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Machining titanium.

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Robin Graham25/04/2021 00:58:18
945 forum posts
295 photos

This is not the first thread on this forum with the title above I know - I found a discussion dating from 2011 (it ran for four years in fits and starts!) but it doesn't give me the info I want. I think the OP in that thread wasn't specific enough in his question, so I'll try to focus:

I have a piece of 20mm diameter Grade 5 (Ti 6-4) round bar which I want to cut, turn, and drill.

  • Q1. Can this stuff be cut with a 'normal' bandsaw? Mine has a 14tpi bimetal blade with M42 teeth. The blade speed given on the plate is 45/min, but it doesn't say if the 45 is in nanometres, parsecs or somewhere between.
  • Q2. If I use carbide insert tools for the turning, should I go for CCMT or CCGT? Or would I be better off with HSS?
  • Q3. I've looked about for advice on drilling the stuff and the recommendation is solid carbide. But that's from suppliers of industrial tooling. I need to drill three holes. Can I get away with HSS drills?

Any advice would be welcome.

Robin.

Neil Lickfold25/04/2021 02:03:56
836 forum posts
166 photos

Hi Robin, I use a low speed in the bandsaw for cutting G5 Ti, I use around 40ft/min to saw off. I don't use an older blade that has dulled. Use a new or new or new blade. You want low chlorine water and coolant. It only catches fire if it gets really hot and often there will be sparks or something like that. Never seen it catch fire with plenty of water based soluble oil coolants. I use the concentration of 8% to 12%. Where possible I use deionised distilled water for mixing my soluble coolants in a bottle. I drill with new centre point style drills. An 8mm drill I use 300 rpm or so. I use as a drilling speed of 8m/min surface speed and just use the squirt bottle for the coolant. Ti will work harden if you take too fine a drill feedrate, and if the drill dulls. I use about 1.5mm to 2mm pecks. For outer turning I use the coated CCGT inserts , with a coating for Ti,/ Nickel/ tough to turn materials. Ti like cutting with the positive very sharp inserts. I use R0.4 for roughing, and the R0.2 for finishing. As for turning speed I use 15 to 16 m/min surface speed or no faster than 720 rpm that my lathe is speed limited to. So for the 20mm bar , can take 0.5mm cuts/ 1mm diameter at 19mm I would run around 250 rpm, and feed at around 0.2mm / rev or so if you have the power and coolant from the squirt bottle or from the coolant tap.

Neil

ChrisB25/04/2021 07:17:09
659 forum posts
212 photos

At work we often use grade 5 titanium for aircraft parts. Mostly drilling and cutting operations and some turning.

Drilling can be done with hss bits, but be careful...do not creep to the final size using small increments. Drill a pilot hole to clear the next drill's point and then go to final size using coolant. I find that if I use small incremental steps to drill, the drill tip edges will overheat and go blunt immediately. Use a new sharp drill !

As for turning, the sharper the tip the better, I have machined Ti with TNMG inserts tho, which don't have the sharpest geometry with good results.

Cutting it with a band saw is the way to go, tried with grinder and thin cut off discs, eats up the discs in seconds, overheats and gets harder.

As for fire hazard, I have never seen a titanium fire in 20years. Just control the ammount of thin swarf and keep the workarea clear and you'll be safe.

Kettrinboy25/04/2021 08:38:13
94 forum posts
49 photos

HSS turning tools and drills can do Ti but must be sharp, use a brand new drill if you can and keep the suds on it , if it loses it's edge up the hole it will melt the end if the drill , for turning i use brazed carbide tools for touching and HSS for finishing, tapping is difficult , it's not the material the taps are made of but the angles need to be right or it takes ages, when you know the ins and outs it's actually pretty good stuff to machine, ive made tons of components at work and in my workshop shame ive used all my stock up as its expensive to buy.

Hollowpoint25/04/2021 09:10:13
471 forum posts
58 photos

I'm not an expert with titanium by any means but have done some work with it.

The thing to remember is that it work hardens very quickly if you don't keep the cutting temps down. Incidentally it heats up very fast and seems to hold heat. Therefore sharp tooling, slow speeds and coolant are a must. Expect to ruin plenty of tooling if it is too hot!

IMO turning doesn't present much of a problem, drilling and tapping on the other hand can be difficult. It is sometimes easier to bore holes in titanium than drill in my experience. With tapping you might find the tap has a tendency to get stuck often, again if you can "single point" screw cut that can be an advantage.

SillyOldDuffer25/04/2021 10:17:28
Moderator
8513 forum posts
1914 photos

Interesting stuff Titanium, no experience myself but this web page gives a good summary of what makes Titanium awkward and what to do about it, see answers above!

Briefly, Titanium has low heat conductivity and elasticity, high reactivity and it work hardens in a blink. The answer is low rpm and high feed-rate, sharp tools, plenty of coolant at the cutting edge, never stop with the cutter in contact, maximised tool, machine and work rigidity and replace tools as soon as they wear.

The need to replace cutters quickly jumps out at me relative to Robin's question: 'Can I get away with HSS drills?' The answer is yes, but start with sharp ones and expect to consume several. Unlikely to 'get away' with blunt drills.

My casual approach to drilling mild-steel would certainly cause trouble if applied to Titanium. Mild-steel tolerates blunt drills and wobbly set-ups, cuts over a wide range of speeds and feeds, and isn't fussy about coolant. Titanium reminds me of Stainless, another special needs metal: I'm much more careful machining it, and avoid the rapid work hardening alloys if at all possible. Nonetheless stainless can be machined - it just has to be cut appropriately.

