JP2016170165A - Evaluation device and evaluation method for bending resistance of metal plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate a critical bending radius of a steel plate by V-shape bending with drastic suppression of increase of the man-hour and cost for an evaluation test in comparison to conventional evaluation methods.SOLUTION: An evaluation device 10 includes a punch 11 and a die 12, and performs a V-shape bending work to a steel-plate 13 in one direction to evaluate a critical bending radius. A bending radius R1 at a tip 11a of the punch 11 and a bending radius R2 at a bottom 12a of the die 12 continuously and gradually change in a direction intersecting the one direction, respectively.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an evaluation apparatus and an evaluation method for bending resistance of a metal plate.

  The plating layer of the alloyed hot-dip galvanized steel sheet is composed of a Zn-Fe intermetallic compound, so it has the property of being hard and brittle, and the surface galvanized layer is peeled off in powder form by deformation during press molding. May occur.

  When the plating powder peeled off by powdering adheres to the molded product, various problems such as indentation marks, damage to the mold, and deterioration of the appearance during painting occur. In the case of bending deformation, powdering is said to be affected by the bending radius of the bent portion, the alloying degree of the alloyed hot-dip galvanized layer, the alloying treatment temperature, and the like. Therefore, for example, the limit bending radius that does not cause powdering is obtained in advance, and the powdering characteristics of the plated steel sheet (for example, the limit bending radius that does not cause powdering (limit bending punch R)) It is necessary to evaluate in advance for each degree of conversion and alloying treatment temperature.

  Patent Documents 1 to 3 disclose inventions relating to the evaluation of powdering characteristics of plated steel sheets. There are various methods for evaluating powdering characteristics, but most generally, evaluation is performed by V-shaped bending and bending back as described in Patent Documents 1 to 3.

  Moreover, it is necessary to evaluate the limit bend radius at which the surface layer does not peel, not only for the alloyed hot-dip galvanized steel sheet but also for a metal plate having a surface layer with poor toughness that may be peeled off by bending. Here, “having a surface layer with poor toughness” means that a layer with less toughness than the metal inside the metal plate is formed between the metal and the surface of the metal plate, for example, alloyed molten zinc In addition to the plated steel sheet, alloy electroplated steel sheet, Al—Zn hot dipped steel sheet, Zn—Al—Mg hot dipped steel sheet, chemical coated steel sheet such as chromium-free coated steel sheet, and the like can be mentioned.

  On the other hand, since the ductility of a steel sheet decreases as the strength of the steel sheet increases, cracks (hereinafter referred to as “bending cracks” in this specification) tend to occur in the press-formed steel sheet. When bending cracks occur, the yield of press-formed products decreases. For this reason, the limit bending radius which does not produce a bending crack is calculated | required in advance, and the bending cracking property (for example, the limit bending radius which does not produce a bending crack (limit bending punch R)) is evaluated beforehand for every tensile strength of a steel plate. There is a need.

  As a method for evaluating the bending cracking property of a steel sheet, a V-bending test method is generally known. In the V bending test method, a plurality of punches having a V-shaped cross section having a plurality of different bends R at the tip and a die facing the punch are prepared, and a steel sheet is sandwiched between the plurality of punches and dies, and press forming is performed many times. This is a method for obtaining a minimum bending radius at which a bending crack does not occur in the steel sheet.

  However, in order to perform the V-bending test method, it is necessary to prepare punches and dies having a large number of bends R at the tip and perform a large number of experiments, which increases the cost and man-hours required for the test.

  Patent Document 4 discloses a method of determining a bending limit value of a steel sheet as a function of a punch bending R and a V-shaped die span W in a V-bending test, and Patent Document 5 discloses a method after bending deformation of a metal plate. An evaluation method for cracking in bending that occurs inside the bending at the time of bending back deformation is disclosed.

JP 2014-201818 A JP 2014-238282 A JP-A-11-6827 JP 2011-173136 A JP2015-47605A

  FIG. 8 is an explanatory view schematically showing a method for evaluating the powdering characteristics of a plated steel sheet by conventional V-shaped bending bending back.

