4130 welded frame anyone?!?! - Page 2
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  1. #21
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    4130 was specifically designed for o/a welded air frames, TIG welding came later and must be adapted to the material's needs.

    Nice little buggy. I have been building mountain bikes and off road race cars for a long time. Built something similar to yours in the 80's that got featured in 'Dirt Wheels' mag. 300lb, 12" travel, 60hp = lots of fun. Now I build and race class 10 cars in SCORE races.

    Tubing companies make special tubes for bikes. The tubes are already heat-treated for high strength. To prevent the welds from being a weak spot, or require reheat-treating, the tubes are thicker at the ends. The tubes are swaged in the middle to about .024 wall and the last few inches taper to about .035 wall.

  2. #22
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    When heat-treating 4130:

    For .065 wall and less I use ER70S2. I make the joints tight so not much rod is needed. Welding causes a concentration of carbon, so the low carbon rod will balance it out.

    Thicker welds I will use 4130 filler.

  3. #23
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    Sloeit, I wanted to do a series of similar test for the minibaja team here at UMBC, but our faculty adviser thought it was a waist of time. I still cringe when I go into the shop and see them welding on the car frame without even having cleaned the scale off the tubbing. And they wounder why we have problems with welds failing.

    Ray

  4. #24
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    M1,

    I think that is what is sorely lacking in our (and it sounds like your) mini baja/formula teams. An inherient lack of understanding of material properties. My feeling on the subject is that we are Mechanical Engineers, we should have a good understanding of the matierlas we are designing with.

    There is a group of Engineering students at my school who are designing a the seating portion of a roller coaster for Disney. Since they didnt know what materials to use, they asked the material science department (?!?!?!). When asking another ME professor he was amazed that they were now using a steel with a yield strength of 190 ksi!!!!. When a Mech. Engineer cant spec out A36, or maybe even "mild steel" for a project, its time to worry.....

    I hope to change a SMALL portion of that ignorance...

    Nick

  5. #25
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    Application of materials is very important. Once saw an SAE buggy just like yours with an aluminum brake rotor. They said they thought 6061 T6 would be up to the task, after all the numbers in the book said it was as hard as some steel , and 1/2 the weight. They couldn't understand why the brake pads were galling the rotor surface so bad, and why it got worse after everything cooled down once or twice. Are these the same engineers designing tires and other critical components in our vehicles and other critical components?Also saw an aluminum brake rotor on a motorcycle that was hard chromed to avoid the same problems as the above lads, only problem there was differental in expansion rates that de-laminated the chrome, throwing shrapnel on all the competitors behind him.Your test with the 4130 is a good example of what happens when the proper procedure for fabrication/welding is not followed,as stated by the many posts above.Have been repairing /fabricating with 4130 for 15 years, and see a lot of improperly welded 4130 fail,from little more than vibration from a motorcycle engine in 1 hrs. riding.It is very important to post weld anneal the HAZ with a OA rosebud to 1320 and play the flame back until the color is gone, and let cool in STILL AIR, no open doors, overhead heaters or fans. Have had very good luck with this method,and many happy customers that otherwise would have scrapped their frame,(motorcycle). I have seen some catostropic failures on motorcycle chassis where the whole steering head has ripped off, because the chassis builder did not do post weld treatment to his chassis. This was easy to see in the wreckage as the joints failed next to the weld, in the HAZ. One crack propigated from a crater at the end of the weld. (slammn' off the gas at the end of the weld). Every material has its place, but if assembled incorrectly,or used improperly , they will fail. Remember that when collecting your data.

  6. #26
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    In re aluminum rotors I've used both the Hunt rotors which had a plasma-sprayed ceramic coating and also the Buell rotos that had a stainless steel surface bonded/clad to the aluminum core. Both worked fine but the Hunt rotors could have the coating chipped if they were struck hard enough with something. The Zanzanis in Italy supplied aluminum rotors to many small GP bikes, but I don't know what kind of surface treatment they had.

    cheers,
    Michael

  7. #27
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    Yer baja team is funny...ours just mig welded everything together.

    I'm almost certain they used 1020 though.

    I usually ended up doing their CV shafts, or at least what they wanted...which was just cut them, drill them and make a bushing so they could shorten them. Flat sided bushing, round pin. Failed constantly...I was just the "machinist" (wasnt' even on the team...I was FSAE)

    Ours was just as bad though. We TIG welded 4130. I brought up the point of heat treating the weld and was laughed at, after all, at the time I was just a sophomore...the seniors did the design work and made the decisions. I can thankfully say that none of my welds ever failed. We had a little accident with an inexperiened driver (didn't push the clutch in), a stuck throttle cable and a curb at around 50 miles an hour. It rolled in the air. He walked away with bruises and a sprained ankle, the car was mangled. For those that dont know, an FSAE car is a mini formula car using a street bike motor. Weight is around 550 lbs and ours was putting out 120 HP at the axles.

