JP2007245187A - Method for manufacturing object having closed cross sectional shape by hot working press - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an object having a closed cross sectional shape by a hot working press, which method can manufacture a formed object having a nearly or completely closed hollow cross sectional shape while allowing the best use of merits of the hot press forming to simultaneously carry out the shaping and quenching to a metal plate. <P>SOLUTION: The metal plate M having a first formed portion M1 and a second formed portion M2 is prepared, and is heated to a temperature capable of quenching. First, a primarily formed item having an opened cross sectional shape given to the first formed portion M1 is achieved by press-forming the first formed portion M1 at a temperature capable of quenching using a first press die mechanism held at a low temperature, and is quenched at the same time. Next, a secondarily formed item having a hollow closed cross sectional shape formed by the second formed portion M2 bent from the opened cross sectional shape of the primarily formed item is achieved by bending the second formed portion M2 at a temperature capable of quenching by press-forming using a second press die mechanism held at a low temperature, and is quenched at the same time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to hot press forming in which shape imparting and quenching are simultaneously performed on a metal plate material, and in particular, a hot-formed product (closed cross-sectional shape product) having a hollow closed cross-sectional shape whose cross section is almost or completely closed. The present invention relates to a method for manufacturing a product having a closed cross-sectional shape by hot pressing which can be manufactured by press molding.

  2. Description of the Related Art Conventionally, it has been proposed to manufacture a vehicle collision reinforcing material such as a door impact beam or bumper reinforcement by hot press molding (see, for example, Patent Documents 1 and 2). “Hot press forming” means that metal sheet material that has been heated to a predetermined quenching temperature and is in a high temperature state is press-formed (and constrained as necessary) using a relatively low-temperature press die. This refers to a press molding technique in which shape imparting and quenching are simultaneously performed on a plate material. According to hot press molding, a lightweight and high-strength molded product can be produced at a relatively low cost without impairing the moldability of the metal plate material and the shape accuracy after molding.

Japanese Patent Application Laid-Open No. 2003-231915 (the product of FIG. 4 has an open cross-sectional shape) JP 2002-102980 A

  However, the conventional hot press forming method is based on a simple procedure in which a metal plate material in a high temperature state is normally press formed by a one-time stamping operation. For this reason, the conventional hot press molding method is applied only to products having an open cross-sectional shape (for example, a hat-shaped cross-sectional shape) in which a cross-section after molding is opened in one side (for example, Patent Document 1). There is no case where a product having a closed cross-sectional shape with a hollow cross section is manufactured by a hot press molding method. In other words, in the conventional hot press forming method, the entire metal plate material (or the molded product) is cooled at once when the stamping is performed with a press die, and the whole is rapidly cured. It will be difficult to process. Therefore, the application target of the conventional hot press forming method has been limited to products whose cross section is an open cross section.

  The object of the present invention is to provide a molded product (closed cross-sectional shape product) having a hollow closed cross-sectional shape in which the cross section is almost or completely closed while taking advantage of the hot press forming that simultaneously imparts the shape to the metal plate and quenching. ) Can be manufactured, and a manufacturing method of a closed cross-sectional shape product by hot pressing is provided.

  The invention according to claim 1 is a plate material preparation step of preparing a metal plate material having a flat plate-shaped first formed portion and a flat plate-shaped second formed portion, and heats the entire metal plate material to a quenchable temperature. Using the heating step and a first press die mechanism having a temperature lower than the quenchable temperature, press forming the first molded portion in the quenchable temperature state of the metal plate material, thereby A first hot press molding step for obtaining a primary molded product having an open cross-sectional shape with a cross section opened on one side with respect to one molded part, and quenching the first molded part, and the quenchable temperature. The first molded part of the primary molded product is subjected to press bending molding on the second molded part that is in a quenchable temperature state of the primary molded product by using a second press mold mechanism at a lower temperature. The open cross-sectional shape at A second hot press for obtaining a secondary molded product whose cross section is changed into a hollow closed cross-sectional shape which is almost or completely closed by the second molded part formed by brazing and quenching the second molded part It is a manufacturing method of the closed cross-sectional shape goods by the hot press characterized by including a formation process.

