JP4933788B2 - Bulge molding method and hollow molded body - Google Patents

Description

  The present invention relates to a bulge forming method in which a pressure fluid is circulated through a hollow workpiece to perform a forming process, and a hollow formed body obtained by the method.

  As a method for producing a hollow molded body that is long and has a different cross-sectional shape or dimension in a direction orthogonal to the longitudinal direction, the molding is performed while circulating a pressure fluid (generally high-pressure water) through the hollow workpiece. The applied bulge forming process is adopted.

  The case where the straight pipe is used as a raw material will be described as an example. First, the straight pipe is accommodated in a preforming mold, and in this state, the pressure fluid is supplied into the straight pipe. As a result, the inner peripheral wall of the straight pipe is pressed by the pressure fluid, and as a result, a portion that expands radially outward is formed in the straight pipe. In addition, since the straight pipe is accommodated in the mold, the expanded portion is finally blocked by the mold. This process is also called a pipe expansion process.

  Next, the straight pipe having the expansion portion is transferred to another mold, and the expansion portion is mainly pressed under the action of the compression mechanism to be pressed into a predetermined shape. Further, the main forming process is performed with another mold, and thereby a hollow molded body is obtained.

  In this type of bulge forming process, various attempts are being made to obtain the cross-sectional shape or dimensions with high accuracy. For example, Patent Document 1 proposes setting the temperature of the preforming die to be equal to or higher than the recrystallization temperature of the hollow workpiece and setting the temperature of the main molding die to be equal to or lower than the recrystallization temperature of the hollow workpiece. Yes.

  Patent Document 2 proposes providing a temperature distribution along the longitudinal direction of the hollow workpiece in order to facilitate the control of the thickness distribution of the hollow molded body. In this case, the thickness of the portion heated to a high temperature increases, so that the thickness decreases. On the other hand, the extension of the portion heated to a relatively low temperature decreases, so the thickness increases.

JP 2003-126923 A JP 2003-103327 A

  In the prior art described in Patent Document 1, attention is paid to the reduction of dislocations in the metal that is the material of the hollow work, and the preforming process is performed by heating above the recrystallization temperature, but the hollow work is made of an Al alloy. When a material is used and heated to such a temperature range, uniform solid solution of Al and other metal atoms may occur. In this case, depending on the cooling rate, coarse particles containing the metal atoms are precipitated in the metal structure of the hollow workpiece, and as a result, there is a problem that a low-strength portion is formed in the hollow molded body.

  In addition, there is a demand for hollow molded bodies having different strengths depending on the part. For example, it is a case where a hollow molded body is used as a frame member constituting a frame of an automobile body. In this case, if the frame member has a strength, and hence a portion that does not bear the shock absorption, and a portion that does not bear the shock, it is not necessary to separately prepare the frame member that bears the shock absorption and the frame member that does not bear the shock, and the number of the frame members is reduced. Become. Therefore, there are advantages such as a reduction in the number of processes when the frame members are welded to form a frame.

  In this regard, in the prior art described in Patent Document 2, it is possible to vary the strength by varying the thickness, but it is difficult to vary the strength while the thickness is substantially equal.

  The present invention was made in order to solve the above-mentioned problem, and while avoiding the formation of a low-strength portion other than a predetermined portion, a bulge forming method that makes it easy to obtain a hollow molded body, It aims at providing the hollow molded object from which intensity | strength changes with parts.

In order to achieve the above object, the present invention is a bulge forming method in which a pressure fluid is circulated through a hollow work made of an alloy to perform a forming process,
Heating the hollow workpiece;
A preforming step in which preforming is performed while circulating a pressure fluid through the hollow workpiece in a preforming mold set at a temperature equal to or higher than a precipitation temperature at which a metal phase that does not contribute to improving the strength of the hollow workpiece is precipitated in the metal structure of the alloy. When,
The hollow work that has been preformed is housed in a main mold set at a temperature at which quenching can be performed, and the hollow work is cooled by the main mold at a cooling rate at which the metal phase does not precipitate. However, a main molding process for subjecting the hollow workpiece to a main molding process,
An aging treatment step of performing an aging treatment on the hollow workpiece subjected to the main forming process and precipitating a metal phase contributing to an improvement in the strength of the hollow workpiece in a metal structure,
It is characterized by having. In the following, the metal phase may be simply referred to as “phase”.

