Press molding method

Abstract

To achieve both reduction in a press load and excellent dimensional accuracy.SOLUTION: A press molding method includes an intermediate molded article molding step of pressing a metal plate and molding an intermediate molded article, an additional processing step of subjecting the intermediate molded article to additional processing by pressing, and a specification step of specifying a part under a low pressure where a low pressure is acted on the intermediate molded article in the additional processing step, wherein the additional processing step performs the additional processing so that the pressure acted on the part under the low pressure is equal to or less than a predetermined pressure.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a press forming method. [Background technology]

[0002] The press forming load when press forming a metal plate increases as the material strength or plate thickness increases. The press forming load also increases as the press-formed product becomes larger and the formed shape becomes more complex. On the other hand, a press machine has an upper limit to the load that can be applied to a metal plate. Therefore, depending on the existing press machine, it may not be possible to apply the target load to the metal plate, and it may not be possible to manufacture a press-formed product of the target shape.

[0003] For the purpose of reducing the press load, Patent Document 1 discloses a manufacturing method for a press-formed product in which the press-formed shape is arranged so as to be inclined with respect to the press direction and formed using a cam mechanism, thereby converting the load acting in the press direction to the inclined surface side and reducing the load in the press direction.

[0004] For example, in a transfer press, a metal plate is pressed multiple times to produce a press-formed product. In a press process in which multiple presses are performed, a portion formed in a previous press may be pressurized again. In the following description, the re-pressurization of a portion formed in a previous press may be referred to as overlapping pressurization.

[0005] As a technology for reducing overlapping pressure, for example, Patent Document 2 discloses a press forming method in which vehicle body parts are press-formed from plate material through multiple processes, in which the clearance between the die and the material to be formed in the formed portion of the intermediate product at locations that have a large effect on springback in the next process is made larger than the plate thickness. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-75275 A [Patent Document 2] JP 2020-163416 A Summary of the Invention [Problem to be solved by the invention]

[0007] The technology described in Patent Document 1 reduces the apparent load by changing the direction of the load, but it may be difficult to apply it to the actual part shape because it inclines the forming part. Also, as in the technology described in Patent Document 2, simply making the clearance between the die and the formed material in the part that has a large effect on springback larger than the plate thickness may change the springback after forming, making it impossible to achieve both load reduction and dimensional accuracy.

[0008] The present invention has been made in consideration of the above circumstances, and has an object to provide a press forming method that can achieve both a reduction in press load and excellent dimensional accuracy. [Means for solving the problem]

[0009] The inventors have found that portions in which the difference in strain before and after press working is small are portions in which the amount of deformation is small, and that by reducing the pressure applied to such portions, the press load can be reduced, and further, a press-worked product with excellent dimensional accuracy can be produced.

[0010] The gist of the present invention, which has been made based on the above findings, is as follows. [1] A press forming method according to one embodiment of the present invention includes an intermediate product forming process in which a metal plate is pressed to form an intermediate product, an additional processing process in which the intermediate product is further processed by press processing, and an identification process in which a low-pressure portion is identified in the additional processing process where a low pressure is applied to the intermediate product, and in the additional processing process, additional processing is performed by setting the pressure applied to the low-pressure portion to be equal to or lower than a predetermined pressure. [2] In the press molding method described in [1] above, in the additional machining step, the additional machining may be performed with a pressure of 100 MPa or less applied to the low-pressure portion. [3] In the press molding method described in [1] or [2] above, in the specified step, the low reduction portion may be a portion in which the difference in plastic strain before and after press processing, in which the intermediate molded product is additionally processed without providing a relief portion, is 0.02 or less. [4] In the press forming method according to any one of the above items [1] to [3], the metal sheet may be a steel sheet having a tensile strength of 590 MPa or more. [5] In the press molding method according to any one of the above items [1] to [4], the intermediate product molding step and the additional processing step may be steps in which cold press working is performed. Effect of the Invention

[0011] According to the embodiment of the present invention, it is possible to achieve both a reduction in press load and excellent dimensional accuracy. [Brief description of the drawings]

[0012] [Figure 1] 1 is a flowchart illustrating a flow of a press molding method according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a model diagram of a molded product in an embodiment. [Diagram 3] FIG. 2 is a contour diagram showing the dimensional difference between the molded product of Example 1 of the present invention and the molded product of the reference example. [Figure 4] FIG. 1 is a contour diagram showing the dimensional difference between the molded product of Example 2 of the present invention and the molded product of the reference example. [Diagram 5] FIG. 1 is a contour diagram showing the dimensional difference between the molded product of the comparative example and the molded product of the reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The press forming method according to this embodiment includes an intermediate product forming process for forming an intermediate product by pressing a metal plate, an additional processing process for additionally processing the intermediate product by pressing, and a specifying process for specifying a low-pressure portion where a low pressure is applied to the intermediate product in the additional processing process, and in the additional processing process, the pressure applied to the low-pressure portion is set to a predetermined pressure or less.

