Numerical control bend springback compensation calculation method

Abstract

The invention provides a numerical control bend springback compensation calculation method, which comprises the following steps of: (1) bending two arc sections on a test piece pipe according to set angles Ca and Cb by using a numerical control pipe bending machine, measuring and calculating a proportional springback coefficient k and a fixed springback coefficient b of the bend, measuring and calculating the length of a first straight line section, namely a difference value a of a straight line section in front of the Ca arc section before and after the bend, and calculating a deviation parameter d; (2) a YBC standard driving program of the numerical control pipe bending machine is generated according to the bent pipe three-dimensional model, Y is the linear feeding length, B is the rotation angle, and C is the bending angle; (3) compensating parameters in the YBC standard driving program in the step (2) according to the proportional rebound coefficient, the difference value a and the offset parameter d calculated in the step (1) to generate a new Y 'B' C 'program; (4) calculating the length of the required pipe blank according to the newly generated Y 'B' C 'program, cutting in place after increasing the necessary clamping amount of the pipe bending machine, and then carrying out numerical control pipe bending by utilizing the new Y' B 'C' program; and (5) after numerical control pipe bending is finished, the clamping state of the pipe clamping sleeve of the numerical control pipe bending machine on the pipeline is kept, and online cutting is conducted according to the reserved clamping amount of the pipe bending machine.

Description

Technical Field

[0001] The invention relates to the field of metal pipe bending, in particular to bending thin-walled metal pipes using a bending CNC pipe bending machine, and specifically to a method for optimizing CNC pipe bending accuracy through a springback compensation calculation method. Background Art

[0002] With the rapid development of modern science and technology, especially in the fields of aerospace, weaponry and equipment, the demand for rapid production of single-piece, small-batch metal pipes with high precision and specific bending shapes is increasing.

[0003] The high-precision bending requirements of the pipeline require that the relative position relationship of the two ends of the pipeline be guaranteed when the pipeline is actually used, and at the same time, the avoidance of the surrounding physical constraints and the relative position relationship of specific fixed positions must be guaranteed. Therefore, the bending angle of each arc segment of the pipeline, the length of each straight segment, and the torsion angle accuracy between arc segments will affect the overall accuracy of the pipeline. In recent years, domestic and foreign scholars have conducted more research on the angle compensation of the bending forming machine of the bending type CNC pipe bending machine, but less research on the length change caused by the angle rebound during the forming process (the torsion angle is theoretically only affected by the accuracy of the machine tool and does not need to be compensated). At present, many high-precision manufacturing fields such as aerospace use CNC tube bending equipment from Eaton Corporation of the United States. Compared with domestic equipment, the springback compensation algorithm of Eaton Corporation's CNC tube bending equipment has higher accuracy. However, when dealing with the problem of straight line segment compensation, the springback compensation algorithm embedded in the Eaton tube bending machine focuses on the impact of the springback of the previous bending arc segment on the length of the straight line segment, while the latter bending arc segment only considers the fixed springback part, ignoring the proportional springback part, and does not consider the impact of different materials and different pipe diameters on the compensation algorithm. Therefore, in practical applications, the forming accuracy is higher for materials with lower elastic models (aluminum alloy, stainless steel) and pipes with smaller diameters (4mm, 6mm), while the forming accuracy is poor for other pipes. Moreover, due to the length deviation of the first straight line segment and the process margin required for the tail end clamping, it is usually adopted to reserve process margins at both ends of the pipe bend, and then manually cut off the pipe according to the test results after bending. Summary of the invention

[0004] The technical problem solved by the present invention is to overcome the deficiencies of the prior art and provide a method for calculating springback compensation for bent pipes, which can be used for springback compensation calculation of bent pipes of different materials and different pipe diameters.

