JP2008264829A - Testing method for evaluating formability of extension flange of metallic plate in press forming of sheet metal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a testing method for evaluating the formability of an extension flange, which testing method can be directly utilized for achieving design guidelines or design limits for the shape of the extension flange of an actual automobile component. <P>SOLUTION: In the testing method for evaluating the formability of the extension flange of the metallic plate, a metallic blank having a corner cut to be a V shape is formed by a press machine using a punch, dies, and a pad. In this case, the press forming is repeatedly carried out by changing at least one or more of blank shape variables such as a radius R of curvature, an open angle θ, the height H of the flange at the corner of the blank, and the width W of the blank. Then, the evaluation map for the blank shape variables and the formability of the extension flange is formed to achieve a forming limit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention mainly relates to a technique for evaluating a design shape that avoids stretch flange cracking in designing and manufacturing automotive parts by press forming a metal plate.

  Stretch flange cracking is known as a molding defect when manufacturing automobile parts by press forming of a thin metal plate. Stretch flange cracking is a breaking phenomenon in which the edge of a thin plate is stretched to cause cracking. The forming limit diagram (FLD) obtained by ball head punch extension molding and cylindrical punch extension molding, which has been used for conventional crack evaluation, handles the fracture phenomenon inside the plate and is therefore suitable for evaluation of stretch flange cracks. Absent.

  As a method for evaluating stretch flange formability, a hole expansion test is generally used. However, in the hole expansion test, a stretch flange deformation in which a circular flange edge is extended to a larger circle occurs. Since the contour curve of the hole edge undergoes an isotropic uniform deformation from a small circle to a large circle in the circumferential direction, an axisymmetric strain distribution is generated as shown in FIG. However, in many cases, the stretch flange portion of an actual automobile part has a non-axisymmetric shape different from that of the round hole expansion molding. For example, as shown in FIG. 1B, when the elongated flange portion has a part shape composed of a straight line and a curved portion that continues to the straight flange portion, the elongation deformation of the flange edge portion generates a non-uniform strain distribution in which the strain is concentrated at a specific location. Since such stretch flange deformation is different from the uniform deformation state of the hole expansion test, the conventional hole expansion test cannot reflect the influence of the non-axisymmetric deformation in the actual part, that is, the influence of the shape factor.

  As a stretch flangeability evaluation test method assuming an actual part shape, there is a molding test of a model shape simulating an actual part described in Non-Patent Document 1. In this test, a blank having an edge portion composed of a straight portion and a corner R portion is press-molded, thereby making it possible to perform a molding test having a shape close to an actual component extending flange portion. However, in actual part design and process design, it is necessary to select the optimum shape that does not cause stretch flange cracking from multiple types of shapes, rather than just the presence or absence of cracks of a single shape. An evaluation test method and an evaluation result capable of investigating the influence by changing the form factor are required.

Furthermore, it is also known that the stretch flange formability changes depending on the blank cutting method even in the molding of the same part shape. For example, when a blank is produced by punching, it is known that the stretch flangeability changes depending on the punching clearance. When a blank is produced by laser cutting, the stretch flangeability is generally improved as compared with a blank obtained by punching. Due to this influence, cracks are not observed in the blanks cut by laser at the trial production stage, but there are known cases where stretch flange cracks occur and become a problem when the blank is formed at the mass production stage. For this reason, it is considered that not only the shape factor but also the blank processing method for mass-produced parts, that is, the influence of punching, needs to be reflected in the evaluation test.
The 57th Joint Conference on Plasticity Processing Proceedings, page 137

  It is an object of the present invention to provide an evaluation test method for obtaining a stretch flangeability evaluation result that can be directly used for formulating a stretch flange shape design guideline or design limit of an actual automotive part.

The gist of the present invention is as follows.
Invention 1 is a test method for evaluating the stretch flange formability of a metal plate by press-molding a metal blank having a corner cut into a V shape by using a punch, a die and a pad, the corner of the blank being Of at least one or more of the blank shape variables of curvature radius R [mm], opening angle θ [degree], flange height H [mm] and blank width W [mm], The blank shape variable and stretch flangeability evaluation map are created, and a forming limit is obtained, and the stretch flangeability evaluation test method for a metal plate in thin plate press forming is provided.
However, the stretch flangeability is when a scribed circle with a diameter of a1 [mm] or a grid with a spacing of b1 [mm] is drawn in advance in a blank, the diameter after the test is a2 [mm], and the grid spacing is b2 [mm]. Evaluation value of stretch flangeability = (a2-a1) / a1 × 100 [%] or (b2-b1) / b1 × 100 [%].

