CN104438538A - Three-dimensional curved surface stretch forming method based on surface-changing discrete mould - Google Patents

Abstract

The invention provides a three-dimensional curved surface stretch forming method based on a surface-changing discrete mould, and belongs to the field of metal plastic machining. Nonuniform deformation of a plate in the stretch forming process is the main cause of kinds of defects. According to the method, based on the discrete mould, the forming process of a curved surface is controlled through the change of the mould surface. In the forming process, the plate is kept completely attached to the mould surface all the time, the continuous and uniform change of the mould surface makes the deformation of the plate more and more uniform, the forming defects are avoided, and a high-quality curved-surface part can be obtained through stretch forming. The discrete mould is composed of regularly-arrayed basic body units, and real-time control over the geometrical shape of the surface of the stretch forming mould is achieved by changing the height of the basic body units. Besides, in the stretch forming process, the plate is clamped by a clamp to rotate along with the change of the mould surface, the clamp does not need to move in the horizontal direction or height direction, and therefore a loading structure of stretch forming equipment can be simplified through the forming method.

Description

Based on the three-dimension curved surface method of stretch forming of modification face discrete type mould

Technical field

The invention belongs to Metal Forming field, relate to a kind of sheet forming method, be applicable to the stretch forming of large-scale three dimensional curved surface part.

Background technology

Stretch forming is the important processing mode of one of large-scale curved part.The changeless pull-shaped mould of the pull-shaped employing profile of tradition, the geometry of die face is according to the curved surface part design that will be shaped.In forming process, pull-shaped mould ambilateral clamp clamping plate two ends, by the motion of clamp, plate is contacted gradually with mould, completely last and mould is fitted and is formed curved surface part.Adopt that traditional fixed face mould tool is pull-shaped easily causes distortion uneven, cause break, the wrinkling and defect such as skid wire, coarse-grain, these problems are particularly outstanding when the material forming that the deflection such as aluminium alloy, titanium alloy controlled range is very little.In addition, mould difficult problem is pasted in traditional pull-shaped also existence, and be ensure to paste moulds, plate must leave unsettled section of sufficient length, causes forming larger process residue after being shaped.For improving distortion distribution, improving the subsides mould state of plate, people have carried out many research work in clamp movement locus optimal design, but these problems are difficult to thoroughly solve.

Modification face mould tool is adopted to carry out three-dimension curved surface stretch forming, make plate keep fitting completely with die face all the time in forming process, can realize being out of shape homogenising, and the bad problem of subsides mould can be solved, avoid defect to produce, improve the stretch forming quality of curved surface part.

Summary of the invention

Object of the present invention is: easily occur inhomogeneous deformation for traditional fixed face mould tool is pull-shaped, thus cause the problem of various defect on formation of parts, the present invention will provide a kind of three-dimension curved surface method of stretch forming based on modification face discrete type mould, by the forming process of the change Control curve of die face, in forming process, plate is fitted completely with die face all the time, the distortion of plate is made to be tending towards even, thus avoid various forming defects to produce, obtain high-quality stretch forming curved surface part.

Above-mentioned purpose of the present invention is achieved through the following technical solutions, and accompanying drawings is as follows:

A kind of three-dimension curved surface method of stretch forming based on modification face discrete type mould, the discrete type mould 2 variable using profile and clamp 3 are as forming tool, it is characterized in that: the method passes through the consecutive variations of curve form along with discrete type mould 2 and the conformal rotation of clamp 3 of die face 1, the plate 4 that clamp 3 is clamped is while maintenance is fitted completely with die face 1, stretcher strain gradually, finally forms three-dimension curved surface part 5;

Described discrete type mould 2 arranges an element body unit 6 by the capable n of regularly arranged m and forms.In plate 4 stretch forming process, the change of die face 1 is changed by the relative altitude of each element body and controls, and the motion of discrete type mould 2 comprises the relative motion of short transverse between each element body unit 6 in the lifting of discrete type mould 2 entirety and discrete type mould 2;

