Wishbones in aluminum

[J.Pedro]

Hi!

I'm thinking in making the wishbones of aluminum. I also recognise that teams in Formula Student or Formula FSAE don't have aluminum wishbones. Usually they're made of carbon fiber or steel.

Even in our previous teams we have used always wishbones made of steel.

Nevertheless, I've made a study and an aluminum alloy come out to be the best suitable material for the wishbones, taking in account some financial constraints.

Is there any reason for not having aluminum wishbones? Can anyone give me an advice on this?

Buckling is not a problem, I've studied for that.

I look forward for an answer.

Best Regards,

João Pedro

Projecto FST
www.projectofst.com (http://www.projectofst.com)

[Aaron@Kaist]

fatigue/heat treating

[J.Pedro]

Hi Aaron!

Thank you for your reply.

I'm not thinking in welding the insert to the tube. I'm thinking in bonding it. So, I'll not have to give a new heat treating to the aluminum, right?

Can you specify what you mean by fatigue and heat treating?

Fatigue doesn't seem a problem,if we make a fatigue analysis for the life time of the car.

João Pedro

[Pico]

I think people are more afraid of impact toughness of the aluminium tubing

[Adambomb]

Hmm...just one question:

What bonding method are you considering, and how does the bond strength compare to material strength? As for the design, I'm picturing something along the lines of a typical CFRP wishbone, only using Al tubes instead of CFRP tubes. Is that the plan? Along those lines, I can tell you why we use 4130: I actually tried designing an a-arm several years ago that used machined Al blocks and CFRP tubes. Not only was it heavier than our steelies, but much more expensive and labor intensive. Never mind the possibility of screwing up a bond...

[J.Pedro]

Hi Adam!

Thank you for your reply.

The idea is pretty much what you said: " I'm picturing something along the lines of a typical CFRP wishbone, only using Al tubes instead of CFRP tubes ".

Regarding to the bond strength in comparison with the material strength, I'm thinking in tested it in an "traction machine", I’m not sure if it this name, but basically it is a machine used to determine the tensile strength, and other properties of the materials. I'll manufacture an insert in aluminum, bond it to tube and traction it.

Regarding to the final mass of the A-arms. In my calculations it's less, somehow between 10 to 30% less.

Regarding to the overall cost, I'm not sure yet, because I'm going to buy tubes and then machine both inserts in aluminum and bond them to the tube. The problem that could come out, it's the cost of the blocks to do the inserts, because it's a very small quantity and probably we'll have to buy more than that.

The possible setbacks that I foresee are:

- the small young's modulus of aluminum in comparison to the AISI 4130, that could allow the A-arms to deflect more then what we want it! I have to test that;

- the lower fracture toughness of the aluminum in comparison to the AISI 4130, it's 2x lower more a less;

- the fact that the aluminum alloys are more fragile than AISI 4130.

What do you think of this? Can you give any advice?

I look forward to your reply.

Best Regards,

João Pedro

Projecto FST
www.projectofst.com (http://www.projectofst.com)

[Mike Cook]

I have looked at alternatives to steel a-arms several times. If anyone notices our lower a-arms as this years competition, you will understand why...

With aluminum a-arms, if your main concern is buckling, then they are much better per weight in that regard then steel. The reason I have shy'd away from them is mostly because firstly, welding thin wall aluminum tubes scares me a bit. I have seen lots of guys be able to pick up tig welding steel, but tig welding thin aluminum takes a lot of practice, and for us, we don't have anyone that can do it all that well. The second reason is, that even welded well, we would have to heat treat, which can warp the arms, takes extra jigging time, manufacturing time, extra cash, etc. The third reason is, I would want to helicoil the inserts, and this just adds more money and time into the arms.

In terms of bonding inserts in, I feel like this is really a lateral migration- I would actually feel better with a welded arm. Your also going to have to make a more complicated spherical bearing housing with nubs coming out of it, which requires more machine time. In the end, unless your really trying to shave every ounce off the car I don't think its worth it.

Finally, we tend to break a-arms more than anything else, I like being able to throw together a steel one in an hour and have the car repaired.

Mike

[EPMAl]

I have been looking into Aluminum and titanium wishbones in the past but abandoned it for one simple reason: I didn't think the very small saving in weight was worth the higher manufacturing complexity and cost.

[Adambomb]

I think the tensile test is a really really good idea to test the bond strength. Fracture toughness is something to worry about too, I find that no matter how hard you try, if you're pushing the car at all you're eventually going to nail a cone against an a-arm. In fact, you'll probably carry one around the track a half a lap or so. Several times. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Also had people drop things on them, dented one of them once or twice. Outside of that, biggest thing for us is manufacturing time and cost. Getting the end-nub-pieces light enough to justify the effort could require some pretty tedious machining.

[t21jj]

Originally posted by Adambomb:
I think the tensile test is a really really good idea to test the bond strength. Fracture toughness is something to worry about too, I find that no matter how hard you try, if you're pushing the car at all you're eventually going to nail a cone against an a-arm. In fact, you'll probably carry one around the track a half a lap or so. Several times. http://fsae.com/groupee_common/emoticons/icon_wink.gif

Also had people drop things on them, dented one of them once or twice. Outside of that, biggest thing for us is manufacturing time and cost. Getting the end-nub-pieces light enough to justify the effort could require some pretty tedious machining.

+1 on hitting cones with the a-arms.

And as said by others you have to ask your self is the extra manufacturing time and cost worth the weight savings.