Invention 2 is a test method for evaluating the stretch flangeability of a metal plate by press-molding a metal blank having a corner cut into a V shape using a punch, a die and a pad, the punch and the The radius of curvature Rp and Rd [mm] and the opening angles θp and θd [degrees] of the corners forming the V-shape of each die, and the die shape variables of the punch and die height Hp and Hd [mm] Stretch flangeability of a metal plate in thin plate press forming characterized in that at least one of them is changed, repeatedly press-molded, the mold shape variable and stretch flangeability evaluation map are created, and a forming limit is obtained. This is an evaluation test method.
However, the stretch flangeability is when a scribed circle with a diameter of a1 [mm] or a grid with a spacing of b1 [mm] is drawn in advance in a blank, the diameter after the test is a2 [mm], and the grid spacing is b2 [mm]. Evaluation value of stretch flangeability = (a2-a1) / a1 × 100 [%] or (b2-b1) / b1 × 100 [%].

  Invention 3 is a blank shape variable of a corner radius R [mm], an opening angle θ [degree], a flange height H [mm] and a blank width W [mm] of a blank obtained by cutting a metal plate into a V shape. 3. The invention according to claim 2, wherein at least one or more of them are changed, repeatedly press-molded, the blank shape variable and the mold shape variable and an evaluation map of stretch flangeability are created, and a molding limit is obtained. It is a stretch flangeability evaluation test method of a metal plate in thin plate press forming.

  Invention 4 performs a repeated test by changing two or more of either or both of the blank shape variable and the mold shape variable, and the first variable and the two types of any one of the two or more types. The evaluation map of the presence or absence of stretch flangeability or crack occurrence is created with the other second variable of the above, and the forming limit is obtained. It is a stretch flangeability evaluation test method of a metal plate in thin plate press forming.

  Invention 5 makes a blank by punching a V-shaped corner part, The stretch flangeability evaluation test method of the metal plate in the thin-plate press forming of any one of the said invention 1-4 characterized by the above-mentioned It is.

  The invention 6 is characterized in that a blank is created by changing either or both of the blanking conditions of the punching clearance and the pad pressure when the corner portion is punched, and the forming limit is determined including the blanking conditions. It is the stretch flangeability evaluation test method of the metal plate in the thin plate press molding of the invention 5.

  According to the present invention, the influence of the shape factor on stretch flangeability in press forming of a metal plate can be investigated and an evaluation map of stretch flangeability effective for selecting an optimum shape can be provided, and an actual blank punching method can be provided. Effects can also be reflected in test results. This facilitates the adoption of an optimal stretch flange shape that does not cause cracks at the design stage of actual parts, and contributes to shortening the design and prototyping process and further reducing the cost of new product development.

The inventors changed the shape of the stretch flange portion by changing the corner R, the straight portion opening angle θ, the stretch flange height H, and the blank width W [mm]. We have invented a method to obtain an evaluation result that quantitatively incorporates the influence. And the method of obtaining the evaluation result in consideration of mass production processing conditions by making those blank shapes by changing the punching processing method was also invented. The present invention requires the following.

  The evaluation test method in the present invention 1 is a blank having a V-shaped stretch flange portion as shown in FIG. 2 in order to realize a forming test of the stretch flange portion causing non-axisymmetric deformation as shown in FIG. More model molded products are formed by press working. The shape of the stretch flange portion of the blank is defined by the shape variables of corner radius of curvature R [mm], opening angle θ [degree], flange height H [mm], and blank width W [mm]. A plurality of blanks having at least one of these blank shape variables are prepared, and a scribed circle or a grid is transferred in advance. After the blank is molded by the molding die, the in-plane principal strain is obtained from the diameter of the scribed circle at the cracked portion or the change in the side length of the grid, and the hole edge limit strain is evaluated as the stretch flangeability evaluation value. The initial diameter of the scribed circle to be transferred or the initial side length of the grid is preferably not less than the plate thickness and not more than 10 mm.

