In the machining of mechanical parts, the proportion of hole machining is quite large. High-speed, high-precision drilling processing similar to high-speed milling has been put on the agenda. High-efficiency hole processing is indispensable for promoting the rationalization of parts production. crafting process. In recent years, most parts and components have been produced in the form of CNC machine tools. When machining holes, most of them use advanced equipment such as machining centers and CNC electric machines. Regardless of the hole processing in any field, achieving high precision and high speed is an important competitive means to obtain user orders.
1 Machining Center (MC) Conditions for High-Speed ​​Hole Machining The prerequisite for high-speed hole machining is that high-speed machining centers must be used, and the speed of the machine must meet the following conditions.
1.1 Equipped with a high-speed rotary spindle The drill has the same center tooth as the end mill. Since there is a peripheral speed near the center tooth, the spindle speed must be increased when the cutting speed is increased. In particular, when a small-diameter drill is used, the speed of the spindle is indispensable. In the future, with the progress of high-speed hole processing, the demand for spindles with a rotational speed of 30,000 to 100,000 r/min is expected to increase. At the same time, since the time required to reach the specified high-speed rotation is short and the length of the spindle extending in the Z-direction (bit cutting direction) is required to be controlled to a minimum, the configuration of the high-speed spindle is indispensable for achieving high-speed and high-precision hole machining. condition.
1.2 The movable part has the function of agile action. The movable part such as the main shaft and the worktable should be as light as possible to achieve quick action, which is also a condition for high-speed hole machining. The processing time of one hole only takes a few seconds. Therefore, it is necessary to shorten the tool movement time between the hole and the hole, which is a key problem for achieving high-efficiency cutting. The solution to this problem is firstly that the movement of the movable part must be flexible. Fast. For example, even if high-precision positioning accuracy is achieved, if the movement of the movable part of the machine tool is not sensitive enough, it is impossible to meet the requirements of the current user for high-speed hole machining. Usually, the acceleration characteristic (G value) is used to judge the quick performance of the movable part of the machine. When G=0.8~1.5, the machine tool can be judged to be a machining center with high speed performance.
1.3 The ratio of the worktable to the overall area of ​​the machine tool should be small. As a user of the machining center, they hope that the space outside the workbench and the workbench should be as small as possible. In particular, in the field of processing where the processing cost is high and the added value is low, it is preferable to use a compact machining center. For example, the high-speed CNC milling machine prototyped by the Japan Institute of Physical and Chemical Research has a processing range of 300mm2, and the machine body occupies an area of ​​950mm2. The machine tool occupies about three times the largest workpiece size, and the whole structure is quite compact. The milling machine has a spindle speed of 45000r/min for high-speed cutting. The spindle is a moving structure in the XY direction (the table is only moved by the Z axis), and its acceleration characteristic value is G=1.5, indicating that the machine has a quick action function.
1.4 The main shaft can directly supply the coolant. During the drilling process, the hole with the L/D (the ratio of the drill diameter to the hole depth) of 5 or more must pay special attention to the chip removal problem. It is best to use the drill bit with the oil supply hole for the purpose of Stable processing. It is more convenient to replace the locking bolts of the fixture by adopting the method of supplying the coolant from the center of the spindle.
1.5 CNC tool interpolation function for hole machining CNC cutting is characterized by reasonable machining of the tool path. In the CNC machining of the hole, it can be used for helical cutting, contour cutting, and cutting. CNC control systems with these functions can be used in hole machining.
2 A new era of high-speed drilling. The long-term use of drills for high-precision holes, threaded holes and other through-holes and bolt holes has been processed. Recently, such machining has rapidly developed in the direction of high-speed cutting.
In the hole processing operation, high-speed steel twist drills are still widely used, but the gap between the processing precision and processing efficiency of various enterprises has gradually widened. The material of the high-speed cutting bit is mainly made of ceramic-coated cemented carbide. For example, when MAZAK and Mori Seiki manufacture the cast iron, the ceramic coated drill bit is used. In the processing of colored materials such as aluminum alloys, diamond-coated carbide drills, DLC coated carbide drills or drill bits with diamond sintered body teeth may be used. In short, many new high-speed cutting bits will be developed in the future.
