JP6925706B2 - Press molding simulation method - Google Patents

Description

The present invention relates to a method for simulating press molding.

When a metal plate (blank material) is press-molded, springback occurs in the molded product at the time of mold release, so that it is inevitable that the dimensional accuracy deteriorates. Therefore, in order to improve the dimensional accuracy of the molded product, the shape of the molded product is calculated in advance by performing a press molding simulation, and the mold shape and the like are adjusted based on the calculation result (for example,). See Patent Documents 1 and 2 below).

Japanese Unexamined Patent Publication No. 2002-45920 Japanese Unexamined Patent Publication No. 2012-153045

In the press molding simulation as described above, the calculation is usually performed by regarding the die as a rigid body and the work as a deformed body. However, in this case, since the bending deformation of the molding surface of the mold due to the molding reaction force during processing is not taken into consideration, the output accuracy of the simulation is lowered.

For example, by using an elastic solid element model of a mold (an elastic model in which a mold is divided into a large number of three-dimensional solid elements), it is possible to perform a molding simulation in consideration of bending deformation of the mold. Specifically, the press molding process is performed by calculating the molding reaction force that changes from moment to moment during processing and calculating the amount of deformation of the elastic solid element model of the die at each time point based on this molding reaction force. It is possible to dynamically reproduce the bending deformation of the mold in the above, and the output accuracy of the molding simulation is improved. However, the simulation using such a three-dimensional elastic solid element model of the mold requires a huge calculation time because the calculation load is very large.

Therefore, the problem to be solved by the present invention is to improve the accuracy of the simulation in consideration of the bending deformation of the molding surface of the mold during molding in the press molding simulation method, and reduce the calculation load to shorten the calculation time. To do.

In order to solve the above problems, the present invention is a press molding simulation method, which reflects a step of calculating the amount of bending of the molding surface of a mold at a plurality of stages of a molding stroke process and the amount of bending at each stage. While molding the material model with the step of creating a rigid shell element model of a plurality of molded surfaces and the rigid shell element model of the first molding surface that reflects the amount of deflection at a certain stage, the amount of deflection at the next stage is reflected. Provided is a press molding simulation method including a step in which the rigid shell element model of the second molding surface overtakes the rigid shell element model of the first molding surface to perform a simulation of molding the material model.

As described above, in the present invention, the forming stroke process is divided into a plurality of stages, and a forming simulation is performed using a rigid body shell element model of the forming surface (a rigid body model in which the forming surface is divided into a large number of flat shell elements) in each stage. I do. Specifically, the amount of bending of the molding surface of the mold is calculated from the molding reaction forces in a plurality of stages during the stroke, and a rigid shell element model of the molding surface reflecting the amount of bending in each stage is created. Then, at each stage in the middle of the stroke, by using the rigid body shell element model corresponding to each stage, the bending deformation of the molded surface in the molding stroke process can be reproduced step by step, so that the accuracy of the simulation is improved. .. In addition, by performing the simulation using the two-dimensional rigid shell element model of the molded surface, the calculation load is significantly smaller than when using the three-dimensional solid element model of the mold, so the calculation time Is greatly shortened.

In this case, in the middle of the forming stroke, the rigid shell element model of the first forming surface in which the force is balanced in contact with the material model is replaced with the rigid shell element model of the second forming surface having a different shape (deflection amount). There is a need. When the rigid shell element model of the molded surface is replaced in this way, the positional relationship (contact state) between the material model and the rigid shell element model of the molded surface suddenly changes, and the balance of forces between the two is lost. It becomes difficult to continue the molding simulation while maintaining the continuity of contact.

