JP2007229784A - Method for preparing correction shape data of press die - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparing the correction shape data of a press die capable of considerably enhancing the precision of the correction shape of a press die. <P>SOLUTION: In a formed component mesh data preparing step, the formed component mesh data for the FEM simulation is prepared to give the deformation corresponding to the spring back amount to the formed component mesh data. In an FEM simulation step, the FEM simulation is performed by using the formed component mesh data and the die mesh data; the residual stress forming the motive power of the spring back is calculated from the deformation corresponding to the spring back amount of the formed component mesh data; the stress distribution of the residual stress is subjected to ± inversion; the elastic recovery is performed with the inverted residual stress as the motive power; the amount of the elastic recovery is operated; the die shape data is obtained based on the amount of the operated elastic recovery, and the correction shape of the die is stored as the data. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for creating press mold correction shape data for correcting spring back.

  When a plate material is press-molded using a molding die, a molded part taken out from the molding die after press molding is elastically deformed (springback) by releasing residual stress generated during press molding. For this reason, the molded part has a shape different from that of the molding die, and it is impossible to mold a molded part having the correct shape with a molding die created in the same shape as the part drawing. For this reason, in order to mold a molded part having the same shape as the design drawing, it is necessary to weave the shape in consideration of the spring back amount into the molding die.

  Conventionally, the following method is used as a method of creating a molding die into a shape incorporating a springback amount.

  (1) A method of weaving a mold correction shape by trial and error. In this method, the material is press-molded with the created molding die, the finished molded part panel is measured using a panel gauge, and the corrected shape is taken into account from the error amount of each part and woven into the die shape. . Furthermore, it is a method in which a panel, which is a molded part that has been press-molded with a modified molding die, is woven into the molding die again considering the corrected shape from the error amount.

  (2) A method of measuring the shape of a panel, which is a press-formed molded part, in three dimensions, and weaving a corrected shape into a molding die based on the shape data. This method uses a three-dimensional shape measuring machine to measure the shape of a press-formed molded part. In this method, the point cloud data obtained as a result of the measurement is compared with the part shape data, the correction amount is calculated from the error amount, and the part shape data is deformed to obtain the corrected shape of the molding die.

(3) A method of predicting the amount of springback using a forming simulation and weaving a corrected shape into the forming mold using a stress value generated there. In this method, the residual stress generated at the bottom dead center during press molding is obtained by molding simulation, the stress value is inverted ±, and the plate material that is the molded part is elastically recovered (spring forward) using the stress. This is a method for obtaining the corrected shape of the molding die (see Patent Document 1).
JP 2003-33828 A

  The above-described method (method of forming a molding die into a shape incorporating a springback amount) has the following problems.

  In the above methods (1) and (2), the measured shape (the shape of the panel that is a molded part) is compared with the part drawing shape, and the correction amount is obtained from the error amount. If the correction is performed with these methods, if the press mold is performed with the corrected molding die, the residual stress will be different from the previous part in the molded part. There is a new difference in shape. For this reason, it is necessary to rotate the cycle of the correction of the molding die and the molding of the pressed part many times to gradually approximate the part drawing shape.

  In the method (3) described above, the residual stress at the time of press forming, which becomes the starting force of the springback, is calculated by a forming simulation, and the die correction shape is obtained based on the amount. For this reason, when the residual stress is correctly determined, the corrected shape of the molding die may be correctly determined. It is difficult to accurately determine the residual stress at the current technical level.

  For this reason, when press molding is performed with the molding die created by this method, the molded part often has an error from the part drawing shape, and thereafter, the above methods (1) and (2) are used. Therefore, it is necessary to correct the mold shape.

  The present invention solves the above-described problems, and an object of the present invention is to provide a method for creating press die correction shape data that makes the die correction shape extremely high in accuracy.

