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

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

Crimp (fig.17.46, b) - reduction of the perimeter of the cross-section of the hollow workpiece. In the deformation center, the wall thickness of the product increases slightly. To avoid the formation of longitudinal folds in the crimped part, the crimp ratio must be observed

K = ~ - = 1.2 ... 1.4,

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

Cold stamping is carried out mainly on crank presses. Technologically, mechanical presses are divided into single, double and triple action presses (one-, two- and three-slide, respectively). The kinematic diagram of a single-acting crank stamping press is in many respects similar to that of a crank hot stamping press.

A double-acting press (fig. 17.47) is designed for deep drawing of large parts. It has two slides - an internal 3 driven by a crank and an external 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 attached to the inner slider, the outer slider is stationary. At the end of the drawing, the sliders rise.

Fig. 17.47. Diagram of a single-crank double-acting press

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

As a tool for cold sheet stamping, stamps are used. They consist of blocks of parts and working parts - dies and punches. The working parts directly deform the workpiece. The parts of the block (upper and lower plates, guide columns and bushings) serve to support, guide and fasten the working parts of the stamp. Technologically, there are simple, sequential and combined action stamps.

In the stamp simple action (Fig. 17.48) in one stroke of the slider, one operation is performed, therefore it is called single-operation. The stamp is placed on the press table with the lower plate and fastened to it with bolts and brackets, the upper plate of small stamps is attached to the slider using a shank, and the upper plate of large stamps is attached to the slider in the same way as the lower plate to the press table. The strip or tape is fed into the stamp between the guide rails until it stops, which limits the strip or tape feed pitch. A stripper is used to remove the die cut from the punch.

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

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

of the slider down, the punch 5 and the matrix 8 cut the workpiece out of the strip 6, and the punch 7 simultaneously draws the product in the 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-operation. 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.

Flanging is divided into two main types: flanging of holes and flanging of the outer contour. They differ in the nature of deformation, stress state diagram, and industrial purpose.

Flanging of holes is the formation of beads around pre-punched holes (sometimes without them) or along the edge of hollow parts, produced by stretching the metal.

Figure 7 - Sequence of the flanging process

Flanging of holes is widely used in stamping production, replacing drawing operations, followed by punching the bottom. Especially great efficiency is provided by the use of flanged holes in the manufacture of parts with a large flange, when drawing is difficult and requires several transitions.

Conclusion

The developed schemes and methods for calculating technological processes make it possible to accurately assess and calculate their characteristic indicators. The calculation method helps to study in more depth the possible options for the high-quality work of the metalworking industry, namely the sheet stamping process. The manual makes it easier for students to navigate the proposed calculation methodology, developing logical thinking; makes it possible to come up with new schemes of technological processes for implementation in production and their successful work.

The manual can be used to calculate the technological processes of any operations of the HLS process. Due to the proposed calculations, the shaping of metal blanks can almost always be carried out ambiguously. There are many possible options for calculating any technological process.

To get the best option for a particular example, you need to calculate along several possible paths. For a more efficient and convenient use of the calculation material, a certain computer program is required.

APPENDIX I

An example of the calculation of the technological process of sheet stamping

Example:

Obtain a part from steel 35 in the form of a hemisphere with dimensions S = 0.8 mm, H = d / 2 = 25 mm, d = 50 mm.

1.1 Analysis of methods of obtaining a product

The hemisphere is a three-dimensional product, so it is not possible to get it by rolling (cold or hot), because This process allows you to obtain only flat products (sheet, plate, profile), the only exception is pipes obtained by rolling, therefore, we will exclude this process of shaping immediately without further analysis. It is also impossible to obtain a hemisphere by pressing, because It involves the production of flat products, as in rolling, with the exception of pipes (angles, channels, T-beams, I-beams, other complex profiles), therefore, similar to rolling, we will not conduct a more detailed analysis of the manufacture of this product.

