CN105855324A - Metal plate high-speed forming limit testing method - Google Patents

Abstract

The invention relates to a metal plate high-speed forming limit testing method. The metal plate high-speed forming limit testing method comprises the following specific steps that 1, before an experiment is started, a capacitance charging switch (25) is confirmed to be in a disconnected state, and a launching switch (29) is confirmed to be in a launching gear; 2, a test plate material (4) is manufactured; 3, a lifting bracket (9) and a blank holder (6) are lifted, and the test plate material (4) is placed on a female die (3); 4, the lifting bracket (9) is descended to enable a punching head (8) to be closely attached to the test plate material (4); 5, the angle of two high-speed cameras (20) is adjusted to enable imaging centers to be both aligned to one test plate material (4) grid point irradiated by laser light spots, and included acute angles theta 1 and theta 2 among the two cameras and a vertical line are recorded; and 6, the voltage-withstanding value and the capacitance value of a capacitor group (28) are adjusted, and the voltage value of a transformer and the voltage-withstanding value of the capacitor group (28) are adjusted to be corresponding. According to the metal plate high-speed forming limit testing method, the deformation process of the plate material printed with grids can be shot through the high-speed cameras, and the strain rate and the fracture strain can be calculated; and electromagnets can fix the punching head in the experiment preparation stage and are disconnected at the same time at the capacity discharge moment.

Description

A kind of sheet metal high-speed molding limit test method

Technical field

The present invention relates to sheet metal high-rate forming manufacture field, particularly to a kind of sheet metal high-rate forming limit test method.

Background technology

High energy rate metal forming includes kinds of processes method, mainly includes explosive forming, electro-magnetic forming, electro-hydraulic forming, namely utilizes high-energy electric, chemical, machinery storage to release in moment and be processed.Electro-magnetic forming and explosive forming are attained by the process velocity of 15～300 meter per seconds, can improve working (machining) efficiency greatly.Meanwhile, under the high strain rate of a lot of metal materials, its forming limit relatively room temperature low speed process improves a lot.Explosive forming, electro-magnetic forming, electro-hydraulic forming have abroad begun to research as far back as the middle of last century, come into now the practical stage.

In room temperature low speed forming process, the formability evaluation of sheet material has multiple way, wherein forming limit diagram (FLD) is to judge and the easiest and method intuitively of evaluation sheet material forming performance, is the very effective instrument solving sheet stamping forming problem.FLD is by sheet material local buckling limit logarithmic strain ε under differently strained path₁And ε₂The strip-type region constituted, reflects sheet material forming limit under unidirectional tension, two-way tension, plane strain and intermediateness effect comprehensively.In sheet material forming, the combination in any of two principal strains in board plane, as long as on the shaping limit curve fallen in forming limit diagram, will produce during sheet deformation and rupture, otherwise be then safety.

But, relate to strain rate factor during high-rate forming, and under differently strained speed, the plastic deformation law of material has very big difference, and the plasticity of different materials also differs widely with strain rate situation of change.As a rule, plate usual plasticity under Under High Strain speed is preferable, but plasticity is poor under middling speed strain rate.And, during sheet forming there is very big difference in the strain rate of plate various location, and this is by the prediction of appreciable impact plate failpoint.Therefore, what the forming limit of high energy rate metal forming can not be simple sets up principal strain and the relation of time strain, and is considered as effect of rate of strain, and conventional forming limit method of testing is the most applicable.

At present, the strain value measured under the high strain rate of material generally uses Hopkinson pull rod or depression bar to obtain high-speed stretch or the compression stress strain curve of material；Middle strain rate then can use high-speed stretch machine to test.In addition to common high-speed stretch machine, also utilize electromagnetism power-actuated superelevation speed one directional tensile test device and method just like a set of described in patent CN102944474A.But no matter use Hopkinson bar or high-speed stretch machine, all can only obtain the strain regime of simple tension or Uniaxial Compression, be far from being enough.

