JP5855914B2 - Hydraulic forming method - Google Patents

Description

The present invention relates to a hydroformed how the liquid is formed into a shape with a corner while applying a pressing to fluid pressure encapsulated tubular member radially inward.

  Conventionally, as one of hydraulic forming methods for a vehicle member having a closed cross section such as a front lower arm or a torsion beam, for example, a pipe member is set in a plurality of forming dies, and the inside of the set pipe member is processed. Liquid sealing molding (liquid sealing molding) is known in which a tubular member having a circular cross section is plastically deformed by molding a vehicle member having corners by enclosing a liquid and applying a hydraulic pressure.

The hydraulic forming method described in Patent Document 1 will be described with reference to FIG.
As shown in FIGS. 12 (a) and 12 (b), the hydroforming apparatus 50 of Patent Document 1 includes a nozzle 51 that is attached to both ends of the pipe member WO in a sealed state and injects a working liquid into the pipe member WO. , A pair of first molds 52 that sandwich the pipe member WO to which the hydraulic pressure is applied from both left and right sides and press it radially inward, and a pipe member prior to the pressing operation of the pair of molds 52 The pair of second molding dies 53 sandwiching the WO from above and below and the pair of second molding dies 53 previously pressing the pipe member WO from above and below are brought into contact with each other to prevent movement in the mold opening direction. A stopper 54 and the like are provided.

Normally, in such a hydraulic forming method, the hydraulic pressure inside the pipe member is controlled so that the molding time and the internal pressure of the pipe member are in a relationship as shown in FIG. 13, and the pipe member is processed into a desired product shape. ing.
First, after enclosing the working fluid inside the pipe member, the pipe member internal pressure suddenly rises from T1 when the preceding mold that sandwiches the pipe member in advance contacts the pipe member, and reaches a predetermined pipe member internal pressure. The machining fluid is discharged from the inside of the pipe member, and the internal pressure of the pipe member is kept constant regardless of the pressing operation of the pre-molding die. The succeeding mold clamping operation is started after the preceding mold clamping operation. The subsequent mold contacts the tube member at T2. After T2, the discharge of the machining fluid is controlled so that the internal pressure of the pipe member becomes constant according to the sandwiching operation between the preceding mold and the subsequent mold.
The internal pressure of the pipe member is kept constant from T3 when the preceding mold and the subsequent mold reach the bottom dead center to T4 after a predetermined time has elapsed, and then the machining fluid is discharged from the inside of the pipe member.

  In the hydroformed product, the shape is formed by flowing the metal material of the pipe member in the circumferential direction. Therefore, the hydroformed product with corners has a large amount of deformation at the corners, so the metal material that flows from the corners to parts other than the corners increases, and the plate thickness of the corners is other than the corners. There was a problem that it was thinner than the thickness of the part. In view of this, there has been proposed a technique for equalizing the thickness of the hydroformed product by suppressing the reduction in the thickness of the corner.

  In the hydraulic molding method described in Patent Document 2, the molding die is divided into a plurality of fixed dies that mold corners of a hydraulic molded product and a plurality of movable dies that can slide toward the molding space. After dividing the fixed die and movable die into positions corresponding to the corners, where the tangent line drawn with respect to the molding surface does not cross the molding space at the division position, and after clamping the mold, The movable die is pushed and operated radially inward of the pipe member while applying a predetermined hydraulic pressure to the pipe member in the space. Thereby, it can form, without making the metal material of pipe members other than a corner | angular part flow actively to a corner | angular part, and reducing the corner | angular part cross section of a hydraulic-molded article.

JP 2004-181477 A JP 2000-343141 A

The hydroforming method of Patent Document 2 can control the thickness of the corners of the hydroformed product and suppress the decrease in the thickness of the corners to equalize the thickness of the hydroformed product. Is possible.
However, in this hydraulic molding method, it is necessary to provide a plurality of fixing dies corresponding to each corner of the hydraulic molded product, which may complicate the molding apparatus and increase the production cost. Moreover, as the number of fixed dies corresponding to the corners increases, the dividing line between the fixed die and the movable die increases, so it is necessary to rework the dividing line transferred to the hydroformed product, and further increase the production cost. May increase.

