To all the welders out there

[kozak]

Hey fellow welders i just recently got our tig up and "operating", i've been messing around with alum welding and i think i got it down. But steel is whats giving me problems. today i tried welding some 4130 chromo we had laying around the shop. it took a little time but i think i got my techneque down, but the welds are turning our very crappy. Three things i noticed; way to much slag on the weld, there is a brown red powder that forms near the weld after, and lots of porosity. i did search the forums earlier and did get some info but not specifically what i needed, so i'm just wondering what you all think.

[Marshall Grice]

sounds like dirty steel. you get some nice colors if you touch the tip to the puddle.

[Chris Allbee]

Are you running pure argon? you should be, it works out easier. and make sure you have plenty of gas flowing while you weld.

[Alexandre D.]

Yep dirty steel is probably the problem... Clean the steel and brush it with a steel only brush.

You may want to add some post flow too but i doubt it will change anything.

Personnally i think 4130 is much easier than aluminium.

[kozak]

yes i am running pure argon. i wouldn't think that a little dirt wopuld have that much of a bad effect on the weld. i know dirt is not good but it completely destroyed the weld. i will clean the tube better and try again. i should also add that the alum i am welding is like 1/8 in.

[Jeff The Pyro]

i doubt this is the problem but dont forget... use dc electrode negative for steel, ac for aluminum

[mtg]

TIG welding is really picking about everything being very clean. Its not like MIG welding where you can weld through rust.

Its not as important welding aluminum, or anytime using AC or DC+ because when the electrons flow from the metal to the electrode, the crap on the surface is blasted off.

Watch your tungsten electrode also- if you touch it to the work while welding, go regrind it. Dirty tungsten screws up welds as well.

As another tip, Lincoln and Miller have pretty good online resources for welding "how to".

[Alan]

I have found that if you clean the area with acetone first, then brush it with a SS brush, that helps a lot.

As far as gas coverage goes, for 4130 I think 10-12 CFH is a good starting point. A good habit to form is to not move the torch for a few seconds at the end of the bead (assuming you have post-flow). This will prevent the end of the bead from oxidizing. Depending on the joint, you might want to try different shape/size ceramic cups or even use a gas lens.

[kozak]

yeah right now i have a short small cup on the end do you think this could be affacting the flow of the gas and causing oxidation.

[Alan]

Originally posted by kozak:
yeah right now i have a short small cup on the end do you think this could be affacting the flow of the gas and causing oxidation.

Its very possible. If you post a picture of your torch setup and the joint you are trying to weld it might help.

[Cement Legs]

Originally posted by mtg:

Its not as important welding aluminum, or anytime using AC or DC+ because when the electrons flow from the metal to the electrode, the crap on the surface is blasted off.

Watch your tungsten electrode also- if you touch it to the work while welding, go regrind it. Dirty tungsten screws up welds as well.



I would disagree... even with the AC squarewave feature on a Lincoln welder you will still have way more trouble welding semi dirty aluminum than dirty steel! The grit just does not diffuse as nicely as it does with steel. But your welds always show your preparation.

I do agree that grounding your tungsten to the part while welding makes things a little harder but if you are patient and a little more careful you can continue welding (to a certain point), your arc will just behave like a dull pencil instead of a sharp one. If you ground down too many times your arc will look like a garden sprinkler rather than a water jet http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Someone already suggested using DC- which to me sounds like what the problem may be assuming that your gas flow is good (between 15-25 CFH, too little and you wont have adequate shielding unless your cone is right on top of your bead and too high will blow your puddle around). Be sure to use a good quality filler rod (ER80S-D2, ER-70S-2, ER70S-6; in this order for strength). Also be sure to use a 2% thoriated tungsten tip and sharpen it like a pensil (on the grinder of course). Allthough the diameter of your tungsten tip wont affect the welds in the way you have described it will help with your precision and heat affected area.

PS if you are still having problems post 2-3 pictures of the welds that you are concerned about....

