material for drive axle 8

[mechanodan]

I would like to have some feedback on some material we are considering for half shafts in a custom car application.The app.is a shaft 24" long with a 1.2"spline journal diam.with 29 splines 45 degree pressure angle 24-48 pitch angle.The axle is exposed (visually)and I didn't want corrosion.I would also like to avoid any paint.Ford uses a necked down or waisted area of 1.437 down to the 1.2 spline diam.My concern is that if I make these shafts from 17-4 or 15-5 and use H-900 cond.Would it compromise the spline area in a torsional shock load? The parallel would be 4340 material which is used in the aftermarket and is presumably stronger than stock.

 

[tbuelna]

mechanodan:

I would not recommend 17-4 in the H900 condition, due to potential SCC. 15-5PH or 13-8 would be better choices for that strength level.

Hope that helps.
Terry

 

[salmon2]

Generally, I will say 17-4 H900 won't be good for shock load as the strength is so high and impact toughness will be poor.

 

[mechanodan]

I do know that 17-4 is used in formula 1 cars as drive axle material but I don't know the H condition.Kirkham team uses metalore or pankl style and they are 17-4.I am inclined to say 15-5 sounds better but?????my concern is the spline toughness in a stainless grade of steel.I have had this question thrown at me be several customers with Cobra or independent suspension systems that are the focal point of the car.I was told if they told me the secret they would have to kill me.

 

[salmon2]

Why 17-4PH H900 is considered? Is it the strength level you really need by stress analysis? Talking about best combination of strength, ductility and toughness, you won't get much better than 4340. You can get 150+ ksi YS and 50+ ft-lb toughness easy. Or if you prefer even higher toughness, 4330V. Then use QPQ for corrosion. This combination is much cheaper than 17-4 and performs better. QPQ is not a coating but a surface modification technique so it won't peel off or anything. The thin and hard surface offers excellent wear and corrosion resistance. The only problem is it is black color, not as shiny as stainless, but not dull either. I am in oilfield downhole tools business, not automotive though. Hope this helps.

 

[MikeHalloran]

I could swear that Ford's standard axles (from decades ago when I worked there) used 28 tooth splines. I.e., if you're using Ford parts, count those teeth again.



Mike Halloran
Pembroke Pines, FL, USA

 

[mechanodan]

The spline you are referring to is a differential spider gear,generally for a flanged axle.As I mentioned this is an independent suspension system where the spline intersects a cv joint at both ends.Even though the axle may be referred to as a 28 -31 spline an independent half shaft has a short stub shaft with the same count as a standard third member type and plugs into the same spider gear. At that point a cv or tripod joint is attached to the stub shaft which can and most often is a different spline to accommodate the multitude of cv's available.You are right about the spline you're thinking of as a ford 28-31.The half shaft definitely is a 29 spline cv intersect on an 8.8 ford in this case.

 

[metman]

Vascomax C250 or C300 maraging steel depending on stress level and/or fatigue life.

Or Ferrium 53 or 54.

C300 doubled fatigue life in one case for splined shaft of (4340 with most sophisticated surface hardening and core treatments available including shot peening and electro-polishing). Also these maraging steels have excellent corrosion and SCC resistance.

But these are not cheap alloys. How custom is it?

Design for RELIABILITY, manufacturability, and maintainability

 

[mechanodan]

We are manufacturing a new kit car which will be made available in a nearly completed form.The entire car is comprised of polished aluminum and stainless steel pieces.The suspension system and all the wheels,brakes,a-arms and drive axles will be focal points.Most of these components are built and or machined in house.I have been building custom suspension systems for a number of years.We are attempting to do this at very reasonable cost to the customer.To paint a very nicely machined part goes against my grain.As salmon2 mentions there are some coatings which to me are are very appealing but the overall cost gets crazy.I am not fond of the black look fad on most vehicles today.The people I build for like the machined look and I am trying to incorporate it into all exposed areas of the car.This is an electric car with roughly 400 hp and 600 ft.lbs.of torque.It is all wheel drive with one front motor and one rear.Each axle receives half of the above number so that torque loads are not as great per axle.Please note that I am capable of learning even after 50 years of being a toolmaker/machinist. I appreciate all interest or comments that people have to say.Thank you one and all for any pieces of wisdom you can contribute.

