See above for my comments.Originally Posted by nixrox
Just for clarification, you were an inspector, not a weldor correct? I see in your list of tools that you have mig welders and a stick welder, so I am guessing you yourself do not do, or teach aerospace welding? Just trying to get an idea what your experience level and type is?
Last edited by Aaron Novak; 10-10-2018 at 11:24 AM.
to add my small idea the forum. maybe the welder could cut into some of his welds , one poor weld ,one good weld , and one of his best welds. To see how to see his welding / heating penetrates the metal.........and on seeing photos ,the original poster. is using, some nice jigs / fixtures ..... good day /// rick
Well you guys certainly are extremely sensitive and very easy to get a rise out of.
However, in the interests of clearing the air, I decided to go straight to the horses mouth - Miller Welding.
I found an article that covers best practices for welding 4130 chrome-moly, low alloy tubing.
Surprise, surprise - if you follow this article carefully, you should notice that the 'novice' home built welders on this forum have been giving you totally wrong information.
So if you want the correct information you need to go to the specialist who actually do this for a living.
Enjoy the article.
Best Practices for TIG Welding of 4130 Chrome-Moly Tubing
In General Motorsports and Aerospace Applications
Chrome-moly steel offers a good blend of strength, weight and ductility
for many motorsports and aerospace applications. The following article
discusses some of the recommended procedures and equipment for
successfully TIG welding 4130 chrome-moly steel.
Just as a NHRA (National Hot Rod Association) drag racing team depends
on blend of team talent to win races, the material selected for a
particular application requires a blend of properties to withstand the
stresses involved. For a drag racing chassis, and for many other
motorsports and aerospace applications, that material is 4130
chromium-molybdenum, or chrome-moly, which is selected for its blend of
ductility, strength, weight and fabrication advantages.
The 4130 grade of chrome-moly is a high-strength low-alloy (HSLA) steel
that contains molybdenum (0.15 - 0.25 percent by weight) and chromium
(0.8 - 1.1 percent by weight) as strengthening agents. However, it has
relatively low carbon content (nominally 0.30 percent), so it welds,
machines and bends almost as easily as 1018 DOM mild steel tubing (which
has an 0.18 percent carbon content).
*Material* *Tensile Strength* *Yield Strength *Hardness, Rockwell B* *Elongation*
4130 chrome-moly 97,200 psi 63,100 psi 92 25.5%
Chrome-moly is not lighter than steel, a common misconception. Both
weigh about 491 lbs. per cubic foot.
However, chrome-moly offers a better strength-to-weight ratio and better
elongation (a measure of ductility), which enables designers to use
thinner wall and/or smaller diameter tubing to reduce overall weight.
Because many motorsports, aerospace and sporting goods applications
involve welding normalized 4130 chrome-moly tubing with a wall
thicknesses of less than .125-in., this article will focus on best
practices for these applications.
Welding Consumables and Variables
Material 4130 chrome-moly tubing (normalized).
Thickness < 0.125 in. Most chassis tubing has a wall thickness ranging
from 0.035 – 0.083 in. and diameters from 1/4in. - 1-5/8in.
Amperage 1 amp per .001 in. of wall thickness.
Polarity DC Electrode Negative. HF for arc starts only.
Pulsing Optional.
Filler Material ER70S-2 or ER80S-D2.
Filler Diameter 0.030 – 1/8-in. Generally, do not use a rod larger than the thickness of the base metal.
Tungsten Type 2% type (Ceriated is first choice, then Thoriated)
Tungsten Diameter 1/16 – 3/32 (smaller diameter for thinner wall).
Tungsten Prep Pointed.
Arc Length
Less than or equal to the electrode diameter. Generally, the tighter
the better, as shorter arc lengths reduce heat input.
Electrode Stickout
No further than the distance of the inside diameter
of the cup being used. However using a gas lens can extend this distance.
Gas Lens Not required, but helpful if a tight joint configuration
demands a longer stickout or involves multiple tubes. Keep the screen
free of debris and spatter.
Shielding Gas
100% argon, 15 – 20 CFH. More is not better, as
turbulence could suck atmosphere into the weld.
Pre-flow
.4 to .6 seconds.
Post-flow
10 – 15 seconds.
Backing Gas
Follow applicable codes/standards, if any; not required for NHRA applications.
