Splines that don't slide - but should.

[CMcF]

I am designing an assembly station in which a splined hub and shaft are assembled. "99 times out of 100"", the shaft will just slide into the hole under its own weight. But some times it will need a bit of help. Call me cynical but I was not surprised to learn that nobody could quantify a maximum insertion load before the assembly should be rejected. But I have to design the machine anyway. It would be nice if I could justify using a medium sized pneumatic cylinder, instead of a hydraulic ram. Your comments and help will be much apreciated.

 

[Barry1961]

Well I would assume you don't want to damage the spline if it does not go together easily. You probably do not want to damage the device/fixture if there is a problem either. If one of the parts is bad you want to know it and reject it.

I would concentrate on getting the 99 out of 100 and providing a quick and smooth solution for rejecting or recycling the 1 in 100. Keep the line going!

The ultimate goal is to produce the maximum number of assemblies in a given time period at the least cost. If during the shift you have 20 spline assemblies that need manual rework or need to be checked and re-loaded into parts bins would it be acceptable?

The customer/boss is probably asking for 100% but knows it will not happen.

Barry1961

 

[CESSNA1]

CMCF: Assuming that the splines are supposed to slide relative to each other in operation, then you want a very low assembly force. The force should be enough to overcome the lubricated friciton to assemble.

If on the other hand the splines are for positioning or for strength then you may wnat a large press fit type of force.

Which do you have?

Regards
Dave

 

[BillPSU]

The "bit of help" is it a tap with a hammer or a shoove with hand? Depending on how much help its needs I would use an air cylinder due to reduced cost, faster speed and no oil leakage. Pressure control and flow control could be added. Experience should give you an insertion force needed.

 

[CMcF]

Thank you all for your inputs. I will be trying to persuade my boss, that we should be avoiding damage to the "good" component (I expect both will be good after a wipe). This needs to be more of a "verification" operation.

Thanks again,

Colin.

 

[TheTick]

Have you checked the straightness of the apparently defective shafts? Can yo chack straightness before adding the spline?

 

[CMcF]

TheTick,
These are automotive components (Land Rover Discovery Rear Hub), so I would expect them to have been inspected every way you could imagine and a few more besides! I posted this to see if anybody out there had heard of "transition fit" splines. I am pretty sure that they do not exist.

 

[MikeHalloran]

Of course there could be 'transition fit' splines. Ford used to put a tiny 'twist' in their pinion splines so there would never be fretting between them and the companion flange; they _had_ to be assembled with some axial force.

I suspect you are suffering from contamination, burrs or nicks, rather than a statistical tolerance stackup.



Mike Halloran
Pembroke Pines, FL, USA

 

[gearguru]

CMcF,
the splines can have any fit - even the press (interference) fit. I am talking about the "side fit" and also the "OD fit".
Check the widely used standard DIN5480, Part 1 and Part 14.
In that standard you can also find the methods for calculating the gages for checking splines with any of those fits.
You should have the detailed info about both splines - the customer's and obviously yours. Do some math and check the fit. It is not simple, but doable. And proper gage for both internal and external splines is a must; how can you proove that the customer's splines are really correct?

 

[GregLocock]

CMcF if you work at LandRover find me on Outlook, I can give you the gory details on our various splines.



Cheers

Greg Locock

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

 

[CMcF]

GregLocock,
thanks but I do not work for LandRover, I am a subcontractor to a subcontractor of a partner that supplies Land Rover. I am not sure you can talk to me.

GearGuru and MikeHalloran thank your info.

[highlight #FF99FF]"You should have the detailed info about both splines - the customer's and obviously yours.?"[/highlight]

You would have thought so wouldn't you....



If any body from an automotive company is listening... The reality is:- The factories where components are assembled are not where the components were designed. The companies that manufacture mass produced components have process sheets and op sheets and dedicated machine tools, and drawings for each process, but not drawings of the finished component, because they do not need them.
Companies like mine would love to have drawings of finished components, which is obvious to every one , and they always say that they will give them to us. But normally they do not exist!

Sorry forgive my little bit of a rant. Thank you again for all your help.

Colin

 

[BillPSU]

The problem with splines, threads and gears are they are composite structures. Splines and gears can meet the measurement over wires and pins but be off on the lead or involute tooth form and cause problems. Runout of the spline can also cause problems as well as heat treatment size growth. The process which makes the splines can also cause problems. I believe the parts which do not go together without a little help are parts made to the extreme limits of the tolerance band of one of the critical dimension and with the other dimensions having variation causing interference at assembly.