JP2010162677A - Small-diameter cbn ball end mill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-service life CBN (cubic boron nitride) small-diameter ball end mill which can suppress vibration and chattering of a tool during cutting work, has high bending-breakage strength, and can provide a good cutting surface, particularly a small-diameter ball end mill which, even in the case of a long neck having a length L of the neck which is five times or larger the diameter D of the cutting edge, is less likely to cause vibration and has no possibility of bending-breakage. <P>SOLUTION: The small-diameter CBN ball end mill has a cutting edge diameter D of not more than 3 mm and includes a ball cutting edge, which constitutes a cutting part and has an arcuate radius of R mm, and a peripheral cutting edge formed of CBN. In the small-diameter CBN ball end mill, the rake face of the ball cutting edge and the rake face of the peripheral cutting edge which is not less than R/5 of the length of the peripheral cutting edge are provided on the same plane, the peripheral cutting edge is formed in a right hand cut left hand helix form, and the axial rake angle of the ball cutting edge is -5&deg; to -25&deg;. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a small-diameter CBN ball end mill using a sintered body of cubic boron nitride (hereinafter referred to as CBN) for a blade portion. In particular, the present invention is a long neck having a blade diameter D of 3 mm or less and a length under the neck of the end mill of L, and L / D is 5 or more, and the sintered body and shank serving as a blade at the neck. The present invention relates to a small-diameter CBN ball end mill having a joint with a cemented carbide which is the side.

  A rotary tool using a CBN sintered body for a blade portion is mainly used as a tool for machining a mold. A ball end mill is often used for machining a die that requires three-dimensional machining. In particular, a small-diameter ball end mill having a blade diameter of 3 mm or less is often used in rib groove processing, deep corner processing, and finishing processing of uncut portions. In recent years, the neck length L of this small-diameter ball end mill is required to be at least 5 times the blade diameter D. Furthermore, since the machining is performed in a closed region where the clearance with the work material (hereinafter also referred to as a workpiece) is small, there is a problem of tool deflection and vibration, and chip discharge is not sufficient. This causes breakage and chipping of the tool.

  On the other hand, Patent Document 1 discloses a technique for improving the chip discharging performance by providing a large chip pocket in the ball portion of the ball end mill. Further, Patent Document 2 proposes a CBN end mill in which the outer peripheral blade is inclined with respect to the shaft center so as to be twisted in the opposite direction to the cutting rotation direction seen from the shank side, and the rake angle is made negative to improve the edge strength. Has been.

Japanese Patent Application Laid-Open No. 11-114717 JP 2008-110411 A

  In recent years, miniaturization of home appliances and machine products has been remarkable, and electronic parts and semiconductor-related parts have become more precise and complicated. For example, in a connector-related mold, it is necessary to use a small-diameter end mill to cut a high-hardness steel material exceeding HRC60 (for example, heat-treated JIS SKD11). In recent years, for example, the thickness of mobile phones has been decreasing year by year, and the structure of the ribs has been changed in order to give the frame strength even if it is thin. In other words, a mold material that is harder than before has been required for press processing of fine ribs, and a small-diameter end mill with a blade diameter of 3 mm or less is particularly required for cutting because of the need for fine processing. Yes. However, the above-described machining of a hard steel material with a cutting tool has a problem with tool wear, and it is difficult to perform high-efficiency and high-precision machining for a long time. For this reason, electrical discharge machining with extremely low machining efficiency is still often employed.

  When cutting these high-hardness materials without using electric discharge machining, generally a coated tool made of cemented carbide is used. In order to perform high-precision processing of a material with high hardness over a long period of time, it is necessary to increase the hardness of the tool material itself and improve wear resistance. In such a background, in recent years, the number of cases in which a CBN sintered tool having a blade portion formed of a CBN sintered body is used. However, CBN sintered tools are extremely fragile compared to cemented carbide tools, and have the disadvantage that they are prone to chipping and chipping during cutting, and high-efficiency cutting with high cutting speed and high feed rate is impossible and limited. It is only used as a super-finishing process in an environment.

  In order to solve the problems peculiar to the CBN sintered material, a proposal for improving the shape of the CBN end mill with emphasis on sharpness and cutting edge strength has been made in Patent Document 2 described above. However, as described above, there is a problem in performing high-efficiency processing, and there remains a problem that chipping and breakage occur when the high-efficiency processing is performed and the cutting conditions are increased. As a major cause of this problem, in addition to a small diameter tool of 3 mm or less, a ratio of the machining depth to the blade diameter is 5 times or more, that is, a long neck small diameter ball end mill has been required. This is because the current situation is. Specifically, in order to process fine and deep grooves, the use of elongated ball end mills in which the ratio of the neck length L to the blade diameter D is about 5 to 10 is rapidly increasing. Such a ball end mill generates chatter and vibration during cutting, and in particular, in the case of a CBN sintered body, the cutting edge tends to be chipped and often causes a breakage accident. Such problems cannot be dealt with by the prior art including the above-mentioned patent documents.

