Method of producing polygonal closed cross-section structural component with a curved form and polygonal closed cross-section structural component produced by the method

A method of producing a polygonal closed cross-section structural component includes press-forming a metal sheet into a gutter-shaped pre-processed part with a curved form along its longitudinal direction having plural ridge lines corresponding to corner portions of the polygonal closed cross-section in a cross-sectional form developed by cutting the component at a position corresponding to the ridge line located at the innermost side in the radial direction to provide a flange portion extending along the ridge line at the resulting respective ends, and press-forming the pre-processed part to deform inwardly in the cross-sectional direction at a position of one or more of the plural ridge lines to butt the ridge lines located at the innermost side and the flange portions to each other.

TECHNICAL FIELD

This disclosure relates to a method of producing a polygonal closed cross-section structural component with a curved form along its longitudinal direction, which is used in automobiles, domestic electric appliances and the like, and a polygonal closed cross-section structural component produced by the method.

BACKGROUND

In the field of automobiles, domestic electric appliances and the like is known a component having a closed cross-section structure formed by shaping two parts separately and joining these parts to each other. Also, hydroforming or roll forming is known as a method of producing a closed cross-section structural component with a curved form along its longitudinal direction.

In the conventional hydroforming method, it is necessary to weld all of peripheral edge portions before the pouring of a machining fluid. JP-A-2008-119723 discloses a hydroforming machine, a hydroforming method and a hydroformed product, in which deep drawn products having an excellent sealing property in bulging can be obtained from two or more metal sheets without lap-welding all peripheral edge portions and the production efficiency capable of simultaneously shaping plural components is excellent.

JP-A-2000-263169 discloses a method of producing a closed cross-section curved long material comprising a roll forming step of shaping a band plate into nearly a closed cross-section with multistage forming rollers, joining butt portions thereof with a caulking roller and curving the resulting closed cross-section long material with many bending rollers along a moving direction of the band plate.

JP-A-2003-311329 discloses a technique capable of obtaining a pressed product with a distortion on the way of a closed cross-section form from a raw material in which a high-quality closed cross-section pressed product having a light weight and a high-rigidity distorted portion is provided at a low cost.

JP-A-2011-062713 discloses a method of producing a closed cross-section structural component having a curved form along its longitudinal direction through press forming by joining two folded steel sheets each having a curved form at their both flange portions to each other and deforming to move the flange portions close to each other.

However, the hydroforming method disclosed in JP '723 and the roll forming method disclosed in JP '169 have problems that the production rate is slow and equipment cost is high compared to the press forming. Also, the press forming method disclosed in JP '329 has a problem that it is difficult to perform butting of the end faces in a component having a curved form in its longitudinal wall portion. Further, the method disclosed in JP '713 has a problem that there is a limitation in the weight reduction because it is required to join flange portions of two press formed steel sheets to each other by welding.

It could therefore be helpful to provide a method of producing a polygonal closed cross-section structural component with a curved form along its longitudinal direction that is capable of reducing the weight of a product at a low cost only by press forming, and a polygonal closed cross-section structural component produced by the method.

SUMMARY

We examined a method of producing a polygonal closed cross-section structural component with a curved form along its longitudinal direction from a metal sheet to reduce a weight of the product by minimizing a flange portion and found that when a pre-processed part with a curved form along its longitudinal direction has a radius of curvature equal to a radius of curvature of the curved form along the longitudinal direction of the polygonal closed cross-section component at each ridge line corresponding to each corner portion of the component, if it is intended to reduce the form of the pre-processed part into the form of the component in a cross-sectional direction by press forming, a length of a ridge line in the component becomes shorter than a length of a ridge line located in the pre-processed part inward in the radial direction of the curved form and, hence, a surplus portion is produced in the sheet material and causes wrinkles in the component so that when the radius of curvature in the curved form along the longitudinal direction of the pre-processed part to cause a length difference in the each ridge line between the component and the pre-processed part or to make the each length of the ridge line in the component longer, the polygonal closed cross-section structural component with the curved form along its longitudinal direction can be produced by press forming without causing wrinkles.

