JP5902599B2 - Tailored blank manufacturing method and tailored blank - Google Patents

Description

  The present invention relates to a method for manufacturing a tailored blank and a tailored blank. Specifically, the present invention relates to a tailored blank manufacturing method and a tailored blank in which a thick plate and a thin plate are abutted and welded so that one surface is a flat surface.

Conventionally, as a technique related to arc welding, there is a technique disclosed in Patent Document 1 (see Patent Document 1).
In the technique disclosed in Patent Document 1, after arc welding, a laser beam is irradiated around the weld metal to heat it above the martensite transformation point and below the melting point. According to this technique, it is said that high hardness joints can be formed in a wide range around the weld metal, the strain concentrated only on the weld metal can be reduced, and the fatigue strength can be improved.

Moreover, there exists a technique disclosed by patent document 2 as a technique regarding laser welding (refer patent document 2).
In the technique disclosed in Patent Document 2, butt welding is performed with a laser beam, and then a laser beam absorption coating treatment is performed on the joint, and further, the laser beam unfocused on the joint is irradiated and softened by heating. According to this technique, the joint is softened by irradiation with a laser beam to reduce its hardness, and since it has bending ductility, stress concentration can be alleviated.

JP 07-118757 A Japanese Patent Publication No. 60-54837

  However, in the technique disclosed in Patent Document 1, since the hardness of the joint is high, stress concentration still occurs in the joint. For this reason, the joint portion is broken due to the stress concentration, or the elongation concentrates on the thin plate near the joint portion and the thin plate is excessively reduced.

  Further, in the technique disclosed in Patent Document 2, when the joint is irradiated with a non-focused laser beam and softened by heating, the joint is not melted, so that unevenness formed at the time of welding remains on the surface of the joint. However, stress concentration starting from unevenness on the surface of the joint cannot be prevented.

  This invention solves the said subject, The objective is to provide the manufacturing method of a tailored blank and the tailored blank which form the surface of a junction part smoothly while reducing the hardness of a junction part.

A welding process (for example, a welding process S1 to be described later) in which a thick plate (for example, a later-described thick sheet 2) and a thin plate (for example, a later-described thin sheet 3) are welded so that one surface is a flat surface; A remelting step (for example, a remelting step S2 described later) for remelting a welded portion (for example, a welded portion 5 described later) welded in the welding process, and in the remelting step, the welded portion Remelting scanning speed and heat input density for remelting are set to values at which cooling of the remelting part (for example, remelting part 6 described later) proceeds by annealing the welded part, Is welded from a side (for example, a vehicle interior side I to be described later) that generates a step (for example, a step D to be described later) when the thick plate and the thin plate are brought into contact with each other. The side that becomes a flat surface when the plate and the thin plate are abutted (for example, the rear Method for producing tailored blanks from the design surface side O), characterized in that to re-melt the weld (for example, later tailored blanks 1).

According to the present invention, the remelting scanning speed and the heat input density in the remelting step are set to values at which cooling of the remelting portion proceeds by annealing the welded portion. That is, by reducing the remelting scanning speed, the time for heat conduction from the remelting part to the periphery of the remelting part at the time of remelting is increased, and the heating area is widened. Therefore, by maintaining a large heating area around the weld zone at a high temperature, the temperature difference between the remelt zone and the heating zone can be reduced, the cooling rate of the remelt zone can be reduced, and the weld zone is annealed. Cooling proceeds at a speed.
Thus, the hardness of a junction part can be reduced by putting an annealing and cooling a welding part.
Moreover, the surface of a junction part can be smoothly formed by remelting the unevenness | corrugation formed in the surface of the weld part at the time of welding.
As a result, stress concentration at the joint and cracking of the joint can be alleviated.

In addition, according to the present invention, in the welding process, since the thick plate and the thin plate are welded from the side where the step is generated, the thick plate and the thin plate are not affected even if a large thickness difference occurs. It is possible to join the portion where the thick plate and the thin plate are butted together by dissolving the protruding portion.
Also, in the remelting process, the welded portion is remelted from the side that becomes flat when the thick plate and the thin plate are abutted, so the surface on the side that becomes flat when the thick plate and the thin plate are abutted Can be formed smoothly.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a tailored blank and the tailored blank which form the surface of a junction part smoothly while reducing the hardness of a junction part can be provided.

