Types of blanks, methods of obtaining them. Types and methods of manufacturing blanks Technology for obtaining a blank part by casting

The main direction of mechanical engineering technology is the improvement of procurement processes in order to reduce the cost of machining, limit the technological operations of final processing, and ensure low-waste or waste-free technology.

The method of obtaining the workpiece is determined by the size of the program task and the technological capabilities of the procurement workshops; opportunities to obtain blanks from specialized enterprises; the material of the part, the shape of its surface, dimensions and technical requirements for manufacturing. The method of obtaining the workpiece, in addition, is determined by the possibilities of manufacturing technological equipment (manufacturing of stamps, models, molds). The cost of manufacturing a part consists of the cost of procurement and machining. And in the end, it is important to ensure the reduction of the entire amount, and not just one component. Creating a design that allows cutting to be replaced by stamping or upsetting, in many cases, leads to a decrease in material consumption and a decrease in labor intensity. There are the following methods for obtaining blanks:

1. Casting. When choosing a casting as a workpiece, the following factors are taken into account: the suitability of this method for the required shaping, taking into account the dimensions; compliance of the material from which it is possible to perform casting, the requirements of the part drawing; technological capabilities of the casting method to obtain dimensional accuracy and surface roughness under specific production conditions.

The most common casting methods include shell mold casting, sand-clay mold casting, investment casting, metal mold casting, pressure casting, and centrifugal casting.

The method of casting in sand-clay molds is used for all casting alloys, types of production, workpieces of any mass, configuration and dimensions. In the total volume of production of castings by casting in sand-clay molds, 80% of all castings are obtained and only 20% of castings are produced by special casting methods. It is distinguished by technological versatility and low cost. By changing the molding methods, the materials of the models and the composition of the molded mixtures, blanks are made with a given accuracy and quality of the surface layer. The method is distinguished by a large flow of molding and auxiliary materials, it is characterized by large machining allowances, 15-25% of the metal from the mass of the workpiece goes into chips.

Casting into shell molds Using this method, workpieces of complex configuration are obtained: crankshafts and camshafts, ribbed cylinders and impellers. Part of the surfaces of the workpieces does not require machining. By the time the metal solidifies, the molds are easily destroyed without preventing the metal from shrinking, the residual stresses in the casting are not significant. The consumption of molding materials is 10-20 times less than when casting into sand-clay molds. At the same time, with hot metal products it presents a certain difficulty.

Investment casting is a method for producing complex and precise blanks for hard-to-form and hard-to-machine alloys with a high melting point. It features the most labor-intensive production method of all casting methods. The cost-effectiveness of the method is achieved by a correctly developed nomenclature of castings, especially when the requirements for roughness and dimensional accuracy can be met in the cast state and only the mating surfaces need to be machined. The use of blanks obtained by investment casting instead of stamped ones reduces metal consumption by 55-75%, the labor intensity of machining up to -60% and the cost of the part by 20%.

2. Hot plastic deformation. About 90% of steels produced are processed by pressure, which shows the importance of this method for obtaining blanks. Depending on the serial production of parts, various methods of processing blanks by pressure are used. In single and small-scale production, blanks are most often made by free forging. This method can only obtain forgings of a simple configuration. In medium and small-scale production, hot stamping is used on hammers, presses and GCM. In mass production, specialized forging machines are used. Machines of this type include high-speed stamping hammers, forging rolls, crimping, rolling, rolling, bending, etc.

Low-waste processes of shaping parts by pressure treatment include precision stamping, knurling of gear wheels, slots and threads, hot and cold extrusion, radial and rotational forging. When introducing low-waste processes of pressure treatment, it is necessary to solve problems associated with their specifics - obtaining an accurate mass and volume of the original workpiece, preliminary preparation of the workpiece - applying protective and lubricating coatings, increasing tool life, using non-oxidizing heating of the workpiece.

3. Cold stamping. With the introduction of this production method, it is possible to obtain the final dimensions and shape of complex parts (gears, spindles, connecting rods, valves, camshafts, etc.), and subsequent machining is minimized or eliminated. This method eliminates the loss of metal in waste and waste in the scale, provides high quality surfaces of the product. As a result of cold deformation in the metal, the uniformity of the structure is ensured, and the surface layer is hardened. Cold stamping is a method of obtaining blanks from a sheet or tape by punching, drawing, punching, bending, flanging, etc. The feasibility of its use is determined by a number of conditions - the serial production of products, the configuration of products, the mechanical properties of the material, the accuracy of manufacturing parts.

The use of cold stamping to obtain a workpiece is beneficial if the part has a complex shape, while the dimensions do not need to be performed accurately; if the parts have slots with sharp corners; in the manufacture of parts, the blanks of which have the form of whole washers or washers with a central hole; for the manufacture of parts, if the costs of manufacturing and operating the die are justified.

• 4. Rental. Rolled products are used when the geometry of the product corresponds to the shape of the sectional material (round, hexagonal, etc.). Seamless pipes and shaped rolled products (corners, channels, beams) are widely used. Using bent, open and closed profiles, the weight of the part is significantly reduced.
• 5. Plastic blanks. Plastics are widely used for the manufacture of simple parts (impellers, pumps, pulleys, bushings). It should be taken into account that plastics are characterized by low impact strength, insufficient strength, aging, low heat resistance (250 - 300 ° C).

The method of obtaining the workpiece is made at the qualitative and quantitative levels. The decision on the choice of the technological process for obtaining the workpiece is made on the basis of a comparative assessment of comparable options. It is considered economically feasible that option for obtaining a workpiece, which will provide the minimum reduced costs for the procurement and machine shops of the plant. The calculation of the reduced costs is carried out in accordance with the methods of the feasibility study of the technological process option. Such calculations are performed by the technical services of the plant, who have experience in calculating technological developments. We make calculations at a qualitative level, i.e. we use an approximate method for choosing a workpiece. Its essence is that for simple products, for educational purposes, the task of choosing a workpiece is solved by analyzing the technological properties of the material of the product, the complexity of the product, the dimensions and the release program. The analysis is performed according to 4 criteria:

Technological properties of the material of the product: In accordance with the data of the drawing, the material from which the spool is made is 40X steel. This steel has high strength, good machinability, low sensitivity to stress concentration. Technological features of blank production determine the following methods for obtaining a blank: casting, forging, stamping and rolling

• 2. Product design: Since the spool has a simple configuration, i.e. insignificant differences in the diameters of the cylinders, then from the possible methods of obtaining we assign stamping and rolling.
• 3. Dimensions of the product.: Such a method of blank production as stamping has limitations on the dimensions of the blank, therefore, from all possible methods, we choose rolled products.
• 4. Type of production: we assign small-scale production of a thousand parts.

Thus, taking into account the production program, the simple configuration of the part, and based on the data of the machine-builder technologist's handbook, the most rational way of blanking for the spool is round rolled steel 40X GOST4543-71.

Workpiece length:

Lz \u003d Ld + 2P + T,

where Ld = part length; P - allowance; T is the width of the cutter.

