JP2005205416A - Hot press-forming method and hot press-forming die - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot press-forming method and a hot press-forming die by which drawing forming is possible without causing forming cracks. <P>SOLUTION: In a hot press-forming method by which quenched formed products are obtained by performing the press-forming and the cooling of a heated steel sheet W simultaneously with a forming die 1, the peripheral part of the charged heated steel sheet W is held with a blank holder 4 and the holder face 10 of a die 2 facing the blank holder 4 which are heated to a temperature where rapid cooling is not caused on the heated steel sheet W, respectively, the peripheral part of the heated steel sheet W is pressed with the blank holder 4 and the holder face 10 of the die 2 in accordance with the forming starting motion of the forming die 1 and the steel sheet W is drawn by forming motion after that. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hot press forming method and a hot press forming die for press forming a heated steel sheet in a hot state, and more particularly to a hot press forming method and a hot press forming die suitable for draw forming. .

  As a method of improving the strength of the panel material for the purpose of weight reduction, for example, in a vehicle body or the like that is assembled and formed from a conventional panel material, instead of the conventional method using a high-strength steel plate, the heated steel plate is in a hot state. It has been proposed to perform press molding (see Patent Document 1).

In this method, a steel sheet is heated to around 1000 degrees Celsius, put into a forming die, and press-formed in a hot state of about 850 degrees Celsius. The steel sheet to be press-formed has a low material strength due to high temperature, and deforms straight along the forming die, thereby improving the dimensional accuracy of the formed product. In addition, when the heated steel sheet is sandwiched between the forming dies, heat is taken away from the forming dies and rapidly cooled and quenched, so that the strength of the base material of the formed product can be greatly improved. Since the molded product is formed in a quenched state, there are very few dimensional accuracy defects such as a spring back. In addition, the steel plate applied to this shaping | molding method uses what has a little carbon amount (C) and an alloy component etc. are added in order to improve the hardenability of material.
Japanese Patent No. 3389562

  However, in the above conventional example, bending molded parts such as a door impact beam or a center pillar member are targeted, and when a drawing molded (draw molded) part is targeted, molding defects such as molding cracks are likely to occur. It was a thing. That is, in draw forming, it is necessary to sandwich the heated steel sheet between the blank holder and the die prior to forming, and the heated steel sheet is cooled by the blank holder before forming by the forming die, and the temperature of the steel sheet decreases. It is necessary to solve the problem that the strength of the portion is increased, the inflow resistance of the material is increased, and the amount of material inflow necessary for the drawing is not ensured, and the molded product is cracked.

  Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a hot press molding method and a hot press mold that can be drawn without causing molding cracks.

  The present invention is hot press forming that obtains a molded product by cooling a heated steel sheet simultaneously with press forming with a forming die, and a temperature at which the peripheral edge of the heated steel sheet is not rapidly cooled in the heated steel sheet. The blank holder heated at the same time or held on the holder surface of the die facing the blank holder, the peripheral edge of the heated steel plate is pressed by the blank holder and the die holder surface according to the molding start operation of the mold, The heated steel sheet was drawn by a subsequent forming operation.

  Therefore, in the present invention, the peripheral portion of the heated steel plate is held on the holder surface of the die that faces the blank holder or the blank holder that has been heated in accordance with the temperature at which the heated steel plate is not rapidly cooled. The heated steel plate is held by the die holder surface and the blank holder surface in order to press the peripheral edge of the heated steel plate with the blank holder and the die holder surface according to the starting operation, and to draw the heated steel plate by subsequent forming operation. Even during blank holding, the heated steel sheet is not rapidly quenched and quenched, does not hinder material flow into the forming part, and can be drawn without forming cracks even in hot pressing.

  Hereinafter, a hot press molding method and a hot press mold of the present invention will be described based on each embodiment.

(First embodiment)
FIG. 1 is a cross-sectional view showing a first embodiment of a hot press mold to which the present invention is applied.

  In FIG. 1, a hot press mold 1 is configured such that each element constituting a mold composed of a die 2, a punch 3, and a blank holder 4 is cooled and heated at a site described below.

  In the punch 3, a cooling means, for example, a cooling pipe 7 or the like for cooling the molding surface 6 that is the product shape is installed, and the cooling water is circulated in the cooling pipe 7 so that the surface of the molding surface 6 is circulated. It is configured to be kept at a low temperature (for example, normal temperature to 100 degrees Celsius).

