Types of heat treatment

Metal forming, or metal forming, is possible due to the fact that such materials are characterized by high ductility. As a result of plastic deformation, a finished product can be obtained from a metal blank, the shape and dimensions of which correspond to the required parameters. Metal forming, which can be performed using various technologies, is actively used to produce products used in mechanical engineering, aviation, automotive and other industries.

Physics of metal forming process

The essence of metal pressure processing is that their atoms of such a material, when exposed to an external load, the magnitude of which exceeds the value of its elastic limit, can occupy new stable positions in the crystal lattice. This phenomenon, which is accompanied by metal pressing, is called plastic deformation. During the process of plastic deformation of a metal, not only its mechanical, but also its physicochemical characteristics change.

Depending on the conditions under which OMD occurs, it can be cold or hot. Their differences are as follows:

1. Hot metal processing is performed at a temperature that is higher than its recrystallization temperature.
2. Cold working of metals is accordingly carried out at a temperature below the temperature at which they recrystallize.

Types of processing

The metal processed by pressure, depending on the technology used, is subjected to:

1. rolling;
2. forging;
3. pressing;
4. drawing;
5. processing performed by combined methods.

Rolling

Rolling is a pressure treatment of metal blanks, during which they are exposed to rolling rolls. The purpose of such an operation, which requires the use of specialized equipment, is not only to reduce the geometric parameters of the cross-section of a metal part, but also to give it the required configuration.

Today, metal rolling is carried out using three technologies, the practical implementation of which requires appropriate equipment.

This is rolling, which is one of the most popular processing methods using this technology. The essence of this method of metal forming is that the workpiece passing between two rolls rotating in opposite sides, is compressed to a thickness corresponding to the gap between these working elements.

Using this technology, metal bodies of rotation are processed by pressure: balls, cylinders, etc. Performing processing of this type does not imply that the workpiece undergoes translational motion.

This is a technology that is something intermediate between longitudinal and transverse rolling. It is mainly used to process hollow metal workpieces.

Forging

A technological operation such as forging belongs to high-temperature forming methods. Before forging, the metal part is subjected to heating, the magnitude of which depends on the grade of metal from which it is made.

Metal can be processed by forging using several methods, which include:

• forging performed using pneumatic, hydraulic and steam-air equipment;
• stamping;
• forging done by hand.

In machine and hand forging, which is often called free forging, the part, while in the processing zone, is not limited by anything and can take on any spatial position.

Machines and technology for metal forming using the stamping method assume that the workpiece is previously placed in a die matrix, which prevents its free movement. As a result, the part takes exactly the shape that the cavity of the die matrix has.

Forging, which is one of the main types of metal forming, is used mainly in single and small-scale production. When performing such an operation, the heated part is placed between shock units hammers, which are called strikers. In this case, the role of supporting tools can be played by:

• regular ax:
• crimps of various types;
• rolling out.

Pressing

When performing a technological operation such as pressing, metal is forced out of the matrix cavity through a special hole in it. In this case, the force necessary to carry out such extrusion is created by a powerful press. Parts that are made of metals that are highly brittle are mainly subjected to pressing. The pressing method produces products with a hollow or solid profile from alloys based on titanium, copper, aluminum and magnesium.

Depending on the material of the processed product, pressing can be performed in a cold or hot state. Parts that are made of ductile metals, such as pure aluminum, tin, copper, etc., are not subjected to preheating before pressing. Accordingly, more brittle metals, in particular chemical composition which contain nickel, titanium, etc., are pressed only after preheating both the workpiece itself and the tool used.

Pressing, which can be performed on equipment with a replaceable matrix, allows the production of metal parts of various shapes and sizes. These can be products with external or internal stiffeners, with a constant or different profile in different parts of the part.

Drawing

The main tool with which such a technological operation as drawing is performed is a die, also called a die. During the drawing process, a round or shaped metal blank is pulled through a hole in the die, resulting in a product with the required cross-sectional profile being formed. Most a shining example The use of such technology is the wire production process, which assumes that the workpiece large diameter is sequentially pulled through a number of dies, eventually turning into a wire of the required diameter.

Drawing is classified according to a number of parameters. So, it could be:

• dry (if done using soap shavings);
• wet (if a soap emulsion is used to perform it).

According to the degree of cleanliness of the surface being formed, drawing can be:

• rough;
• finishing

Depending on the frequency of transitions, dragging occurs:

• one-time, performed in one pass;
• multiple, performed in several passes, as a result of which the cross-sectional dimensions of the workpiece being processed are gradually reduced.

By temperature conditions this type of metal forming can be:

• cold;
• hot.

Volume stamping

The essence of this method of metal forming, such as die stamping, is that the production of a product of the required configuration is carried out using a stamp. The internal cavity, which is formed by the structural elements of the die, limits the flow of metal in an unnecessary direction.

Depending on the design, dies can be open or closed. In open dies, the use of which makes it possible not to adhere to the exact weight of the workpiece being processed, a special gap is provided between their moving parts, into which excess metal can be squeezed out. Meanwhile, the use of stamps open type forces specialists to remove flash that forms along the contour of the finished product during its formation.

Between structural elements of stamps closed type there is no such gap, and the formation of the finished product occurs in a confined space. In order to process a metal workpiece using such a stamp, its weight and volume must be accurately calculated.

Heat treatment of products promotes softening and better absorption of food by the human body.

In addition, at high temperatures, food is disinfected as a result of the death of microorganisms. The products acquire a pleasant taste and aroma.

However, improper heat treatment can lead to discoloration and the formation of substances in products that have bad taste and odor, which have a carcinogenic effect. Vitamins and aromatic substances may be destroyed, and the content of soluble nutrients may decrease. Therefore, it is necessary to strictly observe the cooking mode and cooking time.

Cooking

Cooking is the heating of food in a liquid or atmosphere of saturated water vapor. Cooking is one of the main ways culinary processing, and boiled dishes reign supreme in any national cuisine, in clinical nutrition - especially.

