JP5428881B2 - Tailored blank and manufacturing method thereof - Google Patents

Description

  The present invention relates to a tailored blank and a method for manufacturing the tailored blank. Specifically, the present invention relates to a tailored blank made of, for example, a thick plate and a method for manufacturing the same.

FIG. 10 is an explanatory view showing the underfill of the butt welds of the steel plates 1 and 2.
The steel plates 1 and 2 that are the materials for butt laser welding have sharp cut end faces due to changes in the cut end face due to fluctuations in the cut clearance when the end faces are cut, for example, blade wear and mold deflection. There may not be. For this reason, when the steel plates 1 and 2 are joined by butt laser welding, a large gap 3 is formed in the abutted portion, and the weld metal is perforated due to insufficient molten metal volume to fill the gap 3 during welding. Dents (underfill; (T-Tw) / T × 100 ((%)) are likely to occur. The dents reduce the fatigue strength of the pressed product. In this way, two steel plates are joined by butt laser welding. In that case, it was not easy to ensure stable welding quality.

  Conventionally, in order to ensure the quality of the welded portion of the tailored blank, it is known that it is important to accurately cut the end faces of the steel plates to be abutted. For example, it is desirable that the straight line accuracy in the cutting direction is increased as much as possible, the occurrence of burrs and sagging on the end face is small, and the end face of the steel sheet is perpendicular to the surface of the steel sheet.

FIG. 11 is an explanatory view schematically showing a state of cutting the steel plate 4, and FIG. 12 is an explanatory view showing a cut end face of the steel plate 4. The die cutting will be described with reference to FIGS.
As shown in FIGS. 11 and 12, in the shear cutting performed on the steel plate 4 by pressing or shearing, a shear surface S is formed by the descending upper blade 5, and further cracks are generated from the tips of the upper blade 5 and the lower blade 6, respectively. The fracture surface B is formed by the generation and growth, and the association thereof, leading to cutting.

  Usually, the cut end face on the side having the plate restraint 7 shown in FIG. 11 is used as an end face to be welded because an end face having high linearity in the cutting longitudinal direction is obtained. When the clearance Cl {(the distance between the upper blade 5 and the lower blade 6 in the direction perpendicular to the cutting direction / plate thickness) × 100 (%)} between the upper blade 5 and the lower blade 6 becomes wider, the angle θ ( Since the gap 8 (surface sag angle) becomes large and a gap 8 (hereinafter referred to as “end face gap”) that does not come into contact with the mating material is formed at the time of butting, the volume of the weld metal is insufficient at the time of butt welding, A concave underfill occurs.

  Non-Patent Document 1 states that the weld thickness is 0.8 or more (underfill 20% or less as defined in this specification) with respect to the base metal plate thickness from the viewpoint of formability, and welding quality in laser welding. If the plate thickness is 1.2 mm or less, the shear area ratio (shear length / plate thickness) should be greater than 0.8, and if the plate thickness is greater than 1.2 mm It is disclosed that the cross-sectional ratio is larger than 0.2.

  Therefore, in the production of tailored blanks, cutting is performed under the condition that the clearance of the blade at the time of cutting is reduced so that the surface sag angle θ shown in FIG. 12 is reduced. Specifically, cutting is often performed with a clearance of 10% or less. However, with a thick plate, particularly a high-tensile thick steel plate, it is difficult to cut with such a small clearance in terms of management of the cutting die and blade.

  In Patent Document 1, the cut end surface of the plate remaining on the fixed blade side is used, the plate on one side is turned upside down, and the sag surface (shear surface) and the burr surface (fracture surface) are abutted to form a gap between the abutting portions. Is small, and it is disclosed that a good weld can be obtained. Further, in Patent Document 1, by welding the cutting end surface on the side that remains on the fixed blade and the end surface that is cut off by the moving blade, the sag surface and the burr surface are abutted and welded without turning the plate upside down. It is disclosed.

JP 2001-205432 A

Press Technology, Vol. 40, No. 10 (October 2002) 49-53

  According to the examination results of the present inventors, it has been found that even with the invention disclosed in Patent Document 1, good welding quality cannot always be obtained.

