WO2009139379A1 - 異形断面筒状部材のプレス成形方法とこのプレス成形方法により成形した異形断面筒状部材 - Google Patents
異形断面筒状部材のプレス成形方法とこのプレス成形方法により成形した異形断面筒状部材 Download PDFInfo
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- WO2009139379A1 WO2009139379A1 PCT/JP2009/058832 JP2009058832W WO2009139379A1 WO 2009139379 A1 WO2009139379 A1 WO 2009139379A1 JP 2009058832 W JP2009058832 W JP 2009058832W WO 2009139379 A1 WO2009139379 A1 WO 2009139379A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G21/00—Interconnection systems for two or more resiliently-suspended wheels, e.g. for stabilising a vehicle body with respect to acceleration, deceleration or centrifugal forces
- B60G21/02—Interconnection systems for two or more resiliently-suspended wheels, e.g. for stabilising a vehicle body with respect to acceleration, deceleration or centrifugal forces permanently interconnected
- B60G21/04—Interconnection systems for two or more resiliently-suspended wheels, e.g. for stabilising a vehicle body with respect to acceleration, deceleration or centrifugal forces permanently interconnected mechanically
- B60G21/05—Interconnection systems for two or more resiliently-suspended wheels, e.g. for stabilising a vehicle body with respect to acceleration, deceleration or centrifugal forces permanently interconnected mechanically between wheels on the same axle but on different sides of the vehicle, i.e. the left and right wheel suspensions being interconnected
- B60G21/051—Trailing arm twist beam axles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
- B21D22/02—Stamping using rigid devices or tools
- B21D22/025—Stamping using rigid devices or tools for tubular articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D53/00—Making other particular articles
- B21D53/88—Making other particular articles other parts for vehicles, e.g. cowlings, mudguards
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G2200/00—Indexing codes relating to suspension types
- B60G2200/20—Semi-rigid axle suspensions
- B60G2200/21—Trailing arms connected by a torsional beam, i.e. twist-beam axles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G2202/00—Indexing codes relating to the type of spring, damper or actuator
- B60G2202/10—Type of spring
- B60G2202/13—Torsion spring
- B60G2202/136—Twist-beam type arrangement
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G2206/00—Indexing codes related to the manufacturing of suspensions: constructional features, the materials used, procedures or tools
- B60G2206/01—Constructional features of suspension elements, e.g. arms, dampers, springs
- B60G2206/20—Constructional features of semi-rigid axles, e.g. twist beam type axles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G2206/00—Indexing codes related to the manufacturing of suspensions: constructional features, the materials used, procedures or tools
- B60G2206/01—Constructional features of suspension elements, e.g. arms, dampers, springs
- B60G2206/20—Constructional features of semi-rigid axles, e.g. twist beam type axles
- B60G2206/202—Constructional features of semi-rigid axles, e.g. twist beam type axles with a radially deformed tube as a cross member
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G2206/00—Indexing codes related to the manufacturing of suspensions: constructional features, the materials used, procedures or tools
- B60G2206/01—Constructional features of suspension elements, e.g. arms, dampers, springs
- B60G2206/20—Constructional features of semi-rigid axles, e.g. twist beam type axles
- B60G2206/203—Constructional features of semi-rigid axles, e.g. twist beam type axles with outwardly bent trailing arms to increase the width of the support or wheelbase
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G2206/00—Indexing codes related to the manufacturing of suspensions: constructional features, the materials used, procedures or tools
- B60G2206/01—Constructional features of suspension elements, e.g. arms, dampers, springs
- B60G2206/70—Materials used in suspensions
- B60G2206/72—Steel
- B60G2206/724—Wires, bars or the like
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60G—VEHICLE SUSPENSION ARRANGEMENTS
- B60G2206/00—Indexing codes related to the manufacturing of suspensions: constructional features, the materials used, procedures or tools
- B60G2206/01—Constructional features of suspension elements, e.g. arms, dampers, springs
- B60G2206/80—Manufacturing procedures
- B60G2206/81—Shaping
- B60G2206/8102—Shaping by stamping
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49616—Structural member making
- Y10T29/49622—Vehicular structural member making
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/51—Plural diverse manufacturing apparatus including means for metal shaping or assembling
- Y10T29/5199—Work on tubes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/53—Means to assemble or disassemble
- Y10T29/53996—Means to assemble or disassemble by deforming
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/12—All metal or with adjacent metals
- Y10T428/12299—Workpiece mimicking finished stock having nonrectangular or noncircular cross section
Definitions
- the present invention relates to a method for press-forming a modified cross-section tubular member used for an automobile undercarriage member such as an axle beam, and a modified cross-section tubular member formed by this press forming method.
