JP2004090192A - End mill and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an end-mill-like tool using an ultra-high pressure sintered body with improved blade vibration, outer diameter dimension accuracy of the tool, and surface roughness by burnishing, causing no chattering. <P>SOLUTION: The end mill employs the ultra-high pressure sintered body 2, the sintered body 2 is joined to a support section 12, the end mill has an outer peripheral round land connecting to 6 or more twisted cutting edges, and core thickness ratio is 80 to 95%. Especially, the surface roughness Rz of the outer peripheral round land is 0.5 μm or less. Such end mill provides a tool having high dimension accuracy and no run-out, by grinding the outer periphery of a hard sintered body material 11 and then forming the cutting edge. <P>COPYRIGHT: (C)2004,JPO

Description

【００３３】
上記は一つの実施例であるが、硬質焼結体素材からは任意形状に切刃を削り出すことができるため、設計においては刃数、ネジレ角、すくい角などの要素を本発明の範囲内で自由に設定することができる。特に小径サイズ（工具回転径が４ｍｍ以下）の場合には従来のロー付け方法では不可能であったような６枚刃以上の多くの刃数を持つ工具を作ることができる。また、前述の通り工具径寸法も円筒研削により±０．００５ｍｍでの管理が容易にできるようになり、刃振れも０．００３ｍｍ以内にすることができた。
【００３４】
【発明の効果】
以上述べたように、本発明の製造方法により、小径多刃構造のネジレ刃エンドミルを寸法精度及び刃振れ精度良く得ることができる。また、原理的に刃振れが生じることなく精度の高い、研削ダレのない工具を得ることができる。更に、本発明によって得られた工具で切削すると、ランド面によるバニシング効果により仕上げ面粗さも良好な結果が得られる。
【図面の簡単な説明】
【図１】図１は本発明エンドミルの製造工程を示す模式図で、図１（Ａ）は先端部に超高圧焼結体を有する円柱状素材の模式図、図１（Ｂ）は円柱状素材をシャンクにロー付けした状態を示す模式図、図１（Ｃ）は研削仕上げした先端形状を示す模式図、図１（Ｄ）は刃溝加工（外周部はランド面を残す）を施した完成品の模式図である。
【図２】図２は本発明の一つの実施例で、図２（Ａ）はスクエアエンドミルの正面図で、図２（Ｂ）はその側面図である。
【図３】図３は、従来の外周丸ランドを有するスパイラルエンドミルで、図３（Ａ）はその正面図、図３（Ｂ）は切刃部の拡大正面図、図３（Ｃ）は側面図である。
【図４】図４は従来のエンドミルの外周研削の状況を模式的に示すもので、図４（Ａ）は外周研削の模式図、図４（Ｂ）はエンドミル切刃の拡大模式図である。
【符号の説明】
１　　切刃部
２　　超高圧焼結体
３　　外周丸ランド
４　　エンドミル
５　　円筒研削砥石
６　　研削ダレ
１１　　硬質焼結体素材
１２　　支持部
１３　　シャンク
１４　　ポケット溝
Ｗ　　丸ランドの幅[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an end mill having a torsion blade and a method for manufacturing the same, and particularly to a cubic boron nitride sintered body (CBN sintered body) used for hardened steel processing and cast iron processing among steels, and non-ferrous metal processing. The present invention relates to an end mill having a diamond sintered body (PCD sintered body) used for a cutting edge.
[0002]
[Prior art]
Compared to the conventional tool materials such as cemented carbide and high-speed steel, and tools whose surfaces are coated with a ceramic material, ultra-high pressure sintered bodies such as CBN sintered bodies and diamond sintered bodies (PCD sintered bodies) are more It is a tool material with high hardness. For this reason, the CBN sintered body has come to be used for cutting hardened steel having a hardness of HRC 55 or higher, and for cutting cast iron materials under high-speed cutting conditions. PCD sintered bodies are used for processing non-ferrous metal materials.
[0003]
However, the ultrahigh-pressure sintered body has a very high hardness, but is a relatively brittle material. Therefore, when the ultrahigh-pressure sintered body is formed into an end mill shape, various problems occur as described in detail below.
[0004]
The main ones are as follows.
(1) Tool dimensional accuracy: It is difficult to finish the tool dimensions such as the tool dimensional size and the blade runout accuracy with high accuracy.
