Elucidation of Metallic Plume and Spatter Characteristics Based on SVM During High-Power Disk Laser Welding

During deep penetration laser welding,there exist plume(weak plasma) and spatters,which are the results of weld material ejection due to strong laser heating.The characteristics of plume and spatters are related to welding stability and quality.Characteristics of metallic plume and spatters were investigated during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW.An ultraviolet and visible sensitive high-speed camera was used to capture the metallic plume and spatter images.Plume area,laser beam path through the plume,swing angle,distance between laser beam focus and plume image centroid,abscissa of plume centroid and spatter numbers are defined as eigenvalues,and the weld bead width was used as a characteristic parameter that reflected welding stability.Welding status was distinguished by SVM(support vector machine) after data normalization and characteristic analysis.Also,PCA(principal components analysis) feature extraction was used to reduce the dimensions of feature space,and PSO(particle swarm optimization) was used to optimize the parameters of SVM.Finally a classification model based on SVM was established to estimate the weld bead width and welding stability.Experimental results show that the established algorithm based on SVM could effectively distinguish the variation of weld bead width,thus providing an experimental example of monitoring high-power disk laser welding quality.     

紫外激光烧蚀Cu诱导发光羽外观特征动力学研究

通过测定脉冲紫外激光在氦气中烧蚀金属Cu诱导发光羽的发射光谱及其强度随时间的分布,拍摄了发光羽的照片。实验结果表明：在低压下,发光羽的中心区与中间层均为混合色,外围层为黄绿色;中压下,发光羽的中心区和中间层均为白色,外围层为淡绿色;高压下,发光羽的中心区和中间层均为白色,外围层为微绿色。发光羽区域随着环境气压的增大而减小,其颜色随环境气压的增大而变淡。结合实验结果,对发光羽的发光机理进行了探讨。中压及低压下以电子与原子、离子的碰撞传能激发以及原子与原子、离子的碰撞传能激发为主要机理;高压下以电子韧致辐射及电子与离子的复合激发为主要机理。并用此机理定性地解释了所观察到的实验现象。     

铍/铝镁合金YAG激光焊接工艺及微观组织分析

利用YAG激光焊接了铍/铝镁合金环,探索出合理的焊接工艺参数,采用扫描电镜及电子探针对铍/铝镁合金焊接接头的组织结构进行了研究。冷却速度对显微组织的形成影响明显,在靠母材的焊缝两侧,焊缝的显微组织为树枝晶,而焊缝的中心为等轴晶;在焊缝处主要存在焊接热裂纹及夹杂物,对夹杂物的能谱分析表明,其主要由C、O、Al、Mg、F、Cl等元素组成;对焊缝的面扫描结果表明,C、O等元素在焊缝的表面存在偏析,而Be与Mg分布较为均匀。     

316不锈钢激光焊接中离焦量对热裂纹的影响

采用最大平均功率为500 W的脉冲激光焊机开展了316不锈钢焊接试验,通过测试表面形貌、微观组织、显微硬度及能谱（EDS）等,分析了离焦量对焊缝组织和热裂纹的影响。研究结果表明,在其他焊接参数不变的条件下,离焦量增大时焊缝组织逐渐细化和致密,热裂纹倾向性逐渐减小。焊缝熔深和熔宽均随离焦量的增大而减小,但宽深比增大,当宽深比大于7.5时焊接热裂纹彻底消失。增大离焦量改变了激光能量的分布状态,导致焊缝凝固过程中S、P等元素向熔池表面偏析,消除了焊缝凝固后期液膜及低熔点组织的不利影响,有效控制了脉冲激光焊接316不锈钢热裂纹的产生。     

Hastelloy C-276/316L脉冲激光异质焊接微观组织研究

为评价激光焊接AP1000部件工艺的可靠性,探究Hastelloy C-276与316L异质焊接焊缝的元素偏析及组织结构,利用Nd:YAG脉冲激光进行焊接,借助光学显微镜和电子探针X射线微区分析仪等分析测试仪器,对焊缝显微组织、元素成分及金相形貌进行分析。结果表明：焊缝组织晶粒细化,焊缝中部以细小等轴晶为主、边缘以柱状晶为主,且焊接接头两侧热影响区极窄;依据元素宏观分布,焊缝可分为3个区域,焊缝两侧元素成分急剧变化,中部均匀;元素存在微观偏析,晶界处Mo元素富集。焊缝组织以γ奥氏体为主,并未发现明显δ铁素体生成。     

铍环电子束焊接温度场和应力场的有限元分析

采用ADINA/ADINAT对铍环电子束焊接过程的温度场和应力场进行了有限元分析 ,结果表明 :铍环焊接过程中焊缝外表面最高温度达 2 73 4℃ ,内表面最高温度仅 3 78℃ ,位于外止口铍钚一侧 ;铍环电子束焊接后 ,在焊缝附近 2 0mm范围内焊接残余应力较大 ,焊缝处于复杂的三维应力状态 ,焊缝根部的残余应力达到最大 ;内外止口铍环由于结构差异 ,焊接残余应力分布并不完全相同。     

Preliminary Study of Isotopic Methanes Analysis by Laser Raman Spectroscopy for In-Situ Measurement at Fusion Fuel Gas Processing

Application of laser Raman spectroscopy for fusion fuel gas processing was studied by measuring isotopic methanes exchanged with hydrogen isotopes, which are considered to be a major impurities in the processing. For experimental gases, isotopically equilibrated deuterium and methane were prepared in the presence of solid catalyst. Large Raman scattering peaks of v ₁, bands were observed at 2,917 cm^?1 for CH₄ and at 2,100-2,200 cm_?1 for deuterated derivatives of methane C(H,D)₄. Under a spectral resolution of 5 cm_?1, the v ¹ bands of CH₃D and CH₂D₂ were observed as an overlapped peak, the relative absolute Raman intensity ratio of each isotopic methane was obtained as CH₄: CH₃D+CH₂D₂: CHD₃: CD₄=230: 74: 144: 100. On the other hand, the Raman intensity ratio obtained from pure deuterated standard methane was CH₄: CH₃D: CH₂D₂: CHD₃: CD₄=230: 53: 33: 115: 105. It was confirmed that isotopically equilibrated hydrogen isotopes and methane mixed gas would be applicable for an alternative standard gas for fusion fuel processing gas analyzing system.