JP2020179401A - Method for manufacturing hot press molding - Google Patents

Abstract

To provide a method for manufacturing a hot press molding which can suppress occurrence of cracking and wrinkles of a molding.SOLUTION: In a method for manufacturing a hot press molding, a hot press molding includes a top plate surface, the hot press molding has a recess retreated in an in-plane direction on the top plate surface, the hot press molding includes a continuous vertical wall on the edge of the top late surface, a blank is heated to a temperature equal to or higher than Ac3 transformation point of the blank, bending molding of the blank at the temperature equal to or higher than Ac3 transformation point is started, and the bending molding is switched to drawing molding.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for producing a hot press molded product.

Conventionally, when hot press forming an automobile pillar, a composite forming is performed by combining bending forming and drawing forming (see, for example, Patent Document 1).

In this composite molding, the shrinking flange portion where wrinkles may occur is formed by drawing molding using a blank holder. Further, the portion other than the shrinking flange portion is formed by bending molding.

JP-A-2017-159359

However, in draw forming using a blank holder, the temperature of the blank portion sandwiched between the blank holder and the die drops sharply, and the ductility decreases. Then, the inflow of the material is hindered during drawing molding, and cracks may occur. This phenomenon is remarkable when the molded product has a recess that retracts inward.

In particular, when a thin steel plate is used to reduce the weight of the vehicle body, this phenomenon becomes remarkable, and it takes a lot of trouble to take measures to suppress cracking of the molded product.

An object of the present disclosure is to provide a method for producing a hot press molded product capable of suppressing the occurrence of cracks and wrinkles in the molded product.

Aspect 1 is a method of manufacturing a hot press-molded product, wherein the hot press-molded product has a top plate surface, and the hot press-molded product retracts inward in the in-plane direction to the top plate surface. The hot press molded product is provided with a recess, and the hot press molded product is provided with a continuous vertical wall at the edge of the top plate surface, the blank is heated to a temperature equal to or higher than the Ac3 transformation point of the blank, and the blank has a temperature equal to or higher than the Ac3 transformation point. This is a method for manufacturing a hot press-molded product, in which bending molding is started and the bending molding is switched to drawing molding.

In the second aspect, the radius of curvature of the edge of the recess is 100 mm or more and less than 300 mm, and the vertical wall formed by the bending molding is 30% to 80% of the molding height of the vertical wall of the hot press molded product. The method for producing a hot press-molded product according to the first aspect, wherein the bending molding is switched to the drawing molding in the meantime.

In the third aspect, the radius of curvature of the edge of the recess is 50 mm or more and less than 100 mm, and the vertical wall formed by the bending molding is 40% to 70% of the molding height of the vertical wall of the hot press molded product. The method for producing a hot press-molded product according to the first aspect, wherein the bending molding is switched to the drawing molding in the meantime.

In the fourth aspect, the radius of curvature of the edge of the recess is 25 mm or more and less than 50 mm, and the vertical wall formed by the bending molding is 50% to 60% of the molding height of the vertical wall of the hot press molded product. The method for producing a hot press-molded product according to the first aspect, wherein the bending molding is switched to the drawing molding in the meantime.

According to this aspect, the occurrence of cracks and wrinkles in the molded product can be suppressed.

It is a perspective view which shows the hot press molded article which concerns on this embodiment. It is a schematic diagram which shows the main part of the die of the press machine in the hot press apparatus used in this embodiment. It is sectional drawing of the main part which shows the state which the blank is set in the mold of this embodiment. It is sectional drawing of the main part which shows the state of bending and molding a blank with the mold of this embodiment. It is sectional drawing of the main part which shows the state which draw-molds a blank with the mold of this embodiment. FIG. 5 is a cross-sectional view of a main part showing a state in which a blank is further drawn and molded following FIG. It is a figure which shows the state which operated the mold of this embodiment to the bottom dead center. It is a perspective view which shows the main part of the hot press molded article molded by this embodiment. It is a figure which shows the test result.

