Patent Abstract:
The present invention provides a hot press molding method for molding a heated metallic plate (K) using a molding die ( 20, 60 ) comprising an upper die ( 21 ) and a lower die ( 20 ). According to the method, the heated metallic plate is arranged between the upper die and the lower die, the upper die and the lower die are brought together, and the metallic plate held between the dies is pressed. After the metallic plate is pressed, a refrigerant in the form of a liquid or mist is supplied via a plurality of supply holes provided to the lower die to a surface of the metallic plate held between the dies, and once the refrigerant has finished being supplied, a gas is sprayed onto the surface of the metallic plate via the plurality of supply holes. It is thereby possible to remove, with maximum speed, liquid refrigerant adhering to the metallic plate when the supply of liquid refrigerant is stopped.

Full Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a hot press forming method and a hot press forming die of a metal sheet. 
       BACKGROUND ART 
       [0002]    In recent years, as means for shaping steel sheet for auto parts using high strength steel sheet, hot press forming has increasingly been employed. Hot press forming shapes the steel sheet at a high temperature to thereby form it at a stage of a low deformation resistance and then rapidly cools it to quench harden it. With hot press forming, it is possible to press-form parts which are high in strength and are high in shape precision without causing deformation or other shaping problems after shaping. 
         [0003]    Specifically, with the hot press forming method, first, steel sheet which has been heated in advance by a heating furnace to a predetermined temperature is supplied to a press die. After this, in a state placed on the bottom die (die) or in a state lifted from the bottom die by lifters or other fixtures built in the bottom die, a top die (punch) is descended to the bottom die limit. Next, the steel sheet is cooled for a certain time (usually 10 seconds to 15 seconds) to cool the steel sheet to a desired temperature. Further, after the cooling finishes, the shaped steel sheet is taken out from the die, then a new steel sheet which has been heated to a predetermined temperature is supplied to the press die. The steel sheet is quenched, tempered, and otherwise heat treated in the cooling process. Therefore, in hot press forming, freely controlling the cooling rate from the viewpoint of the heat treatment characteristics of the steel sheet, obtaining a uniform cooling rate at the steel sheet as a whole from the viewpoint of stability of quality, and shortening the time required for the cooling process after shaping the steel sheet from the viewpoint of productivity, are important. 
         [0004]    As means for shortening the cooling time of the shaped steel sheet, it has been proposed to not make the die directly rob heat from the steel sheet, but to feed another medium, for example, water, to the surface of the steel sheet (for example, PLT 1). In particular, in the hot press forming apparatus which is described in PLT 1, the inside surface of the die is provided with a plurality of independent projections of certain heights and channels for water which are communicated with plurality of locations at the inside surface of the die are provided inside the die. Due to this, it is possible to run coolant through the channels inside of the die in the clearances, which are formed by the projections, between the inside surface of the die and the steel sheet. For this reason, it is possible to cool the metal sheet in a short time and raise the productivity of the hot press forming operation. Further, this quenching by rapid cooling enables the steel sheet to be raised in hardness and the strength of the shaped part to be greatly improved. 
         [0005]    Further, as means for shortening the time which is required for the cooling process after shaping the steel sheet, it has been proposed to arrange a storage container storing a coolant as close to the steel sheet as possible (for example, PLT 2). In particular, the die which is described in PLT 2 is provided with a storage container which stores a coolant, a plurality of feed holes which feed coolant which is stored in the storage container to the steel sheet, and a coolant feed control device which is provided between the storage container and the feed holes. By having a storage container of coolant arranged inside the die in this way, it is possible to shorten the distance between the storage location of the coolant and feed locations of the coolant. Due to this, it becomes possible to immediately feed coolant to the steel sheet after the control device is sent a coolant feed instruction, and therefore the time from press forming the steel sheet to the end of the cooling process can be shortened. 
       CITATIONS LIST 
     Patent Literature 
       [0000]    
       
         PLT 1: Japanese Patent Publication No. 2005-169394 A 
         PLT 2: Japanese Patent Publication No. 2007-136535 A 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    In this regard, in general the heat conduction rate of a liquid is higher than the heat conduction rate of a gas, and therefore when using a liquid state coolant as a coolant for cooling the metal sheet after being pressed, the metal sheet can be cooled quickly compared with the case of using a gas state coolant. From this viewpoint, in both the above PLTs 1 and 2, as the coolant, a liquid, in particular water, is used. 
         [0009]    In this regard, when using a liquid state coolant for cooling the metal sheet, even after stopping the feed of the liquid state coolant, the liquid state coolant remains on the surface of the metal sheet. This liquid state coolant does not remain on the entire surface of the metal sheet uniformly, but locally deposits on the surface of the metal sheet. In this case, regions where the liquid state coolant remains are rapidly cooled, while regions where liquid state coolant does not remain are not cooled that much. For this reason, the metal sheet is unevenly cooled and as a result the metal sheet becomes uneven in strength. Further, when using a liquid state coolant comprised of water or another highly corrosive liquid (liquid which easily causes a metal etc. to corrode), if the liquid state coolant remains on the surface of the metal sheet, corrosion of the metal sheet will be invited. 
         [0010]    For this reason, to suppress uneven strength or corrosion of a metal sheet, it is considered necessary to remove the liquid state coolant which has deposited on the surface of the metal sheet as quickly as possible after pressing. 