It is a top view which shows the tailored blank which concerns on embodiment of this invention. It is process drawing which shows the manufacturing method of the tailored blank which concerns on the said embodiment. It is a figure which shows the state at the time of welding of the tailored blank which concerns on the said embodiment, (a) shows the junction part at the time of welding, (b) shows the junction part and hardness distribution after welding. It is a figure which shows the state at the time of remelting of the tailored blank which concerns on the said embodiment, (a) shows the junction part at the time of remelting, (b) shows the junction part and hardness distribution after remelting. The state of the welding point and remelting point at the time of manufacture of the tailored blank which concerns on the said embodiment is shown, (a) shows the welding point and heating area | region in a welding process, (b) is the remelting point in a remelting process. And the heating zone.

  Embodiments of the present invention will be described below with reference to the drawings.

First, the tailored blank 1 according to the present embodiment will be described.
The tailored blank (“TWB”) method is a method of placing a blank material (semi-processed product) having a required strength at a required site. The tailored blank method has been adopted in various fields with the progress of analysis technology. Especially in the automobile industry, the weight reduction is achieved by the tailored blank method, and the yield of blank materials is improved to greatly contribute to the reduction of production cost. Therefore, the automobile industry is often applied to vehicle structures that require mass production.

FIG. 1 is a plan view showing a tailored blank 1 according to this embodiment.
A tailored blank 1 shown in FIG. 1 is used for an outer side panel of a vehicle, and is formed by joining two steel plates having different thicknesses and materials before press molding to form one blank material.

The tailored blank 1 is composed of a thick plate 2 and a thin plate 3.
The thick plate 2 is made of a high-strength material for safety in the event of a vehicle collision and constitutes the lower part of the outer side panel of the vehicle.
The thin plate 3 is made of a lightweight material for reducing the weight of the vehicle, and constitutes an upper portion of the outer side panel of the vehicle. The hardness h2 of the thin plate 3 is lower than the hardness h1 of the thick plate 2 (see FIG. 3B).

As shown in FIG. 1, the tailored blank 1 has a joint portion 4 to which a thick plate 2 and a thin plate 3 are joined.
The joining portion 4 welds the thick plate 2 and the thin plate 3 so that the surface on the design surface side O, which is the outside of the vehicle assembled using the tailored blank 1, is a flat surface (the same surface). The welded welded portion 5 is remelted and finally joined (see FIGS. 3 and 4).

Next, the manufacturing method of the tailored blank 1 is demonstrated.
FIG. 2 is a process diagram showing a method for manufacturing the tailored blank 1 according to this embodiment.
The manufacturing method of the tailored blank 1 includes a welding step S1 and a remelting step S2.

  In the welding step S1, the thick plate 2 and the thin plate 3 are brought into contact with each other so that the surfaces 2f and 3f on the design surface side O become a single plane, and the portion to be the joint portion 4 is welded (FIG. 3A). reference).

FIG. 3 is a diagram showing a state of the tailored blank 1 according to the present embodiment during welding, where (a) shows the joint 4 during welding, and (b) shows the joint 4 and hardness distribution after welding. Show.
In the welding step S1, as shown in FIG. 3 (a), when the thick plate 2 and the thin plate 3 are brought into contact with each other, the respective surfaces 2b and 3b are on the side where the step D is generated, and the tailored blank 1 is used. The surfaces 2b and 3b are welded to the surfaces 2b and 3b from the vehicle interior side I of the vehicle assembled in this manner.
Welding is performed continuously by emitting a laser beam L from the laser beam device 10 and moving the welding point Pw in the direction in which the portion to be the joint 4 extends.

  On the vehicle interior side I, the welded portion 5 (welded portion 4) that has been welded is in a weld bead state in which the step D between the surfaces 2b and 3b of the thick plate 2 and the thin plate 3 is dissolved in the inclined surface 5b. . Further, the surface 5f on the design surface side O of the welded portion 5 (joint portion 4) is in a state in which minute irregularities are formed as shown in FIG.

  Further, when the hardness h3 of the welded part 5 (joint part 4) is measured from the surface 5f, it becomes higher than the hardnesses h1 and h2 of the thick plate 2 and the thin plate 3 as shown in the hardness distribution of FIG.