  In order to achieve the above-mentioned object, the method of creating the press mold correction shape data according to the present invention is based on the difference between the measurement data of the molded part after press molding by the molding die and the shape of the molding die. This is a method of creating press mold correction shape data to create mold correction shape data, a point cloud data measurement process for measuring a molded part as point cloud data, and FEM simulation by creating surface data based on the point cloud data Molding part mesh data creation process in which deformation corresponding to springback amount is given to the molding part mesh data by creating molding part mesh data for the mold, and a mold for FEM simulation from the mold shape data of the molding die Mold mesh data creation process to create mesh data, FEM simulation using molded part mesh data and mold mesh data FEM simulation process to calculate the residual stress that becomes the starting force of the spring back from the deformation corresponding to the spring back amount of the molded part mesh data, the stress distribution inversion process to reverse the residual stress stress distribution ±, and the inversion Elastic recovery using the residual stress as a starting force and calculating the amount of elastic recovery, and obtaining mold shape data based on the calculated amount of elastic recovery, A mold shape data correcting step for converting the corrected shape into data is provided.

  Therefore, since the shape of the spring back is obtained by measuring a press-molded molded part, a method of creating a shape incorporating the spring back amount as the background art (3) described above (spring using a molding simulation) Predicting the back amount and using the stress value generated there to weave the corrected shape into the mold)) The accuracy of the spring back predicted by using the FEM simulation described above is much higher, and the spring from this shape Since only the residual stress component that becomes the starting force of the back is obtained using the FEM, it can be obtained with high accuracy. In addition, since the deformation amount of the entire part is calculated based on the residual stress, even a molded part composed of a three-dimensional shape is created in a shape that incorporates the springback amount as the background art (1) described above. To create a shape incorporating the spring back amount as the background technology (2) described above (three-dimensional shape of the panel, which is a press-molded molded part) Thus, the mold correction shape data can be obtained with higher accuracy than the method of measuring the shape of the mold and weaving the correction shape into the molding die based on the shape data.

  According to the press die correction shape data creation method according to the present invention, since the shape of the pulling back is obtained by measuring a press-molded molded part, the FEM simulation described in the background art (3) above. Since the accuracy is much higher than the shape of the springback predicted by using the FEM, and only the residual stress component that becomes the starting force of the springback is obtained from this shape using the FEM, it can be obtained with high accuracy. Further, since the deformation amount of the entire part is calculated based on the residual stress, the spring back amount described in the background arts (1) and (2) described above is incorporated even in a molded part composed of a three-dimensional shape surface. The mold correction shape data can be obtained with higher accuracy than the method of creating the shape.

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

  FIG. 1 is a block diagram showing the configuration of a support system used for carrying out the method for creating press die correction shape data according to the present invention, FIG. 2 is a block diagram depicting the configuration of the CPU of FIG. 1, and FIG. FIG. 4 is a perspective view of a molded part, and FIG. 4 is a flowchart showing the operation in the method for creating press die correction shape data according to the invention.

  The mold shape data creation method according to the present invention creates modified shape data of a molding die for manufacturing a molded part accompanied by plastic deformation such as a pressed part of any equipment. In particular, it is assumed that the shape of the molding part of the first molding die is equal to the part shape.

  By forming a flat plate with a molding die having a molding part of this shape, measuring the shape of the resulting molded part (spring-backed shape), and obtaining a corrected shape from the difference in shape from the molding die. is there.

  At this time, the material used for the molded part is particularly effective when the material has a large amount of spring back, such as a high-tensile steel plate or an aluminum plate. However, the material of the molded part is not limited to the above.

  Here, the springback characteristic means that the metal material that has been subjected to the forming process returns to its original shape.

  For example, when a plate-shaped blank is pressed, a part bent at a predetermined angle returns the processed product to an angle shallower than the angle when the mold is released.

  In particular, a high-tensile steel material, an aluminum plate, or the like has a large amount of springback (amount of deformation due to springback characteristics).

  As shown in FIG. 1, a support system used to implement a method for creating press die correction shape data according to the present invention includes a CPU (arithmetic unit) 11 having a predetermined arithmetic processing capability, and a predetermined storage capacity. A computer 1 having a hard disk 12 is used.

  The computer 1 is a computer such as a workstation, a server computer, or a personal computer.

  The computer 1 includes a CPU 11, a hard disk 12, a RAM 13 that temporarily stores predetermined data to be processed, a keyboard (input device) 14 for an operator to input predetermined data, A general computer has equipment such as a display (output device) 15 for displaying processing results to an operator.

  Accordingly, although not shown, a ROM for storing a program frequently used in the computer 1, a drive for reading predetermined data from another storage medium (for example, CD-ROM) (for example, a CD-ROM drive), etc. It also has.

