Sheet bending technology. How is sheet metal bending? Self-production of the machine

Bending sheet metal is one of the most common hot and cold forming operations. The process is notable for its low energy consumption and makes it possible to successfully manufacture spatial products of various shapes and sizes from flat blanks.

Classification and process features

Sheet metal bending technology is developed in accordance with the assigned tasks and is classified into:

one-angle (V-shaped);
two-corner (U-shaped);
multi-angle;
radius (seaming).

Bending is usually carried out in a cold state, since the applied forces are low. An exception is the bending of a steel sheet made of low-plasticity metals. These include steels with a high carbon content, duralumin, titanium and its alloys. Materials with a thickness of 12 to 16 mm are usually hot bent. In the process of bending, rolled metal can get the following shape distortions:

change in thickness (mainly for thick-sheet blanks);
the appearance of metal flow lines;
springing / springing (spontaneous change of the final bending angle);
folding of a metal sheet.

Bending is often combined with other sheet metal stamping operations: cutting, punching, punching. For this reason, for the production of complex multidimensional parts, dies are used, which are designed for several transitions. A special case of sheet metal bending is the stretching operation, designed to produce narrow and long parts with large radii.

Depending on the type and size of the workpiece, as well as the required characteristics of the products after deformation, the following can be used as bending equipment:

horizontal hydraulic presses with two sliders;
vertical press brakes with hydraulic or mechanical drive;
pipe and profile bending;
blacksmith bulldozers;
universal bending machines.

The main features of plate bending devices are the increased size of the die space, reduced deformation rates and low energy consumption.

Stages and sequence of technology

In the future, we will focus on the processes of processing rolled metal in a cold state. Development of technological process sheet metal bending is carried out in the following sequence:

analysis of the design of the part;
calculation of the effort and work of the process;
selection of the standard size of production equipment;
preparation of a drawing of the original workpiece;
calculation of deformation transitions;
design of the project of technological equipment.

Checking the compliance of the capabilities of the source material - important process, which must be performed to determine the suitability of rolled metal for stamping according to the specific dimensions indicated on the drawing of the finished part. This stage includes:

studying the plastic abilities of the material and checking the compliance of the result with the level of stresses arising during bending. For low-plastic alloys and metals, it is necessary to split the process into several transitions and use interoperative annealing, which is designed to increase the plasticity;
the possibility of obtaining a bend radius at which the risk of material cracking is reduced to zero;
determination of possible distortions of the profile or thickness of the workpiece after the completion of pressure treatment with complex contours of the product.

According to the results of this analysis, a decision can be made on:

replacing the original material with a more plastic one;
preheating the workpiece before deformation;
performing preliminary softening heat treatment.

An extremely important point in the development of a technological process is the calculation of the minimum allowable bending angle, its radius and spring angle.

Bending radius (rmin) is calculated based on the level of plasticity of the workpiece metal, the ratio of its dimensions and the rate of deformation. With a decrease in rmin, all metals experience a decrease in the initial thickness of the workpiece. This process is called thinning. Its intensity determines the coefficient of thinning λ, the percentage of which depends on how much the thickness will decrease finished product... If this value is higher than the critical value, then it is necessary to increase the initial thickness of the workpiece metal (s). Correspondence between the above parameters:

It is also important to define minimum bending radius, which depends on the ductility, thickness and location of the fibers of the rolled metal. This is necessary if the bending radius is small, since in this case the outer steel fibers can break, as a result of which the integrity of the finished product will be violated. For this reason, the minimum radii should be calculated from the greatest deformations of the extreme parts of the workpiece, based on the relative narrowing (ψ) of the metal subjected to deformation. In this case, the amount of deformation of the workpiece must be taken into account.

The effect of the possible springback taken into account by means of data on the actual angles of spring (β):

Determination of the bending force

The strength indicators of bending directly depend on the plasticity of the metal and the intensity of its hardening during deformation. These parameters have the direction of rolling of the original billet. Upon completion of rolling, the material acquires the property of anisotropy (in the direction of the rolling axis, the residual stresses are less than in the opposite direction). Thus, if the metal is bent along the fibers, then with the same degree of deformation, the risk of destruction of the part is significantly reduced. For this reason, the bending rib is positioned so that the angle is minimal between the position of the workpiece in the sheet and the rolling direction.

