METHOD OF TRIMMING ULTRA HIGH STRENGTH HOT STAMPING STEEL SHEET USING COINING

Abstract

The present invention may provide a method of trimming a ultra high strength hot stamping steel sheet using coining, which includes a forming step and a coining step which are simultaneously performed on a hot stamping steel sheet.

Claims

1. A method of trimming a ultra high strength hot stamping steel sheet using coining, the method comprising: forming and coining a hot stamping steel sheet.

2. The method of claim 1, wherein a coining bushing, which is used for the coining, is mounted at an end portion of flanges of dies.

3. The method of claim 2, wherein the dies include an upper die and a lower die and coining bushings are mounted on the flanges of the upper die and the lower die which are used for the forming.

4. The method of claim 3, wherein the coining bushings are made of a material identical to a material applied to the upper die and the lower die which are used for the forming.

5. The method of claim 3, wherein the coining bushings are attachable and detachable to the upper die and the lower die respectively.

6. The method of claim 3, wherein when a thickness of the hot stamping steel sheet is greater than 0 mm and equal to or smaller than approximately 1.5 mm, the coining bushings protrude to the outside of the upper die and the lower die at a height of approximately 0.5 mm, respectively.

7. The method of claim 3, wherein when a thickness of the hot stamping steel sheet is greater than approximately 1.5 mm, the coining bushings protrude to the outside of the the upper die and the lower die at a height which is approximately 30% of the thickness of the hot stamping steel sheet.

8. The method of claim 1, wherein after the forming and the coining are simultaneously performed, hard trimming is performed on the hot stamping steel sheet by using a press.

9. The method of claim 8, further comprising: before the forming and the coining are simultaneously performed on the hot stamping steel sheet, blanking a steel sheet in a form of a coil, and heating the blank steel sheet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a photograph of a laser trimming apparatus in the related art.

[0024] FIG. 2 is a photograph of scattered welding chips produced by laser trimming in the related art.

[0025] FIG. 3 is a photograph illustrating corrosion of a ultra high strength hot stamping steel sheet which occurs due to welding chips or spatters produced during a laser trimming process in the related art.

[0026] FIG. 4 is a step-by-step configuration diagram of a laser trimming method in the related art.

[0027] FIG. 5 is a step-by-step configuration diagram of a method of trimming a ultra high strength hot stamping steel sheet using coining according to an exemplary embodiment of the present invention.

[0028] FIG. 6 is a configuration diagram of a sheared surface of a typical steel sheet which is formed by hard trimming in the related art.

[0029] FIG. 7 is a configuration diagram of a sheared surface of a ultra high strength hot stamping steel sheet which is formed by hard trimming according to the exemplary embodiment of the present invention.

[0030] It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

[0031] In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

[0032] Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

[0033] Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. Terms or words used in the specification and the claims should not be interpreted as a general and dictionary meaning and should be interpreted as a meaning and a concept which conform to the technical spirit of the present invention based on a principle that an inventor can appropriately define a concept of a term in order to describe his/her own invention by the best method. Therefore, the exemplary embodiments disclosed in the present specification and the configurations illustrated in the drawings are just the best exemplary embodiments of the present invention and do not represent all the technical spirit of the present invention. Accordingly, it should be appreciated that various equivalents and modified examples capable of substituting the exemplary embodiments may be made at the time of filing the present application.

[0034] The present invention relates to a method of trimming a ultra high strength hot stamping steel sheet using coining. Recently, the ultra high strength hot stamping steel sheet is increasingly applied to a vehicle in order to ensure weight reduction and stability of the vehicle. In general, the ultra high strength hot stamping steel sheet is produced by blanking a steel sheet in the form of a coil, heating the blank material, and then pressing and cooling a hot stamping steel sheet 20. The steel sheet is formed by being heated at a high temperature, such that the steel sheet is easily formed, and the hot stamping steel sheet 20 is rapidly cooled in a die, such that the hot stamping steel sheet 20 has super high strength, and the residual stress caused by phase transformation is eliminated, such that dimension precision of the ultra high strength hot stamping steel sheet is improved.

