How Can I Estimate the Tonnage Needed for a Smooth Press Fit?

[microman]

Hi All!
I have an application where a bush is press fitted into a housing with repeated blows from a 1kg hammer.
Is there a way to calculate(estimate) the tonnage of the press which can do the same,in a smooth (non impact) manner ?
TIA !

 

[Bystander]

bush[insert]ing[/insert] is press fitted into a housing with repeated blows from a 1kg hammer.
Is there a way to calculate(estimate) the tonnage of the press which can do the same,in a smooth (non impact) manner ?

In a word, "No;" materials, properties, and relevant particulars need to be specified, and have not been.

 

[FEAnalyst]

This could be done using special software for numerical simulations (FEA). Results will be very accurate if you set such analysis properly.

 

[jrmichler]

Yes, there is. I used to have a spreadsheet to do those calculations because we used a lot of shrink fits where I used to work. The equations are in many books on advanced strength of materials, and also in Formulas for Stress and Strain by Roark. I had better luck using those formulas because they were as accurate as my assumptions, while the FEA packaged with SolidWorks had problems with contact formulations. SolidWorks FEA may have been improved in the last three years, but as of three years ago, it was pretty useless for shrink fit calculations. And the spreadsheet was many times faster.

Be sure to check the tolerance stackup, and calculate two cases - maximum and minimum interence. I strongly suggest that you get an advanced strength of materials book and work your way through the chapter on thick wall pressure vessels. Resist the temptation to look up a calculator online because you will not understand exactly what is happening, so will have no way to check your results.

 

[microman]

Thanks for the replies.
I was wondering if there is a quick and reasonably approximate way to convert the impact force into tonnage,if the mass of the hammer is known,velocity of the strike is measured ?

 

[jrmichler]

I was wondering if there is a quick and reasonably approximate way to convert the impact force into tonnage,if the mass of the hammer is known,velocity of the strike is measured ?

No.

In theory, there is, but there are too many variables to make it practical. Some of the variables include:
Hardness of the hammer face
How straight the hammer hits it
Velocity of the hammer at impact
Steel vs dead blow hammer
Mass of the hammer
Mass of the bushing
Mass of the housing
Mass of what the housing is setting on
Elasticity (springiness) of the bushing
Elasticity of the housing
Elasticity of what the housing is setting on

Some of these variables drop out under certain specific cases, but they all factor into a calculation. Your best bet is do the press fit calculation. If you do not want to do that, just go out and buy a Harbor Freight 10 ton press, and try. If it gets the job done, use it until the press falls apart, then get a better press. If it pushes the bushing halfway and stalls, get a 50 ton press. If it barely starts the bushing, try again with a 100 ton press. A local machine shop will have a press, you could hire them to press in a few bushings, and report the peak force from the gauge on the press.

Note that I use shrink fits and press fits interchangeably. In both cases, parts are assembled with an interence fit. The only difference is that shrink fits use heat to eliminate the interference during assembly, while press fits force the parts together.