I read about such an interesting processing method. I want to implement on a CNC machine :)
From the book "Handbook of Process Engineer in Mechanical Engineering" (Babichev A.P.):
Electrochemical sizing is based on the phenomenon of anodic (electrochemical) dissolution of a metal when a current passes through an electrolyte supplied under pressure to the gap between the electrodes without direct contact between the tool and the workpiece. Therefore, another name for this method is anodic-chemical treatment.
The tool electrode during processing is the cathode, and the workpiece is the anode. The tool electrode moves progressively at a speed Vн. The electrolyte is fed into the interelectrode gap. The intensive movement of the electrolyte provides a stable and highly efficient flow of the anodic dissolution process, the removal of dissolution products from the working gap and the removal of heat generated during the processing. As the metal is removed from the anode blank, the cathode tool is fed.
The smaller the interelectrode gap, the higher the rate of anodic dissolution and the processing accuracy. However, with a decrease in the gap, the process of its regulation becomes more complicated, the resistance to pumping of the electrolyte increases, and a breakdown may occur causing damage to the treated surface. Due to the increase in gas filling at small gaps, the rate of anodic dissolution decreases. Should choose
the size of the gap, which achieves the optimum metal removal rate and the accuracy of shaping.
To obtain high technological parameters of ECM, it is necessary that the electrolytes meet the following requirements: complete or partial elimination of side reactions that reduce the current efficiency of the anodic dissolution of the workpiece metal only in the processing zone, excluding the dissolution of untreated surfaces, i.e. the presence of high localizing properties, ensuring the flow of an electric current of the calculated value in all areas of the processed surface of the workpiece.
The most common electrolytes are neutral solutions of inorganic chloride salts, sodium and potassium nitrates and sulfates. These salts are cheap and harmless to service personnel. An aqueous solution of sodium chloride (table salt) NaCl has been widely used due to its low cost and long-term performance, which is ensured by the continuous reduction of sodium chloride in the solution.
Installations for ECHO must have filters for cleaning the electrolyte.
The roundness of the hole itself pleases. But the funnel shape is not encouraging.
Now I will try to pump electrolyte through a medical needle.
Modified April 18, 2008 by destiK .: Tehnika, 1989 .-- 191 p.
ISBN 5-335-00257-3
Download (direct link) :
sputnik_galvanika.djvu Previous 1 .. 8\u003e .. \u003e\u003e Next
In electrochemical milling, a coating of any acid-resistant paint applied on a stencil can serve as a protective coating. The pickling solution in this case consists of 150 g / l sodium chloride and 150 g / l nitric acid. Etching occurs at the anode at a current density of 100-150 A / dm2. Copper plates are used as a cathode. After the termination of the process, the cathodes are removed from the bath.
Electrochemical milling is more accurate than chemical milling.
PRE-TREATMENT OF ALUMINUM AND ITS ALLOYS
To ensure a strong adhesion of the electrolytic coating to aluminum, an intermediate layer of zinc, iron or nickel is applied to the surface of the latter (Table 21).
CHEMICAL AND ELECTROCHEMICAL POLISHING
A smooth metal surface can be obtained by chemical or electrochemical (anodic) polishing (Tables 22, 23). The use of these processes makes it possible to replace mechanical polishing.
When oxidizing aluminum, mechanical polishing is not enough to achieve a shiny surface; after it, chemical or electrical
21. Solutions for pretreatment of aluminum
Orthophosphoric Ki Ice Acetic Orthophosphoric Ki
280-290 15-30 1-6
Acid Orange * For:
dye 2
pinned surface
1st treatment with intermediate
ratu-ra. FROM
4. ORTHOPHOSPHORE!
Triethane! lamin
500-IfXX) 250-550 30-80
Triethanolamine Catalin BPV
850-900 100-150
Ortofs of phrtoic acids Chromic thhydrnd
* PS mining products are processed by the washing line in the same flow rate 6A / dm2
trochemical polishing When polishing precious metals by chemical or electrochemical methods, their losses are completely eliminated. Electrochemical and chemical polishing can be not only a preparatory operation before applying electroplating, but also the final stage of the technological process. It is most widely used for aluminum. Electrochemical polishing is more economical than<ими-ческое.
