WO1996001717A1

WO1996001717A1 - Concentric cold wire gas tungsten arc welding

Info

Publication number: WO1996001717A1
Application number: PCT/US1995/008472
Authority: WO
Inventors: Larry W. Cherne; David A. Cherne
Original assignee: Cherne Larry W; Cherne David A
Priority date: 1994-07-08
Filing date: 1995-07-07
Publication date: 1996-01-25
Also published as: AU2962795A

Abstract

This invention involves a cold wire GTAW welding method and apparatus in which the filler wire (36) is concentrically fed through the welding apparatus (10) with the nonconsumable electrode (18) placed off-center within the welding apparatus (10). The nonconsumable electrode (18) can be positioned parallel to or at an angle to the filler wire (36) depending on the welding application.

Description

CONCENTRIC COLD WIRE GAS TUNGSTEN ARC WELDING Technical Field

The present invention relates to cold wire gas tungsten arc welding, and more particularly to a welding method that uses a torch with the wire guide concentrically disposed within the torch at the central longitudinal axis and the tungsten electrode is offset from that axis. The invention can also include placing the tungsten electrode at an angle relative to the filler wire. Background Art Gas tungsten arc welding (GTAW) and more particularly cold wire gas tungsten arc welding (CWGTAW) , is a process wherein an electric arc is created between base material to be welded and a nonconsumable tungsten electrode, using either AC or DC± current. The heat created by the arc melts the base material creating a weld pool into which consumable filler wire is added to add reinforcement, compensate for shrinkage or provide alloys required for the desired results. The filler wire is added to the weld pool as the torch moves along the welding joint.

In cold wire GTAW the filler wire must be kept electrically cold. In other words, the filler wire must be insulated to prevent the power being supplied to the tungsten electrode from diverting to the filler wire. Further, once the filler wire exits its insulated guide to be placed in the weld pool the filler wire must be kept a controlled distance from the tungsten electrode. If the filler wire is too close to the tungsten electrode, it will be deflected toward the tungsten electrode causing contamination and requiring replacement of the tungsten electrode. The minimum distances required between the filler wire and the tungsten electrode vary with the welding parameters and are known to those skilled in the art. GTAW is further characterized by the use of an inert shielding gas to protect the welding process from oxidation and to aid in electrical conductivity. A shielding gas is fed through the torch and flows from the gas nozzle at the open end of the torch to shield the tungsten electrode and the weld pool and to aid in electrical conductivity. The filler metal must enter the weld pool within the protection of the shielding gas to prevent oxidation.

GTAW is the preferred method of welding for certain applications. GTAW is particularly adapted for joining and overlaying aluminum, stainless, magnesium, titanium and tool steel. GTAW is a precise and accurate welding process that produces a high quality weld. However, historically the deposition rate and weld travel speed are sacrificed, as compared to other welding techniques, for the higher quality weld achieved through GTAW. Further, GTAW requires a high level of operator skill as compared to other welding techniques such as Metal Inert Gas (MIG) welding. GTAW has the advantage of being safer than MIG welding because it produces significantly less metal oxide fumes, some of which, such as Chrome-6 and Nickel oxides, are known carcinogens.

GTAW processes can be operator controlled, semi-automatic, or fully automatic. Traditional hand-held fully operator controlled GTAW requires extraordinary skill and dexterity. The operator must hold the welding torch in one hand, hold and feed the filler wire with the other hand while controlling the power supply to the tungsten electrode with his foot or his thumb. The arc length must be held at 0.040 to 0.250 inches in order to maintain a consistent weld. If the operator errs even slightly in positioning the filler wire, the filler metal may deflect and contaminate the tungsten. Time is then wasted having to replace the tungsten electrode.

