JP5367998B2 - Warm forming method of aluminum alloy sheet - Google Patents

Description

  The present invention relates to a method of warm forming an aluminum alloy plate that can be integrally formed without dividing a panel such as an automobile panel having a relatively large planar shape and a deep forming depth for press forming. It is about.

  In recent years, automobiles have been actively reduced in weight by using aluminum alloy plates instead of conventional steel plates for the outer plate parts (hoods, doors, fenders, roofs, trunks, etc.) for the purpose of reducing fuel consumption. ing. In this aluminum alloy plate, a 5000 series aluminum alloy to which Mg is added as a main additive element for emphasizing formability, or 6000 to which Mg and Si are added as main additive elements with the aim of improving the strength after painting and baking. Often, an aluminum alloy is used.

  In general, press molding of automobile parts is performed by cutting a steel plate or an aluminum alloy plate from a sheet or coil state into a blank of an appropriate size for obtaining a press-formed product (molded panel), and then drawing the blank. (Draw), restructuring, piercing, etc., and then commercialized (panelized).

  On the other hand, domestic and overseas safety standards for automobile (car body) collision safety are becoming stricter year by year, and the vehicle body side part structure including doors must meet the safety standards for side barrier collisions. It has been. In order to satisfy these safety standards, it is necessary to install various safety members inside the door, and in order to secure this space, the dimension in the thickness direction of the door is thicker than the dimension in the thickness direction of the conventional door. Tend to be. As a result, among the members constituting the door, the door inner panel having a particularly large rectangular shape is subjected to deep drawing with a deep molding depth.

  However, since aluminum alloy sheet material is inferior in formability compared to conventionally used mild steel sheets, cracks and wrinkles are generated during deep drawing, and the door inner has a deep forming depth as described above. There was a situation that the formability of the panel could not be secured, and as a result, aluminum doors (lightening) did not progress.

  In such deep drawing, a resistance force (this is referred to as a flow-in resistance F) due to a material deformation resistance accompanying shrinkage deformation when the blank flange portion moves in a direction toward the punch pressure portion due to pressurization of the punch. On the other hand, the molding force sufficient to overcome this is transmitted from the punch shoulder to the blank to perform molding. At this time, when the fracture resistance (referred to as S) of the punch shoulder portion is larger than the flow-in resistance F of the flange portion, molding can be performed without fracture. Moreover, both the deformation resistance and the breaking resistance S of the blank depend on the deformation stress of the material of each part. Therefore, if the blank has a high deformation stress in the blank part that comes into contact with the shoulder of the punch and the deformation stress in the flange part is low, press molding compared to a blank with uniform material properties in the same plate The squeezability at the time is improved.

  As a method for forming an aluminum alloy plate adopting this idea, there is a warm forming method as shown below. For example, a warm forming method has been proposed in which the material temperature of the flange portion is locally increased by heating and the blank central portion is kept at a low temperature, and it has been proved by tests that the formability is improved. Patent Document 1 discloses a method of forming a peripheral portion (flange portion) of the material with a predetermined heating time, holding time, and forming time.

JP 2006-205244 A

  As described above, warm forming in which there is a temperature difference (strength difference) within the same plate during forming is considered effective for deep drawing. However, the optimal temperature distribution differs depending on the press-formed product (molded panel) that is the object of molding, and the optimal temperature distribution for each press-formed product (molded panel) has not necessarily been clear so far. It was. Therefore, even if a temperature difference is provided in the same plate, in the blank for forming an actual press-molded product, it is difficult to obtain an optimal temperature distribution, and thus problems such as partial cracks occur. The actual situation is that the molded product has not been successfully molded.

  Moreover, a press-molded product having a relatively large rectangular shape such as the above-described door inner panel can be obtained only by setting a rough temperature distribution condition that regulates the temperature and heating time (holding time, molding time) of the flange portion. Actually, warm forming is difficult. In a press product with such a large rectangular shape and a deep molding depth, as will be described later, it is difficult to actually perform warm molding integrally unless the temperature distribution of each part of the blank is controlled more finely. there were.