To obtain a highly accurate calculation of the force parameters, it is necessary to clarify how the deformation will be carried out. There are two options:

bending element- the workpiece is laid on the stops with subsequent free deformation;
effort- at the final moment of the process, the part rests on the working surface of the matrix.

The first method is the simplest and less power-consuming, the second one allows you to get more accurate parts.

Metal bending is a method of changing the shape of a workpiece. Such a change is carried out without any material sampling, namely cutting or electric welding.

The required result is obtained through the use of metal deformation. When bending, the inner layer of the material is squeezed and the outer layer is stretched. In some ways, the bending operation is akin to straightening, the use of which eliminates defects - bulges and waviness.

Varieties and design of bending machines

Sheet metal bending is performed on specialized equipment - sheet bending machines. According to the principle of operation, metal bending machines can be conditionally divided into several types:

Universal. During the operation of this machine, the sheet is laid in a fixed matrix and, with the assistance of a punch, is given the required shape. Punches are made in several versions, which differ from each other in shape and size, for example, in angle. On the matrix, as a rule, an angle-shaped groove is made.

Universal presses are easily reconfigured and capable of solving many technological problems.

Turning. This machine consists of a traverse, as they call a bending beam, a bending beam and a back stop. The clamping beam is necessary to fix the metal sheet to the bed. The bending of the sheet is carried out by a bending beam. In fact, it is the main working element of this machine.

Rotary. The design of such equipment may include several shafts (rolls). They rotate around their axis. In addition, the work rolls can move in a vertical plane. A sheet of metal is placed in the space between the shafts and by moving them vertically, the future bending radius is adjusted. After the sheet has passed between the rotating shafts, it will get the desired shape.

The metal bending machine can be powered by human muscle force, hydraulic, pneumatic, electrical (electromechanical) or mechanical drive.

To work with metal of small thickness, folding or folding machines are used. They are widely used when working with a roofing sheet, creating ventilation ducts etc.

Types of bending machines

To get a complete picture of the work of a bending machine, you need to understand how it works. The structure of this equipment includes such units as a table on which the workpieces are placed. The workpiece will move along its surface in the specified direction. In addition, a cutter can be installed on the table, cutting off finished parts from the sheet of starting material. A roller knife or a reciprocating guillotine can be used as a cutter.

The bending machines include a protractor. It is used when setting the angle at which the sheet should be bent. In addition to this unit, limiters that regulate the maximum height of the resulting product play an important role.
The working length of the bending and the limiting metal thickness for each type of machine is strictly individual.

In practice, the following types of bending machines are used.

Hand-held equipment is small in size and can be easily transported from one place to another. It is used in one-off production. On manual machines, work is performed to obtain parts made of different materials, for example, aluminum, copper, galvanized steel. Working on such a machine does not require any special training.

Mechanical equipment uses in its work the energy of the flywheel, which is specially unwound for this. Electromechanical driven machines are powered by a drive station that includes an electric motor, gearbox, belts or chains. Hydraulic power packs are powered by energy from a hydraulic cylinder.

By the way, for careful bending of sheets, especially those on which the coating is applied, bending machines using compressed air are used.
There are also devices such as electromagnetic. They are often used in the manufacture of boxes and boxes. The working tool in such equipment is powerful electromagnets, under the influence of which the sheet is bent.

A separate class of bending equipment is portable (mobile), as a rule, they are used directly at the workplace, for example, at a construction site.

Advantages and disadvantages of bending machines

Like any bending equipment, it has a number of advantages. These include - the strength of the finished parts obtained. The use of bending machines allows you to form parts without the use of welding and cutting. After the bending operation has been completed, the likelihood of corrosion phenomena in the place of its implementation is reduced.

The use of bending machines allows you to create one-piece structures, and as part of such a product, it is possible to obtain versatile bends and angles.
But, one must also understand that bending equipment is quite expensive. Sheet bending operations are very laborious, especially if these works are performed on equipment designed for manual work.
But the listed disadvantages are more than compensated by the quality of the products obtained.

The operating principle of various plate bending machines

Technological equipment used on modern production on the creation of metal structures, allows you to obtain finished parts from sheet material with different dimensions and shapes.

Manual bending machines

These structures have a number of features, in particular, they have restrictions on the depth of the workpiece, the maximum thickness of the metal, its width, or rather the length of the bending. How thinner metal, the longer the bending length. Most often, they are used for bending thin sheet metal.