At cooking using the main method the product is completely immersed in a large amount of liquid (water, milk, broth, syrup, etc.). Before boiling, the process is carried out over high heat in a container with a closed lid; after boiling, the heat is reduced and cooking is continued at low simmer until the product is completely cooked. Full boiling is undesirable, as this quickly boils away the liquid, destroys the shape of the product, and evaporates aromatic substances.

In pressure cookers or autoclaves, excess pressure is created, and the temperature rises to 132 C, which speeds up cooking. When cooking using the main method, a large amount of nutrients are lost from the product due to their transition into a decoction, and the boiled product becomes tasteless. However, if the environmental purity of the product is questionable, cooking in large quantities water is a necessity, since radionuclides, xenobiotics, etc. are extracted.

Allowance

Poaching is a more rational type of cooking that allows you to preserve as much as possible. nutrients product. In this case, the product is immersed in boiling water by approximately 1/3 of its volume, and 2/3 is cooked with steam with the lid tightly closed. Juicy fruits are simmered without adding liquid, in own juice released when heated. It is advisable to use poaching, and not cooking, as the main method when preparing vegetable side dishes.

Steaming

Steaming is the main type of heat treatment when preparing main courses for therapeutic diets that require gentle gastrointestinal tract. To do this, use steam ovens or steam pans with a tightly closed lid. Water is poured into the pan, a grate is placed on the bottom, on which the food is placed.

When the water boils, the pan is filled with steam, in which the food is cooked. The products are juicy, with a delicate texture and well-preserved shape. The loss of nutrients is less than with poaching.

There is another method of steam cooking. Pour up to half boiling water into a large pan, tie a linen napkin around the top of the pan so that it sags slightly in the middle. They put it in a napkin, like in a hammock. food products(most often rice) and put the pan on the fire, and cover the food in napkins with an overturned plate. Rice or other grains turn out crumbly, not unsaturated with excess water.

Much less commonly used is the so-called contactless cooking food. With it, there is no direct contact of the environment in which the food is cooked, or even the container itself where the food is located, with fire. This is achieved by placing the vessel (pan, pot, cast iron with a tightly closed lid) with food not on the fire, but in a larger vessel into which water is poured, and this large vessel is placed on the fire (water bath).

Non-contact cooking requires much more heat and time for cooking, but the taste, consistency and aroma of omelettes, meat, fish, and vegetables becomes unusual. If the lid is on the pan with food, and the cauldron of water where it sits is tightly closed with a lid, then the cooking will not be called a water bath, but a steam bath. The food will be cooked by the steam coming from the boiler. The taste of food with these non-contact cooking methods is different.

Frying

Frying is heating a product without liquid, in fat or heated air. As a result of frying, a crust forms on the surface of the product; the products lose some of their moisture due to evaporation, so they retain a higher concentration of nutrients than when boiled.

Fat plays an important role when frying, as it protects the product from burning, ensures uniform heating, improves the taste of the dish and increases its calorie content. Before frying, the fat must be overheated, since only overheated fat does not burn, does not smoke, does not smoke and remains clean from the beginning to the end of cooking.

Pour vegetable oil into a frying pan in a half-centimeter layer and heat it over medium heat, without bringing it to a boil. After 2-3 minutes, the oil will lighten, and after another couple of minutes a white, barely noticeable, but acrid smoke will appear above it. If you throw a pinch of salt into the oil, it will bounce off the surface with a bang. This means that the oil has overheated and evaporated excess water, gases, various impurities. This oil will not change as it is further heated and will be easier to fry with.

At the time of overheating, you can add some spices (onion, garlic, anise, fennel, dill seeds), which must be removed after 3-4 minutes. Spices fight off the specific odors of fats and give the corresponding aroma. Another way to improve oil is to use a mixture of animal and vegetable fat: sunflower oil and lard, olive oil and chicken fat, beef fat and mustard oil, etc.

There are several types of frying. The most common of them is frying in the main way, in which the product is heated with a small amount of fat (5-10% by weight of the product) at a temperature of 140-150 C. The best utensils for frying on an open surface are frying pans or roasting pans with a bottom thickness of at least 5 mm. In them, the temperature is distributed more evenly, the possibility of sticking and burning of the product is reduced. IN last years use non-stick pans.

At deep frying take 4-6 times more fat than the product, heat it to 160-180C and place the product for 1-5 minutes. Frying is carried out in a deep dish (deep fryer), the products are removed with a slotted spoon or a special mesh. Products are coated smooth, beautiful, golden crust, but the temperature inside them does not reach 100 C and is often insufficient to bring them to full readiness and destroy all microorganisms. In this regard, after deep frying, the products can be placed in the oven for some time.

At roasting over an open fire the product is placed on a metal rod or placed on a greased metal grid. The rod or grate is placed over hot coals or electric coils in electric grills and grilled. To ensure uniform frying of the product, the rod is rotated slowly. Frying occurs due to radiant heat.

Roasting in a broiler (in the oven)

A shallow dish (baking tray, frying pan or pastry sheet) is greased and food is placed on it, then placed in an oven at a temperature of 150-270 C. From below, the product is heated due to heat transfer, and from above - due to infrared radiation from the heated walls of the cabinet and the movement of warm air.

The process of formation of a crispy crust occurs more slowly than when frying in the main way, as a result of which the products are heated evenly. To obtain a more golden brown crust and increase the juiciness of the finished product during the frying process, the product is turned over, poured with fat or brushed with sour cream and egg.

Frying in a field of infrared rays (IR) carried out in special devices, while frying time is reduced by 2-6 times and the juiciness of the product is better preserved.

Roasting in a microwave field (in microwave ovens) helps reduce the time of heat treatment, the product retains nutrients well, however, with this method of heat treatment, a crispy crust does not form on the surface of the product. Some technologists consider this method of heat treatment to be cooking.

