JP2006061980A - Method for press-forming metallic sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for press-forming a metallic sheet by which formed parts having high dimensional accuracy is obtained by suppressing cracks, wrinkles and shock lines without increasing the number of forming steps in the press-forming of the metallic sheet. <P>SOLUTION: The method for press-forming the metallic sheet while imparting blank holding force is characterized in that the blank holding force at the starting of the forming is set to be ≥5% of the tensile strength (TS) of the metallic sheet in terms of tension, punch speed is set to be ≤500 mm/s, and the blank holding force is increased and the punch speed is lowered on the midway of a stroke. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a press forming method for a thin metal plate such as a steel plate, stainless steel, aluminum, titanium, etc., and more particularly to a forming method for adjusting a wrinkle holding force and a speed during press working.

  In press forming, various inventions have been disclosed regarding a forming method for changing the wrinkle holding force. For example, Patent Document 1 discloses that wrinkle generation is caused by increasing the wrinkle holding force during drawing from the initial stage to the middle stage. While suppressing growth, a method for preventing wrinkles from occurring due to generation of cracks and excessive flow of material is disclosed by reducing the pressure to an appropriate value in the later stage of molding.

  Further, Patent Document 2 discloses a method of using a spacer to avoid cracking without applying a wrinkle holding force until reaching a forming bottom dead center, and to provide a wrinkle holding force near the bottom dead center to ensure shape accuracy. Has been.

  Regarding the punch speed, there is a method of reducing the impact load by lowering extremely slowly near the bottom dead center at the time of pressing and pressing in Patent Document 3, and then rapidly descending from the vicinity of the bottom dead center to the bottom dead center. It is disclosed.

JP-A-9-38728 Japanese Patent Laid-Open No. 10-15932 JP-A-9-124363

  Even if an invention for suppressing the generation of cracks / wrinkles by changing or controlling the wrinkle holding force in Patent Documents 1 and 2, etc., the wrinkle holding force is reduced to an appropriate value in the later stage of molding, There is a limit to the suppression of cracks and wrinkles and improvement of shape accuracy only by the control of applying a wrinkle holding force near the bottom dead center. Further, even though a method for reducing the impact load with respect to the punch speed is disclosed, a method for suppressing cracks / wrinkles and improving shape accuracy is not shown.

  Further, when the punch starts to contact with the metal thin plate, a linear mark called a shock line is attached, which may cause deterioration of the quality of the molded product and further cause cracking, which may cause noise.

  An object of the present invention is to provide a press molding method that suppresses cracks, wrinkles, and shock lines and has high surface accuracy and dimensional accuracy, and further provides a press molding method that reduces noise during press molding. To do.

The present invention has been made to solve the above-described problems, and the gist thereof is as follows.
(1) A method of press-forming a thin metal sheet while applying a wrinkle holding force, wherein the wrinkle holding force at the start of forming is 5% or more of the tensile strength (TS) of the metal thin plate in terms of tension, and the punch speed is 500 mm / sec. A press forming method for a thin metal plate, characterized in that the pressing force is decreased while increasing the wrinkle holding force in the middle of the stroke.
(2) A method of press forming a thin metal sheet while applying a wrinkle holding force, wherein the wrinkle holding force at the start of forming is 5% or more of the tensile strength (TS) of the thin metal sheet in terms of tension, and the punch speed is 500 mm / sec. A press forming method for a thin metal sheet, characterized in that when the punch shoulder comes into contact with the thin metal sheet, the pressing force is increased and the punch speed is decreased.
(3) The press forming method for a thin metal plate according to (1) or (2), wherein when the punch starts to contact the thin metal plate, the punch speed is set to 20 mm / sec or less, and then the punch speed is increased.
(4) In (1), the wrinkle holding force after the increase is 50% or more of the tensile strength (TS) in terms of tension, and the punch speed after the reduction is 0.5-50 mm / sec. A method for press forming a thin metal sheet.
(5) In (2), the wrinkle holding force when the punch shoulder is in contact with the metal material is 30% or more of the tensile strength (TS) in terms of tension, and the punch speed is reduced to 0.5 to 50 mm / sec. Press forming method for thin metal sheet.
(6) The method according to any one of (1) to (3), the method according to any two or more methods, or the method according to any one of (3) to (5) A method for press forming a metal thin plate, comprising a combination of any two or more methods.