The present invention relates to a first steel plate having an end surface constituted by a fracture surface and a shear surface having a surface sag angle of 5 ° or more, and an end surface constituted by a fracture surface and a shear surface having a surface sag angle of 5 ° or more. And a second steel plate having a face to face each other to form a butt face, and irradiating a high energy beam to weld the butt face to produce a tailored blank, wherein the butt face is The shear surface in the first steel plate and the fracture surface in the second steel plate are opposed to each other, and the fracture surface in the first steel plate and the fracture surface in the second steel plate are at least one place in the longitudinal direction of the butt surface. Forming a high energy beam on the shear surface side of the thin steel plate of the first steel plate and the second steel plate with high energy. The tailored blank manufacturing method is characterized in that the irradiation is performed while being arranged on the beam irradiation side and with the surface in the height direction of the irradiation side of two steel plates substantially matched .

In the present invention, it is desirable that the shear plane ratio at the end face of each of the first steel plate and the second steel plate is 35% or less .

In the present invention, the first steel plate and the second steel plate are both sandwiched between the plate supporting means provided facing the moving blade and the plate restraining means provided facing the fixed blade. However, it is desirable that the steel plate is cut with a moving blade and a fixed blade.

  From another viewpoint, the present invention is a tailored blank manufactured by the above-described method for manufacturing a tailored blank according to the present invention, wherein the underfill amount is 25% or less.

  The surface sag angle is also called a fracture surface angle.

  ADVANTAGE OF THE INVENTION According to this invention, production management is easy and it can provide favorable welding quality reliably, for example, can provide the tailored blank of a thick board, and its manufacturing method.

FIG. 1 shows the relationship between the clearance and the quality of the shear end face when a 780 MPa grade hot-rolled steel sheet having a thickness of 2.3 mm is cut using a mold having an upper blade and a lower blade having the structure shown in FIG. It is a graph. FIG. 2 is a graph showing the relationship between the area of the gap (gap area) of the butted portion and the underfill when the shear surfaces of the steel plates are butted and welded. FIG. 3A and FIG. 3B are explanatory views showing a butted state of end faces having a small blade clearance and a small shear plane ratio. FIG. 4A and FIG. 4B are explanatory views showing the difference in the size of the shearing surface and the butt state. FIG. 5 (a) is an explanatory view showing a cutting mechanism of a conventional cutting method in which a support mechanism is not disposed under the upper blade, and FIG. 5 (b) is a diagram illustrating the present invention in which the support mechanism is disposed under the upper blade. It is explanatory drawing which shows the cutting mechanism of this cutting method. FIG. 6A shows a cut end face shape (shear surface ratio, sagging angle) when a 440 MPa class hot-rolled steel sheet (JSH440) having a thickness of 2.6 mm is cut without arranging the support mechanism shown in FIG. 5B. ) And the clearance, and FIG. 6B is a graph showing the relationship between the cut end face shape (shear surface ratio, sagging angle) and the clearance when this support mechanism is disposed and this hot-rolled steel sheet is cut. It is a graph which shows a relationship. FIG. 7A to FIG. 7C are explanatory views showing the form of butting of the first steel plate and the second steel plate, which have different plate thicknesses. FIG. 8 is a graph showing the fatigue test results showing the influence of underfill on the fatigue strength. FIG. 9 is an explanatory view schematically showing the support mechanism as seen from the plate feed direction. FIG. 10 is an explanatory view showing the underfill of the butt weld of the steel plate. FIG. 11 is an explanatory view schematically showing a state of cutting a steel plate. FIG. 12 is an explanatory view showing a cut end face of a steel plate.

A mode for carrying out the present invention will be described with reference to the accompanying drawings. First, the technical idea of the present invention will be described.
In shear cutting performed on a steel sheet by pressing or shearing, a shear surface is formed from a position in contact with the blade, and then cracks are generated and grow to form a fracture surface, leading to cutting.

  FIG. 1 shows a state where a 780 MPa class hot rolled steel sheet 4 having a thickness of 2.3 mm is cut using a mold having an upper blade (moving blade) 5 and a lower blade (fixed blade) 6 having the structure shown in FIG. It is a graph which shows the relationship between clearance and the quality of a shear end face. In FIG. 1, the shear end surface is an end surface on the side sandwiched between the plate presser 7 and the lower blade 6, and the “sag angle” means a surface sag angle θ.

