Because cutting tools generate high temperatures during machining and reduce the tool life, the actual cutting speed is low. Various cutting tool materials need to combine high cutting performance and high life. High-speed steel and carbide are most common.
High-speed steel has very good strength and toughness, but its high temperature performance is generally. Tungsten carbide is generally preferred to high speed steel because of its higher hardness and its ability to maintain its hardness at high cutting temperatures.
Specifically pointed out, the cutting speed of carbide cutting tools can be at least 4 times higher than high-speed steel cutting tools, and has a longer tool life. However, compared with high-speed steel, the fracture toughness of cemented carbide is low, which limits its application in some processes, especially tapping.
Unlike most turning, milling and drilling tools, the inherent processing of tapping determines its relatively weak cutting edge and cross-section. The cutting edge can easily collapse or break, causing the tool to fail, even in the case of relatively easy-to-machine materials such as steel.
In low-carbon steel processing, long, continuous chips can clog the tap flutes, limiting carbide taps to only those materials that are easier to machine than steel, such as aluminum and cast iron.
Steel and other ferrous materials are the most commonly used materials for threaded joints. This also means that carbide cutting tools will have more potential advantages than high speed steels if they can solve the problems of chipping and cracking.
The accuracy of the internal thread of rigid tapping determines the accuracy of the thread itself and the precision of the thread fit.
When tapping a tapped hole, the tap is usually driven by a drill press or the tap is placed on a machine tool with a floating tapping chuck to rotate the tap and the feed rate is approximately equal to the pitch value of the internal thread.
In previous flexible tapping equipment, the feed was only an approximation. The pitch of the thread after machining was determined by the pitch of the tap, but the error between the feed of the machine and the pitch of the tap was caused by a floating attack. The wire chucks are adjusted for coordination. The axial direction of the floating tapping chuck has a certain amount of expansion and contraction. As long as the error accumulated between the feed of the machine tool and the pitch of the tap does not exceed this amount of expansion and contraction, the machining can be performed normally without causing any clasp (or " Bad teeth").
In addition, tapping chucks allow the tap to oscillate in the radial direction during tapping, which reduces the accuracy of the threading process. These conditions can lead to extremely low rigidity and uneven tapping loads.
It is well-known that the successful use of carbide tools usually requires high machine rigidity and uniform feed. The development of materials for CNC cutters from high-speed steels to harder materials such as cemented carbides can increase processing speeds, but brittleness is also avoided. The development of science and technology has not yet enabled us to economically obtain cutting tool materials that can both take into account high hardness and high toughness. Therefore, we must consider how to maintain the rigidity of the tool and how to control the feed in order to avoid high brittle tool materials during processing. Normally damaged.
For most machining methods, these are no longer a major issue for the use of carbide cutting tool materials, but for tapping, this is an issue that must be considered.
Today's CNC machine control technology has long been developed to maintain spindle rotation and feed synchronization, eliminating the need for floating tapping chucks. In the past, CNC machine control, the machine can reach a stable speed when the two synchronization can be achieved, but in the start and stop phase can not be synchronized - disorderly buckle often occurs at this time.
In addition, when gripping other tools that rotate the shank, such as carbide drills and end mills with precision shanks, the technology has evolved into chucks that can be heated and expanded first and then shrunk. This allows the shank of the tool to fit tightly and transmit sufficient torque. There is also a chuck that uses hydraulic pressure to grip the shank of the tool, which can also transmit a large amount of torque.
Another advantage of using thermal expansion and hydraulic chucks is that they have very little radial runout compared to the tapping head when gripping the tool: for example, the chuck can rotate at a concentricity of 3 μm or more Small, these methods can also be used to hold a cylindrical shank and have a higher clamping force and rigidity.
The powerful TGHP precision chucks with high clamping force, although they do not have the same accuracy as thermal expansion and hydraulic chucks, are effectively used in tapping.
The creation of such conditions of use has resulted in a smaller radial run-out and a higher rigidity of the carbide taps, resulting in the possibility of machining threads that far exceed the cutting speed of the high-speed steel cones.
However, since the current taps are used with flexible tapping heads, the size of the expression of the amount of run-out does not need to be limited to a strict tolerance. For example, a high-speed wire cone with a 0.5 inch (12.7 mm) thread diameter can achieve an industry standard for eccentricity of the drill shank of up to 20μ (0.0008 inch).
In addition, we do not need to strictly control the thread diameter and the concentricity of the cutting cone and tap shank.
Solid Carbide Taps Amplify New High-Performance Carbide Tap Designs In order to take full advantage of the advantages of carbide, a new tap fully exploits the advantages of rigid tapping machines and high-precision tool chucks.
As with precision drills and end mills, the shank of the tap is also completely cylindrical, but unlike the current high speed steel cones, the shank diameter is a common size.
