The present invention relates to a manufacturing method and a manufacturing line of the press-molded product made of steel plate.
BACKGROUND
[0002]
　Recently, the automobile, improvement of fuel efficiency from the viewpoint of global environmental conservation is demanded, also required further ensure crashworthiness. Therefore, higher strength and weight of the automobile body has been promoted. Such background, skeletal parts and underbody parts or the like constituting the vehicle body (hereinafter, also referred to as "body components") to tend to press molded article comprising a plate thickness of thin high-strength steel sheet is applied. Strength of the steel sheet to be used as a press-molded product materials are becoming more and more.
[0003]
　Strength of the steel sheet deformability higher steel (press formability) decreases. Therefore, it is difficult to obtain by cold pressing a high strength of the press-molded product with high quality. As strategy, for example, Japanese 2004-353026 (Patent Document 1) in hot stamping as disclosed (hot pressing, also called breath quenching) tends to is employed. In hot stamping, and supplies to the press device steel which is a material after heating up to, for example, about 950 ° C.. The steel plate at the same time hardening the pressing by the mold.
[0004]
　In car body parts, in order to further weight reduction while securing a component performance, the thickness difference thickening is valid. The difference thickening here, a portion governing the component performance, and is less affected portion of the component performance, in which by varying the plate thickness. Conventionally, in order to realize the difference thickening of the body part, as a steel sheet is subjected to press working, tailored blanks are used. Tailored blank is a kind of tailor welded blank having a thickness of thick portion (hereinafter, also referred to as "thick part") and thin portion of the thickness (hereinafter, also referred to as "thin portion") and a.
[0005]
　Tailored blanks, for example, JP 2005-206061 (Patent Document 2) as disclosed in a tailored welded blank (hereinafter, also referred to as "TWB") and, for example, Japanese 2002-316229 (Patent Document 3) tailored rolled blanks as disclosed in (hereinafter, also referred to as "TRB") are classified into. TWB is obtained joining by welding a plurality of steel plates in which the plate thickness and the like are different. Meanwhile, TRB by adjusting the gap between the rolling rolls paired in making the steel sheet is obtained by changing the plate thickness.
[0006]
　However, the TWB and TRB, not so large plate thickness difference between the thick part and the thin part. That is, the ratio "t1 / t2" with the thickness t2 of the plate thickness t1 and a thin portion of the thick part is only about 1.8 at most. Furthermore, the TWB, there is undeniable to occur localized intensity changes due to welding. In TRB, the size of each area of ​​the thick part and the thin part inevitably large also. Therefore, a low degree of freedom in designing the body parts. Therefore, the weight of the press molded article using the tailored blank is limited.
CITATION
Patent Document
[0007]
Patent Document 1: JP 2004-353026 Patent Publication
Patent Document 2: JP 2005-206061 Patent Publication
Patent Document 3: JP 2002-316229 JP
Summary of the Invention
Problems that the Invention is to Solve
[0008]
　The present invention has been made in view of the above circumstances. One object of the present invention is to provide a manufacturing method and a manufacturing line for high-strength, yet the weight reduction is a press-molded article as possible.
Means for Solving the Problems
[0009]
　Method for producing a press-molded product according to an embodiment of the present invention includes a steel plate heating step, a hot forging step, and hot stamping step. The steel plate heating step, heating the steel sheet to above 950 ° C.. The hot forging process, using a pressing device, forged steel, shaping the tailor welded blank. The hot stamping process, using different pressing device and said pressing device, by pressing and molding a press molded product of tailor welded blank by the mold, the molded press formed product is cooled in the mold.
[0010]
　Production line of the press-molded product according to an embodiment of the present invention comprises a forging press apparatus, and a press device for hot stamping, and at least one heating furnace, and at least one manipulator, a.
The invention's effect
[0011]
　According to the manufacturing method and a manufacturing line of the press-molded product according to an embodiment of the present invention can be produced press-molded product capable of high-strength, yet lightweight.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012]
[1] Figure 1 is a flow diagram illustrating a method for manufacturing a press molded article according to an embodiment of the present invention.
FIG. 2 is a diagram schematically showing a process of the method for manufacturing a press molded article according to an embodiment of the present invention.
FIG. 3 is a schematic diagram showing an example of a production line for producing the press molded product.
[Figure 4A] Figure 4A is a cross-sectional view showing an initial state in the hot stamping of the first embodiment.
[Figure 4B] Figure 4B is a cross-sectional view showing a state of a medium-term in hot stamping of the first embodiment.
[Figure 4C] Figure 4C is a cross-sectional view showing a state of the end of the hot stamping of the first embodiment.
[Figure 5A] Figure 5A is a cross-sectional view showing an initial state in the hot stamping of a second embodiment.
[Figure 5B] Figure 5B is a cross-sectional view showing a state of a medium-term in the hot stamping of a second embodiment.
[Figure 5C] Figure 5C is a cross-sectional view showing a state of the end of the hot stamping of a second embodiment.
[Figure 6A] Figure 6A is a cross-sectional view schematically showing an analysis model of the comparative example used in the bending test examples.
