Nugget Formation Research Articles

Gold nugget formation from earthquake-induced piezoelectricity in quartz

Gold nugget formation from earthquake-induced piezoelectricity in quartz

Gold nugget formation from piezoelectric quartz

Gold nugget formation from piezoelectric quartz

Effect of Welding Parameter on the Nugget Overlap and Nugget Formation in Resistance Seam Welding of Secondary Coated Steels

Effect of Welding Parameter on the Nugget Overlap and Nugget Formation in Resistance Seam Welding of Secondary Coated Steels

Lap-Shear Performance of Weld-Bonded Mg Alloy and Austenitic Stainless Steel in Three-Sheet Stack-Up

With the growing interest in utilizing Mg and austenitic stainless steel (ASS) in the automotive sector, joining them together in three-sheet configuration is inevitable. However, achieving this task presents considerable challenges due to the large differences in their physical, metallurgical and mechanical properties. To overcome these challenges, the feasibility of using weld-bonding to join Mg alloy/ASS/ASS was investigated. The nugget formation, interface characteristics, microstructure and mechanical properties of the joints were investigated. The results show that the connection between the Mg alloy and upper ASS was achieved through the combined effect of the cured adhesive and weld-brazing in the weld zone. On the other hand, a metallurgical bond was formed at the ASS/ASS interface. The Mg nugget microstructure exhibited fine columar grains composed predominantly of primary α-Mg grains along with a eutectic mixture of α-Mg and β-Mg17Al12. The nugget formed at the ASS/ASS interface consisted largely of columnar grains of austenite, with some equiaxed dendritic grains formed at the centerline of the joint. The weld-bonded joints exhibited an average peak load and energy absorption of about 8.5 kN and 17 J, respectively (the conventional RSW joints failed with minimal or no load application). The failure mode of the joints changed with increasing welding current from interfacial failure via the Mg nugget/upper ASS interface to partial interfacial failure (part of the Mg nugget was pulled out of the Mg sheet). Both failure modes were accompanied by cohesive failure in the adhesive zone.

An investigation on bending fatigue in a corrosive environment of dual-phase 1000 sheet steel RSW joints and damage model via experiment and numeric analysis

Fatigue, corrosion, and fatigue damage models are best addressed to improve and understand the service performance of materials, particularly automotive steel. This study is an attempt to experimentally and finite element investigates plain bending fatigue performance and damage model of DP 1000 sheet steel resistance spot welding (RSW) joints in 3% NaCl aqueous corrosive treatment. RSW applications were carried out using different weld currents. The joint samples were then subjected to optical image analysis, tensile shear, and fatigue tests (3% NaCl-aqueous and normal atmosphere). A proper damage model of RSW junctions was developed and corrected by numeric analysis. Besides, RSW nugget formation, tensile shear, and plain bending fatigue tests were also applied. Consequence, fatigue behavior, tensile load carrying capacity, and effective fracture behavior of resistance spot welded joint specimens were evaluated. Results showed that a corrosive environment negatively affected fatigue performance. With the developed model, it was observed that the fatigue life of the samples decreased by 30–35% in the fatigue tests performed in the corrosive environment. Experimental and numerical analysis results of plain bending were compatible.

Detection of electrode misalignment and its effect on joint quality in resistance spot welding: a low-cost computer vision-based approach

Electrode misalignment in resistance spot welding can be caused by poor fitting or deformation of electrode with continuous usage. This leads to asymmetric weld nugget formation, porosity and expulsion. This paper presents a novel low-cost real-time inspection system for angular misalignment using an image processing approach. The proposed solution can effectively segment the electrode tips even from the image captured at noisy industrial background such as automotive assembly line, by using a regional convolutional neural network based object identification method. The trained model has a mean average precision and recall of 99.01% and 96.6%, respectively. A series of image processing tools and mathematical operations were used to identify the edge line contours of electrode tips accurately from the detection mask, and determine the angular misalignment with a maximum deviation of less than 0.06°. Experimental results showed that the weld nuggets exhibited porosity, shrinkage voids, and cracks when performed under angular misalignment conditions.

