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Tool breakage problems Due to the high hardness of the workpiece material, the tool is prone to breakage even in semi-finished cars. The following measures can be taken during processing:
Cut with a negative rake angle. The negative rake angle value does not have to be large, for example, the arbor groove has a longitudinal negative rake angle (gp=-11° or so), so that when both the main yaw angle and the sub yaw angle are 45°, the rake angle and the back angle of the blade itself are both For O, the front cutting angle of the main cutting edge after installation is -8°, the rake angle is -8°, and the back angle of the cutting edge and the minor cutting edge are both 8°. A blade has eight corners for cutting.
A negative chamfer is sharpened 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 large, but also the cutting temperature is very high. If the thickness of the blade is insufficient, the rigidity of the groove surface which is in contact with the lower surface of the blade is insufficient, so that the blade surface is cracked. For example, cutting with a 16×16×4.5 mm blade produces a visible crack in the direction of the vertical cutting edge, and no crack occurs when cutting with a 16×16×8 mm blade.
Compared with cemented carbide tools, the cutting speed of chilled cast iron is only 10~15m/min, and the tool wear is more serious. The margin of the grinding process. Cutting chilled cast iron with silicon nitride ceramic tool, the cutting speed can reach 35 ~ 40m / min, such as the turning hardness of 66 ~ 78HS (49 ~ 58HRC), the length of 803mm rolls, after processing one, the flank wear Only 0.2 to 0.3 mm, one corner of the blade can be used to turn 3 to 4 rolls. It can be seen that the use of silicon nitride ceramic tools instead of hard alloy tool semi-finished chilled cast iron workpieces, the cutting speed is at least doubled, and higher tool durability and machining accuracy can be obtained. The cost of cutting tools has not increased much, but the economic benefits have increased significantly.
2 Cutting high hardness steel cutting high manganese steel high manganese steel, although the original hardness is not necessarily high, but the work hardening is very serious, the hardness after processing can be doubled, the cutting process is very poor, it is difficult to use the general hard alloy tool Machining, especially when machining accuracy or surface roughness is high, carbide tools are even more powerless. For example, a factory processing active wheel, the material is ZG55Mn, quenching and tempering, hardness is 169 ~ 225HB, 380mm inner hole tolerance is only 0.045mm, inner hole taper requirement is 0.014/455mm, roughness requirement is Ra1.6μm. The selection of a variety of carbide tools, can not meet the above quality requirements; later changed to silicon nitride ceramic tools, successfully solved the problem.
Another high-manganese steel has a raw hardness of 280HB, and the hardness after initial cutting is 500-600HB. It is difficult to machine with ordinary cemented carbide tools. Although high-performance carbide tools can be processed, the efficiency is low. The speed is only 16m/min. With silicon nitride ceramic inserts, the cutting speed can reach 65m/min and the machining efficiency is more than three times with the cutting depth and feed rate unchanged. The cutting is smooth and brisk, the surface roughness of the workpiece is small, and the tool wears. Very small.
Matters needing attention during use: 1 For continuous cutting, that is, roughing and continuous or semi-finishing. Avoid roughing the rough and then finish the finishing; 2 The cutting depth should be above 0.5mm to avoid cutting in the hardened layer; 3 Both ends should be chamfered beforehand, otherwise the cutting head will be easy to crack at the infeed and exit.
Cutting hardened steel Some alloy hardened steels such as W18Cr4V, Gr15, 38CrMoAlA, etc. can have a hardness of 58-62HRC, which is difficult to cut, and is usually processed by grinding, but the grinding efficiency is very low. For example, the oil pump sleeve material of a factory is 38CrMoAlA, and the allowance to be cut after nitriding is 0.5mm. If it is grinding, it takes 3 to 4 hours, but it is only 10 minutes to turn it with 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 strong scratching effect, which makes the tool wear very fast.
Cutting chilled cast iron chilled cast iron has high hardness, rough surface, and there are casting defects such as blisters and pores. The machining allowance is large. Generally, the cutting depth is large when roughing, and there is a large impact load. Quite harsh, it is still difficult to rough the car with ceramic tools. Usually, the outer circumference of the car is roughened with a cemented carbide tool, leaving a margin of about 0.3 mm (single side), and then semi-finishing with a silicon nitride ceramic tool.
Tool breakage problems Due to the high hardness of the workpiece material, the tool is prone to breakage even in semi-finished cars. The following measures can be taken during processing:
Cut with a negative rake angle. The negative rake angle value does not have to be large, for example, the arbor groove has a longitudinal negative rake angle (gp=-11° or so), so that when both the main yaw angle and the sub yaw angle are 45°, the rake angle and the back angle of the blade itself are both For O, the front cutting angle of the main cutting edge after installation is -8°, the rake angle is -8°, and the back angle of the cutting edge and the minor cutting edge are both 8°. A blade has eight corners for cutting.
