JP2009190146A

JP2009190146A - Tool material

Info

Publication number: JP2009190146A
Application number: JP2008035474A
Authority: JP
Inventors: Masayuki Imai; 真之今井
Original assignee: Hitachi Tool Engineering Ltd
Current assignee: Moldino Tool Engineering Ltd
Priority date: 2008-02-18
Filing date: 2008-02-18
Publication date: 2009-08-27

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tool material using a cBN sintered body for a blade, having a high breakage strength. <P>SOLUTION: The tool material in a columnar shape is formed of the cBN sintered body at one end and a WC-based cemented carbide at the other, wherein: the WC-based cemented carbide comprises a cemented carbide A and a cemented carbide B longitudinally, with one end of the cemented carbide A having a faying surface C with the cBN sintered body and the other having a faying surface D with the cemented carbide B; the cemented carbide A has a WC average grain size d1 (μm) within a range of 2≤d1≤4 and contains Co in an amount of 6-12% by mass; the cemented carbide B has a WC average grain size d2 (μm) within a range of 0.3≤d2≤1 and contains Co in an amount of 5-11%; and the tool material 1 has a length L (mm) and a diameter D (mm) within the ranges of 3≤L≤60 and D≤6, respectively. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本願発明は、ｃＢＮ焼結体を刃部に用いる工具素材に関する。特に、刃径が１ｍｍ以下の回転工具に関するものである。 This invention relates to the tool raw material which uses a cBN sintered compact for a blade part. In particular, the present invention relates to a rotary tool having a blade diameter of 1 mm or less.

特許文献１は、超硬合金が裏打ちされたｃＢＮ焼結体円板と、これを用いて形成した回転工具の技術を開示している。 Patent Document 1 discloses a technique of a cBN sintered body disk lined with a cemented carbide and a rotary tool formed using the cBN sintered body disk.

特開２００４−２６８２０２号公報JP 2004-268202 A

本願発明は、折損強度の高い工具素材を提供することを目的とする。 An object of this invention is to provide the tool raw material with high fracture strength.

本願発明は、円柱形状の工具素材（１）の一方の端部がｃＢＮ焼結体（２）、他の端部がＷＣ基超硬合金（３）で形成され、該ＷＣ基超硬合金（３）は長手方向に超硬合金Ａ（４）と超硬合金Ｂ（５）とからなり、該超硬合金Ａ（４）の一方の端部は、該ｃＢＮ焼結体（２）との接合面Ｃ（６）を有し、該超硬合金Ａ（４）の他の端部は、該超硬合金Ｂ（５）との接合面Ｄ（７）を有し、該超硬合金Ａ（４）は、ＷＣ平均粒径をｄ１（μｍ）としたとき、２≦ｄ１≦４、Ｃｏ含有量は質量％で、６％以上、１２％以下であり、該超硬合金Ｂ（５）は、ＷＣ平均粒径をｄ２（μｍ）としたとき、０．３≦ｄ２≦１、Ｃｏ含有量は５％以上、１１％以下であり、工具素材（１）の長さ（ｍｍ）をＬ、直径（ｍｍ）をＤとしたとき、３≦Ｌ≦６０、Ｄ≦６、であることを特徴とする工具素材である。上記の構成を採用することによって折損強度の高い工具素材を提供することができる。また、本願発明の工具素材は、ｃＢＮ焼結体（２）の長さ（ｍｍ）をＬ１、超硬合金Ａ（４）の長さ（ｍｍ）をＬ２、超硬合金Ｂ（５）の長さ（ｍｍ）をＬ３、としたとき、Ｌ２／Ｌ１≧２、（Ｌ１＋Ｌ２）／Ｌ３≦０．７、であることが好ましい。また、ｄ１値が、２．５≦ｄ１≦３．５、ｄ２値が、０．３≦ｄ２≦０．６、であることが好ましい。 In the present invention, one end of a cylindrical tool material (1) is formed of a cBN sintered body (2) and the other end is formed of a WC-based cemented carbide (3), and the WC-based cemented carbide ( 3) is composed of cemented carbide A (4) and cemented carbide B (5) in the longitudinal direction, and one end of the cemented carbide A (4) is connected to the cBN sintered body (2). The other end of the cemented carbide A (4) has a bonding surface D (7) with the cemented carbide B (5), and the cemented carbide A (4), when the WC average particle diameter is d1 (μm), 2 ≦ d1 ≦ 4, the Co content is 6% by mass and 12% by mass, and the cemented carbide B (5) Is 0.3 ≦ d2 ≦ 1, when the WC average particle diameter is d2 (μm), the Co content is 5% or more and 11% or less, and the length (mm) of the tool material (1) is L When the diameter (mm) is D, 3 ≦ L ≦ 60, D It is a tool material characterized by ≦ 6. By adopting the above configuration, a tool material with high break strength can be provided. The tool material of the present invention is such that the length (mm) of the cBN sintered body (2) is L1, the length (mm) of the cemented carbide A (4) is L2, and the length of the cemented carbide B (5). When the thickness (mm) is L3, it is preferable that L2 / L1 ≧ 2 and (L1 + L2) /L3≦0.7. Further, it is preferable that the d1 value is 2.5 ≦ d1 ≦ 3.5, and the d2 value is 0.3 ≦ d2 ≦ 0.6.

