JP2006142917A - Shock absorbing member having excellent shock absorbing property and welding method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shock absorbing member having an excellent shock absorbing property by optimizing a shape of a laser welding part in the light of a collapse form and welding strength of a shock absorbing member applied to an automobile or the like, and a welding method therefor. <P>SOLUTION: In a shock absorbing member having a closed cross sectional structure in which at least one side is formed by a hat-shaped cross sectional shape steel plate, a ratio (L/λ) of a welding length L to a welding pitch λ per one spot of a welding bead intermittently formed along the longitudinal direction of a flange part made of the hat-shaped cross sectional shape steel plate is 0.2 to 0.95. In addition, the ratio (W/t) of a welding width W to a plate thickness t on the lapped face of the flange part is 1.0 to 3.0. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an impact-absorbing member excellent in impact-absorbing characteristics used for automobile members and the like, and a welding method thereof. In particular, the present invention relates to a welding member having improved shock absorption characteristics and a welding method related to a method for improving the shock absorption characteristics.

  Currently, the automobile industry is working on the development of car bodies with excellent collision safety for the purpose of ensuring the safety of passengers in car collisions. Excellent collision safety means that the kinetic energy that the car had while driving can be converted into strain energy and heat energy efficiently without causing significant damage to the occupant's maneuvering space and by causing large deformation of the surrounding skeleton members It can be said. For example, on both sides of the front part of the vehicle body, there is an impact absorbing member having a closed cross section structure sandwiching the engine, which is called a front side member. As an example, a front side member perspective view is shown in FIG. The front side member shown in FIG. 1 has a closed cross-sectional structure in a cross section perpendicular to the longitudinal direction of a member in which a welded portion 4 is formed and joined to a flange portion 3 in which a steel plate 1 and a steel plate 2 bent into a hat shape are overlapped. Form the member shape. When the automobile collides with an object from the front, the front side member is crushed like a bellows in the longitudinal direction of the member, and efficiently absorbs the energy of impact. In general, if the front side member falls down in the middle of a collision or breaks easily at the weld, regular bellows-like crushing does not occur in the longitudinal direction of the member. End up.

Conventionally, it has been known that it is effective to reduce the welding interval of spot welding or use a high-tensile steel plate as a method of improving the impact absorbing characteristics when manufacturing an impact absorbing member using resistance spot welding. Yes. Usually, the distance between the resistance spot welds is within the range of 25-60 mm, and the size of the resistance spot weld is within the range of 3t ^{0.5 to} 6t ^0.5 (t = plate thickness), so that the weld is easily broken at the time of collision. The member itself can absorb the impact. However, resistance spot welding is a process that presupposes the formation of spot-like welds, and it is not preferable in terms of production efficiency to reduce the interval and form a number of resistance spot welding points. Further, when the interval between the welded portions is shortened, a shunt phenomenon in which current flows through the previously formed welded portion occurs, making it difficult to control the welded portion size.

  On the other hand, the application of laser welding in place of resistance spot welding is expanding with the aim of reducing the weight of automobile bodies and improving the rigidity and collision safety when welding automotive parts. Laser welding provides a good penetration depth with a narrow bead width compared to resistance spot welding, and therefore features such as shortening the flange width forming the weld and improving productivity by continuous welding at high speeds. Can be mentioned.

  When manufacturing an impact-absorbing member (welding member) by laser welding or the like, methods for improving the impact-absorbing characteristics of the welding member are known (for example, see Patent Documents 1 to 4).

  That is, in a vehicle body frame structure formed in a closed cross section with a vehicle body panel and a hat section member, a large number of notches are arranged in parallel in the longitudinal direction of the flange portion of the hat section member, and are sequentially deformed at the notches at the time of a collision. A method is known in which the bellows are regularly deformed to improve the shock absorption characteristics (see, for example, Patent Document 1).

  Also, in the frame structure in which the panel and the flange portion of the hat-shaped frame member are welded to form a closed cross section, the side edge in the width direction of the flange portion is intermittently connected in the longitudinal direction of the flange portion by high energy beam welding such as laser. In general, a method of welding is known (see, for example, Patent Document 2).

Effective in the width direction of the flange from the center of the corner adjacent to the flange in the long tubular weld strength member composed of the first member and the second member of the plate thickness t having the flange and n corners. A method is described in which a welded portion is provided in the range of width a = 4 nt ^0.46 , and the welded portion is intermittently formed at a predetermined pitch (interval) in the longitudinal direction of the flange to improve the shock absorption characteristics (for example, And Patent Document 3).

  However, these methods are methods for optimizing the weld length and weld pitch (interval) at the welded part in the longitudinal direction of the flange part and the melt (bead) width at the welded part in the widthwise direction of the flange part from the viewpoint of crushing mode control. However, it has been difficult to stably improve the shock absorption characteristics compared to the conventional art by suppressing the lateral collapse and fracture of the welded portion during crushing and maintaining a regular crushing configuration.