Described clamp 3 clamps plate 4, in stretch forming process, rotate, but the position of occurred level and short transverse is not moved with the tangential variations at die face 1 edge;

The motion of described discrete type mould 2 and the rotation of clamp 3 ensure that plate 4 is fitted completely with die face 1 all the time in forming process, make distortion be tending towards even, obtain high-quality stretch forming curved surface part 5;

The concrete steps of the control forming process of the method are as follows:

A. the initial profile of discrete type mould 2 is adjusted to plane, and clamp 3 clamps plate 4, fits with the initial plane of mould;

B. according to the shape of profile surface, at the uniform velocity rise based on each element body unit 6 and the principle of clamp 3 uniform rotation, determine the hard-over θ of short transverse displacement w at each element body of forming process t and clamp _maxand the amount of movement d in discrete type mould 2 whole height direction;

C. according to the short transverse displacement w of required element body unit 6 and the global displacement d course over time of discrete type mould 2, control moving up and down of discrete type mould 2 and each element body unit 6, carry out the stretch forming of three-dimension curved surface.

Wherein, determine in step c that each element body unit 6 of discrete type mould in the detailed process of forming process t z direction displacement and the overall z direction displacement of discrete type mould 2 is:

A. the coordinate x at element body unit 6 center of the i-th row jth row is extracted _ijand y _ij(i=1,2 ..., m; J=1,2 ..., n; Wherein m is the line number of element body unit 6, and n is the columns of element body unit 6); Determine the maximum tangential tilt θ of discrete type mould 2 edges at two ends place curved surface _max, and determine the surface parameter equation of three-dimension curved surface part 5:

$P(u,v)=\left\{\begin{array}{c}x(u,v)\\ u(u,v)\\ z(u,v)\end{array}\right\}---I$

Wherein x, y are the coordinate of horizontal direction, and z is short transverse coordinate; U, v are the parameter coordinate of three-dimension curved surface part 5;

B. solving equation II, calculates the element body unit 6 of the i-th row jth row and the parameter coordinate u of the contact point of three-dimension curved surface part 5 _iand v _j

$\left\{\begin{array}{c}x(u_i,v_j)-(r+H+\frac{h}{2})n_x(u_i,v_j)=x_{\mathrm{ij}}\\ y(u_i,v_j)-(r+H+\frac{h}{2})n_y(u_i,v_j)=y_{\mathrm{ij}}\end{array}\right.(i=\mathrm{1,2},...,m;j=\mathrm{1,2},...,n)---\mathrm{II}$

Wherein x (u _i, v _j), y (u _i, v _j) provided by profile surface equation I, r is the Probe-radius of element body unit (6), and h is plate 4 thickness, and H is the thickness of cushion 7, n _x(u _i, v _j) and n _y(u _i, v _j) be normal component outside the unit of three-dimension curved surface part 5, calculated by following formula

$n(u_i,v_j)=\left\{\begin{array}{c}{n}_x(u_i,v_j)\\ n_y(u_i,v_j)\\ n_z(u_i,v_j)\end{array}\right\}=\frac{\frac{\∂P(u_i,v_j)}{\∂u}\×\frac{\∂P(u_i,v_j)}{\∂v}}{|\frac{\∂P(u_i,v_j)}{\∂u}\×\frac{\∂P(u_i,v_j)}{\∂v}|}---\mathrm{III}$

Wherein P (u _i, v _j) provided by profile surface equation (I);

C. the final height at the end of the element body utilizing equation IV to calculate the i-th row jth row is shaped

${z^f}_{\mathrm{ij}}=z(u_i,v_j)-(r+H+\frac{h}{2})n_z(u_i,v_j)+r,(i=\mathrm{1,2},..,m;j=\mathrm{1,2},..,n)---\mathrm{IV}$

Wherein z (u _i, v _j) provided by profile surface equation I, normal component n outside the unit of curved surface _z(u _i, v _j) provided by equation III;

