Small Vehicle Uprights

[Chris Boon]

Hey all,
I am looking at the possibility of using an older Barina or Mini uprights and machine them to use as uprights for the car. I have heard a couple of teams have looked into this in the past. If anyone has any information, opinions, advice on this could they let me know. I have been trying to find some sort of drawings on the net but to no avail. Thinking I might have to do a trip to the Wreckers in the coming days.

Cheers,
Chris

Suspension, UQ Racing

[Jersey Tom]

You certainly could. But is it worth your trouble? You have to get them first, CAD them, determine their material and HT condition, check their strength as a FSAE part, and then jig and post machine them for your application. At the 2006 FSAE East competition I saw one team that used old cast uprights post-machined as FSAE uprights, but.. I personally wouldn't take that route.

I'd much rather machine my own uprights. DFM is key. You can design good machined uprights that only take 1-2 setups and are rigidly fixtured such that you can be taking full-slot bites with a 3/4" carbide flat endmill at 5500+ rpm / 80+ ipm. Massive MRRs. < 1hr total machine time. And you can tailor-fit all your geometry to your suspension's needs.

Then again, I'm a machinist. I love taking billet blocks of aluminum and reducing them down to nothing.

[Nihal]

We used 1st generation VW Rabbit uprights, CV's, axles, hubs, and bearings last year and they all worked great. We had no failures. We didn't have any CNC capabilities and the like. Using parts off of an OEM car is a great idea if you don't have alot of money, time, and a set knowledge base (1st year cars etc.).
The uprights and wheel package will be a bit on the heavy side, but you can machine some weight out of them if you understand the loads etc.

[murpia]

If you are planning on using OEM kit then take a look at the 4WD or IRS quads, the uprights on them could be suitable.
But as Tom says, you need to verify them as suitable for the task in hand. That means analysing the load cases they are subjected to, analysing their dimensions, materials, HT specs etc. to determine suitability, then rig-testing at least 1 item (to destruction?) to verify your analysis.
You _might_ get that info from your OEM but I doubt it.
If you just fit them, and justify the design with 'they haven't broken yet' you will get nowhere.
Regards, Ian

[LU-Bolton]

Do you have a welder? consider steel plate uprights. Plate steel is very cheap as compared to billet aluminum and it wouldn't require an expensive machine. I also would not use someone else's upright design. Are KPI, caster, and tie rod location all in the right spot? I've seen some bad fabrication of cast uprights in SAE cars, i.e. welding to cast steel and aluminum uprights to get the right geometry(looking through an album from the late 90's in our SAE room). If you decide to go that route, just do your homework. All I have to say is if you can make an entire frame accurately, why can't you make uprights? Good luck.

Aaron Cassebeer
2007 Lehigh Team Leader

[Jersey Tom]

The only things I have against the popular welded steel uprights...

Are you going to leave them in the as-welded state, or go through a true normalizing process after welding? In either, how repeatable is your welder? The uprights see all sorts of fatigue through varying loads, and see all the forces the car generates though acceleration, braking, an cornering. So how much do you trust your FEA? How many of your welds have been cut up and examined? Is the quality consistent? Is there any porosity? Undercut? Full-depth penetration? You'd be surprised how poor a weld can be, even if you think its solid. We had an aluminum diff casing crack last year on one of our old cars. It had been made from two parts, welded together by our best TIG guy. On machining it down to reweld it, we saw all sorts of porosity through the depth of it, which is where the crack had initiated.

If left in the as-welded state, the actual weld seam tensile strength should be easy to approximate. But how you do quantify the HAZ? The vast, vast majority of welded parts on FSAE cars are overwelded, due mostly I think to typical lack of formal training. The leg of a fillet weld need only be 1-1.5 times the thickness of the thinnest part you're welding. So for most upright and chassis work, we're talking about welds on the order of 1/16" leg.. at most 1/8" accross. Since so many parts are overwelded, there's an excess of heat input and a much larger HAZ than necessary. I don't even know where you start in mechanical analysis for such a thing. For a chassis its not a huge deal since they're so overbuilt anyway. For uprights though, I'd be worried about it.

If you do normalize the part, how do you know you've reached full-depth recrystallization? How do you constrain the upright so it doesn't pull? Are you going to drill a couple holes in it to release gas pressure buildup inside the upright that might otherwise distort the part?

And even then, with any welded upright you're going to need to go back in and spot-machine areas. Since these are hand-jigged and every welded part is going to be a little different... how do you build your fixture to locate each part repeatedly with weld dimension variance?

The material for a welded steel upright is cheap, sure. But then you have to cut it to shape somehow (by hand with a plasma cutter and ground? machined? waterjet? cnc plasma cutter? a large shear?). Then I imagine its going to be TIG welded, which is the slowest of all welding processes. Most of the welded steel uprights have a lot of sides to them which all need to be hand-fitted, cleaned, tacked, and final welded. The time adds up.

How expensive is billet aluminum? It depends. The machined upright design we had rolled with for some years required stock 7075-T6xx around 12 x 6 x 3" .. 216 CI of stock.. as much as $800 for 4 uprights. Took something ridiculous like 10 hours minimum and 4 setups of machine work to get EACH done. Last year I got it down to 72 CI ($270? for a full set of uprights), 3 vice setups, and ~2 hours each of machine time. This year I might be able to get it down to 54 CI ($200 for a full set of uprights) and 1-1.5 hrs of machine time in 1 or 2 setups through better fixturing and tooling. We also managed to get an aluminum sponsor, so the stock was free anyway.