  In evaluating the stretch flangeability, a scribed circle having a diameter a1 [mm] or a grid having a spacing b1 [mm] is drawn in advance in a blank, the diameter after the test is a2 [mm], and the grid spacing is b2 [mm]. ], The stretch flangeability evaluation value = (a2-a1) / a1 × 100 [%] or (b2-b1) / b1 × 100 [%].

  The corner radius of curvature Rp and opening angle θp of the punch used for forming, or the corner radius of curvature Rd and opening angle θd of the die are the same as those in the blank shape, and the test is performed. The flange height H and blank width W are set in consideration of the actual part shape to be simulated. In addition, since the occurrence of cracks may vary, it is desirable to repeat the molding test for the same blank shape at least three times, and to determine that the molding has failed when one or more cracks are observed.

  As a test result, by plotting the success or failure of molding against the selected blank shape variable, a map showing the success or failure of molding (evaluation map for occurrence of cracking) is obtained. Moreover, the stretch flangeability evaluation value = (a2-a1) / a1 × 100 [%] or (b2-b1) / b1 × 100 [%] is plotted against the blank shape variable to evaluate the stretch flangeability. A map is obtained. Hereinafter, in the inventions 2 to 6, the stretch flangeability evaluation value is obtained from a scribed circle or grid that has been transferred in advance, and the criteria for determining the success or failure of molding are the same as in the invention 1.

  The evaluation test method according to the second aspect of the present invention is that the radius of curvature Rp, Rd [mm] and the opening angle θp, θd [degree] of the corners of the punch and the die, and the height of the punch and the die are determined for a specific blank shape. A molding test is carried out by changing at least one of the mold shape variables of height Hp and Hd [mm]. From the result, a crack evaluation map showing the influence of the punch shape and the die shape is created.

  The evaluation test method according to the present invention 3 employs the blank shape variable as a variable in the above-mentioned invention 2, and obtains the stretch flange crack evaluation map when each of the punch shape, the die shape, and the blank shape affects each other. This is a test method. That is, a plurality of types of blank shapes are prepared by changing at least one of the punch shape, the die shape, and the blank shape, and a molding test is performed.

  The evaluation test method according to the fourth aspect of the present invention is the evaluation test method according to any one of the first to third aspects, wherein a test is repeatedly performed by changing two or more of either or both of the blank shape variable and the mold shape variable. This is a test method for obtaining an evaluation map of stretch flangeability or crack occurrence with respect to any one first variable of two or more species and one other second variable of the two or more species. In this case, in the stretch flangeability evaluation map or the crack occurrence evaluation map, the result of molding success or failure is assigned to a plurality of shape variables.

  In the evaluation test method according to the fifth aspect of the present invention, in any one of the first to fourth aspects of the present invention, in order to investigate the influence of the punching process frequently used in the mass production process on the stretch flange formability, the specified punch and die are used. The V-shaped corner of the blank to be molded is created by punching. In this case, the V-shaped corner portion that undergoes stretch flange molding needs to be created by punching, and other straight side portions that do not cause stretch flange deformation may be created without necessarily being punched. Good. The punching clearance is preferably fixed at a value in the range of 5 to 25% that is frequently used in mass production.

  In the evaluation test method according to the sixth aspect of the present invention, a blank is created by a punching process frequently used for mass production processing, and a punching clearance and a pad for punching the corner portion are punched for the same blank shape. A blank is created by changing either or both of the blank blanking conditions for pressure, a blank created under a plurality of blank blanking conditions is prepared, and a stretch flangeability evaluation map is created including the blank blanking conditions. It is desirable to carry out the punching clearance at the time of blank production by selecting 3 levels or more from the range of 5-25% frequently used in mass production.

  As Example 1 of the present invention, a mold for evaluation test of stretch flangeability as shown in FIG. 3 was prepared and tested. The mold is composed of three parts, a punch A, a die B, and a pad C, each of which can be replaced independently. D is blank. When the punch A moves downward, the blank D is press-formed, the V-shaped corner is flanged up, and is formed into a member having a flange height H [mm]. FIG. 4 is an explanatory diagram of mold shape variables (punch shape variables and die shape variables). Punches and dies having 6 levels shown in Table 1 were prepared. The punch and die corners were used in combination so that the curvature radii Rp and Rd were equal and the opening angles θp and θd of the punch and die corners were equal. The corner radius of curvature Rp and the opening angle θp of the punch are equal to the radius of curvature R [mm] and the opening angle θ [degree] of the corner of the blank, and the corner radius of curvature Rd and the opening angle θd of the die are also It was made equal to the curvature radius R [mm] and the opening angle θ [degree].

