Pressing. The essence of the pressing process

Pressing - the process of obtaining products by squeezing the heated metal out of a closed cavity (container) through the hole of the tool (matrix). There are two ways of pressing: direct and reverse. At direct pressing(Fig. 17, but) the metal is extruded in the direction of movement of the punch. At reverse pressing(Fig. 17, b) the metal moves out of the container towards the movement of the punch.

The initial workpiece for pressing is an ingot or a hot-rolled bar. To obtain a high-quality surface after pressing, the workpieces are turned and even polished.

Heating is carried out in induction installations or in furnaces-baths in molten salts. Non-ferrous metals are pressed without heating.

Rice. 17. Direct pressing (but) and vice versa (b):

1 - container; 2 - punch; 3 - blank; 4 - needle; 5 - matrix; 6 - profile

Deformation during pressing

During pressing, a scheme of all-round uneven compression is realized, while there are no tensile stresses. Therefore, even steels and alloys with low ductility, such as tool alloys, can be pressed. Even such fragile materials as marble and cast iron can be pressed. Thus, pressing can process materials that, due to low plasticity, cannot be deformed by other methods.

Draw ratio µ when pressed, it can reach 30-50.

Press tool

The tool is a container, a punch, a matrix, a needle (to obtain hollow profiles). The profile of the resulting product is determined by the shape of the matrix hole; holes in the profile - with a needle. The working conditions of the tool are very difficult: high contact pressure, abrasion, heating up to 800-1200 С. It is made from high quality tool steels and heat resistant alloys.

To reduce friction, solid lubricants are used: graphite, nickel and copper powders, molybdenum disulfide.

Pressing equipment

These are hydraulic presses with a horizontal or vertical punch.

Pressing products

By pressing, simple profiles (circle, square) are obtained from alloys with low ductility and profiles of very complex shapes that cannot be obtained by other types of OMD (Fig. 18).

Rice. 18. Pressed prof
or

Benefits of pressing

The accuracy of pressed profiles is higher than that of rolled profiles. As already mentioned, you can get profiles of the most complex shapes. The process is versatile in terms of moving from size to size and from one type of profile to another. Tool change does not require a lot of time.

The ability to achieve very high degrees of deformation makes this process highly productive. Pressing speeds reach 5 m/s and more. The product is obtained in one stroke of the tool.

Disadvantages of pressing

Large waste of metal press balance(10-20%), since all the metal cannot be squeezed out of the container; uneven deformation in the container; high cost and high tool wear; the need for powerful equipment.

Drawing

Drawing – production of profiles by pulling the workpiece through a gradually narrowing hole in the tool – in about loke.

The initial workpiece for drawing is a bar, thick wire or pipe. The workpiece is not heated, i.e. drawing is a cold plastic deformation.

The end of the workpiece is sharpened, it is passed through the die, grasped with a clamping device and pulled (Fig. 19).

Drawing deformation

P When drawing, tensile stresses act on the workpiece. The metal should deform only in the tapering channel of the die; deformation outside the tool is not allowed. The reduction in one pass is small: drawing µ = 1.1÷1.5. To obtain the desired profile, the wire is pulled through several holes of decreasing diameter.

Since cold deformation is carried out, the metal is riveted - hardened. Therefore, between pulling through adjacent dies, annealing(heating above the recrystallization temperature) in tube furnaces. The hardening is removed, and the metal of the workpiece again becomes ductile, capable of further deformation.

Drawing tool

AND tool is portage, or die, which is a ring with a profiled hole. Draw dies are made from hard alloys, ceramics, industrial diamonds (for very thin wire, with a diameter of less than 0.2 mm). Friction between tool and workpiece is reduced by solid lubricants. Mandrels are used to obtain hollow profiles.

The working hole of the die has four characteristic zones along the length (Fig. 20): I - inlet, or lubrication, II - deforming, or working, with an angle α = 8÷24º, III - calibrating, IV - outlet cone.

The wire size tolerance averages 0.02 mm.

Drawing equipment

Exist drawing mills various designs - drum, rack, chain, hydraulically driven, etc.

drum mills(Fig. 21) is used for drawing wire, rods and pipes of small diameter, which can be wound into riots.

Drum mills for multiple drawing can include up to 20 drums; between them are drawing dies and annealing furnaces. The wire speed is in the range of 6-3000 m/min.

Chain drawing countries(fig. 22) are intended for products of large section (bars and pipes). The length of the resulting product is limited by the length of the frame (up to 15 m). Pipe drawing is performed on a mandrel.

R
is. 22. Chain drawing machine:

1 - drag; 2 - ticks; 3 - carriage; 4 - traction hook; 5 - chain; 6 - leading sprocket;

7 - reducer; 8 - electric motor

Drawing products

By drawing, a wire with a diameter of 0.002 to 5 mm is obtained, as well as rods, shaped profiles (various guides, dowels, slotted rollers) and pipes (Fig. 23).

Rice. 23. Profiles obtained by drawing

Advantages of drawing

These are high dimensional accuracy (tolerances of no more than hundredths of a mm), low surface roughness, the ability to obtain thin-walled profiles, high productivity, and a small amount of waste. The process is universal (you can simply and quickly replace the tool), so it is widely used.

It is also important that it is possible to change the properties of the resulting products due to work hardening and heat treatment.

Disadvantages of drawing

The inevitability of hardening and the need for annealing complicates the process. The compression in one pass is small.

Forging

TO ovkoy called obtaining products by sequential deformation of a heated workpiece by blows of a universal tool - strikers. The resulting workpiece or finished product is called forging.

The initial workpiece is ingots or blooms, long products of a simple section. Preforms are usually heated in chamber-type furnaces.

Forging deformation

Deformation in the forging process follows the scheme of free plastic flow between the tool surfaces. Deformation can be performed sequentially in separate sections of the workpiece, so its dimensions can significantly exceed the area of the strikers.

The amount of deformation expresses forging:

where F max and F min - the initial and final cross-sectional area of the workpiece, and the ratio of the larger area to the smaller one is taken, therefore the forging is always greater than 1. The larger the forging value, the better the metal is forged. Some of the forging operations are shown in Fig. 25.

Rice. 25. Forging operations:

but- broach; b- firmware (getting a hole); in- felling (separation into parts)

Forging tool

The tool is universal (applicable for forgings of various shapes): flat or cut-out dies and a set of backing tools (mandrels, shims, piercings, etc.).

Forging Equipment

Machines of dynamic, or percussion, action are used - hammers and machines of static action - hydraulic presses.

Hammers are divided into pneumatic, with a mass of falling parts up to 1 t, and steam-air, with a mass of falling parts up to 8 tons. Hammers transfer the impact energy to the workpiece in a fraction of a second. The working fluid in hammers is compressed air or steam.

Hydraulic presses with a force of up to 100 MN are designed to process the heaviest workpieces. They clamp the workpiece between the strikers for tens of seconds. The working fluid in them is a liquid (water emulsion, mineral oil).

Application of forging

Forging is most often used in single-piece and small-scale production, especially for heavy forgings. From ingots weighing up to 300 tons, products can only be obtained by forging. These are shafts of hydrogenerators, turbine disks, crankshafts of ship engines, rolls of rolling mills.

The benefits of forging

This is, first of all, the versatility of the process, which makes it possible to obtain a wide variety of products. Forging does not require complex tools. During forging, the structure of the metal improves: the fibers in the forging are arranged favorably in order to withstand the load during operation, the cast structure is crushed.

Disadvantages of forging

This, of course, is the low productivity of the process and the need for significant machining allowances. Forgings are obtained with low dimensional accuracy and high surface roughness.

Pressing

Pressing- a type of pressure treatment, in which the metal is squeezed out of a closed cavity through a hole in the matrix corresponding to the section of the extruded profile.

This modern way obtaining various profile blanks: bars with a diameter of 3 ... 250 mm, pipes with a diameter of 20 ... 400 mm with a wall thickness of 1.5 ... 15 mm, profiles of complex section, solid and hollow with a cross-sectional area of up to 500 cm 2.

For the first time, the method was scientifically substantiated by Academician Kurnakov N.S. in 1813 and was mainly used to produce rods and pipes from tin-lead alloys. Currently, ingots or rolled products from carbon and alloy steels, as well as from non-ferrous metals and alloys based on them (copper, aluminum, magnesium, titanium, zinc, nickel, zirconium, uranium, thorium) are used as the initial billet.

Technological process pressing includes operations:

preparation of the workpiece for pressing (cutting, preliminary turning on the machine, since the quality of the surface of the workpiece affects the quality and accuracy of the profile);

heating of the workpiece with subsequent cleaning from scale;

· laying the workpiece in the container;

Direct pressing process

Finishing of the product (separation of the press residue, cutting).

Pressing is carried out on hydraulic presses with a vertical or horizontal plunger, with a capacity of up to 10,000 tons.

There are two pressing methods: straight And back(Fig. 11.6.)

With direct pressing, the movement of the press punch and the outflow of metal through the die hole occur in the same direction. With direct pressing, much more force is required, since part of it is spent on overcoming friction when moving the workpiece metal inside the container. The press residue is 18...20% of the mass of the workpiece (in some cases - 30...40%). But the process is characterized by a higher surface quality, the pressing scheme is simpler.

Rice. 11.6. Scheme of bar pressing by direct (a) and reverse (b) method

1 - finished bar; 2 - matrix; 3 - blank; 4 - punch

During reverse pressing, the workpiece is placed in a blind container, and during pressing it remains motionless, and the outflow of metal from the hole of the matrix, which is attached to the end of the hollow punch, occurs in the direction opposite to the movement of the punch with the matrix. Reverse pressing requires less effort, the press residue is 5 ... 6%. However, less deformation results in the pressed bar retaining traces of the structure of the cast metal. The design scheme is more complex

The pressing process is characterized by the following main parameters: elongation ratio, degree of deformation, and metal outflow rate from the die point.

The elongation ratio is defined as the ratio of the cross-sectional area of the container to the cross-sectional area of all holes in the matrix.

Degree of deformation:

The metal outflow rate from the matrix point is proportional to the elongation ratio and is determined by the formula:

where: - pressing speed (punch speed).

During pressing, the metal is subjected to all-round uneven compression and has a very high ductility.

The main advantages of the process include:

the possibility of processing metals that, due to low ductility, cannot be processed by other methods;

Possibility of obtaining practically any cross-sectional profile;

obtaining a wide range of products on the same press equipment with the replacement of only the matrix;

· high productivity, up to 2…3 m/min.