As shown in the graph of FIG. 1, when the distance (clearance) between the upper blade 5 and the lower blade 6 is increased, the surface sag angle is increased and the shear surface ratio is also increased.
FIG. 2 is a graph showing the relationship between the area of the gap (gap area) and the underfill when the shear surfaces of the steel plates 9 and 10 are butted and welded. The amount of the gap is a value measured from a cross-sectional photograph of the cut end face, and the end face state, that is, the gap at the time of matching is changed by changing the clearance of the blade at the time of cutting.

As shown in the graph of FIG. 2, it can be seen that the underfill of the weld metal depends on the gap at the time of butting, and reducing the gap amount is effective for suppressing the underfill.
FIG. 3A and FIG. 3B are explanatory views showing a butted state of end faces having a small blade clearance and a small shear plane ratio.

  As shown to Fig.3 (a), when the end surfaces are faced | matched so that the shearing surfaces and fracture surfaces of the steel plates 9 and 10 may oppose, the big clearance gap 11 will arise in the part of the fracture surface of abutting part. When such a part is laser-welded, molten metal is insufficient and underfill is likely to occur. On the other hand, as shown in FIG. 3 (b), when the fracture surface of the steel plate 9 and the shear surface of the steel plate 10 face each other and the fracture surfaces of the steel plates 9, 10 are in contact with each other, the gap 12 Is small and effective in preventing underfill.

FIG. 4A and FIG. 4B are explanatory views showing the difference in the size of the shearing surface and the butt state.
As shown to Fig.4 (a), when the shear plane ratio of the steel plates 9 and 10 is small, the fracture surface of the steel plate 9 and the shear surface of the steel plate 10 oppose, and the fracture surfaces of the steel plates 9 and 10 are mutually adjacent. The gap 12 is reduced by bringing the steel plates 9 and 10 into contact with each other. However, as shown in FIG. 4B, when the shear plane ratio of the steel plates 9 and 10 is increased, the steel plates 9 and 10 may be abutted so that the fracture surface of the steel plate 9 and the shear plane of the steel plate 10 face each other. Since the shearing surfaces of the steel plates 9 and 10 abut each other and the gap 13 resulting from the surface sag of the fractured surface remains as it is, the molten metal is insufficient and underfill is likely to occur.

  That is, even if a large clearance is set in order to maintain the quality of the cutting blade, the shear surface becomes large in the normal cutting method. Therefore, even if the shear surface of the steel plates 9 and 10 abut against the fracture surface, welding is performed. It does not lead to quality improvement.

  Therefore, by welding the steel plates 9 and 10 so that the fracture surface of the steel plate 9 and the shear surface of the steel plate 10 face each other and the fracture surfaces of the steel plates 9 and 10 are in contact with each other, good welding with small underfill is achieved. In order to obtain quality, it is important to obtain a cut end face with a small shear surface even under conditions where the blade clearance is large. For this purpose, a cutting method in which a shear surface hardly occurs even under a condition with a large clearance is effective.

  FIG. 5 (a) is an explanatory view showing a cutting mechanism of a conventional cutting method in which a support mechanism is not disposed under the upper blade, and FIG. 5 (b) is a diagram illustrating the present invention in which the support mechanism is disposed under the upper blade. It is explanatory drawing which shows the cutting mechanism of this cutting method.

  As shown in FIG. 5A, in the conventional cutting method, the upper blade 17 is not disposed below the upper blade 17 while the steel plate 14 is sandwiched between the plate retainer 15 and the lower blade 16. Is lowered, the steel plate 14 is cut.

  As a result of intensive studies on the cutting method, the present inventors have arranged a support mechanism 18 that supports the steel plate 14 facing the upper blade 17 that is a moving blade, as shown in FIG. While holding the steel plate 14 with the lower blade 16 and holding the steel plate 14 with the upper blade 17 and the support mechanism 18, the upper blade 17 and the support mechanism 18 are lowered to cut the steel plate 14. It has been found that even when the clearance is large, it is possible to obtain a cut surface in which a shear surface is hardly generated.

