Forming method of aluminum alloy large-curvature automobile back door outer plate cold stamping die

Abstract

The invention discloses a cold stamping die forming method for an aluminum alloy large-curvature automobile back door outer plate. The cold stamping die forming method comprises the following steps that 1, a V-shaped forming frame is constructed; 2, forming difficulty analysis; 3, surface drawing and weak rib control are carried out; 4, the step 4.1 of small-area draw bead treatment, the step 4.2 of reverse drawing forming compensation and the step 4.3 of over-drawing forming compensation are included; 5, performing comprehensive treatment optimization; 6, progressive drawing strengthening is carried out; step 7, turning over for secondary compensation; 8, area strengthening and connection forced pressing are carried out; and 9, trimming and debugging. The forming problem of the back door outer plate is successfully solved, a low-cost and high-efficiency forming scheme without increasing other equipment or auxiliary material consumption is provided for cold stamping forming of light-weight, large-curvature and few-control-point parts, and technical support is provided for combination of attractiveness and mechanical property of an automobile. And rapid application of light-weight materials and beautiful development of automobile modeling are promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of automotive panel dies, and particularly to a cold stamping die forming method for the outer panel of the large-curvature aluminum alloy automotive rear door. Background Art

[0002] With the increasingly obvious achievements of China's new energy vehicles in overtaking on a curve, China's automotive technology stands at the world's forefront with a high standard. The competition in the automotive industry has shifted from a comfortable driving experience to an all-round progress leapfrog stage. As the core image part of the vehicle, the automotive rear door has attracted much attention because of its many laps, which is related to the overall appearance effect of the vehicle and the vehicle's hydrodynamic performance.

[0003] However, there are few forming control points for the outer panel of the automotive rear door, and the appearance accuracy requirements are high. Therefore, the shape design is relatively strict due to the influence of the forming ability. Therefore, it is necessary to use shapes such as side lines and ridge lines to reduce the forming difficulty, but in this way, the aesthetics is limited within a certain range; especially with the rise of new energy vehicles, the pursuit of the application of lightweight materials is more urgent. The forming of the outer panel of the automotive rear door with large curvature, few control points and lightweight has become an urgent aesthetic demand and a pain point in the industry. The main reasons are as follows.

[0004] On the one hand, lightweight materials such as aluminum alloy and high-strength steel have large springback, poor formability, and are prone to cracking and distortion, and are prone to a series of problems such as scratches and orange peel, resulting in high cost, long cycle and poor quality effect for realizing cold stamping die forming; on the other hand, the forming state of parts with large curvature and few control points is inherently poor, and problems such as springback, cracking, distortion, poor strength and serious surface defects emerge in an endless stream. The superposition of these two factors has caused the forming of the outer panel of the automotive rear door with large curvature and few control points made of lightweight materials to be in a state where no one has tried, seriously affecting the process of the perfect combination of the aesthetics, lightweight and mechanical properties of automotive design.

[0005] To solve the above problems, the global automotive industry has also carried out relevant explorations, such as trying to explore by means of electromagnetic assisted forming, graphene lubricated forming, and residual stress compensation forming. However, due to the influence of various factors such as cost, efficiency and forming effect, it is still very difficult to form the outer panel of the automotive rear door with large curvature and few control points made of lightweight materials. As a result, it has to continue to use traditional shapes or use easily formable ordinary steel plates and other methods for forming. It is still the industry's expectation to solve this problem in a simple and easy way.

[0006] It should be particularly noted that the above technical information is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or any form of implication that the above technical information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0007] In view of the deficiencies in the above-mentioned background art, the present invention proposes a cold stamping die forming method for the outer panel of an aluminum alloy automotive back door with a large curvature, and the technical problems to be solved are: how to achieve the reliability of the cold stamping die for the outer panel of an automotive back door with a large curvature made of lightweight materials and few control points, how to significantly shorten the development cycle of the cold stamping die for the outer panel of an automotive back door with a large curvature made of lightweight materials and few control points, and how to reduce the application cost of the cold stamping die for the outer panel of an automotive back door with a large curvature made of lightweight materials and few control points.

[0008] The technical solution of the present invention is as follows: A cold stamping die forming method for the outer panel of an aluminum alloy automotive back door with a large curvature, comprising the following steps: Step 1: Construct a V-shaped forming frame; Step 2: Analyze the forming difficulties; Step 3: Surface drawing and weak rib control; Step 4: Include Step 4.1 Treatment of draw beads in small areas, Step 4.2 Compensation for reverse drawing forming, and Step 4.3 Compensation for over-drawing forming; Step 5: Comprehensive treatment and optimization; Step 6: Progressive drawing strengthening; Step 7: Second compensation for flanging; Step 8: Area strengthening and connection strong pressing; Step 9: Trimming and debugging.

[0009] The specific method of the above-mentioned Step 1 is as follows: On the basis of the above technical solution, as a preferred technical solution of the cold stamping die forming method for the outer panel of an aluminum alloy automotive back door with a large curvature, Step 1.1: Taking the overall trend of the product type as a reference, with the vertex of the large curvature as the center and the vertical downward direction as the direction line, make the angles between the main trend direction lines of the two sides of the L-shaped product of the part and the vertical downward direction line equal. At this time, the part placement mode is the standard inverted V mode.

