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Machining Titanium

*ANY* advice sought

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Alf Jones30/10/2011 08:33:16
14 forum posts
Hello all.
 
I have a model project in the works that I am building up to. It's still in the planning stage so I won't get too deeply into it (mostly because I'm still trying to decide if I'm biting off too much!! ), but one of the elements is an engine, likely a V-twin, dealing with super hot steam, in a situation where weight is a major issue.
 
Myself and a couple of friends are currently looking at aluminium, some of the hotter working alloys, and they don't seem to do what we need, so thoughts are turning to titanium.
 
I've done some reading about titanium, and here is the total of everything I know to date:
1) It work hardens like the devil
2) Use milk as the lubricant while cutting
3) Welding it is essentially impossible in the home workshop - too many specialised factors and tools needed.
 
4) Erm... thats it.
 
Obviously a period of attacking poor innocent lumps of titanium with machine tools is called for, but I was hoping to get advice from you good gentlemen before I start.
 
Given the absolute lack of knowledge, ANY advice you can give me would be very valuable.
 
I'm looking for basic information really - is there a knack to driling? Do you sharpen tools at different angles? What sort of methods can I use to avoid work hardening? feeds and speeds in lathes and mills etc etc etc.
 
Like I say - ANY advice or war stories you've picked up over the years will be hugely useful to me.
 
 

Edited By Alf Jones on 30/10/2011 08:33:45

Tony Pratt 130/10/2011 10:51:40
929 forum posts
3 photos
Alf, from my limited machining of Titanium it does work harden so don't let the cutters rub and don't use dull cutting tools. Milk as a lubricant sounds very old school, it may work but I'm sure there must be a better alternative?
Tony
John Stevenson30/10/2011 11:02:29
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5068 forum posts
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Depends on grades.
Grade 2 works a lot like stainless, good with tipped tooling but can work harden when drilling and tapping.
Grade 9 is a total bitch, try to avoid.
 
Neat cutting oil is best, can be TiG welded.
 
John S.
Andrew Johnston30/10/2011 11:24:50
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4936 forum posts
560 photos
As far as machining goes, use the same techniques as for stainless steel. I'll reinforce what Tony says; don't let the cutters rub, positive feedrates all the time.
 
Some titanium alloys can be welded at home; but with two caveats. One, you will need a decent DC TIG welder. Two, the main problem is that titanium has great affinity for oxygen and nitrogen when it is hot. So you will need to be innovative in organising gas shielding while the metal is hot. This is similar to stainless steel, but more elaborate.
 
The main safety issue with titanium is that the fine dust or swarf from machining can spontaneously combust. This isn't very likely, but if it does burn you are not going to be able to put it out unless you are prepared. The official means is a class D fire extinguisher; but these are expensive. About £200 last time I looked, before turning down a titanium machining job. The basic class D extinguishers, suitable for titanium, contain sodium chloride (salt!) plus other ingredients. An alternative (but don't quote me) is a bucket of dry sand; essentially you need to prevent oxygen getting to the fire.
 
Regards,
 
Andrew
Alf Jones30/10/2011 11:38:33
14 forum posts
Thank you gentlemen.
 
With drilling, is it better to "peck" at the work, as you would brass, which might keep the heat down, or push it through in one go, which is more positive, but will increase heat?
 
Does any one have any information about what properties Ti has as an engine block, and suitable pistons to go with it? Can you make a Ti-Ti interface? Ti-Cast Iron etc?
 
I will also need to bore the Ti - any thoughts? Boring generally is a bit of a delicate operation - I'm not sure how to combine boring with "positive feed rates"?
 
Lastly, do anyone have any advice on tapping and threading?
Graeme Starkey14/06/2012 15:16:32
11 forum posts

Yes you can weld Ti you need to have a gas shield that covers the back of the weld as well as the front,

you will also need gas to cover the heat affected zone until it is cool you will need a good quality T.I.G welding M/C. Machining treat it like cooper for speeds and feeds, tapping if say you are tapping a 6mm thread drill size would normaly be 5mm I would go for 5.2mm drill using a machine tap and a thick cutting compound helps take it very easy clear the tap often of swarf .As for cutting fluid water based cutting fluid is best and plenty of it, also When cutting Ti if you use carbide tips the carbide absorbs Ti after a period of use I got near to size with H.S.S tooling and changed to carbide

Tim Stacey23/06/2012 08:19:11
5 forum posts

Hi,

One small comment on the machining is that it is counter intuitive. Think of doing big slow cuts, if things start to get hot go deeper on the cuts. If you go for shallow cuts you will end up with bits of burning powder.

