Machining characteristics of stainless steel

1.Basic requirements for stainless steel machining tools.When machining stainless steel, the geometric shape of the cutting tool part,generally, we should consider from the front Angle and the back Angle.When choose the front corner, we need consider the factors for chip groove, chamfering and the size of plus or minus Angle of the tool blade Angle.No matter what kind of tool,we must use a larger front Angle when processing stainless steel,it can reduce the resistance encountered in the process of separation and removal by increasing the tool's front Angle.The selection requirements for the back Angle are not very strict, but should not be too small,if the back Angle is too small, it will cause serious friction with the surface of the workpiece, which will worsen the roughness of the machining surface and accelerate the tool wear.And because of the strong friction, enhances the stainless steel surface work hardening effect;the tool back Angle should not be too large, if it is too large, the tool wedge Angle decreases, it also reduce the cutting edge strength, speed up the tool wear.In general, the back Angle should be suitably larger than for ordinary carbon steel parts.Requirements for the surface roughness of the cutting part of the tool,it can reduce the resistance of the chip when forming crimp by improve the surface finish of the cutting part of the tool,then improve tool durability.Compared with processing ordinary carbon steel,we should properly reduce the cutting amount when processing stainless steel to reduce tool wear; At the same time, the appropriate cooling lubricant should be selected to reduce the cutting heat and cutting force in the cutting process and prolong the service life of the tool. 

1.2. Requirements for the material of cutter arbor.

When processing stainless steel, due to the larger cutting force, the tool must have enough strength and rigidity, so as to avoid chatter and deformation in the cutting process.This requires the selection of an appropriately large cross-sectional area of the cutter arbor,it should also be made of stronger materials to make the cutter arbor, such as steel 45 or steel 50.

1.3. Material requirements for tool cutting position.

When processing stainless steel, the material requiring the cutting position of the tool has high wear resistance and can maintain its cutting performance at a higher temperature.At present, the commonly used materials are: high-speed steel and cemented carbide. Because high speed steel can only maintain its cutting performance below 600 ℃, it is not suitable for high speed cutting, and only suitable for processing stainless steel at low speed. Due to the cemented carbide has better heat and wear resistance than high-speed steel,therefore, the tool made of cemented carbide is more suitable for the cutting of stainless steel.Cemented carbide can be divided into tungsten-cobalt alloy (YG) and tungsten-cobalt titanium alloy (YT).Tungsten cobalt alloy has good toughness,the tool can be made by using a larger front Angle and edge to grind out a sharper edge.It is not easy to deformation and light, not easy to stick the knife in the cutting process,so in general,it is more suitable to process stainless steel with tungsten cobalt alloy.Tungsten and cobalt alloy blades should be used especially in rough machining and intermittent cutting machining with large vibration.vIt is not as hard and brittle as tungsten cobalt titanium alloy, hard to grind, easy to broken blade.Tungsten-cobalt titanium alloy has better red hardness and is more resistant to wear at high temperature than tungsten-cobalt alloy, but its brittleness is larger and it is not resistant to impact and vibration,it is generally used stainless steel precision turning tool.

2. Selection of tool material brand.

The cutting performance of tool materials is related to the tool's durability and productivity,the process property of cutting tool material affects the manufacture of cutting tool and grinding quality.It is advisable to choose tool materials with high hardness, good adhesion resistance and toughness, such as YG cemented carbide,It is better not to choose YT cemented carbide, especially in the processing of 1Gr18Ni9Ti austenitic stainless steel should absolutely avoid using YT cemented carbide.Because the titanium (Ti) in stainless steel and the Ti in YT cemented carbide will produce the affinity cooperation,the chip is easy to take away the Ti in the alloy, which makes the tool wear worse.The production practice shows that the selection of YG532 YG813 and YW2 three kinds of cutting tools to process stainless steel has a good processing effect (see the attached table).

Attached table: performance comparison of three cemented carbide brands.

3. Selection of tool geometric parameters.

3.1. Selection of front corner.

       In terms of the generation and heat dissipation of cutting heat, increasing the front Angle can reduce the generation of cutting heat, and the cutting temperature is not too high.However, if the front Angle is too large, the cooling volume of the cutting head will decrease and the cutting temperature will increase.Reducing the front Angle can improve the cooling conditions of the cutting head, and the cutting temperature may be reduced,but the front Angle is too small, the cutting deformation is serious, cutting heat is not easy to disperse.Practice shows that the front Angle go=15 ~20 is most suitable.

3.2. Selection of rear Angle.

      During rough machining, the cutting edge strength is required for the cutting tool with strong cutting force, and the back Angle should be smaller; During fine machining, tool wear mainly occurs in the cutting edge area and the back surface of the tool.For stainless steel material prone to work hardening,the friction of the tool surface has a great influence on the machining surface quality and tool wear.The reasonable back Angle should be: when processing austenitic stainless steel (below 185HB), the back Angle can be 6 ~8;When processing martensite stainless steel (above 250HB), the back Angle is 6 ~8.When processing martensitic stainless steel (below 250HB), the rear Angle should be 6 ~10.

3.3. Selection of blade Angle.

      The size and direction of the dip Angle of the blade determine the direction of the chip flow. The reasonable choice of the dip Angle of the blade is usually is ls-10°~20.When turning the outer circle, the hole and the plane with a small amount of finishing,the tool with a large angle of inclination should be used: LS45°~ 75 °.

3.4. Selection of cutting parameters.

      In order to inhibit the built-up edge and improve the surface quality,when machining with carbide tools, the cutting parameters are slightly lower than that of turning ordinary carbon steel workpiece,especially the cutting speed should not be too high.Generally, the recommended cutting speed is Vc=60~80m/min, cutting depth is ap=4~7mm, and feed f=0.15~0.6mm/r.