We thus provide a method of producing a polygonal closed cross-section structural component with a curved form along its longitudinal direction having plural ridge lines corresponding to corner portions of the polygonal closed cross-section and two flange portions extending in parallel to a flat face including a ridge line located at an innermost side in a radial direction of the curved form of the component along the longitudinal direction among the above ridge lines from a metal plate, characterized in that the metal sheet is first press-formed into a gutter-shaped pre-processed part with a curved form along its longitudinal direction having plural ridge lines corresponding to the corner portions of the polygonal closed cross-section of the component in a cross-sectional form developed by cutting the component at a position corresponding to the ridge line located at the innermost side in the radial direction to provide a flange portion extending along the ridge line at the resulting respective ends wherein each of the ridge lines corresponding to the corner portions has a radius of curvature equal to or smaller than a radius of curvature of the corresponding ridge line of the component to have a length equal to or shorter than the length of the corresponding ridge line; and the pre-processed part is then press-formed to deform inwardly in the cross-sectional direction at a position of one or more of the plural ridge lines to butt the ridge lines located at the innermost side and the flange portions to each other.

In the method of producing a polygonal closed cross-section structural component with a curved form, a polygonal line of a groove-shaped cross-section may be press-formed along one or more of the plural ridge lines of the pre-processed part at such a ridge line to easily deform the pre-processed part inward in the cross-sectional direction at a position of such a ridge line whereby the pre-processed part is surely deformed inward in the cross-sectional direction at the position of the ridge line so that the component can be press-formed from the pre-processed part in a high accuracy.

A polygonal closed cross-section structural component with a curved form is characterized by producing through the aforementioned method of producing a polygonal closed cross-section structural component with a curved form.

In the method producing a polygonal closed cross-section structural component with a curved form, when a metal sheet is shaped into a polygonal closed cross-section structural component with a curved form along its longitudinal direction having plural ridge lines corresponding to corner portions of the polygonal closed cross-section and flange portions extending in parallel to a flat face including a ridge line located at an innermost side of the curved form along the longitudinal direction in a radial direction of the component among the above ridge lines, a gutter-shaped pre-processed part with a curved form along its longitudinal direction is first press-formed from the metal sheet. The pre-processed part has plural ridge lines corresponding to the corner portions of the polygonal closed cross-section of the component in a cross-section form developed by cutting the component at a position corresponding to the ridge line located at the innermost side in the radial direction to provide a flange portion extending along the ridge line at the resulting respective ends wherein each of the ridge lines corresponding to the corner portions has a radius of curvature equal to or smaller than a radius of curvature of the corresponding ridge line of the component to have a length equal to or shorter than the length of the corresponding ridge line. Then, the pre-processed part is press-formed to deform inwardly in the cross-sectional direction at a position of one or more of the plural ridge lines to butt the ridge lines located at the innermost side and the flange portions to each other.

Therefore, the polygonal closed cross-section structural component with the curved form produced by the method to producing a polygonal closed cross-section structural component with a curved form can be shaped from a metal sheet by press forming so that the cost is low. Also, the flange portion exists only in the inside of the curved form of the component, which can contribute to reduce the weight of the component. Furthermore, when the component is press-formed from the pre-processed part, the difference of the length of the each ridge line is not produced between the component and the part or the length of the each ridge line is made longer in the form of the component so that the occurrence of wrinkles in the form of the component can be prevented.

DESCRIPTION OF REFERENCE SYMBOLS

DETAILED DESCRIPTION

An example will be described in detail with reference to the drawings.FIG. 1(A)is a side view of a closed cross-section structural component produced in an example of the method of producing a polygonal closed cross-section structural component with a curved form, andFIG. 1(B)is a sectional view taken along a line A-A in the side view, andFIG. 2(A)is a side view of a pre-processed part produced in the example of the method of producing a polygonal closed cross-section structural component with a curved form, andFIG. 2(B)is a sectional view taken along a line B-B in the side view.