[mtg]

Originally posted by Cement Legs:
I would disagree... even with the AC squarewave feature on a Lincoln welder you will still have way more trouble welding semi dirty aluminum than dirty steel!

Someone already suggested using DC-

We're thinking different ballparks. When I say "not as clean", I mean really damn clean, not super ultra-mega clean.

You want to use DC- on steel. I've tried all three (DC+, AC, DC-) on steel, aluminum, and Ti. DC+ on steel zorches the tungsten. AC somewhat zorches the tungsten on steel. Maybe if you use a He-Man sized tungsten, you could use DC+ on steel and have it turn out pretty good (but then it would be hard to control the heat with such a fat electrode).

If you're using 15-25 CFH, you might be using a much bigger ceramic cup than the rest of us (allowing more gas flow without turbulence). What size tungsten are you using?

[kozak]

3/32 tung, and the cup is actually fairly small i think.

[DaveC]

I like gas lenses, they're a little bulkier, but its not a problem too often. Different machines react with slight differences due to the tungsten formulation, I'd buy a couple different types that are made for DC, and see how it works out. I'd also seek an alternative to thoriated tungsten, it's radioactive. Maybe buy a tungsten grinder that captures the dust if you feel you have to have thoriated. I definately second the cleaning with acetone after everything else is ready to weld. It seemed to get rid of a couple various problems that arose when I didnt use it first.

[Dave M]

Ive found that cutting oil is usually the culprit for bad steel welds, like everyone else said cleaner is better

[Jarrod]

The powder and porosity sound like either dipping the tungsten in the weld pool, or poor gas coverage. I have found that with small nozzles, too much gas can often be worse, as the gas flow will be turbulent, and pull air into the argon stream. Also be aware if you have fume extraction or a cooling fan on the welder, that they are not blowing your gas away.

[Kirk Feldkamp]

Jarrod is right about high flow and a small cup.. make sure first that you have proper Argon flow with a big enough cup. If I need to use a really small cup for whatever reason, i tend to turn down the flow to compensate.

My experience is that either oil or rust cause the reddish brown color, but more often than not, it's oil. Unless the thing is dripping oil, however, rust is usually the culprit for red stuff and a lot of porosity. It seems like something is outgassing when you weld rust and that's causing the pores.

My welding instructor used to always say "cleanliness is godliness." I pretty much require than most anything i'm welding is hit with a wire wheel and a little wipe of acetone before it gets welded. A piece can look clean, but usually even if you wipe it off with a clean rag, it still has a thin film of oil that messes everything up.

-Kirk

[Cement Legs]

Originally posted by mtg:

You want to use DC- on steel. I've tried all three (DC+, AC, DC-) on steel, aluminum, and Ti. DC+ on steel zorches the tungsten. AC somewhat zorches the tungsten on steel. Maybe if you use a He-Man sized tungsten, you could use DC+ on steel and have it turn out pretty good (but then it would be hard to control the heat with such a fat electrode).



Exactly. My grammer may have been a bit confusing but I was referring to the fact that someone had already suggested using DC-. When I mentioned that might be the problem I was reffering to the possibility that the machine was set on something else http://fsae.com/groupee_common/emoticons/icon_biggrin.gif.

[jsmooz]

...use a 2% thoriated tungsten tip...

If also depends on the type of tungsten. You should be using the red type for steel and green type for aluminum. The color is found on one end of a new electrode. The color code has something to do with the tungsten composition. It think one is more suited for AC welding and one for DC.

Usually when I get a lot of the red/brown stuff and porosity it has to do with the gas flow.

[DaveC]

If also depends on the type of tungsten. You should be using the red type for steel and green type for aluminum. The color is found on one end of a new electrode. The color code has something to do with the tungsten composition. It think one is more suited for AC welding and one for DC.


While this is the general rule of thumb, red being thoriated, green being pure, there are other alternatives that I've found perform better than either pure or thor for AC / DC respectively. Thorium is also radioactive, and while its only %2 of the total formulation, grinding it into fine dust might not be a good idea. The specific tungsten that will work best depends on the machine youre using...

