JP4795176B2 - Mold temperature simulation method and simulation program - Google Patents

Description

  The present invention relates to a mold temperature simulation method and a simulation program for simulating a mold temperature when a heated workpiece is pressed with a mold.

  In recent years, high-strength steel sheets are actively used in vehicles such as automobiles from the viewpoint of weight reduction and collision safety improvement. However, since the complex shape cannot be easily formed when the steel plate strength is increased, a press forming method called hot press or hot stamp is generally used. This hot press (hot stamp) forming is a method for increasing the strength of a steel sheet by heating the steel sheet to an austenite region of approximately 900 ° C. and quenching it by cooling it with a mold. In Japanese Patent Application Laid-Open No. H11-228561 and Patent Document 2, the improved technique is disclosed.

In the technique of Patent Document 1, a steel sheet is heated to a temperature not lower than the Ac3 transformation point, press-molded with a mold heated to a temperature not lower than 400 ° C and not higher than 500 ° C, and then cooled to room temperature at a rate lower than air cooling. By doing so, the toughness of the molded product is improved. Moreover, the technique of patent document 2 heats a steel plate in the temperature range of 800-1200 degreeC, and the time required for quenching is calculated based on the steel plate thickness and the steel plate temperature at the time of a press start. The product productivity is enhanced by quench forming while pressing so as to satisfy the above conditions.
JP 2005-177805 A JP 2005-205453 A

  By the way, in hot press molding, it is important to control the temperature of the mold to quickly cool the workpiece. If the mold temperature during the pressing process is simulated in advance using a computer, the mold design and product It is extremely effective in improving quality.

  However, when trying to simulate the mold temperature during the pressing process, the workpiece deforms as the pressing process proceeds, and the amount of heat transfer due to the change in the contact surface between the workpiece and the mold due to the deformation of the workpiece is calculated. Generally, it is necessary to perform a simulation by coupling a plastic deformation analysis of a workpiece and a heat conduction analysis of the workpiece and a mold. In plastic deformation analysis and heat conduction analysis, when modeling the object to be analyzed, a mesh such as FEM (finite element method) is created according to each purpose, so calculation of a plastic deformation analysis model that requires precise analysis The result is used by mapping it to a heat conduction analysis model.

  For this reason, it is necessary to match the time interval of the analysis calculation of the heat transfer phenomenon with a relatively large time constant to the plastic deformation analysis that requires a minute time step, which increases the amount of computation and calculation time required for the entire simulation. Therefore, a high-speed and large-scale system is required, and the cost and man-hour required for the simulation increase. Furthermore, it is difficult to flexibly cope with a design change or the like by quickly changing a model and executing a re-simulation.

  The present invention has been made in view of the above circumstances, and it is possible to simply simulate the mold temperature in hot press molding without coupling plastic deformation analysis and heat conduction analysis. It is an object of the present invention to provide a mold temperature simulation method and a simulation program that can be applied to a system.

  In order to achieve the above object, a mold temperature simulation method according to the present invention is a mold temperature simulation method for simulating a mold temperature when a heated workpiece is pressed with a mold. Assuming the state of plastic deformation and pressurization / holding, the shape data of the workpiece and the mold is divided into a plurality of elements, and a model construction step for constructing an analysis model for heat transfer calculation, and the analysis model A boundary condition setting step for setting a thermal boundary condition corresponding to a boundary surface between the workpiece and the mold; and a temperature distribution of the mold calculated from the thermal boundary condition as an initial state to heat the workpiece and the mold The amount of movement is calculated in predetermined time increments. When the workpiece is pressed by the mold, the metal mold is analyzed without analyzing the plastic deformation of the workpiece. Characterized in that it comprises a heat transfer amount calculation step of calculating the heat transfer amount of the workpiece and the die on the basis of the contact thermal resistance is set between.

