JP2021186833A - Rigidity evaluation method and shape determination method of press molding product, and press molding product - Google Patents

Abstract

To provide a rigidity evaluation method which can accurately evaluate whether dents are generated or not so as to supply a press molding product without dents due to rigidity improvement.SOLUTION: A method evaluating rigidity of a press molding product is given in which: by the elastic analysis using displacement-load measuring experiment or CAE, when supposing two points in circumference of a molding product or molding shape data and when one side of the circumference divided by the two point is restricted and displacement in the press direction is provided to one point in the other side, it evaluates whether dents are generated or not on the basis of the relation between displacement and load at the point to which displacement is applied. A molding shape without dents is determined based on the method and a rigidity improvement measure by which a rigidity addition shape is added, and the press molding product is press-molded by use of the molding shape determination method.SELECTED DRAWING: Figure 5

Description

The present invention relates to a rigidity evaluation method for determining the presence or absence of stickiness in a press-molded product, a method for determining a shape of a press-molded product without stickiness using the same, and a press-molded product.

In recent years, there has been an increasing demand for weight reduction of automobile bodies for the purpose of improving fuel efficiency due to energy problems and global environmental problems, while demands for improving collision characteristics, for example, body rigidity, for occupant protection in the event of a collision. Is increasing year by year. In order to meet these two conflicting demands, the application of high-strength steel sheets is expanding. By applying a high-strength steel plate, it is possible to increase the strength and rigidity of the automobile body and the absorbed energy at the time of a collision without increasing the plate thickness.

However, in press molding, which is generally used frequently for processing vehicle body parts, a shape freezing defect called springback becomes a problem. Springback occurs when a press-molded product press-molded from a steel plate as a plate-like material is released from a die, and increases as the material strength of the steel plate increases. Since springback not only impairs the appearance quality but also causes welding defects during assembly, it is indispensable to take measures against springback in order to expand the application of high-strength steel sheets.

The cause of the springback is the elastic recovery due to the bending moment caused by the non-uniformity of the residual stress being released at the time of mold release of the press-molded product. Therefore, conventionally, as a measure against springback, a method of alleviating the non-uniformity of residual stress has been proposed.

In Patent Document 1, an intermediate product in which an emboss is arranged in an elongated flange portion and a surplus bead is arranged in a contracted flange portion is formed, and in the molding of a final molded product, compressive stress is applied to the elongated flange portion by crushing the embossing. A technique has been proposed for leveling the residual stress distribution of a press-formed product by applying tensile stress to the shrinking flange portion by means of a surplus bead.

In Patent Document 2, an intermediate part is manufactured by press-molding to a radius of curvature smaller than the radius of curvature of the product shape, and the manufactured intermediate part is press-molded into the product shape due to the stress difference between the top plate portion and the flange portion. A technique has been proposed in which the bending moment generated is reduced and the camber back is suppressed.

In Patent Document 3, the surface of a metal panel after press molding is divided into N regions, and an indenter is pressed against the surface of the metal panel in each region to measure the relationship between displacement and load, and the distribution of stickiness is generated. And a method for evaluating the tensile rigidity of a metal panel that can obtain the load distribution of stickiness has been proposed.

Japanese Unexamined Patent Publication No. 2009-255117 International release 2017/149955 Japanese Unexamined Patent Publication No. 2013-29332

As a method for leveling the residual stress, Patent Document 1 proposes a method of forming an embossing in the extension flange portion and forming a surplus bead in the contraction flange portion, but the low rigidity which is the main object of the present invention is proposed. Since springback occurs in parts even at low stress, it may not be sufficient to reduce the stress in a specific part. In addition, another form of springback may occur in a new stress state resulting from reducing the stress in a particular portion.

Patent Document 2 deals with the case where the continuous hat shape is curved, but the low-rigidity part mainly targeted by the present invention has a shallow molding depth and is in a stress state depending on the presence or absence of the overhanging shape of the top plate. Therefore, it is not possible to reduce the stress by a uniform method as in the technique of Patent Document 2.

In Patent Document 3, it is effective when a part of the panel is sticky, but since the measurement is performed by restraining the entire outer circumference, the stickiness causes twisting or distortion of the entire panel, and raising a part of the outer circumference. There was a problem that it could not be judged effectively when it led to a depression. In addition, there is a problem that the number of measurement points increases in order to measure accurately.

