Grinding wheels are an indispensable tool for grinding. Whether the grinding wheel is suitable or not is an important condition that affects the quality of grinding and the cost of grinding. The company produces a series of surface grinders, which need to be equipped with different grinding wheels to adapt to the surface processing of various workpieces. In order to facilitate the selection of users and the design and process personnel of this company, this article focuses on the selection of grinding wheels for surface grinders and the selection of grinding wheels for different workpiece materials, for your reference.
There are many types of grinding wheels, and there are various shapes and sizes. Due to the different abrasives, bond materials and manufacturing processes of the grinding wheels, various grinding wheels have different working performances. Each type of grinding wheel has a certain scope of application according to its own characteristics. Therefore, when grinding, you must select the appropriate grinding wheel according to the specific conditions (such as the material properties of the workpiece to be ground, heat treatment method, workpiece shape, size, processing form and technical requirements, etc.). Otherwise, the machining accuracy, surface roughness and production efficiency will be directly affected by improper selection of the grinding wheel. The basic principles of wheel selection are listed below for reference.
1. Selection of ordinary grinding wheels
1. The choice of abrasives The choice of abrasives mainly depends on the workpiece material and heat treatment method.
a. When grinding materials with high tensile strength, use abrasive materials with high toughness.
b. When grinding materials with low hardness and high elongation, use brittle abrasives.
c. When grinding materials with high hardness, use abrasives with higher hardness.
d. Use abrasives that are not easily chemically reacted by the processed material.
The most commonly used abrasives are brown corundum (A) and white corundum (WA), followed by black silicon carbide (C) and green silicon carbide (GC), and the rest commonly used are chromium corundum (PA) and single crystal corundum (SA) , Microcrystalline corundum (MA), zirconium corundum (ZA).
Brown corundum grinding wheel: Brown corundum has high hardness and high toughness, suitable for grinding metals with high tensile strength, such as carbon steel, alloy steel, malleable cast iron, hard bronze, etc. This abrasive has good grinding performance and wide adaptability. It is commonly used to cut off rough grinding with a large margin, 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 the toughness is lower than that of brown corundum. When grinding, the abrasive particles are easily broken. 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, and has higher hardness than white corundum. It is suitable for grinding materials with low mechanical strength, such as cast iron, brass, aluminum and refractory materials.
Green silicon carbide grinding wheel: Green silicon carbide has higher hardness and brittleness than black silicon carbide, sharp abrasive particles, good thermal conductivity, suitable for grinding hard and brittle materials such as cemented carbide, optical glass, ceramics and so on.
Chrome corundum grinding wheel: suitable for grinding workpieces with high surface quality requirements such as cutting tools, measuring tools, meters, threads, etc.
Single crystal corundum grinding wheel: suitable for grinding stainless steel, high vanadium high speed steel and other materials with high toughness and high hardness and workpieces that are easily deformed and burned.
Microcrystalline corundum grinding wheel: suitable for grinding stainless steel, bearing steel and special nodular cast iron, etc., used for forming grinding, plunge grinding and mirror grinding.
Zirconium corundum grinding wheel: suitable for grinding austenitic stainless steel, titanium alloy, heat-resistant alloy, especially for heavy-duty grinding.
2. The choice of particle size mainly depends on the surface roughness and grinding efficiency of the workpiece to be ground.
The particle size refers to the particle size of the abrasive, and its size is indicated by the particle size number.
When grinding with a coarse-grained grinding wheel, the production efficiency is high, but the surface of the workpiece is rough. When grinding with a fine-grained grinding wheel, the surface roughness of the workpiece is good, and the productivity is low. Under the premise of meeting the roughness requirements, the coarse-grained grinding wheels should be selected as much as possible to ensure higher grinding efficiency. Generally, coarse-grained wheels are used for rough grinding, and fine-grained wheels are used for fine grinding.
When the contact area between the grinding wheel and the workpiece is large, a coarser grinding wheel should be selected. For example, to grind the same plane, the grinding of the end face of the grinding wheel is coarser than the grinding of the grinding wheel.
The scope of application of different sizes of grinding wheels.
3. The choice of hardness mainly depends on the workpiece material to be ground, the grinding efficiency and the quality of the machined surface.
Hardness refers to the difficulty of grinding wheel falling off under the action of external force. In order to meet the requirements of different workpiece materials, the grinding wheel is divided into different hardness grades.
