Method for manufacturing a forged product

Abstract

To provide a method for manufacturing a forged, molded article whereby occurrence of quenching strain in a forged body can be prevented without using an additive, a jig, or the like in a quenching step.SOLUTION: A forging temperature range in a heating step is in a range of 450°C or more to 550°C or less. A surface temperature of an upper molding portion of a first upper mold in a primary forging step and a surface temperature of an upper molding portion of a second upper mold in a secondary forging step are each in the range of 150°C or more to 190°C or less. A surface temperature of a lower molding portion of a first lower mold and a surface temperature of a lower molding portion of a second lower mold are each in the range of 190°C or more to 230°C or less. The surface temperature of the lower molding portion of the first lower mold and the surface temperature of the lower molding portion of the second lower mold are higher than the surface temperature of the upper molding portion of the first upper mold and the surface temperature of the upper molding portion of the second upper mold, respectively, by 5°C or more.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a forged product for manufacturing a forged product of a suspension arm for an automobile.

Background Art

[0002] In recent years, from the viewpoint of improving the fuel efficiency of automobiles by reducing the weight of the vehicle body, a forged body made of a lightweight aluminum alloy is used as a suspension arm such as a lower arm or an upper arm, which is a component of the undercarriage of an automobile. When forging such a suspension arm, for example, it is common to manufacture it by heating a linear round bar-shaped aluminum alloy material to a predetermined forging temperature and performing two-stage forging such as upset forging and finish forging (for example, see Patent Documents 1 and 2).

[0003] With the increase in demand for such suspension arms made of aluminum alloy, in a production line for manufacturing suspension arms by hot forging a bar-shaped forged material, for example, hundreds of thousands of suspension arms are mass-produced per month. Such mass production equipment for suspension arms is disclosed in, for example, Patent Document 3. That is, a continuously cast aluminum alloy casting rod with a relatively small diameter suitable for forging a suspension arm is subjected to homogenization heat treatment, and many processes leading to hot forging (die forging) such as mechanical forging and hydraulic forging are made highly efficient by automation.

[0004] The suspension arm made of aluminum alloy thus produced constitutes a control arm as an automotive underbody part. Automotive suspension arms often have a non-axisymmetric and complex shape, and while high strength and fatigue strength similar to those of steel materials are required, high impact resistance is also necessary. Therefore, 6000 series (Al-Mg-Si series) aluminum alloy, which is a JIS standard, is generally used as the forging material for suspension arms. The 6000 series aluminum alloy is high in strength, high in toughness, and excellent in corrosion resistance. In addition, it is excellent in recyclability because the amount of alloying elements is small and it is easy to reuse scrap as the melting raw material for 6000 series Al alloy again.

[0005] As a method for manufacturing such a suspension arm made of aluminum alloy, for example, Patent Document 4 discloses hot forging using an upper die and a lower die. According to this, the die temperature is preferably 100°C to 300°C if it is an aluminum alloy, and the forging material temperature is preferably 400°C to 550°C if it is an aluminum alloy.

[0006] Further, the forged and formed suspension arm made of aluminum alloy is then subjected to heat treatment processes such as solution treatment, quenching treatment, and artificial aging hardening treatment. In a suspension arm made of aluminum alloy, in order to achieve high strength and high toughness, in addition to controlling the composition of the aluminum alloy and the microstructure in forging, setting the conditions for each of the solution treatment, quenching treatment, and artificial aging hardening treatment is important.

[0007] Also, as described above, in the production line of the suspension arm made of aluminum alloy, in order to carry out mass production reaching hundreds of thousands of pieces per month, it is also important to improve the efficiency of the heat treatment process. For this reason, in order to efficiently perform heat treatment on relatively small forgings such as suspension arms, in these solution treatment, quenching treatment, and artificial aging hardening treatment, it is common to arrange and accommodate a large number of forgings in a case. Specifically, a case containing a plurality of forgings is placed in a solution treatment furnace, a quenching treatment water tank, and an artificial aging hardening treatment furnace for each case without transferring the forgings in the case for each individual process, and the plurality of forgings are processed collectively.

