Welding Polarity Effects on Weld Spatters and Bead Geometry of Hyperbaric Dry GMAW

Welding polarity has influence on welding stability to some extent, but the specific relationship between welding polarity and weld quality has not been found, especially under the hyperbaric environment. Based on a hyperbaric dry welding experiment system, gas metal arc welding（GMAW） experiments with direct current electrode positive（DCEP） and direct current electrode negative（DCEN） operations are carried out under the ambient pressures of 0.1 MPa, 0.4 MPa, 0.7 MPa and 1.0 MPa to find the influence rule of different welding polarities on welding spatters and weld bead geometry. The effects of welding polarities on the weld bead geometry such as the reinforcement, the weld width and the penetration are discussed. The experimental results show that the welding spatters gradually grow in quantity and size for GMAW with DCEP, while GMAW with DCEN can produce fewer spatters comparatively with the increase of the ambient pressure. Compared with DCEP, the welding current and arc voltage waveforms for DCEN is more stable and the distribution of welding current probability density for DCEN is more concentrated under the hyperbaric environment. When the ambient pressure is increased from 0.1 MPa to 1.0 MPa, the effects of welding polarities on the reinforcement, the weld width and the penetration are as follows： an increase of 0.8 mm for the weld reinforcement is produced by GMAW with DCEN and 1.3 mm by GMAW with DCEP, a decrease of 7.2 mm for the weld width is produced by DCEN and 6.1 mm by DCEP; and an increase of 3.9 mm for the penetration is produced by DCEN and 1.9 mm by DCEP. The proposed research indicates that the desirable stability in the welding procedure can be achieved by GMAW with DCEN operation under the hyperbaric environment.

Correlative spatter and vapour depression dynamics during laser powder bed fusion of an Al-Fe-Zr alloy

Spatter during laser powder bed fusion(LPBF)can induce surface defects,impacting the fatigue performance of the fabricated components.Here,we reveal and explain the links between vapour depression shape and spatter dynamics during LPBF of an Al-Fe-Zr aluminium alloy using high-speed synchrotron x-ray imaging.We quantify the number,trajectory angle,velocity,and kinetic energy of the spatter as a function of vapour depression zone/keyhole morphology under industry-relevant processing conditions.The depression zone/keyhole morphology was found to influence the spatter ejection angle in keyhole versus conduction melting modes:(i)the vapour-pressure driven plume in conduction mode with a quasi-semi-circular depression zone leads to backward spatter whereas;and(ii)the keyhole rear wall redirects the gas/vapour flow to cause vertical spatter ejection and rear rim droplet spatter.Increasing the opening of the keyhole or vapour depression zone can reduce entrainment of solid spatter.We discover a spatter-induced cavity mechanism in which small spatter particles are accelerated towards the powder bed after laser-spatter interaction,inducing powder denudation and cavities on the printed surface.By quantifying these laser-spatter interactions,we suggest a printing strategy for minimising defects and improving the surface quality of LPBF parts.

Welding characteristics of AZ31B magnesium alloy using DC-PMIG welding

Direct current pulsed metal inert-gas （DC-PMIG） welding was carried out on AZ31B magnesium alloy to obtain continuous welding joints of 3 mm and 8 mm thickness with 1.6 mm diameter of filler wire. The behavior and mechanism of metal transfer, the parameter ranges of stable welding process, the microstructure and mechanical properties of magnesium alloy were investigated. The results show that the metal transfer form of magnesium alloy using DC-PMIG welding is realized in modes of globular transfer, projected transfer and spray transfer. Welding spatter with a large size will be produced in the mode of globular transfer, and high-quality joints with few spatters can be obtained in the mode of projected transfer and spray transfer when the linear energy of filler wire is 242-27l J/cm, droplet diameter is 1.6-0.9 mm tensile strength of weld beads is 94.2% of that of base metals. and transition frequency is 30-69 Hz. The average ultimate

Analysis of high-power disk laser welding stability based on classification of plume and spatter characteristics

Classification of plume and spatter images was studied to evaluate the welding stability. A high-speed camera was used to capture the instantaneous images of plume and spatters during high power disk laser welding. Characteristic parameters such as the area and number of spatters, the average grayscale of a spatter image, the entropy of a spatter grayscale image, the coordinate ratio of the plume centroid and the welding point, the polar coordinates of the plume centroid were defined and extracted. Karhunen-Loeve transform method was used to change the seven characteristics into three primary characteristics to reduce the dimensions. Also, K-nearest neighbor method was used to classify the plume and spatter images into two categories such as good and poor welding quality. The results show that plume and spatter have a close relationship with the welding stability, and two categories could be recognized effectively using K-nearest neighbor method based on Karhunen-Loeve transform.