The current density and the duration of the electropolishing process are selected depending on the shape, size and material of the products.
TECHNOLOGY OF COATING PROCESSES
SELECTION OF ELECTROLYTES AND PROCESSING MODES
The quality of the metal coating is characterized by the structure of the deposit, its thickness and uniformity of distribution on the surface of the product. The structure of the precipitate is influenced by the composition and pH of the solution, the hydrogen released together with the metal, the electrolysis mode - by the
polishing
M 41
with SS
Density
„|§..
Cathodes
From sent
Carbonaceous
I-IL
15-18
1,63-1,72
12XI8H9T, svshsho
1-5
10-100
From steel 12Х18Н97
H: rust
From styles 12Х18Н9Т Aluminum and 3-5 20-50 - (aluminum) stainless
0.5-5.0 20-50 1.60-1.61 Of copper or Evin - Copper and its
temperature, flow density, swing, filtration, etc.
To improve the structure of the precipitate, various organic additives (glue, gelatin, saccharin, etc.) are introduced into the electrolytes, complex salts are precipitated from solutions, the temperature is raised, continuous filtration is used, etc. The released hydrogen can be absorbed by the precipitate, contributing to an increase in fragility and porosity. , and the appearance of points of the so-called pitting. To reduce the effect of hydrogen on the quality of the precipitate, the parts are shaken during the process, oxidizing agents are introduced, the temperature is raised, etc. The porosity of the precipitate decreases with an increase in its thickness.
The uniform distribution of sediment on the surface and the delium depends on the scattering power of the electrolyte. The best scattering power is possessed by alkaline and cyanide electrolytes, much less - by acidic ones, and the worst - by chromic ones.
When choosing an electrolyte, it is necessary to take into account the configuration of the products and those requirements that are imposed on the NNM. For example, when covering products of a simple shape, you can work with simple electr\u003e -
lntamn that do not require heating, ventilation, filtration; when coating products of complex shape, solutions of complex metal salts should be used; for covering internal and hard-to-reach surfaces - internal and additional anodes, filtration, mixing; to obtain a shiny coating - electrolytes with complex gloss-forming and leveling additives, etc.
GENERAL DIAGRAM OF THE TECHNOLOGICAL PROCESS
The coating process consists of a series of sequential preparatory, coating and finishing operations. Preparatory operations include machining [parts, degreasing in organic solvents, chemical or electrochemical degreasing, pickling and polishing. Finishing treatment of coatings includes dehydration, clarification, passivation, impregnation, polishing, and brushing. After each operation
B. Rau
Processes electrochemical processing of metals are used in all industries. With their help, you can perform operations such as drilling, turning, grinding or polishing, milling parts of the most complex configurations, and even removing burrs. In this case, the essence of the processes of electrochemical sizing consists in the anodic dissolution of the metal during electrolysis with the regular removal of the resulting waste. That is why - and this is the most valuable thing - there are practically no hard-to-machine metals for electrochemical "cutting" processes.
All these advantages of electrochemical processing processes can be successfully used at home for many interesting and useful work. For example, they can be used to cut out an elastic plate from a razor blade in 20-30 minutes, cut a hole of complex shape in a thin sheet of metal, and carve a spiral groove on a round rod. To carry out all these works, it is enough to have an AC rectifier giving an output voltage of 6-10 volts, or a rectifier for micromotors for 6 volts, 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 a in some workpiece, you need to make a recess of a complex configuration - for example, cut out an apartment number - then for this you need to take a sheet of Whatman paper and draw on it in full size the contour of the recess that you want to get. Then, with a razor blade or scissors, cut and remove the drawn outline, and cut the sheet in accordance with the shape and dimensions of the workpiece. Glue the template-mask obtained in this way (1) with rubber glue or BF-88 glue on the surface of the workpiece (2), attach a wire to the workpiece from the positive pole of the rectifier or a set of batteries and apply 1-2 layers to all its surfaces without insulation any varnish or nitro paint. It's a good idea to varnish or paint the mask template itself. After letting the coating dry, lower the workpiece into a glass with a concentrated solution of sodium chloride, opposite the mask template, install a cathode plate (3) made of any metal and connect it to the negative pole of the rectifier or power source.
