Most of the die steel is cut before heat treatment. It is mainly used for face milling and end milling of cavities, punches, and grooving. After cutting, heat treatment such as quenching and tempering is performed. At this time, the hardness can reach HRC50～ 60 or even higher. The high hardness can guarantee the wear resistance of the mold and prolong its service life. However, after the heat treatment, the parts are easily deformed, the materials become hard, and the processing performance is deteriorated. In order to achieve the final accuracy, only the grinding or even manual grinding can be used for finishing. . This processing method has low efficiency, long cycle, late delivery and high cost, and it is difficult to meet customer needs. At present, in fact, a situation has been formed in which a company can efficiently manufacture molds, shorten the delivery period and reduce the corresponding cost, and can expand the market, expand sales, and win the competition.
In order to meet the above requirements, people have changed their minds. Whether or not the material can be used for cutting after the heat treatment is hardened, especially if all types of cavities and profiles can also be processed with end mills, making them not only semi-smooth Machining, even for finishing, partial or complete "milling". The cutting volume of the cutting tool in the unit time is much larger than that of the grinding wheel, that is, its machining efficiency is much higher than that of grinding, and it can bring about in equipment investment, land occupation, environmental protection, and reducing the total cost. Many economic and social benefits. The following describes the improvements made by the integral end mill to meet the requirements for cutting hardened steel.
Development and Innovation of Tool Materials: CBN Material Begins to Be Used in Endmills
In recent years, when talking about car-generation grinding and milling and grinding of hardened steel, the first thing to think about is the use of cubic boron nitride (CBN) tool materials. The particle hardness of CBN reaches HV8000-9000, and the hardness of sintered body PCBN can reach HV3000 ~ 5000, heat resistance up to 1400 ~ 1500 °C. PCBN hardness at 800 °C is still higher than the hardness of ceramic and hard alloy at room temperature, it can be carbide 3 to 5 times the cutting speed for cutting, and its chemical stability is good, in the 1200 ~ 1300 °C high temperature, nor It reacts with iron-based materials and reacts with carbon at 2000°C. CBN's adhesion to various materials and its diffusion at high temperatures are also much smaller than cemented carbide, making it particularly suitable for processing steel materials. The thermal conductivity of CBN is 20 times that of cemented carbide, second only to diamond, and its thermal conductivity increases with temperature. The friction coefficient of CBN with different materials is only 0.1-0.3, and with the increase of cutting speed, the friction coefficient will decrease, while the friction coefficient of cemented carbide is 0.4-0.6.
Mitsubishi Materials has developed an end mill for CBN materials earlier. Its CBN-2XLB type R1x5 ball end mills (with a ball nose radius of 1mm and a neck length of 5mm) can be used at speeds of up to 20000r/min and 1700mm/min. The SKD11 die steel of 60HRC was milled with a depth of 0.05 mm (backing amount). After cutting 800 meters, the flank wears only 0.03mm. If the depth of cut is increased to 0.1 mm (ie, at a higher cutting load), after cutting 400 meters, the flank wear height is only 0.022 mm. Due to its high ball-end accuracy (R tolerance of ±5μm, outer diameter tolerance of 0 to 10μm), high machining accuracy, in order to maintain the same high accuracy, a CBN high-precision ball end mill can process the surface, if To use the same precision carbide ball end mill, you need 7 to 8.
When cutting hardened die steels, if CBN material is selected, although the price is more expensive, due to the high cutting speed, the machining time can be shortened, the tool life can be prolonged, and the product quality can be improved. Therefore, it may be more economical.
Of course, if you choose to use new tool materials, you may increase the processing cost if you disengage from the actual processing conditions (the price of CBN tools is about 6 to 10 times that of cemented carbide tools). In addition, the use of new tool materials, if the cutting conditions are not properly selected, will also affect the quality of processing and tool life. Therefore, the entire processing task should be evaluated, comprehensively weighed production batches, processing time, machine tools and tool performance. Under the premise of ensuring the processing quality, under the conditions of low cutting speed, the lower coating hardness can also be used. Alloy cutters can also achieve better machining results.