Experimental Study on Metal Transfer and Welding Spatter Characteristics of Cellulose Electrode

Welding spatter cause many problems during the welding process and this issue is particularly important for cellulose electrode welding. The hot flying spatter balls often deteriorate the working environment, and decrease the welding efficiency. Many factors affect the welding spatter, and metal transfer behavior is one of the main factors. Many studies concerning the spatter mechanism in arc welding process were made; most of them focused on the solid wire welding and the study on cellulose electrode is rarely reported. In this paper the metal transfer behavior and the weld spatter characteristics of three commercial cellulose electrodes were studied experimentally by using a high speed camera for visually capturing the metal transfer. The relationship between the metal transfer and the welding spatter was analyzed experimentally by comparing the spatter loss coefficient, which is for quantitative evaluation of welding spatter, with the statistical analysis of the large droplet transfer mode. The results showed that short circuiting transfer, large droplet spray transfer, fine droplet spray transfer and explosive transfer govern the metal transfer modes in cellulose electrode welding. Weld spatter occurred mainly in the deflection of large droplet process, explosive transfer process and fine droplet spraying process. Different metal transfer modes lead to different spatter. The deflection of large droplet and explosive transfer are the main factors of the spatter formation. Minimizing the droplet size and reducing the deflection of large droplet and explosive transfer leads to the reduction the amount of spatter in cellulose electrode welding.

Investigation into Spatter Particles and Their Effect on the Formation Quality During Selective Laser Melting Processes

During the selective laser melting process,a high-energy laser beam acts on the powder,a molten pool is rapidly generated and the characteristic parameters are constantly changing.Among them,temperature is one of the important parameters in the forming process.Due to the generation of splash particles,there will be defects in the microstructure,which will seriously affect the formation quality of the prepared parts.Therefore,it is necessary to study the relationships between the splash behavior,molten pool characteristics and product quality.The finite element simulation of the transient temperature field was performed by ANSYS software.Time-series images at different frame rates were obtained with a high-speed camera,and the dynamic process of splashing was observed.Using IN718 alloy powder,the influence of the laser energy density on the light intensity of the molten pool was studied.The appearance of splash particles and the deviation of the powder chemical elements caused by the splash were analyzed.The results show that the transient temperature field with drastic change is easy to cause spatter,which is consistent with the experimental results.There are large differences in the splash at different shooting frame rates.Increasing the frame rate can allow the observation of details such as the shape,size and number of splash particles,which is beneficial for studying the process of splash formation.At the moment when the splash occurs,the light intensity of the molten pool always first increases and then decreases,depending on the energy input.The higher the energy input is,the more intense the light intensity of the molten pool and the higher the peak interval distribution.Compared with fresh powder,the contents of Al and Ti in powder reused 5 times were reduced by 0.15%and 0.02%,respectively.The increases of these two elements in the splash were 16.18%and 29.62%,respectively,and the content of Nb even exceeded the standard range.When the energy density decreased from 229.17 J/mm3 to 130.95 J/mm3,the relative density of the part increased from 91.82%to 99.83%.This shows that reducing the energy input can reduce the splash to suppress the generation of defects,along with the weakening of the overall light intensity of the molten pool.These results can provide a basis for feature extraction of the molten pool,which is of great significance for real-time monitoring and online control in manufacturing processes and ensuring product quality.

Effects of current waveform parameters during droplet transfer on spatter in high speed waveform controlled Short-circuiting GMAW

Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.