  That is, in the present invention, when the hollow work after completion of the preforming process is quenched with a mold for performing the forming process, a supersaturated solid solution is formed at a cooling rate at which a phase that does not contribute to strength improvement does not precipitate, By applying an aging treatment to the supersaturated solid solution, a phase contributing to strength improvement is precipitated. Thereby, the molded object excellent in intensity | strength is obtained. Thus, by controlling the temperature and cooling rate of the hollow workpiece, it is possible to avoid the occurrence of a low strength portion in the hollow molded body due to precipitation of a phase that does not contribute to strength improvement. Of course, both of the phase that does not contribute to the improvement of strength and the phase that contributes to the improvement of strength include solute atoms forming the alloy.

Here, whether or not the precipitated phase contributes to improving the strength is determined by, for example, testing a test piece made of an alloy as a raw material, and by cooling the test piece at various cooling rates after heat treatment. It can be judged by comparing the strength with a heat-treated test piece in which the above phase is precipitated. When the hollow workpiece is an Al—Mg—Si alloy, the β phase (Mg ₂ Si) corresponds to a phase that does not contribute to strength improvement.

In addition, the phase which contributes to strength improvement, and the phase which does not contribute can be deposited in another site | part, and the site | part from which intensity | strength differs mutually can also be provided in the same member. That is, the present invention is a bulge forming method for performing a forming process by circulating a pressure fluid through a hollow work made of an alloy,
Heating the hollow workpiece;
There are provided a first part set to be equal to or higher than a precipitation temperature at which a metal phase that does not contribute to improving the strength of the hollow workpiece is precipitated in the metal structure of the alloy, and a second part set to a temperature lower than the precipitation temperature. In a preforming mold, a preforming step for preforming while circulating a pressure fluid through the hollow work,
The hollow workpiece that has been preformed is accommodated in a main mold set at a temperature at which quenching can be performed, and the hollow workpiece is formed at a cooling rate at which the metal phase does not precipitate in the first part. by cooling the mold, subjected to the molding against the hollow workpiece while precipitating the metal phase and the second portion of the metal structure without precipitation of the metal phase in the first portion of the metal structure The main molding process,
An aging treatment is performed on the hollow work subjected to the main forming process, and a metal phase contributing to the strength improvement of the hollow work is precipitated in the metal structure of the first part;
It is characterized by having.

  In this case, when the preforming process is performed, the hollow workpiece has a high-temperature portion (first portion) that rises above the precipitation temperature at which a phase that does not contribute to strength improvement is precipitated, and a low-temperature portion (first portion) that is lower than the precipitation temperature. 2 sites). When the hollow workpiece is rapidly cooled during the main forming process, the phase does not precipitate from the high temperature part, but the phase precipitates from the low temperature part. As described above, when an aging treatment is performed at a portion where the phase does not precipitate, another phase is precipitated and the strength becomes relatively large. On the other hand, at a portion where the phase is precipitated, the strength is increased even when the aging treatment is performed. Not much improvement. Accordingly, the low temperature portion has a lower strength than the high temperature portion.

  Thus, by providing a high temperature part and a low temperature part in a preforming mold, it is possible to easily produce a hollow molded body having different strengths depending on the part. Moreover, in this case, it is not necessary to change the wall thickness in order to change the strength.

  Further, in this case, since it is not necessary to separately provide hollow molded bodies having different strengths, raw material costs can be reduced and the number of molding steps can be reduced. In addition, the number of bonding steps is reduced.

  The preforming step may include a tube expansion step for expanding the hollow workpiece. In this case, the outer peripheral dimension of the cross section exposed by cutting the expanded portion of the expanded hollow work obtained in the tube expansion process in a direction perpendicular to the longitudinal direction of the hollow work is subjected to the main forming process in the main forming process. It is preferable that the molded part of the hollow work after being made is substantially the same as the outer peripheral dimension of the cross section exposed by cutting in the same direction as described above.

