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  #16 (permalink)  
Old 12-20-2009, 10:21 AM
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Fellows look at the amp ratings on the 110 machines, you are asking for trouble trying to weld a frame with an amp rating that low without preheating first. Theoretically you could heat each joint but in addition to the extra work you would most likely run into warpage problems. The problem is the heavier metal acts as a heat sink and will chill that low amp weld bead much too fast which will result in thermal shock to both the bead and the base metal. What happens then is that even if the bead appears ok it will usually be brittle and there will be under-bead cracking.



Try this, take 2 pieces of 1/4" plate about 4" square and butt weld with the 110 machine edge to edge without any sort of preheat then try it again after heating both pieces to about 400 deg. (just too hot to touch with your bare hand). Look at the difference in the welds, that's the problem and a 110 machine simply does not have the energy available to get around this. I know there have been improvements in 110 machines but that does not make up for the fact that the total energy input available is too low to avoid the problem, those bigger coils may increase the duty cycle but they can not create energy and only have what energy is available to them to convert to welding current.


AddShoe, A 110 welder could be used to weld some areas with proper preparation and proper pre-heat but to build a frame this becomes impractical. There are some other very skilled and experienced MIG welders (weldors) here that will probably chime in soon and some of these guys will recommend not even trying small frame welds with pre-heat, I can not disagree with them as their reasoning is not only sound it is the accepted industry practice. I personally have had good success welding heavier sections with a 110 MIG using preheat and for the occasional small job I believe this to be acceptable but the extra weld prep and extra attention required really makes it impractical for something like an entire frame.

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Old 12-21-2009, 02:45 AM
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The only thing that would worry me about pre-heating a frame is that the chance to overheat it and change the carateristics of the material it self. There is a reason why they tell you not to drill or heat frames on Heavy equipment and Trucks (in my pick-up's book also). I have seen bulldozer frames (made a Cat d3 dozer from low track to a high track in a few seconds with the idler being pushed into the cab), excavator booms fail because of overheating the material and in some cases the material is greater than 2 inches thick!
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Old 12-21-2009, 06:20 AM
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Quote:
Originally Posted by jonahb
The only thing that would worry me about pre-heating a frame is that the chance to overheat it and change the carateristics of the material it self. There is a reason why they tell you not to drill or heat frames on Heavy equipment and Trucks (in my pick-up's book also). I have seen bulldozer frames (made a Cat d3 dozer from low track to a high track in a few seconds with the idler being pushed into the cab), excavator booms fail because of overheating the material and in some cases the material is greater than 2 inches thick!
Heavy Equipment and Bigger truck's frames are made of a hardened steel,not mild steel,same with all crane and excavator booms and dozers.Most being a hardened wear plate steel,completely different animal from car and pickup truck's frames
Car frames and most pickup trucks up to 1 ton are mild steel frames.
Pre-heating is common practice for frame welding by the professionals on mild steel frames.
The reasons why they say not to drill and weld on them is most people don't know or have the capability to do the job properly.
Drilling a hole close to the edge of a frame will cause a crack and breakage,that's why a plate welded over the area the hole is needed and drilled is the common practice for added structural strength.

I've drilled and welded on many mild steel frames ,Jeeps,trucks..rods..etc and never seen a problem,jeep and 4x4 frames are regularly modified for different spring setups regularly by hobby garage welders and do just fine and these things are abused to the EXTREME,but they always take the advice of pro's on the setup and right way to do it,prep,preheat,fish plates,,etc
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Old 12-21-2009, 08:30 AM
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Quote:
Originally Posted by jonahb
The only thing that would worry me about pre-heating a frame is that the chance to overheat it and change the carateristics of the material it self. There is a reason why they tell you not to drill or heat frames on Heavy equipment and Trucks (in my pick-up's book also). I have seen bulldozer frames (made a Cat d3 dozer from low track to a high track in a few seconds with the idler being pushed into the cab), excavator booms fail because of overheating the material and in some cases the material is greater than 2 inches thick!


Exactly what SuthnCustoms said about frames but just to add a bit more.

One of the (mis-guided) arguments about preheating is that you will get the metal too hot when the heat from the weld is added but it simply does not work that way, if welded properly the base metal will be no hotter when finished than if preheat had not been used and preheating is nowhere near hot enough to damage the metal. The base metal will sink off the heat and weld temperatures will be controlled by welding rate. When done this way the weld starts out much closer to the same conditions that it will be when finished as opposed to starting out cold with not only thermal shock to both the weld and base metal to contend with but also rapid and localized expansion of the base metal. Think about what is happening when you start out welding on cold base metal, you will be inducing a difference of thousands of degrees of heat into a tiny area which is not only going to cause high stress as the hot metal tries to expand against the cold metal but this same cold metal is going to chill the weld bead much too fast. You would not quench a red hot weld bead with water would you? While the effect is not nearly as severe as quenching with water it is still happening to some degree until the base metal reaches a workable temperature. When properly preheated the metal will have already expanded over a much larger area and thermal shock to both weld and base will be minimized, the temperature differences between the weld and base will still be significant but after the base reaches about 400 or so degrees the adverse effects are reduced to the point of no longer being a problem.


BTW, it is standard procedure to preheat bulldozer parts. I spent 35 years maintaining Caterpillar mining equipment and made just about every conceivable weld on everything from D4 bulldozers to the D11's.
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