Showing papers in "Welding Journal in 2007"

Effects of fusion zone size and failure mode on peak load and energy absorption of advanced high-strength steel spot welds

Abstract: This paper examines the effects of fusion zone size on failure modes, static strength and energy absorption of resistance spot welds (RSW) of advanced high strength steels (AHSS). DP800 and TRIP800 spot welds are considered. The main failure modes for spot welds are nugget pullout and interfacial fracture. Partial interfacial fracture is also observed. The critical fusion zone sizes to ensure nugget pull-out failure mode are developed for both DP800 and TRIP800 using limit load based analytical model and micro-hardness measurements of the weld cross sections. Static weld strength tests using cross tension samples were performed on the joint populations with controlled fusion zone sizes. The resulted peak load and energy absorption levels associated with each failure mode were studied for all the weld populations using statistical data analysis tools. The results in this study show that AHSS spot welds with fusion zone size of can not produce nugget pullout mode for both the DP800 and TRIP800 materials examined. The critical fusion zone size for nugget pullout shall be derived for individual materials based on different base metal properties as well as different heat affected zone (HAZ) and weld properties resulted from different welding parameters.

Laser engineered net shaping advances additive manufacturing and repair

Abstract: The LENS® technology is transitioning into a process accepted by a growing number of commercial, aerospace, and Department of Defense customers.

Application of magnetic pulse welding for aluminum alloys and SPCC steel sheet joints

Abstract: Magnetic pulse welding (MPW) is a cold process for welding conductive metals to similar or dissimilar materials. Magnetic pulse welding uses magnetic pressure to drive the primary metal against the target metal sweeping away surface contaminants while foreing intimate metal-to-metal contact, thereby producing a solid-state weld. In this paper, the MPW method and its application for several aluminum alloys (A1050, A2017, A3004, A5182, A5052, A6016, and A7075) and joints in steel (SPCC) sheets were investigated, and the welding process parameters and characteristics are reported.

Technical note : Martensite formation in austenitic/ferritic dissimilar alloy welds

Abstract: Electron microprobe analysis was utilized to examine the gradient of alloying elements across the weld interface of austenitic/ferritic dissimilar alloy welds. The concentration gradients were converted to martensite start (Ms) temperature gradients and used to explain the differences in martensite layer widths that have been observed in the partially mixed zone (PMZ) of dissimilar welds.

Metallurgical investigation into ductility dip cracking in Ni based alloys

Abstract: In this second of two papers, the microstructural and microchemical evolution of Alloy 600 (A600), Alloy 690 (A690), Filler Metal 82H (FM82H), and Filler Metal 52 (FM52) during the weld thermal cycle was investigated and compared to the hot ductility data presented in the first paper (Ref. 1). The Gleeble® hot ductility test was used to subject these four alloys to a simulated weld thermal cycle. Water quenching was conducted at select temperatures so that the elevated temperature microstructure could be subsequently characterized. Microstructural and microchemical characterization was carried out using scanning electron microscopy, transmission electron microscopy, and analytical electron microscopy techniques. Complete dissolution of intergranular carbides was observed in A690 and FM52 at ∼2400°F (1316°C), both of which exhibit an on-cooling ductility minimum at 1600°F (871°C). Of all four alloys, the greatest resistance to ductility dip cracking (DDC) was observed in A600 and A690 during on-heating, which had coarse, homogenously distributed intergranular carbides. FM82H, which formed NbC intergranular carbides, had the most stable intergranular microstructure and serrated grain boundaries, which corresponded to the best overall DDC resistance. Modifications to the thermal cycle that resulted in increased intergranular carbide coverage in FM82H and FM52 also reduced DDC susceptibility. AEM analysis did not reveal any sulfur or phosphorous segregation in FM52 at 1600°F (871°C) on-heating, on-cooling, or after a 60s hold. Samples with microstructures that consisted of coarsened carbides and/or serrated grain boundaries, which are expected to decrease grain boundary sliding, were found to be resistant to DDC. Based on the results of this work and the results previously presented in Paper I (Ref. 1), grain boundary sliding contributes to DDC. Conversely, sulfur and phosphorous embrittlement do not play a role in DDC of FM52 at the concentrations investigated. The dynamic precipitation of partially coherent intergranular M 23 C 6 carbides at intermediate temperatures may exacerbate DDC in A690 and FM52, but requires further investigation.