A negative chamfer is sharpened 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 large, but also the cutting temperature is very high. If the thickness of the blade is insufficient, the rigidity of the groove surface which is in contact with the lower surface of the blade is insufficient, so that the blade surface is cracked. For example, cutting with a 16×16×4.5 mm blade produces a visible crack in the direction of the vertical cutting edge, and no crack occurs when cutting with a 16×16×8 mm blade.
Compared with cemented carbide tools, the cutting speed of chilled cast iron is only 10~15m/min, and the tool wear is more serious. The margin of the grinding process. Cutting chilled cast iron with silicon nitride ceramic tool, the cutting speed can reach 35 ~ 40m / min, such as the turning hardness of 66 ~ 78HS (49 ~ 58HRC), the length of 803mm rolls, after processing one, the flank wear Only 0.2 to 0.3 mm, one corner of the blade can be used to turn 3 to 4 rolls. It can be seen that the use of silicon nitride ceramic tools instead of hard alloy tool semi-finished chilled cast iron workpieces, the cutting speed is at least doubled, and higher tool durability and machining accuracy can be obtained. The cost of cutting tools has not increased much, but the economic benefits have increased significantly.
2 Cutting high hardness steel cutting high manganese steel high manganese steel, although the original hardness is not necessarily high, but the work hardening is very serious, the hardness after processing can be doubled, the cutting process is very poor, it is difficult to use the general hard alloy tool Machining, especially when machining accuracy or surface roughness is high, carbide tools are even more powerless. For example, a factory processing active wheel, the material is ZG55Mn, quenching and tempering, hardness is 169 ~ 225HB, 380mm inner hole tolerance is only 0.045mm, inner hole taper requirement is 0.014/455mm, roughness requirement is Ra1.6μm. The selection of a variety of carbide tools, can not meet the above quality requirements; later changed to silicon nitride ceramic tools, successfully solved the problem.
Another high-manganese steel has a raw hardness of 280HB, and the hardness after initial cutting is 500-600HB. It is difficult to machine with ordinary cemented carbide tools. Although high-performance carbide tools can be processed, the efficiency is low. The speed is only 16m/min. With silicon nitride ceramic inserts, the cutting speed can reach 65m/min and the machining efficiency is more than three times with the cutting depth and feed rate unchanged. The cutting is smooth and brisk, the surface roughness of the workpiece is small, and the tool wears. Very small.
Matters needing attention during use: 1 For continuous cutting, that is, roughing and continuous or semi-finishing. Avoid roughing the rough and then finish the finishing; 2 The cutting depth should be above 0.5mm to avoid cutting in the hardened layer; 3 Both ends should be chamfered beforehand, otherwise the cutting head will be easy to crack at the infeed and exit.
Cutting hardened steel Some alloy hardened steels such as W18Cr4V, Gr15, 38CrMoAlA, etc. can have a hardness of 58-62HRC, which is difficult to cut, and is usually processed by grinding, but the grinding efficiency is very low. For example, the oil pump sleeve material of a factory is 38CrMoAlA, and the allowance to be cut after nitriding is 0.5mm. If it is grinding, it takes 3 to 4 hours, but it is only 10 minutes to turn it with 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 strong scratching effect, which makes the tool wear very fast.
For example, a factory uses a YG6 carbide tool to turn a piston. The material is a high-silicon aluminum alloy. When the cutting speed is v=465m/min, the tool durability is only about 20 minutes. If a silicon nitride ceramic blade is used, the cutting speed is the same. In this case, the durability is 2 to 3 times that of YG6. Turning pistons are interrupted cuts, but silicon nitride ceramic tools are still capable. For aluminum alloys with higher silicon content, the machinability is even worse. If the silicon nitride ceramic tool is still not satisfactory, it can be changed to diamond tool processing.
4 Cutting surfacing cobalt-based alloy The exhaust valve material of a factory is a cobalt-based alloy with a hardness of 40-50 HRC. The surface of the blank is the hard skin of the surfacing, which is uneven, and is in an intermittent turning state during processing. When roughing with a carbide tool, the cutting conditions are ap=1mm, f=0.15mm/r, v=21m/min; when machining with a silicon nitride ceramic tool, the depth of cut and the feed amount remain unchanged. The cutting speed is increased to 53m/min, the cutting efficiency is increased by 1.5 times, and the tool durability is extended by 2 to 4 times.
