JP2014176883A - Automobile panel press molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automobile panel press molding method capable of suppressing generation of surface distortion following to molding of a recess part even if a large-sized automobile outer panel is subjected to press molding by normal temperature (room temperature) using a heat treatment type aluminum alloy plate as a raw material.SOLUTION: A raw material heat treatment type aluminum alloy plate such as 6000 base is subjected to special restoration processing at high temperature in a short time. Then, on an automobile panel 11 having a recess 12 on a part of continuous curved surfaces, press molding is performed by using molds 2, 3 capable of moving a mold 5a for molding the recess 12 partially at normal temperature, and generation of surface distortion is suppressed.

Description

  The present invention relates to a method for press-molding a material heat-treatable aluminum alloy plate on an automobile panel (vehicle panel).

  Conventionally, aluminum alloy plates have also been used as panel materials for panels such as outer panels (outer plates) and inner panels (inner plates) of automobile panel structures. These aluminum alloy panel materials include Al-Mg-based 5000 series that is thin, high-strength and excellent in formability, and heat-treatable Al-Mg-Si-based series that are also excellent in bake hardenability (BH). Aluminum alloy plate materials such as 6000 series are used. These aluminum alloy sheets (hereinafter also simply referred to as aluminum alloy sheets) are rolled sheets of hot rolled sheets and cold rolled sheets, and are formed into a panel (product) shape by press forming.

  Large automotive outer panels such as doors, luggages, fenders, hoods, trunk lids, etc. of automobile panels have a concave shape on a part of a continuous curved surface, for example, handle seats, lamp seats, licenses (number plates) A recessed portion (an overhang portion or an embossed portion) having a predetermined depth is provided partially, for mounting an instrument or member such as a seat or drawing a wheel arch.

  Usually, the molds for forming these recesses are integrally arranged in a mold for molding the overall shape (overall curved surface) of the automobile panel, and the recesses and the overall shape of the automobile panel are simultaneously press-molded. However, this recess (overhang) needs to have a certain depth, and when the recess connected to the entire curved surface as described above, including the continuous curved surface around the recess shape, is press-molded, Distortion tends to occur, and surface distortion (surface distortion, surface distortion) is unavoidable.

  When press-molding an aluminum alloy plate with a lower cracking limit than a steel plate, it is necessary to lower the tension at the time of molding than in the case of a steel plate, which is the surface when pressing an aluminum alloy plate. Helps to generate distortion. When this surface distortion occurs, the aluminum alloy sheet has a lower elastic coefficient than that of the steel sheet, and therefore it is difficult to eliminate the surface distortion once generated by further press forming or correcting. Therefore, the problem of surface distortion becomes a fatal problem in the above-described large-sized automobile outer panel in which the design is important.

  On the other hand, there is a great limitation to suppress the surface distortion by improving the formability on the aluminum alloy material side. For this reason, various improvements from the processing side have been proposed in the past in forming into an aluminum alloy panel such as an automobile panel having the concave portion in part.

  For example, conventionally, various special molding methods such as warm molding, blow molding, hydroforming, and electromagnetic molding have been studied as methods for suppressing the occurrence of such surface distortion. If such a special molding method is used, there is a possibility that molding can be performed while suppressing occurrence of surface distortion. However, such a molding method requires a special press working method, a special molding die, or a new device, and there is a problem that the manufacturing cost of the panel increases.

  For this reason, various methods for suppressing the occurrence of surface distortion have been proposed in the past using basic press forming at normal temperature (room temperature).

  For example, in Patent Document 1, when forming a concave portion (an overhang portion, an embossed portion) provided partially such as a handle seat in an automobile side door outer panel or the like for a metal plate such as a steel plate, the concave portion is formed. There has been proposed a method for suppressing the occurrence of surface distortion by using a mold in which a mold that is divided and movable is integrated. In this patent document 1, the molding location of the metal plate in the concave portion is partially heated to a temperature of 200 to 300 ° C., and the continuous curved surface of the entire panel other than the concave portion is pressed by a die (pressing die). After forming, only the concave portion is formed using the mold that is divided and movable, thereby suppressing the occurrence of surface distortion accompanying the formation of the concave portion.

  Patent Document 2 also proposes a method of forming an automobile panel having a concave portion in a part of a continuous curved surface for a steel plate. In Patent Document 2, a mold in which a mold that can be divided and formed to form the concave portion is integrally incorporated, and a curved surface other than the concave portion is cold-cooled using a first male die and a female die. There has been proposed a two-stage molding method in which, after molding, the concave portion is partially cold-molded using a second male mold and a female mold. This Patent Document 3 is also a steel plate, and the second-stage molding in which the concave portion is partially molded using a second male mold and a female mold is similar to the first-stage overall molding. It is said that it can be molded cold.

  In Patent Document 3, for a 5000 series aluminum alloy plate such as 5182, molding is performed using a mold in which a mold that can be divided and formed to form the concave portion is integrated. In Patent Document 3, cold forming of the cup-shaped overall shape and warm forming by partial heating of the protruding portion (concave portion) of the top of the cup at 150 to 250 ° C. are performed simultaneously to obtain a high protruding portion. It has been described. However, what is actually formed in Patent Document 3 is a punch diameter of 200 mm and a recess diameter of only about 30 mm.

