Form-changing operations of sheet stamping. Forming and flanging

metal hole punching superplasticity

Hole flanging is widely used in stamping production, replacing drawing operations with subsequent cutting of the bottom. Hole flanging is especially effective in the manufacture of parts with a large flange, when drawing is difficult and requires several transitions. At present, holes with a diameter of 3 h 1000 mm and a material thickness of 0.3 h 30 mm are obtained by flanging.

Flanging is understood as the operation of cold sheet stamping, as a result of which a bead is formed along the inner (inner flanging) or outer (outer flanging) contour of the workpiece. Basically, internal flanging of round holes is performed. The formation of the bead in this case is carried out by pressing a part of the workpiece into the hole of the matrix with a punched hole previously or simultaneously with the flanging. The scheme of flanging round holes is shown in Figure 2.1. A variation of flanging is flanging with wall thinning.

Figure 2.1 - Schemes for flanging round holes: a) with a spherical punch; b) cylindrical punch

Flanging of round holes is performed spherical (Figure 2.1 A) or a cylindrical punch (Figure 2.1 b). In the latter case, the working end of the punch is made in the form of a retainer (catcher), which ensures the centering of the workpiece along the hole, with a conical transition to the working part of the diameter d P.

The deformation of the metal during flanging is characterized by the following changes: elongation in the tangential direction and a decrease in the thickness of the material, as evidenced by the radial-annular mesh applied to the workpiece (Figure 2.2). The distances between the concentric circles remain unchanged.

Figure 2.2 - Workpiece before and after flanging

The degree of deformation during the flanging of holes is determined by the ratio between the diameter of the hole in the workpiece d and side diameter D or the so-called flanging factor:

TO = d/D,

Where D determined by the midline (see Figure 2.2).

If the flanging ratio exceeds the limit value TO before, then cracks form on the walls of the board.

The limiting flanging factor for a given material can be analytically calculated using the formula:

where h is the coefficient determined by the flanging conditions;

d is elongation determined from tensile tests.

The value of the limiting flanging coefficient depends on the following factors:

1) the nature of processing and the condition of the edges of the holes (drilling or punching, the presence or absence of burrs);

2) relative workpiece thickness s/D;

3) the type of material and its mechanical properties;

4) the shape of the working part of the punch.

There is a direct dependence of the maximum allowable flanging coefficient on the relative thickness of the workpiece, i.e. with a decrease d/s the value of the maximum allowable flanging coefficient TO before decreases and the degree of deformation increases. In addition, the value TO pre depends on the method of obtaining a flanged hole, as shown in table 2.1 for mild steel. Table 2.2 lists the flanging factor limits for non-ferrous materials.

The allowable value of bead wall thinning during flanging due to hole edge defects (burrs, hardening, etc.) is significantly lower than the value of transverse narrowing during a tensile test. The smallest thickness at the edge of the board is:

Table 2.1 - Estimated values TO pre for mild steel

The calculation of the technological parameters of the flanging of round holes is carried out as follows. The initial parameters are the inner diameter D ext flanged hole and side height H specified by the detail drawing. According to the specified parameters, the required diameter is calculated d technological hole.

Table 2.2 - Values TO pre for non-ferrous metals and alloys

For a relatively high side diameter calculation d are performed based on the equality of the volumes of the workpiece before and after flanging:

Where D 1 = d n + 2( r m+ s).

In this formula, the geometric parameters are determined according to Figure 2.1.

For a low bead, the calculation can be performed from the condition of conventional bending in a radial section:

d = D + 0,86r m - 2 H - 0,57s.

Then check the possibility of flanging in one transition. To do this, compare the flanging factor (see page 14) with the limit value TO before: TO > TO prev.

The flanging force of round holes with a cylindrical punch can be approximately determined by the formula

where s T is the yield strength of the material.

The nature of the change in force during flanging is shown in Figure 2.3, depending on the shape of the outline of the working part of the punch.

