Metal deforming – By use of tool acting during relative rotation between tool... – With tool surface orbiting around axis parallel to direction...
Reexamination Certificate
1999-09-22
2001-10-16
Tolan, Ed (Department: 3725)
Metal deforming
By use of tool acting during relative rotation between tool...
With tool surface orbiting around axis parallel to direction...
C140S147000
Reexamination Certificate
active
06301944
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of fabricating welding wire and particularly relates to fabricating weld wire having increased hardness and low cast in a continuous length for winding on a spool.
BRIEF SUMMARY OF THE INVENTION
Welding in locations having severely restricted physical access requires mechanized welding equipment to deliver the welding torch to the work surface. For processes using a non-consumable electrode and a wire feed such as tungsten inert gas welding, laser or electron beam welding (with wire feed) and plasma arc welding, the position of the wire as it enters the weld pool and the clearance of the wire to the electrode or power beam are difficult to control if the wire has continuously changing curvature, commonly called “cast.” Cast is the permanent curvature remaining in wire which has been bent past its elastic limit, such as typically remains in wire after being unwound from a spool. Low-cast wire therefore has a very large radius of curvature; cast-free wire is essentially straight. The cast of spooled wire is a result of having been permanently bent as it was wound onto a spool hub and varies greatly as the wire on the outer layers is consumed and the take-off point progresses to the remaining wire on the inner layer on the spool, which has a significantly smaller radius of curvature.
For consumable electrode mechanized welding such as gas metal arc welding and submerged arc welding, variable wire cast can produce a variable position of the weld deposit. This, in turn, can lead to a lack of fusion, incomplete joint penetration and other significant weld defects.
In addition to cast control, the yield strength, commonly referred to as “hardness,” of the wire controls its ability to be bent while being pushed through curved nozzles or guides without unnecessarily increasing its cast. Since the yield strength of commercial wire is not well controlled, the response of the wire as it is fed through a conduit and nozzle system is variable, resulting in variable welding performance as the wire cast varies. In addition, the value of the wire material's yield strength is not kept at its practical maximum value, i.e., just below its value at breaking during fabrication, but is significantly weaker.
A third problem of wire feeding during mechanized welding is catastrophic buckling of the wire in the wire feeder due to relatively high frictional resistance in the wire path. For a given alloy, the buckling strength is controlled by the wire diameter and its degree of cold work-hardening before use. The wire drawing/rolling (diameter reduction) processes are inherently limited in their ability to harden many alloys to their maximum strength, without damaging the drawing dies or risking tensile fracture of the wire. This effect is especially true for thin wire which is desirable for use with improved efficiency, lower heat input welding processes.
A fourth problem is the difficulty of sufficiently work-hardening the metallurgically preferred high-purity materials, such as vacuum-induction melted heats due to their inherently lower initial (soft condition) yield strength and/or rate of work-hardening when plastically strained in a wire straightener. The reduced final hardness of wires made from these materials makes them prone to various soft wire feeding problems described above, particularly if the wires are thinned as desired.
The above problems of existing wire strength are currently minimized or eliminated, in some cases, by locating the wire push mechanism such as a pair of drive rolls close to the torch so as to reduce the conduit length and corresponding friction. In other cases, a push mechanism is located remotely to the torch and a supplementary wire pull mechanism is located near the torch. Both of these means do not address the important case, where the access at the weld area is so severely reduced or limited that there is insufficient space for a pull mechanism and where the weld area is also far from the push mechanism, such as when small inside diameter pipes are joined by welding or are weld clad. Another situation not optimized by the existing wire fabrication and feed methods is welding inside pipes at locations where the weld head (including the wire feeder) is on the near side of elbows or other internal access restrictions and the torch is used on the far side of these restrictions.
Prior spooled welding wire fabrication relies on stationary offset-roll straightening of continuous lengths of welding wire to provide straight wire before it is wound on a spool and/or as it is unwound for use on a welding machine. Other than the drawing process itself, no attempt is made to work-harden the wire and increase its yield strength so that it cannot be permanently strained from its straight cast when wound on a storage spool of a predetermined diameter. Conventional roll straightening provides only a minimum degree of work-hardening, even if repeated a number of times.
The minimum diameter of a spool hub on which wire can be wound without plastic straining (exceeding the yield stress of the material at its given degree of hardness) is a function of the material type, its diameter and metallurgical history. However, for all known orbital or robotic welding applications where the spool must be low weight and dimensionally small enough to be manipulated as the work progresses, a significant and problematic small cast occurs in the wire due to being wound on the relatively small surface of the moving spool. This cast may vary in degree as the spool is emptied and the diameter of the remaining wound material is reduced, eventually to the hub diameter of the spool, where the smallest cast occurs.
In accordance with a preferred embodiment of the present invention, an improved method is provided for the manufacture of low-cast, full-hard spooled wire for use in automated or mechanized welding procedures. The low-cast wire is produced by using a modified commercial rotary arbor type of wire straightening machine originally designed for straightening short rigid lengths to both simultaneously straighten and significantly work-harden continuous flexible lengths. After hardening, these continuous lengths maintain sufficient elasticity to be wound on a spool without the typical high degree of cast and can be fed against high frictional forces in a welding system without buckling. This reduced-cast, increased yield strength spooled wire significantly improves the accuracy and reliability of feeding filler material into the molten pool during the welding process. The method is especially suited to critical applications such as remotely controlled cladding of small inside diameters (e.g., nuclear reactor vessel penetrations) and joining of limited access internal components where variations in cast are difficult to compensate for during welding. The method is also suited for welding with very low heat input where the weld pool size is small, requiring the wire aiming accuracy to be maintained to tight tolerances.
Weld wire formed in accordance with the preferred embodiment hereof has the technical advantage of being able to be reliably pushed against the higher friction of very long conduit lengths and/or through severely curved feed nozzles without catastrophic buckling of the wire which typically occurs in unsupported gaps of the wire feed mechanism. This buckling occurs when the compression in the wire required to push forward exceeds the wire's column strength in the longest unsupported span of its path to the final feed nozzle.
The present method also improves the productivity of making the wire by reducing/minimizing the number of straightening steps required to achieve a predetermined degree of straightness and hardness, as compared to the conventional drawing and straightening method. Since the needed straightening and hardening of the disclosed method is achieved primarily in a single pass through the final straightener, the prior inter-pass annealing steps normally required may be increased as desired to main
General Electric Company
Nixon & Vanderhye
Tolan Ed
LandOfFree
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