[0035] However, the ultra high strength hot stamping steel sheet is impossible to be subjected to trimming (hard trimming) using a typical press due to high strength of a 120 K level or higher. FIG. 1 is a photograph of a laser trimming apparatus 17 in the related art. Because the ultra high strength hot stamping steel sheet is impossible to be subjected to hard trimming in the related art, a laser trimming process or the like was used as illustrated in FIG. 1. The laser trimming has problems in that productivity is low, and a large amount of process costs are required, that is, a large amount of costs for purchasing equipment and maintenance are required.

[0036] FIG. 2 is a photograph of scattered welding chips produced by laser trimming in the related art. FIG. 3 is a photograph illustrating corrosion of a ultra high strength hot stamping steel sheet which occurs due to welding chips or spatters produced during a laser trimming process in the related art. The laser trimming has problems in that as illustrated in FIG. 2, welding chips, spatters, and the like are produced after the process of trimming components because of the nature of laser, and as illustrated in FIG. 3, the components may be corroded due to the welding chips, spatters, and the like, and may be softened due to heat from laser.

[0037] To solve the aforementioned problems in the related art, the present invention provides a method of trimming a ultra high strength hot stamping steel sheet using coining, which includes a forming step and a coining step which are simultaneously performed on a hot stamping steel sheet 200. Coining bushings 107, which are used for the coining step, may be mounted at end portions of a flange, and the coining bushing 107 may be mounted on an upper die 101 and a lower die 103 which are used for the forming step. In addition, the coining bushing 107 may be made of a material identical to a material applied to the upper die 101 and the lower die 103 which are used for the forming step, and the coining bushings 107 may be attached to and detached from the upper die 101 and the lower die 103. Moreover, in a case in which a thickness of the hot stamping steel sheet 200 is greater than 0 mm and equal to or smaller than 1.5 mm, the coining bushings 107 may protrude to the outside of the dies at a height of 0.5 mm, respectively, and in a case in which a thickness of the hot stamping steel sheet 200 is greater than 1.5 mm, the coining bushings 107 may protrude to the outside of the dies at a height which is 30% of the thickness of the hot stamping steel sheet 200. Furthermore, after the forming step and the coining step are simultaneously performed on the hot stamping steel sheet 200, the hot stamping steel sheet 200 may be subjected to hard trimming by a press, and before the forming step and the coining step are simultaneously performed on the hot stamping steel sheet 200, a material blanking step of blanking a steel sheet in the form of a coil, and a heating step of heating the blank material may be further included.

[0038] FIG. 4 is a step-by-step configuration diagram of a laser trimming method in the related art. In the related art, after the blank is manufactured, the blank is conveyed to a hydraulic press while being heated from a room temperature up to 950° C. Thereafter, the heated blank is pressed by the hydraulic press, and an upper die 11 and a lower die 13 of the hydraulic press are cooled by a coolant 15 of a cooling apparatus installed in advance. Thereafter, the ultra high strength hot stamping steel sheet, which has been completely formed, is ejected, and then cut by a laser trimming apparatus 17. However, the ultra high strength hot stamping steel sheet, which is manufactured in the related art as described above, has a problem in that the ultra high strength hot stamping steel sheet cannot be cut by a typical press because of high strength thereof, and for this reason, the ultra high strength hot stamping steel sheet was cut by the laser trimming apparatus 17 as illustrated in FIG. 4. Therefore, to solve the aforementioned problems, the present invention provides a method of trimming a ultra high strength hot stamping steel sheet using coining in which a forming step and a coining step are simultaneously performed. FIG. 5 is a step-by-step configuration diagram of a method of trimming a ultra high strength hot stamping steel sheet using coining according to an exemplary embodiment of the present invention. In an exemplary embodiment of the present invention, a blank is manufactured by blanking a steel sheet in the form of a coil. Thereafter, the blank is heated up to 950° C. while being conveyed to a hydraulic press. Thereafter, as illustrated in the FIG. 4, the blank is pressed by the press dies having the coining bushings 107 mounted at end portions of flanges of the upper die 101 and the lower die 103 The coining is performed on the end portion of the flange simultaneously with the forming step. If the coining is performed after the forming step, there is a problem in that it is impossible to perform the coining because strength of the hot stamping steel sheet 200 becomes higher. The present invention solves the aforementioned problem by simultaneously performing the forming step and the coining step. In the forming step, the heated hot stamping steel sheet 200 is compressed by the coining bushings on the dies. Thereafter, the upper die 101 and the lower die 103 of the hydraulic press are cooled by a coolant 105 of a cooling apparatus installed in advance. Next, hard trimming is performed on the compressed and cooled hot stamping steel sheet 200 by using the press.

