Stuart Ackerman
13-04-05, 12:51 AM
Hi all,
I was sent this a while back, and perhap could be a sticky? Titanium is HARD to work with, as this might help...
Titanium and its alloys have been in use in the commercial-industrial sector for over four decades. However, very little information has been available to address the needs of the knifemaker. For example, in a recently completed survey, we asked the general public and knifemakers alike, "how many grades of titanium do you think there are?" The most frequent answers were "two" and "three". There are actually over 50 titanium grades used worldwide, with each being designed for applications as wide ranging as rotating components for jet engines to submarine hulls to medical implants and bicycle frames. Since many knifemaking artisans are using titanium as bolsters, liners, handles and even blades, I felt it might be of benefit to share what we have learned working with titanium over the past several years. Five important properties need to be considered when working with titanium;
Titanium heats up faster than steel.
Titanium, being a poor conductor, will tend to retain the heat being generated in the specific area being worked. Therefore, it is easy to quickly overheat that specific area which causes work-hardening.
Alloyed Titanium is very abrasion resistant.
Titanium has a fairly low modulus of elasticity. This gives titanium its "springiness" property. This, in turn, causes titanium to "chatter", which causes tooling to break if not fixtured correctly.
Titanium has a tendency to gall.
These material properties require slowing down of all of your machinery (both speeds and feeds), keeping the titanium cool, keeping the titanium fixtured correctly, and keeping the cutting tool surfaces free of chips.
II. PROCESSES
I felt the best way to approach this topic would be to discuss each of the knifemaking processes.
A) PROFILING
Begins with taking a piece of metal, and ending up with something that resembles the outline of a knife blade. Listed below are most of the processes that we have investigated.
1. Blanking/Stamping - a metal "mold" is made of a high strength steel which resembles the final profile of a knifeblade. This "mold" is then attached to a large hydraulic press which then closes down on the metal plate. The mold then shears out the knifeblade from the plate.
Advantages -can be successfully used for thinner sections of titanium (generally, a maximum of, 0.0625" for highly alloyed titanium, 0.080" for alloyed titanium and 0.125" for commercially pure). Low to medium strength titanium (alloys) work best. For a high volume shop, this might be a good way to make titanium liners.
Disadvantages - mold wear and potential breakage increase exponentially as the thickness of the titanium plate increases linearly. Also, even on thin titanium sections, shearing on corners can be excessive such that grinding, buffing, and polishing steps are required.
2. Stock Removal (milling and belt grinding) - If you have access to a milling machine, you can use carbide cutters. Again, you will need to slow down the speeds and feeds, and use ultra sharp tools. Although more people have access to belt grinders, this is not a very attractive approach. For heavy stock removal with belt grinding, we recommend using a 50 or 60 grit belt with a HARD and SERRATED contact wheel. Another tip is to SLOW your belts surface feet per minute (SFPM).
For example, using the standard 8" contact wheel, the standard 960 Burr-King knifemaker grinder runs 4,398 SFPM. By changing to the 5" wheel you can drop the speed down to 2,747.5 SFPM. This is still too fast to efficiently grind titanium. Titanium prefers to be ground between 1,200 (Beta titanium) and 1,800 (6Al-4V titanium) SFPM. In general, the more highly alloyed the titanium is, the slower you need to work it. Table 1 shows the actual formula used to calculate SFPM for a two pulley knifemaker grinder. Table 2 shows the results of these pulley and wheel changes. Instead of a constant speed machine, you might want to investigate a variable speed unit.