  According to the method of the present invention, in the first hot press forming step, only the first forming part of the metal plate material is provided with an open cross-sectional shape and quenched to be formed into an open cross-sectional shape. A primary molded product having a first molded part and an unmolded second molded part is provisionally completed. In the subsequent second hot press forming step, by performing press bending forming and quenching on the second forming portion of the primary molded product, the open cross-sectional shape in the first forming portion is bent. As a result, a secondary molded product (that is, a closed cross-sectional shape product) whose cross section is changed to a hollow closed cross-sectional shape is completed. In this way, the first forming part and the second forming part of the metal sheet heated to a quenchable temperature are subjected to press forming and quenching step by step while the respective parts maintain the quenchable temperature state. By adopting a series of procedures, it is possible to change the primary molded product with an open cross-sectional shape into a secondary molded product with a hollow closed cross-sectional shape while partially simultaneously quenching the molded product at each stage. It became. Therefore, according to this method, a molded product (closed cross-sectional shape) having a hollow closed cross-sectional shape in which the cross-section is almost or completely closed while taking advantage of the hot press forming that simultaneously imparts the shape to the metal plate and quenching. Product) can be manufactured smoothly and reliably.

  According to a second aspect of the present invention, in the method for manufacturing a product having a closed cross-sectional shape by hot pressing according to the first aspect, the metal plate material prepared in the plate material preparing step is a flat plate including a pair of protruding piece portions at both ends. In the first hot press forming step, the first plate forming portion of the metal plate material is provided in the first hot press forming step. A central flange extending in the longitudinal direction with respect to one molded part, a pair of webs whose front ends are connected by the central flange, a pair of side flanges extending outward in the width direction from the rear end of each web, and Then, by forming the pair of protruding pieces bent at substantially right angles with respect to the side flanges, a primary molded product having an open cross-sectional shape with a transverse section opened to the opposite side to the central flange is obtained. And the second hot press forming process Then, the open cross-sectional shape of the first molded portion of the primary molded product is the pair of protrusions bent substantially perpendicular to the central flange, the pair of webs, the pair of side flanges, and the side flanges. To obtain a secondary molded product in which the transverse section is changed to a substantially closed or closed closed shape with a substantially convex shape, which is defined by the one part and the second molded part formed by bending. It is characterized by.

  According to the second aspect of the present invention, a secondary of a hollow closed cross-sectional shape in which the transverse cross section is substantially convex or substantially closed while taking advantage of the hot press forming that simultaneously imparts the shape to the metal plate and quenching. A product having a closed cross-sectional shape derived from a molded product can be produced smoothly and reliably.

  According to a third aspect of the present invention, in the method for manufacturing a closed cross-sectional product by hot pressing according to the second aspect, the first press die mechanism used in the first hot press forming step includes a fixed base, and A primary molding fixed mold composed of a two-stage switching mold supported by the fixed base so as to be able to switch between a hat mold cross-section molding position and a protruding piece bending molding position, and the primary molding fixed mold And a primary molding movable mold provided so as to be able to approach and separate, and the two-stage switching mold presses the primary molding fixed mold arranged at the hat mold cross-section molding position with the primary molding movable mold. Thus, a hat-shaped cross-sectional shape defined by the central flange, the pair of webs, and the pair of side flanges is imparted to the first molded portion of the metal plate material, and then the two-stage switching By further pressing the primary forming fixed mold with the primary forming movable mold until the position of the mold is switched from the hat cross section forming position to the protruding piece bending forming position, a pair of protrusions of the first forming portion of the metal plate material are pressed. The primary molded product is obtained in which a piece is bent at a substantially right angle with respect to each of the side flanges.

  According to the third aspect, by using the first press mold mechanism including the fixed mold for primary molding composed of the fixed base and the two-stage switching mold and the movable mold for primary molding, the two-stage switching mold. Based on the stepwise pressing operation of the movable mold for primary molding against the center flange, the center flange, the pair of webs, the pair of side flanges, and the pair of projecting portions bent substantially at right angles to the side flanges. However, it is possible to smoothly and reliably obtain a primary molded product having an open cross-sectional shape in which the cross section is opened to the opposite side to the central flange.

  The invention of claim 4 is the method for producing a closed cross-sectional product by hot pressing according to claim 1, 2, or 3, wherein the second press die mechanism used in the second hot press forming step is: Of the primary molded products, a secondary molding fixed mold for holding the first molded part to which the open cross-sectional shape is given, and a second of the primary molded products held by the secondary molding fixed mold. In order to bend down the forming portion, the secondary forming movable die is provided so as to be slidable so as to cross the secondary forming fixed die in the width direction.

