Patent Application
20240261841
The present disclosure relates to a hot press device configured such that a formed product that is obtained in a forming area and is in a high temperature state is held under pressure, cooled, and thereby hardened, in a cooling die set in a cooling area.
Conventionally, hot press forming using a hot press device is known as a forming method for obtaining a high-strength formed product without increasing the thickness of the sheet. For example, a hot press device as disclosed in Patent literature 1 includes a forming die set within which liquid coolant flows through, and is configured such that when the forming die set moves to close, a steel sheet in a high temperature state is drawn to obtain a formed product, and the formed product is held under pressure, cooled, and thereby hardened, in the state where the forming die set is closed. The forming die set includes an upper die having a pressing surface in which a plurality of cooling grooves are formed. When the liquid coolant fills spaces between a surface of the formed product held under pressure and the cooling grooves in the state where the forming die set is closed, the liquid coolant thereby directly cools the formed product, and the rate of cooling the formed product is improved during the hardening.
[Patent Literature 1] Japanese Laid-Open Patent Publication No. 2018-012113
In this respect, when the cooling grooves are provided in the pressing surface of the forming die set as described in Patent literature 1, the cooling grooves may be transferred to the surface of the formed product to have grooved shapes on the surface of the formed product as the steel sheet is at high temperatures and softened during forming in hot press forming, and thus, desired accuracy of the surface of the formed product may not be able to be ensured.
To avoid this phenomenon, it can be considered that the accuracy of the surface of the formed product is ensured such that a cooling area is provided separately of the forming area, and a primary formed product that is obtained in the forming area and is in a high temperature state is held under pressure and cooled in a cooling die set placed in the cooling area to thereby obtain a hardened final formed product.
In this respect, when the cooling area is separately provided for hot press forming, the primary formed product in the high temperature state which is transferred from the forming area to the cooling area is necessary to be mounted firstly on a pressing surface of a lower die of the cooling die set that is opened, and thus the lower die of the cooling die set is more likely to be at increased temperatures than the upper die. Thus, for example, when the hot press forming is repeatedly performed, the lower die of the cooling die set is kept at higher temperatures and the liquid coolant cools not only the primary formed product but the lower die during the hardening. This may result in significant decrease in the rate of cooling the primary formed product during the hardening and adversely affect the strength of the final formed product.
The present disclosure is made in view of the foregoing and an object of the present disclosure is to provide a hot press device that improves a rate of cooling a formed product while ensuring the accuracy of a surface of the formed product, and that is further capable of reducing an increase in temperature of a lower die of a cooling die set to obtain the formed product appropriately hardened.
To achieve the object, the present disclosure is characterized by using liquid coolant in a liquid reservoir provided in a lower cooling die in order to cool the lower cooling die.
Specifically, the present disclosure is directed to a hot press device configured such that a primary formed product that is obtained in a forming area and is in a high temperature state is held under pressure and cooled on respective pressure-holding surfaces of an upper die and a lower die in a cooling die set to thereby obtain a hardened final formed product, and the following aspects are then applied.
According to a first aspect of the present disclosure, the lower die includes a liquid reservoir for retaining liquid coolant.
According to a second aspect of the present disclosure which is an embodiment of the first aspect, at least one of the upper die or the lower die includes a liquid supply portion for depositing the liquid coolant on the primary formed product held under pressure, and a first liquid reservoir is provided in the lower die as the liquid reservoir, the first liquid reservoir configured to collect and retain the liquid coolant deposited from the liquid supply portion on the primary formed product.
According to a third aspect of the present disclosure which is an embodiment of the second aspect, the first liquid reservoir includes a cooling opening that is open at the pressure-holding surface of the lower die for the primary formed product, and the liquid supply portion includes a jetting nozzle disposed in the first liquid reservoir, and is configured such that the liquid coolant jetted from the jetting nozzle is sprayed via the cooling opening onto the primary formed product held under pressure, or that compressed air jetted from within the liquid coolant retained in the first liquid reservoir by the jetting nozzle passes through a surface of the liquid coolant so that the liquid coolant is scattered and sprayed via the cooling opening onto the primary formed product held under pressure.
According to a fourth aspect of the present disclosure which is an embodiment of the second or third aspect, the upper die includes a cooling recess that is open at the pressure-holding surface of the upper die for the primary formed product, and the liquid supply portion is capable of supplying the liquid coolant to the cooling recess.
According to a fifth aspect of the present disclosure which is an embodiment of the fourth aspect, the cooling recess is provided at a location corresponding to the pressure-holding surface of the lower die, and the first liquid reservoir is provided at a location corresponding to the pressure-holding surface of the upper die.
According to a sixth aspect of the present disclosure which is an embodiment of the fourth or fifth aspect, a plurality of upper cooling grooves are formed in the pressure-holding surface of the upper die, and the upper cooling grooves each having an end portion that is open to the cooling recess.
According to a seventh aspect of the present disclosure which is an embodiment of any one of the second to sixth aspects, a plurality of lower cooling grooves are formed in the pressure-holding surface of the lower die, and the lower cooling grooves each having an end portion that is open to the first liquid reservoir.
According to an eighth aspect of the present disclosure which is an embodiment of the seventh aspect, a second liquid reservoir is provided in an outer region of the first liquid reservoir of the lower die as the liquid reservoir, the second liquid reservoir extending to surround the first liquid reservoir and being capable of retaining the liquid coolant, and the second liquid reservoir configured such that when an amount of the liquid medium retained in the first liquid reservoir increases, the liquid coolant moves via the lower cooling grooves to the second liquid reservoir and is retained in the second liquid reservoir.
According to a ninth aspect of the present disclosure which is an embodiment of the first aspect, a third liquid reservoir is provided in the lower die as the liquid reservoir, the third liquid reservoir being open upward and capable of retaining the liquid coolant, and the pressure-holding surface of the lower die is located on an inner side of the third liquid reservoir , and an outer wall of the third liquid reservoir includes a volume varying wall, and the volume varying wall includes an upper end provided at a level higher than the pressure-holding surface of the lower die, and the volume varying wall is configured to move in a horizontal direction to vary a retaining volume of the third liquid reservoir.
According to a tenth aspect of the present disclosure which is an embodiment of the ninth aspect, the volume varying wall is configured to move toward or away from the pressure-holding surface of the lower die to vary the retaining volume of the third liquid reservoir.
According to an eleventh aspect of the present disclosure which is an embodiment of the tenth aspect, a lower sloping surface is formed on a side of the volume varying wall opposite the third liquid reservoir, the lower sloping surface inclined to extend progressively away from the third liquid reservoir toward a lower portion, and an upper sloping surface is formed at a location of the upper die corresponding to the volume varying wall, the upper sloping surface inclined to correspond to the lower sloping surface, and configured such that when the upper die is moved downward with respect to the lower die, the upper sloping surface makes sliding contact with the lower sloping surface to press the volume varying wall toward a pressure-holding surface side of the lower die to move the volume varying wall toward the pressure-holding surface of the lower die.
According to a twelfth aspect of the present disclosure which is an embodiment of any one of the ninth to eleventh aspects, a recess that is open upward is provided in the pressure-holding surface of the lower die as the liquid reservoir.
According to a thirteenth aspect of the present disclosure which is an embodiment of the twelfth aspect, a communication passage is formed in the lower die, the communication passage configured to provide communication of an inner space of the recess with the third liquid reservoir.
According to a fourteenth aspect of the present disclosure which is an embodiment of the first aspect, the lower die includes a lower recess as the liquid reservoir, a first cylinder portion, and a first communication passage, the lower recess being open at a location corresponding to the pressure-holding surface of the lower die, the first cylinder portion including a first cylinder chamber in which a first piston is housed such that the first piston is reciprocally movable, and the first communication passage configured to provide communication of the first cylinder chamber with the lower recess, the first cylinder chamber includes a first reservoir chamber as the liquid reservoir, the first reservoir chamber bounded by the first piston, associated with the first communication passage, and configured to retain the liquid coolant.
According to a fifteenth aspect of the present disclosure which is an embodiment of the fourteenth aspect, the first cylinder chamber is open upward, the first piston is configured to be reciprocally movable in a vertical direction, the first reservoir chamber is located under the first piston, and a first pressing portion is provided at a location of the upper die corresponding to the first piston, the first pressing portion configured to push the first piston downward as the upper die is moved downward.
According to a sixteenth aspect of the present disclosure which is an embodiment of the fourteenth or fifteenth aspect, the upper die includes an upper recess, a second cylinder portion, and a second communication passage, the upper recess being open at a location corresponding to the pressure-holding surface of the upper die, the second cylinder portion including a second cylinder chamber in which a second piston is housed such that the second piston is reciprocally movable, and the second communication passage configured to provide communication of the second cylinder chamber with the upper recess, a second reservoir chamber is formed in the second cylinder chamber, the second reservoir chamber bounded by the second piston, associated with the second communication passage, and configured to retain the liquid coolant.