TABLE 1
SFPM = RMP of the Motor
Multiplied by ( * ) Diameter (inches)
of the Driving (Motor) Pulley
Divided by ( / ) Diameter (inches)
of the Driven (Contact Wheel) Pulley
Multiplied by ( * ) Diameter (inches)
of the Contact Wheel
Multiplied by ( * ) pi (3.14159)
Divided by ( / ) 12
For Example: BurrKing 960
SFPM =
(1750 * 3 / 2.5 * 8 * 3.14159 / 12) = 4,398
TABLE 2
Contact Wheel Driving
Pulley Driven
Pulley SFPM SPEED
8"
5"
8"
5"
8"
5"
8"
5"
8"
5"
8"
5"
8"
5"
8"
5" 2.5"
2.5"
3"
3"
2.5"
2.5"
2"
2"
2"
2"
1.5"
1.5"
1.5"
1.5"
1.5"
1.5" 3"
3"
2.5"
2.5"
2.5"
2.5"
3"
3"
2.5"
2.5"
3"
3"
2.5"
2.5"
2"
2" 3053
1908
4396
2748
3663
2289
2442
1526
2931
1832
1832
1145
2198
1374
2747
1717 Too Fast Good BurrKing (Baseline) Too Fast
Too Fast
Too Fast
Too Fast Better
Too Fast Good
Good
Best
Too Fast Better
Too Fast Good
**Note: Pulleys come in many more sizes than just the 1.5", 2", 2.5", and 3" described here
Keep the titanium cool with a water mist unit or frequent dunkings in water. Once the titanium heats up, you can easily create a case hardened area on the spot being worked. This case hardened area has the appearance of blue colored stripes and is basically a hard ceramic. Belt grinding can be used with lower strength titaniums in thinner gauges. Also, the type of belt makes a big difference along with the abrasive pattern. ALuminum OXide (ALOX) belts/random pattern are almost useless. For example, the first time I attempted stock removal on beta titanium, I used a new 50 grit ALOX belt. Sparks flew, but nothing happened. I stopped my Burr-King and looked at the piece of 0.25" titanium. Just a few small scratches on the titanium. Then I looked at the belt. To my surprise, there was no grit left on it - and that was after only 5 seconds of grinding. I thought to myself, "I'm going to have to try something different, this just ain't going to work."
At a minimum, the next step up in performance would be silicon carbide belts. The key to belts (and abrasive cutting wheels) is this, you want the abrasive grains to fracture to expose a fresh, sharp cutting edge every time it comes into contact with the titanium. Silicon carbide works well initially, but wears down quickly. As soon as the carbide dulls slightly, you are not "cutting" anymore, all you are doing is heating up the titanium.
Since we have all of our blades water jet cut, most of our belts are used for buffing out the tooling marks from the milling operation. We do not use belts courser than 100 grit, and usually start with a 120 grit ceramic.
If I can get away with it, I like to start out with a 150 grit ceramic, then jump right to the 180 grit 3M Apex.
I have very recently tried the "Compact Grain" belts from VSM abrasives (#CK742J). These are also silicon carbide, but nothing like you have seen before. I have had exceptionally good belt life from these belts. They come in 80, 120, 180, and 320, and work exceedingly well on titanium.
The belts we now use and keep in stock are the following:
100 grit, usually zirconia or ceramic. For heavy work there does not seem to be any measurable difference in belt life between the two. The drawbacks are that it takes extra work to grind out the deeper scratches from this grit.
120 grit, usually zirconia or ceramic. This is where we usually start our "buffing" process. This step takes most of the tooling marks out. I have recently shifted to exclusively using VSM compact grain belts in this grit size.
150 grit, usually ceramic. Takes out the 120 grip scratches.
180 grit, use 3M Apex or VSM compact grain. These "buff" great. For even better buffing, flip the 3M Apex around so the belt runs in the reverse direction - there will still be a lot of belt life remaining - acts like a fresh 240 grit.
320 grit, if you want even finer buffing, use the 3M Apex or VSM. Both belts work very well.
3. Sawing - this includes abrasive cutting wheels, hacksaws, and bandsaws. Power sawing works reasonably well for commercially pure titanium, and less and less well for higher and higher strength titanium alloys. Chips, which are a result from the sawing action, can destroy a saw blade almost immediately, therefore, abrasive wheel cutting is usually the preferred approach. Here are some recommended parameters when sawing (assuming maximum titanium thickness of 1/4").