Figure 2.3 - Diagrams of force and transitions of flanging of round holes with various punch shapes: a) curvilinear; b) spherical; c) cylindrical

d 0 \u003d A-K (r M + S / 2) -2ft,

Where!)! - outer diameter of the side; g m - the radius of curvature of the matrix; S is the thickness of the workpiece; h - board height.

crimping (Fig. 17.46, b) - reduction of the perimeter of the cross section of the hollow workpiece. In the deformation zone, the wall thickness of the product slightly increases. In order to avoid the formation of longitudinal folds in the crimped part, it is necessary to observe the crimping ratio

K \u003d ~ - \u003d 1.2 ... 1.4,

where £ zag, d m - the diameter of the workpiece and part.

Cold sheet forging is carried out mainly on crank presses. According to the technological basis, mechanical presses are divided into single, double and triple action presses (respectively, one-, two- and three-sliders). The kinematic scheme of the single-acting crank press is in many respects similar to the scheme of the crank hot forging press.

Double action press (Fig. 17.47) is designed for deep drawing of large parts. It has two sliders - inner 3 driven by a crank and outer 2 driven by cams 1 mounted on the shaft. First, the outer slider overtakes the inner one and presses the workpiece flange against the die. During drawing with a punch fixed on the inner slider, the outer slider is stationary. At the end of the hood, the sliders rise.

Rice. 17.47. Scheme of a double-acting single-crank press

Hydraulic presses are used for cold stamping of large-sized products.

Stamps are used as a tool for cold sheet stamping. They consist of blocks of parts and working parts - dies and punches. The working parts directly deform the workpiece. Block parts (top and bottom plates, guide columns and bushings) serve to support, guide and fasten the working parts of the stamp. According to the technological feature, there are stamps of simple, sequential and combined action.

In stamp simple action (Fig. 17.48) in one move of the slider, one operation is performed, therefore it is called single-operation. The bottom plate of the stamp is installed on the press table and fastened to it with bolts and brackets, the upper plate of small stamps is attached to the slider with the help of a shank, and the upper plate of large stamps is attached to the slider in the same way as the bottom plate, to the press table. The strip or tape is fed into the stamp between the guide bars until it stops, which limits the step of feeding the strip or tape. A puller is used to remove the punch from the punch.

In stamp sequential action for one stroke of the slider, two or more operations are performed simultaneously in different positions, and the workpiece after each stroke of the press moves to the feed step. On fig. 17.49 shows a diagram of a sequential stamp for punching and punching. For each press stroke, the workpiece is fed to the stop 1, then punch 3 punches a hole in the workpiece, and punch 2 during the next press stroke cuts out the part.

In stamp combined action (Fig. 17.50) in one stroke of the press slider, two or more operations are performed in one position without moving the workpiece in the feed direction. When driving

slider down, punch 5 and matrix 8 cut the workpiece from strip 6, and punch 7 simultaneously draws the product in matrix 5. The sequence of drawing operations is indicated in the figure by positions 10 ... 12.

Stamps of sequential n combined action are called multi-operational. They are more productive than single-operation ones, but more complicated and more expensive to manufacture. They are used in large-scale and mass production.

Hood

Drawing - shaping of a sheet blank into a bowl- or box-shaped shell or a blank in the form of such a shell into a deeper shell, which occurs due to the retraction by the punch into the matrix of a part of the material located on the mirror behind the contour of the opening (cavity) of the matrix, and stretching of the part located inside the contour . There are varieties of drawing - axisymmetric, non-axisymmetric and complex. non-axisymmetric hood - hood of a non-axisymmetric shell, for example, box-shaped, having two or one plane of symmetry. Complex hood - an hood of a shell of complex shape, usually not having a single plane of symmetry. axisymmetric drawing - drawing a shell from an axisymmetric workpiece with an axisymmetric punch and a matrix (Fig. 9.39, 9.40).

Rice. 9.39. Extraction scheme (A ) and the type of the resulting workpiece (b )

Rice. 9.40.The appearance of blanks after drawing (A ) and technological waste cutoff(b)

When drawing a flat workpiece 5 is drawn in by a punch 1 into the matrix hole 3. In this case, significant compressive stresses arise in the workpiece flange, which can cause wrinkling.

Clamps are used to prevent this. 4. They are recommended to be used for drawing from a flat workpiece when D h - d 1 = 225 where D h – slab diameter; d 1 - diameter of a part or semi-finished product; δ is the sheet thickness. The process is characterized by an elongation ratio t =d 1/D h. To prevent tearing off the bottom, it should not exceed a certain value. Deep parts that, due to strength conditions, cannot be drawn out in one transition, are pulled out in several transitions. Coefficient value T are selected according to reference tables depending on the type and condition of the workpiece. For mild steel, at the first drawing, the value T take 0.5–0.53; for the second - 0.75–0.76, etc.