Process Disadvantages:

· increased consumption of metal per unit of product due to losses in the form of a press residue;

the appearance in some cases of a noticeable unevenness of mechanical properties along the length and cross section of the product;

high cost and low durability of the pressing tool;

high energy intensity.

Drawing

The essence of the drawing process is to pull the blanks through a tapering hole (die) in a tool called a die. The hole configuration determines the shape of the resulting profile. The drawing scheme is shown in Fig. 11.7.

Fig.11.7. Drawing scheme

By drawing, a wire with a diameter of 0.002 ... 4 mm, rods and profiles of shaped section, thin-walled pipes, including capillary ones, are obtained. Drawing is also used to calibrate the cross section and improve the surface quality of workpieces. Drawing is more often performed at room temperature, when hardening accompanies plastic deformation; this is used to improve the mechanical characteristics of the metal, for example, the tensile strength increases by 1.5 ... 2 times.

The starting material can be hot-rolled bar, long products, wire, pipes. Drawing processes steels of various chemical composition, non-ferrous metals and alloys, including precious ones.

The main tool for drawing - dies various designs. The die works in difficult conditions: high stress is combined with wear during pulling, so they are made of hard alloys. To obtain particularly precise profiles, dies are made from diamond. The design of the tool is shown in fig. 11.8.

Fig.11.8. General form portages

Voloka 1 fixed in the cage 2. The filaments have a complex configuration, its constituent parts are: intake part I, including the inlet cone and the lubricating part; deforming part II with an angle at the top (6…18 0 for bars, 10…24 0 for pipes); cylindrical gauge belt III 0.4…1 mm long; exit cone IV.

The technological process of drawing includes the following operations:

· preliminary annealing of workpieces to obtain a fine-grained structure of the metal and increase its ductility;

Etching of blanks in a heated solution of sulfuric acid to remove scale, followed by washing, after removing the scale, a sublubricating layer is applied to the surface by copper plating, phosphating, liming, the lubricant adheres well to the layer and the friction coefficient is significantly reduced;

drawing, the workpiece is sequentially pulled through a series of gradually decreasing holes;

· annealing to eliminate work hardening: after 70…85% reduction for steel and 99% reduction for non-ferrous metals;

finishing of finished products (cutting ends, straightening, cutting to lengths, etc.)

The technological process of drawing is carried out on special drawing machines. Depending on the type of pulling device, mills are distinguished: with rectilinear movement of the drawn metal (chain, rack); with winding of the processed metal on a drum (drum). Drum mills are usually used to produce wire. The number of reels can be up to twenty. The drawing speed reaches 50 m/s.

The drawing process is characterized by the following parameters: the drawing ratio and the degree of deformation.

The elongation ratio is determined by the ratio of the final and initial length or the initial and final cross-sectional area:

The degree of deformation is determined by the formula:

Usually, in one pass, the elongation ratio does not exceed 1.3, and the degree of deformation is 30%. If it is necessary to obtain a large amount of deformation, repeated drawing is performed.

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Production

Pressing makes it possible to obtain bulk products of any cross section, including pipes;
Pressing ensures the best quality of the surface of the original workpiece;
Pressing provides the greatest uniformity of the mechanical properties of the material along the length; The process is easily automated and allows plastic deformation of aluminum and its alloys in a continuous mode. Supplier Evek GmbH offers to buy aluminum at an affordable price in a wide range. We will provide delivery of products to any point of the continent. The price is optimal.

Forward and reverse pressing

In the first case, the direction of the metal flow coincides with the direction of movement of the deforming tool, in the second, it is opposite to it. The back pressing force is higher than direct pressing (regardless of whether it is performed in a cold or hot state of the alloy), but the surface quality of the finished product is also higher. Therefore, for the production of aluminum bars of increased and high accuracy, as well as rolled products of short length, reverse pressing is used, in other cases direct pressing is used. The stress-strain state of the metal during pressing is a comprehensive non-uniform compression, in which aluminum has the highest ductility. Therefore, this technology has practically no restrictions on the limiting degrees of deformation.

hot deformation

In the technology of hot pressing, before the start of deformation, the workpiece is heated in special continuous electric furnaces. The heating temperature depends on the brand of aluminum alloy. All other operations of the process are identical to cold pressing.

cold deformation

For highly ductile aluminum alloys (for example, AD0 or A00), the deformation is carried out in a cold state. Aluminum wire rod of round or square cross section is cleaned from surface impurities and oxide films, richly lubricated, and fed into the pressing die. There it is picked up by a press ram, which first pushes it into the container, and then, with an increase in the technological pressing force, into a matrix, the cross section of which corresponds to the cross section of the final rod. The direction of flow, as mentioned earlier, is determined by the method of pressing. As production equipment I use special bar-piercing hydraulic presses of horizontal type.

Edit

After the end of the pressing cycle, the aluminum bar is fed to a straightening press, where such a defect as the curvature of the axis of the bar due to the presence of residual stresses in the metal is removed. Straightening is followed by cutting to size and subsequent trimming of the bar.

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The device is designed to produce ring blanks of high grinding and polishing wheels on ceramic, bakelite, vulcanite and other bonds. It contains a housing installed with the possibility of vertical movement with horizontal guides. Inside the housing there is a mandrel with molding plates. The mechanism of vertical movement of the housing is made in the form of two-rack gears. One of the rails is fixed on the lower traverse of the device, the second - on the upper one. The gear is connected to horizontal guides. The device allows to reduce the difference in density of circles in height. 2 ill.

The invention relates to the abrasive industry, in particular to devices for producing ring blanks of high abrasive grinding and polishing wheels on ceramic, bakelite, volcanic and other bonds. A device for one-sided molding of blanks of grinding wheels is known, including a housing, upper and lower molding plates mounted on a mandrel. The disadvantage of this device, designed for one-sided pressing, are limited technological capabilities, since when forming ring blanks with a height of 50 mm or more, it is impossible to ensure the uniform density of the blanks, and therefore, the uniform mechanical properties of the finished circles in height and their required quality. The specified device is installed permanently on the table of a general-purpose hydraulic press. Pressing high blanks in this case is impossible, since it is impossible to load the initial mass into the device and push the compact out of the device (the working space of a general-purpose press is small). A device is also known for one-sided pressing of blanks of abrasive wheels with pre-pressing, including a vertically movable housing, an upper molding plate, a mandrel, a lower molding plate and a housing movement mechanism containing guides and elastic elements. The specified device for one-sided pressing with pre-pressing partially eliminates the uneven density of the resulting blanks and expands the technological capabilities of the pressing process. At the same time, at the stage of completion of one-sided pressing with the help of the upper molding plate, the molding sand is pre-pressed by the lower molding plate due to the downward movement of the matrix. In this case, the device is also installed permanently on a general-purpose press table, which limits its technological capabilities. A significant disadvantage of the device designed for one-sided pressing of workpieces with pre-pressing is the different path traveled in the matrix by the upper and lower molding plates, i.e., different compression of the molding sand, as well as different forces acting on the pressing from the upper and lower molding plates. Moreover, this difference in efforts will depend on the height of the filling of the mixture in the device and on the height of the pressing. This disadvantage leads to a significant difference in density of the compacts and the heterogeneity of the mechanical properties (strength and hardness) of the abrasive wheels obtained from them in height. The closest in technical essence and the achieved effect to the proposed invention is a device for pressing blanks of abrasive wheels, including a body mounted on horizontal guides, inside of which there is a mandrel with upper and lower molding plates installed on it, a mechanism for vertical movement of the body and horizontal guides, a lower crosshead with stops for the lower molding plate and mounted with the possibility of vertical movement of the upper traverse with a punch fixed on it. In this device, first, the process of one-sided pressing is carried out by the upper molding plate, and then, after compression of the elastic elements by moving the body down, the abrasive mixture is subjected to pre-pressing by the lower molding plate. But prepressing does not ensure the uniform density of the workpieces in height. Thus, the main disadvantage of the closest analogue is the uneven density of the workpieces in height, and consequently, different mechanical properties, primarily the strength and hardness of the abrasive wheels obtained from them in height. The technical result is to reduce the density variation in the height of the circles (the density is equal to the mass per unit volume of the body). The difference in density in this solution is understood as a decrease in fluctuations in the numerical values of this density over the entire height of the circle, and, consequently, a decrease in hardness fluctuations along the height of the circle. The task is achieved by the fact that in the device for pressing blanks of abrasive wheels, containing a housing mounted on horizontal guides, inside of which there is a mandrel with upper and lower molding plates installed on it, a mechanism for vertical movement of the housing and horizontal guides, a lower traverse with stops mounted on it for the bottom plate and installed with the possibility of vertical movement of the upper traverse together with the punch fixed on it, according to the invention, the mechanism for vertical movement of the body and horizontal guides is made in the form of two-rack gears, with one of the rails of which is fixed on the lower traverse, the second - on the upper traverse, and the gear is connected to the horizontal guides. The fact that the mechanism of vertical movement of the body with horizontal guides is made in the form of double-rack gears makes it possible to link the movement of the upper movable crosshead with the movement down of the body together with the horizontal guides. Moreover, as follows from the laws of mechanics (cf. Yablonsky A.A., Nikiforova V.M. Course of theoretical mechanics. Part 1. -M. : high school, 1977, p. 234, fig. 310), the punch of the device, fixed on the upper traverse and the rails fixed on it, will move down at a speed twice the speed of the gears, and, consequently, the speed of the device body. Such a ratio of the speeds of movement of the upper punch and the body downwards, provided that the same distance between the punch and the upper molding plate, as well as between the lower molding plate and the stops of the lower molding plate installed on the lower traverse, is set, will ensure the performance of two-sided pressing of the abrasive mixture with equal reductions from the upper and bottom plates. Bilateral pressing, for its part, will ensure the uniform density of the workpiece, the uniformity of its mechanical properties, and, consequently, will improve the quality of the obtained high abrasive wheels. The proposed device is illustrated in Fig.1 - 2, where in Fig. 1 shows a general view of the device (view from the loading position) in the initial position (left side) and at the beginning of pressing (right side), in Fig. 2 - view of the device (front view) at the beginning of pressing (left side) and at the end of pressing (right side). The device for pressing blanks of abrasive wheels includes a housing 1 with wheels 2, inside which is placed a mandrel 3 with top 4 and bottom 5 molding plates. The body 1 is mounted with its wheels 2 on horizontal guides (rails) 6 fixed on the base plate 7. There are upper and lower traverses 8 and 9. The upper traverse 8 is made with the possibility of vertical movement. The mechanism for the vertical movement of the body 1 with horizontal guides (rails) 6 is made in the form of racks 10, 11 and gears 12. The racks 10 are fixed on the lower traverse 9 of the device, the slats 11 on the upper traverse 8. The gears 12 are connected by means of a base plate 7 with horizontal guides 6. A punch 13 is fixed on the upper traverse 8. Two stops 14 of the lower molding plate 5 are installed on the lower traverse 9. The device operates as follows. In the annular cavity of the housing 1 in the loading position (not shown), the molding sand 15 is loaded onto the lower molding plate 5, the upper molding plate 4 is installed on top of it. After that, along the horizontal guides (rails) 6, the housing 1 is set in working area devices (Fig. 1 and 2). Turn on the drive device (Fig. 1 - 2 is not shown). In this case, the upper traverse 8, together with the punch 13 and the slats 11, begin to move down. At the same time, due to the interaction of racks 11 with gears 12 and racks 10, gears 12, base plate 7, horizontal guides (rails) 6, wheels 2 and body 1. From the initial position (left part of Fig. 1) to the moment of contact with the upper molding plate 4, the punch 13 passes a path equal to 2h 1, since the body 1 simultaneously with the punch 13 goes down. In this case, the body 1 of the device, together with the mandrel 3, the upper and lower molding plates 4 and 5 and the abrasive mixture 15, pass a path equal to h 1 . If h 1 =h 2 , where h 2 is the distance between the lower molding plate 5 and the supports 14, then at this moment the plate 5 will come into contact with the supports 14. From the moment the punch 13 touches the upper molding plate 4 and the lower molding plate 5 stops 14 the pressing process starts. When pressing, the molding sand 15 is compressed by the value h by the upper molding plate 4 when it moves down together with the punch 13 (figure 2) and is compressed by the value h by the lower molding plate 5 by moving this value h down the body 1 together with the pressing 16. In this case, the punch 13, together with the upper molding plate 4, travels a path equal to 2h. After the end of the pressing operation, the body 1, together with the wheels 2, the horizontal guides 6 and the plate 7, are returned to their original position by means of the racks 10, 11 and gears 12 due to the upward movement of the traverse 8. Then, along the horizontal guides 6, the body 1 on the wheels 2 is fed into position pressing extrusion 16. A prototype device for pressing workpieces of electrocorundum abrasive wheels on a ceramic bond with dimensions of 100 x 80 x 32 mm (GOST 2424-83) has been developed. This device is equipped with two-rail mechanisms with the following characteristics: - movable rails have a length of 800 mm with a length of the rack part of 300 mm, their cross section is 25x25 mm, material 40X; - fixed rails have a length of 400 mm with a length of the rack part of 300 mm, their cross section is 25x25 mm, material 40X; - gears have a pitch circle diameter of 80 mm, the number of teeth is 40, the tooth module is 2 mm, the material is 35X; - gear axles made of steel 45 with a diameter of 25 mm are welded to the base plate. The blanks obtained on the prototype device after the heat treatment operation were subjected to mechanical properties control in accordance with GOST 25961-83. The hardness of the wheels was determined by the acoustic method using the device "Sound 107-01". The control results showed that the hardness is uniform in the height of the circles, and their quality after machining meets the requirements of the standard of the Chelyabinsk Abrasive Plant. The proposed device is advisable to use for the manufacture of high (height from 50 to 300 mm or more) grinding wheels on ceramic, bakelite and volcanic bonds. Sources of information 1. Equipment and equipment for enterprises of the abrasive and diamond industries /V. A. Rybakov, V.V. Avakyan, O.S. Masevich and others - L .: Mashinostroenie, p. 154 -155, fig.6.1. 2. Ibid., p. 155, fig.6.2. 3. Patent RU 2095230 C1, B 24 D 18/00, 1997.