According to a seventeenth aspect of the present disclosure which is an embodiment of the sixteenth aspect, the second cylinder chamber is open downward, the second piston is configured to be reciprocally movable in a vertical direction, the second reservoir chamber is located over the second piston, and a second pressing portion is provided at a location of the lower die corresponding to the second piston, the second pressing portion configured push the second piston upward as the upper die is moved downward.
According to an eighteenth aspect of the present disclosure which is an embodiment of the seventeenth aspect, the first pressing portion includes a lower end portion of the second piston, and the second pressing portion includes an upper end portion of the first piston.
According to a nineteenth aspect of the present disclosure which is an embodiment of the eighteenth aspect, a first biasing member is provided in the first reservoir chamber, the first biasing member configured to press the first piston in a direction in which a retaining volume of the first reservoir chamber increases, a second biasing member is provided in the second reservoir chamber, the second biasing member configured to press the second piston in a direction in which a retaining volume of the second reservoir chamber increases, and the first elastic member has smaller biasing force than the second elastic member.
According to a twelfth aspect of the present disclosure which is an embodiment of the nineteenth aspect, a fourth liquid reservoir capable of retaining the liquid coolant is further included, and a third communication passage is formed in the upper die, the third communication passage configured to provide communication of the second reservoir chamber with the fourth liquid reservoir.
In the first aspect, the liquid coolant retained in the liquid reservoir takes the heat from the lower die of the cooling die set to cool the lower die so that an increase in the temperature of the lower die can be effectively reduced. Thus, the cooling of the lower die is performed by using the liquid coolant during hardening, and thereby, a decrease in the rate of cooling the primary formed product can be reduced. Further, the cooling grooves in the forming die set as described in Patent literature 1 thus do not need to be provided, and this allows avoidance of the situation where the accuracy for the surface of the formed product is unable to ensure in hot press forming.
In the second aspect, the liquid coolant supplied from the liquid supply portion is directly deposited on the primary formed product in a high temperature state so that a larger amount of the heat is lost from the primary formed product to the liquid coolant. Therefore, the cooling of the primary formed product is efficiently performed and the rate of cooling the primary formed product can be improved during the hardening. Also, the liquid coolant is collected and retained in the first liquid reservoir after cooling the primary formed product, and thus, the liquid coolant retained in first liquid reservoir takes the heat from the lower die to cool the lower die. Thus, the liquid coolant retained in the first liquid reservoir after cooling the primary formed product can be reused to cool the lower die of the cooling die set so that an increase in the temperature of the lower die of the cooling die set can be effectively reduced. Further, the cooling grooves in the forming die set as described in Patent literature 1 thus do not need to be provided, and this allows avoidance of the situation where the accuracy for the surface of the formed product is unable to ensure in hot press forming.
In the third aspect, the liquid coolant upwardly makes direct contact with the primary formed product being in the high temperature state and held under pressure in the cooling die set, so that the liquid coolant hitting a back surface of the primary formed product absorbs the heat from the formed product in the high temperature state and is vaporized in the first liquid reservoir. Thus, the heat of vaporization generated by vaporizing the liquid coolant can be used to improve the rate of cooling the primary formed product. Also, the liquid coolant splashed off from the back surface of the primary formed product is collected and retained in the first liquid reservoir via the cooling opening, and thus, the liquid coolant used for cooling the primary formed product can be reused to cool the lower die, so that the lower die of the cooling die set can be efficiently cooled.
In the fourth aspect, when the liquid coolant is supplied to the cooling recess in the state where the cooling die set is closed, the liquid coolant is supplied to a space formed between a front surface of the primary formed product under the pressure and the cooling recess to make contact with the front surface of the primary formed product in the high temperature state. Thus, the liquid coolant made contact with the front surface of the primary formed product takes the heat from the primary formed product in the high temperature state and is vaporized, and by using the heat of vaporization, the rate of cooling the primary formed product can be efficiently improved.
In the fifth aspect, the liquid coolant directly, uniformly, cools different regions of the front and back surface sides of the primary formed product held under pressure in the cooling die set, so that the rate of cooling the formed product is prevented from varying from one region to another during the hardening and appropriate hardening can be performed.
In the sixth aspect, when the amount of the liquid coolant deposited on the front surface of the primary formed product held under pressure is increased in the cooling recess, the liquid coolant flowing out from the cooling recess along the front surface of the primary formed product then fills spaces formed between the front surface of the primary formed product held under pressure, and the upper cooling grooves. Thus, the liquid coolant after directly cooling the front surface of the primary formed product in the cooling recess is used again to directly cool the primary formed product so that the primary formed product can be efficiently cooled.
In the seventh aspect, when the amount of the liquid coolant retained in the first liquid reservoir increases, the liquid coolant overflowing from the first liquid reservoir fills spaces formed between the back surface of the primary formed product held under pressure in the cooling die set, and the lower cooling grooves. Thus, the liquid coolant retained in the first liquid reservoir is used again to directly cool the primary formed product so that the primary formed product can be efficiently cooled.
In the eighth aspect, when the amount of the liquid coolant retained in the first liquid reservoir increases, the liquid coolant flows into the second liquid reservoir via the lower cooling grooves to be retained in the second liquid reservoir. Thus, the liquid coolant directly cools the primary formed product as passing through the lower cooling grooves, and thereafter, is further reused in the second liquid reservoir for cooling the lower die, so that the lower die of the cooling die set can be efficiently cooled.
In the ninth aspect, when the volume varying wall moves to reduce the third retaining volume of the liquid reservoir, the level of the liquid coolant retained in the third liquid reservoir gradually increases and becomes higher than the pressure-holding surface of the lower die of the cooling die set, and the liquid coolant thus flows toward the pressure-holding surface side of the lower die, so that the pressure-holding surface is immersed in the liquid coolant. Thus, the primary formed product in the high temperature state which is mounted on, or held under pressure on, the pressure-holding surface of the lower die of the cooling die set is immersed in the liquid coolant, and hence the liquid coolant directly takes the heat from the primary formed product, so that the rate of cooling the primary formed product can be increased during the hardening. The liquid coolant retained in the third liquid reservoir also takes the heat from the lower die of the cooling die set to cool the lower die so that an increase in the temperature of the lower die can be effectively reduced. Further, the cooling grooves in the forming die set as described in Patent literature 1 thus do not need to be provided, and this allows avoidance of the situation where the accuracy for the surface of the formed product is unable to be ensured during hot press forming as a result of providing the cooling grooves.
In the tenth aspect, when the volume varying wall moves toward the pressure-holding surface of the lower die, a wave of the liquid coolant from a volume varying wall side toward the pressure-holding surface side of the lower die is formed near the surface of liquid in the third liquid reservoir. When the wave of the liquid coolant reaches the primary formed product in the high temperature state, which is mounted on, or held under pressure on, the pressure-holding surface of the lower die of the cooling die set, the wave of the liquid coolant spreads to cover over the entire front surface of the primary formed product so that the liquid coolant directly contacts the front surface of the primary formed product. Thus, the liquid coolant directly takes the heat from the primary formed product to efficiently cool the primary formed product so that the rate of cooling the primary formed product can be improved during the hardening.
In the eleventh aspect, the level of the liquid coolant in the third liquid reservoir can increase synchronously as the upper die of the cooling die set is moved downward, so that the state of holding the primary formed product under pressure in the cooling die set and the state of immersing the primary formed product in the liquid coolant are enabled simultaneously or with a relatively small time difference. Thus, this can reduce the time during which the primary formed product in the high temperature state is mounted on, or held under pressure on, the pressure-holding surface of the lower die of the cooling die set without being immersed in the liquid coolant, so that heat transfer from the primary formed product in the high temperature state to the pressure-holding surface of the lower die can be reduced to lower an increase in the temperature of the lower die of the cooling die set. Also, the volume varying wall can be moved by using the downward movement of the upper die, and thus a cost increase caused by separately including a driving source for moving the volume varying wall can be avoided.
In the twelfth aspect, the area of the pressure-holding surface in the lower die of the cooling die set is smaller due to the provided opening region of the recess so that the amount of heat transfer to the pressure-holding surface from the primary formed product in the high temperature state which is mounted on, or held under pressure on, the pressure-holding surface of the lower die can be reduced to lower an increase in the temperature of the lower die of the cooling die set.
In the thirteenth aspect, when the volume varying wall moves to reduce the retaining volume of the third liquid reservoir, the liquid coolant flows from the third liquid reservoir via the communication passage to a space formed between the recess and the back surface of the primary formed product mounted on, or held under pressure on, the pressure-holding surface of the lower die of the cooling die set so that the liquid coolant flowing in fills the space. Thus, the liquid coolant directly contacts the back surface of the primary formed product in the high temperature state, and a larger amount of the heat is lost from the primary formed product in the high temperature state to the liquid coolant, so that the rate of cooling the primary formed product can be further improved.
