Titanium

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McGizmo

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The major problem with welding titanium is not having it catch on fire. I have never heard of this happening but imagine it might be possible. The problem is weld contamination. The metal and welding rod need to be clean and the weld needs to be in a clean and inert atmosphere; typically with the parts flooded with argon gas. I have made some welds that looked beautiful to my eye and yet had them fail catastrophically. I recall having lunch with a professional welder quite some time ago and we got around to discussing titanium and he told me of one job he had where they were welding titanium and they did it in a room that was filled with argon wearing suits and hoods with air supplied and pumped into and out of the suits, beyond the welding room. I guess it was a type of clean room in which one could not survive due to lack of breathable air. He said they dressed up like space men before entering and getting to the job at hand. Apparently when titanium is elevated way up there in temperature it gladly reacts with other elements and can be contaminated with its physical properties significantly altered.
 

rasnum

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how did you manage to fix that beat up light with elbow grease? What did you do exactly?
 

fyrstormer

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The owner fell off a motorcycle and scratched up the light. My understanding is they just used a grinder to remove the damaged metal, then sanded and polished the new surface until it was smooth again. Not the same as new, of course, but not jagged either.
 

fyrstormer

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I guess it was a type of clean room in which one could not survive due to lack of breathable air. He said they dressed up like space men before entering and getting to the job at hand. Apparently when titanium is elevated way up there in temperature it gladly reacts with other elements and can be contaminated with its physical properties significantly altered.
Sounds about right. Not only does titanium oxidize instantly when exposed to oxygen, but when heated to glowing-hot it will also react with the nitrogen in the air to produce titanium nitride. TiN is far more abrasion-resistant than TiO2, of course, but it's just as unweldable.

I had disc brake mounting tabs welded onto the aluminum swingarm of my mountain bike a couple years ago. From the description of the guy who did it, welding the aluminum was hard enough; I'm amazed (though grateful) that anyone even tries to weld titanium.
 

fyrstormer

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That is a cool bit of information and now I'm thinking about what light I want to color gold...
The article I read said the titanium burns, it doesn't just form a surface coating. I was just suggesting one way that ambient air would contaminate a titanium weld joint. Professional application of a TiN coating is recommended if you want it to look good at all.
 

kaichu dento

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The article I read said the titanium burns, it doesn't just form a surface coating. I was just suggesting one way that ambient air would contaminate a titanium weld joint. Professional application of a TiN coating is recommended if you want it to look good at all.
I was mostly joking and it's good to have you point out the caution necessary in attempting such a process.

I'm not as much a TiN fan as I am of TiCN and AlTiN, which is what I've got on my Draco and Haiku!
 

js

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how did you manage to fix that beat up light with elbow grease? What did you do exactly?

So, here is the original thread from which I used the before and after images:

Ti PDS vs. Highway

knifebright is the one who did it, and here is what he said he used (I have excerpted from three different posts of his--see thread for full text):

Not much that cant' be fixed with a hand file, DMT stones, various grit wet dry paper, a leather strop paddle, flitz, dremmel, microfiber cloth

I really recomend flitz polish but its not going to remove deeper scratches just refurb the surface.
as far as wet/dry paper it really depends on how deep your scratches are and what type of finish your trying to achieve.
It really really is kind of a case by case as far as grit but if you have pics i may be able to give you a starting point.

I do really really recomend you take most of this by hand but you really do need a dremmel regardless :0 . Get yourself some wet dry in the following pieces

2-200
4-400
6-800

that should get you started then hit it up with some Flitz. you could use the dremmel felt wheels with the flitz from here but by hand does it as wel and won't leave "wheel marks"

Note that he does NOT suggest using a grinder! Do this sort of thing by hand. Take your time. Go slowly and constantly check yourself.
 

fyrstormer

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Heh. Actually I was thinking of using a bench grinder, not a handheld grinder, because it's big and heavy and stable, and it won't skip around like a handheld grinder would. I wouldn't try to completely erase the scratches, though, just remove the top layer of jagged metal. I suppose it all depends on how confident you are with using any given tool, though. I can sharpen steak knives on a bench grinder, so I'm pretty confident with it.
 

js

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I'm going to add the machining info as a separate post, since most won't be interested, but I'll reference this post in the OP. OK. Here goes:

Traditional Machining of Titanium

The technology supporting the machining of titanium alloys is basically very similar to that for other alloy systems. Efficient metal machining requires access to data relating the machining parameters of a cutting tool to the work material for the given operation. The important parameters include:

Tool life
Forces
Power requirements
Cutting tools and fluids

Guidelines. The following guidelines, based in large part on the inherent factors affecting the machinability of titanium described above, contribute to the efficient machining of titanium:

Use low cutting speeds: A low cutting speed helps to minimize tool edge temperature and maximize tool life. Tool tip temperature is strongly affected by cutting speed. Lower speeds are required for alloys such as Ti-6Al-4V than are necessary for unalloyed titanium.

