Use silicon nitride ceramic tools to cut difficult-to-machine materials
Author:Kaixin Special Materials - Silicon Nitride CeramicSource:Kaixin Special Materials - Silicon Nitride Ceramic
1 cutting chilled cast iron
The hardness of chilled cast iron is very high, the rough surface is rough, and there are casting defects such as sand holes and blowholes. The machining allowance is large, the general cutting depth is selected larger during rough machining, and there is a large impact load, and the cutting conditions are quite severe. It is also difficult to use a ceramic tool for roughing. Usually the carbide former is used to rough out the outer circle, leaving a margin of about 0.3 mm (one side), and then semi-finishing with a silicon nitride ceramic tool.
Tool damage problem
Due to the high hardness of the workpiece material, the tool is susceptible to damage even in semi-finish vehicles. The following measures can be taken during processing:
Use negative rake for cutting. The negative rake angle does not have to be large. For example, the shank groove has a longitudinal negative rake angle (gp=-11° or so). Thus, when the main deviation angle and the sub-offset angle are both 45°, the rake and back angles of the insert itself are For O, the rake angle of the main cutting edge after installation is -8°, the inclination angle of the cutting edge is -8°, and the relief angles of the cutting edge and the auxiliary cutting edge are both 8°. One blade has eight corners for cutting.
Sharpen the negative chamfer on the cutting edge. For example bg1=0.2mm, g01=-30° to protect the cutting edge.
Use a thicker blade. When cutting, not only the cutting force is great, but also the cutting temperature is very high. If the thickness of the blade is not enough, the rigidity of the groove surface that is in contact with the lower surface of the blade is not enough, so that the surface of the blade is cracked. For example, cutting with a 16 x 16 x 4.5 mm blade produces a visible crack in the direction of the vertical cutting edge, and cracking occurs with a 16 x 16 x 8 mm blade.
Contrast with cemented carbide tools
The cutting of chilled cast iron with hard alloy cutting tools usually has a cutting speed of only 10 to 15 m/min, and due to the relatively heavy tool wear, there is a more pronounced taper in the workpiece, which will increase the margin of the subsequent grinding process. With silicon nitride ceramic cutting chilled cast iron, cutting speed can reach 35 ~ 40m/min, such as the turning hardness of 66 ~ 78HS (49 ~ 58HRC), length 803mm roll, after processing a flank wear Only 0.2 to 0.3mm, one corner of the blade can turn 3 to 4 rolls. It can be seen that the use of silicon nitride ceramic tool to replace semi-finished carbide tool chilled cast iron workpiece, the cutting speed at least more than doubled, you can get a higher tool durability and machining accuracy. The cost of cutting tools has not increased much, but the economic benefits have been significantly improved.
2 cutting high hardness steel
Cutting high manganese steel
Although the original hardness of high manganese steel is not necessarily very high, but the work hardening is very serious, the hardness after processing can be increased by about twice, the cutting process is very poor, it is very difficult to use ordinary carbide tool processing, especially when the processing accuracy or rough surface When the degree of demand is high, carbide tools are even more powerless. For example, a factory processing active wheels, material ZG55Mn, hardening, hardness 169 ~ 225HB, 380mm inner hole tolerance is only 0.045mm, inner hole taper requirements 0.014/455mm, roughness requirements Ra1.6μm. The use of a variety of carbide tool processing, can not reach the above quality requirements; later use silicon nitride ceramic tool, smooth solution to the problem.
Another kind of high manganese steel's original hardness is 280HB, after the initial cutting hardness is 500~600HB, it is very difficult to process with the ordinary hard alloy cutting tool, although the high-performance hard alloy cutting tool can process, but the efficiency is low, cutting Speed is only 16m/min. With silicon nitride ceramic inserts at constant cutting depth and feed rate, the cutting speed can reach 65m/min, the machining efficiency is increased by more than 3 times, and the cutting is smooth and light, the surface roughness of the workpiece is small, and the tool wears. Extremely small.
Matters needing attention in use: 1 Continuous cutting, that is, roughing and finishing cars or semi-finishing car continuous. Avoid roughing the rough stock first, and then finish machining; 2 Cutting depth should be more than 0.5mm to avoid cutting in the hardened layer; 3 Both ends must be chamfered in advance, otherwise the cutter heads at the feeding and the outlet are easy to crack.
Cutting hardened steel
Some alloy quenched steels, such as W18Cr4V, Gr15, 38CrMoAlA, etc., have a hardness of 58-62HRC and are difficult to cut. Grinding methods are usually used, but the grinding efficiency is very low. For example, the oil pump sleeve material of a factory is 38CrMoAlA, and the allowance to be removed after nitriding is 0.5mm. If grinding is used, it takes 3 to 4 hours, but it takes only 10 minutes to turn it with a silicon nitride ceramic tool. Greatly improved cutting efficiency.
3 cutting high silicon aluminum alloy
Although the hardness of high-silicon aluminum alloy is not high, due to the high silicon content, the fine-grained silicon and other alloy components contained in the material have a strong abrasion effect, which makes the tool wear quickly.
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