Sequential forming method

Abstract

To solve the problem that a conventional sequential forming method may cause deformation by spring back after forming, and is desirable to be improved.SOLUTION: A sequential forming method includes a forming step of forming a metal plate W into a three-dimensional shape along a forming die 1, using a rod-like tool T arranged on one main surface side of the metal plate W and the forming die 1 arranged on the other main surface side of the metal plate W, while moving the metal plate W with the tip of the rod-like tool T pressed against the metal plate W, and a correction step of imparting compressive stress to a necessary correction region Wc as a part of a forming part Wf of the metal plate W passing through the forming step between the rod-like tool T and the forming die 1, while pressing and moving the rod-like tool T with respect to the necessary correction region Wc, and suppresses deformation by spring back in the formed metal plate W.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an incremental forming method for forming a metal sheet into a three-dimensional shape using a rod-shaped tool and a forming die. [Background technology]

[0002] A conventional incremental forming method is described, for example, in Patent Document 1. Patent Document 1 describes an incremental forming method in which a metal plate and a rod-shaped tool are placed above a forming die, and the metal plate is formed into a three-dimensional shape along the forming die while the rod-shaped tool is pressed against the metal plate and moved. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-244493 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional incremental forming method as described above, when the metal plate is released from restraint after forming, deformation due to springback may occur. Deformation is particularly noticeable in aluminum metal plates, so improvements to suppress this deformation were needed.

[0005] The present invention has been made in consideration of the above-mentioned conventional situation, and has an object to provide an incremental forming method capable of suppressing deformation due to springback in a metal sheet after forming. [Means for solving the problem]

[0006] The incremental forming method according to the present invention uses a rod-shaped tool arranged on one main surface side of a metal plate and a mold arranged on the other main surface side of the metal plate. The incremental forming method is characterized by including a forming process in which the metal plate is formed into a three-dimensional shape along the mold while pressing and moving the tip of the rod-shaped tool against the metal plate, and a straightening process in which the rod-shaped tool is pressed against and moved against a straightening-requiring region, which is a part of the formed part of the metal plate that has undergone the forming process, and compressive stress is applied to the straightening-requiring region between the rod-shaped tool and the mold. In the above configuration, the straightening-requiring region is a region where springback is likely to occur, and is set according to the shape of the formed part. Effect of the Invention

[0007] By adopting the above-mentioned configuration, the incremental forming method according to the present invention can suppress deformation due to springback in the metal sheet after forming, and can improve the shape accuracy of the metal sheet. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a cross-sectional view showing a state at the start of molding as a first embodiment of the incremental molding method. [Diagram 2] FIG. 2 is a cross-sectional view illustrating a molding step subsequent to FIG. [Diagram 3] FIG. 4 is a plan view showing a moving path of a rod-shaped tool. [Figure 4] FIG. 3 is a cross-sectional view illustrating a straightening step following FIG. 2. [Diagram 5] 10A to 10C are cross-sectional views of the main parts in a straightening process. [Figure 6] FIG. 4 is a cross-sectional view showing the metal plate after forming. [Figure 7] 5A to 5D are cross-sectional views showing a second embodiment of the incremental molding method in the order of steps (A) to (D). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] First Embodiment 1 to 6 are diagrams illustrating a first embodiment of an incremental forming method according to the present invention. As shown in Fig. 1, the incremental forming method uses a rod-shaped tool T arranged on one main surface side (upper side in the figure) of a metal sheet W and a forming die 1 arranged on the other main surface side of the metal sheet W. The metal sheet W is a flat plate that is the raw material for a formed product.

[0010] The rod-shaped tool T is held by a driving device (not shown) in a position with its axis in the up-down direction, and its lower tip portion forms a spherical surface. Examples of the driving device include a multi-axis controlled work robot and an NC machine tool. This drives the rod-shaped tool T in three orthogonal axial directions, or in three orthogonal axial directions and around each axis.

[0011] The forming die 1 has a shoulder 1A around its periphery, and a forming recess 1B that is open upward inside the shoulder 1A. After the metal sheet W is placed in a horizontal position on the shoulder 1A of the forming die 1, the peripheral edge of the metal sheet W is sandwiched between the shoulder 1A and a frame-shaped clamp 2 that can be raised and lowered to firmly hold it. The incremental forming method according to the present invention can be carried out even if the metal sheet W is inclined or vertical, and the rod-shaped tool T and the forming die 1 are positioned according to the attitude of the metal sheet W.

