Recent advances in the design and use of PCBN (polycrystalline cubic boron nitride) and PCD (polycrystalline diamond) cutting tools have provided new incentives for manufacturers in different industries to increase productivity. For example, the automotive industry's use of new large-particle monolithic PCBN inserts makes it possible to efficiently machine hard-to-machine alloy cast iron, which was previously only possible by grinding.
“Increased granularity in the latest overall PCBN grade has significantly improved performance,†said David Huddle, Detroit Seco Carboloy Advanced Materials Product Manager. “The larger PCBN particle size improves wear resistance and impact resistance, which is highly processed like iron. Cast iron materials with a eutectic content of less than 10% are critical.†Huddle explains that good impact toughness when roughing these parts is important to withstand cracks, blisters and other defects left in the casting process. Very good wear resistance is required for finishing, because the parts contain 28% to 30% chromium and the hardness is between 68 and 72 Rockwell.
The latest PCBN blades also offer better reliability and economy. The blade thickness is increased from the traditional 3.18mm to 4.76mm and can be safely mounted on a standard carbide insert with a knife holder. In addition, the monolithic PCBN structure provides multiple cutting edges on both sides, reducing the cost of dispensing the blades to each part.
In addition to this new type of integral thick blade, today's PCBN inserts are also available in "surface sintered" and "insert" versions. The surface sintered type is to sinter a complete PCBN surface on a cemented carbide substrate. The most widely used PCBN inserts are the less expensive inserts. This type of insert is a small piece of PCBN that is welded to the corner of the carbide insert and typically provides one or two cutting edges. Both surface sintered and insert types meet industry standard specifications. Like the latest monolithic inserts, they can be mounted on the holders of standard carbide shanks and milling cutters.
Cutting conditions and parameters According to Carboloy's Huddle, cutting hard parts with PCBN is best suited for parts with a Rockwell hardness value of 45 or higher. “That’s the lower limit of practical work that most people in the industry recognize,†he said. “We don't say that you can't use PCBN to machine lower hardness parts, but in those applications the guillotine wear on the rake face is a problem.â€
For PCBN roughing, the maximum depth of cut of the blade is: white cast iron and other hard high chromium cast irons of about 4.76mm, and chromium-free "clean" cast irons up to 6.35mm. The line speed of finishing is from 105~120m/min for processing high chromium cast iron to 2100m/min for processing gray cast iron. Huddle emphasizes that there must be a solid configuration for all PCBN processing. “It usually includes the tool itself, the fixture, the machine spindle and the machine itself.â€
Huddle says that the right PCBN finishing speed will vary dramatically depending on the material of the workpiece, the hardness of the material, and the shape of the part. “When processing hardened steel with a Rockwell hardness range of 60 to 62, the line speed can reach 180 m/min at a depth of cut of 0.5 mm,†he suggested. When the feed amount is in the range of 0.05 to 0.1 mm/r, a good finish of less than 0.3 μm is usually obtained. When processing a slightly harder material, it can be cut faster, but even then, the upper limit is about a line speed of 200 m/min, above which the wear is exacerbated. Obviously, the cutting speed can be much faster when processing ordinary cast iron.
Choosing the Right Blade Type Huddle said that another important thing in PCBN machining is the right choice for monolithic, surface-sintered, insert-to-blade inserts. “PCBN insert inserts are both economical and reliable in a wide range of rough finishing applications, but some applications are certainly better with monolithic or surface sintered.â€
Huddle said that a cylinder liner with a cast flash in the middle of the rough is an example. “If you use a insert blade here, even if the depth of cut is completely correct, the flash edge will inevitably deviate from the PCBN part. This is generally not the case with a more solid monolithic or surface-sintered PCBN insert.†Surface-sintered inserts also have the benefit of regrind, and continued use offsets the high cost of the initial investment.
Huddle emphasizes that monolithic or surface-sintered PCBN inserts are well-suited for use with flash liners and add misleading instructions. “Integrated inserts have higher initial costs. For cost-effective use, you have to make sure The application allows you to use two-sided cutting edges."
At present, the biggest growth of PCBN blade applications is hard turning, especially for automobile engine parts such as gears, shafts, bearings and other alloy steel materials with hardness between 60 and 65. “These parts are traditionally ground to a very high dimensional accuracy and high finish,†Huddle explains. The same effect can be achieved with a CNC lathe, and the cost of a CNC lathe is only half that of a CNC grinding machine, and the maintenance cost is much lower than that of a CNC grinding machine.
