In the process of cutting, elastic deformation, plastic deformation and friction deformation occur in the three deformation zones, 99.5% of the cutting power is transformed into shear slip deformation (the first deformation zone), the friction deformation of the rake face (the second deformation zone), and the energy consumed by extrusion, excess deformation and friction deformation of the back face (the third deformation zone), and it is transformed into heat energy in an instant, resulting in the temperature rise of chip, cutting edge area and workpiece surface.
Cutting heat is an inevitable physical phenomenon in the process of metal cutting, which has a significant impact on the quality of workpiece and tool life. In low-speed cutting, mechanical wear is the main reason for tool wear; while in high-speed cutting, high-temperature induced tool wear changes from mechanical wear to diffusion wear, phase change wear and carbonization wear, and leads to adhesive wear on the tool surface. Cutting heat also causes the thermal expansion of cutting tools and workpieces, aggravates the friction and wear of the flank of the cutting tool, and causes the surface roughness of the workpiece to rise. Therefore, the ultra precision machining process emphasizes that the conduction of cutting heat in the workpiece and tool must be controlled timely and effectively. It is also very important to control the temperature rise of tool and workpiece for NC machining.
The cutting heat of metal originates from the strength, hardness, toughness, plasticity and elasticity of materials. The research also shows that the temperature rise of cutting tool and workpiece is closely related to the contact area, heat transfer coefficient, temperature difference, contact time and so on. Generally speaking, reducing the cutting rate can reduce the contact area between the tool and the heat source; increasing the flow rate and flow rate of the cooling medium is to increase the heat transfer coefficient; reducing the temperature of the cooling medium can increase the heat capacity and temperature difference effect of the cutting tool and workpiece; and increasing the machine speed and cutting speed actually shortens the heat conduction time of cutting.
It can be seen that in order to control the cutting heat of metal and the temperature rise of cutting tools and workpieces, various factors must be considered comprehensively. In addition to the reasonable selection of cutting tools and cutting process parameters according to the characteristics of metal materials and machining technical indicators, the most direct measure is to use various cooling media to quickly take away the cutting heat on the tool and workpiece and reduce the temperature.
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