Welding In Order Research Articles

Investigations on the multiple-sector hard-copper X-band accelerating structures

The development of advanced, high gradient accelerating structures is one of the leading activity of the particle accelerator community. In the technological research of new construction methods for these devices, high-power testing is a critical step for the verification of their viability.Recent experiments showed that accelerating cavities made out of hard copper, fabricated without high-temperature processes, can achieve better performance as compared with soft copper ones. Recently, we have built cavities using Tungsten Inert Gas welding and the high-power experiments confirmed that this joining process is a robust and low-cost alternative to brazing or diffusion bonding. This is a good solution for high-gradient operation, with a gradient of about 150 MV/m in X-band, at a breakdown rate of 10−3/pulse/meter using a shaped RF pulse with a 150 ns flat part.We continue the design, construction and high power tests of three-cells standing-wave X-band accelerating cavities fabricated with a split-open geometry, made of hard copper and vacuum-sealed by welding. Our aim is the fabrication of accelerating structures made out of hard copper alloys by using innovative cost-effective technologies. Moreover, our method of multiple-sector structures opens the way to new technological approaches and design methods, for example providing the possibility of placing dampers of the parasitic higher-order modes. Such structures with dampers allow for acceleration of multi-bunch beams, both in standing and in travelling-wave accelerating modality.This paper describes the design of two cavities made of multiple sectors that were fabricated at the Italian Institute for Nuclear Physics in Frascati, Italy (INFN-LNF), assembled by means of clamping and then joined with the Tungsten Inert Gas welding in order to preserve the hardness of the metal. These are three-cell standing-wave X-band accelerating cavities, to be operated in the π-mode. We report the low-power RF tests of the first one, made of two halves, and the RF design of the second one, made of four quadrants. Both structures were built for high-gradient tests at SLAC National Accelerator Laboratory.

The short- and long-term properties of welded high-temperature-resistant thermoplastics

AbstractHigh-performance plastics, such as polyphenylene sulfide or polyphthalamide, are increasingly being used in highly stressed areas, primarily due to their outstanding thermal and mechanical properties. Due to the increasing demands on plastic components in terms of geometry, functional integration, etc., components produced by primary molding often have to be welded in an additional process step. Furthermore, there are often restrictions with regard to component cleanliness, which is why converting, non-contact welding processes are of great industrial interest. However, as a result of the changeover-step in these processes, the previously plasticized areas cool down. For materials with high melt temperatures this circumstance can lead to inadequate weld seam qualities.The aim of the investigations was therefore to expand the understanding of the process of welding high-temperature-resistant plastics, to identify optimum welding parameters and to determine the mechanical short- and long-term properties of the welds. Furthermore, a comparison was made between the changeover welding processes and single-stage vibration welding in order to clarify the relevance of short changeover times.It could be shown that a significant correlation exists between the changeover time, the melting temperature and the resulting weld strength. Furthermore, the selection of the welding process and thus the type of heat input seems to have an influence on the long-term properties of the welds at high test temperatures.

Effect of low frequency vibration-assisted shielded metal arc welding on the properties of mild steel

Vibration-assisted welding (VAW) has emerged to be a feasible alternative to thermal and post-weld vibration treatments for arc welds in order to minimize stress concentrations and distortions thereby improving mechanical characteristics. Limited research is available considering low frequency vibration. The main objective is to develop an experimental setup to analyze the properties of welded connections made with shielded metal arc welding (SMAW) using low-frequency mechanical vibrations. Mild steel (MS) plates with dimensions of 100 mm by 50 mm and thickness of 5 mm are considered in this study. Heat inputs of 80 Amps, 100 Amps and 120 Amps were taken into consideration as input current. Vibration was varied between 0 and 100 Hz at every 20 Hz interval to study the Hardness, Tensile Strength and Impact Strength of welded joints. Microstructure of welded MS plates has been analyzed using SEM analysis. Experimental results revealed improved mechanical properties due to the application of low-frequency vibrations that may tend to increase the welding speed thus reducing time and enabling stronger, durable and reliable welded joints. A fine grain structure is seen for Low-frequency vibration-assisted welded butt joints implying improved mechanical properties due to excitation of weld pool.