pressing (extruding) is a type of metal processing by pressure, which consists in giving the metal being processed a given shape by squeezing it out of a closed volume through one or more channels made in a shaping press tool.

This is one of the most progressive metal forming processes, which makes it possible to obtain long products - extruded profiles, which are economical and highly efficient when used in structures.

The essence of the pressing process on the example of direct pressing (Fig. 5.1) is as follows. blank 1, heated to the pressing temperature, placed in a container 2. From the output side of the container in the matrix holder 3 matrix 5 is placed, forming the contour of the press product 4. Via press ram 7 and press washer 6 pressure is transferred to the workpiece from the main cylinder of the press. Under the influence high pressure the metal flows into the working channel of the matrix, forming a given product.

The widespread use of pressing is explained by the favorable scheme of the stress state of the deformed metal - all-round non-uniform compression. The choice of temperature conditions for pressing is determined mainly by the value of the deformation resistance of the metal.

Hot pressing is used much more often than cold pressing. However, with an increase in the production of high-strength tool steels, as well as as a result of the creation of powerful specialized equipment, the scope of cold pressing is expanding for metals and alloys with low deformation resistance. Typically, the pressing cycle is a repetitive process (discrete pressing), but now semi-continuous and continuous pressing methods are also used, and processes based on the combination of casting, rolling and pressing operations are being developed.

Rice. 5.1. Scheme of direct pressing of a solid profile:

1 - blank; 2 - container; 3 - matrix holder;
4 - press product; 5 - the matrix; 6 - press washer;
7 - press stamp

The pressing process has many varieties that differ in a number of features: the presence or absence of movement of the workpiece in the container during pressing; the nature of the action and the direction of friction forces on the surface of the workpiece and tool; temperature conditions; speed and methods of application of external forces; workpiece shape, etc.

The place of pressing in the production of long metal products can be assessed by comparing pressing with competing processes, such as hot section rolling and pipe rolling.

With this comparison, the advantages of pressing are as follows. During rolling, large tensile stresses arise in many parts of the plastic zone, which reduce the ductility of the metal being processed, and during pressing, an uneven all-round compression scheme is implemented, which makes it possible to manufacture in one operation various press products that are not obtained by rolling at all or are obtained, but for a large number of passes. The area of application of pressing is especially expanded when the degree of deformation per transition exceeds 75%, and the drawing ratio has a value of more than 100.

By pressing it is possible to obtain products of almost any cross-sectional shape, and by rolling only profiles and pipes of relatively simple cross-sectional configurations.

When pressing, it is easier to transfer the technological process of obtaining one type of press product to another - it is enough just to replace the matrix.

Press products are more accurate in size than rolled ones, which is due to the closedness of the die caliber, in contrast to the open caliber formed by rotating rolls during rolling. The accuracy of the product is also determined by the quality of the matrix, its material and the type of heat treatment.

High degrees of deformation during pressing, as a rule, provide high level product properties.

Pressing, in contrast to rolling, can be used to obtain molded products from low-plastic materials, semi-finished products from powder and composite materials, as well as clad composite materials, consisting, for example, of combinations of aluminum-copper, aluminum-steel, etc.

Along with the listed advantages, discrete pressing has the following disadvantages:

the cyclic nature of the process, which leads to a decrease in productivity and yield of suitable metal;
improving the quality of press products requires low pressing speeds for a number of metals and alloys and is accompanied by large technological waste due to the need to leave large press residues and remove the weakly deformed output end of the press product;
the limited length of the workpiece, due to the strength of the press rams, the power capabilities of the press and the stability of the workpiece during unpressing, reduces the productivity of the process;
uneven deformation during pressing leads to anisotropy of properties in the press product;
severe operating conditions of the pressing tool (a combination of high temperature, pressure and abrasive loads) necessitate frequent replacement and the use of expensive alloy steels for its manufacture.

A comparison of the advantages and disadvantages of the process allows us to conclude that it is most expedient to use pressing in the production of pipes, solid and hollow profiles of complex shape with increased dimensional accuracy when processing hard-to-form and low-plastic metals and alloys. In addition, unlike rolling, it is profitable in medium and small-scale production, as well as in the implementation of continuous or combined processing methods.

To describe the deformation during pressing, the following characteristics are used.

1. Draw ratio A, cp, defined as the ratio of the cross-sectional area of the container R to k cross-sectional area of all channels of the matrix I/ 7 ,

When pressing pipes, the elongation coefficient A. cf is determined by the formula

K IG

m 1 IG

where R sh R k, R IG - respectively, the cross-sectional area of the matrix, container and mandrel needle.

2. Pressing factor, which quantitatively characterizes the ratio of the diameter of the workpiece and the container:
3. Relative degree of deformation e, related to the elongation ratio and calculated by the formula

(5.4)
4. Pressing speed etc. (speed of movement of the press stamp):

where AL- the length of the pressed part of the workpiece; ? - pressing time.

5. Expiration rate and ist, which characterizes the speed of movement of the press product.

^ist ^^pr- (5.6)

Types of pressing

direct pressing

In press production, several types of pressing are used, the main ones are discussed here.

With direct pressing, the direction of extrusion of the press product from the die channel and the direction of movement of the press ram are the same

(Fig. 5.2). This type of pressing is the most common and makes it possible to obtain solid and hollow products with a wide range of cross sections close to the size of the container cross section. A characteristic feature of the method is the obligatory movement of the metal relative to the fixed container. Direct pressing is carried out without lubrication and with lubrication. In direct pressing without lubrication, the workpiece, usually in the form of an ingot, is placed between the container and the press ram with a press washer (Fig. 5.2, but), pushed into the container (Fig. 5.2, b) upset in a container (Fig. 5.2, in), extruded through the matrix channel (Fig. 5.2, G) before the formation of the press weight (Fig. 5.2, e).

Rice. 5.2. Scheme of direct pressing stages: but - starting position; 1 - press stamp; 2 - press washer; 3 - blank; 4 - container; 5 - matrix holder; 6 - the matrix; in- loading of workpiece and press washer; in - workpiece pressing; d - stable flow of metal: 7 - press product; d - the beginning of the outflow from the zones of difficult deformation and the formation of a press sink; e - press-residue department

and extracting the press item: 8 - knife

The result of the action of friction forces on the surface of the workpiece during direct pressing are high shear deformations, which contribute to the renewal of the metal layers that form the peripheral zones of the profile. This method makes it possible to obtain products with a high surface quality, since in the volume of the workpiece adjacent to the matrix, a large elastic metal zone is formed, which practically excludes the ingress of defects on the surface of the product from the zone of contact between the workpiece and the container.

However, direct pressing is characterized by the following disadvantages.

1. Additional efforts are expended to overcome the force of friction of the surface of the workpiece against the walls of the container.
2. An uneven structure and mechanical properties of press products are formed, leading to anisotropy of properties.
3. The yield is reduced due to the large size of the press residue and the need to remove the weakly formed part of the output end of the press product.
4. Parts of the pressing tool wear out quickly due to friction with the deformable metal during the pressing process.

Back pressing

During reverse pressing, the outflow of metal into the matrix occurs in the direction opposite to the movement of the press ram (Fig. 5.3).

