JP3653258B2 - Fastening part manufacturing method and fastening part - Google Patents

Description

【００３１】
表中の直径（ｄｉａｍｅｔｅｒ）は、伸線加工により線引きダイス２５（図３）を通して引き抜かれた伸線素材１０（図３）の引抜径ｄである。直径の測定には、精度の良いレーザースキャンマイクロメータが使用されている。
【００３２】
伸線素材１０は、複数回引き抜かれることで最終の引抜径ｄに整形されるが、１パス当たりの断面減少率（以下、Ｒ／Ｐという）は５〜１０％に調整されている。Ｒ／Ｐを増加させると、形状記憶合金の形状回復力が低下し、伸線素材１０が破断することがあるからである。
【００３３】
図３に示すように、線引きダイス２５には円すい形状のコニカルダイスが使用される。線引きダイス２５は、導入部２５ａと、絞り部２５ｂと、整形部２５ｃと、逃げ部２５ｄとからなっている。コイル状の素材が挿入される入口側の導入部２５ａは、潤滑剤の受け部の役目を果たしている。
【００３４】
潤滑剤には、窒化硼素（ＢＮ）や二硫化モリブデン（ＭｏＳ₂）などの極圧添加剤を加えた被膜剤と金属石鹸が使用されている。伸線加工においては、潤滑材の選択は殊に重要であり、選択を誤ると焼付きが生じて仕上げ面が荒れることがある。
【００３５】
絞り部２５ｂは、ダイス半角αで傾斜するアプローチ部であり、素材の絞りを行う部分である。ダイス半角αは任意であり、本実施形態では６゜に設定されている。ダイス半角αを小さくするほど引抜力が小さくなり、Ｒ／Ｐも小さくなる。
【００３６】
整形部２５ｃは、素材の整形を行う部分であり、ごく僅かの勾配に形成されている。整形部２５ｃの長さは、引抜径ｄの１／４〜３／４に設定されている。逃げ部２５ｄは、線引きダイス２５の出口に相当し、素材に強度を持たせるための部分である。
【００３７】
線引きダイス２５は、十分な強さを有し、耐摩耗性が高く、焼付き等が生じないことが重要である。このため、本実施形態では、超硬合金（ＷＣ−Ｃｏ系）の線引きダイス２５が使用されている。なお、セラミックダイスやダイヤモンドダイスを用いることもできる。
【００３８】
再び表１に戻って説明する。変態温度Ｍｓは、オーステナイト相（高温相）がマルテンサイト相（低温相）に変態するときの変態開始温度を示しており、変態温度Ａｆは、マルテンサイト相がオーステナイト相に逆変態するときの変態終了温度を示している。
【００３９】
変態温度は、予め７７３Ｋで焼なまし処理された形状記憶合金の変態温度である。変態温度の測定には、変態に伴う熱発生の変化を測定する示差走査熱量計が使用され、変態量と温度の関係から変態温度が測定されている。
【００４０】
各種形状記憶合金の成分組成は、重量％で示されている。Ｎｉ量はＴｉ量より５％程度多くなっている。このような成分組成の形状記憶合金を用いたのは、硬度が低く加工性の良いことが明らかにされているからである。なお、鉄を含まない３種類の試料は、僅かにＮｉ量が異なっている。鉄を含むをＮｏ．４の試料は、鉄が０．２１ｗｔ％含まれている。
【００４１】
図１には、表１のＮｏ．１〜４の各試料についての、伸線限界（Ｄｒａｗｉｎｇ ｌｉｍｉｔ）が示されている。各試料の伸線限界は、図３に示す線引きダイス２５を用い、潤滑剤にはステアリン酸ナトリウム石鹸を用い、Ｒ／Ｐ７〜９％の条件の下で調べられた。ここで、伸線限界とは、線引きダイス２５を通して引き抜かれた伸線素材１０が断線したときの断面減少率をいう。
【００４２】
図示するように、Ｎｉ量が最も多くＡｆ点が低いＮｏ．１の試料は、伸線限界が４０％程度と低い結果となっている。Ｎｏ．２〜４の試料は、５０％以上の伸線限界を示している。Ｆｅを添加したＮｏ．４の試料は、最も伸線限界が高く６４％の伸線限界を示している。従って、ねじの加工には、Ｎｏ．４の試料が最も成形性が良いと考えられ、後述するねじの加工に供することとされた。
【００４３】
次に、焼なまし処理における焼なまし温度と伸線限界の関係が、図２に示されている。この図は、Ｎｏ．２の試料で調べられたものである。試料は、大気中で７７３〜１１７３Ｋの温度に加熱され、３０分保持され、除冷された後、図３に示す線引きダイス２５で伸線限界が調べられた。なお、素材にスケールを付着させないアルゴン雰囲気中での焼なまし処理も試みられたが、ねじの加工中に割れの生じることが判明している。
【００４４】
加工条件は、Ｒ／Ｐを１０％とした。線引きダイス２５による引抜きは、試料が断線するまで繰り返し行われた。その結果、処理温度が高くなるにしたがい伸線限界が向上し、８７３Ｋ以上では約５０％の伸線限界が得られた。９７３Ｋを越えると、伸線限界曲線は横軸に水平となった。一方、硬さはばらついてはいるものの、硬さ曲線は伸線限界曲線に対して鏡面対称となり、処理温度が高くなるにしたがい硬さは低下した。