For example, the shank diameter of the new unified threading UNF1/4-20 carbide tap is 0.25 inch (6.35 mm), and the 0.201 inch (5.1 mm) high precision cemented carbide commonly used to machine UNF 1/4-20. The shank diameter of the screw drill is the same.
In order to make full use of hot-fit, hydraulic or precision chucks, the diameter deviation of the shank is maintained at h6 of the German Industrial Standard 7160.
For example, a 0.5 inch (12.7 mm) shank has a diameter tolerance of -0.0110 mm (-0.000040 in.) and a roundness of 3 μm (0.00012 inch.).
The square head is not necessary because when the shank diameter is within the specified tolerances, these chucks have sufficient clamping force to meet the tapping needs.
Further, the concentricity of the threaded portion of the new tap and the cutting cone to the shank is within 10 μm. The use of high-precision chucks can create a completely rigid process system and reduce the amount of bouncing of the tap, meeting the two conditions for successful use of carbide taps: rigid and uniform loads.
Together with good rigidity and neutrality, a newly developed carbide grain with excellent characteristics, tap geometry and PVD coating greatly increase tapping speed and service life!
For Kennametal, two materials are used for tapping. Among them, KC7542 is specially designed for processing new steel taps and cast iron taps. It is coated with a newly developed nano-TiAlN coating on a high-strength cemented carbide substrate. This new tap guarantees the strength of the cutting edge and Wear resistance. The KC7512 is used to machine aluminum and other non-ferrous metals. The material consists of a wear-resistant cemented carbide substrate and a two-layer coating, where TiN is the coating on the substrate and CrC/C (chromium carbide) is the coating on the surface. Floor. In the processing of non-ferrous metals, the outermost coating has a small coefficient of friction, which prevents scales and built-up edges.
The performance of carbide taps in rigid tapping advances in the design of machine tools, tapping chucks and cutting tools. The well-designed carbide taps are not only used for "short-cutting" materials such as aluminum and cast iron, but are now starting to be used for the first time. Applied to "long chip" materials, including carbon steel, alloy steel and tool steel.
In the "short chip" material, nodular cast iron, malleable cast iron, and gray cast iron. These carbide taps can be successfully machined with the above mentioned metallic materials within the specified speed range. The cutting speed can be up to 4 times that of high-performance high-speed steel coated taps, thereby substantially improving the production efficiency.
It is worth noting that not all CNC machines can achieve rigid tapping when machining blind holes. Because the tap and the spindle must all decelerate when they reach the bottom of the hole, a pitch error may occur during the reversal. The thrust on the tap will increase the size of the tap. In the process of deceleration during the machining of blind holes, the tap is still in the workpiece, the tap is reversed and re-accelerated, and the tap speed must be reduced to 40% of the recommended machining speed listed in the table above.
When the tap spindle rotates, not all CNC machines can be considered synchronous or rigid, so that the feed is equal to the pitch, but a large number of tap holders with compensation have been used in rigid tapping. These chucks allow slight axial movement to compensate for errors.
The chuck of the "sub-rigid" tap allows a certain amount of axial movement but it has a very high rotational stiffness and can achieve better results with carbide taps. Because they were already on the market two years ago, these taps have been extensively tested. Manufacturers have changed their tapping processes to take advantage of the new carbide taps. The cutting technology website believes that because the pitch of the tap will always have some manufacturing errors, the axial feed of the machine tool will not be exactly the same. The error of the two will make one side of the tap shape bear more than the other side. A large load, thereby accelerating the wear of the tap. Therefore, using a small amount of compensation (for example, ±0.2mm) can effectively solve this problem, which is more significant for hard alloy taps with relatively large brittleness.
For example, when an automated component supplier supplied the KC7542 Tap A536 ductile iron, the tapping speed could be increased from 110 feet per minute (33m/min) to 400 feet per minute (122m/min), reducing the tapping cycle by 65 %. The life of the tap has also been increased to 40,000 holes (4 times that of powder metallurgy high-speed steel cones), and the total tapping cost has been reduced by 66% when considering the cost of processing machine tools and tools.
Another manufacturer discovered that the new KC7512 carbide tap can process 310 feet per minute (94.5m/min) when machining silicon-aluminum alloy brake elements, and can increase the life of the tap more than 3 times to 300,000 hole. In this case, the manufacturer's tapping costs were reduced by 49%.
Conclusion With the development of machine tools, control technology, tapping chucks and carbide tapping material levels, the design target range of taps has exceeded that of conventional materials that can be processed, including not only aluminum and cast iron, but also carbon and alloy steels for the first time. . The new carbide taps have a cylindrical shank and high tolerances that can be used for hot-fitting, hydraulic or ER, or higher-precision TGHP fixtures (with high clamping force), can be rigid or Synchronous tapping on a CNC machine.