Tim

Richard Parsons23/06/2012 09:25:36
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645 forum posts
33 photos

Alf

We had one shop which worked exclusively in Titanium. There was a very strict anti fire policy and there were special fire extinguishers everywhere. All the staff were specially trained as firemen.

What I am saying is be careful and clean up very well every day and put the swaff and dust well away form anything you care about

Rdgs

Dick

methusala23/06/2012 20:16:47
32 forum posts

Alf,

I agree with Graeme on the size of the tapping drill i.e 5.2mm, if you have difficulty

tapping titanium you could try using 2 stage taps.

As an aside you can also electron beam weld titanium, but it would be very expensive

Colin.

Ady123/06/2012 21:24:09
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3463 forum posts
513 photos

"*ANY* advice sought"

To prevent heat buildup in Aluminium, (stickyness and clogging) I used my backgear

For a material like stainless though, you would need exceptional power, stiffness and hardness

Ian S C24/06/2012 10:56:50
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7447 forum posts
230 photos

Collin, I would suggest using a larger size tapping drill, and cutting thethread in one go, to cut in two stages invites work hardening on the first cut, and difficulties with the second tap. Just my small expiriance when tapping stainless steel, similar problem when using a die on stainless and trying to take it down in stages. Ian S C

methusala24/06/2012 21:42:48
32 forum posts

Ian, Way back in the eighties I worked for a firm that produced components for the

oil industry. These were manufactured from titanium and had numerous tapped

holes ranging from m3 to m6, and as you can imagine we had a heck of a job

tapping them. The firm got a rep in from a specialist firm for advice, and he reccomended

the two stage taps. It was still a "cork in the bottom " job to tap them, especially the m3

but it was definitely a lot easier.

Colin

John Haine24/06/2012 22:46:58
2693 forum posts
138 photos

Surely the "super hot steam" won't be hotter than petrol vapour burning with air? Why not use aluminium alloy for the block with inserted liners made of steel or meehanite? It sounds from everyone's experience above that titanium will be an absolute b***h to machine with no end of opportunities for things to go wrong.

Ady125/06/2012 01:08:31
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3463 forum posts
513 photos

but one of the elements is an engine, likely a V-twin, dealing with super hot steam, in a situation where weight is a major issue.

Ian S C25/06/2012 09:57:44
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7447 forum posts
230 photos

Thanks Colin, Its good to get the info from someone who knows, I'm teaching myself, and finding out how as I go.

If weight is so important, is the motor for an aeroplane? Ian S C

Ady125/06/2012 10:56:28
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3463 forum posts
513 photos

It would definitely help if we knew its purpose, there's a lorra braincells and experience in this place

Trevor Wright25/06/2012 13:27:06
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139 forum posts
36 photos

have machined a lot of Titanium in my time, mostly grade5, and on serious machines, would not recommend it as a material for engine blocks and Ti-Ti rubbing is an absolute no-no.

Have recently cut plate with an angle grinder, the fire aspect that was mentioned earlier was not an issue. In fact it cut better when the plate glowed red.......the sparks are ridiculously hot though and burnt a hole in my trousers and jacket......

Tapping is a nightmare unless you use cobalt style taps and drill at least Ø5.3mm for M6. Work hardening is not an issue but heat transfer is. Titanuim absorbs heat slowly so your cutting action will cause the immediate area to swell and expand and will "grab" your tool with a heart-stopping squeal. Don't try to force it - instead, go and make a cuppa and by the time you return it will be loose enough to retract.......then get another tap......

If you burn a drill out in the metal you are stuffed. The work hardening mentioned earlier is akin to a chilled casting. Cut low revs, feed hard and plenty of lube, pecking every 2-3 seconds maximum.

Have fun.........

Trevor

Chris12318/04/2013 23:51:18
108 forum posts

Only used titanium a few times but I agree with the above. The heat doesn't distribute anywhere near as well as steel or aluminium, it stays local for longer.

Windy19/04/2013 00:44:04
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747 forum posts
221 photos

It would be interesting to know why the weights so critical is it for an aircraft? Something like HH Groves steam driven aircraft.

As a user of high temperature steam (engine steam feed pipe glowing) and always having to keep weight down due to regulations could there be an alternative to titanium to reduce machining problems.

There are ceramic coatings on aluminium pistons on one fullsize flash steam engine I know of and maybe other applications it can be applied to.

Experimenting is great when it all comes together.

Paul

M0BND19/04/2013 06:50:33
81 forum posts
9 photos

**LINK** I work in a company that make and assemble these and have also machined some of the parts on them. Tapped holes range from M2 to M6, this is grade 2 titanium and machines like mild steel to a fashion. We weld these together too and again, not a problem - TIG with argon shielding. Hand dressing was easily done but quite labour intensive.

Andy.

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