Author Topic: Titanium Cutting Capacity At a Plateau  (Read 13807 times)

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Offline regentag

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Titanium Cutting Capacity At a Plateau
« on: September 16, 2007, 08:49:17 PM »
Looks like  "a Titanium flashlight in every home" is not going to happen any time soon.  :rolleye:

The accompanying chart illustrates the progress of cutting tool technologies, beginning with the development of high-speed steel cutting tools in the early part of the last century, through the use of computer software to optimize cutting programs. Titanium machining, which began in aerospace in the 1940s, is graphed as having a modest-but-steady growth in removal rate per hour through the 1970s, then rapidly advancing from the late 1970s through 2000. However, since 2000, titanium cutting capacity has leveled out, restricted by advances in materials that have made titanium alloys nearly as hard as the tools that are used to cut them, and by slower advances in cutting tool technologies. This plateau in cutting technology is presenting a serious problem as Boeing Company and other aircraft manufacturers increase their use of these advanced titanium alloys, and require more titanium products to be machined.



(Courtesy of American Machinist)
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Offline MR Bulk

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Re: Titanium Cutting Capacity At a Plateau
« Reply #1 on: September 17, 2007, 03:56:55 AM »
INTERESTING!  No wonder the machine shops seem to balk when I ask about a new Ti light project...
MR Bulk
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Offline regentag

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Re: Titanium Cutting Capacity At a Plateau
« Reply #2 on: September 17, 2007, 06:03:11 AM »
Sounds like you and Boeing are in the same boat. :rolleye:

(At least you're in good company)
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Offline Geologist

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Re: Titanium Cutting Capacity At a Plateau
« Reply #3 on: September 17, 2007, 09:56:50 AM »
Glad I wasn't waiting for Mr. B's new 767!  I am sure I'd still be waiting - even w/o tritium slots!

Very interesting information - thanks for sharing - you get a free gift!
Dragon, Ti, and Classic Chammies, Blk, Bare, & Brass LCs, Blk & Bare LHs, X990, Rayzorlite, The Torch, Mag85, MagGH24, SF C3, C2, 6P, G2, & Winelights, Peak Caribbean, Pacific, McKinnleys, + more , Exolion Ti, Orb Raw NS, SS Gatlight, Eternalights, Nuwai QIII, Inova X5THAs, X1, ARCs, + more?

Offline MR Bulk

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Re: Titanium Cutting Capacity At a Plateau
« Reply #4 on: September 17, 2007, 10:08:05 AM »
YEah, Regs gets FREE TRIT SLOTS! :headbang:
MR Bulk
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Offline herbsandspices

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Re: Titanium Cutting Capacity At a Plateau
« Reply #5 on: September 17, 2007, 10:16:28 PM »
Sounds like you and Boeing are in the same boat. :rolleye:

Don't you mean the same plane? :D

Offline regentag

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Re: Titanium Cutting Capacity At a Plateau
« Reply #6 on: September 17, 2007, 10:35:18 PM »
No, boat.



 ;)
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Offline be.irenic

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Re: Titanium Cutting Capacity At a Plateau
« Reply #7 on: October 20, 2007, 10:57:41 AM »
Just when I thought my baby brother would be no help to all my flashaholic fantasies since he's an engineer and all...he works at Boeing!


hmmmmmmm......

Offline 45/70

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Re: Titanium Cutting Capacity At a Plateau
« Reply #8 on: October 24, 2007, 04:16:12 PM »
Looks like  "a Titanium flashlight in every home" is not going to happen any time soon.  :rolleye:

Shoot!  There goes my dream of Ti paper weights and fishing sinkers as well.

:'(

Dave
Eveready Economy Bright Light w/PR4 and "Heavy Duty" batteries

Offline fläshgreëniè

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Re: Titanium Cutting Capacity At a Plateau
« Reply #9 on: October 24, 2007, 05:03:57 PM »
I guess we are talking more about milling here more than cutting. Did they mention anything about new harder alloys coming???

Offline milkyspit

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Re: Titanium Cutting Capacity At a Plateau
« Reply #10 on: October 29, 2007, 04:53:52 PM »
Interesting chart! Seems like the rough-cut end of things has progressed a heck of a lot more than the finer finishing work...