Lz,1 = 205+2*1+6 = 213 mm

Lz,1000 \u003d 1000 * Ld + 2P * 10 + 9 * T \u003d 1000 * 205 + 2 * 1 * 10 + 9 * 6 \u003d 205074 mm

We accept the required length of the workpiece, equal to Lz \u003d 213000 mm

Part volume:

Vd = Vp1+ Vp2+ Vp3+ Vp4+ Vp5+ Vp6+ Vp7+ Vp8+ Vp9+ Vp10+ Vp11-Vp12-Vp13

Vts1=3.14 *R12*H1 = 3.14*22.52*4 = 6358.5 mm3

Vts2 \u003d 3.14 * 182 * 8 \u003d 8138.88 mm3

Vp3=3.14*22.52*38= 60405.75 mm3

Vp4=59*1/2*38*35=39235 mm3

Vp5 \u003d 2 * 3.14 * 202 * 8 \u003d 3925 mm3

Vp6 \u003d 1/3 * 3.14 * 15 * (17.52 + 242 + 17.5 * 24) \u003d 15.70 * 1302.25 \u003d 20445.53 mm3

Vp7= 3.14*242*7=12660.48mm3

Vp8 \u003d 3.14 * 5 * 22.52 \u003d 7948.125mm3

Vp9 \u003d 1/3 * 3.14 * 242 * 25 \u003d 45216 mm3

Vp10 \u003d 3.14 * 182 * 8 \u003d 8138.88 mm3

Vp11 \u003d 3.14 * 242 * 30 \u003d 54259.2 mm3

Vp12 = 1/3*3.14*4(122 +162 +12*16)+3.14*144*40+1/3*3.14*144*8=

2478.704+18086.4 +1205.76=21770.864mm3

Vp13 \u003d 3.14 * 144 * 20 \u003d 9043.2 m3

Vd = 235917.281 mm3 = 235.917281 cm3

Workpiece volume:

Vz \u003d 3.14 * (26.5) 2 * 213 \u003d 469678.84 mm3 \u003d 469.67884 cm3

Part and workpiece weight:

M = *V; where is the density of steel for steel 40X \u003d 7.85 g / cm3

Md \u003d 7.85 * 235.917281 \u003d 1851.951 kg

Mz \u003d 7.85 * 469.67884 \u003d 3686.kg

Material utilization rate:

c.m. = Md/Mz

c.m. =1851.951 /3686=0.5024

Conclusion: The choice of workpiece is carried out at a qualitative level. blank for

1000 products - rolled steel 40X with a diameter of 53, a length of 207 mm. Equipment - milling and cutting semiautomatic device brand 8A641.

The main types of blanks: castings, stampings, forgings, rolled products, blanks from metal powders, plastics and stamp-welded. Qualitative characteristics of blanks depending on the method of their production. Technical and economic conditions for the selection of blanks. Influence of the design and material of the part on the choice of the method for obtaining blanks. Tasks of rational and economical use of metals by improving the design of automotive equipment and increasing the accuracy of workpieces. Tasks of environmental protection, working conditions. Zero Waste Technology

The following main blanks are used in the transport industry:

a) castings from iron, steel and non-ferrous metals; b) forgings and stampings from steel and some non-ferrous metals; c) rolled steel and non-ferrous metals; d) stamp-welded from rolled steel and other metals; e) stampings and castings from plastics; f) cermet (powder metallurgy).

The cost of a part consists of the cost of the workpiece and the cost of its processing, so it is necessary to consider the manufacturing process of the part as a whole, including the process of obtaining the workpiece and its processing. Of the many possible ways to obtain a workpiece, it is necessary to choose the optimal one for the given production conditions, which ensures the minimum cost of manufacturing the part. For example, in the mass production of parts, it is economically justified to obtain blanks that are closest in shape and size to the finished part.

For an objective technological characteristic of the workpiece (except for assessing the correctness of the geometric shape and dimensions, as well as the physical properties of the metal), the metal removal factor is applied

Where - workpiece weight; - part weight.

Production of blanks by casting

Blanks can be cast into one-off, semi-permanent and permanent molds.

Casting in disposable molds. This method is used in the manufacture of blanks from ferrous and non-ferrous metals with any size and weight. Casting is carried out in disposable wet or dry sand molds, in shell (shell) molds and on investment models (precision).

sand molds are carried out in flasks or without flasks (soil molding). Forms without flasks are made by hand, and in flasks - by hand and machine.

Dry (rod) molds used to obtain critical castings of complex configuration (engine cylinder, hydraulic turbine impellers, etc.). The form is assembled from rods according to templates and conductors; it provides a high accuracy of the workpiece. Billets obtained by casting in shell forms , made from sand-resin mixtures, have higher dimensional and shape accuracy and surface finish compared to castings obtained by casting in conventional sand molds. In shell molds, castings are made from gray, malleable and ultra-strong cast iron, steel and non-ferrous alloys. This method usually produces complex and critical workpieces weighing up to 100 kg. . Shell molds have strong thin walls with a thickness of 5-8 mm , consisting of a mixture of 92-95% quartz sand and 8-5% thermosetting resin (phenol-formaldehyde resins such as bakelite, etc.). Fast-hardening mixtures with liquid glass, concrete, etc. are also used.

The method of casting into shell molds reduces the consumption of foundry earth by 10 times, increases labor productivity by 10-15 times, and significantly improves working conditions in the foundry. This method is especially beneficial for large-scale and mass production of parts. It allows you to get steel castings with a wall thickness of 3 mm , and castings from aluminum alloys with a wall thickness of 1 mm . The accuracy of the castings corresponds to the 4th-5th accuracy classes, and the surface cleanliness to the 3rd-4th classes.

Investment casting allows you to get workpieces of complex shape, so close to the finished part that in some cases, mechanical processing is partially or completely excluded. Castings of light weight (up to 3 kg ), although in some cases they can be performed and much larger weight. The minimum wall thickness of cast iron castings is 0.15 mm, and from aluminum alloys - 0.8 mm . It is possible to cast blanks of gear wheels with teeth, splined rollers with splines, etc. To obtain a higher metal density in the casting, a centrifugal or centrifugal-vacuum casting method is used. To increase the productivity of the casting process, it is advisable to cast a group of blanks according to investment patterns in one mold. In this case, castings are obtained with an accuracy of 4-5 classes and a surface finish of 3-4 classes.

Casting in semi-permanent molds. With this method, molds are made from gypsum, cement, brick and stone. Gypsum molds are used for the manufacture of cast iron and non-ferrous alloy castings weighing up to 1 ton . Castings in plaster molds can have a wall thickness of 1-1.5 mm , and castings from aluminum alloys using vacuum - wall thickness 0.2 mm . This method is used to manufacture gear castings with tooth shaping, splined shafts, turbine blades, etc. Cement molds and brick molds are not used in the automotive industry.

Stone molds provide cast iron and bronze castings with a surface finish of the 6th class and do not require surface layer bleaching. Forms of talc-actinolith-chlorite slate are used instead of metal molds in mass production.

Casting into permanent moulds. Casting in metal molds is widely used - chill mold. This type of casting makes it possible to obtain castings with an accuracy of 4-7 classes and with a surface finish of 3-4 classes. It is possible to cast blanks from steel, cast iron and non-ferrous alloys weighing from several grams to several tons into metal molds.

To increase the resistance of metal molds, they are cooled with water. This method is economically feasible to apply in serial and mass production. It allows you to increase labor productivity in comparison with sand casting by 2 times or more, reduce production areas by more than 4 times and reduce the cost of molding materials by 2 times.

Injection molding It is produced mainly in permanent molds and is used for the manufacture of complex thin-walled castings with deep planes and complex wall intersections. Castings have a fine-grained structure, which increases the strength of the metal by 1.5 times compared to the strength of castings obtained in sand molds.

The cost of injection molds is high, so this method is used in large-scale and mass production.

For casting bushings, rings, pipes and other rotating parts, centrifugal casting is used on centrifugal machines.

A feature of this process is the formation of an internal cavity without the use of rods and the possibility of obtaining multilayer castings. Pouring metal into a metal mold provides a better casting than pouring into a lined mold, but the service life of the latter is longer due to less heating. The accuracy of steel and iron castings obtained by centrifugal casting corresponds to 6-8 classes and the surface cleanliness - to the 3rd class.

Obtaining workpieces by pressure treatment

Metal forming processes are characterized by high productivity, relatively low labor intensity, provide economical metal consumption and, as a rule, improve the mechanical properties of the metal.

Blanks can be obtained by forging, hot forging, cold forging and cold sheet forging.

Free forging. It is produced on forging hammers. Pneumatic or steam-air hammers are used to obtain shaped blanks for car and tractor parts made from long products. It is expedient to use free forging only for single production. Hammer forging is also carried out in backing dies. The use of backing dies allows increasing the productivity of forging by 5-6 times. This type of forging is used in small-scale production. Before stamping in backing dies, the workpiece is free forged into a shape close to the shape of the given forging. The tolerance for the size of forgings obtained in backing dies is approximately 2-3 times less than the tolerance for free forging. In small-scale production, forging is used on a radial forging machine with program control. This machine performs periodic compression and pulling of a bar or pipe billet along the ledges with the help of successive and quick blows by two or more strikers, working according to a given program embedded in the machine's software device. On a radial forging machine, hot and cold forging can be performed. Dimensional accuracy during cold forging ranges from ±0.02 to ±0.2 mm and surface finish corresponds to 7-9 grades, with hot forging, the accuracy ranges from ± 0.05 to 0.3 mm and surface cleanliness corresponds to 1-3 classes.