    Nice to see a SAE team that is actually doing some homework instead of blindly relying on FEA numbers.

    On your A-Arms..I recommend running a bar between the legs of the A (make it more like the shape of an A instead of a V). It serves as a safety if you were to snag a wheel on something and break the arm loose. Keeps it from breaking through the wall and smashing your foot.

    -Jacob

  8. #28
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    Snowman, u mean a bar to prevent this?



    This was after a couple barrel rolls/cartwheels. First thing to fly off was the drivers helmet, didnt strap in. Luckily he came out unhurt. You can see where the upper A arm penetrated the .028 al skin.

    The one thing I am happy about, this was the first time weve broken a 1/4" hiem joint that we use on out front suspension!

    Nick

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    Yah...that.

    Only in my scenario, it would be the rear that would fail and then it would pivot in through the skin and into the driver compartment [img]smile.gif[/img]

    Are you using 4130 heim joints? Breaking a 1 1/4" is quite the feat!

    -Jacob

  10. #30
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    Snowman...

    no thats 1/4 hiem joints [img]smile.gif[/img] 0.25"!!!

    FSAE now uses carbon monocoque tubs, so they are pretty damn safe in that thing. We currently have a student doing my project but on the carbon. He is going to drop 450 lbs on an old tube to verify calcs.

    Nick

  11. #31
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    it's a slow day, brain hasn't came up to speed yet.

    1/4 sounds more like it [img]smile.gif[/img] It'd take a heck of a force to snap 1 1/4 [img]smile.gif[/img]

    I guess this year the school I went to is using a titanium frame...that means they'll finish the car the night before and wont be able to tune it at all.

    -Jacob

  12. #32
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    Ti frame?!? Welded or machined out of a giant block? Do they have a welding chamber or what?!

    Scary...kinda like the teams that used to use AL for frames on bajas (till it was banned) Some of the welds were frightening!

    Nick

  13. #33
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    i guess they made a welding chamber.

    idk...

    just saw something in the local newspaper

    haven't been back to visit in a while...try to avoid such things.

    -jacob

  14. #34
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    I thought that the rules stated that the frame had to be made out of steel for baja?

    Ray

  15. #35
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    M1,

    3 years ago they banned non-ferrous spaceframe materials. Before then they were allowed.

    Nick

  16. #36
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    Kinda OT ,but maybe of interest...
    Some years NMSU's ME Mini Baja does well, others, well...
    A couple years ago the Mechanical Engineering Technology students made a REALLY NICE Mini Baja whereas the ME students made a TURD .
    1. Their welding was so bad that visiting high school students made comments about it...( I took the HS students to show them the MEtech "good" car without making any negative comments...)They didn't use jigs at ALL, no heat treating at all (they used ChromMolly tubing)and the welds were really, really slaggy.
    2. They used a disk from a dividing head (!)as brake disks to save time because "it is ventilated and is available" and "we'll give them back". When I saw this I said -" Hey-that's part of the dividing head-you can't use that!" This served to teach me more about human nature that year than anything...it was like something out of an Ayn Rand novel[not that SHE is the last word,but, as usual, I digress again]
    Well, when the guy that owned the shop found out (Tony)... MAN was he PO'd, and I can't blame him! He liked to say "Their work is their signature."
    That year's team made us ALL look bad...
    The comment about the sophmore bringing up the heat treating (Snoman)and the seniors COMPLETELY blowing it off pretty much sums up my experience with a LOT of engineers-if you are newer, your opinion isn't even worth poop...
    I saw that a LOT in school and see it from time to time at work...oh well...
    I think being a good listener and humble teaches you more...
    In any case, the good team took great pride in their work without swelled egos or egregious short cuts...They placed above average, wheras the ME team -if I remember correctly-had to work on their car AT the race....

  17. #37
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    OT:
    He is one of our cars this year. We just got it rolling last month. Finishing up drivetrain and brakes. heres a pic




    A few years back we built an aluminum chassis and suspension. I think the chassis weighed as much as one of the chromoly ones. go figure.

  18. #38
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    I have just about stoped worrying about trying to help with designing our car and are starting to figure out repairs to fix the "Features" that the other "Engineers" have designed into it. I will try to post some pictures Saturday evening.

    Ray


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