In the fourteenth aspect, when the first piston moves through the first cylinder chamber in a direction in which the retaining volume of the first reservoir chamber decreases, the liquid coolant retained in the first reservoir chamber is pushed by the first piston to flow into the lower recess via the first communication passage. The level of the liquid coolant in the lower recess then increases and thus, the pressure-holding surface of the lower die, and the primary formed product in the high temperature state which is mounted on, or held under pressure on, the pressure-holding surface are immersed in the liquid coolant. Thus, the liquid coolant directly takes the heat from the primary formed product so that the rate of cooling the primary formed product can be improved during the hardening. The liquid coolant retained in the first reservoir chamber also takes the heat from the lower die of the cooling die set to cool the lower die so that an increase in the temperature of the lower die can be effectively reduced. Further, the cooling grooves in the forming die set as described in Patent literature 1 thus do not need to be provided, and this allows avoidance of the situation where the accuracy for the surface of the formed product is unable to be ensured during hot press forming as a result of providing the cooling grooves.
In the fifteenth aspect, the first piston moves downward to reduce the retaining volume of the first reservoir chamber synchronously as the upper die of the cooling die set is moved downward, and hence the liquid coolant retained in the first reservoir chamber can move to the lower recess to increase the level of the liquid coolant retained in the lower recess. Thus, this enables the state of holding the primary formed product under pressure in the cooling die set and the state of immersing the primary formed product in the liquid coolant, simultaneously or with a relatively small time difference, and allows reduction of the time during which the primary formed product in the high temperature state is mounted on, or held under pressure on, the pressure-holding surface of the lower die of the cooling die set without being immersed in the liquid coolant. The heat transfer from the primary formed product in the high temperature state to the pressure-holding surface of the lower die is thus reduced so that an increase in temperature of the lower die of the cooling die set can be reduced. Also, the first piston can be moved by using the downward movement of the upper die, and thus a cost increase caused by separately including a driving source for moving the first piston can be avoided.
In the sixteenth aspect, when the second piston moves through the second cylinder chamber in a direction in which the retaining volume of the second reservoir chamber decreases, the liquid coolant retained in the second reservoir chamber is pushed out by the second piston to flow into the upper recess via the second communication passage. The liquid coolant then falls through the opening of the upper recess to contact the front surface of the primary formed product being in the high temperature state and mounted on, or held under pressure on, the pressure-holding surface of the lower die of the cooling die set. Thus, the liquid coolant contacting the front surface of the primary formed product directly takes the heat of the primary formed product in the high temperature state so that the rate of cooling the primary formed product can be further improved during the hardening.
In the seventeenth aspect, the second piston moves upward to reduce the retaining volume of the second reservoir chamber synchronously as the upper die of the cooling die set is moved downward, and hence the liquid coolant retained in the second reservoir chamber moves to the upper recess to fall via the opening of the upper recess toward the front surface of the primary formed product in the high temperature state which is mounted on, or held under pressure on, the pressure-holding surface of the lower die of the cooling die set, so that the liquid coolant poured onto the primary formed product can efficiently cool the front surface of the primary formed product in the high temperature state. Also, the second piston can be moved by using the downward movement of the upper die, and thus a cost increase caused by separately including a driving source for moving the second piston can be avoided.
In the eighteenth aspect, the second piston is moved by using the first piston configured to control the movement of the liquid coolant in the lower die, and the first piston is moved by using the second piston configured to control the movement of the liquid coolant in the upper die, and thus there is no need to separately provide pressing structures only for moving the first piston and the second piston, so that the number of parts is reduced to keep manufacturing cost under control, and a horizontal increase in size of the cooling die set by providing pressing structures in a region exclusive of the both pistons can be reduced.
In the nineteenth aspect, when the upper die of the cooling die set s moved downward, the second piston starts to move later than the first piston in the direction in which the retaining volume of the second reservoir chamber decreases, and the cooling of the back surface of the primary formed product due to the increased level of the liquid coolant in the lower recess and the cooling of the front surface of the primary formed product by the liquid coolant supplied via the lower opening of the upper recess are thus enabled simultaneously or with a relatively small time difference, so that the front and back surfaces of the primary formed product are uniformly cooled and the rate of cooling the entire primary formed product can be improved.
In the twelfth aspect, when the upper die of the cooling die set is moved upward, the second piston moves by means of the biasing force of the second biasing member in the direction in which the retaining volume of the second reservoir chamber increases, so that a negative pressure is generated in the second reservoir chamber. The negative pressure then causes part of the liquid coolant flowing out from the second reservoir chamber to the second communication passage to return to the second reservoir chamber, and brings the liquid coolant to flow from the fourth liquid reservoir via the third communication passage into the second reservoir chamber, so that the second reservoir chamber is filled with the liquid coolant. Thus, even when the upper die of the cooling die set repeatedly performs the upward and downward movements, the second reservoir chamber is constantly filled with the liquid coolant. This can reduce a decrease in the rate of cooling the front surface of the primary formed product by means of the liquid coolant, as a result of a reduced amount of the liquid coolant flowing out from the second reservoir chamber when the upper die of the cooling die set is moved downward.
First, second, and third embodiments of the present disclosure are described in detail below with reference to the drawings. It is noted that the following description of preferred first, second, and third embodiments is merely an example in nature.
A heating furnace 20 of a far-infrared rays type is placed in the heating area 2, and includes a lower furnace body 20a that is mounted on a floor, and an upper furnace body 20b that is placed above and opposite the lower furnace body 20a.
A heater (not shown) configured to increase the temperature of atmospheric gas between the upper furnace body 20b and the lower furnace body 20a is attached to the upper furnace body 20b to heat the steel sheet S for a predetermined heating time to increase its temperature to about 900° C., which is a predetermined hardening temperature.
A first robot R1 is disposed between the heating area 2 and the forming area 3, and configured to transport to the forming area 3 the steel sheet S having its temperature increased in the heating furnace 20 and being in a high temperature state.
The forming area 3 includes a forming die set 30 for hot press forming, and a mechanical press machine 5.
The forming die set 30 includes an upper forming die 31 and a lower forming die 32 facing each other, and the upper forming die 31 is configured to move upward and downward with respect to the lower forming die 32 by means of the mechanical press machine 5.
A first pressing surface 31a recessed upward to have a generally concave cross section is formed on the upper forming die 31, and a second pressing surface 32a bulging upward to have a generally convex cross section is formed on the lower forming die 32.
When the steel sheet S in the state where its temperature is increased to the hardening temperature is placed on the second pressing surface 32a of the lower forming die 32 and thereafter, the upper forming die 31 is moved downward to close the forming die set 30, the primary formed product P having a generally hat-shaped cross section can be then obtained from the steel sheet S.
A second robot R2 is disposed between the forming area 3 and the hardening area 4, and configured to transport to the hardening area 4 the primary formed product P obtained in the forming area 3.
A cooling die set 40 for hardening, and a servo press machine 6, are placed in the hardening area 4, the cooling die set 40 including an upper cooling die 41 and a lower cooling die 42 facing each other, and the servo press machine 6 configured to move the upper cooling die 41 upward and downward with respect to the lower cooling die 42.
As shown in
A first jetting nozzle 51 (liquid supply portion) is attached generally in a middle of a ceiling surface 43a of each cooling recess 43, and is capable of jetting liquid coolant (for example, industrial water) to supply the liquid coolant in the cooling recess 43.
On the other hand, a lower pressure-holding surface 42a bulging upward to have a generally convex cross section is formed on the lower cooling die 42. A plurality of first liquid reservoirs 44 are provided at locations of the lower pressure-holding surface 42a corresponding to the respective cooling recesses 43 of the upper cooling die 41, and are each recessed downward to be concave, and have a lower cooling opening 44b that is open at the lower pressure-holding surface 42a.
A second jetting nozzle 52 (liquid supply portion) is attached generally in a middle of a bottom surface 44a of each first liquid reservoir 44, and is capable of jetting liquid coolant toward the lower cooling opening 44b. The first liquid reservoir 44 is capable of retaining the liquid coolant jetted from the second jetting nozzle 52.
A second liquid reservoir 45 is provided in an outer region of the first liquid reservoir 44 of the lower cooling die 42, is open upward to be recessed, extends to surround the first liquid reservoir 44, and is capable of retaining the liquid coolant.
A plurality of cooling grooves 46 (lower cooling grooves) are formed in regions of the lower pressure-holding surface 42a of the lower cooling die 42 exclusive of the lower cooling openings 44b, and extend in a direction of a row of the first and second liquid reservoirs 44, 45, and are open upward.
That is, the cooling grooves 46 are each open at the lower pressure-holding surface 42a and have end portions being open to the first liquid reservoir 44 or the second liquid reservoir 45. Adjacent two first liquid reservoirs 44 or adjacent first and second liquid reservoirs 44, 45 are thus in communication with one another via the cooling grooves 46.
An outer wall 47 forming the second liquid reservoir 45 includes an upper end face 47a that is provided at a height generally same as that of a bottom surface 46a of the cooling groove 46.
A liquid coolant pump 10 is placed laterally outward of the lower cooling die 42 and is capable of pressure feeding the liquid coolant.