Laser hybrid welding in the automotive industry

Abstract: Combining lasers with other welding techonoliges promises greater versatility and speed for high-production applications.

Variable AC polarity GTAW fusion behavior in 5083 aluminum

Abstract: Aluminum alloys are typically welded on AC with the gas tungsten arc welding (GTAW) process. Many power sources have "max penetration" indicated when more than 50% of the AC cycle is spent on electrode negative polarity and "max cleaning" when more than 50% of the cycle is on electrode positive polarity. In the work reported here, weld bead dimensions, notably penetration and bead width, increase with the percentage of electrode positive polarity during the unbalanced square wave AC welding of aluminum alloys with the GTAW process. This is in direct contradiction of conventional assumptions about the role of electrode positive and electrode negative contributions to surface cleaning and fusion behavior during AC welding. The primary source of the extra base metal melting during electrode positive operation is in the nature of cold cathode field emission of electrons from the base metal. The dielectric breakdown of surface oxide as electrons are emitted also contributes to the increased fusion, but this is not a contributory factor once the weld metal surface is completely clean. Both phenomena require extra energy to be supplied to the cathode, which results in the increased fusion. Earlier works on the gas metal arc welding (GMAW) process confirm this behavior of enhanced melting at the cathode. Positive ion bombardment, thermal convection from the plasma jet, and radiation from the plasma complete the thermal input to the cathode for metal fusion.

The effect of coatings on the resistance spot welding behavior of 780 MPa dual-phase steel

Abstract: Dual-phase steels are commercially available with hot-dipped galvanneal (HDGA) or hot-dipped galvanize (HDGI) coatings. An investigation was undertaken to examine whether differences exist in the resistance spot welding behavior of 780 MPa dual-phase steel with HDGA coating compared to the one coated with HDGI coating. The resistance spot welding evaluations consisted of determining the welding current ranges for the steels with HDGA and HDGI coatings by determining the current required to obtain the minimum weld size and the current required to cause expulsion of weld metal. Shear-tension and cross-tension tests were performed on spot welds made on steels with both HDGA and HDGI coatings. Weld cross sections from both types of coatings were examined for weld quality. Weld microhardness profiles were determined to examine hardness variations across the welds. Cross sections of HDGA and HDGI coatings as well as the electrode tips after welding were examined using a scanning electron microscope. Composition profiles across the coating depths were analyzed using a glow-discharge optical emission spectrometer to understand the role of coating in resistance spot welding. Contact resistance was measured to examine its contribution to the current required for welding. The results indicated that 780 MPa dual-phase steel showed similar overall welding behavior with HDGA and HDGI coatings. Further, weld shear and cross-tension strengths were independent of the type of coating. The results of the study are presented along with a discussion of the structure and the role of coatings in welding. A brief discussion of the physical metallurgy of 780 MPa dual-phase steel is presented to explain weld microstructural evolution.

Reducing shrinkage voids in resistance spot welds

Abstract: Key factors that contribute to the formation of shrinkage voids in resistance spot welds of advanced high-strength steels were investigated.

Practical applications for hybrid laser welding

Abstract: This technology offers potential for significant improvement in weld quality and process efficiency for fabrication applications.

Prediction of element transfer in submerged arc welding

Abstract: The transfer of elements across the molten weld pool has been predicted by developing quadratic models in terms of flux ingredients with the application of statistical experiments for mixture design. Bead-on-plate weld deposits were made at fixed welding parameters using submerged are welding fluxes prepared as per extreme vertices algorithm of mixture experiments in a CaO-MgO-Caf 2 -Al 2 O; flux system. The results show that some of the individual flux ingredients and their binary mixtures have a predominant effect on weld metal transfer of oxygen, manganese, silicon, and carbon contents. The analysis of experimental data also indicates that transfer of oxygen is affected by several properties of flux ingredients such as oxygen potential, thermodynamic stahility, and viscosity. In the element transfer of silicon, both thermochemical and electrochemical reaction mechanisms operate simultaneously. Transfer of manganese is principally related to the weld metal oxygen contents as well as electrochemical reaction in the molten weld pool. The transfer of carbon was generally governed by the oxidation reaction. Iso-response contour plots were also developed to quantify the transfer of elements against different flux compositions.

