Drawing forming process of complex profile part

Abstract

The invention relates to a drawing forming process for a complex profile part, and belongs to the technical field of drawing forming, the drawing forming process comprises the steps that S1, intelligent partitioning is conducted, specifically, the part is at least divided into two regions, one region is a first deformation region, and the other region is a second deformation region; s2, drawing for the first time, drawing the first deformation area by taking the outer contour of the first deformation area as a blank holder to form a high deformation area, forming a low deformation area corresponding to the second deformation area, and enabling the material to flow from the low deformation area to the high deformation area; and S3, secondary drawing is conducted, specifically, the outer contour of the part face serves as a blank holder to conduct drawing on the low-deformation area, and wrinkles are avoided. According to the method, cracking of the high-deformation area is restrained through high-speed drawing, wrinkles of the low-deformation area are reduced through low-speed drawing, precise regulation and control over material flowing are achieved, the process requirements of the high-deformation area and the low-deformation area in the complex part face can be met, and the product quality is improved. And cracks or wrinkles of molded surfaces of parts are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of drawing forming, and in particular relates to a drawing forming process for parts with complex profiles. Background Art

[0002] As vehicles become increasingly lightweight and styling becomes more complex, hood hinge reinforcement panels and other covering components are becoming increasingly demanding, with deep interiors and complex surface curvatures. These components must meet not only structural strength requirements but also aesthetically pleasing appearance.

[0003] In traditional stamping processes, such parts are usually formed using a one-step stretching solution. However, due to the complexity of the product surface, the flow resistance of the material in the deep cavity area increases significantly, leading to the following technical bottlenecks: The amount of deformation in a single stretch is limited by the elongation of the material. When the deformation exceeds the plastic limit of the material, macro cracks or micro cracks are likely to occur in the fillet transition area or at the sudden change of the mold surface, which directly affects the fatigue life and safety of the part. To avoid cracking, traditional processes require reducing the blank holder force or optimizing the layout of the drawing ribs, but this will cause uncontrolled material flow and form wrinkles in the concave area of ​​the mold surface, significantly reducing the appearance quality of the part. Existing technologies attempt to improve formability by optimizing mold surfaces, adjusting lubrication conditions, or using variable-strength plates, but these methods can only partially alleviate the defects and cannot fundamentally break the contradiction between material elongation and complex surfaces.

[0004] Therefore, a new drawing process is urgently needed to achieve high-quality forming of complex surface parts. Summary of the Invention

[0005] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a drawing forming process for parts with complex profiles, which solves the problem that the existing parts with complex profiles are usually drawn in one time, resulting in the deep drawing ribs of the parts being prone to cracking or the shallow drawing ribs being prone to wrinkling.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A drawing forming process for complex surface parts includes the following contents: S1: Intelligent partitioning, dividing the part into at least two areas, one is the first deformation area and the other is the second deformation area; S2: First drawing, using the outer contour of the first deformation zone as a blank holder to draw the first deformation zone to form a high deformation zone, and forming a low deformation zone corresponding to the second deformation zone, and the material fluidity flows from the low deformation zone to the high deformation zone; S3: The second drawing is to use the outer contour of the part surface as the blank holder to draw the low deformation area to avoid wrinkles.

[0007] Preferably, the method for implementing the intelligent partitioning includes the following steps: S101: obtaining an equivalent plastic strain cloud diagram during the drawing process of the part through finite element simulation, taking a strain gradient greater than X% as a threshold, defining the area where the strain gradient is higher than the threshold as the first deformation zone, and the remaining area as the second deformation zone; S102: performing topological optimization on the part based on the part's service condition, extracting the optimized stress concentration factor distribution, and including the area with a stress concentration factor greater than Y into the first deformation zone; Among them, the value range of X is 10%-20%, and the value range of Y is 1.5-2.0.