[0005] The technical solution of the present invention is: a CNC bending pipe springback compensation calculation method, comprising:

[0006] Step 1: Use the CNC pipe bending machine to bend the test pipe according to the set angle C a and C bBend two arc segments, measure and calculate the proportional springback coefficient k and the fixed springback coefficient b of the bent pipe, as well as the length of the first straight segment, which is C a The difference a between the straight segment before the arc segment before and after bending the pipe, and calculate the offset parameter d;

[0007] Step 2: Generate the YBC standard drive program for the numerically controlled pipe bender according to the 3D model of the bent pipe, where Y is the linear feed length, B is the rotation angle, and C is the bending angle;

[0008] Step 3: Compensate the parameters in the YBC standard drive program in Step 2 according to the proportional springback coefficient, difference a, and offset parameter d calculated in Step 1 to generate a new Y'B'C' program;

[0009] Step 4: Calculate the required length of the pipe blank according to the newly generated Y'B'C' program, intercept it in place after adding the necessary clamping amount of the pipe bender, and then perform numerical control pipe bending using the new Y'B'C' program;

[0010] Step 5: After the numerical control pipe bending is completed, keep the pipe clamp of the numerical control pipe bender in the clamped state of the pipeline, and perform on-line truncation of the reserved clamping amount of the pipe bender.

[0011] Preferably, the calculation formula for the offset parameter d is:

[0012] d = [a - k·R·tan(C a / 2) - b·π·R / 360] - tan(C a / 2),

[0013] where b = C a - C a ' - k·C a ;

[0014] a is the difference between the straight segment before the C a arc segment before and after bending the pipe; R is the theoretical pipe bending radius; C a ' is the measured angle after bending the C a arc segment.

[0015] Preferably, according to the proportional springback coefficient k, difference a, and offset parameter d calculated in Step 1, compensate the parameters in the YBC standard drive program in Step 2. The compensation algorithm is to establish a theoretical model of pipe bending springback compensation based on the springback characteristics of the material and the geometric characteristics of the bending process, compare the calculation results of the theoretical model with the actual bending results, and numerically fit the differences to form a correction term for the compensation algorithm to further improve the accuracy of the compensation algorithm.

[0016] Preferably, the compensation algorithm f(YBC) i :

[0017] Ci ' = C i + k * C i + b;

[0018] B i ' = B i ;

[0019] Y1' = Y1 - g·k·R·tan(C1 / 2) - b·π·R / 360 - d / tan(H1 / 2);

[0020] Y i ' = Y i+1 - g·k·R·tan(C i / 2) - b·π·R / 360 + d / tan(H i / 2) - g·k·R·tan(C i+1 / 2) - b·π·R / 360

[0021] - d / tan(H i+1 / 2);

[0022] Y n ' = Y n - g·k·R·tan(C n-1 / 2) - b·π·R / 360 + d / tan(H n-1 / 2)

[0023] Where Y is the length of the straight line segment, B is the rotation angle, C is the bending angle; R is the theoretical radius of the bent pipe; n is the total number of straight line segments on the pipeline; the subscript i is the serial number of the bending arc segment of the pipeline; when C i > C a , H i = C i , when C i < C a , H i = C a ; g is a preset material coefficient.

[0024] Preferably, for the preset material coefficient g, when the titanium alloy pipe is set to (0.8 - 1.2), the stainless steel pipe is set to (0.5 - 0.7), and the aluminum alloy pipe is set to 0.4 (0.3 - 0.5).

[0025] Preferably, for the preset material coefficient g, when the titanium alloy pipe is set to 1, the stainless steel pipe is set to 0.6, and the aluminum alloy pipe is set to 0.4.

[0026] Preferably, the method further includes step 6: performing precision detection on the formed bent pipe. If the precision requirements are not met, correcting the parameters in the newly generated Y'B'C' program, and jumping to step 4 to perform numerical control pipe bending again until the pipe bending precision meets the requirements, and using the output result for the manufacture of formal workpieces.

[0027] Preferably, the correction is to modify the preset material parameter g. According to the detection result after pipe bending, record the actual length of the straight line segment before each bent arc segment i after bending as L i , and record the theoretical length of the straight line segment before each bent arc segment i as M i , if ∑|L i -M i |≥0, increase and adjust the preset material parameter g. If ∑|L i -M i |<0, decrease and adjust the preset material parameter g.