[0014] <Intermediate molding process> In the intermediate product forming process, the metal plate is pressed to form the intermediate product. There is no particular limitation on the metal plate, and various metal plates can be used as the material. Examples of the metal plate include steel plate, stainless steel plate, aluminum steel plate, copper plate, titanium plate, etc. However, the higher the strength, the larger the load required for press working, and the more remarkable the effect of this embodiment can be obtained. For example, the metal plate is preferably a steel plate having a tensile strength of 590 MPa or more, more preferably a steel plate having a tensile strength of 980 MPa or more, and even more preferably a steel plate having a tensile strength of 1180 MPa or more, 1470 MPa or more.

[0015] The thickness of the metal plate is not particularly limited, but as the plate thickness increases, the load required for press working increases, and the effect of this embodiment can be obtained more significantly. Therefore, the plate thickness of the metal plate is preferably 1.0 mm or more, more preferably 1.4 mm or more, and even more preferably 1.8 mm or more. The plate thickness may be, for example, 3.2 mm or less.

[0016] The press working in the intermediate product forming step is cold press working, and as the press working, for example, drawing, pad drawing, pad bending, stamping, deep drawing, stretching, bending, or the like can be applied.

[0017] <Additional work process> In the additional processing step, the intermediate molded product is additionally processed by press processing. In the additional processing step, the pressure applied to the low-pressure reduction portion specified in the later-described specifying step is set to a predetermined pressure or less to perform additional processing. The pressure applied to the low-pressure reduction portion varies depending on the type of metal plate, the plate thickness, the shape of the molded product, etc., and can be determined according to the following method. For example, for various molded shapes, the contact pressure between the intermediate molded product and the die when plastic deformation occurs is observed, and the pressure at which elastic deformation occurs is set as the pressure applied to the low-pressure reduction portion. By setting the pressure applied to the low-pressure reduction portion to a predetermined pressure or less, the load can be reduced. In addition, since a low pressure is applied only to a portion that has little effect on deformation before and after press processing, and a high pressure is applied only to a portion that is deformed, a press molded product with excellent dimensional accuracy can be manufactured. The pressure applied to the low-pressure reduction portion is preferably 100 MPa or less. If the pressure is 100 MPa or less, the load can be sufficiently reduced to a degree that press processing can be performed at or below the limit load of the press processing machine. The pressure applied to the low pressure portion is 0 MPa, in other words, the low pressure portion does not need to come into contact with the die.

[0018] The press working in the additional processing step is cold press working, and as the press working, for example, drawing, pad drawing, pad bending, stamping, deep drawing, stretching, bending, or the like can be applied.

[0019] <Specific process> In the identification process, a low-pressure portion where a low pressure is applied in the intermediate molded product in the additional processing process is identified. As mentioned above, when a press-molded product is manufactured by performing press processing multiple times, there may be cases where a portion molded in a previous press processing is pressurized again in a later press processing, resulting in overlapping pressurization. If the overlapping pressurized portion is not deformed in the later press processing, the load acting on that portion does not contribute to the deformation. Therefore, by reducing the load on the portion where deformation does not occur, the load acting on the intermediate molded product by the press processing machine can be reduced. Therefore, in this process, a portion where the amount of deformation is small between the previous press processing (intermediate molded product molding process) and the later press processing (process of processing the intermediate molded product without providing a relief portion) is identified. In the additional processing process, the pressure acting on that portion is set to a predetermined pressure or less.

[0020] The low-stressed portion is identified, for example, by finite element method (FEM) analysis. In detail, FEM analysis is performed as a condition for applying a load when pressing into a desired shape without providing a relief portion (clearance), and the low-stressed portion is a portion where the difference in plastic strain before and after pressing is equal to or less than a predetermined value. Identification of the low-stressed portion is not limited to FEM analysis, and may be performed by performing a preliminary test, etc.