[0008] Also, in the quenching treatment process, for the sake of efficiency, cases in which these forgings are arranged in a plurality are further stacked vertically and then submerged in a quenching treatment water tank for quenching treatment. That is, a large number of forgings made of aluminum alloy arranged and stacked in a large number are quenched simultaneously in a batch.

[0009] However, as described above, in the quenching treatment process, when relatively small forgings are arranged in a large number in a case and these cases are stacked on top of each other, there is a problem that the temperature distribution of the cooling water for cooling the forgings tends to be uneven, and there is a high likelihood that there will be a difference in the cooling rate for each forging. This is because, for the sake of efficiency of the quenching treatment, due to the large number of arrangements and stacking, the forgings in the case are accommodated in a state where they are densely arranged.

[0010] That is, in the arrangement and stacking in the case, it is difficult to secure sufficient space (gap, interval) for the forgings arranged on the upper side or the central part side to come into contact with the relatively low-temperature cooling water that has just been supplied. For this reason, only the cooling water that has been heated to a high temperature by cooling the forgings located on the lower side or the peripheral part side comes into contact with the forgings arranged on the upper side or the central part side, and depending on the position arranged in the case, there may be a difference in the water temperature of the cooling water in contact with the forgings.

[0011] On the one hand, in order to forge a high-strength suspension arm, it is necessary to rapidly cool the forged body in the quenching process after solution treatment. However, on the other hand, the faster the cooling rate during quenching, the more likely quenching distortion (bending of the forged body) occurs. A suspension arm with quenching distortion may cause interference with other components when assembled into a vehicle.

[0012] In order to suppress the occurrence of quenching distortion in such a quenching process, a method of increasing the temperature of the cooling water to reduce the cooling rate can be considered. However, there is a concern that sufficient strength cannot be ensured for the suspension arm due to the decrease in the cooling rate.

[0013] For this reason, for example, Patent Documents 5 and 6 disclose using a jig to individually restrain a forged body made of an aluminum alloy during quenching to suppress distortion. Adding an additive such as ethylene glycol to the cooling water is also disclosed.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0015] However, although the quenching distortion prevention jig disclosed in Patent Documents 5 and 6 described above is effective when the forged body has a simple shape such as a cylindrical shape, in the case of a forged body with a complex shape such as a suspension arm, the locations where distortion occurs are diverse, and it is difficult to effectively prevent the occurrence of distortion in the entire suspension arm with the jig. Also, in the case of mass-produced suspension arms, it is not realistic in terms of manufacturing cost to prepare a number of quenching distortion prevention jigs corresponding to the production quantity.

[0016] On the other hand, in the method of adding an additive such as ethylene glycol to the cooling water, there are problems such that this additive adheres to the forged body and causes contamination, and also the effect of suppressing quenching distortion is limited.

[0017] An object of the present invention is to provide a method for manufacturing a forged molded product capable of suppressing the occurrence of quenching distortion in the forged body without using an additive, a jig, or the like in the quenching process.

Means for Solving the Problems

[0018] In order to solve the above problems, the present invention proposes the following means. That is, the method for manufacturing a forged molded product of the present invention is a method for manufacturing a forged molded product for a suspension arm for an automobile, comprising a heating step of heating a cylindrical forged material made of an aluminum alloy to a forging temperature range, a primary forging step of forging the forged material maintained in the forging temperature range between a first upper mold having an upper molding portion imitating the shape of the forged product and a first lower mold having a lower molding portion to obtain a primary forged body, a secondary forging step of forging the primary forged body between a second upper mold having an upper molding portion imitating the shape of the forged product and a second lower mold having a lower molding portion to obtain a secondary forged body, a solutionizing step of solutionizing the secondary forged body, a quenching step of quenching the secondary forged body, and an aging step of subjecting the secondary forged body to age hardening treatment to obtain the suspension arm. The forging temperature range in the heating step is in the range of 450°C or higher and 550°C or lower. The surface temperature of the upper molding portion of the first upper mold in the primary forging step and the surface temperature of the upper molding portion of the second upper mold in the secondary forging step are each in the range of 150°C or higher and 190°C or lower, and the surface temperature of the lower molding portion of the first lower mold and the surface temperature of the lower molding portion of the second lower mold are each in the range of 190°C or higher and 230°C or lower. Moreover, the surface temperature of the lower molding portion of the first lower mold and the surface temperature of the lower molding portion of the second lower mold are each 5°C or higher than the surface temperature of the upper molding portion of the first upper mold and the surface temperature of the upper molding portion of the second upper mold, respectively.