An inlet line L1 is provided on an upstream side of the liquid coolant pump 10, and has one end connected to an inlet port 10a of the liquid coolant pump 10 and another end connected to a liquid coolant supply source (not shown). The inlet line L1 is configured to introduce the liquid coolant stored in the liquid coolant supply source, via the inlet port 10a, into the liquid coolant pump 10, when the liquid coolant pump 10 is driven.
A first supply line L2 is provided on a downstream side of the liquid coolant pump 10, and has one end connected to the first jetting nozzles 51 and another end connected to an outlet port 10b of the liquid coolant pump 10.
The first supply line L2 includes a channel provided between the outlet port 10b and the upper cooling die 41, and a communication hole connecting the channel and the first jetting nozzle 51 and formed inside the upper cooling die 41. The first supply line L2 is configured to pressure feed the liquid coolant discharged from the outlet port 10b, to the first jetting nozzles 51, when the liquid coolant pump 10 is driven.
A second supply line L3 is also provided on the downstream side of the liquid coolant pump 10, and has one end connected to the second jetting nozzles 52 and another end connected to the outlet port 10b.
The second supply line L3 includes a channel provided between the outlet port 10b and the lower cooling die 42, and a communication hole connecting the channel and the second jetting nozzle 52 and formed inside the lower cooling die 42. The second supply line L3 is configured to pressure feed the liquid coolant discharged from the outlet port 10b, to the second jetting nozzles 52, when the liquid coolant pump 10 is driven.
When the primary formed product P obtained in the forming area 3 and being in a high temperature state is mounted on the lower pressure-holding surface 42a of the lower cooling die 42 that is opened, and the upper cooling die 41 is then moved downward to close the cooling die set 40, the primary formed product P is thereby held under pressure by the upper pressure-holding surface 41a and the lower pressure-holding surface 42a.
When the liquid coolant is supplied from the liquid coolant pump 10 to the cooling die set 40 in the state where the primary formed product P is held under pressure in the cooling die set 40, the primary formed product P is then cooled by the cooling die set 40 cooled by means of the liquid coolant, and is also cooled by the liquid coolant sprayed from the first jetting nozzles 51 via the upper cooling openings 43b, and by the liquid coolant sprayed from the second jetting nozzles 52 via the lower cooling openings 44b, and is thus hardened, and the vehicle frame F serving as the final formed product is obtained.
As shown in
Next, a method for hardening using the cooling die set 40 in the harden area 4 is described in detail with respect to
First, once a primary formed product P is formed in the forming die set 30, the primary formed product P is transported by using the second robot R2 to mount on the lower pressure-holding surface 42a of the lower cooling die 42 that is opened, as shown in
Next, the upper cooling die 41 is moved downward to close the cooling die set 40 as shown in
Thereafter, the liquid coolant pump 10 is driven to send the liquid coolant to the first jetting nozzles 51 and the second jetting nozzles 52. The liquid coolant is then jetted from the first jetting nozzles 51 and the second jetting nozzles 52 toward the primary formed product P held under pressure by the upper cooling die 41 and the lower cooling die 42.
The liquid coolant jetted from the first jetting nozzles 51 is directly deposited on a front surface of the primary formed product P to absorb the heat primarily from a front surface side of the primary formed product P. On the other hand, the liquid coolant jetted from the second jetting nozzles 52 is directly deposited on a back surface of the primary formed product P to absorb the heat primarily from a back surface side of the primary formed product P.
In this instance, the liquid coolant deposited on the primary formed product P is vaporized in insides of the cooling recesses 43 and insides of the first liquid reservoirs 44. In so doing, the heat of vaporization generated by the vaporization is used to perform the cooling of the primary formed product P.
The liquid coolant jetted from the second jetting nozzles 52 is deposited on the back surface of the primary formed product P to use for cooling the primary formed product P, and thereafter falls from the back surface of the primary formed product P, and is collected and retained into the first liquid reservoirs 44 via the lower cooling openings 44b.
Part of the liquid coolant jetted from the second jetting nozzles 52 then hits the back surface of the primary formed product P to use for cooling the primary formed product P, and is thereafter splashed off to be collected and retained into the first liquid reservoirs 44 via the lower cooling openings 44b.
The liquid coolant retained in the first liquid reservoirs 44 directly absorbs the heat from a body portion of the lower cooling die 42. Thus, the liquid coolant used for directly cooling the primary formed product P is reused to cool the lower cooling die 42.
Thereafter, when the primary formed product P is continued to be cooled and a certain period of time has passed, the amount of the liquid coolant retained in the first liquid reservoirs 44 increases. As shown in
Further, when the amount of the liquid coolant in the first liquid reservoirs 44 increases, the liquid coolant flows into the second liquid reservoir 45 via the cooling grooves 46 to be retained in the second liquid reservoir 45, as shown in
The liquid coolant retained in the second liquid reservoir 45 absorbs the heat directly from the body portion of the lower cooling die 42. Thus, the liquid coolant used in the cooling grooves 46 for directly cooling the primary formed product P is reused to cool the lower cooling die 42.
Thereafter, the cooling die set 40 is opened and the hardened vehicle frame F is removed by the third robot R3 to be transported to a next area.
According to the first embodiment of the present disclosure, the liquid coolant supplied from the first jetting nozzles 51 and the second jetting nozzles 52 is directly deposited on the primary formed product P in the high temperature state so that a larger amount of the heat is lost from the primary formed product P to the liquid coolant. Thus, the cooling of the primary formed product P is efficiently performed and the rate of cooling the primary formed product P can be improved during the hardening.
Also, the liquid coolant is collected and retained in the first liquid reservoirs 44 after cooling the primary formed product P, and thus, the liquid coolant retained in first liquid reservoirs 44 takes the heat from the lower cooling die 42 to cool the lower cooling die 42. Thus, the liquid coolant retained in the first liquid reservoirs 44 after cooling the primary formed product P, can be reused to cool the lower cooling die 42 of the cooling die set 40, so that an increase in the temperature of the lower cooling die 42 of the cooling die set 40 can be effectively reduced. Further, the cooling grooves in the forming die set as described in Patent literature 1 thus do not need to be provided, and this allows avoidance of the situation where the accuracy for the surface of the formed product is unable to ensure in hot press forming.
The liquid coolant jetted from the second jetting nozzles 52 then upwardly makes direct contact with the primary formed product P being in the high temperature state and held under pressure in the cooling die set 40, so that the liquid coolant hitting the back surface of the primary formed product P absorbs the heat from the formed product in the high temperature state and is vaporized in the first liquid reservoirs 44. Thus, the heat of vaporization generated by vaporizing the liquid coolant can be used to improve the rate of cooling the primary formed product P.
Also, the liquid coolant splashed off from the back surface of the primary formed product P is collected and retained in the first liquid reservoirs 44 via the lower cooling openings 44b, and thus, the liquid coolant used for cooling the primary formed product P can be reused to cool the lower cooling die 42, so that the lower cooling die 42 of the cooling die set 40 can be efficiently cooled.
When the liquid coolant is then supplied to the cooling recesses 43 in the state where the cooling die set 40 is closed, the liquid coolant is supplied to spaces formed between the front surface of the primary formed product P under the pressure and the cooling recesses 43 to make contact with the front surface of the primary formed product P in the high temperature state. Thus, the liquid coolant made contact with the front surface of the primary formed product P takes the heat from the primary formed product P in the high temperature state and is vaporized, and by using the heat of vaporization, the rate of cooling the primary formed product P can be efficiently improved.
When the amount of the liquid coolant retained in the first liquid reservoirs 44 increases, the liquid coolant overflowing from the first liquid reservoirs 44 fills the spaces formed between the back surface of the primary formed product P held under pressure in the cooling die set 40, and the cooling grooves 46. Thus, the liquid coolant retained in the first liquid reservoirs 44 is used again to directly cool the primary formed product P so that the primary formed product P can be efficiently cooled.
When the amount of the liquid coolant retained in the first liquid reservoirs 44 increases, the liquid coolant also flows into the second liquid reservoir 45 via the cooling grooves 46 to be retained in the second liquid reservoir 45. The liquid coolant thus directly cools the primary formed product P as passing through the cooling grooves 46, and thereafter, is further reused in the second liquid reservoir 45 for cooling the lower cooling die 42, so that the lower cooling die 42 of the cooling die set 40 can be efficiently cooled.