[0010] On the basis of the above technical solution, as a preferred technical solution of the cold stamping die forming method for the outer panel of an aluminum alloy automotive back door with a large curvature, Step 1.2: In the standard inverted V mode, rotate the product type upward along the long side of the L-shaped product of the product at a unit of every 5 degrees until there is no negative angle state when looking at the product type from top to bottom, and define the state at this time as the non-negative angle inverted V mode.

[0011] On the basis of the above technical solutions, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automotive rear door, step 1.3: Rotate the product model upward along the long side of the product model in the shape of L until the outermost sides of the products on both sides of the L shape are on the same horizontal plane. The mode at this time is defined as the plane inverted V mode; compare the included angle between the plane inverted V mode and the non-negative angle inverted V mode. If the included angle is less than 15°, the non-negative angle inverted V mode is used as the die stamping normal direction. If it is greater than 15°, the midline direction of the two included angles is selected as the reference direction, and check whether there is a negative angle on the surface in this direction. If there is no negative angle, the reference direction is the stamping direction. If there is a negative angle, rotate the part clockwise and counterclockwise until there is no negative angle, and take the minimum rotation angle direction of the two rotation modes as the stamping direction.

[0012] On the basis of the above technical solutions, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automotive rear door, step 1.4: Taking the stamping direction as the frame state, establish the process supplement according to the conventional mode and optimize it. At this time, the product model state is in a suitable state where it is basically evenly distributed on both sides and the cavity depth is relatively shallow. Practical experience shows that this state can provide better force dispersion and compensation space for subsequent forming control and compensation, so as to complete the construction of the V-shaped frame.

[0013] On the basis of the above technical solutions, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automotive rear door, the forming difficulty analysis in step 2 is to perform a conventional process supplement on the product model under the V-shaped frame, establish a process digital model, and perform CAE batch analysis of different parameters on the process digital model, set different parameters, so as to find the forming difficulties of the overall process digital model and generate the first process digital model; on this basis, establish the regional distinction of the overall forming difficulties and the overall sorting of the forming difficulties, and optimize the process of the forming difficulty area, improve the process digital model of the forming difficulties, find the best state, and generate the first process digital model.

[0014] On the basis of the above technical solutions, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automotive rear door, the specific method of step 3 is as follows: Step 3.1: On the basis of the first process digital model, eliminate the draw beads in the forming difficulty areas in the L long direction and L short direction, retain the draw beads at both ends, and eliminate all the draw beads in the middle to convert it into an open draw environment.

[0015] Step 3.2: Adopt a weak bead control method for the left and right directions. The method is to increase the width of the draw bead to 1-3 times the normal draw bead width. The algorithm is to set the normal draw bead width as H, and the length D from the outside of the product model to the inside in the defect area. Then the draw bead width h is: h = 3H - D / 5, h >= H; (if D / 5 is greater than 2, then D / 5 = 2).

[0016] At the same time, adjust the height of the draw bead to 60% - 80% of the state calculated by the primary process type, and the specific value is adjusted according to the later CAE analysis, so as to reduce the forming influence of the draw bead.

[0017] On the basis of the above technical solution, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile back door, the specific method for the draw bead treatment in the small area in step 4.1 is as follows: Step 4.1.1: In the defect-free areas formed by the primary process type on both the left and right sides, add draw beads for the second time. The adding method is that the height of the draw bead is half of the normal height, the width is 2 times the normal width, and the position is 20 - 30 mm outside the draw bead, which is specifically set according to the product shape.

[0018] Step 4.1.2: In the four-corner areas of the product type, since springback and material dropping problems are likely to occur, force sorting needs to be done. The method is to make diffused melon seeds beads centered on the vertices of the four corners, and the maximum width of the beads is 6 mm.

[0019] On the basis of the above technical solution, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile back door, the specific method for the reverse drawing forming compensation in step 4.2 is as follows: Step 4.2.1: In the springback area inside the product type, perform over-drawing compensation in the product type area according to the springback amount calculated by the primary process digital model. Starting from the starting point of the springback amount calculated by the primary process digital model and ending at the outermost side of the product type, perform over-drawing compensation, and the compensation amount is 1.2 times the springback amount, with uniform transition.

[0020] Step 4.2.2: Starting from 30 mm below the product type, start constructing the reverse drawing process type. The curvature of the reverse drawing process type is 1.5 - 2 times the curvature of the V-shaped profile. The specific transition depth and shape are determined according to the later CAE analysis.

[0021] On the basis of the above technical solution, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile back door, the specific method for the over-drawing forming compensation in step 4.3 is as follows: It is mainly carried out in the L-longitudinal area of the product. Use over-drawing to process the data of the difficult forming areas in this area, and its compensation mode is the same as the compensation method for the springback area inside the product type in the reverse drawing forming compensation; at the same time, in the outer process supplementary area in this direction, a simple wide draw bead mode needs to be established, with a height of 1 / 2 of the normal draw bead and a width of 2.5 times the normal draw bead.