  According to the fourth aspect, by using the second press mold mechanism including the secondary molding fixed mold and the secondary molding movable mold, the secondary molding movable mold has a width of the secondary molding fixed mold. The first molded part with the open cross-sectional shape is smoothly formed into a hollow closed cross-sectional secondary molded article based on the bending and pressing operation of the second molded part of the primary molded product accompanying sliding in the direction. And it can change reliably. At the same time, the second molded part that has been bent over can be quenched.

  According to the method for producing a product with a closed cross-section by hot pressing according to the present invention, the hollow cross-section is substantially or completely closed while taking advantage of the hot press forming that simultaneously imparts the shape to the metal plate and quenching. A molded product having a closed cross-sectional shape (closed cross-sectional shape product) can be manufactured smoothly and reliably.

  Hereinafter, an embodiment in which the present invention is applied to the manufacture of a body portion of a door impact beam, which is a kind of vehicle impact reinforcement, will be described with reference to the drawings. In this embodiment, the main body portion 10 of the door impact beam as a product with a closed cross section as shown in FIGS. 10 and 11 is manufactured from a steel plate M as a metal plate as shown in FIG.

  First, a steel plate as a metal plate as a starting material is prepared. As shown in FIG. 9, the steel plate M is formed as a flat plate material having a uniform thickness (for example, 0.5 to 2 mm), and includes a flat plate-shaped first molded portion M1 and a flat plate-shaped second molded portion M2. It consists of two parts. The first forming part M1 of the steel plate is composed of a large rectangular main body part and a pair of left and right protruding piece parts 14 each having a small rectangular shape at both ends in the width direction of the main body part. The second forming portion M2 (the hatched portion in FIG. 9) of the steel steel plate is configured as a rectangular extending portion continuous with the left protruding piece portion 14. In addition, the steel steel which comprises this steel plate M is C: 0.18-0.25 mass%, Si: 0.15-0.35 mass%, Mn: 1.15-1.40 mass% as an additive element. Cr: 0.15-0.25 mass%, B: 0.0005-0.0020 mass%, The remainder consists of Fe and an impurity element.

  Next, the metal plate M is heated to about 900 ° C. in an electric heating furnace, for example. This heating temperature is a temperature sufficient to make the steel steel into austenite and be hardened. When the metal plate M is heated to about 900 ° C., it is taken out from the heating furnace, quickly set in the first press mold mechanism (see FIG. 2), and subjected to the first hot press forming. In the present embodiment, the metal plate material M is taken out of the heating furnace and set in the first press mold mechanism, and the time until the shaping and quenching operation by the first press mold mechanism is started is about 3 seconds. (See FIG. 13).

[About the first hot press forming process]
As shown in FIG. 1, the first press mold mechanism used in the first hot press molding step includes a lower mold 20 as a primary mold fixed mold and an upper mold 30 as a primary mold movable mold. Yes. The lower mold 20 includes a fixed base 21 and a two-stage switching mold 25 supported by the fixed base 21 so that the vertical position can be switched.

  The fixed base 21 has a pair of left and right support walls 22, and a two-stage switching mold 25 is held between the both support walls 22. The fixed base 21 has a pair of left and right shaped protrusions 23 that protrude upward from a horizontal reference surface 22 a corresponding to the upper surface of each support wall 22. Each of the shaped protrusions 23 has a substantially rectangular parallelepiped shape, and each has a horizontal top surface 23a and a vertical inner wall surface 23b.

  The two-stage switching mold 25 has a horizontal upper surface 26 that functions as a shaping surface, and a shaping groove 27 that extends in the longitudinal direction at the center of the switching mold and opens in the upper surface 26. This two-stage switching mold 25 is fixed so that it can be switched between the upper stage position (hat mold cross-section molding position) shown in FIGS. 1 to 3 and the lower stage position (projection piece bending molding position) shown in FIG. It is supported by the pedestal 21. When the two-stage switching mold 25 is arranged at the upper position, the upper surface 26 of the two-stage switching mold 25 is flush with the top surface 23a of each shaping protrusion of the fixed base 21, so that these surfaces (23a, 23a, 26) It becomes possible to place the metal plate M horizontally on the top. When the two-stage switching mold 25 is disposed at the lower position, the upper surface 26 of the two-stage switching mold 25 is substantially flush with the reference surface 22 a of the fixed base 21.