Additionally, in the middle of the experiment of the high-rate forming limit, the collection of experimental data is also a difficult problem.The method of traditional forming limit test uses print grid on plate, sheet-metal press working extremely produces the moment ruptured and stops immediately testing, now measure the Gridding length of plate rent, reach the purpose of strain measurement.But, the high-rate forming limit is tested, it is impossible to Control release terminates when plate produces and ruptures.Being referred to a kind of sheet metal formability test device utilizing the online image measurement technology of DIC in patent CN102305745A, device can measure the strain that plate produces in real time, it is not necessary to Control release terminates, it is not necessary to plate is carried out manual measurement.But this patent has following defects that 1, owing to DIC technology is when the strain measured on curved surface, data are the most inaccurate, therefore the flat-bottom punch that device uses, flat-bottom punch compares round punch, exists and easily ruptures at fillet, needs use to require many defects such as higher lubricant method.2, the when of drift upwards punching press plate, the distance of plate to camera shutter can produce the change of distance, and this can cause the enlarge-effect of image, cause measurement error.3, device can only measure the right half part of forming limit, and left-half needs to rely on one directional tensile test and empirical equation.4, tack drift quality is excessive, moves up, it is impossible to realize high velocity experiments.

Therefore, one is not still had directly to measure under high strain rate at present, the apparatus and method of Sheet Metal Forming Limit, there is the biggest limitation in existing high strain rate plate failure prediction method, in the urgent need to a kind of new forming limit diagram, and test device and method of testing carry out effective evaluation sheet metal forming property during high-rate forming, instruct foundation for the offer of the production process such as actual explosive forming, electro-magnetic forming, electro-hydraulic forming.

Summary of the invention

Problem to be solved by this invention is to provide a kind of sheet metal high-rate forming limit experimental provision, it is obtained in that under differently strained speed, Sheet Metal Forming Limit under differently strained path, it is provided that a kind of can accurately, convenient wrinkling, the method for splintering problem evaluated during sheet metal high-rate forming.

A kind of sheet metal high-speed molding limit test method of offer is provided, specifically includes following steps:

Step 1, start experiment before, confirm electric capacity charge switch be off, emission switch is in transmitting gear, treats that capacitor set discharge completes；Opening laser range finder, then by after on drift two pieces of armature alignment electric magnet suction nozzles and drift round end top alignment laser facula, make armature clash into the collision block of electric magnet head, emission switch is bound to electromagnetism adhesive gear, closes circuit general switch；

Step 2, making test plate；

Step 3, rise lifting support, rise blank holder, is placed and on die by test plate；

Step 4, fall lifting support, make drift press close to test plate；

Step 5, two high-speed camera angles of adjustment, the mesh point making imaging center all be irradiated by laser facula in alignment with test plate, record two cameras and the acute angle theta folded by vertical curve₁,θ₂；

Step 6, the pressure voltage adjusting Capacitor banks and capacitance, adjust transformer voltage value corresponding with Capacitor banks pressure voltage；

Step 7, complete charging after, it is ensured that disconnect capacitor charge switch；

Step 8, open high-speed camera, confirm that laser range finder is opened, carry out high-speed camera initially focus, image length to mark, initial camera length d of two high-speed cameras of measuring and calculating₁,d₂, i.e. high-speed camera focus is to the distance of initial focusing；

Step 9, high-speed camera, confirm that both laser range finders carry out the time to mark, press emission switch；Drift is launched, and plate will be recorded by high-speed camera by high speed bulging, Bulging Process, until drift reaches range, remaining kinetic energy is absorbed by adjustable bump rubber and buffer；Closing high-speed photographing unit, disconnects main power after test, confirm that electric capacity charge switch is off；Breakdown point is found according to the photo of photographing unit shooting, strain rate when confirming to rupture, try to achieve breaking strain.

The beneficial effects of the present invention is:

1) Electromagnetic Launching mode launching lightweight high intensity drift is used, equipment is simple, easy to maintenance, drift can be accelerated in very short time and launch with flank speed, plate can be made to obtain the high strain rate that can adjust within the specific limits, simultaneously because use the downward radiation pattern of drift, reach gravitional force and supplement kinetic energy consumption, have employed electric magnet, drift can be fixed before experiment is launched.