COMPUTER SIMULATION OF NEURAL NETWORK CONTROL SYSTEM FOR CO_2 WELDING PROCESS

In this paper, neural network control systems for decreasing the spatter of CO2 welding have been created. The Generalized inverse Learning Architecture(GILA), the SPecialized inverse Learning Architecture(SILA)-I & H and the Error Back Propagating Model(EBPM) are adopted respectively to simulate the static and dynamic welding control processes. The results of simulation and experiment show that the SILA-I and EBPM have betted properties. The factors affecting the simulating results and the dynamic response quality have also been analyzed.

Narrow gap space contributes to chemical metallurgy of self-shielded arc welding

The slag-free self-shielded flux-cored wire was fabricated to apply for the narrow gap welding.The results showed that narrow gap welding shows lower welding spatter compared with hardfacing except under voltage of 30 V and current of 260 A.The deposition efficiency keeps over 90%for both 12 mm and 8 mm narrow gap welding.For 12 mm narrow gap welding,when the voltage is 28 V and the current is 264 A(or 286 A),no pores are found in the narrow gap weld.In the continuous welding process,manganese vapor,aluminum vapor and CO continuously generate to form gasbag and occupy the narrow gap space,thus protecting the droplet and molten pool from the invasion of air.

Study on arc characteristics and behavior of metal transfer in pulse current flux-cored arc welding of mild steel

The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative study of similar nature has also been carried out during flux-cored arc weld deposition in globular and spray transfer modes.The effect of pulse parameters has been studied by considering their mean current and arc voltage.The arc characteristics studied by its root diameter,projected diameter and length,and the behavior of metal transfer noted by the metal transfer model and the droplet diameter have been found to vary significantly with the pulse parameters.The observation may help in understanding the arc characteristics with respect to the variation in pulse parameters which may be beneficial in using pulse current FCAW to produce desired weld quality.

Elucidation of Metallic Plume and Spatter Characteristics Based on SVM During High-Power Disk Laser Welding

During deep penetration laser welding,there exist plume（weak plasma） and spatters,which are the results of weld material ejection due to strong laser heating.The characteristics of plume and spatters are related to welding stability and quality.Characteristics of metallic plume and spatters were investigated during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW.An ultraviolet and visible sensitive high-speed camera was used to capture the metallic plume and spatter images.Plume area,laser beam path through the plume,swing angle,distance between laser beam focus and plume image centroid,abscissa of plume centroid and spatter numbers are defined as eigenvalues,and the weld bead width was used as a characteristic parameter that reflected welding stability.Welding status was distinguished by SVM（support vector machine） after data normalization and characteristic analysis.Also,PCA（principal components analysis） feature extraction was used to reduce the dimensions of feature space,and PSO（particle swarm optimization） was used to optimize the parameters of SVM.Finally a classification model based on SVM was established to estimate the weld bead width and welding stability.Experimental results show that the established algorithm based on SVM could effectively distinguish the variation of weld bead width,thus providing an experimental example of monitoring high-power disk laser welding quality.

The Influence of Annealing Temperature on the Structure and Properties of TiO_2 Films Prepared by Sputtering

The TiO2 fihus were prepared on slides by dc reactive magnetron spattering, then the samples were annealed at 300 ℃ ,350 ℃ ,400 ℃ ,450 ℃ ,500 ℃ and 550 ℃ , respectively. X-ray diffraction （XRD） was used to obtain the TiO2 film crystalline structure; X-ray photoelectron spectroscopy （ XPS ） was used to study the film surface stoichiometries ; surface morphologies were studied by scanning electron microscopy （SEM） ; the coatact angle was tested to indicate the TiO2 film wettability ; and the photocatalytic activity testing was couducted to evaluate the photocatalysis properties. The photocatalytic activity and contact angle testing results were correlated with the crystallinity , surface morphologies aud surface · OH concentration of TiO2 films. The samples with a higher polycrystalline anatase structure, rough surface and high · OH concentration displayed a better photoinduced hydrophilicity aud a stronger photocatalysis.

Comparison of the pulsed MIG welding process for different median current

Based on the high speed video system with electrical signals collecting and wavelet analyzing, the welding processes under three different median currents with the same median time were detected. The experimental results show that, when the median current is higher, the input peak energy is lower. And the droplet transfer is almost in spray mode. The welding process is the stablest.