  Actually, when an aluminum alloy plate is used for a door inner panel, the door inner panel itself is divided into about 2 to 3 parts, and each part is separately press-molded and then re-applied by spot welding or the like. The fact is that we have to take the method of assembling together. Therefore, in addition to the increase in the number of parts in the middle of manufacturing, a separate joining process is required, and in reality, there has been a problem that the manufacturing cost is significantly increased. This problem is one of the main reasons why the door panel is not made aluminum (light weight).

  The present invention has been made as a solution to the above-described conventional problems, and even a press-molded product such as a door inner panel having a large rectangular shape and a deep molding depth is not divided. It is an object of the present invention to provide a warm forming method of an aluminum alloy plate that can be formed integrally and without forming cracks or wrinkles during forming.

The present invention relates to a method for warm forming an aluminum alloy plate in which an aluminum alloy plate blank having a substantially rectangular shape is flat-drawn into a flat, substantially rectangular shaped product having a flange portion around it. The temperature at the time of forming the central portion where the punch bottom contacts when forming the alloy plate blank is T0, and among the peripheral portions (four laps) of the aluminum alloy plate blank that is blank-held during forming, T0 <T3, T0 ≦ (T1, T2) where T1 is the molding temperature, T2 is the molding temperature at the center of the long side of the blank, and T3 is the molding temperature at the center of the four corners. ), (T1, T2) <after having to satisfy each expression of T3, the T1 and T2 are 0.99 ° C. or more and a T3, so that the temperature difference between T1 and T2 becomes equal to or higher than 50 ° C. It is a warm molding method of an aluminum alloy sheet, which comprises forming Te.

  That is, the requirements for the warm forming method of the aluminum alloy sheet of the present invention are that the forming temperature of the central part of the four corners of the aluminum alloy sheet blank to be deep drawn in the warm condition is formed in all other parts. If the temperature at the center of the center where the punch bottom contacts is higher than the molding temperature of the short side part and the long side part of the blank, good.

  According to the present invention, even a press-molded product such as a door inner panel having a large rectangular shape and a deep molding depth is integrated without being divided, and cracks (cracking) during press working There is no generation or wrinkle generation, and the aluminum alloy plate can be warm-formed stably.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.

  In describing the present invention, first, a deformation mechanism of the aluminum alloy sheet blank 1 by a general cylindrical diaphragm will be described with reference to FIGS. 2 and 3. FIG. 2 is a vertical cross-sectional perspective view showing a state in which the aluminum alloy plate blank 1 is warm-formed by a cylindrical drawing, and FIG. 3 is a vertical cross-sectional perspective view showing a press product warm-formed by the cylindrical drawing. In FIG. 2, reference numeral 2 denotes a punch for press forming the aluminum alloy plate blank 1 and drawing, 3 denotes a material deformed portion by the punch 2 when the aluminum alloy plate blank 1 is formed, and the periphery of the blank 1. A die 4 for blank-holding the part 4 is a blank holder for blank-holding the peripheral part of the aluminum alloy plate blank 1 together with the die 3.

  Whether or not the drawing is established depends on the force that resists shrinkage deformation in the circumferential direction when the material in the peripheral part of the aluminum alloy sheet blank 1 moves in the central direction by pressurization by the punch 2, that is, flows in. It is determined by the magnitude relationship between the resistance F and the material breaking resistance S of the cross section of the portion where the load is transmitted from the punch 2 to the material. In order for the drawing to be established, the condition of S> F needs to be satisfied.

  Therefore, drawing molding is more easily established as the material breaking resistance S is higher and the flow resistance F is lower. In other words, as the material deformation stress σ0 is larger at the central portion of the aluminum alloy plate blank 1 where the bottom of the punch 2 contacts during molding, the material breaking resistance S is higher, and the aluminum alloy plate held blank during molding The smaller the deformation stress σ1 of the material in the periphery of the blank 1, the smaller the flow resistance F and the higher the drawability.

  FIG. 4 shows a temperature distribution at the time of forming the aluminum alloy plate blank 1 having a substantially rectangular shape by a conventional warm forming technique in which only the peripheral portion (four rounds) held by the blank is heated during forming. Show. The aluminum alloy plate blank 1 is provided with a temperature distribution by heating only the peripheral portion of the four circumferences with the blank hold surface of the die 3 that is blank-held or the blank holder 4. In addition, this warm forming technique is a warm forming technique employed for forming a press-formed product having a small planar shape and a shallow forming depth as compared with a door inner panel or the like.