Coating Technology and New Developments in Cemented Carbide Materials
According to different application requirements, the hardness of hardened steel can reach HRC45-68. In order to smoothly cut the workpiece, the hardness of the cutting tool usually needs to be 3 to 5 times more than the hardness of the workpiece. The hardness of the coating is usually measured by Vickers hardness (Hv). Take Mitsubishi's product as an example, the hardness of the TiN coating end mill is Hv1900, and the hardness of the Mstar end mill with (Al,Ti)N coating is Hv2800. The hardness of the VC-type end mill with (Al,Ti,Si)N coating is Hv3200, and the recently developed Impact Miracle nano-grade (Al,Ti)N-coated VF end mill is further enhanced in hardness to Hv3700 It can be said that the hardness of PCBN is approaching. The oxidation initiation temperature and the coating adhesion force are further increased, and the friction coefficient is continuously decreasing. HRC68 is roughly equal to Hv940 when the HRC value is simply compared with the Hv value. Although the hardness values ​​are not related to the improvement of the hardness, it can be seen that the (Al,Ti)N coated Mstar end mill can be hardened and cut. The Impact Miracle-coated VF series end mills for steels with higher hardness and oxidation initiation temperatures can achieve better processing results.
Cutting Example of Impact Miracle-coated VF End Mills:
(1) High-speed steel SKH51 (M2) die (hardness HRC65) is machined with VF-2SB R1 ball end mill. The cutting amount is: 20,000 rev/min, feed rate 6000mm/min, 0.15mm/teeth, back The amount of knife is 0.07mm, the amount of side knife is 0.2mm, and the air is cold. After the cutting length reaches 30m, the tool has not been damaged.
(2) The tool steel SKDII (HRC60) was machined with a VF-MD φ6 right-angle end mill. The cutting rate was 8000 rpm, feed rate 2160 mm/min (0.045 mm/tooth), and air-cooled. After the cutting length reaches 100m, the tool has not been damaged.
(3) Using VF-2SB R3 ball end mill for machining hot-pressing die (material: DH315, hardness HRC52), cutting rate: 16000 rpm, feed rate 1600mm/min, feed per tooth 0.05mm/tooth, back blade (cut depth) 2mm, side blade 0.2mm, straight milling, air-cooled. Despite the toughness of the material, the tool was damaged after more than 120 meters of cutting.
(4) The powder metallurgy high-speed steel mold with HRC68 or more is cut with a VF-2SB R1 ball nose end mill. The cutting amount is: the rotational speed is 8000 rpm, the feed speed is 1260 mm/min, and the feed per tooth is 0.08 mm/teeth. The amount of back knife 0.2mm, side knife 0.07mm, air-cooled, followed by milling. The cutting length can reach more than 50 meters, which is several times longer than that of ordinary end mills.
(5) The tool steel SKDII (HRC60) was machined with VF-2SB R10 ball end mill, and the cutting amount was: 1200 rev/min, feed rate 240 mm/min, feed per tooth 0.1 mm/teeth, back feed Knife volume can be up to 8mm, knife side volume 0.5mm, followed by milling, air-cooled. Under such a large depth of cut, 30 meters can still be cut, which is 3 times that of the old product.
(6) The deep groove of the die is machined with a long-necked VF-2XLB R1×20 ball end mill. The material is SKDII (HRC60). The cutting amount is: the rotational speed is 10000 rpm, the feed rate is 1000 mm/min, and the per tooth The amount of 0.05mm / tooth, air-cooled, crushing. Reciprocating cutting length up to 20 meters, double the life expectancy of other similar products.
(7) Simultaneously machine the side and bottom of the hardened steel with hardness of HRC60 with VF-MD right-angle end mill, stable cutting, good surface quality, normal chip shape and color, cutting speed of 151m/min, per tooth With a feed rate of 0.1 mm/tooth, the bottom edge has good defect resistance and outer edge wear resistance.
(8) SKDII (60HRC) was machined with an arc head end mill VF-MDRB at a cutting speed of 50 m/min, a feed per tooth of 0.05 mm/tooth, a depth of cut of 0.5 mm, and a cut width of 8 mm, followed by milling, and air cooling. After a cutting length of 8 meters, the tool has almost no damage.
