[Spartan]

Most regulars here probably know that I'm primarily a TIG welder, and as such, I'm fairly adamant about material prep. However, I'm looking into offering more furniture and utility-type products to my customers (benches, tables, chairs...non-critical things of that nature) and have started getting back into MIG to speed up the process (make it more affordable for the customers), and since two of my helpers are not TIG welders, but are proficient at MIG (keeps them busy and paid).

So my question is this: If the beads are flowing fine and the welds look fine, is there any practical reason that you MUST remove the mill scale before doing this type of welding? Have I just been running TIG for too long and shouldn't even be this concerned about it??

[sbaker56]

You'll be fine, especially since it's non critical, I've done break tests with and without removing mill scale and not seen any sort of pattern in regard to a difference in strength. If the scale is exceptionally thick I'd probably remove it, but on tubing, pipe and light plate I wouldn't worry. I do like to take a power wire wheel to things however to take off anything loose be it rust, scale or just dirt.

[tweake]

crank the heat up a bit and burn through the mill scale.
however on things where you want fairly clean welds to cut down on finishing time, your far better to take the time to clean the mill scale off.
structurally, mill scale can cause issues especially when your using bare minimum amps due to it being thin wall tubing.
welds can look perfectly fine but are just sitting on top of mill scale and not actually bonding.

the danger with mig is that welds can look perfect and not actually be bonding.
i highly recommend testing all weld settings, go break the welds and see how it holds up. i've had perfectly looking beads pop right off before its a real eye opener.

[Oscar]

So long as you are not getting excessive under-cut from having to weld over millscale or other impurities, then I suspect it will be fine. It also depends what MIG wire you use. ER70S-6, while very common, inexpensive, and has nice wet-out, won't deal with impurities (such as millscale) as well as ER70S-2. S-2 is "triple deoxidized", meaning it contains trace amounts of Titanium, Zirconium, and Aluminum that work as deoxidizing agents that will help eat up the millscale and thus help prevent undercut under the correct & proper conditions. It is, of course, more expensive than S-6.

Cranking up the heat and burning through the millscale does make it get out of the way, but without deoxidizers, it has no where to go and stays mixed in the puddle and affects (reduces) puddle fluidity if is excessive. That's why there's a higher chance of getting undercut, because the puddle is less fluid and the arc cuts to much into the steel without molten steel flowing into the freshly cut metal.

[TraditionalToolworks]

Aside from if it's ok or not, is that the type of work you want to sell?

3 years down the road a welder is looking at it saying, "Look some wanker didn't even clean off the mill scale..."

Certainly not trying to tell you how to run your own business, I wouldn't cut corners for the cost of a happy meal...

[Spartan]

Thanks for the info, fellas. Very helpful!

TTW - I'm with you 100% on that, and it's actually a big part of why I'm asking here. The thing is, after doing an analysis on the pricing structure, I'm having to make decisions on whether or not going down this road can even be profitable for the business. In this situation, a welder (or apprentice) spending an extra 20-30 mins on prep can be the difference between losing or making money on things like this...the margins are that thin. And please note that when I say "profitable" I don't mean squeezing out as much profit as possible, I mean can the shop even make $20 in profit when one of these goes out there door in order to help keep the lights on? These will not be made-to-order items for customers that come to us, but rather items that are advertised in their own right, so pricing can be tricky.

A big part of this is also my desire to increase the MADE IN USA items that are available off-the-shelf. And I'm finding out exactly how hard that is...

[tweake]

so the question is do you want to compete with the cheap nasty stuff or do better quality?
also can you absorb any comeback if one of these items fails, customer gets hurt etc?

i have family who run a farm type workshop. they mig over mill scale all the time. however the gear is over welded to start with and it doesn't need to be a tidy finish. so its fit for purpose.
your situation is somewhat different.

[sbaker56]

Might seem kind of like a dumb answer, by why not test it out? Others have brought up a good point about bead appearance and wetting out, but like mentioned it depends on the level of scale and your machine settings. It's not possible to be entirely sure until you test on the kind of materials you use with the machine and settings you plan to use.

I do have to disagree on the point of having to always remove scale or it's not a quality job, if it's going to be a stool and you can weld it without showing undercut, lack of fusion, cratering or any other weld discontinuities then it's better than 99% of what's out there mill scale or no mill scale. If not grinding to bright shiny metal means you do get undercut or other issues, then yes it would mean you didn't do a quality weld, but it's not always necessary to avoid those things.

[Spartan]

so the question is do you want to compete with the cheap nasty stuff or do better quality?

Yes and yes!

also can you absorb any comeback if one of these items fails, customer gets hurt etc?

Yes, I can. But an item would never leave my shop if it were likely to cause injury or a structurally inferior weld. My original question was not so much: what can I get away with?, but rather: is this an acceptable practice?

[Oscar]

My original question was not so much: what can I get away with?, but rather: is this an acceptable practice?

I echo with what tweake was getting at. When see the garbage welds on a lot (some, but not all) of mass-produced stuff at big box tool stores, Tractor Supply, Harbor freight, etc, heck almost anything could be better than that stuff!