Back pressing begins with the fact that the workpiece is placed between the container and the hollow press ram (Fig. 5.3, but), then it is pushed into the container, upset (Fig. 5.3, b) and extruded through the die channel (Fig. 5.3, in), after which the press product is removed, the press residue is separated (Fig. 5.2, d), the matrix is removed and the press stamp is returned to its original position (Fig. 5.3, e).

During reverse pressing, the ingot does not move relative to the container, so there is practically no friction at the container-blank contact, except for the corner cavity near the die, where it is active, and the total pressing force is reduced due to the absence of energy consumption to overcome friction forces.

The advantages of reverse pressing compared to direct pressing are:

reduction and constancy of the magnitude of the pressing force, since the influence of friction between the surface of the workpiece and the walls of the container is eliminated;
increasing the productivity of the press plant due to an increase in the speed of the expiration of alloys by reducing the unevenness of deformation;
an increase in the yield due to an increase in the length of the workpiece and a decrease in the thickness of the press residue;
increasing the service life of the container due to the absence of friction of its walls with the workpiece;
increasing the uniformity of mechanical properties and structure in the sectional section of the press product.
12 3 4 5 6 7

Rice. 5.3. Scheme of the stages of reverse pressing: but - starting position: 1 - shutter press stamp; 2 - container; 3 - blank; 4 - press washer; 5 - press stamp; 6 - magic holder; 7 - matrix; b - loading a workpiece with a matrix and pressing out the workpiece; in- the beginning of the outflow from the zones of difficult deformation and the formation of a press sink: 8 - press product; d - separation of the press residue and extraction of the press product: 9 - knife; d- removal of the matrix and return of the container

and press ram to original position

The disadvantages of reverse pressing compared to direct pressing are:

reduction of the maximum transverse size of the press product and the number of simultaneously pressed profiles due to the reduction in the size of the through hole in the matrix block;
the need to use workpieces with preliminary surface preparation to obtain press products with a high-quality surface, which requires preliminary turning or scalping of workpieces;
reduction in the range of press products due to an increase in the cost of a tool kit and a decrease in the strength of the matrix assembly;
increase in auxiliary cycle time;
complication of the design of the matrix node;
reduction in the allowable force on the press ram due to its weakening due to the central hole.

Semi-continuous pressing

The length of the blank depends on the strength of the press ram and the size of the working stroke of the press; therefore, blanks of no more than a certain length are used for pressing. In this case, each workpiece is pressed with a press residue. Yield is an indicator of efficiency, equal to the ratio of finished products to the mass of the workpiece. This limitation leads to a decrease in the yield and a decrease in the productivity of the press. This drawback is partially eliminated by the transition to semi-continuous pressing (the method is also called "blank-by-blank" pressing), which, depending on the alloy and the purpose of the press products, is carried out without lubrication and with lubrication. Semi-continuous pressing of blanks without lubrication consists in the fact that each successive blank is loaded into a container after the previous one has been extruded approximately three-quarters of its length. When using this technique, the workpieces are welded at the ends. The length of the workpiece left in the container is limited by the fact that further continuation of pressing will lead to the formation of a press sink, therefore, when loading the next workpiece into the container, the risk of formation of a shrink cavity is eliminated and conditions are created for obtaining high-quality press products. In this case, it is possible to obtain such a press product, the length of which is theoretically unlimited and will be determined only by the number of pressed blanks. Sometimes, during the pressing process, the product is wound into a coil of great length.

The sequence of operations for semi-continuous pressing is shown in fig. 5.4.

At the first stage, the workpiece is fed into the press container and, after de-pressing, it is extruded to a predetermined length of the press residue (Fig. 5.4, a-d). After that, the press stamp is withdrawn together with the press washer fixed on it and the next ingot is loaded. When extruding the next workpiece, it is welded with the press residue from the previous workpiece and the entire metal is extruded through the die channel (Fig. 5.4, d-f). After pressing each workpiece, it is necessary to return the press washer to its original position, which can only be done through the container. The lack of lubrication in the container makes this operation difficult, therefore, a special fastening of the press washer to the press tool and a change in the design of the press washer are required, for example, to facilitate the withdrawal of the press washer from the sleeve of the container, the press washer is equipped with an elastic element.

The disadvantage of semi-continuous pressing is the low welding strength of parts of the press product obtained from individual blanks due to various contaminants that usually remain in the press residue. It was also noted that the welding site in the press product, as a result of the nature of the outflow of the metal, can be strongly stretched.

Rice. 5.4. Scheme of the stages of semi-continuous pressing: but - starting position: 1 - prss-stamp; 2 - press washer; 3 - blank; 4 - container; 5 - the matrix; 6 - matrix holder; - rasprssssovka workpiece; G - billet extrusion; d- loading the next workpiece: 7 - the next workpiece; e - extrusion of the press residue with another blank; w - extrusion

another blank

In semi-continuous pressing of well-welded alloys, the press residue is welded with the next ingot along the end surface. In a prsss product, this surface will be curved, which, with good welding, increases the strength of the joint. In this process, for better weldability, lubrication is unacceptable and the container must be heated to a temperature close to the pressing temperature. In the same way, it is possible to press products from unsatisfactory weldable metals and alloys using lubricants. However, to obtain a flat line of articulation of press products from successively pressed blanks with their easy subsequent separation, it is necessary to use cone dies with an angle of inclination of the generatrix to the axis of less than 60° and concave press washers.

Another scheme of semi-continuous pressing with a prechamber is currently widely used for the production of press products from aluminum alloys (Fig. 5.5).

Rice. 5.5. Scheme of semi-continuous pressing using a prechamber: I- press stamp;

2 - press washer; 3 - preparation; 4 - container; 5 - "dead" zones; 6 - matrix holder; 7 - matrix;
8 - prechamber

A characteristic feature of this pressing scheme is the use of a special pre-chamber tool that provides pressing with butt welding and tension.

Continuous pressing

One of the main disadvantages of pressing is the cyclic nature of the process, therefore, in recent years, much attention has been paid to the development of continuous pressing methods: conforming, extrolling, line-nsks. The conformal method has found the greatest application in industry. A feature of the installation of conforms is (Fig. 5.6) that in its design the container is formed by the surfaces of the groove of the movable drive wheel 6 and a protrusion of a fixed insert 2, which is pressed against the wheel using a hydraulic or mechanical device. Thus, the section of the container, using the terminology of section rolling, is a closed pass. The workpiece is drawn into the container due to friction forces and fills it with metal. When the stop 5 is reached in the workpiece, the pressure increases to a value that ensures the extrusion of the metal in the form of a pressed semi-finished product 4 through the matrix channel 3.

A rod or a conventional wire can be used as a workpiece, and the process of deformation - retraction into the pressing chamber as the wheel turns, preliminary profiling, filling the groove in the wheel, creating a working force and, finally, extrusion is continuous, i.e. continuous pressing technology is implemented .

Rice. 5.6. Scheme of continuous pressing by conformal method: I- supply of bar stock; 2 - fixed insert; 3 - the matrix; 4 - semifinished; 5 - emphasis; 6 - wheel

All-round uneven compression that occurs in the deformation zone makes it possible to achieve high drawings even for low-plasticity alloys, and ductile alloys can be pressed at room temperature with high flow rates. By the method of conforms it is possible to obtain wire and low-section profiles with a high drawing (more than 100). This is especially true for wire, which is more profitable to manufacture by conforming instead of drawing. Currently, the conformal method is used for pressing aluminum and copper alloys. And, finally, it is advisable to use this method to obtain semi-finished products from discrete metal particles: granules, chips. Moreover, there is domestic experience in the industrial use of the conformal method for obtaining, for example, a ligature rod from aluminum alloy granules.

However, the lack of detailed studies of metal shaping, taking into account the boundary forces of friction, studying the laws of deformation of various metals and alloys revealed a number of shortcomings that significantly limit the possibilities of this method of continuous pressing.

1. The maximum linear size of the cross section of the workpiece should not exceed 30 mm to ensure its bending when moving along the gauge.
2. There are difficulties in observing the temperature regime of pressing, since the tool is very hot as a result of the action of friction forces.
3. The process is accompanied (especially for aluminum alloys, most often used for this method) by sticking of metal to the tool, extrusion of metal into the gap of the caliber with the formation of a “whisker” type defect, etc.

Metal flow during pressing

Control of the pressing process and improvement of the quality of pressed semi-finished products is based on knowledge of the patterns of metal flow in the container. An example is direct compression without lubrication, which is the most common. This process can be divided into three stages (Fig. 5.7).

The first stage is called pressing out blanks. At this stage, the workpiece, introduced into the container with a gap, is subjected to upsetting, as a result of which the container is filled with compressible metal, which then enters the die channel. Effort at this stage increases and reaches a maximum.

The second stage begins with the extrusion of the profile. This stage is considered the main one and is characterized by a steady metal flow. As the billet is extruded and the size of the contact surface of the billet with the container decreases, the pressing pressure decreases, which is explained by a decrease in the magnitude of the press force component spent to overcome friction over the container. At this stage, the workpiece volume can be conditionally divided into zones in which plastic and elastic deformations occur. In the main part of the workpiece, the metal is deformed elastically and plastically, and in the corners of the mating of the matrix and the container and near the press washer, elastic deformation is observed (Fig. 5.8).

It has been established that the ratio of the volumes of elastic and plastic zones of the main part of the workpiece depends mainly on the friction between

workpiece and container surfaces. At high values of friction forces, plastic deformation covers almost the entire volume of the workpiece; if the friction is small, for example, the pressing is lubricated, or it is completely absent (reverse pressing), then the plastic deformation is concentrated in the crimping part of the plastic zone around the matrix axis.

Stroke of the press ram

Rice. 5.7. The scheme of pressing with a graph of the distribution of the pressing force by stages: I - workpiece crushing;

II - steady flow of metal; III - final stage

Rice. 5.8. Scheme of the formation of a press sinker during pressing: 1 - zone of plastic deformation; 2 - press weight; 3 - zone of elastic deformation ("dead" zone)

Relatively small elastic zones near the matrix have a significant impact on the course of the metal outflow and the quality of the pressed products. Particular attention should be paid to the volume of metal located in the corners between the matrix and the wall of the container, which is deformed only elastically. This elastic zone of the metal is also called the "dead" zone, and depending on the pressing conditions, its dimensions can change. The elastic zone at the matrix forms an area similar to a funnel, through which the workpiece metal flows into the matrix. In this case, the metal from the “dead” zone itself does not expire into the press product. During direct pressing, the volumes of metal adjacent to the surface of the workpiece, due to the large friction forces on the contact surfaces, as well as plastically non-deformable metal zones near the matrix, delay the peripheral layer from flowing into the channel of the matrix, so it does not participate in the formation of the surface of the product. This is one of the advantages of direct pressing, which lies in the fact that the surface quality of the workpiece has little effect on the surface quality of the molded product.