Among various coated drill bits, ceramic coated carbide drills pay special attention to wear resistance, heat resistance and lubricity. The coating process also adopts multi-layer coating methods, such as using TiAlN, TiN, TiCN and other composite nitrogen. The compound forms a composite coating structure. The general trend of the cutting conditions of the drill bit is high speed, and the cutting speed can reach 200-300 m/min respectively depending on the material to be processed. High-speed drill cutting is a trend of high-speed and large-feeding, similar to the development trend of ball-end end mill cutting conditions. Cutting practice shows that increasing the cutting speed is beneficial to the rationalization of the chip shape and improving the roughness of the machined surface. It is expected to develop along the direction of high-speed cutting in the future; increasing the feed rate is very beneficial for chip breaking and tool life extension. In the future, it will continue to develop along the direction of the big feed.
At present, high-speed hole processing mostly uses a machining center with a spindle with a liquid supply hole, which is advantageous for improving the cutting speed of the drill bit. For example, when machining a shallow hole on a S45C material with a φ10mm coated carbide drill, the cutting speed can reach 250m/min and the feed rate can reach 1600mm/min (equivalent to 0.2mm/r). Under this condition, processing It takes only about 1 second for one hole. Hitachi Seiki Co., Ltd. and Brass Industries Co., Ltd. use this condition for shallow hole processing. Under this condition, the Brass company uses a diamond-coated carbide drill to machine small diameter holes on the aluminum alloy rod. One hole can be completed in about 0.2 to 0.5 seconds. It is expected that the small-diameter hole processing will enter the high-speed machining period of one hole for one second.
High-speed cutting has many factors affecting the life of the drill bit, such as blade wear due to high cutting heat. Cutting vibration will cause chipping, chip entanglement, and even breakage of the drill bit. In order to reduce the impact of the above faults on the life of the drill bit, the following technical measures can be taken:
(1) It is suitable for tool materials with high wear resistance and suitable for high-speed drilling, such as coated carbide.
(2) Select the shape of the cutting edge that is suitable for high-speed cutting, such as determining the appropriate drill angle and edge chamfering. Generally, the drill tip angle can be selected from 130° to 140°, which can effectively reduce the cutting torque. In addition, the cross-shaped grinding or the like can be adopted to minimize the contact area between the cutting edge and the cut surface. At the same time, the runout accuracy of the shank and the cutting edge portion and the height accuracy of the flange portion should be maximized.
(3) Select the fixture with high clamping rigidity and high vibration accuracy, and reduce the weight of the fixture to facilitate quick operation. For example, the hot-fit structure of the HSK tool holder is currently the ideal clamping system.
(4) In high-speed drilling, in order to improve the edge cooling and chip removal effect, the liquid supply method of directly supplying the coolant to the cutting edge can be used to obtain a stable cutting effect. In the coolant, in addition to the cutting fluid, a small amount of vegetable oil and air may be added to form a mixed mist-like coolant.
3 Development trend of indexable drill bit The indexable drill bit is a replaceable tool for the cutting edge. It has a larger diameter than the conventional drill bit, but a small indexable drill bit of φ10 mm has recently been developed. At present, indexable drill bits have been serialized and can cover almost all types of products in the integrated drill series. Drill blades are generally made of coated cemented carbide materials, and only a few products use sintered high speed steel, diamond sintered body, CBN sintered body and other materials. Indexable drills usually have only one blade or two blades, namely the center tooth and the outer tooth. When machining large diameter holes, the drill can be installed with more than 2 blades. A drill with a single insert is similar to an integral drill with a triangular shape at the tip to reduce cutting resistance; the insert has a chipbreaker for easy chip breaking. The method of clamping the blade varies from manufacturer to manufacturer. In most cases, the blade is fastened with one or several screws. When there are more than 2 blades, the shape of the blade and the shape of the chip breaker are different. This trend is particularly evident recently. At the beginning of the development of indexable drill bits, only holes with a depth of about 3 times the diameter of the drill can be processed. At present, deep holes capable of processing 5D to 8D (D is the diameter of the drill) have been developed. The use of indexable drill bits is most effective when machining parts with uniform hole sizes. For example, by using a multi-blade drill bit, it is possible to perform chamfering and boring at the entrance of the hole at the same time, which is extremely advantageous for improving the hole processing efficiency.