  A blank specimen was a cold-rolled steel sheet having a thickness of 1.6 mm and a tensile strength of 780 MPa. The blank width W was constant at 140 mm. A blank created by punching using a dedicated punching die was prepared for the V-shaped corner portion subjected to stretch flange deformation. Punching was performed under the conditions of 11% punching clearance and pad back pressure of 5 tons, based on a thin plate with 1.6mm thickness. Among blank shape variables, the corner portion shapes R and θ were prepared in six levels having the same dimensions as the punch shapes Rp and θp shown in Table 1. Blanks with different flange heights H of 10, 15, 20, 25, and 30 mm were prepared.

  By preparing the above mold and blank, there are three types of form factors: blank flange height H, punch corner radius of curvature Rp (= Rd = R), punch corner opening angle θp (= θd = θ) The molding test was carried out while changing. This time, the molding test under the same conditions was repeated three times, and only when no stretch flange cracking was observed in all three specimens, cracking was observed even in one of the three. About the test piece, it determined with shaping | molding failure.

  FIG. 5 shows an evaluation map for occurrence of cracks obtained as a result of the molding test. The case of successful molding is indicated by a circle, and the case of molding failure is indicated by a cross. From this evaluation map, if it is within the range of conditions for successful molding, it can be seen that the molding can be performed without causing stretch flange cracks, and can be used as a design guideline for actual parts.

  FIG. 6 shows an evaluation map of stretch flangeability, which is a graph with the blank shape variable as the vertical axis and the stretch flangeability evaluation value as the horizontal axis. It is possible to quantitatively evaluate that the greater the corner radius of curvature R (= Rp = Rd) and the larger the opening angle θ (= θp = θd), the smaller the generated strain and the lower the risk of stretch flange cracking. It became.

  As Example 2 of the present invention, the test described later was performed using the mold for evaluation test of the stretch flange used in Example 1 of the present invention. Of the six levels of punch and die shapes shown in Table 1, a die with Rp = Rd = 60 mm and θp = θd = 120 ° was used. The blank had a constant width W of 140 mm. The blank shape variables were constant at R = 60 mm and θ = 120 °. A blank created by punching using a special punching die was prepared for the V-shaped corners subjected to stretch flange deformation. At this time, the blank flange height H was adjusted so that three levels of 10, 15, and 25 mm could be prepared, and punching was performed. The die of the special punching die has a mechanism that can be slid and fixed at a plurality of specified positions, and punched with 3 levels of punching clearance of 5%, 11%, and 20% based on a thin plate material of 1.6mm thickness Processing was performed to prepare a blank. In addition, a blank was also prepared in which punching was carried out by changing the pad back pressure to three levels of 0 tons, 2.5 tons, and 5 tons in punching with an 11% punch clearance. The condition of 0 tons of pad back pressure was realized by removing the pad and punching.

  FIG. 7 shows an evaluation map for occurrence of cracks obtained as a result of the molding test. The case of successful molding is indicated by a circle, and the case of molding failure is indicated by a cross. From this evaluation map, it became clear that stretch flange cracks could be formed with respect to punching clearance and punching conditions for pad back pressure during punching, and that evaluation was used as an actual part design guideline considering the impact of punching during mass production. It is possible to utilize maps. FIG. 8 shows an evaluation map of stretch flangeability, which is a graph with the blank punching condition as the vertical axis and the stretch flangeability evaluation value as the horizontal axis. When the punching clearance is small or when the pad back pressure is not applied, it can be quantitatively grasped that the stretch flange crack occurs with a small strain.

