Application of diamond wheel | Prctools.com

1. Select the right grinding wheel

Different grinding wheels should be used for different workpiece materials and different processing requirements.

Even if grinding the same workpiece material, the grinding ratio of different brands of grinding wheels may differ by 2~5 times, so the appropriate grinding wheel should be selected.

Diamond grinding wheel is the best grinding tool for hard alloy, optical glass, ceramics, gemstones and stone non-metallic materials with high hardness and high brittleness.

But because diamond is easy to be carbonized at 700℃~800℃, it is not suitable for grinding steel.

CBN slightly inferior to the hardness of diamond, but its thermal stability (which can withstand temperatures up to 1300 ℃ ~ 1400 ℃), it is not like a diamond in the high temperature decomposition, namely, oxidation and graphitization, and the elements of iron group chemical inertness, high thermal conductivity (46 times that of corundum), made of the grinding wheel long life (up to several dozen times the corundum grinding wheel to into more than one hundred times), is the alternative corundum grinding wheel grinding of hardened steel, high-speed tool steel, bearing steel, stainless steel, heat-resistant steel and titanium alloys such as the best abrasive hardness toughness of metal materials.

The bonding agent of super hard abrasive wheel is resin, metal, ceramics, electroplating and brazing.

Resin bonded grinding wheel is mainly used for cutting tool measuring tool, grinding hole, cylindrical grinding and plane grinding.

Metal bonded grinding wheels are used for cutting into the shape grinding of optical curve grinding machines, single edge cutting tools, spiral groove grinding of small bits, and also for electrolytic grinding.

Ceramic binder grinding wheel of high grinding efficiency, good shape retention, high durability, easy dressing, grinding wheel service life is long, and because of ceramic bond itself has good chemical stability, heat resistant, oil resistant, resistant to acid and alkali erosion, can adapt to all kinds of grinding fluid, grinding cost is low, and therefore has to make the first selection of high efficiency, high precision grinding abrasive;

Electroplated grinding wheels are suitable for high speed fine grinding and forming grinding, as well as for efficient grinding of holes (wet grinding) and use on coordinate grinders.

Brazing wheel is suitable for ultra-high speed grinding.

It must be pointed out that abrasive of different brands has different crystal shape and particle shape due to different manufacturing processes, and has different strength, thermal stability and crushing characteristics. Different abrasive materials should be selected according to binder type, workpiece material and grinding method.

For high-strength, high-precision grinding of ceramic binder wheels, use abrasive with sharp grain shapes such as PDA (synthetic diamond) and ABN800 (CBN) from DeBeers or other similar brands.

There are two kinds of clothes on the surface of the abrasive, which should be selected according to different conditions, such as binder type, workpiece material, dry grinding and wet grinding.

Copper clothes are generally used for dry grinding, such as RVD-Cu and CBN-Cu.

Wet grinding nickel coating, such as RVD-Ni, CBN-Ni. At present, the metal plating has developed from nickel, copper to titanium, tungsten alloy, non-metallic ceramics, from single coating to composite coating, and has developed from abrasive coating to micro powder coating.

The concentration of hard abrasive grinding wheel should not be too low. High concentration can lead to a high grinding ratio. The 200% concentration of super hard abrasive wheel is actually a kind of ordinary grinding wheel with super hard abrasive as auxiliary material, so it is generally not recommended to use the name.

At present, the high concentration of high speed and high efficiency grinding is adopted, and the high concentration of ceramic binder CBN grinding wheel is adopted. The concentration of ceramic binder CBN grinding wheel is generally selected above 125%, and the concentration of imported matching ceramic CBN grinding wheel is generally 175%~200%.

The hardness grade of the grinding wheel indicates the amount of holding force of the cement on the abrasive.

Uniform and stable hardness of grinding wheel and reasonable choice of hardness are important prerequisites to ensure grinding quality.

Foreign super hard abrasive grinding wheels generally have 3~7 hardness levels to choose from, but the super hard abrasive wheels produced in China are not standard hardness levels, and corresponding standards are not stipulated in GB6409, so the quality is not easy to guarantee, bringing inconvenience to users, and it is urgent to be supplemented and improved.

2. choose the appropriate amount of grinding

The grinding speed of the superhard abrasive wheel should be selected according to the grinding type, grinding mode and cooling conditions.

Increasing the working speed of the grinding wheel can significantly improve the grinding efficiency and grinding ratio (for example, the grinding speed of the grinding wheel can be increased by 40% and the grinding ratio can be doubled) and reduce the grinding cost.

The grinding speed of metal and resin bonded diamond wheel is usually 35~60m/s. The grinding speed of ceramic bonded CBN wheel can be increased to 45~160m/s. The linear speed of single-layer CBN wheel can be 125~250m/s.80~125m/s.

The grinding depth is generally 0.002~0.010mm, the workpiece speed is usually 10~30m/min, and the longitudinal feed speed is 0.3~1.5m/min.

