JP2011125882A - Method and apparatus for manufacturing drawn product consisting of galvannealed steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the formability by achieving the consistent slidability when drawing a GA steel sheet. <P>SOLUTION: When manufacturing a drawn product by drawing a GA steel sheet 14 by using a press forming device having a punch 11 and a die 13, the maximum value of the forming stroke or the forming load in which the forming load is maximized is previously obtained. Based on the obtained maximum value of the forming stroke or the forming load, the last punch speed is maintained at least in a part of an area to the forming stroke with the forming load being maximum after the contact of the punch 11 with the GA steel sheet 14 is started, and the punch forming speed is increased together with the forming stroke. In this area of the forming stroke, the forming load become maximum after the forming load reaches the maximum 90% of the forming load. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and apparatus for producing a drawn product made of an alloyed hot-dip galvanized steel sheet.

  A method for producing a drawn product by drawing an alloyed hot-dip plated steel plate (hereinafter also referred to as “GA steel plate”) whose surface is coated with a steel plate is used for the production of automobile parts and home appliance parts. In draw forming, by using a press device including a punch, a die and a holder, the steel plate to be formed is fixed by the die and the holder, and the punch is raised or lowered with respect to the die while applying a pressing force to the steel plate. Then, the steel plate is formed into a punch-shaped drawn product.

  A crank press using a crank mechanism has been conventionally used in a press device. The steel plate has a punch speed (forming speed) that draws a sine curve that is zero at the top dead center and bottom dead center of the punch forming stroke and fastest at the middle position of the top dead center and bottom dead center by the crank press. ). A link motion press in which the punching speed is reduced by attaching a link mechanism to the crank press is also used. Recently, a servo press that can freely set a punch molding speed curve by using a servo motor as a drive source of the punch is also used.

When producing a drawn product by drawing a steel plate, it is known that a forming defect such as a crack occurs in the steel plate.
Patent Document 1 discloses a method of improving the forming limit at which cracks occur in a metal plate by restarting the forming after separating the punch from the metal plate in the middle of the forming of the metal plate.

  In Patent Document 2, the forming speed is reduced immediately before the punch touches the metal plate, and further, the forming speed is increased after forming at least the punch diameter × 0.25 height in order to increase productivity. Discloses a method of processing a metal plate into a cylindrical drawn product while suppressing the occurrence of shock lines.

JP 2005-199318 A JP 2007-98428 A

  In general, GA steel plates have unstable slidability between a steel plate and a tool such as a punch as compared with a normal steel plate (hereinafter also referred to as “CR steel plate”). For this reason, cracks are likely to occur in the steel sheet during press forming and lack mass stability. Recently, it has been increasing that the GA steel plate and the CR steel plate are press-formed with the same press mold. For this reason, it is required to stabilize the slidability of the GA steel sheet with respect to the tool.

  So far, for example, a method for improving the slidability of the GA steel sheet by forming a new film on the surface of the GA steel sheet or performing special production management related to alloying of the plating on the surface of the GA steel sheet. Has been proposed. However, when these methods are implemented, an increase in the manufacturing cost of a drawn product made of a GA steel plate is inevitable.

  Also, even based on the methods disclosed in Patent Documents 1 and 2, quality defects due to instability of slidability in drawing of GA steel sheet cannot be sufficiently suppressed, and productivity Also decreases.

  The present invention has been made in view of these problems of the prior art, and is made of a GA steel plate that can stabilize the slidability and improve the formability when drawing the GA steel plate. It aims at providing the manufacturing method and manufacturing apparatus of a molded article.

The present inventors examined the influence of the friction coefficient between a steel plate and a press tool on the quality of a press-formed product in drawing of the steel plate.
FIG. 11A to FIG. 11D are explanatory diagrams schematically showing the state of drawing of the steel plate 1.

