Fume formation from spatter oxidation during arc welding

Abstract

Spatter and fume formation rates during arc welding both increase and decrease in a similar manner as welding parameters change. Previously, this fume–spatter relationship has been attributed to evaporation of the spatter caused by oxidation. In this work, a simulated spatter oxidation test did not detect significant fume formation, but high speed videography showed fume trails behind large spatter droplets. Heat balance calculations show that only spatter droplets larger than a few millimeters evaporate and produce fume in significant amounts. Since most spatter particles are smaller than 2 mm, it is not likely that evaporation from spatter contributes significantly to fume. It is proposed that the correlation between spatter and welding fume is instead related to how the temperature of the welding surface affects formation rates of both spatter and fume.     

Application of optical sensor for arc welding

Summary

In CO₂ gas-shielded arc welding, spatter is scattered and adheres to the base metal surface. The main factors affecting any difference in the bonding force remain obscure. This paper examines the bonding force of spatter adhering to the surface of SS400 base metal (rolled steel sheets) under different temperature conditions in CO₂ gas-shielded arc welding using 1.2 mm dia. solid wire. The following four types of base metal surface condition were adopted:

Type 1: As-received surface covered with an oxide film;

Type 2: Ground surface machined with a plain grinder (R_max = 0.6 μm);

Type 3: Surface with fume adhering to the ground surface;

Type 4: Free-ground surface machined with a disc grinder (R_max = 7–16 μm).

The base metal was heated by a 14 mm dia. x 600 mm ceramic heater arranged on the back of the base metal. The bonding force was measured as the shearing force of the spatter. Some 400 spatter particles on each surface were examined. The particles mostly have diameters ranging between 0.4–1.4 mm.

At a base metal temperature below around 450 K, the spatter on the scaled surface is insufficiently hot to melt the base metal and cannot adhere by melting the base metal surface. The shear stress is mostly below around 40 MPa. Despite a rising base metal temperature, however, spatter removal is still possible at less than 300 MPa.

Fume on the surface or the surface roughness do not affect the bonding force as directly as scale on the surface. The temperature, however, affects the bonding force. At a base metal temperature below around 450 K, the bonding force is slightly smaller.

When spatter adheres to the surface, heat causes the microstructure to change with corresponding hardening. The spatter and HAZ of the base metal here show a slightly higher Vickers hardness value (some spatter particles having HV470) than the base metal hardness (HV156–165), although this depends on the surface conditions and temperature.     

Features of Coatings Obtained by Supersonic Laser Deposition

The three types of coatings that can be deposited by supersonic laser deposition, namely coatings built without the melting of the processed powder particles, coatings built from molten particles and coatings made from molten particles and with solid particles embedded in the coating, are discussed. For instance, with no melting of the powder material, a titanium alloy coating without transformation of the structure and with a uniform distribution of the chemical elements in the coating cross-section was obtained. Self-fluxing coatings (NiCrCBSiFe) with high hardness were achieved by melting the powder and mixing it with the substrate. The mixing of the coating metal with the substrate metal led to a significant increase in the concentration of the main alloying elements in the coating–substrate interface. X-ray diffraction analysis also showed that the mixing of the NiCrCBSiFe coating with a medium-carbon steel substrate led to the formation of new Fe_xNi phases, while their concentration decreased through coating thickness.     

Sensing approach for the in-situ determination of spatter motion within PBF-LB/M

Within powder bed fusion of metals by a laser-beam (PBF-LB/M) spatter particles evolve due to the entrainment of powder particles and their ejection along the vapor plume. Motion properties of the evolving spatter particles are directly linked to the process zone topography, qualifying them as an interesting process signature for in-situ sensing. This work shows an industrially applicable sensing approach which allows the determination of three-dimensional spatter positions in real-time. A camera setup is derived reducing ambiguity within the reconstruction at high framerates. The presented parallel image processing and reconstruction algorithm allows for the determination of three-dimensional spatter coordinates in real-time.     

