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Flanging products on special stamps. Flanged outer contour.Hole flanging (internal).
Scheme for calculating the flanging of the product. Force for flanging with a cylindrical punch. Forming.
A distinction is made between a hole flanging (inner) and an outer flange. Flanging of products is performed on special dies. To make flanging in a flat or hollow workpiece, you must first punch a hole in it. With deep flanging, a hood is first made, then a hole is punched and then flanging is performed. In order to perform flanging without breaks and cracks in one operation, it is necessary to take into account the degree of deformation (or the so-called flanging coefficient) K ot \u003d d / D, where d is the diameter of the previously punched hole, mm; D - hole diameter obtained after flanging, mm.
Flanging of a product made of a thin material is carried out by pressing the product against the surface of the die matrix. The diameter of the flange hole for a low flange can be approximately determined by the method that is used when calculating a workpiece with a rounding, obtained flexible. For example, for the product shown in fig. 9, the hole diameter (mm) in the workpiece is determined by the formula d \u003d D 1 - π - 2h. Hence the height of the side H \u003d h + r 1 + S \u003d D - (d / 2) + 0.43r 1 + 0.72S.
Figure: nine. Scheme for calculating the flanging of the product
Practice has established that the limiting flanging factor depends on the mechanical properties of the material, the relative thickness of the workpiece (S / d). 100, the roughness of the surfaces of the edges of the holes in the workpiece, the shape of the working part of the die punch.
The radius of rounding of the cylindrical punch must be at least four material thicknesses.
Force for flanging with cylindrical punch can be determined by the formula of A. D. Tomlenov: P out \u003d π (D-d) SCσ т ≈1,5π (D-d) Sσ в, where D is the diameter of the flange of the product, m; d - hole diameter for flanging, m; S - material thickness, m; C is the coefficient of metal hardening and the presence of friction during flanging Cσ t \u003d (1.5 ÷ 2) σ in; σ t and σ in - yield strength and ultimate tensile strength of the material, MPa (N / m 2).
Outer contour flange parts are used with convex and concave contours. Flanging with convex contour is similar to the shallow drawing process, and flanging of concave contour is similar to flanging of holes.
The amount of deformation with the outer flanging of the convex contour K n.otb \u003d R 1 / R 2, where R 1 is the radius of the contour of the flat workpiece; R 2 is the radius of the beaded contour of the product.
Molding is an operation in which the shape of a product previously obtained by drawing is changed. Such an operation includes, for example, forming from the inside (bulging), obtaining a bulge, a depression, a drawing, an inscription. The dies for forming from the inside have split dies and an elastic expanding device (liquid, rubber, mechanical).
Geometric parameters of the flanging tool. Flanging of holes The process of flanging holes consists in the formation in a flat or hollow product with a pre-punched hole, sometimes without it, a larger hole with cylindrical flanges or flanges of another shape. Particularly great efficiency is provided by the use of a 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 number 16
Form-changing operations of sheet stamping. Forming and flanging
Lecture plan
1. Forming.
1.1. Determination of permissible degrees of deformation during forming.
1.2. Technological calculations during molding.
2. Flanging.
2.1. Flanged holes.
2.2. Geometric parameters of the flanging tool.
1. Forming
Relief molding is a change in the shape of a workpiece, which consists in the formation of local depressions and bulges due to stretching of the material.
In addition to local depressions and convex - concave reliefs, patterns 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 mass. The use of forming 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 the strength obtained as a result of work hardening exceeds the decrease in strength due to the 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: in contact with the punch and a free section where there are no external loads.
Picture 1 - Forming stiffeners and hemispherical recesses
When forming hemispherical depressions, cracks may appear at some distance from the pole of the hemisphere. This is due to the fact that in the pole and its vicinity the workpiece adheres tightly to the punch and the contact friction forces arising when the workpiece slides (during its thinning) relative to the punch restrain deformation at the pole more intensively than at the peripheral sections.