  In an impact absorbing member obtained by laser welding a steel plate with a hat cross-sectional shape and a flat steel plate or a steel plate with a hat cross-sectional shape at the flange portion, the melt width in the width direction of the weld portion formed on the flange portion is 1.4 to There is also known a method of improving impact absorption characteristics by continuously welding the longitudinal direction of the flange end so as to be 3.0 times (see, for example, Patent Document 4). This method is intended to improve the shock absorption characteristics by forming a welded portion continuous in the longitudinal direction on the flange portion to increase the joint strength. However, according to the results of the crush test by the present inventors, the shock absorbing member in which the flange portion is continuously welded with the laser has a high probability of causing the member to fall down during the buckling progress at the time of collision. It was found that the shock absorption characteristics could not be obtained.

  As described above, various methods for improving the impact absorbing characteristics of the impact absorbing member by changing the welding method and the welded portion shape (melting width and length) have been proposed. However, in all cases, the shape of the welded part is not adequately optimized from the viewpoint of crushing mode control and welded part strength, and the shock absorbing characteristics of the shock absorbing member using laser welding can be improved dramatically and stably. Was difficult.

  In order to further improve the collision safety of automobiles, which are increasingly demanded, the structure of the shock absorbing member, the strength of the welded part that greatly affects the crushing form of the shock absorbing member, and the shape of the welded part that determines it are determined. The practical application of optimization technology is strongly desired.

JP 58-116268 A JP-A-6-170568 JP-A-7-125651 Japanese Patent Laid-Open No. 2002-079388

  In view of the current state of the prior art as described above, the present invention optimizes the shape of a laser weld from the viewpoint of the crushing form and welding strength of an impact absorbing member applied to automobiles and the like, and is excellent in impact absorbing characteristics. Another object is to provide a shock absorbing member and a welding method thereof.

  The present invention solves the above-mentioned problems, and the gist thereof is as follows.

  (1) In an impact-absorbing member having a closed cross-section structure in which at least one is made of a hat-shaped cross-sectional steel plate, per weld bead formed intermittently along the longitudinal direction of the flange portion of the hat-shaped cross-sectional steel plate The ratio (L / λ) of the welding length L and the welding pitch λ is 0.2 or more and 0.95 or less, and the ratio (W / t) of the melt width W and the plate thickness t on the overlapping surface of the flange portion. Is an impact-absorbing member excellent in impact-absorbing characteristics, characterized by being 1.0 or more and 3.0 or less.

(2) The weld bead is formed within a distance d = 12 × t ^{0.5 in the} flange width direction from the vertical wall portion of the hat-shaped cross-sectional steel plate with respect to the plate thickness t of the flange portion. The shock absorbing member having excellent shock absorbing characteristics as described in (1).

  (3) In the hat-shaped cross-sectional steel plate, the average length D = (a + b) / 2 of the thickness t of the flange portion, the length a in the width direction of the hat-shaped cross section, and the length b in the height direction, The ratio (t / D) is 0.020 or less, and the shock absorbing member having excellent shock absorbing characteristics according to (1) or (2).

  (4) In the method of welding a shock absorbing member having a closed cross-sectional structure, at least one of which is a hat-shaped cross-section steel plate, the ratio (L / λ) of the welding length L to the welding pitch λ per point is 0.2 or more and 0 The hat is formed by laser welding so that the ratio (W / t) of the melt width W to the plate thickness t on the overlapping surface of the flange portion is 1.0 or more and 3.0 or less. A welding method for an impact-absorbing member excellent in impact-absorbing characteristics, wherein a weld bead is intermittently formed along the longitudinal direction of a flange portion of a steel plate having a cross-sectional shape.

(5) The welding bead is formed within a range of a distance d = 12 × t ^{0.5 in the} flange width direction from the vertical wall portion of the hat-shaped cross-sectional steel plate with respect to the plate thickness t of the flange portion. A method for welding an impact-absorbing member having excellent impact-absorbing characteristics as described in (5).

  (6) An average length D = (a + b) / 2 of the thickness t of the flange portion, the length a in the width direction of the hat-shaped cross section, and the length b in the height direction in the hat-shaped cross-sectional steel plate. The ratio (t / D) is 0.020 or less. The method for welding an impact-absorbing member having excellent impact-absorbing characteristics according to (4) or (5).

  ADVANTAGE OF THE INVENTION According to this invention, the crushing form and welding strength of the impact-absorbing member manufactured using laser welding are optimized, and the impact-absorbing member which has the outstanding impact-absorbing characteristic compared with the past, and its welding method can be provided. .

