温差拉伸和随焊激冷配合使用控制焊接变形

对温差拉伸和随焊激冷配合使用控制铝合金薄板焊接变形的联合工艺进行了数值模拟和试验研究。数值分析表明 ,随焊激冷更倾向于在焊缝中心造成显著的纵向塑性拉伸 ,而温差拉伸则倾向于在近缝区造成显著的塑性拉伸。将二者配合使用 ,不仅可以靠温差拉伸将焊缝和近缝区在加热阶段形成的纵向塑性压应变控制在较低的水平 ,还可以靠随焊激冷增加冷却阶段的纵向塑性拉伸进一步抵消焊缝区已经形成的压应变。因而充分发挥二者的作用 ,有效地控制焊件的残余变形。试验研究与数值模拟得到的结论基本一致 ,随焊激冷和温差拉伸联合使用 ,可使 5 4 0mm× 3 0 0mm× 2mm的LY1 2CZ薄板焊后纵向挠曲由单独使用温差拉伸时的 2 .87mm和单独使用随焊激冷时的 4 .88mm降低到 0 .80mm的水平     

Stress and distortion mitigation technique for welding titanium alloy thin sheet

Abstract

A stress and distortion mitigation technique for Gas Tungsten Arc Welding (GTAW) of titanium alloy Ti–6Al–4V thin sheet is presented. The proposed welding technique incorporates a trailing heat sink (an intense cooling source) with respect to the welding torch, and it is also called the Dynamically Controlled Low Stress No-Distortion (DC-LSND) technique. The development of this mitigation technique is based on both detailed welding process simulation using the advanced finite element technique and systematic laboratory experiments. The finite element method is used to investigate the detailed thermomechanical behaviour of the weld during conventional GTAW and DC-LSND GTAW. With detailed computational modelling, it is found that by the introduction of a heat sink at some distance behind the welding arc, a saddle shaped temperature field is formed as a result of the cooling effects of the heat sink; the lowest temperature exists in the zone where the heat sink is applied. High tensile action on the surrounding zone is generated by abrupt cooling and contraction of the metals beneath the heat sink, which increases the tensile plastic strain developed during the cooling process and decreases the compressive plastic strain developed in the heating process, and therefore mitigates the residual stresses and plastic strains within and near the weld. The experimental results confirmed the effectiveness of the DCLSND technique and the validity of the computational model. With a proper implementation of the DC-LSND technique, welding stress and distortion can be reduced or eliminated in welding titanium alloy Ti–6Al–4V thin sheet, while no appreciable detrimental effects are caused on the mechanical properties of welded joints by applying the heat sink in the GTAW process.     

薄板高强铝合金LY12CZ焊接工艺参数的优化

从力学角度出发，通过调整焊接温度场，控制焊缝及近缝区的应力应变发展，实现了高强铝合金LY12CZ薄板的低应力少变形无热裂焊接。运用正交试验设计来安排试验、筛选因子，并用一次回归正交设计调优运算优化因子的匹配，找到了影响铝合金薄板焊接变形的主要因子和最佳工艺参数匹配，揭示了主要工艺参数对减小变形效果的影响规律。     

热沉影响钛合金薄板焊接残余应力的试验分析

采用切条应力释放法测量了钛合金TC4薄板常规钨极氩弧焊(GTAW)和动态控制低应力无变形GTAW对接试件中的纵向残余应力和纵向残余塑性应变的分布。测量结果表明,钛合金常规GTAW缝中残余拉应力峰值小于其母材屈服强度,焊缝附近存在残余压缩塑性应变;动态控制低应力无变形GTAW焊技术中热沉的冷却作用使得热源与热沉之间的高温金属承受强烈的拉伸作用,产生拉伸塑性变形,部分抵消了焊接过程中已产生的缩短的塑性变形,使得试件中纵向残余塑性应变减小,焊接残余拉应力峰值降低,残余压应力水平降低。切条应力释放法是一种简便有效的薄板焊后残余应力测量方法,能够满足工程应用的精度要求。     

焊接塑性应变演变过程——低碳钢、不锈钢及钛合金塑性应变演变特点及规律

采用数值模拟方法对低碳钢、不锈钢及钛合金3种材料薄板电弧焊接塑性应变演变过程进行了分析.结果表明,在焊接过程中,焊缝及近缝区内无论是纵向塑性应变还是横向塑性应变均为压缩塑性应变,熔池凝固及高温区冷却产生的拉伸卸载不足以完全抵消加热过程产生的压缩塑性应变,最终残留在焊缝及近缝区内的塑性应变仍保持压缩状态,压缩塑性区的宽度明显宽于材料"力学熔化"区宽度.     

