The essence of the chemical milling process is the controlled removal of material from the surface of the workpiece by dissolving it in an etchant due to a chemical reaction. Areas of the workpiece that are not subject to dissolution are covered with a protective layer of chemically resistant material.

The removal rate of many materials is up to 0.1 mm/min.

Advantages of the process:

· high productivity and quality of processing,

· the ability to obtain parts of complex configurations of both small and significant thickness (0.1-50) mm;

· low energy costs (chemical energy is mainly used);

· short production preparation cycle and ease of automation;

· waste-free due to regeneration of process products.

During processing, material removal can be carried out from the entire surface of the workpiece, to various depths or to the entire thickness of the part (through milling). Chemical milling includes the following main stages: preparation of the workpiece surface; applying a protective layer of the pattern; chemical etching; removal of the protective layer and quality control of products (see Fig. 3.1).

Surface preparation means cleaning it from organic and inorganic substances, for example, using electrochemical degreasing. The degree of purification is determined by the requirements for subsequent operations.

The application of the protective layer of the design is carried out using the following methods: manual and mechanized engraving on the mistaken (varnish, wax) layer, xerography, screen printing, offset printing, as well as photochemical printing.

In instrument making, the most widely used method is photochemical printing, which ensures small product sizes and high accuracy. IN in this case To obtain a protective layer of a given configuration, a photomask is used (photocopy of the part on an enlarged scale on transparent material). Liquid and film photoresists with photosensitivity are used as a protective layer. Liquids, the most developed in industry, require high quality cleaning the surface of workpieces. To apply them to the surface, one of the following methods is used: immersion, watering, spraying, centrifuging, rolling with rollers, spraying in an electrostatic field. The choice of method depends on the type of production (continuous application or on individual workpieces); requirements for the thickness and uniformity of the film formed, which determine the accuracy of the pattern dimensions and the protective properties of the resist.

Rice. 3.1. General scheme technological process chemical milling.

Photochemical printing of a protective pattern, in addition to the operation of applying photoresist and drying it, includes the operations of exposing a layer of photoresist through a photomask, developing the pattern and tanning the protective layer. During development, certain areas of the photoresist layer dissolve and are removed from the surface of the workpiece. The remaining layer of photoresist in the form of a pattern defined by a photomask, after additional heat treatment - tanning - serves as a protective layer during the subsequent chemical etching operation.

The chemical etching operation determines the final quality and yield of the product. The etching process proceeds not only perpendicular to the surface of the workpiece, but also sideways (under protective layer), which reduces processing accuracy. The amount of etching is assessed through the etching factor, which is equal to , where H tr is the etching depth, e is the amount of etching. The rate of dissolution is determined by the properties of the metal being processed, the composition of the etching solution, its temperature, the method of supplying the solution to the surface, the conditions for removing reaction products and maintaining the etching properties of the solution. Timely termination of the dissolution reaction ensures the specified processing accuracy, which is approximately 10% of the processing (etching) depth.

Currently, etchants based on salts with an amine oxidizer are widely used, among which the most commonly used are chlorine, oxygen compounds of chlorine, dichromate, sulfate, nitrate, hydrogen peroxide, and fluorine. For copper and its alloys, kovar, steel and other alloys, the most widely used solutions are ferric chloride (FeCl 3) solutions with a concentration of 28 to 40% (by weight) and a temperature within (20 - 50) C, which provide a dissolution rate of (20 - 50) µm/min.

Among known methods etching distinguishes between immersing the workpiece in a calm solution; into a stirred solution; spraying the solution; spraying the solution; jet etching (horizontal or vertical). The best processing accuracy is ensured by jet etching, which consists in the fact that an etching solution under pressure is supplied through nozzles to the surface of the workpiece in the form of jets.

Parts quality control includes visual inspection their surfaces and measurement of individual elements.