An object of the present invention is to provide while achieving a reduction in the simplicity and production cost of the apparatus, hydroformed how that can increase the thickness of the corner portions of the hydroformed product a.

  According to a first aspect of the present invention, there is provided a hydraulic molding method comprising: a first molding die that presses a tube member enclosing a liquid radially inward; and a tube member that presses the pipe member radially inward from a direction different from the first molding die. Alternatively, in the hydraulic molding method in which the tube member is pressed by a plurality of second molding dies to form a shape having corners while applying hydraulic pressure, the first and second molding dies are formed on the tube member. After the contact, the hydraulic pressure holding step of holding the hydraulic pressure inside the pipe member at the post-contact hydraulic pressure, and the hydraulic pressure inside the pipe member before the first and second molds reach bottom dead center And a hydraulic pressure lowering step for lowering the pressure to the hydraulic pressure before bottom dead center set lower than the post-contact hydraulic pressure.

  In this hydraulic pressure forming method, before the first and second molds reach the bottom dead center, the hydraulic pressure inside the tube member is reduced to the hydraulic pressure before the bottom dead center set lower than the post-contact hydraulic pressure. Since the hydraulic pressure lowering step is provided, the hydraulic pressure inside the tube member before the first and second molding dies reach the bottom dead center can be lowered, and the bottom dead center by the first and second molding dies. The pressing operation before reaching can be used as a flow promoting operation for causing the metal material of the pipe member to flow from a portion other than the corner to the corner.

According to a second aspect of the present invention, in the first aspect of the invention, the second molding die has a preceding pressing step of pressing the pipe member inward in the radial direction prior to the pressing operation of the first molding die. It is a feature.
The invention of claim 3 is characterized in that, in the invention of claim 2, when the second mold is in a position near the bottom dead center, the first mold contacts the pipe member.

  The invention of claim 4 is the invention of any one of claims 1 to 3, wherein in the hydraulic pressure holding step, the post-contact hydraulic pressure is P1 (MPa), the thickness of the pipe member is L (mm), and the pipe When the yield strength of the member is A (MPa) and the outer diameter of the pipe member is D (mm), P1 ≧ L × (A / D) × 3.25 is satisfied.

  The invention of claim 5 is the invention of any one of claims 1 to 4, wherein, in the hydraulic pressure lowering step, the hydraulic pressure before bottom dead center is P2 (MPa), and the plate thickness of the pipe member is L (mm). When the tensile strength of the pipe member is B (MPa) and the outer diameter of the pipe member is D (mm), L × B / 108 ≦ P2 ≦ L × B / 36 is satisfied.

  According to the first aspect of the present invention, the hydraulic pressure inside the pipe member before the first and second molds reach the bottom dead center can be lowered and the pressure before the bottom dead center is reached by the first and second molds. Since the operation can be used as a flow promoting operation in which the metal material of the pipe member flows from the portion other than the corner to the corner, the reduction in the plate thickness of the corner of the tube member is suppressed and the molding die dedicated to the corner is omitted and It is possible to omit the process of repairing the dividing line by the mold. Therefore, it is possible to increase the thickness of the corner of the hydroformed product while simplifying the apparatus and reducing the production cost.

According to invention of Claim 2, the metal material of the pipe member for making it flow to a corner | angular part can be collected in the press part by a 1st shaping | molding die.
According to invention of Claim 3, the metal material of the pipe member for making it flow to the corner | angular part collected by the press part by a 1st shaping | molding die can be increased.

According to the fourth aspect of the present invention, it is possible to obtain a pressure range of the post-contact hydraulic pressure in which the pipe member can be expanded and the pipe member is not damaged.
According to the invention of claim 5, the lower limit value of the hydraulic pressure before the bottom dead center at which the shape of the hydraulic molded product can be molded, and the upper limit of the hydraulic pressure before the bottom dead center at which the metal material of the pipe member can flow while being clamped. Value.

