JP2009019229A - Manufacturing method of structural member of closed section of vehicle body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a structural member of a closed section of a vehicle body for easily manufacturing a structural member coping with any collision deformation, wherein the strength difference between works during the bend-forming is reduced, the bend-formability is enhanced by performing the bend-forming of a heated work, the strength of necessary parts requested for a vehicle body is secured by hardening the work by cooling the work after the bend-forming to provide the strength difference. <P>SOLUTION: A second blank having the strength and the thickness substantially equal to those of a first blank and having the hardenability higher than that of the first blank is arranged adjacent to the first blank arranged at a predetermined part in the axial direction. Both blanks are welded S1 at a welding line of both blanks only diagonal to the axial direction, end faces of the welded blanks are welded to each other to form S2 a cylindrical workpiece. Then, the workpiece is heated S3 to the temperature equal to or higher than the hardening temperature to perform the bend-forming S4 of the workpiece. The workpiece is subjected to the cooling and hardening S5 after the bend-forming S4. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a vehicle body closed cross-section structure member such as a center pillar or a front side frame using a tailored blank material.

Conventionally, when a vehicle body closed cross-section structural member is manufactured, a vehicle body structural member having a closed cross-section is generally manufactured by joining two members pressed into a cross-sectional hat shape by sheet metal.
When a vehicle body closed cross-section structural member consisting of two members of this sheet metal press is adopted as a part of the vehicle body, there are a portion where high strength is not required and a portion where sufficient high strength is required. Since both members were formed in accordance with the required strength, there was a problem that caused an increase in weight and cost.

  On the other hand, as disclosed in Patent Documents 1 and 2, a method of manufacturing a structural member using a tailored blank material has already been invented.

  The manufacturing method of the tailored blank press-molded product disclosed in Patent Document 1 includes a first metal material made of steel obtained by adding an alloy element in an amount capable of improving hardenability to an iron-based material, and an amount capable of improving hardenability. A second metal material made of an iron-based material to which no alloying element is added, and the materials and / or plate thicknesses of the first and second metal materials are made different, and the two metal materials are welded together. Then, after forming a connection substrate (tailored blank) in which these two metal materials are integrated, the connection substrate is heated to a temperature range where the first metal material can be quenched, and the heated connection substrate is pressed, The first metal material is quenched and the connecting substrate is press-molded at the same time to form a press-formed product having a hat-shaped cross section.

  According to the conventional method disclosed in Patent Document 1, there is an advantage that a difference in strength can be imparted to the connection substrate by the presence or absence of quenching (containing or not containing an alloy element that can enhance hardenability) The press-formed product formed by this conventional method does not form a cylindrical workpiece that becomes a closed cross-section structural member, nor does it apply the necessary bending to the vehicle body closed cross-section structural member. There is no disclosure of any specific issues.

When bending a cylindrical workpiece, in the case of a tailored tube made of a tailored blank material, the strength varies locally due to the difference in material thickness and material. When the lower part is located, there is a problem that buckling occurs due to compressive stress or wrinkles are formed. Conversely, when a part with low strength is located outside the bend during bending, the action of tensile stress is caused. Therefore, there is a problem that a crack is generated in the portion.
In the conventional method disclosed in Patent Document 1, there is no description about the technical problem at the time of bending.

Moreover, the manufacturing method of the tailored tube disclosed in Patent Document 2 is a method of manufacturing a tailored tube by tailoring welding a plurality of steel plates (tailored blanks) having different materials or wall thicknesses. A plurality of steel plates are tailored with a welding line that is slanted with respect to the axial direction of the tube when it is made into a tailored tube, and sudden changes in material and strength in the axial direction of the tube are eliminated during this tailored welding. It is designed so that welding can be completed under certain welding conditions, but this tailored tube is made into a steel member with a predetermined shape by applying hydroforming to the raw material. Incidental facilities such as outer molds will be enlarged.
Although the technical idea of the above-described planing is disclosed in Patent Document 2, no technical problem at the time of bending is disclosed as in Patent Document 1.

JP 2004-58082 A JP 2004-314102 A

  Therefore, the present invention is adjacent to the first blank material arranged at a predetermined portion in the axial direction of the cylindrical workpiece, and the strength and the plate thickness are substantially equal to the first blank material, and the hardenability is the first blank. A second blank material higher than the material is arranged, and both blank materials are welded to each other at a welding line between both blank materials constituted only obliquely with respect to the axial direction, and the end face portion of the welded blank material welded Welding each other to form a cylindrical workpiece, and then heating the cylindrical workpiece above the quenching temperature of the workpiece, bending the heated workpiece, then cooling the workpiece and quenching Depending on the method, the difference in strength of each part of the cylindrical workpiece during bending can be reduced, and the bending workability can be improved by bending the heated workpiece. Later The vehicle body can be manufactured by a simple method to ensure the strength of the necessary part required for the vehicle body by cooling and quenching the steel plate to ensure the strength of the necessary part required for the vehicle body An object of the present invention is to provide a method for producing a closed cross-section structural member.

