JP4679257B2 - Thread groove processing method for ball screw shaft - Google Patents

Thread groove processing method for ball screw shaft Download PDF

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JP4679257B2
JP4679257B2 JP2005176501A JP2005176501A JP4679257B2 JP 4679257 B2 JP4679257 B2 JP 4679257B2 JP 2005176501 A JP2005176501 A JP 2005176501A JP 2005176501 A JP2005176501 A JP 2005176501A JP 4679257 B2 JP4679257 B2 JP 4679257B2
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thread groove
groove
ball screw
screw shaft
tool
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JP2006349058A (en
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守久 吉岡
恵介 数野
清仁 石川
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NTN Corp
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Description

本発明は、多数のボールが転動する螺旋状のねじ溝が形成されたボールねじのボールねじ軸のねじ溝加工方法に関するものである。
The present invention, number of balls is related to the screw groove processing method of ball Lumpur screw shaft of a ball screw with a helical screw groove is formed to roll.

ボールねじは、外周に螺旋状のねじ溝が形成されたボールねじ軸と、円筒面内に螺旋状のねじ溝が形成されたボールねじナットと、対向する両ねじ溝で構成されたボール転動路内に転動自在に収容された多数のボールとからなり、ボールねじ軸あるいはボールねじナットの回転を軸方向の並進運動に変換する機械要素である。   A ball screw has a ball screw shaft composed of a ball screw shaft having a spiral thread groove formed on the outer periphery, a ball screw nut having a spiral thread groove formed in a cylindrical surface, and both opposing screw grooves. It is a mechanical element that is composed of a large number of balls that are rotatably accommodated in the road, and converts the rotation of the ball screw shaft or ball screw nut into translational motion in the axial direction.

従来、自動車用のアクチュエータ等に使用されるボールねじにおいて、そのボールねじ軸またはナットのねじ溝は、生材にねじ溝を旋削する工程と、焼入工程と、ねじ溝を研削する工程を経て加工されている。なお、旋削工程では、ねじ溝と同じ形状の工具（総型バイト）を使用している。   2. Description of the Related Art Conventionally, in a ball screw used in an actuator for an automobile, the thread groove of the ball screw shaft or nut is subjected to a process of turning the thread groove on a raw material, a quenching process, and a process of grinding the thread groove. Has been processed. In the turning process, a tool (total type bite) having the same shape as the thread groove is used.

しかしながら、総型バイトで旋削すると、バイトに対する切削抵抗が大きくて剛性の不足が生じ、バイトの振動、所謂ビビリが生じ易い。その結果、加工精度が悪化すると共に、研削取代を大きく残しておく必要があり、研削工程に時間がかかる。こうした問題を解決するため、本出願人は、ねじ溝の形状変化に容易に対処でき、かつ総加工時間の短縮が図れるボールねじのねじ溝加工方法を既に提案している。   However, when turning with a full-size bite, the cutting resistance against the bite is large and the rigidity is insufficient, so that vibration of the bite, so-called chattering easily occurs. As a result, the machining accuracy deteriorates, and it is necessary to leave a large machining allowance, which takes time for the grinding process. In order to solve these problems, the present applicant has already proposed a method of processing a thread groove of a ball screw that can easily cope with a change in the shape of the thread groove and can reduce the total processing time.

このねじ溝加工方法は、図８に示すように、ねじ軸５１におけるねじ溝５２の加工を行う方法であって、生材からなるワークＷにねじ溝５２を旋削する工程と、この旋削したワークＷを焼入れする工程と、焼入後のワークＷのねじ溝５２を研削する工程とを含む。まず、同図（Ａ）に示すように、生材の棒状ワークＷにねじ溝５２を旋削する。（ａ）は、ワークＷを旋盤の主軸チャック５３で把持した状態を示し、（ｂ）は旋削が進んだ段階におけるねじ溝５２の拡大断面を示す。この場合の旋削は、所謂ポイント切削で行う。すなわち、切刃５４ａのノーズＲがねじ溝５２の曲率半径よりも小さな汎用バイト５４を用い、この汎用バイト５４をねじ溝５２の有効長さ分だけ複数回移動させて、各回の移動経路Ｐ１、Ｐ２〜Ｐｎをねじ溝５２の断面形状の円弧方向に順次ずらせることによりねじ溝５２の全体を旋削する。ねじ溝５２の旋削が完了した後、ワークＷを加熱炉５５で焼入れし（図８（Ｂ））、この焼入れしたワークＷを砥石５６で研削してねじ軸５１が完成する（図８（Ｃ））。
特開平６−２４９３１７号公報 As shown in FIG. 8, the thread groove machining method is a method of machining the thread groove 52 in the screw shaft 51, and includes a step of turning the thread groove 52 into a workpiece W made of raw material, and the turned workpiece. A step of quenching W and a step of grinding the thread groove 52 of the workpiece W after quenching. First, as shown in FIG. 2A, the thread groove 52 is turned in the raw bar work W. (A) shows the state where the workpiece W is gripped by the spindle chuck 53 of the lathe, and (b) shows an enlarged cross section of the thread groove 52 at the stage where the turning has proceeded. The turning in this case is performed by so-called point cutting. That is, using a general-purpose tool 54 in which the nose R of the cutting edge 54a is smaller than the radius of curvature of the screw groove 52, the general-purpose tool 54 is moved a plurality of times by the effective length of the screw groove 52, and each movement path P1, The entire thread groove 52 is turned by sequentially shifting P2 to Pn in the arc direction of the cross-sectional shape of the thread groove 52. After the turning of the thread groove 52 is completed, the workpiece W is quenched in the heating furnace 55 (FIG. 8B), and the quenched workpiece W is ground by the grindstone 56 to complete the screw shaft 51 (FIG. 8C )).
JP-A-6-249317

