Method for setting processing path for incremental forming

Abstract

When a workpiece is processed into a processed product having a prescribed target shape by incremental formation, a control device (15) uses a prescribed setting method to set a first processing path, for the incremental formation, corresponding to a defined target shape, uses numerical analysis to obtain the shape of the processed product when the workpiece is incrementally molded in the first processing path, actually processes the workpiece in the first processing path and measures the shape of the processed product thereof, and sets a second processing path by correcting the first processing path by using a shape error between the analyzed shape of the processed product as obtained by the numerical analysis and the actual shape of the processed product as actually processed and measured.

Description

Method for Setting Machining Path of Sequential Forming

[0001] The present invention relates to a method for setting a machining path of sequential forming.

[0002] Patent Document 1 below describes a method for setting a machining path of a tool when machining a workpiece by sequential forming. Sequential forming, also called incremental forming, refers to a machining method in which local plastic deformation is sequentially applied to a workpiece without using a forming die to form a machined part. Also, the machining path refers to the movement path of a tool that locally plastically deforms a workpiece. In the method for setting the machining path described in this patent document, for example, using existing machining software or the like, a reference machining path corresponding to the specified target shape (design shape) of the machined part is set, and the shape of the machined part machined along this reference machining path is obtained by numerical analysis such as the finite element method. In this numerical analysis, springback, i.e., the return of the machined part after plastic deformation machining in sequential forming, is also taken into account, and the shape of the springbacked machined part after machining along the reference machining path can be calculated. Then, based on the shape error between the analyzed shape of the numerically analyzed machined part and the specified target shape, the reference machining path is repeatedly corrected to set a final machining path that makes the shape of the machined part the specified target shape or within a predetermined shape error range.

[0003] Japanese Patent Application Laid-Open No. 2023-56138

[0004] However, in the method for setting the machining path of sequential forming described in Patent Document 1 above, it is necessary to repeatedly correct the machining path many times to set a machining path that can machine the machined part to the specified target shape. Also, in numerical analysis, although the machining path can make the shape of the machined part the specified target shape or within a predetermined shape error range, the shape of the actual machined part may deviate from the specified target shape. In sequential forming, the springback after machining is larger than that in machining a machined part by press forming using a forming die, and accordingly, it is difficult to set a machining path with a small shape error only by numerical analysis. The present invention aims to provide a method for setting a machining path of sequential forming that can quickly set a machining path that does not deviate the shape of the machined part from the specified target shape.

[0005] One aspect of the present invention is a method for setting sequential forming processing paths in a calculation processing unit when processing a workpiece into a workpiece of a specified target shape by sequential forming, wherein the calculation processing unit sets a reference processing path for sequential forming according to the specified target shape using a predetermined setting method, determines the shape of the workpiece when the workpiece is sequentially formed using the reference processing path by numerical analysis, measures the shape of the workpiece by actually processing the workpiece using the reference processing path, and corrects the reference processing path using the shape error between the analytical shape of the workpiece determined by numerical analysis and the actual shape of the workpiece measured by actual processing to set a corrected processing path.

[0006] According to one aspect of the present invention, a standard machining path containing analytical errors that cannot be fully corrected by numerical analysis alone can be corrected using the shape error between the actual shape of the machined product measured by actual machining and the analytical shape of the machined product obtained by numerical analysis. This allows for the rapid establishment of a machining path that does not cause the shape of the machined product to deviate from a defined target shape. The objectives and advantages of the present invention are embodied and achieved using the elements and combinations thereof set forth in the claims. Both the above general description and the following detailed description are merely illustrative and explanatory and should be understood as not limiting the present invention in the manner of the claims.

[0007] This is a block diagram showing one embodiment of the molding apparatus according to the present invention. This is a flowchart of the calculation process performed by the control device in Figure 1. This is an explanatory diagram of the operation by the calculation process in Figure 2. This is an explanatory diagram of the operation by conventional calculation process (numerical analysis). This is an explanatory diagram of the efficiency rate of achieving a specified target shape by the calculation process in Figure 2.