It is required for aircraft to reduce potetial contamination on the backside of the weld.
Pre-heat
Not required as long as tubing is above 60 – 70 degrees F.
Stress Relief
Not required on material < 0.125 inch; simply allow the weld to air-cool.
Tack Welds
Four tacks made 90 degrees apart; tacks ideally should be longer than wide.
Joint Preparation
Tubing notcher for coping, drum sander for final
fit-up, deburring for edge preparation, Scotch-Brite™ or 120 grit sand
paper to clean about 1 in. back from the joint, and final clean with
acetone, lacquer thinner or similar solvent to remove oil.
Joint Gap
None! Realistically, gaps smaller than 0.010 are permissible; larger
gaps promote poor quality.
Weld Size
Keep welds to within their specified size: a weld needs to be no larger
than its thinnest section, which will be the “weakest link” in the
chain. Larger-than-necessary welds add excess heat and waste gas, filler
rod and time.
Weld Technique
Weld in one continuous motion, pulsing the foot control
and adding filler rod to create the “stack of dimes” appearance (or use
the machine’s pulsing controls). Do not stack separate puddles on top of
each other, as this may lead to incomplete fusion.
End-of-Weld Procedure
Avoid pinholes by tapering off heat input at the end of the weld and
maintaining a constant distance between the tungsten and the weldment.
Weld Appearance
A good weld looks shiny and has a bluish tint. A dirty, gray-looking
weld may indicate poor shielding gas coverage or excess heat.
Perfect Fit-Up
When welding thin-wall tubing, whether chrome-moly or other metals, the
welders at Cagnazzi Racing joke that their tolerances range from perfect
to almost not perfect. That is, if the parts don’t fit perfectly, they
start over because thin-wall tubing does not have sufficient mass to
absorb excess heat.
The usual “trick” to filling gaps with GTAW is to use a larger diameter
filler rod. However, larger rods require more heat and excess heat
promotes burn-through, warping and embrittlement. Using a larger rod
might be an acceptable solution in a non-critical application, but it’s
a poor practice when welding chrome-moly.
Consistency
Cagnazzi uses hundreds of jigs and fixtures bolted to a surface that is
flat to within a few thousandths of an inch for fabricating even the
smallest items to help ensure tight fit-up and consistent tube
placement, which provides repeatability
Chrome Moly Tubing Consistency
By producing a new chassis nearly identical to the previous, the crew
chief can hone his craft of gear ratio and clutch management without
worrying about a new chassis introducing unknown variables. Many
fabricators believe that they cannot afford to build fixtures for all of
their components or for larger weldments. However, if repeatability and
accuracy are important, good fixturing is mandatory.
Coping Mechanism
Most of Cagnazzi’s jigs have a go/no-go type fit, which enables
“sneaking up” on a perfect fit by making small incremental adjustments.
After cutting to approximate length with a band saw, Cagnazzi uses a
tube notcher for rough coping. The fabricator will then check
the length and use a drum sander to sneak up on a perfect fit by slowly
sanding away excess metal from the mouth of the tube. Before
welding, the fabricator will deburr the edge , clean back 1 in.
from edge using Scotch-Brite or 120 grit sandpaper and remove oils or
other contaminants with a solvent. Be sure to wear nitrile
gloves, as the natural oils from your fingers can ruin a weld just as
thoroughly as grease or cutting fluid. Don’t forget to use the sandpaper
and solvent on the filler rod, too.
Filler Metal Selection
In many motorsports and aerospace applications, engineers want some
degree of ductility in the weld to help absorb impacts and prevent
cracking. For this reason, most NHRA fabricators intentionally dilute
the strength of the parent material by selecting ER70S-2 for filler for
roll cages, chassis and other applications requiring more flexibility.
While actual tensile strength of the weld will vary and depend on other
factors, 4130 diluted with ER70S-2 filler likely produces a weld with a
tensile strength in the 80,000 to 82,000 psi range.
For areas requiring higher strength, such as spindles and upper and
lower control arms, fabricators select ER80S-D2 filler, which produces
welds with a high tensile strength (as a side note, consider that S-2
fillers clean impurities better than D-2 fillers). In any event, do not
use 4130 filler, as the weld will not have sufficient ductility unless
it undergoes stress relief.