[0028] Preferably, the tolerance of the cut length of the pipe blank needs to be less than 0.5 times the tolerance of the pipeline length.

[0029] Preferably, the numerical control pipe bender is a rotary draw type numerical control pipe bender, and the radius of the pipe bending die equipped is consistent with the theoretical pipe bending radius R.

[0030] The beneficial effects of the present invention compared with the prior art are:

[0031] The present invention discloses a high-precision pipe bending springback compensation algorithm that can adapt to different materials and different pipe diameters, and can achieve high-precision non-remnant pipe bending through algorithm control and online cutting of the pipe bender. The compensation algorithm can be independent of the numerical control pipe bender control system, realize the springback compensation of pipe bending by correcting the pipe bending program, and reduce the redevelopment of the existing numerical control pipe bending equipment system.

[0032] A numerical control pipe bending springback compensation calculation method provided by the present invention, compared with the traditional springback compensation represented by the Eaton numerical control pipe bender, considers the offset parameters of the springback difference between the two sections before and after the pipe bending arc section, and also considers the material coefficient due to the material and the cross-sectional size of the pipe, and provides corresponding calculation and correction methods, with higher pipe bending forming precision and wider pipe material applicability.

[0033] A numerical control pipe bending springback compensation calculation method provided by the present invention can achieve accurate pre-cutting and accurate pipe bending forming with online removal of clamping remnants, avoiding the redundant process of manually cutting according to the measurement results after forming the remaining margins at both ends before pipe bending, improving the automation level of accurate pipe bending and the pipe bending efficiency.

[0034] A numerical control pipe bending springback compensation calculation method provided by the present invention. The provided springback compensation calculation method can be independent of the numerical control pipe bending machine control system, and realizes the springback compensation of pipe bending by modifying the pipe bending program, reducing the redevelopment of the existing numerical control pipe bending equipment system, and is widely applicable to the current general-purpose rotary pipe bending numerical control pipe bending machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow description of a numerical control pipe bending springback compensation calculation method of the present invention.

[0036] Figure 2 It is the multi-view detection result of a 6mm diameter numerical control pipe bending after adopting the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0037] The following will further elaborate on the present invention in conjunction with the Figure 1-2 drawings and embodiments.

[0038] Aiming at the problem of low accuracy of the springback compensation algorithm of the traditional rotary pipe bending numerical control pipe bending machine in the current existing technology, the present invention designs a pipe bending springback compensation calculation method by considering the geometric characteristics during pipe forming and increasing the adjustable material coefficient, which can adapt to the springback compensation algorithms for pipes with different materials and different diameters. The compensation algorithm can be independent of the numerical control pipe bending machine control system, and realizes the springback compensation of pipe bending by modifying the pipe bending program, reducing the redevelopment of the existing numerical control pipe bending equipment system, and is widely applicable to the current general-purpose rotary pipe bending numerical control pipe bending machine. And through the algorithm control and the online cutting of the pipe bending machine, high-precision and zero-remainder pipe bending can be achieved.

[0039] A numerical control pipe bending springback compensation calculation method is as follows:

[0040] Step 1:

[0041] Open the numerical control pipe bending machine. On a test piece pipe of appropriate length, bend two arc segments according to the set angles C a and C b (C a <<C b , usually C a =20°, C b =120°). Then use a pipeline shape measurement device such as a multi-view detection device or a laser fork detection device to measure and calculate the proportional springback coefficient k and the fixed springback coefficient b of the pipe bending, as well as the difference a in the length of the first straight segment (the straight segment before the C a arc segment) before and after pipe bending, and calculate the offset parameter d.

[0042] Where: k = 1 - (C b '-C a ') / (C b -C a );

[0043] b = C a -C a '-k·C a ;

[0044] d = [a - k·R·tan(C a / 2) - b·π·R / 360] - tan(C a / 2).

[0045] The materials of the test pipe and the formal workpiece are thin-walled metal materials, and the cross-sectional shapes of the pipes include, but are not limited to, round pipes and square pipes. The numerical control pipe bender is a rotary draw bending numerical control pipe bender, and the radius of the pipe bending die equipped is consistent with the theoretical pipe bending radius R.