Hot stamping, which is a volumetric process, should have made it possible to obtain this product, but in reality this is not the case, since it is carried out in the so-called. special technological cavities that follow the contour of the part. Although, by such a deformation process, it is possible to obtain a rough workpiece and, after a number of additional operations, to make a hemisphere, but due to the duration, increased labor intensity and economic inexpediency, this process of manufacturing a hemisphere can be excluded (forging will not even be considered, since it is impossible to forge such a part due to laboriousness of manufacturing its geometry for this operation). Cold stamping is similar to the hot stamping process in terms of obtaining various volumetric products (but it also allows flat products, such as a corner, a circle, etc.). Sheet stamping is divided into several operations: punching, punching, broaching, distribution, crimping, drawing, forming, cutting, bending. Cutting, punching and punching allows you to get only flat products, so we immediately exclude these punching operations. Bending also allows you to get only flat parts, but with a different orientation, therefore, this operation is also excluded. Crimping and expanding allow you to get parts that, after these operations have proceeded, will have a different cross-sectional diameter in relation to the original. In this case, the workpiece is a circle of a specially calculated diameter, it is clearly impossible to distribute such a workpiece, to compress it too, because in the latter case, corrugations will necessarily take place, which cannot be removed by any additional processing method, therefore, these operations are also not suitable in this case. Stretching, broaching and forming can be referred to one general group of operations. Broaching and forming are special cases of drawing. Broaching is the same drawing operation, but there is a thinning of the wall in the process of deformation, which we do not have due to the unnecessary pressing of the workpiece to the matrix, which causes

thinning of the wall as a result of the action of the punch on the workpiece. Forming is also a special case of extrusion, but such an operation allows you to obtain a similar part with a smaller extrusion radius (in our case, we have a deep extrusion radius). Thus, having carried out a complete analysis of the methods for producing a hemisphere, we choose the process of cold sheet stamping, the drawing operation. Stretching is a process of shaping, which leads to a characteristic volumetric scheme of the stress-strain state.

The technological process of manufacturing a hemisphere is as follows: cold-rolled sheet with a thickness of 0.5 mm is supplied to the stamping section as a blank material. Further, separating operations are carried out, i.e. blanks are cut from the sheet in the form of a circle of the calculated diameter. After that, the workpiece is placed in a drawing die and a pre-calculated force for a given deformation is given. The resulting product (hemisphere) is checked for external defects, if they are visible, then the part is either rejected or eliminated (depending on the degree of the defect). If additional mechanical actions are needed, then the part is sent for mechanical processing (drilling, punching, grinding, etc.). Further, the part is subjected to more thorough quality control and studies are carried out for the suitability of work in real conditions (not all parts are subjected to control, but three pieces taken from one batch). At the end of all the above operations, the parts are marked, packaged and sent to the warehouse, from where the products are delivered to the customer.

1.2 Calculation of cutting strips into blanks

To calculate the technological process, you first need to calculate the cutting of the material. We will assume that the punching process of this part is automated, so we will use single-row cutting. The material for the workpiece will be a strip, the size (width) of which should be calculated. First, let's find the diameter of the workpiece that will be cut from the strip. From table 19, the diameter of the workpiece for the hemisphere is found by the formula

The length of the strip is GOST and is 1000, 2000, 3000 mm, etc. Let's take a strip with a width of 1000mm. Determine the width of the strip, for this we will find out the size of the jumper between the blanks to be cut

∆ = (2-3) S = 2 * 0.8mm = 1.6mm

Feed step

W = D z + ∆ = 70.7 + 1.6 = 72.3 mm

The width of the line

B = D z + 2∆ = 70.7 + 2 * 1.6 = 73.9 mm

According to GOST, there is no approximate width of the strip, but only the exact one, therefore, we take a strip with a width of 74 mm.

The number of workpieces to be placed on a strip 1000 mm long and 74 mm wide

The strip holds as many as 13 blanks.

The area of ​​one workpiece

Strip area

F p = B * L = 74 * 1000 = 74000 mm 2

Let's find the utilization factor of the material according to the formula

Thus, 31.1% of the metal is wasted.

