Written by Ed Craig www.weldreality.com



Tungsten Inert Gas Welding - Tig Welding Tips







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Question. Ed please provide some guidelines and general data for establishing automated TIG welding parameters

Answer. When automated TIG welding, an important first requirement is determine the approximate weld current required for the specific welds. Once the approximate weld current range is determined, then select the correct tungsten electrode size. The following enables the correct size tungsten electrode.




 


TUNGSTEN SIZE AND APPROX. WELD CURREN
T RANGE FOR REGULAR TIG, DCEN.


Tungsten
Ceriated
Lanthanaum

0.020
(0.5mm)

0.040
(1.0mm)
Tungsten
DCEN Amp
Range

5 - 20A

15 - 70A

BEST EQUIPMENT FOR ALUMINUM WELDS IS A POWER SOURCE WITH AN EN-EP WAVE BALANCE CONTROL.

WITH THE BALANCE CONTROL, THERE IS NO NEED FOR AC CURRENT / TUNGSTEN CONCERNS. WITH ALUMINUM BALANCE CONTROL SIMPLY USE A LANTHANUM OR CERIATED TUNGSTEN AND USE THE SIMILAR CURRENT AS USED WITH DCEN,


0.062
(1.6mm)


70-140A

3/32
(2.4mm)

130- 210A

1/8
(3.2mm)

200- 310A

5/32
(4mm)

 

250 - 500A

 

Try and ensure with the TIG tungsten selected that the weld current frequently used is not > 80% of the recommended weld amp range.

 



TIG Weld Tips



Anyone who has worked with TIG Welders and automated and orbital TIG systems, knows the TIG weld quality is highly dependent on retaining the shape and quality of the tungsten welding tips. Weld start data is critical with automated TIG welding applications. Tungsten life is improved with a start ramp up from a low current start point then ramp to the operating current.

The Cobra TIG 150A power source is shown below. This is one of the best, economical, small pulsed TIG power sources designed for "orbital tube welds" that I ever had the pleasure working with. No bell and whistles, just logical, practical process control features. The equipment delivers consistent, controlled weld results and the company that provides the equipment provides excellent equipment product support. The Cobra TIG power source is available from MK products California.








Cobra TIG Welding  Power Source




TIG TUNGSTEN ELECTRODE PROFILES:

 



Best Included angle for most welds > 50 amps,
45 - 50 degrees with small flat.

For automated TIG welds with AVC controls or good tungsten to work height control, with the use of correct tungsten size and weld parameters, both a tungsten point and a tungsten with a small flat spot with a 20 to 25 degree (40 - 50 included angle should be able to get the tungsten through at least a high duty 6 to 8 hours of arc on time without tungsten regrind or change.



PULSED TIG WELDING DATA:


Pulsed TIG Welding

 

Use pulsed as a LOWER ENERGY solution to heat related weld problems that occur with a TIG welding arc. The most consistent TIG arc, is an arc without a pulse.

Note: With TiP TiG, ninety nine percent of the weld applications get not benefits from the pulsed mode.





Pulsed
TIG is not required with the
superior TiP TiG process

Tig Welding Videos

 



GENERAL TIG WELDING DATA:

 

 


For steel and alloy steel applications, avoid radiation concerns with thoriated tungsten and use 1.5% Lanthium or Ceriated Tungstens.


FOR CONSISTENT ARC STARTS AND CONSISTENT
WELD QUALITY TIG "ARC LENGTH" IS CRITICAL:

APPROX. ARC LENGTH. Gap between tungsten and weld surface,

Arc length (AL) with applications that weld at 15 to 30 amps = 0.025 - 033
Arc length (AL) with applications that weld at 30 to 50 amps = 0.030 - 038
Arc length (AL) with applications that weld at 50 to 70 amps = 0.040
Arc length (AL) with applications that weld at 70 to 150 amps = 0.070 - 0.080
Arc length (AL) with applications that weld > 150 amps = 0.125 - 0.165



TIG WELDING SPEEDS - TIG WELD, TECHNIQUES

If you don't know the traditional TIG weld speed, start at in the range of 2 - 5 ipm. With TIP TIG start at 12 - 20 ipm) then change the speed to suit the desired weld size and penetration requirements.

Use a fore hand position for the tungsten as this helps break up the metal oxides in front of the welds.


RAMPING DOWN CURRENT AT THE WELD END ASSISTS IN REDUCING
WELD CRATER CRACKS AND ADDS TO THE TUNGSTEN LIFE.