钛合金带热沉钨极氩弧焊中热沉作用

采用数值模拟和实验相结合的方法研究了钛合金TC4薄板常规及带热沉的钨极氩弧焊焊接过程中温度及应力应变的分布,考察了热沉对温度场和应力应变场的影响规律,探讨了使用该技术实现应力和变形控制的机理.结果表明:带热沉的钨极氩弧焊焊接过程中,紧随热源之后热沉急冷作用使得试件形成马鞍形温度场,而热沉作用部位温度最低.热沉作用部位的急冷收缩对周围金属产生拉伸作用,使得焊缝及近缝区金属升温过程中产生的压缩塑性应变减小,冷却过程中产生的拉伸塑性应变增大,接头中不协调应变减小,残余应力降低.实验测量与有限元模拟结果吻合良好,证实了采用热沉控制应力与变形的有效性和有限元模型的正确性.     

焊接塑性应变演变过程——不锈钢薄板焊接塑性应变演变过程

采用数值模拟方法对不锈钢薄板电弧焊接塑性应变演变过程进行了分析.结果表明,在焊接过程中焊缝及近缝区内无论是纵向塑性应变还是横向塑性应变均为压缩塑性应变,熔池凝固冷却产生的拉伸回复不足以完全抵消加热过程已产生的压缩塑性应变,最终残留在焊缝及近缝区内的塑性应变仍保持压缩状态,压缩塑性区的宽度明显大于材料"力学熔化区"宽度.     

随焊冲击碾压减小应力变形防止热裂纹应变场分析

随焊冲击碾压法(weld with Trailing Impact Rolling，WTIR)是一种降低应力、减小变形防止热裂纹的新方法。文中分析了在前后冲击碾压轮作用下，焊缝金属塑性流动和应变场的变化规律，揭示了这种方法的机理。前轮周面内凹，迫使焊缝金属由焊趾处向焊缝中心流动，对处于脆性温度区间的焊缝金属施加一个横向挤压塑性应变，减小甚至抵消致裂的拉伸应变，防止了焊接热裂纹的产生。后轮缘稍向外凸，将焊缝金属冷却产生的压缩塑性变形充分碾开，减小了工件的应力和变形。试验结果表明，随焊冲击碾压能有效地防止焊接热裂纹的产生，将试件的纵向挠曲变形与横向收缩变形量控制到常规焊接状态的1／10和1／5左右，同时能将薄壁构件焊接残余应力控制到非常低的水平，甚至由拉应力状态转变为压应力状态，验证了应变场分析的正确性。     

用旋转挤压方法控制薄板的焊接变形

提出了旋转挤压控制薄板焊接变形的新方法,它足利用特定形状的挤压头对焊缝及近缝区金属进行旋转挤压,产生拉伸塑性应变,减小甚至抵消残余压缩塑性应变,以此来消除焊接残余变形.该方法处理后的焊道表面平整光滑,减小了应力集中.结果表明,旋转挤压法能将薄壁构件焊接变形降到非常低的水平,选择适当的工艺参数,该方法能将焊接残余变形控制在常规焊接状态的3%以下.旋转挤压控制薄板焊接变形的效果与多个工艺参数有关,只有当各个工艺参数取值适当且匹配良好时,才能取得良好的焊接变形控制效果.     