The following is a summary of current issues common to small-diameter CBN ball end mills having a blade at the cutting edge.
1) The biggest problem when using a CBN tool with higher performance than carbide is that CBN is essentially a brittle material and it is necessary to ensure rigidity. In particular, when the CBN ball end mill has a small diameter of 3 mm or less, it is necessary to ensure the rigidity of the entire tool.
2) Recent small-diameter CBN ball end mills used for machining dies have long neck lengths for deep engraving, which increases the deflection of the tool neck, making it easy to generate vibration and chatter during cutting. To occur. In the cutting of narrow and deep groove dies, not only the bottom cutting with the ball blade of the ball end mill, but rather the gradient cutting with the outer peripheral blade must be considered the mainstream. However, when a small-diameter ball end mill is used for slope surface cutting, the contact length of the cutting edge to the workpiece is longer than that of a radius end mill having the same cutting diameter, and the tool itself is likely to vibrate.
3) Generally, in the case of machining using a CBN tool, a mist coolant is often used. When deep rib machining is performed using a right-handed right-twisted CBN tool that has been widely used in the past, the mist-like coolant flows to the shank side with the air around the blade edge, so supply sufficient coolant to the blade edge. Can not be.

  In response to the above-mentioned problems, the present invention suppresses vibration and chatter, and has a small breakage strength and a small diameter CBN ball end mill, particularly a long neck whose neck length is 5 times the blade diameter or less, and has little vibration. An object is to provide a small-diameter CBN ball end mill.

  The present inventor has examined in detail the overall configuration from the blade tip to the shank of the small diameter CBN end mill and the shape of the blade tip. As a result, especially in the case of a small-diameter CBN ball end mill with a blade diameter of 3 mm or less, if at least the blade portion is made of a CBN sintered material, the flank on the back of the blade portion and the back metal portion are also CBN sintered material. Therefore, it has been found that when the overall rigidity is small and a lateral force is applied by contact with the workpiece during cutting, the vibration is increased due to the small diameter and chipping and breakage occur due to insufficient strength.

  Therefore, in the small-diameter CBN ball end mill of the present invention, the outer peripheral blade of the blade portion is formed with a right-handed left-handed twist in order to ensure essential rigidity. Furthermore, the small-diameter ball end mill of the present invention has a step difference between most of the rake face of the ball blade and the rake face of the outer peripheral blade so that vibration is not increased due to a lateral force from the workpiece being cut especially on the outer peripheral blade. There is no coplanarity. In order to ensure the rigidity of the blade and optimal supply of mist coolant, the axial rake should be at a negative angle.

  That is, the present invention is a small-diameter CBN ball end mill having a blade diameter of 3 mm or less and an arcuate radius Rmm forming a blade portion and an outer peripheral blade made of CBN, the rake face of the ball blade and the outer peripheral blade The outer peripheral edge rake face of R / 5 or more in length is formed in the same plane, the outer peripheral edge is formed by right-handed left-handed twist, and the axial rake of the ball blade is −5 ° to −25 °. Is a small diameter CBN ball end mill. Here, R means the radius of the ball blade.

  In particular, the present invention realizes a long neck small-diameter CBN ball end mill due to the above-mentioned feature of the tool shape. That is, another invention of the present invention is a long neck tool having a blade diameter D of 3 mm or less and a ratio L / D of a neck length L to the blade diameter D of 5 or more. A small-diameter CBN ball end mill in which a ball blade having an arcuate radius Rmm and an outer peripheral blade are made of CBN, and the rake face of the ball blade and the outer peripheral rake face of R / 5 or more of the outer peripheral blade length are coplanar. A small-diameter CBN ball end mill characterized in that the outer peripheral blade is formed of a right blade left-handed twist, and the axial rake of the ball blade is -5 ° to -25 °.

  Further, in the present invention, there is no portion where the rigidity is lowered by the conventional method for forming a blade groove. In other words, the blade groove can be formed shorter than before. This effect of ensuring the tool rigidity is a very important effect in order to realize a brittle tool called CBN with a small-diameter ball end mill with a blade diameter of 3 mm or less targeted by the present invention. In particular, in the case of a long-necked small-diameter ball end mill, vibration is likely to occur due to insufficient rigidity of the tool, so ensuring the rigidity of the blade is very important.

  In the present invention, the axial rake of the ball blade is set to −5 ° to −25 °. This improves the chipping resistance against the resistance applied in the axial direction, and the tool which is the biggest problem of the conventional small-diameter CBN ball end mill even in the case of non-uniform machining in the previous process of the finishing process. This has the effect of preventing the drop of CBN particles, chipping and chipping, and instability of cutting caused by vibration and insufficient strength.

  In the small-diameter CBN ball end mill of the present invention, the outer peripheral blade is formed by a right blade left-handed twist. Due to this effect, the end mill is applied with a force in the direction of being pulled toward the main spindle side of the machine tool, so that the holding rigidity of the cutting tool is increased and the vibration toward the workpiece side can be reduced. Further, the cutting edge rigidity is increased, and there is an effect of suppressing chipping. In particular, in the case of a long neck where L / D is 5 or more and vibration is likely to occur, the blade portion is often hit by the workpiece, but the axial rake of the ball blade is -5 ° to -25 °. By doing so, since the rigidity of the blade portion itself can be increased, damage such as chipping and chipping can be made difficult to occur.

  When a steel material is cut using a CBN sintered body, a mist-like coolant is often used for cooling the cutting edge. The reason why the coolant is used in the form of mist is that CBN tends to drop off and wear easily when it is rapidly cooled. Since the mist-like coolant is sprayed in the atmosphere in the form of a mist, the coolant also flows along the air flow. Especially in the small-diameter CBN tool that is used by increasing the number of revolutions during cutting, the right-handed right-handed shape of the right blade as well as the mist-like coolant flows to the shank side together with the air around the blade edge. Difficult to spread on the cutting edge. As in the present invention, by setting the axial rake of the ball blade to -5 ° to -25 ° as the shape of the right blade left-handed twist, the mist coolant can be efficiently spread to the tip of the blade portion. Thereby, the cooling effect of the cutting edge can be enhanced to further increase the tool life, and the surface roughness quality of the machined surface can be improved by enhancing the lubricity.