[0019] According to the present invention, when manufacturing a suspension arm, the surface temperature of the upper molding part of the first upper die in the primary forging process and the surface temperature of the upper molding part of the second upper die in the secondary forging process are each in the range of 150°C or higher and 190°C or lower, and the surface temperature of the lower molding part of the first lower die and the surface temperature of the lower molding part of the second lower die are each in the range of 190°C or higher and 230°C or lower, and the surface temperature of the lower molding part of the first lower die and the surface temperature of the lower molding part of the second lower die are each set 5°C or higher than the surface temperature of the upper molding part of the first upper die and the surface temperature of the upper molding part of the second upper die, respectively. By doing so, it is possible to reduce the strain generated in the secondary forged body forged from the forging material. Thereby, the suspension arm for an automobile obtained through a heat treatment process including a solutionizing process, a quenching process, and an aging hardening process can have no strain and high strength with dimensions as designed.

[0020] Further, in the present invention, the forging material may be one whose surface has been peeled in advance.

[0021] Further, in the present invention, in the solutionizing process, the quenching process, and the aging hardening process, the plurality of secondary forged bodies may be stored in a storage case that holds them at a constant interval such that their longitudinal directions are parallel to each other.

[0022] Further, in the present invention, in the quenching process, the water temperature of the cooling water for quenching and cooling the secondary forged body may be in the range of 60°C or higher and 65°C or lower.

[0023] Further, in the present invention, the aluminum alloy may be a 6000 - series aluminum alloy.

Effects of the Invention

[0024] According to the present invention, it becomes possible to provide a method for manufacturing a forged molded product capable of suppressing the occurrence of quenching distortion in the forged body without using additives, jigs, etc. in the quenching process.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0026] Hereinafter, with reference to the drawings, a method for manufacturing a forged molded product according to an embodiment of the present invention will be described. The following embodiments are specifically described in order to better understand the gist of the invention, and do not limit the present invention unless otherwise specified. In addition, the drawings used in the following description may show the main parts enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component are not necessarily the same as the actual ones.

[0027] In the following embodiment, for example, a suspension arm 100 for an automobile in the form shown in FIG. 1 is forged and molded. Such a suspension arm 100 is an arm for controlling the movement of the wheels of an automobile and is also referred to as a control arm. Such a suspension arm 100 is usually installed one by one on the left and right of the vehicle in the direction along the traveling direction, but 3 to 5 may be used to resist lateral forces. For this reason, the suspension arm 100 needs to be high-strength and lightweight.

[0028] FIG. 2 is a flowchart showing step by step the manufacturing method of a forged molded product according to an embodiment of the present invention. The manufacturing method of the forged molded product of this embodiment for manufacturing the suspension arm 100 as described above includes a heating step S1 of heating the forging material to the forging temperature range, a primary forging step S2 of forging the forging material between a first upper die and a first lower die to obtain a primary forged body, a secondary forging step S3 of forging the primary forged body between a second upper die and a second lower die to obtain a secondary forged body, a solutionizing step S4 of solutionizing the secondary forged body, a quenching step S5 of quenching the secondary forged body, and an aging hardening step S6 of aging hardening the secondary forged body, and these steps are performed in order.

[0029] The forging material, which is a raw material for manufacturing the suspension arm 100 by the manufacturing method of the forged molded product of this embodiment, may be an aluminum alloy formed into a cylindrical (round bar) shape. As an example of the dimensions, the diameter is about 40 to 60 mm and the length is about 500 to 600 mm. As the aluminum alloy, for example, a 6000 series aluminum alloy defined in JIS may be used. As an example of its composition, Si: 0.65 mass% to 0.80 mass%, Fe: 0.20 mass% to 0.40 mass%, Cu: 0.27 mass% to 0.40 mass%, Mn: 0.08 mass% to 0.15 mass%, Mg: 0.97 mass% to 1.20 mass%, Cr: 0.20 mass% to 0.30 mass%, and the balance is an Al-Mg-Si alloy composed of Al and inevitable impurities. Further, it may contain B: 0.0001 mass% to 0.03 mass%.

