Numerical simulation of inertia friction welding process of GH4169 alloy

Transcription

1 J. Phys. IV France 120 (2004) EDP Sciences, Les Ulis DOI: /jp4: Numerical simulation of inertia friction welding process of GH4169 alloy Zhang Liwen, Liu Chengdong, Qi Shaoan, Yu Yongsi, Zhu Wenhui, Qu Shen and Wang Jinghe Dalian University of Technology, Materials Engineering Department, China Abstract. Friction welding is a solid state welding technology with good quality and high automation. It has been widely used in many industry fields especially in automobile and aerospace industry. Because of the characters of less process parameters and high automation, inertia friction welding is popular in many fields. In this paper, a 2-D thermo-mechanical FEM model was developed to simulate inertia welding process. In this model, the temperature dependency of the thermal and mechanical properties of material was considered. The finite-element software MSC.Marc was used to calculate the temperature field, stress field and strain field during inertia friction welding process. The transient temperature field and the deformation of GH4169 superalloy during inertia friction welding process were predicted. The temperature filed during inertia friction welding process was measured by means of thermocouples. The calculated temperature filed is in good agreement with the experimental result. 1. INTRODUCTION As an important member of friction welding family, inertia friction welding is a complicated process in which the heat for welding is produced by direct conversion of kinetic energy stored in rotational flywheel to thermal energy at the welding interface of the welding parts. It does not need apply electrical energy or heat from other sources to the welding parts. Compared with the continuous-drive friction welding process, the inertia friction welding process has only three parameters( pressure, initial rotating speed and moment of inertia). This makes it easy to be controlled and monitored. Temperature field, stress field and strain field are three important factors of welding process and directly affect the quality of the welded joint. Most literatures about simulation of friction welding are focus on the calculation of the three fields. On the temperature aspects of friction welding, C.J.Cheng and K.K.Wang have done some pioneering work. C.J.Cheng [2,3] has studied the transient temperature distribution during continuous drive friction welding process of two similar and dissimilar metal parts respectively. He established a one-dimensional model for the process using the finite difference method. K.K.Wang [4] proposed a two-dimensional finite differential model to simulate the transient temperature distribution of inertia friction welding process. A.FRANCIS [5] provided a model for frictioning stages in friction welding of thin tubes. With rapid development of computer technology and finite element method, the thermo-mechanical coupled model was introduced into the simulation of the inertia welding process. ANDRZEJ SLUZALEC [6] and A.MOAL [7] have respectively provided a complete thermo-mechanical finite element method model to simulate the welding process. L.FU and L.DUAN [8] calculated the temperature, stress and strain distribution of the inertia process of GH4169 superalloy by thermo-mechanical method.

2 682 JOURNAL DE PHYSIQUE IV The models described in literatures are about the welding process of small diameter parts. In this paper, a 2-D thermo-mechanical FEM model was developed to simulate the inertia welding process of large diameter GH4169 superalloy workpiece. Temperature dependency of the thermal and mechanical properties of material was considered in this model. The finite-element software MSC.Marc was used to calculate the temperature field, stress field and strain field during inertia friction welding process. 2. THE FINITE ELEMENT MODEL The inertia friction welding process is a complicated process with the interaction of the heat and friction force. The friction force directly decides the heat generated at the friction interface. A change in the temperature distribution contributes to the deformation of the body through thermal strains and influences the material mechanical and thermal physical properties. In return, the plastic deformation converts mechanical work into heat through an irreversible process. The dimension of weldment is shown in Fig.1. R 1 is the inner radius of weldment near the frictional Figure 1. The dimension of weldment. interface and R 2 is the outer radius. The balance relation of heat flow is expressed in the analyed domain by the following two-dimension axisymmetric nonlinear heat transfer equation T T k( T ) T T C p T kt kt q, r, (1) t r r r r k is thermal conductivity, (T ) parameters vary with the temperature. T is current temperature. The expression of q is q a q i Where Where (T ) C p is the heat specific, the two thermal property (2) a is the coupling factor for the thermo-mechanical action and denotes the rate of internal heat generation during the plastic deformation. a is thermal efficiency of plastic deformation. q i is the internal heat source. The initial temperature of the parts is uniform and is described as and T t T 0 0 (3) On the free surface, the boundary condition is given as following T k ( T ) 0 (4) n 1 T k( T ) ( h1 h2 )( T n 2 Where h 1 is the convection coefficient and h 2 is the radiation coefficient. T s is the surrounding temperature. On the friction surface, the boundary condition is written in the following equation T k( T ) q( r, (6) n 3 T s ) (5)