D. equation V is utilized to calculate the z direction displacement of element body unit 6 in t of the i-th row jth row of discrete type mould 2

$w_{\mathrm{ij}}\left(t\right)=({z^f}_{\mathrm{ij}}-z_{\min })\frac{t}{T},(i=\mathrm{1,2},...,m;j=\mathrm{1,2},...,n)---V$

Wherein z _minfor the minimum of a value in the final height of element body unit (6) that equation (IV) calculates, T is the total time that stretch forming needs;

Equation VI is utilized to calculate the global displacement of discrete mold 2 in the z direction of t

$d\left(t\right)=\frac{l{\mathrm{\θ}}_{\max }}{T}t---\mathrm{VI}$

Wherein l is the distance of die edge to clamp, θ _maxfor the maximum tangential tilt of both mold ends edge curved surface.

In the method for the invention, described element body unit 6 is made up of cell cube 8, element body adjusting lever 9 and element body control unit 10, described element body control unit 10 comprises adjusts shape motor, decelerator and encoder, and the height of element body unit 6 is controlled in real time by element body control unit 10; Regularly arranged m capable n row element body unit fixedly forms the variable discrete type mould 2 of profile by fixed head and base 11.

Further, between discrete type mould 2 and plate 4, use cushion 7, to avoid occurring impression on the curved surface part be shaped.

Further, described cushion 7 can adopt polyurethane sheet or rubber slab.

Compared with prior art the invention has the beneficial effects as follows:

Because plate is contacted by cushion all the time completely with die face in curve generating process, the distortion of plate can be made to be tending towards even, thus the generation of various forming defects can be avoided, obtain high-quality curved surface part; In addition, compared with the pull-shaped technology of existing employing fixed face mould tool, improve and paste mould state, can significantly reduce technique clout, save material; Finally, in stretch forming process, clamp clamping plate rotates with the change of die face, and clamp does not need the motion of level and short transverse, and thus this manufacturing process can also simplify the loading structure of pull-shaped equipment.

Accompanying drawing explanation

Fig. 1 is modification face of the present invention discrete type mould structure schematic diagram;

Fig. 2 is modification face of the present invention discrete type mould Stretch Forming Process schematic diagram;

Fig. 3 is element body cellular construction schematic diagram;

Fig. 4 is clamp corner, suspension area length and discrete type mold integral displacement diagram;

Fig. 5 is t i-th row jth row element body cell height direction displacement diagram;

Fig. 6 is the sphere drip molding equivalent strain distribution map adopting modification face discrete type mould pull-shaped;

Fig. 7 is the sphere drip molding equivalent strain distribution map adopting traditional fixed face mould tool pull-shaped;

Fig. 8 is that modification face is pull-shaped and tradition is pull-shaped sphere drip molding is along the strain comparison diagram that draw direction symmetry axis distributes;

Fig. 9 is that modification face is pull-shaped and tradition is pull-shaped sphere drip molding is along the strain comparison diagram that stretched vertically direction symmetry axis distributes.

In figure:

1. die face, 2. discrete type mould, 3. pulling-in dog, 4. plate, 5. three-dimension curved surface part, 6. element body unit, 7. cushion, 8. cell cube, 9. element body adjusting lever, 10. element body control unit, 11. fixed heads and base.

The whole height direction amount of movement of d-discrete type mould

θ-clamp anglec of rotation

Z _minminimum of a value in the final height of-element body unit

L-die edge is to the distance of clamp

Z _ijthe final height of the element body unit of the-the i-th row jth column position

R-element body unit Probe-radius

Detailed description of the invention

Detailed content of the present invention and detailed description of the invention thereof is further illustrated below in conjunction with Figure of description:

As depicted in figs. 1 and 2, the discrete type mould 2 of stretch forming is made up of regularly arranged m capable n row element body unit 6.In the stretch forming process of plate 4, the change of die face 1 is changed by the relative altitude of each element body and controls, and the motion of discrete type mould 2 comprises the relative motion in the lifting of discrete type mould 2 entirety and discrete type mould 2 between each element body unit 6.

