A drawing process for a complex profile part

Abstract

The application relates to a drawing forming process of a complex profile part, and belongs to the technical field of drawing forming, S1: intelligent partitioning, at least two regions are divided for the part, one is a first deformation region, and the other is a second deformation region; S2: first drawing, the outer contour of the first deformation region is taken as a blank holder ring to draw the first deformation region to form a high deformation region, a low deformation region is formed for the second deformation region, and the material flowability flows from the low deformation region to the high deformation region; S3: second drawing, the outer contour of the part surface is taken as a blank holder ring to draw the low deformation region, and wrinkles are avoided, the application inhibits cracking of the high deformation region through high-speed drawing, wrinkles of the low deformation region are reduced through low-speed drawing, precise regulation and control of material flow are realized, the process requirements of the high deformation region and the low deformation region in the complex part surface can be met, and cracking or wrinkles of the part surface are reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of drawing forming, and particularly relates to a drawing forming process for a complex profile part. BACKGROUND

[0002] With the development of automobile lightweighting and complex modeling, engine hood hinge reinforcement plate assemblies and other coverings gradually exhibit the characteristics of deep inner cavity and complex profile curvature. Such parts not only need to meet the structural strength requirements, but also need to meet the requirements of appearance aesthetics.

[0003] In the traditional stamping process, such parts usually adopt a one-time drawing forming scheme. However, due to the complexity of the product profile, the flow resistance of the material in the deep cavity area increases significantly, resulting in the following technical bottlenecks:

[0004] The one-time drawing deformation amount is limited by the material elongation rate. When the deformation amount exceeds the material plastic limit, macroscopic cracking or microscopic dark cracking is easily generated at the corner transition zone or profile mutation, directly affecting the fatigue life and safety of the part. To avoid cracking, the traditional process needs to reduce the blank holder force or optimize the layout of the drawing bead, but this will lead to material flow out of control, forming wrinkles in the profile recessed area, significantly reducing the appearance quality of the part.

[0005] The prior art attempts to improve the formability by optimizing the die profile, adjusting the lubrication conditions, or using variable strength sheet materials, but these methods can only partially alleviate the defects and cannot fundamentally break through the contradiction between material elongation rate and complex profile.

[0006] Therefore, there is an urgent need for a new drawing forming process to achieve high-quality forming of complex profile parts. SUMMARY

[0007] To solve the above problems in the prior art, the present application provides a drawing forming process for a complex profile part, which solves the problem that the existing complex profile part is usually one-time drawing forming, which causes the deep drawing bead to easily crack or the shallow drawing bead to easily wrinkle.

[0008] The purpose of the present application can be achieved by the following technical solutions:

[0009] A drawing forming process for a complex profile part, comprising the following contents:

[0010] S1: Intelligent partitioning, dividing the part into at least two regions, one being a first deformation zone and the other being a second deformation zone;

[0011] S2: First drawing, drawing the first deformation zone with the outer contour of the first deformation zone as the blank holder to form a high deformation zone, and the second deformation zone to form a low deformation zone, with the material flowability flowing from the low deformation zone to the high deformation zone;

[0012] S3: Second drawing, drawing the low deformation zone with the outer contour of the part surface as the blank holder, to avoid wrinkles.

[0013] Preferably, the implementation method of the intelligent partitioning comprises the following steps:

[0014] S101: Obtain the equivalent plastic strain cloud map in the drawing forming process of the part through finite element simulation, take the strain gradient greater than X% as the threshold, and define the area with a strain gradient higher than the threshold as the first deformation zone, and the remaining area as the second deformation zone;

[0015] S102: Topology optimization of the part based on the service condition of the part, extract the stress concentration coefficient distribution after optimization, and include the area with a stress concentration coefficient greater than Y in the first deformation zone;

[0016] Wherein, the value range of X is 10%-20%, and the value range of Y is 1.5-2.0.

[0017] Preferably, the entrance fillet of the high deformation zone adopts a gradual fillet structure, the fillet radius R changes continuously along the drawing depth direction, and satisfies the following relationship:

[0018]

[0019] R min is the minimum fillet radius, the value range is 3t-5t; R max is the maximum fillet radius, the value range is 8t-12t, and R max ≥2R min , t is the sheet thickness; z is the depth of the current point from the drawing bottom, H is the total drawing depth; k is the gradual change index.

[0020] Preferably, the value of k is related to the determination standard 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.

[0021] Preferably, the surface roughness Ra of the gradual fillet structure is ≤0.8μm, and the contact surface with the part is coated with a graphene-based lubricating layer.

[0022] Preferably, during the first drawing, the high deformation zone corresponds to a die gap of 0.95-0.98t, and the low deformation zone gap is set to 1.02-1.05t, t is the thickness of the part.