A GAN-based method for diagnosing bodywork spot welding defects in response to small sample condition

Due to the hidden nature and complexity of resistance spot welding weld nugget formation, how to avoid the time-consuming and money-consuming problem of traditional defect diagnosis methods and accurately grasp the weld nugget status is still an urgent problem. In this paper, an improved GAN model is proposed to solve the corresponding problem by combining the weld nugget defects with the dynamic resistance curve. Aiming at the problem that traditional GAN algorithms are prone to pattern collapse, this paper utilizes a variational autoencoder integrated with a channel attention mechanism as the generator part of the generative adversarial network, which helps the model pay better attention to the high-weight part of the defective sample data and combines the encoding and decoding processes to highlight defective features, thus reconstructing the defective samples with higher quality. Convolutional neural networks are then utilized to identify the features of the generated samples and diagnose the type of weldment defects. The test results show that the proposed scheme is highly reliable and the model outperforms other schemes in diagnosing welded nugget defects under the same conditions, avoiding undesirable effects such as underfitting. The validation of the actual dataset shows that, compared with other diagnostic methods that generally have an accuracy rate of less than 75%, the accuracy of the weld nugget defects diagnosis of this paper's method reaches more than 94%, which is a positive impetus to the development of auto body welding diagnosis.

Experimental Analysis on Ultrasonic Resistance Spot Welding of Aluminum Alloys

A recently developed hybrid joining process known as ultrasonic resistance spot welding (URW) was used on various pairs of similar and dissimilar aluminum (Al) alloys with different thicknesses, including AA5182–AA5182, AA6111–AA6111, AA7075–AA6111, and AA7075–AA5182, and comprehensively studied. Compared to conventional resistance spot welding (RSW), URW of the alloys showed consistently enhanced mechanical behavior in lap shear and crosstension tests. This can be attributed to the multiple perspectives on microstructure improvements. For different stacks of Al alloys and welding conditions, nugget formation was promoted with a larger nugget size in URW. In the nugget center, ultrasonically assisted (UA) vibration facilitated the formation of an equiaxed crystal zone. At the nugget boundary, URW showed a narrower coarse columnar zone and partially melted zone, which are associatedwith the lowest hardness in the weld. Specifically in dissimilar Al welds, UA vibration moved the nugget more centered toward the weld interface. These microstructure improvements indicated UA vibration can homogenize temperature and elemental distribution, which modifies solidification behavior.

An Optimization Study on Resistance Spot Welding of DP600 Sheet Steel via Experiment and Statistical Analysis

Resistance Spot Welding (RSW) is widely used in many automotive, boiler, and ship manufacturing industries. Therefore, the optimization and effectiveness of the RSW process are very useful and cost-efficient processes in addition to improving weld quality. This study used various welding parameters to investigate the optimization of the RSW process of Advanced High Strength Steel (AHSS). RSW was carried out using different welding times, currents, and electrode pressure values. Microstructural analysis, nugget formation, and tensile shear test were performed on samples. This study applied the Taguchi method and ANOVA to set up the welding process and optimize its results. Microstructural characterization showed that the weld nugget microstructures had a high-volume fraction of martensite. Using the Minitab software, Taguchi (DOE) and ANOVA on the tensile shear test results showed that welding current is more effective than clamping pressure on the tensile shear load-bearing capacity (TLBC). However, clamping pressure affects the weld current effects on weld performance. Additionally, the TLBC of RSW samples increases, whereas increasing the clamping pressure leads to a decrease in TLBC and nugget dimensions. Consequently, a detailed analysis of the RSW coefficients and their effects led to optimized results.

Critical effect of heat input on joint quality in resistance element welding of Al and steel

Resistance element welding (REW) has recently attracted increasing interest, especially in the joining of high-strength steels and aluminum alloys. However, the intensity of heat input is a critical factor for the joint quality due to the possibility of excessive melting of the aluminum sheet around the element shank, which often degrades the joint's performance. This study evaluates the influence of heat input on the joint formation and mechanical performance of REW joints between ultra-high strength steel and aluminum alloy. In addition to the experimental investigations, a finite element method (FEM) was used to analyze the temperature distribution, nugget formation, and aluminum sheet melting characteristics as a function of heat input. The results show that the nugget dominates the joint's strength if the heat input is comparatively low. When heat is increased, however, the aluminum sheet plays a significant role in the joint's strength. Excessive melting of aluminum sheets reduces the load-bearing area of the joint. The competition between the weld nugget and aluminum sheet determines the joint's strength. The failure mode changes from interfacial to aluminum sheet failure as the heat input increases. The combined effect of aluminum sheet thickness and heat input on the joint strength was also evaluated. The results indicate that determining the appropriate heat input level is crucial to achieving an excellent performance of the REW joints.

