CN117299965A

CN117299965A - Method for obtaining right half part of automobile plate forming limit diagram and corresponding mold

Info

Publication number: CN117299965A
Application number: CN202210711477.5A
Authority: CN
Inventors: 胡晓; 杨兵; 张文; 曹零勇; 刘俊涛
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2022-06-22
Filing date: 2022-06-22
Publication date: 2023-12-29

Abstract

The method for obtaining right half part of the forming limit diagram of the automobile plate and the corresponding mould, wherein the deformation strain path of the fracture part takes linearity as a constraint condition in a period from the set time before fracture to the fracture time, and the corresponding secondary strain in the fracture of the plate is uniformly distributed in at least three intervals between 0 and 10 percent as a target, so that the mould is arranged; the strain, stress and displacement of the to-be-measured point from the beginning of pressurization to the full period of fracture are obtained through one-time stamping by combining the measurement based on the three-dimensional digital speckle strain measurement analysis system. According to the method for obtaining the right half part of the forming limit diagram of the automobile plate and the corresponding die, the forming limit strain of the metal plate in a plurality of two-way stretching deformation states can be obtained through a single test, so that the right half part of the Forming Limit Diagram (FLD) of the plate can be obtained rapidly.

Description

Method for obtaining right half part of automobile plate forming limit diagram and corresponding mold

Technical Field

The utility model belongs to the technical field of metal plastic processing and dies, and particularly relates to a method for obtaining the right half part of a forming limit diagram of an automobile plate and a corresponding die.

Background

The stamping forming has the advantages of stability, high efficiency, low cost and the like, can process parts with light weight, thin wall, high precision and complex shape, and becomes an important processing mode in the field of automobile manufacturing. The covering part is used as an important component of an automobile product, and has the characteristics of large deformation, complex space curved surface, high surface quality and dimensional accuracy requirements and the like. In the production process, cracking defects are often caused by mismatch of material properties and a stamping process, so that the production efficiency and the manufacturing cost are greatly influenced. Therefore, the engineering is generally to draw a forming limit diagram to comprehensively evaluate the forming performance of the sheet, has an important effect on evaluating the forming quality of the sheet, and is widely applied to the design for guiding the stamping die and the production process.

The concept of sheet forming limit diagrams was originally proposed by Keeler in 1965 and has been improved, developed and perfected by Goodwin, marciniak, ghosh, hecker and Nakazima et al. Finally, a lot of automobile companies, steel companies and scientific research institutions are combined with the 2008 published ISO12004FLD test standard, and the acquisition method of the current sheet metal forming limit diagram is determined.

The current FLD measurement method is to first process the plate into dumbbell-shaped test pieces (the length, width and radius of the transitional arc of the parallel parts are defined by the arrows in the figure) as shown in fig. 1, and print a selected grid or random spot pattern with precise size on the surface of the plate. The sheet was then deformed until broken, using either the Nakajima (shown in fig. 2) or Marciniak method (shown in fig. 3), stopping the test. And measuring the strain of the deformed sample, and then determining the maximum strain which can be borne by the material without failure through interpolation, so as to obtain the forming limit strain value under a given strain state. By varying the width of the parallel portions of the specimen, the strain path measured ranges from unidirectional to bi-directional. And connecting the single forming limit data points collected under different strain states to obtain a forming limit curve.

The limit diagram of the forming performance in the prior art is obtained based on multiple bulging tests, complex machining is required to be carried out on the sample plate, and the defect of the characteristic notch of the edge part is possibly introduced during machining, so that a longer test process is required, the complex sample plate is required to be machined, and the test precision is inevitably influenced due to the hard damage of the machining body; meanwhile, due to the fact that the test sample with the notch is adopted to form different stress characteristics, edge cracks are easy to occur in the test process of the narrower test sample, and the test accuracy is affected.