  That is, as shown in FIG. 5A, when the support mechanism 18 is not disposed facing the upper blade 17, if the blade clearance is large, the steel plate 14 is bent and deformed during cutting, and the steel plate 14. Since the upper blade 17 bites greatly while accompanying shear deformation, the shear surface becomes large. On the other hand, as shown in FIG. 5B, when the support mechanism 18 is disposed facing the upper blade 17, the bending deformation of the steel plate 14 after the upper blade 17 bites into the steel plate 14 is caused by the support mechanism 18. Therefore, the portion of the steel plate 14 in contact with the tip end of the upper blade 17 easily reaches the breaking limit, breaks after a small shear surface occurs, and the fracture surface becomes large.

  FIG. 6A shows a cut end face shape (shear surface ratio, sag) when a 440 MPa class hot rolled steel sheet (JSH440) having a thickness of 2.6 mm is cut without the support mechanism 18 shown in FIG. 5B. FIG. 6B is a graph showing the relationship between the angle) and the clearance, and FIG. 6B shows the cut end face shape (shear surface ratio, sag angle) and clearance when the support mechanism 18 is disposed and the hot-rolled steel sheet is cut. It is a graph which shows the relationship.

  As shown in the graphs of FIGS. 6A and 6B, by arranging the support mechanism 18 shown in FIG. 5B and cutting the steel plate, an end face having a small shearing surface can be obtained even under a large clearance condition. It turns out that it is obtained.

  As described above, according to the present invention, by arranging the support mechanism shown in FIG. 5B and cutting the steel plate, it is possible to obtain an end surface with a small shear surface even under a condition where the clearance is large. Therefore, using the first steel plate and the second steel plate having end faces with a small shear surface obtained in this manner, the fracture surface of the first steel plate and the shear surface of the second steel plate are opposed to each other, and The technical idea is that the gap between the butted portions can be reduced by abutting the first steel plate and the second steel plate so that the fracture surfaces of the first steel plate and the second steel plate contact each other. Is based.

Next, rules relating to the present invention will be described.
<Thickness>
When the thickness of each of the first steel plate and the second steel plate is increased, the load applied to the blade is increased, and when the clearance is decreased, the wear of the blade is increased. For this reason, cutting with a large clearance is directed and large underfill is likely to occur. Therefore, both the first steel plate and the second steel plate in the present invention desirably have a thickness of 2 mm or more. The upper limit of the plate thickness is not particularly limited, but the upper limit is about 6 mm in automobile parts that are assumed to be applied as tailored blanks.

<Tensile strength, material>
The tensile strength and material of the first steel plate and the second steel plate as the base material are not particularly limited. The present invention is applicable to all types of steel plates used as automotive steel plates. Specific examples include cold-rolled steel sheets, hot-rolled steel sheets, alloyed hot-dip galvanized steel sheets plated on these surfaces, hot-dip galvanized steel sheets, electrogalvanized steel sheets, and aluminum-plated steel sheets. Is done.

<Formation of butt surface>
In the present invention, as shown in FIG. 3 (b), the fracture surface at the end surface of the first steel plate 9 and the shear surface at the end surface of the second steel plate 10 face each other, and the end surface of the first steel plate 9 faces the end surface. The first steel plate 9 and the second steel plate 9 and the second steel plate 9 so that the formed fracture surface and the fracture surface formed on the end surface of the second steel plate 10 are in contact with each other in at least one region in the longitudinal direction (welding direction) of the end surface. The steel plates 10 are butted together to form a butted surface.

  The part contacting in the thickness direction does not need to be the entire fractured surface, and at least one fractured surface may be in contact with each other. For example, the state where the boundary between the fracture surface of one steel plate and the shear plane is in contact with the fracture surface of the other steel plate, or the surface side end of the fracture surface of one steel plate may be in contact with the other fracture surface.

  By forming the butt surface in this way, the gap at the time of butting is reduced, and the occurrence of underfill can be suppressed. Preferably, the 1st steel plate 9 and the 2nd steel plate 10 are faced | matched so that the torn surfaces of each of the 1st steel plate 9 and the 2nd steel plate 10 may contact in the area | region of the multiple places of a longitudinal direction.

