TWI589367B - Method of analyzing press forming - Google Patents

Description

Stamping forming analysis method

The present invention relates to a method of forming press forming, and more particularly to a press forming analysis method for predicting a shape after cooling in the case of press-formed heated press-formed material. Further, the press forming analysis method in the present specification includes: press forming analysis, which is formed by pressing a formed material and analyzing until the state before demolding; and rebound analysis, which performs springback after demolding Analysis; and shape analysis, which analyzes the shape change caused by temperature changes after rebound.

The press forming refers to a method in which a die is pressed against a press-formed material (metal material) as an object, and the shape of the mold is transferred to a press-formed material and processed. In the press forming, there is often a problem that the press-formed product is rebounded (elastically deformed) after being taken out from the mold (after demolding), and is different from the desired shape.

The reason why such a rebound is known is the residual stress of the object to be molded before demolding, which is conventionally analyzed by a numerical analysis method such as a finite element method, and after the rebound is completed. The prediction of the shape, and the analysis of its causes.

As a conventional example of the analysis of the main cause of the rebound, there is a "press forming analysis method" disclosed in Patent Document 1. "Press forming" disclosed in Patent Document 1 The parsing method includes the following three processing.

. Treatment 1: Based on the calculation of data such as the shape of the molded article before demolding and the data before demolding, the shape of the molded product after demolding is calculated, and a certain definition related to the rebound is calculated. the amount.

. Process 2: Changing the residual stress distribution in a certain region of the molded article before demolding, and calculating the shape of the molded article after demolding based on the changed data, and calculating the residual stress distribution after a certain region is changed. The rebound is related to a defined amount.

. Process 3: Calculate how a certain amount is defined before changing the residual stress distribution for a certain region.

The "Pressing and Forming Analysis Method" of Patent Document 1 predicts in a short time and accurately predicts which of the molded articles after press forming (before demolding) affects the rebound and rebounds. The researcher of the countermeasures.

The conventional rebound analysis method is a cold press forming in which press forming is performed without heating the press-formed material, as represented by the above-mentioned Patent Document 1.

Recently, in order to simultaneously achieve fuel consumption improvement and collision safety performance, as a steel sheet used in automobile parts, the ratio of high strength steel sheets has increased.

High-tensile steel sheets have large deformation resistance, so in the cold press forming of high-tensile steel sheets, there is a problem that the life of the mold is lowered, and the forming is limited to the deep drawing forming or the high-stretching flange forming, which is not subjected to strong processing. Processing problems.

Therefore, in order to avoid such a problem, a so-called warm press forming in which a press-formed material is heated to a predetermined temperature and then press-formed is applied to a high-tensile steel sheet. Warm stamping is a technique as described below: by cold stamping to form a high temperature The forming is performed to lower the deformation resistance of the high-tensile steel sheet and to improve the deformability, thereby preventing defects such as punching and chipping. Such a warm press forming technique is disclosed, for example, in Patent Document 2.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2007-229724

Patent Document 2: Japanese Patent Laid-Open Publication No. 2001-314923

The inventors and the like have studied the shape defect after the warm press forming of the high-tensile steel, and performed the rebound analysis after the demolding by the finite element method. The shape obtained in the rebound analysis was compared with the shape of the molded article actually obtained by the warm press forming, and a large deviation was found.

From this, it is understood that the temperature of the molded article immediately after demolding in the warm press forming is high, and if the heat shrinkage during the cooling process is not considered, it is impossible to analyze the shape of the final shape or the reason.

However, in the conventional technique for studying the shape defect by the press forming analysis and the rebound analysis, the cold press forming is premised, so that the temperature distribution generated in the press-formed material is not considered, and the warm press forming cannot be analyzed. In the case of shape defects.

The present invention has been made to solve the above problems, and an object of the invention is to provide a press forming analysis method capable of predicting a shape after cooling in warm press forming.

The inventors have obtained the knowledge that the temperature of the molded article immediately after demolding in the warm press forming is high, and the shape defect occurring in the warm press forming affects not only the residual stress in the bottom dead point, but also the residual stress in the bottom dead point. It also affects the temperature distribution, and further needs to consider the heat shrinkage during the cooling process based on the temperature distribution. Based on this finding, it is considered that the above problem can be solved by the method of press forming a heated press-formed material, and obtaining a temperature distribution at the time of rebound, based on the temperature distribution due to the cooling process. The deformation caused by heat shrinkage is analyzed.

The present invention is based on such an idea, and specifically includes the following constituents.

(1) A press forming analysis method comprising: a press forming analysis step of setting an initial temperature distribution to a heated press-formed material, coupling the temperature analysis and the structural analysis to perform press forming analysis, and obtaining the peeling after press forming Shape information, temperature distribution, stress distribution and strain distribution in front of the mold; rebound analysis step based on shape information, temperature distribution, stress distribution and strain distribution obtained in the analysis step of the press forming without considering the mold and being stamped The contact heat transfer between the forming materials couples the temperature analysis and the structural analysis to perform springback analysis, and obtains shape information, temperature distribution, stress distribution, and strain distribution after rebound; and a shape analysis step based on the rebound The shape information, the temperature distribution, the stress distribution, and the strain distribution obtained in the analysis step are coupled to the temperature analysis and the structural analysis, and the temperature distribution of the material to be press-formed is within ±5° C. during cooling and after cooling. The changes are resolved.

(2) A press forming analysis method comprising: a press forming analysis step of setting an initial temperature distribution to a heated press-formed material, coupling the temperature analysis and the structural analysis to perform press forming analysis, and obtaining the peeling after press forming Shape information, temperature distribution, stress distribution and strain distribution before the mold; a rebound analysis step that combines temperature analysis and structural analysis based on shape information, temperature distribution, stress distribution, and deformation distribution obtained in the press forming analysis step and considering contact heat transfer between the mold and the material to be stamped. Performing springback analysis, and obtaining shape information, temperature distribution, stress distribution, and deformation distribution after rebound; and shape analysis step based on shape information, temperature distribution, stress distribution, and deformation obtained in the rebound analysis step The distribution is analyzed by combining temperature analysis and structural analysis to change the shape during the cooling process and the cooling after the temperature distribution of the press-formed material is within ±5°C.

(3) The press forming analysis method according to (1) or (2), wherein the structural analysis in the shape analysis step includes a structural analysis of a final step of the structural analysis by a static implicit method.

(4) A press forming analysis method comprising: a press forming analysis step of setting an initial temperature distribution to a heated press-formed material, combining temperature analysis and structural analysis to perform press forming analysis, and obtaining a shape before demolding Information, temperature distribution, stress distribution, and deformation distribution; a rebound analysis step based on shape information, temperature distribution, stress distribution, and deformation distribution obtained in the press forming analysis step and regardless of the relationship between the mold and the material to be stamped Contact heat transfer, combine temperature analysis with structural analysis to perform springback analysis, and obtain shape information, temperature distribution, stress distribution, and deformation distribution after rebound; a first shape analysis step based on the rebound analysis step The obtained shape information, temperature distribution, stress distribution, and deformation distribution are combined with temperature analysis and structural analysis to analyze the shape change of the temperature of the press-formed material within ±5° C. during cooling and after cooling. a second shape analysis step obtained in the above-described rebound analysis step Temperature points The cloth is changed, and the temperature distribution after the change and the shape information, the stress distribution, and the strain distribution obtained in the rebound analysis step are coupled to the temperature analysis and the structural analysis, and the temperature distribution of the material to be pressed is ±5. Analysis of the shape change during cooling and after cooling within °C; and a shape comparison step of the cooled press-formed material obtained by the analysis of the second shape analysis step and the first shape analysis step The shape is compared.

(5) A press forming analysis method comprising: a press forming analysis step of setting an initial temperature distribution to a heated press-formed material, coupling the temperature analysis and the structural analysis to perform press forming analysis, and obtaining a shape before demolding Information, temperature distribution, stress distribution and strain distribution; rebound analysis step based on shape information, temperature distribution, stress distribution and strain distribution obtained in the stamping analysis step and considering contact between the mold and the material to be stamped Heat transfer, performing temperature analysis and structural analysis coupling for rebound analysis, and obtaining shape information, temperature distribution, stress distribution, and strain distribution after rebound; a first shape analysis step based on the rebound analysis step Obtaining the shape information, the temperature distribution, the stress distribution, and the strain distribution, and coupling the temperature analysis and the structural analysis to analyze the shape change in the cooling process and the cooling after the temperature distribution of the press-formed material is within ±5 ° C; a second shape analysis step that is obtained in the rebound analysis step The temperature distribution is changed, and the temperature distribution after the change and the shape information, the stress distribution, and the strain distribution obtained in the rebound analysis step are coupled to the temperature analysis and the structural analysis, and the temperature distribution of the material to be pressed is ± Analysis of the shape change during cooling and after cooling within 5 ° C; and a shape comparison step by the second shape analysis step and the first shape solution The shape of the cooled press-formed material obtained by the analysis of the analysis step was compared.