  The mold temperature simulation program according to the present invention is a mold temperature simulation program that can be executed by a computer that simulates a mold temperature when a heated workpiece is pressed with a mold, and the workpiece is plastically deformed into a product shape. Assuming a state of pressing and holding, the shape data of the workpiece and the mold is divided into a plurality of elements, a model construction step for constructing an analysis model for heat transfer calculation, and the analysis model, A boundary condition setting step for setting a thermal boundary condition corresponding to the boundary surface between the workpiece and the mold, and a heat transfer amount of the workpiece and the mold with the temperature distribution of the mold calculated from the thermal boundary condition as an initial state Is calculated in predetermined time increments, and plastic deformation analysis of the workpiece is performed when the workpiece is pressed by the mold. Characterized in that it comprises a heat transfer amount calculation step of calculating the heat transfer amount of the workpiece and the die on the basis of no contact thermal resistance is set between the mold.

  According to the present invention, the mold temperature in the hot press molding can be simulated without coupling the plastic deformation analysis and the heat conduction analysis, and the amount of calculation and the calculation time required for the simulation can be reduced. It can be applied to large-scale systems, can reduce the cost and man-hours required for simulation, and can also flexibly respond to design changes etc. by quickly changing the model and executing re-simulation. Become.

  Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 relate to an embodiment of the present invention, FIG. 1 is a basic configuration diagram of a simulation apparatus, FIG. 2 is an explanatory diagram showing an example of a mold and a workpiece, and FIG. 3 is an explanatory diagram showing a contact thermal resistance. 4 is an explanatory diagram showing an example of a calculation mesh, FIG. 5 is an explanatory diagram showing an example of setting boundary conditions, FIG. 6 is an explanatory diagram showing the contact thermal resistance height, and FIG. 7 is a flowchart of a simulation program.

  As shown in FIG. 1, the simulation apparatus 1 according to the present embodiment is a so-called hot press that heats a workpiece such as a high-strength steel plate and presses it with a mold at room temperature. This simulates the mold temperature in press (or hot stamp) molding. The simulation apparatus 1 is configured using a single computer such as a microcomputer or a personal computer, or a plurality of computers connected to each other via a network.

  Below, the example which comprises the simulation apparatus 1 with a single computer for convenience is demonstrated. The simulation apparatus 1 includes an arithmetic device 10, an input device 11 such as a keyboard and a mouse, a display device 12 such as a CRT and a liquid crystal display, an external storage device 13 such as a magnetic disk and an optical disk, and the like.

  The arithmetic device 10 includes an internal memory such as a CPU, a ROM and a RAM, an input / output interface, and the like, and includes a simulation program stored in an internal ROM, an external storage device 13 and an external storage medium, or a network (not shown) The simulation program loaded from the outside via the communication device is executed by the CPU, and the heat between the workpiece and the mold when the workpiece (object) to be analyzed instructed via the input device 11 is press-molded. Simulate the movement phenomenon.

  The function of the simulation program executed in the arithmetic device 10 can be expressed by a model construction unit 10a, an attribute setting unit 10b, a boundary condition setting unit 10c, a heat transfer amount calculation unit 10d, and a post processing unit 10e. The arithmetic unit 10 simulates the temperature distribution of the mold using an analysis model obtained by dividing the mold and the workpiece into a plurality of elements and numerically modeling the result, and outputs the simulation to the display device 12. On the display device 12, for example, the mold temperature distribution during the simulation or at the end of the simulation is displayed graphically.

  As a feature of the temperature distribution simulation of the mold according to the present invention, the mold temperature in the molding process is simply calculated from the temperature distribution calculated in a steady state in the initial state without performing plastic deformation analysis of the press-molded work, and compared. High-speed simulation is possible.

  In other words, since the contact surface between the mold and the workpiece changes due to the deformation of the workpiece in the pressing process, strictly speaking, the heat transfer between the mold and the workpiece is a plastic deformation analysis program using a finite element method or the like. It is necessary to perform calculations by coupling with a heat conduction analysis program, which increases the amount of computation and time required for simulation, and requires a high-speed and large-scale system.

