Setting method of metal sheet anisotropy information and sheet thickness information for analysis model of press-formed panel, and stiffness analyzing method

Abstract

A method of setting metal sheet anisotropy information and sheet thickness information for an analysis model of a press-formed panel includes spreading the analysis model of the press-formed panel into a blank shape by analysis of reverse press-forming; acquiring sheet thickness information obtained by the analysis of reverse press-forming; based on a spread-blank-shape and a panel-taking blank shape, acquiring a reference direction of the spread-blank-shape; calculating an angle formed between the reference direction of the spread-blank-shape and each element in the spread-blank-shape, and setting the reference direction for each element of the analysis model of the press-formed panel based on the calculated angle; and setting the sheet thickness information acquired in the sheet-thickness-information acquiring step for each element of the analysis model of the press-formed panel.

Claims

1. A method of designing an automotive body by using a CAE (computer aided engineering) analysis executed by a computer, the CAE analysis comprising, setting metal sheet anisotropy information and sheet-thickness-information for an analysis model of a press-formed panel subject to the CAE analysis for designing the automotive body, wherein the setting method comprises: acquiring a spread blank-shape by spreading the analysis model of the press-formed panel into a spread blank-shape by analysis of reverse press-forming; acquiring sheet-thickness-information changed by the analysis of reverse press-forming; acquiring a reference-direction based on the spread blank-shape and a panel-taking blank-shape which is taken from a steel sheet having in-plane anisotropy of a mechanical characteristic, the panel-taking blank-shape having a predetermined reference-direction relating to the in-plane anisotropy of a mechanical characteristic of the metal sheet, acquiring the reference-direction of the spread blank-shape; setting a reference-direction by calculating an angle formed between the acquired reference-direction of the spread blank-shape and a line joining nodes of each element in the spread blank-shape, adjusting the calculated angle based on a change of a shape of each element in the analysis of reverse press-forming that spreads the analysis model of the press-formed panel into the spread blank-shape, and setting the reference-direction for each element of the analysis model of the press-formed panel based on the adjusted angle; and setting the acquired sheet-thickness-information for each element of the analysis model of the press-formed panel.

2. The setting method according to claim 1, wherein the mechanical characteristic is at least one selected from Young's modulus, yield strength, tensile strength, r value, and a stress-strain curve.

3. A method of analyzing stiffness comprising executing a stiffness analysis while the analysis model of the press-formed panel after the reference-direction setting and the sheet-thickness-information setting in the method described in claim 2 serves as an analysis subject.

4. A method of analyzing crashworthiness comprising executing crashworthiness analysis while the analysis model of the press-formed panel after the reference-direction setting and the sheet-thickness-information setting in the method described in claim 2 serves as an analysis subject.

5. A method of analyzing stiffness comprising executing a stiffness analysis while the analysis model of the press-formed panel after the reference-direction setting and the sheet-thickness-information setting in the method described in claim 1 serves as an analysis subject.

6. A method of analyzing crashworthiness comprising executing crashworthiness analysis while the analysis model of the press-formed panel after the reference-direction setting and the sheet-thickness-information setting in the method described in claim 1 serves as an analysis subject.

7. A method of designing an automotive body by using a CAE (computer aided engineering) analysis executed by a computer, the CAE analysis comprising, setting metal sheet anisotropy information and sheet-thickness-information for an analysis model of a press-formed panel subject to the CAE analysis for designing the automotive body, wherein the setting method comprises: spreading the analysis model of the press-formed panel into a spread blank-shape by analysis of reverse press-forming; acquiring sheet-thickness-information changed by the analysis of reverse press-forming; based on the spread blank-shape and a panel-taking blank-shape which is taken from a steel sheet having in-plane anisotropy of a mechanical characteristic, acquiring a reference-direction of the spread blank-shape; calculating an angle formed between the reference-direction of the spread blank-shape and a line joining nodes of each element in the spread blank-shape, adjusting the calculated angle based on a change of a shape of each element in the analysis of reversed press-forming that spreads the analysis model of the press-formed panel into the spread blank-shape, and setting the reference-direction for each element of the analysis model of the press-formed panel based on the adjusted angle; and setting the sheet-thickness-information acquired in the sheet-thickness-information acquiring for each element of the analysis model of the press-formed panel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1(a)-(d) provide explanatory views each showing an example of my method.

(2) FIGS. 2(a)-(c) provide explanatory views each showing an example of a result of press-forming analysis.

(3) FIGS. 3(a)-(c) provide explanatory views each showing an example of a result of the press-forming analysis.

(4) FIGS. 4(a)-(b) provide explanatory views each showing an example of a result of conventional press-forming analysis.

(5) FIG. 5 is a graph showing results of stiffness analysis of Example 1 and Comparative Example 1 compared to experimental values.

