Titanium cold forming

"grade 1" is meaningless.

Why?

It could mean anything without knowing the alloy at least. A grade is a variation of the basic material as described and required by a material specification. You have not stated either an alloy or a specification let alone a heat treat condition. With a few more details we can usually provide an educated guess. I can't do even that with "grade 1".
For example, in comercially pure titanium there are four common variations with different properties. Some specs might call this grades. For Ti 6Al-4V there are two major chemistry variants and three major heat treatment condictions. Are those grades? There are also several minor variants of heat treatment for Ti 6Al-4V. This does not include literally dozens of other alloys and heat treatments of each.
Help narrow the field. Learn enough to ask an answerable question. Start with the material you are considering. Get alloy and spec then tell us your intended purpose.
#! rnews 1085 Xref: xyzzy sci.engr.metallurgy:28144 Newsgroups: sci.engr.metallurgy Path: xyzzy!nntp From: "bainite" Subject: Re: How corrosion resistant is CPM M4 tool steel? X-Nntp-Posting-Host: l0129594.mw.nos.boeing.com Message-ID: X-Mimeole: Produced By Microsoft MimeOLE V6.00.2800.1441 X-Priority: 3 X-Msmail-Priority: Normal Lines: 10 Sender: snipped-for-privacy@news.boeing.com (Boeing NNTP News Access) Organization: The Boeing Company X-Newsreader: Microsoft Outlook Express 6.00.2800.1437 References: Date: Mon, 18 Apr 2005 17:17:42 GMT
Why wouldn't a 400 series CRES be a much better choice?

For Ti (certainly in UK practice) the "grade" implies the alloy.
"Grade 1" (and several others) is pure Ti, with no deliberate alloying and the impurites below certain quanitifed levels. There are something like two dozen grades and about six of these are "pure", for varying levels of purity. I'm unsure of the precise values (I'm a smith, not a metallurguist) and you no doubt have better references than I do, but "grade" is certainly a recognised way of specifying Ti alloys, at least in my country. "Grade 4" is the general grade of CP that I encounter, but that might be a grade mainly used for drawing seamless tube.
I'm not certain if grade also implies the heat treatment (I'm going to hand forge this stuff, so I don't care). However my suppliers offer particular grades as "standard" and "annealed", so they consider it worthwhile to separate the grades, even when they've all been annealed.

For sheet titanium, I'd refer to MIL-T-9046. Composition 1 through 4 is commercially pure titanium with minium yield strengths of 70, 55, 40, 25 ksi.

Even in UK, specs you must go to the specification to get the definition of grade. "Grade" is meaningless without it. And yes, I am a metalurgist. I earn my living answering these questions. BTW- "Bainite" is a steel microstructure.
#! rnews 1077 Xref: xyzzy sci.engr.metallurgy:28169 Newsgroups: sci.engr.metallurgy Path: xyzzy!nntp From: "bainite" Subject: Re: The Naming of Metals X-Nntp-Posting-Host: l0129594.mw.nos.boeing.com Message-ID: X-Mimeole: Produced By Microsoft MimeOLE V6.00.2800.1441 X-Priority: 3 X-Msmail-Priority: Normal Lines: 16 Sender: snipped-for-privacy@news.boeing.com (Boeing NNTP News Access) Organization: The Boeing Company X-Newsreader: Microsoft Outlook Express 6.00.2800.1437 References: Date: Wed, 20 Apr 2005 16:47:59 GMT
Try Google. There are many excellent sites with this info. Iron is Ferrum Copper is Cuprum Steel is an alloy of iron and iron-carbide not an element. The name is different in different languages.

As Mr. Dingley wrote, Ti grade 1 is commercially pure unalloyed titanium (you can find a lot of specification surfing on internet); it seems to be the best for cold forming operations, expecially when low in oxygen. I will be glad if anyone could indicate me how to form it in order to obtain a titanium dome for tweeters. Have a nice day. lele

No, you don't need to go the specification, because you (or at least I) very rarely need to know the definition. A piece of steel labelled "Extra crunchy tool steel" _is_ meaningless, because no-one else knows what that means. For Ti though, these grade numbers are well-defined and controlled. I don't know what their _definition_ is, and given how scary Ti phase diagrams are, I don't want to know. But with my engineer's hat on I can order some stock over the phone as "Grade 4" and know that what I'm getting is up to the job. Somewhere a metallurgist once worked out what it was good for and how much unobtainium impurity was permissable, but that's just not my problem any more - I deal with a part number, not a composition.
"Grade 1" is meaningful for Ti in a way that "Grade 1" wouldn't be meaningful for steel (although EN45A or 316 might be). Even if I don't know what this implies, I can still choose the stuff, buy some and make things out of it.
BTW - The one on the left is grade 1 Ti, the others are just plain mild steel is about 2" across
No shit ! Ever thought that people bothering to read an obscure sci.* group might already know things like that ?