[0039] In the method of trimming the ultra high strength hot stamping steel sheet using coining according to an exemplary embodiment of the present invention, a material of the die used for the forming step may be SKD11, or other materials, which are typically used and subjected to vacuum heat treatment, may be applied as a material of the die. Moreover, the coining bushing 107, which is applied to the present invention, may be made of a material identical to a material of the die, and the coining bushing 107 may be attached to and detached from the upper die 101 and the lower die 103 according to an exemplary embodiment of the present invention. If a thickness of the hot stamping steel sheet 200 is 0 to 1.5 mm, the coining bushing 107 applied to the upper die 101 and the coining bushing 107 applied to the lower die 103 may protrude to the outside of the dies at a height of 0.5 mm, respectively. In addition, in a case in which a thickness of the hot stamping steel sheet 200 is greater than 1.5 mm, the coining bushing may protrude at a height which is 30% of the thickness of the hot stamping steel sheet 200.

[0040] FIG. 6 is a configuration diagram of a sheared surface of a typical steel sheet which is formed by hard trimming in the related art. It can be seen that in a case in which a steel sheet is sheared by a typical press in the related art, burrs are formed at a lower side of a sheared surface as illustrated in FIG. 6. FIG. 7 is a configuration diagram of a sheared surface of a ultra high strength hot stamping steel sheet which is formed by hard trimming according to the exemplary embodiment of the present invention. In an exemplary embodiment of the present invention, the forming step and the coining step are simultaneously performed, and as a result, indentations are formed at an end portion of the flange of the ultra high strength hot stamping steel sheet. It can be seen that in a case in which hard trimming is performed by using a press, burrs are not formed as illustrated in FIG. 7.

[0041] In an exemplary embodiment of the present invention, the forming step and the coining step, which use the press, are simultaneously performed on the hot stamping steel sheet 200, such that the hot stamping steel sheet 200 is cut by hard trimming using the press instead of laser trimming, and as a result, there is a great effect in producing the hot stamping steel sheet and components made by using the hot stamping steel sheet, costs are reduced by 50% compared to the related art because high-priced laser trimming equipment is substituted, and cycle time is increased by 500% in an exemplary embodiment of the present invention compared to laser trimming in the related art, such that productivity is improved by hard trimming which makes production efficiency and a production speed excellent. Moreover, it is possible to prevent components from being corroded by welding chips and spatters which are scattered when the laser trimming is performed, quality of the sheared surface is excellent compared to the related art, and it is possible to inhibit burrs from being formed.

[0042] For convenience in explanation and accurate definition in the appended claims, the terms “upper”, “lower”, “inner”, “outer”, “up”, “down”, “upper”, “lower”, “upwards”, “downwards”, “front”, “rear”, “back”, “inside”, “outside”, “inwardly”, “outwardly”, “interior”, “exterior”, “inner”, “outer”, “forwards”, and “backwards” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures.

[0043] The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and their practical application, to thereby enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.