[0008] Preferably, the entrance fillet of the high deformation zone adopts a gradual fillet structure, and the fillet radius R changes continuously along the drawing depth direction and satisfies the following relationship: R min is the minimum fillet radius, ranging from 3t to 5t; R max is the maximum fillet radius, ranging from 8t to 12t, and R max ≥2R min , t is the sheet thickness; z is the depth from the current point to the bottom of the drawing, H is the total drawing depth; k is the gradient index.

[0009] Preferably, the value of k is associated with the judgment criterion of the first deformation zone: when X>15% and Y>1.8, k=1.2-1.5; when X≤15% or Y≤1.8, k=0.8-1.2.

[0010] Preferably, the surface roughness of the gradually rounded corner structure is Ra≤0.8 μm, and the contact surface with the part is coated with a graphene-based lubricating layer.

[0011] Preferably, during the first drawing, the mold gap corresponding to the high deformation zone is set to 0.95-0.98t, and the gap in the low deformation zone is set to 1.02-1.05t, where t is the thickness of the part.

[0012] Preferably, during the second drawing, the die gap in the low deformation zone is 1.05-1.10t, where t is the thickness of the part.

[0013] Preferably, the blank holder is embedded with a shape memory alloy, and the contour of the shape memory alloy is actively deformed according to the strain distribution measured after the first drawing. Before the second drawing, the actual contour data of the low deformation area is obtained by laser scanning. The blank holder produces a shape memory effect under current excitation and clamps the low deformation area.

[0014] Preferably, the working surface of the blank holder is processed into annular grooves of alternating depths and shallownesses, and the grooves are filled with a silicone rubber damping layer, the silicone rubber hardness in the shallow groove area is Shore 70±5, and in the deep groove area is Shore 40±3.

[0015] The beneficial effects of the present invention are: This application breaks through the limitation of traditional single blank holding force through the staged blank holding strategy of "vertical high pressure in high deformation zone + inclined low pressure in low deformation zone", suppresses cracking in high deformation zone through high-speed drawing, and reduces wrinkling in low deformation zone through low-speed drawing, thereby realizing precise control of material flow, meeting the process requirements of high deformation zone and low deformation zone in complex part surface, reducing cracking or wrinkling of part surface, and improving the forming quality of complex surface parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0017] Figure 1 A flow chart of the drawing process for complex profile parts provided in one embodiment of the present invention; DETAILED DESCRIPTION

[0018] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0019] The traditional drawing process for complex surface parts usually adopts a single overall drawing mode, usually with the overall outer contour of the part as the blank holder, and one-time forming is performed through a single blank holder force (usually in the vertical direction) and a fixed drawing speed; complex surfaces have high and low deformation areas such as curved surface transition areas and flat areas. Single drawing causes the material to easily accumulate and wrinkle when flowing from the low deformation area to the high deformation area, or excessive stretching causes cracking in the high deformation area, resulting in geometric mutation areas in complex surface parts such as engine hood hinge assemblies. Traditional single drawing cannot simultaneously meet the process requirements of high and low deformation areas. like Figure 1 As shown in FIG, a drawing forming process for complex surface parts includes the following: S1: Intelligent partitioning, dividing the part into at least two areas, one is the first deformation area and the other is the second deformation area; S2: In the first drawing, the outer contour of the first deformation zone is used as the blank holder to isolate the material flow interference in the low deformation zone. The vertical pressure P1 is 1.2 to 1.5 times the traditional blank holder force, which promotes the rapid filling of the material into the high deformation zone to avoid cracking. High-speed drawing, with a speed of 1.5 times that of the traditional process, can reduce the frictional heat generated between the material and the mold, and inhibit the deterioration of the structure caused by local overheating, cracking or dark cracking. S3: The second drawing is carried out with the overall outer contour of the part as the blank holder. The low deformation area is subjected to low-speed drawing. Pressure is applied at an angle of 5° to 15° to the part contour. The tangential component of force is used to guide the material to flow along the mold surface, reducing the tendency to wrinkle. In summary, this application proposes a staged blank holding strategy of "vertical high pressure in high deformation zone + inclined low pressure in low deformation zone", breaking through the limitation of traditional single blank holding force, suppressing cracking in high deformation zone through high-speed drawing, and reducing wrinkles in low deformation zone through low-speed drawing, thereby realizing precise control of material flow, meeting the process requirements of high deformation zone and low deformation zone in complex part surface, reducing cracking or wrinkling of part surface, and improving the forming quality of complex surface parts.