  As shown in FIG. 3A, when the first steel plate 9 and the second steel plate 10 are abutted so that the shear surfaces of the first steel plate 9 and the second steel plate 10 face each other, a butt surface is formed. Since a large gap is generated on the fracture surface side, the volume of the welded portion is insufficient, and good welding quality cannot be expected.

<Matching form>
FIG. 7A to FIG. 7C are explanatory views showing the form of butting of the first steel plate 19 and the second steel plate 20 with different plate thicknesses.

  As shown to Fig.7 (a), it is a case where the board thickness of the 1st steel plate 19 and the 2nd steel plate 20 to match is different, Comprising: Thickness is thick among the 1st steel plate 19 and the 2nd steel plate 20. As shown in FIG. When the surface 19a on the shear surface side of the first steel plate 19 is disposed on the irradiation side of the high energy beam, the positions in the height direction of the surfaces 19b, 20b on the counter-irradiation side of the first steel plate 19 and the second steel plate 20 It is desirable to irradiate a high-energy beam with substantially the same.

  Moreover, as shown in FIG.7 (c), it is a case where the plate | board thickness of the 1st steel plate 19 and the 2nd steel plate 20 to match is different, Comprising: The surface by the side of the fracture surface of the 1st steel plate 19 with thick plate | board thickness When the 19b is arranged on the irradiation side of the high energy beam, the high energy beam is irradiated with the positions in the height direction of the surfaces 19a, 20a on the opposite side of the first steel plate 19 and the second steel plate 20 substantially coincided with each other. Is desirable.

  By disposing the first steel plate 19 and the second steel plate 20 as shown in FIGS. 7A and 7C, the fracture surfaces of the first steel plate 19 and the second steel plate 20 are in contact with each other. Since the length in the plate thickness direction is increased, the gap at the time of butting can be reduced. It should be noted that if the surface of the second steel plate 20 having a small plate thickness is present outside the surface of the first steel plate 19 having a large plate thickness, a welding failure such as a misunderstanding will occur, so such arrangement is avoided. Should.

  On the other hand, as shown in FIG. 7B, the surface 19b on the fracture surface side of the first steel plate 19 having a large plate thickness is arranged on the irradiation side of the high energy beam, and the first steel plate 19 and the second steel plate 19 are arranged. When the positions in the height direction of the surfaces 19a, 20a on the counter-irradiation side of the steel plate 20 are substantially matched, the length in the plate thickness direction where the shear surface of the first steel plate 19 and the shear surface of the second steel plate 20 are in contact with each other. Shortens and gaps increase.

<Shear plane ratio>
The shear plane ratio (shear plane length / plate thickness × 100) of each of the first steel plate and the second steel plate is preferably 35% or less. Thereby, it becomes possible to contact each fracture surface of a 1st steel plate and a 2nd steel plate reliably, and the clearance gap in the case of abutting can be made small. When the shear surface ratio is excessive, the gap formed is not limited even if the first steel plate and the second steel plate are abutted with each other so that the fracture surface of the first steel plate and the shear surface of the second steel plate face each other. It becomes large and good welding quality cannot be obtained. Usually, in a tailored blank, the plate thickness difference is assumed to be about 1.5 times. In this case, the effect of the present invention can be stably obtained if the shear ratio is 35% or less.

  If the shear plane ratio is greater than 35%, the first steel plate and the second steel plate may not be connected due to unavoidable variations in the set of the first steel plate and the second steel plate in the height direction at the time of matching. The risk that the cross sections will collide with each other increases, leading to variations in weld quality. The shear surface ratio should be small, more preferably 30% or less. The lower limit of the shear plane ratio is not particularly required, but the lower limit of the shear plane ratio is substantially about 10%.

<Fracture surface angle (sag angle)>
As shown in the graph of FIG. 1, the angle of the fracture surface depends on the clearance of the blade, and the larger the clearance, the larger the angle of the fracture surface.

  Conventionally, in order to obtain a good weld with a small underfill, the clearance is reduced and cutting with a small angle of the fracture surface is directed. However, when cutting a thick plate, it is not easy to manage the clearance to be small.