【００４５】
従って、最適な焼なまし処理の下限温度は、伸線限界が５０％を越え、かつ硬さが低くなる８７３Ｋ以上が適当であると判断された。他方、焼なまし処理の上限温度は、図２からは判断されないが、試料の酸化やスケールの厚みなどを考慮して、１１７３Ｋが最適であると判断された。１１７３Ｋを越えると、酸化が進行しスケールが厚くなりすぎ、試料の表面性状が悪くなるとともに、試料が脆くなるためである。焼なましの保持時間は、素材の硬さやスケールの密着性を考慮すると、１０〜６０分が適当であることが明らかにされている。
【００４６】
次に、図３〜図６に基づいて締結部品としてのねじの製造方法について説明する。製造されたねじ１５（図５）は、なべ状の頭部を有するメートル並目ねじであり、呼び径が２．５ｍｍでピッチが０．４５ｍｍの小ねじと、呼び径が１．２ｍｍでピッチが０．２５ｍｍの小ねじの２種類である。ねじ部の長さは、１０ｍｍ程度である。ねじ頭部１５ａは、ＪＩＳ Ｂ １１０１相当の寸法に形成されている。ねじ頭部１５ａの端部には、図示しないすりわり（十字穴でもよい）が形成されていて、ねじ回しで回すことができるようになっている。
【００４７】
先ず、線引きダイス２５を通され引き抜かれた伸線素材１０が、図示しない切断機により所定の長さに切断されて、円柱状の素材片１１が製作される。続いて、素材片１１が図示しないヘッダーマシンに供給され、ねじ頭部１５ａ（図６）が圧造加工にて成形される。ヘッダーマシンは、素材片１１を保持するダイス２０及び予備成形用の第１のヘッダー２１と本成形用の第２のヘッダー２２とを備えている。２つのヘッダー２１，２２はダイス２０に対して往復動作し、素材片１１を軸方向に圧縮する。ヘッダー２１，２２の往復動作するストローク長は２５ｍｍに設定されている。
【００４８】
圧造加工は、予備成形加工と本成形加工とからなっている。予備成形加工と本成形加工の間には、上述した条件で焼なまし処理が行われる。焼なまし処理では、素材片１１に適度な膜厚のスケール１６（図５）を形成するとともに、素材片１１を軟質化する。スケール１６は、素材片１１の両側の切断面に形成される（片側のみを図示する）。
【００４９】
焼なまし処理において、スケール１６を切断面に形成し、圧造及び転造することが本発明の特徴である。スケール１６は、表面被覆処理剤や潤滑剤を保持する効果があり、圧造時に表面割れや中心割れを生ずることを防止する。また、パンチとしてのヘッダー２１，２２と切断面との焼付きを防止して、ヘッダー２１，２２の寿命を向上させる。スケール１６は、酸化物や窒化物を主成分とし、切断面に密着性良く付着する。なお、スケール１６が厚く成りすぎると、素材片１１が脆くなり、割れが生じるため、焼なまし処理を上述した条件で行うことが重要である。
【００５０】
図４及び図５は、ヘッダーマシンにより行われた予備成形加工と本成形加工の加工状態をそれぞれ示したものである。図４に示すように、予備成形加工は、ダイス２０から突出した素材片１１の突端部１２をヘッダー２１で軸方向に一押しで圧縮する加工である。素材片１１の他側端部１３は、ダイス２０に保持されており、圧縮された素材片１１が座屈しないように支持されるようになっている。据え込み長さと素材片１１の直径との比である据え込み比は、２．５〜３以下に設定されている。
【００５１】
予備成形加工では、素材片１１の突端部１２が笠状になる程度で加工を一旦終了する。続いて、上述した焼なまし処理に続いて本成形加工が行われる。図５に示すように、本成形加工は、鍋状になるよう突端部１２を圧縮するとともに、突端部１２の端面にねじ回し用のすりわりや図示しない十字穴を打ち込む加工である。
【００５２】
表２には、ヘッダー２２の１分当たりのストローク数とねじ頭部１５ａの割れの関係を示したものである。表から明らかなように、ヘッダー２２のストローク数が多くなるほど、言い換えるとヘッダー２２の動作速度が早くなるほど加工割れの生じない加工を行えることが明らかにされた。
【００５３】
【表２】

【００５４】
このようにして、割れを生ずることなくねじ頭部１５ａが成形される。ねじ１５の頭部形状は、鍋状に限らずさら状や丸状などにもすることが可能である。また、突端部１２の端面には、すりわりに変えて十字穴を形成することも可能である。さらに、リベットなどのように、突端部１２の端面に凹みを形成しない場合には、素材片１１を切断した後に、焼なまし処理を行い、予備成形と本成形を一度に行うことも可能である。