Traditional semi-automatic GTAW frees one of the operator's hands by mounting a wire feeder to the exterior of the torch. While this system requires less dexterity, the wire feeder must be positioned precisely in the proper X, Y and Z position each time that the welding direction changes. Further, this type of wire guide can become difficult to handle and control in applications involving adjacent structures and tight clearances. Disclosure of Invention

An object of this invention is to improve welding travel speed, deposition rates, weld quality, consistency of deposits, control over the welding process, and the weld types available in cold wire gas tungsten arc welding. Another object is to reduce the level of operator skill needed to perform cold wire GTAW welding.

A further object is to provide a lightweight, ergonomic welding torch suitable for hand-held manual, hand-held semiautomatic or automatic cold wire GTAW welding.

Additional objects, advantages, and novel features of the invention will be set forth in part of the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

Brief Description of Drawinσs

The objects and advantages of this invention will become more apparent from reading the following detailed description in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic partial cutaway side view of a welding gun made in accordance with this invention;

FIG. 2 is an enlarged schematic sectional view of the distal portion of the torch head;

FIG. 3 is a schematic of the cross-sectional aspects of various prior art welds and various welds made in accordance with this invention;

FIG. 4 is a schematic perspective exploded view of another embodiment of the welding gun; FIG. 5 is a schematic cross-sectional view of the distal portion of another embodiment of the conductive holder;

FIG. 6 is a schematic sectional view of the distal end of the torch head of another embodiment of this invention.

Common elements between the drawings are designated by the same numeral. Modes for Carrying Out the Invention Referring now to the Figures, and in particular to FIGS. 1 and 2, there is shown the preferred embodiment of the cold wire gas tungsten arc welding apparatus of the invention identified generally by reference numeral 10. As shown in FIG. 1, a GTAW welding gun 10 comprises a torch head 12 attached to a neck 14 which is in turn secured to a handle 16. The particular design of the welding gun 10, including the torch head 12, neck 14, and handle 16 are a matter of choice for those skilled in the art.

As shown in greater detail in FIG. 2, the tungsten electrode 18 is attached to a conductive holder 20 which in turn is secured by a friction fit to the torch head 12 in a manner which preferably allows the conductive holder 20 to be attached and removed from the torch head 12 in order to facilitate replacement of the tungsten electrode 18. The size of the tungsten electrode 18 is predetermined by the operator depending on the application and other factors. Any available size of tungsten electrode 18 can be used with this invention, including the smallest diameters. Further, the tip of the tungsten electrode 18 can be shaped to either a frustro- conical or hemispherical head depending on which is needed for the application. The tungsten electrode 18 can be composed of either pure tungsten or a tungsten alloy containing cerium, lanthanum, thorium, or zirconium, such as, for example, 1% thoriated tungsten, or 2% thoriated rare earth blend. Hereinafter, any reference to a tungsten electrode should be understood to include both pure tungsten and tungsten alloy electrodes.

The tungsten electrode 18 is disposed on the conductive holder 20 so that when the conductive holder 20 is attached to the torch head 12 the tungsten electrode 18 does not intersect the central longitudinal axis of the torch head 12. The conductive holder 20 can be composed of any type of conductive material such as copper.

Electrical current is supplied to the tungsten electrode 18 by the current conductor 22 which extends through the handle 16, neck 14, and the torch head 12 to supply current to the conductive holder 20 which thereby conducts current to the tungsten electrode 18. The power supply is amperage controlled and of the constant current, constant potential current, and/or inverter type with AC and/or DC± output which are common in the industry. A remote amperage control, which can also be programmable, can be used with this invention. When current is supplied to the tungsten electrode 18, an arc 24 will form between the tungsten electrode 18 and the base metal 25 to be welded causing the base metal 25 to melt and create a weld pool 26. The shielding gas supply tube 28, which extends through the GTAW welding gun 10, supplies shielding gas through the torch head 12 to the gas nozzle 30 which directs the shielding gas to surround the welding zone adjacent to the tip of the tungsten electrode 18. The gas nozzle 30 is attached to the torch head 12. Welding must occur within the shielding gas in order to prevent oxidation. The shielding gases useful with this invention are the same as those presently used by the industry with GTAW welding.

