高压液氨装置用大型锻件的焊接修复

介绍了大型锻件的焊接修复工艺的制订以及焊后热处理,通过两年的运行表明,该焊接工艺可靠安全。     

Numerical analysis of welding residual stress using heat source models for the multi-pass weldment

Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the development or refinement of welded product designs. Various researchers have studied several thermal models associated with the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated. These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared. Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results in reasonable agreement with the experimental data.     

Improving the service properties of metal structures working in the conditions of low climatic temperatures by methods of adaptive pulsed-arc welding

Experimental results confirm that the application of adaptive pulsed-arc welding with regulated heat input to welded material refines the structure of the metal, lowers the degree of softening of the fusion zone of the welded joint and greatly increases the mechanical properties of the welded joints, including structures working at low temperatures.     

Lower limit law of welding windows for explosive welding of dissimilar metals

The influence of explosive charge thickness on the quality of explosive welding of dissimilar metals was in-vestigated.The lower limit law should be followed in the course of explosive welding.Three welding ex-periments of stainless steel (410S) and steel (Q345R) were carried out in three different kinds of explo-sive charge thicknesses, namely 15, 25 and 35 mm.Interfaces of morphology and mechanical properties of three samples were observed and tested.It was found that micro and small wavy bonding is mainly formed for charge thickness of 15 mm whose strength is the highest with minor deformation and few defects in the interface; small and middle wavy bonding are mainly formed for charge thickness of 25 mm whose strength is comparatively mediocre; big wavy bonding is mainly formed for charge thickness of 35 mm whose strength is the lowest.The cause of high bonding strength of the micro and small wavy interface was analyzed and verified on the basis of the results of Electron Probe Micro-Analyzer (EPMA) tests of three selected samples.     

Development and comparison of residual stress measurement on welds by various methods

Abstract

Residual stress constitutes an integral part of the total stress acting on any component in service. It is imperative to determine residual stress to estimate the life of critical engineering components, especially those that are welded. The stresses caused by non-uniform temperature distribution due to welding and the effect of these multiaxial stresses upon service performance are discussed. A controlled thermal severity test (CTS) was performed on mild steel plates bolted together, with anchor welds deposited on opposite sides. After cooling, bithermal and trithermal test welds were deposited one after the other. Varying welding stresses were deliberately introduced by using different thicknesses of both plates to change the thermal severity numbers (TSN). The main experimental technique used here to determine the magnitude and nature of residual stress is based on X-ray diffraction (XRD). It was utilised to develop and standardise other techniques. The XRD method is based on the peak shiftin the diffraction profile due to the presence of stress using a sin² ψ method. The peak shift is determined by orienting the sample at different angles ± ψ to the incident X-ray beam. The semidestructive technique of hole drilling and use of a strain gauge was also employed to determine residual stress in CTS specimens. The magnitude, nature, and direction of principal stresses were determined by relieving stresses through incremental blind hole drilling and measuring strain values at each step. The surface displacements arising due to hole drilling can also be determined by laser holography. A sandwich holography technique was developed to avoid unwanted rigid body motions of samples due to hole drilling when relieving stresses. Stress values were obtained by measuring fringe displacement between two exposures of a sandwich hologram, due to hole drilling. Results on the change in residual stress values with TSN are discussed. The residual stress values determined by XRD and sandwich holography were found to be comparable, and stress values obtained by hole drilling/strain gauge measurement were higher than these values. The reasons are discussed.     

Development of a new hybrid plasma torch for materials processing

The main objectives of this study were to construct a plasma generator device and to investigate its applications in welding, cutting, and surface hardening. The device was derived from the union of two plasma-generating technologies, non-transferred-arc plasma and magnetoplasmadynamic thruster (MPDT), and characterised by the simultaneous formation of two plasma arcs in one device, generating a plasma jet with high energy density. Initially, trials were conducted to analyse the influence of the physical variables (gas flow rate and electric current intensities – primary and secondary) on the plasma jet, for which the thruster and the length of the plasma jet expulsed from the chamber were determined. The relevant parameters for welding, cutting and surface hardening were determined by trial and error, in which the trials were conducted using various plate thicknesses and materials. The results have shown that this device can be used for welding, cutting and surface hardening.     

Exploiting robotic link deflection for low-cost force measurement in manufacturing

A custom, low-cost force measurement system for manufacturing is presented that exploits robotic link deflection for measurement purposes instead of utilizing a commercially purchased load cell. Force measurement can be an important aspect to many manufacturing processes, as it can allow for force feedback control or other process-planning related operations, such as tool-workpiece autozero or through-the-tool joint tracking. This system is demonstrated on a machine that is used for Friction Stir Welding research, and a Finite Element Analysis is also conducted on the robotic link that is used for axial force measurement purposes. This system may be particularly attractive to small businesses or low-volume manufacturers whose smaller operating budgets may normally prohibit them from implementing force measurement systems.     

Comprehensive study on hydrogen induced cracking of electrical resistance welded API X52 pipeline steel

Different heat treatment cycles were designed in order to investigate the effect of microstructural changes on hydrogen induced cracking resistance (HIC) and mechanical properties of the electric resistance welded steel. The heat treating of the as-welded specimen improved the ductility and impact toughness. After heat treatment, the uniform hardness profile was obtained for the welded specimens. The removal of local hard zones reduced the risk of HIC. The chemical composition and clustering of inclusions have a deleterious effect on cracking resistance in the H₂S environment. Aluminosilicate compounds and MnS inclusions were favorite sites for HIC. The most promising post weld heat treatment for improving mechanical properties and the resistance to HIC was the application of two-cycle quenching followed by tempering.     

A Review on Dissimilar Friction Stir Welding of Copper to Aluminum: Process,Properties, and Variants

Copper and aluminum materials are extensively used in different industries because of its great conductivities and corrosion resistant nature. It is important to join dissimilar materials such as copper and aluminum to permit maximum use of the special properties of both the materials. The joining of dissimilar materials is one of the most advanced topics, which researchers have found from last few years. Friction stir welding (FSW) technology is feasible to join dissimilar materials because of its solid state nature. Present article provides a comprehensive insight on dissimilar copper to aluminum materials joined by FSW technology. FSW parameters such as tool design, tool pin offset, rotational speed, welding speed, tool tilt angle, and position of workpiece material in fixture for dissimilar Cu–Al system are summarized in the present review article. Additionally, welding defects, microstructure, and intermetallic compound generation for Cu–Al FSW system have been also discussed in this article. Furthermore, the new developments and future scope of dissimilar Cu–Al FSW system have been addressed.