The drawing force of a cylindrical semi-finished product in a stamp with a clamp is determined approximately by the formula

Where R 1 – own drawing force, ; Р2 – clamping force, ; P- coefficient, the value of which is chosen according to the reference tables depending on the coefficient T;σv is the ultimate strength of the material; F 1 - cross-sectional area of ​​the cylindrical part of the semi-finished product, through which the drawing force is transmitted; q– specific drawing force; F 2 – the contact area of ​​the clamp and the workpiece at the initial moment of drawing.

Meaning q choose from guides. For example, for mild steel it is 2–3; aluminum 0.8–1.2; copper 1–1.5; brass 1.5–2.

Depending on the type of semi-finished product being drawn, punches and dies can be cylindrical, conical, spherical, rectangular, shaped, etc. They are made with rounded working edges, the value of which affects the drawing force, the degree of deformation, and the possibility of wrinkling on the flange. The dimensions of the punch and die are chosen so that the gap between them is 1.35–1.5 of the thickness of the deformed metal. An example of a punch for producing cylindrical parts is shown in fig. 9.41.

Rice. 9.41.

1 – stamp body; 2 – punch body; 3 - punch

flanging

This is a form change in which a part of a sheet blank located along its closed or open contour is displaced into a matrix under the action of a punch, simultaneously stretched, rotated and turned into a bead. The formation of a bead from an area located along a convex closed or open contour of a sheet blank is a shallow drawing, and along a straight contour it is bending.

There are two types of flanging - internal flanging of holes (Fig. 9.42, A) and external flanging of the outer contour (Fig. 9.42, b), which differ in the nature of the deformation and the stress pattern.

Rice. 9.42.

A- holes; b- outer contour

The process of flanging holes consists in the formation in a flat or hollow product with a pre-punched hole (sometimes without it) of a larger diameter hole with cylindrical sides (Fig. 9.43).

Rice. 9.43.

For several operations in a flat workpiece, it is possible to obtain holes with flanging of complex shape (Fig. 9.44).

Rice. 9.44.

Flanging of holes allows not only to obtain structurally successful forms of various products, but also to save stamped metal. At present, parts with a hole diameter of 3–1000 mm are obtained by flanging with a material thickness of 0.3–30.0 mm (Fig. 9.45).

Rice. 9.45.

The degree of deformation is determined by the ratio of the diameter of the hole in the workpiece to the diameter of the bead along the center line D(Fig. 9.46).

Geometric parameters of the flanging tool. Flanging of holes The process of flanging of holes consists in the formation in a flat or hollow product with a pre-punched hole, sometimes without it, larger holes with cylindrical sides or sides of a different shape. Especially great efficiency is the use of hole flanging in the manufacture of parts with a large flange, when drawing is difficult and requires several transitions...

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Page 113

LECTURE #16

Form-changing operations of sheet stamping. Forming and flanging

Lecture plan

1. Molding.

1.1. Determination of permissible degrees of deformation during molding.

1.2. Technological calculations during molding.

2. Flanging.

2.1. Hole punching.

2.2. Geometric parameters of the flanging tool.

1. Molding

Relief molding is a change in the shape of the workpiece, which consists in the formation of local depressions and bulges due to the stretching of the material.

In addition to local recesses and convex concave reliefs, drawings and stiffeners are obtained by molding. Rationally made stiffening ribs can significantly increase the rigidity of flat and shallow stamped parts, it becomes possible to reduce the thickness of the workpiece and its weight. The use of molding replacement hoods in the manufacture of shallow parts with a flange allows you to save metal due to a decrease in the transverse dimensions of the workpiece. The increase in strength obtained as a result of work hardening exceeds the decrease in strength due to thinning of the workpiece in the deformation zone.

The shape of the punch significantly affects the location of the deformation zone. When deformed by a hemispherical punch, the plastic deformation zone consists of two sections: one in contact with the punch and a free section where there are no external loads.

