Flanging calculation. The method of flanging holes in a sheet blank

Usage: area of ​​metal forming. Essence: a method of flanging holes, in which the workpiece is deformed with simultaneous processing of the deformation zone to a plastic state by electric current. In this case, the current is supplied by pulses to the central part of the deformation zone for a processing width equal to 0.35 ... 0.45 of the diameter of the beaded hole. 1 tab., 2 ill.

The invention relates to the field of metal forming, in particular to methods for intensifying the operation of flanging holes in sheet and tubular blanks of various materials, and can be used in aviation and related industries of mechanical engineering. It is known from the scientific and technical literature that flanging is an operation often used in the production technology of aircraft parts. Flanging is used to form a bead along the edges of the holes and along an open, but concave contour. In most cases, the flanges produced by flanging are stiffening elements of sheet parts or transition elements used for subsequent connection of parts into a single structure. An increase in the limiting possibilities of the operation of flanging holes in sheet blanks leads to an increase in the height of the manufactured sides and, therefore, either to an increase in the rigidity of the manufactured parts while reducing their weight, which is especially important for aircraft parts, or to an improvement in the possibilities for using various methods of joining parts. Thus, the intensification of the flanging operation seems to be very important. A known method of flanging operations based on changing the scheme of the stress-strain state in the deformation zone. As is known, in the traditional scheme of deformation (flanging with a moving punch), bilateral tension occurs in the deformation zone. When a compressive force is applied to the end of the beaded hole, in accordance with the described method of intensification, due to the occurrence of intense compressive stresses in the radial direction, it is possible to largely compensate for the effect of stretching in the tangential direction on the deformation process. This method, in addition to a significant increase in the degree of shaping, makes it possible to produce boards without changing the thickness of the original workpiece. Among the disadvantages of the method of intensifying the flanging operation, it should be noted: a significant complication of the tooling and an increase in the cost of its production, an increase in contact stresses, leading to a decrease in the durability of the die parts. A known method of intensifying the operation of flanging holes, according to which the center of deformation of the workpiece before its shaping is heated to temperatures corresponding to the increase in the plastic properties of deformable materials. Moreover, heating is performed differentially. Near the edge of the hole, the material is heated to higher temperatures than in the area where the bead meets the wall. The described method of intensification makes it possible to increase the limiting possibilities of the forming process. Among the disadvantages of the described method, it should be noted: the duration of the production cycle of one part, due to the duration of heating of the parts of the stamping equipment and the workpiece itself, the significance of energy costs. The problem to be solved by the present invention is to increase the technological capabilities of the hole flanging operation, improve the quality of parts and reduce production costs. This goal is achieved by the fact that in the method of intensifying the operation of flanging holes, including the processing of the deformation zone by electric current to a plastic state in the plane of the sheet during its deformation, the electric current is supplied by pulses to the central part of the deformation zone of the workpiece, to the processing width B arr. equal to: B arr. \u003d (0.35.0.45) D hole, where: D hole is the original diameter of the hole. In FIG. 1 shows a fragment of a sheet with a beaded hole and a schematic representation of the contacts and electric current lines of the processing; in fig. 2 dependence of the flanging coefficient on the value of the ratio of the width of the processing zone B arr to the diameter of the original hole D holes. When implementing this method of processing blanks in the process of their deformation, a model of non-uniform electric pulse processing is implemented. As noted above, when implementing uniform electric pulse machining in the radial direction of workpieces in the process of flanging holes, the edge of the hole is processed by pulsed electric current only at the initial moment of deformation. Subsequently, as the zone of contact between the workpiece and the conductive punch increases, the edge of the hole is driven by current and is not processed or plasticized. When implementing the model of non-uniform current processing in the plane of the sheet, the central parts of the workpiece between the current-carrying elements 1 are processed with maximum intensity, as evidenced by the graphical representation of the current lines 2. The intensity of processing the edges of the holes 3 in this case increases even more due to the additional current concentration due to "bending" "obstruction" current, in the role of which the hole itself acts. The edge parts of the workpiece are processed due to the scattering of current lines with a decrease in the intensity of processing as they move away from the current-carrying elements. Thus, the machinability of the beaded hole 3 does not depend on the degree of fit to the punch and is carried out due to the "leakage" of the current, which is explained by the unevenness of the electropulse processing. The implementation of this method in the formation of beads along the edges of holes or along an open one, but the development in order