Double-electrode GMAW process and control : A novel welding process adds a GTAW torch to a conventional GMAW system to create a bypass arc for increasing melting current while controlling base current

Abstract: Double-electrode gas metal arc welding (DE-GMAW) is a novel process that decouples the melting current into base metal current and bypass current by adding a bypass torch to a conventional GMAW system to establish a bypass arc. This makes it possible to increase the melting current while the base metal current can be controlled at a desired level. Experiments have been done to find the conditions that can assure a stable bypass arc is established/maintained between the welding wire and the bypass torch. To control the base metal current at the desired level, a group of power resistors is added in the bypass loop. The resistance of the power resistor group is adjusted real-time by changing the combination of the resistors, and the change in the resistance results in a change in the bypass current and thus a change in the base metal current. A model has been developed to correlate the change of the resistance needed to achieve the desired base metal current to the deviation of the base metal current from its desired level. Experiments demonstrated that the developed control system can adjust the bypass current in a great range to maintain the base metal current at the desired levels.

Soldering aluminum matrix composites

Abstract: The improvement of tin-based solder alloys by the addition of ceramic particles was investigated.

Fusion-boundary macrosegregation in dissimilar-filler welds : Fundamental solidification and macrosegregation in welds made with filler metals different in composition from the workpiece are presented

Abstract: More often than not, the filler metal in arc welding is different (dissimilar) in composition from the base metal. It can cause macrosegregation along the fusion boundary and degrade the weld quality, but the formation of such macrosegregation is still not well understood. In the present study, the liquidus temperature of the weld metal T LW and that of the base metal T LB were considered, in addition to the stagnant or laminar-flow layer of liquid base metal along the weld pool boundary suggested by Savage. The following solidification concepts were presented: 1) The melting front is at T LB and not T LW ; 2) the solidification front is no longer isothermal at T LW everywhere - only the homogeneous bulk weld pool begins to solidify at T LW ; 3) the liquid base metal can freeze quickly in a different liquid cooler than T LB before much mixing occurs, so can the liquid weld metal freeze quickly in a different liquid cooler than T LW , and macrosegregation is promoted either way; and 4) complete mixing throughout the weld pool is impossible with T LW > T LB . Even when the filler metal is mixed completely with the bulk weld pool, macrosegregation can still occur by the following two mechanisms. In Mechanism 1, for filler metals making T LW T LB , the layer of liquid base metal is below T LW . The liquid weld metal pushed by convection from the bulk weld pool into this cooler layer can freeze quickly. Filler-deficient features, including "beaches," "peninsulas," and "islands," formed by Mechanism 1 are distinctly different from those formed by Mechanism 2. Macrosegregation reported by previous investigators can be explained by Mechanism 1, but macrosegregation by Mechanism 2 has not been reported. The mechanisms were verified with gas metal arc welds of 1100 Al (pure Al) made with filler 4145 Al (Al-4Cu-10Si) and of Cu made with filler ER-CuNi (Cu-30Ni).

Comparison of friction stir weldments and submerged arc weldments in HSLA-65 steel

Abstract: Friction stir welding (FSW) is of interest to the shipbuilding community because of the need to reduce weld distortion in thin structures to improve fairness. The project objectives were to evaluate FSW tools and equipment, develop procedures, and demonstrate the feasibility of FSW 0.25-in.- (6-mm-) thick HSLA-65 steel weldments fabricated from 10-ft- (3-m-) long plate sections, on a production-size, purpose-built FSW machine. Measurements were taken to compare the amount of weld distortion with that of a conventional submerged arc weldment (SAW). In addition, the mechanical properties and microstructures of the weld regions were evaluated to further compare the two welding processes. Two types of tool materials were evaluated: a polycrystalline cubic boron nitride (PCBN) tool and a tungsten-25% rhenium (W-25%Re) tool. W-Re was evaluated as a pin material in a two-piece FSW tool using a Mo-1%Ti-0.3%Zr-0.15%C (Mo-TZM) shoulder. The W-Re pin performed well with minimal wear, but the Mo-TZM shoulder wore excessively during fabrication of the 10-ft weldment. Transverse and longitudinal weld distortion measurements were obtained on a usable 6.0-ft (1.8-m) length of this weldment and compared to those of a similar length of the submerged arc weldment. Transverse weld tensile, Charpy V-notch (CVN) impact and guided bend tests were obtained from the W-Re friction stir and submerged arc weldments. Both the friction stir and submerged arc weldments exhibited significant longitudinal weld distortion. The submerged arc weldment was bowed in the transverse direction, while the friction stir weldment exhibited no transverse distortion. The transverse weld tensile strengths of both weldments were acceptable, and the CVN toughness of the FSW stir zone was significantly higher than that of the submerged arc weld metal. There was little difference in heat-affected-zone toughness. The present trials indicate that FSW is technically feasible for joining HSLA-65 steel for structural applications.