Hot forging. Hot die forging can be performed on hammers, horizontal forging machines (HCM), stamping presses and forging rolls. Hammer stamping is used in series and mass production. The workpiece of the required configuration is mostly obtained by sequential processing in several streams made in one stamp.

By stamping on the GCF, blanks weighing 0.1-100 kg are made . It is possible to ensure high quality of forgings at GCF due to the arrangement of material fibers in the most favorable direction. Blanks that are simple in shape can be obtained without flash when manufactured at the GCF, while blanks that are complex in shape can be obtained with a small flash, not exceeding 1% of the weight of the blank. It is possible to obtain stamped billets with a through hole and with deep blind holes on the GCM. Stamped blanks can be obtained from bars and pipes of increased accuracy.

Stamping on hydraulic, friction and crank presses in the automotive industry is widely used. Stamping on hydraulic presses is used to obtain blanks from light and low-plastic alloys that require low deformation rates. The low productivity of hydraulic presses due to their low speed increases the cost of stamped blanks compared to the cost of stamped blanks obtained on other types of presses.

Stamping on friction presses is used in small-scale and mass production to obtain steel blanks mainly in single-strand dies and for cutting in two or more strands, as well as for precision stamping of complex blanks from non-ferrous alloys.

The most widespread in the transport industry is stamping on crank presses. Almost all types of hot stamping of workpieces weighing up to 100 kg are produced on these presses. . The constancy of deformation modes ensures the stability of the dimensions and mechanical properties of forged blanks. The productivity of friction and crank presses is 2-3 times higher than the productivity of hammers. On the presses, it is possible to stamp blanks by extrusion (extruding), which ensures the exact shape, dimensions and increases the mechanical properties of the metal.

Billets can also be obtained by rolling. Rolling is the process of forming metals by pressure, in which the deformation of the workpiece occurs in rotating die sectors located in rows.

Cold forging. One of the most economical technological processes for obtaining blanks of fasteners and other types of small parts (screws, bolts, rollers, balls, valve lifters, etc.) in large quantities is cold forging (disembarkation) on special automatic cold heading presses. Productivity of the automatic machine - to 400 pieces/min. . The initial semi-finished product for the manufacture of bolts is a coil of wire with a diameter from tenths of a millimeter to 10-15 mm or calibrated bar with a diameter of more than 8 mm .

Cold stamping The starting material is thin sheets of metal and tape.

Cold forming operations can be divided into two groups.

• 1. Separating operations, by means of which one part of the material is completely or partially separated from another: cutting, cutting, punching, notching, trimming, trimming, cleaning and sizing.
• 2. Form-changing operations, by means of which a flat or three-dimensional workpiece is transformed into a three-dimensional part of a given shape and size: bending, flanging, drawing.

Cold profile drawing. Cold drawing produces workpieces with a small cross section, usually with sides or diameters not exceeding 25-30 mm. This method produces fine-grained gears, ratchet wheels, screws and parts of any complex profile.

The deviations of the dimensions of the cross section of the workpiece correspond to the 4th class of accuracy, the surface cleanliness of the 6th class. With repeated drawing, the accuracy of the shape and dimensions in the cross section is achieved up to the 2nd class and the surface cleanliness is at the 8th class. The application of this method ensures the production of a workpiece, the machining of which is carried out only along its ends.

Control questions:

• 1. What are the casting methods?
• 2. What types of blanks obtained by pressure treatment are there?
• 3. What is the metal removal factor for?

Blanks obtained by casting methods. Casting produces blanks of almost any size from simple to very complex configurations from all metals and alloys. The quality of the casting depends on the conditions of crystallization of the metal in the mold, determined by the method of casting.

Casting method in sand-clay molds used for all casting alloys, types of production, workpieces of any mass, configuration and dimensions. In the total production of castings by casting in sand-clay molds, 80% of all castings are obtained, and only 20% of castings are produced by special casting methods. It is distinguished by technological versatility and low cost. By changing the molding methods, the materials of the models and the composition of the molding sands, blanks are made with a given accuracy and quality of the surface layer. The method is characterized by large allowances for machining, 15 ... 25% of the metal from the mass of the workpiece goes into chips.

Casting in shell molds receive workpieces of complex configuration: crankshafts and camshafts, ribbed cylinders, impellers. Part of the workpiece surfaces does not require machining. By the time of solidification of the metal of the mold, it is easily destroyed, without preventing the shrinkage of the metal, the residual stresses in the casting are insignificant. The consumption of molding materials is 10…20 times less than when casting into sand-clay molds.

Shell molds are made according to hot model equipment 1 (Fig. 2, A), heated to 200…250 °C, from a special molding sand 3, consisting of fine-grained quartz sand, thermosetting binders, moisturizers (kerosene, glycerin), solvents (acetone, ethyl alcohol) and other substances in the tipping hopper 2. The pattern slab is rotated 180° and molding sand is poured onto it.

Rice. 2. Schemes of the molding operation when casting into shell

foundry molds

The molding sand on a heated pattern plate is kept until a shell with a thickness of 5…15 mm is formed (Fig. 2, b). After returning the plate to its original position (Fig. 2, V) the mixture is calcined in a furnace at a temperature of 300 ... 350 ° C. The hard shell 4 obtained in this way is removed from the model by a special ejector 5 (Fig. 2, G). Molten metal can be poured into such molds both vertically and horizontally. When pouring in a vertical position, the molds are placed in a flask 6 and covered with cast-iron shot 7 to prevent premature destruction (Fig. 2, b). Castings are knocked out of the mold on vibrating gratings or on special knock-out machines. When casting into shell molds, the volume of mechanical processing is reduced by 30...50%, the metal consumption of blanks is reduced by 10...15% compared to casting into sand molds. At the same time, the accuracy of the workpiece is ensured, corresponding to 13 ... 14 qualifications, the surface roughness parameter Ra= 25…10 µm.

At the same time, working with hot metal models presents a certain complexity and is expensive.

Investment casting– a method for manufacturing complex and precise thin-walled (up to 0.5 mm thick) workpieces from hard-to-deform and hard-to-machine alloys with a high melting point. It is distinguished by the longest and most labor-intensive TC among all casting methods.

Investment models 1 are formed in detachable molds 2 (Fig. 3, A) of two or more parts with a vertical or horizontal split. The molding sand, consisting of wax, stearin, RZ model composition containing paraffin, synthetic ceresin, lignite wax and VAT residue, as well as other materials with a melting point of 50 ... 70 ° C, is fed under pressure into the mold. After the model composition has hardened and the model has been removed from the mold, the models are assembled into blocks 3 (Fig. 3, b). The block of models is covered with a heat-resistant layer 4 by repeated dipping into a special creamy mixture consisting of marshallite and a binder composition (ethyl silicate or liquid glass) (Fig. 3, V), followed by sprinkling in three to ten layers of fine quartz sand 5 (Fig. 3, G) and curing in air or in ammonia vapor 6 (Fig. 3, d). Then, the model composition is smelted from the resulting multilayer shell mold and the latter is molded into the mold by backfilling with quartz sand 5 (Fig. 3, e) followed by calcination in furnace 7 at a temperature of 850...950 °C (Fig. 3, and). The calcined mold 8 is poured with liquid metal (Fig. 3, h). After cooling, the casting molds are knocked out, cleaned and the elements of the gating system are separated from them.

The dimensional accuracy of the casting corresponds to 11 ... 12 qualifications, the values ​​of their surface roughness Ra= 25…10 µm.