Auxiliary methods of heat treatment include sautéing and blanching. With these methods, the product is not brought to a state of complete culinary readiness.

Sauteing

Sautéing is a short-term frying of a product until half cooked in a small amount of fat (15-20% by weight of the product) at a temperature of 110-120 C without the formation of a crispy crust. Moreover, part essential oils, coloring matter and vitamins pass from food into fat, giving it the color, taste and smell of food. Sauteed vegetables, roots, tomato puree and flour are used to prepare soups, sauces and other culinary products.

Blanching (scalding)- this is short-term (1-5 minutes) cooking or scalding with steam followed by rinsing the food cold water. Blanch some varieties of vegetables to remove bitterness (young White cabbage, turnip, rutabaga); preservation of color, taste and consistency of peeled vegetables and fruits (potatoes, apples) during their subsequent processing; to prevent products from sticking together in the broth (scalding homemade noodles); to facilitate mechanical cleaning sturgeon fish; for partial removal of extractives and purine bases from animal products.

Stewing, baking and frying after cooking are combined methods of heat treatment.

Extinguishing- this is the poaching of a pre-fried product with the addition of spices and aromatic substances. It should be simmered in a tightly sealed container for 45-60 minutes on the stove, then 1-1.5 hours in the oven. At the end of stewing, when the water evaporates, denser or more acidic liquids (sour cream, juice, vinegar, cream, grape wine) should be added, which prevents the dish from burning and improves its taste and consistency. Salt and spices are added at the end to artificially restore what was lost during long stewing natural taste products.

Baking- this is the frying of a pre-boiled (sometimes raw) product in oven to form a golden brown crust. Products are baked at 200-300 C, both with the addition of sauces, eggs, sour cream, and without sauces. This type of heat treatment is necessary for diets without mechanical sparing of the gastrointestinal tract, but with a sharp limitation of purine bases (for example, for gout).

Roasting after cooking used for preparing side potatoes, as well as those products that cannot be cooked by frying alone (fried brains, kidneys). In diet, this technique is used to reduce the content of nitrogenous extractives in meat and fish products.

Metal machining is a necessary process before a metal part can be used.

There are different ways to work with different types of metals - they all have their pros and cons and can be used in different situations depending on your goals.

From the article you will learn what mechanical processing of metals is, and what types of it exist, and you will be able to choose which procedure for working with metal is required for you.

There are only two options for finishing metal parts: this can be done by pressure or by cutting.

Most often it is used when it is necessary to give a metal sheet a shape, or in the process of creating parts from long rolled metal.

This method of influence includes the following types of work: bending, stamping, upsetting, etc. Below we will consider various methods of influencing metal using pressure in more detail.

Manual hot forging is often used to process non-ferrous metals.

To carry it out, the material is preheated to a temperature exceeding its recrystallization, and then it is given the required form.

To do this, use the simplest tools: a hand hammer or hammer. The degree of heating of a material depends on its properties: how much carbon it contains.

The lower this value, the higher the operating temperature should be.

Such mechanical finishing of different types of metals is considered quite effective, since it makes it possible to create solid parts of high strength without losing natural properties material.

There is also a more perfect one - mechanical method hot processing.

In this case, the material is also heated to the desired temperature, but the effect is carried out using a special device.

Mechanical forging can be free or done using a forging die.

In the first case, the impact on the metal coating occurs with the help of an anvil and a hammer, which is used to act on the metal.

Another option is when the metal is exposed to a special press, which gives it the desired shape.

Both the hammer and the press are mechanical devices, but the first gives the workpieces the desired shape by blows, and the second uses pressure.

The hammer device can be steam, steam-air, falling with a friction disk or spring.

The press can be hydraulic, steam-hydraulic, screw, friction, eccentric, crank or spring.

Hammering is used less frequently because it is very noisy and less efficient and is used only in large industries.

In addition to hot impact, there is also cold impact - it is used more often because it is capable of giving workpieces made of non-ferrous and ferrous metals the desired shape without affecting its physical characteristics.

Unlike hot exposure, with the cold method there is no need to heat the surface - all work is done at room temperature.

The cold method of influence is called stamping, it is divided into different types. Stamping can be single or multi-operational, depending on the functions of a particular device.

Work with the material can be carried out either while maintaining a continuous coating or with its division - this also depends on the type of device with which the workpiece is given the desired shape.

The most popular types of cold pressing are the following: impact by bending, stretching, crimping, molding, buckling or beading.

Bending allows you to change the axial shape of a part; it is done using a special vice that is installed on bending dies and presses.

Using extrusion, you can make parts of complex shapes. For this type of work, a pressing machine is required.

By crimping cross section The hollow part is reduced, and molding allows you to turn the workpiece into a part that has a spatial shape.

This type of processing requires drawing dies or special forming dies.

When bulging, the workpiece also takes on the appearance of a spatial shape, and when beading, sides and other additional elements are created on the part.

Processing by cutting

Mechanical processing of different types of metals by cutting also requires special equipment. This is a more complex process, which is why the types of machines used here are more complex.

For non-ferrous metals that are resistant to external influences and difficult to deform, most often a special laser is used for processing, or a plasma processing method, which became less relevant after the advent of the laser.

Today, metal machining on machines and lines is carried out using a fiber laser, which consists of a resonator, a light guide and a special pumping module.

With this method of exposure, the laser beam hits the metal surface through a special light guide that stores the energy of the beam, due to which the power of the device is sufficient for high-quality cutting of non-ferrous metals.

It is quite easy to work with a fiber laser - it is automated and has high quality characteristics: in addition to cutting, it provides cooling of the product, and is also able to withstand high power and temperature.

This tool has functions not only for cutting, but also for other types of processing: engraving and welding.

There are the following types of metal processing by cutting: turning, drilling, milling, planing and grinding.

When turning the material, its changes are minimal, since this procedure is performed in cases where the size of the workpiece practically corresponds to the final size of the part.

You can do the turning on the equipment different types: Lathe, drilling, grinding and other types of machines may be suitable for this.