  Application of the present invention to an impact absorbing member used for automobiles and the like further improves the reliability and safety of welded structures such as automobile parts, and also improves productivity by laser welding with excellent welding efficiency. This makes it possible to contribute greatly to industries such as the automobile field.

  Embodiments of the present invention will be described below.

  In the following description, it goes without saying that the present invention is not limited to the following embodiments and conditions as long as the objects and effects of the present invention are achieved without departing from the gist of the present invention.

  The present invention is implemented, for example, in an embodiment as shown in FIG. A hat-shaped cross-section steel plate 1 bent into a hat shape and a flat steel plate 2 are overlapped, and a laser beam (not shown) is irradiated in a direction substantially perpendicular to the steel plate surface to the overlapping portion of the flange 3. Then, the bead 4 is formed and joined by melting and solidifying at least the thickness region including the steel plate overlapping surface. As a result, an impact-absorbing member having a hat-shaped closed cross-sectional structure with a cross section perpendicular to the longitudinal direction of the member can be manufactured. The formation of the bead 4 by laser welding at the overlapping portion of the flange 3 is performed by welding a target position on the surface of the flange 3 with a laser beam (not shown) focusing optical system (not shown) at a predetermined speed, for example. It is formed by moving along the line direction. At the time of laser welding, a gap between the steel plate overlapping surfaces in the flange 3 is large by pressing with a roll-shaped clamp that moves with the condensing optical system or a non-movable clamp that is in surface contact with the flange (not shown). In this case, it is preferable because the melted portion can be prevented from dropping and a sound welded portion can be formed.

  In FIG. 1, an embodiment in which the flange 3 of the hat-shaped cross-sectional steel plate 1 and the flat steel plate 2 are overlapped and laser-welded to manufacture the shock absorbing member is shown, but as shown in FIG. Embodiments in which the flanges 3 of the two hat-shaped cross-sectional steel plates 1 are overlapped with each other and laser-welded to manufacture an impact absorbing member can also be adopted.

  The present invention is premised on being applied to an impact absorbing member manufactured by using laser welding as shown in the above embodiment and a welding method thereof.

  Laser welding is compared to a method in which a steel plate overlapped with a pair of electrodes is sandwiched from the surface side, such as resistance spot welding and mash seam welding, and then energized to form a weld between the overlapping surfaces. Irradiation of high energy density laser beam from one side of the combined steel sheets can maintain a good penetration depth even with a narrow bead width, reduce welding deformation, minimize high-speed continuous welding and welding flange width Is possible. In the present invention, in order to realize the weight reduction and productivity improvement of the shock absorbing member by taking advantage of the above-mentioned advantages of laser welding together with the improvement of shock absorbing characteristics of the shock absorbing member described later, welding is performed when manufacturing the shock absorbing member. Laser welding is applied as a method.

  Further, in the present invention, as a main component for improving the impact absorbing characteristics of the impact absorbing member described later, at least one of the shock absorbing members having a closed cross-sectional structure made of a hat-shaped cross-sectional steel plate, The ratio (L / λ) of the weld length L to the weld pitch λ per portion of the weld beads formed intermittently along the longitudinal direction of the flange portion is 0.2 or more and 0.95 or less, and the flange The melt width W at the overlapping surface of the portions is 1.0 to 3.0 times the plate thickness t.

  In addition, the weld length L per one place of the weld bead is an average value of the weld length of each weld bead formed intermittently along the longitudinal direction of the flange portion of the hat-shaped cross-sectional steel plate shown in FIG. Welding pitch λ is obtained as an average value of the distance between adjacent weld bead centers shown in FIG.

  Further, the shock absorbing characteristic of the shock absorbing member is, for example, a load-displacement curve as shown in FIG. 4 based on measured values of load and displacement in a crush test in which a load is applied in the longitudinal direction (axial direction) of the shock absorbing member. (Solid line) can be created and evaluated based on the impact absorption energy obtained as the integrated value of the load in the predetermined displacement range of the load-displacement curve. In other words, whether the shock absorbing member is good or bad can be evaluated by the magnitude of the measured value of the absorbed energy in the crushing test of the shock absorbing member.

  In order to sufficiently and stably improve the shock absorbing characteristics of the shock absorbing member laser-welded by such an action of the present invention, it is necessary to define the following conditions. The reasons for limiting the conditions defined in the present invention will be described below.

  (Ratio of welding length L to welding pitch λ (L / λ)

  The inventors of the present invention intermittently formed along the longitudinal direction of the flange portion of the hat-shaped cross-sectional steel plate when laser-welding a shock-absorbing member having a closed cross-sectional structure made of a steel plate having a hat-shaped cross-sectional shape. The influence of the ratio (L / λ) of the weld length L to the weld pitch λ (L / λ) per location on the weld bead on the impact absorbing characteristics of the impact absorbing member was examined in detail.

