Narrow Gap Welding Process Research Articles

Metallurgical and Mechanical Characterization of Pure Titanium Thick Welds Made Using Laser Narrow Gap Welding Process

Metallurgical and Mechanical Characterization of Pure Titanium Thick Welds Made Using Laser Narrow Gap Welding Process

Numerical Simulation of Constricted Sheet Tungsten Electrode Arc Characteristic with Insulating Solid Wall in Ultra Narrow Gap Welding Process

Numerical Simulation of Constricted Sheet Tungsten Electrode Arc Characteristic with Insulating Solid Wall in Ultra Narrow Gap Welding Process

Process stability and parameters optimization of narrow-gap laser vertical welding with hot wire for thick stainless steel in nuclear power plant

Incomplete fusion, pore and melt sagging are common defects for multi-layer narrow-gap laser welding with filler wire in vertical positions for large and heavy structures. This investigation showed that vertical-up laser welding had a lower sensitivity to pores than vertical-down welding, whereas increasing welding speed could improve welding stability and reduce the formation possibility of pores. For laser vertical welding with hot wire, surface tension transfer mode could effectively guarantee pre-heating of filler wire and achieve a stable welding process. The keyhole stability and melt flow varied with welding directions. The melt sagging defect was usually observed and mainly caused by the concentrated laser energy, which easily led to discontinuous weld bead. Laser beam oscillation technology increased laser melting area and promoted wetting behavior of filler wire with base metal. The weld width increased and concave weld metal surface was obtained with suitable process parameters. Narrow-gap welding process could be carried out at a small defocusing position with a lower laser power, further decreasing tendency of melt slagging. The 20-mm defect-free joint was obtained by vertical-up and vertical-down narrow-gap laser oscillation welding with hot wire.

Research on the seam tracking of narrow gap P-GMAW based on arc sound sensing

Arc sensor is important in the automation of narrow gap welding process because only the arc signal can reflect the position of the arc in the groove in real time, as well as the heat input to the side wall. Except the current and voltage of the arc, the deviation state of the welding arc can be identified by experienced welders by the associated arc sound, therefore, the arc sound signal presents a potential welding seam tracking signal. In this study, arc sounds were acquired and processed to examine the correlation with weld deviation during narrow gap pulsed gas metal arc welding (P-GMAW). The influences of groove sidewall on the arc sound signal and the sensitive of arc sound features to welding torch deviation were studied, and the short-time energy was determined as the best parameter to reflect the arc deviation in the narrow gap grooves. Furthermore, a system was established for seam tracking using the arc sound short-time energy and the results show that the arc sound can be used as the control signal to realize seam tracking to a certain degree of precision, thus, providing a new control signal for narrow gap P-GMAW welding seam tracking based on multi-information fusion.

Fatigue crack growth of 316NG austenitic stainless steel welds at 325 °C

316NG austenitic stainless steel is a commonly-used material for primary coolant pipes of pressurized water reactor systems. These pipes are usually joined together by automated narrow gap welding process. In this study, welds were prepared by narrow gap welding on 316NG austenitic stainless steel pipes, and its microstructure of the welds was characterized. Then, fatigue crack growth tests were conducted at 325 °C. Precipitates enriched with Mn and Si were found in the fusion zone. The fatigue crack path was out of plane and secondary cracks initiated from the precipitate/matrix interface. A moderate acceleration of crack growth was also observed at 325°Cair and water (DO = ∼10 ppb) with f = 2 Hz.

Numerical analysis of heat transfer and fluid flow in swing arc narrow gap GMA welding

A three-dimensional model is developed for swing arc narrow gap welding process considering the effect of moving trajectory of arc and joint geometric shape, which can calculate the temperature field and fluid flow in transient state. The arc heat source model also allows for the inclination of arc in the plane perpendicular to weld beam and the variation of the arc moving direction through coordinate system transformation, its distribution parameters being determined based the arc behavior captured by a high speed video system. The droplet heat transfer is assumed as the process of liquid metal with high temperature flowing into the weld pool from the certain area above it. The major forces acing on liquid molten pool, including arc pressure, arc plasma drag force, electromagnetic force, surface tension, Marangoni stress and buoyancy force are taken into account in this model. The characteristics of weld pool dynamic behavior and temperature profile are analyzed and the effect of different welding parameters on them is discussed. In swing arc narrow gap GMA welding, there exists a large vortex in the whole weld pool cross section and fluid flow pattern is beneficial to the growth of sidewall penetration depth. The width of high-temperature region outside weld pool is smaller than that of non-swing arc welding process. The arc swing frequency has minor influence on the cooling rate.