The cost-effectiveness of the method is achieved by a properly selected nomenclature of castings, especially when the requirements for surface roughness and dimensional accuracy can be met in the cast state and machining of only mating surfaces is required. The use of blanks obtained by investment casting instead of stamped ones reduces metal consumption to 55...75%, the labor intensity of machining up to 60% and the cost of the part by 20%.

Rice. 3. Schemes of the molding operation during casting

investment models

Casting in metal molds (chill mold). A chill mold is a metal mold filled with a melt under the action of gravitational forces. The essence of the process lies in the repeated use of a metal mold. The resistance of the molds depends on technological factors: the temperature of the metal pouring, the material of the mold, dimensions, weight and configuration of the casting. A feature of the formation of castings in a mold is the high intensity of heat exchange between the casting and the mold. Rapid cooling of the melt reduces fluidity, so the walls are much thicker when casting into a mold. For aluminum and magnesium alloys, it is 3 ... 4 mm, for cast iron and steel 8 ... 10 mm. The method completely eliminates sticking, increases the yield of workpieces up to 75 ... 95%.

The sequence of manufacturing a casting in a mold, consisting of a small number of basic operations, is shown in Fig. 4.

Preparing the mold for work includes cleaning the surfaces of half-moulds 1 and 3 (Fig. 4, A), plates 4 and connectors from traces of dirt and oil; checking possible displacements, centering and fastening of the moving parts of the chill mold. Then the mold is preheated to 150...200 °C by gas burners or electric heaters, which is necessary for better adhesion of the cladding and paint to the working surfaces of the mold and metal rod 5. These refractory coatings are applied in the form of an aqueous suspension. Coatings are applied with a spray gun 2 or with a brush, while the mold is open. The cladding can consist of several layers; the cladding is coated on top with paint for less surface roughness. Paints have the same composition as facings, but more liquid.

Rice. 4. Scheme for the manufacture of castings in a metal mold (chill mold):

a - cleaning of half-forms; b - installation of rods; c - pouring the melt;

d - partial removal of the metal rod; e - casting extraction

Linings and paint protect the mold from sudden heating and setting with the casting, and also regulate the cooling rate of the casting, which predetermines the properties of the casting metal. After applying the refractory coating, the mold is heated to a working temperature, the value of which (usually 150–350 °C) is determined by the wall thickness and dimensions, as well as by the specified properties of the casting metal.

When assembling molds (Fig. 4, b) is installed, if necessary, a sand core 6. After that, the halves of the mold are connected and fastened with special clamps or using the locking mechanism of the chill machine.

With the help of pouring ladles or automatic pouring devices, the mold is poured with melt 7 (Fig. 4, V).

After reaching sufficient strength of the casting during its solidification, the metal rod is partially removed from the casting (Fig. 4, G) to avoid being over-compressed by the shrinking casting.

From an open mold (Fig. 4, d) the hardened and cooled casting is removed; before that, the metal rod is finally removed.

A sand core is knocked out of the casting, sprues, profits and upstreams are cut off; if necessary, conduct heat treatment of castings. Castings are inspected.

The technological process of mold casting makes it possible to create highly efficient automatic casting complexes.

This type of casting is used in large-scale and mass production. Castings are made from cast iron, steel and non-ferrous alloys with a wall thickness of 3 ... 100 mm and a mass of tens of grams to hundreds of kilograms. In accordance with GOSTs, the accuracy of castings reaches 12 ... 15 qualifications, and the surface roughness Ra= 25…2.5 µm. Castings are characterized by stability in terms of mechanical properties and density.

However, the method is characterized by the presence of defects in castings: deformations, cracks, gas porosity.

Injection molding is the most productive way to obtain cast billets.

Molten metal is poured into a metal mold (usually steel) under pressure (about 100 MPa) using a special compressor or piston type machine with a cold or hot pressing chamber.

Schemes of the process of manufacturing blanks on a machine with a cold chamber are shown in fig. 5. A portion of the molten metal is fed into the pressing chamber 1 (Fig. 5, A), where, under the action of piston 2, it fills the cavity of the metal mold through the sprue channels (Fig. 5, b). After cooling and solidification of the metal, rod 3 is removed (Fig. 5, V) and the mold is opened, at the same time the casting is removed from it by ejector 4 (Fig. 5, G).

Injection molding produces castings, mainly from non-ferrous alloys, in shape, weight and dimensions that are most suitable for finished parts (for example, mixing chamber bodies, carburetors and other body and box-type parts). This method can be used to produce complex thin-walled castings with wall thicknesses up to 0.5 mm and holes up to 1 mm in diameter with bosses, protrusions, threads, etc. When casting under pressure, the accuracy of the dimensions of the workpiece corresponds to 8 ... 12 degrees of accuracy and the values ​​of the surface roughness parameters Ra= 5.0…0.63 µm.

The main advantages of the method are the production of castings with a wall thickness of less than 1 mm and the possibility of automating the process.

Rice. 5. Diagrams of injection molding machine with cold

pressing chamber

Centrifugal casting. A characteristic feature of the method is the weighting of particles under the action of centrifugal forces during pouring and solidification. This improves the nutrition of castings, however, chemical heterogeneity (segregation) in such blanks is more pronounced than in others. This method produces workpieces such as bodies of revolution: bushings, cylinder liners, disks, pipes made of cast iron, steels, hard alloys and non-ferrous metals.

The sequence of manufacturing castings on centrifugal machines with horizontal and vertical axes of mold rotation is shown in fig. 6. After preparation, the mold 1 is closed with a lid 2 and poured with melt through the chute 4 from the ladle 3. Position I corresponds to the stage of pouring the rotating molds with the melt, II - the formation and solidification of castings, III - the extraction of finished castings from the molds using grippers or pushers. Machines with a horizontal axis of rotation are used for the production of castings - pipes with a diameter of 50 to 1500 mm and a length of 4 ... 5 m; various bushings, rings, etc. can also be cast. Shaped castings (bushings, rings, etc.) with diameters exceeding height are produced on machines with a vertical axis of rotation.

Rice. 6. Schemes of the process of obtaining castings by centrifugal casting:

a - on machines with a horizontal axis of rotation; b - with vertical

axis of rotation

Centrifugal casting is a productive method that lends itself well to mechanization and automation. This type of casting ensures the manufacture of castings weighing from a few grams to several tons.

The advantages of centrifugal casting are good filling of the mold with melt, increased density of castings due to the reduction of pores, cavities and other defects, high mechanical properties of castings, the possibility of obtaining castings from two or more metals arranged in layers.

This method has the following disadvantages: contamination of the inner surface of the castings with non-metallic inclusions, obtaining an uneven inner surface of the castings, the introduction of relatively large machining allowances for the internal dimensions. Casting accuracy reaches 12…14 grades, surface roughness Ra= 12.5…1.25 µm.

Preforms obtained by pressure treatment.

Forging is a universal method for the production of forgings on a hammer or press. Forging produces blanks for a wide variety of parts weighing from 10 g to 350 tons with an allowance of 5 to 34 mm (forging on hammers) and from 10 to 80 mm (forging on presses).

Forging allows you to obtain large-sized workpieces by successive deformation of its individual sections. During the forging process, the physical and mechanical properties of the material are improved, especially the impact strength.

Hot forging- the main method for obtaining blanks for critical parts weighing from 0.5 to 20 ... 30 kg. Depending on the type of die used, there are stamping in open or closed dies, as well as in extrusion dies. Depending on the equipment used, stamping is divided into stamping on hammers, presses, GCM, hydraulic presses, as well as on special machines.

Progressive technological processes of hot forging are forging on radial forging machines, as well as liquid and volumetric isothermal forging (Fig. 7).

Simultaneous compression of the workpiece by four strikers on radial forging machines (RKM) (Fig. 7, A) creates a scheme of all-round uneven compression in the deformation zone. Strikers 1, located radially and symmetrically with respect to workpiece 2, make short-term impacts-compressions (160...1800 beats per minute). The process is highly productive: one RCM with a force of 10 MN replaces, for example, six 2.5-ton hammers and one hydraulic press with a force of 6.3 MN. Radial reduction ensures the production of forgings with diameters of 18…600 mm and significant metal savings, increases equipment productivity and improves wear resistance of machine parts.