The chemical milling process is most beneficial in the manufacture of flat parts of complex configurations, which in some cases can also be produced by mechanical stamping. Practice has established that when processing batches of parts up to 100 thousand, chemical milling is more profitable, and over 100 thousand, stamping is more profitable. For very complex configurations of parts, when it is impossible to make a stamp, only chemical milling is used. It should be taken into account that the chemical milling process does not allow the production of parts with sharp or right angles. The radius of curvature of the internal corner must be at least half the thickness of the workpiece S, and external corner- more than 1/3 S, the diameter of the holes and the width of the grooves of the parts must be more than 2 S.

Found the method wide application in electronics, radio engineering, electrical engineering and other industries in production printed circuit boards, integrated circuits, in the manufacture of various flat parts with complex configurations (flat springs, raster masks for picture tubes of color TVs, masks with circuit patterns used in thermal spraying processes, meshes for razors, centrifuges and other parts).

Electrochemistry in a glass

Electrochemical metal processing processes are used in all industries. With their help, you can perform operations such as drilling, turning, grinding or polishing, milling parts of complex configurations, and even removing burrs. At the same time, the essence of the processes of electrochemical dimensional processing is the anodic dissolution of the metal during electrolysis with the regular removal of generated waste. And therefore - and this is the most valuable thing - there are practically no hard-to-cut metals for electrochemical “cutting” processes.

All these advantages of electrochemical processing processes can be successfully used at home to perform many interesting and useful works. For example, with their help you can cut an elastic plate from a razor blade in 20-30 minutes, cut a hole complex shape in a thin sheet of metal, carve a spiral-shaped groove on a round rod (Fig. 1). To perform all these works, it is enough to have a rectifier AC, giving an output voltage of 6-10 volts, or a rectifier for 6-volt micromotors, or, finally, a set of 2-3 batteries for a flashlight. Pieces of wire, metal, glue and other auxiliary materials can be found in any home workshop.

Milling.

If you need to make a recess of a complex configuration in some blank - for example, cut out an apartment number (Fig. 2) - then to do this you need to take a sheet of Whatman paper and draw on it life size outline of the indentation you want to achieve. Then use a razor blade or scissors to cut and remove the drawn outline, and cut the sheet in accordance with the shape and size of the workpiece. Glue the mask template (1) obtained in this way using rubber glue or BF-88 glue onto the surface of the workpiece (2), attach the wire from the positive pole of the rectifier or a set of batteries to the workpiece and apply 1-2 layers to all its remaining surfaces without insulation any varnish or nitro paint. It’s a good idea to varnish or paint the mask template itself. After allowing the coating to dry, lower the workpiece into a glass with a concentrated solution of table salt, install a cathode plate (3) made of any metal opposite the mask template and connect it to the negative pole of the rectifier or current source.

As soon as the current is turned on, the process of electrochemical dissolution of the metal inside the contour of the mask template will begin. But after some time, the intensity of the process will decrease, which can be seen by a decrease in the number of bubbles released at the cathode (3). This means that an insulating layer of process waste has formed on the surface being treated. To remove them and at the same time measure the depth of the recess, the part must be removed from the glass and, being careful not to damage the mask template, use a small hard brush to clean off the loose layer of waste from the surface being treated. After this, periodically removing the part to control the dimensions and remove waste, the process can be continued until the excavation depth reaches the required value. And when the processing is completed, having removed the insulation and mask template, the part must be washed with water and lubricated with oil to prevent corrosion.

Stamping and engraving.

When it is necessary to make a hole of a complex configuration in a thin sheet of metal, the principles of electrochemical processing remain the same as for milling. The only subtlety is that in order for the edges of the hole to be smooth, the mask template (1) must be glued to the workpiece on both sides. To do this, the contours of the mask template (1) should be cut out in a sheet of paper folded in half and, gluing the template onto the workpiece (2), orient it along one of its sides (Fig. 3). And in addition, in order to speed up processing and ensure uniform removal of metal from both sides, it is advisable to bend the cathode plate (3) in the shape of the letter “U” and place the workpiece into it.

To make parts of any profile from sheet steel - for example, from a razor blade - parts of any profile are done somewhat differently. The profile of the part itself (1) is cut out of paper and glued to the workpiece (2) (Fig. 4). Then the entire the opposite side steel sheet, and on the template side, varnish insulation is applied so that it does not adjoin the template. And only in one place should the applied insulation be brought to the template using a narrow bridge (3) - otherwise, the dissolution of non-insulated surfaces around the template may end before the outline of the part is formed. To obtain more precise parts, you can cut out two templates, stick them on the workpiece on both sides and carry out processing in a U-shaped cathode. Using similar methods, you can make various inscriptions on metal, both convex and “pressed”.

Threading and spiral grooving.

One variation of the milling process is electrochemical cutting of spiral grooves and threads. This method can be useful for making, for example, wood screws or twist drills at home. When cutting a thread on a screw (Fig. 5), as a mask template (1), you need to take a thin rubber cord with a square section of 1x1 millimeter, wind it in a spiral with tension on a cylindrical workpiece (2) and secure its ends with threads (3). And then those surfaces of the workpiece that are not subject to etching are insulated with varnish. As a result of electrochemical processing, a spiral thread cavity is formed between the turns of rubber on the workpiece. Now you need to sharpen or, more precisely, make conical that end of the workpiece, which will serve as the tip of the screw entering the tree. To do this, you need to remove the workpiece from the bath, remove the rubber from it and dry it. And then, having varnished its surface so that only the first 2-3 threads remain open, the workpiece is returned to the bath and the electrochemical processing is continued for some more time.

To make a twist drill at home as a mask template (1), you need to take three rubber cords of the same cross-section and wind them onto a heat-treated cylindrical workpiece (2), but in two passes (Fig. 6). Then the surfaces of the workpiece that are not to be processed, and for reliability, the rubber cords must be varnished and, lowering the part into a glass bath, electrochemical milling of the drill grooves to the required depth. Now these grooves need to be expanded to form the so-called “back” of the drill (3). To do this, two out of three cords are removed from each strip of rubber insulation, and electrochemical milling continues for some time. After this, by removing the remaining insulation and sharpening the lead, you will have an excellent twist drill.

B. Rau

Processes Electrochemical metal processing is used in all industries. With their help, you can perform operations such as drilling, turning, grinding or polishing, milling parts of complex configurations, and even removing burrs. At the same time, the essence of the processes of electrochemical dimensional processing is the anodic dissolution of the metal during electrolysis with the regular removal of generated waste. And therefore - and this is the most valuable thing - there are practically no hard-to-cut metals for electrochemical “cutting” processes.
All These advantages of electrochemical processing processes can be successfully used at home to perform many interesting and useful jobs. For example, with their help you can cut an elastic plate from a razor blade in 20-30 minutes, cut a complex-shaped hole in a thin sheet of metal, or carve a spiral-shaped groove on a round rod. To perform all this work, it is enough to have an AC rectifier that produces an output voltage of 6-10 volts, or a 6-volt rectifier for micromotors, or, finally, a set of 2-3 batteries for a flashlight. Pieces of wire, metal, glue and other auxiliary materials can be found in any home workshop.

Milling.

If in some workpiece you need to make a recess of a complex configuration - for example, cut out an apartment number - then to do this you need to take a sheet of whatman paper and on it draw a life-size outline of the recess that you want to get. Then use a razor blade or scissors to cut and remove the drawn outline, and cut the sheet in accordance with the shape and size of the workpiece. Glue the mask template (1) obtained in this way using rubber glue or BF-88 glue onto the surface of the workpiece (2), attach the wire from the positive pole of the rectifier or a set of batteries to the workpiece and apply 1-2 layers to all its remaining surfaces without insulation any varnish or nitro paint. It’s a good idea to varnish or paint the mask template itself. After allowing the coating to dry, lower the workpiece into a glass with a concentrated solution of table salt, install a cathode plate (3) made of any metal opposite the mask template and connect it to the negative pole of the rectifier or current source.
How As soon as the current is turned on, the process of electrochemical dissolution of the metal inside the contour of the mask template will begin. But after some time, the intensity of the process will decrease, which can be seen by a decrease in the number of bubbles released at the cathode (3). This means that an insulating layer of process waste has formed on the surface being treated. To remove them and at the same time measure the depth of the recess, the part must be removed from the glass and, being careful not to damage the mask template, use a small hard brush to clean off the loose layer of waste from the surface being treated. After this, periodically removing the part to control the dimensions and remove waste, the process can be continued until the excavation depth reaches the required value. And when the processing is completed, having removed the insulation and mask template, the part must be washed with water and lubricated with oil to prevent corrosion.

Stamping and engraving.

When in a thin sheet of metal you need to make a hole of a complex configuration; the principles of electrochemical processing remain the same as when milling. The only subtlety is that in order for the edges of the hole to be smooth, the mask template (1) must be glued to the workpiece on both sides. To do this, the contours of the mask template (1) should be cut out in a sheet of paper folded in half and, gluing the template onto the workpiece (2), orient it along one of its sides. And in addition, in order to speed up processing and ensure uniform removal of metal from both sides, it is advisable to bend the cathode plate (3) in the shape of the letter “U” and place the workpiece into it.
For Manufacturing parts of any profile from sheet steel - for example, from a razor blade - proceeds somewhat differently. The profile of the part itself (1) is cut out of paper and glued to the workpiece (2). Then the entire opposite side of the steel sheet is coated with varnish, and varnish insulation is applied on the template side so that it does not adjoin the template. And only in one place should the applied insulation be brought to the template using a narrow bridge (3) - otherwise, the dissolution of non-insulated surfaces around the template may end before the outline of the part is formed. To obtain more precise parts, you can cut out two templates, stick them on the workpiece on both sides and carry out processing in a U-shaped cathode. Using similar methods, you can make various inscriptions on metal, both convex and “pressed”.

Threading and spiral grooving.

One One of the varieties of the milling process is electrochemical cutting of spiral grooves and threads. This method can be useful for making, for example, wood screws or twist drills at home. When cutting a thread on a screw, as a template-mask (1), you need to take a thin rubber cord with a square section of 1x1 millimeter, wind it in a spiral with tension on a cylindrical workpiece (2) and secure its ends with threads (3). And then those surfaces of the workpiece that are not subject to etching are insulated with varnish. As a result of electrochemical processing, a spiral thread cavity is formed between the turns of rubber on the workpiece. Now you need to sharpen or, more precisely, make conical that end of the workpiece, which will serve as the tip of the screw entering the tree. To do this, you need to remove the workpiece from the bath, remove the rubber from it and dry it. And then, having varnished its surface so that only the first 2-3 threads remain open, the workpiece is returned to the bath and the electrochemical processing is continued for some more time.
For To make a twist drill at home, as a template-mask (1), you need to take three rubber cords of the same cross-section and wind them onto a heat-treated cylindrical workpiece (2), but in two passes. Then the surfaces of the workpiece that are not to be processed, and for reliability, the rubber cords must be varnished and, lowering the part into a glass bath, electrochemical milling of the drill grooves to the required depth. Now these grooves need to be expanded to form the so-called “back” of the drill (3). To do this, two out of three cords are removed from each strip of rubber insulation, and electrochemical milling continues for some time. After this, by removing the remaining insulation and sharpening the lead, you will have an excellent twist drill.

Grinding.

To To polish the surface of cylindrical parts using the electrochemical method, in addition to traditional equipment, you need to have a small electric motor or drill. Having previously insulated the surfaces of the part that are not to be treated with varnish, fasten it on the electric motor shaft (1), install the motor vertically on some bracket and lower the end of the part to be treated (2) into a bath of electrolyte. In this case, it is best to supply the anode part (2) with current using a sliding contact going to the motor shaft, and make the cathode (3) flat, equal in length to the surface being treated. Now all that remains is to turn on the electric motor and power to the bath. With the beginning of the process, the surface will begin to darken - the formation of waste. To get the correct cylindrical the surface being treated, this waste must be continuously removed. This can be conveniently done using a toothbrush with bristles shortened for rigidity, which, pressed against the part, should be moved steadily up and down. By periodically removing the part to measure the diameter, in this way you can obtain a surface with dimensional accuracy of the second class.

