JP2004268096A - Hydroforming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydroforming method which attains a forming upto a large tube expansion ratio without causing burst or buckling. <P>SOLUTION: In the hydroforming method in which a metallic tube is set in a die and in which, after clamping, an internal pressure and an axial thrusting force are imparted to the metallic tube; while being expanded in one direction of the tube cross section, the metallic tube is deformed for two times the wall thickness to 1.4 times the diameter of the base tube (except the equal diameter) in the direction orthogonal to that one direction. Then, while being expanded in the direction orthogonal to that one direction in the cross section, the metallic tube is formed to two times the wall thickness to 1.4 times the post-deformation width in that one direction. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is used for manufacturing exhaust system parts, suspension system parts, and the like for automobiles. A metal pipe is put into a divided mold, and after clamping the mold, the internal pressure and the pipe axial direction are filled in the metal pipe. The present invention relates to a hydroforming method for forming into a predetermined shape by applying a pressing force.
[0002]
[Prior art]
In recent years, hydroforming technology has been attracting attention in the automotive field as one of the means of cost reduction and weight reduction by reducing the number of parts, and has been adopted in actual vehicles in Europe and the United States for several years, and in Japan since 1999 Application has also started. Since then, the number of parts to which hydroforming has been applied has been increasing year by year, and the market size has been greatly expanded.
[0003]
[Problems to be solved by the invention]
One of the technical advantages of hydroforming when comparing hydroforming and pressing is that large deformation is possible. FIG. 1 shows a distortion state diagram generated in hydroforming (marked by ●) and press working (marked by □). In general, in press working, deformation is performed in a region from a biaxial tension state to a uniaxial tension state through a plane strain state. The equibiaxial tension state refers to a state in which the tensile strain in the X direction acts equally to the tensile strain in the direction perpendicular to the X direction. The plane strain state refers to a state in which the strain in the X direction is 0 and the tensile strain in the direction perpendicular to the X direction. The uniaxial tension state refers to a state in which only the strain acts, and the uniaxial tensile state refers to a state in which the tensile stress in the X direction is 0 and only the tensile stress in the direction perpendicular to the X direction acts. Therefore, in the press working, deformation occurs in a region where the deformability is small in view of the forming limit of the material, and it is easy to break when the strain progresses particularly in a plane strain state. On the other hand, in the hydroforming process, since the axial pressure is applied simultaneously with the application of the internal pressure, the material can be subjected to shear deformation, and the deformation progresses in the range from uniaxial tension to pure shear. The pure shear state refers to a state in which the compressive strain in the X direction works equally to the tensile strain in the direction perpendicular to the X direction. Therefore, when viewed from the forming limit of the material, processing is performed in an area where the deformability is very wide, and as a result, large deformation is possible. In other words, in other words, it is not an exaggeration to say that in order to realize a large deformation process by the hydroforming process, it depends on how a strain state is brought to the pure shear side.
[0004]
Needless to say, it is effective to simply apply the axial pushing positively in order to deform on the pure shear side. However, if the axial pushing is simply increased, the problem of buckling naturally occurs. Increasing the internal pressure is effective in preventing this buckling, but increasing the internal pressure means that the strain state shifts from the shear side to the plane strain side, and therefore, it is easy to break. Therefore, in a free bulge having no mold as shown in FIG. 2, molding can be performed only on the plane strain side from the uniaxial tension state in order to prevent buckling (extracted from Non-Patent Document 1).
[0005]
The reason why the shear deformation was realized by the T-forming (hydroforming) as shown in FIG. 1 is due to the effect of the constraint of the mold. Since the mold is present around the buckle, buckling can be suppressed more than in the case of the free bulge. In addition, since the mold is provided, the internal pressure can be made higher than in the case of the free bulge, whereby the adhesion with the mold is further increased, which is effective in suppressing buckling. As described above, in the T-molding, shear deformation can be realized while suppressing buckling due to the presence of the mold, so that large deformation is possible.
[0006]
In addition to the T-molding, there is an example shown in FIG. 3 as a shape that is easily sheared. However, what is common to these examples is that all of them expand or branch on one surface. For example, in the example of the rectangular tube expansion, the raw tube is expanded only in the Y direction on the YZ plane, but not in the Z direction.