【００５５】
図６は、一対の平形ダイス２７，２８を備えた図示しないローリングマシンにて、素材片１１の他側端部１３にねじ部１５ｂを成形している状態を示したものである。転造では、一方の平形ダイス２７を固定し、他方の平形ダイス２８を長手方向に往復移動させて、一対の平形ダイス２７，２８の間に挿入された素材片１１にねじ山を成形する。他方の平形ダイス２８は、１５０ｍｍのストローク長で往復動作する。平形ダイス２７，２８がねじに食い付いてから５〜６回転でねじ山が完成する。平形ダイス方式は、素材片１１の供給と排出が容易に行われるため、小ねじの大量生産に適する。
【００５６】
表３には、平形ダイス２８の１分当たりのストローク数とねじ山の成形性の関係を示したものである。表から明らかなように、平形ダイス２８のストローク数が多くなるほど、言い換えると平形ダイス２８の動作速度が早くなるほどねじ山の成形性の良い加工を行えることが明らかにされた。
【００５７】
【表３】

【００５８】
従来は、加工初期において素材片１１に平形ダイス２７，２８を強く押し付けた際、又は加工終期において素材片１１が加工硬化した際に、素材片１１の端部において割れを生ずることがあったが、焼なまし処理にてスケールを素材片１１の切断面に密着性良く形成することで、潤滑剤などの潤滑効果が保持されて、欠陥のないねじを成形することが可能となった。
【００５９】
【発明の効果】
以上の如く、請求項１記載の発明によれば、焼なまし処理にて密着性の良いスケールが素材片の切断面に形成されるから、表面被覆処理剤や潤滑剤がスケールによって保持される。従って、成形体に表面割れや中心割れが生ずることが防止され、欠陥のない成形体が得られる。また、ヘッダやダイスの焼付きが防止され、工具寿命が向上する。
【００６０】
また、請求項２記載の発明によれば、素材片の切断面に形成されるスケールが、適度な膜厚に形成されて潤滑剤の潤滑効果が保持される。従って、素材片が脆くなることが防止されて、成形性が向上し、割れのない加工を行うことができる。
【００６１】
また、請求項３記載の発明によれば、据込み加工などの予備成形が行われた後に、焼なまし処理が行われるから、潤滑剤の潤滑効果が維持されるとともに、加工硬化した素材片が軟化する。従って、割れを生ずることなく、すりわり加工や十字穴加工などの本成形を行うことができる。
【００６２】
また、請求項４記載の発明によれば、素材片の両側の切断面にスケールが形成されることで、圧造及び転造の成形性が向上する。従って、割れを生ずることなく、ねじ頭部及びねじ部を成形することができる。
【００６３】
また、請求項５記載の発明によれば、Ｎｉ−Ｔｉ系の形状記憶合金であるから、伸線限界が向上し、圧造及び転造加工時の成形性が向上し、形状記憶合金からなる締結部品を得ることができる。
【００６４】
また、請求項６記載の発明によれば、超弾性を有する締結部品としての成形体が得られるから、締結部品に引張りの軸力が働き、ねじ面や座面の摩擦係数が高くなり、締付け保持力が向上して、締結部品の緩みが防止される。従って、締結信頼性の高い締結部品を提供することができる。
【図面の簡単な説明】
【図１】本発明に係る締結部品の製造方法において、各形状記憶合金と伸線限界の関係を示すグラフである。
【図２】同じく締結部品の製造方法において、焼なまし処理温度と伸線限界の関係を示すグラフである。
【図３】同じく締結部品の製造方法において、形状記憶合金を線引きダイスに通し引き抜いた状態を示す断面図である。
【図４】同じく締結部品の製造方法において、形状記憶合金の素材片を圧造により予備成形している状態を示す断面図である。
【図５】同じく締結部品の製造方法において、形状記憶合金の素材片を圧造により本成形している状態を示す断面図である。
【図６】同じく締結部品の製造方法において、転造により形状記憶合金の素材片にねじ部を成形している状態を示す斜視図である。
【図７】従来の締結部品の製造方法の一例を示す図である。
【符号の説明】
１０ 伸線素材
１１ 素材片
１２ 突端部
１５ ねじ
１５ａ ねじ頭部
１５ｂ ねじ部
１６ スケール
２０ ダイス
２１ 第１のヘッダー
２２ 第２のヘッダー
２５ 線引きダイス
２７ 一方の平形ダイス
２８ 他方の平形ダイス[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a fastening part used in glasses, medical equipment, electrical equipment, automobile equipment, and the like, and the fastening part.