  The method for manufacturing a vehicle body closed cross-section structural member according to the present invention has a strength and a plate adjacent to a first blank material arranged at a predetermined position in the axial direction of the cylindrical workpiece when formed into the cylindrical workpiece in the next step. A second blank material having a thickness substantially equal to that of the first blank material and a hardenability higher than that of the first blank material is disposed, and the two blank materials are welded to each other only obliquely with respect to the axial direction. The blank material welding process which welds the said both blank materials with a wire, and the cylindrical workpiece formation process which welds the end surface parts of the welding blank material welded in the said blank material welding process, and forms a cylindrical workpiece And bending the workpiece into a workpiece heated above the quenching temperature by the workpiece heating step, the workpiece heating step heating the cylindrical workpiece formed at the cylindrical workpiece forming step above the quenching temperature of the workpiece. Bending and shaping step is performed to, in which and a quenching step of performing quenching to cool the workpiece after the bending process.

  According to the above configuration, in the blank material welding step, the second blank is adjacent to the first blank material arranged at a predetermined site in the axial direction and has the same strength and plate thickness as the first blank material and high hardenability. The two blank materials are welded to each other at a weld line between the blank materials that are arranged only obliquely with respect to the axial direction.

In the next cylindrical workpiece forming step, the end surfaces of the welded blank materials welded in the blank material welding step are welded to form a cylindrical workpiece (a so-called tailored tube).
In the next workpiece heating step, the cylindrical workpiece formed in the cylindrical workpiece forming step is heated to a temperature equal to or higher than the quenching temperature of the workpiece.
In the next bending process, the work heated above the quenching temperature by the work heating process is bent.
In the next quenching process, the workpiece is cooled and quenched after the bending process.

As described above, since the cylindrical workpiece is formed by substantially equalizing the strength and thickness of the first blank material and the second blank material, it is possible to reduce the strength difference of each part of the cylindrical workpiece during bending. .
Further, since bending is performed on the heated workpiece, it is possible to improve the bending property.

  In addition, since the first blank material and the second blank material are welded with only an oblique weld line, there is no sudden change in strength in the axial direction of the cylindrical workpiece, and the workpiece is cooled and quenched after bending. In order to provide a difference in strength, it is possible to easily manufacture a closed cross-section structural member that supports the required deformation required for the vehicle body, and compared to hydroforming, There will be no increase in size.

  In one embodiment of the present invention, the bending in the bending step is to apply a compressive stress to a portion that is inside the workpiece.

The above configuration has the following effects.
In other words, in the case of a cylindrical workpiece (tailored tube) with different materials and plate thickness, there is a difference in strength locally, so when bending this cylindrical workpiece, a portion with low strength is located inside the bend. In this embodiment, the first blank member and the second blank member have substantially the same strength and plate thickness, so that the difference in strength of each part of the cylindrical workpiece is reduced. Thus, it is possible to prevent the occurrence of buckling of the bending inner portion during bending.

In one embodiment of the present invention, both the blank materials are made of an iron-based material.
According to the said structure, even if it is a workpiece | work consisting of the iron-type material for which the closed cross-section shaping | molding by extrusion is difficult, a desired closed cross-section structural member can be manufactured by a simple method.

  In one embodiment of the present invention, the second blank material contains more alloy elements that can improve the hardenability than the first blank material.

The alloy elements that can improve the hardenability described above include C (carbon), Si (silicon), Mn (manganese), Ni (nickel), Cr (chromium), Ti (titanium), Mo (molybdenum), B ( Boron) may be used.
According to the said structure, the hardenability of a 2nd blank material can be improved with a simple method rather than a 1st blank material.

In one embodiment of the present invention, the first blank material is disposed at an intermediate portion in the axial direction of the cylindrical workpiece, and the second blank material is disposed at each part on both sides in the axial direction of the cylindrical workpiece. Each joint part with a vehicle body other member is provided.
According to the said structure, the intensity | strength (joining strength) of each junction part with respect to a vehicle body other member is securable.

In one embodiment of the present invention, the plurality of first blank materials having low hardenability are arranged apart from each other in the middle of the cylindrical workpiece in the axial direction, and the second blank material having high hardenability is separated. It is arrange | positioned between the 1st blank materials and the axial direction both sides of a cylindrical workpiece.
According to the above configuration, the vehicle body closed cross-section structural member can be configured by the plurality of first blank materials and the plurality of second blank materials, so that the compatibility with the collision deformation of the vehicle body, and the versatility can be improved. Can do.