A hollow cylindrical wire guide 32 composed of nonconductive, low friction material is disposed within the GTAW welding gun 10 and extends to the distal end of the torch head 12 to the location where the conductive holder 20 is attached to the torch head 12. The wire guide 32 can be composed of a material which has a low coefficient of friction, such as teflon, nylon or ceramic, to allow a smooth feeding of the filler wire 36. In the manner of the invention, the wire guide 32 is concentrically disposed within the torch head 12 so that the central longitudinal axis of the wire guide 32 is substantially coaxial with the central longitudinal axis of the torch head 12.

A ceramic tube 34 is disposed within the conductive holder 20 and is even with or extends past the distal edge of the conductive holder 20. The ceramic tube 34 is disposed within the conductive holder 20 in a position such that when the conductive holder 20 is attached to the torch head 12 the central longitudinal axis of the ceramic tube 34 is substantially coaxial with the central longitudinal axis of the wire guide 32. The ceramic tube 34 can be composed of a ceramic material or any electrically insulating material that will prevent current from passing from the conductive holder 20 to the filler wire 36.

With this design, the filler wire 36 is fed through the wire guide 32 and continues through the ceramic tube 34 where it is fed into the weld pool 26 during welding. The filler wire 36 can be fed by an automatic wire feed unit such as the cold wire feed system sold by Jetline, Inc. The filler wire 36 may have a diameter between 0.015 and 0.125 inches and may be composed of any suitable metal composition appropriate for the particular welding application, including stainless, nickels, monels, inconels, steels, aluminum tool steel, bronzes, brass and other designations of the American Welding Society.

The concentric or coaxial placement of the wire guide 32 within the torch head 12 leads to many advantages over the prior art. The welding process will be much simpler for the operator because the filler wire 36 is, by design, placed into the proper location in the weld pool 26. The filler wire 36 defines the tool point of the weld. The tool point should travel along the joint to be welded. In other words, in order to achieve a proper weld, the filler wire 36 should be inserted at the point where the two base metal pieces to be joined meet. Where, in the manner of the invention, the filler wire 36 is fed from the center of the torch head 12, the operator can more easily keep the tool point on the weld joint. Thus, the operator need not be as skilled as is required for traditional GTAW welding. Because less operator skill is required, higher travel speeds and greater deposit rates are achieved. Further, for automatic operations, programming the robot or dedicated welder is less time consuming if the filler wire 36 is concentrically disposed in the torch head 12 because the tool point is concentric to the barrel of the torch. Additionally, the welding process is faster with the filler wire 36 placed concentrically because the tool point does not change when the torch is rotated for a new direction of welding.

The invention also permits a simple, light weight torch design. Feeding the filler wire 36 concentrically through the welding gun 10 permits an ergonomic design. The operator can hold the welding gun 10 in a comfortable position without added torsional stress being placed on his wrist during welding.

Further, the concentric feeding of the filler wire 36 through the welding gun 10 reduces the potential for contamination of the tungsten electrode 18 due to feeding problems. Most spooled wire has a cast, a helix, and a twist which causes the wire to naturally curl. The filler wire 36 will tend to curl more when it is subjected to more force on one side over the other. The smaller the diameter of the wire, the more the wire will curl upon exiting the ceramic tube 34. Feeding the filler wire 36 concentrically reduces the chance that uneven forces will be applied to the filler wire 36 during feeding. Thus, the concentric feeding of the filler wire 36 increases welding efficiency and reduces costs by decreasing the chance that the filler wire 36 will deflect and contaminate the tungsten electrode 18. Placing the filler wire 36 concentrically within the torch head 12 gives the operator the ability to better control the width to depth ratio of the weld to achieve several different types of weld profiles. FIG. 3 illustrates the cross-section of various types of welds, including a traditional MIG weld 38, a traditional GTAW weld 40, and three categories of welds that can be achieved by this invention, an alloy transfer weld 41, a buried transfer weld 42, and a plasma transfer weld 43. As FIG. 3 demonstrates, all three types of welds possible with this invention 41, 42, 43 result in a lower profile weld than is possible with traditional GTAW welding 40. The lower profile reduces manufacturing costs because it requires less grinding to achieve a finished product.

