X80管线钢多道激光-MIG复合焊残余应力分析

采用试验和数值模拟结合的方法对X80管线钢多道激光-MIG复合焊焊接过程的温度场和焊接残余应力场进行了研究,分析了激光功率对复合焊接头的显微组织、温度分布和残余应力分布的影响规律. 结果表明,激光功率增加,熔池最高温度明显上升,焊后冷却速度下降;粗晶热影响区组织中粒状贝氏体、针状铁素体增加,条状贝氏体减少. X80管线钢激光-MIG复合焊接头残余应力水平较高,纵向残余应力、横向残余应力和厚度方向残余应力的拉应力峰值均出现在焊缝区. 激光功率在2.0 ~ 3.5 kW范围时,等效残余应力、纵向残余应力、横向残余应力和厚度方向残余应力的峰值随着激光功率增加均出现下降趋势. 但激光功率从3.5 kW上升至4.0 kW时,各应力的峰值有所上升.     

铝合金激光拼焊应力场数值模拟

利用有限元分析软件ANSYS模拟铝合金激光拼焊时应力场的变化.选取的热源模型为高斯热源,利用ANSYS软件的APDL语言编写程序实现移动热源的加载.在模拟中不但要考虑一般激光焊接中参数对应力场的影响,还要考虑铝合金激光拼焊的特性.结果表明,在焊缝区工件处于拉应力状态,远离焊缝逐渐过渡到压应力状态.当激光功率3000～4500 W、焊接速度2～4 m/min时,随着激光功率增大和焊接速度降低,焊缝附近的拉应力峰值及应力分布范围增大.     

CO2激光焊残余应力测试与分析

采用盲孔研究了CO2激光焊工艺参数对焊接残余应力的影响，并对激光焊接工件残余应力的形成过程进行了初步的研究，试验结果表明，激光功率，爆接速度，试板尺寸等因素对残余应力分布情况有明显的影响。     

同轴送粉激光增材制造Al-Zn-Mg-Cu合金应力场数值模拟

采用Ansys软件建立了同轴送粉激光增材制造Al-Zn-Mg-Cu合金的有限元模型，对该模型进行了试验验证，模拟分析了不同激光功率和扫描速度单层单道成形过程中的温度场和应力场。结果表明，模拟得到的应力与试验结果误差约为5.2%,验证了模型的准确性。激光成形过程中，激光作用产生“端部效应”,熔池前端的温度梯度大，后端的温度梯度小。随着激光功率的增加和扫描速度减小，熔池温度增加，激光功率的影响更加显著。随着激光功率与扫描速度的增加，沉积层的三向应力也随之增大，最大Von mises等效应力与垂直于扫描方向的应力σ_y呈“W”形分布，沿扫描方向的应力σ_x先增大后减小，且σ_x>σ_y。当沉积层冷却至室温时，其表面残余应力主要为拉应力，且沉积层中部位置的残余应力高于边缘位置的残余应力。     

工艺参数对异厚度铝合金激光拼焊板残余应力场的影响

采用小孔释放法检测异厚度铝合金激光拼焊后的残余应力场,分析残余应力产生的规律和原因,对比薄厚两板残余应力场的差异,分析激光功率、焊接速度、离焦量、添加粉末对残余应力场的影响.测量分析结果表明:异厚度铝合金激光拼焊残余应力场分布规律与普通熔焊方法相似,但分布区域较窄.对于不同的工艺参数,焊接功率越小、焊接速度越快、离焦量越大、不添加粉末时,残余应力场分布范围越窄.     

激光功率变化对蠕墨铸铁相变硬化热力耦合场的影响

为了防止蠕墨铸铁气门座激光相变硬化缺陷的形成,通过对其热力耦合场进行数值模拟,探究激光功率的变化对气门座温度场和残余应力场的影响,并在模型中考虑了相变潜热和材料性能参数随温度的变化。结果表明:激光相变硬化是一个快速加热和冷却的过程,能够针对材料局部和表面进行硬化和强化;激光功率增加可以提高气门座的峰值温度;气门座截面的温度和周向残余拉应力均呈月牙形分布,峰值均出现在硬化层表面区域;伴随激光功率的增加,相变硬化区域的周向残余拉应力呈上升趋势。基于模拟结果,得到了气门座在不同激光功率下热力耦合场的分布规律,为优化激光参数提供了指导。     

