DOM vs CDS
 

to start with this is NOT PIPE

As most of us know DOM is expensive, over $10 a foot in most places. CDS is about $2 a foot.

DOM-
DOM is cold drawn through a die and over a mandrel resulting in improved surface finish, excellent concentricity and dimensional accuracy. Lower cost alternative to CDS with equal or superior physical properties. Can be used for
machined parts, rollers, shafts, sleeves and is most readily adaptable in cylinder applications
tensile strength 80,000psi
Yield 70,000 psi
elongation 10%
wedlability - good to excellent

DOM: made from 1020 steel, in walls 10 ga and lighter (0.134"), 1026 steel in walls greater than 10 ga. Meets ASTM A513 Type 5.

CDS-
General purpose seamless tubing, CDS allows selection of chemistry and rough tube size. Cold drawing produces higher physical properties without heat treating. Offers widest range of sizes and chemistries in mechanical tubing. Better tolerances and reduced machining allowances over HFS. Typically ordered as either OD and wall or OD and ID.
Machined parts, rollers, shafts, sleeves and cylinders.
tensile 75,000 psi
yield 65,000 psi
elongation 5%
wedlability good to excellent

CDS: made from 1026 steel, sizes up to 9.5" OD. Meets ASTM A519

Acording the specs above:

The DOM has an elongation of 10% vs. the CDS 5%. This means that at that elongation, the material will have yeilded, and will not return to its original shape.

So yes, the DOM will "flex more" under load before failing. However the load that it will flex under isn't much more than the CDS, and with less flex there will be less recoil when something lets loose, or the load changes suddenly.

The flip side is that a well designed part will suffer less fatigue with the greater flexability that DOM provides.

For a load bearing part the DOM would be a better choice, but for bumpers and the like the CDS would be fine when you compare what you are getting for what you pay for it.

That is just from the specs listed above, there may be some metalurgical intracies that will make the DOM superior, but steel is steel, and when you weld it you change the worked structure anyway (when cold or hot forming, it won't matter at the weld because you just basically annealed it, so all the dislocations put into it during a cold work process are negated) and the joints are where the loads do weird things when they combine in the first place (unless you build funky parts with extreme slenderness ratios, like really long control arms that have tendency to buckle) which is why everybody preaches more gussets. If you built your joints strong then a tube will fail, but the joints are where the care should be taken.

The Score racing rulebook allows for CDS, I quote from CR33 Roll Cages, "Minimum design and tubing size based on seamless 4130 chromoly tubing or ASTM 1018/1026 CDS/DOM, no aluminum or other non-ferrous metal permitted"......


Just a little food for thought here.

man that is some good info :thumbsup:

Looks like you're talking tubing. There are three basic types:

DOM - Drawn Over Mandrel. You've pretty well nailed this one down. However, note that DOM can be pretty much any AISI alloy, with "chrome-moly" (41xx and 43xx) being probably most common (and therefore also driving the cost up.)

HREW - Hot Rolled/Electrically Welded. Usually covered with scale formed during cooling, this is easier to form (no work hardening,) and can be pretty much any AISI alloy. The scale on the surface and the slight "burr" on the inside diameter at the seam give this one away. Most often 10xx or 11xx steel.

CREW - Cold Rolled/Electrically Welded. Clean surface, closer tolerances than HREW, but not as good as DOM. Formability somewhat less than HREW due to work hardening. The burr on the ID is usually not as great.

HREW and CREW can be readily identified by the presence of a seam (which looks different due to the HAZ of the weld,) while DOM is usually made from drawing a rod through a die and over a mandrel - literally punching a hole through it (this is why DOM is so limited in lengths, while HREW and CREW are not so much. Longer DOM sticks are, natch, going to cost more.) The seam in HREW/CREW can be a weak point, and should be allowed for when designing and forming your project (unless effective heat-treatment is part of the forming process.)

DOM, typically being 41xx/43xx alloys, will respond well to being "gas torch-welded" - while HREW and CREW do not. This is because the chrome-moly alloys were actually originally formulated for use with oxyacetylene torch welding, and a slight carburising (read: "rich") flame will give best results for the weld.

I could expound on this, but I don't have my notebooks handy and I'm about to leave to go pick up The Blonde Thing (tm.) It's her birthday to-day - all those years ago, she was released unto the world. The world has yet to recover (I came along rather later. It's been twelve years, and I haven't recovered yet either...:naughty:)

Amen brother!

Same thing happens when you put a torch to it. Kind of defeats the purpose of buying a $150 piece of DOM just to heat it up to bend it.

not all DOM is chromoly, but some chromoly is DOM.