As shown in Figure 2 and Figure 4, clamp 3 clamps plate 4, in stretch forming process, rotate, but the position of occurred level and short transverse is not moved with the tangential variations at die face 1 edge.

As shown in Figure 2 and Figure 4, ensure that plate 4 is fitted completely with die face 1 all the time in forming process by the motion of discrete type mould 2 and the rotation of clamp 3, make distortion be tending towards even, obtain the three-dimension curved surface part 5 of high-quality stretch forming.

As shown in Figure 2, the concrete steps based on the control forming process of the three-dimension curved surface method of stretch forming of modification face discrete type mould are as follows:

A. the initial profile of discrete type mould 2 is adjusted to plane, clamp 3 clamps plate 4, fits, is set as the initial time of forming process this moment with the initial plane of discrete type mould 2;

B. according to the shape of three-dimension curved surface part 5, at the uniform velocity rise based on each element body unit 6 and the principle of clamp 3 uniform rotation, determine the hard-over θ of short transverse displacement w at each element body unit 6 of forming process t and clamp 3 _maxand the whole height direction amount of movement d of discrete type mould 2;

C. according to required element body unit 6 displacement w and discrete type mould 2 global displacement d course over time, control the motion of discrete type mould 2 and each element body unit 6, carry out the stretch forming of three-dimension curved surface.

As shown in Figure 4 and Figure 5, determine that each element body unit 6 of discrete mold in the detailed process of forming process t z direction displacement and mold integral z direction displacement is:

A. the coordinate x of each element body center in x, y direction is determined _ijand y _iji=1,2 ..., m; J=1,2 ..., n; The wherein columns of m to be the line number n of element body be element body; Determine the maximum tangential tilt θ of both mold ends edge curved surface _max, and determine the parametric equation of three-dimension curved surface part 5:

$P(u,v)=\left\{\begin{array}{c}x(u,v)\\ u(u,v)\\ z(u,v)\end{array}\right\}---I$

Wherein u, v are the parameter coordinate of curved surface.

B. solving equation II, calculates the parameter coordinate u of the element body of the i-th row jth row and the contact point of target three-dimension curved surface part 5 _iand v _j

$\left\{\begin{array}{c}x(u_i,v_j)-(r+H+\frac{h}{2})n_x(u_i,v_j)=x_{\mathrm{ij}}\\ y(u_i,v_j)-(r+H+\frac{h}{2})n_y(u_i,v_j)=y_{\mathrm{ij}}\end{array}\right.(i=\mathrm{1,2},...,m;j=\mathrm{1,2},...,n)---\mathrm{II}$

Wherein x (u _i, v _j), y (u _i, v _j) provided by profile surface equation I, r is element body Probe-radius, and h is plate 4 thickness, and H is the thickness of cushion 7, n _x(u _i, v _j) and n _y(u _i, v _j) be normal component outside the unit of curved surface, calculated by following formula

$n(u_i,v_j)=\left\{\begin{array}{c}{n}_x(u_i,v_j)\\ n_y(u_i,v_j)\\ n_z(u_i,v_j)\end{array}\right\}=\frac{\frac{\∂P(u_i,v_j)}{\∂u}\×\frac{\∂P(u_i,v_j)}{\∂v}}{|\frac{\∂P(u_i,v_j)}{\∂u}\×\frac{\∂P(u_i,v_j)}{\∂v}|}---\mathrm{III}$

C. the final height at the end of the element body utilizing equation IV to calculate the i-th row jth row is shaped

${z^f}_{\mathrm{ij}}=z(u_i,v_j)-(r+H+\frac{h}{2})n_z(u_i,v_j)+r,(i=\mathrm{1,2},..,m;j=\mathrm{1,2},..,n)---\mathrm{IV}$

Wherein z (u _i, v _j) provided by profile surface equation I, normal component n outside the unit of curved surface _z(u _i, v _j) provided by equation III.