  According to the present invention, the strength and plate thickness are substantially equal to the first blank material, and the hardenability is the first blank adjacent to the first blank material arranged at a predetermined site in the axial direction of the cylindrical workpiece. A second blank material higher than the material is arranged, and both blank materials are welded to each other at a welding line between both blank materials constituted only obliquely with respect to the axial direction, and the end face portion of the welded blank material welded Welding each other to form a cylindrical workpiece, and then heating the cylindrical workpiece above the quenching temperature of the workpiece, bending the heated workpiece, then cooling the workpiece and quenching Since it is a method to be performed, it is possible to reduce the difference in strength of each part of the cylindrical workpiece during bending molding, and by bending the heated workpiece, it is possible to improve the bending moldability, After bending By cooling the workpiece and quenching it to give a difference in strength, it is possible to secure the strength of the necessary part required for the vehicle body and to produce a closed cross-section structural member corresponding to collision deformation by a simple method. effective.

  Necessary parts required for the vehicle body by reducing the strength difference of each part of the cylindrical workpiece during bending and improving the bending property, cooling the workpiece after bending and quenching it, and giving the strength difference The purpose of ensuring a sufficient strength and easily manufacturing a closed cross-section structural member corresponding to collision deformation is to be arranged at a predetermined position in the axial direction of the cylindrical workpiece when it is formed in the cylindrical workpiece in the next step. Adjacent to the blank material, a second blank material having a strength and a plate thickness substantially equal to those of the first blank material and having a hardenability higher than that of the first blank material is disposed, and only obliquely with respect to the axial direction. Welding a blank material welding step of welding the two blank materials with each other at a welding line between the two blank materials, and welding the end surfaces of the welded blank materials welded in the blank material welding step, Shape cylindrical workpiece A cylindrical workpiece forming step, a workpiece heating step for heating the cylindrical workpiece formed in the cylindrical workpiece forming step to a temperature higher than the quenching temperature of the workpiece, and a workpiece heated to a quenching temperature or higher by the workpiece heating step. And a bending process for performing bending, and a quenching process for cooling and quenching the workpiece after the bending process.

An embodiment of the present invention will be described in detail with reference to the drawings.
The drawing shows a manufacturing method of a center pillar of a vehicle body as an example of a vehicle body closed cross-section structural member. In the blank material welding step S1 of the process diagram shown in FIG. 1, as shown in FIG. The second blank members 2A and 2B are disposed adjacent to both sides of the first blank member 1 disposed in the intermediate portion in the axial direction of the cylindrical workpiece when formed on the workpiece, and only oblique to the axial direction. The two blank materials 1, 2A, 2B are laser welded to each other at the welding lines L1, L2 between the two blank materials 1, 2A, 2B, thereby forming a single flat welding blank material 3. To do.

Here, the first blank material is formed in a triangular shape, one second blank material 2A is formed in a right triangle shape, and the other second blank material 2B is formed in a substantially trapezoidal shape, which is rectangular as a whole. The welding blank material 3 (so-called tailored blank) is formed.
Further, both the first blank material 1 and the second blank materials 2A and 2B are made of an iron-based material having substantially the same strength and thickness, and the second blank materials 2A and 2B are in contrast to the first blank material 1. It is comprised so that hardenability may become high.

That is, the second blank materials 2 </ b> A and 2 </ b> B contain more alloy elements that can improve the hardenability than the first blank material 1.
The alloy element is at least one of C (carbon), Si (silicon), Mn (manganese), Ni (nickel), Cr (chromium), Ti (titanium), Mo (molybdenum), and B (boron). Although it is good to contain a kind, it is especially effective to increase content of Mo (molybdenum) and B (boron).

  In FIG. 2, x is a portion corresponding to the outside of the center pillar cabin, y is a portion corresponding to the inside of the center pillar, z is a portion corresponding to the center pillar in the vehicle width direction, and BL is a belt line. In this embodiment, the first blank material 1 is disposed only below the belt line BL. Moreover, in order to distinguish the 1st blank material 1 and 2nd blank material 2A, 2B in drawing, the hatching is given to the 1st blank material 1 for convenience of illustration, but this hatching does not show a cross section. .

Next, in the cylindrical workpiece forming step S2 in FIG. 1, the end face portions 4 and 5 of the welding blank material 3 welded in the blank material welding step S1 are welded to each other, and the cylindrical workpiece 6 (so-called “so-called”) shown in FIG. Tailored tube).
In this case, as shown in FIG. 3, pressure is applied to the welding blank 3 from the left, right, and lower three directions by the pressure rollers 7... In the example, the end face) is abutted and the end face portions 4 and 5 are laser welded using a laser beam (LB) to form the cylindrical workpiece 6 shown in FIG. Instead of the butt welding of the end surface portions 4 and 5, the end surface portions 4 and 5 may be overlap-welded.

  In FIG. 4, the first blank material 1 is disposed at the intermediate portion in the axial direction of the cylindrical workpiece 6 described above, and the second blank materials 2 </ b> A and 2 </ b> B are disposed at respective portions on both sides in the axial direction of the cylindrical workpiece 6. The joint portions 8 and 9 with other members of the vehicle body are provided.

