JP4457671B2 - 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 without taking the steps.

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

  For press molding, as shown in FIG. 5, (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 definition of the limit molding height LDH is shown in FIG. The larger the limit drawing ratio and the limit molding height, 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. 1 (a), conventionally, press forming has generally been performed by punching a material metal plate (blank) 100, for example, a die 20 on the upper side in the figure and a lower side in the figure. 10 until the final target shape is reached (the punch reaches the top dead center). The punch 10 is moved at a substantially constant speed (even 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. In addition, the wrinkle presser 30 may not be arranged.

  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. 5A, the metal plate (blank 100) sandwiched between the wrinkle retainer 30 and the die 20 is slid with the wrinkle retainer 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. 5B, 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 provides a press molding method in which a lubricant is present between a punch and a metal plate at the start of molding, and the metal plate is clamped with a punch and a die, after the punch first contacts the metal plate and molding is started. , Until the punch reaches the stroke end and the forming is completed, the punch is once separated from the metal plate, and the metal plate is formed again using the punch and the die, at least, The problem is solved by passing one or more times.

  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. The circular blank is drawn into a cylindrical cup of the desired size, and the maximum size (diameter) of the circular blank before press forming that can be formed without breaking, cracking or wrinkling is evaluated as the forming limit. It is a method to do.

  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.

  On the other hand, as shown in FIG. 1 (b), according to the method of the present invention, after the punch 10 first contacts the blank 100 and molding is started, the punch reaches the stroke end and the metal plate Until the formation of the (blank 100) is completed, the blank 100 and the punch 10 are once separated, and the operation of forming the metal plate (blank 100) again using the same punch 10 and the die 20 is performed once or more. It passes.

  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.

  If the state in the middle of molding is imagined, the mold surface such as the punch 10 and the die 20 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 at the start of molding or between the die 20 and the blank 100 is temporarily thinned as the molding proceeds. Thus, as shown in the upper part of FIG. 2, the metals are partly in direct contact with each other.

  As a result, the coefficient of friction between the mold such as the punch 10 and the die 20 and the blank 100 temporarily increases, the slidability decreases and the blank 100 is cracked, or the mold and the blank 100 are broken. Adhesion occurs between the two and troubles such as mold galling occur. 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 blank 100 and the punch 10 are once separated until the punch reaches the end of the stroke and the forming of the metal plate (blank 100) is completed. Here, the separation includes not only the case where the blank 100 and the punch 10 are completely separated as shown in FIGS. 1B and 1B, but also the case where only the bottom surface of the punch 10 is separated and the side surfaces are in contact with each other. Meaning.

  In this way, as shown in the lower part of FIG. 2, the film thickness of the lubricant 50 is recovered, and when the operation of forming the metal plate (blank 100) again using the same punch 10 is started, the slidability is reached. Is recovered and cracks in the blank 100 or mold galling can be suppressed.

  The reason why the slidability is restored when the blank 100 and the punch 10 are separated is not clear, but as shown in FIG. 2, the surface of the blank 100 or the mold (punch 10 in the figure) is minute. This is probably due to the action of the lubricant 50 enclosed in the recesses being drawn 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 punch 10 are once separated, and the metal plate (blank 100) is formed again using the same punch 10 and the die 20 more than twice. That's fine.

  The punch 10 is separated from the punch 10 and the metal plate (blank 100) is formed again using the same punch 10 and the die 20, and the punch 10 is applied to the metal plate (blank 100). The effect of the present invention can be obtained as long as it is at least once after the first contact and before the formation of the metal plate (blank 100) to the final target shape 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 cylindrical cup drawing as an example. However, the present invention is not limited to cylindrical cup drawing, but is also drawn and formed by parts such as stretch molding and parts having complicated shapes. It can be applied to press molding in general, such as mixed molding.