In this example, a cylindrical component1of a quadrangular closed cross-section structure as shown inFIGS. 1(A)and (B) is produced from a steel sheet. The component1has a curved form along a longitudinal direction of the component1and is provided with four ridge lines1a,1b,1c,1dextending along the longitudinal direction of the component1at positions corresponding to corner portions of the quadrangular closed cross-section and flange portions1eextending on a flat face including the ridge line1d(flat face parallel to a paper inFIG. 1(A)) along the ridge line1dlocated at an innermost side in a radial direction of the curved from along the longitudinal direction of the component1(uppermost position inFIG. 1) among the ridge lines1a-1din the quadrangular closed cross-section of the component1and protruding inward in the radial direction. Also, the curved form of the component1has a radius of curvature R1, a center of which is located on a flat face including the ridge line1dat the innermost side in the radial direction of the quadrangular closed cross-section or at the position of the ridge line1d.

In this example of producing the component1, a gutter-shaped pre-processed part2with a curved form along a longitudinal direction thereof as shown inFIGS. 2(A)and (B) is first press-formed from a steel sheet previously trimmed to a given contour shape, for example, with a bending and drawing mold. The pre-processed part2has an opened cross-section form developed by cutting the component1at a position of the ridge line1dlocated at the innermost side to have a flange portion1eextending along the ridge line1dat the resulting respective ends as shown inFIG. 2(B), in which the part has four ridge lines corresponding to the corner portions of the polygonal closed cross-section of the component1and one ridge line increased by the above cutting or five ridge lines2a-2din total and two flange portions2eextending along the two ridge lines2dlocated at the innermost side in the radial direction (uppermost position inFIG. 2).

Each of the ridge lines2a-2dhas a radius of curvature equal to or smaller than a radius of curvature of the corresponding ridge lines1a-1dto have a length equal to or shorter than a length of the corresponding ridge lines1a-1din the component1. For example, a radius of curvature R2of the ridge line2dlocated at the innermost side in the radial direction (uppermost position inFIG. 2) is made smaller than a radius of curvature R1of the corresponding ridge line1din the component1. Also, a polygonal line2fof U-shaped groove type cross-section extending along each of the ridge lines2a-2dis formed at an inner position sandwiched between both sides of each of the ridge lines2a-2din the pre-processed part2to easily deform the pre-processed part2at positions of such ridge lines in a cross-sectional direction at subsequent press-forming as enlarged and shown inFIG. 3.

The curved form of the each ridge line2a-2dand flange portions2ein the pre-processed part2extends on a flat face parallel to a paper face ofFIG. 2(A)and along the flat face when the pre-processed part2is deformed so that the ridge lines other than the ridge line2aare not parallel to the paper face and the each ridge line2b-2dis moved to the same position of the corresponding ridge line1b-1dof the component1. The center of the radius of curvature R2is located at a position separated vertically from the paper face (for example, on a flat face including the flange portion2e) instead of the paper face ofFIG. 2(A).

In the subsequent step, the pre-processed part2is press-formed into a closed cross-section form corresponding to the cross-section of the component1as shown by a phantom line inFIG. 2(B)by pushing the part with a usual cam mold (not shown) having a shaping form corresponding to the curved form of the component1to deform from the original cross-section form shown by a solid line inFIG. 2(B)in a horizontal direction inFIG. 2(B)inwardly in the cross-sectional direction to butt the ridge lines2dlocated at the innermost side and the flange portions2eextending along the ridge lines2dto each other.

At this moment, the pre-processed part2is bent inwardly at the position of the each ridge line2a-2cand outwardly at the position of the each ridge line2d, wherein a length of a portion moving inward in the radial direction of the curved form of the component1is generally shortened by the bending along the curved form of these ridge lines. However, the pre-processed part2is deformed with the cam mold to make the radius of curvature in the each ridge line2a-2dequal to that of the corresponding each ridge line1a-1din the component1while accepting the enlargement of the radius of curvature, whereby the length of the each ridge line2a-2dis maintained or extended to match with a length of the each ridge line1a-1din the component1, while the length of the flange portion2eis extended to match with the length of the flange portion1ein the component1.