  In Patent Document 4, a split mold method (hereinafter, also simply referred to as a split mold method) using a mold in which a split movable mold that forms a recess is integrated is referred to as an automobile side door made of an aluminum alloy plate. It has also been proposed as a method for suppressing surface distortion when molding an outer panel or the like. In Patent Document 4, a curved surface other than the concave portion is formed using a first male die and a female die, and then the concave portion is partially formed using a second male die and a female die. When forming into the concave portion of the aluminum alloy plate is partially heated to a temperature of 150 to 400 ° C., and a curved surface other than the concave portion is pressed with a press mold, and then the concave portion is formed. It describes that it is formed by an overhanging process and suppresses the occurrence of surface distortion accompanying the formation of the recess.

JP 59-229242 A Japanese Utility Model Publication No.59-1429 JP-A-6-170453 JP 2010-227978 A

As described above, the occurrence of surface distortion associated with the formation of the concave portion (the overhang portion) is more remarkable in the aluminum alloy plate, which is inferior in formability compared to the steel plate, and its influence and problem are large. And the generation | occurrence | production of this surface distortion becomes remarkable, so that the magnitude | size and depth of the said recessed part (overhang | projection part) are large, so that the automotive panel which uses an aluminum alloy plate as a shaping | molding raw material becomes large. Here, the above-described large-sized automobile panel in which the problem of occurrence of surface distortion becomes remarkable refers to a panel having an area of 0.5 m ² or more in plan view as a guide.

  In the molding method based on the split mold method of Patent Documents 1 to 4, there is a limit in suppressing the occurrence of surface distortion associated with the molding of the concave portion in the molding of the exemplified large automobile outer panel made of an aluminum alloy plate. is there.

  Further, in Patent Documents 1, 3, and 4, in common, the mold structure is more complicated and the molding operation is complicated because the recess is partially heated, and the production efficiency of the molding process is significantly reduced. It also leads to things.

  The limit of the suppression of the occurrence of surface distortion in these prior arts depends on the complexity of the design (shape) of the exemplified large automobile outer panel. The door outer panel, which is a representative example of a large automobile panel, is provided with a linear convex shape as shown in FIG. 4 and a partial concave portion in the vicinity thereof as a door handle due to recent design requirements. A concave design having a more complicated cross-sectional shape is employed. In order to obtain such a concave design with good shape accuracy, not only advanced molding technology is required, but the material plate is molded in a situation where it does not stick to the mold (not pressed), so the surface around the handle The distortion tends to get worse. Incidentally, FIG. 4 shows the door outer panel in a front perspective view on the left side and a sectional view on the right side.

  Furthermore, when a heat-treatable aluminum alloy plate such as 6000 series is used as the panel material, there is also a problem of age hardening at normal temperature (room temperature). Usually, after a solution treatment (high-temperature heat treatment and quenching treatment) is performed by a material manufacturer and then processed by an automobile or parts manufacturer, it is kept at room temperature for a certain period of time for industrial transportation or storage. Be drunk. In the meantime, the heat-treatable alloy is age-hardened by natural aging (normal temperature aging, room temperature aging), and the yield strength of the material increases, so that the springback during press forming becomes remarkable. Such a tendency further makes it difficult to ensure shape accuracy such as molding of a panel part having a complicated shape as described above and suppressing surface distortion.

  For this, conventionally, in order to cancel the natural aging, there is also a means for reducing the strength such as the proof stress by performing a restoration process (recovery process) for heating the material aluminum alloy plate before press forming. is there. However, if the proof stress is too low by this restoration process, the bake hardness (hereinafter also referred to as BH property) during the artificial age hardening process in the paint baking process (heat treatment, hereinafter also referred to as bake) of the automobile body is likely to deteriorate, There was a problem that the performance as an automobile panel material deteriorated. That is, in the conventional restoration process, it is difficult to achieve both formability and BH property.

  The present invention has been made in view of such problems. Even if the above-described large-sized automobile outer panel is press-molded at room temperature (room temperature) using a heat-treatable aluminum alloy plate as a raw material, surface distortion caused by the formation of the recess is generated. It is an object of the present invention to provide a press molding method for an automobile panel that can suppress the above.

  In order to achieve the above object, the gist of the press molding method of the automobile panel of the present invention is that the heat treatment-type aluminum alloy plate is subjected to a restoration treatment in a temperature range of 220 ° C. to 280 ° C. for a time of 0.1 seconds or more and 150 seconds or less. After holding, it is cooled to room temperature at an average cooling rate of 10 ° C./second or more, and then at a room temperature, a mold part for molding the recess is made movable in a shape having a recess on a part of a continuous curved surface. It is to perform press molding using a mold.

  In the present invention, first, unlike a conventional restoration process, the material aluminum alloy plate is subjected to a restoration process under a specific condition of a relatively high substantial temperature and an absolute short-time holding. And it press-molds in the subsequent short time. Then, press molding is performed by molding at room temperature by a split mold method using a mold in which a split movable mold that forms a recess is integrated.

  With the combination of such a special restoration process in advance and press molding of the split mold method, even with a naturally aged high-strength heat-treatable aluminum alloy sheet as a material, the door outer panel having a complicated cross-sectional shape shown in FIG. Without using the above-described special molding method, basically, press molding that is generally used can be used to suppress the occurrence of surface distortion accompanying the molding of the concave portion and to ensure the shape accuracy.

  In addition, due to the heat-treatable aluminum alloy sheet, the strength varies depending on the degree of natural age hardening and how it progresses, and the problem of variations in strength and springback amount is solved. The mechanical properties and springback amount of the formed sheet material are also eliminated. Can be made uniform. Furthermore, if the 0.2% proof stress of the material aluminum alloy sheet after the restoration treatment is reduced to a specific 80 to 150 MPa, the member strength is increased to 200 MPa or more with a 0.2% proof stress in the artificial age hardening treatment after forming. It can be secured. As a result, both formability and BH properties can be achieved.