[0012] The incremental forming method includes a forming step in which, as shown in FIG. 2, the tip of a rod-shaped tool T is pressed against and moved against a metal plate W, while the metal plate W is formed into a three-dimensional shape along the inner surface of the forming recess 1B of the forming mold 1.

[0013] In the above forming process, as shown by the arrow A in Fig. 3, the rod-shaped tool T is moved in a circular motion along a contour line, and a pitch feed is performed in which the rod-shaped tool T is moved inward and downward for each revolution. In this way, in the incremental forming method, the bottom of the metal sheet W is gradually pressed down to form a formed part Wf having a three-dimensional shape.

[0014] In addition, as shown in Figure 4, the incremental forming method includes a straightening process in which a rod-shaped tool T is pressed against and moved against a region requiring straightening Wc, which is part of the formed portion Wf of the metal plate W that has undergone the above-mentioned forming process, and compressive stress is applied to the region requiring straightening Wc between the rod-shaped tool T and the forming die 1.

[0015] The area requiring correction Wc is an area in the formed portion Wf where the forming angle is relatively small when the angle between the main surface of the metal sheet W before forming and the inclined surface after forming is taken as the forming angle, and in this embodiment, it is the bottom surface area of ​​the formed portion Wf shown by matte hatching in Fig. 4. In short, the area requiring correction Wc is an area where springback is likely to occur after forming.

[0016] In the above-mentioned straightening process, as shown by the arrow B in Fig. 3 and Fig. 4, the rod-shaped tool T is moved in one direction, and then moved in the other direction so as to shift the trajectory in parallel, and such reciprocating movement is repeated to apply compressive stress to the entire area requiring straightening Wc. Note that the movement of the rod-shaped tool T can be appropriately selected, and for example, a starting point may be set at the center or outer periphery of the area requiring straightening Wc to make a spiral trajectory.

[0017] Furthermore, in the above-mentioned straightening process, as shown in FIG. 5, it is preferable that the relationship between the distance c from the rod-shaped tool T to the inner surface of the forming recess 1B of the forming die 1 and the sheet thickness t of the metal sheet W is t>c>0.7t, whereby a compressive stress capable of suppressing springback can be applied to the region Wc requiring straightening.

[0018] Furthermore, in the above-mentioned straightening step, the rod-shaped tool T used in the forming step may be used as it is, or a different rod-shaped tool T may be used, and in any case, it is preferable to use a rod-shaped tool T having a spherical tip as described above. Note that, although the above-mentioned straightening step can be performed multiple times on the region Wc requiring straightening, it is possible to impart sufficient compressive stress even with only one time.

[0019] Incidentally, in the case where only the forming process is performed on the metal sheet W, when the restraint by the clamp 2 is released, the bottom part of the metal sheet W, which has a small forming angle, deforms in the direction of returning to a flat state due to springback, as shown by the dotted line in Figure 6, and the metal sheet W deforms into an overall open state.

[0020] In contrast, in the above-mentioned incremental forming method, a straightening process is performed following the forming process to impart compressive stress to the region requiring straightening Wc, so that deformation due to springback in the metal sheet W after forming can be suppressed as shown by the solid line in Fig. 6, and the shape accuracy of the metal sheet W can be improved. As a result, in the above-mentioned incremental forming method, even when using a metal sheet W made of aluminum, which is prone to springback, a formed product with good shape accuracy can be obtained.

[0021] As a test, the straightening step was carried out by varying the distance (clearance) c from the rod-shaped tool T to the forming die 1. The results are shown in Table 1 below.

[0022] [Table 1]

[0023] As is clear from Table 1, when the clearance c was set to 1.0t, that is, when the clearance c was set to be equal to the thickness t of the metal sheet W, no tool marks were left, but the application of compressive stress was insufficient, and deformation occurred at the peripheral portion of the metal sheet W. Furthermore, when the clearance c was set to 0.6t, the application of compressive stress was excessive, and tool marks occurred. In contrast, it was confirmed that when the clearance was set to 0.7t or 0.8t, sufficient compressive stress was applied, and no deformation occurred, and no tool marks were left.

[0024] As a result, in the above-mentioned incremental forming method, by setting the relationship between the distance c from the rod-shaped tool T to the forming die 1 and the thickness t of the metal sheet W to be t>c>0.7t, the springback of the metal sheet W after forming can be suppressed, resulting in good shape accuracy, and good surface quality without tool marks can be obtained, making it possible to produce high-quality formed products.