基板预变形对不锈钢激光立体成形件应力应变的影响

采用316不锈钢粉末和304L基板,通过一系列预变形矩形试样的激光立体成形正交实验,并通过小孔释放法进行应力测试,分析了基板预变形处理对激光立体成形试样的残余应力和变形的影响.结果表明:预变形量对预变形条件下的激光立体成形试件的平整度影响最大,其次为激光功率,激光速率.基板预变形后的应力分布显著影响激光立体成形后试样最终的变形形状.激光成形件上部熔覆层的残余应力σx先增大后减小,σz先减小后增大.研究结果为优化预变形条件下的激光立体成形工艺提供了参考依据.     

激光重熔合成Fe-Al涂层温度场及应力场数值模拟

依据有限元建模思想,采用高斯表面热源,同时考虑相变潜热与温度的关系,应用ABAQUS软件建立了Q235钢基体上激光重熔合成Fe-Al涂层的温度场和应力场计算模型,研究了激光功率和扫描速度对温度场和应力场的影响。结果表明,提高激光功率对增大热影响区深度效果不大,反而会形成较大的熔池而使重熔表面粗糙;与激光功率相比,扫描速度对温度场影响较小;涂层与基体合金化区沿着激光扫描方向的拉应力远大于垂直扫描方向的拉应力;结合界面处的残余应力与扫描速度成正比,与激光功率成反比,且扫描速度对残余应力的影响较激光功率显著。实验结果较好地验证了模拟结果,表明所建立的温度场和应力场计算模型是正确和可靠的。     

曲面基底工件激光熔覆温度场与应力场数值模拟

目的 研究曲面基底工件激光熔覆的温度场和应力场分布情况。方法 采用数值模拟的方法模拟激光熔覆及冷却过程中的温度场和应力场。通过Ansys软件,采用高斯热源模型模拟圆环柱曲面基底外表面上的激光熔覆过程。在加工过程中,激光头与基底的相对运动为螺旋运动。分析不同功率和扫描速度对温度场和残余应力的影响,以及应力场随时间的变化和残余应力的分布情况。结果 扫描速度对温度场的影响较大,功率和扫描速度对残余应力无明显直接影响,不同功率和扫描速度的残余应力最大值都出现工件外壁中部。在XZ轴面上的径向应力呈现出漏斗形,四周高,中间低,大部分都在–20～20 MPa,起伏较小;周向应力在XZ轴面对角线方向上呈近似抛物线,两端高,中间低,最高值为100 MPa,最低值为–50 MPa,起伏较大;厚度方向的应力分布呈近似半圆锥三维形状,在Z轴方向上为近似直线,在X轴方向上为近似半抛物线,呈现出一端高、一端低、中间部分逐渐下降的趋势,最高值为110 MPa,最低值为–30 MPa,起伏较大。结论 成功研究了曲面基底工件激光熔覆的温度场和应力场分布情况,对曲面基底激光熔覆的工艺参数优化和提高产品质量有一定指导作用。     

基于计算机有限元分析的激光冲击强化钛合金疲劳性能研究

基于限元分析软件ABAQUS和MSC.Fatigue,建立了激光冲击TC17钛合金标准紧凑拉伸试样及其疲劳裂纹扩展的有限元分析模型。对不同区域下激光冲击强化TC17钛合金后的残余应力分布及疲劳裂纹扩展性能进行分析,进而探讨了残余应力场对疲劳裂纹扩展的影响。结果表明,激光冲击TC17钛合金经后,试样上下表面处理区域均呈现压应力分布,最大残余压应力达-473 MPa,残余压应力层深度达0.76 mm,同时,表面残余压应力随激光功率密度和冲击区域的增大,逐渐增大并达到饱和。相对于未冲击件,激光冲击使TC17试样疲劳寿命大幅延长,疲劳裂纹扩展速率显著降低;且随冲击区域的增大,疲劳寿命不断延长,表明激光冲击诱导的残余应力场对TC17钛合金疲劳裂纹扩展具有较好的抑制作用。     

Thermal–mechanical analysis on the transient deformation during pulsed laser forming

The transient deformation of thin grade 304 stainless steel metal sheets heated by a single pulse of a CO₂ laser beam is simulated in this paper. The laser beam is assumed to be Gaussian mode and the coupled thermo-elastoplastic problem is treated as three-dimensional. The temperature field, deformation pattern, stress–strain states, and the residual stress distribution of the specimens have been calculated numerically and the transient response of the bending angle has been validated by experiments. Good agreement has been obtained between the numerical simulation and the experiments under various operating conditions. The numerical study reveals that a high temperature gradient exists for a positive bending angle and a low one for a negative angle. It transpires that the mechanisms of pulsed laser forming are dependent mainly upon the laser power, the heating time, the clamping arrangement, as well as the geometry, the thermal properties, and the original stress states of the specimen.     