[0002]
[Prior art]
The Ni—Ti-based shape memory alloy is the most widely used shape memory alloy among various shape memory alloys. Shape memory alloys are well known to exhibit shape memory properties, superelasticity, vibration absorption and high corrosion resistance, and are expected to be further applied to various fields such as medical equipment and electrical equipment.
[0003]
However, shape memory alloys are also known to have poor plastic workability due to their properties, and are listed as one of difficult-to-work materials. In particular, it is not suitable for a cutting process in which a material is sheared to discharge chips.
[0004]
Applications as shape memory alloys include springs, pipe joints, regulating valves, eyeglass frames, orthodontic wires, brass cores, mobile phone antennas and the like.
[0005]
Furthermore, it is expected to be used as fastening parts such as screws and bolts. However, since a fastening part made of a shape memory alloy is difficult to be plastically processed as described above, various studies have been conducted from the processed surface.
[0006]
FIG. 7 is described in Japanese Patent Application Laid-Open No. 11-207525 as an example of a method for manufacturing a screw made of a shape memory alloy. As shown in the drawing, the screw 51 as a fastening part has a screw portion 52 on one side and a screw head (not shown) on the other side.
[0007]
The threaded portion 52 is formed by pressing a tapered material piece 50 against a round die or a flat die. A screw head (not shown) is considered to be formed by forging.
[0008]
The material piece 50 is manufactured by drawing the shape memory alloy through a drawing die (not shown). The distal end side 51a of the material piece 50 on which the threaded portion 52 is formed has a small diameter, and the root side 51b has a large diameter, and is processed into a tapered shape by polishing. For this reason, when the threaded portion 52 is formed by rolling, a complete screw is not formed on the distal end side 51a, and the thread 52a gradually increases from the distal end side 51a toward the root side 51b. Yes.
[0009]
The screw 51 thus molded is a screw having a nominal diameter of 3 mm, a pitch of 0.5 mm, and a screw length of 5 mm. When the screw 51 is screwed to a mating member or nut (not shown), the incomplete thread 52a on the tip side 51a does not completely screw with the mating member, and only the complete thread 52a on the root side 51b is mated. Screwed into the member.
[0010]
[Problems to be solved by the invention]
However, the conventional screw manufacturing method has the following problems to be solved.
[0011]
First, one side of the material piece 50 having a diameter of about 3 mm has to be formed into a tapered shape by polishing. In addition to the difficulty in processing, there is a concern that the production cost of the screw 51 is increased.
[0012]
That is, by processing the material piece 50 into a tapered shape, even if the wear of the rolling die forming the screw portion 52 is reduced and the life of the rolling die is improved, the processing cost at the time of taper processing increases. Therefore, there is a concern that production costs will increase overall.
[0013]
For example, since the tip 51a of the screw 51 is an incomplete thread 52a, the number of effective threads is small, the fastening holding force is insufficient, and the screw 51 is loosened due to vibration or the like. I'm worried about 51 coming out.
[0014]
Furthermore, there is a concern that cracking or the like may occur during the rolling process for forming the screw portion 52. This is because cracks due to work hardening of shape memory alloys have been reported in various directions as one of the reasons why it is difficult to plastically process screws made of shape memory alloys.
[0015]
An object of this invention is to provide the manufacturing method of a fastening component and fastening component which can prevent the crack of the molded object at the time of plastic working, and can improve a moldability in view of an above-described point.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 is a method of manufacturing a fastening part in which a molded body is obtained by plastic processing of a shape memory alloy. make, make blanks by cutting該伸line material, prior to plastic working of said workpiece strip, said workpiece as a lubricating effect is maintained during the plastic working I rows annealing process to said workpiece piece A method of manufacturing a fastening part in which a scale is formed on a cut surface of a piece , wherein the fastening part is a screw or a rivet .