  On the other hand, the present invention constructs an analysis model of a workpiece and a mold assuming that the workpiece is pressed by a mold and plastically deformed into a product shape. Set the contact thermal resistance between. Basically, the heat transfer due to the change in the contact surface between the mold and the workpiece due to the plastic deformation of the workpiece is calculated as the heat transfer based on the change in the contact thermal resistance in the process of pressing the workpiece. It is a simple algorithm.

  As a result, it is possible to simulate the mold temperature without performing plastic deformation analysis of the workpiece, and it is possible to reduce the amount of computation and processing time required for the simulation. That is, in the present invention, the mold temperature distribution can be simulated without executing a large-scale operation in which the plastic deformation analysis of the work and the heat conduction analysis between the work and the mold are coupled. It can also be applied to small-scale systems.

  In the following, as a simulation of mold temperature distribution, as shown in FIG. 2, an upper mold 3 movable in the vertical direction and a lower mold 4 disposed and fixed via a predetermined gap with the upper mold 3 The case where the steel plate 5 as a workpiece is hot-pressed using the mold 2 having the above will be described as an example. In this simulation, as shown in FIG. 3, the steel plate 5 includes a forming portion A that forms a substantially cylindrical recess provided in the upper die 3 and a forming portion that forms a substantially cylindrical protrusion provided in the lower die 4. Assuming a state in which the product is pressed and drawn into a shape B and pressed into a product shape having a substantially hat-shaped projection, the product-shaped steel plate 5 and the upper die 3 and the lower die 4 are mutually connected. Set the contact thermal resistance RPU, RPL on the contact surface. And the amount of heat transfer between the steel plate 5 and the metal mold | die 2 is calculated by changing the value and position of this contact thermal resistance RPU, RPL every moment.

  2 and 3 show an example in which the coolant passage 6 is provided in the upper die 3 and the lower die 4, and when such a coolant passage 6 is provided, heat dissipation by the coolant is also taken into consideration. . In addition, the subscript PL in the contact thermal resistance RPU, RPL indicates the contact thermal resistance between the steel plate 5 and the upper die 3, and the subscript PL is the contact thermal resistance between the steel plate 5 and the lower die 4. It shows that there is.

  In this case, in the present embodiment, the one-cycle process of pressing the heated sheet metal material to the product shape is roughly divided into the following first process to sixth process, and this one-cycle process is repeated a plurality of times. Calculate the temperature distribution of the mold in the state of being pressed (that is, the state of pressing a plurality of workpieces continuously).

(1) 1st process It is a conveyance process of a workpiece | work, takes out the heat-treated steel plate 5 from a heating furnace, and carries it to the press machine in which the metal mold | die 2 was set.

(2) 2nd process It is the mounting process to the press of a workpiece | work, and puts the steel plate 5 on the lower mold | type 4 of the metal mold | die 2. FIG.

(3) 3rd process It is an operation | movement process of a metal mold | die, the upper mold | type 3 descend | falls and the steel plate 5 is gradually plastically deformed.

(4) 4th process It is the pressurization process of a workpiece | work, and the upper mold | type 3 reaches | attains a bottom dead center. The steel plate 5 is pressed and held in this state to have a product shape.

(5) Fifth step This is a die opening step, and the upper die 3 rises from the bottom dead center. The steel plate 5 in the product shape is left in the upper mold 3 or the lower mold 4.

(6) Sixth step This is a step of taking out the workpiece from the press machine. The steel plate 5 in the product shape is taken out and transported to a subsequent step or storage place.

  Next, the function of each part of the arithmetic unit 10 for executing the simulation in the above steps will be described.

  The model construction unit 10a constructs an analysis model that assumes a workpiece pressurizing step (fourth step). As the analysis model, the mold 2 and the steel plate 5 are divided into a plurality of elements, and an analysis model for numerical calculation based on the data of each element is constructed. As an element of the analysis model, a mesh such as a triangle, a rectangle, or a polygon is employed. For the upper mold 3, the lower mold 4, and the steel plate 5 in the pressurizing process (fourth process) shown in FIG. An analysis model MDL with a plurality of meshes Mi as shown in FIG. Each mesh has, for example, data such as a mesh number for identifying itself, a coordinate value for a predetermined reference point of a node (node) of the mesh, and these data are stored in the external storage device 13. In addition, when considering the flow of the coolant in the coolant passage 6 for cooling the mold, a mesh for the coolant is generated.

