Processing of metals by cutting

1) Metalworking machines and tools

To ensure the accuracy of dimensions and surface roughness established by the drawing, most parts of machines and mechanisms are machined on the machines by chip removal. The surfaces to be treated can be flat, cylindrical, conical, shaped or complex curvilinear. Movement of executive bodies of machine tools is divided into working and auxiliary. Workers call movements in which chips are removed; Auxiliary – movements, in which the chip is not removed from the workpiece. The work movement can be divided into main movement and feed motion. The main movement is motion, the speed of which is the greatest.
When turning the workpiece, the rotational main motion is communicated, and the tool (cutter) – the feed motion
When milling, the main movement is communicated to the tool (milling cutter), and the feed motion to the workpiece.
When drilling, both the main movement and the feed motion are usually communicated to the tool, however in special machines this may not be observed.
When planing on cross-planer machines and processing blanks on slotting machines, the main movement is communicated to the tool (cutter), and the feed movement to the workpiece or cutter.
When planing on planer planers, the main movement is communicated to the workpiece, and the feed to the tool (tool).
When pulling, the main movement (rectilinear) is communicated to the tool (broach).
With round and flat grinding, the main motion is always rotational (grinding wheel).

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2) Elements of cutting

The main elements of cutting are:

1) t – depth of cutting between the treated and treated surface, mm.

T = (D-d) / 2

2) feed s – displacement of the tool in one turn of the workpiece, mm / rev

3) width of the cut layer b – distance between the treated and machined surface measured along the cutting surface, mm.
The surface of the workpiece with which the chips is removed is called processed (1); The surface formed by the cutting edge of the tool during cutting is called the cutting surface (3). The surface formed after chip removal is called processed (2).

3) Cutter geometry

The cutter is the most common tool used in the processing of materials.
Cutters are distinguished by the type of processing and equipment (turning, boring, planing, grooving, special); On the work performed (through, undercut, cut-off, boring, threaded, shaped, as well as roughing, finishing and diamond turning); In the direction of feed (radial and tangential, as well as right and left); By the kind of tool material (from low and medium-alloy steels, high-speed, hard-alloy, diamond, mineral-ceramic); Depending on the shape of the rod section (rectangular, square, round); By the shape of the head (straight, bent, curved, drawn); By the method of production (solid, with soldered or mechanically fixed plate, with a welded head).
In the processing of soft, carbonaceous steels, copper, the chip is formed; When machining solid steels, chipping chips are formed; When processing cast irons and other brittle metals, shavings of the nelomium are formed.

4) Lathes, types of processing, tools, devices

The group of lathes includes lathe-screw-cutting, turning-turret, multi-lathe turning, carousel-turning, frontal, automatic and semiautomatic machines, drilling-cutting (with rotating workpiece) and special lathes.
The main tools for turning machines are: cutters of different types, drills, countersinks, countersinks, reamers, dies.
The main types of work on lathes: grinding (cylindrical and conical surfaces), grinding and cutting end surfaces, boring cylindrical and tapered holes, threading.
As devices on lathes are: centers, self-centering cartridges (3x – 4x cams), face plates, lunettes.

Milling machines and work performed on them

Milling machines are divided into cantilever, longitudinal, portal, carrousel-milling, drum-milling, copying and special.
Cantilever lathes are designed for processing small and tall workpieces, which is determined by the size of the tables (up to 500-2000 mm) and the largest distance (up to 500 mm) from the table to the end of the spindle (vertical) or to its axis (horizontal).

Milling, milling cutters and auxiliary tools

Milling is one of the high-performance and common methods of cutting, it is used to produce flat or profile (shaped), smooth, corrugated, surfaces of parts, grooves, various grooves.
Mills, depending on the position of the cutting edge with respect to the axis, are with a straight and screwed tooth; On the shape of the posterior surface of the tooth, the milling cutters can be flattened and unkempt (spiky).

