Siemens SINUMERIK 840D Maintenance Manual page 96

FADAL MACHINING CENTERS
This process is also effective for inspecting parts. By cooling the part prior to the finish
cuts, the temperatures at final cut and at inspection can be brought closer. In this
situation, the target temperature should also be close to the temperature at which the
gauge is calibrated.
Monitoring Position Changes
The home position of the part will change as the temperature of the screws change.
The operator can follow the home position changes throughout the production run and
change the fixture home position and offsets accordingly.
Coolant
Using soluble and synthetic coolants that are mixed with water is the single most
effective factor in removing the heat generated during cutting. Coolant is formulated
specifically to absorb a great deal of heat within its molecular structure without having
to radiate that heat onto the next material it contacts. Cutting oils are formulated for
cutting, and lack the cooling quality of soluble and synthetic coolants mixed with water.
Flood coolant is a better choice than either mist coolant or cutting oils because it
benefits the cutting process in addition to providing heat removal.
The temperature of the coolant can be conditioned further through any of a few simple
actions. Bags of ice floating in the coolant tank can be used to maintain the
temperature. Pumping the coolant through a radiator, or through a copper coil in the
coolant tank, or through a copper coil placed in a small refrigerator can all be used to
condition the temperature of the coolant.
One side benefit of coolant is its cooling effect on the table as well as the part. As it is
splashed around, the coolant's direct contact and its evaporation tends to keep the
table at or near the temperature of the coolant, directly compensating for the effect of
hot chips falling on the table. If the coolant temperature is being conditioned through
some of the steps just mentioned, the thermal stability of the table benefits even more.
Cooled Ballscrews and Spindle
The only effective way to greatly reduce the thermal expansion of the ball screws is to
provide coolant through the center of the screws. Building on the Coolant Through
Spindle concept, machines equipped with this feature pump a fluid through the screws
and the spindle. A refrigeration unit, coupled to a thermostat, is used to control the
temperature of the fluid, which consequently conditions the temperature of the screws
and spindle as the fluid flows through them.
90 GENERAL INFORMATION MAN-0126_ R1