How to calculate the machining time for face milling, parting off, and deep grooving?

 

Calculating the machining time for face turning, finishing, and deep grooving is challenging due to the following reasons:

 

• The spindle speed continuously changes.
• The machine's maximum speed limits the cutting speed.

 

 

 

Units:

• Time is measured in minutes.
• Diameter is measured in inches or millimeters.
• Cutting speed (SFM) is in meters/minute.
• Feed rate is in units of IPR or millimeters/revolution.

 

The following parameters apply to the formula used below:

– Starting diameter of machining

– Ending diameter of machining

– Maximum spindle speed of the machine

– Cutting speed

– Feed rate

– Clamping diameter: the diameter at which the machine's maximum spindle speed limits the cutting speed

– Machining time for diameters greater than the clamping diameter

– Machining time for diameters less than the clamping diameter

T – Total cycle time

 

Due to the constant diameter, calculating the operation time for longitudinal turning is quite simple. Therefore, during the entire operation, the cutting and spindle speeds remain unchanged, and the following simple formula applies (where l is the distance to be turned).

 

T =

 

In face turning, cut-off turning, and grooving, the diameter continuously changes, and the total cutting time should be calculated through integration.

 

= = π ×

 

In metric units, the constant 12 should be replaced with 1000.

 

The situation becomes more complex due to the maximum spindle speed limit (n max) of each machine. To maintain the cutting speed (Vc), the spindle speed (n) will increase as the machine moves from d1 to d2.

 

n =

 

In metric units, the constant 12 should be replaced with 1000.

 

At a certain diameter, n will reach n max. This diameter is called the "clamping diameter" (dc), because from this diameter onwards, the spindle speed is "clamped" and the cutting speed begins to decrease.

 

=

 

In metric units, the constant 12 should be replaced with 1000.

 

The first formula t1 only applies to diameters greater than the clamping diameter. For diameters smaller than the clamping diameter, a different and simpler formula applies.

=

 

Clamping Conditions

 

To perform the correct calculation, you need to determine the situation relative to the clamping diameter.

 

 

Situation 1: Both the starting and ending machining diameters are greater than the clamping diameter.

T = =

 

Situation 2: The clamping diameter is between the starting and ending machining diameters.

T = =

 

Situation 3: Both the starting and ending machining diameters are less than the clamping diameter.

T = =

 

In metric units, the constant 12 should be replaced with 1000.