How to call out staking on a print

[JsTyLz]

A ground pin is slip fit through a housing into another housing. These housing are to rotate about each other, and neither is fixed (only when in a locked state are they fixed). The pin allows them to move when the mechanism in unlocked.
Question is that on the print there is a callout for staking. "Stake two places on diameter 180deg apart"
After reviewing the dFMEA this is not sufficient for the possible failure mode.
In the past I have called out stakes two ways, or a combination of both.
1.Dimensionally, with a minimum depth of the deformed stake. Also someone recommended calling out a "deforemed materail minimum ID. This method would allow QE to check with a gage pin.
2.With Minimum pull/push out force. I think this method to be preferred, but also know that it is a destructive test.

I was wondering how other called out mechanical staking and if any recommmendations on how the staking should be called out. (I also know that putting manufacturing processes on prints is not recommended, but this has to be the fastening method as it was proven and PPAPed this way)


Thanks in advance!!

 

[sbozy25]

Perhaps you should ask "super engineer" Pat G. how to do this?

 

[sreid]

Would you be better off with an interferrence fit for the dowel pin. This is done all the time.

 

[MikeHalloran]

Staking tools are not standardized. It's commonly done with prick punches, or chisels, or whatever is available, and sometimes, rarely, an actual custom tool is produced and used.

You need to define what you want. I.e., design and dimension the tool to be used, and/or fully dimension the deformed condition to be achieved.




Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

One way to test it would be to establish a proof load that is greater than the service load, but less than the capacity of the joint, and test each part to that.

We occasionally do that for safety critical welds in tension, for example.



Cheers

Greg Locock

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

 

[KENAT]

I've done similar to Greg, trouble is it turned out we could only just exceed the service load with out breaking our test rig!

Your minimum pull/push test is probably only destructive if the component fails. If it passes the pin is still in place and serviceable, right? This may be a good way to go, although testing adds time to manufacture.

What exactly do you mean by staking? I think we used a different term back in the UK.

Are you deforming the actual pin or the ends of the holes to stop it coming out (we used the term peening for this)

When I had a similar situation we actually put a dimple (think it was center drilled) in the ends of the pin which then facilitated deforming it more easily. I think we used a press type tool, probably modified from a rivet press.

Sadly I can't remember the wording we use. The deformed ends of the pin stuckout, almost like a small rivet head, they weren't flush.

Trying to equate a level of deformation to match the equivalent/required push/pull force may be timeconsuming. Especially if your 'staking' method doesn't give consistent results.

KENAT, probably the least qualified checker you'll ever meet...

 

[berkshire]

KENAT (Mechanical)
The term Staking in the US usually means deforming the body of the part surrounding the part to be held. Most often it is done with a center punch or a staking punch, a small chisel like punch about 1/8" wide. I think this is the custom tool Mike talked about.
B.E.

 

[MDAPSEY]

You may want to look at using a pin with a groove already on the part. The part will have an area of the pin swedged to a larger diameter giving you an interference fit in that location.

This way you don't have to have a separate operation in your process for the staking. Look at this website for an idea of what you could use.

http://www.driv-lok.com

 

[KENAT]

Thanks berkshire.

After that clarification I like MDAPSEY idea or equivalent.

Can it be made some kind of interference fit in one part while free to rotate in the other?

KENAT, probably the least qualified checker you'll ever meet...

 

[MDAPSEY]

Yes in the case of JsTyLz application where you are locating two housing together and you would want them to rotate about each other. You would design a pin with grooves in the section of one housing thus locking the pin in place. You would then be able to rotate the other housing on the other portion of the pin.

 

[KENAT]

MDAPSY, sorry I should have been clearer.

I knew generally it's possible, I think I've done it. I meant in the OP application is this a workable solution.

I've investigated the groove pin idea before but it didn't work out, as I recal we couldn't get them made in the quantity we wanted for a good price (they would have had to be a special) and we would have had to do qualification testing for the application.

Is there a design guide somewhere for this type of thing though?

KENAT, probably the least qualified checker you'll ever meet...

 

[JsTyLz]

All,
Thanks for the comments and suggestions. I need to restate a portion of my original post. The Ground pin "IS" press fit into one housing, but the stake is a countermeasure because their is also a lateral load applied which theoretically, and once in a real world application worked its way out. I think if I draw a sketch you will get the idea better.

<a href="

http://photobucket.com"

target="_blank"><img src="

http://i224.photobucket.com/albums/dd23/james_sweet/GlobalColumnStakingSummary.jpg"

border="0" alt="Photo Sharing and Video Hosting at Photobucket"></a>

or try the link:

http://i224.photobucket.com/albums/dd23/james_sweet/GlobalColumnStakingSummary.jpg

 

[MDAPSEY]

Perfect application for a groove pin.

 

[JsTyLz]

Yes a groove pin might work but this part is already in production. I am a product engineer, and do really miss the days of design engineer work (pre-production), when such changes could be made. I must make a callout on the print to satisfy the countermeasure WITHOUT adding cost.

I think the grooved pin is probably a good idea, but not as common of a part as a ground machine dowel pin. THe pin is right out of ASME standards and thus costs less than special application items. Automotive industry has no room for cost increase as margins are at a premium already. Anyways I appreciate all the comments and feedback but was wondering if anyone had worked with staking. Like bearing crosses in a u-joint yoke. These are sometimes captured by staking the yoke.

I have to make a change within the current process capability. Changing the pin is not an option. Changing the amount of press fit by increasing/decreasing the hole sizes is an option. Also how and how much I stake is an option.