Figure 1 Forming the stiffener and hemispherical recesses

When forming hemispherical recesses, cracks may appear at some distance from the pole of the hemisphere. This is explained by the fact that in the pole and its vicinity, the workpiece fits snugly against the punch, and the contact friction forces that arise when the workpiece slides (when it is thinned) relative to the punch restrain the deformation in the pole more intensively than in the peripheral areas.

Forming with a cylindrical punch with a flat end, one can obtain recesses with a height of (0.2 0.3) of the punch diameter. To obtain deeper cavities, molding is used with a preliminary set of metal in the form of an annular ledge (rift), and when stamping parts of their aluminum alloys, differential heating of the flange is used.

Figure 2 Forming with a cylindrical punch with a flat face and forming with a pre-set

During molding, the workpiece is partially fitted along the punch, and partially along the matrix, so the depth of the matrix must be greater than the height of the rib or recess, and the radius of the corner section of the punch is significantly less than the radius of the rounding of the die edge, otherwise pinching of the walls of the molded part may occur, leading to cracks and irreparable defects.

Molding can be carried out with an elastic and liquid medium (stamping with rubber, polyurethane, used in small-scale production: aircraft building, car building, instrument making, radio engineering) liquid molding of corrugated thin-walled axisymetric shells (compressors in pipeline systems and as sensitive elements of devices).

1.1. Determination of permissible degrees of deformation during molding

The peripheral annular section of the flange is limited by radii and deforms elastically.

The greatest depth of the stiffening rib, which can be obtained as a result of relief molding of parts made of aluminum, mild steel, brass, can be approximately determined by the empirical formula:

where is the rib width, mm;

Thickness of the stamped material, mm.

Figure 3 Plastic and elastic areas during molding

When depth; , but to prevent the destruction of the material.

For large workpiece sizes, the boundary between the plastic and elastic regions is

In other respects, the boundary between the elastic and plastic regions is where

The depth of local drawing is determined by the equation:

Increasing the gap at small radii of curvature allows you to get a deeper local hood.

For relief molding in the form of recesses of a spherical shape:

A; .

Figure 4 Scheme for molding spherical recesses

Possible sizes of local recesses can be determined based on the relative elongation of the stamped material according to the dependence:

where is the length of the middle line of the relief section after stamping;

The length of the corresponding section of the workpiece before stamping.

When forming with a cylindrical punch with a flat end and a small radius of rounding of the working edge, the annular section of the flange is plastically deformed, limited by the radius and, as well as the flat section of the bottom of the part.

Figure 5 Scheme of forming stiffeners, spherical recesses

1.2. Technological calculations during molding

The force of relief stamping can be determined by the formula:

where is the specific strength of relief molding, taken:

for aluminum 100 200 MPa,

for brass 200 250 MPa,

for mild steel 300 400 MPa,

Projection area of ​​the stamped relief on a plane perpendicular to the direction of the force, mm 2 .

The force for relief stamping on crank presses of small parts (), from thin material (up to 1.5 mm) can be determined by the empirical formula:

where is the area of ​​the stamped relief, mm 2

Coefficient: for steel 200 300 MPa,

For brass 150 200 MPa.

The force during molding with a hemispherical punch without taking into account contact friction and uneven thickness of the workpiece in the deformation zone can be determined by the formula:

at

When forming a stiffener (rift) with a punch with a cross section in the form of a circular segment.

where is the length of the rib, at

Or,

where - coefficient, depends on the width and depth of the rift

2. Flanging

2.1. Hole flanging

The process of flanging holes consists in the formation in a flat or hollow product with a pre-punched hole (sometimes without it) of a larger hole with cylindrical sides or sides of a different shape.

Flanging produces holes with a diameter of 3 ... 1000 mm and a thickness= 0.3…30mm. This process is widely used in stamping production, replacing drawing operations with subsequent cutting of the bottom. Hole flanging is especially effective in the manufacture of parts with a large flange, when drawing is difficult and requires several transitions.

In the process under consideration, there is an elongation in the tangential direction, and a decrease in the thickness of the material.

For a relatively high bead, the calculation of the diameter of the original workpiece is performed from the condition of equality of the volumes of the material before and after deformation. The initial parameters are the diameter of the flanged hole and the height of the side of the part (Fig. 6). Based on these parameters, the required diameter of the original hole is calculated:

Where.