  In the remelting step S2, the welded portion 5 (joint portion 4) welded in the welding step S1 is remelted.

FIG. 4 is a diagram showing a state at the time of remelting of the tailored blank 1 according to the present embodiment, where (a) shows the joint 4 during remelting, and (b) shows the joint 4 after remelting and The hardness distribution is shown.
In the remelting step S2, as shown in FIG. 4A, when the thick plate 2 and the thin plate 3 are brought into contact with each other, the respective surfaces 2f and 3f become one plane from the design surface side O to the surface 5f. On the other hand, the welded part 5 (joint part 4) is remelted by the laser beam L.
The remelting is continuously performed by emitting the laser beam L from the laser beam device 20 and moving the remelting point Pr in the extending direction of the welded portion 5 (joint portion 4).

  FIG. 5 shows the state of the welding point Pw and the remelting point Pr during manufacture of the tailored blank 1 according to the present embodiment, (a) shows the welding point Pw and the heating region Rw in the welding step S1, ) Shows the remelting point Pr and the heating region Rr in the remelting step S2.

  In welding process S1, as shown to Fig.5 (a), the welding speed (movement speed of the welding point Pw) is Va, and the heating area | region from the welding point Pw to the thick plate 2 and the thin plate 3 is Rw. is there.

In the remelting step S2, the remelting scanning speed and the heat input density for remelting the welded portion 5 (joint portion 4) are annealed in the welded portion 5 (joint portion 4), and the remelted portion 6 (joint portion 4). Set to a value at which cooling of the battery proceeds.
Here, the remelting scanning speed is a speed at which the remelting point Pr irradiated with the laser beam L is advanced in the extending direction of the welded portion 5 (joint portion 4).

Specifically, in the remelting step S2, as shown in FIG. 5B, the remelting scanning speed (moving speed of the remelting point Pr) is Vb (<Va) lower than the welding speed Va. The heating region from the remelting point Pr to the thick plate 2 and the thin plate 3 is Rr (> Rw) wider than the heating region Rw during welding.
Further, the heat input density for remelting the welded portion 5 is also set to a value lower than the heat input density at the time of welding so that it can be slowly heated at a relatively low temperature at the remelting scanning speed Vb that is lower than the welding step S1. .

  By setting the remelting scanning speed and the heat input density, the remelting part 6 (joint part 4) to the remelting part 6 (joint part 4) with respect to the thick plate 2 and the thin plate 3 at the time of remelting in the remelting step S2. The heating region Rr that conducts heat to the periphery becomes wider. Thereby, the cooling rate of the remelting part 6 (joining part 4) is slowed by heating the wide heating area | region Rr around the welding part 5 (joining part 4). As a result, since the remelting part 6 (joint part 4) after the remelting point Pr is moved is cooled slowly, the welded part 5 (joint part 4) is annealed to remelt the remelting part 6 (joint part 4). Cooling (curing) proceeds.

  Here, annealing means removing internal strain when the welded part 5 (joined part 4) is hardened by welding, softening the structure to lower the hardness of the joined part 4, and improving the ductility. .

Further, since the remelting scanning speed is Vb and the surface 6f of the remelting part 6 (joint part 4) is not vibrated when the remelting point Pr is moved, minute irregularities are formed on the surface 6f. It is hard to be done. Moreover, even if the remelting part 6 (joint part 4) after the movement of the remelting point Pr is slowly cooled and minute irregularities are formed on the surface 6f, before the remelting part 6 (joint part 4) is cured. The convex portion sinks due to its own weight, and the surface 6f is leveled.
As a result, the minute unevenness formed on the surface 5f on the design surface side O of the welded portion 5 (joined portion 4) is remelted and leveled.

  In addition, although it is preferable to remelt the whole welded part 5 (joint part 4), the remelt process S2 was formed in the surface 5f of the design surface side O of the weld part 5 (joint part 4) at the time of welding. What is necessary is that the minute irregularities are remelted and the main portion of the welded portion 5 (joint portion 4) can be annealed during cooling after remelting.

  The surface 7f of the final joint portion 7 (joint portion 4) subjected to remelting was formed on the surface 5f on the design surface side O of the weld portion 5 (joint portion 4) as shown in FIG. 4B. The minute irregularities are remelted and cooled in a uniform state to form a flat surface.