- a modified cross-section cylindrical member has been widely used as an undercarriage member for an automobile such as an axle beam disposed between wheels of an automobile and a suspension member around the axle beam.
- Such a modified cross-section tubular member is repeatedly subjected to impact load, torsion load, and the like during traveling, and therefore needs high fatigue resistance in addition to high strength.
- an automobile undercarriage member such as an axle beam is formed by pressing a single steel pipe, rather than using a plurality of members.
- Patent Document 1 listed below discloses an axle beam having a hollow structure in which a high-strength steel pipe is pressed into an irregular cross-sectional shape.
- the axle beam of Patent Document 1 performs a heat treatment such as quenching in order to control the residual stress in the stress concentration portion and increase the fatigue resistance of the material. Furthermore, an atmosphere control and a descaling process are required to prevent oxide scale caused by heat treatment. As a result, there is a problem that not only heat treatment costs but also extra costs are required to cope with the oxide scale. In addition, there is a problem that the product accuracy is lowered by the heat treatment, and the assembly work to the vehicle body becomes difficult.
- the present invention has been made in view of the above circumstances, and when manufacturing a deformed cross-section cylindrical member such as an ASKUL beam by press forming of a steel pipe, fatigue resistance is eliminated without conventional heat treatment such as quenching. Improved method of reducing the cost and the number of processes, ensuring the accuracy of the product and improving the workability of assembling to the car body, and the deformed section tubular member press forming method, and the deformed shape formed by this press forming method It aims at provision with a cross-section cylindrical member.
- the present invention employs the following means in order to solve the above problems and achieve the object. That is, (1)
- the present invention is a modified cross-section cylindrical member having a V-shaped cross section manufactured by the method for press-forming a modified cross-section cylindrical member described in (1) above.
- the V groove surface has the compressive residual stress formed by the spring back.
- the modified cross-section tubular member described in (3) above may be an automobile suspension member.
- the residual stress of the member can be controlled. Therefore, heat treatment such as quenching is not required after press forming as in the prior art, and high fatigue resistance can be obtained by applying compressive residual stress only at a predetermined position where fatigue damage is likely to occur by only the pressing step.
- the modified cross-section tubular member described in (3) has a compressive residual stress on the V-groove surface at the bottom of the member, high fatigue resistance can be obtained and a long life can be achieved.
- the modified cross-section cylindrical member (3) is applied to an automobile suspension member, it is possible to reduce the cost and extend the life of the automobile.
- FIG. 2 is a cross-sectional view taken along the line AA in FIG. It is sectional drawing which shows before an upper mold
- FIG. 6 is a diagram showing residual stresses of test pieces in Comparative Examples 2 to 4.
- FIG. 5 is a diagram showing an example of destruction of test pieces in Comparative Examples 2 to 4.
- FIG. 1 shows an axle beam 1 which is an embodiment of a modified cross-section tubular member formed by the method for press-forming a modified cross-section tubular member of the present invention.
- FIG. 2 is a cross-sectional view taken along the line AA in FIG. As shown in FIG. 2, this axle beam 1 is formed by crushing one steel pipe between a pair of upper and lower molds (described later) and press-molding it into a V-shaped cross section.
- Reference numeral 1a is an upper plate corresponding to the upper arc in the cross-sectional shape of the pre-processed steel pipe of the axle beam 1
- reference numeral 1b is a lower plate corresponding to the lower arc in the same cross-sectional shape.
