Research On Forming Method And Experiment Of Nanocrystalline/Ultra-fine Grain Structure Cylindrical Parts By Counter-roller Spinning

Power spinning contains lots of advantages such as high accuracy, great smoothness,high material utilization, and so on, so it is widely used in aerospace, ordnance industry,petrochemical and transportation and other sectors.With the development of precision fromplastic forming technology, not only requires high precision, high material utilization, butalso the workpiece with higher performance. In the21st century, with the continuousdevelopment of nano or ultrafine grained technology, the use of strong plastic deformationtechniques to prepare nano or ultrafine materials has become a hot research topic of more andmore scientists. Studies have shown that the nano or ultrafine materials make by severeplastic deformation have lots of excellent performance and good application prospect, whichare seen as one to achieve bulk metallic nano or ultrafine crystallized the most effective way.In this paper, with the help of MARC finite element software for finite elementnumerical simulation of the stagger spinning, the isometric spinning and the counter-rollerspinning, and on this basis, the required design spinning technology and equipment anddevelop appropriate experimental program to study the changes in the dimensional accuracyof the spinning parts and their microstructure and mechanical properties of power spinningafter large deformation. The main contents and conclusions are as follows:Firstly, by means of finite element numerical simulation software (MARC), with20steelas research material, using the forming methods of the stagger spinning, the isometricspinning and the counter-roller spinning to study the equivalent stress, strain and wallthickness distribution of spinning parts, so select one power spinning method with poorsmallest equivalent stress, strain, and lay the foundation for subsequent tests.The simulationresults showed that when using the method of counter-roller spinning, the inner and outersurface of the spinning parts with the equivalent stress, strain difference and maximum wallthickness deviations, which are much less than the stagger spinning and the isometricspinning, stagger spinning is less than the isometric spinning. Of counter-roller spinning withdifferent sets of rollers for spinning parts in the equivalent stress, strain of the inner and outersurface, and wall thickness distribution of influence is relatively large.Secondly, depending on the choice of the size of the tube material, the mechanicalproperties as well as theoretical knowledge combined with the corresponding spinning and numerical simulation results to design process equipment for counter-roller spinning testsneeded(rollers, the clamping device etc.), and to20steel and H62brass tube, using thecombining methods of counter-roller spinning forming and recrystallization annealingprocess, studying the changes of dimensional accuracy, surface quality and microstructureand mechanical properties of the spinning parts. The experimental results showed that withthe increasing of reduction ratio, spinning parts improving the uniformity of the wallthickness, increasing diameter and ovality, and decreasing surface roughness.Thirdly, to study the microstructure evolution of spinning cylindrical parts by opticalmicroscopy (OM) and other analytical techniques. The experimental results showed that withthe increasing of reduction ratio, original equiaxed grain is constantly stretched and orientedto give an ordered microstructure. Further, after severe plastic deformation of the20steelspinning parts under580℃annealing and H62brass spinning parts under650℃annealing,as the annealing time prolonged, the slender elongated shape grain began to get more uniformin heat preservation after one hour of fine equiaxed grain (the average grain size ofrespectively about0.6μm and10μm), further overtime of heat preservation, equiaxed graingrowing into big grain.Fourthly, study on mechanical propertis of spinning for different thinning rate and afterrecrystallization annealing. The experimental results showed that the hardening of thematerial after the plastic deformation, so that increasing the strength and hardness of thespinning parts, decreasing the ductility and toughness. After severe plastic deformation(Reduction ratio is about90%)of the20steel spinning parts under580℃annealing and H62brass spinning parts under650℃annealing, as the annealing time prolonged, strength andhardness reduced, plasticity increased of the spinning parts after recrystallization annealing.And the holding time of one hour of20steel and H62brass spinning parts, the comprehensivemechanical properties of the best(20steel: tensile strength is640MPa, vickers hardness valueis201HV, elongation is21%; H62brass: tensile strength is490MPa, vickers hardness valueis155HV, elongation of23%).