Weld Length Research Articles

Profiling stainless steel welding processes to reduce fume emissions, hexavalent chromium emissions and operating costs in the workplace

ABSTRACTNine gas metal arc welding (GMAW) processes for stainless steel were assessed for fume generation rates, fume generation rates per g of electrode consumed, and emission rates for hexavalent chromium (Cr6+). Elemental manganese, nickel, chromium, iron emissions per unit length of weld, and labor plus consumables costs were similarly measured. Flux-cored arc welding and shielded metal arc (SMAW) processes were also studied. The objective was to identify the best welding processes for reducing workplace exposures, and estimate costs for all processes. Using a conical chamber, fumes were collected, weighed, recovered, and analyzed by inductively coupled atomic emission spectroscopy for metals, and by ion chromatography for Cr6+. GMAW processes used were Surface Tension Transfer, Regulated Metal Deposition, Cold Metal Transfer, short-circuit, axial spray, and pulsed spray modes. Flux-cored welding used gas shielding; SMAW used E308 rods. Costs were estimated as dollars per m length of a ¼ in (6.3 mm) thick horizontal butt weld; equipment costs were estimated as ratios of new equipment costs to a 250 ampere capacity SMAW welding machine. Results indicate a broad range of fume emission factors for the processes studied. Fume emission rates per g of electrode were lowest for GMAW processes such as pulsed-spray mode (0.2 mg/g), and highest for SMAW (8 mg fume/g electrode). Emission rates of Cr6+ ranged from 50–7800 µg/min, and Cr6+ generation rates per g electrode ranged from 1–270 µg/g. Elemental Cr generation rates spanned 13–330 µg/g. Manganese emission rates ranged from 50–300 µg/g. Nickel emission rates ranged from 4–140 µg/g.Labor and consumables costs ranged from $3.15 (GMAW pulsed spray) to $7.40 (SMAW) per meter of finished weld, and were measured or estimated for all 11 processes tested. Equipment costs for some processes may be as much as five times the cost of a typical SMAW welding machine.The results show that all of the GMAW processes in this study can substantially reduce fume, Cr6+, manganese and costs relative to SMAW, the most commonly used welding process, and several have exceptional capabilities for reducing emissions.

Effect of the Welding Parameters on the Structural and Mechanical Properties of Aluminium and Copper Sheet Joints by Electromagnetic Pulse Welding

Aluminium-copper hybrid parts, as a substitution to copper parts, result in weight and cost reduction, and are relevant in applications related to the electronic, heating and cooling sector. However, aluminium to copper joined by thermal welding processes presents challenges in terms of achieving good joint quality. This is attributed to their dissimilar mechanical and thermal properties which result in large stress gradients during heating. This study investigated joining of aluminium to copper sheets by electromagnetic pulse welding, which is a solid-state process that uses electromagnetic forces for joining of dissimilar materials. Hybrid sheet welds were obtained for all parameters conditions, selected according to a Taguchi L18 design. The structural and mechanical characteristics were examined and related to the welding parameters by means of a Pareto analysis and response graphs. The welded zone started with a wavy interface with interfacial layers and defects and evolved to a flat interface without interfacial layers. The maximum transferable force depended on the minimum specimen thickness and the strength of the hybrid sheet weld. In case of aluminium sheet thickness reduction, the maximum transferable force was linearly correlated with the aluminium sheet thickness. High quality joints were obtained for no aluminium sheet thickness reduction and for a sheet weld strength which was at least as high as that of the base material. The most effective way to increase the transferable force was to lower the initial gap and to increase the free length, which resulted in no aluminium sheet thickness reduction. Alternatively, the use of a rounded spacer decreased the effect of the aluminium sheet thickness on the transferable force. An increase in weld width was achieved for an increase in capacitor charging energy and gap, whereas an increase in weld length was obtained for a decrease in gap. An increase in weld width did not necessarily result in an increase in the transferable force. In the regarded cases, a hybrid sheet with narrow weld width could therefore have higher quality.