Bandsaw:
8 to 10 teeth per inch
Use 60 to 70 (Feet Per Minute) FPM speed on the more highly alloyed titaniums (including 6Al-4V).
Use 150 to 200 FPM on commercially pure grades.
Slow feed.
Liberal Lubrication. Alternatively, you can friction saw cut titanium with a dull blade.
Here you are essentially burning thru the material.
Power Hacksaw:
8 to 10 teeth per inch
Use 25 to 30 (Strokes Per Minute) SPM speed on the more highly alloyed titaniums (including 6Al-4V).
Use 120 to 180 SPM on commercially pure grades.
Slow feed
Liberal Lubrication.
Hacksaw (by hand):
6 teeth per inch.
Liberal Lubrication.
Extremely slow, almost to the point of being impractical, especially with the alloy grades.
Abrasive wheels work very well given the proper characteristics:
Wheel Composition - the abrasive grains should fracture for continuous exposure of fresh and sharp cutting edges. A silicon carbide wheel works very well. Use 60 to 120 grit wheels.
Hardness - too soft equals rapid wheel wear, too hard equals loading up. A wheel hardness of "L" is recommended.
Wheel Speeds and Feeds - 7000 to 12,000 SFPM works well given that adequate flood cooling is used.
Wheel Width - recommended widths are 0.090" to 0.125"
4. Laser Cutting - has its advantages and disadvantages.
Advantages:
Usually lower cost than water jet (per inch).
Usually faster than water jet (per inch).
Good for thin stock (ex. liners) usually up to a maximum of 0.100"
Disadvantages:
Not recommended for thicker stock over 0.100". Need to use a shop that has done titanium before (usually higher shop rates), because mixtures and pressures are different than when cutting steel.
Cannot cut parts as close together as water jet, therefore, less yield per plate.
Expect "blown out" parts if pressures and mixes fluctuate when cutting.
Expect to grind off burr from the back side of the knife blank. We have noticed an exponential increase in burr with a linear increase in titanium thickness.
Expect to surface grind away the "weld splatter" generated from the laser cutting.
Will leave 0.050" to 0.125" Heat Affected Zone (HAZ). Will need to grind or peripheral mill away this HAZ.
5. Water Jet Cutting - the best overall cutting technique. Water jet cutters have come a long way in a very short period of time and are actually more precise than lasers (no HAZ, splatter, and burr), and can yield more parts per plate due to this lack of heat. The key to this technique is to slow down the cutter to obtain as square an edge as possible. In other words, the faster the cutter goes, the more deflection that can be seen in the part, while the slower the cut, the less deflection. A slow cutter speed translates into as close to a 90 degree cut edge as possible. This is the technique we have had the most success with for cutting out our blades from plate.
6. Wire EDM - the most expensive, but also, the most accurate. Even though the titanium is submersed in a coolant tank, the spark of the wire is what actually does the cutting, therefore, a small HAZ is still created. While not nearly as bad as with laser cutting, you still must remove this HAZ before continuing with the processing. On the positive side, the metal can be cut to near finished size so that very little, if any, peripheral milling needs to be done.
(B) EDGING (Tapers or Hollow Grinds)
1. CNC Machining/Milling - Stiff and Ridgid Vertical flatbed mills with flood coolant is required. For anyone requiring any sort of production or semi production work, CNC machining or CNC Grinding is the only solution for heavy stock removal on titanium alloys.
2. Knife Grinding Machines - Most importantly, stiff and rigid grinders are required. Here, two models come to mind:
Berger, and
American Siepmann
3. Belt Grinding - Again, most important to slow the SFPM. Table 3 will show our experience with different types of belts and belt wear in a "buffing" type operation. Grinding Performance is defined as how much of the MPK blade a belt was able to grind on until the belt went "dead". This operation removes tool marks caused by the CNC mill - 180 grit belts are used.
