JP2004058082A - Method for producing tailored blank press formed article - Google Patents

Method for producing tailored blank press formed article Download PDF

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JP2004058082A
JP2004058082A JP2002217451A JP2002217451A JP2004058082A JP 2004058082 A JP2004058082 A JP 2004058082A JP 2002217451 A JP2002217451 A JP 2002217451A JP 2002217451 A JP2002217451 A JP 2002217451A JP 2004058082 A JP2004058082 A JP 2004058082A
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press
metal plate
plate
metal
heating
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JP2002217451A
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JP4316842B2 (en
Inventor
Masashi Ozawa
小澤 正史
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Aisin Takaoka Ltd
アイシン高丘株式会社
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Abstract

An object of the present invention is to provide excellent press formability and controllability of work hardening by press working so that molding defects are less likely to occur, quality control is easier than before, and quality can be improved relatively inexpensively. The present invention provides a method for producing a tailored blank press molded product.
SOLUTION: A first metal plate X and a second metal plate Y having different materials and / or plate thicknesses are welded to obtain a connection board in which both metal plates are integrated. The connecting substrate is heated to a temperature range in which the first or second metal plate can be hardened. The connection substrate in the quenching temperature state is subjected to press working using press dies 10 and 20 having relatively low temperatures, so that a desired shape is imparted and quenched at a time.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a tailored blank press molded product.
[0002]
[Prior art]
For example, in the field of automotive parts, various press-formed products using a so-called tailored blank material are manufactured. Generally, in the case of a press-formed product made of a tailored blank material, two or more base plates (including those having different materials and thicknesses) are butt-joined, and the butt portions are continuously welded to connect the two base plates integrally. Thereafter, it is manufactured through a series of steps in which a desired shape is imparted by subjecting the connection substrate to cold pressing (see, for example, JP-A-11-104750 and JP-A-2001-1062).
[0003]
However, conventional tailored blank press molded articles have various disadvantages. For example, the connection substrate undergoes work hardening by cold pressing, but even with the same connection substrate, the degree of work hardening is not stable and the quality tends to be uneven, and the degree of work hardening is also very halfway There is a disadvantage that it is. For this reason, it was difficult to control the tensile strength in consideration of the work hardening by the cold press, and it was difficult to stably produce a press-formed product of uniform quality. In particular, when a high-strength steel (also referred to as a steel material having a high tensile strength by adding a small amount of alloying element to a low-carbon steel, also referred to as a high-tension material) is used for the base plate, Internal stress tends to remain in the product due to damage. For this reason, when the product is removed from the press die (molding die) immediately after the cold pressing, a phenomenon (spring back) occurs in which the intended shape is not given to the product and the product partially returns to the shape, It has been difficult to ensure the quality of the product due to the phenomenon that the product self-disintegrates with time (delayed destruction).
[0004]
Furthermore, since changes in the material and plate thickness are concentrated at the welded portion of the connecting board, strain is concentrated at the welded portion or in the vicinity thereof by cold pressing, and cracks or cracks occur in a part of the product after pressing. There is a serious drawback that molding defects such as wrinkles are likely to occur.
[0005]
On the other hand, new attempts have been made in the field of tailored blanks for automobiles. For example, when manufacturing a collision-reinforcing material for a vehicle (eg, a center pillar reinforce) that requires a locally high strength, a tailored blank having a quenched steel plate portion and a normal steel plate portion is prepared, and the tailored blank is prepared. A processing technique has been attempted in which partial induction hardening is performed on a quenched steel plate portion of a blank material to selectively increase the strength of only that portion. The partial induction quenching refers to a quenching method in which a high-frequency induction coil is brought close to a part to be quenched to generate heat by an induced current, and quenching is achieved by quenching the heated part with water.
[0006]
However, even when partial induction hardening is performed on the tailored blank material, a "twist" due to local heating occurs in the tailored blank material, and the dimensional accuracy is reduced. In addition, steel sheets with the required tensile strength must be used from the beginning for ordinary steel sheet parts that are not subject to partial induction quenching, and if the required strength of that part is high, a steel sheet with a high strength corresponding to the required strength must be used. Grade and expensive steel plates have to be adopted. As described above, the partial induction quenching technology for the tailored blank material also has many problems in terms of both the technology perfection and the material cost.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances. An object of the present invention is to improve the formability of press-formed products and the controllability of work hardening by press working, so that molding defects are less likely to occur, quality control is easier than before, and the quality is improved relatively inexpensively. It is an object of the present invention to provide a method for producing a tailored blank press-formed product that can be used.