Offline Anglepoise

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Re: Titanium Cutting Capacity At a Plateau
« Reply #11 on: October 30, 2007, 02:22:13 AM »
Interesting graph and article, but can be looked at from two angles.

Titanium can be turned and milled with comparative ease as long as you are not in a hurry.
Now Ti has got a bad reputation with the machine shops as they are profit motivated and always in a hurry. Time is
money to them. Now Ti machining needs to be slowed right down and if automated ( CNC machine ) needs constant monitoring.
This is always 100% opposite to what a machine shop wants. Set the machine up and push a few buttons and let 100 perfectly machined and knurled flashlights pop out the other end. Just won't happen with Ti. When the tooling looses its sharpness edge ( from being hurried ) it rubs as opposed to cuts and this causes work hardening. Once work hardening sets in , things go from bad to worse as the cutting can completely stop and in extreme cases machine tool damage can and will occur.

But slow things down to a crawl and Ti and its alloys can machine nicely with very sharp tooling that is kept very sharp throughout the run.

Also equally relevant is the fact that most job shops that we ask to machine Ti have very little experience working with it.
And the ones that have are not interested in our small runs as they are doing aero and government stuff
« Last Edit: October 31, 2007, 03:59:04 PM by Anglepoise »

Offline griff

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Re: Titanium Cutting Capacity At a Plateau
« Reply #12 on: November 13, 2007, 03:06:53 AM »
Take a Bite Out of Titanium
Machining Titanium Alloys doesn't have to be difficult!
The right approach, the right tools and the right parameters,
puts the profit back in the job.

 

Titanium's reputation for being difficult to machine is, in many ways, undeserved. Properly approached, this light weight metal machines as easily as most other materials.

Few manufacturers realized the potential of titanium alloys when they first appeared on the industrial market during the early 1950's. Today, however, there seems to be almost no limit to the possible uses for these alloys.

Manufacturers of aerospace and defense components, engines, turbines, automotive parts, and commercial products all capitalize on the unique properties of titanium alloys. And their usage is rising. The Rockwell B-1B aircraft contains almost 200,000 lbs. of these materials.

Comparatively Speaking

Compared to steel, titanium alloys offer several advantages. Their density is only about half that of steel, so parts made from them weigh roughly half as much as steel parts. Yet their strength exceeds steel's, and they have twice the elasticity. That makes them ideal for applications that require flexible materials that don't crack or rupture. Titanium alloys resist corrosion better than the best stainless steels. And, like steel, titanium alloys can be readily cast or forged and are widely available to the industrial market.

There are drawbacks, however. Most titanium alloys are poor thermal conductors. Heat generated during cutting doesn't dissipate through the part and machine table, but tends to concentrate in the cutting area. The high temperatures - 2000 deg. F in some cases - temper and dull cutting edges. These dull edges generate even more heat, further shortening tool life. Cutting temperatures can get so high that chips sometimes burst into flames.

Titanium alloys' elasticity, so beneficial to finished parts, makes them especially difficult to machine. Under cutting pressures, the "springy" materials move away from the tool. Consequently, the cutting edges rub rather than cut, particularly when making light cuts. The rubbing process generates more heat, compounding problems caused by poor thermal conductivity.

As a result of the normal cutting process, titanium alloys tend to workharden. This is especially true when an inappropriate tool is applied. Instead of cutting the part, the wrong tool "pushes" it, straining the alloy. As the material moves away from the cutting edge it deforms plastically rather than elastically. Plastic deformation increases the material's strength - and, unfortunately, its hardness - at the point of cut. As the alloy reaches a higher level of hardness and strength, cutting speeds that were appropriate at the start of the cut become excessive, and the tool wears dramatically.

Many shops misunderstand these peculiarities, and take a trial-and-error approach to machining titanium alloys. They spend considerable sums on cutting tools, trying to find the ones that work. Some have even gone out of business as a result. Other shops, intimidated by the prospector ruining parts worth thousands of dollars, avoid working with the materials altogether.

Despite titanium alloys' reputation for toughness, they can be machined successfully and cost-effectively. Those shops that have taken the time to learn how to machine the materials, in fact, consider them a "piece of cake."

Understanding Titanium

Applying the proper tools and operating at the correct cutting parameters are key elements to the successful machining of titanium alloys. It's also important to realize that different alloys are machined differently, so users must be able to identify the alloy to be cut.