[0008] The embodiments of the present invention will be described below with reference to the drawings. Note that the drawings are schematic and may differ from actual ones. The molding apparatus 1 shown in Figure 1 is an apparatus for forming a workpiece by processing a workpiece with a tool using sequential forming. As mentioned above, sequential forming refers to a processing method in which a workpiece is formed by sequentially applying local plastic deformation to a workpiece without using a mold. Sequential forming is broadly classified into sequential stretch forming, sequential reverse stretch forming, and sequential compression forming. As an example, in sequential stretch forming, which is the subject of this embodiment, the outer periphery of the workpiece, which is a metal plate member, is fixed, and stretch forming is performed sequentially from the outer periphery to the center by pushing the workpiece with a rod-shaped tool. The workpiece and tools used in sequential stretch forming are described in detail in the above-mentioned Patent Document 1, so please refer to that.

[0009] The molding apparatus 1 shown in Figure 1 is equivalent to that described in Patent Document 1, but in order to understand the processing path setting method for sequential molding in this embodiment, it is necessary to understand the configuration and function of this apparatus, so we will outline them below without hesitation, even if it is repetitive. The molding apparatus 1 in Figure 1 comprises a fixing device 11, a processing device 12, a display device 13, an input device 14, and a control device 15. The arrangement and configuration of each device are examples and can be set as appropriate. The fixing device 11 is a device for fixing the outer periphery of a workpiece, which is a metal plate member, during processing by sequential molding. The processing device 12 is a device for moving a tool used in sequential molding in a three-dimensional direction and pressing and applying pressure to the workpiece with the tool, for example, a multi-axis controlled robot arm is applied. By attaching a tool to the robot hand at the tip of this robot arm, the tool can be moved freely in a three-dimensional direction and the tool can be pressed against the workpiece to perform plastic deformation processing. The display device 13 is a device for providing information for operating the molding apparatus 1 to the operator (user), for example, a display. The input device 14 is a device for an operator to input instructions for operating the molding apparatus 1, and examples include a keyboard, mouse, or touch panel.

[0010] The control device 15 is a device for controlling each device of the molding apparatus 1 so that they work together. Specifically, it receives instructions from the input device 14, sets a machining path for moving the tool, controls the machining apparatus 12 so that the tool moves along the set machining path, measures the shape (dimensions) of the workpiece, and displays the necessary information on the display device 13. Therefore, the control device 15 is constructed by a computer system (arithmetic processing unit) with high arithmetic processing capabilities. The control device 15, being a computer system, includes a CPU (Central Processing Unit) 151 which is a processor, a ROM (Read Only Memory) 152 which stores programs and various data, and a RAM (Random Access Memory) 153 which functions as an accessible storage device. The CPU 151, being a processor, is an operating circuit, and the control device 15 functions when the CPU 151 executes the program stored in the ROM 152. The program executed by the control device 15 constitutes the control unit 2 as a functional block for making the control device 1 function. The control unit 2 includes a setting unit 21, a measurement unit 22, a calculation unit 23, and an output unit 24.

[0011] The setting unit 21 has the function of setting the machining path, which is the movement path of the tool, in order to process a workpiece by sequential forming and obtain a workpiece. The machining path, which is the movement path of the tool, is the path the tool takes when moving from a position set as the starting point to a position set as the ending point, and in particular refers to the path taken by the tip of the tool that comes into contact with the workpiece. The machining path is set according to the desired shape of the workpiece. For example, when the tool is moved from the outer circumference to the center of a workpiece, which is a metal plate member, in accordance with the desired shape (design shape, which is a specified target shape), the trajectory drawn by the intersection of the surface of the tip of the tool and the central axis of the tool is set as the machining path. In addition, the setting unit 21 also has the function of setting or correcting the machining path so that the workpiece becomes the specified target shape after springback, taking into account the springback of the workpiece. For example, when the measurement unit 22, which will be described later, calculates the shape of the workpiece after springback following the set machining path using numerical analysis, the machining path is corrected based on the shape error between the analyzed shape and the specified target shape. Furthermore, if the specified target shape is changed to a different target shape, such as a virtual target shape, the system also has a function to set or readjust the machining path according to that virtual target shape. As described in Patent Document 1 above, commercially available machining software can be used to set and correct the machining path.