  Another invention of the present invention is a small-diameter CBN ball end mill having a blade diameter of 3 mm or less and an arcuate radius Rmm forming a blade portion and an outer peripheral blade made of CBN, The outer peripheral edge rake face of R / 5 or more of the outer peripheral edge length is formed in the same plane, the outer peripheral edge is formed by right-handed left-handed twist, and the axial rake of the ball edge is −5 ° to −25 °. Further, the range of 20% of the entire length of the ball blade with the tip of the ball blade as the center includes an angular range in which the radial rake is 0 ° to −10 °, and 20% of the total length of the ball blade. The radial rake of the ball blade on the outer peripheral side exceeding% is a small-diameter CBN ball end mill characterized in that the minus angle gradually increases until it reaches the outer peripheral blade in the range of more than −10 ° and 25 °. Here, the range of 20% of the total length of the ball blade includes the angle range of 0 to -10 ° in the radial rake means that the angle of 0 to -10 ° in the radial rake means that the angle of the ball blade is That is, it is surely in the range of 20% of the entire length of the ball blade with the tip as the center. For example, the radial rake is −15 ° at the position of 10% of the entire length of the ball blade, and the radial rake is −5 ° at the position of 15%. The conditions of this axial rake and radial rake are effective when a long-necked tool having an L / D of 5 or more is used. That is, for example, the above-described radial rake conditions ensure the biting property in the vicinity of the tip of the ball blade and ensure the strength on the outer peripheral side of the tool of the ball blade, so that the small diameter CBN combines both cutting performance and strength. It becomes a ball end mill.

  According to the present invention, for example, in precision parts using a CBN small-diameter ball end mill having a blade diameter of 3 mm or less, or in mold processing of a frame part different from the rib structure of a mobile phone, even if the mold material is a high-hardness material. In addition, even with a long neck shape in which the ratio (L / D) of the neck length L to the blade diameter D is 5 times or more, the rigidity of the ball end mill can be ensured and chatter and vibration during cutting can be ensured. Generation can be suppressed and chipping is not caused.

  The small-diameter CBN ball end mill of the present invention makes it easy to spread mist coolant to the tip of the blade by setting the axial rake of the ball blade to -5 ° to -25 ° as a right-handed left-handed twist shape. Further, it is possible to improve the surface roughness quality of the work surface of the workpiece by enhancing the cooling effect of the cutting edge to further extend the tool life and enhancing the lubricity. That is, high-precision machining for a long time can be realized stably even in rib groove machining and deep corner machining, and the present invention is effective for cost reduction such as precision component machining mainly targeted.

  In the small diameter CBN ball end mill of the present invention, the radial rake is changed depending on the position of the ball blade. The ball end mill has poor chamfering because the cutting speed does not increase near the tip of the ball blade, but due to the above radial rake conditions, the chamfering property near the center of the ball blade is ensured and the tool outer side of the ball blade is secured. Since the strength can be ensured, a small-diameter CBN ball end mill having both cutting performance and strength is obtained.

It is a front view which shows the small diameter CBN ball end mill which concerns on embodiment of this invention. (A) is the figure seen from the A direction of FIG. 1, (b) is an enlarged view of the periphery of the blade part of FIG. It is the figure which compared the difference in the contact length of the cutting edge at the time of processing the workpiece which has a gradient surface with a general ball end mill and a radius end mill, (a) is a figure of a ball end mill, (b ) Is a diagram of a radius end mill. BRIEF DESCRIPTION OF THE DRAWINGS It is an enlarged view of the periphery of the blade part of the CBN ball end mill of this invention, (a) is a front view of the CBN ball end mill of this invention, (b) is the figure seen from the arrow B direction of (a). (C) is an enlarged view of a P portion of (b). It is an enlarged view of the periphery of the blade part of the conventional CBN ball end mill, (a) is a front view of the conventional CBN ball end mill, (b) is a view seen from the arrow B direction of (a), (C) is an enlarged view of a Q portion in (b). It is a schematic diagram which shows the cutting resistance of the conventional ball end mill and the CBN ball end mill of the present invention. It is a schematic diagram which shows the flow direction of the mist-like coolant of the conventional ball end mill and the CBN ball end mill of the present invention, wherein (a) is a view of the conventional ball end mill, and (b) is the CBN ball end mill of the present invention. FIG. (A) is the figure seen from the blade tip direction of the conventional ball end mill, (b) is the figure seen from the blade tip direction of the CBN ball end mill of the present invention. It is a figure explaining the angle range of the condition of the ball blade whole length of the CBN ball end mill of the present invention, and radial rake. (B) is a figure which shows the AA cross section of FIG. 9 of the CBN ball end mill of this invention, (a) is a figure which shows the cross section of the conventional ball end mill in the position corresponded to the said AA cross section. (C) is the schematic which shows the direction of the cutting resistance in the bottom face cutting of the ball end mill which has the cross section of (a), (d) is the direction of the cutting resistance in the bottom face cutting of the ball end mill which has the cross section of (b). FIG. (B) is a figure which shows the BB cross section of FIG. 9 of the CBN ball end mill of this invention, (a) is a figure which shows the cross section of the conventional ball end mill in the position corresponded to the said BB cross section. (C) is the schematic which shows the direction of cutting resistance in the cutting of the gradient surface of the ball end mill which has the cross section of (a), (d) is in the cutting of the gradient surface of the ball end mill which has the cross section of (b). It is the schematic which shows the direction of cutting resistance. It is the figure which showed the processing method of the Example.