to improve the plastic properties of materials and restore their plasticity resource during the entire deformation stage, which leads to an increase in the degree of forming. Example. When experimentally determining the effectiveness of the proposed method of the flanging operation, a comparison was made of the limiting degrees of shape change of parts manufactured in accordance with the prototype and manufactured in accordance with the claims of the proposed invention. As a parameter for comparison, the value of the flanging coefficient k reb was taken, defined as the ratio of the diameter of the original hole D rem to the diameter of the resulting board D b. Electric pulse processing of workpieces in the process of their deformation was carried out from a source of pulsed current, which included: a step-down transformer with a power of 250 kW; a welding type current interrupter used to regulate the energy and time parameters of the processing current over a wide range. To change the energy and time parameters of the processing current, a S8-13 storage oscilloscope and a measuring current transformer were used. The deformation of blanks from various materials was carried out on a hydraulic press with a maximum force of 300 kN. A specially designed and manufactured experimental equipment with a replaceable punch and die made it possible to deform blanks in accordance with both compared methods. The use of conductive electrically insulated punch and matrix made it possible to carry out the deformation process in accordance with the method adopted for the prototype. The use of a punch, a matrix and a clamp made of insulating heat-resistant materials with electrical contacts built into the clamp made it possible to deform the materials according to the method proposed in the claims. Moreover, when deforming workpieces in accordance with the invention, due to the use of different-sized conductive pads, it was possible to vary the current treatment zone and, therefore, vary the degree of non-uniformity of the electric pulse treatment. To match the experimental data obtained by both deformation schemes, the shaping was carried out by cone punches with a taper angle of 30. The effectiveness of the proposed method for intensifying the flanging operation was revealed in the process of deformation of workpieces from alloys: D16M, V95M, 12Kh18N10T, OE4. The thickness of sheet blanks from all the investigated alloys was 2 mm. The holes in the workpieces were obtained by drilling with subsequent cleaning of the edges. The ratio of the values ​​of the flanging coefficients obtained during deformation in accordance with the method adopted for the prototype and in accordance with the invention are shown in the table. From the analysis of the data given in the table, it follows that the use of electric pulse processing of materials in the process of their deformation, carried out in accordance with the essence of the present invention, allows an average of 35% to reduce the value of the flanging coefficient and, therefore, significantly increase the marginal possibilities of the operation in relation to method of processing workpieces with pulsed current in the process of their shaping, taken as a prototype. This clearly indicates the advantages of this method of intensifying the flanging operation in relation to the method adopted as a prototype, and confirms the goals described in the distinctive part of the claims. To determine the optimal size of the treatment zone with a pulsed electric current, flanging of holes was carried out with a wide variation in the width of the contacts of the conductors. For this, equal-sized conductive spacers were used in the experiments. When using these gaskets, the size of the processing zone changed from B arr 0.25 D resp. to B arr 0.7 D resp. with a step of B 0.05 D resp. The experiments were carried out on all the materials listed above. As a comparison parameter, as before, the value of the flanging coefficient k reb was used. The results obtained in this part of the described experimental studies for the D16M aluminum alloy are shown in Fig. 2. From the analysis of the dependence of the flanging coefficient k otb on the value of the ratio B rev /D otv, which determines the processing zone of the pulsed alloy D16M in the process of its deformation during the operation of flanging holes (Fig. 2), we can draw the following conclusions: with a decrease in the processing zone with a pulsed electric current and, consequently, an increase in the uneven processing of the deformation zone, a decrease in the flanging coefficient is observed, which indicates an increase in the limiting degrees of shape change; the minimum values ​​of the flanging coefficient are taken when processing workpiece zones corresponding to the width B arr (0.25.0.45) D resp; when the size of the processing zone B arr with a pulsed current is less than 0.35 of the diameter of the original hole for flanging D rem due to significant current concentrations near the contacts, an intense material of the workpiece is observed, leading to the occurrence of burns, burns and other irreparable surface defects (the dashed part of the line in Fig. . 2). Thus, it is impractical when performing the operation of flanging holes to reduce the processing area with pulsed electric current B arr less than 0.35 from the diameter of the original hole D holes. The results of experimental studies to determine the optimal zone for processing blanks from other materials listed above by pulsed electric current when flanging holes on them are completely similar to those given above for the V16M aluminum alloy, therefore, they, as well as conclusions on them, are not given. The above experimental studies confirm the proposed in the claims range of zones of electric pulse processing of sheet blanks in the process of flanging holes on them. The invention is applicable in the aerospace industry and related branches of engineering.