  As shown in FIG. 8, the evaluation method by V-shaped bending and bending back uses a punch 1 having a predetermined punch tip radius and a die 2 having a predetermined die bottom radius as a test piece (alloyed galvanized steel sheet). 3) V-shaped bending was performed on 3 and then bent back using the flat punch 4 and the flat die 5, and then the tape 6 was applied to and peeled from the bending inner surface of the test piece 3. To evaluate the presence or absence of powdering. This is performed on the test piece 3 using a number of other punches and dies having different punch tip radii and die bottom radii. In this way, the limit bending radius that does not cause powdering has been obtained.

  For this reason, even when the degree of alloying of the test piece 3 to be tested and the alloying treatment temperature are one condition, it is necessary to use a plurality of solid molds and perform a plurality of V-shaped bending and unbending operations. There is a need to do. For this reason, the increase in the man-hour and cost which an evaluation test requires cannot be avoided. The situation is the same when evaluating an allowable limit bending radius at which the surface layer does not peel against a metal plate having a surface layer that may be peeled off by other bending.

  In the inventions disclosed in Patent Documents 4 and 5, it is necessary to prepare a large number of molds and perform a large number of experiments, which increases the cost and man-hour required for the test.

  The present invention has been made in view of such problems that the conventional evaluation method for the powdering property of, for example, a plated metal plate by V-shaped bending bending back and the conventional evaluation method for the bending crack of a steel sheet by the V-shaped bending test method have. The surface layer that can be peeled off by bending, such as the powdering characteristics of galvannealed steel sheets, which can greatly suppress the increase in man-hours and costs required for evaluation tests as compared to conventional evaluation methods. It is to provide an evaluation device and an evaluation method for a metal plate having a limit bending radius of a metal plate or a metal plate that may cause a bending crack.

As a result of intensive studies to solve the above problems, the present inventors have
(A) Using a punch and die in which both the punch tip radius and the die bottom radius are continuously changed, V-shaped bending and bending back with a bending radius continuously changed on the metal plate is performed on the surface of the metal plate. If compressive strain is applied to cause peeling of the surface layer, the bending resistance of the metal plate can be properly evaluated by a single bending process from the occurrence of peeling of the surface layer accompanying the continuous change of the bending radius R, and (B ) Using a punch and die whose punch tip radius and die bottom radius both change continuously, V-shaped bending with a continuously changing bending radius was performed on the metal plate, and the ridgeline of the bent metal plate Knowing that if the strain is intermittently changed in the direction, the bending cracks of the metal plate accompanying the continuous change of the bending radius R can be properly evaluated by a single bending, and the present invention is completed through further studies. did. The present invention is listed below.

(1) An apparatus that includes a punch and a die and evaluates a limit bending radius of the metal plate by performing a V-shaped bending process in one direction on the metal plate,
An apparatus for evaluating a limit bending radius of a metal plate, wherein the bending radius at the tip of the punch and the bending radius at the bottom of the die both continuously and gradually change in a direction intersecting the one direction.

  (2) The evaluation apparatus for the limit bending radius of the metal plate according to item 1, wherein the metal plate is a metal plate having a surface layer with poor toughness, and the limit bending radius is a limit bending radius that does not cause surface layer peeling.

  (3) The evaluation apparatus for the limit bending radius of the metal plate according to item 2, wherein the bending radius at the tip of the punch has a location 10 times the thickness of the metal plate.

  (4) The apparatus for evaluating a limit bending radius of a metal plate according to item 2, wherein the bending radius at the tip of the punch has a portion within a range of 3 to 26 mm.

  (5) The apparatus for evaluating a limit bending radius of a metal plate according to item 2, wherein the bending radius at the tip of the punch includes a portion of less than 3 mm and a portion of more than 26 mm.

  (6) The apparatus for evaluating powdering characteristics of a metal plate according to any one of 2 to 5, wherein the metal plate is an alloyed hot-dip galvanized steel plate.

  (7) The apparatus for evaluating a limit bending radius of a metal plate according to item 1, wherein the metal plate is a metal plate that generates a bending crack, and the limit bending radius is a limit bending radius that does not generate a bending crack.

  (8) The tip of the punch has a portion where R / t is 3 or less when the bending radius of the tip is R (mm) and the thickness of the metal plate is t (mm). The evaluation apparatus of the limit bending radius of the metal plate of Claim 7.