For TIG Welding crater fill, both ramp down current and back stepping is common.





ORBITAL TIG WELDING AND REQUIRED WELD SCHEDULES.



Orbital TIG welds typically require a minimum of 4 weld parameter schedules to compensate for the increased weld heat that occurs as the TIG weld travels 360 degrees around the tube. For example an orbital weld schedule may drop the weld current by 10 - 20% between each of the 4 schedules as the weld heat builds up during the TIG torch rotation.TIG Arc Machine

Note, the smaller and thinner the tube welds, the faster the weld heat builds up.

Typical Orbital Weld Procedure.
Provide ramp up weld start 20 amps leading into weld schedule 1. Schedule 1 travels from 12 to 3 o'clock with 60 amps. For the schedule 2. the torch travels 3 to 6 o'clock at 55 amps. For weld schedule 3. The TIG torch travels between 6 to 9 o'clock at 50 amps. For the final weld schedule 4. The torch travels between 9 to 12 o'clock at 48 amps. Then apply the crater fill and finish data that could ramp the current down as low as 1 amp.


For great orbital tube or pipe auto TIG equipment check out MK and AMI, California. For manual, conventional TIG applications my choice is typically Miller followed by ESAB.

Note: FRONIUS has some interesting TIG equipment but tends to be overpriced with too many bells and whistles for the weld shop.





TIG GASES:

To eliminate tungsten oxidation, iner argon is utilized for TIG. When the argon purity is a concern, the use of liquid argon provides the highest purity. Gas contamination is common in high pressure cylinders that have not been purged before use, or possibly the cylinders have been previously used for MIG gas mixes that contain reactive gases such as O2 or CO2.

For most common TIG welds, Use a flow rate of 15 to 20 cuft/hr, start out at 15 cuft/hr. For high speed or deeper TIG penetration welds, flow rates will typically be increased between 20 and 40 cuft/hr.


When requiring higher energy TIG welds, before considering costly argon - helium or argon - hydrogen gas mixes, for any TIG application start out on a piece of scrap with straight argon and ensure the weld current required is compatible with the tungsten size utilized. It's a fundamental fact, that for all weld applications and all alloys that will require less than 200 amps, that straight argon should be the logical choice. Its also a fact that if you need high energy TIG weld you should be using the TIP TIG process which rarely requires helium or hydrogen gases.

I believe all TIG applications benefit from the use a gas lens. The use of gas lens also allows for greater tungsten extension which is beneficial on groove joints and joints with tight restriction.


WELD SPEEDS AND AUTOMATED TIG APPLICATIONS:

If you using high current and are utilizing the largest possible tungsten, to further increase weld speeds (automated applications only) with steel applications, try a 60 - 70% helium with 40- 30% argon mix. With austentitic and some nickel welds, the addition of hydrogen in the range of 5 - 30% may provide faster and cleaner welds. With most austenitic 300 series applications, nitrogen may be used for the back up / purge gas. Remember that when TIG welding, with approx. 90% of TIG applications, you will get ther job done with straight argon.

Note: Ed developed three of the most common MIG gas mixes used in North America, visit the MIG gas section if you want to get the saesmanship out og gas selection. Consider argon with 5 - 30% hydrogen if you want more weld wetting or faster faster weld speeds. Remember an increase in weld speed may have little value if the weld cycle time is measured in seconds. The hydrogen addition to argon can increase arc stability on specific, very thin low amp applications <10 amps. When welding specific alloy steels with hydrogen gas, be beware of the potential for hydrogen embrittlement. Hydrogen can also decrease the potential life of the tungsten, depending on the hydrogen content and tungsten type.


Note: TIP TIG Welding enables the fastest possible TIG weld speeds and typically requires
only argon:


GAS PRE FLOW - GAS POST FLOW.
Starting the TIG arc and finishing the arc without sufficient pre - post gas flow will cause instant damage to the tungsten. Using a controlled pre- and post flow is critical if you wish to retain the integrity of the tungsten / weld and minimize tungsten inclusions in your weld. Examine the contact tip at the arc start for the first inch of weld if the tip end gray or black your pre - flow gas is inadequate. Then examine the tip at the weld completion and look for the same contamination to tell you if the post flow time is effective. For TIG welds in which many welds are required it may pay to keep the shielding gas flowing continuously If the weld current used is over 200 amps I would set a post flow time of 20 - 25 seconds to protect the hot tungsten from oxidation with the air


FLOW RATES:

As mentioned , use a flow rate of 15 to 20 cuft/hr and start out at 15 cuft/hr.
Gas flow can be increased as weld sizes get bigger. With some automated applications, increasing gas flow can also enable a slight increase in the weld fusion and increase arc stability and weld speed


OZONE FORMATION:
Ozone forms in both MIG and TIG arcs. The greater the weld current density and the greater the reflective weld surface, the greater the ozone content. For more info, visit MIG weld gases at this site.







