A dynamic springback compensation method in incremental forming process

Abstract

The present invention discloses a dynamic springback compensation method for a progressive forming process. Based on the type of original sheet material, sheet material thickness, forming angle and forming depth of the workpiece being processed, as well as the tool head radius, x-axis feed rate, and z-axis feed rate, the springback angle of the part is determined, and the theoretical contact range between the tool head and the sheet material and the index of the node to be processed are calculated. Based on the tool head feed rate, nodes can be located on the sheet material. Based on the nodes, the theoretical minimum distance between the sheet material and the tool head is determined, thereby calculating the number of nodes when a springback collision occurs. In other words, if a springback collision occurs during processing, the node closest to the tool head will become the first impact point. Therefore, by simply controlling the tool head to perform springback compensation on the node before the springback of the node reaches the theoretical minimum distance, the part forming quality can be guaranteed, and the efficiency is far higher than that of a multi-pass springback compensation method.

Description

Technical Field

[0001] The invention belongs to the technical field of incremental forming material processing, and in particular relates to a dynamic springback compensation method in an incremental forming process. Background Art

[0002] The springback deformation problem in the CNC incremental forming process seriously affects the shape and dimensional accuracy of parts, and is one of the main reasons that hinder the actual production of incremental forming. To address this problem, the "springback prediction + springback compensation" strategy is currently adopted. Li Junchao et al. proposed a real-time compensation method, dividing the workpiece processing into n passes, measuring after each pass, and performing springback compensation in the next pass. However, in practice, real-time measurement is very difficult, the workload is huge, and the measurement results are often inaccurate. Multi-pass processing will also increase the cutting force of the tool head on the sheet metal; other scholars, such as Han Fei, Mo Jianhua, Zhang Bin, Gong Pan, etc., use various algorithms to predict springback, and then use tool path compensation method to compensate for the springback of the side wall of the formed part. However, the algorithm is difficult and complicated to operate, making it difficult to go beyond the laboratory.

[0003] Currently, the industry mostly uses traditional stamping as a theoretical model to study the springback of sheet metal in incremental forming. Under this theoretical model, the sheet metal forming process is relatively fast, and springback mainly occurs after the tool head separates from the sheet metal (that is, after processing is completed). Therefore, compensation for springback is often established after the springback occurs, and the springback is often corrected during the complete processing process.

[0004] The unique processing method of incremental forming differs from traditional stamping in that the tool head remains in contact with the sheet metal for extended periods of time. Therefore, springback can occur not only after the process is complete but also during the process itself. As time passes, the sheet metal accumulates internal stress, increasing the severity of the springback. However, since the process is not yet complete, the tool head and sheet metal are still in contact, causing the sidewall of the part to collide with the tool head, affecting the final part quality.

[0005] In summary, on the one hand, in traditional multi-pass springback correction, the sheet metal will be subjected to repeated cutting over a large area by the tool head, which will make the wall thickness thinner and the surface quality of the workpiece deteriorate. At the same time, the tool head and the sheet metal need to be in contact for a long time, which can easily cause springback accumulation and affect the accuracy of the workpiece. On the other hand, other real-time compensation measurements for springback require real-time monitoring and real-time measurement of the entire processing process, which requires the machine tool to be upgraded. This makes the processing cost extremely high and labor-intensive and time-consuming, which is contrary to the high economy of incremental forming. At the same time, the academic community is still controversial about the forming principle of incremental forming of sheet metal, so the prediction algorithm developed faces problems such as insufficient explanatory power.

[0006] Therefore, it is of practical significance to develop a new processing method program to achieve more efficient dynamic springback compensation by combining existing CNC machining equipment and progressive forming processing technology. Summary of the Invention

[0007] In response to the above problems, the present invention designs a dynamic rebound compensation method in the progressive forming process. Through the design of the processing method and steps, more efficient dynamic rebound compensation can be achieved without changing the hardware equipment environment.

[0008] The present invention provides a method for dynamic springback compensation in an incremental forming process, comprising the following steps:

[0009] S1. Calculate the springback angle ψ. Based on the type and thickness of the original sheet material, the forming angle θ (in degrees) of the workpiece being processed, the forming depth h, the tool head radius r, the x-axis feed Δx, and the z-axis feed Δz, use a CAE (Computer Aided Engineering) simulation system to determine the springback angle ψ of the part.