  FIG. 7 shows the relationship between the ratio of the weld length L to the weld pitch λ (L / λ) and the shock absorption energy in the weld bead of the shock absorbing member.

  Note that the shock absorbing characteristics of the shock absorbing member are obtained by calculating the shock absorbing energy from the load-displacement curve (solid line) in the result of the crushing test of the shock absorbing member as shown in FIG. 4, and the ratio of the welding length L to the welding pitch λ (L / Λ) was evaluated as a relative ratio to the measured value (reference = 1.0) of the impact absorption energy of the impact absorbing member under the condition of 0.1.

  The ratio (W / t) of the melt width W to the plate thickness t in the weld bead of the impact absorbing member was 1.5.

  When the ratio (L / λ) of the weld length L and the weld pitch λ is less than 0.2, buckling progresses while the non-welded part opens when the impact absorbing member is crushed, and the impact absorbing member is deformed into a part of the impact absorbing member. The non-linear portion remains, that is, the impact absorption energy cannot be sufficiently improved due to the reduction in the buckling resistance of the flange and the reduction in the member strength increase due to the reduction in the work hardening region (deformation region). This is thought to be because the deformation stress locally decreases, the average crushing load of the shock absorbing member decreases, and the shock absorbing energy also decreases.

  On the other hand, when the ratio (L / λ) of the welding length L to the welding pitch λ exceeds 0.95, the impact absorbing member is tilted from the longitudinal direction (axial direction) of the impact absorbing member in the middle of crushing and rolls over to cause impact. The probability that the absorbed energy decreases increases. Considering the actual frontal collision of an automobile, the axial direction of the impact absorbing member may not always coincide with the load loading direction. Therefore, if L / λ exceeds 0.95, the impact absorbing member will fall sideways even in an actual vehicle. There is a high possibility that the shock absorption characteristics will deteriorate.

  For the above reasons, at least one of the present invention is intermittently formed along the longitudinal direction of the flange portion of the hat-shaped cross-sectional steel plate when laser-welding the shock absorbing member having a closed cross-sectional structure made of a hat-shaped cross-sectional steel plate. The ratio (L / λ) of the weld length L and the weld pitch λ per place of the weld bead is 0.2 or more and 0.95 or less.

(Ratio of melt width W to sheet thickness t (W / t))
Next, the inventors of the present invention have a ratio of the melt width W and the plate thickness t at the overlapping surface of the flange portion in the weld bead formed on the shock absorbing member having a closed cross-sectional structure made of a steel plate having a hat-shaped cross section. The effect of (W / t) on the impact absorbing characteristics of the impact absorbing member was examined in detail.

FIG. 6 shows the relationship between the ratio (W / t) of the melt width W to the plate thickness t in the weld bead of the shock absorbing member and the shock absorbing energy.
The shock absorbing characteristic of the shock absorbing member is obtained by calculating the shock absorbing energy from the load-displacement curve (solid line) in the result of the crushing test of the shock absorbing member as shown in FIG. / T) was evaluated as a relative ratio to the measured value (reference = 1.0) of the impact absorption energy of the impact absorbing member under the condition of 0.7.

  Further, the ratio (L / λ) of the weld length L to the weld pitch λ in the weld bead of the shock absorbing member was set to 0.5.

  When the ratio (W / t) of the melt width W to the plate thickness t is less than 1.0, the strength of the welded portion is insufficient and the welded portion is broken during the crushing of the shock absorbing member, and an irregular crushing mode occurs. Occurrence (regular bellows deformation does not occur) reduces the average crushing load of the shock absorbing member, and as a result, the shock absorbing energy of the shock absorbing member decreases.

  On the other hand, when the ratio (W / t) of the melt width W to the plate thickness t exceeds 3.0, the molten metal partially sags or completely melts during laser welding. Part cannot be obtained. In this case, not only the strength of the welded portion is reduced, but it is also judged defective in terms of the appearance of the parts.

  For the above reasons, at least one of the present invention is intermittently formed along the longitudinal direction of the flange portion of the hat-shaped cross-sectional steel plate when laser-welding the shock absorbing member having a closed cross-sectional structure made of a hat-shaped cross-sectional steel plate. The ratio (W / t) of the melt width W and the plate thickness t at the overlapping surface of the flange portion of the weld bead is set to 1.0 or more and 3.0 or less.

(Relationship between L / λ and W / t)
Furthermore, the inventors have determined the ratio (L / λ) of the welding length L and the welding pitch λ per point in the weld bead of the shock absorbing member, and the ratio of the melt width W and the plate thickness t on the overlapping surface. The relationship between (W / t) and the impact absorbing characteristics of the impact absorbing member was examined in detail.