By designation, the milling cutters are divided into the following:

A) for the treatment of planes – cylindrical and face;
B) for grooving grooves and splines – disc, groove, end, single-corner, double-angle, T-shaped;
C) to produce shaped surfaces – shaped, modular, worm;
D) for cutting metals – cutting (circular saws).

Grinding

The process of abrasive processing is called grinding. Abrasive materials (grains of high hardness with sharp edges) can be in free form (powders) or in bound (cemented) in the form of circles, bars, segments.
In the majority of cases, grinding is a finishing operation that provides high accuracy (up to 0.002 mm) and the required grade of surface roughness, and is used for processing the outer and inner cylindrical and conical, flat and curved surfaces of all metals and alloys.
Grinding is also used for grinding work, for sharpening cutting tools. The greatest number of grinding operations is performed using a rapidly rotating abrasive wheel.

Depending on the size of the grains of abrasives, they are divided into grinding grains – granularity from No. 200 to No. 16, grinding powders – from No. 12 to No. 3 (number indicates the average grain size in hundredths of a millimeter) and micropowders – from M40 to M5 (number specifies Grain size in μm). The choice of grain size depends on the required roughness: coarse abrasives are used for roughing, fine-grained for finishing and finishing.

Bundle provides a compact abrasive tools of the desired shape and size and determines their strength and hardness. Inorganic and organic ligaments are used. The most common inorganic bond – ceramic K, composed of refractory clay, liquid glass and other components. Organic bonds – volcanic B and bakelite B have great strength and elasticity and are used for the production of thin (cutting) circles, for tools used in finishing operations; Circles on the vulcanite bond are also used as the leading ones for centreless grinding.
A group of grinding Stoics includes machines for round grinding (center-circular grinding, centerless grinding, intragrinding), machines for flat grinding, lapping and polishing, grinding, abrasive grinding, as well as specialized and special.

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Methods of metal forming

The preforms are heated in order to reduce the resistance to deformation. Heating of the metal for hot processing is carried out in flame and electric furnaces.

Electric furnaces for non-oxidizing heating of metals are chamber and methodical. In chamber furnaces, the temperature is the same throughout the entire working space. In methodical furnaces, the preforms are heated gradually according to a given regime. Contact electric heaters are used to heat a large current (at low voltage) through a heated workpiece, which in this case serves as a resistance. The workpiece heats up very quickly, which ensures high productivity and a small loss of heat (efficiency of the installation is 70-80%). Induction heating is performed with an induction electric heater consisting of a closed inductor in which the preforms are heated and the capacitor bank being mounted below it. Placed inside the inductor, the metal heats up under the influence of magnetic hysteresis and eddy currents excited in it. The high efficiency (60-70%) of the induction heater is achieved by selecting the current of the corresponding frequency.

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Compared with the heating of blanks in other furnaces or induction heating, the time is sharply reduced (by 15-20 times) (at a selection of the corresponding frequencies, a steel preform 40 mm in diameter is heated to a forging temperature in 30-35 s), the scale layer decreases 4-5 times , The decarburized layer is practically absent, the metal burns down, the working conditions improve (no irradiation from heating furnaces, noiseless heating, etc.). With contact and induction heating, the danger of crack formation disappears, because under the action of the heat generated in the metal itself, more uniform heating results.

Before processing metals, metals and alloys are heated to increase ductility and reduce resistance to deformation.
During heating, scale is formed on the surface of the workpiece, and below it is a layer of decarburized Me. The thickness of the layer forming the scale depends on the duration of heating, from chemical. Composition of the alloy, and temperature. Less scale scale occurs when the preforms are heated in the electrical installation.
When heating, do not overheat the workpieces (overheating is eliminated by annealing) and burnt (the final marriage – the workpieces go for remelting).
Heating is carried out in flaming furnaces (chamber, methodical) and in electric heating devices (contact, induction).