  When such dimension setting is performed, it is not necessary to stretch the hollow workpiece with the internal pressure during the main forming process, and therefore there is almost no change in the outer peripheral dimension (peripheral length) of the molding part. For this reason, even if it is a case where temperature is not raised in this shaping | molding process, it becomes easy to ensure the dimensional accuracy of a hollow molded object and by extension, the precision of a shape.

  Here, the set temperature of the present molding die is not particularly limited as long as it is a temperature at which a cooling rate at which a phase containing solute atoms does not precipitate is obtained, and it is not more than an artificial aging temperature, for example, about 200 ° C. or less. However, it is preferable that the temperature is room temperature because the cooling rate increases.

Furthermore, the present invention is a long hollow molded body made of an alloy and having a different cross-sectional shape or dimension in a direction orthogonal to the longitudinal direction, depending on the site,
A first part containing in the metal structure a first metal phase that does not contribute to improving the strength, and a second part containing a second metal phase contributing to improving the strength in the metal structure and having a higher strength than the first part. It is the single member which has these.

  This hollow molded body integrally has portions with different strengths. Therefore, when providing structures having different strengths according to the portions, it is not necessary to individually provide a plurality of hollow molded bodies having different strengths and to join them. For this reason, raw material costs can be reduced, and the number of molding steps can be reduced.

A suitable example of the material of such a hollow molded body is an Al alloy containing Mg and Si. In this case, Mg ₂ Si (β phase) is formed as the first phase, while β ′ phase is formed as the second phase.

  In the present invention, the predetermined part of the preforming mold is held at a predetermined temperature so that the corresponding part in the hollow workpiece is set to the predetermined temperature to control the precipitation / non-precipitation of the phase that does not contribute to the strength improvement. . The strength of each part of the hollow molded body (hollow workpiece) is set according to this precipitation / non-deposition.

  That is, according to the present invention, a predetermined portion of the hollow molded body (hollow workpiece) can be set to a predetermined strength. In other words, it is possible not only to avoid the formation of a low-strength part other than the predetermined part, but also to easily produce a hollow molded body having a different strength depending on the part.

  Hereinafter, preferred embodiments of the bulge forming method and the hollow molded body according to the present invention will be described in detail with reference to the accompanying drawings.

  Flowcharts of the bulge forming method according to the first embodiment are shown in FIGS. 1A to 1E exemplifying a case where a hollow molded body is obtained from a straight pipe (hollow workpiece). In this bulge forming method, a heating step S1 for heating the straight pipe 10, a tube expanding step S2 and a press forming step S3 as a preforming step, a main forming step S4, and an aging treatment step S5 are performed, and the tube expanding step In each of S2, press molding process S3, and main molding process S4, the 1st semi-finished product 12, the 2nd semi-finished product 14, and the hollow molded object 16 are produced.

  In this case, the bulge forming apparatus that performs the bulge forming process includes a heating station, a tube expansion station, a press forming station, and a main forming process station, and each step of the heating process S1 to the main forming process S4 is performed in each station. . The aging treatment step S5 is performed in a heat treatment furnace.

  In the first embodiment, the straight pipe 10 is made of a so-called 6000 series Al alloy standardized by JIS, in other words, an Al-Mg-Si series alloy. A specific example of this type of Al alloy is A6063 alloy.

  The straight pipe 10 is clamped from both ends by a clamping mechanism, and is conveyed to the heating station in this state. Thereafter, as shown in FIG. 1A, the straight pipe 10 is heated by heating means provided in the heating station, for example, the electrodes 20 and 22, and is heated to 500 ° C. or higher. Thereby, heating process S1 is implemented.

  The heated straight pipe 10 is transferred to a pipe expansion station that performs the pipe expansion step S2, and is positioned between the pipe expansion lower mold 30 and the pipe expansion upper mold 32 that are disposed in the pipe expansion station and separated by a predetermined distance (see FIG. 2). ).