5 Turning and milling spray (heap) welding Nickel-based alloy Nickel-based alloy features: 1 high temperature strength, even at 600 ~ 800 °C, still maintain high strength and hardness, which will greatly improve the cutting force It requires high hardness and high temperature strength of the tool; 2 severe work hardening, which will further increase the cutting force, make the tool bear a large load, easily cause the tool to break, and require the tool to have high fracture toughness; The coefficient is low, high temperature will be generated on the surface of the tool during cutting, and the tool material is required to have high high temperature hardness. 4 It contains many hard points such as carbides and nitrides, which are easy to wear and require good resistance. Grinding. Due to the third and fourth points, the tool material can be selected from cemented carbide or ceramic, but the two materials have lower strength, higher brittleness and easy breakage. Especially in the processing of spray (heap) welding of nickel-based alloys, due to the serious surface roughness, it is interrupted cutting. Among the two types of tools, ceramic tools are more susceptible to breakage, but even if applied properly, even ceramic tools are fully qualified.
Measures to Solve Tool Breakage The following is an example of how to prevent tool breakage by using end milled nickel-based alloy as an example. The workpiece is a well valve gate valve plate, and a nickel-based alloy is sprayed on the surface of the steel substrate. The composition is: C O.5～1.0%, Fe 10～13%, Cr 9～12%, B 3.0～ 4.0%, Si 2.5 to 3.5%, Ni balance. The hardness of the spray-welded nickel-based alloy is 50 to 55 HRC. The workpiece is a rectangular flat plate with a milling area of ​​184 x 85 mm2. The surface of the spray welding is extremely rough, and the height difference is 1 to 1.5 mm. It is machined on X53 vertical milling machine with Ø200mm face milling cutter. The single-tooth, blade is a silicon nitride blade developed by Shanghai Silicate Research Institute. The size is 16×16×4.5mm. It is clamped in the milling cutter by mechanical clamping method. On the plate.
Cutting with a negative rake angle: The choice of the rake angle is the key to solving the chipping. Since the blade has an axial rake angle of 4° and a radial rake angle of 0°, when the main declination is 45°, if the rake angle of the blade itself is 0°, the actual rake angle of the cutting edge after installation is 2.8. °. To protect the cutting edge, a negative chamfer with a width of 0.1 mm should be ground with a negative chamfering rake angle of -30°. Since the contact length of the nickel-base alloy and the rake face is large, the main cutting action is the rake face after the negative chamfering. When the blade itself is 0° front angle, it is actually cut in the form of positive rake angle. Under such heavy impact load, the blade strength is obviously insufficient. At a cutting speed of 47 m/min, whether the milling depth is reduced from 1.0 mm to 0.5 mm or 0.3 mm, the feed rate is reduced from 0.31 mm/tooth to 0.2 or O.12 mm/tooth, or YG6 cemented carbide is used. Blades, or higher-strength hot-pressed silicon nitride blades, do not solve the chipping problem. Only when the front corner of the blade itself is sharpened to -10° or a 15°, the stress distribution state in the tool is improved, and the chipping can be effectively prevented.
Control cutting speed: If the cutting speed is not properly selected, that is, a negative rake angle is used, and chipping still occurs. If the above processing conditions are used, at the cutting speed of 47m/min, there is no chipping in the milling stroke; but when the cutting speed is increased to 60m/min, although the other conditions are the same, the milling is less than one stroke, the cutter The tooth collapsed. As the cutting speed is increased, the impact load is also increased, so that the chipping is inevitable. Milling spray-welded nickel-base alloy is different from milling gray cast iron. When milling gray cast iron, when the milling depth is ap=1mm and the feed rate is 0.787mm/tooth, even if the cutting speed is increased to v=589m/min, it will not collapse. blade.
For example, a factory uses a YG6 carbide tool to turn a piston. The material is a high-silicon aluminum alloy. When the cutting speed is v=465m/min, the tool durability is only about 20 minutes. If a silicon nitride ceramic blade is used, the cutting speed is the same. In this case, the durability is 2 to 3 times that of YG6. Turning pistons are interrupted cuts, but silicon nitride ceramic tools are still capable. For aluminum alloys with higher silicon content, the machinability is even worse. If the silicon nitride ceramic tool is still not satisfactory, it can be changed to diamond tool processing.
