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Titanium 6-AL-4V spur gears hobbing 1
- Thread starter israelkk
- Start date
I don't remember the Ti alloys we tried but the results were extremely bad. Every known coating at the time (early 90's) was tried but the results were the same mainly failure from galling and tremendous wear with any load at all.
I haven't keep up with the coatings for Ti alloys so there maybe a better one available. The only one I recall being used was Tiodize, which one no recall.
We eventually we with a high strength steel gear designed to the 9's. The thing was so light I was kinda scared of it during testing. A TiN coating was eventually used on the gear
Have you checked the NASA site?
I haven't keep up with the coatings for Ti alloys so there maybe a better one available. The only one I recall being used was Tiodize, which one no recall.
We eventually we with a high strength steel gear designed to the 9's. The thing was so light I was kinda scared of it during testing. A TiN coating was eventually used on the gear
Have you checked the NASA site?
- Thread starter
- #4
unclesyd
Thank you for your posts.
Fellow and hobbing are the same from my point of view and my question is basically referring to both methods and any other gear machining process.
My problem is not just the machining issues but basically how two spur gears made of high strength titanium will work together in mesh under quite heavy loads and high speeds.
Thank you for your posts.
Fellow and hobbing are the same from my point of view and my question is basically referring to both methods and any other gear machining process.
My problem is not just the machining issues but basically how two spur gears made of high strength titanium will work together in mesh under quite heavy loads and high speeds.
- Thread starter
- #6
Carburize
The gears are fine pitch gears DP 72, 64, 48 ,32 PIC SDP BERG and others make gears from AL 2024-T4 with no problems. We did custom aluminum gears too with no problem.
We are now facing some "managers" who believe that switching from small 38RC stainless steels fine pitch gears to titanium "will save some weight".
We are sure this is a bad idea but we will be glad to find "outside help" to help those mangers climb down the tree.
1. This will make the gears much more expensive
2. The time to get them manufactured will be much longer
3. We expect galling etc.
It takes 100 smart guys to pull a stone some fool throw into a deep well
The problem currently that we have to confront some "managers" who believe they can lower some weight of a small 38RC steel gears by changing them to titanium gears.
The gears are fine pitch gears DP 72, 64, 48 ,32 PIC SDP BERG and others make gears from AL 2024-T4 with no problems. We did custom aluminum gears too with no problem.
We are now facing some "managers" who believe that switching from small 38RC stainless steels fine pitch gears to titanium "will save some weight".
We are sure this is a bad idea but we will be glad to find "outside help" to help those mangers climb down the tree.
1. This will make the gears much more expensive
2. The time to get them manufactured will be much longer
3. We expect galling etc.
It takes 100 smart guys to pull a stone some fool throw into a deep well
The problem currently that we have to confront some "managers" who believe they can lower some weight of a small 38RC steel gears by changing them to titanium gears.
- Thread starter
- #7
- Thread starter
- #9
Carburize
The gears have to be made from a material that does not corrode such as stainless steel. Nitriding may be an option and was considered but as far as we know grinding of fine pitch gears is a problem or not possible. The tooth of the fine pitch gear is too small for case hardening because there will be no base metal left just only the brittle case (the sum of thickness of the case on both sides can be more than the tooth width).
The gears have to be made from a material that does not corrode such as stainless steel. Nitriding may be an option and was considered but as far as we know grinding of fine pitch gears is a problem or not possible. The tooth of the fine pitch gear is too small for case hardening because there will be no base metal left just only the brittle case (the sum of thickness of the case on both sides can be more than the tooth width).
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1
- #11
diamondjim
Mechanical
How thick are these fine pitch little gears?
- Thread starter
- #12
Another process which is used on aerospace applications such as shafts, sealing diameters, turbine wheels and high speed and cryogenic temperatures applications is hard chrome on titanium. It prevents galling and fretting with this much harder coating. For this application a thin, uniform deposition would be required using a conforming anode. Most of the wear would occur on the tooth working surfaces and not the root or crown. USChrome Corp has performed this process on many Sundstrand, Honeywell, Boeing parts.
- Thread starter
- #14
repdevman
Hard chrome is usually quite thick compared to the size and dimensions of these gear teeth. According to QQ-C-320 CHROMIUM PLATING (ELECTRODEPOSITED) class 2 which is hard chromium plating should be at least 0.002" thick.