[0017]
According to the above configuration, the shape memory alloy that has been annealed in advance is drawn through a wire drawing die to be formed into a wire drawing material having a predetermined thickness, and the wire drawing material is cut to form a cylindrical material. A piece is produced. Since the material piece is compressed in the axial direction by plastic processing performed later, it is manufactured to a length that allows for the compression rate. Then, in order to improve the moldability of a raw material piece, an annealing process is performed and a scale is formed on a cut surface. Then, it is formed into a predetermined shape by plastic working.
[0018]
The scale is mainly composed of oxide and nitride, adheres well to the cut surface, and retains the surface coating agent and lubricant, preventing surface cracks and center cracks from occurring in the molded product. A molded body free from defects is obtained.
[0019]
Further, the invention according to claim 2 is the method of manufacturing a fastening part according to claim 1, wherein in the annealing treatment, the material piece is heated to 873 K to 1173 K in the atmosphere and held for 10 to 60 minutes, The scale is formed by slow cooling.
[0020]
According to the said structure, the scale formed in the cut surface of a raw material piece is formed in a moderate film thickness, and lubrication effects, such as a lubricant, are maintained. Moreover, softening is sufficient and the moldability is improved.
[0021]
The invention according to claim 3 is characterized in that, in the method for manufacturing a fastening part according to claim 1 or 2, the annealing treatment is performed on the material piece after preforming the material piece.
[0022]
According to the above-described configuration, the annealing effect is performed after the preforming such as upsetting, so that the lubricating effect of the lubricant and the like is maintained and the work-cured material piece is softened. For this reason, the main molding of the next process can be performed without causing cracks.
[0023]
According to a fourth aspect of the present invention, in the method of manufacturing a fastening part according to any one of the first to third aspects, a scale is formed on the cut surfaces on both sides of the material piece by the annealing treatment. A screw head is formed on one of the material pieces by forging, and a thread portion is formed on the other of the material pieces by rolling.
[0024]
According to the said structure, a screw head and a thread part can be shape | molded without producing a crack in a forging and a rolling process by forming a scale in the cut surface of the both sides of a raw material piece.
[0025]
The invention according to claim 5 is the method for manufacturing a fastening part according to any one of claims 1 to 4, wherein the shape memory alloy is a Ni-Ti alloy. .
[0026]
According to the above configuration, since the shape memory alloy is a Ni-Ti-based alloy, the wire drawing limit is improved, the wire drawing property at the time of wire drawing, the formability at the time of forging and rolling, the cracking, etc. It is possible to obtain a molded body having no defects.
[0027]
The invention described in claim 6 is characterized in that it is molded by the method for manufacturing a fastening part according to any one of claims 1 to 5.
[0028]
According to the above configuration, since a fastening part having super elasticity can be obtained, when the mating member is fastened with the fastening part, a tensile axial force acts on the fastening part, and the friction coefficient of the thread surface and the seating surface is high. Thus, the tightening holding force is improved, and the looseness of the fastening parts is prevented.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Specific examples of the embodiments of the present invention will be described in detail below.
Table 1 shows component compositions of four types of Ni—Ti shape memory alloys having different compositions. A sample having the best moldability is selected from the four types of samples, and is used for processing a screw as a fastening part described later. This is because, as described in the section of the prior art, since it is difficult to process a screw made of a shape memory alloy, it is necessary to use a material having the best formability.
[0030]
[Table 1]

[0031]
The diameter in the table is the drawing diameter d of the wire drawing material 10 (FIG. 3) drawn through the wire drawing die 25 (FIG. 3) by wire drawing. An accurate laser scanning micrometer is used for measuring the diameter.
[0032]
The wire drawing material 10 is shaped to the final drawing diameter d by being drawn a plurality of times, but the cross-sectional reduction rate (hereinafter referred to as R / P) per pass is adjusted to 5 to 10%. This is because when the R / P is increased, the shape recovery force of the shape memory alloy is lowered, and the wire drawing material 10 may break.
[0033]
As shown in FIG. 3, a conical die having a conical shape is used for the drawing die 25. The drawing die 25 includes an introduction part 25a, a narrowing part 25b, a shaping part 25c, and an escape part 25d. The inlet side introduction portion 25a into which the coil-shaped material is inserted serves as a lubricant receiving portion.