[0008]
[Means for Solving the Problems]
The present invention (a method for producing a tailored blank press molded product) can be expressed as a production method described below.
[0009]
The first method for producing a tailored blank press-formed product includes welding a first metal base plate and a second metal base plate having at least one of a material, tensile strength, and plate thickness different from each other. A welding step of obtaining a connecting board in which the board is integrated, a heating step of heating the connecting board to a temperature range in which the first metal plate or the second metal plate can be hardened, A press step of applying a desired shape and quenching at once by subjecting the connected substrate in a temperature state to press working using a relatively low-temperature press die.
[0010]
According to this manufacturing method, the connection substrate serving as the base of the tailored blank is formed by welding the first metal plate and the second metal plate having at least one of a different material, tensile strength, and thickness. can get. At the stage before pressing, the connection substrate is heated to a temperature range that can be hardened for the first metal plate or the second metal plate, so that all or a part of the connection substrate is easily plastically deformed. Become. Then, by performing press working using a press die on the connection substrate holding the quenchable temperature state, the connection substrate is given a desired shape with excellent molding accuracy and at a relatively low temperature. By contacting the press die, the connecting substrate is rapidly cooled and quenching is performed.
[0011]
As described above, the tailored blank press is manufactured by adopting the technique of hot pressing the connected substrate heated to a predetermined temperature range to achieve giving (forming) a desired shape and hardening (rapid cooling) at a time. Residual internal stress in the molded product is avoided or reduced, and the formability of the press molded product is improved. In addition, by using a hot press, the controllability of work hardening by the press is greatly improved, the quality is stable, and the quality control becomes easier than before. Furthermore, by performing quenching at the same time as molding, it is possible to reliably and inexpensively improve the quality of a tailored blank press molded product as compared with the related art.
[0012]
The second method for producing a tailored blank press-molded product includes a first metal plate made of a steel material obtained by adding an alloying element capable of increasing hardenability to an iron-based material, and an alloy having an amount capable of improving hardenability. A welding step of welding a second metal base plate made of an iron-based material to which no element is added to obtain a connection substrate in which both metal base plates are integrated, and connecting the connection substrate to the iron-based material. A heating step of heating the steel material to which an alloying element capable of enhancing hardenability is added to a quenching temperature range for a steel material, and using a relatively low-temperature press die for the connection substrate in the quenching temperature state. And press working to give a desired shape and quench at a time.
[0013]
According to this manufacturing method, the connection substrate serving as the base of the tailored blank is made of a first metal base plate made of a steel material obtained by adding an alloy element in an amount capable of enhancing hardenability to an iron-based material, and a hardenability. It can be obtained by welding a second metal base plate made of an iron-based material to which an increasing amount of alloying element is not added. At the stage before pressing, the connecting substrate is heated to a temperature range in which hardening is possible for a steel material in which an amount of alloying element capable of enhancing hardenability is added to the iron-based material. It becomes easy to deform. Then, by performing press working using a press die on the connection substrate holding the quenchable temperature state, the connection substrate is given a desired shape with excellent molding accuracy and at a relatively low temperature. By contacting the press die, the connecting substrate is rapidly cooled and quenching is performed.
[0014]
As described above, the tailored blank press is manufactured by adopting the technique of hot pressing the connected substrate heated to a predetermined temperature range to achieve giving (forming) a desired shape and hardening (rapid cooling) at a time. Residual internal stress in the molded product is avoided or reduced, and the formability of the press molded product is improved. In addition, by using a hot press, the controllability of work hardening by the press is greatly improved, the quality is stable, and the quality control becomes easier than before. Furthermore, by performing quenching at the same time as molding, it is possible to reliably and inexpensively improve the quality of a tailored blank press molded product as compared with the related art.
[0015]
The second metal base plate is made of an iron-based material to which no alloying element is added in an amount capable of enhancing hardenability, that is, a normal steel plate designed without any post-quenching process. It has been experimentally confirmed that the hot pressing of the connection substrate also exerts a certain quenching effect on the second metal plate portion to improve the tensile strength (see Example 1 described later). That is, an ordinary steel plate which is relatively inexpensive and can be easily procured from anywhere in the world can be used as the base plate of the tailored blank material, and it is possible to significantly reduce the cost of the tailored blank press molded product.
