Laser beam welding of dissimilar stainless steels in a fillet joint configuration

This paper investigates laser beam welding of dissimilar AISI 304L and AISI 430 stainless steels. Experimental studies were focused on effects of laser power, welding speed, defocus distance, beam incident angle, and line energy on weld bead geometry and shearing force. Metallurgical analysis was conducted on a selected weld only to show various microstructures typically formed at different zones and consequent change in microhardness. Laser power and welding speed were the most significant factors affecting weld geometry and shearing force. All the bead characteristics but radial penetration depth decreased with increased beam incident angle. The focused beam allowed selecting lower laser power and faster welding speed to obtain the same weld geometry. Weld shape factor increased rapidly due to keyhole formation for line energy input ranging from 15 kJ/m to 17 kJ/m. Fusion zone microstructures contained a variety of complex austenite-ferrite structures. Local microhardness of fusion zone was greater than that of both base metals.     

辅助增强匙孔气流对激光焊接不锈钢组织和显微硬度的影响

以HR-2抗氢钢为试验材料,利用板条型CO2连续激光器,采用喷嘴在前、入射角为60°的匙孔增强气流,进行了不同参数下的激光焊接试验.结果表明,在气流辅助增强匙孔激光焊中,匙孔气喷嘴在前的布局对熔池扰动小,能获得较好的焊缝成形;与传统激光焊接相比,熔深增加、熔宽明显减小,焊缝形状呈葫芦型,这是匙孔气流压制等离子体、使匙孔向底部凹陷的结果;从焊缝组织来看,增强激光焊焊缝的柱状晶较短小,焊缝中心呈现等轴晶形态,属于FA的不锈钢凝固模式.与传统激光焊不同,气流辅助增强匙孔激光焊的焊缝、热影响区显微硬度与母材相当,这可能是引入的增强匙孔气流改善了焊缝金属的冷却条件,更少铁素体析出的结果.     

铝合金脉冲YAG激光焊脉冲调制参数对焊缝形状参数的影响

以2mm厚LF3铝合金薄板为对象,研究了在平均功率和焊接速度不变时脉冲YAG激光焊脉冲调制参数(脉宽、频率及单脉冲能量)对热导焊缝形状参数(熔深、熔宽及深宽比)的影响规律,并结合脉冲激光焊间断作用的特征,引入"有效峰值功率密度"综合考虑焊接速度、频率、脉宽以及光斑大小对焊缝形状参数的影响.此外,还对脉冲激光焊所形成的特殊的层状焊缝形貌进行研究和分析.结果表明,焊缝形状参数受脉宽及峰值功率密度双重作用的影响.脉冲焊得到的焊缝呈现多层状形貌,层数随频率升高而增多.     

Experimental investigation on laser beam welding of martensitic stainless steels in a constrained overlap joint configuration

This paper presents experimental investigation of laser beam welding of martensitic stainless steels in a constrained overlap configuration. Experimental studies were focused on the effects of laser power, welding speed and fiber diameter on bead geometry and mechanical properties of the weld. Metallurgical study of a selected welded joint was done only to show various microstructures typically formed at different zones. Laser power and welding speed were found the most significant factors affecting the weld geometry and shearing force. The contour plots showing constant response lines indicated the evidence of two-factor interaction effects of laser power-welding speed, welding speed-fiber diameter, and fiber diameter-laser power on all the responses except the weld width. Moreover, energy density plots illustrated its linear relationship with penetration depth and limited nonlinear effects on others. Additionally, metallurgical analysis of fusion zone showed dendritic structures consisted of martensitic with eutectic ferrite along solidification grain and subgrain boundaries.     

Effect of heat input on weld bead geometry of submerged arc welded ASTM A709 Grade 50 steel joints

A series of measurements was carried out on specimens of submerged arc welded plates of ASTM A709 Grade 50 steel to determine how variation in heat input achieved using single and double wires affected bead reinforcement, bead width, penetration depth, contact angle, heat affected zone (HAZ) size, deposition area, penetration area and total molten area. The level of dilution and different melting efficiencies were calculated and their variation with heat input was analyzed based on the acquired measurements. The cooling time from 800 to 500 °C was also related to various weld bead characteristics (e.g., total nugget area, heat transfer boundary lengths, bead width-to-depth ratio, and nugget parameter). The bead reinforcement, bead width, penetration depth, HAZ size, deposition area and penetration area increased with increasing heat input, but the bead contact angle decreased with it. The electrode melting efficiency increased initially and then decreased with increasing heat input, but the plate melting efficiency and percentage dilution changed only slightly with it. Cooling time exhibited a very good linear relationship with the total nugget area, heat transfer boundary length, and nugget parameter.     