[0020] When traditional complex surface parts need to be drawn multiple times, the middle area is usually used as the first drawing, and the parts are gradually drawn outward from the middle area. This division method does not distinguish based on the flow characteristics of the material, which leads to the fact that in subsequent drawing, the drawing process required by the high deformation area and the low deformation area cannot be performed. In the drawing process, the material utilization rate is not sufficient, and some areas are over-stretched while some areas are not stretched.

[0021] In one embodiment, the method for implementing intelligent partitioning includes the following steps: S101: Build a geometric model of the part and define process parameters such as material properties (such as anisotropy coefficient and hardening curve), friction coefficient, and drawbead resistance. Use a dynamic explicit algorithm to simulate the drawing process and obtain the forming limit diagram and EPS cloud diagram. The determination of X% requires combining the material forming limit (FLD0 value) and the part safety margin. For example, if the material FLD0 = 20%, X can be set to 15% to 18% to ensure that the first deformation zone is within the safe deformation range. S102: Define load conditions (such as tensile force and residual stress), use the variable density method (SIMP) or level set method for optimization, generate a material distribution cloud map, perform static analysis on the optimized structure, and calculate the stress at each node; The value range of X is 10%-20%. The safe deformation threshold of the first deformation zone needs to be less than the material's FLD0 value to avoid cracking. For high-strength steel (such as DP780, FLD0≈12%), X may be 8%-10%. For aluminum alloys (such as AA5754, FLD0≈25%), X can be relaxed to 18%-20%. The value range of Y is 1.5-2.0. High-fluidity materials (such as aluminum alloys) require a larger Y value (such as 1.8-2.0) to limit local excessive flow, while low-fluidity materials (such as high-strength steel) can take Y=1.5-1.7 to avoid cracking due to excessive resistance. The intelligent zoning technology of this embodiment controls the safety boundary of the initial deformation zone through the X value and adjusts the material flow resistance through the Y value, thereby achieving efficient and high-quality forming of complex surface parts.

[0022] After the high deformation zone and the low deformation zone are distinguished by intelligent zoning, the high deformation zone is designed to allow the material to flow fully from the low deformation zone to the high deformation zone, but it will not cause material accumulation in the high deformation zone.

[0023] In one embodiment, the entrance fillet of the high deformation zone adopts a gradual fillet structure, and the fillet radius R changes continuously along the drawing depth direction and satisfies the following relationship: R min is the minimum fillet radius, ranging from 3t to 5t; R max is the maximum fillet radius, ranging from 8t to 12t, and R max ≥2R min , t is the sheet thickness; z is the depth from the current point to the bottom of the drawing, H is the total drawing depth; k is the gradient index; the K value is different for different materials Initial stage <0.3, R≈R min , by increasing the bending resistance through small rounded corners, the material flow rate is limited to 0.8-1.2m / s to avoid initial impact; Transition stage 0.3≤ ≤0.7, R increases exponentially, matching the material hardening effect, reducing the flow resistance gradient and maintaining a stable flow rate; Final forming stage >0.7, R→R max , rounded corners reduce friction coefficient by 30%-40%, release residual stress and inhibit springback; The gradual rounded corner structure is used to form a resistance decreasing field in the depth direction, guiding the material to be replenished from the low deformation area. In the initial stage: through R min Constructing a high-pressure area to force the material to flow preferentially to the high-deformation area; in the later stage: R max Creates a low-pressure buffer zone to avoid overstretching of the formed area.