  In the present invention, the thin plate is not particularly limited as long as it can be press-molded. However, in order to obtain good workability, the thickness is preferably 5 mm or less, more preferably 3 mm or less. .

  According to the present invention, it is possible to obtain a press-molded product that suppresses cracks, wrinkles, and shock lines and has high surface accuracy and dimensional accuracy. Moreover, the noise at the time of press molding can also be reduced by this invention.

  Details will be described below with reference to the drawings.

  FIG. 1 shows an example of adjusting the wrinkle pressing force and speed in the press forming described in (1) above.

  In the prior art, if the wrinkle holding force is increased, wrinkles are suppressed. However, if the wrinkle holding force is increased from the initial stage of molding, that is, from a small punch stroke, cracking occurs. In order to avoid this, conventionally, after the punch stroke has increased to some extent, the wrinkle holding force is increased to generate tension on the workpiece (metal sheet) to suppress wrinkles and improve shape freezing. It has been broken. However, it is difficult to generate sufficient tension only by increasing the wrinkle holding force after the punch stroke is increased to some extent, and therefore it is necessary to further increase the tension by another method.

  On the other hand, the friction coefficient can be increased by decreasing the speed when the wrinkle holding force is increased in the middle of the stroke, so that the tension applied to the thin metal plate can be further increased. With this effect, the tension that is insufficient with only the wrinkle pressing force can be sufficiently increased, and the shape freezing property and the like can be ensured. The stroke for reducing the speed is not particularly limited, but it is particularly desirable that 80%, preferably 90%, of the entire stroke is completed. In addition, the wrinkle holding force / punch speed is changed in a rectangular wave shape in FIG. 1, but the same effect can be obtained even if the changing portion is changed in a slanting or curved manner in the drawing.

  The wrinkle holding force at the start of forming is defined as 5% or more of the tensile strength (TS) of the metal thin plate in terms of tension in order to suppress wrinkles generated in the flange portion and the like during the forming process. On the other hand, the upper limit of the wrinkle pressing force is not particularly limited, but is preferably 120% or less of the tensile strength (TS) in order to suppress breakage at the vertical wall portion.

  Also, the punch speed at the start of molding is defined as 500 mm / sec or less due to equipment limitations. On the other hand, the lower limit of the punch speed is preferably set to 0.1 mm / sec or more in order to prevent the productivity from being extremely lowered.

  FIG. 2 shows an example of adjusting the wrinkle pressing force and speed in the press forming described in (2) above.

  As explained in the invention according to (1) above, cracks and wrinkles are suppressed by increasing the wrinkle holding force and decreasing the punch speed in the middle of the stroke, especially at the later stage of molding, that is, when the punch stroke becomes large. As a result, it is possible to improve the shape freezing property and obtain a molded product with good dimensional accuracy. However, the shape of the bottom surface of the punch called surface accuracy is already formed when the punch stroke is large, and even if the wrinkle holding force is increased or the speed is decreased at this stage, the surface accuracy cannot be increased.

  On the other hand, in the invention according to (2), the punch stroke area where the shape of the bottom surface of the punch is transferred, that is, when the punch shoulder comes into contact with the metal thin plate, the wrinkle holding force is increased, and the punch speed is decreased. The accuracy can be improved. In order to improve the surface accuracy, in the case of forming with a shallow forming depth such as a panel, the stroke area for changing the wrinkle holding force and punch speed starts from about 20% of the entire stroke and ends at about 40%. desirable. In forming the bottom surface by deep drawing, it is desirable that the ratio be set to the above-described ratio with respect to the stroke in which the processing of the panel bottom surface is completed and the vertical wall is formed. Further, although the wrinkle holding force and the punch speed are changed in a rectangular wave shape in FIG. 2, the same effect can be obtained even if the changing portion is changed so as to be inclined or curved in the drawing.

  In the present invention, the “punch shoulder” refers to a ridge line portion that becomes the boundary between the bottom surface of the punch and the vertical wall.

  The reason for limiting the wrinkle holding force and punch speed at the start of molding is the same as in the invention according to (1).

  FIG. 3 shows an example of adjusting the wrinkle holding force and speed in the press forming described in (3) above.

