WHAT KIND OF STEELS??

[Rob Davies]

When looking at the specs of some of the space frames of other teams there is a high use of alloy steels such as 4130, 1020, T4 etc..

From what I can see the alloy steels have practically the same properties as the simple mild steel we use. Plus Im led to believe that 4130 requires stress relieving ad heat treatment after welding.

So I know you guys are more intelligent than me ! and you are using alloy steels, so there must be some justification for it that I cant seem to find. Any help?

Thanks, Rob

[John Lankes]

I was just wondering the exact same thing, the standard Mild steels, and the alloys have the same modulus of elasticity at about 205Gpa. In my eyes this would be the main criteria for designing a chassis or suspension component. The only justification I can find to using the more expensive alloy steels would be the significantly higher UTS in the event of a crash or other high load condition.

[Charlie]

Can you get mild steel tubing in such thin wall thicknesses? Such as .028"?

[Frank]

Agreed with Charlie,

Even with an efficient structure (well triangulated), most beams will still see significant bending.

Therefore, the section inertia is most important, and you seek to use the thinnest wall tubing possible in all places.

This year we only used .028" in a few places, and .035" everywhere possible (.028" was a bit scary to weld, except when you mate it to a thicker section).

If you can get thin wall mild, then go for it (do check stresses before hand, particularly diff mounts, and near front pickups).

http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp

We usually use the ER70S-2 filler

As for heat-treating, not on chassis, tubular anti-roll bars maybe (use 4130VM filler for heat treated applications).

[RagingGrandpa]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Frank:
... This year we only used .028" in a few places, and .035" everywhere possible (.028" was a bit scary to weld, except when you mate it to a thicker section)... <HR></BLOCKQUOTE>
Now .016" Aluminum is a bit scary to weld (pissed me off yesterday), but come on, 0.028" wall steel is butta

[J. Schmidt]

I heard that in the past, design points were awarded for using alloy steels (true?) but not any more. Considering that 4130 and the like need to be TIG welded (our TIG welder graduated), add to the cost report over mild steel, and is generaly more expensive for the team to buy, and should be heat treated...I'm looking into mild steel for next year's car. Is there that much weight savings by going with chrom-moly?

[J. Schmidt]

I just read Frank's link, good info. I see that 4130 tubing doesn't need to be heat treated. We had to heat treat ours because we used 4130 filler rod. Thanks Advance Heat Treat (http://www.ahtweb.com)! (tastless sponsor plug)

[Storbeck]

I've seen so much conflicting opinions, theories, and whatnot about welding 4130, normalize, heat treat, use this kind of filler rod... I'm pretty well baffled. What do other teams do? filler rod? normalize don't normalize?

Even Caroll Smith has somewhat vague conflicting info on this.

I haven't been TIG welding for very long, but man it's wretched bitch to weld on these cars, I don't know how you guys do it.

[Denny Trimble]

For highest strength (a-arms, swaybars, uprights): 4130 filler rod, full heat treat (quench + temper)

For low-stress applications (spaceframe): ER-70 (mild steel) filler rod, stress relieve if you like, but not necessary on thin-wall stuff.

[Gonzo]

Denny do you need to use 4130 filler wire for a-arms?

We are a first year team but have used ER-70s for all steel welds. A-arms are moly but spaceframe is MS.

Our midget chassis builder, who I have been consulting, does all his moly work with ER-70s and reckons its better than 4130 wire coz it doesn't need heat treating and its easier to get.

[Denny Trimble]

Well, to paraphrase Carroll Smith, welding a-arms out of 4130 and not heat treating them is stupid, because you could have built the parts from 1020 and ended up with the same strength. The only advantage of 4130 is that it is heat-treatable up to a high strength. This isn't important for the frame, which is usually low-stress if it's stiff enough and designed well, but your a-arms and swaybars (definitely!) see much higher stresses. 4130 can save you weight on these parts if you heat treat it; otherwise, it's the same as 1020.

If you're heat treating the parts, you want 4130 filler rod.

[Cement Legs]

We've dicided to use aluminum for the frame for our car. I know with the thicker wall thickness required, weight savings pretty much go out the window so the decision has a big "experimental tag" on it. Everyting except the main roll hoop and main roll hoop supports will be 6061 1" OD .75" ID. We plan on heat treating our a-arms before knurling them and wraping them with carbon fibre for extra stiffness. Any suggestions from all of the materials engineers out there?

[James Waltman]

Why knurling? Are you doing it to help the carbon fiber attach better?