[0030] It is preferable that such a forging material is previously subjected to peeling processing for grinding the outer peripheral surface with a predetermined thickness to remove the oxide film and smooth the peripheral surface.

[0031] In the heating step S1, the forging material as described above is heated to the forging temperature range. The heating may be performed by using a heating furnace to heat a large number of forging materials collectively. The forging temperature range of the forging material is in the range of 450°C or higher and 550°C or lower. In this embodiment, the forging material is heated to 500°C. By heating such a forging material, the plastic fluidity of the forging material increases.

[0032] FIG. 3 is an external perspective view showing the molds used in the primary forging process S2 and the secondary forging process S3, respectively. The primary forging process S2, also known as rough forming, forges the forging material heated to the forging temperature range in the heating process S1 into a rough shape of the suspension arm 100, which is a forged product. In this primary forging process S2, the first upper die 11 and the first lower die 12 are used.

[0033] The first lower die 12 is a fixed die fixed to a horizontal pedestal or the like, and a lower molding portion 12a, which roughly resembles the shape of the lower half of the suspension arm 100, which is a forged product, is formed. The lower molding portion 12a may be a concave portion that opens on the surface side facing the first upper die 11. During forging, the forging material heated to the forging temperature range is placed on this lower molding portion 12a.

[0034] The first upper die 11 is a movable die that can move up and down along the vertical direction, and is moved up and down between the top dead center and the bottom dead center in contact with the first lower die 12 by a vertical movement mechanism (not shown) such as a hydraulic cylinder. An upper molding portion 11a, which roughly resembles the shape of the upper half of the suspension arm 100, which is a forged product, is formed on the first upper die 11. The upper molding portion 11a may be a concave portion that opens on the surface side facing the first lower die 12.

[0035] In the primary forging process S2, the surface temperature of the upper molding portion 11a of the first upper die 11 is heated to be in the range of 150°C or higher and 190°C or lower as described above. Also, the surface temperature of the lower molding portion 12a of the first lower die 12 is heated to be in the range of 190°C or higher and 230°C or lower. At this time, the surface temperature of the lower molding portion 12a of the first lower die 12 is made to be at least 5°C or higher than the surface temperature of the upper molding portion 11a of the first upper die 11.

[0036] As an example, in the primary forging process S2, the surface temperature of the lower molding portion 12a of the first lower die 12 was set to 150°C, the surface temperature of the lower molding portion 12a of the first lower die 12 was set to 190°C, and the temperature difference was set to 40°C.

[0037] After heating the temperatures of the first upper die 11 and the first lower die 12 to a predetermined temperature, a forging material heated within a forging temperature range is placed on the lower molding portion 12a of the first lower die 12, and the first upper die 11 is lowered along the vertical direction to the bottom dead center where it contacts the first lower die 12. As a result, the cylindrical forging material undergoes metal flow (plastic flow) so as to spread within the molding space formed by the upper molding portion 11a and the lower molding portion 12a, and a primary forged body roughly shaped like the suspension arm 100 is obtained.

[0038] The primary forged body thus obtained undergoes the next secondary forging process S3 while maintaining the forging temperature range. The secondary forging process S3 is also referred to as finish forming, and the primary forged body within the forging temperature range is forged so as to have the designed shape of the suspension arm 100 which is the forged product. In this secondary forging process S3, the second upper die 21 and the second lower die 22 are used.

[0039] The second lower die 22 is a fixed die fixed to a horizontal pedestal or the like, and a lower molding portion 22a shaped like mainly the lower half of the suspension arm 100 which is the forged product is formed. The lower molding portion 22a may be a concave portion that opens on the surface side facing the second upper die 21. During forging, the primary forged body within the forging temperature range is placed on this lower molding portion 22a.