[0016]
The third method for manufacturing a tailored blank press-formed product is a method of welding a first metal base plate and a second metal base plate having different plate thicknesses to obtain a connection substrate in which both metal base plates are integrated. A heating step of heating the connecting substrate to a temperature range in which the first metal plate or the second metal plate can be quenched; When a low-temperature press die is used, when both surfaces of the larger metal plate of the first and second metal plates contact the forming surface of the press die, the plate thickness is smaller. Press working in such a manner that a predetermined clearance can be secured between at least one surface of one of the metal base plates and the forming surface of the press die facing the surface, thereby giving and quenching a desired shape. And press at once Characterized in that it obtain.
[0017]
According to this manufacturing method, the connection substrate serving as the base of the tailored blank material is obtained by welding the first metal plate and the second metal plate having different plate thicknesses. At the stage before pressing, the connection substrate is heated to a temperature range that can be hardened for the first metal plate or the second metal plate, so that all or a part of the connection substrate is easily plastically deformed. Become. Then, by performing press working using a press die on the connection substrate holding the quenchable temperature state, the connection substrate is given a desired shape with excellent molding accuracy and at a relatively low temperature. By directly or indirectly contacting (including approaching) the press die, the connected substrate is rapidly cooled, and quenching is performed according to the degree of the contact or rapid cooling. That is, in the press working using the press die having a relatively low temperature, both surfaces of the metal plate having the larger thickness of the first and second metal plates are in contact with the forming surfaces of the press die, respectively. Then, the pressing is performed in such a manner that a predetermined clearance can be secured between at least one surface of the metal plate having a smaller thickness and the forming surface of the press die facing the surface. Therefore, the metal plate with a larger thickness has a greater quenching effect due to rapid heat removal due to the direct contact of both sides with the forming surface of the press die, while the metal plate with a smaller thickness is smaller. Since at least one surface of the plate approaches or indirectly contacts the forming surface of the press die through the predetermined clearance, the plate receives relatively low heat removal and has a relatively small quenching effect. That is, the quenching effect is adjusted by intentionally securing a clearance in a part of the connection substrate to be pressed, and the quality (mainly strength) of the press-formed product is locally controlled.
[0018]
As described above, the tailored blank press is manufactured by adopting the technique of hot pressing the connected substrate heated to a predetermined temperature range to achieve giving (forming) a desired shape and hardening (rapid cooling) at a time. Residual internal stress in the molded product is avoided or reduced, and the formability of the press molded product is improved. In addition, by using a hot press, the controllability of work hardening by the press is greatly improved, the quality is stable, and the quality control becomes easier than before. Furthermore, by performing quenching at the same time as molding, it is possible to reliably and inexpensively improve the quality of a tailored blank press molded product as compared with the related art. In this method, in particular, at the time of hot pressing, control of hardenability according to the degree of heat removal is achieved by intentionally securing a clearance between a part of the connection substrate and the molding surface of the press die. It becomes possible, and the range of quality design and quality control of tailored blank press molded products is expanded.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the technical contents described in the section of “Means for Solving the Problems” will be further supplemented, and preferred embodiments of the present invention will be described in detail.
[0020]
(Welding process and conditions of metal plate)
The connection substrate serving as the base of the tailored blank is formed by welding and integrating two or more metal plates (two of which are a first metal plate and a second metal plate). For example, the ends of adjacent metal plates are butted, and continuous welding is performed on the butted portions, whereby the integration of a plurality of plates is achieved. Examples of welding techniques that can be used at that time include laser welding, mushroom welding, electron beam welding, TIG welding, MIG welding, plasma welding, seam welding, spot welding, arc welding, electric welding, and the like.
[0021]
At least one (one item) of the material, the tensile strength, and the plate thickness of the two or more metal base plates constituting the connection substrate is different. In particular, when the material is different between two or more metal base plates and / or when the plate thickness is different, the usefulness of the present invention is remarkable.
[0022]
As a material of each of the metal base plates constituting the connection substrate, for example, an iron-based (including high-strength steel, stainless steel, or the like), a titanium-based, an aluminum-based, or a copper-based can be used. However, the features of the present invention are best exhibited when the metal plate is an iron-based material (that is, a steel material).
