Resistance Spot Welding Of Aluminum Alloy Research Articles

Quality prediction of aluminum alloy resistance spot welding with shunting by introducing spacing factor

Shunting is a very common phenomenon in the practical manufacturing of aluminum alloy resistance spot welding (RSW). Effective quality prediction method for RSW with shunting is still insufficient. In this study, after dimensionality reduction by principal component analysis (PCA), the ensemble learning model AdaBoostRegressor was used to predict the weld diameter under shunting conditions in aluminum alloy RSW. The prediction effects of various signals collected during the welding process on the welding quality were compared and discussed. After the introduction of the spacing factor, except for the welding voltage and dynamic resistance signals, the effects of other signals in predicting the welding quality have been significantly improved. The electrode displacement signal introduced with the spacing factor has the best effect on the quality prediction of welds among all the collected signals, and the coefficient R2 reaches 0.88. It is concluded that the electrode displacement signal is suitable for quality monitoring of aluminum alloy RSW under various conditions. Undersized welds can be quickly identified by calculating the work done by the weld spots to the upper electrode. Our study lays a foundation for the real-time quality monitoring in the process of aluminum alloy RSW.

Numerical and experimental study of the hot cracking phenomena in 6061/7075 dissimilar aluminum alloy resistance spot welding

In this study, a CALPHAD-coupled finite element model was established to reveal the formation mechanism of hot cracks (including liquation and solidification cracks) in the dissimilar 6061/7075 resistance spot welding joints. The partially melting zone (PMZ) and the fusion zone solidified under tension during the cooling stage. When the composition of the local area is susceptible to hot tearing, crack initiation would take place. This can be revealed by the CALPHAD-coupled finite element model. At the 6061/nugget interface, the PMZ was torn apart under the thermal strain to form cracks which are perpendicular to the nugget border (Type I liquation cracks). At the 7075/nugget interface, the PMZ was torn apart by the solidification contraction of the nugget ((fS)nugget>(fS)7075) to form cracks along the tangent line of the nugget border (Type II liquation cracks). The calculation of the ∣dT/d(fS)1/2∣ index shows that the solidification cracking susceptibility of the 6061/7075 nugget is fairly high. The metallographic and energy dispersive spectrometer analysis shows that the Type I liquation cracks were filled by the liquid within the nugget while the Type II liquation cracks and solidification cracks created a local no-bonding area. The Type I liquation cracks did not affect the mechanical properties of the joints while the Type II liquation cracks deteriorated the mechanical properties of the joints.

Efecto de la velocidad de rotación y la indentación en soldadura de punto por fricción agitación de aleaciones de aluminio disimilares

En los últimos años, dentro de a la industria automotriz, se busca introducir partes de aluminio en reemplazo de componentes de acero para la disminución en peso de los vehículos. Estas piezas deben ser unidas entre sí, por ejemplo, mediante soldadura. El proceso de soldadura más utilizado dentro de la industria automotriz es la soldadura de punto por resistencia (RSW). Sin embargo, la soldadura RSW de aleaciones de aluminio presenta desventajas importantes. Dentro de este contexto se ha desarrollado una variante del proceso de soldadura por Fricción Agitación denominado Soldadura de Punto por Fricción Agitación (FSSW), el cual presenta un fuerte interés en relación a la soldadura de aleaciones de aluminio y de materiales disímiles en chapas finas. Los parámetros de soldadura afectan a las características de las juntas obtenidas. Sin embargo, es escasa la información disponible sobre la influencia de estos sobre las características de la unión, en particular para juntas disimilares y en chapa fina. El objetivo de este trabajo fue estudiar el efecto de la velocidad de rotación y la profundidad de indentación de la herramienta sobre las características de uniones disimilares soldadas por FSSW. Uniones soldadas sin defectos pudieron obtenerse con propiedades mecánicas superiores a lo que se reporta hasta el momento. La carga de rotura máxima fue de 5800 N. La longitud efectiva de unión aumentó con la indentación de la herramienta, mientras que la carga de rotura aumenta y luego disminuye. Finalmente, al soldar con 1200 RPM las propiedades mecánicas de las uniones disminuyeron, respecto a lo obtenido con 680 y 903 RPM.

Weld Growth Mechanisms and Failure Behavior of Three-Sheet Resistance Spot Welds Made of 5052 Aluminum Alloy

This paper investigates the weld nugget formation in three-sheet aluminum alloy resistance spot welding. The nugget formation process in three equal thickness sheets and three unequal thickness sheets of 5052 aluminum alloy were studied. The results showed that the nugget was initially formed at the workpiece/workpiece interfaces (i.e., both upper interface and lower interface). The two small nuggets then grew along the radial direction and axial direction (welding direction) as the welding time increased. Eventually, the two nuggets fused into one large nugget. During the welding process, the Peltier effect between the Cu-Al caused the shift of the nugget in the welding direction. In addition, the mechanical strength and fracture mode of the weld nuggets at the upper and lower interfaces were also studied using tensile shear specimen configuration. Three failure modes were identified, namely interfacial, mixed, and pullout. The critical welding time and critical nugget diameter corresponding to the transitions of these modes were investigated. Finally, an empirical failure load formula for three-sheet weld similar to two-sheet spot weld was developed.