Metallurgical Characteristics on PGMA Welding of Dissimilar 304 Austenitic Stainless Steel and HSLA Steel

Welding of dissimilar metal between austenitic stainless steel (γ-SS) and, high strength low-alloy (HSLA) steel are widely used in high-temperature applications in power station and petrochemical plants. Fusion welding is one of the most widely used methods for joining of dissimilar metal. Therefore, continuous efforts are made to apply this method for joining of dissimilar metal of various combinations and despite many difficulties encountered. These difficulties include problems associated with microstructure of the weld metal and heat-affected zone (HAZ). Considering the lack of such knowledge some understanding in this regard has been presented in reference to dissimilar Austenitic stainless steel (γ-SS) and high strength low alloy (HSLA) steel under controlled pulsed current GMAW. This paper focus on effect of grain size, microstructure and the width of the heat affected zone by pulsed current gas metal arc welding (PGMAW) of dissimilar γ-SS and HSLA steel. The observations show that in PGMA welds, the decrease in grain size at heat affected zone and lower HAZ Width in both HSLA steel and γ-SS especially with the lowering of summarized influence of pulse parameters factor () at similar heat input per unit length of weld (Ω) has been observed.

Weld Effective Lengths for Rectangular HSS Overlapped K-Connections

One large-scale, 33-ft-span, simply supported, Warren truss was tested to assess the performance of welds in rectangular hollow structural section (HSS) overlapped K-connections. Nine overlapped connections, within the truss, were designed to be weld-critical and sequentially failed by producing an axial force distribution with a point load, applied quasi-statically, to strategic panel points. The structural reliability (or safety index) of the existing AISC specification formulas for the effective length of welds in rectangular HSS overlapped K-connections, in Table K4.1 of the 2010 AISC Specification for Structural Steel Buildings, was determined from the tests. The results indicate that these provisions are conservative; hence, a modification to the current requirements that limits the effective width of the transverse weld elements is proposed. The proposal establishes a more economical and yet still safe weld design method for rectangular HSS overlapped K-connections.

Pulsed current gas metal arc welding of P91 steels using metal cored wires

A detailed experimental study was undertaken to examine the suitability of pulsed current gas metal arc welding of 12mm thick P91 steels in groove joint configurations with metal cored filler wire. Both the single and multipass welds showed satisfactory bead morphology, tensile strength and toughness especially at higher groove angles of 60° and 75° for the selected range of welding current and speeds. The weld metal compositions showed considerably high presence of Ni, Mn and Si with little loss of other alloying elements. The weld properties were primarily affected by the heat input per unit length of weld and the groove angle. The maximum ultimate tensile strength and toughness of the welds were found to be around 845MPa and 125J, respectively, for a heat input of 1.38kJ/mm and a groove angle of 75°. The use of metal cored filler wires could enhance the welding speed by 20% and filler wire deposition rate by 42% compared to that with the solid wires. Overall, the present study showed that the pulsed current gas metal arc welding of medium to high thickness P91 steels using metal cored filler wires could provide higher deposition rate and welding speed, and enhanced weld bead properties in comparison to solid wires.

Optimizing the Welding Parameters of Reinforcing Steel Bars

Welding is highly recommended for splicing concrete reinforcing bars in all concrete structures. SMAW lap-welded and butt-welded joints made from Tempcore and hot-rolled reinforcing steel bars were studied. The results give an insight into the effect of metallurgical structure and the chemical composition on the effective lap weld length of reinforcing steel bars. It was found that the hot-rolled bars gave shorter acceptable lap length than the Tempcore bars. This was because of the higher amount of pearlite/bainite phases in weld area. In the other hand, the HAZ hardening resulted in the most pronounced changes in ductility of hot-rolled joints. Preheating the hot-rolled bars up to 200 °C was insufficient to prevent the formation of HAZ hard phases.

Corrosion susceptibility of dissimilar friction stir welds of AA5083 and AA6082 alloys

The corrosion susceptibility of dissimilar friction stir welds of AA5083-O and AA6082-T6 alloys has been investigated. Two different tool traverse speeds were compared, revealing that the faster welding speed resulted in increased susceptibility to corrosion because of the reduced tool rotation rate per weld length for heat generation and mixing of materials. The heat affected zones of both alloys and the transition regions between the AA5083-O and the AA6082-T6 rich zones have been identified to be the regions that are most susceptible to corrosion. Grain boundary sensitization in the heat affected zones of both alloys, distribution of Mg2Si particles along the boundary between the two alloys (in the thermomechanically affected zones of the welds) and the galvanic interactions between the AA5083 rich zones and the AA6082 rich zones were observed to be responsible for the corrosion susceptibility in the welds.

