There are many different types of grinding tools, and they come in all shapes and sizes. Each type of grinding wheel has a certain range of application depending on the abrasive of the grinding wheel, the bonding material, and the manufacturing process. If you choose improperly, it will directly affect the processing accuracy, surface roughness and production efficiency. Therefore, when grinding, the appropriate grinding wheel must be selected according to the actual situation. How to choose the right wheel? A summary of the grinding wheels commonly used in grinding allows you to clearly select the wheels.
First, the choice of ordinary grinding wheel:
Selection of Abrasives
The choice of abrasive depends mainly on the workpiece material and heat treatment method.
a. When grinding materials with high tensile strength, choose tough abrasives.
b. When the material with low hardness and high elongation is used, use a relatively fragile abrasive.
c. When grinding high hardness materials, use abrasives with higher hardness.
d. Use abrasives that are not easily chemically processed.
The most commonly used abrasives are brown corundum (A) and white corundum (WA), followed by black silicon carbide (C) and green silicon carbide (GC). Others are commonly used chrome corundum (PA), single crystal corundum (SA). , microcrystalline corundum (MA), zirconia corundum (ZA).
Brown corundum grinding wheel: Brown corundum has high hardness and high toughness. It is suitable for grinding metals with high tensile strength, such as carbon steel, alloy steel, malleable cast iron, and hard bronze. This kind of abrasive has good grinding performance and wide adaptability. It is often used to remove coarse grinding with a large margin. It is inexpensive and can be widely used.
White corundum wheel: The hardness of white corundum is slightly higher than brown corundum, and the toughness is lower than that of brown corundum. During grinding, the abrasive grains are easy to crack. Therefore, the grinding heat is small, and it is suitable for the production of refined hardened steel, high-carbon steel, High-speed steel and grinding wheels for thin-walled parts cost more than corundum.
Black silicon carbide wheel: Black silicon carbide is brittle and sharp, with higher hardness than white corundum. It is suitable for grinding materials with lower mechanical strength, such as cast iron, brass, aluminum and refractory materials.
Green silicon carbide grinding wheel: Green silicon carbide ‘s hardness and fragility is higher than black silicon carbide, featured with sharp abrasive particles, good thermal conductivity, suitable for grinding carbide steel, optical glass, ceramics and other hard and brittle materials.
Chrome corundum grinding wheel: Suitable for grinding tools, measuring tools, instruments, threads and other surface processing high quality workpiece.
Mono crystalline corundum grinding wheel: Suitable for grinding stainless steel, high vanadium high speed steel and other toughness, high hardness materials and easy deformation of the burned workpiece. The
Microcrystalline corundum grinding wheel: suitable for grinding stainless steel, bearing steel and special ductile iron, etc., used for forming grinding, cutting into grinding, mirror grinding.
Zirconium corundum grinding wheel: suitable for grinding austenitic stainless steel, titanium alloy, heat-resistant alloy, especially for heavy-duty grinding.
The choice of particle size
The choice of particle size mainly depends on the surface roughness and grinding efficiency of the workpiece being ground.
Particle size refers to the particle size of the abrasive, and its size is indicated by the size number. Grinding with a coarse-grained grinding wheel results in high production efficiency, but the surface of the milled workpiece is rough. When grinding with a fine-grained grinding wheel, the surface roughness of the milled workpiece is good, and the productivity is low. Under the premise of satisfying the roughness requirements, coarse-grained grinding wheels should be used as far as possible to ensure high grinding efficiency. The coarse-grained grinding wheel is generally used for coarse grinding, and the fine-grained grinding wheel is used for fine grinding.
When the contact area between the grinding wheel and the workpiece is large, a coarser grinding wheel should be used. For example, grinding the same plane and grinding the end face of the grinding wheel is coarser than the grain size selected by grinding around the circumference of the grinding wheel.
The choice of hardness
The choice of hardness depends mainly on the workpiece material being ground, grinding efficiency and surface quality.
Hardness refers to the degree of difficulty that the grinding wheel falls off under the action of the external force. In order to meet the requirements of different workpiece material grinding and processing, the grinding wheel is divided into different hardness levels.
