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08-25-2011
12:19 PM

08-25-2011
12:19 PM

Determine force required to assemble 2 parts with pressfit

Good Day All,

Does Pro/e Mechanica have the ability to determine force required to assemble 2 parts with a pressfit?

Looking to determine the Press tonnage require to assemble 2 parts that have a complex profile and an interference fit.

Goal would be to use a displacement constraint to move one part into the otherpart in it'sfinal assemble state and then

have it report back what press tonnage would be required to assemble the 2 parts.

Trying to bypass the hand calculations.

Can this be done and if so how?

Thanks for any help you can provide,

Don Anderson

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3 REPLIES 3

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08-25-2011
09:32 PM

08-25-2011
09:32 PM

Determine force required to assemble 2 parts with pressfit

Don,

I assume you are looking for "sliding" reaction force, not normal force. If so, you are on the right track. However, you will need to include friction in the contact analysis. You may run into issues with MECHANICA attempting to solve large translations - although without seeing your model, I do not know how far you have to go for complete assembly overlap ... and the "complex profile" worries me a bit.

You do not actually have a "large deformation" problem (somewhat related to "large translations"), and you are not able to combine large deformation and contact in the same analysis anyway (I believe). Those are two different types of nonlinear analysis (contact and large deformation).

MECHANICA does a good job in solving this type of problem on simple geometry. That is, you can have initial overlap (interference) in two separate parts, and MECHANICA will "push" them away from each other until equilibrium is reached. Measures are automatically defined for the contact regions, but perhaps not in the direction you are looking for. There is a tolerance for the amount of overlap which will remain and it defaults to a percentage of your overall model size (like 0.001). So you may need to adjust that. Be sure to converge on the measure you are interested in, a reaction force in the tangential direction.

I would also recommend comparing the FEA solution, if you are able to get one, with your hand calc method since the problem is highly dependent on friction.

Good luck.

Randy Speed

President & CEO

Speed Consulting, LLC

4715 Harvest Hill Road

Dallas, Texas 75244

(214) 213 4440

(214) 853-9221 fax

www.speedconsulting.com

I assume you are looking for "sliding" reaction force, not normal force. If so, you are on the right track. However, you will need to include friction in the contact analysis. You may run into issues with MECHANICA attempting to solve large translations - although without seeing your model, I do not know how far you have to go for complete assembly overlap ... and the "complex profile" worries me a bit.

You do not actually have a "large deformation" problem (somewhat related to "large translations"), and you are not able to combine large deformation and contact in the same analysis anyway (I believe). Those are two different types of nonlinear analysis (contact and large deformation).

MECHANICA does a good job in solving this type of problem on simple geometry. That is, you can have initial overlap (interference) in two separate parts, and MECHANICA will "push" them away from each other until equilibrium is reached. Measures are automatically defined for the contact regions, but perhaps not in the direction you are looking for. There is a tolerance for the amount of overlap which will remain and it defaults to a percentage of your overall model size (like 0.001). So you may need to adjust that. Be sure to converge on the measure you are interested in, a reaction force in the tangential direction.

I would also recommend comparing the FEA solution, if you are able to get one, with your hand calc method since the problem is highly dependent on friction.

Good luck.

Randy Speed

President & CEO

Speed Consulting, LLC

4715 Harvest Hill Road

Dallas, Texas 75244

(214) 213 4440

(214) 853-9221 fax

www.speedconsulting.com

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08-25-2011
09:37 PM

08-25-2011
09:37 PM

Determine force required to assemble 2 parts with pressfit

Don,

Mechanica does not handle finite friction, so using it to estimate the load required to press a pin into a hole is not possible ... directly. If you use the resultant radial reaction load at the press fit, you can estimate the axial load required to move the pin by multiplying it by the coefficient of friction you will assume exists at the interface. Your problem, with the OD profile of the pin, will have a bit of reaction backward against the motion to press the pin in, so you will see this value using your method. But, again, without any consideration for friction being present. Hope this helps.

Chris

Mechanica does not handle finite friction, so using it to estimate the load required to press a pin into a hole is not possible ... directly. If you use the resultant radial reaction load at the press fit, you can estimate the axial load required to move the pin by multiplying it by the coefficient of friction you will assume exists at the interface. Your problem, with the OD profile of the pin, will have a bit of reaction backward against the motion to press the pin in, so you will see this value using your method. But, again, without any consideration for friction being present. Hope this helps.

Chris

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08-26-2011
09:25 AM

08-26-2011
09:25 AM

RE: Determine force required to assemble 2 parts with pressfit

Randy & Chris,

Thanks,

Don Anderson

Quote Start

http://www.eng-tips.com/viewthread.cfm?qid=151892

Pa= f*3.142*d*L*Pc

where f=friction coefficient

Pc=contact pressure between the two members

d= nominal shaft dia

L=length of external member.

Pa= axial force required to interference fit

to calculate Pc for a given interference use the formula:-

Pc=x/[Dc*[((Dc^2+Di^2)/(Ei(Dc^2-Di^2))+....................

((Do^2+Dc^2)/(Eo*(Do^2-Dc^2))-((Ui/Ei)+

Ui/Eo))]

where x = total interference

Dc=dia of shaft

Di = dia of inner member(this is zero for solid shaft)

Do= outside dia of collar

Uo=poissons ratio for outer member

Ui=poissons ratio for inner member

Eo=modulus of elasticity for outer member

Ei=modulus of elasticity for inner member

This formula for Pc will simplify if the materials are the same.

Quote End

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