薄壁件粘性介质外压成形失稳起皱及成形极限研究

Outer pressure forming of thin-wall parts, mainly due to the influence of buckling and wrinkling, will give rise to wrinkling when forming pressure exceeds buckling pressure, leading to the forming tube blank changed from stable state to instable state, and the forming process is hard to control. All these restrict the application of outer pressure forming process. In consideration of these problems, the applicant carried out the outer pressure forming method of viscous medium, which, due to the unique performance of viscous medium, can alleviate the influence of buckling and wrinkling on outer pressure forming under certain conditions,and improre the outer pressure forming limit. Aiming at the problems of stability of the tube blank and the elimination of wrinkles under the outer pressure of viscous medium, systematic study is made in this project,and influences of the viscous medium properties on delaying the occurrence of buckling and the elimination of wrinkles are concluded, and then the viscous medium used in the outer pressure forming process is optimized. According to the deformation features of outer pressure forming of viscous medium,combined with the stability theory and the forming limit theory, the outer pressure forming limit diagram of viscous medium is built which can reflect the influence of buckling and wrinkling on outer pressure forming, which gives solution to basic problems that restricted the application of outer pressure forming of thin-wall parts and technical support for the application of this technology.

薄壁件外压成形主要问题是失稳起皱，当成形压力超过失稳压力就会产生起皱，导致成形筒坯由稳态转变为非稳态变形，成形过程不易控制，制约成形方法的应用。针对这些问题申请者开展的粘性介质外压成形方法，由于介质特有性能一定条件下减缓了失稳起皱对外压成形的影响，较大幅度的提高外压成形极限。本项目针对粘性介质外压作用下的筒坯稳定性及褶皱消除问题进行系统研究，确定介质性能对延缓失稳、消除褶皱的影响规律，优化外压成形用粘性介质；根据粘性介质外压成形变形特点，结合稳定性理论和成形极限理论建立能够反映失稳起皱过程对外压成形影响的粘性介质外压成形极限图,解决制约薄壁件外压成形的基础性问题,为该技术的应用提供技术支持。

本项目旨在研究粘性介质自身特性对外压成形失稳起皱过程影响，建立能够反映失稳起皱过程对外压成形影响的粘性介质外压成形极限图。研究过程中，通过粘性介质动态剪切流变实验和压缩实验，确定出不同分子量粘性介质的粘度、速率敏感性、压缩性能等流变性能，及对筒坯（无缝筒坯和焊接筒坯）稳定性的影响规律；基于板材YBT起皱原理，确定出不同分子量粘性介质压力条件下板材消皱能力，及褶皱不同受力状态对消除能力的影响；得到了既有助于筒坯稳定性提高，又有助于褶皱消除的粘性介质分子量及所对应的流变特性，从而优化了外压成形用粘性介质；在此基础上，基于粘性介质外压成形工艺窗口，建立了以变形区长度、筒坯直径为参数、极限变量为指标的粘性介质外压成形极限图，并进行了实验验证，该成形极限图较好反映了筒坯的失稳起皱、褶皱消除和极限变形能力。上述研究结果不仅揭示了粘性介质性能对外压失稳及褶皱消除过程的影响，还为该工艺的应用提供了较好的技术支持。