Processing of hard materials. Hard alloy

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Five-spindle machine from Fives.
Fives Cincinnati XT copy router equipped with five spindles for machining titanium parts

New Kennametal spindle connections improve the reliability and productivity of Cincinnati's high-volume contour milling machine for titanium parts.

In a time of resilience in demanding industries such as civil aircraft manufacturing, the entire supply chain is under rigorous scrutiny. This is due to the need to maintain high standards quality and meeting deadlines.

This is familiar to Fives Cincinnati's machine builder: The company's Hebron, Kentucky plant manufactures Cincinnati's multi-tasking machines, composite fiber winding systems and multi-spindle contour milling machines. The company, which has 650 contour milling machines in operation worldwide, claims that every jet aircraft used in civil aviation has been manufactured using Cincinatti's contour milling technology in one way or another.

The center of the highest activity.
Work area of Fives Cincinnati XT five-spindle copy-milling machine

The latest generation of Cincinnati XTi machines, with the option of a three- or five-spindle gantry layout, is impressive in many ways. They have been designed for companies involved in the processing various kinds materials. Thus, 7000 rpm spindles can cut aluminum and steel, while high torque spindles (2523 Nm) can cut titanium and other hard alloys. What's more, the company bills XTi as "the only multi-spindle platform for titanium roughing" and claims its 100 cubic inches per minute metal removal rate is industry-leading.

For XTi with travel of 4267mm (increased by 3658mm) in X-axis, 3683mm in Y-axis and 711mm in Z-axis, Kennametal Inc. KM4X100 spindle connections can now be selected.

The hardness of titanium when it is contoured or milled with finer or coarser pitches constantly creates a challenge in terms of metal removal. Efficiency gains in carbide machining require maximum metal removal rates despite high forces and low cutting speeds.

The connection to delete.
The KM4X100 spindle connection plays an important role in achieving top speed metal removal

Fives Cincinnati, like other machine builders, has responded to this challenge by increasing machine rigidity and dampening performance. These improvements have minimized the vibration that negatively impacts part quality, output and tool life, while increasing productivity. However, the tool-spindle connection is still a structural element that requires greater reliability and durability.

The amount of material removed during a particular operation is determined by the secure connection between the machine and the cutting tool, which must withstand high loads, remaining strong enough even in the event of severe bending of the tool or the occurrence of vibrations.

More stable metal removal rate (MRR).
Thanks to the combination of high clamping force and optimal level interference KM4X provides a strong spindle connection with high rigidity and maximum resistance to bending loads. This improves the reliability and productivity of the machine when machining hard alloys and other materials.

Spindles are capable of transmitting a certain amount of torque, while cutting forces also create bending moments that exceed the limits set for the connection even before reaching the maximum torque. This is seen in face milling where the overhang is usually longer and the limiting factor is the bending resistance of the spindle connection. For example, an 80mm helical cutter with 250mm protrusion from the spindle nose generates a bending moment of 4620Nm and a torque of up to 900Nm when cutting Ti6Al4V at 360cm3/min, cutting width 12.7mm and cutting depth of 63.5 mm.

Combining high clamping force and optimum interference levels, the company's new generation of KM4X spindle connections provide reliability, extremely high rigidity and significant resistance to bending forces. In the case of titanium machining tools, this means a significant increase in machine productivity when machining hard alloys, the ability to develop incredibly high metal removal rates and produce more finished parts per shift.

Fives Cincinnati Analyst Robert Snodgrass, along with Kennametal's General Account Manager Mike Malott, began looking into the KM4X's specifications about 4 years ago. “The engineering concept struck me,” Snodgrass recalls. “She made it clear to us that the possibilities of machine design are endless: increased spindle rigidity not only allows us to meet customer requirements for more efficient process cutting, but also to increase the volume of products.

Progress in contouring.
Titanium contouring process

Mark Huston, vice president of Kennametal, explains: “It should be remembered that typical aircraft structural components are made from forgings, with significant material removal to obtain finished parts with the required parameters. The material utilization ratio - the ratio of the weight of purchased raw materials to the weight of the finished part - can be 4:1, 8:1 or even more, depending on the part.