  As shown in FIGS. 11 (a) to 11 (d), the steel plate 1 uses a press die 5 including a punch 2, a holder 3, and a die 4, and the steel plate 1 as a material is sandwiched between the holder 3 and the die 4. Thus, it is constrained (the clamping force is referred to as “BHF”), and then the punch 2 and the die 4 are moved to form the drawn product 6. At that time, in order to ensure the quality of the drawn product 6, the inflow of the material into the punch portion 6 a is controlled by adjusting the frictional resistance generated between the steel plate 1 and the tools 2 to 4.

  If the frictional resistance is too small, the material excessively flows into the punch portion 6a, wrinkles are generated in the punch portion 6a and the flange portion 6b of the press-formed product 6, and molding defects occur. On the other hand, if the frictional resistance is excessive, the inflow of material to the punch bottom is excessively hindered and breakage occurs during press forming, resulting in a failure. The frictional resistance force per unit area is expressed by the frictional resistance force per unit area = contact surface pressure × friction coefficient (μ), and the contact surface pressure is a die generated by BHF, material deformation resistance, or the like. It is the contact surface pressure of the material.

  If the friction coefficient fluctuates greatly during the drawing process, the frictional resistance fluctuates greatly, resulting in a reduction in quality. Further, in the latter half of the molding process, for example, in the vicinity of the bottom dead center of the molding, the contact surface pressure increases and the frictional resistance increases. As a result, the punch molding load increases and exceeds the fracture limit, and cracking is likely to occur. .

In order to reduce the frictional resistance in the latter half of the forming process in which the contact surface pressure is increased in the GA steel sheet drawing process, for example, in the vicinity of the forming bottom dead center, the friction coefficient between the steel sheet and the punch The present invention was completed by paying careful attention to slidability and obtaining findings (1) to (8) listed below. In the following description, the steel plate 1 in FIG. 11 is assumed to be a GA steel plate.
(1) The smaller the coefficient of friction between the GA steel sheet 1 and the punch 2 in FIG. 11, the smaller the variation in the frictional resistance and the better the press formability.
(2) The friction coefficient between the GA steel sheet 1 and the punch 2 varies depending on the amount of ζ phase during plating of the GA steel sheet 1, and the smaller the amount of ζ phase, the smaller the friction coefficient.
(3) The GA steel sheet 1 has a large variation in the amount of ζ phase during plating, and as a result, the slidability during press forming becomes unstable.
(4) The friction coefficient between the GA steel sheet 1 and the punch 2 varies depending on the contact surface pressure, and the friction coefficient increases as the contact surface pressure increases.
(5) The friction coefficient between the GA steel sheet 1 and the punch 2 varies depending on the punch forming speed, and the friction coefficient decreases as the punch forming speed increases.
(6) Therefore, in a region where the contact surface pressure is high, that is, in the vicinity of the molding load, for example, in the vicinity of the molding bottom dead center, the slidability is improved and cracking is suppressed by increasing the punch molding speed.
(7) When the GA steel sheet 1 is press-formed by a general crank press, that is, a press whose punch speed is represented by a sine curve, the punch speed is remarkably lowered with the forming stroke in the latter half of the forming process in which the forming load increases. For this reason, the coefficient of friction is increased, the slidability is lowered, and cracking is likely to occur.
(8) In a crank press having a servo press or a link motion mechanism, the punch forming speed can be increased in the latter half of the forming process in which the forming load increases. Thereby, generation | occurrence | production of the crack at the time of drawing-forming GA steel plate 1 can be suppressed.

  In the present invention, when producing a drawn product by drawing a GA steel sheet using a press forming apparatus having a punch and a die, a maximum value of a forming stroke or a forming load at which a forming load is maximized is obtained in advance. Based on the maximum value of the molding stroke or molding load obtained, the previous punch speed is maintained in at least a part of the area between the start of contact between the punch and the GA steel plate and the molding stroke at which the molding load is maximized. Or a method of manufacturing a drawn product made of a GA steel sheet, wherein the punch forming speed is increased with the forming stroke.