The manual installation work is structured as follows:
The top beam presses the sheet against the working table. The required bending angle is obtained by lifting the lower, pivoting beam. When using this machine, it must be borne in mind that the thickness of the sheet that can be processed should not exceed 2 mm.

Manual bending machines have a low weight, and this allows them to be used both in stationary conditions and directly at the workplace, for example, at a construction site.

These machines use liquid as a source of energy. The pump, built into the system, creates an overpressure, under the action of which the plunger moves the movable crossbeam.
The sheet to be processed is pressed against the work table, and the movement of the crossbeam is performed, straightening and bending of the sheet.

Sheet bending machines of this class are used for processing workpieces along the entire length of the working table, in addition, with their help, deep drawing of metal is performed.
The hydraulic cylinders feature positioning accuracy and high working efficiency. Their use allows you to control the amount of movement, speed and movement of parts of the hydraulic system.

Machines with a hydraulic drive are used for the production of additional components, air ducts, roofing parts. With the help of this equipment, advertising structures are manufactured, external and internal decoration of buildings and structures is performed.
The use of hydraulic equipment makes it possible to process sheets with a greater thickness, for example, up to 4 - 8 mm. Of course, this value depends on the grade of the processed material.

The structure of this equipment consists of a bed, a swing beam for bending the sheet. In addition to the rotary beam, a beam assembled from profile senments is installed on the machine, which presses the sheet. For the operator's safety, this type of machine is equipped with a foot pedal control.

Bending machines of this type allow you to bend metal with a long length. They are used to process various materials, including galvanized steel, 2.5 mm thick cold rolled steel.

Machines of this type are used in the production of ebb, window sills, structures for ventilation systems.

Metal bending and its main methods

Sheet bending

It should be understood that bending operations are not limited to sheet metal work. When creating metal structures for various purposes, there is a need to use bent pipes or profiles.

Radial bending of sheet metal is carried out on the equipment described above. When performing it, it is important to choose the correct linear size of the workpiece. The designer should remember that the length of the workpiece should be slightly larger than the length of the finished part. This is due to the specifics of the bending operation. The fact is that when you change the position of one part of the sheet relative to another, the inner layers of the metal are compressed, and the outer ones are stretched. That is, before performing radius bending of metal, it is necessary to carefully calculate the geometric parameters of the workpiece.

To calculate the bend radius, it is enough to use tabular data, which can be found in almost any engineering reference book.

Pipe bending

Pipes can also be bent in accordance with the requirements of the working documentation. There are several methods - manual and mechanized. By the way, in everyday life, bent pipes can be found on fences and railings installed in residential buildings and other premises.

Most often, the pipes are slashed along the radius. This process allows the formation of a partial or complete bend of the pipe. Moreover, it will not depend on the shape and size of the section. The process of deformation of pipes looks like this - when bending a hollow profile, several forces act on the workpiece, one affects the surface of the inner wall, and the other affects the outer side of the profile.

When bending the pipe, there is a danger that the interaction of these forces could deform the pipe profile. As a result, misalignment may occur. Moreover, if a number of technological rules are not followed, the pipe can be ruptured. If the bend is uneven, folds may form at the bend. The reason for this is the effect of tangential forces arising during the deformation of the pipe.

To avoid such phenomena, cold and hot pipe bending is used. The first method is used for processing pipes with a small diameter. But in this case, you need to know the minimum allowable bend radius, which runs along the center line. It should be noted that the use of local heating of the pipe creates more comfortable conditions for performing pipe bending. After heating, the metal acquires ductility sufficient to perform a given deformation. The hot bending method is used on large diameter pipes.

Metal bending on CNC machines advantages

Increasingly, the use of computer-controlled hardware is becoming the norm rather than the exception. Such machines can be seen in almost any production, moreover, regardless of its scale. The use of specialized software allows not only to increase the speed of processing parts, but also leads to significant savings in metal, increasing the accuracy of processing workpieces.

Work on processing blanks on CNC bending machines is as follows:

with the help of data carriers or via a LAN, a control program is entered into the control system.
it encodes the signals necessary for the operation of the equipment, on the basis of which the workpiece will be processed. That is, the actuators, receiving the appropriate commands, set in motion the working body (punch) pressing the workpiece into the matrix.