Mechanical behavior of AA5083/AA6061 friction stir welds using modal analysis

Abstract Solid-state joining is used for welding similar or dissimilar materials due to its many advantages like avoiding fusion and formation of a thick intermetallic layer, etc. Determination of the right process parameters (feed rate and rotation speed) and tool geometry (shoulder and pin) is of critical importance in friction stir welding in order to achieve adequate weld quality. The experiments were performed using three process parameters: feed rate (mm min−1), rotation speed (rpm) and pin geometry for friction stir welding of Al5083 and Al6061. Eighteen experiments were performed with different process parameters and mechanical tests (microhardness and tensile measurements) have been carried out to determine the weld quality. Results showed that the best results of ultimate strength (198.5 MPa) were achieved by the triangle pin geometry, 1250 rpm rotation speed and 100 mm min−1 feed rate. Similar results were observed in microhardness tests. Effects of tool geometry, feed rate, and rotation speed on the vibration properties and weld quality are also investigated experimentally. The effects of the FSW parameters used were assessed using vibration analysis.

Structural Behaviour of Castellated Beam: A Review

The use of castellated beams has gained popularity due to their excellent performance in terms of strength, stiffness, and economy. Castellated beams are fabricated by cutting I-sections or H-sections along the web in the desired shape and re-joining the two halves on one another through welding in order to improve the beam's overall depth. Most often, hexagonal, circular, diamond, and sinusoidal shapes are used for the web opening. This pattern increases the surface area and reduces the weight of the beam without compromising its structural integrity. The idea incorporates the technique of offering the best section in accordance with the most essential need. This paper presents an overview of the behavior of castellated steel beams with several shape openings having an I-shaped cross-section, modeling is conducted using the finite element software package ANSYS14 and ABAQUS. With uniform distributed load and simply support conditions, an analysis is conducted. The investigation of various failure patterns and the deflection at the middle of the beam are done

Dissimilar metal welding of S690 QL with DOCOL 1400 M steel for the structures of various means of transport

Purpose: The novelty and the aim of the article is to check the possibility of dissimilar welding of two grades of steel with significantly different properties. Design/methodology/approach: Two various materials have been checked in welding in order to obtain a high-quality joint of various means of transport. The properties of the joint were checked by NDT (Non Destructive Test) and also bending and tensile strength were tested. Findings: Relations between process parameters and the quality of welds. Research limitations/implications: In the future, it can be suggested to investigate the effect of micro addition of nitrogen and oxygen in gas shielding mixtures of the MIG/MAG welding process. Practical implications: The proposed innovation will not cause problems in the production process provided that the technological regime will be respected. Social implications: Modifying the welding method will not affect the environment and production management methods. Producing dissimilar welds (although it is very difficult) translates into large savings. Originality/value: It is to propose a new solution with its scientific justification. The article is addressed to manufacturers of high-strength steel and advanced high-strenth steel for automotive industry and other means of transport. Keywords: dissimilar welding, S690 QL, DOCOL 1400 M, transport, shielding gas mixture, production savings. Category of the paper: Research paper.

Numerical Prediction for the Effects of Welding Interpass Temperature on the Thermal History and Microstructure of Duplex Stainless Steels

Numerical simulation was used to predict the thermal behavior and the resulting microstructure at the heat-affected zone (HAZ) of a 170 mm diameter and 3.5 mm thickness super duplex stainless steel (SDSS) UNS S32750 tube. In order to evaluate the thermal response from the model, a usual welding situation involving interpass temperature (IT) and its influence on the HAZ microstructure was exploited. Thus, two superimposed autogenous welding passes were simulated, the first clockwise with the tube in the room temperature and the second, counterclockwise, with the tube at the temperature of 250oC. Even subjected to successive thermal cycles and high interpass temperature, the proportion and morphology of the phases at the HAZ and Fusion Zone (FZ) did not present significant differences when comparing the two welding passes. Meanwhile, nitrogen losses should be avoided during welding in order to obtain a balanced microstructure in DSS welds, contributing to guarantee satisfactory toughness in addition to resistance to pitting corrosion. The predictions from the simulation were validated by using experimental results obtained from the autogenous TIG (Tungsten Inert Gas) process.