  From another point of view, the present invention is a manufacturing apparatus that includes a punch and a die, press-forms the GA steel sheet to manufacture a drawn product, and includes a speed adjusting unit that adjusts a punch forming speed. The speed adjusting means is based on the forming stroke at which the forming load is maximized or the maximum value of the forming load, and at least a part of the forming stroke from when the punch and the GA steel plate start to contact until the forming stroke at which the forming load is maximized. An apparatus for producing a drawn product characterized by having a function of maintaining the immediately preceding punching speed in a region or increasing the punching speed with the molding stroke.

  In the present invention, the “punch forming speed” means the moving speed of the punch when the punch is moved while the die is fixed, and the die is moved while the punch is fixed. In the case of molding, it means the moving speed of the die. Further, when molding is performed by moving both the die and the punch, it means the sum of the moving speed of the punch and the moving speed of the die.

In the present invention, it is desirable that the region is a region from when the forming load reaches 90% of the maximum forming load to the forming stroke at which the forming load becomes maximum.
In these present inventions, it is desirable that the molding stroke that maximizes the molding load be the molding bottom dead center.

Further, in these inventions, the punching speed of the region is set such that the stroke position from the bottom dead center is SP (mm), the number of strokes per minute is SN (number of times / minute), When the total stroke to the dead point is ST (mm), it is desirable that the stroke is larger than the reference speed calculated by the following equation (1).
Reference speed (mm / s) = 2 × 3.14 / (60 / SN) × sin (T × 2 × 3.14 / (60 / SN)) × ST / 2 (1)
Here, SP = −cos (T. × 2 × 3.14 / (60 / SN)) × ST / 2 + ST / 2, where T is the stroke position SP (distance from bottom dead center) to bottom dead center. Means the time in seconds.

  According to the present invention, it is possible to stabilize the slidability when drawing the GA steel sheet and to suppress cracking during press forming in the drawing of the GA steel sheet, thereby improving the formability. become able to.

  In addition, according to the present invention, the occurrence of cracks when drawing the GA steel plate and the CR steel plate with the same mold is suppressed, and the press forming can be stably performed.

FIG. 1 is a graph showing a transition of a punch speed pattern of a conventional crank press system. FIG. 2A is an explanatory view showing the state of drawing by the manufacturing apparatus of the present invention, and FIG. 2B is a graph showing an example of the relationship between the forming load and the stroke in the present invention. FIG. 3 is a graph showing an example of the relationship between the punch forming speed (forming speed) and the stroke in the present invention. FIG. 4 is a graph illustrating types of punch forming speeds in the present invention. FIG. 5 (a) is an explanatory view schematically showing a state at the completion of molding in another manufacturing method of the present invention, and FIG. 5 (b) shows the transition of the molding load in another manufacturing method of the present invention. It is a graph to show. FIG. 6 is a graph illustrating the transition of the punching speed in another manufacturing method of the present invention. FIG. 7 is an explanatory view schematically showing a configuration of a manufacturing apparatus having a servo press mold used in the examples. FIG. 8 is a graph showing a speed pattern of crank motion. FIG. 9 is a graph showing the transition of the molding load when the BHF is 39.2 kN in the speed pattern shown in FIG. FIG. 10 is a graph showing types of molding speeds in Examples. Fig.11 (a)-FIG.11 (d) are explanatory drawings which show typically the condition of the drawing forming of a steel plate.

The present invention will be described with reference to the accompanying drawings.
FIG. 1 is a graph showing a transition of a punch speed pattern of a conventional crank press system. The punch speed of this crank press system is SP (mm) as the stroke position from the bottom dead center, SN (number of times / minute) as the number of strokes per minute, and the total stroke from the top dead center to the bottom dead center. When ST (mm) is used, the pattern is expressed by the following formula (1), and in the molding region from the start of molding to the bottom dead center, the punch speed is monotonously reduced with the punch stroke. In addition, the punch speed represented by Formula (1) is called a reference speed.
Reference speed (mm / s) = 2 × 3.14 / (60 / SN) × sin (T × 2 × 3.14 / (60 / SN)) × ST / 2 (1)
Here, SP = −cos (T × 2 × 3.14 / (60 / SN)) × ST / 2 + ST / 2, where T is the stroke position SP (distance from bottom dead center) to bottom dead center. Time (seconds).

