THE OPTIMIZATION OF SEVERAL TECHNOLOGICAL PARAMETERS OF ULTRASONIC VIBRATION AIDED FLOW-FORMING Chengcheng Zhu, Shengdun Zhao, Chao Zhang and De an Meng Xi'an Jiaotong Universityg, Xi an, China email: 573652551@qq.com When using the flow-forming method to manufacture tubes which have big diameter or thick wall, the spinning power will be very large. Too big spinning power leads destabilization and other problems. As we all know, ultrasonic vibration could reduce the power in metal forming process, so the ultrasonic vibration aided flow-forming method has been put out. The effect of ultrasonic vibration in this method is complicated, and some studies use experiment or general FEM to find the ultrasonic vibration influence on metal flow characters at present. Rollers feed speed and the amplitude of ultrasonic vibration is important in this forming process, but there are few studies on optimization problem under given conditions. We used the finite element software ABAQUS to analyse this kind flow-forming process. By using different amplitudes of ultrasonic vibration and feed speed of spinning rollers, a typical flow forming process was simulated. According to the simulation result, the ultrasonic vibration could effective reduce flowforming power. With the amplitude of ultrasonic vibration increasing, the material is easier to shape. Otherwise, with the feed speed improving, the forming power will be bigger and bigger. Depending on the simulation result, some process parameters were analysed. This study confirmed the effect of ultrasonic vibration aided flow-forming in forming force side. 1. Introduction The flow-forming process is a kind of near-net shaping method [1]. Compared with other forming technologies, the flow-forming process has some significant advantages: better efficient, better accuracy, and smaller forming force. Nowadays, this method is widely used in many domains. For high performance big parts, a mass of new flow-forming methods are raised such as counter-rollers flow-forming process [2]. The ultrasonic vibration method could alter metal formability [3]. So the ultrasonic vibration process becomes an important means to ameliorate traditional machining and forming technologies [4]. Ultrasonic vibration aided flow-forming is a typical combination in this mind. This flow forming method could increase the hardness of work surface and the roughness of the mandrel contact surface. The major forming forces could be reduced with high ultrasonic vibration [5]. The ultrasonic vibration could be applied on mandrel or rollers [6]. During the flow-forming process, the mandrel rotates by itself. The roller feeds in the axial direction to shape the tube blank in Fig 1. Just like the way to vibrate machine tool cutter, there are three modes of vibration can be selected: bend, torsion and longitudinal tension-compression. The longitudinal vibration is the most common used method. In this way, the roller will vibrate in the radial direction and the mandrel will vibrate in axial direction. The difference between the forward and the back-forward flow forming is whether the free end of the tube blank move with the roller. They have similar simulation method. Both of them could use ultrasonic vibration to improve processing capability. 1
Figure 1: Ultrasonic vibration aided flow forming process. With the help of the Finite Element Method (FEM), the metal forming process could be efficiently and accurately analysed. So the ABAQUS which is an excellent research-based FEM software is chosen to study the influence of ultrasonic vibration in the flow forming process. The flow forming process could be considered as plane deformation, so the 2D FEM method is used in this study. The feed speed and vibration amplitude was considered. 2. FEM model 2.1 Material performance The ultrasonic vibration has complicated influence on the material performance. Nowadays, three theories are put forward to explain the characters which happen in the ultrasonic aided metal forming process: surface effect, volume effect and rotary forging effect. The volume effect is the most important phenomenon in majority forming method. The volume effect could significantly cause material softening and other transformations. So it is important to find a suitable material model which consider the volume effect to study the forming process with FEM. Many different kinds of material model are used in FEM to deal simulation problems. The most common used material model is the quasi-static model which is revised with attenuation factor. These model has been proved to approximate evaluate the vibration influence in some forming process such as drawing [7]. A better idea is to overall considering the rain rate hardening method and the ultrasonic vibration aided tensile curve. The ultrasonic vibration aided tensile curve has considered the different vibration effect on various forming process. One kind of high-quality carbon steel was chosen to study the flow-forming process: ASTM 1020 [8]. This material is widely used in manufacture. The basic material parameters are shown in Table 1. Table 1: The basic material parameters of ASTM 1020. Name Density Yong s modulus Poisson s ratio (kg/m 3 ) (GPa) ASTM1020 7850 209 0.3 330 Yield strength (MPa) 2.2 Preprocess Because of the roller and the mandrel are much hard than the tube blank, they almost keep their shape in the flow forming process. So they were both set as rigid part. Some important parameters of the forming process which are similar as Rasoli M A used in the experiment [5] are presented in Table2. The 2D model is shown as Fig. 2. Table 2:Model parameters. Blank thickness (mm) Thickness Mandrel Roller Feed speed Frequency Amplitude reduction diameter diameter % (mm) (mm) (mm/s) (khz) (mm) 3 25 38 115 0.3 0.6 0.9 20000 0.01 0.001 2 ICSV23, Athens (Greece), 10-14 July 2016