The application number is: the utility model application of CN 2014108463726 discloses a device and a test method for measuring the left half part of a metal plate forming limit diagram, wherein the device comprises two sample fixing mechanisms and a sample lifting mechanism, and the two sample fixing mechanisms are arranged at two sides of the sample lifting mechanism; the sample jacking mechanism comprises a cylindrical roller and a lifting device, wherein the cylindrical roller is arranged above the lifting device, and the lifting device drives the cylindrical roller to move up and down. The cylindrical roller gradually rises to enable two ends of the sample to be broken or directly broken, and as one end of the sample material is broken or broken in advance, the other end of the sample material is just in a critical state of just necking or just breaking, so that the problem that the critical state of just necking or breaking of the sample is difficult to control is solved, and then the left half part of a strain limit diagram can be drawn more accurately by measuring the strain of the area.

The application number is: the utility model application of CN 201920392531.8 discloses a forming limit curve testing mould and device, comprising: the die, the blank holder, the punch and the punch backing plate; the female die is provided with a plurality of first through holes penetrating through the female die, the first ends of the first through holes are provided with observation windows, and the second ends of the first through holes are provided with grooves which are expanded radially; the edge pressing die is provided with a plurality of second through holes which penetrate through the edge pressing die and have the same number as the first through holes, the arrangement mode of the second through holes is consistent with that of the first through holes, and the first through holes and the second through holes at the same arrangement point are coaxial; the number of the punches is consistent with that of the second through holes, and the punches are embedded in the second through holes in a one-to-one correspondence and axially movable manner; the punch is fixed on the punch backing plate.

The application number is: the utility model application of CN201910850955.9 discloses a method for testing the limit of edge forming of a metal plate, and establishes a spherical male die expansion type test device comprising a blank holder, a male die, a female die and a plate center positioning mechanism; preparing a sheet sample with a circular arc notch in the middle part of one side, and processing different edge quality of the sample according to requirements; placing the test sample on one side of a spherical male die expansion die, aligning the arc center of the test sample with the center of the spherical male die, and causing cracking of the edge at the arc center under the action of pull-up and lateral force in the rising process of the male die. Testing samples with better edge quality and materials with poor edge quality or different tissues with the same edge quality, and measuring displacement change and main strain change of a cracking position through a digital image measuring system; by comparing the displacement or the principal strain, the edge forming limit of the material in a specific edge state and the sensitivity of the material to the edge quality are determined.

The application number is: the utility model application of CN 2021109899751 discloses a method for constructing a non-contact forming limit diagram, which adopts a tensile test method, accurately obtains main strain and secondary strain of a frame before material fracture by using a DIC technology, and accurately constructs the forming limit diagram of a metal material. The main deformation part in the whole test process is not required to be contacted with any mold, so that the problem that the strain at the breaking position and the friction force caused by the contact of the male mold and the plate material in the traditional forming limit test can not be collected and the influence on the test result is effectively solved.

Disclosure of Invention

In order to solve the problems, the utility model provides a method for obtaining the right half part of an automobile plate forming limit diagram and a corresponding mold, and the technical scheme is as follows:

a method for obtaining the right half of a forming limit diagram of an automobile panel, which is characterized by comprising the following steps:

setting a die by taking the linear deformation strain path of a fracture part as a constraint condition in a period from a set time before fracture to a fracture time and taking the uniform distribution of corresponding secondary strain in at least three intervals between 0 and 10 percent as a target when a plate material is broken;

the strain, stress and displacement of the to-be-measured point from the beginning of pressurization to the full period of fracture are obtained through one-time stamping by combining the measurement based on the three-dimensional digital speckle strain measurement analysis system.

The method for acquiring the right half part of the forming limit diagram of the automobile plate is characterized by comprising the following steps of:

the method is characterized in that the corresponding secondary strain of the plate material is uniformly distributed in at least three intervals between 0 and 10 percent when the plate material breaks, and the secondary strain of the plate material when each deformation area is pressed to break corresponds to a target secondary strain interval by arranging at least three independent deformation areas on the die.

