阅读说明：本技术 冲压成型品的制造方法 (Method for producing press-molded article ) 是由 飞田隼佑 新宫丰久 山崎雄司 于 2018-12-17 设计创作，主要内容包括：本发明提供一种能够在不使模具形状变得复杂且也不过度实施加热处理的情况下抑制拉伸凸缘裂纹、没有成型不良的冲压成型品。冲压成型品的制造方法如下：对将由1张板材构成的金属板进行剪切加工(剪切工序(1))后的单一金属板实施包含拉伸凸缘成型的冲压加工(冲压加工工序(4))而制造。将推断为对上述单一金属板利用上述冲压加工进行冲压成型时容易产生拉伸凸缘裂纹的区域作为拉伸凸缘裂纹区域的情况下,在上述剪切加工后的单一金属板中,对位于上述拉伸凸缘裂纹区域内的金属板端面及其附近中的至少金属板端面进行加热、冷却后(加热工序(2)和冷却工序3(3)),实施上述冲压加工(冲压加工工序(4))。(The invention provides a press-formed product which can restrain the tensile flange crack and has no bad forming without complicating the shape of a die and applying heat treatment without excess. The method for producing the press-molded article comprises: the single metal plate is produced by subjecting a metal plate made of 1 sheet material to a shearing process (1)) and then subjecting the single metal plate to a press process (4)) including stretch flange forming. When a region in which stretch flange cracking is likely to occur when the single metal plate is press-formed by the press working is regarded as a stretch flange cracking region, the single metal plate after the shearing working is subjected to the press working (press working step (4)) after at least the end face of the metal plate located in the stretch flange cracking region and the vicinity thereof is heated and cooled (heating step (2) and cooling step (3)).)

1. A method for producing a press-molded article, characterized in that a single metal plate obtained by shearing a metal plate consisting of 1 sheet is subjected to press working including stretch flange molding,

when a region in which a stretch flange crack is likely to occur when the single metal plate is press-formed by the press working is defined as a stretch flange crack region,

in the single metal sheet after the shearing, at least one of the end surface of the metal sheet located in the stretch flange cracking region and the vicinity thereof is heated and cooled, and then the press working is performed.

2. The method of producing a press-molded article according to claim 1, wherein a heating temperature T of the heated portion at the time of the heating is set to 200 ℃ or higher and Ac1 point or lower of the metal plate, and the unit of the heating temperature T is set to C.

3. The method of producing a press-molded article according to claim 1 or 2, wherein a heating range X from an end face position of the metal plate when the heating is performed on the surface of the single metal plate is set to be within a range of formula (1), and a unit of the heating range X is mm,

0mm≤X≤20mm···(1)。

4. the method of manufacturing a press-formed article according to any one of claims 1 to 3, wherein the metal plate is a steel plate having a tensile strength of 440MPa or more.

Technical Field

The present invention relates to a method for manufacturing a press-formed product by performing press working after reducing the risk of stretch flange cracking in press forming a metal plate. The present invention is a technique particularly suitable for manufacturing a vehicle body structural member for an automobile.

Background

In recent years, high tensile materials of 590MPa or more have been applied to vehicle body structural members in order to achieve both improvement in collision safety and weight reduction of automobile bodies. Since the high tensile material has a small hole expansion ratio, a molding failure such as a stretch flange crack is a problem when press molding is performed.

One of the press-formed articles used for automobile chassis parts is a structural member having a shape curved in a plan view, such as a lower arm. When the member is formed into a shape curved in a plan view by press forming, a tensile flange crack may occur in the curved portion.

In addition, when automobile parts are mass-produced by press forming, a press working process is often performed after shearing such as a trimming process and a punching process. In this case, the stretch flange crack is likely to occur from the sheared edge formed in the trimming step or the punching step.

When a high-tensile material is applied to the above-described shape of the member and the molding process, the above-described stretch flange crack tends to occur.