  The die 2 is provided with cooling means for cooling the molding surface 8 that is the product shape, for example, a cooling pipe 9 through which cooling water circulates, and the surface of the molding surface 8 is cooled to a low temperature (for example, normal temperature to Celsius). A heating means for heating a cooling part held at 100 degrees) and a holder face 10 such as a die face facing the blank holder 4, for example, a heating device 11 such as an electric heater is installed, and the surface of the holder face 10 is And a heating part that is maintained at a high temperature (for example, 200 degrees Celsius or higher).

  A heat insulating layer 12 made of a heat insulating material is interposed at the boundary between the cooling part and the heating part so that heat is not transmitted to each other. That is, the die 2 is divided into a cooling part and a heating part, and both are integrated via the heat insulating layer 12. The heat insulating layer 12 does not need to have a cylindrical shape extending in the pressing direction, and for example, as shown in the drawing, it is configured in an L-shape bent toward the outer peripheral side of the die 2 from the middle extending from the boundary portion in contact with the molding material. However, it is desirable to ensure the mechanical strength of the die 2.

  The boundary portion where the heat insulating layer 12 is disposed is placed outside the trim end that trims the molded product peripheral flange after molding. If it does in this way, the part by which the hardness fell rapidly in the peripheral part of a molded article will not be generated.

  Also in the blank holder 4, heating means for heating the holding surface 14 facing the heating portion on the surface of the holder surface 10 of the die 2, for example, a heating device 15 such as an electric heater is installed, and the holding surface 14 is heated to a high temperature. (E.g., 200 degrees Celsius or higher). On the inner peripheral side of the blank holder 4 in the mold 1, there is a cooling portion that is in contact with the punch 3 and maintained at the same temperature as the punch 3.

  And the heat insulation layer 16 by a heat insulating material is interposed in the boundary part of the said heating site | part and a cooling site | part, and it is comprised so that heat may not mutually transmit. That is, the blank holder 4 also has a structure that is divided into a cooling part and a heating part, and both are integrated via the heat insulating layer 16. Similarly, the boundary where the heat insulation layer 16 is disposed also trims the trim flange of the molded product peripheral flange so as not to generate a portion whose hardness has been sharply reduced at the peripheral portion of the molded product. It is located on the outside.

  The operation of the hot press mold 1 having the above configuration will be described. During the molding operation, the heating parts of the die 2 and the blank holder 4 are kept at high temperatures by heating means 11 and 15 such as an electric heater, and the cooling parts of the punch 3 and the die 2 are supplied with cooling water to the cooling pipes 7 and 9. The surfaces of the molding surfaces 6 and 8 are kept at a low temperature by cooling means such as circulation. In the mold open state shown in FIG. 1, the die 2 is in the raised standby position, and the blank holder 4 is also in the standby position in which the hold surface 14 is raised from the tip of the punch 3 by a cushion (not shown).

  The steel sheet W to be formed is first heated to about 1000 degrees Celsius via a heating furnace, and then placed on the blank holder 4 of the press mold 1 as shown in FIG. The loaded steel plate W is supported by the holding surface 14 (heating part) of the blank holder 4 without contacting the punch 3. Since the heating part of the blank holder 4 is heated to high temperature by the heating means 15 such as an electric heater, rapid cooling of the steel plate W is suppressed.

  Next, the process proceeds to a pressing process, and the die 2 is lowered. When the lowering of the die 2 reaches a predetermined position, the heating portion which is the holder surface 10 of the die 2 comes into contact with the peripheral portion of the steel plate W supported by the blank holder 4, and the heating portion of the holder surface 10 and the blank holder 4 and the heating part of the holding surface 14. Since the heating part of the holder surface 10 of the die 2 is also heated to high temperature by the heating means 11 such as an electric heater, the steel plate W in this part is not rapidly cooled to the extent that quenching occurs.

  As the die 2 and the blank holder 4 are subsequently lowered, as shown in FIG. 2, the steel plate W is sandwiched between the molding surfaces 6 and 8 of the punch 3 and the die 2 and along the molding surfaces 6 and 8 of the punch 3 and the die 2. Thus, it is drawn and pressed. As the drawing process proceeds, an inflow of material is generated in which the blank material W held on the holding surface 14 of the blank holder 4 and the holder surface 10 of the die 2 is drawn between the molding surfaces 6 and 8 formed of the punch 3 and the die 2. Finally, it is molded along the molding surfaces 6 and 8 and simultaneously quenched and quenched. During the inflow of this material, the temperature of the steel sheet W is held between the heated portions of the holding surface 14 of the blank holder 4 and the holder surface 10 of the die 2 and is therefore not rapidly cooled to the extent of quenching. It is possible to prevent the strength from increasing and increase the inflow resistance of the material, to secure the amount of material inflow necessary for drawing, and to prevent the occurrence of molding cracks in the molded product.

