Incremental molding method

Abstract

To improve accuracy of a shape in incremental molding for molding a plate material without using a mold.SOLUTION: An incremental molding method includes a step of controlling residual stress, in a state in which the periphery of a plate material P is restrained after sequential molding of pressing and working the plate material, and eliminating or reducing spring back. The incremental molding method corrects a tool trajectory from a target shape from a shape difference between the shape of the plate material obtained after control of the residual stress and the target shape.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an incremental forming method. [Background technology]

[0002] In addition to press processing using dies, parts such as body panels can also be produced by processing methods that do not use dies and are used when only a small number of parts, such as repair items, are produced; such processing methods can be called dieless molding.

[0003] Dieless forming is a method that applies incremental forming, in which a plate material is deformed little by little by a tool attached to a robot, etc. As a technology related to dieless forming, a system equipped with a forming control unit that corrects the tool path assuming that springback occurs in the plate material in incremental forming is disclosed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-1381 Summary of the Invention [Problem to be solved by the invention]

[0005] In incremental forming, since the shape of the plate material may be significantly deformed by springback when the plate material is processed, the shape of the plate material needs to be frozen after processing. The present inventors have been making intensive studies on improving the dimensional accuracy of the plate material when freezing the shape after incremental forming.

[0006] An object of the present invention is to improve the accuracy of shape in a method for forming a plate material without using a die. [Means for solving the problem]

[0007] One aspect of the present invention includes a process for controlling residual stress in a state where the periphery of the sheet material is restrained after incremental forming to eliminate or reduce springback in incremental forming, and a tool trajectory is corrected from the target shape using a shape difference between the shape obtained after the incremental forming and the target shape. Effect of the Invention

[0008] According to the above molding method, it is possible to improve the accuracy of the shape in a molding method that does not use a metal mold. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing a device configuration of an incremental forming method according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing a molding section constituting the incremental molding device according to the embodiment. [Diagram 3] FIG. 2 is a diagram showing a residual stress control unit constituting the incremental forming device according to the first embodiment. [Figure 4] 4 is a flowchart illustrating an incremental forming method according to an embodiment. [Diagram 5] 1 is a diagram showing an actual shape, a target shape, and a corrected path before considering springback of a conventional sheet material. FIG. [Figure 6] 1A and 1B are diagrams showing a shape of a plate material processed by a conventional correction pass in which the plate material has a deflection caused by residual stress and a shape of the plate material after the deflection caused by the residual stress is eliminated. [Figure 7] 1A to 1C are diagrams showing a shape of a plate material having deflection due to residual stress before considering springback in an embodiment, a shape after the deflection due to residual stress is eliminated, a target shape, and a correction path. [Figure 8] 1A to 1C are diagrams showing a shape of a plate material processed by a correction pass according to an embodiment, the shape of the plate material being bent due to residual stress, and the shape of the plate material after the residual stress is eliminated. [Figure 9] The upper figure shows the plate material after molding by the molding part according to the embodiment and before residual stress control, and the lower figure shows the atomic level state of the plate material in the state shown in the upper figure. [Figure 10] The upper figure shows a plate material after residual stress control according to an embodiment, and the lower figure shows the atomic level state of the plate material in the state shown in the upper figure. [Figure 11] 13A to 13C are diagrams illustrating the correction of a tool trajectory on a plate material. [Figure 12] 13A to 13C are diagrams illustrating the correction of a tool trajectory on a plate material. [Figure 13] FIG. 4 is a diagram showing a residual stress control unit according to Modification 1 of the first embodiment. [Figure 14] FIG. 11 is a diagram showing a portion for controlling residual stress in Modification 2 of the first embodiment. [Figure 15] FIG. 11 is a diagram showing a residual stress control unit according to Modification 2 of the first embodiment. [Figure 16] FIG. 11 is a diagram showing a residual stress control unit according to Modification 3 of the first embodiment. [Figure 17] FIG. 11 is a diagram showing a residual stress control unit according to Modification 3 of the first embodiment. [Figure 18] FIG. 11 is a diagram showing a residual stress control unit according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (First embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. In the drawings, the same components are denoted by the same reference numerals, and duplicated explanations will be omitted. In the drawings, the size and ratio of each component are exaggerated to facilitate understanding of the embodiment, and may differ from the actual size and ratio.