[0034]
As the lubricant, a coating agent and a metal soap to which an extreme pressure additive such as boron nitride (BN) or molybdenum disulfide (MoS ₂ ) is added are used. In the wire drawing process, the selection of the lubricant is particularly important. If the selection is wrong, seizure may occur and the finished surface may be roughened.
[0035]
The narrowing portion 25b is an approach portion that is inclined at a die half angle α, and is a portion that narrows the material. The die half angle α is arbitrary, and is set to 6 ° in this embodiment. As the die half angle α is reduced, the pulling force is reduced and the R / P is also reduced.
[0036]
The shaping part 25c is a part for shaping the material, and is formed with a very slight gradient. The length of the shaping part 25c is set to 1/4 to 3/4 of the drawing diameter d. The escape portion 25d corresponds to the exit of the drawing die 25 and is a portion for giving strength to the material.
[0037]
It is important that the wire drawing die 25 has sufficient strength, has high wear resistance, and does not cause seizure or the like. For this reason, in this embodiment, the drawing die 25 of a cemented carbide (WC-Co system) is used. Ceramic dies and diamond dies can also be used.
[0038]
Returning to Table 1 again, explanation will be given. The transformation temperature Ms indicates the transformation start temperature when the austenite phase (high temperature phase) transforms into the martensite phase (low temperature phase), and the transformation temperature Af transforms when the martensite phase reversely transforms into the austenite phase. The end temperature is indicated.
[0039]
The transformation temperature is the transformation temperature of the shape memory alloy that has been previously annealed at 773K. For the measurement of the transformation temperature, a differential scanning calorimeter that measures the change in heat generation accompanying transformation is used, and the transformation temperature is measured from the relationship between the transformation amount and temperature.
[0040]
The component compositions of the various shape memory alloys are shown in weight percent. The amount of Ni is about 5% larger than the amount of Ti. The reason why the shape memory alloy having such a component composition is used is that it is clear that the hardness is low and the workability is good. In addition, three types of samples which do not contain iron differ slightly in the amount of Ni. Including iron. Sample No. 4 contains 0.21 wt% of iron.
[0041]
In FIG. Drawing limits for each of the samples 1-4 are shown. The drawing limit of each sample was examined using a drawing die 25 shown in FIG. 3, sodium stearate soap as a lubricant, and R / P of 7 to 9%. Here, the wire drawing limit means a cross-sectional reduction rate when the wire drawing material 10 drawn through the wire drawing die 25 is disconnected.
[0042]
As shown in the figure, the Ni content is the highest and the Af point is the lowest. Sample No. 1 has a low drawing limit of about 40%. No. Samples 2 to 4 show a drawing limit of 50% or more. No. to which Fe was added Sample No. 4 has the highest drawing limit and shows a drawing limit of 64%. Therefore, no. The sample No. 4 was considered to have the best moldability, and was used for screw processing described later.
[0043]
Next, the relationship between the annealing temperature and the wire drawing limit in the annealing treatment is shown in FIG. This figure is No. It was investigated by 2 samples. The sample was heated in the atmosphere to a temperature of 773 to 1173 K, held for 30 minutes, cooled, and then the drawing limit was examined with a drawing die 25 shown in FIG. An annealing treatment in an argon atmosphere in which no scale is attached to the material has been attempted, but it has been found that cracking occurs during the machining of the screw.
[0044]
The processing conditions were such that R / P was 10%. Drawing with the drawing die 25 was repeated until the sample was disconnected. As a result, the wire drawing limit improved as the processing temperature increased, and a wire drawing limit of about 50% was obtained at 873 K or higher. Beyond 973K, the wire drawing limit curve became horizontal on the horizontal axis. On the other hand, although the hardness varies, the hardness curve is mirror-symmetrical with respect to the drawing limit curve, and the hardness decreases as the processing temperature increases.
[0045]
Therefore, it was judged that the optimum lower limit temperature of the annealing treatment is appropriate to be 873 K or more, at which the wire drawing limit exceeds 50% and the hardness becomes low. On the other hand, the upper limit temperature of the annealing treatment is not judged from FIG. 2, but 1173K was judged to be optimal in consideration of the oxidation of the sample, the thickness of the scale, and the like. If it exceeds 1173K, the oxidation proceeds, the scale becomes too thick, the surface properties of the sample deteriorate, and the sample becomes brittle. It has been clarified that the annealing holding time is suitably 10 to 60 minutes considering the hardness of the material and the adhesion of the scale.