At the end of the main stage, a phenomenon occurs that has a great influence on the entire pressing process - the formation press weights, which happens as follows. As the pressing washer moves towards the die, due to friction, the movement of the metal parts in contact with the pressing washer slows down, and a funnel-shaped cavity is formed in the central part of the workpiece, into which counter flows of peripheral metal are directed. Due to the fact that volumes of metal from the end and side surface of the workpiece, containing oxides, lubricants and other contaminants, rush into this "funnel", the press tie can penetrate into the press product. In a high-quality press product, the presence of this defect is unacceptable. The formation of a press sink is the most characteristic phenomenon of the third stage of pressing.

In order to completely exclude the transition of the press sinker into the press product, the pressing process is stopped until the extrusion of the workpiece is completed. The underpressed part of the workpiece, called press balance, is removed for waste. The length of the press residue, depending on the conditions of pressing, primarily the value of contact friction, can vary from 10 to 30% of the initial diameter of the workpiece. If, nevertheless, the press sinker has penetrated into the press product, then this part of the profile is separated and discarded.

The formation of a press sink sharply decreases during reverse pressing, but the transition to this type is accompanied by a decrease in the productivity of the process. There are the following measures to reduce the press sink while maintaining productivity:

reduction of friction on the side surfaces of the container and matrix through the use of lubrication and the use of containers and dies with good surface finish;
heating the container, which reduces the cooling of the peripheral layers of the ingot;
jacketed pressing.

Forced pressing conditions

The choice of equipment, the calculation of the tool, the establishment of energy costs and other indicators are calculated based on the determination of the force conditions of pressing. In the practice of press production, these indicators are determined experimentally, analytically or using computer simulation.

The force conditions of pressing determined under production conditions are the most accurate, especially if the tests are carried out on existing equipment, but this method is laborious, high cost and often practically impossible to implement for new processes. Simulation of hot metal processing processes in production, and more often in laboratory conditions, is associated with a deviation from real conditions, especially in temperature regime due to differences in the specific surfaces of the model and nature, hence the inaccuracies of this method. The simplest and most common method, which allows a fairly accurate assessment of the total pressing force, is the method of measuring the pressure of the liquid in the working cylinder of the press according to the pressure gauge. Of the experimental methods that make it possible to indirectly determine the force conditions of pressing, the method of measuring the elastic deformations of the press columns, as well as tensometric tests, is used.

For computer modeling of pressing processes and determination of force costs, such programs as DEFORM (Scentific Forming Technologies Corporation, USA) and QFORM (KvantorForm, Russia) are widely used recently, which are based on finite element method. When preparing data for modeling using these programs, information is usually required on the deformation resistance of the workpiece material, the characteristics of the lubricant used, and the technical parameters of the deforming equipment.

Of great interest are analytical methods for determining the force conditions of pressing, which are based on the laws of solid mechanics, the results of experiments on studying the stress-strain state of a pressed material, differential equilibrium equations, the power balance method, etc. All these calculation methods are quite complex and are described in a special literature. In addition, in analytical methods, it is necessary to know that in any formula it is impossible to take into account all the conditions and varieties of the process in a mathematical expression, and therefore there are no necessary calculation coefficients that accurately reflect the actual conditions and factors of the process.

In practice, for common types of pressing, simplified formulas for determining the total force are often used. The most famous is the formula of I. L. Perlin, according to which the force R, required to extrude the metal from the container through the die hole is equal to

P = R M + T K + T M + T n , (5.7)

where R M- the force required for the implementation of plastic deformation without friction; T to - the force expended to overcome the friction forces on the side surface of the container and the mandrel (with the reverse pressing method, there is no movement of the ingot relative to the container and T to - ABOUT); Г m - the force required to overcome the friction forces arising on the side surface of the compressing part of the deformation zone; T p- the force expended to overcome the friction forces acting on the surface of the calibrating band of the matrix.

Pressing pressure and is calculated as the ratio of effort R, at which pressing takes place, to the cross-sectional area of the container R to

To calculate the components of the pressing force, the formulas contained in the reference books for different cases pressing.

Often simplified formulas are used, for example:

P \u003d P 3 M P pX, (5.9)

where ^3 is the cross-sectional area of the workpiece; M p - pressing module, which takes into account all the conditions of pressing; X- draw factor.

For practical calculations of the pressing force, we can recommend the formula of L. G. Stepansky, which is written in the following form:

P \u003d 1.15aD (1 + 1.41p? 1). (5.10)

where a 5 - resistance to deformation of the material of the workpiece.

The main factors affecting the magnitude of the pressing force include: strength characteristics metal, the degree of deformation, the shape and profile of the channel of the matrix, the dimensions of the workpiece, the friction conditions, the speed of pressing and expiration, the temperature of the container and the matrix.

Pressing pipes and hollow profiles

Pipe pressing

Pressing produces pipes and other hollow profiles. For this, direct and reverse pressing with a fixed and movable needle, as well as pressing using a combined matrix, are used. Pressing with a fixed needle is a process in which at the moment of extrusion of metal into the annular gap that forms the pipe wall, the needle remains in a stationary state.

Direct and reverse pressing of pipes with a fixed needle does not fundamentally differ from the schemes for pressing solid products. However, the presence of an additional detail - mandrel needles to form the inner channel of the pipe, it changes the nature of the metal flow. A special drive is required for the mandrel needle, the task of which is to provide different kinematic conditions depending on the ratio of the speed of movement of the mandrel needle, press ram and container.

Pressing pipes with a fixed needle requires the use of blanks with central holes previously made in them, which also serve as guide holes for the needle. The cavity in the blank for the mandrel needle is made by piercing on a press, drilling or casting. The scheme of direct pipe pressing is shown in fig. 5.9.

Rice. 5.9. Scheme of the stages of direct pressing of pipes with a fixed needle: but- starting position: I- needle-mandrel; 2 - the top of the mandrel needle; 3 - press stamp; 4 - prss-washer; 5 - blank; 6 - container; 7 - matrix; 8 - matrix holder; 6 - loading the workpiece into the container; in - workpiece crushing; d - stage of steady flow; d- the beginning of the outflow from the zones of difficult deformation and the formation of a press sink; e - retraction of the press ram and container, separation of the press residue and press washer: 9 - knife

Pressing begins with the movement of the press ram, then the mandrel needle passes through the hole in the workpiece until its end rests against the die, after which the workpiece is pressed with subsequent extrusion of the metal into the annular gap formed by the die channel (forms the outer diameter of the pipe) and surface of the needle (forms the inner diameter of the pipe). Just like when pressing a bar, a friction force arises between the surfaces of the workpiece and the walls of the container. After reaching a certain length of the press residue, the needle moves back, then the container is retracted, and the press residue is removed from it. When the press ram is retracted, the scissors fixed on the front cross member of the press separate the press residue. It should be noted that during metal extrusion, the mandrel needle is held by the piercing system in the matrix in the same position, therefore this pressing method is called pipe pressing with a fixed mandrel needle. But pipes can also be pressed on bar-profile presses without a piercing system. In this case, the mandrel needle is attached to the press ram and enters the blank cavity, and then into the matrix. When the ram moves and the metal is extruded, the mandrel needle also moves forward, and this method is called moving needle pressing.

The sequence of reverse pressing of pipes with a fixed needle is shown in fig. 5.10. At the initial moment, the mandrel 1 inserted into the workpiece cavity 4 until its top enters the die channel 5, then the ingot is pressed out and the billet metal is extruded into the annular gap between the die channel and the surface of the needle. Upon reaching the predetermined length of the press residue, the needle is retracted to its original position and the press residue is removed.

The main advantages of the direct method of pipe pressing in comparison with the reverse can be formulated as follows:

1. Ability to use any type of press.
2. High quality of a surface of the received pipes.
3. The possibility of obtaining pipes of almost any configuration.

At the same time, a number of shortcomings should be avenged:

1. High energy costs to overcome friction forces.
2. Anisotropy of properties along the length and cross section of pipes.
3. Wear on the surfaces of the container and the needle-mandrel.
4. Significant metal waste due to press residue (10% or more).

For pressing pipes with a fixed needle, pipe profile presses equipped with a piercing system are used, which does not require the use of only a hollow billet. With direct pressing of pipes after loading the workpiece 4 and press washers 3 into the container 5, the workpiece is first pressed out. In this case, the needle 7, located inside the hollow press ram 3, slightly push forward and lock the opening of the press washer 2 (Fig. 5.11, b). After pressing out, the pressure is removed from the press ram and the ingot is pierced with a needle that is pulled out of it. Then served operating pressure to the press ram and the workpiece is squeezed out into the annular gap between the needle 1 and matrix 6 (Fig. 5.11, d). At the end of pressing, the press package (press residue with press washer) is cut off with a knife 8 (Fig. 5.11, e). With this method, it is necessary to carefully center the axes of the container, the press ram and the mandrel relative to the matrix axis in order to avoid the eccentricity of the resulting pipes.

Rice. 5.10. Scheme of the stages of reverse pressing of pipes with a fixed needle: but- starting position: 1 - needle-mandrel; 2 - shutter press stamp; 3 -container; 4 - preparation; 5 - matrix; 6 - press stamp; 7 - mouthpiece; insertion of the needle and pressing the workpiece in the container; g - pipe pressing; d - pressing to a predetermined length of the press residue, retraction of the locking ram and needle: 9 -knife; 10- pipe; e- pushing the matrix out of the container; w - return to starting position

The described schemes have the following disadvantages:

1. Making a hole in the workpiece (drilling, piercing, etc.) requires a change in the design of equipment and tools, additional operations, which increases the complexity of the process, reduces the yield, etc.
1 2 3 4 5 6 7

Rice. 5.11. Scheme of the stages of direct pressing of pipes with a fixed needle: but- starting position: 1 - needle; 2 - press stamp; 3 - press washer; 4 - preparation; 5 - container; 6 - the matrix; 7 - matrix holder; b - feeding the workpiece into the container; in- rasprssssovka workpiece; g - firmware of the workpiece with a needle: 8 - Cork; d- pressing to a predetermined length of the press residue; e - press-residue department

with press washer: 9 - knife; 10 - pipe

2. Obtaining the exact geometry of the pipe makes it necessary to center the mandrel relative to the axis of the matrix channel, which complicates the design of the tool setting.
3. Applying lubricant to the mandrel needle increases the likelihood of defects in the workpiece being pierced.