[0011] The incremental forming according to the present embodiment can be used, for example, for large parts such as car body panels, in cases where parts such as repair parts are not mass-produced. The incremental forming according to the present embodiment can also be called dieless forming, since the plate material P is formed without using a die.

[0012] Fig. 1 is a block diagram showing the device configuration of the incremental forming method according to this embodiment. As shown in Fig. 1, the device configuration of the incremental forming method according to this embodiment includes an input unit 10, a position information acquisition unit 20, a storage unit 30, a forming unit 40, a residual stress control unit 50, and a device control unit 60. The details will be described below.

[0013] (Input section) The input unit 10 is used by an operator to input and instruct the position information acquired by the position information acquisition unit 20, the contents stored in the storage unit 30, the tool trajectory of the plate material P formed by the forming unit 40, the control contents of the residual stress control unit 50, etc. The input unit 10 can include at least one of a mouse, a keyboard, a touch screen, etc. In addition, the device for the incremental forming method according to this embodiment can communicate with the Internet, etc., and can connect to storage media such as various disks and memory sticks, so that shape data such as drawings of the parts to be manufactured can be imported.

[0014] (Location information acquisition unit) The position information acquisition unit 20 is configured to be able to acquire information on the path of the tool inputted and instructed by the input unit 10. The position information acquisition unit 20 can be configured to include a light projecting unit that irradiates light to image the plate material P to be processed, a light receiving unit that receives the light from the light projecting unit, and a display that processes and displays the information received by the light receiving unit. Examples of devices that include the above-mentioned light projecting unit, light receiving unit, display, etc. include a three-dimensional shape measuring device and a 3D scanner. By imaging the formed plate material P using the position information acquisition unit 20, data including the coordinate position of a specific portion of the plate material P can be acquired.

[0015] (Storage part) The storage unit 30 is configured to be capable of storing information such as applications required for incremental forming, physical properties of the plate material P input / instructed by an operator, position information by the position information acquisition unit 20, forming information by the forming unit 40, and operation details by the residual stress control unit 50. The storage unit 30 may include a RAM and a ROM. In addition to the position information acquired by the position information acquisition unit 20 described above, the storage unit 30 may store data related to a target shape, etc. The storage unit 30 may store drawing data, design data such as part shape data and data related to a tool trajectory calculated by the device control unit 60.

[0016] (molding part) 2 is a diagram showing a forming unit 40 included in the device for the incremental forming method according to this embodiment. The forming unit 40 is configured to form the plate material P under the control of the device control unit 60 based on the tool trajectory stored in the storage unit 30. The forming unit 40 can include, for example, a multi-axis robot 41 having a linear tool 42 or the like attached to its tip.

[0017] 2 shows one robot 41, but the number of robots does not have to be one if incremental forming is performed without using a metal mold. The forming unit 40 can include, in addition to the multi-axis robot 41, a jig 43 for fixing the outer periphery or the vicinity of the outer periphery of the plate material P, a placement unit 44 such as a table on which the plate material P is placed, and the like. The plate material P is pressed by the forming unit 40 to perform incremental forming.

[0018] (Residual stress control section) Fig. 3 is a diagram showing a residual stress control unit 50 included in the device for the incremental forming method according to this embodiment. The residual stress control unit 50 is configured to control the residual stress of the sheet material P formed by the forming unit 40 in order to improve the forming accuracy of the sheet material P. The residual stress control unit 50 can be configured to accommodate a heating furnace in its internal space in which the sheet material P after being formed by the forming unit 40 can be placed. Fig. 3 is a diagram showing the inside of the heating furnace.

[0019] Hot air heated to a predetermined temperature can be blown into the internal space of the heating furnace. This makes it possible to remove or reduce residual stress from the plate material P after it has been formed by the forming section 40. Furthermore, in the heating furnace, the plate material P can be arranged by the pedestal 51 so as to be separated from the ground of the heating furnace. Furthermore, the pedestal can be formed in a frame shape so that the contact surface of the pedestal 51 with the plate material P is as small as possible (see FIG. 3).