4 CNC hole machining technology CNC cutting is a machining method that makes the cutting process more rational. When performing CNC hole machining, it is possible to use an end mill with multi-directional cutting function, spiral cutting interpolation and contour cutting interpolation. Use as few tools as possible to make the most reasonable machining of a small number of holes. Recently, the use of high-speed milling for hole machining in production is an application example of such machining. High-speed milling has the following features:
(1) boring and chamfering can be performed by using a ball end mill and a helically inserted drill bit;
(2) Ball end mill with spiral interpolation method for continuous processing of taper holes;
(3) The end mill for machining threads and the helical interpolation method can perform various thread hole machining;
(4) The end mill can be semi-finished and finished with the contour cut-in interpolation.
In short, the tool interpolation function enables high-efficiency precision machining of high-precision holes of any size. Especially in high-speed milling, the load on each tooth is relatively light, so the same coated carbide end mill can be used for high-speed and high-precision hole machining of a variety of materials. In the future, this processing method is expected to be further used in the field of dry cutting.
5 High-speed and high-precision hole machining In addition to precision machining of holes by CNC cutting method, high-precision machining of holes can be performed by boring and reaming. With the high speed of the machining center spindle, the boring tool can be used to perform high-speed precision machining of the hole. It has been reported that the cutting speed can be increased to more than 1500 m/min when φ40 mm boring is performed on an aluminum alloy material. Such a cutting speed can also be employed when machining a steel, cast iron, and high hardness steel using a CBN sintered body as a cutting edge. It is expected that the speed of boring and processing will be popularized in the future.
In order to achieve high speed and high precision of boring, it is necessary to pay attention to the influence of tooth vibration on the surface roughness and tool life. In order to prevent machining accuracy and tool life from falling, the selected machining center must be equipped with a spindle with excellent dynamic balance. The selected boring tool must also have high dynamic balance characteristics. Especially for the cutter part of the boring tool, the geometry, tool material and the clamping method suitable for high-speed cutting should be selected. The R of the end of the cutting edge should be larger to improve the processing efficiency; the feed rate should be increased under the premise of ensuring the same surface roughness. However, increasing the feed rate should be adequate, otherwise it will increase the cutting resistance, which is not conducive to improving the processing efficiency. The cutting edge should be set with a negative chamfer of 0.1mm or less, which can effectively maintain the stability of the tool life. As for the tool material, it varies depending on the nature of the material being processed. For materials such as steel below 40HRC, cermet cutters can be used. This tool can achieve good surface roughness and long tool life under high-speed cutting conditions of v=300m/min. Coated cemented carbide tools are suitable for high-speed cutting of steels below 60HRC. The tool life is very stable, but the cutting speed is slightly lower than that of cermet tools.
CBN sintered body cutter is suitable for processing high hardness steel, cast iron and other materials, cutting speed can reach more than 1000m / min, and the tool life is very stable. The edge portion of the CBN cutter should be properly chamfered, which is extremely beneficial for stable high speed cutting and extended tool life. In the case of ultra-high-speed cutting of non-ferrous metals and non-metallic materials such as aluminum alloys, diamond sintered body tools are available, which are stable in cutting and long in tool life. It should be noted that when using a diamond tool, the blade edge must be chamfered, which is an important condition for ensuring the stability of the cutting.
In terms of reaming, there has not been a new high-speed, high-precision tool, and the research and development work in this field seems to be in a state of stagnation. High-speed reamers have so far been used by some specific users for high-speed, high-precision hole machining. This reamer has a negative rake angle, high rigidity, good chip breaking effect, and stable precision hole machining under high-speed cutting conditions. The reamer is characterized by a large negative rake angle and an odd number of teeth, and the speed of high-speed cutting is unachievable by the past reamer. Therefore, it can be said that this design has bolded the traditional concept of the reamer. Breakthrough is a highly efficient reaming tool.