Further, even if the springback can be reduced by the above-mentioned technique and the conventional countermeasure technique, stickiness may occur due to slight distortion of the panel. Further, in the case of a part having low shape rigidity, stickiness may occur even if the springback is zero. Therefore, in order to reduce stickiness, conventional springback measures alone are not sufficient, and the presence or absence of stickiness itself is evaluated, the shape rigidity of the part is increased, and the part shape that does not cause stickiness. We need a way to determine.
That is, the problems to be solved by the conventional technology are listed below.
(1) There is a need for a method to evaluate the stickiness itself.
(2) There is a need for a method to determine the shape of parts that do not cause stickiness by repeating the process multiple times, with the evaluation of stickiness and the improvement of rigidity as one process.

The present invention has been made in view of the above problems, and proposes a rigidity evaluation method capable of determining the presence or absence of stickiness in a press-molded product, and proposes a method for determining the shape of a press-molded product that does not cause stickiness. At the same time, it is an object of the present invention to provide a press-molded product having a determined press-molded shape.

The method for evaluating the rigidity of a press-molded product of the present invention, which advantageously solves the above problems, is a method for evaluating the rigidity of a press-molded molded product, which is divided into two points on the outer periphery of the molded product and the two points. One of the outer circumferences is restrained, a displacement in the pressing direction is given to one point on the other outer circumference, and the presence or absence of stickiness is determined from the relationship between the displacement amount and the load at the point where the displacement is applied.

Further, the rigidity evaluation method of the press-molded product of the present invention is a method of evaluating the rigidity of the press-molded molded product, and is divided into two points on the outer periphery of the molded product shape data and the two points using CAE analysis. One of the outer circumferences is restrained, a displacement in the pressing direction is given to one point on the other outer circumference, and the presence or absence of stickiness is determined from the relationship between the displacement amount and the load at the point where the displacement is applied. There is.

Further, the method for determining the shape of the press-molded product of the present invention includes a rigidity evaluation step of determining whether or not stickiness occurs in the press-molded product by the above-mentioned rigidity evaluation method of the press-molded product, and a press-molded product to which a rigidity-added shape is added. It is characterized by repeatedly applying the design rigidity improvement measures process to determine a non-sticky press molding shape.

Further, the press-molded product of the present invention is characterized in that the press-molded shape is determined by the above-mentioned method for determining the shape of the press-molded product, and the press-molded product is press-molded.

According to the rigidity evaluation method of the press-molded product of the present invention, two points on the outer circumference of the molded product and one of the outer circumferences divided by the two points are restrained, and one point on the outer circumference of the other is given a displacement in the pressing direction. Since it was decided to determine the presence or absence of stickiness from the relationship between the amount of displacement at the point where the displacement was applied and the load, it is possible to accurately determine the stickiness due to twisting or distortion of the press-molded product.

Further, according to the rigidity evaluation method of the press-molded product of the present invention, CAE analysis is used to restrain two points on the outer circumference of the molded product shape data and one of the outer circumferences divided by the two points, and the other outer circumference. Since the presence or absence of stickiness is determined from the relationship between the displacement amount and the load at the point where the displacement is applied, the displacement in the press direction is given to one point, so the press-molded product is not pressed in advance. You can judge the stiffness accurately.

Further, in the rigidity evaluation method of the press-molded product of the present invention, it is preferable to restrain three points among the four corners of the outer periphery of the molded product or the molded product shape data and give a displacement to the other one point. A press-molded product having a substantially square outer circumference can be easily and efficiently evaluated for rigidity.

Further, according to the method for determining the shape of the press-molded product of the present invention, the rigidity evaluation step of determining whether or not the press-molded product is sticky by the rigidity evaluation method of the press-molded product and the press molding with the added rigidity added. Since it was decided to repeatedly apply the rigidity improvement measure process for designing the product once or twice or more to determine the press-molded shape without stickiness, the press-molded product has excellent shape freezeability and other When joining parts, it is possible to make parts with less displacement of the joints, which can contribute to improving the productivity of automobiles, for example.

