K-TIG vs GMAW

K-TIG vs GMAWKeyhole TIG and Gas Metal Arc Welding Compared

What is K-TIG?Keyhole GTAW explained

Overview

A high energy density variant of GTAW, K-TIG (Keyhole TIG) is a high speed, single pass,full penetration welding technology that welds up to 100 times faster than TIG welding inmaterials up to 5/8in (16mm) in thickness, and typically operates at twice the speed ofplasma welding.

K-TIG works across a wide range of applications, and is particularly well suited to lowerconductivity materials such as stainless steels, nickel alloys, titanium alloys and mostcorrosion resistant and exotic materials. It easily handles longitudinal and circumferentialwelds on pipe, plate, spooling, vessel, tank and other materials in a single pass:

Titanium at 3mm to 16mm (1/8 to 5/8 inch) Stainless steel at 3mm to 13mm (1/8 to 1/2 inch) Carbon steel at 3mm to 9mm (1/8 to 11/32 inch)

K-TIG’s extremely fast welding times result in dramatic reductions in labor costs, weldingcycle times, rework and repair costs, gas and power usage. K-TIG’s single pass, fullpenetration welds significantly reduce or eliminate grinding and reworking. The K-TIGprocess dramatically reduces or eliminates the need for wire, eliminates edge bevelling,and requires only a square butt joint, but can also weld into all standard GTAWpreparations. No root gap is required.

The Process

Keyhole TIG is not a Plasma welding process. It is a much simpler, high productivity GTAWvariant developed by the Australian Government’s Commonwealth Scientific & IndustrialResearch Organisation (CSIRO), in conjunction with the Cooperative Research Centre forWelded Structures before being acquired and commercialised by K-TIG.

The System

The K-TIG 1000 System has been precision engineered to deliver the Keyhole GTAWprocess in a robust, intelligent and user friendly form. The K-TIG 1000 System ismanufactured in Adelaide, South Australia, is being used by many of the world’s mostproductive fabricators and has been exported to 18 countries.

K-TIG welding is a new productivity benchmark.The speed, penetration, quality and overall savingsgenerated by the process are extraordinary.

Attila Szabo, Principal Joining Engineer, GE

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PENETRATION Up to 16mm Up to 2mm

SPEED Up to 1000mm/min Up to 400mm/min

WELD QUALITY Very high due to benefitsfrom keyhole mode

Medium level, frequentproblems with porosity, lackof fusion, inclusions due tohigh wire deposition rates

JOINT PREPARATION Very low cost, simple squarebutt design

High, due to V- or J-groovepreparation for any thicknessabove 2 mm, due to limitedpenetration

WELDING CYCLE TIMES Very fast, high speed anddeep penetration

Medium travel speed and theneed for multiple weldpasses

KEYHOLE STABILITY High inherent stability, self-correcting keyhole

No keyhole; slow, multi-passpenetration + fill passes

CIRCUMFERENTIAL WELD OVERLAPTIE-IN

Very simple, just slope down,no voids

Often experience lack offusion or incompletepenetration at overlap dueto weld metal build up fromstart of weld, limited pencapability

WELD APPEARANCE

Very smooth and goodcontour; no dressing orgrinding required on eithercrown or root

Rough with lots of spatter;frequently require grindingor dressing of weld bead

DISTORTION

Very low overall distortiondue to high energy density,low heat input, and hightravel speeds

Very high overall distortiondue to low energy density,high heat input, and slowtravel speeds

PROCESS CONSISTENCY Very consistent keyhole, noprocess drift

Inconsistent due to high wirefeed, spatter, differentwelding modes (globular,spray, short circuit)

CONSUMABLES COSTS Very low, long electrode lifeHigh wire consumables cost,nozzles require frequentcleaning due to weld spatter

SKILL OF OPERATOR Very low High

DUTY CYCLE 100% Typically 60%

K-TIG GMAW


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PENETRATION

Up to 16mm

K-TIG comfortably performs single passwelds in 16mm thick titanium, 13mmaustenitic stainless steels, Hastelloys,Inconels and a wide range of nickel andcobalt alloys, and 9mm in conductivematerials such as ferritic steels & carbonsteels.

Up to 2mm

The practical upper limit for single passGMAW welding is generally considered tobe 2mm. Beyond this thickness, a V-groove root pass is normally applied,followed by filler passes.

SPEED

Up to 1000mm/min

K-TIG welding is significantly faster thanGTAW or GMAW. Typical speeds are:• 3mm material at up to 1000mm/min• 4mm material at up to 750mm/min• 6mm material at up to 600mm/min• 8mm material at up to 500mm/min• 12mm material at up to 350mm/min• 14mm material at up to 250mm/min• 16mm material at up to 200mm/min

Up to 400mm/min

GMAW welding is significantly slower thanK-TIG. Typical speeds are:• 1mm material at up to 400mm/min• 2mm material at up to 300mm/min• 6mm material – multipass• 8mm material – multipass• 12mm material – multipass• 14mm material – multipass• 16mm material – multipass

WELDQUALITY

Very high

One of the benefits of keyhole welding isthe exit path available for any vaporizedimpurities to leave the weld through theback of the keyhole. This prevents theevolved gases from becoming trapped asporosity in the solidifying weld. Anotherbenefit is the simple square butt jointdesign, which eliminates the possibility of"bridging" during fill passes and resultantlack of fusion.

