CN211528095U

CN211528095U - Test platform for realizing thin plate forming limit under nonlinear and linear strain path

Info

Publication number: CN211528095U
Application number: CN202020040448.7U
Authority: CN
Inventors: 柳泉潇潇
Original assignee: Changsha Jinbang Electromechanical Equipment Co Ltd
Current assignee: Huaxun (Shenzhen) Intelligent Equipment Co.,Ltd.
Priority date: 2020-01-08
Filing date: 2020-01-08
Publication date: 2020-09-18
Anticipated expiration: 2030-01-08

Abstract

The utility model provides a realize nonlinear and linear test platform who meets an emergency sheet metal limit of taking shape under route, include: the device comprises an upper end die fixing component, a lower end die fixing component, an image acquisition device and a die component; wherein: the upper-end die fixing assembly comprises a die handle (1), an upper die base (3) and an upper connecting base (6), and the die handle (1) is connected with the upper die base (3) through threads; the upper die holder (3) is connected with the upper connecting seat (6) through a bolt (2); the lower end die fixing component comprises a supporting seat (17), a lower die seat (19), a lower punch fixing block (24) and a lower punch positioning seat (25); the image acquisition device comprises a light source (26) and a camera (4), wherein the light source (26), the camera (4) and an equipment fixing support are fixed on the upper die base (3). The test platform punches a sample by adopting the upper male die and the ellipsoidal lower male die in the form of the flat-like punch head, and can realize a complex strain path of a surface fracture point of the sample.

Description

Test platform for realizing thin plate forming limit under nonlinear and linear strain path

Technical Field

The utility model relates to a test platform especially relates to a realize the test platform of the limit that the sheet metal takes shape under nonlinear and linear strain path, and this platform can cooperate non-contact strain test system to acquire panel surface limit strain.

Background

In the manufacturing industry today, stamping parts are used in a large number of applications for reasons of high production efficiency, stable quality and ease of production. Taking an automobile as an example, the steel consumed by stamping parts on the automobile accounts for more than 60% of the steel consumed by the whole automobile, and with the application of a new stamping process, the proportion can be further increased in the future, so that the importance of the stamping parts to the manufacturing industry can be seen. The material used for the stamping process is generally a metal sheet with the thickness of less than 6mm, and the metal sheet is subjected to drawing, bending and bulging deformation or combination of the deformation in a die to obtain a stamping part with a required shape.

However, due to the unreasonable process design or the poor formability of the metal sheet, the sheet may have wrinkles or cracks during the punching process. Therefore, in actual production, in order to obtain an acceptable stamping part, it is important to know the formability of the metal material. The forming performance of the metal sheet in engineering is generally characterized by a traditional Forming Limit Curve (FLC). During testing, the primary and secondary strains near the failure area can be obtained by changing the size of the test piece when the plate is cracked or necked under different linear strain paths. The strain at these failure points is plotted on the primary and secondary strain axes to form a forming limit plot.

However, in actual production, the forming limit curve under a linear strain path is found, and the fracture prediction of a local profile with a complex strain path has deviation from the test result. At present, the forming limit research of a plate under a nonlinear strain path is mainly divided into two parts of theoretical research and experimental research. In the theoretical part, expert scholars deduce forming limits under different strain paths according to stress and strain states and based on damage criteria such as M-K and the like, but theoretical derivation is based on various assumptions, and at present, no generally accepted derivation method exists, so theoretical research cannot be popularized to engineering application. In the experimental research part, Graf, Hosford and the like perform pre-strain on a plate and then perform bulging experiments, and disclose the evolution process of forming limit after different pre-strains, but the unloading process after the pre-strains is not in accordance with the actual engineering; in addition, the patent "composite strain path forming experimental device" (application number: 201110194526.4) proposes a composite strain path forming device which can realize a composite deformation mode of sheet bulging and drawing, but the device has a complex structure and a limited range of nonlinear strain paths, and the position of a fracture point appears on a fillet or a side wall part, so that the strain system is inconvenient to observe.

Therefore, a multifunctional test platform capable of realizing the plate forming limit under the linear strain path and the nonlinear strain path is needed, and the test mold is required to be simple in structure and convenient to replace.

SUMMERY OF THE UTILITY MODEL

The utility model aims at providing a can realize the mould that the limit test takes shape under linear strain path and the nonlinear strain path of sheet metal to can acquire the test platform that the limit of sample surface full field meets an emergency and the position of breaking meets an emergency through non-contact strain test system.

