Hot presses and methods for producing products through hot pressing.
Patent Information
- Application Number
- TH2201006256
- Authority / Receiving Office
- TH · TH
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2021-03-30
- Publication Date
- 2026-08-28
- Estimated Expiration
- 2041-03-29
AI Technical Summary
Conventional hot press methods struggle to achieve both shape accuracy and productivity in hot press-formed products due to temperature differences and cooling rate variations, leading to potential shape defects and increased bottom dead center holding time.
A hot press apparatus with a movable mold that alternates between contact and non-contact positions during the bottom dead center holding period, allowing for controlled cooling rates to ensure uniform temperature distribution and maintain shape accuracy without extending the holding time.
The controlled cooling conditions using the movable mold ensure shape accuracy and characteristic strength distribution in hot press-formed products, reducing the risk of defects and improving manufacturing efficiency.
Abstract
Description
Hot press device and method for manufacturing hot press-molded product
[0001] The present invention relates to a hot press apparatus and a method for manufacturing a hot press-formed product.
[0002] In metal structural components, strength and other properties may be locally changed. For example, when applying high-strength components to vehicle frame members, the strength of specific areas may be reduced rather than increasing the strength of the entire component. There are several reasons for this. For example, low-strength areas may be subjected to processing such as drilling. In other cases, when a component deforms, the low-strength areas may be deformed early to control the deformation behavior.
[0003] One method for manufacturing components with low strength sections involves hot stamping a tailor-welded blank made by welding steel materials with different properties. For example, Japanese Patent Publication No. 5,864,414 describes a method for hot press-forming a steel sheet blank consisting of separate plates welded together. In this method, a heated steel sheet blank is hot press-formed in a cooled tool pair, and the formed product is hardened while the blank is still in the tool pair. The weld between the two plates is cooled at a reduced cooling rate relative to the portions on both sides of the weld. This results in a portion with a low martensite content along the weld. The cooling rate is reduced by maintaining a gap between the tool pair and the final product.
[0004] JP 2015-226936 A discloses a manufacturing method that allows for localized adjustment of the structure of a metal structural component. In this manufacturing method, a steel member is hot-formed and hardened over at least several sections by contact with a tool surface. At least one of two sections of the tool surface has a surface coating that reduces or increases thermal conductivity. The sections of the tool surface with different thermal conductivities result in different cooling rates. The partial regions of the steel member with different cooling rates have different microstructures after hardening.
[0005] Japanese Patent No. 5864414 Japanese Patent Application Laid-Open No. 2015-226936
[0006] In the above-mentioned conventional techniques, the cooling rate of a metal sheet can be partially reduced by using the gap (clearance) between the molded product and the mold or the distribution of thermal conductivity on the mold surface. However, when the molded product is removed from the mold, the temperature of the parts with slower cooling rates is high. Subsequently, these parts may thermally shrink as they cool, resulting in defective shape. Furthermore, if there is a large temperature difference within the molded product when it is removed from the mold, the molded product may deform due to thermal shrinkage, resulting in defective shape. To reduce the temperature of the molded product upon removal from the mold and the temperature difference within the molded product, the molded product must be held in the mold until the temperature within the molded product becomes uniform. On the other hand, from the perspective of production costs, etc., a shorter holding time of the molded product in the mold (bottom dead center holding time) is preferable. In other words, it is difficult to achieve both productivity and shape accuracy with conventional methods.
[0007] Therefore, the present disclosure provides a hot press device and a method for manufacturing a hot press-molded product that can ensure the shape accuracy of a molded product with a characteristic distribution without having to extend the time that the molded product is held at bottom dead center during hot pressing.
[0008] A hot press apparatus according to an embodiment of the present invention includes a first die, a second die movable in a pressing direction relative to the first die, and a control unit that controls the relative movement of the first die and the second die. At least one of the first die and the second die has a recess on a surface facing the other die in the pressing direction. A movable die is disposed in the recess and is movable in a direction intersecting the facing surface. The control unit controls the movable die so that a heated and press-formed metal sheet is held between the first die and the second die, and a bottom dead center holding period during which the first die and the second die are at bottom dead center includes a contact period during which the movable die contacts the metal sheet and a non-contact period during which the movable die does not contact the metal sheet.
[0009] According to the present disclosure, in hot pressing, the shape accuracy of a molded product having a characteristic distribution can be ensured without increasing the time for which the molded product is held at bottom dead center by a die.
[0010] FIG. 1 is a cross-sectional view showing an example of the configuration of a press apparatus in this embodiment. FIG. 2 is a view showing a state in which the press apparatus shown in FIG. 1 is at bottom dead center. FIG. 3 is a view showing a state in which the movable mold 4 abuts against the metal plate B at bottom dead center. FIG. 4 is a graph showing an example in which there is a contact period at the beginning of the bottom dead center holding period. FIG. 5 is a graph showing an example in which there is a contact period at the end of the bottom dead center holding period. FIG. 6 is a view showing a modified configuration of the clearance portion. FIG. 7 is a view showing another modified configuration of the clearance portion. FIG. 8 is a view showing a modified configuration of the movable mold 4. FIG. 9 is a view showing another modified configuration of the clearance portion. FIG. 10 is a view showing the evaluation position of the shape accuracy of the molded product of this example. FIG. 11 is a graph showing the results of the hardness distribution of the molded product. FIG. 12 is a graph showing the results of the twist angle of the molded product. FIG. 13 is a graph showing the results of the out-of-plane deformation of the molded product.
[0011] (Configuration 1) A hot press apparatus according to an embodiment of the present invention includes a first die, a second die movable relative to the first die in a pressing direction, and a control unit that controls the relative movement of the first die and the second die. At least one of the first die and the second die has a recess on a surface facing the other die in the pressing direction. A movable die that is movable in a direction intersecting the facing surface is disposed in the recess. The control unit controls the position of the movable die so that a bottom dead center holding period during which a heated and press-formed metal sheet is held between the first die and the second die and the first die and the second die are at bottom dead center includes a contact period during which the movable die is in a contact position in contact with the metal sheet and a non-contact period during which the movable die is in a retracted position not in contact with the metal sheet.
[0012] According to the above-described configuration 1, during the bottom dead center holding period, the cooling rate can be slowed, i.e., slow cooling, during the non-contact period when the movable die is not in contact with the metal sheet. Furthermore, during the contact period when the movable die is in contact with the metal sheet during the bottom dead center holding period, the cooling rate can be increased, i.e., rapid cooling. This allows the temperature distribution of the metal sheet to be made closer to uniform, even while differentiating the cooling conditions of the portion of the formed metal sheet that is in contact with the movable die from those of other portions. Therefore, the formed metal sheet removed from the die is given a characteristic distribution due to the difference in cooling conditions, and deterioration in the shape accuracy of the formed product due to temperature differences is suppressed. In this way, the shape accuracy of the formed product with the characteristic distribution can be ensured without increasing the bottom dead center holding time of the formed product using the die.