3 ICTPMCS 683 Where q ( r, is the heat flux at friction surface and described as q( r, 2 r ( r, p( r, ( (7) Where p ( r, = pressure at the frictional surface, ( = angular speed, r = friction coefficient. (, The friction coefficient during the initial stage of the inertia friction welding process is described as following [9] a b f0p ( T 273) exp( cv) (8) Where T, P,V are the temperature [9], pressure and linear velocity in the frictional interface. a,b, c, f are the constant obtained from experiments. During the steady- friction stage of 0 the inertia friction welding process, the friction coefficient is described as * I d( ( (9) P S r dt Where ( = friction coefficient, I = Inertia moment, * ( = Measured angular speed, P = Thrust pressure, S = Area of friction interface. The calculation model for stress and strain fields of the welding process is described by Kirchhoff balance equation V 0 S E dv ij ij V 0 P u dv oi j S ot T u ds Where S ij is Kirchhoff stress tensor, E is Green strain tensor, u ij i is component of virtual displacement, P and oi T oi are unit volume force component acting on the deformed body respectively[8]. The strain increment d consists of the elastic strain increment d e and the plastic train increment d p The stress increment is calculated as follows ep Where D is the elastic-plastic matrix. oi d d e d p j (10) (11) d [ D d (12) The nonlinear governing equation group could be obtained when the above two models were dispersed through finite element method. ep] K ( T ) u f C ( T ) T K 1 ( T ) T Q (13)

4 684 JOURNAL DE PHYSIQUE IV 3. NUMERICAL SIMULATION RESULTS AND DISCUSSIONS The material to be welded is GH4169 superalloy (Inconel 718 superalloy). A two-dimensional axisymmetric coupled thermo-mechanical finite element model for this process was set up based on the Msc.Marc software. The domain of the circular cross-section of weld joint is divided into a number of four-noded isoparametric elements (type 10 elements). Temperature dependent thermal physical properties, time dependent heat inputs, contact condition of welding interface during welding are taken into consideration. At the same time, the convection and radiation heat losses at the surface of part are also considered. The temperature at some points near the welding interface was measured by thermocouple. Figure 2 and figure 3 show the temperature distribution of the welding one at 0.25 sec and 1.5sec. At 0.25sec, the temperature is very high near the friction interface, and the gradient of temperature is very steep in the axial direction (). So the heat affected one is very narrow. While at 1.50sec, the layer of higher temperature deform partly near the friction interface. The temperature gradient is not as steep as before. Figure 2. Distribution of temperature at 0.25sec. Figure 3. Distribution of temperature at 1.5sec. Figure 4. Calculated temperature-time history plot. Figure 5. Comparison of calculated vs. measured temperature. Figure 4 shows the temperature-time history plot of some points near the friction interface. First, the temperature in the welding part increase rapidly especially at the friction interface, and the heating rate is very high because of the interaction between the frictional heating power and the frictional characteristics on the surface. Then the temperature at the friction interface becomes uniform and almost constant. The temperature near the friction interface increases for the heat conduction. Last, the heating process is finished and temperature decreases gradually. Figure 5 shows the comparison