Measuring on-line and off-line noncontact ultrasound time of flight weld penetration depth

Abstract: Welding is the primary technique used for joining structural components. However, weld penetration depth measurement is not done in real-time resulting in open-loop control of it. The major obstacle to on-line weld penetration depth measurement is a lack of accurate and high-resolution nondestructive and noncontact sensors that can operate in high temperatures and harsh environments typical of welding processes. The use of ultrasonic sensors to measure weld penetration depth of butt joint welds has focused on using a direct reflection of either a longitudinal or shear wave from the bottom of a weld bead. During laser generation of ultrasound, it was observed that a Rayleigh (surface) wave was generated on the bottom of weld samples. This Rayleigh wave traveled to the bottom of the weld bead where it mode converted into a longitudinal (pressure) and shear (transverse) wave. The mode-converted longitudinal wave traveled to the bottom of the weld sample where it generated a shear (RGLS) and longitudinal (ROLL) wave reflection. Similarly, the mode converted shear wave also generated a shear (RGSS) and longitudinal (RGSL) wave reflection. The development of a new RGLS time of flight (TOF) technique for weld penetration measurements will be presented. Experimental results using the RGLS TOF technique for weld penetration depth measurement has proven to be accurate, precise, and repeatable both off-line after welding and on-line during welding. Additional RGLL, RGSL, and RGSS TOF techniques related to the RGLS TOF technique will also be presented. This new technique for measuring weld penetration depth can enable closed loop control of weld penetration depth.

Image Processing for Measurement of Three-Dimensional GTA Weld Pool Surface Algorithms are explored for processing the image of a dot-matrix laser pattern reflected from the weld pool surface

Abstract: Observing and measuring the weld pool surface is a key to develop- ing next-generation intelligent welding machines and to understanding the weld- ing process better. In this paper, a dot- matrix pattern is used to project a com- mercially available low-power continuous laser onto the weld pool surface. The re- flected laser beam is intercepted by an image plane, which is placed at a distance from the arc. While the reflection of the laser travels without reducing much of the intensity, the intensity of the arc radiation rapidly decays with the distance. To utilize the reflection to reconstruct the weld pool surface, the correspondence of the reflec- tion points with their projected points must be found. This paper addresses the algorithms used to extract the reflected points from the image and then match the reflected points with their projected points. The establishment of the corre- spondence provides the data needed to re- construct the weld pool surface based on the reflection law.

P91 and beyond : Welding the new-generation Cr-Mo alloys for high-temperature service

Abstract: reep strength-enhanced ferritic steel (CSEF) and advanced chromium-molybdenum steels are experiencing worldwide usage. The desire to increase efficiency has introduced a need for advanced materials with superior material properties at higher temperatures. Advanced chromium-molybdenum pipe and tubing such as 9 CrMoV [P(T)91], tungsten, and/or boron-enhanced materials (i.e., Grades 92, 122, E911, 23, 24, etc.) are now being specified. The lessons learned thus far with P(T)91 weldments have truly demonstrated that CSEF steels are quite different and require significantly more attention than the P(T)22 and lesser materials. Of the candidate advanced base materials and consumables, T23 appears to have the highest priority among challenges to P91, followed by P92 and then to a lesser extent the higher chromiumand nickel-based alloys. Emphasis placed herein on Grade 91 and the importance of maintaining preheat, interpass temperature, and dangers inherent in interrupted heating cycles or improper postweld heat treatment plus detailed attention to filler metal procurement to avoid metallurgical complications is equally true for the other advanced chromium-molybdenum alloys.

