Modelling the spot shape influence on high-speed transmission lap welding of thermoplastics films

Modelling high-speed laser lap welding of thermoplastic films has been accomplished and the influence of laser beam spot shape, dimensions, and position relative to sample displacement was analysed.Engineering parameters predicted by the model were applied to lap weld of high- and low-density polyethylene transparent samples with thickness between 10 and 100 μm, and experimentally validated. Experimental set-up allowed reaching welding constant linear velocities up to 10 m/s.Theoretical and experimental data show coincidence. Weld strength increases for larger beam spot diameters, and elliptical beam spots increase weld efficiency, allowing higher processing speeds or decreasing required laser power. An angular deviation of elliptical beam spot with regard to the sample's movement direction causes an increase of weld strength and a decrease of welding speed.     

Parametric optimisation and microstructural analysis on high power Yb-fibre laser welding of Ti–6Al–4V

In this work thin sheets of Ti–6Al–4V were full penetration welded using a 5 kW fibre laser in order to evaluate the effectiveness of high power fibre laser as a welding processing tool for welding Ti–6Al–4V with the requirements of the aircraft industry and to determine the effect of welding parameters including laser power, welding speed and beam focal position on the weld microstructure, bead profile and weld quality. It involved establishing an understanding of the influence of welding parameters on microstructural change, welding defects, and the characteristics of heat affected zone (HAZ) and weld metal (WM) of fibre laser welded joints. The optimum range of welding parameters which produced welds without cracking and porosity were identified. The influence of the welding parameters on the weld joint heterogeneity was characterised by conducting detailed microstructural analysis.     

RAFM钢TIG焊和电子束焊疲劳性能实验和分析模拟

利用ANSYS 对低活化铁素体马氏体(RAFM)钢进行非熔化极气体保护焊(TIG 焊)与电子束焊的抗疲劳模拟分析，再利用SDS200 电液伺服疲劳试验机对TIG 焊和电子束焊的两种RAFM 钢试件进行实验。通过施加相同梯度负荷对TIG 焊和电子束焊试件进行焊缝的疲劳性能实验。与实验结果对比分析，结果显示电子束焊优于 TIG 焊，但在一定负载下可以用TIG 焊代替电子束焊。     

Optimal design for laser beam butt welding process parameter using artificial neural networks and genetic algorithm for super austenitic stainless steel

Laser welding input parameters play a very significant role in determining the quality of a weld joint. The joint quality can be defined in terms of properties such as weld bead geometry, mechanical properties and distortion. Therefore, mechanical properties should be controlled to obtain good welded joints. In this study, the weld bead geometry such as depth of penetration (DP), bead width (BW) and tensile strength (TS) of the laser welded butt joints made of AISI 904L super austenitic stainless steel were investigated. Full factorial design was used to carry out the experimental design. Artificial Neural networks (ANN) program was developed in MatLab software to establish the relationships between the laser welding input parameters like beam power, travel speed and focal position and the three responses DP, BW and TS in three different shielding gases (Argon, Helium and Nitrogen). The established models were used for optimizing the process parameters using Genetic Algorithm (GA). Optimum solutions for the three different gases and their respective responses were obtained. Confirmation experiment has also been conducted to validate the optimized parameters obtained from GA.     

Transient interaction of a boiling melt with a pulsed Nd:YAG-laser

The boiling front induced by a pulsed Nd:YAG-laser at very slow translation speed was studied. The purpose is to understand fundamental melt movement mechanisms. The melt was observed by high speed imaging, with and without illumination. When switching on the laser beam a hole is drilled through a bulk of melt. The hole expands and the boiling pressure gradually opens the melt bridge, instead developing an interaction front similar to cutting. These conditions remain in quasi-steady state during the pulse. The ablation pressure from boiling shears waves down the front and keeps the melt downwards in a stable position. When switching off, the waves smoothen and in absence of boiling the surface tension drags the melt back upwards, to semi-torus-like Catenoid shape. Evidence on the large melt pool and its shape was achieved by three-dimensional reconstruction from cross section macrographs. The basic findings how melt can move with and without ablation pressure can enable controlled melt dynamics for various laser processing techniques, like remote cutting, ablation, keyhole welding or drilling.     

