JP5121040B2 - Hydroform molding method - Google Patents

Description

  The present invention relates to a steel pipe for hydrofoam and a hydrofoam molding method in which a steel pipe is put into a mold and clamped and then molded into a predetermined shape while applying an internal pressure and a shaft pressing force in the pipe.

  Hydroform can obtain a more complicated shape than the press molding and welding, and has advantages such as reduction in the number of parts, weight reduction of parts, increase in strength, and cost reduction. Hydrofoam is attracting attention especially in the field of manufacturing automobile parts and has been applied to actual vehicles in Japan since 1999. Since then, the application parts of Hydroform have been increasing year by year, and the market size has been greatly expanded.

  Hydroform is a method of inserting a steel pipe into a mold having an overhanging cavity and clamping it, and then applying an internal pressure to the pipe while axially pressing both ends thereof with an axial push punch. For example, a technique of forming a T-shaped branch pipe. When hydroforming is performed, if the bulge amount is increased and the length of the branch pipe or the like can be increased, the number of parts that can be processed increases accordingly, and the versatility increases.

  On the other hand, in hydrofoam, if the amount of bulging is excessively large, there is a problem that wrinkles and cracks are generated with molding. Further, when the bulge amount increases, the wall thickness of the bulge portion becomes thin, and there is a concern that strength is insufficient or breakage occurs.

Therefore, conventionally, when hydroforming is performed, wrinkles and cracks associated with molding are generated by moving the mold that forms the projecting cavity and appropriately controlling the width of the projecting cavity during molding. A method for avoiding this is disclosed (Patent Document 1). In addition, in order to prevent insufficient strength and breakage of the bulging part, a so-called tailored tube in which a plurality of short steel pipes having different strengths and wall thicknesses are joined in the longitudinal direction of the steel pipe is used. A technique for increasing the strength and wall thickness of the paper is disclosed (Patent Document 2).
Japanese Patent Laid-Open No. 2002-153917 JP 2001-321844 A

  However, in the technique of the above-mentioned Patent Document 1, it is necessary to control the width of the projecting cavity in order to suppress the generation of wrinkles and cracks associated with molding, and the operation becomes complicated. In addition, a mechanism for moving the mold is required, and the apparatus configuration is complicated.

  Further, when a tailored tube is used as in the above-mentioned Patent Document 2, there is a problem that it is not easy to increase the bulge amount although it is possible to prevent insufficient strength and breakage of the bulge portion. For example, when forming a T-shaped branch pipe, the height of the branch pipe that can be easily formed is limited to approximately the same as the diameter D (mm) of the steel pipe, and the height is 2D (mm) or more. In order to form such a branch pipe, the control as described in Patent Document 1 is required. Further, since a branch pipe having a sufficient height cannot be formed, a process such as joining a short pipe member by welding after hydroforming is required, and work efficiency has not been improved.

  Accordingly, an object of the present invention is to provide a steel pipe for hydrofoam capable of performing a hydroforming with a high bulge amount without causing wrinkles or cracks by a relatively simple operation. It is to provide a hydroforming method used.

In order to solve such a problem, according to the present invention, a steel pipe in which two types of steel materials having different tensile strengths are arranged in parallel so as to be continuous in the pipe axis direction between both ends is provided. The steel material having a large tensile strength is bulged in a state where the steel material is aligned so as to face the cavity for projecting the mold, and in the steel material having the high tensile strength, the steel pipe is formed along the inner peripheral surface of the cavity. A pair of front and rear vertical parts bent at 90 ° with respect to the tube axis direction, and at the back of the cavity part, the hollow part is disposed across the tip of the vertical part so as to cross the tube axis direction of the steel pipe. A steel material having a small tensile strength that is surrounded by the pair of front and rear vertical portions of the steel material having a high tensile strength and the horizontal portion and deformed along the inner peripheral surface of the cavity portion. Is characterized by bulging the T-shaped branch pipe by flowing To, hydroformed method is provided. In this hydroform molding method, for example, when the diameter of the steel pipe is D (mm), the circumferential width of the steel material having a large tensile strength is (0.5 to 0.99) D (mm). Further, the circumferential width of the steel material having a high tensile strength may be constant in the tube axis direction or may be continuously changed.

In this case, the steel pipe may be inserted into a mold and molded while applying an internal pressure and a shaft pressing force. When the diameter of the steel pipe is D (mm), the molding height is 2D (mm). ) You may shape | mold so that it may become the above.

