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Dynamic simulation of the temperature field of stainless steel laser welding
Materials & Design Materials and Design 28 (2007) 240–245 www.elsevier.com/locate/matdes
Technical report
Dynamic simulation of the temperature field of stainless steel laser welding Han GuoMing *, Zhao Jian, Li JianQang School of Material Science and Engineering, Tianjin University, Tianjin, PR China Received 12 January 2005; accepted 8 June 2005 Available online 8 August 2005
Abstract The distribution of the temperature field in laser welding based on stainless steel 304 sheet was dynamically simulated by the FEA software – ANSYS in this paper. In view of the characters of laser welding, a travel heat source combined with the body loads was designed by analyzing both the temperature relativity of the thermal physical parameters of material and latent heat of fusion and the effect of convection radiation on temperature field. Considering the high nonlinear of the laser welding process, the transition element modeling was adopted. During load history, a residue control method was taken to ensure the precision of node selection. Through the calculation, it was shown that the simulation results of weld shape were in accordance with the experimental results. 2005 Elsevier Ltd. All rights reserved. Keywords: Laser welding; Temperature field; Finite-element analyze; Numerical simulation
1. Introduction Laser welding, using laser beam of high energy density as heat source, is a highly efficient and precise welding method. It has some excellence, such as high energy density, focalization, deep penetration, high efficiency and strong applicability, and is widely applied to welding field requiring high precision and high quality, including aviation and spaceflight, automobile, microelectronics, light industry, medical treatment and nucleus industry. As laser welding is a fast but unbalanced heat-circulation process, the larger temperature grads appear around the weld, therefore the residual stress and deformation of different extent can also appear in the post welding structure. All of these phenomena become the important factors, influencing the quality of welding structure and the usable capability. Understanding the
*
Corresponding author. Fax: +86 22 274 070 22. E-mail address: [email protected] (H. GuoMing).
0261-3069/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2005.06.006
heat-process of welding is important for the analysis of welding structure mechanical and microstructure and controlling of welding quality. It is difficult to measure the temperature field of welding, especially in the laser welding process. It always needs many prior tests to set down suitable laser welding process for some materials. That will use a great deal of manpower, material resources and financial resources. With the high-speed development of the technology in the software and hardware of computer, the virtual technology of manufacture gives rise to the upsurge, including the numerical simulation of heat-process in welding. The appearance of numerical simulation technology in welding creates some conditions for the development of welding manufacture towards ‘‘theory–numerical simulation–production’’. The development of numerical simulation technology in welding makes the leaps both from experience to science and from qualitative to quantitative [1–4]. In this paper, the main investigative object is laser welding of stainless steel sheet. The quasi-steady-state temperature field of laser welding was simulated with
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
2. Testing methods and materials In this experiment, the PRC4000 tape CO2 laser device was used as laser welder, its maximal output power is 4 kW, the pattern of laser output is radical model, the diameter of laser faculae is 0.4 mm, the focus of lens is 190.5 mm (7.5 in.), protective gas is Ar, adding gas by the same axis, and the flow of gas is 6 L/min. The test sample stainless steel 304 was adopted in the test, the dimension of testing board is 200 · 100 · 5 mm. The travel speed of heat source, namely welding speed, is 1.5 m/ min, its outputting power is 3 kW, its initial temperature is 20 C.
3. The simulation of temperature field in laser welding 3.1. Numerical models The welding process is high nonlinear transient state. The thermal physical nature of material properties changed rapidly with the change of temperature. Its controlling equation of heat conduction is: oT o oT o oT o oT qc ¼ k k k þ þ þ Q. ð1Þ ot ox ox oy oy oz oz In the equation, q, c and k are the density of material, the specific thermal capacity of material and the heat conductance of material these are the functions of temperature Q is the intensity of inner heat source.
ture (0–3000 C), was defined firstly [5]. And the thermal physical property parameters are achieved by the interpolation method in the unknown temperature range. The latent heat of fusion is considered by the thermal enthalpy of material for calculation of phase transition problem. In the analysis, as the transient integrated parameter is taken into account, THETA needs to be equal to one for the setup of Euler fro-difference, because the material property must be confirmed by the temperature acquired from formerly iterative one-step. 3.3. Creating model In this paper, finite element model is created from the top down. Reseaus are carved up with transition element, for reducing the element number and increasing calculative speed. The solid70 element is adopted in the weld and far away from the weld; the solid90 element is adopted in the transition region. In order to save the calculative time, the degenerative tetrahedron element of 20 nodes may be translated into non-degenerative solid87 unit element of 10 nodes after the solid90 creates the transition pyramid element. So the random storage element needed by every element can be decreased. In the research, half of the workpiece is chosen for calculation due to symmetric and regular weld. The workpiece is divided into three parts: the hexahedron element is adopted in the weld region and far away from
B SH
the FEA software – ANSYS as well as tests. During calculation, the simulation result of welding shape was compared with the experimental results.