(6) FIG. 6 is a graph showing results of stiffness analysis of Example 2 and Comparative Example 2 compared to experimental values.

(7) FIG. 7 is an explanatory view explaining a precondition.

(8) FIG. 8 is an illustration explaining anisotropy information.

REFERENCE SIGNS LIST

(9) 1 analysis model (before setting of anisotropy information and sheet thickness information) 2 blank 3 metal sheet (metal sheet from which blank is taken) 4 panel-taking blank shape 5 analysis model (after setting of anisotropy information and sheet thickness information)

DETAILED DESCRIPTION

(10) A press-formed panel is typically obtained by taking a blank from an anisotropic metal sheet such as a rolled metal sheet and obtained by press-forming the blank. Hence, data on blanking (panel-taking blank shape) is additionally available. In the blanking data, the relative positional relationship between the anisotropic metal sheet and the blank member is obtained. Hence, the reference direction of the anisotropy information for the blank member can be acquired as long as the reference direction of the anisotropic metal sheet can be acquired.

(11) Meanwhile, if analysis of reverse press-forming is executed for the analysis model of the press-formed panel, a spread-blank-shape obtained by spreading the analysis model into the blank shape is expected to be the same shape as the panel-taking blank shape. Accordingly, by comparing both shapes to each other, the reference direction in the spread-blank-shape can be acquired.

(12) Then, I provide a method of setting the reference direction for the analysis model of the press-formed panel when the reference direction in the spread-blank-shape is acquired.

(13) Since each element in the analysis model of the press-formed panel is very small, even if the analysis model of the press-formed panel is spread into the blank shape by the analysis of reverse press-forming, the deformation thereof is very small. Also, even if deformation occurs, the deformation is from a square into a rectangle or a parallelogram.

(14) Hence, if each element is not deformed or if each element is deformed into a rectangle, the relative positional relationship between a side of each element and a certain direction in the element, for example, the reference direction, is not changed before and after the analysis of reverse press-forming.

(15) Also, even if the element is deformed into a parallelogram, by taking into account a displacement of an orthogonal side of the element, the relative relationship between the side of the element and the certain direction in the element can be obtained before and after the analysis of reverse press-forming.

(16) The analysis model has coordinate information of nodes before and after the deformation of each element, that is, before and after the analysis of press-forming or analysis of reverse press-forming, the side of the element can be obtained by using a line joining the nodes of the element.

(17) Hence, by acquiring an angle formed by the line joining the nodes of each element in the spread-blank-shape and the reference direction in the anisotropy information, the relative positional relationship between the side and the reference direction of the element in the spread-blank-shape can be obtained, and the reference direction can be easily set for the analysis model of the press-formed panel based on the angle.

(18) Also, by executing the analysis of reverse press-forming in which the press-formed panel is spread into the blank shape, the sheet thickness information of each element can be acquired.

(19) Hereinafter, analysis is entirely executed by a computer. FIG. 1 provides explanatory views each showing an example of my method. Reference sign 1 denotes an analysis model of a press-formed panel. Anisotropy information or sheet thickness information is not set for the analysis model 1.

(20) The metal sheet of the analysis model 1 is an anisotropic metal sheet (in this example, cold-rolled steel sheet). Anisotropy information of this metal sheet is correspondence information between an azimuth angle with respect to the reference direction and a mechanical characteristic. In this case, the anisotropy information is stored in the form of a table.

(21) The reference direction is a direction rotated counterclockwise from the C direction by an angle (this angle is also referred to as reference-direction-to-C-direction angle) (see FIG. 8). The table holds mechanical characteristic values corresponding to three angles of =0, =45, and =90. By designating in the table, the reference direction can be set or changed. If =0 is designated, the C direction serves as the reference direction. If =45 is designated, a direction rotated counterclockwise from the C direction by 45 serves as the reference direction. If =90 is designated, a direction rotated counterclockwise from the C direction by 90 (=L direction) serves as the reference direction. The mechanical characteristic values in the table are respective pieces of data of Young's modulus, yield strength, tensile strength, r value, and stress-strain curve. Depending on the type of analysis to be executed (the above-described stiffness analysis or crashworthiness analysis), data required for the analysis is selected from these pieces of data, and is used.

(22) In the following description, an example of reference-direction-to-C-direction angle =0, that is, an example, in which the C direction serves as the reference direction, is described.

(23) In CAE analysis, the analysis model 1 is divided into a plurality of regions in a mesh form as shown in FIG. 1(a). Each of the plurality of divided regions is an element.

(24) In a first step [1] ((A), (B) spread-blank-shape acquiring step, and (B) sheet-thickness-information acquiring step, described below), the analysis of reverse press-forming is executed for the analysis 1 so that the analysis model 1 is spread into a blank having a planar shape (spread-blank-shape 2) (see FIG. 1(b)), and sheet thickness distribution information for the analysis model 1 is acquired.

