Research On Microstructure Evolution Of Cold Rolled Ring

Cold ring rolling is a kind of continuous local plastic deformation technology used for manufacturing seamless rings. Nowadays this technology is widely applied to processing a variety of ring products such as bearing races, flanges and gear rings owing to its advantages of uniform quality, smooth surface, close tolerances and considerable saving in energy and material. Combining numerical and experimental methods, this dissertation explored the strain distribution of the cold rolled ring in the beginning part. Subsequently the influence of lubrication condition in roller-ring contact boundary upon the surface quality of ring products was investigated. What's more, evolution of microstructure of the ring was studied as well. As a result, the effects of processing parameters upon the microstructure of the ring products were elucidated and links were forged between microstructural properties and mechanical performances of the cold rolled ring.Analytical method was conducted to calculate the thickness reduction in outer and inner surface of the rolled ring on certain dimensional conditions of roller and ring blank. A rational FE model of cold ring rolling was set up in ABAQUS software environment, and the strain distribution of the ring was analyzed. Results indicate that the outer surface of the rolled ring shows a higher level of strain than that of inner surface. Practical experiment was carried out on D56G90 CNC cold ring rolling mill with the same processing parameters used for FE simulation. And the microstructures of the cold rolled ring were investigated with Quanta 200 SEM. Results show that the deformation degree of outer surface layer was greater than that of inner surface layer, which shows good qualitative agreement with the results of analytical and numerical method.To investigate the influence of cold ring rolling process on the surface quality of the raceway of bearing race, the cold ring rolling test of 6308 inner-groove ball bearing race was carried out with a D56G90 CNC cold ring rolling mill. The surface topography of the cold rolled bearing race was investigated with a Philips Quanta 200 SEM. Results show that the rolling feed rate has a remarkable influence on the lubrication condition of roller-ring contact boundary and on the surface topography of the bearing race. A rational rolling feed rate will preclude the deterioration of micro defects on the surface of the bearing race, and therefore guarantees the surface quality of the raceway.Red copper ring was processed with several processing parameters, and the evolution of dislocation and diffraction patterns on longitudinal section of the ring was observed with a JEM2010--HT TEM. Results indicate that with the increasing of thickness reduction the original integral grains were subdivided into subgrains, and dislocation cells of high density were observed. In addition to that, the diffraction pattern of selected region was observed to be changed from spots to rings, which suggests that a preferential orientation of the grains was obtained. With feeding rate increased, the density of dislocation was increased and the subgrains diameter became smaller.