241
SB
An important problem is lack of the available data the time of high material temperature for the welding simulation. In the research, the physical parameter value of stainless steel 304, changing with the variety of tempera-
H
3.2. The material property
Fig. 2. Model of thermal source: (a) frontal view of floating thermal source; (b) bottom view of floating thermal source.
Fig. 1. Meshing of model: (a) frontal view of meshing; (b) frontal side elevation of meshing.
242
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
Fig. 3. Movement of thermal source: (a) frontal view of floating thermal source; (b) bottom view of floating thermal source.
Fig. 4. The distribution of temperature field in the sheet: (a) the frontal view of temperature field distribution at 0.30 s; (b) the frontal view of temperature field distribution at 0.425 s; (c) three-dimension the equivalence surface of temperature field at 0.425 s.
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
welding line; the pyramid element transition is adopted in the middle part. The result of partition is shown in Fig. 1. 3.4. Thermal source model The satisfying results can be acquired by adopting the surface thermal source of gauss distribution for the normal welding method, but the request could not be contented with it for the laser welding of big impact force effect. Based on the characteristic of laser welding thermal source, the model is built by the superposition of body thermal source. The model of thermal source is shown in Fig. 2. In the plot, the position of thermal source is the function of time, namely t1 < t2 < t3, shown in Fig. 3. 3.5. Initial condition and boundary condition The initial condition: when t = 0, workpiece has uniform primary temperature. The environmental temperature is commonly chosen as 20 C. In the welding process, the workpiece exchanges heat with the medium around it in the pattern of convection and radiation, because there is intense difference in the
243
temperature between its boundary and ambience. The higher temperature is the more intense thermal radiation is, but convection is less relatively. Owing to the different calculative methods between thermal radiation and thermal convection, the radiant exchange heat and convection contact with the difference of temperature on the surface of object are considered with the total exchange heat coefficient b in the calculation for convenience. So the loss of boundary exchange heat can be shown as q0 ¼ bðT T 0 Þ.
ð2Þ
During calculation, it is shown that the exchange heat coefficient changed with the variety of temperature. It is shown that exchange heat coefficient changed with the variety of temperature. Meanwhile, the model is built according to half of the object in the orientation of length and width for reducing the calculation. The symmetrical boundary acts as an absolute heat condition. 3.6. Convergent rule and solver As the convergent rule is confirmed, ANSYS procedure gives a series of choices. The convergent test can be based on the power, moment, running and tempera-
Fig. 5. Vertical interfacial distribution of the temperature field.
Fig. 6. The distribution of temperature in the Y-orient.
244
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
Table 1 The comparison between simulative size and measured size Depth of penetration (H/mm) Width of penetration (B/mm) Height of weld waist (SH/mm) Width of weld waist (SB/mm) Measured value Simulative value
3.26 2.36
2.5 3.0
ture or the random combination of them. Otherwise, every item can have different convergent tolerant values. The convergent rule, defaulted by the procedure, is suitable with the structural calculation and based on the power and displacement. When calculating the temperature field, it needs to be adjusted to check up the problem of thermal analytical astringency with temperature and thermal current rate. The condition conjugate gradient method in the ANSYS is adopted as solver. The condition conjugate gradient method starts out from cell matrix formula as well as direct method; however, it does not make the whole matrix into triangle, but makes it assembling. Then, the result of free degree was calculated by the method of iteration. When meeting an infinite matrix, solver transfers arithmetic to deal with infinite matrix automatically. If the method cannot derive the result (while the equation system is ill or morbid), ANSYS procedure touched an external Newton–Raphson circulation automatically and performed a halve manipulation. At the same time, the stiffness matrix can become benign, and the condition conjugate gradient method may compute all the nonlinear sub-steps finally.