  The temperature distribution of the aluminum alloy sheet blank 1 includes a temperature T0 between a portion where the bottom of the punch 2 contacts when the blank 1 is formed and a temperature T1 of the peripheral portion where the blank is held when the blank 1 is formed. The relationship T1 is established. Conventionally, a warm forming method has been adopted by deep drawing using an aluminum alloy sheet blank 1 having a temperature distribution in which this relationship is established. By setting the temperature distribution as described above, the deformation stress σ0 of the material at the portion where the bottom of the punch 2 is in contact with the center of the aluminum alloy plate blank 1 during molding and the aluminum alloy plate blank 1 that is blank-held during molding. A relationship of σ0> σ1 is established between the deformation stresses σ1 of the material in the peripheral portion of.

  By making the conditions of the aluminum alloy plate blank 1 at the time of forming in this way, the material fracture resistance S of the cross section of the portion where the load is transmitted from the punch 2 to the material, the material of the peripheral portion of the aluminum alloy plate blank 1 is the punch 2 Considering that it is possible to improve the formability by increasing the relative resistance to the inflow resistance F, which is the force resisting the movement in the pressurizing direction and the deformation accompanying the movement. Molding was done.

  However, when deep drawing is performed using a relatively large flat, substantially rectangular aluminum alloy plate blank 1 used in the molding of a door inner panel with a temperature distribution as shown in FIG. In the material constituting the portion, the short side portion and the long side portion excluding the corner portions of the four corners, in particular, the material in the central portion thereof flows in the direction pressed by the punch 2 preceding the corner portion. As shown in FIG. 5, a phenomenon that cracks 5 and wrinkles occur near the die shoulder occurs at a very high frequency. That is, even if this conventional warm forming technology is adopted, in the deep drawing forming of a press-molded product such as a door inner panel having a large rectangular shape and a deep forming depth, the formability is improved. Was impossible.

  On the other hand, in the warm forming method of the aluminum alloy plate of the present invention, as shown in FIG. 1, the temperature distribution of the aluminum alloy plate blank 1 during forming is more finely defined.

  In the method of warm forming an aluminum alloy plate according to the present invention, the temperature at the time of forming the central portion of the blank where the bottom of the punch 2 contacts when forming the aluminum alloy plate blank 1 is T0, and the aluminum alloy plate blank 1 is blank-held during the forming. Among the peripheral parts, the molding temperature at the center of the short side part of the blank 1 is T1, the molding temperature at the center of the long side part of the blank 1 is T2, and the center part of the corners of the four corners is molding. When the temperature was T3, the molding was performed under the conditions satisfying the following expressions.

  First, the first condition is a condition of T0 <T3. The first is to raise the molding temperature T3 at the center of the corners of the four corners of the aluminum alloy sheet blank 1 from the molding temperature T0 at the center of the blank where the bottom of the punch 2 contacts when the aluminum alloy sheet blank 1 is molded. Is the condition.

  The second condition is a condition of T0 ≦ (T1, T2). The temperature T1 at the time of forming the central part of the short side portion excluding the corners at the four corners of the aluminum alloy plate blank 1 and the temperature T2 at the time of forming the central part of the long side portion are the bottom of the punch 2 at the time of forming the aluminum alloy plate blank 1 Is the temperature T0 or more at the time of molding of the central part of the blank that comes into contact. It is more desirable that T0 <(T1, T2).

  The third condition is a condition of (T1, T2) <T3. The temperature T3 at the center of the corners of the four corners of the aluminum alloy sheet blank 1 is the temperature T1 at the center of the short side part excluding the corners of the four corners of the aluminum alloy sheet blank 1 and the temperature at the long side part. The temperature is higher than the molding temperature T2 at the center.

  In the above description, the temperatures at the time of forming the central portion of each part of the aluminum alloy sheet blank 1 are shown as T0, T1, T2, and T3, respectively, strictly speaking, only the temperatures at the time of forming the central part of each part. However, since parts other than the central part of each part have the same or similar temperatures as those temperatures, the following description will be given without particularly focusing on the central part of each part.

