JP4556432B2 - Metal plate press forming method - Google Patents

Description

  Press molding refers to forming a desired shape by sandwiching a metal plate with a pair of molds (in many cases, a mold) such as a punch and a die.

  The present invention relates to a press forming method of a metal plate when manufacturing parts of automobiles and home appliances, and special measures such as mold shape correction (grinding etc.) and changing the material of the metal plate to a special one. The present invention relates to a press forming method of a metal plate that can improve the forming limit at which a crack occurs in the metal plate, and more particularly to a press forming method called draw forming.

  For manufacturing parts of automobiles and home appliances, press forming of a metal plate such as a thin steel plate is often used.

  In press molding, as shown in FIG. 4, (a) draw forming (a material metal plate (referred to as a blank) 100 flows from the periphery into the die (die 20)), (b) overhang forming (bead 40). And the material metal plate 100 is not allowed to flow into the mold (20) from the periphery) (Non-patent Document 1). Incidentally, the definition described in the document is shown in FIG. The larger the limit drawing ratio, the better the moldability. In the figure, 10 is a punch that constitutes a press mold together with a die 20, and 30 is a wrinkle presser.

  As shown in FIG. 1A, conventionally, generally, in press forming, a raw metal plate (blank) 100 is raised from, for example, a die 20 on the upper side in the drawing and a lower side in the drawing. The punch 10 was formed so as to move at a substantially constant speed until it reached the final target shape (the punch reaches the top dead center) (when the die is on the lower side and the punch is on the upper side) In that case, the punch reaches the bottom dead center and the molding is completed). In the meantime, in order to suppress the occurrence of wrinkles on the outer edge of the blank 100, in many cases, the wrinkle presser 30 is arranged, and the punch 10 is moved with the metal plate (blank 100) sandwiched between the dies 20. To complete the molding.

  The force for sandwiching the metal plate (blank 100) between the wrinkle retainer 30 and the die 20 is sufficient to suppress the occurrence of wrinkles on the outer edge of the blank 100, and does not need to be excessively large. As shown in the example of drawing shown in FIG. 4A, the metal plate (blank 100) sandwiched between the wrinkle presser 30 and the die 20 slides with the wrinkle presser 30 and the die 20, respectively. This is because if it is excessively increased, sliding is hindered, and cracks are likely to occur in the metal plate (blank 100) during press forming. Incidentally, in the case of the overhang forming example shown in FIG. 4B, this bead 40 rather positively prevents this sliding and suppresses the metal plate (blank 100) from being drawn into the back side of the die 20. .

  By the way, various types of molding defects can occur in press molding. Especially when the shape of the part to be press-molded is complicated or the material metal plate (blank) has high strength, There is a problem that cracking is likely to occur.

  As a general method to suppress this, the shape of press molds (such as punches and dies) such as punches and dies (simply called molds) is modified, or the blank shape is changed to a different shape from the beginning. Or changing the blank material to a special one.

  However, it takes a lot of time, labor, and costs to correct the shape of the mold or change the shape or material of the blank. A method capable of suppressing the occurrence of the occurrence has been studied and developed.

  For example, in Non-Patent Document 2 and Patent Document 1, the frictional force between the mold and the blank is reduced by microvibrating a press-molding mold such as a punch or a die using ultrasonic waves. A method for improving the formability is described.

JP-A-1-122624 Steel Handbook VI p252, p259 Plasticity and processing Vol. 23 no. 256 (1982-5), p458

  However, in this method, it is necessary to apply minute vibrations to the mold by ultrasonic waves or the like, and in actual press molding machines for automobiles and the like having large molding load and wrinkle holding force specifications, regardless of small experimental devices. However, there has been a problem that an output sufficient to vibrate the mold cannot be obtained, or that it would be very expensive to apply to an actual machine.

  Even if it can be applied fortunately, high-frequency vibrations are applied to the mold, so the force of tension and compression is repeatedly applied to each part of the actual press molding machine. There was also a problem of durability of the actual machine.