It is a schematic flow chart which shows the process of determining the molding shape of the press-molded article without stickiness which concerns on one Embodiment of this invention. It is a perspective view which shows typically the press molding shape before applying this invention. It is a perspective view which shows typically the measurement point and the restraint point for the rigidity evaluation which concerns on one Embodiment of this invention. It is a graph which shows the displacement-load measurement result which concerns on embodiment of FIG. It is a perspective view which shows typically the press molding shape which added the rigidity addition shape by the method of determining the molding shape which concerns on one Embodiment of this invention. It is a graph which shows the displacement-load measurement result which concerns on embodiment of FIG. It is a perspective view which shows typically the press molding shape which added the rigidity addition shape by the method of determining the molding shape which concerns on other embodiment of this invention.

As a result of diligent studies to solve the above problems, the inventors restrained two points on the outer circumference of the press-molded molded product and one of the outer circumferences of the molded product divided by the two points, and restrained one of the outer circumferences of the other. It has been found that it is possible to determine the presence or absence of stickiness by giving a displacement in the press direction to one point and evaluating the rigidity of the press-molded product from the relationship between the displacement amount and the load at the point where the displacement is applied. We also found that for press-molded products that generate stickiness, it is effective to take measures to improve rigidity by adding a rigidity-added shape consisting of beads and overhanging shapes that improve rigidity. rice field. In addition, it has been found that rigidity evaluation and rigidity improvement measures can be repeated once or twice or more to determine a non-sticky press-molded shape.

In the method for evaluating the rigidity of a press-molded product according to an embodiment of the present invention, one of the two points on the outer circumference of the molded product and one of the outer circumferences of the molded product divided by the two points is supported or constrained, and the outer periphery of the other is supported. A load in the pressing direction is applied to one point, the rigidity is evaluated using the relationship between the displacement amount and the load at the point where the displacement is applied, and the presence or absence of stickiness is determined. Here, the restraint point, the support point, and the displacement point are not strictly located on the outer circumference, but may be located inward from the outer circumference with a predetermined length, if necessary. Further, the outer circumference on the side to be supported or restrained may be supported or restrained at one point, but may be a plurality of points or a linear support / restraining method. When supporting, it is necessary to support the support point so that it will not be displaced when a load is applied to the displacement point. Further, the pressing direction is, for example, the plate thickness direction of the flat plate portion. For example, two diagonal corners of the four corners of the molded product after press molding are completely restrained, one of the other diagonals is supported or restrained, and the remaining one corner is loaded in two positive and negative directions in the press direction. It is preferable to add. In the case of a quadrangle or a rectangular shape and a shape that can be approximated to them, the four corners can be determined at four points corresponding to the vertices. In the case of other polygonal shapes or complex shapes, both ends of the diagonal line connecting any two points on the outer circumference of the part, one point on one outer circumference divided by the diagonal line, and one point on the other outer circumference. And, it is preferable to choose. Here, a diagonal line that divides the outer circumference into approximately 1/2 can be selected, one of the divided outer circumferences can be supported or constrained, and one point on the other outer circumference can be used as a measurement point (displacement point). Further, it is preferable that two points other than the points at both ends of the diagonal line among the points defined as the four corners are positioned axially symmetric with respect to the diagonal line. "Approximately 1/2 of the outer circumference" can be configured so that, for example, the diagonal line passes through the center of gravity of the press-molded product. When determining the four corners, for example, a place with extremely low rigidity such as a protruding shape is shifted in the circumferential direction or inward to avoid deformation only in the vicinity of the displacement point when a displacement is applied. It is preferable to measure. It is also possible to use 5 or more points on the outer circumference, and 4 or more points may be constrained as long as they are on the outer circumference. The range on the outer circumference to be restrained depends on the shape of the press-molded product, but the line length is preferably 1/6 or more and 2/3. If the restrained range is too narrow or too wide, the evaluation accuracy of stickiness based on the twist of the entire molded product and the distortion of the outer circumference will be low.

In the present embodiment, three points out of the four corners determined as described above are constrained, and the remaining one point is evaluated for two conditions in the positive and negative directions of the press direction, and a total of eight conditions are evaluated for rigidity. .. This stiffness evaluation investigates the displacement-load relationship of the target position by experiment or by CAE (Computer Aided Engineering) analysis.