In general hot press molding, when drawing and molding cross-section hat-shaped parts such as side sills and pillars, which are automobile parts, the temperature of the blank part sandwiched between the blank holder and the die drops sharply and ductility occurs. Can be reduced. Then, when the draw forming is started by the punch, the inflow of the material is hindered, and there is a possibility that cracks occur in the vertical wall or the like.

This phenomenon becomes remarkable when a thin steel plate is used. For this reason, in hot press forming using a thin steel plate, bending forming is often performed without using a blank holder.

Further, when a suddenly changing shape portion such as a shrinking flange is formed by bending molding, wrinkles are likely to occur, and the wrinkles are remarkable when a thin steel plate is used.

On the other hand, in automobile parts, thinning is required in order to reduce the weight of the vehicle, and hot press forming using a thin steel plate is required.

However, it has been difficult to suppress the occurrence of wrinkles and the occurrence of cracks at the same time while reducing the weight of the hot press molded product.

Therefore, the present inventor repeated research and found the following.

That is, in hot press forming, when the forming depth of bending forming increases, the amount of strain due to forming increases and wrinkles occur.

Further, when the molding depth is increased by drawing molding, cracks occur. This phenomenon can be explained as follows. If a blank is sandwiched between a blank holder of a mold and a die during drawing molding, the temperature of that portion drops sharply and ductility decreases. If drawing molding by punching is started in this state, the inflow of the material in the portion where the ductility is lowered is hindered, and cracks occur in the vertical wall of the hot press molded product or the like.

As described above, both bending molding and draw molding have problems when the molding depth is increased. However, the inventor of the present application paid attention to the fact that the causes of both problems are different.

It seems possible to increase the molding depth without causing problems by switching to the other molding after performing one of the bending molding or the drawing molding.

However, if draw forming is performed first, the blank that has been cooled and has reduced ductility is bent and formed. Then, there is a possibility that cracks occur during bending molding. To avoid this, bending molding is performed first, and then drawing molding is performed.

In this way, in the molding of a hot press molded product using a thin steel plate, bending molding is performed at the initial stage of molding. Then, in the shape suddenly changing portion where wrinkles may occur, drawing molding (partial drawing molding) is partially performed using a blank holder from the middle of molding.

As a result, hot press molding capable of suppressing the occurrence of cracks and wrinkles can be realized.

Further, in this manufacturing method, since the temperature of the entire blank is not lowered, the hardness after quenching can be ensured, and a lightweight and high-strength hot press molded product can be obtained.

<Embodiment>
Hereinafter, this embodiment will be described with reference to the drawings.

FIG. 1 is a diagram showing a hot press molded product 10 formed by the method for manufacturing a hot press molded product according to the present embodiment, and as an example of the hot press molded product 10, a pillar which is an automobile part is shown. Has been done.

(Hot press molded product)
The hot press molded product 10 has a long shape and includes a flat top plate surface 12 extending in the length direction.

[Top plate surface]
The width dimension of the base end portion of the top plate surface 12 expands toward one side IH of the width direction HH toward the base end side.

As a result, on the top plate surface 12, a wide portion 12A having a wide width dimension is formed at the base end portion, and a general portion 12B having a narrow width dimension is formed on the tip end side of the wide portion 12A. Further, the top plate surface 12 is formed with a recess 14 that recedes inward in the in-plane direction of the top plate surface 12 between the wide portion 12A and the general portion 12B.

[Vertical wall]
From one side edge of one side IH of the top plate surface 12, a continuous first vertical wall 20 extends toward the back side of the top plate surface 12 via the first bent portion 18. Further, from the other side edge of the other side TH of the top plate surface 12, a continuous second vertical wall 24 extends toward the back side of the top plate surface 12 via the second bent portion 22.