Figure 2: 2D FEM model. The ABAQSU Standard Code was used to simulate the forming process. The ultrasonic vibration was load by shake the mandrel in the axial direction to imitate the mandrel longitudinal wave. Because the vibration tensile model has considered the ultrasonic influence, the simulation process is much more like traditional flow forming. By the way, in this FEM simulation, the roller vibrating in the radial direction has also been test, but there is little difference between this situation and the one vibrating the mandrel. 3. Result and discussion 3.1 Simulation result The forming process during both of the traditional flow forming and the one with ultrasonic vibration help were steady. After the simulation, the thickness of blank obviously decreased. The Von-Mises stress nephogram in the forming process is shown as Fig 3.1. The radial force in the ultrasonic vibration aided flow forming process is shown as Fig 3.2. The black points in the picture are calculate result(simulation data). The output time interval is bigger than calculate time interval, so it look like straight line. When the vibration load on the flow forming process, the shaping force will cyclical change as the vibration frequency. The max in this break line was defined as the vibration aided flow forming force in following sections. Figure 3.1 Von-Mises stress nephogram. Figure 3.2 Radial force with ultrasonic vibration. Figure 3: Stress and strain nephogram. 3.2 The influence of feed speed The feed speed is determined by the feed rate and mandrel rotational speed. In 2D FEM simulation, the feed speed is the representative of these two important parameters. The absolute value of the radial direction force and the axial direction force is shown as Fig. 4. It can be seen that the forming force rise with feed speed increasing. The absolute increment of axial force is smaller than the radial s, but their relative increments are similar. With the help of the ultrasonic vibration, both of the axial and the radial force is decreased. These three feed speed in FEM simulation is low, so the vibration influence isn t highly significant. Considering the working efficiency, in this parameter range, the higher feed speed is appropriate. ICSV23, Athens (Greece), 10-14 July 2016 3
Figure 4: The influence of feed speed. 3.3 The influence of vibration amplitude When the amplitude is ZERO, the vibration will disappear. The influence of the vibration amplitude is shown as Fig.5. With the amplitude increasing, the flow forming force decrease. The amplitude of flow forming force is controlled by the amplitude of the vibration. When the vibration is too little, the forming process would not be affected. Initiate the mandrel vibration, and the forming force will become wave. The large amplitude could provide more effective power.with the effective power increasing, the material in the deformation zone will soften. But too small amplitude can t effect the material in deep. When we used the 0.001mm amplitude, the flow forming force remained unaffected. So 0.01mm or even bigger amplitude is necessary in ultrasonic vibration forming process. Figure 5: Stress and strain nephogram. 4 ICSV23, Athens (Greece), 10-14 July 2016
4. Conclusion By way of the FEM simulation method, it can be seen that the ultrasonic vibration could decrease the flow forming force in both axial and radial direction. The feed speed increasing leads flow forming force rise. Large vibration amplitude could clearly decrease the forming force. REFERENCES 1 Sivanandini, M., Dhami,S. S.and Pabla, B. S. Flow Forming of Tubes A Review, International Journal of Scientific Engineering Research, 3, (2012). 2 Zhu, Chengcheng. An Algorithm of Counter-roller Flow-forming Force, 7th International Conference on Tube Hydroforming (TUBEHYDRO2015), Xi an, (2015). 3 Langenecker, Bertwin. Effects of ultrasound on deformation characteristics of metals, Sonics and Ultrasonics, IEEE Transactions on, 13(1), 1-8, (1966). 4 Astashev, V. K., Babitsky, V. I. Ultrasonic processes and machines: dynamics, control and applications, Springer Science & Business Media, (2007). 5 Rasoli, M. A., et al. Influence of ultrasonic vibrations on tube spinning process, Journal of Materials Processing Technology, 212(6), 1443-1452, (2012). 6 Qin, Qingyuan., Research of Ultrasoni-aided Spinning Plastic Deformation Mechanism and design of resonance system, Master of Engineering Thesis, Central South University, (2013). 7 Hayashi, Masahiro, et al. Simulation of ultrasonic-vibration drawing using the finite element method (FEM), Journal of Materials Processing Technology, 140(1-3), 30-35, (2003). 8 Qin, Jun., Study on mechanical property of 20# steel under ultrasonic vibration simple tension, Master of Engineering Thesis, Henan Polytechnic University, (2007). ICSV23, Athens (Greece), 10-14 July 2016 5