In the first embodiment of the present disclosure, the cooling recesses 43 are provided at locations corresponding to the respective first liquid reservoirs 44; however, the cooling recesses 43 may be provided at locations corresponding to the lower pressure-holding surface 42a as shown in
Also, in the first embodiment of the present disclosure, the first supply line L2 directly connects the outlet port 10b of the liquid coolant pump 10 to the first jetting nozzles 51; however, for example, a third liquid reservoir 48 capable of retaining the liquid coolant may be provided in the upper cooling die 41 to indirectly connect the outlet port 10b of the liquid coolant pump 10 and the first jetting nozzles 51 via the third liquid reservoir 48, as shown in
Also, in the first embodiment of the present disclosure, the second jetting nozzles 52 is connected to the outlet port 10b of the liquid coolant pump 10 via the second supply line L3; however, the second jetting nozzles 52 may be connected to a compressed air pump 11 via a third supply line L21, and the liquid coolant may be retained in the first liquid reservoirs 44 such that the second jetting nozzles 52 are located within the liquid coolant, and compressed air that is pressure fed from the compressed air pump 11 may be jetted within the first liquid reservoirs 44 from the second jetting nozzles 52, as shown in
Also, in the first embodiment of the present disclosure, the first liquid reservoirs 44 are open at the lower pressure-holding surface 42a; however, for example, a communication groove 55 (upper cooling groove) may be provided, the communication groove 55 being open at the upper pressure-holding surface 41a of the upper cooling die 41 and having end portions that are open to an inner surface of the cooling recess 43 and an outer surface of the upper cooling die 41, respectively, and a collecting recess 60 and a coolant passage 49 may be also provided in the lower cooling die 42, the collecting recess 60 being open upward at a location corresponding to an opening end of the communication groove 55 on an outer surface side of the upper cooling die 41, and capable of collecting the liquid coolant moving downward after passing through the communication groove 55, and the coolant passage 49 connecting the collecting recess 60 and the first liquid reservoir 44, as shown in
In the first embodiment of the present disclosure, the cooling grooves 46 are then provided to extend in the direction of the row of the first and second liquid reservoirs 44, 45; however, the embodiment is not limited to this configuration and, for example, a cooling groove 46 generally cross-shaped in planar view may be provided which includes a first cooling groove 46b extending in the direction of the row of the first and second liquid reservoirs 44, 45, as well as a second cooling groove 46c extending horizontally, orthogonally to the direction of the row of the first and second liquid reservoirs 44, 45, from generally a middle of the first cooling groove 46b in the direction of the row, as shown in
Also, in the first embodiment of the present disclosure, the cooling grooves 46 are provided in the lower pressure-holding surface 42a; however, in addition to the cooling grooves 46 in the lower pressure-holding surface 42a, an upper cooling groove (not shown) which is open at the upper pressure-holding surface 41a and has end portions open to the inner surfaces of the cooling recesses 43, may be also provided, or only the upper cooling groove may be provided. Further, the upper cooling groove may have end portions that are open to the inner surface of the cooling recess 43 and the outer surface of the upper cooling die 41, respectively, or end portions that are open only to the inner surfaces of the cooling recesses 43. In this way, when the amount of the liquid coolant deposited on the front surface of the primary formed product P held under pressure is increased in the cooling recesses 43, the liquid coolant flowing out from the cooling recesses 43 along the front surface of the primary formed product P then fills a space formed between the front surface of the primary formed product P held under pressure, and the upper cooling groove. Thus, the liquid coolant after directly cooling the front surface of the primary formed product P in the cooling recesses 43 is used again to directly cool the primary formed product P so that the primary formed product P can be efficiently cooled.
Also, in the first embodiment of the present disclosure, the second jetting nozzle 52 is provided on the bottom surfaces 44a of the first liquid reservoirs 44; however, it may be also provided on the cooling grooves 46, in addition to the bottom surfaces 44a.
A heating furnace 120 of a far-infrared rays type is placed in the heating area 102, and includes a lower furnace body 120a that is mounted on a floor, and an upper furnace body 120b that is placed above and opposite the lower furnace body 120a.
A heater (not shown) configured to increase the temperature of atmospheric gas between the upper furnace body 120b and the lower furnace body 120a is attached to the upper furnace body 120b to heat the steel sheet S for a predetermined heating time to increase its temperature to about 900° C., which is a predetermined hardening temperature.
A first robot R101 is disposed between the heating area 102 and the forming area 103, and configured to transport to the forming area 103 the steel sheet S having its temperature increased in the heating furnace 120 and being in a high temperature state.
The forming area 103 includes a forming die set 130 for hot press forming, and a mechanical press machine 105.
The forming die set 130 includes an upper forming die 131 and a lower forming die 132 facing each other, and the upper forming die 131 is configured to move upward and downward with respect to the lower forming die 132 by means of the mechanical press machine 105.
A first pressing surface 131a recessed upward to have a generally concave cross section is formed on the upper forming die 131, and a second pressing surface 132a bulging upward to have a generally convex cross section is formed on the lower forming die 132.
When the steel sheet S in the state where its temperature is increased to the hardening temperature is placed on the second pressing surface 132a of the lower forming die 132 and thereafter, the upper forming die 131 is moved downward to close the forming die set 130, the primary formed product P having a generally hat-shaped cross section can be then obtained from the steel sheet S.
A second robot R102 is disposed between the forming area 103 and the hardening area 104, and configured to transport to the hardening area 104 the primary formed product P obtained in the forming area 103.
A cooling die set 140 for hardening, and a servo press machine 106, are placed in the hardening area 104, the cooling die set 140 including an upper cooling die 141 and a lower cooling die 142 facing each other, and the servo press machine 106 configured to move the upper cooling die 141 upward and downward with respect to the lower cooling die 142. In the hardening area 104, the primary formed product P is cooled by means of liquid coolant and is thereby hardened, and the vehicle frame F serving as the final formed product is obtained.
As shown in
Next, the cooling die set 140 is described in detail.
As shown in
An upper groove 147 is formed in regions of the upper pressure-holding surface 141a exclusive of opening portions of the first upper recesses 143, and extends in a direction of a row of the first and second upper recesses 143, 145, and is open downward.
That is, the upper groove 147 is open at the upper pressure-holding surface 141a and has end portions being open to the first upper recess 143 or the second upper recess 145. Adjacent two first upper recesses 143 or adjacent first and second upper recesses 143, 145 are thus in communication with one another via the upper groove 147.
An upper outer wall 149 protruding downward is provided outside the second upper recess 145. The upper outer wall 149 includes an inner surface having an upper sloping surface 149a inclined to extend progressively outward toward a lower portion, i.e., to extend progressively away from the second upper recess 145 toward the lower portion.
On the other hand, the lower cooling die 142 is wide and has a cross section in the shape of comb teeth oriented upward. The lower cooling die 142 includes an inner region of its top surface that has a lower pressure-holding surface 142a at a location corresponding to the upper pressure-holding surface 141a, and an outer periphery region of its top surface that has a lower outer wall 151 protruding upward.
A plurality of lower recesses 144 being open upward are provided at locations of the lower pressure-holding surface 142a corresponding to the first upper recesses 143 of the upper cooling die 141. The liquid coolant is retained in the lower recesses 144, and the liquid coolant retained in the lower recesses 144 takes the heat from the lower cooling die 142 to cool the lower cooling die 142.
A liquid reservoir 146 is provided in the lower cooling die 142 outside the lower pressure-holding surface 142a, is open upward to be recessed, and extends to surround the lower recesses 144. The liquid reservoir 146 is capable of retaining the liquid coolant. The liquid coolant retained in the liquid reservoir 146 then takes the heat from the lower cooling die 142 to cool the lower cooling die 142.
A plurality of communication passages 148 are formed in a portion of the lower cooling die 142 downward of the lower pressure-holding surface 142a, and extend in a direction of a row of the lower recesses 144 and the liquid reservoir 146.
The communication passage 148 has end portions being open to the lower recess 144 or the liquid reservoir 146. Inner spaces of adjacent two lower recesses 144, or an inner space of the lower recess 144 and the liquid reservoir 146 which are adjacently located are in communication with one another via the communication passage 148.
The communication passages 148 are located downward of the level of liquid in the lower recesses 144 and the liquid reservoir 146, and thus constantly filled with the liquid coolant.
A volume varying wall 150 having a generally trapezoidal cross section is provided between the lower pressure-holding surface 142a and the lower outer wall 151, and includes an upper end 150c provided at a level higher than the lower pressure-holding surface 142a.
The volume varying wall 150 is provided at a location corresponding to the upper sloping surface 149a of the upper cooling die 141, and includes an inner wall surface 150b forming the liquid reservoir 146 on a lower pressure-holding surface 142a side of the volume varying wall 150.
That is, the volume varying wall 150 constitutes a part of an outer wall of the liquid reservoir 146.
A lower sloping surface 150a is formed on an outer wall surface of the volume varying wall 150, i.e., a wall surface opposite the inner wall surface 150b, and is inclined to extend progressively away from the liquid reservoir 146 toward a lower portion. The lower sloping surface 150a is inclined to correspond to the upper sloping surface 149a.
The volume varying wall 150 is movable toward and away from the lower pressure-holding surface 142a in a horizontal direction. Thus, when the volume varying wall 150 is moved, a retaining volume of the liquid reservoir 146 varies, that is, the retaining volume changes. Specifically, when the volume varying wall 150 is moved toward the lower pressure-holding surface 142a, the retaining volume of the liquid reservoir 146 decreases, and when the volume varying wall 150 is moved away from the lower pressure-holding surface 142a, the retaining volume of the liquid reservoir 146 increases.