  By performing hydroforming using the steel pipe for hydroforming of the present invention, it becomes possible to perform molding with a high bulge amount without generating wrinkles or cracks. In this case, when hydroforming, the operation of moving the mold can be omitted, and the processing becomes easy. According to the present invention, for example, when manufacturing a T-shaped branch pipe, a branch pipe having a molding height of 2D (mm) or more is easily formed with respect to the diameter D (mm) of the steel pipe. Can do. As a result, the number of applicable parts for hydroform increases, and the range of applicable automotive parts and the like expands. Moreover, the welding of the short pipe member which was conventionally required can be omitted, and it can contribute to the improvement of work efficiency and cost reduction. Furthermore, the weight reduction of automobiles will lead to improved fuel efficiency, which can contribute to the improvement of the global environment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted. FIG. 1 is a perspective view of a steel pipe 1 for hydroforming according to an embodiment of the present invention.

  This steel pipe 1 for hydrofoam has a structure in which two types of steel materials 10 and 11 having different strengths expressed by thickness x tensile strength are arranged so as to be continuous in the pipe axis direction of the hydroform steel pipe 1. have. By connecting the side surfaces of the steel materials 10 and 11 integrally, the hydroform steel pipe 1 is formed in a hollow cylindrical shape having both ends opened, and the two types of steel materials 10 and 11 are composed of the hydroform steel pipes. 1 is continuously arranged between both ends.

In the illustrated example, the strength of the steel material 10 (represented by the thickness t _{10 of the} steel material ₁₀ × tensile strength Ts ₁₀ = t ₁₀ · Ts ₁₀ ) is the strength of the steel material 11 (the thickness t _{11 of the} steel material ₁₁ × tensile. It is designed to be greater than the strength Ts ₁₁ = t ₁₁ · Ts ₁₁ . That is, t ₁₀ · Ts ₁₀ > t ₁₁ · Ts ₁₁ .

In order to preferentially deform the steel material 10 having high strength (thickness × tensile strength), the total surface area of the steel materials 10 and 11 is smaller than the total area of the steel material 11 having low strength. It has become. To the above 2D the forming height of the later (D is the diameter of the steel pipe), the circumferential width L ₁₀ of the large steel 10 of intensities, the diameter D of the hydroforming steel pipe 1 (mm), The width L _{11 in} the circumferential direction of the steel material 11 having a small strength is set to L ₁₀ = (0.5 to 1.5) D (mm). L ₁₁ = (π−0.5 to 1.5) D ( mm).

  2 and 3 show an example of a manufacturing method of the steel pipe 1 for hydroform. First, as shown in FIG. 2, the steel materials 11a and 11b with low strength divided into two are arranged on both sides of the steel material 10 with high strength. And one side of steel materials 11a and 11b is joined to both sides of steel material 10 by laser welding etc., respectively.

  In this way, the steel material 10 and the steel materials 11a and 11b having an integral plate shape are rounded and formed into a cylindrical shape, and the other side surfaces of the steel materials 11a and 11b are joined together by laser welding or the like as shown in FIG. Through the above steps, the tubular hydroforming steel pipe 1 described in FIG. 1 can be manufactured.

  4 and 5 show another example of the manufacturing method of the steel pipe 1 for hydroform. First, as shown in FIG. 4, a cylindrical steel pipe 1 ′ is inserted into a container 16 in which a cooling liquid 15 such as water is placed, and a portion 10 ′ of the steel pipe 1 ′ is separated from the liquid surface of the cooling liquid 15. Set it to the top. In this case, a portion 10 ′ located on the liquid level is made to be continuous in the tube axis direction of the steel pipe 1 ′.

  Then, a portion 10 ′ of the steel pipe 1 ′ that is on the liquid surface of the coolant 15 is heated by a laser or the like. In addition, while heating the part 10 ′ of the steel pipe 1 ′ in this way, the other part 11 ′ of the steel pipe 1 ′ immersed under the liquid surface of the coolant 15 is cooled by the coolant 15. Therefore, it is not heated and only part 10 'of steel pipe 1' can be heated.

  Thus, after heating only a portion 10 ′ of the steel pipe 1 ′, the entire steel pipe 1 ′ is immersed under the liquid level of the coolant 15 as shown in FIG. 5. Then, the portion 10 ′ of the steel pipe 1 ′ heated on the liquid surface of the coolant 15 is quenched in the coolant 15, so that only the portion 10 ′ of the heated steel tube 1 ′ is quenched. Through the above steps, a part 10 ′ of the steel pipe 1 ′ is transformed into a steel material 10 having a high strength, and the other part 11 ′ is a steel material 11 having a strength lower than that of the steel material 10, and the hydroform described in FIG. The steel pipe 1 can be manufactured.

