JP7496664B2 - Method for determining material dimensions for UO bending - Google Patents

Description

The present invention relates to a method for determining material dimensions for UO bending through simulation.

The parts that make up an automobile body are often manufactured by press-molding metal sheets. Specifically, a blank of a given shape is punched out of a flat metal sheet, and after press-molding this blank, unnecessary parts of the molded product are cut away and removed. In this process, if the blank before press-molding is made to have the minimum size (shape) required for the molded product after press-molding, material yield can be increased.

For example, the following Patent Document 1 shows a method for optimizing the shape of a blank material through repeated calculations using computer simulation.

JP 2009-45627 A JP 2014-4626 A

Optimization of the blank shape using computer simulation is performed, for example, in the following procedure. First, a flat blank 101 shown in FIG. 12(A) is press-formed using simulation to form a molded product 102 shown in FIG. 12(B). The contour (position of the end) of this molded product 102 is compared with the contour (position of the end) of a finished part 103 shown in FIG. 12(C) to calculate the surplus or deficiency ΔL' of the dimensions of the blank 101. The shape of the blank 101 is modified based on the surplus or deficiency ΔL' thus calculated, and press forming is performed again. The above steps are repeated until the molded product 102 meets the required quality (i.e., until the difference between the contour of the molded product 102 and the contour of the finished part 103 falls within a predetermined range).

As a type of press forming, a so-called UO bending process is known in which a flat blank material is formed into a tubular shape (see, for example, the above-mentioned Patent Document 2). In a typical UO bending process, a flat blank material is first pressed with a U-bending die to form a U-shaped formed product (U-bending process). Next, as shown in FIG. 13, a U-shaped formed product 201 is pressed with O-bending dies 202 and 203 to butt the ends of the formed product 201 together (see FIG. 13(B)). After that, by further pressing, the formed product 201 protrudes to the outer periphery (see FIG. 13(C)), and is pressed against the die 201 to form a tubular part 204 (see FIG. 13(D)). The tubular part 204 is provided with an butt joint 205 between the ends.

When trying to optimize the shape of such a material (blank material) for UO bending using a method similar to that shown in FIG. 12, it is necessary to compare the outline (position of the end) of the tubular part 206 obtained by UO bending in simulation with the outline (position of the end) of the tubular part on the design drawing. However, since the ends of the tubular part 204 are butted together, it is difficult to calculate the excess or deficiency of the material dimensions at the end positions. For example, even if a molding defect occurs in the tubular part 204 formed by simulation as shown in the upper diagram of FIG. 14 (A) (B), the position (horizontal position) of the butt joint 205 of this tubular part 204 and the butt joint 205' of the tubular part 204' on the design drawing shown in the lower diagram of the same work does not change, so it is not possible to calculate the excess or deficiency of the material dimensions from the position of the butt joint.

Therefore, the present invention aims to provide a method for optimizing the material shape of UO bending through simulation.

To solve the above problem, the present invention provides a material dimension determination method for UO bending, which includes a first step of forming a tubular part by performing UO bending on a flat plate material through simulation, a second step of comparing the circumferential length at multiple longitudinal cross sections of the tubular part with a target value, and a third step of correcting the dimensions of the flat plate material based on the comparison result between the circumferential length and the target value.

In this way, in the present invention, the circumferential length in the cross section of the tubular part is compared with its target value, rather than the position of the end (butt) of the tubular part. For example, when a molding defect such as that shown in the upper diagram of FIG. 14(A) occurs, the circumferential length will be longer than the target value (the circumferential length in the lower diagram), and when a molding defect such as that shown in the upper diagram of FIG. 14(B) occurs, the circumferential length will be shorter than the target value (the circumferential length in the lower diagram), so these molding defects can be detected. Then, by correcting the dimensions of the flat plate material based on the result of comparing this circumferential length with its target value, the shape of the flat plate material can be optimized.

Even when the ends of the tubular part material are butted together (i.e., when the circumferential length matches the target value), if the circumferential compressive stress applied to the material during the O-bending process (see Figure 13) is insufficient, the material may not be pressed against the die with sufficient force, resulting in molding defects. Such molding defects cannot be detected by simply comparing the circumferential length of the tubular part with the target value.