[Figure 6B] Figure 6B is a cross-sectional view schematically showing an analysis model of the present invention examples used in bending test examples.
[7] FIG. 7 is a diagram summarizing the test results of Examples.
DESCRIPTION OF THE INVENTION
[0013]
　Method for producing a press-molded product according to an embodiment of the present invention includes a steel plate heating step, the hot forging process, hot stamping (hereinafter, also referred to as "HS") and step. The steel plate heating step, heating the steel sheet to above 950 ° C.. The hot forging process, using a pressing device, forged steel, formed into tailor welded blank. The HS step, using different pressing device and said pressing device, by pressing and molding a press molded product of tailor welded blank by the mold, cooling the press-molded product in the mold.
[0014]
　In a typical example, the manufacturing method of the present embodiment further comprises a preparation step. The preparation process, the thickness is prepared certain steel. Further, in a typical example, the manufacturing method of the present embodiment further includes a tailor welded blank heating step. The tailor welded blank heating step, after the hot forging process, before the HS process, the tailor welded blank A c3 transformation point or higher, "A c3 heated to a temperature of less than transformation point + 150 ℃". Further, in a typical example, the manufacturing method of the present embodiment further includes a cooling step. In the cooling step after hot forging step, prior to the tailor welded blank heating step, cooling the tailor welded blank. Tailor welded blank here, it has a thick portion and a thin portion of the thick thickness.
[0015]
　According to this manufacturing method, by hot forging, it can be molded a large different thickness steel sheet having a thickness difference between the thick portion of the thickness (thick part) and a thin portion (thin portion) thick. Then, HS by, subjected to press working and quenching the tailor welded blank, thereby, the strength of each part is high, it is possible to obtain a weight of lighter press-molded product. Therefore, according to the manufacturing method according to the present embodiment can produce dramatically press molded article that can be lightweight even only high strength.
[0016]
　Press-molded product is applied, for example, to the body part of an automobile. Body parts, skeletal parts (for example: pillar, side members, side sills, cross members, etc.), underbody parts (for example, toe control link, suspension arm, etc.), other reinforcing component (for example, bumper beams, door impact beams, etc. ), and the like.
[0017]
　In tailor welded blank according to the above manufacturing method, the thickness of the thick portion of the thickness t1 and the ratio "t1 / t2" with the thickness of the thin portion of the thickness t2 (hereinafter, also referred to as "ItaAtsuhi") of 1.8 it is possible to exceed the. In this case, it is possible to further reduce the weight of the press-molded product. The upper limit of the ItaAtsuhi "t1 / t2" is not particularly limited. Considering the uniformity of press formability and hardening in the HS process, the upper limit of ItaAtsuhi "t1 / t2" is 3.5.
[0018]
　The above manufacturing method, comprising the tensile strength of the press-molded product can be at least 1300 MPa. In this case, part performance is improved in terms such as strength and weight of the press-molded product (lighter).
[0019]
　In the above manufacturing method, the steel sheet contains, by mass%, C: 0.15 ~ 0.60%, Si: 0.001 ~ 2.0%, Mn: 0.5 ~ 3.0%, P: 0. 0.05% or less, S: 0.01% or less, sol. Al: 0.001 ~ 1.0%, N: 0.01% or less and B: containing 0.01% or less, the balance being Fe and impurities, it is preferable. This steel sheet, instead of a part of Fe, Ti, Nb, V, Cr, Mo, containing 0.03 to 1.0% in total of one or two or more selected from the group consisting of Cu and Ni it may be. In this case, it is possible to make the tensile strength of the press-formed article more than 1300 MPa.
[0020]
　Production line of the press-molded product according to an embodiment of the present invention comprises a forging press apparatus, and HS a press device, and at least one heating furnace, and at least one manipulator, a. According to the production line of the present embodiment can be produced above the press-molded product.
[0021]
　Hereinafter, the manufacturing method and manufacturing line of the press-molded product of the present invention will be described in detail embodiments thereof.
[0022]
　[Manufacturing Method]
　Fig. 1 is a flow diagram illustrating a method for manufacturing a press molded article according to an embodiment of the present invention. Figure 2 is a schematic diagram showing a process of the method for manufacturing a press molded article according to an embodiment of the present invention. 1, the manufacturing method of this embodiment includes a preparing step (Step # 5), a first heating step (step # 10), and hot forging step (step # 15), the second comprising heating step (step # 20), a hot stamping process (step # 25), the. The first heating step is steel heating step. The second heating step is tailor welded blank heating step. Hereinafter, with reference to FIGS. 1 and 2 will be described in detail for each step.
[0023]
　In the present embodiment, as shown in FIG. 2 illustrates a case where the cross-sectional shape to manufacture a press-molded article 1 of the hat-shaped. Press-molded product 1 includes a top plate 2, the two vertical wall portions 3, the two flanges 4, and two upper ridge portion 5, and two lower ridge portion 6, a. The upper ridge portion 5 connecting the top plate portion 2 and the vertical wall portion 3. Lower ridge portion 6 connects the vertical wall portion 3 and the flange portion 4.
