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Steel material that is magnetic and stable when machined? 2

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battleship81

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Aug 4, 2010
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Hello-
I am designing a series of inspection plates for a family of aluminum parts. Each inspection plate will hold an array of 25 machined, cylindrical (2-3 in. o.d., .375 in. tk.) aluminum parts. The plate will hold each part in a 3 pt. kinematic seat machined into the surface of the plate. The part will lay flat on the plate, and the kinemtic seat in the plate will hold the part on a critical (datumed) plane. The part will not be constrained diametrically, but will be loosely clocked using a locator pin to mate up into one of the tapped holes of the part. A bar will span the part, contacting the part near the "i.d." so as not oil can the bottom surface of the part as it will be constrained axially by a screw that runs through the bar and part and threads into a machined hole in the plate (not pictured).
I want the plate to be steel so that it won't wear when switching out batches of parts. I don't really need a super hard steel, just as long as it’s tougher than aluminum. I would like the steel to be stable when machined and magnetic, so that a grinder can be used to achieve the .0004in./3.0X3.0in. flatness tolerance that I need. Right off the top of my head, 416 SS is the only steel that would work, but its pretty pricey. I had considered 01 tool steel, but I couldn't confirm whether or not it is magnetic, and I know it would be harder to machined than the 416 SS.

What other steel is magnetic and will stay stable when machined?

The part in the picture is just a concept test that holds one of the aluminum parts.


Thanks!
 
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Not a material I've used yet but would continuous cast gray Iron be remotely suitable? It would need an appropriate plating finish - maybe even a post plating lap to get your .0004" flatness.

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Please refrain from double posting

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Is O1 tool steel magnetic? Certainly. Is it stable? Probably not to your tolerances.

My recommendation would be as KENAT said, cast iron. If flatness is an issue, it is possible to get it surface ground and scraped (if necessary).
 
Pardon my ignorance, but why does it need to be magnetic? Could you use a steel grade sufficient for your tolerances and another steel for whatever magnetic features you required?
 
Thanks for the replies. Sorry for double posting; it won't happen again.

You're right, Mike. I'm looking for magnetic so that a surface grinder can be used.
 
AFAIK most "normal" steels can be magnetized, so can't you just magnetize after you've machined the part?

If it has to be stainless steel, you're looking for ferritic or martensitic SS.
Contact your suppliers to see what they have in stock.

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Almost all ferrous materials are magnetic (will stick to a magnet)

The only reason to use stainless is if you need the corrosion resistance, otherwise you are just adding unnecessary costs.

Grey Cast Iron is a pretty good choice if you're looking for long term dimensional stability during use and over environmental changes.

Otherwise using a common tool steel such as O1, A2, etc.. is probably your best bet. A rough machining pass, heat-treat (temper for best stability, not highest hardness), then finish grinding, whether surface or jig, to get within your tolerances is the process I would use to make this tooling.

This looks like a pretty easy job for a tool and die shop.


Nick
 
Nick-
Pardon my ignorance here, but why are you saying i'd want to heat treat? I really don't think I need the plates to be that hard, but I just need something tougher than the aluminum parts that will be inspected. Is it just for dimensional stability? I like that you mentioned grinding after the first machining of the surface. I was wondering if that would be a good idea.
 
I think he's talking stress relieving after major machining before finish machining - we do this a lot on complex/precise Invar pieces.

If you use the continuous cast gray Iron I don't think you'd necessarily need it.

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