Shaping with a cylindrical punch with a flat end can be used to obtain indentations with a height (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 protrusion (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 end and forming with a preliminary set
During molding, the workpiece is partially tightened along the punch, and partially along the matrix, therefore, 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 rounding of the edge of the matrix, otherwise the appearance of pinching of the walls of the formed part, leading to cracks and irreparable rejects.
Molding can be carried out with an elastic and liquid medium (stamping with rubber, polyurethane, used in small-scale production: aircraft construction, car building, instrumentation, radio engineering) liquid molding - corrugated thin-walled axisometric 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 a stiffener, which can be obtained as a result of relief molding of parts made of aluminum, mild steel, brass, can be roughly determined by the empirical formula:
where is the rib width, mm;
Thickness of the stamped material, mm.
Picture 3 - Plastic and elastic areas during molding
At depth; , but to prevent destruction of the material.
With large dimensions of the workpiece, the boundary between the plastic and elastic regions is.
For other ratios, the boundary between the elastic and plastic regions is where
Local draft depth is determined by the equation:
Increasing the clearance at small radii of curvature allows for deeper localized drawing.
For relief molding in the form of spherical recesses:
AND; ...
Figure 4 - Scheme of forming spherical recesses
The possible dimensions 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, limited by the radius and, as well as the flat section of the bottom of the part, are plastically deformed.
Figure 5 - Scheme of forming stiffeners, spherical recesses
1.2. Technological calculations during molding
The strength of the relief stamping can be determined by the formula:
where is the specific force of relief molding, taken:
for aluminum 100 - 200 MPa,
for brass 200 - 250 MPa,
for mild steel 300 - 400 MPa,
The area of \u200b\u200bthe projection of the stamped relief onto the plane perpendicular to the direction of the force action, mm2 .
The force for relief stamping on crank presses of small parts (), made of thin material (up to 1.5 mm) can be determined by the empirical formula:
where is the area of \u200b\u200bthe stamped relief, mm2
Coefficient: for steel 200 - 300 MPa,
For brass 150 - 200 MPa.
The force during forming 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 edge length, at
Or,
where is the coefficient, depends on the width and depth of the rift
2. Flanging
2.1. Flanging holes
The process of flanging holes consists in the formation of a larger hole with cylindrical sides or sides of a different shape in a flat or hollow product with a pre-punched hole (sometimes without it).
Holes with a diameter of 3 ... 1000 mm and a thickness of= 0.3 ... 30mm. This process is widely used in stamping production, replacing drawing operations followed by punching the bottom. Especially great efficiency is provided by the use of a flanged hole in the manufacture of parts with a large flange, when drawing is difficult and requires several transitions.
In the process under consideration, elongation occurs in the tangential direction, and the thickness of the material decreases.
For a relatively high flange, the calculation of the diameter of the original workpiece is performed from the condition of equality of the volumes of material before and after deformation. The initial parameters are the diameter of the flanged hole and the height of the bead of the part (Fig. 6). These parameters are used to calculate the required diameter of the original hole:
where.
If the flange height is specified in the detail drawing (fig. 6), then the diameter of the flange hole for the low flangeroughly calculated, as in the case of simple bending by the formula:
where;
Radius of rounding of the working edge of the matrix,
or
where is the bead height, mm, is the flange radius, is the thickness of the starting material
In the case of a given flanging diameter, the flange height can be determined by the dependence:
Figure 6 - Scheme for calculating flange parameters - flange height and - flange hole diameter
The radius has a large influence on the flange height. With its large values, the side height increases significantly.
When receiving small holes for threading or pressing in axles, 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 using the operation under consideration 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 performed 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 rounding of the matrix and a small gap, b - with a large gap
The number of transitions required to obtain flanging is determined by the flanging ratio:
where is the hole diameter before flanging;
Diameter of the flange at the center line.
The maximum permissible coefficient for a given material can be determined analytically:
where is the relative elongation of the material;
Factor determined by flanging conditions.
The smallest thickness at the edge of the bead is:
The value of the flanging factor depends on:
- From the nature of the flanging and the condition of the edges of the hole (drilling or punching a hole was obtained, the presence or absence of burrs).
- From the relative thickness of the workpiece.
- 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.
