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How to choose the correct grinding wheel when tool grinding?

How to choose the correct grinding wheel when tool grinding?

Hope 2024-04-30 11:33:01

Abstract There are many types of grinding wheels with various shapes and sizes. Each type of grinding wheel has a certain scope of application depending on the abrasives, bond materials and manufacturing processes of the grinding wheel. Improper selection will directly affect processing accuracy, surface roughness and production efficiency. Therefore, grinding...

 

Grinding wheel Abrasive tools There are many types and come in various shapes and sizes, depending on the grinding wheel Abrasive , bond materials and manufacturing processes, each grinding wheel has a certain scope of application. Improper selection will directly affect processing accuracy, surface roughness and production efficiency. therefore, grinding When processing, the appropriate grinding wheel must be selected according to the specific situation. So how to choose the correct grinding wheel? This article summarizes the grinding wheels commonly used in grinding so that everyone can choose the grinding wheel clearly.

1. Selection of ordinary grinding wheels

1. Selection of abrasives The selection of abrasives mainly depends on the workpiece material and heat treatment method.

a. When grinding materials with high tensile strength, choose abrasives with high toughness.

b. When grinding materials with low hardness and high elongation, use brittle abrasives.

c. When grinding materials with high hardness, choose abrasives with higher hardness.

d. Choose abrasives that are not prone to chemical reactions in the materials being processed.

The most commonly used abrasive is brown corundum (A) and white corundum (WA), followed by black silicon carbide (C) and green silicon carbide (GC), and other commonly used ones include chromium corundum (PA), single crystal corundum (SA), microcrystalline corundum (MA), and zirconium corundum (ZA).

brown corundum Grinding wheel: Brown corundum has high hardness and toughness, and is suitable for grinding metals with high tensile strength, such as carbon steel, alloy steel, malleable iron, hard bronze, etc. This abrasive has good grinding performance and wide adaptability, and is often used Rough grinding that removes larger margins is cheap and can be widely used.

White corundum grinding wheel: The hardness of white corundum is slightly higher than that of brown corundum, and its toughness is lower than that of brown corundum. During grinding, the abrasive grains are easily broken. Therefore, the grinding heat is small, and it is suitable for manufacturing fine grinding quenched steel, high carbon steel, etc. The cost of high-speed steel and grinding wheels for grinding thin-walled parts is higher than that of brown corundum.

Black silicon carbide grinding wheel: Black silicon carbide is brittle and sharp, with a higher hardness than white corundum. It is suitable for grinding materials with low mechanical strength, such as cast iron, brass, aluminum and Refractory materials wait.

Green silicon carbide grinding wheel: Green silicon carbide has higher hardness and brittleness than black silicon carbide, sharp abrasive grains, and good thermal conductivity. It is suitable for grinding hard and brittle materials such as cemented carbide, optical glass, and ceramics.

Chrome corundum grinding wheel: suitable for grinding tools, measuring tools, instruments, threads and other workpieces with high surface processing quality requirements.

Single crystal corundum grinding wheel: suitable for grinding stainless steel, high-vanadium high-speed steel and other materials with high toughness and hardness, as well as workpieces that are prone to deformation and burns.

Microcrystalline corundum grinding wheel: suitable for grinding stainless steel, bearing steel and special ductile iron, etc., used for form grinding, plunge grinding and mirror grinding.

Zirconium corundum grinding wheel: suitable for grinding Austrian stainless steel, titanium alloy, heat-resistant alloy, especially suitable for heavy-duty grinding.

2. The selection of particle size mainly depends on the surface roughness and grinding efficiency of the workpiece to be ground.

Particle size refers to the particle size of the abrasive, and its size is expressed by the particle size number. When grinding with a coarse-grained grinding wheel, the production efficiency is high, but the surface of the ground workpiece is rough; when grinding with a fine-grained grinding wheel, the surface roughness of the ground workpiece is good, but the productivity is low. On the premise of meeting the roughness requirements, coarse-grained grinding wheels should be used as much as possible to ensure higher grinding efficiency. Generally, a coarse-grained grinding wheel is used for rough grinding, and a fine-grained grinding wheel is used for fine grinding.

