material thickness ratings on welders

[lostcause]

am i the only one perplexed by these? i'll confess i'm not a trained welder. i've had zero training other than hands on. in the last 20+ years since i struck my first arc i've welded many things - all with structural success and many with cosmetic success

my experience is almost 20 years as a steel detailer. in that time, i always worked under the premise that all welds are sized as needed, and you can't weld anything full-strength in a single pass. as i look at new welders, i see max thickness 1/4", 5/16", and 3/8" for the small-medium sized home shop welders in the range i want. my experience told me that with most all types of welding - gmaw, smaw, fcaw - that a 5/16" fillet weld was the maximum effective weld for a single pass. with saw you could get 3/8", and we never considered gtaw for structural, so i have no knowledge there, though i assume it to be smaller. we designed all welds based on the load, and if we did not know the exact load, it was sized for the strength of the material. any time we needed to match the full strength of the material you were generally talking about a complete penetration weld, generally square groove or bevel groove.

all welder specs now list a maximum thickness welded in one pass, but does anyone know how they are deriving these numbers? are they talking about a weld strength based on x/16ths of an inch with 70ksi filler material and 36ksi base metal? if so, it seems a little useless to me. whenever i build something i only consider whether i can generate enough heat to create proper adhesion of the two metals i am attaching. very seldom does a weld need to be the full strength of the material in my experience. i recently welded 1/2" plates to a 1/4"-3/8" channel web with a 120v flux cored welder maxed on the 90a setting. those plates will never come off, and they will carry any load they could possibly have put on them. guaranteed that the plate will rupture at the 7/8" pin holes before the welds let go, and probably the channel web will yield before that.

can anyone enlighten me as to the theory behind these ratings that all manufacturers love to toss out now? the spokesman for the new forum welding sponsor seems to be pretty well educated and versed in these matters, and surprisingly doesn't really seem too biased how bout it mark? can ya help me stop scratching my head about this?

 

[yomax4]

The Ratings are skewed at best. Most 115v Welders say they will weld 1/4" plate single pass. Anyone would be nuts to build a Trailer out of 1/4" welded with a 115v unit unless they Pre-Heated to 600 degrees prior to every weld. Its like that with output too. Take the Miller 210, They call it a 210 but the plate on the front says 150 amps output. Comon Sense has to take over at some point. Will a 250 amp mig unit really weld 1/2" Plate with one pass? Maybe if you Spray with
.045 but its not designed for that thickness. Bottom Line, There is a lot of competition out there and with that comes a lot of Hype..

 

[Mark @ Everlast]

Not all manufacturers rate them the same either. Sometimes its even in multipasses. (Which a multipass weld is typically better anyway). These are "marketing" tools that some company started a while back. Its sort of the one upsmanship game that is being played. I personallly don't like the "maximimum" weld capacity because it cannot take into account variables.
For example in aluminum tig welding:

Preheat
Tungsten size/type
AC balance
AC frequency
Ambient temperature
Pulse
Oxidation
Alloy type
etc.

I have that question a lot. My typical answer is that its really unlimited, if you have the skills and patience to make multi passes. We have added what I think is realistic expectations from our units to our website for a single pass weld...however, it was done only to give a point of comparison to other models...after literally scores of phone calls asking "how thick will this thing weld". Rather than tie up our resources answering these questions all day, between me and another guy, we put in the time to figure out a reasonable expectation under fairly good circumstances. Most people report that the units are exceeding their expectations, occasionally, others report less achievements. Most of the time I think it can be traced to experience, though.


Except for welding solid 3 inch thick slabs of plate together...1/4" is all that is recommended to weld at a single pass for quality in most circumstances. Even that is a bit much for most people. The reasons large single pass welds are discouraged are that it is easier to get large inclusions or other defects in the weld and less heat stress and HAZ formation is obtained with smaller welds.

I'll put it in perspective:

I am a proud owner of an 1958 Lincoln SA 200. The serial number indicates it has the parts of a short hood, but carries the "long hood" look. Its only 200 amps, yet, this machine and others like it have built pipelines, powerplants, factories, skyscrapers, tanks, ships, etc since the 1930's with only 200 amps@ 60% duty cycle. It still is a preferred welder on pipelines and construction sites. In fact on some job sites, if you pull up with something that isn't old drab gray, they will run you off!! A used unit like mine can go for as high as 7k on the right day with a fresh skin of paint. Now of course, later there came a SA 250,400 etc. Now there are welders putting out over 600 amps. There are real applications for these, and they can make quality welds at great thicknesses...however, I don't want to be doing it. The intensity of the heat and arc that is given off is great and keeping cool is a serious undertaking. Welding is hot enough work. Most people couldn't stand the heat very long from welding a 3/8, 1/2 or even 5/8" pass. It just isn't practical.