The technical scheme of the utility model a test platform that sheet metal takes shape limit under realization nonlinear and linear strain path is provided, include: the device comprises an upper end die fixing component, a lower end die fixing component, an image acquisition device and a die component; wherein:

the upper-end die fixing assembly comprises a die handle, an upper die base and an upper connecting base, wherein the die handle is connected with the upper die base through threads; the upper die holder is connected with the upper connecting seat through a bolt;

the lower die fixing assembly comprises a supporting seat, a lower die seat, a lower punch fixing block and a lower punch positioning seat, wherein the lower punch fixing block is connected with the lower punch positioning seat through a screw, and the lower punch positioning seat is driven by hydraulic pressure below the lower punch positioning seat on the lower die seat; the supporting seat is fixed with the lower die holder through a lower die holder connecting bolt;

the image acquisition device comprises a light source and a camera, and the light source, the camera and the equipment fixing bracket are fixed on the upper die base; the light source bracket is used for fixing the light source;

the die assembly comprises an upper male die, a lower male die, a blank holder and a female die, wherein the upper male die is a hollow conical male die with a flange and is connected with an upper connecting seat through a male die connecting bolt; the upper part of the lower convex die is an ellipsoidal curved surface; the lower surface of the lower convex die positioning seat is provided with an inward sunken platform which is rigidly connected with the lower convex die supporting rod; the blank holder and the female die are fixed on the female die, and the female die is fixed on the supporting seat through a female die fixing bolt; the supporting plate is used for supporting the concave die.

Furthermore, the upper die base is positioned and guided through the guide sleeve and the guide pillar; the guide post is fixed on the lower die base in an interference fit manner;

furthermore, the sample is positioned between the blank holder and the female die, the blank holder is connected to the upper die holder through the suspension spring, and the sample is fixed on the female die through downward blank holding force applied to the blank holder by the compression spring.

Furthermore, the lower male die and the lower male die supporting rod are connected through a bayonet lock and fixed on the lower male die fixing block.

The beneficial effects of the utility model reside in that:

the utility model discloses the beneficial effect who brings is: an upper male die and an ellipsoidal lower male die in the form of a flat-like punch the sample to realize a complex strain path of a surface fracture point of the sample; the interior of the upper male die in the die is hollow, so that a camera is matched with a light source to observe and collect the deformation process of the sample; through replacing the accessories, one set of die tool can realize the forming limit test of the thin plate under a linear strain path and a nonlinear strain path.

Drawings

FIG. 1 is a schematic view of the complex strain path experimental apparatus

FIG. 2 shows a schematic diagram of a conventional forming limit experiment sample

FIG. 3 is a schematic view of a traditional forming limit experiment blank holder

FIG. 4 is a schematic view of a hemispherical male die for a traditional forming limit experiment

FIG. 5 is a cross-sectional view of the male mold of the complex strain path experimental device of the present invention

FIG. 6 is a top view of the upper connection plate of the complex strain path experiment device

FIG. 7 is a plan view of a supporting plate of the complex strain path experimental device

FIG. 8 is a cross-sectional view of the lower punch of the complex strain path experimental apparatus of the present invention

FIG. 9 is a three-view diagram of the lower punch of the complex strain path experimental apparatus of the present invention

Fig. 10 is a schematic diagram showing the complex strain path experimental apparatus according to the present invention using a series of sample sizes;

FIG. 11 shows a first arrangement of the lower punch and the sample;

FIG. 12 shows a second arrangement of the lower punch and the test piece;

FIG. 13 shows a sample obtained after one-step bulging;

FIG. 14 is a schematic view showing the shape of a sample after the long axis of the lower punch is formed perpendicular to the rolling direction and the shape of the sample after the long axis of the lower punch is formed in the rolling direction.

Wherein: 1-die shank, 2-upper die holder screw, 3-upper die holder, 4-camera and fixing support, 5-guide bush, 6-upper connecting holder, 7-web fixing screw, 8-upper web, 9-punch fixing screw, 10-upper punch, 11-guide post, 12-blankholder fixing screw, 13-blankholder, 14-die, 15-support plate, 16-die fixing screw, 17-lower die holder, 18-lower die holder connecting screw, 19-lower die holder, 20-lower punch, 21-bayonet, 22-lower punch support bar, 23-index plate, 24-lower punch fixing block, 25-lower punch positioning seat, 26-light source, 27-light source support, 28-suspension spring, 29-sample, 30-reverse bulging male die.

