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Differential Material?
5

Differential Material?

Differential Material?

(OP)
I am trying to get an idea of what material to use if I want to build a differential for a very small vehicle?  Does anyone have recommendations?  What do most automobiles have?

Blessings :)
 

RE: Differential Material?

4340-or-4140 (4130)

 Seriously a good alloy steel will work great for the gears, and teh case could be aluminium or plastic. The trouble with building your own is that it is almost never cheaper.

RE: Differential Material?

(OP)
   Thanks alot for your responses!  I'm not too worried about the cost.  I'm actually designing rear-ends for motorcycles.  We are converting bikes to trikes and I need a good idea of the correct material to use for a pumkin (differenctial housing).

Blessings

RE: Differential Material?

8620 makes a good gear material, 9310 is better.  You can get into exotic stuff but I don't believe your application warrants it unless you are trying to reduce weight or size.

For maximum strength and durability, vacuum carburize the above materials and give them a real -320F cryogenic process with proper ramp down, hold and ramp up, followed by a proper tempering.

RE: Differential Material?

(OP)
Frederick

 Thanks for giving me details.  Do you have any suggestions for the carrier material.  I know ductile iron could be used but I also heard that aluminum alloys work well too.  I was thinking of a AA 356 sandcast or a 6061 T6?

Blessings
Drew

RE: Differential Material?

I agree with Fredrick and have used 8620 in carburized condition for a gear box. Also used it in a PSRU for an aircraft Mzda engine. The carrier could be made with lost wax casting if you are using 3D model definition that is able to transfer to a STP or STL file and the caster can use SLA as a pattern and 5 to 15 days later there is your carrier.

Regards

RE: Differential Material?

I would caution you aganst using a cast aluminum housing, but a housing made from extruded 6061 and welded should work well and reduce weight.

RE: Differential Material?

(OP)
carnage1

Thanks for the warning.  What are your concerns with using a cast housing?

Blessings

RE: Differential Material?

I would like to know why carnage1 doesnt reccommend a cast housing also. Considering that most if not all production differential housings are cast.

RE: Differential Material?

(OP)
NickE

I should have specified aluminum casting in my reply to carnage1.  I think it is the "aluminum" casting that he is cautioning me against.

Blessings

RE: Differential Material?

I can think of at least one cast aluminium diff that is good for 300 hp.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Differential Material?

A cast aluminum diff could work but I would be very cautious. I have not cast any aluminum parts. my experiance comes from machining. none of the cast aluminums I have worked with were nearly as good as 6061 extruded. the cast aluminums tend to have almost no spring to them so they either permanantly deform or start stress cracks, depending on how soft or brittle they are. Extruded aluminum seems to be able to handle some overloading without failure a lot better than cast aluminum.
As for cast iron it is great stuff,a bit heavy, but it never warps. (unless my grandmother has been cooking with it)

RE: Differential Material?

(OP)
carnage1

  My only problem with extrusion is the price of material will be more and the process of machining will be quite extensive.  A cast part comes already hollowed out and close to the dimensions of the finished product leaving only a little left to machine.  The die will cost a fair bit but we plan an making alot of parts.

Blessings

RE: Differential Material?

If you plan on making "alot of parts" then definately a cast housing will be more cost effective. Also a proper design of the casting can produce a part with optimized geometry and gussets so that it is effectively stronger than a machined and welded part.

RE: Differential Material?

maybe an extruded tube for the center and cast front and rear covers? It sounds like cast may be the only cost effective option if you are doing a large number of units.
Could you stamp a thick enough aluminum to make the rear cover out of?

RE: Differential Material?

carnage1- I know that you have some experience with this, but I beg to differ. If he is going to make "alot" of these, the best method is casting.

Many people think that casting makes brittle, failure prone components. They are wrong, just tell GE or PCC that casting is not the best method to make turbine blades and they'll tell you to jump off a long dock.

The steering knuckles in most (if not all) of the production vehicles in the US are cast. They are not brittle; in fact quite the opposite.

An A356-T6 sand cast housing would be the optimum, there is geometry that can be cast in that will provide plenty of stiffining and strength. Once the patterns are made and tested the cost per pound drops spectacularly. The rear cover could easily be die cast/permanant mold cast. (at least thats how the one on my car is made) I dont know about front cover, mainly because I've never seen an automotive diff with one. (well on front axle, but then it doesn't have a "rear" cover)

Sure a highly engineered machining from billet 6061-T6 would be awesome - the costs would be through the roof. So would the swarf. (or the production efficency would be really low.)

Also welding on 6061-T6 is only possible if you are going to re-solutionize and age after welding. (otherwise the weld is going to be really soft.)