         [0011]    Therefore, in consideration of the above problem, an object of the present invention is to provide a hot press forming method and a hot press forming die which can remove the liquid state coolant which has deposited on the surface of the metal sheet as fast as possible when stopping the feed of the liquid state coolant. 
       Solution to Problem 
       [0012]    The inventors studied various hot press forming methods and various hot press forming dies relating to the removal of the liquid state coolant which deposited on the surface of a metal sheet when stopping the feed of the liquid state coolant. 
         [0013]    As a result, they discovered that by providing the hot press forming die with a plurality of feed holes able to feed fluid to the metal sheet and by not only feeding liquid state coolant through these feed holes to the surface of the metal sheet, but also blowing a gas on the surface of the metal sheet, it is possible to remove the liquid state coolant which has deposited on the surface of the metal sheet member as fast as possible when stopping the feed of the liquid state coolant. 
         [0014]    The present invention was made based on the above findings and has as its gist the following: 
         [0000]    (1) A hot press forming method which shapes a heated metal sheet using a forming die which is comprised of a first die and a second die, comprising steps of: arranging the heated metal sheet between the first die and the second die; making the first die and the second die approach to press the metal sheet which is clamped between the two dies; after pressing the metal sheet, feeding liquid state or mist state coolant to the surface of the metal sheet which is clamped between the two dies through a plurality of feed holes which are provided at least at one of the first die and the second die; and, after the coolant finishes being fed, blowing a gas through the plurality of feed holes to the surface of the metal sheet.
 
(2) The hot press forming method as set forth in (1) wherein the first die and second die are separated before feeding the gas to the surface of the metal sheet.
 
(3) The hot press forming method as set forth in (1) or (2) wherein a fluid switching means for switching the coolant and the gas which are fed to the plurality of feed holes is provided inside at least one of the first die and second die.
 
(4) The hot press forming method as set forth in (3) wherein at least one of the first die and the second die has an outside die at which the feed holes are provided and an inside die which is arranged slidably inside the outside die; the outside die is provided inside it with outside pipes which are arranged between a sliding surface between the outside die and the inside die, and the feed holes; the inside die is provided inside it with first inside pipes which are arranged between the sliding surface and a connecting part which is connected to a coolant feed source and with second inside pipes which are arranged between the sliding surface and a connecting part which is connected to a gas feed source; and the fluid switching means makes the outside die and the inside die slide relative to each other to connect the outside pipes with the first inside pipes or second inside pipes and thereby switch between the coolant and the gas which is fed to the plurality of feed holes.
 
(5) The hot press forming method as set forth in any one of the above (1) to (4) wherein the coolant is either water or anti-rust oil.
 
(6) A hot press forming die which presses and cools a heated metal sheet, comprising: an outside die provided with feed holes which feed fluid to the metal sheet; and an inside die which is arranged slidably inside the outside die, wherein the outside die is provided inside it with outside pipes which are arranged between a sliding surface between the outside die and the inside die and the feed holes; the inside die is provided inside it with first inside pipes which are arranged between the sliding surface and a connecting part which is connected to a coolant feed source and with second inside pipes which are arranged between the sliding surface and a connecting part which is connected to a gas feed source; and the outside pipes, first inside pipes, and second inside pipes are formed so that the outside pipes can be switched between at least a state connected to the first inside pipes and a state connected to the second inside pipes by making the outside die and the inside die move relative to each other.
 
(7) The hot press forming die as set forth in the above (6) wherein the outside pipes, first inside pipes, and second inside pipes are formed so that the outside pipes to be switched between a state connected to the first inside pipes, a state connected to the second inside pipes, and a state not connected to the two inside pipes, by making the outside die and the inside die move relative to each other.
 
(8) The hot press forming die as set forth in the above (6) or (7) wherein the pipeline lengths of the outside pipes are equal.
 
(9) The hot press forming die as set forth in any one of the above (6) to (8) wherein the die which is comprised of the inside die and the outside die is used as at least one of a top die and bottom die for press forming.
 
(10) The hot press forming die as set forth in any one of the above (6) to (9) wherein the coolant is any of water, an anti-rust oil, and mists of the same.
 
       Advantageous Effects of Invention 
       [0015]    According to the present invention, it is possible to quickly remove the liquid state coolant which was deposited on the surface of a metal sheet at the time of stopping the feed of the liquid state coolant and, as a result, it is possible to suppress uneven strength of the shaped metal sheet and corrosion of the metal sheet. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  is a side view which schematically shows the configuration of a hot press forming apparatus. 
           [0017]      FIG. 2  is a plan view which schematically shows the configuration of the hot press forming apparatus. 
           [0018]      FIG. 3  is a longitudinal cross-sectional view which schematically shows the configuration of a bottom die. 
           [0019]      FIG. 4  is a lateral cross-sectional view which schematically shows the configuration of the bottom die. 
           [0020]      FIG. 5  is a longitudinal cross-sectional view which shows the configuration near a forming surface of the bottom die. 
           [0021]      FIG. 6  is a longitudinal cross-sectional view which schematically shows the configuration of the bottom die which is used in a hot press forming die of a second embodiment. 
           [0022]      FIG. 7  is a lateral cross-sectional view which schematically shows the configuration of the bottom die which is used in a hot press forming die of a second embodiment. 