It is a right side top view of the hydraulic forming apparatus which concerns on the Example of this invention. It is the II-II sectional view taken on the line of FIG. It is process drawing which concerns on a hydraulic forming method, (a) shows the initial state of a preceding press process, (b) shows the late stage state of a preceding press process, (c) shows the initial state of a hydraulic pressure holding process. (D) The latter-stage state of the hydraulic pressure holding process is shown. It is a time chart of the pipe member internal pressure of the hydraulic forming method concerning an example. It is a perspective view of the fluid pressure molded product concerning the 1st verification experiment. It is an experimental result which concerns on a 1st verification experiment. It is a graph of a 1st experimental result. It is an experimental result which concerns on a 2nd verification experiment. It is a graph of a 2nd experimental result. It is an experimental result which concerns on a 3rd verification experiment. It is a graph of a 3rd experimental result. It is a conventional hydraulic forming apparatus, (a) shows a side view, (b) shows a longitudinal sectional view. It is a time chart of the pipe member internal pressure concerning the conventional hydraulic forming method.

Hereinafter, modes for carrying out the present invention will be described based on examples. In this embodiment, an example applied to forming a torsion beam for a vehicle having a closed cross section is shown. The direction in which the cam mold moves is the left-right direction, and the axial direction of the tube member arranged in the fixed mold is the front-back direction. Explain .

A first embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 and 2, a hydraulic forming apparatus 1 used in this hydraulic forming method includes a lower mold 2 fixed on a floor, and an upper part that can be vertically separated from the lower mold 2 in the vertical direction. A die 3, a pair of left and right cam dies 4 (second molding die) as a pre-molding die that forms the shape of the left and right side portions perpendicular to the axis of the metal pipe member W having a circular cross section, and the pipe member W The fixed mold 5a and the movable mold 5b (first mold) as the subsequent molds that form the shape of the upper and lower side parts orthogonal to the left and right side parts of the tube member W A pair of nozzle members 6 and the like are provided. In addition, since the hydraulic forming apparatus 1 has a left-right symmetric structure, the description of the left side portion will be omitted and the description of the right side portion will be mainly given below.

  The lower mold 2 is positioned and mounted on the tube member W, and has a fixed mold 5a provided with a molded part, and a pair of left and right cam molds 4 provided on both the left and right sides with the fixed mold 5a interposed therebetween. Each of the left and right paired cam molds 4 is mounted, and the upper part of the lower mold 2 is configured by a pair of left and right slide members 7 formed to be slidable in the left-right direction. The right end of the right slide member 7 is formed with an inclined portion that moves downward toward the right.

  The upper mold 3 is connected to a drive device (not shown) that can reciprocate in the vertical direction, and a movable mold 5b having a molding portion and a pair of left and right disposed on both the left and right sides of the movable mold 5b. The cam member 8 or the like. At the left end portion of the right cam member 8, an inclined portion that moves downward toward the right side is formed, and is formed to be slidable with respect to the inclined portion of the right slide member 7.

  The pair of front and rear nozzle members 6 are attached to the front and rear ends of the tube member W in a sealed manner, and at least one nozzle member 6 fills the inside of the tube member W with a processing liquid such as water or processing oil. At the same time, in order to adjust the liquid pressure inside the pipe member W, the machining fluid can be adjusted and discharged from the inside of the pipe member W. As a result, when the upper mold 3 is lowered after the machining liquid is sealed in the tube member W, the pair of left and right slide members 7 approaches the tube member W in synchronization with the downward movement of the pair of left and right cam members 8. The pair of left and right cam molds 4 press the tube member W radially inward from the left and right sides. After the start of pressing by the pair of left and right cam molds 4, the movable mold 5 b presses the tube member W from the upper side in the radial direction, and the pair of left and right cam molds 4 and the movable mold 5 b are simultaneously positioned at the bottom dead center in the pressing operation. Is set to reach.

  Next, based on the process diagram of FIG. 3 and the time chart of the pipe member W internal pressure of FIG. The hydraulic molded product molded by the present hydraulic molding method is a vehicle member having a closed cross section with a rectangular cross section having four corners extending in the axial direction. These corners are formed at a boundary (divided) portion between the fixed mold 5 a and the cam mold 4 or between the movable mold 5 b and the cam mold 4.

  First, as a preparatory step prior to the start of processing, the tube member W is positioned and fixed at a processing position on the fixed mold 5a, and a pair of front and rear nozzle members 6 are attached to both ends of the tube member W and a processing liquid is enclosed. Performed in advance.