TABLE 3
BELT
Aluminum Oxide Silicon Carbide Zirconia
Ceramic
APEX (Ceramic) VSM CK742J GRINDING
PERFORMANCE
1 Side of 1 Knife
2 Sides of 6 Knives
2 Sides of 10 Knives
2 Sides of 12 Knives
2 Sides of 15 Knives
2 Sides of 25 Knives INCREASE OVER BASELINE
Baseline
12 Times
20 Times
24 Times
30 Times
50 Times
(C) DRILLING - There are six main rules when drilling:
1. Slow
2. Keep part cool
3. Keep part lubricated
4. Keep drill bit sharp
5. Keep drill bit clean/free of chips
6. Rigid machines and firm holding fixtures are mandatory
Cobalt and Carbide drills work best, although carbide requires a slower feed rate.
Whenever possible, use stub length bits to minimize chatter.
Keep the titanium cool and use frequent lubrication or flood coolant.
A coolant free of trichloroethane, sulpher and chlorine is recommended where follow-up heat treating will be used.
COOL TOOL II by Monroe is a good choice. Maximum RPM we use is 80.
You especially want slow speeds when using carbide drills, reams and counterbores.
Most drill presses cannot go that slow, although there are some which can be slowed with the use a third reduction pulley. This might be an option for you to explore for your own drill press.
We use a Flat bed CNC mill for most of our automated operations and a Bridgeport mill for "manual" drilling, reaming, and countersinking. Both of these mills can achieve speeds down to 80 RPM.
Keep drill bits free of chips.
If you see a chip forming on the drill bit, stop immediately and remove the chip(s).
A chip welded to the bit is the quickest way to fracture the cutting edge of the tool.
Point angle is also an important factor, and is dependent on the hole diameter.
Use a blunt point (140 degrees) for smaller diameter holes (less than 1/4")
Use a sharp point (90 degrees) for larger diameter holes (1/4" to 1/2").
(D) REAMING
Same issues as above. Water/Laser jet holes should be 0.010" to 0.020" undersize. Again, cobalt and carbide reamers work the best. For chip clearing considerations, textbooks recommend using reamers with a minimum number of flutes. We have found that for the higher alloyed titaniums, the maximum number of flutes work best.
(E) COUNTERSINK
Same issues as above, except we have found that if the countersink bit is cleaned frequently of chips, a 90 degree by 6 flute bit works best.
(F) TAPPING
One of the most difficult machining operations due to the difficulty of getting cutting lubricants to the surface being cut. Titanium tends to gall and smear on the tap which causes the tap to bind in the hole. Back the tap off frequently and clear the chips for best results. Also recommended are a 65% thread.
(G) SAFETY ISSUES
General Safety
When belt grinding, we have found it best to let the sparks burn out all of the way. This causes the titanium dust to burn out (oxidize), thereby greatly reducing the risk of fire. Actually, what happens is that the heat of the titanium spark is very high (over 3,000 degrees F) and these hot sparks are known to ignite other metals (dust) which do not readily oxidize when ground. This has caused much confusion in the industry. In other words, the titanium spark is the igniter for the other dust. Coupled with the fact that almost every metal in dust form will burn, it is therefore of utmost importance to remove all grinding residue from the entire area (including exhaust systems) before working with titanium. Do not let the titanium dust mix with the other metals dust.
UV Damage
Use UV rated safety glasses or face shield. If you are concerned, they now make welders glasses and welders flip-down lenses.
Sound
At a minimum, use the new style foam ear plugs.
Smoke
Generated from the dry grinding operation, consists of both titanium dioxide and belt dust. Titanium Dioxide is inert to the body, but it is characterized as a dust irritant. I have checked with a couple of the belt manufacturers and they have said the same thing about the belts - an inert dust irritant. Just to be sure, I use a half face dual cartridge respirator system, with a dust/vapor/fume/mist HEPA cartridge filter.
General
Knifemaking is an inherently dangerous endeavor. Take it slow and easy, and by all means, stay safe.