Turning of a part is most often done on a lathe using a special cutter, which effectively removes the excess layer of metal and brings the workpiece to the desired size.

Using drilling, you can make the necessary holes in the workpieces, thereby changing their shape.

For this type of processing, any equipment that has a drill and a vice is suitable: you need to install a workpiece between them, the drill will move towards it progressively, and as a result we will get a hole of the size and shape we need.

Milling also changes the shape of the part. This is a rather complex type of processing that requires special equipment - a horizontal milling machine.

Processing of the workpiece is carried out using a cutter, which is on this device.

The cutter impacts the workpiece at an angle, while the part itself does not move - before starting work, it must be clearly fixed on the surface of the equipment.

The planing method of work involves influencing the workpiece with a cutter. This process requires a special planing machine because... only he is equipped with the necessary tools.

During operation, the cutter gradually enters the metal and then comes back out, performing intermittent movements.

This the hard way processing of non-ferrous metals, because it requires calculations of idle and working strokes for correct execution work.

The last method of working with metal is grinding. This is a fairly simple method that you can often do yourself if you have a sanding wheel available.

For professional processing, special grinding machines are used.

Work with workpieces made of non-ferrous metals occurs due to rotational movements with linear and circular feed.
Video:

This method of exposure is used to produce parts that have a cylindrical shape.

If a flat workpiece is processed, then the feed direction can only be straight.

Metal processing in modern industry is usually distinguished by types and methods. The most “ancient” type has the greatest number of types of processing. mechanical method: turning, drilling, boring, milling, grinding, polishing, etc. The disadvantage of mechanical processing is large waste of metal into shavings, sawdust, waste. A more economical method is stamping, used as steel sheet production develops. But over the past decades, new methods have emerged that have expanded the capabilities of metalworking - electrophysical And electrochemical.

In previous articles you got acquainted with stamping and cutting of metals. And now we will tell you about electrophysical methods (electrical erosion, ultrasonic, light, electron beam) and electrochemical.

Electrical discharge machining

Everyone knows what a destructive effect an atmospheric electrical discharge - lightning - can produce. But not everyone knows that electrical discharges reduced to small sizes are successfully used in industry. They help create the most complex parts of machines and devices from metal blanks.

Many factories now operate machines in which the tool is a soft brass wire. This wire easily penetrates the thickness of workpieces made of the hardest metals and alloys, cutting out parts of any, sometimes downright bizarre, shape. How is this achieved? Let's take a closer look at the working machine. In the place where the wire tool is closest to the workpiece, we will see luminous lightning sparks that strike the workpiece.

The temperature at the site of exposure to these electrical discharges reaches 5000-10000 ° C. None of the known metals and alloys can withstand such temperatures: they instantly melt and evaporate. Electric charges seem to “corrode” the metal. Therefore, the processing method itself received the name electroerosive(from the Latin word "erosion" - "corrosion").

Each of the resulting discharges removes a small piece of metal, and the tool is gradually immersed in the workpiece, copying its shape in it.

Discharges between the workpiece and the tool in electroerosive machines follow one after another with a frequency of 50 to hundreds of thousands per second, depending on what processing speed and surface cleanliness we want to obtain. By reducing the power of the discharges and increasing their frequency, the metal is removed in ever smaller particles; At the same time, the purity of processing increases, but its speed decreases. The action of each discharge must be short-lived so that the evaporating metal is immediately cooled and cannot reconnect with the metal of the workpiece.

Scheme of operation of an electroerosive machine for contour cutting of holes of complex profiles. The necessary work here is carried out by an electric discharge that occurs between the tool - the brass wire and the workpiece.

During electrical discharge machining, a workpiece and a tool made of a refractory or heat-conducting material are connected to a source of electric current. To ensure that the effect of current discharges is short-lived, they are periodically interrupted either by turning off the voltage or by quickly moving the tool relative to the surface of the workpiece. Necessary cooling of the melted and evaporated metal, as well as its removal from working area are achieved by immersing the workpiece in a tokone-conducting liquid - usually machine oil, kerosene. The lack of current conductivity in the liquid means that the discharge acts between the tool and the workpiece at very small distances (10-150 µm), i.e., only in the place to which the tool is connected and which we want to expose to current.

An electrical discharge machine usually has devices for moving the tool in the desired direction and an electrical power source that excites the discharges. The machine also has an automatic tracking system for the size of the gap between the workpiece being processed and the tool; it brings the tool closer to the workpiece if the gap is too large, or moves it away from the workpiece if it is too small.

As a rule, the electroerosive method is used in cases where processing on metal-cutting machines is difficult or impossible. due to the hardness of the material or when the complex shape of the workpiece does not allow the creation of a sufficiently strong cutting tool.

Not only a wire, but also a rod, a disk, etc. can be used as a tool. Thus, using a tool in the form of a rod of a complex three-dimensional shape, one gets, as it were, an impression of it in the workpiece being processed. A rotating disk is used to burn narrow slots and cut strong metals.

Electroerosive machine.

There are several varieties of electrical erosion method, each of which has its own properties. Some varieties of this method are used for burning complex-shaped cavities and cutting holes, others are used for cutting workpieces made of heat-resistant and titanium alloys, etc. We list some of them.

At electrospark During electrical processing, short-term spark and spark-arc discharges with temperatures up to 8000-10,000 ° C are excited. The tool electrode is connected to the negative pole, and the workpiece being processed is connected to the positive pole of the electrical power source.

Electropulse processing is carried out by electrically excited and interrupted arc discharges with temperatures up to 5000 ° C. The polarity of the electrode-tool and the workpiece is reverse in relation to electric spark processing.

At anodic-mechanical During processing, an electrode-tool is used in the form of a disk or an endless belt, which quickly moves relative to the workpiece. With this method, a special liquid is used, from which a non-conducting film falls onto the surface of the workpiece. The electrode tool scratches the film, and in places where the surface of the workpiece is exposed, arc discharges occur that destroy it. They do the necessary work.