  In addition to the above-described constituent features of the present invention, modes for carrying out the invention will be described below with reference to FIGS. FIG. 1 is a front view showing a small-diameter CBN ball end mill according to an embodiment of the present invention. 2 and 9 are enlarged views of the periphery of the blade portion. FIG. 3 is a diagram comparing the difference in contact length between cutting edges of a general ball end mill and a radius end mill. 4 and 5 are enlarged views of the periphery of the blade portion. FIG. 6 is a schematic diagram showing the direction of cutting resistance. FIG. 7 is a schematic diagram showing the direction in which the mist coolant flows. FIG. 8 is a view seen from the tip direction of the blade edge. FIG. 10 is a schematic diagram showing the AA cross-sectional view of FIG. 9 and the direction of cutting resistance in bottom cutting. FIG. 11 is a schematic cross-sectional view taken along the line BB of FIG. 9 and the direction of cutting resistance in the cutting of the inclined surface.

  As shown in FIG. 1, the small-diameter CBN ball end mill of the present invention has a blade portion 1 and a neck portion 2 made of a CBN sintered body having a blade diameter D, joined to a cemented carbide at a joint portion 3 and has a neck length L And is connected to the shank 4.

  As shown in FIG. 2, the small-diameter CBN ball end mill of the present invention includes a ball blade 5 having an arcuate radius Rmm and an outer peripheral blade 6 forming a blade portion 1 as a blade shape, and is formed of a CBN sintered body. The rake face 8 and the outer peripheral edge rake face 9 of R / 5 or more of the outer peripheral edge length 7 are formed in the same plane and are characterized by a right-handed left-handed twist. In the CBN ball end mill of the present invention, the ball blade 5 constituting the blade portion 1 is not necessarily a circular arc in a strict sense, but the blade portion has a ball shape close to the circular arc in the cross section including the axis. The parts are generically called an arc shape. A black circle point O in the figure indicates the center point of the radius R.

  FIG. 3 shows a comparison of the difference in contact length 11 between the cutting edges of a general ball end mill and a radius end mill when a sloped surface such as a mold is machined. When machining a sloped surface, if the blade diameter D is the same, the ball end mill has a longer contact length 11 for the cutting edge than the radius end mill. Problems arise.

  That is, when the ball end mill is used for slope surface machining, it is important to take measures to prevent tool vibration. On the other hand, as shown in FIGS. 4A to 4C, the small-diameter CBN ball end mill of the present invention has the ball blade rake face 8 and the outer peripheral rake face 9 formed of the same rake face. In the present invention, it is desirable that the rake surfaces of the ball blade and the outer peripheral blade are the same plane. However, the length of the outer peripheral edge rake face may be equal to or greater than R / 5. The ball edge of the conventional ball end mill and the outer peripheral edge rake face 9 of the outer peripheral edge are formed of different surfaces. In this case, the vibration is increased due to resistance from at least two directions during cutting. However, according to the present invention, since the ball blade rake face 8 of the ball blade and the outer peripheral rake face 9 of the outer peripheral blade are formed in the same plane, the resistance during cutting is received from one direction, so that vibration is hardly generated and stable machining is performed. It becomes possible to do.

  The features of the ball blade rake face 8 and the outer peripheral rake face 9 of the present invention are exerted as a great effect when cutting a gradient surface such as a mold having a small draft angle. When the gradient angle of the workpiece 12 is as small as 0.5 °, in the small diameter CBN ball end mill of the present invention, the ball blade 5 and the outer peripheral blade 6 are simultaneously involved in cutting.

This effect of the present invention will be described with reference to FIGS. 5 (a) to 5 (c) and FIGS. 6 (a) to 6 (c) in comparison with a conventional small diameter CBN ball end mill. Fig.5 (a) shows the conventional shape of a right blade left twist. In the conventional CBN ball end mill, as shown in FIG. 5 (b), the ball blade rake face 8 and the rake face 9 of the outer peripheral edge are formed separately, so that a partial enlarged view of the outer peripheral edge 6 in FIG. 5 (c). As shown in FIG. 2, an angle difference is generated between the ball blade rake face 8 and the outer peripheral rake face 9.
As a result, in the case of the conventional tool shape, since the directions of the ball blade rake face 8 and the outer peripheral rake face 9 are different as shown in FIG. 6A, the cutting force is received from two different directions. Therefore, vibration is likely to occur. On the other hand, in the small diameter CBN ball end mill of the present invention, as shown in FIG. 6 (b), since the cutting resistance is received from only one direction, the neck length L is particularly 5 times the blade diameter D or more. In such a long case, the occurrence of vibration can be suppressed and more stable machining can be performed.