Here, in both of the lower pipe expansion mold 30 and the upper pipe expansion mold 32, heaters 34a to 34e, 36a to 36a, which are elongated cylindrical bodies extending along the longitudinal direction of the lower pipe expansion mold 30 and the upper pipe expansion mold 32. 36e is embedded. The temperature of the expanded pipe lower mold 30 and the expanded pipe upper mold 32 is such that the heaters 34a to 34e and 36a to 36e are energized in advance so that an Al—Mg—Si based alloy (for example, A6063 alloy) that is the material of the straight pipe 10 is used. ) Of the β-phase precipitation temperature. Since the precipitation temperature of Mg ₂ Si as the β phase is about 480 ° C., the holding temperature of the lower pipe expansion die 30 and the upper pipe expansion die 32 may be set to about 500 ° C. or more, for example.

  Thereafter, the lower mold 30 is raised toward the straight pipe 10 to clamp the mold, and as shown in FIG. 2, the straight pipe 10 is inserted into the cavity 38 formed by the lower pipe mold 30 and the upper pipe mold 32. Be contained. In the cavity 38, a part of the circumferential direction orthogonal to the longitudinal direction is set to be larger than the diameter of the straight pipe 10. For this reason, in the said part, the outer peripheral wall of the straight pipe 10 is in the state spaced apart from both the pipe expansion lower mold | type 30 and the pipe expansion upper mold | type 32. FIG.

  Next, compressed air is supplied into the straight pipe 10 via the clamping mechanism, and the pressure inside the straight pipe 10 increases accordingly. That is, in the portion where the straight pipe 10 is pressed from the inside by the compressed air and separated from the pipe expansion lower mold 30 and the pipe expansion upper mold 32, the straight pipe 10 expands toward the pipe expansion lower mold 30 and the pipe expansion upper mold 32. start.

  The expanded portion is finally dammed by the expanded lower die 30 and the expanded upper die 32. Accordingly, the expansion is stopped, and the first semi-finished product 12 (see FIG. 1B) having a shape corresponding to the cavity 38 is formed.

  While this pipe expansion step S <b> 2 is performed, heat is transmitted to the straight pipe 10 from the pipe expansion lower mold 30 and the pipe expansion upper mold 32. In the straight pipe 10 that has received heat, the temperature of the lower pipe expansion die 30 and the upper pipe expansion die 32 is maintained at or above the β-phase precipitation temperature of the Al—Mg—Si alloy that is the material of the straight pipe 10. , The solid solution of Si as a solute atom in Al is promoted.

  After a predetermined time has passed after the mold is clamped, the compressed air in the first semi-finished product 12 is exhausted, and the expanded pipe lower mold 30 is lowered to open the mold. The exposed first semi-finished product 12 is then transferred to a press molding station and placed between a press molding lower die 40 and a press molding upper die 42 that are separated from each other by a predetermined distance (see FIG. 3).

  Similarly to the pipe expansion lower mold 30 and the pipe expansion upper mold 32, the press molding lower mold 40 and the press molding upper mold 42 extend along the longitudinal direction of the press molding lower mold 40 and the press molding upper mold 42. Long cylindrical body-shaped heaters 44a to 44e and 46a to 46e are respectively embedded. And when these heaters 44a to 44e and 46a to 46e are energized in advance, the temperature of the press-molding lower mold 40 and the press-molding upper mold 42 is equal to or higher than the precipitation temperature of the β phase of the Al—Mg—Si alloy. For example, it is maintained at about 500 ° C.

  When the press-molding lower mold 40 rises with the start of the press-molding step S3, the first semi-finished product 12 is pressed toward the press-molding upper mold 42. Immediately before the press-molding lower mold 40 comes into contact with the first semi-finished product 12, compressed air is supplied through the clamping mechanism. The supply pressure at this time may be set to such an extent that the first semi-finished product 12 is not expanded.