Therefore, the accuracy will be less than Q10C after the chrome plating. Grinding of fine pitch gears is a problem or even impossible to my best knowledge.
The gears are not subjected to only wear, there are high Hertz line or point contact stresses where the involutes contact. The chrome plate if not really thick will tend to break. Chrome plating is commonly used on shafts and surfaces that are not subjected to point or line loads.
.
Hard chrome is usually quite thick compared to the size and dimensions of these gear teeth. According to QQ-C-320 CHROMIUM PLATING (ELECTRODEPOSITED) class 2 which is hard chromium plating should be at least 0.002" thick.
Therefore, the accuracy will be less than Q10C after the chrome plating. Grinding of fine pitch gears is a problem or even impossible to my best knowledge.
The gears are not subjected to only wear, there are high Hertz line or point contact stresses where the involutes contact. The chrome plate if not really thick will tend to break. Chrome plating is commonly used on shafts and surfaces that are not subjected to point or line loads.
.
gearcutter
Industrial
A company over here in Australia makes a planetary drive for actuators on aircraft fuel tank vents that spin at around 30,000 rpm. The pitch is around 0.5 module. They wire cut the sun, planets and ring; then finish them off by lapping the set together. I'm told that the material is induction hardened 4340 to around 55-60 Rc. I'm not shore on the achieved quality but I figure for that speed and aplication it must be pretty good. Hope this gives you some ideas.
- Thread starter
- #16
gearcutter
I am aware of this process (wire EDM). We did it many years ago for first and quick prototypes and NASA did some research on it too in order to use 60RC fully harden gears for space use. The got close to the accuracy I am fter but not exactly, and the price is accordingly.
However, the issue here is fine pitch gears made of titanium alloy. It seems that no one in this forum have any experience or knowledge about it.
I am aware of this process (wire EDM). We did it many years ago for first and quick prototypes and NASA did some research on it too in order to use 60RC fully harden gears for space use. The got close to the accuracy I am fter but not exactly, and the price is accordingly.
However, the issue here is fine pitch gears made of titanium alloy. It seems that no one in this forum have any experience or knowledge about it.
diamondjim
Mechanical
I too was thinking of lazer or edm cutting
that is why I asked for the thicknesses.
I assume cost is not a factor and that weight
is their greatest concern. I also assume
that you will not be able to test several
prototypes. I would look at recess action
gearing to help reduce the chances of gaulling.
Will you be able to run-in these gears?
Plazma coating may be an option.
that is why I asked for the thicknesses.
I assume cost is not a factor and that weight
is their greatest concern. I also assume
that you will not be able to test several
prototypes. I would look at recess action
gearing to help reduce the chances of gaulling.
Will you be able to run-in these gears?
Plazma coating may be an option.
- Thread starter
- #18
diamondjim
Although weight is crucial the cost is a major factor too.
As far as I know all recess gears are intended for one direction rotation. In our case the gear is used both as a speed increasing gear and as a reduction gear. The gears were designed and corrected for minimum specific sliding in both ways.
What to you mean by "run-in"? Is it as it was used with old cars for the first 500 miles run-in to let the parts match themselves by wearing out the imperfections of the involute profile? No, we do not have this option.
Our problem is even bigger because we may need to use the gears with dry lubrication (MoS2) and no grease or oil.
Although weight is crucial the cost is a major factor too.
As far as I know all recess gears are intended for one direction rotation. In our case the gear is used both as a speed increasing gear and as a reduction gear. The gears were designed and corrected for minimum specific sliding in both ways.
What to you mean by "run-in"? Is it as it was used with old cars for the first 500 miles run-in to let the parts match themselves by wearing out the imperfections of the involute profile? No, we do not have this option.
Our problem is even bigger because we may need to use the gears with dry lubrication (MoS2) and no grease or oil.
diamondjim
Mechanical
Your are right about recess action gearing.
Is the MoS2 simply sprayed on with an alcohol
base? I was fairly certain that these would
be run dry. I also assume that lead or mercury
cannot be used to surface coat these.
Is the MoS2 simply sprayed on with an alcohol
base? I was fairly certain that these would
be run dry. I also assume that lead or mercury
cannot be used to surface coat these.
- Thread starter
- #20
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