The first vertical wall 20 includes a vertical wall general portion 20B continuous with the general portion 12B of the top plate surface 12, and a vertical wall wide portion 20A continuous with the wide portion 12A. An arcuate vertical wall curved portion 20D is formed in a portion where the vertical wall general portion 20B and the vertical wall wide portion 20A are continuous, and the vertical wall curved portion 20D recedes inward in the width direction HH.

[Flange]
From the edge of the first vertical wall 20, the first flange 28 extends outward in the width direction HH via the third bent portion 26. Further, from the edge of the second vertical wall 24, the second flange 32 extends outward in the width direction HH via the fourth bent portion 30.

The first flange 28 includes a flange general portion 28B continuous with the vertical wall general portion 20B of the first vertical wall 20, and a flange wide portion 28A continuous with the vertical wall wide portion 20A.

A flange curved portion 28D forming a shape sudden change portion curved in an arc shape is formed in a portion where the wide flange portion 28A and the general flange portion 28B are continuous. The flange curved portion 28D is retracted inward in the width direction HH, and the flange curved portion 28D is elongated in the first vertical wall 20 direction and contracted in the length direction of the flange curved portion 28D during molding. It constitutes the shrinking flange that occurs.

(Mold)
FIG. 2 is a schematic view showing a mold of a press machine 36 in a hot press apparatus used in the method for manufacturing a hot press molded product according to the present embodiment. FIG. 2 shows how the blank 42 is arranged between the upper die 38 and the lower die 40 of the press machine 36.

[Upper mold]
As shown in FIGS. 3 to 7, the upper mold 38 is composed of a die mold provided with a refrigerant flow path. The upper die 38 is formed in a long shape according to the length of the hot press molded product 10.

The upper die end surface 46 of the upper die 38 is provided with a die hole 48 for forming the hot press molded product 10 at the center of the width direction HH.

As shown in FIG. 2, the die hole portion 48 has a wide portion 48A having a wide width dimension formed at the base end portion and a general portion 48B having a narrow width dimension on the tip side of the wide portion 48A. .. Further, in the die hole portion 48, a recess 48C that retracts inward in the in-plane direction of the die hole portion 48 is formed on a side portion between the wide portion 48A and the general portion 48B.

As shown in FIGS. 3 to 7, the inner surface of the die hole portion 48 has a first concave wall surface 52 continuous with the upper die end surface 46 via the first corner portion 50, and a first corner on the first concave wall surface 52. It is provided with a recessed bottom surface 56 that is continuous via a portion 54. Further, the inner surface of the die hole portion 48 is provided with a second recessed wall surface 60 that is continuous with the upper die end surface 46 via the second corner portion 58, and the second recessed wall surface 60 is provided via the second corner portion 62. It is continuous with the bottom surface 56 of the recess.

[Lower mold]
The lower die 40 is composed of a long punch die provided with a refrigerant flow path. The lower die 40 is formed in a long shape according to the length of the hot press molded product 10.

The lower die upper surface 72 of the lower die 40 is provided with a punch convex portion 74 for forming the hot press molded product 10 at the center of the width direction HH.

As shown in FIG. 2, the punch convex portion 74 has a wide portion 74A having a wide width dimension formed at the base end portion, and a general portion 74B having a narrow width dimension on the tip end side of the wide portion 74A. .. Further, in the punch convex portion 74, a concave portion 74C that retracts inward in the in-plane direction of the punch convex portion 74 is formed on a side portion between the wide portion 74A and the general portion 74B.

As shown in FIGS. 3 to 7, the punch convex portion 74 has a first convex portion wall surface 78 continuous from the lower mold upper surface 72 via the first folding portion 76, and a first shoulder on the first convex portion wall surface 78. It is provided with a convex top surface 82 that is continuous via the portion 80. Further, the punch convex portion 74 is provided with a second convex portion wall surface 86 that is continuous with the lower mold upper surface 72 via the second folding portion 84, and the second convex portion wall surface 86 is provided via the second shoulder portion 88. It is continuous with the convex top surface 82.