Characteristics of GMAW Narrow Gap Welding on the Armor Steel of Combat Vehicles

The primary purpose of this investigation was to study the characteristics of the armor steel weldment of combat vehicles by using GMAW narrow gap welding (NGW). The results showed that the mechanical properties and residual stress distribution of NGW weldment were improved, compared with conventional X-groove weldment. Additionally, ballistic tests according to MIL-HDBK-1941 were carried out to verify the ballistic ability of NGW weldment and the result showed that the NGW process was qualified for welding the armor steel of combat vehicle.

Development of narrow gap multi-layer welding process using oscillation laser beam

The oscillation laser beam is considered to be effective as a heat source of narrow gap multi-layer welding because oscillation laser welding can control the penetration shape and prevent the lack of fusion. In this study, in order to establish a narrow gap welding process by oscillation laser beam, butt welding experiments of 50 mm thickness carbon steel plate were performed. By the appropriate control of the heat input area using the in-process sensor for recognizing the groove shape, narrow gap welding of a thick plate with groove which was cut by gas cutting was achieved. Properties of the welded joint had been confirmed by nondestructive testing, tensile test and side bend test. A two-dimensional numerical calculation model for welding deformation was developed. This calculation model was used for investigation of the optimal groove angle. The results of calculations were in quantitative agreement with the experimental results. Microstructure of the weld zone had multiple thermal histories. According to the hardness test results, maximum hardness of the heat affected zone of the upper layer has been lowered than that of the lower layer.

Fundamental study of narrow-gap welding with oscillation laser beam

Laser welding with oscillation laser beams enables control of the heat input distribution. In this study, we attempted to develop a narrow-gap welding process with oscillation laser welding. This process is expected to prevent a lack of fusion because the entire bottom to the groove can be melted by the oscillation laser. As the first step of the study, bead-on-plate welding experiments with an oscillation laser beam were performed to investigate the relationship between the welding conditions and welding results. The experiments revealed that the oscillation conditions strongly affect the welding penetration shape. It was clarified that the wire melting phenomena in oscillation laser welding differed from those of straight (non-oscillation) laser welding. Additionally, narrow-gap laser welding experiments were performed to investigate the relationship between the oscillation conditions and gap width. The results confirmed the effectiveness of oscillation laser welding for narrow-gap welding.

Experimental Investigation of Wire Arrangements for Narrow-Gap Triple-Wire Gas Indirect Arc Welding

A new narrow-gap welding process is proposed by applying triple-wire gas indirect arc (TW-GIA). There are double power supplies and triple wires in this system. Power supplies are only connected between electrode wires and base materials are not linked to power supplies. Since there are different wire arrangements with TW-GIA, this article studies these wire arrangements and their effects on sidewall fusion for narrow-gap welding. Results show that different wire arrangements lead to variant arc behaviors and metal transfer, and consequently they lead to different situation of sidewall fusion. The heat to melt sidewalls is mainly from the indirect arc column and metal transfer with narrow-gap TW-GIA. When side wires deviate from the main wire to opposite directions, heat from arc columns and metal transfer can concentrate toward groove sidewalls. When the whole weld torch is lowered, heat from the indirect arc column and metal transfer increases at the weld bead root.

