JP2008001135A - Automobile member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a door beam whose structural strength is improved by quenching and hardening only a quenching section set in a main body part while using direct electric conductive quenching. <P>SOLUTION: The main body part 11 is divided into the quenching section 14 and a non-quenching section 15 which are arranged in an extending direction in a door beam 1 having the main body part 11 extending in one direction. The electric resistance per a unit length in the quenching section 14 is made larger than that per a unit length in the non-quenching section 15 by making the cross section in the quenching section 14 smaller than that in the non-quenching section 15. The main body part 11 is directly energized by allowing at least all the quenching sections 14 to be sandwiched. The quenching section 14 is heated to a phase transition temperature by direct energization prior to the non-quenching section 15, and thereafter the door beam 1 is formed by quickly cooling at least the quenching section 14 and quenching and hardening it. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an automobile member partially quenched by direct energization.

Many automotive parts are required to have high structural strength (high bending strength, high torsional strength, high tensile strength, etc.). The above requirements can be satisfied by selecting a material such as a high-strength steel plate / ultra-high-strength steel plate (590 N / mm ² or more), increasing the thickness of an automobile member, or adding a reinforcing member. In addition, it is possible to produce a member for an automobile using a general steel plate / high-tensile steel plate (270 N / mm ^{2 to} 440 N / mm ² ) that is inexpensive and has good workability, and realize high structural strength.

  As described above, a door beam can be exemplified as a member for an automobile that is required to be inexpensive and easily processed with a high structural strength and to be lightweight. For example, in the door beam of Patent Document 1, a door beam is configured by three members, a main body portion and a pair of mounting portions (mounting brackets). After the mounting portions are integrated by welding to both ends of the main body portion, It is said that “hardening and annealing” will be applied.

  The door beam of Patent Document 2 is made of high strength steel that is not quenched for the purpose of reducing the costs associated with quenching while forming the door beam with one member by press molding and preventing the occurrence of residual stress due to quenching. Selected. On the other hand, the door beam of Patent Document 3 is composed of a single member like the door beam of Patent Document 2, but has a thin plate thickness due to the increase in the plate thickness and the increase in weight caused by not quenching. The required structural strength is satisfied by quenching.

Japanese Patent No. 3139984 ([0076] and others) Japanese Patent Laid-Open No. 10-166860 ([0019] and others) JP 2003-094943 A ([Claim 1], [0043] and others)

  As described above, automobile members are required to have high structural strength, but at the same time, the amount of energy required for processing for improving structural strength is small, the processing time or processing steps are short, and productivity is high. It is also required to have excellent quality. These latter demands relate not only to automobile members, but also to processing methods and processing equipment used for processing to improve structural strength. From this point of view, it is necessary to select and use an appropriate processing method and processing apparatus in view of the required structural strength in accordance with the automobile member.

  In the door beam of Patent Document 1, since the main body portion and the mounting portion are separate members, these assembly steps are required, and it is difficult to improve productivity, and an increase in cost due to the assembly step is unavoidable. The door beam of Patent Document 2 has a problem that it is difficult to improve the structural strength by devising the cross-sectional shape because there is a restriction that the drawing process of the high-tensile steel plate cannot be made so deep. On the other hand, the door beam of Patent Document 3 is improved in structural strength by quenching while being press-formed using a relatively low tensile steel plate, that is, a relatively inexpensive steel plate. Compared to cost-effectiveness.

  Patent Document 3 uses high-frequency quenching (hereinafter referred to as high-frequency quenching) using an electromagnetic induction coil for quenching the door beam. This induction hardening is also frequently used for other automobile members. However, induction hardening requires complicated processing equipment and an induction coil is configured for each automobile member. Therefore, the induction coil is subject to design restrictions, and the objects that can be actually quenched are limited. Since it takes time to heat even a member, there is a problem that it is difficult to improve productivity. Therefore, the automotive member having a main body extending in one direction, such as a door beam, is preferably quenched by direct energization (hereinafter referred to as direct energization quenching). Direct current quenching has the advantage that the processing apparatus is simple, the time required for heating is short, and the productivity is easily improved as compared with induction quenching.

