A method and system for jointly planning bending processes and stop positions in sheet metal work.

Abstract

This invention discloses a method and system for joint planning of bending processes and stop positions in sheet metal processing. Based on the target bending node of the sheet metal, preliminary planning of bending processes and candidate stop positions is performed. The bending length error is calculated based on the spatial relationship between the bending node and the stop. Considering the influence of the stop position and bending length error on dimensional accuracy, an equivalent accuracy model is established. Considering the adjustment operations between bending processes during the bending process, an equivalent efficiency model is established. Using the equivalent accuracy model and equivalent efficiency model as fitness functions, and with bending accuracy and efficiency as dual objectives, a genetic algorithm is used to solve the problem, obtaining a Pareto optimal solution set. Based on the objective preferences, the optimal combination of bending processes and the corresponding stop position sequence are obtained. By clarifying the inherent correlation between dimensional error and bending process planning and stop position selection, the joint planning simultaneously obtains the processing sequence and the stop position sequence, effectively improving bending accuracy and efficiency.

Description

Technical Field

[0001] This invention relates to automated sheet metal bending processing, specifically to a method and system for jointly planning the bending process and stop position for sheet metal. Background Technology

[0002] Sheet metal bending, as a sheet metal forming process, aims for high precision and efficiency. Improving efficiency through rational process planning is an effective approach. In recent years, various process planning methods and technologies have emerged, including: obtaining feasible bending processes using branch and bound, heuristic search algorithms; and transforming bending process planning into an optimization problem, solving it using classical genetic algorithms and non-dominated sorting genetic algorithms with efficiency as the objective, considering the interference between the workpiece, machine tool, and mold, as well as processing constraints, to obtain the optimal process sequence. However, these methods often neglect the correlation between processes and length errors, and fail to consider the impact of bending processes on processing accuracy and the optimization of stop positions. Summary of the Invention

[0003] Purpose of the invention: To address the above-mentioned shortcomings, this invention provides a method for jointly planning the bending process and the stop position for sheet metal to improve bending accuracy and efficiency. This invention also provides a system for jointly planning the bending process and the stop position for sheet metal.

[0004] Technical Solution: To solve the above problems, the present invention provides a method for jointly planning the bending process and stop position in sheet metal, comprising the following steps:

[0005] Step 1: Determine the target bending node of the sheet metal, initially plan several feasible bending process combinations, and based on the stopability analysis, determine the candidate node set of the stop position for each bending step. The candidate nodes include the bending node and the edge node of the sheet metal. Analyze the impact of the change of the stop position on the bending length accuracy, and determine the bending length error calculation formula based on the spatial position relationship between the current bending node and the stop during the bending process.

[0006] Step 2: Based on the formula for calculating bending length error, considering the influence of the stop position and bending length error on the machining dimensional accuracy, establish an equivalent accuracy model that characterizes the variation characteristics of bending machining dimensional accuracy.

[0007] Step 3: Consider the time consumed by the adjustment operations on the sheet metal between bending processes during the bending process, and establish an equivalent efficiency model for the bending process based on the number of adjustment operations.

[0008] Step 4: Using the equivalent accuracy model and equivalent efficiency model as fitness functions, and taking bending accuracy and efficiency as dual objectives, solve the problem using a genetic algorithm to obtain the Pareto optimal combination of bending processes and the corresponding stop position sequence. Determine the priority of the optimization objectives of bending accuracy and efficiency, and take the optimization objective with higher priority as the preference to obtain the optimal combination of bending processes and the corresponding stop position sequence under the preference.

[0009] Furthermore, the material stop position includes direct material stop and indirect material stop. Direct material stop is defined as no bent node between the current bending node and the material stop position. Indirect material stop is defined as at least one bent node between the current bending node and the material stop position. The consideration of the influence of the material stop position on the machining dimensional accuracy includes considering the principle of priority for direct material stop and the principle of indirect material stop based on proximity.

[0010] Furthermore, it also includes identifying critical length segments in sheet metal. In the equivalent accuracy model, critical length segments are considered to be processed earlier, and weights are added to them. The greater the weight, the more important their accuracy.

[0011] Furthermore, the equivalent precision function in the equivalent precision model for:

[0012] ;

[0013] Where G represents the number of critical length segments. For the first Priority weights for each key length, This is the determination coefficient for direct stop, when the direct stop condition is met. , The determination coefficient for indirect material blocking, The ranking coefficient for the critical length segment. The influence coefficient of bending length error is given when the bending length error is minimized. , , , and These are the weighting coefficients.