Rolling production

Renting is the process of deformation of Me by means of its compression between rotating rolls of a rolling mill.
Rolling is the primary treatment of steel ingots. Rolling is carried out with heating of blanks. Do not heat the workpiece at the final operations. Depending on the location of the workpiece and rolls, there are 3 types of rolling

1. Longitudinal

The axes of the rolls of the workpiece rolls rotate in different directions. Due to friction, the workpiece is drawn into the gap between the rollers and moves translationally along its axis. With smooth rolls, sheets are produced; If the wolves have streams, then they get a long-distance rolling.

2. Transversal

The rolls have a cylindrical shape. The axes of the workpiece blank. Rolls rotate in one direction, the workpiece in the opposite and transverse? Is pushed into the gap between the rollers. As a result, the transverse section decreases. Blanks at a length approximately equal to the length of the roll.

3. Cross-screw

The axes of the rolls are arranged at an angle to each other and to the workpiece, so that the workpiece, apart from the rotating motion, has a yield. In this way, non-existent pipes, bodies of revolution (balls) are obtained.

The rolling mill is distinguished:

• by designation (leaf, varietal);
• by the number of wolves (2, 3-wolves, etc.)
• by the number of working stands and the layout of the location.

Drawing. Pressing. Forging, free forging operations. Equipment. Stamping, volume and sheet.

Drawing is the process of deformation of a metal by pulling it through holes in a drawing, which has a smaller cross section than the workpiece. As a result of drawing, the cross-section of the workpiece decreases and takes the form of a section of the hole in the die, the length of the workpiece is increased, the products receive precise dimensions and a clean smooth surface.
Drawing is the only way to get a wire d = 0.006 mm.

When drawing, the tool is a drawing die, the equipment is drawing mills:

1) Chain
2) Drum.

Pressing is the process of hot deformation of Me by extruding it from the closed plane of the container through the holes in the matrix.
Press differentiate the direct and the reverse. With direct pressing more effort, a cleaner surface, but more waste Me. With reverse compaction less effort, less waste Me, but on the surface you can see traces of cast Me.
When pressing, profiles of different sections, pipes, tubes are obtained.

Forging – the process of hot deformation of Me with the help of bikes or other tools on a hammer or press is called. The flow of Me during forging is limited in the direction of movement of the tool.

With the help of forging, shaped blanks are obtained for subsequent machining, which are called forgings. Forgings have high mechanical properties. Their mass can be from 50g. Up to 250 tons (oxen, staples, hooks, oxen of rolling mills).

Forging and stamping

Forging is an inefficient operation, therefore it is used in conditions of a single multi-series production. Forging forging is rolled (round or cross-section). Forging is produced on hammers or presses in the conditions of the enterprises, except for it distinguish art forging. The main operations of forging are: draft, broaching, flashing, cutting, bending, twisting. Two types of hammers are used for forging: pneumatic, steam-air. And presses: hydraulic, forging with a nominal force of up to 31.5 mN.

Stamping. The workpieces are rolled (a circle, a square). Stamping is a high-performance operation, it is used in mass production. There are stamping volumetric and sheet, cold and hot. Bulk stamping – is performed on hammers or presses. The flow of metal is limited by the die cavity. Stamps distinguish: one-hand and multi-arm. They are fastened with the help of a wedge and the “swallow’s tail”. Surplus metal flowing into the annular groove near the creek is called obloy or burr. They are cut off on the press. Heating of the workpiece is carried out to increase the ductility of the metal. Cold volumetric stamping is pre-pressing of hot stamped forgings (chasing), by small deformations. Sheet stamping is carried out on presses, screw, crank. For cutting metal, use scissors (guillotine). The main operations are: cutting, punching, drawing, flanging, crimping, dispensing. Hot sheet stamping is used for sheets with a thickness of more than 6 mm.

Welding and cutting of metal

Arc welding is possible on a constant and alternating current; The arc at a constant current is more stable, by the consumption of el. The energies are higher. To power the arc with direct current, generators and rectifiers are used.