  The method of the present invention is premised on the use of a steel plate having an end face cut with a relatively large clearance, specifically, a clearance of 10% or more, which is industrially easy to manage. However, even if the set clearance is small, the substantial clearance may increase due to the deflection of the mold or the blade, or the substantial clearance may increase due to the consumption of the blade. Therefore, in the present invention, a state in which the clearance is large is indirectly defined using not the clearance but the angle of the fracture surface having a correlation with the clearance.

  As shown in the graph of FIG. 1, when the clearance is 10% or more, the angle of the fracture surface is 5 ° or more. Therefore, in this invention, the angle of a torn surface is prescribed | regulated as 5 degrees or more. The upper limit of the fracture surface angle is not particularly limited. The effect of the present invention can be obtained even when the angle of the fracture surface is large. However, according to experiments, even if the cutting conditions are changed, the fracture surface angle is 40 degrees as the upper limit, and no further fracture surface is produced.

<Underfill>
If the underfill of the weld is excessive, the fatigue strength of the molded product is greatly reduced. This is because the underfill portion becomes a stress concentration portion, and the stress concentration increases as the underfill increases. Therefore, the underfill of the weld metal is desirably 25% or less. Details will be described below.

  FIG. 8 is a graph showing the fatigue test results showing the influence of underfill on the fatigue strength. In the fatigue test, as shown in FIG. 5A, a 780 MPa class hot rolled steel sheet 14 having a thickness of 2.6 mm and 2.3 mm is cut with a clearance of 10%, and 2.6 mm and 2 on the sheet presser 15 side. .3 Fatigue test with different underfill by butt-welding 3mm steel plates 14, 14 and changing the gap amount during butt to 0-0.15mm, butt welding with laser at output 4.5kW, speed 4m / min A piece was manufactured, and a double swing plane bending test with a frequency of about 30 Hz was performed using this fatigue test piece.

  Fatigue tests were performed on test pieces having the same underfill under various stresses, the number of repetitions (breaking life) was determined, and a fatigue strength characteristic diagram (SN diagram) was created from the stress and the breaking life. From the SN diagram, the breaking stress at 1 million times for each underfill was determined.

  As shown in FIG. 8, the fatigue strength decreases as the underfill increases. The fatigue strength is greatly reduced when the underfill is 20% to 30%. For this reason, the underfill is preferably 25% or less. When the underfill is excessive, a hole in the welded portion is likely to occur. More desirably, the underfill is 20% or less.

<Welding method>
As a welding method, it is effective to use a high energy beam welding method having a small melting portion such as laser welding or electron beam welding.

<Support mechanism>
As shown in FIG. 5B, the first steel plate and the second steel plate both use a cutting device including a support mechanism 18 that supports the steel plate 14 so as to face the upper blade 17 that is a moving blade. It is desirable to be cut.

FIG. 9 is an explanatory view schematically showing the support mechanism 18 as viewed from the plate feed direction.
The support mechanism 18 is exemplified by a structure in which a support member 21 made of a block-like or pin-like metal body or hard rubber is pressed against the steel plate 14 by an urging member 22 such as an air spring.

  By disposing the support mechanism 18 so as to face the moving blade 17, the steel plate 14 is always pressed against the lower surface of the moving blade 17, and bending deformation (bending deformation) of the steel plate 14 due to the lowering of the moving blade 17 is suppressed. As shown in FIG. 9, when the cutting blade or the moving blade 17 has a shear angle (an angle formed by the shearing blade and the moving blade), the block-shaped support member 21 cannot be disposed, so that the pin shape Using the support member 21 is exemplified. If the interval between adjacent pins in the pin-shaped support member 21 is too wide, a sufficient effect cannot be obtained.

  The support region of the support member 21 is preferably supported as close to the cutting blade or the moving blade 17 as possible. If it is away from the cutting blade or the moving blade 17, the steel plate 14 is likely to be bent and deformed, and the aiming effect of the support mechanism 18 is hardly achieved. Preferably, the cutting blade or the moving blade 17 is supported to a position within 10 mm, and more preferably within 2 mm.

  The support load that acts on the support mechanism 18 is set according to the strength and thickness of the steel plate 14. If the supporting load is insufficient, bending deformation occurs and a sufficient effect cannot be obtained. For example, the support load is desirably 1 kgf / mm or more per unit width of the steel plate 14.

