Analysing a scissor lift table in NX 9

[magnusrm]

Hello guys.
Im making a scissor lift table and struggle abit with the FEA.
I have never tried this kind of coupled mechanism analysis before, so have patience.
I have tried several different methods of coupling the two parts trough center holes where it will have an axle / bolt. There is also a cylinder acting, but this is simplified by a rigid RBE2 element, as max load will occur at the most lower position. (I have also tried CROD). The load is a total of 18kN total. The scissor mechanism is coupled by a manual coupling, and i have also tried RBE2 elements only.


The stresses get far higher than i have expected. Any input? Thanks.

FEM and SIM file:

https://dl.dropboxusercontent.com/u/3095226/scissor_fem_sim.zip

the scissor table is similar to this in the mechanism:

 

[Toost]

I don't think i can help you solve this but i see something worth checking, you have very high stress in two areas where there should be quite low stress. - The stress should be the same at all 8 ends, but it isn't.
See attached image.


Regards,
Tomas

 

[magnusrm]

Hi. I originally though that this high stress came from the mechanism forced the two parts in different directions, but you are right. Those forces should be taken up by the lateral beams and not the constraints.
Thanks for the tip!