T-shaped ball head profile stretch forming method based on a cantilever stretch-bending machine tool

Abstract

The application discloses a T-shaped ball head profile stretching forming method based on a cantilever type stretch bending machine tool. Through a novel stretch bending forming structure and a novel stretch bending forming filler, the process method of the asymmetric web profile stretch bending forming is realized for the first time. The application uses the filler which is different from the filler used in the traditional complex profile stretch bending forming, uses the novel filler to change the stress layer of the stretch bending forming from asymmetric to approximate symmetry, and calculates the position of the centroid of the section edge strip width direction, so that the stretch bending data acquisition position is consistent with the inertia moment axis position of the stretch bending profile blank and the filler as a whole; the part forming efficiency is greatly improved, the original asymmetric web surface distortion of the part is basically eliminated, and the stretch bending forming efficiency of the part is greatly improved. The parts processed by the novel stretch bending forming process method have good batch part quality, high processing efficiency and low production cost, and high technical benefits and economic benefits can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aircraft manufacturing, and particularly relates to a T-shaped ball head profile stretching forming method based on a cantilever type stretch bending machine tool. BACKGROUND

[0002] Generally, the frame rib part on an aircraft belongs to a planar part with a bent edge. The edge bending forming is a main process in part manufacturing. The edge bending can be divided into two types, i.e., a type with aerodynamic shape requirement and a type without aerodynamic shape requirement. The former has a relatively strict shape accuracy requirement, and the latter can be appropriately relaxed. Generally, the frame rib part can also be distributed with a weight-reducing hole, a pipeline through hole, a longeron notch, a depression, a reinforcing nest and a reinforcing ridge, and a reference hole and a positioning hole used as a reference, etc. Since the aircraft shape is a smooth streamline body, the edge bending around the frame rib part has different bending angles and different heights along the contour; the contour line of the edge bending has a straight line, a convex arc line, a concave arc line and a comprehensive line of the three; in addition, the directions of the edge bending on the same part are the same or opposite. Since the latter needs to be formed twice, it should be avoided as much as possible. The frame rib part is mostly located on the control section of the size and shape of the aircraft body, so the planar part is required to be kept flat and is not allowed to be twisted and relaxed. Overall, the shape of the frame rib part is mostly planar.

[0003] The outer nacelle frame strip is a sheet metal part formed by bending a T-shaped ball head profile, and the forming process is complex. The forming process adopts pre-drawing in an annealed state, quenching and secondary bending, and multiple sheet metal manual correction. Due to the influence of the cross-sectional shape, the bending radius, the material performance and the like, the part is prone to forming defects such as web surface wrinkling, cross-sectional distortion, angle flatness change and springback in the drawing and bending process, and needs to be repeatedly manually corrected. The cold work hardening phenomenon is serious, and the forming quality of the part cannot be guaranteed. Since the ball head is not at the center of the vertical rib and has no stress point, when the part shape is corrected, the web surface is prone to wrinkling. SUMMARY

[0004] In order to solve the above problems, the present application provides a T-shaped ball head profile stretching forming method based on a cantilever type stretch bending machine tool.

[0005] The technical scheme of the present application is as follows:

[0006] A T-shaped ball head profile stretching forming method based on a cantilever type stretch bending machine tool, comprising the following steps:

[0007] Step 1: blanking the raw material, hoisting the stretch bending die, installing and debugging the stretch bending die, and fixing the stretch bending die on the workbench of the stretch bending machine tool;

[0008] Step 2: installing the stretch bending chuck of the stretch bending machine, and then cleaning the butt joint surface of the stretch bending chuck with compressed air to remove impurities in the stretch bending chuck;