When the upper cooling die 141 is moved downward, the upper sloping surface 149a makes sliding contact with the lower sloping surface 150a and thereby, the volume varying wall 150 is pressed by the upper cooling die 141 to move toward the lower pressure-holding surface 42a of the lower cooling die 142.
Next, a method for hardening using the cooling die set 140 in the harden area 104 is described in detail with respect to
First, once a primary formed product P is formed in the forming die set 130, the primary formed product P is transported by using the second robot R102 to mount on the lower pressure-holding surface 142a of the lower cooling die 142 that is opened, as shown in
In this instance, the area of the lower pressure-holding surface 142a of the lower cooling die 142 is smaller due to the provided opening regions of the lower recesses 144 so that the amount of heat transfer to the lower pressure-holding surface 142a from the primary formed product P in a high temperature state which is mounted on the lower pressure-holding surface 142a, is reduced, and the temperature of the lower cooling die 142 is less likely to increase.
Next, as shown in
When the volume varying wall 150 is moved toward the lower pressure-holding surface 142a, the retaining volume of the liquid reservoir 146 is reduced. The level of the liquid coolant retained in the liquid reservoir 146 then gradually increases and becomes higher than the lower pressure-holding surface 142a of the lower cooling die 142, so that the liquid coolant in the liquid reservoir 146 flows to the lower pressure-holding surface 142a side to immerse the lower pressure-holding surface 142a in the liquid coolant. The primary formed product P mounted on the lower pressure-holding surface 142a is thus immersed in the liquid coolant so that the liquid coolant directly takes the heat from the primary formed product P to cool the primary formed product P.
Further, when the volume varying wall 150 is moved toward the lower pressure-holding surface 142a, a wave of the liquid coolant from a volume varying wall 150 side toward the lower pressure-holding surface 142a side is formed near the surface of liquid in the liquid reservoir 146. The wave of the liquid coolant spreads to cover over an entire front surface of the primary formed product P mounted on the lower pressure-holding surface 142a and being in the high temperature state, and the liquid coolant directly contacts the front surface of the primary formed product P, so that the contacting liquid coolant cools the front surface of the primary formed product P.
Also, when the volume varying wall 150 is moved toward the lower pressure-holding surface 142a to reduce the retaining volume of the liquid reservoir 146, the liquid coolant flows from the liquid reservoir 146 via the communication passages 148 into spaces formed between the lower recesses 144 and a back surface of the primary formed product P mounted on the lower pressure-holding surface 142a. The liquid coolant flowing into fills the spaces so that the liquid coolant directly contacts the back surface of the primary formed product P mounted on the lower pressure-holding surface 142a, and this liquid coolant thus cools the back surface of the primary formed product P.
Then, the upper cooling die 141 is further moved downward to close the cooling die set 140 as shown in
When the cooling die set 140 is closed, the liquid coolant fills the first upper recesses 143 and the upper groove 147 of the upper cooling die 141, as well as the lower recesses 144 and the communication passages 148 of the lower cooling die 142.
The level of the liquid coolant in a space formed by the second upper recess 145, the liquid reservoir 146, and the inner wall surface 150b of the volume varying wall 150 is then located higher than ceiling surfaces of the first upper recesses 143 and lower than the upper end 150c of the volume varying wall 150 so that the entire primary formed product P held under pressure by the upper pressure-holding surface 141a and the lower pressure-holding surface 142a is immersed in the liquid coolant. In this way, the level of the liquid coolant can increase synchronously as the upper cooling die 141 of the cooling die set 140 is moved downward, i.e., is closed, and thus the state of holding the primary formed product P under pressure in the cooling die set 140 and the state of immersing the primary formed product P in the liquid coolant are enabled simultaneously or with a relatively small time difference. Thus, this can reduce the time during which the primary formed product P in the high temperature state is mounted on the lower pressure-holding surface 142a of the lower cooling die 142 without being immersed in the liquid coolant, so that heat transfer from the primary formed product P in the high temperature state to the lower pressure-holding surface 142a of the lower cooling die 142 can be reduced.
Thereafter, the cooling die set 140 is opened and the hardened vehicle frame F is removed by the third robot R103 to be transported to a next area. In this respect, the volume varying wall 150 returns to an original location shown in
According to the second embodiment of the present disclosure, when the volume varying wall 150 is moved to reduce the retaining volume of the liquid reservoir 146, the level of the liquid coolant retained in the liquid reservoir 146 then gradually increases and becomes higher than the lower pressure-holding surface 142a of the lower cooling die 142 of the cooling die set 140, so that the liquid coolant flows to the lower pressure-holding surface 142a side of the lower cooling die 142 to immerse the lower pressure-holding surface 142a in the liquid coolant. Thus, the primary formed product P in the high temperature state which is mounted on, or held under pressure on, the lower pressure-holding surface 142a of the lower cooling die 142 of the cooling die set 140 is immersed in the liquid coolant, and hence the liquid coolant directly takes the heat from the primary formed product P, so that the rate of cooling the primary formed product P can be increased during the hardening. Also, the liquid coolant retained in the liquid reservoir 146 takes the heat from the lower cooling die 142 of the cooling die set 140 to cool the lower cooling die 142 so that an increase in the temperature of the lower cooling die 142 can be effectively reduced. Further, the cooling grooves in the forming die set as described in Patent literature 1 thus do not need to be provided, and this allows avoidance of the situation where the accuracy for the surface of the formed product is unable to be ensured during hot press forming as a result of providing the cooling grooves.
Also, when the volume varying wall 150 is moved toward the lower pressure-holding surface 142a of the lower cooling die 142, the wave of the liquid coolant from the volume varying wall 150 side toward the lower pressure-holding surface 142a side of the lower cooling die 142 is formed near the surface of liquid in the liquid reservoir 146. When the wave of the liquid coolant reaches the primary formed product P in the high temperature state, which is mounted on, or held under pressure on, the lower pressure-holding surface 142a of the lower cooling die 142 of the cooling die set 140, the wave of the liquid coolant spreads to cover over the entire front surface of the primary formed product P so that the liquid coolant directly contacts the front surface of the primary formed product P. Thus, the liquid coolant directly takes the heat from the primary formed product P to efficiently cool the primary formed product P so that the rate of cooling the primary formed product P can be improved during the hardening.
Also, the level of the liquid coolant in the liquid reservoir 146 can increase synchronously as the upper cooling die 141 of the cooling die set 140 is moved downward, so that the state of holding the primary formed product P under pressure in the cooling die set 140 and the state of immersing the primary formed product P in the liquid coolant are enabled simultaneously or with a relatively small time difference. Thus, this can reduce the time during which the primary formed product P in the high temperature state is mounted on, or held under pressure on, the lower pressure-holding surface 142a of the lower cooling die 142 of the cooling die set 140 without being immersed in the liquid coolant, so that heat transfer from the primary formed product P in the high temperature state to the lower pressure-holding surface 142a of the lower cooling die 142 can be reduced to lower an increase in the temperature of the lower cooling die 142 of the cooling die set 140. Also, the volume varying wall 150 is moved by using the downward movement of the upper cooling die 141, and thus a cost increase caused by separately including a driving source for moving the volume varying wall 150 can be avoided.
Additionally, the area of the lower pressure-holding surface 142a in the lower cooling die 142 of the cooling die set 140 is smaller due to the provided opening regions of the lower recesses 144 so that the amount of heat transfer to the lower pressure-holding surface 142a from the primary formed product P in the high temperature state which is mounted on, or held under pressure on, the lower pressure-holding surface 142a of the lower cooling die 142 can be reduced to lower an increase in the temperature of the lower cooling die 142 of the cooling die set 140.
Additionally, when the volume varying wall 150 is moved to reduce the retaining volume of the liquid reservoir 146, the liquid coolant flows from the liquid reservoir 146 via the communication passages 148 into the spaces formed between the lower recesses 144 and the back surface of the primary formed product P mounted on, or held under pressure on, the lower pressure-holding surface 142a of the lower cooling die 142 of the cooling die set 140 so that the liquid coolant flowing into fills the spaces. Thus, the liquid coolant directly contacts the back surface of the primary formed product P in the high temperature state, and a larger amount of the heat is lost from the primary formed product P in the high temperature state to the liquid coolant, so that the rate of cooling the primary formed product P can be further improved.
In addition, in the second embodiment of the present disclosure, the upper sloping surface 149a and the lower sloping surface 150a corresponding to each other are provided, and the volume varying wall 150 moves synchronously as the upper cooling die 141 is moved downward; however, the present embodiment is not limited to this configuration and, for example, a dedicated driving source 155 may be separately provided for moving the volume varying wall 150 toward and away from the lower pressure-holding surface 142a of the lower cooling die 142, as shown in
Also, in the second embodiment of the present disclosure, the lower recesses 144 and the communication passages 148 are provided in the lower cooling die 142; however, as shown in
In addition, in the second embodiment of the present disclosure, when the primary formed product P is mounted on the lower pressure-holding surface 142a before being held under pressure by the upper pressure-holding surface 141a and the lower pressure-holding surface 142a, the primary formed product P is immersed in the liquid coolant, and may be, however, immersed in the liquid coolant after being held under pressure by the upper pressure-holding surface 141a and the lower pressure-holding surface 142a.
