| The technology of hot rolling microgroove combines advantages of roll forming and hot forming, not only increases material utilization and production efficiency but also improves the material performance of plastic forming, therefore it is suitable for mass production of micro structure on surface of sheet. However, machining micro groove on the surface of sheet is different from the traditional macro plastic forming, its mechanical properties, formability and plastic flow behavior are affected by grain size, geometry and feature size of micro groove on the roller. The main research contents of this paper are as follows: craft of hot rolling microgroove, microstructure evolution and the influence of size effect.In this paper, the finite element model of hot rolling microgroove is established by Deform-3D software, different craft parameters, geometry and feature sizes are set, including rolling temperature, rolling speed, groove width on the roller, rolling depth, top and bottom radius of groove. In addition, the actual experiment is carried to verify the exactness of the simulation. In this paper, the main research contents and results are as follows:1. A finite element model of roll forming microgroove on surface of plate is set up with different temperatures, width of channels on the roller, rolling depth. The flow of material is compared to conclude the reasonable parameters. Results are as follows: hot rolling microgroove has a continuous distribution of metal fiber streamline, so the comprehensive mechanical performance is obviously better than machining. Continuous metal streamline makes microgroove excellent mechanical properties such as resistance to fatigue strength. The distribution of streamline is rational, at the bottom and the fillet of the groove, the density is the largest. The more populated area of metal streamlines, the higher the density of the metal, the better the wear resistance. Rising temperature is beneficial to the flow of metal, decreasing the groove space can increase the metal flow range firstly and decrease it after that, and enlarging the rolling depth can improve the flow and deformation degree.2. On the basis of finite element model of roll forming microgroove on surface of plate, the microstructure evolution model is established. By changing the rolling temperature, forming rate, the channel width on the roller and rolling depth. By analyzing morphology of the average grain size and grain topography of selected sections, the optimum processing conditions are obtained to deform desired grain size. The reasonable rolling temperature is between 430 ℃ to 480 ℃, the forming rate is between 0.1mm/s to 1mm/s. The effect of channel width on the roller and rolling depth is not obvious.3. By the effect of grain size, the channel width on the roller and the top and bottom fillets on the roller to the forming height and rolling loads, size effect is studied. The feature height of microgroove decreases with the increasing of grain size. When grain size increases, the grain boundary strengthening effect, the yield strength and the deformation resistance reduce, so the rolling load reduces. Inside the groove spacing, greater the space is, more the grain boundary is, higher the flow stress during deformation process, so higher the rolling load is. The influence of top and bottom are the same, with the increase of radius, the rolling load decreases.4. The experiment result of material flow and microstructure evolution are the same as simulation, which proves that the simulation result is exact. Changing the rolling depth, different height of microgroove can be deformed. In order to make the best drag reduction effect, the rolling depth should be controlled more than 35%. By comparing the hardness distribution on the cross section, it is verified that the simulation results of the grain size effect is correct. At the same time, the distribution of hardness can also prove the change of depth will also cause size effect. |
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