It is sectional drawing of the press apparatus which shows the one aspect | mode of the press molding of this invention. It is a top view which shows the door outer panel shape | molded by the press apparatus of FIG. It is sectional drawing of the press apparatus which shows another aspect of the press molding of this invention. It is explanatory drawing which shows the door outer panel example which this invention shape | molds. It is explanatory drawing which shows the out-of-plane displacement measuring device by a 3 point gauge. It is explanatory drawing which shows the generation | occurrence | production mechanism of a surface distortion. It is explanatory drawing which shows the relationship between the position of a peripheral part of a recessed part, and a surface distortion amount in an Example.

Mechanism of surface distortion generation:
As a premise, first, the mechanism of occurrence of surface distortion, which is a problem in the present invention, will be described below with reference to FIG. Note that the mechanism and state of occurrence of surface distortion, which is a subject of the present invention, are also disclosed in the above-mentioned Patent Documents, particularly Patent Document 4. First, FIG. 6A is a cross-sectional view of the press device, illustrating a method of forming the recess (grip seat) 12 of the side door outer panel 11 after the entire shape is formed. In FIG. 6A, the outer panel 11 is fixed by the wrinkle presser 40, and the molding surface 20 b of the recess (grip seat) 12 of the mold 20 is partially formed in the downward arrow direction by the punch 30. Press molding.

  In such a case, as shown in FIG. 6 (b) in plan view, the outer panel 11 being molded is shown in a plan view, and as the material (aluminum alloy) flows into the recess 12 in the direction of the arrow A1, the horizontal direction of the arrows A2 and A3. In addition, the material inevitably and unevenly moves. For this reason, surface distortion X occurs at the four corners of the peripheral portion 12 a of the recess 12. When surface distortion X occurs in this way, the mold is removed and the outer panel 11 is opened, and the outer panel 11 after molding is shown in a perspective view in FIG. As a result, a convex portion Y is generated. The occurrence of such surface distortion deteriorates the shape accuracy such as the flatness of the automobile panel, and in particular, the outer panel for the above-mentioned use impairs the appearance or the appearance. For this reason, if a troublesome correction work is required or the occurrence of surface distortion is significant, the correction cannot be made even by correction, and it cannot be employed as a side door outer panel.

  Other causes of surface distortion X include flaking due to circumferential compressive stress due to minute inflow of material at the corners of recesses 12, and bulges around recesses due to bending moments (overhangs and embossed parts) The increase in surface distortion due to elastic recovery is raised. Further, surface distortions unique to these parts are also generated in the license seat and the lamp seat of the luggage outer panel, and the wheel arch of the fender outer panel other than the recess 12 of the door outer panel 11.

In addition, such a problem of surface distortion is not only a problem of the above-described concave portion (projecting portion), but is a door outer panel, a vertical wall portion of a front fender outer panel, a wind corner portion of a rear fender outer panel, a trunk lid, Aluminum alloy with an area of 0.5 m ² or more in plan view, with some of the recesses (overhangs) that cause surface distortion, such as the disappearance of the character line of the outer panel of the hood and the base of the rear fender pillar outer panel This is a problem common to large automobile panels.

  Hereinafter, embodiments of the present invention will be specifically described in order for each requirement.

Material aluminum alloy plate:
In the present invention, a 6000 series aluminum alloy plate of Al-Mg-Si type is particularly preferable as a heat treatment type alloy excellent in formability and bake hardenability, which is a material aluminum alloy plate for automobile panel materials. The material aluminum alloy plate is a rolled plate material such as a hot-rolled plate or a cold-rolled plate, and is tempered from these rolled plates, and is formed into a panel (product) shape by press forming.

(composition)
In order for the 6000 series aluminum alloy plate to satisfy the basic performance such as the necessary strength, tension rigidity, dent resistance, bending rigidity, torsional rigidity, etc. as the door outer panel of FIG. It is preferably made of a plate of 6000 series aluminum alloy composition containing Si: 0.4 to 1.5%, Mg: 0.4 to 1.0%, with the balance being Al and inevitable impurities. . In addition, in the production of the material plate, there is an impurity element that is inevitably mixed by using a low-purity metal or scrap material during melting and casting of the aluminum alloy, and is included in the unavoidable impurities. As specific examples, the following elements are allowed to be contained. Fe: 0.5% or less, Zn: 0.5% or less, Cu: 1.0% or less, Mn: 0.5% or less, Cr: 0.5% or less, Zr: 0.3% or less, Ti: 0.1% or less. In addition, all the element amounts described in% are mass%.

(Production method)
A material plate made of such a 6000 series composition or other 3000 series aluminum alloy composition is produced by a conventional method or a known method. That is, an aluminum alloy ingot having a desired composition is subjected to homogenization heat treatment after casting, and hot rolling or further cold rolling is performed to obtain a predetermined material plate thickness. In addition, the aluminum alloy sheet (hot rolled sheet, cold rolled sheet) with a predetermined thickness is subjected to tempering such as normal solution treatment and quenching treatment, and subsequent reheating treatment at low temperature or pre-aging treatment. It is processed and manufactured as a raw material aluminum alloy plate.

Restoration process:
In the present invention, the material aluminum alloy plate after the tempering process manufactured in this way is subjected to a restoration process before press molding to an automobile panel material without artificially tempering except natural aging. Artificial age-hardening treatment and heat treatment other than natural aging are not necessary for the tempered aluminum alloy sheet, and it hinders the manifestation of the effect of restoration treatment and is harmful.