Detailed Description

The technical solution in the embodiments of the present invention will be further illustrated and described with reference to the drawings in the embodiments of the present invention. It is to be understood that the embodiments described are only some embodiments of the invention, and not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by the skilled in the art without creative work belong to the protection scope of the present invention.

As shown in fig. 1, the present embodiment provides a testing platform for realizing the forming limit of a thin plate under nonlinear and linear strain paths, including: the device comprises an upper end die fixing component, a lower end die fixing component, an image acquisition device and a die; wherein:

the upper-end die fixing assembly comprises a die shank 1, an upper die base 3 and an upper connecting seat 6, and the die shank 1 is connected with the upper die base 3 through threads; the upper die holder 3 is connected with the upper connecting seat 6 through a bolt 2; the upper connecting seat 6 is of a hollow structure and has enough height;

the image acquisition device comprises a light source 26 and a camera 4, wherein the light source 26, the camera 4 and the equipment fixing bracket are fixed on the upper die holder 3; the light source holder 27 is used to hold the light source 26.

The lower die fixing assembly comprises a supporting seat 17, a lower die seat 19, a lower punch fixing block 24 and a lower punch positioning seat 25, wherein the lower punch fixing block 24 is connected with the lower punch positioning seat 25 through a screw, and the lower punch positioning seat 25 is driven by lower hydraulic pressure on the lower die seat; the supporting seat 17 is fixed with the lower die holder 19 through a lower die holder connecting bolt 18.

The non-linear strain path lower thin plate forming limit die assembly comprises an upper male die 10, a lower male die 20, a blank holder 13 for clamping and pressing a plate material, and a female die 14, as shown in fig. 6 and 7. As shown in fig. 5, the upper male die 10 is a hollow conical male die with a flange, the lower part of the conical male die is in round corner transition, and the conical male die is connected with the upper connecting seat 6 through a male die connecting bolt 9; the upper connecting seat 6 and the upper connecting plate 8 are fixed through a connecting plate fixing bolt 7. The upper part of the lower convex die 20 is an ellipsoidal curved surface, as shown in fig. 8 and 9; the lower surface of the lower punch positioning seat 25 is provided with an inward sunken platform and is rigidly connected with the lower punch supporting rod 22. The lower punch 20 can be positioned and adjusted at different angles relative to the rolling direction of the sample by rotating the upper dividing disc 23 on the sliding chute of the supporting seat 17, and the relative position of the lower punch ellipsoid is shown in fig. 11 and 12;

the linear strain path lower sheet forming limit die assembly comprises a lower male die 20, a blank holder 13 and a female die 14, wherein the effective sizes of the blank holder and the female die are determined according to the description in the linear strain path lower sheet forming limit test standard as shown in figure 3, the lower male die is hemispherical, and the size is determined according to the description in the linear strain path lower sheet forming limit test standard as shown in figure 4. The connection form is consistent with the thin plate forming limit die assembly under the nonlinear strain path;

the upper die holder 3 is positioned and guided through the guide sleeve 5 and the guide post 11; the guide post 11 is fixed on the lower die base 19 through interference fit; the sample is positioned between the blank holder 13 and the female die 14, the blank holder 13 is connected to the upper die holder 3 through a suspension spring 28, and the sample is fixed on the female die 14 through downward blank holder force applied to the blank holder 13 by a compression spring;

the blank holder 13 and the female die 14 are fixed on the female die 14 through blank holder bolts 12, and the female die 14 is fixed on a supporting seat 17 through female die fixing bolts 16; the support plate 15 is used to support the female die 14.

The lower punch 20 and the lower punch supporting rod 22 are connected through a bayonet 21 and fixed on a lower punch fixing block 24.

The device is arranged on a double-acting hydraulic press and is provided with two power sources.