[0013] In conventional methods that slow the cooling rate by using clearance or the thermal conductivity of the die surface, the cooling conditions for slow cooling of a portion of a workpiece are predetermined cooling conditions based on the die configuration. Therefore, the metal structure obtained by slow cooling and the temperature distribution of the workpiece removed from the die also depend on the die configuration. To change these, the die configuration must be modified or remanufactured. In contrast, with the above-mentioned configuration 1, the cooling conditions can be controlled by adjusting the length of the contact period during the bottom dead center holding period. Therefore, in press working using a hot press device, the cooling conditions for slow cooling of a portion of a formed metal sheet can be easily changed.
[0014] In the above configuration 1, the movable mold is configured to be movable between an abutment position and a retracted position. The control unit switches the movable mold between a state in the abutment position and a state in the retracted position during a period in which the bottom dead center is maintained. When the movable mold is in the abutment position, the abutment surface of the movable mold with the metal plate is in a position corresponding to the molding surface. When the movable mold is in the retracted position, the movable mold is retracted to the back of the recess and is in a position separated from the molding surface. The retracted position is set to a position where the metal plate does not come into contact with the movable mold even if the portion of the metal plate corresponding to the recess is deformed out-of-plane at the bottom dead center. The retracted position is determined, for example, according to at least one of the area of the recess and the thickness of the metal plate to be processed.
[0015] (Configuration 2) In the above configuration 1, the control unit may bring the movable die into contact with the metal plate at the beginning of the bottom dead center holding period, and then move the movable die away from the metal plate at the end of the bottom dead center holding period. That is, the control unit may move the movable die from the contact position to the retracted position during the bottom dead center holding period. This allows the metal plate to be formed by the movable die during the bottom dead center holding period, when the temperature of the metal plate is relatively high and it is easy to form. This makes it easier to ensure local shape accuracy of the portion of the formed metal plate that corresponds to the movable die.
[0016] (Configuration 3) In the above configuration 1, the control unit may separate the movable mold from the metal plate at the beginning of the bottom dead center holding period, and then contact the movable mold with the metal plate at the end of the bottom dead center holding period. That is, the control unit may move the movable mold from a retracted position to a contact position during the bottom dead center holding period. This allows the movable mold to contact the metal plate and rapidly cool it when the temperature of the metal plate is relatively low during the bottom dead center holding period. This also makes it easier to make the temperature distribution of the metal plate more uniform. This also makes it easier to ensure shape accuracy throughout the formed metal plate. Furthermore, controlling the contact period makes it easier to adjust the cooling conditions.
[0017] In the above configuration 1, the control unit may contact the movable mold with the metal plate at the beginning of the bottom dead center holding period, then separate the movable mold, and then contact the movable mold with the metal plate again at the end of the bottom dead center holding period. That is, the control unit may move the movable mold from the contact position to the retracted position during the bottom dead center holding period, and then move the movable mold back to the contact position. This allows the movable mold to be rapidly cooled during a relatively high period and a relatively low period during the bottom dead center holding period. This makes it easier to control shape accuracy.
[0018] The control unit may, for example, control the movable mold so that the contact period is 10 to 90% of the entire bottom dead center holding period. In this case, the contact period is preferably 80% or less of the entire bottom dead center holding period, more preferably 70% or less, and even more preferably 50% or less. In other words, the control unit may control the movable mold so that the non-contact period is 10% or more of the entire bottom dead center holding period. This makes it easy to partially vary the cooling rate of the metal plate during the bottom dead center holding period and partially vary the metal structure of the molded product. In this way, the control unit can control the length of the contact period and non-contact period during the bottom dead center holding period.
[0019] (Configuration 4) In any of the above configurations 1 to 3, the recesses may include a first recess in the first mold and a second recess in the second mold facing the first recess. In this case, the movable mold is disposed in at least one of the first recess and the second recess facing each other. This allows clearance to exist on both sides of the metal plate during a non-contact period when the movable mold is not in contact. This can improve the robustness of the cooling conditions.
[0020] (Configuration 5) In the above configuration 4, the movable mold may be disposed in both the first recess and the second recess that face each other, thereby further increasing the robustness of the cooling conditions.
[0021] (Configuration 6) In any of the above configurations 1 to 5, the surface of the movable mold that contacts the metal plate may be formed to be flush with the surface of the mold around the recess in which the movable mold is disposed when the movable mold is in contact with the metal plate at the bottom dead center. This allows a characteristic distribution to be imparted to a planar portion of the formed metal plate.
[0022] (Configuration 7) In any of the above configurations 1 to 6, the top surface of the movable mold may have a convex portion that contacts the metal plate and a concave portion that does not contact the metal plate when the movable mold is in contact with the metal plate at the bottom dead center. Even during the contact period when the movable mold is in contact with the metal plate, a clearance exists in the concave portion of the movable mold. This allows for gentle cooling. Furthermore, by changing the shapes of the convex portion and the concave portion on the top surface of the movable mold, the cooling conditions can be changed. The top surface of the movable mold is the end surface closest to the position where the metal plate is placed, of both end surfaces of the concave portion of the movable mold in the movement direction.
[0023] (Configuration 8) In any of the above configurations 1 to 7, the top surface of one of the movable dies of the first die and the second die may have irregularities that protrude or recess in the pressing direction. The opposing surface of the other die or movable die that faces the one movable die in the pressing direction may have a shape that corresponds to the irregularities of the top surface of the one movable die. The configuration may be such that when the one movable die is in contact with the metal plate at the bottom dead center, the opposing surface of the other die or movable die also abuts against the metal plate. This allows the metal plate to be formed into a shape that corresponds to the irregular shape of the movable die.
[0024] (Configuration 9) In any of the above configurations 1 to 8, the control unit may adjust the distance between the metal plate and the movable mold when the movable mold is in the retracted position. This makes it possible to set an appropriate retracted position so that the metal plate and the movable mold are less likely to come into contact at the retracted position. At bottom dead center, a portion of the metal plate corresponding to the recess may undergo out-of-plane deformation. The degree of this out-of-plane deformation varies depending on the area of the recess and the thickness of the metal plate. Therefore, the control unit can make it less likely that the metal plate, which undergoes out-of-plane deformation at bottom dead center, will come into contact with the movable mold in the retracted position by adjusting the retracted position of the movable mold, for example, depending on the thickness of the metal plate.
[0025] In any of the above configurations 1 to 9, the hot press device may include a cooling mechanism for cooling the first mold and the second mold. For example, at least one of the first mold and the second mold may have a pipe or a groove for passing a cooling medium.