  FIG. 5 shows the ratio of the weld length L to the weld pitch λ (L / λ) in the weld bead of the shock absorbing member, the ratio of the melt width W to the plate thickness t (W / t) on the overlapping surface, and the shock absorption. The relationship between characteristics and collapsed form is shown.

  Note that both the hat-shaped cross-section steel plate and the flat steel plate forming the shock-absorbing member have a thickness of 1.2 mm and a tensile strength of 294 MPa, and the width in the hat-shaped cross-section of the shock-absorbing member is long. The length (horizontal wall length) a was 60 mm, and the length in the height direction (vertical wall length) b was 40 mm.

  Symbols in the figure indicate that ◯ is excellent in shock absorption characteristics (when the shock absorption characteristics are L / λ = 0.1, relative ratio to the shock absorption energy at W / t = 0.7, 1.05 or more), □ Is a case where the shock absorbing member falls sideways and the shock absorbing characteristics are deteriorated, △ is a case where peeling occurs at the welded portion of the shock absorbing member during crushing, and x is a weld failure due to melting of a part of the welded portion during welding. Shows the case.

  From this result, the ratio (L / λ) of the welding length L to the welding pitch λ (L / λ) in the weld bead of the shock absorbing member is 0.2 or more and 0.95 or less, and the melt width W on the overlapping surface of the flange portion is By setting the ratio (W / t) of the plate thickness t to 1.0 or more and 3.0 or less, a favorable crushing form of the shock absorbing member can be stably maintained, and the shock absorbing characteristics can be sufficiently improved. .

  For these reasons, in the present invention, when laser-welding a shock absorbing member having a closed cross-sectional structure, at least one of which is a hat-shaped cross-sectional steel plate, intermittently along the longitudinal direction of the flange portion of the hat-shaped cross-sectional steel plate. The ratio (L / λ) of the formed weld length L to the weld pitch λ (L / λ) is 0.2 or more and 0.95 or less, and the melt width W at the overlapping surface of the flange portion of the weld bead And the plate thickness t (W / t) is 1.0 or more and 3.0 or less.

  In the present invention, as described above, in the weld bead of the shock absorbing member, the ratio of the weld length L to the weld pitch λ (L / λ) and the ratio of the melt width W to the plate thickness t (W / t) are set. By controlling and welding within the appropriate range, it is possible to stably maintain a good crushing shape and to manufacture an impact absorbing member having sufficiently high impact absorbing characteristics.

  Furthermore, in the present invention, in order to maintain a good crushing shape of the shock absorbing member more stably and to further improve the shock absorbing characteristics, in addition to the above definition, the weld bead position, the hat type for the following reasons. It is preferable to appropriately control the cross-sectional shape as follows.

(Welding bead position: flange width direction distance d from the vertical wall)
From the analysis result of the crush test, the present inventors have contributed greatly to the R portion (corner portion) adjacent to the flange portion in the hat-shaped cross-sectional shape of the shock absorbing member, as shown in FIG. As described above, the position of the weld bead formed on the flange portion is within a range away from the vertical wall portion of the hat-shaped cross-sectional steel plate by a distance d = 12t ^{0.5 with} respect to the plate thickness t of the flange portion. Has been confirmed to be preferable in order to stably improve the shock absorbing characteristics of the shock absorbing member.

  If the position of the weld bead formed on the flange portion is larger than the distance d in the flange width direction from the vertical wall portion of the hat-shaped cross-section steel plate, the end of the R portion (corner portion) adjacent to the hat-shaped cross-section flange portion, Since the distance to the position of the weld bead increases and deformation in the vicinity of the R portion of the shock absorbing member cannot be restricted during crushing, the shock absorbing characteristics of the shock absorbing member are deteriorated. In addition, the buckling strength in the vicinity of the R portion increases as the thickness t of the steel plate constituting the shock absorbing member increases, and the range in which the vicinity of the R portion restrains the surrounding deformation during crushing is expanded. The appropriate position of the distance d in the flange width direction to be formed increases as the thickness t of the steel plate increases.

For these reasons, in the present invention, in order to stably improve the shock absorbing characteristics of the shock absorbing member, the ratio (L / λ) of the weld length L to the weld pitch λ, the melt width W, and the plate thickness. In addition to the above definition of the ratio of t (W / t), the position where the weld bead is formed is the distance d in the flange width direction from the vertical wall portion of the hat-shaped cross-sectional steel plate with respect to the plate thickness t of the flange portion. It is preferable to be within a range separated by 12 × t ^0.5 .

(Ratio of plate thickness t and average side length D (= (a + b) / 2) (= t / D))
From the analysis results of the crush test, the present inventors have determined that the crushing mode of the shock absorbing member is not only the shape of the weld bead formed on the flange portion, but also the geometric shape of the shock absorbing member, particularly a hat-shaped cross-section steel plate. It was confirmed that the hat-shaped cross section was affected by the length a in the width direction and the length b in the height direction.