  When the drawing process is completed, the molded product is also raised with the rise of the die 2 and the blank holder 4, and the interval between the molded product and the die 2 is increased by returning the blank holder 4 to the initial position. The upper molded product is taken out and drawing is completed. Since the taken-out molded product is processed by being sandwiched between the cooled molding surfaces 6 and 8 of the die 2 and the punch 3, the molded product is rapidly cooled and quenched by the die 2 and the punch 3. For this reason, even when the steel sheet W was kept at a temperature of about 800 degrees Celsius or more at the time of charging, the shape part of the molded product is lowered to the temperature of the press mold 1 at the time of taking out, and the flange part at the periphery of the molded product Also, since the temperature rapidly decreases after being removed from the mold 1, it can be handled easily.

  In the present embodiment, the following effects can be achieved.

  (A) The blank holder 4 heated to a temperature at which the heated steel plate W is not rapidly cooled, or the peripheral edge of the heated steel plate W placed on the holder surface 10 of the die 2 facing the blank holder 4 is held, and a forming die In order to press the peripheral edge of the heated steel plate W by the blank holder 4 and the holder surface 10 of the die 2 in accordance with the forming start operation of No. 1, and to draw the steel plate W by the subsequent forming operation, Even during blank holding in which the heated steel plate W is held with the blank holder 4 surface 14, the heated steel plate W is not rapidly quenched and quenched, and does not hinder material flow into the formed part. Even in a hot press that obtains a molded product that is cooled and quenched simultaneously with the press molding by the mold 1, it is possible to perform drawing without a molding crack.

  (A) heating means 11 and 15 for locally raising the holding surface 14 of the blank holder 4 of the mold 1 and the holder surface 10 of the die 2 facing the blank holder 4 to a temperature at which the heated steel plate W does not cause rapid cooling; Since the cooling means 7 and 9 for cooling the molding surfaces 6 and 8 of the mold 1 for directly molding the molded product are provided, quenching due to rapid cooling of the heated steel plate W in the blank hold portion can be prevented, and material flow into the molding portion Thus, even if hot press drawing is performed, a quenched drawn product without forming cracks can be obtained.

  (C) The holding surface 14 of the blank holder 4 heated by the heating means 11 and 15 and the holder surface 10 of the die 2 facing the blank holder 4 are thermally insulated from the other parts of the mold 1 by the heat insulating layers 12 and 16. Therefore, the inflow of the material can be surely performed, while the molding surfaces 6 and 8 forming the molded product can be reliably cooled, and the steel sheet W can be reliably cooled by molding to give sufficient quenching hardness. it can. In addition, it is possible to deliberately separate the parts that require hardness from the parts that do not require hardness because it becomes scrap, and the cutting part in the trim process that cuts the scrap part in the subsequent process is easy because the hardness is not as high as that of the molded part. Can be cut.

(Second Embodiment)
FIG. 3 is a cross-sectional view showing a second embodiment of a hot press molding method and a hot press mold using the present invention. In the present embodiment, the temperature of the portion that contacts the steel plate at the initial stage of clamping such as the punch edge and the die edge is set to a high temperature until the initial stage of clamping and to a low temperature after the final stage of clamping so as to improve the formability of the steel material. It is a thing. The same devices as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In FIG. 3, the hot press mold 1 of the present embodiment has a configuration similar to the first embodiment, in addition to the edge portion 6A of the molding surface 6 of the punch 3 and the edge portion 8A of the molding surface 8 of the die 2. Is locally provided with a heating area by (second) heating means 18, 19 such as an electric heater, and is provided with cooling means 7A, 9A as necessary. Then, from the mold open state to the mold clamping initial stage, the heating means 18 and 19 are operated so that the edge portion 6A of the molding surface 6 of the punch 3 and the edge portion 8A of the molding surface 8 of the die 2 are in a high temperature state. From the end to the mold opening, the operation of the heating means 18 and 19 is stopped, and instead the cooling means 7A and 9A are operated so as to be in a low temperature state.

  As described above, when the punch edge 6A and the die edge 8A are maintained at a high temperature until the initial stage of mold clamping, the steel sheet W heated to about 1000 degrees Celsius by the heating furnace is brought into contact with the punch edge 6A and the die edge 8A that are in contact with the initial stage of forming. It is possible to suppress the rapid cooling that precedes locally, and it is possible to suppress the hardness from increasing locally in advance.