Development of a 16-Channel Broadband Piezoelectric Micro Ultrasonic Transducer Array Probe for Pipeline Butt-Welded Defect Detection.

Butt welding is extensively applied in long-distance oil and gas pipelines, and it is of great significance to conduct non-destructive ultrasonic testing of girth welds in order to avoid leakage and safety accidents during pipeline production and operation. In view of the limitations of large transducer size, single fixed beam angle, low detection resolution and high cost of conventional ultrasonic inspection technologies, a 16-channel piezoelectric micro ultrasonic transducer (PMUT) array probe was developed through theoretical analysis and structural optimization design. After the probe impedance characterization, the experimental results show that the theoretical model can effectively guide the design of the ultrasonic transducer array, offering the maximum operating frequency deviation of less than 5%. The ultrasonic echo performance tests indicate that the average −6 dB bandwidth of the PMUT array probe can be up to 77.9%. In addition, the fabricated PMUT array probe has been used to successfully detect five common internal defects in pipeline girth welds. Due to the multiple micro array elements, flexible handling of each element, large bandwidth and high resolution of defect detection, the designed PMUT array probe can provide a good application potential in structural health monitoring and medical ultrasound imaging fields.

Numerical simulation for determination of temperature field and residual stress of stainless steel butt joints with and without clamping

Many welded structures are fabricated from stainless steels because these steels have good mechanical properties and good corrosion resistance. It is necessary to predict the residual stress after welding in order to evaluate the performance of the welded joint. In this paper, the butt welded joint of AISI 316L stainless steel plates is studied. The Metal Inert Gas (MIG) welding process is selected for this material. A SYSWELD software based on the Finite Element Method (FEM) is used to determine the temperature field and residual stresses of two stainless steel plates. The welding simulation includes a sequential coupled thermomechanical analysis. The elemental generation and death technique is utilized to simulate metal deposition in welding. The double ellipsoidal heat source model is used for the heat input of the MIG welding process. The temperature distribution for various time steps at some important points is presented. Cooling times and cooling rates over a temperature range of 800 oC to 500 oC at these points are determined. The residual stress distribution in the longitudinal and transverse direction in two cases with and without clamping is obtained and compared. Obtained results show that: the temperature field in the case of clamping is the same as in the case of no clamping; only the longitudinal stress and transverse stress components are important, the other stress components are not important; the longitudinal stress at the middle of weld line is very high; the transverse stress in the case of clamping is greatly increased, so it is necessary to limit clamping to reduce residual stress after welding

Temperature Distribution of Vessel Tissue by High Frequency Electric Welding with Combination Optical Measure and Simulation.

In clinical surgery, high frequency electric welding is routinely utilized to seal and fuse soft tissues. This procedure denatures collagen by electrothermal coupling, resulting in the formation of new molecular crosslinks. It is critical to understand the temperature distribution and collagen structure changes during welding in order to prevent thermal damage caused by heat generated during welding. In this study, a method combining optical measurement and simulation was presented to evaluate the temperature distribution of vascular tissue during welding, with a fitting degree larger than 97% between simulation findings and measured data. Integrating temperature distribution data, strength test data, and Raman spectrum data, it is discovered that optimal parameters exist in the welding process that may effectively prevent thermal damage while assuring welding strength.

Evosys' advanced quasi‐simultaneous welding

AbstractEvosys Laser GmbH is developing a new method for laser welding of polymers, so‐called ‘advanced quasi‐simultaneous welding’ (AQW). The patented technique combines two different processing wavelengths with the method of quasi‐simultaneous welding in order to achieve a significant reduction of welding time and enhanced weld seam quality. By the use of differing wavelengths – alternated in a certain time pattern – it is possible to improve and better control the deposition of specific amounts of energy into each item to be joined.

