Behavior of vapor/plasma within the keyhole and above the workpiece during CO_2 laser penetration welding

In this paper, a high-speed camera and an optical emission monitor were used to study the behavior of vapor/ plasma during CO2 laser welding of SUS304 stainless steel. Results of optical emission from vapor/plasma show that two characteristic frequency bands exist, 100 -500 Hz and 1 500 -3 500 Hz. At the same time, the changing images of vapor/ plasma and bottom pool also confirm that there are two different fluctuation frequency bands. One of the frequency bands represents the characteristic of vapor/plasma within the keyhole, and it is within 167 -500 Hz. Another frequency band is within 1 500 - 3 500 Hz, and it obviously derives from the shielding gas. Some factors may cause these frequency differences between the keyhole plasma and the shielding gas plasma. One of them is that the vapor/plasma pressure within the keyhole will increase slowly.

A study on the porosity of CO_2 laser welding of titanium alloy

The CO2 laser welding of BT20 titanium alloy and Ti-23Al-17Nb titanium aluminide was conducted to investigate into the porosity in titanium alloy weld. The results show that there are two sorts of porosities observed in welds of titanium alloy laser welding based on the microscopic characteristics of the porosities. One is the metallurgical porosity with round and smooth inner wall, which results from the surface contamination. The other is the processing porosity with irregular and rough inner wall that displays the trace of the pool flowing, which results from the ruffle on the keyhole wall gathering together locally and closing down the gas in the keyhole into bubbles because of the keyhole fluctuating. The CO2 laser welding could break down easily the surface oxide film and produce little metallurgical porosity, but produces easily processing porosity when partial penetration or unstable-full penetration laser welding is conducted, which always occurs in the center of weld.

Macrostructural and microstructural features of 1000 MPa grade TRIP steel joint by CO_2 laser welding

Bead-on-plate CO2 laser welding of 1 000 MPa grade transformation induced plasticity （TRIP） steel was conducted under different welding powers, welding speeds and shield gases. The macrostructural and microstructural features of the welded joint were investigated. The increase of welding speed reduced the width of the weld bead and the porosities in the weld bead resulting from the different flow mode of melted metal in weld pool. The decrease of welding power or use of shield gas of helium also contributed to the reduction of porosity in the weld bead due to the alleviation of induced plasma formation, thus stabilizing the keyhole. The porosity formation intimately correlated with the evaporation of alloy element Mn in the base metal. The laser welded metal had same martensite microstructure as that of water-quenched base metal. The welding parameters which increased cooling rate all led to fine microstructures of the weld bead.

Mechanism of laser welding of SiC reinforced LD2 aluminum metal matrix composite

In this paper the mechanism of SiC_P/LD2 aluminum matrix composites during laser welding was investigated. The emphasis was laid on the study of the distribution of aluminum carbides in whole welds. The joint can be divided into three regions both in depth and in width. The depth is divided into severe reaction region, partial reaction region, and no reaction region. In these regions, the extent of interfacial reaction varies gradually, the shape of reactants varies from long to fine. In width it can also be divided into severe reaction region, partial reaction region, and initial reaction region from the center of the weld to about the welding junction. In the initial reaction region, nucleation and growth of the reaction products on the surface of SiC particles can be observed by using TEM. The investigation showed that the quantity and size of SiC are relative to the temperature gradient in the molten pool.

Multipass welding of thick section steels using autogenous CO2 laser welding and CO2 laser-MIG hybrid welding

Laser multipass welding techniques for thick section steels have been developed using a new type of UV combined narrow groove. The shape and sizes at the bottom of groove are determined by analyzing the plasma behavior using high speed photographic equipment. A stable autogenous CO2 laser welding process and greater penetration are generated at the root pass because of strong reduction of the plasma volume. According to the waveforms of welding current and arc voltage, and the interaction between the arc and the laser induced plasma, a suitable groove angle is obtained. Laser-double MIG hybrid welding process is studied and the optimum distances between the laser and two arcs are determined. By using autogenous CO2 laser welding, CO2 laser-MIG hybrid welding and laser-double MIG hybrid welding, 28 mm thick steel plates are welded with four passes. The welds produced are assessed by X-ray. No crack is found and there is only a small amount of pores. The experimental results show that the multipuss welding procedures proposed can realize the joining of thick section steels with high efficiency and good quality.

