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Steel vs. Aluminum in flexability

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Steel vs. Aluminum in flexability
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flag ricar
Posted: Jan 28, 2008 at 14:32 Quote
Have to say I would never MIG a frame or buy a frame that has been MIG welded.


EDIT: I forgot to add that steel is also more forgiving of twisting forces. If you deflect a steel tube it has more "spring", there is a greater range before you perminantly deform the tube. Alu has a tendancy to stay bent once deflected.
flag huckoveraduck
Posted: Jan 28, 2008 at 14:35 Quote
ricar wrote:
Have to say I would never MIG a frame or buy a frame that has been MIG welded.

i would buy a MIG welded frame - it it was made from 13mm steel sections and had no use.
flag doctorz
Posted: Jan 28, 2008 at 14:38 Quote
i use a mig welded steel frame that i made myself and it hold perfectly the only problem i find is on the rear swingarn it has so much tensile and spring strenght it bash the rear derailleur against the rear part like there is no tomorrow i go thru 3 or 4 derailleur each year
best of all i use a home depot lincoln mig pak 10 welder with legend high tensile 70 000psi ts fluxcore wire with on 14 gauge steel it give great result
you would be surprise
cheers
Dr Z
flag srobinson
Posted: Jan 28, 2008 at 15:53 Quote
huckoveraduck wrote:
ricar wrote:
Have to say I would never MIG a frame or buy a frame that has been MIG welded.

i would buy a MIG welded frame - it it was made from 13mm steel sections and had no use.

MIG welding a frame really isn't that bad, I'd still never buy one. If the welder has enough skill it can be made as strong as a tig weld. The problem is becuse you can't really change the amount of metal deposited, you will end up with a larger bead. Also if the weld is done improperly (not enough heat, too much feed) the heat will be concentrated on the weld puddle, not your work, causing less penetration and creating a situation where the weld is more likely to break. If done proplerly though, it will be ok, but probably won't look as good.
flag terrance
Posted: Jan 28, 2008 at 15:59 Quote
s-t-e-v-e wrote:
huckoveraduck wrote:
well steel frames can melt at the welds if you use them for excessive downhill. But aluminium is pretty flexible too, which means sometimes if your not careful it will rust where it bends or flexes.

Aluminium doesn't rust.

aluminium doesn't rust, IT CORRODES
flag BMX8000
Posted: Jan 28, 2008 at 16:56 Quote
srobinson wrote:
huckoveraduck wrote:
ricar wrote:
Have to say I would never MIG a frame or buy a frame that has been MIG welded.

i would buy a MIG welded frame - it it was made from 13mm steel sections and had no use.

MIG welding a frame really isn't that bad, I'd still never buy one. If the welder has enough skill it can be made as strong as a tig weld. The problem is becuse you can't really change the amount of metal deposited, you will end up with a larger bead. Also if the weld is done improperly (not enough heat, too much feed) the heat will be concentrated on the weld puddle, not your work, causing less penetration and creating a situation where the weld is more likely to break. If done proplerly though, it will be ok, but probably won't look as good.

Could some one enlighten me on what you guys are talking about in a language I would understand???
flag Hummeroid
Posted: Jan 28, 2008 at 17:05 Quote
MIG= you set the feed speed for your filler wire, heat settings and such, and pull the trigger to weld.

TIG= You hold the filler rod, and vary the welders power with your foot pedal if it needs to be.

Google either one, and theres a ton of info im sure.

(for all the fabricators and welders out there, that is soo over-simplified, but still, itll help him out)
flag doctorz
Posted: Jan 28, 2008 at 17:13 Quote
terrance wrote:
s-t-e-v-e wrote:
huckoveraduck wrote:
well steel frames can melt at the welds if you use them for excessive downhill. But aluminium is pretty flexible too, which means sometimes if your not careful it will rust where it bends or flexes.

Aluminium doesn't rust.

aluminium doesn't rust, IT CORRODES
exactly when its scrat bad and not treated
flag doctorz
Posted: Jan 28, 2008 at 17:15 Quote
mig is the easiest but i only recommend welding with mig when you have experience and getting the right type of flux core wire
as for what he said yes it right its hard to weld correclty with a mig because a cheap one will vary the current and lose power once a awhile when your welding i should have gotten a mig pak 170 with 70amp of power or the latest model
flag signorvince2
Posted: Jan 28, 2008 at 17:18 Quote
terrance wrote:
s-t-e-v-e wrote:
huckoveraduck wrote:
well steel frames can melt at the welds if you use them for excessive downhill. But aluminium is pretty flexible too, which means sometimes if your not careful it will rust where it bends or flexes.

Aluminium doesn't rust.

aluminium doesn't rust, IT CORRODES

rust is iron oxide, but it still oxidation/corrosion

aluminum doesn't "rust" per se, but whenever someone says that, they aren't talking about the chemical "rust" they are talking about oxidation/corrosion.

