Laser Spot Welding of Thermoplastic and Ceramic: An Experimental Investigation

Laser welding of dissimilar materials classes has vast potential in a variety of applications due to the non-contact nature of the process. This study investigates the effects of CO₂ laser process parameters on the characteristics of spot welded joint between ceramic and thermoplastic. Using a full-factorial design an experimental investigation is carried out studying the effect of welding parameters (laser exposure, number of spots, stand-off distance) on the tensile strength and the diameter of spot weld. The study reveals an increase of joint tensile strength with the increase in the number of spots and the duration of exposure. However at low laser power, the effect of stand-off distance on the spot weld diameter is found to be inconclusive. Optimal process parameters are estimated using the multi-objective optimization on the basis of ratio analysis. The analysis shows that the higher number of spots and the longest duration of laser exposure result in optimal weld characteristics. Alongside these conditions, a larger stand-off distance is seen to have beneficial impact on the weld characteristics.     

6063铝合金单模光纤激光焊接工艺研究

目的 针对采用脉冲激光点焊的6063铝合金焊点拉力较低,无法满足实际需求的问题,研究6063铝合金激光焊接的最优工艺方案,以提升焊点拉力.方法 采用单模光纤激光对6063铝合金进行焊接,通过极细的线宽组成螺旋点,代替单个脉冲激光点焊.对激光功率、焊接速度及离焦量等工艺参数进行正交实验,得到最佳工艺参数,并通过分析焊缝外...     

Qualitätssicherung von Widerstandspunktschweißverbindungen mit Hilfe der Schallemissionsanalyse (SEA)

Quality Control of Spot Weldings by Acoustic Emission The quality control of spot weldings has to be performed continuously during welding. Acoustic Emission (AE) is a suitable method for online surveillance of the welding process. Several measuring parameters of AE are tested with regard to the characterization of the spot weld quality during the welding process. It is shown that the quality of the spot weld can be evaluated by measuring the energy of the AE signals during the welding process. This parameter can be applied also for controlling the welding time of each spot weld under constant current load. On the other hand, the quality of the spot welds can be estimated by measuring the AE count during cooling after finishing the weld spot. By this method the welding process can be controlled with regard to the tendency in the long run.     

Comparative study on CO2 laser overlap welding and resistance spot welding for galvanized steel

The CO₂ laser overlap welding and the resistance spot welding are respectively investigated on DC56D galvanized steel used for auto body. The characteristics of the two types of welding methods are systematically analyzed in terms of the weld molding, tensile-shear performance, microstructure, hardness, and corrosion resistance of welding joint. The results show that, the fusion widths of the upper and lower surface are almost the same for the resistance welding joint, and the weld nugget is surrounded by the heat-affected zone. While the laser welding joint belongs to deep penetration welding, the weld fusion width presents wide at the top and narrow at the bottom, and the heat-affected zone is situated on both sides of the weld pool. Compared with resistance spot welding joint, laser welding joints have much more ultrafine microstructures, much smaller heat-affected zones, as well as greater resistance to deformation and corrosion. In addition, the tensile-shear performance of laser weld joints is superior to that of resistance welding joints under certain conditions.     

Elektrodenauswahl für das WIG‐Unterwasser‐Schweißen

Selection of electrode for GTA‐Underwater Welding Reproducible good weld quality and economical benefit of underwater‐welding require a complete automation. For this purpose Gas Tungsten Arc‐welding (GTA or TIG) offers numerous advantages, especially for the root and the following hot pass run. Disadvantages of GTA‐welding are the low weld deposit rate and the limited lifetime of the tungsten electrode. Already small wear damages cause wide alterations of the arc under high surrounding pressure, so that a suited choice of the electrode enables to increase the productivity considerably. Therefore the influence of the electrode features on welding process, arc stability, arc ignition, weld geometry and electrode wear has been investigated. For quick and elementary selection of electrode an assessment catalogue was elaborated.     

Effect of ultrasonic welding parameters on microstructure and mechanical properties of dissimilar joints

Ultrasonic spot welding has received significant attention during past few years due to their suitable applications in comparison to conventional fusion welding techniques. Fusion welding of dissimilar Aluminum and Stainless steel alloys is always a challenging task because of poor control on grain size and formation of undesirable brittle intermetallic compounds in the weld metal, which have deleterious effect on mechanical properties. In the past, welding of dissimilar alloys has been performed using electron beam welding, laser beam welding and friction stir spot welding, resistance spot welding, etc. However, little work has been reported on dissimilar welding of Aluminum and Stainless steel alloys using ultrasonic spot welding. The objective of the present work is to optimize ultrasonic spot welding parameters for joining 3003 Aluminum alloy with 304 Stainless steel. Welding was performed at various clamping pressures (i.e. 30, 40, 50 and 60 psi) and energy levels for investigating its effect on microstructure, mechanical properties and bond quality of the weld. Different levels of weld quality i.e. ‘under weld’, ‘good weld’ and ‘overweld’ were identified at various welding parameters using physical attributes. The weld specimens prepared with energy 125 and 150 J showed the maximum bond strength and were rated as “good” weld. It was also revealed that for a good quality weld, the maximum tensile strength is achieved once a reasonable amount of bond density and material thinning (required for the formation of metallurgical bonds) is attained.     