6 High-speed thread cutting tools With the development of CNC cutting, some corresponding compound tool products have been developed, such as a new thread cutting tool that combines drilling and thread cutting. Drilling and thread cutting are completed in one stroke. . This composite tool makes the threaded hole processing more reasonable and the machining efficiency is greatly improved. The new end mill for thread cutting adopts the helical cutting interpolation method. The end mill can process the threaded holes of M3 or more, and the chip discharging performance is good, and stable high-precision machining effect can be obtained. General taps are also moving toward high-speed cutting and machining of high-hardness steels, and the range of applications for tapping tools is expanding. The basic conditions for high-speed cutting of taps are as follows: (1) The cutting function of the cutter teeth should be emphasized. For example, the taps with the back angle of the cutter teeth are selected, and the cutting effect is ideal. (2) The clamps should be clamped with good rigidity. For example, spring clamps, hot-mounted fixtures, etc. are used. (3) Machine tools such as machining centers should have high synchronization accuracy during the cutting and turning process.
For high-speed tapping operations, stable high-precision and high-efficiency thread cutting can be achieved by satisfying the functions of tapping tools, tool paths and cutting conditions, fixtures, and machining centers used.
7 Micro-hole processing technology required in the future With the development of IT-related industries, the demand for parts and components of devices used in the optical and electronic industries has increased rapidly in recent years. This growth has stimulated the rapid development of micro-shape and high-precision processing technology. . Among them, the development and application of micro-hole processing technology is particularly eye-catching. Micro-hole processing has long been applied in the processing of printed circuit boards, etc., and a variety of materials to be processed, including steel, can be processed by small diameters with drill bits. For example, Dijet has recently developed a new twist drill that sinter polycrystalline diamond and cemented carbide into a single cutting edge for high-speed, high-precision machining of aluminum alloys, magnesium alloys, graphite and plastics. The tool life is also greatly extended. The drill has a helix angle of 30° and a minimum diameter of φ0.4 mm. At the same time, a drill bit is produced with a minimum diameter of φ0.88 mm. These types of drill products have been serialized, and the most notable feature is that the surface roughness of the machine is greatly improved.
Mitsubishi Materials Corporation has developed a diamond-coated carbide drill with a diameter of φ0.2 to 3.0 mm. When the aluminum alloy is processed, the speed can be as high as 32000r/min, the feed rate is 0.09mm/r, and the feed speed is 3008mm/min. Under this condition, the tool life is 300,000 holes. Among the drill bits for machining high-hardness workpieces, the drills developed by MMC Kobelco Tools have performed extremely well. When the SKD11 material (60HRC) is machined with the company's φ0.4mm drill, it can perform long-term stable cutting at a speed of 6000r/min and a feed rate of 30mm/min. Mitsubishi Materials Corporation recently introduced a small-diameter drill bit (φ2mm) with oil supply hole. SUS630 material is processed under the conditions of cutting speed of 60m/min and feed rate of 0.02mm/r (length to diameter ratio is L/D= 6) Deep hole, the tool life is more than 600 holes.
At present, in the processing of small-diameter holes, the diameter of cutting with a drill can be as small as about φ50 μm. Holes smaller than φ50 μm are mostly fabricated by electrical machining. In order to suppress the occurrence of burrs, many researchers have proposed that ultrasonic vibration cutting can be used. At present, an ultrasonic vibration cutting mode with a wide range of applications and reasonable processes is being explored, including research on the adaptability of machine tools. With the smooth resolution of these problems, it is expected that in the future, small deep hole machining with smaller diameter and larger L/D value will be realized, the drilling speed will be faster, and the machining accuracy will be higher.