[0024]
　Such press-molded article 1 having a hat-shaped cross-section is applied to, for example, a bumper beam of the vehicle body parts. Usually, the bumper beam, the top plate portion 2 is arranged to face the inside or outside of the vehicle body. In either case, the load caused by collision propagates the vertical wall portion 3. Parts performance required of the bumper beam is high maximum load that the impact load can withstand when it is loaded, is that large absorbed energy. Therefore, in the bumper beam, the portion which governs the component performance, vertical wall portions 3, a top ridge portion 5 and the lower ridge part 6, part is less affected on component performance top plate 2 and the flange portion 4. Therefore, the thickness of the top plate 2 and the flange portion 4, the vertical wall portion 3, as compared to the thickness of the upper ridge part 5 and the lower ridge part 6, may be thinned. Higher intensity of each part bumper beam, particularly the thinner the thickness of the top plate portion 2, the bumper beam is also lighter only high strength. In press-molded article 1 shown in FIG. 2, the thickness of the top plate 2 is made significantly thinner than the plate thickness of the other portions.
[0025]
　Preparing process (step # 5), as the material press-formed article 1, to prepare a steel sheet 10. Steel 10 is a thick, was cut from a fixed hot rolled steel sheets, cold-rolled steel plate or the like. Thickness constant hot rolled steel sheet, conventional hot-rolled steel sheets and cold-rolled steel sheet, means cold rolled steel sheet, the thickness difference between 25mm from the widthwise center and the edge of the steel strip in the state of a coil after rolling it is 0.2mm or less. Hot-rolled steel sheet, thickness variation within the steel sheet was cut from the cold-rolled steel sheet 10 (blank) is natural 0.2mm or less. The thickness of the steel plate 10 is about 2.0 ~ 6.0 mm. In FIG. 2, so as to correspond to the shape of the press-molded product 1 having a hat-shaped cross-section, illustrating the steel plate 10 which is cut in a rectangular shape.
[0026]
　In the first heating step (step # 10), placed steel plate 10 in the first heating furnace 20 and heated to above 950 ° C.. The steel plate 10 in the next step is to hot forging. Preferably, the heating temperature of the steel sheet 10 is 1000 ° C. or higher. The upper limit of the heating temperature, as long as it is below the melting point of the steel material of the steel plate 10 is not particularly limited. Preferably, the heating temperature of the steel sheet 10 is 1350 ° C. or less.
[0027]
　In the hot forging step (step # 15), the heated steel sheet 10 taken out from the first heating furnace 20, and supplies the steel sheet 10 to the forging press apparatus 21, carrying out the forging. In forging, paired upper and lower dies 21a, using 21b. Mold 21a, by 21b, is rolling repeatedly in the thickness direction of the part of the area of ​​the steel plate 10. Its reduction region may be a whole of the steel plate 10. Forging, may be a die forging, it may be a free forging.
[0028]
　By hot forging, shaping the steel plate 10 to the tailor welded blank 11. Tailor welded blank 11 has a thick part 12 and the thin portion 13. Since the thick portion by hot forging adding repetitive pressure 12 and the thin portion 13 is molded, it is possible to increase the plate thickness difference between the thick part 12 and the thin portion 13. That is, the thickness ratio of the thickness t2 of the plate thickness t1 and a thin portion 13 of the thick part 12 "t1 / t2" is also possible to exceed 1.8. TWB, in tailored blanks, such as TRB, it is difficult to realize such a large thickness ratio. FIG 2 is a thick part 12 and the plate thickness ratio of the thin portion 13 "t1 / t2" is 1.8 or more, the thin portion 13 is formed along the longitudinal direction in the central portion in the width direction difference illustrate the steel plate 11.
[0029]
　Moreover, since the thick part 12 and the thin portion 13 is formed on the basis of freely designing can mold 21a, the shape of the 21b, the size of each area of ​​the thick part 12 and the thin portion 13 is not limited. In TRB, the size of each of those regions are limited to some extent large. Furthermore, since the grain flows are continuous over the entire of the thick portion 12 and the thin portions 13, decrease in strength at the boundary of the thick portion 12 and the thin portion 13 does not occur. This can not be a TWB. Further, since the tailor welded blank 11 by hot forging is molded, the internal structure of the tailor welded blank 11, in particular the internal tissue of the reduction amount of large thin portion 13 is made dense and homogeneous.
[0030]
　Incidentally, during forging, prior to the geometry of the desired tailor welded blank 11 is obtained, the temperature is the predetermined temperature (eg: 950 ° C.) of the steel plate 10 When the lower, the steel plate 10 back to the first heating step it may be heated to a predetermined temperature or more. Then, it is sufficient again moves to hot forging process.
[0031]
　After hot forging, the tailor welded blank 11 A c3 it is desirable to cool to a temperature lower than the transformation point. When carrying out the cooling, toughness of the final product than in the case of not performing the cooling (press molding) is excellent, there is a advantage. In this case, the tailor welded blank 11 may be cooled to room temperature. This cooling may be air-cooled, it may be a rapid cooling such as water cooling.