Electron beam weld parameters and thermal efficiency improvement

Thermal efficiency is considered in connection with welding regimes and seam parameters by applying a statistical approach. This approach allows one to establish empirically (by fitting a mathematical model) the type of relationship that is present between performance characteristics and its influencing factors. Optimal regimes are found through thermal efficiency optimisation. The study leads to new proposals for the position of the focus with respect to the surface of the welded material, under conditions of maximum thermal efficiency or maximum welding depth. The values of the ratio of power to weld depth (P/H) and weld width times velocity of weld front (vB) are confirmed to be the main characteristic parameters of electron beam welding, considered as a self-organising process.     

Modellierung des Ermüdungsrisswachstums in Schweißverbindungen unter Berücksichtigung von Schweißeigenspannungen

The present paper contains research results determined within the framework of a project called IBESS (?Integrale Bruchmechanische Ermittlung der Schwingfestigkeit von Schweißverbindungen“) by the Materials Mechanics Group of the Technische Universität Darmstadt [1]. Aim is to calculate the fatigue life of welded joints by taking into account the effect of residual stresses and the influence of the weld toe geometry. Here, the fatigue life is regarded as period of short fatigue crack growth. Two and three dimensional finite element models, with cracks as initial defects, are constructed for this purpose. Fatigue crack growth analyses are performed by using the node release technique together with the finite element program ABAQUS. The welding residual stresses as well as the plasticity induced crack closure effects are considered. Structural calculations are performed in order to introduce residual stress fields in finite element models. The calculated compressive residual stress field matches the measured one especially in the weld notch area. The effective cyclic J‐integral (ΔJ_eff) is used as crack tip parameter in a relation similar to the Paris equation for the calculation of the fatigue life. For this purpose, a Python code was written for the determination of ΔJ_eff at every crack length phase. The calculated fatigue lives were compared with experimental data and a good accordance between both results was achieved. The impact of welding residual stresses on ΔJ_eff as well as on the fatigue life during short crack growth was investigated. As expected, results revealed that at lower stress amplitude, a compressive residual stress field is favorable to the fatigue life, whilst a tensile residual stress field is unfavorable. The influence of residual stresses can be neglected only for large load amplitudes.     

Mechanical performance of three thickness resistance spot welded low carbon steel

Abstract

Resistance spot welding is the dominant process for joining sheet metals in automotive industry. Despite the application of three thickness resistance spot welds in this industry, present guidelines and recommendations are limited to two thickness spot welds. Study towards better understanding of weld nugget growth and mechanical properties is the first step to understanding the welding behaviour and developing proper guidelines for the three thickness resistance spot welding. In this paper, weld nugget growth, mechanical performance and failure behaviour of three thickness low carbon steel resistance spot welds are investigated. Macrostrcutural and microstructural investigations, microhardness tests and quasi-static tensile–shear tests were conducted. Mechanical performance of the joint was described in terms of peak load, energy absorption and failure mode. In order to understand the failure mechanism, micrographs of the cross-sections of the spot welded joints during and after tensile–shear are examined by optical microscopy. Unlike two thickness resistance spot welded joint, weld nugget was formed in the geometrical centre of the joint (i.e. centre of the middle sheet). Weld nugget size along sheet/sheet interface was greater than that of along geometrical centre of the joint. Increasing welding time leads to increases in peak load and energy absorption of the joint and transition of interfacial failure mode to pullout failure mode, primarily due to the enlargement of weld nugget size along sheet/sheet interface.     

Dissimilar Resistance Spot Welding of Q&P and TWIP Steel Sheets

Dissimilar resistance spot welding of twinning induced plasticity (TWIP) and quenching and partitioning (Q&P) steel grades has been investigated by evaluating the effects of clamping force, welding current, and welding time on the microstructure, shear tension strength, and fracture of welded samples. The spot welding of TWIP and Q&P steels promotes the occurrence of an asymmetrical weld nugget with a greater dilution of TWIP steel because of its lower melting temperature and thermal conductivity. As a result, weld nuggets exhibit an austenitic microstructure. TWIP steel undergoes a grain coarsening in the HAZ, whereas Q&P steel undergoes some phase transformations. Welded samples tend to exhibit higher shear tension strength as they are joined at the highest welding current, even though an improper clamping force can promote excessive metal expulsion, thereby reducing the mechanical strength of the welded joints. Shear tension welded samples failed through interfacial fracture with partial thickness fracture mode for a low welding current, while partial thickness with button pull fractures were observed when a high welding current was used. The weld spots predominantly failed at the TWIP side. However, as TWIP steel can work harden significantly in the more resistant welded joints, the failures occur, instead, at the Q&P side.     