  FIG. 4 shows load-displacement curves in the compact mode (solid line) and the non-compact mode (dotted line) in the crush test of the shock absorbing member. FIG. 8 shows a compact mode and a non-compact mode crush form in the crush test of the shock absorbing member.

  From the analysis result of the crush test, in the hat-shaped cross-section steel plate, the average length D = (a + b) of the thickness t of the flange portion, the length a in the width direction of the hat-shaped cross section, and the length b in the height direction. When the ratio (t / D) to / 2 is 0.020 or more, when the shock absorbing member is crushed, regular bellows deformation as shown by a solid load-displacement curve in FIG. (See (b) of FIG. 8). On the other hand, when the above t / D is 0.020 or less, that is, with respect to the plate thickness t of the flange portion, the average length D of the length a in the hat-shaped cross section and the length b in the height direction. When (a + b) / 2 is excessively large, stress is concentrated locally in the impact absorbing member during crushing, and a non-compact mode in which a linear portion that does not cause plastic deformation remains in the impact absorbing member ((a) of FIG. 8). , See)). When crushing in such a non-compact mode, a load-displacement curve having no periodicity is obtained as shown by a one-dot chain line in FIG.

  In the present invention, by appropriately controlling the shape of the weld bead formed on the flange portion described above, the shock absorbing property is improved regardless of whether the impact absorbing member is in the compact mode or the non-compact mode. An effect is obtained. In particular, according to the above specification of the weld bead shape of the present invention, when crushing in the non-compact mode, the deformation in the parallel direction or the perpendicular direction to the steel plate overlapping surface of the flange portion is restrained to greatly increase the flange buckling load. Therefore, in order to obtain particularly excellent absorbed energy using the present invention, it is preferable to set the t / D to 0.020 or less in addition to the definition of the weld bead shape.

  As described above, the present invention stably maintains a good crushing shape of the shock absorbing member by controlling the weld bead shape at the time of laser welding, and sufficiently improves the shock absorbing characteristics. There is no need to particularly define the strength of the steel plate constituting the absorbing member. In addition, in the crushing test of the impact absorbing member produced by laser welding a steel material having a tensile strength (TS) in the range of 270 to 1470 MPa, the present inventors have obtained the effect of improving the impact absorbing characteristics by applying the present invention. It is confirmed that

  Of course, it goes without saying that the mechanical properties and types of the steel used for the shock absorbing member can be changed as appropriate without departing from the scope and spirit of the present invention.

  In general, the absolute value of the impact absorbing energy of the impact absorbing member increases with an increase in the tensile strength TS of the steel material used. Therefore, in order to obtain high impact absorbing characteristics without increasing the weight of the impact absorbing member, High high strength steel plates can also be used.

  Furthermore, by using TRIP (Transformin Induced Plasticity) steel and DP (Dual Phase) steel among high-tensile steel plates as steel materials used for impact absorbing members, particularly excellent shock absorbing characteristics can be obtained among steel materials of the same strength. Can do. Since these steel materials have high work hardening characteristics at the time of deformation, the stress level of the portion where buckling progresses increases immediately after the start of deformation, and therefore the load level and impact absorption energy of the entire member are improved. In addition, there is also an advantage that the side wall does not easily fall because the deformation easily propagates from the buckled portion where the stress level suddenly increases to the periphery of the buckled portion having low strength.

  In the present invention, the thickness of the steel material is not particularly limited, but the thickness of the steel material used for the shock absorbing member is set to 0. 0 for the purpose of ensuring sufficient strength and rigidity against a static load as an automobile part. It can also be 6 mm or more.

  Hereinafter, the present invention will be described with reference to examples.

  A steel plate having a tensile strength of 280 MPa class and a plate thickness t of 1.2 mm was bent into the cross-sectional shape shown in FIG. 2A to produce a hat-shaped cross-sectional steel plate. After the flat steel plate having the same tensile strength and thickness as this hat-shaped cross-sectional steel plate is superposed, the superposed portion of the flange portion is intermittently laser-welded in the longitudinal direction as shown in FIG. A shock absorbing member as shown in FIG. At this time, as shown in Table 1 or Table 2, the condition of the weld bead formed on the flange portion by laser welding is the ratio (L / λ) of the welding length L to the welding pitch λ per location, and the overlap of the flange portion. Ratio (W / t) of melt width W and sheet thickness t at the mating surface, weld bead position and flange width direction distance d from the vertical wall of the hat-shaped cross-section steel plate, width-direction length a of the hat-shaped cross section The ratio (t / D) of the average length D = (a + b) / 2 between the height b and the length b in the height direction was varied. A YAG laser was used for laser welding, the processing point output was set at 3.0 kW, the beam diameter at the focal position was fixed at 0.6 mmφ, the welding speed was adjusted, and the melt width W of the weld bead was adjusted. In addition, the fusion width W refers to the width of the weld bead on the steel sheet overlapping surface of the flange portion, and was measured from observation of the weld cross-section after welding. The shield at the time of welding was performed using a center shield torch, and nitrogen gas was used as a shield gas. The focal position of the beam during laser welding was the steel plate surface of the flange portion.