[0020] In the heating furnace, hot air can be circulated in the horizontal direction in Fig. 3 (diagonally upward to the left connecting the lower right and upper left in Fig. 3) below the portion of the pedestal 51 on which the plate material P is placed. This allows hot air to be blown to portions of the plate material P that would not come into contact if the plate material P was placed on the ground when hot air is blown inside the heating furnace, and residual stress can be efficiently removed or reduced. Furthermore, in the heating furnace associated with the residual stress control unit 50, weights (not shown) or a jig similar to the jig 43 in Fig. 2 can be used around the plate material P to restrain the periphery of the plate material P.

[0021] (Device Control Unit) The device control unit 60 includes a CPU and the like, and is configured to control the input unit 10, the position information acquisition unit 20, the storage unit 30, the forming unit 40, and the residual stress control unit 50. The device control unit 60 can also calculate a tool trajectory and the like based on information such as the material and thickness of the sheet material P stored in the storage unit 30, and the tool trajectory.

[0022] (Molding method) Next, the incremental forming method according to this embodiment will be described. Fig. 4 is a flow chart showing an outline of the incremental forming method according to this embodiment. The incremental forming method according to this embodiment will be generally described with reference to Fig. 4, and includes test forming (S1), residual stress control (S2), and main forming (S3). The method will be described in detail below.

[0023] First, in this forming method, the plate material P is set on the placement unit 44, and necessary portions are restrained by the jig 43. Then, the operator inputs and specifies, via the input unit 10, the forming path of the tool 42 required for forming the plate material P.

[0024] Next, when a switch (not shown) is pressed, the device control unit 60 reads out a program designated by the operator from the storage unit 30 and operates the tool 42 of the robot 41 according to the input program. As a result, the robot 41 performs incremental forming on the plate material P using the tool 42 (S1, test forming).

[0025] Here, the difference between the conventional incremental forming and the present embodiment will be described. Fig. 5 is a diagram for explaining the shape of a plate material bent due to residual stress, the target shape, and the correction path in the conventional method, and Fig. 6 is a diagram for explaining the shape of a plate material bent due to residual stress and the shape after the residual stress is eliminated. Fig. 7 is a diagram for explaining the shape of a plate material bent due to residual stress and the shape after the residual stress is eliminated, the target shape, and the correction path in the present embodiment.

[0026] Fig. 8 is a diagram for explaining a shape with deflection due to residual stress according to the embodiment and a shape after the deflection due to residual stress is eliminated. The upper side of Fig. 9 shows the sheet material P after molding by the molding part 40 and before residual stress control, and the lower side is a diagram showing the state of the sheet material P at the atomic level in the upper diagram. The upper diagram of Fig. 10 shows the sheet material P after residual stress control, and the lower side is a diagram showing the state of the sheet material P at the atomic level in the upper diagram.

[0027] In the diagrams at the bottom of Figures 9 and 10, circles represent metal atoms, black solid lines between circles representing metal atoms represent compression, dashed lines represent tension, and gray solid lines represent a balanced state. Also, the roughly circular arc shape shown in Figure 9 represents crystal defects.

[0028] In the case of conventional incremental forming, when forming is performed on the sheet material P without considering the springback of the sheet material P, the sheet material P will have an actual shape L2 compared to the target shape L1 shown in Fig. 5. The tool trajectory is corrected to eliminate the difference between the target shape L1 and the actual shape L2 in Fig. 5, resulting in the corrected path L3 shown in Fig. 5. However, when forming and trimming large parts with low shape rigidity, such as the hood or door of an automobile, the parts will deform to a considerable extent. For this reason, the sheet material P is often heated while its periphery is restrained in order to freeze its shape.

[0029] When considering the state of the sheet material P after forming at the atomic level, some atoms have an imbalance between tensile and compressive forces, and crystal defects exist, as shown in Figure 9. Even if forming is performed in this state using the difference between the target shape and the shape before springback is taken into account as the correction trajectory of the tool, if heating is performed to freeze the shape after forming, the shape of the sheet material P will be formed beyond the target shape.