how As soon as the current is switched on, the process of electrochemical dissolution of the metal inside the contour of the mask template will begin. But after a while, the intensity of the process will decrease, which can be seen from 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 treated surface. To remove them and at the same time measure the depth of the recess, the part must be removed from the glass and, trying not to damage the template-mask, clean off the loose layer of waste from the treated surface with a small hard brush. After that, periodically removing the part for dimensional control and waste removal, the process can be continued until the depth of the excavation reaches the required value. And when the treatment is finished, after removing the insulation and the mask-mask, the part must be rinsed with water and lubricated with oil to avoid corrosion.
Stamping and engraving.
When it is necessary to make a hole with a complex configuration in a thin sheet of metal; the principles of electrochemical machining remain the same as in milling. The subtlety lies only in the fact that in order for the edges of the hole to be smooth, the template-mask (1) must be glued to the workpiece from 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, sticking the template onto the blank (2), orient it along one of its sides. And besides, in order to speed up the processing and ensure uniform metal removal on both sides, it is advisable to bend the cathode plate (3) in the shape of the letter "U" and place the workpiece to be processed in it.
For manufacturing from sheet steel - for example, from the blade of a razor blade - parts of any profile do a little differently. The profile of the part itself (1) is cut out of the paper and glued to the workpiece (2). Then the entire opposite side of the steel sheet is coated with varnish, and from the side of the template, the lacquer insulation is applied so that it does not adjoin the template. And only in one place the applied insulation needs to be brought to the template with a narrow jumper (3) - otherwise the dissolution of uninsulated surfaces around the template may end before the outline of the part is formed. To obtain more accurate details, you can cut out two templates, stick them on the workpiece on both sides and carry out processing in a U-shaped cathode. Similar methods can be used to make various inscriptions on metal, both convex and "depressed".
Threading and spiral grooving.
One of the varieties of the milling process is the electrochemical cutting of spiral grooves and threads. This method can be useful for making, for example, wood screws or twist drills at home. When threading a screw, as a template-mask (1), you need to take a thin rubber cord with a square cross section 1x1 millimeter, wind it with tension in a spiral on a cylindrical workpiece (2) and fasten 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 machining, a spiral thread cavity is formed on the workpiece between the rubber turns. Now you need to sharpen or, more precisely, make the end of the workpiece conical, which will serve as the sting of the screw entering the tree. To do this, 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 of the thread remain open, the workpiece is returned to the bath and the electrochemical processing continues for some time.
For for making a twist drill at home, as a mask-template (1), you need to take three rubber cords of the same 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, by lowering the part into a glass bath, electrochemical milling of the drill grooves to the required depth is performed. Now these grooves need to be widened to form the so-called "back" of the drill (3). For this, two out of three cords are removed from each strip of rubber insulation, and electrochemical milling continues for some time. After that, by removing the remaining insulation and sharpening the lead-in part, you will have an excellent twist drill.
Grinding.
To to grind the surface of cylindrical parts by electrochemistry, in addition to traditional equipment, you must have a small electric motor or drill. Having previously insulated the non-machined surfaces of the part with varnish, fix it on the motor shaft (1), install the motor vertically on a bracket and lower the part to be machined (2) into the electrolyte bath. In this case, the power supply of the anode part (2) with current is best organized with a sliding contact going to the motor shaft, and the cathode (3) should be made flat, equal along the length of the treated surface. Now it remains to turn on the electric motor and power supply to the bath. With the beginning of the process, the surface will begin to darken - the formation of waste. To obtain the correct cylindrical shape of the treated surface, this waste must be continuously removed. It is convenient to do this with a toothbrush with a bristle shortened for rigidity, which, pressing it against the part, should be measured up and down. By periodically removing the part to measure the diameter, this way you can get a surface with dimensional accuracy according to the second class.
