Can you MIg Chromoly

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We are building a roll cage out of chromoly and wanted to know if you can MIG weld it.  We normally build cages out of steel for rock crawlers but are wanting to use chromoly for this particular application.  Neither one of us knows how to TIG weld.  I have read that you can MIG weld it using ER70 filler, is this correct. Any info would be appreciated.
Reply:Yes you can. Some of the new ump modified chassis are might welded moly. From what I understand they don't last as long as a Dom chassis. Take the time and learn to tig
Reply:Is this cage on a crawler? If so I wouldn't recommend using chromoly due to cost it isn't cheap and the only real advantage is some weight savings due to the fact you can use a thinner wall tube. I used to help a guy build sprint car chassis and asked why he didn't mig it and it had something to do with the amount of heat that dissipated to the surrounding area causing the tube to possibly become brittle, but don't quote me that was about 15 years ago.
Reply:Might use 309 stainless mig wire..030 size.Just a couple welders, big hammers, grinders, and torches.Work will free you.Men in dirty jeans built this country, while men in clean suits have destroyed it. Trump/Carson 2016-2024
Reply:If you follow a good welding procedure then yes the mig process can be used. The procedure may consist of pre and post heats etc. In fact Mig, Tig, O/A and even SMAW have been used for quality production fabrication of SAE4130, but each has its own procedure that no filler metal can account for. Material thickness and joint configuration will decide on the best procedure to use. Of course since you are spending the money on the material, I am assuming that you were hoping for some kind of quality finished product.
Reply:preheat is an important factor in welding chromoly's.no problem with MIG this, as long as you follow a WPS that is made for this application.About your filler material, this sums it up nicely:http://www.lincolnelectric.com/en-us...ly-detail.aspxI would advice against using 309.
Reply:Read the technical specifications for whatever racing category your building a cage for. Some require cages to be tig welded
Reply:Why do you want to build it out of CrMo? Often there are better (or at least simpler) options, when you take cost and other drawbacks into account. Many constructions get absolutely no benefit at all from 4130 compared to mild steel, while others designed to use the properties of 4130 can be made slightly lighter with the same strength or stronger with the same weight as mild steel.
Reply:Originally Posted by G-sonWhy do you want to build it out of CrMo? Often there are better (or at least simpler) options, when you take cost and other drawbacks into account. Many constructions get absolutely no benefit at all from 4130 compared to mild steel, while others designed to use the properties of 4130 can be made slightly lighter with the same strength or stronger with the same weight as mild steel.
Reply:My kit airplane has a production MIG welded 4130 fuselage.  There are thousands of these flying currently with no weld failures that I've heard of.  I've seen aftermath pictures of crashed planes and it's always the tubes that give way after buckling, not the welds.  Of course these are highly engineered for strength and light weight.  The manufacturer doesn't provide details on weld procedures so I can't shed any light on the exact process used.-- Paul S
Reply:Go with regular DOM and save the money, you won't really gain anything with CrMo other than a little weight savings in the form of a lighter wallet. DOM is easier to weld, easier to bend, easier to find, and a lot easier to afford.
Reply:I have built 10 chassis out of chromoly tubing; four Formula SAE cars, four Baja SAE cars, and two unmanned robots.  I didn't pre or post heat because all the wall thicknesses were .065" or under (the only tube thicker was the main driver roll bar at .095").  I tigged every vehicle together but you can use MIG as well.  ER70S-2 or S-6 is fine, only used the 4130 filler for parts that I had to have heat treated.  Get your process down pat if you are going to do this but if it's for a rock crawler I wouldn't waste the money on the chromoly tubing.  I was extremely concerned with weight hence the 4130 in all of my applications.  We had a hell of a time with bends due to the thin wall and wasted a lot of tubing before we learned the limitations during bending of the tubing that we used.Feel free to ask if you have any further questions.Mechanical Engineer
Reply:Originally Posted by SedlyMy kit airplane has a production MIG welded 4130 fuselage.  There are thousands of these flying currently with no weld failures that I've heard of.  I've seen aftermath pictures of crashed planes and it's always the tubes that give way after buckling, not the welds.  Of course these are highly engineered for strength and light weight.  The manufacturer doesn't provide details on weld procedures so I can't shed any light on the exact process used.
Reply:Originally Posted by makoman1860Which manufacturer? Kitfox and Rans have had failures that I know of. The biggest drawbacks to Mig and SMAW on 4130 tubing are rapid post weld quenching, and poor reinforcement shape causing stress risers. The quenching you can help by PWHT, but the physical shape of the weld itself is always there.
Reply:Originally Posted by SedlyIt's a Kitfox.  I haven't heard of any weld failures and I follow their forums pretty closely.  Do you know where in the structure the welds failed and what vintage they might be?  I believe current production is still Mig welded.
Reply:Originally Posted by SedlyMy kit airplane has a production MIG welded 4130 fuselage.  There are thousands of these flying currently with no weld failures that I've heard of.  I've seen aftermath pictures of crashed planes and it's always the tubes that give way after buckling, not the welds.  Of course these are highly engineered for strength and light weight.  The manufacturer doesn't provide details on weld procedures so I can't shed any light on the exact process used.
Reply:We are building a Polaris RZR 1000 for the Baja 1000.  We wanted chromoly for the weight savings as the class we are running in requires a stock motor.  Therefore our only advantage is saving weight anywhere we can.  We have actually hired an airplane fabricator to do our tig welding for us.  We do want this to look professional so spending the extra cash to have someone tig weld is not a problem.  Thank you guys for all the info...  One more question, does anyone know what the spring back rate is for 1 3/4" .095 chromoly?