Generally, titanium alloys fall into four major groups, classified by their alloying elements and microstructures. They are:

 Pure titanium (unalloyed).
 Alpha-phase.
 Alpha-beta.
 Beta.

Pure titanium is the easiest to machine and presents no real problems. But it lacks the beneficial properties inherent in its alloys - strength and flexibility and finds limited use.

The most commonly used alloys are the alpha-beta group. A member of this group, Ti-6A1-4V, comprises more than 50 percent of all titanium alloys used today.

Predictably, the more alloying elements added to a particular grade, the more difficult it is to machine. Beta alloys present the most problems because they contain high percentages of vanadium, molybdenum, and chromium.

The alloy the workpiece is made from determines the proper cutting speed needed to cut it. Unalloyed titanium can be machined at speeds up to 180 sfm, while the tougher beta alloys require speeds as low as 30 sfm. In general, the more vanadium (V) and chromium (Cr) in a particular alloy the lower the cutting speed needed. In all cases, titanium alloys demand heavy chip loads to overcome rubbing and the consequent workhardening.

Tool Selection

Most operations on titanium alloys involve relatively shallow profile-milling cuts with end mills. The following, therefore, will concern itself primarily with this type of operation.

The three major factors determining an end mill's performance are:

 Raw material (HSS, premium cobalt HSS, Powder Metallurgy, Carbide, etc.)
 Geometry (angles, shapes, accuracy)
 Treatment (heat treatment, tempering, coatings)

Raw Materials

The tool material chosen should be relatively common, inexpensive, and have good wear resistance, high hot hardness, and adequate toughness.

Lately, some toolmakers have promoted cutting tools made from expensive special raw materials, including powdered metal, 12-percent-cobalt steel, and high hardness (70 Rc) HSS, for machining titanium alloys. Tool material is important to machining these alloys, but tool geometry is most important. Titanium alloys respond far better to HSS tools with proper geometries than to exotic material tools with improper geometries. With sharp edges and higher helix, rake, and relief angles, even ordinary M-2 and M-7 HSS end mills will provide impressive results.

In addition, high-grade tool materials sometimes cause problems. True, a high cobalt content gives HSS higher hot hardness, but it also increases the tool's tendency to chip. Titanium alloys require heavy cuts. Highly alloyed tools, when ground with the optimum geometry for cutting titanium alloys, tend to chip and microchip under the severe cutting conditions encountered during machining.

At present, the most cost-effective, readily available tools for machining titanium alloys have the proper geometry and are made from specially heat treated M-42, 8-percent-cobalt HSS. As cutting tool technology continues to unfold, the issue of tool material is sure to be looked at more closely.

Geometry

Milling titanium alloys requires high chip loads, resulting in high torque being generated. That makes it essential to break chips into smaller pieces, especially when making heavy roughing cuts. Using roughing end mills and various types of chipbreakers considerably reduces cutting-edge pressure.

Unlike a finishing cutter, a roughing end mill's feed per tooth equals the feed per revolution. Each "wave" on the profile operates independently. There is no overlapping of cutting edges, as is the case with a finishing cutter, so we don't divide feed per revolution by the number of teeth. Compared to a 4-flute finishing end mill, which generates four long, thin chips per revolution, a 4-flute rougher produces dozens of short chips that are four times thicker.

Roughers are very effective for cutting a titanium alloy's surface, which may be workhardened. Roughing end mills with a coarser pitch consume less energy than those with a fine pitch, but they don't last as long and their knuckles may peel off under the extreme pressure of shearing the material.

One problem with roughers arises during the milling of pockets. The short, thick chips fall to the pocket's bottom, where the cutter tends to recut them. This problem can be avoided by directing a stream of coolant or shop air at the cut point to evacuate chips.

For finishing passes, use a high-helix tool with sharp edges. Standard, 30 deg.-helix end mills are not recommended.

End mills for titanium alloys must be properly heat-treated to cut effectively. Tool manufacturers should adhere to the right number of tempering cycles for the cutting edges and also draw the shanks to a lower hardness. This will significantly improve the tool's toughness in the spindle.

The shank diameter should equal the cutting diameter. A 2" cutter with a 2" shank, for example, is far more rigid than one with a 1 1/4" shank. When cutting, avoid overhang. Try to use as short a tool as possible to augment rigidity.