  Table 1 shows that the size of the shock absorbing member is a hat-shaped cross-section length in the width direction (horizontal wall length) a: 120 mm, length in the height direction (vertical wall length) b: 80 mm, flange width c: 20 mm, impact The test result in the case of length of the longitudinal direction (axial direction) of an absorption member: 300 mm is shown. In Table 2, the shock absorbing member size is the width in the hat-shaped cross section (horizontal wall length) a: 60 mm, the length in the height direction (vertical wall length) b: 40 mm, the flange width c: 20 mm, The test result when the length in the longitudinal direction (axial direction) of the impact absorbing member is 300 mm is shown.

  In the crushing test of the impact absorbing member, a 110 kg weight was freely dropped and collided with the welding member at a speed of 14 m / sec (50 km / h). The shock absorbing characteristics of the shock absorbing member are obtained by integrating the load (reaction force) of the load-displacement curve as shown in FIG. 4 obtained by the crushing test of the shock absorbing member up to 150 mm displacement to obtain the absorbed energy. No. shown in FIG. 8 or No. 2 shown in Table 2. An absorption energy of 12 is set as a reference (= 1), and an evaluation is made based on an absorption energy ratio with respect to the reference value. When the absorption energy is improved by 5% or more with respect to the reference value, “OK” (good) or less The thing was made into "NG" (defective).

  However, the overall evaluation of this example is that, even if the result of the impact absorption characteristic evaluation (absorption energy ratio) is “OK” (good), the crush test is performed a plurality of times under the same conditions, and the impact absorbing member is Those with a rollover ratio (lateral fall rate) exceeding 30% were evaluated as NG (defective).

Moreover, in Table 1 or Table 2, d shows the distance of the flange width direction from the vertical wall of a hat-shaped cross-section steel plate to a weld bead toe part. Conditional expression of the weld bead position: In the evaluation of d ≦ 12 × t ^0.5 , the case where this conditional expression is satisfied is evaluated as ◯, and the case where it is not satisfied is evaluated as ×.

  Table 1 shows the test results of the impact-absorbing member having a hat-shaped cross-sectional length (horizontal wall length) a: 120 mm and a height direction length (vertical wall length) b: 80 mm.

No. 1-4 are examples of the present invention, the ratio of the welding length L to the welding pitch λ (L / λ) per spot in the laser welding bead, the ratio of the melt width W to the plate thickness t on the overlapping surface of the flange portion. Since (W / t) satisfies the specified range of the present invention, the impact absorption property evaluation result of the impact absorbing member is “OK” (good), and an excellent impact absorbing property can be obtained. .
On the other hand, no. 5-8 is either the ratio of the welding length L to the welding pitch λ per location (L / λ), or the ratio of the melt width W to the plate thickness t (W / t) on the overlapping surface of the flange portion. It is a comparative example outside the specified range of the invention.

  No. No. 5, W / t is within the range of the present invention, but L / λ is out of the range of the present invention, so that the impact absorbing characteristics of the impact absorbing member are excellent. It was determined to be NG because it exceeded.

  No. No. 6 had an L / λ of 0.15, which was out of the scope of the present invention, and the welded part was partially peeled off, and the impact absorbing property of the impact absorbing member was poor.

  No. In No. 7, L / λ was within the range of the present invention, but W / t was out of the range of the present invention, and a weld part was partly peeled during the crushing test, and the impact absorbing characteristics of the impact absorbing member were poor.

  No. In No. 8, L / λ was within the range of the present invention, but W / t was out of the range of the present invention, and the weld was partially peeled during the crush test.

  Table 2 shows the test results of the impact-absorbing member having a hat-shaped cross-sectional length (horizontal wall length) a: 60 mm and a height direction length (vertical wall length) b: 40 mm.

No. 9 and no. 10 is an example of the present invention, where the ratio of the welding length L to the welding pitch λ (L / λ) per spot in the laser weld bead, the ratio of the melt width W to the plate thickness t (W Since / t) is within the specified range of the present invention, the evaluation result of the impact absorbing property of the impact absorbing member is “OK” (good), and an excellent impact absorbing property can be obtained.
But.

  On the other hand, no. 11 and 12 are either the ratio of the welding length L to the welding pitch λ per location (L / λ), or the ratio of the melt width W to the plate thickness t (W / t) on the overlapping surface of the flange portion. It is a comparative example outside the specified range of the invention.