Simulation study of a hybrid process for the prevention of weld bead hump formation : A numerical simulation shows how formation of bead humps in high-speed GMAW is prevented by additional laser heat input

Abstract: A three-dimensional numerical simulation of heat and fluid flow and phase change in pulsed gas metal arc weld (GMAW-P) deposits was used to study hump formation and its suppression by a hybrid laser welding process. The simulation results allowed definition of the events leading to the formation of a humped bead. In the initial stage of hump formation, which occurred at relatively high (in terms of Peclet number) travel speed, a thin elongated molten bead was formed and pinching due to capillary instability resulted in a dramatically reduced cross section. Solidification then divided the molten pool into front and back sections, guaranteeing hump formation. Conditions for formation of a hump at the beginning of a weld bead and formation of subsequent humps were different, but the events leading to hump formation were the same for both. Experimental and simulation results for the hybrid process showed that a defocused laser beam located in front of the GMA weld pool could decrease the size of the initial bead hump and prevent formation of subsequent humps. This was the case if a laser melt pool of sufficient width was created in front of the weld pool to make the broadened weld bead stable from a capillary point of view. Conversely, simulations showed that hump formation was not prevented by the hybrid process if the laser beam did not sufficiently widen the weld bead.

Fusion-boundary macrosegregation in dissimilar-filler metal Al-Cu welds

Abstract: Dissimilar filler metals, that is, filler metals different from the base metal in composition, are routinely used in arc welding but macrosegregation can form and degrade the weld quality. Based on the liquidus temperatures of the weld metal (T LW ) and the base metal (T LB ) as well as the stagnant or laminar-flow layer of liquid base metal along the weld pool boundary suggested by Savage, two new mechanisms have been proposed recently for macrosegregation near the fusion boundary in arc welds made with dissimilar filler metals, one for T LW T LB . To verify the mechanisms, the binary Al-Cu system was selected, and gas metal arc welding was used. In the case of T LW T LB , on the other hand, the Al-33Cu eutectic was selected as the base metal because the eutectic has the lowest liquidus temperature and thus T LW > T LB is met automatically. It was welded with filler metal 1100 Al. The beach along the fusion boundary was significantly thicker < T LB . It was intruded by the weld metal, with peninsulas, and islands randomly oriented in the space between the weld-metal intrusions. These beach, peninsulas and islands were eutectic, that is, they originated from the liquid base metal that solidified without mixing with the bulk weld pool. In either case, the filler-deficient zone was thicker in welds made with a larger difference between T LW and T LB . All these observations were consistent with and thus verified the proposed mechanisms.

The effect of chromium on the weldability and microstructure of Fe-Cr-Al weld cladding

Abstract: Iron-aluminum-based weld cladding is currently being considered as corrosion-resistant coatings for boiler tubes in coal-fired power plants. Although these alloys could potentially be good coating candidates due to their excellent high-temperature corrosion resistance, Fe-Al weld cladding is susceptible to cracking due to hydrogen embrittlement at elevated aluminum concentrations. Additions of chromium to these iron-aluminum alloys have been shown to improve the corrosion resistance of the alloys and could potentially increase the lifetimes of the coatings. The current study investigated the effect of chromium on the hydrogen cracking susceptibility of Fe-Al weld cladding.

Influence of lubricants on electrode life in resistance spot welding of aluminum alloys

Abstract: Rapid electrode tip degradation and inconsistent joint strength are two major problems associated with resistance spot welding of aluminum alloys. A new approach of lubricating the contact between electrode and aluminum sheet to influence and perhaps extend the electrode life was examined. Different metalworking lubricants were placed between the electrode and aluminum sheet to produce different surface conditions. Keeping all weld conditions constant, electrode life experiments were conducted for both lubricated and unlubricated conditions. Joint shear strength values were periodically measured as hundreds of welds were made until either explosion/sticking occurred or a drop in the shear strength indicated the end of the effective electrode tip life. For the same welding conditions and failure criteria, one "good"lubricant was found to extend the electrode life to almost double that of the unlubricated surface (as received). A second set of experiments was performed to examine the action of the good lubricant. These experiments involved a variety of smaller studies including scanning electron microscopy, x-ray diffraction, hardness measurements, and electrical resistance measurements. The results of this second set of experiments suggested that the good lubricant thinned the surface oxide layer, thus reducing the heat generation at the electrode-worksheet interface. This lower heat generation reduced alloying and pitting rate, thus increasing electrode tip life. Future work on improving the good lubricant was contemplated.

