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ok I read about a certain aftermarket axle company advertising "Rolled" splines being stronger that "cut" splines.

When they say "rolled" I'm thinking that they achieve the splines by using a knurling like tool.


I've been machining a long time, never did any external splines on a shaft but have done internal on a EDM. I know alot about tool steels and heat treating because I'm a Tool and Die maker.....

but unless you are hard cutting/rolling (heat treat steel then machine) the splines it would seem to me any affect that machining has on the strength of the materiel (however microscopic) would be essentially moot once the steel is heat treated.

Could someone here please school me on where they get their info from??? What am I missing??
 

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maby its why forged things are sronger than cast. im not sure though. why dont you ask them?
 

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It's because cutting the splines removes the material, rolling the splines takes a LOT of force and mashes them into shape - like a forging. So you get a very dense zone of material making it stronger. Forging provides a much better consistancy of material than casting, pressure does cool stuff!
 

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When you cut something you are actually tearing it very finely. Cutting the splines causes the crystal structure of the material to have very small tears in it that can be made bigger under stress. Rolling the splines compresses the material and does not tear it just slightly reorganizes the crystal structure.
 

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It's because cutting the splines removes the material, rolling the splines takes a LOT of force and mashes them into shape - like a forging. So you get a very dense zone of material making it stronger. Forging provides a much better consistancy of material than casting, pressure does cool stuff!


What he said, and GRAIN STRUCTURE. It changes the way the grain structure is in the material. It actually arc the grain structure and makes it uneven and interlocks the grains. Kinda hard to explain but its a much better way to make threads. The extra strength is prooven in yeild and rotational strength and resistance to twisting at the splines.
 

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Its negligible at best. How many axles have you seen where the splines strip out? You can try to point to root failure in the splines and then proudly pound your chest to rolling the spline instead of cutting them but in the end its just another feature.

My .02$
 

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the real benefit to rolling splines is speed , once the machine is set up you can roll a spline in 30 seconds or so per cycle , so if you have 100,000 axles or so to spline and they are all the same rolling is the way to go , for custom lengths not so much
 

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Its negligible at best. How many axles have you seen where the splines strip out? You can try to point to root failure in the splines and then proudly pound your chest to rolling the spline instead of cutting them but in the end its just another feature.

My .02$
I've seen plenty of splines twist off. But there's always more to it than just the method of spline forming. Fatigue life is still largely dependent on the shaft design. So I will agree with you to a point, however the strength AT the spline, IS stronger.
 

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Kinda like using a roll tap.A roll tap will produce a stronger thread compared to a cut tap.
 

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Its negligible at best. How many axles have you seen where the splines strip out? You can try to point to root failure in the splines and then proudly pound your chest to rolling the spline instead of cutting them but in the end its just another feature.

My .02$
Bullshit.

As mentioned above, rolling the splines is a cold forging operation that aligns the grain structure. I also creates a compressive residual stress on the surface. It makes the spline stronger from an ultimate strength standpoint but also from a fatigue strength standpoin. I don't have a number for the ultimate strength but it doubles the fatigue life.

The other aspect of spline strength is in shock load capacity. The sharp edges left by the machining process are more susceptible to fast fracture that will lead to full shaft failure under one BIG impact load.

The cold worked forging operation increase the fracture toughness of the material and increase the impulse load capacity that causes fast fracture. Simply put it takes a larger impulse to cause fast fracture. Fast fracture doesn't go away, it just takes a bigger hit.

If the shafts are heat treated after the spline are rolled the residual compressive stress on the surface is eliminated and the only advantage is the improved grain structure and the slightly rounded edges left by the process. Still an improvement.
 

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Maybe I didnt say it right I feel the benefts are negligible in an axle shaft. You can quadruple the fatigue life and still be 5 times stronger than the yeild strength over the length of the shaft. I would love to see a case study showing the problems with machining the splines. I know and understand the science behind it but to my expertise it is like adding a 10 bolt 5 ton pattern to a rear axle shaft on a dana 35 axle...it just isnt required.

Take your load values, shock load, material yeild, fatigue numbers, spline count, axle diameters and axle length and then get back to me on rolling vs machining and you may see the benefits drop dramatically after 23 splines (considering std size values for light duty axles)

After you have the data go tell Randy O. his machined 2" 47 spline axles cant stand up. Not trying to pick on you here but there is much more to the story than calling bullshit and pointing out the obvious benefits of rolling.
 

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I have not personally seen the test data myself, but I was trained by one of the guy's that developed the spline design and manufacturing process for Caterpillar over a 45 yr career and was instrumental in Cat's rolled spline axle shaft program. I know Cat did extensive testing to validate the benefits of the process in physical iron. Cat is fully convinced there is a significant benefit.

I do know that Cat puts more emphasis on the fatigue side than the fast fracture side since these components are going in machines that last for 60K+ hrs and see hundreds of thousands of cycles.