Influences of laser in low power YAG laser-MAG hybrid welding process

The influences of laser defocusing amount △z, laser power P, space distance DLA between laser and arc on weld penetration, arc modality and stability are investigated in low power YAG laser and metal active gas （laser-MAG） hybrid welding process. The experimental results indicate that the effects of laser-induced attraction and contraction of MAG arc are emerged in hybrid welding process, which result in the augmentation of hybrid welding energy. When DLA ： -0.5 - 2 mm, △z = -2 - 2 mm and P ≥ 73 W, the synergic efficiency between laser and MAG arc is obvious, the cross section at the root of hybrid arc is contracted and the hybrid weld penetration is increased. The maximal ratio of hybrid/MAG weld penetration is 1.5 and the lowest YAG laser power that augments MAG arc is 73 W. The input of YAG laser makes the stabilities of arc ignition and combustion prominent in hybrid welding process.     

Pulsed Nd:YAG laser welding of AISI 304 to AISI 420 stainless steels

The technique to weld AISI 304 stainless steel to AISI 420 stainless steel with a pulsed Nd:YAG laser has been investigated. The main objective of this study was to determine the influence of the laser beam position, with respect to the joint, on weld characteristics. Specimens were welded with the laser beam incident on the joint and moved 0.1 and 0.2 mm on either side of the joint. The joints were examined in an optical microscope for cracks, pores and to determine the weld geometry. The microstructure of the weld and the heat affected zones were observed in a scanning electron microscope. An energy dispersive spectrometer, coupled to the scanning electron microscope, was used to determine variations in (weight %) the main chemical elements across the fillet weld. Vickers microhardness testing and tensile testing were carried out to determine the mechanical properties of the weld. The results of the various tests and examinations enabled definition of the best position for the incident laser beam with respect to the joint, for welding together the two stainless steels.     

Measurement of micro weld joint position based on magneto-optical imaging

In a laser butt joint welding process,it is required that the laser beam focus should be controlled to follow the weld joint path accurately.Small focus wandering off the weld joint may result in insufficient penetration or unacceptable welds.Recognition of joint position offset,which describes the deviation between the laser beam focus and the weld joint,is important for adjusting the laser beam focus and obtaining high quality welds.A new method based on the magneto-optical(MO)imaging is applied to measure the micro weld joint whose gap is less than 0.2 mm.The weldments are excited by an external magnetic field,and an MO sensor based on principle of Faraday magneto effect is used to capture the weld joint images.A sequence of MO images which are tested under different magnetic field intensities and different weld joint widths are acquired.By analyzing the MO image characteristics and extracting the weld joint features,the influence of magnetic field intensity and weld joint width on the MO images and detection of weld joint position is observed and summarized.     

Measurement of the bead profile and microstructural characterization of a CO2 laser welded AISI 904 L super austenitic stainless steel

Laser welding of AISI 904 L super austenitic stainless steel using a diffusion cooled slab 3.5 kW CO₂ laser and employing two different shielding gases, namely argon and helium, was carried out. The laser weld bead profile depends on various parameters such as beam power (BP), travel speed (TS) and focal position (FP) of the laser spot. These parameters have to be selected suitably to obtain the desirable output. The cross sectioned area of the bead profiles measured using an optical microscope to determine the bead width and depth of penetration. X-ray diffraction used for phase identification confirmed that the weld structure was fully austenitic and dendritic. Hardness was observed to increase in the weld bead with respect to the parent metal and it was related to the microstructural refinement induced by a rapid cooling of the weld zone.     

Features of Laser Through-Cutting of Silicate Glass by a Fiber Ytterbium Laser

Some principal aspects of silicate glass cutting by controlled laser through thermal cleavage are considered. In particular, it is shown that the cutting speed in the case of ytterbium fiber laser radiation with a wavelength of 1.065 μm lying in fact in the glass transmission range (more precisely, in the low absorption region) depends linearly on the laser power. It is shown that the glass end face takes various geometrical shapes under various conditions of bulk heating and cooling. Therefore, to obtain a homogeneous end face, it is required to stabilize both the laser radiation power and the laser beam speed at a corresponding laser beam geometry in the cut region. Methods for obtaining various cross section shapes of the glass end face and methods for obtaining blunt edges of end faces are presented.     