(25) The analysis of reverse press-forming is analysis that press-forming a subject product shape in a reverse manner and, hence, restores the product shape into a flat sheet. To be specific, a finite element model is created for the subject product shape, and the finite element model is spread into a plane so that the strain energy is minimized (i.e., so that elements do not overlap each other and the deformation of each element is minimized).

(26) Further, deformation of each element and the state of the sheet thickness and the like of the spread planar finite element model are reflected on a corresponding element of the finite element model with the product shape before the spread. Accordingly, the sheet thickness distribution state and the like of the product shape before the spread can be obtained.

(27) In a second step [2] ((C) reference-direction acquiring step, described below), the spread-blank-shape 2 is moved and rotated and the direction of the spread-blank-shape 2 is aligned with the direction of a panel-taking blank shape 4. Accordingly, relative positional relationship with respect to a steel sheet 3 of the spread-blank-shape 2 can be acquired. Data of the panel-taking blank shape 4 is previously input (see FIG. 1(c)).

(28) To align the spread-blank-shape 2 in FIG. 1(b) with the panel-taking blank shape 4 in FIG. 1(c), the spread-blank-shape 2 in FIG. 1(b) is rotated by 180. Accordingly, the reference direction can be set at each element of the spread-blank-shape 2, based on the reference direction of the steel sheet 3. As described above, the reference-direction-to-C-direction angle is set at 0 in this example and, hence, the C direction serves as the reference direction. The C direction is already set as the reference direction at the steel sheet 3.

(29) In a third step [3] ((D), (E) reference-direction setting step, and (F) sheet-thickness-information setting step, described below), as shown in FIG. 7, an angle formed between a line joining a node number 1 to a node number 2 and the reference direction, is calculated by an outer product, with reference to X coordinates and Y coordinates of the node number 1 and the node number 2 acquired in (A) ((D) described below).

(30) Regarding a certain element, if the shape of the element is not changed, or if the shape of the element is changed from a square to a rectangle, the angle in the state of the spread-blank-shape 2 is not changed from the angle in the state of the analysis model 1. Hence, based on the angle , the reference direction can be set for the analysis model 1, by calculation in a reverse manner from the line joining the node number 1 to the node number 2.

(31) Also, regarding a certain element, if the shape of the element is deformed from a square to a parallelogram, by obtaining a change amount of an angle formed by adjacent sides and taking into account the change amount to the angle , the reference direction for the analysis model 1 can be set.

(32) Hence, the angles are obtained for all elements of the spread-blank-shape 2, and the reference directions are collectively set for all elements in the analysis model 1 corresponding to the respective elements of the spread-blank-shape 2 based on the angles ((E) described below). Thus, the reference direction can be automatically set in a short time for each element of the analysis model 1.

(33) Then, in (F) described below, sheet thickness information, which is acquired as the sheet thickness information of each element of the analysis model 1 in (B), is input.

(34) In this way, the anisotropy information and the sheet thickness information can be correctly set for the analysis model 1.

(35) The above-described steps can be summarized as follows:

(36) (A) Acquisition of information of original analysis model: the node number 1 and the node number 2 of an element to be calculated are acquired.

(37) (B) Restoration of original analysis model to shape of a blank: by using analysis of reverse press-forming such as Onestep, a product having a three-dimensional shape is changed to a two-dimensional flat sheet state, and the sheet thickness distribution information for the analysis model is acquired.

(38) (C) Arrangement of the blank: the blank is moved and rotated with respect to the LC directions, and is arranged.

(39) (D) Calculation of angle in the blank: the angle formed between the line joining the node number 1 to the node number 2, and the reference direction is calculated by the outer product, with reference to the X coordinates and Y coordinates of the node number 1 and node number 2 acquired in (A).

(40) (E) Setting of angle in the analysis model: the reference direction is set based on the angle calculated in (D) for the element of the original analysis model.

(41) (F) Setting of sheet thickness in the analysis model: the sheet thickness acquired in (B) is input to the sheet thickness information of the element of the original analysis model.

Example 1

(42) Operations and advantageous effects by the calculation method of metal sheet anisotropy are described below based on specific examples.

(43) Experiments were executed for respective cases in which the reference-direction-to-C-direction angle (metal sheet angle ) was 0, 45, and 90, and the analysis models 5, in which the anisotropy information and sheet thickness information were set, were acquired. Also, for these analysis models 5, a stiffness analysis was executed, and stiffness values were calculated (Example 1). A 590-Mpa class cold-rolled steel sheet was used as the metal sheet.

(44) Also, actual press-formed panels corresponding to these models were fabricated, the stiffness test (stiffness check experiment) corresponding to the stiffness analysis was executed, and the stiffness value was obtained (Experimental Value 1).

