Steel grades

If these electronic chassis aren't flying around in a spacecraft, A36 should be your cheapest choice. It usually sold with the mill scale on it and since it is rolled to final shape hot, its dimensions will vary a little. It's commonly called "mild steel" these days. Its carbon content can vary from about 0.15% or so to as much as 0.29%. 1018 is usually cold rolled to its finished size and if so, it is more accurately sized, free of scale and costs more than A36, maybe 2X. The "18" in 1018 means that its carbon content is about 0.018%. Typically, neither of these products is considered "hardenable" by normal processes.

1008 contains 0.08% carbon and, since that's pretty darn low, it's more expensive to produce than the above. One big advantage of this type is that is not as prone to work hardeneing as A36 or 1018. It is used in application when deep drawing is needed.

12L14: the "L" stands for Lead. They put a small quantity of lead in this steel to make it easier to machine. I haven't ever used it in sheet goods, but it probably would be my last choice.

4130 is relatively expensive. They use it a lot in tube to make race car roll cages. Some airplanes (maybe a LOT of airplanes) use it in framing. I even cast some 10Kg anvils from it. Relatively high alloy. I can't think of a good reason to use it in your application, except that it resists cracking at welds well, I think.

Have you tried cheaper grades of aluminum? You'd want to test them. If vibration isn't an issue, you should be able to save some bucks. Check for "gumminess" when drilling and make sure that things don't crack when bent.

Pete Stanaitis

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mkr5000 wrote:

12L14 would be my choice. Machinists love it and consumable costs go way down

Gunner

"Confiscating wealth from those who have earned it, inherited it, or got lucky is never going to help 'the poor.' Poverty isn't caused by some people having more money than others, just as obesity isn't caused by McDonald's serving super-sized orders of French fries Poverty, like obesity, is caused by the life choices that dictate results." - John Tucci,

I guess the primary thing for me to be concerned with is how well it forms. (especially at 050 thickness)

I almost always just do a 90 degree bend.....I was looking at Mc Master Carr and they said 4130 was excellent for this but then they didn't show the others.

4130 was half the price of 5052 aluminum but I suppose what I'm asking is what is the most commonly used.

I know with aluminum (at least for electronics), it's 3003 or 5052.

4130 is used in small planes and bicycles as "chome moly" steel.

this guy goes on and on about it:

None of its merits sound like things you need for your application though.

Others have given you some good answers... I've found aluminum often works out cheaper in relatively small quantities when you count the cost of the finishing required for steel, and shipping costs.

Best regards, Spehro Pefhany

Don't you mean 0.18%?

Jeff

Unless I should be looking at other numbers on aluminum than 3003 and

5052, the part that emachineshop.com is quoting me is over 50% less using the 4130 steel. (compared to 5052)

Naturally, I'll stay away from 4130 if I someone can tell me I shouldn't use it. ( ? )

So, what other numbers of aluminum should I be considering if you're saying the part would be more inexpensive using it than steel ?

I've always heard the opposite.

If you want a lower part cost, use steel......I just never have because of weight.

This particular part though is only about 7" x 3" and 050 thickness would be fine -- weight isn't an issue.

For aluminum, try 6061-T6 if you don't need a sharp bend. It's usually the sheet of choice at the DIY store.

Bob

3003 and 5052 are the best alloys to bend. If your part needs to be folded into a box or something like that, then that material is a good choice. 2024 is very hard to bend, but in a pinch you can anneal it along the bend line and then bend it before it gets hard again. But, I suspect a commercial shop won't want to mess with it. Thin 6061 and the like can also be bent, but the thicker material will start to crack at the outer radius. But, 2024 and 6061 are much better to machine that the 5052 and 3003.

Jon

You don't know the specific properties of the various alloys, which makes me assume they aren't very critical. In which case, why wouldn't you simply ask the shop making the parts to suggest the alloys?

John Martin

I assume you mean sheet metal parts although some of those steels imply machined bar, rod or tubing.

In small quantities aluminum usually is best overall because you don't have to finish it, although you can paint or plate or brush or anodize it if you want to. 6061-T6 is the most common grade for electronics, I think because it's the strongest alloy that can be bent with few problems, and welded. 5052 is somewhat weaker and bends to a sharper corner without cracking. The higher performance alloys all have some gotcha like brittleness or welding issues, the softer ones are better for severe forming but aren't stiff enough when flat. Bud chassis boxes are a good example, they deform easily and don't hold screws well.