In recent years, with the advent of high-speed milling, cutting machining centering on milling tools is entering a high-speed and high-precision machining period. At present, the speed of hole machining is obviously lagging behind other cutting processes. The rapid production of parts is an important condition for the survival of the manufacturing industry. Therefore, the hole processing technology cannot be a bottleneck process for machining. It must follow the direction of high-speed cutting, and step into the high-speed and high-precision processing as soon as possible.
1 Machining Center (MC) Conditions for High-Speed ​​Hole Machining The prerequisite for high-speed hole machining is that high-speed machining centers must be used, and the speed of the machine must meet the following conditions.
1.1 Equipped with a high-speed rotary spindle The drill has the same center tooth as the end mill. Since there is a peripheral speed near the center tooth, the spindle speed must be increased when the cutting speed is increased. In particular, when a small-diameter drill is used, the speed of the spindle is indispensable. In the future, with the progress of high-speed hole processing, the demand for spindles with a rotational speed of 30,000 to 100,000 r/min is expected to increase. At the same time, since the time required to reach the specified high-speed rotation is short and the length of the spindle extending in the Z-direction (bit cutting direction) is required to be controlled to a minimum, the configuration of the high-speed spindle is indispensable for achieving high-speed and high-precision hole machining. condition.
1.2 The movable part has the function of agile action. The movable part such as the main shaft and the worktable should be as light as possible to achieve quick action, which is also a condition for high-speed hole machining. The processing time of one hole only takes a few seconds. Therefore, it is necessary to shorten the tool movement time between the hole and the hole, which is a key problem for achieving high-efficiency cutting. The solution to this problem is firstly that the movement of the movable part must be flexible. Fast. For example, even if high-precision positioning accuracy is achieved, if the movement of the movable part of the machine tool is not sensitive enough, it is impossible to meet the requirements of the current user for high-speed hole machining. Usually, the acceleration characteristic (G value) is used to judge the quick performance of the movable part of the machine. When G=0.8~1.5, the machine tool can be judged to be a machining center with high speed performance.
1.3 The ratio of the worktable to the overall area of ​​the machine tool should be small. As a user of the machining center, they hope that the space outside the workbench and the workbench should be as small as possible. In particular, in the field of processing where the processing cost is high and the added value is low, it is preferable to use a compact machining center. For example, the high-speed CNC milling machine prototyped by the Japan Institute of Physical and Chemical Research has a processing range of 300mm2, and the machine body occupies an area of ​​950mm2. The machine tool occupies about three times the largest workpiece size, and the whole structure is quite compact. The milling machine has a spindle speed of 45000r/min for high-speed cutting. The spindle is a moving structure in the XY direction (the table is only moved by the Z axis), and its acceleration characteristic value is G=1.5, indicating that the machine has a quick action function.
1.4 The main shaft can directly supply the coolant. During the drilling process, the hole with the L/D (the ratio of the drill diameter to the hole depth) of 5 or more must pay special attention to the chip removal problem. It is best to use the drill bit with the oil supply hole for the purpose of Stable processing. It is more convenient to replace the locking bolts of the fixture by adopting the method of supplying the coolant from the center of the spindle.
1.5 CNC tool interpolation function for hole machining CNC cutting is characterized by reasonable machining of the tool path. In the CNC machining of the hole, it can be used for helical cutting, contour cutting, and cutting. CNC control systems with these functions can be used in hole machining.
2 A new era of high-speed drilling. The long-term use of drills for high-precision holes, threaded holes and other through-holes and bolt holes has been processed. Recently, such machining has rapidly developed in the direction of high-speed cutting.
In the hole processing operation, high-speed steel twist drills are still widely used, but the gap between the processing precision and processing efficiency of various enterprises has gradually widened. The material of the high-speed cutting bit is mainly made of ceramic-coated cemented carbide. For example, when MAZAK and Mori Seiki manufacture the cast iron, the ceramic coated drill bit is used. In the processing of colored materials such as aluminum alloys, diamond-coated carbide drills, DLC coated carbide drills or drill bits with diamond sintered body teeth may be used. In short, many new high-speed cutting bits will be developed in the future.