As the molded product or the shape data of the molded product used in the present embodiment, it is preferable to use the regular size, the molded product press-molded according to the regular size, or the shape data of the regular size. When evaluating the rigidity of the molded product after springback, it is preferable to use the molded product data after springback or the molded product data after springback analysis.

Under the above conditions, perform a displacement-load measurement experiment or elastic analysis by CAE to investigate the displacement-load relationship at the displacement measurement point. In a molded product with sufficient rigidity, the displacement-load curve becomes monotonically increasing. On the other hand, when the shape rigidity is insufficient and stickiness occurs, the displacement-load curve descends, stagnates, or vibrates, and does not increase monotonically. This is used to determine the presence or absence of stickiness. The amount of displacement is preferably at least 1.0 times the plate thickness, preferably up to about 100 mm, and more preferably up to the bottom dead center in a normal press. This is because if the amount of displacement to be measured is too small, stickiness cannot be confirmed, and if it is too large, plastic deformation occurs.

In addition to the displacement-load curve, it is also effective to use the displacement distribution in the press direction of the entire molded product panel during the experiment or the elastic analysis by CAE in determining the presence or absence of stickiness. Image analysis, laser ranging, and finite element method analysis can be used.

Next, in the method for determining the shape of a press-molded product as another embodiment of the present invention, first, the presence or absence of stickiness is determined by using the rigidity evaluation method for the press-molded product according to the above embodiment (rigidity evaluation step). ). Next, we will implement rigidity improvement measures to design a press-molded shape by adding rigidity-added shapes such as beads and overhanging shapes to the part where stickiness is determined to occur and its surroundings (rigidity improvement measures). Process). This rigidity evaluation step and the rigidity improvement measure step are repeatedly applied once or twice or more to determine a press-molded shape in which stickiness does not occur.

Further, the press-molded product as another embodiment of the present invention is manufactured by determining a shape that does not cause stickiness by the above-mentioned method for determining the shape of the press-molded product and press-molding the shape to freeze the shape. It is possible to make a part that has excellent properties and is less likely to be twisted or distorted on the outer periphery of the molded product. Therefore, when joining with other parts, it is possible to carry out high-precision and efficient joining with less occurrence of deviation without any trouble. For example, by applying this embodiment to automobile parts, the production efficiency of automobiles can be improved.

(Example 1)
The above embodiment was applied to the molding of the A-pillar lower inner of the actual part, and the rigidity was evaluated by the elastic analysis by CAE. It is a substantially rectangular part having an approximate length of 700 mm and a width of 400 mm. The material is a 980 MPa class cold-rolled steel sheet (HITEN) with a plate thickness of 0.9 mm, and the mechanical properties are yield point (YP) of 620 MPa, tensile strength (TS) of 1030 MPa, and elongation (El) of 15. %Met.

The process flow which shows the shape determination method of the press-molded article which concerns on embodiment applied to FIG. 1 is shown. First, shape data of the press-molded product is prepared (S10). Using the shape data, the displacement-load curve is obtained by elastic analysis by CAE (S11), and the presence or absence of stickiness is determined (S12), and the rigidity is evaluated (rigidity evaluation step). If it is determined that stickiness occurs, a rigidity-added shape is added and rigidity improvement measures are taken (S13: rigidity improvement measures step). The rigidity evaluation process and the rigidity improvement measure process are repeated until the shape does not cause stickiness. A shape that does not cause stickiness is determined as a press-molded shape (S14).

FIG. 2 is a perspective view showing the shape of the press-molded product 100 used in this embodiment. It has a substantially rectangular shape with a large width on the right side in the longitudinal direction, and has a step portion 12 having a Z-shaped cross section on the front side. The flat plate portion 11 is the XY plane, the longitudinal direction is the X axis to the right, the width direction is the Y axis in the direction away from the step portion 12, and the direction in which the step portion 12 is bent perpendicular to the flat plate portion 11 is the negative of the Z axis. Let the coordinate system be. Same below.