Next, in the workpiece heating step S3 in FIG. 1, the cylindrical workpiece 6 formed in the cylindrical workpiece forming step S2 is heated to a temperature equal to or higher than the quenching temperature of the workpiece 6, and in the next bending molding step S4, the workpiece heating step. The cylindrical workpiece 6 heated to the quenching temperature or higher in S3 is bent. In this case, a compressive stress is applied to the portion of the cylindrical workpiece 6 that is on the bending inner side. Further, in the next quenching step S5, after the bending forming step S4, the above-described cylindrical workpiece 6 is cooled, that is, rapidly cooled and quenched.
In each of the above-described steps S3, S4, and S5, the push-through bending machine 10 shown in FIG. 5 is used.

This push-through bending machine 10 is composed of a feed mechanism 11 that sandwiches the cylindrical workpiece 6 and feeds it in the direction of the arrow in FIG. 5 and a plurality of guide rollers 12... Fixing jig 13 for fixing as much as possible, high-frequency induction heating coil 14 as a heating means for heating the cylindrical workpiece 6 to a temperature higher than its quenching temperature, and bending the cylindrical workpiece 6 in any three-dimensional direction The movable jig 15 is provided.
Moreover, the cooling means which quenches the cylindrical workpiece 6 after bending and quenches the workpiece 6 can be configured as shown in FIG. 6a or FIG. 6b.

  In the configuration shown in FIG. 6A, the high-frequency induction heating coil 14 is configured by a copper pipe, and a plurality of injection holes 14a for injecting cooling water in the copper pipe to the rear side of the heating portion by the pipe are provided. An electromagnetic on-off valve (not shown) is interposed in the cooling water supply line that is formed and supplies cooling water to the copper pipe. After the cylindrical work 6 is heated by the high frequency induction heating coil 14, the movable treatment is performed. The cylindrical work 6 is bent by means of the tool 15, and after this bending, the electromagnetic on-off valve of the cooling water supply line is opened, cooling water is ejected from the plurality of injection holes 14a, and the cylindrical work 6 is formed. The workpiece 6 is quenched by quenching.

  The configuration shown in FIG. 6 b is provided with a cooling-dedicated pipe 16 (that is, a cooling coil) that is separate from the high-frequency induction heating coil 14 made of copper pipe and is located at the rear of the high-frequency induction heating coil 14. The pipe 16 is formed with a plurality of injection holes 16a for injecting cooling water in the pipe 16, and an electromagnetic on-off valve (not shown) is provided in a cooling water supply line for supplying cooling water to the pipe 16. After the cylindrical workpiece 6 is heated by the high frequency induction heating coil 14, the cylindrical workpiece 6 is bent by the movable jig 15, and the electromagnetic on-off valve of the cooling water supply line is opened after the bending. In other words, cooling water is ejected from the plurality of injection holes 16a, the cylindrical workpiece 6 is rapidly cooled, and the workpiece 6 is quenched.

Here, when the structure of FIG. 6a is adopted, the number of parts can be reduced and the apparatus can be simplified. When the structure of FIG. 6b is adopted, the cooling pipe 16 is used. It is possible to improve the degree of freedom of the arrangement position (in other words, the degree of freedom of the rapid cooling timing required for quenching).
The heating temperature of the cylindrical workpiece 6 in the workpiece heating step S3 is preferably 850 ° C. or higher and 1050 ° C. or lower. That is, when the heating temperature is less than 850 ° C., a sufficient quenching effect cannot be obtained, and the improvement of the tensile strength in the molded product becomes insufficient. On the other hand, when the heating temperature exceeds 1050 ° C., not only the energy consumption increases, but also the metal crystal becomes coarser as the temperature increases, so that the heating temperature, that is, the quenching temperature is within the range of 850 to 1050 ° C. Is desirable.

Furthermore, after the cylindrical workpiece 6 is heated in the above-described workpiece heating step S3 and the cylindrical workpiece 6 is bent in the next bending molding step S4, in the quenching step S5, the cylinder is immediately injected by water injection. The cylindrical workpiece 6 is quenched and the cylindrical workpiece 6 is quenched.
Cooling of the tubular workpiece 6 described above, A ₁ transformation point may be cooled to (with the exception of retained austenite or the like, pearlite transformation from austenite almost finished temperature on cooling) or less.

Thus, since the cylindrical workpiece 6 is cooled and quenched after bending, a difference in strength is imparted to both the first blank material 1 having low hardenability and the second blank materials 2A and 2B having high hardenability. Therefore, it is possible to easily manufacture a closed cross-section structural member that is capable of collision deformation and ensures the strength of a necessary part required for the vehicle body.
In this case, the strength of the second blank materials 2A and 2B having high hardenability is higher than the strength of the first blank material 1 having low hardenability. In other words, since the strength of the first blank material 1 is lower than the strength of the second blank materials 2A and 2B, the first blank material 1 can be set as a fragile portion.