[0010] S2. Determine the theoretical contact range between the tool head and the sheet metal. According to the tool head radius r and the forming angle θ of the workpiece to be processed, the theoretical contact range for,

[0011]

[0012] S3. Calculate the processing node index a contained in the theoretical contact range,

[0013]

[0014] Int() means rounding up. The above formula is essentially rounding up the result in the brackets. The basic principle is to determine the side wall elongation during a single feed based on the single feed amount of the tool head. According to the theoretical contact range Calculate its node index, although The number of nodes in theoretical contact within the range is a, but considering the rebound factor, the Kth a+1 A node will also contact the tool head, so the theoretical number of contact nodes is a+1;

[0015] S4, computing node K a+1 The theoretical minimum distance from the tool head ΔL1,

[0016]

[0017] S5. Calculate the final number of nodes K1 within the theoretical contact range when springback compensation is considered. Generally, the first set of theoretical contact ranges is taken as an example. The first set of theoretical contact ranges includes the start of asymptotic forming processing from the first K a+1 The range from node to the first K1 node, then

[0018]

[0019] S6, the first group of nodes springback compensation processing, the first group of nodes including the first group of theoretical contact range from K a+1 To the node K1, the springback compensation processing includes performing progressive forming processing on each node from top to bottom. After the tool head finishes processing the K2 node, the tool head is first retracted by Δz and then by Δx, so that the tool head can re-align the node K1. a+1 Processing is then performed, and the tool head is then advanced by a Δx, and then by a Δz, to complete the processing of the K1 node. a+1 The rebound processing of the first group of nodes K1 is completed; the basic principle is that according to theoretical analysis, when the tool head sequentially processes to node K1, node K a+1 It will collide with the tool head, so after the tool head finishes processing K2, the tool head is first retreated by Δz and then retreated by Δx, so that the tool head can collide with node K again. a+1 Perform processing, and then continue to complete the processing of the K1 node, thereby completing the springback compensation processing.

[0020] S7, sequentially perform springback compensation processing on nodes one by one, including performing springback compensation processing on nodes with an integer multiple of K2, i.e. repeat the springback compensation processing operation of step S6, and perform springback compensation processing on nodes with an integer multiple of K2. a+1 The nth group of nodes of nK1 are processed in groups one by one until the processing is completed; that is, after the processing is completed to the nK2 node, the tool head is first retracted by Δz and then by Δx, so that the tool head can re-align with the node nK a+1 Processing is performed, and then the tool head is advanced by a distance Δx and then by a distance Δz to continue processing the nK1th node, where n is a natural number greater than or equal to 2.

[0021] Furthermore, there is no order restriction for step S1 relative to step S2, step S3 and step S4, that is, step S1, step S2, step S3, step S4 can be executed in sequence, or step S2, step S1, step S3, step S4 can be executed in sequence, or step S2, step S3, step S1, step S4 can be executed in sequence, or step S2, step S3, step S1, step S4 can be executed in sequence, or step S2, step S3, step S4, step S1 can be executed in sequence, as long as it is completed before step S5.

[0022] Furthermore, the original sheet material includes a metal sheet.

[0023] The advantages and beneficial effects of the present invention are as follows: the dynamic rebound compensation method designed by the present invention in the incremental forming process adopts a single-pass multi-stage processing strategy, which reduces the number of passes, significantly shortens the processing time, effectively avoids prolonged contact between the tool head and the sheet material and repeated large-area cutting of the sheet material by the tool head, and ensures the wall thickness and surface quality of the workpiece. The single-pass multi-stage processing strategy takes into account the sheet material springback during the processing process, which was previously ignored, and at the same time reduces the accumulation of springback, which is conducive to improving the precision of the workpiece. It does not require the addition of additional equipment or modification of the machine tool, embodies the high economic efficiency of incremental forming, contributes to the promotion of incremental forming technology in actual production, and is applicable to both positive and negative incremental forming technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the theoretical contact range between the tool and the sheet;

[0025] Figure 2 It is a schematic diagram of a set of processing nodes within the theoretical contact range;

[0026] Figure 3 This is a schematic diagram of tool head springback compensation processing;

[0027] Figure 4 It is a schematic diagram of the rebound distance and theoretical distance principle;

[0028] Figure 5 This is a schematic diagram of the sequential node springback compensation processing group by group;

[0029] Figure 6 It is a flow chart of a dynamic springback compensation method in a progressive forming process. DETAILED DESCRIPTION

[0030] The following embodiments are further described in conjunction with the accompanying drawings and examples. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0031] Example 1, as Figures 1 to 6 As shown, the present invention designs a dynamic springback compensation method in a progressive forming process, comprising the following steps:

[0032] S1. Calculate the springback angle ψ. The springback angle ψ of the part is determined using a CAE (Computer Aided Engineering) simulation system based on the type and thickness of the original sheet material, the forming angle θ (in degrees) of the workpiece being processed, the forming depth h, the tool head radius r, the x-axis feed Δx, and the z-axis feed Δz. In this embodiment, the springback angle ψ is obtained using LS-DYNA software, which is widely used in the engineering field. This technology is mature in this field, and existing tool software can directly calculate it based on input parameters. The workpiece includes the target product and / or intermediate product to be processed. The forming angle θ and forming depth h of the workpiece are determined in advance based on the workpiece processing requirements.

[0033] S2. Determine the theoretical contact range between the tool head and the sheet metal. According to the tool head radius r and the forming angle θ of the workpiece to be processed, the theoretical contact range For (such as Figure 1 、 Figure 2 shown),

[0034]

[0035] S3. Calculate the processing node index a contained in the theoretical contact range,

[0036]

[0037] Int() means rounding up. The above formula is essentially rounding up the result in the brackets. The basic principle is to determine the side wall elongation during a single feed based on the single feed amount of the tool head. According to the theoretical contact range Calculate its node index, although The number of nodes in theoretical contact within the range is a, but considering the rebound factor, the Kth a+1 The nodes will also contact the tool head, so the theoretical number of contact nodes is a+1 (e.g. Figure 2 shown);

[0038] like Figure 2 、 Figure 3 、 Figure 4 As shown, the lowest point of the tool head theoretical contact range is node K1, the second to last node is K2, and K a The theoretical contact range The highest node in the tool head, then the node closest to the tool head is K a+1 .

[0039] S4, computing node K a+1 The theoretical minimum distance from the tool head ΔL1,

[0040]

[0041] The specific principle is as follows Figure 4 shown

[0042] ΔL1=L1-L3

[0043] in

[0044] L1=Δx(a+1)

[0045]

[0046] S5. Calculate the final number of nodes K1 within the theoretical contact range when springback compensation is considered. Generally, the first set of theoretical contact ranges is taken as an example. The first set of theoretical contact ranges includes the start of asymptotic forming processing from the first K a+1 The range from node to the first K1 node, then

[0047]

[0048] The specific principle is as follows Figure 4 As shown, node K a+1 The rebound value ΔL2 = L1-L2 at the position can be obtained by using trigonometric functions.

[0049]

[0050] Let ΔL2 = ΔL1, and use Formula 1 to calculate the value of K1. K1 is rounded up to obtain the result of Formula 2.

[0051] Here, it is known that the distance between the theoretical point and the tool is ΔL1 (this is a fixed value), and the distance between the theoretical point and the actual rebound point is ΔL2 (this value will change). Therefore, when the two values ​​are equal, it is considered that a collision has occurred. This is the first collision in the processing process. After the correction of the collision point is completed, the sheet metal will still collide due to rebound in subsequent processing, so the operation needs to be repeated.

[0052] S6, the first group of nodes springback compensation processing, the first group of nodes including the first group of theoretical contact range from K a+1 To the node K1, the springback compensation processing includes performing progressive forming processing on each node from top to bottom. After the tool head finishes processing the K2 node, the tool head is first retracted by Δz and then by Δx, so that the tool head can re-align the node K1. a+1 Processing is then performed, and the tool head is then advanced by a Δx, and then by a Δz, to complete the processing of the K1 node. a+1 The rebound processing of the first group of nodes K1 is completed; the basic principle is that according to theoretical analysis, when the tool head sequentially processes to node K1, node K a+1It will collide with the tool head, so after the tool head finishes processing K2, the tool head is first retreated by Δz and then retreated by Δx, so that the tool head can collide with node K again. a+1 Processing is carried out, and then the processing of the K1 node is continued to be completed, thereby completing the springback compensation processing (such as Figure 3 shown).

[0053] S7, sequentially perform springback compensation processing on nodes one by one, including performing springback compensation processing on nodes with an integer multiple of K2, i.e. repeat the springback compensation processing operation of step S6, and perform springback compensation processing on nodes with an integer multiple of K2. a+1 The nth group of nodes of nK1 are processed in groups one by one until the processing is completed; that is, after the processing is completed to the nK2 node, the tool head is first retracted by Δz and then by Δx, so that the tool head can re-align with the node nK a+1 Processing (such as Figure 5 As shown), the tool head is then advanced by a Δx and then by a Δz to continue processing the nK1th node, where n is a natural number greater than or equal to 2.

