I am a freelance draughtsman under solidworks and, I have a customer asking me to check the resistance of a threaded rod/nut assembly.
The problem is that I rarely use the simulation tool and I wanted to know if such a simulation was possible?
Basically, I have an M45x1.5 threaded axle with a nut + notched washer. In the first prototypes he made, the nut was 15mm high and now, to save space, it is only 10mm and therefore, he is afraid that it will tear the threads on the axle.
Are you asked to do a simulation on SolidWorks? Because in general for the simulation SolidWorks uses a bolt connector since the threads are not shown :
The client doesn't force me to do the simulation, but it can allow me to work a little on the simulations. On the other hand, I really have a hard time understanding how it works... I really have to take the time to read everything.
I tried to do the calculations but, I find a pretty huge result. The axle is made of cast iron and I find a thread pulling force of 24463Kg. So I think it's okay!
@Gt22, it is a KM9 nut from SKF that is M45x1.5. The axle is machined accordingly.
You have to start with the tutorials available in SolidWorks (from the menu on the right, by clicking on the house, then at the bottom) or on the internet:
The (correct) finite element modeling of a screw/nut contact is a relatively tedious exercise. Especially in a case like this where the pitch is very small compared to the diameter. I therefore advise against this kind of test to get started with the simulation.
That said, by doing a first quick calculation by hand, I only arrive at a resistance of about 5000 kg for the shear strength of the screw threads. However, I may not have started with the right assumptions.
Overall, I make the following calculation: F = Rc * (d*3.14)*(n*P/2)
where Rc = permissible shear stress. Considering that Rc = 0.5*Re and Re = 200 MPa for cast iron I have an Rc = 100 MPa (obviously it's debatable but I needed a value).
d = 45 mm. Normally, you would have to take the diameter on the sides of the threads but given the pitch/diameter ratio it won't change much.
n = number of threads in gear = Hnut / P - 2 = 10/1.5 - 2 = 4.5 approximately.
P = pitch of the screw and /2 since half of the height is taken up by the thread of the nut.
Thank you for this calculation! I started with the calculations given in the Wikipedia link given by .pl which give the resistance of the threads as a function of the traction.
Isn't yours just a shear strength calculation?
But it's also good to take as a reference to the handling of the axis, even if in my case, the cast iron has a Re of 320 Mpa.
It is indeed a shear calculation. I hadn't looked at the Wikipedia link but the philosophy is similar. My calculation is just a little more pessimistic because I consider that the first and last thread of the nut are not completely "operational" and are therefore not taken into account.
On a "normal" screw with a large metric pitch, it is often considered that the core of the screw is more limiting beyond a few threads engaged. But in this case, the ratio of core section to fillet section is largely in favor of the core. So there's no need to even talk about it here.