1、 Welding Simulation of Cast Aluminium A356X-T. Pham*, P. Gougeon and F-O. GagnonAluminium Technology Centre, National Research Council Canada Chicoutimi, Quebec, CanadaAbstract Welding of cast aluminium hollow parts is a new promising technical trend for structural assemblies. However, big gap betwe

2、en components, weld porosity, large distortion and risk for hot cracking need to be dealt with. In this paper, the MIG welding of aluminium A356 cast square tubes is studied. The distortion of the welded tubes was predicted by numerical simulations. A good agreement between experimental and numerica

3、l results was obtained. IntroductionAluminium structures become more and more popular in industries thanks to their light weights, especially in the automotive manufacturing industry. Moreover, welding of cast aluminium hollow parts is a new promising technical trend for structural assemblies 1-3. H

4、owever, it may be very challenging due to many problems such as big gap between components, weld porosity, large distortion and risk for hot cracking 4,5. Due to local heating, complex thermal stresses occur during welding; residual stress and distortion result after welding. In this paper, the alum

5、inium A356 cast tube MIG welding is studied. The software Sysweld 6 was used for welding simulations. The objective is to validate the capability of this software in predicting the distortion of the welded tubes in the presence of large gaps. In this work, the porosity of welds was checked after wel

6、ding using the X-ray technique. The heat source parameters were identified based on the weld cross-sections and welding parameters. Full 3D thermal metallurgical mechanical simulations were performed. The distortions predicted by the numerical simulations were compared to experimental results measur

7、ed after welding by a CMM machine. ExperimentsExperimental setup Two square tubes are made of A356 by sand casting and then machined. They are assembled by four MIG welds, named W1 to W4. Their dimensions and the welding configuration are depicted in Figure 1. Both small (inner) and large (outer) tu

8、bes are well positioned on a fixture using v-blocks as shown in Figure 2. The dimensions of the tubes make a peripheral gap of 1 mm between them. This fixture is fixed on a positioner that allows the welding process to be carried out always in the horizontal position. The length of each weld is of 3

9、5 mm. The Fronius welding head, which is mounted on a Motoman robot, was used for the MIG welding process. Table 1 indicates the parameters of the welding process for this welding configuration.Table 1: MIG welding parameters.VoltageAmperageSpeedThick1Thick2Gap(V)(A)(m/min.)(mm)(mm)(mm)23260441a)b)F

10、igure 1: Tube welding configuration: a) cross-section view, b) tube dimensionsFigure 2: Experimental setup for tube weldingTestingThe porosity of welds was observed before and after welding using the X-ray technique to check the quality of these welds according to the standard ASTM E155. The whole w

11、elded tubes were then tested by traction on a MTS testing machine. The final dimensions of the welded tubes are measured on a CMM machine at many points on the tubes. The distortion of the welded tubes is determined by comparing the final positions with the initial positions of the tubes.Numerical a

12、nalysisIn Sysweld, a welding analysis is performed based on a weak-coupling formulation between the heat transfer and mechanical problems. Only the thermal history will affect on the mechanical properties, but not in reverse direction. Therefore, a thermal metallurgical mechanical analysis is divide

13、d into two steps. The first step is a thermal metallurgical analysis, in which the heat transferred from the welding source makes phase changes during the welding process. The results of temperature and phase changes from the first step are then used as input for the second analysis. It is a pure th

14、ermo-elasto-plastic simulation 6.Heat source model identificationBefore running a welding simulation, it is necessary to determine the parameters of the heat source model. This is called heat source fitting. Actually, it is a thermal simulation using this heat source model in the steady state, which

15、 iscombined with an optimization tool to obtain the parameters of the heat source. Figure 3 presents the form of a 3D conical heat source of which the energy distribution is described in Eq (1) as follows:F=Q0exp(-r/r0) (1) in which Q0 denotes the power density; and r，r0 are defined by r=(x-x0)+(x-x

16、0-vt) (2) and r0=re-(re-ri)(ze-z+z0)/(ze-zi) (3) wherex0,y0,z0)is the origin of the local coordinate system of the heat source; re and ri the radius of the heat source at the positions ze and zi,respectively;v the welding speed and t the time.In this study, a metallographic cross-section has been us

17、ed to identify the heat source parameters as shown in Figure 4. The use of a 3D conical heat source fits very well the weld cross-section. The mesh size in the cross-section is around 0.5 mm for this case. The finer is the mesh, the more accurate is the shape of the melting pool, but the longer is t

18、he simulation.Figure 3: 3D conical heat source (Sysweld).a)b)Figure 4: (a) Metallographic cross-section, (b) Melting pool cross-section.Analysis modelThe mesh of the tubes was created in Hypermesh 7.0. Sysweld 2007 has been used as solver and pre/post processor. A full 3D thermal metallurgical mecha

19、nical analysis with brick and prism elements. Two welding sequences have been done such as W1/W2/W3/W4 and W1/W3/W2/W4. The tubes are clamped using four v-blocks during the welding, two for each tube. In the simulations, the positions where the tubes are in contact against the surfaces of the v-bloc