Therefore, it is preferable that in the second step, the circumferential compressive strain at multiple longitudinal cross sections of the tubular part is compared with its target value, and in the third step, the dimensions of the flat plate material are corrected based on the comparison result of the circumferential compressive strain with its target value. In this way, by comparing not only the circumferential length of the tubular part but also the circumferential compressive strain with its target value, it is possible to detect whether the compressive stress applied to the material is excessive or insufficient. By correcting the dimensions of the flat plate material based on the comparison result of this circumferential compressive strain with its target value, the dimensions of the flat plate material can be set to more appropriate values.

As described above, according to the present invention, it is possible to optimize the material shape for UO bending through simulation.

FIG. 2 is a flow diagram of a method for determining blank dimensions for UO bending according to one embodiment of the present invention. 1A to 1D are cross-sectional views showing each step of UO bending forming. 13A and 13B are cross-sectional views of a U-bending process. 11A to 11C are cross-sectional views showing a first O-bending process. 11A to 11C are cross-sectional views of the second O-bending process. FIG. FIG. 2 is a plan view of the tubular part. FIG. 2 is a cross-sectional view of a tubular part. FIG. 2 is a plan view of a flat plate material with a tubular part unfolded. FIG. 11 is a flow chart of a method for determining blank dimensions for UO bending according to another embodiment. FIG. 11 is a flow chart of a method for determining material dimensions for UO bending according to yet another embodiment. 1A shows a comparative example of a method for determining the material dimensions of a press-molded product, in which (A) is a cross-sectional view of a flat plate material, (B) is a cross-sectional view of a press-molded product obtained by simulation, and (C) is a cross-sectional view of a press-molded product on a design drawing. 1A to 1D are cross-sectional views of the O-bending process in conventional UO bending. The upper figures in (A) and (B) are cross-sectional views of a tubular part in which a molding defect has occurred, and the lower figures are cross-sectional views of the tubular part on the design drawings.

The following describes an embodiment of the present invention with reference to the drawings.

The method for determining material dimensions for UO bending according to this embodiment is carried out through steps S1 to S4 shown in FIG. 1. Each of steps S1 to S4 is carried out using a computer equipped with an input unit such as a keyboard, a calculation unit that performs calculations based on information entered through the input unit, and a display unit such as a monitor that displays the results of the calculation unit. Each of steps S1 to S4 is explained in detail below.

(1) First step S1 (UO bending)
In the first step S1, a flat plate material is subjected to UO bending by the above-mentioned computer simulation (for example, a simulation using the finite element method). In this embodiment, first, a flat plate material 2 shown in Fig. 2(A) is subjected to a U-bending process, a first O-bending process, and a second O-bending process to form a tubular part 1 shown in Fig. 2(D). Each process will be described below.

In the U-bending process, the flat plate material 2 is subjected to U-bending processing to form the U-bent product 3 shown in FIG. 2(B). Specifically, as shown in FIG. 3, the flat plate material 2 is pressed with U-bending dies 21, 22 to form the U-bent product 3. The U-bent product 3 has a U-shaped cross section with a bottom 11 and a pair of vertical wall portions 12 rising from both ends of the bottom 11. The flat plate material 2 and the U-bent product 3 formed from it are modeled as solid elements, and the U-bending dies 21, 22 are modeled as rigid bodies. The flat plate material 2 and the U-bent product 3 may also be modeled as shell elements.

In the first O-bending process, the U-bend product 3 is subjected to a first O-bending process to form the first O-bend product 4 shown in FIG. 2(C). Specifically, as shown in FIG. 4, the U-bend product 3 is pressed with first O-bending dies 23, 24 to form a shoulder bend 13 on the vertical wall portion 12 of the U-bend product 3. The U-bend product 3 and the first O-bend product 4 formed from it are modeled as solid elements, and the first O-bending dies 23, 24 are modeled as rigid bodies. The U-bend product 3 and the first O-bend product 4 may also be modeled as shell elements.

In the second O-bending process, the first O-bending product 4 is subjected to a second O-bending process to form the tubular part 1 shown in FIG. 2(D). Specifically, as shown in FIG. 5(A), the first O-bending product 4 is pressed by the second O-bending dies 25 and 26, which are made of a rigid body model, to butt the ends of the material together (see FIG. 5(B)). After that, by further pressing, the vertical wall portion 12 (particularly the area above the die bending portion 13) of the second O-bending product 4 is pushed outward and pressed against the molding surface of the upper die 25. As a result, the tubular part 1 is formed according to the molding surfaces of the dies 25 and 26 (see FIG. 5(C)). The first O-bending product 4 and the tubular part 1 to be formed from it are modeled as solid elements, and the second O-bending dies 25 and 26 are modeled as rigid bodies. The first bent product 4 and the tubular part 1 may also be modeled as shell elements.

The tubular part 1 of this embodiment is used, for example, as the left and right trailing arms of an automobile rear suspension, and has a curved hollow tube shape as shown in FIG. 6. The tubular part 1 in the illustrated example is curved in a plan view as shown in FIG. 7. The tubular part 1 may be curved in other directions as well, for example, one end of the tubular part 1 may be curved upward or downward in the figure. The tubular part 1 has a non-circular cross section. The tubular part 1 has a cross-sectional shape that differs in the longitudinal direction. A butt joint 14 between the ends of the material is provided along the longitudinal direction on the upper surface of the tubular part 1.

Note that UO bending is not limited to the above, and for example, the first O-bending process may be omitted and the U-bending product may be subjected to the O-bending process to form a tubular part. Also, the shape of the tubular part is not limited to the above, and may be, for example, a straight line in the longitudinal direction, a circular cross section, or a cross-sectional shape that does not change in the longitudinal direction.

(2) Second step S2 (checking circumferential length and compressive strain)
In the second step S2, the circumferential length and circumferential compressive strain of the tubular part 1 are checked (see FIG. 1). Specifically, first, as shown in FIG. 7, cross sections P ₁ to P _n are set at multiple locations in the longitudinal direction of the tubular part 1. Each of the cross sections P ₁ to P _n is set on a plane that is approximately perpendicular to the longitudinal direction, for example, on a plane that is perpendicular to the butted portion 14. The pitch of the cross sections P ₁ to P _n is set according to the size of the mesh in the finite element method, and is set to, for example, about 1 to 2 mm (the pitch is shown larger in FIG. 7 for the sake of simplicity).

Then, the circumferential lengths L ₁ to L _n at the plate thickness center of each cross section P ₁ to P _n of the tubular part 1 are calculated (see FIG. 8). Then, the circumferential lengths L ₁ to L _n at the cross sections P ₁ to P _n of the tubular part 1 are compared with the respective target values L0 ₁ to L0 _n . The target values L0 ₁ to L0 _n of the circumferential lengths are the circumferential lengths at the plate thickness center of each cross section P ₁ to P _n of the tubular part on the design drawing. Then, the differences ΔL ₁ to ΔL n between the circumferential lengths L ₁ to L _n of the tubular part 1 by simulation and the respective target values L0 ₁ to L0 _n are calculated. Then, in cross sections where the differences ΔL ₁ to ΔL _n are within a predetermined range, _it is determined that the ends of the materials butt against each other as shown in the design drawing (i.e., the butted portion 14 is disposed at the desired position). On the other hand, in the cross section where the above differences ΔL ₁ to ΔL _n are outside the predetermined range, the butted state of the ends of the blanks is judged to be defective, and the process proceeds to the third step S3.

In addition, the circumferential compressive strain in each cross section P ₁ to P _n of the tubular part 1 is calculated. Specifically, the distribution of the circumferential compressive strains ε ₁ to ε _n in each cross section P ₁ to P _n (the ratio of the circumferential dimension of each element of the flat plate material 2 to the circumferential dimension of each element of the tubular part 1) is calculated. Meanwhile, a target value of the circumferential compressive strain in each cross section P ₁ to P _n of the tubular part 1 is set. This target value can be calculated by simulating the compressive strain distribution in an ideal forming state, or set based on data of actual press forming in the past. Then, the circumferential compressive strains ε ₁ to ε _n in each cross section P ₁ to P _n are compared with the target value. In this embodiment, the differences Δε ₁ to Δε _n between the distribution of the circumferential compressive strains ε ₁ to ε _n in each cross section P ₁ to P _n obtained by simulation and the respective target values ε0 ₁ to ε0 _n are calculated. In the cross section where the differences Δε ₁ to Δε _n are within a predetermined range, it is determined that the material is subjected to an appropriate compressive stress, whereas in the cross section where the differences Δε ₁ to Δε _n are outside the predetermined range, it is determined that the material is subjected to an excessive or insufficient compressive stress, and the process proceeds to the third step S3.

(3) Third step S3 (material size correction)
In the third step S3, first, an inverse operation of UO bending is performed on the tubular part 1 to obtain a flat plate material 2' by developing the tubular part 1 into a flat plate (see FIG. 9). Section lines P ₁ '-P _n ' corresponding to each section P ₁ -P _n of the tubular part 1 are provided on this flat plate material 2'. Ends 2a', 2b' of the flat plate material 2' constituting the butted portion are set at the ends of each section line P ₁ '-P _n '. Then, in the second step S2, the length of the section lines P _{1 '} -P _{n '} of the flat plate material 2' is corrected and the positions of the ends 2a, 2b of the flat plate material 2' are adjusted based on the result of comparing the circumferential length of the material with its target value (ΔL ₁ -ΔL _n ) or the result of comparing the circumferential compressive strain with its target value (Δε ₁ -Δε _n ), or both. At this time, the amount of correction of the lengths of the cross-sectional lines P ₁ ' to P _n ' and which end of the cross-sectional lines P ₁ ' to P _n ' to move to correct the lengths are set based on past data and the like.

Thereafter, using the flat plate material 2' whose dimensions have been corrected in the third step S3, UO bending (first step S1) and checking the circumferential length and strain (second step S2) are performed again. Then, the above steps S1 to S3 are repeated until the differences ΔL ₁ to ΔL _n between the circumferential length at each cross section P ₁ to P _n of the tubular part 1 and its target value, and the differences Δε ₁ to Δε _n between the circumferential compressive strain at each cross section P ₁ to P _n of the tubular part 1 and its target value, are all within predetermined ranges. When ΔL ₁ to ΔL _n and Δε ₁ to Δε _n are all within the predetermined ranges, the process proceeds to the fourth step S4.

(4) Fourth step S4 (determining material dimensions)
In a fourth step S4, the tubular part 1 is developed into a flat plate by performing an inverse operation of the UO bending on the tubular part 1. This makes it possible to obtain a flat plate material whose dimensions (shape) are optimized so as to obtain the desired butt joint state.

The present invention is not limited to the above embodiment. Other embodiments of the present invention will be described below, but duplicate explanations of points similar to the above embodiment will be omitted.

In the embodiment shown in FIG. 10, the second step S2 is divided into a step S2a for checking the circumferential length of the tubular part 1 and a step S2b for checking the circumferential compressive strain of the tubular part 1. Specifically, after the first step S1, the circumferential length of the tubular part 1 is compared with its target value (step S2a), and if the difference between them is outside a predetermined range, the dimensions of the flat plate material 2' are corrected (third step S3), and UO bending is performed again (first step S1). These steps are repeated, and when the difference between the circumferential length and the target value is within a predetermined range, the circumferential compressive strain of the tubular part 1 is compared with the target value (step S2b), and if the difference between them is outside the predetermined range, the dimensions of the flat plate material 2' are corrected (third step S3), and UO bending is performed again (first step S1). These steps are repeated, and when the difference between the circumferential compressive strain and the target value is within a predetermined range, proceed to the fourth step S4.

In the embodiment shown in FIG. 11, the check of the circumferential compressive strain of the tubular part 1 is omitted. Specifically, only the circumferential length of the tubular part 1 is compared with its target value (second step S2), and if the difference between them is outside a predetermined range, the dimensions of the flat plate material 2' are corrected (third step S3), and UO bending is performed again (first step S1). These steps are repeated, and when the difference between the circumferential compressive strain and the target value falls within the predetermined range, the process proceeds to the fourth step S4. In this way, by omitting the step of checking the compressive strain, the calculation load is reduced compared to the above embodiment, and the calculation time is shortened.

Reference Signs List 1 Tubular part 2 Flat plate material 3 U-bent product 4 First O-bent product 14 Butt joint P ₁ -P _n cross section P ₁ '-P _n ' Cross section lines L ₁ to L _n Circumferential length ε ₁ -ε _n Compressive strain in circumferential direction

Claims (2)

A first step of forming a tubular part by performing UO bending on a flat plate material through simulation;
a second step of comparing a circumferential length of an entire circumference at a plurality of cross sections in a longitudinal direction of the tubular part with a target value;
and a third step of correcting the dimensions of the flat plate material based on a comparison result between the circumferential length and its target value. In the second step, a circumferential compressive strain at a plurality of cross sections in a longitudinal direction of the tubular part is compared with a target value;
2. The method for determining material dimensions for UO bending according to claim 1, wherein in the third step, the dimensions of the flat plate material are corrected based on a comparison result between the circumferential compressive strain and its target value.

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