Showing papers in "Welding Journal in 2005"

Chemical analysis of welding fume particles

Abstract: Airborne particle size is the most important factor in determining the accuracy of a method for chemical analysis.

Estimation of cooling rate in the welding of plates with intermediate thickness

Abstract: An innovative method for estimating the actual cooling rate in a welded section is presented. The method is based on applying a weighting factor to the Rosenthal analytical solutions for thick and thin plates. The factor is determined from the heat-affected zone (HAZ) width, obtained from etched sections, and reflects the actual response of the plate to the heat flow condition. Previous formulations in the literature are based on the assumption of either thin-plate or thick-plate conditions, while most actual conditions lie somewhere between the two extremes. Limited experimental measurements of cooling rate, carried out by instrumented welding, showed good agreement with predicted values. The model was further used to predict the peak temperature profile across the HAZ.

Development of requirements for resistance spot welding dual-phase (DP600) steels. Part 1: The causes of interfacial fracture

Abstract: Weld fracture was investigated in relation to weld parameters and steel sheet characteristics.

Particle size distribution of gas metal and flux cored arc welding fumes

Abstract: A cascade impactor was employed to separate the fume particles in order to determine the size distribution of welding fume. Clear images of coarse welding fume particles (microspatter) from scanning electron microscopy are presented. The particle size distribution of the welding fume reveals that gas metal arc welding (GMAW) fume consists predominately of particle agglomerates smaller than approximately one micrometer. Less than 10% of the fume by weight is microspatter, which is larger than a micrometer. This fraction of microspatter does not change greatly as the GMAW parameters are changed. Flux cored arc welding (FCAW) fume contains more microspatter, approximately 30% by weight.

An experimental study determines the electrical contact resistance in resistance welding

Abstract: Electrical contact resistance is of critical importance in resistance welding. In this article, the contact resistance is experimentally investigated for welding mild steel, stainless steel, and aluminum to themselves. A parametric study was carried out on a Gleeble® machine, investigating the influence on the contact resistance of interface normal pressure, temperature, and base metal.

Effects of process parameters on angular distortion of gas metal arc welded structural steel plates

Abstract: Mathematical models were developed to study the effects of process variables on the angular distortion of multipass GMA welded structural steel plates.

Trends in aluminum resistance spot welding for the auto industry

Abstract: Recent advances in resistance welding technology, alloys, and NDE techniques have helped to reduce manufacturing costs for aluminum sheet structures.

Determination of optimal welding conditions with a controlled random search procedure

Abstract: This study proposes a method for determining the near-optimal settings of welding process parameters using a controlled random search (CRS) wherein the near-optimal settings of the welding process parameters are determined through experiments. The method suggested in this study is used to determine the welding process parameters by which the desired weld bead geometry is formed in gas metal arc (GMA) welding. In this method, the output variables (front bead height, back bead width, and penetration) are determined by the input variables (wire feed rate, welding voltage, and welding speed). The number of levels for each input variable and the total search points were determined to be 10 and 1000, respectively.

Reliable calculations of heat and fluid flow during conduction mode laser welding through optimization of uncertain parameters

Abstract: During conduction mode laser beam welding, the quality of numerical simulation of heat transfer and fluid flow in the weld pool is significantly affected by the uncertainty in the values of absorptivity, effective thermal conductivity, and effective viscosity that cannot be easily prescribed from fundamental principles. Traditionally, values of these parameters are either prescribed based on experience or adjusted by trial and error. This paper proposes a deterministic approach to improve reliability of heat transfer and fluid flow calculations. The approach involves evaluation of the optimized values of absorptivity, effective thermal conductivity, and effective viscosity during conduction mode laser beam welding from a limited volume of experimental data utilizing an iterative multivariable optimization scheme and a numerical heat transfer and fluid flow model. The optimization technique minimizes the error between the predicted and the measured weld dimensions by considering the sensitivity of weld dimensions with respect to absorptivity, effective thermal conductivity, and effective viscosity. Five sets of measured weld pool dimensions corresponding to five different welding conditions were utilized for the optimization. However, the procedure could identify the optimized values of the three uncertain parameters even with only three sets of measured weld pool dimensions.

Cold metal transfer has a future joining steel to aluminum

Abstract: Tests showed good results for tensile strength, corrosion resistance, and limiting fatigue strength when welding steel to aluminum with a modified GMAW process.

Ultrasonic spot welding: A new tool for aluminum joining

Abstract: Ultrasonic spot welding offers cost and performance advantages for joining of aluminium vehicle body parts.