1.47 1.25
0.8 0.8
The practice ensures that the nodes between initial coordinate and terminal coordinate could be selected exactly. The moving load was implemented by the circulation of APDL language. For calculation, the load position and magnitude are confirmed every time firstly. The load moves with time. When the load moves to the next load step, the former load step is deleted. In this simulation, power is 3000 kW; the workpiece moves at a speed of 1.5 m/min, thermal efficiency is 0.9. The length of the sheet is a quarter of the whole, namely 0.05 m. The workpiece is welded completely in 1 s. The step length is chosen as 0.025 s. The thermal resource moves to a distance of 0.00125 m.
4. Result and analysis 4.1. The thermal simulation of laser welding temperature field Fig. 4(a) and (b) are the plots of isothermal chart at 0.30 and 0.425 s, respectively; Fig. 4(c) is the threedimensional contour plane at 0.425 s; it figures the equivalence surface of temperature.
3.7. Loading and solving When choosing the nodes, a residue parameter Remain is designed as there is a determinate distance among the nodes of meshing. When choosing the nodes according to the coordinate, the initial coordinate needs to be subtracted from a residue parameter, and the terminal coordinate needs to be added to a residual parameter.
A B C
Fig. 7. Each testing point of the sheet.
Fig. 8. Thermal circulation curve of the sheet.
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
It can be seen from Fig. 4 that the distribution of temperature field changes as the laser resource moves along and the melt pool moves along with the laser source. In the middle of the workpiece, the distribution of temperature field goes to balance, namely it goes into quasisteady-state. It also appears that the isotherm line presents ellipse. And not only the isotherm line is dense in front of the removal thermal source, but also the temperature grads are great there. But in the back of the moving thermal source, the complexion is contrary. 4.2. Thermal simulations of laser welding melt pool The simulated shapes of melt pool are shown in Fig. 5. It is seen from the picture that the maximal temperature of melt pool is 13,332 C. The melting point of stainless steel 304 is selected as 1500 C. The depth of penetration, the width of penetration, the height of weld waist and the width of weld waist can be calculated with the data shown in the picture. And it will be seen that all above are in accordance with the trim size of weld, shown as Table 1. Fig. 6 shows the connection between the distance of the center of the weld and the distribution of temperature. It can be seen from the figure that the temperature dropped rapidly with the increase of distance to the center of the weld. As the distance between nodes and the center is about 0.387 mm, the temperature has fallen to 130 C. At 0.05 s, it is shown in Fig. 7 that three points are chosen in turn in the workpiece. They are A(0.00125, 0.005, 0), B(0.00125, 0.00375, 0), C(0.00125, 0.0025, 0). The thermal circulation curve of each point is shown in Fig. 8. It is seen from Fig. 8 that the upper surface temperature of welding line is the highest. And the further the distance away from the upper surface is, the lower the maximal temperature is.
5. Conclusion On the condition of moving thermal resource, the temperature distribution of workpiece changes quickly with the variety of time and space. Heating and cooling
245
exist at the same time. Compared with other welding methods, the temperature field grads of laser welding are large, and the heat affected zone is small. It is so difficult that the satisfying result is obtained by the traditionally analytical method. In this paper, the temperature distribution of laser welding was investigated by the definite element method. The conclusion is as follows: (1) In view of the high dense characters of laser welding, a heat source combined the body loads has been designed. (2) When analyzing with definite element method, it is considered that the thermal physical parameters depend on the temperature, and each physical parameter is attained in high temperature. (3) A residue control method is taken to ensure the precision of node selection. (4) As a result of the simulation, the maximal temperature is up to 13,000 C, and the temperature grads are much larger in the laser welding. (5) Through the calculation, it is shown that the simulation results of weld shape were in accordance with the experimental results.
References [1] Xiong Jian-Gang, Hu Qiang, Li Zhi-Yuan, et al. The research situation of mathematical modeling in laser keyhole welding currently. J China Mech Eng 2003;14(9):803–7. [2] Wu Xiang-xing, Hu Lun-ji, Du Han-bing, et al. Application of ANSYS software in temperature field value simulation of laser welding. J Electr Weld Mach 2002;32(9):1–3. [3] Li Jian-qiang, Han Guo-ming, He Yu. Study on simulation of laser welding. J Electr Weld Mach 2003;33(9):10–4. [4] Xue Zhong-ming, Gu Lan, Zhang Yan-hua. Temperature field simulation of laser welding. J Trans China Weld Inst 2003;24(2): 79–82. [5] Artemis Agelaridou. Thermal and solidification modeling of weld: a design tool approach. Doctor thesis. US: Tufts University; 2002. Han GuoMing is currently an Associate Professor in materials process engineering at Tianjin University, China. His research interests include Welding process simulation, Arc physics and autocontrol, Welding process and equipment, etc.