Control of diffusible weld metal hydrogen through flux chemistry modification : The influence of fluoride and calcite flux additions on the hydrogen content of shielded metal arc welds was examined

Abstract: This project examined the feasibility of using flux modification to reduce the as-deposited hydrogen content of basic-type shielded metal arc welds. Flux formulations containing additions of fluoride-containing compounds (CaF 2 , NaF, K 2 AlF 6 , and K 2 TiF 6 ) and calcite displayed lower hydrogen levels, with the diffusible weld metal hydrogen content reaching a minimum with increasing additions. Higher levels caused an increase in the weld hydrogen content. Thermodynamic slag modeling attributes the existence of these minima to a decrease in slag water capacity with an increase in slag fluoride content (at constant basicity), brought about by higher concentrations of fluoride-containing compounds in the flux formulation. The effect of flux additions on the weld mechanical properties and the electrode operating characteristics was not evaluated during the course of this investigation.

Weldability evaluation of supermartensitic stainless pipe steels

Abstract: Significant interest exists in the use of supermartensitic materials for oilfield applications. However, the hardness for both the weld deposit and the heat-affected zone (HAZ) of different material combinations may exceed the NACE requirement of 23 HRC (253 HV). Therefore, further studies to quantify the mechanical properties of welded joints and variables controlling the sulfide stress cracking (SSC) resistance in the as-welded condition remain necessary both for economical fabrication and to ensure reliable service operation. In this program, the as-welded mechanical properties of three different supermartensitic pipe steels were compared using different welding consumables and welding procedures. The susceptibility to hydrogen-induced stress corrosion cracking of selected weldments under slightly sour conditions and under cathodic protection was evaluated. Additionally, the influence of short postweld heat treatment (PWHT) on the HAZ mechanical properties and on the microstructure of three supermartensitic stainless pipe steels was studied. The results show that the filler metal and welding procedure combination affect the matching characteristics of the welded joint and their toughness and ductility properties. Additionally, supermartensitic steel welded joints with a maximum hardness ranging from 282 to 313 HV 1 and under an applied stress level equal to the measured yield strength of the base material did not crack under slightly sour conditions. The result also showed that a short PWHT is effective in reducing the micro-hardness of the HAZ to levels very close to the hardness of the base metal in the asreceived condition. It is assumed that the main mechanism responsible for the changes of hardness with PWHT is the amount of reverted and stable austenite.

A look at the statistical identification of critical process parameters in friction stir welding

Abstract: Many fundamental physical relationships governing the friction stir welding (FSW) process remain largely unexplored. Recent studies have aided in the discovery and clarification of many process fundamentals. A 16-run fractional factorial experiment was used to analyze the effects of nine FSW input parameters on measured process outputs. It was confirmed that the most significant input parameters are spindle speed, feed rate, and tool depth. In addition, the distance between the weld and side of the plate had a significant effect on measured Z-force and shoulder depth, and thus should be considered in future studies.

Effects of sheet surface conditions on electrode life in resistance welding aluminum

Abstract: The relatively short electrode life in welding aluminum sheets has been a bottleneck for large-scale production of aluminum vehicles. The rapid deterioration of electrodes during resistance welding aluminum is the collective consequence of high pressure, high temperature, and a rapid metallurgical (alloying) process. This study systematically investigated the effects of sheet surface conditions on electrode life. Using 2-mm 5A02 aluminum sheets, a schedule conducive to electrode life was used for testing the effects of sheet surface conditions. A three-phase, direct-current pedestal-type resistance spot welding machine was used, and the electrodes lasted for about 200 welds for sheets with untreated or original surfaces, up to 1700 welds when they were electric-arc cleaned, and more than 2000 welds if the sheets were degreased or chemically cleaned. This investigation also shows that the appearance of an electrode after a small number of welds provides useful information on the electrode life using the same welding schedule.