TIG Weld Safety & Thoriated Tungsten Concerns:


Thorium the base alloy in thoriated tungsten. Thorium is a radio active alloy used in the manufacture of tungsten arc welding electrodes to assist in arc starting. Although companies involved in welding have been using thoriated electrodes for many years, the industry is becoming more mindful of their potential health hazards and the micro amounts of radiation levels found in the grinding dust and environment where TIG welders work.

The following are notes, warnings, and recommendations form various organizations on the use of thoriated tungsten welding electrodes


American Welding Society: "

Thorium is radioactive and may present hazardous by external and internal exposure. Alternatives tungsten types are available If welding is to be performed in confined spaces for prolonged periods of time or if electrode grinding dust might be ingested, special precautions relative to ventilation and dust disposal should be considered. The user should consult appropriate safety personnel."
Tungsten. Standard Manufacturer's Warning: "Thorium dioxide is a naturally occurring radioactive element. It is an alpha emitter and, as such, its primary hazard lie in inhalation of dust/fumes." "Thorium dioxide has been identified as a carcinogen by the NTP and IARC." (These quotes are from Osram Sylvania MSDS sheets).


The Welding Institute:

Thorium is a radioactive element. The HSWE has recommended to factory inspectors that , where thoriated tungsten electrodes are not necessary, users should be encouraged to look for alternatives.Cancer Assessment: Thorium dioxide has been identified as a carcinogen by the National Toxicology Program and International Agency for Research on Cancer.


TIG TUNGSTEN SAFETY QUESTION.


We use Thoriated TIG electrodes in our factory. We have been told by a sales rep that these electrodes are are associated with health hazards. Can we consider switching to Ceriated or Lanthanated TIG electrodes? What type of tungsten should you replace the thoriated with when using AC and DC TIG welding?


Answer: For welding steels consider a tungsten with 2 percent cerium or a tungsten with 1 to 2 percent of lanthanum. Ceriated and lanthanated tungsten electrodes are equal to other electrodes in terms of their weld properties and are superior in some areas.

In contrast to "pure tungsten" the advantages of a ceriated or lanthanated electrode are:
[] Outstanding in the low current range.
[] Excellent ignition and re-ignition performance.
[] More durable a longer service life.
[] Excellent weld current carrying capacity.
[] Maintains a point instead of tendency to balling.




Remember regular TIG is obsolete.
Welcome to TIP TIG:






Aluminum TIG welds have special considerations,





TIG Aluminum

Question: Ed. We are TIG welding Aluminum. When we use the AC we can set the AC balance control towards electrode positive or negative and yes are welders all use different setting, each swearing that their balance setting is the best. Any logic we should apply as to the optimum setting. Thanks for your web site. Kyle

Answer. With AC welding we get both EP and EN. With EP, the majority of the electrons will flow to the tungsten welding tip while the larger positive gas molecules hit the aluminum surface breaking up the alum oxide skin. Unfortunately EP sends to many electron to the tungsten tip and the heat build will melt the tip end. To avoid the tip damage, with all TIG welds we use EN (electrode negative)in which the electrons are driven away from the tungsten to the work. With AC aluminum welds and a balance control, it's beneficial to use an arc with a little amount of EP added, so set that start balance control at 80% EN and 20% EP. Check the weld cleaning etch if its too wide decrease EP, not enough increase EP. For a tighter narrower TIG plasma increase EN, for the opposite decrease EN.

 

TIG Welding Aluminum with pure tungsten and AC current. The AC current will result in a ball at the tungsten tip, The rounded tip results from the high arc energy generated from the EP portion of the AC arc. With an alloyed rare earth tungsten when welding aluminum with AC the tungsten can be pointed with a flat added at the tip, this can provide welding benefits

As mentioned pure tungsten balls up, producing a wider, less intense plasma arc cone that can result in arc wandering. A rare earth tungsten used in combination with square wave technology that enables a greater ratio of EN rather than EP maintains a point and lets you use smaller tungsten. This type of tungsten provides a more focused arc so you can more precisely control heat input and weld bead profile. For a pointed electrode, use a truncated (flat) point as an overheated tip point can melt or fall into the weld.