[0026] (Manufacturing Method 1) A manufacturing method of a hot press-formed product according to an embodiment of the present invention includes the steps of: placing a heated metal sheet between a first mold and a second mold; press-forming the metal sheet by bringing the first mold and the second mold relatively close to each other in a press direction; holding the metal sheet at bottom dead center with the first mold and the second mold; and moving a movable mold provided in a recess of at least one of the first mold and the second mold relative to the metal sheet during a bottom dead center holding period in which the metal sheet is held at the bottom dead center. The bottom dead center holding period includes a contact period in which the movable mold is located at a contact position in contact with the metal sheet, and a non-contact period in which the movable mold is located at a retracted position not in contact with the metal sheet.
[0027] In the above-described manufacturing method 1, the cooling rate can be slowed during the non-contact period of the bottom dead center holding period. Furthermore, the cooling rate can be increased during the contact period of the bottom dead center holding period. This allows the temperature distribution of the metal sheet to be made more uniform while the cooling conditions of the portion of the formed metal sheet that is in contact with the movable mold are made different from those of the other portions. Therefore, the shape accuracy of the formed product with the characteristic distribution can be ensured without increasing the time the molded product is held at bottom dead center.
[0028] (Manufacturing Method 2) In the manufacturing method 1, the movable die may be brought into contact with the metal plate at an early stage of the bottom dead center holding period, and then the movable die may be separated from the metal plate at an end of the bottom dead center holding period. That is, the movable die may be controlled to move from the contact position to the retracted position during the bottom dead center holding period.
[0029] (Manufacturing Method 3) In the manufacturing method 1, the movable die may be separated from the metal plate at an early stage of the bottom dead center holding period, and then the movable die may abut against the metal plate at a final stage of the bottom dead center holding period. That is, the movable die may be controlled to move from a retracted position to a contact position during the bottom dead center holding period.
[0030] (Manufacturing Method 4) In any of the above manufacturing methods 1 to 3, when the movable mold is in contact with the metal plate at the bottom dead center, the surface of the movable mold that contacts the metal plate may be arranged on the same plane as a surface of the mold that contacts the metal plate around a recess in which the movable mold is arranged.
[0031] (Manufacturing Method 5) In any of the above manufacturing methods 1 to 4, the top surface of the movable mold may have a convex portion that abuts against the metal plate when the movable mold is in contact with the metal plate at the bottom dead center, and a concave portion that does not abut against the metal plate.
[0032] (Manufacturing Method 6) In any of the above manufacturing methods 1 to 5, the top surface of one of the movable dies of the first die and the second die may have irregularities that protrude or recess in the pressing direction. An opposing surface of the other die or movable die that faces the one movable die in the pressing direction may have a shape corresponding to the irregularities of the top surface of the one movable die. When the one movable die is in contact with the metal plate at the bottom dead center, the opposing surface of the other die or movable die may also be in contact with the metal plate.
[0033] In any of the above manufacturing methods 1 to 6, the movable die may be controlled so that the non-contact period is 10% or more of the entire period during which the bottom dead center is held. Note that, a method for manufacturing a hot press-formed product by any of the above manufacturing methods 1 to 6 using a hot press apparatus of any of the above configurations 1 to 9 is also included in embodiments of the present invention.
[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated. In order to make the description easier to understand, the drawings referred to below show simplified or schematic configurations, and some components are omitted.
[0035] (Configuration example of press device) FIG. 1 is a cross-sectional view showing a configuration example of a hot press device in this embodiment. FIG. 2 is a view showing a state in which the mold of the hot press device shown in FIG. 1 is at bottom dead center. The hot press device 1 presses a metal sheet B to produce a press-formed product. The hot press device 1 includes, as molds, a die 2, a punch 3, a die pad 5, a movable mold 4, and a control unit 9. The die 2 is movable in a press direction PD relative to the punch 3. That is, the die 2 and the punch 3 are movable relative to each other. The direction of this relative movement is the press direction.
[0036] The die 2 can be moved in the pressing direction relative to the punch 3 by an elevator mechanism (actuator) 8. The elevator mechanism 8 may include, for example, a hydraulic cylinder, an air cylinder, an air cushion, or a cam. In this example, the die 2 moves relative to the punch 3, but the punch 3 may also be configured to move relative to the die 2. Alternatively, both the die 2 and the punch 3 may be configured to move.
[0037] The hot press device 1 presses the metal sheet B by placing the metal sheet B between a die 2 and a punch 3 and pressing the metal sheet B from both the die 2 and the punch 3. The die 2 and the punch 3 are examples of a first mold and a second mold.
[0038] The die 2 has a concave shape on its inside that corresponds to the shape of the press-molded product. The punch 3 has a convex shape that corresponds to the concave shape of the die 2. The surface of the die 2 that faces the punch 3 includes a pressure surface that contacts and presses the metal sheet B. The surface of the die 2 that faces the punch 3 has a concave portion 2a. The concave portion 2a does not come into contact with the metal sheet B even at bottom dead center. In other words, the concave portion 2a forms a clearance between the metal sheet B and the die 2 (see FIG. 2 ).
[0039] The die pad 5 is movable in the pressing direction relative to the die 2 via an elevating mechanism 6 such as a hydraulic cylinder. The die pad 5 is movable up and down together with the punch 3 with its top surface pressed against the metal plate B. The die pad 5 is provided at a position opposite to the top surface of the punch 3. The top surfaces of the die pad 5 and the punch 3 face each other in the pressing direction. The die pad 5 may be omitted.
[0040] The surface of the punch 3 facing the die 2 includes a pressure surface that contacts and presses the metal sheet B. The surface of the punch 3 facing the die 2 has a recess 3a. A movable mold 4 is disposed in the recess 3a. The recess 3a of the punch 3 is located opposite the recess 2a of the die 2 in the pressing direction. In other words, at least a portion of the recess 3a of the punch 3 overlaps with the recess 2a of the die 2 when viewed from the pressing direction.
[0041] The movable die 4 is provided in the recess 3a of the punch 3 and is movable relative to the punch 3 in a direction intersecting the surface of the punch 3 facing the die 2. The movable die 4 is movable in the depth direction of the recess 3a by an elevator mechanism (actuator) 7. In the example shown in FIG. 1, the movable die 4 can be pressed into the recess 3a of the punch 3. That is, the top surface of the movable die 4 can enter the recess 3a deeper than the edge of the opening of the recess 3a. In the example shown in FIG. 2, the top surface 4u of the movable die 4 is retracted deep into the recess 3a at the bottom dead center. In this case, the movable die 4 does not contact the metal sheet B between the die 2 and the punch 3. In this way, the movable die 4 is configured to be movable between a position where it contacts the metal sheet B held at the bottom dead center, i.e., a contact position, and a position where there is clearance between the metal sheet B, i.e., a retracted position. Note that, although the movable die 4 is movable in the pressing direction in the example shown in FIG. 2, the moving direction of the movable die 4 is not limited to the pressing direction. The lifting mechanism 7 can be configured, for example, by a hydraulic cylinder, an air cylinder, a cam, or a gas cushion.
