JP2010125594A - Minor diameter cbn end mill - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a minor diameter CBN end mill in a new shape capable of performing the cutting of a high-hardness material such as a precision component with high accuracy and efficiency for a long time without the occurrence of abrasion and chipping, and especially to provide a minor diameter CBN square end mill and a radius end mill with an edge diameter of 3 mm or less. <P>SOLUTION: A minor diameter end mill in which a part of cemented carbide material integrally sintered to a CBN sintered material is inserted and fixed to a shank hole part is provided with a cutting edge on its tip with an edge diameter of 3 mm or less. In the minor diameter CBN end mill, a peripheral cutting edge is formed so as to be a right edge torsional to left, and at least 60% of the peripheral cutting edge, desirably whole of it, is formed by a gash. The axial rake of the cutting edge at the tip of the end mill is -5&deg; to -25&deg;, and further desirably the radial rake of the tip of the cutting edge is +10&deg; beyond -5&deg;. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a small-diameter CBN end mill having a structure in which at least a part of a blade portion is composed of a CBN sintered portion and integrally sintered with a cemented carbide portion, and the blade diameter is 3 mm or less.

  The cubic boron nitride (CBN) cutting tool is a cutting tool obtained by sintering boron nitride (BN) having hardness next to diamond at an ultrahigh pressure. Since diamond is not suitable for cutting iron-based materials, CBN is used for cutting iron-based high-hardness materials and difficult-to-cut materials, or for high-speed cutting and intermittent cutting of low-hardness iron-based materials. However, CBN cutting 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 a large cutting volume is not possible. It is only used for super finishing. Particularly in the case of a small-diameter CBN end mill, at least the blade portion is made of a CBN sintered material, and the flank on the rear side of the blade portion and the back metal portion are also CBN sintered material. For this reason, if a lateral force is applied during cutting, chipping occurs due to insufficient strength. Therefore, in a small-diameter end mill having a blade diameter of 3 mm or less, machining with low accuracy is forced by using a carbide end mill having excellent toughness compared to a CBN sintered material. In some cases, electric discharge machining with extremely low machining efficiency is required. Is still adopted.

Non-Patent Document 1 describes a small-diameter CBN radius end mill, and as a tool for preventing chipping, a chamfer ring, that is, the entire cutting edge, from an end mill end cutting edge including an end cutting edge and a corner cutting edge to an outer peripheral cutting edge. An end mill having a large negative rake angle has been proposed.
Another Patent Document 1 uses a CBN end mill having at least a tip portion made of an ultra-high pressure CBN sintered body and having an outer peripheral blade having a twist in a direction opposite to the cutting rotation direction when viewed from the shank side. It has been proposed that efficiency can be improved.
JP 2008-110411 A "Type Technology" Vol. 21, No. 8, July 2006 (P.38-39)

  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 60 HRC. In recent years, the thickness of mobile phones has become thinner year by year, and the structure of the ribs has changed in order to give the frame strength even if it is thin. In other words, a mold material that is harder than before is 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, such hard steel materials as described above have a problem in tool wear when processed with a cutting tool, and it is difficult to perform highly efficient and highly accurate processing over a long period of time. For this reason, electric discharge machining with extremely low machining efficiency is still employed.

  When machining these materials with high hardness 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 cutting edge formed of a CBN sintered body is used has increased. 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 a large cutting volume is impossible. It is only used for super finishing. Here, in the case of a ball end mill having a ball blade at the cutting edge, the shape is not finished unless the pitch is made fine, so that highly efficient cutting cannot be performed. That is, it is difficult to perform highly efficient finishing even with an end mill made of cemented carbide. In addition, in the case of a CBN ball end mill having a cutting edge formed of a CBN sintered body, if the cutting condition is increased by forcibly performing high-efficiency processing, the cutting edge will be lost, and it will not be adopted for use. In order to solve the problems peculiar to CBN sintered materials, proposals for improving the shape of the CBN ball end mill have been proposed in Non-Patent Document 1 and Patent Document 1 described above. There is a problem in performing, and there remains a problem that if the cutting condition is raised by forcibly performing high-efficiency machining, the chip is lost.

  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 end mill with a diameter of 3 mm or less, if at least the blade portion is made of a CBN sintered material, the flank and the back metal portion behind the blade portion are also made of the CBN sintered material. Therefore, it was found that when a lateral force is applied during cutting, chipping occurs due to insufficient strength due to the small blade diameter.