20、ks are considered as fixed conditions (i.e. Ux = Uy = Uz = 0). In the release phase, the tubes are free from the v-blocks. ResultsThe distortion of the welded tube is measured when it is released from the constraints. The distortion is determined by measuring the displacement of the small tube on th

21、e top and lateral surfaces along the centre line of the tube. These measures are relative to the large tube. Figures 5a-b depict the distortion predicted by the numerical simulations of the sequence W1/W2/W3/W4 and W1/W3/2/W4, respectively. Good agreements between experimental and numerical results

22、were obtained in the two welding sequences as indicated in Tables 2-3, in both the distortion tendency and distortion range of the process variation. a)b)Figure 5: Tube distortion (Norm U): (a) Sequence W1/W2/W3/W4, (b) Sequence W1/W3/W2/W4.Table 2: Distortion result comparison (welding sequence W1/

23、W2/W3/W4) Displacements(mm)UyUzExperimrntal3D simulationTable 3: Distortion result comparison (welding sequence W1/W3/W2/W4)Displacements(mm)UyUzExperimrntal3D simulationa)b)Figure 7: State of stresses Sxy (a) Clamped, (b) Released. (Red = positive, Blue = negative)a)b)Figure 8: State of stresses Sx

24、z (a) Clamped, (b) Released. (Red = positive, Blue = negative)Figures 6-8 shows the state of the stresses of the welded tubes at room temperature for the sequence W1/W2/W3/W4 after welding when clampled and released from constraints (x is the direction along the axe of the welded tube). To show how

25、the welded tube is distorted, positive-negative values are used instead of the true values of stresses. The distortion of the welded tube can be explained as the new equilibrium position due to the residual stresses when there is no external load. It is remarked that in the presence of large gaps, t

26、he distortion of the welded tube is very likely in the rotational mode around local welds.ConclusionsThe MIG welding is very good for assembling aluminium cast tubes (hollow parts) in the presence of large gaps. The 3D thermal metallurgical mechanical simulation of the cast tube welding using Syswel

27、d has been validated. A very good agreement between numerical and experimental results was obtained for both the distortion tendency and distortion range. The welding sequence has a major influence on the distortion of the welded structure. It turns out that the optimization of the welding sequences

28、 for a reasonable distortion of a welded structure with a large number of welds becomes very important. AcknowledgmentsThe authors would like to thank gratefully Rio Tinto Alcan and General Motor for financial and technical supports, particularly Martin Fortier and Pei-Chung Wang. Also, the authors

29、are grateful to Welding Team at ATC (Audrey Boily, Martin Larouche, Franois Nadeau and Mario Patry) for experimental works.References1. K-H. Von Zengen, Aluminium in future cars A challenge for materials science, Materials Science Forum, 519-521 (Part 2), 1201-1208 (2006). 2. S. Wiesner S., M. Rethm

30、eier and H. Wohlfart, MIG and laser welding of aluminium alloy pressure die cast parts with wrought profiles, Welding International, 19 (2), 130-133 (2005). 3. R. Akhter, L. Ivanchev, C.V.Rooyen, P. Kazadi and H.P. Burger, Laser welding of SSM Cast A356 aluminium alloy processed with CSIR-Rheo techn

31、ology, Solid State Phenomena, 116-117, 173-176 (2006). 4. J.F. Lancaster, Metallurgy of welding, Abington Publishing (1999). 5. . Grong, Metallurgical modelling of welding, The institute of materials (1997). 6. Sysweld, Sysweld reference manual, ESI Group (2005). 譯文鑄造A356鋁合金的焊接模擬X-T. Pham*, P. Gouge

32、on and F-O. Gagnon Aluminium Technology Centre, National Research Council Canada Chicoutimi, Quebec, Canada摘要：空心鋁鑄造件的焊接是一個很有前途的新結構組件技術的趨勢。然而，組件之間的差距較大，焊接孔隙度，大變形和熱裂需要處理的風險。在這篇文章中，對鑄造A356鋁合金的方管的MIG焊接進行了研究。并對焊接管彎曲變形進行了數值模擬預測。實驗結果和數值模擬結果的相似度很高。1前言：由于鋁合金結構自身的重量輕，所以它變得越來越流行，尤其是在汽車制造業。此外，空心鋁鑄造件的焊接是一種新的有前途的

33、結構組件技術的趨勢1-3。但是它可能有很大的挑戰，由于大的差距，例如組件之間，焊接孔隙度，大變形和熱裂的危險等很多問題4,5。由于局部加熱，復雜的熱應力發生在焊接中；焊后會出現剩余應力和變形的結果。在這篇文章中，關于鑄造A356鋁合金的方管的MIG焊接進行了研究。Sysweld軟件6被用于焊接模擬。其目的是驗證這個軟件在大差距的焊接管扭曲變形的預測中的能力。在這項工作中，在焊接后利用X射線技術來檢查焊縫的孔隙率。在熱源參數的根底上，確定了焊縫截面和焊接參數。冶金力學的3D熱量模擬已經被使用。用數值模擬所預測出來的扭曲值與焊后用CCM機器所測量的實驗結果進行了比擬。2實驗：兩個成直角的管子是用A

