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CBN abrasive is a new abrasive developed in modern times. Due to its high hardness and micro-crushing structure, it can achieve good efficiency for grinding high-hardness ferrous metals. Among the abrasives, the hardness of CBN is second only to diamond and much higher than that of general abrasives such as GC.
The body of the CBN grinding wheel is mostly made of metal(Aluminum or steel), and most of the heat energy will be transmitted to the grinding wheel when the CBN grinding wheel is ground. Therefore, during the grinding process, the heat energy will be continuously transferred to the grinding wheel. At this time, the metal body will start to expand due to the accumulation of heat energy.
Because the distance between each position of the grinding wheel and the grinding point of the heat source center is different, the expansion degree of each position is also different. The loss of roundness of the grinding wheel may cause "vibration" and other problems!
In addition, thermal expansion will also change the previous feed. For example, the original feed is 0.01mm, and the feed may become 0.03mm after thermal expansion, so dimensional accuracy is not easy to achieve.
As mentioned earlier, CBN abrasive is harder than ordinary abrasive, and its shape is also sharper. Although the cutting force is good, if the same particle size as the ordinary abrasive is selected, the roughness of the grinding surface will become too coarse (close to the cutting effect).
Therefore, in practice, the grain size of CBN will be 3~4 orders finer than that of conventional grinding wheels. For example, if the grain size of conventional grinding wheels is 80#, CBN will choose 140# or 170#.
However, this increases the difficulty of feeding, because the appropriate feeding amount is about 1/10 of the diameter of abrasive particles. When the selected particle size is small, the diameter of abrasive particles is small, and the range of feeding amount will be reduced.
In addition to the increased difficulty of tool set at the beginning, it is easy to cause burns and other problems if the feed volume suddenly increases due to operation or machine problems. It also leads to the thermal expansion of the grinding wheel mentioned above.
In addition, the bond of the CBN grinding wheel is stronger than that of the general grinding wheel, and the self-sharpening effect is slow, which will make this situation worse.
In order to avoid the above problems, many operators will choose to "slow down the wheel speed" to avoid burns and other problems. However, CBN has a micro crushing structure. Too slow rotating speed is not conducive to giving full play to the characteristics and advantages of CBN, but also reduces the grinding ratio and reduces the service life of the grinding wheel.
① Change the metal body into other materials that will not expand due to temperature: for example, ceramics. It will solve the problem that the metal body expands due to heating and loses its true roundness.
② Choose a special high porosity bond: through the role of pores, achieve the effect of heat dissipation. At the same time, because the contact area is reduced, the grinding resistance is reduced, and the grinding temperature is also reduced.