2) the conventional round punch meeting GB is used, it is to avoid the various defects that flat-bottom punch produces, can be on this experimental provision, by adjusting blank shape, measure the forming limit point in arbitrarily linear strain path on forming limit diagram.

3) punch stroke is limited; stroke can change by adjusting adjustable bump rubber; lower section is also provided with drift buffer unit to buffer drift further; and owing to high-speed camera is placed between buffer unit bearing and die socket; can effectively protect camera will not be damaged by drift; plane mirror system can also be used, change high-speed camera position, protect camera further.

4) speed of experiment can be controlled by regulation capacitor bank voltage and capacitance.

5) two high-speed cameras and laser range finder record is used to print the 3 D deformation process of plate of grid, solve each point strain and a difficult problem for instantankeous strain speed measurement in high-rate forming limit experimentation, solve the uncontrollable difficult problem rupturing termination experiment of high velocity experiments, initial rupture point can be found accurately by the image of record.Have and just can be completed by single test to find the advantage ruptured

6) mould of the present invention can be replaced, and can test under different bead height.

Accompanying drawing explanation

Fig. 1 is schematic diagram and the circuit theory diagrams of a kind of high-rate forming limit experimental provision of the present invention；

Fig. 2 is sectional view and the top view of die socket 2；

Fig. 3 is sectional view and the top view of die 3；

Fig. 4 is sectional view and the top view of blank holder 6；

Fig. 5 is sectional view and the A-A profile of lifting support 9；

Fig. 6 is sectional view and the top view of damping rubber block bearing 19；

Fig. 7 is camera axis plane computations schematic diagram.

In figure: 1-rail brackets, 2-die socket, 3-die, 4-tests plate, 5-packing ring, 6-blank holder, 7-trip bolt, 8-composite drift, 9-lifting support, 10-motorized rails, 11-plate coil, 12-drive block, 13-pitman, 14-is adjustable buffer rubber gasket, 15-stopper slot, 16-electric magnet, 17-armature, 18-drift damping rubber block, 19-damping rubber block bearing, 20-high-speed camera, 21-high-speed camera bearing, 22-laser range finder, 23-circuit general switch, 24-transformator, 25-electric capacity charge switch, 26-protects electric capacity, 27-high-voltage rectifier bridge, 28-Capacitor banks, 29-drift emission switch, 30-protective resistance, 31-rectifier bridge.

Detailed description of the invention

The present invention is elaborated by 1-7 and embodiment below in conjunction with the accompanying drawings.

As it is shown in figure 1, a kind of sheet metal high-speed molding limit experimental provision that the invention provides, including: rail brackets 1, die socket 2, die 3, packing ring 5, blank holder 6, trip bolt 7, composite drift 8, lifting support 9, motorized rails 10, plate coil 11, drive block 12, pitman 13, adjustable buffer rubber gasket 14, stopper slot 15, electric magnet 16, armature 17, drift damping rubber block 18, damping rubber block bearing 19, high-speed camera 20, high-speed camera bearing 21, laser range finder 22 and control circuit.

Wherein, motorized rails 10 is arranged in square rail support 1 upper end, drives lifting support 9 to move up and down and fix with motor, and lifting support 9 structure is as it is shown in figure 5, be the square that communicates of an opposite.It is bonded with plate coil 11 with insulating cement and bakelite on lifting support 9, plate coil 11 is powered by Capacitor banks 28, produce powerful pulse-electromagnetic force, it is arranged can to promote next-door neighbour, the movable downward high-speed mobile of copper drive block 12, thus drive and use the pitman 13 threadeded with it, pitman 13 uses bolt to fix with composite drift 8.Bonding armature 17 on drift 8, is attracted to before experiment on electric magnet 16, and the support column of electric magnet 16 is bolted to lifting support 9 upper end, relative with armature 17 through the perforate of support 9 lower end.

Being designed with incrassation type perforate stopper slot 15 in the middle part of lifting support 9 lower end, pitman 13 passes through.The removable loop buffer block rubber 14 of stopper slot upper ends one piece.