Welding machines and generators are divided into single-post – to supply a single arc, and multi-station – to power several arcs. For welding, the standard voltage is used: 220, 380, 500 V.

DC welding generators are driven by an electric motor or an internal combustion engine. The winding of the welding generators must be protected from destruction by short-circuit currents when the arc is excited. The external volt-ampere characteristic of these generators and transformers should be falling, more precisely, the voltage should decrease with increasing current, and with a short-circuit current decrease to zero; The open circuit voltage must be sufficient to drive the arc.

Welding generators and transformers should have good dynamic properties, more accurately instantly respond to a change in the current-voltage characteristics of the welding arc. The falling characteristic in welding generators is provided by the influence of the magnetic field of the armature on the magnetic field of the poles of the generator, and in welding transformers by the sequential inclusion of the inductive resistance-the throttle.

Arc cutting

Sharp with the use of an arc, the metal is separated not by burning, but by melting. This method is used for cutting carbon and alloy steels, cast iron, aluminum, copper and their alloys, a branch of a sprue, etc. Arc cutting is made by a carbon or metal electrode.
Automatic arc cutting under the flux is used for cutting sheets of corrosion-resistant steel.

Air-arc cutting is made by carbon or graphite electrode, which is fixed in cutting or cutting head. In the contact-nozzle part of the cutter (head) there are holes through which air jets blow the molten metal out of the cut

Electric arc welding by robots

In recent years, more and more arc-welding is being introduced by robots in place of manual welding. In addition to releasing the welder from heavy labor, an increase in productivity and quality of welding is achieved, determined by the accuracy and uniformity of the movement of the arc. Automatic arc control software guarantees the absence of pores, cracks, non-welded craters, burns and other defects.

Plasma cutting, welding and surfacing

Plasma surface and plasma-mechanical treatments are becoming increasingly widespread; A plasma jet is also used to apply protective and decorative coatings, to obtain thin metal filaments, fine-dispersed powders of metals, for heat treatment.

1. Plasma cutting is the most productive type of thermal cutting, which is widely used in machinery and shipbuilding, in factories of lifting and transport equipment, in pipe production, where the volume of cutting sheet metal is particularly large. The compression and stabilization of the arc is accomplished by the flow of gas passing along with the column of the arc through the nozzle of the plasmatron, as a result of which the temperature of the acute plasma arc torch reaches 12,000-20,000 ° C, and the properties of the metal with such a powerful directional flow of thermal energy practically do not affect the cutting process. As a result of the local removal of the cut layer, the surface of the cutting is obtained accurately along the contour with a small degree of roughness.

2. Welding of plasma jet gives good results both for the combination of refractory metals, corrosion-resistant steels, and for alloys of aluminum and other non-ferrous metals. The seams obtained by plasma welding have a small zone of thermal influence.

3. In plasma surfacing, filler material can be fed in the form of wire, tape or powder, so this method can be used to weld all kinds of surfacing materials. High concentration of energy in the plasma jet, stability of the arc discharge, as well as the possibility of separate regulation of heating of the main and filler materials are an advantage of this type of surfacing.

Electroslag Welding

Electroslag welding is a method of arc-free electric butt welding in molten slag. To guide the slag, the same fluxes are used. As with electroslag remelting steel. In an overheated slag, the electrode wire melts, and the welded edges of the preform are melted, the metal is drained in a common bath and a weld is formed upon hardening. Copper creepers, cooled by water, automatically move upward as they weld and ensure the formation of a seam

Contact welding

In the case of contact welding, heat generated during the passage of current through the welding location is used to heat the welded parts. After reaching the required temperature in the welding zone, the welded parts are squeezed. There are three types of contact welding: butt, dot, roller.