[0040] The second upper die 21 is a movable die that can move up and down along the vertical direction, and is moved up and down between the top dead center and the bottom dead center where it contacts the second lower die 22 by a vertical movement mechanism (not shown) such as a hydraulic cylinder. The second upper die 21 has an upper molding portion 21a shaped like mainly the upper half of the suspension arm 100 which is the forged product. The upper molding portion 21a may be a concave portion that opens on the surface side facing the second lower die 22.

[0041] In the secondary forging process S3, the surface temperature of the upper molding portion 21a of the second upper die 21 as described above is heated to be in the range of 150°C or higher and 190°C or lower. Also, the surface temperature of the lower molding portion 22a of the second lower die 22 is heated to be in the range of 190°C or higher and 230°C or lower. At this time, the surface temperature of the lower molding portion 22a of the second lower die 22 is made to be at least 5°C or higher than the surface temperature of the upper molding portion 21a of the second upper die 21.

[0042] As an example, in the secondary forging process S3, the surface temperature of the lower molding portion 22a of the second lower die 22 was set to 160°C, the surface temperature of the lower molding portion 22a of the second lower die 22 was set to 200°C, and the temperature difference was set to 40°C.

[0043] After heating the temperatures of the second upper die 21 and the second lower die 22 to a predetermined temperature, the primary forged body that has been in the forging temperature range is placed on the lower molding portion 22a of the second lower die 22, and the second upper die 21 is lowered vertically along the direction to the bottom dead center in contact with the second lower die 22. As a result, the primary forged body undergoes metal flow within the molding space formed by the upper molding portion 21a and the lower molding portion 22a, and a secondary forged body that is precisely finish-forged into the shape of the suspension arm 100 is obtained.

[0044] The secondary forged body immediately after the secondary forging process S3 is, for example, about 350°C. After this secondary forged body is cooled naturally in a room temperature environment by slow cooling to 300°C, it is cooled from 300°C to room temperature by air cooling with blowing. During this cooling, it is preferable that the secondary forged body maintains the same posture as during forging. After that, burrs and preformed parts generated during the forging of the secondary forged body are removed.

[0045] Next, this secondary forged body is processed in the order of the solution heat treatment process S4, the quenching process S5, and the aging hardening process S6, which are heat treatment processes. The solution heat treatment process S4 is a process of uniformly dissolving the undissolved elements in the aluminum alloy to improve corrosion resistance and the like. In the solution heat treatment process S4, the secondary forged body is heated to the solution heat treatment temperature, for example, by a heating furnace. In the case of an aluminum alloy, it may be heated to a range of 500°C or higher and 530°C, for example.

[0046] In the quenching process S5, the secondary forged body heated to the solution treatment temperature in the previous solution treatment process S4 is rapidly quenched and cooled with cooling water. At this time, it is preferable that the water temperature of the cooling water is in the range of 60°C or higher and 65°C or lower.

[0047] In the quenching process S5, since the immersion speed of the secondary forged body heated to the solution treatment temperature in the cooling water is very fast, if the water temperature of the cooling water is less than 60°C, there is a concern that distortion may easily occur in the arm portions 100a, 100b, 100c (see FIG. 1) of the suspension arm 100 which is the secondary forged body during quenching. Also, if the water temperature of the cooling water exceeds 65°C, there is a concern that the rapid cooling effect will be reduced. For this reason, for example, using a warm water circulation system, a heater, etc., the water temperature of the cooling water in the water tank is set in the range of 60°C or higher and 65°C or lower.

[0048] The aging hardening process S6 is a process of performing artificial aging hardening treatment on the secondary forged body that has undergone the previous quenching process S5 using an artificial aging hardening treatment furnace. Thereby, the elements dissolved by supersaturation can be artificially precipitated, and the hardness of the secondary forged body can be increased due to the strain of the crystal. Such an aging hardening process S6 can be performed by heating the secondary forged body that has undergone the quenching process S5 to about 200°C, for example.

[0049] In the heat treatment process including the above-described solution treatment process S4, quenching process S5, and aging hardening process S6, for example, in order to mass-produce suspension arms on a scale of hundreds of thousands per month, while a large number of secondary forged bodies are accommodated in a heat treatment storage case 110 as shown in FIG. 4, without transferring the secondary forged body in each of the solution treatment process S4, quenching process S5, and aging hardening process S6, it is preferable to perform each heat treatment process while keeping the storage case as it is or together with the storage case.