  The attribute setting unit 10b sets attributes representing a mold (upper mold, lower mold) and a steel plate corresponding to the upper mold 3, the lower mold 4, and the steel plate 5 in each mesh. In addition, when generating the mesh for cooling liquid, the attribute (usually water attribute) of a cooling liquid is set to the mesh for cooling liquid. The mesh attribute data is stored in, for example, the external storage device 13. The external storage device 13 stores various types of data necessary for the simulation process. For example, the external storage device 13 has a database composed of attribute record groups with individual identification numbers (record numbers) assigned to the objects. In the attribute record, mesh numbers, node point coordinate values, attribute data, and the like of each mesh are described in association with each other.

  The boundary condition setting unit 10 c sets a boundary condition for heat transfer for each boundary surface of the mold 2 and the steel plate 5 for each step of press forming. As shown in FIG. 2, the boundary surfaces of the respective parts in this heat transfer are the base surface (reference surface) 3 a, the side surface 3 b, the bottom surface (surface facing the lower mold 4) 3 c of the upper mold 3, and the base surface of the lower mold 4. (Reference surface) 4a, side surface 4b, upper surface (surface facing upper die 3) 4c, side surface 5a of steel plate 5, contact surface 7 between upper die 3 and steel plate 5, contact surface 8 between steel plate 5 and lower die 4 Etc. When heat dissipation by the cooling liquid is taken into consideration, boundary conditions are also set for the mold contact surface 9 of the cooling liquid.

  FIG. 5 shows an example of thermal boundary conditions set for each process. Basically, there is no contact between the mold 2 and the steel plate 5 through all the first to sixth processes, or there is no contact. For the part that can be determined not to exist, the temperature of each part, the heat transfer coefficient by the convection of the surrounding air, the ambient atmosphere temperature, etc. are set. When considering heat dissipation by cooling water (cooling liquid), set the heat transfer coefficient and cooling water temperature by cooling water convection, and if the cooling water temperature changes greatly in the passage, the cooling water Consider the heat flow.

  Further, for the second to fifth steps in which the mold 2 and the steel plate 5 are in contact, the contact thermal resistance due to the temperature difference between the lower die 4 and the steel plate 5 in the second step, the third to fourth steps. The contact thermal resistance at the contact surface between the upper die 3 and the lower die 4 and the steel plate 5 is set, and heat insulation or convection to the surroundings is performed according to the remaining state of the steel plate 5 in the mold in the fifth step. Set the heat dissipation rate.

  The heat transfer amount calculation unit 10d steadily calculates the temperature distribution inside the mold under the thermal boundary condition of the first process, and uses this temperature distribution as the initial state of the first cycle to determine the relationship between the mold and workpiece in the subsequent processes. The amount of heat transfer between them is calculated unsteadyly. This unsteady calculation of heat transfer is mainly based on the change in contact thermal resistance in the third and fourth steps until the upper die 3 is lowered and the steel plate 5 is pressurized and reaches the bottom dead center. .

  When calculating the heat transfer, set the calculation time increment Δt, set the time distribution for each process from the total process time (first to sixth process times), and set the number of repeated cycles. If necessary, the calculation result at the time specified in advance is output. When the calculation for one cycle is completed, the temperature distribution state is updated as the initial state in the calculation for the next cycle, and the calculation for N cycles is executed.

  Since the time constant Δt of the heat transfer calculation has a relatively large time constant of the heat transfer phenomenon, it is not necessary to set it to a small time step width as in plastic deformation analysis, and it can be changed arbitrarily as a constant value. May be.