[0046] Step 2: Generate the YBC standard drive program for the numerical control pipe bender according to the 3D pipe bending model. This part is prior art and will not be elaborated here.

[0047] Step 3: Compensate the YBC program according to the measured parameters k, b, and d according to the springback compensation algorithm f(YBC) to generate a new Y'B'C' program;

[0048] f(YBC) i : C i ' = C i +k*C i +b;

[0049] B i ' = B i ;

[0050] Y1' = Y1 - g·k·R·tan(C1 / 2) - b·π·R / 360 - d / tan(H1 / 2);

[0051] Y i ' = Y i+1 -g·k·R·tan(C i / 2) - b·π·R / 360 + d / tan(H i / 2) - g·k·R·tan(C i+1 / 2) - b·π·R / 360

[0052] -d / tan(H i+1 / 2);

[0053] Y n ' = Y n -g·k·R·tan(C n-1 / 2) - b·π·R / 360 + d / tan(H n-1 / 2)

[0054] Where Y is the linear feed length, B is the rotation angle, C is the bending angle; R is the theoretical pipe bending radius; n is the total number of straight segments on the pipeline; the subscript i is the serial number of the bending arc segment of the pipeline; when C i > C a , H i = C i , when C i < C a , H i = C a ; g is a preset material coefficient.

[0055] Step 4: Calculate the required length of the pipe blank according to the newly generated Y'B'C' program (adding the necessary clamping amount of the pipe bender), and cut it in place, and then perform numerical control pipe bending.

[0056] Calculating the pipe blank is a well-known algorithm in the industry. The pipe blank length is cut in place by a cutting operation that disengages from the pipe bender before pipe bending. The pipe blank cutting length tolerance usually needs to be less than 0.5 times the pipeline length tolerance.

[0057] Step 5: After the numerical control pipe bending is completed, keep the clamping state of the pipe clamp sleeve of the numerical control pipe bender on the pipeline, and use a cutter to cut the clamping allowance of the bent pipeline at the origin position of the Y axis of the pipe bender. When cutting, keep the clamping state of the pipe bender for on-line cutting.

[0058] On-line cutting is to use a cutting tool or a cutting mechanism equipped on the numerical control pipe bender to cut the bent pipeline at the origin position of the numerical control pipe bender.

[0059] Complete the initial setting according to the setting of g given by this invention based on experience. The titanium alloy pipe is set to (0.8 - 1.2), the stainless steel pipe is set to (0.5 - 0.7), and the aluminum alloy pipe is set to 0.4 (0.3 - 0.5). In a preferred embodiment given by this invention, the titanium alloy pipe is initially set to 1, the stainless steel pipe is initially set to 0.6, and the aluminum alloy pipe is initially set to 0.4, which can generally meet the final pipe bending requirements at one time. Step 6 can also be added according to your own usage needs.

[0060] Step 6: Use a pipeline shape measuring device such as a multi-purpose detection device or a laser fork detection device to detect the accuracy of the formed bent pipe. If the accuracy requirements are not met, correct the preset material parameter g in the springback compensation algorithm f(YBC) i . Specifically, the correction method of the preset material parameter g is to record the actual length of the straight segment before each bending arc segment i as L i , and record the theoretical length of the straight segment before each bending arc segment i as M i , if ∑|L i - M i|≥0, the preset material parameter g is increased and adjusted, if ∑|L i -M i |<0, the preset material parameter g is adjusted to decrease. After completing the correction of the material parameter g, jump to step 3 and perform CNC tube bending again until the bending accuracy meets the requirements, and use the output results for the manufacture of formal workpieces. When each batch of tubes is bent using the same mold, it is only necessary to make corrections before bending the first product, and the corrected material parameters can be applied to the remaining products.

[0061] The following is further described in conjunction with specific embodiments:

[0062] The tube to be bent is a stainless steel thin-walled round tube with a diameter of 6 mm, a wall thickness of 0.8 mm, and a grade of 1Cr18Ni9Ti. The tube bending equipment uses Eaton VB2500 CNC tube bending machine with a bending radius of R24. The tube bending model consists of 5 original arcs with angles ranging from 34° to 113.5° and 6 straight line segments.