Due to their design and the limitations of the spindle connection, the first generation of Cincinnati contour milling machines were capable of metal removal rates of up to 4 cubic inches per minute when machining titanium parts. The new generation of Cincinnati XT machines, combined with the HSK 125 spindle end connection, increased this speed to 50 inches, and with the introduction of the KM4X100, it was able to double it to 100 cubic inches per minute.

“Even at 100 cubic inches per minute, XT machine tool evaluation results using the KM4X were far below theoretical bending moment limits,” added Snodgrass. Noting that the previous generation was tested using CAT60 taper toolholders, he compared using the 50 taper version to "driving a tank and an SUV." The KM4X connection helped achieve twice the metal removal rate of a 60-taper tool post. Compared to CAT50, HSK100 or KM4X100, CAT60 weighs almost twice as much.

Maximum torque, maximum power.
During the test run, the spindle connection is tested with maximum torque and cutting forces. However, this is not a problem for the Fives Cincinnati XT contour milling machine with KM4X spindle connection.

Fives Cincinnati Product Manager Ken Wichman commented, “This is a game changer in spindle and machine tool design. Many gantry machines use manual tool change, even with an auto changer/magazine. The increased bending moment resistance of the KM4X allows the use of lighter tools than CAT or HSK with the same tool life. Ergonomically, this is a huge advantage for the operator. For a customer who opts for an automatic tool changer, the KM4X will fit more tools into the available space.”

The issue of finishing hardened steel is solved in modern production mainly abrasive. Until recently, this was explained different levels equipment for grinding and blade processing. Lathes could not guarantee the same accuracy that was achieved on grinding machines. But now modern machines CNC machines have sufficient motion accuracy and rigidity, so the share of turning and milling of hard materials is constantly expanding in many industries. Turning of hardened blanks has been used in the automotive industry since the mid-eighties of the last century, but today a new era begins in this type of processing.

Heat treated blanks

Many steel parts require heat treatment or surface hardening to obtain additional wear resistance and the ability to withstand significant loads. Unfortunately, high hardness adversely affects the machinability of such parts. Gear parts and various shafts and axles are typical hardened parts that are turned, milled and hardened by dies and molds. Heat-treated parts - rolling elements, as a rule, require finishing and finishing, which removes shape errors and provides the required accuracy and surface quality. As far as die and mold parts are concerned, there is now a tendency to process them in a hardened state already at the roughing stage. This results in a significant reduction in die production time.

Processing of hard materials

The processing of parts after heat treatment is a matter that requires a flexible approach. The range of solutions depends on the type of tool material chosen for processing. For a tool, the ability to process hard materials means high heat resistance, high chemical inertness, and abrasion resistance. Such requirements for tool material are determined by the machining process itself. When cutting hard materials, high pressure is applied to the cutting edge, which is accompanied by the release of a large amount of heat. Higher temperatures aid the process by weakening the chips, thereby reducing cutting forces, but have a negative effect on the tool. Therefore, not all tool materials are suitable for processing heat-treated parts.

Carbide grades are used to machine materials with hardness up to 40HRc. For this, fine-grained hard alloys with a sharp cutting edge are recommended, which resist abrasive wear well and have high thermal and plastic deformation resistance. Uncoated carbide grades such as H13A from Sandvik Coromant have such properties. But it is also possible to successfully use grades with wear-resistant coatings for finishing and P05 and K05 applications, such as GC4015, GC3005.

The most inconvenient workpiece for machining is a workpiece with a hardness of 40…50HRc. Hard alloys when working in this range are no longer satisfied with their heat resistance. At the same time, CBN and ceramic wear out quickly, because due to insufficient hardness of the material being processed, a build-up is formed on the front surface of the tool, causing chipping of the cutting edge when it is torn off. Therefore, the problem of choosing a tool material for working in this range of hardness is solved on the basis of economic considerations. Depending on the serial production, one has to either put up with low productivity and dimensional accuracy when working with a hard alloy, or work more productively with ceramics and CBN, but with the risk of breaking the insert.

