Thread: Welding an octagonal box

What grade of aluminium?

What thickness?

Welding difficulty increases as material gets thinner. Some aluminium alloys are easier to weld than others.

PDW

Welcome Mike!,
As PDW has said its gets harder as the metal becomes thinner. Thin aluminium (say below 3mm ) is in realm of experienced welders and with a machine ( AC DC & argon cover gas for aluminium).

Your type (grade) of aluminium used may well depend on the application for your job. So, if can drop a few hints here and there, maybe some other forumites may be able to help you further.
Details like metal thickness ,dimensions of height and across flat measurement will yield much better answers as people are otherwise guessing on what the requirements are? Also a badly welded thin section may distort and ruin the work. Give as much detail as you are able and get the most appropriate answers without people having to question and answer back and forth.It saves time!

Tht thickness may not permit welding but could be suited to being developed (laid out flat and then folded up) and secured by pop rivets.

If it is to be welding subject its best placed in the welding forum. If welding doesn't suit the thickness you we will keep it herein this metalworking forum. To get to welding scroll up the page ,click on METALWORK FORUMS
This will bring up a list of the specific forums found under metalwork forums.Scroll down to find welding at the bottom.

More info then OK?
Welcome
Grahame

Knowing nothing about the box, I'd probably do it by bending a piece of strip up in an octagon, joining that and then welding a base in. A word of warning here. Aluminium has a lower melting point than it's oxide skin, so it will melt and only the skin stops it running away. As a result on the 'other side' of an Al weld it will look a little saggy and lumpy. Will both sides of the weld be visible surfaces? This may mean that it needs to be dressed.

Michael

Aluminium brazing rod is cheap and simple to use. I love it (because even I can weld aluminium with it) and thin material is not a problem. I'm sure everyone has seen the demonstrator at the show welding a coke can.
You can get some here.
Would be the cheapest option for a small, one off job.

Originally Posted by NCArcher

Aluminium brazing rod is cheap and simple to use. I love it (because even I can weld aluminium with it) and thin material is not a problem. I'm sure everyone has seen the demonstrator at the show welding a coke can.
You can get some here.
Would be the cheapest option for a small, one off job.

Sorry to be pedantic, but the boilermaker in me is coming out.
You can't WELD aluminium with these rods, you can only BRAZE with them. Personally, I don't like them at all, but I accept that they are an option for those without the gear or experience to weld ally. One point I would make in relation to this application, they are a terrible colour match for ally, so this may be an issue aesthetically.
If the thickness is over 1.2mm then I would simply fold the octagons in 2 halves and weld them together, or have them welded. If you back the joint up with some stainless, then you could weld the corners with no over penetration and then sand the outside to profile and polish or otherwise. Accurate fabrication will be the key to the success or otherwise of this project. There are a couple of ways to avoid over penetration when the base is welded on.
Anything is possible with enough time (money) and effort.

As yet another boilermaker, I too will jump in and add my voice to the opinion that the product is just a brazing rod not a welding rod despite the website that was linked to it,suggesting it is a welding rod.

Its quite simple, aluminium melts about 660C where as the melting point given for this rod was in the 300C region. Welding, as occurs with the fusion ( mixing) of parent and filler metal, cannot occur.

Brazing is where one metal( the filler) ,in a molten state,bonds to the other un-melted (the parent ) metal. Think of water flowing over a sponge and then freezing. The filler(water, as ice when cooled) is locked into the cells of the sponge. Thats similar to what occurs in the brazing process and helps describe the action of the bonding a purely mechanical attachment which occurs.

Welding is the mixture of a filler and parent metals to give one homogenous mix.

The aluminum brazing rod MAY be suitable but we will not know if it is applicable until the original poster offers more information.
Grahame