Deformation Of Loose Powder Filled Tubes During Forward Extrusion With Superimposed High-frequency Vibration

Discrete medium such as loose powder filled thin-walled tubes are frequently used as integer structures for special purpose, e.g., in certain materials processing(produce superconducting MgB2 strands or drawing technology with solid granules process)or architectural components. The deformations of such composite structures are complicate mechanics processes, involving coupled elastic-plastic deformation of dense metal, compaction of discrete particles, along with the interaction between the filler and tube wall.However, the studies regarding the frame of mechanics condition in the integral forming of powder filled tubes are still rare which could not guide the manufacture. For example, in the preparation of superconducting materials by drawing and so on, it is frequently encountered that the technology parameters of the processes were inappropriately selected, resulted in fracture at interface and uneven distribution of microstructure. And many studies indicate that formation with vibration can improve the process which could be used by such composite structures to increase the forming ability. While, studies about loose powder filled thin-walled tubes with high frequency vibration are rare. Therefore, it has important theoretical and engineering significance to examine the coupled deformation behaviors of discrete medium filled thin-walled tubes during forming.This paper examined the forward extrusion of Al 6061 tubes filled with two kinds of particles with different granularities and materials by means of experiment and numerical simulation with and without vibration. First, the study regarding the internal volume variation of hollow tubes during forward extrusion indicates that, with the reduction of diameter the decrease of internal volume of tubes is a common phenomenon. The volume-reduction degree increases with the increasing die conical angle ?, relative thickness t0/D0, extrusion ratio D0/D, and friction coefficient ?. The cavity shrinkage brings about triaxial pressure on the filler, resulted in compaction and densification of it.Then, experiment and simulation of loose powder filled thin-walled tubes extrusion show that the higher the pressure is, the more the particles are compacted. Particle filling resulted in higher extrusion load; meanwhile the load-stroke curves of the tubes filled with fine powders and coarse balls are different due to dissimilar migration behaviors of the media. Furthermore, small r-value leads to higher hydrostatic pressure of the filler and then the powders are compacted more.Next, the experiment of testing friction angle with vibration by straight scissors indicates that vibration has good influence on mobility of powders and then a smaller friction angle. And, the friction of Fe powders is smaller than steel balls'. The simulation shows that vibration leads to a reduction of friction of contact surfaces and a increase of deformed powders' pressure.Moreover, in the vibration moment, forward extrusion of thin-walled tubes filled with various discrete particles with different sizes and materials were investigated by means of experiment. The effect of processing and geometrical parameters on variation of tube inner volume was analyzed; the relationship between the densification of powder and the internal stress condition during extrusion was also examined. Vibration results in reduction of extrusion load and the increase of internal powders' hardness as well as the uniformity of wall thickness.