As for filler rod diameter, use a rod diameter that matches the
thickness of the base metal. Trying to weld 0.035-in. tubing with a
1/16th inch filler (0.063-in.) is a bad idea because the tubing wall
will melt before the filler rod is up to temperature. Cagnazzi
predominantly uses 0.030-, 0.045- and 0.063-in. (1/16th) filler rods
, with .045 and .063 being the most common. For thicker, larger
diameter tubing they use 3/32- and 1/8-in. rods.
Heat Control
Successfully welding 4130 requires preserving its mechanical properties
by heating and cooling the weld in a controlled manner. Excess heat
causes carbide precipitation, and cooling too quickly causes
embrittlement. Fortunately, the GTAW process provides sufficient heat
control. Welds made on tubing 1/8-inch or thinner do not require
pre-heating or post-weld stress relief, yet they will have sufficient
penetration as long operators follow the general rule of the thumb by
using 1 amp per 0.001 in. of metal thickness.
Note that if the tubing is below 60 degrees F, use a small propone torch
to heat the base metal to up to 300 degrees F. Otherwise, the metal
could cool too quickly and become brittle. Welding cold metal may also
promote hydrogen cracking, so that’s another reason to preheat 4130 if
it’s cold.
Puddle Size and Arc Length
While welding too slowly increases overall heat input, operators should
not necessarily focus on welding travel speed. Rather, they should focus
on controlling their body (Fig. 11), controlling puddle size by making
the puddle only as wide as necessary and holding a tight arc length of
1/8-in. or less.
Note that a longer arc length, or tungsten tip-to-work distance,
increases overall heat input, because a GTAW power source automatically
increases voltage when arc length increases. If the joint configuration
limits access because of cup size, do not try to weld with a longer arc.
Rather, use a smaller cup or a gas lens and extend the tungsten.
To better control heat input, and to enable repositioning the body to
better control torch movement, do not weld the circumference of a tube
in one pass. Rather, weld it in four quarters. Weld only two of the
quarters (on opposite side of the tube) then move to another joint. When
the first joint cools, come back and complete the remaining sections.
No Slacking Allowed — EVER
The authors of this article weld 4130 tubing in critical applications,
and they have a combined 50 years of welding experience. As such, they
take every step of the fabrication process seriously.
“Close enough” is simply not good enough for NHRA or AEROSPACE work,
nor should it be, for a child’s go-kart or bicycle.
Miller is not an authority on aerospace weldments on 4130, they are a company that makes welding equipment ( To be fair NONE of the welding machine manufacturers should be considered design experts for weldments). They have no materials lab, no NDT lab, no MTS lab, do no structural or fatigue testing of any kind. This is not their job, they are not something like edison welding institute or southwest research or NASA, they are a tool maker. Their suggestions are kind of sketchy do you not agree? How can you use material thickness alone to determine if you need PWHT? No mention of joint configuration at all? It looks like they grabbed that thickness from what I am guessing is a jominy bar test and misunderstood the data or totally missed the material thickness equivalency calculations. This is not a bash on Miller at all, they are a fine company that I have visited many times. I'm really trying to figure out where you are going here? You claim nobody knows what they are doing in aviation, yet post a copy and paste off the internet from a company that has no authority in aviation. Considering your push to put engineering into weldments I am just surprised.
obviously you have a reading handicap.
Miller never wrote the article - they just put it in the magazine.
The article was written by two journeyman welders with 50 years of experience.
I trust journeyman far more than part-time trainee welders - like you.
You should not be giving welding advice to anyone, because you do not have the license, training nor experience.
The difference between you and me is that I always take welding projects to journeyman welders.
I may be a certified weld inspector and licensed NDT Inspector but my welding sucks.
I complete all the mechanical work and farm out the welding and upholstery to the experts.
have a nice day.
I don’t know why I try but here goes...
What was the point of insulting him? And where exactly did you give a link or cite for the text you posted? When I read your post I see no links, no author names, no dates, no magazine name, nothing but your assertion that Miller is your authoritative “from the horses mouth” source and what looks like you commentary at the end about the authors. What exactly is in your post that he could have read better?
The article itself, and even better a link to where everyone can see it in context, is the sort of thing you could have come in and posted along with some questions about what you saw, how it looked imperfect to you, and how it could be done better. The article is helpful. It is your condescending attitude that is keeping you from doing any good.