  Here, since the door beam is an impact absorbing member with a beam structure in which the main body is installed over both attachment parts attached to the vehicle body, the entire main body is limited to improving the structural strength due to the complicated cross section, and the central section of the main body Only in a certain section with the central symmetry axis interposed therebetween, the structural strength may be further improved by direct current quenching. Hereinafter, the “central section of the main body” is referred to as a “quenching section”. In the simplest case, it is only necessary that the energizing electrode of the processing apparatus is brought into contact with the quenching section, and only the quenching section can be energized directly. However, as described above, the main part of the door beam has a complicated cross section, and it is difficult to bring the current-carrying electrode of the processing apparatus into close contact with the main part. From this point of view, in order to realize stable and reliable direct energization, it has been assumed that the energization electrode of the processing apparatus is brought into contact with the mounting portion sandwiching the main body portion and the entire main body portion is directly energized.

  In order to quench only the quenching section while directly energizing the entire main body, it is conceivable that the rapid cooling after heating necessary for quenching is limited to the quenching section. Specifically, after the entire main body is uniformly heated to the phase transition temperature, only the quenching section may be jetted and rapidly cooled. However, it is difficult to limit the injection range of the coolant to the quenching section, and it is difficult to quench only the quenching section as designed. Further, since the injection range of the coolant cannot be accurately controlled, quenching is not uniform, and the quality of the door beam may be deteriorated. Furthermore, direct energization generates an oxide scale on the entire surface of the main body, which is the energization range, but since the injection of the coolant also serves to remove the oxide scale, it is possible to partially inject the coolant to the oxide scale. This is not desirable because it requires a separate post-treatment to remove the.

  From this, the direct energization quenching of the door beam is performed by directly energizing the entire main body part to uniformly heat the entire main body part to the phase transition temperature, and then uniformly cooling the entire main body part to form a structure of the entire main body part. There was nothing but to improve the strength. As a result, in theory, compared with direct energization quenching only in the quenching section, actual direct energization quenching increases the processing time for uniformly heating the entire main body and the amount of energy required for the heating. There was a problem to do. Here, in order to reduce the processing time and the amount of energy, it is conceivable that the current value to be energized is increased to rapidly heat the entire main body. However, if rapid heating is performed by increasing the current value, the dispersion of heat generation due to heat conduction cannot catch up with the heating, and local fluctuations in the temperature rise of the metal material (steel material in the case of a door beam) due to heating. When a general heat generation occurs, an increase in temperature is further promoted by an increase in electrical resistance, resulting in a large temperature variation. As a result, satisfactory structural strength cannot be expected, and the quality of the door beam may be deteriorated. Therefore, when the door beam is directly energized and quenched, it is necessary to keep the current value low and to gently heat the entire main body.

  As described above, in the direct electric quenching of the door beam, it is difficult to improve only the structural strength of the quenching section, and as a result, there is a problem of increasing the processing time and the amount of energy. Like a door beam, an automotive member having a main body extending in one direction can reduce the processing time and energy amount by direct current quenching compared to induction quenching, but still shortens the processing time, It is expected to reduce the amount of energy required. Therefore, in order to develop an automobile member such as a door beam, which is hardened and hardened only in the quenching section set in the main body while using direct electric quenching, the structural strength is improved.

  What has been developed as a result of the study is a metal automotive member having a body portion extending in one direction. The body portion is divided into a quenching section and a non-quenching section aligned in the extending direction. By making the sectional area of the section smaller than the sectional area of the non-quenched section, the electrical resistance per unit length of the quenched section (hereinafter simply referred to as electrical resistance) is made larger than the electrical resistance of the non-quenched section. Then, the main body is directly energized across at least all the quenching sections, and the quenching section is heated to the phase transition temperature prior to the non-quenching section by the direct energization, and then at least the quenching section is rapidly cooled. It is a member for automobiles that has been quenched and hardened. The automotive member to which the present invention can be applied includes a door beam having a main body portion of an open section structure (for example, a hat type) or a closed section structure (for example, a pipe type), a bumper beam, a side member, and a cross having the same sectional structure as described above. A member, a pillar, a roof bow, etc. can be mentioned.