Electrodeposition of copper applied to the manufacture of seamless superconducting rf cavities

Niobium thin film coated copper superconducting radio frequency elliptical cavities have demonstrated for many years their strong potential as an alternative to bulk niobium cavities. The thin film lower performance at high rf field is often attributed to the defects observed in the elaborated Nb layer, sometimes originated from defects inherited from the substrate itself. The currently used methods of manufacturing the copper elliptical substrates include several steps of electron-beam welding in order to join the half cells and the cutoffs which can contribute to defects and porosities. Seamless methods are nowadays developed in order to avoid welding steps and to decrease the global manufacturing cost of the cavities. We propose in this study an innovative alternative route in which the cavity is formed by electrodeposition of copper on a sacrificial aluminum mandrel. The strength of the process relies on the total absence of welding joints. Two different electroforming techniques using either direct current or pulsed plating have been investigated. The electroformed copper exhibited similar mechanical robustness, cryogenic properties and purity as the oxygen-free copper. In addition, the fabrication process was validated on test mandrels which mimic the geometry of 1.3 GHz cavities.

Effect of vibration treatment during welding on technological strength of chromium martensitic steel P91

The paper shows the possibility of using the technology of vibration treatment in the process of welding of high-temperature chromium steel of martensitic class P91 applied to the product to increase the technological strength of welded joints and the effect of this technology on mechanical properties before and after thermal treatment. Application of vibration action on welding bath and weld seam in process of manufacturing of welded structure may allow to reduce inhomogeneity of weld metal structure in liquid phase, as well as increase its microchemical inhomogeneity within crystallites during crystallization, reduce grain size due to more efficient heat removal and increase of number of crystallization centers. On the example of manufacturing the turbine support housing of the gas turbine drive, it is shown that it is necessary to replace part of the heat treatment operations with other more energy - efficient and less labor-intensive operations. Results of studies of influence of vibration treatment of welded joint on tendency of welded joint metal to form cold cracks, strength, hardness and impact toughness are given. Based on the obtained results, diagrams of average values of parameters are constructed and conclusions are drawn on the possibility of using the technology of vibration treatment of the turbine casing in the process of welding in order to reduce the number of heat treatment operations during its manufacture.

Optimization of Percentage Dilution in Butt Welds to Prevent Weld Porosity Using Response Surface Methodology

A detailed analysis to optimize percentage dilution in butt welds in order to prevent weld porosity has been carried out in this study. The response surface steepest ascent was used to optimize values of percentage dilution in a butt weld using gas tungsten arc welding process. Predictions for percentage dilution were made using the second order mathematical model for response surface methodology and results obtained showed that percentage dilution value of 45.73% was able to eradicate weld porosity in butt welds. Overall results of percentage dilution analyzed, recorded an optimal value of 45.73% with values of welding current, welding voltage and welding speed as 131.5amperes, 17.4 volts and 100mm/min respectively. A defined quantity of percentage dilution value of 45.73% established in this study should be used at a GTAW process to provide sufficient amount of dilution for controlled solidification of molten metal during welding operation in order to produce porosity-free welds. This work presented results that revealed percentage dilution values that will prevent weld porosity in butt welds with no gas traps or voids in welded joints produced.

Microstructure investigation of duplex stainless steel welds using arc heat treatment technique

A heat treatment technique was applied on standard duplex stainless steel welds in order to investigate the influence of thermal treatments, e.g., multi-pass welding, on the microstructure. By using a stationary arc, a spatial steady-state temperature field ranging from liquidus to room temperature evolves within a single sample and results in a graded microstructure. The arc heat treatment was applied for 10 and 60 min respectively, and the experimental results were compared against thermodynamic calculations. Metallographic investigations revealed the formation of secondary phases within distinct zones. For the 10 min arc heat treated sample, the formation of sigma phase was observed in a temperature range of 730–1000 °C and chi phase was found above 700 °C. For the 60 min sample, sigma phase formed between 675 and 1025 °C, while chi phase formed above 600 °C. In both samples, transformation of chi phase to sigma phase as well as the formation of secondary austenite at 575–1100 °C was observed. Hardness measurements identified brittle regions, which correlated with the regions enriched in sigma phase and decomposition of ferrite. Compared to the initial microstructure, regions with secondary phases showed increased sensitization to local corrosion, when tested according to ASTM A262-Practice A.