(6) The press forming analysis method according to (4) or (5), wherein the structural analysis in the first shape analysis step and the second shape analysis step includes a final step of performing the structural analysis by a static implicit method. Construction analysis.

According to the present invention, since the shape after cooling in the warm press forming can be predicted, it is possible to take measures against the shape defects in the warm press forming, and effects such as reduction in test man-hours or cost in the design stage of the press-formed product can be expected.

1‧‧‧Compression forming analysis device

3‧‧‧Display device

5‧‧‧ Input device

7‧‧‧Main memory device

9‧‧‧Auxiliary memory device

11‧‧‧Operation Processing Department

13‧‧‧Compression forming method

15‧‧‧Rebound analysis

17‧‧‧Shape analysis

19‧‧‧Changes in temperature distribution

20‧‧‧Shape comparison means

21‧‧‧B pillar upper part

23‧‧‧Adjustment rod

31‧‧‧Shaped shape

33‧‧‧Resolved shape after rebound

35‧‧‧Shape after shape analysis (shape after first shape analysis)

37‧‧‧Shape surface shape

39‧‧‧Second shape after shape analysis

S1~S11‧‧‧ steps

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow chart showing the flow of processing of an embodiment of the present invention.

Fig. 2 is a block diagram showing the configuration of an apparatus according to an embodiment of the present invention.

Fig. 3 is a schematic view showing a solid stamped product of an embodiment of the present invention.

Fig. 4 is a view showing a sectional shape of a mold used in an embodiment of the present invention.

Fig. 5 is a view showing a comparison of the shapes of the mold, the actual stamped product, and the analysis result in the examples of the present invention.

Fig. 6 is a flow chart showing the flow of processing of an embodiment of the present invention.

Fig. 7 is a block diagram showing the configuration of an apparatus according to an embodiment of the present invention.

Fig. 8 is a view showing a temperature distribution of a wrinkle cross section of a hat cross-sectional shape in an embodiment of the present invention.

Fig. 9 is a view showing only half of the temperature distribution of the entire hat-shaped cross-sectional shape as another example of the embodiment of the present invention.

Fig. 10 is a schematic view showing a solid stamped product of an embodiment of the present invention.

Fig. 11 is a view showing the temperature distribution of a solid stamping product according to an embodiment of the present invention.

Fig. 12 is a view showing a sectional shape of a mold used in an embodiment of the present invention.

Fig. 13 is a view for explaining the shape obtained in the first shape analysis step in the embodiment of the present invention.

Fig. 14 is a view for explaining a shape comparison step in the embodiment of the present invention.

[Embodiment 1]

The press forming analysis method according to the first embodiment is performed by a device such as a personal computer (PC, Personal Computer) that executes a program processing, and therefore, first, based on the block diagram shown in FIG. 2 (hereinafter referred to as a "stamping and forming device" The structure of 1") is summarized.

(press forming analysis device)

The press forming analysis apparatus 1 of the first embodiment includes a PC (personal computer) or the like, and includes a display device 3, an input device 5, a main memory device 7, an auxiliary memory device 9, and an arithmetic processing unit 11 as shown in Fig. 2 .

Further, the arithmetic processing unit 11 is connected to the display device 3, the input device 5, the main memory device 7, and the auxiliary storage device 9, and performs functions by the command of the arithmetic processing unit 11. The display device 3 is used for display of calculation results and the like, and includes a liquid crystal monitor or the like.

The input device 5 is used for input from an operator, etc., including a keyboard or a mouse.

The main memory device 7 is used for temporary storage or calculation of data used in the arithmetic processing unit 11, and includes a random access memory (RAM). The auxiliary memory device 9 is used for data storage and the like, and includes a hard disk or the like.

The arithmetic processing unit 11 includes a central processing unit (CPU, Central Processing Unit) such as a PC, and the like, and includes, in the arithmetic processing unit 11, a press forming analysis means 13, a rebound analyzing means 15, and a shape analyzing means 17. These means are implemented by executing a predetermined program by a CPU or the like. The following means will be described below.

<Press forming analysis means>

The press forming analysis means 13 sets an initial temperature distribution to the heated press-formed material, combines temperature analysis and structural analysis, and performs press forming analysis, and obtains shape information, temperature distribution, and stress distribution after press forming (before demolding). And deformation distribution.

<Rebound analysis method>

The rebound analysis means 15 performs the springback analysis by combining the temperature analysis and the structural analysis based on the information obtained by the press forming analysis means 13, and acquires the shape information, the temperature distribution, the stress distribution, and the deformation distribution after the rebound. .

<Shape analysis means>

The shape analysis means 17 combines the temperature analysis and the structural analysis based on the shape information, the temperature distribution, the stress distribution, and the deformation distribution acquired by the rebound analysis means 15, and the temperature distribution of the material to be press-formed is ±5. The analysis is performed during the cooling process within the °C and during the cooling process.

(Pressing analysis method)

The press forming analysis method according to the first embodiment is completed by performing the respective processes by the respective means of the "press forming analysis means", the "rebound analysis means", and the "shape analysis means", and includes the following Stepper.

That is, the press forming analysis method according to the first embodiment includes a press forming analysis step of setting an initial temperature distribution to the heated press-formed material, combining the temperature analysis and the structural analysis to perform press forming analysis, and obtaining the press forming ( Shape information, temperature distribution, stress distribution and deformation distribution before demolding; rebound analysis step based on shape information, temperature distribution, stress distribution and deformation distribution obtained in the analysis step of the press forming without considering the mold and The contact heat transfer between the press-formed materials is combined with the temperature analysis and the structural analysis to perform springback analysis, and the shape information and temperature distribution after the rebound are obtained. a force distribution and a strain distribution; and a shape analysis step of coupling the temperature analysis and the structural analysis based on the shape information, the temperature distribution, the stress distribution, and the strain distribution obtained by the rebound analysis step to the stamped molding material The temperature distribution was analyzed during the cooling process up to within ±5 ° C and the shape change after cooling.

In the press forming analysis method according to the first embodiment, as described above, the temperature analysis and the structural analysis are coupled to each other to perform analysis. The analysis that couples the temperature analysis and the structural analysis means that the temperature distribution of the material to be pressed is analyzed (temperature analysis) in consideration of air cooling, contact heat transfer between the mold and the material to be pressed, and the like. Based on the temperature distribution obtained thereby, temperature dependent data corresponding to the temperature (Young's modulus, Poisson's ratio, thermal expansion coefficient, relief stress, stress-strain line diagram, specific heat, thermal conductivity, etc.) are used. ) Analysis of the stress state and the like (structural analysis).

Hereinafter, each of the above steps in the press forming analysis method according to the first embodiment will be described in detail based on the flowchart of Fig. 1 .

<Press forming analysis step>

In the press forming analysis step, an initial temperature distribution is set for the heated press-formed material, and temperature analysis and structural analysis are coupled to perform press forming analysis, and shape information, temperature distribution, stress distribution and after stress forming (before demolding) are obtained. The strain distributor (step S1).

The setting of the initial temperature distribution for the heated press-formed material will be described below.

In the actual warm press forming, the press-formed material is sufficiently heated by the electric furnace to have a uniform temperature, and then transferred to a press machine by a transfer robot to perform press forming. Therefore, in the press forming analysis step, it is assumed that the actual press-formed material is heated, and the entire press-formed material is set to a uniform temperature (for example, 600 ° C) as the initial temperature. Furthermore, in order to expect more accuracy, you can also consider The air in the middle of the conveyance after the electric furnace is heated is cooled to calculate the temperature distribution and set as the initial temperature distribution.