[Didier Beaudoin]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Cement Legs:
We've dicided to use aluminum for the frame for our car. I know with the thicker wall thickness required, weight savings pretty much go out the window so the decision has a big "experimental tag" on it. Everyting except the main roll hoop and main roll hoop supports will be 6061 1" OD .75" ID. We plan on heat treating our a-arms before knurling them and wraping them with carbon fibre for extra stiffness. Any suggestions from all of the materials engineers out there? <HR></BLOCKQUOTE>

The team from Université de Québec Ã* Chicoutimi did an aluminium frame this year. I'm not here to discourage you, but basically, the judges told them aluminium frames were not meant to be in motor racing, basically because there is no weight gain, tha the welding is more difficult and that you need difficult heat treatment (6061-O to 6061-W, and 6061-W to 6061-T6). Also, if you want to modify something afterwards and you weld something on the frame, you have to do the heat treatments again. So if you have a trouble at the competition and that you have to modify your frame for safety, or any other reason, you won't be able to keep your frame in the T6 state, which is pretty bad...

If you really do it in aluminium, don't forget to bring some heat treatment proofs at the competition or you won't pass the tech inspection, based on the experience of this team.

[Cement Legs]

Did the team from Université de Québec Ã* Chicoutimi fail the tech inspection because they didnt have the frame heat treated or becasue "the equivalent yield stregth in the AS-WELDED condition" was not strong enough. If they had a better frame design without the heat treatment would they have passed? I'm just curious because the rules do not specify that heat treatment is required? Maybe they should clarrify this point.

Further to this point, does anyone have any info on section 3.3.3.2.3 of the 2004 rules. Specifically what do the judges 'take away' from your design if the frame is considered in the "AS WELDED" condition?

[Vector006]

To answer the questions on welding 4130, this should answer your questions:

http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp

Hope this helps.

[Erik Whoa]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Cement Legs:
We've dicided to use aluminum for the frame for our car. I know with the thicker wall thickness required, weight savings pretty much go out the window so the decision has a big "experimental tag" on it. Everyting except the main roll hoop and main roll hoop supports will be 6061 1" OD .75" ID. We plan on heat treating our a-arms before knurling them and wraping them with carbon fibre for extra stiffness. Any suggestions from all of the materials engineers out there? <HR></BLOCKQUOTE>

Just wondering, but why not go with a larger diameter, smaller wall thickness tube? Although all of the frame won't be in a pure torsion state, it could help.

[Charlie]

I was under the impression that aluminum and titanium space frames were outlawed for 2005, this being stated in 2003 as an early warning to 2 year teams.

[Cement Legs]

Yeah weve decided to go with steel. We are still gonna have some fun thaking this aluminum chasis throuth the paces but after testing for ergonomics we will re-tig for steel. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Angry Joe]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Charlie:
I was under the impression that aluminum and titanium space frames were outlawed for 2005, this being stated in 2003 as an early warning to 2 year teams. <HR></BLOCKQUOTE>

I think this was in reference to roll hoops only if I'm not mistaken. Still, that complicates an aluminum chassis.

Lehigh did a really cool aluminum honeycomb monocoque in '96, but I have very little information on it...

[rjwoods77]

When I went through the rules I found that it would be a waste of time(maybe?) to try to use anything else then steel for metal spaceframes. The rules say the main roll hoop and front roll hoop have to be steel. I think the bulkhead too but I dont have my rulebook next to me. Based on that you either do the whole car as a mild steel or chromo frame or use the mild steel/chromo hoops with a monocoque of whatever sorts. You can braze aluminum to mild steel but you cant braze alum to chromo(Welders Handbook). Brazing alum to mild would be an intersting situation but the od of the alum. really couldnt be greater that the od of the mild steel and based on the properties of alum you would be losing out of strength in the frame because weight for strength you would have to use a really thick sidewall on the aluminum which kills your "weight advantage" going to aluminum. Joining titanium with mild steel would be an absolute nightmare if you could do it(dont know off hand). You could do something like they do with bikes(the cast nodes that the tubes go into) that get brazed to the mild steel which would allow you to use larger od alum. than the od of the steel(sort of like a hollow tab for the alum tube) but again that wouldnt make up for the weight difference.

It basically seems like the rules are setup to say steel spaceframe or steel hooped monocoque or the whole car out of titanium which is frankly just masterbation(too much money). The examples I gave are just a couple and there are more ways of doing it but for the size of our cars, it wouldnt make sense to do it. Not to say that it cant be done though. Maybe a steel hooped car that uses huge alum. side tubes with aluminum shear panels(Western washington university but aluminum insted of carbon).

[rjwoods77]

Also the price of steel these days is sick. Distributors that bought huge stocks years ago(chassis shop,etc.) still have prices on chromoly down around the $2.5/ft range. But any of the new purchased mill stock is up aroun $4-5/FT. Mild steel is from a 1/3 to 1/2 of that cost. While chromo is superior in strength, the strength of the bars based on minimum wall thickness in the rules are already more than what is needed really. On our car 50% of the tubing in our car is mandated by rules but we dont have much in our car. There is an advantage to going chromo the more that percentage drops with the scope of your frame. Also having built a number of chassis in different racing fors over the years, chromo is a bitch. I hate working with it. Bends hard, cut hard, hits the pocketbook hard, weld finicky. Nice thing about mild steel is that it is way easier to work with, bends alot easier in small wall thickness percentages(all the way down to 4% which chromo hates), easier of tooling to cut, way cheaper and you can put as much heat into you want within reason of course. Its jsut generally a dead material. Another side benefit is if you plan to sell this to people you can figure that some idiot is gunna want to add this that and the other too it and weld on it all day. Mild steel is less sensitive to shitty welds than chromo. Just something to consider since we are designing these things for a consumer.