When the contact area between the grinding wheel and the workpiece is large, a grinding wheel with a coarser particle size should be selected. For example, when grinding the same plane, the end face of the grinding wheel should be ground with a coarser grain size than the peripheral grinding of the grinding wheel.

3. The choice of hardness mainly depends on the workpiece material to be ground, grinding efficiency and machined surface quality.

Hardness refers to the ease with which abrasive grains of a grinding wheel fall off under the action of external force. In order to adapt to the grinding requirements of different workpiece materials, grinding wheels are manufactured into different hardness levels.

If the grinding wheel is chosen too hard, the dull abrasive grains will not fall off easily, the grinding wheel will be easily clogged, the grinding heat will increase, the workpiece will be easily burned, and the grinding efficiency will be low, affecting the surface quality of the workpiece; if the grinding wheel is chosen too soft, the abrasive grains will fall off while they are still sharp. , which increases the wear of the grinding wheel and easily loses the correct geometric shape, affecting the accuracy of the workpiece. Therefore, the selection of the grinding wheel hardness should be appropriate, and should also be comprehensively considered based on factors such as the contact area between the grinding wheel and the workpiece, the shape of the workpiece, the grinding method, the cooling method, the type of bonding agent of the grinding wheel, and other factors.

The following grinding wheel hardness selection principles are for reference:

a. When grinding soft materials, choose a harder grinding wheel, and when grinding hard materials, choose a soft grinding wheel;

b. When grinding soft and tough non-ferrous metals, the hardness should be softer;

c. When grinding materials with poor thermal conductivity, softer grinding wheels should be selected;

d. When end face grinding is compared with circumferential grinding, the hardness of the grinding wheel should be softer;

e. Under the same grinding conditions, the hardness of a resin-bonded grinding wheel is 1 to 2 grades higher than that of a ceramic-bonded grinding wheel;

f. When the grinding wheel rotation speed is high, the hardness of the grinding wheel can be selected from 1 to 2 small grades softer;

g. Grinding with coolant has a grinding wheel hardness that is 1 to 2 grades higher than that of dry grinding.

 

4. The selection of bonding agent should be considered based on conditions such as grinding method, usage speed and surface processing requirements.

The most commonly used grinding wheel bonds are vitrified bond (V) and resin bond (B).

Ceramic bond is an inorganic bond with stable chemical properties, good heat resistance, corrosion resistance, and large porosity. The grinding wheel made with this bond has high grinding efficiency, low wear, and can better maintain the geometric shape of the grinding wheel. , has the widest range of applications. The grinding wheel is suitable for grinding ordinary carbon steel, alloy steel, stainless steel, cast iron, carbide, non-ferrous metals, etc. However, vitrified bonded grinding wheels are relatively brittle and cannot withstand severe vibrations. Generally it can only be used at speeds within 35 meters/second. .

Resin bond is an organic bond. The grinding wheel made with this bond has high strength, certain elasticity, low heat resistance, good self-sharpening, easy production, and short process cycle. It can manufacture grinding wheels with working speeds higher than 50 m/s and very thin grinding wheels. Its application scope is second only to ceramic bonding agent, and it is widely used in rough grinding, waste grinding, cutting off and free grinding, such as grinding steel ingots, deburring castings, etc. It can manufacture high-speed, high-finish grinding wheels, heavy-duty, cutting-off and various special requirements grinding wheels.

5. The selection of tissue mainly considers the pressure on the workpiece, grinding method, workpiece material, etc.

Structure refers to the percentage of abrasive grains in the grinding wheel that accounts for the volume of the grinding wheel. The grinding wheel structure grade is divided into 62% abrasive grain volume percentage as "0" structure. Every time the abrasive grain volume decreases by 2%, the structure increases by one size, and so on, and is divided into 15 numbers in total. The larger the number, the looser the organization.