As conventional techniques for stretch flange cracking, there are, for example, patent documents 1 to 3.

The method described in patent document 1 is a technique for preventing a stretch flange crack generated when a high-strength steel sheet is press-formed. Patent document 1 describes the following: when a steel sheet is stretch-flange-formed by this technique, dynamic recovery of dislocations occurs during processing by heating the steel sheet to 400 to 1000 ℃ during forming, accumulation of dislocations is less likely to occur, and stretch-flange cracks are suppressed.

The method described in patent document 2 is a technique of enhancing formability in press working by applying a strengthening treatment for enhancing mechanical strength to a predetermined portion of a plate-like panel as a press material. Patent document 2 describes that cracks caused by stress concentration accompanying the progress of press working can be suppressed by this technique.

The method described in patent document 3 is a technique for press-forming an integrated sheet material produced by welding end portions of a plurality of sheet materials to each other by irradiating laser light to butt joint edges thereof in a state where the end portions are butted. Patent document 3 describes the following: when the welded end portions of the plate materials and the vicinity thereof are press-formed into a curved shape in a plan view, the peripheral portion of the plate material including the welded end portions and the vicinity thereof are irradiated with a laser beam before the press-forming to perform a softening treatment. It is described that this treatment prevents stress concentration from occurring in the peripheral portion of the plate material, makes it easy to stretch the softened portion during press forming, and prevents stress concentration at the welded end portion.

Disclosure of Invention

However, in the method described in patent document 1, in order to heat the steel sheet during press forming, a heating device needs to be installed in the die, and the shape of the die becomes complicated. Further, since the mold is easily damaged by heating to 400 to 1000 ℃, there is a possibility that the mass production cost increases.

The method described in patent document 2 is a method for suppressing cracks by increasing the strength, and is difficult to apply to stretch flange cracks that require stretching. Is a process that is particularly unsuitable for high tensile materials having high tensile strength.

In addition, the method described in patent document 3 is a method of suppressing the stretch flange cracking in the vicinity of the welded portion by dispersing the strain in the stretch flange cracking risk region. However, the method described in patent document 3 does not describe the heating temperature of each material, the heating region, and the condition of steel type, and there is a possibility that sufficient stretch flange formability cannot be obtained in the local stretch flange forming. In addition, in the method described in patent document 3, since the welding end portion is softened to prevent cracking, a region where the heating treatment is possibly performed is relatively wide.

The present invention has been made in view of the above points, and an object thereof is to provide a press-formed product capable of suppressing a stretch flange crack and suppressing a molding failure without complicating a die shape and without excessively performing heat treatment.

In order to solve the above problems, a method of manufacturing a press-formed article according to an aspect of the present invention is a method of manufacturing a press-formed article by subjecting a single metal plate, which is a metal plate made of 1 sheet, to a press working including a stretch flange forming, wherein, when a region where a stretch flange crack is likely to occur when the single metal plate is press-formed by the press working is estimated to be a stretch flange crack region, an end face of the metal plate located in the stretch flange crack region and at least an end face of the metal plate located in the vicinity thereof are heated and cooled in the single metal plate after the shear working, and then the press working is performed.

According to one aspect of the present invention, it is possible to provide a press-formed product in which the risk of cracking of a member in which a stretch flange crack occurs can be greatly reduced without heating an unnecessary region, and molding defects can be suppressed. As a result, a member having good moldability is obtained, and the yield is improved.

Drawings

Fig. 1 is a diagram illustrating a process of manufacturing a press-molded product according to an embodiment of the present invention.

Fig. 2 is a diagram illustrating an example of a region where a stretch flange crack occurs, where (a) shows a metal plate, and (b) shows an example of a press-formed product.

Fig. 3 is a schematic view of a hole expansion test.

FIG. 4 is a schematic view of a hole-enlarging test piece.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

As shown in fig. 1, the method of manufacturing a press-molded article according to the present embodiment includes a shearing step 1, a heating step 2, a cooling step 3, and a press working step 4 in this order. The method of manufacturing a press-molded article according to the present embodiment includes the stretch flange crack region estimation process 5.