Milling Substrate Substrate Carbide Grain Ultrafine
End mill teeth are subjected to repeated impact loads during processing and therefore must have sufficient toughness. When cutting a hardened material, the cutting force is large and the toughness should be increased. Today, the hardness of the coating is getting higher and higher, the coating ensures the wear resistance of the tool when cutting hardened steel, and machinability and toughness are more depend on the matrix material to ensure. The substrate material of the coated cemented carbide end mills is mainly high toughness and good vibration resistance K type cemented carbide (the main component is WC). In order to improve the toughness, it is necessary to refine the WC crystal particles, the harder the coating surface, the more the crystal grains of the matrix should be refined, and the higher the performance of the hardened steel. Impact Miracle coating matrix material grain size up to 1μm, making it both wear resistance and toughness increased.
In order to adapt to the hardened steel processing, the structure of the end mill is improved
(1) Improvement of ball end mill structure: Make the two main blades form a point at the center of the top edge so as not to generate a chisel edge to reduce the cutting force, improve the cutting performance of the center part, eliminate the pinching phenomenon, and help to form and eliminate chips. There should be a smooth transition between the ball edge and the peripheral edge, no joint marks.
(2) Improvement of the right-angle end milling cutter and the circular-arc end mill on the bottom edge: making the bottom edge position staggered, easy to manufacture, improving the cutting conditions at the center of the bottom edge, and improving the groove shape to facilitate chip removal; Rounding improves the cutting edge resistance to the cutting of high hardness materials.
(3) In order to increase the lifespan and enhance the rigidity, the VF-2SSB type short-blade end mill has been specially designed. The overall length is also shorter and it is an end mill that is suitable for the sleeve-type clamping shank.
(4) In order to achieve "milling and grinding" and achieve high precision of grinding, the accuracy of the end mill itself must be improved. Mitsubishi's high-precision ball end mills have a ball nose radius R accuracy of ±0.002 mm and a diameter accuracy of 0 to 0.01 mm. Circular arc end milling cutter corner arc R accuracy of 0 ~ ± 0.01mm. If the group of endmills is divided into several groups according to the dimensional tolerances within the range of the diameter tolerance, the grouping size tolerance will inevitably be reduced, and the machining accuracy of the end mills of each group will be improved. With such a high-precision end mill, the precision The side of the processing mold can reach a high precision of ± 0.005mm, thus realizing efficient and high-precision machining of the mold with an end mill, completely eliminating the grinding process.
In order to meet the above requirements, people have changed their minds. Whether or not the material can be used for cutting after the heat treatment is hardened, especially if all types of cavities and profiles can also be processed with end mills, making them not only semi-smooth Machining, even for finishing, partial or complete "milling". The cutting volume of the cutting tool in the unit time is much larger than that of the grinding wheel, that is, its machining efficiency is much higher than that of grinding, and it can bring about in equipment investment, land occupation, environmental protection, and reducing the total cost. Many economic and social benefits. The following describes the improvements made by the integral end mill to meet the requirements for cutting hardened steel.
Development and Innovation of Tool Materials: CBN Material Begins to Be Used in Endmills
In recent years, when talking about car-generation grinding and milling and grinding of hardened steel, the first thing to think about is the use of cubic boron nitride (CBN) tool materials. The particle hardness of CBN reaches HV8000-9000, and the hardness of sintered body PCBN can reach HV3000 ~ 5000, heat resistance up to 1400 ~ 1500 °C. PCBN hardness at 800 °C is still higher than the hardness of ceramic and hard alloy at room temperature, it can be carbide 3 to 5 times the cutting speed for cutting, and its chemical stability is good, in the 1200 ~ 1300 °C high temperature, nor It reacts with iron-based materials and reacts with carbon at 2000°C. CBN's adhesion to various materials and its diffusion at high temperatures are also much smaller than cemented carbide, making it particularly suitable for processing steel materials. The thermal conductivity of CBN is 20 times that of cemented carbide, second only to diamond, and its thermal conductivity increases with temperature. The friction coefficient of CBN with different materials is only 0.1-0.3, and with the increase of cutting speed, the friction coefficient will decrease, while the friction coefficient of cemented carbide is 0.4-0.6.