4 Cutting surfacing cobalt-based alloy The exhaust valve material of a factory is a cobalt-based alloy with a hardness of 40-50 HRC. The surface of the blank is the hard skin of the surfacing, which is uneven, and is in an intermittent turning state during processing. When roughing with a carbide tool, the cutting conditions are ap=1mm, f=0.15mm/r, v=21m/min; when machining with a silicon nitride ceramic tool, the depth of cut and the feed amount remain unchanged. The cutting speed is increased to 53m/min, the cutting efficiency is increased by 1.5 times, and the tool durability is extended by 2 to 4 times.
5 Turning and milling spray (heap) welding Nickel-based alloy Nickel-based alloy features: 1 high temperature strength, even at 600 ~ 800 °C, still maintain high strength and hardness, which will greatly improve the cutting force It requires high hardness and high temperature strength of the tool; 2 severe work hardening, which will further increase the cutting force, make the tool bear a large load, easily cause the tool to break, and require the tool to have high fracture toughness; The coefficient is low, high temperature will be generated on the surface of the tool during cutting, and the tool material is required to have high high temperature hardness. 4 It contains many hard points such as carbides and nitrides, which are easy to wear and require good resistance. Grinding. Due to the third and fourth points, the tool material can be selected from cemented carbide or ceramic, but the two materials have lower strength, higher brittleness and easy breakage. Especially in the processing of spray (heap) welding of nickel-based alloys, due to the serious surface roughness, it is interrupted cutting. Among the two types of tools, ceramic tools are more susceptible to breakage, but even if applied properly, even ceramic tools are fully qualified.
Measures to Solve Tool Breakage The following is an example of how to prevent tool breakage by using end milled nickel-based alloy as an example. The workpiece is a well valve gate valve plate, and a nickel-based alloy is sprayed on the surface of the steel substrate. The composition is: C O.5～1.0%, Fe 10～13%, Cr 9～12%, B 3.0～ 4.0%, Si 2.5 to 3.5%, Ni balance. The hardness of the spray-welded nickel-based alloy is 50 to 55 HRC. The workpiece is a rectangular flat plate with a milling area of ​​184 x 85 mm2. The surface of the spray welding is extremely rough, and the height difference is 1 to 1.5 mm. It is machined on X53 vertical milling machine with Ø200mm face milling cutter. The single-tooth, blade is a silicon nitride blade developed by Shanghai Silicate Research Institute. The size is 16×16×4.5mm. It is clamped in the milling cutter by mechanical clamping method. On the plate.
Cutting with a negative rake angle: The choice of the rake angle is the key to solving the chipping. Since the blade has an axial rake angle of 4° and a radial rake angle of 0°, when the main declination is 45°, if the rake angle of the blade itself is 0°, the actual rake angle of the cutting edge after installation is 2.8. °. To protect the cutting edge, a negative chamfer with a width of 0.1 mm should be ground with a negative chamfering rake angle of -30°. Since the contact length of the nickel-base alloy and the rake face is large, the main cutting action is the rake face after the negative chamfering. When the blade itself is 0° front angle, it is actually cut in the form of positive rake angle. Under such heavy impact load, the blade strength is obviously insufficient. At a cutting speed of 47 m/min, whether the milling depth is reduced from 1.0 mm to 0.5 mm or 0.3 mm, the feed rate is reduced from 0.31 mm/tooth to 0.2 or O.12 mm/tooth, or YG6 cemented carbide is used. Blades, or higher-strength hot-pressed silicon nitride blades, do not solve the chipping problem. Only when the front corner of the blade itself is sharpened to -10° or a 15°, the stress distribution state in the tool is improved, and the chipping can be effectively prevented.
Control cutting speed: If the cutting speed is not properly selected, that is, a negative rake angle is used, and chipping still occurs. If the above processing conditions are used, at the cutting speed of 47m/min, there is no chipping in the milling stroke; but when the cutting speed is increased to 60m/min, although the other conditions are the same, the milling is less than one stroke, the cutter The tooth collapsed. As the cutting speed is increased, the impact load is also increased, so that the chipping is inevitable. Milling spray-welded nickel-base alloy is different from milling gray cast iron. When milling gray cast iron, when the milling depth is ap=1mm and the feed rate is 0.787mm/tooth, even if the cutting speed is increased to v=589m/min, it will not collapse. blade
Cutting difficult materials with silicon nitride ceramic tools
Cutting chilled cast iron chilled cast iron has high hardness, rough surface, and there are casting defects such as blisters and pores. The machining allowance is large. Generally, the cutting depth is large when roughing, and there is a large impact load. Quite harsh, it is still difficult to rough the car with ceramic tools. Usually, the outer circumference of the car is roughened with a cemented carbide tool, leaving a margin of about 0.3 mm (single side), and then semi-finishing with a silicon nitride ceramic tool.