[0023]
As an iron-based material for a metal base plate, a steel material (a so-called special steel plate for quenching or a special quenching material) obtained by adding an alloy element in an amount capable of enhancing hardenability to an iron-based material, An iron-based material to which an increasing amount of alloying element is not added (also called a so-called ordinary steel plate or a general material) can be given. Examples of alloying elements (alloying elements having a high quench multiple) applicable to iron-based materials for enhancing hardenability include carbon, silicon, manganese, nickel, chromium, titanium, molybdenum, and boron. Usually, such alloying elements are added in combination to a plurality of iron-based materials as a base material to adjust the transformation point of the metal and adjust the tensile strength and other physical properties. In the case of iron-based materials, not only the presence or absence of the addition of the alloying element as described above does not matter, but it goes without saying that the hardenability is controlled according to the amount of the alloying element added.
[0024]
A high-strength steel can be given as a typical example of "a steel material in which an alloy element is added to an iron-based material in an amount capable of enhancing hardenability". As the high-tensile steel, it is preferable to add a small amount of alloying element to low-carbon steel, which is a kind of iron-based material, and to impart a tensile strength of about 400 to 1000 MPa (preferably, a tensile strength of 500 to 600 MPa). More preferably, “iron is used as a base material, and 0.18 to 0.25 wt% of carbon, 0.15 to 0.35 wt% of silicon, 1.15 to 1.40 wt% of manganese, and 0.15 to 0. High-strength steel containing at least 25% by weight of chromium and 0.01 to 0.03% by weight of titanium. " In general, high-tensile steel has high tensile strength but plastic deformation is not always sufficient. Therefore, according to the present invention in which heating is performed prior to pressing, the plastic deformation of a metal plate made of high-strength steel is reduced by pressing. Can be enhanced before.
[0025]
Examples of the "iron-based material to which no alloying element capable of enhancing hardenability is added" include hot-rolled steel sheets having a tensile strength of less than 400 MPa, such as JIS (Japanese Industrial Standard) SHP270 hot-rolled steel sheet (tensile strength of 270 MPa). Steel plates and cold-rolled steel plates can be exemplified. Incidentally, the SHP270 material is widely used as a general material (ordinary steel plate) in Japan.
[0026]
The connection substrate obtained by welding two or more metal base plates in this way is subjected to a press working through a heating process (see FIG. 1).
[0027]
(Heating process)
In the heating step, the connection board is heated to a temperature range where it can be hardened by any one of the two or more metal base plates constituting the connection board. Particularly, when any one of the two or more metal base plates constituting the connection substrate is made of a steel material in which an alloy element in an amount capable of enhancing hardenability is added to the iron-based material, the iron-based material is particularly used. The steel is heated to a temperature range where hardening is possible for a steel material to which an amount of alloying element capable of enhancing hardenability is added.
[0028]
When the metal base plate is an iron-based material, the “quenching temperature range” conceptually refers to a temperature range equal to or higher than the A1 transformation point (quenching temperature). The temperature region above the A1 transformation point means a temperature region higher than the austenite formation temperature. The upper limit of the heating temperature is preferably the liquid phase generation temperature of the base material of the metal plate. In addition, by contacting or approaching a relatively low-temperature press mold at the time of pressing, the metal phase is promoted to martensite and quenched.
[0029]
The preferred range of the “quenching temperature range” in the heating in the heating step is, specifically, a temperature of 850 ° C. or higher and lower than the lowest melting point among the melting points of the metal base plates constituting the connection substrate. It is. In particular, when the metal base plate constituting the connecting substrate is made of an iron-based material, a more preferable range of the “quenching temperature range” is 850 ° C. or more and 1050 ° C. or less. When the heating temperature is lower than 850 degrees Celsius, the quenching effect by hot pressing is not sufficiently exhibited, and the improvement in tensile strength of the press-formed product becomes insufficient. In particular, when the metal plate is a high-tensile steel, if the heating temperature is lower than 850 degrees Celsius, not only the improvement in tensile strength is insufficient, but also the improvement in formability (such as avoidance of springback and delayed fracture) is also insufficient. Become. On the other hand, when the heating temperature is higher than 1050 degrees Celsius, the improvement in tensile strength tends to level off or tends to decrease, and there is little benefit in raising the temperature to above 1050 degrees Celsius. Note that a reason why good results cannot be obtained even when heating to a temperature exceeding 1050 degrees Celsius is considered to be that the connection of the crystal structure becomes rather coarse due to the increase in the size of the metal crystal due to the high temperature.
[0030]
As a specific method for heating the connection substrate, at least one of a method of holding the connection substrate in a heating furnace, a method of inductively heating the connection substrate, and a method of heating the connection substrate by resistance by energizing the connection substrate is adopted. Can be. Of course, two or more methods may be used in combination.