           [0023]      FIG. 8  is a view for explaining the state where the top die is pushed down to a bottom die limit. 
           [0024]      FIG. 9  is a longitudinal cross-sectional view which schematically shows the configuration of the bottom die according to a modification of the second embodiment. 
           [0025]      FIG. 10  is a lateral cross-sectional view which schematically shows the configuration of a bottom die according to a modification of the second embodiment. 
           [0026]      FIG. 11  is a longitudinal cross-sectional view which schematically shows the configuration of a bottom die according to a modification of the second embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    Below, referring to the figures, embodiments of the present invention will be explained in detail. Note that, in the following explanation, similar components are assigned the same reference numerals. 
         [0028]      FIG. 1  is a side view which schematically shows the configuration of a hot press forming apparatus  1  according to a first embodiment of the present invention.  FIG. 2  is a plan view which schematically shows the configuration of the hot press forming apparatus  1 . 
         [0029]    As will be understood from  FIG. 1  and  FIG. 2 , the hot press forming apparatus  1  comprises a hot press forming die  10  for shaping a steel sheet K, a coolant feed source  11  which feeds coolant (in the present embodiment, water) to the hot press forming die  10 , a gas feed source  12  which feeds gas (for example, compressed air) used for being blown to the hot press forming die  10 , and a control unit  13  which controls the hot press forming apparatus  1 . 
         [0030]    The hot press forming die  10  has a bottom die  20  which is disposed in a lower side and a top die  21  which is disposed in a upper side. The bottom die  20  is arranged on the base  22 . The top die  21  is arranged vertically above the bottom die  20  and facing the bottom die  20  and is configured to be able to be lifted by a lift mechanism  23  in the vertical direction. The lift mechanism  23  performs a lift operation based on a control signal from the control unit  13 . 
         [0031]    The bottom die  20  is provided with positioning pins  30  for positioning with prepierced holes P which are preliminarily provided in the steel sheet K. The positioning pins  30  are arranged so as to pass through the inside of the bottom die  20  and stick out vertically upward from the top surface of the bottom die  20 . 
         [0032]    The top ends of the positioning pins  30  are formed into substantially conical shapes. For this reason, by fitting the top ends of the substantially conical shapes in the prepierced holes P of the steel sheet K, as shown in  FIG. 1  by the broken line, the steel sheet K is supported and positioned. In particular, since the top ends of the positioning pins  30  are substantially conical, by suitably setting the sizes of the prepierced holes P of the steel sheet K, the steel sheet K can be supported in a state with a clearance H of a predetermined distance provided from the bottom die  20 . 
         [0033]    Further, the positioning pins  30  are slidable with respect to the bottom die  20 . Further, they are supported at the top surface of the base  22  through not shown biasing means (for example, springs). For this reason, if the top die  21  descends and the positioning pins  30  are pushed down, the steel sheet K is pushed down together with the positioning pins  30 . 
         [0034]      FIG. 3  is a cross-sectional view when viewing the bottom die  20  from the front direction, while  FIG. 4  is a cross-sectional view when viewing the bottom die  20  from the side direction. As shown in  FIG. 3  and  FIG. 4 , the bottom die  20  has a forming surface  20   a  which contacts the steel sheet K at the time of pressing. Inside of the bottom die  20 , a header  40  which is connected to the coolant feed source  11  and gas feed source  12 , and a plurality of pipes  41  which run through the inside of the bottom die  20  between the header  40  and the forming surface  20   a , are provided. In the thus configured bottom die  20 , the fluid which is fed from the coolant feed source  11  and gas feed source  12  is fed through the header  40  and pipes  41  to the surface of the steel sheet K. Therefore, the ends of the pipes  41  at the forming surface  20   a  sides act as feed holes  41   a  which feed fluid to the surface of the steel sheet K. Note that, in the example which is shown in  FIG. 3 , to facilitate understanding of the drawing, the feed holes  41   a  are provided at only the left and right sides of the bottom die  20  and are not provided at the center, but in actuality they are preferably arranged evenly over the entire forming surface  20   a  including the center part. 
         [0035]    Further, at the forming surface  20   a  of the bottom die  20 , as shown in  FIG. 5 , a plurality of constant height independent projections  42  are formed over the entire surface of the region which faces the steel sheet K. Conversely speaking, the forming surface  20   a  of the bottom die  20  is formed with recesses which are formed between the projections  42  over the entire surface of the region which faces the steel sheet K. Due to this, when the top die  21  pushes down the bottom surface of the steel sheet K to a position which contacts the forming surface  20   a  of the bottom die  20 , a clearance is formed between the forming surface  20   a  and the bottom surface of the steel sheet K between the plurality of projections  42 . For this reason, by feeding coolant to the clearance from the pipes  41 , the steel sheet K can be rapidly cooled. 
         [0036]    The header  40 , as shown in  FIG. 4 , is connected through a coolant feed pipe  45  to the coolant feed source  11  and is connected through a gas feed pipe  46  to the gas feed source  12 . The coolant feed pipe  45  is provided with a valve  47 , while the gas feed pipe  46  is provided with a valve  48 . The valve  47  and valve  48  are connected to the control unit  13 . The control unit  13  is used to operate the valve  47  and the valve  48  to open and close. Therefore, by operating the valve  47  which is provided at the coolant feed pipe  45 , the feed and stopping of the coolant are controlled, while by operating the valve  48  which is provided at the gas feed pipe  46 , the feed and stopping of the gas are controlled. 