  When the press-molding lower mold 40 is displaced up to a predetermined position, a cavity 48 shown in FIG. 3 is formed. In this case, the expansion part or the like in the first semi-finished product 12 is press-molded by a part of the press-molding lower die 40 and the press-molding upper die 42, and finally the second semi-finished product 14 (see FIG. 1C) is produced. The While the pressure molding step S3 is performed in this manner, the heat of the pressure molding lower die 40 and the pressure molding upper die 42 is transmitted to the first semi-finished product 12 as in the tube expansion step S2. Therefore, the solution treatment is performed on the first semi-finished product 12 and the second semi-finished product 14.

  When the press molding step S3 is completed, the compressed air in the second semi-finished product 14 is exhausted, and then the press molding lower mold 40 is lowered to open the mold. The exposed second semi-finished product 14 is rotated about 90 ° along the circumferential direction of the straight pipe 10, and then the main molding lower mold 50 and the main molding upper mold 52 of the main molding station separated from each other by a predetermined distance. (See FIG. 4).

  The main molding lower mold 50 and the main molding upper mold 52 are respectively provided with refrigerant passages 54a to 54e and 56a to 56e for circulating the cooling medium. A cooling medium such as water, oil, or compressed air is circulated through each of the refrigerant passages 54a to 54e and 56a to 56e, whereby both the main molding lower mold 50 and the main molding upper mold 52 are maintained at room temperature. .

Accordingly, when the main forming step S4 is started and the main lower mold 50 is raised and the mold is clamped, the second semi-finished product 14 is rapidly cooled to a room temperature from a temperature equal to or higher than the β phase precipitation temperature. In the second semi-finished product 14 that has been subjected to such rapid cooling, it is avoided that Mg ₂ Si as the β phase is precipitated in the metal structure of the Al—Mg—Si alloy as the material.

As described above, in the first embodiment, the straight pipe 10, the first semi-finished product 12, and the second semi-finished product 14 are heated to the β-phase precipitation temperature or higher in the preforming step, that is, the tube expanding step S 2 and the press forming step S 3. On the other hand, in this molding process S4, the hollow molded body 16 is produced while the second semi-finished product 14 is rapidly cooled to room temperature. Thereby, the precipitation of β phase (Mg ₂ Si) is avoided, and a hollow molded body 16 (see FIG. 1D) made of a supersaturated solid solution is formed.

  In addition, in the second semi-finished product 14, the outer shape (peripheral length) of the cross section exposed by cutting the portion molded in the press molding step S <b> 3 along the direction orthogonal to the longitudinal direction is the same as that in the hollow molded body 16. It is set to be substantially the same as the perimeter of the corresponding part. The peripheral length is controlled by measuring the peripheral dimensions of the corresponding portion of the cavity 48 formed by the press molding lower mold 40 and the press molding upper mold 42, and the cavity 58 formed by the main molding lower mold 50 and the main molding upper mold 52. This can be done by substantially matching the circumferential dimension of the corresponding part.

  As described above, when the second semi-finished product 14 is deformed to the hollow molded body 16, the dimensional accuracy of the hollow molded body 16, and thus the accuracy of the shape, can be improved by performing this molding process step S 4 with almost no change in the peripheral length. It is easy to ensure. In this case, there is almost no need to stretch the second semi-finished product 14 by internal pressure, and therefore there is almost no dimensional change in the process of deforming from the second semi-finished product 14 to the hollow molded body 16.

  Further, compressed air is supplied to the inside of the second semi-finished product 14 while the main forming step S4 is performed.

  Thereafter, an aging treatment step S5 is performed. That is, the hollow molded body 16 is accommodated in the heat treatment furnace and subjected to artificial aging treatment. The aging treatment condition may be, for example, 180 ° C. and 6 hours. Or you may make it perform natural aging.

  By this aging treatment, Mg and Si as solute atoms are precipitated as β ′ phase in the metal structure of the Al—Mg—Si based alloy (supersaturated solid solution) that is the material of the hollow molded body 16. The β ′ phase is a phase that contributes to improving the strength of the Al—Mg—Si alloy, and therefore the strength of the hollow molded body 16 is higher than that of the straight pipe 10. A typical form of the β ′ phase is fine particles, but is not particularly limited thereto.