  A die cushion mechanism (not shown) made of, for example, a strong spring is disposed below the two-stage switching mold 25. By this die cushion mechanism, the two-stage switching mold 25 is normally placed at the upper position. On the other hand, when receiving a strong pressing force from the top to the bottom, the two-stage switching mold 25 is switched to the lower stage position against the action of the die cushion.

  The upper mold 30 as a primary mold movable mold is disposed above the lower mold 20 so as to be vertically movable (that is, close to and away from the lower mold 20). The length and width of the upper mold 30 substantially match the length and width of the two-stage switching mold 25 of the lower mold 20, and the upper mold 30 and the lower two-stage switching mold 25 are arranged to face each other. And the upper mold | type 30 has the shaping | molding protrusion 31 which can be fitted in the shaping groove | channel 27 of the two-step switching type | mold 25 in the lower surface side.

  As shown in FIG. 1, at the time of standby, the lower two-stage switching mold 25 is disposed at the upper position, and the upper mold 30 is disposed at the upper standby position. The metal plate M heated in the heating furnace is conveyed there, and as shown in FIG. 2, the metal plate M is set on the upper surface 26 of the two-stage switching mold 25 and the top surface 23a of the left and right shaping protrusions ( Place). Immediately after the setting is completed, the upper die 30 is moved vertically downward from the standby position shown in FIG. 2, and the upper die 30 is pressed against the first forming portion M1 of the metal plate material, and the upper die shaping protrusion 31 is moved in two stages. It is inserted into the switching type shaped groove 27. Then, as shown in FIG. 3, the first forming part M1 of the metal plate material is formed into a cross-sectional hat shape so as to match the fitting relationship between the upper die 30 (shown by a broken line) and the two-stage switching die 25. The More specifically, a central flange 11, a pair of left and right webs 12, and a pair of left and right side flanges 13 are formed on the first molded part M1 of the metal plate (see FIGS. 10 and 11), and thereby a cross section hat is formed. An open cross-sectional shape of the mold is formed.

  When the two-stage switching mold 25 is further pressed with the upper mold 30 from the state of FIG. 3, the upper mold 30 and the two-stage switching mold 25 are apparently integrated and further moved downward, and the two-stage switching mold 25 is shown in FIG. 3 is switched to the lower position in FIG. With the switching of the two-stage switching mold 25, the left and right protrusions of the first forming part M1 of the metal plate material that have only been placed on the top surfaces 23a of the right and left shaping protrusions in the state of FIG. 14 receives a relative thrust by the left and right shaped projections 23 and is bent at a substantially right angle with respect to the side flange portion 13 as shown in FIG. 4, along the inner wall surface 23b of each shaped projection. Molded to stand vertically.

  As described above, by the series of pressing operations from FIG. 2 to FIG. 4, the first flange M1 of the metal plate material has the center flange 11, the pair of left and right webs 12, the pair of left and right side flanges 13, and the side flanges. A pair of left and right projecting pieces 14 bent at a substantially right angle with respect to the portion 13 are formed, and thereby, a primary molded product having an open cross-sectional shape with a transverse section opened to the opposite side to the central flange 11 is formed. Is done.

  When the embossing shown in FIG. 4 is finished, the left and right projecting pieces 14 contact the inner wall surface 23b of the shaped projecting portion, so that they are rapidly cooled by conduction heat transfer, but continue to the left projecting piece 14. The second molding portion M2 that is not in contact with any part of the lower mold 20 and the upper mold 30 and therefore is not cooled by conduction heat transfer.

  The graph of FIG. 13 shows the change with time of the temperature of the first forming part M1 and the second forming part M2 after the metal plate material M is taken out from the heating furnace. In the graph of FIG. 13, the range of 3 to 5 seconds corresponds to the first hot press molding process, and the range of 5 to 6 seconds corresponds to the mold removal / conveyance time of the primary molded product for process switching. At the time of taking out from the heating furnace (at 0 second), the metal plate M was heated to about 900 ° C., but when the metal plate M was set on the lower mold 20 and the embossing by the upper mold 30 was started ( 3 seconds), both the first molding part M1 and the second molding part M2 of the metal plate were at about 800 ° C. At the end of the press after 2 seconds from the start of the press (at 3 seconds) (at the time of 5 seconds), the first molding part M1 that has been sandwiched by the lower mold 20 and the upper mold 30 drops to about 400 ° C. did. On the other hand, during this time, the temperature drop of the second molding part M2 that was not directly contacted by the lower mold 20 and the upper mold 30 was limited to natural cooling. When the primary molded product obtained in the first hot press molding process is removed from the lower mold 20 and set in the second press mold mechanism (at 6 seconds), the first molding part M1 is about 400 ° C. On the other hand, the 2nd shaping | molding part M2 maintained the high temperature state of about 700 degreeC.