Appearance and characteristics of non explosive short circuit transfer using basic electrodes

By means of high-speed photograph and synchronous oscillograph, the appearance and technical features of non-explosive short circuiting transfer using basic electrodes are investigated, and the conditions to form this metal transfer mode are discussed. It is shown that the metal transfer mode has its high frequency of droplet, short period of arc extinguishing and long arc igniting period. This metal transfer mode is expected for basic electrodes for its less spatter and higher deposition efficiency.

Eigenvalue extraction of current signal during spot welding based on space-phase reconstruction

Nonlinear methods are used to analyze current signal of spot welding and the minimum embedding dimension, correlation dimension, the optimal time delay and the largest Lyapunav exponent of current signal time series are calculated in this paper. The chaotic character of current signal time series is discovered. Then a chaotic neural network is built and used to predict the future current signal. Means of residual error out of the network are used as eigenvalue of current signal during spot welding. It is shown that spatter can greatly affect the means of residual error of spot welding after analysis, the mean values of output errors of signal contaminated by spatter noise are more than 0. 08, but the mean values of output errors of the signal with no spatter noise are less than 0. 04, so mean of residual errors can be employed as the character of spatter.

Effect of arc physics on developing CO_2 arc welding

The mechanisms of weld formation, spatter and projected transfer in CO2 arc welding are revealed based on the experiment and study of the arc physics. The views are beneficial to develop CO2 arc welding technology.

Fronius TPS/i焊接系统的先进工艺及其应用

简要阐述了Fronius伏能士TPS/i智能焊接平台中几种先进的焊接工艺,同时介绍了几种工艺的焊接应用,为客户的实际应用提供参考与借鉴。

A wave controlling method for CO_2 welding using saturable inductor

A new current wave controlling method for short circuit transition CO 2 welding using saturable inductor is put forward in this paper. Theory analysis and experiment results prove that the inverter's dynamic characteristics is greatly improved, the declining speed of current during liquid bridge neck shrinking is quicker, subsequently the energy accumulated in the bridge and the radius of the bridge before rupturing is reduced thus the low spatter result is achieved.

In-situ monitoring plume,spattering behavior and revealing their relationship with melt flow in laser powder bed fusion of nickel-based superalloy

Laser powder bed fusion(LPBF)is a highly dynamic and complex physical process,and single-track de-fects tend to accumulate into non-negligible internal defects of parts.The nickel-based superalloy single track was fabricated by LPBF,and its plume and spattering behavior were monitored in situ and recorded in real time based on image recognition and tracking in this study.The relationship among laser energy density,melt flow,plume and spattering behavior during LPBF was discussed.Volumetric energy density had limitations as a design parameter for LPBF.However,we found that plume and spattering behavior can be used as real-time design parameters for the processing of LPBF parts and implemented the initial velocity statistics for LPBF single-track spattering based on the centroid extraction algorithm.The influ-ence of melt flow evolution paths on the spattering and plume behavior in three different melting modes was revealed,and a shift in plume behavior was found in the overlap region of the additive substrate.This study provides a new method for obtaining statistics of spattering-related physical quantities in the melting mode,which is beneficial for the development of processing methods to mitigate the instability of the LPBF process.

Modeling and Experimental Investigation of Laser Drilling with Jet Electrochemical Machining

As two kinds of defects, recast layers and spatters, commonly accompanied by laser-drilled holes always prevent the laser drilling technique from extending its applications in aerospace and aircraft industries, therefore, a novel hybrid process incorpo- rating laser drilling with jet electrochemical machining （JECM-LD） has been developed to solve these problems as well as improve the overall quality of laser-drilled holes. It is executed by directing an electrolyte jet coaxially aligned with a laser beam onto the workpiece surface. During the process, the electrolyte jet produces electrochemical reaction with the surface material, effective cooling of it and carries away the process scraps. A two-dimensional mathematical model is proposed to describe the shape of the holes machined by JECM-LD. The model is verified through comparison between the results from simulation and those from experiments conducted on the test pieces made of 321 stainless steel 0.5 mm thick processed by the pulsed Nd：YAG laser at second harmonic wavelength. An examination of the experimental results under an optical microscope discovers that, by contrast with the laser drilling in air, the JECM-LD has effectively removed the recast layers and spatters, but its efficiency dropped by about 30%.