The use of control systems allows you to achieve certain advantages over other methods of metal processing:

The quality of the finished product, it is ensured, including the fact that during the operation of the CNC, the influence of the human factor is completely excluded.
The dimensions and shape of the resulting product fully comply with the requirements of the working documentation.

In addition to the named parameters, one cannot fail to mention the fact that the work on the manufacture of products can be performed in 7/24 mode without attracting additional human resources.

Metal bending stages of the technological process

The metal bending process consists of several steps:

Cutting of sheet material and obtaining blanks, which are subject to processing on bending equipment, are obtained in a variety of ways. Almost all types of blanking equipment can be used for cutting.
Then, the blanks are transferred to the production site, where the operator, who must have all the necessary working documentation on hand, performs the appropriate operations and finally receives the finished part.

After receiving it, it is necessary to perform control and measuring operations. This work is performed either by a shift foreman or by an employee of the department technical control... To perform this operation, you must use a verified measuring tool - a ruler, tape measure, goniometer, etc.

If any defects are detected, it is necessary to make changes either to the equipment settings or to the text of the control program.

Only after passing the technical control, the part can be allowed for further use. Otherwise, substandard products must be sent either for alteration or disposal.

Metal bending subsequent processing

In fact, bending operations are intermediate in the manufacture of certain assemblies, for example, elements of metal stairs. That is, after bending, the resulting parts are sent to the assembly production, where they are installed in the place specified in the working documentation for the product.

If the product will not be used as part of other structures, then a protective corrosion-resistant coating is applied to its surface. It can be a primer such as GF 21, or powder paint. It all depends on the purpose and operating conditions of the finished product.

Why do you need a homemade sheet bending machine

Bending sheet metal with your own hands is a feasible operation that can be done at home. But, many home craftsmen are stopped by the rather high price of sheet bending machines. For the needs of small-scale production or for housework, there is no need to install complex machines with a hydraulic wire, but it will be enough manual machine.

In order to make a machine of this kind, you must have at least sketch documentation. It can always be found on the Internet, where you can either simply download it or buy it. But it is best to study the work of an existing hand-held machine and implement the knowledge gained in metal.

In fact, for the construction of such a machine, a certain amount of rolled metal, sheet material, welding machine and locksmith tools.

DIY sheet bending machine

The sheet metal bending machine consists of the following main components:

bed;
pressure beams;
rotary bending beam;
crimping beam;
knife (roller, saber) for cutting blanks;
receiving tray, which can be made of wood or sheet metal.

When making such a machine, the master must remember that he is controlled by muscular strength and, therefore, rely on the fact that it will be possible to process metal with a thickness of up to 2 mm.

Base for the machine

For the manufacture of the bed, a certain amount of profile metal rolling will be required. It can be a channel or an I-beam.

Bed - base for the machine

When assembling it, it must be remembered that the structure must be rigid. The quality of metal processing depends on this parameter.

Clamping device

As a clamp, steel plates are used in mass-produced equipment. In a home-made machine, you can use profile rolled products, for example, channel number 12.

Roller knife

To cut the resulting part, you can use several types of knives, for example, saber, or roller. Most often they are used to work with thin sheet material. When assembling a homemade listogib, it is advisable to purchase a roller knife from a company that supplies such equipment.

The thing is that for the manufacture of roller shears, as well as others, tool steels are used. To obtain working bodies, it is necessary to use heat treatment, but at home it is unlikely to be possible to do this.

Service and safety

Persons who have the qualifications of a locksmith MCP may be allowed to work on bending machines. Before starting work, personnel must undergo appropriate training and pass qualification exams.
The personnel who will work on the bending machine must undergo an initial safety briefing.
Meanwhile, on machines intended for bending sheet metal, certain safety measures are provided, for example, on some models, a swing beam or plate can be set in motion only after the operator presses two control buttons. This solution will avoid injury to the operator's hands.

On some models, you must also press the pedal to start the mechanism.
In construction mechanical equipment, there are end sensors that limit the stroke of the punch or rotary plate. In addition, the safety of work is ensured by of various kinds guards that restrict the operator's access to the work area.

They are installed in such a way that even turning off one of them will lead to the fact that the machine simply will not turn on.

Bending of steel products with small overall dimensions cross section performed, as a rule, in a cold state. The process consists in an irreversible change in the longitudinal or transverse axis of the deformable workpiece.