With a higher hardness of 50-70HRc, the choice clearly leans towards machining using a tool with a cutting part made of ceramic or cubic boron nitride. Ceramic allows even interrupted machining, but provides a slightly higher surface roughness than CBN. With CBN machining, roughness up to 0.3Ra can be achieved, while ceramic creates a surface roughness of 0.6Ra. This is explained by different models of tool material wear: under normal conditions, CBN has uniform wear along the flank surface, and microchipping is formed on ceramics. In this way, CBN keeps the line of the cutting edge continuous, which allows you to get the best values for the roughness of the machined surface. Cutting conditions in the processing of hardened materials varies over a fairly wide range. This depends on the material of the workpiece, the machining conditions and the required surface quality. When machining a workpiece with a hardness of 60HRc with new grades of cubic boron nitride CB7020 or CB7050, the cutting speed can reach 200 m/min. CB7020 is recommended for finishing with continuous cutting, and CB7050 for finishing heat treated materials under adverse conditions, i.e. with blows. Plates from these grades are produced with a thin coating of titanium nitride. According to Sandvik Coromant, this measure makes it much easier to control insert wear. The company also produces plates from similar grades of cubic boron nitride CB20 and CB50, but without coating.

Various grades of ceramics are commonly used for machining hardened steels. Sandvik Coromant currently produces all types of ceramics and is actively developing new grades. CC 620 oxide ceramics are produced on the basis of aluminum oxide with small additions of zirconium oxide to increase strength. It has the highest wear resistance, but can only be used in good conditions due to low strength and thermal conductivity. More versatile is the CC650 mixed ceramic based on aluminum oxide with additives of silicon carbide. It has higher strength and good thermal conductivity, which allows it to be used even with interrupted processing. The so-called whiskered ceramics CC670 has the highest strength. The composition of which also includes silicon carbide, but in the form of long crystalline fibers that penetrate the base material. The main area of application of this ceramic grade is the machining of nickel-based heat-resistant alloys, but due to its high strength, it is also used for machining hardened steel under adverse conditions. The cutting conditions when using ceramic inserts, as well as in the case of cubic boron nitride, vary widely. This is explained to a greater extent not by differences in the properties of the tool material, but by a variety of processing conditions, when sufficient heating is achieved in the cutting zone and, accordingly, a decrease in effort and wear. Usually the optimal cutting speed is in the range of 50-200 m/min. Moreover, a decrease in cutting speed does not necessarily lead to an increase in tool life, as is the case with a hard alloy.

New opportunities

Productivity in the machining of hardened materials has so far been achieved by changing the design of the tool and improving the equipment. Now, new tool materials allow you to work at high speeds, and the geometry of the cutting part to achieve high values of working feeds. In addition, the ability to machine parts in one setup when turning or milling results in a significant reduction in non-productive time.

The amount of feed depends on the geometry of the cutting tool tip. For tools with a radius-shaped tip, the feed is rigidly related to the requirement to provide a given surface quality. The usual feed rate is 0.05…0.2 mm/rev. But now plates called Wiper have appeared on the market, which allow you to increase it. When machining with such inserts, the feed value can in practice be doubled without affecting the surface quality. The wiper effect is created by modifying the insert tip and creating a special large-radius wiper edge that is a continuation of the main fillet radius. The wiper cutting edge provides a minimum auxiliary angle in the insert when working, which allows you to increase the working feed without losing the quality of the machined surface. By doubling the feed rate, the cutting path is also reduced, and, accordingly, the wear of the insert. The revolutionary nature of this solution is that an increase in productivity is achieved simultaneously with an increase in tool life.

Wiper inserts were first introduced by Sandvik Coromant and are now becoming more and more common. So, for CBN and ceramic inserts, there are already two options for the Wiper geometry. Geometry WH - the main geometry that allows you to achieve maximum performance. The optional WG geometry creates low cutting forces and is used for high speed machining with high demands on the quality of the machined surface.

CBN and ceramic Wiper inserts take finishing and finishing of hardened materials to new levels of productivity.

The main advantages of turning hardened materials:

high productivity due to high cutting speeds and reduced non-productive time;
high flexibility of application;
the process is easier than grinding;
no burns;
minimal distortion of the workpiece;
additional productivity gains due to high feed rates when using wiper inserts;
the possibility of unification of equipment for the complete processing of the part;
safe and environmentally friendly processing.