Among various coated drill bits, ceramic coated carbide drills pay special attention to wear resistance, heat resistance and lubricity. The coating process also adopts multi-layer coating methods, such as using TiAlN, TiN, TiCN and other composite nitrogen. The compound forms a composite coating structure. The general trend of the cutting conditions of the drill bit is high speed, and the cutting speed can reach 200-300 m/min respectively depending on the material to be processed. High-speed drill cutting is a trend of high-speed and large-feeding, similar to the development trend of ball-end end mill cutting conditions. Cutting practice shows that increasing the cutting speed is beneficial to the rationalization of the chip shape and improving the roughness of the machined surface. It is expected to develop along the direction of high-speed cutting in the future; increasing the feed rate is very beneficial for chip breaking and tool life extension. In the future, it will continue to develop along the direction of the big feed.
At present, high-speed hole processing mostly uses a machining center with a spindle with a liquid supply hole, which is advantageous for improving the cutting speed of the drill bit. For example, when machining a shallow hole on a S45C material with a φ10mm coated carbide drill, the cutting speed can reach 250m/min and the feed rate can reach 1600mm/min (equivalent to 0.2mm/r). Under this condition, processing It takes only about 1 second for one hole. Hitachi Seiki Co., Ltd. and Brass Industries Co., Ltd. use this condition for shallow hole processing. Under this condition, the Brass company uses a diamond-coated carbide drill to machine small diameter holes on the aluminum alloy rod. One hole can be completed in about 0.2 to 0.5 seconds. It is expected that the small-diameter hole processing will enter the high-speed machining period of one hole for one second.
High-speed cutting has many factors affecting the life of the drill bit, such as blade wear due to high cutting heat. Cutting vibration will cause chipping, chip entanglement, and even breakage of the drill bit. In order to reduce the impact of the above faults on the life of the drill bit, the following technical measures can be taken:
(1) It is suitable for tool materials with high wear resistance and suitable for high-speed drilling, such as coated carbide.
(2) Select the shape of the cutting edge that is suitable for high-speed cutting, such as determining the appropriate drill angle and edge chamfering. Generally, the drill tip angle can be selected from 130° to 140°, which can effectively reduce the cutting torque. In addition, the cross-shaped grinding or the like can be adopted to minimize the contact area between the cutting edge and the cut surface. At the same time, the runout accuracy of the shank and the cutting edge portion and the height accuracy of the flange portion should be maximized.
(3) Select the fixture with high clamping rigidity and high vibration accuracy, and reduce the weight of the fixture to facilitate quick operation. For example, the hot-fit structure of the HSK tool holder is currently the ideal clamping system.
(4) In high-speed drilling, in order to improve the edge cooling and chip removal effect, the liquid supply method of directly supplying the coolant to the cutting edge can be used to obtain a stable cutting effect. In the coolant, in addition to the cutting fluid, a small amount of vegetable oil and air may be added to form a mixed mist-like coolant.
3 Development trend of indexable drill bit The indexable drill bit is a replaceable tool for the cutting edge. It has a larger diameter than the conventional drill bit, but a small indexable drill bit of φ10 mm has recently been developed. At present, indexable drill bits have been serialized and can cover almost all types of products in the integrated drill series. Drill blades are generally made of coated cemented carbide materials, and only a few products use sintered high speed steel, diamond sintered body, CBN sintered body and other materials. Indexable drills usually have only one blade or two blades, namely the center tooth and the outer tooth. When machining large diameter holes, the drill can be installed with more than 2 blades. A drill with a single insert is similar to an integral drill with a triangular shape at the tip to reduce cutting resistance; the insert has a chipbreaker for easy chip breaking. The method of clamping the blade varies from manufacturer to manufacturer. In most cases, the blade is fastened with one or several screws. When there are more than 2 blades, the shape of the blade and the shape of the chip breaker are different. This trend is particularly evident recently. At the beginning of the development of indexable drill bits, only holes with a depth of about 3 times the diameter of the drill can be processed. At present, deep holes capable of processing 5D to 8D (D is the diameter of the drill) have been developed. The use of indexable drill bits is most effective when machining parts with uniform hole sizes. For example, by using a multi-blade drill bit, it is possible to perform chamfering and boring at the entrance of the hole at the same time, which is extremely advantageous for improving the hole processing efficiency.