         [0037]    Note that, in the example which is shown in  FIGS. 1 ,  2 , and  4 , the coolant feed pipe  45  and gas feed pipe  46  are provided with valves  47  and  48 . However, the merged part  49  of the coolant feed pipe  45  and the gas feed pipe  46  may be provided with a three-way valve to control the fluid which is fed to the header  40 . 
         [0038]    Further, in the present embodiment, the forming surface  20   a  of the bottom die  20 , as shown in  FIG. 3  and  FIG. 4 , is provided with exhaust suction holes  50  which suck in the coolant etc. which is fed though the feed holes  41   a  to the surface of the steel sheet K and discharge the coolant from around the surface of the steel sheet K. The exhaust suction holes  50  are connected to a suction pipe  51 , while the suction pipe  51  is connected to for example a vacuum pump or other exhaust mechanism  52 . 
         [0039]    Note that, to enable the coolant etc. which is fed from the feed holes  41   a  to be smoothly discharged through the exhaust suction holes  50 , the exhaust suction holes  50  should be atmospheric pressure or less. That is, for example, if opening the end of the suction pipe  51  at the opposite side to the exhaust suction holes  50  to the atmosphere, the extraneous coolant around the surface of the steel sheet K will be discharged outside of the die. For this reason, the exhaust mechanism  52  need not necessarily be provided. 
         [0040]    Note that, in the present embodiment, water is used as the coolant which is fed from the coolant feed source  11 , but aside from water, anti-rust oil which has a rust prevention function or another liquid state coolant may also be used. Further, a mist of water or anti-rust oil etc. or other mist-like coolant can be used. Further, in the present embodiment, as the gas which is fed from the gas feed source  12 , compressed air is used, but the invention is not limited to this. For example, so long as a gas which is fed at a pressure of atmospheric pressure or more, nitrogen gas or another gas other than air may be used. In particular, when using nitrogen as the gas which is fed from the gas feed source  12 , the surroundings of the steel sheet K may be a nonoxidizing atmosphere, and therefore rusting of the steel sheet K can be further suppressed. 
         [0041]    Next, the method of using the thus configured hot press forming apparatus  1  to form steel sheet K by hot press will be explained next. 
         [0042]    First, when starting the press forming of the steel sheet K, the valves  47  and  48  are closed. Due to this, the pipes  41  of the bottom die  20  are not fed with either coolant or gas. In such a state, a steel sheet K which has been heated to a predetermined temperature (for example, 700° C. to 1000° C.) is placed by a conveyor apparatus (not shown) between the bottom die  20  and the top die  21 . Specifically, the steel sheet K is placed on the positioning pins  30  of the bottom die  20  so that the prepierced holes P fit into the positioning pins  30 . 
         [0043]    Next, the top die  21  is moved in the vertical direction so as to approach the bottom die  20  to press the steel sheet K which is clamped between the top die  21  and bottom die  20 . When the top die  21  descends to the bottom die limit and the press operation is completed, the valve  47  which is provided at the coolant feed pipe  45  is opened. When the valve  47  is opened, coolant is fed from the coolant feed source  11  through the coolant feed pipe  45 , header  40 , pipes  41 , and feed holes  41   a  to the surface of the steel sheet K. Due to this, the steel sheet K starts to be rapidly cooled. 
         [0044]    Further, if the top die  21  is held at the bottom die limit for a certain time and the steel sheet K is cooled to a temperature of for example 200° C. or less, next, the valve  47  which is provided at the coolant feed pipe  45  is closed and the valve  48  which is provided at the gas feed pipe  46  is opened. If the valve  48  is opened, the gas is blown from the gas feed source  12  through the gas feed pipe  46 , header  40 , pipes  41 , and feed holes  41   a  to the surface of the steel sheet K. At this time, if the pressure of the gas which is fed from the feed holes  41   a  is too high, the pressurizing energy becomes high, while conversely if too low, gas is no longer evenly ejected from the feed holes  41   a , and therefore the pressure is set to 0.1 to 1.0 MPa, preferably 0.3 to 0.7 MPa, more preferably 0.4 to 0.5 MPa. The flow rate is determined by the pressure of the gas and the nozzle shape and is set to 20 to 2000 ml/sec, preferably 300 to 1000 ml/sec, more preferably 400 to 700 ml/sec. 
         [0045]    Further, the temperature of the gas which is fed from the feed holes  41   a  is set to 200° C. or less, preferably ordinary temperature. That is, the steel sheet K is cooled by the coolant down to 200° C. or less, whereby it is quenched. For this reason, if blowing 200° C. or more gas, the steel sheet K becomes at a temperature of 200° C. or more, the steel sheet K is annealed, and the hardness falls. 
         [0046]    Further, in the present embodiment, along with the closing of the valve  47  or the opening of the valve  48 , the top die  21  is risen to top die limit. If the top die  21  rises in this way, the positioning pins  30  which had been pushed downward by the top die  21  rise and the steel sheet K is separated from the forming surface  20   a  of the bottom die  20 . Due to this, a clearance is formed between the bottom surface of the steel sheet K and the forming surface  20   a  of the bottom die  20 . 