Low Heat Welding of Titanium Materials with a Pulsed Nd:YAG Laser

Titanium materials exhibit a property profile that is just as versatile as that of steel materials. Titanium materials therefore have outstanding properties, such as excellent resistance to corrosion and high strength values at low densities, which makes them ideal for use in the chemical industry and as structural materials in lightweight construction. Due to the high affinity of titanium to atmospheric gases at increased temperatures above 500 °C, titanium components have to be welded in a sophisticated process under inert shielding gas by TIG welding or by an electron beam in a vacuum. A novel innovative laser beam welding process using a pulsed laser with free pulse shaping will be presented here with which oxidation‐free titanium weld seams with excellent mechanical and technological properties can be produced. For this low heat welding process, the otherwise commonly used inert gas covering can be substituted with a shielding gas nozzle. The process‐specific low heat input and the resulting low energy input per unit length both have a positive effect on the microstructure and thus on the mechanical properties. This welding process offers both technological and economical advantages over the processes used up until now, particularly for the machining of complex components and for series production.     

Laser-based manufacturing concepts for efficient production of tailor welded sheet metals

Laser welding is an established manufacturing technology for a large variety of automotive applications due to its attractive properties such as low heat input,high precision and fast welding speed.Especially when welding high strength steels,which are dominantly used in today's car body construction,the low heat input by laser welding bears significant advantages with regard to the properties of the weld seam.The exploitation of the full application potential of laser welding in mass production requires an appropriate manufacturing concept and corresponding auxiliary technologies.The present paper demonstrates the integration of laser welding into the surrounding manufacturing concepts by a modular setup with different levels of automation.This approach offers flexible solutions for individual needs thereby optimizing investment cost,labor cost and productivity.Recently available laser sources enable exceptionally high welding speed on thin gauged sheet metals but require efficient material handling concepts to utilize the full speed potential.Industrial concepts are presented offering efficient material handling and high process robustness for mass production welding.     

Research and Progress in Laser Welding of Wrought Aluminum Alloys. I. Laser Welding Processes

With the wide application of Al alloys in automotive, aerospace and other industries, laser welding has become a critical joining technique for aluminum alloys. In this review, the research and progress in laser welding of wrought Al alloys have been critically discussed from different perspectives. The primary objective of this review is to understand the influence of welding processes on joint quality and to build up the science base of laser welding for the reliable production of Al alloy joints. Two main types of industrial lasers, carbon dioxide (CO₂) and neodymium-doped yttrium aluminum garnet (Nd:YAG), are currently applied but special attention is paid to Nd:YAG laser welding of 5000 and 6000 series alloys in the keyhole (deep penetration) mode. In this part of the review, the main laser welding processing parameters including the laser-, process-, and material-related variables and their effects on weld quality are examined. In part II of this article in this journal, the metallurgical microstructures and main defects encountered in laser welding of Al alloys such as porosity, cracking, oxide inclusions, and loss of alloying elements are discussed from the point of view of mechanism of their formation, main influencing factors, and remedy measures. In part II, the main mechanical properties such as hardness, tensile, and fatigue strength and formability are also discussed.     

基于机器学习的薄板等离子弧搭接焊的熔深预测

在等离子弧搭接焊中,搭接焊接头的焊缝熔深是评价焊接质量的关键指标之一,而焊接过程中的热输入信息和熔池图像信息都与焊缝熔深有密切关系。本文通过建立304L不锈钢薄板等离子弧搭接焊数据采集系统,利用LabVIEW实时检测电信息,采用视觉传感技术实时获取薄板等离子弧搭接焊过程中的熔池图像,并通过图像处理方法获得熔池的几何参数信息,结合焊接工艺参数,选择峰值电流、峰值电压、焊接速度、离子气流量、保护气流量、熔池宽度和熔池后端长度作为输入量,焊缝熔深作为输出量,建立了基于支持向量机回归和BP神经网络的熔深预测模型。实验验证表明,采用径向基函数的支持向量机回归模型可以有效地对焊缝熔深进行预测,并具有很好的泛化能力,可为进一步实现在线优化焊接工艺参数提供依据。     