The application of artificial neural networks to weld-induced deformation in ship plate

Abstract: An artificial neural network model was developed to be used in a study of factors affecting the distortion of 6- to 8-mm-thick D and DH 36 grade steel plate. The data from a significant number of closely controlled welding trials, and subsequent measurements of distortion were input into the model. From this model development, a sensitivity analysis was carried out, which highlighted a number of apparently key factors, which influenced distortion. From this it was established that the carbon content of the steel plate played a key role in the amount of distortion produced by the welding process. The mechanism of the effect of carbon appears to be linked to its effect on grain size, transformation temperature, mechanical properties and pearlite content at least. It was established that an increase in carbon content was beneficial in reducing thin plate distortion caused by welding.

Friction stir welding of 2219 aluminum: Behavior of θ (Al2Cu) particles

Abstract: An experimental study was conducted to determine if the maximum temperature in the workpiece can reach the lower bound of the melting temperature range and trigger liquation during friction stir welding (FSW) of aluminum alloys as some computer simulation has suggested. Alloy 2219, which is essentially a binary Al-Cu alloy, was selected as the material for study because of its clear lower bound of the melting temperature range, that is, the eutectic temperature 548°C. In addition to FSW, gas metal arc welding (GMAW) of Alloy 2219 was also conducted to provide a benchmark for checking liquation in FSW of Alloy 2219. The microstructure of the resultant welds was examined by both optical and scanning electron microscopy. It was found that in GMAW of Alloy 2219, θ (Al 2 Cu) particles acted as in-situ microsensors, clearly indicating the onset of liquation by reacting with the surrounding aluminum matrix and forming distinct composite-like eutectic particles upon reaching the eutectic temperature. In FSW, on the other hand, no evidence of θ-induced liquation was found as the welds contained θ particles alone and no eutectic particles, suggesting that the eutectic temperature was not reached during FSW. However, in most friction stir welds large θ particles were observed, some exceeding 100 μm and even 1 mm in length as compared to the normal θ particles of only about 10-15 μm in length in both the base metal and the weld, that is, the stir zone or nugget. The large θ particles appeared to have formed during FSW from agglomeration of fractured θ particles and the smaller ones of the θ particles in the workpiece. No apparent correlation between the extent of agglomeration and the welding condition was found.

Exploring temper bead welding

Abstract: With this welding technique, tight control over subsequent weld beads is used to control the properties of previously deposited beads and the heataffected zone.

Development of requirements for resistance spot welding dual-phase (DP600) steels part 2: Statistical analyses and process maps : Weld diameter proved to be the primary factor influencing type of weld fracture

Abstract: The DP600 steels have presented new challenges to the conventional practice of resistance spot welding. In developing process requirements to spot weld stacks of two identical DP600 steel sheets, a statistical method was applied in order to establish empirical relationships between the type of weld fracture during quality control (i.e., interfacial vs. button pullout), the weld current, the weld time, and the sheet thickness independent of chemical composition and galvanized coating. The selected methodology was so successful that maps to select process parameters were developed for spot welding 0.9- to 2.2-mm-thick DP600 steels. This study also confirmed that weld diameter was a primary factor influencing type of weld fracture. A new relationship between minimum weld diameter to prevent interfacial fracture during quality control and sheet thickness was also determined, and compared with several resistance spot weld standards.

Intelligent control of pulsed GTAW with filler metal

Abstract: This paper addresses intelligent control of weld shape for plates with varied root openings during pulsed GTAW with filler metal, and is a development from the work in Refs. 1-3. The newly developed double-sided visual image sensing system could acquire the front topside, back topside, and backside images of the weld pool simultaneously in the same frame. The root opening and the double-sided weld pool geometry parameters were extracted online. A neural network model was established to predict the backside width and topside height through welding parameters and topside shape parameters. Feasible intelligent control schemes were also investigated. In order to eliminate the effect of the root opening and stabilize both backside width and topside height, a double-variable controller was designed, in which the feedback control part regulates the pulse duty ratio to control backside width and, at the same time, the feed-forward control part adjusts the filler metal rate to achieve the desired topside height in order to compensate for the effects of the varying root openings.