stamping like technological process processing of workpieces made of metal, allows you to get finished products of a flat or volumetric type, differing both in their shape and size. A stamp attached to a press or other type of equipment can act as a working tool when performing stamping. Depending on the conditions of execution, metal stamping is hot and cold. These two types of this technology involve the use of different equipment and compliance with certain technological standards.

Technology Features

You can get acquainted with the GOST requirements for metal stamping processing by downloading the document in pdf format from the link below.

In addition to the division into hot and cold, stamping of metal products is also divided into a number of other categories, depending on its purpose and technological conditions. So, stamping operations, as a result of which a part of a metal blank is separated, are called separating. This, in particular, includes cutting, chopping and punching metal parts.

Another category of such operations, as a result of which the stamped sheet of metal changes its shape, are shape-changing stamping operations, often referred to as forming. As a result of their implementation, metal parts can be subjected to drawing, cold extrusion, bending and other processing procedures.

As noted above, there are such types of stamping as cold and hot, which, although they are implemented according to the same principle, which involves metal deformation, have a number of significant differences. , which involves their preheating to a certain temperature, is used mainly in large manufacturing enterprises.

This is primarily due to the rather high complexity of such a technological operation, for the qualitative implementation of which it is necessary to make a preliminary calculation and accurately observe the degree of heating of the workpiece being processed. With the help of hot stamping, such critical parts as boiler bottoms and other hemispherical products, hulls and other elements used in shipbuilding are obtained from sheet metal of various thicknesses.

To heat metal parts before hot stamping, heating equipment is used, which is able to provide accurate temperature conditions. In this function, in particular, electric, plasma and other heating devices can be used. Before starting hot stamping, it is necessary not only to calculate the heating rates of the workpieces, but also to develop an accurate and detailed drawing of the finished product, which will take into account the shrinkage of the cooling metal.

When making metal parts, the process of forming the finished product proceeds only due to the pressure exerted by the working elements of the press on the workpiece. Due to the fact that blanks are not preheated during cold stamping, they are not subject to shrinkage. This allows you to produce finished products that do not require further mechanical refinement. That's why this technology is considered not only more convenient, but also a cost-effective processing option.

If you skillfully approach the issues of designing the dimensions and shape of blanks and the subsequent cutting of the material, then you can significantly reduce its consumption, which is especially important for enterprises that produce their products in large batches. Not only carbon or alloy steels, but also aluminum and copper alloys can act as a material from which blanks are successfully stamped. Moreover, an appropriately equipped punching press is successfully used to process workpieces made of materials such as rubber, leather, cardboard, and polymer alloys.

Dividing stamping, the purpose of which is to separate a part of the metal from the workpiece being processed, is a very common technological operation used in almost every manufacturing enterprise. Such operations, which are performed by means of a special tool mounted on a stamping press, include cutting, punching and punching.

During the cutting process, metal parts are divided into separate parts, and such separation can be carried out along a straight or curved cut line. Various devices can be used to perform cutting: disk and vibration machines, guillotine shears, etc. Cutting is most often used to cut metal blanks for further processing.

Punching is a technological operation during which parts with a closed contour are obtained from a metal sheet. With the help of punching in sheet metal blanks, holes of various configurations are made. Each of these technological operations must be carefully planned and prepared so that as a result of its implementation a high-quality finished product is obtained. In particular, the geometric parameters of the tool used must be accurately calculated.

Perforated metal sheet is obtained by punching holes on a jig punch press

Technological operations of stamping, during which the initial configuration of metal parts is changed, are forming, bending, drawing, flanging and crimping. Bending is the most common form-changing operation, during which sections with a bend are formed on the surface of a metal workpiece.

The hood is a three-dimensional stamping, the purpose of which is to obtain a three-dimensional product from a flat metal part. It is with the help of the hood that the metal sheet turns into products of a cylindrical, conical, hemispherical or box-shaped configuration.

Along the contour of sheet metal products, as well as around the holes that are made in them, it is often necessary to form a ledge. Flanging successfully copes with this task. Such processing, performed by means of a special tool, is also subjected to the ends of the pipes on which it is necessary to install flanges.

With the help of crimping, unlike flanging, the ends of pipes or the edges of cavities in sheet metal blanks are not expanded, but narrowed. When performing such an operation, carried out using a special conical die, an external compression of the sheet metal occurs. Forming, which is also one of the varieties of stamping, involves changing the shape of individual elements of a stamped part, while the outer contour of the part remains unchanged.

Volumetric stamping, which can be performed using various technologies, requires not only careful preliminary calculations and the development of complex drawings, but also the use of specially manufactured equipment, so it is problematic to implement such a technology at home.

Tools and equipment

Even the processing of soft metals, in particular aluminum stamping, requires the use of special equipment, which can be guillotine shears, crank or. In addition, the ability to calculate material consumption and develop technical drawings is necessary. In this case, the requirements contained in the corresponding GOST should be taken into account.

Stamping, which does not require preheating of the workpiece, is carried out mainly on hydraulic presses, the production of which is regulated by GOST. A variety of serial models of this equipment allows you to select a machine for the production of products of various configurations and overall dimensions.

When choosing a press for stamping, first of all, you should be guided by the tasks for which it is needed. For example, to perform such technological operations as cutting or punching, single-acting stamping equipment is used, the slider and washers of which make a small stroke during processing. In order to perform the extraction, double-acting equipment is required, the slider and washers of which make a significantly larger stroke during processing.