[MoboostWRX]

One thing that is a way to make better welds on a mild or certain alloy steel is to use a stainless steel filler rod, it will help cut down on porosity. Makes an ok welder like me, look much better than I am.

[kozak]

yeah i was also thinking that i could be using the wrong filler rod that could explain the crappyness of the weld. DaveC hey don't worry about the radiation i'm a big tuff manly man besides radiation does the body good... right.

[Alan]

Originally posted by MoboostWRX:
One thing that is a way to make better welds on a mild or certain alloy steel is to use a stainless steel filler rod, it will help cut down on porosity. Makes an ok welder like me, look much better than I am.

No offense but I don't think better looking welds = better welds. I don't know the specifics of what alloys and grades of steel you are combining, but in general SS filler on steel will create a very brittle weld.

[DaveC]

Unless there are published standards for using SS rods on other steels, and there could be, I would not do it on anything structural (what do people weld that isn't?).

Kozak, I have not looked into exactly how radioactive Thorium is, but you might want to... http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Mostly, tig welding just takes practice.

[MoboostWRX]

My information came from a professional welder when he was supervising me at Tech College. The real fact is that TIG welding can be done without any filler at all so long as the pieces are machined very well. He said that mild steels are hard to weld with a TIG and that that is why me generally MIG weld mild steels. The big thing with welding 4130 chromoly is that you don't get it to hot otherwise it will become very brittle when it cools and the welds can fail.

[Sgt Slaughter]

There are a few reasons teams have trouble with chromoly. First, most teams don't use chromoly filler rod. A joint is only as strong as its weakest link. Second, as MoboostWRX pointed out, Chromoly is heat affected. A mediocre welder will pour heat into chromo destroying its mechanical properties and requiring a post heat treat to return strength. Another common mistake welders make is undercutting material. it is often difficult to obtain good penetration without cutting a little, the trick is to control the application of filler to stop this. I've welded alot of mild steel and never had a porblem doing this with a tig however. so on that point MoboostWRX, I'm gonna have to disagree with you. As almost any good welder knows there are two secrets to good welds, the first being the machine setup and the second, as turbotwig and others pointed out, is cleanliness. Oil can destroy what started out as a good weld. One more question. You're not trying to seal whatever you welded off are you? Pressure inside a vessel can cause a blowout making the weld look like crap.

Another point which is interesting to bring up is with the price of chromo being what it is, and a team not having a good welder, is it a better choice to go with 1020 DOM which can take heat better than 4130 can?

Comments?

[John Lankes]

A few comments from above:

Regarding the SS filler rod, I've worked with a couple of Pro race shops, and you will find some of the older fabbies still using SS filler rod to do structural work, and I can't say I've ever heard of a failure. That doesn't mean its correct, just that it isn't going to destroy what you are doing. In my experience SS rod might give your chromoly welds better color, but the rod flow is far poorer than a regular mild steel Crown 8 rod.

Second, if you are not heat treating the part I would strongly advise against using chromoly filler rod, or just fusing chromoly pieces. Either of these, without a heat treat, will result in a brittle part. If you are not heat treating (like most spaceframes) I would recommend a mild steel (crown8 or similar) filler rod.

[Cement Legs]

Good point on the heat treat John http://fsae.com/groupee_common/emoticons/icon_wink.gif.

If you dont use heat treatment then using 310 or 312 SS rod is perfectly acceptable for any structure and even recommended.

[DaveC]

I've always thought it was completely necessary to heat treat crmo after welding. For what I've done in the past crmo has not been used for many reasons, 1020 DOM, as sgt said, was a better choice. For fsae crmo might be lighter, I forget the exact weight difference between the two... With 1020 DOM, mig welding is acceptable, so it might take some pressure off youre welder if you only have one tig guy. I know tig is a superior process, but the HAZ will break well before either a tig or a mig weld. I've seen some really badly wrecked rally cars with mig welded cages that were fine, and MANY off road vehicles where the mig weld was not the point of failure.

