In order to reasonably select the grinding amount, the relationship between the surface temperature of the grinding area and the grinding amount must be analyzed first. Taking plane grinding as an example, the calculation problem of reducing the grinding area to a semi-infinite heat field with a continuous uniform heat source AB conducting only below the surface of the workpiece is simplified according to the actual machining situation (see Figure 1).Through the theoretical analysis and calculation of temperature field, the heat generated by the continuous uniform heat source AB in the grinding zone in unit time Q = c0VI0.2AP0.35V sand 0.35F-0.3 (C0 is constant) can be obtained.From the relation between the surface temperature of the grinding zone and the grinding dosage, it can be seen that:
(1) Grinding depth AP When the grinding depth AP increases, the heat generated will increase, which will increase the surface temperature of the workpiece and increase the degree of burn. Therefore, AP cannot be selected too large.
(2) Transverse feed F When the transverse feed F increases, the surface temperature of the grinding zone decreases on the contrary, and the grinding burn decreases.The reason is that with the increase of F, the contact time between the grinding wheel and the workpiece surface is relatively reduced, so the action time of heat is reduced and the heat dissipation condition is improved. In order to make up for the increase of surface roughness caused by the increase of lateral feed, a wider grinding wheel can be used.
When the workpiece velocity vI increases, the surface temperature of the grinding zone rises.However, further study found that the larger vI was, the larger the temperature gradient near the grinding surface was, as shown in Table 1.
This is because although vI increases, the action time of heat is reduced, that is, although the temperature of grinding area is high, the workpiece surface is not burned before it is effectively cooled out of the grinding area. According to the data in Table 1, choosing a larger vI can reduce the burn on the grinding surface and improve the productivity at the same time.
Of course, increasing vI will lead to increased surface roughness, and in order to make up for this defect, the speed of grinding wheel can be improved accordingly. In fact, according to relevant studies, if vI is increased by 3 times, resulting in increased surface roughness, only a 39% increase in V sand can be compensated.Practice has proved that increasing vI and V sand simultaneously can avoid grinding burns.As shown in figure 2 is 18 crniwa steel grinding, vI and v sand not burn the critical ratio curve. Here is the right of the curve is prone to burn the danger zone (Ⅰ area), the curve of the upper left for safe (Ⅱ area).
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