On the base end side of the lower mold upper surface 72 in the length direction, a holder accommodating hole 92 is formed on one side IH of the width direction HH with the punch convex portion 74 as a boundary. As shown in FIG. 2, the holder accommodating hole 92 is formed in a portion of the punch convex portion 74 adjacent to the concave portion 74C.

As shown in FIG. 3, the block-shaped blank holder 96 is housed in the holder housing hole 92.

The blank holder 96 is supported by a rod 98 of a hydraulic cylinder so as to be vertically movable as an example. At the bottom dead center where the blank holder 96 is most lowered, the holder upper surface 96A of the blank holder 96 is at the same height as the lower mold upper surface 72 of the lower mold 40, as shown in FIG.

The upper die end surface 46 of the upper die 38 and the lower die upper surface 72 of the lower die 40 form the flanges 28 and 32 of the hot press molded product 10. The upper die end surface 46 of the upper die 38 and the holder upper surface 96A of the blank holder 96 of the lower die 40 form a flange curved portion 28D in the first flange 28 of the hot press molded product 10.

Further, the concave wall surfaces 52 and 60 of the upper die 38 and the convex wall surfaces 78 and 86 of the lower die 40 form the vertical walls 20 and 24 of the hot press molded product 10. The concave bottom surface 56 of the upper die 38 and the convex top surface 82 of the lower die 40 form the top plate surface 12 of the hot press molded product 10.

[Hydraulic cylinder]
The hydraulic cylinder is controlled by a control device (not shown). The control device sets the extension amount of the rod 98 of the hydraulic cylinder and the pressure required for retracting the rod 98.

Thereby, as shown in FIG. 3, the control device can set the height of the holder upper surface 96A at the top dead center where the upper mold 38 and the lower mold 40 are farthest from each other. Further, the control unit can set the pressure for pressing the blank 42 with the blank 42 sandwiched between the upper mold 38 and the blank holder 96.

[blank]
The blank 42 is a steel plate having a plate thickness of 0.8 mm or more and 3.0 mm or less. Steel plates with a thickness in this range are often used for automobile parts.

The steel material used as the blank 42 is C: 0.1% or more and 0.8% or less, Si: 0.001% or more and 2.0% or less, Mn: 0.5% or more and 3.0% or less in mass%. , P: 0.05% or less, S: 0.01% or less as a chemical composition.

Further, the steel material is sol. It is preferable that Al: 0.001% or more and 1.0% or less, N: 0.01% or less, B: 0.01% or less are contained as a chemical composition, and the balance is composed of Fe and impurities. Further, the chemical composition may contain one or more selected from the group consisting of Ti, Nb, V, Cr, Mo, Cu and Ni instead of a part of Fe.

If the amount of carbon C is too small, it can result in a low-strength product with little quenching effect. Therefore, in the present embodiment, the amount of carbon contained in the blank 42 is set to 0.1% by mass or more. On the other hand, if the amount of carbon C is too large, the product becomes too hard and has poor toughness. Therefore, in the present embodiment, the amount of carbon contained in the blank 42 is set to 0.8% by mass or less, and the amount of carbon contained in the blank 42 is set to 0.1% by mass or more and 0.8% by mass or less.

Si is preferably controlled in the range of 0.001% by mass or more and 2.0% by mass or less. Si is an element that suppresses the formation of carbides in the cooling process from the austenite phase to the low-temperature transformation phase, so that it does not deteriorate the ductility or improves the ductility to increase the strength after quenching. is there. If the Si content is less than 0.001% by mass, it is difficult to obtain the above effect. Therefore, the Si content is preferably 0.001% by mass or more.

When the Si content is 0.05% by mass or more, the ductility is further improved. Therefore, the Si content is more preferably 0.05% by mass or more. On the other hand, when the Si content exceeds 2.0% by mass, the effect of the above action is saturated and economically disadvantageous, and the surface texture is significantly deteriorated. Therefore, the Si content is preferably 2.0% by mass or less. More preferably, it is 1.5% by mass or less.