こうした従来の加工方法によると、小さなバイト５４でポイント切削を行うので、バイト５４の経路変更を行うだけで容易にねじ溝５２の形状変更ができ、バイト５４に対する切削抵抗が小さくてなってビビリの問題もなく、高精度に旋削が行えるという特徴を有している。然しながら、総型バイトを使用する旋削加工に比べ、ある程度のコスト低減は可能であるが、研削工程は、加工の度に砥石５６を成形して形状を管理する必要がある。この研削工程は、ねじ溝５２の加工工程全体の加工コストに対して、大きなウェイトを占めているため、さらなる加工コストの低減を図るには限界があった。   According to such a conventional processing method, since point cutting is performed with a small cutting tool 54, the shape of the thread groove 52 can be easily changed by simply changing the path of the cutting tool 54, and the cutting resistance with respect to the cutting tool 54 is reduced, resulting in chattering. It has the feature that it can be turned with high accuracy without any problems. However, it is possible to reduce the cost to some extent as compared with the turning process using the total tool, but in the grinding process, it is necessary to form the grindstone 56 and manage the shape every time the machining is performed. Since this grinding process occupies a large weight with respect to the machining cost of the entire machining process of the thread groove 52, there is a limit to further reducing the machining cost.

本発明は、こうした従来の問題を解決し、良好な表面粗さが得られ、加工時間が短く低コストなボールねじ軸のねじ溝加工方法を提供することを目的とする。
An object of the present invention is to solve such a conventional problem, and to provide a thread groove machining method of a ball screw shaft that can obtain a good surface roughness, has a short machining time, and is low in cost.

係る目的を達成すべく、本発明のうち請求項１に記載の方法発明は、生材からなるワークにねじ溝を旋削する工程と、この旋削したワークを焼入れする工程とを含むボールねじ軸のねじ溝加工方法において、前記旋削工程で、切刃のノーズ半径が前記ねじ溝の溝曲率半径に近付けて当該溝曲率半径よりも小さな汎用バイトを用い、前記切刃が棒状のワークの軸心方向に送られ、前記ねじ溝の概略形状が当該バイトの切刃によって成形され、この汎用バイトを前記ねじ溝の有効長さ分だけ複数回移動させて、各回の移動経路を当該ねじ溝の断面形状の円弧方向に順次ずらせることにより、前記ねじ溝の全体が旋削されると共に、前記ねじ溝のツールマーク高さが所定値以下となるように前記切刃のノーズ半径と刻み角度が設定されている。
According to an aspect of the method invention of claim 1 of the present invention includes the steps of turning the screw groove on the workpiece consisting of the raw material, the ball screw shaft and a step of hardening the turning Work In the thread groove processing method, in the turning step, a general-purpose tool having a nose radius of the cutting blade that is close to the groove curvature radius of the thread groove and smaller than the groove curvature radius is used, and the cutting edge is in the axial direction of the rod-shaped workpiece. The general shape of the thread groove is formed by the cutting edge of the bite, the general-purpose bite is moved a plurality of times by the effective length of the screw groove, and the cross-sectional shape of the screw groove is moved each time. The entire groove is turned, and the nose radius and the notch angle of the cutting edge are set so that the tool mark height of the screw groove is not more than a predetermined value. Yes.

このように、切刃のノーズ半径をねじ溝の溝曲率半径に近付けて当該溝曲率半径よりも小さな汎用バイトを用い、前記切刃が棒状のワークの軸心方向に送られ、前記ねじ溝の概略形状が当該バイトの切刃によって成形され、この汎用バイトを前記ねじ溝の有効長さ分だけ複数回移動させて、各回の移動経路を当該ねじ溝の断面形状の円弧方向に順次ずらせることにより、前記ねじ溝の全体が旋削されると共に、ねじ溝のツールマーク高さが所定値以下となるように切刃のノーズ半径とポイント切削の刻み角度が設定されているので、ねじ溝に所望の表面粗さが得られ、ポイント切削によってねじ溝の成形加工を完了させることができる。したがって、従来の熱処理後の研削加工あるいは旋削加工を廃止することができ、ボールねじの精度・耐久性を確保することができると共に、加工コストを低減したボールねじを提供することができる。
Thus, using a small general-purpose byte than the groove radius of curvature close to the nose radius of the cutting edge into the groove radius of curvature of the thread groove, the cutting edge is fed in the axial direction of the rod-shaped workpiece, the screw groove The general shape of the cutting tool is formed by the cutting edge of the cutting tool, and the general-purpose tool is moved a plurality of times by the effective length of the thread groove, and the movement path of each time is sequentially shifted in the arc direction of the sectional shape of the thread groove. As a result, the entire thread groove is turned, and the nose radius of the cutting edge and the point cutting step angle are set so that the tool mark height of the thread groove is not more than a predetermined value. A desired surface roughness is obtained, and the thread groove forming process can be completed by point cutting. Therefore, conventional grinding or turning after heat treatment can be abolished, the accuracy and durability of the ball screw can be ensured, and a ball screw with reduced machining costs can be provided.