(2) Chipping of the cutting edge: Fine chipping occurs at the ridgeline (edge) of the cutting edge during grinding, and this causes the finished surface roughness of the processed surface in the end mill to deteriorate.
(3) Occurrence of chattering: Since hardened steel has a large cutting resistance, in the case of an intermittent impact such as an end mill, the chattering phenomenon easily occurs, and the tool is easily damaged. Also, the finished surface becomes worse.
[0005]
The following is a summary of the improvements and ingenuity currently implemented for the above problems.
(1) Tool Dimension Accuracy In addition to drills and reamers, it is common for end mills to have round lands in order to improve tool diameter and outer edge runout accuracy. For example, by attaching a round end land to a spiral end mill, there is obtained an effect that a finished surface to be processed and a falling accuracy are improved (for example, see Patent Document 1). An example is shown in FIG. FIG. 3A is a front view of the spiral end mill 4, and FIG. 3B is an enlarged front view of the cutting edge portion 1. 3 are provided. FIG. 3C is a side view of the spiral end mill 4.
[0006]
A tool using an ultra-high pressure sintered body as disclosed in the above-mentioned publications is used for cutting an end mill by brazing the sintered body to two or four (or more) cutting edges. Make up the blade. In this case, in the cylindrical grinding, the cylindrical grinding wheel 5 and the end mill 4 are rotated in the direction of the arrow as shown in FIG. As is clear from FIG. 4 (A), the round land 3 as a cutting blade and the cylindrical grinding wheel 5 are intermittently contacted and ground. When observing the shape of the outer peripheral round land of the obtained end mill in detail, as shown in FIG. 4B, a grinding sag 6 generated when the grindstone comes off remains near the rake face of the sintered body. Therefore, the round land slightly deviates from the radius of curvature of the tool rotation radius. In addition, the round land is an outer peripheral portion of the cutting edge which is concentric with the outer peripheral portion of the end mill and has the same radius. Further, the sag of the land portion is a portion where the cutting edge shape is shifted from the outer peripheral surface of the end mill.
[0007]
In recent years, the precision required for tools has become increasingly severe, and even slight deviations have become unacceptable. That is, it is clear that a state in which there is no sag is desirable in order to more strictly pursue the performance and sharpness of the tool.
[0008]
(2) The chipping ultrahigh-pressure sintered body of the cutting edge is a material obtained by high-pressure sintering of CBN or diamond powder particles having a size of about 0.5 to 10 μm and as large as about 50 μm together with a binder. Therefore, when a sharp cutting edge is polished by grinding because the powder particles are constituents, chipping due to falling off of particles at the edge tip is inevitable.
[0009]
The size of this chipping is several μm to several tens of μm, and when cutting is performed with a tool having a cutting edge with such chipping, the chipped cutting edge shape is transferred to the work material, and the finished surface Worsens. When this chipping receives an impact at the time of cutting, it causes a larger loss, thereby shortening the tool life.
[0010]
(3) Generation of Chatter To reduce the magnitude of impact resistance during cutting in an end mill, it is most effective to form a torsion blade-shaped cutting blade. Conventionally, there are the following methods for providing a torsion-shaped material in an ultrahigh-pressure sintered material. (For example, see Patent Literature 2, Patent Literature 3, and Patent Literature 4.)
[0011]
In these methods, it is practically impossible to produce a multi-blade end mill having a small diameter of 4 mm or less and a cutting edge of 6 or more blades due to brazing or structural restrictions. there were. In order to obtain an end mill having a multi-blade structure of six or more blades in a small diameter size, a method disclosed in Japanese Patent Application Laid-Open No. H8-336716 discloses a method in which "a cylindrical superabrasive sintered body is manufactured by shaving. Rotary cutting tool ". Here, the method of manufacturing the superabrasive sintered body is not clear. There is also a prior art using an ultra-high pressure sintered body (see Patent Document 5). In this application, a PCD sintered body drill is disclosed.
[0012]
As discussed in detail above, solutions to individual problems have been clarified, but means for solving these problems as a whole have not been clarified yet.
[0013]
[Patent Document 1]
JP-A-8-27631 (pages 3-5, FIG. 1)
[Patent Document 2]
JP-A-5-261613 (FIG. 1)
[Patent Document 3]
JP-A-3-10707 (FIG. 5)
[Patent Document 4]
JP-A-8-85012 (FIG. 5)
[Patent Document 5]
Japanese Patent Publication No. 7-42489 (Pages 4-6, Fig. 6)
[0014]
[Problems to be solved by the invention]
The end mill of the present invention is intended to reduce the surface roughness of the inner surface of a fine deep hole having a diameter of 5 mm and a depth of about 30 mm. In response to such new demands from the market, the present invention seeks to provide a processing method intermediate between conventional cutting and grinding.