Pressing pipes and hollow profiles with welding

Most of the disadvantages listed for the considered types of pipe pressing are eliminated by using combined dies, which makes it possible to obtain products of almost any configuration with complex external and internal contours. Such matrices make it possible to produce profiles with not only one, but also with several cavities of various shapes, both symmetrical and asymmetric. A more precise fixation of the mandrel relative to the matrix channel and its small length, and therefore increased rigidity, make it possible to extrude pipes and hollow profiles with a much smaller thickness variation compared to pressing through simple dies.

The benefits of this process are as follows:

eliminates the loss of metal to obtain a cavity in a solid billet;
it becomes possible to use presses without a piercing system;
the longitudinal and transverse thickness variation of hollow pressed products is reduced due to a rigidly fixed short needle;
it becomes available to obtain products of great length by the method of semi-continuous pressing with the folding of a press product into a bay;
improves the quality of the inner surface of the profiles due to the absence of lubricants;
it becomes possible to press several profiles at once, with the most diverse configuration.

However, when using such a pressing scheme, a number of disadvantages should be taken into account, among which the main ones are a large press residue and the presence of welds that are less strong than the base metal, as well as the high cost of dies and low process productivity.

All combined dies consist of a die body or die sleeve and a splitter with a needle. The matrix and the needle form channels, the cross sections of which correspond to the cross section of the press products. On fig. 5.12 shows that on a solid workpiece 4, placed in a container 3, from the press ram 1 through the press 2 pressure is transferred from the working cylinder of the press.

Pressurized workpiece metal 4, passing through the protruding divider 7, it is divided into two streams, which then enter the common welding zone 8 (the flow of metal is shown by arrows), flow around the divider and, under the influence of high temperatures and pressures, are welded into a pipe 9, with seams along the entire length. Such a matrix is also called reed.

On fig. 5.13. the diagram of assembly of a pressing tool (tool setting) is presented, which is used for pressing a pipe using a combined matrix.

Rice. 5.12. Scheme of pressing a pipe through a single-channel combined matrix with a protruding divider: 1 - press stamp; 2 - press washer; 3 - container; 4 - blank; 5 - matrix body; 6 - the matrix; 7 - protruding divider;

8 - welding zone; 9 - pipe

Rice. 5.13. Tool setting for pressing a pipe through a single-channel combined die with a protruding divider: 1 - press stamp; 2 - container; 3 - press washer; 4 - the matrix; 5 - matrix housing; 6 - insert; 7 - matrix holder; 8 - guide; 9 - pipe

Combined matrices of different design make it possible to obtain not only pipes, but also profiles with one, as well as with several cavities of various shapes, both symmetrical and asymmetric, which cannot be produced by pressing into simple matrices. On fig. 5.14 shows a four-channel combined die for pressing a profile of complex shape.

Rice. 5.14. Combined Quad Matrix (but) and the shape of the pressed profile (b)

A necessary condition for obtaining strong welds is also the use of such temperature and speed pressing modes, at which the temperature of the metal in the plastic zone becomes high enough for setting in the seams, and the duration of contact of the welded surfaces ensures the occurrence of diffusion processes that contribute to the development and strengthening of metal bonds. In addition, the fulfillment of deformation conditions that guarantee a high hydrostatic pressure in the welding zone also ensures a good quality of the weld.

Pressing through a multi-channel die

Metal extrusion, which uses matrices with up to 20 channels (Fig. 5.15), and sometimes more, is called multichannel pressing. The transition from single-channel pressing to multi-channel due to an increase in the total cross section of simultaneously pressed products and a decrease in the total elongation at the same workpiece sizes and equal outflow rates reduces the duration of the pressing process, reduces the total pressing pressure and the thermal effect of deformation, and also leads to an increase in the total area of the contact surface in matrix channels.

Replacing single-channel pressing with multi-channel pressing is beneficial under the following conditions:

productivity will increase;
the nominal force of the press used is many times greater than that required for pressing a given profile through one channel;
it is required to limit the growth of metal temperature in the deformation zone;
it is necessary to obtain profiles with a small cross-sectional area.

The features of the metal flow during multi-channel pressing are that the volume of the pressed metal, when approaching the matrix, is divided into separate flows (according to the number of channels), and the outflow rates from each channel of the matrix will be different. Therefore, the farther from the center of the matrix are the axes of the channels of the matrix, the shorter will be the length of the resulting press products. Such pressing is characterized by an average drawing A, cf:

^p = -^r. (5.11)

where E’k is the cross-sectional area of the container; - cross-sectional area of the channel in the matrix; P- the number of channels in the matrix.

In multi-channel pressing, as the press washer moves towards the die, the outflow rates through the various channels continuously change. To equalize the velocities of the outflow from different channels and to obtain press products of a given length, the channels on the matrix are arranged in a certain way. The values of the outflow velocities will be close if the centers of the channels are located uniformly along the entire circumference with the center on the axis of the workpiece. If the channels are located on several concentric circles, then the center of each channel must coincide with the center of gravity of equal cells of the grid applied to the end surface of the matrix. Cells must be arranged symmetrically about the axis.

In addition to the already considered pressing method using combined matrices (see Fig. 5.14), multi-channel pressing is also used in the production of asymmetric or with one symmetry plane profiles to reduce deformation unevenness (see Fig. 5.15).

The assembly scheme of the pressing tool (tool setting) for multi-channel pressing is shown in fig. 5.16.

Rice. 5.15.

Rice. 5.16. Scheme of tool setting for multi-channel pressing on a horizontal press: 1 - press stamp; 2 - press washer; 3 - preparation; 4 -

5 - the matrix; 6 - matrix holder

In those cases when it is impossible to press a large-diameter profile in more than one thread for a certain size of the press container, it is advisable to press this profile simultaneously with one or two small-diameter profiles to increase the productivity of the press.

Pressing equipment

As equipment for pressing, hydraulically driven presses, which are machines of static action, are most widely used. Hydraulic presses are simple in design and at the same time can develop significant forces with the help of a high-pressure fluid (water emulsion or mineral oil). The main characteristics of hydraulic presses are the nominal force R n, working stroke and speed of movement of the pressing traverse, as well as the dimensions of the container. The nominal force of the press is determined as the product of the pressure of the liquid in the working cylinder of the press and the area (or the sum of the areas) of the plunger. The speed of the stroke of the press plunger is easily regulated by changing the amount of fluid supplied to the cylinders. Presses with a mechanical drive from an electric motor for pressing metal are used less often.

A typical hydraulic press installation consists of a press I, pipelines II, controls III and a drive IV (Fig. 5.17).

The design of the hydraulic press includes a frame 1, serving to close the forces developed, the working cylinder 2, in which the fluid pressure develops, the plunger 3, perceiving this pressure and transmitting this force through the tool 4 on the workpiece 5. To carry out the reverse stroke in hydraulic presses, return cylinders are provided 6.

The drive of hydraulic presses is a system that provides high-pressure fluid production and its accumulation. The drive can be pumps or pumping and storage stations. Pumps are used as an individual drive on presses of low and medium power, operating at low speeds. For powerful presses or a group of presses, a pump-accumulator drive is used, which differs from an individual pump drive in that an accumulator is added to the high-pressure network - a cylinder for accumulating high-pressure liquid. As the presses work, the liquid in the accumulator is periodically consumed and accumulates again. Such a drive provides a high speed of movement of the tool and the necessary force of the press.

Depending on the purpose and design of the press, they are divided into bar-profile and pipe-profile, according to their location - into vertical and horizontal. Unlike bar-profile presses, pipe-profile presses are equipped with an independent needle drive (piercing system).

According to the method of pressing, the presses are divided into presses for direct and reverse pressing, and according to the force - into presses of small (5-12.5 MN), medium (15-50 MN) and large (more than 50 MN) forces.

Rice. 5.17. Scheme of hydraulic press installation: I - press; II - pipelines; III - governing bodies; IV - drive; 1 - bed; 2 - cylinder; 3 - plunger; 4 - tool; 5 - blank; 6 - return cylinders

Domestic plants processing non-ferrous metals and alloys mainly use vertical presses with a force of 6-10 MN and horizontal - 5-300 MN. Foreign enterprises use vertical presses with a force range from 3 to 25 MN, and horizontal ones with forces from 7.5 to 300 MN.

The composition of most press installations, in addition to the press itself, includes devices for heating and transferring ingots from the furnace to the press, as well as equipment located on the exit side of the product from the press: a refrigerator, mechanisms for straightening, cutting and winding products.

Comparison of vertical and horizontal presses reveals the advantages and disadvantages of each of these types of equipment. So, due to the small stroke of the main plunger, vertical presses significantly exceed horizontal ones in terms of the number of pressings per hour. Due to the vertical arrangement of moving parts, these presses are easier to center, have Better conditions to work with container lubrication, which makes it possible to obtain pipes with thinner walls and a smaller variation in wall thickness. At enterprises for the processing of non-ferrous metals, vertical presses are used without a piercing system and with a piercing system. Both types of presses are mainly used to produce pipes of limited length and diameter from 20-60 mm. For presses of the first type, a hollow billet is used, which is turned along the outer diameter to reduce the variation in the thickness of the pipe wall. For presses with a piercing system, a solid blank is used, the firmware of which is carried out on a press. A diagram of a vertical press without a piercing system is shown in fig. 5.19.

After each pressing operation, the slider 12 with the help of a hydraulic cylinder, it moves to the right, the product is cut off, and the matrix with the press residue rolls into the container along the sliding slider. The reverse stroke of the main plunger is carried out thanks to the cylinder 14, fixed on the stand. The design of the vertical press allows 100-150 pressings per hour.

However, despite this, horizontal presses have become widespread due to the possibility of pressing longer products, including those with a large cross section. In addition, this type of press is easier to work with automation tools. On fig. 5.19 and 5.20 are bar-profile and pipe-profile horizontal presses.

Bar-profile presses are simpler in design than pipe-profile presses, mainly because they do not include a piercing device. In the design shown in Fig. 5.19 press included movable container 3, able to move due to the container movement cylinders 9 along the axis of the press, main cylinder 6, into which a high-pressure liquid enters, which ensures the creation of a pressing force transmitted through a press ram 10 and a press washer on the workpiece. With 7 return cylinders due to liquid low pressure moving traverse occurs 8. On such presses, pipes can also be pressed, but for this, either a hollow billet should be used or, with a solid billet, pressing through a combined matrix.