  (9) A metal plate having a surface layer with poor toughness is subjected to a V-shaped bending process in which the bending radius continuously changes, and then bent back to give a compressive strain to the surface of the metal plate to cause surface layer peeling. A method for evaluating a limit bending radius of a metal plate, wherein a limit bending radius of the metal plate that does not cause surface layer peeling is determined from occurrence of surface layer peeling accompanying a continuous change in bending radius.

  (10) By performing V-shaped bending with a bending radius continuously changing on a metal plate that generates a bending crack, the strain is intermittently changed in the direction of the ridgeline of the bent metal plate to cause a bending crack. An evaluation method of the limit bending radius of the metal plate, in which the limit bending radius of the metal plate that does not cause bending cracking is obtained.

  (11) After performing a V-shaped bending process in which the bending radius continuously changes on a metal plate that generates bending-bending back cracks, and the strain is intermittently changed in the direction of the ridgeline of the bent metal sheet. A method for evaluating a limit bending radius of a metal plate, wherein a limit bending radius of the metal plate that does not cause a bending / bending return crack is determined by generating a bending / bending return crack by bending back.

  (12) The V-shaped bending process uses a punch and die in which the bending radius of the punch tip and the bending radius of the die bottom both change continuously and gradually in one direction intersecting the processing direction. The evaluation method of the limit bending radius of the metal plate in any one of 9-11 performed.

  According to the present invention, the number of man-hours and costs required for the evaluation test can be increased more than the conventional evaluation method for peeling the surface of a metal plate, such as the powdering property evaluation of an alloyed hot-dip galvanized steel sheet by V-shaped bending and bending back. Both the man-hour and cost increase required for the test for evaluating the bending crackability of the steel sheet by die bending can be greatly suppressed.

FIG. 1 is an exploded perspective view showing a configuration example of an apparatus for evaluating powdering characteristics of an galvannealed steel sheet according to the present invention. FIG. 2 is an explanatory view showing a state where a tape is stuck on the galvannealed steel sheet after bending back. FIG. 3 is an explanatory view schematically showing the state of the peeled tape. FIG. 4 is a graph showing the relationship between the critical bending radius measured by the present invention and the critical bending radius measured by the conventional method shown in FIG. 8 in the evaluation of the powdering characteristics. FIG. 5 is an explanatory view showing an example of the shape of a bent steel plate. 6 is a view taken in the direction of arrow A in FIG. FIG. 7 is a graph showing the relationship between the critical bending radius measured by the present invention and the critical bending radius measured by the conventional method shown in FIG. FIG. 8 is an explanatory view schematically showing a conventional method for evaluating the powdering characteristics and bending / bending return cracking characteristics of a plated steel sheet by V-shaped bending / bending. Note that when a crack is evaluated after V-bending without bending back, it becomes an evaluation method for bending crack characteristics.

The present invention will be described with reference to the accompanying drawings.
1. Evaluation of Powdering Characteristics In the following description, a case where the metal plate having a surface layer with poor toughness in the present invention is an alloyed hot-dip galvanized steel plate is taken as an example.

(1-1) Evaluation apparatus 10 according to the present invention
FIG. 1 is an exploded perspective view showing a configuration example of an apparatus 10 for evaluating powdering characteristics of an alloyed hot-dip galvanized steel sheet 13 according to the present invention.

  As shown in FIG. 1, the evaluation device 10 includes a punch 11 and a die 12. The evaluation device 10 performs V-shaped bending in one direction (bending direction) on the galvannealed steel sheet 13 with the punch 11 and the die 12.

  Both the bending radius R1 of the tip 11a of the punch 11 and the bending radius R2 of the bottom 12a of the die 12 continuously and gradually change in a direction intersecting one direction.

  In the evaluation of alloyed hot-dip galvanized steel sheets, the powdering characteristics are often evaluated with a single digit% strain. Therefore, it is necessary to provide a portion having a bending radius that is 10 times the thickness of the alloyed hot-dip galvanized steel sheet to be evaluated so as to give, for example, 5% strain to the bending radius R1 of the tip 11a of the punch 11.

  Specifically, since the plate thickness of the galvannealed steel sheet to be evaluated is often in the range of 0.3 to 2.6 mm, the bending radius R1 of the tip 11a of the punch 11 is within the range of 3 to 26 mm. If there is no place.