  In the warm forming method of the aluminum alloy plate of the present invention, forming is performed so as to satisfy the above-mentioned conditions.

  Here, the deformation stress of the material at the center of the aluminum alloy sheet blank 1 where the bottom of the punch 2 contacts at the time of forming is σ0, and the deformation of the peripheral material of the aluminum alloy sheet blank 1 that is blank-held at the time of forming. Among the stresses, the deformation stress of the material at the center of the short side portion of the blank 1 is σ1, the deformation stress of the material at the center of the long side portion of the blank 1 is σ2, and the material at the center of the corners of the four corners is The deformation stress is σ3. Since the temperature and the deformation stress are inversely proportional to each other, the relationships of σ0> σ3, σ0 ≧ (σ1, σ2), (σ1, σ2)> σ3 are established between the deformation stresses of the respective parts.

  When deep drawing is performed, the material on the short side and the long side excluding the corners of the four corners of the material that is blank-held during molding is punched prior to the corner material. There is a high possibility that it will flow in the direction pressurized by 2.

  However, when the deep drawing is performed warm using the conditions of the present invention, the temperatures T1 and T2 of the short side portion and the long side portion, which are portions that often flow in advance, are more at the four corners. Since the temperature is lower than the corner temperature T3, the relationship of (σ1, σ2)> σ3 holds as described above. That is, the deformation stresses σ1 and σ2 of the material of the short side portion and the long side portion excluding the corner portions of the four corners are larger than the deformation stress σ3 of the material of the corner portion of the four corners. The possibility that the material on the long side portion moves and flows in the direction in which the material is previously pressed by the punch 2 is reduced. Even if the inflow phenomenon occurs, cracks 5 or wrinkles near the die shoulder as shown in FIG. 5 do not occur.

  Further, since the temperature T3 at the time of forming the corner portions at the four corners is relatively higher than other portions, the deformation stress σ3 is sufficiently small, and the material of the corner portions also moves in the direction pressed by the punch 2. As a result, it becomes easier to flow and contributes to improvement of moldability.

  For the aluminum alloy plate blank 1, aluminum alloy plates of 1000 series, 3000 series, 5000 series, 6000 series, etc. that are standardized by JIS or equivalent to or close to JIS standards can be used. However, in order to have various properties such as basic strength, formability, and corrosion resistance necessary for automobile panels that are difficult to form such as hoods, doors, fenders, roofs, trunks, etc., it is Al-Mg-Si. It is preferable to use a 6000 series aluminum alloy or a 5000 series aluminum alloy which is Al-Mg series.

  As the aluminum alloy plate blank 1, a JIS 5182 aluminum alloy having a thickness of 1 mm tempered to an O material was used, and a test was conducted by performing deep drawing in a warm manner. As shown in FIG. 6, the molding die used for the test was a flat rectangular punch 2, a die 3 having a recess suitable for the punch 2, and an aluminum alloy plate paired with the die 3. The blank holder 4 is configured to blank-hold the peripheral portion of the blank 1.

  A Teflon (registered trademark) sheet was used as a lubricant and molded with a wrinkle holding force of 350 kN. The blank holder 4 and the die 3 incorporate a plurality of heaters, and the corners of the four corners and the corners of the four corners of the peripheral portion of the aluminum alloy sheet blank 1 blank-held by the blank holder 4 and the die 3 are used. The exothermic temperature of the heater can be controlled for each part so that a temperature difference can be provided between the short side part excluding the portion and the long side part.

  In this test, as shown in FIG. 6A, the center point (point 0) of the bottom of the punch 2 and the center of the short side portion in the region where the peripheral portion of the blank 1 and the die 3 are in contact with each other. (Point 1), the center point of the long side part (Point 2), the center point of the corner part (Point 3), a total of four places, temperature measurement by incorporating a thermocouple in the corresponding part of the molding die went. Moreover, the test was done by changing the temperature of these places variously. Furthermore, the punch 2 also has a built-in heater and cooling water pipe, so that the temperature can be controlled. In this test, by gradually increasing the molding depth, the maximum depth that could be molded without the occurrence of cracks 5 was confirmed, and was used as an evaluation item in the test. The test results are shown in Table 1.