Dressing of grinding wheel with super hard abrasive

Dressing grinding wheel of super hard abrasive is usually divided into two procedures: shaping and sharpening.

Shaping is to micro cut the grinding wheel to achieve the required geometric shape and precision, and make the abrasive tip finely broken to form a micro blade;

Sharpening is to remove the bonding agent between the grinding particles, so that there is a certain chip space between the grinding particles, and make the grinding particles stand out of the binding agent, forming a cutting edge.

Super hard abrasive wheel with multi-porosity ceramic binder (including diamond and CBN wheel), because the binder is loose, usually the shaping and sharpening can be completed at one time.

Binder for dense sand wheel (such as resin, metal binder), then shaping and trimming whisker respectively.

The most effective shaping tool for superhard abrasive wheel is diamond dressing tool.

Due to wear of dressing tool, the precision of mold surface is often affected by single particle diamond dressing.

If diamond wheel dressing is used, the dressing tool can be avoided to wear out too fast, and better grinding wheel morphology can be obtained.

The feeding precision of dressing device should be high, and each feed should be controlled in micron level.

Excessive dressing will not only affect the grinding quality, but also greatly reduce the service life of the grinding wheel.

There are many ways of sharpening, generally using mechanical (such as corundum block cutting sharpening, hydraulic jet sharpening) or electrical machining.

The latter is mostly used in the grinding wheel of metal bonding agent. The grinding wheel is used as the anode to remove the metal bonding agent by electric spark or electrolysis.

If graphite powder is added to the binder, this method is also suitable for resin and ceramic binder grinding wheels.

In recent years, a rotary diamond cup wheel dressing tool was developed in The University of Tokyo.

The mechanism is to make use of the abrasive falling off the cup wheel to impact the bonding bridge between the super hard (diamond or CBN) abrasive particles and the binder, as well as the extruding and grinding effect between the abrasive falling off and the super hard wheel to achieve the purpose of dressing.

Using this method, no matter for the multi-pore ceramic binder superhard grinding wheel or the dense sand wheel, the shaping and sharpening can be completed at one time. At the same time, due to the self-rotation of the cup wheel, the wear is very small, and the shaping force can be almost unchanged during the dressing process, and the value is much smaller than that when dressing with a single particle diamond dressing tool.

Use grinding fluid correctly

When grinding superhard abrasive wheel, dry or wet grinding can be used.

However, wet grinding can not only prolong the life of the grinding wheel, but also prevent the workpiece from grinding burn.

Different grinding fluids will cause the grinding ratio of the grinding wheel to differ several times, even ten times (jiangxi xinxing grinding wheel WeChat ID: zgxxsl_1978 editor-in-chief grinding king told you that this is the most neglected in reality).

The degree of mechanical wear, chemical erosion and thermal damage of grinding wheel is closely related to cooling effect.

However, when using CBN wheel for wet grinding, it should be noted that CBN reacts with water vapor and oxygen in the air at high temperature to produce ammonia and boric acid (BN+3H2O→H3BO3+NH3), which is called hydrolysis and will accelerate grinding wheel wear.

Therefore, water-soluble oils or aqueous solutions with extreme pressure additives are commonly used to reduce the hydrolysis effect.

When wet grinding with different grinding fluids, the relative life of CBN wheel is different. The wheel life cooled by pure oil is the longest, followed by that cooled by water-soluble oil, and the wheel life cooled by water and anti-rust additive is the lowest.

Unconventional use of super hard abrasive wheel

It is generally believed that diamond wheel is not suitable for grinding gray cast iron due to the high chemical inertness between diamond and iron group elements. However, this only happens at high temperature.

For example, when grinding with diamond grinding wheel, when the temperature reaches 650℃, diamond will oxidize in air, while when it reaches 700℃~800℃, it will graphitize.

At low temperatures these materials do not react with each other.

Therefore, as long as the appropriate grinding speed and wet grinding method are chosen and sufficient grinding fluid is supplied, the diamond wheel can grind the casting completely, which has been proved in the production practice.

The grinding ratio (9600) of gray iron with diamond wheel is much higher than (2700) of gray iron with CBN wheel when wet grinding is used

It is also generally believed that CBN grinding wheel is not suitable for grinding low carbon steel and other soft materials, because the grinding chip produced at this time is easy to block the grinding wheel.

However, the current research suggests that the ceramic binder CBN grinding wheel can be used to improve the grinding wheel's linear speed to form fine grinding chips, then remove the grinding chips with high-pressure jet grinding fluid, and provide sufficient grinding fluid to prevent blockage of the grinding wheel.

Therefore, CBN grinding wheel can grind low carbon steel (hardness greater than 30HRC) a class of soft materials.

Using an ordinary grinding wheel is the best choice for most situations.

Specific problem specific analysis.

However, CBN grinding wheel is not effective for grinding any material.

Usually it is not suitable for grinding hard alloy and the combination of hard alloy and steel.

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