That is, in the first embodiment, the second semi-finished product 14 is rapidly cooled at a cooling rate at which the β phase (Mg ₂ Si) does not precipitate in the metal structure of the Al—Mg—Si alloy that is the material of the hollow molded body 16. A supersaturated solid solution is formed, and then the β ′ phase is precipitated from the supersaturated solid solution by an aging treatment. The hollow molded body 16 in which such a metal structure is formed is subjected to a solution treatment, a quenching process (rapid cooling), an aging after the tube expansion process S2, the pressure molding process S3, and the main molding process S4 are performed at about 500 ° C. Compared to the hollow molded body 16 having the same material, shape, dimensions and the like obtained by the treatment, it exhibits excellent physical properties of 1.5 times or more in tensile strength and 2.5 or more times in proof stress.

  As described above, it is possible to avoid the formation of a low-strength portion by setting the cooling condition in which the β phase does not precipitate during the main forming step S4.

  When the heating step S1 to the main forming step S4 are continuously performed in order to continuously produce a plurality of hollow molded bodies 16, the heat of the previously produced hollow molded body 16 is reduced to the main molding lower mold 50. And, it is transmitted to the main molding upper mold 52. In this case, the transferred heat is quickly absorbed by the cooling medium flowing through the refrigerant passages 54 a to 54 e and 56 a to 56 e and is removed from the main molding lower mold 50 and the main molding upper mold 52. Therefore, since the temperature rise of the main molding lower mold 50 and the main molding upper mold 52 is avoided, the hollow molded body is caused by the fact that the amount of thermal expansion of the second semi-finished product 14 differs with the number of times of the main molding processing step S4. A reduction in the accuracy of 16 is avoided.

  Next, a second embodiment will be described.

  In the second embodiment, in the tube expansion step S2 and the press molding step S3, a high temperature region and a low temperature region are provided in the tube expansion lower die 30, the tube expansion upper die 32, the pressure molding lower die 40, and the pressure molding upper die 42. In order to provide a high temperature part and a low temperature part, that is, a part where the temperatures are different from each other, for example, in the heaters 34a to 34e, 36a to 36e, 44a to 44e, 46a to 46e, A heater with a different heat generation capacity may be used. Or you may make it make the energization amount differ in each of heater 34a-34e, 36a-36e, 44a-44e, 46a-46e. Of course, a lower tube expansion die, an upper tube expansion die, a lower pressure forming die, and an upper pressure forming die in which heaters are provided sparsely at low temperature portions and heaters are densely provided at high temperature portions may be used.

  In the lower pipe expansion die 30 and the upper pipe expansion die 32, the low temperature portion corresponding to the low strength portion of the hollow molded body 16 is set to be lower than the precipitation temperature of the β phase. On the other hand, the high-temperature part corresponding to the high-strength part of the hollow molded body 16 is set to a temperature equal to or higher than the β-phase precipitation temperature. Of course, the press molding lower mold 40 and the press molding upper mold 42 are similarly provided with a high temperature portion and a low temperature portion.

  Similarly to the first embodiment, the straight pipe 10 is transferred to the pipe expansion station through the heating process S1, and the pipe expansion process S2 is performed by the pipe expansion lower mold 30 and the pipe expansion upper mold 32 to become the first semi-finished product 12. In the pipe expansion step S2, as described above, the high temperature part and the low temperature part are provided in the pipe expansion lower mold 30 and the pipe expansion upper mold 32. Therefore, in the first semi-finished product 12, the part in contact with the high temperature part is While the temperature rises to a temperature equal to or higher than the β-phase precipitation temperature, the portion in contact with the low temperature portion rises only to a temperature lower than the β-phase precipitation temperature.