         [0047]    Further, if blowing gas to the surface of the steel sheet K and thereby finishing removing the coolant on the surface of the steel sheet K, the shaped steel sheet K is taken off by the conveyor apparatus (not shown) from the positioning pins  30  and is unloaded from the hot press forming apparatus  1 . Further, a heated new steel sheet K is placed by a conveyor apparatus (not shown) on the positioning pins  30  of the hot press forming apparatus  1  and this series of steps in the hot press forming operation is repeated. 
         [0048]    Next, the advantageous effects of the hot press forming die and hot press forming method according to the above embodiment will be explained. 
         [0049]    According to the above embodiment, in the state with a steel sheet K placed on the same hot press forming die  10 , the surface of the steel sheet K was fed with coolant from the coolant feed source  11  and blown with gas from the gas feed source  12 . For this reason, it is possible to blow gas to the surface of the steel sheet K immediately after stopping feeding of the coolant to the surface of the steel sheet K. For this reason, it is possible to quickly remove the coolant which has deposited on the surface of the steel sheet K. 
         [0050]    Note that, the time which is taken for removing the coolant which is deposited on the surface of the steel sheet K depends on the temperature and sheet thickness of the shaped steel sheet K (that is, the heat capacity of the steel sheet K). For example, if making the pressure of the gas which is fed from the feed holes  41   a  0.4 MPa, making the flow rate 60 to 70 ml/sec, and making the temperature ordinary temperature, if the temperature of a sheet thickness 1.4 mm steel sheet K right after pressing is about 150° C., it is possible to remove the coolant which deposited on the steel sheet K in about 3 seconds from the start of blowing of the gas. Further, in the case of sheet thickness 1.2 mm steel sheet K, it is possible to remove the coolant which deposited on the steel sheet K in about 7 seconds from the start of blowing of the gas. 
         [0051]    In this way, it is possible to quickly remove the coolant which deposited on the surface of the steel sheet K, and therefore it is possible to suppress uneven cooling of the steel sheet K due to coolant remaining on the surface of the steel sheet K in an uneven manner. Accordingly, it is possible to keep the strength of the steel sheet K from becoming uneven. Further, even when using water as a coolant, it is possible to keep rust from forming due to the coolant which remains on the surface of the steel sheet K. 
         [0052]    Further, after being pressed by the hot press forming die  10 , the surface of the steel sheet K is sprayed with gas whereby the scale which formed on the surface of the steel sheet K due to the pressing etc. can be removed. In particular, if the coolant is removed from the surface of the steel sheet K and the surface of the steel sheet K is dried, the scale easily peels off, and therefore in the present embodiment, the scale can be removed more efficiently. 
         [0053]    Further, in the above embodiment, the clearance H is formed when blowing gas on the surface of the steel sheet K. By such a clearance H being formed, the gas which is fed from the gas feed source  12  through the feed holes  41   a  is easily exhausted and the flow rate of the gas which passes over the surface of the steel sheet K can be raised. Due to this, the coolant which deposited on the surface of the steel sheet K can be efficiently removed. Note that, if the clearance H is too small, it becomes difficult to draw in the surrounding gas while conversely if too large, the blown gas will disperse and the effect of blowing it will fall, and therefore the clearance is 1 mm to 100 mm or so, preferably 5 to 20 mm, more preferably 8 to 15 mm. 
         [0054]    Next, referring to  FIG. 6  and  FIG. 7 , a second embodiment of the present invention will be explained. The configuration of the hot press forming apparatus of the second embodiment is basically similar to the configuration of the hot press forming apparatus of the first embodiment. However, in the hot press forming apparatus of the second embodiment, the configuration of the bottom die  60  differs from the configuration of the bottom die  20  of the first embodiment. 
         [0055]      FIG. 6  is a longitudinal cross-sectional view similar to  FIG. 3  which schematically shows a bottom die  60  which is used in the hot press forming apparatus of the second embodiment, while  FIG. 7  is a lateral cross-sectional view similar to  FIG. 4  which schematically shows the bottom die  60 . As shown in  FIG. 6  and  FIG. 7 , the bottom die  60  has an outside die  61  which has a forming surface  61   a  which contacts the steel sheet K and an inside die  71  which is provided slidably with respect to the outside die  61  at the inside of the outside die  61 . In the present embodiment, the inside die  71  has a rectangular cross-sectional shape. Note that, in  FIG. 7 , for convenience of illustration, the outside die  61  is drawn slightly shorter than the inside die  71  in the lateral direction of  FIG. 7 . 
         [0056]    The outside die  61  is provided with a plurality of outside pipes  64  which run from the forming surface  61   a  which contacts the steel sheet K to the sliding surface  63  between the outside die  61  and inside die  71 , through the inside of the outside die  61 . The ends of the outside pipes  64  at the forming surface  61   a  sides, in the same way as the feed holes  41   a  of the first embodiment, act as feed holes  64   a  which feed fluid to the surface of the steel sheet K. Therefore, the outside pipes  64  can be said to be arranged between the feed holes  64   a  and the sliding surface  63 . The forming surface  61   a , like the forming surface  20   a  of the first embodiment, is formed with a plurality of projections. 