  FIG. 4B shows an axial rake of the small diameter CBN ball end mill of the present invention. The present invention is characterized in that the axial rake 13 of the ball blade 5 of the ball end mill is set to −5 ° to −25 °. As a result, the outer peripheral blade 6 is formed with a right-handed left-handed twist. However, due to this effect, the end mill is applied with a force in the direction of being pulled toward the main spindle side of the machine tool. Vibration can be reduced. Further, since the axial rake 13 of the ball blade 5 of the ball end mill is −5 ° to −25 °, the rigidity of the ball blade 5 is increased and chipping can be suppressed. Here, if the axial rake 13 of the ball blade 5 is larger in the positive direction than −5 °, the rigidity of the ball blade 5 is insufficient, the strength of the CBN sintered material is not obtained, and the CBN particles fall off. Will cause chipping, and if the axial rake 13 is larger than −25 ° in the negative direction, the rigidity of the ball blade 5 will increase, but the resistance will increase, and conversely, the drop of the CBN particles will proceed, resulting in a large defect. It will be connected. In particular, in the case of a long neck end mill with a small diameter such that the ratio of the neck length L to the blade diameter D is 5 times or more, if the cutting resistance increases, it will affect the occurrence of tilting and vibration. When the axial rake 13 of 5 is set to -5 ° to -25 °, it can be stably processed.

  In the small-diameter CBN ball end mill of the present invention, when using a mist-like coolant in which the cutting fluid used for improving the cooling and lubricity of the ball blade 5 and the outer peripheral blade 6 is used, it is particularly difficult to spray. Even in the processing of the rib groove shape, there is an effect of improving the spraying amount of the cutting fluid to the ball blade 5 and the outer peripheral blade 6. Particularly in the case of a CBN tool, when a water-soluble cutting fluid is directly applied to the blade portion 1 in the processing of a high hardness material, the generated cutting heat is rapidly cooled, cracks are generated inside the CBN, and CBN particles fall off. It is desirable to spray mist-like coolant. Here, the flow direction of the mist coolant is, as shown in FIG. 7A, in the case of the conventional right blade right twist, the airflow around the blade portion 1 is directed toward the shank 4 side of the end mill by high speed rotation. It becomes a flowing direction (arrow M direction), that is, a state in which the atomized cutting fluid sprayed from the direction of the upper surface 18 of the workpiece is pushed back. On the other hand, in the present invention, during high-speed rotation, the mist-like coolant flows in the direction of the mist-like cutting fluid sprayed from the direction of the upper surface 18 of the workpiece as shown in FIG. 7 (b). The amount of cutting fluid sprayed onto the ball blade 5 and the outer peripheral blade 6 can be improved without pushing back the airflow around the blade portion 1 (arrow M direction). In addition to improving the tool life, high-precision finishing can be performed over a long period of time.

  As shown in FIG. 8 (a), the conventional right end twisted ball end mill is a view of the ridgeline of the ball blade 5 as viewed from the tip direction of the blade tip, and has an S shape. On the other hand, the small-diameter CBN ball end mill of the present invention is a right-handed left-handed twist, and the axial rake 13 of the ball-shaped blade 5 is set to -5 ° to -25 °. Therefore, as shown in FIG. The ridgeline of the blade 5 is a view seen from the tip direction of the blade tip, and has an inverted S shape. Thereby, since the radial rake 14 near the tip of the ball blade 5 can be set to a negative rake angle smaller than that of the conventional S-shape, the cutting resistance can be lowered and further stable machining can be performed.

  FIG. 9 is a diagram for explaining the entire length of the ball blade and the angular range of the radial rake condition in the CBN ball end mill of the present invention. The radial rake 14 represented in FIGS. 10 and 11 is centered on the tip 17 of the ball blade 17 in FIG. The radial rake 14 includes an angular range of 0 ° to −10 °, and the radial rake 14 of the ball blade 5 on the outer peripheral side exceeding the 20% range 16 reaches the outer peripheral blade 6 in a range of more than −10 ° and 25 °. The negative angle gradually increases until. Here, the length 15 of the entire ball blade indicates a ball blade length of −90 ° to 90 ° in the front view. In other words, it refers to the range of the curve CC ′ in FIG. As a result, the sharpness near the tip of the ball blade 5 can be improved, and even when the neck length L is long, vibration can be suppressed and stable machining can be performed, and the rigidity of the ball blade 5 near the outer periphery can be improved. As a result, chipping and chipping can be suppressed. A black circle point O in the figure indicates the center point of the radius R.

  Next, a case where bottom cutting is performed using a conventional end mill and the small-diameter CBN ball end mill of the present invention will be described. FIG.10 (b) is a figure which shows the AA cross section of FIG. 9 of the CBN ball end mill of this invention. (A) is a figure which shows the cross section of the conventional ball end mill in the position equivalent to the said AA cross section. (C) is the schematic which shows the direction of the cutting resistance in the bottom face cutting of the ball end mill which has a cross section of (a). (D) is the schematic which shows the direction of the cutting resistance in the bottom face cutting of the ball end mill which has a section of (b). In the conventional end mill of FIG. 10A, the sharpness of the tip is low, so that the tip is easily swung left and right as shown in FIG. On the other hand, in the small diameter CBN ball end mill of the present invention, as shown in FIG. 10B, the radial rake 14 is set on the relatively positive side as compared with FIG. . Further, in the CBN ball end mill of the present invention, the radial rake 14 reduces the cutting resistance as shown in FIG. The demand for a small-diameter CBN end mill is to process the workpiece 12 with high accuracy and high quality in finish cutting, and the biting property of the blade portion 1 is particularly important. In particular, in the case of a small-diameter long neck end mill in which the ratio of the neck length L to the blade diameter D is 5 times or more, vibration is likely to occur when the biting property of the blade portion 1 is low. The quality of the machined surface will be lowered. At the same time, the tilting of the tool becomes large, so that the machining accuracy is lowered, and the uncut amount that is an error with respect to the machining target is increased.

