激光深熔焊接热过程数值模拟的研究进展

激光深熔焊接过程涉及极其复杂的物理化学反应,数值模拟是研究激光深熔焊接过程的温度场、焊件应力与变形、熔池、匙孔演变与反冲压力等问题的基础,而热过程处理是激光深熔焊接数值模拟的关键点。总结和分析了体热源模型、复合热源模型和自适应热源模型的发展情况,论述了材料热物理性能参数在数值模拟中的使用情况,讨论了激光深熔焊接数值模拟中一些关键问题如边界条件,并指出了激光深熔焊接热过程数值模拟需要进一步研究的方向。     

深熔激光焊接熔池温度场的数值模拟

利用旋转Gauss曲面体新型热源模型,忽略深熔激光焊时小孔对传热的影响,建立了移动激光热源作用下的三维数学模型.利用PHOENICS3.4软件,模拟了SUS304不锈钢深熔激光焊接热过程的温度场和熔池熔合线形状,得到了不同焊接速度下的温度场分布云图和"钉头"状的熔池形状.数值模拟结果与试验结果基本吻合.     

熔焊热过程与熔池行为数值模拟的研究进展

熔焊是目前机械制造业中应用最为广泛的材料连接技术。熔焊过程中的传热与熔池流动行为对于焊缝成形、接头微观组织与服役性能等起着决定性作用。准确地分析和计算熔焊热过程与熔池形态,对于焊接冶金分析、应力变形分析、过程控制及工艺优化等都具有十分重要的意义,也是使焊接工艺从"定性"走向"定量"分析、从"经验"走向"科学"的重要途径。对焊接电弧物理、熔滴过渡、熔池形态、高速焊接熔池传热与流动、等离子弧焊和激光焊接的小孔与熔池动态行为、激光-电弧复合热源焊接热过程的数值模拟研究现状与存在问题进行了评述,讨论了上述前沿领域的研究方向与发展趋势,旨在为实现熔焊工艺优化和过程控制提供理论依据。     

铍材激光钎焊温度场和应力场的数值模拟

在综合考虑激光钎焊熔池表面形状和几何参数的基础上,建立了适合于铍材激光钎焊的表面双椭圆热源分布模型;通过对数值模拟与试验获得的熔深、熔宽等参数的对比,可知计算结果与试验结果吻合较好,说明双椭圆表面热源模型能够较好地模拟铍环钎焊.通过对焊接加热和冷却过程中铍环焊缝附近应力状态变化的比较,发现凝固过程中最大轴向拉应力和最大环向拉应力均位于焊缝中心,这正是焊缝中心较易形成凝固裂纹的主要原因.     

双丝电弧焊熔滴过渡形式对熔池影响模拟研究

双丝电弧焊是一种满足了焊缝质量、焊接效率的高效焊接方法,得到了广泛的应用.采用数值模拟方法,建立双丝电弧焊热源模型,考虑到熔滴在不同的过渡形式下以不同的动量、热量滴入熔池,建立了熔滴热源、动量模型,对焊接过程中影响熔池流动的驱动力进行加载,并且考虑了熔池边界能量的辐射和对流.对熔滴不同过渡形式下的熔池热场与流场进行模拟分析,熔池的流场和温度场.结果表明:熔滴喷射过渡可以得到更大的熔深和熔宽,以及熔宽比,大的深宽比有利于形成高质量的焊缝,提高焊接质量.细滴粒过渡熔池可以得到更高的焊接温度,熔池长度相对较短,热量较为集中,在熔池深度和宽度方向上金属流动更剧烈,有利于将气体以及杂质带至熔池表面并排出.     