Another thing to consider is that if you are going to be mass producing something, but still want the added practice of removing millscale, then perhaps making a jig to mass-de-millscale the parts is in order. Something that won't take more than a couple minutes of course. It would have to be precisely made jigs for specific parts, with very abrasive long-lasting abrasives (3M Cubitron II comes to mind) in order to not have to be sitting there going at it pass-after-pass; just one or two quick swipes/turns/etc to remove any and all millscale quick. Otherwise it would still defeat the purpose of saving time which will end up eating profits. I was actually pondering this the other day. You know me and my gedankenexperiments. The hamster wheel is always turning at ludicrous-speed.

[TraditionalToolworks]

TTW - I'm with you 100% on that, and it's actually a big part of why I'm asking here.

This is my take, and I subscribe to this in most everything I do with business. I always want to be recognized for doing some of the best work available. I want people to remember when the chips are down and they need someone to do a good job for them, they'll call me. In some cases I've walked out of companies because of the way they operated.

I'm not a professional welder though, so something to keep in mind.

Seems to me that in many cases I am willing to pay more for something that says "Made In America", so I'm not always looking for the best price, in fact, I'm more often looking for some better quality.

Nowadays it's been a tough choice, most of the stuff we buy seems to be made in China. I think that is going to change though.

Profit is a tough thing, but I would understand how much something costs you to make the way you would want to, and price it accordingly. Maybe the stuff will be too high, maybe not, you'll need to see. However, if you have a reputation of producing quality work that people can rely on, the price could be achieved. As an example, ZTFab produces high quality welding cart kits. The kits themselves are priced higher than most carts are, yet he sells a lot of them and has people buying product from him all the time. I would like nothing better than to buy one of Paul's kits, but it's not in my cards right now...but it is the type of kit I would like to build for my own shop. People that buy them rave over them, so I'm sure they're good. That's kind of extreme as ZTFab is on the really high end.

Another example is Roy Crummrine, he sells a nice little pallet for welding. It's a very high quality product that is not cheap, and he sells them.

https://crummywelding.com/

Yet another example, you may or may not know of The House of Chop. Philip is a great guy, really funny, I like following him on Instagram and YouTube. He makes these third hands, and I would say for $68 they're not cheap. But I know he sells them and he does a really nice job on them, they are 100% made by hand and welded by hand.

https://www.thehouseofchop.com/chop-sho ... third-hand

With all that said, I don't have a success recipe for you, I only offer you advice on producing quality product that you will be proud of and price it accordingly so you can turn a profit. Nothing is easy in life and I don't have any answers to make it easier for you. I just suggest you make the type of product you will be proud of and let China or other 3rd world countries make the rest. I say that with partial tongue in cheek, as I type it seems the hammer is coming down on China and the trade war we have with them will probably not benefit the consumer.

[Coldman]

Thing is with mig , the better the prep the better quality weld results. Mig is renown for lack of fusion, I've seen frames fall apart at the hit of a hammer due to welding over mill scale. Often it works ok. I don't care, any mig weld I do is gonna be on shiny steel.
The bamboo stuff is done on mill scale by unqualified underpaid labour on sh#t steel in disgusting work environment so you are behind the 8 ball already on price. Your point of difference might have to be quality, made to measure with choice of finish, and reasonable but not lowest price.

[Spartan]

Thanks everyone for the advice. You've given me a lot to think about regarding how I'm going to handle this side of the business.

[sbaker56]

MIG absolutely isn't the most contaminate tolerant process, but I'm finding myself wanting to run another experiment on this subject now as honestly in my own experience I've never once experienced an utterly unsound mig weld or been able to create one by welding on lower but semi reasonable settings or even over heavy rust, millscale and contamination. Maybe I could weld one side of some T joints with varying levels of prep out of 3/16 or 1/4 plate and bend them away from the unwelded side, I could post my results somewhere else if anyone else is remotely curious.

Am I saying it doesn't happen? Not at all, I just suspect the culprit is typically a totally improperly set machine ran by a poor welder. Even so If It's going to be subject to any real stress I ALWAYS clean down to bright shiny metal, I'll even do it before stick welding if it's especially important. It's just best practice especially on MIG but I've even see Jody mig weld over scale, short circuit weld 1" steel etc because it just wasn't important or worth the extra cost to the customer.

[tweake]

a I just suspect the culprit is typically a totally improperly set machine ran by a poor welder.

the problem i've seen is it can look perfect.
trouble is every welder likes to do things a bit different. however you can get around this by simply testing it. weld a joint and then break it.

[tweake]

is this an acceptable practice?

yes, if its not relying on the weld for strength. ie even if the welds are bad its still not going to fail.

to me the 2nd issue is weld clean up. i rather have better prep to make better welds so i don't have to spend excessive time cleaning them up. one thing i've been learning the hard way is better prep = easier welding = less clean up.

if your doing mass production its easy enough to set up stations so they can crank out the prep work really quickly.