[0030] In other words, if the processing trajectory is simply determined taking springback into consideration, the sheet material P will bend and deform due to the residual stress immediately after processing. As a result, even if the shape of the sheet material P becomes actual shape L4 in Fig. 6, the actual shape will be deformed by the amount of bending due to the residual stress and will be formed into actual shape L5 shown in Fig. 6. Two types of deformation can occur in parts during forming: plastic deformation and elastic deformation. Although the formed part must ultimately become the target shape through plastic deformation, if the shape is evaluated in a state where elastic deformation remains, such as bending due to residual stress, it becomes difficult to determine the appropriate amount of correction.

[0031] In contrast, in this embodiment, after test forming, the residual stress is controlled while the periphery of the sheet material P is restrained (see actual shape L7 in Fig. 7), and the tool trajectory of incremental forming is corrected based on the shape difference between the actual shape and the target shape so as to eliminate springback (see correction path L8, S2). That is, the residual stress is controlled for the sheet material P that would have the actual shape L6 in Fig. 7 before the tool trajectory correction.

[0032] As a result, the actual shape by the corrected path L8 becomes actual shape L9 shown in Fig. 8. Even if the sheet material P is heated to freeze the shape, the incremental forming according to the embodiment can reduce the influence of deformation caused by residual stress, so that the shape of the sheet material P can be made closer to the target shape as shown in actual shape L10 shown in Fig. 8. This can reduce the influence of deformation caused by residual stress after forming and improve the dimensional accuracy of the final shape.

[0033] In this embodiment, the residual stress is controlled by removing the residual stress in the formed plate material P. In this embodiment, the residual stress is removed by blowing hot air in a heating furnace shown in Fig. 3 and bringing the plate material P into contact with a heated atmosphere.

[0034] In this way, by removing the residual stress by heating as a control of the residual stress, the thermal motion of the atoms is activated, and the atoms are realigned so as to cancel the stress applied by the constraint. This makes it possible to reduce or remove the residual stress and improve the accuracy of the shape of the plate material P. Furthermore, according to the atmospheric heating using the heating furnace as in this embodiment, the temperature of the plate material P is increased by contacting the heated gas with the plate material P, and the residual stress is removed. This allows heating regardless of the material, and makes it easy to adjust the temperature.

[0035] After the residual stress has been removed, the plate material P is imaged from a predetermined direction by the position information acquisition unit 20, and data including coordinate information of each portion is stored in the storage unit 30. Then, the data of the target shape is read out from the storage unit 30, and the data is collated so that the same positions of the actual shape and the target shape correspond to each other, and the actual shape of the formed plate material P is compared with the target shape. Figures 11 and 12 are diagrams provided for explaining the determination of the tool trajectory in the main forming.

[0036] Once the sheet material P from which the residual stress has been removed is prepared, positional information of the shape is acquired and the difference from the target shape is calculated. Fig. 11 shows the acquisition of positional information at a specific position of the sheet material P after residual stress removal, and Fig. 12 shows the positional information of the actual shape and the target shape at the position of the two-dot chain line L11 in Fig. 11. As an example of calculating the difference between the actual shape and the target shape, the difference between the actual shape and the corresponding target shape can be calculated for each specific height in the part, as shown in Fig. 11.

[0037] Once the difference between the shape of the actual sheet metal P and the target shape has been calculated, the shape data, which is the difference between the target shape L1 and the actual shape L12 and is arranged on the opposite side of the displacement direction from the target shape to the actual shape, is stored in the memory unit 30 as corrected tool trajectory data (correction amount). The dashed line L13 in Fig. 12 shows the shape of the tool trajectory. The value of the corrected path from the target shape L1 to the dashed line L13 can be calculated by multiplying the value from the target shape L1 to the actual shape L12 by a constant a.

[0038] The device control unit 60 reads out corrected tool trajectory data such as the dashed line L13 from the storage unit 30, and performs final forming on the plate material P using the tool 42 of the forming unit 40 (S3). In this embodiment, the forming unit 40 is used to perform final forming on a plate material P different from the plate material P used in the test forming. This increases the amount of forming in the areas where forming was insufficient during the test forming, and decreases the amount of forming in the areas where forming was excessive, thereby improving or making better the dimensional accuracy of the formed plate material P compared to the plate material P subjected to the test forming (see FIG. 7).