Even faster movement of the electrode, cooling its surface and interrupting arc discharges, is used when electrical contact processing, usually carried out in air or water.

In our country, they produce a whole range of electrical discharge machines for processing a wide variety of parts, from very small to large ones, weighing up to several tons.

Electroerosive machines are now used in all branches of mechanical engineering. Thus, in automobile and tractor factories they are used in the manufacture of dies for crankshafts, connecting rods and other parts, in aircraft factories they are processed on electric erosion machines for turbojet engine blades and hydraulic equipment parts, in electronic device factories - parts of radio tubes and transistors, magnets and molds, in Metallurgical plants cut rolled rods and ingots from especially hard metals and alloys.

Ultrasound works

Until relatively recently, no one could have imagined that sound would be used to measure the depth of the sea, weld metal, drill glass and tan leather. And now sound is mastering more and more new professions.

What is sound and why has it become an indispensable human assistant in a number of important production processes?

Sound is elastic waves, spreading in the form of alternating compression and rarefaction of particles of the medium (air, water, solids, etc.). The frequency of sound is measured by the number of compressions and rarefaction: each compression and subsequent rarefaction form one complete oscillation. The unit of sound frequency is a complete oscillation, which occurs in 1 s. This unit is called the hertz (Hz).

A sound wave carries with it energy, which is defined as the strength of sound and the unit of which is taken to be 1 W/cm2.

A person perceives vibrations of different frequencies as sounds of different pitches. Low sounds (beat of a drum) correspond to low frequencies (100-200 Hz), high sounds (whistle) correspond to high frequencies (about 5 kHz, or 5000 Hz). Sounds below 30 Hz are called infrasounds, and above 15-20 kHz - ultrasounds. Ultrasounds and infrasounds are not perceived by the human ear.

The human ear is adapted to perceive sound waves of very low strength. For example, a loud scream that irritates us has an intensity measured in nanowatts per square centimeter (nW/cm2), i.e., billionths of W/cm2. If you turn the energy from the loud simultaneous conversation of all Moscow residents during the day into heat, it will not be enough even to boil a bucket of water. So weak sound waves cannot be used to perform any manufacturing processes. Of course, sound waves that are many times stronger can be created artificially, but they will destroy the human hearing organ and lead to deafness.

In the region of infrasound frequencies, which are not dangerous to the human ear, it is very difficult to create powerful vibrations artificially. Another thing is ultrasound. It is relatively easy to obtain ultrasound from artificial sources with an intensity of several hundred W/cm 2, i.e. 10 12 times more than the permissible sound intensity, and this ultrasound is completely harmless to humans. Therefore, to be more precise, it was not sound, but ultrasound that turned out to be the universal master who has found such wide application in industry (see vol. 3 DE, art. “Sound”).

Here we will only talk about the use of ultrasonic vibrations in machine tools for processing brittle and hard materials. How are such machines designed and operated?

Ultrasonic machine.

Scheme of the ultrasonic processing process.

The heart of the machine is energy converter high-frequency oscillations of electric current. The current enters the converter winding from the electronic generator and is converted into the energy of mechanical (ultrasonic) vibrations of the same frequency. These transformations occur as a result magnetostriction - phenomenon, which consists in the fact that a number of materials (nickel, an alloy of iron with cobalt, etc.) in an alternating magnetic field change their linear dimensions with the same frequency with which the field changes.

Thus, a high-frequency electric current passing through the winding creates an alternating magnetic field, under the influence of which the converter oscillates. But the resulting vibration amplitudes are small in size. To increase them and make them suitable for useful work, firstly, the entire system is tuned to resonance (the frequency of oscillation of the electric current and the natural frequency of the converter are achieved), and secondly, a special waveguide concentrator, which transforms small amplitudes of oscillations over a larger area into large amplitudes over a smaller area.

A tool is attached to the end of the waveguide in the shape that the hole is desired to have. The tool, together with the entire oscillatory system, is pressed with little force onto the material in which a hole is to be made, and an abrasive suspension (abrasive grains less than 100 microns, mixed with water) is supplied to the processing site. These grains fall between the tool and the material, and the tool, like a jackhammer, drives them into the material. If the material is fragile, then the abrasive grains break off microparticles 1-10 microns in size. It would seem not much! But there are hundreds of abrasive particles under the tool, and the tool delivers 20,000 blows in 1 second. Therefore, the processing process is quite fast, and a hole measuring 20-30 mm in glass 10-15 mm thick can be made in 1 minute. An ultrasonic machine allows you to make holes of any shape, even in fragile materials that are difficult to process.

Ultrasonic machines are widely used for the production of carbide die matrices, computer “memory” cells from ferrite, silicon and germanium crystals for semiconductor devices, etc.

Now we were talking about only one of many cases of using ultrasound. However, it is also used for welding, washing, cleaning, inspection, measuring and performs these duties perfectly. Ultrasound very cleanly “washes” and degreases the most complex parts of devices, performs soldering and tinning of aluminum and ceramics, finds defects in metal parts, measures the thickness of parts, determines the flow rate of liquids in different systems and performs dozens of other works that cannot be done without it completed.

Electrochemical processing of metals

If solid conductive plates (electrodes) are introduced into a vessel with a conductive liquid and voltage is applied to them, electricity. Such conductive liquids are called conductors of the second kind or electrolytes. These include solutions of salts, acids or alkalis in water (or other liquids), as well as molten salts.

Electrochemical copying and stitching machine.

Electrolysis scheme.

Scheme of electrochemical processing of holes of complex configurations in detail.

Current carriers in electrolytes are positive and negative particles - ions, into which the solute molecules are broken down in solution. In this case, positively charged ions move towards the negative electrode - cathode, negative - to the positive electrode - anode. Depending on the chemical nature of the electrolyte and electrodes, these ions either precipitate at the electrodes or react with the electrodes or solvent. The reaction products are either released at the electrodes or go into solution. This phenomenon is called electrolysis.