Last edited by jim_p; 10-11-2018 at 11:14 AM.
Jim_P
I hate to admit this, but you are absolutely right. I have approached this subject from the wrong perspective. I failed to recognize that I have been dealing with individuals who are not fully cognizant of all the potential problems involved with welding processes, because they have no formal weld training. They don't know enough about welding, to realize they don't know enough and should not be welding critical aircraft structures. I forget that my original mechanic apprenticeship was four years long for a reason - there is just too much that can go wrong on an aircraft, if you are not fully aware all the things that can go wrong.
So I sincerely apologize to everyone for the way that I handled this subject. I hope that this entire conversation is not forgotten or discounted and that it does pass along the fact that welding is not easy. Welding critical aircraft structures should not be attempted by novice trainees unless they are under the direct supervision of a journeyman welder. Your life and the people you care about are much to precious to jeopardize because of ignorance of welding principles and procedures. Please approach welding with caution and take the time to learn as much as you possibly can.
Question: Why do you assume some of us are NOT professionally trained weldors or welding engineers with years of experience? Also, here in the USA there really is no generic journeyman welding card, they are specific for pipe welding, iron workers, etc. Here in the USA you typically attain a technical diploma, then do an apprenticeship in the specific field, or sometimes you can test out of the apprenticeship and go right to work. Aerospace is a little different with production workers usually being trained by the company while there are a couple very experienced people that work in the prototype shop. Canada might be a whole different thing and might be a little confusing for you then.
Last edited by Aaron Novak; 10-11-2018 at 11:33 AM.
Aaron:
Forgive if I am mistaken, but I don't remember seeing anyone on this particular blog (even you) stating they were journeyman welders. Yes, in Canada you cannot weld just about anything without being a journeyman certified by the Canadian Welding Bureau. on the aviation side you also have to pass the semi-annual welder performance testing to remain current and certified as an aircraft welder - and that is a difficult process to ensure only the best, most competent welders remain certified. So in that respect we are way ahead of you. However, I am not going to waste any more of my time arguing semantics with you.
I am going to include an article about purging the back side of shielded gas welding procedures, because it is pretty important. If after reading this article, you and everyone else trying to TIG weld 4130 tube - is not 100% positive their welds are defect free, then there is nothing more I am prepared to explore. This is just like the term we have all heard - 'IGNORANCE' of the law is no excuse. In this case, ignorance of the facts is no excuse.
In the military we introduced that process in 1976. I was working in an engine bay on large P&W turbines, when I noticed a significant crack on the titanium front frame. I took the engine over to the welding shop for repair and went back an hour later to get it. As I pulled it outside in the approx. 0C weather, there was a huge 'CRACK' sounded like a gun shot. Sure enough there was a larger crack in the exact same spot - back into the weld shop. This time they tried a more elaborate weld prep - with pre-heat and post-heat with slow cooling - same damn CRACK noise again. This time there was a 3 day consult involving a metallurgical engineer and a welding engineer. The end result, that no one had thought of before, was maybe contaminants were being introduced into the weld root from the un-shielded back side of the weld. So the welder came up with a way to plug the guide vane and attach a hose to allow Argon gas on the back side, at the same time as all the other things we tried before and it worked.
Purging Methods for Weld Purity
www.huntingdonfusion.com
By Dr Michael Fletcher of Delta Consultants
*Design, fabrication, and maintenance practices that can meet exacting
purity requirements of ASME 31.3 are crucial to the food,
pharmaceutical and semiconductor industries. *
Demands for improvements in piping fabrication quality have risen
exponentially in recent years.
Schematic section through tube joints illustrating gas seals on
each side of the weld. The identifiers show access routes for inert gas
supply/exhaust.The latest version of the ASME 31.3 Process Piping code Ref.
1) is a formal recognition of this emerging requirement that has been
stimulated mainly by the bioprocessing sector, but also by associated
industries such as pharmaceuticals, semiconductors, aviation and food production.
An essential element in pipework is production of welded joints. The
stringent inspection procedures imposed ASME 31.3 apply as much to
welded joints, as they do to all the other fabrication processes involved.
The article noted in Ref. 2 highlighted more general aspects of the
significance in the latest edition of the code, as it applies to the
manufacture of high-quality pipework.