I was sent this a while back, and perhap could be a sticky? Titanium is HARD to work with, as this might help...
Titanium and its alloys have been in use in the commercial-industrial sector for over four decades. However, very little information has been available to address the needs of the knifemaker. For example, in a recently completed survey, we asked the general public and knifemakers alike, "how many grades of titanium do you think there are?" The most frequent answers were "two" and "three". There are actually over 50 titanium grades used worldwide, with each being designed for applications as wide ranging as rotating components for jet engines to submarine hulls to medical implants and bicycle frames. Since many knifemaking artisans are using titanium as bolsters, liners, handles and even blades, I felt it might be of benefit to share what we have learned working with titanium over the past several years. Five important properties need to be considered when working with titanium;
Titanium heats up faster than steel.
Titanium, being a poor conductor, will tend to retain the heat being generated in the specific area being worked. Therefore, it is easy to quickly overheat that specific area which causes work-hardening.
Alloyed Titanium is very abrasion resistant.
Titanium has a fairly low modulus of elasticity. This gives titanium its "springiness" property. This, in turn, causes titanium to "chatter", which causes tooling to break if not fixtured correctly.
Titanium has a tendency to gall.
These material properties require slowing down of all of your machinery (both speeds and feeds), keeping the titanium cool, keeping the titanium fixtured correctly, and keeping the cutting tool surfaces free of chips.
II. PROCESSES
I felt the best way to approach this topic would be to discuss each of the knifemaking processes.
A) PROFILING
Begins with taking a piece of metal, and ending up with something that resembles the outline of a knife blade. Listed below are most of the processes that we have investigated.
1. Blanking/Stamping - a metal "mold" is made of a high strength steel which resembles the final profile of a knifeblade. This "mold" is then attached to a large hydraulic press which then closes down on the metal plate. The mold then shears out the knifeblade from the plate.
Advantages -can be successfully used for thinner sections of titanium (generally, a maximum of, 0.0625" for highly alloyed titanium, 0.080" for alloyed titanium and 0.125" for commercially pure). Low to medium strength titanium (alloys) work best. For a high volume shop, this might be a good way to make titanium liners.
Disadvantages - mold wear and potential breakage increase exponentially as the thickness of the titanium plate increases linearly. Also, even on thin titanium sections, shearing on corners can be excessive such that grinding, buffing, and polishing steps are required.
2. Stock Removal (milling and belt grinding) - If you have access to a milling machine, you can use carbide cutters. Again, you will need to slow down the speeds and feeds, and use ultra sharp tools. Although more people have access to belt grinders, this is not a very attractive approach. For heavy stock removal with belt grinding, we recommend using a 50 or 60 grit belt with a HARD and SERRATED contact wheel. Another tip is to SLOW your belts surface feet per minute (SFPM).
For example, using the standard 8" contact wheel, the standard 960 Burr-King knifemaker grinder runs 4,398 SFPM. By changing to the 5" wheel you can drop the speed down to 2,747.5 SFPM. This is still too fast to efficiently grind titanium. Titanium prefers to be ground between 1,200 (Beta titanium) and 1,800 (6Al-4V titanium) SFPM. In general, the more highly alloyed the titanium is, the slower you need to work it. Table 1 shows the actual formula used to calculate SFPM for a two pulley knifemaker grinder. Table 2 shows the results of these pulley and wheel changes. Instead of a constant speed machine, you might want to investigate a variable speed unit.