[0012] The measuring unit 22 has the function of measuring the dimensions of the workpiece obtained by moving the tool along the machining path and acquiring the shape of the workpiece. Specifically, it measures and acquires the dimensions of the workpiece using a three-dimensional measuring machine. Furthermore, as described above, the measuring unit 22 has the function of calculating the shape of the workpiece obtained by moving the tool along the machining path using numerical analysis such as the finite element method, and calculates the shape error between the analyzed shape of the workpiece and the specified target shape or virtual target shape and outputs it to the setting unit 21, which then (re)sets or corrects the machining path based on these shape errors. In other words, in this numerical analysis of the workpiece shape calculation, the workpiece is not actually machined, and the machining path is readjusted and corrected based on so-called estimations, thereby reducing the time and cost required for machining and measurement. Numerical analysis of the workpiece shape in sequential forming can also be performed using numerous commercially available software programs, and these numerical analyses can also calculate the shape of the workpiece after springback following (virtual) machining by the machining path.

[0013] The measurement unit 22 includes a generation unit 221 and an analysis unit 222, which are functional blocks, to achieve these processes. The generation unit 221 has the function of generating an element model used for numerical analysis from the shape data of the object to be analyzed. That is, the numerical analysis used in this embodiment is the finite element method. The shape data of the object to be analyzed is, for example, three-dimensional CAD data of a machined product input from the input device 14. The generation unit 221 generates an element model used for numerical analysis from the acquired three-dimensional CAD data. An element model refers to a model that represents the shape of the object to be analyzed by dividing it into small regions called elements (discretization). By discretizing, even complex shapes can be numerically analyzed by a computer system. The analysis unit 222 has the function of having a computer system perform numerical analysis using the element model generated by the generation unit 221. When the analysis unit 222 acquires an element model, it uses software stored in the ROM 152 to have hardware such as the CPU 151 and RAM 153 perform calculations. The calculation results are output from the analysis unit 222 to the calculation unit 23. The calculation unit 23 has the function of calculating the difference between the measured or numerically analyzed dimensions of the processed product and the design value (specified target shape) or set value (virtual target shape) as a shape error. The output unit 24 has the function of outputting the processing path set in the setting unit 21, the measured dimensions of the processed product measured or numerically analyzed in the measurement unit 22 and the design value or set value, and the difference between the measured value and the design value or set value calculated by the calculation unit to the display device 13. The output information is displayed on the display device 13.

[0014] Next, the calculation process performed by the control device (arithmetic processing unit) 15 in Figure 1 to set the processing path for sequential forming in this embodiment will be explained using the flowchart in Figure 2. Although referred to as calculation processing, it does not mean a calculation mechanism (algorithm) in which a computer system finds a solution, but rather a logical procedure (logic) for finding the optimal processing path through actual processing of the workpiece. This calculation process is started, for example, by the activation of a program by an operator. First, in step S1, the specified target shape (design shape) of the workpiece is read. The shape is represented by three-dimensional CAD data, i.e., dimensions on a three-dimensional Cartesian coordinate system, as described above, but here it will be explained conceptually as the nature of the "shape". Next, the process moves to step S2, where the first processing path (basic processing path) is set for the specified target shape read in step S1. This first processing path can be set using commercially available processing software, as described above. That is, the first processing path is set using a predetermined setting method. Next, the process moves to step S3, where the shape of the workpiece (analyzed workpiece shape) based on the first processing path is calculated using numerical analysis. In this embodiment, as described above, the finite element method is used as the numerical analysis.

[0015] Next, the process moves to step S4, where the workpiece is actually processed into a workpiece using the pre-configured first processing path. Then, the process moves to step S5, where the shape of the actually processed workpiece (actual workpiece) is measured. As mentioned earlier, this measurement of the actual workpiece's shape is performed by measuring the dimensions of the three-dimensional Cartesian coordinates using a three-dimensional measuring machine, and using these dimensions to represent the shape of the actual workpiece. Next, the process moves to step S6, where the shape error between the actual workpiece shape measured in step S5 and the analyzed workpiece shape calculated in step S3 is calculated. This shape error, as well as the analyzed shape error described later, will be explained in a later section. Next, the process moves to step S7, where the shape error calculated in step S6 is added to the specified target shape to set a virtual target shape. This virtual target shape will also be explained in a later section. Next, the process moves to step S8, where a second processing path (correction processing path) for the virtual target shape is set in the same way as the first processing path. Note that the method for setting the first processing path and the method for setting the second processing path are the same (software), so setting this second processing path is equivalent to correcting the first processing path using the shape error calculated in step S6.