Sensitivity analysis of history dependent material mechanical models for numerical simulation of welding process

Abstract

Yield stress of 6013-T6 aluminium alloy was tested on Gleeble 1500D thermal–mechanical system at predesigned temperatures during different typical thermal cycles, in order to accurately reflect the influence of weld thermal history on material properties. The typical thermal cycles were referred to the temperature field simulation results of real welding process. The changes of yield stress were obtained directly from the stress–strain curves generated by the tensile tests. The tests were more accurate than previous publications, where only the yield stresses at room temperature after thermal history were tested or calculated from microstructure evolution model. Experimental results showed that the changes of yield stress during the cooling stage of typical thermal cycles followed one set of curves. These yield stress–temperature curves were different from those during the heating stage. Temperature and temperature history dependent material model M2 and M3 were established based on the experimental results. M2 model was perfectly plastic model while work hardening effect was considered in M3 model. Compared with conventional temperature dependent material model M1, the distributions of longitudinal residual stress and strain obtained with temperature and temperature history dependent models fit better with published results. Yield stress of the material at the weld zone decreased a lot after having experienced weld thermal history and longitudinal compressive plastic strain at the weld zone recovered to some extent during the cooling stage in M2 and M3 models. These were the main causes for lower peak longitudinal residual tensile stress in M2 and M3 models.     

随焊激冷减小铝合金薄板的焊接变形

研究了随焊激冷减小铝合金薄板焊接变形的效果及夹具的散热条件对该效果的影响,研究表明,随焊激冷能够减小铝合金薄板的焊接变形,其效果受夹具自身冷却作用影响很大。随着夹具散热条件的降低,随焊激冷所起的作用增强,但降低焊接变表的效果仍不够明显,适当预热夹具本身可以减小焊接变形,但更重要的是预热使激冷造成了温差拉伸,因此获得了最小的焊接变形。     

焊接应力场与应变场的计算与讨论

经典的观点认为焊缝存在残余压缩塑性应变,而目前有学者认为焊缝是在冷却的过程中形成的,与加热过程无关,认为焊缝只存在拉伸塑性应变,而不存在压缩塑性应变.针对这一对传统残余塑变理论的质疑,采用有限元方法对薄板熔焊对接接头纵向应力和应变的瞬态变化以及由焊缝中心到母材边缘的纵向应力和应变分布情况进行了计算.结果表明,焊缝及近缝区存在着残余压缩塑性应变,应力状态为拉应力,由焊缝中心到母材边缘其纵向应力由拉应力转变为压应力,纵向压缩塑性变形量逐渐下降,离焊缝较远受温度场影响较小的母材不产生塑性变形.     

铝合金薄板焊件纵向塑性应变场的数值模拟

利用弹塑性有限元分析软件对普通焊件的纵向塑性应变场进行了模拟.结果表明,对于尺寸为200 mm×100 mm ×2 mm的2A12T4铝合金薄板填丝对接焊件,其焊缝部位只存在纵向拉伸塑性应变;在靠近焊缝的区域,既存在纵向压缩塑性应变,也存在纵向拉伸塑性应变;在焊缝长度方向纵向残余塑性应变的分布不均匀,在靠近起弧端和收弧端的区域呈现复杂的分布特征.焊接过程中温度场的变化和热源旁侧金属受力状况的不同是近缝区金属纵向塑性应变不均匀分布的原因.     

New technique to control welding buckling distortion and residual stress with non-contact electromagnetic impact

Abstract

A new technique using non-contact electromagnetic forces has been proposed for controlling welding buckling distortion and residual stresses in welded thin plates. The experimental results show that the method can successfully eliminate the buckling distortion and reduce the residual stresses. Three-dimensional finite element modelling has been developed to study the evolution of the stress and strain throughout the welding and electromagnetic impacts. The predicted welding distortion and residual stresses are in good agreement with the experimental results. The numerical analyses show that the reduction in distortion and stress is a result of the change of the plastic strain field in the weld region: electromagnetic impacts reduce longitudinal compressive plastic strain in the local region near the weld, and even produce the tensile plastic strain. Moreover, it is found that the residual stress can promote the changes of the longitudinal plastic strain state under electromagnetic impact.     