Effects of finish turning on an austenitic weld investigated using diffraction methods

Arc welding generally introduces undesired local residual stress states on engineering components hindering high-quality performance in service. Common procedures to reduce the tensile residual stresses are post-heat treatments or mechanical surface treatments like hammering or shot-peening. Assessments of residual stress profiles of post-weld treatments underneath the weld surface are essential, especially in high safety exigency systems like pressure vessels or piping at power plants. In this study, neutron diffraction is used to determine the stress profile after finish milling of an austenitic steel weld in order to verify a chained finite element simulation predicting the final residual stress fields including milling and welding contributions. Non-destructive measurements with spatial resolutions of less than 0.2 mm within the first 1 mm from the surface were mandatory to confirm the finite element simulations of the coarse-grained austenitic material. In the data analysis procedure, the obtained near-surface data have been corrected for spurious strain effects whenever the gauge volume was partially immersed in the sample. Moreover, constraining the surface data to values obtained by x-ray diffraction and data deconvolution within the gauge volume enabled access of the steep residual stress profile within the first 1 mm.

Efficiency of Vanadium Barrier Layer in a Stainless Steel–Titanium Bimetal at a High Temperature

The efficiency of using a vanadium barrier layer and a bimetallic composition composed of 08Kh18N10T stainless steel + VT1-0 titanium obtained by means of explosion welding in order to prevent occurrence of an intermetallic layer is studied in different temperature ranges. The evolution of the heat-affected zone in the samples subjected to heating to 600, 700, 800, and 900°C with exposure times of 1, 3, 5, and 10 h is studied with the use of scanning electron microscopy and metallography, and also the microhardness is measured. It is shown that the vanadium barrier layer reliably prevents mutual diffusion between steel and titanium at a high temperature, which excludes the formation of intermetallic compounds in the heat-affected zone. The efficiency of the barrier layer is evaluated.

Experimental Investigation of Friction Stir Welding Process on High-Density Polyethylene

In this paper, friction stir welding process of high-density polyethylene was studied. Two tools have been chosen, concave and plate, to explore the influence of the tool on the welding quality of the material. In addition, different parameters, rotational speed and welding speed, were investigated. Tensile tests were performed after welding in order to determine the tensile strength efficiency. The greatest ultimate tensile strength was found for the plates welded by concave shoulder.

Considering Phase Transformation Heat When Modeling Thermal Process of Polyethylene Pipes Welding

Mathematical modeling of heat process, considering phase transformation heat, is used to develop technology of welding polyethylene pipes with built-in heating elements at low outdoor temperatures.Mathematically, task is to control technological parameters of welding in order to ensure flow of thermal process at low temperatures according to consistent patterns of welding at acceptable temperatures. With this control of thermal process, the need of ensuring certain sizes of supramolecular structures is eliminated, which allows us to simplify accounting for phase transformation heat. Instead of traditionally used crystallization kinetics equation, it is proposed to directly use differential scanning calorimeter (DSC) data to ensure given temperature field dynamics. Since during phase transformation heat is released and absorbed only by crystalline part of polymer material, special role is assigned to function of crystallinity degree. Formula is given for determining the effective heat capacity coefficient used in the shock-capturing method for solving heat conduction problem with phase transition in temperature range, based on temperature dependence on crystallinity degree. The calculation results for pipes with diameter of 63 mm at various ambient temperatures are shown. Significant increase in cooling rate at air temperatures below minus 15 ° C has been shown.

A Comparative Study of Abbreviated Heat Treatments for SAE 4130 Steel After Laser Welding

It was verified that SAE 4130 steel plates crack when laser beam welded at room temperature (RT). To overcome this problem, this work proposes a high temperature (HT) laser welding in order to reduce the residual stresses and create a bainitic structure instead of a martensitic one. A conventional post-welding heat treatment (PWHT) had been used as a comparison for HT. The centerline crack disappeared after a heat treatment of both in-situ (HT) or after inserting in a furnace (PWHT) at 500 °C for 10 minutes. The finite element analyses indicated a residual stress reduction from 163.70 to 3.72 MPa in the fusion zone (FZ) of the welds from RT to HT. The hardness obtained in FZ depends on the thermal cycle induced microstructure of the welds as 400 HV, 340 HV and 250 HV, for martensite (RT), tempered martensite (PWHT) and bainite (HT) micro-constituents. The proposed in-situ high-temperature laser beam welding method proved its usefulness to solve the center crack issue in SAE 4130 joints.