The lower-priced PCBN inserts can be used for these hard turning operations because the depth of cut is shallow, between 0.3 and 0.38 mm. When Carboloy tested itself with insert inserts, the surface finish of hardened steel parts with a Rockwell hardness of 60-62 was consistently maintained at 0.3 μm or less.
Optimizing PCBN Applications Generally speaking, PCBN processing should be dry cutting. “The PCBN material is hard enough to resist the deformation caused by heat generation, but it is also brittle until the thermal shock of the coolant creates cracks,†Huddle said. “Especially in the case of interrupted cutting. PCBN machining with interrupted cutting must never use coolant.â€
Blade edge grinding is another processing condition that strongly affects the success of PCBN processing. Huddle explained: “Remember that the PCBN insert is a small piece of hard and brittle cutting material that will be used to machine workpiece materials with a Rockwell hardness of 62.â€
In order to achieve the desired tool life, the cutting edge of the PCBN insert must be reinforced with the correct cutting edge. For finishing cast iron, only a small honing is required, and for heavy-duty roughing of white cast iron, there is a negative chamfer with a width of 3.8 mm at a 15 degree angle. A combination of negative chamfering and honing may also be used. “The cutting edge is increased and strengthened by adding a negative chamfer on the insert,†Huddle explained. “For example, the starting value of the tool nose angle is 90 degrees plus the negative chamfering of 20 degrees. Now the tool nose angle becomes 110 degrees. The larger the tool nose angle, the stronger the cutting edge will be.â€
The general principle of properly grinding a PCBN insert is to maintain the angle of the negative chamfer proportional to the hardness of the workpiece material, as the cutting edge will reinforce the cutting force. Therefore, slight honing during machining of cast iron is suitable for finishing, and a negative chamfer with a 20 degree angular width of 0.02 mm is appropriate for roughing. For steel parts with a hardness of 65 degrees Rough, a reasonable negative chamfer range is 0.01 to 0.02 mm wide and X 20 degrees.
Roughening of aluminum with PCD As with PCBN, the use of PCD (polycrystalline diamond) inserts is growing, albeit not because of the development of the cutting material itself. "People have gone beyond the troubles of stickys 5 to 10 years ago," Huddle said. “Today, they expect PCD blades to outperform carbides in terms of economy because they know that these blades dramatically exceed the performance of cemented carbides in most non-ferrous applications.â€
Most of the PCD inserts used today are "insert" type, which means they contain a small piece of polycrystalline diamond welded to the corner of the carbide insert. The insert inserts are factory-standard, so they can be mounted on the holders of standard carbide shanks and milling cutters. But unlike carbide inserts, insert PCD inserts are not indexable. They only provide one cutting edge.
PCD inserts also have a standardized "surface sintered" type in which a full-face polycrystalline diamond is sintered onto a cemented carbide substrate. The surface sintered type has a higher initial cost, but can be indexed on one side to provide multiple cutting edges. The blades that are commonly purchased are rounded to obtain the most effective cutting edge and are used primarily for special applications.
Huddle said that an important development in the use of PCD inserts is safer blade retention - especially for rotary tools. Today, you have a combination of wedges and screws that improve blade retention—even taper blades and wedges. You can also get a traditional screw or clamping design, or a direct mounting chuck type cutter with PCD tabs soldered directly to the card body. Rigid fixtures are equipped to give users more reliable results with PCD and help them take full advantage of the productivity potential of PCD.
Huddle said that safer part clamping has a similar effect on better machine and spindle rigidity, noting that today's CNC lathes and machining centers provide all the rigid demands for successful PCD or PCBN cutting tools. He further pointed out that as the economy grows, the number of new machine tools grows rapidly, providing a more friendly environment for the use of high-performance PCD and PCBN cutting tools.
An interesting example of today's PCD applications is the finishing of aluminum alloy automotive intake manifolds. According to Huddle, in these applications the cutterheads typically combine a PCD insert blade with a conventional carbide insert to resist the casting of the flash on the blade. The flash has a tendency to separate the intersection of the PCD cutter head and the carbide carrier, creating the risk of eventually causing displacement of the PCD cutter head.