  As shown in FIG. 7, the vehicle body closed cross-section structural member formed through the steps S1 to S5 shown in FIG. 1 is joined to the roof side rail 17 as the vehicle body other member, and the The joint portion 8 is joined to a side sill 18 as another member of the vehicle body and used as a center pillar 19.

  When an external force acts on the center pillar 19 from the outside of the vehicle body at the time of a side collision, the center pillar 19 has a fragile portion on the outside of the passenger compartment (see the portion x of the first blank material 1) as shown by the phantom line in FIG. At the side of the car. Since the fragile portion (see the first blank 1) is provided below the belt line BL, the bent portion of the center pillar 19 is below the belt line BL and is compared with a structure that bends near the belt line BL. Thus, the amount of deformation of the center pillar 19 toward the vehicle interior side is reduced.

  Moreover, since the weak part (refer the part y of the 1st blank material 1) of the vehicle interior side is widely formed with respect to the weak part (refer the part x of the 1st blank material 1) of the vehicle interior side, it is a side collision. Sometimes, the fragile portion on the vehicle interior side is crushed widely, and a part of the external force is absorbed. As a result, the maximum displacement amount of the center pillar 19 at the time of a side collision is suppressed, and the amount of movement of the center pillar 19 toward the vehicle interior side Can be reduced.

  In addition, when employ | adopting a vehicle body closed cross-section structural member in parts other than the center pillar 19 shown in FIG. 7, in order to cope with the collision deformation | transformation of the said part, the 1st blank material 1 and the 2nd blank material 2A. , 2B can be set to a, b, c in FIG. 8 or other patterns not shown.

  Thus, the manufacturing method of the vehicle body closed cross-section structural member of the said Example is the 1st blank material arrange | positioned in the predetermined site | part in the axial direction of the cylindrical workpiece 6 at the time of forming in the cylindrical workpiece 6 at next process S2. 1, the second blank materials 2 </ b> A and 2 </ b> B whose strength and plate thickness are substantially equal to the first blank material 1 and whose hardenability is higher than that of the first blank material 1 are arranged, and with respect to the axial direction. The blank material welding step S1 for welding the blank materials 1, 2A, 2B to each other at the weld lines L1, L2 between the blank materials 1, 2A, 2B, which are configured only diagonally, and the blank material welding step A cylindrical workpiece forming step S2 for forming the cylindrical workpiece 6 by welding the end face portions 4 and 5 of the welding blank material 3 welded in S1, and a cylinder formed in the cylindrical workpiece forming step S2. Quenching the workpiece 6 A workpiece heating step S3 for heating to a temperature higher than that, a bending molding step S4 for bending the cylindrical workpiece 6 heated to a quenching temperature or higher by the workpiece heating step S3, and the cylindrical workpiece 6 after the bending molding step S4. And quenching step S5 for quenching by cooling (see FIG. 1).

  According to this configuration, in the blank material welding step S1, adjacent to the first blank material 1 arranged at a predetermined site in the axial direction, the strength and plate thickness are the same as those of the first blank material 1, and the hardenability is high. 2nd blank materials 2A and 2B are arranged, and both blank materials 1 and 2A, 2A, 2B are formed by welding lines L1 and L2 between the blank materials 1, 2A and 2B that are formed only obliquely with respect to the axial direction. 2B are welded together.

  In the next cylindrical workpiece forming step S2, the end surfaces 4 and 5 of the welding blank material 3 welded in the blank material welding step S1 are welded to form a cylindrical workpiece 6 (so-called tailored tube). .

  In the next workpiece heating step, the cylindrical workpiece 6 formed in S3 and the cylindrical workpiece forming step S2 is heated to a temperature equal to or higher than the quenching temperature of the workpiece 6.

  In the next bending step S4, the cylindrical workpiece 6 heated to the quenching temperature or higher in the workpiece heating step S3 is bent.

  In the next quenching step S5, the cylindrical workpiece 6 is cooled and quenched after the bending step S4.

Thus, since the cylindrical workpiece 6 is formed by forming the first blank member 1 and the second blank members 2A and 2B substantially equal in strength and plate thickness, the difference in strength of each part of the cylindrical workpiece 6 during bending molding. Can be reduced.
Moreover, since bending is performed with respect to the heated cylindrical workpiece 6, it is possible to improve the bending property.

Furthermore, since the first blank material 1 and the second blank materials 2A and 2B are welded with only the welding lines L1 and L2 that are oblique, there is no sudden change in strength in the axial direction of the cylindrical workpiece 6, and bending molding is performed. Later, the cylindrical workpiece 6 is cooled and quenched to give a difference in strength, so that it is possible to easily produce a closed cross-section structural member that supports the required deformation required for the vehicle body, Compared to hydroforming, there is no increase in the size of incidental equipment.
In addition, the bending in the bending step S4 is to apply a compressive stress to a portion of the cylindrical workpiece 6 that is on the bending inner side.