- reference numerals 2a and 2b are bottom portions of the upper plates 1a and 1b, respectively
- reference numerals 2c and 2d are V-groove surfaces of the bottom portions 2a and 2b, respectively.
- the stress generated during the fatigue test is highest on the V groove surface 2c of the bottom 2a of the upper plate 1a.
- the V-groove surface 2c of the bottom 2a of the upper plate 1a is required to have a compressive residual stress. Therefore, in this embodiment, the fatigue resistance is improved by applying compressive residual stress to the V-groove surface 2c of the member bottom 2a.
- the radius of curvature of the tip of the upper mold is R 1 (mm).
- R 1 , R 2 , t are the following (1), where R 2 (mm) is the radius of curvature of the bottom of the lower mold corresponding to the tip of the upper mold, and t (mm) is the thickness of the steel pipe.
- the expression (1) is a condition necessary for eliminating a gap between the mold and the molded article when the upper mold (described later) reaches bottom dead center. Further, as will be described later, in order to leave a gap between the mold and a predetermined position of the steel pipe that is the molded product before the upper mold reaches the bottom dead center, R 1 ⁇ 3t is required. On the other hand, 1.5 t ⁇ R 1 is necessary to prevent molding cracks during press molding. Therefore, it is necessary to satisfy the condition of equation (2).
- 3 to 5 are all cross-sectional views of the press molding process at the bottom 2 of the axle beam 1.
- 3 to 5 are enlarged sectional views of the press molding process before the upper mold reaches the bottom dead center, enlarged sectional views of the press molding process when the upper mold reaches the bottom dead center, and after the mold opening, respectively.
- An enlarged cross-sectional view of the bottom 2 of the axle beam 1 is shown.
- reference numeral 11 is an upper mold
- reference numeral 12 is a lower mold.
- the steel pipe which is a base material is press-molded between the upper mold
- both the upper plate 1a and the lower plate 1b are general bending deformations in which the radii of curvature R 1 and R 2 are reduced. .
- the mold design does not leave a gap between the upper and lower molds 11 and 12 and the product to be molded as limited to the expression (1). Therefore, if molding is continued, the gap 3 between the tip portion 11a of the upper mold 11 and the corresponding portion of the upper plate 1a and the gap 4 between the portions of the bottom 12a both sides of the lower die 12 and the corresponding portion of the lower plate 1b, The deformation which crushes 4 is added. That is, in this case, the V-groove surfaces 2c and 2d of the bottom portion 2 are bent back, that is, deformed to increase the curvature radii R 1 and R 2 .
- the bottom 2a of the upper plate 1a and the bottom 2b of the lower plate 1b are processed to be spread by a mold, and any of the V-groove surfaces 2c and 2d is in a tensile stress state. That is, both the V-groove surfaces 2c and 2d of the bottom portion 2 are subjected to stress that tends to reduce their own radii of curvature R 1 and R 2 .
- an axle beam is shown as an example of a modified cross-section cylindrical member.
- the present invention can be widely applied to other automobile suspension members that require fatigue resistance, such as suspension members in the vicinity thereof.
- the steel pipe material is not limited at all, and any material can be used. That is, if the press molding method of the present invention is used, fatigue resistance can be improved with any steel pipe material.
- the press molding method of the present invention if used, a compressive residual stress can be applied to a portion where the generated stress is high, so that the fatigue life can be greatly improved.
- heat treatment such as quenching is performed after press forming to improve the fatigue life.
- the fatigue life since the fatigue life can be improved without heat treatment, the heat treatment cost can be reduced and the process can be simplified. Furthermore, since heat treatment is not required, there is an advantage that product accuracy can be secured.
- Table 1 shows the residual stress properties of the V-groove surfaces 2c and 2d of the member bottom 2 after press molding.
- a test piece 21 having a width of 20 mm was cut out from the longitudinal center of the tubular member having a V-shaped cross section as shown in FIG.
