Grinding cracks (black broken points) produced by surface grinding are not formed by sudden cracking, but appear sporadically on the surface of the workpiece. Although grinding cracks, novices are still difficult to distinguish. The grinding fluid treated with special drugs is not deep, and the general depth is only 0.05~0.25mm. There are several reasons for the occurrence of grinding cracks: the internal stress of the workpiece exceeds the limit of the fracture, that is, the workpiece has mechanical stress and thermal stress remaining in the surface layer due to previous grinding or heat treatment. Since the part of the stress that just balanced can be worn away during grinding, the residual stress exceeds the strength of the workpiece, and some grinding cracks are generated. Among all the reasons, "cracking by grinding" is the key to the problem. The biggest problem is the stress generated by the grinding heat. Because of the heat of grinding, the local temperature of the surface of the workpiece rises rapidly, and this part is tempered or otherwise heat treated. Cracks are generated by tensile stress due to changes in internal structure and shrinkage of the surface. 1. An example of the relationship between the feed amount of the grinding wheel and the residual stress. 1 The tensile stress will gradually increase as the feed force of the grinding wheel increases, and slowly approach the tensile strength of the workpiece material. Cracks are generated once the tensile strength of the workpiece material is exceeded. 2 The compressive stress does not change too much, because the scale and experimental conditions are different, so the comparison cannot be made, but the almost constant is that when the backing knife is 0.05 mm, the residual tensile stress is the largest, even if it is cut deep and residual. The stress will not be too great. It is generally believed that this is due to abrasive falling. 2. An example of measuring the residual stress after grinding by changing the feed amount of the grinding wheel. The greater the feed of the grinding wheel, the deeper the residual stress exists. 2 The residual stress on the surface acts as a tensile stress in the direction of the grinding, and can also act in the vertical direction of the grinding direction in the form of pressure, and the deeper the interior, the sharp decrease in stress. 3 When acting in the grinding direction and the vertical direction, it first becomes a compressive stress and then suddenly becomes a tensile stress that coincides with the grinding direction. When it reaches the maximum value, it gradually decreases, eventually becoming a tiny compressive stress. The relationship between the hardness of the grinding wheel and the residual pulling force, the hardness between G, H, I, J, the higher the hardness, the greater the residual residual stress. The effect of the speed of the grinding wheel (circumferential speed) on the residual stress. Once the rotational speed (circumferential speed) exceeds 1500 m/min, the residual stress increases sharply. In addition, because of the different materials of the workpiece, there are also differences in the occurrence of grinding cracks and the occurrence of grinding cracks. Caesar door control co.,ltd , https://www.caesar-door.com
Grinding crack generation and solution analysis