Liquid stamping is carried out in stamps (Fig. 7, b), equipped with cavities for pouring liquid metal and storing its excess. The stamp consists of an upper plate 1, in which a block of punches 2 is mounted, consisting of a piercing 3 and a pre-pressing 4 punches. Matrix 7, fixed on the bottom plate 9 of the die of the holder of the matrix 8, is cooled by water supplied through the hose 5 to the channels 6. The forging 11 weighing from 3 to 30 kg is removed from the matrix by the ejector 10.

Volumetric isothermal forging is performed in closed or open dies, in the working area of ​​which the temperature of 800…1100 °C is maintained. In the stamp (Fig. 7, V) the workpiece 1 is squeezed out in the matrix 12 by the punch 7. The finished forging is removed from the die by the ejector 14; for this, the fixing plate 4, the punch holder 5 and the punch, fixed by the ring 2 and the sleeve 3 on the support 6, rise up. The heaters are copper rods 9, they are connected by straps 13, they are isolated from the die body 11 (positions 15, 16 and 17). The current is supplied by devices 8, the temperature is fixed by a thermocouple 10.

Rice. 7. Progressive methods of hot forging:

a - on radial forging machines; b - liquid stamping;

c - isothermal stamping

Hot die forging is widely used to obtain blanks for parts of automobiles, tractors, agricultural machines, etc., as it creates favorable conditions for expanding the range of parts supplied for assembly after minimal machining.

Cold forging workpieces with high physical and mechanical properties are obtained due to the cold flow of metal in the die. In this way, blanks are obtained for parts operating under severe conditions of abrasive wear, under shock and alternating loads, thermal and other harmful factors, for example, ball pins of steering rods, piston pins, valve seats, etc.

rolling blanks are obtained that are used directly for the manufacture of parts on the MRS.

Commercial blanks, sectional and shaped profiles for general, industry and special purposes, pipe and sheet products, bent and periodic profiles represent a wide choice of initial blanks, saving metals and energy at the stage of blanking processes.

Blanks obtained by powder metallurgy. Blanks are made of various compositions with special properties. The application of the method for the production of blanks for structural purposes is justified only by a significant effect. The technology for obtaining workpieces by powder metallurgy includes the following main stages: preparation of powders of raw materials, pressing a workpiece from a prepared charge in special molds; heat treatment, providing the final physical and mechanical properties of the material.

The advantage of powder metallurgy is the possibility of manufacturing blanks from refractory materials, pseudo-alloys (copper-tungsten-iron-graphite), porous materials for plain bearings.

The powder metallurgy method makes it possible to produce workpieces that require only finishing machining. Thus, a gear wheel obtained by powder metallurgy provides gearing according to the 7th degree of accuracy and a fitting inner diameter according to the 7th grade. This allows it to be used without further machining. Typical powder parts are gears, cams, sprockets, ratchets, bushings, etc.

The cost-effectiveness of the powder metallurgy method is manifested at sufficiently large production volumes due to the high cost of technological equipment and raw materials.

Questions for self-examination:

ALLOWANCES FOR MECHANICAL PROCESSING

1. Basic provisions for calculating allowances.

2. Methods for determining allowances.

3. Calculation of the dimensions of the workpiece.

A blank is a product from which a part is made by changing the shape, dimensions, surface properties and (or) material. To obtain a part from a workpiece, it is subjected to mechanical processing, as a result of which, by removing a layer of material from individual (or all) of its surfaces, the geometric shape, size and surface properties of the part specified by the designer in the drawing are obtained. The layer of material that is removed is called the allowance. It is necessary to reliably ensure the geometric characteristics and cleanliness of the working surfaces of the part. Allowance amount depends on the depth of surface defects and is determined by the type and method of obtaining the workpiece, its weight and dimensions.

In addition to allowances during machining, allowances are removed, which make up part of the volume of the workpiece, sometimes added to simplify the technological process of its production.

Blanks of a simple configuration (with overlaps) are cheaper, since they do not require complex and expensive technological equipment in the manufacture. However, such blanks require subsequent labor-intensive processing and increased material consumption. Obviously, for each specific method of manufacturing a workpiece, there is an optimal accuracy and an optimal output.

Procurement production is an integral part of any autotractor plant, forming the first technological redistribution.

It is customary to distinguish blanks according to the form that reflects the characteristic features of the basic technological method of their manufacture.

There are the following types of blanks:

obtained by casting (castings);

obtained by pressure treatment (forged and stamped blanks);

blanks from rolled products (obtained by cutting);

welded and combined blanks;

obtained by powder metallurgy methods.

The blank can be piece (measured) or continuous, for example, a hot-rolled bar, from which individual piece blanks can be obtained by cutting.

The development of mechanical engineering has led to the appearance of blanks obtained from structural ceramics.

A workpiece of each type can be made by one or more methods related to the basic one. So, for example, a casting can be obtained by casting into sand or shell molds, into a chill mold, etc.

Casting produces blanks of virtually any size, simple and very complex configuration, from almost all metals and alloys, as well as from other materials (plastics, ceramics, etc.). The quality of the casting depends on the conditions of crystallization of the metal in the mold, determined by the method of casting. In some cases, the formation of defects (shrinkage looseness, porosity, hot or cold cracks) is possible inside the walls of the castings, which are often detected only after rough machining.

Forged and stamped blanks, as well as machine-building profiles, are obtained by pressure treatment of metals. Forging is used in single and small-scale production, as well as in the manufacture of large, unique blanks and blanks with particularly high requirements for the bulk properties of the material. Stamping allows you to get blanks close in configuration to the finished part. The mechanical properties of workpieces obtained by pressure treatment are higher than cast ones. Machine-building profiles are produced by rolling, pressing, drawing.

Rolled blanks are used in single and mass production. The rolled stock of the selected profile is cut into piece blanks, from which parts are made by subsequent machining. The perfection of the workpiece is determined by the proximity of the selected rolled profile to the cross section of the part (including machining allowances).

Welded and combined blanks are made from separate components, interconnected using various welding methods. In a combined workpiece, in addition, each component is an independent workpiece of the corresponding type (casting, stamping, etc.), made by the selected method according to an independent technological process. Welded and combined blanks greatly simplify the creation of structures of complex configuration. Incorrect workpiece design or incorrect welding technology can lead to defects (warping, porosity, internal stresses) that are difficult to correct by machining.

Blanks obtained by powder metallurgy can correspond in shape and size to finished parts and require minor, often only finishing processing.

Structural ceramic blanks are used for heat-stressed and (or) parts operating in aggressive environments.

The workpiece before the first technological operation of the manufacturing process of the part is called the original.

The blanks received for processing must comply with the approved specifications. Therefore, they are subjected to technical control according to the relevant instructions that establish the control method, frequency, the number of checked blanks as a percentage of output, etc. Usually check the chemical composition, mechanical properties of the material, structure, the presence of internal defects, dimensions, weight of the workpiece.

For workpieces of complex configuration with holes and internal cavities (such as body parts), the dimensions and location of surfaces are checked in the blank shop. To do this, the workpiece is installed on the machine, using its technological base, simulating the installation scheme adopted for the first processing operation. Deviations in the dimensions and shape of the surfaces must comply with the requirements of the workpiece drawing. The blanks must be made of the material indicated on the drawing, have the corresponding mechanical properties, must not have internal defects (for castings - friability, shells, foreign inclusions; for forgings - porosity and delamination, cracks along slag inclusions, "slate" fracture, coarse-grained, slag inclusions; for welded structures - lack of penetration, porosity of the weld metal, slag inclusions).

Defects that affect the strength and appearance of the workpiece must be corrected. The technical specifications should indicate the type of defect, its quantitative characteristics and methods of correction (cutting, welding, impregnation with various chemical compositions, straightening).