After the press forming, the butted flange portions2eof the pre-processed part2are joined to each other, for example, by welding such as spot welding, laser welding or the like or with an adhesive or the like, whereby the component1of the closed cross-section structure can be produced.

According to the method of this example and a component1of a quadrangular closed cross-section structure with a curved form of this example produced by the method, therefore, the component1can be formed from the single metal sheet by press forming so that the cost is low, while the flange portion1eis only an inner portion in the curved form of the component1and can contribute to reduce the weight of the component1. Furthermore, when the component1is press-formed from the pre-processed part2, the difference of length in the each ridge line is not caused or the length of the each ridge line is made longer in the component so that the occurrence of wrinkles can be prevented in the component1.

According to the producing method of this example, the polygonal line2fis formed at the each ridge line2a-2dof the pre-processed part2by press forming so that the pre-processed part2is surely deformed inward at the position of the each ridge line2a-2dat the subsequent step and hence the component1can be press-formed from the pre-processed part2in a high accuracy.

FIGS. 4(A)and (B) are perspective views of a pre-processed part and a closed cross-section structural component produced from the pre-processed part in another example of the method of producing a polygonal closed cross-section structural component with a curved form, andFIGS. 5(A)and (B) are perspective views of a pre-processed part produced in the example of the method of producing a polygonal closed cross-section structural component with a curved form and a press mold to produce a closed cross-section structural component from the pre-processed part.

In the producing method of this example is produced a front pillar component3for a vehicle body as shown inFIG. 4(B). The front pillar component3has a global curved form having a relatively large radius of curvature and a middle curved form having a relatively small radius of curvature and also a closed cross-section structure near to a trapezoid having four ridge lines3a-3dcorresponding to corner portions as seen from an end face and further has a flange portion3elocated at an inside of the curved form.

When the front pillar component3is produced by press forming in the producing method of this example, a gutter-shaped pre-processed part4having a curved form along its longitudinal direction is first press-formed from a metal sheet previously trimmed to a given contour form with, for example, a bending and drawing mold as shown inFIG. 4(A). The pre-processed part4has an opened cross-section form developed by cutting the component3at a position of a ridge line3dlocated at an innermost side in a radial direction of the curved form (lowermost position inFIG. 4) to have a flange portion3eextending along the ridge line3dat the resulting respective ends, in which the part has four ridge lines corresponding to the corner portions of the polygonal closed cross-section of the component3and one ridge line increased by the above cutting or five ridge lines4a-4din total and two flange portions4eextending along the two ridge lines4dlocated at the innermost side in the radial direction.

Each of the ridge lines4a-4dhas a radius of curvature equal to or smaller than a radius of curvature of the corresponding ridge lines3a-3dto have a length equal to or shorter than a length of the corresponding ridge lines3a-3din the component3. For example, a radius of curvature of the ridge line4dlocated at the innermost side in the radial direction (lowermost position inFIG. 4) is made smaller than a radius of curvature of the corresponding ridge line3din the component3.

In the subsequent step, the pre-processed part4is press-formed into a closed cross-section form corresponding to the cross-section of the component3as shown inFIGS. 5(A)and (B) by pushing the pre-processed part4with a usual cam mold5having shaping faces5a,5bof a curved form corresponding to the curved form of the component3to deform from the horizontal direction inward in the cross-sectional direction as shown by an arrow inFIG. 5(B)to butt the ridge lines4dlocated at the innermost side and the flange portions4eextending along the ridge lines4dto each other.

At this moment, the pre-processed part4is bent inwardly at the position of the each ridge line4a-4cand outwardly at the position of the each ridge line4d, wherein a length of a portion moving inwardly in the radial direction of the curved form of the component3is generally shortened by the bending along the curved form of these ridge lines. However, the pre-processed part4is deformed with the cam mold5to make the radius of curvature in the each ridge line4a-4dequal to that of the corresponding each ridge line3a-3din the component3while accepting the enlargement of the radius of curvature, whereby the length of the each ridge line4a-4dis maintained or extended to match with a length of the each ridge line3a-3din the component3, while the length of the flange portion4eis extended to match with the length of the flange portion3ein the component3.