Electrolysis is widely used in industry for the production of metal casts from relief models, for the application of protective and decorative coatings on metal products, for the production of metals from molten ores, for the purification of metals, for the production of heavy water, in the production of chlorine, etc.

One of the new areas of industrial application of electrolysis is electrochemical dimensional processing of metals. It is based on the principle of dissolving a metal under the influence of a current in aqueous solutions of salts.

Light beam machine for processing diamond filters.

Optical quantum generator circuit: 1 - flash lamp; 2 - capacitor; 3 - ruby; 4 - parallel mirrors; 5 - lens.

In electrochemical dimensional machining, electrodes are placed in the electrolyte at very close range from each other (50-500 µm). Electrolyte is pumped between them under pressure. Thanks to this, the metal dissolves extremely quickly, and if the distance between the electrodes is maintained constant, then a fairly accurate representation of the shape of the tool electrode (cathode) can be obtained on the workpiece (anode).

Thus, using electrolysis, you can relatively quickly (faster than the mechanical method) produce parts of complex shapes, cut workpieces, make holes or grooves of any shape in parts, sharpen tools, etc.

The advantages of the electrochemical processing method include, firstly, the ability to process any metals, regardless of their mechanical properties, and secondly, the fact that the electrode tool (cathode) does not wear out during processing.

Electrochemical processing is carried out on electrochemical machines. Their main groups: universal copying and stitching machines - for the manufacture of stamps, molds and other products of complex shape; special - for processing turbine blades; sharpening And grinding - for sharpening tools and flat or profile grinding of difficult-to-cut metals and alloys.

Light works (laser)

Remember "Engineer Garin's Hyperboloid" by A. N. Tolstoy. Ideas that were recently considered fantastic are becoming reality. Today, a light beam is used to burn holes in such strong and hard materials as steel, tungsten, diamond, and this no longer surprises anyone.

Of course, you all had to catch sunbeams or focus with a lens sunlight into a small bright spot and burn different designs on the wood with it. But on a steel object you cannot leave any mark in this way. Of course, if it were possible to concentrate sunlight into a very small point, say a few micrometers in diameter, then the specific power (that is, the ratio of power to area) would be sufficient to melt and even evaporate any material at that point. But sunlight cannot be focused like that.

In order to use a lens to focus light into a very small spot and at the same time obtain a high specific power, it must have at least three properties: be monochromatic, i.e. monochrome, spread in parallel(have a low luminous flux divergence) and be sufficient bright.

The lens focuses rays of different colors at different distances. Yes, rays of blue color come into focus further than red. Since sunlight consists of rays of different colors, from ultraviolet to infrared, it is not possible to focus it accurately - the focal spot turns out to be blurry and relatively large. Obviously, monochromatic light produces a much smaller focal spot.

Gas laser used for cutting glass, thin films and fabrics. In the near future, such installations will be used for cutting metal blanks of considerable thickness.

It is known from geometric optics that the smaller the diameter of the light spot at the focus, the smaller the divergence of the light beam incident on the lens. That is why parallel rays of light are necessary for our goal.

Finally, brightness is needed in order to create a high power density at the focal point of the lens.

No ordinary light source has these three properties at the same time. Monochromatic light sources are low-power, while high-power light sources, such as an electric arc, have a large divergence.

However, in 1960, Soviet scientists - physicists, laureates of the Lenin and Nobel Prizes N. G. Basov and A. M. Prokhorov, simultaneously with the laureate Nobel Prize American physicist Charles Townes created a light source with all the necessary properties. He was named laser, abbreviated from the first letters of the English definition of the principle of its operation: light amplification by stimulated emission of radiation, i.e. amplification of light using stimulated radiation. Another name for laser is optical quantum generator(abbreviated OKG).

It is known that every substance consists of atoms, and the atom itself consists of a nucleus surrounded by electrons. In the normal state, which is called main, electrons are so located around the nucleus that their energy is minimal. To remove electrons from the ground state, it is necessary to impart energy to them from the outside, for example, by illumination. The absorption of energy by electrons does not occur continuously, but in separate portions - quanta(see vol. 3 DE, art. “Waves and quanta”). The electrons that have absorbed energy go into an excited state, which is unstable. After some time, they return to the ground state again, releasing the absorbed energy. This process does not happen all at once. It turned out that the return of one electron to the ground state and the release of a light quantum by it accelerates (stimulates) the return to the ground state of other electrons, which also release quanta, and, moreover, exactly the same in frequency and wavelength. Thus we get an enhanced monochromatic beam.

Principle of operation light beam machine Let's look at the example of an artificial ruby ​​laser. This ruby ​​is obtained synthetically from aluminum oxide in which a small number of aluminum atoms are replaced by chromium atoms.

As external source energy applied flash lamp 1, similar to that used for flash photography, but much more powerful. The lamp's power source is capacitor 2. When irradiated by a lamp, chromium atoms located in ruby 3, absorb light quanta with wavelengths that correspond to the green and blue parts of the visible spectrum, and pass into an excited state. An avalanche-like return to the ground state is achieved using parallel mirrors 4. The released light quanta, corresponding to the red part of the spectrum, are reflected many times in the mirrors and, passing through the ruby, accelerate the return of all excited electrons to the ground state. One of the mirrors is made translucent, and the beam is output through it. This beam has a very small divergence angle, since it consists of light quanta that have been reflected many times and have not experienced significant deviation from the axis of the quantum generator (see figure on page 267).

Such a powerful monochromatic beam with a low degree of divergence is focused lens 5 on the surface to be treated and produces an extremely small spot (up to 5-10 microns in diameter). Thanks to this, colossal power density is achieved, on the order of 10 12 -10 16 W/cm 2 . This is hundreds of millions of times the power that can be obtained by focusing sunlight.

