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.

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.

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.

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.

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.

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.

LASER WELDING OF HIGH T_c CERAMIC BiSrCaCu_2O_y SUPERCONDUCTORS

Joining the bulk high T_c superconducting ceramics is an unavoidable problem people will face in the application of the new material. The primary requirement is that the joints have to have the superconductivities similar to those of the bulk materials. That means the joints must have the same composition with the bulk materials. Fusion welding of the ceramies is thought to be the most reliable and efficient joining process for oxide ceramics.

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.

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.

添加稀土元素的TC4钛合金激光焊接头纵向超塑性能研究

针对钛合金激光焊接接头超塑性能低的难题,提出在焊缝中以Yb_(2)O_(3)的方式添加稀土Yb元素,分析Yb_(2)O_(3)含量对TC4钛合金激光焊接头高温拉伸峰值流变应力、断后伸长率及组织的影响.结果表明,Yb_(2)O_(3)能够促进变形过程的组织等轴化进程,减小焊缝β晶粒尺寸和接头超塑性变形流变应力,并提高断后伸长率.随着Yb_(2)O_(3)含量增加,接头应力应变曲线下移,峰值流变应力呈先降低后升高的趋势,而断后伸长率则为先增大后减小.在超塑性变形过程中,Yb_(2)O_(3)含量6%时峰值流变应力最低为11.9 MPa,断后伸长率为572.3%;焊缝中心β晶粒尺寸最小为127μm,相较于未添加Yb_(2)O_(3)时β晶粒尺寸的337μm细化了62.3%.此时,马氏体组织发生相变,形态转变成片层,焊缝区域组织等轴化程度最高,焊缝的超塑性能最好.

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.

TA1超薄板激光焊接组织与性能的研究

选用0.5 mm工业纯钛TA1作为研究对象,在不同激光功率下采用不同焊接速度对其进行焊接试验,焊后分析了不同焊接速度对TA1焊缝宏观形貌、显微组织、接头力学性能及硬度、接头耐蚀性的影响。结果表明:随着焊接速度增加,焊缝宽度逐渐减小,焊缝表面成形质量提高;焊缝组织中粗大块状α相逐渐减小,针状α相逐渐增多,晶粒细化;接头抗拉强度逐渐增大并趋于母材强度,耐腐蚀性也越来越好。随着焊接功率增加,焊缝宽度逐渐增加,焊缝组织中粗大块状α相逐渐增加,抗拉强度逐渐降低,耐腐蚀性越差。

R60702锆激光焊接接头焊缝区的显微组织及其在硫酸中的耐蚀性研究

为探究不同焊接工艺下(工艺1:激光功率1 600 W,焊接速度1 600 mm/min,线能量60 J/mm,气体流量20 L/min,离焦量0 mm;工艺2:激光功率1 800 W,焊接速度1 200 mm/min,线能量90 J/mm,气体流量20 L/min,离焦量0 mm)R60702激光焊接接头中焊缝区不同组织的耐蚀性,采用金相显微镜(OM)、X射线衍射仪(XRD)、电化学测试仪、扫描电镜(SEM)、三维轮廓仪和能谱(EDS)对其金相组织、物相组成、耐腐蚀性能及机理、腐蚀形貌、腐蚀产物元素组成进行分析。结果表明:2种焊接工艺下的焊缝区呈现出不同的显微组织,工艺1条件下焊缝区为篮网状组织及少量(26.7%)平行板条状魏氏组织的混合,工艺2条件下焊缝区呈现出典型的魏氏组织。在100℃的20%硫酸中浸泡腐蚀72 h后,混合组织焊缝表现为电偶腐蚀,平行板条状魏氏组织焊缝表现为均匀腐蚀,平行板条状魏氏组织焊缝的耐蚀性更优。这是由于混合组织焊缝的显微组织不均匀性形成了电位差,导致氧化膜因电偶腐蚀发生破裂,因此其耐蚀性较差;而平行板条状魏氏组织焊缝的电化学均匀性良好,自腐蚀电位无显著差异,有利于抑制电偶腐蚀。

激光焊接技术在航空工业机械制造中的应用

以激光焊接技术在航空工业中的应用为切入点,介绍了激光焊接的基本原理、主要工艺参数及设备类型,分析了激光焊接技术在航空发动机、飞机结构及航空维修方面的应用情况,提出了该技术目前存在的问题及未来发展前景,旨在为激光焊接技术的进一步发展提供参考。

基于多部件集成的热冲压成形技术研究进展

高性能金属板料热冲压成形技术对汽车轻量化极其重要,目前已被广泛应用。随着超高强钢热冲压成形技术的进步,热冲压成形技术从简单的零件成形正逐步向复杂结构成形发展。以轻量化车身结构件的碰撞能量分布载荷路径为基础,选择不同板厚和强度级别的板料进行激光拼焊,经过一体化热冲压成形后,获得高强塑性区域合理分布的多部件集成热冲压轻量化车身部件。激光拼焊工艺和高效激光加工自动化装备保证了其关键技术的实现。在降低碳排放、提高生产效率、减少材料用量及满足车身结构优化等诸多方面具有突出的优越性和实用价值。

基于激光扫描的工业机器人焊接焊缝跟踪方法

由于工业机器人焊枪和焊接焊缝之间的位置偏差会导致焊接焊缝跟踪结果存在一定的误差,因此提出了一种基于激光扫描的工业机器人焊接焊缝跟踪方法。首先,采用激光扫描传感器采集工业机器人焊接焊缝图像,并对图像进行滤波、增强、黑白化预处理;其次,检测图像边缘后,采取激光扫描方法确定焊接焊缝边缘图像中激光条纹骨架的大概位置,经最小二乘法直线拟合出准确的激光条纹中心线,提取焊接焊缝特征点;再次,结合工业机器人手眼标定矩阵,将激光扫描传感器坐标系中的焊接焊缝特征点坐标转化为工业机器人坐标,从而形成焊接焊缝轨迹;最后,采取3次非均匀有理B样条方法得到工业机器人焊枪和焊接焊缝之间的位置偏差,修正机器人焊枪位置,从而实现工业机器人焊接焊缝的精准跟踪。实验结果表明,该方法不仅能够准确检测出焊接焊缝边缘,而且能够跟踪不同宽度、不同形状的焊接焊缝工件。

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.

以激光飞行焊为例浅析机器人虚拟工具的坐标系设定和校准方法

对比了激光飞行焊和传统接触式焊接区别,提出了一种激光飞行焊机器人工具坐标系设定方法,可以节省仿真建模时间和工装开发成本。机器人虚拟工具的校准方法与实体工具有所不同,在机器人传统实体工具校准方法的基础上开发了适用于此类工具的校准方法。该方法能够节省焊缝批量偏移时的工艺调试时间,快速解决序列化生产中常见的工具偏移问题,在汽车制造领域具有广泛的应用前景。