1.Field of the Invention
The present invention relates to an apparatus and a method for cooling a workpiece in machining such as grinding, dressing, cutting or the like.
2.Description of the Related Art
In machining, especially in grinding, coolant (i.e., grinding fluid) is supplied to a grinding zone between a grinding wheel and a workpiece to cool the machining zone in order to prevent grinding burn and to flush chips from the workpiece.
In the grinding, the coolant carried by high-speed rotation of the grinding wheel generates dynamic pressure at the grinding zone. The dynamic pressure tends to deflect the workpiece having a small diameter so as to decrease accuracy of the grinding, especially roundness of the workpiece is deteriorated. In the case of a workpiece having a recessed portion, e.g., a key way, an oil hole or the like, the recessed portion is possibly deformed after the grinding because the dynamic pressure changes at the recessed portion.
Moreover, the coolant carried by the rotation of the grinding wheel gives additional load to a motor driving the grinding wheel, so that power loss of the motor is increased.
On the other hand, cold-air-grinding is developed to improve working environment. The cold-air-grinding employs air refrigerated at 0.degree. C. or lower instead of the coolant.
FIG. 1 shows one example of the cold-air-grinding including nozzles 30 and 31. The nozzle 30 supplies cold air to a grinding zone P between a grinding wheel G and a workpiece W, thus reduces temperature in the workpiece W. The nozzle 31 feeds lubricating oil to the grinding zone P to prevent friction in the grinding zone P.
However, cooling effect of the cold-air-grinding is insufficient compared with the grinding using the coolant because thermal capacity of the cold air is smaller than one of the coolant.