Yes, that is true. It has been (d)rawn (o)ver a (m)andrel. The process takes out the seam and makes the wall thickness more constant. It also affects the metal properties so that it is stronger than the blue seam tubing.
you seem to know about this, and i dont have a rool book. whats the tubing size requiremtns for a single cab toyota like dans (i have the same model) for DOM? would it be OK to use 1.5" DOM? im just curiouse. any answeres are welcome.
minimum design and tubing size on seamless mild steel for roll cage structures are as follow:
vehicle weight ----- open cockpit----- closed cockpit
under 2000 -------- 1.5 x .090 -------- 1.5 x .900
2000 to 2999 ------ 1.75 x .120 ------ 1.5 x .120
3000 to 3999 ------ 2 x .120 ---------- 1.75 x .120
4000+ ------ ------- 2.25 x .120 ------ 2 x .120
material for roll cage construction may be CRW,DOM,WHR and WCR mild carbon steel or 4130.
i say using mild steel(blue line) for a cage is exceptable. when i put one in my truck it will be 1.75x .120 mild steel or greater. choice in materials really depends on application and or the SCORE rulebook
please stay away from EW tubing and go with DOM. the "weakness" of the electric welded tubing is very evident in how easy in bends in your tubing bender. get 2 samples and try it, then ask yourself if its worth your life to save $.25 per foot on EW tube.
OK PEOPLE HERE WE GO>>>>>>>>>>>>>>>>The tubing with the “blue line is CREW or CRW”, this tubing is the bare minimum that can be used in a cage. It is 1018 mild steel (in most cases) or 1020 mild steel flat stock, that has gone through a series of rollers to shape it into a round tube and then the seam is welded by machine, a.k.a. the blue line. DOM is Drawn Over Mandrel, which means NO WELD SEAM at all. The solid material is forced over a mandrel to form the ID of the tube, which transmits to no seam. DOM tube is also 1020 mild steel yet it is stronger than the CREW. 4130 is made the SAME way as DOM, except with a different alloy, not 1020 but 4130. Use the DOM, you’ll thank me later………….If you have any questions, just ask............
Um, DOM starts out the same way that CREW/CRW/HREW/HRW tubing does. It's flat stock that is rolled into a tube and then the butted edges are resistance welded together. What separates it from the common EW tubing is, as you state, AFTER the welding it is drawn over a mandrel in a cold working process. This cold working imparts an internal stress to the metal that serves to make it less ductile. I have no refs that state or infer that the UTS of the steel is increased by such a process, that is dictated by the alloying and the heat treat. Moving from 1018 alloy to 1020 alloy would increase both.
Do Hoeker's experiment with 1018 and 1020 DOM, there is a difference in bending effort there too. The 1020 is a little harder to find, but worth it.
Just because you can't see the seam doesn't mean it's not there. Acid etch a sample, the seam will show up. Some samples exhibit the seam with really close inspection.
There are hollow rounds available that are 'pierced', that is they start out as round bar stock and then have the hole pushed thru them in a manner similar to DOM's drawing process. That is not how DOM is made.
Thom you left something out; how seamless tubing is made. Some welded tubing is drawn over a mandrel to size it. Most seamless tubing is drawn over a mandrel to create it in the first place. It is often drawn again to size it. Some seamless, like high presure piping, is not drawn again for sizing. If someone uses the term "seamless DOM tubing" they are not incorrect. It is an intersting process.