[0031]
The method of holding the connection substrate in the heating furnace can be performed in a state where the furnace chamber of the heating furnace is in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere include a vacuum atmosphere, a reducing gas atmosphere, and an inert gas atmosphere. Examples of the reducing gas atmosphere include a CO gas atmosphere and a gas atmosphere containing CO. Examples of the inert gas atmosphere include a rare gas atmosphere such as a nitrogen gas atmosphere and an argon gas.
[0032]
The method of inductively heating the connection substrate means that an AC current is supplied to the conductive member in a state where a conductive member for induction heating (for example, a high-frequency induction coil) is brought close to the connection substrate to generate heat by the induction current in the connection substrate. It refers to a method of producing and heating. According to the induction heating method, it is possible to expect a proximity effect that efficiently heats a surface layer of the connection substrate close to the conductive member, and a skin effect in which a current flows through the surface layer of the connection substrate. Can be efficiently heated.
[0033]
The method of heating the resistance by energizing the connection board refers to a method in which the connection terminal is connected to the connection board and the connection terminal is energized to generate Joule heat to heat the connection board. The current flowing may be direct current or alternating current. When the current is an alternating current, a skin effect in which the current flows through the surface layer of the connection substrate can be expected, and the surface layer of the connection substrate can be efficiently heated.
[0034]
In the present invention, in order to maintain good formability at the time of press working, in the heating step before pressing, the entire connection substrate is uniformly heated evenly, particularly, each metal plate and their welded parts It is desirable that there be no difference in the degree of heating between the two. In this regard, of the above heating methods, the method of holding the connection substrate in the heating furnace is most preferable.
[0035]
(Pressing process)
In the pressing step following the heating step, the connection substrate in a quenable temperature state is subjected to press working using a relatively low-temperature press die, so that a desired shape is imparted and quenched at a time.
[0036]
The essence of this method is that the temperature of the connected substrate immediately before being pressed is set to a temperature at which quenching can be performed. The desired effect cannot be obtained. Therefore, when there is a possibility that the temperature of the connected substrate may decrease when the process shifts from the heating process to the pressing process, the temperature of the connected substrate is set to a temperature at which the temperature of the connected substrate can be quenched at the time of pressing, in consideration of the temperature decrease. It is necessary to set a target heating temperature in the heating step so that the temperature can be maintained.
[0037]
“Relatively low-temperature press die” means that the temperature of the press die is relatively lower than that of the connected substrate in a quenching temperature state (that is, a high-temperature state). The temperature is preferably 200 ° C. or lower, and more preferably a room temperature or a temperature around room temperature. In order to ensure that the press die is at a relatively low temperature, the press die may be provided with cooling means for forcibly cooling itself. As an example of the configuration of the cooling means, a system in which a cooling passage is formed inside a press die and a cooling medium (cooling water, refrigerant gas, or the like) is supplied to the cooling passage can be exemplified.
[0038]
If the thickness of two or more metal plates constituting the connection substrate is different, use a relatively low-temperature press die for the connection substrate in a quenable temperature state, and use the metal plate with the larger plate thickness. When both surfaces of the plate are in contact with the forming surface of the press die, a predetermined clearance (between at least one surface of the metal plate having a smaller thickness and the forming surface of the press die facing the surface). It is preferable to perform the press working in such a manner that a gap can be secured.
[0039]
As a form of the press working ensuring the mold clearance, specifically, the forms as shown in FIGS. 2 and 3 can be exemplified. In the press mode of FIG. 2, when the upper and lower surfaces of the thick metal plate contact the forming surfaces 11 and 21 of the upper and lower press dies 10 and 20, respectively, the upper surface of the thin metal plate is A predetermined clearance C1 is secured between the upper surface and the molding surface 11 of the upper press die facing the surface. In the pressing mode of FIG. 3, when the upper and lower surfaces of the thick metal plate contact the forming surfaces 11 and 21 of the upper and lower press dies 10 and 20, respectively, the upper surface of the thin metal plate is A predetermined clearance C2 is ensured between the upper press die forming surface 11 facing the surface and the lower press die forming surface 21 facing the lower surface of the thin metal plate. A predetermined clearance C3 is secured therebetween.