Since the press forming analysis step is performed by the press forming analysis means 13, the temperature dependent data (Young's modulus, Poisson's ratio, thermal expansion coefficient, and the like required for the press forming analysis means 13 are input in the press forming analysis step. The stress, strain-strain diagram, specific heat, thermal conductivity, etc. are applied to the stamped material and the mold to give an initial temperature distribution.

Further, in the actual warm press forming, the press-formed material is cooled in a state where the press-formed material is held for a fixed period of time in the press-down state, whereby the occurrence of springback after demolding is suppressed depending on the shape of the part. And the shape becomes good. Therefore, in the press forming analysis step, the press-formed material can be cooled in the mold for a fixed period of time. However, in the actual warm press forming, since the cooling time is prolonged and the production efficiency is deteriorated, it is preferable to set the cooling time in consideration of the actual working efficiency in setting the cooling time in the press forming analysis step.

The information necessary for the shape information, temperature distribution, stress distribution and strain distribution of the formed material and the mold to be demolded before the demolding is transferred to the next rebound analysis step.

<Rebound analysis step>

The rebound analysis step is based on the shape information, the temperature distribution, the stress distribution, and the strain distribution obtained in the press forming analysis step, and the temperature analysis and the structural analysis are coupled without considering the contact heat transfer between the mold and the material to be stamped. The rebound analysis is performed, and the shape information, the temperature distribution, the stress distribution, and the strain distribution after the rebound are obtained (step S3).

In the rebounding step of the first embodiment, the analysis is performed regardless of the contact heat transfer between the mold and the material to be pressed. Therefore, in the rebounding step, it is stamped and formed The temperature of the material is not reduced due to contact with the mold, and only the temperature drop due to air cooling is considered and calculated. By doing so, the calculation becomes simple, and convergence is easily obtained as compared with the case where the contact heat transfer is considered and analyzed.

The specific analytical method for performing springback analysis without considering the contact heat transfer between the mold and the material to be stamped is based on the information obtained in the analysis step of the press forming, which is an initial condition, and constrains one or several of the material to be stamped. The joints are not moved by the joints, and the stress is released from the state of the bottom dead center and calculated. It is assumed that the time for releasing the stress is a fixed time.

The necessary information such as shape information, temperature distribution, stress distribution, strain distribution, etc. of the formed material after the rebound is transferred to the next shape analysis step.

Further, in the case where the stress is released from the state of the bottom dead center, that is, the assumed time is short, and is equal to or less than 1 second, only a temperature change of a negligible degree is caused, and therefore temperature analysis may not be performed. In this case, the temperature distribution of the press-formed material after the press forming analysis is directly set to the temperature distribution after the rebound, and is transferred to the next shape analysis step. However, even if the temperature analysis is not performed in the present rebound analysis step, the structural analysis is analyzed based on the temperature distribution after the press forming analysis and the temperature dependent data.

<Shape analysis step>

The shape analysis step is based on the shape information, the temperature distribution, the stress distribution, and the strain distribution acquired in the rebound analysis step, and the temperature analysis and the structural analysis are coupled to each other so that the temperature distribution of the material to be pressed is within ±5 ° C. The shape change during cooling and after cooling is analyzed (step S5).

The shape analysis step is performed using the shape analysis means 17, and the shape information, the temperature distribution, the stress distribution, the strain distribution, and the like of the press-formed material after the rebound analysis are The initial conditions analyze the change in the temperature distribution due to cooling, and perform structural analysis considering heat shrinkage.

As a specific analysis method in the shape analysis step, one or a plurality of nodes of the press-formed material are restrained so that the press-formed material does not move during the cooling process. Regarding the constraints of the nodes, the node constraints used in the above-described rebound parsing step can also be used.

The temperature analysis can also be carried out on the assumption of air cooling, but it is assumed that it is placed on the cooling stage for cooling in actual operation, and the analysis of the heat transfer of the contact between the cooling stage and the material to be pressed is considered, which is closer to the actual The temperature analysis result of the operation.

In the shape analysis step, the temperature change of the material to be press-formed is analyzed within a cooling process of ±5° C. and the shape change after cooling, and the reason is as follows.

In the actual warm press forming, when the temperature of the material to be stamped is lowered to the ambient temperature such as room temperature, the temperature distribution of the entire press-formed material converges within ±5 ° C (more preferably within ±1 ° C). At the time, there is almost no change in shape due to temperature. Therefore, in the shape analysis step, the cooling time should be sufficiently ensured so as to satisfy the conditions of the temperature distribution described above.

Furthermore, the structural analysis of the shape analysis step can be performed dynamically or statically in principle. When the dynamic analysis is performed, the time can be compressed and processed on a time scale, so that the calculation time becomes faster. However, when the analysis is completed by the dynamic analysis, the calculation accuracy is lowered due to the influence of the residual inertial force. Therefore, in order to obtain a more accurate calculation result, it is preferable to perform structural analysis of all shape analysis steps statically. Alternatively, in order to enjoy the advantage of dynamic analysis, it is preferable to divide the shape analysis step into two stages, and dynamically perform the initial stage, and statically perform the final stage. example For example, when a cooling time of 1001 seconds is assumed, if the first 1000 seconds are performed by time-compression by dynamic analysis, and the last analysis is performed for the last one second, the calculation accuracy can be improved while the calculation accuracy can be improved. Furthermore, it is more preferable to use the static implicit method at the final stage of the structural analysis of the shape analysis step.

As described above, in the press forming analysis method according to the first embodiment, each of the press forming analysis step and the rebound analysis step is performed by coupling the temperature analysis and the structural analysis, and performing a shape analysis step. Based on the shape and temperature distribution obtained in the rebound analysis step and coupling the temperature analysis and the structural analysis, the shape change due to the temperature change is analyzed, so that the shape after cooling in the warm press forming can be predicted, and It is possible to take measures against the shape defects in the warm press forming, and it is expected to have effects such as reduction in test man-hours or cost in the design stage of the press-formed product.

[Embodiment 2]

The press forming analysis method according to the second embodiment includes a press forming analysis step of setting an initial temperature distribution to a heated press-formed material, coupling the temperature analysis and the structural analysis, performing press forming analysis, and obtaining shape information after press forming. Temperature distribution, stress distribution and strain distribution; rebound analysis step based on shape information, temperature distribution, stress distribution and strain distribution obtained in the analysis step of the press forming and considering the contact heat between the mold and the material to be stamped Transmitting, performing temperature analysis and structural analysis coupling for rebound analysis, obtaining shape and temperature distribution after rebound; and shape analysis step based on shape information, temperature distribution, and stress distribution acquired in the rebound analysis step And the strain distribution, the temperature analysis and the structural analysis are coupled to each other, and the temperature change of the material to be press-formed is analyzed within a cooling process of ±5° C. and a shape change after cooling.

The press forming analysis method in the second embodiment is considered in the embodiment. The contact heat transfer between the mold and the material to be pressed which are not considered in the rebound analysis step of the press forming analysis method in the first embodiment is the same as the press forming analysis method according to the first embodiment.

Therefore, the case where the contact heat transfer between the mold and the material to be press-formed is considered in the rebound analysis step of the second embodiment will be described below.

In the rebound analysis step, the effect produced by considering the contact heat transfer between the mold and the material to be stamped is as follows.

The temperature change due to the mold release can be more accurately considered, and the temperature distribution of the material to be molded after the rebound can be more accurately obtained. As a result, the shape analysis step can be more accurately determined. The shape of the molded article after cooling.

However, in the rebound analysis step as in the first embodiment, the contact heat transfer between the mold and the material to be press-formed is not considered, and the advantage of convergence is easily obtained. Therefore, both of them can be used depending on the specific conditions.

In the rebound analysis step, as a specific method for considering the analysis of the contact heat transfer between the mold and the material to be pressed, the one or several nodes of the press-formed material are restrained so that the material to be stamped does not move, and the mold is moved. And the simulation is demoulding. In this case, temperature analysis is performed by accurately considering the cooling due to contact with the mold and the air cooling of the portion not in contact with the mold.

Furthermore, the initial conditions in the rebound analysis step and the transfer of the data after the rebound are the same as in the first embodiment.

As described above, according to the second embodiment, the temperature change due to the mold release can be more accurately considered as described above, and the temperature distribution of the material to be molded after the rebound can be more accurately obtained. As a result, the following can be obtained as follows. Effect: The shape of the molded article after cooling obtained by the shape analysis step can be more accurately obtained.