  FIG. 2A is an explanatory diagram showing the state of drawing by the manufacturing apparatus 10 of the present invention, and FIG. 2B is a graph showing an example of the relationship between the molding load and the stroke in the present invention. FIG. 3 is a graph showing an example of the relationship between the punch forming speed (forming speed) and the stroke in the present invention.

A manufacturing apparatus 10 according to the present invention will be described with reference to FIG.
As shown in FIG. 2A, the manufacturing apparatus 10 according to the present invention includes a punch 11, a holder 12, and a die 13, and speed adjusting means for adjusting a punch forming speed (not shown). The manufacturing apparatus 14 performs drawing on the GA steel plate 14 to manufacture a drawn product having a stepped portion indicated by a circle in FIG.

  The speed adjusting means (a) sets the immediately preceding punch speed in at least a part of the region from the start of contact between the punch 11 and the GA steel sheet 14 (start of forming) to the forming stroke at which the forming load becomes maximum. Has a function of maintaining or increasing the punching speed with the forming stroke, (b) the stroke position from the bottom dead center is SP (mm), and the number of strokes per minute is SN (number of times / minute), When the entire stroke from the top dead center to the bottom dead center is ST (mm), the punch forming speed in that region is made larger than the reference speed calculated by the above formula (1) defined by the crank motion. It is desirable to have a function. The molding stroke that maximizes the molding load can be obtained in advance by a molding test or by performing analysis using general-purpose molding simulation analysis software or the like.

  It is desirable that the speed adjusting means has a function of increasing the punching speed from the time when the forming load reaches 90% of the maximum forming load until the forming stroke at which the forming load becomes maximum as compared with the reference speed.

As this speed adjusting means, for example, a servo motor used as a drive source of the punch 11 is exemplified.
Also, the punch speed adjustment in the present invention is to obtain the maximum value of the molding load in advance and maintain the previous punch speed based on the measured value of the molding load and the maximum value of the molding load, or punch molding with the molding stroke. This can be done by determining the timing for increasing the speed and transmitting this timing to the speed adjusting means. That is, when the measured value of the molding load becomes a predetermined value with respect to the maximum value of the molding load, the punch speed is maintained or the molding speed is increased.

  Next, the production method of the present invention will be described. Here, as shown in FIG. 2 (b), the case where the molding load is maximum at the molding bottom dead center will be described. However, the present invention is not limited to this case. The same applies when the molding load becomes small at the bottom dead center of molding. Note that the load characteristics as shown in FIG. 2 (b) occur in the non-drawn forming form illustrated in FIGS. 2 (a) and 11 (c), but the deep drawing forming depth is not less than a certain level. It can also be seen in the aperture parts.

  In the drawing of the GA steel sheet according to the present invention, as shown in the graph of FIG. 3, immediately after the punch 11 starts to contact the GA steel sheet 14, the punch forming speed is increased, and then the speed is reduced to the bottom dead center. Thus, molding is performed with a speed pattern in which the punching speed is zero. With this speed pattern, the drawing is performed from the start of molding to the bottom dead center at a higher punch speed than the reference speed.

  As described above, in press forming of the GA steel sheet 14, the higher the forming speed, the smaller the friction coefficient between the GA steel sheet 14 and the tools 11-13. Therefore, as shown in the speed pattern shown in FIG. 3, the punch molding speed is once increased in the molding area, and the molding speed at the stroke at which the molding load increases becomes larger than the reference speed, thereby increasing the molding load area. The coefficient of friction at is reduced, and the frictional resistance is reduced. As a result, the molding load is reduced and the occurrence of cracks is suppressed.

The present invention is a speed pattern in which the punch forming speed is increased immediately after the punch 11 starts to contact the GA steel sheet 14, but the present invention is not limited to this speed pattern.
FIG. 4 is a graph illustrating a pattern of punch forming speed in the present invention.

  As illustrated by the curves a, b, and c in the graph of FIG. 4, punch forming is performed in at least a part of the region from the start of contact between the punch 11 and the GA steel plate 14 to the forming stroke at which the forming load becomes maximum. By increasing the speed with the stroke or maintaining the immediately preceding speed, the punch speed in that region may be set to a speed pattern larger than the reference speed.