Punching holes for flanging should be done from the side opposite to the flanging direction, or lay the workpiece with burrs upwards so that the flared edge is less stretched than the rounded edge.
When flanging the bottom of a pre-stretched glass with a hole (Fig. 8), the total height of the part obtained after deformation can be determined by the formula:
where is the depth of preliminary drawing.
Figure 8- Scheme for calculating the flanging in the bottom of a pre-stretched glass: 1-die, 2-punch, 3-clamp
Due to the significant stretching of the material at the edge of the technological hole, as a result of increasing to, a significant thinning of the edge of the edge occurs:
where is the thickness of the edge after thinning.
In one operation, simultaneously with flanging, the wall can be thinned up to.
When punching a hole, the maximum diameter for each type and thickness of material is usually established empirically. At the same time, the edge of the end of the vertical walls always remains torn, therefore the piercing is applicable only for irrelevant parts.
The technological force required for flanging round holes is determined by the formula:
where is the strength 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 area 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 diameter of the flanging, taking into account some springback of the stamped material and the allowance for wear of the punch:
where is the nominal value of the diameter of the flanged hole;
Specified tolerance for the diameter of the flanged hole.
The matrix is \u200b\u200bmade 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 the pre-stretched glass -
or from table 1.
The working part of the flanging punches can have different geometries (fig. 9):
a) tractrix, providing a 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 punches
Punches with a spherical tip geometry and a small radius of curvature require the greatest flanging force.
Table 1-One-sided flange clearance
|
Treatment type |
Workpiece material thickness |
|||||||
|
Slab |
0,25 |
0,45 |
0,85 |
1,00 |
1,30 |
1,70 |
||
|
Pre-stretched glass bottom |
0,25 |
0,45 |
0,55 |
0,75 |
0,90 |
1,10 |
1,50 |
|
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Flanging holes It is widely used in stamping production, replacing drawing operations, followed by cutting the bottom. This process is especially effective in the manufacture of parts with a large flange, when pulling is difficult and requires several transitions.
The deformation of the metal during flanging is characterized by a change in the radial-ring mesh applied to the workpiece (Figure 8.57)... When the holes are flanged, elongation occurs in the tangential direction and decreases in thickness. The distances between concentric circles remain unchanged.
The geometric dimensions during flanging are determined based on the equality of the volumes of the workpiece and the part... Usually, the height of the side is specified in the drawing of the part. In this case, the diameter of the flange hole is roughly calculated as for simple bending. This is permissible due to the small amount of deformation in the radial direction and the presence of significant thinning of the material.
| Drawing. 8.57. Flanging scheme |
The hole diameter is determined by the formula:
- d \u003d D-2 (H-0, 43r - 0.72 S), (8.96)
The board height is expressed by the relationship:
- H \u003d (Dd) / 2 + 0.43r + 0.72S, (8.74)
As can be seen from the last formula, the board height, other things being equal, depends on the radius of curvature. With large radii of curvature, the height of the bead increases significantly.
Research by R. Wilken showed that with an increase in the gap between the punch and the die to z \u003d (8 ÷ 10) S), there is a natural increase in the height and radius of curvature of the bead (Fig. 8.58).
In this case, the degree of deformation of the bead edge does not increase, since the diameter of the workpiece does not change. But due to the fact that a large amount of metal is involved in the center, the deformation of the bead is dispersed, and the thinning of the edge is somewhat reduced. It was found that with an increase in the gap to z \u003d (8 ÷ 10) S, the flanging force decreases by 30 - 35%. Consequently, the stresses in the walls are correspondingly reduced, since the resistance of the metal to deformation and the flanging force depend on their value.
Thus, this process is best done when the gap between the punch and the die is large or when the die radius is significantly increased.... Such flanging, characterized by a large radius of curvature, but a small cylindrical part of the bead, is quite acceptable in those cases when it is made to increase the rigidity of the structure with its low mass.
The process with a small radius of curvature and a large cylindrical part of the bead can only be used when flanging small holes for threads or pressing in axles or when it is structurally necessary to have cylindrical flanged walls. The size of the force is greatly influenced by the shape of the punch.