5 ICTPMCS 685 between the calculated temperature and the measured temperature. The calculated temperature is in good agreement with the measured temperature. Figure 6. Distribution of the axial stress at 0.25sec. Figure 7. Distribution of the axial stress at 1.5sec. Figure 6 and figure 7 shows the distribution of the axial stress at 0.25sec and 1.5sec respectively. During the initial frictional stage, the distribution of the axial stress appears as a complex state and is affect by the workpiece shape strongly. The stress near the outer surface is higher than that near the inner surface. At 1.5 sec, there is a nearly symmetric axial stress distribution in the whole welded joint. Figure 8 shows the variation of axial stress distribution at the friction interface with time. Before 0.2sec, the axial stress changes linearly with the radius. At the following time, the stress reaches a steady state under the interaction of heat and force. At the external and internal surface of welded joint, the axial stress becomes ero or positive value. While at the center of the friction interface, the axial stress reaches its highest value. Figure 9 shows the variation of stress distribution along the axial direction ( r R2 ) with time. When t<0.7s, is compressive stress. When t>0.7s, the welded joint deforms partly, the stress in the one close to friction interface becomes tensile stress, and in other one is still compressive stress. Figure 8. Variation of stress distribution at the friction interface (=0). Figure 9. Variation of stress distribution along the axial direction ( r R2 ) with time.

6 686 JOURNAL DE PHYSIQUE IV Figure 10. Distribution of the radial stress at 0.25sec. Figure 11. Distribution of the radial stress at 1.5sec. The distribution of the radial stress at 0.25sec and 1.5sec is presented in figure 10 and figure 11. Similar to the axial stress distribution, the one A near the friction interface is compressive stress and the one B closed to one A is tensile stress during initial friction weld stage and steady friction stage. R Figure 12 shows the Variation of stress distribution along the axial direction ( r ( R 1 R2 ) / 2 ) with time. At the initial stage of frictional heating, the radial stress R is almost ero. With the frictional heating time increasing, the stress R in the one close Figure 12. Variation of R along the axial direction with time. to friction interface is compressive stress and the one becomes wider. Adjacent to this compressive stress one, a certain one far away from the friction interface is tensile stress one. The distribution of equivalent Von Mises stress is presented in Figure 13 and figure 14. The equivalent Von Mises stress at the region B of the welded joint is larger than that at the one A. With the frictional heating time increasing, the temperature at the one A rises rapidly. At the same time, the yield strength of the material decreases. Accordingly, the equivalent Von Mises stress becomes small gradually. Figure 13. Distribution of equivalent Von Mises stress t=1.5sec. Figure 14. Distribution of equivalent Von Mises at stress at t=0.25sec.

7 ICTPMCS CONCLUSION In the paper a two-dimension numerical model for inertia friction welding has been set up, according to the characters of inertia welding and friction theory. The transient temperature, stress and strain distribution during the inertia friction welding process of GH4169 super alloy are calculated. 1. During initial friction stage, the temperature in friction interface raises rapidly, while during steady friction stage the temperature becomes uniform and almost constant. The calculated temperature is in good agreement with the temperature measured using thermocouples. 2. There is a complex distribution of radial and axial stress in the welded joint. The stress in the one close to friction interface is compressive stress, and the stress in the one adjacent to the compressive stress one is tensile stress. The stress distribution in welded joint is strongly affected by the interaction of heat and force. References [1] K.K.Wang, Wen Lin, Welding Journal, 1974, p233s. [2] C.J.Cheng, Welding Journal, 1962, p233s. [3] C.J.Cheng, Welding Journal, 1963, p419s. [4] K.K.Wang, Welding Journal, 1970, p419s. [5] A.Francis, Int.J.Heat Mass Transfer, 1985, p1747. [6] Andrej Slualec, Int.J.Mech.Sci, 1990, p467. [7] A.Moal, E.Massoni, Engineering Computation, 1995, p479. [8] L.Fu, L.Duan, Welding Journal, 1998, p202s. [9] Du Suigeng, Duan Liyu, etal, Mechanical Science and Technology, 1997, p703 (In Chinese). [10] V.R.Dave, M.J.Cola, G.N.A.Hussen, Welding Journal, 2001, p246s [11] E.Mssoni, L.D.Alvis, Journal of Material Processing Technology, 2002, p387.