  11 (a) to 11 (d) show a case where a slope is cut using a conventional end mill and a small diameter CBN ball end mill of the present invention. FIG.11 (b) is a figure which shows the BB cross section of FIG. 9 of the CBN ball end mill of this invention. (A) is a figure which shows the cross section of the conventional ball end mill in the position corresponded to the said BB cross section. (C) is the schematic which shows the direction of the cutting resistance in cutting of the inclined surface of the ball end mill which has a cross section of (a). (D) is the schematic which shows the direction of the cutting resistance in cutting of the inclined surface of the ball end mill which has a cross section of (b). Both the conventional end mill of FIG. 11 (c) and the end mill of the present invention of FIG. 11 (d) are in the case of cutting a sloped surface where vibrations are likely to occur. As shown in b), since the radial rake 14 is large on the negative side, the rigidity of the cutting edge is improved, and the occurrence of chipping and chipping can be suppressed. For this reason, in the case of the present invention, especially in the shape of a long neck length L such that the neck length L exceeds 5 times the blade diameter D, in both bottom cutting and sloped surface cutting. Can be processed stably with high efficiency.

  In the present invention, as shown in FIG. 2, it is preferable to provide an interference avoidance portion 10 in which the interference portion between the rotation trajectory of the tool and the workpiece is removed to the rear in the rotational direction of the outer peripheral blade. As a result, it is possible to suppress a decrease in the tool rigidity, that is, the overall rigidity is improved and there is no interference with the workpiece, so that more stable machining can be realized. Here, the shape of the interference avoidance portion 10 may be a concave shape, a convex shape, a polygonal shape, or the like, and any shape can be exerted as long as the minimum necessary interference portion with the workpiece can be removed.

  Hereinafter, although the small diameter CBN ball end mill of the present invention is explained concretely with an example, the present invention is not limited by these examples.

In each of the examples in the following table, the present invention, the conventional example, and the comparative example are shown as categories, and the material numbers are described as consecutive serial numbers regardless of the categories.
Example 1
Example 1 is a comparison of cutting results of a right-handed left-handed torsion having the shape of the present invention with respect to a right-handed right-handed twisted blade which is a typical conventional example. In both Conventional Example 1 and Invention Example 2, the number of blades is 2 blades, the blade diameter is 1 mm, the radius of the ball blade is R0.5 mm, the outer peripheral blade length is 0.1 mm, that is, the blade length is 0.6 mm. This is a small diameter CBN long neck ball end mill having a length of 10 mm (L / D = 10) and a shank diameter of 4 mm. Conventional Example 1 was manufactured with a right-handed right-handed twist, and Example 2 of the present invention was prepared with a right-handed left-handed one. SKD11 (HRC60) hardened steel having a width of 50 mm, a depth of 50 mm, and a height of 50 mm was used as the work material. As shown in FIG. 12, the workpiece shape is a surface with a 1 ° gradient, the workpiece depth is 10 mm, and the bottom surface portion is formed with a plane width of 0.1 mm in order to evaluate the state of the processed surface. . In order to clarify the difference in tool performance, the cutting conditions are set such that the radial cut amount is 0.05 mm, the pitch cut amount is 0.05 mm, and the bottom cut amount is 0.05 mm. did. The rotational speed was 16000 times / min, the feed rate was 960 mm / min, mist coolant was used for cooling, and cutting was performed until the flank wear width of the tool reached 0.1 mm. The cutting results were compared based on the blade damage status, the machining surface state on the slope, the machining surface state on the bottom surface, and the tool life. The results are shown in Table 1.

  As a result of the cutting test, vibration was generated in Conventional Example 1 because the tool rigidity was low as described above. As a result, chipping occurred in the cutting edge, and it seems that the machined surface roughness in the machined surface state on the inclined surface deteriorated. A lot of streaks remained on the sloped surface in which the level difference of the cutting edge due to the chipping of the blade was transferred. On the other hand, Example 2 of the present invention was a very stable processed surface, and the maximum height of the surface roughness of the gradient surface was Rz = 0.68 μm. Also, in the tool life, the comparative example 1 was 120 m and the specified flank wear width reached 0.1 mm, while the inventive example 2 had a flank wear width of 0.07 mm even when scraped to 400 m. It was in a state where it could be continuously processed. Further, when comparing the machined surface state at the bottom surface of the workpiece, the invention example 2 obtained a uniform cutter mark machined surface, while the comparative example 1 produced non-uniform cutter marks. At the same time, the machined surface was in a muddy state. In the prior art example 1, the mist-like coolant was not sufficiently supplied, and the processing surface was muffled. On the other hand, the present invention 2 supplied the mist coolant sufficiently to the tip portion to provide a good surface roughness. It is because it can be obtained.