In fig. 8.59 shows the working diagrams and the sequence of flanging with a different shape of the outline of the working part of the punch (curved - trajectory, circular arc, cylinder with significant roundings, cylinder with small roundings)... The force required for flanging with a cylindrical punch can be determined using the following formula:
- P \u003d lnSσt (Dd), (8.75)
where D is the diameter of the flange, mm; d - hole diameter, mm.
Execution depends on the cleanliness of the deformable edge cut.
The degree of deformation during flanging of holes is determined by the ratio between the diameter of the hole in the workpiece and the diameter of the bead or the so-called flaring ratio:
where d is the hole diameter before flanging; D - flange diameter (along the middle line).
The permissible transverse constriction due to hole edge defects is significantly lower than in the tensile test. The smallest thickness at the edge of the bead is S1 \u003d S.
The value of the flanging coefficient depends:
- 1) on the nature of processing and the state of the edges of the holes (drilling or punching, presence or absence of burrs);
- 2) the relative thickness of the workpiece, which is expressed by the ratio (S / D) 100;
- 3) the type of material and its mechanical properties;
- 4) the shape of the working part of the punch.
The inverse dependence of the maximum permissible flanging factor on the relative thickness of the workpiece has been experimentally proved, i.e. the greater the relative thickness of the workpiece, the lower the value of the permissible flanging ratio, the greater the possible degree of deformation. In addition, the dependence of the limiting coefficients on the production method and the state of the hole edge has been proved.
The smallest coefficients were obtained when flanging drilled holes, the highest - when flanging punched holes. The ratio of drilled holes differs little from the ratio of the punched and annealed workpiece, since annealing eliminates work hardening and increases the ductility of the metal. Sometimes, to remove the work-hardened layer, the hole on the stripping dies is cleaned.
Table 8.42 shows the calculated values \u200b\u200bof the coefficients for mild steel depending on the flanging conditions and the ratio d / S.
Punching holes for flanging should be done from the side opposite to the flanging direction, or enclose the workpiece with a lattice upwards so that the edge with the lattice is less stretched than the rounded edge.
If a large board height is required, cannot be obtained in one operation, then when flanging small holes in artificial workpieces, use thinning process (see below), and in the case of flanging large holes or with successive stretching in the belt - pre-draft, (fig. 8.60).
The calculation of the dimensions h and d is carried out according to the following formulas:
- h \u003d (Dd) / 2 \u003d 0.57r; (8.77)
- d \u003d D + 1.14r - 2h, (8.78)
Flanging of holes is widely used in sequential stamping in a strip.
Table 8.42. The calculated value of the coefficients for mild steels
| Flanging method | Hole making method | The value of the coefficient depending on the ratio d / S | ||||||||||
| 100 | 50 | 35 | 20 | 15 | 10 | 8 | 6,5 | 5 | 3 | 1 | ||
| Spherical punch | 0,70 | 0,60 | 0,52 | 0,45 | 0,40 | 0,36 | 0,33 | 0,31 | 0,30 | 0,25 | 0,20 | |
| Punching in a stamp | 0,75 | 0,65 | 0,57 | 0,52 | 0,48 | 0,45 | 0,44 | 0,43 | 0,42 | 0,42 | - | |
| Cylindrical punch | Drilling with deburring | 0,80 | 0,70 | 0,60 | 0,50 | 0,45 | 0,42 | 0,40 | 0,37 | 0,35 | 0,30 | 0,25 |
| Punching in a stamp | 0,85 | 0,75 | 0,65 | 0,60 | 0,55 | 0,52 | 0,50 | 0,50 | 0,48 | 0,47 | - | |
The operation of rolling the flanges of the cavity parts, carried out to increase the strength of the flange and rounding the edge, has a similar character with the operation of flanging holes, especially with flanging the edge of the cavity parts.
 |
| Drawing. 8.60. Flanging with the previous draw |
In various designs, there are holes and notches that are not round (oval or rectangular) forms with sides along the contour. Often such cutouts are made to lighten the mass. (side members, etc.), And the sides - to increase structural strength.