  In this restoration process, as a specific condition, a heating process is performed in which the body temperature of the plate is maintained for at least 0.1 seconds at a temperature range of 220 ° C. to 280 ° C. and for 150 seconds at a temperature range of 220 ° C. to 280 ° C. Immediately after this heat treatment, it is rapidly cooled to room temperature (room temperature) at an average cooling rate of 10 ° C./second or more. Then, press molding is performed at room temperature as soon as possible. At this time, the form of the material aluminum alloy plate may be a cut plate cut from the coil or may remain the coil. However, since the equipment for performing short-time heating and rapid cooling as the restoration process can be simplified, the form of the material aluminum alloy plate is preferably a cut plate cut into a predetermined size.

  Unlike the above-described conventional restoration process, the restoration process according to the present invention restores the material aluminum alloy plate under a specific condition that the actual temperature is relatively high and the absolute holding time is absolutely short. It is recognized that the above-described conventional restoration process satisfies the conditions (such as a specific substance temperature of a material, a specific extremely short time holding, and a rapid cooling at a specific cooling rate) like the restoration process of the present invention. Absent. Therefore, the probability that the moldability and the BH property cannot be achieved inevitably increases in the conventional restoration process.

  The restoration processing mechanism of the present invention is as follows. In a heat-treatable alloy such as 6000 series, precipitates (made of Mg and Si), which are hardening elements, are dissolved in the matrix by the solution treatment. In this state, the strength is low and the moldability is good. However, during transportation, storage, and other processes from the material plate manufacturer to automobiles and parts manufacturers, a minute room temperature aging product precipitate A is generated and grown by being placed at room temperature (room temperature) for a certain period of time. Increases the strength of the material plate.

  When such a room temperature aging state material plate is heated to a predetermined temperature as in a restoration process, the minute room temperature aging product precipitate A, which is thermally unstable, is dissolved again in the matrix and disappears. And it returns to the structure | tissue state immediately after solution forming. At this time, the conventional restoration process described above is a process in which all the fine precipitates are re-dissolved in the matrix by heating the material plate in the normal temperature aging state to a temperature of 150 to 350 ° C. for a relatively long time. Yes, it is in a state immediately after the solution hardening treatment.

  On the other hand, in the present invention, unlike these conventional restoration processes, the material aluminum alloy sheet is subjected to a restoration process under a specific condition of having a relatively high substantial temperature and being absolutely held for a short time. For this reason, although all the thermally unstable room temperature aging-generated microprecipitates A are re-dissolved in the matrix, not all the microprecipitates are re-dissolved, and the heat contributes to the bake hardness. Stable fine precipitate B remains without being dissolved.

  This fine precipitate B contributes to the bake hardness formed in the aluminum alloy sheet structure by a series of tempering processes at the time of manufacturing the sheet, such as a preliminary aging process after the solution hardening process, It is a stable fine precipitate. In the present invention, the restoration process is performed under specific conditions of a relatively high substantial temperature and an absolute short time retention, so that the fine precipitate B contributing to the bake hardness is not re-dissolved. It can be left. On the other hand, all the thermally unstable room temperature aging-generated microprecipitates A that inhibit the moldability and BH properties can be re-dissolved in the matrix.

  For this reason, when the split mold press molding is performed within a short period of time, such as within 240 hours after the restoration process, the spring back during the press molding is suppressed, and the surface distortion is particularly improved as an excellent shape accuracy. Can be suppressed. That is, even with a naturally aged high-strength material aluminum alloy plate, without using the special molding method described above, such as a door outer panel having a complicated cross-sectional shape adopting a concave design as shown in FIG. Molding with high shape accuracy can be achieved by cold (room temperature) press molding.

  In addition, excellent bake hardness can be exhibited even after the restoration process. Specifically, if the 0.2% proof stress of the material aluminum alloy sheet after the restoration treatment is reduced to the above-described specific 80 to 130 MPa, the member strength is reduced to 0 by the artificial age hardening treatment after forming. It can be secured to 200 MPa or more with a 2% yield strength.

  Also, depending on the material aluminum alloy plate, the strength varies depending on the degree of natural age hardening and how it progresses, and the problem of variations in strength and springback amount is solved, and the mechanical properties and springback amount of the formed material plate are made uniform. Can be planned.

  Furthermore, even a high-strength aluminum alloy plate that is naturally aged, it is also a high-strength aluminum alloy plate that is formed into a member by forming with residual stress selected from bending and punching. However, the residual stress at the position of the member that has undergone the forming process can be reduced. This is particularly advantageous when the automobile material after molding is not subjected to solution treatment and quenching treatment, and the residual stress imparted by molding cannot be removed by these tempering after molding. Since the residual stress can be reduced in this way, the SCC resistance (stress corrosion cracking resistance) at the molding site does not deteriorate.

(Restore processing conditions)
The conditions for the restoration process of the present invention are important for the manifestation of the above-described effect by this restoration process. That is, with respect to the heat treatment conditions, only the re-solution of the thermally unstable room temperature aging-generated fine precipitates A is appropriately performed without re-dissolving the fine precipitates B contributing to the bake hardness. The condition is to remain.

  For this purpose, first, the optimum heating (heating treatment) temperature is set in the range of 220 ° C. or more and 280 ° C. or less as the substantial temperature of the material plate to be restored, not the ambient temperature. When the temperature is lower than 220 ° C., the fine precipitate A is not sufficiently re-dissolved, so that the required amount of proof stress is not lowered and excellent shape accuracy after press molding cannot be obtained. Moreover, BH property also falls and required strength cannot be obtained.