[0063] First, a 500 mm long pipe from the same batch was used to bend two curved arcs of 20° and 120°, and the length of the first straight segment before bending was recorded. After bending, the true angles of the two curved arcs and the length of the first straight segment after bending were measured. According to the results, the proportional rebound coefficient k = 0.0364, the fixed rebound coefficient b = 1.056, and the offset parameter d = 0.0509 were calculated according to the calculation method in step 1.

[0064] Secondly, generate the YBC standard driver program of the CNC pipe bending machine (a method known in the field) according to the three-dimensional model of the bent pipe, as shown in the following table.

[0065] Y (mm) B(°) C(°) 80.00 / 60.20 94.20 0.00 85.20 164.20 -180.00 34.00 113.20 0.00 113.50 113.20 -90.00 66.00 213 / /

[0066] Again, according to the calculation method in step 3, based on YBC, the revised Y1B1C1 is produced, as shown in the following table. The required blank length for the pipe bending is calculated to be 928.14mm, and the clamping amount of the pipe bending machine is set to 170mm. Therefore, the blanking length of the pipe is 1098.14mm.

[0067] <![CDATA[Y1(mm)]]> <![CDATA[B1(°)]]> <![CDATA[C1(°)]]> 79.38715 / 63.44728 93.0043 0.00 89.35728 162.5761 -180.00 36.2936 111.9311 0.00 118.6874 110.8129 -90.00 69.4584 212.5168 / /

[0068] Then, a CNC pipe bender is used to perform CNC pipe bending according to Y'B'C'. After bending, the pipe is clamped by the pipe bender and cut at the origin of the Y axis of the pipe bender.

[0069] Finally, a multi-eye inspection device is used to inspect the tube body that has been bent according to the three-dimensional model.

[0070] In the multi-camera detection data, the difference between the tail section length and the theoretical length is 0.16 mm, and the difference between the head section length and the theoretical length is 0.37. The bending accuracy of each part of the pipe body is relatively high, which fully meets the installation and use requirements of the product. There is no need to iterate and improve the accuracy again. Therefore, the output results will be used for the manufacturing of subsequent formal workpieces. The detection results are as Figure 2 shown.

[0071] As a common method, a numerical control pipe bending springback compensation calculation method provided by the present invention obviously has good universality: it takes into account the offset parameters of the springback differences between the front and rear sections of the pipe bending arc, and also takes into account the material coefficients of the material and the pipe cross-sectional dimensions, improves the forming accuracy, and can achieve accurate blanking in advance and accurate pipe bending forming with on-line removal of clamping allowances, avoiding the redundant process of manually cutting the allowances reserved at both ends before pipe bending according to the measurement results after forming, and improving the automation level of accurate pipe bending. It can be seen that the present invention also has the characteristics of simplicity, reliability, and good operability. It can directly use the existing general equipment conditions without re-developing the system to improve the forming accuracy of pipes made of different materials. It is an economical, easy-to-implement, flexible, and universal method.

[0072] Although the present invention has been disclosed above with preferred embodiments, it is not used to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solution of the present invention by using the disclosed methods and technical contents without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes, and decorations made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention all belong to the protection scope of the technical solution of the present invention.

[0073] The parts not detailed in the present invention belong to the common general knowledge of those skilled in the art.