[0046]
Next, a method for manufacturing a screw as a fastening part will be described with reference to FIGS. The manufactured screw 15 (FIG. 5) is a metric coarse screw having a pan-shaped head, a small screw having a nominal diameter of 2.5 mm and a pitch of 0.45 mm, and a pitch having a nominal diameter of 1.2 mm. Are two types of small screws of 0.25 mm. The length of the thread portion is about 10 mm. The screw head 15a is formed in a size corresponding to JIS B 1101. A not-shown slot (which may be a cross hole) is formed at the end of the screw head 15a so that it can be turned with a screwdriver.
[0047]
First, the drawn wire material 10 drawn through the wire drawing die 25 is cut into a predetermined length by a cutting machine (not shown) to produce a columnar material piece 11. Subsequently, the material piece 11 is supplied to a header machine (not shown), and the screw head 15a (FIG. 6) is formed by forging. The header machine includes a die 20 that holds the material piece 11, a first header 21 for preliminary molding, and a second header 22 for main molding. The two headers 21 and 22 reciprocate with respect to the die 20 to compress the material piece 11 in the axial direction. The stroke length in which the headers 21 and 22 reciprocate is set to 25 mm.
[0048]
The forging process includes a preforming process and a main forming process. Between the preforming process and the main forming process, the annealing process is performed under the above-described conditions. In the annealing treatment, a scale 16 (FIG. 5) having an appropriate film thickness is formed on the material piece 11, and the material piece 11 is softened. The scale 16 is formed on the cut surfaces on both sides of the material piece 11 (only one side is shown).
[0049]
In the annealing process, it is a feature of the present invention that the scale 16 is formed on the cut surface, and is pressed and rolled. The scale 16 has an effect of retaining a surface coating treatment agent and a lubricant, and prevents surface cracks and center cracks from occurring during forging. Further, seizure between the headers 21 and 22 as a punch and the cut surface is prevented, and the life of the headers 21 and 22 is improved. The scale 16 is mainly composed of oxide or nitride, and adheres to the cut surface with good adhesion. In addition, since the raw material piece 11 will become weak and a crack will arise if the scale 16 becomes too thick, it is important to perform an annealing process on the conditions mentioned above.
[0050]
4 and 5 respectively show the processing states of the preforming process and the main forming process performed by the header machine. As shown in FIG. 4, the preforming process is a process of compressing the protruding end portion 12 of the material piece 11 protruding from the die 20 with a header 21 in the axial direction. The other end portion 13 of the material piece 11 is held by a die 20 and is supported so that the compressed material piece 11 does not buckle. The upsetting ratio, which is the ratio between the upsetting length and the diameter of the material piece 11, is set to 2.5 to 3 or less.
[0051]
In the pre-forming process, the process is temporarily finished until the protruding portion 12 of the material piece 11 has a shade shape. Subsequently, the main forming process is performed following the annealing process described above. As shown in FIG. 5, the main forming process is a process of compressing the projecting end portion 12 so as to have a pan shape, and driving a screwing slot or a cross hole (not shown) into the end face of the projecting end portion 12.
[0052]
Table 2 shows the relationship between the number of strokes per minute of the header 22 and the cracking of the screw head 15a. As is clear from the table, it has been clarified that machining with no machining cracks can be performed as the number of strokes of the header 22 increases, in other words, as the operating speed of the header 22 increases.
[0053]
[Table 2]

[0054]
In this way, the screw head 15a is formed without causing cracks. The head shape of the screw 15 is not limited to a pan shape, and may be a flat shape or a round shape. Moreover, it is also possible to form a cross hole on the end face of the projecting end portion 12 in place of the slit. Further, when a dent is not formed on the end face of the projecting end portion 12 such as a rivet, it is possible to perform an annealing process after cutting the material piece 11 to perform preliminary forming and main forming at once. is there.
[0055]
FIG. 6 shows a state in which a threaded portion 15 b is formed on the other end portion 13 of the material piece 11 in a rolling machine (not shown) provided with a pair of flat dies 27 and 28. In rolling, one flat die 27 is fixed, and the other flat die 28 is reciprocated in the longitudinal direction to form a thread on the material piece 11 inserted between the pair of flat dies 27, 28. The other flat die 28 reciprocates with a stroke length of 150 mm. After the flat dies 27 and 28 bite into the screw, the screw thread is completed in 5 to 6 rotations. The flat die method is suitable for mass production of machine screws because the material pieces 11 can be easily supplied and discharged.
[0056]
Table 3 shows the relationship between the number of strokes per minute of the flat die 28 and the thread formability. As is apparent from the table, it has been clarified that as the number of strokes of the flat die 28 increases, in other words, as the operation speed of the flat die 28 increases, the thread can be processed with good formability.