[Second hot press forming step]
As shown in FIG. 5, the second press mold mechanism used in the second hot press molding process includes a holding mold 40 as a fixed mold for secondary molding and a horizontal slide mold 50 as a movable mold for secondary molding. It has.

  The holding die 40 has a horizontal upper surface 41 that functions as a support surface of the side flange 13, and a holding groove 42 that extends in the longitudinal direction at the center of the holding die 40 and opens in the upper surface 41. The holding die 40 has a pair of left and right holding protrusions 43 protruding upward from the horizontal upper surface 41. Each holding projection 43 has a substantially rectangular parallelepiped shape, and each has a horizontal guide top surface 43a and a vertical inner wall surface 43b. In the present embodiment, the holding groove 42 of the holding mold 40, the horizontal upper surface 41, and the vertical inner wall surface 43 b of each holding projection 43 cooperate to provide a first open sectional shape of the primary molded product. A holding means for holding the molding part M1 so as not to move in the width direction of the holding mold 40 is constructed.

  The horizontal slide mold 50 has a substantially rectangular parallelepiped shape that can be bridged on the left and right holding projections 43 of the holding mold 40 (see FIG. 7). The horizontal slide mold 50 is located above the holding mold 40 and can slide along the virtual horizontal plane including the horizontal guide top surface 43a of the left and right holding projections 43 so as to cross the holding mold 40 in the width direction ( That is, it can be horizontally reciprocated). 5 to 8 do not show the support / drive mechanism of the lateral slide mold 50.

  As shown in FIG. 5, when the second press die mechanism is on standby, the lateral slide die 50 is disposed at the standby position on the left side of the holding die 40. There, the primary molded product formed in the first hot press forming step is transported and quickly set on the holding die 40 as shown in FIG. When the setting is completed, the central flange 11 and the pair of webs 12 of the primary molded product are arranged in the holding groove 42, the left and right side flanges 13 are placed on the horizontal upper surface 41, and the left and right protruding pieces 14 are left and right. It arrange | positions along the inner wall surface 43b of a holding | maintenance protrusion. Thereby, the 1st shaping | molding part M1 to which the open cross-sectional shape was provided among the primary molded articles is hold | maintained by the holding die 40 so that a movement is impossible. At this time, the second molding portion M2 continuing to the left protruding piece portion 14 protrudes upward from the guide top surface 43a of the left holding protruding portion 43 and takes a posture of standing substantially vertically.

  Immediately after the setting of the primary molded product is completed, the lateral slide mold 50 is moved rightward in the horizontal direction from the standby position in FIG. Then, the second molding portion M2 is pressed rightward by the front end portion 51 of the lateral slide mold 50, and bent so as to push down the second molding portion M2 as the horizontal slide mold 50 moves horizontally. At this time, as described above, the second molding portion M2 maintains a temperature of about 700 ° C. and has a certain flexibility, so that the boundary line position between the left protruding piece portion 14 and the second molding portion M2 is maintained. Thus, the second molding part M2 bends at a substantially right angle with respect to the left protruding piece part 14. As shown in FIG. 7, when the front end portion 51 of the horizontal slide mold 50 reaches the guide top surface 43a of the right holding projection 43, the second molding portion M2 is bent into a substantially complete horizontal state, It is shaped as a horizontal back plate 15 (see FIGS. 10 and 11) that bridges the projecting piece 14. Thereafter, as shown in FIG. 8, the secondary molded product can be removed from the holding mold 40 by horizontally moving the horizontal slide mold 50 in the left direction and returning it to the original standby position. 10 and 11 show the product after being removed from the mold.