[0014] Furthermore, the determination coefficient of the indirect material stop The calculation formula is:

[0015] ;

[0016] in, This is the current bending node. For material blocking node, Indicates the total number of bending processes;

[0017] The sorting coefficient of the key length segment The calculation formula is:

[0018] ;

[0019] in, and These are the nodes at both ends of the critical length segment. and The corresponding bend position.

[0020] Furthermore, the sheet metal adjustment operations include flipping, turning, mold changing, and sheet material movement. The efficiency function expression of the equivalent efficiency model is:

[0021] ;

[0022] in, The number of times to flip the dough. Number of U-turns For the number of mold changes, The relative movement distance of the sheet metal. Indicates the total number of bending processes; They represent The weighting coefficients.

[0023] Furthermore, the specific steps of the genetic algorithm are as follows: construct an initial set of processes and a set of stop positions, encode the set of processes and the set of stop positions using real number encoding, generate an initial population, operate on the initial population through selection, crossover, and mutation, calculate the two fitness values ​​of the population using the fitness functions of the equivalent accuracy model and the equivalent efficiency model respectively, determine the quality of the population, obtain the solution set of the Pareto optimal bending process combination and the corresponding stop position sequence, determine the priority of the bending accuracy and efficiency optimization objectives, take the optimization objective with the higher priority as the preference, and obtain the optimal bending process combination and the corresponding stop position sequence under the preference.

[0024] The present invention discloses a joint planning system for bending process and stop position in sheet metal, comprising:

[0025] The error calculation module is used to determine the target bending node of the sheet metal, initially plan several feasible bending process combinations, determine the candidate node set of the stop position for each bending step based on the stop analysis, the candidate nodes include bending nodes and edge nodes of the sheet metal, analyze the impact of the change of the stop position on the bending length accuracy, and determine the bending length error calculation formula according to the spatial position relationship between the current bending node and the stop during the bending process.

[0026] The accuracy model building module is used to establish an equivalent accuracy model that characterizes the variation characteristics of bending processing dimensional accuracy, based on the bending length error calculation formula, considering the influence of the stop position and bending length error on the processing dimensional accuracy.

[0027] The efficiency model building module is used to consider the time spent on adjusting the sheet metal between bending processes during the bending process, and to build an equivalent efficiency model for the bending process based on the number of adjustment operations.

[0028] The sequence determination module uses the equivalent accuracy model and equivalent efficiency model as fitness functions, and solves the problem using a genetic algorithm with bending accuracy and efficiency as dual objectives. This yields the Pareto optimal combination of bending processes and the corresponding stop position sequence, determines the priority of the bending accuracy and efficiency optimization objectives, and selects the optimal optimization objective with the highest priority as the preference, thus obtaining the optimal combination of bending processes and the corresponding stop position sequence under the preference.

[0029] Beneficial Effects: Compared with existing technologies, the significant advantages of this invention are: by considering the impact of changes in the stop position on bending length accuracy, it clarifies the inherent correlation between dimensional errors and bending process planning and stop position selection. Joint planning of sheet metal bending processes and stop positions allows for the simultaneous acquisition of bending process sequences and stop position sequences, effectively improving bending accuracy and efficiency. By normalizing the expression of bending accuracy and efficiency, the optimal Pareto combination set of bending process and stop position sequences is obtained to the greatest extent possible, and adjustments are made according to target preferences, making it more suitable for complex bending manufacturing scenarios with multiple bending processes. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the planning method in this invention.

[0031] Figure 2 This is a schematic diagram of the workpiece in an embodiment of the present invention.

[0032] Figure 3 This is a schematic diagram illustrating the principle of bending error formation during the bending process of this invention.

[0033] Figure 4 This is a schematic diagram of direct and indirect material blocking in an embodiment of the present invention.

[0034] Figure 5 This is a diagram showing the combined planning results of the bending process and the material stop position in an embodiment of the present invention. Detailed Implementation

[0035] like Figure 1 As shown in the figure, this embodiment of a method for jointly planning the bending process and the stop position of sheet metal includes the following steps:

[0036] Step 1: Determine the target bending node of the sheet metal, initially plan several feasible bending process combinations, and based on the stopability analysis, determine the candidate node set of the stop position for each bending step. The candidate nodes include bending nodes and edge nodes of the sheet metal. Analyze the impact of the change of the stop position on the bending length accuracy, and determine the bending length error calculation formula according to the spatial position relationship between the current bending node and the stop during the bending process.