D. equation V is utilized to calculate the z direction displacement of element body in t of the i-th row jth row of discrete mold 2

$w_{\mathrm{ij}}\left(t\right)=({z^f}_{\mathrm{ij}}-z_{\min })\frac{t}{T},(i=\mathrm{1,2},...,m;j=\mathrm{1,2},...,n)---V$

Equation VI is utilized to calculate the global displacement of discrete mold 2 in the z direction of t

$d\left(t\right)=\frac{l{\mathrm{\θ}}_{\max }}{T}t---\mathrm{VI}$

Wherein z _minfor the minimum of a value in the final height of element body that equation IV calculates, T is the total time that stretch forming needs, and l is the distance of die edge to clamp, θ _maxfor the maximum tangential tilt of both mold ends edge curved surface.

As shown in Figure 3, the element body unit 6 of discrete type mould 2 is made up of cell cube 8, element body adjusting lever 9 and element body control unit 10, element body control unit 10 comprises adjusts shape motor, decelerator and encoder, and the height of element body is controlled in real time by element body control unit 10.Regularly arranged m capable n row element body unit fixedly forms the variable discrete type mould 2 of profile by fixed head and base 11.

As shown in Figure 2 and Figure 4, should use cushion 7 between discrete mold 2 and plate 4, to avoid occurring impression on the curved surface part be shaped, and cushion 7 can adopt polyurethane sheet or rubber slab.

Specific embodiment

Plate 4 is 400mm × 240mm, thickness h=1mm; The target surface of three-dimension curved surface part 5 is the sphere of radius 360mm, and discrete type mould 2 area that is shaped is 250mm × 250mm; Discrete type mould 2 is made up of 10 × 10 element body unit 6, and element body is of a size of 25mm × 25mm, element body unit 6 Probe-radius r=15mm; Discrete type mould 2 edge is l=45mm to the distance of clamp 3, and cushion 7 is the polyurethane sheet of thickness H=30mm.

Concrete steps based on the control forming process of the three-dimension curved surface method of stretch forming of modification face discrete type mould are:

The first step: the initial profile of discrete type mould 2 is adjusted to plane, clamp 3 clamps plate 4 and fits with the initial plane of mould;

Second step: the coordinate x of center in x, y direction determining each element body unit 6 of discrete type mould 2 _ijand y _ij:

$\left\{\begin{array}{c}{x}_{\mathrm{ij}}=25(i-1)+12.5\\ y_{\mathrm{ij}}=25(j-1)+12.5\end{array}\right.(i=\mathrm{1,2},...,10;j=\mathrm{1,2},...,10)$

The maximum tangential tilt determining discrete type mould 2 edges at two ends place curved surface is θ _max=19.47 °, and the parametric equation determining profile surface:

Wherein R=360mm is the radius of sphere, be that the parameter coordinate of profile surface is (namely in equation I with θ v=θ).

3rd step: according to equation II, the parameter coordinate of the element body unit 6 arranged by equation solution i-th row jth below and target profile surface contact point and θ _j

Wherein spherical radius R=360mm, the Probe-radius r=15mm of element body unit 6, sheet thickness h=1mm, cushion thickness H=30mm, with for normal component outside the unit of profile surface;

4th step: according to equation IV, calculates the final height at the end of element body unit 6 that the i-th row jth arranges is shaped by equation below

Wherein for normal component outside the unit of profile surface;

5th step: the z direction displacement of element body unit 6 in t calculating the i-th row jth row of discrete type mould 2 according to equation V

$w_{\mathrm{ij}}\left(t\right)=({z^f}_{\mathrm{ij}}-z_{\min })\frac{t}{T},(i=\mathrm{1,2},...,10;j=\mathrm{1,2},...,10)$

The global displacement of discrete type mould 2 in the z direction of t is calculated according to equation VI

$d\left(t\right)=l{\mathrm{\θ}}_{\max }\frac{t}{T}$

Wherein z _minfor the minimum of a value in the final height of element body unit 6, T is the total time that stretch forming needs, discrete type mould 2 edge to the distance l=45mm of clamp, the maximum tangential tilt θ of discrete type mould 2 edges at two ends place curved surface _max=19.47 °.