  In the present invention, the speed increase or the speed is maintained so that the speed pattern is larger than the reference speed in the region from the molding load reaching 90% of the maximum molding load to the molding stroke where the molding load is maximum. It is desirable.

  As shown by a curve a in the graph of FIG. 4, a speed pattern that increases the forming speed in at least a part of the region from the start of the contact of the punch 11 to the GA steel plate 14 to the bottom dead center of the forming may be used. desirable. In addition, it is desirable to increase the speed so that the punch forming speed is 100 mm / sec or more.

  FIG. 5 (a) is an explanatory view schematically showing a state at the time of completion of molding in another manufacturing method of the present invention, and FIG. 5 (b) is a graph showing transition of molding load in another manufacturing method of the present invention. It is. FIG. 6 is a graph illustrating the transition of the punching speed in another manufacturing method of the present invention.

  When drawing through as shown in FIG. 5 (a) or when the forming depth is a certain amount or more, as shown in FIG. 5 (b), during the molding from the start of molding to the bottom dead center of molding. In this case, the molding load is maximized.

  In the drawing of the GA steel sheet 14-1 according to the present invention, as exemplified by the curves a and b in the graph of FIG. 6, the punch forming speed is at least in a part of the region from the start of forming to the maximum forming load. Speed pattern in which the punching speed near the forming stroke where the forming load is maximized or maintained is increased at a speed higher than the reference speed and then decelerated to zero at the bottom dead center Molding is performed.

With this manufacturing method, the friction coefficient in the region where the molding load is high is reduced, and the frictional resistance is reduced. As a result, the molding load is reduced and the occurrence of cracks is suppressed.
In addition, according to the present invention, since the slidability in the vicinity of the forming stroke which is the maximum value of the forming load in the drawing of the GA steel plate is stabilized, the GA steel plate and the CR steel plate having different slidability are used in the same press die. Thus, it becomes possible to press-mold stably.

  FIG. 7 is an explanatory view schematically showing the configuration of the manufacturing apparatus 10 having the servo press mold used in this embodiment. In FIG. 7, the same components as those in the manufacturing apparatus illustrated in FIG. 2A and FIG. 5A described above are denoted by the same reference numerals, and redundant description is omitted.

Using the manufacturing apparatus 10 having the servo press mold configured as shown in FIG. 8, the number of strokes per minute (SN) is 27 times / minute, the total stroke from top dead center to bottom dead center is 200 mm, and blank By performing cylindrical drawing with a forming depth of 50 mm in various forming speed patterns on a GA steel plate having a mechanical thickness shown in Table 1 and a thickness of 0.7 mm and a blank diameter of 176 mm as (steel plate) 14, A drawn product was produced. The both sides of the blank 14 were coated with ² g / m ² of general oil-proofing oil.

  First, drawing was performed with a conventional crank motion speed pattern, and the molding load was measured. FIG. 8 is a graph showing the speed pattern of the crank motion, and FIG. 9 is a graph showing the transition of the molding load when the BHF is 39.2 kN in the speed pattern shown in FIG.

As shown in the graph of FIG. 9, the maximum value of the molding load was 78 kN, and the stroke reaching 90% of the maximum molding load was 20 mm from the start of molding (30 mm from the bottom dead center).
Next, based on the molding load-stroke curve obtained in advance, the molding speed in at least a part of the stroke where the molding load is maximum from the start of molding is set to be larger than the reference speed calculated by the above-described equation (1). The speed pattern that increases the molding speed along with the stroke in a part of the stroke where the molding load is maximum from the start of molding, is performed 5 times for each speed pattern, the maximum molding load, the variation in the maximum molding load and the limit BHF investigated. In general, the formability in press molding can be evaluated by the limit BHF, which is the maximum BHF that can be molded without forming defects.