This configuration has the following effects.
In other words, in the case of a cylindrical workpiece (tailored tube) with different materials and plate thickness, there is a difference in strength locally, so when bending this cylindrical workpiece, a portion with low strength is located inside the bend. In this embodiment, the first blank member 1 and the second blank members 2A and 2B have substantially the same strength and plate thickness, so that the strength of each part of the cylindrical workpiece 6 is reduced. A difference becomes small and generation | occurrence | production of buckling to the bending inner side part at the time of such bending forming can be prevented.
Further, both the blank materials 1, 2A, 2B are made of an iron-based material.

  According to this configuration, a desired closed cross-section structural member can be manufactured by a simple method even for a workpiece made of an iron-based material that is difficult to be formed by extrusion.

Further, the second blank materials 2A and 2B contain more alloy elements that can improve the hardenability than the first blank material 1.
The alloy elements that can improve the hardenability described above include C (carbon), Si (silicon), Mn (manganese), Ni (nickel), Cr (chromium), Ti (titanium), Mo (molybdenum), B ( At least one of boron) can be used.

According to this structure, the hardenability of 2nd blank material 2A, 2B can be improved rather than the 1st blank material 1 by a simple method.
And while the said 1st blank material 1 is arrange | positioned in the intermediate part in the axial direction of the said cylindrical workpiece 6, said 2nd blank materials 2A and 2B are in each site | part of the axial direction both sides of the said cylindrical workpiece 6. Each joint part 8 and 9 with a vehicle body other member (refer the roof side rail 17 and the side sill 18 of FIG. 7) is provided.
According to this configuration, it is possible to ensure the strength (joint strength) of each joint 8 and 9 with respect to the other body member.

9 to 11 show another embodiment of a method for manufacturing a vehicle body closed cross-section structural member. In Embodiment 2, a method for manufacturing a front side frame of a vehicle body is shown.
The manufacturing process is the same as in the first embodiment, but in the case of the second embodiment, the arrangement structure of the first and second blank materials 1A, 1B, 1C, 2A, 2B, and 2C is implemented. This is different from Example 1.

  In the blank material welding step S1 of the process diagram shown in FIG. 1, as shown in FIG. 9, a plurality of first blank materials 1A and 1B, 1C having low hardenability are axially (in the next step, cylindrical workpiece 6 The second blank materials 2A, 2B, and 2C, which are spaced apart from each other in the middle and are highly hardened, are separated from each other by the separated first blank materials 1A and 1B. , 1C and on both sides of the cylindrical workpiece 6 in the axial direction, and each of the blanks configured only obliquely with respect to the axial direction are welded lines L3, L4, L5, L6. The blank materials 1A, 1B, 1C, 2A, 2B, and 2C are laser-welded to form a single flat welding blank material 3.

The first blank material 1A is formed in a substantially rhombus shape, and the first blank materials 1B and 1C are formed in a triangular shape, and form a rectangular welding blank material 3 (so-called tailored blank) as a whole.
Moreover, each of the blank materials 1A, 1B, 1C, 2A, 2B, and 2C is made of an iron-based material having substantially the same strength and thickness.

About hardenability, 2nd blank material 2A, 2B, 2C is the highest, 1st blank material 1B, 1C is an intermediate | middle grade, and the amount of contained alloy elements is adjusted so that the 1st blank material 1A may become the lowest.
That is, the second blank materials 2A, 2B, and 2C having the highest hardenability include alloy elements that enhance the hardenability. C, Mn, Mo, Ni, B, Ti, etc. can be used as an alloy element that enhances hardenability.

  Specifically, the second blank materials 2A, 2B, and 2C include 0.20 to 0.70% by weight of carbon, 0.50% by weight or less of silicon, and 0.10 to 2.00% of manganese. %, Phosphorus 0.015%, sulfur 0.003-0.080%, molybdenum 0.05-0.50%, aluminum 0.10% or less, nitrogen 0.0070 Inductive quenching steel or the like containing Fe and impurities is used, which contains 0.0020% by weight or less by weight or less and oxygen by 0.0020% by weight or less.

  In addition, 0.0005 wt% to 0.0050 wt% boron, 0.045 wt% or less of titanium, 0.20 wt% or less of copper, 0.20 wt% or less of nickel, and 0.20 wt% or less of nickel with respect to the above components. Wt% or less, chromium 0.20 wt% or less, niobium 0.30 wt% or less, vanadium 0.20 wt% or less, calcium 0.01 wt% or less, One or more of 0.30% by weight or less of lead, 0.03% by weight or less of bismuth, and 0.10% by weight or less of tellurium may be contained.

  Further, the first blank materials 1B and 1C having an intermediate hardenability have a carbon content of 0.20% by weight to less than the C amount of the second blank materials 2A, 2B and 2C, and the silicon content of 0. It contains 0.05 wt% to the Si amount of the second blank materials 2A, 2B, 2C or less, 0.05 wt% of molybdenum to the Mo amount of the second blank materials 2A, 2B, 2C or less, and the balance from Fe and impurities. A steel material for induction hardening is used.