  Further, the hardness h4 of the final joint portion 7 (joint portion 4) that has been remelted is measured from the surface 7f, as shown in FIG. 4B, the hardness of the welded portion 5 (joint portion 4) indicated by a broken line. Decreases from h3.

  And the tailored blank 1 provided with the last joint part 7 (joint part 4) which put the annealing in the weld part 5 (joint part 4) and cooled through the welding process S1 and the remelt process S2 is manufactured.

  According to the manufacturing method of the tailored blank 1 which concerns on the above this embodiment, there exist the following effects.

(1) Remelting scanning speed Vb and heat input density in remelting step S2 are set to values at which cooling of remelting portion 6 (joint portion 4) proceeds by annealing welded portion 5 (joint portion 4). To do. That is, by setting the remelting scanning speed to a low Vb, the time for heat conduction from the remelting part 6 (joint part 4) to the periphery of the remelting part 6 (joint part 4) at the time of remelting increases. The region Rr is expanded. Therefore, by heating the wide heating region Rr around the welded portion 5 (joined portion 4), the temperature difference between the remelted portion 6 (joined portion 4) and the heated region Rr can be reduced. The cooling rate can be slowed, and the cooling proceeds at a rate at which the weld 5 is annealed.
Thus, the hardness of the final joint part 7 (joint part 4) can be reduced by annealing the weld part 5 and cooling it. In particular, since the cooling rate after remelting is lowered and the final joint portion 7 (joint portion 4) is annealed, the hardness of the final joint portion 7 (joint portion 4) can be further reduced.
Moreover, the surface 7f on the design surface side O of the final joint portion 7 (joint portion 4) is formed smoothly by remelting the irregularities formed on the surface 5f on the design surface side O of the weld portion 5 during welding. Can do.
As a result, stress concentration on the joint 4 and cracking of the joint 4 can be alleviated.

That is, since the surface 7f on the design surface side O of the final joint portion 7 (joint portion 4) is formed smoothly, and unevenness at the time of welding does not remain on the surface 7f, stress concentration starting from the unevenness can be prevented. .
Further, since the hardness of the final joint portion 7 (joint portion 4) is low, stress concentration hardly occurs in the final joint portion 7 (joint portion 4).
As a result, cracks are unlikely to occur in the final joint portion 7 (joint portion 4), elongation does not concentrate on the thin plate 3 in the vicinity of the final joint portion 7 (joint portion 4), and the thin plate 3 is not excessively reduced.

(2) In the welding step S1, since the welding is performed from the vehicle interior side I that generates a step D when the thick plate 2 and the thin plate 3 are abutted, there is a large difference in thickness between the thick plate 2 and the thin plate 3. Even if the thick plate 2 and the thin plate 3 are abutted with each other, the protruding portion of the thick plate 2 can be dissolved.
Moreover, in remelting process S2, in order to remelt the welding part 5 (joining part 4) from the design surface side O used as one plane when the thick plate 2 and the thin plate 3 are faced | matched, the surface of the design surface side O 7f can be formed smoothly.

  Note that the present invention is not limited to the above-described embodiment, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the scope of the present invention.

  In the present embodiment, a laser beam is used as a heat source for welding in the welding step S1 and remelting in the remelting step S2. However, it is not limited to this. For example, other heat sources such as an arc, an electron beam, and a high frequency may be used for welding in the welding step S1 and remelting in the remelting step S2.

DESCRIPTION OF SYMBOLS 1 ... Tailored blank 2 ... Thick plate 3 ... Thin plate 4 ... Joining part 5 ... Welding part 6 ... Remelting part 7 ... Final joining part D ... Step S1 ... Welding process S2 ... Remelting process Vb ... Remelting scanning speed I ... Car Indoor side O ... Design side

Claims (1)

A welding process in which a thick plate and a thin plate are welded so that one surface is a flat surface;
A remelting step of remelting the welded portion welded in the welding step,
In the remelting step, the remelting scanning speed and heat input density for remelting the welded part are set to values at which cooling of the remelted part proceeds by annealing the welded part ,
In the welding process, welding is performed from the side where a step is generated when the thick plate and the thin plate are abutted,
The said remelting process remelts the said welding part from the side used as one plane, when the said thick plate and the said thin plate are faced | matched , The manufacturing method of the tailored blank characterized by the above-mentioned .

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