Polishing.

For In order to polish any steel surface, prepare two wooden “bottles” (1) measuring 40x40 millimeters: one for roughing and the second for finishing polishing. Attach tin plates (2) bent at an angle to them, acting as a cathode, so that their position can be adjusted in height. To debug the polishing process, you need to take the workpiece (3), connect it to the positive pole of the current source and place it in a bath of electrolyte so that the level of the solution lies slightly above the horizontal part of the cathode (2). Then the rough “ball” should be dipped with one of the ends into the solution of table salt in the bath, taken out and a pinch of fine abrasive powder sprinkled on it. Now, turning on the current, begin polishing the part in a circular motion. In this case, it may happen that electrochemical dissolution will proceed faster than the process of removing waste with an abrasive. To eliminate this discrepancy, raise the cathode plate higher and the dissolution rate will decrease. Having polished the entire surface with the first “ball”, change the electrolyte solution to a clean one, wash the part from the abrasive and with the help of the second “roll” proceed to final polishing, which should be done either without any abrasive at all, or using tooth powder instead. With some training in this way you can get on the details mirror surface two to three times faster than mechanical polishing.

"Frost" on tinplate.

Take an empty can or just a piece of tinplate and connect to the wire from the positive pole of the rectifier. And connect any metal rod to the other pole, after making a cotton swab at its lower end. If you now dip this kind of “brush” into a solution of table salt and then begin to slowly move it over the surface of the tin, then amazing things will happen to it. In those places where you swabbed 2-3 times, sparkling crystals of “frost” appear - the crystalline structure of the tin coating will be revealed. If you continue the process, gray islands of waste will soon appear on the metal, firmly bound to the metal. And in the future, the entire surface of the tin will become spotted gray, with a characteristic bizarre pattern.
For To obtain various decorative patterns on metal, you can try using solutions of different salts or acids. So, for example, if instead of a solution of table salt you take a one percent solution of sulfuric acid, then the “developing” crystals will acquire a brown tint. If you sprinkle the tin plate with tooth powder, the “frost” pattern will become more contrasting, with a milky-gray tint. By preheating individual parts of a tin piece until the tin melts locally and quickly cooling them in water, one can obtain the most intricate ornaments on metal. Such ornaments look especially good if they are covered with colored varnish on top. Try it and you will see that it is simple tin can you can do a lot of beautiful things.

Y.M. I'm Polish

METHOD OF ELECTROLYTIC MILLING

INTERNAL CONNECTING WINDOWS

CHANNELS IN PARTS FROM ALUMINUM AND ITS ALLOYS

Announced February 8, 1957 for No. 566488 n Committee on Affairs of Inventions and Discoveries and the Sonnet of Ministers of the USSR

The invention relates to methods electrolytic milling connecting windows internal channels in parts made of aluminum and its alloys.

Known methods of this kind do not make it possible to perform internal connection of channels in hard to reach places. According to the invention, to obtain such channels, copper tubes are used, which serve to supply and discharge electrolyte and act as a cathode. A neutral salt solution, for example, a solution of technical table salt, is used as an electrolyte.

The proposed method of electrolytic milling is illustrated in the drawing.

In product 1, equipped with two or more channels 2, it is required to make a channel 3 connecting the first two channels. To do this, an insulating and sealing tube 4 is inserted into one of the channels 2, inside which copper tubes 5 and 6 are located, which serve for supplying and discharging electrolyte. The product is connected to the positive pole of the current source and serves as an anode, and the copper tubes are connected to the negative pole and serve as a cathode. Electrolyte is continuously supplied through tube 5 by a pump. Under the influence of current and mechanical action of the electrolyte stream, anodic dissolution of the metal of the product occurs in the direction of the electrolyte stream. Through tube 6, the electrolyte enters the collection tank and then again into the supply pump.