A heating furnace 220 of a far-infrared rays type is placed in the heating area 202, and includes a lower furnace body 220a that is mounted on a floor, and an upper furnace body 220b that is placed above and opposite the lower furnace body 220a.
A heater (not shown) configured to increase the temperature of atmospheric gas between the upper furnace body 220b and the lower furnace body 220a is attached to the upper furnace body 220b to heat the steel sheet S for a predetermined heating time to increase its temperature to about 900° C., which is a predetermined hardening temperature.
A first robot R201 is disposed between the heating area 202 and the forming area 203, and configured to transport to the forming area 203 the steel sheet S having its temperature increased in the heating furnace 220 and being in a high temperature state.
The forming area 203 includes a forming die set 230 for hot press forming, and a mechanical press machine 205.
The forming die set 230 includes a lower forming die 231 and an upper forming die 232 facing each other, and the upper forming die 232 is configured to move upward and downward with respect to the lower forming die 231 by means of the mechanical press machine 205.
A first pressing surface 231a bulging upward to have a generally convex cross section is formed on the lower forming die 231, and a second pressing surface 232a recessed upward to have a generally concave cross section is formed on the upper forming die 232.
When the steel sheet S in the state where its temperature is increased to the hardening temperature is placed on the first pressing surface 231a of the lower forming die 231 and thereafter, the upper forming die 232 is moved downward to close the forming die set 230, the primary formed product P having a generally hat-shaped cross section can be then obtained from the steel sheet S.
A second robot R202 is disposed between the forming area 203 and the hardening area 204, and configured to transport to the hardening area 204 the primary formed product P obtained in the forming area 203.
A cooling die set 240 for hardening, and a servo press machine 206 are placed in the hardening area 204, the cooling die set 240 including a lower cooling die 241 and an upper cooling die 242 facing each other, and the servo press machine 206 configured to move the upper cooling die 242 upward and downward with respect to the lower cooling die 241. In the hardening area 204, the primary formed product P is cooled by means of liquid coolant and is thereby hardened, and the vehicle frame F serving as the final formed product is obtained.
As shown in
Next, the cooling die set 240 is described in detail.
As shown in
A lower pressure-holding surface 241a is provided in a region of the top surface of the lower cooling die 241 between the lower outer wall 251 located on one end in a longitudinal direction, and the lower inner wall 253, and the lower pressure-holding surface 241a is provided at a location downward of top surfaces of the lower outer wall 251 and the lower inner wall 253.
A plurality of lower recesses 243 are provided at locations corresponding to the lower pressure-holding surface 241a.
The liquid coolant is retained in the lower recesses 243, and the liquid coolant retained in the lower recesses 243 takes the heat from the lower cooling die 241 to cool the lower cooling die 241.
A first cylinder portion 245 including a first cylinder chamber 245a that is open upward is then provided in a region of the top surface of the lower cooling die 241 between the lower outer wall 251 located on another end in the longitudinal direction, and the lower inner wall 253. A first piston 261 is housed in the first cylinder chamber 245a such that the first piston 261 is reciprocally movable in a vertical direction.
The first piston 261 is in the shape of a cylinder having a vertically oriented center line. The first piston 261 has an upper end including a first upper end portion 261a (second pressing portion) extending horizontally, and a lower end including a first lower end portion 261b extending horizontally.
A first reservoir chamber 255 capable of retaining the liquid coolant is provided in a lower region of the first cylinder chamber 245a bounded by the first piston 261, and the liquid coolant retained in the first reservoir chamber 255 takes the heat from the lower cooling die 241 to cool the lower cooling die 241.
A retaining volume of the first reservoir chamber 255 varies in
accordance with the vertical movement of the first piston 261. That is, when the first piston 261 is moved downward, the retaining volume of the first reservoir chamber 255 decreases, and when the first piston 261 is moved upward, the retaining volume of the first reservoir chamber 255 increases.
A first spring 257 (first biasing member) of a compression coil spring type is also disposed in the first reservoir chamber 255. The first spring 257 has one end that abuts the first lower end portion 261b of the first piston 261 and another end that abuts a bottom surface of the first reservoir chamber 255 to press the first piston 261 in a direction in which the retaining volume of the first reservoir chamber 255 increases, i.e., in an upward direction.
A first communication passage 247 configured to provide communication of the lower recesses 243 with the first reservoir chamber 255 is provided in the lower cooling die 241. The first communication passage 247 has one end being open to the first reservoir 255 and is branched at its midsection, and end portions of the branched portions are open to bottom surfaces of the respective lower recesses 243. The first communication passage 247 is also filled with the liquid coolant, and the liquid coolant takes the heat from the lower cooling die 241 to cool the lower cooling die 241.
On the other hand, as shown in
An upper pressure-holding surface 242a is provided at a location of the bottom surface of the upper cooling die 242 corresponding to the lower pressure-holding surface 241a, and the upper pressure-holding surface 242a is provided at a location downward of bottom surfaces of the upper outer wall 252 and the upper inner wall 254.
A plurality of upper recesses 244 are provided at locations corresponding to the upper pressure-holding surface 242a, and the plurality of upper recesses 244 are formed to face the respective plurality of the lower recesses 243 in the vertical direction.
A second cylinder portion 246 including a second cylinder chamber 246a that is open downward is also provided at a location of the bottom surface of the upper cooling die 242 corresponding to the first cylinder portion 245, and a second piston 262 is housed in the second cylinder chamber 246a such that the second piston 262 is reciprocally movable in the vertical direction.
The second piston 262 is in the shape of a cylinder having a vertically oriented center line. The second piston 262 has an upper end including a second upper end portion 262a extending horizontally, and a lower end including a second lower end portion 262b (first pressing portion) extending horizontally, and the second lower end portion 262b faces the first upper end portion 261a of the first piston 261 in the vertical direction.
A second reservoir chamber 256 capable of retaining the liquid coolant is provided in an upper region of the second cylinder chamber 246a bounded by the second piston 262.
A retaining volume of the second reservoir chamber 256 varies in accordance with the vertical movement of the second piston 262. That is, when the second piston 262 is moved upward, the retaining volume of the second reservoir chamber 256 decreases, and when the second piston 262 is moved downward, the retaining volume of the second reservoir chamber 256 increases.
A second spring 258 (second biasing member) of a compression coil spring type is also disposed in the second reservoir chamber 256. The second spring 258 has biasing force same as that of the first spring 257, and has one end that abuts the second upper end portion 262a of the second piston 262 and another end that abuts a ceiling portion of the second reservoir chamber 256 to press the second piston 262 in a direction in which the retaining volume of the second reservoir chamber 256 increases, i.e., in a downward direction.
A second communication passage 248 configured to provide communication of the upper recesses 244 with the second reservoir chamber 256 is provided in the upper cooling die 242. The second communication passage 248 has one end being open to the second reservoir chamber 256, is branched at its midsection, and includes other ends in the branched portions being open to ceiling portions of the respective upper recesses 244. The second communication passage 248 can also be filled with the liquid coolant.
Next, a method for hardening using the cooling die set 240 in the harden area 204 is described in detail with respect to
First, once a primary formed product P is formed in the forming die set 230, the primary formed product P is transported by using the second robot R202 to mount on the lower pressure-holding surface 241a of the lower cooling die 241 that is opened, as shown in
In this instance, the area of the lower pressure-holding surface 241a of the lower cooling die 241 is smaller due to the provided opening regions of the lower recesses 243 so that the amount of heat transfer to the lower pressure-holding surface 241a from the primary formed product P in a high temperature state which is mounted on the lower pressure-holding surface 241a, is reduced, and the temperature of the lower cooling die 241 is less likely to increase.
Next, as shown in
downward toward the lower cooling die 241 to close the cooling die set 240. Then, the first upper end portion 261a of the first piston 261 abuts the second lower end portion 262b of the second piston 262 so that the second lower end portion 262b pushes the first piston 261 downward and the first upper end portion 261a pushes the second piston 262 upward.
When the first piston 261 is pushed downward to reduce the retaining volume of the first reservoir chamber 255, the liquid coolant retained in the first reservoir chamber 255 is pushed out to the lower recesses 243 via the first communication passage 247 by means of the first piston 261 to increase the level of the liquid coolant retained in the lower recesses 243. The primary formed product P in the high temperature state which is mounted on, or held under pressure on, the lower pressure-holding surface 241a of the lower cooling die 241 is then immersed in the liquid coolant so that the liquid coolant takes the heat from the primary formed product P to cool the primary formed product P.