[0021] The low reduction portion may be specified in consideration of the reduction in applied load and the required dimensional accuracy. However, it is preferable to select the portion where the difference in plastic strain before and after press working is 0.02 or less as the low reduction portion, since this can further improve the dimensional accuracy.

[0022] <Press molding process> The flow of press molding according to the press molding method of this embodiment will be described with reference to Fig. 1. Fig. 1 is a flowchart for explaining the flow of press molding.

[0023] First, a specification step is performed to specify a low pressure portion where a low pressure is applied to the intermediate product in an additional processing step (step S101). Next, an intermediate product forming step is performed to form an intermediate product by pressing a metal plate (step S103), and then an additional processing step is performed to additionally process the intermediate product by pressing (step S105).

[0024] The present invention has been described above with reference to the present embodiment. However, the technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0025] For example, the additional processing step may be performed multiple times. In this case, an intermediate molded product obtained by pressing in a previous additional processing step is pressed in a subsequent additional processing step. In this case, a portion to be pressurized in the subsequent additional processing step with a pressure equal to or lower than a predetermined pressure may be specified in the specific step. EXAMPLES

[0026] Next, examples of the present invention will be described, although the technical scope of the present invention is not limited to the following examples.

[0027] A steel plate having a thickness of 1.4 mm and a tensile strength of 1470 MPa was subjected to deep drawing, cam bending, and stamping in this order to produce a formed product having the shape shown in FIG. 2. As a reference example, stamping was performed without providing a clearance between the die and the intermediate formed product for the overlapping pressurized portion in stamping. The stamping load was 177 tonf. As an example 1 of the present invention, stamping was performed with a clearance between the die and the intermediate formed product (contact pressure 0 MPa) for the portion where the difference in plastic strain before and after stamping calculated by finite element method analysis was 0.02 or less. As an example 2 of the present invention, stamping was performed with a contact pressure of 100 MPa for the portion where the difference in plastic strain before and after stamping calculated by finite element method analysis was 0.02 or less. As a comparative example, stamping was performed by providing a clearance between the die and the intermediate molded product not only for the overlapping pressurized portion where the difference in plastic strain before and after stamping calculated by finite element analysis was 0.02 or less, but also for the portion where the difference was more than 0.02 and 0.06 or less. Figure 3 shows a contour diagram showing the dimensional difference between the molded product of Example 1 of the present invention and the molded product of the Reference Example. Figure 4 shows a contour diagram showing the dimensional difference between the molded product of Example 2 of the present invention and the molded product of the Reference Example. Figure 5 shows a contour diagram showing the dimensional difference between the molded product of the Comparative Example and the molded product of the Reference Example. The numerical values ​​shown in Figures 3 to 5 indicate the dimensional difference (mm) between the molded product of the Reference Example.

[0028] In Example 1 of the present invention, the stamping load was reduced by 42% compared to the reference example to 102 tonf, and the dimensional difference was within ±0.15 mm. In Example 2 of the present invention, the stamping load was reduced by 36.5% compared to the reference example to 112.6 tonf, and the dimensional difference was within ±0.27 mm. On the other hand, in the comparative example, the stamping load was reduced by 54% compared to the reference example, but the dimensional difference was ±1.43 mm. It was found that Examples 1 and 2 of the present invention reduced the stamping load and also had excellent dimensional accuracy.

Claims

1. an intermediate product forming step of forming an intermediate product by pressing a metal plate; an additional processing step of additionally processing the intermediate molded product by press processing; and a step of specifying a low pressure portion where a low pressure is applied to the intermediate molded product in the additional processing step, In the additional machining step, the pressure applied to the low-pressure portion is set to a predetermined pressure or less to perform the additional machining.

2. The press forming method according to claim 1 , wherein in the additional machining step, the additional machining is performed with a pressure applied to the low-pressure portion being 100 MPa or less.

3. 3. The press molding method according to claim 1, wherein in the identifying step, a portion in which a difference in plastic strain before and after press working in which the intermediate molded product is additionally machined is 0.02 or less without providing a relief portion is determined as the low reduction portion.

4. The press forming method according to claim 1 or 2, wherein the metal plate is a steel plate having a tensile strength of 590 MPa or more.

5. The press forming method according to claim 1 or 2, wherein the intermediate product forming step and the additional processing step are steps in which cold press working is performed.

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