Treatment

The "phobia" about using titanium nitride(TiN)-coated tools to cut titanium alloys seems unfounded. There is a fear that chemical reactions eventually will occur between the titanium elements. Experience doesn't bear this out. In fact, TiN coatings have provided some small improvements in certain applications. But in most cases, TiN-coated HSS tools don't perform any better than uncoated ones when machining titanium.

On the other hand, TiN-coated C-2 carbide tools do an excellent job on titanium alloys. In Ti-6A1-4V, these tools can be run at cutting speeds higher than 150 sfm.

Over the past couple of years, succes has also been found with HSS & carbide tools coated with Titanium Carbonitride (TiCN) and Titanium Aluminum Nitride (TiAlN). Combined with the appropriate geometry, the extreme hardness of these coatings provide a tool the ability to run at signifigantly higher surface speed, without creating excessive heat.

At Hanita, evaluating the performance comparison of the two coatings from our own coating center, we've found more consistency in improving performance in machining Titanium on a cost effective basis with TiAlN. However, considering the signifigant difference found with the quality of the various local coating services located throughout the market, it is best to recommend the user evaluate both coatings and make a determination based on his own findings.

Cutting Parameters

Cutting speed selection is critical to machining titanium alloys. this is especially true because of the heat generated at higher speeds. The best speed for a particular alloy within a group will vary, depending on DOC and the particular part's hardness. However, special care should be given to select the right speed. The following chart will provide appropriate speeds for the various groups of titanium.
Cutting Speeds
Group   Condition   Type of Cut   Cutting Speed
Pure Titanium   120 - 160 Bhn

200 - 250 Bhn   Rough
Finish
Rough
Finish   120 - 140 sfm
170 - 180 sfm
70 - 90 sfm
100 - 120 sfm
Alpha Alloys   300 - 330 Bhn   Rough
Finish   60 - 80 sfm
90 - 100 sfm
Alpha-Beta Alloys   300 - 330 Bhn

360 - 400 Bhn   Rough
Finish
Rough
Finish   50 - 60 sfm
70 - 80 sfm
40 - 50 sfm
60 - 70 sfm
Beta Alloys   300 - 330 Bhn

360 - 400 Bhn   Rough
Finish
Rough
Finish   45 - 55 sfm
60 - 70 sfm
30 - 40 sfm
45 - 55 sfm
The part's design dictates the machining procedure. An accurate casting needs little material removed; another may require more machining. For these applications, roughing cutters prove most effective. In both cases, because of the material's elasticity, finishing passes will probably be necessary to achieve dimensional accuracy and good surface finish.

Inexperienced operators sometimes think they can achieve better tool life by making a number of light passes rather than one heavy pass. Just the opposite is true. Because of workhardening and heat transfer problems, the most common cause of reduced tool life is cutting chips that are too small or too thin. The light cut causes the cutter to rub the surface rather than cut, resulting in increased tool pressure and heat.

Titanium alloys respond best to heavy cuts generating thick, well-defined chips. There are limits, though, because of the high torque generated. As a general rule, width of cut should be no more than 30 percent of tool diameter. When taking a heavy profiling cut with a 2 x 2 x 4 finishing tool, for instance, axial depth will be 4" or less, and radial depth should be 0.600" or less.

Climb milling generally works better than conventional milling for machining titanium alloys. The teeth can take a good "bite" out of the material, helping overcome work-hardened surfaces. The values on the following chart are based on a profiling operation with HSS end mills, where width of cut is 1.5 times tool diameter, and can be considered as good starting points. As width of cut changes, feed rates can be increased or decreased up to 25 percent. On small diameters, feed per tooth does not vary with different alloy hardnesses, but rather stays constant. This is because small tools are fragile. High table feed rates can break them regardless of chip thickness.