TABLE 1
SFPM = RMP of the Motor
Multiplied by ( * ) Diameter (inches)
of the Driving (Motor) Pulley
Divided by ( / ) Diameter (inches)
of the Driven (Contact Wheel) Pulley
Multiplied by ( * ) Diameter (inches)
of the Contact Wheel
Multiplied by ( * ) pi (3.14159)
Divided by ( / ) 12
For Example: BurrKing 960
SFPM =
(1750 * 3 / 2.5 * 8 * 3.14159 / 12) = 4,398
TABLE 2
Contact Wheel Driving
Pulley Driven
Pulley SFPM SPEED
8"
5"
8"
5"
8"
5"
8"
5"
8"
5"
8"
5"
8"
5"
8"
5" 2.5"
2.5"
3"
3"
2.5"
2.5"
2"
2"
2"
2"
1.5"
1.5"
1.5"
1.5"
1.5"
1.5" 3"
3"
2.5"
2.5"
2.5"
2.5"
3"
3"
2.5"
2.5"
3"
3"
2.5"
2.5"
2"
2" 3053
1908
4396
2748
3663
2289
2442
1526
2931
1832
1832
1145
2198
1374
2747
1717 Too Fast Good BurrKing (Baseline) Too Fast
Too Fast
Too Fast
Too Fast Better
Too Fast Good
Good
Best
Too Fast Better
Too Fast Good
**Note: Pulleys come in many more sizes than just the 1.5", 2", 2.5", and 3" described here
Keep the titanium cool with a water mist unit or frequent dunkings in water. Once the titanium heats up, you can easily create a case hardened area on the spot being worked. This case hardened area has the appearance of blue colored stripes and is basically a hard ceramic. Belt grinding can be used with lower strength titaniums in thinner gauges. Also, the type of belt makes a big difference along with the abrasive pattern. ALuminum OXide (ALOX) belts/random pattern are almost useless. For example, the first time I attempted stock removal on beta titanium, I used a new 50 grit ALOX belt. Sparks flew, but nothing happened. I stopped my Burr-King and looked at the piece of 0.25" titanium. Just a few small scratches on the titanium. Then I looked at the belt. To my surprise, there was no grit left on it - and that was after only 5 seconds of grinding. I thought to myself, "I'm going to have to try something different, this just ain't going to work."
At a minimum, the next step up in performance would be silicon carbide belts. The key to belts (and abrasive cutting wheels) is this, you want the abrasive grains to fracture to expose a fresh, sharp cutting edge every time it comes into contact with the titanium. Silicon carbide works well initially, but wears down quickly. As soon as the carbide dulls slightly, you are not "cutting" anymore, all you are doing is heating up the titanium.
Since we have all of our blades water jet cut, most of our belts are used for buffing out the tooling marks from the milling operation. We do not use belts courser than 100 grit, and usually start with a 120 grit ceramic.
If I can get away with it, I like to start out with a 150 grit ceramic, then jump right to the 180 grit 3M Apex.
I have very recently tried the "Compact Grain" belts from VSM abrasives (#CK742J). These are also silicon carbide, but nothing like you have seen before. I have had exceptionally good belt life from these belts. They come in 80, 120, 180, and 320, and work exceedingly well on titanium.
The belts we now use and keep in stock are the following:
100 grit, usually zirconia or ceramic. For heavy work there does not seem to be any measurable difference in belt life between the two. The drawbacks are that it takes extra work to grind out the deeper scratches from this grit.
120 grit, usually zirconia or ceramic. This is where we usually start our "buffing" process. This step takes most of the tooling marks out. I have recently shifted to exclusively using VSM compact grain belts in this grit size.
150 grit, usually ceramic. Takes out the 120 grip scratches.
180 grit, use 3M Apex or VSM compact grain. These "buff" great. For even better buffing, flip the 3M Apex around so the belt runs in the reverse direction - there will still be a lot of belt life remaining - acts like a fresh 240 grit.
320 grit, if you want even finer buffing, use the 3M Apex or VSM. Both belts work very well.
3. Sawing - this includes abrasive cutting wheels, hacksaws, and bandsaws. Power sawing works reasonably well for commercially pure titanium, and less and less well for higher and higher strength titanium alloys. Chips, which are a result from the sawing action, can destroy a saw blade almost immediately, therefore, abrasive wheel cutting is usually the preferred approach. Here are some recommended parameters when sawing (assuming maximum titanium thickness of 1/4").