  In the case of a ball end mill having a ball blade at the cutting edge, in processing that does not have a three-dimensional shape, such as precision part processing or mold processing of a frame part that is different from the rib structure of a mobile phone, that is, in two-dimensional or 2.5-dimensional processing Since the shape is not finished unless the pitch is made fine, high-efficiency processing cannot be performed, and it does not fit the application at all. That is, the target end mill shape cannot be obtained.

  Here, in processing such as mold processing of frame parts that are different from precision parts and mobile phone rib structures, a square end mill with a flat cutting edge and a radius end mill with a round corner are used rather than a ball end mill with a ball cutting edge at the cutting edge. Since the bottom blade flat part is wider, highly efficient processing is possible. However, in the processing of the bottom surface portion, as shown in FIG. 1, when both the ball end mill 1 and the radius end mill 2 are cut with the same cutting depth 3, the radius end mill 2 has a wide bottom edge flat portion, so that the work material 4 is divided accordingly. Since the contact area 5 of the cutting blade that comes into contact with the substrate increases, the resistance tends to increase. In FIG. 1, a portion of the contact area 5 of the cutting edge that contacts the work material 4 is drawn by comparison with a thick line, but when compared, the radius end mill 2 has a larger contact area 5 of the cutting edge. I understand that.

  On the other hand, Non-Patent Document 1 proposes a small-diameter CBN radius end mill that has a large negative rake angle for the entire cutting edge to prevent chipping. In this proposed end mill, The cutting resistance is further increased, cannot withstand the resistance, and leads to a larger defect. In other words, in the case of a square end mill having a flat cutting edge or a radius end mill having a round corner, if the material of the tool is formed of a CBN sintered material, it is more likely to cause chipping and stable machining cannot be expected.

  Patent Document 1 proposes a CBN end mill having at least a tip portion made of an ultra-high pressure CBN sintered body and having an outer peripheral cutting edge having a twist in a direction opposite to the cutting rotation direction when viewed from the shank side. . As a result, the edge angle of the corner cutting edge increases and the edge strength increases, and it is not necessary to round the edge by chamfering such as lapping or honing, which suppresses blade chipping. However, in this proposed end mill, as shown in FIG. 2, the rake face 27 of the corner cutting edge and the rake face 28 of the outer peripheral cutting edge are formed by different surfaces. That is, the resistance when the corner cutting edge comes into contact with the outer peripheral cutting edge in the machining of the bottom surface, such as the precision part machining and the die machining of the frame part different from the rib structure of the mobile phone, especially the machining of the corner part of the mold. Since the resistance at this time changes, a large resistance is generated in combination with the vibration generated due to the large contact area of the bottom blade. In particular, when high-efficiency processing is performed, the strength of the cutting edge cannot be withstood, and the chip is lost, and stable processing cannot be expected.

Further, since the rake face 27 of the corner cutting edge and the rake face 28 of the outer peripheral cutting edge that form the chip pocket when chip is discharged are formed with different surfaces, a step is likely to occur at the rake face boundary 29, and at the time of cutting processing. The generated chips are easy to bite in the chip pocket, and the finished surface may be damaged, or the resistance may increase due to the bite and may be lost.
Also, according to the proposal of this end mill, the rake angle of the outer peripheral cutting edge is said to be better as it becomes a negative rake angle, but at the negative rake angle, the biting property deteriorates and the vibration accompanying the increase in resistance is extremely large. It is likely to occur and stable processing cannot be expected.
In view of the conventional circumstances of the present invention, a small-diameter CBN end mill having a blade diameter of 3 mm or less, particularly capable of machining a high-hardness material such as precision part machining with high accuracy and high efficiency over a long period of time. Among them, a small-diameter CBN square end mill and a small-diameter CBN radius end mill of 3 mm or less that can achieve high-efficiency cutting are provided.

  In the present invention, as shown in FIGS. 3 and 4, at least the blade portion 26 is formed of the CBN sintered portion 6, and the rear end portion 7 of the cemented carbide portion 17 integrally sintered with the CBN sintered portion 6 is provided. The blade portion 26 is a small-diameter end mill having a tip edge 11 having a blade diameter of 3 mm or less, and 60% or more of the outer peripheral edge 8 is a gash 9. The outer peripheral cutting edge 8 of the blade portion 26 is formed by a right-handed left-handed twist, and the axial rake of the end mill end cutting edge 11 is −5 ° to −25 °. It is an end mill. The outer peripheral cutting edge 8 includes an outer peripheral cutting edge 10 formed by a gash 9 and a blade groove. Here, the end mill end cutting edge 11 is a combination of the end cutting edge 12, the corner cutting edge 13 and the outer peripheral cutting edge 8, and the axial rakes of the end cutting edge 12, the corner cutting edge 13 and the outer peripheral cutting edge 8 are all the same. To do. The blade portion 26 is a term generically indicating the end mill tip cutting edge, and the blade diameter 30 indicates the maximum diameter portion of the blade portion.