Further, in the above-described first and second embodiments, a method of performing warm press forming and analyzing the material to be press-formed to 600 ° C will be described. However, even in the case of analyzing the cold press forming, the present invention can be applied to analysis in consideration of the influence of heat such as heat generation or frictional heat generation.

Further, by combining the present invention with a method for investigating the influence of the stress distribution as in Patent Document 1, it is an analytical means for press forming which has a high practical value for studying the countermeasure against shape defects.

[Embodiment 3]

The press forming analysis method according to the third embodiment is performed by a device such as a PC (personal computer) that executes a program processing. Therefore, first, based on the block diagram shown in FIG. 7 (hereinafter referred to as "press forming analysis device 1") The composition is summarized.

(press forming analysis device)

The press forming analysis apparatus 1 of the third embodiment includes a PC (personal computer) or the like, and includes a display device 3, an input device 5, a main memory device 7, an auxiliary memory device 9, and an arithmetic processing unit 11 as shown in Fig. 7 .

Further, the arithmetic processing unit 11 is connected to the display device 3, the input device 5, the main memory device 7, and the auxiliary storage device 9, and performs functions by the command of the arithmetic processing unit 11. The display device 3 is used for display of calculation results and the like, and includes a liquid crystal monitor or the like.

The input device 5 is used for input from an operator, etc., and includes a keyboard, a mouse, and the like.

The main memory device 7 is used for temporary storage or calculation of data used in the arithmetic processing unit 11, and includes a RAM or the like. The auxiliary memory device 9 is used for data storage and the like, and includes a hard disk or the like.

The arithmetic processing unit 11 includes a CPU or the like of a PC or the like, and includes, in the arithmetic processing unit 11, a press forming analysis means 13, a rebound analyzing means 15, a shape analyzing means 17, and a temperature distribution. The changing means 19 and the shape comparing means 20. These means are implemented by executing a predetermined program by a CPU or the like. The following means will be described below.

<Press forming analysis means>

The press forming analysis means 13 sets the initial temperature distribution to the heated press-formed material, couples the temperature analysis and the structural analysis, and performs press forming analysis, and obtains shape information, temperature distribution, and stress distribution after press forming (before demolding). And strain distribution.

<Rebound analysis method>

The rebound analysis means 15 performs the springback analysis by coupling the temperature analysis and the structural analysis based on the information obtained by the press forming analysis means 13, and acquires the shape information, the temperature distribution, the stress distribution, and the strain distribution after the rebound. .

<Shape analysis means>

The shape analysis means 17 couples the temperature analysis and the structural analysis based on the shape information, the temperature distribution, the stress distribution, and the strain distribution acquired by the rebound analysis means 15, and the temperature distribution of the material to be pressed is within ±5 ° C. The shape change during cooling and after cooling is analyzed.

Further, the shape analysis means 17 performs the processing of the steps of both the first shape analysis step and the second shape analysis step as described below.

<Means of temperature distribution change>

The temperature distribution changing means 19 applies a change to the temperature distribution acquired by the rebound analyzing means 15. Specifically, the temperature distribution of a predetermined portion of the material to be molded is changed in accordance with an instruction from the operator.

<Shape comparison means>

The shape comparison means 20 compares the shapes of a plurality of cooled press-formed materials obtained by the shape analysis means 17. Specifically, it has the following functions: The shape of the formed material after cooling is displayed on the display device 3 in a state where the operator can visually compare.

(Pressing analysis method)

The press forming analysis method according to the third embodiment is executed by each of the means of the "press forming analysis means", the "rebound analysis means", the "shape analysis means", the "temperature distribution changing means", and the "shape comparison means". The process is completed and is included in the steps shown below.

That is, the press forming analysis method according to the third embodiment includes a press forming analysis step of setting an initial temperature distribution to the heated press-formed material, coupling the temperature analysis and the structural analysis, performing press forming analysis, and obtaining the mold before the mold release. Shape information, temperature distribution, stress distribution and strain distribution; rebound analysis step based on shape information, temperature distribution, stress distribution and strain distribution obtained in the press forming analysis step and regardless of the mold and the material to be stamped The contact heat transfer is performed by coupling the temperature analysis and the structural analysis to perform springback analysis, and obtaining the shape information, the temperature distribution, the stress distribution, and the strain distribution after the rebound; the first shape analysis step is based on the rebound analysis step. The shape information, the temperature distribution, the stress distribution, and the strain distribution are obtained, and the temperature analysis and the structural analysis are coupled to each other, and the temperature distribution of the material to be press-formed is analyzed within a cooling process of ±5° C. and the shape change after cooling. a second shape analysis step, which is in the above-described rebound analysis step The temperature distribution is changed, and based on the temperature distribution after the change and the shape information, the stress distribution and the strain distribution obtained in the rebound analysis step, the temperature distribution and the structural analysis are coupled to the temperature distribution of the formed material. Analysis of the shape change during cooling and after cooling within ±5 ° C; The shape comparison step compares the shape of the cooled press-formed material obtained by the analysis of the second shape analysis step and the first shape analysis step.

In the press forming analysis method according to the third embodiment, as described above, the temperature analysis and the structural analysis are coupled to each of the analysis steps to perform analysis. The analysis that couples the temperature analysis and the structural analysis means that the temperature distribution of the material to be pressed is analyzed (temperature analysis) in consideration of air cooling, contact heat transfer between the mold and the material to be pressed, and the like. Based on the temperature distribution obtained thereby, the temperature dependence data (Young's modulus, Poisson's ratio, thermal expansion coefficient, relief stress, stress-strain diagram, specific heat, thermal conductivity, etc.) corresponding to the temperature is used for stress state, etc. Analysis (structural analysis).

Hereinafter, each of the above steps in the press forming analysis method according to the third embodiment will be described in detail based on the flowchart of FIG. 6. In the following description, a case where a foam molding hat-shaped cross-sectional shape is exemplified is exemplified.

<Press forming analysis step>

The press forming analysis step is performed by setting an initial temperature distribution on the heated press-formed material, coupling the temperature analysis and the structural analysis, and performing press forming analysis, and obtaining shape information, temperature distribution, stress distribution, and after stress forming (before demolding). The strain distributor (step S1).

The setting of the initial temperature distribution for the heated press-formed material will be described below.

In actual hot press forming, the press-formed material is sufficiently heated by the electric furnace to have a uniform temperature, and then conveyed by a transfer robot to a press machine to perform press forming. Therefore, in the press forming analysis step, the actual press-formed material is heated, and the entire press-formed material is set to a uniform temperature (600 ° C) as the initial temperature. Further, in order to make the expectation more accurate, it is also possible to consider the air cooling in the middle of the conveyance after the electric furnace is heated and calculate the temperature distribution and set it as the initial temperature distribution.

Since the press forming analysis step is performed by the press forming analysis means 13, the temperature dependent data (Young's modulus, Poisson's ratio, thermal expansion coefficient, and the like required for the press forming analysis means 13 are input in the press forming analysis step. The stress, strain-strain diagram, specific heat, thermal conductivity, etc. are applied to the stamped material and the mold to give an initial temperature distribution.

Further, in the actual warm press forming, the press-formed material is cooled in a state where the press-formed material is held for a fixed period of time in the press-down state, whereby the occurrence of springback after demolding is suppressed depending on the shape of the part. And the shape becomes good. Therefore, in the press forming analysis step, the press-formed material can be cooled in the mold for a fixed period of time. However, in the actual warm press forming, since the cooling time is prolonged and the production efficiency is deteriorated, it is preferable to set the cooling time in consideration of the actual working efficiency in setting the cooling time in the press forming analysis step.

The information necessary for the shape information, temperature distribution, stress distribution and strain distribution of the formed material and the mold to be demolded before the demolding is transferred to the next rebound analysis step.

<Rebound analysis step>

The rebound analysis step is based on the shape information, the temperature distribution, the stress distribution, and the strain distribution obtained in the press forming analysis step, and the temperature analysis and the structural analysis are coupled without considering the contact heat transfer between the mold and the material to be stamped. The rebound analysis is performed, and the shape information, the temperature distribution, the stress distribution, and the strain distribution after the rebound are obtained (step S3).

In the rebounding step of the third embodiment, the analysis is performed regardless of the contact heat transfer between the mold and the material to be pressed. Therefore, in the rebounding step, the temperature of the press-formed material is not lowered due to contact with the mold, and only the temperature drop due to air cooling is considered and calculation is performed. By doing this, the calculation becomes simple, and considering the contact heat transfer Convergence is also easy to achieve compared to the case of handing and parsing.