[0054] Preferably, the original sheet material comprises a metal sheet.

[0055] The specific flow chart of this embodiment is as follows Figure 6 shown.

[0056] In this embodiment, a frustum workpiece with an opening radius of 40 mm is subjected to progressive forming. The sheet material is 1060 aluminum, the sheet thickness is 1 mm, the forming angle of the workpiece is 60 degrees, the forming depth is 40 mm, the tool head radius is 5 mm, the x-axis single feed amount △x is 0.8 mm, and the z-axis single feed amount △z is 0.6 mm. The springback angle ψ obtained by LS-DYNA software is 3 degrees. The calculated K1 value is 8, so it is necessary to make a correction when k2 is an integer multiple of 7, that is, to make a springback correction when the processing depth h is 7x0.6=4.2 mm. Subsequently, springback correction will be made at depths of 8.4, 12.6, 16.8, 21, 25.2, 29.4, 33.6, and 37.8 mm, respectively.

[0057] The production of this part requires 15 minutes for a single pass without correction, and the quality of the single product is poor; using the method described in the present invention for processing, the process is completed in one go, the processing time is 18 minutes, and the quality is good; using the same raw material and part with two passes and the same trajectory correction requires 33 minutes; using the three-pass correction method, the processing time requires 42 minutes, which is close to the processing quality of the method of the present invention.

[0058] The present invention refers to the above method of predicting and compensating for springback at each node segment as a single-pass multi-segment processing method.

[0059] The difference between Example 2 and Example 1 is that the order of executing the method steps is: steps S2, S1, S3, S4, S5, S6, and S7.

[0060] Example 3 differs from Example 1 in that the method steps are executed in the following order: steps S2, S3, S1, S4, S5, S6, and S7.

[0061] Embodiment 4 differs from Embodiment 1 in that the order of executing the method steps is: steps S2, S3, S4, S1, S5, S6, and S7.

[0062] The basic principle of the present invention is: through the analysis of the incremental forming process, it is found that there is a theoretical contact range between the tool head and the sheet metal. (like Figure 1 As shown in the figure), nodes can be taken on the sheet material according to the feed rate of the tool head, and the theoretical minimum distance between the sheet material and the tool head can be determined based on the nodes (as shown in the figure). Figure 4 If a springback collision occurs during machining, the node closest to the tool head will become the first impact point. Therefore, by simply controlling the tool head to perform springback compensation on that node before the springback reaches the theoretical minimum distance, part forming quality can be guaranteed, and this method is much more efficient than multi-pass springback compensation.

[0063] The above is only a more systematic and comprehensive embodiment of the dynamic rebound compensation method in the incremental forming process of the present invention. It is essentially a timely rebound compensation method. Compared with the rebound compensation from the beginning of multiple passes, it can naturally improve efficiency. In fact, according to the actual processing, rebound compensation processing can be performed in real time at other nodes; in addition, steps S1 to S7 of the present invention can be recombined, etc. Such changes should also be regarded as the scope of protection of the present invention and will not be listed one by one here.

Claims

1. A method for dynamic springback compensation in an incremental forming process, characterized in that: The steps include: S1. Calculate the springback angle ψ. Determine the springback angle ψ of the part based on the type of original sheet material, sheet material thickness, forming angle θ of the workpiece, forming depth h, tool head radius r, x-axis feed △x, and z-axis feed △z. S2. Determine the theoretical contact range between the tool head and the sheet material. for, S3. Calculate the processing node index a contained in the theoretical contact range, Among them, int() means rounding; S4, computing node K a+1 The theoretical minimum distance from the tool head ΔL1, S5, calculate the final number of nodes K1, S6, the first group of nodes rebound compensation processing, the rebound compensation processing includes performing progressive forming processing on each node from top to bottom, when the tool head finishes processing the K2 node, the tool head is first retreated by Δz and then retreated by Δx, so that the tool head can re-process the node K a+1 Perform processing, then move the tool head forward by Δx and then by Δz to complete the processing of the K1 node; S7, sequentially perform springback compensation processing on each node group, including performing springback compensation processing on nodes that are integer multiples of K2, until the processing is completed.

2. The method for dynamic springback compensation in an incremental forming process according to claim 1, characterized in that: There is no order restriction for step S1 relative to step S2, step S3 and step S4.

3. The method for dynamic springback compensation in an incremental forming process according to claim 1, wherein: The raw sheet material comprises a metal sheet.

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