  The computer 1 may be connected to a three-dimensional shape measuring machine or another computer that creates an FEM model as will be described later.

  As shown in FIG. 2, the CPU 11 of the computer 1 includes a point cloud data measuring unit 11a, a molded part mesh data generating unit 11b, a mold mesh data generating unit 11d, an FME simulation unit 11e, and a stress distribution reversal. It has means 11f, elastic recovery amount calculation means 11g, and mold shape data correction means 11h.

  The point cloud data measuring means 11a measures a molded part press-molded with a molding die as point cloud data using a three-dimensional shape measuring machine.

  The molded part mesh data creating means 11b creates surface data based on the point cloud data measured by the point cloud data measuring means 11a, and creates mesh data for FEM simulation. It has a function of giving deformation equivalent to the back amount.

  The mold mesh data creation means 11c creates mold mesh data for FEM simulation from the mold shape data used for press molding stored in the mold mesh data storage means 11d.

  The FEM simulation unit 11e uses the molded product mesh data created by the molded product mesh data creation unit 11b and the mold mesh data created by the mold mesh data creation unit 11c, performs FEM simulation, and generates the mesh data of the molded part. From the deformation corresponding to the amount of spring back, the residual stress that is the starting force of the spring bag is calculated.

  The stress reversing unit 11f has a function of reversing ± the residual stress distribution calculated by the FEM simulation unit 11e.

  The elastic recovery amount calculating means 11g elastically recovers the residual stress reversed by the stress reversing means 11f as a starting force, and calculates the amount of elastic recovery.

  The mold shape data correction means 11h obtains a mold shape based on the amount of elastic recovery calculated by the elastic recovery amount calculation means 11g, and converts the correction shape of the mold into data.

  The point cloud data measuring unit 11a has a function of sampling the entire surface of the molded part 20 shown in FIG. 4 press-molded with a molding die to obtain three-dimensional measured point cloud data.

  This three-dimensional measuring machine includes a laser type that projects laser light and reads reflected light, an optical type that reads images from multiple directions with a video camera, a digital camera, and the like, and a contact type.

  The molded part mesh data creation means 11b uses commercially available software, creates surface data based on the point cloud data measured by the point cloud data measurement means 11a, and creates mesh data for FEM simulation. It has a function.

  The mold mesh data creating means 11d has a function of creating mold mesh data for FEM simulation from mold shape data of a mold used for press molding.

  In this case, a method of measuring the mold shape with a three-dimensional measuring machine may be used. As another method for acquiring mold shape data, there is a method using three-dimensional shape data used for mold processing.

  Mold three-dimensional shape data acquired by these methods is converted into mesh data to create mold mesh data for FEM simulation.

  In the present invention, as a precondition, since the mold shape of the initial mold is equal to the three-dimensional shape of the molded part, the shape data of the mold is basically the three-dimensional shape data of the molded part. Will be equal.

  The FEM simulation means 11e uses the molded part mesh data created by the molded part mesh data creation means and the mold mesh data created by the mold mesh data creation means, performs FEM simulation, and springs back the molded part mesh data. From the deformation corresponding to the amount, it has a function of calculating the residual stress that becomes the starting force of the springback.

  That is, the difference in shape between the molded part mesh data created by the molded part mesh data creating unit 11b and the mold mesh data created by the mold mesh data creating unit 11d corresponds to the springback amount of the molded part.

  Mold material data created by the mold mesh data creation means 11d is defined as mesh data of a molding die, and the molded part mesh data created by the molded part mesh data creation means 11b is used for molding. Define and perform molding simulation. By performing this simulation, deformation of the springback amount is imparted to the molded part mesh.

  As a result, when the molding is completed, the molded part mesh data has the same shape as the molding die, and at this time, a stress is generated when a deformation corresponding to the springback amount is applied. Since the springback is elastically deformed, the stress distribution described above can accurately determine the stress distribution of the elastic deformation when the springback amount of deformation is applied.

  The stress distribution reversing unit 11f has a function of reversing the stress distribution of the residual stress obtained by the FEM simulation unit 11e by ±. That is, the stress obtained by the FEM simulation means 11e corresponds to the residual stress that becomes the starting force of the springback.

  Since the shape required for the molded part is that it becomes a regular part shape after the spring back, the molding die may be deformed from the regular shape by an amount corresponding to the spring back.