Therefore, in the present invention, as described above, the rigid shell element model of the second molding surface is the rigid shell element model of the first molding surface while the material model is molded by the rigid shell element model of the first molding surface. Perform a simulation to overtake and form a material model. Since the simulation does not consider the contact between the molded surfaces, it is possible to perform the simulation in the above-mentioned situation that is not actually possible. As a result, the rigid body of the first molded surface to the rigid body of the second molded surface are maintained while maintaining the force balance and relative positional relationship between the rigid shell element model of the first molded surface and the material model. The material model can be gradually passed to the shell element model. This solves the problem of contact discontinuity between the rigid shell element model of the molded surface at each stage and the material model, so molding simulation using the rigid shell element model of the molded surface considering bending deformation at multiple stages. Is possible.

In the above molding simulation method, for example, after stopping the rigid shell element model of the first molding surface forming the material model, the rigid shell element model of the second molding surface is the rigid body of the first molding surface. When the shell element model is overtaken and comes into contact with the material model, the material model causes the material model to stop when the rigid shell element model of the first molding surface is stopped or when the rigid shell element model of the second molding surface comes into contact with the material model. Since it is deformed by the influence of inertial force, the accuracy of the simulation may decrease. Therefore, while moving the rigid shell element model of the first and second molding surfaces together, the rigid shell element model of the second molding surface overtakes the rigid shell element model of the first molding surface and delivers the material model. Is preferable.

As described above, according to the present invention, the rigid shell element model and the material model of the molding surface of each stage are used by using the rigid shell element model of a plurality of molding surfaces considering the bending deformation in a plurality of stages of the molding stroke process. It is possible to perform molding simulation while maintaining the continuity of contact. By taking into account the bending deformation of the mold in this way, the accuracy of the simulation can be improved. Further, by using the rigid shell element model of the molded surface, the calculation load is reduced as compared with the case of using the solid element model of the mold, so that the calculation time is shortened.

It is sectional drawing of the press molding die. It is a flow chart of the bending analysis method of a mold using a molding simulation. It is a perspective view of the rigid shell element model of the molding surface of the mold of FIG. (A) to (C) are cross-sectional views of a rigid shell element model of the molding surface of the upper mold reflecting the bending deformation at each stage of the molding stroke process. (A) to (C) are cross-sectional views conceptually showing how the material model is passed from the first rigid body shell element model to the second rigid body shell element model.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In this embodiment, a simulation method in the case of drawing and forming a metal plate (blank material) will be described. As shown in FIG. 1, the draw forming is performed by holding the work W between the upper die (die) 1 and the blank holder 2 and lowering them to press the work W against the lower die (punch) 3. This is done by stretching the work W and forming it into a predetermined shape.

Before actually performing drawing molding as described above, analysis is performed by molding simulation using a computer, and the shape of the mold and processing conditions are adjusted based on the analysis results, thereby improving the molding accuracy. Be done. In this embodiment, the analysis is performed according to the procedure shown in FIG. Each procedure will be described in detail below.

First, data on materials (for example, material and thickness of a metal plate), data on processing conditions (for example, molding load), data on the molding surface of a mold, and the like are input to a computer. As data on the molding surface of the mold, a rigid shell element model of the molding surface of the mold is created. Specifically, as shown in FIG. 3, a rigid shell element model 10 on the molding surface (lower surface) of the upper mold, a rigid shell element model 20 on the holding surface (upper surface) of the blank holder 2, and a molding surface of the lower mold. A rigid shell element model 30 (upper surface) is created. Using the data of these materials, the data of the processing conditions, and the data of the forming surface (rigid body shell element models 10, 20, 30), the forming simulation of the elastic body model (material model M) of the work W is performed.

By the above molding simulation, the strain and internal stress generated in the material model M and the machining reaction force applied to the mold are acquired. From the strain and internal stress generated in the material model M, it is possible to analyze whether or not cracks or wrinkles occur in the work, and based on this analysis result, the material, processing conditions, shape of the molded surface, etc. are corrected. ..