The price of aluminum seems to vary wildly between suppliers, I don't know why. I've been quoted $60 for a 4X8 sheet from one local dealer and over $200 from another.

"Cold Rolled Steel" or CRS around 20 to 26 gauge (~ 0.018" - 0.036") is similar in stiffness to 0.050 or 0.062 aluminum. It's used to repair car bodies, often in thinner gauges, and for sheet-metal furniture and appliances. Some of its strength comes from the cold rolling so you can't compare it directly to hot-rolled steel of similar carbon content like A36. It's almost always plated or painted or powder-coated even for indoor use. Some people's fingerprints will rust it.

Hot rolled steel is the cheapest to buy and most expensive to finish. A36 is a common type. It's easy to weld and generally used where strength counts more than appearance.

Galvanized sheet steel is CRS with a zinc coating which protects it from rusting, including the cut edges. I've used it for electronics where I needed magnetic shielding and didn't have enough Mu metal. It works about as well as aluminum but it doesn't look as good and doesn't hold paint well. It's used for heating ducts so it's available in small amounts, which can be a problem for metals. The largest local dealer had a minimum order of $500 last time I checked.

There's a type of galvanized or zinc-primed or whatever steel with a matte grey finish used for computer internals that could be the best answer if you can find some. Common bending machines might scratch the coating. The undersides of my SUV and truck are made of something similar.

12L14 and its free-machining buddies make life easier for the machinist but it rusts badly, as does chrome-moly.

A stainless steel such as 304 could be worth considering. It's more durable than aluminum for things that will be banged around and also doesn't need expensive finishing. Some types like 302 made decent flat springs for no-tool panel latches.

I ask the shop for their recommendations and see if I can save money by fitting my design to their standard practices, for instance not calling out holes they can't punch or bends beyond their brake's capacity. The setup is a large part of the cost for a small batch of parts.

I set up a home shop substantially to learn materials and manufacturing processes so I could design a $5 bracket that didn't cost $3000 to make. Electrical engineers rarely know much about mechanical engineering or production and too often make very expensive design decisions. My machine tools are far too old, slow and small for economical production - that's why they were available cheap - but they are good enough to make a single prototype or machine a small emergency batch of simple parts that the sheet metal shop fabricating the job couldn't handle. Often I notice an improvement or interference when making prototypes that I missed when drawing them.

Jim Wilkins

For general chassis and sheet metal work specify P&O. That is a standard 1018 Hot Rolled (HR) sheet metal that has been Pickled and Oiled (P&O). Usually sold by "gauge", you are probably looking for 16 or

18 gauge.

Sometimes specified as HRP&O-----Hot Rolled Pickled and Oiled. It's a little bit more expensive than regular HR sheet metal, but well worth it for appearance.

3003 is about the softest grade of aluminium going.

since steel in the same thickness is about 3 times the strength of aluminium any annealed grade of mild steel would probably do.

get your local yellow pages out. locate a sheet metal bending outfit and ask them what the easiest grade of steel is for bending and punch forming. that will get you first hand info.

failing that annealed 316 stainless would probably do and give you freedom from corrosion.

Thanks folks....Jim especially, for that primer.

Yes, I'm talking about sheet and forgot to mention that I will be painting the piece with either a 2 part system or a powder coat.

So, I would imagine if it's painted right away -- corrrosion isn't an issue?

The good thing about this software is you can do the part and then put in different material choices for an instant quote....so I'll try some of those numbers.

An 050 steel is ideal for this part because I'm using a thin magnetic strip to hold the piece on.

It's just a 7" by 2.5" lid with (2) sharp 90 bends.

1018 -- 12L14 -- I'll try some of those numbers.

Looks like either 1018 or 12L14 is the way to go.

They're both the very same density and damn near the same price but it says 12L14 machinability is excellent compared to 1018's "good".

?

At 050 thickness which would you use?

Sheet metal?

Ooops...never mind.

Gunner

"Confiscating wealth from those who have earned it, inherited it, or got lucky is never going to help 'the poor.' Poverty isn't caused by some people having more money than others, just as obesity isn't caused by McDonald's serving super-sized orders of French fries Poverty, like obesity, is caused by the life choices that dictate results." - John Tucci,