Model-based approach for quality improvement of electron beam welding applications in mass production

A model-based approach is presented to obtain a definite geometry of the seam as well as to find the regimes where the results will repeat with less deviation from the desired values in the electron beam welding. Using the response surface methodology, polynomial regression models for the behaviour of weld depth and the weld width are found. In order to improve the quality of the process in mass production, by a decrease of the deviation from a target value of the performance characteristic, parameters in two models describing the mean value and the variance for the weld depth and for the weld width in mass production are estimated. Using these models quality improvement, defined as an optimisation problem to produce reproducible welds while keeping the mean value of weld depth or/and width constant, is discussed. This approach is applied to the electron beam welding of stainless steel, for beam powers in the region of 4.2-4.8 kW and welding speeds of 3.333-13.333 mm/s.     

不锈钢与钛合金纳秒激光焊接工艺研究

目的 针对不锈钢与钛合金异种金属焊接时,容易产生间化合物,导致焊点拉力低的现象,通过纳秒激光焊接工艺来提高不锈钢与钛合金异种金属焊接的焊点拉力.方法 采用纳秒光纤激光器进行304不锈钢与TC4钛合金的焊接实验,通过激光运行螺旋线组成焊点,并对工艺参数进行正交试验,得到焊点拉力最大的工艺参数.结果 当激光功率为90 W,...     

Untersuchung einer mehrlagigen Schweißnaht eines dickwandigen Rohres aus dem austenitischen Stahl X6 CrNiNb 18 10

Analysis of a multi pass weld of a thick walled tube made of austenitic stainless steel X6 CrNiNb 18 10 In this paper, microstructure and residual stresses of a multi pass welding of a thick‐walled tube made of austenitic stainless steel X6 CrNiNb 18 10 (1.4550) are systematically characterized and assessed. Results of microstructural and phase analyses, residual stress and hardness measurements as well as of a tensile test using micro specimen and SEM analyses are presented. Using these data, plastic deformations occurring during the welding process in the vicinity of the weld seam are evaluated. Finally, consequences of an additional heat treatment at 400 °C/24 h are studied.     

New parametric study of nugget size in resistance spot welding process using finite element method

Resistance spot welding process (RSW) is one of important manufacturing processes in automotive industry for assembling bodies. Quality and strength of the welds and therefore body mainly are defined by quality of the weld nuggets. The most effective parameters in this process are: current intensity, welding time, sheet thickness and material, geometry of electrodes, electrode force, and current shunting. In present research, a mechanical–electrical–thermal coupled model in a finite element analysis environment is made using. Via simulating this process, the phenomenon of nugget formation and the effects of process parameters on this phenomenon are studied. Moreover, the effects of welding parameters on temperature of faying surface are studied. Using this analysis, shape and size of weld nuggets are computed and validated by comparing them with experimental results from published articles. The methodology developed in this paper provides prediction of quality and shape of the weld nuggets with variation of each process parameter. Utilizing this methodology assists in adjusting welding parameters so that costly experimental works can be avoided. In addition, the process can be economically optimized to manufacture quality automotive bodies.     

双束激光焊接的研究现状

双束激光焊接技术是高能束焊接领域的研究热点之一,其主要目的是解决激光焊接时存在的问题。文章首先根据单束激光焊接冷却速度过快、装配要求精度过高等缺点,提出了采用双束激光焊接技术进行改善,并对其机理进行了概括分析;其次介绍了多种双束激光焊接同种/异种材料的研究现状,包括不同的工艺参数(束间距、光强比、热源布置方式等)、匙孔内的等离子体行为、焊缝性能以及焊接缺陷等方面。     

Zum Einfluss des Schweißens auf das Kriechverhalten moderner Stähle für die thermische Energieerzeugung

The influence of welding on creep behaviour of modern steels for thermal power generation Un‐ and low alloyed ferritic/bainitic Chromium steels as well as high alloyed ferritic/martensitic 9–12 % Chromium steels are widely used for high temperature components in thermal power generation. Welding in all its variety is the major repair and joining technology for such components. The weld thermal cycle has significant influence on the base material microstructure and its properties. The Heat Affected Zone is often regarded as the weakest link during high temperature service. While weldments of un‐ and low alloyed ferritic Chromium steels can show significant susceptibility to Reheat Cracking in the coarse grained heat affected zone, weldments of high alloyed ferritic Chromium steels generally fail by Type IV Cracking in the fine grained heat affected zone during long term service. In this paper the influence of the weld thermal cycle on the base material microstructure is described. Long‐term creep behaviour of weldments is directly related to the main failure mechanisms in creep exposed ferritic weldments and implications for industries using heat resistant ferritic steels are shown.