[0050] The storage case 110 is formed of, for example, a heat-resistant metal, and holds a large number of secondary forged bodies at regular intervals inside such that their longitudinal directions are parallel to each other. Such a storage case 110 may have a configuration that allows heat and cooling water to easily enter the inside.

[0051] By using such a storage case 110 in the heat treatment process, a large number of relatively small secondary forged parts such as suspension arms can be efficiently heat-treated collectively, and the productivity of the suspension arms can be improved. Through the above respective processes, the suspension arm 100 for an automobile can be manufactured from the forged material.

[0052] As described above, according to the method for manufacturing a forged molded product of an embodiment of the present invention, when forging and molding the suspension arm 100 for an automobile, the surface temperature of the upper molding portion 11a of the first upper mold 11 in the primary forging process S2 and the surface temperature of the upper molding portion 21a of the second upper mold 21 in the secondary forging process S3 are each in the range of 150°C or higher and 190°C or lower, and the surface temperature of the lower molding portion 12a of the first lower mold 12 and the surface temperature of the lower molding portion 22a of the second lower mold 22 are each in the range of 190°C or higher and 230°C or lower, and the surface temperature of the lower molding portion 12a of the first lower mold 12 and the surface temperature of the lower molding portion 22a of the second lower mold 22 are each set to be 5°C or higher than the surface temperature of the upper molding portion 11a of the first upper mold 11 and the surface temperature of the upper molding portion 21a of the second upper mold 21, respectively. By doing so, the strain generated in the secondary forged part forged from the forged material can be reduced. As a result, the suspension arm 100 for an automobile obtained through the heat treatment process including the solutionizing process S4, the quenching process S5, and the aging hardening process S6 can have dimensions as designed without strain and can have high strength.

[0053] The embodiments of the present invention have been described above. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Example

[0054] The effects of the present invention were verified. <Example 1 of the present invention> A forged material made of a cylindrical aluminum alloy (diameter 48 mm, length 543 mm) that had been subjected to a peeling process in advance was prepared, and this forged material was heated to 500°C (heating step). Then, for the heated forged material, the surface temperature of the molding part of the first upper die shown in FIG. 2 was set to 150°C, and the surface temperature of the molding part of the first lower die was set to 230°C, and rough forming (primary forging process) was performed to obtain a primary forged body.

[0055] Next, for this primary forged body, the surface temperature of the molding part of the second upper die shown in FIG. 2 was set to 150°C, and the surface temperature of the molding part of the second lower die was set to 230°C, and finish forming (secondary forging process) was performed to obtain a secondary forged body. Then, the secondary forged body, which was about 350°C after the secondary forging process, was cooled to 300°C by natural cooling and then cooled to 50°C by air cooling with a fan from 300°C or lower. The ambient temperature at this time remained at room temperature, and the posture of the secondary forged body was maintained during the implementation. Then, the burrs and excess material parts of the cooled secondary forged body were removed by trimming to produce a secondary forged body having the shape shown in FIG. 1.

[0056] Furthermore, this secondary forged body was heat-treated in the order of solutionizing process, quenching process, and aging hardening process in the same manner as in the above-described embodiment to obtain the suspension arm of Example 1 of the present invention.

[0057] <Comparative Example 1> As a conventional Comparative Example 1, rough forming (primary forging process) was performed by setting the surface temperature of the molding part of the first upper die to 230°C and the surface temperature of the molding part of the first lower die to 150°C, and finish forming (secondary forging process) was performed by setting the surface temperature of the molding part of the second upper die to 230°C and the surface temperature of the molding part of the second lower die to 150°C. Otherwise, the manufacturing conditions were the same as those in Example 1 of the present invention.

[0058] <Comparative Example 2> As a conventional comparative example 1, rough forming (primary forging process) was performed with the surface temperature of the molding part of the first upper die and the surface temperature of the molding part of the first lower die both set to 190°C, and finish forming (secondary forging process) was performed with the surface temperature of the molding part of the second upper die and the surface temperature of the molding part of the second lower die both set to 190°C. Otherwise, the manufacturing conditions were the same as those in Example 1 of the present invention.