[0009] Step 3 calculates the position of the centroid of the flange surface of the profile section in the width direction, and establishes a plane coordinate system with the intersection of the flange surface of the profile section and its adjacent surface as the origin, wherein the X direction is the width direction of the flange surface, and the Y direction is the height direction of the web surface, and the position of the centroid of the flange surface of the profile section in the width direction is calculated according to the following formula: X = (A1 + A2) / (2 * (A1 + A2 + A3 + A4)) c The stretching amount is set on the operation interface of the numerical control stretch-drawing machine, and the position X of the centroid of the flange surface of the profile section in the width direction is calculated c The trajectory line is collected so that the bending action surface coincides with the position of the centroid of the flange surface of the profile section in the width direction, and the numerical control stretch-drawing program is generated

[0010]

[0011] wherein X c is the position of the centroid of the flange surface of the profile section in the width direction, γ i is the ratio of the actual area of the profile section to the theoretical area of the profile section, A i is the simplified area of the profile section, X i is the position of the centroid of the flange surface of the profile section in the width direction corresponding to the simplified area of the profile section

[0012] Step 4: the surface of the raw material is cleaned, and it is observed whether there are burrs, stacking, burrs, inclusions or bubbles on the surface of the raw material, and the next step is performed after the defects are excluded;

[0013] Step 5: first stretch-drawing: the rubber plate is embedded into one side of the cavity of the web surface of the raw material, then the raw material and the rubber plate are slid into the web groove of the stretch-drawing die together, and lubrication is performed, no lubrication is performed between the rubber plate and the raw material, 1% is pre-drawn, then bent, the raw material after the film is taken off from the stretch-drawing die, and the semi-finished raw material is quenched after the rubber plate is separated.

[0014] Step 6: second stretch-drawing: after the semi-finished raw material is quenched, the rubber plate is embedded, and the second stretch-drawing is performed, and 2% to 3% is supplemented.

[0015] Further, the rubber plate is made of 5270 rubber plate, the vulcanization condition is 151±2℃ for 25 minutes, the hardness is 65±5 Shore, the tensile strength is ≥7.8MPa, the elongation at break is ≥450%, the permanent deformation at break is ≤30, and the thickness of the rubber plate is the thickness of the ball head part of the profile section minus the thickness of the web surface of the profile section.

[0016] The advantages of the present application are:

[0017] 1. In the process of one-drawing and two-drawing of profile stretch bending forming, the rubber plate is embedded to eliminate the additional bending moment generated by the asymmetric profile section in the drawing process, limit the deformation of the profile section, and prevent the generation of web surface wrinkling defects. The efficiency of stretch bending forming is improved by more than 45%, and the manual correction amount after part forming is reduced by more than 50%.

[0018] 2. The rubber plate is used instead of traditional cast zinc, fusible alloy, hard aluminum and other hard materials as the filler of drawing, which effectively avoids the damage to the surface of the part caused by hard materials, improves the surface quality of the part, reduces the product scrap rate, and saves the production cost. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Stretch bending die and part main structure;

[0020] Figure 2 Remove the structure of the upper cover of the stretch bending die;

[0021] Figure 3 Main structure cross-sectional view;

[0022] Figure 4 Calculation of the area division of the centroid position of the profile cross-sectional edge strip surface in the width direction;

[0023] Explanation of the numbers in the figure: 1, upper die of stretch bending die; 2, lower die of stretch bending die; 3, lower top plate of stretch bending die; 4, rubber plate; 5, raw material; 6, edge strip surface; 7, web surface. DETAILED DESCRIPTION

[0024] As shown in Figures 1-4 A T-shaped ball head profile stretching forming method based on a stretch bending machine tool, comprising the following steps:

[0025] Step 1: Cut the raw material 5 and the rubber plate 4, hoist the stretch bending die, the stretch bending die is composed of the upper die 1, the lower die 2 and the lower top plate 3 of the stretch bending die, install and debug the stretch bending die, and fix it on the workbench of the stretch bending machine tool. The material used is 2A12-O-XC241-7, with a density of 2850 kg / m3, an elastic modulus of 70 GPa, a Poisson's ratio of 0.33, a yield strength of 135.81 MPa, a stud ball head diameter b = 10 mm, and a web δ1 = 2 mm as Figure 3The rubber plate 4 is shown in the cross section of the middle profile 5. The length of the rubber plate 4 is 726mm, L = 926mm, which is 200mm longer than the length of the stretch-drawing die; the rubber plate 4 is made of 5270 rubber plate, and the vulcanization condition of the rubber plate is 151±2℃ for 25min, the hardness is 65±5 Shore, the tensile strength is ≥7.8MPa, the elongation at break is ≥450%, the permanent set at break is ≤30, and the thickness of the rubber plate 4 is the thickness of the ball head part of the profile cross section minus the thickness of the web of the profile cross section. The thickness = the thickness of the ball head - the thickness of the web = 10-2 = 8mm, and the width size is the height size of the web of the profile minus the diameter of the ball head and the thickness of the edge strip