[0039] (Variation 1) The following describes modified examples of the above embodiment. In the following, the configuration of the residual stress control unit is mainly different from the above, and other configurations are similar, so only the different configurations will be described and the description of the common configurations will be omitted. Figure 13 is a diagram for explaining a residual stress control unit 50a according to Modification 1 of the first embodiment.

[0040] In the first embodiment, the residual stress control unit 50 has been described as having a heating furnace that atmospherically heats the plate material P in a space, but the residual stress control unit 50a may be configured to heat the plate material P in a non-contact manner using a coil or the like that utilizes Joule heat generated by an electric current. As shown in Fig. 13, the residual stress control unit 50a includes a top plate 51a, a coil 52a, a jig 53a that restrains the periphery of the plate material P, an inverter (not shown), and the like.

[0041] The top plate 51a is configured so that a plate material P for controlling residual stress can be placed on the top plate 51a. The coil 52a can be installed on the bottom of the top plate 51a so as to cover a predetermined portion of the plate material P, that is, in this embodiment, substantially the entire plate material P when viewed in a plan view. When power is supplied from the inverter to the coil 52a, magnetic lines of force are generated in the coil 52a, and the plate material P placed above the coil 52a via the top plate 51a generates a current due to the magnetic flux of the coil, which generates Joule heat inside the plate material P.

[0042] In this way, by utilizing the Joule heat from the coil 52a, the residual stress of the formed sheet material P can be removed or reduced, thereby improving the accuracy of the shape of the sheet material P. Furthermore, the residual stress control unit 50a using the coil 52a can perform relatively rapid heating.

[0043] (Variation 2) Fig. 14 is a diagram showing a simulation used to identify a portion for controlling residual stress in Modification 2 of the first embodiment. Fig. 15 is a diagram showing a residual stress control unit 50b according to Modification 2 of the first embodiment.

[0044] In the first embodiment, it has been described that the residual stress control unit 50 heats the entire plate material P by using a heating furnace. However, the plate material P may be configured to identify areas with high residual stress by a simulation and to control the residual stress based on the results of the simulation.

[0045] In the simulation, the restraint parts and pressure (input) parts of the plate material P are specified, and then parts with high residual stress are identified from a contour diagram or the like by stress analysis. Specifically, the simulation is performed by completely restraining the periphery of the plate material P, setting the movement trajectory of the tool 42 as an input, and performing elastic-plastic analysis using a dynamic explicit method or the like with the machining tool as a rigid body and the plate material P as an elastic-plastic body.

[0046] This makes it possible to obtain a contour diagram like that shown in Figure 14, and by setting a threshold value and checking each part of the contour diagram, it is possible to identify the parts that require localized heating. After this, by locally heating only the parts that require the removal of residual stress based on the simulation results, it is possible to remove the residual stress in a time- and energy-saving manner. In addition, by heating only the parts that require the removal of residual stress, heating can be carried out relatively quickly regardless of the material. Note that Figure 14 is an example showing an image of the simulation results.

[0047] The residual stress control unit 50b used for heating can be a heater 52b having an outlet for blowing hot air that can be scanned relative to the component. The heater 52b used in this modification includes a member required for heating, such as a coil, and a member required for blowing air, such as a fan, and is made movable in various directions.

[0048] As a means for moving the heater 52b in various directions, the heater 52b is attached to the tip of a multi-axis robot 51b as an example in Fig. 15. During residual stress control, the plate material P is placed on a table 54b, and hot air from the heater 52b can be blown to various parts by the robot 51b while the periphery of the plate material P is restrained by a jig 53b.

[0049] However, as long as hot air can be blown locally to the plate material P, the configuration for moving the heater 52b is not limited to a multi-axis robot, and the heater 52b may be moved in various directions by linearly moving the heater 52b relative to the plate material P using an X-stage, Y-stage, or the like. In this way, by blowing hot air to remove residual stress, heat from the high-temperature hot air is imparted to the plate material P by convection heat transfer, and the residual stress is used as a driving force to rearrange atoms through heating and remove stress. In addition, by heating only the necessary parts, processing can be performed in less time and energy. In addition, the plate material P can be heated relatively quickly regardless of the material.