[0032]
　Next, in the second heating step (step # 20), placed tailor welded blank 11 in the second heating furnace 22, A c3 transformation point or higher, "A c3 heated to a temperature of less than transformation point + 150 ℃". The tailor welded blank 11 in the next step is to implement the HS (pressing and quenching). Through the second heating step, the internal structure of the tailor welded blank 11 is austenite. The second heating furnace 22 may be dedicated to a second heating step may share a first heating furnace 20 used in the first heating step. However, the second heating step is not necessary. For example, without performing cooling after hot forging, the temperature of the tailor welded blank 11 is A c3 transformation point or higher, "A c3 if it is ensured in the following transformation point + 150 ℃", the second heating step can be omitted . However, when carrying out the cooling after hot forging, the second heating step is required. Even if you did not carried the cooled after hot forging, it is preferable to go through the second heating step. Temperature of tailor welded blank 11 after hot forging or a heterogeneous, A c3 because often has lowered below the transformation point. Or a subsequent temperature of the tailor welded blank 11 fed to the HS step uneven, A c3 when or less than the transformation point, quenching failure occurs or the desired strength in the final product is not locations obtained there is likely to occur.
[0033]
　In HS step (step # 25), A c3 transformation point or higher, "A c3 sends transformation point + 150 ℃" following tailor welded blank 11 in hot stamping for press device 23, to implement the HS. Tailor welded blank 11 A c3 transformation point or higher, "A c3 for the following transformation point + 150 ℃", may be heated to tailor welded blank 11, for example in the second heating furnace 22. Hot stamping for the press device 23 is different from the forging press apparatus 21. In HS, die paired with the upper and lower (eg dies and punches) 23a, using 23b. Mold 23a, by 23b, by forming a press-molded article 1 by pressing the tailor welded blank 11, to cool the press-molded product 1 which is molded mold 23a, within 23b. Die 23a, the press cooling of the molded article 1 in a 23b is rapidly cooled. Rapid cooling means cooling the cooling rate to be transformed into martensite or bainite. When carrying out yet another HS step after the HS process, allowing bainite principal tissue. This cooling mold 23a, cooling water circulating in the interior of the 23b, the mold 23a, performed by heat exchange between 23b and press-molded product 1. In addition, the mold 23a, at the time of press completion by 23b, may be carried out cooling by injecting directly the cooling water to the press-molded article 1 mold 23a, from 23b.
[0034]
　By pressing the HS process, press-molded article 1 of the desired dimensions is formed. At that time, in the example shown in FIG. 2, the thin portion 13 of the tailor welded blank 11 is formed into a top plate 2 of the press-molded product 1. Thick portion 12 of the tailor welded blank 11, the upper ridge part 5 of the press-molded product 1, the vertical wall portion 3 is shaped in the lower ridge part 6, and the flange portion 4. Further, the cooling in the HS process, press-molded article 1 is hardened. By quenching, the internal structure of the press-molded article 1 is transformed into a hard phase such as martensite austenite becomes martensite (including bainite). Strictly speaking, the internal structure of the press-molded article 1, the volume fraction of martensite is 80% or more. Thus, as shown in FIG. 2, thin press-formed article 1 than the plate thickness of the top plate portion 2 is the thickness of the other portion can be obtained.
[0035]
　Such press-molded product 1 which is formed in the order with a martensitic structure over the entire area, the high strength of each part. For example, by adjusting the chemical composition of the steel sheet 10 to be used as the material, the tensile strength of the press-molded article 1 becomes more than 1300 MPa. Furthermore, tailor welded blank 11 having a dense internal structure by hot forging is molded. Since the press-molded product 1 are those molded from the tailor welded blank 11, the toughness of the press-molded product 1 is high. By forging, because coarsening of the particle size of the austenite is the source of martensite (gamma particle diameter) is suppressed. Also, large tailor welded blank 11 of sheet thickness ratio is formed by hot forging. Since the press-molded product 1 are those molded from the tailor welded blank 11, the weight of the press-molded article 1 becomes lighter. Therefore, according to the manufacturing method of this embodiment, the press-molded article 1 capable of high-strength, yet lightweight can be manufactured.
[0036]
　Hereinafter, an example of the chemical composition of the steel sheet as a material in the production method of this embodiment. Steel sheet according to the present embodiment illustrated herein, is intended tensile strength after quenching is equal to or more than 1300 MPa. The chemical composition of this steel sheet contains the following elements. "%" Related elements, unless otherwise specified, it means mass%.
[0037]
　C: 0.15 ~ 0.60%
　strength after quenching is determined primarily by the content of carbon (C), which governs the hardness of the martensite phase. Therefore, C content in accordance with the required strength is determined. To ensure the tensile strength of not less than 1300MPa is, C content is 0.15% or more. More preferably, C content exceeds 0.20%. On the other hand, if the C content is too high, the toughness is deteriorated after quenching, increases risk of brittle fracture occurs. Therefore, the upper limit of the C content is 0.60%. The preferable upper limit of C content is 0.50%.