Next, the upper die 3 is lowered from the initial position, and the preceding pressing process is started.
As shown in FIG. 3A, as the upper mold 3 is lowered, the pair of left and right cam molds 4 are moved from the left and right sides toward the inside in the radial direction of the pipe member W. Similarly, the movable mold 5b is The pipe member W is moved from the upper side toward the radial inner side. As shown in FIG. 4, at the start of the preceding pressing step, at the time T1, a pair of left and right cam dies 4 comes in contact with the left and right side portions of the tube member W in advance of the movable die 5b, and the left and right sides of the tube member W Start pinching the part. By the pressing operation of both cam molds 4, the pipe member W is plastically deformed radially inward, and the hydraulic pressure P inside the pipe member W increases rapidly.

  As shown in FIG. 3B, in the latter stage of the preceding pressing step, the pair of left and right cam molds 4 further press the left and right side portions of the tube member W, so that the tube member W is deformed into an elliptical cross section. To do. As the hydraulic pressure P inside the tube member W increases, the contact area between the molded portions of both cam molds 4 and the tube member W increases according to the elapsed time from the start of molding. As shown in FIG. 4, the hydraulic pressure P inside the pipe member W maintains a post-contact hydraulic pressure P1 that is set so that the pipe member W can be expanded and the pipe member W is not damaged, for example, 70 MPa. Further, the processing liquid discharged through the nozzle member 6 is adjusted.

After the preceding pressing step, a hydraulic pressure holding step is performed.
As shown in FIG. 3C, a position where substantially the entire molding part of both cam molds 4 and the left and right side portions of the tube member W are in surface contact, so-called a pair of left and right cam molds 4 is located near the bottom dead center. At time T2 (see FIG. 4), the movable die 5b comes into contact with the upper portion of the tube member W curved in an arc shape in cross section upward, and the hydraulic pressure holding process is started. As shown in FIG. 4, in the hydraulic pressure holding step, the hydraulic pressure P inside the pipe member W is held at 70 MPa in the same manner as described above according to the pressing operation of the pair of left and right cam molds 4 and the movable mold 5b. It has been adjusted.

  As shown in FIG. 3 (d), after the movable mold 5b contacts the upper portion of the tube member W, the pair of left and right cam molds 4 and the movable mold 5b press the tube member W radially inward, and the tube member W is plastically deformed into a rectangular shape. In the preceding pressing step, the upper curved portion length (area) of the tube member W is formed to be larger than the molded portion length (area) of the movable mold 5b. The length (area) corresponding to the difference is supplied to the boundary (divided) portion between the fixed mold 5a and the cam mold 4 or the movable mold 5b and the cam mold 4 in order to form the corners of the hydroformed product. Yes.

Next, a hydraulic pressure lowering step is performed before the pair of left and right cam molds 4 and the movable mold 5b reach the bottom dead center position. As shown in FIG. 4, immediately before T3 when the pair of left and right cam molds 4 and the movable mold 5b reach bottom dead center, the hydraulic pressure P inside the pipe member W is contacted from the post-contact hydraulic pressure P1 (70 MPa). The pressure is lowered to the fluid pressure P2 before the bottom dead center which is set lower than the rear fluid pressure P1. The hydraulic pressure P2 before the bottom dead center is a pressure value set between a lower limit value at which the shape of the hydraulic molded product can be molded and an upper limit value at which the metal material of the pipe member W can flow while clamping, for example, 10 MPa. Is set to
In the hydraulic pressure lowering step, since the hydraulic pressure P inside the pipe member W is reduced, the metal material inside the pipe member W is moved to a portion other than the corners by the pressing operation of the pair of left and right cam molds 4 and the movable mold 5b. It can be made to flow from the site to the corner.

  After the hydraulic pressure lowering step, a second hydraulic pressure holding step for holding the hydraulic pressure P inside the pipe member W at the hydraulic pressure P2 before the bottom dead center for a predetermined time is performed. In the second hydraulic pressure holding step, the shape of the molded hydraulically molded product is stabilized. As shown in FIG. 4, after the machining fluid is discharged from the inside of the tube member W through the nozzle member 6 at time T4, the upper mold 3 is raised to form a pair of left and right cam molds 4 and a movable mold 5b. Opening this hydraulic pressure forming process ends.