Influences of lumped passes on welding residual stress of a thick-walled nuclear rotor steel pipe by multipass narrow gap welding

The purpose of this study is to investigate the effect of the lumped passes simulation on the distribution of residual stresses before and after heat treatment in a thick-walled nuclear power rotor pipe with a 89-pass narrow gap welding process. The local removal blind hole method was used to measure internal residual stress of the thick-walled pipe after post weld heat treatment (PWHT). Based on the ANSYS software, a two-dimensional axisymmetric finite element model is employed. Two lumped-pass models of M-5th model (five weld beads as one lumped pass) and M-10th model (ten weld beads as one lumped pass) were developed to reduce computational cost. Based on the results in this study, the distributions of residual stresses of a thick-walled welded pipe before and after PWHT are developed. Meanwhile, the distribution of the through-wall axial residual stress along the weld center line is demonstrated to be a self-equilibrating type. In addition, the investigation results show that reasonable and reliable lumped-pass model can not only guarantee the accuracy of the simulated results, but also improve the computational efficiency in the thermo-elastic–plastic FE analysis procedure. Therefore, from the viewpoint of engineering application the developed lumped-pass computational procedure is a promising and useful method to predict residual stress of large and complex welded structures.

揺動レーザを用いた狭開先溶接に関する基礎的検討

Laser welding with oscillation laser beam enables control of the heat input distribution. In this study, we attempted to develop a narrow gap welding process with oscillation laser welding. This process is expected to prevent lack of fusion because the entire bottom of the groove can be melted by the oscillation laser. As the first step of the study, bead-on-plate welding experiments with an oscillation laser beam were performed to investigate the relationship between the welding conditions and welding results. The experiments revealed that the oscillation conditions strongly affect the welding penetration shape. It was clarified that the wire melting phenomena in oscillation laser welding differed from those of straight (non-oscillation) laser welding. Additionally, narrow gap laser welding experiments were performed to investigate the relationship between the oscillation conditions and gap width. The results confirmed the effectiveness of oscillation laser welding for narrow gap welding.

A Digital Control for Swinging Arc Narrow Gap MAG Welding System

This paper presents a digital control system for swinging arc narrow gap MAG welding based on double single-chip microcomputers. The control system utilizes a single-chip microcomputer to set and display welding process parameters, and then uses another single-chip microcomputer to realize the control functions that are necessary for the swing arc process, in which the two single-chip microcomputers can exchange data through asynchronous serial communication circuit. Experimental results show that the control system works stably and reliably with strong anti-interference capabilities, and can completely satisfy the requirements of swinging arc narrow gap welding process.

Numerical Simulation of Weld Metal by Ultra-Narrow Gap Arc Welding

The ultra narrow gap welding process is suitable to the thick plate, ultra-thick plate welding with the characteristic of highly effective, high quality, low cost, low energy consumption and so on, and is easy to realize the mechanization and the automation. In this paper, the numerical simulation and technical experiment are used to study the form, grow and distribution regulation of the welding temperature field, stress field in welding joint with UNG MAW. Using the calculation to the thickness of 32mm, an example to simulate the magnitude and distribution of the residual stress in welding joint is given. Research shows that it is an effective analysis method to heat process and mechanic behavior in the welding by using finite element method numerical simulation and few experiments. Keywords: UNG MAW, Welding residual stress, Finite element method, Numerical simulation

ANALYSIS OF RESIDUAL STRESS FOR NARROW GAP WELDING USING FINITE ELEMENT METHOD

Reactor coolant loop (RCL) pipes circulating the heat generated in a nuclear power plant consist of so large diameter pipes that the installation of these pipes is one of the major construction processes. Conventionally, a shield metal arc welding (SMAW) process has been mainly used in RCL piping installations, which sometimes caused severe deformations, dislocation of main equipments and various other complications due to excessive heat input in welding processes. Hence, automation of the work of welding is required and narrow-gap welding (NGW) process is being reviewed for new nuclear power plants as an alternative method of welding. In this study, transient heat transfer and thermo-elastic-plastic analyses have been performed for the residual stress distribution on the narrow gap weldment of RCL by finite element method under various conditions including surface heat flux and temperature dependent thermo-physical properties.

