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Author Topic: Working with Titanium  (Read 57590 times)
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wobblywalrus
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« on: July 12, 2015, 02:53:58 PM »

Titanium is sometimes referred to as "the titan of metals."  It is also called a number of other unprintable names.  The stuff can be difficult to impossible to work with.  Some methods follow.  They are done using small and old tooling like most of us have.  Suppliers are named so a person will know about a source.  ASTM Grade 5 annealed titanium alloy with 6 percent aluminum and 4 percent vanadium is used.  This is often called "structural ti."  References to "Bradley" are in Volume 2 of John Bradley's "The Racing Motorcycle."  He has a chapter on titanium alloys.

The metal can be machined using conventional high speed steel or carbide bits and drills.  Occasionally there will be a tool that wears quickly.  The carbide boring bar bit shown wore down almost instantly.  There was never a problem when it was used on other metals.  Carbide insert tooling is what I use now for these reasons.  The bits are available with a variety of coatings and some resist wear very well.  This saves a lot of sharpening.  A variety of chip breakers can be had that result in good finish quality and I cannot duplicate them on HSS bits.  Bradley recommends using tools for titanium that are not used to machine other metals.  It is easier to have a supply of bits used for ti rather than a special set of cutting tools.

My little lathe uses 1/4 inch by 1/4 inch tool bits.  It would be very expensive to adapt it to modern tool holders for carbide insert bits.  Instead, an intermediate solution is used.  It is the tool bits shown.  They have carbide inserts and fit in old style tool holders.  A page listing the bits is shown from the 2011 Sam A. Mesher Tool catalog.  They are in Portland ad they specialize in being able to find weird machine tooling.  www.meshertool.com


* 2015 Tit 001.JPG (82.06 KB, 800x528 - viewed 131 times.)

* 2015 Tit 002.JPG (164.22 KB, 800x509 - viewed 136 times.)

* 2015 Tit 003.jpg (92.88 KB, 789x600 - viewed 137 times.)

* 2015 Tit 004.JPG (90.73 KB, 739x600 - viewed 140 times.)
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manta22
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« Reply #1 on: July 12, 2015, 03:13:52 PM »

WW;

I don't do any titanium machining (6Al4V usually) other than drilling & cutting sheet metal. If you treat titanium like stainless steel, you'll be on the right track-- heavy pressure & low rpm with cutting fluid works well with high-speed steel drills.

Cutting 6Al4V sheet metal is problematic. I've tried hacksaws, abrasive cut-off wheels, and anything else I could think of but the only method that works for me is a plasma cutter. To dress up the cut edges, I use an angle grinder with a 3M Cubitron II oriented ceramic abrasive disc.

One more point to add to your excellent post-- even 6Al4V titanium is not necessarily stronger than many good alloy steels; it is its strength to weight ratio that is outstanding.

Regards, Neil  Tucson, AZ
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Regards, Neil  Tucson, AZ
fordboy628
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« Reply #2 on: July 12, 2015, 04:32:43 PM »

Ti is sexy and light, but often not necessary.    Check out the retainers on MM's BMC.

 cheers
Fordboy
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wobblywalrus
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« Reply #3 on: July 12, 2015, 09:04:48 PM »

A post coming up will address this.  Ti is real good for a limited range of applications, like you say.
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aircap
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« Reply #4 on: July 12, 2015, 11:05:23 PM »

Be mindful of your titanium dust when grinding. I ignited my Tshirt once when a spark lit all the dust on my shirt. There was a bright flash, a wave of heat crossed my face, and I suddenly had an 8 inch diameter glowing ring on my stomach with exposed skin showing. It quickly went in the sink while I secured another shirt.
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« Reply #5 on: July 12, 2015, 11:26:45 PM »

Be very aware when machining titanium alloys that it will burn, and can be ignited even in a solid state. It is the only material that will burn in a pure nitrogen atmosphere. In the airplane plants, they keep buckets of a black sand close at hand anywhere that TI is being worked, just in case it ignites. I forget exactly what this substance is, but it is the only thing that will smother and extinguish at titanium fire. Water, dry chemical, Halon, etc will not put it out.

I only saw it happen once. A new guy was trying to drill a hole, not knowing what he was doing. He was almost through when the bit dulled. Instead of getting a new bit, he spun up the drill motor and pushed harder. Before he could be stopped, sparks and then a blinding white glare. The guy next to him covered the area with black sand and put it out. Almost cost several million dollars. New guy got some extra training.
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« Reply #6 on: July 13, 2015, 07:22:42 AM »



Ti can be a real danger:-o
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« Reply #7 on: July 13, 2015, 08:54:33 AM »

I had similar self ignition issues when machining zirconium years ago, (making nozzles for an acid spray cleaner which needed the high corrosion resistance of the zirconium), but I was unaware that Ti could do the same thing, and even in a pure nitrogen atmosphere. 
Gets interesting when your mill catches fire and the spray mist accelerates the fire in the chips because zirconium strips the water just like magnesium does.