For processing aluminum products, a 10-20% HblH solution of technical table salt is used as an electrolyte. The current density should be equal to 10V”

Current source voltage 15V”

25th century When selecting appropriate electrolytes, the method can be applied to the processing of other metals. No. 110679

Subject of the invention

Rep. editor L. G. Golaydsky

Standardgiz. Subp. to the stove 14/1H 1958 Volume O, I25 and. l. Circulation 85O, zeiz 28 iop.

Printing house of the Committee for Inventions and Discoveries under the Council of the USSR Ministry of Construction and Construction

Moscow, Neglinnaya, 23. Zak. 1980

1. A method of electrolytic milling of connecting windows of internal channels in parts made of aluminum and its alloys, consisting in directing a stream of electrolyte onto the surface to be processed, and connecting the product and the stream of electrolyte to a source DC, the difference is that, in order to create the possibility of making holes in hard-to-reach places, copper tubes connected to the negative pole of the current source are used to supply and drain the electrolyte.

2. Method according to and. 1, characterized in that a solution of technical table salt is used as an electrolyte.

Similar patents:

The invention relates to equipment for electrochemical analysis and can be used as a sensor as part of polarographic equipment

The invention relates to the field of electroplating and can be used in the electrical industry, instrument making and for decorative purposes in the production of consumer goods. The method is characterized by the fact that an anode made of silver and silver alloys and a metal cathode are immersed in an electrolytic bath and a voltage of 280-370 V is applied to them at an anode current density of 0.4-0.8 A/cm2 and at a temperature of an aqueous electrolyte solution of 20-40 °C, while an aqueous solution containing ammonium chloride, ammonium citrate and tartaric acid is used as an electrolyte in the following ratio of components, wt.%: ammonium chloride 3-10; ammonium citrate 2-6; tartaric acid 1-3; water the rest. The technical result consists in polishing a silver or silver-containing part - the anode and obtaining silver oxide on the surface of the cathode.

The invention relates to the field of electrochemical processing of non-ferrous metal workpieces, namely to an aqueous electrolyte solution used for processing. The electrolyte solution contains citric acid with a concentration ranging from 1.665 g/l to 982 g/l, ammonium bifluoride with a concentration from 2 g/l to 360 g/l and not more than 3.35 g/l strong acid. Surface treatment of the workpiece involves exposing the surface to a bath of an aqueous electrolyte solution, adjusting the temperature of the bath to less than or equal to 85°C, connecting the workpiece to the anode of the DC power supply and immersing the cathode of the DC power supply in the bath and passing a current of less than 255,000 amperes through the bath. square meter. The invention allows the use of an aqueous electrolyte solution for processing various non-ferrous metals, while the electrolyte is environmentally friendly and does not create hazardous waste. 6 n. and 23 salary files, 12 ill., 9 tables.

The invention relates to the field of electrical chemical methods processing metal surfaces, including decorative processing. The method includes treating the surface of silver in aqueous solution sodium thiosulfate Na2S2O3×5H2O - 790 g/l at a temperature of 35±2 °C using pulsed unipolar and bipolar currents rectangular shape the following amplitude-time parameters: tpulse=0.1-10.0 ms, tneg.impulse=0.1-10.0 ms, delay duration of the current pulse of negative polarity tз=0.1-10.0 ms, tpause=0 ,1-10.0 ms, amplitude current density in a pulse of positive polarity iimp=0-5 A/cm2, amplitude current density in a pulse of negative polarity ineg.imp=0-5 A/cm2 and treatment duration 0.5-15, 0 minutes, and the current is unipolar when iotp.imp = 0. The technical result is the formation of resistant to external influences environment passive decorative films on the surface of 925 silver alloy. 3 ill.

