The interface calculation in shrink fit 1

[LCform]

To shrink fit carbide in steel , there is a formula given in some catalogues , that is kind of blind and not possible to get , cause the P : pressure between the cylinder is unknown , and it's not said how much it should be

please check this link for the formula, page 6

Link

 

[rb1957]

how much interference do you want ?

research Lame equations (as noted in the link, the equations come from Lame's analysis).

The point is with these equations you can calculate the internal stresses due to an amount of interference. IMHO their equation is the opposite way around ... rather than calculating the amount of interference required to create a certain level of pressure, I think it's more obvious to calculate the internal pressure that a certain amount of interference creates. But it depends on where you're starting (ie if you know the stress you want to create, then you want the interference needed, as per the calc).

another day in paradise, or is paradise one day closer ?

 

[LCform]

Thank you for the answer, well usually die makers for metal forming, are making and choosing that interference, I mean , as far as I know, maybe a higher tech company decides and asks the company that makes the shrink fit with a specific interference and procedure, but it seems like usually they just ask for the internal diameter of the die , and based upon that , they make the shrink fit, I am new to metal forming , and among the dies we order , I noticed there is one die with two external supports, not just one, and the middle one had a lower thickness than the others, let's say for a hole diameter of 4mm of the die , we had this

 

[EdStainless]

Typically when we did it we aimed for the yield strength of the case.
With a round hole in a round die you can't have too much pressure.
Multiple layers lets you reach higher pressures. Look in an older machinists handbook.

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P.E. Metallurgy, Plymouth Tube

 

[LCform]

Thank you , I wish I find it, if you meant machinery's handbook ?

 

[Occupant]

It depends, of course, entirely on your application. For draw rings we go as high as H5/u5 because we have to make absolutely sure that the carbide does not separate from the steel housing during the press operation - goes as high as 330/min. - which would create a big mess.

 

[LCform]

Thank you for your answer

just one question , If we order to any manufacturer to do this shrink- fit for us , how can we control and make sure that they have done the right work ? I mean the interference tolerance has acheived ? regarding the fact that there are two methods of doing the shrink fit ,cold and hot

 

[Tmoose]

"How can we control and make sure that they have done the right work. regarding the fact that there are two methods of doing the shrink fit ,cold and hot ?"
Insist they provide Inspection certificates for the Components' ID and OD, and scoop a few out during production, before assembly for you to QC.

Plus a non destructive test pressing the received assemblies into components to a particular value.
Plus careful magnified visual inspection of the joint between the assembled components looking for debris that would indicate there was skiving or galling if the parts were pressed together.

 

[LCform]

Thank you so much , I still need more advice, please if possible share some articles with me, I would be so so thankful

what kind of non destructive test and how much does it help ?

 

[tbuelna]

"If we order to any manufacturer to do this shrink- fit for us , how can we control and make sure that they have done the right work ? I mean the interference tolerance has achieved ? regarding the fact that there are two methods of doing the shrink fit ,cold and hot"

I think the term "thermal fit" is better to use. This covers situations where the bushing is cooled, the housing bore is heated, or some combination of the two is used. Press fitting is not the best approach, since it is easy to damage the parts when applying significant amounts of axial force needed to force them together. Thermal fitting is much better and less likely to cause damage if performed properly.

As for some QA method to verify the proper interference fit was achieved, you can inspect the dimension and profile tolerance of each mating part prior to installation. Check the bore dimension of the bushing after installation. Develop and qualify a controlled manufacturing process that will be used to perform the task.

 

[LCform]

Thank you very much

I was wondering is Visual magnified inspection (magnification with strong lenses and approriate devices ) is the same as checking with an NDT test ?

I mean, once you make sure that the diameter of the bore has increased , is it necessary to check the non visible parts with NDT ?

 

[Tmoose]

Tmoose ( that's me !) said, in addition to inspection certificates proving dimensional compliance of the parts, I'd include "a non destructive test pressing the received assemblies into components to a particular value.
Plus careful magnified visual inspection of the joint between the assembled components looking for debris that would indicate there was skiving or galling if the parts were pressed together."
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By non-destructive test pressing I meant set up fixtures as if to press the bushing out of the housing, but limit the applied force to 1875 lbs, or some empirically derived value low enough not budge a correctly manufactured and installed bushing, but high enough to move a bushing that was made undersize, or was damaged ruing installation.

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The visual inspection is to help identify if the bushing was damaged during installation.

The intent of a press fit is for all the bushing material to remain on the bushing even after it is the housing bore.
The requirement is to prevent bushing material to be skived or broached off, Similar to half the bright damage on half this bushing ( ignore the hole worn through it.)

http://i15.photobucket.com/albums/a377/Jason280_5/Bandsaw/Bushing 2_zpsnalik2da.jpg

If the bushing is pressed into the housing and the parts were not carefully deburred, or the press fixture allowed thing to start off crooked, the Outside diameter can be "skived."
The resulting bronze slivers may be brushed or blown away by the operator.

http://www.bikernet.com/news/images/PhotoID27558.jpg

But often the edge of the fully installed bushing will be damaged.

An undamaged bushing might look like this -

http://i138.photobucket.com/albums/...d Motors/720stuffKA24Epistonrod003Large-1.jpg

The red residue may be loctite.

 

[tbuelna]

If I read your OP correctly, you are asking about a carbide bushing with a shrink fit into a steel bore. This would require heating the steel bore, chilling the carbide bushing, or some combination of the two.

As for some NDI process to verify the required fit is achieved, you can use a controlled process involving dimensional control of the mating parts prior to assembly, heating/chilling the mating parts to specific temperatures at assembly, using specific tooling/fixtures to assemble the parts, and measuring the bushing bore size/shape after assembly.

Proof testing parts that are swaged or press fit is common practice with aircraft components. But this will require some qualification work to develop your QA process.