好ましくは、請求項２に記載の発明のように、前記ねじ溝のツールマーク高さが２μｍ以下に規制されていれば、ねじ溝の表面粗さが０．２５〜１．０Ｒａと、少なくとも従来品の精度以上を確保することができ、精度・耐久性に優れたねじ溝が得られる。   Preferably, as in the invention described in claim 2, if the tool mark height of the thread groove is regulated to 2 μm or less, the surface roughness of the thread groove is at least 0.25 to 1.0 Ra, at least conventional. More than the accuracy of the product can be secured, and a thread groove excellent in accuracy and durability can be obtained.

また、請求項３に記載の発明のように、前記焼入工程の後に、少なくとも前記ねじ溝にショットピーニングによる仕上げ加工が施されていれば、ねじ溝に付着したスケールや表層の粒界酸化層を除去することができ、ボールねじの耐久性を向上させることができる。
Further, as in the invention according to claim 3 , when at least the thread groove is subjected to finish peening by shot peening after the quenching step, the scale or surface grain boundary oxide layer adhered to the thread groove. The durability of the ball screw can be improved.

本発明に係るボールねじ軸のねじ溝加工方法は、生材からなるワークにねじ溝を旋削する工程と、この旋削したワークを焼入れする工程とを含むボールねじ軸のねじ溝加工方法において、前記旋削工程で、切刃のノーズ半径が前記ねじ溝の溝曲率半径に近付けて当該溝曲率半径よりも小さな汎用バイトを用い、前記切刃が棒状のワークの軸心方向に送られ、前記ねじ溝の概略形状が当該バイトの切刃によって成形され、この汎用バイトを前記ねじ溝の有効長さ分だけ複数回移動させて、各回の移動経路を当該ねじ溝の断面形状の円弧方向に順次ずらせることにより、前記ねじ溝の全体が旋削されると共に、前記ねじ溝のツールマーク高さが所定値以下となるように前記切刃のノーズ半径と刻み角度が設定されているので、ねじ溝に所望の表面粗さが得られ、ポイント切削によってねじ溝の成形加工を完了させることができる。したがって、従来の熱処理後の研削加工あるいは旋削加工を廃止することができ、ボールねじの精度・耐久性を確保することができると共に、加工コストを低減したボールねじを提供することができる。
Thread groove processing method of the ball screw shaft according to the present invention includes the steps of turning the screw groove on the workpiece consisting of the raw material, the thread groove processing method of the ball screw shaft and a step of hardening the turning Work, the In the turning process, the cutting blade is fed in the axial direction of the rod-shaped workpiece using a general-purpose tool whose nose radius is close to the groove curvature radius of the thread groove and smaller than the groove curvature radius , and the thread groove The general shape of the cutting tool is formed by the cutting edge of the cutting tool, and the general-purpose tool is moved a plurality of times by the effective length of the thread groove, and the movement path of each time is sequentially shifted in the arc direction of the sectional shape of the thread groove. As a result, the entire thread groove is turned and the nose radius and the notch angle of the cutting blade are set so that the tool mark height of the thread groove is not more than a predetermined value. Surface of It is obtained, thereby completing the molding of the thread groove by a point cutting. Therefore, conventional grinding or turning after heat treatment can be abolished, the accuracy and durability of the ball screw can be ensured, and a ball screw with reduced machining costs can be provided.

生材からなるワークにねじ溝を旋削する工程と、この旋削したワークを焼入れする工程とを含むボールねじ軸のねじ溝加工方法において、前記旋削工程で、切刃のノーズ半径が前記ねじ溝の溝曲率半径に近付けて当該溝曲率半径よりも小さな汎用バイトを用い、前記切刃が棒状のワークの軸心方向に送られ、前記ねじ溝の概略形状が当該バイトの切刃によって成形され、この汎用バイトを前記ねじ溝の有効長さ分だけ複数回移動させて、各回の移動経路を当該ねじ溝の断面形状の円弧方向に順次ずらせることにより、前記ねじ溝の全体が旋削されると共に、前記ねじ溝のツールマーク高さが２μｍ以下となるように前記切刃のノーズ半径と刻み角度が設定されている。
In the threading method of a ball screw shaft including a step of turning a thread groove on a workpiece made of raw material and a step of quenching the turned workpiece, the nose radius of the cutting edge is set to be equal to that of the thread groove in the turning step. Using a general-purpose tool closer to the groove curvature radius and smaller than the groove curvature radius , the cutting blade is fed in the axial direction of the rod-shaped workpiece, and the approximate shape of the thread groove is formed by the cutting blade of the tool. The general-purpose tool is moved a plurality of times by the effective length of the thread groove, and the entire thread groove is turned by sequentially shifting the movement path of each turn in the arc direction of the cross-sectional shape of the thread groove, The nose radius and the notch angle of the cutting blade are set so that the tool mark height of the thread groove is 2 μm or less.

