Machining Titanium

[Alf JonesParticipant @alfjones33318]

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

[Alf JonesParticipant @alfjones33318]

*ANY* advice sought

[Tony Pratt 1Participant @tonypratt1]

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 Stevenson 1Participant @johnstevenson1]

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.

[Anonymous]

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 JonesParticipant @alfjones33318]

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 StarkeyParticipant @graemestarkey91347]

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 StaceyParticipant @timstacey83769]

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 ParsonsParticipant @richardparsons61721]

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

[methusalaParticipant @methusala]

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.

[Ady1Participant @ady1]

"*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 CParticipant @iansc]

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

[methusalaParticipant @methusala]

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 HaineParticipant @johnhaine32865]

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.

[Ady1Participant @ady1]

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 CParticipant @iansc]

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

[Ady1Participant @ady1]

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

[Trevor WrightParticipant @trevorwright62541]

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

[Chris123Participant @chris123]

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.

[WindyParticipant @windy30762]

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

[M0BNDParticipant @m0bnd]

**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.

[Speedy Builder5Participant @speedybuilder5]

Years ago, I was an apprentice machining huge Ti forgings for the engine beams of VC10 aircraft on Droop and Rein hydro copy mills. The forgings were about 8 feet long by 4 feet deep. The cutters were all nitrided HSS and cut using plenty of soluble oil. Machine setters set up the feed and speed of the cutters and as apprentices, we 'rode' the mill, and read our books / playboy mags and LISTENED to the cut as it proceeded. When the sound changed, we stopped the cut and called the machine setter for a new cutter. If we left it, the cutting sound changed to a 'squeak', then either the 2inch diameter cutter snapped, or the forging got pushed away from its mounting jig. In either case, it was hell to pay. The 'damaged' area had to be ground out (removing the work hardened area) before the cut could be resumed. This may have taken a day or so to recover the cut. My experience was that you spent as much time sharpening cutters and setting up as machining.

[richard allen 6Participant @richardallen6]

Cobalt drills cut like butter on Titanium……HSS taps can be used, but carefully….

[Chris HeapyParticipant @chrisheapy71135]

I tried to make some light-weight piston heads for a match target air rifle I was tuning, turning the outside and screw-cutting no problem, last job was to drill and tap an 8mm hole in the centre. No chance, the drill just heated up and that was that. Work hardened. Is it possible to anneal a titanium part that has work hardened like this?

[Trevor WrightParticipant @trevorwright62541]

The only way to salvage the part is to cut through the hardened section with a larger endmill or such, but it will ruin your cutter. Very low revs, hand feed so you can "feel" the cut and lots of oil to lubricate. The hardening is only local so when you are through the hard section it will be ok. If it was the tapping drill that burnt out then tapping will be impossible. If there is material on the diameter then grind a small boring bar up and take small licks until you get a diameter of 7 to 7.1mm for M8

Use a spiral tap with lots of oil and take your time, heat build up at the cutting tip will cause the metal to swell and grab…..

Tips for drilling;

Never pilot drill

grind the tip of the drill offset and it will cut oversize – won't drag on the bore already cut and overheat..

Lots and lots and lots of lube….retract the drill every 2-3seconds.

If you cannot drill finished size, use the biggest drill you can and bore the rest.

Trevor

Edited By Trevor Wright on 24/04/2013 12:58:17

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