[0050] In addition, in the first modification, it has been explained that the plate material P is heated as a whole by utilizing Joule heat from the coil, but the heating range by the coil (Joule heat) may be configured to be a portion of the plate material P by installing the coil. In this way, the residual stress can be removed in a time-saving and energy-saving manner by identifying the portion where the residual stress is to be removed by simulation and configuring to remove the residual stress in the identified portion. In addition, the plate material P can be heated rapidly by utilizing the Joule heat from the coil for localized heating.

[0051] (Variation 3) Fig. 16 is a diagram showing a residual stress control unit 50c during the incremental forming method according to Modification 3, and Fig. 17 is a diagram showing a residual stress control unit 50d during the incremental forming method according to Modification 3. In Modification 2, it has been described that the plate material P is locally heated by blowing hot air onto it with the heater 52b. However, the method of heating the plate material P is not limited to the above, and the residual stress may be controlled by radiant heat transfer in which a laser is irradiated onto the plate material P using a head 51c shown in Fig. 16. Note that the configuration of the device for irradiating the laser is known, and therefore a detailed description thereof will be omitted.

[0052] Also, the residual stress control unit 50d may be configured to include a heat source 51d such as a halogen lamp as shown in FIG. 17, and to control the residual stress by radiation heat transfer that radiates infrared rays or the like to the plate material P. Heating by a halogen lamp is similar to a known device configuration, and therefore a description thereof will be omitted. In both of FIGS. 16 and 17, a configuration similar to the jig 53a shown in FIG. 13 or the like can be used to restrain the periphery of the plate material P. With this configuration, the plate material P can be heated by absorbing the energy of the electromagnetic waves to increase the temperature of the plate material P, and the plate material P can be heated relatively quickly, and the irradiation position can be easily selected.

[0053] (Variation 4) In the second modification, when the plate material P is locally heated, the portion having a relatively high residual stress is identified by simulation. In this regard, the simulation may calculate a shape in which springback is eliminated or reduced (see actual shape L9 in FIG. 8) by simulation. The shape in which springback is reduced or removed can be obtained by the conditions such as the physical properties and input load of the plate material P when the above-mentioned simulation is performed, and the stress and strain generated in the plate material P by analysis. Such data can be displayed on a display, or the coordinate data of each portion of the shape in which springback is reduced, etc. can be stored in the storage unit 30. In this way, by confirming the shape in which springback is eliminated or reduced by simulation, the dimensional accuracy of the plate material P in which springback occurs can be improved.

[0054] Second embodiment 18 is a diagram showing a residual stress control unit 50e in the incremental forming method according to the second embodiment. In the first embodiment, it has been described that the residual stress control unit 50 controls the residual stress by removing or reducing the residual stress from the formed sheet material P by heating or the like, but the method of controlling the residual stress is not limited to removing the residual stress. The residual stress may be controlled by applying a residual stress other than the above.

[0055] Specifically, the residual stress control unit 50e includes a nozzle 51e that causes countless micrometer-order granular materials such as metal to collide and be sprayed onto the sheet material P. The locations of the granular materials to be sprayed onto the sheet material P can be identified from the results of simulating the sheet material P by the molding unit, as described in Modification 2. When applying residual stress, the periphery of the sheet material P can be restrained using a configuration similar to that of a jig 53a similar to that shown in FIG. 13, etc.

[0056] With this configuration, the device control unit 60 can adjust the range over which the granular material is to collide, the speed of the granular material, or the type of granular material so that the residual stress after the granular material is applied is balanced according to the state of residual stress such as in a simulation, etc. When determining the range over which the granular material is to collide, the nozzle 51e for colliding the granular material is illustrated as one in FIG. 18, but multiple nozzles may be used.