In this embodiment, the upper die base functions to:

(1) clamping and pressing the edge ring in the preforming process of the draw bead;

(2) clamping a male die in the formal test process;

(3) providing a space for erecting two CCD cameras and an illumination light source in a non-contact strain measurement system; the lower die holder has the following functions: providing a space for clamping the lower male die and fixing the female die in the whole test process; the blank holder provided with the draw bead and the female die are matched with the drawn bead in the process of drawing bead preforming, and are matched with the female die to clamp a sample in the formal testing process; the upper male die is mainly used for causing first-step deformation to a sample in the formal test process and pressing the sample in the second-step deformation process, and a hollow structure is arranged in the middle of the upper male die, so that a CCD camera can be matched with an illuminating light source to shoot the surface of the sample, as shown in FIG. 4; the lower male die is mainly used for punching a sample in the second step in the formal test process.

In this embodiment, the lower die holder functions as:

providing a male die clamping space and fixing a female die in the whole test process; the blank holder provided with the draw bead and the female die are matched with the drawn bead in the process of drawing bead preforming, and are matched with the female die to clamp a sample in the formal testing process; the male die is mainly used for bulging the test sample until the test sample is broken in the formal test process.

To obtain the forming limit under the nonlinear strain path, the test was performed by a two-step bulging method.

After a sample is placed on the surface of the female die 14, the die shank 1 is pushed by a hydraulic cylinder of a hydraulic press, the blank holder 13 is connected to the upper die holder 3 through the suspension spring 28, the upper die holder 3, the upper connecting plate 8 and the upper male die 10 are connected through bolts, the die shank 1 moves downwards to drive the suspension spring 28 and the upper male die 10 to move downwards together, the blank holder 13 is driven to be matched with the female die 14 to punch a draw bead, then the sheet is clamped, the upper male die 10 continues to move downwards to be in contact with the sample, the sample is subjected to plastic deformation to a certain degree, and the sample is kept still after the upper male die 10 moves for a certain stroke, the stage is preliminary bulging, and the shape of the sample is as shown in.

And then the hydraulic cylinder at the lower end of the double-acting hydraulic press outputs a driving force to push the push rod 20 connected with the hydraulic cylinder to move upwards and drive the lower punch 20 to move upwards, the lower punch 20 starts to contact with the sample until the surface of the sample starts to be necked or cracked, the stage is secondary bulging, the shape of the sample after the long axis of the lower punch is formed perpendicular to the rolling direction is shown as (a) of fig. 14, and the shape of the sample after the long axis of the lower punch is formed along the rolling direction is shown as (b) of fig. 14.

In the whole process of plastic deformation of the sample, a camera in the cavity of the upper connecting seat 6 photographs and records the deformation condition of the surface of the sample, and then the deformation condition is submitted to a computer for processing to obtain the time-related full-field strain of the surface of the sample in the experimental process.

To obtain the forming limit under the linear strain path, the test was performed using the forming limit test standard procedure.

After a sample is placed on the surface of a female die 14, a die shank 1 is pushed by a hydraulic cylinder of a hydraulic press, a blank holder 13 is connected to an upper die holder 3 through a suspension spring 28, the die shank 1 moves downwards to drive the suspension spring 28 and an upper male die 10 to move downwards together, the blank holder 13 is driven to be matched with the female die 14 to punch a draw bead, then a plate is clamped, the hydraulic cylinder at the lower end of the hydraulic press outputs a pushing force to push a push rod 20 connected with the hydraulic cylinder to move upwards and drive a lower male die 20 to move upwards, the lower male die 20 starts to be in contact with the sample until the surface of the sample begins to be necked or cracked, during the whole process of plastic deformation of the sample, a camera in a cavity of an upper connecting seat 6 is used for photographing and recording the deformation condition of the surface of the sample, and then the deformation condition is submitted to a computer for processing to obtain.

When the experimental device and the testing method are used for obtaining the formability of the material under the nonlinear strain path, the specific implementation process comprises the following steps:

step 1, preparation of a sample, wherein the sample is prepared by wire cutting. And (4) testing the forming limit under the nonlinear strain path, and forming the shape as shown in figure 10.

And 2, obtaining surface speckles, namely for metal, in order to obtain better surface speckles, spraying matte white paint on the surface of a sample to prevent the surface of the metal sample from reflecting light to influence the quality of a picture, and then spraying matte black paint on the surface of the sample with white paint as a primer.

And 3, calibrating the DIC equipment, namely adjusting the shooting angle of the camera 4 and the light intensity of the light source 26 to obtain a picture with better quality for subsequent data processing.

And 4, clamping the sample, wherein the relative position of the sample and the lower male die is shown in figures 11 and 12.