(1) Improvement of Tool Dimensional Accuracy In the case of a brazing tool having an ultrahigh-pressure sintered body at the cutting edge, when the outer peripheral cutting edge portion of an end mill, a reamer, or the like is cylindrically ground, sagging occurs as described above. As a result, there occurs a problem that the outer peripheral diameter is reduced by performing the third surface processing for reducing the land width of the outer peripheral portion. In this method, a tool having a desired size can be obtained without changing the dimensional accuracy by eliminating the polishing dripping of the outer peripheral round land. Further, in the case of a multi-blade tool, if a round land is not generally provided, a shift of the blade tip position (blade runout) occurs.
[0015]
(2) Improvement of Finished Surface Roughness Generally, it is known that by attaching a round land (margin) to an outer peripheral cutting edge of an end mill, a finished surface is improved by a burnishing effect. The present invention intends to further improve the machined surface roughness by smoothing the surface roughness in the round land, and to provide such a tool manufacturing method.
[0016]
(3) Suppression of Chatter As described above, the means for solving chatter is to use a cutting blade as a torsion blade and to use multiple blades to reduce the load applied to one cutting blade.
[0017]
In summary, the conventional processing techniques can be roughly divided into cutting and grinding, and any of the above-mentioned prior arts can be distinguished into either one. A large chip is a cutting process, and as described above, a chip, such as CBN, which produces a chip having a size of powder particles is called grinding. The present invention seeks to solve this problem by opening up a new processing field that cannot be solved by such conventional techniques. That is, by providing a tool positioned between cutting and grinding, it is intended to achieve the above-described improvement in dimensional accuracy, improvement in finished surface roughness, and prevention of chatter.
[0018]
[Means for Solving the Problems]
In the end mill using the ultrahigh-pressure sintered body provided by the present invention, the ultrahigh-pressure sintered body is bonded to a support portion, and has six or more torsion-shaped cutting blades and an outer peripheral round land (margin), The core thickness ratio is 80 to 95%. Here, the core thickness is a value obtained by multiplying 100 by a value obtained by dividing the diameter of a circle having the bottom of the pocket groove as a circumscribed circle by the diameter of the cutting edge. If the core thickness ratio exceeds 95%, the grooves are too shallow, resulting in poor machining efficiency. On the other hand, if the core thickness ratio is less than 80%, the rigidity of the tool is insufficient and the object cannot be achieved.
[0019]
Here, the ultra-high pressure sintered body is obtained by sintering CBN powder or diamond powder under ultra-high pressure and high temperature. In the case of a CBN sintered body, a very high hardness sintered body can be obtained by mixing and sintering a CBN powder with a Co powder or a TiN powder. In the case of a diamond sintered body, it is manufactured by sintering a Co powder or a Co plate and a diamond powder. The support portion of the present invention is preferably made of a cemented carbide or a W alloy directly bonded to a CBN sintered body or a diamond sintered body when sintering CBN or diamond. However, the ultrahigh-pressure sintered body and the support may be brazed.
[0020]
Further, by making the cutting blade to have a twisted shape, the cutting resistance is reduced and the discharge of the cutting powder is assisted. Providing a land on the outer periphery of the cutting blade has the effect of burnishing the surface of the work material, and cleans the surface of the finished surface. By attaching a round land (margin) to the outer peripheral cutting edge of the end mill, the finished surface can be improved by the burnishing effect. In the present invention, the surface roughness of the outer peripheral round land is set to 0.5 μm or less in Rz to further improve the processed surface roughness. A pocket groove is formed along the cutting edge, and this groove is extremely shallow. By reducing the cutting allowance during cutting by making the groove shallow, reducing the cutting resistance applied to the tool, increasing the number of blades to supplement the processing speed, and maintaining the rigidity of the tool by increasing the core thickness ratio, The intended tool can be obtained.
[0021]
The end mill using the ultra-high pressure sintered body provided by the present invention prepares a hard sintered body material in which the ultra-high pressure sintered body is joined to a supporting portion, and has an outer peripheral surface of the hard sintered body material having a surface roughness. Is manufactured through a process of polishing to an Rz (maximum height) of 0.5 μm or less and then forming six or more torsion-shaped cutting blades while leaving an outer peripheral round land (margin).