  The present invention has been made to solve the above-described problems in the prior art. The shape of a press mold such as a punch or a die is corrected, or the shape or material of a blank is changed to a special one. If the shape of the part to be press-molded is complicated without taking special measures such as micro-vibrating a press-molding die such as a punch or die using ultrasonic waves, To provide a low-cost method that can improve the forming limit at which cracks occur in the metal plate even when the material metal plate is high-strength, and can be easily applied to large-scale press forming machines. Let it be an issue.

The present invention relates to a press forming method in which a wrinkle presser is arranged and a metal plate is clamped by a punch and a die, and the punch first contacts the metal plate in a state where the metal plate is held by the wrinkle presser and the die. After the forming is started and before the punch reaches the stroke end and the forming is completed, the wrinkle presser is once separated from the metal plate, and the metal is again used by using the punch, the die, and the wrinkle presser. The operation of stopping the movement of the punch until starting the forming of the plate, applying the wrinkle holding force again using the punch, the die and the wrinkle holding member, and then starting the forming of the metal plate again. The above problem is solved by passing at least once.

  According to the present invention, the shape of a press molding die such as a punch or a die is modified, the shape or material of a blank is changed to a special one, or the press molding die such as a punch or a die is ultrasonicated. A method that can improve the forming limit of cracks in metal plates without taking special measures such as micro-vibration using etc., is easy to apply to the actual press molding machine, and is a low-cost method Can provide.

  The operation of the present invention will be described using the example of cylindrical cup drawing shown in FIG. Cylindrical cup drawing is widely used as a test method for evaluating the deep drawability of a blank metal plate. In this method, a circular blank is drawn into a cylindrical cup of a desired size, and the maximum dimension (diameter) of the circular blank before the start of press molding, which can be formed without breaking or cracking, is set as the forming limit. It is a method to evaluate.

  As shown in FIG. 1 (a), according to the conventional method before the present invention, the blank 100 is sandwiched between the die 20 and the wrinkle press 30 on the upper side in the drawing, and the wrinkle press force is applied. Thereafter, as soon as the punch 10 comes into contact with the blank 100 for the first time, forming is started. Until the punch reaches the end of the stroke and the forming of the metal plate (blank 100) is completed, that is, the punch 10 is in the position where the forming is to be completed (top dead The punch 10 moves at a substantially constant speed until reaching the point (point), and the punch 10 and the blank 100 are completely formed in a state of being in contact from the start to the end of the forming.

  In contrast, as shown in FIG. 1B, according to the method of the present invention, the punch 10 first contacts the blank 100 with the metal plate (blank 100) sandwiched between the wrinkle presser 30 and the die 20. After the punching is started and before the punch reaches the stroke end and the forming of the metal plate (blank 100) is completed, the wrinkle presser 30 is once separated from the metal plate (blank 100), The operation of forming the metal plate (blank 100) again with the wrinkle retainer 30 and the die 20 using the die 20 and the wrinkle retainer 30 is performed at least once.

The movement of the punch 10 stops after the wrinkle retainer 30 is separated from the metal plate (blank 100) until the metal plate (blank 100) is formed again by using the same punch 10 and the die 20 and the wrinkle retainer 30. Keep it .

  The inventors have found that according to the method of the present invention, the deep drawability is improved and the molding limit can be improved as compared with the conventional method.

  The effect was estimated as follows.

  When the state in the middle of molding is imagined, the mold surface such as the punch 10, the die 20 and the wrinkle presser 30 and the surface of the blank 100 slide while being pressed. Thus, the film of the lubricant 50 existing between the punch 10 and the blank 100, between the die 20 and the blank 100, or between the wrinkle presser 30 and the blank 100 at the start of molding is molded. As it progresses, it becomes thin temporarily, and the metals are partially in contact as shown in the upper part of FIG.