  In the graph of FIG. 13, the range of 6 to 8 seconds corresponds to the second hot press forming step, and the range of 8 to 9 seconds is the removal of the secondary molded product from the holding mold 40 and to the cooling place. Corresponds to the transport time. At the time (6 seconds) when the pressing by the horizontal slide mold 50 was started simultaneously with the completion of the setting of the primary molded product to the holding mold 40, the second molded part M2 of the primary molded product maintained a temperature of about 700 ° C. However, at the end of the stamping after 2 seconds from the start of stamping (at 6 seconds) (at 8 seconds), the second molding part M2 dropped to about 300 ° C. During this time, the first molding part M1 starts at about 400 ° C. at the start of stamping (at 6 seconds), becomes about 220 ° C. at 7 seconds after 1 second, and about 180 at 8 seconds after 2 seconds from the start of stamping. Fell to a degree. The second molded part M2 of the primary molded product was about 300 ° C. immediately after being transferred to the cooling place (at 9 seconds), but then dropped to about 200 degrees at 13 seconds after about 4 seconds. did.

[Summary of Embodiment]
Quenching of steel refers to the martensitic transformation of the austenitic metal structure at a high temperature of about 800 to 900 ° C. or higher by rapid cooling, generally from a high temperature of about 900 ° C. to 20 ° C. It is a necessary condition for quenching to cool to 220 ° C. or less at a cooling rate of at least / sec. In this regard, when looking back at the quenching process of the present embodiment, it takes about 8 seconds for the first molded part M1 to reach about 180 ° C., which is definitely below 220 ° C. from about 900 ° C. immediately after furnace exit. The average cooling rate V1 of the first molding part M1 during this period is (900−180) / 8 = 90 ° C./second, which satisfies the above-described quenching requirements. In addition, it takes about 13 seconds for the second molding part M2 to reach about 200 ° C., which is surely below 220 ° C. from about 900 ° C. immediately after exiting the furnace, and the average cooling of the second molding part M2 during this period. The speed V2 is (900−200) / 13 = about 54 ° C./second, which satisfies the requirement for quenching. Therefore, according to the present embodiment, although the quenching conditions are different between the first molding part M1 and the second molding part M2, any part is surely quenched through the first and second hot press molding processes. Thus, strength improvement (hardening of the metal structure) based on quenching is sufficiently achieved.

  As described above, according to the present embodiment, the steps are performed while each part is kept in a quenchable high temperature state with respect to the first molding part M1 and the second molding part M2 of the metal sheet M heated to a quenchable temperature. By adopting a series of procedures of press forming and quenching, a primary molded product with an open cross-sectional shape (Figure 1) while partially simultaneously quenching the primary molded product or secondary molded product at each stage 4) can be changed to a hollow molded article having a closed cross-sectional shape (see FIG. 8). Therefore, according to the stepwise hot press forming method of the present embodiment, the hollow cross-section is substantially or completely closed while taking advantage of the hot press forming in which the metal sheet material M is simultaneously shaped and quenched. The door impact beam main body (see FIGS. 10 and 11) as a molded product having a closed cross-sectional shape can be manufactured smoothly and reliably.

  Incidentally, as shown in FIGS. 10 and 11, the door impact beam main body 10 manufactured through a series of steps from FIG. 1 to FIG. The web 12 and a pair of left and right side flanges 13 are provided. The center flange 11 provides the front surface (lower surface in FIGS. 10 and 11) as a main collision surface with the beam, and the front end portions (FIG. 10 and FIG. 10) of the left and right webs 12 located on both sides in the width direction. 11, the lower ends are connected to each other. Each web 12 is provided at a substantially right angle to the central flange 11, and the two webs 12 are in a substantially parallel facing relationship. At the rear end of each web 12 (the upper end in FIGS. 10 and 11), side flanges 13 are provided so as to extend outward in the width direction, and both side flanges 13 are also substantially parallel to the center flange 11. is there. In addition, the center flange 11, the web 12, and the side part flange 13 shape | mold the main-body part of the 1st shaping | molding part M1 of a metal plate material in the cross-sectional hat type | mold.

  Further, a pair of left and right protruding pieces 14 are provided in the middle of each side flange 13. These projecting piece portions 14 are connected to the outer end portion of the side flange 13 and are erected substantially perpendicular to the side flange 13. Further, a back plate portion 15 is provided at the upper end portion of the left protruding piece portion 14, which is constituted by a second molding portion M <b> 2 bent at a right angle with respect to the left protruding piece portion 14. The back plate portion 15 is provided so as to bridge between the left and right projecting piece portions 14, and has a substantially parallel relationship with the central flange 11 and the side flange 13. 10 and 11, the center flange 11, the left and right webs 12, the left and right side flanges 13, the left and right projecting piece portions 14, and the back plate portion 15 (second molding portion M2) are crossed. A substantially closed closed cross-sectional shape having a substantially convex surface is defined.