以下、本発明の実施の形態を図面に基いて詳細に説明する。
図１は、本発明に係るボールねじ軸のねじ溝加工方法を適用するボールねじの一例を示す縦断面図、図２は、本発明に係るねじ軸のねじ溝加工状態を示す説明図、図３は、本発明に係るねじ軸のねじ溝加工工程を示すねじ溝の拡大断面図、図４は、ねじ軸のねじ溝を示す要部拡大図である。
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing an example of a ball screw to which a thread groove machining method for a ball screw shaft according to the present invention is applied. FIG. 2 is an explanatory view showing a thread groove machining state of the screw shaft according to the present invention. 3 is an enlarged sectional view of a thread groove showing a thread groove machining step of the screw shaft according to the present invention, and FIG. 4 is an enlarged view of a main part showing the thread groove of the screw shaft.

このボールねじ１は、Ｓ５５Ｃ等の中炭素鋼やＳＣＭ４１５等の肌焼き鋼からなり、外周に螺旋状のねじ溝２ａが形成されたねじ軸２と、ＳＣＭ４３０等の肌焼き鋼からなり、このねじ軸２に外挿され、内周にねじ溝２ａに対応する螺旋状のボールねじ溝３ａが形成されたナット３と、両ねじ溝２ａ、３ａ間に転動自在に収容された多数のボール４と、円筒状のナット３の胴部に装着され、ねじ溝３ａを連結する連結溝５ａが形成された駒部材５とを備えている。そして、ねじ溝２ａ、３ａによりボール転動路が構成され、駒部材６の連結溝５ａによって多数のボール４が無限循環することができる。   The ball screw 1 is made of medium carbon steel such as S55C or case-hardened steel such as SCM415, and is made of a screw shaft 2 having a spiral thread groove 2a formed on the outer periphery and a case-hardened steel such as SCM430. A nut 3 that is extrapolated to the shaft 2 and has a spiral ball screw groove 3a corresponding to the screw groove 2a on the inner periphery, and a large number of balls 4 that are rotatably accommodated between the screw grooves 2a and 3a. And a piece member 5 that is mounted on the body of the cylindrical nut 3 and has a connecting groove 5a that connects the thread groove 3a. Then, a ball rolling path is constituted by the thread grooves 2a and 3a, and a large number of balls 4 can be infinitely circulated by the connecting groove 5a of the piece member 6.

ここで、ねじ溝２ａ、３ａは、ボール４の半径よりも僅かに大きい曲率半径からなる２つの円弧を組み合わせたゴシックアーチ溝に形成されている。無論、ねじ溝２ａ、３ａは、このゴシックアーチ形状以外にも、ボール４とサーキュラコンタクトする円弧状の形状であっても良い。なお、ボール循環方式は駒式に限らず、リターンチューブ式やエンドキャップ式であっても良い。   Here, the thread grooves 2 a and 3 a are formed in a Gothic arch groove in which two arcs having a radius of curvature slightly larger than the radius of the ball 4 are combined. Of course, the thread grooves 2a and 3a may have an arcuate shape in circular contact with the ball 4 other than the Gothic arch shape. The ball circulation method is not limited to the piece type, and may be a return tube type or an end cap type.

図２は、ねじ軸２におけるねじ溝２ａの加工状態を示している。生材の棒状ワークＷ（２）が図示しない旋盤の主軸チャックで把持され、所定の方向に回転された状態で汎用バイト６によって旋削加工される。このバイト６は、径方向に進退自在に、かつ軸方向に移動自在に支持されたホルダー７に固定されている。この場合の旋削は、所謂ポイント切削で行われる。すなわち、バイト６の切刃６ａのノーズ半径Ｒ２が、ねじ溝２ａの溝曲率半径Ｒ１よりも小さな汎用バイト６を用い、このバイト６をねじ溝２ａの有効長さ分だけ複数回移動させてねじ溝２ａの成形が行われる。   FIG. 2 shows a machining state of the thread groove 2 a in the screw shaft 2. A raw material bar-shaped workpiece W (2) is gripped by a spindle chuck of a lathe (not shown), and is turned by a general-purpose tool 6 while being rotated in a predetermined direction. The cutting tool 6 is fixed to a holder 7 supported so as to be movable back and forth in the radial direction and movable in the axial direction. The turning in this case is performed by so-called point cutting. That is, a general-purpose cutting tool 6 having a nose radius R2 of the cutting edge 6a of the cutting tool 6 smaller than the groove curvature radius R1 of the thread groove 2a is used, and the cutting tool 6 is moved a plurality of times by the effective length of the thread groove 2a. The groove 2a is formed.