  As explained in the invention according to (1) above, particularly at the latter stage of molding, that is, at the stage when the punch stroke becomes large, the wrinkle holding force is increased and the punch speed is lowered, and the invention according to (2) is explained. As described above, when the punch shoulder comes into contact with the metal thin plate, the wrinkle holding force is increased, and the punch speed is decreased, so that cracks and wrinkles can be suppressed, and a molded product with good dimensional accuracy and surface system can be obtained. However, when the punch starts to come into contact with the metal thin plate, a shock line is attached, which may cause deterioration of the quality of the molded product, and may be a starting point of cracking. Moreover, it causes a loud noise.

  On the other hand, in the invention according to (3), when the punch starts to contact the metal thin plate, the punch speed V3 is lowered to 20 mm / sec or less, and then the punch speed is increased to suppress the shock line and the noise. can do. In FIG. 3, the position where the punch starts to contact the thin metal plate corresponds to the intersection of the punch stroke indicated by the dotted line and the Y coordinate (punch speed V).

  The punch speed after the start of contact is preferably increased to 50 mm / sec or more in order to improve moldability and productivity. Further, the wrinkle holding force and punch speed after the punch speed increase is changed to a rectangular wave shape in FIG. 3, but it is the same even if the changing portion is changed to be diagonal or curved in the figure. An effect is obtained.

  FIG. 4 shows an example of adjusting the wrinkle pressing force and speed in the press forming described in (4) above.

  This shows how much the wrinkle holding force of the invention according to the above (1) is raised and how much the punch speed is lowered to obtain the best effect. A sufficient effect can be obtained if the appropriate wrinkle holding force F1 is a value converted into a tension by dividing by the cross-sectional area of the plate and is 50% or more of the tensile strength (TS) of the metal thin plate. The upper limit is not particularly defined, but is preferably 120% or less of the tensile strength (TS) in order to suppress breakage at the vertical wall portion.

  Further, an effect can be obtained if the punch speed V1 is 50 mm / sec or less, but molding is not possible if the speed is 0 mm / sec. Good results can be obtained by setting it to 0.5 mm / sec or more.

  FIG. 5 shows an example of adjusting the wrinkle holding force and speed in the press forming described in (5) above.

  This shows how much the crease pressing force is raised and how much the punch speed is lowered in the stroke of forming the bottom surface of the punch according to the invention of (2). A sufficient effect can be obtained if the appropriate wrinkle holding force F2 is a value converted into a tension by dividing by the cross-sectional area of the plate and is 30% or more of the tensile strength TS of the metal thin plate. The upper limit is not particularly defined, but is preferably 120% or less of the tensile strength (TS) in order to suppress breakage at the vertical wall portion.

  Examples of adjusting the wrinkle pressing force and speed in the press forming described in the above (6) are as shown in FIGS.

  When the wrinkle holding force is increased in the middle of the stroke, the speed is lowered (the inventions according to the above (1) and (4)), and the punch pressing speed is increased when the punch shoulder comes into contact with the metal thin plate. (Invention according to (2) and (5) above), and when the punch starts to contact the metal sheet, the punch speed V3 is reduced to 20 mm / sec or less (invention according to (3) above). If two or more are combined, it is possible to obtain the combined effects of securing the shape freezing property, improving the surface accuracy, suppressing the shock line and noise.

  Based on the above-mentioned invention, press molding was performed by the molding method shown in FIG. 4 as an example of the present invention.

  Table 1 shows the characteristics of the steel plates used. A 780 MPa class TRIP steel with a plate thickness of 1.6 mm was used.

  In the molding test, a hat-shaped cross section with a width of 120 mm and a height of 110 mm shown in FIG. 6 was drawn. The plate width was 100 mm. As Example 1 of the present invention, the wrinkle pressing force of 10% of the tensile strength in terms of tension is applied up to 10 mm before the stroke end in FIG. 4, and the wrinkle pressing force (F1 in FIG. 4) from 10 mm before the stroke end in terms of tension. Multiplied by 80% of the tensile strength. The punch speed was set to 100 mm / sec from the start of molding, and the punch speed was reduced to 5 mm / sec (V1 in FIG. 4) 10 mm before the end of the stroke.