The method for acquiring the right half part of the plate-shaped limit diagram of the automobile is characterized by comprising the following steps of:

the deformation zone is formed by an elliptic punch head arranged on the punch bottom plate and an adaptive ellipse arranged at the corresponding position on the die;

the length-diameter ratio of the ellipsoidal punch of each male die is different, and the deformation areas are separated by a draw bead arranged on the female die.

the ratio of the length to the diameter of each ellipsoidal punch is determined based on finite element simulation according to the target secondary strain corresponding to each deformation zone.

at least one of the at least three zones is a zone that encompasses planar strain.

the number of the sections is 5, and the corresponding secondary strain of each section is 6% -8%, 4% -6%, 3% -5% and 1% -3%0% -2% respectively.

the number of the sections is 5, and the corresponding secondary strain of each section is 6% -8%, 4% -6%, 3% -5%, 1% -3% and 0% -2% respectively; correspondingly, the length-diameter ratio of the ellipsoidal punch is as follows: 6:6, 6:5, 6:4, 6:3, 6:2.

the one-time punching is repeated for at least three times, and all phase images obtained by the three times are used as a phase image set for analysis.

A die for obtaining the right half of a forming limit diagram of an automobile plate, which is characterized in that:

the die forms different times of strain of the plate material at the breaking moment of each deformation zone during one-time stamping through the set different characteristic deformation zones, and the deformation strain path of the breaking part is linear within the period from the set moment before breaking to the breaking moment of the plate material.

The die for obtaining the right half part of the forming limit diagram of the automobile plate is characterized in that:

setting 5 different deformation areas, wherein different times of strain of the plate material when each deformation area is broken are as follows: 6 to 8 percent, 4 to 6 percent, 3 to 5 percent, 1 to 3 percent and 0 to 2 percent.

setting a plurality of ellipsoidal punches on a male die base plate, and setting adaptive ellipses at corresponding positions on a female die, so as to establish linear response of deformation strain paths of fracture parts in a period from a set time before fracture to a fracture time of a plate;

forming different deformation areas for each ellipsoidal punch by arranging draw beads on the female die;

by setting different length-diameter ratios of the ellipsoidal punch, different secondary strains of the plate at the breaking moment of each deformation area during secondary stamping are formed.

the different length-diameter ratios are determined through finite element simulation according to the target fracture times strain corresponding to each deformation region.

setting 5 different deformation areas, wherein different times of strain of the plate material when each deformation area is broken are as follows: 6 to 8 percent, 4 to 6 percent, 3 to 5 percent, 1 to 3 percent and 0 to 2 percent;

the corresponding sequential length-diameter ratio is as follows: 6:6, 6:5, 6:4, 6:3, 6:2.

The method for obtaining the right half part of the forming limit diagram of the automobile plate and the corresponding die can realize the stress and deformation process consistent with the actual stamping process of the plate, and have good reference significance for the development and process design of the actual automobile plate stamping die; based on the three-dimensional digital speckle dynamic strain measurement analysis system, the breaking strain of the automobile plate in a plurality of characteristic deformation states can be accurately measured; the forming limit strain of the metal plate in a plurality of biaxial stretching deformation states can be obtained through a single stamping process, so that the right half part of a plate Forming Limit Diagram (FLD) is rapidly obtained; the required plate sample has a simple shape, no characteristic gap, no complex machining is required, and the influence of the sample processing quality on the test precision is small.

In summary, the method for obtaining the right half part of the forming limit diagram of the automobile plate and the corresponding mold can obtain the forming limit strain of the metal plate in a plurality of two-way stretching deformation states through a single test, so that the right half part of the Forming Limit Diagram (FLD) of the plate is rapidly obtained, and effective experimental guarantee is provided for guiding the development and process design of the stamping forming mold of the automobile plate; the method is well applicable to metal plates with different materials and various thickness specifications; the designed die is simple to manufacture, convenient to operate and low in test cost.

Drawings

FIG. 1 is a schematic diagram of a prior art dumbbell-shaped specimen with parallel portions;

FIG. 2 is a schematic cross-sectional view of a Nakajima test mold in accordance with the prior art of the present utility model;

FIG. 3 is a schematic cross-sectional view of a Nakajima test mold in accordance with the prior art of the present utility model;

FIG. 4 is a schematic illustration of a test abrasive article of the present utility model;

FIG. 5 is a schematic diagram of a male die structure in the present utility model;

FIG. 6 is an exploded front view of a test die in an embodiment of the utility model;

FIG. 7 is a cross-sectional view taken along the direction A-A of FIG. 6;

FIG. 8 is a B-B sectional view of FIG. 6;

FIG. 9 is a schematic diagram of a female die structure in an embodiment of the utility model;

FIG. 10 is a schematic view in the C-C direction of FIG. 9;

FIG. 11 is a schematic view of a structure of a pressing plate according to an embodiment of the present utility model;

FIG. 12 is a D-D sectional view of FIG. 11;

FIG. 13 is a forming limit graph of a sheet material measured in accordance with an embodiment of the present utility model.