What means more to me in welding is duty cycle. How long can you sustain the weld that you are making?

60% used to be the industrial standard. Now Miller has dumbed down its former ratings and publish on their site that anything over 20-30 percent is industrial duty cycle. I am not a fan of this rating method. Again, its a game they are playing. But if you go back and look at all the "old" machines, duty cycle was never less than50-60% at full amps. Either industrial workers have gotten lazier and won't weld very long at a time or Miller and others have been cheapening up their machines and trying to "upsell" their machines capability.

 

[yomax4]

Well Said!!!:thumbsup:

 

[lostcause]

thanks for the replies guys. pretty much just telling me what i already assumed - it pretty much means nothing and is totally useless, but it still leaves me with the nagging question - what is it based on? this kind of leads me right back where i started:

Will a 250 amp mig unit really weld 1/2" Plate with one pass?

as a really basic straightforward theoretical approach, let's just say that it's a 1/4 fillet weld on one side of a 3/8" plate, 12" long, welded to another 3/8" plate. this assumes a shear loading condition with no eccentricity on the weld group, and the use of a 70Ksi electrode. the weld strength would be:

R = D * L * C = 4(16ths) * 12in * 0.928 K/in = 44.544K = 44,544 LB

now the plate: assuming A36 steel with no eccentricity between the applied load and the shear plane:

R = 0.4Fy * L * T = 0.4 * 36Ksi * 12in * 0.375in = 64.8K = 64,800 LB

now, it's entirely possible i made a mistake in my calculation. i've been out of the industry for almost 2 years, and i may have jumbled something up. based on a 1/4 fillet, this doesn't add up. i've seen 5/16 max fillets, but not with the size hardware that people here consider, and even then, we're still not there. if this was a 2 sided weld, then we're up around 89K, so yeah, we're well over the plate capacity, but that's not the advertised number.

any ideas on how these numbers come up? i know these calculations have safety factors engineered in, so maybe they're doing a destructive test and physically breaking parts to prove that the steel yields before the weld? to be honest, i really don't care too much, because i see the rating as bogus, but i see so many people toss these max numbers around when someone asks a question about a welder they may be buying. at this point i feel like i'm mulder trying to debunk some alien welder myths.

duty cycle doesn't really bother me too much either. personally, i find that even on my old 120v century, heat maxed on the 90a setting, 0.035 flux cored, welding 1/8" through 1/2" i never hit the duty cycle, which is probably 20% or less. i fit up a piece, then tack it, check location again, then weld. there's a lot of off time for the welder in a one man operation. now, where i used to work, people would totally fit up and tack all components together and then pass the assembly on to a certified welder, and he would do nothing but weld. in that case i can see a duty cycle issue.

personally, i'm inches away from buying a miller 211. i want a total replacement for my old 230a craftsman and the 120v century. the miller should do both. i always seem to use the stick at 75a-150a, and the miller is capable of that. the other big perk is that it's a small package and will also run at a downgraded output on 120v, so i can take it anywhere to do lighter work if needed. mail order it's just over $1200 delivered, including sales tax. i even got the local place (25 miles away) to do $1260 with tax, so it's not too horrible, and that price includes the spool gun.

 

[Mark @ Everlast]

lost cause,

There is a basic formula that a lot of people toss around. Its 1 amp for every thousandths of an inch. This is probably how a lot of the units are rated.

 

[woodlandfarms]

So I have a project that is all 1/2" steel. An AC/DC Tombstone, What would be a recommended Rod and Setting (I think I hav 7014 (thick, like 3/8") and run the weld at around 210 Amps DC+

This is all said from a VERY novice welder (was given a buzz box, some stick and about a half hour you aren't going to kill yourself lesson) and I have been welding ever since. Everything I have done for the most part has held, but pretty would not be a word I would use.

Carl

 

[Mark @ Everlast]

Well you have a problem.:confused2: The tombstone is only good for 125 amps DC. It won't burn a 3/8" electrode even if it were 200 amps.

A 1/8" inch 7014 set around 110 amps will probably wet in quite nicely. V it out at about a 60 degree total angle to about 1/16 land. It'll take somewhere between 4-6 passes to fill it completely and properly. Then grind out the backside about 1/8 deep and run a weld that fills the groove completely on the backside. That is about as proper as you can get for farm work. My first pass would be with a 6010 or 6011, and my preferred rod of choice is a 7018, but unless you have a rod oven, I'd go with the 7014 you have.

 

[travis potter]

Mark you are very helpful and give good info. Thanks!

 

[woodlandfarms]

Thank you very much mark. I am going to come back to this question once I get back home and can really look at what I have. Clearly I am giving you the wrong specs as I have welded a lot of stuff up.

I have to go take a class, or get someone to teach me. I bet I can find a local guy who is a good welder and teacher and slip him a couple for the "class".

Carl