  As a result, the friction coefficient between the mold such as the punch 10, the die 20, the wrinkle presser 30, and the blank 100 temporarily increases, the slidability decreases and the blank 100 is cracked, Adhesion occurs between the mold and the blank 100, causing troubles such as mold galling. In general, the above estimation seems to be correct even from the empirical fact that such molding defects occur more frequently in the case of molding with a longer sliding distance between the mold and the blank 100. .

  Therefore, in the present invention, the wrinkle presser 30 is once released from the blank 100 until the punch reaches the stroke end and the forming of the metal plate (blank 100) is completed.

  In this manner, as shown in the lower part of FIG. 2, the film thickness of the lubricant 50 is recovered, and the metal plate (blank 100) is formed again using the same punch 10, die 20 and wrinkle presser 30. When entering, the slidability is recovered and cracking of the blank 100 or mold galling can be suppressed.

  The reason why the slidability is restored when the wrinkle retainer 30 and the blank 100 are separated is not clear, but as shown in FIG. This is probably due to the action of the lubricant 50 that had been pulled out to the surface.

  When the operation of forming the metal plate (blank 100) again is started, the film of the lubricant 50 becomes thin again in the process of forming, and the blank 100 is cracked, or gold Adhesion may occur between the mold and the blank 100, and there is a possibility that problems such as mold galling and the like are likely to occur again.

  Therefore, in such a case, the metal plate (blank 100) and the wrinkle retainer are once released, and the metal punch (blank 100) is formed twice using the same punch 10, the die 20 and the wrinkle retainer 30 twice. All that is required is to pass through.

  The number of times that the wrinkle presser 30 and the metal plate (blank 100) are separated, the same punch 10 and the die 20 and the wrinkle presser 30 are used to apply the wrinkle presser force again to form the metal plate (blank 100) is After the punch 10 first contacts the metal plate (blank 100) with the metal plate (blank 100) sandwiched between the crease presser 30 and the die 20, the punch reaches the end of the stroke and the metal plate (blank 100) The effect of the present invention can be obtained if the molding is completed at least once before the molding is completed.

  The molding limit can be further improved by increasing the number of times, but if the number is increased too much, the effect is saturated and the time required for molding becomes longer, and the productivity is deteriorated. Therefore, the maximum molding depth that does not reach the molding limit and the minimum required number of times are experimentally determined according to the final target shape of the part to be molded, especially the depth, and press molding is performed at the minimum number of times necessary for mass production. This will ensure maximum productivity.

  Here, for the sake of convenience, the operation of the present invention has been described by taking a cylindrical cup drawing as an example. However, the present invention is not limited to a cylindrical cup drawing, but also a component having a complicated shape, such as a combination of drawing and stretch forming. For example, the blank 100 is slid between the wrinkle retainer 30 and the die 20 while the metal plate (blank 100) is sandwiched between the wrinkle retainer 30 and the die 20, and molding is performed while the material flows into the back side of the die 20. Applicable to general press molding.

  When the present invention is applied to a large-scale press molding machine for mass production, such as press molding of parts of automobiles and home appliances, a force to sandwich the metal plate (blank 100) by the wrinkle presser 30 and the die 20 is generated. A control device such as a servo valve may be installed for a drive source such as hydraulic pressure, and the force for sandwiching the metal plate (blank 100) between the wrinkle retainer 30 and the die 20 or the stroke of the wrinkle retainer 30 may be controlled. When the punch 10 is moved to the maximum forming depth that does not reach the limit, the sensor is sensitive to a sensor such as a limit switch (not shown) so that it is sensitive to a sensor such as another limit switch (not shown) in the retracted position. By doing so, the sequence circuit may be assembled in such a manner that the metal plate is automatically sandwiched again by the wrinkle presser 30 and the die 20 again.

  In any case, the effect of the present invention is not affected by the type of the press molding machine or the like, and the punch 10 is a metal plate with the metal plate (blank 100) sandwiched between the crease presser 30 and the die 20. After the first contact with the blank 100), until the punch reaches the end of the stroke and the forming of the metal plate (blank 100) is completed, the wrinkle retainer 30 is separated from the blank 100, and the same punch 10 and die 20 are moved. The molding limit can be improved as long as the operation of sandwiching and forming the metal plate (blank 100) with the crease presser 30 and the die 20 can be performed at least once.