[0040]
As shown in FIG. 2 and FIG. 3, a thick metal plate whose upper and lower surfaces are in direct contact with the molding surfaces 11 and 21 of the press mold is subjected to rapid heat removal by the upper and lower press molds 10 and 20. The quenching effect is also great. On the other hand, a thin metal plate whose upper and lower surfaces cannot be directly in contact with the molding surfaces 11 and 21 of the press die at the same time is relatively moved by approaching or indirect contact with the upper and lower press dies 10 and 20. As a result of the low degree of heat removal, the quenching effect is relatively small. That is, due to the difference in plate thickness between the two metal plates constituting the connection substrate, a difference occurs in the contact condition when each metal plate comes into contact with the forming surface of the press mold during hot pressing, This results in a difference in heat removal performance, and as a result, it is possible to locally adjust the hardenability in one press-formed product. In this way, it is possible to manufacture tailored blank press-formed products having different strengths depending on the parts.
[0041]
As described above, according to the method for manufacturing a tailored blank press-formed product of the present invention, the connection substrate heated to a predetermined temperature region is hot pressed to give a desired shape (forming) and quenching (rapid cooling) once. By adopting the technique of achieving the above, the residual internal stress in the tailored blank press molded product is avoided or reduced, and the moldability of the press molded product is improved. In particular, the formability at and around the welded portion is greatly improved as compared with the related art, the incidence of molding defects such as cracks and wrinkles is reduced, and the welded portion can be deeply bent. In addition, by using a hot press, the controllability of work hardening by the press is greatly improved, the quality is stable, and the quality control becomes easier than before. By performing quenching at the same time as molding, it is possible to reliably and inexpensively improve the quality of a tailored blank press molded product as compared with the related art. Furthermore, even when high-tensile steel is used as a part of two or more metal base plates constituting the connecting substrate, excellent formability is ensured, and springback and delayed fracture are effectively prevented.
[0042]
The application field of the tailored blank press molded product is not limited to the field of automobile parts, but it is preferable to apply the present invention to the production of automobile parts, and particularly to the production of collision reinforcing materials for vehicles. Is preferred. When the present invention is applied to the production of a collision reinforcement for a vehicle, a product having high tensile strength can be produced even with a small thickness, and the weight of the collision reinforcement can be further reduced. In addition, the strength of a material that is easily available and inexpensive from anywhere in the world can be effectively increased, thereby contributing to a reduction in the manufacturing cost of the collision reinforcing material. The term "vehicle collision reinforcing material" refers to a member attached to each part of the vehicle to protect occupants in the vehicle in the event of a vehicle collision or other accident, and does it alone exert a protective function? It does not matter whether the protection function is exhibited in cooperation with other members.
[0043]
【Example】
Next, Examples 1 and 2 in which the present invention is embodied in the manufacture of automobile parts will be described. The shape of each metal plate, the final shape of the press-formed product, and the manufacturing procedure in Examples 1 and 2 are as shown in FIG. 1 (including a perspective view and a cross-sectional view).
[0044]
(Example 1)
As the first metal plate X, a special steel material A having a plate thickness t1 = 1.8 mm was used, and as the second metal plate Y, an SHP270 steel plate having a plate thickness t2 = 1.2 mm was used. The special steel material A is an iron-based material classified as a high-strength steel and has a component composition as described in Table 1 below. The melting point of the special steel material A is 1300 to 1400 degrees Celsius, and its tensile strength is about 600 MPa. SHP270 steel plate is a so-called general material, and its tensile strength is about 270 MPa. As shown in FIG. 1, the ends of these two metal plates X and Y were butted, and the butted portions were laser-welded to integrate them, thereby obtaining a single flat connecting substrate.
[0045]
Subsequently, the connection substrate was sealed in an electric heating furnace having a nitrogen gas atmosphere inside, and heated to a predetermined target temperature (930 ° C. in this example). The connected substrate heated to the target temperature was transferred from the electric furnace between the pressing dies 10 and 20 at high speed and immediately subjected to press working. The time taken to set the connection substrate from the electric furnace to the press mold and start pressing was set to 5 seconds or less, and care was taken that the temperature of the connection substrate immediately before pressing did not fall below 850 degrees Celsius. On the other hand, the temperatures of the press dies 10, 20 were kept at room temperature (around room temperature). The pressing pressure was about 5,000 MPa. As shown in FIG. 2, the pressing of the connecting substrate composed of the metal base plates X and Y having different plate thicknesses involves a clearance C1 (=) between the thin second metal base plate Y and the molding surface 11 of the press die. 0.6 mm). The temperature of the press-formed product taken out of the press mold immediately after pressing was 100 to 200 ° C.