The grinding wheel is too hard, the blunt abrasive particles are not easy to fall off, the grinding wheel is easy to block, the grinding heat is increased, the workpiece is easy to burn, the grinding efficiency is low, which affects the surface quality of the workpiece; the grinding wheel is too soft, the abrasive particles fall off when they are sharp , Increased grinding wheel loss, easy to lose the correct geometry, affecting the accuracy of the workpiece. Therefore, the selection of the hardness of the grinding wheel should be appropriate, and it should be comprehensively considered according to factors such as the size of the contact area between 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 principles of hardness selection for grinding wheels 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 nonferrous metals, the hardness should be selected to be softer;
c. For materials with poor thermal conductivity, the softer wheels should be selected;
d. When face grinding is better than circumferential grinding, the hardness of the grinding wheel should be softer;
e. Under the same grinding conditions, the hardness of the resin bond grinding wheel is 1 to 2 grades higher than that of the ceramic bond grinding wheel;
f. When the rotation speed of the grinding wheel is high, the hardness of the grinding wheel can be selected from soft grades 1 to 2;
g. Grinding with coolant is 1 to 2 grades higher than that of dry grinding.
4. The choice of bonding agent should be considered according to the grinding method, speed and surface processing requirements.
The most commonly used grinding wheel bonding agents are ceramic bonding agents (V) and resin bonding agents (B).
Ceramic bonding agent is an inorganic bonding agent with stable chemical properties, good heat resistance and corrosion resistance, and large porosity. The grinding wheel made of this bonding agent has high grinding efficiency and low wear, which can maintain the geometry of the grinding wheel , The most widely used. Suitable for grinding ordinary carbon steel, alloy steel, stainless steel, cast iron, cemented carbide, non-ferrous metals, etc. However, the ceramic bond wheel is brittle and cannot be subjected to severe vibration. Generally, it can only be used at a speed within 35 meters/second.
Resin bond is an organic bond. The grinding wheel manufactured by this bond has high strength, certain elasticity, low heat resistance, good self-sharpness, easy manufacture, and short process cycle. It can manufacture grinding wheels with working speed higher than 50m/s and very thin grinding wheels. Its scope of application is second only to ceramic bonding agents, and it is widely used for rough grinding, rough grinding, cutting and free grinding, such as grinding steel ingots and casting burrs. It can manufacture high-speed, high-finish grinding wheels, heavy-duty, cut-off and various special requirements.
5. The choice of organization mainly considers the pressure on the workpiece, grinding method, workpiece material, etc.
Microstructure refers to the percentage of abrasive wheel volume in the grinding wheel. The organization grade of the grinding wheel is organized by 62% of the abrasive grain volume percentage as “0”. For every 2% of the abrasive grain volume, the organization is increased by one, and so on, divided into 15 numbers. The larger the number, the looser the organization (see Table 4).
The tightly-organized grinding wheel can grind a better surface of the workpiece. The loose-structured grinding wheel can ensure that the grinding chip is accommodated during the grinding process due to the large gap. Generally, when rough grinding and grinding soft metal, the grinding wheel is easy to be blocked, and a loose-structured grinding wheel should be used; when forming grinding and precision grinding, in order to maintain the geometry of the grinding wheel and obtain a better roughness, the tighter-structured one should be selected Grinding wheels; when grinding machine tool guides and cemented carbide tools, in order to reduce thermal deformation of the workpiece and avoid burn cracks, it is appropriate to use loose-structured grinding wheels; grinding materials with large thermal sensitivity, non-ferrous metals, and non-metallic materials should be larger than 12#. Grinding wheel.
6. The choice of shape and size should be selected according to the grinding machine conditions 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 grinding wheel (PB), cylindrical grinding wheel (N), bowl-shaped grinding wheel (BW), dish-shaped one Grinding wheel (D1), etc.
The shape and size of the grinding wheel that can be used for each grinder have a certain range. Under possible conditions, the outer diameter of the grinding wheel should be selected as large as possible to improve the linear speed of the grinding wheel, obtain higher productivity and the surface quality of the workpiece, and increase the width of the grinding wheel can also obtain the same effect.
The writing order of the current national standard grinding wheel: grinding wheel code, size (outer diameter × thickness × aperture), abrasive grain, particle size, hardness, structure, bonding agent, maximum working linear speed.