[0022] The process digital model formed by the draw bead treatment in the small area in step 4.1, the reverse drawing forming compensation in step 4.2, and the over-drawing forming compensation in step 4.3 is the secondary process digital model.

[0023] On the basis of the above technical solutions, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile rear door, the main method of comprehensive treatment optimization is to perform CAE analysis on the secondary process digital model, and adjust the process digital model according to the defect conditions of the analysis results. The adjustment method is as follows: in the left-right direction, adjust the forming result by adjusting the length and height of the small-area draw beads; in the L-short direction area, adjust the result by adjusting the reverse drawing depth, width and shape of the reverse drawing forming compensation; in the L-long direction, adjust the process result by adjusting the compensation amount of the over-drawing forming compensation and the height of the external draw beads until the process analysis reaches the state that meets the quality requirements; thereafter, reserve a low process step at the starting position of the reverse drawing forming compensation in the L-short direction. Taking the starting position of the reverse drawing forming compensation as the center, establish an adjustment ridge with a width of 10 mm and a height of 0.3 - 0.5 mm for later craftsmen to debug and trim; then perform comprehensive analysis and calculation to determine the final process forming attributes. When all data are within the qualified range, the final process digital model design is completed.

[0024] On the basis of the above technical solutions, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile rear door, the specific method of progressive drawing strengthening is as follows: taking the vertex of the V shape as the center and the midlines of the middle parts in the L-long direction and L-short direction as the endpoints, perform a strong pressing transition. The strong pressing center in the vertex area uses strong coloring, and gradually transitions to normal coloring in the midline area, so as to ensure that the top of the overall large-curvature shape is in a state of strong pressing force, promote the force dispersion in the external area, and transfer the overall defect area to the outside.

[0025] On the basis of the above technical solutions, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile rear door, the main compensation areas of the trimming secondary compensation are the four corner areas of the product shape and the areas with large springback amounts in the overall drawing. For this area, perform strong pressing shaping in the flanging and shaping process, and perform reverse compensation processing on the process digital model of this area. The compensation amount is a transition from 0.2 - 0.3 mm to 0 mm from the outside to the inside in the four corner areas, with a transition width of 25 - 40 mm, and implement strong pressing; for the areas with large springback amounts in the middle, compensate according to 20% - 30% of the over-drawing compensation of the final process digital model; On the basis of the above technical solutions, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile rear door, the area strengthening adopts the mode of area strong pressing: mainly aiming at the corner areas of each forming part, the stress concentration in the corner areas affected by flanging causes surface product defects. Therefore, perform strong pressing treatment on this area. The strong pressing reserved amount is 0.1 mm, and the strong pressing range transitions 30 - 50 mm from the corner to the surrounding area according to the shape; On the basis of the above technical solutions, as an optimized technical solution for the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile back door, the connection strong pressing mainly aims at the surface quality defects such as surface warping, convexity and concavity, and slip lines caused by subsequent flanging during the forming process of the back door outer panel. Taking the line 4 mm inward along the flanging line of the product shape as the center line, on both sides of the long side L and the short side L, bulges with a height of 0.05 mm are made, and it transitions outward to the flanging line where the height returns to zero, and transitions inward to 5 mm where the height returns to zero. During the subsequent debugging process, the debugging craftsman evenly transitions it into a coherent coloring mode with strong coloring at the midpoint and weak coloring on both sides, so as to correct the adverse effects of surface quality caused by flanging forming and achieve a perfect surface quality effect.

[0026] Compared with the prior art, the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile back door provided by the present technical solution has the following beneficial effects: 1. Through the analysis of the typical characteristics of the special product and the material forming analysis, the present invention innovates the surface drawing and weak rib control mode, and conducts targeted technical solutions for the forming characteristics of different regions, successfully solving the forming problem of the outer panel of the large-curvature automobile back door with few control points. It provides a low-cost and high-efficiency forming solution for the cold stamping forming of lightweight large-curvature parts with few control points without adding other equipment or auxiliary material consumption, provides technical support for the combination of the aesthetics and mechanical properties of automobiles, and promotes the rapid application of lightweight materials and the aesthetic development of automobile styling.

[0027] 2. The comprehensive forming mode of small-area draw bead treatment, reverse drawing forming compensation, and over-drawing forming compensation provides new innovative ideas for the forming of automobile panel dies and provides a new technical solution for solving the forming difficulties of the frame type.

[0028] 3. The regional strengthening and connection strong pressing are remarkable in solving surface quality problems, which can reduce the workload of craftsmen for surface quality improvement by more than 40%, provide a mature and transplantable technical solution for surface quality control, and provide comprehensive assistance for reducing the labor of craftsmen and the product development cost and cycle. Description of the Drawings

[0029] In order to more clearly illustrate the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 It is a flow block diagram of the cold stamping die forming method of the outer panel of the large-curvature aluminum alloy automobile back door. Detailed Embodiments

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the core concept of the present invention and the following embodiments, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0032] These embodiments are provided in this application to make this application thorough and complete, and to fully convey the scope of this application to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, the components of materials, numerical expressions and values described in these embodiments should be construed as merely exemplary, rather than as limitations.