Die socket 2, independent of rail brackets 1, is positioned between rail brackets 1, can be lined with one piece of rubber blanket below, and die socket is as in figure 2 it is shown, its upper end is an annular groove, and annular die 3 is positioned in the groove of die socket 2 upper end.Annular die 3 outer ring has been circular layout screwed hole, and inner ring has a circle bead, as shown in Figure 3.

There is the boring relative with die 3 upper screwed hole that is circular layout the outer ring of blank holder 6, and inner ring is disposed with the bead corresponding with on die 3, as shown in Figure 4.

Plate 5 is killed on plate by blank holder 6 screw 7 circumferentially.The acquisition system of experimental data is installed below die socket, it is two to be arranged symmetrically, the high-speed camera 20 that camera axis can intersect at a point all the time, He Yitai is arranged vertically, in real time measure drift 8 and two camera focuses the laser range finder 22 of straight vertical dimension.

High-speed camera 20 is arranged on camera bearing 21, laser range finder is arranged in the circular hole of damping rubber block bearing 19 central authorities, as shown in Figure 6, damping rubber block bearing 19 is fixed on immediately below drift 8, its central circular hole just to drift 9 central authorities on it circular groove be placed with the drift damping rubber block 18 of same central openings.

The pattern of the downward pressing sheet material 4 of drift 8 that sheet metal high-speed molding limit experimental provision uses so that gravitional force can supplement a part by drift 8 forces sheet material 4 to deform the energy consumed.The semicircle drift of a diameter of 100mm that drift 8 used is recommended for GB, for alleviating drift 8 mass, drift 8 uses high strength composite to make, inner hollow, is divided into cup head and cover plate two parts, two-part being connected by glued joint.The purpose using light material is to make under certain plate coil 11 discharge energy, and drift 8 can obtain bigger speed.Device provides the drift 8 of two kinds of different qualities so that under same discharge energy, drift can obtain two kinds of different grades of speed.

Pitman 13 passes in the stopper slot 15 on lifting support 9 so that drift 8 can only move up and down.Drive block 12 and the stroke that distance is drift 8 of adjustable bump rubber 14 on stopper slot 15; this distance is slightly larger than the distance of drift 8 to lower platen damping rubber block 18; ensure that plate camera before rupturing can photograph the photo of plate clearly; the kinetic energy of drift 8 is mainly absorbed by adjustable bump rubber 14; excessive remaining kinetic energy will be by drift damping rubber block 18, and it will play a protective role simultaneously.

Block rubber 14 hoop designed openings so that it need not dismantle drive block 12, pitman 13, the connection of drift 8, and take out pitman 13 and just can change block rubber.

The data collecting system of the experiment of sheet metal high-speed molding limit experimental provision includes that two high-speed cameras being arranged symmetrically 20, high-speed camera 20 axis can intersect at a point all the time；Also include one vertically arranged, in real time measure drift 8 and two camera focuses the laser range finder 22 of straight vertical dimension.

High-speed camera 20 is arranged on camera bearing 21, laser range finder is arranged in the circular hole of damping rubber block bearing 19 central authorities, damping rubber block bearing 19 is fixed on immediately below drift 8, its central circular hole just to drift 9 central authorities on it circular groove be placed with the drift damping rubber block 18 of same central openings.

The control circuit of sheet metal high-speed molding limit experimental provision includes circuit general switch 23, transformator 24, electric capacity charge switch 25, protects electric capacity 26, high-voltage rectifier bridge 27, Capacitor banks 28, drift emission switch 29, protective resistance 30, rectifier bridge 31.

Control circuit part uses mains-supplied, the keying of circuit general switch 23 control circuit, charged for high-voltage capacitor group by transformator 24 and high-voltage rectifier bridge 27, the voltage of Capacitor banks 28 and capacitance can be by changing connection in series-parallel electric capacity quantity regulating, to change discharge energy, regulate drift 8 speed.

