The Research Of Vibration Granule Medium Forming Technology In Bi-cone Parts Of Magnesium Alloy AZ31B

Solid Granule Medium Forming technology（SGMF） presented on the basis of conventional flexible die forming is a new flexible die forming process in which solid granule medium is used to replace the rigid male die. The technology takes full advantages of granule medium such as seal easy, loading easy and nonuniform internal pressure to provide a new way for the forming of magnesium alloy and other light weight alloy. Vibration plastic processing technology is a new process in which a ultrasonic vibration excitation is applied in the process of metal forming to improve the contact conditions at the material-die interface and the forming limit of sheet. Many key problems in the field of hard-processing material forming, such as high work hardening and heavy wear of the mould cavity, have been solved by this technology. Ultrasonic Vibration Granule Medium Forming technology（UGMF） in which the ultrasonic vibration is applied in SGMF has the characteristics of both.In order to study the influence of UGMF on the forming property of magnesium alloy and other hard forming material as well as the forming of parts with complex shape section, UGMF is applied in the forming of magnesium alloy AZ31B bi-cone part in this paper. The characteristic of bi-cone part forming and the affect of ultrasonic vibration in UGMF are researched by numerical simulation and experimental study.Based on the theory of vibration anti-friction and powders mechanics, a pressure-transfer model of solid granule under the condition of vibration is built. The expressions of equivalent friction coefficient at granule medium-barrel wall interface and reactive force given by barrel bottom along axial direction are also obtained. All the theoretical work is compared with the result of numerical simulation. The study shows that the friction at the granule-die interface has decresed and the pressure-transfer property of solid granule has been improved with the applition of ultrasonic vibration in the model.Combining with the material performance tests of magnesium alloy AZ31B, bi-cone part is studied as a research subject to establish the stimulation model of UGMF. The change rules of part outline, wall thickness, forming force and equivalent stress in the forming process of bi-cone part are studied. Moreover, the forming parameters of filler height, blank-hold force and amplitude are also analysized in this process. This study shows that the effect of amplitude is the most obvious. Compared with that without vibration, the biggest wall thickness reduction decreased from 22.8% to 12.5% and the reduction of forming force can be up to 1200 N with the function of ultrasonic vibration.The effect of amplitude on forming property is studied by the UGMF process test for the bi-cone part. At 250℃ a bi-cone part of magnesium alloy AZ31B has been achived with a blank in diameter D₀=44mm with ultrasonic vibration.