Heat generation is one of the most important problems in grinding, because high temperature can limit the wheel life and also induce defects, such as tensile residual stress and micro cracks, in the workpiece. Coolant is extensively used in order to reduce the heat effect. _{c w s}...[ Read more ]

Heat generation is one of the most important problems in grinding, because high temperature can limit the wheel life and also induce defects, such as tensile residual stress and micro cracks, in the workpiece. Coolant is extensively used in order to reduce the heat effect.

In order to deal with the problems associated with conventional cooling methods and combine their advantageous, an actively cooled and activated cooling approach is examined in this project. Characteristic studies were carried out to find the relationship between the input and output parameters. The cooling performances were compared for the proposed approach and other 3 cooling methods.

In order to deal with the multiple input parameters, including, depth of cut d_c, table speed v_w, wheel speed n_s, coolant temperature t_c, coolant concentration c_c, coolant flow rate Q_c and nozzle diameters d_nzl, and reduce the huge number of experiments, an orthogonal test was conducted and the order of importance of the 7 input parameters was obtained. Based on this result, 4 input parameters with higher order of importance were selected to be further studied.

Coolant velocity v_c related parameters, including coolant flow rate Q_c and nozzle diameter d_nzl were studied. Effects of Q_c and d_nzl on surface roughness were analyzed. It was found that when Q_c increased from 90 to 110 l/h, surface roughness R_a can be reduced by up to 3.99%. When d_nzl decreased from 5.1mm to 3.8mm, surface roughness R_a can be reduced by up to 12.15%. When v_c increased from 1200 to 2700mm/s, surface roughness R_a can be reduced by 14.75%.

In v_c test, compared with normal coolant, an average reduction up to 7.16% in R_a can be obtained for cooled coolant, an average reduction up to 4.79% in R_a can be obtained for the activated coolant and an average reduction up to 20.82% in R_a can be obtained for the actively cooled and activated coolant.

SEM images for v_c test show that the best surface quality was obtained by using actively cooled and activated coolant under the largest coolant velocity of 2700mm/s.

Effects of depth of cut d_c and coolant temperature t_c on loading current I, radial wheel wear R_ww and surface roughness R_a were also studied. When d_c decreased from 5μm to 1μm, loading current can be reduced by up to 42%, radial wheel wear R_ww can be reduced by up to 384.21% and surface roughness can be reduced by up to 7.56%. When tc decreased from 23 to 4ºC, loading current can be increased by up to 29%, radial wheel wear R_ww can be reduced by up to 86.27% and surface roughness can be reduced by up to 11.95%.

In d_c and t_c test, compared with normal coolant, an average increase up to 28.94% in I can be obtained for cooled coolant, an average reduction up to 9.39% in I can be obtained for activated coolant and an average increase up to 8.65% in I can be obtained for the actively cooled and activated coolant.

In d_c and t_c test, compared with normal coolant, an average reduction up to 83.33% in R_ww can be obtained for cooled coolant, an average reduction up to 57.78% in R_ww can be obtained for activated coolant and an average reduction up to 91.67% in R_ww can be obtained for actively cooled and activated coolant.

In d_c test, compared with normal coolant, an average reduction up to 11.65% in R_a can be obtained for cooled coolant, an average reduction up to 4.88% in R_a can be obtained for activated coolant and an average reduction up to 11.26% in R_a can be obtained for the actively cooled and activated coolant.

Through the experiment results in d_c and t_c tests, it was found that when coolant temperature decreases, the hardness of both workpiece material and grinding wheel will increase. Firstly, the increase in workpiece material, on one hand, leads to an increase in grinding force and loading current; on the other hand, it leads to a decrease in lateral plastic flow in workpiece material and thus a reduction in surface roughness. Secondly, the increase in grinding wheel can lead to a significant reduction in wheel wear which will be good for surface roughness reduction.

SEM images for d_c and t_c test show that the best surface quality was obtained by using the actively cooled and activated coolant under the smallest depth of cut 1μm and lowest coolant temperature 4ºC.

Computational test was conducted to study the thermal transfer and temperature distribution in the grinding zone. It was found that average temperature in the grinding zone T_avg increases with the increases in depth of cut d_c and table speed v_w. The heat can be taken away more effectively by the actively cooled and activated cooling approach.