Polishing.
For In order to polish any steel surface, prepare two wooden "kolobashki" (1) measuring 40x40 millimeters: one for rough and one for final polishing. Fasten the sheet metal plates (2) that act as a cathode on them so that their position can be adjusted in height. To debug the polishing process, you need to take a workpiece (3), connect it to the positive pole of the current source and place it in a bath with electrolyte so that the solution level lies slightly above the horizontal part of the cathode (2). Then the rough "kolobashka" should be dipped with one of the ends in a solution of sodium chloride in the bath, removed and a pinch of fine abrasive powder should be poured onto it. Now, turning on the current, begin to polish the part in a circular motion. In this case, it can happen that the 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. After polishing the entire surface with the first "kolobashka", change the electrolyte solution to a clean one, wash the part from the abrasive and, with the help of the second "kolobashka", proceed to fine polishing, which should be carried out either without abrasive at all, or using tooth powder instead. With some training in this way, you can get a mirror surface on parts two to three times faster than mechanical polishing.
"Frost" on a tinplate.
Take an empty canned food can or just a piece of tinplate and connect to the wire from the positive pole of the rectifier. And to the other pole, connect any metal rod, having previously made a cotton swab at its lower end. If now this kind of "shaving brush" is dipped into a solution of table salt and then slowly begin to drive it over the surface of the tin, then amazing things will happen to it. In those places where you have applied a "shaving brush" 2-3 times, sparkling crystals of "frost" appear - the crystal structure of the tin coating will be revealed. If you continue the process, then gray islands of waste will soon appear on the metal, firmly attached to the metal. And in the future, the entire surface of the tin will turn spotty gray, with a characteristic bizarre pattern.
For getting various decorative patterns on the metal, you can try to use solutions of different salts or acids. So, for example, if instead of a solution of sodium chloride to take a one-percent solution of sulfuric acid, the "emerging" crystals will acquire a brown tint. If a tin plate is sprinkled with tooth powder, the "frost" pattern will become more contrasting, with a milky-gray tint. By preheating individual parts of the tin part to local melting of the tin and quickly cooling them in water, you can get the most intricate patterns on metal. Such ornaments look especially good if they are covered with colored varnish on top. Try it and you will see that a lot of beautiful things can be made from a simple tin can.
Electrochemical sizing is based on the local anodic dissolution of the workpiece material in an electrolyte solution with intensive movement of the electrolyte between the electrodes.
The machinability of metals and alloys by the electrochemical method depends on their chemical composition and does not depend on their mechanical properties and structural state. The advantages of the method include a high surface quality with an increase in processing productivity, no thermal effect on the part, and no wear of the tool electrode. Due to this, during electrochemical processing, a layer of a changed structure is not formed and the formation of burns, cracks, residual stresses, etc. on the surface is excluded.
Feasibility of application
The use of electrochemical processing turns out to be highly effective and economically feasible in the following main cases:
- for processing parts made of particularly hard, brittle or ductile materials (heat-resistant, hard and titanium alloys, stainless and hardened steels);
- for processing structurally complex assemblies and parts (gas turbine blades, dies, molds, casting molds, internal channels and cavities, etc.) even from materials that can be cut;
- to replace particularly laborious (including manual) operations (deburring, edge rounding, etc.);
- to obtain a high quality, including polished surface without defects in the surface layer.
It is advisable to classify the known types of electrochemical processing according to two defining characteristics - the mechanism of the metal destruction process itself and the method of removing the reaction products from the working zone. Based on this, we can name three main directions in which the development and implementation of electrochemical processing methods is going on: electrochemical-hydraulic (anode-hydraulic) processing, electrochemical mechanical processing and combined processing methods.