Peripheral Milling (Profiling) with HSS Endmills
Chip Load per Tooth
Group   Depth of Cut   1/2 " DIA.   3/4 " DIA.   1 " DIA.   1 1/4 " DIA.   2 " DIA.
Pure Titanium    .050
.250
.400   .0016
.0013
NR   .0032
.0025
NR   .0070
.0054
NR   .0090
.0062
.0050   .0150
.0120
.0090
Alpha Alloys    .050
.250
.400   .0016
NR
NR   .0032
.0025
NR   .0065
.0048
.0034   .0080
.0058
.0044   .0140
.0110
.0080
Alpha-Beta Alloys   .050
.250
.400   .0016
NR
NR   .0028
.0022
NR   .0050
.0038
.0028   .0075
.0054
.0042   .0125
.0100
.0070
Beta Alloys   .050
.250   .0016
NR   .0025
.0020   .0032
.0020   .0060
.0045   .0095
.0060
NR: Not recommended, too heavy a cut.
For endmills of the long type, reduce feed rates by 30 %.
To calculate the proper table feed rate, use the following formula:

Table feed = rpm x number of flutes x feed per tooth

Cut titanium alloys at continuous feed rates. Never allow the tool to "dwell" in the workpiece. Inexperienced operators, again, in an effort to extend tool life, sometimes reduce the table feed rate below the recommended rate. This error reduces productivity and tool life.

Proper chip thickness is very important. Theoretically, chip thickness equals feed per tooth. In a profiling operation, theoretical chip thickness often is different from actual thickness. Maximum chip thickness is achieved only when DOC is equal to or greater than half the end mill's diameter.

For relatively light cuts, avoid cutting too thin a chip. This is especially important when using end mills smaller than 1/2" in diameter, because table feeds are already set low to prevent tool breakage. It's better to use a lower spindle rpm while maintaining the recommended table feed in these cases.

Unlike cutting speed, the selected feed has an optimum range. Feed rates directly affect tool life. Low feed rates can cause tools to wear as fast as high rates.

While calculating speeds and feeds, it is also important to remember that titanium alloys tend to clog cutter flutes. This, together with the need for a thick chip, explains the greater success of tools with fewer flutes instead of more, as would be the case when cutting conventional materials. Besides proper tool geometry and feed rates, ample chip clearance is necessary as well.

Other aspects of the machining operation must be controlled, too. A rigid machine tool is necessary, accurately leveled and with all leadscrews, gears, and belts properly adjusted. It's critical to secure the workpiece adequately and avoid runout in the tool and spindle. Runout will lead to uneven chip loads and premature tool wear.

Tool Life

Getting sufficient life from a tool is important. But when cutting titanium alloys, it's far more important to know when to resharpen the tool. Although the wear process is nonlinear, it's quite predictable. As the tool dulls it begins to "push" material rather than cut it, building up excess heat. Often, the tool breaks within minutes, and sometimes the part is damaged as well.

Check the tool frequently to avoid this, especially on new jobs where there are no records on which to base tool-life predictions.

Some indicators of tool wear are:

 Burrs on the upper edges of the workpiece.
 A change in chip color from white to gray, black, or blue.
 A dimensional change in the workpiece.
 Noise and or smoke suddenly generated at the point of cut.

As soon as these or any other suspicious changes develop during the machining process, stop the machine and check the tool. Don't try to make "one more pass." The tool could easily break.

Catching worn tools early ensures that they can be reground more effectively, besides avoiding possible damage to expensive workpieces.

Extend tool life by cutting at low metal-removal rates. (Not low feed rates!) Busier shops may prefer to maximize productivity regardless of tool life. But since a 2" end mill can cost $200 and machine time usually is $50 per hour, it's best to try to achieve a balance between productivity and tool life.

When comparing tool life to machine productivity, consider net milling time, or actual time in cut. For rough-milling titanium alloys, tool life of 45 minutes is good, while 90 minutes is desirable for finishing passes.

Sometimes the individual has to decide whether tool life or productivity is more important. Extended tool life may be preferable during night shifts when the tool crib is closed, but reduced cycle time might be more important for all-out daytime production.

No matter which route is chosen, machining titanium alloys doesn't have to be traumatic. They respond to the appropriate feeds, speeds, and tool geometries, just like other materials. There's nothing secret about them.
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Offline aikiman44

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Re: Titanium Cutting Capacity At a Plateau
« Reply #13 on: November 13, 2007, 04:03:26 AM »
Got it!
I said I liked it.  I didn't say I wanted to kiss it.
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Offline knot

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Re: Titanium Cutting Capacity At a Plateau
« Reply #14 on: November 13, 2007, 06:34:44 AM »
I'm not understanding the touted strength. Titanium does not make good mountain bike spokes, at all. They are light and they look cool but they break so easily.
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