  On the other hand, when the heating temperature exceeds 280 ° C., the solid precipitate B is re-dissolved together with the fine precipitate A, and the strength after the restoration treatment is excessively lowered. As a result, although good shape accuracy can be obtained, an increase in strength (BH property) due to heat treatment at the time of subsequent coating baking cannot be obtained, and the function as an automobile panel material cannot be achieved.

  Next, the heating and holding time is also important, and the heat treatment time in the restoration process is that the temperature of the material plate is in the temperature range of 220 ° C. or higher and 280 ° C. or lower, It is effective if the temperature of the board body is within this temperature range. For example, even if the heating body is in direct contact with the plate and immediately separated, the actual temperature of the material plate is within this temperature range even if it is about 0.1 seconds, which is a measure of instantaneous holding (time). Is effective. On the other hand, if this holding time is too long, although depending on the temperature conditions, the fine precipitates B that contribute to the bake hardness due to the restoration process are re-dissolved, or conversely, precipitation proceeds. For this reason, the heating and holding time is set to 0.1 to 150 seconds, preferably 0.1 to 100 seconds, as described above.

  The cooling after the heat treatment is immediately cooled to normal temperature (room temperature) at an average cooling rate of 10 ° C./second or more immediately (without time delay) after the heat treatment is completed. The reason for rapid cooling to room temperature is to allow subsequent press molding to be used as it is by a general-purpose press molding method and apparatus at normal temperature. In addition, when the cooling rate is too slow, fine precipitates may be formed again. Therefore, the cooling rate is preferably not less than the appropriate cooling rate. However, if the cooling rate is too fast, cooling distortion due to non-uniform temperature distribution is likely to occur, and deformation of the material remains even after press processing, so that the quality as a pressed product is deteriorated. For this reason, the average cooling rate to room temperature is preferably in the range of 10 to 500 ° C./second. As the cooling means, air cooling, water cooling, mist cooling, or the like can be selected as the forced quenching means for obtaining the optimum cooling rate range. Control of the cooling rate by these forced quenching is possible by the amount of each refrigerant used (the amount sprayed or immersed in the material) in accordance with the thickness and size of the plate.

  Here, normal temperature or synonymous room temperature referred to in the present invention is, for example, a normal season in a factory or outdoors, such as about 40-30 ° C., about 18-30 ° C., several ° C., 0 ° C., about 0 ° C. or less. It means the temperature and temperature range (area) considering factors.

  The heating during the heat treatment is rapid heating (rapid heating) at an average heating rate of 0.5 ° C./second or more, so that the material temperature of the material plate can be kept within the heating temperature range for only a short time. This is preferable because it is possible. In relation to this, the restoration process may be, for example, a method based on contact with a heating body in addition to a non-contact method such as charging and unloading into an atmospheric furnace, induction heating, laser heating, or the like.

Press molding:
In order to exhibit the effect of the restoration process described above in press molding, it is preferable to perform press molding as soon as possible (without time delay) after the restoration process. That is, it is preferable to carry out the 6000 series material aluminum alloy plate while the natural aging after the restoration treatment has not progressed or while the natural aging has progressed.

  As a guideline, of course, it depends on the manufacturing conditions of the material aluminum alloy plate. However, if these are determined by pushing them, the (required) time from immediately after the rapid cooling to the room temperature of the restoration process to the start of press forming is 240. Within time (hr). Exceeding this, the higher the strength of the aluminum alloy sheet, the more the natural aging after the restoration treatment proceeds, and the formability is remarkably lowered, and the significance of the restoration treatment is lost. However, after the restoration process (cooling) and before press molding, pre-processing and pre-preparation of the material plate, which is generally performed prior to press molding, such as providing an oiling process for lubrication if necessary, It may be made naturally during this time.

  Here, the press forming which the present invention presupposes is cold (room temperature) press forming, and a blank made of a raw material aluminum alloy plate (thin plate) is locally heated in advance (prior to press forming), Cooling means that molding is performed at room temperature = cold as it is (with uniform strength regardless of the part) without providing a soft part. And even during press molding, the blank is not heated to a hot or hot state, and without using a pressure medium such as a special liquid (hydraulic pressure), the blank is dies, a blank holder, a punch, etc. It is said to be in direct contact with a mold composed of

(Split molding machine with split mold)
Below, the embodiment of a press molding apparatus is demonstrated using drawing. FIGS. 1A, 1B, and 1C are partial cross-sectional views of a press apparatus showing an embodiment of press molding of the present invention. FIG. 2 is a plan view showing an embodiment of the door outer panel 11 formed by the pressing device of FIG. FIG. 1 shows the molding of the AA cross section of the panel 11 of the product part of FIG. 3 (a) and 3 (b) are cross-sectional views of the press device showing an enlarged main part near the recess 12 in FIG.

  FIG. 1 shows a mold part for forming a recessed part which is movable in a split manner with respect to the restored aluminum alloy plate (blank). After the concave part is partially formed in advance, the automobile shown in FIG. The aspect which draw-draws to the whole shape (continuous curved surface other than the recessed part 12) of the side outer panel 11 is shown.

  In FIG. 1, first, partial press molding of the recess 12 shown in FIGS. 1A and 1B is performed, and then continuous curved press molding other than the recess 12 shown in FIG. 1C is performed. In the same press machine. Finally, an automobile side outer panel 11 shown in a plan view in FIG. 2 is formed. Here, the molded recess 12 in FIG. 2 is a door handle portion (grip seat) of the door outer panel.