- the number of occurrences of fatigue cracks is less than 10,000 times with short fatigue life (C), 10,000 times or more and less than 100,000 times (B), and excellent fatigue life of 100,000 times or more Evaluation was performed in three stages (A).
- the modified cross-sectional cylindrical member of the present invention has sufficient compressive residual stress applied to the V-groove surfaces 2c and 2d of the bottom 2 as shown in FIG. It was confirmed that the fatigue property was greatly improved.
- Comparative Example 1 shows a case where the radius of curvature R 1 is (2) less than formula. In this case, cracks occur in the bottom 2 at the time of molding due to the radius of curvature R 1 is too small, could not be molded. Comparative Example 2 shows a case the radius of curvature R 1 is (2) greater than expression. In this case, since the radius of curvature R 1 is too large, during the pressing process, while there is no gap at all times the molded article is molded in close contact with the mold. Therefore, when the bottom portion 2 is not bent back and the upper mold 11 reaches the bottom dead center, the stress of the V groove surface 2c of the bottom portion 2a of the upper plate 1a is a compressive stress.
- the V spring surface 2c causes a tensile residual stress as shown in FIG. 8B due to the subsequent spring back, and the fatigue resistance decreases.
- a crack 30 as shown in FIG. 8C is generated in the V-groove surface 2c of the bottom 2a of the upper plate 1a in a short time that cannot be practically used.
- the radius of curvature R 2 does not satisfy the formula (1) is shown. Since the curvature radius R 2 does not satisfy the expression (1), when the upper mold 11 reaches the bottom dead center, a gap between the product to be molded and the mold remains.
- the bottom 2 is not sufficiently bent back, and the stress of the V-groove surface 2c of the bottom 2a of the upper plate 1a is a compressive stress. Therefore, the V spring surface 2c causes a tensile residual stress as shown in FIG. 8B due to the subsequent spring back, and the fatigue resistance decreases. As a result, a crack 30 as shown in FIG. 8C is generated in the V-groove surface 2c of the bottom 2a of the upper plate 1a in a short time that cannot be practically used. As described above, in the comparative example that does not satisfy the conditions of