         [0057]    Further, the outside die  61  is supported through elastic members  65  on the base  22 . As the elastic members  65 , for example, springs of predetermined stroke lengths are used. For this reason, if the top die  21  descends and pushes the outside die  61 , the outside die  61  is guided by the sliding surface  63  while being pushed downward. The guide mechanism for sliding the outside die  61  and the inside die  71  may be provided separately from the sliding surface  63 . 
         [0058]    Inside of the inside die  71 , a plurality of first inside pipes  72 , a plurality of second inside pipes  73 , a first header  74  which connects the plurality of first inside pipes  72  and coolant feed source  11 , and a second header  75  which connects the plurality of second inside pipes  73  and gas feed source  12  are provided. The first inside pipes  72  are provided in the same number as the outside pipes  64  of the outside die  61  and run from the sliding surface  63  to the first header  74  through the inside of the inside die  71 . The second inside pipes  73  are also provided in the same number as the outside pipes  64  of the outside die  61  and run from the sliding surface  63  to the second header  75  through the inside of the inside die  71 . 
         [0059]    The first header  74 , as shown in  FIG. 7 , connects through the coolant feed pipe  45  to the coolant feed source  11  and therefore acts as a connecting part which is connected to the coolant feed source  11 . On the other hand, the second header  75  connects through the gas feed pipe  46  to the gas feed source  12  and therefore acts as a connecting part which is connected to the gas feed source  12 . The coolant feed pipe  45  is provided with the valve  47 , while the gas feed pipe  46  is provided with the valve  48 . The valve  47  and the valve  48 , in the same way as the first embodiment, are connected to the control unit  13 . The control unit  13  is used to operate the valve  47  and the valve  48  to open and close. 
         [0060]    The ends of the second inside pipes  73  at the sliding surface  63  sides are arranged so as to be aligned with the ends of the outside pipes  64  at the sliding surface  63  sides in the state where the outside die  61  is not pushed by the top die  21 . Conversely, the ends of the first inside pipes  72  at the sliding surface  63  sides are arranged so as not to be aligned with the ends of the outside pipes  64  at the sliding surface  63  sides in the state where the outside die  61  is not pushed by the top die  21 . Therefore, in the state where the outside die  61  is not pushed by the top die  21 , only the second inside pipes  73 , that is, only the gas feed source  12 , is connected to the outside pipes  64 . 
         [0061]    On the other hand, the ends of the first inside pipes  72  at the sliding surface  63  sides are arranged so as to be aligned with the ends of the outside pipes  64  at the sliding surface  63  sides in the state where the outside die  61  is pushed down to the bottom die limit by the top die  21 . Conversely, the ends of the second inside pipes  73  at the sliding surface  63  sides are arranged so as not to be aligned with the ends of the outside pipes  64  at the sliding surface  63  sides in the state where the outside die  61  is pushed down to the bottom die limit by the top die  21 . Therefore, in the state where the outside die  61  is pushed down to the bottom die limit by the top die  21 , only the first inside pipes  72 , that is, only the coolant feed source  11 , is connected to the outside pipes  64 . 
         [0062]    In other words, in the present embodiment, the outside die  61  and the inside die  71  slide relative to each other linked with the operation of the top die  21 . Due to this, it is possible to switch between a state where the outside pipes  64  are connected to the first inside pipes  72  and a state where they are connected to the second inside pipes  73 . Note that, when with just the metal surfaces sliding together, it is difficult to seal in the coolant against the pressure of the coolant, the ends of the inside pipes  72  and  73  at the sliding surface  63  sides or the ends of the outside pipes  64  at the sliding surface  63  sides may be provided with rubber rings or other seal members. 
         [0063]    Next, the method of using the thus configured hot press forming apparatus to hot press form steel sheet K will be explained. 
         [0064]    First, when starting the press forming of the steel sheet K, the valve  48  which is provided at the gas feed pipe  46  is closed and the valve  47  which is provided at the coolant feed pipe  45  is opened. At this time, the outside die  61  is not pushed by the top die  21 , and therefore is lifted by the elastic members  65 . Therefore, the outside pipes  64  are connected, with the second inside pipes  73 . For this reason, even if the valve  47  is opened, the coolant feed source  11  feeds coolant to the first inside pipes  72  at a predetermined pressure and does not feed coolant to the outside pipes  64 . In other words, the coolant which is fed to the first inside pipes  72  is stopped by the sliding surface  63  of the outside die  61  and is filled at a predetermined pressure to the ends of the first inside pipes  72 . On the other hand, the valve  48  is closed, and therefore even if the second inside pipes  73  and the outside pipes  64  are connected, the outside pipes  64  are not fed with gas. 
         [0065]    Next, a high temperature steel sheet K is placed by a conveyor apparatus (not shown) on the positioning pins  30  of the bottom die  60 . Next, the top die  21  is moved in the vertical direction so as to approach the bottom die  60  to, for example, as shown in  FIG. 8 , make it descend to the bottom die limit. Along with this, the steel sheet K and the outside die  61  of the bottom die  60  are pushed down in the vertical direction and the steel sheet K which is clamped between the top die  21  and the bottom die  60  is pressed. 
         [0066]    At this time, the outside die  61  is pushed down to the bottom die limit, whereby the outside pipes  64  of the outside die  61  are disconnected from the second inside pipes  73  of the inside die  71  and are connected to the first inside pipes  72 . Due to this, the coolant which had been filled to the end of the first inside pipes  72  is immediately fed from the outside pipes  64  to the steel sheet K. The steel sheet K starts to be rapidly cooled right after the steel sheet K is pressed. 