[Courtney Waters]

Right you are about steel prices! Man, even when buying "ornamental" (ERW) mild steel it's still expensive (compared to a couple years ago). I think it makes a lot of sense to use mild steel for the space frame if you were really building a car for the weekend autocrosser due to its ease of repair (and modification if need be). However, one might argue that it's an autocross car and accidents should be much less frequent than a road race car. Plus, ultimate performance will win out in the comp and for the potential buyers of the car.

Bulding an aluminum car doesn't make much sense if you're just going to replace steel tubes with aluminum ones. Besides a sheetmetal/honeycomb monocoque, what might be interesting is if a team explored the use of aluminum extrusions. Dies can be built for all kinds of custom sections. For building one car it may be expensive due to the tooling costs, but for mass production it makes a lot of sense.

[Mark TMV]

I have a question; if we're to heat treat our suspensions arms (4130 tubing and 4130 filler rod) what should be heat treat them to (Rc)?

[Bill Kunst]

Stop me if I am wrong, but you aren't looking to "heat treat" to a hardness, but looking to normalize the stresses within the HAZ. What is the Rc for noraml condition on 4130? That is what you are looking for.
Bill

[Mark TMV]

Hmmm, well, I'm getting a bit confused, because I've read that the 4130 suspension arms should have a full heat treat (quench and temper).
Normalizing, on the other hand would just relieve the stress from welding and make material softer.

what to do, what to do?

[Bete Noir]

GoKart chassis have been welded using 4130 for many years. The stress relieving vibrations resulting from usage have very often caused a shift in dimension and a resulting distortion of alignment. For serious competition, all heat treated steels should be heat treated after welding to prevent dimensional relaxation.

In many applications, advanced design is more important than strength of materials. Has anyone seriously considered the use of sheet metal tacked to tubular structures to produce stressed skin designs which have much greater torsional stiffness than big tubes? An interesting paper delivered at the Motorsport Engineering conference a few years ago demonstrated how a NASCAR chassis was made much stiffer using fewer and smaller tubes.

[Greg 08]

Hmmm, well, I'm getting a bit confused, because I've read that the 4130 suspension arms should have a full heat treat (quench and temper).
Normalizing, on the other hand would just relieve the stress from welding and make material softer.

what to do, what to do?

I would look at what your design goals are and how you plan to acheive them. When I designed some a-arms, I designed them with buckling in mind and found that tensile stresses were basically insignificant. It was a while back, but I didn't see any reason to heat treat, even to relieve weld stresses. Not relieving the stresses was probably not the best call, but it would have been some work to actually get a furnace and do it, so we didn't bother. We never considered the elusive cone impact as a reason to heat treat because we would just fab up another set of arms if they got bent.

Our baja team did explore heat treating a long while ago. They had some very motivated materials engineers and some very reckless drivers who loved hitting stuff. Given that, they justified higher hardness that way, but when I was on formula we never could justify the extra work to ourselves.

What book told you that they must be heat treated?

Greg Ehlert

[BStoney]

We also design our a-arms with buckling in-mind, so the heat treat is not an issue and thus has not been explicitly explored.

However, one must consider that if you stick an a-arm in a furnace, heat it up, then quench it and it wasn't in a fixture the whole time, it will likely turn into a giant pretzel (I'm exaggerating a bit here) when its complete. And oh yea, your fixture better be made of a very similar material (with respect to properties) so that it expands and contracts at the same rate as the part you are heat treating. This obviously presents an issue IMHO. Weldments that need to hold dimensional tolerance characteristics (i.e., a-arms) are tricky beasts when it comes to sticking them in an oven to achieve improved material properties. Even simple stress relief on 4130 can be an issue if not done properly...

[KU_Racing]

I think maybe there is a little confusion about the heat treat process on this post. The hardness is not the goal of the heat treatment, but it is diretly related to the properties of the finished product, and it is the easiest way to measure the properties of a weldment.. Think about it- would you rather do a simple hardness test on a piece of material, or use a instron to do a full tensile test? the hardness test is easier, and gives the exact same information about the state of the material. In most cases, however, achieving a certain hardness target is not the goal of the heat treatment.

[Jersey Tom]

I can't imagine you'd need to quench and temper a-arms. From a stress standpoint they are overbuilt, unless you curb it in which case you're screwed anyway.

We normalize the area around the wheel side welding while the a-arms are in their jig just so they stress relieve to where we want em to be. As-welded they've usually pulled in a bit.

Talk to the guy who weld a-arms for Swift.. they don't bother heat treating their a-arms.