What benefits are attained from using TIG inverter (balance control power sources) with the rare earth tungstens?

Through the benefits of balance AC control, some power sources allow up to 90 percent EN in the AC cycle with variable output frequency (20 to 250 Hz) you can dramatically reduce the heat at the tungsten tip and direct the majority of electrons to the work piece. This provides;

* Narrower heat affected zones
* Improved control over weld depth-to-width ratios.
* Initiate the weld puddles much faster.
* Faster weld travel speeds.
* Reduction in porosity.
* Less tungsten and gas consumption.
* Eliminate arc wandering.

Aluminum TIG Welding

Question
: Ed We are trying to AC - TIG weld a plug in an Alum 60 series tube. The tube rotates. The tube is only 12 mm OD, and to add to the problems it's only 0.050 thick. The plug is the same alloy, however it's solid, 1/8 thick 3/8 in length and fits in the end of the tube. The pulsed weld is made between the plug surface and tube end. We have extensive GTAW issues in controlling the weld fluidity in this single pass weld and frequently melt through the thin tubes.

TIG Welding Answer.
This is a difficult, automated TIG application. The following adds to your weld issues.


[a] The tube is thin aluminum, rapid heat build up..
[b] The tube is small diameter, rapid heat buildup.
[c] The plug thickness is different to the tube creating different weld heat requirements.
[d] The plug length is short creating rapid heat build up in contrast to the tube which is a good heat conductor.
[c] AC with pure tungsten is used. The weld arc width and length may change with variations in the tungsten length and shape.

SOMETIMES WHEN THE PROBLEM IS GENERATED BY WELD HEAT, THE TIG WELD SOLUTION IS MORE WELD PASSES.

The answer to this difficult weld issue may lie in the opposite of what you would expect. Instead of a high current single pass (single tube rotation) weld try two or possibly three smaller weld passes.

[1] First start out with a low weld current TIG pass. This weld pass will preheat the tube and plug and reduce the alum oxides.

[2] For the second pass, slightly ramp up the weld current, just enough to let the tube and plug alum melt and form a weld.

[3] For the third pass if necessary, use one more tube rotation. Use a lower current then the weld pass, this pass is to blend the weld.

[4] Ensure you use at least a 3 - 5 second current tail out with the finish weld current less than 5 amps.

[5] The best weld equipment for this application is to use a balance wave and set the EN between 80-90%.



~~~~~~~~~ AC GTAW Arc Rectification~~~~~~~~



For those of you that use AC current on your TIG aluminum applications and you may wonder about that occasional plasma arc instability that may occur in the TIG arc. The following is a brief description of AC arc rectification.

During the AC cycle, the tungsten is both positive and negative and the electrons flow in two directions 120 times per-second from the tungsten to work and from the work to the tungsten. First the tungsten in the negative mode is a superior conductor than the metals being welding. When the AC cycle is in its negative mode the electrons will flow from tungsten to work. During the negative mode we have more stable electron flow than when the electron flow in the positive cycle in which the electrons flow from negative alum metal surface to the positive tungsten tip.

Another reason for AC rectification is the condition of the aluminum weld surface. For example when welding multipass TIG welds one weld pass will remove the alum metal surface oxide, the next pass made on top of the weld may present a cleaner weld surface, (a weld surface that presents less surface oxides). When the alum metal surface has less impurities (less oxides) the HF used to reignite the AC arc may have a difficult time as oxides add to arc stability, (that's one of the benefits of oxygen or CO2 in a MIG gas to weld steel).

Remember it's the argon gas molecules and tungsten positive cycle that provides the arc cleaning action. The positive cycle is when the electrons flow from the work (breaking up the minuscule aluminum surface oxides) to the tungsten, this provides the arc cleaning action. Once the alum oxides have decreased from the weld surface its harder for the HF to reignite the arc so we see arc stability issues also affected by the condition of the alum weld surface.
Today we use square wave weld equipment to minimize the effects of AC rectification however the arc rectification will still occur, it's just less noticeable.

View more about TIG Aluminum.






For steels - alloy steels welcome to TIP TIG:

 

Learn more about TIG Welding Techniques on Titanium || Stainless Steel TIG Welding || Aluminum ||
Duplex Steels || Nickel || Automated TIG Welding




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