[0023] Preferably, during the second drawing, the low deformation zone die gap is 1.05-1.10t, t is the thickness of the part.

[0024] Preferably, the blank holder is embedded with a shape memory alloy, the profile of the shape memory alloy is actively deformed according to the measured strain distribution after the first drawing, and the actual profile data of the low deformation area is obtained by laser scanning before the second drawing. The blank holder is excited by current to generate shape memory effect and press the low deformation area.

[0025] Preferably, the working surface of the blank holder is processed with annular grooves with different depths, and the grooves are filled with a silicon rubber damping layer. The hardness of the silicon rubber in the shallow groove area is Shore 70±5, and the hardness of the silicon rubber in the deep groove area is Shore 40±3.

[0026] The beneficial effects of the present application are:

[0027] The present application adopts a staged blanking strategy of "high vertical pressure in high deformation area + low inclined pressure in low deformation area", breaks through the limitation of traditional single blanking force, suppresses cracking in high deformation area through high-speed drawing, reduces wrinkles in low deformation area through low-speed drawing, realizes precise control of material flow, meets the process requirements of high deformation area and low deformation area in complex part surface, reduces cracking or wrinkling of part surface, and improves the forming quality of complex part surface. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to facilitate the understanding of those skilled in the art, the present application will be further described below with reference to the accompanying drawings.

[0029] Figure 1 A complex part surface drawing forming process flowchart provided in an embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0030] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the specific embodiments, structures, features and effects according to the present application are described in detail below with reference to the accompanying drawings and preferred embodiments.

[0031] The traditional complex part surface drawing forming process usually adopts a single whole drawing mode, which usually takes the whole outer contour of the part as the blank holder, and performs one-time forming through a single blanking force (usually in the vertical direction) and a fixed drawing speed. The complex part surface has high and low deformation areas such as curved surface transition area and flat area. Single drawing leads to easy accumulation and wrinkling when the material flows from the low deformation area to the high deformation area, or causes excessive stretching and cracking in the high deformation area, resulting in geometric mutation area in the complex part surface such as engine cover hinge assembly. The traditional single drawing cannot meet the process requirements of high and low deformation areas at the same time.

[0032] As shown in the figure, a drawing forming process for a complex part surface includes the following contents: Figure 1

[0033] ​S1: Intelligent partitioning, dividing the part into at least two regions, one as the first deformation region and the other as the second deformation region;

[0034] S2: First drawing, taking the outer contour of the first deformation region as the blank holder, isolating the material flow interference of the low deformation region, applying a vertical pressure P1 of 1.2~1.5 times the traditional blank holding force, promoting the material to quickly fill the high deformation region, and avoiding cracking; high-speed drawing, the speed is 1.5 times of the traditional process, which can reduce the frictional heat between the material and the mold, and inhibit the organization deterioration and cracking caused by local overheating;

[0035] S3: Second drawing, taking the overall outer contour of the part as the blank holder, low-speed drawing for the low deformation region, applying a pressure with a 5°~15° inclination angle to the part contour, guiding the material to flow along the profile by using the tangential component force, and reducing the tendency of wrinkles;

[0036] In summary, the present application proposes a "high deformation region vertical high pressure + low deformation region inclined low pressure" staged blank holding strategy, which breaks through the limitation of traditional single blank holding force, inhibits cracking in the high deformation region by high-speed drawing, reduces wrinkles in the low deformation region by low-speed drawing, realizes precise control of material flow, and can meet the process requirements of complex part surface high deformation region and low deformation region, reduce the cracking or wrinkles of the part surface, and improve the forming quality of complex surface parts.

[0037] When the traditional complex surface part needs multiple drawings, it is usually drawn from the middle region to the outside, which does not distinguish the material flow characteristics, and thus cannot be drawn according to the drawing process required by the high deformation region and the low deformation region, and the material utilization rate is not sufficient during the drawing process, and there are some areas that are stretched and some areas that are not stretched.

[0038] In an embodiment, the implementation method of intelligent partitioning includes the following steps:

[0039] S101: Establish a geometric model of the part, define material properties (such as anisotropy coefficient, hardening curve), friction coefficient, drawing rib resistance, etc. Process parameters; obtain the forming limit diagram and EPS cloud diagram by dynamic explicit algorithm simulation of the drawing process; the determination of X% needs to combine the material forming limit (FLD0 value) and the part safety margin, for example, if the material FLD0=20%, X=15%~18% can be taken, to ensure that the first deformation region is within the safe deformation range;

[0040] S102: Define the load case (such as drawing force, residual stress), use variable density method (SIMP) or level set method for optimization, generate material distribution cloud diagram, and perform statics analysis on the optimized structure to calculate the stress of each node;

[0041] Wherein, the value range of X is 10%-20%, the safety deformation threshold of the first deformation zone needs to be less than the FLD0 value of the material to avoid rupture, for high-strength steel (such as DP780, FLD0≈12%), X can be 8%-10%; for aluminum alloy (such as AA5754, FLD0≈25%), X can be widened to 18%-20%; the value range of Y is 1.5-2.0; high-fluidity materials (such as aluminum alloy) need a larger Y value (such as 1.8-2.0) to limit local excessive flow, and low-fluidity materials (such as high-strength steel) can take Y=1.5-1.7 to avoid cracking due to excessive resistance;

[0042] The intelligent partitioning technology of the embodiment controls the initial deformation zone safety boundary through the value of X and adjusts the material flow resistance through the value of Y, so as to realize efficient and high-quality forming of complex-shaped parts.