The surfaces of the castings must be clean and must not have burns, junctions, shrinkage, captivity, alluvium and mechanical damage. The workpiece must be cleaned or chopped off, the points of supply of the gating system, bays, burrs and other defects must be cleaned, scale removed. The cavities of the castings must be especially carefully cleaned. The unprocessed outer surfaces of the workpieces, when checked by a ruler, should not have deviations from straightness more than specified. Workpieces, in which the deviation from the straightness of the axis (curvature) affects the quality and accuracy of the machine, are subject to mandatory natural or artificial aging according to the technological process, which ensures the removal of internal stresses, and straightening.

The blanks of the base for machining marked on the drawing should serve as initial bases for the manufacture and verification of technological equipment (models and fixtures), they must be clean and smooth, without burrs, remains of sprues, profits, uplifts, casting and stamping slopes.

In modern production, one of the main directions in the development of machining technology is the use of rough workpieces with economical structural forms that provide the possibility of using the most optimal methods for their processing, i.e., processing with the highest productivity and the least waste. . This direction requires a continuous increase in the accuracy of workpieces and the approximation of their structural shapes and dimensions to finished parts, which makes it possible to correspondingly reduce the amount of machining, limiting it in some cases to finishing, finishing operations.

The reduction in the labor intensity of the machining of workpieces, achieved by a rational choice of the method of their manufacture, ensures the growth of production on the same production areas without a significant increase in equipment and tooling. Along with this, the rational choice of methods for manufacturing blanks in relation to various production conditions determines the degree of mechanization and automation of production.

Mechanical engineering is the largest consumer of metal. So, in the past five-year plan in mechanical engineering, it was used 40% of the total output of rolled metal products and more than 77% of the total output of iron, steel and non-ferrous metals, while about 53% of the mass of the metal went to waste, including irretrievable ones.

Given the significant importance in the production technology of improving the quality indicators of the manufacture of blanks, in "The main directions of the economic and social development of the USSR for 1981 - 1985 and for the period up to 1990", approved at the XXVI Congress of the CPSU, it is indicated that it is necessary to accelerate the development of specialized capacities for the production of castings and stampings through the reconstruction of existing ones and the construction of new foundry and forging and stamping plants and workshops on a new technical basis, improving the quality and accuracy of castings and stampings through the introduction of metal-saving (non-waste and low-waste) technological processes.

The consistent use of advanced technological processes for the manufacture of blanks will provide the necessary material base for the advanced development of mechanical engineering, create the prerequisites for a radical improvement in the use of materials with a sharp reduction in their losses and waste and bring the average utilization factor of metal processing to 0.59 ... 0.6.

The choice of the type of workpiece for further machining in many cases is one of the very important issues in the development of the manufacturing process of the part. P correct workpiece selection- establishing its shape, the size of the processing allowances, the accuracy of dimensions (tolerances) and the hardness of the material, i.e., parameters depending on the method of its manufacture - usually has a very strong effect on the number of operations or transitions, labor intensity and, as a result, on the cost of the manufacturing process details. The type of workpiece in most cases largely determines the further processing process.

Thus, the development of the manufacturing process of a part can go in two fundamental directions:

• obtaining a workpiece that approximates in shape and size to the finished part, when the blank shops account for a significant proportion of the labor intensity of manufacturing the part, and a relatively smaller proportion falls on machine shops,
• obtaining a rough workpiece with large allowances, when machine shops account for the bulk of the labor intensity and cost of manufacturing the part.

Depending on the type of production, one or another of the indicated directions or some intermediate between them turns out to be rational. The first direction corresponds, as a rule, to mass and large-scale production, since the expensive modern equipment of blanking shops, which provides high-performance processes for obtaining precise blanks, is economically justified only with a large volume of product output. The second direction is typical for single or small-scale production, when the use of the specified expensive equipment in blank shops is uneconomical. However, the foregoing should not be understood in such a way that expedient decisions on the satisfactory quality of the blanks cannot be achieved within the limits of single and serial production. On the contrary, the quality of blanks that is economically expedient for any production can always be predetermined in advance with the right approach to their choice, and, consequently, to the establishment of a method for their manufacture.

The main types of blanks, depending on the purpose of the parts, are:

• castings from ferrous and non-ferrous metals;
• metal-ceramic blanks;
• forged and stamped blanks;
• blanks stamped from sheet metal;
• rolled blanks; welded blanks;

castings from ferrous and non-ferrous metals (Fig. 36) are performed in various ways. For blanks of simple shapes with a flat surface in conditions of single and small-scale production, casting into open earthen molds is used, for large blanks - casting into closed molds. Manual molding in flasks according to models or templates is used for small and medium-sized castings of parts that have the shape of bodies of revolution. At present, casting into liquid quick-hardening mixtures is gaining popularity. This method eliminates the need for drying molds in ovens. In serial and mass production, machine molding is used on wooden or metal models. Castings of complex configuration are made in molds, which are assembled from rods according to templates and conductors.

Castings of complex shapes from hard-to-cut alloys are made investment models, while ensuring dimensional accuracy in 12…11-th qualifications and surface roughness R a =6.3…1.6 µm. Investment castings are made from both ferrous and non-ferrous alloys, and in the production of castings from alloys, which must be poured into cold molds, a combination of investment casting and the gypsum molding method is used.

Precision castings with small machining allowances are obtained with shell casting. This method, widely used at present, is based on the property of a thermosetting resin-sand mixture to take the form of a heated metal model and form a dense and fast-hardening shell. This casting method expands the possibilities of automation. The castings have a dimensional accuracy of 14…12 grades and a roughness R a =0.4 µm.

Progressive methods for the manufacture of cast billets include the method casting in metal molds(chill mold), which eliminates the molding process, provides favorable cooling conditions, as well as ease of removal of castings from the mold. P It is promising to use pliable metal molds made from packages of fine steel, as well as thin-walled water-cooled molds in which the working cavity is made in the form of replaceable stamping. The use of vacuum suction in chill casting expands the scope of its use for the manufacture of thin-walled body parts from aluminum and magnesium alloys, and pouring into an open mold with subsequent squeezing when the mold halves are closed (book molding method) makes it possible to obtain large-sized thin-walled castings.

For the manufacture of castings with a fine-grained metal structure and enhanced mechanical properties, centrifugal casting method, which is most widely used in the manufacture of castings of parts having the shape of bodies of revolution (bushings, coarse, etc.), with an accuracy of the 12th grade.

For the manufacture of blanks for parts of complex configuration, the method is successfully used. injection molding. The strength of castings made by this method is 30% higher than the strength of castings made by casting into earthen molds. This method is widely used in serial and mass production in the manufacture of small parts of complex shape. Modern machines for injection molding castings weighing up to 300 g provide productivity up to 6000…8000 castings per hour. The surface roughness of the workpieces R a = 2.5 ... 0.32 microns.

Metal-ceramic blanks are made from powders, various metals or from a mixture of them with powders, for example, graphite, silica, asbestos, etc. This type of blanks is used for the production of parts that cannot be made by other methods - from refractory elements (tungsten, molybdenum, magnetic materials and etc.), from metals that do not form alloys, from materials consisting of a mixture of metal with non-metals (copper - graphite), and from porous materials.

The method for producing cermet materials is based on pressing fine metal powders in the required mixture in molds under a pressure of 100...600 MPa and subsequent sintering at a temperature slightly below the melting point of the main component. This method is called powder metallurgy, and it is used to manufacture plain bearings ( with anti-friction properties), brake discs ( with friction properties), self-lubricating bushings, in which the pores are filled by 20 ... 30% of the volume under pressure with lubricant (porous), as well as parts for the electrical and radio engineering industry (magnets). The advantage of powder metallurgy is also the possibility of manufacturing parts that do not require subsequent machining.

Forged and stamped blanks(Fig. 37) are manufactured in various ways, the technological characteristics of which are given in table. 5.

Thus, forging hammers and hydraulic forging presses are used to obtain blanks for parts in single-piece and small-scale production. The workpieces are characterized by a relatively rough approximation to the shape of the finished part and require high costs for subsequent machining.

For a closer approximation of the shape of the workpiece to the shape of the finished part in small-scale production, they use underlay stamps. The billet, previously made by free forging using a universal forging tool, is placed in a backing die, where it takes a shape that is closer to the shape of the finished part.

