CNC Turning SS304 Stainless Steel

Austenitic 304 stainless steel is a very common stainless steel with corrosion resistance, heat resistance, low temperature strength and overall mechanical properties. Widely used in food equipment, chemical equipment and nuclear industry equipment.

Austenitic 304 stainless steel has a relative machinability Kr of about 0.4, which is a relatively difficult material to process. The cutting force is large, the work hardening is large, the cutting area is high, and the local temperature is high. Therefore, the following items are required for turning.

1. High cutting force

Austenitic 304 stainless steel has low hardness ≤ Cr, Ni, Mn and other elements = 5, has 187 HbS and good plasticity (elongation after fracture) ≥ 40%, area ψ reduction ≥ 60%). The plastic deformation during cutting is large, and the strength can be maintained even at high temperatures (generally, the strength of steel decreases significantly when the cutting temperature rises). Under previous cutting conditions, the unit cutting force of austenitic 304 stainless steel is 2450mpa, which is more than 25% higher than that of 45 steel.

2. Hard work hardening

Austenitic 304 stainless steel is accompanied by obvious plastic deformation during processing, and the material lattice is severely deformed; at the same time, due to the stability defect of the austenite structure, the austenite part becomes martensite, and the impurities in the austenite During the cutting process, it is decomposed by heating to form a hardened layer on the surface, and the work hardening phenomenon is very obvious. After curing +B to 1500 MPa, the depth of the solidified layer is 0.1 to 0.3 mm.

3. The local temperature of the cutting area is high

Austenitic 304 stainless steel requires a large cutting force and is difficult to chip, so the operation by blade separation is also large. Under previous conditions, the cutting of stainless steel is about 50% higher than that of mild steel, generating more cutting heat. Austenitic stainless steels have poor thermal conductivity. The thermal conductivity of austenitic 304 stainless steel is 0. 321.5 w/m.k is one-third of the thermal conductivity of 45 steel. Therefore, the temperature of the cutting area is higher (generally speaking, the heat generated by the blade during the cutting process accounts for more than 70% of the cutting heat). A large amount of cutting heat is concentrated on the cutting area and the surface of the cutting tool, and the heat transferred to the tool is as high as 20% (only 9% when cutting common carbon steel). Under the same cutting conditions, the cutting temperature of austenitic 304 stainless steel 200~300°C higher than 45 steel.

4. Tools are easy to stick and wear

Due to the high temperature strength and high work hardening of austenitic stainless steel, the cutting load is large, and the affinity of austenitic stainless steel with tools and inserts is greatly improved due to the affinity of austenitic stainless steel with tools during cutting, resulting in bonding and diffusion phenomena. The result of tool sticking and wear. In particular, hard inclusions are formed by a small piece of cemented carbide, which promotes tool wear and causes edge collapse, which greatly shortens the service life of the tool and affects the surface quality of the machined parts.

Choose a reasonable CNC turning process

Due to the poor machinability of AISI 304 austenitic stainless steel, in order to improve productivity and processing quality, it is necessary to select appropriate turning, including cutting tool material, tool shape parameters, cutting parameters, and reasonable selection of cooling materials.

Tool material

Proper selection of tool material is critical to efficient machining of austenitic stainless steels. The reduction in turning performance of austenitic 304 stainless steel indicates that the selected cutting tool has high strength and toughness characteristics. At the same time, it has excellent wear resistance and has little affinity with stainless steel. At present, cemented carbide and high-speed steel are still the most commonly used cutting tool materials.

1. Carbide

Due to the high cutting force of difficult-to-cut materials and the short contact between chips and the lake surface, the cutting force is mainly concentrated near the edge, and edge collapse is prone to occur. Therefore, you can choose yg carbide tools for processing. The toughness, wear resistance, red hardness and thermal conductivity of yg cemented carbide are excellent. Suitable for processing austenitic stainless steel. You can also choose the YG 8 N tool. By adding nb, the cutting performance is 1~2 times higher than that of yg 8, and the effect is good in rough machining and semi-precision machining.

2. High speed steel

High-speed steel tools can effectively avoid the phenomenon that hard tools are easy to be damaged according to the size, shape and structure of the turning of stainless steel processed products. Conventional high-speed steel tools such as W 18 CR 4 V do not meet current machining conditions in terms of durability, new high-speed steel tools with excellent cutting performance such as high-speed steel (W 6 Mo 5 Cr 4 V 2 Al) and Nitrogen-containing high-speed steel (W 12 Mo 3 Cr 4 V 3 N).

Tool shape parameters

Reasonably determining the geometric parameters of the selected tool is an important factor to effectively improve the durability and processing effect of the austenitic 304 stainless steel tool. Generally speaking, knives must have large front and rear angles and sharp cutting edges.

1. Cutting parameters

AISI 304 stainless steel is usually a difficult-to-cut material, and the cutting parameters should be selected reasonably. Cutting parameters have a great influence on work hardening, cutting force, heat and processing efficiency. Cutting speed has a great influence on cutting temperature and tool durability. The second is the feed rate F, and the reverse feed rate AP has the greatest influence.

2. Cutting oil

Due to the insufficient cutting performance of austenitic 304 stainless steel, the selected cutting fluid has better cooling, lubricity and permeability (ie, anti-bonding performance). In addition, emulsifiers and vulcanized oils contain extreme pressure additives, such as S and Cl, which must be selected as much as possible.

Emulsion has good cooling properties and is mainly used for rough turning of stainless steel. Vulcanized oil has certain cooling and lubricating properties and low cost. It can be used for semi-finishing and finishing of stainless steel. Adding extreme pressure and oily additives to cutting fluids can significantly improve lubrication performance. Usually used for stainless steel finishing. The cutting fluid composed of a mixture of carbon tetrachloride, kerosene and oleic acid greatly improves the permeability of cooling lubricating oil, and is especially suitable for the finishing of AISI 304 austenitic stainless steel. Through the large cutting heat of austenitic stainless steel, methods such as spray cooling and high-pressure cooling can be performed to improve the cooling effect.

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