  The elastic recovery amount calculating means 11g has a function of elastically recovering the inverted residual stress as a starting force and calculating the amount of this elastic recovery (spring forward).

  This amount is a value close to the amount of spring back when the residual stress of the entire molded part, which is the starting force of spring back obtained by the FEM simulation means 11e, is reversed.

  The mold shape data correcting unit 11h has a function of obtaining mold shape data based on the amount of elastic recovery calculated by the elastic recovery amount calculating unit 11g and converting the corrected shape of the molding die into data.

  That is, the mold shape data is obtained by elastically deforming the residual stress as a starting force, and the corrected shape of the molding die is converted into data.

  Next, the operation of the method of the present invention will be described based on the flowchart shown in FIG.

  When the process is started, the CPU 11 of the computer 1 obtains measurement data of the shape of the molded part 20 that is actually press-molded with a molding die. In this case, the molded part 20 is measured as point cloud data by a three-dimensional shape measuring machine connected to the computer 1 (step S101).

  For example, the three-dimensional measuring machine obtains point coordinates of each point from the reflected light of the curved surface of the molded part 20 that is the object to be measured, using laser light from one direction. The point coordinates of these points become the actual measured point group data of the surface.

  Then, either one of the molded part 20 or the laser scanner is rotated by 90 °, the measured point cloud data of the curved surface is sampled with laser light from this direction, and the measured point cloud data is sequentially sampled from each direction and molded. Sampling is performed on the entire surface of the component 20 to obtain three-dimensional measured point cloud data.

  Next, surface data is created based on the point cloud data described above (step S102), and molded part mesh data for FEM simulation is created (step S103).

  That is, the three-dimensional measured point cloud data obtained in step S101 is a collection of many points. From the data sampled from each direction in this collection of points, the operator sorts and selects the overlapping data and unnecessary data of the boundary line, and only the ordered processing point group data is three-dimensionally with a mouse etc. Are plotted on the display 15, and based on the plotted processing point cloud data, the computer creates curved surface data by the NURBS method or the like.

  Next, the computer 1 connects the points of the point group constituting the acquired point group data to generate a measurement point approximate mesh to obtain molded part mesh data for FEM simulation. A known mesh generation algorithm is used to generate the measurement point approximate mesh.

  Next, die mesh data for FEM simulation is created from the die shape data of the molding die used for press molding of the molded part 20 (step S104). That is, the CPU 11 converts the input mold shape data into mesh data to create mold mesh data for FEM simulation.

  Next, an FEM simulation is performed using the finite element method using the molded part mesh data for FEM simulation created in step S103 and the mold mesh data created in step S104 (step S105).

  Here, as is well known, the finite element method uses a stiffness matrix that divides a material into a plurality of finite elements and correlates stress and displacement at each node of each element, and solves static problems. This is a numerical analysis method in which the iterative calculation of the stiffness equation, which is a simultaneous equation, is repeated until the solution converges to a true solution on the condition that the external force and the internal force at each node of each element are balanced.

  Since the shape error between the molding die shape and the molded part shape corresponds to the springback amount, in this FEM simulation, deformation corresponding to the springback amount is given to the molded part mesh data.

  As a result, in the final stage of the FEM simulation, the residual stress that is the starting force of the springback is calculated.

  Since the springback phenomenon is a deformation in the elastic range, the accuracy of the FEM simulation performed here is the same as the FEM simulation shown in the prior art (3) (simulation by elastic-plastic deformation from the flat plate state to the bottom dead center). In general, a higher-precision simulation is possible than

  For this reason, the residual stress which becomes the starting force of the spring back at the time of press molding can be obtained correctly.

  Next, a spring forward simulation is performed (step S106). This spring forward simulation inverts the residual stress distribution acting in the plate material of the plate material model 21 calculated by the spring back simulation (see FIG. 5).

  This is a process of calculating the amount of elastic recovery (spring forward) when the inverted stress distribution acts on the plate material model 21. FIG. 6 is a diagram illustrating the shape 20-1 after the spring back of the molded part 20 and the shape 20-2 after the spring forward.

  Since the spring back is caused by the uneven distribution of the residual stress in the plate material, when the residual stress acting in the plate model 21 is reversed, as shown by 20-2 in FIG. A shape will be obtained.