  In FIG. 1 (a), reference numeral 1 denotes a heat-treatable aluminum alloy plate that is the restored forming material (blank), and 1a denotes a formed portion corresponding to the recessed portion 12 to be stretch-formed. In FIG. 1C, 11 is a door outer panel in which the heat-treatable aluminum alloy plate 1 is formed, 12 is a recessed portion (door outer panel holding seat) 1a, and 12a is a periphery of the recessed portion 12 that has been formed. Each part (flat part) is shown.

  In the press apparatus shown in FIG. 1, 2 is a die which is a first female die, 3 is a punch which is a first male die, and 4 is a wrinkle presser. Drawing is performed to form the entire curved surface shape.

  On the other hand, 3a is a second female mold for projecting the recess 12 and is provided in a space in the punch 3 which is the first male mold and is integrated into the punch 3. Yes. The second male mold 5a is provided at a position corresponding to the molding of the recess 12 of the aluminum alloy plate 1 so as to be separated from the punch 3 and to be able to advance and retreat independently.

  The punch 5 only needs to have a structure in which a predetermined support reaction force is applied from the tip 5a to the material plate 1 during the overmolding of the recess 12 and is supported on the die 2 main body by a spring 6 as illustrated. Has been. As a structure for applying the predetermined support reaction force, support by a hydraulic pressure, a gas spring, or the like may be used in addition to the spring 6. Further, the peripheral portion of the punch 5 of the die 2 may be divided from the die 2 main body so as to be movable independently so as to be a plate presser type in the overhang processing of the concave portion 12.

(Split molding method using split mold)
The material aluminum alloy plate (blank) 1 subjected to the restoration process is press-molded on the automobile side outer panel 11 shown in FIG. 2 by the press molding apparatus shown in FIG. 1 without time delay (immediately after the restoration process). Is done. At this time, prior to drawing into the entire shape of the automobile side outer panel 11 shown in FIG. 1 (c) (a continuous curved surface other than the recess 12), as shown in FIG. Molded.

  In FIG. 1 (b), the concave portion corresponding portion 1 a is pressurized by the punch 5 (tip 5 a) that is elastically supported by a spring and can be divided (independently) moved, and the concave portion 3 a of the mold 3. Thus, the concave portion 12 is formed. At this time, the punch 5 which is a divided movable portion is arranged on the die 2 side from the bottom dead center at the initial stage of molding in FIG. 1A, and moves to the bottom dead center together with the die 2 as the molding proceeds. ing.

  Next, following the formation of the concave portion 12, as shown in FIG. 1 (c), a drawing process is performed to the overall shape of the automobile side outer panel 11 (a continuous curved surface other than the concave portion 12). . This press molding itself is the same as a conventionally known method, and the drawing is performed by the cooperation of the punch 3 that is the first male mold, the die 2 that is the female mold, and the wrinkle presser 4 of the aluminum alloy plate 1. Processing is performed. At this time, although not shown, a draw bead on the outer periphery of the product shape is provided on the wrinkle presser 4 to control the amount of material flowing into the die 2 from the outer periphery of the product shape.

  As described above, in the present invention, for the blank 1 that has been subjected to the restoration process, the body of the automobile side outer panel 11 is molded using a mold in which the recess 12 is movable with respect to the mold body. Apart from that, it is partially press-molded. As a result, when forming a continuous curved surface other than the concave portion 12 which is the latter stage of molding the door outer panel 11, as shown in FIG. 1 (c), a larger tension indicated by left and right arrows is applied to the material around the concave portion 12. can do. For this reason, during the formation of the recess 12, “wrinkles” generated on the peripheral edge of the punch 5 (both left and right sides in the figure) as shown in FIG. 3B can be eliminated by this tension, and FIG. As shown in c), the occurrence of surface distortion around the recess 12 is suppressed.

  Further, when forming the concave portion 12, by holding the peripheral portion 12a around the concave portion 12 with the die 2 and punch 3 serving as a pressing mold, the material inflow into the concave portion 12 can be suppressed. The curved shape of the entire panel formed in advance can be maintained, and the occurrence of surface distortion can be further suppressed.

  In the overhanging process to the concave portion 12, the pressing force of the peripheral surface (peripheral molding surface) 3b of the second female die 3a, which is a presser die of the plate, or further expanded, the die 2 (the punch in the die 2) 5) and the punch 3 surface are preferably set to 0.6 MPa or more. If these pressures are small, depending on the conditions, the material inflow into the female mold 3a in the overhang processing of the concave portion 12 can not be sufficiently suppressed, the curved shape of the entire pre-formed panel cannot be maintained, There is a possibility that the occurrence of surface distortion cannot be suppressed.

  Here, the peripheral surface (peripheral molding surface) 3b of the second female die (extension molding surface) 3a in the punch 3 is flat in order to mold the flat peripheral portion 12a around the recess (extension portion) 12. And However, the peripheral portion 12a is not necessarily flat as in this aspect, depending on the design shape of the panel and the panel application, and may have an arbitrary oblique side shape or curved surface shape. In such a case, the peripheral surface (peripheral molding surface) 3b of the second female die (extrusion molding surface) 3a does not necessarily have to be a flat portion as in this embodiment, and corresponds to the shape of the peripheral portion 12a. Arbitrary shape.