The first type of weld possible with this invention, an alloy transfer weld 41, is achieved by setting the wire feed speed at a relatively slower rate so that the heat that is reflected back toward the torch from the arc 24 and the weld pool 26 melts the filler wire 36 before it enters the arc 24 or the weld pool 26. The filler wire 36 thus melts and droplets of the molten filler wire 36 fall into the weld pool 26. The weld profile achieved with alloy transfer welding 41 is relatively wide and shallow like the weld profile achieved in traditional MIG welding 38 though with a lower profile. Again, the lower profile reduces manufacturing costs because it requires less grinding to achieve a finished produc . The second type of weld possible with this invention, a buried transfer weld 42, is achieved by increasing the feed speed of the filler wire 36 so that the reflected heat does not have time to melt the filler wire 36. Thus the filler wire 36 can be driven deep into the weld pool 26 achieving a weld profile 42 with a large depth to width ratio. This increased depth to width ratio results in reduced manufacturing costs because less edge preparation is required. Further, energy costs are reduced because less heat input is required to achieve a weld with a larger depth to width ratio. The third type of weld possible with this invention is a plasma transfer weld 43. The wire feed speed is balanced in this process so that the filler wire 36 is not fed so slowly that the reflective heat causes it to melt before entering the arc 24 as with alloy transfer welding 41, yet the wire feed speed is not so fast that the filler wire 36 enters the weld pool 26 before melting as with buried transfer welding 42. Rather the filler wire 36 enters the arc 24, also known as the plasma, which is at a temperature between 6000 and 8000 degrees

Fahrenheit, and the filler wire 36 is melted within the arc or plasma 24. The melted filler wire then enters the weld pool 26. A distinct humming or hissing sound is heard if plasma transfer welding is occurring. Any size filler wire can be used in plasma transfer welding, although it can be difficult to melt the larger diameter filler wires within the arc or plasma in order to achieve plasma transfer welding.

The welding speed is greatly increased in plasma transfer welding 43 because the temperature of the filler wire 36 is increased before being placed in the weld pool 26 thereby reducing the distortion, shrinkage, and, with certain alloys, cracking that is caused when a cold filler wire 36 enters and chills the weld pool 26. Further, the total energy input is reduced because the energy in the arc or plasma 24 is transferred to the filler wire 36 and therefore to the deposit. The depth to width ratio of a plasma transfer weld 43 is also greater than the depth to width ratio possible with traditional GTAW welding 40, though the ratio is not as great as the ratio possible with buried transfer welding 42. Thus, the manufacturing and energy costs are reduced in plasma transfer welding 43.

Several other embodiments of this invention are depicted in FIGS. 4, 5 and 6. As FIG. 4 demonstrates, the welding gun 10 can be designed such that the wire guide 32 is not disposed within the handle 16 but rather is inserted directly into the torch head 12. In this design, the neck 14 and the handle 16 are combined in one structure. The shielding gas supply tube 28 and the current conductor 22 enter through the combined neck 14 and handle 16. The ceramic tube 34, the conductive holder 20, the tungsten electrode 18, the gas nozzle 30, and the filler wire 36 are also shown in FIG. 4. This design is less preferable than the design shown in FIG. 1 because the torsional stress placed on the operator's wrist during welding is increased. The preferred embodiment of FIG. 1 minimizes any such torsional stress.

FIG. 5 depicts the distal end of another embodiment of the conductive holder 20. The conductive holder 20 can be more conically shaped as shown in FIG. 5, rather than the substantially cylindrical shape as shown in FIG. 2, to facilitate welding when the base metal 25 forms a corner

or other similarly restricted joint. Again, the ceramic tube 34 is disposed within the conductive holder 20 such that when the conductive holder 20 is attached to the torch head 12 the longitudinal axis of the ceramic tube 34 is coaxial with both the wire guide 32 and the torch head 12. The gas nozzle 30 surrounds the conductive holder 20. The tungsten electrode 18 is behind and obscured by the filler wire 36 and the ceramic tube 34.