  The “quenched section” is, for example, a central section of the door beam, that is, a section that requires improvement of structural strength by direct electric quenching, and the “non-quenched section” is a section excluding the central section of the door beam, for example, directly Each section does not require improvement of structural strength by electric quenching. When the automotive member is a door beam, only the non-quenched sections are arranged on both sides in the extending direction of the main body across the quenching section, but a plurality of quenched sections or non-quenched sections may be provided.

  “Directly energizing the main body with at least all of the quenching sections” means that the processing device has a positional relationship between all of the quenching sections of the quenching section and the non-quenching section in the extending direction of the main body section. This means that the current-carrying electrode is brought into contact with the main body. For example, out of the quenching section and the non-quenching section arranged in the extending direction of the main body, if there is a quenching section on the outermost side, the outermost part of the quenching section and the non-quenching section on the outermost side The energizing electrode of the processing apparatus is brought into contact with any position in the non-quenching section. “Electrical resistance per unit length” means the electrical resistance in the extending direction of the unit length section in the extending direction of the main body.

  “At least quenching the quenching section” means, for example, injecting the coolant into the quenching section that has been heated to the phase transition temperature in advance, and also in the non-quenching section that has not yet reached the phase transition temperature. Including the case of injecting coolant. In the latter case, the quenching zone that has reached the phase transition temperature is quenched before the non-quenching zone reaches the phase transition temperature, so that the non-quenching zone is not directly energized and quenched. From this, the member for motor vehicles of the present invention can use the processing device which supplies electricity directly to the whole main-body part seen conventionally. However, as will be described later, even when direct energization as in the prior art is applied to the main body, the processing time required for heating can be shortened, and the amount of energy required can be reduced.

  The present invention utilizes the fact that heating by direct energization varies depending on the difference in electrical resistance, and provides a quenching section and a non-quenching section with different electrical resistance in inverse proportion to the cross-sectional area in the main body portion of the automobile member. It is characterized in that only the insertion section is directly energized and quenched. When energization is started directly on the entire main body across all the quenching sections, the quenching section having a relatively high electrical resistance starts to be heated prior to the non-quenching section having a relatively low electrical resistance. The hardened section with a small cross-sectional area has a smaller heat capacity per unit length than the non-quenched section, and as already mentioned, the metal material used for automotive parts increases the electrical resistance when heated. Further, the heating in the quenching section precedes the non-quenching section. As a result, since the quenching section reaches the phase transition temperature prior to the non-quenching section, if the quenching section reaches the phase transition temperature, the direct energization is stopped and the quenching section is rapidly cooled, so that the quenching section Only the section can be directly energized and quenched.

  The main body of the present invention divides the main body into a quenching section and a non-quenching section due to the difference in electrical resistance, and it is sufficient that the main body can be directly energized across all the quenching sections. In the case of having a mounting part made of metal at both ends, the main body part may be directly energized via the mounting part. The mounting part may be separate from the main body part. In addition to the difference in electrical properties with the main body part, it is not desirable that the electrical resistance of the joint part to the main body part is generated. Therefore, the mounting part is integrally formed with the main body part. Is preferred. Even if the main body is directly energized through the mounting portion in this way, it is only necessary to heat only the quenching section, so that the processing time can be shortened and the required energy amount can be reduced. Furthermore, the amount of energy can be further reduced if direct energization can be performed at the shortest distance across all quenching sections. As a result, the risk of deformation due to quenching can be reduced, so that the quality of the automobile member can be improved.

  Since the quenching section and non-quenching section of the main body are continuous sections of the main body, changing the cross-sectional area of both forms a structural boundary in the direction of extension of the main body. It may also be done, which is not preferable. Therefore, the main body may be configured such that the cross-sectional area of the quenching section is made smaller than the cross-sectional area of the non-quenching section by gradually decreasing the cross-sectional area of the non-quenching section toward the quenching section. Thus, although the cross-sectional area of the non-quenched section may change, the cross-sectional area is made constant because the quenching section needs to be able to be directly and electrically quenched. The method of making the cross-sectional area of the quenching section smaller than the cross-sectional area of the non-quenching section is, for example, an automotive member having a flange. Or the method of reducing height can be illustrated. In addition, a long hole may be provided in the range of the quenching section.