One of the most effective ways cutting and processing of hard materials is waterjet cutting. It can cut hard materials such as marble and granite, metal, concrete and glass. This type cutting is widely used in construction in the processing of composite and ceramic materials, sandwich structures.

The waterjet cutting method consists in a narrowly directed jet of water under high pressure, hitting the material at high speed. Initially, only water was used, and the method was called water jet cutting. It was used for processing not too hard materials, which required a more delicate effect than other types of cutting. It was optical fiber and cables, laminated materials that did not tolerate high temperatures and the occurrence of a fire hazard.

Later, an abrasive was added to the water, which significantly increased the cutting power of the water jet. Finely dispersed garnet sand is used as an abrasive. With the use of abrasive particles, it has become possible to cut much harder materials such as rocks and metals.

In this regard, waterjet cutting is widely used in various industries, in construction and in the manufacture of monuments. Granite is often used for the manufacture of monuments, and the prices for monuments in Moscow allow you to make a choice for any budget. However, not everyone thinks that when ordering a monument, not only the cost of material and work matters, but also the method of processing.

Waterjet cutting can be called very gentle in the sense that there is no intense impact on the material, which means that its strength is not reduced. To order monuments, prices are formed based, among other things, on the method of cutting and processing stone. Waterjet cutting avoids cracks and chips and minimizes stone loss during processing. This is just one of the benefits of waterjet cutting.

Waterjet cutting: advantages and features

1. No strong heating of the material

This parameter is critical for both metal and natural and artificial stone, tiles. When cutting with a water jet with an abrasive, the temperature is maintained in the range of 60-90ºС. Thus, the material is not exposed to high temperatures, as with other types of cutting, which increases its service life.

2. Versatility of application

With the help of a waterjet "blade" it is possible to equally successfully cut both hard and medium-hard materials. True, in the case of working with the latter, it is not necessary to use an abrasive.

3. Excellent cut quality

The cut edge roughness when using water jet cutting is Ra 1.6. Using this method will help to get a clear cut without excess dust and loss of material.

4. Fire safety

All components used in cutting are fire and explosion-proof, including due to low temperature. When cutting, flammable substances are not used, which significantly reduces the risk during work.

5. No material melting

This property also follows from the temperature at the cut. When cutting, the material does not burn either in adjacent areas or directly on the cut, which is especially important when working with metals.

6. Multi-use

Using waterjet cutting, it is possible to cut both a sheet of steel with a thickness of 200 mm, and many thin sheets stacked together. This saves time and increases productivity.

The disadvantages include the high cost of consumables (namely sand) and the limited resource of the cutting head and some other components of the machine. The waterjet cutting machine consists of a pump (several) in which water is injected at a pressure of up to 4000 bar, a nozzle, a mixing chamber and a second carbide nozzle.

How waterjet cutting works:

With the help of a pump, water is pumped under pressure up to 4000 bar;

FRAGMEHT BOOKS (...) § 81. CUTTING OF CERAMIC MATERIALS AND COATINGS
Machining of ceramic-metal parts (cermets), the workpieces of which are obtained by powder metallurgy, occupies a significant place in their manufacture. This is explained, on the one hand, by the need to obtain more complex shapes than pressing allows, for example, parts with two collars, holes perpendicular to the movement of punches, and mutually intersecting axes, recesses, chamfers, grooves, threads, and, on the other hand, obtaining products with an accuracy of more than 4 - 5 classes, as well as cheaper production in cases where it is easier to apply cutting than using complex molds.
Hard alloys are a very common type of cermet materials; they are used to make, for example, stamps, tools. For their cutting, electroerosive, anode-abrasive, ultrasonic and mechanical processing are most often used.
The electroerosion method is an effective means of processing hard alloys. Hard alloys are well cut by high-frequency EDM using a continuously moving wire as a tool. So, the VK20 alloy is processed with a copper wire with a diameter of 0.2 mm with a tension of 500 g at a rewind speed of 3 mmmin in microfarad modes, the resulting processing speed with a part thickness of 5 mm is 0.65 mmmin.
Anodic abrasive processing is used for the manufacture of high-precision carbide parts. To do this, conventional modernized grinding machines are powered from DC sources (machine generators or rectifiers) with a voltage of 25–30 V. The working medium is a mixture of oils. A step change in the current strength within 3 - 800 A sets a sequential change in the processing conditions from roughing, which ensures the removal of the main allowance and cleanliness of the 5th class, To finishing, giving cleanliness of the 9th class; then finishing with an abrasive is carried out up to the 11th class. Anode-abrasive treatment is used for sharpening carbide tools (Table 77 - data from A. G. Ryabinyuk).
Machining of hard alloys is carried out with blade and abrasive tools. The main method of processing hard-alloy inserts for cold heading tools is abrasive and diamond grinding: it is used to obtain flat, round outer and inner (P> 5-g-8 mm) and also shaped surfaces and provides, with a productivity of 40 - 100 mm3 min, the accuracy of the 1st class and surface cleanliness up to the 13th class.
Obtaining cylindrical outer surfaces on parts made of hard alloys is carried out by grinding with green silicon carbide wheels and diamond wheels, and cutting off workpieces - with diamond cutting wheels and the electroerosive method. The removal of the material of the cut layer when grinding hard alloys with green silicon carbide wheels occurs by pulling out of the base material, crushing and splitting tungsten carbide grains. These processes are accompanied by a high temperature (~ 1500°C), which causes softening and melting of the relatively lower-melting cobalt bond, its oxidation, and the formation of microcracks. These phenomena lead to poor quality surfaces. In diamond grinding, due to the high hardness and sharpness of the cutting edges, material is removed by cutting; the temperature in the cutting zone in this case is much lower (500 - 600°C); all this contributes high quality surfaces.
The blade tool in a number of operations for the manufacture of products from hard alloys shows high efficiency. It has been established that hard alloys in a state of all-round uneven compression can be plastically deformed. The deformation proceeds by displacement of individual blocks of crystallites of the carbide phase, shifts in them, as well as crushing of carbide grains. The process of cutting hard alloys, as well as other materials, is based on the difference in hardness between the workpiece and the tool; however, they have a small degree of plastic deformation in the chip formation zone. When processing alloys with a cobalt content of more than 15%, a fracture chip is formed, individual pieces of which consist of sheared layers. The cutting temperature of hard alloys is 300 - 370 ° C; this ensures the absence of microcracks and structural transformations. The surface layer of the hard alloy after cutting is a compacted thin layer, under which there are alloy grains that have undergone shearing, chipping and plastic deformation.
Turning of hard-alloy inserts of dies from VK20, VK25 alloys is carried out with cutters equipped with VKZM alloy plates, which are strengthened by soldering brass “7162. The following modes are recommended: for rough turning t=0.2 - 0.5 mm,
so \u003d 0.3-j-0.5 mmob, v \u003d 2-1-3 mmin for finishing \u003d 0.2 - 0.3 mm, s0 \u003d 0.08-i-0.12 mmob, o \u003d 3 - 4 mm. The cutting is carried out in the modes so=0.05 mmob, o=4-5 mm.
Ceramic-metal porous materials are widely used for the manufacture of plain bearings; according to the level of permissible cutting speeds, they are also classified as difficult to machine. So, if the cutting speed corresponding to the 20-minute resistance of a hard-alloy (VK8) cutter, when machining molybdenum is 100 mm, then when turning porous iron graphite grade ZhGZ, it does not exceed 25 - 45 mm. The most common porous materials based on iron and copper. Iron-based materials have irregularly shaped pores that communicate with each other. Bronze graphite is characterized by spheroidal pores, isolated from each other, as a result of which, when machining deformation of the surface layer is greater.
Cutting porous materials is difficult due to the instability of the cutting process due to the discontinuity of the material, low thermal conductivity, leading to high temperatures in the cutting zone (up to 600 ° C), increased tendency to oxidation; the resulting iron oxides have an increased abrasive effect on the tool.
In terms of machinability, porous materials are closer to cast irons; tool wear during their processing also occurs only on the back surface. Taking into account the deterioration of the antifriction properties of bearings when machining with a blunt tool, the blunting criterion is relatively small: r3 = 0.4-0.5 mm.
The requirements for machining are determined by the purpose of the surface - for sliding surfaces, free access of lubricant to the friction zone is required, i.e., a slightly deformed surface; for fixed joints, a sealed surface is needed that provides the necessary mating strength. Therefore, the processing modes according to the quality of the resulting surface are divided into non-compacting and sealing.
Hard alloys of grades VK8, VKZM, VK6M are most suitable for processing porous materials. The cutting speed when machining porous cermet materials should be high enough to go beyond the built-up edge zone and provide uniform roughness with moderate work hardening of the surface layer material. Taking this into account, with a porosity of the processed material of 15%, the cutting speed is 85 - 250 mSmuh, with a porosity of 20% v = 100 - 400 mmin, with a porosity of 30% u = 110 - 500 mmin. Feeds should be small: when processing highly porous materials (more than 25%) s0 = = 0.035 mmob, low-porous - so=0.07 mmob.
Ceramic-metal materials obtained by flowing down a mixture of powders of metals and their alloys (AI2O3 - Al, AI2O3 - Cr, TiC - Ni, ZrC - Fe, Si - S) find significant industrial application; the machinability of even such low-strength materials as iron graphite (Fe +, + Cu + C), as a rule, is much worse than steel 40 X and gray cast iron SCH 15 - 32. This is due to the fact that when turning these materials, the cutting temperature is high, despite their lower--; which strength and ductility, as well as the magnitude of the acting cutting forces. An increase in temperature is obtained due to a significantly lower (1.5 - 2 times) thermal conductivity. In addition, poor machinability is due to their higher abrasion ability and also unfavorable working conditions of the tool material due to the periodic fatigue action of the pores.
The machinability of cermet materials is determined primarily by the structure; materials with a ferritic structure have the best machinability, then, in order of deterioration, there are frito-pearlitic, pearlitic and pearlitic structures with the inclusion of cementite. The shape of the cementite particles included in perlite has a significant effect on machinability; granular perlite provides better tool life than lamellar perlite. This is explained by the fact that the cutting temperature increases with an increase in the content of pearlite and cementite inclusions in the structure of metal-ceramic materials and, conversely, decreases with an increase in the amount of ferrite. In addition, the ratio of the abrasive ability of cermet materials with different structures is similar to ordinary steels; granular perlite shows the least abrasion ability, lamellar pearlite shows the highest.
The machinability of cermet products also depends on their porosity and the degree of impregnation with oil; increasing the porosity from 15 to 30% increases the cutting speed v60 when turning workpieces impregnated with oil by 50% and unimpregnated by 20%. This is explained by the fact that an increase in porosity leads to a decrease in cutting temperature by 154-20°. Oil impregnation also increases the o6o value from 20% (for the same 15% porosity) to 50% (for 30% porosity). The effect of oil impregnation on increasing the cutting speed is greater for cermet materials that do not contain graphite, since in the latter case the cutting temperature is 1.4-4-1.5 times higher. This is due to the fact that graphite plays the role of a lubricant, while the effectiveness of the lubricating and cooling effect of the oil decreases. When using oil impregnation as a means of increasing productivity, it must be taken into account that it worsens the sanitary and hygienic conditions of the operation, since the oil burns out during the cutting process and its balls pollute the atmosphere.
Metal coatings are widely used as a means of improving the heat-resistant, wear-resistant and anti-corrosion characteristics of parts. Coatings are applied in various ways, usually by spray electroplating. Most often, the processing of coatings by cutting is carried out by turning and grinding; this is due to the peculiarities of the processed products, as well as the fact that the processing of coatings by other methods (drilling, milling, planing) is associated with certain difficulties due to intense chipping of the treated layer.
A distinctive feature of the structure of metal coatings is their layering - metal particles are strongly elongated and separated from each other by oxide films. In addition, the material has a large porosity and heterogeneity of the structure, it contains oxides, nitrides and other chemical compounds with high hardness. The sprayed metal is more brittle than the original one. The hardness of the sprayed metal is much higher than the original one. So, when applying low-carbon steel, the hardness of the coating is 35-60% higher, and the microhardness due to the presence of pores and cracks is even greater (several times). All this brings the properties of coatings closer to those of cast metal; however they have their specific features. Characteristic features machining of metal coatings are:
1) fragility of the processed material; causes a specific chip formation process (see page 46), where the loads from the cutting process are concentrated directly at the cutting edge. The stress concentration causes increased wear of the cutters at the tip. In order to avoid chipping of the surface layer, sharp edges and sharp transitions should not be processed on parts;
2) high abrasion (abrasive) effect on the working surfaces of the tool; it is due to the presence in the treated coating of the smallest inclusions of high hardness, which also prevent plastic deformation in the process of chip formation; %
3) reduced thermal conductivity of coatings due to their porosity and the presence of oxides; as a result, when cutting coatings, burns often occur; to eliminate them, effective coolants should be used;
4) the difficulty of obtaining surfaces high purity due to the specific structure of the metallization layer. Tool wear during machining causes local destruction of the coating surface: its chipping, flaking, and the appearance of scales.
Sanding of coatings has distinguishing feature- quick salting of the circle; in addition, the reduced thermal conductivity of coatings during grinding often leads to the formation of burns. To avoid this, liquids with an effective cooling effect should be used.