Mn is preferably controlled in the range of 0.5% by mass or more and 3.0% by mass or less. Mn is a very effective element for enhancing the hardenability of steel and stably securing the strength after quenching. However, if the Mn content is less than 0.5% by mass, the effect cannot be sufficiently obtained even under rapid cooling conditions, and it becomes very difficult to secure a tensile strength of 1200 MPa or more in terms of strength after quenching. Therefore, the Mn content is preferably 0.5% by mass or more.

P is preferably controlled to 0.05% by mass or less. P is an impurity that is inevitably contained in steel in general, but it may be positively contained because it has an effect of increasing strength by solid solution strengthening. However, when the P content exceeds 0.05% by mass, the resistance weldability between the member of the present embodiment and the other member is significantly deteriorated. Therefore, the P content is preferably 0.05% by mass or less. The P content is more preferably 0.02% by mass or less. In order to obtain the above action more reliably, the P content is preferably 0.003% by mass or more.

S is preferably controlled to 0.01% by mass or less. S is an impurity inevitably contained in steel, and combines with Mn and Ti to form sulfide and precipitate. If the amount of the precipitate is excessively increased, the interface between the precipitate and the main phase may become the starting point of fracture, so the lower the amount, the more preferable. If the S content exceeds 0.01% by mass, the adverse effect becomes remarkable. Therefore, the S content is preferably 0.01% by mass or less. It is more preferably 0.003% by mass or less, still more preferably 0.0015% by mass or less.

sol. Al is preferably controlled in the range of 0.001% by mass or more and 1.0% by mass or less. Al is an element having an action of deoxidizing steel to make the steel material sound, and also an element having an action of improving the yield of a carbonitride forming element such as Ti. sol. If the Al content is less than 0.001% by mass, it becomes difficult to obtain the above effect. Therefore, sol. The Al content is preferably 0.001% by mass or more. More preferably, it is 0.015% by mass or more. On the other hand, sol. When the Al content exceeds 1.0% by mass, the weldability is remarkably lowered, oxide-based inclusions are increased, and the surface texture is remarkably deteriorated. Therefore, sol. The Al content is preferably 1.0% by mass or less. More preferably, it is 0.080% by mass or less.

N is preferably controlled to 0.01% by mass or less. N is an impurity inevitably contained in steel, and the lower it is, the more preferable it is from the viewpoint of weldability. If the N content exceeds 0.01% by mass, the weldability is significantly reduced. Therefore, the N content is preferably 0.01% by mass or less. More preferably, it is 0.006% by mass or less.

B is preferably controlled to 0.01% by mass or less. B is an element having an action of enhancing low temperature toughness. Therefore, B may be contained. However, if it is contained in an amount exceeding 0.01% by mass, the hot workability deteriorates and hot rolling becomes difficult. Therefore, the B content is preferably 0.01% by mass or less. In order to obtain the effect of the above action more reliably, it is more preferable that the B content is 0.0003% by mass or more.

As other additive elements, Ti, Nb, V, Cr, Mo, Cu, and Ni may be added as necessary in order to improve the hardenability of steel and to stably secure the strength after quenching.

(Manufacturing method of hot press molded products)
A method for manufacturing a hot press molded product will be described.

"Heating process"
In the method for producing a hot press-formed product according to the present embodiment, the blank 42 is heated to a temperature equal to or higher than the Ac3 transformation point of the blank 42 to be austenitic in the heating step.

The Ac3 transformation point, which indicates the austenitic transformation point temperature, is the temperature at which the above-mentioned blank 42 made of steel is completely austenitized, and is represented by the following equation as an example.

Ac3 (° C.) = 910-203 x √C (mass%) +44.7 x Si (mass%) -30 x Mn (mass%) -11 x Cr (mass%) + 700 x S (mass%) + 400 x Al (Mass%) + 50 x Ti (Mass%)

Here, C is carbon, Si is silicon, Mn is manganese, Cr is chromium, S is sulfur, Al is aluminum, and Ti is titanium.