The massive base of the pipe press (see Fig. 5.21) is the foundation slab 12, on which the front 1 and rear cross members 2, which are connected by four powerful columns 3. These parts of the press bear the main load during pressing. The main cylinder, with the help of which the working pressing force is generated, and the return cylinder, designed to move the press ram to its original position, are fixed in the rear cross member. 2.

Rice. 5.18. General view of the vertical press: 1 - bed; 2 - master cylinder; 3 - main plunger; 4 - movable traverse; 5 - head; 6 - press stamp; 7 - needle; 8 - container; 9 - container holder; 10- the matrix; 11- plate; 12 - slider; 13 - knife; 14 - cylinder; 15 - brackets

13 12 11 10 9 in

Rice. 5.19. General view of the horizontal bar profile press: 1 - matrix board; 2 - Column; 3 - container;

4 - container holder; 5 - pressing traverse; 6 - master cylinder; 7 - return cylinder; 8 - rear crossbar;
9 - container movement cylinder; 10 - press stamp; 11- matrix node; 12 - front cross member; 13 - press bed
11 10 1 8

9 4 5 3 16 7 8
13 TO

Rice. 5.20. General view of the horizontal pipe press: 1 - front cross member; 2 - rear crossbar; 3 - Column; 4 - matrix node; 5 - container; 6 - cylinder; 7 - receiving table; 8 - wedge gate; 9 - hydraulic cylinder; 10 - saw; 11 - scissors; 12 - base plate; 13 - master cylinder; 14 - main plunger; 15 - movable crossbar; 16 - press stamp; 17 - shank; 18 - the stem of the piercing system; 19 - traverse of the firmware system; 20 - plunger; 21 - cylinder

firmware system; 22 - needle

In the described design of the press, the rear cross member is integral with the main cylinder. 13. Movable traverse 15 with press stamp 16 connected to the front neck of the main plunger 14. Movable stem 18, fixed on a movable traverse 19 piercing system, enters the cavity of the main plunger and its shank 7 7. In the channel of the movable hollow rod 18 there is a pipe through which water is supplied to cool the piercing needle 22. Cooling water from the needle is discharged through the channel of the hollow rod. The entire telescopic system is enclosed in the casing of the shank 77. In turn, the traverse is fixed on the plunger 20 firmware cylinder 21. Piercing traverse 19 and stem 18 when piercing, they move autonomously from the main plunger, and when pressing, they move synchronously with it. matrix node 4 with adjoining container 5 through wedge gate 8 rests on the front crossbar. The wedge gate is equipped with a hydraulic cylinder 9. When separating the press residue and changing the die, the mouthpiece with the die holder is removed from the cross member by a cylinder 6, which is mounted in the frame of the receiving table 7. The product is cut off from the press residue with a saw 10 or scissors 77. The saw is raised or lowered by means of hydraulic oil-powered cylinders to complete the cutting operation.

Pressing pipes on a pipe press consists of the following operations. The workpiece, heated in the furnace, rolls down the troughs onto the intermediate table, being enveloped in lubricant, and transferred to the tray. In front of the ingot, on the same tray in front of the billet, an extrusion washer is installed and the tray is moved to the level of container 5 until the axis of the ingot is aligned with the axis of the container. After that, the workpiece with a press washer using a press stamp 16 idling master cylinder plunger 14 stuffed into a heated container. To stop the movable traverse 75 at the moment of reaching a predetermined height by the press residue in front of the container, a stroke limiter is installed. Then, under the action of high-pressure fluid in the cylinder of the piercing system 21 a working stroke is made, and the workpiece is stitched with a needle 22. Pressing the pipe by extruding the metal into the gap between the matrix channel and the needle is carried out by the pressure of the press ram 16 through the press washer onto the workpiece due to the high pressure fluid in the main cylinder. At the end of the pressing cycle, the piercing and pressing traverses move back to the rearmost position, the container is retracted to allow the passage of the saw 10, which is supplied by hydraulic cylinders, cuts off the press residue and is retracted to its original position. This is followed by operations to remove the press residue with the rest of the pipe and separate them using scissors 77. Then the needle is pulled out for cooling and lubrication.

In accordance with the pressing technology, the hydraulic press must also have auxiliary mechanisms used to perform such operations as feeding the ingot to the heating furnace, cutting off the press residue and cleaning it, transporting the pressed bars and their finishing, and, if necessary, heat treatment. Typical for modern presses is their complete mechanization and automation with program control for the main and auxiliary operations, from feeding the workpiece to the heating furnace, the pressing process itself and ending with the packaging of finished products.

Press tool

The main parts of the pressing tool

The set of tools installed on the press is called tool setting, the design of which varies depending on the device of the press and the type of pressed products.

For pressing on hydraulic presses, several types of adjustments are used, which differ depending on the type of press products, the pressing method and the type of pressing equipment used.

Typically, tool setups are systems consisting of a matrix set, container and press ram or matrix set, container, mandrel and press ram and differ either in the design of the matrix set or the insertion of a mandrel. One of the main types of tool setting is shown in Fig. 5.21.

In hydraulic presses, the main pressing tools are dies, die holders, needles, press washers, press dies, needle holders and containers.

Compared with bar-profile presses, tool adjustments used on pipe-profile presses have their own characteristics associated with the presence of parts necessary for piercing a solid billet.

The tool of hydraulic presses is conditionally divided into parts of a movable unit and parts of a fixed unit. A fixed assembly in direct pressing includes a container and a device for attaching dies, which do not move with the pressed metal during the extrusion of products.

The composition of the movable unit includes a press-stamp, a press-washer, a needle holder and a needle. Such a division of the tool is advisable for analyzing the conditions of its operation, methods of fastening and maintenance.

When considering the issues of resistance and durability of the tool, a heavily loaded working tool for hot pressing of metals can be divided into two groups.

Rice. 5.21. Scheme of tool setting for direct pressing on a horizontal press: 1 - press stamp; 2 - press washer; 3 - preparation; 4 - container inner sleeve; 5 - the matrix; 6 - matrix holder

The first group includes parts that are in direct contact with the metal during the pressing process: needles, dies, press washers, die holders and inner sleeves of containers. The second group includes intermediate and outer bushings of containers, press-stampsli, heads of matrix holders or matrix boards, which do not come into direct contact with the pressed metal.

In the most difficult conditions, the tool of the first group, which is subjected to high voltage(up to 1,000-1,500 MPa), cyclic alternating loads, exposure to high temperatures, accompanied by sharp surges and temperature changes, intense abrasive action of deformable metal, etc.

The operation features of the tool belonging to the first group are explained by the fact that the cost of the tool of this group can reach 70 - 95% of all costs for the working tool of a typical press. Here, the main designs of the parts included in the pressing tool are considered.

Serves as a receiver of the heated ingot. During the extrusion process, it takes the full pressure from the pressed metal under conditions of intense friction at high temperature. To ensure

chsniya sufficient resistance containers are made composite of two to four bushings. In terms of dimensions, the container is the largest part of the press tool assembly, the mass of which can reach 100 tons. A typical design of a three-layer container is shown in fig. 5.22.

1 2

Rice. 5.22. Container: 1 - inner sleeve; 2 - middle sleeve; 3 - outer sleeve; 4 - holes for copper rods of container heater

Matrix holder locks the outlet side of the container and enters into connection with it along the conical surface. In the central part of the matrix holder there is a nest for landing the matrix. Matrices are installed either from the end of the matrix holder or from its inner side. The conical mating surface of the die-holder with the container experiences heavy loads, therefore, the die-holders are made of heat-resistant die steels with high strength characteristics.

(38KhNZMFA, 5KhNV, 4Kh4NVF, etc.).

Press stamp transfers the force from the main cylinder to the pressed metal and perceives the full load from the pressing pressure. To protect the end of the press ram from contact with the heated workpiece, replaceable press washers are used that are not fastened to the press ram and after each pressing cycle are removed from the container along with the press residue for separation and use in the next cycle. The exception is semi-continuous pressing, in which the press washer is fixed on the press ram and, after the end of the cycle, returns to its original position through the cavity of the container. Based on the operating conditions, the press dies are made from forged alloy steels with high strength characteristics (38KhNZMFA, 5KhNV, 5KhNM, 27Kh2N2MVF).

In the practice of pressing, bar and pipe press dies are used. Solid section press rams are used for pressing solid profiles, as well as pipes on bar-profile presses with a movable mandrel fixed on the press ram and moving with it. The design of the press dies is shown in fig. 5.23.

At the non-working end of the press ram there is a shank that serves to fasten the press ram to the press traverse of the press. Press stamps are made both solid and prefabricated. The use of prefabricated dies makes it possible to use smaller diameter forgings for their manufacture.

The main purpose of workers press washer is to exclude direct contact between the press ram and the heated workpiece. Press washers in the process of deformation perceive the full pressing pressure and are subjected to cyclic temperature loading, therefore they are made from forgings of die steels (5KhNM, 5KhNV, 4Kh4VMFS, ZKh2V8F, etc.).

Rice. 5.23. Press dies: but - solid; b - hollow

Needle holder is designed to secure the needle and transfer force to it from the movable traverse of the piercing device, to the stem of which it is attached by a threaded section.

The tool for flashing a workpiece is called needle, and for the formation of an internal cavity in pipes and hollow profiles - mandrel. Sometimes these functions are performed by one tool. When pressing a hollow billet, the mandrel is fixed in a press ram (pressing with a movable needle on a bar-profile press) or in a needle holder (pressing on a pipe-profile press with a piercing system). When pressing hollow profiles from a solid billet, the mandrel needle is an integral part of the combined matrix.

For the manufacture of needles, steels such as KhN62MVKYU, ZhS6K, 5KhZVZMFS, ZKh2V8F, 4Kh4VVMFS, ZKh2V8F, and others are used. 5.24 schematically shows the needles of vertical and horizontal presses used in the pressing of pipes and profiles of constant cross section.

Rice. 5.24. Needles: but - vertical press; b - horizontal press

A part of a pressing tool that, when pressed, provides a profile of the required dimensions and the quality of its surface is called matrix. Typically, the matrix is made in the form of a disk with a channel cut through it, the cross-sectional shape of which must correspond to the section of the pressed profile. The diameter of the matrix depends on the dimensions of the container and the workpiece, and the thickness of the matrix is chosen based on design and technological considerations.

The die operates under extremely severe conditions of high temperatures and specific forces with minimal lubrication and cooling opportunities. This part is considered the most critical and most subject to wear of all the parts included in the press tool assembly. According to the number of holes, matrices are single- and multi-channel. The number of holes in the matrix is determined by the type of product and the required productivity of the press. According to the design of the matrix, they are divided into two groups: the first is intended for obtaining products of a solid cross-section or hollow profiles pressed by the pipe method from a hollow billet, and the second is used for pressing hollow profiles from a solid billet and is a combination of a matrix with a mandrel (combined matrix). The matrix forms the contour of the press product and determines its dimensional accuracy and surface quality.