[0037] Sheet metal bending length error mainly includes initial length error and bending process length error. Initial length error: Dimensional deviations in the sheet metal blank caused by processes such as blanking, shearing, or cutting before entering the bending process. Bending process length error: During the bending process, inaccurate positioning of the stop device leads to different length errors at different stop positions. This paper mainly considers the error caused by stop positioning. To further understand the formation and transmission rules of bending process length error, a direct stop method is defined as having no "bent" node between the current bending position and the stop position; an indirect stop method is defined as having at least one "bent" node between the current bending position and the stop position. Different stop methods result in different length errors.

[0038] In this embodiment, for example, Figure 2 The diagram illustrates the bending process and stop position planning for a typical two-dimensional bent sheet metal part. Its length segment consists of bending nodes and sheet metal edge nodes, numbered sequentially as 0, 1, 2, 3, 4, 5, 6, 7, and 8. First, the process is planned using a reverse state propagation method, generating 5 feasible bending processes. Then, combined with a stopability check, a set of candidate nodes for the corresponding stop position is determined for each bending step. In this embodiment, the critical length segment is set as... The priority weights of the two are set as follows: .

[0039] Calculate the length error caused by different material stopping methods, such as Figure 3 , 4 As shown, for the direct blocking method, The segment directly affects the size. The segment size indirectly affects the size. The error introduced by the segment size is , The segment dimensions include the newly introduced length tolerance. And the original Segment size error Therefore Compared to direct blocking, indirect blocking introduces more dimensional errors. The segment size directly affects the overall size, while and The two dimensions are indirectly affected dimensions. The error introduced by the segment size is , The dimensional error of the segment is , The error in segment size is then... .

[0040] Step 2: Based on the formula for calculating bending length error, considering the influence of the stop position and bending length error on the machining dimensional accuracy, establish an equivalent accuracy model characterizing the variation of bending machining dimensional accuracy. The influence of the stop position on machining dimensional accuracy includes considering the principle of prioritizing direct stop and the principle of indirect stop based on proximity; it also includes considering the influence of setting critical length segments in the sheet metal on machining dimensional accuracy, and considering that critical length segments are processed earlier; and considering the influence of bending length error on machining dimensional accuracy.

[0041] Equivalent precision function in the equivalent precision model for:

[0042] (1)

[0043] In equation (1), G represents the number of critical length segments. For the first The priority weights of key length segments are assigned, with larger weights indicating greater importance for accuracy. This is the determination coefficient for direct stop, when the direct stop condition is met. , The determination coefficient for indirect material blocking, The ranking coefficient for the critical length segment. The influence coefficient of bending length error is given when the bending length error is minimized. , , , and These are the weighting coefficients.

[0044] Determination coefficient of indirect material blocking The calculation formula is:

[0045] (2)

[0046] In equation (2), This is the current bending node. For material blocking node, This represents the total number of bending steps;

[0047] Ranking coefficient of key length segment The calculation formula is:

[0048] (3)

[0049] In equation (3), and These are the nodes at both ends of the critical length segment. and The corresponding bend position.

[0050] In this embodiment, the priority order of their values ​​in the accuracy constraints is set. The weighting coefficients are 0.4, 0.5, 0.7, and 0.8, respectively, for the equivalent precision function. for:

[0051] (4)

[0052] In equation (4), when the direct material blocking priority is satisfied... If not satisfied When the bending length error is minimized. If not satisfied .

[0053] Step 3: Consider the time consumed by sheet metal adjustment operations between bending processes during the bending process. Based on the number of adjustment operations, establish an equivalent efficiency model for the bending process. Focus on the flipping, turning, mold changing, and sheet metal movement stages. By minimizing the number of flipping and turning operations, optimizing the mold changing sequence, and compacting the process design, the time consumption of each stage can be effectively reduced, bending efficiency improved, and the time consumed in the sheet metal bending process minimized. The efficiency function expression of the equivalent efficiency model is:

[0054] (5)

[0055] In equation (5), The number of times to flip the dough. Number of U-turns For the number of mold changes, The relative movement distance of the sheet metal. Total number of bends; They represent The weighting coefficients.