Electrochemical-hydraulic processing
Electrochemical-hydraulic treatment (also called electrochemical treatment in a flowing electrolyte) is based on the anodic dissolution of metal and the removal of reaction products from the working area by an electrolyte flow. In this case, the speed of the electrolyte flow in the interelectrode gap is maintained within 5-50 m / s (using a pump providing a pressure of 5-20 kgf / cm2, or due to the rotation of the cathode-tool, continuously wetted by the electrolyte). The operating voltage is maintained within 5-24 V (depending on the material and technological operation), the gap between the electrodes is from 0.01 to 0.5 mm; the size of the gap is regulated by automatic tracking systems. Stainless steel, brass, graphite (the latter when processing at alternating or impulse voltage) are used as the material for the manufacture of the electrode-tool.
The energy intensity of this group of processes depends on the chemical composition of the processed material and the current efficiency. For most technological operations, it is 10-15 kWh / kg. The most common at present are the following types of electrochemical hydraulic processing.
Copy-stitching operations carried out with the translational movement of the cathode-tool, the shape of which is copied on the product simultaneously over the entire surface (Fig. 5).
These operations are used in the manufacture of turbine blades, forging dies, etc. At a metal removal rate of 0.1-0.5 mm / min, a surface finish of 6-7 is achieved; with an increase in the processing speed to 1-2 mm / min, the surface finish rises to 8-9. The highest productivity obtained when machining cavities on the MA-4423 machine is 15000 mm3 / min at a current of 5000 amperes. The feed rate of the tool in the direction of metal removal is 0.3-1.5 mm / min when processing dies, molds and blades and 5-6 mm / min when piercing holes. Surface finish 6-9; processing accuracy 0.1-0.3 mm. Processing is carried out with minimal gaps (0.1-0.15 mm); the largest gaps (5-6 mm) - while processing large surfaces.
Figure: 5. Scheme of piercing a hole by electrochemical method
Figure: 6. Machining with a rotating disc tool
Processing with a rotating disk tool (Fig. 6), which allows you to carry out profile, flat and circular external grinding with a non-abrasive tool to obtain a surface finish of 7-9 with a productivity on stainless steels up to 150-200 mm3 / min from a working area of \u200b\u200b1 cm2 and 60-80 mm3 / min for hard alloys, it is used to obtain the profile of carbide threaded dies, shaped cutters, knurling rollers, making external spline grooves, cutting narrow slots, cutting workpieces (cutting width 1.5-2.5 mm; surface finish 6-7) as well as for the processing of permanent magnets. Processing is carried out with gaps of 0.01-0.1 mm; processing accuracy 0.01-0.05 mm, surface finish 6-9. The feed rate, depending on the depth of processing, ranges from 1 to 40 mm / min, the voltage is 6-10 V. When machining cemented carbide, alternating or pulsed currents are used.
Figure: 7. Scheme of electrochemical deburring: 1 - tool; 2 - insulating sleeve; 3-blank (anode); 4 - removable burr
Wire complex contour cutting by copy of products from hardened, stainless steels and other difficult-to-machine materials allows the manufacture of die matrices, templates, through and blind grooves. Productivity of processing is up to 40 mm2 / min with a surface finish of 8 - 9. Accuracy of processing with straight cutting 0.02 mm, with cutting along the contour 0.06 mm. The maximum thickness of the workpiece to be cut is 20 mm (the given data were obtained on the MA-4429 machine).
Removing burrs from gears (Fig. 7), parts of hydraulic equipment, small radio engineering products, etc.
Manufacturing of grooves in special products.
Figured processing of bodies of revolution both at the end of the product, and outside and inside. The processing accuracy when using a shaped cathode is 0.05-0.1 mm.
Electrochemical mechanical treatment
Electrochemical-mechanical treatment is based on the anodic dissolution of metal and the removal of reaction products from the treated surface and from the working area using an abrasive and an electrolyte flow. This type of machining includes electrochemical grinding (electro-abrasive or electro-diamond machining), electrochemical machining with a neutral abrasive (grinding, honing and polishing) and anodic abrasive machining. In electro-abrasive and electro-diamond machining, metal removal is carried out not only due to the reaction of anodic dissolution, but also by grains of abrasive or diamond.