While all three of the types of welds possible with this invention can be achieved where the tungsten electrode 18 is parallel to the filler wire 36, in most applications, the preferred embodiment involves placing the tungsten electrode 18 at an angle to the filler wire 36. Angling the tungsten allows the operator to vary the size and shape of the arc 24 and the weld pool 26, increasing the welding options available and the operator's control over the process.

As shown in FIG. 6, the tungsten electrode 18 is mounted in the conductive holder 20 such that the longitudinal axis of the tungsten electrode 18 forms an angle 44 with the longitudinal axis of the filler wire 36 measured from the point of convergence of their respective axes. Depending on the application, the angle 44 can be between negative 10 degrees (-10°) and forty five degrees (45°) . The larger the angle 44 the larger the conductive holder 20 must be in order to accommodate the tungsten electrode 18. Similarly, as the angle 44 increases, the diameter of the gas nozzle 30 may need to be increased to allow for the larger conductive holder 20. Thus, the larger angles may only be practical in automatic welding due to the size of the torch required.

What has been described is an improved method of cold wire gas tungsten arc welding in which filler wire is added concentrically through the welding torch while the tungsten electrode is offset from the central longitudinal axis. As such, this method can improve deposition rates, travel speed, quality and profile of the weld, and control of the welding process. Though the embodiments disclosed herein are preferred, numerous changes and modifications which do not part from the true scope of the invention will become apparent to those skilled in the art. Accordingly, all such changes and modifications are intended to be covered by the following claims.

Claims

Claims What is claimed is:

1. A method of cold wire gas tungsten arc welding, said welding method capable of being performed by a human operator using a hand-held device, or by a partially or fully automated system, comprising the steps of: connecting a single nonconsumable electrode and a filler wire guide to an arc welding torch head such that said single nonconsumable electrode is not concentrically disposed within said torch head and said filler wire guide is concentrically disposed within said torch head; connecting said single nonconsumable electrode to a power source; feeding a filler wire through said concentric filler wire guide; enveloping said single nonconsumable electrode and said filler wire with a shielding gas; generating an arc between said single nonconsumable electrode and a base metal by passing electrical current through said single nonconsumable electrode and bringing said single nonconsumable electrode in proximity to the base metal to form a molten metal pool on the base metal; and inserting said filler wire into the molten metal pool.

2. The method of claim 1 wherein the longitudinal axis of said single nonconsumable electrode and the longitudinal axis of said filler wire guide form an angle, said angle being between negative 10 degrees (-10°) and forty five degrees (45°) .

3. The method of claim 1 wherein said inserting step comprises inserting said filler wire in a solid state into the molten metal pool.

4. The method of claim 1 wherein said inserting step comprises melting said filler wire and inserting said filler wire in said melted state into the molten metal pool.

5. The method of claim 4 wherein said melting step occurs by placing said filler wire in the proximity of the arc wherein heat generated by the arc reflects towards said filler wire and melts said filler wire.

6. The method of claim 4 wherein said melting step occurs by placing said filler wire in the arc wherein the heat generated by the arc melts said filler wire.

7. The method of claim 1 wherein said enveloping step is accomplished by attaching a gas nozzle to said torch head such that said single nonconsumable electrode and said filler wire guide are substantially surrounded by said gas nozzle and said shielding gas is supplied to said gas nozzle.

8. The method of claim 1 wherein said power source is a source of AC current.

9. The method of claim 1 wherein said power source is a source of DC current.

10. The method of claim 1 wherein said filler wire feeding step further comprises using an automatic feeder to insert said filler wire through said concentric filler wire guide.

