Machinability of Aluminum vs. Steel

D

deker

Joined
Nov 14, 2005
Messages
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I'm working on a non-knife project where I'd have some stuff machined for me. The machinist I'm talking to has told me that his concern is that the tool
pressure would be more than the fixtures were designed to hold since they are
designed to machine aluminum.

So, my question is, would low-carbon steel after a spheriodize anneal be soft enough to work? He's willing to give it a shot, so I'm going to run with it and see, but I was wondering if the big brains here could give me some insight on aluminum vs. soft steel.

Thanks,

-d
 
I don't quite understand. You can machine some very hard steels. Carbide cutters will cut most hardened steels, Not all and maybe not efficently. As we speak I have a piece of annealed 5160 on my mill and I am cutting it from .250 to .135 using a regular high speed steel mill. (I need some thinner stock for a couple folder locks) He should be able to get a tool and fixture to machine low carbon easy.
If you or he has some special tool and it was designed for cutting aluminum it may not last long with steel, but, you should be able to get a similar tool for cutting steel. If the piece you are going to machine is attached to something made of aluminum it may break or come loose during the machining operation. A fixture is usually something holding an object or tool.
 
I'm having him make something he usually machines from aluminum out of steel (it'll be damascus of some sort. Probably 1008 and A203E) so he's already got fixtures set up for machining these parts from aluminum. My guess is his concern is that the extra pressure on his tools to cut steel will cause the work to shift in the fixtures he has.

-d
 
I machine both on a daily basis with the same tooling. If he slows down his feed, and cutting speeds and his depth of cut is shallower he should be fine.Dave:)
 
I machine steel and aluminum all the time. The main thing is, he needs to go with carbide end mills and the speed has to be slow on steel. I generally keep it in the 60-80 rpm range.

Actually, what I normally do is use high speed steel hogger end mills, then refine with carbide (saves your carbide bits).

As long as he doesn't try to take more than .010 to .020 at a time, he should be fine provided the speed is slow (and he needs to use coolant for the HSS end mills).

The main thing to avoid, especially with high carbon Damascus is work hardening. Most high carbon steels tend to work harden very easily, hence the need for coolant.


Mark T.
 
Mark Terrell said:
The main thing to avoid, especially with high carbon Damascus is work hardening. Most high carbon steels tend to work harden very easily, hence the need for coolant.
Click to expand...

We're going strictly low carbon on this one since it's a purely decorative item. Much as I'd LIKE to do hight carbon to get a nice dark etch, first shot will be soft materials. If he finds it's no big deal, I may send him some higher carbon stuff as well...

Thanks for all the info folks. When the secret project is done, I'll post about it ;)

-d
 
Generally speaking, aluminum is much easier to machine than steel and is typically run at higher spindle speeds and much higher feed rates.

Yeah, fixtures designed for aluminum or plastic often lack the rigidity needed for steel, leading to reduced tool longevity, accuracy and surface finish issues and even safety issues.

You've already been given good advice (by most). I'm sure you have no problem separating the wheat from the chafe, but I'll reiterate a few points.

Reduced speeds and feeds (50 surface feet per minute rotational speed, .001" per tooth chip load feed rate on a 1/2" cutter works out to 400 RPM and 1 to 2 inches per minute.) and shallow depth of cut will reduce the loads on the fixture for most any machining. That's a glacial pace, can't get much more conservative than that. Not so for tapping and broaching etc obviously. And remember that too small of a chip load is just as bad as too much. But your machinist should be able to do it, just slower and more cuts = $$$

There is a large range of machinability ratings for different steels in different conditions. What you've described sounds like it would be somewhat on the "bad" side.
 
Quote:
Originally Posted by Mark Terrell
The main thing to avoid, especially with high carbon Damascus is work hardening. Most high carbon steels tend to work harden very easily, hence the need for coolant.


deker said:
We're going strictly low carbon on this one since it's a purely decorative item. Much as I'd LIKE to do hight carbon to get a nice dark etch, first shot will be soft materials. If he finds it's no big deal, I may send him some higher carbon stuff as well...

Thanks for all the info folks. When the secret project is done, I'll post about it ;)

-d
Click to expand...


Coolant won't have an effect on work hardening, which is a function of crystalline dislocations, not temperature. Work hardening is best avoided with sharp tooling, maintaining high enough chip load, and avoid pausing. Low carbon high alloy steels like 316 stainless are really bad about it.
 
Thanks for the info Nathan! Would 1018 or the like tend to work harden? I'd like to make this gentleman's life as easy as possible (not to mention, I don't want to contribute to the breakage of his standard fixtures).

Thanks!

-d
 
I would take Nathan's word on it (hence his user name on here). I'm kind of the knifemaker who machines stuff, not the machinist who makes knives.


MT
 
deker said:
Thanks for the info Nathan! Would 1018 or the like tend to work harden? I'd like to make this gentleman's life as easy as possible (not to mention, I don't want to contribute to the breakage of his standard fixtures).

Thanks!

-d
Click to expand...


1018 machines fairly well. The cold rolled version of it can be a bit of a pill at times but not too bad. It you're looking for steel that's really easy to cut you might try 12L14 or the like.

Though I haven't seen your part or your fixture, I still think you could machine your annealed damascus that you're wanting, and just use conservative speeds and feeds and very shallow depth of cut to keep loads down...
 
I thought I might have some constructive input when I opened this thread, but instead I find myself staring at Mark's avatar, and completely forgot what I was going to say. :D
 
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