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In this paper, the thermal field of double wire welding is simulated by using ANSYS software. Simulation results were shown that the total heat input (E) is the most significant parameters to change the value of t8/5; By the mean of rationally controlling the proportion of the front arc heat input (E1) in the total heat input (E) and appropriately selecting double wire spacing (L), It is effective means to get the double wire welding thermal cycle. By the way of simulation, it is possible to manage the thermal input in the double welding wires and to control the temperature field and cooling rate that are fundamental for the final joint quality, it is great importance guidance to optimize the double wire welding process parameters.

Welding thermal cycle is a dynamic thermal process, which involves arc physical, material, metallurgy and chemical change, heat transfer, mass transfer and the mechanical property variation. During the welding process and after welding, because of the welding residual stress and distortion, welding thermal affects the manufacturing precision of welding structure, strength, toughness and operational performance. The practical significance of welding the three dimensional numerical simulation lies in the fact that comprehensive prediction weld defects, analysis of laws of welding residual stress and deformation, to optimize the welding structure and process, control of welding stress and deformation [

Welding thermal process directly determine the microstructure and mechanical properties of welded joint. There are four principal parameters in welding thermal cycle as following: The welding speed (ν) which influence the austenitic homogenization and microstructure; the heating the highest temperature (Tp) which determine metal phase change and austenitized after welding; the cooling welding rate (t_{8/5}, t_{8/3}) affect the joint process of phase transformation; And cooling time of temperature from 400˚C to 150˚C is for the spread of the hydrogen cold cracks. So it is very necessary to optimize parameters of the welding thermal cycle to study the influence of welding thermal process on the microstructure and mechanical properties, to control phase transformation of HAZ (heat affected zone), stress, and strain of welded joint [

The tests welding plate materials is 10Ni3CrMoV steel, Its chemical components are shown in

According to symmetry of the simulation calculation of geometric objects and the applied load, the simulation calculation of geometric model and finite element model are half, and the model is divided into three areas: far away from the weld zone (base zone), transition zone (fusion zone) and weld zone, for greatly reduce the number of units in the finite element calculation process.

In this paper, the size of simplified half geometric model is 500 mm × 75 mm × 16 mm, as shown in

Elements | C | Si | Mn | Cr | P | S | Section shrinkage/% | Elongation/% |
---|---|---|---|---|---|---|---|---|

Percent | 0.796 - 0.834 | 0.195 - 0.305 | 0.7 - 0.8 | 0.14 - 0.22 | <0.015 | <0.005 | >30 | >10 |

and displacement constraints on finite element model are shown in

Double ellipsoid heat source model is more suitable for the simulation of fusion welding process with the characteristic of width and deep welding pool [_{f} and f_{r} respectively, and the f_{f} + f_{r} = 2. Heat flux distribution function is following Formulas (1) and (2).

Among them, the characteristic parameters such as a_{ij}, b_{i}, c_{i} (i = 1, 2; j = 1, 2) are related to the shape of molten pool, desirable different values and independent of each other, by the adjusting of a, b, c parameters, we can adjust the temperature field simulation. The arc energy distribution coefficient of the front (f_{f}) and rear (f_{r}) were f_{f} = 0.48, f_{r} = 1.52.

Because of the effect of moving welding heat source, the temperature of spot in the workpiece changing with time, called the point of welding thermal cycle. Influence of welding thermal cycle curve parameters mainly includes electric arc voltage (U), as well as double wire welding current(I), welding speed (ν), distance (L) between the two wires. And heat flow calculation and load the program were designed and published in my literatures [

The total heat input E(KJ/cm) of double wire submerged arc welding calculation expression is: E = η(U_{1}I_{1} + U_{2}I_{2})/ν, to the double wire submerged arc welding (_{1}, I_{1}, and U_{2}, I_{2} and ν, the E_{1}, E_{2} and E can be taken different values, as shown in

the smallest E value of 20.03 KJ/cm; And, the heat input value of frontal arc (E_{1}) and back arc (E_{2}) are different, The length of red, green histogram are respectively shown the value of the heat input of before and after the arc. The position of blue plus sign is shown the average value of E, when it landed in the red areas indicating E1 > E2, fell on the green area indicating the E_{1} < E_{2}. Therefore, based on the 21 sets of different welding parameters and double wire spacing, the welding temperature field is simulated, and the relationship of the heat input E and double wire spacing L with the thermal cycle characteristic parameters were analyzed. Also, the double wire distance L affects the overall welding energy distribution.

In simulation and test, the model size is the same of 500 × 75 × 16 (mm), the welding parameters (L is constant 60 cm) is been chosen as shown in

According to the actual welding seam size and the finite element model, in order to convenient analyses, the taken points in finite element nodes are shown in

For different double wire spacing L and different heat input E, points in different positions have different thermal cycle curve, organization transformation is closely related to the cooling rate. According the double wire welding specification shown in

In order to study the effect of heat input E on t_{8/5} and Tp, The values (L = 60 mm) of t_{8/5} and Tp of each special points along penetration direction were statistics, shown in _{8/5} is significant positive correlation with heat input E, and with the increase of heat input E the values of t_{8 /5} are closer. From

With different heat input E and different double wire spacing L, how about the law of the peak temperature (Tp)? Peak temperature (Tp) of butt welding plate is unfavorable to the microstructure. The following analysis mainly is to find out law of Tp.

Selected the welding process parameters 2 in

With double wire spacing L (50 mm), along penetration direction, the variation of Tp to heat input E is shown in _{1} to E_{2} could be found in

From the _{1} is the more

sensitive factor than E_{2}.

(1) Along the points of further from the center of the heat source, the peak temperature (Tp) is lower, the t_{8/5} constantly is increasing. while the double wire spacing L only have affect on the peak temperature (Tp), almost less affect t_{8/5}. Therefore, it is effective method by the mean of increasing the double wire spacing (L) to reduce the peak temperature (Tp) without changing the t_{8/5}. On the one hand, we can prevent microstructure of HAZ from burnt, on the other hand, we can guarantee the microstructure transformation of weld fusion line by control cooling process.

(2) By the secondary development of ANSYS, the thermal field of double wire welding was simulated, the part laws of thermal cycle of double wire welding was found. We can improve the microstructure and mechanical properties by the way of adjusting weld process parameters.

This work was partly supported by the “Hubei Province Education Department youth project (No.Q20123001). Hubei province natural science foundation of China (No.2014 CFB 177), Dr. Field introduced project (No.11yjz01R), Field introduced project (2015A05)”.

Yang, X.Z., Yang, C.J., Dong, C.F., Xiao, X.H., Hua, W.L. and Wang, X.J. (2016) Finite Element Simulation of Thermal Field in Double Wire Welding. Journal of Materials Science and Chemical Engineering, 4, 10-21. http://dx.doi.org/10.4236/msce.2016.412002