(Example 2)
In Example 2, the number of blades is two blades, the blade diameter is 1 mm, the radius of the ball blade is R0.5 mm, the outer blade length is 0.1 mm, that is, the blade length is 0.6 mm, and the neck length is 10 mm (L / D = 10). ), Although the shank diameter was 4 mm and the right blade left-twisted small diameter CBN long neck ball end mill shape, the influence due to the difference in the shape of the ball blade rake face and the outer edge rake face was confirmed. In Example 5 of the present invention, the ball blade rake face and the outer peripheral edge rake face were manufactured using a method of simultaneously grinding so that the ball blade rake face and the outer peripheral edge rake face were formed on the same plane. As a comparative example, Comparative Example 3 in which the angle difference between the ball blade rake face and the outer peripheral edge rake face formed by separate processes of the ball edge rake face and the outer peripheral edge rake face was 10 °, and the ball blade rake face and the outer peripheral edge rake face. A cutting test was carried out using Comparative Example 4 in which the angle difference was as small as 3 °. The rake face of the outer peripheral cutting edge of Comparative Examples 3 and 4 was formed by the method of grinding the outer peripheral groove in the same manner as the conventional ball end mill shown in FIG. The cutting test was performed under the same cutting conditions, workpiece shape, and machining method as in Example 1, and the cutting results were evaluated by comparing the blade damage status, the machining surface condition on the gradient surface, and the tool life. The results are shown in Table 2.

  As a result of the cutting test, vibration was generated in both Comparative Examples 3 and 4, and as a result, large cracks were generated on the flank surface at the stage where 150 m was cut in Comparative Example 3 and at the stage where 240 mm was cut in Comparative Example 4. As for the machined surface state on the gradient surface, more waviness was generated with many cutter marks remaining on the gradient surface. In addition, streaks occurred in the pitch direction on the gradient surface, and the maximum height of the surface roughness of the gradient surface was Rz = 2 μm or more. On the other hand, Example 5 of the present invention was in a stable machined surface state with no chatter vibration. In particular, the maximum height of the surface roughness of the sloped surface was Rz = 0.66 μm, and a very small surface roughness could be obtained compared to the comparative example. In Example 5 of the present invention, there was no particularly large defect even at the stage of cutting 400 m, and the flank wear width was as small as 0.056 mm.

(Example 3)
In Example 3, the influence of the axial rake of the ball blade was confirmed. Comparative Example 6, Invention Examples 7 to 11 and Comparative Example 12 were prepared by changing the axial rake of the ball blade as shown in Table 3 with the same basic tool shape as that of Invention Example 5. It used for the cutting test. SKD11 (HRC60) hardened steel having a width of 50 mm, a depth of 50 mm, and a height of 50 mm was used as the work material. In this test, the ball tip was evaluated by bottom cutting. The cutting conditions were an axial depth of cut of 0.05 mm, a pitch direction depth of cut of 0.05 mm, a rotational speed of 16000 times / min, a feed rate of 960 mm / min, and mist coolant was used for cooling. Evaluation was performed until the cutting distance reached 400 m. The cutting results were compared based on the state of damage to the blade and the machined surface state at the bottom. The results are shown in Table 3.

  As a result of the cutting test, Examples 7 to 11 of the present invention have no chatter vibration, and the blade edge is in a worn state having a stable flank wear width of 0.1 mm or less even after being cut by 400 m, and can be continuously machined. Met. In addition, the processed surface was a good finished surface, and the maximum height of the surface roughness of the bottom surface portion was Rz = 1 μm or less, and a uniform cutter mark could be obtained. On the other hand, since Comparative Example 6 is weak against the resistance from the bottom surface because of the low rigidity of the blade edge, a large chip occurred on the rake face side. Further, in Comparative Example 12, large chipping occurred on the flank side, and thereafter wear progressed on the rake face side. This is presumably because chipping to the flank side occurred because the axial rake was too large on the negative side and the resistance of the cutting edge received during cutting increased.

Example 4
Example 4 is an example of the present invention in which the influence of radial rake at the tip of the ball blade was confirmed. Invention Examples 13 to 17 are manufactured by changing the radial rake from the tip of the ball blade to the shank side as shown in Table 4 with the same basic tool shape as the present invention 10, as shown in Table 4. And subjected to a cutting test. From the tip of the ball blade to the place where it enters 0.02 mm on the shank side is a range corresponding to 20% of the entire length of the ball blade. SKD11 (HRC60) hardened steel having a width of 50 mm, a depth of 50 mm, and a height of 50 mm was used as the work material. In this test, the ball tip was evaluated by bottom cutting. The cutting conditions were an axial depth of cut of 0.05 mm, a pitch direction depth of cut of 0.05 mm, a rotational speed of 16000 times / min, a feed rate of 960 mm / min, and mist coolant was used for cooling. Evaluation was performed until the cutting distance reached 400 m. The cutting results were compared based on the blade damage status and the machined surface roughness at the bottom. The results are shown in Table 4.

  As a result of the cutting test, in all of Examples 13 to 17 of the present invention, the blade edge was in a worn state with a stable flank wear width of 0.1 mm or less even after being cut by 400 m, and could be continuously machined. . Therefore, the tool life was better than that of the conventional ball end mill. Comparing the processed surface roughness at the bottom surface, the processed surface roughness is satisfactory from the object of the invention, but the present invention example 15 was able to obtain the smallest processed surface roughness. In the present invention example 17, the maximum height Rz of the processed surface roughness is relatively large in this group, and when the radial rake becomes positive as in the present invention example 17, the biting property is improved, but the rigidity of the cutting edge is increased. It is thought that minute chipping of the cutting edge affects the surface roughness of the machined surface. On the other hand, when the radial rake becomes large negative as in Example 13 of the present invention, the cutting resistance received by the cutting edge is improved, which slightly affects the generation of vibration. From this result, it was confirmed that when the radial rake in the range of 20% of the entire length of the ball blade is in the range of 0 ° to −10 °, it is possible to perform machining more stably for a long time.