In the drawing the view of the figure,

1-grooves;

2-a material pressing plate;

3-convex grooves;

4-a male die bottom plate;

1 a-bolt holes;

1 b-a draw bead;

2 A-A draw groove;

3 b-an elongated positioning block.

Detailed Description

The method for obtaining the right half part of the forming limit diagram of the automobile plate and the corresponding mould according to the utility model are further specifically described below according to the attached drawings and the specific embodiments.

The method for obtaining the right half part of the forming limit diagram of the automobile plate takes the set time before fracture to the time of fracture continuously, the deformation strain path of the fracture part is linear as a constraint condition, and takes the distribution of corresponding secondary strain in at least three intervals between 0 and 10 percent as a target when the plate material is broken, so as to set a die;

Wherein,

A die for obtaining the right half part of a forming limit diagram of an automobile plate,

Wherein,

Principle of operation

1 design thought

Bulging deformation is more common during stamping of automotive panels, which corresponds to the right half of FLD. In addition, different stamping die shapes can generate different deformation effects on the plate materials with the same shape. Starting from the two points, the method and the device can obtain the plate forming limit under a specific strain state by changing the shape profile of the bulging die, and simultaneously ensure that the stress state of the metal plate in the forming process is similar to that of stamping.

2 composition of test die

The test die consists of a female die, a material pressing plate and a male die, as shown in fig. 4. Five ellipsoidal punches with different length-diameter ratios (6:6, 6:5, 6:4, 6:3 and 6:2) are respectively arranged on the male die, and each punch can respectively generate 6-8%, 4-6%, 3-5%, 1-3% and 0-2% secondary strain when the sheet is broken from large to small according to the ellipsoidal short diameter; the secondary strain setting sets a section covering the plane strain state according to the plane strain state, the ellipsoidal setting can well represent the plane strain state, and meanwhile, the fact that a certain period of time lasts to the breaking moment before stamping to breaking can be guaranteed, the strain path of the secondary strain is linear, and the testing precision can be well guaranteed; the length-diameter ratio is obtained by continuous iterative calculation through a finite element method according to the respective secondary strain interval; wherein the secondary strain setting is set with 0-10% as a first target and the secondary strain having been continuously distributed in this interval as a second target, and with the fracture in the measured plane strain state as a third target.

The female die and the pressing plate are both provided with hollow structures matched with the shapes of the male die and the punch heads, and the die is divided into five independent bulging forming areas by arranging drawing beads at the periphery of each punch head forming area, so that the occurrence of plate flow between the areas is avoided, and the stability of the test is improved.

Method for obtaining right half part of forming limit diagram of automobile plate

The specific evaluation flow of the acquisition of the right half of the automobile sheet forming limit diagram is as follows:

(1) Processing three rectangular samples of 400mm multiplied by 400mm from the measured plate material;

(2) Spraying paint for measuring speckle on the surface of the sample;

(3) Mounting a test die on a press and sufficiently lubricating the surface of the test die;

(4) And placing the sample on a pressing plate, starting a press machine to deform the plate, and measuring the strain state of the surface of the plate through a three-dimensional digital speckle dynamic strain measurement analysis system.

(5) Strain data of the fracture position of each area is acquired according to the method, the test is finished until the last area is fractured, and the test is repeated for three times;

(6) And connecting the measured data points to obtain the right half part of the forming limit diagram of the measured plate.