[0038]
　Si: 0.001 ~ 2.0%
　silicon (Si) are in the course of cooling from the austenite phase to be transformed into low-temperature transformation phase, suppresses the formation of carbides. That, Si, without degrading the ductility, to improve the ductility in some cases, increasing the strength after quenching. If Si content is too low, the effect can not be obtained. Therefore, Si content is 0.001% or more. More preferably, Si content is 0.05% or more. On the other hand, if the Si content is too high, on the above effects is economically disadvantageous saturated, deterioration of the surface properties of the steel becomes significantly. Therefore, Si content is 2.0% or less. More preferably, Si content is 1.5% or less.
[0039]
　Mn: 0.5 ~ 3.0%
　manganese (Mn) increases the hardenability of steel to stabilize the strength after quenching. However, if the Mn content is too low, it is difficult to secure a tensile strength of not less than 1300 MPa. Therefore, Mn content is 0.5% or more. More preferably, Mn content is 1.0% or more. If Mn content is 1.0% or more, it is possible to secure a tensile strength of not less than 1350 MPa. On the other hand, if the Mn content is too high, the band-like martensite structure becomes uneven, deterioration of impact properties becomes remarkable. Therefore, Mn content is 3.0% or less. Considering the alloy cost, the upper limit of the Mn content is 2.5%.
[0040]
　P: 0.05% or less
　Phosphorus (P) is generally is an impurity which is inevitably contained in the steel, the solid solution strengthening, enhancing the strength. On the other hand, if the P content is too high, weldability markedly deteriorate. In addition, the risk of brittle fracture increases when aimed at the tensile strength of not less than 2500MPa. Accordingly, P content is 0.05% or less. More preferably, P content is 0.02% or less. The lower limit of the P content is not particularly limited. To obtain the effect of the more reliably the lower limit of the P content is 0.003%.
[0041]
　S: 0.01% or less
　Sulfur (S) is an impurity which is inevitably contained in the steel combines with Mn and Ti is deposited to produce a sulfide. If the amount of the precipitate is too increased, the interface of the deposit and the main phase may become starting points of fracture. Therefore, S content is low it is preferable. Thus, S content is 0.01% or less. More preferably, S content is 0.008% or less. The lower limit of the S content is not particularly limited. Considering the production cost, the lower limit of the S content is 0.0015%, more preferably 0.003%.
[0042]
　sol. Al: 0.001 ~ 1.0%
　aluminum (Al) is to deoxidation steel and soundness steel, also improving the yield of carbonitride-forming elements such as Ti. If the Al content is too low, it is difficult to obtain the above effect. Therefore, Al content is 0.001% or more. More preferably, Al content is 0.015% or more. On the other hand, if the Al content is too high, reduction in weldability is significantly oxide inclusions deterioration of surface properties of the steel is remarkably increased. Therefore, Al content is 1.0% or less. More preferably, Al content is less 0.080%. In this specification, Al content sol. Means Al (acid soluble Al).
[0043]
　N: 0.01% or less
　Nitrogen (N) is an impurity which is inevitably contained in the steel. Considering weldability, N content is low it is preferable. On the other hand, if the N content is too high, decrease the weldability becomes significant. Therefore, N content is 0.01% or less. More preferably, N content is 0.006% or less. The lower limit of the N content is not particularly limited. Considering the production cost, the lower limit of the N content is 0.0015%.
[0044]
　B: 0.01% or less
　boron (B) increases the low-temperature toughness. However, if the B content is too high, hot workability is degraded, the hot rolling becomes difficult. Therefore, B content is 0.01% or less. More preferably, B content is 0.0050%. The lower limit of the B content is not particularly limited. To obtain the effect of the more certainly, B content is 0.0003% or more.
[0045]
　The remainder of the chemical composition of the steel sheet according to the present embodiment is composed of Fe and impurities. Here, the impurities, in producing the steel sheet industrially, ore as a raw material, there is to be mixed from scrap, or manufacturing environment, the allowable range of the steel sheet of the present embodiment does not adversely affect It is the means something.
[0046]
　The above steel sheet is further, in place of part of Fe, Ti, Nb, V, Cr, Mo, 0.03 ~ total one or two or more selected from the group consisting of Cu and Ni 1. 0% may be contained. All of these elements are also optional element to enhance the hardenability of steel to stabilize the toughness or strength of the steel after quenching. If the inclusion of these optional elements, if is too low content of optional elements, the above effects do not effectively expressed. Accordingly, the lower limit of the total content of any element is 0.03%. On the other hand, even if too high content of optional elements, the above effect is saturated. Therefore, the upper limit of the total content of any element is 1.0%.
[0047]
　A steel plate according to the present embodiment c3 transformation point is calculated for example by equation (1) below.
　A c3 = 910-203 × √C) -15.2 × Ni + 44.7 × Si + 104 × V + 31.5 × Mo-30 × Mn-11 × Cr-20 × Cu + 700 × P + 400 × Al + 50 × Ti ... (1)
　where , each element symbol in the formula (1), the content of the corresponding element (mass%) is substituted. Al is sol. It means Al.
[0048]
　[Production Line]
　FIG. 3 is a schematic diagram showing an example of a production line for producing the press molded product. Referring to FIG. 3, the production line for producing the press molded article, the forging press apparatus 21, and the HS press device 23, and at least one heating furnace 20, and at least one manipulator 50, the provided. In fact, the production line is provided with a control unit 51 for controlling all of these devices 21,23,20 and 50.