The specific analytical method for performing springback analysis without considering the contact heat transfer between the mold and the material to be stamped is based on the information obtained in the analysis step of the press forming, which is an initial condition, and constrains one or several of the material to be stamped. The joints are not moved by the joints, and the stress is released from the state of the bottom dead center and calculated. It is assumed that the time for releasing the stress is a fixed time.

The necessary information such as shape information, temperature distribution, stress distribution, and strain distribution of the formed material after the rebound is transferred to the next first shape analysis step.

Further, in the case where the stress is released from the state of the bottom dead center, that is, the assumed time is short, and is equal to or less than 1 second, only a temperature change of a negligible degree is caused, and therefore temperature analysis may not be performed. In this case, the temperature distribution of the press-formed material after the press forming analysis is directly set to the temperature distribution after the rebound, and is transferred to the next first shape analysis step. However, even if the temperature analysis is not performed in the present rebound analysis step, the structural analysis is analyzed based on the temperature distribution after the press forming analysis and the temperature dependent data.

Fig. 8 is a graph showing an example of a temperature distribution of a specific portion of the press-formed material obtained by the rebound analysis step. In the graph of Fig. 8, the vertical axis represents the temperature (°C) of the material to be press-formed, and the horizontal axis represents the distance (mm) measured along the cross-section of the material to be press-formed.

In the case of foaming and forming the hat-shaped cross-sectional shape, wrinkles may be formed in the flange portion depending on the molding conditions and the like during the press forming process. After the rebound, the temperature of the wrinkle portion becomes higher than the temperature around it. The reason for this is that the flange portion is in contact with the mold during the press forming process, so that heat is transferred to the mold, which causes a decrease in temperature, and a portion which does not come into contact with the mold at the wrinkle portion does not cause a temperature drop at the portion.

The graph of Fig. 8 shows the temperature distribution of the section including the vicinity of the bottom of the wrinkle centering on the top of the generated wrinkle, and the solid line is the temperature distribution obtained by the rebound analysis step. If the graph of the solid line in Fig. 8 is observed, the two hills are connected, and the valley portion appears therebetween. This valley is equivalent to the top of the wrinkle. The top of the wrinkle contacts the mold to cause a temperature drop.

As shown in Fig. 8, a temperature distribution is generated in the material to be press-formed due to wrinkles.

<First shape analysis step>

The first shape analysis step is based on the shape information, the temperature distribution, the stress distribution, and the strain distribution acquired in the rebound analysis step, and the temperature analysis and the structural analysis are coupled to each other, and the temperature distribution of the material to be pressed is within ±5° C. The shape change during the cooling process and after the cooling is performed (step S5).

In this example, the temperature distribution in the first shape analysis step is performed based on the temperature distribution including the temperature distribution of the wrinkle portion shown by the solid line in FIG. 8 .

The first shape analysis step is performed by the shape analysis means 17, and the shape information, the temperature distribution, the stress distribution, and the strain distribution of the press-formed material after the rebound analysis are used as initial conditions, and the temperature distribution due to cooling is performed. The change is analyzed and the structure analysis considering heat shrinkage is performed.

The specific analysis method in the first shape analysis step is performed by restraining one or a plurality of nodes of the press-formed material so that the press-formed material does not move during the cooling process. Regarding the constraints of the nodes, the node constraints used in the above-described rebound parsing step can also be used.

The temperature analysis can also be performed assuming air cooling, but it can be obtained closer to the actual operation as long as it is assumed to be placed on the cooling stage for cooling in actual operation, and considering the analysis of the contact heat transfer between the cooling stage and the material to be stamped. Temperature analysis results.

In the first shape analysis step, the temperature change of the material to be press-formed is analyzed within a cooling process of ±5° C. and the shape change after cooling, and the reason is as follows.

In the actual warm press forming, when the temperature of the material to be stamped is lowered to the ambient temperature such as room temperature, the temperature distribution of the entire press-formed material converges within ±5 ° C (more preferably within ±1 ° C). At the time, there is almost no change in shape due to temperature. Therefore, in the first shape analysis step, the cooling time should be sufficiently ensured so as to satisfy the conditions of the temperature distribution described above.

<Second shape analysis step>

The second shape analysis step applies a change to the temperature distribution acquired in the rebound analysis step, and causes the temperature based on the changed temperature distribution and the shape information, the stress distribution, and the strain distribution acquired in the rebound analysis step. The analysis and the structural analysis are coupled to analyze the shape change in the cooling process and the cooling after the temperature distribution of the press-formed material is within ±5° C. (steps S7 and S9).

The second shape analysis step is the same as the first shape analysis step except that the temperature distribution acquired in the rebound analysis step is changed and the shape is analyzed.

As a method of changing the temperature distribution of the press-formed material after the rebound analysis, in this example, the temperature distribution of the wrinkle-forming portion is a broken line as shown in FIG. That is, it is in a state like a temperature distribution which is not generated at a portion where wrinkles are generated, in other words, it can be inferred that a temperature distribution can be obtained if no wrinkles are generated.

After changing the temperature distribution, the shape analysis means 17 is used to analyze the change in the temperature distribution due to the cooling based on the temperature distribution after the change, the shape information, the stress distribution, and the strain distribution obtained in the rebound analysis step, and Conducting a structure that takes into account heat shrinkage Analysis.

<Shape comparison step>

The shape comparison step compares the shape of the cooled press-formed material obtained by the analysis of the first shape analysis step and the second shape analysis step (step S11).

The shape comparison step is a state in which the shape of the cooled press-formed material obtained by the analysis of the second shape analysis step and the first shape analysis step is comparable (for example, a state in which the two are arranged side by side or a state of coincidence) Displayed on the display device 3, the operator visually compares.

In the case where there is no difference in the shape of the cooled press-formed material obtained by the analysis of the first shape analysis step and the second shape analysis step, it is understood that the temperature distribution change does not affect the shape of the formed material after cooling. Make an impact. Therefore, it is understood that there is no problem in that the temperature distribution before the temperature distribution change does not occur after the rebound.

On the other hand, when there is a difference in the shape of the cooled press-formed material obtained by the analysis of the first shape analysis step and the second shape analysis step, it is understood that the temperature distribution is changed to the cooled press-formed material. The shape has an effect. In this case, if the shape obtained by changing the temperature distribution is close to the target shape, it is understood that the temperature distribution before the temperature distribution change after the rebound is a problem, and the press forming such that the temperature distribution is not generated is performed. The case is related to the case where the shape of the material to be formed after cooling is subjected to the target shape. According to the present example, the temperature distribution due to the occurrence of wrinkles is a problem, and therefore, a press forming method such as no wrinkles may be considered. As such a method, for example, a method is considered in which, during the movement of the mold from the top dead center to the bottom dead center, stretching is performed by pressing the press-formed material by wrinkle pressing, or The initial shape of the formed material is changed.

As described above, according to the third embodiment, it is known that the temperature distribution after the rebound is What effect is caused by the shape after cooling, whereby the countermeasure against the shape defects in the warm press forming becomes possible, and the effects such as the reduction of the test man-hour or the cost in the design stage of the press-formed product can be obtained.

In the above description, the method of changing the temperature distribution after the rebound is a method of changing the temperature distribution of a part (wrinkled portion) of the material to be press-formed, but it is also possible to set the temperature of the entire material to be press-formed. Apply changes in a uniform manner.

In the following, a case where the temperature distribution of the entire material to be press-formed is uniform is changed, that is, a case where the press-formed material has a hat-shaped cross-sectional shape will be described as an example.

Fig. 9 is a graph showing the temperature distribution after a rebound of a hat-shaped cross-sectional shape. Fig. 9 is a longitudinal axis of the material to be press-formed (°C), and the horizontal axis represents the length (mm) of the center in the width direction measured along the cross-section, and shows only one half of the width direction of the hat-shaped cross-sectional shape.

In the case of press-forming the hat-shaped cross-sectional shape, the time at which the top plate portion of the hat-shaped cross-sectional shape comes into contact with the vertical wall portion and the mold is short, so that the temperature drop due to the contact is less likely to occur, and the temperature is kept high. On the other hand, the time at which the curvature portion and the flange portion connecting the top plate portion and the vertical wall portion come into contact with the mold is long, and thus the temperature is lowered. Therefore, it becomes an uneven temperature distribution as shown by the graph of the solid line in Fig. 9.