本願発明によって、折損強度の高い工具素材を提供することができた。 By this invention, the tool raw material with high breaking strength was able to be provided.

本願発明の工具素材（１）の例を図１に示す。円柱形状の工具素材（１）の一方の端部がｃＢＮ焼結体（２）、他の端部がＷＣ基超硬合金（３）で形成されている。またＷＣ基超硬合金（３）は長手方向に超硬合金Ａ（４）と超硬合金Ｂ（５）とからなっている。更に、超硬合金Ａ（４）の一方の端部は、ｃＢＮ焼結体（２）との接合面Ｃ（６）を有し、超硬合金Ａ（４）の他の端部は、超硬合金Ｂ（５）との接合面Ｄ（７）を有している。例えば、ｃＢＮ焼結体を刃部とする切削工具は、切削加工時に刃部の温度が約８００から１０００℃の高温となる。特に切削条件が高速高送り等の過酷な場合、刃部の温度上昇は著しい。従って、ｃＢＮ焼結体と超硬合金Ａとの接合面Ｃは、高温域での密着強度が要求される。そこで超高圧高温条件下で両者を一体焼結処理することによって形成された接合面Ｃを有することが必要である。またこの一体焼結処理は、ｃＢＮ焼結体と超硬合金とを接合させるために必要な処理でもある。一方、超硬合金Ａと超硬合金Ｂとの接合面Ｄは、超硬合金Ａの厚さの分、ｃＢＮ焼結体からの距離が離れているため、例えば拡散接合法をよって形成された接合面Ｄを選択することができる。
本願発明の工具素材のＷＣ基超硬合金において、ｃＢＮ焼結体との接合面Ｃを有する超硬合金Ａは、ＷＣ平均粒径をｄ１（μｍ）としたとき、２≦ｄ１≦４、より好ましくは、２．５≦ｄ１≦３．５であり、Ｃｏ含有量は質量％で、６％以上、１２％以下である。また、この超硬合金Ａの別の端部と接合面Ｄを有する超硬合金Ｂは、ＷＣ平均粒径をｄ２（μｍ）としたとき、０．３≦ｄ２≦１、より好ましくは０．３≦ｄ２≦０．６であり、Ｃｏ含有量は５％以上、１１％以下である。ｃＢＮ焼結体と接合面Ｃを介している超硬合金Ａも熱伝導によって６００から７００℃の高温域での機械的強度が要求され、破壊、亀裂の進展を回避しなければならない。そのため、高温となる接合面Ｃ近傍の超硬合金Ａの亀裂が進展し難いｄ１値が２μｍ以上の粗粒超硬合金を用いれば、高温域となる接合面Ｃ近傍の超硬合金Ａの折損強度を向上させることができる。しかし、ｄ１値の増大により曲げ変形が起こりやすくなるため、ｄ１値は４μｍ以下にする必要がある。このためｄ１値は２≦ｄ１≦４、より好ましくは、２．５≦ｄ１≦３．５とする。また、超硬合金Ａには、加熱と冷却が加わるため、熱衝撃抵抗Ｒも大きいことが必要となる。熱衝撃抵抗Ｒは、次の化１によって定義される。ここで、ｋは定数、λは熱伝導率、σｍは抗折力、αは熱膨張係数、Ｅはヤング率である。 An example of the tool material (1) of the present invention is shown in FIG. One end of the cylindrical tool material (1) is formed of a cBN sintered body (2), and the other end is formed of a WC-based cemented carbide (3). The WC-based cemented carbide (3) is composed of cemented carbide A (4) and cemented carbide B (5) in the longitudinal direction. Furthermore, one end of the cemented carbide A (4) has a joint surface C (6) with the cBN sintered body (2), and the other end of the cemented carbide A (4) It has a joint surface D (7) with the hard alloy B (5). For example, a cutting tool having a cBN sintered body as a blade portion has a high temperature of about 800 to 1000 ° C. during cutting. In particular, when the cutting conditions are severe such as high speed and high feed, the temperature rise of the blade portion is remarkable. Therefore, the bonding surface C between the cBN sintered body and the cemented carbide A is required to have an adhesion strength in a high temperature range. Therefore, it is necessary to have a joint surface C formed by subjecting both to integral sintering under ultrahigh pressure and high temperature. This integrated sintering process is also a process necessary for joining the cBN sintered body and the cemented carbide. On the other hand, the bonding surface D between the cemented carbide A and the cemented carbide B is formed by, for example, a diffusion bonding method because the distance from the cBN sintered body is increased by the thickness of the cemented carbide A. The joining surface D can be selected.
In the WC-based cemented carbide of the tool material of the present invention, the cemented carbide A having the joint surface C with the cBN sintered body has a WC average particle diameter of d1 (μm), 2 ≦ d1 ≦ 4, Preferably, 2.5 ≦ d1 ≦ 3.5, and the Co content is 6% or more and 12% or less by mass%. Further, the cemented carbide B having another end portion of the cemented carbide A and the joint surface D has a WC average particle size of d2 (μm), and 0.3 ≦ d2 ≦ 1, more preferably 0.8. 3 ≦ d2 ≦ 0.6, and the Co content is 5% or more and 11% or less. The cemented carbide A through the cBN sintered body and the joint surface C is also required to have mechanical strength in a high temperature range of 600 to 700 ° C. due to heat conduction, and the development of fracture and cracks must be avoided. For this reason, if a coarse cemented carbide having a d1 value of 2 μm or more, in which the crack of the cemented carbide A in the vicinity of the joining surface C that becomes high temperature is difficult to progress, breakage of the cemented carbide A in the vicinity of the joining surface C that becomes the high temperature region. Strength can be improved. However, since the bending deformation is likely to occur as the d1 value increases, the d1 value needs to be 4 μm or less. For this reason, the d1 value is 2 ≦ d1 ≦ 4, more preferably 2.5 ≦ d1 ≦ 3.5. In addition, since the cemented carbide A is heated and cooled, the thermal shock resistance R needs to be large. The thermal shock resistance R is defined by the following chemical formula 1. Here, k is a constant, λ is thermal conductivity, σm is a bending strength, α is a thermal expansion coefficient, and E is a Young's modulus.