 

[TVP]

mechanodan,

I think that the most important issue is to understand the contact stress in the spline area, as that should determine the strength that is required, and hence the alloy and heat treatment that can meet it. Based on your further clarification, as long as the contact stresses are not so high that surface hardening (case carburizing or induction hardening) is required, one of the PH stainless steels should be ok. 17-4 PH is somewhat cheaper than 15-5, and certainly more readily available. I would suggest using the H1100 temper rather than the H900, if you want this to be a bullet-proof part that doesn't require extensive inspection, replacement, etc. Shot peening or roller burnishing will go a long way toward improving durability, and are not that costly, especially if you can do the latter in house.

 

[mechanodan]

I have looked into the maraging materials and they are the choices of formula 1 for drive axles(vascomax 300-350).I have attempted buying the material but was told they don't have this size.When I approached the problem (challenge)my goal was to make a no maintenance repairable axle by just replacing cv joints and a bulletproof axle that does not need replacing.These axles are longer than stock and are not available commercially.The constant velocity joints are.I am not a metallurgist but I do know people in this industry are approaching these issues but in the box engineering causes a little constipation of imagination.I am in this forum because it seems that people examine the issues at hand. Paralyses of analysis comes about when you don't have enough information to make an intelligent choice.To make an axle which stands up better than the stock configuration, won't rust,and be able to handled without damage should be achievable.Thanks again to all.

 

[swall]

Mechanodan--how will you reconsilde the cosmetics of using a nice ss axle shaft mated to plain old steel CV joints?

 

[salmon2]

Did you check out Aermet alloy yet? It is something the same league as maraging.

 

[swall]

Neither Vascomax nor Aermet are corrosion resistant. Both would need to be coated.

 

[mechanodan]

Good question about the cv joints.They are presently 2 part epoxy coated then baked at 275f but there is consideration about having A PVD coating done.They really don't show very much and they are the most expendable part.The boots cover a great deal of the joint area and we make sure that all the exposed areas are cosmetically appealing.If damage occurs we will stock an exact replacement free to the original buyer.I have a good reputation for building parts that are dependable and for all intent and purpose bulletproof.Thank you for being observant it's a good point.As far as the vascomax goes this is the reason I'm on the quest.

 

[swall]

I used to work for a CV joint manufacturer and we were developing product for a Korean OEM (no longer in the automotive business). They were very picky about coating cosmetics to the point of requiring special masks to prevent any "overspray" exstending into areas that were supposed to be bare that were covered by the boot. So I am well aware of the importance of cosmetics to certain customers. Where I was going with this was the possibility of capitalizing on the need to powder coat the joints and extending this to the I/C shaft with some sort of custom color. There are some really nice metallic hues available, etc. Probably out of the question, though, if you are buying stock CV joints and the supplier only does black epoxy.

 

[metman]

mechanodan,

I think you should look strong and hard at this suggestion --ALL OF IT including

Shot peening or roller burnishing will go a long way

:

17-4 PH is somewhat cheaper than 15-5, and certainly more readily available. I would suggest using the H1100 temper rather than the H900, if you want this to be a bullet-proof part

Because if TVP says, "bullet proof" he must have looked at impact values for H1100 condition and this could be the simple answer to:

...if they told me the secret they would have to kill me.

My concern is that if I make these shafts from 17-4 or 15-5 and use H-900 cond.Would it compromise the spline area in a torsional shock load?

mechanodan, Have you gone thru the numbers? This can be calculated and if the shaft couples with the CV joint, you need to calc bending load (stress) from the CV joint. This is a complex stress pattern including torsion, bending, and spline root stress, which I think requires Mohrs Circle analysis with contact stress as an adjunct .

Dana Convel is the largest automotive aftermarket CV joint supplier and designers/builders of humongous special CV joints if you desire some technical expertise in that area.

I am also a machinist/Toolmaker and a metallurgist and I have great confidence in TVP's expertise on this forum.

Please keep us informed on this fascinating project!



Design for RELIABILITY, manufacturability, and maintainability

 

[tbuelna]

I have looked into the maraging materials and they are the choices of formula 1 for drive axles(vascomax 300-350)

Race engineer Carroll Smith doesn't think using maraging steels for drive axles is a good idea, due to load reversals.

http://books.google.com/books?id=Jy...page&q=maraging steel stress reversals&f=true

Regards,
Terry

 

[CoryPad]

One of the worst mistruths ever published.

 

[tbuelna]

Mistruth or misinterpretation?

300M is a good material for driveshafts. But it's not the same as C300. I couldn't find any published fatigue data for maraging steels.