  Next, the press molding step S3 is performed on the first semi-finished product 12, and the second semi-finished product 14 is produced. In this process, when the first semi-finished product 12 is molded, the high-temperature portion that has risen to a temperature equal to or higher than the β-phase precipitation temperature contacts the high-temperature portions of the press-molding lower mold 40 and the press-molding upper mold 42. In addition, a low temperature portion having a temperature lower than the β-phase precipitation temperature contacts the low temperature portions of the press-molding lower mold 40 and the press-molding upper mold 42. For this reason, also in the 2nd semi-finished product 14, each temperature of the high temperature site | part and low-temperature site | part in the 1st semi-finished product 12 is maintained.

  Thereafter, the second semi-finished product 14 is transferred to the main molding processing station, and the main molding processing S3 is performed. At this time, the second semi-finished product 14 is cooled as it is sandwiched between the main molding lower mold 50 and the main molding upper mold 52 held at room temperature. Accordingly, the temperature of the second semi-finished product 14 drops rapidly.

  As described above, in the second embodiment, the second semi-finished product 14 is provided with a high-temperature portion that is equal to or higher than the β-phase precipitation temperature and a low-temperature portion that is lower than the β-phase precipitation temperature. When these high-temperature parts and low-temperature parts are rapidly cooled, a supersaturated solid solution is formed at the high-temperature parts, and the β phase is precipitated in the metal structure at the low-temperature parts.

  When the hollow molded body 16 is subjected to an aging treatment, a β ′ phase is precipitated in a portion made of a supersaturated solid solution, as in the first embodiment. That is, in the second embodiment, the hollow molded body 16 is produced in which the portion where the β phase is precipitated and the portion where the β ′ phase is precipitated are mixed.

  In the hollow molded body 16, the portion where the β ′ phase is precipitated has higher strength than the portion where the β phase is precipitated. That is, the hollow molded body 16 having a high strength portion (high strength portion) and a low strength portion (low strength portion) while being a single member is obtained. Such a hollow molded body 16 is suitable, for example, as a frame member constituting a frame of an automobile body. In this frame member, there are a part responsible for shock absorption and a part not responsible for shock absorption based on the difference in strength. Therefore, it is not necessary to separately produce a frame member that bears shock absorption and a frame member that does not bear shock, and the number of frame members can be reduced for this purpose.

  As can be understood from the above, in the second embodiment, the ultimate temperatures of the first semi-finished product 12 and the second semi-finished product 14 in the tube expansion step S2 and the press molding step S3 are made different depending on the part in order to make the strength different. I have to. Therefore, it is not particularly necessary to make the thicknesses different in order to make the strengths different. That is, according to the second embodiment, it is possible to make the strengths different without making the thicknesses different.

  Also in the second embodiment, for the same reason as in the first embodiment, the peripheral length of the press forming portion of the second semi-finished product 14 formed in the press forming step S3 is formed in the main forming step S4. It is preferable to set substantially the same as the peripheral length of the corresponding portion of the hollow molded body 16.

  In each of the above-described embodiments, the molding process is performed using compressed air, but it goes without saying that a liquid may be used.

  Further, instead of circulating a cooling medium through the main molding lower mold 50 and the main molding upper mold 52, a heat dissipation plate made of a material having high thermal conductivity, such as Cu, is used as the main molding lower mold 50 and the main molding upper mold. 52 may be attached. Of course, the circulation of the cooling medium and the mounting of the heat sink may be used in combination.

  Further, the heating means for maintaining the expanded pipe lower mold 30, expanded pipe upper mold 32, press molded lower mold 40 and pressed molded upper mold 42 at predetermined temperatures are heaters 34a to 34e, 36a to 36e, 44a to 44e, 46a to 46a. It is not limited to 46e, Other heating means, such as a high frequency induction heating means, may be sufficient.

  Furthermore, in each of the above-described embodiments, the straight pipe 10 is used, but the workpiece is not particularly limited to this, and may be a hollow body capable of circulating a pressure fluid.

  The material of the hollow workpiece is not particularly limited to the Al—Mg—Si alloy, and may be any alloy that precipitates a phase contributing to strength improvement and a phase not contributing to strength improvement.