  In the manufacturing method shown in FIGS. 4 and 5, even when a steel pipe 1 ′ (general steel pipe) having a uniform thickness and material is used, two kinds of steel materials having different strengths are obtained by performing a partial heat treatment. The steel pipe 1 for hydroforming in which 10 and 11 are continuously arranged in the pipe axis direction can be manufactured. In addition, in order to change the portion 10 ′ of the steel pipe 1 ′ into the steel material 10 having a high strength as described above, a strengthening method such as a processing effect or a carburizing process may be used in addition to the heat treatment.

The widths L ₁₀ and L ₁₁ of the two types of steel materials 10 and 11 having different strengths may be constant with respect to the tube axis direction or may be continuously changed with respect to the tube axis direction. 6 (a) is the width L ₁₀ of the steel material 10 indicates a hydroformed steel pipe 1 is fixed to the tube axis direction. Meanwhile, Hydro shown in FIG. 6 (b) (c), the width L ₁₀ of the steel material 10 shows the hydroformed steel pipe 1 which continuously changes with respect to the tube axis direction, and FIG. 6 (b) In the foam steel pipe 1, the width L ₁₀ of the steel material 10 is narrow at the center portion in the tube axis direction. Conversely, the hydroform steel pipe 1 shown in FIG. 6C is a steel material at the center portion in the tube axis direction. A width L10 of ₁₀ is widened. Incidentally, in the case of thus changing the width L ₁₀ with respect to the tube axis direction, reducing the width L ₁₀ always in the center of the tube axis direction (or, broadly) it needs not to be. Depending on the portion to which hydroformed may be desired setting of the position of narrowing the width L ₁₀ (or, broadly).

  Next, the hydroforming method using the steel pipe 1 for hydroforming concerning embodiment of this invention is demonstrated. As an example of hydroforming, a process of forming a T-shaped branch pipe 25 by bulging the central portion of the hydroforming steel pipe 1 perpendicular to the pipe axis direction will be described.

  First, as shown in FIG. 7, the hydroforming steel pipe 1 is inserted between a pair of molds 20. In this case, the hydroforming steel pipe 1 is appropriately rotated so that the steel material 10 having a high strength faces the projecting cavity 21. In addition, although the metal mold | die 20 is comprised by a pair of pair which has the inner surface shape of object mutually, the steel pipe 1 for hydroforming will be inserted in the inside of a pair of metal mold | die 20, In order to explain this state, in FIG. 7, the mold 20 disposed on the near side is omitted.

  After the molds 20 are clamped together, both ends of the hydroform steel pipe 1 inserted between the molds 20 are pressed by a shaft push mold 22 as shown in FIG. A shaft pressing force (compression force) is applied to the. In addition, a high-pressure liquid is supplied into the hydroforming steel pipe 1 from the supply hole 23 disposed on the distal end surface of the axial push die 22 to apply an internal pressure. In this way, by applying the internal pressure and the axial pressing force, the hydroforming steel pipe 1 is expanded toward the hollow portion 21, and the T-shaped branch pipe 25 is bulged to produce the product 26.

  FIG. 9 is a front view of the product 26 thus molded, and FIG. 10 is an enlarged view of the distal end portion of the branch pipe 25. In the product 26 manufactured using the steel pipe 1 for hydrofoam according to the embodiment of the present invention, as described above, the steel material 10 having high strength is aligned so as to face the cavity 21. Therefore, in the steel material 10 having high strength, a pair of front and rear vertical portions bent along the inner peripheral surface of the cavity portion 21 at approximately 90 ° with respect to the tube axis direction of the steel tube 1 for hydroform. 30 and the horizontal part 31 arrange | positioned ranging over the front-end | tip of the vertical part 30 so that the hollow part 21 may be crossed in the pipe-axis direction of the steel pipe 1 for hydroforms in the inner part of the hollow part 21 will be formed. And the steel material 11 with small strength which deform | transformed along the internal peripheral surface of the cavity part 21 flows into the both sides of a pair of front-and-back vertical part 30 and the horizontal part 31 which were bent in this substantially U shape, and T The letter-shaped branch pipe 25 can be bulged.

In this case, the steel material 10 having high strength is bent at approximately 90 ° twice each at the base of the branch pipe 25 (the entrance side of the cavity 21) and the back of the cavity 21. In order to prevent the steel material 10 from being cracked at the location where it is bent in this manner, the tensile strength Ts ₁₀ of the steel material 10 is preferably 590 MPa ≦ Ts ₁₀ ≦ 1180 MPa. As the steel material 10, for example, high-tensile steel can be used.