Ｃｏ量が６％未満の場合、Ｒ値が減少するが、Ｃｏ量が１２％を超えて大きくてもλ値の低下によりＲ値が減少してしまう。そこで、超硬合金ＡのＣｏ量を６％以上、１２％以下とする。本願発明の工具素材における超硬合金Ａは、主に回転工具における首部を構成することになる。
一方、超硬合金Ｂは、回転工具におけるシャンク部やシャンク部よりも径が絞られる首部、又はシャンク部から首部に跨った構成をすることになる。そこで、径が絞られる首部とシャンク部の境界は応力が集中するため、超硬合金Ｂは、折損強度の高い超微粒系超硬合金を用いることになる。例えば、特に首下が長い小径工具においてその影響は大きい。超硬合金Ｂは、ｄ２値が１μｍ以下の折損強度の高い超微粒系超硬合金を用いることにより、応力の集中する首部とシャンク部の境界部の強度を向上することができる。しかし、ｄ２値が０．３μｍ未満の超硬合金では、焼結時に異常成長するＷＣ粒子の影響のため、抗折力は低下してしまう。このため超硬合金Ｂのｄ２値を０．３≦ｄ２≦１、とする。また、首部は振動や曲げ変形を抑制する必要があり、同時に小径工具では耐衝撃性を高める必要がある。破壊靱性値Ｋ１ｃは、Ｃｏ量の増加とともに増大するため首部においてもＣｏ量を規定する必要がある。Ｃｏ量が５％未満の場合、Ｋ_１ｃの減少により耐衝撃性が低下してしまい、Ｃｏ量が１１％を超えて大きいいと、耐振動性が低下する他、曲げ変形を生じやすくなってしまう。そこで、超硬合金ＢのＣｏ含有量を５％以上、１１％以下に規定する。
本願発明の工具素材において、Ｌ値、Ｄ値は、３≦Ｌ≦６０、Ｄ≦６、である。これは、回転工具、特に小径工具における工具の全長とシャンク径のサイズを配慮している。 When the Co amount is less than 6%, the R value decreases. However, even if the Co amount exceeds 12% and is large, the R value decreases due to a decrease in the λ value. Therefore, the Co content of the cemented carbide A is set to 6% or more and 12% or less. The cemented carbide A in the tool material of the present invention mainly constitutes the neck of the rotary tool.
On the other hand, the cemented carbide B has a configuration in which the diameter is narrower than that of the shank part or the shank part in the rotary tool, or a straddle from the shank part to the neck part. Therefore, since stress concentrates at the boundary between the neck and the shank where the diameter is reduced, the cemented carbide B uses an ultra-fine grain cemented carbide with high break strength. For example, the influence is large especially in a small diameter tool having a long neck. The cemented carbide B can improve the strength of the boundary between the neck portion and the shank portion where stress is concentrated by using an ultrafine grained cemented carbide having a high fracture strength with a d2 value of 1 μm or less. However, in a cemented carbide with a d2 value of less than 0.3 μm, the bending strength is reduced due to the influence of WC particles that grow abnormally during sintering. For this reason, the d2 value of the cemented carbide B is set to 0.3 ≦ d2 ≦ 1. Moreover, it is necessary to suppress vibration and bending deformation at the neck, and at the same time, it is necessary to improve impact resistance with a small diameter tool. The fracture toughness value K1c increases as the amount of Co increases, so it is necessary to define the amount of Co also at the neck. When the Co content is less than 5%, the impact resistance is reduced due to the decrease in K _{1c. When} the Co content is more than 11%, vibration resistance is lowered and bending deformation is likely to occur. . Therefore, the Co content of the cemented carbide B is specified to be 5% or more and 11% or less.
In the tool material of the present invention, the L value and the D value are 3 ≦ L ≦ 60 and D ≦ 6. This takes into account the overall tool length and the size of the shank diameter in rotating tools, particularly small diameter tools.