Productivity with electro-diamond grinding of hard alloys is 1.5-2 times higher than with diamond grinding, and the wear of a diamond wheel is 1.5-2 times less (when working with wheels on a bronze bond of Ml, on bonds M5, MB1 and MO13E, the wear of a wheel approximately the same as for diamond grinding); the surface finish is the same as for diamond grinding. In electrochemical grinding, the power consumed to drive the grinding wheel decreases several times. At the same time, the temperature of the surface layer drops sharply, due to which the appearance of cracks and burns is completely excluded. This method is widely used for sharpening carbide tools.
Electrochemical machining with neutral abrasives is used for flat, cylindrical and profile grinding, honing of internal cylindrical surfaces, and superfinishing. In all cases, the productivity of these operations is four to eight times that of machining.
Combined processing methods
Combined processing methods include electroerosive and electrochemical - ultrasonic.
The electroerosive-chemical processing method is based on the simultaneous occurrence of the processes of anodic dissolution and erosional destruction of the metal and the removal of reaction products from the working area by an electrolyte flow. During piercing operations, the cathode feed rate reaches 50-60 mm / min for steel, 20-30 mm / min for high-temperature alloys and 10 mm / min for hard alloys. In this case, the wear of the cathode-tool does not exceed 2.5%; processing accuracy 0.1-0.4 mm (according to experimental data).
This method can also be used for circular, flat and profile grinding, cutting workpieces made of difficult-to-machine materials. When cutting stainless steel blanks, the productivity is 550-800 mm2 / min; tool wear reaches 4-5%; processing accuracy 0.1-0.3 mm. Machines for this processing method are currently not produced.
The electrochemical method of processing is based on the destruction of the metal by its simultaneous anodic dissolution and exposure to ultrasonic vibrations. This method is used for machining carbide drawing dies.
Methods of processing materials are called chemical methods in which the removal of a layer of material occurs due to chemical reactions in the processing zone. Advantages of chemical processing methods: a) high productivity, provided by relatively high reaction rates, primarily the lack of dependence of productivity on the size of the area of \u200b\u200bthe treated surface 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 a 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 workpieces with a large; the number of places to be processed (perforation of the cylindrical surfaces of pipes). By local removal by this method from excess material in unloaded or lightly loaded, it is possible to reduce the total weight of aircraft and missiles without reducing their strength and rigidity. In the United States, the use of chemical milling has reduced the weight of a supersonic bomber wing by 270 kg. This method allows you to create new structural elements, such as sheets 1 of variable thickness. Chemical milling is also used in the manufacture of printed circuits for electronic equipment. In this case, in a panel made of insulating material, covered on one or both sides with copper foil, the sections specified by the circuit are removed by etching.
The technological process of chemical milling consists of the following operations.
1. Preparation of 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; rinsing in warm and cold waters and clarification in nitric acid followed by rinsing and drying. For stainless and titanium alloys, preparation of parts is carried out by etching for descaling in a bath with hydrofluoric (50-60 g / l) and nitric (150-160 g / l) acids or in a bath with electric heating up to 450-460 ° C in caustic soda and sodium nitrate (20%), followed by washing and drying, degreasing and light pickling with repeated washing and drying.
2. Application of protective coatings to the areas of the workpiece that are not subject to etching. It is produced by installing special pads, chemically resistant adhering type templates or, most often, by applying paints and varnishes, which are usually perchlorovinyl varnishes and enamels, polyamide varnishes and materials based on non-oprene rubbers. So, for aluminum alloys it is recommended to enamel PVC510V, solvent RS1 TU MHP184852 and enamel KhV16 TU MHPK-51257, solvent R5 TU MHP219150, for titanium alloys - glue AK20, thinner RVD. For better adhesion of these coatings to 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 sites with templates or by immersion in a bath; in the latter case, the contour is marked on the dried protective film, then it is cut and removed.
3. Chemical dissolution is carried out in baths in compliance with the 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 rinsing in running water at a temperature of 50 + 70 ° C, 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 with soft brushes in a solution of ethyl acetate with gasoline (2: 1). Then produce clarification or light pickling and drying.