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
The end mill of the present invention manufactures a tool by the steps shown in FIGS. Grinding sag can be prevented by bringing a step (D) of performing blade cutting after a step (C) of grinding the outer peripheral surface of the cylinder using a cylindrical grinder or the like. This order of steps is particularly important in the present invention. Referring to the drawings, as shown in FIG. 1A, a columnar hard sintered body material 11 having an ultrahigh-pressure sintered body 2 at the tip of a support portion 12 is prepared. If necessary, it is brazed to the shank 13 to obtain the shape shown in FIG. 1B, or is used as it is as an end mill shank by round grinding.
[0023]
First, the tip sintered body is finished to a required shape. The shape illustrated in FIG. 1C is rectangular (square) in a side view. In addition, it is finished with a cylindrical grinder or the like into a predetermined shape and dimensions, such as a radius (one with an R at the tip corner of the square) or a tapered shape (one with an inclined ridge on the outer periphery).
[0024]
At this time, by leaving the surface of the created ultra-high pressure sintered body as the outer peripheral round land of the tool as it is, it is less likely that factors such as sagging and runout in the outer peripheral round land deteriorate the tool shape accuracy. For this reason, a tool having good shape accuracy is inevitably obtained. Since this outer peripheral surface is finally a round land and has the effect of improving the finished surface by the burnishing effect on the processed surface, it is preferable that the surface roughness of this portion is excellently finished.
[0025]
In order to obtain a sintered body surface with good surface roughness, improve the tool performance by raising the grinding wheel number in cylindrical grinding or improving the roughness of the ground surface by film wrap etc. after cylindrical processing Can be done. At this time, the surface roughness of the sintered body surface is desirably 0.5 μm or less in maximum height Rz.
[0026]
Thereafter, as shown in FIG. 1 (D), a pocket groove 14 is formed in the outer peripheral portion, and at this time, the outer peripheral surface of the sintered body is left in a range of 0.02 mm to 0.5 mm in width of the round land. . If it exceeds 0.5 mm, the cutting resistance increases, the friction between the tool and the work material increases, and the temperature of the cutting edge also increases, so that the tool life is shortened. If it is less than 0.02 mm, the effect of the round land cannot be obtained.
[0027]
It is desirable that the twist angle of the twist shape is 10 ° to 45 °. When the helix angle is less than 10 °, there is no effect of lowering the cutting resistance and there is no effect on the discharge of the chips, and when it exceeds 45 °, the cutting resistance is rather increased and the discharge of the chips becomes worse.
[0028]
Another feature of the end mill of the present invention is that the outer diameter of the support portion is smaller than the outer diameter of the ultrahigh-pressure sintered body, and the cutting edge is formed on the surface of the ultrahigh-pressure sintered body. Therefore, the outer diameter of the support portion is smaller than the outer diameter of the cutting blade formed of the ultrahigh-pressure sintered body. In use, the support can be further joined to the shank.
[0029]
(Example)
FIG. 2A is a front view of the square end mill of the present invention. In this end mill, a cutting edge 1 and a round land 3 having a width W are formed in an ultrahigh-pressure sintered body 2, and the sintered body 2 is joined to a support portion 12. The pocket grooves 14 for discharging chips are formed over the entire length of the ultrahigh-pressure sintered body 2. FIG. 2B is a side view of the end mill, and shows that the pocket groove 14 is twisted.
[0030]
The above squared end mill was manufactured by the method shown in FIG. 1, and the dimensions of each part were as follows. The diameter of the cutting blade is 4mm, the length of the cutting blade is 4mm, the width W of the round land is 0.05mm, the depth of the groove is 0.3mm, the number of blades is 8 blades, and the super high pressure sintered body is CBN sintered. BN250 manufactured by Sumitomo Electric Industries, Ltd. was used as the binder. The diameter of the support was 3.5 mm, the torsion angle of the cutting blade was 15 °, and the surface roughness of the round land was 0.3 μm in Rz. Since the core thickness ratio of the end mill used in this example was 3.4 / 4 × 100, it was 85%.
[0031]
The result of working the side surface of the hardened steel using this tool is shown below. The cutting conditions are shown in Table 1. The work material is SKD11 (HRC60). As a result of the cutting test, Rz = 0.52 μm was obtained as the roughness of the finished surface, and the roughness of the conventional tool, which was about 1 to 2 μm, could be greatly improved.