[0043] After the high deformation zone and the low deformation zone are distinguished by the intelligent partitioning method, the material flow in the high deformation zone can be fully flowed from the low deformation zone to the high deformation zone, and the material accumulation phenomenon in the high deformation zone can be avoided.

[0044] In an embodiment, the entrance fillet of the high deformation zone adopts a gradual fillet structure, the fillet radius R continuously changes along the drawing depth direction, and satisfies the following relationship:

[0045]

[0046] R min is the minimum fillet radius, the value range is 3t-5t; R max is the maximum fillet radius, the value range is 8t-12t, and R max ≥2R min , t is the sheet thickness; z is the depth of the current point from the drawing bottom, H is the total drawing depth; k is the gradual change index; when corresponding to different materials, the value of K is also different

[0047] Initial stage <0.3, R≈R min , the bending resistance is increased by the small fillet, the material flow rate is limited to 0.8-1.2 m / s, and the initial impact is avoided;

[0048] Transition stage 0.3≤ ≤0.7, R increases according to the exponential law, matches the material hardening effect, makes the flow resistance gradient decrease, and maintains the flow rate stable;

[0049] Final forming stage >0.7, R→R max , the fillet reduces the friction coefficient by 30%-40%, releases the residual stress, and suppresses the springback;

[0050] The gradual round corner structure forms a resistance decreasing field in the depth direction, guiding the material to supplement from the low deformation area. In the initial stage: through R min a high-pressure area is constructed to force the material to flow preferentially to the high deformation area; in the later stage: R max a low-pressure buffer area is formed to avoid excessive stretching of the formed area.

[0051] In the drawing forming of complex profile parts, the material flow balance of high and low deformation areas is a key process problem. The traditional fixed round corner structure cannot simultaneously meet the flow inhibition in the initial stage and the stress release requirement in the final forming stage. Through intelligent partitioning combined with gradual round corner, a dynamic resistance field is constructed, and the gradual change index k value is scientifically selected based on material constitutive parameters and deformation characteristics to realize precise control of material flow.

[0052] In an embodiment, the value of k is associated with the determination standard of the first deformation area: 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, so the K value is selected between 1.2-1.5 to delay the influence of high deformation area on the drawing of low deformation area. By strictly selecting the value of K, the material flow during drawing is ensured; when the material is aluminum alloy, the material behavior characteristics show low strain and uniform strain, so the K value is selected between 0.8-1.2 to accelerate the transition of the accelerated round corner, thereby compensating for the slow flow of low plasticity materials.

[0053] In an embodiment, the surface roughness Ra of the gradual round corner structure is ≤0.8μm, and the contact surface with the part is coated with a graphene-based lubricating layer.

[0054] In an embodiment, during the first drawing, the gap between the molds corresponding to the high deformation area is set to 0.95-0.98t, which slightly suppresses the excessive thinning of the material. Combined with the strain gradient control of intelligent partitioning, the gap in the low deformation area is set to 1.02-1.05t, t is the thickness of the part, which reserves the material flow space and reserves the allowance for the second drawing, avoiding the early constraint of the first drawing leading to hidden wrinkles.

[0055] In the second drawing process of complex profile parts, the low deformation area needs to achieve two major goals: eliminating the springback distortion caused by the work hardening layer formed in the first drawing, controlling the local material flow through gap compensation to avoid instability wrinkling caused by sudden change of the blank holder force; along the drawing depth direction, the gap at the inlet is 1.05t, and the gap at the outlet gradually increases to 1.10t, forming a horn-shaped flow channel.

[0056] After the first drawing, the low deformation area has a work hardening layer, which causes springback distortion, which needs to be eliminated through gap compensation and flow control to suppress wrinkles.

[0057] In an embodiment, the die gap of the low deformation zone is 1.05-1.10t during the second drawing, t is the thickness of the part. The small gap at the inlet: restricts the initial flow direction of the material, eliminates the rebound distortion of the work-hardened layer. The large gap at the outlet: reduces the frictional resistance, releases the stress accumulated by the material at the end of the secondary drawing, avoids instability wrinkling; the die gap between the first deformation zone and the second deformation zone forms a horn-shaped flow channel to guide the material to flow along the axial direction, and suppresses the wrinkle initiation caused by circumferential compression.