次に、図３（ａ）〜（ｊ）を用いてねじ溝２ａの加工工程を説明する。
図３（ａ）は、旋削加工前の棒状の生材を示し、（ｂ）〜（ｄ）の順に、切刃６ａがワークＷの軸心方向に送られて、ねじ溝２ａの概略形状がバイト６の切刃６ａによって成形される。ここで、切刃６ａのノーズ半径Ｒ２をねじ溝２ａの溝曲率半径Ｒ１に近付けて寸法設定することにより、切刃６ａを軸方向に移動させることなくねじ溝２ａの概略形状が得られ、加工時間を短縮することができる。 Next, the process of processing the thread groove 2a will be described with reference to FIGS.
FIG. 3A shows a rod-shaped raw material before turning, and the cutting edge 6a is fed in the axial direction of the workpiece W in the order of (b) to (d), and the schematic shape of the thread groove 2a is as follows. It is formed by the cutting edge 6 a of the cutting tool 6. Here, when the nose radius R2 of the cutting edge 6a is set close to the groove curvature radius R1 of the thread groove 2a, the approximate shape of the thread groove 2a is obtained without moving the cutting edge 6a in the axial direction. Time can be shortened.

そして、図３（ｅ）に示すように、ねじ溝２ａの旋削加工がある程度進んだ段階でポイント切削が開始される。（ｅ）〜（ｊ）に示すように、切刃６ａをねじ溝２ａの有効長さ分だけ複数回移動させて、各回の移動経路をねじ溝２ａの円弧方向に順次ずらせることによりねじ溝２ａの全体形状が旋削される。   Then, as shown in FIG. 3E, point cutting is started when the turning of the thread groove 2a has progressed to some extent. As shown in (e) to (j), the cutting edge 6a is moved a plurality of times by the effective length of the thread groove 2a, and the thread path is sequentially shifted in the arc direction of the thread groove 2a. The entire shape of 2a is turned.

なお、本実施例では、ねじ溝２ａがゴシックアーチ形状であっても、バイト６の切刃６ａのノーズ半径Ｒ２がねじ溝２ａの溝曲率半径Ｒ１よりも小さく設定されているので、加工するねじ溝２ａと対向するねじ溝２ａに干渉することはない。ところが、従来の総型バイトによるねじ溝加工と違い、この種のポイント切削においては、図４に示すようなツールマークの発生を免れない。ここで、本実施例では、ポイント切削時のツールマーク高さＨは、ねじ溝２ａの溝曲率半径Ｒ１と切刃６ａのノーズ半径Ｒ２および刻み角度αによって決定されている。すなわち、ツールマーク高さＨが２μｍ以下となるように切刃６ａのノーズ半径Ｒ２と刻み角度αが設定されている。   In this embodiment, even if the thread groove 2a has a Gothic arch shape, the nose radius R2 of the cutting edge 6a of the cutting tool 6 is set smaller than the groove curvature radius R1 of the thread groove 2a. There is no interference with the thread groove 2a facing the groove 2a. However, unlike the conventional thread groove machining with a general-purpose tool, this kind of point cutting cannot avoid the generation of tool marks as shown in FIG. Here, in this embodiment, the tool mark height H at the time of point cutting is determined by the groove curvature radius R1 of the thread groove 2a, the nose radius R2 of the cutting edge 6a, and the step angle α. That is, the nose radius R2 and the cut angle α of the cutting edge 6a are set so that the tool mark height H is 2 μm or less.

ねじ溝２ａの表面粗さはボールねじの精度や耐久性に影響する重要な特性であり、一般的にこのねじ溝２ａの表面粗さはＲａで管理されるが、ここで、ツールマーク高さＨは、ねじ溝２ａの粗さ曲線においてＲｚに相当する。なお、Ｒｚは、ＪＩＳの粗さ形状パラメータの一つで（ＪＩＳ Ｂ０６０１−１９９４）、１０点平均粗さ、すなわち、基準長さ毎の山頂の高い方から５点、谷底から低い方から５点を選び、その１０点の平均高さを言う。また、Ｒａは算術平均粗さで、平均線から絶対値偏差の平均値を言う。これらのパラメータＲｚ、Ｒａ間には、概ねＲａ≒Ｒｚ／４の関係がある。したがって、ツールマーク高さＨが２μｍ以下となるように切刃６ａのノーズ半径Ｒ２および刻み角度αを設定することにより、ねじ溝２ａの表面粗さが０．２５〜１．０Ｒａと、少なくとも従来品の精度以上を確保することができ、精度・耐久性に優れたねじ溝２ａが得られる。   The surface roughness of the thread groove 2a is an important characteristic that affects the accuracy and durability of the ball screw. Generally, the surface roughness of the thread groove 2a is controlled by Ra, where the tool mark height is H corresponds to Rz in the roughness curve of the thread groove 2a. Rz is one of JIS roughness shape parameters (JIS B0601-1994), 10-point average roughness, that is, 5 points from the top of the peak for each reference length, 5 points from the bottom to the bottom. And say the average height of the 10 points. Ra is an arithmetic average roughness, which means an average value of absolute value deviations from the average line. There is a relation of Ra≈Rz / 4 between these parameters Rz and Ra. Therefore, by setting the nose radius R2 and the notch angle α of the cutting edge 6a so that the tool mark height H is 2 μm or less, the surface roughness of the thread groove 2a is at least 0.25 to 1.0 Ra, which is at least conventional. More than the accuracy of the product can be ensured, and the thread groove 2a excellent in accuracy and durability can be obtained.

このように、本実施例では、切刃６ａのノーズ半径Ｒ２をねじ溝２ａの溝曲率半径Ｒ１よりも小さくしてねじ溝２ａがポイント切削によって成形加工されると共に、切刃６ａのノーズ半径Ｒ２とポイント切削の刻み角度αを所定値に設定することにより、ツールマーク高さＨが１μｍ以下に規制するようにしたので、ねじ溝２ａに所望の表面粗さが得られ、ポイント切削によってねじ溝２ａの成形加工を完了させることができる。したがって、従来の熱処理後の研削加工あるいは旋削加工を廃止することができ、ボールねじ１の精度・耐久性を確保することができると共に、加工コストを低減したボールねじ１を提供することができる。   Thus, in this embodiment, the nose radius R2 of the cutting edge 6a is made smaller than the groove curvature radius R1 of the thread groove 2a, and the thread groove 2a is formed by point cutting, and the nose radius R2 of the cutting edge 6a. Since the tool mark height H is regulated to 1 μm or less by setting the step angle α of the point cutting to a predetermined value, a desired surface roughness is obtained in the thread groove 2a, and the thread groove is obtained by point cutting. The molding process 2a can be completed. Therefore, conventional grinding or turning after heat treatment can be abolished, the accuracy and durability of the ball screw 1 can be ensured, and the ball screw 1 with reduced processing costs can be provided.

図５は、本発明に係るポイント切削によるねじ溝加工方法と従来の総型バイト（タップ）により成形されたねじ溝の母線崩れ（理論Ｒに対する崩れ量）を比較したグラフである。また、図６は、同じくねじ溝の表面粗さを比較したグラフである。測定値は、ゴシックアーチ溝の左右フランク（ボールが転動する接触角が４５°付近）の平均値を示している。なお、サンプルは、ねじ軸の材質がＳＣＭ４１５で、軸径が１６ｍｍ、リードが３ｍｍ、ボール径が２．３８１ｍｍ、溝曲率半径が１．４ｍｍである。それぞれのサンプルは、実施例の方は超硬製のチップを使用してワーク回転数が２００ｒｐｍでポイント切削され、また、比較例の方はチタンコーティング（ＴＩＮ）されたタップを使用し、ワーク回転数が４５ｒｐｍで総型旋削されてたものである。図５および図６のグラフからも明らかなように、ねじ溝の母線崩れは従来のタップ加工に比べ、１１．５μｍから８μｍと略３０％改善することができると共に、表面粗さにおいては、３０％以上の改善が認められた。   FIG. 5 is a graph comparing the thread groove machining method by point cutting according to the present invention and the bus line collapse (the collapse amount with respect to the theory R) of a thread groove formed by a conventional general-purpose tool (tap). FIG. 6 is a graph comparing the surface roughness of the thread grooves. The measured value shows the average value of the left and right flank of the Gothic arch groove (the contact angle at which the ball rolls is around 45 °). In the sample, the material of the screw shaft is SCM415, the shaft diameter is 16 mm, the lead is 3 mm, the ball diameter is 2.381 mm, and the groove curvature radius is 1.4 mm. Each sample is point-cut at a workpiece rotation speed of 200 rpm using a cemented carbide tip in the example, and a titanium coating (TIN) tap is used in the comparative example to rotate the workpiece. The number is the total turning at 45 rpm. As apparent from the graphs of FIGS. 5 and 6, the collapse of the thread groove bus line can be improved by approximately 30% from 11.5 μm to 8 μm as compared with the conventional tapping, and the surface roughness is 30%. % Improvement was observed.

さらに、本実施例では、ポイント切削によってねじ溝２ａの成形加工を完了させた後、熱処理によってその表面に５５〜６２ＨＲＣの範囲の硬化層が形成されている。熱処理は、浸炭焼入れでも高周波誘導加熱による焼入れでも良いが、表層に粒界酸化層が抑制でき、また、局部加熱ができて硬化層深さの設定が比較的容易にできる高周波焼入れが好適である。   Furthermore, in this embodiment, after the forming process of the thread groove 2a is completed by point cutting, a hardened layer in the range of 55 to 62HRC is formed on the surface by heat treatment. The heat treatment may be carburization quenching or quenching by high frequency induction heating, but it is preferable to use induction hardening that can suppress the grain boundary oxide layer on the surface layer and that can locally heat and set the hardened layer depth relatively easily. .

さらに、熱処理によりねじ溝２ａ等に付着したスケールや表層の粒界酸化層を除去するためにショットピーニングによる仕上げ加工（図示せず）が行われている。このショットピーニングは、スチールビーズの粒径を２０〜１００μｍ、噴射時間は約９０秒、噴射圧は１〜３ｋｇ／ｃｍ２、噴射ノズルとワークの表面までの距離は略１４０ｍｍとした。 Further, finish processing (not shown) by shot peening is performed in order to remove scales and surface grain boundary oxide layers adhering to the screw grooves 2a and the like by heat treatment. In this shot peening, the particle size of the steel beads was 20 to 100 μm, the injection time was about 90 seconds, the injection pressure was 1 to 3 kg / cm 2 , and the distance between the injection nozzle and the surface of the workpiece was about 140 mm.

図７は、本発明に係るナットにおけるねじ溝の加工状態を示している。なお、前述した実施例と同一あるいは同一機能を有する部品や部位には同じ符号を付して重複した説明を避ける。   FIG. 7 shows a machining state of the thread groove in the nut according to the present invention. In addition, the same code | symbol is attached | subjected to the components and site | part which have the same or the same function as the Example mentioned above, and the duplicate description is avoided.

ここでは、前述したねじ軸２におけるねじ溝２ａの加工と同様、生材の筒状ワークＷ（３）が図示しない旋盤の主軸チャックで把持され、所定の方向に回転された状態で汎用バイト６によって旋削加工される。このバイト６は、径方向に進退自在に、かつ軸方向に移動自在に支持されたホルダー７に固定されている。この場合の旋削もポイント切削で行われる。すなわち、バイト６の切刃６ａのノーズ半径Ｒ２が、ねじ溝３ａの溝曲率半径Ｒ１よりも小さな汎用バイト６を用い、バイト６をねじ溝３ａの有効長さ分だけ複数回移動させて、各回の移動経路をねじ溝３ａの円弧方向に順次ずらせることによりねじ溝３ａが旋削される。   Here, in the same manner as the processing of the screw groove 2a in the screw shaft 2 described above, the general-purpose tool 6 (3) in which the raw material cylindrical workpiece W (3) is gripped by a spindle chuck of a lathe (not shown) and rotated in a predetermined direction. Is turned by. The cutting tool 6 is fixed to a holder 7 supported so as to be movable back and forth in the radial direction and movable in the axial direction. Turning in this case is also performed by point cutting. That is, using a general-purpose tool 6 in which the nose radius R2 of the cutting edge 6a of the tool 6 is smaller than the groove curvature radius R1 of the screw groove 3a, the tool 6 is moved a plurality of times by the effective length of the screw groove 3a, and each time The thread groove 3a is turned by sequentially shifting the movement path in the arc direction of the thread groove 3a.

本実施例においても、切刃６ａのノーズ半径Ｒ２をねじ溝３ａの溝曲率半径Ｒ１よりも小さくしてねじ溝３ａがポイント切削によって成形加工されると共に、切刃６ａのノーズ半径Ｒ２とポイント切削の刻み角度αを所定値に設定することにより、ツールマーク高さＨが２μｍ以下に規制するようにしたので、ねじ溝３ａに所望の表面粗さが得られ、ポイント切削によってねじ溝３ａの成形加工を完了させることができる。   Also in the present embodiment, the nose radius R2 of the cutting edge 6a is made smaller than the groove curvature radius R1 of the thread groove 3a, and the thread groove 3a is formed by point cutting, and the nose radius R2 of the cutting edge 6a and point cutting are performed. Since the tool mark height H is regulated to 2 μm or less by setting the step angle α to a predetermined value, a desired surface roughness is obtained in the thread groove 3a, and the thread groove 3a is formed by point cutting. Processing can be completed.

以上、本発明の実施の形態について説明を行ったが、本発明はこうした実施の形態に何等限定されるものではなく、あくまで例示であって、本発明の要旨を逸脱しない範囲内において、さらに種々なる形態で実施し得ることは勿論のことであり、本発明の範囲は、特許請求の範囲の記載によって示され、さらに特許請求の範囲に記載の均等の意味、および範囲内のすべての変更を含む。   The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

本発明に係るボールねじ軸のねじ溝加工方法は、特に自動車等のアクチュエータや電動パワーステアリング装置に用いられボールねじにおけるねじ軸のねじ溝の加工に適用できる。
The ball screw shaft thread groove machining method according to the present invention can be applied to machining of a thread groove of a screw shaft in a ball screw used in an actuator or an electric power steering device of an automobile or the like.