If the height of the side is specified in the detail drawing (Fig. 6), then the diameter of the flare hole for the low sideapproximately calculated, as in the case of simple bending according to the formula:

Where;

The radius of curvature of the working edge of the matrix,

or

where is the bead height, mm, is the flanging radius, is the thickness of the starting material.

In the case of a given diameter for flanging, the height of the side can be determined from the dependence:

Figure 6 Scheme for calculating the parameters of the flanging - the height of the side and - the diameter of the hole for flanging

The height of the flanging is greatly influenced by the radius. At high values, the height of the side increases significantly.

When obtaining small holes for threading or pressing axes, when it is structurally necessary to have cylindrical walls, flanging with a small radius of curvature and a small gap is used (Fig. 7, a).

When applying the operation in question to increase the rigidity of the structure: when flanging large holes, windows of aviation, transport, shipbuilding structures, flanging hatches, necks, sockets, etc., the process is best done with a large gap between the punch and the matrix and with a large radius of curvature matrices (Fig. 7, b). In this case, a small cylindrical part of the bead is obtained.

a) b)

Figure 7 Flanging options: a- with a small radius of the matrix and a small gap, b with a large gap

The number of transitions required to obtain a flanging is determined by the flanging factor:

where is the diameter of the hole before flanging;

Flanging diameter along the midline.

The maximum allowable coefficient for a given material can be determined analytically:

where is the relative elongation of the material;

Coefficient determined by flanging conditions.

The smallest thickness at the edge of the board is:

The value of the flanging coefficient depends on:

1. From the nature of the flanging and the state of the edges of the hole (a hole was obtained by drilling or punching, the presence or absence of burrs).
2. From the relative thickness of the workpiece.
3. From the type of material, its mechanical properties and the shape of the working part of the punch.

The smallest value of the coefficient should be taken when flanging drilled holes, the largest punched. This is caused by work hardening after punching. To remove it, annealing or cleaning of the hole in the cleaning dies is introduced, which makes it possible to increase the plasticity of the material.

Flanging holes should be punched from the side opposite to the flanging direction, or the workpiece should be laid with the burrs up so that the burr face is less stretched than the rounded edge.

When flanging the bottom of a pre-drawn cup with a hole (Fig. 8), the total height of the part obtained after deformation can be determined by the formula:

where is the pre-draw depth.

Figure 8 - Scheme for calculating the flanging in the bottom of a pre-drawn glass: 1-matrix, 2-punch, 3-clamp

Due to the significant stretching of the material at the edge of the technological hole, as a result of an increase in to, a significant thinning of the edge edge occurs:

where is the thickness of the edge after thinning.

In one operation, simultaneously with the flanging, it is possible to make the wall thinning up to.

When punching a hole, the maximum diameter for each type and thickness of material is usually established empirically. In this case, the edge of the end of the vertical walls always remains torn, so the piercing is applicable only for non-critical parts.

The technological force required for flanging round holes is determined by the formula:

where is the strength limit of the stamped material, MPa.

The clamping force during flanging can be taken equal to 60% of the clamping force during drawing under similar conditions (thickness, type of material, diameter of the annular platform under the clamp).

2. Geometric parameters of the flanging tool

The dimensions of the working parts of dies for flanging round holes can be determined depending on the flanging diameter, taking into account some springback of the stamped material and the wear allowance of the punch:

where is the nominal value of the flanged hole diameter;

Specified tolerance for flanged hole diameter.

The matrix is ​​made on a punch with a gap.

The gap depends on the thickness of the starting material and the type of workpiece and can be determined by the following relationships:

• in a flat workpiece -
• in the bottom of a pre-stretched glass -

or from table 1.

The working part of punches for flanging can have different geometry (Fig. 9):

a) tractrix providing minimum flanging force;

b) conical;

c) spherical;

d) with a large radius of curvature;

e) with a small radius of curvature.

A B C D E)

Figure 9 Forms of the working part of the punches

Punches with a spherical geometry of the working part and with a small radius of curvature require the greatest flanging force.