Effect of Ti content on TiN morphology,microstructure and toughness in coarse‐grained heat affected zone of Ti‐containing steels

It is well known that weld distortion, which has a negative influence on material properties, structural fabricability and structural integrity, should be controlled appropriately. There are many methods to control or reduce weld distortion, but most of them involve some costly process in addition to welding. In-process control of weld distortion becomes more preferable than post-welding process or other methods, when manufacturing efficiency is considered. In recent years, in-process control welding by additional cooling has been proposed as one of techniques for reducing weld distortion and partially applied for thin-plate structure in industries. However, the effectiveness of additional cooling method has not yet been fully clarified. In this study, the effectiveness of additional cooling method and appropriate cooling condition for effective reduction in weld distortion are investigated by three-dimensional thermal elastic–plastic analysis. In addition, the effect of locally cooled temperature distribution on generation behaviour of plastic strain is discussed. As a result, it is concluded that the effectiveness of additional cooling and appropriate cooling condition for reduction in weld distortion are dependent on weld distortion under consideration and welding conditions. Especially, it is necessary for reduction in weld distortion to set the cooling torch at the appropriate position. For example, in order to reduce angular distortion effectively, the appropriate cooling position is dependent on the mechanical melting length during welding.     

关于焊接塑性应变的计算与讨论

采用数值模拟的方法计算了平板熔焊对接接头的纵向塑性应变的分布和动态演变过程.就目前学者所提出的焊缝存在的拉伸塑性应变的观点与传统的残余压缩塑性应变理论所存在的分歧,对比了考虑熔化现象和不考虑熔化现象两种情况,分析了焊缝中心和热影响区焊接准稳态时纵向塑性应变的变化规律.结果表明,考虑熔化现象和不考虑熔化现象纵向塑性应变结果基本相同,在焊接加热过程中所产生的压缩塑性应变始终大于冷却过程中所产生的拉伸塑性应变,在考虑熔化现象的情况下,其热影响区也始终处于压缩塑性应变状态,只是在移动热源经过后,其压缩塑性应变值在冷却的过程中有所减小.     

A new method for welding aluminum alloy LY12CZ sheet with high strength

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NUMERICAL SIMULATION OF CONTROLLING IN TITANIUM ALLOY SHEETS WELDING RESIDUAL STRESS BY TRAILING PEENING

It is a promising and new technology to apply welding with trailing peening to control welding stress and distortion of titanium alloy. Numerical simulation of conventional welding and welding with trailing peening of the titanium alloy sheet is carried out, using nonlinear finite element theory and the engineering analysis software MARC. The result shows that welding with trailing peening technology reduces longitudinal residual stress in welding joint effectively, and it is more effective to reduce residual stress to peen the weld than to peen the weld toe. It is a effective result that other technolooy and method used in welding can never achieved.     

预拉伸对铝合金焊接残余应力和变形的影响

在预拉伸应力作用下，进行了厚度为4mm的5A05铝合金试板的焊接，焊后残余应力及变形的测定结果表明．预拉伸焊接法可有效减小铝合金薄板焊后的纵向残余应力、纵向挠曲变形和平面变形。在弹性应力范由内，随着预应力的增大，试板的残余应力峰值、纵向挠曲变形及平面变形均逐渐减小。分析认为，预拉伸应力部分抵消了焊接区热膨胀产生的压缩应力，从而减小了压缩塑性变形，进而减小了冷却时焊接区域的拉伸应力水平，相应地远离焊缝区域的压缩应力也随之减小。     

Trailing heat sink effects on residual stress and distortion of pulsed laser welded Hastelloy C-276 thin sheets

A three-dimensional finite element model (FEM) was established to reveal the thermal-mechanical behaviors of pulsed laser welding (PLW) with and without trailing heat sink. Experiments were carried out to measure the welding temperature histories, residual distortions and solidification profiles. The simulation results agree well with the corresponding experimental measurements. The peak values of the temperature and transient longitudinal tensile stresses valleys in the weld increase as the cooling intensity increases from 5000 to 15,000 W/(m² K), while those of the temperature and transient longitudinal compressive stresses near the weld decrease. The peak values of the longitudinal residual compressive stresses and plastic strains, and the maximum deflections in longitudinal and transverse direction decrease as the cooling intensity increases from 5000 to 15,000 W/(m² K). The magnitudes of the transverse shrinkage distortions increase as the cooling intensity increases from 5000 to 15,000 W/(m² K). The proper cooling intensity to reduce the residual stresses and distortions of the PLW with the trailing heat sink is detected at 10,000 W/(m² K). The trailing heat sink is technically feasible for actual pulsed laser restraint welding in Hastelloy C-276 thin sheet structures.