[0042] 3 is a diagram showing the state in which the movable mold 4 contacts the metal sheet B at the bottom dead center. In this way, the movable mold 4 can move from the state in which it is inserted into the recess 3a until the top surface 4u of the movable mold 4 is at least at the same height as the pressure surface 3u around the recess 3a. In this example, the top surface 4u of the movable mold 4 is shaped so that it can be positioned on the same plane as the pressure surface 3u around the recess 3a. The entire top surface 4u of the movable mold 4 contacts the metal sheet B.
[0043] The control unit 9 controls the die 2, punch 3, and movable mold 4. In the example shown in FIGS. 1 to 3, the control unit 9 controls the relative movement of the die 2 and punch 3 by controlling the lifting mechanism 8 of the die 2. The control unit 9 also controls the movement of the movable mold 4 by controlling the lifting mechanism 7. The control unit 9 can supply control signals to the lifting mechanisms (actuators) 8 and 7 to control their driving.
[0044] The control unit 9 moves the die 2 and punch 3 from a state in which the heated metal sheet B is disposed between the die 2 and punch 3, which are spaced apart, toward each other in the pressing direction until they reach bottom dead center. This press-forms the metal sheet B. The control unit 9 then holds the die 2 and punch 3 at bottom dead center. As a result, during the bottom dead center holding period, the portions of the formed metal sheet B in contact with the die 2 and punch 3 are rapidly cooled and hardened.
[0045] The control unit 9 controls the movable mold 4 so that the bottom dead center holding period includes a contact period in which the movable mold 4 is in contact with the metal sheet B and a non-contact period in which the movable mold 4 is not in contact with the metal sheet B. In other words, the control unit 9 controls the operation of the movable mold 4 so that the movable mold 4 is held in a position in contact with the metal sheet B for a contact period that is shorter than the bottom dead center holding period. During the bottom dead center holding period, the control unit 9 switches the position of the movable mold 4 from the contact position to the retracted position, or from the retracted position to the contact position.
[0046] During the non-contact period of the bottom dead center holding period, the control unit 9 retracts the movable mold 4 to the back of the recess 3a, as shown in Fig. 2, for example. That is, the top surface 4u of the movable mold 4 is controlled to be located behind the edge of the opening of the recess 3a, i.e., in a retracted position where the top surface 4u does not contact the metal sheet B. This creates a clearance between the movable mold 4 and the metal sheet B. The control unit 9 may also control the amount of clearance. For example, the control unit 9 can adjust the retracted position of the top surface 4u of the movable mold 4 by controlling the lifting mechanism 7.
[0047] 3, for example, the control unit 9 moves the movable mold 4 to a position where it reaches at least the opening of the recess 3a. That is, the top surface 4u of the movable mold 4 is controlled to be at the position of the opening of the recess 3a, i.e., at the contact position where the top surface 4u is in contact with the metal sheet B. This causes the movable mold 4 to come into contact with the metal sheet B.
[0048] The control unit 9 controls the movable mold 4 so that, during the bottom dead center holding period, at least one of an operation of separating the movable mold 4 from a state in which it is in contact with the metal sheet B, or an operation of bringing the movable mold 4 from a state in which it is separated from the metal sheet B into contact with the metal sheet B is performed. The control unit 9 also controls the movable mold 4 so that the contact period and non-contact period during the bottom dead center holding period are of predetermined lengths. Data indicating the contact period or non-contact period during the bottom dead center holding period may be recorded, for example, in a recording device accessible to the control unit 9. As an example, data indicating at least one of the time (timing) when the movable mold 4 is brought into contact with the metal sheet B and the time when the movable mold 4 is separated from the metal sheet B, based on the start of the bottom dead center, may be recorded in the recording device. The control unit 9 can control the contact period and non-contact period during the bottom dead center holding period using the recorded data.
[0049] The control unit 9 can be configured, for example, by a computer including a processor and a storage device (memory). The processor executes a program stored in the storage device to realize the function of supplying control information to the lifting mechanisms 7 and 8 for the die 2, punch 3 (first and second dies), and movable die 4. As an example, the control unit 9 determines the timing and amount of movement (or direction of movement) of the die 2, punch 3, and movable die 4 based on external input and / or data pre-recorded in the memory, and determines the control information required for this movement. The control unit 9 outputs the control information to the lifting mechanism 7.
[0050] (Example of Manufacturing Process) Here, an example of a manufacturing process of a hot press-formed product using the hot press apparatus 1 will be described. First, a metal plate B, which is the raw material, is heated. Note that the metal plate B may be, for example, a flat plate or a press-formed intermediate product. As an example, the metal plate B is a steel plate. In the heating step, the metal plate B is heated to the Ac3 point or higher to austenitize the metal structure. The heated metal plate B is transported and placed between the die 2 and punch 3 of the hot press apparatus 1.
[0051] In the hot press apparatus 1, a heated metal sheet B is placed between the die 2 and the punch 3, and at least one of the die 2 and the punch 3 is moved to the bottom dead center. This causes the metal sheet B to be hot-press-formed. The formed metal sheet B is held between the die 2 and the punch 3 at the bottom dead center. During this bottom dead center holding period, the metal sheet B in contact with the die 2 and the punch 3 is rapidly cooled. A recess 2a of the die 2 and a recess 3a of the punch 3 are provided as clearances in some of the dies of the hot press apparatus 1. A movable die 4 is provided in the recess 3a. At the bottom dead center, the recess 2a does not contact the metal sheet B. When the movable die 4 is retracted into the recess 3a, i.e., in the retracted position, it does not contact the metal sheet B. As a result, the portion of the metal sheet B corresponding to the clearance between the recesses 2a and 3a cools at a slower rate than the portion in contact with the die 2 and the punch 3. This allows a portion of the metal sheet B to be slowly cooled.
[0052] During the bottom dead center holding period, the control unit 9 operates the movable mold 4 to bring it into contact with the metal sheet B. This makes it possible to switch the cooling rate from slow cooling to rapid cooling. Alternatively, the control unit 9 keeps the movable mold 4 in contact with the metal sheet B at the start of the bottom dead center, and operates the movable mold 4 during the bottom dead center holding period to separate the movable mold 4 from the metal sheet B. This makes it possible to switch the cooling rate from rapid cooling to slow cooling. This allows for slow cooling of a portion of the formed metal sheet B to change the cooling conditions, while making the temperature distribution in the metal sheet B at the end of the bottom dead center holding period closer to uniform. Furthermore, by controlling the operation of the movable mold 4 during the bottom dead center holding period, it is possible to control the cooling conditions for the portion to be slowly cooled.
[0053] When the bottom dead center holding period is over, the formed metal plate B (formed product) is removed from the mold (die 2 and punch 3). The obtained formed product has a strength distribution and excellent shape precision.