"Quenching process"
As shown in FIGS. 3 to 7, the blank 42 heated above the Ac3 transformation point in the heating step is hot-pressed by the press machine 36 of the hot-pressing apparatus. After hot pressing, the hot press molded product 10 is transformed into martensite by rapidly removing heat from the press molded product with the upper die 38 and the lower die 40 while the mold is being fastened and cooling.

The quenching process will be specifically described below.

[set]
That is, the blank 42 heated above the Ac3 transformation point in the heating step is set between the lower mold 40 and the upper mold 38 as shown in FIG.

At this time, the hydraulic cylinder is controlled in advance by the control device, and the height BH from the lower mold upper surface 72 to the holder upper surface 96A of the lower mold 40 is the height from the lower mold upper surface 72 to the convex top surface 82 on the blank holder 96 side. The height should be within the range of 30% to 80% of the h.

The pressure for pressing the blank 42 is appropriately determined while the blank 42 is sandwiched between the upper mold 38 and the blank holder 96.

[Bending molding]
In this set state, as shown in FIG. 4, the upper mold 38 is lowered toward the lower mold 40 as an example.

Then, while both side portions of the blank 42 are supported by the shoulder portions 80 and 88 of the lower mold 40, they are pushed downward by the corner portions 50 and 58 of the upper mold 38, and the blank 42 is bent and molded. As a result, bending molding is started for the blank 42 having a temperature equal to or higher than the Ac3 transformation point.

[Drawing]
As the upper mold 38 continues to descend, as shown in FIG. 5, one side of the bent-formed blank 42 is sandwiched between the upper mold end surface 46 of the upper mold 38 and the holder upper surface 96A of the blank holder 96. Then, one side portion of the bent-molded blank 42 is pressed by the upper mold 38 and the blank holder 96, and the occurrence of wrinkles is suppressed.

As a result, bending molding can be switched to drawing molding.

Then, as shown in FIGS. 5 to 6, as the punch convex portion 74 of the lower mold 40 is inserted into the die hole portion 48 of the upper mold 38, the blank 42 that is drawn and formed becomes the die hole portion 48. Pulled in. Then, the central portion of the blank 42 in the width direction HH is formed into a shape based on the shapes of the punch convex portion 74 of the lower mold 40 and the die hole portion 48 of the upper mold 38.

Then, when the upper mold 38 reaches the bottom dead center closest to the lower mold 40, the molding of the blank 42 is completed in a state of being sandwiched between the upper mold 38 and the lower mold 40 as shown in FIG. To do.

[cooling]
When the upper mold 38 reaches the bottom dead center, the molded blank 42 comes into close contact with the upper mold 38 and the lower mold 40. This state is called mold clamping. In the molded state, the heat of the blank 42 is rapidly taken away by the upper mold 38 and the lower mold 40. As a result, the blank 42 undergoes martensitic transformation. That is, quenching is performed. In this way, the blank 42 becomes the hot press molded product 10.

Examples of the heat removal method for removing heat from the blank 42 include a method of indirectly cooling with a refrigerant flowing inside the upper mold 38 and the lower mold 40. Further, as another heat removal method, there is a method of directly cooling the blank 42 by injecting a refrigerant from the upper mold 38 and the lower mold 40.

The time from the heating step to the start of cooling shall be within 8 seconds. That is, the time from when the blank 42 heated in the heating step leaves the heating furnace until the upper mold 38 reaches the bottom dead center is within 8 seconds.

When the blank 42 is made of a steel plate having the fastest cooling rate and a thickness of 0.8 mm, the temperature of the blank 42 becomes 600 ° C. or less in about 12 seconds from the Ac3 transformation point in a room temperature atmosphere. During press molding, the portion of the blank 42 in contact with the die is cooled at an even faster rate. Therefore, the time from the heating step to the start of cooling needs to be within 8 seconds. Otherwise, the hot press molded product 10 cannot be hardened.