喷射电镀Ni镀层激光重熔温度场的数值模拟

利用ANSYS有限元软件，综合考虑材料的热物理性能参数、激光的热源模型，建立了激光重熔喷射电镀层的数值模型。在不同激光工艺参数下，数值模拟所得到的熔池截面尺寸和试验所测得的熔池截面尺寸相吻合，表明所建立的连续移动激光重熔温度场的计算模型是正确的。数值模拟结果可作为激光加工工艺参数选择的依据。     

TC4钛合金激光熔覆熔池凝固传热研究

基于有限元法对单道单层激光熔池的凝固过程进行数值模拟,得到熔覆过程中激光熔池的温度场分布及温度梯度分布等数据信息,结合测温实验,分析了激光熔池在凝固过程中的热行为,阐述了激光工艺参数对熔池凝固传热过程的影响。结果表明:在激光单道熔覆过程中,熔池前端热量集中、熔深较大,尾部热量传递迅速、熔深较小。温度梯度在熔池前端最大值变化范围是3.04～3.89×10~6℃/m~(-1)。激光功率对熔池热传递的影响效应大于扫描速度影响效应的规律。模拟和实验结果吻合。     

铍材钎焊熔池动态行为的影响因素研究

在综合分析激光钎焊的焊缝形状特征和热源作用特点的基础上,根据流体力学和传热学原理,建立瞬态熔池三维数值分析模型和混合热源分布模型,模型考虑熔池液态金属对流传热、熔池外工件的固态导热、焊接过程中的相变潜热、侧吹气流方式、对接界面的结构几何特性以及材料热物理性能参数随温度变化等因素.利用Visual Fortran语言编写数值分析程序,分析相变潜热、侧吹气流和对接间隙等对熔池内流场和温度场分布的影响.研究表明,相变潜热的影响不是总可以忽略的,尤其是在移动热源作用下相变潜热的影响比固定热源更为突出.侧吹气流主要是通过改变熔池内液态金属的流动状态进而影响到熔池的三维形态,因此,选择合适的吹气方式能够有效地提高激光钎焊的稳定性和焊深.间隙的存在造成温度场分布不连续造成熔池形状呈“钉头”形,考虑间隙时计算得到的熔池形状与试验结果吻合更好.     

双椭球热源参数调整在预测在役焊接熔池尺寸上的应用

双椭球热源模型常用于在役焊接过程的数值模拟,模型中参数的合理选用对于计算结果的正确性具有决定性的作用。以往进行热源参数的调整,常运用经验反复进行试算以确定热源参数,具有很大的不确定性且工作量较大。为此,运用解析法对在役焊接常用的二氧化碳气保焊双椭球热源模型参数的确定进行了计算,通过模拟计算与试验相结合的方式对其进行验证,确定了该模型熔池尺寸参数的经验公式。研究结果表明,运用该方法,热源参数的确定过程大大简化,提高了数值模拟的效率和精度,较好地预测了在役焊接熔池的尺寸。     

激光直接烧结成形多层金属薄壁件的温度场有限元模拟

为掌握多层粉末烧结过程中激光熔池的加热冷却规律以及各烧结层之间的相互影响,综合考虑热传导、热辐射和热对流以及材料的高度非线性,基于ANSYS平台建立了多层金属薄壁件的三维温度场有限元模型,利用APDL语言编程实现模拟中激光热源的移动,采用"单元生死"技术描述粉末材料动态增长过程。模拟结果表明:在现有工艺参数下,烧结获得的熔深在0.15mm以上,熔宽在0.61mm左右,烧结成形件与基体以及层层之间搭接牢固;成形件中,与x方向的热梯度相比,z方向热梯度占绝对优势,这说明成形件在冷却过程中热量的散失以堆积方向为主。将模拟结果与实验结果进行了对比,实验结果较好地验证了模拟结果。     

Numerical modeling of heat transfer and fluid flow in hybrid laser–TIG welding of aluminum alloy AA6082