[0033] It should be noted that in the description of this application, unless otherwise specified, the meaning of "several" is greater than or equal to two; the orientation or positional relationships indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", "axial", "radial", etc. are only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of this application. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0034] In addition, the "first", "second" and similar terms used in this application do not denote any order, quantity or importance, but are only used to distinguish different parts. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range. Terms such as "including" or "comprising" mean that the elements before this term cover the elements listed after this term, and do not exclude the possibility of also covering other elements.

[0035] It should also be noted that in the description of this application, unless otherwise clearly specified and limited, the terms "mounted", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations. When it is described that a specific device is located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0036] All terms used in this application have the same meanings as understood by those of ordinary skill in the art to which this application pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries, such as those, should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such herein.

[0037] Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and devices should be regarded as part of the specification.

[0038] This invention patent relates to the field of automotive dies and is an forming method applied to the cold stamping die forming process of the lower section of the outer panel of a large-curvature automotive rear door made of aluminum alloy sheet. It reduces springback, distortion, and forming cracking of automotive parts with large curvatures and few control points, and achieves precise forming.

[0039] To solve the problems raised in the background art, through the analysis of forming difficulties and industry technologies, this invention adopts the method of in-depth analysis of typical features of a single part. Taking the lightweight material aluminum alloy sheet as the research object, through multi-batch forming performance tests of the material, combined with simulation experiments and the collection of batch craftsman experience, and using the mode of continuous innovation through multiple experiments, it has developed a cold stamping die forming technology for the outer panel of a large-curvature automotive rear door made of aluminum alloy. This technology creates a V-shaped forming framework using the typical part features of the outer panel of the rear door, evenly disperses the force application directions and modes, and optimizes the forming space layout. Through the modes of surface drawing and weak rib control, it reduces defects such as distortion, cracking, and scratching of the aluminum alloy sheet. Through the production of draw beads in small areas, reverse drawing forming compensation, and over-drawing forming compensation, it uses the combination control of shape features to solve the problem of uncontrolled springback. Through comprehensive processing and optimization, it makes the springback control smooth and avoids the occurrence of forming warping and distortion. Through progressive drawing strengthening, it deepens the depth control of large-curvature features and ensures forming stability and part strength. Through flanging secondary compensation, it optimizes the springback and distortion problems of the product in the subsequent process. Finally, through regional strengthening and connection strong pressure, it eliminates surface product warping, non-connection, and concavity and convexity problems caused by flanging and forming, thereby achieving high-precision forming of the outer panel of the rear door without improving the manufacturing equipment and process requirements. It enables the design of the automotive rear door to have a perfect smooth streamline and hydrodynamic effect, greatly shortens the die development cycle of large-curvature parts, reduces the application cost, and provides technical support for the application of lightweight materials and cost reduction and quality improvement.

[0040] That is, based on the CAE analysis of typical part features and the integration and innovation of craftsmen's experience, through batch deep experiments on special problems, a V-shaped forming framework is created using product features, and the problems of springback, distortion, and cracking are solved while ensuring product strength by means of multi-compensation of surface drawing and typical features. The forming effect is optimized and solidified by progressive drawing strengthening and trimming secondary compensation, and the surface quality problems are solved by process technology, regional strengthening, and connection strong pressing. Thus, high-precision cold stamping forming of large-curvature and few-control-point back door parts made of lightweight materials is completed using normal production equipment and production rhythm, and low-cost, short-cycle, and high-quality cold stamping forming of the outer panel parts of the back door is achieved. The present invention is applicable to ordinary aluminum plates and 5xxx, 6xxx, 7xxx series aluminum alloys, and the thickness of the test plates used in the present invention is 0.5 - 1.2 mm.

[0041] As Figure 1 shown, the main process of the present invention is as follows: A cold stamping die forming method for the outer panel of a large-curvature automotive back door made of aluminum alloy, 1. Construction of the V-shaped forming framework; the outer panel of the automotive back door is generally L-shaped. To utilize its typical features to construct a dispersion mode of forming force and reduce the forming difficulty, it is necessary to construct an approximately inverted V-shaped stamping direction so as to better utilize the typical features to make the forming force counteract and disperse, and provide guarantee for the forming effect. The specific method is as follows: 1) Taking the overall trend of the product type as a reference, with the vertex of the large curvature as the center and the vertical downward direction as the direction line, make the angles between the main trend direction lines of the two sides of the L-shaped product of the part and the vertical downward direction line equal. At this time, the part placement mode is the standard inverted V mode.

[0042] 2) In the standard inverted V mode, taking every 5 degrees as a unit, rotate the product type upward along the long side of the L-shaped product type until there is no negative angle state when looking at the product type from top to bottom. Take the state at this time and define it as the non-negative angle inverted V mode.