In addition, the bending analysis of the mold is performed from the processing reaction force applied to the mold and the information on the mold structure. As information on the mold structure, for example, an elastic solid element model of the mold can be used. By this deflection analysis, the amount of deflection of the molded surface of the mold due to the machining reaction force can be obtained. In the present embodiment, the amount of bending of the molding surface of the mold at a plurality of stages of the molding stroke process (the process of lowering the upper mold 1 in the present embodiment) is acquired. Since most of the bending deformation of the molding surface of the mold occurs at the end of the molding stroke process (near the bottom dead center of the upper mold 1), the amount of bending of the molding surface at a plurality of stages immediately before the bottom dead center is obtained. It is preferable to do so.

Specifically, for example, the machining reaction force at each predetermined time (for example, starting point) of the first step a, the second step b, and the third step c of the molding stroke process shown in FIG. 3 is calculated. Based on this calculation result, the amount of bending of the molding surface of the mold (for example, the molding surface of the upper mold 1) is calculated as shown in exaggeratedly shown in FIGS. 4 (A) to 4 (C). Normally, as the machining stroke progresses, the machining reaction force increases, and the amount of deflection of the molded surface increases accordingly. Then, the amount of bending in each stage is reflected in the rigid shell element model 10 of the molding surface of the upper mold 1, and the rigid shell element model 10A of the first molding surface reflecting the amount of bending in the first stage a (hereinafter, hereinafter, It is referred to as a "first molding surface model 10A"), and a rigid shell element model 10B of the second molding surface reflecting the amount of deflection in the second stage b (hereinafter referred to as a "second molding surface model 10B"). ), And a rigid shell element model 10C of the third molded surface (hereinafter referred to as “third molded surface model 10C”) reflecting the amount of deflection in the third step c is created (arrow in FIG. 2). See X).

Next, the molding simulation is performed again using the molding surface models 10A to 10C of each stage. Specifically, as shown in FIG. 3, in the first step a, the material model M is molded by the first molding surface model 10A. In the arrows showing the strokes of the molded surface models 10A to 10C in FIG. 3, the solid line arrow indicates the state of contact with the material model M, and the dotted line arrow indicates the state of not contacting the material model M.

Then, in the transition period from the first stage a to the second stage b, the second molding surface model 10B overtakes the first molding surface model 10A while molding the material model M with the first molding surface model 10A. .. Since the contact between the molding surface models is not considered in the molding simulation, the second molding surface model 10B can pass through the first molding surface model 10A and come into contact with the material model M as described above. ..

Specifically, as shown in FIG. 5A, in the first step a, only the first molding surface model 10A (chain line) comes into contact with the material model M to mold it. On the other hand, the second molding surface model 10B (dotted line) moves behind the first molding surface model 10A (upper part in the drawing) in the same direction as the first molding surface model 10A. At this time, both the molded surface models 10A and 10B are moving at substantially the same speed (Va≈Vb).

Then, by gradually reducing the speed of the first molding surface model 10A (Va <Vb), as shown in FIG. 5 (B), the second molding surface model 10B makes the first molding surface model 10A. Start overtaking. As a result, a part of the second forming surface model 10B protrudes toward the material model M side (lower in the figure) from the first forming surface model 10A, and the material model M has the first forming surface model 10A and the first forming surface model 10A. Both of the molded surface models 10B of 2 come into contact at the same time. That is, in the transition period, the first forming surface model 10A and the second forming surface model 10B cooperate to form the material model M.

Then, as shown in FIG. 5C, the second forming surface model 10B completely overtakes the first forming surface model 10A. As a result, the material model M is passed to the second forming surface model 10B, and the material model M is formed only by the second forming surface model B (second step b). The first molding surface model 10A is stopped (or may be eliminated) after the material model M is delivered to the second molding surface model 10B.

In this way, the second forming surface model 10B overtakes the first forming surface model 10A, so that the positional relationship and the force balance between the forming surface models 10A and 10B and the material model M at each stage are maintained. The material model M can be gradually passed from the first molding surface model 10A to the second molding surface model 10B. As a result, the continuity of contact between the molding surface models 10A and 10B at each stage and the material model is maintained, so that molding simulation using the molding surface model that reflects the amount of deflection at each stage becomes possible, and the accuracy of the simulation is improved. Be done. In addition, by performing the simulation using the rigid shell element model of the molded surface, the calculation load is significantly reduced compared to the case of using the elastic solid element model of the mold, so the calculation time is significantly shortened. ..