The figure which shows the difference in the strain distribution in the board edge part of a hole expansion test piece (a) and an actual component expansion flange (b). Explanatory drawing of the blank shape used for the evaluation test of stretch flangeability, and a blank shape variable. Explanatory drawing of the metal mold | die structure used for the evaluation test of stretch flangeability. It is explanatory drawing of a punch shape variable and die shape variables, (a) Punch shape variable, (b) Die shape variable The figure of the evaluation map of the presence or absence of the crack generation obtained from the test result of Example 1. The figure which shows the influence of the shape variable with respect to the stretch flangeability evaluation value obtained from the test result of Example 1. FIG. The figure of the evaluation map of the presence or absence of the crack generation obtained from the test result of Example 2. The figure which shows the influence of blank punching conditions with respect to the stretch flangeability evaluation value obtained from the test result of Example 2. FIG.

Explanation of symbols

W: Width of practical evaluation test blank
R: radius of curvature of the corner of the blank for practical evaluation test θ: opening angle of the corner of the blank for practical evaluation test
Lp: Punch edge shape curve
Htotal: Total length of blank center
Hflat: The length of the central part of the blank flat part between the punch and pad
H: Flange height subjected to stretch flange deformation (H = Htotal−Hflat)
A: Punch
B: Dice
C: Pad
D: Blank
Rp: radius of curvature of the corner of the punch θp: opening angle of the corner of the punch
Hp: punch height
Rd: radius of curvature of the corner of the die θd: opening angle of the corner of the die
Hd: Die height

Claims (6)

A test method for evaluating the stretch flangeability of a metal plate by press-molding a metal blank having a corner cut into a V shape using a punch, a die and a pad, the radius of curvature of the corner of the blank At least one of the blank shape variables of R [mm], opening angle θ [degree], flange height H [mm], and blank width W [mm] is changed, repeatedly press-molded, and the blank shape A method for evaluating the stretch flangeability of a metal plate in thin plate press forming, wherein a variable and stretch flangeability evaluation map is created and a forming limit is obtained.
However, the stretch flangeability is when a scribed circle with a diameter of a1 [mm] or a grid with a spacing of b1 [mm] is drawn in advance in a blank, the diameter after the test is a2 [mm], and the grid spacing is b2 [mm]. Evaluation value of stretch flangeability = (a2-a1) / a1 × 100 [%] or (b2-b1) / b1 × 100 [%]. A test method for evaluating stretch flangeability of a metal plate by press-molding a metal blank having a corner cut into a V shape using a punch, a die and a pad, each of the punch and the die At least one of mold shape variables of curvature radius Rp, Rd [mm] and opening angles θp, θd [degrees] of corners forming a V shape, and heights Hp, Hd [mm] of the punch and the die. Stretch flangeability evaluation test method for metal plate in thin plate press forming characterized in that the mold shape variable and stretch flangeability evaluation map are created by changing the seeds or more, and the mold shape variable and stretch flangeability evaluation map are created. .
However, the stretch flangeability is when a scribed circle with a diameter of a1 [mm] or a grid with an interval of b1 [mm] is drawn in advance in a blank, the diameter after the test is a2 [mm], and the grid interval is b2 [mm]. Evaluation value of stretch flangeability = (a2-a1) / a1 × 100 [%] or (b2-b1) / b1 × 100 [%]. At least one of blank shape variables of a curvature radius R [mm], an opening angle θ [degree], a flange height H [mm], and a blank width W [mm] of a blank obtained by cutting a metal plate into a V shape. 3. The thin plate press forming according to claim 2, wherein the press forming is repeatedly performed by changing the seeds or more, the blank shape variable, the mold shape variable and the stretch flangeability evaluation map are created, and the forming limit is obtained. Test method for evaluation of stretch flangeability of metal plates in Two or more of the blank shape variable and the mold shape variable or both of them are changed to perform a repeated test, and the first variable of any one of the two or more and the two or more of the two or more The thin plate press molding according to any one of claims 1 to 3, wherein an evaluation map for the presence or absence of stretch flangeability or crack occurrence is created using another one of the second variables, and a molding limit is obtained. Test method for evaluation of stretch flangeability of metal plates in The blank flange is created by punching a V-shaped corner portion, and the stretch flangeability evaluation test method for a metal plate in thin plate press forming according to any one of claims 1 to 4. 6. The blank is created by changing either or both of the blanking conditions of the punching clearance and the pad pressure when the corner part is punched, and the forming limit is determined including the blanking conditions. Test method for evaluating the stretch flangeability of a metal plate in the thin plate press forming.