Next, the effect of this hydroforming method demonstrated by three types of verification experiments will be described with reference to FIGS.
First, the first verification experiment will be described with reference to FIGS.
In the first verification experiment, a hydraulically molded product having a rectangular cross section (Comparative Examples Y1 to Y3) formed by varying the hydraulic pressure corresponding to the post-contact hydraulic pressure P1 inside the pipe member in the conventional hydraulic molding method. The plate thickness of the corners is compared with that of a hydraulically molded product having a rectangular cross section formed by the hydraulic molding method of this example.

The experimental conditions for the first verification experiment will be described.
As shown in FIG. 5, the material: SUS429 (steel pipe formed by seam welding of a stainless steel plate), material strength: 540 MPa, plate thickness: 2 mm, the hydraulic forming method and the hydraulic pressure lowering step of the present example. By using a conventional hydroforming method that does not have, the hydroformed products having the same shape were molded, and the plate thicknesses of the corners X1 to X4 of the hydroformed products were compared. The mold clamping force of the molding machine is 400 t.

  In Comparative Examples Y1 to Y3, the same hydraulic molding apparatus 1 as in this example is used. Similarly to this example, after a pair of left and right cam molds 4 press the pipe member, the pipe member is formed by the movable die 5b. Even after the pair of cam molds and the movable mold reach the bottom dead center, the internal pressure of the pipe member is maintained until the machining liquid is discharged (see FIG. 4). In Comparative Examples Y1 to Y3, the hydraulic pressure during the hydraulic pressure holding period is set to 40 MPa, 50 MPa, and 70 MPa, respectively. Note that, as described above, the hydraulic forming method of the present embodiment is less than the post-contact hydraulic pressure P1 (70 MPa) inside the pipe member immediately before the pair of left and right cam molds and the movable mold reach the bottom dead center. It is a specification to reduce to the fluid pressure P2 before dead center (10 MPa).

  As shown in FIGS. 6 and 7, in the plate thicknesses of the corner portions X1 to X4 of the comparative examples Y1 to Y3, none of the corner portions exceeded the original plate thickness of 2 mm of the tube member. However, in the hydroformed product by the hydroforming method of the present embodiment, all the corners X1 to X4 are molded to a plate thickness exceeding the original plate thickness of 2 mm of the pipe member. The thicknesses of X1 and 4 are increased by 10% or more than the original thickness.

The second experimental result will be described with reference to FIGS.
In the second experiment, the correlation between the post-contact hydraulic pressure P1 and the peripheral length increase rate of the pipe member is detected, and the relationship between the post-contact hydraulic pressure P1 and the formability of the pipe member is determined. The experimental condition of this second experiment is that when forming a pipe member having an outer diameter of 65 mm and an initial peripheral length of 204.2 mm by the hydraulic molding method of this embodiment, the post-contact hydraulic pressure P1 is set to 0 to 70 MPa every 10 MPa. Molded differently.

Generally, in order to ensure the moldability by the hydraulic molding method, at least a circumference increase rate of about 2% is required. Therefore, as shown in FIG. 9, in the hydraulic pressure holding step, the post-contact hydraulic pressure is P1 (MPa), the tube member thickness is L (mm), the tube member yield strength is A (MPa), and the tube member. When the outer diameter is D (mm), by satisfying the relational expression shown in the following equation (1), it is possible to obtain the lower limit value of the post-contact hydraulic pressure P1 at which the pipe member can be expanded and the pipe member is not damaged. And the optimum pressure range of the post-contact hydraulic pressure P1 can be set.
P1 ≧ L × (A / D) × 3.25 (1)

A third experiment will be described based on FIGS.
The third experiment detects the correlation between the fluid pressure P2 before the bottom dead center and the corner plate thickness of the pipe member, and determines the relationship between the fluid pressure P2 before the bottom dead center and the increasing tendency of the corner plate thickness. doing. The experimental conditions of the third experiment are the same as the hydraulic molding method of the present example in the first experiment. In molding, the hydraulic pressure P2 before bottom dead center is varied from 0 to 70 MPa every 10 MPa. ing.