the present invention, cracking occurs during the processing of the bottom 2 or tensile residual stress is generated in the V-groove surface 2c of the bottom 2a of the upper plate 1a. The fatigue could not be obtained. From the above results, it was confirmed that the deformed cross-section tubular member produced by press-molding a steel pipe under the conditions of the present invention has excellent fatigue resistance because sufficient compressive residual stress is applied.
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Abstract
Description
本願は、2008年5月12日に、日本に出願された特願2008-124787号に基づき優先権を主張し、その内容をここに援用する。
このような異形断面筒状部材は、走行中に衝撃荷重やねじり荷重等を繰り返し受けるため、高強度に加え、高い耐疲労性が必要である。また、最近では、アクスルビーム等の自動車用足廻り部材は、複数の部材を用いて成形するのではなく、1本の鋼管をプレス加工して成形することが要求されている。
加えて、熱処理を施すことによって製品精度が低下し、車体への組み付け作業が困難になるという問題もあった。
(1)本発明は、上型及び下型の間で鋼管を潰して断面V字状とする、異形断面筒状部材のプレス成形方法であって、前記上型の先端部の曲率半径をR1、この上型の前記先端部に対応する前記下型の底部の曲率半径をR2、前記鋼管の板厚をtとしたとき、R1、R2、tが、R1+2t=R2、かつ、1.5t≦R1≦3tを満たす。
特に、上記(3)の異形断面筒状部材を自動車用足廻り部材に適用した場合は、自動車の低コスト化及び長寿命化が達成できる。
図1は、本発明の異形断面筒状部材のプレス成形方法により成形した異形断面筒状部材の一実施形態であるアクスルビーム1を示す。また、図2は、図1のA-A断面図を示す。
このアクスルビーム1は、図2に示されるように、上下一対の型(後述)間で1本の鋼管を潰して断面V字状にプレス成形されたものである。符号1aは、アクスルビーム1の加工前鋼管の断面形状中の上の弧に対応する上板であり、符号1bは、同断面形状中の下の弧に対応する下板である。さらに、符号2a、2bは、それぞれ上板1a、1bの底部であり、符号2c、2dは、それぞれ底部2a、2bのV溝面である。
前記アクスルビーム1において、疲労試験時に発生する応力は、上板1aの底部2aのV溝面2cでもっとも高くなる。そのため、上板1aの底部2aのV溝面2cに圧縮の残留応力を有することが要求されている。したがって、本実施形態では、部材底部2aのV溝面2cに圧縮残留応力を付与して耐疲労性を改善させている。
R1+2t=R2・・・・・(1)
1.5t≦R1≦3t・・・・・(2)
本実施形態においては、スプリングバック後のアクスルビーム1の底部2のV溝面2c、2dの残留応力を圧縮にする、即ち、スプリングバックにより底部2のV溝面2c、2dに圧縮の残留応力を形成するためのプレス加工条件を規定している。
図3~図5は、いずれもアクスルビーム1の底部2におけるプレス成形工程の断面図である。図3~図5は、それぞれ、上型が下死点に至る前のプレス成形工程の拡大断面図、上型が下死点に達した際のプレス成形工程の拡大断面図、型開き後におけるアクスルビーム1の底部2の拡大断面図を示す。
なお、図3~図5において、符号11は上型、符号12は下型である。また、母材である鋼管を上型11及び下型12の間でプレス成形した場合、型間では、上板1aと下板1bとが密着される。
図3に示されるように、上型11が下死点に至る前のプレス成形工程においては、上板1a、下板1bともに曲率半径R1、R2が小さくなる一般的な曲げ変形である。しかしながら、V字状のアスクルビーム1の底部2を形成する上型11と下型12の曲率半径R1、R2は、(2)式で制限したように小さいため、被成形品が型になじまずに曲げ過ぎが生じる。この結果、上型11の先端部11aと上板1aの対応部分との間に隙間3が生じる。同様に、下型12の底部12a両サイドの部分と下板1bの対応部分との間にも隙間4、4が生じる。
そして、上型11が下死点に至る前は、前記隙間3、4を有したままプレス成形が進行する。なお、この状態においては、上板1aの底部2aのV溝面2c及び下板1bの底部2bのV溝面2dは、圧縮応力状態である。
なお、この状態においては、上板1aの底部2a及び下板1bの底部2bは、型により押し広げられる加工であり、いずれのV溝面2c、2dも、引張応力状態となる。即ち、底部2のV溝面2c、2dには、ともに自身の曲率半径R1、R2を小さくしようとする応力が生じる。