And 5, lubricating the surface of the sample, namely coating lubricating oil on the upper surface and the lower surface of the sample to reduce friction in order to reduce the interference of the friction on the test.

And 6, testing the forming limit under the nonlinear strain path, setting the strokes of the upper male die 10 and the lower male die 20, starting the DIC data acquisition system, starting the bulging test, performing the downward bulging test on the upper male die 10, and performing the upward bulging test on the lower male die 20 until the surface of the sample is necked or cracked. Note that the sample surface is not allowed to neck or crack during the bulging of the punch 10 at the initial stage.

And 7, processing the photos obtained by the DIC, obtaining a strain path of a necking point or a fracture point of the sample by using post-processing software carried by the DIC equipment, and drawing a Forming Limit Diagram (FLD) based on the strain path.

When the experimental device and the testing method are used for obtaining the formability of the material under the linear strain path, the specific implementation process comprises the following steps:

step 1, preparation of a sample, wherein the sample is prepared by wire cutting. The forming limit test specimen under the linear strain path was shaped as shown in fig. 2 according to the national standard.

And 4, lubricating the surface of the sample, namely coating lubricating oil on the upper surface and the lower surface of the sample to reduce friction in order to reduce the interference of the friction on the test.

Step 5, testing the forming limit under the linear strain path, after the sample is clamped, starting a DIC data acquisition system, and ascending a spherical male die to start a bulging test until the surface of the sample is necked or cracked;

and 6, processing the photos obtained by the DIC, obtaining a strain path of a necking point or a fracture point of the sample by using post-processing software of the DIC equipment, and drawing a Forming Limit Diagram (FLD) based on the strain path.

Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that the present invention is not limited to the specific embodiments, but rather, various modifications, alterations and substitutions can be made without departing from the spirit and scope of the present application.

Claims

1. A test platform for achieving sheet forming limits under nonlinear and linear strain paths, comprising: the device comprises an upper end die fixing component, a lower end die fixing component, an image acquisition device and a die component; wherein:

the upper-end die fixing assembly comprises a die handle (1), an upper die base (3) and an upper connecting base (6), and the die handle (1) is connected with the upper die base (3) through threads; the upper die holder (3) is connected with the upper connecting seat (6) through a bolt (2);

the lower end die fixing assembly comprises a supporting seat (17), a lower die seat (19), a lower punch fixing block (24) and a lower punch positioning seat (25), wherein the lower punch fixing block (24) is connected with the lower punch positioning seat (25) through a screw, and the lower punch positioning seat (25) is driven by hydraulic pressure below the lower die seat; the supporting seat (17) is fixed with the lower die holder (19) through a lower die holder connecting bolt (18);

the image acquisition device comprises a light source (26) and a camera (4), wherein the light source (26), the camera (4) and an equipment fixing support are fixed on the upper die base (3); the light source bracket (27) is used for fixing the light source (26);

the die assembly comprises an upper male die (10), a lower male die (20), a blank holder (13) and a female die (14), wherein the upper male die (10) is a hollow conical male die with a flange and is connected with an upper connecting seat (6) through a male die connecting bolt (9); the upper part of the lower male die (20) is an ellipsoidal curved surface; the lower surface of the lower convex die positioning seat (25) is provided with an inward sinking platform and is rigidly connected with a lower convex die supporting rod (22); the blank holder (13) and the female die (14) are fixed on the female die (14), and the female die (14) is fixed on the supporting seat (17) through a female die fixing bolt (16); the support plate (15) is used for supporting the concave die (14).

2. The test platform for achieving sheet forming limit under nonlinear and linear strain path as claimed in claim 1, wherein: the upper die holder (3) is positioned and guided through the guide sleeve (5) and the guide pillar (11); the guide post (11) is fixed on the lower die base (19) through interference fit.

3. The test platform for achieving sheet forming limit under nonlinear and linear strain path as claimed in claim 1, wherein: the test sample is positioned between the blank holder (13) and the female die (14), the blank holder (13) is connected to the upper die holder (3) through a suspension spring (28), and the test sample is fixed on the female die (14) through downward blank holding force applied to the blank holder (13) by a compression spring.

4. The test platform for achieving sheet forming limit under nonlinear and linear strain path as claimed in claim 1, wherein: the lower male die (20) and the lower male die supporting rod (22) are connected through a clamping pin (21) and fixed on a lower male die fixing block (24).