Quantitative Interpretation of Dynamic Resistance Signal in Resistance Spot Welding

Dynamic resistance is one of the most common and important signals used to monitor and control the resistance spot welding (RSW) process. However, existing studies on the signal evolution mechanism are limited to qualitative analysis, resulting in an ambiguous interpretation of the formation mechanism for the signal features. In this paper, a collaborative simulation approach was applied for the RSW of bare DP590 steel to obtain high-precision computation of the temperature and potential distributions inside the weld. On this basis, an analytical mapping model between the dynamic resistance signal and the weld profile was developed based on basic physical laws, and the signal evolution mechanism was quantitatively revealed through the model. It was found that the main factors determining the signal evolution trend are average sheet temperature and electrode/sheet contact diameter rather than the nugget growth process. The peak resistance feature was attributed to the bilinear relationship between sheet resistivity and temperature rather than nugget formation. The resistance drop after the peak mainly arose from the increase of the electrode/sheet contact diameter rather than nugget growth. This study can help improve the comprehension of the dynamic resistance signal and the interpretability of some data-driven methods used for RSW quality monitoring and control.

Quantitative characterization of fracture spatial arrangement and intensity in a reservoir anticline using horizontal wellbore image logs and an outcrop analogue

Using image logs from horizontal wells in the asymmetric East Painter Reservoir anticline in Wyoming, scanlines and petrographic observations from nearby outcrops, and methods that allow statistical quantification of fracture spatial arrangement patterns (including clustering), we show that in early Jurassic Nugget Formation sandstone degree of clustering and intensity of fractures varies with structural position. In the backlimb, fractures are markedly more clustered than random, and hierarchical and regularly spaced clusters are present, but intensity is low. In the forelimb, arrangements are mostly indistinguishable from random, but intensity is high. Based on image log response, the backlimb contains a higher proportion of open fractures, although the forelimb has greater numbers of open fractures. Spatial arrangement and intensity patterns are similar in a forelimb outcrop. Petrography reveals that quartz seals fractures less than 0.15 mm wide. Wider fractures are open with quartz rinds or are quartz lined and sealed with calcite or filled by quartzose cataclasite. The proportion of open fractures depends on quartz and calcite deposits and closure by reactivation (shearing) of pre-existing quartz-lined fractures. Based on increased abundance and greater strike dispersion, results suggest that in forelimbs, high fracture intensities reflect shear on preexisting fractures, possibly resulting in more numerous but less spatially correlated open fractures. The most prolific gas and water production wells are in the backlimb, suggesting that clustered but sparse quartz-lined open fractures are more effective fluid conduits than closely spaced partly damaged/sheared arrays.

Microstructure and joining mechanism of Al/CFRTP resistance element welded joints

Resistance element welding (REW) is an effective method for joining dissimilar materials by applying an auxiliary element in resistance spot welding (RSW). In this paper, 6061-T6 aluminum alloy/carbon fiber reinforced thermoplastic (CFRTP) joints were produced via REW. The macrostructure, microstructure, microhardness distribution and tensile shear performance of the joints obtained via REW were investigated. The effects of welding parameters on the nugget formation and joint performance during REW were investigated. Studied the joining mechanism by microscopic observation and mapping. Conducted fractography by macroscopic 3D observation and scanning electron microscope (SEM) observation. It is found that in a certain range, the interface nugget diameter increases with the increase of heat input, resulting in the increase of tensile peak load. The maximum peak tensile shear loads of the REWed joints were 3788.06 N. The failure mode of the REW joints changed from interface mode to partial button fracture with an increase in welding current under the same welding time and electrode pressure.

Nugget formation, microstructural features and strength of resistance spot welded cold-rolled dual-phase steel lap joints for automotive applications

Abstract The main objective of this research paper is to investigate the nugget formation, microstructure and strength performance of DP 800 steel joints developed using resistance spot welding (RSW) process for automotive application. The influence of RSW parameters on nugget formation was studied using one variable at a time approach. The RSW joint showing optimum nugget area was further characterized for microstructural features and strength performance. The microstructural features of nugget were studied using optical and scanning electron microscopy (SEM). The lap tensile shear fractured specimens were analyzed using SEM for optimized condition. The microstructural features were correlated to the tensile shear strength and hardness of RSW joints. Results showed that welding current significantly influences the nugget formation than electrode force and welding time. The DP 800 RSW joints made using a welding current of 5.5 kA, an electrode pressure of 4.0 MPa and a welding time of 2.0 s disclosed defect free weld nugget of 7.28 mm diameter. It showed a higher tensile shear strength of 20 kN and microhardness of 564 HV thereby satisfying the requirement of automotive applications.