The shape after cooling obtained by performing the first shape analysis step based on the uneven temperature distribution is changed to a temperature at which the uneven temperature distribution is changed to a uniform shape of the hat-shaped cross-sectional shape (dotted line in FIG. 9). When the results of the second shape analysis step are compared based on the temperature, it is clear that the shape is poor, the temperature distribution of the unevenness is a problem, or the heat shrinkage is uniformly performed as a whole.

Furthermore, the configuration solution of the first shape analysis step and the second shape analysis step The analysis can be carried out dynamically or statically. When the dynamic analysis is performed, the time can be compressed and processed on a time scale, so that the calculation time becomes faster. However, when the analysis is completed by the dynamic analysis, the calculation accuracy is lowered due to the influence of the inertial force remaining. Therefore, in order to obtain a more accurate calculation result, it is preferable to perform structural analysis of all shape analysis steps statically. Alternatively, in order to enjoy the advantage of dynamic analysis, it is preferable to divide the first shape analysis step and/or the second shape analysis step into two stages, and to perform the initial stage dynamically, and to perform the final stage statically. For example, if a cooling time of 1001 seconds is assumed, if the first 1000 seconds are performed by time-compression by dynamic analysis and the last one second is statically analyzed, the calculation accuracy can be shortened while calculating the calculation time. improve. Furthermore, it is more preferable to use the static implicit method at the final stage of the structural analysis of the first shape analysis step and the second shape analysis step.

[Embodiment 4]

The press forming analysis method according to the fourth embodiment includes a press forming analysis step of setting an initial temperature distribution to the heated press-formed material, coupling the temperature analysis and the structural analysis, and performing press forming analysis. Obtaining shape information, temperature distribution, stress distribution and strain distribution before demolding; a rebound analysis step based on shape information, temperature distribution, stress distribution and strain distribution obtained in the press forming analysis step and considering the mold and the The contact heat transfer between the press forming materials couples the temperature analysis and the structural analysis to perform springback analysis, and obtains shape information, temperature distribution, stress distribution, and strain distribution after rebound; the first shape analysis step is based on The shape information, the temperature distribution, the stress distribution, and the strain distribution obtained by the rebound analysis step are coupled to the temperature analysis and the structural analysis, and the temperature distribution of the material to be pressed is within ±5° C. during cooling and after cooling. The shape change is analyzed; a second shape analysis step of changing a temperature distribution acquired in the rebound analysis step, and based on the temperature distribution after the change and the shape information, the stress distribution, and the strain distribution acquired in the rebound analysis step, The temperature analysis and the structural analysis are coupled to each other, and the temperature distribution of the material to be press-formed is analyzed within a cooling process of ±5° C. and the shape change after cooling; and the shape comparison step is performed by the second shape analysis step. The shape of the cooled press-formed material obtained by the analysis of the first shape analysis step is compared.

The press forming analysis method according to the fourth embodiment is carried out in consideration of the contact heat transfer between the mold and the material to be pressed which are not considered in the rebound analysis step of the press forming analysis method in the third embodiment, and other aspects are The press forming analysis method of the third embodiment is the same.

Therefore, the case where the contact heat transfer between the mold and the material to be press-formed is considered in the rebound analysis step of the present embodiment will be described below.

In the rebound analysis step, the effect produced by considering the contact heat transfer between the mold and the material to be stamped is as follows.

The temperature change due to the mold release can be more accurately considered, and the temperature distribution of the material to be pressed after the rebound can be obtained more accurately, and as a result, the shape analysis step can be more accurately obtained. The shape of the molded article after cooling.

However, in the rebound analysis step as in the third embodiment, the contact heat transfer between the mold and the material to be press-formed is not considered, and the advantage of convergence is easily obtained. Therefore, the two may be used as needed.

In the rebound analysis step, as a specific method for considering the analysis of the contact heat transfer between the mold and the material to be pressed, the one or several nodes of the press-formed material are restrained so that the material to be stamped does not move, and the mold is moved. And simulate demoulding. This situation is Temperature analysis is performed by accurately considering cooling due to contact with the mold or air cooling of a portion not in contact with the mold.

Furthermore, the initial conditions in the rebound analysis step and the transfer of the data after the rebound are the same as in the third embodiment.

As described above, according to the fourth embodiment, the temperature change due to the mold release can be more accurately considered as described above, and the temperature distribution of the material to be molded after the rebound can be more accurately obtained. As a result, the following can be obtained as follows. Effect: The shape of the molded article after cooling obtained by the shape analysis step can be more accurately obtained.

Further, in the above-described third and fourth embodiments, a method of performing warm press forming and analyzing the material to be press-formed to 600 ° C will be described. However, even in the case of analyzing cold press forming, the present invention can be applied to analysis in consideration of the influence of heat such as heat generation or frictional heat generation.

Further, by combining the present invention with a method for investigating the influence of the stress distribution as in Patent Document 1, it is an analytical means for press forming which has a high practical value for studying the countermeasure against shape defects.

Example 1

The experiment for confirming the effects related to the first and second embodiments is performed, and therefore, the following description will be made.

In the experiment, the upper part 21 of the B pillar (the column between the front seat and the rear seat) of the automobile shown in Fig. 3 is subjected to actual temperature press forming, and the simulation analysis using the press forming analysis method of the present invention is applied. And compare the results of these.

First, an outline of the actual warm press forming will be described. The stamped forming material is a high tensile steel of 980 MPa. The initial shape is a parallelogram with a bottom edge of 650 mm and a height of 300 mm, and the plate thickness is 1.4 mm. Heating the stamped material by an electric furnace After the temperature is 680 ° C, the transfer robot is mounted between the molds of the press machine to perform press forming. The press forming start temperature was 600 ° C (a thermocouple was attached to the center of the material to be press-formed in advance, and the temperature change under the same conditions was measured, and the material temperature at the end of mounting in the press was 600 ° C). The press forming method is stretch forming by a wrinkle pressing force of 45 tonf. The average press forming speed is 100 mm/s. After the film was released to the bottom dead center, it was released from the mold and air-cooled to room temperature to obtain a press-formed product (hereinafter referred to as "skin-pressed product"). Finally, the shape of the surface of the stamped product was measured by a non-contact three-dimensional shape measuring device.

Next, the simulation analysis performed by applying the press forming analysis method of the present invention will be described.

This simulation analysis system sequentially performs a press forming analysis step, a rebound analysis step, and a shape analysis step in the same manner as the press forming analysis method of the present invention.

Hereinafter, input conditions, analysis conditions, and the like will be described for each analysis step.

<Press forming analysis step>

First, necessary information and conditions are input to the press forming analysis means 13, and press forming analysis is performed using the press forming analysis means 13. The following is a summary of the information and conditions of the above input.

Each of the material properties was determined in advance for the steel grades which were the same as those of the press-formed materials which were subjected to the above-described actual warm press forming. Specifically, temperature dependence data of specific heat, thermal conductivity, thermal expansion coefficient, Young's modulus, and Poisson's ratio are measured, and tensile tests are performed at 400 ° C, 500 ° C, and 600 ° C, and used to form stress-strain lines. Figure modeler.

Further, the press-formed material is modeled by the outer shape element in the thickness of the initial shape used in the actual warm press forming described above. The mold is formed by modeling the surface of the mold used in the actual warm press forming described above by the shape factor. By. Further, the material to be press-formed is assumed to be a deformed body, and the mold system is assumed to be a rigid body.

In the press forming analysis, when the distance between the surface of the press-formed material and the surface of the mold is less than 0.01 mm, it is considered that the press-formed material is in contact with the mold, and the heat flow rate is calculated by contact heat transfer. Further, when the distance is 0.01 mm or more, the material to be press-formed is air-cooled, and radiation and convection are considered. The emissivity of the material to be stamped was set to 0.75.

Moreover, the initial temperature of the press-formed material was fixed at 600 °C.

<Rebound analysis step>

Then, rebound analysis is performed using the rebound analysis means 15. The rebound analysis system constrains the movement of the two nodes of the bottom of the punch and the nodes of the flange, and the stress is released from the state of the bottom dead center. The stress release time was set to 0.5 second, and the press-formed material was air-cooled and also subjected to temperature analysis during this period.