Numerical and experimental study on nugget formation process in resistance spot welding of aluminum alloy

The weld nugget formation in the resistance spot welding (RSW) of aluminum alloy was investigated in the present study. The nugget formation process was directly observed by using a digital high-speed camera. Numerical simulation was also employed to investigate the nugget formation process. The results showed that for the RSW of two aluminum alloy sheets, a nugget was first formed in the workpiece/workpiece (W/W) interface and grew along the radial direction and axial direction of the sheets, and then it became a large elliptical nugget. For the RSW of three aluminum alloy sheets, two small nuggets were firstly formed in two W/W interfaces and grew along the axial direction and radial direction; finally they fused into one nugget. Besides, there existed a critical welding time, after which the nugget size remained nearly unchanged. This indicates that a long welding time is unnecessary for the RSW of aluminum alloy. In addition, the calculated nugget radius was compared with the experimental results, which showed that the simulation results agreed well with the experimental results.

Modeling, identification and simulation of DC resistance spot welding process for aluminum alloy 5182

Currently the aluminum alloy resistance spot welding (AA-RSW) has been extensively used for light weight automotive body-in-white manufacturing. However the aluminum alloys such as AA5182 have inferior weld ability for forming the joint due to their high reflective ness to heat and light. Therefore it is necessary to further develop the high performance control strategy and the set-up of a new welding schedule. The welding process identification is the essential issue where the difficulty arises from the fact that the AA-RSWis a nonlinear time-varying uncertain process which couples the thermal, electrical, mechanical and metallurgical dynamics. To understand this complicated physical phenomenon a novel dual-phase M-series pseudo-random electrical pattern is adopted to excite the AA-RSW electrical-thermal process and the thermal response is recorded according to the welding power outputs. Based on the experimental information, the transfer function of an AA-RSW electrical thermal mechanism is identified, and the optimum model order and parameters are determined. Subsequently a control-oriented DC AA-RSW model is established to explore the welding power control algorithm. The simulated results of the control model show agreement with the experimental data, which validates its feasibility for the corresponding welding control.

Multi-field dynamic modeling and numerical simulation of aluminum alloy resistance spot welding

In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical–thermal–mechanical and metallurgical analysis was established to numerically display the resistance spot welding (RSW) process within multiple fields and understand the AA-RSW physics. A multi-disciplinary finite element method (FEM) framework and a empirical sub-model were built to analyze the affecting factors on weld nugget and the underlying nature of welding physics with dynamic simulation procedure. Specifically, a counter-intuitive phenomenon of the resistance time-variation caused by the transient inverse virtual variation (TIVV) effect was highlighted and analyzed on the basis of welding current and temperature distribution simulation. The empirical model describing the TIVV phenomenon was used for modifying the dynamic resistance simulation during the AA spot welding process. The numerical and experimental results show that the proposed multi-field FEM model agrees with the measured AA welding feature, and the modified dynamic resistance model captures the physics of nugget growth and the electrical-thermal behavior under varying welding current and fluctuating heat input.

Multiple information fusion and quality classification of aluminum alloy resistance spot welding

Resistance spot welding quality real-time monitoring of aluminum alloy is realized by distributed multiple-sensor synchronous collection system and the related data processing software is also developed by using LABVIEW graphical language.The results show that the endo-expulsion in spot welding is related to the notching curve of voltage and electrode displacement signal.Moreover,there is a correlation between the high frequency impulse amplitude and duration of the electrode pressure signal and the expulsion strength index,and three characteristics simultaneously or separately occur according to the expulsion strength index in spot welding. Resistance spot welding quality can be reflected by nine characteristics of high signal-to-noise ratio,and they become the base of on-line quality classification of aluminum alloy spot welding in future.Furthermore,using principal component analysis may implement the information fusion and data compression.The percentage of spot welding quality classification accuracy can reach 98%.

EFFECT OF ELECTRODE PITTING ON WELDING QUALITY IN RESISTANCE SPOT WELDING OF ALUMINIUM ALLOYS

The effect of electrode pitting on the welding quality in resistance spot welding (RSW) of aluminum alloy AA5182 is investigated using both finite element analysis and physical modeling methods. Results show that with the increasing of the pitted area at the electrode tip, the actual contact area at elec- trode/sheet interface does not change so much, while the con- tact area at sheet/sheet interface is increased significantly, therefore, the current density at the sheet/sheat interface is re- duced greatly, and the thickness and diameter of the nugget formed are both decreased. Dimensions and shapes of the nug- gets from physical modeling are in very good coincidence with numerical predictions. Only a donut shape nugget with very limited thickness is formed when the diameter of the pitting hole is 5.0 mm. These results reveal that the increasing of con- tact area at sheet/sheet interface by the increasing pitting hole diameter at the electrode tip is one of the major causes for worse and worse welding quality durin RSW of aluminum alloys.