In serial and mass production, blanks are made on stamping hammers and presses in open and closed dies. In the first case, flash is formed, i.e., the waste of excess metal as a result of the outflow; flash compensates for the inaccuracy in the mass of the original workpiece. In the second case, there is no flash, therefore, the metal consumption per workpiece is less. Technological processes that intensify the technology of stamping are: stamping of blanks from centrifugal castings and castings in a chill mold, stamping by extrusion in conventional closed and split dies, flashless stamping, stamping from periodic rolled products, volumetric stamping from blanks obtained by continuous casting of steel.

Forging blanks cast by centrifugal and chill casting methods, is intended for the manufacture of blanks such as hollow cylinders, bypassing the processes of pouring steel into ingots and their subsequent rolling and forging. In this process, workpieces for subsequent stamping or rolling are cast on a centrifugal machine, and then hot (at t = 1250 ... 1300 ° C) are removed from the mold or centrifugal machine.

extrusion method especially effective when combined with induction heating for the manufacture of such large workpieces as shafts, rolls, rotors, etc.

Significantly greater savings in metal can be obtained by introducing advanced technological processes for stamping on crank hot forging presses, stamping (hot extrusion) in solid and split dies, low-waste stamping (flash-free and with back pressure). hot extrusion is an efficient process for obtaining stampings of various configurations, most often in the form of rods with flanges of various shapes, parts with processes, etc. waste is reduced to a burr. An even more effective version of the technological scheme of extrusion - extrusion in split dies. The presence of the second parting line makes it possible to obtain forgings with processes and undercuts close to the configuration of the part. Process essence low-waste stamping consists in obtaining precise blanks (mainly bodies of revolution) without flash in closed dies. Excess metal (inevitable with existing methods of cutting workpieces) is discharged into special die cavities. One of the varieties of the process is the stamping of gears in dies with a wedge flash groove.

An essential factor in saving rolled products is the use for forging and die forging of blanks obtained by continuous casting of steel, which do not require a high degree of forging; moreover, these blanks without preliminary rolling can be stamped.

Of the other progressive technological processes, the introduction of which ensures a more efficient use of metal, includes rolling blanks on forging rolls, including multi-stand and automated, on which the workpiece of the required variable section can be obtained in one pass; radial reduction(reduction), carried out both in a hot and in a cold state; rolling, application of periodic rolling for preliminary shaping of blanks for stamping.

One of the ways to produce blanks from castings is vibroforming method. The advantage of the method is the creation of better deformation conditions due to a decrease in external friction and strain rate. Stamping can be carried out in single and multi-strand dies; small blanks are stamped in multi-piece dies.

Horizontal forging machines are used to produce blanks from bar material by upsetting. This method is efficient and economical. Shaped, as well as hollow cylindrical blanks are stamped on hydraulic presses. Hollow blanks are made by piercing a hole with subsequent drawing through a ring or upsetting, and bolts, rivets and similar parts are made on friction screw presses in special prefabricated dies with split dies. When stamping on friction presses, high accuracy of manufactured blanks, reduced material consumption and high productivity are achieved. So, in the manufacture of rivets, the productivity of presses is up to 1000 pcs. at one o'clock.

For the manufacture of rivets and other similar parts in mass production, cold heading press machines are also used. . The capacity of these presses is 400 pcs. per minute or more. Opals obtained by cold heading from calibrated rolled products are distinguished by high accuracy (8th grade). ForreceivingpreparedToperiodicalprofileorForhoodsmetalVlongitudinalAndtransversesectionsuseforging rolls. A profile of variable section is obtained by passing the workpiece through a stream of rollers, a complex profile is obtained by passing the workpiece through several profiled streams.

Dimensional accuracy and surface roughness of stamped blanks are increased by cold calibration and planar or volumetric ironing (chasing). planar coinage used for small sections of workpieces, and volumetric - for workpieces of small size. Blanks can also be minted in a hot state, however, the accuracy of hot minting is lower than that of cold minting. Hot stamping is used mainly for large stamped preparations.

Sheet metal stamping it is possible to obtain products of simple and complex configuration: washers, bushings, cages of rolling bearings, tanks, car cabs, etc. These products are characterized by almost the same wall thickness, which differs little from the thickness of the original material (Fig. 38).

Cold stamping can be used to obtain blanks on low-carbon steel, ductile alloy steel, copper, brass ( with a copper content of more than 60%), aluminum and some of its alloys, as well as other ductile sheet materials with a thickness from tenths of a millimeter to 6 ... 8 mm. The blanks obtained from the sheet by cold stamping are distinguished by high dimensional accuracy, in many cases they do not require subsequent machining and go directly to the assembly.

Hot sheet stamping can be used to obtain workpieces from material with a thickness of more than 8 ...

Improving the technological processes of sheet stamping production in order to more efficiently use sheet metal carried out in three directions: replacement of a sheet with a wide roll, the use of a sheet without allowances and positive tolerances for dimensions, and the full replacement of stamped parts with parts made from bent profiles.

Further development of cold sheet forming processes is based on the use of targeted, combined and universal equipment using special equipment, namely: universal blocks for batch dies, electromagnetic blocks for plate dies, universal dies for geometrically similar parts and for stamping by elements, tweezers for punching out large parts and for group stamping, dies using rubber, liquid and other elastic media and simplified dies (ribbon , molded, plastic, using concrete, wood, etc.).

In the manufacture of large-sized sheet parts, non-press stamping is currently widely used, called hydraulic extractor and based on the use of static hydraulic pressure, electro-hydraulic effect and the energy of an underwater explosion of explosives. Hydraulic drawing can be used for shaping parts made of aluminum alloys up to 5 mm thick and steel up to 3 mm thick. High pressure of the order of 20 ... 25 MPa is transmitted either directly by the liquid, or through a rubber diaphragm or bag. Hydraulic drawing is characterized by a more uniform distribution of stresses in the metal than when drawing with punches, and creates more favorable conditions for shaping with less thinning during the drawing process.

To processes cold forming includes cold heading and die forging. Disembarkation is used to form local thickenings of the required shape by redistributing and moving the metal volume. Extrusion is used to manufacture hollow parts, parts with a smaller cross-sectional area from a thick workpiece due to the outflow of metal into the gap between the die and the tool. Depending on the direction of movement of the metal in relation to the tool, three extrusion tires are distinguished: direct - the metal flows in the direction of the working movement of the tool, reverse - in the opposite direction to the working movement, and combined - a combination of direct and reverse types. Direct extrusion is used for the manufacture of solid parts, and sometimes hollow parts such as sleeves and pipes. Reverse extrusion is used exclusively to obtain hollow parts. Combined - for the manufacture of parts of complex shape: with a figured bottom, with a bottom with processes, with a bottom located inside a hollow part, etc.

For shaping, calibration, surface finishing of machine parts and their hardening during cold pressure processing, non-stamping processing processes based on the plastic deformation of metals are used. These include the knurling of gears, splines and threads, the knurling and rolling of surfaces with balls and rollers. These methods make it possible to dimensional finishing, improve the microgeometry of surfaces, in some cases eliminating the finishing treatment.

The method of rolling with rollers (hydrospinning) is also used, successfully replacing not only cutting and spinning, but also drawing. This method consists in the gradual compression by rollers of a sheet, stamped or cast workpiece obtained on a forcibly rotating mandrel. High pressures on the rollers, reaching 25 MPa, created by a hydraulic drive, make it possible to very efficiently compress hollow parts of cylindrical, conical and parabolic shapes, to obtain flying parts of complex configuration with a large difference in sections with an accuracy within the 11th grade and surface roughness R a = 0, 8…0.4 µm.

All sheet metal stamping operations can be divide into separators(cutting, punching, punching, cleaning), during which one part of the workpiece is separated from the other, and shape-changing(bending, drawing, crimping, flanging, relief molding, molding), in which one part of the workpiece moves relative to the other without breaking the workpiece (within the limits of plastic deformation).

The original thick sheet is divided into dimensional blanks mainly by gas cutting.

Thin sheets are divided into blanks, usually by cutting on guillotine and circular shears.