Table 1 - One-sided flare clearance

The utility model relates to the field of metal forming, namely to cold stamping of blanks from a sheet, and can be used to increase the height of the side in the manufacture of parts with a cylindrical side. The flanging device contains a cylindrical punch with a section of radius rounding to a flat end, a matrix, a clamp and a lower clamp, while the diameter of the flat end of the punch is made with a size determined by the dependence: where d 0 is the diameter of the hole in the workpiece, [K om ] is the edge the value of the flanging coefficient (less than one), the lower clamp has a radius rounding zone, covering the rounding radius of the punch, with a radius equal to R=R n +S 0 where R n is the punch radius, and S 0 is the thickness of the workpiece. The center of curvature of the radius zone of the clamp is displaced relative to the center of the radius rounding of the punch in the horizontal direction from the axis of the stamp by a distance, the value of which is determined by the dependence: where d is the diameter of the side of the part, and d 0 is the initial diameter of the hole in the workpiece, k=1.05..1.15 is the coefficient characterizing the increase in the plasticity of the material at the edge of the deformable hole as a result of applying additional compressive stresses to it. Fig.3

The utility model relates to the field of metal forming, namely to cold stamping of blanks from a sheet, and can be used in the manufacture of hollow parts with a high edge.

A well-known design of equipment for flanging, in which the workpiece with a hole is completely beaded beforehand, and then the side is turned out, acting simultaneously on the end of the side and the annular part of the workpiece adjacent to the side of the workpiece (AC 1817720, IPC B 21 D 22/00, publ. 1993.05 .23). The creation of axial and radial compressive stresses on the end face of the beaded billet increases the plasticity of the metal and makes it possible to increase the height of the bead compared to conventional flanging.

The disadvantage of this equipment is its complexity. When implementing this method on presses, the die tooling becomes very complicated due to the need to ensure the required movements of the independent elements of the die during the deformation process.

The closest in technical essence to the claimed design, which is taken as a prototype, is the tooling design, which consists of a flanging punch having a radius rounding area, a flat clamp, a flanging die and a lower clamp located under the flanging punch (AU No. 275986, IPC B 21 d 19/06, published 1970.01.01). To increase the allowable degree of deformation, compressive stresses are created on the edge of the hole with the help of a lower clamp and a flanging punch, parallel to the axis of the stamp. As a result of compression of the edge of the hole between the conical surfaces of the lower clamp and the flanging punch, in the latter there are

compressive stresses that increase the plasticity of the metal, which increases the limiting possibilities of the process.

The disadvantage of the design is that in the manufacture of a cylindrical side, at the final stage of the deformation process, the workpiece comes out of contact with the lower clamp. The lower clamp ceases to create compressive stresses on the edge. As a result, the stress state scheme in it again changes to uniaxial tension. Since by this moment the plasticity of the metal has already been exhausted (the value of the flanging coefficient exceeds the limit value), the workpiece is destroyed at the edge of the hole.

In addition, by applying compressive stresses from the very beginning of the flanging process, the radial stresses increase in the zone of radius rounding of the flanging punch and the destruction of the workpiece begins to occur in the form of a bottom tear (similar to the drawing process). This does not allow to achieve large degrees of deformation in the process as a whole. At the initial moment of deformation of the workpiece, the friction forces from the lower clamp are harmful.

The objective of the invention is to increase the marginal flanging factor with the relative simplicity of the die tooling design.

The problem is solved due to the fact that in the device for flanging, containing a cylindrical punch with a section of radius rounding to a flat end, a matrix, a clamp and a lower clamp, the diameter of the flat end of the punch is made with a value determined by the dependence:

where d 0 is the diameter of the hole in the workpiece, [K om ] is the limiting value of the flanging coefficient, the lower clamp has a radius rounding zone, covering the rounding of the punch, with a radius equal to

where R n is the radius of the punch, and S 0 is the thickness of the workpiece, while the center of curvature of the radius zone of the lower clamp is displaced relative to the center of the radius rounding of the punch in the horizontal direction from the axis of the stamp by a distance, the value of which is determined by the dependence:

where d is the diameter of the side of the part, a d 0 is the initial diameter of the hole in the workpiece, k=1.05-1.10 is the coefficient characterizing the increase in the plasticity of the material at the edge of the deformable hole as a result of applying additional compressive stresses to it.

The claimed device is illustrated by a drawing, where figure 1 shows the device in its original position, figure 2 shows the position of the device at the moment when the lower clamp acts on the edge of the beaded hole, creating compressive stresses on it. Figure 3 shows the device at the final stage of the flanging process.