[First step simulation]
In detail, in the simulation of the first process, in the first cycle, according to the boundary condition shown in FIG. 5, heat is radiated from the steel plate 5 to the ambient air, and the mold 2 (upper mold 3 and lower mold 4) is ambient air (cooling). When water is taken into consideration, the heat transfer amount qP of the steel plate 5, the heat transfer amount qU of the upper mold 3, and the heat transfer amount qL of the lower mold 4 are calculated with the heat radiation to the ambient air and the cooling water in the initial state. In the second and subsequent cycles, heat is released to the ambient air of the mold 2 (in the case of considering cooling water, ambient air and cooling water) with the simulation result (temperature distribution) of the sixth step of the previous cycle as an initial state. By calculating, the heat transfer amount qP of the steel plate 5, the heat transfer amount qU of the upper die 3, and the heat transfer amount qL of the lower die 4 are calculated.

[Simulation of the second step]
In the simulation of the second step, since the steel plate 5 is in contact with only the lower die 4, the heat release to the surroundings is calculated for the upper die 3, and the steel plate 5 and The heat transfer amount is calculated from the temperature difference with the lower mold 4 in consideration of the contact thermal resistance.

[Simulation of the third and fourth steps]
In the simulation of the third and fourth steps, the heat transfer amount qP of the steel plate 5, the heat transfer amount qU of the upper die 3, and the heat transfer amount qL of the lower die 4 are mainly used as the upper die 3 and the lower die 4 and the steel plate 5. Calculated based on contact thermal resistance due to contact with. For this reason, as shown in FIG. 6, when the pressing direction is the Z-axis direction, the contact heat resistance heights ZU and ZL, which represent the contact state between the steel plate 5 and the mold 2 in terms of the height in the Z-axis direction, are represented. The contact degree between the upper die 3 and the steel plate 5 and the contact degree between the lower die 4 and the steel plate 5 are examined.

  Specifically, the contact thermal resistance height ZU on the upper mold 3 side is a height to the top surface of the molding part B of the lower mold 4 with respect to the lower surface (surface facing the lower mold 4) 3c of the upper mold 3. It is indicated by a value obtained by removing the rounded corners and chamfered portions from the height (coordinate values). Further, the contact heat resistance height ZU on the lower mold 4 side is determined by rounding or chamfering the corner from the height (coordinate value) to the lower surface 3c of the upper mold 3 with respect to the top surface of the molded part B of the lower mold 4. It is indicated by the value excluding the part. Since these contact heat resistance heights ZU and ZL change as the upper mold 3 is lowered, the contact heat resistance heights ZU and ZL and the upper mold movement amount in the pressurizing step (the lowering amount of the upper mold 3). ) To determine the contact state.

  The upper die movement amount is the time (Time) at the press speed (lowering velocity of the upper die 3) v, where the elapsed time from the initial state (start time of the first step) is Time and the start time of the third step is Time_3. It can be obtained by multiplying by -Time_3). Therefore, by comparing the values obtained by correcting the contact thermal resistance heights ZU and ZL with the correction values ZUC and ZLC in consideration of the rounding and chamfering of the corner portion, and the upper mold movement amount V × (Time-Time_3), The contact state between the upper mold 3 and the lower mold 4 and the steel plate 5 is examined. As shown in the following formulas (1) to (6), the upper mold 3, the lower mold 4, and the steel plate 5 are singly or mutually Calculate the amount of heat transfer.

(The amount of heat transfer between the steel plate 5 and the upper mold 3)
When the upper mold movement amount V × (Time-Time_3) is equal to or less than the value obtained by adding the correction value ZUC to the contact thermal resistance height ZU, that is, when there is a gap between the upper mold 3 and the steel plate 5, (1 As shown in equation (2), the heat transfer amount qP of the steel plate 5 is calculated from the temperature difference between the steel plate temperature θP and the ambient temperature θa in consideration of heat dissipation by convection. Further, as shown in the equation (2), the heat transfer amount qU of the upper mold 3 is calculated from the temperature difference between the upper mold temperature θU and the ambient temperature θa in consideration of heat dissipation by convection.
When (ZU + ZUC) ≧ V × (Time-Time_3),
qP = α (θP−θa) (1)
qU = α (θU−θa) (2)
Where α: Convective heat dissipation rate

