An appropriate choice of wheel
For different workpiece materials, different processing requirements, should use a different wheel. Even the same kind of grinding workpiece material, different grades of grinding wheel grinding ratio may vary from 2 to 5 times, and therefore the appropriate choice of the wheel.
Diamond grinding wheel is grinding carbide, optical glass, ceramics, stones and stone high hardness brittle non-metallic materials, the best abrasive. But the diamond at 700 ℃ ~ 800 ℃ easily when carbonation, so it is not suitable for grinding steel material. CBN is slightly inferior to the hardness of diamond, but it's good thermal stability (the ability of 1300 ℃ ~ 1400 ℃ high temperature), it does not like the diamond that will break down at high temperatures, ie, oxidation and graphite, and iron group elements chemically inert large, high thermal conductivity (46 times corundum), with its production of wheel life long (corundum grinding wheels up to a hundredfold more than a few times), is an alternative corundum grinding wheel hardened steel, high speed tool steel, bearing steel , stainless steel, heat-resistant steel and titanium metal toughness, high hardness materials, the best abrasive.
Grinding wheel with a binder resin, metal, ceramics, plating and brazing. Resin bonded grinding wheel is mainly used for measuring blade sharpening, grinding holes, cylindrical grinding and surface grinding; metal bonded grinding wheel for cutting, shaping optical curve grinder grinding, sharpening single-edged knives, grinding small drill spiral grooves, also applies to electrolytic grinding; vitrified grinding wheel of high efficiency, good shape retention and durability, easy dressing, grinding, long life, and because of vitrified itself has good chemical stability, heat, oil, acid erosion, can be adapted to a variety of grinding fluids, grinding, low cost, and thus has become efficient, high-precision grinding preferred abrasive; electroplated grinding wheel suitable for high speed grinding and forming mill, also suitable hole efficient grinding (wet) and use the jig grinder; brazed wheel suitable for ultra-high speed grinding.
Should be noted that different grades of abrasives, because the manufacturing process is different, the crystal morphology, particle shape are different, and have different strength, thermal stability, and fragmentation characteristics, should be based on type of binding agent, grinding the workpiece material and the grinding means, Select a different abrasives. As for efficient, high-precision grinding of ceramic bonded grinding wheel, the choice of high strength and sharp abrasive particle shape, such as the DeBeers company produces PDA type (synthetic diamond varieties) and ABN800 type (CBN varieties) or other similar properties grades.
Another superhard grinding surface metallization produced clothing (metal coatings can play a reinforcement toughening, slowing the thermal shock as well as in abrasive and binder combination bridge between the role play can improve wheel performance) and non-metallised coat two species, should be based on the binder type, workpiece material, both dry and wet conditions, such as different choices. Dry grinding is generally used copper clothing, such as RVD-Cu, CBN-Cu; wet optional Ni clothing, such as RVD-Ni, CBN-Ni. Currently, metal plating by nickel, copper developed to titanium, tungsten alloy, nonmetal ceramics, etc., by a single coating developed to the composite coating, and has been developed to a fine powder coated abrasive coating.
From hard abrasive wheel can not choose too low concentration and high concentration can bring high grinding ratio, 200% concentration of superabrasive grinding wheel is actually a kind of super abrasive grinding wheel as adjunct general, is generally not recommended Named use. Currently, high-speed and efficient grinding higher concentrations are used, vitrified CBN grinding wheel are made of a high concentration of high-density, vitrified CBN grinding wheel generally choose more than 125% concentration, such as import supporting ceramic CBN grinding wheels concentrations in general are 175% to 200%.
Expressed wheel hardness grade of binder on the size of the abrasive gripping force. Wheel hardness uniformity and stability and hardness of the level of rational choice, is an important prerequisite to ensure the quality of grinding. Foreign grinding wheel generally 3 to 7 hardness levels to choose from, but China's production of superhard grinding wheel hardness level is not standard, GB6409 also does not provide the appropriate standards, so the quality is not guaranteed and inconvenience to users, urgent supplement and perfect.
2 Select the appropriate grinding parameters
Superabrasive grinding wheel speed should be based on the type wheel, grinding mode and cooling and other specific conditions to choose. Improving working speed grinding wheel, can significantly improve the grinding efficiency and grinding ratio (such as grinding wheel speed increased by 40%, grinding ratio doubled), lower grinding costs. Metal and resin bond diamond grinding wheel, grinding speed is usually 15 ~ 35m / s, vitrified CBN grinding wheel speed can be increased to 45 ~ 160m / s, single-CBN grinding wheel speed can choose 125 ~ 250m / s. 80 ~ 125m / s line speed has become the mainstream of the world CBN grinding wheel. Grinding depth is generally 0.002 ~ 0.010mm, the workpiece speed is generally 10 ~ 30m/min, vertical feed rate preferably 0.3 ~ 1.5m/min. Whichever is greater coarse grinding, fine grinding take a small value.
3 superhard grinding wheel for grinding requirements
Superhard grinding wheel, especially high-speed grinding, processing requirements, good stability, small vibration, high linear velocity. For example, in CIMT2001 PLANOMAT series on display plane and shaped grinding wheel operating speed of 170m / s. Therefore, there is a requirement for grinding:
(A) higher precision grinding wheel spindle.
(2) grinding stiffness is better than ordinary grinder generally require about 50% higher, usually not less than 100N/μm of magnitude.
(3) Grinders Feed System accuracy is high, the feed rate should be uniform and accurate, longitudinal feed minimum speed should reach 0.3m/min, infeed (depth of cut) should reach 0.001 ~ 0.002mm / single stroke, in order to ensure size precision grinding, precision geometry and surface roughness.