The device consists of a punch 1, which has a radius rounding from a cylindrical wall to a flat end, a clamp 2, which presses the workpiece 3 to the matrix 4. Under the flanging punch, there is a lower clamp 5, which has a radius rounding zone, covering the rounding zone of the punch for flanging 1.

The device works as follows.

The workpiece 1, having a hole with a diameter d o is installed on the matrix 4 and pressed against it by the clamp 2. After that, the working stroke of the punch 1 begins. The punch has a flat end with a diameter equal to d. During the working stroke of the punch,

shaping of the bead with an increase in the diameter of the beaded hole. The process is carried out as a normal flanging. The diameter of the flat end of the punch is determined by the dependence

where d 0 is the diameter of the hole in the workpiece, is the limiting value of the flanging coefficient.

The presence of the coefficient (0.8-0.9) can be considered as a safety factor that protects the workpiece from destruction during the flanging process, while the lower clamp does not act on the edge of the flanging hole. The value of the marginal flanging coefficient is determined from reference literature (for example, Romanovsky V.P. Handbook of cold forging. - L. Mashinostroyeniye, 1979, p. 221, table 111).

With a further working stroke of punch 1, when the diameter of the flared hole has increased to a value of d (the possibilities of metal with simple flaring have been exhausted), it is necessary to create compressive stresses on the edge of the workpiece for further deformation. These stresses are created as a result of the fact that the edge of the workpiece is compressed between the punch 1 and the lower clamp 5.

That is, when the hole diameter reaches a value close to the largest size that can be obtained by flanging the hole without participating in the process of deformation of the lower clamp, the workpiece edge is compressed between the punch and the lower clamp. In this case, the entire pressing force is concentrated in a small area near the edge of the hole, which makes it possible to change the scheme of the stress state of the workpiece edge from linear tension to a flat opposite scheme, without excessive deformation of the material, and with a minimum deformation force.

The presence of compressive stress on the edge increases the ductility of the metal, allows you to increase the ultimate deformation per transition and make a board of increased height.

In order to ensure the impact of the lower clamp and the punch on the edge of the workpiece during the entire subsequent process of deformation of the workpiece, the lower clamp is made with a radius rounding zone, covering the rounding zone of the punch for flanging.

In the course of further implementation of the process, the edge of the workpiece hole, being under pressure concentrated on a small area applied from the side of the punch, moves between the punch and the lower clamp until the moment of complete shaping, which occurs when the edge of the workpiece hole moves to the cylindrical section of the punch.

At that moment, when the edge of the workpiece moves to the cylindrical section of the punch, the tensile deformation on the edge stops, and therefore, the destruction of the workpiece will no longer occur.

In order for compressive stresses to form only on the edge of the beaded hole, and not along the entire deformation zone, the shape of the tool must ensure that the workpiece is compressed only along the edge. To do this, the centers of curvature of the zones of radius rounding of the flanging punch and the lower clamp are made with an offset in the horizontal direction from the axis of the stamp by an amount

where d is the diameter of the side of the part, a d 0 is the initial diameter of the hole in the workpiece, k=1.05..1.15 is the coefficient characterizing the increase in the plasticity of the material at the edge of the deformable hole as a result of applying additional compressive stresses to it.

A device for flanging a hole, containing a flat clamp, a matrix, a flanging punch with a radius rounding of the transition to a flat end, and a lower clamp located under the flanging punch, characterized in that the flat end of the punch is made with a diameter equal to d:

where d 0 is the diameter of the hole in the original workpiece, [K om ] is the limiting flanging factor, the lower clamp has a radius rounding zone, covering the rounding of the punch, with a radius R equal to:

where R n is the rounding radius of the punch, a S 0 is the thickness of the original workpiece from the sheet;

at the same time, the center of curvature of the radius of the rounding zone of the clamp is displaced relative to the center of the rounding of the punch in the horizontal direction, from the axis of the stamp, by a distance, the value of which is determined by the dependence:

where d is the diameter of the side of the part, a d 0 is the initial diameter of the hole in the workpiece, k=1.05-1.10 is the coefficient characterizing the increase in the plasticity of the material at the edge of the deformable hole as a result of applying additional compressive stresses to it.