Computational analysis of the ultrasonic effects on resistance spot welding process

Ultrasonic resistance welding (URW) is a hybrid welding process that utilizes in situ ultrasonic vibration during resistance spot welding (RSW) process to increase nugget size, enhance weld mechanical properties, and refine microstructure. Despite the promising experimental results, the underlying mechanisms of acoustic effects on the RSW process are elusive as the involved interacting physical phenomena can hardly be revealed with direct experimental methods. In this study, a three-dimensional fully coupled electro-thermo-mechanical model of the URW process for aluminum alloys has been developed and validated, where the ultrasonic effect on nugget formation and evolution is simulated from different perspectives based on a RSW model. It shows that the enlarged nugget in URW welds is a result of coupling interactions among multiple ultrasonic effects on contact resistance and molten metal thermophysical properties, which are based on the ultrasonically assisted fracture of surface oxides, acoustic softening, cavitation and streaming physical phenomena.

Particle simulation of nugget formation process during steel/aluminum alloy dissimilar resistance spot welding and thickness estimation of intermetallic compounds

A steel/aluminum alloy dissimilar resistance spot welding process was simulated by a three-dimensional smoothed particle hydrodynamics method. Furthermore, the time-dependent increase in the intermetallic compound thickness at the joint interface was estimated using the obtained numerical data of temperature history. As a result, the steel sheet started to melt from the center of the sheet in the thickness direction. The convection in the molten aluminum alloy caused by the electromagnetic force promoted the heat transfer at the solid-liquid interface because the temperature gradient becomes steeper. Moreover, the maximum thickness of the intermetallic compound was estimated to be approximately 1 µm. These results support the validity of the computational model developed in this study for simulating the nugget formation process during dissimilar resistance spot welding and estimating the intermetallic compound thickness.

Effect of temperature patterns on iron nugget formation in fluxless processing of titanomagnetite

The technology used to process titanomagnetite is currently limited to the rotary kiln-electric furnace. Other techniques are being developed, including the separation of iron in the form of iron nugget from the reduction of titanomagnetite with coal without any flux addition. The effect of different temperature patterns on the formation of iron nuggets from titanomagnetite was studied. The initial temperature was varied from 700 to 1380 °C, while the final temperature was kept constant at 1380 °C. The experiment results showed that the initial temperature affected the formation of iron nuggets. Initial temperatures of 700–1100 °C produced many iron nuggets up to 3 mm in size and an initial temperature of 1200 °C produced one nugget with a size of about 4 mm. Initial temperatures of 1300 and 1380 °C did not produce any iron nuggets due to the formation of metallic iron crust on the surface of the reduced briquettes. The optimum initial temperature was 1000 °C to achieve high iron recovery in the nuggets.

Substituting Resistance Spot Welding with Flexible Laser Spot Welding to Join Ultra-Thin Foil of Inconel 718 to Thick 410 Steel.

This paper investigated various aspects of replacing existing micro-resistance spot welding (micro-RSW) with micro-laser spot welding for joining Inconel 718 thin foils to thick 410 steel stack-up to allow faster, non-contact joining together with flexibility in spot positioning and removal of tip dressing required for RSW electrodes. The joint quality was evaluated based on the mechanical strength, microstructural characteristics and joint strength at elevated temperature as these joints are often used for high-temperature applications. Experimental investigations were performed using micro-RSW and micro-laser spot welding to obtain the 90° peel and lap shear specimens, each comprising four spots. The obtained strength from laser joints was significantly higher than that of micro-RSW joints due to larger weld nugget formation and interface width. The process map for obtaining good quality welds was also identified, and about a 17% reduction in joint strength was obtained when welded specimens were subjected to elevated temperature (i.e., 500 °C) in comparison with room temperature. This reduction was compensated for using the flexibility of laser welding to add two extra spots. The overall performance of the micro-laser spot welds was found to be better than the micro-RSW considering joint strength, flexibility in placing the spots and time to produce the welds.

Influence of zinc coating on nugget development and mechanical properties in dissimilar welded joints DP600 – AISI304 obtained by the RSW process

This paper researches the influence of zinc coating of galvanized DP600 steel (DP600G) on the nugget development and mechanical properties of dissimilar DP600 - AISI304 welded joints obtained by resistance spot welding process (RSW). The RSW evaluations consisted of determining, from the dynamic resistance curves, the different stages involved in nugget formation. The experimental results showed that the zinc coating on the DP600G steel has a significant influence on the time needed for the start of the nugget formation, two times higher than that used for non-galvanized steel. The expulsion time was delayed by 1.12 times. The presence of Zn in the DP600G/AISI304 welded joints produced smaller nugget diameters compared to the DP600/AISI304 joints for the same experimental conditions, however higher peak failure load values were obtained for the first. The causes of this unusual behavior are also analyzed in this paper.

Effect of zinc coating on delay nugget formation in dissimilar DP600-AISI304 welded joints obtained by the resistance spot welding process

Effect of zinc coating on delay nugget formation in dissimilar DP600-AISI304 welded joints obtained by the resistance spot welding process