High quality welding of stainless steel with 10 kW high power fibre laser

Abstract

The objectives of this research are to investigate penetration characteristics, to clarify welding phenomena and to develop high quality welding procedures in bead on plate welding of type 304 austenitic stainless steel plates with a 10 kW fibre laser beam. The penetration depth reached 18 mm at the maximum at 5 mm s^?1. At 50 mm s^?1 or lower welding speeds, however, porosity was generated at any fibre laser spot diameter. On the other hand, at 100 mm s^?1 or higher welding speeds, underfilling and humping weld beads were formed under the conventionally and tightly focused conditions respectively. The generation of spatters was influenced mainly by a strong shear force of a laser induced plume and was greatly reduced by controlling direction of the plume blowing out of a keyhole inlet. The humping formation was dependent upon several dynamic or static factors, such as melt volume above the surface, strong melt flow to the rear molten pool on the top surface, solidification rate and narrow molten pool width and corresponding high surface tension. Its suppression was effective by producing a wider weld bead width under the defocused laser beam conditions or reduction of melt volume out of keyhole inlet under the full penetration welding conditions. Concerning porosity, X-ray transmission in situ observation images demonstrated that pores were formed not only from the tip of the keyhole but also at the middle part because of high power density. The keyhole behaviour was stabilised using a nitrogen shielding gas, resulting in porosity prevention. Consequently, to produce high quality welds in 10 kW high power fibre laser welding, the reduction procedures of welding defects were required on the basis of understanding their formation mechanism, and 10 kW fibre laser power could produce sound deeply penetrated welds of 18 mm depth in a nitrogen shielding gas.     

Hybrid laser/arc welding process for controlling bead profile

Abstract

A laser hybrid welding process in which a defocused laser beam is applied beside a gas metal arc weld (GMAW) pool to modify the bead shape was studied. The present paper aims to produce welds with improved toe geometry and better fatigue life than those made with GMAW alone and to apply a numerical simulation to help configure the hybrid process. First, stationary hybrid welds were made to validate weld bead shape predictions and to characterise the spreading of the arc weld deposit to the laser heated spot. Next, the travelling hybrid process was configured with the aid of simulations and fatigue test specimens were welded. Proper application of the laser heat input induced molten metal to spread to the laser heated area, increasing the fillet weld leg length. This produced a larger weld toe angle that decreased the stress concentration and increased the fatigue life of the welds relative to standard mean values.     

Optimization of welding parameters for laser bead-on-plate welding using Taguchi method

This paper presents the results obtained by the optimization of laser bead on plate welding parameters for 3.5 kW cooled slab laser using Taguchi technique. The trials were conducted on two different shielding gases 100% Nitrogen and 50% Nitrogen + 50% Argon. The input process parameters such as beam power, travel speed and focal position are selected suitably in order to obtain the desired output i.e., bead width and depth of penetration. The quality of the weld is evaluated by studying the features of weld bead geometry. Grey relational analysis is applied to optimize the input parameters simultaneously considering multiple output variables. In this investigation the nearest optimal solution which would improve the weld quality was found out. Experimental trial on super austenitic stainless steel has been conducted to validate the optimized parameters. Further, the optimized parameters were evaluated through the microstructural characterization and hardness measurements across the weld zone.     

Characterization of deposited layer fabricated by direct laser melting process

Deposition dimensions are important in the final applications of products made by direct laser melting (DLM). This investigation used a 200 W fiber laser to produce single-line beads from stainless steel 316L powder using a variety of different energy distributions. To investigate the deposited layer, deposition width, height, penetration depth, and side surface roughness were measured. In order to validate the effectiveness of the two main process parameters (laser power and scan rate), multi-layered beads were fabricated by the sequential layering of single lines. It was found that with an increase in linear energy density, the wetting angle was reduced, and the average roughness was also increased with linear energy density. An equation that predicts the deposition height for a multi-layered bead is proposed and experimentally validated in this study. For deposited layer applications, the material properties of the deposited layer, such as contact angle, interfacial contact resistance, and flexural strength are estimated. The rougher deposited layers show higher contact angle and interfacial contact resistance. The flexural strength of the DLM fabricated specimen is above 250 MPa.     