[0016] Next, the process moves to step S9, where, similar to step S3, the shape of the workpiece produced by the second processing pass is calculated by numerical analysis. Next, the process moves to step S10, where the shape error between the analyzed workpiece shape calculated in step S9 and the virtual target shape is calculated as the analyzed shape error. Next, the process moves to step S11, where it is determined whether the analyzed shape error calculated in step S10 is less than or equal to a preset processing tolerance threshold. If the analyzed shape error is less than or equal to the processing tolerance threshold, the process moves to step S13; otherwise, the process moves to step S12. The processing tolerance threshold is a value such that, if the analyzed shape error is smaller than or equal to it, the shape of the workpiece can be made to the specified target shape or kept within a predetermined shape error range by sequential forming in the second processing pass. In step S12, it is determined whether the analyzed shape error calculated in step S10 is less than or equal to a preset recalculation threshold. If the analyzed shape error is less than or equal to the recalculation threshold, the process moves to step S18; otherwise, the process moves to step S13. The recalculation threshold is a value below which, if the analytical shape error is small, it is considered possible to gradually reduce the analytical shape error with respect to the virtual target shape by correcting the second machining pass using the analytical shape error. Conversely, if the analytical shape error is large above this value, it is considered that the virtual target shape and the analyzed machined part shape are diverging, and the virtual target shape should be reviewed.

[0017] In step S13, similar to step S4, the workpiece is actually processed into a workpiece using the currently set second processing pass. Next, the process moves to step S14, where the shape of the actual processed workpiece is measured, similar to step S5. Next, the process moves to step S15, where the actual shape error between the actual workpiece shape measured in step S14 and the specified target shape is calculated. Next, the process moves to step S16, where it is determined whether the actual shape error calculated in step S15 is below the processing tolerance threshold. If the actual shape error is below the processing tolerance threshold, the process moves to step S17; otherwise, the process moves to step S19. In step S17, the process is instructed to perform processing (sequential forming) using the currently set second processing pass, and then the process returns. In step S19, the virtual target shape is corrected taking into account the actual shape error calculated in step S15, and then the process moves to step S8. Meanwhile, in step 18, the second processing pass is corrected using the analysis shape error calculated in step S10, and then the process moves to step S9.

[0018] In the calculation process shown in Figure 2, the correction of the second machining path using the analyzed shape error in step S18 is the same as the correction of the machining path by numerical analysis described in Patent Document 1, except that the target for calculating the analyzed shape error is either a virtual target shape or a specified target shape (which is the design shape and the desired shape of the machined product). Therefore, the explanation is omitted here. Below, we will explain the calculation of the shape error in step S6 of the calculation process in Figure 2, the setting of the virtual target shape in step S7, and the setting of the second machining path in step S8. Figure 3 schematically shows the actual machined product shape, the analyzed machined product shape, the virtual target shape, and the specified target shape used in these steps. In Figure 3a, the specified target shape is shown by a dashed line, the analyzed machined product shape by a dashed line, and the actual machined product shape by a solid line. In step S6 of the calculation process in Figure 2, the shape error between the actual machined product shape and the analyzed machined product shape, which are shown by dimension lines in Figure 3a, is calculated. Both the analyzed machined product shape and the actual machined product shape are the shapes of the machined product processed in the first machining path. Assuming that the analyzed part shape is numerically analyzed using processing software based on press molding with a mold, for example, in actual sequential forming, as mentioned above, springback is greater than in press molding, so it is thought that shape errors like those shown in the figure will occur (the actual shape is a combination of multiple elements, as will be explained later).

