how calculate the press fit force
DESCRIPTION
Method for calculate the press fit force in assembly applications through a pressTRANSCRIPT
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Method to calculate the
press fit force
Sometime you shall project a new productive l ine but
you haven't any idea about which size of servo
presses is necessary instal l to press fit your parts. I f
the shape of parts are cylindrical or almost, is
possible calculate the press fit force necessary to
assembly together your parts.
Determinate the minimum force required.
To determinate the minimum force required exist
many formulas that can provide you an approximate
value. This value could be considered good for
determinate your purchase for don't buy an under
sized servo press.
The press fit force is produced by many magnitudes
as: Interference, friction and the elasticity between
the two parts. A small variance of one of these
magnitudes can change dramatical ly the press fit
force. For this reason became important a control of
supply chain to avoid big differences in the features of
your products.
The first step to have a good press fit process wil l be
the determination of the maximum compressive force
applicable on your parts. Cheek in the data sheet of
the material used to made the parts the yield point to
know the elastic l imit.
F= A*
Where :
F: is the Force admissible before the plastic
deformation expressed in Newton (N)
A: is the resistant area of the part expressed in
square mil l imetres (mm^2)
: is the material 's yield point which is made the part
expressed in Newton per square mil l imetres
(N/mm^2)
Calculate this force value is very easy only if the
material fol lows the Hooke's Law, but in case the
material pass from the elastic behaviour immediately
to the rupture consider wil l be necessary use the Von
Misees criteria to calculate the maximum force
allowable. However, to be sure to know what is the
maximum compressive force applicable, our
suggestion is cheek in laboratory the l imit force
before appear some creek or permanent de-
formations.
Press fit force calculation
The maximum force admissible F shall be more
bigger than the Fp force value for fit the parts. To
know prior an approximate value of force to press fit
your parts is necessary know the pressure of contact
1
-
between the two parts and is possible calculate with
this formula :
P=
I
d
Eo
do
2
+ d
2
do
2
- d
2
+Vo
*
+
d
Ei
di
2
+ d
2
di
2
- d
2
-Vi
*
where :
P: means pressure of contacts expressed in N/mm^2
I: means interference between the hub and shaft
expressed in mm
d: Nominal rim diameter expressed in mm
Eo: Hub Young's modulus expressed in N/mm^2
do: Hub outer diameter expressed in mm
vo: Hub Poisson's Modulus
Ei: shaft Young's modulus expressed in N/mm^2
di: shaft internal diameter expressed in mm
vi: shaft Poisson's Modulus
As is demonstrated in the formula above the pressure
of contact depends mainly by the interference
between the two parts joined in press fit process.
To calculate the minimum force necessary to press fit
the parts now is necessary use this formula :
Fp= P**d*pi*L
where :
Fp: means the press fit Force expressed in N
P: means the pressure of contact expressed in
N/mm^2
: means the friction between hub and shaft
d : means the nominal diameter of joint (hub, shaft)
expressed in mm
pi: 3,1 4
L: length of the joint between hub and shaft
expressed in mm.
di
d
do
2
In case the press fit force value Fp result more bigger
than the maximum force admissible F before the
deformation is necessary working on the interference
during the introduction by a cooling down of the shaft
or by a warming up of the hub. Another good
practices easy to implement and very affordable is the
use of lubricant to reduce the friction between the hub
and shaft or with a reduction of the surfaces
roughness. The last instance is the reduction of the
joint length.
The values obtained by the use of the formulas above
are purely indicative. Auloma suggest test in
laboratory to determinate the right press fit force
value. Auloma reject any liabi l ity for any damages for
gods or person about the use of the formula
expressed above.
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3Auloma Holding S.r. l .
Via Mussolina 1 074
4001 8 - S. Pietro in Casale
ITALY
www.auloma.com
Auloma provide
servo presses
until 500 kN