低碳钢TIG焊电涡流传感熔透控制原理的研究

本文提出了一种用电涡流传感控制熔透的新方法。采用步进式ＴＩＧ焊，利用计算机控制，对薄反低碳钢平板堆焊的熔透控制进行了研究。研究结果表明：该方法能够实现对焊点焊接时间的实时控制，获得均匀稳定的焊缝成形。     

数值模拟在超级钢焊接中的应用

本文综述了超级钢焊接温度场的数值模拟方法及研究现状,以及超级钢焊接热影响区微观组织的预测方法及研究现状,论述了超级钢的强化机制及细晶原理。超级钢作为一种性能好、成本低的新型材料,有着广阔的应用前景,但其焊接工艺尚不完善。数值模拟方法能够准确的模拟超级钢焊接温度场,预测超级钢焊接热影响区微观组织,这对了解超级钢焊接机理有很大帮助,并为优化焊接工艺提供指导和依据。     

Relationship between base metal properties and friction stir welding process parameters

Friction stir welding (FSW) is a solid state welding process for joining aluminum alloys and has been employed in aerospace, rail, automotive and marine industries for joining aluminium, magnesium, zinc and copper alloys. In FSW, the base metal properties such as yield strength, ductility and hardness control the plastic flow of the material under the action of rotating non-consumable tool. The FSW process parameters such as tool rotational speed, welding speed, axial force, etc. play a major role in deciding the weld quality. In this investigation, an attempt has been made to establish relationship between the base material properties and FSW process parameters. FSW joints have been made using five different grades of aluminium alloys (AA1050, AA6061, AA2024, AA7039 and AA7075) using different combinations of process parameters. Macrostructural analysis has been done to check the weld quality (defective or defect free). Empirical relationships have been established between base metal properties and tool rotational speed and welding speed, respectively. The developed empirical relationships can be effectively used to predict the FSW process parameters to fabricate defect free welds.     

Study on the all position automatic pipeline backing weld machine

As a result of the lower backing weld efficiency, the applying of automatic welding is seriously limited. So a kind of special automatic welder is designed and manufactured for backing weld. This paper introduces the character of the assembled pulse MAG welding machine which has strong penetrability. It specifies the technology of controlling the parameters of all position automatic welding by computer and multi-axis controller. Moreover typical welding procedure parameters are provided. It is proved by examination that the economical and practical equipment and technology are suitable for the long-distance transmission pipeline, and it has a good foreground of spreading and applying.     

Adaptive mesh technique for thermal–metallurgical numerical simulation of arc welding processes

A major problem arising in finite element analysis of welding is the long computer times required for a complete three‐dimensional analysis. In this study, an adaptative strategy for coupled thermometallurgical analysis of welding is proposed and applied in order to provide accurate results in a minimum computer time. The anisotropic adaptation procedure is controlled by a directional error estimator based on local interpolation error and recovery of the second derivatives of different fields involved in the finite element calculation. The methodology is applied to the simulation of a gas–tungsten‐arc fusion line processed on a steel plate. The temperature field and the phase distributions during the welding process are analyzed by the FEM method showing the benefits of dynamic mesh adaptation. A significant increase in accuracy is obtained with a reduced computational effort. Copyright © 2007 John Wiley & Sons, Ltd.     

Control of submerged arc weld penetration by radiographic means

The application of real-time radiography for in-process weld quality evaluation is discussed. The advantages of this technique are on-line testing of weld penetration and the possibility of using this information for welding current control. The experimental system developed includes the arc welding unit, the welding manipulator, the real-time X-ray machine and the videorecording and computerized image processing units. In this system welding current can be remotely controlled during weld observation. The experimental results are demonstrated for the submerged arc welding process. In this process the welding pool is covered by a thick layer of welding flux and is therefore optically invisible. By using computer data on the grey levels of the weld images and their histogram distributions, the three-dimensional shape of the submerged arc pool can be recognized, image-digitized and analysed in real time at the rate of 30 frames per second. The depth of the welding pool which characterizes the weld penetration is a very important characteristic of the weld quality. This characteristic can be measured in real time and used for weld tracking and welding current control.     

水电站合拢焊缝残余应力的数值模拟

采用有限元方法，通过计算机对水电站合拢焊缝残余应力进行了数值模拟，并将其与实测结果进行了比较，两者基本上一致，证明该方法是一种经济而有效的焊接残余应力预测方法，可为制订焊接工艺时控制残余应力提供参考。     

强规范条件下CO_2焊飞溅产生机理的研究

本文采用自制的 CO_2焊电流波形微机控制系统、微机数据采集分析系统等先进手段,对强规范条件下的 CO_2焊飞溅生成机理等问题进行研究,得出了初步规律。实验研究分析结果表明,瞬间短路与再引燃时的电弧冲击是强规范条件下 CO_2焊飞溅的主要产生原因。研究还表明,在短路过渡开始瞬间及结束后瞬间施加电流负脉冲能明显减少 CO_2焊飞溅。     

Impact of welding research on steel composition development

A review has been made on development of technologies concerning welding and steel making and also on changes in requirements for structural integrity. The purpose is to understand how the development of welding technology has affected progress in steel making processes and especially that in chemical composition.     

Mathematical Modeling of Metal Active Gas (MAG) Arc Welding

In the present paper. a numerical model for MAG (metal active gas) arc welding of thin plate has been developed. In MAG arc welding, the electrode wire is melted and supplied into the molten pool intermittently. Accordingly, it is assumed on the modeling that the thermal energy enters the base-plates through two following mechanisms, i.e., direct heating from arc plasma and "indirect" heating from the deposited metal. In the second part of the paper, MAG arc welding process is numerically-analyzed by using the model. and the calculated weld bead dimension and surface profile have been compared with the experimental MAG welds on steel plate. As the result. it is made clear that the model is capable of predicting the bead profile of thin-plate MAG arc welding, including weld bead with undercutting.     

Study on Shear Test of New Style Automotive Structural Adhesive using Digital Image Correlation Method

In this paper, digital image correlation method (DICM) is employed to measure the shear behavior of the spot welding specimens and the ones using adhesive under quasi-static lap shear testing. The images of the specimens' surfaces are captured in real-time by CCD and corresponding computer system. DICM is subsequently used to obtained strain by correlating the images captured before and after deformation. Then, both force-displacement curves and stress-strain curves of the specimens including the cracking load are obtained. The results and analysis show that the mechanical properties of specimens using adhesive compared with the spot welding specimens have an obvious advantage. This paper provides some experimental basis for improving this new type of structural adhesive. In this experiment, the method of non-contact measurement was used to obtain the strain. It has greater significance.     

焊接双活塞环定位片工装的虚拟设计

置于发动机汽缸内的双活塞环,是一种可以提高发动机效率的新型节能装置,其设计思想简练、结构简单可靠.焊接活塞环上的定位片是保证该技术的重要工序,焊接工装设计是实现节能目标的关键.在工装设计中,应用计算机辅助设计手段,成功地实现了焊接工装的结构设计、装配、干涉检查和运动仿真、由三维模型向二维工程图的转换等工作.设计直观形象,准确可靠,提高了设计效率,降低了生产成本.     

焊接过程宏微观数值模拟与仿真的研究现状

焊接过程的数值模拟与仿真是研究焊接热过程、焊接电弧行为、焊接熔池、焊接应力与变形、焊接结构疲劳与脆断、焊接接头力学性能、焊接接头微观组织、界面形成机理,以及焊接缺陷分析等问题的基础。借助计算机辅助技术对于焊接现象进行模拟研究,可以解决试验和实际生产中诸多的困难问题,对焊接过程控制和工艺优化等具有重要的指导价值。通过对目前国内外焊接领域关于焊接过程宏微观的数值模拟与仿真研究现状的分析,描述了焊接数值模拟技术的主要发展方向,并指出了一些研究中的热点问题,旨在为相关领域的研究工作者提供有效的帮助,开拓新的研究思路。     

图像处理在自动焊接中的应用和展望

图像处理技术在自动焊接领域的应用已引起国内外学者的广泛重视。通过图像传感技术获取焊接熔池直观丰富的图像信息，使用高效的图像处理算法，提取焊接熔池的特征信息，用以实现自动焊接过程质量实时传感与控制。本文综合论述了图像处理技术在自动焊接中的应用原理、数字图像的采集方法、数字图像的特征信息定义、广义数字图像处理技术及其对自动化焊接理论研究和实践应用的推动作用。通过总结图像处理技术的研究和应用现状，综合分析了图像处理技术在现代焊接技术中发展和应用的前景。     

Comparisons between TiO2- and SiO2-flux assisted TIG welding processes

This study investigates the effects of flux compounds on the weld shape, ferrite content, and hardness profile in the tungsten inert gas (TIG) welding of 6 mm-thick austenitic 316 L stainless steel plates, using TiO2 and SiO2 powders as the activated fluxes. The metallurgical characterizations of weld metal produced with the oxide powders were evaluated using ferritoscope, optical microscopy, and Vickers microhardness test. Under the same welding parameters, the penetration capability of TIG welding with TiO2 and SiO2 fluxes was approximately 240% and 292%, respectively. A plasma column made with SiO2 flux exhibited greater constriction than that made with TiO2 flux. In addition, an anode root made with SiO2 flux exhibited more condensation than that made with TiO2 flux. Results indicate that energy density of SiO2-flux assisted TIG welding is higher than that of TiO2-flux assisted TIG welding.     

Comparative evaluation of tungsten inert gas and laser beam welding of AA5083-H321

In this study, the bead-on-plate welds were made on AA5083-H321 alloy plates using both tungsten inert gas (TIG) welding and laser beam (LB) welding processes to study the enhancement of mechanical properties such as weld yield strength and hardness. The low heat input of laser beam welding effectively reduced the size of the fusion zone and heat affected zone compared to tungsten inert gas welding process. High speed LB welding and fast heating and cooling of LB welding process hinders grain growth compared to TIG welding process. The effect of vapourization of volatile alloying elements is also considered. It seems that magnesium evaporation is relatively less in LB welding compared to TIG welding. Tensile testing of the welded joints revealed that LB welding results in superior mechanical properties. It is concluded that LB welding process is more suitable to join AA5083-H321.     

Continuous Drive Friction Welding Studies on AISI 304 Austenitic Stainless Steel Welds

An attempt has been made to study the friction welding characteristics of an austenitic stainless steel AISI 304 employing a continuous drive friction welding machine. The central region in some of the welds exhibited abnormal grain growth. Optimization studies revealed that the optimum parameters depend on the property of interest. In general, friction welds exhibited lower notch tensile strength and impact toughness than the parent metal due to aligned microstructure features. An inverse relationship has been observed between notch tensile strength and impact toughness.     

Single-sided laser beam welding of a dissimilar AA2024–AA7050 T-joint

In the aircraft industry double-sided laser beam welding of skin–stringer joints is an approved method for producing defect-free welds. But due to limited accessibility – as for the welding of skin–clip joints – the applicability of this method is limited. Therefore single-sided laser beam welding of T-joints becomes necessary. This also implies a reduction of the manufacturing effort. However, the main obstacle for the use of single-sided welding of T-joints is the occurrence of weld defects. An additional complexity represents the combination of dissimilar and hard-to-weld aluminium alloys – like Al–Cu and Al–Zn alloys. These alloys offer a high strength-to-density ratio, but are also associated with distinct weldability problems especially for fusion welding techniques like laser beam welding. The present study demonstrates how to overcome the weldability problems during single-sided laser beam welding of a dissimilar T-joint made of AA2024 and AA7050. For this purpose a high-power fibre laser with a large beam diameter is used. Important welding parameters are identified and adjusted for achieving defect-free welds. The obtained joints are compared to double-sided welded joints made of typical aircraft aluminium alloys. In this regard single-sided welded joints showed the expected differing weld seam appearance, but comparable mechanical properties.     

Fatigue Strength Assessment of Laser Beam Welded Joints Made of AA7075 and Magnetic Pulse Welded Joints Made of AA7075 and 3D-Printed AlSi10Mg

The use of 7000 aluminum alloys has an important role in future lightweight structures in the field of mobility due to the low density and high strength. However, these alloys can only be fusion welded to a limited extent because welding defects can rarely be prevented. For this reason, investigations are carried out to identify the most suitable welding parameters for two processes: laser beam and magnetic pulse welding. Herein, laser beam welding is successfully used to manufacture a roll-formed and longitudinally welded pipe made of AA7075 and joined by magnetic pulse welding with a 3D-printed lug-tube made of AlSi10Mg. The fatigue strength of these pipe joints and of laser beam welded butt joint specimens is determined using load-controlled fatigue tests. For the characterization of the specimens, cross sections are prepared and examined metallographically, which reflect the local weld seam geometry in the joining area. A fatigue assessment is made using linear-elastic approaches. The reference radius concept is applied to map the influence of geometric notches on the fatigue strength, assuming linear-elastic stress–strain behavior. It is shown that the recommended notch stress fatigue class FAT 178 (von Mises stress) can be applied for a safe and reliable fatigue assessment.     

Nickel based hardfacing alloys for high temperature applications

Abstract

Conventional nickel based hardfacing alloys deposited by arc welding usually have a nominally single phase microstructure and derive their hot strength primarily from solid solution strengthening. The present work is an attempt at designing improved alloys containing large volume fractions of ordered precipitates or intermetallic compounds. The alloy design has been carried out using a computer model capable of estimating microstructure and strength as a function of many variables. The results are tested experimentally against cast samples which simulate welding conditions during manual metal arc welding.

MST/1035