Bandsaw:
8 to 10 teeth per inch
Use 60 to 70 (Feet Per Minute) FPM speed on the more highly alloyed titaniums (including 6Al-4V).
Use 150 to 200 FPM on commercially pure grades.
Slow feed.
Liberal Lubrication. Alternatively, you can friction saw cut titanium with a dull blade.
Here you are essentially burning thru the material.
Power Hacksaw:
8 to 10 teeth per inch
Use 25 to 30 (Strokes Per Minute) SPM speed on the more highly alloyed titaniums (including 6Al-4V).
Use 120 to 180 SPM on commercially pure grades.
Slow feed
Liberal Lubrication.
Hacksaw (by hand):
6 teeth per inch.
Liberal Lubrication.
Extremely slow, almost to the point of being impractical, especially with the alloy grades.
Abrasive wheels work very well given the proper characteristics:
Wheel Composition - the abrasive grains should fracture for continuous exposure of fresh and sharp cutting edges. A silicon carbide wheel works very well. Use 60 to 120 grit wheels.
Hardness - too soft equals rapid wheel wear, too hard equals loading up. A wheel hardness of "L" is recommended.
Wheel Speeds and Feeds - 7000 to 12,000 SFPM works well given that adequate flood cooling is used.
Wheel Width - recommended widths are 0.090" to 0.125"
4. Laser Cutting - has its advantages and disadvantages.
Advantages:
Usually lower cost than water jet (per inch).
Usually faster than water jet (per inch).
Good for thin stock (ex. liners) usually up to a maximum of 0.100"
Disadvantages:
Not recommended for thicker stock over 0.100". Need to use a shop that has done titanium before (usually higher shop rates), because mixtures and pressures are different than when cutting steel.
Cannot cut parts as close together as water jet, therefore, less yield per plate.
Expect "blown out" parts if pressures and mixes fluctuate when cutting.
Expect to grind off burr from the back side of the knife blank. We have noticed an exponential increase in burr with a linear increase in titanium thickness.
Expect to surface grind away the "weld splatter" generated from the laser cutting.
Will leave 0.050" to 0.125" Heat Affected Zone (HAZ). Will need to grind or peripheral mill away this HAZ.
5. Water Jet Cutting - the best overall cutting technique. Water jet cutters have come a long way in a very short period of time and are actually more precise than lasers (no HAZ, splatter, and burr), and can yield more parts per plate due to this lack of heat. The key to this technique is to slow down the cutter to obtain as square an edge as possible. In other words, the faster the cutter goes, the more deflection that can be seen in the part, while the slower the cut, the less deflection. A slow cutter speed translates into as close to a 90 degree cut edge as possible. This is the technique we have had the most success with for cutting out our blades from plate.
6. Wire EDM - the most expensive, but also, the most accurate. Even though the titanium is submersed in a coolant tank, the spark of the wire is what actually does the cutting, therefore, a small HAZ is still created. While not nearly as bad as with laser cutting, you still must remove this HAZ before continuing with the processing. On the positive side, the metal can be cut to near finished size so that very little, if any, peripheral milling needs to be done.
(B) EDGING (Tapers or Hollow Grinds)
1. CNC Machining/Milling - Stiff and Ridgid Vertical flatbed mills with flood coolant is required. For anyone requiring any sort of production or semi production work, CNC machining or CNC Grinding is the only solution for heavy stock removal on titanium alloys.
2. Knife Grinding Machines - Most importantly, stiff and rigid grinders are required. Here, two models come to mind:
Berger, and
American Siepmann
3. Belt Grinding - Again, most important to slow the SFPM. Table 3 will show our experience with different types of belts and belt wear in a "buffing" type operation. Grinding Performance is defined as how much of the MPK blade a belt was able to grind on until the belt went "dead". This operation removes tool marks caused by the CNC mill - 180 grit belts are used.
