Need some Aluminium Sheet info?
 

Hello guys/gals

I am looking in to making a bespoke car and I will be making the chassis and top deck parts from Aluminium.

Does anyone have any experience of which alloy sheet to use?
I will be using the sheet with a thickness of 3mm.

Any help would be appreciated?

Regards Ian

Depends how you are planning to make it.

CNC/manual machining.
Home powertools.
Or hacking at it with a hacksaw and a dremel..................

Materials suitable for the first, will not be so good for the last. Unless you have a million spare hours to use..........

Many manufacturers will use 7075 or 6061 sheet, either heat treated, or not, depending on their particular design philosophy (stiff or flexible chassis).
But these are a real bugger to cut manually. Or with home powertools.

Go with 7075. It is twice as strong (503 vs 276 MPa Yield strength). It is the same stiffness, (71.0 vs 68.3 GPa). It has a poor rating for workability (bending), but I have made chassis with 25 degree kickups that have had no fatigue or cracking problems. Just a reality check on the strength: it is harder to bend. It's quite dramatic in comparison to 6061.

7075 is the strongest aluminum that is commercially available (easily). I have milled it and also cut it with a jigsaw. Either will work. You will notice the increased force when cutting with hand power tools, but it's not a big deal.

I'm not sure where the idea comes from that hardness is equivalent to stiffness (it isn't; hardness is analogous to strength), but it acts like 6061 until it's time for it to fail (scratches, plastic deformation). Then it is vastly superior.

7075 costs about twice as much as 6061, and it's about twice as strong.

References:

https://online.kaiseraluminum.com/de..._and_Plate.pdf

https://online.kaiseraluminum.com/de..._and_Plate.pdf

Thank you gents for your input.

I won't be cutting it by hand, I have drawn the chassis and will get it laser cut.
I will have to bend up the front section and I was looking at a slight bend longitudinally on each side due to the length of it for stiffness.
I will also be making a top deck as well.

Thank you

I found it difficult to source 3mm (or 3.125 imperial equivalent) thickness 7075 sheet off the shelf from local or national suppliers. No one stocked it, special order only, and you had to order large 3m+ sheets. no one had off cuts or smaller pieces available.
7075 is what you want though, or try 6068.

Watch out with laser cutting and aluminium: Some grades (like 7075) have copper in them, which reflects part of the laser beam. This can (and in the copper fractions in 7075, likely will) lead to damage of the laser! :thumbdown: Some other substances will also reduce the quality of the cut.

Instead, I would consider using water jet cutting: There's no heat build-up and as such less distortion and better retention of material properties near your cutting edges (especially for strain hardened or heat treated grades), you're not restricted in material composition (like you are with a laser), accuracy and edge finish are fine for a chassis plate and as far as my knowledge goes, for small batches and one-off work the costs are very similar.

Agreed, really hard to get hold of 7075 in the UK, I end up making most of my stuff out of 6082, its availible and not bad overall.

If your only making 1 or a handful of items, the expense it will cost to get it laser cut probably won't be worth it. You can cut 7075 T6 ok with a band saw and hand finish by draw filing. As long as your drills and countersink cutter are good and sharp you will be fine.
When you fabricate the chassis, make sure the grain runs length ways along the chassis so the kick up will be against the grain, which will be less prone to cracking (without giving you the long winded scientific answer) when you carry out that process.
It's worth finding out the aviation forums and asking any of the users on there if there workshops have any off cuts, there is an awful lot of "waste" when dealing with that sort of work.
LAS aerospace are usually ok for stock as well, and they do 4' x 2' which is better than the normal 12' x 4' . They are a bit more pricey than most metal suppliers but at least you can some in a smaller quantity.
Don't forget American aircraft will be dealing in imperial, so if you need 2.5 mm, 3/32" is the equivalent and for 3 mm 1/8 will be 0.2 mm thicker.
Hope any of that helps.

Nowhere, but that's the feature you are most likely to want to tune, that's why it was mentioned. And by using the harder/stronger/tougher material you can remove more material (optimise flex) whilst keeping the durability/damage tolerance of the chassis. Basically.

Surely you need the chassis to be as stiff as possible because if the chassis is flexing all over the place it will become uncontrollable.
If the chassis is stiff the suspension tuning will be felt by the driver as the changes will be directly positive or negative.
If you make a suspension change while the chassis is flexing in the middle the results will become unclear?? :confused:

Thank you guys for all your feed back. :)

Ian

I started with this idea in my car, but reality is more complicated than this, unfortunately. I am now trying to figure out when flex is good and how much is good. I haven't seen much clear information on this. I wish it were clearer.

This makes sense. I didn't read it that way the first time.

Sorry for the rough tone in my first response. I shouldn't be allowed to post before coffee in the morning...

No worries, realised it could have been clearer once you'd posted, and if that's considered a rough tone you should try my job :wtf:

There isn't much clear information because its simply down to the particular designer, and how they've dressed it up. Then you have to try and filter out what is real engineered in flex and what is marketing bullshit.

But basically, you need some torsional flex along the long axis of the car to help the suspension and traction, but as little bend in the longitudinal axis as possible. Flex across the chassis is pretty much a non-issue as there isn't really any way to apply a load........

And when we say "flex" we mean giving the chassis a damn good yank will move it slightly, not "flexing all over the place".

As a rule a car with a more flexible chassis will seem to generate more grip, be more forgiving of mid corner bumps, and have a larger setup window.
A car with less flex will be more responsive and consistent in high grip conditions , and more responsive to setup changes, but also ends up with a smaller setup window to the point that you just can't get the car setup.

The theory of a very stiff chassis is sound, but the reality is a little bit of flex tends to make a faster and easier to setup and drive car.