  The present invention improves the structural strength while improving the structural strength appropriately and sufficiently for the automobile member by partially improving the structural strength of the automobile member while using direct current quenching. It has the effect of reducing the required processing time and energy amount. As described above, direct current quenching has a shorter processing time than the currently used high frequency quenching and reduces the amount of energy required. There is an advantage that the processing time required is the shortest and the amount of energy is minimized. In particular, the shortening of the processing time brings about the effect of increasing the productivity of the automobile member of the present invention.

  In addition, the automotive member of the present invention can clearly separate the quenching section and the non-quenching section in the main body portion and directly energize and quench only the quenching section, which may reduce the quality of the automotive member. However, since it is possible to control the section for direct current quenching relatively accurately, an effect of improving the quality can be obtained. Since the present invention realizes these advantages and effects only by providing a relative difference in the cross-sectional area between the quenching section and the non-quenching section in the main body of the automobile member, the present invention is cost-effective. It can be said that an excellent automotive member can be provided.

  Hereinafter, the door beam 1 which is embodiment of this invention is demonstrated, referring a figure. FIG. 1 is a perspective view showing an example of a door beam 1 according to the present invention, FIG. 2 is an enlarged plan view of a portion indicated by an arrow A in FIG. 1, and FIG. 3 is an example of a processing apparatus 2 that directly energizes and quenches the door beam 1 of this example. 4 is a plan view of the processing apparatus 2 of this example, FIG. 5 is a partial cross-sectional view taken along the line BB in FIG. 3, and FIG. 6 is a perspective view corresponding to FIG. FIG. 8 is a perspective view corresponding to FIG. 1 of the door beam 1 after the direct quenching, FIG. 8 is a perspective view corresponding to FIG. 1 showing another example of the door beam 1 according to the present invention, and FIG. 9 is a further view of the door beam 1 according to the present invention. FIG. 2 is a perspective view corresponding to FIG. 1 showing another example.

As shown in FIG. 1, the door beam 1 of this example includes a hat-shaped main body portion 11 extending in the longitudinal direction (one direction), and a pair of attachment portions 13 provided with the main body portion 11 sandwiched in the longitudinal direction. It is the member for motor vehicles which consists of. The door beam 1 is inexpensive and workability good general steel, high-tensile steel plate ^{(270N / mm 2 ~440N / mm} 2) press molding, roll forming or hydroforming (hydroforming etc.), flange 12 on both side edges A hat-shaped main body 11 having (the back side is not visible in FIG. 1) is formed, and the mounting portion 13 is a flat surface as it is.

  In the door beam 1 of this example, a quenching section 14 having a relatively small cross-sectional area is defined as a central section of the main body 11, and the flange 12 in the quenching section 14 is cut off from the edge. A non-quenched section 15 having a relatively large cross-sectional area is defined between each of the mounting portions 13 with the quenched section 14 interposed therebetween. Here, in order to ensure the continuity of the flange 12 across the quenching section 14 and the non-quenching section 15, a gradual change section 16 is formed by continuously cutting the flange 12 obliquely to the quenching section 14. . Since the gradual change section 16 has a larger cross-sectional area than the quenching section 14, it is included in the non-quenched section 15 in the classification according to the present invention. Thus, the electrical resistance of the quenching section 14 is the highest, the electrical resistance gradually decreases by the gradual change section 16, and the electrical resistance of the non-quenching section 15 is the lowest.

  The door beam 1 of this example directly energizes a low-frequency alternating current (50 Hz to 250 Hz, about 3000 A) through the mounting portion 13 through the mounting portion 13 by the processing device 2 shown in FIGS. Only directly energize and quench. The door beam 1 that has been press-molded is sandwiched between the attachment portions 13 by the chuck electrodes 21 and fixed in position to the processing apparatus 2. The processing apparatus 2 uses a lower jig 22 and an upper jig 24 having a cross-sectional shape following the main body 11 of the door beam 1 in order to suppress or prevent deformation of the door beam 1 whose position is fixed by direct energization quenching. Sandwich. However, the lower jig 22 and the upper jig 24 prevent short-circuiting and do not release heat, so that the lower jig 22 and the upper jig 24 are not brought into contact with the main body part 11 but are kept close to the main body part 11. That is, the lower jig 22 and the upper jig 24 abut against the main body 11 that is deformed during cooling, and only suppress the deformation.