On the other hand, the steel material 11 having a low strength can be deformed along the inner peripheral surface of the cavity portion 21 on both sides of the vertical portion 30 and the horizontal portion 31 of the steel material 10 bent into a substantially U shape. The strength Ts ₁₁ is preferably 270 MPa ≦ Ts ₁₁ ≦ 780 MPa. As the steel material 11, for example, mild steel can be used.

Further, in addition to setting the tensile strength Ts ₁₀ of the steel material ₁₀ and the tensile strength Ts ₁₁ of the steel material 11 in an appropriate range as described above, the strength t ₁₀ · Ts ₁₀ of the steel material _{10 is changed} to the strength t _{11 of the} steel material _11. It is also important to design so that the total area of the steel material 10 having a high strength is smaller than the total area of the steel material 11 having a low strength while being larger than Ts ₁₁ . By satisfying these conditions, the T-shaped branch pipe 25 can be easily bulged without cracking or wrinkling.

  Further, particularly in the vicinity of the distal end portion of the branch pipe 25 shown by the region 35 in FIG. 9, it is shown in FIG. 10 by being surrounded by the steel material 10 having a high strength bent into the vertical portion 30 and the horizontal portion 31. Thus, the compressive stress σ in the direction orthogonal to the longitudinal direction of the branch pipe 25 (the pipe axis direction of the hydroform steel pipe 1) acts on the steel material 11 having a low strength. Due to the influence of the compressive stress σ, the deformation mode of the steel material 11 in the vicinity of the distal end portion of the branch pipe 25 becomes a uniaxial tension state that is substantially extended only in the longitudinal direction of the branch pipe 25, and cracks are suppressed. Moreover, in the base part of the branch pipe 25 shown by the area | region 36 in FIG. 9, the deformation | transformation mode of the steel material 11 with small intensity | strength will be in a pure shear (pure shearing) state, and a crack is suppressed similarly. Further, on the side of the pipe opposite to the branch pipe 25 shown by the region 37 in FIG. 9, the deformation mode of the steel material 11 having a low strength is in a plane strain state of compression, so that molding is performed at a higher pressure. And the generation of wrinkles is suppressed.

  From the above, by carrying out hydroforming using the hydroforming steel pipe 1 according to the embodiment of the present invention, the forming height of the branch pipe 25 with respect to the diameter of the hydroforming steel pipe 1 is D (mm). Molding such that H is 2D (mm) or more is possible.

In addition, since the steel material 10 having a high strength and the steel material 11 having a low strength are continuously provided in the pipe axis direction, there is an advantage that a wide range of hydroforming processing conditions can be selected. That is, for example, the steel material 10 having a high strength has a tensile strength Ts ₁₀ = 780 MPa and a steel material having a wall thickness t ₁₀ = 1.6 mm, and the steel material 11 having a low strength has a tensile strength Ts ₁₁ = 440 MPa and a wall thickness t ₁₁ = 1.6 mm. When the diameter D of the hydroforming steel pipe 1 is set to 63.5 (mm), as shown in FIG. 11, the steel material 11 having a low strength (tensile strength Ts ₁₁ = 440 MPa, wall thickness is used. The processing conditions of the axial pressing amount and the internal pressure when hydroforming a steel pipe (diameter D = 63.5 (mm)) consisting only of t ₁₁ = 1.6 mm are as shown by the graph line 40. Further, the amount of axial pressing when hydroforming a steel pipe (diameter D = 63.5 (mm)) consisting only of a steel material 10 having a high strength (tensile strength Ts ₁₀ = 780 MPa, wall thickness t ₁₀ = 1.6 mm) The processing conditions for the internal pressure are as shown by the graph line 41. On the other hand, in the case of hydroforming a hydroforming steel pipe 1 (diameter D = 63.5 (mm)) in which a steel material 10 having a high strength and a steel material 11 having a low strength are continuously arranged in the pipe axis direction. With respect to the processing conditions of the axial pressing amount and the internal pressure, molding without cracks and wrinkles is possible in the range between the graph line 40 and the graph line 41.

In addition, when a steel pipe (diameter D = 63.5 (mm)) composed only of a steel material 11 having a low strength (tensile strength Ts ₁₁ = 440 MPa, wall thickness t ₁₁ = 1.6 mm) is hydroformed, FIG. As shown, the height H of the moldable branch pipe 25 is about 1.5 D (mm). Further, when a steel pipe (diameter D = 63.5 (mm)) made only of a steel material 10 having a high strength (tensile strength Ts ₁₀ = 780 MPa, wall thickness t ₁₀ = 1.6 mm) is hydroformed, it can be formed. The height H of the branch pipe 25 is about 1.0 D (mm). On the other hand, when hydroforming steel pipe 1 (diameter D = 63.5 (mm)) in which steel material 10 having a high strength and steel material 11 having a low strength are arranged so as to be continuous in the pipe axis direction, As shown in FIG. 12, the height H of the moldable branch pipe 25 increases to about 2.5 D (mm).

