Tungsten
Inert Gas Welding - Tig Welding Tips
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TIG Welding
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.
TIG
Welding Parameters:
TUNGSTEN SIZE AND APPROX.
WELD CURRENT
RANGE FOR 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 BALANCE CONTROL.
WITH THIS EQUIPMENT THERE IS NO NEED FOR AC CURRENT / TUNGSTEN CONCERNS. WITH
ALUMINUM 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 Welding 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 tip. 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.
TIG
TUNGSTEN PROFILES:
TIG Welding Tips for Electrodes
1) Low current (under 20 amps) grind tips to 20 degees to a point
2) Over 20 amps grind tips to 20 degrees to a point and add a flat spot
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 30 degree 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:
Use
pulsed as a solution to a problem that occurs with a consistent TIG arc. However
remember with most pulsed carbon steel or stainless steel TIG welding applications
pulsed TIG the most consistent arc, is an arc without a pulse
PEAK
TO BACK GROUND THIN PARTS:
If using pulsed, set the weld current for the "average pulsed current"
For example welding a part 0.040 thick requires approx. 40 amps. To attain 40
amps start out with a peak current to back ground ratio of 3 to 1. Back Ground
- 20 amps. Peak current - 60 amps, this provides an average weld current of 40
amps.
PULSED WIDTH OR TIME. The time at which the peak current
is maintained. The more sensitive the part to weld heat the smaller the width
or the less percentage of time. Start in the range of 30 to 50 %.
PULSED
FREQUENCY. Examine the pulsed overlap weld pattern 60 to 80 percent overlap
is good. For thin metals <0.030 it's usually beneficial to decrease the pulsed
frequency. For more weld penetration or a smoother more continuos weld surface,
increase the pulsed frequency.
Pulsed
TIG is not required with the
latest and superior
TIG Welding process
GENERAL
TIG WELDING DATA:
Tungstens.
Avoid radioactive concerns from thoriated electrodes, use Lanthium or Ceriated
Tungstens. Information below.
[] With those low current TIG applications under 20 amps, grind the tip of the
tungsten to 20 degrees to a point.
[] With steel applications that require
> 20 amps, to avoid the tip melting and becoming a tungsten inclusion in the
weld, grind the tip to an included angle of 20 - 30 degrees and add a small flat
spot approx. 0.005 to 0.010 on the tip.
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 4 - 5 ipm, (with TIP TIG
start at 12 - 15 ipm) then change the speed to suit the desired weld size and
penetration requirements. Use a fore hand position welding technique with the tungsten to help break
up the oxides in front of the welds.
RAMP
DOWN CURRENT FOR WELD CRATER REDUCTION
AND TUNGSTEN PROTECTION.
For TIG Welding crater fill, ramp down and back stepping is common. About 3 to 4 mm
from end of weld, ramp down from the weld current to 1-5 amps for 1 to 2 seconds...
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 a 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.
Note, the smaller and thinner the tube welds, the faster the weld heat builds
up.
Orbital Tube Typical 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 and comparing Miller, ESAB and Lincoln
TIG power sources, my choice is typically Miller followed by ESAB. FRONIUS also
has some interesting products.
TIG Welding 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.
View more about TIG Welding Aluminum
 TIG
WELD GASES:
Argon is the most economical
gas and when provided in liquid form eliminates concern for gas contamination
which is common in high pressure cylinders that have not been purged before use
or when the cylinders have been previously used for MIG gas mixes that contain
reactive gases (O2 or CO2). For most common welds, Use a flow rate of 10 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 50 cuft/hr.
When
requiring higher energy 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 (99.995% pure) 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 is the
logical choice. Its also a fact that if you need high energy TIG weld you should
be using TIP TIG 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 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 / 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 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:
PRE FLOW
- POST FLOW. Starting the 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. FLOW RATES: As
mentioned , use a flow rate of 10 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 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
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 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.
03/2009 Regular TIG is obsolete.
Welcome to
TIP TIG:
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