Medium

GMAW is a high wire deposition weldingprocess, so the weld quality can beacceptable but not easy to control. It ishighly dependent on the welder's skilllevel for manual weldingapplications. Penetration is achieved bymelting through the joint thickness, anddue to the high amount of molten fillermetal being added to the pool, porosity isoften trapped in the solidifying weld. Lackof fusion is also a significant concern, asbridging a V-groove occurs regularlywithout properly fusing the joint sidewalls.

JOINT PREPARATION

Low cost, simple square butt design

A simple square butt joint design isrequired, no groove to fill (unless morethan 14-16 mm thick).

Costly V- or J-groove preparation

Machined groove preparation is preferredfor the sake of process consistency, whichadds cost, and the removed joint metalmust be replaced with fillermetal. Manually beveled joints often leadto inconsistent welding results.

K-TIG GMAW


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WELDING CYCLETIMES

Very fast

The high energy density keyhole permitssingle pass penetration of thick joints at avery high travel speed, resulting inminimal weld passes accomplished in veryshort times.

Rather slow

The low energy density arc has limitedpenetration capability, and the root and fillpasses are performed at fairly slow travelspeeds, resulting in numerous weld passesaccomplished in fairly lengthy weldingtimes.

KEYHOLE STABILITY

High inherent stability, self-correctingkeyhole

K-TIG keyholes have extremely highstability, due to the high travel speeds andsurface tension in the weld pool. As aresult, there is no requirement to seek abalance between arc force (plasmacolumn) and surface tension - the natureof the keyhole surface is such that itnaturally and dynamically self-corrects forfluctuations in the arc forces.

No keyhole; penetration and fill passes

There is no keyhole, simply a "meltthrough" approach. Beyond 2mmthickness, a V-groove root pass is normallyapplied, followed by filler passes. Thisapproach takes much longer, costs more interms of labor and consumables, and isprone to welding defects.

CIRCUMFEREN-TIALWELD OVERLAP TIE-IN

Very simple, just slope down, no voids

The K-TIG keyhole is produced from a highenergy density arc and patented torchdesign, without any plasma gas or complexconstricted arc required. As a result, atthe overlap and slope out of acircumferential weld, the process isextremely simple to slope down to closeout the keyhole and end the weld.

Potential for Lack of Fusion at overlap

Due to the limited penetration capabilityof the process, the overlap can be difficultto "tie in" or fuse properly, as the weldmetal from the original start of the weld(with considerable filler wire added) canbe a barrier to full penetration at theoverlap point.

WELD APPEARANCE

Very good and smooth contour

With proper gas shielding of the face androot sides of the weld, the K-TIG processinherently produces a very smooth anduniform weld appearance that requires nofurther grinding or dressing.

Rough appearance with plenty of weldspatter

Even with proper gas shielding of the faceand root sides of the weld, the GMAWprocess inherently produces a rough anduneven weld appearance, due to theviolent addition of filler metal. There istypically considerable spatter that requiresgrinding or dressing.

DISTORTION

Very low

Due to the high energy density of theprocess, the high travel speeds that can beachieved with single pass penetrationresult in remarkably low weld shrinkageand distortion.

Very high

Due to the low energy density of theprocess, the slow travel speeds that aretypical with multiple weld passes result insubstantial weld shrinkage and distortion.

K-TIG GMAW


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PROCESSCONSISTENCY

Very high

The high energy density arc from K-TIGproduces a smooth and consistent keyholethrough the joint, with very little variationfor the duration of the weld. The processis simple enough, and the electrode islarge enough, that erosion (and processdrift) are negligible.

Medium

The GMAW process can be "dialed in" toachieve sound welds in a mechanizedmode, with a root pass followed bymultiple fill passes typically. However, theweld can vary significantly depending onwhether it is in short circuit, globular, orspray transfer mode, and the transfer oflarge amounts of filler wire to the weldpool creates a level of inconsistency.

CONSUMABLES COSTS

Very low

Long electrode life, nothing else erodes orwears, 100% duty cycle power supply.

High

High cost of wire consumables. GMAWtorch nozzles and contact tips requirecleaning or replacement on a regular basisdue to the high amount of weld spatter.

SKILL OF OPERATOR

Very low

K-TIG requires minimal training due to thesimplicity of the process and thesophistication of the K-TIG controller. Anunskilled operator is sufficient.

High

GMAW requires extensive welder trainingfor manual welding.

DUTY CYCLE

100%

K-TIG utilises a 1000 amp power supply,which is considerably more than isrequired for any keyhole process, and israted for 100% duty cycle.

Typically 60%

GMA welding systems are typicallyprovided with power supplies in the rangeof 300-600 amps, and are typically onlyrated for 60% duty cycle.

K-TIG GMAW


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K-TIG vs GMAW