Chemical methods of processing materials are called in which the removal of a layer of material occurs due to chemical reactions in the processing area. Advantages of chemical processing methods: a) high productivity provided by relatively high speeds the course of reactions, first of all, the absence of dependence of productivity on the size of the surface area being treated and its shape; b) the ability to process particularly hard or viscous materials; c) extremely low mechanical and thermal effects during processing, which makes it possible to process parts of low rigidity with sufficiently high accuracy and surface quality.

Dimensional deep etching (chemical milling) is the most common chemical processing method. It is advisable to use this method for processing surfaces of complex shapes on thin-walled parts, obtaining tubular parts or sheets with a smooth change in thickness along the length, as well as when processing a significant number of small parts or round blanks with big; number of treated areas (perforation of cylindrical pipe surfaces). By local removal of excess material in unloaded or lightly loaded areas by this method, it is possible to reduce total weight aircraft and missiles, without reducing their strength and rigidity. In the USA, the use of chemical milling made it possible to reduce the weight of a supersonic bomber wing by 270 kg. This method allows you to create new structural elements, for example sheets 1 of variable thickness. Chemical milling is also used in the manufacture of printed circuits of electronic equipment. In this case, from a panel made of insulating material, covered on one or both sides with copper foil, the areas specified by the circuit are removed by etching.

The technological process of chemical milling consists of the following operations.

1. Preparing parts for chemical milling to ensure subsequent tight and reliable adhesion of the protective coating to the surface of the part. For aluminum alloys this preparation is carried out: by degreasing in B70 gasoline; light etching in a bath with caustic soda 45-55 g/l and sodium fluoride 45-55 g/l at a temperature of 60-70 ° C for 10-15 minutes to remove the clad layer; washing in warm and cold water and clarification in nitric acid, followed by washing and drying. For stainless and titanium alloys, parts are prepared by etching to remove scale in a bath with hydrofluoric (50-60 g/l) and nitric (150-160 g/l) acids or in a bath electrically heated to 450-460 ° C in caustic soda and sodium nitrate (20%), followed by washing and drying, degreasing and light etching with repeated washing and drying.

2. Application protective coatings to areas of the workpiece that are not subject to etching. It is produced by installing special overlays, chemically resistant adhesive-type templates or, most often, applying paint coatings, which are usually used perchlorovinyl varnishes and enamels, polyamide varnishes and materials based on non-oprene rubbers. Thus, for aluminum alloys, we recommend enamel PKhV510V, solvent RS1 TU MKhP184852 and enamel KhV16 TU MKhPK-51257, solvent R5 TU MKhP219150, for titanium alloys - glue AK20, thinner RVD. For better adhesion of these coatings to the metal, the surface is sometimes pre-anodized. The application of paint and varnish coatings is carried out with brushes or spray guns with preliminary protection of the etching areas with templates or by immersion in a bath; in the latter case on dried protective film The contour is marked, then cut and removed.

3. Chemical dissolution is carried out in baths in compliance with temperature regime. Chemical milling of aluminum and magnesium alloys is carried out in solutions of caustic alkalis; steels, titanium, special heat-resistant and stainless alloys - in solutions of strong mineral acids.

4. Cleaning after etching of parts made of aluminum alloys with an enamel protective coating is carried out by washing in running water at a temperature of 50+70° C, by soaking the protective coating in hotter running water at a temperature

70-90°C and subsequent removal of the protective coating with knives manually or soft brushes in a solution of ethyl acetate and gasoline (2:1). Then they are clarified or lightly etched and dried.

The quality of the surface after chemical milling is determined by the initial roughness of the workpiece surface and etching modes; usually it is 1-2 grades lower than the cleanliness of the original surface. After etching, all previously existing defects on the workpiece are removed. (risks, scratches, irregularities) retain their depth, but widen, acquiring greater smoothness; The greater the etching depth, the more pronounced these changes are. The quality of the surface is also influenced by the method of obtaining workpieces and their heat treatment; rolled material gives better surface compared to stamped or pressed. High surface roughness with pronounced irregularities is obtained on cast workpieces.

