work hardening ?

[morpheus]

Night before last I cut a piece out of 5/16" plate and after some machining I was going to chuck it up in my buddy's lathe and turn the O.D. of it down a bit to clean it up and much to my shock the piece had become work hardened and I couldn't hardly work it with his small lathe. This is the first time I've noticed something like this .... is this a common occurence ?

If I had used a plasma cutter instead of a torch would the same thing have happened ?

- jack

[aircraft]

The answer to your question is no.

did you get it hot on the mill or the lathe?

[morpheus]

I don't think it got very hot on the mill. Just really drilled a bunch of 3/8" holes in it. Though we did use a hanson drill to bore a 1.25" hole in the center.

- jack

[BillC]

Hey Jack,

I have usually associated work hardening with a forming operation like bending or drawing rather than from heat, but I can't think what else to call it right now...

Anyway, it happens with low or high carbon steels, and is also a problem with lasers. We have tried lasering holes in plate with the intention of reaming them to final dimensions, but found that the hard "skin" on the burned hole made tool life too short.

Aircraft, does PAC truly leave no skin, or is it just thin enough that it does not pose an issue?

Regards,

[Franz]

Jack, sounds like you may have carmelized the steel when you cut it. If you grind it down about .020 you may be back to machinable steel.

[morpheus]

Thanks Franz. Last night I took my angle grinder and got the piece into a much "rounder" shape. I took off more than franz recommends but will see how it goes tonight. thanks ...

- jack

[bobad]

High mangnaese steel will work harden a bit from dull tools, hammering, and bending. It usually will not work harden enough to make it impossible to machine, however.

Cutting and welding is another matter. Some steels leave a layer of super nasty slag when cut and oxidized. This slag is not only pretty hard, but very abrasive to tools. All I can say is cut conservitavely and grind off the slag.

[aircraft]

Originally posted by BillC
Aircraft, does PAC truly leave no skin, or is it just thin enough that it does not pose an issue?

All burned holes have some skin (oxidation) thickness of that skin is influenced by a number of variables. I have always been taught to be a useable piece of metal all oxidation must be removed.

I have no personal experience with a lasers but I thought it could be used in a purge chamber with no oxidation?

[morpheus]

well I got one of these pieces of plate turned down the night before last. It turned out to be user error

The pieces I was attempting to turn down were right at the max OD for his lathe and I had the cutting tool just a bit above the centerline of the piece which was making it to where it wouldn't really cut.

It was also my first attempt at using carbide tools in the lathe and all my buddy has are angled tool holders which evidently don't hold the carbide pieces at the right angle for cutting.

so, it was a compound of errors. once the tool holder was adjusted better and I switched to another type of cutting tool it worked fine.

- jack

[jason]

Originally posted by aircraft


All burned holes have some skin (oxidation) thickness of that skin is influenced by a number of variables. I have always been taught to be a useable piece of metal all oxidation must be removed.

I have no personal experience with a lasers but I thought it could be used in a purge chamber with no oxidation?

I used to run a couple of co2 cnc lasers, both Mitsubishi, one was 2000 watt the other 3000 watt. On those machines it depended on what assist gas was used (assist gas pushes the molten metal out). We used either oxygen or nitrogen. The Nitrogen was capable of clean cutting (no or exremely little oxidisation) but required more power and hence thickness was limited. With oxygen there was of course oxidisation (as with a cutting torch) but the thickness and speed were increased significantly.

Jason

[Franz]

Jason, if I'm readin this right, laser cutting isn't a whole lot different from O/A cutting other than the initial heat source. Laser + Oxygen is really using the molten iron as a fuel source.
No wonder they won't let me in that room to see how it really works. Now I am definitely gettin in there and checking that machine out.

[jason]

Franz, yes that's right. With oxygen the metal is burning just like an o/a cutting torch only difference is the process is started by the energy of the laser. Clean cutting (nitrogen) however relys solely on the energy of the laser.

The lolerances are quite impressive though, much better and cleaner than o/a cutting or even plasma. They are pretty neat machines.

Here's the sample parts page from the place I used to work.

https://www.jobsite-us.com/j-parts.html#laser

Jason

[Franz]

A buddy of mine sells reproduction Corvette fuely parts that he's having laser cut at one of the local shops. These parts look better than the original stamped parts.
The machine owner encourages their employees to bring in short run work that will fill time on the machine, so if you need something made, they will often beat anybody's prices, especially since their major customers have cut back bigtime.
Definitely a nice toy, but I don't have room for one.