In this case, the depth of the side is taken small (4 ÷ 6%) S with low requirements for its accuracy.
When building a sweep, one should take into account the different nature of deformation along the contour: bending in straight sections and flanging with stretching and a slight decrease in height in the corners. However, due to the integrity of the metal, the deformation extends to the straight sections of the bead, the metal of which partially compensates for the deformation of the corner beads. Therefore, there is no big difference in the board height.
To eliminate possible errors, the width of the flanged field on corner roundings should be slightly increased compared to the width of the field on straight sections.
About:
- b cr \u003d (1.05 ÷ 1.1) b pr, (8.79)
where b cr and b pr is the width of the field on the rounding and on the straight sections.
When flanging NOT round holes, the allowable deformation is calculated for areas with the smallest radius of curvature. It has been experimentally established that when flanging NOT round holes limiting factors are slightly lessthan when flanging round holes (due to the unloading effect of neighboring areas), but the magnitude of this decrease is practically insignificant. Therefore, in this case, you can use the coefficients set for round holes.
The relative thickness of the material S / r or S / d has a great influence on the value of the coefficient, and an even greater influence is the state and nature of the opening edge.
The limiting coefficient of flanging of holes obtained by punching due to edge work-hardening is 1.5 - 1.7 times higher than in milled ones. However, milling is unproductive and impractical.
In fig. 8.62 shows the sequence of manufacturing a part by drawing from a rectangular flange. For the first step (1), a rectangular drawing of the inner cavity is carried out, for the second step (II) - cutting the technological hole, after the third (III) - drawing the outer contour and flanging the inner contour.
Cutting technological holes or using notches for relief are often used when pulling parts of complex shapes. They can significantly reduce the movement of the outer flange and use the deformation of the bottom of the workpiece.
The utility model relates to the field of metal forming, namely cold stamping of blanks from a sheet, and can be used to increase the height of the bead in the manufacture of parts with a cylindrical bead. The flanging device contains a cylindrical punch with a radius rounding area 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, [К om] the value of the flanging factor (less than one), the lower clamp has a radius rounding zone covering the radius rounding of the punch, with a radius equal to R \u003d R n + S 0 where R n is the radius of the punch, and S 0 is the thickness of the workpiece. The center of curvature of the clamping radius zone is displaced relative to the center of the radius rounding of the punch in the horizontal direction from the punch axis by a distance, the value of which is determined by the dependence: 
where d is the diameter of the bead of the part, and d 0 is the initial diameter of the hole in the workpiece, k \u003d 1.05..1.15 is the coefficient characterizing the increase in the plasticity of the material at the edge of the deformed hole as a result of applying additional compressive stresses to it. Fig. 3
The utility model relates to the field of metal forming, namely, cold stamping of blanks from a sheet, and can be used in the manufacture of hollow parts with a high flange.
Known design of equipment for flanging, in which the workpiece with a hole is completely flanged, and then the bead is inverted, acting simultaneously on the bead end and the annular part of the workpiece adjacent to the workpiece board (AC 1817720, IPC 21 D 22/00, publ. 1993.05 .23). The creation of axial and radial compressive stresses on the end face of the flanged workpiece increases the ductility of the metal and makes it possible to increase the flange height as compared to conventional flanging.
The disadvantage of this rig is its complexity. When this method is implemented on presses, the die tooling is greatly complicated due to the need to ensure the required movements of the independent die elements during deformation.
The closest in technical essence to the claimed design, which is taken as a prototype, is the design of the tooling, which consists of a flanging punch having a radius rounding zone, a flat clamp, a flanging matrix and a lower clamp located under the flanging punch (AC No. 275986, IPC B 21 d 19/06, publ. 1970.01.01). To increase the permissible degree of deformation, compressive stresses parallel to the die axis are created at the edge of the hole with the help of the lower clamp and the flanging punch. As a result of the compression of the edge of the hole between the conical surfaces of the lower clamp and the flanging punch, in the latter,
compressive stresses that increase the ductility of the metal, which increases the limiting capabilities of the process.