本願発明の工具素材において、Ｌ２／Ｌ１値が２未満であると、超硬合金Ｂまで高温となるため、超硬合金Ｂの折損強度が低下してしまう。この理由は、超硬合金Ｂは高温での折損強度の低いからである。（Ｌ１＋Ｌ２）／Ｌ３≦０．７に規定する理由は、刃先先端より長手方向に離れるに従って急速に温度は低下し２００℃以下の低温となる。このため、（Ｌ１＋Ｌ２）値が０．７＊Ｌ３値以下であれば、低温となる部分で折損強度の高い微粒の超硬合金Ｂを用いることができるため小径工具の折損強度が向上する。一方、回転工具は刃先先端に力が作用するため、作用点より離れた部分の応力が大となる。そこで、（Ｌ１＋Ｌ２）値が０．７＊Ｌ３値を超えて長いと超硬合金Ａの応力負荷が大となってしまい不都合である。本願発明の工具素材において、超硬合金Ｂの抗折力は３５００ＭＰａ以上であることが好ましい。この理由は、応力の集中する首部とシャンク部の境界の折損強度をより向上できるからである。 If the L2 / L1 value is less than 2, the tool material of the present invention has a high temperature up to the cemented carbide B, so that the fracture strength of the cemented carbide B is lowered. This is because the cemented carbide B has a low breaking strength at high temperatures. The reason for defining (L1 + L2) /L3≦0.7 is that the temperature rapidly decreases as the distance from the tip of the blade edge increases in the longitudinal direction, and the temperature becomes 200 ° C. or lower. For this reason, if the (L1 + L2) value is 0.7 * L3 or less, the fine cemented carbide B having a high breaking strength can be used at a low temperature portion, and the breaking strength of the small-diameter tool is improved. On the other hand, since the force acts on the tip of the cutting edge of the rotary tool, the stress in the part away from the point of action becomes large. Therefore, if the (L1 + L2) value is longer than 0.7 * L3, the stress load of the cemented carbide A becomes large, which is inconvenient. In the tool material of the present invention, the bending strength of the cemented carbide B is preferably 3500 MPa or more. This is because the break strength at the boundary between the neck portion and the shank portion where stress is concentrated can be further improved.

本願発明の工具素材における超硬合金のｄ１、ｄ２値は、超硬合金の断面を鏡面研磨した後、村上試薬で０．５分、王水で３分間エッチングすることによりＷＣ粒子以外の金属を除去し、ＷＣ粒子の結晶粒界を明確にした後、顕微鏡による観察した。例えば、ＦＥ−ＥＰＭＡ（日本電子社製ＪＸＡ−８５００Ｆ型）を用いて倍率１０ｋ〜２０ｋ倍で観察を行い、その観察画像をコンピュータに取り込み、画像解析装置にて解析した。例えば、一定の面積の１０〜３０ｍｍ２の範囲に存在するＷＣの平均粒径を測定することができる。Ｃｏ含有量は蛍光Ｘ線分析装置により、また抗折力はＪＩＳ規格、Ｒ１６０１に記載の３点曲げ試験法により求めることができる。次に、本願発明の工具素材を実施例により具体的に説明する。 The d1 and d2 values of the cemented carbide in the tool material of the present invention are obtained by mirror polishing the cross section of the cemented carbide and then etching the metal other than the WC particles by etching with Murakami reagent for 0.5 minutes and aqua regia for 3 minutes. After removing and clarifying the grain boundaries of the WC particles, they were observed with a microscope. For example, observation was performed at a magnification of 10 k to 20 k using FE-EPMA (JXA-8500F type manufactured by JEOL Ltd.), the observed image was taken into a computer, and analyzed by an image analyzer. For example, the average particle diameter of WC existing in a range of 10 to 30 mm 2 having a certain area can be measured. The Co content can be determined by a fluorescent X-ray analyzer, and the bending strength can be determined by a three-point bending test method described in JIS standard, R1601. Next, the tool material of the present invention will be specifically described with reference to examples.