[0054] The mechanism by which the strength distribution is imparted is as follows. During hot press working, the cooling modes of the clearance portion of metal sheet B, i.e., the portion corresponding to the recesses 2a and 3a, are (1) heat conduction within metal sheet B, (2) heat transfer between metal sheet B and the atmosphere, and (3) radiation between metal sheet B and the mold. Therefore, the cooling rate in the clearance portion is slower than the heat transfer between metal sheet B and the mold due to contact with the mold. If the cooling rate from austenite is slower than the critical cooling rate determined by the steel sheet material, a diffusional transformation occurs in the steel, resulting in the formation of soft metal structures such as ferrite and bainite. Meanwhile, the portion in contact with the mold undergoes a non-diffusional transformation, resulting in a hard metal structure primarily composed of martensite. In other words, by reducing the cooling rate in part of the metal sheet, a press-formed product with a partially softened structure can be produced.
[0055] If there is a large temperature difference within the molded product when the molded metal plate (molded product) is removed from the mold, the molded product may be deformed due to thermal contraction, resulting in a defective shape. In contrast, in this embodiment, the bottom dead center holding period includes a contact period in which the movable mold 4 contacts the metal plate B and a non-contact period in which a clearance is generated between the movable mold 4 and the metal plate B. Therefore, the temperature difference within the molded product at the end of the bottom dead center holding period can be made closer to uniform. This makes it easier to ensure the shape accuracy of the entire molded product. Furthermore, during the contact period of the bottom dead center holding period, the metal plate is cooled while being restrained by the movable mold 4. Therefore, it is easier to ensure the shape accuracy of the portion restrained by the movable mold 4 compared to when the metal plate is not restrained for the entire bottom dead center holding period.
[0056] During the bottom dead center holding period, the movable mold 4 is brought into contact with the metal plate B at the beginning, and then, at the end of the bottom dead center holding period, the movable mold 4 is separated from the metal plate B. That is, during the bottom dead center holding period, there is an operation in which the movable mold 4 moves away from the state in which it is in contact with the metal plate B.
[0057] FIG. 4 is a graph showing an example in which there is a contact period at the beginning of the bottom dead center holding period. In FIG. 4, line L1 indicates the temperature of the portion of the metal sheet B being press-formed that corresponds to the movable die 4. Line L2 indicates the temperature of the portion (other portion) of the metal sheet B that is in contact with the die throughout the bottom dead center holding period. In the example shown in FIG. 4, at the start of the bottom dead center holding period, the movable die 4 is in contact with the metal sheet B. That is, at this time, the clearance CL between the movable die 4 and the metal sheet B is 0 mm. Thereafter, the movable die 4 separates from the metal sheet B and remains separated at the end of the bottom dead center holding period. At this time, the clearance is, for example, 13 mm. That is, in the example of FIG. 4, at the start of the bottom dead center, there is an initial contact period in which the movable die 4 is in contact with the metal sheet B, and after the contact period, there is a non-contact period until the end of the bottom dead center. During the contact period, the portion of the metal plate B corresponding to the movable mold 4 is restrained by the movable mold 4 as shown by line L1, maintaining its shape, and is rapidly cooled like the other portions. Therefore, the temperature difference between the portion of the metal plate B corresponding to the movable mold 4 and the other portions does not widen. During the non-contact period, the portion of the metal plate B corresponding to the movable mold 4 is cooled at a slower rate than during the contact period, and is cooled slowly.
[0058] In this way, during the bottom dead center holding period, there are periods when part of the metal plate is rapidly cooled and periods when it is slowly cooled, so the temperature difference between the slowly cooled part and the other parts is reduced. This makes it easier to ensure the shape precision of the entire molded product. In addition, because the slowly cooled part is also restrained by the mold during part of the bottom dead center holding period, it is easier to ensure the shape precision of the slowly cooled part.
[0059] In the example shown in FIG. 4 , the portion of the metal sheet B corresponding to the movable die 4 is rapidly cooled during the contact period, and then separates from the movable die 4 before reaching the Ms point (the start point of martensitic transformation), and slow cooling begins. This results in the production of a soft metal structure. Meanwhile, as shown by line L2, the other portions of the metal sheet B other than the portion corresponding to the movable die 4 are in contact with the die throughout the bottom dead center holding period and are rapidly cooled. The other portions are cooled to below the Mf point (the end point of martensitic transformation) during the bottom dead center holding period. This results in the production of a hard metal structure mainly composed of martensite. In this way, the properties (in this example, strength) of the formed metal sheet B can be made different between the portion corresponding to the movable die 4 and the other portions.
[0060] 4, the portion of the metal sheet B is rapidly cooled during the contact period when the temperature is relatively high at the beginning of the bottom dead center holding period. Since the metal sheet B is constrained by the movable mold 4 while the temperature of the metal sheet B is high and soft, it becomes easier to ensure the shape precision of the constrained portion.
[0061] During the bottom dead center holding period, the movable mold 4 is brought into contact with the metal plate B at the beginning, and then, at the end of the bottom dead center holding period, the movable mold 4 is separated from the metal plate B. That is, during the bottom dead center holding period, there is an operation in which the movable mold 4 moves away from the state in which it is in contact with the metal plate B.
[0062] FIG. 5 is a graph showing an example in which a contact period occurs at the end of the bottom dead center holding period. In FIG. 5, line L3 indicates the temperature of the portion of the metal sheet B being press-formed that corresponds to the movable die 4. Line L2 indicates the temperature of the portion (other portion) of the metal sheet B that contacts the die throughout the bottom dead center holding period. In the example shown in FIG. 5, at the start of the bottom dead center holding period, the movable die 4 is separated from the metal sheet B. At this time, the clearance CL is, for example, 13 mm. Thereafter, the movable die 4 contacts the metal sheet B, the clearance becomes 0 mm, and the contact period continues at the end of the bottom dead center holding period. That is, in the example of FIG. 5, at the start of the bottom dead center, there is an initial non-contact period, and after the non-contact period, the contact period continues until the end of the bottom dead center. Because the bottom dead center holding period includes both a non-contact period and a contact period, the shape accuracy of the molded product is easily ensured.
[0063] In the example shown in FIG. 5 , the contact period ends before the temperature of the portion of the metal sheet B corresponding to the movable die 4 drops to the Ms point, as shown by line L3. This results in the production of a soft metal structure. On the other hand, as shown by line L2, the other portions of the metal sheet B other than the portion corresponding to the movable die 4 are rapidly cooled during the bottom dead center holding period and cooled to below the Mf point. This results in the production of a hard metal structure mainly composed of martensite. In this way, the portion of the formed metal sheet B corresponding to the movable die 4 can have different properties (e.g., strength) from the other portions.
[0064] In the example of Figure 5, the temperature is relatively low at the beginning of the bottom dead center holding period, and the metal plate B is rapidly cooled during the contact period when the cooling rate slows down. In this case, the temperature difference due to rapid cooling is small, making temperature control easy. In addition, since the metal plate B is restrained and rapidly cooled when the temperature drops and it becomes slightly hard, it is easier to ensure shape precision.