         [0067]    Further, if the outside die  61  is pushed down to the bottom die limit and thereby the outside pipes  64  and the second inside pipes  73  are disconnected, the valve  48  which is provided at the gas feed pipe  46  is opened. For this reason, the second inside pipes  73  are fed with gas of a predetermined pressure. In other words, the coolant which was fed to the second inside pipes  73  is stopped by the sliding surface  63  of the outside die  61  and is filled at a predetermined pressure to the ends of the second inside pipes  73 . 
         [0068]    Further, if the top die  21  is held at bottom die limit for a certain time and the steel sheet K is cooled down to a temperature of for example 200° C. or less, next, the top die  21  is risen to top dead center. If the top die  21  rises to top die limit, the outside die  61  which was pushed down to the bottom die limit is pushed vertically upward by the elastic members  65  which support the outside die  61 . As a result, the outside pipes  64  are disconnected from the first inside pipes  72  and are connected to the second inside pipes  73 . For this reason, the feed of coolant from the outside pipes  64  to the steel sheet K is immediately stopped. In addition, the gas which filled up to the ends of the second inside pipes  73  is immediately fed from the outside pipes  64  to the steel sheet K, and therefore gas starts to be blown to the steel sheet K immediately after stopping the feed of the coolant. At this time, the pressure etc. of the gas which is fed from the feed holes  64   a  are set in the same way as in the first embodiment. 
         [0069]    Further, when coolant finishes being removed from the surface of the steel sheet K by blowing gas to the surface of the steel sheet K, the shaped steel sheet K is removed by the conveyor apparatus (not shown) from the positioning pins  30  and is unloaded from the hot press forming apparatus. After this, a heated new steel sheet K is placed by the conveyor apparatus (not shown) on the positioning pins  30  of the hot press forming apparatus and this series of steps of the hot press forming operation are repeated. 
         [0070]    Next, the advantageous effects of the hot press forming die and hot press forming method according to the above embodiment will be explained. 
         [0071]    According to the present embodiment, the outside pipes  64  and the first inside pipes  72  and second inside pipes  73  are switched to be connected and disconnected by making the outside die  61  and the inside die  71  move relative to each other. Therefore, in the present embodiment, a fluid switching means for switching the fluid which is fed to the plurality of feed holes  64   a  between a coolant and gas can be said to be provided inside of the bottom die. For this reason, the outside pipes  64  and the first inside pipes  72  and second inside pipes  73  are switched to be connected and disconnected at positions close to the feed holes  64   a  which feed fluid (coolant and gas) to the steel sheet K. In other words, control may be performed to feed and stop the fluid at positions close to the forming surface  61   a  of the outside die  61 , that is, positions close to the steel sheet K to which the fluid is to be fed. 
         [0072]    For this reason, in the state where the second inside pipes  73  are closed by the sliding surface  63  of the outside die  61 , the gas is fed in advance to the second inside pipes  73  to fill the gas up to the ends of the second inside pipes  73 . After this, the outside die  61  can be pushed up to connect the outside pipes  64  and the second inside pipes  73 . Due to this, the gas which had been filled in the second inside pipes  73  can be quickly blown from the outside pipes  64  to the steel sheet K. Therefore, compared with the first embodiment, it is possible to more quickly blow gas to the surface of the steel sheet K after stopping the feed of coolant to the surface of the steel sheet K. 
         [0073]    Similarly, in the state where the first inside pipes  72  are closed by the sliding surface  63  of the outside die  61 , the coolant is fed in advance to the first inside pipes  72  to fill the coolant up to the ends of the first inside pipes  72 . After this, the outside die  61  can be pushed down to the bottom die limit to connect the outside pipes  64  and the first inside pipes  72 . Due to this, coolant which is filled in the first inside pipes  72  can be quickly blown from the outside pipes  64  to the steel sheet K. 
         [0074]    Further, for example, at the bottom die  60  which is shown in  FIG. 4 , for example, the total pipeline lengths from the valves  47  and  48  to the feed holes  41   a  closest to the valves  47  and  48  (feed holes at right side of  FIG. 4 ) and the total pipeline lengths to the feed holes  41   a  furthest from the valves  47  and  48  (feed holes at left side of  FIG. 4 ) greatly differ in length. For this reason, at the positions close to the valves  47  and  48  and the positions far from the valves  47  and  48 , the timings of start of cooling of the steel sheet K and the timings of start of blowing of gas to the steel sheet K differ. As opposed to this, in the hot press forming apparatus of the present embodiment, it is possible to obtain similar effects to the case where valves are provided at the ends of the outside pipes  64  at the sliding surface  63  sides, and therefore it is possible to make the differences in pipeline lengths extremely small compared with the bottom die  60  which is shown in  FIG. 4 . 
         [0075]    Note that, the outside pipes  64  of the outside die  61  are preferably the same in pipeline lengths. By making the outside pipes  64  the same in pipeline lengths, the times from connection of the outside pipes  64  and the inside pipes  72  and  73  to the start of feed of coolant or gas to the steel sheet K become the same. In this case, it is possible to make the timings of start of cooling and the timings of start of blowing of gas uniform over the surface of the steel sheet K. As a result, the hardness of the steel sheet K after hot press forming can be uniform over the surface. 