[0049]
　[Forging press apparatus]
　forging press apparatus 21 is used in the above hot forging process. Forging press apparatus 21, the high temperature of the steel sheet (the blank) hit repeatedly by the mold 21a and 21b, forging the tailor welded blank. Forging press apparatus 21 is preferably provided with a water cooling device for cooling the tailor welded blank forged. In order to obtain excellent final product (press molding) toughness.
[0050]
　[For hot stamping press device]
　HS for press device 23 is used in the above HS steps. HS for press apparatus 23, the high temperature of tailor welded blank by pressing by the mold 23a and 23b, forming a press-molded product. Furthermore, HS for press device 23, the cooled mold 23a and 23b, or the press-molded product in the mold 23a and 23b to cool the mold 23a and 23b by the cooling water sprayed, quenching.
[0051]
　Here, the HS, from tailor welded blank including a thick portion and a thin portion, in order to obtain a press-molded article having a desired strength, A c3 and the cooling rate of the press-molded article molded by the transformation point or higher it is desirable to appropriately control the cooling end point temperature. In press-thick part it is less likely to be cooled than the thin portion. The heat capacity of the thick part is because larger than that of the thin portion. Therefore, it is desirable to apply a strong cooling than the thin portion in the thick part.
[0052]
　In the thick portion, if not given the cooling rate of the aim, the insufficient production of the desired hard metal structure. In this case, the press-molded product, the metal structure becomes uneven, strength becomes uneven. Furthermore, the difference and phase transformation strain difference in thermal contraction resulting from the difference in the metal structure, it is difficult to obtain the aimed shape dimensional accuracy. Further, if it is cooled at a faster rate than the thick part and the boundary portion is thick portion and thin portion of the thin portion, the strength of the boundary portion becomes higher than other portions. In this case, when a collision load in the press-molded article was given, there is a risk that the boundary portion by the secondary deformation is broken.
[0053]
　Thus it is desirable to enhance the cooling of the thick part at the time of the HS. An example of such adaptable HS for press device to the situation below.
[0054]
　FIGS. 4A ~ 4C are cross-sectional views showing a first embodiment of the HS press. 4A shows a machining initial state, FIG. 4B shows a state of the machining metaphase, Fig. 4C shows the state of the working end. The HS for press apparatus 30 includes a upper die 31 and lower die 32. The upper die 31 includes a first surface 31a that corresponds to the thick part 12, a second surface 31b that corresponds to the thin portion 13, a. The height of the step of the first face 31a and second face 31b of the upper die 31 h2 is smaller than the height h1 of the step of the thick portion 12 and the thin portion 13 in the tailor welded blank 11. The upper die 31 is supported by the upper holder (not shown). Cooling water is circulated inside the upper die 31.
[0055]
　Referring to Figure 4A, the high temperature of the tailor welded blank 11 comprising a thick part 12 and the thin portion 13 is placed on the lower die 32. Referring to FIG. 4B, when the upper holder is lowered, first, the first surface 31a in the upper die 31 is in contact with the thick portion 12 of the tailor welded blank 11. Further the upper holder descends, the thick portion 12 is processed by the first surface 31a.
[0056]
　Further when the upper holder descends, as shown in FIG. 4C, the second surface 31b of the upper die 31 is in contact with the thin portion 13 of the tailor welded blank 11. Further, when the upper die holder is moved down to the bottom dead center, the thin portion 13 is processed by the second face 31b.
[0057]
　FIGS. 5A ~ 5C are sectional views showing a second embodiment of the HS press. Figure 5A shows the processing initial state, FIG. 5B shows a state of the machining metaphase, Fig. 5C shows a state of processing end. The HS for press apparatus 40 includes a first upper die 41, a second upper die 42 and lower die 43. The first upper die 41 is disposed at a position corresponding to the thick part 12. The second upper die 42 is disposed at a position corresponding to the thinned portion 13. The first upper die 41 through the first pressure member 45 is supported by the upper holder 44. The second upper die 42, through the second pressing member 46 is supported by the upper holder 44. First and second pressure members 45 and 46 is a hydraulic cylinder or a spring or the like. Cooling water is circulated inside the first and second upper die 41 and 42.
[0058]
　Referring to Figure 5A, the high temperature of the tailor welded blank 11 comprising a thick part 12 and the thin portion 13 is placed on the lower die 43. Referring to FIG 5B, when the upper die holder 44 moves downward, first, the first upper die 41 is in contact with the thick portion 12 of the tailor welded blank 11. Further the upper holder 44 descends, the first pressing member 45 shrinks while applying pressure to the first upper die 41, the thick portion 12 is processed by the first upper die 41.
[0059]
　Further when the upper holder 44 descends, as shown in FIG. 5C, the second upper die 42 is in contact with the thin portion 13 of the tailor welded blank 11. Further the upper holder 44 lowered to the bottom dead center, the second pressing member 46 shrinks while applying a pressure to the second upper die 42, the thin portion 13 is processed by the second upper die 42.