FIG. 2 shows a side door outer panel molded product molded in the embodiment of FIG. The side door outer panel 11 and the like, which is the subject of the present invention, is a large-sized automobile outer panel exemplified as described above, in which the problem of occurrence of surface distortion becomes significant and the area in plan view is 0.5 m ² or more. It is.

  In the molded article 11, the occurrence of surface distortion accompanying the molding of the concave portion (overhang portion) 12 is suppressed, and the convex portion Y as shown in FIG. Excellent shape accuracy such as flatness and aesthetics. In addition, since the generation of surface distortion is suppressed by such a concave portion forming method, deeper (higher) and larger concave portions can be formed (overhang processing) as compared with press molding. The advantage of increasing the degree of freedom in designing the shape of the recess (projecting portion) is also great.

  According to this aspect, since the press apparatus to be used can be modified only by partially providing the punch 5 and the female mold 3a, which are the second male mold, to the existing press apparatus, It is not necessary to modify the press device.

(Other press molding aspects)
3 (a) and 3 (b) show in advance in FIG. 2 before forming the recess 12 partially, contrary to FIG. 1, when the blank subjected to the restoration process is quickly formed. A mode in which the overall shape of the automobile side outer panel 11 (a continuous curved surface other than the recess 12) is first drawn is shown.

  In FIG. 3, 1 is a heat-treatable aluminum alloy plate that is the reprocessed forming material (blank), and 1a indicates a formed portion corresponding to the recessed portion 12 to be stretch-formed. 11 is a molded door outer panel, 12 is an overmolded recess (door outer panel handle seat), and 12a is a peripheral portion (flat portion) of the overmolded recess. The press apparatus shown in FIG. 3 has basically the same structure as the press apparatus shown in FIG.

  In FIG. 3, first, as shown in FIG. 3A, the material aluminum alloy plate 1 subjected to the restoration process is drawn into the entire curved surface of the automobile side outer panel 11 without delay. This press molding itself is the same as in FIG. 1 (c), and is due to the cooperation of the punch 3 which is the first male mold, the die 2 which is the female mold, and the wrinkle presser 4 of the aluminum alloy plate 1. Drawing is performed. At this time, although not shown in the figure, a draw bead on the outer periphery of the product shape is provided on the wrinkle retainer 4 to control the amount of material flowing into the die 2 from the outer periphery of the product shape.

  After drawing the entire shape, as shown in FIG. 3 (b), the concave portion (projecting portion) 12 of the door outer panel 11 includes a punch 5 as a second male die, a female die 3a, Is partially stretched and molded.

  Also in this case, a large tension can be applied to the material around the recess 12 by press-molding using the mold in which the recess 12 is movable with respect to the mold body. For this reason, as in the case of FIG. 1, the wrinkles generated on the periphery of the punch 5 (on the left and right sides in the figure) during the formation of the recess 12 are eliminated by this tension, and the occurrence of surface distortion is suppressed. Is done.

  The method for forming the side door outer panel has been described above. However, according to the present invention, the method can be applied to the formation of the concave portion of the other large automobile outer panel as described above.

  The automotive panel material after press molding is subjected to an artificial age hardening treatment in a paint baking (heat treatment) process by itself or after assembling the automobile body to increase the strength. By such an artificial age hardening treatment, for example, in an automotive panel material of a 6000 series aluminum alloy, the 0.2% proof stress after BH can be increased to 200 MPa or more.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not restrict | limited by the following Example from the first.

  Examples of the present invention will be described. A molding test simulating the molding of the automobile side door outer panel shown in FIG. 2 was performed, and the surface distortion around the recess (door handle portion) 12 was evaluated. These results are shown in Table 1.

  The forming aluminum alloy sheet was an AA6022-T4 tempered 6000 series aluminum alloy sheet and mild steel sheet (regular steel sheet) that were aged at room temperature for 3 months after production and had a 0.2% proof stress of 140 MPa. The size of these blanks (cutting plates) was set to a size commensurate with the size of the following molded panel, including the peripheral portion removed by trimming.

The panel 11 of the product part in FIG. 2 has an arcuate curved surface with a continuous curved surface (cross section) of R1000 mm, except for the peripheral part removed by trimming, and the overall planar shape of the panel 11 is 600 mm wide and 1000 mm long. It has a rectangular parallelepiped shape and the area in plan view is 0.6 mm ² . And the handle seat 12 which is a recessed part was made into the rectangular shape of length 100mm, width 50mm, and depth 15mm.

  As the surface distortion evaluation method by measuring the shape of the molded panel of FIG. 2, the evaluation method based on out-of-plane displacement using a three-point gauge with a spacing of 40 mm shown in FIG. 5 is adopted, and the amount of surface distortion is maximized. As shown in FIG. 6, the lower 10 mm portion of the concave portion (door handle portion) 12 shown in FIG. 6 was measured and evaluated as the maximum change amount (hmax, unit: mm) of the out-of-plane displacement.

  The panel after press molding is subjected to artificial age hardening treatment (BH) simulating a paint baking (heat treatment) process after assembling the body of an automobile panel under the condition of 170 ° C. × 20 minutes, 0.2% after BH The proof stress was investigated. Further, the 0.2% proof stress of the aluminum alloy plate and the mild steel plate (regular steel plate) before press forming was also investigated. This mechanical property (0.2% proof stress) was measured by cutting out a test material from a plate or a molded panel and preparing a 50 mm × 25 mm JIS No. 5 tensile test piece perpendicular to the rolling direction. The test piece was subjected to a tensile test at room temperature according to JISZ2241, and 0.2% proof stress was measured.