Low-speed laser welding of aluminum alloy 7075-T6 using a 300-W, single-mode, ytterbium fiber laser

Abstract: Heat-treatable aluminum alloys are important structural materials due to their increased strength-to-weight ratio. However, it is challenging to weld heat-treatable aluminum alloys successfully. Some of the factors affecting the weld quality include very high reflectivity, loss of strength, different kinds of porosity formation, hot tearing, solidification cracking, oxide inclusions, loss of alloying elements, and destruction of temper. In this paper, we explored the use of a 300-W, single-mode, ytterbium fiber-optic laser for low-speed keyhole welding of heat-treatable aluminum (7075-T6). The optimum welding speed was found to be between 2 and 3 mm/s, focused slightly into the workpiece (no deeper than 0.75 mm), for a maximum penetration of 1.02 mm. By defining the fluence per weld length and specific weld energy per weld length metrics, we were able to examine the results with respect to power, speed, and focus simultaneously and also get further insight into welding efficiency. The specific weld energy per weld length indicates how "well" the energy was used to produce a high aspect ratio weld. Furthermore, the slope of the plotted curves has a physical meaning as good weld conversion efficiency, indicating how much energy deposited into the material is actually used to produce a "good" weld. Steeper slopes indicate higher weld conversion efficiencies. Results show that with decreasing processing speed, the weld conversion efficiency decreased.

Estimation of weld quality in high-frequency electric resistance welding with image processing

Abstract: In high-frequency electric resistance welding (HF-ERW), the weld quality is determined by the welding phenomenon in the welding spot proximity. Methods to eliminate or minimize defects, therefore, include real-time monitoring of the weld quality and problem solving as problems arise. It is possible to estimate weld quality qualitatively by using the weld image data during HF-ERW A method to predict the weld quality using image processing in the heating process of the HF-ERW point is proposed. An algorithm, which predicts the weld quality by using a vision sensor to obtain the image of the welding spot proximity thus best expressing the welding phenomenon, is developed. The heated area, which shows the image data with the highest correlation to the weld quality and the smallest amount of noise, is consequently calculated.

Tailoring fillet weld geometry using a genetic algorithm and a neural network trained with convective heat flow calculations

Abstract: A desired weld feature such as geometry can be produced using multiple sets of welding variables, i.e., different combinations of arc current, voltage, welding speed, and wire feed rate. At present, there is no systematic methodology that can determine, in a realistic time frame, these multiple paths based on scientific principles. Here we show that the various combinations of welding variables necessary to achieve a target gas metal arc (GMA) fillet weld geometry can be systematically and quickly computed by a real-number-based genetic algorithm and a neural network that has been trained with the results of a heat transfer and fluid flow model. The neural network is computationally efficient and, because of its origin, its input and the output obey the equations of conservation of mass, momentum, and energy. A genetic algorithm is used to determine a population of solutions by minimizing an objective function that represents the difference between the calculated and the desired values of the penetration, throat, and leg length. The model proposed here is different from traditional reverse models, since they cannot provide a choice of solutions and usually do not confirm to any phenomenological laws. The computational methodology provided a choice among various sets of current, voltage, welding speed, and wire feed rate for achieving a given fillet weld geometry specified by a set of leg length, penetration, and throat. The computed results were adequately verified by comparing with experimental results. The results provide hope that other weld attributes can also be tailored based on scientific principles in the future.

Transferring Electron Beam Welding Parameters Using the Enhanced Modified Faraday Cup

Abstract: A procedure for transferring electron beam welding parameters between different machines using the Enhanced Modified Faraday Cup (EMFC) electron beam diagnostic tool is described. Unlike existing qualitative methods based on the transfer of machine settings, this procedure utilizes quantitative measurements of specific beam parameters, which can be correlated to the size and shape of the welds produced by the different welding machines. As a demonstration of this transfer procedure, a sharply focused 100-kV, 10-mA beam produced on one machine at a work distance of 457 mm is replicated on another machine with a defocused beam at a work distance of 210 mm. Measurements made with this diagnostic tool show that the peak power densities of the resulting beams vary by only 2%, while the beam distribution parameters, which are a measure of the beam width, vary by 4 to 7%. Using these well-characterized beams, autogenous welds with similar shapes and depths were then produced on 304L stainless steel samples. The measured depths of these welds vary by only approximately 8%, thus providing evidence for the utility of the use of this diagnostic tool in the transfer of beam parameters between different machines.