34、356通過砂型鑄造然后在加工形成的。他們是由四個管MIG焊接組裝而成 ，命名為W1至W4子都很好的定位在一個采用V形塊的夾具上，如圖2所示。管子的規模使它們之間產生了一個1毫米厚的不主要的縫隙。這個夾具固定在一個定位上，使焊接過程中總是保持水平位置。每個焊縫的長度是35毫米。被安裝在Motoman機器人上的Fronius焊頭是用于MIG焊過程中的。表1說明了這個焊接結構的焊接工藝參數。表1：MIG焊接參數電壓電流速度厚板1厚板2縫隙(V)(A)(m/min.)(mm)(mm)(mm)23260441a)b)圖1：鋼管焊接配置:a截面圖 b鋼管尺寸圖2：管焊接實驗裝置 焊接前后利用X射線技術觀察

35、焊縫氣孔，按ASTM E155標準檢查這些焊縫質量。然后整個焊接管子通過一個MTS試驗機上的牽引來測試。焊接管最終的尺寸被定位在管子上的多個點的CMM機器所測量。扭曲的焊接管的最終位置與初始位置的管子進行比擬。 3數值分析 在Sysweld軟件中，焊接分析是基于熱傳導和力學問題之間的微弱鏈接而制定的。只有熱學經歷在相同方向上才將影響力學性能 。因此，熱學冶金力學分析分為兩個步驟。第一步是一種熱學冶金分析，其中在焊接過程的相變過程中從焊接電源的熱量被轉移。第一步溫度和相變的結果將作為第二次的分析。它是一個純熱彈塑性模擬6。4熱源模型的鑒定 焊接模擬運行之前，有必要確定熱源模型的參數。這就是所謂的

36、熱源配件。實際上，它是一種熱模擬中的穩定狀態，在這種穩定狀態中用一種優化工具來獲得的熱量來源的參數。圖3給出了一個三維錐形熱源形式，它的能量分布在方程中描述：舉例如下:F=Q0exp(-r/r0) (1) 其中Q0 表示功率密度; r，r0 被定義為：r=(x-x0)+(x-x0-vt) (2) 和 r0=re-(re-ri)(ze-z+z0)/(ze-zi) (3) 其中x0,y0,z0)是局部坐標系原點熱源，re和 ri 在位置ze 和zi,分別為半徑熱源；v為焊接速度，t為時間。 在這項研究中，金相截面已被用來確定熱源，如圖4所示的參數。一個三維錐形熱源使用非常適合的焊接橫截面。在橫截面

37、的網狀尺寸是這種情況下約為0.5毫米。越細的網狀，越是更準確的熔池形狀，但不再是模擬。圖3:三維錐形熱源 (Sysweld).a)b)圖4: (a) 金相截面(b) 熔池截面5模型分析在Hypermesh7.0上創立了管網。Sysweld2007已被用來作為求解器和前后處理器。一個完整的三維熱學冶金力學分析用磚和棱鏡為元素。兩種焊接序列已完成，如W1/W2/W3/W4和W1/W3/W2/W4。在焊接過程中，夾住管子的過程中使用四個V形塊，每個管子兩個。在模擬中，管子的立場是反對接觸的V形塊的外表被認為是固定的條件如Ux = Uy = Uz = 0。在釋放階段，管子在V形塊中是不受力的。6結果

38、當焊接管子從束縛狀態被釋放時，它的變形被控制。失真是通過測量沿管子的中心線從頂部到兩側面的小管的位移。這些措施是相對于大管的。圖5a,b的描述失真通過數值模擬預測序列為W1/W2/W3/W4和W1/W3/W2/W4。在數值計算結果和實驗中獲得了良好的協議的兩種焊接順序如表2-3所示，在這兩種傾向的扭曲和變形的過程中變化的范圍。a)b)圖5：電子管失真標準U：a序列W1/W2/W3/W4，b序列W1/W3/W2/W4表2：扭曲結果的比擬焊接順序W1/W2/W3/W4 位移 (mm)UyUz實驗至至三維模擬表2：畸變結果比擬焊接順序W1/W2/W3/W4 位移 (mm)UyUz實驗至至三維模擬a)b)圖6：規定壓力 Sxx a夾緊b放松紅=正，藍=負a)b)圖7：規定壓力 Sxy a夾緊b放松紅=正，藍=負a)b)圖8：規定壓力 Sxz a夾緊b放松紅=正，藍=負 圖6-8顯示了在夾緊和放松后的焊接在室溫的規定壓力下焊接序列W1/W2/W3/W4的狀態x是沿焊接管斧頭