  0.0005 to 0.0050% by weight of boron and 0.045% by weight or less of titanium, and 0.008% by weight of copper to the amount of Cu in the second blanks 2A, 2B, and 2C based on the above components The nickel content is 0.008 wt% to the Ni amount of the second blank 2A, 2B, 2C, the chromium is 0.20 wt% or less, the niobium is 0.01 wt% to the second blank 2A, 2B, Nb amount of 2C or less, vanadium 0.01 wt% to V amount of the second blank 2A, 2B, 2C, calcium 0.01 wt% or less, lead 0.30 wt% or less, One or more of 0.03 wt% or less of bismuth and 0.10 wt% or less of tellurium may be included.

  The first blank material 1A having the lowest hardenability does not contain more alloy elements that enhance the hardenability than the second blank materials 2A, 2B, and 2C. Specifically, carbon is 0.20 to 0.70% by weight, silicon is 0.50% by weight or less, manganese is 0.1 to 2.0% by weight, phosphorus is 0.04% by weight or less, and sulfur is 0%. A steel material containing 0.04% by weight or less, 0.4% by weight of chromium, and 0.04 to 0.15% by weight of titanium is used.

  Next, in the cylindrical workpiece forming step S2 in FIG. 1, the end face portions 4 and 5 of the welding blank material 3 welded in the blank material welding step S1 are welded to each other, and the cylindrical workpiece 6 (so-called so-called “working”) shown in FIG. Tailored tube).

  In FIG. 10, the second blank members 2 </ b> A and 2 </ b> C are provided with respective joint portions 20 and 21 with other members of the vehicle body at respective portions on both sides in the axial direction of the cylindrical workpiece 6 described above.

Next, in the workpiece heating step S3 in FIG. 1, the cylindrical workpiece 6 formed in the cylindrical workpiece forming step S2 is heated to a temperature equal to or higher than the quenching temperature of the workpiece 6, preferably in the range of 850 to 1050 ° C., and then bent. In the forming step S4, the cylindrical workpiece 6 heated to the quenching temperature or higher in the workpiece heating step S3 is bent and formed into a shape as shown in FIG. In this case, a compressive stress is applied to the portion of the cylindrical workpiece 6 that is on the bending inner side. Further, in the next quenching process S5, the cylindrical workpiece 6 above after the molding step S4 bending cooled quenched than the A ₁ transformation point, perform quenching.

Here, in each of the above-described steps S3, S4, and S5, the push-through bending machine 10 shown in FIG.
After the above-described quenching step S5 is completed, quenching with different hardenability is performed on each blank material, so that a difference in strength can be imparted to each blank material, which is required for the vehicle body. It is possible to easily manufacture a closed cross-section structural member corresponding to a collision deformation in which the strength of a necessary part is ensured.

  In this case, the strength of the second blank materials 2A, 2B, 2C is the highest, the strength of the first blank materials 1B, 1C is intermediate, and the strength of the first blank material 1A is the lowest, so the first blank materials 1A, 1B and 1C can be effectively used as weak parts.

As shown in FIG. 12, the vehicle body closed cross-section structural member formed through the steps S1 to S5 shown in FIG. 1 is joined to a bumper beam 22 as a vehicle body other member, as shown in FIG. The joining portion 21 is joined to a floor frame 23 serving as a vehicle body other member, and used as a Freon and a side frame 24.
In FIG. 12, 25 is an engine, 26 is a dash lower panel, 27 is a floor panel, 28 is a tunnel part, 29 is a hinge pillar, and 30 is a side sill.

When an external force is applied to the bumper beam 22 from the front of the vehicle body at the time of a frontal collision of the vehicle, the hardenability is set to the weakest part due to the difference in area between the vehicle outer side and the vehicle inner side of the first blank 1A in the front side frame 24. 12 is deformed inward in the vehicle width direction in front of the engine 25 as indicated by a virtual line α in FIG. 12, and between the vehicle outer side and the vehicle inner side of the first blank members 1B and 1C in the front side frame 24. Due to the area difference, the hardenability is intermediate and the portion set as the weakened portion is deformed outward in the vehicle width direction on the side of the engine 25 as shown by the phantom line β in FIG. 12 to absorb the collision energy. At the same time, it is possible to avoid the deformed front side frame 24 from interfering with the engine 25.
10 and 11, arrow F indicates the front of the vehicle when the vehicle body closed cross-section structural member is assembled to the vehicle body, arrow IN indicates the vehicle inward, and arrow OUT indicates the vehicle outward.

  As described above, the manufacturing method of the vehicle body closed cross-section structural member shown in FIGS. 9 to 12 has a plurality of first blanks 1A, 1B, 1C having a low hardenability (in this embodiment, a plurality of types of first blanks having a low hardenability). 1 blank material 2A, 2B, and 2C having high hardenability are arranged apart from each other in the middle of the cylindrical workpiece 6 in the axial direction, and the separated first blank materials 1A, 1B, and 1C are separated. And on both sides of the cylindrical workpiece 6 in the axial direction.