(Action and effect)
The action and effect of this embodiment will be described.

In the initial stage of molding, bending molding is performed. Therefore, as compared with the case where drawing molding is performed from the initial stage of molding, heat is not taken from the blank 42 by sandwiching the blank 42 by the mold, and the decrease in ductility of the blank 42 can be suppressed. As a result, the fluidity of the material constituting the blank 42 can be ensured, so that cracking of the hot press molded product 10 can be suppressed.

Then, before the molding depth becomes large, bending molding is switched to draw molding, and draw molding is performed from the middle of molding. As a result, it is possible to suppress the occurrence of wrinkles as compared with the case where the molding depth in the bending molding becomes large and the strain becomes large by continuing the bending molding to the bottom dead center.

Further, by switching to drawing molding, the flange curved portion 28D of the first flange 28, which is a shape sudden change portion, can be molded in a state of being sandwiched between the upper mold end surface 46 of the upper mold 38 and the holder upper surface 96A of the blank holder 96. , The effect of suppressing wrinkles can be enhanced.

Therefore, it is possible to provide a method for producing a hot press-formed product that can suppress the occurrence of cracks and wrinkles in the hot press-formed product 10.

Since it is possible to suppress a local temperature drop of the blank 42 until the molding is completed, it is possible to secure the hardness of the hot press molded product 10 after quenching, and it is lightweight and has high strength hot press molding. Item 10 can be obtained.

In the present embodiment, at the bottom dead center where the upper mold 38 is closest to the lower mold 40, the portion of the first flange 28 that becomes the flange curved portion 28D is sandwiched between the upper mold 38 and the blank holder 96. However, it is not limited to this.

For example, if the blank holder 96 is moved to one side IH of the width direction HH and installed, the portion to be the flange curved portion 28D is sandwiched between the upper mold 38 and the blank holder 96 just before reaching the bottom dead center. It can be released from the dead center. In this case, the rocking mechanism of the blank holder 96 becomes unnecessary.

Further, if the blank holder 96 is provided with a distance block and a gap is formed between the holder upper surface 96A and the blank 42, it is possible to suppress heat removal due to contact between the blank holder 96 and the blank 42.

<Test>
8 and 9 are diagrams for explaining the test, and FIG. 9 shows the test results.

In this test result, the relationship between the timing of starting drawing molding and the presence or absence of cracks and wrinkles generated in the hot press molded product 10 is the recess in the first bent portion 18 constituting one side edge of the top plate surface 12. It is shown for each radius of curvature R at 14.

The timing for starting draw forming is 0.0 to 1.0 times the molding height H from the flanges 28 and 32 of the hot press molded product 10 shown in FIG. 8 to the top plate surface 12. Switch from bending to drawing at each height position.

As shown in FIG. 3, the molding height H is determined by the height h from the lower mold upper surface 72 to the convex top surface 82 of the lower mold 40, and the lower mold is raised from the holder upper surface 96A of the blank holder 96. The timing at which draw forming is started is determined by the height BH up to the upper surface 72.

Specifically, in FIG. 9, at 0.1H, the height BH from the lower mold upper surface 72 to the holder upper surface 96A is a blank so as to be 0.1H (10% of the molding height H). The height of the holder 96 is determined and molded.

Further, at 0.0H, the height BH from the lower mold upper surface 72 to the holder upper surface 96A is 0.0H, that is, the holder upper surface 96A and the lower mold upper surface 72 are formed at the same height. At 1.0H, the height BH from the lower mold upper surface 72 to the holder upper surface 96A is 1.0H, that is, the height h from the holder upper surface 96A and the lower mold upper surface 72 to the convex top surface 82 is the same height. Mold it.