FIG. 10 is a graph showing types of molding speeds in this example.
In the graph of FIG. 10, the speed pattern of (a) is a crank motion pattern (comparative example) calculated by Expression (1), and the speed patterns of (b) and (c) are from the start of molding. The speed is increased before the stroke reaches 20 mm, and the speed between the stroke 20 mm and the stroke 50 mm (molded bottom dead center) is higher than the speed pattern of the speed pattern (a) (example of the present invention). The speed pattern is a pattern (invention example) in which the speed is increased 30 mm before the stroke, the molding speed after the stroke 30 mm is larger than the speed pattern of the speed pattern (a), and the speed pattern (e) It is a pattern (invention example) in which the speed is increased 40 mm before and the molding speed after the stroke 40 mm is larger than the speed pattern of (a).

  Table 2 summarizes the maximum molding load, the variation in the maximum molding load, and the investigation results of the limit BHF in each speed pattern.

  As shown in Table 2, in the trial patterns 2 to 5 of the speed patterns (b) to (e), the maximum molding load is lower than that of the trial pattern 1 of the speed pattern (a), and the maximum molding load is not uniform. Results in an increase in the critical BHF. Thereby, according to this invention, it turns out that the formability of GA steel plate improves.

  In particular, the speed is increased before the stroke from the start of molding becomes 20 mm, and the speed between the stroke 20 mm and the stroke 50 mm (molded bottom dead center) becomes a pattern larger than the speed pattern of (a) (b). In the speed pattern of (c), it can be seen that the limit BHF is increased by 20% or more and the moldability is remarkably improved.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Punch 3 Holder 4 Die 5 Press die 6 Drawing molded product 6a Punch part 6b Flange part 10 Manufacturing apparatus 11 Punch 12 Holder 13 Die 14, 14-1 GA steel sheet

Claims (5)

  When producing a draw-formed product by drawing an alloyed hot-dip galvanized steel sheet using a press-forming device equipped with a punch and a die, obtain the maximum value of the forming stroke or forming load that maximizes the forming load in advance. Based on the determined molding stroke or the maximum value of the molding load, at least a part of the region from the start of contact between the punch and the galvannealed steel sheet until the molding stroke at which the molding load is maximized. Then, the manufacturing method of the draw-formed article which consists of an alloying hot-dip galvanized steel plate characterized by maintaining a punch speed immediately before or increasing a punch forming speed with a forming stroke.   The said area | region is an area | region from the alloying hot-dip galvanized steel plate described in Claim 1 to the shaping | molding stroke from which the shaping | molding load reaches | attains the maximum 90% of a shaping | molding load until the shaping | molding load becomes the maximum. Product manufacturing method.   The method for producing a drawn product made of an alloyed hot-dip galvanized steel sheet according to claim 1 or 2, wherein the forming stroke with the maximum forming load is a forming bottom dead center. The punching speed of the area is SP (mm) as the stroke position from the bottom dead center, SN (number of times / minute) as the number of strokes per minute, and ST for all strokes from the top dead center to the bottom dead center. When it is set to (mm), it is larger than the reference speed calculated by the following formula (1), and is drawn by the alloyed hot-dip galvanized steel sheet according to any one of claims 1 to 3. Product manufacturing method.
Reference speed (mm / s) = 2 × 3.14 / (60 / SN) × sin (T × 2 × 3.14 / (60 / SN)) × ST / 2 (1)
Here, SP = −cos (T. × 2 × 3.14 / (60 / SN)) × ST / 2 + ST / 2
T: Time from stroke position SP (distance from bottom dead center) to bottom dead center (seconds) A manufacturing apparatus comprising a punch and a die, press-molding an alloyed hot-dip galvanized steel sheet to produce a drawn product,
Comprising a speed adjusting means for adjusting the molding speed of the punch,
The speed adjusting means is based on the forming stroke at which the forming load is maximized or the maximum value of the forming load, and until the forming stroke at which the forming load is maximized after the punch and the galvannealed steel sheet are brought into contact with each other. An apparatus for producing a drawn product, which has a function of maintaining the immediately preceding punch speed or increasing the punch molding speed with the molding stroke in at least a part of the area between the two.

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