  If the bending radius R1 of the tip 11a of the punch 11 is less than 3 mm and more than 26 mm, almost all of the galvannealed steel sheets can be evaluated with one mold.

  By providing the punch 11 and the die 12, the evaluation apparatus 10 evaluates the limit bending radius of the alloyed hot-dip galvanized steel sheet 13 that does not cause powdering.

  The configurations of the punch 11 and the die 12 other than those described above may be the same as punches and dies commonly used as this type of punch and die, which are well known to those skilled in the art, and thus further description thereof is omitted.

  The evaluation device 10 is configured as described above. Next, the evaluation method according to the present invention will be described. In the following description, the case where the evaluation apparatus 10 shown in FIG. 1 is used is taken as an example, but the evaluation method according to the present invention is also applied to the case where the evaluation apparatus 10 is not used.

(1-2) Evaluation Method According to the Present Invention First, as shown in FIG. 1, using a punch 11 and a die 12, a V-shaped bending in which a bending radius continuously changes in an alloyed hot-dip galvanized steel sheet 13 Processing.

  Next, for example, using the flat punch 4 and the flat die 5 shown in FIG. 1, the alloyed hot-dip galvanized steel sheet 13 which has been V-shaped bent is bent back into a flat plate.

  Compressive strain is imparted to the surface of the galvannealed steel plate 13 by V-shaped bending, and tensile strain is imparted by bending back. Will occur.

  The tape is applied to and peeled from the bent inner surface of the test piece 3. The tape may be attached before bending the V-shaped die, after bending the V-shaped die, or after bending back to a flat plate. However, the tape must be peeled off after being bent back to a flat plate.

  FIG. 2 is an explanatory view showing a state in which the tape 6 is pasted on the galvannealed steel plate 13 after being bent back.

  Reference numeral 14 in FIG. 2 indicates a side where the bending radius R1 is 0 mm and the bending radius R2 is tmm, and reference numeral 15 indicates a side where the bending radius R1 is 20 mm and the bending radius R2 is 20 + tmm. Moreover, the area | region enclosed by the straight lines L1 and L2 shows the sticking range of a tape, and the straight line L3 shows the site | part which was the ridgeline of bending by V-shaped bending.

  FIG. 3 is an explanatory diagram schematically showing the state of the peeled tape 6.

  As shown in FIG. 3, the amount of adhesion of the plating powder 16, that is, the amount of powdering, gradually changes on the peeled tape as the bending radius of the V-shaped bending is continuously changed. For this reason, powdering in the galvannealed steel sheet 13 is measured by measuring the distance D from the side 14 where the bending radius R1 is 0 mm and the bending radius R2 is tmm to the position 17 where the plating powder is not adhered. The limit bend radius that does not cause the problem can be obtained by one V-shaped bending and bending back.

  The critical bending radius measured according to the present invention coincided with the critical bending radius measured by the conventional method shown in FIG.

  For this reason, according to this invention, the increase in the man-hour and cost which an evaluation test requires can be suppressed significantly rather than the conventional evaluation method of the powdering property of the galvannealed steel plate by V-shaped bending bending back.

  When performing an evaluation test on a plurality of types of alloyed hot-dip galvanized steel sheets having different plate thicknesses, the die 12 is arranged in one direction according to the thickness of the alloyed hot-dip galvanized steel sheet 13 used for the evaluation test. The V-shaped die can be bent into a shape along the punch 11 -alloyed hot-dip galvanized steel plate 13 -die 12. That is, the powdering properties of various alloyed hot-dip galvanized steel sheets of various plate thicknesses can be evaluated by one set of punch 11 and die 12, and from this viewpoint, the number of molds required for the evaluation test can be reduced. This can reduce the cost required for the evaluation test.

2. Evaluation of bending cracking property (2-1) Evaluation device 10 according to the present invention
In the following description, a case where the metal plate in the present invention is a steel plate 13 (for example, a high-tensile steel plate having a tensile strength of 300 MPa or more) 13 that may cause a bending crack is taken as an example.

  The case where the bending cracking property of the steel plate 13 is evaluated using the apparatus 10 shown in FIG.

  As shown in FIG. 1, the evaluation device 10 includes a punch 11 and a die 12. The evaluation apparatus 10 performs a V-shaped bending process in one direction (bending process direction) on the steel plate 13 by the punch 11 and the die 12.