Bending types differ in the following parameters:

Bending technology with profiled tools

All the processes considered below are carried out using a specialized tool - stamps... The working parts of any bending die are punch and die. Punch- the movable part of the stamp is fixed. As a rule, in its upper half, and when the slider moves, it moves back and forth. Matrix- the stationary part of the stamp is located in its lower half, which is fixed on the equipment table.

The accuracy of punching with a profiled tool depends on:

When designing the working profile of bending punches and dies, the main factor is not the technological force (for all bending options it is small), but the so-called elastic aftereffect of the workpiece metal, called springing.

As a result of springing, the metal always strives to return to its original form, and the intensity of this striving depends on the plasticity limit. Soft metals(aluminum, copper, steel with a carbon percentage of up to 0.1%, etc.) spring-loaded by 3 ... 8%, and brass, medium and high-carbon steels - by 12 ... 15%.

The springback is taken into account in several ways:

Production of punches and dies with a working profile that takes into account future springback(for example, if you want to bend the workpiece at an angle of 60 0, with the expected springback of the metal 10 0, then the tool profile is performed at an angle of 70 0). The spring rates are determined from tables, depending on the grade of the material and the thickness of the workpiece.
Undercut punches where the deformable metal flows. In this case, the forces of elastic aftereffect are neutralized by the force of plastic deformation of the workpiece.
Introducing an additional calibrating transition when the product is stamped. The method is unproductive, since it increases the complexity of the bending.
Reducing the rate of deformation and retention of metal under load for some time, until the forces of inertia in the deformable section disappear. This is only possible on hydraulic presses, or presses with a special, crank-crank drive.

The wear of the bending tool is uneven: wear out more intensively punches and dies in places of inflection of the original profile, while the resistance of the peripheral areas is much higher. Nevertheless, the tool must be restored or repaired (most often the worn areas are welded and then ground to size).

For bending plastic materials use punches and dies, made of U10 or U12 type carbon tool steels in accordance with GOST 1435... Workpieces made of materials with an increased value of ultimate tensile strength are deformed by punches and dies from alloyed tool steels of type 9ХС or Х12М in accordance with GOST 5950.

The main types of equipment for bending in dies include:

Vertical sheet bending presses with a mechanical drive (in the domestic press building, these machines are designated I13_ _ and the last two digits indicate the nominal force).
Horizontal bending presses (I12_ _ series).
Universal multi-slide plate bending machines (A72_ _ series).

The technology of bending with profiled tools has its limitations:

When stamping on presses, there is always a stage return stroke when no deformation occurs, therefore productivity decreases;
On one set of stamps you can make a part strictly defined standard size... A partial way out of the situation is to install several sets of different punches and dies on the press table, for parts requiring the same value of the press slider working stroke;
Stamps are a technically complex tool, the cost of which is quite high. This negatively affects the price of the final product;
When bending profiled sections, cracks are possible in the places of differences in the cross-section of the workpiece.

Based on this, bending with non-profiled tools should only be used with significant production programs for parts.

This bending method is based on the use of rotary instrument... In this case, deformation occurs due to passing the workpiece into the gap between continuously rotating rolls... The rolls are arranged so that as a result of this passage, the product acquires the required curvature.

High-quality bending of long products - channel, I-beam, corner- is possible only in this way, since the result will not be affected in any way by the parameters of the cross-section of the workpiece.

When processing thin-sheet metal products, bending occurs along the circumference, and long products - along an arc of a circle, which is set by changing the distance between the work rolls.

The most widespread are three-roll plate and section bending machines.... Two rolls - the lower ones - are supporting, in the third - the upper one - push. Roll bending machines can be classified according to the following criteria:

By the arrangement of the rolls relative to the vertical axis of the equipment - symmetrical and asymmetrical. With symmetrically located rolls, the pressure roll is located strictly in the middle, and with an asymmetric scheme, the pressure roll is located above one of the back-up rolls.
Along the width of the rolls, which determines the technological capabilities of the equipment: the longer the rolls, the wider the sheet can be bent on this installation.
By the presence of additional rolls installed either before or after the main ones. Such equipment performs not only bending, but also the subsequent straightening of products.
By the relative position of the work rolls which can be horizontal or vertical. The latter is less convenient, but sometimes it is advisable, since as a result, the overall dimensions of the equipment in plan are reduced.