• When the butt welded parts are clamped in the contact pads of the welding machine and a large current flows through them. In addition, a large amount of heat is generated in the welding zone and parts of the joint are heated to a plastic state. The heated parts are squeezed. Butt welding is possible with a cross section of up to 50000 mm or more. It is also used for joining stamping sheets. The strength of the butt weld is not inferior to the strength of the base metal, so this welding can be taken for responsible connections.

• When spot welding, the parts are clamped between the electrodes, through which a large current flows from the secondary winding of the transformer. Due to the large resistance, the contact point of the welded parts is heated to the thermoplastic state and welding takes place under the action of the electrode pressure. Water inside the hollow electrodes circulates to cool them.

• In the case of roller welding (seam), sheets of 0.1-3 mm thick are made of low-carbon steel and sheets up to 1.5 mm thick are made of corrosion-resistant chromium-nickel steel, brass, bronze, and aluminum alloys. The welded parts are passed between the rotating rollers – the electrodes of the suture machine, through which the current flows, which generates heat at the place of contact of the welded parts, as a result of which a continuous seam is formed.

Gas welding and cutting

Gas welding is performed by butt and onboard connections. Angle, T-shaped, overlapping is avoided by gas welding due to the occurrence of deformations and thermal stresses in products.

Gas press welding is used for butt joints of pipes. The joints are heated by an annular multi-flame burner and the parts to be welded are squeezed. This method is also used for welding rails, drilling equipment and tools.

Gas cutting in an oxygen jet is used for steel with a mass content of carbon up to 0.7% and some grades of low-alloy steel. Cast iron, aluminum, copper and its alloys, as well as highly alloyed steels, are not cut directly by the jet of oxygen, powder fluxes consisting mainly of iron powder and quartz sand are used for gas cutting of these metals. The flux burns in a stream of oxygen and raises the temperature at the cutting site to such an extent that the resulting refractory oxides are slagged with iron oxides and the liquid slag is blown with a gas jet.

Types of welding, cutting, soldering of metal

Welding refers to the technological process of obtaining permanent joints of blanks by means of establishing interatomic and intermolecular bonds between the welded parts.

Welding processes are used for the manufacture of welded structures, repair of defects in the casting of parts, for the restoration of broken, worn parts.

Welded together as homogeneous parts, and heterogeneous (steel with copper, copper with aluminum, etc.), as well as metals with non-metals (ceramics, glass). There are three classes of welding: thermal, mechanical and thermomechanical.

• Thermal welding includes fusion welding. This type includes arc, electroslag, plasma, electron-beam, laser, gas, termite welding.

• Mechanical welding includes those in which plastic deformation is the determining factor. The mechanical class includes cold, ultrasonic welding, explosion welding, and friction.

• The thermomechanical class includes those types in which thermal energy and external pressure are used to form welded joints. This class includes contact, gas-press, diffusion, etc.

For the production of welded structures, the following types of joints are used: butt joint, lapping, riveted, T-shaped, angled.
Other types of welding (electron beam, laser, plasma) are performed in fractions of a second, give a thin and clean seam, free from defects.

Fire cutting is used to separate blanks into parts, burn holes, surface processing (planing).

The parts are joined together by soldering, using a more low-melting filler metal-solder. When soldering, the base metal is solid, and the solder is melted.

Arc welding and cutting

In 1802 Academician VV Petrov discovered the phenomenon of arc discharge. In 1882, the Russian inventor NN Benardos proposed the use of e-mail. Arc for welding metals with a carbon electrode. In 1888 the mining engineer Slavyanov replaced the graphite electrode with a metallic one. At present, about 99% of the work performed by arc welding is carried out according to the method of Slavyanova.

Welding by the method of Benardos

Welding is carried out with a graphite electrode with or without a filler metal; welding with this method has limited application. It is used for joining with the flanging of thin steel billets, where no filler metal is required, for non-ferrous metals and cast iron, as well as for welding hard powder alloys. Usually direct current is used, and for the stability of the arc and better heating of the joint during welding, the direct polarity is used: the workpiece includes an anode (+) and the electrode is cathode (-).