The method for producing a press-molded article according to the present embodiment is particularly effective in the case of a steel sheet in which the tensile strength of the metal sheet is 440MPa or more. In the present embodiment, a high tensile material of 440MPa or more is targeted for the metal plate to be subjected to the press working. However, the steel sheet and the aluminum sheet having a tensile strength of less than 440MPa can be used.

< cutting Process 1 >

The shearing step 1 is a step of trimming the outer peripheral outline shape of a metal plate made of 1 sheet material formed by rolling and other steps into a predetermined shape or shearing to form an opening portion to obtain a single metal plate.

In the present embodiment, the "single metal plate" refers to a metal plate made of the same metal material, rather than an integrated plate material in which a plurality of plates are joined by welding.

Here, when the metal plate is cut by shearing, the end face is largely damaged as compared with the end face produced by machining, and the stretch flange formability is degraded because the end face is in a non-uniform end face state.

< stretch flange crack region inference processing 5 >

The stretch flange crack region estimation process 5 is a process of specifying the position of a stretch flange crack region estimated to be a region in which a stretch flange crack is likely to occur when a single metal plate is press-formed in the press working step 4.

The determination of the stretch flange crack region (the stretch flange crack risk portion) may be determined by a CAE analysis based on the press forming conditions in the press working step 4, or may be determined by actual pressing. In general, a bent portion, a burr portion, or the like in a plan view is a stretch flange crack region. Therefore, in the area where the stretch flange is formed, the flange portion having a radius of curvature equal to or larger than the predetermined radius of curvature in the press working can be easily made to be the stretch flange crack area.

< heating Process 2 >

The heating step 2 and the cooling step 3 which is the next step are pretreatment before the single metal plate after the shearing step 1 is subjected to press working including stretch flange forming.

The heating step 2 is a step of heating at least the end face of the metal sheet in the stretch flange crack region determined by the stretch flange crack region estimation process 5 and the end face of the metal sheet in the vicinity thereof.

In the heating step 2, after it is estimated that the temperature of the end face of the metal plate reaches the target heating temperature, the heated state thereof may be maintained for a certain period of time. Since a long holding time leads to a decrease in production efficiency, the holding time is preferably within 5 minutes. More preferably, the holding time is 1 minute or less.

Only the end face of the metal plate in the flange crack region may be heated. However, it is difficult to heat only the end face, and therefore it is preferable to set the end face of the metal plate and the vicinity thereof so as to heat the region as close as possible to the end face by laser, induction heating, or the like which can perform local heating.

In view of mass production, it is difficult to heat the end face of the metal plate with the laser beam, and therefore it is preferable to heat the vicinity of the end face from the surface side of the metal plate.

For example, the heating range X [ mm ] from the end face position of the metal plate in the surface of the single metal plate is set within the range of the formula (1). That is, the region of the heating range X [ mm ] or less is defined as the end face and the vicinity thereof.

0[mm]≤X≤20[mm]···(1)

Here, if the heating range X [ mm ] exceeds 20mm, the fatigue characteristics of the component may be reduced with the softening of the material strength (tensile strength), which is not preferable. In addition, if the apparatus is capable of further heating only the vicinity of the end face, the heating range X [ mm ] is more preferably within 5 mm.

From the viewpoint of suppressing the trouble due to heating, the heating range X [ mm ] is preferably as close as possible to the end face, and more preferably within the range of the following formula (2).

0[mm]≤X≤8[mm]···(2)

The heating method is not limited to heating by laser light, and for example, a heating device such as an induction coil may be brought close to the end face side of the metal plate to heat the metal plate. However, heating by laser is preferred because it is simple.

The heating temperature T [ ° c ] of the heated portion when heating is a temperature at which softening of the material can occur at the heating position, and is, for example, an annealing temperature of the target metal.