Capacitor charge switch 25 controls the break-make of Capacitor banks 28；Protection electric capacity 26 by the alternating current in certain limit, and can block the reverse breakdown unidirectional current caused due to too high capacitor bank voltage, for the safety of protective condenser group 28 charging circuit.

Firing button 29 controls electric discharge and the power-off of electric magnet 16 of Capacitor banks 28 simultaneously, and during by low punch firing button 29, plate coil 12 is discharged by Capacitor banks 28, simultaneously electric magnet 16 power-off, is launched by drift 8.Electric magnet 16 head design has collision block, when armature clashes into collision block when, can play firing button 29 by appliance for releasing single, and Capacitor banks 29 path disconnects, and electric magnet 16 is energized, and holds drift 8, thus fixing before facilitating the experiment of drift 8.

The data collecting system of experiment can also use plane mirror system that camera is arranged on other places, but its equivalent light path should meet aforementioned claim.Design to restriction, damping rubber block bearing 19 and the die socket 2 of drift 8 range of movement can be played expensive high-speed camera 20 Pleiotropic Protections so that it is will not be broken by drift 8 out of control.

Utilize above-mentioned experimental facilities to carry out the method tested additionally, present invention also offers, specifically include following steps:

Step 1, start experiment before, confirm that electric capacity charge switch 25 is off, emission switch 29 is in transmitting gear, treats that Capacitor banks 28 discharge, and to ensure circuit safety, plate coil will not burn, and Capacitor banks adjusts front electric capacity and is in not charged state.Opening laser range finder 22, then after two blocks of armature 17 on drift 8 are directed at electric magnet suction nozzle 16 and drift 8 round end top alignment laser facula, make armature 17 clash into the collision block of electric magnet 16 head, emission switch 29 is bound to electromagnetism adhesive gear, closes circuit general switch 23.

Step 2, making test plate 4.

Square net is printed on test plate 4.Grid is the least, tests the most accurate.

Step 3, rise lifting support 9, rise blank holder 6, test plate 4 is placed with on die 3；

To make the upper grid lines of test plate (4) be parallel or perpendicular to the camera axis place plane of two high-speed cameras (20) during placement as far as possible, facilitate the data of subsequent pictures to process, close blank holder 6, compress plate 4.This step can change different blank holder bead height according to each experiment needs.

Step 4, fall lifting support 9, make drift 8 press close to plate 4；

But a segment distance need to be reserved, its purpose is to make drift 8 have the acceleration distance of abundance to complete moment acceleration, after completing to accelerate, drift relies on inertia high speed impact plate 4, plate 4 will be risen brokenly within the extremely short time, simultaneously because the compensating action of gravity, it is believed that plate is during being risen brokenly, and strain rate change is little.

Step 5, two high-speed camera 20 angles of adjustment, make the mesh point that imaging center is all irradiated by laser facula in alignment with plate 4, and this can make two captured images all without being blocked a part owing to panel surface arches upward.Record two cameras and the acute angle theta folded by vertical curve₁,θ₂.The two angle will be used for follow-up image procossing.

Step 6, the pressure voltage adjusting Capacitor banks 28 and capacitance, adjust transformer voltage value corresponding with Capacitor banks 28 pressure voltage.Guan Bi capacitor charging 25 switch, completes the charging of Capacitor banks 28.

Step 7, complete charging after, it is ensured that disconnect capacitor charge switch 25.

If the most directly pressing emission switch 29, plate coil 11 may burn.One fusing insurance can be set.

Step 8, open high-speed camera 20, confirm that laser range finder 22 is opened, carry out photographing unit 20 initially focus, image length to mark, measuring and calculating initial rapid photographing unit length d₁,d₂(high-speed camera focus is to the distance of initial focusing).