Such power density It is enough to evaporate even such a refractory metal as tungsten in the area of ​​the focal spot in thousandths of a second and burn a hole in it.

Now light-beam machines are widely used in industry to make holes in watch stones made of ruby, diamonds and hard alloys, and in diaphragms made of refractory, difficult-to-cut metals. New machines made it possible to increase productivity tenfold, improve working conditions and, in some cases, produce such parts. which cannot be obtained by other methods.

The laser not only produces dimensional processing of micro-holes. Light-beam installations for cutting glass products, micro-welding of miniature parts and semiconductor devices, etc. have already been created and are successfully operating.

Laser technology, in essence, has just appeared and is becoming an independent branch of technology before our eyes. There is no doubt that, with the help of humans, the laser will “master” dozens of new useful professions in the coming years and will begin to work in factory shops, laboratories and construction sites along with cutters and drills, electric arcs and discharges, ultrasound and electron beams.

Electron beam processing

Let's think about the problem: how to cut a tiny surface area - a square with a side of 10 mm - from a very hard material into 1500 parts? Those who are engaged in the manufacture of semiconductor devices - microdiodes - encounter this problem every day.

This problem can be solved using electron beam - accelerated to high energies and focused into a highly directed flow of electrons.

Processing of materials (welding, cutting, etc.) with an electron beam is completely new area technology. She was born in the 50s of our century. The emergence of new processing methods is, of course, not accidental. In modern technology we have to deal with very hard, difficult-to-process materials. In electronic technology, for example, plates made of pure tungsten are used, in which it is necessary to drill hundreds of microscopic holes with a diameter of several tens of micrometers. Man-made fibers are made using dies, which have holes of a complex profile and are so small that the fibers pulled through them are much thinner human hair. The electronics industry requires ceramic plates with a thickness of 0.25 mm. Slots with a width of 0.13 mm should be made on them, with a distance between their axes of 0.25 mm.

Old processing technology cannot handle such tasks. Therefore, scientists and engineers turned to electrons and forced them to perform technological operations of cutting, drilling, milling, welding, smelting and cleaning metals. It turned out that the electron beam has attractive properties for technology. When it hits the material being processed, it can heat it up to 6000° C (the temperature of the surface of the Sun) at the point of impact and almost instantly evaporate, forming a hole or depression in the material. In the same time modern technology allows you to quite easily, simply and within a wide range regulate the energy of electrons, and therefore the heating temperature of the metal. Therefore, the flow of electrons can be used for processes that require different powers and occur at very different temperatures, for example, for melting and cleaning, for welding and cutting metals, etc.

An electron beam can cut a tiny hole even in the hardest metal. On the image: electron gun circuit.

It is also extremely valuable that the action of the electron beam is not accompanied by shock loads on the product. This is especially important when processing fragile materials such as glass and quartz. The processing speed of micro-holes and very narrow slots on electron beam machines is significantly higher than on conventional machines.

Installations for electron beam processing are complex devices based on the achievements of modern electronics, electrical engineering and automation. The main part of them is electron gun, generating a beam of electrons. Electrons emitted from the heated cathode are sharply focused and accelerated by special electrostatic and magnetic devices. Thanks to them, the electron beam can be focused on an area with a diameter of less than 1 micron. Precise focusing also makes it possible to achieve a huge concentration of electron energy, thanks to which it is possible to obtain a surface radiation density of the order of 15 MW/mm 2. Processing is carried out in high vacuum (residual pressure approximately equal to 7 MPa). This is necessary to create conditions for electrons to travel freely, without interference, from the cathode to the workpiece. Therefore the installation is equipped vacuum chamber And vacuum system.

The workpiece is placed on a table that can move horizontally and vertically. The beam, thanks to a special deflection device, can also move over short distances (3-5 mm). When the deflector is turned off and the table is stationary, the electron beam can drill a hole with a diameter of 5-10 microns in the workpiece. If you turn on the deflection device (leaving the table stationary), then the beam, moving, will act like a cutter and will be able to burn small grooves of various configurations. When it is necessary to “mill” longer grooves, the table is moved, leaving the beam stationary.

It is interesting to process materials with an electron beam using the so-called masks. In the setup, I place* a mask on a moving table. Its shadow on a reduced scale is projected onto the part by the forming lens, and the electron beam processes the surface limited by the contours of the mask.

The progress of electronic processing is usually monitored using optical microscope. It allows you to accurately set the beam before starting processing, for example cutting along a given contour, and monitor the process. Electron beam installations are often equipped with programming device which automatically sets the pace and sequence of operations.

High frequency current treatment

If a crucible with a piece of metal placed in it is wrapped with several turns of wire and passed along this wire (to the inductor) high frequency alternating current, the metal in the crucible will begin to heat up and after a while will melt. This is circuit diagram the use of high frequency currents (HFC) for heating. But what happens?

For example, the heated substance is a conductor. The alternating magnetic field, which appears when alternating current passes through the turns of the inductor, causes electrons to move freely, i.e., it generates eddy induced currents. They heat up a piece of metal. The dielectric heats up due to the fact that the magnetic field vibrates the ions and molecules in it, “rocking” them. But you know that the faster the particles of a substance move, the higher its temperature.

Schematic diagram of the installation for heating products with high frequency currents.

For high-frequency heating, currents with frequencies from 1500 Hz to 3 GHz and higher are now most widely used. At the same time, heating installations using HDTV often have a power of hundreds and thousands of kilowatts. Their design depends on the size and shape of the heated objects, on their electrical resistance, on what kind of heating is required - continuous or partial, deep or superficial, and on other factors.

How larger sizes object being heated and the higher the electrical conductivity of the material, the lower frequencies can be used for heating. And vice versa, the lower the electrical conductivity, the smaller the dimensions of the heated parts, the higher frequencies are required.

What technological operations in modern industry are carried out using HDTV?

First of all, as we already said, fuse. High-frequency melting furnaces are now operating in many enterprises. They produce high-quality steels, magnetic and heat-resistant alloys. Melting is often carried out in a rarefied space - in a deep vacuum. Vacuum melting produces metals and alloys of the highest purity.

