Due to different mechanical properties and chemical composition in different kind of stainless steel, the CNC machinng difficulties are also different. To some stainless steel in cutting, it is difficult to achieve satisfactory machining surface roughness, to the other stainless steel, although it is easy to meet the requirements of machining surface roughness, but also easy to wear. In summary, the reasons caused difficulties for cutting stainless steel are below,
High thermal strength, toughness is not suitable for high-speed CNC cutting, hardness and tensile strength of austenitic stainless steel and martensitic stainless steel are not high, only equivalent to C40 steel, but the elongation, section shrinkage and impact value is very high. For example, the elongation of 1Cr18Ni9Ti is 210% of the C40 steel, so it is not easy to be cut off in the high-speed CNC cutting process, and power consumption when cutting deformation is quite large. Relatively, the strength of stainless steel at high temperature is reduced less, eg. 45 steel at 500° its lasting strength of 7kg/mM2, and 1Cr18Ni9Ti at 550° its lasting strength is still maintained at 19 ~ 24kg/mM2. Practice has proved that under the same cutting temperature, cutting stainless steel is more difficult than ordinary carbon steel, its high thermal strength is an extremely important factor.
Machining hardening trend is unfavorable to CNC turning, in the process of high-speed CNC turning, Due to cutting tools extrudes woirkpieces which will cause deformation, crystal slip, lattice distortion, dense organization, changes of mechanical properties, its general cutting hardness can also increase by 2 ~ 3 times. After CNC cutting the depth of work hardening layer can vary from dozens of microns to hundreds of microns, so the work hardening phenomenon produced by the first cutting and hinder the next cutting, and the high hardness of the work hardening layer leads to tool wear easily.
Cutting chips’ adhesion, poor thermal conductivity has an impact on CNC machining process, in the process of CNC cutting, cutting chips are easy to firmly adhere to or melt on the tip of the tool and the blade, turning to be scars, effecting bad surface roughness on workpieces, while increasing the vibration in the cutting process, accelerate tool wear. And also a lot of cutting heat can not be conducted out timely, even the heat generated by cutting can not be transmitted to the chip as a whole, resulting in the total heat of the incoming on tool 3 ~ 5 times than ordinary carbon steel, so that tools lose the cutting performance. In the process of CNC cutting, lots of heat energy generated is not quickly discharged, will inevitably be transferred to the tool, then the temperature of the cutting part rises. At the same time, because removal of the cutting chips is more difficult, especially the continuous chips, so that the chips are blocking continually, especially the processing of machining inner holes, chip block more seriously. In addition, because the tool is limited by the shape of the thread section, coupled with its poor strength, vibration in the processing, The tool tip is easy to burn out due to high local temperature in the cutting process, or cracks due to big vibration.