  No. No. 11 has W / t within the scope of the present invention, but L / λ is out of the scope of the present invention, and the impact absorbing characteristics of the impact absorbing member are excellent, but the lateral collapse rate in the crushing test exceeds 40%, which is the standard value. It was determined as NG.

  No. No. 12, W / t was within the range of the present invention, but L / λ was out of the range of the present invention, and peeling of the weld part occurred partially.

It is the perspective view seen from the diagonal front of the welding direction of the impact-absorbing member which shows embodiment of this invention. It is sectional drawing seen from the front of the welding direction of the impact-absorbing member which shows embodiment of this invention. (A) shows the impact-absorbing member which consists of a hat-shaped cross-sectional steel plate and a flat steel plate, (b) shows the impact-absorbing member which consists of a hat-shaped cross-sectional steel plate and a hat-shaped cross-sectional steel plate, respectively. It is the top view seen in the laser irradiation direction of the impact-absorbing member which shows embodiment of this invention. It is a figure which shows the load-displacement curve in the crushing test of an impact-absorbing member. A solid line indicates a case where the crushing mode is the compact mode, and a one-dot chain line indicates a case where the crushing mode is the non-compact mode. The graph which shows the relationship between the ratio (L / λ) of the welding length L and the welding pitch λ, the ratio (W / t) of the melt width W and the plate thickness t on the overlapping surface, and the impact absorption characteristics and the crushing form. It is. It is a graph which shows the relationship between the ratio (W / t) of the fusion | melting width W and plate | board thickness t in the weld bead of an impact-absorbing member, and impact-absorbing energy. It is a graph which shows the relationship between the ratio (L / (lambda)) of the welding length L and the welding pitch (lambda) in the weld bead of an impact-absorbing member, and impact-absorbing energy. It is a figure which shows the crush form in a crush test. (A) shows a case where the crushing mode is a non-compact mode, and (b) shows a case where the crushing mode is a compact mode.

Explanation of symbols

1 Hat-shaped cross-section steel plate 2 Flat steel plate 3 Flange 4 Weld bead 5 R part (corner part)
t: Thickness a: Length of hat-shaped cross section in the width direction (lateral wall length)
b: Length in the height direction of the hat-shaped cross section (vertical wall length)
c: flange width d: distance between the vertical wall portion and the weld bead W: melt width L: weld length λ: weld pitch

Claims (6)

  In an impact absorbing member having a closed cross-sectional structure, at least one of which is made of a hat-shaped cross-sectional steel plate, a weld length L per weld bead formed intermittently along the longitudinal direction of the flange portion of the hat-shaped cross-sectional steel plate. And the welding pitch λ (L / λ) is 0.2 or more and 0.95 or less, and the ratio (W / t) of the melt width W and the plate thickness t on the overlapping surface of the flange portion is 1. An impact-absorbing member excellent in impact-absorbing characteristics, characterized by being 0 or more and 3.0 or less. The weld bead is formed within a range away from the vertical wall portion of the hat-shaped cross-sectional steel plate by a distance d = 12 × t ^{0.5 in the} flange width direction with respect to the plate thickness t of the flange portion. The shock-absorbing member having excellent shock-absorbing characteristics according to claim 1.   In the hat-shaped cross-section steel plate, the ratio of the thickness t of the flange portion to the average length D = (a + b) / 2 of the length a in the width direction and the length b in the height direction of the hat-shaped cross section ( The shock absorbing member having excellent shock absorbing characteristics according to claim 1 or 2, wherein t / D) is 0.020 or less.   In a method of welding a shock absorbing member having a closed cross-sectional structure, at least one of which is made of a hat-shaped cross-sectional steel plate, the ratio (L / λ) of the welding length L to the welding pitch λ per location is 0.2 or more and 0.95 or less. And the hat-shaped cross-sectional shape by laser welding so that the ratio (W / t) of the melt width W to the plate thickness t on the overlapping surface of the flange portion is 1.0 or more and 3.0 or less. A welding method for an impact-absorbing member excellent in impact-absorbing characteristics, wherein a weld bead is intermittently formed along a longitudinal direction of a flange portion of a steel plate. The weld bead is formed within a range of a distance d = 12 × t ^{0.5 in the} flange width direction from the vertical wall portion of the hat-shaped cross-sectional steel plate with respect to the plate thickness t of the flange portion. The welding method of the impact-absorbing member excellent in the impact-absorbing property of Claim 4.   In the hat-shaped cross-section steel plate, the ratio of the thickness t of the flange portion to the average length D = (a + b) / 2 of the length a in the width direction and the length b in the height direction of the hat-shaped cross section ( 6. The method for welding an impact absorbing member having excellent impact absorbing characteristics according to claim 4, wherein t / D) is 0.020 or less.

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