Reply:the chromoly advantage comes when thin tubes are heat treated, thus you gain some weight savings while gaining strength. is the plan to heat treat the roll cage? would a 1026 DOM be more suitable?1026 7.9g/cm385kpsi ultimate tensile75kpsi yield4130 7.8g/cm3 (normalized)97.2kpsi ultimate tensile63.1kpsi yield4130 7.8g/cm3 (annealed)81.2kpsi ultimate tensile52.2kpsi yieldLast edited by welding_kid; 05-19-2014 at 03:30 PM.
Reply:Originally Posted by RyanMcIntire22We are building a Polaris RZR 1000 for the Baja 1000.  We wanted chromoly for the weight savings as the class we are running in requires a stock motor.  Therefore our only advantage is saving weight anywhere we can.  We have actually hired an airplane fabricator to do our tig welding for us.  We do want this to look professional so spending the extra cash to have someone tig weld is not a problem.  Thank you guys for all the info...  One more question, does anyone know what the spring back rate is for 1 3/4" .095 chromoly?
Reply:Originally Posted by welding_kidthe chromoly advantage comes when thin tubes are heat treated, thus you gain some weight savings while gaining strength. is the plan to heat treat the roll cage? would a 1026 DOM be more suitable?1026 7.9g/cm385kpsi ultimate tensile75kpsi yield4130 7.8g/cm3 (normalized)97.2kpsi ultimate tensile63.1kpsi yield4130 7.8g/cm3 (annealed)81.2kpsi ultimate tensile52.2kpsi yield
Reply:Just use Normalized tubing and avoid excessive heat when welding...i.e, use proper prep and fitting techniques to avoid excessively large welds. You shouldn't have anything over .095-.120" wall thickness on that car and most should be .083 and .065 in 4130.  In motorsports many of the components (arms, diff housings, etc) are heat treated but the chassis is left in as welded condition. You're building a RZR, not a spaceship.http://all-a-cart.comWelding Cart Kits and accessories
Reply:Had anyone used bend tech pro?  We are using it to design the cage.  I am great with cad so it's pretty simple to pick up on.  Is it reliable on its spring back calculations and cutting measurements?
Reply:Originally Posted by RyanMcIntire22Had anyone used bend tech pro?  We are using it to design the cage.  I am great with cad so it's pretty simple to pick up on.  Is it reliable on its spring back calculations and cutting measurements?
Reply:Welded our 4130  with 3/32 LH-70 Lincoln before tig and mig and we did USAC approved welds on cars too . Bent with a Hossfield . Our Beady rear engine midget was brazed 4130 and had Mario Andretti and Wally Dalenback as drivers . Floyd Trevis welded his cars with stick too./
Reply:When your super fly chromoly chassis gets bent or broken will you be expecting to fix it your self at the track. hire the repair at the track. or trailer it home and call it a day? If you can't weld the frame your self and your hiring a guy at the track to repair it how do you know the local guy is equiped or skilled enough to repair your ride? I have built and repaired many a vehicle and never depend on the local guy for a repair both because I am concerned about the quality and often I don't have enough time to stand in line to get my repairs done. Be fore warned that you will be very popular at the track as soon as everyone finds out you have a set up for field repairs. Bottom line, gear up for the welding you need or go with mild steel. Good luck with your project.Tthe chassis builder for the winner of King of Hammers this year builds his chassis out of chromoly and mig welds them.  If its good enough for them then its good enough.  They do post weld heat treat the whole chassis after welding.More is never enough.
Reply:Originally Posted by gundog77When your super fly chromoly chassis gets bent or broken will you be expecting to fix it your self at the track. hire the repair at the track. or trailer it home and call it a day? If you can't weld the frame your self and your hiring a guy at the track to repair it how do you know the local guy is equiped or skilled enough to repair your ride? I have built and repaired many a vehicle and never depend on the local guy for a repair both because I am concerned about the quality and often I don't have enough time to stand in line to get my repairs done. Be fore warned that you will be very popular at the track as soon as everyone finds out you have a set up for field repairs. Bottom line, gear up for the welding you need or go with mild steel. Good luck with your project.
Reply:Originally Posted by makoman1860Ahhh, you may want to check the numbers on 1026. My books list 34ksi yield and 63ksi ultimate in the hot roll condition, and 60/71 for cold. Both annealed. The area of the weld is going to be towards the hot roll specs due to loss of strain hardening. My guess is you got the numbers from a tubing manufacturer that has strain hardened the material quite a bit and is perhaps being a bit deceptive. 1026 being a medium carbon steel may start needing some special care and feeding as well depending on welding process and joint config.
Reply:We are running two chase trucks.  Each truck has either a mig or tig machine and someone that can weld so we will be good as far as getting things fixed.  It is correct all we are wanting to do is finish the race so any repairs will be quick band aids until we can get back home and repair them properly.  We are a small team going and most likely have no chance of finishing on the podium, we are looking just to finish.  We also don't want to look out of place with our car so we are going to build it right and spend the money to have it properly done.  Thats why I am asking all the questions that we are unfamiliar with.  Thank you guys for all the help and information we greatly appreciate it.  I will post a picture of the roll cage and chassis when we are finished.
Reply:Originally Posted by RyanMcIntire22We are running two chase trucks.  Each truck has either a mig or tig machine and someone that can weld so we will be good as far as getting things fixed.  It is correct all we are wanting to do is finish the race so any repairs will be quick band aids until we can get back home and repair them properly.  We are a small team going and most likely have no chance of finishing on the podium, we are looking just to finish.  We also don't want to look out of place with our car so we are going to build it right and spend the money to have it properly done.  Thats why I am asking all the questions that we are unfamiliar with.  Thank you guys for all the help and information we greatly appreciate it.  I will post a picture of the roll cage and chassis when we are finished.