On-line quality inspection in laser blank welding using ART2 neural network

Laser blank welding is becoming more and more important in the automotive industry and the quality of the weld is critical for a successful application. A fully automated solution is required to inspect the quality of the blanks. This paper presents a vision inspection system with a CMOS camera which uses ART2 network to inspect the defects on-line to obtain the geometry and the quality of the weld seam. The neural network ART2 has the capability of self-learning fiom the environment. It can distinguish the defects that have been learned before and give new outputs for new defects. So ART2 network is suitable for weld quality inspection in laser blank welding. Additionally, a CO2 laser is used for the blank butt-welding.

Effect of laser characteristics on the weld shape and properties of penetration laser weld of BT20 titanium alloy

The laser beam welding of BT20 titanium alloy was conducted to investigate the weld shape, microstructures and properties. The full penetration weld characteristics produced by CO_2 laser and by YAG laser were compared. The results show that the full penetration weld of YAG laser welding closes to “X” shape, and weld of CO_2 laser welding is “nail-head” shape. Those result from special heating mode of laser deep penetration welding. The tension strength of CO_2 laser and YAG laser joints equal to that of the base metal, but the former has better ductility. All welds consist mainly of the acicular α phase and a few β phase in microstructure. The dendritic crystal of CO_2 laser weld is a little finer than YAG laser weld. According the research CO_2 laser is better than YAG laser for welding of BT20 titanium alloy.

Laser Welding of TC-1 Titanium Alloy

The technology of CO2 laser welding and joint properties of titanium alloy were investigated. The problem of molten pool protection was resolved by designing a shielding trailer and a special clamp. Joints with silvery appearance were obtained, which have no pore and crack. In addition, the welding speed could reach 3 m/min for the plate of 1.5 mm thickness being penetrated. The reason of the porosity formation in partial penetration joints is that the keyholes can be easily cut apart in the radial direction, which makes the gas enclosed in the molten pool. The surface oxide of specimens can not affect the porosity formation in welds directly.

High-temperature Tensile Behavior of Laser Welded Ti-22Al-25Nb Joints at Different Temperatures

The high-temperature tensile behavior of laser welded Ti-22Al-25Nb (at%) joints was investigated at 500,650,800,and 1 000 ℃.The temperatures for tensile tests were selected according to the phase transformation sequence of Ti2AlNb-based alloys.At temperatures lower than the B2+O phase field (500 ℃) and higher than the B2+O phase field (1 000 ℃),the joints fracture in the base metal in ductile fracture mode.By contrast,the joints exhibit obvious high-temperature brittleness in the B2+O phase field (650 °C and 800 ℃).Heat treatments were conducted with respect to the thermal history of tensile specimens.Intergranular microcracks along the grain boundary of B2 phase are found in the fusion zone after the heat treatments at 650 ℃ and 800 ℃.The high-temperature brittleness at 650 ℃ and 800 ℃ is attributed to the B2→O transformation along the grain boundary.The stress concentration caused by the volume change of B2→O transformation also contributes to the high-temperature brittleness of laser welded Ti-22Al-25Nb joints.