[0024] In the drawing forming of complex surface parts, the material flow balance between high and low deformation zones is the core problem of the process. The traditional fixed fillet structure cannot simultaneously meet the flow suppression in the initial stage and the stress release requirements in the final forming stage. Through intelligent zoning combined with gradient fillets, a dynamic resistance field is constructed, and the gradient index k value is scientifically selected based on the material constitutive parameters and deformation characteristics to achieve precise control of material flow.

[0025] In one embodiment, the value of k is associated with the judgment criteria of the first deformation zone: when X>15% and Y>1.8, k=1.2-1.5; when X≤15% or Y≤1.8, k=0.8-1.2. When high-hardness steel is drawn, the material characteristics show high strain concentration behavior. At this time, the K value is selected between 1.2-1.5, which can delay the stress concentration after the high deformation zone to affect the drawing of the low deformation zone. By strictly selecting the K value, sufficient material flow is guaranteed during the drawing process; and when the material is aluminum alloy, the material behavior characteristics show medium and low strain and uniform strain. At this time, the K value is selected between 0.8-1.2, which accelerates the rounded corner transition and compensates for the problem of slow flow of low-plasticity materials.

[0026] In one embodiment, the surface roughness of the gradually rounded corner structure is Ra≤0.8 μm, and the contact surface with the component is coated with a graphene-based lubricating layer.

[0027] In one embodiment, during the first drawing, the mold gap corresponding to the high deformation zone is set to 0.95-0.98t, and excessive thinning of the material is suppressed by slight extrusion. Combined with the strain gradient control of intelligent zoning, the gap in the low deformation zone is set to 1.02-1.05t, where t is the thickness of the part. Space for material flow is reserved to reserve a margin for the secondary drawing, thereby avoiding hidden wrinkles caused by premature constraint during the first drawing.

[0028] In the secondary drawing process of complex-surface parts, the low deformation zone needs to achieve two core goals: eliminating the rebound distortion caused by the work-hardened layer formed in the first drawing, and controlling the local material flow through gap compensation to avoid instability and wrinkling caused by sudden changes in the blank holder force; along the drawing depth direction, the gap at the entrance is 1.05t, and gradually increases to 1.10t at the exit, forming a trumpet-shaped flow channel.

[0029] After the first drawing, a work-hardened layer appears in the low deformation area, resulting in springback distortion. Gap compensation and flow control are required to eliminate springback and suppress wrinkles.

[0030] In one embodiment, during the second drawing, the die clearance in the low deformation zone is 1.05-1.10t, where t is the part thickness. A small inlet clearance constrains the initial material flow direction and eliminates springback distortion in the work-hardened layer. A large outlet clearance reduces frictional resistance, releases material buildup stress at the end of the second drawing, and prevents instability and wrinkling. A trumpet-shaped flow channel is formed between the die clearances in the first and second deformation zones, guiding material flow axially and suppressing wrinkle initiation caused by circumferential compression.

[0031] In one embodiment, the blank holder is embedded with a shape memory alloy. Shape memory alloys, such as NiTi alloy, have a unique shape memory effect and superelasticity. At a specific temperature, current excitation can trigger its martensitic phase transformation, causing the alloy to recover or deform into a predetermined shape. Before the second drawing, the actual contour data of the low deformation zone is obtained by laser scanning. The contour data is input into the control system of the blank holder. The control system calculates the required deformation of the blank holder based on the measured contour and excites the SMA wire through current to cause it to contract or stretch, driving the blank holder to produce a shape memory effect and accurately matching the geometric characteristics of the low deformation zone. The blank holder is divided into multiple independent control areas. The SMA wire in each area can be excited separately to achieve zoned control of the blank holder force. In the wrinkle-prone area of ​​the low deformation zone, the blank holder force in this area is increased by increasing the excitation current of the SMA wire, thereby suppressing the wrinkling tendency of the material. In summary, the blank holder technology embedded with shape memory alloy can effectively suppress the wrinkling tendency of the material in the low deformation area through the active deformation and partitioned pressure of the blank holder.