The numerical simulation result of the draw direction Strain Distribution of the sphere drip molding adopting the three-dimension curved surface method of stretch forming of modification face discrete type mould and the pull-shaped mode of tradition to be shaped is provided by Fig. 6, Fig. 7, longitudinally provided by Fig. 8, Fig. 9 with the Strain Distribution on lateral symmetry axis, the maximum that the longitudinal direction of spherical parts and lateral symmetry axis strain, minimum of a value contrast as follows:

Compared with the pull-shaped mode of tradition, its plastic strain amplitude of curved surface that discrete type mould pull-shaped method in modification face is shaped significantly declines, and Strain Distribution degree of irregularity is greatly improved.Adopt the maximum strain on the pull-shaped method longitudinal axis of modification face discrete type mould to have dropped 11.6%, maximum strain and minimum strain difference have dropped 72%; Maximum strain on axis of pitch have dropped 11.6%, and minimum strain have dropped 18%.

Claims (6)

1. the three-dimension curved surface method of stretch forming based on modification face discrete type mould, using discrete type mould (2) and clamp (3) as forming tool, it is characterized in that: the method is changed along with the consecutive variations of discrete type mould (2) and the conformal rotation of clamp (3) by the curve form of die face (1), the plate (4) that clamp (3) is clamped is while maintenance is fitted completely with die face (1), stretcher strain gradually, final formation three-dimension curved surface part (5);

Described discrete type mould (2) arranges an element body unit (6) by the capable n of regularly arranged m and forms, in plate (4) stretch forming process, the change of die face (1) is controlled by the relative altitude change of each element body, and the motion of discrete type mould (2) comprises the relative motion of short transverse between each element body unit (6) in the overall lifting of discrete type mould (2) and discrete type mould (2);

Described clamp (3) clamping plate (4), in stretch forming process, rotate, but the position of occurred level and short transverse is not moved with the tangential variations at die face (1) edge;

The motion of described discrete type mould (2) and the rotation of clamp (3) ensure that plate (4) is fitted completely with die face (1) all the time in forming process, make distortion be tending towards even, obtain high-quality stretch forming curved surface part (5).

2. a kind of three-dimension curved surface method of stretch forming based on modification face discrete type mould as claimed in claim 1, the concrete steps of the control forming process of the method are as follows:

A. the initial profile of discrete type mould (2) is adjusted to plane, and clamp (3) clamping plate (4), fits with the initial plane of mould;

B. according to the shape of profile surface, at the uniform velocity rise based on each element body unit (6) and the principle of clamp (3) uniform rotation, determine the hard-over θ of short transverse displacement w at each element body of forming process t and clamp _maxand the amount of movement d in discrete type mould (2) whole height direction;

C. according to the short transverse displacement w of required element body unit (6) and the global displacement d course over time of discrete type mould (2), control moving up and down of discrete type mould (2) and each element body unit (6), carry out the stretch forming of three-dimension curved surface.

3. the curved surface method of stretch forming based on modification face mould tool according to claim 2, it is characterized in that, in step c, determine that each element body unit (6) of discrete type mould in the detailed process of the direction displacement of forming process t short transverse and the direction displacement of discrete type mould (2) whole height direction is:

A. the coordinate x at element body unit (6) center of the i-th row jth row is extracted _ijand y _ij(i=1,2 ..., m; J=1,2 ..., n; Wherein m is total line number of element body unit (6), and n is total columns of element body unit (6)); Determine the maximum tangential tilt θ of discrete type mould (2) edges at two ends place curved surface _max, and determine the surface parameter equation of three-dimension curved surface part (5):

$P(u,v)=\left\{\begin{array}{c}x(u,v)\\ y(u,v)\\ z(u,v)\end{array}\right\}---\left(I\right)$

Wherein x, y are the coordinate of horizontal direction, and z is short transverse coordinate; U, v are the parameter coordinate of three-dimension curved surface part (5);