Evaluation of a pyramid die extrusion for a hollow aluminum profile using FE simulation

The pyramid die extrusion for a hollow aluminum profile was analyzed to investigate the potential of such innovative dies. For this purpose, the pyramid and conventional porthole dies were respectively designed for a given hollow aluminum profile. And the extrusion process was comprehensively studied by performing different types of finite element simulation, such as the analysis of steady state, transient state and billet skin tracking. The effects of pyramid angle on the evaluation parameters of extrusion, such as extrusion load, material flow, exit temperature, length of transverse weld, quality of longitudinal weld, back end defect and die stress were overall analyzed and compared with the conventional porthole die. Through this study, the advantages and shortcomings of pyramid die were well concluded, which should be important information for die designers and makers.

Comparative study on CO2 laser overlap welding and resistance spot welding for automotive body in white

Abstract Our previous study included a comparative analysis of the characteristics of CO 2 laser overlap welding and resistance spot welding in terms of the weld fundamentals, tensile–shear performance, microstructure, hardness, and corrosion resistance of welding joints. In this study, the processing properties of the two types of welding methods were further investigated. First, experiments were conducted on dissimilar auto body sheets using resistance spot welding and laser welding with different weld lengths. Next, the layout of the laser welding joints was analyzed. Finally, experiments were performed on an auto door sub-assembly using resistance spot welding and laser welding respectively. Experimental results showed that both the sheet thickness and weld pool width were correlated with the laser weld length (LWL). When the LWL was increased to 20 mm, the tensile–shear performance of the specimen was better than that of one resistance-spot welding point under various conditions. When performing weld joint layout using the “short-length and multi-segment” scheme, it was possible to produce laser welding specimens with a preferable joint morphology and mechanical properties. The laser welded auto door with welding joints having an optimized weld length and layout had better quality and performance, and the laser welding process had higher flexibility.

Effects of ram velocity on pyramid die extrusion of hollow aluminum profile

During the extrusion process of aluminum alloy, the ram velocity should be well controlled, since it is an important parameter affecting the profile quality and extrusion productivity. The effects of ram velocity on conventional porthole die extrusion have been investigated by some researchers, while its influence on pyramid die extrusion has not been fully clarified. Thus, in this study, the pyramid die extrusion process for producing a hollow rectangular aluminum tube was comprehensively investigated by performing analysis of steady state, transient state, and billet skin tracking. Importantly, the effects of ram velocity on some evaluation parameters of pyramid die extrusion, such as the material flow behavior, extrudate temperature, extrusion force, transverse weld, quality of longitudinal weld, and back end defect, were overall investigated. The results show that the flowing velocity, extrudate temperature, extrusion force, and welding pressure tend to increase as the increase of ram velocity, while the length of transverse weld is reduced at higher ram velocity. However, the effect of ram velocity on the back end defect is quite slight. Moreover, the advantages and shortcomings of pyramid die were also discussed by comparing with the conventional porthole die.

Analyzing Fracture Behavior of Beam-Column Joints Using Micromechanical Fracture Models

The micromechanical fracture models were used to study the fracture behavior of the welded connection and welded-bolted connection joints. The Void Growth Model was implemented in commercial finite element software ABAQUS through the user-defined subroutines. The results predicted that cracks initiated at the edge of the welds and extended along the length and thickness of the welds. Comparing the effects of equivalent plastic strain and stress triaxiality for the fracture of the first failure element of both beam-to-column joints, we found that the equivalent plastic strain grew linearly as the loads increased and the weld of the lower flange generated cracks when the stress triaxiality increased at maximum value.