The grinding wheel is selected hard, the blunt abrasive grains are not easy to fall off, the grinding wheel is easy to be blocked, the grinding heat is increased, the workpiece is easy to burn, the grinding efficiency is low, and the surface quality of the workpiece is affected; the grinding wheel is too soft and the abrasive particles are still off when they are sharp , Increased grinding wheel wear, easy to lose the correct geometry, affect the accuracy of the workpiece. Therefore, the choice of hardness of the grinding wheel should be properly considered, and it should be comprehensively considered according to factors such as the contact area of the grinding wheel and the workpiece, the shape of the workpiece, the grinding method, the cooling method, and the type of the bonding agent of the grinding wheel.
The following wheel hardness selection principles are for reference:
a. When grinding soft materials, choose a harder grinding wheel; when grinding hard materials, choose a soft grinding wheel;
b. When grinding soft and tough non-ferrous metals, the hardness should be selected softer;
c. Grinding material with poor thermal conductivity should be selected softer grinding wheel;
d. When the surface grinding is more than circular grinding, the hardness of the grinding wheel should be selected soft;
e. Under the same grinding conditions, the hardness of the resin-bonded grinding wheel is 1 to 2 lower than that of the ceramic-bonding grinding wheel;
f. When the rotation speed of the grinding wheel is high, the hardness of the grinding wheel can be selected from soft 1 to 2 small steps;
g. Grinding with coolant is 1 to 2 orders of magnitude higher than the hardness of the grinding wheel.
The choice of binder
The choice of binder should be considered based on the grinding method, speed of use and surface processing requirements.
The most commonly used abrasive wheel binders are ceramic binder (V) and resin binder (B).
Ceramic binder is an inorganic binder, chemical stability, heat resistance, corrosion resistance, and porosity, the grinding wheel made of this binder has high grinding efficiency, low abrasion, and can well maintain the geometry of the grinding wheel The widest range of applications. Grinding wheel is suitable for grinding ordinary carbon steel, alloy steel, stainless steel, cast iron, hard alloy, non-ferrous metals and so on. However, the ceramic binder wheel is brittle and cannot be subjected to severe vibrations. It can only be used at speeds up to 35m/s. .
The resin binder is an organic binder. The wheel produced by this binder has high strength, certain elasticity, low heat resistance, good self-sharpness, simple manufacture, and short process cycle. Grinding wheels with a working speed higher than 50 m/s and very thin grinding wheels can be manufactured. Its application area is second only to ceramic binders, and is widely used in rough grinding, barren grinding, cutting and free grinding, such as grinding steel ingots, casting burrs and so on. Can produce high speed, high smoothness grinding wheel, heavy load, cutting and various special requirements of the grinding wheel.
The selection of the organization
The selection of the organization mainly considers the pressure on the workpiece, the grinding method, and the workpiece material.
The organization refers to the percentage of the abrasive wheel's volume in the grinding wheel. The classification of grinding wheel organization is based on the fact that 62% of the abrasive grain volume percentage is “0” organization, and the abrasive grain volume is reduced by 2% each time. Its organization is increased by No.1, and so on. It is divided into 15 numbers. The bigger the number, the looser the organization.
The tightly-organized grinding wheel can grind up the surface of the workpiece and loosen the grinding wheel. Due to the large gap, it can ensure that grinding debris is contained in the grinding process and the grinding wheel is not blocked. Usually, when grinding and grinding relatively soft metal, the grinding wheel is easy to be clogged, and the grinding wheel with loose structure should be selected. When forming grinding and precision grinding, in order to maintain the geometry of the grinding wheel and get better roughness, the closer organization should be used. Grinding wheel; Grinding machine tool rails and carbide tools, in order to reduce the thermal deformation of the workpiece, to avoid burn cracks, should be used loose grinding wheel; grinding heat-sensitive materials, non-ferrous metals, non-metallic materials should be used more than 12 # organization Grinding wheel.
The shape and size
The shape and size should be selected according to the conditions of the grinder and the shape of the workpiece.