  According to this configuration, the plurality of first blank members 1A, 1B, 1C and the plurality of second blank members 2A, 2B, 2C can constitute a vehicle body closed cross-section structural member (see the front side frame 24). Therefore, it is possible to improve the response to the collision deformation of the vehicle body and the versatility.

  In the second embodiment shown in FIGS. 9 to 12, the other operations and effects are the same as those in the first embodiment shown in FIGS. The same parts are denoted by the same reference numerals, and detailed description thereof is omitted.

In the correspondence between the configuration of the present invention and the above-described embodiment,
The vehicle body closed section structural member of the present invention corresponds to the center pillar 19 (see FIG. 7) or the front side frame 24 (see FIG. 12) of the embodiment.
Similarly,
Other members of the vehicle body correspond to the roof side rail 17, the side sill 18, the bumper beam 22, and the floor frame 23,
The present invention is not limited to the configuration of the above-described embodiment.

  For example, the toughness may be improved by tempering after the quenching step S5, and the vehicle body closed cross-section structure member of the present invention is another vehicle body such as a hinge pillar, a front pillar, a rear pillar, a side sill, and a tunnel member. You may apply to a structural member.

Process drawing which shows the manufacturing method of the vehicle body closed cross-section structural member of this invention Illustration of blank material welding process Explanatory drawing of cylindrical work forming process Perspective view of cylindrical workpiece Explanatory drawing of work heating process, bending process, quenching process Explanatory drawing which shows the Example of a cooling means The front view which shows the joining structure of the vehicle body closed cross-section structural member with the vehicle body other member Explanatory drawing which shows the other Example of each blank material formation pattern Explanatory drawing of the blank material welding process by the other Example of the manufacturing method of a vehicle body closed cross-section structural member Perspective view of cylindrical workpiece Perspective view of cylindrical workpiece after bending and quenching The top view which shows the joining structure of the vehicle body closed cross-section structural member with the vehicle body other member

Explanation of symbols

S1 ... Blank material welding step S2 ... Cylindrical workpiece forming step S3 ... Work heating step S4 ... Bending molding step S5 ... Quenching steps L1-L6 ... Welding lines 1, 1A, 1B, 1C ... First blank materials 2A, 2B, 2C ... 2nd blank 3 ... Welded blanks 4 and 5 ... End face part 6 ... Cylindrical workpieces 8, 9, 20, 21 ... Joint part 17 ... Roof side rail (vehicle body other member)
18 ... side sill (other body parts)
19 ... Center pillar (body cross-section structural member)
22 ... Bumper beam (other body parts)
23 ... Floor frame (other body parts)
24. Front side frame (body closed cross-section structural member)

Claims (6)

Adjacent to the first blank material arranged at a predetermined site in the axial direction of the cylindrical workpiece when formed on the cylindrical workpiece in the next step, the strength and the plate thickness are substantially equal to the first blank material, and The blank material which arrange | positions the 2nd blank material whose hardenability is higher than the said 1st blank material, and welds the said both blank materials with the welding line of the said both blank materials comprised only diagonally with respect to the said axial direction. Welding process;
A cylindrical workpiece forming step of welding the end faces of the welding blank material welded in the blank material welding step to form a cylindrical workpiece;
A workpiece heating step of heating the cylindrical workpiece formed in the cylindrical workpiece forming step to a temperature equal to or higher than the quenching temperature of the workpiece;
A bending process for bending the work heated above the quenching temperature by the work heating process;
A quenching process in which the workpiece is cooled and quenched after the bending process;
A method for manufacturing a vehicle body closed cross-section structure member comprising: 2. The method of manufacturing a vehicle body closed cross-section structure member according to claim 1, wherein the bending in the bending forming step applies compressive stress to a portion that is on the bending inner side of the workpiece. 3. The method for manufacturing a vehicle body closed cross-section structure member according to claim 1, wherein both the blank materials are made of an iron-based material. The method for manufacturing a vehicle body closed cross-section structure member according to claim 3, wherein the second blank material contains more alloying elements that can improve hardenability than the first blank material. The first blank material is disposed at an intermediate portion in the axial direction of the cylindrical workpiece,
The vehicle body according to any one of claims 1 to 4, wherein the second blank member is provided with respective joint portions with other members of the vehicle body at respective portions on both sides in the axial direction of the cylindrical workpiece. Manufacturing method of closed cross-section structural member. While disposing a plurality of first blank materials with low hardenability spaced apart in the middle in the axial direction of the cylindrical workpiece,
The second blank material having high hardenability is disposed between the first blank materials spaced apart from each other and on both sides in the axial direction of the cylindrical workpiece. A method for manufacturing a vehicle body closed cross-section structural member.

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