Wondering if anyone here at the 'space has done hot shaping work with aluminum, like blacksmiths do with iron.
My first project, if I ever make it there shall be roughly forming ingot to desired shape and then machine finish. I’m not sure if that should be followed up with any sort of heat treating our not. … So I’m wondering if there are folks to ask, materials to read, or classes that might be taught on such topics. …
Have forged aluminum stock before, it’s generally doable but quite a bit harder to work than steel. The main problem is the fairly narrow working temperatures and lack of color change at those temperatures. If you work it too much too cold it will work harden and splinter or fracture. If you let it get too hot it will turn into a powder when you hit it, or melt in the forge. Sheet aluminum is fairly good for raising, generally worked cold then annealed when it starts to work harden, again it’s a tricky material to anneal since the color doesn’t change, there are a couple tricks to get it to the right temp with a torch but you should expect to blow through a few pieces before getting it right. The hot forging I did was for an art project so I wasn’t concerned about material properties much, if this is to be a working part you should plan to test them before use and make a few extra in case you get fractures or other defects.
what’s the project, how large of stock are we talking about, and how much movement do you need to get in it.
2 Likes
As jhaskins has stated aluminum is a difficult material to work with, especially if heated and in the presence of oxygen. What the alloy is greatly affects things, aircraft alloys in the 2XXX & 7XXX series are the most are the most common and specific heat treatment properties.
In aerospace we did what was called “Hot Forming” this is well below melting temperatures and annealing temps, e.g. putting a joggle in a tee-section of extrusion. We controlled the temperature closely, you can buy temperature “crayons” that change once a certain temperature is reached so you know when to work the material. We used two of them: one to show the temperature we needed to reach and another that showed we exceeded the limit which meant scraping the part (of course this is because we were extremely concerned about changes in physical properties of the metal resulting in out of specification for intended purposes).
Google: Temperature Indicator Crayons to find suppliers. One company sells them that range from 104F to over 2100F
3 Likes
I’m hoping to remake some crappy plastic tools I have out of aluminum because the plastic won’t take the torque. We’re talking about 10mm or less diameter, about 3" long or less, so pretty small. I could always just cast the thing and clean it up, and I’ll probably start similarly. I could also just machine it out of cast or extruded stock, and I’ll probably try that too. But I thought it might make a fun piece to try “forging”. I think what I’m actually talking about is “cold forming” or “drop forging”, and not technically “forging” in the same sense as with ferrous materials. Or maybe its “hot forming” as mentioned by @photomancer. At any rate, I think you heat the metal to make it more malleable, but not as near the melting point as iron is heated, and then knock it into shape with a few hammer blows, with or without a die. Then you cut off the flashing, polish, etc. or, if done without a dye, cut to shape. Then I don’t really know what happens. I don’t know if it’s finished, needs heat treated, or what…
Since it’s such an innocuous purpose, I did not intend to worry too much about which alloy I was employing, and will likely be whatever scrap I can find laying around (from soda cans to HAAS waste material, I figure).
Do you mark this and then wait for the mark to change color, or wait for it to melt, or…?
They look pretty cool, but I don’t quite understand how they’re used. The directions are those irretrievably stupid “universal picture directions”, and I don’t get it…
Thank you guys for the info. It’s comforting to know someone here has tried it, and might be able to steer me in better directions when I get to this project!
1 Like
Your just mark the part in the areas concerned, when it reaches its designed temperature it changes visually. Really simple to use. It’s that simple.
While I’ve only witnessed them used on metal there is no reason they couldn’t be used for people forming plastics so you know when you are over heating an area.
Re: Forged Aluminum: If you are buying roll-forged aluminum raw stock and you are going to work it rather than machine it, you will probably work harden it and then anneal it if you have to work it further. If that is the case don’t waste money on forged stock since the annealing will diminish the strength properties that the mill put into the metal at the mill. Just get rolled formed stock.
By machining forged stock you retain the strength properties. Also when you buy forged material it should indicate the gain direction.
You can forge aluminum but we are talking about using a drop hammer forge and forming dies. No hand hammering. You also want something that isn’t nearly pure aluminum like an H-series grade aluminum, I confess I’m mainly familiar with the aerospace alloys: 2XXX, 6XXX, and 7XXX series. These can be brought up a high temperature and quenched to get them harder, they’ll will then artificially age/precipitate harden it over a period time. Immediately after it’s quenched you can work it before the final temper takes place (that or store at about -150F until your ready to work it) 
Follow-up: Found an article discussing Hot Joggling (forming/working an extrusion without annealing or affecting Temper) of 7075 Alloy, temperature range was 300F-350F. I would say this range would pretty much cover the 2XXX, 6XXX, & 7XXX series alloys. Again the 1XXX series of alloys are mainly pure Aluminum and will work harden if you are working with a hammer
If you are going to use Alum cans, I’d be sure to wash them out very well and do several re-melts of the ingots until there is virtually no dross/slag left in the in the crucible after skimming. Then machine off at least .050" of each surface to get rid of the worst of the oxidized surface.
Personally, hit garage sales and look for anything made of Alumin, old screen frames, chairs etc, an throw them in the pot to melt. It’ll be a bastardized alloy but you’ll probably end up with a better tool in the end.
1 Like
Yeah, I have actually found a lot of stock material at Estate sales in the DFW area. I walked away with 20-30 lbs for 3-5 dollars.
Same thing for brass. Lots of items like candle stick holders, small bowls etc. Get 'me, for a buck or two, cheap based on weight (plus no shipping or sales tax). I buy them to cut up for Steam Punk items.