[0057] In this way, by controlling the residual stress by applying it to one side of the plate material P, it is possible to balance the uneven residual stress in the plate thickness direction generated by incremental forming, thereby improving the accuracy of the shape. In addition, by colliding a granular material harder than the plate material P to apply the residual stress, it is possible to balance the residual stress and improve the accuracy of the shape even in materials in which it is difficult to remove stress by heat. In addition, by colliding a granular material with the plate material P, it is possible to selectively apply residual stress only to the necessary parts of the plate material P.

[0058] Furthermore, by adjusting the range, speed, and type of the granular material to be collided by the device control unit 60 according to the state of the residual stress, it is possible to balance the residual stress according to the state of the plate material P, thereby improving the accuracy of the final shape. Furthermore, by specifying the portion to be collided with the granular material from the results of the simulation, it is possible to impart residual stress in a time- and energy-saving manner.

[0059] The present invention is not limited to the above embodiment, and various modifications are possible within the scope of the claims. In the first embodiment, the plate material used for the test molding and the plate material used for the main molding are described as different members. However, the present invention is not limited to the above, and the main molding may be performed by performing additional processing on the plate material that has been subjected to the test molding.

[0060] The following embodiments are also within the scope of the present invention: the incremental molding method as claimed in claim 1 having the features of claim 2; the incremental molding method as claimed in claim 2 having the features of claim 3; the incremental molding method as claimed in claim 3 having the features of claim 4; the incremental molding method as claimed in claim 3 having the features of claim 5; the incremental molding method as claimed in claim 3 or 5 having the features of claim 6; the incremental molding method as claimed in claim 3 or 5 having the features of claim 7; the incremental molding method as claimed in claim 3 or 5 having the features of claim 8; the incremental molding method as claimed in claim 1 having the features of claim 9; the incremental molding method as claimed in claim 9 having the features of claim 10; the incremental molding method as claimed in claim 10 having the features of claim 11; the incremental molding method as claimed in claims 1, 2, 3, 5, 7, 9, 10, 11 having the features of claim 12; the incremental molding method as claimed in claim 12 having the features of claim 13; the incremental molding method as claimed in any one of claims 1 to 13 having the features of claim 14. [Explanation of symbols]

[0061] 50, 50a, 50b, 50c, 50d, 50e Residual stress control section, P plate material.

Claims

1. In incremental forming, where a plate material is pressed and processed, The incremental forming method includes a process of controlling residual stress while constraining the periphery of the plate material after the incremental forming, thereby eliminating or reducing springback, and then correcting the tool trajectory of the incremental forming from the target shape using the shape difference between the obtained shape and a target shape.

2. The method of claim 1 , wherein the residual stress is controlled by removing stress.

3. The incremental forming method of claim 2 , wherein the residual stress is removed by heating the plate.

4. The method of claim 3 wherein the sheet is heated by contacting it with a heated atmosphere.

5. The incremental forming method according to claim 3 , wherein the plate material is locally heated at a portion of the plate material where the residual stress is to be removed.

6. 4. The incremental forming method according to claim 3, wherein the plate material is heated by applying Joule heat by electric current.

7. The method of claim 3 , wherein the plate is heated by blowing heated gas onto it.

8. The incremental forming method according to claim 3 , wherein the plate material is heated by radiation heat transfer.

9. The method of claim 1 , wherein the residual stress is controlled by applying stress to the sheet material.

10. The incremental forming method according to claim 9 , wherein the residual stress is imparted to the plate material by colliding a granular material having high hardness with the plate material.

11. The incremental forming method according to claim 10, wherein the type, range of collision, and speed of the granular material are adjusted according to the state of the residual stress in the plate material.

12. The distribution of the residual stress is specified by simulation; The incremental forming method according to claim 1 , wherein the residual stress is controlled based on the simulation.

13. The incremental forming method according to claim 12 , wherein the simulation calculates a shape of the plate material in which the springback is eliminated or reduced.

14. An incremental forming method according to any one of claims 1 to 13, wherein the tool trajectory reflects a value obtained by calculating a difference between the actual shape of the plate material after controlling the residual stress and the target shape, multiplying the difference by a certain number, and displacing the value in a direction opposite to the direction in which the plate material was displaced from the target shape to the actual shape.

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