  The door impact beam main body 10 shown in FIGS. 10 and 11 is a hollow steel product manufactured by hot press molding, and thus is excellent in mechanical strength and the like despite being relatively lightweight. . In addition, because the cross-sectional shape of the central part of the door impact beam is a substantially convex closed cross-sectional shape, the load resistance in the front-rear direction and the impact absorption performance at the time of collision compared to the door impact beam with a conventional open cross-sectional shape Is greatly improved.

  [Modification] In the above embodiment, as shown in FIG. 9, the metal plate material M in which the second molded part M2 is continuous is used only for one projecting piece part 14 of the first molded part M1, but the first molded part is used. A metal plate material in which the second forming portion M2 ′ is continuous with each of the two projecting piece portions 14 of M1 may be used as a starting material. In that case, as shown in FIG. 12, in the second hot press forming step, a pair of left and right horizontal slide dies 50 are used, and the left and right second moldings respectively continuous with the left and right protruding pieces 14 of the primary molded product. It is preferable that the two back plate portions 15 ′ are hot-formed by bending the portion M2 ′ from the vertical standing state to the horizontal state.

  [Modification] In the embodiment described above, the steel plate as described above is used as the metal plate M, but a rust-proof steel plate to which galvanization has been applied may be used. Usable galvanized steel sheets include, as additive elements, C: 0.15-0.25 mass%, Si: 0.15-0.35 mass%, Mn: 0.5-2.0 mass%, A steel sheet containing Cr: 0.1 to 0.25% by mass and B: 0.0005 to 0.0020% by mass, with the remainder occupied by Fe and impurity elements can be exemplified. In addition, when using the galvanized steel steel plate illustrated here, in order to avoid the grain boundary cracking in the galvanized layer, the start temperature of the first hot press forming is set slightly lower than that in the above embodiment. It is preferable to do.

  [Modification] In the first and second press mold mechanisms, a mold cooling structure such as a cooling water circulation passage may be provided inside each mold. In that case, it is possible to prevent a situation in which the temperature of each mold gradually increases due to the continuous mold pressing operation, and maintain the certainty of quenching.

  [Modification] In the above embodiment, in the second hot press forming step, the primary molded product is held immovably by using the holding mold 40 shown in FIG. 5, but is used in the first hot press forming step. The obtained lower mold 20 may be used as it is in place of the holding mold 40 in the second hot press forming step. Specifically, after the upper mold 30 is separated upward from the state shown in FIG. 4 where the press molding of the primary molded product is completed, the lower mold 20 in a state where the primary molded product is held (= fixed base 21 + two-stage switching) The horizontal slide mold 50 is made to stand by on the upper left side of the mold 25). Then, in the same manner as the series of processes shown in FIGS. 6, 7, and 8 in the above-described embodiment, the second molding part M <b> 2 of the primary molded product held by the lower mold 20 is subjected to the second by the lateral slide mold 50. Hot press molding is performed. According to this modified example, it is not necessary to prepare the holding mold 40 separately from the lower mold 20, and the equipment for press molding can be further simplified. In addition, by making the lower mold 20 after the completion of the first hot press molding function as a holding mold, the continuity between the first hot press molding process and the second hot press molding process is improved, A series of steps can be simplified. The lower mold 20 in this modified example has a role as a fixed mold for primary molding that constitutes the first press mold mechanism and a role as a fixed mold for secondary molding that constitutes the second press mold mechanism. I will also serve.