4 CNC hole machining technology CNC cutting is a machining method that makes the cutting process more rational. When performing CNC hole machining, it is possible to use an end mill with multi-directional cutting function, spiral cutting interpolation and contour cutting interpolation. Use as few tools as possible to make the most reasonable machining of a small number of holes. Recently, the use of high-speed milling for hole machining in production is an application example of such machining. High-speed milling has the following features:
(1) boring and chamfering can be performed by using a ball end mill and a helically inserted drill bit;
(2) Ball end mill with spiral interpolation method for continuous processing of taper holes;
(3) The end mill for machining threads and the helical interpolation method can perform various thread hole machining;
(4) The end mill can be semi-finished and finished with the contour cut-in interpolation.
In short, the tool interpolation function enables high-efficiency precision machining of high-precision holes of any size. Especially in high-speed milling, the load on each tooth is relatively light, so the same coated carbide end mill can be used for high-speed and high-precision hole machining of a variety of materials. In the future, this processing method is expected to be further used in the field of dry cutting.
5 High-speed and high-precision hole machining In addition to precision machining of holes by CNC cutting method, high-precision machining of holes can be performed by boring and reaming. With the high speed of the machining center spindle, the boring tool can be used to perform high-speed precision machining of the hole. It has been reported that the cutting speed can be increased to more than 1500 m/min when φ40 mm boring is performed on an aluminum alloy material. Such a cutting speed can also be employed when machining a steel, cast iron, and high hardness steel using a CBN sintered body as a cutting edge. It is expected that the speed of boring and processing will be popularized in the future.
In order to achieve high speed and high precision of boring, it is necessary to pay attention to the influence of tooth vibration on the surface roughness and tool life. In order to prevent machining accuracy and tool life from falling, the selected machining center must be equipped with a spindle with excellent dynamic balance. The selected boring tool must also have high dynamic balance characteristics. Especially for the cutter part of the boring tool, the geometry, tool material and the clamping method suitable for high-speed cutting should be selected. The R of the end of the cutting edge should be larger to improve the processing efficiency; the feed rate should be increased under the premise of ensuring the same surface roughness. However, increasing the feed rate should be adequate, otherwise it will increase the cutting resistance, which is not conducive to improving the processing efficiency. The cutting edge should be set with a negative chamfer of 0.1mm or less, which can effectively maintain the stability of the tool life. As for the tool material, it varies depending on the nature of the material being processed. For materials such as steel below 40HRC, cermet cutters can be used. This tool can achieve good surface roughness and long tool life under high-speed cutting conditions of v=300m/min. Coated cemented carbide tools are suitable for high-speed cutting of steels below 60HRC. The tool life is very stable, but the cutting speed is slightly lower than that of cermet tools.
CBN sintered body cutter is suitable for processing high hardness steel, cast iron and other materials, cutting speed can reach more than 1000m / min, and the tool life is very stable. The edge portion of the CBN cutter should be properly chamfered, which is extremely beneficial for stable high speed cutting and extended tool life. In the case of ultra-high-speed cutting of non-ferrous metals and non-metallic materials such as aluminum alloys, diamond sintered body tools are available, which are stable in cutting and long in tool life. It should be noted that when using a diamond tool, the blade edge must be chamfered, which is an important condition for ensuring the stability of the cutting.
In terms of reaming, there has not been a new high-speed, high-precision tool, and the research and development work in this field seems to be in a state of stagnation. High-speed reamers have so far been used by some specific users for high-speed, high-precision hole machining. This reamer has a negative rake angle, high rigidity, good chip breaking effect, and stable precision hole machining under high-speed cutting conditions. The reamer is characterized by a large negative rake angle and an odd number of teeth, and the speed of high-speed cutting is unachievable by the past reamer. Therefore, it can be said that this design has bolded the traditional concept of the reamer. Breakthrough is a highly efficient reaming tool.