[0025] In the formed portion Wf of the metal sheet W, the area with a large forming angle has a smaller sheet thickness because a tensile force acts on the material during forming. In contrast, the area with a small forming angle has a very small reduction in sheet thickness, so the relationship between the distance c and the sheet thickness t (t>c>0.7t) as described above can be set. The shape accuracy can be determined by comparing design data such as CAD with the actual measured values ​​of the formed product.

[0026] Furthermore, in the incremental forming method described above, by using a rod-shaped tool T having a spherical tip, the tip of the rod-shaped tool T comes into sufficient contact with the metal sheet W, and the function of suppressing deformation due to springback can be further improved. Note that, although it is best for the tip of the rod-shaped tool T to be spherical, it is also possible to give the tip of the rod-shaped tool T other shapes, such as a curved shape, as long as it can impart sufficient compressive stress to the metal sheet W.

[0027] <Second embodiment> 7 is a diagram showing a second embodiment of the incremental forming method according to the present invention. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0028] As shown in Fig. 7(A), the incremental forming method uses a rod-shaped tool T arranged on one main surface (upper side) of a metal sheet W, a forming die 11 arranged on the other main surface of the metal sheet W, and a clamping device 12 that holds the peripheral portion of the metal sheet W. The forming die 11 in this embodiment has a forming convex portion 11B that bulges upward at its upper portion. The clamping device 12 includes an upper frame 12A and a lower frame 12B that hold the peripheral portion of the metal sheet W from above and below, and is driven to move up and down by a driving device not shown while holding the metal sheet W.

[0029] In the incremental forming method, as shown in Fig. 7(B), the tip of a rod-shaped tool T is pressed against the metal sheet W and moved while the metal sheet W is formed into a three-dimensional shape along the forming protrusion 11B of the forming die 11. At this time, in this embodiment, the clamp device 12 is gradually lowered while the metal sheet W is gradually deformed along the forming die 11. Also, the rod-shaped tool T is moved in a contour trajectory as in the first embodiment.

[0030] In this embodiment, the clamping device 12 may be left stationary and the forming mold 11 may be raised, or the clamping device 12 and the forming mold 11 may be moved relative to each other as shown by the arrow in Figure 7(B).

[0031] 7(C), the incremental forming method performs a straightening step in which a bar-shaped tool T is pressed against and moved against a region requiring straightening Wc, which is part of the formed portion Wf of the metal sheet W that has been subjected to the forming step, while applying compressive stress to the region requiring straightening Wc between the bar-shaped tool T and the forming die 11. The region requiring straightening Wc in this embodiment is a top region of the formed portion Wf of the metal sheet W that has a relatively small forming angle.

[0032] Here, in the case where only the forming process is performed on the metal plate W, when the restraint by the clamping device 12 is released, the bottom part of the metal plate W, which has a small forming angle, deforms in the direction of returning to a flat state due to spring back, as shown by the dotted line in Figure 7 (D), and the metal plate W deforms into an overall open state.

[0033] In contrast, in the above-mentioned incremental forming method, a straightening process is performed following the forming process to impart compressive stress to the region requiring straightening Wc, thereby suppressing deformation due to springback in the metal sheet W after forming, as shown by the solid line in Fig. 7(D). In this way, the above-mentioned incremental forming method can improve the shape accuracy of the metal sheet W, as in the first embodiment, and can obtain a formed product with good shape accuracy even when using an aluminum metal sheet W, which is prone to springback.

[0034] The details of the configuration of the incremental forming method according to the present invention are not limited to the above-described embodiments, and can be appropriately modified without departing from the gist of the present invention. [Explanation of symbols]

[0035] 1,11 Molding mold T bar tool W Metal plate Wc Area requiring correction Wf molded part

Claims

1. Using a rod-shaped tool disposed on one main surface side of a metal plate and a forming die disposed on the other main surface side of the metal plate, a forming step of forming the metal plate into a three-dimensional shape along a forming die while pressing and moving a tip of the rod-shaped tool against the metal plate; and a straightening process in which the rod-shaped tool is pressed and moved against an area requiring straightening, which is part of the formed portion of the metal plate that has undergone the forming process, while applying compressive stress to the area requiring straightening between the rod-shaped tool and the forming die.

2. The angle between the main surface of the metal plate before forming and the inclined surface after forming is defined as a forming angle, The incremental forming method according to claim 1, wherein the area requiring correction is an area in the formed portion where the forming angle is relatively small.

3. 3. The incremental forming method according to claim 1, wherein in the correction step, a relationship between a distance c from the bar-shaped tool to the forming die and a thickness t of the metal plate satisfies t>c>0.7t.

4. The incremental forming method according to claim 3 , wherein the rod-shaped tool is a tool having a spherical tip.

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