  Both the bending radius R1 of the tip 11a of the punch 11 and the bending radius R2 of the bottom 12a of the die 12 continuously and gradually change in a direction intersecting one direction.

  The bending cracking property of the steel plate 13 is correlated with the ratio (R / t) when the bending radius of the steel plate 13 is R (mm) and the plate thickness of the steel plate 13 is t (mm). If the ratio (R / t) is 3 or less, the possibility of bending cracks is increased. Moreover, when the ductility of the steel plate 13 is high, it is 2 or less, and when it is even 1 or less, the possibility of cracking increases. Therefore, it is preferable that the tip 11a of the punch 11 has a portion having a ratio (R / t) of 3 or less.

  Specifically, since the plate thickness when the steel plate 13 to be evaluated is a thin plate is often in the range of 0.3 to 3.2 mm, the bending radius R1 of the tip 11a of the punch 11 is in the range of about 0 to 10 mm. If there is a place inside. That is, the bending radius R <b> 1 may be set so that a portion where the crack occurs and a portion where the crack does not occur are formed.

  When the evaluation object is a thin plate, if there is a location where the bending radius R1 of the tip 11a of the punch 11 is less than 0.3 mm and a location where it is greater than 3.2 mm, almost all the steel plates 13 can be bent and cracked with one mold. Can be evaluated.

  By providing the punch 11 and the die 12, the evaluation device 10 evaluates the limit bending radius of the steel plate 13 that does not cause bending cracking.

  The configurations of the punch 11 and the die 12 other than those described above may be the same as punches and dies commonly used as this type of punch and die, which are well known to those skilled in the art, and thus further description thereof is omitted.

  The evaluation device 10 is configured as described above. Next, the evaluation method according to the present invention will be described. In the following description, the case where the evaluation apparatus 10 shown in FIG. 1 is used is taken as an example, but the evaluation method according to the present invention is also applied to the case where the evaluation apparatus 10 is not used.

(2-2) Evaluation Method According to the Present Invention As shown in FIG. 1, using a punch 11 and a die 12, a V-shaped bending process in which the bending radius continuously changes is performed on the steel sheet 13.

  FIG. 5 is an explanatory view showing an example of the shape of the bent steel sheet 13, and FIG. 6 is a view taken in the direction of arrow A in FIG.

  As shown in FIGS. 5 and 6, the bent steel sheet 13 extends in a direction in which the ridge line 13 a extends to exist in a direction in which the bending radius R <b> 1 is the smallest (for example, R: 0 mm) to the largest part (for example, R: Bending cracks 20 occur toward 5.0 mm).

  For this reason, as shown in FIG. 6, the limit bending radius which does not produce a bending crack can be calculated | required by calculating | requiring the distance from the site | part with the minimum bending radius R1 to the edge part of the bending crack 20. FIG.

  The critical bending radius measured according to the present invention coincided with the critical bending radius measured by the conventional method shown in FIG.

  For this reason, according to this invention, the increase in the man-hour and cost which an evaluation test requires can be suppressed significantly rather than the conventional evaluation method of the bending cracking property of the steel plate by V-shaped bending.

  When performing an evaluation test on a plurality of types of steel plates having different plate thicknesses, V-shaped bending is performed by moving the die 12 in one direction in accordance with the plate thickness of the steel plate 13 provided for the evaluation test. Accordingly, the punch 11-alloyed hot-dip galvanized steel sheet 13-shaped along the die 12 can be bent in a V shape. That is, the powdering properties of various steel plates with various plate thicknesses can be evaluated by one set of punch 11 and die 12, and from this viewpoint, the number of molds required for the evaluation test is reduced and required for the evaluation test. Cost can be reduced.

  Using the apparatus 10 shown in FIG. 1 and the conventional test apparatus shown in FIG. 8, five types of galvannealed steel sheets A to E (tensile strength 340 MPa, plate thickness 0.7 mm) shown in Table 1 are shown in FIG. , 3, an evaluation test by V-shaped bending bending back was performed, and the critical bending radius was measured.

  FIG. 4 is a graph showing the relationship between the critical bending radius measured by the present invention and the critical bending radius measured by the conventional method shown in FIG.

