Need expert metal fab help...

[JUSTA50]

As all of you are aware, there are some very talented metal fab guys on this board. I however am not one of them. I’m hoping the experts can lead me in the right direction.

Recently, I came up with an idea for a specialty product that is made from aluminum. There are 2 pieces that can be slid together and locked into place using a flat stock locking plate mechanism. I’ve been able to make the main body of the parts and thought I came up with a darn good way to lock and unlock the pieces together but trouble arose. The part I need is roughly 4”x0.375”x0.02”.

What I did to make a sample lock section was order some blue tempered spring steel shim stock. Last night the stuff arrived and I pulled out the tin cutters. Cut the piece to the overall size I needed and fit it into the part. The catch (literally) is I then have to have a tight 90 bend to engage the notch in the part to lock, then another 90 in reverse to act as the trigger to release the two pieces. All was going well until I went to bend the thin metal. It broke! I looked at it, then of course, tried it again. Crack! Well at that point I knew I was working with the wrong material. I then tried to heat it, but all this did was produce stress cracks that broke once cooled.

So now I’m stuck. What thin type of steel should I be using? What type of bending method should I incorporate? I’ll try and figure out how to put a drawing up so you all can see what I’m up against. I think I have a good idea, one which will probably have me outsourcing parts once I bring this to market, so if anyone does this for a living, I’d be willing to talk. Thanks

 

[NUTTSGT]

I might be wrong here but you had tempered steel and tried to bend it, that is why it broke or cracked.


What I believe you're going to need to do is get the proper type of steel, machine it to size, bend it then heat treat it.


Surely somebody with a lot more vast knowledge than me will chime in.

 

[bobadame]

A couple of things you might try. With the stock that you have now, try cutting the strip from the sheet at 90 degrees from the way you cut the first piece. Reason for this is that metal has a grain direction that is established when the it's rolled. It is less prone to cracking when you bend it against the grain. You might try less heat in the bend zone. Just enough heat to turn the metal blue. If none of this works, find some 302 half hard stainless steel stock and try that. Also be careful to not use too tight of a bend radius. The bigger the radius, the less prone to failure.

 

[JUSTA50]

NUTTSGT, I believe your right about the not using the proper metal. I'm going to try what bobadame said and cut it the other direction. I've got the material now so why not. I've also been talking with some work collogues and they said I needed a hi yield stainless leaf spring. That would give me the repeated flexing lock action I need and wont break.

 

[ez-duzit]

Unless absolutely necessary for corrosion resistance, stainless will increase your chances of the part failing by cracking as it is apt to work harden.

Possible solution is to form your spring before tempering.

 

[JUSTA50]

Ok, so what type of spring steel material can I get in sheets that is roughly 0.015"-0.02" thick? In researching, it seems like I also need a low carbon steel. Other types I've seen are stress resistant alloy steels?

 

[nehog]

Several times I've needed something like this and successfully used that steel strapping that often is used on larger boxes and pallets. I have some in about 1/2" width and some that is wider. It cuts with snips, bends but has some springiness to it too.

 

[Sureshot]

Have you tried some cheap feeler gauges or shim stock ?

 

[JUSTA50]

The strapping isn't a bad idea to get a design going but I think I'll be needing hundreds at a time.
The original material I ordered was a blue tempered spring steel shim stock. That cracked

 

[Iron Cat]

a quick heads up, stainless steel will erode the aluminum if they're in contact for any amount of time.Paint/powdercoat one or the other or use a different type of steel.

 

[Engineer61]

If you need the springiness of the steel to lock things together, than you really have to do the bending first, and afterwards have it heat-treated to become a spring. What you started with has been heat-treated and tempered to become a spring, but as you have found out when you exceed the springs tension the steel will crack instead of bend. A better steel will help prevent this, but the real solution is to bend first then heat-treat even if you do decide to go with a better steel alloy.
If you don't need the piece to have any spring to it then you can just use standard 1018 or 1020 mild steel sheet metal and bend away.

 

[nehog]

a quick heads up, stainless steel will erode the aluminum if they're in contact for any amount of time.Paint/powdercoat one or the other or use a different type of steel.

And aluminum will erode steel as well...

 

[Boiler]

Best choice if it HAS to be steel on aluminum is a large anodized aluminum object with small stainless objects. The large aluminum bodies will tend to be less affected by electron loss to small stainless item. Like stainless rivets in aluminum sheet.

Aluminum rivets in stainless sheet is a recipe for disaster, but the other way around is usually ok

 

[nehog]

When mixing metals (such as aluminum and steel) if you can isolate (electrically) the two metals you are much better off. Here is the table of metals that I referred to:

http://www.wbdg.org/ccb/FEDMIL/std889b.pdf

This tells you what metal will be sacrificed and what metal will be protected.

 

[gorilla]

I would use 17-4Ph stainless steel. It forms easily at room temperatures and has a simple heat treat. 900*-1175* for one hour and them air cool. Best way to remove the light scale is glass beading. Beryllium copper would be another choice but their are some health risks with beryllium.