High-speed steel has very good strength and toughness, but its high temperature performance is generally. Tungsten carbide is generally preferred to high speed steel because of its higher hardness and its ability to maintain its hardness at high cutting temperatures.
Specifically pointed out, the cutting speed of carbide cutting tools can be at least 4 times higher than high-speed steel cutting tools, and has a longer tool life. However, compared with high-speed steel, the fracture toughness of cemented carbide is low, which limits its application in some processes, especially tapping.
Unlike most turning, milling and drilling tools, the inherent processing of tapping determines its relatively weak cutting edge and cross-section. The cutting edge can easily collapse or break, causing the tool to fail, even in the case of relatively easy-to-machine materials such as steel.
In low-carbon steel processing, long, continuous chips can clog the tap flutes, limiting carbide taps to only those materials that are easier to machine than steel, such as aluminum and cast iron.
Steel and other ferrous materials are the most commonly used materials for threaded joints. This also means that carbide cutting tools will have more potential advantages than high speed steels if they can solve the problems of chipping and cracking.
The accuracy of the internal thread of rigid tapping determines the accuracy of the thread itself and the precision of the thread fit.
When tapping a tapped hole, the tap is usually driven by a drill press or the tap is placed on a machine tool with a floating tapping chuck to rotate the tap and the feed rate is approximately equal to the pitch value of the internal thread.
In previous flexible tapping equipment, the feed was only an approximation. The pitch of the thread after machining was determined by the pitch of the tap, but the error between the feed of the machine and the pitch of the tap was caused by a floating attack. The wire chucks are adjusted for coordination. The axial direction of the floating tapping chuck has a certain amount of expansion and contraction. As long as the error accumulated between the feed of the machine tool and the pitch of the tap does not exceed this amount of expansion and contraction, the machining can be performed normally without causing any clasp (or " Bad teeth").
In addition, tapping chucks allow the tap to oscillate in the radial direction during tapping, which reduces the accuracy of the threading process. These conditions can lead to extremely low rigidity and uneven tapping loads.
It is well-known that the successful use of carbide tools usually requires high machine rigidity and uniform feed. The development of materials for CNC cutters from high-speed steels to harder materials such as cemented carbides can increase processing speeds, but brittleness is also avoided. The development of science and technology has not yet enabled us to economically obtain cutting tool materials that can both take into account high hardness and high toughness. Therefore, we must consider how to maintain the rigidity of the tool and how to control the feed in order to avoid high brittle tool materials during processing. Normally damaged.
For most machining methods, these are no longer a major issue for the use of carbide cutting tool materials, but for tapping, this is an issue that must be considered.
Today's CNC machine control technology has long been developed to maintain spindle rotation and feed synchronization, eliminating the need for floating tapping chucks. In the past, CNC machine control, the machine can reach a stable speed when the two synchronization can be achieved, but in the start and stop phase can not be synchronized - disorderly buckle often occurs at this time.
In addition, when gripping other tools that rotate the shank, such as carbide drills and end mills with precision shanks, the technology has evolved into chucks that can be heated and expanded first and then shrunk. This allows the shank of the tool to fit tightly and transmit sufficient torque. There is also a chuck that uses hydraulic pressure to grip the shank of the tool, which can also transmit a large amount of torque.
Another advantage of using thermal expansion and hydraulic chucks is that they have very little radial runout compared to the tapping head when gripping the tool: for example, the chuck can rotate at a concentricity of 3 μm or more Small, these methods can also be used to hold a cylindrical shank and have a higher clamping force and rigidity.
The powerful TGHP precision chucks with high clamping force, although they do not have the same accuracy as thermal expansion and hydraulic chucks, are effectively used in tapping.
The creation of such conditions of use has resulted in a smaller radial run-out and a higher rigidity of the carbide taps, resulting in the possibility of machining threads that far exceed the cutting speed of the high-speed steel cones.
However, since the current taps are used with flexible tapping heads, the size of the expression of the amount of run-out does not need to be limited to a strict tolerance. For example, a high-speed wire cone with a 0.5 inch (12.7 mm) thread diameter can achieve an industry standard for eccentricity of the drill shank of up to 20μ (0.0008 inch).
In addition, we do not need to strictly control the thread diameter and the concentricity of the cutting cone and tap shank.
Solid Carbide Taps Amplify New High-Performance Carbide Tap Designs In order to take full advantage of the advantages of carbide, a new tap fully exploits the advantages of rigid tapping machines and high-precision tool chucks.
As with precision drills and end mills, the shank of the tap is also completely cylindrical, but unlike the current high speed steel cones, the shank diameter is a common size.