Step 9, to high-speed camera 20, both laser range finders 22 time is carried out mark, then presses emission switch 29.The time of carrying out, to target purpose, is the strain data making high-speed camera record, and the punch stroke of laser range finder record, unifies in time, to avoid the calculating of strain rate to produce error.Drift 8 is launched, and the plate 4 having printed grid will be recorded by high-speed camera 20 by high speed bulging, Bulging Process, until drift 8 reaches range, remaining kinetic energy is absorbed by adjustable bump rubber 14 and buffer 18.Closing high-speed photographing unit 20, disconnects main power after test, confirm that electric capacity charge switch is off.Breakdown point is found according to the photo of high-speed camera shooting, strain rate when confirming to rupture, try to achieve breaking strain.

Experimental provision based on the present invention, present invention also offers one and determines captured space middle conductor length by two high-speed cameras and laser range finder and sit calibration method, and step is as follows:

Step 1. sets up real space coordinate system, and in the plane of two high-speed camera axes intersect, in agreement space, laser range finder focus is initial point, and horizontal direction is x-axis, and vertical direction is z-axis, and vertical x z-plane direction is y-axis, as shown in Figure 7.

Step 2. sets up image coordinate system, laser range finder focus in the captured image of agreement, namely laser range finder focus is projected as initial point on imaging plane in space, two high-speed camera imaging planes set up a with space on the intersection of the plane of two high-speed camera axes intersect respectively₁,a₂Axle, b is set up in vertical intersection direction₁,b₂Axle, as shown in Figure 7.

Any straight line, its a length of l in step 3. space_R, it is projected in the plane of two high-speed camera axes intersect, projected length is l, as shown in Figure 7, it is known that

$l_R^2=l^2+l_y^2---\left(1\right)$

Wherein l_yIt it is space line projected length on the y axis.

Therefore, we have only to know respectively l and l_yLength i.e. may know that l_RLength.

Step 4. seeks l_y, pinhole imaging system principle the projected length and the length positive correlation of b axle, the i.e. l on image that are apparent from y-axis_y=k_b1l_b1=k_b2l_b2, therefore

$l_R^2=l^2+{\left(k_b{l}_b\right)}^2---\left(2\right)$

Wherein, k_bBe the image that determines of high-speed camera length d at the midpoint that focus based on corresponding high-speed camera projects on the y axis to space line to mark coefficient, first we will use initial rapid photographing unit length d previously calculated₁,d₂。

Step 5. seeks l, as shown in Figure 7, l length shown on single camera image, can not the actual length of l in direct reaction space, but by the relation of the different length that l in two cameras is reacted, and camera shutter can obtain the length of l to the distance (camera length) at the midpoint of projection straight line l, concrete grammar is as follows:

Two high-speed camera axis and the angle theta of vertical curve₁,θ₂It is known that in measurement image coordinate system, space line is respectively at a₁,a₂Length l on axle₁,l₂, they relations in the plane of two high-speed camera axes intersect as it is shown in fig. 7, may certify that,

$l^2={\[\frac{k_{a1}{l}_1}{sin({\mathrm{\θ}}_1+{\mathrm{\θ}}_2)}\]}^2+{\[\frac{k_{a2}{l}_2}{sin({\mathrm{\θ}}_1+{\mathrm{\θ}}_2)}\]}^2-\frac{2k_{a1}{k}_{a2}{l}_1{l}_{2}cos({\mathrm{\θ}}_1+{\mathrm{\θ}}_2)}{{\[sin({\mathrm{\θ}}_1+{\mathrm{\θ}}_2)\]}^2}---\left(3\right)$

Wherein, k_a1And k_a2It is camera length d based on corresponding camera respectively_a1,d_a2To mark coefficient, (midpoint of straight line on image might not be presented as in the midpoint of space line projection straight line to the image determined, this needs according to high-speed camera axis and straight line relative tilt angle and the measuring and calculating of high-speed camera length, high-speed camera length is the biggest, relative tilt angle is closer to right angle, closer to midpoint), first we will use initial rapid photographing unit length d of previously measuring and calculating₁,d₂。