  When the energization of the main body 11 is started by the processing device 2, the entire main body 11 starts to be heated by the direct energization, but the quenching section 14 having a relatively high electrical resistance precedes and starts to rise in temperature. As shown in FIG. 6, when the non-quenching zone 15 has not yet reached the phase transition temperature, the quench zone 14 first reaches the phase transition temperature. In FIG. 6, the quenching section 14 that has reached the phase transition temperature is illustrated by cross hatching, and the non-quenching section 15 that has not reached the phase transition temperature is illustrated by normal hatching. Actually, the gradual change section 16 included in the non-quenching section 15 is heated to an intermediate temperature of each of the quenching section 14 and the non-quenching section 15; The gradual change section 16 included in the quenching section 15 is also illustrated by normal hatching similar to the non-quenching section 15.

  When the quenching section 14 of the main body 11 reaches the phase transition temperature or higher, direct energization is stopped. Whether or not the quenching section 14 has reached the phase transition temperature can be measured by directly measuring the temperature of the quenching section 14, but the energization time of the predetermined alternating current, the quenching section 14 and the non-quenched section 14 in advance. Measure the relationship with each temperature rise in the quenching section 15, set the energization time that the quenching section 14 reaches the phase transition temperature while the non-quenching section 15 does not reach the phase transition temperature, and only the energization time directly Energize. Here, the energization time required to reach the quenching section 14 above the phase transition temperature depends on the structure and size of the main body 11, but the direct energization quenching with the main body 11 as a whole above the phase transition temperature. Compared with the energization time of the above, the ratio is shortened in proportion to the ratio of the length of the quenching section 14 with respect to the entire main body 11, and naturally the amount of energy required is greatly reduced.

  When the direct energization is stopped, the temperature of the quenching section 14 and the non-quenching section 15 no longer increases, and the quenching section 14 is further removed from the lower injection hole 23 and the upper injection hole 25 provided in the lower jig 22 and the upper jig 24. As shown in FIG. 7, only the quenching section 14 is directly energized and quenched, and the phase transition temperature is not reached. Cool the quenching section 15. In this way, by spraying the coolant on the entire main body 11 including the non-quenched section 15, the oxide scale generated on the entire main body 11 by direct energization heating can be washed away. Here, the generation of oxide scale is mainly in the quenching section 14 and the generation amount is suppressed because the energization time is short. That is, the cooling liquid injection time in the sense of removing the oxide scale can be shortened as compared with the case where the entire main body 11 is directly energized and quenched.

  Here, as described above, the processing apparatus 2 of the present example is provided in each of the lower jig 22 and the upper jig 24 that suppress the deformation of the main body 11 of the door beam 1 due to rapid cooling. The portion that may be deformed by the door beam 1 is mainly a quenching section 14, and since this quenching section 14 is relatively short with respect to the entire main body 11, the amount of deformation is limited. In other words, the door beam 1 of the present invention is less likely to be deformed by direct electric quenching, and even when it is deformed, the amount of deformation is kept extremely small. From this, there are few cases where the deformation of the main body part 11 is actually suppressed by the lower jig 22 or the upper jig 24. Nevertheless, the present invention has the advantage of providing a highly accurate product with no or little deformation. is doing.

In order to apply the present invention, for example, the electrical resistance of the quenching section 14 in the main body 11 of the door beam 1 illustrated above may be larger than the electrical resistance R of the non-quenching section 15. First, the electrical resistance R of the quenching zone 14 or the non-quenching zone 15 is proportional to the temperature T of each zone 14 and 15 and inversely proportional to the cross-sectional area A of each zone 14 and 15.
R∝T / A (1)
The temperature increase unit ΔT from the temperature T is proportional to the power consumption W and inversely proportional to the heat capacity Q of the sections 14 and 15.
ΔT∝W / Q (2)
Here, the specification power W is represented by the product of the square of the alternating current I to be energized and the electric resistance R of each section 14, 15.
W = I ² R (3)
The heat capacity Q of each section 14 and 15 is proportional to the mass M of each section 14 and 15, and the body portion 11 and the mounting portion 13 are integrally formed of the same material as the door beam 1 illustrated above. From the above, the heat capacity Q is proportional to the volume of each section 14, 15, that is, the product of the length L and the cross-sectional area A of each section 14, 15.
Q∝AL (4)
From the above formulas (1) to (4), the rising temperature unit ΔT is proportional to the electrical resistance of each section 14 and 15, and the volume of each section 14,15, that is, the length L of each section 14,15. It is inversely proportional to the product of area A.
ΔT∝I ² R / AL∝I ² T / A ² L (5)