（実施例１）
図１にｃＢＮ焼結部材（８）の模式図示す。ｃＢＮ焼結部材（８）は、ｃＢＮ焼結体、超硬合金Ａと超硬合金Ｂとから構成される。まず、図２に示すｃＢＮ焼結部材（９）の超硬合金Ａを作製した。超硬合金Ａは、配合時のＷＣ平均粒径を３．８μｍ、Ｃｏ量を８．０％にし、１４００℃６０分真空中で焼結し、その後、１３５０°Ｃ５０ＭＰａ、３０分の条件でＨＩＰ処理をすることにより作製した。その後、研削加工により、厚み２．４ｍｍ、直径３０ｍｍの円板に加工した。次に、得られた超硬合金Ａの円板上に６５容量％のｃＢＮ粉末と、残りがＴｉＮとＡｌからなる粉末を混合した粉体からなるｃＢＮ成形体を配置し、５．６ＧＰａ、１４５０℃の超高圧高温条件で一体焼結後に研削加工を施し、ｃＢＮ焼結体の厚さが０．６ｍｍ、超硬合金Ａの厚さが２．４ｍｍの総厚３．０ｍｍのｃＢＮ焼結部材（９）を得た。
次に、超硬合金Ｂを作製した。超硬合金Ｂは、配合時のＷＣ平均粒径を１．２μｍ、Ｃｏ量を８％にし、１４００℃、６０分真空中で焼結し、その後、１３５０℃、５０ＭＰａ、３０分の条件でＨＩＰ処理をすることにより作製した。その後、厚み４７ｍｍ、直径３０ｍｍの円柱（１０）に加工した。同時に超硬合金Ｂの抗折力試験片も作成した。
先に作製した厚さ３ｍｍのｃＢＮ焼結部材（９）と、超硬合金Ｂの円柱（１０）との間に厚さ１０μｍのＮｉ箔をはさみ、ホットプレス法を用いて、真空中で１０５０℃、３０ＭＰａ、１０分の条件で拡散接合を施し、ｃＢＮ焼結体、超硬合金Ａ、Ｂで構成した厚さ５０ｍｍ、直径３０ｍｍのｃＢＮ焼結部材（８）を作成した。
図１に示す様に本願発明の工具素材の作製方法は、ｃＢＮ焼結部材（８）よりワイヤー放電加工により直径４．０１ｍｍの円柱部材を作製した後、Ｄ値が４ｍｍ、Ｌ値が５０ｍｍの丸棒にセンタレス加工した。図３に作成した本発明例１の工具素材を示す。ここで、工具素材の各種測定を行った。ｄ１、ｄ２値の測定結果、Ｃｏ含有量、超硬合金Ｂの抗折力値、Ｌ１、Ｌ２、Ｌ３の値を表１に示した。 Example 1
FIG. 1 shows a schematic diagram of a cBN sintered member (8). The cBN sintered member (8) is composed of a cBN sintered body, cemented carbide A and cemented carbide B. First, the cemented carbide A of the cBN sintered member (9) shown in FIG. 2 was produced. Cemented carbide A has a WC average particle size of 3.8 μm and a Co amount of 8.0% at the time of blending, and sintered in vacuum at 1400 ° C. for 60 minutes, and then HIP under the conditions of 1350 ° C. and 50 MPa for 30 minutes. It produced by processing. Then, it was processed into a disk having a thickness of 2.4 mm and a diameter of 30 mm by grinding. Next, a cBN compact made of powder obtained by mixing 65% by volume of cBN powder and the remaining powder of TiN and Al on the disc of the cemented carbide A is placed, and 5.6 GPa, 1450 is placed. CBN sintered member with a total thickness of 3.0 mm, with the thickness of the cBN sintered body being 0.6 mm and the thickness of the cemented carbide A being 2.4 mm, after being integrally sintered under an ultrahigh pressure and high temperature condition of ° C. (9) was obtained.
Next, cemented carbide B was produced. Cemented carbide B has a WC average particle size of 1.2 μm and a Co content of 8% at the time of blending, and is sintered in vacuum at 1400 ° C. for 60 minutes, and then HIP under the conditions of 1350 ° C., 50 MPa, 30 minutes. It produced by processing. Then, it processed into the cylinder (10) of thickness 47mm and diameter 30mm. At the same time, a bending strength test piece of cemented carbide B was also prepared.
A Ni foil having a thickness of 10 μm is sandwiched between the cBN sintered member (9) having a thickness of 3 mm previously prepared and the cylinder (10) of the cemented carbide B, and 1050 in a vacuum using a hot press method. Diffusion bonding was performed under the conditions of 10 ° C., 30 MPa, and a cBN sintered member (8) having a thickness of 50 mm and a diameter of 30 mm composed of a cBN sintered body and cemented carbides A and B was prepared.
As shown in FIG. 1, the method for producing a tool material according to the present invention is that a cylindrical member having a diameter of 4.01 mm is produced from a cBN sintered member (8) by wire electric discharge machining, and then a D value is 4 mm and an L value is 50 mm. Centerless processing was performed on a round bar. FIG. 3 shows the tool material of Example 1 of the present invention created. Here, various measurements of the tool material were performed. Table 1 shows the measurement results of the d1 and d2 values, the Co content, the bending strength value of the cemented carbide B, and the values of L1, L2, and L3.

