Hub Splines - Aluminum?

[Muldert]

For our vehicle I'm looking into different hub designs.

The idea is to manufacture a tripod housing/stub axle out of aluminum and connect it to the hub(rotor) part that the brakedisc and wheel is bolted on to.

Local problems like the tripod eating away in the aluminum tripod housing can be helped with steel inserts.
Are there other teams out there that have used aluminum stub axles with splines or other interfaces?

[exFSAE]

Could you do it? Sure, in theory. Particularly if you take an aluminum part and have it properly toleranced, hard coated, cleaned, and well taken care of... can do a lot of things.

Now think about all who is going to be banging and wrenching on this car. How well is it maintained? What's the general attention to detail?

The position you most certainly don't to be in, is having an aluminum wheel galled and stuck on an aluminum hub, and pretty much no way of getting it off. Bending and yielding 1/2" bolts trying to craft up wheel pullers. At 2am. With a track day the next morning.

Ask me how I know...

Valid exercise worth considering. It's one I went through... ultimately decided to go away from the billet aluminum hubs we had been doing for several years and go with a billet steel design - which was smaller, equal weight or lighter, cheaper, easier to manufacture, AND more durable / reliable!

[Z]

Muldert,

In general, I agree with exFSAE that steel is better.

However, as an educational exercise you might want to look up the tripod CVs used on early Citroen DSs (~1960). These had aluminium housings with C-shaped steel liners for the rollers. They are generally considered superior (longer lasting, etc.) to the later all-steel tripod housings. These would be too big for FSAE, and were inboard so no wheel bearings, etc., but are interesting from the "what actually works" point of view.

Z

[Chapo]

On Z's example:

That is exactly the style of the hubs that UNSW@ADFA uses. Al hubs with wirecut C shaped hardened steel inserts that are press fit into machined holes for the tripod to run in. That hub has been running for almost three years now over 4 competitions and there has not been a problem with them.

If you have a look through the FSAE-A photos from 2009 onwards you should be able to see some examples of our setup.

[Bemo]

Our team is running aluminum hubs with steel inserts for years. Works fine. The first car with this design was the 08 car and they still work.
The problem is how to manufacture the steel inserts. But I won't tell you all the secrets http://fsae.com/groupee_common/emoticons/icon_wink.gif.

[Kevin Hayward]

Cole,

UWA ran Al hubs with steel inserts as discussed while I was a student there. They can be quite difficult to machine, but I wouldn't bother machining them now. Try and find a local source that has EDM capabilities. That way you can have the steel inserts cut from incredibly hard steel with no more difficulty than any other type of conductive material. Also not very expensive.

Kev

[Muldert]

Thanks everybody for the quick replies!

Im not that worried about the tri-pod housings.
Steel inserts inspired by the taylor racing tri-pod housings: http://www.taylor-race.com/images/ATP2BANNER.JPG. These will suffice imho.

We have the opportunity to produce everything out of 7075 and also the proper facilities.
What worries me is; the splines and the thread of the stub axle in Al. I can hardly find info on splined axles in Al.

It's interesting that the replies are so varied on this subject.

[JWard]

http://gallery.uwracing.com/main.php?g2_view=core.DownloadItem&g2_itemId=583164&g2_serialNumber=2

Not strictly the same as what you asked, but i believe wisconsin use ali stubs between the dif and their tripods (which mesh with a housing which is iternal to their halfshafts, which also look to be ali. not sure if there are steel inserts in there but i imagine so?)

I believe they're faily approachable.

[RCV Performance]

Those axles are actually a prototype of carbon fiber axles that we are producing now. The aluminum splines have worked with no failures to date. That being said, they must be closely inspected after any long period of driving just to make sure no major deformations have occurred.

I would like to note something that we discovered in running these axles with then UW team. If you can see in that pic, the actual CV joints in the carbon tubes were aluminum at this point. Even with hard coat anodizing and using 7075, the balls from the CV's ended up deforming the aluminum quite a bit in a fairly short time. Therefore we have switched to steel CV housings. We did try using steel inserts on these CV's but had a lot of trouble getting them to stay in. Another interesting concept we tried was using ceramic tracks in aluminum housings, but finish machining them was pretty much impossible with CNC's we have in our shop.

[McDZ]

Originally posted by exFSAE:
Could you do it? Sure, in theory. Particularly if you take an aluminum part and have it properly toleranced, hard coated, cleaned, and well taken care of... can do a lot of things.

Now think about all who is going to be banging and wrenching on this car. How well is it maintained? What's the general attention to detail?

Ask me how I know...