[0032]
[Table 1]

[0033]
Although the above is one embodiment, since the cutting blade can be cut into an arbitrary shape from the hard sintered material, elements such as the number of blades, the torsion angle, and the rake angle are within the scope of the present invention in the design. Can be set freely. In particular, in the case of a small-diameter size (the tool rotation diameter is 4 mm or less), a tool having a large number of 6 or more blades, which cannot be obtained by the conventional brazing method, can be manufactured. Further, as described above, the tool diameter can easily be controlled to ± 0.005 mm by cylindrical grinding, and the blade runout can be reduced to 0.003 mm or less.
[0034]
【The invention's effect】
As described above, according to the manufacturing method of the present invention, a spiral blade end mill having a small-diameter multi-blade structure can be obtained with high dimensional accuracy and high blade runout accuracy. In addition, it is possible to obtain a high-precision tool free of grinding sag without occurrence of blade runout in principle. Further, when cutting is performed with the tool obtained according to the present invention, good results can be obtained in terms of the finished surface roughness due to the burnishing effect of the land surface.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a manufacturing process of an end mill of the present invention, FIG. 1 (A) is a schematic diagram of a columnar material having an ultra-high pressure sintered body at a tip, and FIG. 1 (B) is a columnar material. FIG. 1 (C) is a schematic diagram showing a state in which a material is brazed to a shank, FIG. 1 (C) is a schematic diagram showing a shape of a ground end, and FIG. 1 (D) is a blade groove processing (an outer peripheral portion leaves a land surface). It is a schematic diagram of a completed product.
FIG. 2 is an embodiment of the present invention, FIG. 2 (A) is a front view of a square end mill, and FIG. 2 (B) is a side view thereof.
FIG. 3 is a conventional spiral end mill having a round outer peripheral land, FIG. 3 (A) is a front view thereof, FIG. 3 (B) is an enlarged front view of a cutting edge portion, and FIG. 3 (C) is a side view. FIG.
4A and 4B schematically show the state of the outer peripheral grinding of the conventional end mill. FIG. 4A is a schematic view of the outer peripheral grinding, and FIG. 4B is an enlarged schematic view of the end mill cutting blade. .
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cutting edge part 2 Ultra-high pressure sintered body 3 Outer round land 4 End mill 5 Cylindrical grinding wheel 6 Grinding sag 11 Hard sintered material 12 Support part 13 Shank 14 Pocket groove W Width of round land

Claims (11)

In an end mill using an ultra-high pressure sintered body, the ultra-high pressure sintered body is bonded to a supporting portion, has six or more torsion-shaped cutting blades and an outer peripheral round land, and has a core thickness ratio of 80 to 95%. An end mill characterized in that: The end mill according to claim 1, wherein the torsion angle of the torsion-shaped cutting blade is 10 ° to 45 °. The end mill according to claim 1, wherein a width of the outer peripheral round land is 0.02 to 0.5 mm. The end mill according to any one of claims 1 to 3, wherein a surface roughness of the outer peripheral round land is 0.5 m or less in Rz. The end mill according to any one of claims 1 to 4, wherein the ultra-high pressure sintered body is a cubic boron nitride sintered body or a diamond sintered body. The end mill according to any one of claims 1 to 5, wherein an outer diameter of the support portion is smaller than an outer diameter of the ultrahigh-pressure sintered body. The end mill according to any one of claims 1 to 6, wherein the support portion is joined to a shank. In a method of manufacturing an end mill using an ultra-high pressure sintered body, a hard sintered body material in which the ultra-high pressure sintered body is joined to a support portion is prepared, and an outer peripheral surface of the hard sintered body material has a surface roughness of A method for manufacturing an end mill, comprising: polishing to 0.5 μm or less in Rz (maximum height), and then forming six or more torsion-shaped cutting blades while leaving an outer peripheral round land (margin). The method for manufacturing an end mill according to claim 8, wherein the torsion angle of the torsion shape is 10 ° to 45 °. The method for manufacturing an end mill according to claim 8 or 9, wherein the width of the outer peripheral round land is 0.02 to 0.5 mm. The method for manufacturing an end mill according to any one of claims 8 to 10, wherein an outer diameter of the support portion is smaller than an outer diameter of the ultrahigh-pressure sintered body.

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