Combination of laser keyhole and conduction welding: Dissimilar laser welding of niobium and Ti-6Al-4V

Pulsed Nd:YAG laser welding of pure niobium plate to titanium alloy Ti-6Al-4V sheet in butt joint is studied regarding the laser/metal interaction modes. To obtain the optimized process parameters in dissimilar welding of Ti-6Al-4V/Nb, the melting ratio of laser beam energy for each weld counterpart is evaluated experimentally. Different laser welding modes of keyhole and conduction are predicted regarding the absorbed energy from the similar laser pulses on each weld counterpart. Laser keyhole and conduction welding were observed simultaneously through direct visualization of laser interaction with dissimilar metals using High Speed Imaging (HSI) system.     

Optimization of Nd:YAG laser welding onto magnesium alloy via Taguchi analysis

The use of an Nd:YAG laser for thin plate magnesium alloy butt welding was optimized using the Taguchi analytical methodology. The welding parameters governing the laser beam in thin plate butt welding were evaluated by measuring of the ultimate tension stress. The effectiveness of the Taguchi method lies in clarifying the factor that dominates complex interactions in laser welding. The factors can be the shielding gas, laser energy, convey speed of workpiece, point at which the laser is focused, pulse frequency, and pulse shape. Furthermore, 18 combinations of these six essential welding parameters were set and Taguchi's method followed exactly. The optimal result was confirmed with a superior ultimate tension stress of 169 MPa, 2.5 times larger to that from original set for laser welding.     

Prediction of weld strength and seam width for laser transmission welding of thermoplastic using response surface methodology

In the present work, a study is made to investigate the effects of process parameters, namely, laser power, welding speed, size of the laser beam and clamp pressure, on the lap-shear strength and weld-seam width for laser transmission welding of acrylic (polymethyl methacrylate), using a diode laser system. Response surface methodology (RSM) is employed to develop mathematical relationships between the welding process parameters and the output variables of the weld joint to determine the welding input parameters that lead to the desired weld quality. In addition, using response surface plots, the interaction effects of process parameters on the responses are analyzed and discussed. The statistical software Design-Expert v7 is used to establish the design matrix and to obtain the regression equations. The developed mathematical models are tested by analysis-of-variance (ANOVA) method to check their adequacy. Finally, a comparison is made between measured and calculated results, which are in good agreement. This indicates that the developed models can predict the responses adequately within the limits of welding parameters being used.     

Optimization of laser welding of DP/TRIP steel sheets using statistical approach

Generally, the quality of a weld joint is directly influenced by the welding input parameter settings. Selection of proper process parameters is important to obtain the desired weld bead profile and quality. In this research work, numerical and graphical optimization techniques of the CO₂ laser beam welding of dual phase (DP600)/transformation induced plasticity (TRIP700) steel sheets were carried out using response surface methodology (RSM) based on Box–Behnken design. The procedure was established to improve the weld quality, increase the productivity and minimize the total operation cost by considering the welding parameters range of laser power (2–2.2 kW), welding speed (40–50 mm/s) and focus position (?1 to 0 mm). It was found that, RSM can be considered as a powerful tool in experimental welding optimization, even when the experimenter does not have a model for the process. Strong, efficient and low cost weld joints could be achieved using the optimum welding conditions.     

Optimization of weld bead geometry in laser welding with filler wire process using Taguchi’s approach

In the present work, laser welding with filler wire was successfully applied to joining a new-type Al–Mg alloy. Welding parameters of laser power, welding speed and wire feed rate were carefully selected with the objective of producing a weld joint with the minimum weld bead width and the fusion zone area. Taguchi approach was used as a statistical design of experimental technique for optimizing the selected welding parameters. From the experimental results, it is found that the effect of welding parameters on the welding quality decreased in the order of welding speed, wire feed rate, and laser power. The optimal combination of welding parameters is the laser power of 2.4 kW, welding speed of 3 m/min and the wire feed rate of 2 m/min. Verification experiments have also been conducted to validate the optimized parameters.     