When the second piston 262 is pushed upward to reduce the retaining volume of the second reservoir chamber 256, the liquid coolant retained in the second reservoir chamber 256 is pushed out to the upper recesses 244 via the second communication passage 248 by means of the second piston 262 to fall via openings of the upper recesses 244 toward a front surface of the primary formed product P in the high temperature state which is mounted on, or held under pressure on, the lower pressure-holding surface 241a of the lower cooling die 241, so that the liquid coolant poured onto the primary formed product P cools the front surface of the primary formed product P in the high temperature state.
When the cooling die set 240 is closed, the primary formed product P is hardened by holding the primary formed product P under pressure by the lower pressure-holding surface 241a of the lower cooling die 241 and the upper pressure-holding surface 242a of the upper cooling die 242, and filling the lower recesses 243 and the upper recesses 244 with the liquid coolant to cool the primary formed product P with the liquid coolant.
Thereafter, the cooling die set 240 is opened and the hardened vehicle frame F is removed by the third robot R203 to be transported to a next area. In this respect, when the upper cooling die 242 of the cooling die set 240 is moved to open, the first piston 261 and the second piston 262 respectively move upward and downward by means of the biasing force of the first spring 257 and the second spring 258 to return to original locations as shown in
According to the third embodiment of the present disclosure, when the first piston 261 moves through the first cylinder chamber 245a in a direction in which the retaining volume of the first reservoir chamber 255 decreases, the liquid coolant retained in the first reservoir chamber 255 is pushed by the first piston 261 to flow into the lower recesses 243 via the first communication passage 247. The level of the liquid coolant in the lower recesses 243 then increases so that the lower pressure-holding surface 241a of the lower cooling die 241 and the primary formed product P being in the high temperature state and mounted on, or held under pressure on, the lower pressure-holding surface 241a are immersed in the liquid coolant. Thus, the liquid coolant directly takes the heat from the primary formed product P so that the rate of cooling the primary formed product P can be improved during the hardening. Also, the liquid coolant retained in the first reservoir chamber 255 takes the heat from the lower cooling die 241 of the cooling die set 240 to cool the lower cooling die 241 so that an increase in the temperature of the lower cooling die 241 can be effectively reduced. Further, the cooling grooves in the forming die set as described in Patent literature 1 thus do not need to be provided, and this allows avoidance of the situation where the accuracy for the surface of the formed product is unable to be ensured during hot press forming as a result of providing the cooling grooves.
Also, the first piston 261 moves downward to reduce the retaining volume of the first reservoir chamber 255 synchronously as the upper cooling die 242 of the cooling die set 240 is moved downward, and hence the liquid coolant retained in the first reservoir chamber 255 can move to the lower recesses 243 to increase the level of the liquid coolant retained in the lower recesses 243. Thus, this enables the state of holding the primary formed product P under pressure in the cooling die set 240 and the state of immersing the primary formed product P in the liquid coolant, simultaneously or with a relatively small time difference, and allows reduction of the time during which the primary formed product P in the high temperature state is mounted on, or held under pressure on, the lower pressure-holding surface 241a of the lower cooling die 241 of the cooling die set 240 without being immersed in the liquid coolant. The heat transfer from the primary formed product P in the high temperature state to the lower pressure-holding surface 241a of the lower cooling die 241 is also reduced so that an increase in the temperature of the lower cooling die 241 of the cooling die set 240 can be reduced. Also, the first piston 261 is moved by using the downward movement of the upper cooling die 242, and thus a cost increase caused by separately including a driving source for moving the first piston 261 can be avoided.
Also, when the second piston 262 moves through the second cylinder chamber 246a in a direction in which the retaining volume of the second reservoir chamber 256 decreases, the liquid coolant retained in the second reservoir chamber 256 is pushed out by the second piston 262 to flow into the lower recesses 244 via the second communication passage 248. The liquid coolant then falls through the openings of the upper recesses 244 to contact the front surface of the primary formed product P being in the high temperature state and mounted on, or held under pressure on, the lower pressure-holding surface 241a of the lower cooling die 241 of the cooling die set 240. Thus, the liquid coolant contacting the front surface of the primary formed product P directly takes the heat of the primary formed product P in the high temperature state so that the rate of cooling the primary formed product P can be further improved during the hardening.
Additionally, the second piston 262 moves upward to reduce the retaining volume of the second reservoir chamber 256 synchronously as the upper cooling die 242 of the cooling die set 240 is moved downward, and hence the liquid coolant retained in the second reservoir chamber 256 moves to the upper recesses 244 to fall via the openings of the upper recesses 244 toward the front surface of the primary formed product P in the high temperature state which is mounted on, or held under pressure on, the lower pressure-holding surface 241a of the lower cooling die 241 of the cooling die set 240, so that the liquid coolant poured onto the primary formed product P can efficiently cool the front surface of the primary formed product P in the high temperature state. Additionally, the second piston 262 can be moved by using the downward movement of the upper cooling die 242, and thus a cost increase caused by separately including a driving source for moving the second piston 262 can be avoided.
Also, the second piston 262 is moved by using the first piston 261 configured to control the movement of the liquid coolant in the lower cooling die 241, and the first piston 261 is moved by using the second piston 262 configured to control the movement of the liquid coolant in the upper cooling die 242, and thus there is no need to separately provide pressing structures only for moving the first piston 261 and the second piston 262, so that the number of parts can be reduced to keep manufacturing cost under control, and a horizontal increase in size of the cooling die set 240 by providing pressing structures in a region exclusive of the first piston 261 and the second piston 262 can be reduced.
According to the third aspect of the present disclosure, the first cylinder portion 245 and the first piston 261 are configured to face the second cylinder portion 246 and the second piston 262 in the vertical direction; however, as shown in
Also, in the third embodiment of the present disclosure, the first upper end portion 261a of the first piston 261 is placed opposite the second lower end portion 262b of the second piston 262 in the vertical direction, and the first piston 261 and the second piston 262 move synchronously as the upper cooling die 242 is moved downward; however, the present embodiment is not limited to this configuration and, for example, dedicated driving sources 263, 264 may be separately provided for moving the first piston 261 and the second piston 262, as shown in
Also, in the third embodiment of the present disclosure, a liquid reservoir is not provided for supplying the liquid coolant to the second reservoir chamber 256, and in this respect, as shown in
In addition, in the third embodiment of the present disclosure, the biasing force of the first spring 257 and the second spring 258 is set as same; however, the first spring 257 may be set to have smaller biasing force than the second spring 258. In this way, when the upper cooling die 242 of the cooling die set 240 is moved downward, the second piston 22 starts to move later than the first piston 262 in the direction in which the retaining volume of the second reservoir chamber 256 decreases, and the cooling of the back surface of the primary formed product P due to the increased level of the liquid coolant in the lower recesses 243 and the cooling of the front surface of the primary formed product P by the liquid coolant supplied via the lower openings of the upper recesses 244 are thus enabled simultaneously or with a relatively small time difference, so that the front and back surfaces of the primary formed product P are uniformly cooled and the rate of cooling the entire primary formed product P can be improved.
In addition, in the third embodiment of the present disclosure, the first spring 257 and the second spring 258 of a compression coil spring type apply the biasing force to the first piston 261 and the second piston 262; however, a biasing member, such as a leaf spring, rubber, piston, may be used to apply the biasing force to the first piston 261 and the second piston 262.
Also, in the third aspect of the present disclosure, the first cylinder portion 245 and the first piston 261 are provided in the lower cooling die 241, and the second cylinder portion 246 and the second piston 262 are provided in the upper cooling die 242; however, the second cylinder portion 246 and the second piston 262 may not be necessarily provided in the upper cooling die 242.
In the third embodiment of the present disclosure, the first piston 261 and the second piston 262 have a cylindrical shape, but may also have a rectangular prism shape, the cross section of which is rectangular, or may not be columnar.
Also, in the third aspect of the present disclosure, a sealing member is not disposed in gaps between an outer surface of the first piston 261 and an inner surface of the first cylinder portion 245 and between an outer surface of the second piston 262 and an inner surface of the second cylinder portion 246; however, a sealing member for sealing both gaps in a watertight manner may be disposed.
Also, in the third aspect of the present disclosure, the lower pressure-holding surface 241a is provided at a location downward of the top surfaces of the lower inner wall 253 and the lower outer wall 251, and the upper pressure-holding surface 242a is provided at a location downward of the bottom surfaces of the upper inner wall 254 and the lower outer wall 251. In this respect, the lower pressure-holding surface 241a may be provided at a location upward of the top surfaces of the lower inner wall 253 and the lower outer wall 251, and the upper pressure-holding surface 242a may be provided at a location upward of the bottom surfaces of the upper inner wall 254 and the lower outer wall 251.
The present disclosure is suitable for a hot press device configured such that a primary formed product in a high temperature state which is obtained in a forming area is held under pressure and cooled on an upper die and a lower die of a cooling die set to obtain a hardened final formed product.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-096650 | Jun 2021 | JP | national |
| 2021-118677 | Jul 2021 | JP | national |
| 2021-131389 | Aug 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/015902 | 3/30/2022 | WO |