[0019] Then, in step S7 of the calculation process in Figure 2, the shape error shown by the dimension lines in Figure 3b (the same as the shape error in Figure 3a) is added to the specified target shape shown by the dashed-dotted line to set a virtual target shape shown by the dashed-dotted line. When setting the virtual target shape, in the example in Figure 3a, for a workpiece made of a flat metal plate member, the actual processed product shape is considered to have less deformation, i.e., less processing than the analyzed processed product shape. Therefore, the virtual target shape is set so that the processing amount is larger, for example, in the case of a recessed shape as shown in the figure, the depth of the recess is increased. With respect to this virtual target shape, in step S8 of the calculation process in Figure 2, the second processing pass is set using the same processing software as the first processing pass. As a result, as shown in Figure 3c, the analyzed processed product shape from the first processing pass can be brought closer to the virtual target shape, which has a larger processing amount than the specified target shape. As a result, as shown by the solid line in Figure 3d, it is possible to make the shape of the actually processed product match or come very close to the specified target shape. By setting a virtual target shape in this way, the shape of the machined part analyzed in the first second machining pass can be brought much closer to the specified target shape. This reduces the number of corrections for the second machining pass in steps S9 to S18 of the calculation process in Figure 2, thereby reducing the time (number of calculations) and the computational load required to reach the optimal machining pass.

[0020] In contrast, in the method of Patent Document 1 described above, which corrects the machining path solely by numerical analysis, as shown in Figure 4a, even if the shape of the analyzed machined part (dashed line) is calculated by the first machining path and the machining path is corrected to match this analyzed machined part shape to the specified target shape (solid line), the shape of the actual machined part will still have a shape error compared to the specified target shape, as shown by the solid line in Figure 4b. If this shape error is, for example, a calculation error in the amount of springback of the machining software based on the aforementioned press molding using a mold, then as long as the machining path is set with the same machining software, the calculation error cannot be easily eliminated. This shape error is considered to be an analysis error in numerical analysis. Numerical analysis cannot reproduce all of the actual phenomenon spatially and temporally, but only reproduces a part of the actual phenomenon under some assumptions. Therefore, the results always contain errors (differences from the actual phenomenon), and errors that occur when performing this analysis include, for example, errors due to modeling, errors due to meshing in the finite element method, errors due to modeling, calculation errors, and errors in result processing. In this embodiment, this analysis error is determined as the shape error (more precisely, including the analysis error) between the actual machined part shape and the analyzed machined part shape, and by adding this to the defined target shape to set a virtual target shape, it becomes possible to bring the analyzed machined part shape in the first second machining pass much closer to the defined target shape.

[0021] In contrast, setting the second machining path using the shape error between the actual machined part shape obtained by the first machining path and the analyzed machined part shape, i.e., setting the virtual target shape, may be inappropriate for bringing the actual machined part shape obtained by the second machining path closer to the specified target shape. Therefore, in this embodiment, if the analyzed shape error is greater than the recalculation threshold in step S12 of the calculation process in Figure 2, the virtual target shape is corrected using the actual shape error between the actual machined part shape obtained by the second machining path and the specified target shape. This makes it possible to reset the second machining path by correcting the virtual target shape when, for example, the actual machined part shape obtained by the second machining path deviates from the specified target shape, thereby bringing the actual machined part shape obtained by the second machining path closer to the specified target shape. Furthermore, in this embodiment, even if the analytical shape error between the analyzed workpiece shape and the virtual target shape obtained by the second processing pass is less than or equal to the processing tolerance threshold (second threshold), the workpiece is processed by the second processing pass, and if the actual shape error between the actual workpiece shape and the specified target shape is less than or equal to the processing tolerance threshold (third threshold), the current second processing pass is determined as the processing pass for sequential forming and processing is instructed. This ensures that the actual workpiece shape of the workpiece processed by the second processing pass matches the specified target shape or is kept within a predetermined shape error range.

[0022] Figure 5 shows the shape (dimension) agreement rate with the specified target shape for each number of machining path corrections, in the case where the machining path is corrected according to the calculation process in Figure 2 (solid line) and in the case where the machining path is corrected only by numerical analysis (dashed line: comparative example). Since the number of corrections is 0, this embodiment and the comparative example are equivalent as it is based on the first machining path. However, in the embodiment where the number of corrections is 1, i.e., where a second machining path is set, the shape of the machined product can be brought much closer to the specified target shape compared to the comparative example where the first machining path is corrected by numerical analysis. Furthermore, by correcting the machining path (second machining path) by numerical analysis, the shape can be made to match the shape error range level.