  As shown in the graph of FIG. 4, the critical bend radius measured by the present invention completely matches the critical bend radius measured by the conventional method shown in FIG. 8, confirming the reliability of the present invention. It was.

  Using the apparatus 10 shown in FIG. 1 and the conventional test apparatus shown in FIG. 8 respectively, five types of high hearing steel plates A to E shown in Table 2 (tensile strength 1025 to 1189 MPa, plate thickness 1.0 to 2.0 mm) In addition, as shown in FIG. 1, an evaluation test by V-shaped bending was performed, and a limit bending radius at which no bending crack was generated was measured. In this evaluation test, evaluation was performed in the state of V bending without performing bending return after V bending.

  FIG. 7 is a graph showing the relationship between the critical bending radius measured according to the present invention and the critical bending radius measured after V bending in the conventional method shown in FIG.

  As shown in the graph of FIG. 7, the critical bending radius measured according to the present invention completely coincides with the critical bending radius measured by the conventional method shown in FIG. 8, confirming the reliability of the present invention. It was.

DESCRIPTION OF SYMBOLS 10 Evaluation apparatus 11 according to the present invention Punch 11a Tip 12 Die 12a Die 13 Alloyed hot-dip galvanized steel sheet

Claims (12)

An apparatus that includes a punch and a die and evaluates a limit bending radius of the metal plate by performing a V-shaped bending process in one direction on the metal plate,
An apparatus for evaluating a limit bending radius of a metal plate, wherein the bending radius at the tip of the punch and the bending radius at the bottom of the die both continuously and gradually change in a direction intersecting the one direction.   The apparatus for evaluating a limit bending radius of a metal plate according to claim 1, wherein the metal plate is a metal plate having a surface layer with poor toughness, and the limit bending radius is a limit bending radius that does not cause surface peeling.   The apparatus for evaluating a limit bending radius of a metal plate according to claim 2, wherein the bending radius at the tip of the punch has a portion that is ten times the thickness of the metal plate.   The apparatus for evaluating a limit bending radius of a metal plate according to claim 2, wherein the bending radius at the tip of the punch has a location within a range of 3 to 26 mm.   3. The apparatus for evaluating a limit bending radius of a metal plate according to claim 2, wherein the bending radius at the tip of the punch includes a portion of less than 3 mm and a portion of more than 26 mm.   The said metal plate is a galvannealed steel plate, The evaluation apparatus of the powdering characteristic of the metal plate in any one of Claims 2-5.   The apparatus for evaluating a limit bending radius of a metal plate according to claim 1, wherein the metal plate is a metal plate that generates a bending crack, and the limit bending radius is a limit bending radius that does not generate a bending crack.   The tip of the punch has a portion where R / t is 3 or less when a bending radius of the tip is R (mm) and a thickness of the metal plate is t (mm). The evaluation apparatus of the limit bending radius of the metal plate according to 7.   A metal plate having a surface layer with poor toughness is subjected to a V-shaped bending process in which the bending radius changes continuously, and then bent back to impart compressive strain to the surface of the metal plate to cause surface peeling, and the bending radius A method for evaluating a limit bending radius of a metal plate, wherein a limit bending radius of the metal plate that does not cause surface layer peeling is determined from the occurrence of surface layer peeling due to a continuous change in the metal plate.   By performing a V-shaped bending process in which the bending radius continuously changes on a metal plate that generates a bending crack, the strain is intermittently changed in the direction of the ridgeline of the bent metal sheet to generate a bending crack. The evaluation method of the limit bending radius of a metal plate which calculates | requires the limit bending radius which does not produce a bending crack of the said metal plate by this.   Bend-bend-back cracking is performed on a metal plate that generates a bending-bending crack, and the bending radius is continuously changed. After bending the plate in the direction of the ridgeline of the bent metal plate, the bending is returned. A method for evaluating a limit bending radius of a metal plate, wherein a limit bending radius of the metal plate that does not cause a bending / bending return crack is determined by generating a bending / bending return crack.   The V-shaped bending process is performed using a punch and a die in which the bending radius of the punch tip and the bending radius of the die bottom both continuously and gradually change in one direction intersecting the processing direction. Item 12. A method for evaluating a limit bending radius of a metal plate according to any one of Items 9 to 11.

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