FIG. 3 shows the positions of the four corners selected in this embodiment with ● marks 1, 2, 3, and 4. According to the above embodiment, three points out of the four corners are set as restraint points, and the remaining one point is set as a displacement-load measurement point. For example, positions 2 and 4 are both ends of the diagonal line, position 3 is a constraint point on the outer circumference 13 of the molded product, and a load is applied to position 1 in the positive and negative directions on the Z axis. Displacement-load curves at points 1, 2, 3 and 4 are obtained by elastic analysis by CAE and are shown in FIG. In FIG. 4, the displacement was analyzed up to 40 mm. The maximum value of the load was 140 N. From the results of FIG. 4, the load at the positions 2 and 3 is stagnant in the displacement in the negative direction of the Z axis, and the load at the positions 1, 2 and 3 is stagnant in the displacement in the positive direction of the Z axis. It can be seen that it is descending or vibrating.

Therefore, as shown in FIG. 5, an overhang shape 14 as an additional rigidity shape is provided on the side closer to the position 3 than the center of the wide portion on the right side of the flat plate portion 11, and the press-molded product 101 after the rigidity improvement measures is provided. .. Then, the same rigidity evaluation as above was performed again. The displacement-load curves at each measurement point 1, 2, 3, and 4 are obtained and shown in FIG. The displacement amount was analyzed up to 40 mm in the same manner as above. The maximum value of the load was 140 N. As is clear from FIG. 6, in the shape of FIG. 5 in which the rigidity is improved, the displacement-load curve at each measurement point increases monotonically, and the occurrence of stickiness is improved.

(Example 2)
A bead 15 was provided as a rigidity-added shape to the molded product having the same outer shape as that of the first embodiment, and the press-molded product 101 was used as a press-molded product after measures for improving the rigidity. In designing the bead, the first bead 15 is linear from position 2 to position 4, the second bead 15 is provided so as to hang a perpendicular line from position 3 to the first bead, and the bead is provided to the outer line on the opposite side. Was extended. However, the second bead 15 from the position 3 is divided before and after crossing the first bead 15 so that the intersecting beads 15 do not overlap.

Similar to Example 1, this rigidity improvement measure product also shows that the displacement-load curve uniformly increases as a result of the rigidity evaluation at the four corners.

Thus, the method for evaluating the rigidity of the press-molded product of the present invention can accurately determine the twist and distortion of the panel due to stickiness. Further, according to the method for determining the shape of the press-molded product and the press-molded product of the present invention, the occurrence of stickiness can be efficiently suppressed. The technique of the present invention is suitable for application to flat plate-shaped parts having low shape rigidity.

100 Press-molded product 101 Press-molded product after measures to improve rigidity 11 Flat plate part 12 Step part 13 Outer circumference 14 Overhanging part (rigidity added shape)
15 beads (additional rigidity)
1, 2, 3, 4 measurement points and restraint points (support points)

Claims (6)

A method for evaluating the rigidity of a press-molded molded product, in which one of the two points on the outer circumference of the molded product and the outer circumference divided by the two points is supported or restrained, and one point on the outer circumference of the other is supported. A method for evaluating the rigidity of a press-molded product, which comprises evaluating the rigidity by applying a load in the press direction and using the relationship between the displacement amount and the load at the point where the displacement is applied. A method for evaluating the rigidity of a press-molded molded product, in which CAE analysis is used to support or restrain two points on the outer circumference of the molded product shape data and one of the outer circumferences divided by the two points. A method for evaluating the rigidity of a press-molded product, which comprises applying a load in the pressing direction to one point on the other outer periphery and evaluating the rigidity using the relationship between the displacement amount and the load at the point where the displacement is applied. Of the four corners of the outer periphery of the molded product or the molded product shape data, two diagonal corners are constrained, one of the other diagonal corners is supported or constrained, and the other corner is displaced. The method for evaluating the rigidity of a press-molded product according to claim 1 or 2. The method for evaluating the rigidity of a press-molded product according to any one of claims 1 to 3, wherein the presence or absence of stickiness is determined from the relationship between the displacement amount and the load. The rigidity evaluation step of determining whether or not the press-molded product is sticky by the rigidity evaluation method of the press-molded product according to claim 4, and the rigidity improvement measure step of designing the press-molded product to which the added rigidity shape is added. A method for determining the shape of a press-molded product, which is repeatedly applied to determine a non-sticky press-molded shape. A press-molded product characterized in that the press-molded shape is determined by the method for determining the shape of the press-molded product according to claim 5, and the press-molded product is press-molded.

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