Technical report
Dynamic simulation of the temperature field of stainless steel laser welding Han GuoMing *, Zhao Jian, Li JianQang School of Material Science and Engineering, Tianjin University, Tianjin, PR China Received 12 January 2005; accepted 8 June 2005 Available online 8 August 2005
Abstract The distribution of the temperature field in laser welding based on stainless steel 304 sheet was dynamically simulated by the FEA software – ANSYS in this paper. In view of the characters of laser welding, a travel heat source combined with the body loads was designed by analyzing both the temperature relativity of the thermal physical parameters of material and latent heat of fusion and the effect of convection radiation on temperature field. Considering the high nonlinear of the laser welding process, the transition element modeling was adopted. During load history, a residue control method was taken to ensure the precision of node selection. Through the calculation, it was shown that the simulation results of weld shape were in accordance with the experimental results. 2005 Elsevier Ltd. All rights reserved. Keywords: Laser welding; Temperature field; Finite-element analyze; Numerical simulation
1. Introduction Laser welding, using laser beam of high energy density as heat source, is a highly efficient and precise welding method. It has some excellence, such as high energy density, focalization, deep penetration, high efficiency and strong applicability, and is widely applied to welding field requiring high precision and high quality, including aviation and spaceflight, automobile, microelectronics, light industry, medical treatment and nucleus industry. As laser welding is a fast but unbalanced heat-circulation process, the larger temperature grads appear around the weld, therefore the residual stress and deformation of different extent can also appear in the post welding structure. All of these phenomena become the important factors, influencing the quality of welding structure and the usable capability. Understanding the
*
Corresponding author. Fax: +86 22 274 070 22. E-mail address: [email protected] (H. GuoMing).
0261-3069/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2005.06.006
heat-process of welding is important for the analysis of welding structure mechanical and microstructure and controlling of welding quality. It is difficult to measure the temperature field of welding, especially in the laser welding process. It always needs many prior tests to set down suitable laser welding process for some materials. That will use a great deal of manpower, material resources and financial resources. With the high-speed development of the technology in the software and hardware of computer, the virtual technology of manufacture gives rise to the upsurge, including the numerical simulation of heat-process in welding. The appearance of numerical simulation technology in welding creates some conditions for the development of welding manufacture towards ‘‘theory–numerical simulation–production’’. The development of numerical simulation technology in welding makes the leaps both from experience to science and from qualitative to quantitative [1–4]. In this paper, the main investigative object is laser welding of stainless steel sheet. The quasi-steady-state temperature field of laser welding was simulated with
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
2. Testing methods and materials In this experiment, the PRC4000 tape CO2 laser device was used as laser welder, its maximal output power is 4 kW, the pattern of laser output is radical model, the diameter of laser faculae is 0.4 mm, the focus of lens is 190.5 mm (7.5 in.), protective gas is Ar, adding gas by the same axis, and the flow of gas is 6 L/min. The test sample stainless steel 304 was adopted in the test, the dimension of testing board is 200 · 100 · 5 mm. The travel speed of heat source, namely welding speed, is 1.5 m/ min, its outputting power is 3 kW, its initial temperature is 20 C.
3. The simulation of temperature field in laser welding 3.1. Numerical models The welding process is high nonlinear transient state. The thermal physical nature of material properties changed rapidly with the change of temperature. Its controlling equation of heat conduction is: oT o oT o oT o oT qc ¼ k k k þ þ þ Q. ð1Þ ot ox ox oy oy oz oz In the equation, q, c and k are the density of material, the specific thermal capacity of material and the heat conductance of material these are the functions of temperature Q is the intensity of inner heat source.
ture (0–3000 C), was defined firstly [5]. And the thermal physical property parameters are achieved by the interpolation method in the unknown temperature range. The latent heat of fusion is considered by the thermal enthalpy of material for calculation of phase transition problem. In the analysis, as the transient integrated parameter is taken into account, THETA needs to be equal to one for the setup of Euler fro-difference, because the material property must be confirmed by the temperature acquired from formerly iterative one-step. 3.3. Creating model In this paper, finite element model is created from the top down. Reseaus are carved up with transition element, for reducing the element number and increasing calculative speed. The solid70 element is adopted in the weld and far away from the weld; the solid90 element is adopted in the transition region. In order to save the calculative time, the degenerative tetrahedron element of 20 nodes may be translated into non-degenerative solid87 unit element of 10 nodes after the solid90 creates the transition pyramid element. So the random storage element needed by every element can be decreased. In the research, half of the workpiece is chosen for calculation due to symmetric and regular weld. The workpiece is divided into three parts: the hexahedron element is adopted in the weld region and far away from
B SH
the FEA software – ANSYS as well as tests. During calculation, the simulation result of welding shape was compared with the experimental results.
