1. Due to the vigorous development of aviation, aerospace, petroleum, chemicals, metallurgy, food and other industries, stainless steel materials have been widely used.
Stainless steel has high toughness, high thermal strength, low thermal conductivity, large plastic deformation during cutting, severe work hardening, high cutting heat, and severe heat dissipation. The cutting edge has a high cutting temperature, and the cutting edge is largely adhered to, which not only worsens the wear of the cutting tool but also tends to cause chipping that affects the roughness of the machined surface. In addition, since the chips do not easily curl and break, the machined surface is also damaged, which affects the quality of the work piece. Accurate selection of tool material, tool shape and amount of cutting is very important for improving stainless steel machining efficiency and machining quality.
2. The accuracy of tool material selection is a decisive factor in ensuring the efficient machining of stainless steel.
Depending on the cutting properties of stainless steel, the tool material must have sufficient strength, toughness, high hardness and high wear resistance and low adhesion to stainless steel. Commonly used tool materials are two types of carbides and high speed steel. Tools with complex shapes are mainly made of high speed steel. Cutting high speed steel The cutting speed of stainless steel cannot be too high, which affects production efficiency.
For simpler turning tools, the tool material should have the high strength and good thermal conductivity of cemented carbide, as its hardness, abrasion resistance and other functions are superior to high speed steel. Commonly used cemented carbide materials are tungsten cobalt (YG3, YG6, YG8, YG3X, YG6X), tungsten cobalt and titanium (YT30, YT15, YT14, YT5), and general class (YW1, YW2).
YG cemented carbide has good toughness and thermal conductivity, and is not easy to join with chips, so it is suitable for roughing stainless steel. YW cemented carbide has excellent hardness, wear resistance, heat resistance, oxidation resistance and toughness, and is suitable for precision turning of stainless steel.
When processing 1Cr18Ni9Ti austenite-based stainless steel, Ti and YT cemented carbide in the stainless steel have tools that promote the combined effect, and the chip easily robs Ti in the alloy and promotes wear, so YT Cemented carbide should not be selected.
3. Select the geometric angle of the tool
The geometric angle of the cutting tool has a great influence on the productivity of stainless steel cutting, the cost of tool resistance, the surface roughness to be machined, the cutting force and the machining hardening. Proper selection and improvement of the tool’s geometric parameters is an effective way to ensure process quality, efficiency and cost savings.
- (1) The size of the rake angle of the rake angle γ0 determines the sharpness and strength of the cutting edge. Increasing the rake angle reduces population deformation, reduces cutting and cutting forces, lowers the cutting temperature, and increases the cost of tool resistance. However, increasing the rake angle reduces the wedge angle, reduces blade strength, produces chips, and reduces tool resistance costs. Rotating the stainless steel should make the front angle suitable for expansion without reducing the strength of the tool. When the rake angle of the tool is large, the plastic deformation is small, the cutting resistance and the cutting resistance are small, the work hardening property is lowered, and the tool resistance is large. Generally, the tool rake angle should be between 12 ° and 20 °.
- (2) Selective turning angle α0 of the turning tool During turning, the flank can reduce the friction between the flank and the cutting surface. If the reverse angle is too large, the wedge angle becomes small, the heat dissipation condition deteriorates, the blade strength decreases, and the tool resistance cost decreases. If the back angle is too small and the friction is large, the cutting edge becomes dull, cutting resistance increases, cutting temperature rises, and tool wear increases. In general, the change in angle is small, but a reasonable value is required, and the cost of resistance facilitates the advancement of the tool. When rotating stainless steel, stainless steel is more elastic and plastic than regular carbon steel. Therefore, if the back angle of the tool is too small, the contact area between the cutting surface and the rear corner of the cutting tool will increase. The high temperature region created by friction then concentrates on the rear corners of the turning tool, accelerating wear on the turning tool and reducing the surface finish of the machined surface. Therefore, when turning stainless steel, the angle of rotation of the lathe is slightly larger than when turning ordinary carbon steel. However, if the rear angle is too large, the strength of the blade will be reduced and it will directly affect the turning cost of the lathe. Therefore, the lathe angle should typically be between 6 ° and 10 °.
- (3) When the cutting depth ap and feed amount f are constant, the corner Kr of the turning tool can be selected by reducing the lead angle Kr to improve heat dissipation conditions, reduce tool damage, and smoothly move the tool in and out. can. However, reducing the main deflection angle increases the radial force and tends to cause vibration during the cutting process. Rotating stainless steel tends to harden and vibrate, resulting in difficulty in working. Therefore, the lead angle should typically be between 45 ° and 90 °. The detailed angle should be selected according to the stiffness of the machine, the part, the tool system, and the amount of cutting.
- (4) The inclination of the cutting edge angle λs of the turning tool can control the flow of the insert. If the current angle λs is negative, the tip will flow to the machined surface. If the blade tilt angle λs is positive, the insert flows to the surface to be machined. The edge angle λs is a positive value during finishing to prevent the chip from scratching the machined surface. If λs is positive, the blade tip strength is low and first contacts the workpiece and is easily damaged. When λs is negative, the tip has high strength and impact resistance, prevents the tip from collapsing, and allows smooth loading and unloading. When turning stainless steel, the angle of the tool tip should be 0 ° to 20 °.
4. Select the cutting amount.
The amount of cutting has a great influence on production efficiency and processing quality. Therefore, after deciding the shape of the tool, you need to select a significant number of cuts. The following factors should be considered when choosing the amount of cut: One is to select the cutting amount according to the hardness of stainless steel and various blanks. The second is to select the cutting amount according to the material of the turning tool, the welding quality and the turning conditions of the turning tool. The third is to select the cutting amount according to the part diameter, machining allowance, and lathe accuracy. At the same time, the amount of cutting should be slightly lower than when rotating a normal carbon steel workpiece, especially the cutting speed should not be too high (vc = 50-80m / min);
The cutting depth ap should not be too small to avoid the cutting edge and the tip passing through the hardened layer, ap = 0.4-4 mm. Therefore, the feed rate f is not as effective as the cutting speed, but it removes and pulls chips and chips, scratches the surface of the workpiece and affects the surface quality. The feed rate is usually f = 0.1-0.5 mm / r. Stainless steels, especially austenitic stainless steels, have good plasticity. During machining, the generated insert is less likely to break, increasing friction between the insert and the rake face of the tool and increasing cutting force. At the same time, work hardening increases the hardness and strength of the material to be cut, as well as the cutting force. Therefore, the cutting forces of stainless steel and 45 steel are compared based on the proper selection of tool material, tool shape and cutting amount. The test results show that when the same amount of cutting is used, the cutting force when machining stainless steel is increased by 8.5% compared to machining 45 steel.
A reasonable choice of tool material, tool geometry and amount of cutting can be achieved to improve the efficiency of stainless steel cutting and the quality of machined workpieces.