（実施例２）
実施例１によって得られた本発明例１の工具素材を用いて、図４に示す様なｃＢＮ小径ボールエンドミルを作製した。ｃＢＮ小径ボールエンドミルは、円筒研削加工で首部を形成した後、溝研削加工で刃部を形成することにより、刃径が１ｍｍ、首下長さＬｎが８ｍｍのｃＢＮ小径ボールエンドミルを得た。更に、同様の方法を用いて、超硬合金作製時における配合ＷＣ粉末の粒径とＣｏ量やＬ１値、Ｌ２値、Ｌ３値を調整して本発明例２〜１３、比較例１６〜２６を作製した。これらの工具素材よりｃＢＮ小径ボールエンドミルを作成した。図５は、本発明例１４、１５の別の実施形態に用いたｃＢＮ小径ボールエンドミルの作製方法の例を説明する模式図を示す。本願発明の工具素材を、丸棒（１１）の先端に設けた孔に差し込みロウ付け後、所定の形状に加工して小径ボールエンドミルを得る方法である。
別に本発明例１と同様の方法で、ｃＢＮ焼結体と１種類の超硬合金からなるｃＢＮ焼結部材を得た。得られたｃＢＮ焼結体部材４からワイヤー放電加工により、円柱部材を切り出した後、直径２ｍｍ長さ１３ｍｍの丸棒にセンタレス加工して従来例２７、２８の工具素材を作成した。超硬合金作製時において、配合ＷＣ粉末の粒径とＣｏ量や厚みを調整した。この工具素材から、ｃＢＮ小径ボールエンドミルを作成した。
工具素材の折損強度を評価するため本発明例１から１５、比較例１６から２６、従来例２７から２９の各々５本の工具素材を使用して作成したｃＢＮ小径ボールエンドミルを評価した。切削試験は下記の試験条件で行った。評価は、切削距離３００ｍまでに折損した本数を測定した。折損数を表１に併せて示した。
（試験条件）
被切削材：ＳＫＤ１１、硬さ、ＨＲＣ６０
工具形状：先端ボール刃、Ｒ：０．５ｍｍ
工具回転数：毎分４００００回転
送り速度：１５００ｍｍ／分
切り込み量：０．０５ｍｍ
加工方法：乾式切削による等高線仕上げ加工、勾配角度：１０° (Example 2)
Using the tool material of Invention Example 1 obtained in Example 1, a cBN small-diameter ball end mill as shown in FIG. 4 was produced. In the cBN small-diameter ball end mill, a neck portion was formed by cylindrical grinding and then a blade portion was formed by groove grinding to obtain a cBN small-diameter ball end mill having a blade diameter of 1 mm and a neck length Ln of 8 mm. Further, by using the same method, the present invention examples 2 to 13 and comparative examples 16 to 26 were prepared by adjusting the particle size and Co amount, L1 value, L2 value, and L3 value of the blended WC powder at the time of producing the cemented carbide. Produced. A cBN small-diameter ball end mill was prepared from these tool materials. FIG. 5 is a schematic view for explaining an example of a method for producing a cBN small-diameter ball end mill used in another embodiment of Examples 14 and 15 of the present invention. This is a method of obtaining a small-diameter ball end mill by inserting the tool material of the present invention into a hole provided at the tip of a round bar (11), brazing, and processing into a predetermined shape.
Separately, a cBN sintered member comprising a cBN sintered body and one kind of cemented carbide was obtained in the same manner as in Invention Example 1. A cylindrical member was cut out from the obtained cBN sintered body member 4 by wire electric discharge machining, and then centerless processed into a round bar having a diameter of 2 mm and a length of 13 mm to produce tool materials of conventional examples 27 and 28. During the production of the cemented carbide, the particle size, Co amount and thickness of the blended WC powder were adjusted. A cBN small-diameter ball end mill was created from this tool material.
In order to evaluate the breaking strength of the tool material, cBN small-diameter ball end mills prepared by using five tool materials of Invention Examples 1 to 15, Comparative Examples 16 to 26, and Conventional Examples 27 to 29 were evaluated. The cutting test was performed under the following test conditions. Evaluation measured the number which broke up to 300m of cutting distance. The number of breaks is also shown in Table 1.
(Test conditions)
Workpiece: SKD11, hardness, HRC60
Tool shape: tip ball blade, R: 0.5 mm
Tool rotation speed: 40000 rotations per minute Feed rate: 1500 mm / min Cutting depth: 0.05 mm
Processing method: Contour finishing by dry cutting, gradient angle: 10 °