CO_2激光焊接600MPa DP钢接头组织与性能

采用CO2激光对抗拉强度为600MPa,厚度1.4mm的DP钢进行焊接.研究焊接速度对焊缝外观和截面成形的影响、接头的组织特点、硬度、强度和成形能力.结果表明,激光功率相同,焊接速度较低时焊缝易产生气孔,焊接速度较高时易发生飞溅;焊接速度对焊缝熔深及熔宽也有影响.焊缝区组织主要由马氏体构成,从焊缝、焊接热影响区到母材,组织中马氏体含量下降,接头的最高硬度出现在焊缝或热影响区.在平行于焊缝方向,焊接接头的抗拉强度高于母材,垂直于焊缝方向,接头的抗拉强度与母材相当.由于焊缝出现马氏体组织,接头的塑性和韧性降低,板材的冲压成形能力下降.     

Nd:YAG激光焊接800 MPa TRIP钢的接头组织与性能

采用Nd:YAG激光对强度为800MPa,厚度为1.2mm的TRIP钢板进行焊接.研究焊接速度对焊缝外观和截面成形的影响及接头的组织特点、硬度、强度和成形能力.激光功率相同,焊接速度较低时焊缝易产生气孔,速度较高时易发生飞溅;焊接速度对焊缝熔深及熔宽也有影响.焊缝组织主要由马氏体构成,从焊缝、热影响区到母材,组织中马氏体含量下降,接头的最高硬度出现在焊缝或热影响区.在平行于焊缝方向,焊接接头的抗拉强度高于母材,垂直于焊缝方向,接头的抗拉强度与母材相当.由于焊缝中出现马氏体,接头的塑性和韧性降低,板材的冲压成形能力下降.     

6kW光纤激光器光束入射角对不锈钢板切割质量的影响

采用大功率光纤激光器进行不同板厚的不锈钢的切割试验,研究了光束入射角对切割质量的影响。结果表明,在切割枪不同的倾斜姿态、不同板厚下,光束入射角对切割质量的影响也不同。     

Application of direct laser melting to restore damaged steel dies

Direct laser melting (DLM) technology can be applied to restore damaged steel dies. To understand the effects of DLM process parameters such as the laser power and scan rate, a series of experiments was conducted to determine the optimal operating parameters. To investigate the laser melting characteristics, the depth/height ratio, depth/width ratio and micro-hardness as a function of the laser energy density were analyzed. Fe-Cr and Fe-Ni layers were deposited on a steel die with 11.38 J/mm² of energy input. The wear-resistance and the friction coefficient of the deposited layer were investigated by a pin-on-disk test. The penetration depth decreased as the scan rate increased as a consequence of the shorter interaction time. The depth/height ratio of the deposited layer decreased with an increase in the scan rate. The depth/width ratio increased as laser power increased and the scan rate decreased. The deposition shape of the Fe-Ni powder was relatively shallow and wide compared with that of the Fe-Cr powder. The scan rate had a substantial effect upon the deposition height, with the Fe-Cr powder melting more than the Fe-Ni powder. The micro-hardness of the layer melted from the powders is higher than that of the substrate, and the hardness of the laser-surface-melted layer without any metal powder is higher compared to that of the metal-powder-melted layer. The direct laser melting process with Fe-Ni powder represents a superior method when restoring a steel die when the bead shape and hardness of the restored surface are important outcome considerations.     

不锈钢激光焊焊缝成形的数学模型

在304不锈钢的激光深熔焊中,通过工艺试验,研究了激光焊接工艺参数与焊缝形状参数之间的关系.采用二次通用旋转回归设计方法设计了试验方案.通过对试验数据的统计检验,求出了置信度较高的以功率、速度和离焦量为因子的熔池形状回归方程.通过相关性分析,揭示了各个因子对焊缝成形的影响规律.随着激光功率的增大,熔深、熔宽、束腰高、束腰宽都增加;焊接速度增加时,熔深、熔宽、束腰高、束腰宽都减小,熔宽到一定水平后不再减小,而熔深则一直减小;当离焦量由负离焦向正离焦转变时,熔深和束腰高都呈现先增大后减小的趋势,而熔宽和束腰宽则呈现出相反的趋势.当离焦量水平为0时,熔宽达到最小值.     