6 High-speed thread cutting tools With the development of CNC cutting, some corresponding compound tool products have been developed, such as a new thread cutting tool that combines drilling and thread cutting. Drilling and thread cutting are completed in one stroke. . This composite tool makes the threaded hole processing more reasonable and the machining efficiency is greatly improved. The new end mill for thread cutting adopts the helical cutting interpolation method. The end mill can process the threaded holes of M3 or more, and the chip discharging performance is good, and stable high-precision machining effect can be obtained. General taps are also moving toward high-speed cutting and machining of high-hardness steels, and the range of applications for tapping tools is expanding. The basic conditions for high-speed cutting of taps are as follows: (1) The cutting function of the cutter teeth should be emphasized. For example, the taps with the back angle of the cutter teeth are selected, and the cutting effect is ideal. (2) The clamps should be clamped with good rigidity. For example, spring clamps, hot-mounted fixtures, etc. are used. (3) Machine tools such as machining centers should have high synchronization accuracy during the cutting and turning process.
For high-speed tapping operations, stable high-precision and high-efficiency thread cutting can be achieved by satisfying the functions of tapping tools, tool paths and cutting conditions, fixtures, and machining centers used.
7 Micro-hole processing technology required in the future With the development of IT-related industries, the demand for parts and components of devices used in the optical and electronic industries has increased rapidly in recent years. This growth has stimulated the rapid development of micro-shape and high-precision processing technology. . Among them, the development and application of micro-hole processing technology is particularly eye-catching. Micro-hole processing has long been applied in the processing of printed circuit boards, etc., and a variety of materials to be processed, including steel, can be processed by small diameters with drill bits. For example, Dijet has recently developed a new twist drill that sinter polycrystalline diamond and cemented carbide into a single cutting edge for high-speed, high-precision machining of aluminum alloys, magnesium alloys, graphite and plastics. The tool life is also greatly extended. The drill has a helix angle of 30° and a minimum diameter of φ0.4 mm. At the same time, a drill bit is produced with a minimum diameter of φ0.88 mm. These types of drill products have been serialized, and the most notable feature is that the surface roughness of the machine is greatly improved.
Mitsubishi Materials Corporation has developed a diamond-coated carbide drill with a diameter of φ0.2 to 3.0 mm. When the aluminum alloy is processed, the speed can be as high as 32000r/min, the feed rate is 0.09mm/r, and the feed speed is 3008mm/min. Under this condition, the tool life is 300,000 holes. Among the drill bits for machining high-hardness workpieces, the drills developed by MMC Kobelco Tools have performed extremely well. When the SKD11 material (60HRC) is machined with the company's φ0.4mm drill, it can perform long-term stable cutting at a speed of 6000r/min and a feed rate of 30mm/min. Mitsubishi Materials Corporation recently introduced a small-diameter drill bit (φ2mm) with oil supply hole. SUS630 material is processed under the conditions of cutting speed of 60m/min and feed rate of 0.02mm/r (length to diameter ratio is L/D= 6) Deep hole, the tool life is more than 600 holes.
At present, in the processing of small-diameter holes, the diameter of cutting with a drill can be as small as about φ50 μm. Holes smaller than φ50 μm are mostly fabricated by electrical machining. In order to suppress the occurrence of burrs, many researchers have proposed that ultrasonic vibration cutting can be used. At present, an ultrasonic vibration cutting mode with a wide range of applications and reasonable processes is being explored, including research on the adaptability of machine tools. With the smooth resolution of these problems, it is expected that in the future, small deep hole machining with smaller diameter and larger L/D value will be realized, the drilling speed will be faster, and the machining accuracy will be higher.
In recent years, with the advent of high-speed milling, cutting machining centering on milling tools is entering a high-speed and high-precision machining period. At present, the speed of hole machining is obviously lagging behind other cutting processes. The rapid production of parts is an important condition for the survival of the manufacturing industry. Therefore, the hole processing technology cannot be a bottleneck process for machining. It must follow the direction of high-speed cutting, and step into the high-speed and high-precision processing as soon as possible.
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