As shown in FIG. 11, when the hydraulic pressure P2 before the bottom dead center is less than 10 MPa, the shape of the hydroformed product is deformed, and when the hydraulic pressure P2 before the bottom dead center exceeds 30 MPa, the increase in the thickness of the corners is insignificant. It was enough.
Therefore, in the hydraulic pressure lowering step, the hydraulic pressure before bottom dead center is P2 (MPa), the plate thickness of the pipe member is L (mm), the tensile strength of the pipe member is B (MPa), and the outer diameter of the pipe member is D ( mm)), the lower limit value of the hydraulic pressure P2 before bottom dead center at which the shape of the hydraulic pressure molded product can be formed by satisfying the relational expression shown in the following formula (2), and the metal material of the pipe member while clamping the mold Can be obtained as the upper limit value of the hydraulic pressure P2 before the bottom dead center.
L × B / 108 ≦ P2 ≦ L × B / 36 (2)
A more preferable range of the hydraulic pressure P2 before the bottom dead center can be expressed by the following formula (3).
L × B / 108 ≦ P2 ≦ L × B / 54 (3)

Next, operations and effects of the hydraulic forming method according to the first embodiment will be described.
In this hydraulic pressure forming method, the bottom dead center in which the hydraulic pressure P in the pipe member W is set lower than the post-contact hydraulic pressure P1 before the pair of left and right cam molds 4 and the movable mold 5b reach the bottom dead center. Since a hydraulic pressure lowering step for reducing the hydraulic pressure to the pre-point hydraulic pressure P2 is provided, the hydraulic pressure P inside the pipe member W before the pair of left and right cam molds 4 and the movable mold 5b reach the bottom dead center is reduced. The pressing operation before reaching the bottom dead center by the pair of left and right cam molds 4 and the movable mold 5b can be used as a flow promoting operation for causing the metal material of the pipe member W to flow from a portion other than the corner portion to the corner portion. Can do. Therefore, it is possible to suppress the reduction of the thickness of the corner portion of the pipe member W, omit the molding die dedicated to the corner portion, and omit the process of correcting the dividing line by the molding die, thereby simplifying the apparatus and reducing the production cost. The thickness of the corners of the hydroformed product can be increased.

Prior to the pressing operation of the movable mold 5b, the pair of left and right cam molds 4 has a preceding pressing process of pressing the tube member W radially inward, so that the metal of the tube member W for flowing to the corner portion The material can be collected in the pressing portion facing the molding portion of the movable mold 5b.
When the pair of left and right cam molds 4 are in the vicinity of the bottom dead center, the movable mold 5b comes into contact with the tube member W, so that the metal material of the tube member for flowing to the corners collected at the pressed portion by the movable mold 5b. Can be increased.

  In the hydraulic pressure holding step, when the post-contact hydraulic pressure is P1 (MPa), the thickness of the pipe member is L (mm), the yield strength of the pipe member is A (MPa), and the outer diameter of the pipe member is D (mm) In order to satisfy P1 ≧ L × (A / D) × 3.25, a pressure range of the post-contact hydraulic pressure P1 in which the tube member W can be expanded can be obtained.

  In the hydraulic pressure lowering step, the hydraulic pressure before bottom dead center is P2 (MPa), the plate thickness of the pipe member is L (mm), the tensile strength of the pipe member is B (MPa), and the outer diameter of the pipe member is D (mm). In order to satisfy L × B / 108 ≦ P2 ≦ L × B / 36, the lower limit value of the fluid pressure P2 before bottom dead center at which the shape of the hydroformed product can be formed, and the metal material of the pipe member while clamping the mold Can be obtained as the upper limit value of the hydraulic pressure P2 before the bottom dead center.

  Since the hydraulic molded product is molded by the hydraulic molding method according to claim 1 and the hydraulic molded product is a vehicle member, the apparatus is simplified and the production cost is reduced. Thus, a vehicle member having an increased plate thickness at the corners can be obtained.

Next, a modification in which the above embodiment is partially changed will be described.
1] In the above-described embodiment, an example in which the present invention is applied to a method for forming a torsion beam for a vehicle has been described. However, a member having a closed cross section, such as a front lower arm, a rear cross member, an exhaust pipe, a front pillar reinforcement, and a roof side rail. As long as it is any member, it may be applied to a member other than the vehicle.

2] In the above embodiment, an example of a pair of cam molds (second molding mold) that moves in the left-right direction and a movable mold (first molding mold) that moves in the vertical direction has been described. However, it is also possible to form a complex hydroformed product using three or more molds in order to mold in three or more molding directions. In this case, the hydraulic pressure reduction step is performed after the last mold comes into contact with the pipe member and before all the molds reach the bottom dead center.