[0007]
On the other hand, in the example of FIG. 4, the expanding direction is not limited to only one surface. For example, in the case of a square tube expansion or a hemisphere tube expansion, the raw tube is expanded not only in the Y direction but also in the Z direction on the YZ plane. In such an example, until a part of the base tube comes into contact with the mold, it becomes the same state as the free bulge, so that it is impossible to realize the shear deformation without buckling, and as a result, the expansion ratio Couldn't be bigger.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide a hydroforming method capable of processing a part having a shape in which the direction of expanding in a plane is not limited to one direction by hydroforming as described above.
[0009]
[Non-patent document 1]
Plasticity and processing, Mori et al .: vol. 29 no. 325 (1988) p. 131
[0010]
[Means for Solving the Problems]
The gist of the present invention to solve such a problem is as follows.
(1) In a hydroforming method in which a metal pipe is mounted on a divided mold and clamped, and then an internal pressure and a pipe axial pushing force are applied to the metal pipe, the metal pipe may be moved in one direction in a cross section of the metal pipe. After expanding the pipe in a direction perpendicular to the one direction to a thickness twice as large as the metal pipe to 1.4 times the diameter of the raw pipe (excluding one time of the raw pipe diameter), the metal pipe is deformed. A hydroform characterized in that the metal tube is expanded in a direction perpendicular to the one direction in a cross section while being twice as thick as the metal tube to 1.4 times as large as the deformed width in the one direction. Processing method.
(2) While expanding the metal tube in one direction of the cross section of the metal tube, in a direction perpendicular to the one direction, the plate thickness of the metal tube is twice to 1.4 times the base tube diameter (excluding one time of the base tube diameter). ), Mounted on a mold having the shape of the final product, and while expanding the metal tube in a direction perpendicular to the one direction in the cross section of the metal tube, the thickness of the metal tube in the one direction is twice or more the thickness of the metal tube. The hydroforming method according to (1), wherein the shape is formed to be 1.4 times the width after the deformation.
(3) In a hydroforming method in which a metal tube is mounted on a divided mold and clamped, then an internal pressure and a pushing force in a tube axial direction are applied to the metal tube. After expanding the pipe in a direction perpendicular to the one direction to a thickness twice as large as the metal pipe to 1.4 times the diameter of the raw pipe (excluding one time of the raw pipe diameter), the metal pipe is deformed. While expanding the metal pipe in a direction perpendicular to the one direction in the cross section, the metal pipe is formed in the one direction to be twice the thickness of the metal pipe to 1.4 times the width after the deformation to be an intermediate product. A hydroforming method characterized by being mounted on a mold having the shape of the final product and subjected to hydroforming.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
In the example of FIG. 5, first, the metal tube 1 is mounted on the lower mold 2 and the upper mold 3 is closed. At this time, the shape of the cavity of the molds 2 and 3 is expanded in the horizontal direction with respect to the diameter of the metal tube 1 and also in the vertical direction, which is larger than one time of the diameter of the tube and is at most the original tube diameter. The shape is such that the tube can be expanded to 1.4 times the diameter (width). Up to 1.4 times the original tube diameter (width), it is possible to apply shear deformation to the material to some extent. Next, an inner pressure is applied to the inside of the set pipe 1 and, at the same time, the right and left ends are pushed in the pipe axis direction by the axial pushing punches 4 and 5 to finish the shape of the intermediate product 6. This is the first hydroforming step.
[0012]
Next, the intermediate product 6 is taken out of the first hydroform molds 2 and 3 and mounted on another lower mold 7 corresponding to the final product shape, and another upper mold 8 is closed. At this time, the shape of the cavity of the molds 7 and 8 is expanded in the vertical direction with respect to the shape of the intermediate product 6, and the diameter (width) of the pipe after the first hydroform molding is also maximum in the horizontal direction. ) Is expanded to 1 to 1.4 times that of (1). If the vertical cavity shape (height) exceeds 1.4 times the diameter (width) of the tube after the first hydroform molding, it becomes difficult to apply shear deformation to the material. Next, an inner pressure is applied to the inside of the set intermediate product 6, and at the same time, the left and right ends are pushed in the tube axis direction by the axial pushing punches 9, 10 to finish to the shape of the final product 11. As a result, finally, a final product 11 expanded in the horizontal and vertical directions with respect to the pipe 1 is completed.
