Hole reduction for a press fit 1

[georgeshm]

For a standard Carr lane press fit bushing,
What is the reduction in diameter in the bushing id
after press fitting?

I have seen several answers and now
I am not exactly sure.

To simplify the question.
Press fit hole -12.000- 12.019 mm
Bushing 12.039-13.038 mm od
Bushing 1144 stress proof steel hardened
Hole 6.005 - 6.014
Plate is 12 mm thick 6061 t6 aluminum.

 

[arto]

You can calculate it as a thick walled cylinder
See Roark or Budynas books

 

[unclesyd]

The Carr Lane Handbook/Catalogue used to have some tables for the expected diameter after pressing.
Have you checked their website?

 

[TheTick]

Usually calculating the change in diameters while keeping cross-section area constant works well for initial estimate.

Due to illness, the part of The Tick will be played by... The Tick.

http://www.EsoxRepublic.com

 

[EdDanzer]

This can be handled as an area problem. Calculate the area of the bushing face, OD – ID, then use the OD of the hole bore area minus the bushing face to determine the actual bore of the bushing after press. If you know the bore you need after press and want a specific bore for the bushing to fit into. Use the bushing face area minus the finish bore area to determine the hole bore.

 

[Cockroach]

Georgeshm, your bushing dimensions should probably read 12.039/12.038 mm rather than 12.039/13.038 mm. Otherwise the interference would be much too great at the upper limit.

For the application given, pressure is 115.5154 MPa given the interference of 0.003 mm. A force of 7.864 kN would be required to press fit the assembly. As a result, the inner diameter would be 5.999 mm, a reduction of 0.001 mm. Easing the interference to 0.002 mm gives a surface pressure of 76.828 MPa, press fit force of 5.300 kN and a negligable reduction in bushing ID, about 0.0006 mm.

Properties for aluminum used in the calculation: E=69 GPa at v=0.33 for 6061 Grade T6 and E=200 GPa at v=0.29 for high strength steel alloy, hardened. (Young Modulus, Poisson Ratio respectively). Von Mises-Hencky was used as the theoretical model since it best justifies Thick Wall Pressure Vessel Theory.

I'm getting 307.3785 MPa hoop, 115.515 MPa radial and 0.061 MPa for longitudinal stresses in the press fitted bearing.



Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[ornerynorsk]

You do not change the id of a hardened tool bushing by pressing in even with a moderately heavy fit. It simply shaves the hole being pressed into.

 

[Cockroach]

Actually Ornerynorsk, this is a typical comment and quite wrong. Metal to metal transfer rarely happens mainly because of the ductility assisting deformity for the bearing housing.

You need to remember that the bearing itself has a hole through it. This is what georgeshm is concerned about.

Think of it like this. Shrink fits present ELEVATED surface pressure on the piece being shrink fit. This contract pressure is typical of thick wall pressure vessels under external loading. No construction is perfectly rigid, so there you have it, the ID must shrink.

Check out the mathematics. It's actually poetic.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[georgeshm]

Thank you all for your comments.

I used the thick wall cylinder calculation.
It worked well.

(the Bushing Od should have read 12.039-12.028 mm od)

Answer:
Mean Interference = 0.024 mm
Pressure 70 MPa.
Inner hole reduction = 0.0056mm