For example, the shank diameter of the new unified threading UNF1/4-20 carbide tap is 0.25 inch (6.35 mm), and the 0.201 inch (5.1 mm) high precision cemented carbide commonly used to machine UNF 1/4-20. The shank diameter of the screw drill is the same.
In order to make full use of hot-fit, hydraulic or precision chucks, the diameter deviation of the shank is maintained at h6 of the German Industrial Standard 7160.
For example, a 0.5 inch (12.7 mm) shank has a diameter tolerance of -0.0110 mm (-0.000040 in.) and a roundness of 3 μm (0.00012 inch.).
The square head is not necessary because when the shank diameter is within the specified tolerances, these chucks have sufficient clamping force to meet the tapping needs.
Further, the concentricity of the threaded portion of the new tap and the cutting cone to the shank is within 10 μm. The use of high-precision chucks can create a completely rigid process system and reduce the amount of bouncing of the tap, meeting the two conditions for successful use of carbide taps: rigid and uniform loads.
Together with good rigidity and neutrality, a newly developed carbide grain with excellent characteristics, tap geometry and PVD coating greatly increase tapping speed and service life!
For Kennametal, two materials are used for tapping. Among them, KC7542 is specially designed for processing new steel taps and cast iron taps. It is coated with a newly developed nano-TiAlN coating on a high-strength cemented carbide substrate. This new tap guarantees the strength of the cutting edge and Wear resistance. The KC7512 is used to machine aluminum and other non-ferrous metals. The material consists of a wear-resistant cemented carbide substrate and a two-layer coating, where TiN is the coating on the substrate and CrC/C (chromium carbide) is the coating on the surface. Floor. In the processing of non-ferrous metals, the outermost coating has a small coefficient of friction, which prevents scales and built-up edges.
The performance of carbide taps in rigid tapping advances in the design of machine tools, tapping chucks and cutting tools. The well-designed carbide taps are not only used for "short-cutting" materials such as aluminum and cast iron, but are now starting to be used for the first time. Applied to "long chip" materials, including carbon steel, alloy steel and tool steel.
In the "short chip" material, nodular cast iron, malleable cast iron, and gray cast iron. These carbide taps can be successfully machined with the above mentioned metallic materials within the specified speed range. The cutting speed can be up to 4 times that of high-performance high-speed steel coated taps, thereby substantially improving the production efficiency.
It is worth noting that not all CNC machines can achieve rigid tapping when machining blind holes. Because the tap and the spindle must all decelerate when they reach the bottom of the hole, a pitch error may occur during the reversal. The thrust on the tap will increase the size of the tap. In the process of deceleration during the machining of blind holes, the tap is still in the workpiece, the tap is reversed and re-accelerated, and the tap speed must be reduced to 40% of the recommended machining speed listed in the table above.
When the tap spindle rotates, not all CNC machines can be considered synchronous or rigid, so that the feed is equal to the pitch, but a large number of tap holders with compensation have been used in rigid tapping. These chucks allow slight axial movement to compensate for errors.
The chuck of the "sub-rigid" tap allows a certain amount of axial movement but it has a very high rotational stiffness and can achieve better results with carbide taps. Because they were already on the market two years ago, these taps have been extensively tested. Manufacturers have changed their tapping processes to take advantage of the new carbide taps. The cutting technology website believes that because the pitch of the tap will always have some manufacturing errors, the axial feed of the machine tool will not be exactly the same. The error of the two will make one side of the tap shape bear more than the other side. A large load, thereby accelerating the wear of the tap. Therefore, using a small amount of compensation (for example, ±0.2mm) can effectively solve this problem, which is more significant for hard alloy taps with relatively large brittleness.
For example, when an automated component supplier supplied the KC7542 Tap A536 ductile iron, the tapping speed could be increased from 110 feet per minute (33m/min) to 400 feet per minute (122m/min), reducing the tapping cycle by 65 %. The life of the tap has also been increased to 40,000 holes (4 times that of powder metallurgy high-speed steel cones), and the total tapping cost has been reduced by 66% when considering the cost of processing machine tools and tools.
Another manufacturer discovered that the new KC7512 carbide tap can process 310 feet per minute (94.5m/min) when machining silicon-aluminum alloy brake elements, and can increase the life of the tap more than 3 times to 300,000 hole. In this case, the manufacturer's tapping costs were reduced by 49%.
Conclusion With the development of machine tools, control technology, tapping chucks and carbide tapping material levels, the design target range of taps has exceeded that of conventional materials that can be processed, including not only aluminum and cast iron, but also carbon and alloy steels for the first time. . The new carbide taps have a cylindrical shank and high tolerances that can be used for hot-fitting, hydraulic or ER, or higher-precision TGHP fixtures (with high clamping force), can be rigid or Synchronous tapping on a CNC machine.
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