Mitsubishi Materials has developed an end mill for CBN materials earlier. Its CBN-2XLB type R1x5 ball end mills (with a ball nose radius of 1mm and a neck length of 5mm) can be used at speeds of up to 20000r/min and 1700mm/min. The SKD11 die steel of 60HRC was milled with a depth of 0.05 mm (backing amount). After cutting 800 meters, the flank wears only 0.03mm. If the depth of cut is increased to 0.1 mm (ie, at a higher cutting load), after cutting 400 meters, the flank wear height is only 0.022 mm. Due to its high ball-end accuracy (R tolerance of ±5μm, outer diameter tolerance of 0 to 10μm), high machining accuracy, in order to maintain the same high accuracy, a CBN high-precision ball end mill can process the surface, if To use the same precision carbide ball end mill, you need 7 to 8.
When cutting hardened die steels, if CBN material is selected, although the price is more expensive, due to the high cutting speed, the machining time can be shortened, the tool life can be prolonged, and the product quality can be improved. Therefore, it may be more economical.
Of course, if you choose to use new tool materials, you may increase the processing cost if you disengage from the actual processing conditions (the price of CBN tools is about 6 to 10 times that of cemented carbide tools). In addition, the use of new tool materials, if the cutting conditions are not properly selected, will also affect the quality of processing and tool life. Therefore, the entire processing task should be evaluated, comprehensively weighed production batches, processing time, machine tools and tool performance. Under the premise of ensuring the processing quality, under the conditions of low cutting speed, the lower coating hardness can also be used. Alloy cutters can also achieve better machining results.
Coating Technology and New Developments in Cemented Carbide Materials
According to different application requirements, the hardness of hardened steel can reach HRC45-68. In order to smoothly cut the workpiece, the hardness of the cutting tool usually needs to be 3 to 5 times more than the hardness of the workpiece. The hardness of the coating is usually measured by Vickers hardness (Hv). Take Mitsubishi's product as an example, the hardness of the TiN coating end mill is Hv1900, and the hardness of the Mstar end mill with (Al,Ti)N coating is Hv2800. The hardness of the VC-type end mill with (Al,Ti,Si)N coating is Hv3200, and the recently developed Impact Miracle nano-grade (Al,Ti)N-coated VF end mill is further enhanced in hardness to Hv3700 It can be said that the hardness of PCBN is approaching. The oxidation initiation temperature and the coating adhesion force are further increased, and the friction coefficient is continuously decreasing. HRC68 is roughly equal to Hv940 when the HRC value is simply compared with the Hv value. Although the hardness values ​​are not related to the improvement of the hardness, it can be seen that the (Al,Ti)N coated Mstar end mill can be hardened and cut. The Impact Miracle-coated VF series end mills for steels with higher hardness and oxidation initiation temperatures can achieve better processing results.
Cutting Example of Impact Miracle-coated VF End Mills:
(1) High-speed steel SKH51 (M2) die (hardness HRC65) is machined with VF-2SB R1 ball end mill. The cutting amount is: 20,000 rev/min, feed rate 6000mm/min, 0.15mm/teeth, back The amount of knife is 0.07mm, the amount of side knife is 0.2mm, and the air is cold. After the cutting length reaches 30m, the tool has not been damaged.
(2) The tool steel SKDII (HRC60) was machined with a VF-MD φ6 right-angle end mill. The cutting rate was 8000 rpm, feed rate 2160 mm/min (0.045 mm/tooth), and air-cooled. After the cutting length reaches 100m, the tool has not been damaged.
(3) Using VF-2SB R3 ball end mill for machining hot-pressing die (material: DH315, hardness HRC52), cutting rate: 16000 rpm, feed rate 1600mm/min, feed per tooth 0.05mm/tooth, back blade (cut depth) 2mm, side blade 0.2mm, straight milling, air-cooled. Despite the toughness of the material, the tool was damaged after more than 120 meters of cutting.
