Patent Application
20100270269
The invention relates to a welding apparatus.
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.
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.
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.
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.
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.
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.
Referring to the drawings, wherein like reference numbers refer to like components throughout the several views,
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.
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 12B, 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.
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.
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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.