<Shape analysis step>

Then, the shape analysis means 17 is used to perform shape analysis on the change in shape due to cooling. The shape analysis system first performs air cooling for 1000 seconds, and the structural analysis therebetween is performed by a dynamic explicit method in consideration of the inertial force, and then the shape analysis, that is, the structure analysis, is performed for one second by the static implicit method. Eliminate the effects of reduced accuracy due to inertial forces. The temperature distribution of the material at the end of the shape analysis is within ±1 °C.

Hereinafter, a method of comparing the shape of the actual press product with the shape of the simulation analysis result will be described.

The measured shape of the surface of the stamped product and the shape obtained in the above-described simulation analysis are the shapes of the different positions of the press-formed material as described above. Therefore, when comparing, the shape is processed in such a manner as to be mutually comparable and to be in contact with the surface of the mold. The processing is carried out in the following manner. The shape of the surface of the stamped product is determined Since the shape can be measured from the above, the lower side is offset by 1.4 mm which is equivalent to the thickness of the sheet, and the shape of the stamped product is obtained.

Further, since the press-formed material processed in the simulation analysis is formed by modeling the center of the plate thickness, the shape obtained in the above-described simulation analysis is approximately 0.7 mm which is one-half of the thickness of the plate. Made by offsetting.

In the following description, the shape of the actual stamping product is set to a solid press forming shape, and the shape obtained by the springback analysis is made into a shape after the rebound analysis, and the shape is analyzed based on the shape. The shape obtained by the obtained shape is set to the shape after shape analysis. Moreover, in addition to these shapes, since the shape of the surface of a mold is used for comparison, it is set as the surface shape of a mold. The mold surface shape was the one used in the above simulation analysis.

Using the shape comparison soft body, the four shapes (the actual press formed shape, the rebound analysis shape, the shape analysis shape, and the mold surface shape) are preferably around the shape of the adjustment rod 23 of the punch bottom of FIG. The alignment is performed in a matching manner, and the shapes are compared by the AA arrow cross section of FIG.

As an example of the A-A arrow cross section, the cross-sectional shape of the mold surface shape 37 is shown in FIG. Comparing the four shapes, as a result, the difference in shape was remarkably found in the circular mark portion in Fig. 4, and therefore, the portion corresponding to the portion of each shape was enlarged and superimposed and displayed in Fig. 5. In Fig. 5, reference numeral 31 denotes a solid press formed shape, 37 denotes a mold surface shape, 33 denotes a shape after rebound analysis, and 35 denotes a shape after shape analysis.

5, it can be seen that the shape 33 and the actual press-formed shape 31 after the rebound analysis are found to have a large deviation, but the shape 35 after the shape analysis is in good agreement with the actual press-formed shape 31. According to the result, it was confirmed that in the warm press forming in which the temperature after the demolding was largely lowered, in addition to the rebound analysis, the accuracy can be obtained by performing the shape analysis. Good analysis.

Example 2

Experiments for confirming the effects related to the third and fourth embodiments are performed, and therefore, the following description will be made.

In the same manner as in the first embodiment, the experiment is performed by performing the actual warm press forming on the upper part 21 of the B pillar (the column between the front seat and the rear seat) of the automobile shown in FIG. And using the simulation analysis using the press forming analysis method to which the present invention is applied, and comparing the results of the above.

First, an outline of the actual warm press forming will be described. The stamped forming material is a high tensile steel of 980 MPa. The initial shape is a parallelogram with a bottom edge of 650 mm and a height of 300 mm, and the plate thickness is 1.4 mm. The press-formed material was heated to 680 ° C by an electric furnace, and then placed between the dies of the press by a transfer robot to perform press forming. The press forming start temperature was 600 ° C (a thermocouple was attached to the center of the press-formed material in advance, and the temperature change under the same conditions was measured, and the material temperature at the end of the press installation was 600 ° C). The press forming method is stretch forming by a wrinkle pressing force of 45 tonf. The average press forming speed is 100 mm/s. After the film was released to the bottom dead center, it was released from the mold, and air-cooled to room temperature to obtain a press-formed product (hereinafter referred to as "solid press product"). Finally, the shape of the surface of the stamped product was measured by a non-contact three-dimensional shape measuring device.

Next, the simulation analysis performed by applying the press forming analysis method of the present invention will be described.

This simulation analysis system sequentially performs a press forming analysis step, a rebound analysis step, a first shape analysis step, a second shape analysis step, and a shape comparison step in the same manner as the press forming analysis method of the present invention.

Hereinafter, input conditions, analysis conditions, and the like will be described for each analysis step.

<Press forming analysis step>

First, necessary information and conditions are input to the press forming analysis means 13, and press forming analysis is performed using the press forming analysis means 13. The following is a summary of the information and conditions of the above input.

Each of the material properties was determined in advance for the steel grades which were the same as those of the press-formed materials which were subjected to the above-described actual warm press forming. Specifically, the temperature dependence data of the specific heat, the thermal conductivity, the thermal expansion coefficient, the Young's modulus, and the Poisson's ratio are measured, and the tensile test is performed at 400 ° C, 500 ° C, and 600 ° C, and the stress-strain line is used. Figure modeler.

Further, the press-formed material is modeled by the outer shape element in the thickness of the initial shape used in the above-described actual warm press forming. The mold is formed by modeling the surface of the mold used in the above-described actual warm press forming by the outer shape element. Further, the press-formed material is assumed to be a deformed body, and the mold is assumed to be a rigid body.

In the press forming analysis, when the distance between the surface of the press-formed material and the surface of the mold is less than 0.01 mm, it is considered that the press-formed material is in contact with the mold, and the heat flow rate is calculated by contact heat transfer. Further, when the distance is 0.01 mm or more, the material to be press-formed is air-cooled, and radiation and convection are considered. The emissivity of the material to be stamped was set to 0.75.

Further, the initial temperature of the press-formed material was fixed at 600 °C.

<Rebound analysis step>

Then, rebound analysis is performed using the rebound analysis means 15. The rebound analysis system constrains the movement of the two nodes of the bottom of the punch and one of the flanges, and releases the stress from the state of the bottom dead center. The stress release time was set to 0.5 second, and the press-formed material was air-cooled and also subjected to temperature analysis during this period.

Fig. 11 is a graph showing the temperature distribution of the press-formed material after the rebound analysis in the cross section taken along the line B-B of Fig. 10. Figure 11 is the longitudinal axis of the material being stamped (°C), and the horizontal axis is the distance (mm) measured along the profile from one end of the material being stamped. As shown in the graph of the solid line, the press-formed material after the rebound analysis becomes a non-uniform temperature distribution. Such uneven temperature distribution is caused by the difference in the time of contact with the mold during the press forming process.

<First shape analysis step>

Then, the shape analysis means 17 is used to analyze the shape of the change due to the cooling based on the temperature distribution after the rebound, the shape information, the stress distribution, and the strain distribution. The shape analysis system first performs air cooling for 1000 seconds, and the structural analysis during this period is performed by a dynamic explicit method in consideration of inertial force, and then one-second shape analysis, that is, construction is performed by a static implicit method. Analyze to eliminate the effects of reduced accuracy due to inertial forces. The temperature distribution of the material at the end of the shape analysis is within ±1 °C.

Here, the shape after cooling obtained by the first shape analysis step will be described in comparison with the shape of the actual press product.

The measured shape of the surface of the stamped product and the shape obtained in the above-described simulation analysis are the shapes of the different positions of the press-formed material as described above. Therefore, in the comparison, the shape is processed so as to be mutually comparable and to be in contact with the surface of the mold. The processing is carried out in the following manner. The measurement shape of the surface of the actual stamped product was measured for the shape which can be observed from above, and therefore the lower side was offset by about 1.4 mm which is equivalent to the thickness of the sheet, and the shape of the stamped product was obtained.

Further, since the press-formed material processed in the simulation analysis is formed by modeling the center of the plate thickness, the shape obtained in the above-described simulation analysis is approximately 0.7 mm which is one-half of the thickness of the plate. Made by offsetting.

In the following description, the shape based on the shape of the actual press product is a solid press formed shape, and the shape obtained by the springback analysis is made into a shape after the rebound analysis, and the shape is based on the first shape. The shape obtained after the analysis is made into a shape after the first shape analysis. Moreover, in addition to these shapes, since the shape of the surface of a mold is used for comparison, it is set as the surface shape of a mold. The mold surface shape was the one used in the above simulation analysis.

