Flame cut steel

tcncj · Jun 18, 2019

Hello

Question....We almost never machine steel.
But got a few steel jobs to do (A572Gr50)
2 local suppliers cut the stuff with a flame/plasma? This leaves a very hard skin on the outside.
Sawcut isn't an option.
How do you guys handle this stuff? special tooling?

L Vanice · Jun 18, 2019

The hard skin is usually not terribly thick. An electric portable disc grinder can get through the skin and let conventional tools cut the rest. You can run a quick test to see if the grinder went deep enough using a file or hammer and center punch.

Larry

Limy Sami · Jun 18, 2019

MMM? AKA A36 - ish

Others have their methods, but I'd conventional mill to avoid cutting through the hard crust from the outside, ……..and like castings, go deep to get under the skin, …...go for tough rather than hard tooling - and if your mill is shall we say ''lacking in rigidity''

use HSS cutters - they're less prone to chipping than carbide.

Plus 1 on Larry's advice ( I keep forgetting that

)

crossthread · Jun 18, 2019

The only thing I know to do is grind it off as L Vanice says.

Larry Dickman · Jun 18, 2019

I take one slow cut around it, taking off about .050, using a regrind or some old used em.
One you get the flame cut edge off, then you can let her rip.

tcncj · Jun 18, 2019

Thanks for the quick replies!

Stupid question maybe.
Is it normal for those kind of big blocks to be flame cut? Or should I find a different supplier who can cut the sizes with a bandsaw? So it doesn't harden near the edges.

gregormarwick · Jun 18, 2019

On low carbon steels like that the HAZ is not usually hard, and the the scale doesn't pose a problem to any decent carbide insert cutter. Cut dry, air on the tool if you have it.

Flame cut is common for carbon plate, yes.

garyhlucas · Jun 18, 2019

When you need to machine it a waterjet cut is really nice, no Haz at all. Maybe a closer tolerance cut too so you can machine less.

Mtndew · Jun 19, 2019

It shouldn't be that hard on A36, but if you're having issues I agree with Lily Sami on your first cut being conventional to get under the scale, then climb cut and hog that shit!

dgfoster · Jun 19, 2019

The only time I have encountered really hard edges on A36 is when machining plasma cut steel. Flame cut does not cause much hardening at all, but plasma actually nitrides the surface and is harder than hard and can be a pain to undercut especially if the plasma cut is not smooth enough to allow getting under it in one pass.

The plasma cutter can reduce or eliminate nitriding by using a proper cover gas rather than just air (80 % nitrogen)

Denis

memphisjed · Jun 19, 2019

grinder with blaze 36 grit or rock, really only need to get it shiny to remove all the hard stuff. depends on block sizes if sawn or torched. If a flat bar or um plate size you can spec saw or shear cut, If odd size or small amount it will be plasma (1-1/2 or less, torched if thicker). Waterjet is outside cheap service center pricing-but way more accurate.

metalmagpie · Jun 19, 2019

I mill flame cut all the time with regular carbide tooling. Try it before you diss it...

Limy Sami · Jun 19, 2019

To all the proponents of waterjet, ……….I feel I should point out the OP is in Zimbabwe, and while I have no actual knowledge, I should think waterjet shops are very few and far between.

dgfoster · Jun 19, 2019

metalmagpie said:
I mill flame cut all the time with regular carbide tooling. Try it before you diss it...

Flame cut sure, but plasma cut? The OP says he deals with both. Plasma can surely be done if the surface is regular, but if it is not, no fun. Been there done that. If the cuts were made CNC or with an accurate guide by someone who knows what they are doing, the plasma surface will be smooth with a very thin nitrided layer. If hand cut by someone of ordinary skill that hard layer can be thick and wavy enough that small/ medium machines can’t take a deep enough cut.

Denis

gregormarwick · Jun 20, 2019

dgfoster said:
Flame cut sure, but plasma cut? The OP says he deals with both. Plasma can surely be done if the surface is regular, but if it is not, no fun. Been there done that. If the cuts were made CNC or with an accurate guide by someone who knows what they are doing, the plasma surface will be smooth with a very thin nitrided layer. If hand cut by someone of ordinary skill that hard layer can be thick and wavy enough that small/ medium machines can’t take a deep enough cut.

Denis

Plasma cut too. Our fab shop has a large plasma, and so we routinely machine plasma cut steel plate up to 80mm thick. The cut quality on the thicker plates can be very poor if the operator wasn't on top of everything.

All the same, any modern steel geometry carbide insert with a good mix of toughness and wear resistance will cut through the skin without difficulty. The key point that a lot of people fall foul off is that it really should be done dry. The combination of coolant and the hard layer is what kills inserts.

tcncj · Jun 20, 2019

Thanks for all the useful information.
My experience with steel is almost 0, still learning everyday

Yes the inserts of my facemill didn't like the coolant...
And my endmills didn't like the stuff either. The sharp edges of the endmills broke off. Running the endmills to the specs of the manufacturer. Maybe a corner radius em would do a better job. But I will keep the worn endmills for other steel jobs. To cut away the hard outside layer.

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