[0046]
When the press-formed product of Example 1 was removed from the press dies 10 and 20, no springback occurred in the press-formed product, and a shape substantially similar to that of the press die was given. Further, no molding defects such as cracks and wrinkles were found in the molded product, and no signs of delayed fracture were observed thereafter. When the tensile strength of each part of this tailored blank press-formed product was measured, the average value of the tensile strength of the part composed of the first metal blank X (t1 = 1.8 mm) was dramatically improved to 1500 MPa, The average value of the tensile strength of the portion composed of the metal base plate Y (t2 = 1.2 mm) was also improved to 440 MPa. The fact that a tensile strength difference of more than 1000 MPa occurred in both parts was caused by the fact that the materials of the two metal base plates X and Y were completely different between the special steel material and the general material, and that the clearance C1 (= 0.6 mm) was secured. It is presumed that the fact that the press working was performed had a synergistic effect. It should be noted that there was little variation in tensile strength even between a plurality of measurement points in each metal plate portion, and the strength distribution was almost uniform. Although a plurality of lots of the press-formed product of Example 1 were manufactured, there was almost no variation in quality among lots, and a tailored blank press-formed product of almost the same quality could be stably manufactured.
[0047]
(Example 2)
As the first metal base plate X, a special steel material A having a plate thickness t1 = 1.8 mm was employed, and as the second metal base plate Y, a special steel material A having a plate thickness t2 = 1.2 mm was employed. This special steel material A is the same steel material used in the first embodiment. Then, as shown in FIG. 1, the ends of both metal base plates X and Y were butted, and the abutted portion was subjected to laser welding to integrate the two to obtain a single flat connecting substrate. . Thereafter, through exactly the same heating step and pressing step as in Example 1, a tailored blank press molded product was obtained.
[0048]
When the press-formed product of Example 2 was removed from the press dies 10 and 20, no springback occurred in the press-formed product, and a shape substantially similar to that of the press die was given. Further, no molding defects such as cracks and wrinkles were found in the molded product, and no signs of delayed fracture were observed thereafter. When the tensile strength of each part of this tailored blank press-formed product was measured, the average value of the tensile strength of the part composed of the first metal blank X (t1 = 1.8 mm) was dramatically improved to 1500 MPa, The average value of the tensile strength of the portion composed of the metal base plate Y (t2 = 1.2 mm) was also dramatically improved to 1200 MPa. The difference in tensile strength of 300 MPa between the two portions is due to the effect of the press working in a mode of securing the clearance C1 (= 0.6 mm), considering that the materials of the metal base plates X and Y are the same. I can understand. It should be noted that there was little variation in tensile strength between a plurality of measurement points in each metal plate portion, and the strength distribution was almost uniform. Although a plurality of lots of the press-formed product of Example 2 were manufactured, there was almost no variation in quality between lots, and a tailored blank press-formed product of almost the same quality could be stably manufactured.
[0049]
[Table 1]
[0050]
(Comparative experiments 1 and 2)
As Comparative Experiment 1, an experiment was performed in which the connected substrate of Example 1 was cold-pressed at room temperature without heating under the same conditions as in Example 1. Further, as Comparative Experiment 2, an experiment was performed in which the connected substrate of Example 2 was cold-pressed at room temperature without heating under the same conditions as in Example 2. In Comparative Experiments 1 and 2, when the press-formed product was removed from the press die, intense springback occurred particularly in the portion using the special steel material A, and the shaping according to the press die could not be performed. In addition, small cracks (defective molding) were observed in the welded portion of the press-formed product and at a bent portion having a large curvature. Further, in Comparative Experiments 1 and 2, although the part using the special steel material A was work-hardened, a high level of tensile strength improvement of 1200 to 1500 MPa class was not seen as in Examples 1 and 2, and the improvement in tensile strength was not observed. At most, it stayed at 700 MPa. In Comparative Experiment 1, the tensile strength of the portion of the second metal base plate Y using the SHP270 steel plate was hardly improved even by the press working.
[0051]
From the fact of the comparative experiment 1, in Example 1, the tensile strength of the portion of the second metal plate Y using the SHP270 steel plate as a general material was improved from 270 MPa to 440 MPa by hot pressing. Worthy of note.