前記筒状部材の底部2の耐疲労性を評価するため、図6に示すように断面V字状筒状部材の長手方向中央部から、幅20mmの試験片21を切り出した。その試験片21を切り出す際に長手方向の残留応力は解放される。しかしながら、周方向の拘束は保たれているため、切断前後での試験片底部2のV溝面2c、2dの残留応力の値は、ほとんど変化がなかった。図7に示すように、切り出したV字状試験片の両端を固定側保持具22と振動側保持具23とで保持し、試験片21に±500MPaの両振り応力がかかるように、振動側保持具23を振動器24により周波数1Hzで図7の矢印で示す水平方向(V形状の幅が増減する方向)に振幅させて疲労試験を行った。この疲労試験によって生じたき裂の発生回数を表1に示す。ここで、疲労き裂発生回数が、1万回未満の疲労寿命の短いもの(C)、1万回以上10万回未満のもの(B)、10万回以上の優れた疲労寿命を有するもの(A)の3段階で評価した。
実施例1~3から明らかなように、本発明の異形断面筒状部材は、図8Aに示すように、底部2のV溝面2c、2dに十分な圧縮残留応力が付与されており、耐疲労性が大幅に改善されていることを確認した。
比較例2として、曲率半径R1が(2)式よりも大きい場合を示す。この場合は、曲率半径R1が大きすぎるため、プレス工程中、隙間がないまま、常に被成形品が型に密着して成形される。そのため、底部2の曲げ戻しがおきず、上型11が下死点に達した際、上板1aの底部2aのV溝面2cの応力は圧縮応力である。故に、その後のスプリングバックによりV溝面2cは、図8Bに示すような引張り残留応力を生じ、耐疲労性が低下する。その結果、実用に耐えない短時間で上板1aの底部2aのV溝面2cに、図8Cに示すような亀裂30を生じる。
比較例3、4として、曲率半径R2が(1)式を満たさない場合を示す。曲率半径R2が(1)式を満たさないため、上型11が下死点に達した際、被成形品と型との隙間が残る。そのため、底部2に十分な曲げ戻しが行われず、上板1aの底部2aのV溝面2cの応力は圧縮応力である。故に、その後のスプリングバックによりV溝面2cは、図8Bに示すような引張り残留応力を生じ、耐疲労性が低下する。その結果、実用に耐えない短時間で上板1aの底部2aのV溝面2cに、図8Cに示すような亀裂30を生じる。
このように、本発明の条件を満たさない比較例では、底部2の加工中に割れが生じたり、上板1aの底部2aのV溝面2cに引張り残留応力が生じたりするため、十分な耐疲労性を得ることができなかった。
以上の結果から、本発明の条件で、鋼管をプレス成形して製造した異形断面筒状部材は、十分な圧縮残留応力が付与されているため、優れた耐疲労性を有することを確認した。
1a 上板
1b 下板
2 底部
2a 上板の底部
2b 下板の底部
2c 上板の底部のV溝面
2d 下板の底部のV溝面
3 隙間
4 隙間
11 上型
11a 上型の先端部
12 下型
12a 下型の底部
21 耐疲労性試験片
22 固定側保持具
23 振動側保持具
24 振動器
30 亀裂
Claims (4)
- 上型及び下型の間で鋼管を潰して断面V字状とする、異形断面筒状部材のプレス成形方法であって、
前記上型の先端部の曲率半径をR1、この上型の前記先端部に対応する前記下型の底部の曲率半径をR2、前記鋼管の板厚をtとしたとき、R1、R2、tが、
R1+2t=R2、かつ、
1.5t≦R1≦3t
を満たすことを特徴とする異形断面筒状部材のプレス成形方法。 - 前記上型がその下死点に至る前までの間に、この上型の前記先端部と前記鋼管との間及び前記下型の前記底部と前記鋼管との間に隙間を設けた状態でプレスする工程と;
前記上型が前記下死点に達した際に、前記隙間を完全に潰すようにプレスして異形断面筒状部材とする工程と;
前記上型及び前記下型を開いた後に前記異形断面筒状部材に生じるスプリングバックにより、同異形断面筒状部材の前記底部におけるV溝面に圧縮残留応力を付与する工程と;
を含むことを特徴とする請求項1に記載の異形断面筒状部材のプレス成形方法。 - 請求項2に記載の異形断面筒状部材のプレス成形方法により製造される断面V字状の異形断面筒状部材であって、
前記異形断面筒状部材の前記V溝面に、前記スプリングバックにより形成される前記圧縮残留応力を有することを特徴とする異形断面筒状部材。 - 自動車用足廻り部材であることを特徴とする請求項3に記載の異形断面筒状部材。
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US12/736,756 US8894080B2 (en) | 2008-05-12 | 2009-05-12 | Press-forming method of tubular part having cross section of irregular shape, and tubular part having cross section of irregular shape formed by the press-forming method |
KR1020107021850A KR101177219B1 (ko) | 2008-05-12 | 2009-05-12 | 이형 단면 통 형상 부재의 프레스 성형 방법과 이 프레스 성형 방법에 의해 성형한 이형 단면 통 형상 부재 |
CN200980111571.XA CN101980804B (zh) | 2008-05-12 | 2009-05-12 | 异型断面筒状部件的加压成形方法和利用该加压成形方法成形的异型断面筒状部件 |
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