11. A method of cold wire gas tungsten arc welding, said welding method capable of being performed by a human operator using a hand-held device, or by a partially or fully automated system, comprising the steps of: connecting a single nonconsumable electrode and a filler wire guide to an arc welding torch head such that a line extending along the longitudinal axis of said single nonconsumable electrode and a line extending along the longitudinal axis of said filler wire guide form an angle, said angle being between negative 10 degrees (-10°) and forty five degrees (45°) ; connecting said single nonconsumable electrode to a power source; feeding a filler wire through said filler wire guide; enveloping said single nonconsumable electrode and said filler wire with shielding gas; generating an arc between said single nonconsumable electrode and a base metal by passing electrical current through said single nonconsumable electrode and bringing said single nonconsumable electrode in proximity to the base metal to form a molten metal pool on the base metal; and inserting said filler wire into the molten metal pool.

12. A cold wire gas tungsten arc welding apparatus, capable of being modified to a hand-held device that can be operated by a human operator, or to a device useful in a partially or fully automated system, comprising: an arc welding torch head; a single nonconsumable electrode connected to said torch head such that said single nonconsumable electrode is not concentric with said torch head; a filler wire guide connected to said torch head such that said filler wire guide is concentric with said torch head; a connection for connecting said single nonconsumable electrode to a power source; a connection for connecting said concentric filler wire guide to a source of filler wire; and a connection for connecting said torch head to a source of shielding gas.

13. The apparatus of claim 12 wherein a line extending along the longitudinal axis of said single nonconsumable electrode and a line extending along the longitudinal axis of said filler wire guide form an angle, said angle being between negative 10 degrees (-10°) and forty five degrees (45°) .

14. The apparatus of claim 12 further comprising a gas nozzle connected to said torch head such that said single nonconsumable electrode and said filler wire guide are substantially surrounded by said gas nozzle and said gas nozzle is further connected to said connection for connecting shielding gas.

15. The apparatus of claim 12 further comprising a power source connected to said power source connection.

16. The apparatus of claim 15 wherein said power source is a source of AC current.

17. The apparatus of claim 15 wherein said power source is a source of DC current.

18. The apparatus of claim 12 further comprising a source of filler wire connected to said filler wire source connection.

19. The apparatus of claim 12 further comprising an automatic filler wire feeder connected to said filler wire source connection.

20. The apparatus of claim 12 further comprising a source of shielding gas connected to said shielding gas source connection.

21. The apparatus of claim 16 further comprising a source of shielding gas connected to said shielding gas source connection.

22. A cold wire gas tungsten arc welding apparatus, capable of being modified to a hand-held device that can be operated by a human operator, or to a device useful in a partially or fully automated system, comprising: an arc welding torch head; a single nonconsumable electrode connected to said torch head; a filler wire guide connected to said torch head; said single nonconsumable electrode being connected to said torch head such that the longitudinal axis of said single nonconsumable electrode and the longitudinal axis of said filler wire guide form an angle, said angle being between negative 10 degrees (-10°) and forty five degrees (45°) a connection for connecting said single nonconsumable electrode to a power source; a connection for connecting said filler wire guide to a source of filler wire; and a connection for connecting said torch head to a source of shielding gas.

23. A method of cold wire gas tungsten arc welding, said welding method capable of being performed by a human operator using a hand-held device, or by a partially or fully automated system, comprising the steps of: connecting a single nonconsumable electrode and a filler wire guide to an arc welding torch head; connecting said single nonconsumable electrode to a power source; feeding a filler wire through said filler wire guide; enveloping said single nonconsumable electrode and said filler wire with a shielding gas; generating an arc between said single nonconsumable electrode and a base metal by passing electrical current through said single nonconsumable electrode and bringing said single nonconsumable electrode in proximity to the base metal to form a molten metal pool on the base metal; and inserting said filler wire into the arc at such a rate that said filler wire melts in the arc, said molten filler wire thereafter entering the molten metal pool.

24. The method of claim 1 wherein said torch head is rotatably attached to a torch handle such that said single nonconsumable electrode can be rotated around said filler wire guide without moving said torch handle.