  In order to make the electrical resistance in the quenching section 14 larger than the electrical resistance R in the non-quenching section 15 from the relational expression (the above formula (5)) of the rising temperature unit ΔT, in addition to reducing the cross-sectional area A, the length L It is conceivable to shorten the length. However, the quenching section 14 is determined for each automobile member to which the present invention is applied, and cannot be easily shortened. For this reason, when the electrical resistance R in the quenching section 14 is made larger than the electrical resistance R in the non-quenching section 15, the sectional area A is exclusively reduced.

  As a structure for reducing the cross-sectional area A, the door beam 1 illustrated above has a flange 12 projecting from the left and right sides of the main body 11 cut off from the edge, but as shown in FIG. The long hole 17 may be provided in the main body 11 of the quenching section 14 as shown in FIG. When the cross-sectional area A is thus reduced, the structure strength of the quenching section 14 may be relatively lower than that of the non-quenching section 15, although it varies depending on the structure of the main body 11, particularly the cross-sectional shape. However, since the reduction in the structural strength can be compensated by quench hardening in the quenching section 14, the main body portion 11 of the door beam 1 that has been subjected to the direct current quenching can have a necessary and sufficient structural strength.

  Specifically, the cross-sectional area A of the quenching section 14 is about 5% to 20%, preferably about 7% to 15% smaller than the non-quenching section 15. If it is the said grade, if it is not a main part of a quite special shape, the cross-sectional area A can be reduced comparatively easily. And the main-body part 11 which provided the quenching area 14 in which the cross-sectional area A was made small is only reduced by about several percent compared with the case where the quenching area 14 is not provided. A decrease in the structural strength of the main body 11 can be hardly caused.

It is a perspective view showing an example of the door beam based on this invention. FIG. 2 is an enlarged plan view of a portion indicated by an arrow A in FIG. It is a side view showing an example of the processing apparatus which directly energizes and quenches the door beam of this example. It is a top view of the processing apparatus of this example. It is a BB partial sectional view in FIG. FIG. 2 is a perspective view corresponding to FIG. 1 showing a door beam during direct energization. FIG. 2 is a perspective view corresponding to FIG. 1 of a door beam that has been subjected to direct current quenching. FIG. 3 is a perspective view corresponding to FIG. 1 showing another example of a door beam according to the present invention. FIG. 5 is a perspective view corresponding to FIG. 1 showing still another example of a door beam according to the present invention.

Explanation of symbols

1 Door beam
11 Body
12 Flange
13 Mounting part
14 Quenching section
15 Non-quenched section
16 Gradual interval

Claims (3)

In a metal automobile member having a body portion extending in one direction, the body portion is divided into a quenching section and a non-quenching section aligned in the extending direction, and the cross-sectional area of the quenching section is non-quenched By making it smaller than the sectional area of the section, the electrical resistance per unit length of the quenching section is made larger than the electrical resistance per unit length of the non-quenched section, and at least the entire quenching section is sandwiched between the main body part For a motor vehicle, wherein the quenching section is heated to the phase transition temperature prior to the non-quenching section by direct energization, and at least the quenching section is quenched and quenched and hardened. Element. The member for an automobile according to claim 1, wherein the main body portion has metal attachment portions for the automobile at both ends, and the main body portion is directly energized through the attachment portion. 3. The main body portion according to claim 1 or 2, wherein the cross-sectional area of the non-quenched section is made smaller than the cross-sectional area of the non-quenched section by gradually decreasing the cross-sectional area of the non-quenched section toward the quenched section. The automotive member described.

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