241
SB
An important problem is lack of the available data the time of high material temperature for the welding simulation. In the research, the physical parameter value of stainless steel 304, changing with the variety of tempera-
H
3.2. The material property
Fig. 2. Model of thermal source: (a) frontal view of floating thermal source; (b) bottom view of floating thermal source.
Fig. 1. Meshing of model: (a) frontal view of meshing; (b) frontal side elevation of meshing.
242
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
Fig. 3. Movement of thermal source: (a) frontal view of floating thermal source; (b) bottom view of floating thermal source.
Fig. 4. The distribution of temperature field in the sheet: (a) the frontal view of temperature field distribution at 0.30 s; (b) the frontal view of temperature field distribution at 0.425 s; (c) three-dimension the equivalence surface of temperature field at 0.425 s.
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
welding line; the pyramid element transition is adopted in the middle part. The result of partition is shown in Fig. 1. 3.4. Thermal source model The satisfying results can be acquired by adopting the surface thermal source of gauss distribution for the normal welding method, but the request could not be contented with it for the laser welding of big impact force effect. Based on the characteristic of laser welding thermal source, the model is built by the superposition of body thermal source. The model of thermal source is shown in Fig. 2. In the plot, the position of thermal source is the function of time, namely t1 < t2 < t3, shown in Fig. 3. 3.5. Initial condition and boundary condition The initial condition: when t = 0, workpiece has uniform primary temperature. The environmental temperature is commonly chosen as 20 C. In the welding process, the workpiece exchanges heat with the medium around it in the pattern of convection and radiation, because there is intense difference in the
243
temperature between its boundary and ambience. The higher temperature is the more intense thermal radiation is, but convection is less relatively. Owing to the different calculative methods between thermal radiation and thermal convection, the radiant exchange heat and convection contact with the difference of temperature on the surface of object are considered with the total exchange heat coefficient b in the calculation for convenience. So the loss of boundary exchange heat can be shown as q0 ¼ bðT T 0 Þ.
ð2Þ
During calculation, it is shown that the exchange heat coefficient changed with the variety of temperature. It is shown that exchange heat coefficient changed with the variety of temperature. Meanwhile, the model is built according to half of the object in the orientation of length and width for reducing the calculation. The symmetrical boundary acts as an absolute heat condition. 3.6. Convergent rule and solver As the convergent rule is confirmed, ANSYS procedure gives a series of choices. The convergent test can be based on the power, moment, running and tempera-
Fig. 5. Vertical interfacial distribution of the temperature field.
Fig. 6. The distribution of temperature in the Y-orient.
244
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
Table 1 The comparison between simulative size and measured size Depth of penetration (H/mm) Width of penetration (B/mm) Height of weld waist (SH/mm) Width of weld waist (SB/mm) Measured value Simulative value
3.26 2.36
2.5 3.0
ture or the random combination of them. Otherwise, every item can have different convergent tolerant values. The convergent rule, defaulted by the procedure, is suitable with the structural calculation and based on the power and displacement. When calculating the temperature field, it needs to be adjusted to check up the problem of thermal analytical astringency with temperature and thermal current rate. The condition conjugate gradient method in the ANSYS is adopted as solver. The condition conjugate gradient method starts out from cell matrix formula as well as direct method; however, it does not make the whole matrix into triangle, but makes it assembling. Then, the result of free degree was calculated by the method of iteration. When meeting an infinite matrix, solver transfers arithmetic to deal with infinite matrix automatically. If the method cannot derive the result (while the equation system is ill or morbid), ANSYS procedure touched an external Newton–Raphson circulation automatically and performed a halve manipulation. At the same time, the stiffness matrix can become benign, and the condition conjugate gradient method may compute all the nonlinear sub-steps finally.
1.47 1.25
0.8 0.8
The practice ensures that the nodes between initial coordinate and terminal coordinate could be selected exactly. The moving load was implemented by the circulation of APDL language. For calculation, the load position and magnitude are confirmed every time firstly. The load moves with time. When the load moves to the next load step, the former load step is deleted. In this simulation, power is 3000 kW; the workpiece moves at a speed of 1.5 m/min, thermal efficiency is 0.9. The length of the sheet is a quarter of the whole, namely 0.05 m. The workpiece is welded completely in 1 s. The step length is chosen as 0.025 s. The thermal resource moves to a distance of 0.00125 m.