  When the present invention is applied to a large-scale press molding machine for mass production, such as press molding of automobile and home appliance parts, the punch 10 after the punch 10 first contacts the metal plate (blank 100). A hydraulic or electric motor type servo press capable of freely controlling the position and moving speed may be used to perform stroke control during press forming, or the punch 10 moves to the maximum forming depth that does not reach the forming limit. When the punch 10 stops by sensing a sensor such as a limit switch (not shown) when the punch 10 is automatically retracted, the sensor 10 senses another sensor such as another limit switch (not shown) in the retracted position. A sequence circuit may be built such that the punch 10 automatically moves again to resume molding.

  In any case, the effect of the present invention is not affected by the type of the press molding machine, etc. After the punch 10 first contacts the metal plate (blank 100), the punch reaches the stroke end. The operation of separating the metal plate (blank 100) and the punch 10 and forming the metal plate (blank 100) again using the same punch 10 and the die 20 until the formation of the metal plate (blank 100) is completed. As long as the molding can be performed at least once, the effect of improving the molding limit can be obtained.

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

  Examples will be described below.

  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), the punch 10 and the blank 100 are once separated at the position where the punch 10 has moved 15 mm, and then the metal plate (blank 100) is again used by using the same punch 10 and the die 20. 100) was performed once, and press molding was completed (drawn out) until the punch reached the end of the stroke.

  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 the present invention, the LDR of the test material A, which is a general cold-rolled steel sheet for drawing, becomes larger than the LDR of the test material B, which is a cold-rolled steel sheet for deep drawing. It was verified that the molding limit was improved. Further, even when the test material B used the conventional method, the LDR was originally large, 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.

  Using the same specimens A, B, and C as shown in Table 1 as in Example 1 and using the same ball head overhang test machine as in Example 1, the movement of the blank 100 was constrained by the bead 40. The effect was verified.

  The ball head overhanging test was a method in which the punch 10 and the blank 100 were once separated during the ball head overhanging test and then molded until press molding was completed (breakage occurred). In this example, after the punch 10 first contacted the metal plate (blank 100), the punch 10 and the blank 100 were once separated at a position where the punch 10 moved 25 mm.

  The punch had a diameter of 100 mm. In the ball head overhang test of the present embodiment, the movement of the blank 100 is restricted by the bead 40 so that the raw metal plate (blank 100) does not flow into the die 20. LDH (limit forming height) was used for evaluation of formability in the stretch forming of this example.

  FIG. 4 shows the test results. The LDH of the test material B of the cold-rolled steel sheet for deep drawing, which is superior in elongation properties to the test material A (high EL), is large, but the LDH of the test material A is large by applying the present invention. It can be seen that the LDH of the specimen A, which is a general cold-rolled steel sheet for drawing, is larger than the LDH of the specimen B of the cold-drawn steel sheet for deep drawing when the present invention is not applied. It has been verified that the forming limit is improved in the overhang forming by applying the 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 metal plate is clamped with a punch and a die, the shape of the press molding die such as a punch or die is modified, the shape or material of the blank is changed to a special one, the punch or die is If the shape of the part to be pressed is complicated or the material metal plate has high strength without taking special measures such as micro-vibrating the press mold using ultrasonic waves. Even in this case, it is possible to improve the forming limit at which cracks occur in the metal plate, and to provide a low-cost method that can be easily applied to a large press forming machine.

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 diagram for demonstrating the effect of this invention in the ball head overhang | projection shaping | molding of Example 2 The figure for demonstrating (a) draw forming and (b) overhang forming The figure for explaining the definition of the limit drawing ratio LDR Diagram for explaining the definition of limit forming height LDH

Explanation of symbols

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

Claims (1)

In a press molding method in which a lubricant is present between a punch and a metal plate at the start of molding, and the metal plate is clamped with a punch and a die , the punch first contacts the metal plate and molding is started. During the period from reaching the stroke end to completion of forming, the punch is once released from the metal plate, and the metal plate is formed again using the punch and the die at least once. A metal plate press forming method.

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