Maintain high feed rates: The highest rate of feed consistent with good practice should be used. Tool temperature is affected less by feed rate than by speed. The depth of each succeeding cut should be greater than the work-hardened layer resulting from the previous cut.

Use a generous quantity of cutting fluid: A coolant provides more effective heat transfer. It also washes away chips and reduces cutting forces, thus improving tool life.
Maintain sharp tools: Tool wear results in a buildup of metal on the cutting edges and causes poor surface finish, tearing, and deflection of the workpiece.

Never stop feeding while tool and titanium are in moving contact: Allowing a tool to dwell when it is in moving contact with titanium causes work hardening and promotes smearing, galling, and seizing. This can lead to a total tool breakdown.

Use rigid setups: Rigidity of the machine tool and workpiece ensures a controlled depth of cut.

Although the basic machining properties of titanium metal cannot be altered significantly, their effects can be greatly minimized by decreasing temperatures generated at the tool face and cutting edge. Economical production techniques have been developed through application of the previously mentioned basic rules in machining titanium.

Tool Life. Tool life data have been developed experimentally for a wide variety of titanium alloys. A common way of representing such data is shown in Fig. 10.2, where tool life (as time) is plotted against cutting speed for a given cutting tool material at a constant feed and depth in relation to Ti-6Al-4V. It can be seen that tools for machining titanium alloys are very sensitive to changes in feed. At a high cutting speed, tool life is extremely short; as the cutting speed decreases, tool life dramatically increases. Industry generally operates at cutting speeds promoting long tool life.

Figure 10.2: Effect of cutting speed and feed on tool life during the turning of Ti-6Al-4V alpha-beta alloy:
figure10-2.tiff


Forces and Power Requirements. Cutting force is important because, when multiplied by the cutting velocity, it determines the power requirements in machining. For general approximations, the power requirements in turning and milling can be obtained by measuring the power input to the drive motor of the machine tool during a cutting operation and by subtracting from it the tare, or idle power. A good approximation of the horsepower required in most machining operations can be predicted from unit power requirements. Table 10.2 shows the power requirements for titanium in comparison with other alloys.

Table 10.2: Average unit power requirements for turning, drilling, or milling of titanium alloys compared with other alloys systems:
table10-2.tiff


Tool Materials. Cutting tools used to machine titanium require abrasion resistance and adequate hot hardness. Despite the use of new tool materials—such as special ceramics, coated carbides, polycrystalline diamonds, and cubic boron nitride—in metal removal of steels, cast irons, and heat-resistant alloys, none of these newer developments have found application in increasing the productivity of titanium machined parts.

Generally, only straight carbide and general-purpose high-speed or highly alloyed tool steels can be used. Carbide tools (such as grades C-2 and C-3), if feasible, optimize production rates. General-purpose high-speed tool steels (such as grades Ml, M2, M7, and M10) also are used. However, better results are generally obtained with more highly alloyed tool steel grades, such as T5, T15, M33, and the M40 series. Cutting tool performance is influenced by many factors. Setup, processing methods, grinding techniques, material quality, and the condition of the machine tool and fixturing all influence cutter performance.

In early studies, the straight tungsten carbide cutting tools, typically C-2 grades, performed best in operations such as turning and face milling, while the high-cobalt, high-speed steels were most applicable in drilling, tapping, and end milling. The situation remains much the same today. C-2 carbides are used extensively in engine and airframe manufacturing for turning and face milling operations. Solid C-2 end mills and end mills with replaceable C-2 carbides find application, particularly in aerospace plants. M7 and the M42 and M33 high-speed steels are recommended for end milling, drilling, and tapping of titanium alloys.

Cutting Fluids. The correct use of coolants during machining operations greatly extends cutting tool life, and this is particularly true for titanium alloys. Chemically active cutting fluids transfer heat efficiently and reduce cutting forces between tool and workpiece. Of course, cutting fluids should not cause any degradation of the properties of the workpiece. Chlorine at one time was considered a suspect element in cutting fluids, regardless of the concentration and specific conditions used in titanium alloy manufacturing operations. The aversion to cutting fluids containing chlorine was based on the early discovery of hot-salt stress-corrosion damage in titanium alloys through mechanical property studies (see Chapter 13) and on the unexpected cracking of titanium alloys in cleaning and heat-treatment operations.