1A to 1E are flowcharts of a bulge forming method according to the first embodiment. It is a principal part schematic longitudinal cross-sectional view which shows the state which pipe-expands with a pipe expansion lower type | mold and a pipe expansion upper type | mold with respect to a straight pipe. It is a principal part schematic longitudinal cross-sectional view which shows a part of state which clamped the 1st semi-finished product with the press-molding lower mold | type and the press-molding upper mold | type. It is a principal part schematic longitudinal cross-sectional view which shows the state which clamped the 2nd semifinished product with the main shaping | molding lower mold | type and the main shaping | molding upper mold.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Straight pipe 12, 14 ... Semi-finished product 16 ... Hollow molded object 20, 22 ... Electrode 30 ... Expanded pipe lower mold 32 ... Expanded pipe upper mold 34a-34e, 36a-36e, 44a-44e, 46a-46e ... Heater 40 ... Press Molding lower mold 42 ... Press molding upper mold 50 ... Main molding lower mold 52 ... Main molding upper molds 54a to 54e, 56a to 56e ... Refrigerant passage

Claims (6)

A bulge forming method in which a pressure fluid is passed through a hollow workpiece made of an alloy to perform a forming process,
Heating the hollow workpiece;
A preforming step in which preforming is performed while circulating a pressure fluid through the hollow workpiece in a preforming mold set at a temperature equal to or higher than a precipitation temperature at which a metal phase that does not contribute to improving the strength of the hollow workpiece is precipitated in the metal structure of the alloy. When,
The hollow work that has been preformed is housed in a main mold set at a temperature at which quenching can be performed, and the hollow work is cooled by the main mold at a cooling rate at which the metal phase does not precipitate. However, a main molding process for subjecting the hollow workpiece to a main molding process,
An aging treatment step of performing an aging treatment on the hollow workpiece subjected to the main forming process and precipitating a metal phase contributing to an improvement in the strength of the hollow workpiece in a metal structure,
A bulge forming method characterized by comprising: A bulge forming method in which a pressure fluid is passed through a hollow workpiece made of an alloy to perform a forming process,
Heating the hollow workpiece;
There are provided a first part set to be equal to or higher than a precipitation temperature at which a metal phase that does not contribute to improving the strength of the hollow workpiece is precipitated in the metal structure of the alloy, and a second part set to a temperature lower than the precipitation temperature. In a preforming mold, a preforming step for preforming while circulating a pressure fluid through the hollow work,
The hollow workpiece that has been preformed is accommodated in a main mold set at a temperature at which quenching can be performed, and the hollow workpiece is formed at a cooling rate at which the metal phase does not precipitate in the first part. by cooling the mold, subjected to the molding against the hollow workpiece while precipitating the metal phase and the second portion of the metal structure without precipitation of the metal phase in the first portion of the metal structure The main molding process,
An aging treatment is performed on the hollow work subjected to the main forming process, and a metal phase contributing to the strength improvement of the hollow work is precipitated in the metal structure of the first part;
A bulge forming method characterized by comprising: In the shaping | molding method of Claim 1 or 2, the said preforming process includes the pipe expansion process which expands the said hollow workpiece,
The outer peripheral dimension of the cross section that is exposed by cutting the expanded portion of the hollow workpiece after expansion obtained in the tube expansion step in a direction perpendicular to the longitudinal direction of the hollow workpiece is subjected to main molding processing in the main molding step. A bulge forming method characterized in that the formed part of the hollow workpiece after the cutting is cut in a direction perpendicular to the longitudinal direction of the hollow workpiece so as to be substantially the same as the outer peripheral dimension of the exposed cross section.   The bulge forming method according to any one of claims 1 to 3, wherein the temperature of the main mold is set to room temperature. A long hollow molded body made of an alloy and having a different cross-sectional shape or dimension in a direction orthogonal to the longitudinal direction, depending on the site,
A first part containing in the metal structure a first metal phase that does not contribute to improving the strength, and a second part containing a second metal phase contributing to improving the strength in the metal structure and having a higher strength than the first part. A hollow molded body characterized by being a single member. 6. The hollow molded body according to claim 5, wherein the alloy is an Al alloy containing Mg and Si, and the first metal phase is Mg ₂ Si.

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