[John Lankes]

The only thing I would look out for on DOM tubing is if it is in a high stress/ high fatigue application like a roll bar, the welded seem would make me a bit nervous, especially on thin walled tubing.

Regarding MIG welding, there is nothing wrong with using it on the chassis, in fact if I had a mig welder that would let me consistantly and accurately weld .028-.035 steel, I would do it. The problem is that with that thin of tubing and the need to constantly pulse the welder, and readjust yourself, I think the TIG is better. With the thinwalled tubing, it is vrey easy to quickly go right through it, or overheat it with a MIG welder.

If you look on Miller's site, they have an article about MIG welding NASCAR chassis, with up close shots of the welds. The welds look nearly as good as TIG welds, and they can produce 40 chassis a year MIG welding most of the major components.

[kozak]

I agree alot of people when you mention mig welding they assume that it is a bad weld but that isn't always the case. mig can be just a good as tig but you need a good welder (person), a good welder (machine), inert gas not flux core wire, and fine adjustment.

[DaveC]

The only thing I would look out for on DOM tubing is if it is in a high stress/ high fatigue application like a roll bar, the welded seem would make me a bit nervous, especially on thin walled tubing.


If thats the case, you didnt get DOM, you got welded seam tubing. DOM (Drawn on Mandrel) has been squeezed thru a mandrel to make it almost seamless. I say almost, because it started out as welded tube before it was DOM. 1020 DOM is actually preferred for high impact applications because it can yield without total failure. Suspension links for off road vehicles and rock buggys are one example. 4130 is also very expensive, and should be heat treated after being tig welding, so its also more difficult to join correctly. Some racing rules (like SCCA rally car rules) dont allow you to use thinner wall material if you use crmo, minimizing any advantage while costing $1.5-2k more, almost doubling the cost of the cage.


It is true tig is better for thinner walled tube, for me, much less than .050 mild steel is getting more challenging with the mig, and worthy of getting the tig out. However, I have sneezed while tig welding and blown a hole thru the piece because I floored the pedal while sneezing. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif


I talked to someone today who said they recently went to the local airgas supply, tried to by a thoriated tungsten, and they told him they werent being made anymore, and sold him a ceriated tungsten. http://fsae.com/groupee_common/emoticons/icon_confused.gif

[CMURacing - Prometheus]

Originally posted by DaveC:
Some racing rules (like SCCA rally car rules) dont allow you to use thinner wall material if you use crmo,

and the formula sae rules (3.3.3.1 and table 3.3.3.?)

[kozak]

yeah so i did a better job of cleaning the steel and it seemed to come out better. just when i went over some areas to smooth out the weld it started to bubble up a little and when i was welding it looked like burning sugar bubbling up it this just dirt and oil i missed?

[DaveC]

Thats most likely contaminants trapped inside the weld. You need to completely grind the weld off, and re - do it.

[Analogue]

Yup, welders are an opinionated bunch. After playing with all sorts of things, here's my recommendations:

1/16 ceriated tungsten for thinwall chromemoly work. The arc is very stable at low currents.

3/32 lanthanated for thin (1/16") aluminmum work (esp. with air cooled torches)

This covers most of an FSAE car.

Both of these hold their tip well with air cooled torches. Word on the street is that zirconiated tungsten is best for aluminum, but only if you can keep it from melting.

The old recommendations of thoriated for steel and pure for aluminum are bunk. The thoriated is a major health concern, and the pure can't hold a sharp tip. The "ball" creates a really diffuse arc. A sharp tip with aluminum is a great help.

I like gas lenses when they fit. I use 15 CFH argon with a #8 small body gas lens anywhere I can get it. Overkill, perhaps...

I use a #4 cup to reach in tight places. These are difficult to make behave. I use abuot 8 CFH argon to prevent entraining air.