For pressing the bulk of pipes and rods made of non-ferrous metals and alloys, various types of dies are used, some of which are shown in Fig. 5.25.

Rice. 5.25. Matrix types: but- flat; b - radial; in - national team:

1 - insert; 2 - clip; g - conical: 3 - working cone; 4 - sizing belt

The surface of the compressing part of the plastic zone of the matrix from the side of the metal entering it can have a different shape. It has been established by practice that the optimal angle of the inlet cone into the matrix channel is 60-100°. With an increase in the cone angle, dead zones appear, which reduce the possibility of contaminated parts of the ingot entering the product.

The product receives its final dimensions when passing through a sizing band, the length of which is determined by the type of pressed metal. Often, to increase the service life, the matrix is made detachable, and the belt is made of hard alloys.

Matrices are made from die and heat-resistant steels (ZKh2V8F, 4KhZM2VFGS, 4Kh4NMVF, 30Kh2MFN), and matrix inserts from hard alloys (VK6, VK15, ZhS6K). Steel matrices are located directly in the matricesdsrzhatsle. When pressing aluminum alloys, the matrices are subjected to nitriding to reduce friction and sticking.

Matrices made of hard and heat-resistant alloys are also used in the form of inserts 1, mounted in clips 2 (Fig. 5.26, in), which allows not only to save expensive materials, but also to increase the durability of matrices.

For pressing hollow profiles, combined matrices are used (Fig. 5.26), the designs of which differ in the shape and size of the welding zone and the geometry of the divider. All designs of combined matrices, depending on the number of simultaneously pressed products, are divided into single- and multi-channel.

Rice. 5.26. Combined matrices: but- a matrix with a protruding divider:

1 - support stand; 2 - splitter comb; 3 - needle; 4 - matrix bushing; 5 - body; b- prefabricated matrix: I- divider; 2 - the matrix; 3 - lining; 4 - matrix holder; 5 - clip; 6 - support ring; 7 - pin; 8 - divider needle

Single-channel matrices, depending on the design, have different types dividers (protruding, semi-recessed, recessed, flat), and can also be capsule and bridge. A matrix with a protruding divider (Fig. 5.26, but) has free access of metal to the welding zone. The splitter section of such a matrix has the shape of an ellipse. When pressing through such a matrix, the press residue is removed after each cycle by tearing it out of the matrix funnel or pressing the next workpiece. This operation is carried out by a sharp withdrawal of the container from the matrix.

In most cases, combined matrices are made prefabricated (Fig. 5.26, b). This facilitates their maintenance and makes it possible to reduce the cost of their manufacture.

Pressing equipment and tools are constantly being improved, which makes it possible to increase the efficiency of this type of metal forming.

Fundamentals of pressing technology

The construction of the pressing process includes: selection of the pressing method; calculation of workpiece parameters (shape, dimensions and method of preparation for pressing); substantiation of the method and temperature range of billet heating; calculations of pressing speed and expiration, as well as pressing force; choice auxiliary equipment for heat treatment, straightening, conservation, as well as the appointment of a quality control operation for press products.

In pressing technology, first of all, a cross-sectional drawing of a given press product is analyzed and the type of pressing and the corresponding type of equipment are selected. At this stage, the alloy grade, the delivery length of the profile are taken into account as initial data, coordinating all calculations with such regulatory documents as technical specifications for extruded profiles, compiled on the basis of current state and industry standards, as well as additional requirements agreed between the supplier and the consumer.

To select the pressing method and its variety, it is necessary to analyze the initial data and requirements for products, taking into account the volume of production and the state of delivery of products to the customer. The analysis should also evaluate the technical capabilities of the existing pressing equipment, as well as the ductility of the pressed metal in the pressed state.

In the practice of press production, direct and reverse pressing are most often used. For profiles of large delivery length and with a minimum value of structural heterogeneity, it is advisable to use the reverse pressing method. In all other cases, the direct method is used, especially for products with a larger cross section, up to dimensions approaching the dimensions of the cross section of the container sleeve.

A typical flow diagram used in the extrusion of profiles, bars and pipes from heat-hardened aluminum alloys on horizontal hydraulic presses is shown in fig. 5.27.

Rice. 5.27.

The workpiece for pressing can be cast or deformed, and its parameters are determined from the sum of the masses of the press product and waste at the press stage. The workpiece diameter is calculated based on the cross-sectional area of the molded product, which is acceptable for the extruded drawing alloy in relation to the type of workpiece (ingot or deformed semi-finished product), and the press force. For molds that do not undergo further deformation, the minimum drawdown should be at least 10, and for molds that are further processed this value can be reduced to about 5. The maximum drawdown is determined by the press force, the durability of the pressing tool and the ductility pressed metal. The higher the plasticity, the greater the maximum allowable stretch. Blanks for pressing bars and tubes typically have a length to diameter ratio of 2-3.5 and 1-2.0, respectively. This is explained by the fact that the use of long workpieces when pressing pipes leads to a significant increase in their difference in wall thickness.

In most cases, ingots are used as blanks for pressing. For example, to obtain ingots from aluminum alloys, at present wide use received the method of semi-continuous casting in an electromagnetic mold. The ingots obtained in this way are distinguished by the best quality of structure and surface. After casting, ingots for products of higher quality are subjected to homogenization annealing, after which the structure of the blanks becomes homogeneous, plasticity increases, which makes it possible to significantly intensify the subsequent pressing process and reduce process waste.

Turning and peeling ingots can eliminate surface defects of foundry origin. However, the subsequent heating of the ingots leads to the formation of a scale layer, which reduces the quality of the molded products. In this regard, one of the most effective is the method of hot scalping of billets, which consists in the fact that the ingot, after heating, is pushed through a special scalping matrix, the diameter of which is smaller than the diameter of the ingot by the value of the scalped surface layer (Fig. 5.28).

12 3 4 5 6 7 8 9

I 1 I I / / !

Rice. 5.28. Ingot scalping scheme: 1 - press stamp; 2 - feeder prism; 3 - ingot; 4 - crimp guide sleeve; 5 - scalped layer; 6 - scalping matrix; 7 - attachment point of the scalping matrix; 8 - output guide; 9 - discharge roller table

Scalping is carried out either on separate installations located between the press and the heating device, or directly at the entrance to the press container.

The temperature of the metal during pressing should be chosen so that the metal in the deformation zone is in a state of maximum plasticity. Aluminum and its alloys are pressed at temperatures of 370-500 °C, copper and its alloys at 600-950 °C, titanium and nickel alloys at 900-1200 °C, and steel at 1100-1280 °C,

The temperature of the metal during pressing and the flow rate are the main technological parameters of the process. Usually, both of these parameters are combined into one concept of the temperature-velocity regime, which determines the structure, properties and quality of press products. Strict observance of the temperature and speed regime is the basis for obtaining high quality products. This is especially important for pressing aluminum alloys, which are pressed at speeds much lower than copper alloys.

The main types of heat treatment of press products are: annealing, hardening, aging.

After pressing and heat treatment, press products may have distortions in length and in cross section. To eliminate the distortion of the shape of press products, stretching straightening machines, pipe-rolling machines, and roller straightening machines are used.

To give press products a commercial appearance, their surface is treated, as a result of which lubricants, scale and various surface defects are removed. A special place in these operations, called finishing, is given to etching. For a number of press products, mainly from aluminum alloys, anodizing is carried out (the process of creating a film on the surface of press products by polarization in a conductive medium) for decorative purposes, as well as a protective coating. The technological process of anodizing press products consists of the operations of degreasing, etching, washing, brightening, anodizing itself, drying and applying an anode film.

Cutting of molded products to cut lengths and cutting of specimens for mechanical tests are carried out different ways. The most common cutting on circular saws is cutting cutters.

After cutting and acceptance by the service of the technical control department, most of the press products are preserved and packed in containers. A greased pack of press products is placed in a thick envelope made of oiled paper, which eliminates direct metal-to-wood contact and moisture penetration to the metal.

Control questions and tasks for chapter 5

1. Define the term "pressing" and explain the essence of this process.
2. What scheme of the stress state is realized during pressing in the deformation zone?
3. List and comment on the advantages and disadvantages of the pressing process compared to bar and tube rolling.
4. List the most appropriate areas for pressing.
5. What formulas can be used to calculate the elongation ratio during pressing?
6. How are the relative degree of deformation and the elongation ratio related?
7. How, knowing the speed of pressing, it is possible to determine the speed of expiration?
8. List the main methods of pressing.
9. Describe the features of direct pressing.
10. What are the advantages of reverse pressing compared to direct pressing?
11. What is semi-continuous pressing?
12. What is the design feature of the press washer for semi-continuous pressing?
13. Describe the principle of continuous pressing according to the method of con-

14. What are the stages of the pressing process?
15. Describe the formation of a press sinker during pressing.
16. List the main patterns that determine the size of the press residue.
17. What methods reduce the size of the press residue during pressing?
18. What is the purpose of a mandrel needle when pressing pipes?
19. Comparison of pipe extrusion by direct and reverse methods.
20. How is the process of pressing pipes with welding organized?
21. Describe the tool setting when pressing pipes through a single-channel combination die.
22. What is the design feature of the combined matrix?
23. List the features of pressing through a multi-channel matrix.
24. In what cases is it advisable to replace single-channel pressing with multi-channel pressing?
25. Give the formula for calculating the elongation ratio for multi-channel pressing.
26. Why is it necessary to determine the force conditions of pressing?
27. What are the methods for determining the force conditions of pressing?
28. Describe the main experimental methods for determining the force conditions of pressing, their advantages and disadvantages.
29. Name and describe analytical methods for evaluating the pressing force.
30. What are the components of the total force of the press?
31. What are the main factors affecting the magnitude of the pressing force.
32. List the basic principles by which pressing speeds are chosen.
33. Describe the typical design of a hydraulic press installation.
34. What types of hydraulic presses are used for pressing?
35. Explain the principle of operation of hydraulic rod-profile and pipe-profile presses.
36. What is included in the pressing tool kit?
37. Describe the purpose and design of the container.
38. What steels are used for the manufacture of pressing tools.
39. What types of dies are used for pressing?
40. What is the procedure for developing a pressing process?
41. What operations are included in technological scheme extrusion of aluminum extrusion products?
42. How are press releases edited?
43. What is the anodizing of aluminum press products for?

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