Hot sheet stamping is carried out mainly on hydraulic sheet stamping and friction screw presses, less often on crank sheet stamping presses. Of the special equipment for processing sheets in a hot state, three- and four-roll bending rolls should be noted, designed to bend a sheet into a shell by reverse rolling the sheet between gradually approaching rolls.

Heating before stamping is usually carried out in flame chamber furnaces of periodic action or in methodical furnaces of continuous action. Induction electric heating is progressive, in which the duration of the process is reduced by 5 ... 6 times, and the thickness of the scale layer is reduced by 2 ... 3 times compared to the scale layer obtained in flame furnaces. The accuracy of stamping sharply increases, possibilities for process automation are created, and working conditions in press (forging and stamping) shops are significantly improved.

Round bars for shafts, in most cases, are more appropriate than forged or stamped blanks. However, if the mass of the rolled blank exceeds the mass of stamping by more than 15%, it is better to use stamped blanks.

The manufacture of blanks from pipes is also one of the rational ways. Despite the fact that a ton of hot-rolled products costs on average 1.5 times less than a ton of pipes, nevertheless, metal savings in the production of parts from pipes compared to production from round steel can cover the difference in cost. An exception can be made only for parts that are subjected to further repeated processing (drilling, milling, etc.), and if the material utilization factor is below 0.5.

The maximum similarity of the structural shapes and dimensions of blanks to finished parts can be achieved by using special metal profiles. Application periodical, i.e., rolled products with the maximum similarity between the workpiece and the part, provides an increase in the utilization rate of metal during stamping by an average of 10 ... On fig. 39 shows diagrams of periodic rolling of various workpieces: camshaft (α); balls made by the method of transverse rolling (b). In the above example, the mass of blanks from conventional profiles: a camshaft - 7.95 kg and balls 300 mm - 0.164 kg, and when using periodic rolling - 6.32 and 0.125 kg, respectively, which is a metal saving of 13 and 24%.

From the finished profile rolled products, billets are produced mainly in mass production. In many cases, this method does not require the use of machining or limits it to finishing operations.

Welded blanks allow to obtain products of such a configuration, which is usually obtained as a result of casting or cutting. Often used in modern engineering stamp-welded blanks(Fig. 40). Replacing parts obtained from castings and manufactured by cutting with stamp-welded ones significantly reduces the cost.

Along with stamping, they are also used welded-cast blanks, for example, in the manufacture of blanks for body parts, which are distinguished by a wide variety of structural shapes, sizes, weights and materials. The workpiece is divided into a number of simple parts, obtained by casting, and then connected by welding. This is how press traverses, turbine stators, machine beds, etc. are made. This type of workpiece drastically reduces the labor intensity of manufacturing and the metal consumption of the product.

Also used are blanks made of stamped and cast parts joined by welding.

Blanks from non-metallic materials. Non-metallic materials widely used in mechanical engineering include: plastics, wood, rubber, paper, asbestos, textiles, leather, etc. Non-metallic materials, providing the necessary strength with a small mass of parts made from them, give the parts the necessary properties: chemical resistance ( solvents), water, gas and vapor impermeability, high insulating properties, etc.

Plastics call materials that, at a certain stage of their production, acquire plasticity, i.e., the ability, under the influence of pressure, to take the appropriate form and subsequently retain it. Depending on the chemical properties of the initial resinous substances, plastics obtained on their basis are divided into two main groups:

• thermoset plastic masses based on thermosetting resins, characterized in that, under the action of elevated temperatures, they undergo a number of chemical changes and turn into infusible and practically insoluble products;
• thermoplastic masses(thermoplastics), obtained on the basis of thermoplastic resins and characterized in that when heated, they soften, while maintaining fusibility, solubility and re-formability.

The variety of physicochemical and mechanical properties and the ease of processing into products determine the widespread use of various types of plastics in mechanical engineering and other sectors of the economy. A relatively low density (1000 ... 2000 kg / m3), significant mechanical strength and high frictional properties make it possible in some cases to use plastic masses as substitutes, for example, for non-ferrous metals and their alloys - bronze, lead, tin, babbitt, etc. , and in the presence of some special properties (for example, corrosion resistance), plastics can also be used as substitutes for ferrous metals. High electrical insulating properties contribute to the use of plastics in the electrical and radio industries as substitutes for materials such as porcelain, ebonite, shellac, mica, natural rubber, and many others. Good chemical resistance to solvents and some oxidants, water resistance, gas and vapor impermeability make it possible to use plastics as technically important materials in the automotive, tractor, shipbuilding and other industries.

Parts made of plastics are obtained by pressing, injection molding and casting into molds. The most common method for obtaining parts from plastics is the method hot pressing at the required pressure and temperature. Hydraulic presses are usually used as the main equipment for pressing plastics. However, in some cases, other types of presses can be used, such as friction, screw. Pressing is carried out in metal molds mounted on presses. Molds are the main type of tooling in the production of plastic products. During pressing, the molds are in very unfavorable operating conditions. They perceive multiple power loads (the pressure of the press reaches 20 ... 30 MPa, and sometimes 60 ... 80 MPa), systematic exposure to high temperatures (up to 190 ° C) and aggressive corrosive effects of chemical transformation products released during the pressing process.

An important industrial method for the production of plastic parts is the method injection molding. It is in many ways similar to the method of injection molding of metals. Its essence is as follows: a plastic mass is placed in the loading devices of special machines, then they are fed into a heating device, where the plastic is melted and injected into the mold under the action of a pressure-transmitting piston (plunger). Injection molding machines for plastics are highly productive: up to 12…16 thousand pieces. for a shift. This method can be used to produce various parts with complex threads and profiles, thin-walled parts, etc. Mold casting used in cases where parts are made from a binder without filler. This method is also used to obtain various molded parts from thermosetting plastics, for example, cast carbolite, neoleukorite, cast resite, as well as from thermoplastic materials - organic glass, polystyrene, etc.

Details from laminated plastics widely used in mechanical engineering. For example, textolite gears differ from metal gears in their quiet operation and resistance to the influence of various aggressive environments. In a number of cases, textolite gears have almost completely replaced gears made of non-ferrous metals. They are used to transmit rotation from electric motors in high-speed metalworking machines, they are installed on the camshafts of internal combustion engines. In the chemical industry, textolite gears are used in various apparatuses and devices, where they resist various aggressive influences much better than gears made of bronze and brass. In addition to gear wheels, rollers, rings, etc. are made from textolite.

Wood various breeds, which is a relatively cheap material, is used in many branches of modern engineering. For example, in agricultural engineering and automotive and tractor construction, wood of pine, spruce, Caucasian fir, larch, oak, beech, ash, birch, maple, hornbeam, elm, and elm is used. Hardwood and larch are used to manufacture critical parts of agricultural machines that are subjected to heavy loads.

Wood materials are used in mechanical engineering as structural materials, mainly in the form of veneer, plywood, pellet pressed wood and wood-based plastics.

To increase the resistance of wood against decay, it is specially treated: dried in air and in special drying chambers, and also impregnated with copper sulphate, zinc chloride or creosote and painted.

From wood materials by methods of cold and hot bending, it is possible to obtain products of complex curvilinear shape. Method cold bending consists in the fact that a workpiece is bent and pressed into the template in the form of a set of thin wooden plates coated with glue, without heating. At hot bending the workpiece is pre-boiled or steamed, as a result of which it acquires plasticity, then it is bent on a template and in this position is clamped and placed in a drying chamber.

Along with ordinary wood (the so-called solid wood), plywood and layered wood materials are used in mechanical engineering. Plywood is a sheet material made by gluing several thin wooden sheets (veneer) together. For the manufacture of loaded parts, multilayer, or tiled, plywood with a thickness of 25 ... 30 mm is used.

Thin sheets (veneer), impregnated with special resins and subjected to hot pressing, form the so-called wood-laminated plastics widely used in textile and electrical engineering, as well as a substitute for non-ferrous metal bearings in hydraulic machines, mechanisms operating in an abrasive environment.

Mechanical processing of wood products is carried out on metal-cutting and woodworking machines.