roll cage

[nipper]

is it possible to weld chrome moly with a mig

 

[hotrodder]

Yes and no... the issue is cooling rate in that rapid cooling = hard and brittle. MIG is a low heat input process compared to TIG and oxyfuel (which was how 4130 aircraft fuselages were origionally welded). Cooling rate can be influenced by pre and post heat BUT if you're fabricating a 4130 tube frame or cage chances are you need to work to the rules for whatever racing class and if you're working to, say, NHRA SFI specs then the general regs say something like...

All 4130 chromoly tube welding must be done by approved TIG heliarc process; mild steel welding must be done by approved MIG wire feed or approved TIG heliarc process. Welding must be free of slag and porosity. Any grinding of welds prohibited.

Personally given how much chromoly (or T45 for the roundy roundy boys and girls) costs i don't see much point in making a cage out of the stuff unless it's race legal

ETA more detail on the metallurgy here... http://www.netwelding.com/Welding%204130.htm

 

[nipper]

thanks for that perhaps i`ll wait and pay someone else to build the cage
( this will be a track car ) not for compitition

 

[langy]

thanks for that perhaps i`ll wait and pay someone else to build the cage
( this will be a track car ) not for compitition

You could always use CDS

 

[bert]

most CDS cages are migged by cage manufacturers like OMP and safety devices and they are fine for FIA/MSA regs.

 

[rocketron]

nothing wrong with a ready made cds cage from a recognised manufacturer such as Safety Devices. The majority of weld in cages (i.e. from a bag of supplied pipes, with scant instructions!) that I inspect for MSA log booking fail at first attempt, for a variety of reasons. The thing with ready made cages is that they are more likely to do the roll over protection job they're meant to do. All you have to do is weld or bolt it in. You need not worry whether the cage itself is up to the task: the manufacturer has sorted that for you!
I accept that with fully weld in cages, often more tubes are added to connect up to suspension points, to stiffen up any flex therein, but you're adding more weight, the bane of performance?

 

[langy]

nothing wrong with a ready made cds cage from a recognised manufacturer such as Safety Devices. The majority of weld in cages (i.e. from a bag of supplied pipes, with scant instructions!) that I inspect for MSA log booking fail at first attempt, for a variety of reasons. The thing with ready made cages is that they are more likely to do the roll over protection job they're meant to do. All you have to do is weld or bolt it in. You need not worry whether the cage itself is up to the task: the manufacturer has sorted that for you!
I accept that with fully weld in cages, often more tubes are added to connect up to suspension points, to stiffen up any flex therein, but you're adding more weight, the bane of performance?

Thats why we use chrome moly for strength & lightness.

 

[nipper]

is CDS cold drawn steel

 

[hotrodder]

CDS = cold drawn seamless, aka CFS (cold finished seamless). It doesn't refer to a specific steel designation, it's just a production method [/pedantic]
I can't remember off the top of my head if the MSA refer to specific grade(s) but IIRC they don't, instead speccing a minimum yield strength (350N/mm^2 ?). The usual suspect would be CFS 3BK which is one of several flavours of CDS