The disadvantage of this design is that in the manufacture of a cylindrical bead, at the final stage of the deformation process, the workpiece comes out of contact with the lower clamp. The lower clamp stops creating compressive stresses on the edge. As a result, the diagram of the stress state changes again into uniaxial tension. Since by this moment the plasticity of the metal has already been exhausted (the value of the flanging coefficient exceeds the limiting value), the workpiece is destroyed at the edge of the hole.
In addition, applying compressive stresses from the very beginning of the flanging process, the radial stresses increase in the radius of the flanging punch and the destruction of the workpiece begins to take place in the form of bottom tearing (similar to the drawing process). This does not allow achieving high 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 limiting flanging factor with the relative simplicity of the die tooling design.
The problem is solved due to the fact that in the flanging device containing a cylindrical punch with a radius rounding section to the 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, [К om] is the limiting value of the flanging factor, the lower clamp has a radius rounding zone covering the radius rounding of the punch, with a radius equal to
where R n is the radius of the punch, a 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 bead of the part, a d 0 is the initial diameter of the hole in the workpiece, k \u003d 1.05-1.10 is the coefficient characterizing the increase in the plasticity of the material at the edge of the deformed hole as a result of the application of additional compressive stresses to it.
The claimed device is illustrated by a drawing, where figure 1 shows the device in its initial position, figure 2 shows the position of the device at the moment when the lower clamp acts on the edge of the flanged 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 having a radius rounding from a cylindrical wall to a flat end, a clamp 2, which presses the workpiece 3 against the matrix 4. Under the flanging punch, there is a lower clamp 5, which has a radius rounding zone covering the rounding area of \u200b\u200bthe flanging punch 1.
The device works as follows.
The workpiece 1, having a hole with a diameter d o, is installed on the die 4 and pressed against it by the clamp 2. After that, the working stroke of the punch 1. 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 flanged hole. The process is carried out like a conventional flanging. The size of 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 factor.
The presence of a 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 flanged hole. The value of the limiting flanging factor is determined by reference literature (for example, V.P. Romanovsky, Reference book on cold stamping. - L. Mashinostroenie, 1979, p. 221, table 111).
With the further working stroke of the punch 1, when the diameter of the flanged hole has increased to the value d (the possibilities of the metal are exhausted with a simple flanging), compressive stresses must be created on the edge of the workpiece for further deformation. These stresses are created as a result of the edge of the workpiece being compressed between punch 1 and lower clamp 5.
That is, when the hole diameter reaches a value close to the largest size that can be obtained when the hole is flanged without participation in the deformation of the lower clamp, the edge of the workpiece is compressed between the punch and the lower clamp. In this case, the entire clamping force is concentrated on a small area near the edge of the hole, which makes it possible to change the stress state pattern of the edge of the workpiece from linear tension to a flat, opposite pattern, 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, makes it possible to increase the ultimate deformation for the transition, and to manufacture a board with an increased height.
In order to ensure the effect 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 curvature zone covering the radius of the punch for flanging.
In the course of the further implementation of the process, the edge of the blank hole, being under pressure concentrated in a small area applied from the punch side, moves between the punch and the lower clamp until the moment of complete shaping, which occurs when the blank hole edge moves to the cylindrical section of the punch.
At the moment when the edge of the workpiece moves to the cylindrical section of the punch, the tensile deformation at the edge stops, and therefore, the destruction of the workpiece will not occur.
In order for compressive stresses to be formed only at the edge of the flanged hole, and not along the entire deformation zone, the shape of the tool should provide compression of the workpiece only along the edge. For this, the centers of curvature of the zones of radius rounding of the flanging punch and the lower clamp are made with a displacement in the horizontal direction from the axis of the stamp by an amount
where d is the diameter of the bead of the part, a d 0 is the initial diameter of the hole in the workpiece, k \u003d 1.05..1.15 is the coefficient characterizing the increase in the plasticity of the material at the edge of the deformed 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 radial 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 hole diameter in the original workpiece, [К om] is the limiting flanging factor, the lower clamp has a radius rounding zone, covering the radius rounding of the punch, with the value of the radius R equal to:
where R n is the radius of rounding of the punch, and S 0 is the thickness of the original blank from the sheet;
in this case, the center of curvature of the radius of the press rounding zone is displaced relative to the center of the radius rounding of the punch in the horizontal direction, from the die axis, by a distance, the value of which is determined by the dependence:
where d is the diameter of the bead of the part, a d 0 is the initial diameter of the hole in the workpiece, k \u003d 1.05-1.10 is the coefficient characterizing the increase in the plasticity of the material at the edge of the deformed hole as a result of the application of additional compressive stresses to it.