表１に示す本発明例１から１５、比較例１６から２６と従来例２７から２８の切削試験の評価結果では、本発明例はいずれも折損はなく、折損強度に優れていた。本発明例１０〜１３、１５は、本願発明の規定範囲を満足しているために、Ｌｎ／Ｄ値が１０以上の首下が長く、刃径が１ｍｍの小径のボールエンドミルにおいても折損はなく、優れた折損強度を示した。本発明例は、１２、１３、１５は、本願発明の規定範囲を満足しているほか、首部を構成する超硬合金Ｂの抗折力が３８００ＭＰａであり強度が高いため、Ｌｎ／Ｄ値が１５以上の首下長さの長い小径ボールエンドミルにおいても、折損はなく、優れた折損強度を示した。本発明例１３は、本願発明の規定範囲を満足しているほか、更に超硬合金Ｂのｄ２値が０．６μｍ、超硬合金Ａのｄ１値が３．１μｍと好ましい値にあり、超硬合金Ｂの抗折力が３８００ＭＰａであるために、Ｌｎ／Ｄ値が２０のような首下がさらに長い小径ボールエンドミルにおいても、折損はなく優れた折損強度を示した。
一方、比較例１６、１７は、ｄ１値が２μｍ未満であり、本発明の規定の範囲よりも小さく、高温での折損強度が弱いため、刃部側での欠損本数が多く、工具の折損強度は低いものであった。比較例１８は、ｄ１値が５．６μｍであり、本発明の規定の範囲よりも大きく、曲げ変形に起因する折損が多く、工具の折損強度は低いものであった。比較例１９は、ｄ２値が０．２μｍであり本願発明の規定の範囲よりも小さく、比較例１６、２０は、ｄ２値が１μｍを超えて大きく本願発明の規定の範囲よりも大きく、伴に強度が弱いため、シャンク側での欠損本数が多く、工具の折損強度は低いものであった。比較例２１は、超硬合金ＡのＣｏ量が５％であり、本願発明の規定の範囲よりも小さく、比較例２２は、超硬合金ＡのＣｏ量が１２．５％であり、本願発明の規定の範囲よりも大きく、伴に熱衝撃に起因する刃部側での欠損本数が多く、工具の折損強度は低いものであった。比較例２３は、超硬合金ＢのＣｏ量が４．５％であり本願発明の規定の範囲よりも小さく、衝撃に起因する折損が多く、工具の折損強度は低いものであった。比較例２４は、超硬合金ＢのＣｏ量が１２％であり本願発明の規定の範囲よりも大きく、振動や曲げ変形に起因する破損が多く、工具の折損強度は低いものであった。比較例２５は、Ｌ２／Ｌ１の値が１．７であり、本願発明の規定の範囲よりも小さく、シャンク側の首部が刃部に近接するため、シャンク側の首部での折損が多く、工具の折損強度は低いものであった。比較例２６は、（Ｌ１＋Ｌ２）／Ｌ３の値が０．７５であり、本願発明の規定の範囲よりも大きく、刃部側の首部の部分が必要以上に長くなるため、刃部側の首部での折損が多く、工具の折損強度は低いものであった。従来例２８、２９は、超硬合金が１層であり本願発明の構成と異なるため、工具の折損強度は低いものであった。 In the evaluation results of the cutting tests of Invention Examples 1 to 15, Comparative Examples 16 to 26 and Conventional Examples 27 to 28 shown in Table 1, all of the invention examples were not broken and were excellent in break strength. Since Invention Examples 10 to 13 and 15 satisfy the specified range of the present invention, there is no breakage even in a ball end mill having a long neck length with an Ln / D value of 10 or more and a small-diameter ball end mill with a blade diameter of 1 mm. Excellent break strength. In the present invention example, 12, 13 and 15 satisfy the specified range of the present invention, and the bending strength of the cemented carbide B constituting the neck portion is 3800 MPa and the strength is high, so the Ln / D value is Even in a small-diameter ball end mill having a long neck length of 15 or more, there was no breakage and excellent breakage strength was exhibited. Invention Example 13 not only satisfies the specified range of the present invention, but also has a d2 value of cemented carbide B of 0.6 μm and a d1 value of cemented carbide A of 3.1 μm, which are preferable values. Since the bending strength of the alloy B was 3800 MPa, even a small-diameter ball end mill having a longer neck length such as an Ln / D value of 20 showed no breaking strength and excellent breaking strength.
On the other hand, in Comparative Examples 16 and 17, the d1 value is less than 2 μm, which is smaller than the specified range of the present invention, and the fracture strength at high temperature is weak, so the number of defects on the blade side is large, and the fracture strength of the tool Was low. In Comparative Example 18, the d1 value was 5.6 μm, which was larger than the specified range of the present invention, had many breakage due to bending deformation, and the breakage strength of the tool was low. Comparative Example 19 has a d2 value of 0.2 μm, which is smaller than the specified range of the present invention, and Comparative Examples 16 and 20 have a d2 value exceeding 1 μm and larger than the specified range of the present invention. Since the strength was weak, the number of defects on the shank side was large, and the breaking strength of the tool was low. In Comparative Example 21, the amount of Co in the cemented carbide A is 5%, which is smaller than the prescribed range of the present invention. In Comparative Example 22, the amount of Co in the cemented carbide A is 12.5%, and the present invention The number of defects on the blade side due to thermal shock was large, and the break strength of the tool was low. In Comparative Example 23, the amount of Co in the cemented carbide B was 4.5%, which was smaller than the specified range of the present invention, had many breakage due to impact, and the break strength of the tool was low. In Comparative Example 24, the amount of Co in the cemented carbide B was 12%, which was larger than the specified range of the present invention, there were many breakages due to vibration and bending deformation, and the break strength of the tool was low. In Comparative Example 25, the value of L2 / L1 is 1.7, which is smaller than the specified range of the present invention, and since the neck on the shank side is close to the blade part, there is a lot of breakage at the neck on the shank side. The break strength was low. In Comparative Example 26, the value of (L1 + L2) / L3 is 0.75, which is larger than the specified range of the present invention, and the neck part on the blade part side becomes longer than necessary. The breakage strength of the tool was low. Conventional examples 28 and 29 have one layer of cemented carbide and are different from the configuration of the present invention, so the break strength of the tool was low.