[0043] 3) Rotate the product type upward along the long side of the L-shaped product type until the outermost sides of the two products of the L shape are on the same horizontal plane. The mode at this time is defined as the planar inverted V mode; compare the included angle between the planar inverted V mode and the non-negative angle inverted V mode. If the included angle is less than 15°, then take the non-negative angle inverted V mode as the die stamping normal direction. If it is greater than 15°, then select the midline direction of the two included angles as the reference direction, check whether there is a negative angle on the surface in this direction. If there is no negative angle, then the reference direction is the stamping direction. If there is a negative angle, then rotate the part clockwise and counterclockwise to the non-negative angle state, and take the minimum rotation angle direction of the two rotation modes as the stamping direction.

[0044] 4) With the stamping direction as the frame state, establish the process supplement according to the conventional mode and optimize it. At this time, the product type state is between the appropriate states of being basically evenly distributed on both sides and having a relatively shallow cavity depth. Practical experience shows that this state can provide better force dispersion and compensation space for subsequent forming control and compensation, thereby completing the construction of the V-shaped frame.

[0045] 2. Analysis of forming difficulties: Under the V-shaped frame, conduct conventional process supplementation for the product type, establish the process digital model, and perform CAE batch analysis with different parameters on the process digital model. Set different parameters to find the forming difficulties of the overall process digital model, such as cracking parts, twisting parts, and springback parts, etc., and determine the magnitude and direction range of the springback value. On this basis, establish the regional distinction of the overall forming difficulties and the overall sorting of the forming difficulties, optimize the process for the forming difficulty areas, improve the process digital model of the forming difficulties, find the optimal state, and generate the primary process digital model. Then, distinguish the forming difficulties according to the position of the product type on the vehicle body to form several forming difficulty block areas. (Note: The outer panel of the rear door is generally symmetric left and right on the vehicle body, and the front and rear are in an L-shaped shape. Therefore, it can be divided into the L long direction, the L short direction, and the left and right directions. Generally, the difficult areas in the forming area are symmetric left and right) 3. Surface drawing and weak rib control: This step is mainly to form an open forming environment, thereby eliminating problems such as twisting, cracking, and defect concentration that occur during the forming process. At the same time, for problems such as surface scratches and difficult secondary forming of aluminum alloy materials, perform pre-treatment. The specific methods are as follows: 1) On the basis of the primary process digital model, eliminate the draw beads in the forming difficulty areas of the L long direction and the L short direction (generally, retain the draw beads at both ends and eliminate all the draw beads in the middle), and convert it into an open drawing environment.

[0046] 2) For the left and right directions, adopt the control method of weak ribs. The method is to increase the width of the draw bead to 1 - 3 times the normal draw bead width. The algorithm is to set the normal draw bead width as H, and the length D from the outside of the product type to the inside of the defect area. Then the draw bead width h is: h = 3H - D / 5, h >= H; (If D / 5 is greater than 2, then D / 5 = 2) At the same time, adjust the height of the draw bead to 60% - 80% of the calculation state of the primary process type (the specific value is adjusted according to the later CAE analysis) to reduce the forming influence of the draw bead.

[0047] 4.1 Small-area draw beads: The function of the small-area draw beads is to disperse the force concentration and defect concentration in the forming difficulty areas on the left and right sides, and at the same time, perform dispersion control on the springback areas at the four corners. Its main forms are two parts: 1) Add two draw beads once on both the left and right sides in the defect-free area of the one-time process forming. The adding method is that the height of the draw bead is half of the normal height, the width is twice the normal width, and the position is 20 - 30 mm outside the draw bead, which is specifically set according to the product shape. Thus, the material locking ability of the easy-forming area is increased. Share the flow difficulty problem in the forming difficult area, and compensate for the weak bead treatment of the previous draw beads.

[0048] 2) In the four-corner area of the product shape, since springback and material dropping problems are likely to occur, stress sorting is required. The method is to make diffused melon seeds beads (small-shaped and densely arranged draw beads with a small inner and large outer shape, and the shape of the melon seeds beads is a new technology existing in the industry) centered on the vertices of the four corners, and the maximum width of the beads is 6 mm.

[0049] 4.2 Reverse drawing forming compensation: The area of reverse drawing forming compensation is mainly located in the short L direction of the product shape. This direction has a large curvature, a short area, few control points, and is prone to cracking, springback, or causing problems such as draw eye material dropping and surface warping. Therefore, the shape of this area needs to be key-treated.

[0050] There is generally a large amount of springback in this area. Due to few control points, conventional forming is not easy to compensate, the effect is unstable, and the surface product defects are serious. Therefore, the draw beads in this area are eliminated, and a reverse drawing compensation mode is adopted to let the internal stresses released by the forward and reverse double drawing forming compensate and offset each other, so as to form an accurate surface. The specific method is as follows: 1) In the springback area inside the product shape, perform over-drawing compensation in the product shape area according to the springback amount calculated by the one-time process numerical model. Starting from the starting point of the springback amount calculated by the one-time process numerical model and ending at the outermost side of the product shape, perform over-drawing compensation, and the compensation amount is 1.2 times the springback amount, with a uniform transition.