Simultaneous formula (2), (3), can space length be asked

$l_R^2={\left(k_b{l}_b\right)}^2+{\[\frac{k_{a1}{l}_1}{sin({\mathrm{\θ}}_1+{\mathrm{\θ}}_2)}\]}^2+{\[\frac{k_{a2}{l}_2}{sin({\mathrm{\θ}}_1+{\mathrm{\θ}}_2)}\]}^2-\frac{2k_{a1}{k}_{a2}{l}_1{l}_{2}cos({\mathrm{\θ}}_1+{\mathrm{\θ}}_2)}{{\[sin({\mathrm{\θ}}_1+{\mathrm{\θ}}_2)\]}^2}---\left(4\right)$

May determine that the space coordinates of straight line end points, in can asking for as shown in Figure 7, space line is projection line l and horizontal angle theta in high-speed camera axial plane simultaneously_l, may certify that

${\mathrm{cos\θ}}_l=\[l^2+{\left(\frac{k_{a2}{l}_2}{{\mathrm{cos\θ}}_2}\right)}^2-{\left(\sqrt{l^2-k_{a2}^2{l}_2^2}-k_{a2}{l}_2{\mathrm{tan\θ}}_2\right)}^2\]/\left(\frac{2k_{a2}{\mathrm{ll}}_2}{{\mathrm{cos\θ}}_2}\right)---\left(5\right)$

Or

${\mathrm{cos\θ}}_l=\[l^2+{\left(\frac{k_{a1}{l}_1}{{\mathrm{cos\θ}}_1}\right)}^2-{\left(k_{a1}{l}_1{\mathrm{tan\θ}}_1-\sqrt{l^2-k_{a1}^2{l}_1^2}\right)}^2\]/\left(\frac{2k_{a1}{\mathrm{ll}}_1}{{\mathrm{cos\θ}}_1}\right)---\left(6\right)$

So can the most tentatively try to achieve the x of space line, z-axis coordinate figure lcos θ_l,lsinθ_l, and y-axis coordinate figure is exactly k_bl_b, this coordinate figure is based on the space coordinates with one end points of space line as initial point, and we also to try to achieve it and set up the coordinate figure in coordinate system in step 1, and this is accomplished by trying to achieve end points to the distance between laser focusing point according to the method for step 3～5.

But the coordinate figure tried to achieve at present is inaccurate, because the camera length now used incorrect, a simply estimated value, accordingly, it would be desirable to revise camera length.The present invention uses the method for optimization to obtain real camera length.

According to current high-speed camera length and axis angle θ₁,θ₂, by pinhole imaging system principle, can calculate in the image of shooting, the actual line segment midpoint (and the non-image section of reaching the standard grade midpoint) of space projection straight line l.On image, midpoint is to the distance at the two ends relational expression more following than meeting:

$\frac{s_1}{s_2}=\frac{d_a-0.5lcos({\mathrm{\θ}}_{1,2}\±{\mathrm{\θ}}_l)}{d_a+0.5lcos({\mathrm{\θ}}_{1,2}\±{\mathrm{\θ}}_l)}---\left(7\right)$

Wherein, s₁And s₂Be respectively on image the midpoint of actual straight line to the minor face of image middle conductor end points and long edge lengths.As shown in Figure 7.

For the line segment l in the y-axis of space_y, its midpoint also is indicated as midpoint on image, thus revises line segment midpoint spatial value further.

The coordinate that step 6. is finally tried to achieve by step 5, the distance of this moment space coordinates initial point recorded by laser range finder to two high-speed camera focus lines, punch diameter 100mm, the angle theta of two high-speed camera axis and vertical curve₁,θ₂, space geometry relation try to achieve corresponding high-speed camera length d_a1,d_a2,d_b1,d_b2, (distance at the high-speed camera a length of spatial line segment midpoint tried to achieve to high-speed camera focal plane) correction map picture is to mark coefficient k_a1,k_a2,k_b1,k_b2, its relation is

$\frac{k^{\′}}{k}=\frac{d^{\′}}{d}---\left(8\right)$

Wherein k', d' and k, d represent that image that mark coefficient, high-speed camera length and previous step use by the image of correction is to mark coefficient, high-speed camera length respectively.

Step 7. uses the data revised, and constantly repeats step 3～6, until being tried to achieve difference limits of error δ less than an agreement of twice coordinate.