Using the shape comparison soft body, the four shapes (the actual press formed shape, the rebound shape after analysis, the shape after the first shape analysis, and the shape of the mold surface) are surrounded by the shape of the adjustment rod 25 of the punch bottom of FIG. The alignment is performed in a best fit manner, and the shapes are compared by the AA arrow cross-section of FIG.

As an example of the A-A arrow cross section, the cross-sectional shape of the mold surface shape 37 is shown in FIG. When the four shapes are compared, as a result, the difference in shape is remarkably found in the circular mark portion in Fig. 12. Therefore, the portion corresponding to the portion of each shape is enlarged and superimposed for display, and is shown in Fig. 13. In Fig. 13, reference numeral 31 denotes a solid press formed shape, 37 denotes a mold surface shape, 33 denotes a shape after rebound analysis, and 35 denotes a shape after shape analysis.

When FIG. 13 is observed, it can be seen that the shape 33 and the actual press-formed shape 31 after the rebound analysis have a large deviation, but the shape 35 after the first shape analysis and the actual press-formed shape 31 are in good agreement. Thus, it can be seen that the shape obtained by the first shape analysis is close to the shape obtained by actual warm press forming. In this sense, it has been confirmed that in the warm press forming in which the temperature drop after the mold release is large, in addition to the rebound analysis, the analysis of the first shape can be performed with high precision.

<Second shape analysis step>

Then, the uneven temperature distribution in the press-formed material after the analysis was changed, and the temperature distribution of the entire press-formed material was made uniform at 510 °C. In Figure 11, by virtual The graph of the line indicates the temperature distribution after the change.

The shape of the shape of the press-formed material after cooling is obtained by shape analysis based on the temperature distribution after the rebound and the shape information, the stress distribution, and the strain distribution after the rebound. The conditions for the analysis other than the temperature distribution in the second shape analysis step are the same as those of the first shape analysis step.

<Shape comparison step>

Then, the shape comparison means 21 compares the first shape analysis shape 35 obtained in the first shape analysis step with the second shape analysis shape 39 (see FIG. 14) obtained in the second shape analysis step. .

The first shape-analyzed shape 35 and the second shape-analyzed shape 39 in the portion corresponding to the portion indicated by the circular symbol in Fig. 12 are shown in Fig. 14 . Further, in Fig. 14, for comparison, the shape 33 and the mold surface shape 37 after the rebound analysis are also shown.

As shown in FIG. 14 , the shape after the first shape analysis is a shape that deviates from the mold surface shape 37 , but the shape after the second shape analysis is close to the shape of the mold surface 37 and is the shape after the spring analysis. 33 close to the shape. This means that by making the temperature distribution after the rebound uniform, there is almost no shape change due to subsequent cooling.

Therefore, it is suggested that the shape defect generated during the cooling process is improved if the temperature distribution after the rebound is made nearly uniform. As a method of making the temperature distribution after the rebound close to uniform, for example, it is considered to accelerate the average press forming speed. By speeding up the average press forming speed, the contact time between the stamped material and the mold can be shortened, and the local temperature drop caused by the contact of the stamped material with the mold can be prevented, and the temperature distribution of the material to be stamped can be made uniform. Chemical.

In this example, the average press forming speed was 150 mm/s which was 1.5 times as high as that of the above-described embodiment, and the others were actually subjected to warm press forming under the same conditions. shape. As a result, an effect of improving the shape defect can be obtained.

Claims (5)

A press forming analysis method comprising: a press forming analysis step of setting an initial temperature distribution to a heated press-formed material, performing a press forming analysis by combining temperature analysis and structural analysis, and obtaining after press forming Shape information, temperature distribution, stress distribution and deformation distribution before demolding; rebound analysis step, which is based on the shape information, temperature distribution, stress distribution and deformation distribution obtained in the analysis step of the press forming, and does not consider the mold and The contact heat transfer between the stamped and formed materials, and the temperature analysis and the structural analysis are combined to perform the springback analysis to obtain the shape information, the temperature distribution, the stress distribution and the deformation distribution after the rebound; and the shape analysis step, which is based on The shape information, the temperature distribution, the stress distribution, and the deformation distribution obtained in the rebound analysis step are combined with the temperature analysis and the structural analysis to cool the temperature distribution of the press-formed material to within ±5 ° C. The shape change after cooling is analyzed; and in the shape analysis step described above The analysis is divided into two stages. The first stage is processed by dynamic analysis and compressed by time scale. The second stage is at least in the final step, and the inertial force is made by static implicit method. The effect does not remain and the resolution accuracy is improved. A press forming analysis method comprising: a press forming analysis step of setting an initial temperature distribution to a heated press-formed material, combining temperature analysis and structural analysis to perform press forming analysis, and obtaining a mold release after press forming Front shape information, temperature distribution, stress distribution and deformation distribution; a rebound analysis step of temperature analysis and structural analysis based on shape information, temperature distribution, stress distribution, and deformation distribution obtained in the press forming analysis step, and considering contact heat transfer between the mold and the material to be stamped Combining to perform springback analysis to obtain shape information, temperature distribution, stress distribution, and deformation distribution after rebound; and shape analysis step according to shape information, temperature distribution, and stress distribution obtained in the rebound analysis step And the deformation distribution, and the temperature analysis of the press-formed material is analyzed within a cooling process of ±5° C. and the shape change after cooling in combination with the temperature analysis; and the structural analysis in the shape analysis step It is divided into two stages. The first stage is processed by dynamic analysis and compressed by time scale. The second stage is at least in the final step, and the influence of inertial force is made by static implicit method. Does not leave to improve the resolution accuracy. A press forming analysis method comprising: a press forming analysis step of setting an initial temperature distribution to a heated press-formed material, and combining temperature analysis and structural analysis to perform press forming analysis to obtain shape information before demolding , temperature distribution, stress distribution and deformation distribution; rebound analysis step, which is based on shape information, temperature distribution, stress distribution and deformation distribution obtained in the analysis step of the press forming, and does not consider between the mold and the material to be stamped Contacting heat transfer, and combining temperature analysis and structural analysis to perform springback analysis to obtain shape information, temperature distribution, stress distribution, and deformation distribution after rebound; a first shape analysis step based on the rebound analysis step Shape information, temperature distribution, stress distribution and deformation distribution obtained in the process, and temperature analysis and structural solution The temperature distribution of the press-formed material is analyzed within a cooling process of ±5° C. and the shape change after cooling, and the second shape analysis step is performed on the temperature obtained in the rebound analysis step. The distribution is changed, and based on the temperature distribution after the change and the shape information, the stress distribution, and the deformation distribution obtained in the rebound analysis step, the temperature distribution and the structural analysis are combined to form the temperature distribution of the material to be pressed. Analysis of the shape change during cooling and after cooling within ±5 ° C; and a shape comparison step of being cooled by the analysis of the second shape analysis step and the analysis of the first shape analysis step The shape of the shaped material is compared. A press forming analysis method comprising: a press forming analysis step of setting an initial temperature distribution to a heated press-formed material, combining temperature analysis and structural analysis, and performing press forming analysis to obtain shape information before demolding, Temperature distribution, stress distribution and deformation distribution; rebound analysis step according to the shape information, temperature distribution, stress distribution and deformation distribution obtained in the analysis step of the press forming, and considering the contact heat between the mold and the material to be stamped Transfer, and combine temperature analysis with structural analysis to perform springback analysis to obtain shape information, temperature distribution, stress distribution, and deformation distribution after rebound; a first shape analysis step according to the rebound analysis step The shape information, the temperature distribution, the stress distribution, and the deformation distribution are obtained, and the temperature analysis and the structural analysis are combined to analyze the shape change of the temperature of the press-formed material within ±5° C. during cooling and after cooling. a second shape analysis step, which is in the above-described rebound analysis step Take the temperature The distribution is changed, and based on the temperature distribution after the change and the shape information, the stress distribution, and the deformation distribution obtained in the rebound analysis step, the temperature distribution and the structural analysis are combined to form the temperature distribution of the material to be pressed. Analysis of the shape change during cooling and after cooling within ±5 ° C; and a shape comparison step of being cooled by the analysis of the second shape analysis step and the analysis of the first shape analysis step The shape of the shaped material is compared. The press forming analysis method according to claim 3 or 4, wherein the structural analysis in the first shape analyzing step and the second shape analyzing step includes structural analysis of the final step of the structural analysis by a static implicit method. .