[0051] 2) Starting from 30 mm below the product shape, start constructing the reverse drawing process shape. The curvature of the reverse drawing process shape is 1.5 - 2 times the curvature of the V-shaped shape. The specific transition depth and shape are determined according to the later CAE analysis.

[0052] 4.3 Over-drawing forming compensation: Over-drawing forming compensation is mainly carried out in the long L direction area of the product. Use over-drawing to process the data of the forming difficult area in this area. Its compensation mode is the same as the compensation method for the springback area inside the product shape of the reverse drawing forming compensation; at the same time, in the outer process supplementary area in this direction, a simple wide draw bead mode needs to be established, with a height of 1 / 2 of the normal draw bead and a width of 2.5 times the normal draw bead.

[0053] After the small-area draw bead treatment, reverse drawing forming compensation, and over-drawing forming compensation, the process numerical model formed is the secondary process numerical model.

[0054] 5. Integrated Process Optimization: The main function of integrated process optimization is to perform multiple CAE analyses and optimizations on the secondary process digital model to form the final process digital model for production use. The main method is to perform CAE analysis on the secondary process digital model and adjust the process digital model according to the defect conditions of the analysis results. The adjustment methods are as follows: In the left-right direction, adjust the forming result by adjusting the length and height of the small-area draw beads; in the short L-direction area, adjust the result by adjusting the reverse drawing depth, width, and shape of the reverse drawing forming compensation; in the long L-direction, adjust the process result by adjusting the compensation amount of the over-drawing forming compensation and the height of the external draw beads until the process analysis reaches a state that meets the quality requirements.

[0055] After that, reserve a low process step at the starting position of the reverse drawing forming compensation in the short L-direction to provide an adjustment point for the craftsman's debugging during the later manufacturing process, and achieve rapid debugging of small-scale defects in the later stage. The method is to establish an adjustment ridge with a width of 10 mm and a height of 0.3 - 0.5 mm centered on the starting position of the reverse drawing forming compensation for the later craftsman's debugging and trimming (this content is the reserved amount for the craftsman, and the process step can be reduced according to the forming defect conditions during the later debugging process to quickly adjust the forming result).

[0056] Then perform comprehensive analysis and calculation to determine the final process forming attributes. When all data are within the qualified range, the design of the final process digital model is completed.

[0057] 6. Progressive Drawing Strengthening: The main function is to perform transitional control on the force during the overall forming process according to the overall V-shaped forming framework to ensure that the upper large-curvature part is fully formed, move the defect area outward, and eliminate the defects by the forming control methods on each side. The specific methods are as follows: Centered on the vertex of the V shape and with the midlines in the middle of the long L-direction and short L-direction as the endpoints, perform strong pressure transition. The strong pressure center in the vertex area uses strong coloring and gradually transitions to normal coloring in the midline area to ensure that the top of the overall large-curvature shape is in a state of strong pressure, promote the dispersion of the force in the external area, and transfer the overall defect area to the outside.

[0058] 7. Flanging Secondary Compensation: The main compensation areas for flanging secondary compensation are the four-corner areas of our product model and the areas with relatively large springback amounts in the overall drawing. For these areas, perform strong pressure flanging during the flanging and shaping process, and perform reverse compensation processing on the process digital model of this area. The compensation amount is a transition from 0.2 - 0.3 mm to 0 mm from the outside to the inside in the four-corner areas, with a transition width of 25 - 40 mm, and implement strong pressure. For the areas with relatively large springback amounts in the middle, compensate according to 20% - 30% of the over-drawing compensation of the final process digital model; In order to correct the springback influence caused by the internal stress after cutting in the flanging process and provide a simplified debugging area for the fitter during the manufacturing process.

[0059] 8. Area strengthening and connection strong pressing: This operation is mainly to improve the surface quality of the product and eliminate various surface defects.

[0060] 1) The area strengthening adopts the mode of area strong pressing: mainly for the corner areas of each formed part. Affected by the flanging, stress concentration occurs in the corner areas, resulting in poor surface quality. Therefore, strong pressing treatment is carried out on this area. The reserved amount of strong pressing is 0.1 mm, and the strong pressing range transitions 30 - 50 mm from the corner to the surrounding according to the shape setting.

[0061] 2) Connection strong pressing: Connection strong pressing mainly aims at the surface defects such as surface warping, convexity and concavity, and slip lines caused by subsequent flanging during the forming process of the outer panel of the rear door. Such problems are affected by the flanging shape. Therefore, strong pressing pretreatment is required. The method is: with a center line 4 mm inward along the flanging line of the product shape, on both sides of the long L side and the short L side, make a bulge with a height of 0.05 mm, transition outward until the height of the flanging line returns to zero, and transition inward until the height of 5 mm returns to zero. During the subsequent debugging process, the debugging craftsman will evenly transition it into a coherent coloring mode with strong coloring at the midpoint and weak coloring on both sides, so as to correct the influence of the surface defects caused by the flanging forming and achieve a perfect surface effect.