典型弧焊电源外特性对焊接飞溅的影响

利用特制的变结构晶闸管整流焊机,研究典型焊机外特性对焊接飞溅的影响;独特的飞溅声波动态跟踪法和飞溅颗粒分类法研究焊接过程各阶段飞溅生成的条件和规律;探讨低飞溅率手工弧焊电源关参数的合理调节范围。     

电弧弧长对激光-电弧复合焊飞溅和底部驼峰的影响

由于热源形式的特殊性,激光-电弧复合焊接过程中激光和电弧间易发生相互干扰,产生飞溅和底部驼峰等缺陷。以590 MPa级船用高强钢为研究对象,研究了电弧弧长对激光-电弧复合焊飞溅和焊缝底部驼峰的影响。为了深入研究激光-电弧复合焊飞溅和底部驼峰的产生机理,利用高速摄像设备对熔滴过渡行为和焊缝底部熔池进行了观察。结果表明,适当缩短电弧弧长可以降低激光和电弧间的相互干扰,提高复合焊接过程的稳定性,进而降低飞溅产生的倾向。底部驼峰是小孔熔透性差和底部熔池流动不连续所引起的。缩短电弧弧长可以对底部驼峰的产生起到抑制作用,这是因为缩短电弧弧长可以降低等离子体对激光的吸收,提高激光的能量利用率,增加小孔熔透性和稳定性。创新点： 研究了电弧弧长对激光-电弧复合焊飞溅和底部驼峰的影响,采用高速摄像方法对底部熔池流动进行了观察,进一步明确了激光-电弧复合焊接焊缝底部驼峰的产生原因。     

Study of molten metal droplet adhesion to organic anti-spatter coatings

In this study, the protection mechanism of four typical anti-spatter products based on polymer coating is investigated. These coatings protect the weld nozzle against weld spatter in a similar way as water droplets on a hot plate. During the short contact of the molten metal droplet with the coating, part of the coating evaporates in the form of carbon monoxide, hydrogen, water and other volatile degradation products. During welding, these gases act as a buffer layer between the coating and the weld spatter and can significantly reduce the potential spatter/substrate adherence and spatter agglomeration.     

Effects of spray conditions on coating formation by the kinetic spray process

The kinetic spray coating process involves impingement of a substrate by particles of various material types at high velocities. In the process, particles are injected into a supersonic gas stream and accelerated to high velocities. A coating forms when the particles become plastically deformed and bond to the substrate and to one another upon collision with the substrate. Coating formation by the kinetic spray process can be affected by a number of process parameters. In the current study, several spray variables were investigated through computational modeling and experiments. The examined variables include the temperature and pressure of the primary gas, the cross-sectional area of the nozzle throat, the nozzle standoff distance from a substrate, and the surface condition of nozzle interior and the powder gas flow. Experimental verification on the effects of these variables was performed primarily using relatively large-size aluminum particles (63–90 μm) as the feedstock material. It was observed that the coating formation is largely controlled by two fundamental variables of the sprayed particles: particle velocity and particle temperature. The effects of different spray conditions on coating formation by the kinetic spray process can be generally interpreted through their influences on particle velocity and/or particle temperature. Though it is limited to accelerate large particles to high velocities using compressed air or nitrogen as carrier gas, increasing particle temperature provides an additional means that can effectively enhance coating formation by the kinetic spray process.     

SLM过程中飞溅形成机制和控制方法综述

由于激光选区熔化(SLM)技术加工周期较短、易于成形结构复杂的零件,现已广泛应用于生物医疗、航空航天、汽车和军工制造业等领域。但是由于在成型过程中激光与粉末间复杂地相互作用,激光选区熔化制件的缺陷呈现出多样化的特点,且控制难度加大,这在一定程度上限制了该技术的发展和应用。对于飞溅缺陷的形成机制和控制方法的研究,是近年来研究的热点之一。总结了近年来的相关研究成果,将粉末、熔池及成形层作为线索,从飞溅物对成形件的影响、飞溅物形成原因、监测和控制方法以及未来研究方向四部分阐述SLM过程中飞溅形成机制和控制方法,并展望了未来的发展方向。     

焊接极性对水下高压干法GMAW影响分析

通过环境压力为0.1~2.0 MPa的水下高压干法熔化极气体保护焊(GMAW)试验,比较了直流反接与直流正接焊接过程特点.结果表明,直流反接时,当压力超过0.2 MPa后开始出现少量飞溅,随着环境压力增加,飞溅数量逐渐增多而尺寸逐渐减小.直流正接时,当环境压力大于0.4 MPa后,焊接过程稳定,几乎无飞溅产生.通过高速摄像分析总结了直流反接产生两种飞溅形式及其特征.熔滴偏离型飞溅是伴随着排斥过渡产生的;熔滴反弹型飞溅是由于熔滴接触母材后受向上方向电磁力作用,脱离母材而产生的,并分析了直流正接时飞溅较小的原因.     