On the other hand, when the upper mold movement amount V × (Time-Time_3) is larger than the value obtained by adding the correction value ZUC to the contact thermal resistance height ZU, that is, when the steel plate 5 is pressed and adhered by the upper mold 3. The heat transfer amount qP from the steel plate 5 is assumed to be equal to the heat transfer amount qU to the upper mold 3. Then, as shown in the equation (3), the contact heat resistance RPU between the upper die 3 and the steel plate 5 and the temperature difference between the steel plate temperature θP and the upper die temperature θU are used to transfer the heat transfer amount qP of the steel plate 5, The heat transfer amount qU of the upper mold 3 is calculated. The contact thermal resistance RPU changes with time.
When (ZU + ZUC) <V × (Time-Time_3),
qP = qU = 1 / RPU × (θP−θU) (3)

(The amount of heat transfer between the steel plate 5 and the lower mold 4)
When the upper mold movement amount V × (Time-Time_3) is equal to or smaller than the value obtained by adding the correction value ZLC to the contact thermal resistance height ZL, that is, when there is a gap between the lower mold 4 and the steel plate 5, (4) As shown in the equation, the heat transfer amount qP of the steel plate 5 is calculated from the temperature difference between the steel plate temperature θP and the ambient temperature θa in consideration of heat dissipation by convection. Further, as shown in the equation (5), the heat transfer amount qL of the lower mold 4 is calculated from the temperature difference between the lower mold temperature θL and the ambient temperature θa in consideration of heat dissipation by convection.
When (ZL + ZLC) ≧ V × (Time-Time_3),
qP = α (θP−θa) (4)
qL = α (θL−θa) (5)

On the other hand, when the upper mold movement amount V × (Time-Time_3) is larger than the value obtained by adding the correction value ZLC to the contact thermal resistance height ZL, that is, when the steel plate 5 is pressed against the lower mold 4 and closely adhered, The amount of heat transfer qP from the steel plate 5 is assumed to be equal to the amount of heat transfer qL to the lower mold 4. And, as shown in the equation (6), the heat transfer amount qP of the steel plate 5 using the contact thermal resistance RPL between the lower die 4 and the steel plate 5 and the temperature difference between the steel plate temperature θP and the lower die temperature θL, The heat transfer amount qL of the lower mold 4 is calculated. The contact thermal resistance RPL varies with time.
When (ZL + ZLC) <V × (Time-Time_3),
qP = qL = 1 / RPL × (θP−θL) (6)

[Fifth step simulation]
In the fifth step, a case in which the steel plate 5 remains in the upper die 3 and a case in which the steel plate 5 remains in the lower die 4 is assumed. In any case, heat insulation is provided between the steel plate 5 and the mold on which the steel plate 5 remains. A gap forming a layer is generated. Therefore, in the simulation of the fifth step, in the case where the steel plate 5 remains in the upper die 3, the temperature distribution is calculated as heat insulation on the upper die 3 side, and convection heat radiation to the surroundings on the lower die 4 side. 4, the upper die 3 side is convectively dissipated to the surroundings, and the lower die 4 side is insulated, so that the heat transfer amount qP of the steel plate 5, the heat transfer amount qU of the upper die 3, and the heat transfer amount qL of the lower die 4. Calculate

[Simulation of the sixth step]
Since the simulation of the sixth step is a step of taking out the steel plate 5, the temperature distribution of the upper die 3 and the lower die 4 is calculated by convection heat radiation to the surroundings. The mold temperature calculated in the simulation of the sixth step is updated as an initial condition in the next cycle.

  The post processing unit 10e performs a visualization process so that the calculation result of the heat transfer amount can be easily grasped and a process of making the calculation result data into a file and outputting it to a storage device or the like. In the visualization process of the calculation result of the heat transfer amount, for example, the temperature distribution inside the mold is identified and displayed by hue, shading, etc., so that the temperature distribution can be easily grasped.

  Next, a simulation program executed by the CPU of the arithmetic unit 10 will be described with reference to the flowchart of FIG.