  The operation of the heating means 18 and 19 is stopped by the progress of the subsequent drawing and the temperature of the punch edge 6A and the die edge 8A is lowered. When the end of the mold clamping is reached, the punch edge 6A and the die edge 8A are operated by the cooling means 7A and 9A. Forcibly set to a low temperature state. For this reason, the steel sheet W that contacts the punch edge 6A and the die edge 8A is rapidly cooled together with the punch 3 and other parts sandwiched by the cooled molding surfaces 6 and 8 of the die 2, and finally formed into the molding surfaces 6 and 8. At the same time, it is quenched and quenched.

  As described above, by setting the temperature of the portion in contact with the steel plate W at the initial stage of clamping such as the punch edge 6A and the die edge 8A to a high temperature until the initial stage of clamping and to a low temperature after the final stage of clamping, the material can be obtained at the initial stage of molding. Since the difference in cooling timing between the part that is rapidly cooled and the part that is not rapidly cooled until the end of molding can be reduced, it is possible to avoid molding cracks due to local hardness increases at the lower part of the punch edge 6A and the part passing through the die edge 8A.

  In the present embodiment, in addition to the effects (a) to (c) in the first embodiment, the following effects can be achieved.

  (D) The second heating means 18 and 19 and the cooling means 7 and 9 are disposed on the forming surfaces 6 and 8 which are in contact with the heated steel plate W at the initial stage of drawing of the forming die 1, and the second heating means 18 and 19 raises the initial contact molding surfaces 6A and 8A to a temperature at which the heated steel sheet W does not rapidly cool at the initial stage of forming, and the cooling means 7A and 9A set the initial contact molding surfaces 6A and 8A to the end after molding. Since the temperature of the heated steel sheet W is lowered to a temperature that causes rapid cooling, a difference in cooling timing between a portion where the material is rapidly cooled at the initial stage of molding and a portion where the material is not rapidly cooled until the final stage of molding can be alleviated, and the lower portion of the punch edge 6A or the die edge 8A. It is possible to avoid molding cracks due to local hardness increases such as passage sites.

  In the above embodiment, the press mold 1 is a cushion draw type mold having a die 2 disposed above and a blank holder 4 supported by a punch 3 and cushion pins below. Although the case where the heated steel sheet W is thrown into the surface 14 has been described, although not shown, a die may be disposed below and a double cushion draw type forming die having a punch and a blank holder above may be used. In that case, the heated steel sheet is put into the holder surface of the die.

Sectional drawing of the hot press molding die which shows one Embodiment of this invention. Sectional drawing of the operating state of a hot press mold similarly. Sectional drawing of the operation state of the hot press molding die which shows 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hot press mold 2 Die 3 Punch 4 Blank holder 6, 8 Molding surface 7, 7A, 9, 9A Cooling pipe as cooling means 10 Holder surface 14 Hold surface 11, 15, 18, 19 Electric heater as heating means 12, 16 Heat insulation layer

Claims (6)

In the hot press forming method of obtaining a molded product by cooling the heated steel sheet simultaneously with press forming with a forming die,
The peripheral part of the heated steel sheet that has been charged is held on the holder surface of the die that faces the blank holder or the blank holder, each of which is heated to a temperature that does not cause rapid cooling of the heated steel sheet,
In accordance with the molding start operation of the molding die, press the peripheral edge of the heated steel plate with the blank holder and the holder surface of the die,
A hot press forming method characterized in that a heated steel sheet is drawn by a subsequent forming operation.   The forming mold raises the temperature of the forming surface portion that contacts the heated steel sheet at the initial stage of drawing to a temperature at which the heated steel sheet is not rapidly cooled at the initial stage of forming, and is lowered to a temperature at which the heated steel sheet is rapidly cooled after the final stage of forming. The hot press molding method according to claim 1, wherein: In a press mold that obtains a quenched product by cooling the heated steel sheet simultaneously with the press mold with the mold,
A hot press mold characterized by comprising heating means for locally raising the hold surface of the blank holder of the mold and the holder surface of the die facing the blank holder to a temperature at which the heated steel plate does not cause rapid cooling.   The hot press forming die according to claim 1, wherein the forming die comprises a cooling means for cooling a forming surface of a forming die for directly forming a formed product.   The holding surface of the blank holder heated by the heating means and the holder surface of the die facing the blank holder are thermally insulated from other parts of the mold. Hot press mold. A second heating means and a cooling means are disposed on the molding surface portion that comes into contact with the heated steel plate at the initial stage of drawing of the mold,
The second heating means raises the temperature of the initial contact forming surface portion to a temperature that does not cause rapid cooling of the heated steel plate at the initial stage of forming, and the cooling means rapidly cools the initial contact forming surface portion of the heated steel plate after the end of forming. The hot press mold according to any one of claims 3 to 5, wherein the temperature is lowered to a temperature to be generated.

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