Thermal and stress modeling of multi-material laser processing

Three-dimensional finite element modeling has been carried out to investigate the temperature field in the processing of multiple material components using a moving laser beam. Transient and residual stresses as well as distortion of the component have also been analyzed. Effects of laser processing conditions such as fabrication sequences, laser scanning patterns and scanning rates have been investigated. It is found that the temperature distribution, transient stress, residual stress and distortion of a multi-material component are dependent on the laser processing conditions as well as the material properties, especially the thermal conductivity and coefficient of thermal expansion. Implications of these results on laser fabrication of multiple materials are discussed.     

Finite element analysis of temperature distribution in single metallic powder layer during metal laser sintering

The metal laser sintering (MLS) is used to make strong or hard metallic models for tools and dies directly from metallic powders. Thermal distortion is the serious problem after cooling of the solidified part rapidly. Uncontrolled temperature distribution in the metallic powder layer leads to thermal distortion of the solidified part. The study of temperature distribution within the metallic layer during MLS is important from the quality of the layer point of view.The high temperature generated in the powder layer leads to thermal distortion of the part and causes thermal as well as residual stresses in the part. In this paper the powder layer is assumed to be subjected to plane stress type of temperature variation and a transient finite element method-based thermal model has been developed to calculate the temperature distribution within a single metallic layer during MLS. A finite element code has been developed and validated with the known results from the literature.The obtained results of temperature distribution show the temperature and temperature gradient variation along X- and Y-axis. The effect of process parameters such as laser power, beam diameter, laser on-time, laser off-time and hatch spacing on temperature distribution within a model made of titanium during MLS is studied. The results computed by the present model agree with experimental results. Temperature increases with increase in laser power and laser on-time but temperature decreases with increase in laser off-time and hatch spacing.     

表面织构对模具钢激光熔覆层性能的影响分析

目的 减少激光熔覆过程中产生较大的应力和裂纹的现象,提高激光熔覆后模具钢的抗疲劳性能,延长其使用寿命.方法 选取激光功率(800、1000、1200 W)、扫描速度(5、10、20 mm/s)、光斑半径(0.5、0.75、1 mm)作为激光熔覆模拟因素,以残余应力为主要试验指标,进行三因素三水平正交模拟试验,并对试验结果进行信噪比及极差分析,确定最优熔覆参数.在最优熔覆参数下,进行预置织构及无织构的激光熔覆模拟,对比分析两次模拟的熔覆层温度及残余应力分布.在最优参数下进行熔覆加工,验证有效性.结果 正交模拟试验得出最优熔覆参数为:激光功率800 W,扫描速度20 mm/s,光斑半径1 mm.得到最小残余应力平均值为360 MPa.此外,激光功率对残余应力的影响最为显著,其次是光斑半径,对残余应力影响最小的是扫描速度.在最优熔覆参数下,对预制织构的模型进行激光熔覆模拟,得出残余应力平均值为149 MPa.相比较于无织构熔覆模拟,预置织构熔覆模拟的平均应力值降低了大约58.56％.对无织构和有织构模具钢表面进行激光熔覆加工,测量残余应力,验证了该方法的有效性.结论 通过在基体预置表面织构的方法,在保证熔覆温度的前提下,降低了残余应力,最终能达到降低残余应力、减少裂纹产生的目的.     

Experimental and numerical modeling of buckling instability of laser sheet forming

New experimental results show that laser bending can be extended to generate a bending angle not only towards but also away from the laser beam, giving more flexibility to the process. In order to explain this buckling instability, a series of experiments have been carried out with real-time measurement of the bending angle for different materials, thicknesses, scanning speeds, laser beam diameters and laser powers, pre-bending conditions, and cooling conditions. Furthermore, a 3-D FEM simulation has been performed that includes a non-linear, transient, indirect coupled, thermal–structural analysis accounting for the nonlinear geometric and material properties. The buckling deformation, bending angle and distribution of stress–strain and temperature, as well as residual stresses, have been obtained from the simulations. The bending angle is affected by the temperature distribution and gradient, the mechanical and thermal properties of the sheet metal material, and the process parameters, such as the laser power, the laser beam diameter, the scanning speed, the material, the sample geometry, and other bending conditions. The buckling mechanism can be illustrated by the simulation results.     