Producers of welding accessories designed specifically to meet the
requirements have been quick to meet the new challenges ASME B31.3 impose.
*The Problem *
Pipe Stoppers Nylon Plugs
One of the fundamental requirements
imposed during the welding of pipes, is to prevent oxidation of the weld
during the first pass. The welding torch provides inert gas coverage of
the top of the fusion zone, but unless precautions are made there is no
coverage of the weld root. The problem has always been recognized and
over the years a variety of solutions have evolved, some eccentric,
others practical but largely ineffective.
While minimum standards are set for fusion welding, the application to
the pharmaceutical, semiconductor, and food production sectors demands
particularly high standards of cleanliness. Hygienic purity is the
driving force for joints destined for use in pharmaceutical and food
production. Elimination of particulate contamination is the crucial
requirement in semiconductor manufacture.
Inflatable Stoppers with some semiconductor manufacturers
producing chips with dimensions at the 32-nanometer (nm) level and
research going on at the 15-nm level, it is easy to see why the design,
fabrication, and maintenance practices required to ensure exacting
purity requirements of their process fluid distribution systems are of
paramount importance.
In the food processing industries, statutory legislation and a plethora
of litigation suits have forced plant manufacturers to introduce quality
control levels previously considered unnecessary. Contamination
introduced during fabrication is now unacceptable.
*The Solution *
Quick Purge Pipe Weld Purge System
Inserting low-quality paper or other barrier material on either side of
the joint and filling the space between them with inert gas may be good
enough for low-level requirements but is unsuitable to meet the
requirements ASME B31.3 imposes.
Significant progress was made in purging equipment in the 1980s when
welding accessory manufacturers developed expanding plugs and inflatable
stoppers (Figs. 1–3). These devices gave assurance of effective sealing
with the pipe wall and prevented leakage of inert gas from the weld
zone, thus precluding backflow of oxidizing gases from the atmosphere.
Hot Purge PreHeated Pipework Purge Systems
Generally effective,
these developments still allowed considerable scope for innovative
improvements. Devices such as shown in Fig. 4 integrate a pair of
inflatable bladders and provides pressure- controlled gas ports for both
inflating and inert gas supplies.
Other systems have been designed to satisfy the requirements of pre- and
postweld heating through the use of thermally resistant materials — Fig.
5. Some are produced with no metallic materials in the weld vicinity so
that postweld nondestructive examination can be undertaken with the
purge system still in place. There have been significant developments
recently in gas-monitoring instruments. These incude devices such as
monitors designed specifically for measurement of low oxygen
levels in purge gases during welding.
The challenges of the ASME Process Piping code have provided a stimulus
for further developments, and advanced versions of commercial purge
systems are becoming available. Some of these employ high-stability
engineering polymers to cover all exposed metal components so that the
risk of transfer of metallic materials onto pipe surfaces is minimized.
Many are able to provide fully automatic control over inert gas flow and
pressure. The welding supply industry is responding proactively to the
demands imposed by the latest edition of ASME 31.3.
/References/
1. ASME B31.3, Process Piping, Chapter X, High Purity Piping. 2010. New
York, N.Y.: American Society of Mechanical Engineers.
2. Huitt, W. M., Henon, B. K., and Molina III, V. B. 2011. New piping
code for high-purity processes. Chemical Engineering, July
Some of us do not feel the need to shove credentials around,and at least in my neck of the woods it is usually considered in poor taste and is seemingly reserved for academic types. Back purge is an interesting topic, and one that quite a lot of research has gone into. When we are dealing with 4130 in diameters typically used in GA there is no back purge as the limited oxygen supply is usually consumed quickly in the formation of an oxide scale. Critical weldments can use a backing flux for additional insurance. We can use the flux instead of a back purge as there is no concern for post weld cleanliness as there is in much of pipe welding. Pipe welding also having a much higher internal volume usually, would need more attention in that area. That being said, I am not aware of any 4130 piping. I know of no GA aircraft manufacturer that back purges any of their 4130 weldments, however I can check with my contacts to verify that. I would be curious if you have any failure reports on 4130 from oxide inclusion, Id love to see them. I have never found this failure mechanism in anything GA, instead finding a lot of HAZ issues and reinforcement (bead) geometry issues.
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