  Although the small-diameter CBN end mill of the present invention can be realized by a ball end mill, a square end mill or a radius end mill that makes the most of the features of the present invention is desirable for the purpose of high-efficiency cutting that is difficult with a ball end mill.

  Another invention of the present invention is a small diameter CBN end mill characterized in that an interference avoidance portion is provided behind the outer peripheral cutting edge. In the case of the present invention, there is no outer peripheral cutting edge 10 formed by the blade groove shown in FIGS. 3 and 4, and the outer peripheral cutting edge 8 consists only of a gash 9 extended to the reference numeral 10 in the figure. In this case, an interference avoidance part at the time of tool rotation is provided behind the outer peripheral cutting edge.

  Another invention of the present invention is a small-diameter CBN end mill characterized in that the radial rake of the end cutting edge 12 and the radial rake of the outer peripheral cutting edge 8 have substantially the same angle. Specifically, the substantially same angle means a difference in angle within ± 1 °. In the case of the present invention, the rake face 27 of the corner cutting edge and the rake face 28 of the outer peripheral cutting edge are substantially the same as shown in FIG. 5, and the rake face generated in the conventional example as shown in FIG. The step 31 does not occur. That is, there is no rake face 36 formed by a blade groove in the end mill tip cutting edge 11.

  In the small diameter CBN end mill of the present invention, it is desirable that the radial rake of the end mill end cutting edge is more than −5 ° and + 10 °. In the small diameter CBN end mill of the present invention, the shape of the blade is preferably a radius end mill having corner radii at both ends of the end mill tip.

The small-diameter CBN end mill of the present invention has the entire configuration from the shank to the blade part,
The rear end portion 7 of the cemented carbide portion inserted into the shank hole portion is fixed at its bottom surface 19 and at least a part of the outer peripheral surface portion 18 to the shank portion 23 via a bonding material. The length 20 in a part of the tool axis direction is preferably set to be 1 or more times the blade diameter. The small diameter CBN end mill of the present invention is manufactured by integrally sintering a CBN sintered part and a cemented carbide part. The rear end part of the cemented carbide part is joined to the shank using a joining agent such as a brazing material. Is done. The said outer peripheral surface refers to the outer peripheral surface of the rear end of a cemented carbide part.

  In the present invention, since the outer peripheral cutting edge of 60% or more is formed only by gash, there is no rake face step in the vicinity of the end cutting edge. As a result, it is possible to suppress the generated chips from being bitten by a step, and to solve the problem of chip biting as in the conventional example.

  Further, even in the case of machining with a non-uniform margin in the previous process of the finishing process, the small-diameter end mill of the present invention forms 60% or more of the outer peripheral cutting edge only with the gash, and the axial rake of the end mill cutting edge is − Since the angle is set to 5 ° to −25 °, there is an effect of preventing the dropping of the CBN particles, chipping, chipping, and instability resulting from the vibration of the tool and insufficient strength, which are the biggest problems of the conventional small diameter CBN end mill.

  In the present invention, 60% or more of the outer peripheral cutting edge can be formed only by the gash, so there is no portion where the rigidity is lowered by the conventional blade groove. This effect of ensuring the tool rigidity is a very important effect for realizing a brittle tool called CBN with a small diameter end mill with a blade diameter of 3 mm or less targeted by the present invention.

  A major feature of the axial rake of the small-diameter end mill tip cutting edge 11 of the present invention is that it is -5 ° to -25 °, and the outer peripheral cutting edge is formed by a right-handed 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.

  When the radial rake of the end mill end cutting edge 11 of the present invention is more than −5 ° and + 10 °, sufficient biting property can be secured, so that there is an effect that more stable processing can be realized. In particular, the radial rake is preferably in the range of + 5 ° to 0 °, and is optimal from the balance of biting property and strength.

  In the small diameter end mill of the present invention, the rear end portion of the cemented carbide portion integrally sintered with the CBN blade portion is inserted into the shank hole portion, and the outer peripheral surface portion and the bottom surface portion of the rear end portion are fixed by brazing or the like. Therefore, the mechanical strength of the insertion portion at the rear end is ensured, the strength in the vicinity of the neck mounting portion is increased, the vibration due to deflection is increased, and the like, combined with the effect of the tool shape, realizes extremely stable machining. be able to.