Further, as described above, while moving the first molding surface model 10A and the second molding surface model 10B together, the material model M is received from the first molding surface model 10A to the second molding surface model 10B. By passing the material model M, the inertial force acting on the material model M is suppressed, so that the accuracy of the simulation is further improved.

After that, in the transition period from the second stage b to the third stage c, the third forming surface model 10C overtakes the second forming surface model 10B, so that the second forming surface model 10B to the third forming surface are overtaken. The material model M is delivered to the model 10C. Since the details in this transition period are the same as those in the transition period from the first stage a to the second stage b described above, the description thereof will be omitted. Then, when the third molding surface model 10C reaches the bottom dead center and stops, the molding of the material model M is completed.

From the calculation result of the molding simulation obtained in this way, the molding reaction force applied to the mold is obtained, and the bending analysis of the mold is performed again from this processing reaction force and the mold structure (elastic solid element model of the mold). conduct. In particular, the deflection analysis at the bottom dead center where the amount of deflection is the largest is performed. Since the bending analysis result of the mold obtained in this way is based on the molding surface in which the bending deformation in the molding stroke process is reproduced stepwise, the first bending calculated based on the molding surface in which the bending deformation is not considered at all. The accuracy is higher than the analysis result. Then, in anticipation of the above-mentioned amount of bending, the dimensions of the mold shape (particularly the molding surface) are corrected. Specifically, for example, the molding surface of the mold is displaced to the side opposite to the direction in which the bending occurs by the amount of bending at the bottom dead center obtained in the above molding simulation. As a result, the influence of the bending of the molding surface of the mold due to the molding reaction force can be offset, so that press molding with higher accuracy becomes possible.

The present invention is not limited to the above embodiments. For example, in the above embodiment, the case where the molding simulation is performed using the rigid shell element model of the molding surface of the upper mold 1 reflecting the bending deformation at each stage of the molding stroke process is not limited to this. A molding simulation similar to the above can also be performed using a rigid shell element model of the molding surface of the lower mold 3 that reflects the bending deformation at each stage of the molding stroke process. Further, in the above embodiment, the case where the deflection analysis is performed in three stages immediately before the completion of molding is shown, but this may be two stages or four or more stages. Further, the above molding simulation can be applied not only to drawing but also to various press molding simulations such as bending, overhanging, and forging.

1 Upper mold 2 Blank holder 3 Lower mold 10 Rigid body shell element model 10A of the upper mold molding surface Considering the bending deformation of the upper mold molding surface Rigid body shell element model 10B Considering the bending deformation in the second stage Rigid body shell element model of the upper mold molding surface 10C Rigid body shell element model of the upper mold molding surface considering the bending deformation in the third stage 20 Rigid body shell element model of the holding surface of the blank holder 30 Rigid body shell of the lower mold molding surface Element model M Material model

Claims (2)

It is a simulation method of press molding.
A step of calculating the amount of bending of the molding surface of the mold at multiple stages of the molding stroke process, and
Steps to create a rigid shell element model of multiple molded surfaces that reflect the amount of deflection at each stage,
While molding the material model with the rigid shell element model of the first molding surface that reflects the amount of deflection at a certain stage, the rigid shell element model of the second molding surface that reflects the amount of deflection at the next stage is the first A method for simulating press molding, which comprises a step of overtaking a rigid shell element model of a molding surface and performing a simulation of molding the material model. While the rigid shell element model of the first molding surface and the rigid shell element model of the second molding surface move together, the rigid shell element model of the second molding surface moves the rigid shell element model of the first molding surface. The method for simulating press molding according to claim 1, wherein the element model is overtaken.

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