Laser Beam Welding of 600 MPa Quenched and Tempered High-Strength Steel

Conventional fusion arc welding of high-strength quenched and tempered steel can be improved through the use of non-conventional laser beam welding. This article presents the investigations of autogenous bead on plate and butt CO2 Laser Welding (LW) of 7 mm thick high-strength quenched and tempered low alloy SM570 (JIS) steel plates. The influence of laser welding parameters, mainly welding speed, defocusing distance and shielding gas flow rate on the weld profile, i.e., weld zone penetration depth and width, microstructure and mechanical properties of welded joints was determined. All welded joints showed smooth and uniform weld beads free from superficial porosity and undercuts. The selected best welding conditions were a laser power of 5.0 kW, welding speed of 500 mm/min, argon gas shielding flow rate of 30 L/min and a defocusing distance of -0.5 mm. It was observed that these conditions gave complete penetration and minimized the width of the weld bead. The microstructure of the welded joints was evaluated by light optical microscopy. The weld metal (WM) and heat-affected zone (HAZ) near weld metal achieved maximum hardness (355 HV). The tensile fractured samples showed the ductile mode of failure and ultimate tensile strength of 580 MPa.

CO_2激光焊接神经组织的电生理改变

目的 :探讨激光焊接法吻合神经的优越性。方法 :选择健康普通家兔 30只 ,离断两侧股神经 ,一侧股神经外膜缝合 1针后 ,进行激光焊接 ,输出功率为 ( 1 5 0± 1 5 ) m W,平均照射时间为 ( 1 8±5 ) s,另一侧神经外膜缝合 3针作对照 ,术后 7、1 4、2 1、2 8和 35 d测定吻合神经的传导速度、动作电位幅值和动作电位持续时间 ,并测量前 4个时间点吻合口外径。结果 :术后各时间点 ,同手法缝合侧相比 ,激光焊接吻合的神经传导速度快 ,动作电位幅值大 ,动作电位持续时间短。结论 :激光焊接吻合的神经 。

BT20钛合金CO_2激光焊接工艺

通过对BT2 0钛合金CO2 激光焊技术开展试验研究 ,对焊前清理、焊接过程中气体保护、离焦量、激光功率、焊接速度等工艺参数进行了优化选择 ,确定了合理的焊接工艺参数。

Ti_3Al-Nb金属间化合物CO_2激光焊工艺

针对高Nb含量的Ti3 Al -Nb基合金Ti -2 3Al-17Nb进行激光焊工艺研究 ,了解影响钛铝金属间化合物激光焊质量和焊缝成形的工艺因素。研究结果表明 ,2 .5mm厚的Ti-2 3Al-17Nb合金采用大功率CO2 激光焊不产生焊接裂纹 ,焊缝气孔是主要的焊接缺陷。采用合理的焊前表面处理工艺、全熔透焊接可获得无气孔的焊缝。在所研究条件下 ,合金具有良好的熔透性 ,部分熔透和临界熔透时焊缝截面呈钉头型 ,而稳定的全熔透焊缝则呈“沙漏”形 ,焊缝熔深并不是完全随焊接热输入的增大而增大 ,还取决于激光功率密度。接头显微硬度分布呈马鞍形 ,焊缝的硬度高于母材 ,近缝区出现峰值 。

折叠式准封离型CO_2激光器及其在切割和焊接中的应用

为满足激光切割、焊接对高光束质量激光器的迫切需求 ,开发了一种折叠式准封离型有自主知识产权的高光束质量、高稳定性、高可靠性、低消耗、长寿命千瓦级CO2 激光器。目前已批量生产 ,成功应用于激光切割与焊接生产 ,打破了高光束质量激光器长期被国外产品垄断局面。

锆4合金的CO_2激光焊接工艺研究

本文研究了锆４合金ＣＯ２激光焊接时的保护措施和适宜的激光焊接工艺参数．结果表明：试验确定的保护装置和工艺参数可以获得满意的锆合金激光焊接接头，其力学性能和母材相近。