[0058] In an embodiment, the blank holder is embedded with shape memory alloy, such as NiTi alloy, which has unique shape memory effect and superelasticity. At a specific temperature, the martensitic phase transition can be triggered by current excitation, causing the alloy to recover or deform to a predetermined shape. Before the second drawing, the actual profile data of the low deformation zone is obtained by laser scanning, and the profile data is input to the control system of the blank holder. The control system calculates the required deformation of the blank holder according to the measured profile, and drives the blank holder to exhibit shape memory effect by exciting the SMA wire to shrink or stretch, so as to accurately match the geometric characteristics of the low deformation zone.

[0059] The blank holder is divided into multiple independent control regions, and the SMA wires in each region can be excited individually to achieve zoned control of the blank holder force. In the wrinkle-prone area of the low deformation zone, the excitation current of the SMA wire is increased to increase the blank holder force in this area and suppress the tendency of material wrinkling.

[0060] In summary, the blank holder embedded with shape memory alloy technology effectively suppresses the tendency of material wrinkling in the low deformation zone through active deformation and zoned pressure of the blank holder.

[0061] In an embodiment, the working surface of the blank holder is processed with deep and shallow interlaced annular grooves. The shallow groove area provides a large static friction coefficient with high-hardness silicone rubber, forming a high-friction resistance area. This area restricts the lateral flow of the material, forcing it to extend along the predetermined main flow direction and reducing disordered shear deformation.

[0062] Deep groove area: low-hardness silicone rubber produces controllable deformation under pressure, forming a low-friction resistance channel to guide the material to flow along the deep groove path and avoid local accumulation. The viscoelastic properties of silicone rubber can absorb the vibration energy generated during the drawing process.

[0063] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content to obtain equivalent embodiments with equivalent changes, as long as the changes or modifications do not deviate from the technical solution of the present application. Any modification, change, equivalent change and modification of the above embodiments made according to the technical essence of the present application still belong to the scope of the technical solution of the present application.

Claims

1. A drawing process for complex-shaped parts, characterized in that, Includes the following: S1: Intelligent partitioning, which divides the part into at least two areas, one as the first deformation area and the other as the second deformation area; S2: First drawing, using the outer contour of the first deformation zone as the blank holder to draw the first deformation zone to form a high deformation zone, corresponding to the second deformation zone to form a low deformation zone, and the material flowability flows from the low deformation zone to the high deformation zone. S3: Second drawing, using the outer contour of the part surface as a pressure ring to draw the low deformation area to avoid wrinkles; The method for implementing the intelligent partitioning includes the following steps: S101: Obtain the equivalent plastic strain cloud map of the part during the drawing process by finite element simulation. Use the strain gradient greater than X% as the threshold, define the area with the strain gradient higher than the threshold as the first deformation zone, and the remaining area as the second deformation zone. S102: Based on the service conditions of the part, perform topology optimization on the part, extract the optimized stress concentration factor distribution, and include the region with stress concentration factor greater than Y into the first deformation zone. Where X ranges from 10% to 20%, and Y ranges from 1.5 to 2.0; The entrance fillet of the high deformation zone adopts a gradient fillet structure, with the fillet radius R continuously changing along the drawing depth direction and satisfying the following relationship: R=R min +( ) k (R max -R min ) R min The minimum fillet radius is defined as R, which ranges from 3t to 5t. max The maximum fillet radius is defined as 8t-12t, and R... max ≥2R min t is the sheet thickness; z is the current distance from the bottom of the drawing; H is the total drawing depth; k is the gradient index.

2. The drawing process for complex surface parts according to claim 1, characterized in that, The value of k is related to the criteria for determining 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.

3. The drawing process for complex surface parts according to claim 1, characterized in that, The surface roughness Ra of the gradient rounded corner structure is ≤0.8μm, and the contact surface with the part is coated with a graphene-based lubricating layer.

4. The drawing process for complex surface parts according to claim 1, characterized in that, During the first drawing process, the die clearance for the high deformation zone is set to 0.95-0.98t, and the clearance for the low deformation zone is set to 1.02-1.05t, where t is the thickness of the part.

5. The drawing process for complex surface parts according to claim 2, characterized in that, During the second drawing process, the die gap in the low deformation zone is 1.05-1.10t, where t is the thickness of the part.

6. The drawing process for complex surface parts according to claim 1, characterized in that, The blank holder is embedded with a shape memory alloy. The shape memory alloy actively deforms 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 undergoes a shape memory effect under current excitation to press the low deformation area.

7. The drawing process for complex surface parts according to claim 5, characterized in that, The working surface of the pressure ring is machined with annular grooves of varying depths. 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 it is Shore 40±3.

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