  Moreover, the present invention can be easily applied to a large press molding machine and can be realized at low cost.

  Cylindrical cup drawing was performed using three types of cold-rolled steel sheets (thickness 1.2 mm) shown in Table 1.

  Specimen A is a general cold-rolled steel sheet for drawing, Specimen B is a deep-drawn cold-rolled steel sheet with a high Rankford value (r value) by a special manufacturing method, and Specimen C is ferrite. A stainless steel SUS430 cold-rolled steel sheet having mechanical properties equivalent to those of a general high-strength carbon steel sheet. Using a ball head overhanging tester, the bead portion was removed, and the punch 10 was replaced with a cylinder for cylindrical drawing and tested. The punch 10 had a diameter of 33 mm and a shoulder radius of 3 mm. The shoulder radius of the die 20 was 3 mm.

  After the punch 10 first contacts the metal plate (blank 100) with the metal plate (blank 100) sandwiched between the wrinkle retainer 30 and the die 20, the wrinkle retainer 30 and the die 20 are temporarily moved at a position where the punch 10 has moved 15 mm. Then, once the metal plate (blank 100) is released, and the same punch 10 and the die 20 are used, the metal plate (blank 100) is again given wrinkle holding force, and then the forming is started once. Press molding was completed (drawn out) until breakage occurred in (blank 100).

  The wrinkle pressing force for sandwiching the metal plate (blank 100) between the wrinkle press 30 and the die 20 was 12 kN.

  LDR (limit drawing ratio) was used for evaluation of the forming limit in cylindrical cup drawing.

  The test results are shown in FIG. By applying this invention, it turns out that LDR of the test material A which is a general cold-rolled steel sheet for drawing becomes larger than LDR of the test material B which is a cold-rolled steel sheet for deep drawing, and this invention It has been verified that the molding limit is improved by the application of. In addition, the sample material B had a large LDR even when the conventional method was used, but the molding limit was further improved by applying the present invention. Further, it was verified that the forming limit of the test material C is improved by applying the present invention as compared with the case of using the conventional method.

  In the press molding method in which a wrinkle presser is arranged and the metal plate is clamped with a punch and a die, the shape of the press molding die such as a punch or a die is replaced with another one, or the shape or material of the blank is special. The shape of the part to be press-molded is complicated without taking any special measures such as changing to, or microvibrating a press-molding die such as a punch or die using ultrasonic waves. Even if the material metal plate is high-strength, it is possible to improve the forming limit where cracks occur in the metal plate, and it is easy to apply to a large press forming machine and provides a low-cost method can do.

The figure for comparing and explaining the case where the conventional method and the method of the present invention are applied to cylindrical cup drawing Enlarged view for estimating and explaining the operation of the present invention The diagram for demonstrating the effect of this invention in the cylindrical cup draw molding of Example 1 The figure for demonstrating (a) draw forming and (b) overhang forming The figure for explaining the definition of the limit drawing ratio LDR

Explanation of symbols

10 ... Punch 20 ... Dice 30 ... Wrinkle retainer 40 ... Bead 100 ... Blank

Claims (1)

In the press molding method in which a wrinkle presser is arranged and the metal plate is clamped with a punch and a die, the punch is first brought into contact with the metal plate with the wrinkle presser and the die sandwiched, and molding is started. After the punch reaches the end of the stroke and the forming is completed, the wrinkle retainer is once separated from the metal plate, and the metal plate is formed again using the punch, the die and the wrinkle retainer. Until the start, the movement of the punch is stopped, and after the wrinkle pressing force is again applied using the punch, the die, and the wrinkle presser, the forming of the metal plate is started again. A metal plate press-forming method characterized in that it passes more than once.

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