Welding by the method of Slavyanova

When welding, use a metal electrode in the form of a wire. The arc is excited between the electrode and the base metal and melts both of them, and a common bath is formed where all the molten metal is mixed. Electrode wire is available in diameters from 0.3 to 12 mm.
Medium, thick and extra thick coatings ensure stability of arc burning, as well as protection and alloying of the metal. The composition of these coatings is selected so that around the arc a gas

The medium that protects the electrode metal flowing in the arc and the metal of the bath from oxidation and dissolution of gases in it. As the electrodes are melted, the coating is hushed, and the slag evenly covers the seam, protecting the metal from oxidation and saturation with nitrogen.
According to the thickness of the coating, electrodes are available with thin, medium, thick and extra thick coatings.
Thin coatings are stabilizing, they consist of chalk and liquid glass.

The electric parameters of the arc can vary over a wide range: currents from 1 to 3000 N at a voltage of 10 to 50 V are used. The arc power is from 0.1 to 150 kW.
This range of arc power makes it possible to use it for welding both smallest and large, heavy products.

The arc voltage, depending on the current strength, is expressed by curves that determine the current-voltage or static characteristic of the arc (1 for an arc of 3 mm, 2 for an arc of 6 mm).

The curves show that at a current exceeding 50 A (most often used in welding), the arc burning voltage is almost independent of the current strength and is determined by the arc length.

Typical disadvantages of welded joints are the local absence of fusion between the deposited and base metal, the porosity of the weld metal, the slag inclusions, cracks, and burns (oxidation of the metal in the seam and the adjacent zone).

The meaning of the properties of metals

Mechanical properties

The first requirement for any product is sufficient strength.
Metals have higher strength compared to other materials, so the loaded parts of machines, mechanisms and structures are usually made of metals.
Many products, in addition to general strength, must also have special properties that are characteristic for the work of this product. For example, cutting tools must have a high hardness. For the manufacture of cutting tools, tool steel and alloys are used.
For the manufacture of springs and springs are used special steels and alloys that have high elasticity
Viscous metals are used in those cases where the workpiece is subjected to impact loading.
Plasticity of metals makes it possible to produce their pressure treatment (forging, rolling).

Physical properties

In aircraft, auto and car building, the weight of parts is often the most important characteristic, therefore alloys of aluminum and especially magnesium are irreplaceable here. Specific strength (ratio of tensile strength to specific gravity) for some, for example aluminum, alloys is higher than for mild steel.

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Fusibility is used to produce castings by pouring molten metal into molds. Light metals (for example, lead) are used as quenching medium for steel. Some complex alloys have a low melting point, which melts in hot water. Such alloys are used for casting typographic matrices, in devices serving to protect against fires.
Metals with high electrical conductivity (copper, aluminum) are used in electric machine building, for the construction of power lines, and alloys with high electrical resistance – for incandescent lamps, electric heaters.

The magnetic properties of metals play a pivotal role in electromechanical engineering (dynamos, motors, transformers), for communication devices (telephone and telegraph apparatus) and are used in many other types of machines and devices.

Thermal conductivity of metals makes it possible to produce their physical properties. Thermal conductivity is also used in the manufacture of soldering and welding of metals.

Some metal alloys have a coefficient of linear expansion, close to zero; Such alloys are used for the manufacture of precision instruments, radiolamps. Expansion of metals should be taken into account when constructing long structures, for example bridges. It should also be borne in mind that two parts made of metals with different coefficients of expansion and fastened together can give bending and even destruction when heated.

Chemical properties. Corrosion resistance is particularly important for products operating in highly oxidizing environments (grate bars, parts of chemical machines and devices). To achieve high corrosion resistance, special stainless, acid-proof and heat-resistant steels are produced, and protective coatings are also used.

Technological properties. They are very important in the manufacture of various technological operations.