Development of flux and filler metal for brazing magnesium alloy AZ31B

Abstract: This study was carried out to develop new flux and filler metal to braze magnesium Alloy AZ31B more easily at a lower temperature. A flux was successfully developed consisting of CaCl 2 , LiCI, and NaCI with Ca and Li ions, which made the magnesium alloy surface active at around 450°C. Additionally, brazing filler metals with a melting temperature below 480°C were successfully developed. Magnesium and indium were the main components , along with 0.2 to 6.4 wt-% zinc to lower the melting temperature. With a small amount of zinc, the flux and filler metals achieved a joint with a high strength equivalent to the base metal. As the amount of zinc increased, the joint strength decreased.

Microstructural characterization of a double-sided friction stir weld on a superaustenitic stainless steel

Abstract: The microstructure of AL-6XN plates joined via a double-sided friction stir weld has been investigated. The microstructural zones that develop during friction stir welding (FSW) reflect decreasing strains and less severe thermal cycles with increasing distance from the weld centerline. The nugget, located around the centerline, has a refined structure of equiaxed grains as a result of the extreme strain and temperatures experienced during welding. Several features are seen within the nugget, one of the most prominent being a steady stream of tungsten inclusions created by accelerated tool wear. The heat-affected zone consists of a mixture of relatively large austenite grains and smaller recrystallized grains present at grain boundaries. These fine grains were shown to be austenite and no evidence of sigma phase in this region was apparent. The thermal mechanical-affected zone, located between the nugget and heat-affected zone, shows a microstructural transition from the completely refined structure to a structure very similar to the base metal. Of particular importance is that, unlike fusion welding, microsegregation has been avoided during FSW. Due to the changing microstructure from base metal to the weld zone, there are corresponding changes in hardness. Moving toward the centerline from the base metal, hardness increases due to refinement of the microstructure.

Fatigue behavior of welded joints Part 1 - statistical methods for fatigue life prediction : A model is investigated where fatigue life and fatigue limit are treated as random variables

Abstract: Statistical models for fatigue life prediction for welded joints are discussed and fitted to experimental data for fillet-welded steel joints where cracks emanate from the weld toe. The models are based on an S-N approach where the number of cycles N to failure is assumed to be directly correlated to the applied nominal stress range ΔS. The models assume the existence of a fatigue limit given as a stress range below which no failure will take place. Emphasis is laid on the modeling of the fatigue life close to this limit where the service stresses for welded details often occur. Experimental data in this stress regime are sparse and do not fit the knee point of the conventional bi-linear S-N curve found in rules and regulations. Consequently, an alternative model where both the fatigue life and the fatigue limit are simultaneously treated as random variables is investigated. The model parameters for this random fatigue-limit model (RFLM) are determined by the maximum likelihood method, and confidence inter vals are obtained by the profile likelihood method. The advantage of the model is that it takes into consideration the variation in fatigue limit found from specimen to specimen and that run-out results are easily included. The median S-N curve obtained from the model coincides with the conventional bi-linear curves in the high-stress regime (stress ranges higher than I 10 MPa), but predicts longer lives as the stress range decreases below 100 MPa. The model gives a nonlinear S N curve for a log-log scale in the fatigue-limit area: the fatigue life is gradually increasing and is approaching a horizontal line asymptotically instead of the abrupt knee point of the bilinear curve. '['he nonlinear curve is more in accordance with experimental data. At stress ranges below 100 MPa, the predicted fatigue lives are between 2 to 10 times longer than predictions made by the bilinear F-class curve. The conclusion is that the rule-based S-N curves may he overly pessimistic in the stress regime where service stresses frequently occur. A more correct statistical model based on a random fatigue-limit model results in S-N curves that give decreased dimensions for a giver fatigue design factor under constant amplitude loading.

Influence of procedure variables on C-Mn-Ni-Mo metal cored wire ferritic all-weld metal

Abstract: Different shielding gases, welding position, number of weld passes, and arc energy were all studied to assess their influence on the all-weld-metal properties of a metal cored filler metal.

Properties and sulfide stress cracking resistance of coarse-grained heat-affected zones in V-microalloyed X60 steel pipe