[0062] When the overall mold enters the debugging stage, the debugging craftsman will trim and debug the width, height of the draw bead and the transition form outside the draw bead according to the minor defective state of the forming, thereby forming a comprehensive debugging and forming mode of surface forming and draw bead control forming, so as to quickly form high-quality products.

[0063] 9. When all the debugging is completed, high-quality finished products are formed and sold to customers.

[0064] The above content shows and describes the basic principles, main features and the beneficial effects of the present invention. The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cold stamping die forming method for the outer panel of a large-curvature aluminum alloy automobile rear door, characterized in that: It includes the following steps: Step 1: V-shaped forming frame construction; Step 2: Analysis of forming difficulties; Step 3: Surface drawing and weak rib control; Step 4: It includes Step 4.1 Treatment of draw beads in small areas, Step 4.2 Compensation for reverse drawing forming, and Step 4.3 Compensation for over-drawing forming; Step 5: Comprehensive treatment and optimization; Step 6: Progressive drawing strengthening; Step 7: Flanging secondary compensation; Step 8: Area strengthening and connection strong pressing; Step 9: Trimming and debugging.

2. The cold stamping die forming method for the outer panel of the aluminum alloy large-curvature automobile rear door according to claim 1, wherein: The specific method of the said Step 1 is as follows: Step 1.1: Taking the overall trend of the product type as a reference, with the vertex of the large curvature as the center and the vertically downward direction as the direction line, make the angles between the main trend direction lines of the two sides of the L-shaped product of the part and the vertically downward direction line equal. At this time, the part placement mode is the standard inverted V mode; Step 1.2: In the standard inverted V mode, taking every 5° as a unit, rotate the product type upward along the long side of the L shape of the product type until there is no negative angle state when looking at the product type from top to bottom. Take the state at this time and define it as the non-negative angle inverted V mode; Step 1.3: Rotate the product type upward along the long side of the L shape of the product type until the outermost sides of the two products on both sides of the L shape are on the same horizontal plane. The mode at this time is defined as the plane inverted V mode; Compare the included angle between the plane inverted V mode and the non-negative angle inverted V mode. If the included angle is less than 15°, then take the non-negative angle inverted V mode as the die stamping normal direction. If it is greater than 15°, then select the midline direction of the two included angles as the reference direction, and check whether there is a negative angle on the surface in this direction. If there is no negative angle, then the reference direction is the stamping direction. If there is a negative angle, then rotate the part clockwise and counterclockwise until there is no negative angle state, and take the direction of the minimum rotation angle of the two rotation modes as the stamping direction; Step 1.4: Taking the stamping direction as the frame state, establish and optimize the process supplement according to the conventional mode. At this time, the product type state is in a suitable state between basically uniform distribution on both sides and relatively shallow cavity depth. Practical experience shows that this state can provide better force dispersion and compensation space for subsequent forming control and compensation, so as to complete the construction of the V-shaped frame.

3. The cold stamping die forming method for the outer panel of the aluminum alloy large-curvature automobile rear door according to claim 1 or 2, characterized in that: The analysis of forming difficulties in the said Step 2 is to carry out conventional process supplement to the product type under the V-shaped frame, establish a process digital model, and conduct CAE batch analysis with different parameters on the process digital model, set different parameters, so as to find out the forming difficulties of the overall process digital model and generate a primary process digital model; On this basis, establish the regional distinction of the overall forming difficulties and the overall sorting of the forming difficulties, and optimize the process of the forming difficulty area, improve the process digital model of the forming difficulties, find the best state, and generate a primary process digital model.

4. The cold stamping die forming method for the outer panel of the large-curvature aluminum alloy automobile rear door according to claim 3, wherein: The specific method of the said Step 3 is: Step 3.1: On the basis of the primary process digital model, eliminate the draw beads in the forming difficulty areas in the L long direction and L short direction, retain the draw beads at both ends, and eliminate all the draw beads in the middle, and convert it into an open drawing environment; Step 3.2: Adopt a control method with weak ribs in the left - right direction. The method is to increase the draw bead width to 1 - 3 times the normal draw bead width. The algorithm is as follows: Assume the normal draw bead width is H, and the length from the outer side of the product shape to the inside in the defect area is D. Then the draw bead width h is: h = 3H - D / 5, h >= H; (if D / 5 is greater than 2, then D / 5 = 2); At the same time, adjust the draw bead height to 60% - 80% of the first - process type calculation state. The specific value is adjusted according to the later CAE analysis to reduce the forming influence of the draw bead.

5. The cold stamping die forming method for the outer panel of the large-curvature automobile rear door made of aluminum alloy according to claim 1 or 4, characterized in that: The specific method for the small - area draw bead treatment in Step 4.1 is as follows: Step 4.1.1: In the defect - free area of the first - process type forming on both sides in the left - right direction, add secondary draw beads. The addition method is that the draw bead height is half of the normal height, the width is 2 times the normal width, and the position is 20 - 30 mm outside the draw bead, specifically set according to the product shape; Step 4.1.2: In the four - corner areas of the product shape, since springback and material - dropping problems are likely to occur, force combing is required. The method is to make diffused melon - seed ribs centered on the vertices of the four corners, and the maximum width of the ribs is 6 mm.