  By applying the present invention, for example, in the machining of precision parts using a CBN small diameter end mill with a blade diameter of 3 mm or less and the frame processing of a frame part different from the rib structure of a mobile phone, the mold material is made of a high hardness material. Even in such a case, high-precision machining can be realized stably for a long time without causing chipping, which is effective for cost reduction of precision parts machining.

  The present invention is a structure in which at least the blade portion is made of a CBN sintered portion, and the rear end portion of the cemented carbide portion integrally sintered with the CBN sintered portion is inserted and fixed in the shank hole portion, The blade part is a small-diameter end mill having a cutting edge with a blade diameter of 3 mm or less, and 60% or more of the outer peripheral cutting edge of the small-diameter end mill is formed by gash, and the outer peripheral cutting edge of the blade part is right A small-diameter CBN end mill, which is formed by blade left-hand twist and has an axial rake of the cutting edge of the blade portion of −5 ° to −25 °. As will be described later in Examples, it has been confirmed that it is preferable that 75% or more of the outer peripheral cutting edge is formed only by gash.

  In case of 2D or 2.5D shape processing in high hardness material, in case of small diameter CBN square end mill or small diameter CBN radius end mill where the blade is made of CBN sintered material, Since the contact area of the substrate becomes large, the resistance tends to increase, leading to chipping of the cutting edge and leading to a large defect. In other words, it is necessary to reduce the cutting resistance. However, if the rake angle of the cutting edge is set to an acute angle, the cutting edge has insufficient rigidity, which causes a large defect.

  The present invention is characterized in that as a shape of the blade, 60% or more of the outer peripheral cutting edge 8 is formed only by gash. As a result, as shown in FIG. 7, the end cutting edge 12, the corner cutting edge 13, and the outer peripheral cutting edge 9 formed only by the gash are all formed with the same rake face. The feature of this outer peripheral cutting edge is exhibited as a great effect in corner processing of high-hardness material processing, such as die processing of a frame part different from the precision parts and the rib structure of a mobile phone. For example, as shown in FIG. 8, in corner processing, resistance is applied to the end cutting edge 12 and the corner cutting edge 13, and an outer peripheral cutting edge 10 formed only by a gash and an outer peripheral cutting edge 10 formed by a blade groove. However, the resistance is constant because it is formed by the same rake face except for the outer peripheral cutting edge 10 formed by the blade groove. In other words, only the outer peripheral cutting edge 10 formed by the blade groove changes the cutting resistance and causes vibration, but the present inventor vibrates if 60% or more of the outer peripheral cutting edge is formed only by the gash. I found that the suppression has a big effect. Further, if the outer peripheral cutting edge of 60% or more is formed only by gash, there is no rake face step 31 in the vicinity of the end cutting edge 12 as shown in FIG. 7, and thus generated chips are bitten by the step. As shown in FIG. 6 of the conventional example, it is possible to solve the problem of chip biting in which a rake face step 31 exists in the vicinity of the end cutting edge 12.

  In addition, the main feature is that the axial rake of the end mill cutting edge 11 is set to -5 ° to -25 °. As a result, the outer peripheral cutting edge 8 is formed with a right-handed left-handed twist, but this effect applies a force in the direction in which the end mill is pulled to the spindle side of the machine tool. Can reduce vibration. Further, since the axial rake of the end mill tip cutting edge 11 is −5 ° to −25 °, the cutting edge rigidity is increased and chipping can be suppressed. Here, if the axial rake of the tip cutting edge is larger than -5 ° in the plus direction, the cutting edge rigidity is insufficient, the strength of the CBN sintered material does not exist, and the CBN particles fall off, eventually chipping. If it is larger than −25 ° in the minus direction, the cutting edge rigidity increases, but the resistance increases, and conversely, the CBN particles fall off, leading to a large defect.

  It is one of the features of the present invention that the outer peripheral cutting edge 8 is formed by gasching only 60% or more of the length of the blade. As a more preferable embodiment of the present invention, as shown in FIG. It is desirable to form the cutting edge 8 only by gash. As a result, even during the machining shown in FIG. 8, all the cutting edges that come into contact with each other are formed with the same rake face, so that stable machining without any change in resistance can be expected. Further, as shown in comparison between the example of the present invention in FIG. 5 and the conventional example in FIG. 6, there is no rake face step 31 on the end mill end cutting edge 11, so that no chips are generated due to the step and the cutting is not performed. Changes in cutting resistance, chipping, and the like due to scraping can be more reliably suppressed. Further, since the blade groove is not necessary, a portion where the rigidity is reduced, such as the blade groove length 14 shown in FIGS. 3 and 4 when the blade groove is provided, is not necessary. That is, the inventor deleted unnecessary blade grooves as shown in FIG. 9, and provided an interference avoidance portion 25 at the rear of the outer peripheral cutting blade from which only a necessary minimum interference portion of the rotation locus of the tool was removed. As a result, it is possible to suppress the reduction of the waste tool rigidity, that is, the overall rigidity is improved and more stable machining is realized. Here, the shape of the interference avoidance portion 25 may be a concave shape, a convex shape, a polygonal shape or the like, and any shape can be effective as long as the minimum necessary interference portion can be removed.