[0060]
　Any of the first embodiment and the second embodiment, when the HS, the processing of the thick portion 12 precedes the machining of the thin portion 13. Therefore, cooling of the thick portion 12 precedes the cooling of the thin portion 13. As a result, it is possible to enhance the cooling of the thick portion 12.
[0061]
　[Furnace]
　Referring to FIG 3, the heating furnace 20 is used in the first heating step and the second heating step described above. Furnace 20 heats hot forging preceding steel sheet (blank). The heating furnace 20 heats the tailor welded blank obtained by hot forging. Steel sheet is heated above 950 ° C.. Tailor welded blank is A c3 transformation point or higher, "A c3 is heated to a temperature of less than transformation point + 150 ℃". Production line comprises one of the heating furnace 20 may share the heating furnace 20 in the first and second heating steps. However, there are a heating temperature of a target in a first heating step, also the heating temperature of a target in the second heating step does not match. Therefore, when sharing one of the heating furnace 20, it is desirable to divide into two or more different sections of the target heating temperature inside the heating furnace 20. However, the production line is provided with two or more heating furnace 20, may each heating furnace 20 as a dedicated in each heating step. To the production line in a compact, inside the heating furnace 20 is partitioned by the shelves plurality of stages, it is desirable that the steel sheet or tailor welded blank to each of the shelves is stored.
[0062]
　[Manipulator]
　steel (blank) and tailor welded blank (hereinafter collectively referred to as "flat products") is to be heated above 900 ° C., humans flat products can not be handled directly. Accordingly, conveyance of flat products is carried out by the machine. Flat products is or are charged into between the molds of the forging press apparatus 21, or retrieved. Furthermore, flat products is or are charged into between the molds of the HS press device 23, or withdrawn. Therefore, the transport of the flat products is performed by the manipulator 50 (transport robot) that can lift a flat products.
[0063]
　Conveying the manipulator 50 is carried out is as follows.
And transportation to forging press apparatus 21 from the furnace 20
the conveying from forging press apparatus 21 in the case-reheat is required to the heating furnace 20
heating furnace from forging press apparatus 21 after-hot forging is completed transport of up to 20
from and heating furnace 20 conveyed to the HS press device 23
removal of the press-molded product from-HS for press device 23
[0064]
　Production line comprises a single manipulator 50, it may be borne all conveyed to the manipulator 50. Furthermore, the manufacturing line comprises a plurality of manipulators 50 may be allocated to transport to each manipulator 50. Movable range of the manipulator 50, the transport destination transport origin of each device 21, 23 and 20 are set to fall.
[0065]
　[Control Device
　Temperature blank taken out from the heating furnace 20 is gradually reduced. Therefore, it is necessary to manage the heating temperature of the transfer time and the heating furnace 20 by the manipulator 50. Further, it is necessary to take-out operation and the charging operation by the manipulator 50 works with the heating furnace 20 and the press device 21 and 23. Each device 21, 23 and 20 constituting the production line this reason are controlled by a control device 51.
[0066]
　Controller 51 outputs a signal for controlling the operation of the opening and closing manipulator 50 of the door of the heating furnace 20. A plurality of steel plates (blank) or tailor welded blank is inside the heating furnace 20 is stored. Storing status of each flat products in the heating furnace 20 is recorded in the memory of the control device 51. The control unit 51, based on furnace temperature and standing furnace time of each flat products of the heating furnace 20, take-out whether flat products from the heating furnace 20 is determined. The control device 51, for example, comprises the following functions.
And heating furnace 20 removal determination of the steel sheet from
-furnace 20 forging press apparatus 21 to the manipulator 50 motion control from
-furnace 20 in the management of free space
forging press apparatus sometimes necessary, reheating operation control of the manipulator 50 to the heating furnace 20 from 21
control the operation of the manipulator 50 from the forging press apparatus 21 after-hot forging is after the completion to the heating furnace 20
takeout whether tailor welded blank from-heating furnace 20 determination
operation control of the manipulator 50 from-heating furnace 20 to the HS press device 23
controlling the operation of the manipulator 50 for taking out the press-molded product from the-HS for press device 23
[0067]
　To perform these functions, the control unit 51, signals such as processing ready and processing completion is inputted from the forging press apparatus 21 and the HS press device 23. Operation control of the manipulator 50 may control every moment the position of the manipulator 50. The operation control of the manipulator 50, manipulator 50 may be one that a predetermined operation by a signal output from the controller 51. The control device 51 may have a function of changing in accordance with ejection temperature of the blank from the furnace 20 to the temperature. The control device 51, the transport time from the heating furnace 20 to the forging press apparatus 21 and the HS press device 23 may have a function of changing in accordance with temperature.
Example
[0068]
　To confirm the effects of the manufacturing method of a press-molded product of the present embodiment was carried out numerical analysis the following test. Specifically, to fabricate two types of analysis model having assumed hat-shaped cross-section a bumper beam. Then, for each model, it was performed numerical analysis simulating the crush test three-point bending. Generally, crush test three-point bending is used to evaluate the performance of the bumper beam.