6. The cold stamping die forming method for the outer panel of an aluminum alloy automotive rear door with large curvature according to claim 5, characterized in that: The specific method for the reverse drawing forming compensation in Step 4.2 is as follows: Step 4.2.1: In the springback area inside the product shape, perform over - drawing compensation in the product - shape area according to the springback amount calculated by the first - process digital model. Starting from the starting point of the springback amount calculated by the first - process digital model and ending at the outermost side of the product shape, perform over - drawing compensation. The compensation amount is 1.2 times the springback amount, and make a uniform transition; Step 4.2.2: Starting from 30 mm below the product shape, start constructing the reverse - drawing process type. The curvature of the reverse - drawing process type is 1.5 - 2 times the curvature of the V - shaped profile. The specific transition depth and shape are determined according to the later CAE analysis.

7. The cold stamping die forming method for the outer panel of the large-curvature aluminum alloy automobile rear door according to claim 6, characterized in that: The specific method for the over - drawing forming compensation in Step 4.3 is as follows: Mainly carried out in the L - length direction area of the product. Use over - drawing to process the data of the forming - difficult areas in this area. Its compensation mode is the same as the compensation method for the springback area inside the product shape in the reverse - drawing forming compensation; at the same time, in the outer - side process - supplementary area in this direction, a simple wide draw - bead mode needs to be established, with a height of 1 / 2 of the normal draw bead and a width of 2.5 times the normal draw bead; The process digital model formed after the small - area draw bead treatment in Step 4.1, the reverse - drawing forming compensation in Step 4.2, and the over - drawing forming compensation in Step 4.3 is the secondary process digital model.

8. The cold stamping die forming method for the outer panel of the aluminum alloy large-curvature automobile back door according to any one of claims 1, 2, 4, 6, and 7, characterized in that: The main method of the comprehensive treatment and optimization is to perform CAE analysis on the secondary process digital model and adjust the process digital model according to the defect conditions of the analysis results. The adjustment method is as follows: In the left - right direction, adjust the forming result by adjusting the length and height of the small - area draw beads; in the L - short direction area, adjust the result by adjusting the reverse - drawing depth, width, and shape of the reverse - drawing forming compensation; in the L - long direction, adjust the process result by adjusting the compensation amount of the over - drawing forming compensation and the height of the outer draw beads until the process analysis reaches a state that meets the quality requirements; After that, a short process step is reserved at the starting position of the reverse drawing compensation in the L short direction. With the starting position of the reverse drawing compensation as the center, an adjustment step with a width of 10mm and a height of 0.3-0.5mm is established for later debugging and trimming by craftsmen. Then a comprehensive analysis and calculation is carried out to determine the final process molding properties. When all data are within the qualified range, the final process digital design is completed.

9. The cold stamping die forming method for the outer panel of the large-curvature aluminum alloy automobile rear door according to claim 8, characterized in that: The specific method of the progressive drawing strengthening is: with the apex of the V-shape as the center and the middle midline of the L long direction and L short direction as the end point, a strong pressure transition is performed, the center of the apex area is strongly pressed, strong coloring is used, and the transition to normal coloring is gradually made to the midline area, so as to ensure that the top of the overall large curvature shape is in a state of stress and strong pressure, promote the dispersion of force in the external area, and transfer the overall defect area to the outside.

10. The cold stamping die forming method for the outer panel of the large-curvature automobile back door made of aluminum alloy according to claim 9, characterized in that: The main compensation areas of the flanging secondary compensation are the four corners of the product and the area with large springback due to overall drawing. In the flanging forming process, strong pressure forming is performed on these areas, and reverse compensation is performed on the process number of these areas. The compensation amount is a transition from 0.2-0.3mm to 0mm from outside to inside in the four corners, with a transition width of 25-40mm, and strong pressure is applied. For the area with large springback in the middle, compensation is performed according to 20% to 30% of the over-drawing compensation of the final process number. The regional strengthening adopts the regional strong pressure mode: it is mainly aimed at the corner area of each molding. The stress concentration in the corner area is affected by the flanging, resulting in poor surface quality. Therefore, the area is subjected to strong pressure treatment. The strong pressure reserve is 0.1mm, and the strong pressure range is 30-50mm from the corner as the center to the periphery, which is set according to the shape. The connection strong pressure is mainly aimed at the surface defects such as warping, convexity and concaveness, and slip lines caused by the subsequent flanging during the forming process of the back door outer panel. Along the flanging line of the product type, 4mm inward is used as the center line. On both sides of the L long item and the L short item, a ridge with a height of 0.05mm is made. The height transitions outward to zero at the flanging line, and transitions inward to zero at 5mm. In the subsequent debugging process, the debugging craftsmen evenly transition it to a continuous coloring mode with strong coloring at the midpoint and weak coloring on both sides, so as to correct the adverse effects of the flanging molding on the surface and achieve a perfect surface effect.

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