“The maximum depth of cut designed for PCD insert inserts for milling is approximately 60% of the length of the PCD cutter head,†explains Huddle. “You may have a deeper cut to the PCD head or a little less, but in the case of a flash, you still have the risk of the PCD head being displaced from the blade.†Huddle says the remedy is to adjust the cutter. The disc slightly offsets some of the conventional cemented carbide inserts up and down in the axial and radial directions. The carbide insert will cut the flash edge immediately before the finished PCD insert.
Another major use of PCD insert inserts is the roughing of automotive parts called “granulationâ€. “In order to save on transportation costs and to recover aluminum alloy chips, this is done well by foundries like aluminum cylinder heads,†Huddle said. “At the machining site, PCD is used for semi-finishing of the top, bottom and side of the cast parts with a high metal removal rate. All this is done very quickly. Then, the chips are recycled to the foundry – the machined parts are The rectangular shape makes them easy to handle and package. The parts are also small, so they take up less space and can be transported at a lower cost."
“In fact, PCD insert blades are increasingly being used to process a wide variety of high silicon aluminum parts,†Huddle said. In the automotive industry, they include cylinder heads, cylinder blocks, intake manifolds, gearboxes and a large variety of aluminum wheels. Applications also extend to other industries such as home appliances, medical equipment and aviation. Huddle explained that the range of parts covered is familiar with everything from washing machine parts to lawn mower bodies used in the home gardening industry.
Huddle said that in order to replace cemented carbide with PCD in these applications, manufacturers are looking for higher productivity, as well as eliminating the need for longer tool life and part finish requirements for frequent tool changes. He pointed out that to achieve these benefits, good chip evacuation is a key condition.
“The chip generation after PCD is so fast that you have to have an effective way to get them out of the work area continuously,†Huddle said. “You can use coolant, air, oil mist, cooling air or any combination. Before using any method, you need to ensure good part quality and blade life.â€
Huddle says that with effective chip evacuation and rigid fixtures and machine tools, PCD cutting speeds of up to 3,000 meters per minute. “Today's CNC machining centers and turning centers are easy to produce the necessary spindle speeds.†To be clear, Huddle quoted the car factory's production line as a whole consisting of CNC machines. “One day they will use a PCBN and carbide tool to machine the cast iron cylinder block and another tool with PCD and carbide to machine the aluminum alloy cylinder block.â€
Finding different tooling techniques on the same machine is not straightforward. These days, more and more manufacturers are using both traditional and advanced cutting materials to make them the best and most economical for every object of the application.
“Increased granularity in the latest overall PCBN grade has significantly improved performance,†said David Huddle, Detroit Seco Carboloy Advanced Materials Product Manager. “The larger PCBN particle size improves wear resistance and impact resistance, which is highly processed like iron. Cast iron materials with a eutectic content of less than 10% are critical.†Huddle explains that good impact toughness when roughing these parts is important to withstand cracks, blisters and other defects left in the casting process. Very good wear resistance is required for finishing, because the parts contain 28% to 30% chromium and the hardness is between 68 and 72 Rockwell.
The latest PCBN blades also offer better reliability and economy. The blade thickness is increased from the traditional 3.18mm to 4.76mm and can be safely mounted on a standard carbide insert with a knife holder. In addition, the monolithic PCBN structure provides multiple cutting edges on both sides, reducing the cost of dispensing the blades to each part.
In addition to this new type of integral thick blade, today's PCBN inserts are also available in "surface sintered" and "insert" versions. The surface sintered type is to sinter a complete PCBN surface on a cemented carbide substrate. The most widely used PCBN inserts are the less expensive inserts. This type of insert is a small piece of PCBN that is welded to the corner of the carbide insert and typically provides one or two cutting edges. Both surface sintered and insert types meet industry standard specifications. Like the latest monolithic inserts, they can be mounted on the holders of standard carbide shanks and milling cutters.