Surface roughness is influenced by the structure of the material, grain size and grain orientation. Aged hardened aluminum sheets have a higher grade of surface finish. If the structure is coarse-grained (for example, the metal is annealed), then the final processed surface will have large roughness, uneven, and bumpy. The fine-grained structure should be considered most suitable for chemical processing. It is better to process carbon steel workpieces by chemical milling before hardening, since in the case of hydrogenation during pickling, subsequent heating helps remove hydrogen. However, it is advisable to harden thin-walled steel parts before chemical treatment, since subsequent heat treatment may cause their deformation. The surface processed by chemical milling is always somewhat loosened due to etching, and therefore this method significantly reduces the fatigue characteristics of the part. Taking this into account, for parts operating under cyclic loads, it is necessary to carry out polishing after chemical milling.

Chemical milling accuracy ±0.05 mm. depth and not less than +0.08 mm along the contour; The radius of curvature of the cutout wall is equal to the depth. Chemical milling is usually carried out to a depth of 4-6 mm and less often up to 12 mm; With a greater milling depth, the surface quality and processing accuracy deteriorate sharply. The minimum final thickness of the sheet after etching can be 0.05 mm, so chemical milling can be used to process parts with very thin bridges without warping; processing can be carried out on a cone by gradually immersing the part in the solution. If it is necessary to etch on both sides, you must either position the workpiece vertically so as to allow the released gas to freely rise from the surface, or etch in two stages - first on one side and then on the other. The second method is preferable, since when the workpiece is positioned vertically, the upper edges of the cutouts are processed worse due to gas bubbles entering there. When making deep cuts, special measures (for example, vibration) should be used to remove gas from the surface being processed, which interferes with the normal process. Control of depth and etching during processing is carried out by immersion Simultaneously with the preparation of control samples, direct control of dimensions using thickness gauges such as an indicator bracket or electronic, as well as through automatic weight control.

The productivity of chemical milling is determined by the rate of material removal in depth. The etching rate increases with increasing solution temperature by approximately 50-60% for every 10 ° C, and also depends on the type of solution, its concentration and purity. The solution can be stirred during the etching process using compressed air. The etching process is determined by an exothermic reaction, so the feed compressed air It cools it somewhat, but basically the constant temperature is ensured by placing water coils in the bath.

Immersion etching has a number of disadvantages - the use of manual labor, partial breakdown protective films on untreated surfaces. When processing a number of parts, the jet etching method, in which alkali is supplied by nozzles, is more promising.

A means of increasing the productivity of chemical milling is the use of ultrasonic vibrations with a frequency of 15-40 kHz; in this case, processing productivity increases by 1.5-2.5 times - up to 10 mm/h. The chemical treatment process is also significantly accelerated by exposure to infrared radiation directed action. Under these conditions, there is no need to apply protective coatings, since the metal is subjected to strong heating along a given heating circuit, and the remaining areas, being cold, practically do not dissolve.

The etching time is determined experimentally on control samples. The pickled workpieces are removed from the pickling machine, washed in cold water and to remove emulsion, paint and glue, BF4 is treated at a temperature of 60-80 ° C in a solution containing 200 g/l caustic soda. The finished parts are thoroughly washed and dried in a stream of air.

Improving the conditions for rough cutting of workpieces by preliminary removal of the skin by etching is another example of the dissolving effect of the reagent. Before etching, the workpieces are blasted with sand to remove scale. Titanium alloys are etched in a reagent consisting of 16% nitric and 5% hydrofluoric acids and 79% water. According to foreign literature For this purpose, etching in salt baths is used, followed by rinsing in water and then re-etching in acid etchants to finally clean the surface.

The chemical effect of the technological environment is also used to improve conventional cutting processes; Material processing methods based on a combination of chemical and mechanical influences are becoming increasingly used. Examples of already mastered methods are the chemical-mechanical method of grinding hard alloys, chemical polishing etc.