Titanium fire hazards should be low in a small workshop: the real danger is when a large pile of swarf catches fire and pouring water on it converts an exceptionally hot local fire into an explosion scattering flaming metal over a large area. A ton of burning Titanium is a big problem! I suppose Titanium could catch fire in a home workshop if the operator did absolutely everything wrong: made a big pile of dry swarf under the job, allowed the cut to work-harden, and then insisted on forcing a blunt drill into the job whilst ignoring all the danger signs! Most fire extinguishers are unsuitable for reactive metal fires, so don't use them on burning Titanium or Magnesium without reading the small print first. Doesn't seem likely Titanium soaked in water coolant would catch fire, but a bucket of sand in the workshop would be sensible, just in case.

What fun. Please report what happens Robin. Although my money is on success, failures are educational too!

Dave

Chris Evans 625/04/2021 10:44:53
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2052 forum posts

I have limited experience of machining titanium and can not remember which grade i have used. However I do have a friend that spent his working life at IMI titanium division (Now Timet) His advise to me was always "Think Stainless" so all the above comments re dull tools etc hold good.

Andrew Johnston25/04/2021 10:48:21
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6577 forum posts
701 photos
Posted by SillyOldDuffer on 25/04/2021 10:17:28:
Most fire extinguishers are unsuitable for reactive metal fires..............

A Class D extinguisher is what you need. Types that are water based just make things worse.

Andrew

old mart25/04/2021 15:53:02
3728 forum posts
233 photos

As already mentioned, don't let the tools rub. We had a titanium fire in the toolmakers bandsaw when the apprentices were cutting tooling lugs off part machined aircraft parts. It caused a lot of smoke.

Mick B126/04/2021 12:00:12
2162 forum posts
119 photos

I've managed to machine - usually small items - out of titanium using sharp HSS tools.

I think the issue with low thermal conductance is compounded by its mechanical toughness - the chip is difficult to separate from the parent material and doing so requires energy expenditure, manifesting itself as heat generated in both.

Drilling, IME especially with small diameters, can quickly produce temperatures high enough to let down the drill and, if the swarf jams in the 'ole, twist off the end of the drill bit. If that happens it can obviously present a difficult problem in saving the workpiece unless you're very comprehensively equipped. I once did that when trying (foolishly) to drill 1,8mm through a 50 mm long workpiece, and could only save it by finding a way to substitute a M3 x 10 dp tapped hole. Carbide drills might be an answer if you're prepared to splash the cash.

Robin Graham27/04/2021 00:23:13
945 forum posts
295 photos

Thanks for replies - I think my questions have been answered. Neil Lickfold's detailed report on speeds, feed &c is especially useful.

It seems that I shall have to don my bio-hazard gear and crawl under the lathe to inspect the suds sump. I rarely use flood coolant (messy) but it sounds like I should for this task.

 

Posted by SillyOldDuffer on 25/04/2021 10:17:28:

...

Doesn't seem likely Titanium soaked in water coolant would catch fire, but a bucket of sand in the workshop would be sensible, just in case.

What fun. Please report what happens Robin. Although my money is on success, failures are educational too!

Dave

I don't intend to invest in a class D extinguisher, but might run to a tub of finely-powdered salt which might be better than sand in the event of an emergency. Apparently that's what's in the extinguishers - the salt melts and make a crust over the blazing inferno. And presumably sucks out some energy in the latent heat of fusion.

Something in the article Dave linked to confused me at first:

"Use of relatively high speeds of travel. Temperature is less influenced by speed of travel than by cutting speed. Travel speeds should therefore be as high as compatible with efficient working."

I initially read that as the statement of a general principle, which I couldn't understand. On reflection I think it's to do with the low thermal conductivity of titanium. Presumably the high rate of travel just distributes the heat over the work more rapidly than thermal diffusion, and therefore results in lower local temperatures. Is that right?

Mick - I had thought about carbide drills but was put off by the cost. Nearly £50 for a 5mm drill from RS! But Ive found that Zoro list a 5mm Dormer carbide stub drill, which will do me fine, for £5.99. I don't need to drill deeper than 8mm  so I'll probably go that way.

Robin.

Edited By Robin Graham on 27/04/2021 00:25:39

Edited By Robin Graham on 27/04/2021 00:26:11

Neil Lickfold27/04/2021 01:40:52
836 forum posts
166 photos

Titanium is a very poor conductor of heat. Which is why it will work harden very quickly. Some say treat it like stainless steel, and to a point that is true. Sharp tools with relatively high feed rates. But you have to keep the cutting edge tool. So they use through coolant drills etc. The only way to keep the heat low Ti is sharp tools and going slow rpm. The carbide tools as long as they are sharp will last about 5 times that of a hss drill before it needs resharpening. Some coated drills like the gold coated , can pick up with the Ti. There is a coating for Ti and it is a browny black colour. The other coating is a silvery colour as it is a diamond like coating. Uncoated carbide works well too , if it is the shiny one for Al. As you drill it, it will feel a little tough but easy if that can make sence. Then when it starts to work hardend, it will feel hard to push the drill, and it will squeel a little too. That means that the drill is dulling off or the speed is too high or not enough coolant or feeding too slow. With a 5mm drill you want to feed from 2 thou per rev to 4 tho per rev. On at 400 rpm you will be drilling at a feedrate of 1-1-/2 inches per min (40mm per min) to 3/4 inches per min(20mm per min) So your 8mm hole will be drilled in 12 seconds to 24 seconds as a guide example.

Neil

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