Fagor QC-PDS - 5.3 Asynchronous motor selection; 5.3.1 Power demanded from a motor for a particular load

 Selection criteria
5.
SELECTING CRITERIA
Asynchronous motor selection
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Ref.2003
QC-PDS
HARDWARE
5.3 Asynchronous motor selection
On the spindles of machine tools, it is important to maintain a constant
turning speed of the spindle. To control this speed, the drive applies torque
to the load according to the characteristics of this load as well as to the
adjusted accelerations and decelerations.
Procedure to calculated the needed motor power:
 Based on the load characteristics, determine the rated power values (in
continuous duty cycle, instantaneous and periodically).
 Increase the value of that needed power, considering the efficiency of
the power transmission and load dispersion.
 Select the drive that offers the current needed to govern the motor in all
duty cycles for that machine.
5.3.1 Power demanded from a motor for a particular load
Use the following formula to determine the required motor power:
The power of the motor must be greater than the sum of the power required
by the load and the power required for the machine’s accelerations and
decelerations.
Power required by the load
The power demanded from an asynchronous spindle motor in a turning or
machining center is determined by the cutting power.
A good cutting process required the asynchronous spindle motor to be
working at constant power and with a power range between 1:3 and 1:5.
The power values used for a cutting operation on a lathe, mill or
machining center with a drill are calculated using the following formulas.
For a more accurate calculation of the power required, one must bear in
mind different factors such as cutting oil, material, shape of the tools,
hardness of the material machined, etc.
F. H5/2
Constant power required from the motor for a load regardless of the load.
T. H5/4 Constant motor power demanded by a load.
Constant motor power
Load type Constant power, regardless of speed
Examples
Winding machines at constant tenstion
Milling spindle
Lathe spindle
Torque / speed
characteristics
The torque decreases from base speed on
Motor power
The rated power of the drive will be the one
demanded by the load.
P
MOTOR
P
LOAD
P
ACCEL/DECEL
+>
0
power
speed
n
0
base
torque