1. Select the geometric parameters of the tool
When machining stainless steel, the geometry of the cutting part of the tool should generally be considered from the choice of rake angle and back angle. When selecting the rake angle, factors such as the flute profile, the presence or absence of chamfering and the positive and negative angle of the blade inclination should be considered. Regardless of the tool, a larger rake angle must be used when machining stainless steel. Increasing the rake angle of the tool can reduce the resistance encountered during chip cutting and clearing. The selection of the clearance angle is not very strict, but it should not be too small. If the clearance angle is too small, it will cause serious friction with the surface of the workpiece, worsening the roughness of the machined surface and accelerating tool wear. And due to strong friction, the effect of hardening of the stainless steel surface is enhanced; the tool clearance angle should not be too large, too large, so that the wedge angle of the tool is reduced, the strength of the cutting edge is reduced, and the wear of the tool is accelerated. Generally, the relief angle should be appropriately larger than when processing ordinary carbon steel.
The choice of rake angle From the aspect of cutting heat generation and heat dissipation, increasing the rake angle can reduce the cutting heat generation, and the cutting temperature will not be too high, but if the rake angle is too large, the heat dissipation volume of the tool tip will decrease, and the cutting temperature will be opposite. Elevated. Reducing the rake angle can improve the heat dissipation conditions of the cutter head, and the cutting temperature may decrease, but if the rake angle is too small, the cutting deformation will be serious, and the heat generated by the cutting will not be easily dissipated. Practice shows that the rake angle go=15°-20° is the most appropriate.
When selecting the clearance angle for rough machining, the cutting edge strength of powerful cutting tools is required to be high, so a smaller clearance angle should be selected; during finishing, the tool wear mainly occurs in the cutting edge area and the flank surface. Stainless steel, a material that is prone to work hardening, has a greater impact on the surface quality and tool wear caused by the friction of the flank surface. A reasonable relief angle should be: for austenitic stainless steel (below 185HB), the relief angle can be 6°— —8°; for processing martensitic stainless steel (above 250HB), the clearance angle is 6°-8°; for martensitic stainless steel (below 250HB), the clearance angle is 6°-10°.
The choice of blade inclination angle The size and direction of the blade inclination angle determine the direction of the chip flow. A reasonable selection of the blade inclination angle ls is usually -10°-20°. Large-blade inclination tools should be used when micro-finishing the outer circle, fine-turning holes, and fine-planing planes: ls45°-75° should be used.
2. Selection of tool materials
When processing stainless steel, the toolholder must have sufficient strength and rigidity due to the large cutting force to avoid chattering and deformation during the cutting process. This requires the selection of a suitably large cross-sectional area of the tool holder, and the use of higher-strength materials to manufacture the tool holder, such as the use of quenched and tempered 45 steel or 50 steel.
Requirements for the cutting part of the tool When processing stainless steel, the material of the cutting part of the tool is required to have high wear resistance and maintain its cutting performance at a higher temperature. Currently commonly used materials are: high-speed steel and cemented carbide. Because high-speed steel can only maintain its cutting performance below 600°C, it is not suitable for high-speed cutting, but is only suitable for processing stainless steel at low speeds. Because cemented carbide has better heat resistance and wear resistance than high-speed steel, tools made of cemented carbide materials are more suitable for cutting stainless steel.
Cemented carbide is divided into two categories: tungsten-cobalt alloy (YG) and tungsten-cobalt-titanium alloy (YT). Tungsten-cobalt alloys have good toughness. The made tools can use a larger rake angle and a sharper edge to grind. The chips are easy to deform during the cutting process, and the cutting is brisk. The chips are not easy to stick to the tool. In this case, it is more appropriate to process stainless steel with tungsten-cobalt alloy. Especially in rough machining and intermittent cutting with large vibration, tungsten-cobalt alloy blades should be used. It is not as hard and brittle as tungsten-cobalt-titanium alloy, not easy to sharpen, and easy to chip. Tungsten-cobalt-titanium alloy has better red hardness and is more wear-resistant than tungsten-cobalt alloy under high temperature conditions, but it is more brittle, not resistant to impact and vibration, and is generally used as a tool for stainless steel fine turning.
The cutting performance of the tool material is related to the durability and productivity of the tool, and the manufacturability of the tool material affects the manufacturing and sharpening quality of the tool itself. It is advisable to choose tool materials with high hardness, good adhesion resistance and toughness, such as YG cemented carbide, it is best not to use YT cemented carbide, especially when processing 1Gr18Ni9Ti austenitic stainless steel, you should absolutely avoid using YT hard alloy Alloy, because titanium (Ti) in stainless steel and Ti in YT-type cemented carbide produce an affinity, chips can easily take away Ti in the alloy, which promotes increased tool wear. Production practice shows that the use of YG532, YG813 and YW2 three grades of materials to process stainless steel has a good processing effect
3. Selection of cutting amount
In order to suppress the generation of built-up edge and scale spurs and improve the surface quality, when processing with cemented carbide tools, the cutting amount is slightly lower than that of turning general carbon steel workpieces, especially the cutting speed should not be too high, the cutting speed is generally recommended Vc=60——80m/min, the cutting depth is ap=4——7mm, and the feed rate is f=0.15——0.6mm/r.
4. Requirements for the surface roughness of the cutting part of the tool
Improving the surface finish of the cutting part of the tool can reduce the resistance when the chips are curled and improve the durability of the tool. Compared with processing ordinary carbon steel, when processing stainless steel, the cutting amount should be appropriately reduced to slow down tool wear; at the same time, appropriate cooling and lubricating fluid should be selected to reduce the cutting heat and cutting force during the cutting process, and to extend the service life of the tool.
Post time: Feb-28-2021
