Titanium or Chrome moly....

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I  was wondering what the characteristics of titanium are. I have used chrome moly in the past for lightweight parts but am thinking of trying titanium.I have never welded titanium before. Is titanium more brital than chrome moly? I understand it's stronger but will it snap before it flexes? Once i get my answer i can ask the questions i have regarding the welding process of it. thanks for the help in advance
Reply:Hello sweet73, in a sense you are somewhat comparing apples to oranges. I put it that way based on a couple of things: weight comparison, Ti, light, CrMoly, heavy, Ti, very expensive, CrMoly, not nearly so much, Ti, requires much more attention to parameters and specifics for welding, CrMoly, not nearly so much. Titanium is also very grade specific and requires using the right filler for the right grade, it is also suggested heavily, that you don't intermix grades of Titanium. When you go to buy Titanium materials or the filler metals to weld them, they will be expensive, the fillers might very well require buying minimums of a quantity which might additionally add to and run up the cost. I would say that CrMoly and it's fillers, although not being cheap won't compare to Ti. Titanium is among one of the most sensitive materials that is commercially welded, it will tolerate next to no amounts of oxidation without sacrificing it's structural and other characteristics integrity. So when you mentioned your comment regarding whether it is brittle, I would say yes, if it is welded or handled improperly. A few items for you to think about. Best regards, Allanaevald
Reply:thanks Allan,   I am looking for the lightest material to use.I realize that ti is very light and very strong .I also am aware that it is very expensive.I don't mind spending the extra money on it if i have huge weight savings.What i am afraid of is the welding process.I am not experienced with it but am not afraid to give it a try,especially with people like yourself who are there to give advise. Does every joint to be welded need to be shielded both inside and out of the tube? what about the places where i can't get the gas inside of the joint? This is for a snowmobile chassis to be drag raced..It has to have some give to it as they leave the line very hard at take off.I usually build them out of ch moly but am looking to go lighter.
Reply:anything that is hollow will have to be back purged, no exceptions. with tube structures it can be difficult to know when the gas has gotten to everything. if you have several tubes coming together it can also create problems because you have several tubes that need to be back purged at once. Ti also loves to pull when welded much more so than stainless. their was a guy not to long ago doing research on building a motorcycle frame out of Ti, their were some good answers in their that would pertain to you as well. how much weight are you looking to save? just a guess but you probably aren't going to be able to drop more than a couple pounds doing a Ti chassis and you are going to give up some things to do it. you would probably want to use larger diameter tubes as well which could create problems as well.
Reply:Very generally Ti is around half the density of steel and around half the stiffness regardless of specific alloy. UTS and yield strengths obviously vary with different alloys i.e 4130 has higher UTS and yield strengths than 1018 but is no lighter or stifferData sheets for 4130, grade 5 and grade 9 Ti... http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=m4130rhttp://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTP641http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MTA321The steel versus aluminium versus titanium debate has gone on forever in the bicycle world, many articles have been written on the subject weighing the pros and cons of each material. Here's one of the better ones... http://www.sheldonbrown.com/frame-materials.htmlTi (like steel) has a defined endurance/fatigue limit and while harder/stronger generally means more brittle Ti is quite 'springy' (for want of a better word). It can be hard to work with the harder Ti alloys using DIY tools- more 'spring back' while bending/forming not that big a deal but machining it can be a bear/tedious without suitable kit. Have a play with google, terms like 'titanium springback' and 'machining titanium' should get quite a few hitsTi is lovely to weld, probably a lot to do with the extra cleanliness and gas coverage needed. Keep it clean and covered with argon (including the end of the filler wire) and it's very easy to weld. Only thing that can take a little getting used to or at least catch you out the first time it happens is that the filler wire has a tendancy to 'stick' to the part especially if you're not accurate with the wire and catch the edges of the puddle.
Reply:thanks for all who reply'd. In answer to a couple of questions, i am looking to save as much weight as possible.That being the reason i am researching this. I don't feel that alum would work for me as well as a tube chassis.I am currently running an alum chassis but it seems to have alot of twist off the line. I'm thinking that i might have to look at other parts of the sled and maybe work on saving weight in other areas.At least Ch moly is readily avail when i'm from and ti has to be ordered in special order.Although i would really like to build this chassis all in ti. The tricky part is back purgeing more than a couple of tubes at a time. Thanks for all the input.
Reply:Is is not that different to weld, but Hotrodder said it best with his "stickey" comment. The filler will stick to the base metal any time it touches it like it is magnetic, but it is not. I have hardly ever welded ti except for at an Air Force welding school. Ti in the sheet form, as in firewall pieces surrounding a jet engine, seems to crack quite often from vibration or poor design. I don't have much experience with tubing.Miller Syncrowave 200
Reply:With regards to purging, again plenty of examples in the bicycle world freely available... [ame="http://www.youtube.com/watch?v=j-SFvp4L734"]http://www.youtube.com/watch?v=j-SFvp4L734[/ame]Sticking 'titanium bicycle welding' into youtube will get some hits too, should be some more examples of purging set upsTube intersections need a 'breather hole' anyway, place the holes within the footprint of the joint and each tube vents into another. Obviously need to give it some thought to prevent pockets of air becoming trapped (bicycle frame is pretty simple as it's easy to move around and there's plenty of options for purge entries and exits what with bottle bosses and the like). Key thing to remember is that argon is heavier than air i.e it'll displace air from the bottom up