[0065] The beginning of the bottom dead center holding period is a period that includes at least a part of the first half of the bottom dead center holding period and may or may not include the start of bottom dead center. The end of the bottom dead center holding period is a period that includes at least a part of the second half of the bottom dead center holding period and may or may not include the end of bottom dead center.
[0066] The contact period and non-contact period during the bottom dead center holding period are not limited to the above example. For example, there may be two or more separate contact periods during the bottom dead center holding period. As an example, there may be contact periods at the beginning and end of the bottom dead center holding period, and a non-contact period in the middle between the beginning and end.
[0067] The bottom dead center holding period is not limited to this, but can be, for example, 2 to 90 seconds. From the viewpoint of uniforming the temperature distribution of the molded product at the end of the bottom dead center holding period, a longer bottom dead center holding period is preferable, but from the viewpoint of manufacturing efficiency, a shorter bottom dead center holding period is preferable. Therefore, the lower limit of the bottom dead center holding period is preferably 10 seconds, and more preferably 15 seconds. The upper limit of the bottom dead center holding period is preferably 90 seconds, and more preferably 30 seconds. In this embodiment, since the bottom dead center holding period includes the contact period and the non-contact period, even if the bottom dead center holding period is, for example, 30 seconds or less, uniforming the temperature distribution of the molded product at the end of the bottom dead center holding period is easy.
[0068] The clearance CL during the non-contact period, i.e., the distance between the movable mold 4 at the retracted position and the metal plate B, is not limited to 13 mm in the above example. The distance between the movable mold 4 at the retracted position and the metal plate B can be, for example, 2 mm or more, preferably 4 mm or more, and more preferably 6 mm or more. The distance between the movable mold 4 at the retracted position and the metal plate B may be determined depending on the area of the recess 3 a as viewed from the pressing direction and the thickness of the metal plate B. For example, when the area of the recess 3 a is 1800 mm ２ (60 x 30 mm) and the thickness of the metal plate is 2.6 mm, it is preferable that the distance between the movable mold 4 in the retracted position and the metal plate be 2 mm or more. This makes it difficult for the metal plate to come into contact with the movable mold in the retracted position even if it undergoes out-of-plane deformation. The control unit 9 can adjust the clearance CL by adjusting the retracted position of the movable mold 4. As an example, the control unit 9 may determine the retracted position of the movable mold 4 in accordance with input from the operator. The control unit 9 may determine the retracted position of the movable mold 4 according to the input values of the clearance CL or the thickness of the metal plate B, etc.
[0069] The position of the movable die 4 during the period from the start of pressing until the die reaches bottom dead center is not particularly limited, and may be a contact position or a retracted position. For example, as shown in FIG. 4 , if there is a contact period at the beginning of the period during which bottom dead center is held, the movable die 4 can be kept in the contact position from the start of pressing until bottom dead center is reached. This eliminates the need to move the movable die 4 at the start of the period during which bottom dead center is held. From a similar perspective, if there is a non-contact period at the beginning of the period during which bottom dead center is held, as shown in FIG. 5 , the movable die 4 can be kept in the retracted position from the start of pressing until bottom dead center is reached.
[0070] (Modified Example of Movable Mold) Figure 6 is a diagram showing a modified example of the configuration of the clearance portion. In the example shown in Figure 6, a recess 2a of the die 2 is formed at a position facing the recess 3a of the punch 3. A movable mold 4 is disposed in the recess 3a of the punch 3, and further, a movable mold 21 is disposed in the recess 2a of the die 2. The movable mold 4 and the movable mold 21 are disposed in positions facing each other. In other words, when viewed from the direction of movement of the movable mold 4 in the recess 3a, at least a portion of the top surface 4u of the movable mold 4 is disposed in a position overlapping at least a portion of the top surface 21u of the movable mold 21.
[0071] 6, during the contact period of the bottom dead center holding period, the top surface 4u of the movable mold 4 contacts one surface of the metal sheet B, and the top surface 21u of the movable mold 21 contacts the other surface (opposite surface) of the metal sheet B. As a result, during the contact period, the metal sheet B can be cooled from both sides and both sides can be restrained by the movable mold. This makes it easy to ensure the cooling rate and shape accuracy.
[0072] FIG. 7 shows another modified example of the clearance configuration. In the example shown in FIG. 7 , no recess in the die 2 is formed at a position facing the recess 3 a of the punch 3. The movable die 4 is disposed in the recess 3 a of the punch 3. During the contact period of the bottom dead center holding period, the top surface 4 u of the movable die 4 contacts one side of the metal sheet B, and the die 2 contacts the other side (opposite side) of the metal sheet B. During the non-contact period, a clearance is generated between the movable die 4 and the metal sheet B, but no clearance is generated between the metal sheet B and the portion of the die 2 facing the movable die 4. Even with this configuration, the effect of ensuring shape accuracy can be achieved by having a contact period and a non-contact period during the bottom dead center holding period.
[0073] Fig. 8 is a diagram showing a modified example of the movable mold 4. In the example shown in Fig. 8, the top surface 4u of the movable mold 4 has a convex portion that is convex in the pressing direction. During the contact period when the bottom dead center is held, the convex portion of the top surface 4u of the movable mold 4 contacts the metal sheet B. The portion of the top surface 4u other than the convex portion, i.e., the concave portion, does not contact the metal sheet B. In this way, the movable mold 4 can be formed so that during the contact period, a portion of the top surface 4u of the movable mold 4 contacts the metal sheet B and another portion does not contact the metal sheet B.
[0074] 8 , during the contact period, the movable mold 4 and the metal plate B come into contact with each other, and a clearance is generated between the top surface 4u of the movable mold 4 and the metal plate B. For example, the cooling conditions can be changed by changing the proportion of the top surface 4u of the movable mold 4 that comes into contact with the metal plate B during the contact period. In other words, the cooling conditions can be controlled by the shape of the movable mold 4.
[0075] FIG. 9 is a diagram showing another modified example of the clearance portion configuration. In the example shown in FIG. 9 , the concave-convex shape of the top surface 4u of the movable mold 4 and the concave-convex shape of the opposing surface 2f of the die 2 opposing the top surface 4u are complementary shapes that correspond to each other. That is, each surface is formed so that the convex portion of the top surface 4u fits into the concave portion of the opposing surface 2f. During the contact period of the bottom dead center holding period, while the movable mold 4 is in contact with the metal sheet B, the opposing surface 2f of the die 2 also abuts against the metal sheet B. In this configuration, the metal sheet B is formed into a shape corresponding to the shape of the top surface 4u of the movable mold 4. Note that in the example shown in FIG. 9 , the surface of the die 2 faces the movable mold 4, but the movable mold of the die 2 may be positioned opposite the movable mold 4.