         [0076]    Note that, the bottom die  60  of the second embodiment can be changed in various ways. Below, modifications of the bottom die  60  are shown. 
         [0077]    In the above embodiments, the outside die  61  which is supported by the elastic members  65  is pushed down by the top die  21  whereby the outside die  61  is slid against the inside die  71 . However, if the outside die  61  and the inside die  71  can be slid relative to each other, the inside die  71  can be slid and, further, both the outside die  61  and the inside die  71  can be slid. When making the inside die  71  side, for example as shown in  FIG. 9 , the outside die  61  may be directly arranged on the top surface of the base  22  and the inside die  71  may for example be slide by an actuator or other drive mechanism  80  in the up-down direction. In this case, the timing of ending the press operation of the steel sheet K and the timing of start of feed of the coolant can be separately controlled. 
         [0078]    Further, when using the drive mechanism  80 , the state where the ends of the outside pipes  64  at the sliding surface  63  sides are connected with the first inside pipes  72 , the state where the ends of the outside pipes  64  at the sliding surface  63  sides are connected with the second inside pipes  73 , and, in addition, the state where the ends of the outside pipes  64  at the sliding surface  63  sides are not connected to either the first inside pipes  72  and second inside pipes  73  (that is, the state where the ends of the outside pipes  64  at the sliding surface  63  sides face the inside wall surface of the inside die  71 ) can be switched between. In this case, the valves  47  and  48  no longer need be provided. 
         [0079]    Further, in the above embodiments, the dies  61  and  71  were slid in the up-down direction to connect the outside pipes  64  and the inside pipes  72  and  73 . However, the arrangements of the pipes  64 ,  72 , and  73  and the directions of relative sliding of the dies  61  and  71  are not limited to those of the present embodiments and can be freely set. For example, when making the dies  61  and  71  slide in the horizontal direction, as shown in  FIG. 10 , it is possible to arrange the outside die  61  and the inside die  71  offset in the horizontal direction and shift the inside pipes  72  and  73  from the corresponding outside pipes  64  in the horizontal direction. Further, for example, it is possible to slide the inside die  71  in the horizontal direction by the horizontal movement mechanism  85  so as to connect the first inside pipes  72  and the outside pipes  64  or connect the second inside pipes  73  and the outside pipes. Further, for example, it is possible to make the inside die  71  substantially cylindrical in shape and to slide the inside die  71  in the circumferential direction so that the inside pipes  72  and  73  and the outside pipes  64  are connected. 
         [0080]    Alternatively, as shown in  FIG. 11 , the inside die  71  need not be provided with the second inside pipes  73  and second header  75  and may be provided with only the first inside pipes  72  and first header  74 . In this case, the first header  74 , in the same way as the header  40  of the first embodiment, may be connected to both the coolant feed source  11  and gas feed source  12 . When configuring the inside die  71  in this way, the feed of coolant is started by using the drive mechanism  80  to slide the inside die  71  with respect to the outside die  61 , but the feed of gas is started by controlling the operation of the valves  47  and  48 . 
         [0081]    Note that, in the above embodiments, the bottom die  60  was configured by an outside die  61  and an inside die  71 , but the top die  21  may be configured by an outside die and inside die. Alternatively, both the bottom die  60  and the top die  21  may be configured by outside dies and inside dies. Further, the die comprised of the outside die and inside die may be used for either the projecting die and recessed die which are used for press forming or may be used for both of the projecting die and recessed die. 
         [0082]    Further, in the above embodiments, the inside die  71  was provided with only a single header for each kind of fluid, but it is also possible to provide a plurality of headers for each kind of fluid. In this case, for example, taking a coolant as an example, when stopping the feed of coolant to one part of the headers, it is possible to stop the feed of coolant from the first inside pipes  72  and outside pipes  64  which are connected to the first headers  74  to which feed has been stopped, and continue the feed of coolant from the remaining first inside pipes  72  and outside pipes  64 . That is, it is possible to selectively stop the feed of coolant. Due to this, it is possible to control the portions of the steel sheet K which are fed with coolant and change the hardness in the plane of the steel sheet K. 
         [0083]    Further, in the above embodiments, the hot press forming operation of the steel sheet K as explained, but the invention can also be used for hot press forming a metal sheet other than steel sheet. 
         [0084]    Note that, the present invention was explained in detail based on specific embodiments, but a person skilled in the art can make various changes, corrections, etc. without departing from the claims and concept of the present invention. 
       INDUSTRIAL APPLICABILITY 
       [0085]    The present invention is useful when hot press forming steel sheet. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  hot press forming apparatus 
           10  hot press forming die 
           11  coolant feed source 
           12  gas feed source 
           13  control unit 
           20  bottom die 
           20   a  forming surface 
           21  top die 
           22  base 
           23  lift mechanism 
           30  positioning pin 
           40  header 
           41  pipe 
           42  projection 
           60  bottom die 
           61  outside die 
           63  sliding surface 
           64  outside pipe 
           71  inside die 
           72  first inside pipe 
           73  second inside pipe 
           74  first header 
           75  second header 
         K steel sheet 
         P prepierced hole

Technology Classification (CPC): 2