Abstract: Evaluation of heat-affected zone (HAZ) properties after postweld heat treatment (PWHT) is important not only for selection of suitable chemical composition of microalloyed steel pipes, but also for development of welding procedures, including PWHT, for sour service. In this study, coarse-grained heat-affected zones (CGHAZ) were induced in V-microalloyed X60 steel pipe specimens using a Gleeble weld thermal simulation. Cooling rates from 5 to 80°C/s were used to represent a broad range of welding conditions. The CGHAZ specimens were subjected to PWHT at temperatures from 635 to 670°C (1175 to 1238°F) for 3 to 15 hours. Microhardness and microstructure of the CGHAZ were evaluated in the simulated as-welded and PWHT condition as functions of weld cooling rate and PWHT schedule. The tensile properties and sulfide stress cracking resistance (SSC) of CGHAZ with selected hardness level were determined as well. The maximum hardness of the CGHAZ increases from 233 to 392 HV-10, and its microstructure changes from ferrite with aligned second phases to martensite by increasing the cooling rate from 5 to 80°C/s. None of the PWHT schedules used in this study induced hardening of the CGHAZ of the microalloyed steel. However, the rate of softening may have been retarded because of VC secondary hardening. For a holding time between 3 and 15 hours, the softening effect induced by the PWHT can be described by the Larson-Miller tempering parameter. The apparent activation energy for tempering in the different softening regimes observed during PWHT was determined. The behavior of the CGHAZ during tensile testing depends on the degree of overmatching between the CGHAZ and the base material. Coarse-grained heat-affected zones with a maximum hardness of 264 HV did not crack during exposure to sour testing according to procedure specified in standard NACE TM0177 (Method A).

Constraints-based modeling enables successful development of a welding electrode specification for critical navy applications

Abstract: An innovative constraints-based modeling approach was used to successfully specify the chemical composition range for advanced consumable electrodes intended for gas metal arc welding (GMAW) of high-strength steels for critical US Navy applications Initially, various US Navy requirements for advanced consumable electrodes were converted into a set of constraints that related chemical composition of steels to certain metallurgical characteristics with appropriate numerical ranges The metallurgical characteristics and their numerical ranges, in turn, were used to identify critical elements for compositional control, and to specify the compositional ranges for the individual alloy elements Subsequently, a 2 3 factorial design of experiments was used to develop a batch of welding electrodes, and limited experiments were carried out to evaluate the performance of the welding electrodes Results showed that two of the eight electrodes met or exceeded ER-100S requirements, while one of the eight electrodes met or exceeded ER-120S requirements Additional weld evaluations performed over a much wider welding operational envelope using one of the eight electrodes provided weldments with acceptable weld mechanical properties for ER-100S over the entire range of welding conditions Thus, use of the constraints-based modeling approach greatly reduced the risks inherent in developing electrode specification, while allowing one to meet or exceed US Navy requirements at minimal cost and schedule, thereby validating the exceptional utility of this novel modeling approach

Influence of molybdenum on ferritic high-strength SMAW all-weld-metal properties: As molybdenum increased, hardness, yield, and tensile strengths increased

Abstract: The investigation described in this paper is part of a long-term study on the influence of alloying elements on the mechanical properties and microstructure of high-strength SMAW electrode weld metal of the ANSI/AWS A5.5-96 E10018/11018/12018M type. The objective of this work was to study the influence of Mo variations from nominal 0 to 0.90% for an all-weld metal alloyed with C 0.05%, Ni 1.8%, and two values of Mn: 1 and 1.5% in both the as-welded and stress-relieved conditions in order to contribute to a comprehensive picture on the influence of alloying elements on high-strength weld deposits. Tensile, impact, and CTOD testing were employed to assess the mechanical properties. Full chemical and microstructural analyses were conducted and complemented with a hardness survey. It was found that as Mo increased, hardness, yield, and tensile strengths increased. The same effect was achieved with an increment of Mn. As a general tendency, Mo was deleterious for toughness for 1% Mn, but a maximum of toughness was achieved at 0.25% Mo for 1.5% Mn. Postweld heat treatment (PWHT) produced a drop in tensile properties and a benefit on toughness, especially for Mo contents up to 0.5%. Some suggestions concerning the electrode formulation to obtain an optimum combination of tensile strength and toughness are presented.

A mechanism of spatter production from the viewpoint of the integral of specific current action : A model is proposed to quantitatively explain the mechanism of spatter production and the role of waveform parameters

Abstract: Numerous earlier studies have investigated the mechanism of spatter production, and the waveform parameters affecting spatter production, because more procedures are necessary to remove spatter. These studies explain the spatter mechanism qualitatively, but do not clarify it quantitatively. Also, they do not illustrate how waveform parameters influence spatter production. In this study, the integral of specific current action is introduced to quantitatively explain the mechanism of spatter production. Based on the pi revious studies, this study proposes a model that suggests there is a constant value of the integral of a specific current action to determine the moment of spatter production. By comparing the spatter calculations with the welding experiments, this model was validated. Simulations were carried out to investigate the influence of the waveform parameters on spatter production. This quantitatively explains the role of the waveform parameters, such as peak current and arc time, in spatter production.