  For comparison, as Comparative Example 1, only the crease pressing force was adjusted as described above, and the punch speed was fixed at 100 mm / sec.

  Table 2 shows a comparison of the shape accuracy between the inventive example and the comparative example. As an index of shape accuracy, the molding width W is measured as shown in FIG. 7 as an index that can comprehensively evaluate the wall warp and angle opening caused by the springback, and the deviation from the design width W0 is the width opening ratio (W−W0). ) / W0 as an indicator.

  Although the invention example 1 and the comparative example 1 were able to be molded without cracks and wrinkles, as shown in Table 2, with respect to the shape accuracy, a good shape accuracy was obtained in the invention example 1.

  Based on the above-described invention, press molding was performed by the molding method shown in FIG. 5 as an example of the present invention.

  Table 3 shows the characteristics of the steel sheet used. A mild steel plate having a thickness of 0.8 mm was used.

  In the molding test, the bottom surface of the punch shown in FIG. 8 had a radius of curvature of 2000 mm and a punch shoulder radius of 3 mm, and a 500 mm × 500 mm rectangular tube drawing was performed at a drawing depth of 40 mm. The molding conditions were the wrinkle pressing force and punch speed shown in FIG. Specifically, 30% of the tensile strength is applied to the punch stroke corresponding to punch bottom formation from 8mm to 20mm and converted to tension, and the wrinkle is suppressed from 6mm before the end of the stroke, which is the latter stage of molding, to the end of molding. The force was applied to 70% of the tensile strength in terms of tension, and the wrinkle pressing force was applied to 10% of the tensile strength in terms of tension in the other stroke sections. Regarding the punch speed, the punch stroke was set to 50 mm / sec from 8 mm to 20 mm, 5 mm / sec from 6 mm before the end of the stroke which is the latter stage of molding to the end of molding, and 100 mm / sec in the other stroke sections.

  Further, as Comparative Example 2, the wrinkle pressing force is applied to 70% of the tensile strength in terms of tension from the start of molding to 6 mm before the end of the stroke, which is the latter stage of molding, and the wrinkle pressing force is tensile strength in terms of tension in the other stroke sections. Of 10%. The punch speed was 100 mm / sec over the entire stroke.

Table 4 shows a comparison of shape accuracy between the inventive example and the comparative example. As an index of surface accuracy, the bottom surface of the molded product was measured with a three-dimensional shape measuring instrument, and the molding curvature (κ = 1 / R) was calculated along arc 1 and arc 2 in FIG. This molding curvature range Δκ and the ratio Δκ to the design curvature κ ₀ (= 1 / R ₀ = 1 / 2.0 [1 / m]) Δκ / κ ₀ were defined as surface accuracy indicators.

  Although the present invention example 2 and the comparative example 2 were able to be molded without cracks or wrinkles, as shown in Table 4, in the present invention example 2, good shape accuracy was obtained.

  Based on the above-mentioned invention, press molding was performed by the molding method shown in FIG. 3 as an example of the present invention.

  Table 5 shows the characteristics of the steel sheet used. A 590 MPa class steel plate having a thickness of 1.2 mm was used.

  The molding test was performed in a shape having a step on the bottom surface shown in FIG. 9 and having a curvature radius of 4000 mm as a whole including the flange surface in the longitudinal direction. The molding conditions were the wrinkle holding force and punch speed shown in FIG. Molding was performed under the conditions shown in FIG. From a stroke of 5 mm to 20 mm, 40% of the tensile strength was applied in terms of tension. In addition, from the 8 mm before the end of the stroke to the end of the molding, 75% of the tensile strength was applied to the wrinkle holding force in terms of tension. In the other stroke sections, 10% of the tensile strength was applied in terms of tension. The punch speed was 5 mm / sec from the start of contact with the material to a stroke of 2 mm, and increased linearly from a punch speed of 5 mm / sec to 100 mm / sec from a stroke of 2 mm to a stroke of 5 mm. Further, the punch speed was 10 mm / sec for strokes from 5 mm to 20 mm, and then the punch speed was 120 mm / sec. The punch speed was 10 mm / sec from 8 mm before the end of the stroke until the end of molding.

