How to bend thin-wall aluminum tubing

A. There are a couple of things you may want to know about 6061 AL. There are three ways to readily manipulate this material to work it. You can Cold Work, Hot Work, or Anneal and Cold Work. Each of these will provide different results (and you may be limited based on readily available apparati). Some basic facts:

Cold working in the O temper condition is readily performed. The alloy is notably less easy to cold form in the T 4 and T 6 tempers. Hot working may be done in the temperature range of 700 °F to 500 °F. Annealing should be done at 775 °F for 2 to 3 hours followed by controlled cooling at 50 °F per hour down to 500 °F, then air cool. (Then see cold working)

Oftentimes if you're trying to bend thin walled tubing, you can fill it with sand and TIGHTLY cap the ends before bending (no sand leakage). My recommendation would be to try the easiest (cold working) first, then if acceptable results are not achieved, try either of the other two (as they produce similar results).

I hope that helps.

A. Gary,
The info that Tom gave you was highly informative !

I know NOTHING about aluminum ... but your bend ratio of 5:1 sounds OK.
As Tom says, try it cold first of all, preferably around a mandrel ... and use DRY sand and tamp very tight.
The professionals use a liquid that solidifies on becoming cold, ie. the pipe benders do.

A. Hi, Heinz here; there are plenty of ways to bend tubing, some often involve filling the tube to be bent with non-compressible things. I've seen bismuth and heat used with good success. Heard of sand, water, even coil springs being used inside to mitigate wrinkling on the inside of the bend. I've had excellent success with a rotary compression type bender that I got from pro-tools.com.

I had to modify the bender in several areas to bring up the bend quality. First, the clamp area was made to hold the tube with more surface area, and the clamp was bead blasted for max grip. The transition from grip area to start-of-bend was made as smooth as possible. Both the compression element and the die contact surfaces were polished to a very smooth finish. The die must be absolutely grease free and the compression element must be well lubricated at its two contact points. I bend 1' tubing 180 deg. + around a 3&1/2' die no wrinkles and minor flattening at bend with 1010 low carbon .095 wall thickness. No wrinkles but notably more flattening with same material in .065 wall. I tried .049 wall 1' cro-mo and had even more flattening, no wrinkles, but the stuff wanted to "spring"out of place in the die and would "cripple" or kink unless I allowed zero back creep of the comp. element during the entire bend. I bent .095 wall, 1' 6061 T6 with minor flattening and no wrinkles to 180 deg+.

This is the extent of my experiments to date. I will continue in this, and my colleague, Fritz, and myself will post our findings as we prove them out. I must make clear that we will NEVER post any of these findings as fact unless we have personally proved them out. I chose this method of bending because I did not want to be constrained, or even slowed down by additional steps or variables like heat, grit in tool, etc. Mandrels being used in the process calls for a more costly bender, but will theoretically produce a higher quality bend in thinner wall tubing. I wanted to have the best quality bend for the least cash outlay. To date it has taken about 11 mo. to get to this level of understanding, and has not been without some problems. Fritz and myself are applying this capability to constructing all-metal bicycle sidecars for utility purposes. Thanks, HEINZ

A. Hi, you have to anneal your 6061 t6 tubing in order for it to bend nicely. After you bend it, it will return to t6 temper in about a week as 6061 is an age hardening material. If it still wrinkles you must then fill the tube with fine sand and compact it. To anneal the tubing I wrap it in fiberglass and foil tape a heat gun ⇦ this on eBay or Amazon [affil links] to one end and heat it to 750 to 800 degrees for an hour or so, let it cool down slowly in the insulation. When cool enough to hold without gloves it is ready to bend.

A. Mark: yes, the insulation that I use is just standard house fiberglass. The trick is to get it hot and let it cool in its blanket until about 100 °F and bend it from there. Pack with fine sand and with the radius and length of bend you shouldn't have any problems . The material will return to a t-6 temper within a week (age hardening aluminum alloy); watch for any (orange peeling) of the surface as this is a sign of work hardening that you want to stress relieve before you go any further.