Although the presence of chlorine ions (e.g., those found in fingerprints on a part) can cause stress corrosion in some alloys during processing, it is not thought to always damage titanium alloys during machining. Nevertheless, cutting fluids used in machining titanium alloys require special consideration. If chlorinated cutting fluids are used on alloys that may be subject to stress-corrosion cracking, carefully controlled postmachining cleaning operations must be followed. The general prohibition against the use of cutting fluids containing chlorine is not universally observed.

When specifying cutting fluids for machining titanium, some companies have practically no restrictions other than the use of con-trolled-washing procedures on parts after machining. Other manufacturers do likewise, except that they do not use cutting fluids containing chlorine on parts that are subjected to higher temperatures in welding processes or in service. Also, when assemblies are machined, the same restrictions apply due to the difficulty of doing a good cleaning job after machining. Still other organizations in aerospace manufacturing permit no active chlorine in any cutting fluid used for machining titanium alloys.

Mechanical property evaluations to define the effect of experimental chlorinated and sulfurized cutting fluids on Ti-6Al-4V alloy indicated that no degradation of mechanical properties relative to those obtained from neutral cutting fluids occurred. Similar results were obtained by using chlorinated and sulfurized fluids in machining, or by having those cutting fluids present as an environment during testing. These results and others suggest that under certain conditions, chlorine-containing cutting fluids are not detrimental to titanium alloys.

Usually the heavy chlorine-bearing fluids excel in operations such as drilling, tapping, and broaching. The use of chlorine-containing (or halogen-containing) cutting fluids generally is not a recommended practice, however. There are excellent cutting fluids available that do not contain any halogen compounds. Actually, for certain alloys and operations, dry machining is preferred. Figure 10.3 shows the effect of various cutting fluids on tool life in drilling Ti-6Al-4V.
figure10-3.tiff


Machining Speeds and Feeds. Cutting speed and feed are two of the most important parameters for all types of machining operations. Table 10.3 gives some speed and feed data on turning of selected titanium alloys. Because speed and feed rates have a direct influence on tool life, it is desirable to have charts or graphs for all possible tool and titanium alloy combinations, as well as machining techniques. Considering the range of alloys, tool compositions, and machining techniques possible, such charts are not likely to be available for all situations. However, charts such as Table 10.3 have been compiled for some other machining techniques.
table10-3a.tiff

table10-3b.tiff

table10-3c.tiff


Machining recommendations, such as noted above in Table 10.3 and similar sources, can require modification to fit particular circumstances in a given shop. For example, cost, storage, or other requirements can make it impractical to accommodate a very large number of different cutting fluids. Savings achieved by making a change in cutting fluid can be offset by the cost of changing fluids. Likewise, it might not be economical to inventory cutting tools that have only infrequent use. Furthermore, the design of parts can limit the rate of metal removal in order to minimize distortion (e.g., of thin flanges) and to corner without excessive inertia effects.

An illustration of typical machining parameters used to machine Ti-6Al-4V bulkheads containing deep pockets, thin flanges, and floors at an airframe manufacturer is given in Table 10.4. A bulkhead frequently contains numerous pockets and some flanges as thin as 0.76 mm (0.030 in.). Typical bulkhead rough forgings can weigh in excess of 450 kg (1000 lb), but the finished part is less than 67.5 kg (150 lb) after machining. Extensive machining is done on gas turbine engine components, just as is done on the larger airframe components. Table 10.5 lists typical parameters for machining Ti-6Al-4V jet engine components, such as fan disks, spacers, shafts, and rotating seals.

Table 10.4: Some typical machining parameters used to machine airframe bulkheads from an alpha-beta (Ti-6Al-4V) alloy:
figure10-4.tiff



Table 10.5: Example of typical parameters for machining gas turbine components from an alpha-beta (Ti-6Al-4V) alloy:
table10-5.tiff



Increased Productivity with Special Techniques. The inability to improve cutting tool performance for titanium alloys by developing new cutting tool materials—coatings in particular—has been very frustrating. Likewise, very little improvement in productivity has been experienced by exploring new combinations of speeds, feeds, and depths. Some developments of interest include specially designed turning tools and milling cutters, along with the use of a special end-mill pocketing technique.