[0023] In this embodiment, when processing a workpiece into a workpiece of a specified target shape by sequential forming, the control device 15 sets a first processing pass (reference processing pass) for sequential forming according to the specified target shape using a predetermined setting method, determines the shape of the workpiece when the workpiece is sequentially formed in the first processing pass using numerical analysis, measures the shape of the workpiece by actually processing it in the first processing pass, and corrects the first processing pass using the shape error between the analytical shape of the workpiece determined by numerical analysis and the actual shape of the workpiece measured by actual processing to set a second processing pass (corrected processing pass). As a result, it is possible to set an appropriate second processing pass that greatly reduces the analytical error that cannot be corrected by numerical analysis alone included in the first processing pass, and as a result, it is possible to quickly set a processing pass that does not deviate the shape of the workpiece from the specified target shape. Furthermore, by taking shape errors into account in addition to the specified target shape to set a virtual target shape for the processed product, and by setting a second processing pass for sequential forming corresponding to this virtual target shape using the same setting method as the first processing pass, it is possible to appropriately reduce analysis errors that cannot be fully corrected by numerical analysis alone included in the first processing pass.

[0024] Furthermore, the shape of the workpiece when the workpiece is sequentially formed in the second processing pass is determined by numerical analysis. If the analytical shape error between the analyzed workpiece shape and the virtual target shape exceeds the recalculation threshold, the workpiece is actually processed in the second processing pass, and the virtual target shape is corrected using the actual shape error between the actual workpiece shape and the specified target shape. This allows the second processing pass to be reset by correcting the virtual target shape when the actual workpiece shape produced by the second processing pass deviates from the specified target shape, making it possible to bring the actual workpiece shape produced by the second processing pass closer to the specified target shape. Additionally, the shape of the workpiece when the workpiece is sequentially formed in the second processing pass is determined by numerical analysis. If the analytical shape error between the analyzed workpiece shape and the virtual target shape is below the processing tolerance threshold, the workpiece is actually processed in the second processing pass, and if the actual shape error between the actual workpiece shape and the specified target shape is below the processing tolerance threshold, the second processing pass is determined as a processing pass for sequential forming. This makes it possible to make the actual shape of the workpiece processed in the second processing pass match the specified target shape, or to keep it within a predetermined shape error range.

[0025] 1... Molding device, 2... Control unit, 12... Processing device, 15... Control device (arithmetic processing unit), 21... Setting unit, 22... Measurement unit, 221... Generation unit, 222... Analysis unit

Claims

1. A method for setting sequential forming processing paths in a calculation processing unit when processing a workpiece into a workpiece of a specified target shape by sequential forming, wherein the calculation processing unit sets a reference processing path for sequential forming according to the specified target shape using a predetermined setting method, determines the shape of the workpiece when the workpiece is sequentially formed using the reference processing path by numerical analysis, actually processes the workpiece using the reference processing path and measures the shape of the workpiece, and corrects the reference processing path using the shape error between the analytical shape of the workpiece determined by the numerical analysis and the actual shape of the workpiece measured by the actual processing to set a corrected processing path.

2. The sequential forming processing path setting method according to claim 1, characterized in that the processing unit sets a virtual target shape of the workpiece by taking the shape error into account the predetermined target shape, and sets the correction processing path by setting the sequential forming processing path according to the virtual target shape using the predetermined setting method.

3. The processing device for sequential forming according to claim 2, characterized in that it determines the shape of the workpiece when the workpiece is sequentially formed in the corrected processing path using the numerical analysis, and if the shape error between the analyzed shape of the workpiece determined by the numerical analysis and the virtual target shape exceeds a predetermined threshold, it actually processes the workpiece in the corrected processing path and corrects the virtual target shape using the shape error between the actual shape of the workpiece and the specified target shape.

4. The method for setting a processing path for sequential forming according to claim 2, characterized in that the calculation processing device determines the shape of the workpiece when the workpiece is sequentially formed in the corrected processing path using the numerical analysis, and if the shape error between the analyzed shape of the workpiece determined by the numerical analysis and the virtual target shape is less than or equal to a predetermined second threshold, the workpiece is actually processed in the corrected processing path, and if the shape error between the actual shape of the workpiece and the specified target shape is less than or equal to a predetermined third threshold, the corrected processing path is determined as the processing path for sequential forming.

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