THE INTERFACIAL BEHAVIORS OF ALUMINUM MATRIX COMPOSITE IN DIFFERENT WELDING METHODS

Non-interlayer liquid phase diffusion welding (China Patent) and laser welding methods for aluminum matrix composite are mainly described in this paper. In the non-interlayer liquid phase diffusion welding, the key processing parameters affecting the strength of joint is welding temperature. When temperature rises beyond solidus temperature, the bonded line vanishes. The strength of joint reaches the maximum and becomes constant when welding temperature is close to liquid phase temperature. Oxide film in the interface is no longer detected by SEM in the welded joint. With this kind of technique, particle reinforced aluminum matrix composite Al2 O3p/6061Al is welded successfully, and the joint strength is about 80% of the strength of composite (as-casted). In the laser welding, results indicate that because of the huge specific surface area of the reinforcement, the interfacial reaction between the matrix and the reinforcement is restrained intensively at certain laser power and pulsed laser beam. The laser pulse frequency directly affects the reinforcement segregation and the reinforcement distribution in the weld, so that the weldability of the composite could be improved by increasing the laser pulse frequency. The maximum strength of the weld can reach 70% of the strength of the parent.

CO_2激光深熔焊接光致等离子体吸收及其控制

研究高功率密度 CO2 激光焊接过程中光致等离子体对入射激光的吸收以及侧吹辅助气体对等离子体控制的影响。采用准基模 CO2 激光束在 1 Cr1 8Ni9Ti不锈钢表面进行扫描焊缝 ,通过光谱检测装置检测等离子体辐射谱线强度 ,从而计算等离子体对激光的吸收系数 ;采用侧吹喷嘴分别通CO2 、N2 、Ar、He4种气体压缩等离子体。研究结果表明 ,光致等离子体对入射激光能量的吸收损失高达 2 0 % ;随着侧吹辅助气体流量的增加 ,焊缝呈现3个区间 :当气体压力低于金属蒸汽压力时 ,焊缝为“酒杯”状 ,深宽比很小 ;当辅助气体操作压力稍高于金属蒸汽压力 ,等离子体可被有效控制从而获得最佳焊缝。

新型4通道2×2光开关的设计

针对光开关小型化、快速化、多样化发展趋势,提出了一种采用一个继电器、一个楔角棱镜、应用自动调光路和激光对焊、采用严格的金属化密封封装技术、利用光的折射原理来实现光路交换的新型4通道2×2光开关。最后通过试验,得出可靠的性能指标,并能实现批量性生产。

热输入对Al/TiB_2铝基复合材料激光焊接粒子分布影响

采用光纤激光焊接技术,研究了4 mm厚纳米级Ti B2粒子增强纯铝基体复合材料板材的焊接性能。通过光学显微镜及扫描电子显微镜等方法,分析了焊后纳米级Ti B2粒子在焊缝中的分布及形态。结果表明,纳米级Ti B2粒子增强纯铝基复合材料具有较好的焊接性能。激光焊接后焊缝中Ti B2粒子分布比母材中更加均匀,但当焊接热输入过大时(功率4. 0 k W,1 m/min),Ti B2粒子有破裂现象,但粒子与基体的结合面界面仍然致密,基本不影响焊缝的性能。

Microstructure,mechanical properties and post-weld heat treatments of dissimilar laser-welded Ti_(2)AlNb/Ti60 sheet

Dissimilar joining of Ti_(2)AlNb and Ti60 rolled sheet was performed by laser beam welding.The microstructures and mechanical properties of as-welded and post-weld heat-treated Ti_(2)AlNb/Ti60 joints were investigated by microstructure observation and mechanical properties testing.The fusion zone(FZ)of the as-welded joint consisted of B_(2)/βmatrix and small S2 balls.The heataffected zones HAZ-Ti_(2)AINb and HAZ-Ti60 for the aswelded joint were characterized asα_(2)+B_(2)/β+O andα'+α+β+S_(2),respectively.The tensile strength and elongation of as-welded sheet were 597.5 MPa and 6.2%at650℃,respectively.Most of the plastic deformation was taken place at the side of Ti60 alloy.With the increase in the heat treatment temperature,the anchoring strength between each other of B_(2)/βgrains was enhanced by the precipitated lamellarα'and O grains at the FZ.The depth of the fracture dimples increased with the heat treat temperature increasing.The heat-treated welding joint at970℃presented a good balance of the tensile strength and plasticity,where the tensile strength and the elongation were enhanced to 669.7 MPa and 7.1%at 650℃,respectively.