One of the practical techniques for increasing productivity is to determine the optimum cost in machining a given titanium part for a specific machining operation. If specific data are available relating tool life to speed, feed, and depth for a given operation and cutter, it is possible to calculate the overall cost and time of machining as a function of the cutting parameters. Some companies are using computers to perform such cost analyses and to arrive at minimum costs and optimum production rates for specific machining operations.

Fire Prevention. Fine particles of titanium can ignite and burn. Use of water-base coolants or large volumes of oil-base coolants generally eliminates the danger of ignition during machining operations. However, an accumulation of titanium fines can pose a fire hazard. Chips, turnings, and other titanium fines should be collected regularly to prevent undue accumulation and should always be removed from machines at the end of the day.

Salvageable material should be placed in covered, labeled, clean, dry, steel containers and stored, preferably in an outside yard area. Unsalvageable fines should be properly disposed. Titanium sludge should not be permitted to dry out before being removed to an isolated, outside location.

Dry powders developed for extinguishing combustible metal fines are recommended for the control of titanium fires. For maximum safety, such extinguishers should be readily available to each machinist working with titanium. Dry sand retards, but does not extinguish, titanium fires. Carbon dioxide and chlorinated hydrocarbons are not recommended.

Water should never be applied directly to a titanium fire.
 
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js

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And here's what Donachie has to say about welding titanium:

Joining a Reactive Metal

Titanium has a strong chemical affinity for oxygen, and a stable, tenacious oxide layer forms rapidly on a clean surface, even at room temperature. This behavior leads to a natural passivity that provides a high degree of corrosion resistance. The strong affinity of titanium for oxygen increases with temperature and the surface oxide layer increases in thickness at elevated temperatures. At temperatures exceeding 500 °C (930 °F), the oxidation resistance of titanium decreases rapidly and, as noted previously, the metal becomes highly susceptible to embrittlement by oxygen, nitrogen, and hydrogen, which dissolve interstitially in titanium. Therefore, the melting, solidification, and solid-state cooling associated with fusion welding must be conducted in completely inert or vacuum environments. Similarly, the temperatures and times used for solid-state bonding or for brazing require that processing be conducted in an inert or vacuum environment.

Open-air techniques can be used with fusion welding when the area to be joined is well shielded by an inert gas. By and large, however, atmospheric control by means of a "glove box," temporary bag, or chamber is preferred.

Temperatures for all of the customary metallic joining processes can range from low in the alpha-beta range, above approximately 538 °C (1000 °F), to above the melting temperature of the respective alloys. Solidified cast structures can arise in the cast weld metal area. Coarse structures can form in the weld fusion zone or in the heat-affected zone (HAZ) of a fusion-welded joint, due to holding at high temperatures or due to slow cooling rates from the joining temperatures. Coarse structures can arise in solid-state bonding processes, especially because the joining temperature can be high in the alpha-beta range, and cooling rates from joining can be low.

Special Considerations. Because titanium is a very reactive material and interacts with many atmospheres, special considerations are required both before and during joining to ensure successful joints and acceptable strength of titanium and its alloys. Titanium and titanium alloys can be successfully joined for applications ranging from subzero levels to elevated temperatures when proper precautions are taken and correct preparations are made. Most welding techniques are available for titanium. Titanium alloys can be fusion and solid-state welded, as well as brazed. No fluxes are used when fusion or solid-state welding titanium and its alloys, but fluxes can be used in some situations for brazing.

Because titanium alloy welds are commonly used in fatigue-critical applications, a stress-relief operation is generally required following welding. Specific stress-relief temperatures and times depend on the base-metal.

Three principal conditions need to be met in titanium joining:

Detrimental interstitial elements must be excluded from the joint region
Contaminants (e.g., scale and oil) must be excluded from the joint region
Detrimental phase changes must be avoided to maintain joint ductility

The essence of welding titanium and its alloys is adherence to these principles.
 

fyrstormer

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The repeated emphasis on lowering the cutting-surface temperature makes me wonder if it would be beneficial to run the (filtered) cutting fluid through a refrigeration unit to further reduce the temperature of the cutting surface.
 

precisionworks

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Nicely done JS :)

... heavy chlorine-bearing fluids excel in operations such as drilling, tapping, and broaching.
+1

If it's black, nasty & smelly (which describes heavy chlorinated cutting oils) it works like magic in the most difficult Ti operations. Hate to use it as it stains everything but there's nothing better.

For general purpose lathe or mill work the latest development is MQL (minimum quantity lubrication) using vegetable based oils. Many automated machine tools have through the spindle MQL which applies the oil exactly where needed.