  As a more preferable mode of the present invention, it is desirable that the radial rake of the end mill tip cutting edge 11 is more than −5 ° and + 10 °. By setting the radial rake within the above range, sufficient biting property is secured and more stable processing is realized. Further, the inventor has clarified that the range of + 5 ° to 0 ° is optimal from the balance of biting property and strength.

  As a more preferable embodiment of the present invention, a radius end mill having a corner R at the end mill edge is desirable. By having the corner R at the leading edge, the strength of the leading edge is further increased, and the effect of suppressing chipping and the like is further increased.

  In a more preferred embodiment of the present invention, in the small diameter CBN end mill of the present invention, the rear end portion 7 of the cemented carbide portion inserted into the shank hole portion has a bottom surface 19 and at least a part of the outer peripheral surface 18 containing a bonding agent. The length 20 in the tool axis direction of at least a part of the outer peripheral surface is preferably 1 time or more of the blade diameter. The reason why the length 20 in the tool axis direction is at least one times the blade diameter is to ensure the fixing to the shank by the bonding agent. As a means for inserting the rear end portion 7 of the cemented carbide portion integrally sintered with the CBN sintered portion into the shank hole portion, the cemented carbide portion inserted into the hole portion is inserted into the taper portion 15 at the insertion start position. It is fixed by brazing etc. the outer peripheral surface part 18 and the bottom face part 19 of the part 7 of the cemented carbide material inserted in the hole of the cemented carbide part 17 fixed from 16 and sintered integrally. desirable. As a result, the mechanical strength of the insertion portion from the tip of the hole portion is ensured, the strength in the vicinity of the neck mounting portion is increased, the vibration is also increased due to deflection, and the extremely stable machining is realized in combination with the effect of the tool shape.

Next, the production of a material of an integrally sintered body of cemented carbide inserted into the CBN forming the blade portion of the present invention and the shank hole will be described.
The CBN sintered material and the cemented carbide material that forms the lower part are cut to the required size from the material on the disc that is integrally sintered, and one part of the cemented carbide material is fixed to the hole in the shank. To manufacture. Examples of the fixing method include brazing, crimping, and fitting. Brazing is preferable because it has high accuracy and reliability after fixing and is economically convenient. As the brazing material, it is preferable to use a Ni—Cr brazing material, an Ag—Cu—Ti, or an Ag—Cu—Zn system. For example, an ultra-high hardness sintered material is brazed at a higher temperature, such as 890 to 1173 ° K. for Ag—Cu—Ti and Ag—Cu—Zn brazing materials, and 1200 to 1490 ° K. for Ni—Cr brazing materials. Even when the cutting edge temperature rises during cutting, a more reliable small-diameter end mill can be realized without lowering the brazing strength.
Hereinafter, the present invention will be described based on examples.

Example 1
7 and 10 show the shape of an embodiment of the small-diameter CBN radius end mill according to the present invention. As Example 1 of the present invention, a part 7 of a cemented carbide material integrally sintered with a CBN sintered material having a CBN content of 65% and an average particle size of 3 μm is 0.3 mm, which is 0.3 times the blade diameter. The outer peripheral surface portion 18 and the bottom surface portion 19 were fixed by brazing. As shown in FIG. 10, Example 1 is a CBN radius end mill including a CBN sintered portion 6 made of a CBN sintered material and a cemented carbide portion 21 made of a cemented carbide material. An end cutting edge 12, a corner cutting edge 13, an outer peripheral cutting edge 8, a neck portion 22, a taper portion 15, and a shank portion 23 are provided from the tip of the tool, the number of blades is two, and the twist angle of the outer peripheral cutting edge 8 is -20. °. That is, the axial rake of the end mill end cutting edge 11 was −20 °, and the radial rake of the end mill end cutting edge 11 was 0 °. The blade diameter 30 of the CBN radius end mill is 1 mm, the size of the corner R is 0.2 mm, the length of the outer peripheral cutting edge 9 formed only by the gash is 0.3 mm, and the length of the outer peripheral cutting edge 10 formed by the blade groove Was 0.1 mm, that is, the length of the end mill cutting edge (hereinafter referred to as an effective cutting edge length) was 0.6 mm. The neck was straight, and the neck diameter was 0.94 mm, the neck length was 3 mm, 3 times the blade diameter, and the shank diameter was 4 mm.