[0069]
　[Test conditions]
　Figures 6A and 6B are sectional views showing an analysis model used in bending test of Example schematically. Figure 6A shows an analysis model of the comparative example, FIG. 6B shows an analysis model of the present invention embodiment. As shown in FIG. 6A, the model A of the comparative example was the plate thickness over the entire area at a constant 2.0 mm. As shown in FIG. 6B, the model B of the present invention example was the thickness of the top plate 2 to 1.0mm half of the thickness of the other portion.
[0070]
　Tensile strength, none of the models A and B was 1300 MPa. In both models A and B also joined the common closing plate (not shown) in the flange portion 4 was closed between the flange portion 4 with each other by the closing plate.
[0071]
　Each model A and B supported from closing plate side two points. Supporting point interval of each model A and B was 800 mm. The center of the support point of each model A and B, to collide with the impactor from the top plate portion 2, and crushing the models A and B. The radius of curvature of the tip of the impactor was 150 mm. Collision speed of the impactor was 9km / h.
[0072]
　[Test Results]
　Fig. 7 is a diagram summarizing the test results of Examples. It is shown that from the results shown in FIG.
[0073]
　Distribution of load in accordance with the stroke of the impactor, there is almost no difference in the Model B Model A and Invention Example Comparative Example. In other words, the maximum load and absorbed energy at the time when the collision load is loaded is comparable with Model B Model A and Invention Example Comparative Example. Nevertheless, the weight is lighter better model B of the present invention embodiment. Therefore, the thickness of the top plate portion 2 is less affected by the component performance, by reducing the thickness of the top plate 2, while securing the components performance was found to be lighter weight.
[0074]
　Others The invention is not limited to the above embodiments, without departing from the scope of the present invention, it is needless to say various modifications are possible.
Industrial Applicability
[0075]
　The method of press-molded article produced the present invention can be effectively utilized in the production of the press-molded product for automobile high strength is required.
DESCRIPTION OF SYMBOLS
[0076]
　　1 press-molded product
　　2 the top plate
　　3 the vertical wall portion
　　4 flange
　　5 upper ridge portion
　　6 lower ridgeline portion
　　10 steel
　　20 first heating furnace
　　21 for forging press apparatus
　　21a, 21b dies
　　11 tailor welded blank
　　12 thick part
　　13 thin portion
　　t1 thick part of the plate thickness
　　t2 thin portion of the thickness
　　22 second heating furnace
　　23,30,40 hot stamping a press device
　　23a, 23b die
　　50 the manipulator
　　51 controller

WE claims

[Requested item 1]
　And the steel sheet heating step of heating the steel sheet to above 950 ° C.,
　using a press device, and forging the steel sheet, and hot forging step of forming a tailor welded blank,
　using different press apparatus as the press apparatus, the difference steel plate was molded into a press-molded product by pressing by the mold, including a hot stamping step of cooling the press-molded product in the mold, the manufacturing method of the press-molded product.
[Requested item 2]
　A method of press-molded product produced according to claim 1,
　after the hot forging process, prior to the hot stamping step, the difference steel plate A c3 transformation point or higher, "A c3 transformation point + 150 ℃ tailor welded blank includes a heating step, the manufacturing method of the press-molded product is heated "to a temperature below.
[Requested item 3]
　A method of press-molded product produced according to claim 2,
　after the hot forging step, prior to said difference steel plate heating step includes a cooling step of cooling the difference steel plate, of the press-molded product Production method.
[Requested item 4]
　A method of press-molded product produced according to any one of claims 1 to 3,
　wherein the difference steel plate has a thick portion and a thin portion of the thickness of the thickness, the thickness of the thick portion of the thick t1 and the ratio between the thickness of the thin portion of the thickness t2 't1 / t2 "is greater than 1.8, the manufacturing method of the press-molded product.
[Requested item 5]
　A method of press-molded product produced according to claims 1 to any one of 4,
　the press tensile strength of the molded article is not less than 1300 MPa, the manufacturing method of the press-molded product.
[Requested item 6]
　A method of press-molded product produced according to any one of claims 1 to 5,
　wherein the steel sheet contains, by mass%, C: 0.15 ~ 0.60% , Si: 0.001 ~ 2. 0%, Mn: 0.5 ~ 3.0 %, P: 0.05% or less, S: 0.01% or less, sol. Al: 0.001 ~ 1.0%, N : 0.01% or less and B: containing 0.01% or less, the balance being Fe and impurities, the manufacturing method of the press-molded product.
[Requested item 7]
　A method of press-molded product produced according to claim 6,
　wherein the steel sheet, instead of a part of Fe, Ti, Nb, V, Cr, Mo, 1 kind selected from the group consisting of Cu and Ni or containing 0.03 to 1.0% of two or more in total, the production method of the press-molded product.
[Requested item 8]
　And forging press apparatus,
　and a press device for hot stamping,
　and at least one heating furnace,
　and a least one manipulator of the press-molded product manufacturing line.
[Requested item 9]
　A production line of the press-molded product according to claim 8,
　wherein the forging press apparatus, wherein a hot stamping press apparatus, the heating furnace, and a control unit for controlling the manipulator, the press-molded product manufacturing line .