Avaliação do Uso de Curto-Circuito Controlado em Soldagens de Passes de Enchimento por MIG/MAG Duplo Arame

Neste trabalho foi realizada uma avaliação técnico-econômica do processo de soldagem MIG/MAG Duplo Arame para soldagens de passes de enchimento na posição plana, empregando o modo operacional Curto-Circuito Controlado (CCC) no arame-seguidor, como forma de melhorar o controle da poça de fusão e reduzir respingos. A avaliação foi feita através de um estudo comparativo entre a técnica MIG/MAG Duplo Arame convencional (com uso da corrente pulsada em ambos os arames) e uma combinação de Pulsado no arame-líder e CCC no arame-seguidor. Foram mantidos constantes os valores das correntes médias para cada arame, o volume de material depositado por unidade de comprimento de solda, o tipo e dimensão do chanfro e o arame, a composição do gás de proteção e a DBCP. Avaliou-se o acabamento superficial e a geometria dos cordões de soldas, a taxa e a eficiência de deposição e as velocidades limites de soldagem resultantes do uso de cada técnica. Os resultados mostram que o uso do modo CCC no arco seguidor aumenta levemente a capacidade de produção do processo, faz gerar menos respingos, melhora o acabamento do cordão, produz ZF e ZAC menores e ainda mantem similar envelope operacional (quanto à faixa de velocidades de soldagens úteis), o que são fatores positivos. Por outro lado, como desvantagem, o uso de CCC levou a cordões mais convexos e com uma penetração menor.

Assessment of the Use of Negative Polarity in Double-Wire MIG/MAG-Welding Filling Passes

The aim of this work was to evaluate the use of negative polarity in the trail wire in double-wire MIG/MAG-welding filling passes. A comparative study of the conventional technique (two wires working with pulsed DCEP) and the proposed combinations of pulsed DCEP in the lead wire with pulsed DCEN in the trail wire and pulsed DCEP in the lead wire with controlled short-circuit CSC(-) in the trail wire was carried out. The mean current in each wire and the ratio of travel speed to wire feed rate (for the same bead volume per unit weld length), as well as wire type and size, shielding gas composition and joint type (a butt joint in a flat position), were kept constant. Bead surface finish and geometry, deposition efficiency and maximum travel speed for each combination were evaluated. In conclusion, the use of negative polarity in the trail wire increased the deposition rate (higher travel speeds for the same bead) compared with the use of pulsed DCEP in both wires but at the cost of reduced operational robustness, as the conventional technique allowed a sound bead to be produced over a wider range of travel speeds. In addition, beads welded using negative polarity had smaller fusion zones and narrower heat-affected zones but higher convexities.

Computational analysis of the effect of welding parameters on energy consumption in GTA welding process

The electrical energy needed in welding processes is a major factor of energy consumption in manufacturing processes that use welds to fabricate structures. In the arc welding process an intense electrical arc is used as the heat source to melt locally metallic materials to join them once they solidify. Although the arc is focused at the joint, a large portion of energy is dissipated as heat through the base metals to the surroundings. In this paper it is shown that selecting the welding parameters appropriately, viz., the power supplied to the arc and the translation speed of the arc, can reduce the energy consumed per unit length of weld. The range of parameters examined was selected such that the vaporization of the molten metal was negligible. It is shown that increasing the arc power in conjunction with increasing the travel speed of the arc leads to reduced energy consumption per unit length of weld; this reduction in energy consumption is for equivalent welds, i.e., welds with identical geometric features.

Effect of Tool rotation speed and feed rate on the formation of tunnel defect in Friction Stir Processing of AZ31 Magnesium alloy

Friction Stir Processing (FSP) is a relatively new material processing technique, which is used to refine the grain structure of metals and to impart improved material properties. In the current research, FSP of magnesium alloy AZ31 was conducted at different parameters. Two type of tool profiles, namely cylindrical and truncated conical probe tool, were used to analyze the defects produced at two different feed rate viz. 40mm/ min and 50mm/min. Studies indicate that thedefects produced with truncated conical tool were lesser than the cylindrical tool. Also the tunnel defect increases with the weld length. Negligible tunnel defect was found during FSP with the truncated conical tool at the rotational speed of 2000rpm and welding speed of 40mm

Multi-Objective Evolutionary Optimization of Sandwich Structures: An Evaluation by Elitist Non-dominated Sorting Evolution Strategy

