Aluminium chassis design problem 1

[EsoEng]

I'm designing a chassis for a cargo trailer to be pulled by a motorcycle. It needs to be as compact as possible; there are severe limits on the thickness of the chassis, and the overall height, length, and width, and also weight, of the final trailer.

With the above in mind, the image, below, shows the first design, which consists primarily of extruded aluminium members all on the same plane. This minimises the thickness of the chassis, and thus the overall height of the trailer.

However, the problem I am having is that the design will not be strong enough, once welded, in the heat affected zones (HAZ) using standard heat treated 6000-series stock aluminium extrusions. Maintaining the geometric envelope of the chassis, and without significantly increasing its weight (such as by using a high-strength steel, which would at least double its weight), how can I mitigate the loss in yield strength in the HAZ? (I'm not talking about pre-/post-welding heating, and welding techniques to minimise the problem, as I believe they cannot prevent the significant yield strength loss I am concerned about.)I'm trying to think of ideas, but I would very much like to hear from someone with aluminium fabrication experience/knowledge as to what would be the standard solution(s), please? This is actually my first real project of the type. Pretty much, all I was taught in the classroom were the fundamentals of metallurgy, and how heat affects the strength. The easy answer (in a didactic sense) would be to fabricate the chassis, and then have it heat treated to restore its full yield strength value. However, in practise, this is awkward, and expensive (so I'm told). It makes me wonder what fabricators do to avoid the loss of strength in the HAZ, including, for example, mountains bike frame manufacturers. Perhaps, they just design-in more material in the HAZ, which is not something that would be easy to achieve for my project if I continue to use stock extrusions.

Thanks for any help.

 

[drawoh]

Most bicycle frames use 7005, because it's relatively easy to heat treat.

I have a tent with 7005-T6 poles. The first indication you will get that you are overstressing that stuff is when it shatters. I would want a trailer on the road to bend and deform a bit before everything flies apart.

--
JHG

 

[CWB1]

There's no need to stamp every feature into a panel simultaneously or buy expensive tooling. As dvd mentioned, a decent fab shop should have a selection of press brake dies capable of stamping individual ribs and other common features into aluminum. You'll need to ask the supplier for size/shape details. You could also simply design everything to be folded.

 

[Steven_D_P]

Some ways to make this design simpler is to scrap the round corners and cut the extrusions at an angle to make the corner. Scrap the little cross members in all 4 round corners, I don't think they're very useful. Scrap all the triangular pieces, I don't think they are very useful.

I also did a quick google search for trailer chassis:
1
2
3
4
5

Some things I noticed:
They are all a lot simpler than your design.
They use only bracing members along the width of the trailer and not along it's length.
They use the axle as a bracing member so there are almost no other bracing members. This is only possible if you have no suspension. If you're going to use suspension look at number 5. (you might need suspension for a motorcycle trailer. You probably also need brakes, unlike these trailers. If you don't the trailer will probably jackknife your motorcycle.)

If you use aluminium sandwich panels you might not need any crossmembers at all besides the axle.

If you want to get an idea of the load the trailer has to withstand just take a g-meter with you on your motorcycle trips. It's probably going to be less than 3gs.