  Further, as a conventional example 2, after forming an axial rake of the end mill end cutting edge 11 at 0 °, a crusher ring 24 gives a large negative rake angle of −40 ° to the entire blade portion 26 and a radial rake of −40 °. The other specifications were the same as those of Example 1 of the present invention. As Conventional Example 3, an outer peripheral cutting edge is formed with a blade groove as shown in FIG. 6, axial rake is −10 °, radial rake is 20 °, and other specifications are the same as those of Example 1 of the present invention. Each was subjected to a cutting test.

  As a workpiece to be used for the cutting test, an L-shaped bottom cut having a corner portion having a height of 1 mm and a radius of 0.2 mm was performed on the work material with SKD11 (HRC60). Cutting conditions are as follows: the rotational speed is 40,000 min-1, the feed rate is 2.4 m / min, the cutting depth in the tool axis direction is 0.02 mm, and the cutting depth in the tool radial direction is 0.3 mm. The mist was used.

As an evaluation method, transition of tool wear, measurement of cutting resistance at the initial stage of cutting at the corner, and the state of the finished surface at each cutting distance of 100 m were observed. Regarding tool wear, observe with a scanning electron microscope at a magnification of 250 times, and determine that the wear width of the flank surface reaches 0.1 mm or that cannot be cut due to chipping or the like is the life, and finally Cutting was performed to 500 m. The evaluation of the finished surface is ◎ marked for practically good, ○ marked for some dullness, △ marked for the chatter surface, and the cutting judged as unsatisfactory or glossy or tool failure. The distance is shown, and the x is indicated at that distance.
Table 1 shows the specifications and results of each sample.

As a result, Example 1 of the present invention was in a stable cutting state with almost no wear after cutting at a cutting distance of 500 m. Furthermore, the finished surface was also a glossy surface, and the maximum finished surface roughness in the direction perpendicular to the tool feed direction was 0.98 μm in Rz, which was a very excellent result. On the other hand, in Conventional Example 2, when the cutting distance was 100 m, a large chipping occurred due to the drop of CBN from the end cutting edge to the corner cutting edge, making cutting impossible. In addition, the finished surface was very bad with no gloss. Further, the cutting resistance value at the corner portion at the initial stage of cutting was as large as 22N. This is because the end mill of Conventional Example 2 is provided with the chamfer ring 24 having a large negative rake angle of −40 ° on the entire end mill cutting edge, so that a wide range of the end cutting edge can be used for the workpiece particularly when cutting the bottom surface. This is probably because the cutting resistance increased when contacted, and the strength of the CBN sintered material could not withstand and was lost. Here, FIG. 11 shows a comparison of the tool wear state between Example 1 of the present invention when cutting 500 m and Conventional Example 2 when cutting 100 m. It can also be seen from FIG. 3 that the resistance in the conventional example 2 is increased by the influence of the chamfer ring 24 and the boundary portion between the end cutting edge 12 and the corner cutting edge 13 is already missing at the time of 100 m cutting.
On the other hand, in Example 1 of the present invention, the axial rake of the tip cutting edge is set to -20 °, so that the cutting edge is formed with a right-handed left-handed twist, and the end mill is pulled in the direction of being pulled toward the spindle side of the machine tool Since force is applied, the holding rigidity is increased, the vibration to the workpiece side can be reduced, and the stability is improved, and the cutting edge rigidity is also increased.

  The end mill of Conventional Example 3 was stable with almost no wear at a cutting distance of 100 m, but the cutting resistance value at the corner portion was as high as 14 N from the beginning of cutting, and the finished surface was chattered at a cutting distance of 200 m. In the tool, a small amount of chipping was observed, and a large amount of deposit was observed at the rake face step 31, and finally the chip was lost at the end of 400 m.