Its so much easier to just load a chunk of aluminum in a machine, press the start button, and have a finished part an hour later, while you can be off doing other things. Plus you know the geometry is going to be very consistent from part to part, and the mechanical properties of your part very uniform throughout.

[RacingManiac]

IMO Sheet steel vs CNC is a choice of the available resources. We don't have in-house CNC capability and as such have to rely on outside CNC sponsor, and we've had to wait for the upright to come to physically finish the car. With sheet steel this year it was one of the earliest component to be completed, and can pretty much be built completely in house(we sourced out the sides to be laser cut as we have a pretty reliable sponsor for that with quick-ish turn around time, and ditto with post welding thermal process with another sponsor).

I'd love to make a CNC upright, as I've seen a lot this year that looks absolutely amazing(not to mention not having to mess with Pro/Mechanica to do sheet metal FEA with connection with solids and others...), but until it's feasible for us to do it quickly I'll have to stick with sheet steel...

At any rate either is not that hard to make, if the design is simple enough you may even be able to hand machine the thing. At least you'll have your geometry where you want it instead of compromising on an existing design...

[Jeff The Pyro]

I think that obtaining a reliable structural weld with steel (even moreso with mild steels)is much, much easier than with aluminum. We've had welded 4130 a-arms for three years and never had a failure. the first year they were not heat treated, the second two years they were. In fact the only weld fracture we've ever had in the past 3 years (basically our team's entire existence in FSAE) was an anti-roll bar, but we knew that part had a sketchy FOS to begin with and it still took over a year of abuse at local autocrosses after competition before it finally gave out. I wouldnt be the least bit concerned about running welded steel uprights, we're actually looking into it for next year, despite having access to a 3 axis cnc mill.

[Jersey Tom]

Can you get away with it on an FSAE car... sure. Buts its poor design practice not inspecting welds on structural parts.

And I'm convinced you could get a machined upright to crank out faster than a welded one. But then again, I've got more CNC than TIG experience.

[TomF]

I think the discussion so far does not lead to either of the two solutions. The wat to go imho is to go for the production method that suits your team the best. For us, it will be CNC-ing aluminium, but welding steel was also a good alternative. Our main concern was the accuracy of the final product, but outsourcing CNC stuff also leads to inaccurate products, we learned the hard way. I do believe milling is more accurate than welding, although it all depends on your jig. We did weld our A-arm inserts (carbon fibre tubing was bonded on these) this year and they came out quite accurate. We only had one insert that was inaacurate, so we had to redo that one, but the others were extremely close to their design. I would have to agree with Tom on validation though, it does make a big difference, both in confidence as in good engineering practice.

[LU-Bolton]

ouch, that hurt Tom. lol. Luckily, we had a $6,000 Miller welder donated to us last year by the company, an experienced welder, the uprights were heat treated with the help of a materials science professor, water jetted plates, holes for built up gas pressure already existed due to the design, and a sweet jig was made using your favorite material, aluminum. Also, there was no post-machining necessary.

I started out with an aluminum design myself, but then changed it because I didn't enjoy all of the stress concentrations that exist at every edge/corner of an open section part. Plus we weren't as blessed in the CNC department last year. I saw your uprights also Tom, my first thought was that they were heavy. lol. I don't doubt that they are stiff though. Our car has also been the lightest at Formula SAE the past three years, so we are definitely not the normal design team here at Lehigh. (carbon fiber flexures, cut and fold chassis, etc.)

It's good to see two totally different ways to approach the same design. That's probably why I enjoy designing uprights so much.

Aaron Cassebeer
2007 Lehigh Team Leader

[jack]

the Ariel Atom has hand TIGed uprights. they are cheaper and lighter than a compairable CNCed upright. Given the liability selling a car liKe that, I bet the quality control is outstanding. Fabbed uprights is ot as hard as (the CNC guy) Tom makes them out to be.

[Jersey Tom]

Like I said, you can definately get away with it in an FSAE car with such a short service life (relatively speaking). I just think some of it is poor design practice. It was certainly out of the question for us last year, not even knowing who our main TIG welder was going to be and having to rely on an alumnus for a lot of stuff.

My uprights were indeed heavy. 2lb. But, the reason for that is my original alloy selection, 7068-T6, our sponsor couldn't come through with at the last minute. So I had to go back right before manufacturing and bulk everything up for a 7075-T7 design. Universal and modular though, allowing for swapping out different brake calipers and rotors.. different Ackermann geometry.. diferent camber. and this year will add caster adjustability.

Sweet hookup on the welder. Our welding facilities are being redone this year and I'm pushing really hard to replace our early 80's Syncrowave 300 with a new Dynasty 200DX.

We're not all that blessed in the CNC department, relative to what I'd like to be running. If I had a nice 15000rpm spindle VMC these uprights would be 45 minute parts, easily. If not less. As it was, the most ballsy I got was running 3/4" solid carbide endmills around that billet at I think it was 5500rpm and 70ipm. Still pretty quick.

[Brian Evans]

Jersey Tom, how long would it take you to machine your uprights on a manual Bridgeport? That's the fair comparison to hand-fabbing a welded upright. Honestly interested in the answer, BTW, not a "smart" question.

Brian

[Jersey Tom]

Beats me. I could design the uprights to be pretty damn easy to do on a Bridgeport. Each setup just uses the machine table (setup 1) or a vice (the next couple).

Its a good analogy. At the same time though, I think many many more schools have CNC mills than CNC welders. In fact I don't know of any with CNC TIGs.

Would be pretty sweet.