Since during rotational bending, the force is applied not at the point of contact, but along the arc, the specific load on the rollers is small, which, firstly, increases their durability, and, secondly, makes it possible to use less expensive tool steels for their manufacture.

The roller tool, in contrast to the die tool, is universal, therefore rotary bending is effective in any programs for the release of the final product.

Sequence of action of sheet and section bending machines. Bending of shells.

Bending on sheet bending equipment with a symmetrical arrangement of work rolls includes the following stages:

Refueling the sheet into the space between the rolls, while the leading edge of the workpiece must lie on the second backup roll;
Lowering the upper roll to a position at which the required curvature of the bent profile is guaranteed;
Turning on the drive, as a result of which the sheet is captured by the rolls by friction forces and passes through the working area, acquiring the required shape;
Refueling the next workpiece, with a repetition of the deformation cycle.

A product that has passed through the working area will not be deformed at the front and rear edge of the sheet by an amount equal to half the distance between the backup rolls. Folding is done manually, which is inconvenient. Therefore, if it is necessary to bend the profile along the entire length of the workpiece, use rotary machines with asymmetric layout... At the same time, the rear end is guaranteed to bend, and for the front end, it is enough to start a sheet with back side... Thus, sheet metal produces shell(open cylindrical or conical structural member).

For the possibility of bending sheets of different thickness, the machines provide adjustment of the distance between the lower rolls... For this, the bearings are moved, in which the axes of these rolls rotate. It is also available to replace the roll with a tool with an increased diameter, which will be required when rotary bending of thicker workpieces.

Bending machines operate in a similar way. They are also available in three-roll design, and consist of the following nodes:

Bed.
Rollers, the working profile of which corresponds to the section of long products.
Side rollers ensuring the straightness of the workpiece movement.
Crossbeams, limiting the movement of the workpiece in the transverse direction (for symmetric profiles, for example, channels, the crossbar is transferred to the non-working position.
Filling mechanism profile into the working space between the rolls.
Electric motor.
Intermediate gears.
Drive engagement systems.

Adjustment of the section bending machine to the required bending radius is made by the handwheel of the screw mechanism. Small standard sizes of long products are bent on machines with horizontal work rolls. Bending machines with a vertical arrangement are considered more versatile.

Domestic rotary bending machines markings:

I22_ _ - three-roll bending machines;
И42_ _ - four-roll bending machines;
И32_ _ - three-roll sort-bending machines;
I33 - sort-bending multi-roll.

Sheet metal bending is one of the common hot and cold forming operations. It is distinguished by low energy consumption, and with the correct development of the technical process, it can successfully produce spatial products from flat blanks of various shapes and sizes.

In accordance with the tasks set, the sheet metal bending technology is being developed for the following options:

Single angle (sometimes called V-flex).
Double-angle or U-shaped bending.
Multi-angle bending.
Radial bending of sheet metal (rolling) - obtaining products such as hinges, galvanized clamps, etc.

The bending effort is low, so it is predominantly performed in a cold state. The exception is the bending of a steel sheet made of low-plasticity metals. These include duralumin, high-carbon steels (additionally containing a significant percentage of manganese and silicon), as well as titanium and its alloys. They, as well as blanks made of thick-sheet metal with a thickness of more than 12 ... 16 mm, are bent mainly in the hot.

Bending is combined with other sheet stamping operations: cutting and bending, punching or punching is often combined. Therefore, for the manufacture of complex multidimensional parts, dies designed for several transitions are widely used.

Stretch bending is considered a special case of sheet metal bending, which is used to produce long and narrow parts with large bending radii.

Depending on the size and type of the workpiece, as well as the required characteristics of the product after deformation, the following are used as:

Vertical with mechanical or hydraulic drive;
Horizontal hydraulic presses with two sliders;
Forging bulldozers - horizontal bending machines;
Pipe and profile benders;
Universal bending machines.

To obtain structures that are unique in shape and size, in particular, turbine boilers, etc., exotic technologies are also used for bending sheet steel, for example, by explosive energy. In contrast to this, the question of how to bend tin is not difficult, since the plasticity of this material is very high.

A characteristic feature of plate bending machines is reduced deformation rates, increased dimensions of the stamping space, and relatively low energy consumption. The latter is the basis for a wide production, designed for the deformation of galvanized material. They are especially popular in small workshops as well as individual users.

