FORMING PROCESSES (Extrusion)
EXAMPLE 3.11 (EXTRUSION)
Estimate the maximum force required for extruding a
cylindrical Aluminium billet of 50 mm diameter and 75 mm length to a final
diameter of 10 mm. The average tensile yield stress for Aluminium is 170 N/mm2.
What percent of the total power input will be lost in friction at the start of
the operation?
FORMULAE
SOLUTION
The ram force is
obviously maximum just after the start of the extrusion process as l is
maximum. For the given dimensions and assuming a 45°-dead zone, the value of l
at the beginning is given as
Next, the value of µ is determined by solving
equation (1) through a trial and error method. Thus, we get µ = 0.15.
Now, σx|BB is found out from equation (2) with
this value of µ. Hence,
Finally, using equation (3), we have
If the velocity of the ram is VB
mm/sec, then the frictional power loss (using equations (4) and (5)) is given
as
Now, the total input power is
Therefore, the power loss in friction is
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