[0013]
In the above example, the pipe was expanded mainly in the horizontal direction in the first hydroforming step, and the pipe was expanded mainly in the vertical direction in the second hydroforming step. The effect of the present invention can be similarly obtained by expanding the pipe in the vertical direction and mainly in the horizontal direction in the second hydroforming step.
When the intermediate product formed in the first hydroforming step is set in the second hydroforming step, it is not necessary to insert the intermediate product in the same direction. For example, the intermediate product may be set in a direction inclined by 90 °. In this case, the direction of the mold cavity in the second hydroforming step is the same as the direction of the mold cavity in the first hydroforming step.
[0014]
Further, the same effect can be obtained by expanding the tube after the cross section is flattened in the mold clamping direction at the time of mold clamping. In the example of FIG. 6, first, the metal tube 1 is mounted on the lower mold 2 and the upper mold 3 is closed. At this time, the shape of the hollow portions of the dies 2 and 3 is expanded in the horizontal direction with respect to the diameter of the metal tube 1 and also in the vertical direction from twice or more the plate thickness to the original tube diameter (width). ) Make the shape smaller. If the thickness is more than twice the plate thickness and is smaller than the original tube diameter (width), shear deformation can be imparted. However, since the adhesion to the mold is increased, a highly lubricating lubricant is applied. It is preferable to improve the lubrication between the tube 1 and the upper and lower molds 2, 3. Next, an inner pressure is applied to the inside of the set pipe 1 and, at the same time, the right and left ends are pushed in the pipe axis direction by the axial pushing punches 4 and 5 to finish the shape of the intermediate product 6. This is the first hydroforming step.
[0015]
Next, the intermediate product 6 is taken out of the first hydroform molds 2 and 3 and mounted on another lower mold 7 corresponding to the final product shape, and another upper mold 8 is closed. In the example of FIG. 6, when setting the intermediate product formed in the first hydroforming step in the second hydroforming step, the intermediate product was set in a direction inclined by 90 °.
That is, in this case, the shape of the cavity of the molds 7 and 8 is expanded in the horizontal direction with respect to the shape of the intermediate product 6, and is perpendicular to the expanding direction (the vertical direction in FIG. 6). ) Was formed so that the deformation from twice the plate thickness to 1.4 times the width (height in FIG. 6) after the deformation in the first hydroforming step (see FIG. 6). If the mold clamping is smaller than twice the plate thickness, it becomes difficult to impart shear deformation. Further, if the width exceeds 1.4 times the width after the deformation, it becomes difficult to apply shear deformation to the material.
[0016]
Next, an inner pressure is applied to the inside of the set intermediate product 6, and at the same time, the left and right ends are pushed in the tube axis direction by the axial pushing punches 9, 10 to finish to the shape of the final product 11. As a result, finally, a final product 11 expanded in the horizontal and vertical directions with respect to the pipe 1 is completed.
[0017]
In the above example, the intermediate product formed in the first hydroforming step was tilted by 90 ° when it was set in the second hydroforming step, but the intermediate product may be set without tilting. In this case, the direction of the mold cavity in the second hydroforming step is perpendicular to the direction of the mold cavity in the first hydroforming step. At this time, the pipe may be expanded in the horizontal direction in the first hydroforming step and may be expanded in the vertical direction in the second hydroforming step, or vice versa. That is, the effects of the present invention can be similarly obtained by expanding the pipe mainly in the vertical direction in the first hydroforming step and in the horizontal direction in the second hydroforming step.
[0018]
When the inventions described in FIGS. 5 and 6 are combined, the deformation in the direction perpendicular to the pipe expanding direction is reduced from twice the sheet thickness to 1.4 times the original diameter (width) of the process (the first step). The effect of the present invention can be obtained in the same manner as long as the diameter is increased (except for one time the diameter of the base tube in one hydroforming step).
[0019]
As a method of preventing bursting and buckling during molding and increasing the expansion ratio, there is a counter punch or a movable mold movable in the axial direction of the tube as shown in FIG. 7 (excerpted from Schuler's Metal Forming Handbook). When the method is used in each hydroforming step, the pipe expansion rate in each step can be further increased, and the final pipe expansion rate can be further improved.