[0056] Efficiency function The execution efficiency of the bending process is quantified, and in this embodiment, it is set based on its operational cost. The values ​​are 0.8, 0.3, 0.5, and 0.2. The total number of bends for the sheet metal parts is... The specific formula is:

[0057] (6)

[0058] In equation (6), For the number of times to flip, For the number of U-turns, For mold change times, This represents the relative movement distance of the sheet metal.

[0059] Step 4: Using the equivalent accuracy model and equivalent efficiency model as fitness functions, and with bending accuracy and efficiency as dual objectives, a genetic algorithm is used to solve for the Pareto optimal combination of bending processes and the corresponding stop position sequence. The priority of the bending accuracy and efficiency optimization objectives is determined, and the optimal optimization objective with the highest priority is selected as the preference, thus obtaining the optimal combination of bending processes and the corresponding stop position sequence under this preference. The specific steps of the genetic algorithm are: constructing the initial process set... and material stop position set The process set and stop position set are encoded using real-number encoding to form a single chromosome vector, generating an initial population. Selection, crossover, and mutation are applied to this initial population. The fitness functions of the equivalent accuracy model and the equivalent efficiency model are used to calculate two fitness values ​​for the population, determining its quality and yielding the Pareto-optimal solution set for the bending process combination and corresponding stop position sequence. Based on process decision requirements, the priorities of the optimization objectives for the bending process combination and stop position sequence are determined. First, the sequence set with the best fitness value for the highest priority optimization objective is identified. Then, the sequence combination with the best fitness value for another optimization objective is selected from this set, thus obtaining the optimal bending process combination and corresponding stop position sequence under the preferred conditions. When process engineers desire better accuracy, they can select the optimal bending process combination and corresponding stop position sequence under the most accurate preference.

[0060] In this embodiment, the total number of bends in the sheet metal part is In terms of algorithm settings, the population size was set to 50, and the maximum number of iterations was 30. Based on these settings, a joint planning solution for the "process-stop" relationship was performed. Decoding the optimal solution revealed that the algorithm ultimately selected the optimal bending process node sequence as [7,2,6,5,1,3,4], and the corresponding stop node sequence as [8,0,7,6,2,2,5]. The planning results for the process and stop positions are as follows: Figure 5 As shown, the arrows from left to right indicate the sequence of bending processes. The starting point of the arrow corresponds to the material stop node of the bending step, and the ending point of the arrow is the bending node. The critical dimensions (2, 3) and (5, 6) are both formed by direct material stop bending, achieving the highest accuracy.

Claims

1. A method for jointly planning the bending process and stop position in sheet metal work, characterized in that, Includes the following steps: Step 1: Determine the target bending node of the sheet metal, initially plan several feasible bending process combinations, and based on the stopability analysis, determine the candidate node set of the stop position for each bending step. The candidate nodes include the bending node and the edge node of the sheet metal. Analyze the impact of the change of the stop position on the bending length accuracy, and determine the bending length error calculation formula based on the spatial position relationship between the current bending node and the stop during the bending process. Step 2: Based on the formula for calculating bending length error, considering the influence of the stop position and bending length error on the machining dimensional accuracy, establish an equivalent accuracy model that characterizes the variation characteristics of bending machining dimensional accuracy. Step 3: Consider the time consumed by the adjustment operations on the sheet metal between bending processes during the bending process, and establish an equivalent efficiency model for the bending process based on the number of adjustment operations. Step 4: Using the equivalent accuracy model and equivalent efficiency model as fitness functions, and taking bending accuracy and efficiency as dual objectives, solve the problem using a genetic algorithm to obtain the Pareto optimal combination of bending processes and the corresponding stop position sequence. Determine the priority of the optimization objectives of bending accuracy and efficiency, and take the optimization objective with higher priority as the preference to obtain the optimal combination of bending processes and the corresponding stop position sequence under the preference.

2. The method for jointly planning the bending process and stop position for sheet metal according to claim 1, characterized in that, The material blocking position includes direct material blocking and indirect material blocking. Direct material blocking is defined as having no bent node between the current bending node and the material blocking position. Indirect material blocking is defined as having at least one bent node between the current bending node and the material blocking position. The consideration of the impact of material blocking position on the machining dimensional accuracy includes considering the principle of prioritizing direct material blocking and the principle of indirect material blocking based on proximity.