[0026] =60mm-10mm-3mm = 47mm, and the size of the rubber plate 4 is 726mm×47mm×8mm as shown in Figure 3 The stretch-drawing die is installed and debugged, and is fixed on the workbench of the stretch-drawing machine. The outer shape area of the upper surface of the upper die 1 of the stretch-drawing die and the upper surface of the lower die 2 of the stretch-drawing die is lubricated with a brush dipped in lubricating oil. Figure 1

[0027] Step 2: The stretch-drawing chuck of the stretch-drawing machine is installed, and then compressed air is blown to clean the butt joint surface of the stretch-drawing chuck and remove impurities in the stretch-drawing chuck. The compressed air should not contain water, oil, grease and solid particles.

[0028] Step 3: The centroid position of the edge strip surface of the profile cross section in the width direction is calculated as shown in Figure 4 A plane coordinate system is established with the intersection point of the edge strip surface 6 of the profile cross section and its adjacent surface as the origin, wherein the X direction is the width direction of the edge strip surface 6, and the Y direction is the height direction of the web surface 7. The centroid position coordinate value X of the edge strip surface 6 of the profile cross section in the width direction is calculated according to the following formula: c The approximate area of the edge strip surface 6 is A1 = 50mm×3mm = 150mm 2 The approximate area of the combination of the rubber plate 4 and the divided area of the stud ball head is A2 = 10mm×57mm = 570mm 2 ;

[0029]

[0030] X c is the centroid position of the edge strip surface in the width direction of the profile cross section, and γ i is the correction coefficient of the fillet at the joint of the profile cross section (wherein γ1 is 1 because the fillet is connected to the divided area of the rubber plate and the stud ball head, and the approximate area of the combination of the divided area of the rubber plate and the stud ball head; γ2 is the ratio of the actual area of the combination of the divided area of the rubber plate and the stud ball head to the approximate area of the combination of the divided area of the rubber plate and the stud ball head, and in actual production, for the convenience of calculation, the actual area of each fillet can be approximated to half of the square area with the same radius length of the fillet,

[0031] ​ Set the stretching amount on the CNC stretch bending machine's operating interface, and locate the centroid position X in the calculated profile cross-section flange width direction. c The trajectory line of the CNC bending data is collected at position 28.1, ensuring that the centroid of the bending surface coincides with the centroid of the profile cross-section flange in the width direction. This guarantees that the bending moment and tension acting on the overall moment of inertia of the profile are consistent during the bending process, avoiding bending defects caused by force misalignment. The swing arm speed range of the CNC bending machine is set to 0-4 degrees / second, ideally 1-2 degrees / second. The tension cylinder speed range is 0-0.5 inches / second, ideally 0.3 or 0.4 inches / second. The trajectory line is collected to generate the CNC bending program.

[0032] Step 4: Wipe the surface of the fabric 5 with gauze soaked in acetone, and visually inspect the surface of the fabric 5 for defects such as burrs, lumps, rough edges, inclusions or air bubbles. After eliminating any defects, proceed to the next step.