[0057]
[Table 3]

[0058]
Conventionally, when the flat dies 27 and 28 are strongly pressed against the material piece 11 at the initial stage of processing, or when the material piece 11 is work-hardened at the end of processing, a crack may occur at the end of the material piece 11. By forming the scale with good adhesion to the cut surface of the material piece 11 by annealing, it is possible to retain a lubricating effect such as a lubricant and to form a screw having no defect.
[0059]
【The invention's effect】
As described above, according to the first aspect of the present invention, since the scale having good adhesion is formed on the cut surface of the material piece by the annealing treatment, the surface coating agent and the lubricant are held by the scale. . Accordingly, surface cracks and center cracks are prevented from occurring in the molded body, and a molded body having no defects can be obtained. Further, seizure of the header and the die is prevented, and the tool life is improved.
[0060]
Further, according to the invention described in claim 2, the scale formed on the cut surface of the material piece is formed in an appropriate film thickness, and the lubricating effect of the lubricant is maintained. Therefore, the material piece is prevented from becoming brittle, the formability is improved, and processing without cracking can be performed.
[0061]
According to the invention of claim 3, since the annealing treatment is performed after the preforming such as upsetting, the lubricating effect of the lubricant is maintained, and the work-hardened material piece Softens. Therefore, it is possible to perform main forming such as slitting and cross hole processing without causing cracks.
[0062]
In addition, according to the invention described in claim 4, by forming scales on the cut surfaces on both sides of the material piece, the formability of the forging and rolling is improved. Therefore, the screw head and the screw portion can be formed without causing cracks.
[0063]
Further, according to the invention of claim 5, since it is a Ni-Ti type shape memory alloy, the wire drawing limit is improved, the formability at the time of forging and rolling is improved, and the fastening made of the shape memory alloy Parts can be obtained.
[0064]
According to the invention described in claim 6, since a molded body as a fastening part having superelasticity is obtained, a tensile axial force acts on the fastening part, the friction coefficient of the thread surface and the seat surface is increased, and the fastening part is tightened. The holding force is improved and loosening of the fastening parts is prevented. Therefore, it is possible to provide a fastening component with high fastening reliability.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between each shape memory alloy and the wire drawing limit in the method of manufacturing a fastening part according to the present invention.
FIG. 2 is a graph showing the relationship between the annealing temperature and the wire drawing limit in the same fastener manufacturing method.
FIG. 3 is a cross-sectional view showing a state in which a shape memory alloy is drawn through a drawing die in the same fastener manufacturing method.
FIG. 4 is a cross-sectional view showing a state in which a shape memory alloy material piece is preformed by forging in a method of manufacturing a fastening part.
FIG. 5 is a cross-sectional view showing a state in which a shape memory alloy material piece is finally formed by forging in a method of manufacturing a fastening part.
FIG. 6 is a perspective view showing a state in which a thread portion is formed on a shape memory alloy material piece by rolling in the same fastening part manufacturing method.
FIG. 7 is a diagram showing an example of a conventional method for manufacturing a fastening part.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Wire drawing material 11 Material piece 12 Protruding end part 15 Screw 15a Screw head part 15b Screw part 16 Scale 20 Die 21 1st header 22 2nd header 25 Drawing die 27 One flat die 28 The other flat die

Claims (6)

In a manufacturing method of a fastening part for obtaining a formed body by plastic processing a shape memory alloy,
The shape memory alloy is drawn to produce a drawn material, the drawn material is cut to produce a piece of material, and the piece of material is annealed before being plastically processed. A method of manufacturing a fastening part in which a scale is formed on a cut surface of the material piece so as to maintain a lubricating effect during the plastic working , wherein the fastening part is a screw or a rivet. Method.   2. The fastening part according to claim 1, wherein, in the annealing treatment, the scale is formed by heating the material piece to 873 K to 1173 K in the atmosphere, holding it for 10 to 60 minutes, and gradually cooling the piece. Production method.   3. The method of manufacturing a fastening part according to claim 1, wherein the annealing treatment is performed on the material piece after preforming the material piece. The fastening component is a screw, and by annealing, a scale is formed on the cut surfaces on both sides of the material piece, and a screw head is formed by forging on one of the material pieces, and the material piece The method of manufacturing a fastening part according to any one of claims 1 to 3, wherein a threaded portion is formed by rolling on the other of the above.   The method for manufacturing a fastening part according to any one of claims 1 to 4, wherein a Ni-Ti alloy is used as the shape memory alloy.   A fastening part formed by the method for producing a fastening part according to any one of claims 1 to 5.

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