One point to remember whenever lathe turning is that the unbroken chips may form a bird's nest which requires stopping the machine to remove the turnings. Ti ribbons are razor sharp & cut like a knife. I forgot this recently & have a deep cut on the tip of my middle finger. Bled like a stuck hog which is inconvenient as blood causes rusting on the highly finished guide ways on a lathe - took probably half an hour to finally stop :devil:
 

fyrstormer

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Interesting. I've been lubricating my titanium screw threads with Group 5 gear oil, which, while not chlorinated, does have exposed sulfur atoms on the ends of the molecular strands. (Group 5 oil molecules were once described to me as looking like Koosh balls, albeit with fewer strands, as opposed to older oils which are just single strands.) Stuff works great, but it smells a bit like rotten eggs when put under stress. No idea how it would do as a cutting fluid though.
 

tino_ale

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I keep hearing about the work hardening issue while machining titanium, but I don't recall anyone mentionning heat treatment being offered on a titanium flashlight.

Pointless since it's tough enough un-treated ? Probably, but then does a SPY007 actually need to be so perfectly machined the way it is ? Do we actually need sapphire front lens ?

Since some high-end custom offering are seeking the best among the best, why is heat treatment never offered ?
 

precisionworks

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I don't recall anyone mentioning heat treatment being offered on a titanium flashlight.
Grade 5 can be hardened ... as received (annealed condition) hardness is about 36 HRc or 334 Brinnel. When solution heat treated & aged the hardness rises only to 41 HRc or 379 Brinell. For higher hardness a Beta alloy is needed (Mission Knives uses one of the Beta alloys & their knives test 47 HRc). Beta alloys are more expensive than Grade 5, harder to machine, and not significantly tougher unless the application is a jet turbine blade spinning at 100k rpm.
 

McGizmo

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I keep hearing about the work hardening issue while machining titanium, but I don't recall anyone mentionning heat treatment being offered on a titanium flashlight.

Pointless since it's tough enough un-treated ? Probably, but then does a SPY007 actually need to be so perfectly machined the way it is ? Do we actually need sapphire front lens ?

Since some high-end custom offering are seeking the best among the best, why is heat treatment never offered ?

I put out some feelers on heat treating but haven't heard anything back. The aerospace fastener company I worked for where I first encountered and got to mess with titanium sent out their parts for heat treatment as a rule and the resulting finish was pretty cool looking although not at all important or part of the reason for heat treating. Although a significant structural consideration for many titanium parts I think in the case of flashlights it is more a cosmetic consideration. I personally like the darker and duller oxide finish I have seen on heat treated titanium but I have no idea how much additional cost would be involved or if it is even feasible for the parts I have machined. I asked the machine shop that turns my Ti to look into it but I didn't make the request as a must know the answer. I view it as something that if reasonably inexpensive then something I might just add to all of the parts or something I just pass on just as I don't get involved in any plating or film coatings of my offerings. At least with the bead blasted Haiku option I can do it in my garage as needed.

On a similar note, I have noticed that with my anodizing rig, if I bump the voltage above say 80 V I get essentially a silver finish in the titanium but it seems to be a thick oxide film and rather hard and more scratch resistant. I have also tumbled some titanium parts with some granite rock and they too seem to have a dull and somewhat harder surface.

I suspect that heat treating of Ti is not very common and I imagine it needs to be done in an inert atmosphere which would add to the cost and may not be that readily available. You have the alpha and beta molecular structuring of Ti and as I recall heat treating can alter the surface structure. Some of my failed welds I believe were due to really hard and embrittled (sp) surface metal; probably nitrogen contamination. Mission Knives is one company who doesn't stop with machined titanium but takes it further with heat treating and I think they even have some proprietary processes involved.

I worked in the R&D lab of that aerospace fastener company and it was located in down town Newport Beach, CA right on PCH. There was even a small boatyard as part of the property and the owner of the company kept his private yacht docked at the facility (before my time). I heard of a time that the owner had the R&D shop fabricate a fishing gaff for him out of titanium and he insisted that it be sent out for heat treatment. I gathered that the guys had made a beautiful gaff and one that would never be duplicated due to the effort involved. It had a great curve to it and perfectly sharpened point. They sent it out for heat treatment against their better judgment and certainly a case of major overkill in their opinions. It came back from the heat treatment straight as an arrow. Apparently the treatment process induced some form of memory from the Ti and it completely lost its bent form. Strange metal!

A sapphire window may indeed be overkill but IMHO the alternatives are inadequate in some realistic applications and uses. Heat treating Ti is also an overkill in these lights, in my opinion, but with non heat treated titanium as a viable alternative.
 
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