[0033] Step 5: First bending: Use 2A12-O-XC241-7 wool for the first bending. Figure 2 , Figure 3 As shown, rubber sheet 4 is embedded into one side of the cavity on the web surface of the ball-head profile blank 5. The assembled workpiece is then slid together into the web groove of the bending die 5. Note that lubrication should not be applied between rubber sheet 4 and blank 5 to prevent displacement of the rubber sheet during bending, which could lead to part deformation. Press "Stretch ~ Bending" to pre-stretch by 1%, then bend. During bending, observe whether blank 5 adheres to the die. If not, use a wooden hammer to tap and repair the non-adherent area until it adheres. After adhering, remove blank 5 from the bending die. After separating rubber sheet 4, wipe the surface of the blank with gauze soaked in acetone to remove lubricant and prevent overheating during quenching. After cleaning, quench the semi-finished blank.

[0034] Step 6: Second bending: After the semi-finished raw material is quenched, it is embedded in rubber plate 4 and bent for the second time, with an additional 2% to 3% bending.

[0035] The key point of this invention lies in effectively eliminating the problem of bending moment and tension not acting on the overall moment of inertia of the profile due to the misalignment of the forming bending surface and the centroidal plane of the profile cross-section. This prevents phenomena such as torsion, deflection, and cross-sectional distortion that occur during bending. This improves the efficiency of stretch bending forming by more than 45% and reduces the amount of manual correction after part forming by more than 50%. Furthermore, replacing the traditional use of hard materials such as zinc, fusible alloys, and duralumin as fillers in stretch bending with flexible rubber fillers effectively avoids damage to the part surface caused by hard materials, improves the surface quality of the parts, reduces product scrap rates, and saves production costs.

Claims

1. A method of stretch forming a T-head profile based on a draw-bender machine, the head not being centered on the web, characterized in that The method is as follows: Step 1: discharging the wool material, discharging the rubber plate, hoisting and installing the stretch-drawing die, and installing and debugging the stretch-drawing die to fix it on the workbench of the stretch-drawing machine; Step 2: installing the stretch-drawing chuck of the stretch-drawing machine, and then cleaning the butt joint surface of the stretch-drawing chuck with acetone to remove impurities in the stretch-drawing chuck; Step 3: calculating the centroid position of the profile section edge surface in the width direction, establishing a plane coordinate system with the intersection of the profile section edge surface and its adjacent surface as the origin, the X direction as the edge surface width direction, and the Y direction as the web surface height direction, calculating the centroid position Xc of the profile section edge surface in the width direction according to the following formula, setting the stretching amount on the numerical control stretch-drawing machine operation interface, collecting the track trajectory line at the calculated centroid position Xc of the profile section edge surface in the width direction to make the bending action surface coincide with the centroid position, and generating a numerical control stretch-drawing program, wherein Xc is the centroid position of the profile cross-section edge strip in the width direction, γ i is the ratio of the actual area of the profile cross-section divided area to the theoretical area of the division, A i is the profile cross-section divided simplified area, X i is the centroid position of the profile cross-section divided simplified area in the width direction of the profile cross-section edge strip Step 4: cleaning the surface of the wool material, and visually observing whether there are burrs, accumulated places, burrs, inclusions or bubble defects on the surface of the wool material, and then performing the next step after excluding the defects; Step 5: first stretch-drawing, the specific process is as follows: embedding the rubber plate into one side of the web cavity of the wool material, then sliding the wool material and the rubber plate into the web groove of the stretch-drawing die together, lubricating, not lubricating between the rubber plate and the wool material, pre-drawing 1%, then bending, taking out the wool material after the die from the stretch-drawing die, separating the rubber plate, and then quenching the semi-finished wool material; Step 6: second stretch-drawing, the specific process is as follows: after quenching the semi-finished wool material, embedding the rubber plate, and performing the second stretch-drawing forming, the stretch-drawing is 2%-3%.

2. A method of stretch forming a T-head profile based on a toggle stretcher bender machine bed as claimed in claim 1, characterized in that The rubber plate is made of 5270 rubber plate, the vulcanization condition is 151±2℃ for 25min, the hardness is 65±5 Shore, the tensile strength is ≥7.8MPa, the elongation at break is ≥450%, and the thickness of the rubber plate is the thickness of the profile section ball part minus the thickness of the profile section web surface.

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