Hood
Stretching - the 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 punch drawing 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 the part inside the contour ... There are varieties of hoods - axisymmetric, non-axisymmetric and complex. Nonaxisymmetric hood - a hood of a nonaxisymmetric shell, for example, a box-shaped one, having two or one planes of symmetry. Complex drawing - drawing of a shell of complex shape, usually without a single plane of symmetry. Axisymmetric drawing - drawing of a shell from an axisymmetric workpiece by an axisymmetric punch and a matrix (Fig. 9.39, 9.40).
Figure: 9.39. Exhaust scheme (and ) and the type of the resulting workpiece (b )
Figure: 9.40. The appearance of the blanks after drawing (and ) and cutoff of technological waste(b)
During drawing, the flat workpiece 5 is drawn in by the punch 1 into the die hole 3. In this case, significant compressive stresses arise in the flange of the workpiece, which can cause the formation of folds.
To prevent this, clamps are used 4. It is recommended to use them for drawing from a flat workpiece when Ds - d1 \u003d 225, where Ds – diameter of the flat workpiece; d1 - diameter of a part or semi-finished product; δ - sheet thickness. The process is characterized by a drawing ratio t \u003d d1/ Dh. To prevent the bottom from tearing off, it should not exceed a certain value. Deep parts, which, according to strength conditions, cannot be pulled out in one pass, are pulled out in several passages. Coefficient value t chosen 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 pulling force of a cylindrical semi-finished product in a stamp with a clamp is determined approximately by the formula
where R1 - own pulling force,; P2 - clamping force,; p - coefficient, the value of which is selected according to look-up tables depending on the coefficient t; σv is the ultimate strength of the material; F1 - cross-sectional area of \u200b\u200bthe cylindrical part of the semi-finished product through which the drawing force is transmitted; q - specific pulling force; F2 – contact area of \u200b\u200bthe clamp and the workpiece at the initial moment of drawing.
Value q choose according to reference books. 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 pulled out, punches and dies can be cylindrical, conical, spherical, rectangular, shaped, etc. They are made with rounding of the working edges, the value of which affects the pulling force, the degree of deformation, the possibility of folds on the flange. The dimensions of the punch and matrix are chosen so that the gap between them is 1.35-1.5 times the thickness of the metal being deformed. An example of a punch for producing cylindrical parts is shown in Fig. 9.41.
Figure: 9.41.
1 – die body; 2 - punch body; 3 - punch
Flanging
This is a shaping in which a part of the sheet blank, located along its closed or open contour, under the action of the punch is displaced into the matrix, simultaneously stretched, rotated and turned into a board. 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 rectilinear contour is bending.
There are two types of flanging - internal flanging of holes (fig.9.42, and) and external flanging of the outer contour (Fig.9.42, b), which differ in the nature of the deformation and the stress pattern.
Figure: 9.42.
and - 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) a hole of a larger diameter with cylindrical sides (Fig. 9.43).
Figure: 9.43.
For several operations in a flat workpiece, you can get holes with a flanging of a complex shape (Figure 9.44).
Figure: 9.44.
The flanging of holes allows not only to obtain constructively successful shapes of various products, but also to save the stamped metal. Currently, flanged parts are obtained with a hole diameter of 3–1000 mm with a material thickness of 0.3–30.0 mm (Figure 9.45).
Figure: 9.45.
The degree of deformation is determined by the ratio of the hole diameter in the workpiece to the bead diameter along the centerline D (fig.9.46).