(4) The powder metallurgy high-speed steel mold with HRC68 or more is cut with a VF-2SB R1 ball nose end mill. The cutting amount is: the rotational speed is 8000 rpm, the feed speed is 1260 mm/min, and the feed per tooth is 0.08 mm/teeth. The amount of back knife 0.2mm, side knife 0.07mm, air-cooled, followed by milling. The cutting length can reach more than 50 meters, which is several times longer than that of ordinary end mills.
(5) The tool steel SKDII (HRC60) was machined with VF-2SB R10 ball end mill, and the cutting amount was: 1200 rev/min, feed rate 240 mm/min, feed per tooth 0.1 mm/teeth, back feed Knife volume can be up to 8mm, knife side volume 0.5mm, followed by milling, air-cooled. Under such a large depth of cut, 30 meters can still be cut, which is 3 times that of the old product.
(6) The deep groove of the die is machined with a long-necked VF-2XLB R1×20 ball end mill. The material is SKDII (HRC60). The cutting amount is: the rotational speed is 10000 rpm, the feed rate is 1000 mm/min, and the per tooth The amount of 0.05mm / tooth, air-cooled, crushing. Reciprocating cutting length up to 20 meters, double the life expectancy of other similar products.
(7) Simultaneously machine the side and bottom of the hardened steel with hardness of HRC60 with VF-MD right-angle end mill, stable cutting, good surface quality, normal chip shape and color, cutting speed of 151m/min, per tooth With a feed rate of 0.1 mm/tooth, the bottom edge has good defect resistance and outer edge wear resistance.
(8) SKDII (60HRC) was machined with an arc head end mill VF-MDRB at a cutting speed of 50 m/min, a feed per tooth of 0.05 mm/tooth, a depth of cut of 0.5 mm, and a cut width of 8 mm, followed by milling, and air cooling. After a cutting length of 8 meters, the tool has almost no damage.
Milling Substrate Substrate Carbide Grain Ultrafine
End mill teeth are subjected to repeated impact loads during processing and therefore must have sufficient toughness. When cutting a hardened material, the cutting force is large and the toughness should be increased. Today, the hardness of the coating is getting higher and higher, the coating ensures the wear resistance of the tool when cutting hardened steel, and machinability and toughness are more depend on the matrix material to ensure. The substrate material of the coated cemented carbide end mills is mainly high toughness and good vibration resistance K type cemented carbide (the main component is WC). In order to improve the toughness, it is necessary to refine the WC crystal particles, the harder the coating surface, the more the crystal grains of the matrix should be refined, and the higher the performance of the hardened steel. Impact Miracle coating matrix material grain size up to 1μm, making it both wear resistance and toughness increased.
In order to adapt to the hardened steel processing, the structure of the end mill is improved
(1) Improvement of ball end mill structure: Make the two main blades form a point at the center of the top edge so as not to generate a chisel edge to reduce the cutting force, improve the cutting performance of the center part, eliminate the pinching phenomenon, and help to form and eliminate chips. There should be a smooth transition between the ball edge and the peripheral edge, no joint marks.
(2) Improvement of the right-angle end milling cutter and the circular-arc end mill on the bottom edge: making the bottom edge position staggered, easy to manufacture, improving the cutting conditions at the center of the bottom edge, and improving the groove shape to facilitate chip removal; Rounding improves the cutting edge resistance to the cutting of high hardness materials.
(3) In order to increase the lifespan and enhance the rigidity, the VF-2SSB type short-blade end mill has been specially designed. The overall length is also shorter and it is an end mill that is suitable for the sleeve-type clamping shank.
(4) In order to achieve "milling and grinding" and achieve high precision of grinding, the accuracy of the end mill itself must be improved. Mitsubishi's high-precision ball end mills have a ball nose radius R accuracy of ±0.002 mm and a diameter accuracy of 0 to 0.01 mm. Circular arc end milling cutter corner arc R accuracy of 0 ~ ± 0.01mm. If the group of endmills is divided into several groups according to the dimensional tolerances within the range of the diameter tolerance, the grouping size tolerance will inevitably be reduced, and the machining accuracy of the end mills of each group will be improved. With such a high-precision end mill, the precision The side of the processing mold can reach a high precision of ± 0.005mm, thus realizing efficient and high-precision machining of the mold with an end mill, completely eliminating the grinding process.
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