(Example 2)
Next, as Examples 5 to 8, 10, and 11 of the present invention and Comparative Examples 4, 9, and 12, tests were performed in order to optimize the axial rake of the end mill end cutting edge. As a test method, the radial rake is 0 ° with the same specifications as in the first example of the present invention, the axial rake of the end mill end cutting edge 11 is -2 ° in the comparative example 4, the -5 ° to -25 in the present invention examples 5-8. °, Comparative Example 9 was -30 °.
Further, in Examples 10 and 11 of the present invention and Comparative Example 12, the axial rake is −20 °, the effective blade length is 0.5 mm, the interference avoiding portion 25 is provided behind the outer peripheral cutting edge, and the outer peripheral cutting edge is 100%. Example 10 of the present invention formed with a gash, 60% of an outer peripheral cutting edge with an effective blade length of 0.7 mm, an example of an invention 11 with an effective blade length of 0.7 mm, 50% of an outer peripheral cutting edge with an effective blade length of 0.8 mm The same processing and evaluation as in Example 1 were performed using Comparative Example 12 formed by gassing. The results are shown in Table 2.

  As a result, all the tools of Invention Examples 5 to 8, 10, and 11 could be stably processed even after cutting to 500 m. In the tools of Invention Examples 5 and 8, fine chipping and slight dullness were confirmed on the finished surface after 500 m cutting, but almost no wear was confirmed. In addition, the tool of Invention Example 11 showed a slight chatter surface in the finished surface state after cutting 500 m, but showed excellent performance without chipping and the like. In particular, the tool of Inventive Example 10 showed no wear even after cutting 500 m, and the finished surface was in a very good state.

  On the other hand, in Comparative Example 4, when the tool was confirmed at the time of cutting 200 m, chipping occurred on the rake face of the end cutting edge, and the finished surface was also found to be in a very glossy state that was very bad. This is probably because the end mill end cutting edge has insufficient rigidity, the strength of the CBN sintered material does not exist, and the CBN particles fall off and eventually cause chipping. Similarly, in Comparative Example 9, when the tool was checked at the time of cutting 100 m, large chipping occurred from the end cutting edge, and the finished surface due to this resulted in extremely bad results. This is presumably because the axial rake has a large negative rake angle, the resistance increases, and on the contrary, the dropout of the CBN particles proceeds, leading to the occurrence of large chipping. Further, in the tool of Comparative Example 12, a slight chatter surface was confirmed at the time of cutting 100 m, but it was stable without chipping. However, at 200 m, a minute chipping was caused, and the chatter surface was observed as a finished surface state. Missing along the way. This is considered to be due to the fact that the effective groove length is increased, the blade groove length is increased, and the rigidity of the tool itself is reduced, resulting in loss due to vibration.

Here, as a representative tool wear state, FIG. 12 shows a comparison of the tool wear state at the time of 100 m cutting of the present invention example 10 and the comparative example 4 at the time of 500 m cutting. From the same figure, it can be considered that the tool of Comparative Example 4 does not have sufficient rigidity at the end mill end cutting edge, and CBN particles began to fall off from the vicinity of the boundary between the end cutting edge 12 and the corner cutting edge 13 and eventually led to chipping. . On the other hand, it can be seen that the tool of Invention Example 10 is not worn at all.
From the results of Example 1 and Example 2, it was confirmed that more preferably 75% or more of the outer peripheral cutting edge is formed only by the gash.

(Example 3)
Next, as Examples 13 to 17 of the present invention, tests were performed in order to find a more optimal range of the radial rake of the end mill end cutting edge. The axial rake of the end mill end cutting edge is fixed at -20 °, the radial rake of the end mill end cutting edge 11 is changed from 15 ° to -10 °, and the others are manufactured according to the same specifications as Example 1 of the present invention. did. As an evaluation method, the same processing and evaluation as in Example 1 were performed. The results are shown in Table 3.

  As a result, all of the tools of Examples 13 to 17 of the present invention were able to perform stable processing even after cutting to 500 m. The tool of Example 13 of the present invention was confirmed to have fine chipping during 400 m cutting and a slight dullness on the finished surface, but it did not cause large chipping after 500 m cutting and was good. Further, in the tool of Invention Example 17 as well, a slight chatter surface was confirmed on the finished surface when cutting 400 m, but there was no chipping or the like on the finished surface, and minute drop wear was confirmed when cutting 500 m. On the other hand, Example 15 of the present invention showed very good results with almost no wear after cutting 500 m and a finished surface roughness of 0.96 μm. Preferably, the radial rake range of the end mill end cutting edge is presumed that the range of + 5 ° to 0 ° is more optimal.

Example 4
Next, with the same specifications as Example 1 of the present invention, a square end mill without corner R is used as Example 18 of the invention, and a corner end R of 0.2 mm is set as Example 19 of the invention, and the super sintered body is integrally sintered with a CBN sintered material. The same processing and evaluation as in Example 1 were carried out using a hard alloy portion having a rear end 7 inserted into the shank hole by a length of 1 mm. The results are shown in Table 4.