TABLE 3
BELT
Aluminum Oxide Silicon Carbide Zirconia
Ceramic
APEX (Ceramic) VSM CK742J GRINDING
PERFORMANCE
1 Side of 1 Knife
2 Sides of 6 Knives
2 Sides of 10 Knives
2 Sides of 12 Knives
2 Sides of 15 Knives
2 Sides of 25 Knives INCREASE OVER BASELINE
Baseline
12 Times
20 Times
24 Times
30 Times
50 Times
(C) DRILLING - There are six main rules when drilling:
1. Slow
2. Keep part cool
3. Keep part lubricated
4. Keep drill bit sharp
5. Keep drill bit clean/free of chips
6. Rigid machines and firm holding fixtures are mandatory
Cobalt and Carbide drills work best, although carbide requires a slower feed rate.
Whenever possible, use stub length bits to minimize chatter.
Keep the titanium cool and use frequent lubrication or flood coolant.
A coolant free of trichloroethane, sulpher and chlorine is recommended where follow-up heat treating will be used.
COOL TOOL II by Monroe is a good choice. Maximum RPM we use is 80.
You especially want slow speeds when using carbide drills, reams and counterbores.
Most drill presses cannot go that slow, although there are some which can be slowed with the use a third reduction pulley. This might be an option for you to explore for your own drill press.
We use a Flat bed CNC mill for most of our automated operations and a Bridgeport mill for "manual" drilling, reaming, and countersinking. Both of these mills can achieve speeds down to 80 RPM.
Keep drill bits free of chips.
If you see a chip forming on the drill bit, stop immediately and remove the chip(s).
A chip welded to the bit is the quickest way to fracture the cutting edge of the tool.
Point angle is also an important factor, and is dependent on the hole diameter.
Use a blunt point (140 degrees) for smaller diameter holes (less than 1/4")
Use a sharp point (90 degrees) for larger diameter holes (1/4" to 1/2").
(D) REAMING
Same issues as above. Water/Laser jet holes should be 0.010" to 0.020" undersize. Again, cobalt and carbide reamers work the best. For chip clearing considerations, textbooks recommend using reamers with a minimum number of flutes. We have found that for the higher alloyed titaniums, the maximum number of flutes work best.
(E) COUNTERSINK
Same issues as above, except we have found that if the countersink bit is cleaned frequently of chips, a 90 degree by 6 flute bit works best.
(F) TAPPING
One of the most difficult machining operations due to the difficulty of getting cutting lubricants to the surface being cut. Titanium tends to gall and smear on the tap which causes the tap to bind in the hole. Back the tap off frequently and clear the chips for best results. Also recommended are a 65% thread.
(G) SAFETY ISSUES
General Safety
When belt grinding, we have found it best to let the sparks burn out all of the way. This causes the titanium dust to burn out (oxidize), thereby greatly reducing the risk of fire. Actually, what happens is that the heat of the titanium spark is very high (over 3,000 degrees F) and these hot sparks are known to ignite other metals (dust) which do not readily oxidize when ground. This has caused much confusion in the industry. In other words, the titanium spark is the igniter for the other dust. Coupled with the fact that almost every metal in dust form will burn, it is therefore of utmost importance to remove all grinding residue from the entire area (including exhaust systems) before working with titanium. Do not let the titanium dust mix with the other metals dust.
UV Damage
Use UV rated safety glasses or face shield. If you are concerned, they now make welders glasses and welders flip-down lenses.
Sound
At a minimum, use the new style foam ear plugs.
Smoke
Generated from the dry grinding operation, consists of both titanium dioxide and belt dust. Titanium Dioxide is inert to the body, but it is characterized as a dust irritant. I have checked with a couple of the belt manufacturers and they have said the same thing about the belts - an inert dust irritant. Just to be sure, I use a half face dual cartridge respirator system, with a dust/vapor/fume/mist HEPA cartridge filter.
General
Knifemaking is an inherently dangerous endeavor. Take it slow and easy, and by all means, stay safe.