  In the simulation program of FIG. 7, first, in step S1, shape data (CAD data or the like) of the mold 2 and the steel plate 5 is read, and a plurality of the molds 2 and the steel plates 5 are added in a state where the steel plate 5 is pressed into the product shape. An analytical model for calculating the amount of heat transfer divided by the mesh is constructed.

  Next, the process proceeds to step S2, and the attributes of the steel plate and the mold are set for each mesh of the analysis model (including the cooling liquid attribute if a cooling liquid mesh is provided). In step S3, the analysis model is set. 5 is set on the boundary surface between the mold 2 and the steel plate 5 in FIG.

  In the subsequent step S4, the calculation time increment Δt is set, and in step S5, the distribution of the total process time T_cycle of one cycle to each process (first process to sixth process) is set, and the number of repeated cycles N is set. Set. Then, in step S6, the temperature distribution inside the mold, which is regularly calculated under the boundary conditions of the first process, is set as an initial state, and the elapsed time Time from this initial state (start time of the first process) is reset to zero. .

  The next step S7 is a step of calculating the amount of heat transfer qP of the steel plate 5, the amount of heat transfer qU of the upper die 3 and the amount of heat transfer qL of the lower die 4 for each time step Δt, and the intermediate result in step S8. In step S9, the calculation data is output to the external storage device 13 or the like. When the elapsed time Time has not reached the total process time T_cycle of one cycle in step S10, the time Time is calculated in step S11. Advance by the time step Δt and continue the calculation process in step S7.

  As described above, the temperature difference between the lower die 4 and the steel plate 5 is calculated in the second step of placing the steel plate 5 on the lower die 4 from the temperature distribution in the initial state (first step), as described above. The amount of heat transfer qP of the steel plate 5 due to the above, the amount of heat transfer qL of the lower die 4, and the amount of heat transfer qU of the upper die 3 due to the surrounding convection heat radiation are calculated. In the third and fourth steps in which the steel plate 5 is pressed and pressed into a product shape, the amount of heat transfer qP of the steel plate 5 based mainly on the contact thermal resistance RPU, RPL between the steel plate 5 and the mold 2, The heat transfer amount qU of the upper die 3 and the heat transfer amount qL of the lower die 4 are calculated.

  Furthermore, the amount of heat transfer in the sixth step of taking out the steel plate 5 is calculated. After that, when the elapsed time Time reaches the total process time T_cycle of one cycle, the process proceeds from step S10 to step S12, and the calculation of N cycles is completed. Check whether or not. As a result, if N cycles have not yet been reached, the initial state is updated with the calculation result of the temperature distribution in the sixth step in step S13, and the process returns to step S6 to continue the simulation. On the other hand, if N cycles have been reached in step S12, the simulation program is terminated.

  As described above, according to the present embodiment, when simulating the mold temperature in hot press (hot stamp) molding of a heated workpiece, the workpiece is pressed by the mold and plastically deformed into a product shape. For the analytical model that was assumed and constructed, the contact thermal resistance between the workpiece and the mold was set, and the heat transfer due to the change in the contact surface between the mold and the workpiece due to plastic deformation of the workpiece It is calculated as heat transfer based on the change of contact thermal resistance in the process of pressing.

  For this reason, it is not necessary to couple the plastic deformation analysis of the workpiece and the heat conduction analysis between the workpiece and the mold, and the time step size of the calculation in the heat transfer analysis must be matched to the minute time step size of the plastic deformation analysis. Therefore, heat transfer can be calculated in a relatively large time step, and the amount of calculation required for the simulation and the total calculation time can be reduced.

  As a result, simulation with a relatively small system is possible without requiring a large-scale system, and the cost and man-hour required for simulation can be reduced. It is possible to flexibly cope with such a case that the re-simulation is executed after changing the above.

