The cutting tool cuts the metal by breaking the metal layer. The fracture of the metal layer means that the external force destroys the metal structure and at the same time releases the internal energy of the metal in the form of heat. During cutting, on the one hand, the chips transfer the heat of the crack to the surface of the cutting tool. On the other hand, the chips are pressed into contact with the cutting tool by bending stress and move relatively quickly to generate frictional heat. The combined reasons make the cutting tool and metal surface The temperature rises rapidly. During the cutting process, the high-heat solid metal will be rapidly cooled by the quenching action of the cutting fluid to produce a quenching effect, which destroys the crystal phase structure. At the same time, the molecular dislocation in the crystal phase increases, making the metal hard and fragile at the same time . When the cutting tool finishes cutting and leaves the workpiece, the hot tip will contact the coolant to produce a “quenching reaction” that makes the cutting tool hard and fragile, especially the coated cutting tool, which affects the life of the cutting tool. Since the intensity of the quenching effect is proportional to the temperature difference, increasing the cutting speed will make the cutting tool higher temperature, and the strong quenching reaction produced by the greater temperature difference will further reduce the life of the cutting tool. This is why the higher the cutting speed, the shorter the life of the cutting tool.
During micro-lubrication processing, the lubricant is sprayed to the machined surface in the form of mist particles, which will not produce quenching effect or quenching effect. Moreover, when the cutting speed is increased, the cutting fracture point of the workpiece will appear in advance, and the heat source of the fracture point will be far away from the knife. tip. Since the heat is all concentrated on the workpiece and chips,
The heat source of the cutting tool is only a small part of the heat conduction and friction at the contact point of the chip. Increasing the cutting speed will cause the chip to bend and leave the workpiece and cutting tool at a faster speed, effectively reducing the time for the chip to conduct heat. The high temperature remaining on the workpiece can soften the surface of the workpiece and make the cutting tool easier to cut. Therefore, in general, micro-lubrication processing is suitable for increasing the cutting speed.