This paper describes a three-dimensional numerical model based on finite volume method to simulate heat transfer and fluid flow in laser–tungsten inert gas (TIG) hybrid welding process. To simplify the model and reduce the calculation time, keyhole dynamics are not considered; instead, a new modified volumetric heat source model is presented for the laser source to take into account the effect of the keyhole on the heat transfer into the workpiece. Due to the presence of arc current, an appropriate electromagnetic model based on the Maxwell equations are also solved to calculate electromagnetic forces in the weld pool. The results of computer simulation, including temperature, current density, electromagnetic, and melted material velocity field, are presented here. Furthermore, several dimensionless numbers are employed to recognize the importance of fluid flow driving forces in the weld pool. It is deduced that the fluid flow has an important effect on the weld pool shape. It is also founded that among the driving forces, Marangoni force is dominant fluid force in the weld pool. Besides, calculated results of hybrid welding process are compared with those of TIG and laser welding processes. The weld pool depth is relatively the same, but the width of the weld pool is highly larger in hybrid welding than lone laser welding. Eventually, the presented model is validated by comparison between calculated and experimental weld pool shape. It is founded that there is a good agreement as the capability of this model can be proved.     

Numerical simulation of laser�Ctungsten inert arc deep penetration welding between WC�CCo cemented carbide and invar alloys

In order to optimize the laser?Ctungsten inert arc (TIG) welding process of cemented carbide to steel, a novel combined model consisting of circular disk source, line source, and double ellipsoidal TIG heat source was put forward to simulate the deep penetration phenomena and bead profile. In contrast, laser heat source model was validated using macrostructure analysis results. The effects of the circular disk of radius and the material properties on the bead profile were discussed. For mechanism surface formation, surface depression or humps was discussed based on the high-speed photography technique to verify bead profile characterization. The results manifested that in the model, the circular disk radius played a key role in the formation of bead profile. And the penetration coefficient chiefly affected the root of weld and the keyhole formation. During the hybrid welding, the main forces influencing the surface depression or humping were intrinsic stress from coefficient of thermal expansion gradient, surface tension, buoyancy force, stirring action, and shock waves at the end of the keyhole. Before the solidification of the upper part of the melt, the melt was driven by the fluctuated plasma, plumes, or other forces. While the amount of melt filling the back welds metal of keyhole was larger than that caused by plume losses and the shrinkage of weld metal, the humps came into being.     

Hybrid heat source model designing and parameter prediction on tandem submerged arc welding

In submerged arc welding simulation, the heat source parameters are always decided by experience, and it usually leads to a high simulation error. This work is aimed to develop a methodology for the estimation of the heat source in submerged arc welding. A hybrid heat source model was applied on submerged arc welding simulation. The new heat source model was combined by a surface heat source model and the double ellipsoid heat source model. The surface heat source model was designed based on the Gaussian heat source model. The width and penetration of the weld pool were simulated and compared with the measurement results, and the width at 2?mm depth from the top surface was also considered to describe the shape of the weld pool more accurately. In order to reduce the simulation complexity, the sensitivity of heat source parameters was discussed. The heat source parameter corresponding to different experimental processes was obtained by modified pattern search method. The artificial neural network algorithm and the support vector machine algorithm were applied to predict the relationship between all possible process and the heat source parameters. The validation experiment showed that the prediction model was accurate.     

Laser micro-welding of aluminum alloys: experimental studies and numerical modeling

Experimental and numerical studies were conducted on the effects of the laser beam pulse shaping in the time domain on the quality of the welding seam in laser micro-welded AlMg3 with a thickness of 0.2 mm and 1 mm thick AlMg4.5 Mg foils, respectively. The pulse shaping was realized by a time sequence of three different rectangular pulses with different duration and power level. The first pulse was used to pre-heat the sample, welding occurred with the second pulse and the third pulse controlled the melt pool behavior. The power level and the duration of the single pulses were varied systematically and the resulting microstructure was analyzed by scanning electron microscope. The experiments were accompanied by numerical simulations based on a finite volume model which considers the transient heat flow, melt convection and the evolution of a gas capillary during the deep penetration welding process.     