Effects of microstructure and residual stress on fatigue crack growth of stainless steel narrow gap welds

The effects of weld microstructure and residual stress distribution on the fatigue crack growth rate of stainless steel narrow gap welds were investigated. Stainless steel pipes were joined by the automated narrow gap welding process typical to nuclear piping systems. The weld fusion zone showed cellular–dendritic structures with ferrite islands in an austenitic matrix. Residual stress analysis showed large tensile stress in the inner-weld region and compressive stress in the middle of the weld. Tensile properties and the fatigue crack growth rate were measured along and across the weld thickness direction. Tensile tests showed higher strength in the weld fusion zone and the heat affected zone compared to the base metal. Within the weld fusion zone, strength was greater in the inner weld than outer weld region. Fatigue crack growth rates were several times greater in the inner weld than the outer weld region. The spatial variation of the mechanical properties is discussed in view of weld microstructure, especially dendrite orientation, and in view of the residual stress variation within the weld fusion zone. It is thought that the higher crack growth rate in the inner-weld region could be related to the large tensile residual stress despite the tortuous fatigue crack growth path.

The Study on Mechanical Properties in Narrow-Gap Welds for SA312 TP347

Conventionally, shielded-metal arc welding (SMAW) process has been applied to join pipes of reactor coolant loop, which caused defects and lot of loss in time and cost due to excessive heat input in joining section. Recently, narrow-gap welding (NGW) process was introduced to overcome the disadvantages of SMAW. However, the application of NGW to nuclear power plant is not yet commonly used, because safety of NGW process is not fully proven. In the present paper, welded coupons are made of stainless steel. They are manufactured under different processes; general welding (GW), and repair welding after GW. Performed are various mechanical tests to investigate microstructure, tensile strength and so on. It is verified that the mechanical properties of stainless steel are slightly changed after repair welding process. It is also found from stress corrosion cracking tests that the failure time of repair welding is shorter than that of general welding.

Evaluation of Mechanical Properties for Narrow-Gap Weld Zone in Reactor Coolant Loop

Conventionally, shield metal arc welding (SMAW) process was applied to join pipes of RCL, which caused lot of loss in time and cost due to excessive heat input and defects in joining section. Recently, narrow-gap welding (NGW) process was introduced to overcome the disadvantages of SMAW. However, the application of NGW to nuclear power plant is not yet common because safety of NGW process is not proven. In present paper, the welded coupons are manufactured under different welding processes in carbon steel. Then, microstructure observations and various mechanical tests are performed. It is verified that the mechanical properties of carbon steel are greatly changed after repair welding process due to applied heat flux, and that the effect of post-welding heat treatment is beneficial.

Optimization of residual welding stresses in austenitic steel piping: prooftesting and numerical simulation of welding and postwelding processes

The development/modification and qualification of welding technology for generating compressive stresses in austenitic stainless steel piping welds are discussed. The following welding processes are considered: 1. A modified, orbital gas tungsten arc (GTA) narrow-gap welding process with significant improvements over conventional and standard narrow-gap orbital pipe welding, 2. The heat sink welding (HSW) process with internal cooling of the pipe with water or liquefied CO 2 gas, and 3. The postwelding process. Last pass heat sink welding (LPHSW) for altering residual stresses in an existing weld. Residual stresses have been measured by using the so-called ring-core as well as radiographic procedures. In support of experimental work required to qualify these welding techniques a numerical simulation effort was undertaken.

Sensors for narrow-gap welding

Narrow-gap welding is an important technique for increasing productivity in the manufacture of thick-walled components. The nature of the process demands an automated approach and requires precise control to ensure consistently high weld quality. The work described in the paper gives the design, construction and development of appropriate sensors and sensing techniques for the control of the narrow-gap TIG welding (GTAW) process. Sensing systems based on arc-voltage sensing and direct vision sensing were developed and successfully tested on an experimental welding system. The arc-voltage sensing included the design of a digital technique for calculating the size of the voltage drop as the welding torch approaches a sidewall. The vision-based work involved the development of a very fast access framestore and highly optimised techniques for extracting the position of contrast features within a live image. The relative merits of arc-based and vision-based techniques are discussed.