[0076] The hot press apparatus and the method for manufacturing a hot press-formed product according to the present embodiment can be applied to, for example, the manufacture of vehicle structural members, although this is not limited thereto. Vehicle structural members may be provided with a strength distribution and require shape precision. The embodiments can be suitably applied to such vehicle structural members. For example, the hot press apparatus according to the present embodiment can be used to manufacture vehicle structural members that are hot press-formed products (hot stamped members) having a partially softened portion within a single component to achieve weight reduction and high functionality of the vehicle body. Examples of such vehicle structural members include high-strength center pillars with soft flanges, and rear side members or bumper beams in which the fracture mode during a collision is controlled by the arrangement of the softened portion.
[0077] (Example) A clearance-controllable B-pillar die (hereinafter referred to as the clearance control die) was fabricated and tested. The clearance control die had the same configuration as that shown in FIG. 1 . This clearance control die is characterized by the presence of a clearance portion in a region corresponding to the flange portion of the B-pillar. The clearance portion includes a recess (blank) of the die 2 and a recess of the punch 3 facing it, and a movable die is disposed in the recess of the punch. The movable die allows the clearance amount of the recess of the punch to be changed to 0 mm or 13 mm. Since the clearance portion is not cooled by the die, it is cooled slowly, and the metal structure of the corresponding portion of the metal sheet is softened. For the test, a hot-rolled sheet (thickness 2.6 mm) for hot stamping (hereinafter referred to as HS) was used as the metal sheet. The metal sheet was heated in a furnace set at 900°C for 5 minutes, transported to the clearance control die, held at bottom dead center for 30 seconds, and then released from the die and allowed to cool. The clearance conditions while the bottom dead center was maintained were set to the four conditions shown in Table 1 below.
[0078]
[0079] In Table 1, (a) is the condition for press forming using a die with no clearance, which is a general HS condition in which the entire surface of the metal sheet, including the flange portion, contacts the die. (b) is the condition for press forming using a die with a fixed clearance at the flange-corresponding portion. The clearance is provided on both the die and the punch. The clearance amount is constant throughout the entire bottom dead center holding period. At the end of the bottom dead center holding period, the flange-corresponding portion is released from the die in a high temperature state. Conditions (c) and (d) are conditions for changing the punch-side clearance amount while the bottom dead center is being held. The thermal history for (c) is the same as the example shown in Figure 4, and the thermal history for (d) is the same as the example shown in Figure 5. Under condition (c), the clearance amount between the movable die and the metal sheet at the start of bottom dead center holding was 0 mm, and 5 seconds after the start of bottom dead center holding, the clearance amount was changed from 0 mm to 13 mm to switch to slow cooling. Under condition (d), the clearance was 13 mm at the start of the bottom dead center hold, and 25 seconds after the bottom dead center hold, the clearance was changed from 13 mm to 0 mm, and the die was switched to cooling. The movable die was provided in a recess on the punch side. A recess was provided on the surface of the die facing the movable die, and no movable die was provided. In other words, the clearance on the die side was constant throughout the entire bottom dead center hold period.
[0080] The hardness and shape accuracy of the flange portion of the molded product after hot press molding were evaluated. The shape accuracy was evaluated based on the torsion of the molded product and the out-of-plane deformation of the flange portion. The evaluation positions for the shape accuracy of the molded product of this example are shown in Figure 10. The shape accuracy was evaluated under conditions (b), (c), and (d) based on the data in (a).
[0081] Figure 11 is a graph showing the hardness distribution results of the molded products. Compared to the molded product under condition (a), the molded products under conditions (b) and (c) have lower hardness in the clearance area. The clearance area is the part of the molded product that corresponds to the mold clearance. The results shown in Figure 11 demonstrate the effect of local softening due to the clearance area of the fixed clearance mold and the clearance-controlled mold.
[0082] Fig. 12 is a graph showing the results of the twist angle of the molded products. The twist angle in the graph of Fig. 12 is a value that indicates the degree to which the twist evaluation cross section C1 is twisted relative to the molded product (a) when the molded products (a) to (d) are aligned with the twist alignment surface W1 shown in Fig. 10.
[0083] The results shown in Figure 12 show that the molded product (b) molded using a fixed clearance mold has worse shape accuracy with more twist than the no-clearance condition (a). On the other hand, the molded products (c) and (d) press-molded using clearance-controlled molds have twist angles less than half of that of (b), confirming an improvement in shape accuracy.
[0084] Figure 13 is a graph showing the results of out-of-plane deformation of a molded product. The amount of out-of-plane deformation shown in the graph in Figure 13 indicates the amount of deformation of the molded product surface (a) at the out-of-plane deformation evaluation position F1 shown in Figure 10. The out-of-plane deformation evaluation position F1 is a position that includes the portion corresponding to the mold clearance of the flange portion in (b) to (d). In the example shown in Figure 13, it was found that the local shape accuracy of the flange portion corresponding to the clearance portion was also improved by using the clearance-controlled mold in (c) and (d).
[0085] Although one embodiment of the present invention has been described above, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and carried out within the scope of the spirit of the present invention.
[0086] 1: Pressing device 2: Die 3: Punch 4: Movable die 9: Control unit
Claims
DEPCT6621 / 11 / 25651. A hot press assembled with a first die, a second die that is relative to the first die in the pressing direction, and a control unit optimized for controlling the relative movement of the first and second dies, where at least one die of the first and second dies, including a cavity in the surface facing the other die in the pressing direction, is placed in that cavity. The movable die can move in a direction perpendicular to the surface facing the other die, and the control unit controls the position of the movable die in such a way that the heated and pressed metal sheet is clamped between the first and second dies, and the clamping period is at the bottom dead center where the first and second dies are at the bottom dead center, as well as the bracing period where the movable die is in the bracing position where it is bracing against the metal sheet, and the non-bracing period where the movable die is in the retraction position where it is not bracing against the metal sheet.2.
1. A hot press under claim 1 in which the control unit causes the movable die to be braced against the metal plate at the beginning of the clamping period at bottom dead center and then causes the movable die to be separated from the metal plate at the end of the clamping period at bottom dead center.
3. A hot press under claim 1 in which the control unit causes the movable die to be separated from the metal plate at the beginning of the clamping period at bottom dead center and then causes the movable die to be braced against the metal plate at the end of the clamping period at bottom dead center.
4. Any hot press under claims 1 through 3 in which the cavities, including the first cavity, are provided in the first die and the second cavity are provided in the second die and are positioned facing the first cavity, and the movable die is provided in at least one cavity of the first and second cavities.
5. A hot press under claim 4 in which the movable die is provided in each of the first and second cavities. 6.
7. Any hot press under claims 1 to 6 in which the top surface of the movable die, including the protrusions, is made suitable for bracing against the metal plate and the cavity is made suitable for not bracing against the metal plate when the movable die is bracing against the metal plate while the die is at bottom dead center.