The surface quality after chemical milling is determined by the initial roughness of the workpiece surface and etching modes; usually it is 1-2 classes lower than the purity of the original surface. After etching, all defects previously present on the workpiece. (risks, scratches, irregularities) retain their depth, but broaden, acquiring greater smoothness; the deeper the etching depth, the more pronounced these changes are. The surface quality is also influenced by the method of obtaining the workpieces and their heat treatment; a rolled material gives a better surface than a stamped or extruded material. A large surface roughness with pronounced irregularities is obtained on cast blanks.
Surface roughness is influenced by material structure, grain size and grain orientation. Hardened and aged aluminum sheets have a higher surface finish grade. If the structure is coarse-grained (for example, the metal is annealed), then the finished surface will have large roughness, uneven, bumpy. The most suitable for chemical treatment should be considered a fine-grained structure. It is better to treat carbon steel blanks by chemical milling before quenching, since in the case of hydrogenation during pickling, subsequent heating helps to remove hydrogen. However, it is advisable for thin-walled steel parts to be hardened before chemical treatment, as subsequent heat treatment can cause them to deform. The chemical milled surface is always somewhat loosened due to etching, and therefore this method significantly reduces the fatigue characteristics of the part. Considering this, for parts operating under cyclic loads, it is necessary to polish after chemical milling.
Accuracy of chemical milling ± 0.05 mm. depth and not less than +0.08 mm along the contour; the radius of curvature of the notch 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; at a greater depth of cut, the surface quality and machining accuracy deteriorate sharply. The minimum final thickness of the sheet after etching can be 0.05 mm, therefore, chemical milling can be used to machine parts with very thin bridges without warping, to process them on a cone by gradually immersing the part in the solution. If it is necessary to etch from both sides, it is necessary either to position the workpiece vertically so as to allow the evolved gas to rise freely from the surface, or etch in two steps - 1 first on one side and then on the other. The second method is preferable, since with a vertical position of the workpiece, 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 treated surface that interferes with the normal process. Control of depth, etching during processing is carried out by immersion. Simultaneously with the preparation of control samples, direct control of dimensions with thickness gauges such as an indicator bracket or electronic, as well as through automatic weight control.
Chemical milling performance is determined by the rate at which material is removed in depth. The etching rate increases with an increase in the temperature of the solution by about 50-60% for every 10 ° C, and also depends on the type of solution, its concentration and purity. Stirring the solution during the etching process can be done with compressed air. The etching process is determined by an exothermic reaction, therefore, the supply of compressed air cools it somewhat, but mainly the constancy of temperature is ensured by placing water coils in the bath.
Immersion etching has a number of disadvantages - manual labor, partial breakdown of protective films on untreated surfaces. When processing a number of parts, the jet etching method is more promising, in which the supply of alkali is carried out by nozzles.
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, the processing productivity increases by 1.52.5 times - up to 10 mm / h. The chemical treatment process is also significantly accelerated by the directional infrared radiation. Under these conditions, there is no need to apply protective coatings, since the metal is subjected to strong heating along a given heating circuit, the rest of the sections, being cold, practically do not dissolve.
The etching time is set empirically on control samples. The etched workpieces are removed from the pickling machine, washed in cold water and treated at a temperature of 60-80 ° C in a solution containing 200 g / l of caustic soda to remove the emulsion, paint and glue BF4. The finished parts are thoroughly washed and dried in a stream of air.
Improving conditions for roughing workpieces by cutting by first removing the skin by pickling is another example of the dissolving effect of a reagent. Before pickling, the workpieces are blasted with sand in order to remove scale. Etching of titanium alloys is carried out in a reagent consisting of 16% nitric and 5% hydrofluoric acids and 79% water. According to foreign literature, etching in salt baths is used for this purpose, followed by rinsing in water and then repeated etching in acid etchants for final cleaning of the surface.
The chemical action of the technological environment is also used to improve the processes of conventional cutting; Methods of material processing based on a combination of chemical and mechanical action are finding more and more widespread use. Examples of already mastered methods are the chemical-mechanical method of grinding hard alloys, chemical polishing, etc.