Chill out buddy.
flag nwatkins
Posted: Jan 28, 2008 at 17:25 Quote
hey thanks for all the help guys. I am definatly going to go for the suburban. I am so stoked!
flag srobinson
Posted: Jan 28, 2008 at 17:30 Quote
First you need to understand the funtion of a mig and tig welders. They are both electic welders so the heat comes from and arc forming between the metal and the torch (not with a flame, just what it's called). The torch is usually positive (I think, been a while science i set one up) and the "ground" (a clamp you attach to you the metal) is negative. They can also be set up reverse, for reasons I am unsure of. When the positive and negative are brought into close proximity, an arc is formed as the electricty jumps the air gap from one to the other. This creates heat and you "weld puddle" (a small molten puddle of metal, usualy around 1/8" in diamater). Both mig and tig operate on this prinicipal. The differnce is, mig uses the filler wire (metal added to the weld to make the weld bead) as a carrier for the current. When the trigger is pulled, the wire moves towards the metal, the arc jumps, the metal and the wire get hot, a puddle is formed, and the end of the wire is burned off. More wire is constantly fed to replace the burnt off wire and to maintain the arc. This happens hundreds of times a second to make a weld. A tig on the other hand, is much like gas welding. There is an electrode (metal to carry the positive current) that the arc jumps from, but the metal (a form of tungsten) has an extremely high melting point so it does not burn and add filler metal to the metal. Filler is added manualy via a rod held in your other hand. Another huge difference is a mig's heat and wire speed are adjsuted on the machine, and remain constant throughout the weld. A tig uses a foot pedal to adjust the heat and the filler (essentialy wire speed, not really but we are going to assume it is) is added manualy. That's the basic funtion of both machines

Now the difference is when welding frames with a mig, you need to have the right heat and wire speed set up prior to welding, which takes a lot of experience. Also, on a mig, heat and wire speed must be matched to a certain degree. ie. if you want to weld at 18v you must run between about 190-240 feet per hour of wire feed. You need to have a certain amount of filler to make a decent weld. The problem is if the welder heat is set to low, the feed is also set too low. This means the travel has to be slower to make a wider bead. Ideally when when welding the wire should be right at the front of the weld bead, this causes the wire to be closer to the center of the puddle. The wire is the center of most of the heat, so this means instead of the heat going into the metal, it goes into the already molten metal, and the penteration desired is not achieved. (pentration being how much metal is bonded below the surface of the metal) This makes the metal more liley to break. Also on a mig, it is easy to make a good looking weld that wont hold ten pounds where as other welders generally if it looks good, it is good.

A tig, heat can be adjusted as nessacary to create constant pendatration all the way around. You can also weld with no filler if nessacary, creating a cleaner looking weld. You can also travel any speed you want (provided the weld is not super hot) so you have more time to anaylize the weld as you are performing it without creating a huge glob of metal.

Thats welding in a nutshell hope it made a bit of sense, got a little rushed at the end.
flag nwatkins
Posted: Jan 28, 2008 at 18:48 Quote
Well here is the bike. Just wanted to get some final opinions and the welds and tubing:

Unsecure image, only https images allowed: http://img246.imageshack.us/img246/1783/subbie08wl1gk8.jpg(put the zoom level on 200% to see it better)
flag ricar
Posted: Jan 28, 2008 at 19:57 Quote
TIG now called GTAW (gas tungston arc welding) is simply the most controllable form of welding. It puts also more heat into a peice than any other form of welding. That sounds bad but what it means is you can get in and out before the heat spreads. To get the basic idea of how to TIG weld hold a pencil above a line on a peice of paper. Move the pencil across the line about 1/4" off the sheet. About every 1/8" touch the line with a marker. DO NOT touch the pencil with the marker, touch the line directly below the pencil, DO NOT touch the paper with the pencil. If you can do this TIG welding is about 100 times harder. It is the scalpel of the welding world.

Normally you weld with DC straight, steel ect.. A/C current is Aluminium alloys and sutch. DC reverse is for things like pop cans and tin foil.

As for mig I don't think you are using the right filler. Flux core wire would torch the tubes I use in a heart beat and it's not the strength of the filler that is the problem. The problem is the high carbon content of the steel. When you weld 4130 you get too much carbon in the weld. Carbon is brittle and it will crack. You need a filler like stainless that will dilute the carbon. Still only 310 and 312 stainless. Non stainless, ER80S-D2 is the best. Sure a MIG welder can do great things but I've never seen a MIG touch a pop can (not the rim, the middle). I am not some hard core welder but my teacher is, the only stuff I have spent time welding is thin wall 4130.


EDIT: as for the tungston, you ues pure tungston to weld ALU and 2 percent thoriated tungston is the most common for everythingels, but the dust is radioactive.
flag huckoveraduck
Posted: Jan 28, 2008 at 23:57 Quote
terrance wrote:
s-t-e-v-e wrote:
huckoveraduck wrote:
well steel frames can melt at the welds if you use them for excessive downhill. But aluminium is pretty flexible too, which means sometimes if your not careful it will rust where it bends or flexes.

Aluminium doesn't rust.

aluminium doesn't rust, IT CORRODES

hmm you missed the part where I said I was taking the piss.....

 


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