Choice of a bunch of abrasive tools

The bond determines the strength and hardness of the tool, has a great influence on the modes, productivity and quality of processing. Ligaments are inorganic (ceramic) and organic (bakelite, volcanic).
CERAMIC BOND It has high fire resistance, water resistance, chemical resistance, retains the profile of the working edge of the wheel well, but is sensitive to shock and bending loads. Vitrified bonded tools are used for all types of grinding, except for roughing (due to the brittleness of the bond): for cutting and cutting narrow grooves, flat grinding of grooves of ball bearing rings. The vitrified bonded tool retains its profile well, has high porosity, and removes heat well.
BAKELITE BOND has higher strength and elasticity than ceramic. Bakelite bonded abrasive tools can be made various forms and sizes, including very thin ones - up to 0.5 mm for slotted work. The disadvantage of the bakelite bond is the low resistance to the action of coolants containing alkaline solutions. When using a bakelite bond, the coolant must not contain more than 1.5% alkali. The bakelite bond has a weaker adhesion to the abrasive grain than the ceramic bond, so the tool on this bond is widely used in flat grinding operations where self-sharpening of the wheel is necessary. Bakelite bonded tools are used for rough roughing work performed manually and on suspended walls: flat grinding with the end of a circle, cutting and cutting grooves, sharpening tools, when processing thin products where burning is dangerous. Bakelite bond has a polishing effect.

Choice of brand of abrasive material

Abrasives(fr. abrasif - grinding, from lat. abradere - scrape off) - these are materials with high hardness and used for surface treatment of various materials. are used in the processes of grinding, sharpening, polishing, cutting materials and are widely used in blank production and final processing of various metal and non-metal materials. Natural abrasives - flint, emery, pumice, corundum, garnet, diamond and others. Artificial: electrocorundum, silicon carbide, borazone, elbor, synthetic diamond and others.

ELECTROCORUNDUS NORMAL

It has excellent heat resistance, high bond adhesion, mechanical strength of the grains and significant toughness, which is important for operations with variable loads Machining materials with high tear resistance. This is the peeling of steel castings, wires, rolled products, high-strength and chilled cast irons, malleable cast iron, semi-finishing of various machine parts from carbon and alloy steels in non-hardened; and hardened form, manganese bronze, nickel and aluminum alloys. 25A

ELECTROCORUNDUM WHITE

It is more homogeneous in physical and chemical composition, has a higher hardness, sharp edges, good self-sharpening, better eliminates surface roughness in comparison with normal electrocorundum Processing hardened parts made of carbon, high-speed and stainless steels, chrome-plated and nitrated surfaces. Processing of thin parts and tools, sharpening, flat, internal, profile and finish grinding. 38A

ELECTRIC CORUNDUS ZIRCONIUM

Fine-grained, dense and durable material. Tool life in roughing operations is 10-40 times higher than a similar tool made of normal electrocorundum. Rough grinding of steel billets at high speed, feed and clamping force. Power rough grinding of steel workpieces. 54C

SILICON CARBIDE BLACK

It has high hardness, abrasive ability and brittleness. The grains are in the form of thin plates, which increases their fragility in work. Machining hard materials with low tear resistance (cast iron, bronze and brass castings, hard alloys, precious stones, glass, marble, graphite, porcelain, hard rubber, bones and etc.), as well as very viscous materials (heat-resistant steels, alloys, copper, aluminum rubber). 63C

SILICON CARBIDE GREEN

Differs from black silicon carbide in increased hardness, abrasive ability and brittleness For processing parts made of cast iron, non-ferrous metals, granite, marble, hard alloys, processing titanium, titanium-tantalum hard alloys, honing, finishing work for parts made of gray cast iron, nitrided and ball bearing become. 95A

ELECTROCORUNDUS TITANIUM CHROME

It has higher mechanical strength and abrasive ability compared to normal electrocorundum

Rough grinding with high metal removal

Tool Grain Selection

Grain	Type of processing
LargeF6-F24	Peeling operations with a large depth of cut, cleaning of workpieces, castings. Processing of materials that cause clogging of the wheel surface (brass, copper, aluminum).
F24-F36	Flat grinding with the end face of a circle, sharpening of cutters, dressing of abrasive tools, cutting off.
MediumF30 - F60	Preliminary and combined grinding, sharpening of cutting tools.
F46-F90	Fine grinding, processing of profiled surfaces, sharpening of small tools, grinding of brittle materials.
smallF100-F180

Fine grinding, finishing of hard alloys, finishing of cutting tools, steel blanks, sharpening of thin blades, preliminary honing.

Coarse-grained tools are used:
- during peeling and preliminary operations with a large depth of cut, when large allowances are removed;
- when working on machines of high power and rigidity;
- when processing materials that cause the filling of the pores of the circle and the clogging of its surface, for example, when processing brass, copper and aluminum;
- with a large contact area of the wheel with the workpiece, for example, when using high circles, when flat grinding with the end of the circle, when internal grinding.
Medium and fine-grained tools are used:
- to obtain a surface roughness of 0.320-0.080 microns;
- when processing hardened steels and hard alloys;
— at final grinding, sharpening and fine-tuning of tools;
- with high requirements for the accuracy of the processed profile of the part.
With a decrease in the size of abrasive grains, their cutting ability increases due to an increase in the number of grains per unit of the working surface, a decrease in the grain rounding radius, and less wear of individual grains. Reducing the grain size leads to a significant reduction in the pores of the wheel, which makes it necessary to reduce the depth of grinding and the amount of allowance removed during the operation. The finer the abrasive grains in the tool, the less material is removed from the workpiece per unit time. However, fine-grained tools are less self-sharpening than coarser-grained tools, resulting in faster dulling and clogging. The rational combination of the processing mode, tool dressing and grit allows you to obtain high accuracy and excellent surface finish.

Selection of tool hardness

O, P, Q Profile grinding, intermittent surfaces, honing and thread grinding of coarse pitch workpieces. MediumM-N Surface grinding with segments and annular wheels, honing and thread grinding with Bakelite bonded wheels. Medium softK-L Finishing and combined round, external centerless and internal grinding of steel, flat grinding, thread grinding, sharpening of cutting tools. SoftH-F Sharpening and finishing of cutting tools equipped with hard alloys, grinding of hard-to-machine special alloys, polishing.

The hardness of the tool largely determines the productivity of labor during processing and the quality of the machined.
Abrasive grains, as they become blunt, must be renewed by chipping and chipping particles. If the wheel is too hard, the bond continues to hold the grains that have become dull and have lost their cutting ability. At the same time, a lot of power is consumed for work, the products heat up, their warping is possible, traces of cutting, scratches, burns and other defects appear on the surface. If the wheel is too soft, the grains that have not lost their cutting ability crumble, the wheel loses its correct shape, its wear increases, as a result of which it is difficult to obtain parts of the required size and shape. During processing, vibration appears, more frequent dressing of the circle is necessary. Thus, one should responsibly approach the choice of the hardness of the abrasive tool and take into account the characteristics of the workpieces.

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