铸铁表面激光熔凝行为及温度场数值模拟

为明确铸铁表面激光熔凝过程的热响应规律,考虑随温度变化的材料热物性参数和相变潜热影响,建立铸铁表面激光动态熔凝的三维数值模型并进行了验证,预测值与试验值吻合良好,采用该模型分析了热响应温度场规律及不同工艺参数的映射关系.结果表明,铸铁表面激光熔凝较钢材可获得更大的熔透深度,熔池内、外形成较大温度梯度且分别以深、宽方向分...     

Effect of active flux addition on laser welding of austenitic stainless steel

Abstract

The use of active flux in tungsten inert gas (TIG) welding is known to increase its weld depth. The present paper involves study of active flux laser beam welding (ALBW) of austenitic stainless steel sheets with respect to its effect on plasma plume, microstructure and mechanical properties of the resultant weldments. ALBW performed with SiO₂ as the flux significantly modified shape of the fusion zone (FZ) to produce narrower and deeper welds. Plasma plume associated with the process was considerably smaller and of lower intensity than that produced during bead on plate laser beam welding (LBW). Flux addition during LBW produced thin and rough weld bead associated with humping. The development of such a weld bead is cause by reversal in the direction of Marangoni flow by oxygen induced inversion of surface tension gradient, widely fluctuating plasma plume and presence of oxides on the weld pool surface preventing free flow of the melt. Active flux laser weldments exhibited lower ductility than that of bead on plate laser weldments.     

Experimental study on welding characteristics of CO2 laser TIG hybrid welding process

Abstract

The experiments of CO₂ laser TIG paraxial hybrid welding with 4 mm thick AISI 321 stainless steel sheet have been performed. The arc images and welding characteristics have been investigated with different energy ratios between laser and arc. The experimental results indicate that the hybrid welding is similar to laser welding and has also two welding mechanisms: deep penetration welding and heat conduction welding. Because of the effect of keyhole induced by laser, the arc root can be stabilised and compressed, and the current density and the penetration depth are all increased significantly, which show the characteristics of deep penetration welding. However, when the current is increased to a critical value, the laser induced keyhole disappears and the arc expands obviously, which decreases the penetration depth, so that the welding mechanism has been changed from deep penetration welding to heat conduction welding. Furthermore, the effects of distance between laser beam and electrode, pulsed laser and hybrid manners on hybrid welding characteristics have also been studied.     

Correlation between weld formation and processing parameters in CO2 laser welding of steels

Abstract

Laser welding, which has undergone rapid development in the past few decades, is one of the most important applications in laser materials processing. Although some general data are available, precise welding parameters are equipment specific. In the present study, a series of autogenous laser welds on mild and stainless steels has been investigated, using a Trumpf 3·0 kW CO² laser system, to establish welding parameter windows. The correlation between laser power, welding speed, and weld bead profile for bead on plate welding has been obtained. For a constant laser power, penetration depth reaches a stable value as welding speed exceeds 11 000–13 000 mm min^-1. This value is defined as the penetration threshold. Lower welding speed produces deeper penetration. However, under such conditions, the unstable keyhole and weld pool could result in undercut and porosity. The maximum penetration achievable for sound welds on both mild steel and stainless steel was investigated. The correlation between penetration threshold and power level was also established. The parameter windows established for autogenous welds can be adopted effectively on butt jointsif welding speed is reduced by 25%.     

不锈钢基体多模CO2激光熔覆工艺研究

采用多模CO2激光器在不锈钢表面进行激光熔覆,研究了激光熔覆工艺参数对熔覆层微观组织和界面形状的影响。研究表明,离焦量(聚焦镜高度)、扫描速度和激光功率变化将影响激光熔覆层高度和宽度,以及熔化深度。激光熔覆层的宽度为激光线能量和光斑直径的函数,其线性回归方程为W1=AD(1-90VS/P),其相关系数R=0.9976。多模激光熔覆可通过调节离焦量得到界面熔合完整、熔覆质量良好的熔覆层。     

A simplified energy-based model for laser welding of ferritic stainless steels in overlap configurations

A theoretical model is developed for predicting the weld shape produced by a Continuous Wave (CW) Nd:YAG laser in a constrained overlap configuration on a ferritic stainless steel, and verified by means of experiments. Tests demonstrate that, as assumed in the modelling phase, penetration depth is linearly dependent on the energy density input, within the hypothesis of conduction dominated welding. Penetration depth determines the weld resistance length at the interface since the weld profile is found to change from approximately semicircular to parabolic when the energy density input is varied in the range from 22 J/mm² to 32 J/mm².