本発明に係るボールねじ軸のねじ溝加工方法を適用するボールねじの一例を示す縦断面図である。It is a longitudinal cross-sectional view which shows an example of the ball screw to which the thread groove processing method of the ball screw shaft which concerns on this invention is applied. 本発明に係るねじ軸のねじ溝加工状態を示す説明図である。It is explanatory drawing which shows the thread groove processing state of the screw shaft which concerns on this invention. （ａ）〜（ｊ）は、本発明に係るねじ軸のねじ溝加工工程を示すねじ溝の拡大断面図である。(A)-(j) is an expanded sectional view of the thread groove which shows the thread groove processing process of the screw shaft concerning this invention. 同上、ねじ軸のねじ溝を示す要部拡大図である。It is a principal part enlarged view which shows the thread groove of a screw shaft same as the above. 本発明に係るポイント切削によるねじ溝加工方法と従来の総型バイトにより成形されたねじ溝の母線崩れを比較したグラフである。ねじ溝の表面粗さを比較したグラフである。It is the graph which compared the screw-groove processing method by the point cutting which concerns on this invention, and the bus-line collapse of the thread groove shape | molded by the conventional total type | mold bite. It is the graph which compared the surface roughness of the thread groove. 同上、ねじ溝の表面粗さを比較したグラフである。It is a graph which compared the surface roughness of a screw groove same as the above. 本発明に係るナットのねじ溝加工状態を示す説明図である。It is explanatory drawing which shows the thread groove processing state of the nut which concerns on this invention. 従来のねじ軸のねじ溝加工方法を示す工程説明図である。It is process explanatory drawing which shows the thread groove processing method of the conventional screw shaft.

符号の説明Explanation of symbols

１・・・・・・・・・・・ボールねじ
２・・・・・・・・・・・ねじ軸
２ａ、３ａ・・・・・・・ねじ溝
３・・・・・・・・・・・ナット
４・・・・・・・・・・・ボール
５・・・・・・・・・・・駒部材
５ａ・・・・・・・・・・連結溝
６・・・・・・・・・・・汎用バイト
６ａ・・・・・・・・・・切刃
７・・・・・・・・・・・ホルダー
５１・・・・・・・・・・ねじ軸
５２・・・・・・・・・・ねじ溝
５３・・・・・・・・・・主軸チャック
５４・・・・・・・・・・汎用バイト
５４ａ・・・・・・・・・切刃
５５・・・・・・・・・・加熱炉
５６・・・・・・・・・・砥石
Ｈ・・・・・・・・・・・ツールマーク高さ
Ｐ１〜Ｐｎ・・・・・・・バイトの移動経路
Ｒ１・・・・・・・・・・ねじ溝の溝曲率半径
Ｒ２・・・・・・・・・・切刃のノーズ半径
Ｗ・・・・・・・・・・・ワーク
α・・・・・・・・・・・刻み角度 1 ... Ball screw 2 ... Screw shaft 2a, 3a ... Screw groove 3 ... ··· Nut 4 ······························ 5 ········ General purpose tool 6a ························································· Holder shaft 52 ················································································································· ···························································································· of tool mark height P1 to Pn Movement path R1 ........... Nose radius W ··········· work α ··········· increments angle of the cutting edge

Claims (3)

生材からなるワークにねじ溝を旋削する工程と、この旋削したワークを焼入れする工程とを含むボールねじ軸のねじ溝加工方法において、
前記旋削工程で、切刃のノーズ半径が前記ねじ溝の溝曲率半径に近付けて当該溝曲率半径よりも小さな汎用バイトを用い、前記切刃が棒状のワークの軸心方向に送られ、前記ねじ溝の概略形状が当該バイトの切刃によって成形され、この汎用バイトを前記ねじ溝の有効長さ分だけ複数回移動させて、各回の移動経路を当該ねじ溝の断面形状の円弧方向に順次ずらせることにより、前記ねじ溝の全体が旋削されると共に、前記ねじ溝のツールマーク高さが所定値以下となるように前記切刃のノーズ半径と刻み角度が設定されていることを特徴とするボールねじ軸のねじ溝加工方法。 In a thread groove machining method for a ball screw shaft including a step of turning a thread groove on a workpiece made of raw material and a step of quenching the turned workpiece,
In the turning step, the cutting blade is fed in the axial direction of the rod-shaped workpiece by using a general-purpose tool in which the nose radius of the cutting blade approaches the groove curvature radius of the thread groove and is smaller than the groove curvature radius , and the screw The general shape of the groove is formed by the cutting edge of the bite, and this general-purpose bite is moved a plurality of times by the effective length of the screw groove, and the movement path of each turn is sequentially shifted in the arc direction of the cross-sectional shape of the screw groove. Thus, the entire thread groove is turned, and the nose radius and the notch angle of the cutting blade are set so that the tool mark height of the thread groove is not more than a predetermined value. A thread groove processing method for ball screw shafts . 前記ねじ溝のツールマーク高さが２μｍ以下に規制されている請求項１に記載のボールねじ軸のねじ溝加工方法。 The thread groove machining method for a ball screw shaft according to claim 1, wherein a tool mark height of the thread groove is regulated to 2 µm or less. 前記焼入工程の後に、少なくとも前記ねじ溝にショットピーニングによる仕上げ加工が行われる請求項１または２に記載のボールねじ軸のねじ溝加工方法。The thread groove machining method for a ball screw shaft according to claim 1 or 2, wherein at least the thread groove is subjected to finish machining by shot peening after the quenching step.
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