Productive process for 3mm sq tubing?

[Oswelds]

Hello!
I am trying to choose between welding processes for mainly 3mm steel square tubing used in exercise equipment.

The biggest question is, how can I skip cleaning millscale and still trust the welds?

Im leaning towards the dual shield process, but I am mainly a tig welder and need the help with choosing the right mig process.

Thank you!

 

[Prajna]

Hello!
I am trying to choose between welding processes for mainly 3mm steel square tubing used in exercise equipment.

The biggest question is, how can I skip cleaning millscale and still trust the welds?

Im leaning towards the dual shield process, but I am mainly a tig welder and need the help with choosing the right mig process.

Thank you!

Arc will do that but then you'll be cleaning up the welds afterward, so take your choice.

 

[Robert Weaver]

Mill scale contains a load of different types of iron oxides, which will react with weld metal in the pool if welded over. The resultant solidified weldment will have unknown inclusions and defects. Why risk it? What are you saving by skipping cleaning the surface?

If you're in a production environment, the time and cost of cleaning needs to be balanced by weld quality and impact if they fail in service (assuming it's for personal use).

 

[Oswelds]

Mill scale contains a load of different types of iron oxides, which will react with weld metal in the pool if welded over. The resultant solidified weldment will have unknown inclusions and defects. Why risk it? What are you saving by skipping cleaning the surface?

If you're in a production environment, the time and cost of cleaning needs to be balanced by weld quality and impact if they fail in service (assuming it's for personal use).

The risk might not be worth it, considering its a human potentially getting hurt if the weld fails. I am trying to save time by hopefully skipping the pregrinding. I have been super thorough so far in cleaning because ive only used a tig welder but it certainly is tedious. I have a whole bunch of projects that need to get done and the cleaning time adds up.

 

[hotponyshoes]

As said, it's not worth trying to save time on the cleaning.

If it's for your own/low volume/hobby projects then look at easier ways of removal.
Cordless grinder with suitable disc, bench grinder with a custom rest and suitable wheel and so on.

Tig is a slow welding process but you can visually assess (and correct) any weld issues during welding. Very little clean-up needed afterwards and zero investment (as you already have a tig) Make up some guide blocks if you are doing loads of welds the same and the tig process might actually save you time overall.

For production look into buying/making dedicated scale removal/weld prep tools or chemical strip it.
Or a combination. It would be easy to make up a tool to clean full lengths of 30mm box if thar is the main material.
Then do the other sections by hand.
Downsides are space needed for the extra equipment, initial financial outlay and staffing the cleaning process.
Advantages include being able to set up to clean the whole tube which then has time and appearance advantages when it comes to paint/powdercoat/whatever.

Other options, see if a 'bright steel" version of the tube is available. Or ask if it can be supplied descaled.

 

[Oswelds]

As said, it's not worth trying to save time on the cleaning.

If it's for your own/low volume/hobby projects then look at easier ways of removal.
Cordless grinder with suitable disc, bench grinder with a custom rest and suitable wheel and so on.

Tig is a slow welding process but you can visually assess (and correct) any weld issues during welding. Very little clean-up needed afterwards and zero investment (as you already have a tig) Make up some guide blocks if you are doing loads of welds the same and the tig process might actually save you time overall.

For production look into buying/making dedicated scale removal/weld prep tools or chemical strip it.
Or a combination. It would be easy to make up a tool to clean full lengths of 30mm box if thar is the main material.
Then do the other sections by hand.
Downsides are space needed for the extra equipment, initial financial outlay and staffing the cleaning process.
Advantages include being able to set up to clean the whole tube which then has time and appearance advantages when it comes to paint/powdercoat/whatever.

Other options, see if a 'bright steel" version of the tube is available. Or ask if it can be supplied descaled.

Thank you and everyone else replying. I got a good idea now how to move forward.

 

[Erie Fred]

How much millscale is on your material ?

 

[Oswelds]

How much millscale is on your material ?

All the tubing I use has a pretty light scale on it but the flat stock has a heavy millscale on it. Flat stock is pretty easy to soak in vinegar overnight to remove the millscale. Tubing is more difficult to soak for as I would need many drain pipes in different diameters to soak them efficiently.

 

[DaveB]

Will you not need to remove the mill scale to apply some sort of cosmetic finish ?

 

[Kram]

All the tubing I use has a pretty light scale on it but the flat stock has a heavy millscale on it. Flat stock is pretty easy to soak in vinegar overnight to remove the millscale. Tubing is more difficult to soak for as I would need many drain pipes in different diameters to soak them efficiently.

I use a 1.5 meter length of 3" square drainpipe and it works very well. Drainpipe is cheap. Using hot citric is relatively quick although a pain to keep hot.

 

[Oswelds]

Will you not need to remove the mill scale to apply some sort of cosmetic finish ?

Just a light sanding and degreasing before paint.

 

[Erie Fred]

All the tubing I use has a pretty light scale on it but the flat stock has a heavy millscale on it. Flat stock is pretty easy to soak in vinegar overnight to remove the millscale. Tubing is more difficult to soak for as I would need many drain pipes in different diameters to soak them efficiently.

You said tubing, now flat stock ?....2 completely different materials.

yes, HR flat stock has some mill scale on it.
Enough you should remove it.

Box tube I find does not have anything to warrant cleaning before welding.

Are you having problems welding it with out cleaning ?

Have you inquired to your supplier about P&O material ?
That is "Pickled & Oiled" so the mill scale is gone when you get it, oiled to not rust.

 

[chip]

I've done a few years in production welding (unfortunately) and tons of mass production jig work and never ever seen or needed to or clean square tube, at most a de-burr a little chamfer on the ends. If your mig welds are up to scratch, I can't see it being an issue. Edited to say I would probably be hitting the ends with a 60 grit for a little prep, but that's it.