(45) Also, the stiffness analysis was similarly executed on an analysis model 5 after the anisotropy information and the sheet thickness information were set, obtained by a press-forming analyzing method, in which the anisotropy information was manually input and the sheet thickness was constant, for a three-dimensional shape having the same target value as a comparative example (case of =0 is illustrated in FIG. 4, but =45 and =90 are not illustrated), and the stiffness value was calculated (Comparative Example 1).

(46) First, the direction of an arrow indicative of the reference direction in the analysis model 5 is described.

(47) FIGS. 2 and 3 show the analysis models 5 having the finally calculated shapes obtained through the press-forming analysis. In each of FIGS. 2 and 3, (a) represents the reference-direction-to-C-direction angle is 0, (b) represents the angle is 45, and (c) represents the angle is 90. I found that the arrow indicative of the reference direction is set to match the actual state of every element of the analysis model 5.

(48) FIG. 4 shows the results when the reference-direction-to-C-direction angle is 0 according to the comparative example. The reference-direction-to-C-direction angle is 0. However, since the arrow indicative of the reference direction is input based on the guesswork in each element of the three-dimensional shape, the arrows indicate opposite directions between adjacent elements in a straight portion (FIG. 4(a)), and the arrow indicative of the reference direction is input on a large block basis in a curve portion (FIG. 4(b)). Hence, the setting does not match the actual state.

(49) Table 1 shows an example in which the time required for setting the reference direction (arrow input) is compared with that of the comparative example. Referring to Table 1, the required time for setting the reference direction is of the conventional time even when the number of elements is as small as 1000, and the required time is 1/27 of the conventional time when the number of elements is as large as 10000. I found that the required time is markedly reduced as compared to the conventional time.

(50) TABLE-US-00001 TABLE 1 My Method Comparative Method 1000 meshes 10 30 10000 meshes 11 270

(51) Next, the results of the stiffness analysis are described based on Tables 2 and 3, and FIG. 5.

(52) TABLE-US-00002 TABLE 2 Stiffness value (kN .Math. mm/mm) Metal sheet Experimental angle () Value 1 Example 1 Comparative Example 1 0 1872 1875 1904 45 1743 1743 1867 90 2135 2142 1941

(53) Table 2 shows the stiffness values (kN.Math.mm/mm) according to Experimental Value 1, Example 1, and Comparative Example 1 corresponding to the respective metal sheet angles ().

(54) Table 3 shows how the values of Example 1 and Comparative Example 1 deviate from Experimental Value 1 (rate of deviation (%)) based on Table 2.

(55) TABLE-US-00003 TABLE 3 Rate of deviation from experiment (%) Metal sheet angle () Example 1 Comparative Example 1 0 0.2 1.7 45 0.0 7.1 90 0.3 9.1

(56) As shown in FIG. 5, in Example 1, any reference-direction-to-C-direction angle (metal sheet angle) is extremely close to Experimental Value 1. In contrast, in Comparative Example 1, the angle is a value relatively close to that of Experimental Value 1 when =0. However, the values are largely different from the experimental values when =45 and =90.

(57) As described above, in Example 1, the prediction accuracy of the stiffness value according to the deformation simulation of the stiffness analysis is markedly increased as compared to Comparative Example 1. That is, according to my method, the analysis model 5 with the finally calculated shape in which the anisotropy and sheet thickness are more correctly set could be acquired.

(58) Even when the crashworthiness analysis was executed instead of the stiffness analysis, the analysis was similarly executed, and the similar result could be obtained.

Example 2

(59) Also, to check the difference in advantage caused by the difference in anisotropy of the metal sheet, a 270-Mpa class cold-rolled steel sheet with larger anisotropy than that of the 590-Mpa class cold-rolled steel sheet used in aforementioned Example 1 was used and the similar experiment was executed. The results are shown in Tables 4 and 5, and FIG. 6. The way of looking at the drawing and tables is similar to that of Tables 2 and 3, and FIG. 5.

(60) TABLE-US-00004 TABLE 4 Stiffness value (kN .Math. mm/mm) Metal Experimental sheet angle () Value 2 Example 2 Comparative Example 2 0 1950 1954 1983 45 1825 1827 1971 90 2210 2217 2005

(61) TABLE-US-00005 TABLE 5 Rate of deviation from experiment (%) Metal sheet angle () Example 2 Comparative Example 2 0 0.2 1.7 45 0.1 8.0 90 0.3 9.3

(62) Referring to Table 5, the deviation between Comparative Example 2 and Experimental Value 2 is substantially the same as that of Example 1 (see Table 4) when the metal sheet angle is 0. However, the values become large when the metal sheet angle is 45 and 90. This may be because the deviation more noticeably appeared since the metal sheet with the larger anisotropy was used. In this viewpoint, in Example 2, I found that the value at any metal sheet angle matches Experimental Value 2 well, and the CAE analysis accuracy is markedly increased.