Valid exercise worth considering. It's one I went through... ultimately decided to go away from the billet aluminum hubs we had been doing for several years and go with a billet steel design - which was smaller, equal weight or lighter, cheaper, easier to manufacture, AND more durable / reliable!

exFSAE,

Currently we have a steel stub/CV with a polygon connection to an Al hub. And the stub runs through the hub and a castle nut keeps them together. I want to switch to a steel hub, so it is more durable, and either have a polygon or maybe a sinusoidal spline connection to the stub. But I'm not sure how to keep them together while keeping about the same weight and was wondering how you did that?

The position you most certainly don't to be in, is having an aluminum wheel galled and stuck on an aluminum hub, and pretty much no way of getting it off. Bending and yielding 1/2" bolts trying to craft up wheel pullers. At 2am. With a track day the next morning.

[AxelRipper]

Hard Anodizing.

http://sphotos.xx.fbcdn.net/hphotos-snc6/267552_523741272937_180600938_30510424_7314600_n.j pg

[coleasterling]

How does hard anodizing help in this situation? It is like a thin sheet of ice floating on water. The underlying material will yield and then the anodizing fails...Not to mention the fatigue life reduction from the anodizing.

[Ben K]

Originally posted by coleasterling:
How does hard anodizing help in this situation? It is like a thin sheet of ice floating on water. The underlying material will yield and then the anodizing fails...Not to mention the fatigue life reduction from the anodizing.

-Cole

+1 for Fatigue Life reduction due to Anodizing.

Ben

[RBbugBITme]

Here is a good high school level explanation..

http://www.experimentalhelo.com/Anodizing&Fatigue.pdf

[AxelRipper]

Unfortunately I don't have any pictures of our non-hard anodized ones that we ran the prior year, but they were significantly more worn after the season was over than our hard anodized ones. It seemed to add life to the wear surfaces of the tripod bores.

[Canuck Racing]

In reference to the above,

What exactly is the point of hard anodizing then?

Everyone here does realize there are several different classes of anodizing and post anodizing treatments that all affect fatigue life, hardness, cosmetics, bond adhesion etc.

If anodizing was so bad for everything, it wouldn't exist. We better ways to make things pretty.

Now, lets get back on topic shall we? For the life of a typical formula car, well machined aluminum hubs would work fine. The thickness they have to be to meet the strength required probably doesn't warrant any weight savings, and the extra tight tolerances will be more difficult to machine but there is no reason at all they can't work. If we we discussing OEM cars and trucks that's another story.

[Kevin Hayward]

Canuck,

Hard anodizing is great for protecting items from scratches and damage due to handling and assembly (and similar loads). It is not very helpful in contact stress situations where the peak shear stresses will occur below the anodized level.

Kev

[Canuck Racing]

You need to model your contact stresses and see how your material will yield with and without anodizing and better dang sure be designing with the fatigue life reduction in mind.

That's what I was trying to point out. Everybody here is so opinionated and close minded that their way is the right way and only way they never stop to actually crunch numbers, gather data and think about how to solve the problem rather than how to defend their solution.

I mention the tolerances because if you have steel hubs and tripods that have a bit of play in them it's not the end of the world. But a tripod flopping around in aluminum is going to wear a lot faster than if it has a nice tight fit.

And I agree with you Kevin. However, what everyone has failed to consider is how much you are actually yielding and deforming the material compared to how much the axle plunge is rubbing the tulip across your tripod bore. Which do you think is going to cause more wear? And as I said above, how much yielding is really taking place? (That's all rhetorical by the way http://fsae.com/groupee_common/emoticons/icon_wink.gif)

[Subsonic]

We used steel inserts with aluminum hubs for the first time this year. They were press fit, and it was a pain to machine them. They worked great though.

[Muldert]

Hey guys, thanks for all the replies.


Here is a picture of the finished product.
We'll be testing them soon and race it at the silverstone race. https://lh5.googleusercontent.com/-tGiWNi9lBN4/T-s76LkpIvI/AAAAAAAACpM/v-Jmyqz88PE/s1024/IMG_1210.JPG

https://lh3.googleusercontent.com/-xCOAJLkMaqY/T-4hxgGWA1I/AAAAAAAACsI/vsSwFIgTcAU/s1024/IMG_1251.JPG

[Chapo]

Those bearing housings look nice, just a suggestion for you though, if you were to just make an insert for the C shaped running section of the tripod you can then nest them for manufacture and use a lot less material and save your self a bit of money in the future. (this is assuming that you have access to a EDM wirecutter or similar)

chappy

[Muldert]

Dear Chapo, Your suggestion is exactly how I designed it at first. But the company that produced the parts for us using a waterjet cutter, suggested we'd do it this way.

Today one of the hubs snapped while testing. The spline is more than strong enough as you can see on the pictures, but there wasn't enough space to properly let the stresses flow out. Then this happens:
http://i.imgur.com/Ne9CW.jpg

[Paul Achard]

Wow... thanks for posting this!
Was this tempered 7000-series?
It's hard to see on your pictures; can you see beach-lines from cracking? If so, how far did they progress before failure?