3. The method for jointly planning the bending process and stop position for sheet metal according to claim 2, characterized in that, It also includes identifying critical length segments in sheet metal, considering the critical length segments in the early stages of the process in the equivalent accuracy model, and assigning weights to the critical length segments, with the greater the weight, the more important the accuracy.

4. The method for jointly planning the bending process and stop position for sheet metal according to claim 3, characterized in that, The equivalent precision function in the equivalent precision model for: ； Where G represents the number of critical length segments. For the first Priority weights for each key length, This is the determination coefficient for direct stop, when the direct stop condition is met. , The determination coefficient for indirect material blocking, The ranking coefficient for the critical length segment. The influence coefficient of bending length error is given when the bending length error is minimized. , , , and These are the weighting coefficients.

5. The method for jointly planning the bending process and stop position for sheet metal according to claim 4, characterized in that, The determination coefficient of the indirect material stop The calculation formula is: ； in, This is the current bending node. For material blocking node, Indicates the total number of bending processes; The sorting coefficient of the key length segment The calculation formula is: ； in, and These are the nodes at both ends of the critical length segment. and The corresponding bend position.

6. The method for jointly planning the bending process and stop position for sheet metal according to claim 1, characterized in that, Adjustments to sheet metal include flipping, turning, mold changing, and sheet material movement. The efficiency function expression of the equivalent efficiency model is: ； in, The number of times to flip the dough. Number of U-turns For the number of mold changes, The relative movement distance of the sheet metal. Indicates the total number of bending processes; They represent The weighting coefficients.

7. The method for jointly planning the bending process and stop position for sheet metal according to claim 6, characterized in that, The specific steps of the genetic algorithm are as follows: construct an initial set of processes and a set of stop positions; encode the process set and the set of stop positions using real number encoding to generate an initial population; operate on the initial population through selection, crossover, and mutation; calculate the two fitness values ​​of the population using the fitness functions of the equivalent accuracy model and the equivalent efficiency model respectively; determine the quality of the population; obtain the solution set of the Pareto optimal bending process combination and the corresponding stop position sequence; determine the priority of the bending accuracy and efficiency optimization objectives; take the optimization objective with the higher priority as the preference; and obtain the optimal bending process combination and the corresponding stop position sequence under the preference.

8. A joint planning system for bending processes and stop positions in sheet metal processing, characterized in that, include: The error calculation module is used to determine the target bending node of the sheet metal, initially plan several feasible bending process combinations, determine the candidate node set of the stop position for each bending step based on the stop analysis, the candidate nodes include bending nodes and edge nodes of the sheet metal, analyze the impact of the change of the stop position on the bending length accuracy, and determine the bending length error calculation formula according to the spatial position relationship between the current bending node and the stop during the bending process. The accuracy model building module is used to establish an equivalent accuracy model that characterizes the variation characteristics of bending processing dimensional accuracy, based on the bending length error calculation formula, considering the influence of the stop position and bending length error on the processing dimensional accuracy. The efficiency model building module is used to consider the time spent on adjusting the sheet metal between bending processes during the bending process, and to build an equivalent efficiency model for the bending process based on the number of adjustment operations. The sequence determination module uses the equivalent accuracy model and equivalent efficiency model as fitness functions, and solves the problem using a genetic algorithm with bending accuracy and efficiency as dual objectives. This yields the Pareto optimal combination of bending processes and the corresponding stop position sequence, determines the priority of the bending accuracy and efficiency optimization objectives, and selects the optimal optimization objective with the highest priority as the preference, thus obtaining the optimal combination of bending processes and the corresponding stop position sequence under the preference.

9. The joint planning system for bending process and stop position in sheet metal according to claim 8, characterized in that, The material blocking position includes direct material blocking and indirect material blocking. Direct material blocking is defined as having no bent node between the current bending node and the material blocking position. Indirect material blocking is defined as having at least one bent node between the current bending node and the material blocking position. The consideration of the impact of material blocking position on the machining dimensional accuracy includes considering the principle of prioritizing direct material blocking and the principle of indirect material blocking based on proximity.

10. The joint planning system for bending process and stop position in sheet metal according to claim 9, characterized in that, It also includes identifying critical length segments in sheet metal, considering the critical length segments in the early stages of the process in the equivalent accuracy model, and assigning weights to the critical length segments, with the greater the weight, the more important the accuracy.

Images