Claims

1. A calculation method for springback compensation in numerical control tube bending, characterized in that Including: Step 1: Use a numerically controlled pipe bender to bend two arc segments on the test pipe at the set angles C a and C b Measure and calculate the proportional springback coefficient k, the fixed springback coefficient b of the bent pipe, and the length of the first straight segment, i.e., C a The difference a between the straight segments before and after bending of the arc segment, and calculate the offset parameter d; Step 2: Generate the YBC standard drive program for the numerical control pipe bender according to the 3D model of the bent pipe, where Y is the linear feed length, B is the rotation angle, and C is the bending angle; Step 3: Compensate the parameters in the YBC standard drive program in Step 2 according to the proportional springback coefficient, difference a, and offset parameter d calculated in Step 1 to generate a new Y'B'C' program; Step 4: Calculate the required length of the pipe blank according to the newly generated Y'B'C' program, intercept it in place after adding the necessary clamping amount of the pipe bender, and then perform numerical control pipe bending using the new Y'B'C' program; Step 5: After the numerical control pipe bending is completed, keep the clamping state of the pipe clamp sleeve of the numerical control pipe bender on the pipeline, and perform on-line cutting of the reserved clamping amount of the pipe bender.

2. The method according to claim 1, wherein: The calculation formula for the offset parameter d is: d = [a - k·R·tan(C a / 2) - b·π·R / 360] - tan(C a / 2), where b = C a -C a '- k·C a ; a is C a The difference in the straight section before the arc section before and after the bent pipe; R is the theoretical radius of the bent pipe; C a ' is C a The measured angle after the arc section is bent.

3. The method according to claim 1, wherein: According to the proportional springback coefficient k, difference a, and offset parameter d calculated in Step 1, compensate the parameters in the YBC standard drive program in Step 2. The compensation algorithm is to establish a theoretical model for pipe bending springback compensation based on the springback characteristics of the material and the geometric characteristics of the bending process, compare the calculation results of the theoretical model with the actual bending results, and perform numerical fitting on their differences to form a correction term for the compensation algorithm, further improving the accuracy of the compensation algorithm.

4. The method according to claim 3, characterized in that: Compensation algorithm f(YBC) i :[[-END]] C i ' = C i + k * C i + b; B i ' = B i ; Y1' = Y1 - g·k·R·tan(C1 / 2) - b·π·R / 360 - d / tan(H1 / 2); Y i ' = Y i+1 -g·k·R·tan(C i / 2) - b·π·R / 360 + d / tan(H i / 2) - g·k·R·tan(C i+1 / 2) - b·π·R / 360 -d / tan(H i+1 / 2); Y n ' = Y n -g·k·R·tan(C n-1 / 2) - b·π·R / 360 + d / tan(H n-1 / 2) where Y is the length of the straight segment, B is the rotation angle, C is the bending angle; R is the theoretical pipe bending radius; n is the total number of straight segments on the pipeline; the subscript i is the serial number of the bending arc segment of the pipeline; when C i > C a , H i = C i , when C i < C a , H i = C a ; g is a preset material coefficient.

5. The method according to claim 4, wherein: The preset material coefficient g is set to (0.8 - 1.2) for titanium alloy pipes, (0.5 - 0.7) for stainless steel pipes, and 0.4(0.3 - 0.5) for aluminum alloy pipes.

6. The method according to claim 5, characterized in that: The preset material coefficient g is set to 1 for titanium alloy pipes, 0.6 for stainless steel pipes, and 0.4 for aluminum alloy pipes.

7. The method according to claim 4, wherein: It further includes Step 6: Perform precision detection on the formed bent pipe. If the precision requirements are not met, correct the parameters in the newly generated Y'B'C' program, and jump to Step 4 to perform numerical control pipe bending again until the pipe bending precision meets the requirements, and use the output result for the manufacturing of the formal workpiece.

8. The method according to claim 7, wherein: The correction is to modify the preset material parameter g. According to the detection results after pipe bending, the actual length of the straight segment before each bent arc segment i after bending forming is denoted as L i , and the theoretical length of the straight segment before each bent arc segment i is denoted as M i , if ∑|L i -M i |≥0, the preset material parameter g is increased and adjusted. If ∑|L i -M i |<0, the preset material parameter g is decreased and adjusted.

9. The method according to claim 1, wherein: The tolerance of the cut-off length of the pipe blank needs to be less than 0.5 times the tolerance of the pipeline length.

10. The method according to claim 1, characterized in that: The numerical control pipe bender is a rotary pipe bender, and the radius of the pipe bending die equipped is consistent with the theoretical pipe bending radius R.

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