Most of the CBN grinding wheel substrate is made of metal, and when the CBN grinding wheel is grinding, most of the heat energy will be transmitted to the direction of the grinding wheel. Therefore, in the grinding process, heat energy will be continuously transferred to the grinding wheel. The metal matrix then begins to expand as heat accumulates.
Because the distance between each position of the grinding wheel and the grinding point in the center of the heat source is different, the degree of expansion of each position is also different, the roundness of the grinding wheel is lost, and there may be "vibration" and other problems!
In addition, thermal expansion will also change the amount of feed originally set. For example, the original set feed is 0.01mm, after thermal expansion feed may become 0.03mm, dimensional accuracy is not easy to achieve.
As mentioned before, CBN abrasive is more general abrasive hard, coupled with the shape is also more sharp, although the cutting force is good, but if you choose the same size as general abrasive, the roughness of the grinding surface will become too coarse (close to the effect of cutting).
Therefore, in application, the choice of CBN granularity will be 3~4 orders finer than the general grinding wheel, such as the general grinding wheel granularity is 80#, CBN will choose 140# or 170#.
However, this increases the difficulty of feeding, because the appropriate feeding amount is approximately 1/10 of the diameter of the abrasive grain. When the selected particle size is small, the diameter of the abrasive grain is also small, and the feeding range is narrowed accordingly
In addition, the bond of CBN grinding wheel is stronger than that of 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 grinding wheel speed" to avoid burns and other problems. However, CBN has a micro-crushing structure, and too slow speed is not conducive to play the characteristics and advantages of CBN, will also reduce the grinding ratio, and reduce the life of the grinding wheel
Solutions:
Change the metal wheel body to other materials that will not be thermal expansion due to temperature: such as ceramics. In order to solve the metal inner plate heat expansion, loss of roundness. Or you can choose a new type of special binder containing a large number of pores: through the role of pores, to 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 will also drop.
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