(Example 5)
In Example 5 to 18 of the present invention, the basic tool shape is the same as that of the present invention 15 (therefore, the radial rake at the tip of the ball blade is −5 ° confirmed to be optimal in Example 4), and the outer peripheral blade. A side ball blade with a different radial rake was produced and used for testing. SKD11 (HRC60) hardened steel having a width of 50 mm, a depth of 50 mm, and a height of 50 mm was used as the work material. As shown in FIG. 12, the workpiece shape is a surface with a 1 ° gradient, the workpiece depth is 10 mm, and the bottom surface portion is formed with a plane width of 0.1 mm in order to evaluate the state of the processed surface. . Cutting conditions were set such that the radial cutting depth was set to 0.05 mm and the pitch cutting depth was set to 0.05 mm, and the rotational speed was increased to 30000 in order to intentionally generate vibration. The test was performed using a mist-like coolant for cooling at a speed / min and a feed rate of 1250 mm / min. Cutting results were compared based on the damage status of the blade, the machined surface condition on the bottom surface, the machined surface roughness on the gradient surface, and the amount of uncut material. The results are shown in Table 5.

  As a result of testing with all the tools generating slight chatter vibrations, the inventive examples 19 to 22 show stable wear in the blade damage state, and the maximum height of the surface roughness on the inclined surface is high. Rz = 1 μm or less, the processing surface state at the bottom surface portion was free of streaks and stuffiness, and the uncut amount was good at 0.015 mm or less, and extremely high-precision processing could be realized. In particular, Example 20 of the present invention was the most excellent in both the machined surface roughness and the uncut amount. Further, in terms of the rigidity and biting property of the blade edge, the radial rake was good at around −20 °, and it was confirmed that the blade shape can be machined more stably and efficiently in the present invention. In the example 18 of the present invention, the maximum height of the surface roughness was Rz = 1 μm or less, and the processed surface state at the bottom surface portion was good with stable wear without streaks or stuffiness, but within this group, The amount of uncut material was relatively large at 0.025 mm. This is considered to be because the radial rake on the outer peripheral side is large on the negative side and the cutting resistance is large. On the other hand, in the inventive examples 23 and 24, the blade damage status, the maximum height of the surface roughness, and the machined surface status at the bottom surface were all good as in the inventive examples 19-22. When the radial rake is small on the negative side, it is considered that the abrasion has progressed due to a slight decrease in the rigidity of the cutting edge, and the amount of uncut material has increased. From this result, it is more preferable that the radial rake of the outer peripheral side ball blade exceeds −10 ° and reaches −25 °.

  If the industrial field to which the small-diameter CBN ball end mill of the present invention can be applied is exemplified, in the processing of molds and parts, etc., particularly high-hardness materials with HRC50 or higher, and stable and high-precision processing over a long time. Is possible. Specific application fields are, for example, suitable for finishing plastic molds such as mobile phones, finishing forging dies that are work materials of HRC60 or higher such as gears, and also in molds with a wide processing range. A single tool can cut a wide area. Since it can be machined with higher accuracy than conventional products, it is suitable for machining precision molds that require higher-precision cutting.

DESCRIPTION OF SYMBOLS 1 Blade part 2 Neck part 3 Joint part 4 Shank 5 Ball blade 6 Peripheral blade 7 Peripheral blade length 8 Ball blade rake face 9 Perimeter blade rake face 10 Interference avoidance part 11 Contact length of cutting edge 12 Work material (also called workpiece) )
13 Axial rake 14 Radial rake 15 Overall length of ball blade 16 20% range 17 Ball blade tip 18 Upper surface of workpiece 19
20
D Blade diameter L Neck length R Radius

Claims (4)

  A small-diameter CBN ball end mill having a blade diameter of 3 mm or less and an arcuate radius Rmm forming a blade portion and an outer peripheral blade made of CBN, wherein the rake face of the ball blade and the R / 5 or more peripheral blade rake surfaces are formed in the same plane, the outer peripheral blade is formed by right-handed left-handed twist, and the axial rake of the ball blade is -5 ° to -25 °. Small diameter CBN ball end mill.   A long-necked end mill having a blade diameter D of 3 mm or less and a ratio L / D of the length L of the neck under the tool to the blade diameter of 5 or more, and a ball blade having an arcuate radius Rmm forming a blade portion of the end mill; A small-diameter CBN ball end mill having an outer peripheral blade made of CBN, wherein the rake face of the ball blade and an outer peripheral rake face of R / 5 or more of the outer peripheral blade length are formed in the same plane, A small-diameter CBN ball end mill characterized in that the blade is formed of a right blade left-handed twist, and the axial rake of the ball blade is -5 ° to -25 °.   3. The small diameter CBN ball end mill according to claim 1, wherein the range of 20% of the entire length of the ball blade centered on the tip of the ball blade is an angular range where the radial rake is 0 ° to −10 °. A small-diameter CBN ball end mill characterized in that the radial rake of the outer peripheral ball blade exceeding 20% gradually increases in a minus angle from −10 ° to −25 ° until reaching the outer peripheral blade.   The small diameter CBN ball end mill according to any one of claims 1 to 3, wherein an interference avoidance portion with a work material is provided behind the outer peripheral blade.

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