[0020]
Further, the example of FIG. 8 is an example in which the counter punches 12 and 13 are used in the first hydroforming step, and the movable dies 14, 15, 16 and 17 are used in the second hydroforming step.
[0021]
FIG. 9 shows an example in which the first hydroforming step and the second hydroforming step are processed in the same molds 20 and 21. The pair of dies 20 and 21 have a cavity in which the metal tube 1 can be expanded in the horizontal direction, and a vertical shape (up and down direction) perpendicular to the expansion direction corresponding to the cavity from the outer surface of the metal tube at the beginning of molding to the final shape. It has movable dies 24 and 25 whose position can be controlled to the outer surface of the metal tube. By doing so, the mold mechanism becomes complicated, but the number of molds can be reduced, which is advantageous in cost.
In addition, when a counter punch or a movable mold as in the example of FIG. 7 is used in combination with the integrated mold, molding can be performed up to a larger pipe expansion ratio, which is advantageous.
[0022]
8 and 9 are examples in which, in both the first hydroforming step and the second hydroforming step, there is no deformation at all in the direction perpendicular to the expanding direction. However, it goes without saying that almost the same effect can be obtained if the deformation is 1.4 times or less the original diameter (width) of the process (see FIG. 5).
[0023]
In any of the above examples, when expanding in the horizontal direction, expansion in the vertical direction is restricted, and when expanding in the vertical direction, expansion in the horizontal direction is restricted. In many cases, the final product shape becomes a simple shape. Therefore, it is effective to add one more step to finish a complicated shape like an automobile part. That is, the pipe is expanded to the expansion ratio corresponding to the final product by the above-described first and second hydroforming steps (or a processing step using an integrated die), and the intermediate product 26 is formed. A hydroforming process is carried out so that only the shape is prepared by mounting (see FIG. 10). By this method, it is possible to hydroform a part having a complicated shape and a large pipe expansion ratio. For the molding of the intermediate product 26, the first and second hydroforming steps may be performed using the same mold.
As the metal pipe, a steel pipe, a stainless steel pipe, an aluminum pipe, a titanium pipe, or the like can be used.
[0024]
【Example】
Examples of the present invention will be described below.
As the raw tube, an outer diameter of 63.5 mm, a plate thickness of 2.3 mm, a length of 500 mm, and a material of JIS standard STKM11A (carbon steel pipe for machine structure) were used. As shown in FIG. 5, the shape of the product to be processed was such that the tube was expanded into a square, the length of one side of the square was 150 mm, the corner R was 8 mm, and the length of the expanded portion in the tube axis direction was 100 mm.
[0025]
First, in the first hydroforming step, the pipe was expanded in the horizontal direction and also in the vertical direction to obtain an intermediate product. At this time, molding was performed with an axial pushing amount of 50 mm on both sides and an internal pressure of 30 MPa at the maximum. By the first hydroforming step, the pipe was expanded about 1.9 times in the horizontal direction and about 1.1 times in the vertical direction with respect to the diameter of the raw pipe.
Next, the intermediate product formed as described above was mounted on a second hydroform mold having a final product shape, and expanded in a vertical direction. At that time, the shaping amount was 40 mm on both the left and right sides, and the internal pressure was formed at a maximum of 30 MPa. By this second hydroforming step, the pipe was expanded about 1.2 times in the horizontal direction and about 2.1 times in the vertical direction with respect to the diameter (width) of the pipe after the first hydroform molding.
[0026]
For comparison, molding was performed by a conventional method other than the method of the present invention. That is, the first hydroforming step was omitted, and the raw tube was directly inserted into the mold of the second hydroforming step and molded. As a result, no matter how much the axial pressing and the internal pressure were adjusted, there was no contact with the mold at the expanded portion, and bursting or buckling occurred and molding could not be performed.
[0027]
【The invention's effect】
According to the present invention, it is possible to perform hydroforming with a large pipe expansion ratio that could not be processed due to a conventional burst or buckling as a neck. As a result, the range of parts to which hydroforming is applied is expanded. As a result, it is possible to contribute to the effects of cost reduction and weight reduction of automobile parts as described at the beginning.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a strain state in press working and hydroforming.