(4) grinding of the moving parts, such as the shaft and bearing part of the head frame, the feed movement of the guide portion and so should be reliable sealed to prevent access superhard abrasive, accelerated wear of parts.
(5) have a fairly complete grinding fluid filtration and supply systems, filtration should be less than 0.5μm.
(6) Grinders each part should be a corresponding vibration and vibration isolation measures, wheel balancing should be fine.
4 grinding wheel dressing
Grinding wheel dressing, shaping and sharpening is usually divided into two processes. For trace shaping the grinding wheel cutting, to achieve the required geometry and precision, and to a fine abrasive tip broken, the formation of micro blade; dressing is removed by a combination of abrasive agent, the abrasive grains have a chip space between , binding agent and to highlight the abrasive, the formation of the cutting edges.
For multi-pore vitrified grinding wheel (including diamond and CBN grinding wheels), as binders for the loose type, usually shaping and sharpening can be completed; while for binding agent is dense wheel (such as resin, metal binding agent) , then shaping and sharpening required separately.
Grinding wheel of the most effective tool for shaping diamond dressing tools devaluation. With a single particle diamond dresser, dressing tool wear due, often affect-surface precision. As with diamond wheel dresser, dressing tool to avoid excessive wear and tear, and to get a better wheel topography. Trimming device feeding accuracy is higher, the amount of each feed should be controlled at the micron level. Excessive trim only affects the grinding quality, will greatly reduce wheel life.
Dressing in many ways, generally using mechanical methods (such as corundum block cut dressing, hydraulic jet sharpening method) or electrical processing method. Latter binding agent for metal grinding, the grinding wheel as an anode electrolysis by spark or erosion of the metal binding agent; if the binding agent is added to the graphite powder, this method is also applicable to the resin, vitrified grinding wheels.
In recent years, the University of Tokyo has developed a rotary-type diamond cup wheel dressing tools. The mechanism is the use of cup-shaped wheel from falling down superhard abrasive (diamond or CBN) abrasive grains and binder combination bridge between the impact and the falling down of superhard abrasive and squeezed between the abrasive wheel to achieve the trimming purposes. With this method, both the multi-pore ceramic bonded superhard grinding wheels, or dense wheel, shaping and sharpening can be completed, but because of the cup-shaped grinding wheel from rotating, so wear is very small, almost finishing the process of shaping forces can remain change, and the value than using a single particle is much smaller when dressing diamond dressing tools.
5 correct use of grinding fluid
Superabrasive grinding wheel, can be used either wet or dry. But the use of wet, can prolong wheel life, but will also prevent the workpiece grinding burn. Different grinding fluid, causes wheel grinding ratio difference times, even 10 times. Grinding wheel during grinding mechanical wear, chemical attack and thermal damage, and is closely related to the cooling effect. However, wet grinding with CBN to be noted that as the CBN and the steam at a high temperature together with oxygen in the air from the reaction of ammonia and boric acid (BN 3H2O → H3BO3 NH3), this reaction is called hydrolysis, will accelerate the wheel wear . Therefore, the use of common water-soluble oil or with an aqueous solution of an extreme pressure additive to weaken hydrolysis. When using different wet grinding fluid, CBN grinding wheel relative life differently to pure oil cooling longest wheel life, water-soluble oil-cooled wheel life, followed by cooling water plus anti-rust additives minimum wheel life.
6 superabrasive grinding wheels unconventional use
Usually people think, because diamond and iron group elements chemically inert large, so is not suitable for grinding diamond wheel for a class of gray cast iron parts, however this only occurs at high temperatures only. For example, using a diamond grinding wheel, when the temperature reaches 650 ℃, the diamond will be oxidized in the air, and to achieve 700 ℃ ~ 800 ℃ when it will graphite. At low temperatures, these materials do not react between. So, as long as the appropriate choice of grinding speed and the use of wet methods, and adequate supply of grinding fluid, diamond grinding wheel is perfectly cast, and this has been confirmed in the production practice. When using wet grinding, diamond grinding wheel grinding ratio of gray cast iron (9600) than gray cast iron with CBN grinding wheel for grinding ratio (2700) is much higher.
It is also generally considered, CBN grinding wheel is suitable for a class of low-carbon steel soft material, because then easily generated wear debris clogging the wheel. But the current study suggests that vitrified CBN grinding wheel can be taken to increase the wheel speed to form small debris, and then cleared by high pressure liquid jet grinding debris, as well as adequate supply of grinding fluid and other measures to prevent the wheel blocked. Therefore, CBN grinding wheel is low carbon steel (hardness greater than 30HRC) a class of soft materials. However, CBN grinding wheel is not valid any material. Usually it is not suitable for grinding carbide and carbide and steel assembly, this time with a diamond grinding wheel for better results.
7 Conclusion
Production of synthetic superhard abrasive though started late, but rapid development, China in 1997, synthetic diamond production has reached about 500 million karats, CBN annual output of 800 million carats. Has initially formed a superhard abrasives, special grinding fluid, specialized finishing techniques and devices and specialized grinders a complete technology system. At present, China has been able to produce RVD, CBN and gold-plated high-grade abrasive products are clothing, such as "metal matrix ceramic CBN wheel", "65m / s vitrified CBN grinding wheel," and so on, grinding wheel has formed a series of different specifications, ultra- hard abrasive wheel diameters up φ750mm (under trial φ1100mm wheel), the maximum line speed of up to 80m / s, and in the development of 125m / s high-speed grinding wheel for grinding wheel to create the conditions to promote the use. Can be expected, with the widespread use of super abrasive grinding wheels, grinding industry will promote the transformation and development, and the development of efficient high-performance grinding machine, will lead to further promote the use of super abrasive grinding wheels.