[0059] The strains of the suspension arms of Example 1 of the present invention, Comparative Example 1, and Comparative Example 2 obtained as described above were measured. In the measurement, the gauge device G shown in FIG. 5 was used, and the positioning in the height direction was measured at three points g1, g2, and g3. The positioning in the longitudinal direction was performed at g4, and the positioning in the short-side direction (the depth direction in FIG. 5) was performed at g5 and g6. The strain measurement location was the location g6 where the curvature of each suspension arm was large, and it was measured with a linear gauge in the vertical direction. The evaluation method was to zero-adjust the linear gauge with a master sample having a design strain of "0", and the difference from the master sample was taken as the strain. The results of such strain measurements are shown in a graph in FIG. 6.

[0060] According to the strain measurement results shown in FIG. 6, the strain value of the suspension arm of Example 1 of the present invention obtained by the manufacturing method of the forged molded product of the present embodiment remained at -0.01 mm. On the other hand, the strain value of the suspension arm of Comparative Example 1 was -0.20 mm, and the strain value of the suspension arm of Comparative Example 2 was 0.07 mm. In both cases, larger strains occurred compared to Example 1 of the present invention. Therefore, it was confirmed that according to the manufacturing method of the forged molded product of the present embodiment, it is possible to manufacture a suspension arm with less error with respect to the design value and suppressed strain.

Industrial Applicability

[0061] The manufacturing method of the forged molded product of the present invention enables the manufacture of an automobile suspension arm with less strain using a round bar-shaped forged material. Therefore, it has industrial applicability.

[0062] 11... First upper die 11a... Upper molding part 12…First lower mold 12a…Lower forming part 21…Second upper mold 21a…Upper forming part 22…Second lower mold 22a…Lower forming part 100…Suspension arm

Claims

1. A method for manufacturing a forged molded product for a suspension arm for an automobile, comprising: a heating step of heating a cylindrical forged material made of an aluminum alloy to a forging temperature range; a primary forging step of forging the forged material maintained in the forging temperature range between a first upper mold having an upper molding portion imitating the shape of the forged product and a first lower mold having a lower molding portion to obtain a primary forged body; a secondary forging step of forging the primary forged body between a second upper mold having an upper molding portion imitating the shape of the forged product and a second lower mold having a lower molding portion to obtain a secondary forged body; a solution treatment step of solution-treating the secondary forged body; a quenching step of quenching the secondary forged body; a aging hardening step of aging-hardening the secondary forged body to obtain the suspension arm, and having at least; the forging temperature range in the heating step is in the range of 450°C or higher and 550°C or lower; the surface temperature of the upper molding portion of the first upper mold in the primary forging step and the surface temperature of the upper molding portion of the second upper mold in the secondary forging step are each in the range of 150°C or higher and 190°C or lower, and the surface temperature of the lower molding portion of the first lower mold and the surface temperature of the lower molding portion of the second lower mold are each in the range of 190°C or higher and 230°C or lower, and the surface temperature of the lower molding portion of the first lower mold and the surface temperature of the lower molding portion of the second lower mold are each 5°C or higher than the surface temperature of the upper molding portion of the first upper mold and the surface temperature of the upper molding portion of the second upper mold. A method for manufacturing a forged molded product characterized by this.

2. The method for manufacturing a forged molded product according to claim 1, wherein the surface of the forged material is pre-peeled.

3. In the solution treatment step, the quenching step, and the aging hardening step, a plurality of the secondary forged bodies are stored in a storage case and held at a constant interval so that their longitudinal directions are parallel to each other. The method for manufacturing a forged molded product according to claim 1 or 2, characterized by this.

4. In the quenching step, the water temperature of the cooling water for quenching and cooling the secondary forged body is in the range of 60°C or higher and 65°C or lower. The method for manufacturing a forged molded product according to any one of claims 1 to 3, characterized by this.

5. The method for manufacturing a forged molded product according to any one of claims 1 to 4, wherein the aluminum alloy is a 6000 series aluminum alloy.

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