The perspective view of a 1st press type | mold mechanism. The perspective view of the 1st hot press molding process (at the time of the setting of a workpiece | work). The perspective view of the 1st hot press molding process (at the time of shallow die pressing). The perspective view of the 1st hot press molding process (at the time of deep die pressing). The perspective view of a 2nd press type | mold mechanism. The perspective view of the 2nd hot press molding process (at the time of the setting of a workpiece | work). The perspective view of the 2nd hot press molding process (at the time of a die pressing). The perspective view of the 2nd hot press molding process (at the time of mold return). The top view of a metal plate material. The perspective view which shows an example of a closed cross-section shape goods. FIG. 11 is a schematic cross-sectional view of a closed cross-sectional portion of the closed cross-sectional shape product of FIG. 10. The schematic sectional drawing of the closed cross-section part of the closed cross-section shape goods of the example of a change. The graph which shows the time-dependent change of the temperature of each part in a hot press molding process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Body part (closed cross-section shape product) of door impact beam, 11 ... Center flange, 12 ... Web, 13 ... Side flange, 14 ... Projection piece part in metal plate material and closed cross-section shape product, 15, 15 '... Back Plate part (according to second molding part M2 or M2 '), 20 ... lower mold (primary molding fixed mold constituting the first press mold mechanism), 21 ... fixed base, 25 ... two-stage switching mold, 30 ... upper Mold (movable mold for primary molding that constitutes the first press mold mechanism), 40 ... Holding mold (fixed mold for secondary molding that constitutes the second press mold mechanism), 50 ... Horizontal slide mold (second press) Movable mold for secondary forming constituting mold mechanism), M ... metal plate material, M1 ... first molding part, M2, M2 '... second molding part.

Claims (4)

A plate material preparation step of preparing a metal plate material having a flat plate-shaped first formed portion and a flat plate-shaped second formed portion;
A heating step of heating the entire metal plate to a quenchable temperature;
Using the first press die mechanism having a temperature lower than the quenchable temperature, press forming is performed on the first molded portion in the quenchable temperature state of the metal plate material, whereby the first molded portion is formed. A first hot press molding step of obtaining a primary molded product having an open cross-sectional shape with a transverse cross section opened on one side and quenching the first molded portion;
Using the second press die mechanism having a temperature lower than the quenchable temperature, the primary molded product is subjected to press bending to the second molded part in the quenchable temperature state of the primary molded product. A secondary molded product is obtained in which the open cross-sectional shape in the first molded part is changed to a hollow closed cross-sectional shape in which the transverse cross-section is almost or completely closed by the second molded part formed by bending, and the second molded part is obtained. A method for producing a closed cross-sectional shape product by hot pressing, comprising: a second hot press forming step of quenching the part. The metal plate material prepared in the plate material preparation step includes a flat plate-shaped first forming portion including a pair of protruding piece portions at both ends, and a flat plate-shaped first shape continuous with at least one of the pair of protruding piece portions. 2 molding parts,
In the first hot press forming step, a center flange extending in the longitudinal direction with respect to the first forming portion of the metal plate material, a pair of webs whose front end portions are connected by the center flange, and a rear end of each web By forming a pair of side flanges extending outward in the width direction from the section and the pair of projecting pieces bent substantially at right angles to each side flange, the cross section is opposite to the center flange While obtaining a primary molded product having an open cross-sectional shape opened to the side,
In the second hot press molding step, the open cross-sectional shape of the first molded part of the primary molded product is substantially the same with respect to the central flange, the pair of webs, the pair of side flanges, and the side flanges. The cross section is changed to a substantially convex, almost closed, closed closed section shape defined by the pair of protruding pieces bent at right angles and the bent second molded portion. A method for producing a closed cross-sectional product by hot pressing according to claim 1, wherein a secondary molded product is obtained. The first press die mechanism used in the first hot press molding step is:
A fixed mold for primary molding composed of a fixed base, and a two-stage switching mold supported by the fixed base so as to be able to switch between the hat mold cross-section molding position and the protruding piece bending molding position;
A primary molding movable mold provided so as to be able to approach and separate from the primary molding fixed mold,
By pressing the primary molding fixed mold in which the two-stage switching mold is arranged at the hat mold cross-section molding position with the primary molding movable mold, the central flange, Giving a hat-shaped cross-sectional shape defined by a pair of webs and the pair of side flanges,
Next, the primary molding stationary mold is further pressed by the primary molding movable mold until the position of the two-stage switching mold is switched from the hat mold cross-section molding position to the projecting piece bending molding position, whereby the first of the metal plate material is 3. A product with a closed cross-sectional shape by a hot press according to claim 2, wherein the primary molded product is obtained by bending a pair of projecting pieces of the molded portion substantially at right angles to the side flanges. Production method. The second press die mechanism used in the second hot press molding step is
A fixed mold for secondary molding for holding the first molded part provided with the open cross-sectional shape of the primary molded product;
For secondary molding provided to be slidable across the secondary molding fixed die in the width direction so as to bend over the second molding part of the primary molded product held by the secondary molding fixed die. A method for producing a product with a closed cross-section by hot pressing according to claim 1, 2 or 3, further comprising a movable die.

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