  In the above description, the case where the movable blade 17 moves from above to below is taken as an example. However, depending on the structure of the cutting device, the movable blade 17 may move from below to above. In this case, needless to say, a support mechanism that presses the steel plate downward from above may be disposed above the movable blade 17.

<Sheet board>
For the plate restraint disposed to face the fixed blade, a plate retainer conventionally disposed to face the fixed blade may be used.

<Applicable parts>
Although the application object of the tailored blank which concerns on this invention is not specifically limited, For example, it is suitable for manufacture of vehicle suspension parts, such as a wheel, a suspension arm, and a suspension member. This is because an automobile undercarriage part has a large plate thickness and it is difficult to cut the end face with high accuracy, and the present invention becomes more effective.

  A 780 MPa class hot rolled steel sheet having a plate thickness of 2.9 mm and a sheet width of 100 mm and a 780 MPa class hot rolled steel sheet having a sheet thickness of 2.3 mm and a sheet width of 100 mm are cut with various clearances to obtain a plate. A welding test was performed by using the steel plate on the restraining side so that the plate end surfaces were in contact with each other in various butt forms (fracture surface arrangement, plate alignment position).

  For cutting the hot-rolled steel sheet, a shear cutting machine having a mechanism shown in FIG. Welding was performed using a YAG laser and focused on the thick plate side surface at an output of 4.5 kW, a welding speed of 4.5 m / min, and a beam focal spot diameter of 0.6 mm.

  The end face shape obtained by cutting was determined by polishing the cut end face and measuring its contour. The underfill amount of the welded portion was measured by measuring the welded portion thickness with a micrometer, and was calculated as the thickness of the thin plate side, that is, the ratio of the welded portion thickness to 2.3 mm as shown in the following equation. A weld with an underfill amount of 25% or less was considered good.

(Underfill (%) = (2.3-Weld thickness) /2.3×100)
Table 1 shows the welding test results together with the end face shape and the butt form.

  The numbers A and B in Table 1 are both reference examples, and since the clearance of the cutting blade is as small as 5% and 10%, a sharp end face with a small angle of the fracture surface is obtained. The fracture surfaces are butted against each other and welded, but the underfill at the weld is small.

  No. 1 is a comparative example, which was cut under the condition of a clearance of 15%, and butt-welded so that the fracture surfaces with a fracture surface angle of 11 degrees were both on the lower side. As a result, a large amount of underfill occurred.

No. 2 is a reference example, and the same end face shape as No. 1 is obtained by cutting under the same conditions as No. 1, with the broken surface on the thick plate side as shown in FIG. Welding was carried out with the fractured surface of the steel plate placed on the top and the bottom surfaces of the two steel plates aligned at the same height. Welding was performed in a state in which the fracture surface on the thick plate side and the fracture surface on the thin plate side were in contact with each other, and good welding quality was obtained with a small underfill comparable to No. B, which could ensure sufficient fatigue strength.

No. 3 is the same as No. 2 except that the broken surface on the thick plate side is placed up, the broken surface on the thin plate side is placed down, and the broken surfaces are brought into contact with each other, as shown in FIG. Although it is a reference example of conditions, a relatively good weld was obtained, but the underfill is slightly larger than number 2.

No. 4, as shown in FIG. 7 (c), except that Aligns the height of the upper surface of the two steel plates are examples of the present invention under the same conditions as the number 3, good welding underfill is small Part was obtained.

  No. 5 is a comparative example, which was cut under the condition of a clearance of 20%, and the fracture surface on the thick plate side was placed on the bottom and the fracture surface on the thin plate side was placed on the top, but a hole was generated in the weld. It is considered that the shear plane ratio on the thin plate side is more than 35%, the fracture surfaces are not in contact with each other, and the volume of the weld metal is remarkably insufficient.

  No. 6 is obtained by cutting the clearance on the thin plate side smaller than that of No. 5, bringing the shear plane ratio on the thin plate side to 35% or less and bringing the fracture surfaces into contact with each other, and a welded portion having an underfill of 25% or less. was gotten.