B. solving equation (II), calculates the element body unit (6) of the i-th row jth row and the parameter coordinate u of the contact point of three-dimension curved surface part (5) _iand v _j

$\left\{\begin{array}{c}x(u_i,v_j)-(r+H+\frac{h}{2})n_x(u_i,v_j)=x_{\mathrm{ij}}\\ y(u_i,v_j)-(r+H+\frac{h}{2})n_y(u_i,v_j)=u_{\mathrm{ij}}\end{array}\right.(i=\mathrm{1,2},\·\·\·,m;j=\mathrm{1,2},\·\·\·,n)---\left(\mathrm{II}\right)$

Wherein x (u _i, v _j), y (u _i, v _j) provided by profile surface equation (I), r is the Probe-radius of element body unit (6), and h is plate (4) thickness, and H is the thickness of cushion (7), n _x(u _i, v _j) and n _y(u _i, v _j) be normal component outside the unit of three-dimension curved surface part (5), calculated by following formula

$n(u_i,v_j)=\left\{\begin{array}{c}{n}_x(u_i,v_j)\\ n_y(u_i,v_j)\\ n_z(u_i,v_j)\end{array}\right\}=\frac{\frac{\∂P(u_i,v_j)}{\∂u}\×\frac{\∂P(u_i,v_j)}{\∂v}}{|\frac{\∂P(u_i,v_j)}{\∂u}\×\frac{\∂P(u_i,v_j)}{\∂v}|}---\left(\mathrm{III}\right)$

Wherein P (u _i, v _j) provided by profile surface equation (I);

C. the final height at the end of the element body utilizing equation (IV) to calculate the i-th row jth row is shaped

${z^f}_{\mathrm{ij}}=z(u_i,v_j)-(r+H+\frac{h}{2})n_2(u_i,v_j)+r(i=\mathrm{1,2},\·\·\·,m;j=\mathrm{1,2},\·\·\·,n)---\left(\mathrm{IV}\right)$

Wherein z (u _i, v _j) provided by surface parameter equation (I), normal component n outside the unit of curved surface _z(u _i, v _j) provided by equation (III);

D. equation (V) is utilized to calculate the z direction displacement of element body unit (6) in t of the i-th row jth row of discrete type mould (2)

$w_{\mathrm{ij}}\left(t\right)=({z^f}_{\mathrm{ij}}-z_{\min })\frac{t}{T}(i=\mathrm{1,2},\·\·\·,m;j=\mathrm{1,2},\·\·\·,n)---\left(V\right)$

Wherein z _minfor the minimum of a value in the final height of element body unit (6) that equation (IV) calculates, T is the total time that stretch forming needs;

Equation (VI) is utilized to calculate the global displacement of discrete mold (2) in the z direction of t

$d\left(t\right)=\frac{{\mathrm{l\θ}}_{\max }}{T}t---\left(\mathrm{VI}\right)$

Wherein l is the distance of die edge to clamp, θ _maxfor the maximum tangential tilt of both mold ends edge curved surface.

4. a kind of three-dimension curved surface method of stretch forming based on modification face discrete type mould according to claim 1-3, it is characterized in that, described element body unit (6) is made up of cell cube (8), element body adjusting lever (9) and element body control unit (10), described element body control unit (10) comprises adjusts shape motor, decelerator and encoder, and the height of element body unit (6) is controlled in real time by element body control unit (10); Regularly arranged m capable n row element body unit fixedly forms the variable discrete type mould (2) of profile by fixed head and base (11).

5. a kind of three-dimension curved surface method of stretch forming based on modification face discrete type mould according to claim 1-3, it is characterized in that, cushion (7) is used, to avoid occurring impression on the curved surface part be shaped between discrete type mould (2) and plate (4).

6. a kind of three-dimension curved surface method of stretch forming based on modification face discrete type mould according to claim 1-3, it is characterized in that, described cushion (7) can adopt polyurethane sheet or rubber slab.