IIRC there was a company in Rockford Illinois that developed a training program on spur gears and splines. They may have data to back up the differences. They were working closely with Cat when I worked in the powertrain group back in the late 90's.
 

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I have not seen studies for splines but I have seen studies for threads. If you don't harden the bolt then yes rolling the thread is stronger then cutting. If you harden the bolt there is little to no increase in fatigue strength. You would only get a stronger bolt if you roll the threads after heat treatment which is what companies like ARP do.

Maybe I didnt say it right I feel the benefts are negligible in an axle shaft. You can quadruple the fatigue life and still be 5 times stronger than the yeild strength over the length of the shaft. I would love to see a case study showing the problems with machining the splines. I know and understand the science behind it but to my expertise it is like adding a 10 bolt 5 ton pattern to a rear axle shaft on a dana 35 axle...it just isnt required.

Take your load values, shock load, material yeild, fatigue numbers, spline count, axle diameters and axle length and then get back to me on rolling vs machining and you may see the benefits drop dramatically after 23 splines (considering std size values for light duty axles)

After you have the data go tell Randy O. his machined 2" 47 spline axles cant stand up. Not trying to pick on you here but there is much more to the story than calling bullshit and pointing out the obvious benefits of rolling.
 

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After you have the data go tell Randy O. his machined 2" 47 spline axles cant stand up. Not trying to pick on you here but there is much more to the story than calling bullshit and pointing out the obvious benefits of rolling.
I never said anyones splines couldn't hold up. I did say that if the splines are rolled there is a benefit from both impulse loading and from fatigue. So if Randy O want's to improve his product he can roll the splines.

If you take strain rate out of the equation and only want to look at a load applied slowly to failure I think you'd see a lower benefit.

In rock crawling the primary failure mode is impulse loading or high loads leading to fatigue cracks that ultimately fail due to impulse loading.

I've seen only a handful of shafts that failed at the splines. Typically because the designers neck the shafts down so the highest stress is in the shaft body not in the splines.

In some aftermarket shafts I see the splines cut into the major diameter with only a small relief at the splines. There is a much higher likelihood of spline failure with this design and a rolled spline would improve the design.
 

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Benefits are the same as coldheading parts versus machining. Less material waste, stronger grain structure and less chances for crack propogation since the grain lines are uninterrupted.

MC is looking at it more from a marketing requirement standpoint, and lt1yj is looking at it from an engineers standpoint. I'd dare say that heavy equipment manufacturers like CAT would benefit more from rolled splines due to the very aggressive application, size/cost of part material and labor involved to replace said shaft. I wouldn't see it fit for our application unless market demand increased i.e. lots of people started bitching about failed splines. :D

In theory you'd want it to break the shaft, rather than gears, lockers, pinions. You beef up the shaft, something else thats more expensive will break unless thats beefed up and on and on...
 

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i would bet cat puts serious time into engineering axles to get the required lifespan with a minimal amount of material. those in the offroad axle business probably don't have the engineering dollars that cat does and i would guess over build things in order to survive. i would guess the 2" axles mentioned earlier could be engineered by cat and be made with less material and still hold up to the same loads.

if you can't engineer it, over build it.
 

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Discussion Starter #18
What he said, and GRAIN STRUCTURE. It changes the way the grain structure is in the material. It actually arc the grain structure and makes it uneven and interlocks the grains. Kinda hard to explain but its a much better way to make threads. The extra strength is prooven in yeild and rotational strength and resistance to twisting at the splines.
This I get.

Grain structure I understand.

I had no idea that Cat did this. I've built some equipment for them, they are a solid group of engineers.Based on my experience with dealing with them I have no problem believing what they say about thing like this.

Great answers guys, just the kind of info I was looking for. Can't say that it would make a difference when I was shopping for axle shafts, but at least now I know the why.

:beer:
 

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When you start seeing a bunch of breakage from machined splines then we should really examine the benefits of rolled splines. CAT most likely was looking at a number of factors but lets not rule out that the main concern might have been production time of cutting the splines. I will not dispute the engineering of the rolled splines only an idiot would do that but if you look at the real world applications for light duty axles you may find most of it is marketing hype. How many root failures and failed splines have you seen on aftermarket axles. I know they are out there but could rolling the splines made a huge difference in the outcome...thats the part I believe to be a negligible factor. Huge shock loads can tear splines apart but what we dont have proof of is that rolling will create such a greater strength in the spline area than machining that it is worth it to pay more money for rolling (Which should actually be cheaper in production).

I do believe in beef beef beef that is why I no longer mess with light duty axles but that is not to say old tech cannot be improved upon.
 

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I don't really have much to add except one thing. Somebody said machined splines are weaker because they have sharp edges. They can be machined any shape they can be rolled.
 
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