I have gotten two bottles of bad gas in the same week, from different suppliers. This is the only time I have ever had it happen. This is probably from the bottle not getting evacuated after some chump drained it completely. For the love of Bog, return the bottle with some gas in it. Bad gas shows up as a bubbling puddle, sparks (on steel), tungstens that magically contaminate themself, a greenish arc, and ugly welds with a dark oxidized look. These are the same things that happen if you weld after dipping. Always resharpen after dipping the tungsten into the puddle. I keep the grinder about 40 feet from the chassis for punishment. This prevents getting lazy about dipping.

Also, a tunsten only grinder is a good idea. Use a fine grit, soft wheel, and don't let anybody near it.

As for filler, the stainlesses are ductile. Look at elongation. 4130 will be brittle unless heat treated, and even then, I have some doubts that a overheated weld will retain the material properties of the 4130. ER80-S2 is a good choice for strength, but is also a bit brittle. I use it and like it. If you find yourself overheating the metal, then ER70-S2 is probably a better choice.

As far as a burned sugar look goes, DaveC is probably correct in moisture or air trapped in the weld. Try again with clean metal. The burning sugar also happens when welding stainless. When working on headers, purge the inside with argon. Stainless is no longer stainless when exposed to oxygen at welding temperatures. It also isn't much of a steel after that...

[DaveC]

So, are there any advantages to using alloy steels to make the frame of an FSAE car? 4130 is .283 lb / cu in , and 1020 is .284, so there is a very, very slight difference in weight. I'm not sure for a car weighing 650 lb w/ driver that 4130 would be an advantage... Maybe someone can offer some more insight on this?

Analogue, I've gotten a bottle of bad gas before. After hours of frustration, I decided to get a new bottle, and it solved the problem. I was not happy...

[Allen]

Dave, aside from the density, 4130 is almost 50% stronger than 1020 in the normalized state, which is the main merit, IMO. It's also marginally stiffer than 1020 by about 2.4%, but it's pretty insignificant. I dunno about the fatigue limits or notch sensitivity or corrosion properties of the two steels, however.

[Garlic]

Think about what you want in a frame. Only a few members are restricted by wall thickness, and even those are up for a change with a equivalency form.

Do they make 1020 mild steel in .028 wall thickness?

[DaveC]

Only a few members are restricted by wall thickness, and even those are up for a change with a equivalency form.

The rules specifically state no differences in wall thicknesses for different steels. I thought the equilivency forms were for other designs besides steel cages. http://fsae.com/groupee_common/emoticons/icon_confused.gif You could go with really thin 4340 or 300M (for aircraft frames, landing gear, etc...) if thats the case...

If one tubing isnt available in the size you want and another is, that would be a consideration.

I only ask because alloy adds to the price, and should be tigged and heat treated, where 1020 is cheap, and can be mig welded with no compromise in stregnth. So if there is negligable advantage to using more expensive material that is also more expensive to properly join, using cheap 1020 DOM would be a cost advantage without sacraficing performance.

As far as %50 stronger, I just wonder how much that matters in a light car with a fairly overbuilt frame that will never impact anything at high speed (you'd hope http://fsae.com/groupee_common/emoticons/icon_eek.gif). Once the cage is formed, will the %2.4 advantage in stiffness change?

[Garlic]

Wall thicknes is required for only a couple roll hoops, and side imapct protection. Everything else is wide open! That's a big part of the frame.

Equivalency is for anything; of course it has to be equivalent, which means you can't go thinner unless you go bigger. There wouldn't be much weight loss there but some.

[DaveC]

So, are all steels considered equal as far as equivilancy rules? If not, you could concievably use 300M or similar tubing and save a good bit of weight...

[CMURacing - Prometheus]

there is no change in minimum wall thickness for alloy steels. our team had this argument very early on (my freshman year, our second), and its one of the tenets we're trying to pass on every year in terms of chassis design. there's minimal weight savings/stiffness gains/etc., and there's a significant cost increase.

[DaveC]

OK, thats clear. I guess if that wasnt the case, frames would be made of the most expensive superalloy the team could afford. Since that isnt the case, I'm thinking 1020 DOM might be the best thing to use, maybe other materials can be used for non-rule-specified members...