The basic elements of CNC machining stainless steel

The basic elements of CNC machining stainless steel

In the field of mechanical parts processing, parts of automation equipment, medical equipment and other accessories use stainless steel materials more, and the machinability of stainless steel materials is much worse than that of medium carbon steel. The relative machinability of austenitic stainless steel 1Cr18Ni9Ti is 40%; 48% for ferrite stainless steel 1cr28; 55% for martensitic stainless steel 2Cr13. Among them, the machinability of austenitic and austenitic + ferritic stainless steels is the worst. In the cutting process of stainless steel, the following factors should be paid attention to:

The work hardening of stainless steel is serious: in stainless steel, the work hardening of austenite and austenite + ferrite stainless steel is the most prominent. For example, the strength of austenitic stainless steel after hardening σ B is 1470 ~ 1960mpa, and it increases with time σ B, yield limit σ S increased; Austenitic stainless steel in annealed state σ S not more than σ B 30% ~ 45%, and 85% ~ 95% after work hardening. The depth of work hardening layer can reach 1 / 3 or more of cutting depth; The hardness of the hardened layer is 1.4-2.2 times higher than that of the original one. Because of the large plasticity of stainless steel, the character of plastic deformation is distorted, and the strengthening coefficient is very large; The austenite is not stable enough, and part of austenite transforms into martensite under the action of cutting stress; In addition, compound impurities are easy to decompose and disperse under the action of cutting heat, resulting in hardened layer during cutting. The work hardening phenomenon caused by the previous feed or the previous process seriously affects the smooth progress of the subsequent process.

Large cutting force of stainless steel: large plastic deformation of stainless steel in the cutting process, especially austenitic stainless steel (its elongation is more than 1.5 times of 45 steel), which increases the cutting force. At the same time, the work hardening of stainless steel is serious and the heat intensity is high, which further increases the cutting resistance and makes it difficult to curl and break the chip. Therefore, the cutting force for machining stainless steel is large. For example, the unit cutting force for turning 1Cr18Ni9Ti is 2450mpa, which is 25% higher than 45 steel.

The cutting temperature of stainless steel is high: the plastic deformation and friction between stainless steel and cutting tool are very large, resulting in more cutting heat; In addition, the thermal conductivity of stainless steel is about 1 / 2 ~ 1 / 4 of that of 45 steel. A lot of cutting heat is concentrated in the cutting area and the tool chip contact interface, and the heat dissipation condition is poor. Under the same conditions, the cutting temperature of 1Cr18Ni9Ti is about 200 ℃ higher than that of 45 steel.

Stainless steel chip is not easy to break, easy to bond: stainless steel plasticity, toughness are very big, turning chip continuous, not only affect the smooth operation, chip will crush the machined surface. Under high temperature and high pressure, the affinity between stainless steel and other metals is strong, so it is easy to produce adhesion phenomenon and form chip accumulation tumor, which not only aggravates tool wear, but also causes tearing phenomenon and worsens the machined surface. This characteristic is more obvious in martensitic stainless steel with lower carbon content.

Stainless steel tools are easy to wear: the affinity effect in the process of cutting stainless steel makes the tool chip bond and diffuse, resulting in the tool bond wear and diffuse wear, resulting in crescent depression on the tool rake face, and micro spalling and notch on the cutting edge; In addition, the hardness of carbide particles (such as TIC) in stainless steel is very high, and the tool wear will be aggravated by direct contact, friction, tool scratch and work hardening.

Large coefficient of linear expansion of stainless steel: the coefficient of linear expansion of stainless steel is about 1.5 times that of carbon steel. Under the action of cutting temperature, the workpiece is easy to produce thermal deformation, and the dimensional accuracy is difficult to control.

The above are the basic elements of stainless steel cutting in mechanical parts processing.

ken. tang@chengcg.com

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