3] Further, in the present invention, by controlling the positions of the fixed mold and the movable mold when the bottom dead center is reached, it is possible to mold the shape of the hydraulic molded product in which the shear center is eccentric by a predetermined amount from the centroid. is there. By performing the eccentricity, the roll rigidity changes. Therefore, the controllability can be improved by controlling the amount of eccentricity according to the vehicle type. As the equipment configuration when decentering, for example, the lower side is a fixed type and the upper side, the left side and the right side are movable types, the lower side and the left side are fixed types, the upper side and the right side are movable types, and the entire side is movable type In order to decenter the hydroformed product, a combination in which the lower side and the left side are fixed types and the upper side and the right side are movable types is effective.

As a specific eccentric method, each mold is formed so that the central axis of the cross-sectional shape of the hydroformed product formed by the stop position of each mold when reaching bottom dead center and the centroid of the pipe member at the initial position are different. By setting so as to operate, the hydroformed product can be decentered. Further, after preliminarily bending the single centroid tube member, it can be easily decentered by applying a part of the hydroforming process.
4] When the short side and the long side are present in the hydroformed product, the mold for forming the long side is set to be a fixed mold (or a pre-molding mold), and the short side is a movable mold as a subsequent mold. It is possible to increase the thickness of the sheet further by molding.

5) In the above-described embodiment, an example in which the corner portion of the hydraulic-molded product has a substantially right-angle shape has been described. However, the shape of the molded product may be such that the upper side (lower side) and the side side are connected in a gently curved shape. In this case, even if the mold split position is set in the curved portion, the hydraulic pressure is lowered before the bottom dead center of the succeeding mold, so that the pipe member can be prevented from being damaged by the edge of the mold split portion. .
6) In addition, those skilled in the art can implement the present invention in various forms added with various modifications without departing from the spirit of the present invention, and the present invention includes such modifications. is there.

The present invention Oite the hydroformed how the liquid is formed into a shape with a corner while applying a pressing to fluid pressure encapsulated tubular member radially inward, first, second mold By reducing the hydraulic pressure inside the pipe member before reaching the bottom dead center, it is possible to increase the thickness of the corners of the hydraulic molded product while simplifying the device and reducing the production cost. it can.

DESCRIPTION OF SYMBOLS 1 Hydraulic forming apparatus 4 Cam type | mold 5a Fixed mold | type 5b Movable type P Hydraulic pressure P1 Hydraulic pressure P2 after contact Hydraulic pressure W before bottom dead center W Pipe member

Claims (5)

The first mold for pressing the tube member in which the liquid is sealed radially inward, and the one or more second molds for pressing the tube member radially inward from a direction different from the first mold. In the hydraulic forming method of forming a shape with corners while pressing the pipe member and applying hydraulic pressure,
After the first and second molds are in contact with the pipe member, a hydraulic pressure holding step for holding the hydraulic pressure inside the pipe member at the post-contact hydraulic pressure;
Before the first and second molds reach the bottom dead center, the fluid pressure lowering step of reducing the fluid pressure inside the pipe member to the fluid pressure before the bottom dead center set lower than the fluid pressure after the contact. When,
A hydraulic forming method characterized by comprising:   The hydraulic molding method according to claim 1, further comprising a preceding pressing step in which the second molding die presses the pipe member inward in the radial direction prior to the pressing operation of the first molding die.   3. The hydraulic molding method according to claim 2, wherein when the second mold is in a position near the bottom dead center, the first mold comes into contact with the pipe member. In the hydraulic pressure holding step, the post-contact hydraulic pressure was P1 (MPa), the pipe member plate thickness was L (mm), the pipe member yield strength was A (MPa), and the pipe member outer diameter was D (mm). When
P1 ≧ L × (A / D) × 3.25
The hydraulic forming method according to any one of claims 1 to 3, wherein: In the fluid pressure lowering step, the fluid pressure before bottom dead center is P2 (MPa), the plate member thickness is L (mm), the tube member tensile strength is B (MPa), and the tube member outer diameter is D (mm). When
L × B / 108 ≦ P2 ≦ L × B / 36
The hydraulic forming method according to any one of claims 1 to 4, wherein: