Estimation of Machining Time in Facing in a CNC Turning Centre using constant spindle speed and constant cutting velocity
Estimation
of Machining Time in Facing in a CNC Turning Centre using constant spindle
speed and constant cutting velocity
Facing is the machining process of removing metal
from the end of a workpiece to produce a flat surface. It is done to create a
smooth, flat face perpendicular to the axis of a cylindrical part.
Machining time is the time needed to process or
machine a material under some operation(s). The machining time needs to be determined
or assessed from time to time for several purposes, such as, assessment of
productivity, evaluation of machining cost per piece, determination of
man-machine hour cost per piece, assessment of relative performance or
capability of any machining methods, machine tool, cutting tool, or any
specific techniques in terms of saving in machining time.
The machining time required for a particular
operation can be determined either by approximately calculation (estimation) or
by actual measurement. Measurement generally provides accurate and precise
information but it is tedious and expensive. On the other hand, though
estimation by simple calculation may not be accurate, is much more simple,
quick and inexpensive. Therefore, machining time is regularly evaluated for
different purposes by simple calculation.
Facing of a disc in a CNC turning centre can be done
in two cases. One with constant spindle speed and another with constant cutting
velocity.
Consider a cylindrical shell with outer diameter d2
and inner diameter d1 and other parameters as shown in figure.
(a) Facing with constant Spindle Speed
(n):
If the spindle speed (n) is constant, then the
machining time (tm) can be estimated neglecting the approach and
over-travel as:
Where d2 (mm) is outer diameter of the
cylinder workpiece, d1 (mm) is the inner diameter of the workpiece,
s is feed in (mm/rev) and n is spindle speed in (rpm).
(b) Facing with constant Cutting
Velocity:
If the spindle speed is automatically compensated by
the CNC system and the cutting velocity is kept constant, then the machining
time (t’m) can be estimated as:
Also, we can estimate this machining time using
another method as shown below:
Let for a infinitesimally small change of time, dt,
the change in length be –dR = –dD/2
Here, tm is machining time in minutes, d2
(mm) is outer diameter of the cylinder workpiece, d1 (mm) is the
inner diameter of the workpiece, s is feed in (mm/rev) and vc
is cutting velocity in mm/min.
Good one, Thank you
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