The black sand was probably magnetite (black iron oxide).
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« Reply #8 on: July 13, 2015, 09:39:22 AM »

We work with titanium all the time on a daily basis.

If you keep in mind certain basic safety guidelines, it is as safe to work with as any of the reactive metals.

Titanium is very reactive to oxygen and will start oxidizing in short order at room temperature, if heat is added that oxidation may rapidly escalate into a fire. So keep your work area and machines clean and free of chip buildup. A chip pan fire will do in a a machine in a matter of minutes.

When machining feed rate and surface footage is the key to success. When that combination is just right chips will come off the part as easy as machining aluminum, whoever, if your surface footage is to high you will eat up a lot of tooling in short order. Keep coolant on your part at all times while machining, flood coolant is best, dry machining will get you in trouble if your not very careful.

High speed tooling works fine if you watch you surface footage, all in all a little slower than carbide, but it works fine.

Keep your chip pan clean. Have fun.

Rouse    
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wobblywalrus
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« Reply #9 on: July 14, 2015, 12:43:29 AM »

It looks like I need to do some research.  Geez.  I was using a torch to heat up the stuff to bend it on Sunday.  Maybe fool's luck saved my butt. 

   
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Peter Jack
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« Reply #10 on: July 14, 2015, 01:26:51 AM »

I've cut it with a cutting torch. It cuts beautifully. I'm now realizing I may have been playing with fire so to speak. I'll look for further advice before I try that again. The material was fairly heavy titanium pipe. the customer wanted it for an inert liner. We never did solve the cracking problem then, but I think I could do it now knowing what I know now about welding the material.

This is an interesting thread because I also weld magnesium with great success on a fairly regular basis.

Pete
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« Reply #11 on: July 14, 2015, 08:55:12 AM »

I, personally, love the way magnesium welds.    I have done it a lot on Vw and Hewland gearboxes, and side plates.    Most guys are sh** scared to do it.   Have not done any for a number of years now though.

Like everything else tricky, you need to make the proper preparations of the material, use the correct filler rod, and take the proper precautions for fire.

 cheers
Fordboy
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« Reply #12 on: July 14, 2015, 09:54:56 AM »

One key to machining Ti is the basic machines rigidity.
CNC mills/lathes with ball guides have high speed capability, box way machines are very rigid.

Never had an issue with Ti, cut and weld very nicely.

I used to weld Mag parts all the time, injected Hydrogen with Argon to get better heat and penetration.

Keep making chips to get to the hidden parts within, J
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« Reply #13 on: July 14, 2015, 10:18:57 AM »

If you heat Ti up with a torch you probably just destroyed it. Ti will start oxidizing at temps over 600 F and even faster as the temp goes up from there. Chances are good that the part you heat is now brittle as glass, especially if the part had white powder on the surface once you were finished heating it.

Ti does indeed cut very good with a cutting torch, when working with large sections such as plate. You would use a very undersized tip for the plate thickness you're working with, because you need as little preheat as possible. Once you get the initial cut stared, the reaction to the oxygen keeps the cut going. You will need to cut at 3 or 4 times the speed of steel plate. Lots of white smoke, so do it outside.

Rouse
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wobblywalrus
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« Reply #14 on: July 15, 2015, 12:49:02 AM »

The part was chucked up in a vise with an piece of strap aluminum alongside it.  This keeps the vise jaw from dimpling the part when it is bent.  The aluminum tube protects the part that will be hit with the hammer.

I started out by heating the part with a propane torch and wacking it with a ball peen.  No bending at all.  I was going to put the propane away and get out the torch and give the part some serious heat.  Then I decided to get out Bradley's book and read the Ti chapter.  My testosterone level is dropping, I guess.  The brain engaged itself.  This would never happen in my younger days.  Bradley says that major heat with a non-oxygenating source, like a vacuum furnace, is needed for structural Ti.  He said lesser applications of flame are a waste of time.  I decided to do a cold bend.

It was time for the mini sledge.  Some big banging barely bent the part.  This is a piddly little 0.410 inch diameter rod.  Then I got out the big mama sledge.  Ones like this are used on the railroad to spike tracks.  It must have taken over 30 blows and some major cussing to bend the rascal.  Dishes were rattling upstairs. 

Steel with this much strength would have had a brittle fracture during the bend.  The annealed 6V4Al Ti part has the needed ductility with enormous strength.  The picture shows the thick steel shaft I am replacing with the slimmer and much lighter Ti one.  Both have identical resistance to bending according to calculation.


* 2015 Tit 005.JPG (118.84 KB, 800x526 - viewed 143 times.)

* 2015 Tit 006.JPG (144.87 KB, 800x562 - viewed 135 times.)

* 2015 Tit 007.JPG (117.57 KB, 800x597 - viewed 142 times.)
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