9. Any hot press under claims 1 to 7 in which the top surface of one of the movable dies of the first and second dies, including any cavities or protrusions that are collapsed or protruded in the direction of the press, the surface of the other die or movable die facing one of the movable dies in the direction of the press has a shape that is consistent with the cavity or protrusion on the top surface of one of the movable dies, and when one of the movable dies is braced against the metal plate while the die is at bottom dead center, the surface of the other die or movable die is braced against the metal plate facing one of the movable dies.
10. Any hot press under claims 1 to 8 in which the control unit adjusts the distance between the metal plate and the movable die that is found when the movable die is in the retraction position.The method of producing products from hot pressing involves positioning a sheet of metal by heating it between the first and second dies, pressing the sheet by moving the first and second dies closer together in the direction of pressing, clamping the sheet of metal while the first and second dies are at bottom dead center, and moving the movable die, which has been positioned in at least one die cavity of the first and second dies, during the bottom dead center clamping period, where the sheet of metal is clamped to the bottom dead center. This bottom dead center clamping period includes the bracing period, where the movable die is at the bracing position and braces against the sheet of metal, and the non-bracing period, where the movable die is at the retracted position and braces against the sheet of metal.11.
11. A method of producing hot pressed products under claim 10 in which the movable die is pressed against the metal plate at the beginning of the clamping period at bottom dead center and then the movable die is separated from the metal plate at the end of the clamping period at bottom dead center.
12. A method of producing hot pressed products under claim 10 in which the movable die is separated from the metal plate at the beginning of the clamping period at bottom dead center and then the movable die is pressed against the metal plate at the end of the clamping period at bottom dead center.
13. Any one of the methods of producing hot pressed products under claims 10 to 12 in which the surface of the movable die that will contact the metal plate when the movable die is pressed against the metal plate while the die is at bottom dead center is leveled with the die surface that will contact the metal plate surrounding the cavity provided for the movable die. 14.Any method of producing products from hot pressing under claims 10 through 13 where the top surface of the movable die includes protrusions made suitable for bracing against the sheet metal and cavities made suitable for not bracing against the sheet metal when the movable die braces against the sheet metal while the die is at bottom dead center.15.Any method of producing products by hot pressing under claims 10 to 14 where the top surface of one of the movable dies of the first and second dies, including any cavities or protrusions that are collapsed or protruding in the direction of pressing, the surface of the other die or movable die facing one of the movable dies in the direction of pressing has a shape that is consistent with the cavity or protrusion on the top surface of one of the movable dies, and when one of the movable dies is pressed against the metal plate while the die is at bottom dead center, the surface of the other die or movable die facing one of the movable dies is pressed against the metal plate.-----------------------------------------------------------DEPCT661.A hot press assembled with a first die, a second die that can move relative to the first die in the direction of pressing, and a control unit optimized for controlling the relative movement of the first and second dies, where at least one die of the first and second dies, including a cavity in the surface facing the other die in the direction of pressing, is placed in that cavity. The movable die can move in a direction perpendicular to the surface facing the other die, and the control unit controls the position of the movable die in such a way that the heated and pressed metal sheet is clamped between the first and second dies, with clamping periods at bottom dead center (where the first and second dies are at bottom dead center), bracing periods (where the movable die is at the bracing position where it is bracing against the metal sheet), and non-bracing periods (where the movable die is in the retraction position where it is not bracing against the metal sheet).
1. A hot press under claim 1 in which the control unit causes the movable die to be braced against the metal plate at the beginning of the clamping period at bottom dead center and then causes the movable die to be separated from the metal plate at the end of the clamping period at bottom dead center.
3. A hot press under claim 1 in which the control unit causes the movable die to be separated from the metal plate at the beginning of the clamping period at bottom dead center and then causes the movable die to be braced against the metal plate at the end of the clamping period at bottom dead center.
4. Any hot press under claims 1 through 3 in which the cavities, including the first cavity, are provided in the first die and the second cavity are provided in the second die and are positioned to face the first cavity, and the movable die is provided in at least one cavity of the first and second cavities.
5. A hot press under claim 4 in which the movable die is provided in each of the first and second cavities. 6.
7. Any hot press under claims 1 to 6 in which the top surface of the movable die, including any overhangs, is made suitable for bracing against the metal plate and the cavity is made suitable for not bracing against the metal plate when the movable die is bracing against the metal plate while the die is at bottom dead center.
9. Any hot press under claims 1 to 7 in which the top surface of one of the movable dies of the first and second dies, including any cavities or protrusions that are collapsed or protruded in the direction of the press, the surface of the other die or movable die facing one of the movable dies in the direction of the press has a shape that is consistent with the cavity or protrusion on the top surface of one of the movable dies, and when one of the movable dies is braced against the metal plate while the die is at bottom dead center, the surface of the other die or movable die is braced against the metal plate facing one of the movable dies.
10. Any hot press under claims 1 to 8 in which the control unit adjusts the distance between the metal plate and the movable die that is found when the movable die is in the retraction position.The method of producing products from hot pressing involves positioning a sheet of metal by heating it between the first and second dies, pressing the sheet by moving the first and second dies closer together in the direction of pressing, clamping the sheet of metal while the first and second dies are at bottom dead center, and moving the movable die, which has been positioned in at least one die cavity of the first and second dies, during the bottom dead center clamping period, where the sheet of metal is clamped to the bottom dead center. This bottom dead center clamping period includes the bracing period, where the movable die is at the bracing position and braces against the sheet of metal, and the non-bracing period, where the movable die is at the retracted position and braces against the sheet of metal.11.
11. A method of producing hot pressed products under claim 10 in which the movable die is pressed against the metal plate at the beginning of the clamping period at bottom dead center and then the movable die is separated from the metal plate at the end of the clamping period at bottom dead center.
12. A method of producing hot pressed products under claim 10 in which the movable die is separated from the metal plate at the beginning of the clamping period at bottom dead center and then the movable die is pressed against the metal plate at the end of the clamping period at bottom dead center.
13. Any one of the methods of producing hot pressed products under claims 10 to 12 in which the surface of the movable die that will contact the metal plate when the movable die is pressed against the metal plate while the die is at bottom dead center is leveled with the die surface that will contact the metal plate surrounding the cavity provided for the movable die. 14.Any method of producing products from hot pressing under claims 10 through 13 where the top surface of the movable die includes protrusions made suitable for bracing against the sheet metal and cavities made suitable for not bracing against the sheet metal when the movable die braces against the sheet metal while the die is at bottom dead center.15.Any method of producing products by hot pressing under claims 10 to 14 where the top surface of one of the movable dies of the first and second dies, including any cavities or protrusions that are collapsed or protruding in the direction of pressing, the surface of the other die or movable die facing one of the movable dies in the direction of pressing has a shape that is consistent with the cavity or protrusion on the top surface of one of the movable dies, and when one of the movable dies is pressed against the metal plate while the die is at bottom dead center, the surface of the other die or movable die facing one of the movable dies is pressed against the metal plate.