The heating temperature (target temperature for heating) is, for example, preferably 200 ℃ or higher and Ac1 point or lower of the metal plate.

The heating rate in heating is preferably rapid.

Here, if the heating temperature T [ ° c ] is equal to or higher than the Ac1 point of the material, the hardness increases when rapid cooling is performed, and conversely, the stretch flange formability may decrease, which is not preferable. It is considered that the softening treatment is performed by heating at 200 ℃ or higher as long as the metal is a metal such as a normal steel sheet.

< Cooling Process 3 >

The cooling step 3 is a step of cooling at least the end face of the metal plate in the metal plate heated in the heating step 2 and the end face of the metal plate in the vicinity thereof.

The cooling treatment after heating may be any of rapid cooling by water cooling or the like, air cooling, and slow cooling. In the case of rapid cooling, if the heating temperature is not lower than the Ac1 point of the material, the stretch flange formability may be deteriorated. The air cooling may be natural air cooling or air cooling by blowing air through a nozzle. The slow cooling can be adjusted by adjusting the output at the time of laser heating or induction heating to adjust the cooling rate.

In the cooling step 3, for example, the end face of the heated metal plate is cooled to a temperature lower by 30 ℃ or more than the target temperature of heating.

< Press working Process 4 >

The press working step 4 is a step of subjecting the metal plate subjected to the heating and cooling treatment on the end face to press working including stretch flange forming to produce a press-formed product having a desired shape. The press-formed product of the press working step 4 may not be the final formed product.

< action on other >

As shown in fig. 2 (a), an attempt has been made to simply press-form a plate material 10 made of a flat metal plate into a press-formed product 11 shown in fig. 2 (b) to which deformation by flange stretching is applied at the time of press-forming. At this time, if the metal plate 10 is press-formed using a high-tensile material, a stretch flange crack occurs at a portion indicated by a symbol a in fig. 2 (b). Whether or not such a stretch flange crack is generated depends on material strength (tensile strength), material structure, shear end face condition, surface treatment, and the like.

For example, in the case of a composite structure material which occurs in an ultra-high tensile material, stretch flange formability is reduced compared with a material having a single-phase structure due to the difference in hardness of the structure.

Further, stretch flange formability depends on the method of cutting the end of the material subjected to stretch flange forming deformation. When a metal plate is cut by, for example, shearing, the end face is damaged more largely than the end face formed by machining, and the end face becomes uneven, so that stretch flange formability is lowered. In addition, in the case of the shearing process, stretch flange formability is also changed by the gap.

In order to reduce the tensile flange cracking caused by such materials or processing conditions that are unfavorable for the tensile flange forming, in the method for producing a press-formed article according to the present embodiment, the end face of the metal plate that is likely to become a starting point of the crack in the shear processing in the tensile flange cracking risk region is heated and cooled, and then press-formed.

As a result, in the present embodiment, the stretch flange formability is improved by performing the structural change of the material in the stretch flange crack risk portion, that is, softening or strain removal of the material by heating and cooling as the pretreatment.

In particular, by performing a heating process for softening the material to the end face of the metal plate and at least the end face in the vicinity of the end face, and then performing a cooling process, it is possible to minimize the reduction in fatigue characteristics of the member that accompanies the softening of the material strength (tensile strength) due to heating.

When the present embodiment is applied to an integrated plate material including a welded end portion formed by welding 2 plate materials as in conventional document 3, the following problem arises when the region including the welded end portion is a stretch flange crack region. That is, in the present embodiment, the heating process and the subsequent cooling process are performed only around the end face and its vicinity, that is, the end face. Therefore, if this embodiment is applied, there is a possibility that cracks may occur at the time of press forming of the end face of the welded end portion having relatively weak tensile strength. Therefore, the production of a press-formed product intended for a metal plate having a welded end portion in a stretch flange crack region is not the subject of the present embodiment.