CO2短路过渡过程检测及应用

分析了ＣＯ２气体保护焊短路过渡飞溅产生的机理,阐述了导致飞溅产生的三个重要过程,即瞬时短路,液桥缩颈后爆断和重新燃时冲击熔池。提出了ＣＯ２短路过渡液桥状态检测的新方法,并介绍了液桥状态传感器系统的工作原理,组成及此方法在抑制短路电弧飞溅产生的新型工艺质量控制法中的应用,并取得了满意的工艺效果。     

我国实现低碳经济所面临的挑战自蔓延焊接的安全与防护

分析了自蔓延焊接过程中高温、飞溅、烟尘和爆炸等危害现象产生的杌理和因为,以及时焊接操作人员和环境的影响和危害.并且结合焊接工艺和个人保护,提出了安全有效的针对性防护措施,形成了切实有效的自蔓延焊接安全生产管理方案.     

An experimental and numerical study on laser percussion drilling of thick-section alumina

A major challenge in laser percussion drilling of thick-section ceramics is to obtain a low taper and low spatter deposition hole leading to high quality post-processing. In order to achieve the fine hole drilling, it is important to understand the mechanism of laser percussion drilling. In this paper, an experimental and numerical study on laser percussion drilling was carried out. A two-dimension (2D) axisymmetric finite element (FE) model for simulation of temperature field and proceeding of hole formation during percussion drilling was developed. The FE model was validated by the corresponding experiment. Furthermore, a theoretical model for evaluation of temperature at melt front and velocity of melt ejection was presented in order to further validate the FE model and study the spatter deposition. The effects of laser peak power, pulse duty cycle and pulse repetition rate on hole diameter and spatter deposition were investigated by the developed models and experiments, in which the simulated results were in good agreement with the experiments. The study indicated that the size and temperature of the melt front significantly affected the hole diameter formation and spatter deposition during laser percussion drilling. The characteristic of melt front was mainly determined by the employed laser peak power, pulse repetition rate and pulse duty cycle. Based on the experimental and numerical study, the process parameters were optimised and a drilled-hole with low taper and low spatter deposition was obtained using a 3.5 kW CO₂ laser. A microstructural and element compositional study was also performed in this work, by which the characteristics of microstructure and element composition in HAZ around laser drilled hole were revealed.     

Latest Researches Advances of Plasma Spraying: From Splat to Coating Formation

The plasma spray process with solid feedstock, mainly ceramics powders, studied since the sixties is now a mature technology. The plasma jet and particle in-flight characterizations are now well established. The use of computer-aided robot trajectory allows spraying on industrial parts with complex geometries. Works about splat formation have shown the importance of: the substrate preheating over the transition temperature to get rid of adsorbates and condensates, substrate chemistry, crystal structure and substrate temperature during the whole coating process. These studies showed that coating properties strongly depend on the splat formation and layering. The first part of this work deals with a summary of conventional plasma spraying key points. The second part presents the current knowledge in plasma spraying with liquid feedstock, technology developed for about two decades with suspensions of particles below micrometers or solutions of precursors that form particles a few micrometers sized through precipitation. Coatings are finely structured and even nanostructured with properties arousing the interest of researchers. However, the technology is by far more complex than the conventional ones. The main conclusions are that models should be developed further, plasma torches and injection setups adapted, and new measuring techniques to reliably characterize these small particles must be designed.     

薄板铝合金高功率CO2激光与光纤激光焊接飞溅特性对比分析

铝合金激光深熔焊接飞溅影响焊接稳定性并部分反映激光焊过程特性.对比研究了CO2及光纤激光焊接6061-T6铝合金的飞溅特性,探讨了两种激光焊飞溅特性差异的原因.借助高速摄像仪记录飞溅运动特性,收集并测量焊接飞溅,采用X2检验和最小二乘法拟合飞溅速度及尺寸分布.结果表明,两种激光焊飞溅速度均服从高斯分布,飞溅尺寸均呈对数正态分布,但光纤激光焊飞溅统计平均速度更大,表明光纤激光焊时更需注重聚焦系统保护;光纤激光焊飞溅统计平均直径更小,拟合结果更服从对数正态分布,表明光纤激光焊过程比CO2激光焊过程更稳定.     