Example: P 400×150×203 A60 L 5 B 35
Second, the choice of diamond grinding wheel
Diamond wheels are sharper than abrasive wheels made of boron carbide, silicon carbide, corundum and other general abrasive grains, with low wear, long life, high productivity, and good processing quality, but they are expensive, so they are suitable for fine grinding of hard alloys and ceramics. , Semiconductors and other high-hardness brittle and difficult-to-process materials.
The characteristics of diamond grinding wheels include abrasive type, particle size, hardness, concentration, binder, grinding wheel shape and size.
Abrasive: Artificial diamond (JR) is widely used. According to its crystal shape and particle strength, it is divided into various models, and the model is selected according to its specific purpose.
Granularity: Comprehensive consideration should be given to the three aspects of workpiece roughness, grinding productivity and diamond consumption.
Hardness: Only resin bonded diamond grinding wheels have the “hardness” characteristic. Generally, S (Y1) grade or higher is adopted.
Binders: There are four commonly used binders. Their binding capacity and wear resistance are in order of resin, ceramics, bronze, and electroplated metal, and then gradually strengthen. The resin bond diamond grinding wheel has high grinding efficiency, good roughness of the workpiece to be processed, wide application range, good self-sharpness, not easy to block, low calorific value, easy to dress, and is mainly used in the finishing process. Ceramic bond diamond grinding wheels are mainly used for grinding various non-metallic hard and brittle materials, cemented carbide, super hard materials, etc.
Concentration: The choice of concentration depends on the requirements of the particle size, binder, shape, processing method, production efficiency and life of the grinding wheel. The high-concentration diamond grinding wheel has a strong ability to maintain the shape of the grinding wheel. When grinding the low-concentration grinding wheel, the diamond consumption is often lower, and it should be selected according to the needs.
Shape and size: Select according to the shape, size and machine condition of the workpiece.
3. Selection of Cubic Boron Nitride (CBN) Grinding Wheel
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. Large, high-temperature strength, low thermal conductivity of difficult-to-grind steel and high-speed or ultra-high-speed grinding. Its application range and artificial diamond play a complementary role. Diamond grinding wheels have a unique effect when grinding cemented carbide and non-metallic materials, but when grinding steel, especially when grinding special steel, the effect is not significant. The efficiency of cubic boron nitride grinding wheels for grinding steel parts is nearly a hundred times higher than corundum grinding wheels, and five times higher than diamond grinding wheels, but the grinding of brittle materials is not as good as diamond.
The choice of cubic boron nitride grinding wheels is similar to the choice of diamond grinding wheels. But in the selection of bonding agents, most of them are resin bonding agents, followed by electroplating and metal bonding agents. The ceramic bond CBN grinding wheel is mainly used for the grinding of difficult-to-machine ferrous metals such as titanium alloys, high-speed steel, and malleable cast iron. The resin bond CBN grinding wheel is suitable for grinding ferromagnetic materials and is an ideal choice for processing steel. The concentration of CBN grinding wheel is generally more economical and reasonable between 100% and 150%. It can not use ordinary cutting fluid and requires special cutting fluid.
4. Selection of Atmospheric Grinding Wheel
Atmospheric hole grinding wheels have the advantages of not being easily blocked, high durability and strong cutting ability during grinding. It is suitable for rough and fine grinding of non-metallic materials such as soft metals and plastics, rubber and leather. At the same time, it has the characteristics of fast heat dissipation, so it has a good effect in the grinding of some thermally sensitive materials, thin-walled workpieces and dry grinding processes (such as sharpening carbide tools and machine tool guides, etc.).
The manufacturing method of the atmospheric hole grinding wheel and the general ceramic bond grinding wheel are basically the same. The difference is that a certain amount of pore-increasing agent is added to the ingredients, which is completely volatilized or burned before the grinding wheel is sintered, thereby generating atmospheric pores.
The production range of atmospheric pore grinding wheels is: abrasives generally choose carbides and corundum, such as commonly used black silicon carbide (C), green silicon carbide (GC) and white corundum (WA), etc. These abrasives have high hardness and performance Brittle and sharp, with good thermal and electrical conductivity; abrasive particle size (36#~180#); bond (ceramic bond); hardness (G~M levels); shape (flat, cup, bowl or dish) Shape, etc.); stomatal size (about 0.7 ~ 1.4 mm).