In this study, an application of evolutionary multi-objective optimization algorithms on the optimization of sandwich structures is presented. The solution strategy is known as Elitist Non-Dominated Sorting Evolution Strategy (ENSES) wherein Evolution Strategies (ES) as Evolutionary Algorithm (EA) in the elitist Non-dominated Sorting Genetic algorithm (NSGA-II) procedure. Evolutionary algorithm seems a compatible approach to resolve multi-objective optimization problems because it is inspired by natural evolution, which closely linked to Artificial Intelligence (AI) techniques and elitism has shown an important factor for improving evolutionary multi-objective search. In order to evaluate the notion of performance by ENSES, the well-known study case of sandwich structures are reconsidered. For Case 1, the goals of the multi-objective optimization are minimization of the deflection and the weight of the sandwich structures. The length, the core and skin thicknesses are the design variables of Case 1. For Case 2, the objective functions are the fabrication cost, the beam weight and the end deflection of the sandwich structures. There are four design variables i.e., the weld height, the weld length, the beam depth and the beam width in Case 2. Numerical results are presented in terms of Paretooptimal solutions for both evaluated cases.

Laser Beam Welding of Titanium Additive Manufactured Parts

In this paper the joinability of titanium Additive Manufactured (AM) parts is explored. Keyhole welding, using a pulsed laser beam, of conventionally produced parts is compared to AM parts. Metal AM parts are notorious for having remaining porosities and other non-isotropic properties due to the layered manufacturing process. This study shows that due to these deficiencies more energy per unit weld length is required to obtain a similar keyhole geometry for titanium AM parts. It is also demonstrated that, with adjusted laser process parameters, good quality welds for aerospace applications in terms of pressure resistance and leak tightness are achievable. Video abstract [Display omitted]

Weld Efficiency Factors Revisited

In recognition that pressure equipment welds that have not undergone a full volumetric inspection may contain internal defects, a weld efficiency is introduced. For spot volumetric inspection which is typically 10% of the weld length the weld efficiency is taken as 0.85. Of interest is that this factor is universally adopted in all known pressure equipment codes around the world. Its origins are obscure and to the authors’ best knowledge, has gone unchallenged for the past 88 years. Additional interest is the use of 0.7 weld efficiency for a weld that has undergone no volumetric inspection. This is prevalent in many international pressure equipment code, but not all.This paper revisits these factors. It considers how they were developed and explores a more rigorous probabilistic approach based on the amount of volumetric inspection and the likelihood of defects. It also considers the closely associated design factors. Understanding also that weld technology has developed since the early 1900 and in particular with the introduction of new technologies such as submerged arc welding, it may not be unreasonable to expect these weld efficiencies to differ from that initially developed. While the paper is not conclusive in its findings, it highlights there is justification to question the weld efficiencies adopted and proposes a program to develop more rigorous values.

Effects of Process Parameters on Charge Weld Length during Multi-Hole Porthole Die Extrusion

The evolution of charge weld during multi-hole porthole die extrusion was studied by means of finite element simulation and Taguchi’s design. Moreover, based on S/N analysis, the optimal process parameters that can reduce the charge weld length was obtained, where the billet diameter is 100 mm, extrusion speed is 2.0 mm/s, tool temperature is 430 °C and billet temperature is 465 °C. The accuracy and effectiveness of such optimal process parameters were also verified. The purpose of the present study is to provide some information about the controlling of charge weld for extrusion engineers.

Behavior and design of stainless steel tubular member welded end connections

Among the various alternatives to make a steel tubular member connection, making a slotted and gusset plate welded connection is one of the most frequently preferred alternatives. This type of connection is essentially an end connection that is made by slotting the tube longitudinally, inserting the gusset plate and then placing longitudinal fillet welds at the tube-to-plate interface. In this paper an experimental study on the behaviour of such connections in stainless steel is presented. 24 specimens were tested under concentrically applied axial tensile forces for varying tube-to-gusset plate weld lengths. Both circular and box section members were considered in the test program. Load-deformation curves were obtained and comparisons were made in terms of strength and ductility. The results obtained from the study were then critically examined and compared with currently available design guidance for slotted gusset plate welded tubular end connections. It is noted that no specific rules exist in international specifications on structural stainless steel which cover the design of such connections. Therefore, the results of this study are compared with the existing design rules for carbon steel.