparatus may have a design advantage in that only the relatively inexpensive and easily removable second nozzle body portion  212 B may need replacement after wear. 
         [0019]    Referring to  FIG. 4 , another embodiment of a robotic welding apparatus  310  is shown. The welding apparatus  310  has a weld gun  311  that has a nozzle body  312 A,  312 B formed from a first nozzle body portion  312 A and a second nozzle body portion  312 B. The second nozzle body portion  312 B is a coil spring that is connected to the first nozzle body portion  312 A at an annular shoulder  360  of the first nozzle body portion  312 A. The second nozzle body portion  312 B may be referred to as a nozzle extension, and defines a distal opening  314  and a gas nozzle orifice  315  for laminar flow of the shielding gas  34 . Similar to the embodiment of  FIG. 2 , the nozzle body  312 B is temporarily compressed if work piece  16  bumps the second nozzle body portion  312 B. The second nozzle body portion  312 B will compress relative to the first nozzle body portion  312 A, and then return to the position shown in  FIG. 4 , under the control of the controller  24 , to provide laminar flow of the shielding gas  34 . Weld spatter  28 J is shown in the process of being deflected by the inner surface  331  of the second nozzle body portion  312 B toward the weld pool  32 . The spring pitch (i.e., axial distance between turns of the spring of the second nozzle body portion  312 B) and the spring diameter (i.e., diameter of the spring wire of second nozzle body portion  312 B) may be optimized to produce optimal laminar gas flow and spatter redirecting capability. 
         [0020]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.