Studies Of Varying Parameters Processing Methods Of Die-less Spinning Based On Optimization Of Hoop Strains

The spinning forming technology has been widely applied in mechanical processing field due to its advantages such as simple equipment, small forming forces,improving material properties and chipless forming. However, the requirement of specific mandrels restricts the flexibility of spinning. As a novel technology with great potential, the die-less spinning, in which the specific mandrel is replaced by the cylindrical mandrel with general purpose, has broad research and application prospects.As the forming parameters of spinning usually have opposite influences on forming quality, spinning processes with fixed parameters cannot meet the requests of development such as parameterized, precise and intelligent forming.For solving the above problems, the parametric characterization model of forming quantity of the spinning process is developed, with the parametric model of the roller paths, as the base of the influence model of the forming parameters and the forming qualities. The free deforming mechanism of the blank in die-less spinning is obtained by the combination of the explicit analysis model of the deforming process and the implicit analysis model of the springback process of the blank. Based on the independent-developed composite metal sheet spinning machine, the experimental platform for die-less spinning and the measurement technology of quality parameters are developed. The mechanism of varying parameters methods of die-less spinning is analyzed to obatain the way of adjusting the processing parameters.The designing technique of the roller path with mutative shapes based on optimal allocation of the hoop strains is proposed. The optimal design of the gaps between the roller paths is obtained as a foundation of subsequent research, based on the optimal allocation of the hoop strains between passes. Four processing methods with different roller path profiles and with three deformation allocation methods are discussed. The "similar geometry principle for restraining shape deviation" and the"small curvature principle for maintaining wall thickness" are presented for optimal design of roller path profiles; in addition, the "uniformly allocation principle for maintaining wall thickness" and the "large deformation principle for restraining shape deviation" are brought forward. Based on these principles, a comprehensive optimum schedule is presented based on the final-pass priority.The processing technique of mutative feed ratios based on hoop strains decomposition among and within the passes is proposed. The total hoop strain is decomposed among the passes, based on which the processing time is optimally allocated among the passes accorrding to the hoop strains. The "uniformly decomposition principle for hoop strains" and “sufficiently forming principle for the final pass" for restraining the shape deviation are proposed. Uniform deformation of the blank is realized through mutating the feed ratios of the passes according to the hoop strains between the passes. The hoop strain of the final pass is decomposed by optimally allocating the processing time in the final pass accorrding to the local hoop strain, based on which the "sufficiently forming principle for large hoop strain part" is proposed for restraining the shape deviation.The roller-path adjustment technique with mutative path shapes based on a divide-and-conquer methodology of the hoop strains and the shape deviations. The impact model between the hoop strain and the shape devations is built by dynamic and implict step-by-step solution technology and corresponding forming mechaism and distribution characteristic analysis of springback and over-forming shape devations. The"uniformly distribution principle for hoop strains" is proposed to control the springback shape error. The "uniformly variation principle for hoop strains" is proposed to control the overforming shape error. Separation of springback and overforming shape errors is realized, and the first adjustment of the roller path is conducted based on the shape error data. The pre-compensation of the "secondary" shape error brought by the adjustment of the roller path is realized by the relation of hoop strains and shape errors.For the validation of the varying parameters technology proposed in this paper, the designing technique of the roller path with mutative shapes, the processing technique of mutative feed ratios and the roller-path adjustment technique with mutative path shapes are applied to the die-less spinning processes of three shell type rotary parts, by which the cracking failure, wrinkling failure are prevented and the shape precision is improved.As a result, actual effects of the varying parameters technology of die-less spinning are verified.