Teh cover could be fine-blanked, but if you think molds/patterns/dies for casting cost a pretty penny, you should see what a good stamping die costs!

RE: Differential Material?

Alright I give, it sounds like the only plausable solution is casting due to cost.
aprox. how many units does it take to make casting break even?
or are there multiple types of aluminum casting with various setup costs?
can you weld annealed 6061 and then heat treat or does the entire piece need annealed again before heat treatment?

RE: Differential Material?

For things like diff housings I'd have said a wilely guy could make a cost effective sand casting for ones or tens off. I had a cast part made that cost, for a one off, less than the welded proto cost, including the pattern. The reason is that with a sandcasting you can make your pattern any old how, including basing it on an existing part. You'll have to include draft angles and allow for contraction, of course, but for a complex shape an existing part makes a great basis for the pattern. Talk to or work with the pattern maker at the foundry.

Commercial automotive components are more likely to be low pressure die cast. There is a slight improvement in porosity and shut lines, but if you can afford the time to remelt the failures, there is not a whole lot wrong with sandcast, as, in this case, stiffness is more important than strength. I'd say that in the case of wheels, where strength is more important, that I would be wary of sandcast parts.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Differential Material?

(OP)
  Thanks a lot guys!  You have all been really helpfull. The A356 T6 sandcast sounds attractive but it's elogation before break is only 3% and it's strength is 20ksi. The differential will take a fair amount of pounding since it is part of the unsprung mass in the suspension rather than the sprung mass.  Also, we intend to enlarge the design to fit bigger gears.  Do you think the Aluminum will take this kind of pounding? It would be nice to go with the aluminum since it is so light.  Originally the design used ductile iron with renforcement straps. Prhaps I should stick with the ductile iron in order to maintane enough strength and ductility.  Ductile iron has a much greater yeild and better ductility as far as I can determine.

Blessing to you all!

RE: Differential Material?

If you need more strength (and it sounds like you do) then you might have to go to an iron casting, this of course will drop cost of material. You might want to try ADI (austempered ductile iron) it was pretty cool stuff another grad student was working on when I was doing my Ms on Grey iron.

Try here for more info on ADI:
http://www.castsolutions.com/WebsiteOnly/0503/WebOnly0503.pdf


google it for tons of links (including foundries that can cast it up for you)

RE: Differential Material?

We've got at least half a million cast iron diffs on beam axles out there. I think you can be happy that they are strong enough.

I really doubt that aluminium would not be up to the job, but you would have to design it. I mean, we are engineers, right?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Differential Material?

(OP)
Thanks alot guys!

Yeah, I think I would like to design an aluminum differential, but I will have to see how soon my boss wants the first prototype ready.  I have a few other major tasks to complete first before I can start redesigning a differential.

You guys have been a great help!  I hope one day I can return the favour.

Blessings!

RE: Differential Material?

Let me chime in again with a plug for rapid fab or the trademark name of 'Quick Cast" this is done with SLA which is your pattern made from a 3D data base. Check with John List http://www.protocastjlc.com/  in Conoga Park  he can tell you how many parts he can run, with that pattern.

Check with Gary Vassighi at 3DCam  http://www.3d-cam.com/
for help with the stereolithography pattern.

One other point is I have made housings out of welded 6061 and treated to T6 and it was a miserable twisted piese of crap. If I did it again I would jig weld it and leave plenty of room for post machining.

Also when you talk to John List he can help you with alum material that is  stronger than 356 T6.


Regards

RE: Differential Material?

One last thing ansd I will let this rest...

I worked at a place that made turbine blades and they were forged ...

    That being said I wouldn't dismiss any option even forging without a cost inquery.
    
    I once had a manager at Rocketdyne tell me that cnc was to expensive..and my point is look at evrything even forgings..   
  NickE will tell you that its strength is it the grain direction.

Regards

RE: Differential Material?

(OP)
thundair

Thanks for the heads up.  I have sent an email to John List.  Hopefully he can help.

Blessings

RE: Differential Material?

I have seen a few SAE papers on this that may be of use if you have access to them, based around the design of housings for Formula SAE torsen differnetials. May be of use as these are bike engined single seat cars, so will use a very similar chain driven differential rear axle

RE: Differential Material?


Part geometry and material must be part of the design to be successful.

here is a production rear axle housing apparently fabbed as weldment.  The diff proper is still a ferrous casting of some sort.

http://www.4x4wire.com/toyota/reviews/rockplate/05.jpg

------------------
Keeping bearing bores/seats to size in aluminum and even Stainless steel housings is a painful process, frought with unhappy compromises.  British motorcycles using aluminum connecting rods with insert type bearings develop negative clearances in real cold weather.  Not that I'd expect one to start or run in those circumstances.

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