A grinding wheel with a tight structure can grind a better workpiece surface, while a grinding wheel with a loose structure can ensure that grinding debris is accommodated during the grinding process and avoid clogging of the grinding wheel due to its large gaps. Generally, when rough grinding and grinding softer metals, the grinding wheel is easy to clog, so a loose-structured grinding wheel should be selected; in form grinding and precision grinding, in order to maintain the geometry of the grinding wheel and obtain better roughness, a denser-structured grinding wheel should be used. Grinding wheel; when grinding machine tool guide rails and carbide tools, in order to reduce thermal deformation of the workpiece and avoid burn cracks, a loose-structured grinding wheel should be used; for grinding heat-sensitive materials, non-ferrous metals, and non-metallic materials, a grinding wheel with a structure larger than 12# should be used Grinding wheel.

6. The selection of shape and size should be based on the grinding machine conditions and the shape of the workpiece.

Commonly used grinding wheel shapes include flat grinding wheel (P), single-sided concave grinding wheel (PDA), double-sided concave grinding wheel (PSA), flake grinding wheel (PB), cylindrical grinding wheel (N), bowl-shaped grinding wheel (BW), dish-shaped No. 1 Grinding wheel (D1), etc.

Each grinder has a range of wheel shapes and sizes that can be used. When possible, the outer diameter of the grinding wheel should be selected as large as possible to increase the linear speed of the grinding wheel and obtain higher productivity and workpiece surface quality. The same effect can be obtained by increasing the width of the grinding wheel. .

The writing order of the current national standard grinding wheel: grinding wheel code, size (outer diameter × thickness × hole diameter), abrasive grain, particle size, hardness, structure, bonding agent, and maximum working line speed.

Example: P400×150×203A60L5B35

two, diamond Grinding wheel selection

Diamond grinding wheels have sharper edges, less wear, longer life, higher productivity, and better processing quality than grinding wheels made of general abrasive grains such as boron carbide, silicon carbide, corundum, etc., but are expensive, so they are suitable for fine grinding of cemented carbide and ceramics. , semiconductors and other high-hardness, brittle, difficult-to-machine materials. .

Characteristics of diamond grinding wheels include abrasive type, particle size, hardness, concentration, bond, and wheel shape and size.

Abrasives: Synthetic diamond (JR) is widely used. It is divided into various types according to its crystal shape and particle strength, and the type is selected according to its specific use.

Particle size: It should be comprehensively considered from three aspects: workpiece roughness, grinding productivity and diamond consumption.

Hardness: Only resin-bonded diamond grinding wheels have the property of "hardness". Generally, S (Y1) level or higher is used.

Bonding agent: There are four commonly used bonding agents. Their bonding ability and wear resistance are in the order of resin, ceramics, bronze and electroplated metal, and the order is getting stronger. Resin bonded diamond grinding wheels have high grinding efficiency, good roughness of the workpiece to be processed, wide application range, good self-sharpening properties, not easy to clog, low heat generation, easy to trim, and are mainly used in fine grinding processes. Ceramic bond diamond grinding wheels are mainly used for grinding various non-metallic hard and brittle materials, cemented carbide, superhard materials, etc.

Concentration: The concentration selection depends on the particle size, binder, shape, processing method, production efficiency and grinding wheel life requirements of the grinding wheel. High-concentration diamond grinding wheels have a strong ability to maintain the shape of the grinding wheel. When grinding with low-concentration grinding wheels, diamond consumption is often lower and should be selected according to needs.

Shape and size: Select according to the shape, size and machine tool conditions of the workpiece.

 

3. Selection of cubic boron nitride (CBN) grinding wheels

The cubic boron nitride (CBN) grinding wheel has only a thin layer of cubic boron nitride particles adhered to the surface of the ordinary grinding wheel. Its abrasive grain toughness, hardness and durability are 100 times that of corundum grinding wheels. It is most suitable for processing high hardness and stickiness. Large, difficult-to-grind steel materials with high high-temperature strength and low thermal conductivity and high-speed or ultra-high-speed grinding. Its application range and artificial diamond play a complementary role. Diamond grinding wheels have unique effects when grinding carbide and non-metallic materials, but when grinding steel materials, especially when grinding special steel, the effect is not significant. The efficiency of cubic boron nitride grinding wheels in grinding steel parts is nearly a hundred times higher than corundum grinding wheels and five times higher than diamond grinding wheels, but it is not as efficient as diamond in grinding brittle materials.