Cutting conditions and parameters According to Carboloy's Huddle, cutting hard parts with PCBN is best suited for parts with a Rockwell hardness value of 45 or higher. “That’s the lower limit of practical work that most people in the industry recognize,†he said. “We don't say that you can't use PCBN to machine lower hardness parts, but in those applications the guillotine wear on the rake face is a problem.â€
For PCBN roughing, the maximum depth of cut of the blade is: white cast iron and other hard high chromium cast irons of about 4.76mm, and chromium-free "clean" cast irons up to 6.35mm. The line speed of finishing is from 105~120m/min for processing high chromium cast iron to 2100m/min for processing gray cast iron. Huddle emphasizes that there must be a solid configuration for all PCBN processing. “It usually includes the tool itself, the fixture, the machine spindle and the machine itself.â€
Huddle says that the right PCBN finishing speed will vary dramatically depending on the material of the workpiece, the hardness of the material, and the shape of the part. “When processing hardened steel with a Rockwell hardness range of 60 to 62, the line speed can reach 180 m/min at a depth of cut of 0.5 mm,†he suggested. When the feed amount is in the range of 0.05 to 0.1 mm/r, a good finish of less than 0.3 μm is usually obtained. When processing a slightly harder material, it can be cut faster, but even then, the upper limit is about a line speed of 200 m/min, above which the wear is exacerbated. Obviously, the cutting speed can be much faster when processing ordinary cast iron.
Choosing the Right Blade Type Huddle said that another important thing in PCBN machining is the right choice for monolithic, surface-sintered, insert-to-blade inserts. “PCBN insert inserts are both economical and reliable in a wide range of rough finishing applications, but some applications are certainly better with monolithic or surface sintered.â€
Huddle said that a cylinder liner with a cast flash in the middle of the rough is an example. “If you use a insert blade here, even if the depth of cut is completely correct, the flash edge will inevitably deviate from the PCBN part. This is generally not the case with a more solid monolithic or surface-sintered PCBN insert.†Surface-sintered inserts also have the benefit of regrind, and continued use offsets the high cost of the initial investment.
Huddle emphasizes that monolithic or surface-sintered PCBN inserts are well-suited for use with flash liners and add misleading instructions. “Integrated inserts have higher initial costs. For cost-effective use, you have to make sure The application allows you to use two-sided cutting edges."
At present, the biggest growth of PCBN blade applications is hard turning, especially for automobile engine parts such as gears, shafts, bearings and other alloy steel materials with hardness between 60 and 65. “These parts are traditionally ground to a very high dimensional accuracy and high finish,†Huddle explains. The same effect can be achieved with a CNC lathe, and the cost of a CNC lathe is only half that of a CNC grinding machine, and the maintenance cost is much lower than that of a CNC grinding machine.
The lower-priced PCBN inserts can be used for these hard turning operations because the depth of cut is shallow, between 0.3 and 0.38 mm. When Carboloy tested itself with insert inserts, the surface finish of hardened steel parts with a Rockwell hardness of 60-62 was consistently maintained at 0.3 μm or less.
Optimizing PCBN Applications Generally speaking, PCBN processing should be dry cutting. “The PCBN material is hard enough to resist the deformation caused by heat generation, but it is also brittle until the thermal shock of the coolant creates cracks,†Huddle said. “Especially in the case of interrupted cutting. PCBN machining with interrupted cutting must never use coolant.â€
Blade edge grinding is another processing condition that strongly affects the success of PCBN processing. Huddle explained: “Remember that the PCBN insert is a small piece of hard and brittle cutting material that will be used to machine workpiece materials with a Rockwell hardness of 62.â€
In order to achieve the desired tool life, the cutting edge of the PCBN insert must be reinforced with the correct cutting edge. For finishing cast iron, only a small honing is required, and for heavy-duty roughing of white cast iron, there is a negative chamfer with a width of 3.8 mm at a 15 degree angle. A combination of negative chamfering and honing may also be used. “The cutting edge is increased and strengthened by adding a negative chamfer on the insert,†Huddle explained. “For example, the starting value of the tool nose angle is 90 degrees plus the negative chamfering of 20 degrees. Now the tool nose angle becomes 110 degrees. The larger the tool nose angle, the stronger the cutting edge will be.â€
The general principle of properly grinding a PCBN insert is to maintain the angle of the negative chamfer proportional to the hardness of the workpiece material, as the cutting edge will reinforce the cutting force. Therefore, slight honing during machining of cast iron is suitable for finishing, and a negative chamfer with a 20 degree angular width of 0.02 mm is appropriate for roughing. For steel parts with a hardness of 65 degrees Rough, a reasonable negative chamfer range is 0.01 to 0.02 mm wide and X 20 degrees.