図１は、本願発明の実施形態に用いたｃＢＮ焼結部材の模式図を示す。FIG. 1 shows a schematic diagram of a cBN sintered member used in an embodiment of the present invention. 図２は、ｃＢＮ焼結部材の模式図を示す。FIG. 2 shows a schematic diagram of a cBN sintered member. 図３は、本願発明の工具素材の模式図を示す。FIG. 3 shows a schematic diagram of the tool material of the present invention. 図４は、本願発明のｃＢＮ小径ボールエンドミルの模式図を示す。FIG. 4 is a schematic diagram of a cBN small-diameter ball end mill according to the present invention. 図５は、本願発明の別の実施形態に用いたｃＢＮ小径ボールエンドミルを示す。FIG. 5 shows a cBN small-diameter ball end mill used in another embodiment of the present invention.

Explanation of symbols

１：工具素材
２：ｃＢＮ焼結体
３：ＷＣ基超硬合金
４：超硬合金Ａ
５：超硬合金Ｂ
６：接合面Ｃ
７：接合面Ｄ
８：ｃＢＮ焼結部材
９：ｃＢＮ焼結部材
１０：超硬合金Ｂの円柱
１１：丸棒 1: Tool material 2: cBN sintered body 3: WC-based cemented carbide 4: Cemented carbide A
5: Cemented carbide B
6: Joint surface C
7: Bonding surface D
8: cBN sintered member 9: cBN sintered member 10: Column of cemented carbide B 11: Round bar

Claims

One end of the cylindrical tool material (1) is formed of a cBN sintered body (2) and the other end is formed of a WC-based cemented carbide (3), and the WC-based cemented carbide (3) is elongated. It consists of cemented carbide A (4) and cemented carbide B (5) in the direction, and one end of the cemented carbide A (4) is joined surface C (with the cBN sintered body (2) 6), the other end of the cemented carbide A (4) has a joint surface D (7) with the cemented carbide B (5), and the cemented carbide A (4) , When the WC average particle diameter is d1 (μm), 2 ≦ d1 ≦ 4, the Co content is 6% or more and 12% or less by mass%, and the cemented carbide B (5) has a WC average When the particle size is d2 (μm), 0.3 ≦ d2 ≦ 1, the Co content is 5% or more and 11% or less, the length (mm) of the tool material (1) is L, and the diameter (mm ) Is D, 3 ≦ L ≦ 60 and D ≦ 6. Tool material characterized by that.

The tool material according to claim 1, wherein the length (mm) of the cBN sintered body (2) is L1, the length (mm) of the cemented carbide A (4) is L2, and the cemented carbide B (5 ), When the length (mm) is L3, L2 / L1 ≧ 2, and (L1 + L2) /L3≦0.7.

3. The tool material according to claim 1, wherein the d1 value is 2.5 ≦ d1 ≦ 3.5 and the d2 value is 0.3 ≦ d2 ≦ 0.6. .