FIG. 2 is an explanatory diagram of a forming limit in free bulge processing.
FIG. 3 is an explanatory diagram of an example of a hydroform shape suitable for shear deformation.
FIG. 4 is an explanatory diagram of an example of a hydroform shape when shear deformation is difficult.
FIG. 5 is an explanatory view of the present invention in the case where the deformation in the direction perpendicular to the expanding direction is from 1 to 1.4 times the original diameter (width).
FIG. 6 is an explanatory view of the present invention in the case where the deformation in the direction perpendicular to the direction in which the tube is expanded is twice the plate thickness to one time the original diameter (width).
FIG. 7 is an explanatory view of a counter punch and a movable mold.
FIG. 8 is an explanatory diagram of a case where a counter punch or a movable mold is used in combination with the hydroforming method.
FIG. 9 is an explanatory view of an example of a hydroforming method using an integrated mold.
FIG. 10 is an explanatory view of an example of a hydroforming method in which a third hydroforming step of the present invention is added.
[Explanation of symbols]
Reference numeral 1: Metal tube 2: Lower mold 3 in the first hydroforming step 3 ... Upper mold 4 in the first hydroforming step 5: Left punch for the first hydroforming step 5: Right press for the first hydroforming step Punch 6: Intermediate product after the first hydroforming step 7: Die 8 below the second hydroforming step 8: Die 9 above the second hydroforming step 9: Left punch 10 for the second hydroforming step Second hydroforming step right-axis pressing punch 11: final product 12: counter punch 13 before first hydroforming step 13: counter punch 14 after first hydroforming step: lower left movable mold for second hydroforming step 15: second hydroforming step lower right movable mold 16: second hydroforming step upper left movable mold 17: second hydroforming step Upper movable mold 18: second hydroforming step left mold pressing tool 19: second hydroforming step right mold pressing tool 20: first second step integrated lower mold 21: first Second step integrated type upper mold 22... First second step integrated type left axis pressing punch 23... First second step integrated type right axis pressing punch 24... First second step integrated type front counter punch ( Movable mold)
25: First and second step integrated type front counter punch (movable mold)
26: Intermediate product 27 after the second hydroforming step 27: Lower mold 28 in the third hydroforming step Upper mold 29 in the third hydroforming step Left punch 30 in the third hydroforming step 3 hydroforming process right axis pushing punch

Claims (3)

In a hydroforming method in which a metal pipe is mounted on a divided mold, and after clamping, the internal pressure and the pipe axial pushing force are applied to the metal pipe, the metal pipe is expanded in one direction of the cross section of the metal pipe. After being deformed in a direction perpendicular to the one direction to twice the plate thickness of the metal tube to 1.4 times the tube diameter (excluding one time of the tube diameter), the metal tube cross section is A hydroforming method, wherein the metal pipe is formed in the one direction so as to have a thickness of twice the thickness of the metal pipe to 1.4 times the width after the deformation while expanding the metal pipe in a direction perpendicular to one direction. While expanding the metal tube in one direction of the cross section of the metal tube, the metal tube is deformed in a direction perpendicular to the one direction to twice the plate thickness of the metal tube to 1.4 times the base tube diameter (excluding one time of the base tube diameter). After that, the metal pipe is mounted on a mold having the shape of the final product, and while the metal pipe is expanded in a direction perpendicular to the one direction in the cross section of the metal pipe, the thickness of the metal pipe is twice as large in the one direction to after the deformation. The hydroforming method according to claim 1, wherein the width is 1.4 times the width of the hydroform. In a hydroforming method in which a metal pipe is mounted on a divided mold, and after clamping, the internal pressure and the pipe axial pushing force are applied to the metal pipe, the metal pipe is expanded in one direction of the cross section of the metal pipe. After being deformed in a direction perpendicular to the one direction to twice the plate thickness of the metal tube to 1.4 times the tube diameter (excluding one time of the tube diameter), the metal tube cross section is While expanding the metal tube in a direction perpendicular to one direction, the metal tube is formed in the one direction to a thickness twice as large as the thickness of the metal tube to 1.4 times the width after the deformation to form an intermediate product, and the intermediate product is formed into a final product shape. A hydroforming method characterized by being mounted on a mold and hydroforming.

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