Commonly used grinding wheel shapes are flat grinding wheel (P), single-sided concave grinding wheel (PDA), double-sided concave grinding wheel (PSA), thin-section grinding wheel (PB), cylindrical grinding wheel (N), bowl-shaped grinding wheel (BW), dish-shaped No. 1 Grinding wheel (D1) and so on.
There is a certain range of shapes and sizes of grinding wheels that can be used for each type of grinding machine. Under the possible conditions, the outer diameter of the grinding wheel should be selected as large as possible to increase the line speed of the grinding wheel, and the higher productivity and surface quality of the workpiece can be achieved. The same effect can be obtained by increasing the width of the grinding wheel. .
The current national standard wheel writing sequence: wheel code, size (outside diameter × thickness × aperture), abrasive, grain size, hardness, organization, binder, maximum working line speed.
Exemplary: P 400 × 150 × 203 A 60 L 5 B 35
Second, the choice of diamond grinding wheel
Compared to diamond grinding, wheels made of boron carbide, silicon carbide, corundum and other general abrasive grains, diamond grinding wheels have sharp edge angles, low wear, long service life, high productivity, and good processing quality, but are expensive, and are therefore suitable for fine grinding of hard alloys and ceramics. , semiconductors and other high-hardness brittle materials difficult to process. .
The characteristics of the diamond wheel include the type of abrasive, particle size, hardness, concentration, binder, shape and size of the wheel.
The use of synthetic diamond (JR) is widely used. According to its crystal shape and particle strength, it can be divided into various models according to their specific purposes.
Granularity: Comprehensive consideration should be given to the workpiece roughness, grinding productivity and diamond consumption.
Hardness: Only the resin bond diamond wheel has the characteristic of "hardness". S(Y1) or higher is generally used.
There are four commonly used binders, and their binding capacity and wear resistance are in order of resins, ceramics, bronzes, and electroplated metals. The resin-bonded diamond grinding wheel has high grinding efficiency, good workpiece roughness, wide application range, good self-sharpening property, and is not easy to be blocked, has small heat generation, is easy to trim, and is mainly used in the refining process. Ceramic bond diamond grinding wheels are mainly used for the grinding of various non-metallic hard and brittle materials, hard alloys and superhard materials.
The choice of concentration depends on the size of the grinding wheel used, the binder, the shape, the processing method, the production efficiency, and the life of the grinding wheel. The high-strength diamond grinding wheel has a strong ability to maintain the shape of the grinding wheel. When the grinding wheel is grinded at a low concentration, the consumption of diamond is often lower and should be selected as appropriate.
Shape and size:
It is selected according to the shape, size and machine conditions of the workpiece.
Third, the choice of cubic boron nitride (CBN) grinding wheel
The Cubic Boron Nitride (CBN) grinding wheel' s particles adhere to the surface of ordinary grinding wheels with only a thin layer. Its abrasive grain toughness, hardness, and durability are 100 times that of corundum type grinding wheels. It is most suitable for processing high hardness and viscosity. Large, high-temperature high-strength, low thermal conductivity hard-to-grind steel and high-speed or ultra-high-speed grinding. Its application range and synthetic diamonds play complementary roles. Diamond grinding wheels have unique effects when grinding hard alloys and non-metallic materials, but when grinding steel materials, especially when grinding special steels, the effect is not significant. Cubic boron nitride grinding wheels are nearly 100 times more efficient than corundum grinding wheels and five times higher than diamond grinding wheels, but grinding brittle materials are inferior to diamond.
The choice of cubic boron nitride grinding wheel is similar to the choice of diamond grinding wheel. However, most of the binders are resin binders, followed by electroplating and metal binders. The ceramic binder CBN grinding wheel is mainly used for the grinding of difficult-to-machine ferrous metals such as titanium alloy, high-speed steel, and malleable cast iron. The resin binder CBN grinding wheel is suitable for grinding ferromagnetic materials and is an ideal choice for processing steel materials. The concentration of CBN grinding wheel is generally more economical and reasonable between 100% and 150%. It cannot use ordinary cutting fluid and requires special cutting fluid.
(To be continued)