  As shown in Table 1, Examples 1 and 2 and Comparative Example 8 were subjected to the restoration processing of the plate before press molding under the conditions specified in the present invention. On the other hand, in Comparative Examples 3, 4, and 5, restoration processing was performed under conditions that deviated from this regulation. In Comparative Examples 6, 7, and 9, no restoration process was performed.

  Here, in Table 1, the maximum surface strain amount of 0.07 mm of Comparative Example 9 obtained by press-forming a mild steel plate that is less likely to generate surface strain by the conventional method of FIG. 5 is a criterion for suppressing the surface strain. .

  FIG. 7 shows the amount of surface distortion h (mm) according to the position of the peripheral portion of the recess 12 in Invention Example 1 and Comparative Examples 6, 7, and 9 in Table 1. The horizontal axis in FIG. 7 represents the position of the peripheral portion as a distance (mm) from the concave portion 12 as 0 mm. The vertical axis represents the amount of surface distortion h (vertical axis: mm). In FIG. 7, Invention Example 1 in Table 1 is a thick solid line (lowest surface strain level), Comparative Example 6 is a thin dotted line (highest surface strain level), and Comparative Example 7 is a thick dotted line. 9 (example of steel plate) is indicated by a thin solid line (having fine jaggedness).

  According to Table 1 and FIG. 7, while performing the decompression | restoration process of the board before press molding on the conditions prescribed | regulated by this invention, the invention examples 1 and 2 press-molded by the split movable type of FIG. 1 are comparative examples of a mild steel plate. 9 is the same as the maximum surface strain amount of 0.07 mm, the surface strain amount level is low, and the surface strain is remarkably suppressed. Moreover, the panel strength after the artificial age hardening treatment after molding can be secured to 200 MPa or more with a 0.2% proof stress. As a result, it can be seen that the inventive examples can achieve both formability and BH properties.

  On the other hand, in Comparative Example 3 in which the restoration processing temperature is too high, the surface strain is improved, but the 0.2% proof stress after BH is too low and the BH property is not satisfied. Further, in Comparative Example 4 in which the restoration processing temperature is too low and Comparative Example 5 in which the restoration processing time is too long, the effect of the restoration processing is not exhibited, and the mild steel plate is formed in spite of being press-molded by the split movable type in FIG. Compared to Comparative Example 9 and Inventive Examples 1 and 2, the maximum surface strain amount is significantly large, and the surface strain is not suppressed.

  This is the same in Comparative Examples 6 and 7 in which the restoration process was not performed, and the remarkably large maximum surface distortion amount, the surface distortion amount level is high, and the surface distortion is not suppressed. However, as shown in Table 1 and FIG. 7, in comparison between those not restored, Comparative Example 6 press-molded by the conventional method of FIG. 6 is Comparative Example 7 press-molded by the split movable type of FIG. 1. Compared to the above, the maximum surface distortion amount is large, and the effect of suppressing the surface distortion of the press molding by the split movable type in FIG. 1 is supported.

  Further, Comparative Example 8 is also press-formed by the conventional method of FIG. 5 in spite of performing the restoration process of the plate before press forming under the conditions specified in the present invention. The maximum surface strain amount is significantly larger than the maximum surface strain amounts of Invention Examples 1 and 2, and the surface strain is not suppressed.

  From the results of the above-described embodiments, the complex cross section shown in FIG. 4 can be obtained by using a combination of a special restoration process in advance and press-molding of a split mold method as a raw material of a heat-treated aluminum alloy sheet that is naturally aged. It can be seen that the door outer panel can be molded. Even without using the special molding method described above, it is basically a molding that ensures shape accuracy by suppressing the occurrence of surface distortion associated with the molding of the recesses at room temperature by using generally used press molding. I understand that I can do it. In other words, the significance of exhibiting the synergistic effect by the combination of the requirements defined by the special restoration processing defined by the present invention and the press molding of the split mold method is supported.

  According to the present invention, an automotive panel that can suppress the occurrence of surface distortion associated with the formation of a concave portion even when the above-exemplified large-sized automobile outer panel is press molded at room temperature (room temperature) using a heat-treatable aluminum alloy plate as a raw material Can be provided. For this reason, the present invention uses the above-mentioned special molding method for large automobile outer panels such as doors, luggages, fenders, hoods, trunk lids and the like having complicated shapes as shown in FIG. 4 using an aluminum alloy plate as a material. It can be suitably used for press molding at room temperature.

1: aluminum alloy plate (blank), 2: mold, 3: punch, 4 wrinkle retainer, 5: punch, 6: spring, 11: side door outer panel (panel molded product), 12: handle seat (concave), X : Surface distortion, Y: Convex

Claims (4)

  The material heat-treatable aluminum alloy plate is cooled to room temperature at an average cooling rate of 10 ° C./second or more after holding for 0.1 seconds or more and 150 seconds or less in the temperature range of 220 ° C. to 280 ° C. A press for an automobile panel characterized in that press molding is performed on a car panel having a concave portion on a part of a continuous curved surface by using a mold in which a mold part for molding the concave part is movable. Molding method.   The press molding method of the automobile panel according to claim 1, wherein the press molding at the room temperature is performed within 240 hours after cooling to the room temperature after the restoration process.   The method for press-molding an automobile panel according to claim 1 or 2, wherein a 0.2% yield strength of the heat-treated aluminum alloy sheet is 80 to 130 MPa when press-molded after the restoration treatment. The press molding method of the automobile panel according to any one of claims 1 to 3, wherein the automobile panel is a side door outer panel and the concave portion is a door handle portion.

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