1.3 Selection of technological process and its calculation

Knowing the diameter of the workpiece, we will calculate the force of the drawing process. Because it was previously assumed that the drawing goes in one transition, then we will not refine this assumption using additional formulas.

Р = πD s Sσ in k 1

This is the formula for determining the effort of the drawing process, where π = 3.14 (constant), S = 0.8 mm, D z = 70.7 mm, k 1 = 0.5-1.0, we take k 1 = 0.75 , σ in is the ultimate strength for steel 35, according to the tables of mechanical properties for this steel σ in = 540-630 MPa, we take σ in = 600 MPa.

Since the thickness of this product is 0.8 mm, the clamp can be omitted.

Then the total process force is equal to the drawing force.

Determine the work of the process

where P max = 79.92 MPa, C = 0.6-0.8, we take C = 0.7, h = 25 mm (drawing depth)

The resulting data is consistent with the workflow for this part. On the basis of the obtained values, the equipment for the implementation of this process is selected, and the values ​​of the parameters of the press must be higher than the calculated values ​​for the implementation of its normal operation.

APPENDIX II

Elementary areas of the simplest figures:

Area of ​​a circle

Square area

Ring area

Area of ​​a triangle

Formula for determining the length of an arc of a circle:

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-annular mesh applied to the workpiece (Figure 8.57)... When the holes are flanged, the elongation occurs in the tangential direction and the thickness decreases. 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.

Picture. 8.57. Flanging scheme

The hole diameter is determined by the formula:

• d = D-2 (H-0, 43r - 0.72 S), (8.96)

The height of the side is expressed by the relationship:

• H = (Dd) / 2 + 0.43r + 0.72S, (8.74)

where the designations correspond to (fig. 8.57).

As can be seen from the last formula, the height of the side, 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 up to z = (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 hearth, 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 = (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 force of the flanging depend on their value.

Thus, this process is best performed 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 rounding, cylinder with small rounding)... The force required for flanging with a cylindrical punch can be determined using the following formula:

• P = lnSσt (Dd), (8.75)

where D is the diameter of the flange, mm; d - hole diameter, mm.

Execution depends on the cleanliness of the cut of the deformable edge.

The degree of deformation when flanging 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 = 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, that is, 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 ​​of the coefficients for mild steel depending on the flanging conditions and the d / S ratio.

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 = (Dd) / 2 = 0.57r; (8.77)

• d = 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.

Picture. 8.60. Flanging with 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. (spars, etc.), And the sides - to increase structural strength.

In this case, the height of the side is taken small (4 ÷ 6%) S with low requirements for its accuracy.

When constructing a sweep, one should take into account the different nature of the deformation along the contour.: bending in straight sections and flanging with tension 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 height of the side.

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 = (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 non-circular 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 coefficients are slightly less than 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 edge of the opening.

The limiting coefficient of flanging of holes obtained by punching, due to work-hardening of the edge, 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 operation (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.

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Flanging of products on special stamps. Flanged outer contour. Hole flange (internal).

Scheme for calculating the flanging of the product. Force for flanging with a cylindrical punch. Forming.

A distinction is made between flanging holes (internal) and flanging of the outer contour. 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 otd = d / D, where d is the diameter of the pre-punched hole, mm; D is the diameter of the hole obtained after flanging, mm.

Flanging of a product made of a thin material is carried out with pressing the product to 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 = D 1 - π - 2h. Hence the height of the side H = h + r 1 + S = D - (d / 2) + 0.43r 1 + 0.72S.

Fig. 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, roughness of the surfaces of the edges of the holes in the workpiece, the shape of the working part of the punch of the stamp.

The radius of rounding of a cylindrical punch must be at least four material thicknesses.

Force for flanging with a cylindrical punch can be determined by the formula of A.D. Tomlenov: P out = π (D-d) SCσ t ≈1.5π (D-d) Sσ in, where D is the diameter of the flange of the product, m; d is the diameter of the flanging hole, m; S - material thickness, m; C - coefficient of metal hardening and the presence of friction during flanging Cσ t = (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 at the outer flanging of the convex contour K notb = 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).