Reference example 1

  Using a hot-rolled steel plate of 440 MPa class with a plate thickness of 2.6 mm and a plate width of 100 mm, as shown in FIG. 5 (b), a support mechanism 18 is arranged facing the upper blade 17 serving as a movable blade and fixed. The upper blade 17 and the lower blade 16 were cut while the steel plate 14 was held between the plate presser 15 and the support mechanism 18 provided to face the lower blade 16 as the blade.

  Next, the steel plates 14 and 14 on the plate restraining side cut under the same conditions were butted together and welded. The butting was arranged so that the shear plane and the fracture surface face each other, and the clearance was 12% to 19%. For welding, a YAG laser was used and the surface was focused at an output of 4.5 kW, a welding speed of 4 m / min, and a beam focal spot diameter of 0.6 mm. At the time of butting, the plate end faces were brought into contact with each other.

  For cutting, a cutting die provided with a support mechanism 18 having a block-like support tool 21 that supports 20 mm from the shearing blade tip to a position of 2 mm to 22 mm under the upper blade 17 that is a moving blade was used. The support 21 was supported by an air spring 22 and the support load was set to 10 kgf / mm per unit width of the steel plate 14. Further, the shear angle of this test mold was set to zero.

The end face shape was obtained by polishing a cross section of the cut end face of the steel plate 14 and measuring the shape from the contour. The underfill amount was determined by measuring the weld thickness with a sharp micrometer at the tip and calculating the underfill amount using the following equation. A weld with an underfill amount of 25% or less was considered good.
(Underfill (%) = (2.6-welded wall thickness) /2.6×100)
Table 2 shows the welding test results together with the end face shape.

Reference numeral 1 is a reference example, but the support mechanism 18 is not used. Since the clearance was relatively small and the fracture surface angle was small, the underfill was 25% or less.
No. 2 is a comparative example, which is a condition where the clearance is larger than that of No. 1. Like number 1, the support mechanism 18 is not used. The cut end surface has a large shear surface ratio and a large fracture surface angle. As a result of welding, a hole was formed and a continuous weld could not be obtained.

Reference numeral 3 is a reference example, and the support mechanism 18 is used for the reference example of number 1. Compared with No. 1, the underfill is slightly smaller.
Reference numerals 4 and 5 are reference examples, and the support mechanism 18 is used. Although the fracture surface angle was increased, the shearing surface was small, and as a result, no welded holes were generated in the welded portion, and a continuous welded portion was obtained.

1, 2 Steel plate 3 Gap 4 Steel plate 5 Upper blade 6 Lower blade 7 Plate restraint 8 Clearance 9, 10 Steel plate 11-13 Gap 14 Steel plate 15 Plate restraint 16 Lower blade 17 Upper blade 18 Support mechanism 19 First steel plate 20 Second Steel plate 21 Support member 22 Biasing member

Claims (4)

A first steel plate having an end surface constituted by a fracture surface and a shear surface having a surface sag angle of 5 ° or more, and a second steel plate having an end surface constituted by a fracture surface and a shear surface having a surface sag angle of 5 ° or more. A steel sheet, and abutting each of the end faces to form a butt face, and irradiating a high energy beam to manufacture the tailored blank by welding the butt face,
The abutting surface is such that the shear surface in the first steel plate and the fracture surface in the second steel plate are opposed to each other, and the at least one location in the longitudinal direction of the abutting surface is the first steel plate. The fracture surface and the fracture surface of the second steel plate are in contact with each other and formed ; and
The high energy beam is arranged on the irradiation side of the high energy beam while the shear surface side of the thin steel plate of the first steel plate and the second steel plate is disposed on the irradiation side of the two steel plates. A method for producing a tailored blank, characterized by irradiating with the surface in the height direction being substantially matched .   The method for manufacturing a tailored blank according to claim 1, wherein a shear plane ratio at the end face of each of the first steel plate and the second steel plate is 35% or less.   Both the first steel plate and the second steel plate are sandwiched between the plate support means provided facing the moving blade and the plate restraining means provided facing the fixed blade. The method for manufacturing a tailored blank according to claim 1, wherein the steel plate is cut by the fixed blade. A tailored blank manufactured by the method for manufacturing a tailored blank according to any one of claims 1 to 3 , wherein an underfill amount is 25% or less.

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