After the press forming, the butted flange portions4eof the pre-processed part4are joined to each other, for example, by welding such as spot welding, laser welding or the like or with an adhesive or the like, whereby the component3of the closed cross-section structure can be produced.

According to the method of this example and the component3of an approximately trapezoidal closed cross-section structure with a curved form of the example produced by the method, therefore, the component3can be formed from the single metal sheet by press forming like in the previous example of the method so that the cost is low, while the flange portion3eis only an inner portion in the curved form of the component3and can contribute to reduce the weight of the component3. Furthermore, when the component3is press-formed from the pre-processed part4, the difference of length in the each ridge line is not caused or the length of the each ridge line is made longer in the component so that the occurrence of wrinkles can be prevented in the component3.

FIGS. 6(A)and (B) are perspective views of a pre-processed part and a closed cross-section structural component produced from the pre-processed part in a comparative example of the method of producing a polygonal closed cross-section structural component with a curved form. In the producing method of this comparative example is produced a front pillar component6for a vehicle body as shown inFIG. 6(B). The front pillar component6has a global curved form having a relatively large radius of curvature and a middle curved form having a relatively small radius of curvature and also a closed cross-section structure near to a trapezoid having four ridge lines6a-6dcorresponding to corner portions as seen from an end face and further has flange portions6elocated at an inside of the curved form like the front pillar component3produced in the previous example.

When the front pillar component6is produced by press forming in the producing method of the comparative example, a gutter-shaped pre-processed part7having a curved form along its longitudinal direction is first press-formed from a metal sheet previously trimmed to a given contour form with, for example, a bending and drawing mold as shown inFIG. 6(A). The pre-processed part7has an opened cross-section form developed by cutting the component6at a position of a ridge line6dlocated at an innermost side in a radial direction of the curved form (lowermost position inFIG. 6) to have a flange portion6eextending along the ridge line6dat the resulting respective ends, in which the part has four ridge lines corresponding to the corner portions of the polygonal closed cross-section of the component6and one ridge line increased by the above cutting or five ridge lines7a-7din total and two flange portions7eextending along the two ridge lines7dlocated at the innermost side in the radial direction. The each ridge line7a-7dhas the same radius of curvature as that of the corresponding ridge line6a-6dto have the same length as that of the ridge line6a-6dof the component6.

In the subsequent step, the pre-processed part7is press-formed into a closed cross-section form corresponding to the cross-section of the component6by pushing with a usual cam mold (not shown) having shaping faces of a curved form corresponding to the curved form of the component6to deform from the horizontal direction of the pre-processed part6inward in the cross-sectional direction to butt the ridge lines6dlocated at the innermost side and the flange portions6eextending along the ridge lines6dto each other.

At this moment, the pre-processed part7is bent inward at the position of the each ridge line7a-7cand outward at the position of the each ridge line7d, wherein a length of a portion moving inwardly in the radial direction of the curved form of the component6is shortened by the bending along the curved form of these ridge lines to cause a surplus of a sheet in the longitudinal direction of the component6. According to the producing method of the comparative example, therefore, vertical wrinkles6fare caused at a side face of the curved form in the component6as shown inFIG. 6(B)different from the producing method of the aforementioned examples.

Although the illustrated examples are explained, our methods are not limited to the above examples and may be properly modified within the scope described in the appended claims. For example, the number of ridge lines in the component may be other than four, and the polygonal line may be formed in a V-shaped cross-section or may not be produce a protrusion at its opposite side.

INDUSTRIAL APPLICABILITY

According to the method of producing a polygonal closed cross-section structural component with a curved form, polygonal closed cross-section structural components with a curved form can be produced from a metal sheet through press forming by this method so that the cost is low, while the flange portion is only an inner portion in the curved form of the component and can contribute to reduce the weight of the component. Furthermore, when the component is press-formed from the pre-processed part, the difference of length in the each ridge line is not caused or the length of the each ridge line is made longer in the component so that the occurrence of wrinkles can be prevented in the component.