[0032] In one embodiment, the working surface of the blank holder is machined with annular grooves of alternating depths and shallownesses. The high-hardness silicone rubber in the shallow groove area provides a larger static friction coefficient, forming a high friction resistance area. This area restricts the lateral flow of the material, forcing the material to extend along the predetermined main flow direction, thereby reducing disordered shear deformation. Deep groove area: Low-hardness silicone rubber produces controllable deformation under pressure, forming a low-friction resistance channel, guiding the material to flow directional along the deep groove path and avoiding local accumulation; the viscoelastic properties of silicone rubber can absorb the vibration energy generated during the drawing process.

[0033] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A drawing process for complex surface parts, characterized in that: Includes the following: S1: Intelligent partitioning, dividing the part into at least two areas, one is the first deformation area and the other is the second deformation area; S2: First drawing, using the outer contour of the first deformation zone as a blank holder to draw the first deformation zone to form a high deformation zone, and forming a low deformation zone corresponding to the second deformation zone, and the material fluidity flows from the low deformation zone to the high deformation zone; S3: The second drawing is to use the outer contour of the part surface as the blank holder to draw the low deformation area to avoid wrinkles.

2. The drawing forming process of a complex profile part according to claim 1, characterized in that: The method for implementing the intelligent partitioning comprises the following steps: S101: obtaining an equivalent plastic strain cloud diagram during the drawing process of the part through finite element simulation, taking a strain gradient greater than X% as a threshold, defining the area where the strain gradient is higher than the threshold as the first deformation zone, and the remaining area as the second deformation zone; S102: performing topological optimization on the part based on the part's service condition, extracting the optimized stress concentration factor distribution, and including the area with a stress concentration factor greater than Y into the first deformation zone; Among them, the value range of X is 10%-20%, and the value range of Y is 1.5-2.

0.

3. The drawing forming process of a complex surface part according to claim 2, characterized in that: The entrance fillet of the high deformation zone adopts a gradual fillet structure, and the fillet radius R changes continuously along the drawing depth direction and satisfies the following relationship: R min is the minimum fillet radius, ranging from 3t to 5t; R max is the maximum fillet radius, ranging from 8t to 12t, and R max ≥2R min , t is the sheet thickness; z is the depth from the current point to the bottom of the drawing, H is the total drawing depth; k is the gradient index.

4. The drawing process for complex profile parts according to claim 3, characterized in that: The value of k is associated with the judgment criteria of the first deformation zone: when X>15% and Y>1.8, k=1.2-1.5; when X≤15% or Y≤1.8, k=0.8-1.

2.

5. The drawing process for complex surface parts according to claim 3, characterized in that: The surface roughness of the gradient fillet structure is Ra≤0.8μm, and the contact surface with the parts is coated with a graphene-based lubricating layer.

6. The drawing process for complex profile parts according to claim 1, characterized in that: During the first drawing, the mold gap corresponding to the high deformation zone is set to 0.95-0.98t, and the gap in the low deformation zone is set to 1.02-1.05t, where t is the part thickness.

7. The drawing process for complex surface parts according to claim 4, characterized in that: During the second drawing, the die gap in the low deformation zone is 1.05-1.10t, where t is the thickness of the part.

8. The drawing process for complex profile parts according to claim 1, characterized in that: The blank holder is embedded with a shape memory alloy, and the contour of the shape memory alloy is actively deformed according to the strain distribution measured after the first drawing. Before the second drawing, the actual contour data of the low deformation area is obtained by laser scanning. The blank holder produces a shape memory effect under current excitation and clamps the low deformation area.

9. The drawing process for complex profile parts according to claim 7, characterized in that: The working surface of the blank holder is processed into annular grooves with alternating depths and shallownesses, and the grooves are filled with a silicone rubber damping layer. The hardness of the silicone rubber in the shallow groove area is Shore 70±5, and that in the deep groove area is Shore 40±3.

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