The selection of cubic boron nitride grinding wheels is similar to the selection of diamond grinding wheels. However, in terms of bonding agent selection, most of them are resin bonding agents, followed by electroplating and metal bonding agents. Ceramic-bonded CBN grinding wheels are mainly used for grinding difficult-to-machine ferrous metals such as titanium alloys, high-speed steel, and malleable iron. Resin-bonded CBN grinding wheels are suitable for grinding ferromagnetic materials and are ideal for processing steel. The CBN grinding wheel concentration is generally between 100% and 150%, which is more economical and reasonable. It cannot use ordinary cutting fluid and requires special cutting fluid. 

4. Selection of large hole grinding wheel

The large hole grinding wheel has the advantages of not being easily clogged during grinding, high durability and strong cutting ability. Suitable for rough and fine grinding of soft metals and non-metallic materials such as plastics, rubber and leather. At the same time, it has the characteristics of fast heat dissipation, so it has good effects in grinding some heat-sensitive materials, thin-walled workpieces and dry grinding processes (such as sharpening carbide cutting tools and machine tool guide rails, etc.).

The manufacturing methods of large-pore grinding wheels and general vitrified bond grinding wheels are basically the same. The difference is that a certain amount of pore increasing agent is added to the ingredients, which completely volatilizes or is burned before the grinding wheel is sintered, thus producing large pores.

The production range of large-pore grinding wheels is: the abrasives generally choose carbide and corundum, such as black silicon carbide (C), green silicon carbide (GC) and white corundum (WA). These abrasives have high hardness and durability. Brittle and sharp, with good thermal and electrical conductivity; abrasive particle size (36#~180#); bonding agent (ceramic bonding agent); hardness (G~M levels); shape (flat, cup, bowl or dish shape, etc.); pore size (about 0.7~1.4 mm).

Generally speaking, grinding wheels will be marked with a row of values ​​when they leave the factory. The general order is shape code, size, abrasive, particle size number, hardness, structure number, bond and the maximum allowable linear speed. For example, the specific analysis of the letters and numbers of "P400×40×127WA60L5V35" is as follows:

"P" indicates that the grinding wheel shape is a parallel grinding wheel.

The number "400×40×127" represents the size of the grinding wheel (outer diameter × thickness × hole diameter). "WA" indicates that the abrasive material of the grinding wheel is white corundum grinding wheel. “60” indicates the grinding wheel size, which is 60# (preferably fine grinding). "L" indicates that the hardness of the grinding wheel is medium-soft. "5" indicates the structure number of the grinding wheel, which is relatively dense. "V" indicates the bond of the grinding wheel, which is a ceramic bond and is relatively brittle. “35″ indicates the grinding wheel linear speed, and the speed of 35m/s is medium. 1. Principles for Selection of Grinding Wheels 1. When grinding steel, use corundum grinding wheels; when grinding hard cast iron, cemented carbide and non-ferrous metals, use silicon carbide grinding wheels. 2. When grinding soft materials and hard materials, use hard grinding wheels and soft grinding wheels respectively. 3. When grinding soft and tough materials, use coarse abrasives (such as 12~36#); when grinding hard and brittle materials, use fine abrasives (such as 46~100#). 4. When the roughness value of the grinding surface is required to be low, fine abrasive grains are used; when the metal removal rate is high, coarse abrasive grains are used. 5. When the machined surface quality is required to be good, choose a resin or rubber bonded grinding wheel; when the maximum metal removal rate is required, choose a ceramic bonded grinding wheel. 2. Commonly used grinding wheels

There are two opinions about the hardness of abrasive tools:

1. Abrasive tool hardness refers to the resistance of the bond to resist the detachment of abrasive particles from the surface of the abrasive tool under the action of external force, or the ease with which the abrasive particles detach from the surface of the abrasive tool.

2. The hardness of abrasive tools refers to the comprehensive strength of the bond and abrasive particles when they break from the surface of the grinding wheel due to resistance to external forces during work.

Choose the core of the grinding wheel - how much do you know about hardness?

The hardness of the abrasive reflects the ability of the bond to hold the abrasive particles, not the hardness of the magic itself.

 

When selecting the hardness of abrasive tools, the most basic principles are: to ensure that the abrasive tools have appropriate self-sharpening properties during the grinding process, to avoid excessive wear of the abrasive tools, and to ensure that excessively high grinding temperatures are not generated during grinding.

As mentioned before, the hardness of the abrasive tool is related to the amount of binder. The higher the hardness of the abrasive tool, the greater the number of binders. The thicker the binder bridge, the greater the binder's holding power on the abrasive, making the grinding tool more durable. The grains can withstand large grinding forces without breaking or falling off. On the contrary, when the hardness of the abrasive tool is low, the binding force of the binder on the abrasive grains is small, and the abrasive grains are easy to break or fall off. Therefore, if the hardness of the abrasive tool is selected too high, not only will the blunt abrasive grains be less likely to break or fall off and lose cutting ability, but it will also increase the friction between the abrasive tool and the workpiece, and the surface of the workpiece will easily heat up and cause burns. In order to remove dull abrasive grains in time, the abrasive tools must be frequently trimmed, causing a large amount of wear of the abrasive tools. If the hardness of the abrasive tool is selected to be soft, the abrasive grains will fall off while they are still sharp, causing unnecessary wear. At the same time, the grinding tool wears too fast and its working surface wears extremely unevenly, which also affects the machining accuracy of the workpiece.

To sum up, only by correctly selecting the hardness of the grinding tool can it maintain its normal grinding state and meet the needs of processing. Especially when sharpening Golem writing tools, even a small deviation in the hardness of the abrasive tool will affect the sharpening quality. It can be seen that the influence of the hardness of the abrasive tool is very important.

 

When selecting the hardness of the abrasive tool, the most basic method is: if the hardness of the workpiece is high, the hardness of the abrasive tool must be low; if the hardness of the workpiece is low, the hardness of the abrasive tool must be high. Because when the hardness of the workpiece is low, the pressure on the abrasive grains on the abrasive tool when cutting into the workpiece is correspondingly smaller, and the abrasive grains are not easily blunted. In order to prevent the abrasive grains from breaking or falling off before they are dulled, the abrasive grains with high hardness are selected. Some abrasive tools are more suitable; on the contrary, when the hardness of the workpiece is high, the pressure the abrasive grains bear when cutting into the workpiece is correspondingly greater and becomes dull. Choosing abrasive tools with softer hardness can produce self-sharpening in time and maintain the grinding performance of the abrasive tool. However, when the workpiece material is softer and has high toughness (such as soft bronze, brass, etc.), since the cut metal is easy to block the abrasive tool, it is better to use a softer abrasive tool with a coarser grain size for processing.

The hardness of the grinding tool is also an important factor affecting the temperature of the grinding area. When grinding workpieces with low thermal conductivity (such as alloy steel), because the surface temperature of the workpiece is relatively high, burns and cracks are often easily generated. At this time, a grinding wheel with lower hardness and looser structure should be selected, and at the same time, it should be strengthened. Cooling, so as to effectively avoid burns of the workpiece. Similarly, when grinding thin workpieces, it is also necessary to use a grinding wheel with a loose structure and lower hardness. When grinding the outer circle of a thin-walled hollow workpiece, the hardness of the grinding wheel is lower than when grinding a solid workpiece. This is also to prevent the deformation of the workpiece caused by the increase in grinding temperature.

When selecting the hardness of abrasive tools, the following conditions should generally be considered:

1. When the contact area between the grinding tool and the workpiece is large, the hardness of the grinding tool should be lower to prevent the workpiece from overheating and affecting the grinding quality. For example, the grinding tools used for vertical axis flat grinding have lower hardness; the grinding wheels used for flat grinding and internal soft grinding have lower hardness than the grinding wheels used for cylindrical grinding. However, when grinding a thin and long inner hole, due to the low speed of the grinding wheel, the grinding wheel is easy to wear and causes the workpiece to have a taper (flare mouth). Therefore, the hardness of the grinding wheel is higher than that of general internal grinding. Similarly, a harder grinding wheel can be used to grind workpieces with small apertures, while softer grinding wheels should be used to grind workpieces with large apertures.

2. When grinding intermittent surfaces and burring castings, you should use a hard-grade or super-hard-grade grinding wheel; when grinding steel billets with heavy loads, you should also choose a hard-grade or super-hard grade grinding wheel to prevent the grinding wheel from wearing out too quickly.

3. Diamond abrasives (grinding wheels or oilstones) used for dressing. Due to the high pressure during dressing, high hardness is required, so super-hard abrasives are often used.

4. Heavy-duty grinders and grinders with higher rigidity can use grinding wheels with lower hardness because they vibrate less during grinding and the abrasive grains are not easily damaged.

5. During cylindrical plunge grinding, in order to avoid burns to the workpiece, the hardness of the grinding wheel should be lower than during axial feed.

6. An automatic grinder can use a softer grinding wheel than a manual grinder.

7. When the roughness value of the processed surface is smaller and the size of the workpiece is more precise, a grinding wheel with lower hardness should be selected to avoid excessive grinding heat and deterioration of the surface structure of the workpiece. For example, a super-soft mirror grinding resin bonded grinding wheel can grind a surface with a roughness Rz of 0.05 μm. However, for general fine grinding grinding wheels, the hardness must be higher, otherwise unevenness will occur on the working surface of the grinding wheel. Wear affects the machining accuracy of the workpiece.

 

8. Scratches on the surface of the workpiece are often related to improper selection of abrasive tool hardness. When the hardness of the abrasive tool is too low, the abrasive grains fall off easily, and the fallen abrasive grains will scratch the surface of the workpiece due to extrusion or friction. Therefore, the hardness of the abrasive tool must be appropriately increased at this time.

9. The workpiece is prone to heat during dry grinding, so a grinding wheel 1 to 2 grades softer should be used than during wet grinding.

10. When the production efficiency requirements are high, you can choose a softer grinding wheel to facilitate the self-sharpening of the grinding wheel and reduce the number of dressings. However, the wear of the grinding wheel will increase accordingly, so a comprehensive analysis and comparison of technical and economic indicators must be carried out.

11. During high-speed grinding, when the feed speed remains unchanged, the chips cut by the abrasive grains become thinner, the cutting force endured by the abrasive grains decreases accordingly, and the wear of the grinding wheel becomes slower. At this time, in order to improve the self-sharpening of the grinding wheel In this case, the hardness is 1 to 2 grades softer than that of general grinding. This is the case during high-speed fine grinding. Similarly, for some unbalanced workpieces (such as crankshafts, etc.), since the workpiece speed during grinding cannot be too high, the hardness of the grinding wheel must also be selected lower to avoid burning the workpiece. For high-speed grinding with the main purpose of improving cutting efficiency, the cutting feed rate must be increased. At this time, the grinding force on the abrasive grains increases. In order to ensure that the abrasive grains do not fall off prematurely, the hardness of the grinding wheel should be 1 to 2 grades higher than that of ordinary grinding.

12. When grinding steel balls (balls), a super-hard grade grinding wheel should be selected; for general cutting of workpieces, the hardness of the grinding wheel should be selected to a medium-hard grade.

13. When sharpening carbide and high-speed steel tools, you should choose a grinding wheel with a hardness of J~G.

14. During form grinding, in order to maintain the correct geometry of the workpiece, the wear of the grinding wheel should not be too great, so the hardness of the grinding wheel should be higher.

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