Step 8. due on plate grid be on the disc of drift 8, punch radius R, sheet thickness t it is known that chord length turns arc length, grid lines physical length s after deformation_RHave

$s_R=2(R+t)arcsin\[\frac{l_R}{2(R+t)}\]---\left(9\right)$

Here after have ignored sheet metal deformation, the change of sheet thickness t.s_RIt is required, can be used for calculating strain, and continuous two pictures calculate gained strain, can be used for calculating strain rate.

In order to improve computational efficiency, reducing and calculate intensity, according to test needs, above computational methods can be by following several ways reduction amount of calculation:

1. by the picture of experimental record, determine the initial rupture position of plate, only the grid being in initial rupture position is carried out as above trace analysis.

2. using plane mirror system, change the position of photographing unit, make camera focus the longest to the distance of shooting point, the photographing unit length change caused during such sheet metal deformation is relatively small, and calculating convergence will faster.Meanwhile, plane mirror system is used can also preferably to protect photographing unit.

3., when calculating the strain rate in deformation process and strain, if photographing unit length is longer, mark coefficient can not be modified by image, or revise at a certain distance once.

Above-described detailed description of the invention, has carried out further detailed description to the present invention, the foregoing is only a kind of detailed description of the invention of the present invention, is not limited to the present invention.The mode such as compressing blank holder can use the hydraulic cylinder of hydraulic pump drive.The photographing unit that experiment uses can be arranged in bottom, and bottom can use two plane mirrors to replace, and two high-speed cameras are arranged in the light path of plane mirror.Also include using existing DIC equipment and flat-bottom punch.The one that especially present invention provides determines captured space middle conductor length by two photographing units and laser range finder and sits calibration method, it is not limited to the mode using print grid described in this patent, it further comprises and sprays speckle at plate, use the image processing techniques being similar to DIC, by the way of image transition matrix, it is achieved On-line data processing.

Claims (1)

1. a sheet metal high-speed molding limit test method, it is characterised in that comprise the following steps:

Step 1, start experiment before, confirm electric capacity charge switch (25) be off, emission switch (29) It is in transmitting gear, treats that Capacitor banks (28) has discharged；Open laser range finder (22), then by drift (8) After upper two pieces of armature (17) alignment electric magnet suction nozzle (16) and drift (8) round end top alignment laser facula, make Armature (17) clashes into the collision block of electric magnet (16) head, and emission switch (29) is bound to electromagnetism adhesive gear, Guan Bi Circuit general switch (23)；

Step 2, making test plate (4)；

Step 3, rise lifting support (9), rise blank holder (6), test plate (4) is placed and die (3) On；

Step 4, fall lifting support (9), make drift (8) press close to test plate (4)；

Step 5, two high-speed camera (20) angles of adjustment, make imaging center all in alignment with test plate (4) The mesh point irradiated by laser facula, records two cameras and the acute angle theta folded by vertical curve₁And θ₂；

Step 6, the pressure voltage adjusting Capacitor banks (28) and capacitance, adjust transformer voltage value and Capacitor banks (28) pressure voltage is corresponding；

Step 7, complete charging after, disconnect capacitor charge switch (25)；

Step 8, open high-speed camera (20), confirm that laser range finder (22) is opened, carry out high-speed camera (20) initial focusing, image length to mark, initial camera length d of two high-speed cameras of measuring and calculating₁And d₂, i.e. High-speed camera focus is to the distance of initial focusing；

Step 9, to high-speed camera (20), the two time of laser range finder (22) is carried out mark, presses transmitting Switch (29)；Drift (8) is launched, and plate (4) is by high speed bulging, and Bulging Process will be by high-speed camera (20) Recording, until drift (8) reaches range, remaining kinetic energy is by adjustable bump rubber (14) and buffering Device (18) absorbs；Closing high-speed photographing unit (20), disconnects main power after test, confirm that electric capacity charge switch is in Off-state；Breakdown point is found according to the photo of photographing unit shooting, strain rate when confirming to rupture, try to achieve breaking strain.