  Further, as Comparative Example 3, 70% of the tensile strength is applied in terms of tension from the start of molding to 8 mm before the end of the stroke, which is the latter stage of molding, and the wrinkle pressing force is tensile strength in terms of tension in other stroke sections. Of 10%. The punch speed was 100 mm / sec over the entire stroke.

  Table 6 shows a comparison of shape accuracy between the inventive example and the comparative example. As an index of shape accuracy, the molding width W is measured as shown in FIG. 10 as an index that can comprehensively evaluate the wall warp and angle opening caused by the springback, and the deviation from the design width W0 is the width opening ratio (W−W0). ) / W0 as an indicator.

  Although Example 3 and Comparative Example 3 were able to be molded without cracks and wrinkles, as shown in Table 6, with respect to shape accuracy, good shape accuracy was obtained in Example 3 of the present invention.

Table 7 shows a comparison of surface accuracy between the inventive example and the comparative example. As an index of surface accuracy, the bottom surface of the molded product was measured with a three-dimensional shape measuring instrument, and the molding curvature (κ = 1 / R) was calculated along the longitudinal direction of FIG. The molding curvature range Δκ and the ratio Δκ to the design curvature κ ₀ (= 1 / R ₀ = 1 / 4.0 [1 / m]) Δκ / κ ₀ were defined as surface accuracy indicators.

  Regarding the surface accuracy, as shown in Table 7, in Example 3 of the present invention, good shape accuracy was obtained.

  Further, in Example 3 and Comparative Example 3, 10 sheets were molded, and the presence or absence of shock lines was observed. As shown in Table 8, in Comparative Example 3, shock lines were observed on all 10 sheets. In Example 3, no shock line was observed.

  In addition, Table 9 shows a comparison result of the noise measurement. By adopting the speed / wrinkle pressing force pattern of the above-described Invention Example 3, 5 dB noise was reduced compared to Comparative Example 3.

The adjustment example of the wrinkle pressing force and punch speed | rate which concerns on this invention is shown. Another adjustment example of the wrinkle holding force and punch speed according to the present invention will be shown. Another adjustment example of the wrinkle holding force and punch speed according to the present invention will be shown. Another adjustment example of the wrinkle holding force and punch speed according to the present invention will be shown. Another adjustment example of the wrinkle holding force and punch speed according to the present invention will be shown. The hat type cross section in drawing is shown. FIG. 7 is a cross-sectional view defining the width opening ratio of FIG. 6. An outline view of a molded product in rectangular tube drawing is shown. The outline figure of the molded article which has a step in the bottom and has a flange in the longitudinal direction is shown. FIG. 10 is a cross-sectional view defining the width opening ratio of FIG. 9.

Claims (6)

  A method of press-forming a thin metal sheet while applying a wrinkle holding force, wherein the wrinkle holding force at the start of forming is 5% or more of the tensile strength (TS) of the thin metal sheet in terms of tension, and the punch speed is 500 mm / sec or less. A press forming method for a thin metal sheet, characterized by increasing a wrinkle holding force in the middle of a stroke and lowering a punch speed.   This is a method of press-molding a thin metal sheet while applying a crease-pressing force. The crease-pressing force at the start of molding is set to 5% or more of the tensile strength (TS) of the metal sheet in terms of tension, and the punch speed is set to 500 mm / sec or less A press forming method for a thin metal sheet, characterized in that when the punch shoulder comes into contact with the thin metal sheet, the wrinkle holding force is increased and the punch speed is decreased.   3. The press forming method for a thin metal plate according to claim 1, wherein when the punch starts to contact the thin metal plate, the punch speed is set to 20 mm / sec or less, and then the punch speed is increased.   The wrinkle holding force after the increase is 50% or more of the tensile strength (TS) in terms of tension, and the punch speed after the decrease is 0.5 to 50 mm / sec. Press forming method for metal sheet.   3. The wrinkle pressing force when the punch shoulder is in contact with the metal material is 30% or more of the tensile strength (TS) in terms of tension, and the punch speed is reduced to 0.5 to 50 mm / sec. Press forming method for metal sheet.   The method according to any one of claims 1 to 3, a method combining any two or more methods, or the method according to any one of claims 3 to 5, any two or more. A method for press forming a thin metal sheet, comprising a combination of the above methods.

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