Tensile strength Ts ₁₀ = 590 to 1180 MPa (two types of steel materials SPFC590Y and SPFC780Y of JIS G 3155, and three types of tensile strength 1180 MPa), wall thickness t ₁₀ = 1.2 to 2.0 mm Steel pipe 1 for hydrofoam (diameter D = 63) manufactured using steel material 10 and steel material 11 having a small strength consisting of tensile strength Ts ₁₁ = 440 MPa (steel material SPFC440 of JIS G 3155) and wall thickness t ₁₁ = 1.6 mm. .5 (mm)) was hydroformed. Note that changing the width _{L 10} greater steel 10 strength to 39～63Mm. As a result, as shown in Tables 1 to 3, the width L ₁₀ = 39, 45, 63 mm (Table 1) and the wall thickness t ₁₀ = 1.2, 1.6, 2.0 mm (Table 1) of the steel material 10 having high strength. 2) In any case of tensile strength Ts ₁₀ = 590, 780, 1180 MPa (Table 3), the height H of the branch pipe 25 could be formed to a height of 2.0 D (mm) or more. .

  The present invention is useful for manufacturing, for example, truck frames, suspension parts, lower arms, and the like for automobiles.

It is a perspective view of the steel pipe for hydroforming concerning an embodiment of the invention. It is explanatory drawing which shows an example of the manufacturing method of the steel pipe for hydroforms. It is explanatory drawing which shows an example of the manufacturing method of the steel pipe for hydroforms. It is explanatory drawing which shows another example of the manufacturing method of the steel pipe for hydroforms. It is explanatory drawing which shows another example of the manufacturing method of the steel pipe for hydroforms. It is explanatory drawing of the width | variety of steel material with big intensity | strength, (a) shows the case where a width is changing with respect to a pipe-axis direction, (b) (c) shows the case where the width is changing with respect to a pipe-axis direction. ing It is explanatory drawing of the hydroforming method using the steel pipe for hydroforming concerning embodiment of this invention, and has shown the state before shaping | molding. It is explanatory drawing of the hydroforming method using the steel pipe for hydroforming concerning embodiment of this invention, and has shown the state after shaping | molding. It is a front view of the molded product. It is an enlarged view of the front-end | tip part of a branch pipe. It is a graph which shows the processing conditions of hydroform. It is a graph which shows the height of the branch pipe which can be shape | molded.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel pipe for hydroforming 10 Steel material with high strength 11 Steel material with low strength 15 Cooling liquid 16 Container 20 Mold 21 Cavity for overhang 22 Shaft pushing die 25 Branch pipe 26 Product 30 Vertical portion 31 Horizontal portion

Claims (5)

Two types of steel materials having different tensile strengths are arranged in parallel so that each of the two types of steel materials is continuous in the direction of the tube axis between both ends , and the steel materials having high tensile strength face the cavity for projecting the mold. In the steel material having a large tensile strength, the pair of front and rear members bent at 90 ° with respect to the tube axis direction of the steel pipe is formed along the inner peripheral surface of the hollow portion. And a horizontal portion disposed across the tip of the vertical portion so as to cross the hollow portion in the tube axis direction of the steel pipe at the back of the hollow portion, and the tensile strength of A steel material with a small tensile strength, which is surrounded by a pair of front and rear vertical parts and a horizontal part of a large steel material and deformed along the inner peripheral surface of the cavity, flows into a bulge. A hydroform molding method characterized by comprising:   The diameter of a steel pipe is set to D (mm), The width | variety of the circumferential direction of the steel material with the said large tensile strength is (0.5-0.99) D (mm), It is characterized by the above-mentioned. The hydrofoam molding method as described.   The hydroform molding method according to claim 1 or 2, wherein a circumferential width of the steel material having a high tensile strength is constant in the pipe axis direction or continuously changes. .   The hydroform molding method according to claim 1, wherein the steel pipe is inserted into a mold and molded while applying an internal pressure and a shaft pressing force.   5. The hydroform molding method according to claim 4, wherein when the diameter of the steel pipe is D (mm), molding is performed so that a molding height is 2 D (mm) or more.

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