Study On The Ultrasonic Effect Of Ultrasonic Assisted Upsetting-extrusion Forming

Ultrasonic assisted bulk forming process is a plastic deforming method assisted by using ultrasonic mechanical vibration energy.The ultrasonic effect can not only reduce the material flow stress,but also improve the contact state between work-piece and mould.Previous studies focused on ultrasonic material effect,and paid little attention to the material flow patterns.In this paper,we study the ultrasonic effect and its mechanism from the view of material deformation patterns.In order to study the effect of ultrasonic vibration on the material flow,a design technique for integrated booster with die was established.An ultrasonic assisted plastic forming device was designed.The experimental studies on material flow rules of the ultrasound assisted small-hole and big-hole upsetting-extrusion process were performed.The experimental results shows that the material flow pattern is different from those without ultrasonic vibration.The extruded material length is larger;when the height-diameter ratio of is equal to 1.5,the deformed shape of the work-piece looks like a “waist”;when the ratio is equal to 1.0,the deformed shape is quite uniform.The extruded radial material curl into a roll during the big-hole upsetting-extrusion which is similar with that of an ultrasonic assisted material cutting.Then,ultrasonic effect and its mechanism were studied by using the finite element simulation technology,impact dynamics theory and material characterization techniques.(1)It is investigated that the macro equivalent performance of ultrasonic effect in the process of upsetting-extrusion process based on the performance equivalent method and finite element simulation technology,it is found that the material softening effect of ultrasonic vibration is related to the decrease of the plastic modulus,and the boundary effect is related to the decrease of the equivalent friction stress on the interface of work-piece and mould.(2)The impact effect of ultrasonic assisted plastic forming process was analyzed by using the dynamic method.Results show that: the impact effect of ultrasonic boundary effect will lead to the accumulation of deformation in the contact area,forming a large plastic deformation in the contact areas and small deformation in the middle of the work-piece for the inhomogeneous propagation of elastic waves and plastic waves in the materials;ultrasonic vibration causes the work-piece to be loaded and unloaded,so that there is a reciprocating friction shear stress between the die and the work-piece,the reciprocating friction force cannot significantly improve the uniformity of work-piece,the deformation uniformity of work-piece is related with the ultrasonic impact and contact condition.(3)The black substance generated during of ultrasonic assisted upsetting-extrusion process is analyzed by using material characterization techniques,and then the mechanism of ultrasonic assisted upsetting extrusion process of contact is analyzed: first,the surface oxide film of aluminum is destroyed,then the new material is rapidly oxidized under the help of friction heat,which then functions as lubricating medium,so that the original sliding friction is changed to a certain degree of rolling friction,thereby friction force is reduced.