Study on mechanics and key technologies of laser nondestructive mirror-separation for KDP crystal

KDP crystal is an important electro-optic material in various laser systems. At present, the greatest difficulty is the cutting and polishing of large-scale crystals. In this study, a laser nondestructive mirror-separation technology (LNMS) for KDP crystal has been developed for the first time by skillfully adopting femtosecond laser pretreating and fiber laser separating. The separating efficiency of LNMS is at least 200 times faster than that of traditional mechanical cutting, and a nondestructive mirror-separated crystal sidewall with surface roughness (S_a) of 4.7 nm (P−V) and 2.1 nm (RMS), flatness of 5.433 μm and an angular precision about 0.06° could be obtained using the LNMS method. The effects of laser separating parameters, including laser power, laser moving speed and internal stress release on separating accuracy and quality, were investigated and optimized; meanwhile its principle was expounded as well as its mechanism was discussed. The experimental and analyzed results show that the LNMS technology may also have a prospect in the analysis of residual stress distribution inside KDP crystal. A numerical simulation on the thermal stress in the LNMS separating process of KDP crystal was developed to analyze the separating mechanism, which is in good agreement with the theoretical analysis and experimental results.     

常压/真空环境激光焊接焊缝成形特性及残余应力与变形对比

在高功率激光焊接中,采用增大激光功率的方法以获得更大熔深时,面临焊接过程稳定性差、焊接缺陷频发等问题,目前国内外普遍认为真空激光焊接是解决以上问题的有效手段. 文中采用工艺试验和数值模拟的方法,研究了常压和真空环境下中厚度全熔透激光焊接在焊缝成形及残余应力与变形分布的差异. 结果表明,降低环境压力可显著增加激光焊接熔透深度,真空环境可以将常压环境10 mm全熔透激光焊接所需激光功率从10 kW降低到6 kW,并获得更好的焊接质量. 常压环境和真空环境下,全熔透激光焊接工件展现出类似的横向残余应力、纵向残余应力和变形分布规律,但由于真空环境下热输入较低,焊缝深宽比大,焊后残余应力的峰值和变形程度均显著小于常压环境.     

激光工艺参数对PC/Cu/PC焊接性能及残余应力影响

实现聚碳酸酯(PC)材料高品质焊接是拓展其工程应用的重要方向. 焊接件残余应力聚集的位置易产生变形、裂纹等缺陷,使用过程中进而会形成应力腐蚀,导致强度降低,缩短焊接件的使用寿命. 为了实现PC材料的高质量焊接,提出了以表面涂有碳黑的铜膜为激光吸收材料的透射焊接新方法,并探究了不同激光工艺参数(激光功率和焊接速度)对焊接性能、铜膜变形量及残余应力的影响规律. 结果表明,随着激光功率和焊接速度的增大,焊缝抗剪强度和铜膜变形量均先增大后减小;焊缝宽度与激光功率成正比,与焊接速度成反比;残余应力与激光功率成正比,与焊接速度成反比;且发现铜膜变形在一定程度上有利于提高焊接性能和减小残余应力.     

脉冲激光离散熔凝加工的熔池几何形态研究

研究了Ｎｄ∶ＹＡＧ脉冲激光离散加工时功率密度和作用时间对熔池几何形态的影响。５ＣｒＭｎＭｏ钢的实验结果表明：在一定加工条件下,熔池存在热传导型和深熔型两种形态。激光作用时间小于４ｍｓ时,随着激光功率密度的增加,熔池深宽比显著增加;作用时间超过４ｍｓ后,功率密度对深宽比的影响减弱。基于线性热传导模型的计算结果表明：熔凝起始阶段固态加热过程可忽略;熔池几何尺寸在激光脉冲结束后某个时刻达到最大值;当平均功率密度大于５×１０５Ｗ／ｃｍ２,同时激光作用时间大于２ｍｓ时,热传导型激光熔池向深熔型激光熔池转变