Basic configuration diagram of the simulation device Explanatory drawing showing examples of molds and workpieces Explanatory drawing showing contact thermal resistance Explanatory drawing showing an example of calculation mesh Explanatory drawing showing an example of setting boundary conditions Explanatory drawing showing contact thermal resistance height Simulation program flowchart

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Simulation apparatus 2 Mold 3 Upper mold 4 Lower mold 5 Steel plate 10 Arithmetic unit 10a Model construction unit 10b Attribute setting unit 10c Boundary condition setting unit 10d Heat transfer amount calculation unit RPU, RPL Contact heat resistance qP Heat transfer amount (steel plate)
qU Heat transfer (upper mold)
qL Heat transfer (bottom mold)
Δt time increment

Claims (12)

In the mold temperature simulation method for simulating the mold temperature when pressing a heated workpiece with a mold,
Model building step that divides the shape data of the workpiece and the mold into a plurality of elements and builds an analysis model for heat transfer calculation assuming a state where the workpiece is plastically deformed into a product shape and pressed and held. When,
A boundary condition setting step for setting a thermal boundary condition corresponding to the boundary surface of the workpiece and the mold in the analysis model;
The temperature distribution of the mold calculated from the thermal boundary condition is used as an initial state to calculate the heat transfer amount of the workpiece and the mold in a predetermined time interval. A heat transfer amount calculating step for calculating a heat transfer amount of the work and the mold based on a contact thermal resistance set between the mold and the plastic deformation analysis of the work. Mold temperature simulation method. In the boundary condition setting step,
2. The mold temperature simulation method according to claim 1, wherein the thermal boundary condition is set based on convective heat radiation to the surrounding atmosphere. In the boundary condition setting step,
3. The mold temperature simulation method according to claim 2, wherein the thermal boundary condition is set in consideration of convection heat radiation to a cooling liquid for cooling the mold. In the heat transfer amount calculation step,
4. The mold temperature simulation method according to claim 1, wherein the contact thermal resistance is changed with time. In the heat transfer amount calculation step,
When the heat transfer amount calculation at the stage corresponding to the step of taking out the work from the mold after the work is press-molded into a product shape is completed, the initial temperature is calculated in the temperature distribution state by the heat transfer amount calculation. 5. The mold temperature simulation method according to claim 1, wherein the state is updated and the heat transfer amount calculation step is repeated for the set number of cycles.   The post-processing step of visualizing the temperature distribution inside the mold based on the heat transfer amount calculated in the heat transfer amount calculation step is further provided. Mold temperature simulation method. In a mold temperature simulation program that can be executed by a computer that simulates the mold temperature when pressing a heated workpiece with a mold,
Model building step that divides the shape data of the workpiece and the mold into a plurality of elements and builds an analysis model for heat transfer calculation assuming a state where the workpiece is plastically deformed into a product shape and pressed and held. When,
A boundary condition setting step for setting a thermal boundary condition corresponding to the boundary surface of the workpiece and the mold in the analysis model;
The temperature distribution of the mold calculated from the thermal boundary condition is used as an initial state to calculate the heat transfer amount of the workpiece and the mold in a predetermined time interval. A heat transfer amount calculating step for calculating a heat transfer amount of the work and the mold based on a contact thermal resistance set between the mold and the plastic deformation analysis of the work. Mold temperature simulation program. In the boundary condition setting step,
8. The mold temperature simulation program according to claim 7, wherein the thermal boundary condition is set based on convective heat radiation to the surrounding atmosphere. In the boundary condition setting step,
9. The mold temperature simulation program according to claim 8, wherein the thermal boundary condition is set in consideration of convective heat radiation to a cooling liquid for cooling the mold. In the heat transfer amount calculation step,
10. The mold temperature simulation program according to claim 7, wherein the contact thermal resistance is changed with time. In the heat transfer amount calculation step,
When the heat transfer amount calculation at the stage corresponding to the step of taking out the work from the mold after the work is press-molded into a product shape is completed, the initial temperature is calculated in the temperature distribution state by the heat transfer amount calculation. 11. The mold temperature simulation program according to claim 7, wherein the state is updated and the heat transfer amount calculation step is repeated for a set number of cycles.   The post processing step for visualizing the temperature distribution inside the mold based on the heat transfer amount calculated in the heat transfer amount calculation step is further provided. Mold temperature simulation program.

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