Despite the apparent simplicity of the technology, it is difficult to determine the balance of stresses and deformations of the state in the workpiece. In the process of bending the material, stresses arise in it, at first - elastic, and then - plastic. At the same time, the bending of the sheet material is characterized by a significant uneven deformation: it is more intense in the corners of the bending, and is practically invisible at the ends of the sheet blank. Bending of thin sheet metal differs in that its inner layers are compressed, and the outer ones are stretched. The conditional line that separates these zones is called the neutral layer, and its precise definition is one of the conditions for defect-free bending.

In the process of bending, rolled metal receives the following shape distortions:

Changes in thickness, especially for heavy plate blanks;
Springing / springing - spontaneous change of the final bending angle;
Folding of a metal sheet;
The appearance of metal flow lines.

All these circumstances must be taken into account when developing a stamping technological process.

Stages and sequence of technology

Here, and in what follows, we will focus on the processes of stamping sheet metal in the cold state.

Development is carried out in the following sequence:

The design of the part is analyzed.
The effort and work of the process is calculated.
The standard size of the production equipment is selected.
A drawing of the original workpiece is being developed.
Deformation transitions are calculated.
Technological equipment is being designed.

An analysis of the compliance of the capabilities of the starting material is necessary in order to find out its suitability for stamping according to the dimensions given in the drawing of the finished part. The stage is performed in the following positions:

Checking the plastic ability of the metal and comparing the result with the level of stresses that arise during bending. For low-plasticity metals and alloys, the process has to be split into several transitions, and between them to plan interoperative annealing, which increases the plasticity;
Possibility of obtaining a bend radius at which no cracking of the material occurs;
Determination of possible distortions of the profile or thickness of the workpiece after pressure treatment, especially with complex contours of the part;

According to the results of the analysis, sometimes a decision is made to replace the initial material with a more plastic one, the need for preliminary softening heat treatment, or the workpiece is heated before deformation.

A compulsory point in the development of a technological process is the calculation of the minimum permissible bending angle, bending radius and springback angle.

The bending radius r min is calculated taking into account the plasticity of the metal of the workpiece, the ratio of its dimensions and the speed at which deformation will be carried out (hydraulic presses, with their reduced speeds of movement of the slider, are preferable to higher-speed mechanical presses). With a decrease in the value of r min, all metals undergo so-called thinning - a decrease in the initial thickness of the workpiece. The intensity of thinning determines the coefficient of thinning λ,%, which shows how much the thickness of the final product will decrease. If this value turns out to be more critical, then the initial thickness s of the workpiece metal must be increased.

For low-carbon sheet steels, the correspondence between the above parameters is given in the table (see table. 1).

Thus, under certain conditions, the metal of the workpiece may even bulge somewhat.

Equally important is the determination of the minimum bending radius, which also depends on the initial metal thickness, the arrangement of the rolled fibers and the plasticity of the material (see Table 2). In the event that the bending radius is too small, the outer fibers of the steel can break, which violates the integrity of the finished product. Therefore, the minimum radii are usually counted according to the largest deformations of the extreme parts of the workpiece, taking into account the relative narrowing ψ of the deformable material (set according to the tables). In this case, the amount of deformation of the workpiece is also taken into account. For example, for small deformations, the dependence

and for large deformations, a more accurate equation of the form

The effect of probable springback can be taken into account using the data on the actual springback angles β, which are given in table 3. The data in the table correspond to the conditions of one-angle bending.

Determination of the bending force

The strength parameters of bending depend on the plasticity of the metal and the intensity of its strengthening during deformation. In this case, the direction of rolling of the original billet is important. The fact is that after rolling the metal acquires the property of anisotropy, when the residual stresses in the direction of the rolling axis are less than in the opposite direction. Accordingly, if along the fibers, then with the same degree of deformation, the probability of destruction of the workpiece significantly decreases. Therefore, the bending rib is positioned in such a way that the angle between the rolling direction and the arrangement of the blanks in the sheet, strip or strip is minimal.

To calculate the power parameters, it is specified how the deformation will be performed. It is possible by a bending moment, when the workpiece is laid on the clamps / stops, and then deforms freely, or by force, when at the end of the process the semi-finished product rests on the working surface of the matrix. Free bending is simpler and less energy intensive, but calibration bending gives you more accurate parts.

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