Parameters optimization of laser brazing in crimping butt using Taguchi and BPNN-GA

The laser brazing (LB) is widely used in the automotive industry due to the advantages of high speed, small heat affected zone, high quality of welding seam, and low heat input. Welding parameters play a significant role in determining the bead geometry and hence quality of the weld joint. This paper addresses the optimization of the seam shape in LB process with welding crimping butt of 0.8 mm thickness using back propagation neural network (BPNN) and genetic algorithm (GA). A 3-factor, 5-level welding experiment is conducted by Taguchi L₂₅ orthogonal array through the statistical design method. Then, the input parameters are considered here including welding speed, wire speed rate, and gap with 5 levels. The output results are efficient connection length of left side and right side, top width (WT) and bottom width (WB) of the weld bead. The experiment results are embed into the BPNN network to establish relationship between the input and output variables. The predicted results of the BPNN are fed to GA algorithm that optimizes the process parameters subjected to the objectives. Then, the effects of welding speed (WS), wire feed rate (WF), and gap (GAP) on the sum values of bead geometry is discussed. Eventually, the confirmation experiments are carried out to demonstrate the optimal values were effective and reliable. On the whole, the proposed hybrid method, BPNN-GA, can be used to guide the actual work and improve the efficiency and stability of LB process.     

Spectroscopic, energetic and metallographic investigations of the laser lap welding of AISI 304 using the response surface methodology

Spectroscopic signals originated by the laser-induced plasma optical emission have been simultaneously investigated together with energetic and metallographic analyses of CO₂ laser welded stainless steel lap joint, using the Response Surface Methodology. This statistical approach allowed us to study the influence of the laser beam power and the laser welding speed on the following response parameters: plasma plume electron temperature, joint penetration depth and melted area. A clear correlation has been found between all the investigated response parameters. The results have been shown to be consistent with quantitative considerations on the energy supplied to the workpiece as far as the laser power and travel speed were varied. The regression model obtained in this way could be a valuable starting point to develop a closed loop control of the weld penetration depth and the melted area in the investigated process window.     

Analysis of mechanism of plasma and spatter in CO2 laser welding of galvanized steel

In laser welding, quality, reproducibility and formability are required. That is the great problem in the automation of the laser welding process. Therefore, construction of an on-line process monitoring system of high accuracy is requested.The light which is emitted from plasma and spatter in laser welding was detected by photo-diodes. It was found that the light intensity depends on welding speed, laser power and flow rate of assist gas. The relationship between the plasma and spatter and the bead shape, and the mechanism of plasma and spatter were analyzed for on-line laser weld monitoring systems.     

5083铝合金光纤激光-TIG复合焊接工艺研究

采用IPG YLS-6000光纤激光器和Fronius MagicWave3000job数字化焊机,对4mm厚5083H116铝合金进行了复合焊接试验。研究了电源特性、电流大小和热源间距等工艺参数对光纤激光-钨极惰性气体保护焊(TIG)复合焊接焊缝成形的影响规律,并分析了焊接接头的缺陷、显微硬度及力学性能。结果表明,光纤激光-TIG复合焊接5083铝合金,能够明显改善焊缝成形,提高焊接过程稳定性,特别是与变极性TIG电弧复合效果更为显著;光纤激光与变极性TIG电弧复合焊接,采用激光在前的方式,电弧电流150A,且热源间距不大于4mm,可以得到具有明亮金属光泽和均匀鱼鳞纹的焊缝,焊缝无气孔和裂纹缺陷,其表面有少量的下凹;复合焊接接头抗拉强度为318MPa,达到母材强度的93%,延伸率为7.6%,高于单光纤激光焊接,断口分析为韧性断裂。     

5083铝合金光纤激光-TIG复合焊接工艺研究

采用IPG YLS-6000光纤激光器和Fronius MagicWave3000job数字化焊机,对4 mm厚5083 H116铝合金进行了复合焊接试验。研究了电源特性、电流大小和热源间距等工艺参数对光纤激光-钨极惰性气体保护焊（TIG）复合焊接焊缝成形的影响规律,并分析了焊接接头的缺陷、显微硬度及力学性能。结果表明,光纤激光-TIG复合焊接5083铝合金,能够明显改善焊缝成形,提高焊接过程稳定性,特别是与变极性TIG电弧复合效果更为显著;光纤激光与变极性TIG电弧复合焊接,采用激光在前的方式,电弧电流150 A,且热源间距不大于4 mm,可以得到具有明亮金属光泽和均匀鱼鳞纹的焊缝,焊缝无气孔和裂纹缺陷,其表面有少量的下凹;复合焊接接头抗拉强度为318 MPa,达到母材强度的93%,延伸率为7.6%,高于单光纤激光焊接,断口分析为韧性断裂。