The second most important “profession” of HDTV is hardening metal (see article "Protection of metal").

Many important parts of cars, tractors, metal-cutting machines and other machines and mechanisms are now hardened by high-frequency currents.

HDTV heating allows you to obtain high-quality high-speed soldering various solders.

HDTV heats steel blanks for processing them by pressure(for stamping, forging, rolling). When heating the HDTV, no scale is formed. This saves metal, increases the service life of dies, and improves the quality of forgings. The work of workers is made easier and healthier.

So far we have talked about HDTV in connection with metal processing. But the range of their “activities” is not limited to this.

HDTVs are also widely used for processing important materials such as plastics. In plastic products factories, blanks are heated in HDTV installations before pressing. Heating with HDTV helps a lot when gluing. Multilayer safety glass with plastic gaskets between the layers of glass is made by heating HDTV in presses. By the way, wood is also heated during the production of particle boards, some types of plywood and shaped products made from it. And for welding seams in products made of thin sheets plastics are used special machines HDTV, reminiscent of sewing. Covers, cases, boxes, and pipes are made using this method.

In recent years, HDTV heating has been increasingly used in glass production - for welding various glass products (pipes, hollow blocks) and when melting glass.

HDTV heating has great advantages over other heating methods also because in some cases the technological process based on it is better amenable to automation.

Above we discussed indicators characterizing the quality of parts due to their intended purpose in the machine. Economic achievement of quality of parts is one of the main tasks of mechanical engineering technology.

The most economical, apparently, would be such a technological process, as a result of which the raw product of nature would directly produce a finished part that meets its intended purpose.

The practice of mechanical engineering at the present stage of development does not have such processes, and therefore parts are made from various types of semi-finished products.

Thus, in mechanical engineering, the manufacture of parts consists of transforming a selected semi-finished product into a finished part. From the point of view of achieving the required accuracy of a part, the task comes down to choosing the required volume of a semi-finished product, giving it a shape and size that is close to the future part, and “refining” them to deviations limited by tolerances for the finished part.

1. Manufacturing of blanks machine parts are produced:

a) metal casting in various ways;

b) processing of metals by pressure (plastic deformation), forging, stamping (hot and cold), pressing (extrusion), rolling, drawing;

c) plastic molding;

d) stamping of plastics.

2. Workpiece processing machine parts are produced:

a) mechanically:

Removing chips - cutting metal with blade tools and abrasives on metal-cutting machines;

Plastic deformation (without removing chips) – metal compaction; rolling and rolling with rollers, punching - calibration of holes with a ball or mandrel; rolling (to obtain a corrugated surface);

Cold straightening of metal parts;

shot blasting of metal parts;

plastic deformation of plastics.

b) chemical-mechanical methods :

Finishing (grinding) with laps made primarily of cast iron, copper or brass, micropowders and pastes. The lap material is usually softer than the material of the workpiece;

Polishing with soft circles (from cloth, calico, felt, paper, leather) using polishing pastes containing (like lapping pastes) surfactants that chemically affect the material being processed;

Processing (sharpening and finishing) of a carbide tool in a solution of copper sulfate using abrasive powder and a metal disc.

c) electrochemical methods, the essence of which is the use of electrical energy in the form of electrolysis.

d) thermal methods, which are used to modify the structure of the metal to obtain its mechanical and physical properties that meet technical requirements.

d) X imico-thermal processing methods are used for metal parts in order to improve their physical, chemical and mechanical properties - increase their heat resistance, wear resistance, etc. by changing the chemical composition of the surface layer of the metal, which is artificially saturated with nitrogen (the process is called nitriding), aluminum (alitizing), carbon and nitrogen simultaneously with subsequent hardening (cyanidation) and some other elements. This also sometimes includes the widespread process of heat treatment - saturation of low-carbon steel with carbon followed by hardening (cementation).

3. Aging of parts blanks. Aging aims to bring the structure of the casting into a state of equilibrium, i.e., to free the workpiece from internal stresses that arise both during the solidification of the metal and during preliminary mechanical processing (grinding).

Aging happens natural And artificial. The natural aging method is that the blank after casting or after peeling is kept in the open air under the influence of the atmosphere for 0.5-6 months or more.

Due to the duration of this process, the method of artificial aging is more often used. Artificial aging is mainly carried out by heat treatment of the workpiece by heating it in a furnace (electric, gas, oil) at a temperature of 450-500 ° C, holding for 12-15 hours and cooling for 2.5-3 hours together with the furnace, after which the workpiece is finally cooled in air.

Aging is used primarily for large cast parts that require the greatest possible stability of shape and size, for example, for the beds of metal-cutting machines.

4. Metal welding– one of the ways to connect metal parts; is divided into chemical (gas, thermite, etc.) and electrical (electric arc, contact, etc.). Welding can replace soldering, riveting, forging, casting; in many cases, with the help of welding, significant savings in metal are achieved (the labor intensity of manufacturing products is reduced, production is cheaper).

5. Balancing parts. To avoid vibration, parts rotating at high speeds must be balanced. A rotating part will be balanced or balanced when its center of gravity and main axis of inertia coincide with the axis of rotation. The reasons for the unbalance of parts and assemblies may be inhomogeneity of the material, inaccuracy in the size and shape of surfaces, asymmetrical arrangement of the metal mass relative to the axis of rotation, mismatch of the axes of mating parts rotating together.

Parts that perform reciprocating motion (for example, a piston with a connecting rod in an internal combustion engine) are adjusted according to weight (mass).

6) Cleaning, rinsing and coating parts with lubricant. During processing and after processing, parts are cleaned, washed, dried and coated with lubricant. Cleaning is carried out by mechanical or chemical methods, washing - in washing tanks or washing machines, drying - by blowing with compressed air. Parts are coated with lubricant to protect them from corrosion.