  Therefore, by correcting the shape of the molding die model so as to match the shape of the plate material model 21 that has been elastically restored to the inside, it is possible to more easily design a highly accurate die model in consideration of springback. .

  When the spring forward simulation is performed, the meshes constituting the die model (die face) are corrected so as to match the shape of the plate model 21 after the spring forward, that is, the nodes of the meshes constituting the die model are corrected. Processing is performed, and the corrected shape of the molding die is converted into data (step S107).

  When the corrected data of the corrected mold model is generated in this way, the corrected data of the corrected mold model is output to the controller of the NC processing machine as data for NC processing, for example.

  As described above, according to the embodiment of the present invention, the molding part mesh data for FEM simulation is created in the molding part mesh data creation step, thereby deforming the molding part mesh data corresponding to the springback amount. In the FEM simulation process, FEM simulation is performed using the molded part mesh data and mold mesh data, and the residual stress that is the starting force of the springback is calculated from the deformation corresponding to the springback amount of the molded part mesh data. Then, the stress distribution of the residual stress is reversed ±, the reversed residual stress is elastically restored as the starting force, the amount of this elastic recovery is calculated, and the mold shape data is obtained based on this calculated amount of elastic recovery By making the corrected shape of the mold into data, the corrected shape of the mold is remarkably accurate. It is possible to create a press mold Modify shape data to casting.

  In particular, since the shape of the springback is obtained by measuring a press-molded molded part, the accuracy is much higher than the shape of the springback predicted using the flat plate FEM simulation described in the background art (3) above. Since only the residual stress component which becomes the starting force of the springback is obtained from this shape using the FEM, it can be obtained with high accuracy.

  Further, since the deformation amount of the entire part is calculated based on the residual stress, the spring back amount described in the background arts (1) and (2) described above is incorporated even in a molded part composed of a three-dimensional shape surface. The mold correction shape data can be obtained with higher accuracy than the method of creating the shape.

  In the present invention, since the shape of the pullback is obtained by measuring a press-molded molded part, the shape is much more accurate than the shape of the springback predicted using the FEM simulation described in the background art (3) above. Since the FEM is used to determine only the residual stress component that is the starting force of the springback from this shape, the amount of deformation of the entire part can be determined based on the residual stress. Therefore, even a molded part composed of a three-dimensional shape surface is more accurate than the method of creating a shape incorporating the springback amount described in the background arts (1) and (2). This has the effect that the mold correction shape data can be obtained, and is useful as a method for creating press mold correction shape data for correcting spring back.

It is a block diagram which shows the structure of the assistance system used for enforcing the production method of the press die correction shape data which concerns on this invention. It is a block diagram which shows the structure of CPU of FIG. It is a flowchart which shows operation | movement in the production method of the press die correction shape data which concerns on this invention. It is a perspective view of a molded part. It is explanatory drawing explaining the process in which the stress distribution which acts on the plate | board thickness direction of a board | plate material model is reversed. It is a figure which illustrates the shape after the springback of a molded part, and the shape after a spring forward.

Explanation of symbols

1 Computer 11 CPU
12 Hard disk 13 RAM
14 Keyboard (input device)
15 Display (output device)
20 Molded parts 21 Plate model

Claims (1)

A method of creating press mold correction shape data for creating correction shape data of a molding die from a difference between measurement data of a molded part after press molding by a molding die and the shape of the molding die,
A point cloud data measuring step for measuring the molded part as point cloud data;
By creating surface data based on the point cloud data and creating molded part mesh data for FEM simulation, a molded part mesh data creating step in which deformation corresponding to a springback amount is given to the molded part mesh data;
A mold mesh data creation step of creating mold mesh data for FEM simulation from the mold shape data of the mold;
A FEM simulation step of performing a FEM simulation using the molded part mesh data and the mold mesh data, and calculating a residual stress as a springback starting force from a deformation corresponding to a springback amount of the molded part mesh data;
A stress distribution reversal step of reversing the stress distribution of the residual stress ±,
An elastic recovery amount calculation step of elastically recovering the inverted residual stress as a starting force and calculating the amount of this elastic recovery;
Based on the calculated amount of elastic recovery, mold shape data is obtained, and a die shape data correction step for converting the corrected shape of the molding die into data is provided. How to make.

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