  As a result, both the inventive examples 18 and 19 were able to be processed stably even after cutting to 500 m. In the tool of Inventive Example 18, fine chipping was observed at the corner cutting edge when cutting 400 m, and the finished surface was slightly dull, but chipping did not increase even after cutting 500 m. Further, the tool of Inventive Example 19 showed no wear even after cutting 500 m, and the finished surface was in a very good state. This is because the mechanical strength of the insertion part is secured from the tip of the hole part by inserting the rear end part 7 of the cemented carbide part sintered integrally with the CBN sintered material deeply into the shank hole part, and in the vicinity of the neck part attachment part This is thought to be due to the fact that the strength of the film increased and the vibration caused by the deflection increased.

FIG. 1 shows a diagram comparing the difference in cutting resistance between a ball end mill and a radius end mill. FIG. 2 shows an example of a rake face of a conventional small diameter CBN end mill. FIG. 3 shows an example of a small diameter CBN radius end mill according to the present invention. FIG. 4 shows an example of a small diameter CBN square end mill according to the present invention. FIG. 5 shows that there is no step on the rake face in the enlarged part of the rake face of the small diameter CBN end mill according to the present invention. FIG. 6 shows an enlarged portion of a rake face with a step of a conventional small diameter CBN end mill. FIG. 7 shows the rake face of another small diameter CBN end mill according to the present invention. FIG. 8 shows the resistance of the radius end mill cutting edge in the corner machining of the mold. FIG. 9 shows a small-diameter CBN end mill according to the present invention in which the outer peripheral cutting edge is formed only by a gash and an interference avoidance portion is provided behind the outer peripheral cutting edge. FIG. 10 shows an example of another small-diameter CBN radius end mill according to the present invention. FIG. 11 shows a comparison of the tool wear state between Example 1 of the present invention and Example 2 of the prior art. FIG. 12 shows a comparison of the tool wear state between the inventive example 10 and the comparative example 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ball end mill 2 Radius end mill 3 Cutting depth 4 Work material 5 Cutting blade contact area 6 CBN sintered part 7 Rear end part 8 of cemented carbide integrally sintered with CBN sintered material Outer peripheral cutting edge 10 formed Outer peripheral cutting edge 11 formed by a blade groove End mill tip cutting edge 12 End cutting edge 13 Corner cutting edge 14 Cutting groove length 15 Taper portion 16 Insertion start position 17 Solid sintered cemented carbide Part 18 Peripheral surface part 19 Bottom part 20 Length of rear end part of cemented and sintered cemented carbide part 21 Carbide part 22 Neck part 23 Shank part 24 Chamfer ring 25 Interference avoiding part 26 Blade part 27 Corner cut Edge rake face 28 Edge edge rake face 29 Edge face boundary 30 Edge diameter 31 Edge face step 32 Corner flank face 33 Edge flank face 34 End edge edge Rake face 35 Rake face formed by gash 36 Rake face formed by blade groove

Claims (5)

At least the blade portion is composed of a CBN sintered portion, and the rear end portion of the cemented carbide portion integrally sintered with the CBN sintered portion is inserted into the shank hole portion and fixed, and the blade portion is A small-diameter end mill having a cutting edge with a tip diameter of 3 mm or less, wherein 60% or more of the outer peripheral cutting edge of the small-diameter end mill is formed by gash, and the outer peripheral cutting edge of the blade portion is a right-handed left-handed twist. A small-diameter CBN end mill that is formed and has an axial rake of the cutting edge of the blade portion of −5 ° to −25 °. 2. The small diameter CBN end mill according to claim 1, wherein an interference avoidance portion is provided behind the outer peripheral cutting edge. The small-diameter CBN end mill according to claim 1 or 2, wherein the radial rake of the tip cutting edge of the blade portion and the radial rake of the outer peripheral cutting edge are substantially the same angle. The small-diameter CBN end mill according to any one of claims 1 to 3, wherein a radial rake of the end mill cutting edge exceeds + 5 ° and is + 10 °. 5. The small diameter CBN end mill according to claim 1, wherein a rear end portion of the cemented carbide portion inserted into the shank hole portion has a bottom surface and at least a part of an outer peripheral surface of the cemented carbide via a bonding material. The small-diameter CBN end mill is characterized in that the length in the tool axis direction of at least a part of the outer peripheral surface is at least one times the blade diameter.

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