[0052]
【The invention's effect】
As described in detail above, according to the method for producing a tailored blank press-formed product of the present invention, the moldability of the press-formed product and the control of work hardening by press working are excellent, and molding defects are less likely to occur. The management is easy, and the quality can be improved relatively inexpensively. In particular, since the press working is performed by hot pressing, the formability particularly at the welding portion of the connecting substrate and the vicinity thereof is significantly improved as compared with the related art, and as a result, the incidence of forming defects such as cracks and wrinkles is reduced. At the same time, it is possible to perform a deep bending process on the welded portion.
[0053]
Further, according to the present invention, as a metal base plate for forming a connection substrate, a metal base plate made of an expensive material having a tensile strength of 1000 MPa or more, which can be obtained only in Japan, is not used, and it can be compared from anywhere in the world. It is possible to use a metal base plate made of an inexpensive material that is easily available, and a high-quality tailored blank press-formed product can be manufactured from such an inexpensive metal base plate at low cost.
[Brief description of the drawings]
FIG. 1 is an explanatory view conceptually showing a series of steps for manufacturing a press-formed product.
FIG. 2 is a cross-sectional view showing one mode of press working with a clearance secured.
FIG. 3 is a cross-sectional view showing one mode of press working with a clearance secured.
[Explanation of symbols]
10, 20 ... press mold, 11, 21 ... molding surface of press mold, C1, C2, C3 ... clearance.

Claims (6)

  1. Welding a first metal plate and a second metal plate different in at least one of the material, tensile strength and plate thickness to obtain a connection substrate in which both metal plates are integrated,
    A heating step of heating the connection substrate to a temperature range in which the first metal plate or the second metal plate can be hardened;
    A press step of applying a desired shape and quenching at once by performing press working using a relatively low-temperature press die on the connection substrate in the quenching temperature state. Manufacturing method of tailored blank press molded products.
  2. A first metal plate made of a steel material in which an amount of alloying element capable of increasing hardenability is added to an iron-based material, and a second metal plate made of iron-based material not added with an amount of alloying element capable of improving hardenability. Welding step of obtaining a connection board in which both metal base plates are integrated by welding with the metal base plates of
    A heating step of heating the connection substrate to a temperature range in which hardening is possible for a steel added with an amount of an alloying element capable of enhancing hardenability in the iron-based material,
    A press step of applying a desired shape and quenching at once by performing press working using a relatively low-temperature press die on the connection substrate in the quenching temperature state. Manufacturing method of tailored blank press molded products.
  3. A welding step of welding a first metal base plate and a second metal base plate having different plate thicknesses to obtain a connection substrate in which both metal base plates are integrated;
    A heating step of heating the connection substrate to a temperature range in which the first metal plate or the second metal plate can be hardened;
    A relatively low-pressure press die is used for the connection substrate in the quenching temperature state, and both surfaces of the first and second metal plate having a larger plate thickness are pressed by the press die. In a mode in which a predetermined clearance can be secured between at least one surface of the smaller metal plate and the molding surface of the press die opposed to that surface when each comes into contact with the molding surface of A step of applying a desired shape and quenching at a time by performing press working at the same time.
  4. The plate thickness of the first metal plate is set to be larger than the plate thickness of the second metal plate, and the first metal plate has an amount capable of enhancing hardenability in an iron-based material. The second metal element plate is made of an iron-based material that does not contain an alloying element in an amount capable of enhancing hardenability, and the connecting substrate is made of the steel material to which the alloying element is added. 4. The method for producing a tailored blank press-formed product according to claim 3, wherein the iron-based material is heated to a temperature range in which hardening is possible for a steel material in which an alloying element capable of enhancing hardenability is added.
  5. The thickness of the first metal plate is set to be greater than the thickness of the second metal plate, and both the first and second metal plates are hardenable to an iron-based material. In the heating step, in the heating step, the connecting substrate is set to a temperature range that can be hardened for a steel material to which an alloy element in an amount capable of improving hardenability is added to the iron-based material. The method for producing a tailored blank press-molded product according to claim 3, wherein the product is heated up to the temperature.
  6. The temperature range in which the quenching is possible in the heating step is 850 degrees Celsius or more, and is lower than the lowest melting point among the melting points of the metal base plates constituting the connection substrate. , 3, 4 or 5, the method for producing a tailored blank press molded article.
JP2002217451A 2002-07-26 2002-07-26 Method for manufacturing tailored blank press molded products Expired - Fee Related JP4316842B2 (en)

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