In Invention Example 1, the temperature of T3 (corner portion) was set higher than the temperatures of all other parts, and the temperatures of T1 (short side portion) and T2 (long side portion) were the same. In Invention Example 2, the temperature of T3 (corner part) was set higher than the temperatures of all other parts, and the temperatures of T1 (short side part) and T2 (long side part) were different. Furthermore, in Invention Example 3 and Reference Example , the temperature of T3 (corner portion) is made higher than the temperatures of all other portions, and the temperatures of T1 (short side portion) and T0 (center portion) are the same. . The difference between Invention Example 3 and the reference example is the temperature other than T3 (corner portion).

  In these invention examples, the maximum depth that can be molded without cracks being evaluation items is in the range of 140 mm to 150 mm, and the molding depth usually required for door inner panels or the like that are press products having a large molding depth. Then, it was confirmed that the molding can be performed satisfactorily without generating cracks.

  On the other hand, Comparative Examples 1 to 4 are examples that do not satisfy the requirements of the present invention. In Comparative Example 1, molding was performed at room temperature without controlling the temperature of each part. In Comparative Examples 2 to 4, molding was performed by a conventional method in which the temperatures of the peripheral portions (T1, T2, and T3) were uniformly increased. The differences between Comparative Examples 2 to 4 are the temperatures of T0 to T3.

  In these comparative examples, the maximum depth that can be molded without cracking of the evaluation items is in the range of 60 mm to 80 mm, and the molding depth normally required for door inner panels or the like that are press products having a large molding depth. It was confirmed that it could not be used for molding door inner panels.

    In addition, in order to confirm that the temperature and the deformation stress of the material are in an inversely proportional relationship, a tensile test of an aluminum alloy sheet blank was also performed separately. The test results are shown in Table 2 for reference.

  In this test, the deformation stress at the time of 10% tensile deformation at each temperature of the material used in the test (JIS 5182 aluminum alloy) was confirmed. As is apparent from this test result, the temperature and the deformation stress of the material are in an inversely proportional relationship.

It is explanatory drawing which shows the temperature distribution at the time of shaping | molding of the aluminum alloy plate blank used for the warm forming method of the aluminum alloy plate of this invention. It is a longitudinal cross-sectional perspective view which shows the state which is warm-forming the aluminum alloy board blank with a cylindrical aperture_diaphragm | restriction. It is a longitudinal cross-sectional perspective view which shows the press product warm-formed by the cylindrical aperture_diaphragm | restriction. It is explanatory drawing which shows the temperature distribution at the time of shaping | molding at the time of shaping | molding an aluminum alloy plate blank with the warm shaping | molding technique conventionally employ | adopted as shaping | molding of a press product. It is a perspective view which shows the state of the press product which shape | molded the aluminum alloy plate blank with the warm forming technique conventionally employ | adopted for shaping | molding of a press product. The state at the time of shaping | molding of the shaping die used for the test of an Example and an aluminum alloy plate blank is shown, (a) is the top view, (b) is a longitudinal cross-sectional view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Aluminum alloy plate blank 2 ... Punch 3 ... Die 4 ... Blank holder 5 ... Crack

Claims (1)

In a warm forming method of an aluminum alloy plate in which a plane substantially rectangular shape aluminum alloy plate blank is deep-drawn into a flat, substantially rectangular shaped product having a flange portion around it,
Molding of the central part of the short side portion of the blank among the peripheral parts of the aluminum alloy sheet blank that is held by blanking at the time of molding T0 at the center part where the punch bottom contacts with the molding of the aluminum alloy sheet blank T0 <T3, T0 ≦ (T1, T2) where T1 is the molding temperature at the center of the long side of the blank, T2 is the molding temperature at the center of the four corners, and T3 is the molding temperature at the center of the four corners. , (T1, T2) <T3 after satisfying each expression,
A method of warm-forming an aluminum alloy plate, characterized in that the forming is performed such that T1 and T2 are 150 ° C or higher , and the temperature difference between T3 and T1 and T2 is 50 ° C or higher .