自保护药芯焊丝飞溅的形成机理及其影响因素

详细研究了自保护药芯焊丝飞溅的形成机理及其影响因素.高速摄影观察表明,自保护药芯焊丝在焊接过程中的飞溅主要有以下三种形式,电弧力引起的大颗粒飞溅、气泡放出型飞溅和气体爆炸引起的飞溅.通过混料回归试验分析了药粉中氟化物、氧化物、碳酸盐、脱氧剂、合金元素对焊接飞溅的影响规律.结果表明,氟化物和碳酸盐对飞溅的影响较大,氧化物、脱氧剂和合金元素对飞溅的影响较小.     

润滑相尺寸对自润滑膜形成的影响

采用高能球磨制备细小的复合粉末,再通过感应烧结制备耐高温自润滑IS304涂层,涂层致密且润滑相明显细化,其中Ag粉尺寸为5μm左右、氟化物尺寸小于2μm,且氟化物粒子与Cr2O3粒子形成复合结构。室温时IS304摩擦系数较大,磨损机制主要为微观脆性断裂;随着温度的升高,由于润滑相尺寸减小、且氟化物粒子与Cr2O3粒子形成复合结构,使得摩擦副在高速滑动过程中接触点的瞬态温度迅速升高,此瞬态温度有效地激活了氟化物粒子的润滑性能,在摩擦力和压力的作用下,氟化物粒子经塑性变形后形成表面润滑膜,使得接触面的摩擦系数急剧减小。有限元计算也表明润滑相的细化和分布位置的改变可明显提高润滑相的瞬态温度。     

低C高Si高Mn合金高温氧化动力学及形貌特征分析

研究低C高Si高Mn钢氧化皮随温度的变化,对Fe2SiO4和基体外侧氧化物的分布、形貌进行观察。结果表明,850～960℃时Fe2SiO4在Fe1-xO层中呈颗粒状均匀分布,随着温度升高致密化,呈层状分布,1140℃时首次观察到Fe2SiO4呈岛状分布,1200℃时变成网状分布。基体中Si、Mn元素在850～960℃时先在晶界处氧化,形成网状氧化物,随着温度升高,氧化物在三角晶界处发生球化。     

Effect of REM addition of wire on CO2 gas shielded arc phenomenon

Carbon dioxide (CO₂) gas shielded arc welding is the main arc welding method, but it generates a large amount of spatter during welding. The root cause of spatter lies in the fact that the droplet undergoes repeated irregular shaking. To solve this problem, spatter generation modes were clarified and the effects of polarity and rare earth metal (REM) addition of the wire on CO₂ gas shielded arc welding were investigated. As a result, when welding is performed with an electrode negative (DCEN) polarity using REM added wire, it was found that a conical arc plasma is formed, and the droplet which is transferred from the wire tip to the molten pool is fine and continuous, in what is termed ‘spray transfer’. Thus, spatter generation was reduced to 10% of amount of the conventional CO₂ gas shielded arc welding (from 0.058 to 0.005g/s).     

Effect of substrate temperature on the splat formation of flame sprayed polypropylene

Polypropylene (PP) powder particles were thermally sprayed via a flame spray onto mild steel substrates at room temperature (RT), 70 °C , 120 °C, and 170 °C. Single solidified splats were collected from polished substrates. The splat morphology was characterized using optical microscopy and scanning electron microscopy (SEM). Micro-Raman spectroscopy examined the effect of substrate preheating on the molecular structure of the PP splats. The splat-substrate interface, porosity and a qualitative interpretation of the interface adhesion were obtained by cross-sectioning and imaging using the focused ion beam (FIB) technique.This study indicated that increasing the substrate temperature from room temperature to 170 °C produces PP splats of larger diameter that would be expected to exhibit improved adhesion. The influence of preheating dominates the splat formation and splat morphology. The Raman spectra indicate that the degree of crystallinity of the PP particles rises with increasing substrate temperature. Comparison of the spectra of the feedstock and the deposited PP particles confirms that there is no thermal degradation of the material under these processing conditions.This work demonstrates the influence of substrate chemistry on the PP splat morphology. Microstructural characteristics are related to the flame spray process variables for polymeric coatings.