Testing Research on the Deformation Mechanism of High Manganese Steel and the Model of Surface Roughness Machined at High-Speed Cutting

摘要

To study the deformation mechanism of high manganese steel at high-speed machining and the influence of cutting parameters on a quality of machined surface and on a tool wear, we conducted a serial of tests cutting high manganese steel with metal ceramic tool. By observing the macroscopic chip and measuring its micro-morphology with optical microscope under the condition of five groups of cutting parameters, the effect of cutting speed and amount of feed on chip shape was analyzed. The main mechanism of chip deformation and its effect on chip morphology and tool wear has been studied, and a linear model of surface roughness has been built with regression test method for predicting machined quality. The results show that the deformation mechanism of high manganese steel at high-speed cutting is the concentrated shear or adiabatic shear, and the reason of tool wear is a coherent wear combining abrasive wear and oxidative wear. The model of surface roughness obtained can preferably be used to forecast the machined surface quality by given cutting parameters, or determine cutting parameters with the required roughness height. High manganese steel is the typical wear-resistant steel with advantages of good castability and low cost. Under the condition of a strong load, the surface of high manganese steel part is intensified due to work hardening, and its surface texture becomes martensite from austenite, and hardness increase to 450～550HB from 180～220HB while its keeps the original property in nexine. Therefore, high manganese steel has been widely used because of its high abrasive resistance, shock resistance and antifatigue crack. However, no other than the surface hardening, low heat conductivity coefficient, large elongation and deformation coefficient, it presents high cutting temperature, big cutting force, serious wear of tool and formed built-up edge when high manganese steel is being machined, which is then hard to control the machining precision and surface quality and to break up the chip. Hence, high manganese steel belongs to difficult-to-process material. The cost to process it is high and the range of application is limited. Hu yong-ke [1] makes a research on the processing technic of high manganese steel, summarizing the method of choosing tool material and geometrical parameters. Xu li et al. [2] set up a constitutive model of the plastic deformational behavior of high manganese steel, which can provide a basis for emulate study the cutting property. Xu yu-dong et al. [3-4] studied the matching of metal ceramic tool to process the high manganese steel, which indicates that the tool is not suit for cutting chilled cast iron. Liu zhan-qiang, Ai Xing et al[5-6]. studied the synthesis technique of high-speed cutting (HSC) and abrasion morphology of tool surface, which proved the advantages of high speed cutting. In consideration of the character of high manganese steel and the advantage of HSC, the cutting deformation morphology was observed and analyzed by an experiment of HSC with metal ceramic tool to cut high manganese steel in this paper so as to research the behavior of chip transformation and tool wear mechanism. The model of surface roughness with cutting parameters is obtained, which can offer a basis for choosing process parameters before HSC.