Some studies on temperature profiles in AISI 304 stainless steel sheet during laser beam welding using FE simulation

The investigation of transient temperature profiles of a weld joint produced by the laser welding process is presented. A three-dimensional finite element model is developed using a commercial finite element code ANSYS in order to obtain the behavior of temperature field and molten pool shape during the welding process. A three-dimensional conical Gaussian heat source is employed as a heat source model for performing a non-linear transient thermal analysis. The temperature-dependent material properties of AISI 304 stainless steel sheet are taken into account, which has a great influence on the temperature fields indicated by the simulation results. The effect of latent heat and the convective and radiative boundary conditions are also included in the model. A series of laser welds are performed using a 2-kW continuous wave Nd:YAG laser welding system. The experimental trials are conducted by varying the laser input parameters namely beam power, welding speed, and beam incident angle to validate the model. The results show that there is a good agreement between the finite element simulation and the experimental observations.     

铝合金变极性等离子弧焊温度场数值模拟

通过高速摄像对正、负极性等离子弧形态进行分析,并分析变极性等离子电弧正、反极性不同产热机理的基础上,采用“高斯+双椭球”组合热源模型,建立正、反极性期间不同热源模型。采用ANSYS参数化设计语言(ANSYS parametric design language, APDL)编程语言实现与实际变极性焊接参数对应热载荷的循环交替加载,计算出铝合金变极性等离子弧焊接温度场及熔池形状。对比分析不同变极性电流和焊接速度条件下焊接熔池的穿透深度,并通过实际焊接试验验证热源模型的准确性。研究结果为准确掌握铝合金变极性等离子弧热源形态、产热机理和等离子弧力等特性,并合理选择焊接工艺参数提供理论依据。     

Analysis of weld pool dynamic during stationary laser–MIG hybrid welding

A mathematical model was established to simulate the weld pool development and dynamic process in stationary laser–metal inert gas (MIG) hybrid welding. Surface tension and buoyancy were considered to calculate liquid metal flow pattern; moreover, typical phenomena of MIG welding such as filler droplets impinging weld pool, electromagnetic force in the weld pool, and typical phenomena of laser beam welding such as recoil pressure, inverse Bremsstrahlung absorption, and Fresnel absorption were all considered in the model. The laser beam and arc couple effect was introduced into this model by the plasma width during hybrid welding. Transient weld pool shape and complicated liquid metal velocity distribution from two kinds of weld pool to a unified weld pool were calculated. Furthermore, the simulated weld bead geometries were in good agreement with experimental measurement.     

Online detection method of weld penetration based on molten pool morphology and metallic vapor radiation for fiber laser welding

A novel detection method of penetration status was presented for a high-power fiber laser welding. The metallic vapor and molten pool was recorded by a high-speed camera during welding process. The radiation intensity of metallic vapor, as well as the morphology of molten pool end, was calculated by image processing algorithm as image features. Four image features, the radiation intensity of metallic vapor (RIMV), the area of molten pool end (AMPE), the rear angle of molten pool end (RAMPE), and the aspect ratio of molten pool end (ARMPE), were extracted. The mean value, relative range, variation coefficient, and frequency ratio were computed for the four features to obtain the 16 characteristic parameters. Aiming at penetration status, the characteristic parameters were reorganized to form two complex indicators by the principal component analysis. Experimental results showed that the detection method was potential for online detection on the penetration status in a high-power laser welding process.     

Face milling for hypoid internal bevel gear using new type of tilt milling machine

An hourglass-like heat source model is developed to simulate the geometry of weld beads of laser beam welding. The welding experiments with different welding parameters were carried out to find whether the welds are full-penetrated or not. The laser powers ranged between 1.0 and 5.0 kW with steps of 1.0 kW. Five levels of the welding speed were used: 1.0, 2.0, 3.0, 4.0, and 5.0 m/min. The numerical analysis based on finite element method was used to predict the shape of weld pools during welding. To give a better representation of weld bead, an hourglass-like heat source model is developed to describe the unique shape of 1060 steel weld bead for laser beam welding without filler metal instead of the commonly used conical heat source. Comparing the predicted fusion profile with the experimental cross section of weld, it is found that hourglass-like heat source model is more consistent with the experimental results than the conical heat source for 1060 steel. In addition, the best heat source parameters are obtained by an error analysis. Compared to the experimental results, the simulated results for the welds using Power = 4000 W and Speed = 2.0 m/s and 5000 W and 2.0 m/s match the experimental results well.