4. Result and analysis 4.1. The thermal simulation of laser welding temperature field Fig. 4(a) and (b) are the plots of isothermal chart at 0.30 and 0.425 s, respectively; Fig. 4(c) is the threedimensional contour plane at 0.425 s; it figures the equivalence surface of temperature.
3.7. Loading and solving When choosing the nodes, a residue parameter Remain is designed as there is a determinate distance among the nodes of meshing. When choosing the nodes according to the coordinate, the initial coordinate needs to be subtracted from a residue parameter, and the terminal coordinate needs to be added to a residual parameter.
A B C
Fig. 7. Each testing point of the sheet.
Fig. 8. Thermal circulation curve of the sheet.
H. GuoMing et al. / Materials and Design 28 (2007) 240–245
It can be seen from Fig. 4 that the distribution of temperature field changes as the laser resource moves along and the melt pool moves along with the laser source. In the middle of the workpiece, the distribution of temperature field goes to balance, namely it goes into quasisteady-state. It also appears that the isotherm line presents ellipse. And not only the isotherm line is dense in front of the removal thermal source, but also the temperature grads are great there. But in the back of the moving thermal source, the complexion is contrary. 4.2. Thermal simulations of laser welding melt pool The simulated shapes of melt pool are shown in Fig. 5. It is seen from the picture that the maximal temperature of melt pool is 13,332 C. The melting point of stainless steel 304 is selected as 1500 C. The depth of penetration, the width of penetration, the height of weld waist and the width of weld waist can be calculated with the data shown in the picture. And it will be seen that all above are in accordance with the trim size of weld, shown as Table 1. Fig. 6 shows the connection between the distance of the center of the weld and the distribution of temperature. It can be seen from the figure that the temperature dropped rapidly with the increase of distance to the center of the weld. As the distance between nodes and the center is about 0.387 mm, the temperature has fallen to 130 C. At 0.05 s, it is shown in Fig. 7 that three points are chosen in turn in the workpiece. They are A(0.00125, 0.005, 0), B(0.00125, 0.00375, 0), C(0.00125, 0.0025, 0). The thermal circulation curve of each point is shown in Fig. 8. It is seen from Fig. 8 that the upper surface temperature of welding line is the highest. And the further the distance away from the upper surface is, the lower the maximal temperature is.
5. Conclusion On the condition of moving thermal resource, the temperature distribution of workpiece changes quickly with the variety of time and space. Heating and cooling
245
exist at the same time. Compared with other welding methods, the temperature field grads of laser welding are large, and the heat affected zone is small. It is so difficult that the satisfying result is obtained by the traditionally analytical method. In this paper, the temperature distribution of laser welding was investigated by the definite element method. The conclusion is as follows: (1) In view of the high dense characters of laser welding, a heat source combined the body loads has been designed. (2) When analyzing with definite element method, it is considered that the thermal physical parameters depend on the temperature, and each physical parameter is attained in high temperature. (3) A residue control method is taken to ensure the precision of node selection. (4) As a result of the simulation, the maximal temperature is up to 13,000 C, and the temperature grads are much larger in the laser welding. (5) Through the calculation, it is shown that the simulation results of weld shape were in accordance with the experimental results.
References [1] Xiong Jian-Gang, Hu Qiang, Li Zhi-Yuan, et al. The research situation of mathematical modeling in laser keyhole welding currently. J China Mech Eng 2003;14(9):803–7. [2] Wu Xiang-xing, Hu Lun-ji, Du Han-bing, et al. Application of ANSYS software in temperature field value simulation of laser welding. J Electr Weld Mach 2002;32(9):1–3. [3] Li Jian-qiang, Han Guo-ming, He Yu. Study on simulation of laser welding. J Electr Weld Mach 2003;33(9):10–4. [4] Xue Zhong-ming, Gu Lan, Zhang Yan-hua. Temperature field simulation of laser welding. J Trans China Weld Inst 2003;24(2): 79–82. [5] Artemis Agelaridou. Thermal and solidification modeling of weld: a design tool approach. Doctor thesis. US: Tufts University; 2002. Han GuoMing is currently an Associate Professor in materials process engineering at Tianjin University, China. His research interests include Welding process simulation, Arc physics and autocontrol, Welding process and equipment, etc.