Roughening of aluminum with PCD As with PCBN, the use of PCD (polycrystalline diamond) inserts is growing, albeit not because of the development of the cutting material itself. "People have gone beyond the troubles of stickys 5 to 10 years ago," Huddle said. “Today, they expect PCD blades to outperform carbides in terms of economy because they know that these blades dramatically exceed the performance of cemented carbides in most non-ferrous applications.â€
Most of the PCD inserts used today are "insert" type, which means they contain a small piece of polycrystalline diamond welded to the corner of the carbide insert. The insert inserts are factory-standard, so they can be mounted on the holders of standard carbide shanks and milling cutters. But unlike carbide inserts, insert PCD inserts are not indexable. They only provide one cutting edge.
PCD inserts also have a standardized "surface sintered" type in which a full-face polycrystalline diamond is sintered onto a cemented carbide substrate. The surface sintered type has a higher initial cost, but can be indexed on one side to provide multiple cutting edges. The blades that are commonly purchased are rounded to obtain the most effective cutting edge and are used primarily for special applications.
Huddle said that an important development in the use of PCD inserts is safer blade retention - especially for rotary tools. Today, you have a combination of wedges and screws that improve blade retention—even taper blades and wedges. You can also get a traditional screw or clamping design, or a direct mounting chuck type cutter with PCD tabs soldered directly to the card body. Rigid fixtures are equipped to give users more reliable results with PCD and help them take full advantage of the productivity potential of PCD.
Huddle said that safer part clamping has a similar effect on better machine and spindle rigidity, noting that today's CNC lathes and machining centers provide all the rigid demands for successful PCD or PCBN cutting tools. He further pointed out that as the economy grows, the number of new machine tools grows rapidly, providing a more friendly environment for the use of high-performance PCD and PCBN cutting tools.
An interesting example of today's PCD applications is the finishing of aluminum alloy automotive intake manifolds. According to Huddle, in these applications the cutterheads typically combine a PCD insert blade with a conventional carbide insert to resist the casting of the flash on the blade. The flash has a tendency to separate the intersection of the PCD cutter head and the carbide carrier, creating the risk of eventually causing displacement of the PCD cutter head.
“The maximum depth of cut designed for PCD insert inserts for milling is approximately 60% of the length of the PCD cutter head,†explains Huddle. “You may have a deeper cut to the PCD head or a little less, but in the case of a flash, you still have the risk of the PCD head being displaced from the blade.†Huddle says the remedy is to adjust the cutter. The disc slightly offsets some of the conventional cemented carbide inserts up and down in the axial and radial directions. The carbide insert will cut the flash edge immediately before the finished PCD insert.
Another major use of PCD insert inserts is the roughing of automotive parts called “granulationâ€. “In order to save on transportation costs and to recover aluminum alloy chips, this is done well by foundries like aluminum cylinder heads,†Huddle said. “At the machining site, PCD is used for semi-finishing of the top, bottom and side of the cast parts with a high metal removal rate. All this is done very quickly. Then, the chips are recycled to the foundry – the machined parts are The rectangular shape makes them easy to handle and package. The parts are also small, so they take up less space and can be transported at a lower cost."
“In fact, PCD insert blades are increasingly being used to process a wide variety of high silicon aluminum parts,†Huddle said. In the automotive industry, they include cylinder heads, cylinder blocks, intake manifolds, gearboxes and a large variety of aluminum wheels. Applications also extend to other industries such as home appliances, medical equipment and aviation. Huddle explained that the range of parts covered is familiar with everything from washing machine parts to lawn mower bodies used in the home gardening industry.
Huddle said that in order to replace cemented carbide with PCD in these applications, manufacturers are looking for higher productivity, as well as eliminating the need for longer tool life and part finish requirements for frequent tool changes. He pointed out that to achieve these benefits, good chip evacuation is a key condition.
“The chip generation after PCD is so fast that you have to have an effective way to get them out of the work area continuously,†Huddle said. “You can use coolant, air, oil mist, cooling air or any combination. Before using any method, you need to ensure good part quality and blade life.â€
Huddle says that with effective chip evacuation and rigid fixtures and machine tools, PCD cutting speeds of up to 3,000 meters per minute. “Today's CNC machining centers and turning centers are easy to produce the necessary spindle speeds.†To be clear, Huddle quoted the car factory's production line as a whole consisting of CNC machines. “One day they will use a PCBN and carbide tool to machine the cast iron cylinder block and another tool with PCD and carbide to machine the aluminum alloy cylinder block.â€
Finding different tooling techniques on the same machine is not straightforward. These days, more and more manufacturers are using both traditional and advanced cutting materials to make them the best and most economical for every object of the application.
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