According to its design, as GOST indicates, equipment for stamping is divided into several types, namely:

• single crank;
• double-crank;
• four-crank.

On the presses of the last two categories, sliders of larger sizes are installed. However, regardless of the design, each punching press is equipped with a die. The main movement, due to which the workpiece is processed on a stamping press, is performed by a slider, the lower part of which is connected to the movable part of the stamp. To communicate such a movement to the press slider, the drive motor is connected to it by means of such elements of the kinematic chain as:

• V-belt transmission;
• starting clutch;
• washers;
• crank shaft;
• connecting rod, with which you can adjust the amount of stroke of the slider.

To start the slider, which reciprocates towards the working table of the press, a foot press pedal is used, which is directly connected to the starting clutch.

A four-rod press differs in a slightly different principle of operation, the working bodies of which create a force with a center falling in the middle of a quadrangle formed by four connecting rods. Due to the fact that the force generated by such a press does not fall on the center of the slider, this device is successfully used in order to manufacture products of even very complex configurations. Presses of this category, in particular, are used to produce asymmetric products that differ in significant dimensions.

To manufacture products of a more complex configuration, pneumatic-type press equipment is used, design feature which lies in the fact that it can be equipped with two or even three sliders. In a double-acting press, two sliders are used simultaneously, one of which (external) provides fixation of the workpiece, and the second (internal) performs the drawing of the surface of the processed metal sheet. The first in the operation of such a press, the design parameters of which are also regulated by GOST, is an external slider that fixes the workpiece when it reaches the lowest point. After the inner slider has done its work of stretching the sheet metal, the outer working body rises and releases the workpiece.

For stamping sheet metal, mainly special friction presses are used, the technical parameters of which are also established by GOST. To process thicker sheet metal, it is best to use hydraulic punching equipment, which is equipped with more reliable washers and other structural elements.

A separate category is the equipment with which explosion stamping is performed. On such devices, in which the energy of a controlled explosion is converted into a force exerted on the metal, metal blanks of considerable thickness are subjected to processing. The operation of such equipment, which is considered innovative, looks very impressive even on video.

To ensure that the resulting bend and the overall configuration of the finished metal product are of high quality, recently presses equipped with built-in vibration shears have been actively used. The use of such equipment with shorter legs allows the manufacture of products of almost any configuration.

Thus, sheet metal stamping requires not only specialized equipment, but also appropriate skills and knowledge, so it is rather difficult to implement such a technology at home.

Flanging of products on special stamps. Flanging of the outer contour. Hole flanging (internal).

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

Distinguish between flanging of the hole (internal) and flanging of the outer contour. Flanging of products is carried out on special stamps. To make flanging in a flat or hollow workpiece, you must first punch a hole in it. With deep flanging, the hood is first made, then a hole is punched and then the flanging is performed. In order to perform flanging without gaps and cracks in one operation, it is necessary to take into account the degree of deformation (or the so-called flanging coefficient) K otb =d/D, where d is the diameter of the pre-punched hole, mm; D is the diameter of the hole obtained after flanging, mm.

The flanging of the product from a thin material is carried out with the product pressed against the surface of the stamp matrix. The diameter of the flare hole for a low side can be approximately determined by the method that is used when calculating the workpiece with a rounding, resulting in a flexible one. 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 \u003d h + r 1 + S \u003d D - (d / 2) + 0.43r 1 + 0.72S.

Rice. nine. Scheme for calculating the flanging of the product

It has been established by practice that the limiting flanging coefficient depends on the mechanical properties of the material, the relative thickness of the workpiece (S / d) . 100, the surface roughness of the edges of the holes in the workpiece, the shape of the working part of the die punch.

The radius of curvature of the 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 ot = π(D-d)SCσ t ≈1.5π(D-d)Sσ in, where D is the diameter of the product flanging, m; d - diameter of the hole for flanging, m; S - material thickness, m; C is the coefficient of metal hardening and the presence of friction during flanging Сσ t = (1.5÷2)σ in; σ t and σ in - yield strength and tensile strength of the material, MPa (N / m 2).

Flanging of the outer contour parts are used with convex and concave contours. Convex flare is similar to shallow drawing process, and concave flare is similar to hole flare.

The amount of deformation during external flanging of the convex contour K n.otb = R 1 /R 2 , where R 1 is the radius of the contour of a flat workpiece; R 2 is the radius of the flanged contour of the product.

Molding is an operation in which the shape of the product, previously obtained by drawing, is changed. Such an operation includes, for example, molding from the inside (bulging), obtaining a bulge, depression, pattern, inscription. Dies for molding from the inside have split dies and an expandable elastic device (liquid, rubber, mechanical).

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 lower 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 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 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.