As shown in FIG. 1, the hot press-molded product 10 formed in this test has, as an example, a length L of the top plate surface 12 of 1540 mm and a width W1 of the general portion 12B of the top plate surface 12. It is set to 100 mm. Further, in this hot press molded product 10, the width W2 of the wide portion 12A is 230 mm, and the height H from the flanges 28 and 32 to the top plate surface 12 is 60 mm.

Then, as shown in FIG. 8, the hot press molded product 10 having a radius of curvature R of the recess 14 of 25 mm or more and less than 50 mm and the hot press molded product 10 having a radius of curvature R of 50 mm or more and less than 100 mm are described above. Molded with a hot press. Further, the hot press molded product 10 having the radius of curvature R of the recess 14 of 100 mm or more and less than 300 mm was molded by the above-mentioned hot press device.

As a result, in the hot press molded product 10 having a radius of curvature R of 25 mm or more and less than 50 mm, no cracks or wrinkles were observed when drawing molding was started at a timing of 0.5H to 0.6H.

Further, in the hot press molded product 10 having a radius of curvature R of 50 mm or more and less than 100 mm, no cracks or wrinkles were observed when drawing molding was started at a timing of 0.4H to 0.7H.

In the hot press molded product 10 having a radius of curvature R of 100 mm or more and less than 300 mm, no cracks or wrinkles were observed when drawing molding was started at a timing of 0.3H to 0.8H.

Therefore, when the radius of curvature R of the edge of the recess 14 is 100 mm or more and less than 300 mm, the vertical wall formed by bending is 30% to 80% of the molding height H of the first vertical wall 20 of the hot press molded product 10. It can be seen that it is better to switch bending molding to draw molding when it is between%.

When the radius of curvature R of the edge of the recess 14 is 50 mm or more and less than 100 mm, the vertical wall formed by bending is 40% to 70% of the molding height H of the first vertical wall 20 of the hot press molded product 10. It can be seen that it is better to switch the bending molding to the drawing molding when it is between%.

Further, when the radius of curvature R of the edge of the recess 14 is 25 mm or more and less than 50 mm, the vertical wall formed by bending is 50% to 60% of the molding height H of the first vertical wall 20 of the hot press molded product 10. It can be seen that it is better to switch the bending molding to the drawing molding when it is between%.

The hot press molded product 10 may be a final molded product or an intermediate molded product. When the hot press molded product 10 is used as an intermediate molded product, the hot press molded product 10 may be further quenched.

10 Hot press molded product 12 Top plate surface 14 Recession 20 First vertical wall 28 First flange 28D Flange curved part 36 Press machine 96 Blank holder R Radius of curvature

Claims (4)

A method of manufacturing hot press molded products.
The hot press molded product has a top plate surface and has a top plate surface.
The hot press molded product has a recess on the top plate surface that retracts inward in the in-plane direction.
The hot press molded product has a vertical wall continuous with the edge of the top plate surface.
The blank is heated to a temperature equal to or higher than the Ac3 transformation point of the blank.
Bending molding was started for the blank having a temperature equal to or higher than the Ac3 transformation point.
Switching from the bending molding to the drawing molding,
A method for manufacturing a hot press molded product. The radius of curvature of the edge of the recess is 100 mm or more and less than 300 mm.
The heat according to claim 1, wherein when the vertical wall formed by the bending molding is between 30% and 80% of the molding height of the vertical wall of the hot press molded product, the bending molding is switched to the drawing molding. A method for manufacturing a press-molded product. The radius of curvature of the edge of the recess is 50 mm or more and less than 100 mm.
The heat according to claim 1, wherein when the vertical wall formed by the bending molding is between 40% and 70% of the molding height of the vertical wall of the hot press molded product, the bending molding is switched to the drawing molding. A method for manufacturing a press-molded product. The radius of curvature of the edge of the recess is 25 mm or more and less than 50 mm.
The heat according to claim 1, wherein when the vertical wall formed by the bending molding is between 50% and 60% of the molding height of the vertical wall of the hot press molded product, the bending molding is switched to the drawing molding. A method for manufacturing a press-molded product.