Examples

Fig. 6, 7 and 8 show exploded views of the test die of the present utility model, including: the die 1, the pressure plate 2, the punch 3 and the punch bottom plate 4. In the installation process, the female die is fixedly connected with the female die fixing plate of the press through bolts, the pressing plate is fixedly connected with the lower die fixing plate of the press through bolts, the male die punch is fixedly connected with the male die bottom plate through bolts, and the male die bottom plate is fixedly connected with the ejection device of the press through bolts. In the testing process, the plate material is placed on the upper end surface of the pressing plate, and the female die moves downwards to press the plate material; at the moment, the punch head of the male die moves upwards, so that a plurality of areas of the plate are deformed; and stopping the operation of the male die punch after the last region is broken.

The test die has the following components:

(1) Female die

The female die is shown in fig. 9 and 10, five elliptic hollow structures are arranged in the middle of the female die, and the die is divided into five independent areas (the areas are marked as an area one to an area five in sequence from large to small according to the elliptic short diameters) by a drawing bead 1b arranged on the periphery; bolt holes 1a are arranged at the four vertex angle positions of the die and are used for being connected with a press female die fixing plate.

(2) Material pressing plate

The pressing plate is shown in fig. 11 and 12, five elliptic hollow structures are arranged in the middle of the pressing plate, and drawing grooves 2b corresponding to the die drawing ribs are arranged on the periphery of each hollow region; the four vertex angle positions are provided with bolt holes for connecting with a lower die fixing plate of the press.

(3) Male die

The male die is shown in fig. 5 and consists of a male die base plate and five ellipsoidal male die punches with different length-to-diameter ratios (6:6, 6:5, 6:4, 6:3 and 6:2 respectively). Each punch head of the male die is provided with 2 bolt holes and a strip-shaped positioning block 3b; the four top corners of the male die bottom plate are provided with bolt holes for being connected with a press ejection device.

In order to verify the feasibility and the working precision of the method and the die, the 5182 aluminum alloy automobile plate with the thickness of 1mm is subjected to simulation test based on an Autoform simulation calculation platform, and the simulation test process is as follows:

(1) Establishing a discretization model of the die and the plate according to the geometric parameters;

(2) Setting a movement track of the die according to the working mode of the die;

(3) Setting the coulomb friction coefficient of the plate and the die and the blank holder force;

(4) Submitting the sheet material to an algorithm device for calculation to obtain a sheet material test process simulation file;

(5) Opening a simulation file, and reading strain data of a fracture position of each area at first;

(6) The measured data points are connected to obtain the right half of the measured sheet forming limit graph as shown in fig. 13 (epsilon 1 in the graph is the primary strain, epsilon 2 is the secondary strain, and the selected time period is a certain time duration before fracture to the moment of fracture). The strain track of each fracture position is also marked, and the result shows that the strain path of the sheet deformation of each fracture position is nearly linear, and the effectiveness of forming limit is high; so that the accuracy of the mold of the present utility model is simulated and verified.

Claims

1. A method for obtaining the right half of a forming limit diagram of an automobile panel, which is characterized by comprising the following steps:

2. A method of obtaining the right half of a vehicle panel forming limit diagram according to claim 1, wherein:

3. A method of obtaining the right half of a vehicle panel limit map according to claim 2, wherein:

the deformation zone is formed by an ellipsoidal punch head arranged on the punch bottom plate and an adaptive ellipsoidal hollow structure arranged at the corresponding position on the die;

4. A method of obtaining the right half of a vehicle panel forming limit diagram according to claim 3, wherein:

5. A method of obtaining the right half of a vehicle panel forming limit diagram according to claim 1, wherein:

6. A method of obtaining the right half of a vehicle panel forming limit diagram according to claim 1, wherein:

7. A method of obtaining the right half of a vehicle panel forming limit diagram according to claim 4, wherein:

8. A method of obtaining the right half of a vehicle panel forming limit diagram according to claim 1, wherein:

9. A die for obtaining the right half of a forming limit diagram of an automobile plate, which is characterized in that:

10. A die for obtaining the right half of the forming limit diagram of an automobile panel according to claim 1, characterized in that:

11. A die for obtaining the right half of the forming limit diagram of an automobile panel according to claim 9, wherein:

12. A die for obtaining the right half of the forming limit diagram of an automotive panel according to claim 11, characterized in that:

13. A die for obtaining the right half of the forming limit diagram of an automotive panel according to claim 12, characterized in that: