Showing papers on "Welding published in 1997"

Duplex stainless steels : microstructure, properties and applications

Abstract: Developments, grades and specifications Alloy design Microstructure Forming and machining Physical and mechanical properties Corrosion Stress corrosion cracking Welding metallurgy Welding processes Weld properties Non-destructive testing of welds Applications Service experience.

Thermal plasmas

Abstract: Although many thermal plasma processes have been developed for industrial applications, the wide acceptance as a manufacturing technology is prevented due to economical and competitive reasons, and/or reproducibility and reliability aspects. This paper is devoted to an assessment of the present knowledge in the following topics: (1) plasma torch and performance of blown arc (dc or ac), transferred arc and radio frequency torches; (2) established industrial applications with special emphasis on cutting, welding, spraying, transferred arc reclamation, reheating and purification, reheating metal melts, smelting reduction, chemical operations, and waste destruction; (3) recent developments in the knowledge of fundamental processes in plasma torches with power sources, cathodes (hot and cold), anodes (static and dynamic behavior), and torch components; (4) modeling-thermodynamic and transport properties, plasma flow with and without the Maxwell's equations; (5) measurement techniques including emission and absorption spectroscopy, laser scattering, enthalpy probes, video cameras, spectral analysis, shadowgraphy, and particle diagnostics either in flight with statistical measurements and those giving characteristics of a single particle upon flattening on a substrate; and (6) plasma-processing development in the presently used industrial processes and also in prospective processes with surface hardening, ultrafine powder production, plasma-assisted CVD, and plasma-fluidized or spouted bed reactors.

Prediction of welding distortion

Abstract: This paper presents a numerical analysis technique for predicting welding-induced distortion. The technique combines two-dimensional welding simulations with three-dimensional structural analyses in a decoupled approach. The numerical technique is particularized on evaluating welding-induced buckling. The numerical predictions can be utilized either as a design evaluation or manufacturing analysis tool. As a design tool, the effect of the welding procedures can be determined and incorporated into the evaluation and optimization of the design configurations. As a manufacturing analysis tool, for a fixed design, different welding processes and procedures can be evaluated to minimize welding distortion. Experimental results obtained from small- and large-scale mock-up panels verify the numerical modeling approach.

Fracture toughness of type 304 and 316 stainless steels and their welds

Abstract: Fracture toughness data for type 304 and 316 stainless steels and their welds are reviewed. The material and operational parameters evaluated in this paper include: heat to heat variability; weld process variations; welding induced, heat affected zones; crack orientation; cold work; monotonic and cyclic prestrain; long term thermal aging; neutron irradiation; temperature; and loading rates. Statistical analyses of literature data are provided to establish minimum expected fracture toughness values for use in fracture mechanics design evaluations. Guidance is also provided concerning the potential for component failure and when fracture mechanics assessments are required to guard against unstable fracture. Macroscopic fracture toughness properties are correlated with key microstructural features and operative fracture mechanisms.

An analytical thermodynamic model of laser welding

Abstract: An earlier model of deep-penetration laser welding has been simplified in order to provide a useful model of process analysis. This work involves the modelling of the various energy-absorption mechanisms which determine the keyhole shape and thus the dimensions of the melt pool. The penetration depth and weld width (top and bottom) predicted by the model are shown to be in close agreement with experimental results. The widening of the top of the weld seam as a result of Marangoni flow is accurately modelled by introducing an artificially enhanced value for the workpiece's thermal conductivity towards the top of the weld. The model allows analysis of the dependence of the weld profile on the process parameters.

Auto-adjustable pin tool for friction stir welding

Abstract: An auto-adjusting pin tool for friction stir welding is presented wherein the pin tool automatically adjusts for welding materials of varying thicknesses, and the pin can be incrementally withdrawn from the workpieces thus eliminating any crater or keyhole in the weld. The inventive apparatus is comprised of a welding head housing a motor connected to a controller instrument package and an arbor supported by bearings. The arbor forms an interior cylinder and is encircled by a stationary slip ring though which are ported hydraulic passageways into the interior cylinder of the arbor such that a piston housed therein may be moved axially. Coupled to the piston is a pin tool which is treaded on its lower end and which is moveably seated in, and extending through, a shoulder housing having concave lower face. When welding, the rotating treaded end of the pin enters and stirs the workpieces while the lower face of the shoulder housing compacts the workpieces. As the welding head traverses the shoulder housing the controller senses any rising pressure on the lower face of the shoulder housing and withdraws the arbor to keep the pressure constant. At the same time, the piston moves towards the workpieces thus extending the pin further from the shoulder. This keeps the pin at a proper depth in the workpieces regardless of their thicknesses. As the weld terminates this same operation can be used to incrementally withdraw the pin during the final part of the traverse, thus eliminating any keyhole or crater that would otherwise be created.

Spectroscopic characterization of laser-induced plasma created during welding with a pulsed Nd:YAG laser

Abstract: A spectroscopic study of a laser-induced plume created during the welding of stainless steel and other materials (iron and chromium) has been carried out A pulsed Nd:YAG laser of 1000 W average power is used The evolutions of the electron temperature and electron density have been studied for several welding parameters We use working powers from 300 to 900 W and pulse durations between 15 and 5 ms The influence of shielding gases like nitrogen and argon has been taken into account Temperature and density calculations are based on the observation of the relative intensities and shapes of the emission peaks We assume that the plasma is in local thermal equilibrium The temperature is calculated with the Boltzmann plot method and the density with the Stark broadening of an iron line The electron temperatures vary in the range of 4500–7100 K, electron density between 3×1022 and 65×1022 m−3 The absorption of the laser beam in the plasma is calculated using the Inverse Bremsstrahlung theory

Weld microstructure refinement in a 1441 grade aluminium-lithium alloy

Abstract: Clad 2 mm thick sheets of Russian 1441 grade Al-Li alloys were welded using a gas tungsten arc welding process (GTAW). Comparisons were made between the weld beads obtained under (i) continuous current (CC), (ii) pulsed current (PC), and (iii) arc oscillation (AO) conditions for their macro- and microstructural details. In the case of CC GTAW, sound welds could be produced only under a narrow range of welding parameters. Centre line cracks, which occurred in CC GTAW welds under certain conditions, were halted by switching to PC or AO conditions while the welding was in progress. Microstructural refinement was significant in the case of PC and AO GTA welding.

Mobile automated pipeline welding and quality control system

Abstract: A mobile automated pipeline welding and quality control system comprising a gas metal arc welding carriage and a weld data monitor and acquisition unit The welding carriage carries a welding torch, wire feed device for feeding consumable wire to the torch, an oscillator for oscillating the torch and a motorized drive mechanism for moving the carriage about a weldment A controller for the carriage includes digital control circuitry for dosed loop control of the drive, oscillator and wire feed devices By default, the controller operates each device at one of a plurality of pre-programmed nominal speeds selected from a mode table The controller is responsive to drive, oscillation and wire feed speed variation signals under the control of an operator, and varies the speed of each device within speed ranges which are selected to ensure compliance with welding specifications The monitor has voltage and current transducers for measuring current and voltage at the welding torch The controller supplies the monitor with speed data relating to the drive, oscillator and wire feed devices All of this information can be displayed and recorded in the monitors memory In addition, the monitor can compute and display the heat input into the weld based on the detected welding parameters This information allows the operator to make minute adjustments during the welding process to ensure that a weld falls within specifications

Panel structure, a friction welding method, and a panel

Abstract: This invention provides a configuration of a joint that allows a satisfactory welded joint to be formed with reduced deformation of the joint region when two-face structures (panels) are friction-welded end to ends The panels 31, 32 each have two substantially parallel plates 33, 34 and a third member 35 connecting the two plates 33, 34. The end portions of the plates 33, 34 of one panel 32 are friction-welded to the end portions of the plates 33, 34 of the other panel 32. At least one of the panels has a plate 36 at its end for connecting the plates 33 and 34 and has a rigidity to support a pressing force produced during the friction welding.

Adhesives in engineering

Abstract: When considering methods for joining materials, there are many advantages that engineering adhesives can offer, compared to the more traditional methods of joining such as bolting, brazing, welding...

Joining of nickel base superalloy single crystals

Abstract: The welding and weldability characteristics of single crystal nickel base superalloy PWA 1480 were investigated over a range of welding conditions and orientations using electron beam and laser welding processes. Using differential thermal analysis, the freezing range for this alloy was established and the formation of the γ/γ′ eutectic during the last stages of solidification was identified. Both electron beam and laser welds showed extensive fusion zone cracking, and the cracks were identified as solidification cracks, i.e. hot cracks. Crack free welds could be made over a very narrow range of welding conditions with preheat. Most of the microstructural features observed in the weld are similar to those previously observed in Fe–Ni–Cr alloy single crystal welds. The welds contain misoriented stray grains which playa critical role in the promotion of hot cracks in the welds. The origin of these grains is explained in terms of constitutional supercooling and the growth conditions. Detailed atom pr...

Fused loop filamentous material

Abstract: A fused loop of an elongated material, such as a surgical suture, and apparatus for making the loop. Portions of one or more segments to be joined together are fused in a welding process to form a welded joint. The shear area of the fused portion of the joint determines the strength of the joint and is thus preferably relatively large. Various configurations for the welding apparatus facilitate the creation of relatively large fused portions of the joint by maximizing contact between at least one of the welding members of the apparatus and at least one of the segments to be joined.

Metallurgy of Basic Weld Metal

Abstract: Experimental techniques. Part 1 C-Mn weld metals: Manganese and carbon Effects of welding process variables Effects of heat treatment Silicon and impurities Nitrogen and strain ageing. Part 2 Low alloy steel weld metals: Single additions: with varying manganese Elements in combination i?½ Cr-Mo. Part 3 High purity weld metal: Titanium Combinations with oxygen Combinations with nitrogen. Part 4 Microalloying of C-Mn steel weld metals: Single microaolloying elements (with and without titanium) Combinations of microalloying elements. Part 5 Microalloying of high purity low alloy steel weld metals: Titaniumm and single additions of Cr, Mo, Ni and Cu Titanium and multiple alloying elements: Mn-Ni-Mo weld metals. Part 6 Metallography: Metallographic features.

Mathematical modeling of three-dimensional heat and fluid flow in a moving gas metal arc weld pool

Abstract: Mathematical models capable of accurate prediction of the weld bead and weld pool geometry in gas metal arc (GMA) welding processes would be valuable for rapid development of welding procedures and empirical equations for control algorithms in automated welding applications. This article introduces a three-dimensional (3-D) model for heat and fluid flow in a moving GMA weld pool. The model takes the mass, momentum, and heat transfer of filler metal droplets into consideration and quantitatively analyzes their effects on the weld bead shape and weld pool geometry. The algorithm for calculating the weld reinforcement and weld pool surface deformation has been proved to be effective. Difficulties associated with the irregular shape of the weld bead and weld pool surface have been successfully overcome by adopting a boundary-fitted nonorthogonal coordinate system. It is found that the size and profile of the weld pool are strongly influenced by the volume of molten wire, impact of droplets, and heat content of droplets. Good agreement is demonstrated between predicted weld dimensions and experimently measured ones for bead-on-plate GMA welds on mild steel plate.

Welding of nickel-base superalloys having a nil-ductility range

Abstract: An article made of a nickel-base superalloy having a nil-ductility range from the solidus temperature of the alloy to about 600° F. below the solidus temperature is welded, as for example in the weld repair of surface cracks, by removing foreign matter from the area to be welded, first stress relieving the article, adjusting the temperature of the article to a welding temperature of from about 1800° F. to about 2100° F., welding a preselected area in an inert atmosphere at the welding temperature, and second stress relieving the article. Welding is preferably accomplished by striking an arc in the preselected area so as to locally melt the alloy in the preselected area, providing a filler metal having the same composition as the nickel-based superalloy of the article, and feeding the filler metal into the arc so that the filler metal is melted and fused with the article to form a weldment upon solidification.

Friction stir welding with simultaneous cooling

Abstract: A method and apparatus for friction stir welding that produces a weld of significantly reduced surface roughness at significantly higher welding rates, in materials that are difficult to weld, such as non-extrudable aluminum alloys. The method includes cooling the stir welding tool during the welding process, thereby reducing the tendency of softened metal to adhere to the rotating pin and shoulder of the tool. The apparatus includes a tool with internal spaces or an external jacket, through which coolant can be pumped to remove heat and cool the tool during welding operations. In another embodiment, the apparatus includes a device for spraying a coolant onto exterior surfaces of the distal end of the welding tool to thereby remove heat from the tool, and the surrounding workpiece, during welding.

Analysis and Optimum Design of Metal Structures

Abstract: Detailing a number of structural analysis problems such as residual welding stresses and distortions and behaviour of thin-walled rods loaded in bending, this text also explores mathematical function minimization methods, expert systems and optimum design of welded box beams.

A mathematical model for penetration laser welding as a free-boundary problem

Abstract: A detailed model is constructed in order to determine the full 3D weld pool and keyhole geometry by setting the appropriate energy and pressure balances. The energy balance takes into account heat conduction, ablation losses and evaporation effects at the keyhole open surfaces, as well as the most relevant energy-absorption mechanisms, namely Fresnel and inverse Bremsstrahlung. The pressure balance ensures mechanical stability of the keyhole by including ablation pressure against surface tension pressure. The model provides a full description of the temperature field, electronic density, degree of ionization and absorption coefficient within the plasma, as well as setting the maximum penetration depth for a given set of laser parameters such as power, focusing radius and oscillation transversal mode. The keyhole boundary is initially taken to be an unknown free boundary and is obtained as a part of the solution of the problem. For low and medium welding speeds this boundary is successfully described with a family of ovoids. Good agreement with experimental results is achieved for a wide range of laser powers and plate thicknesses.

Effect of various driving forces on heat and mass transfer in arc welding

Abstract: In this study the heat transfer and fluid flow of the molten pool in stationary gas tungsten arc welding using argon shielding gas were investigated. Transporting phenomena from the welding arc to the base material surface, such as current density, heat flux, arc pressure, and shear stress acting on the weld pool surface, were taken from the simulation results of the corresponding welding arc. Various driving forces for the weld pool convection were considered: self-induced electromagnetic, surface tension, buoyancy, and impinging plasma arc forces. Furthermore, the effect of surface depression due to the arc pressure acting on the molten pool surface was considered. Because the fusion boundary has a curved and unknown shape during welding, a boundary-fitted coordinate system was adopted to precisely describe the boundary for the momentum equation. The numerical model was applied to AISI304 stainless steel and compared with the experimental results.

Portable welding unit

Abstract: A portable welding unit (10) comprises a housing (12) containing a first battery (34) and a second battery (35) connected in series. Each of the batteries (34, 35) is a sealed non-spillable battery and has a positive terminal and a negative terminal. The welding unit has a first clamp (14) electrically connected to the positive terminal of the first sealed, non-spillable battery (34). The first clamp (14) extends outside the housing (12) and is adapted to be connected to the negative terminal of the second sealed, non-spillable battery (35). The welding gun (17) extends outside the housing (12). A wire feed mechanism is located in the housing (12) and is connected to the battery (34) for extending wire through the welding gun (17). A spool of consumable electrode wire is rotatably connected to the housing (12). This wire is supplied to the welding gun (17) via the wire feed mechanism.

Laser Materials Processing

Abstract: Theory of laser operation propagation of laser light considerations for real-world laser beams laser-material interactions safety cutting welding heat treatment laser weld overlay excimers.