Resistance Spot Welding Process Research Articles

Understanding the mechanisms behind ultrasonic vibration in resistance spot welding of aluminum and steel

An ultrasonic-assisted resistance spot welding process, which can improve the quality of aluminum/steel spot-welded joints, has been developed. However, the mechanism of the thermal-electrical-mechanical behavior caused by the ultrasonic longitudinal vibration to welding process has not been clarified. In this study, the role and impact mechanisms of ultrasonic longitudinal vibration during the welding process to form joints were confirmed by combining the microstructural characterization of the formed joints with the signal analysis of the process, as well as the analysis of the independent finite element numerical calculation results. Additionally, the interface metallurgical reaction behavior, welding defects, fracture behavior, and joint strength characteristics of ultrasonic-assisted aluminum/steel resistance spot welding joints were comprehensively analyzed, and the results indicated that the sizes of the aluminum/steel nuggets decreased. It could be attributed to the competition among multiple ultrasonic effects. Specifically, ultrasonic vibration decreased the contact resistance between the aluminum/steel sheets, whereas the acoustic cavitation and acoustic streaming effects increased the electrical conductivity of molten steel and thermal conductivity of molten aluminum, respectively. Moreover, ultrasonic vibration promoted the radial creep of molten and near-molten aluminum, which expanded in the effective bonding area between the two workpieces. Furthermore, ultrasonic vibration effectively reduced the thickness of the intermetallic compound layer (<3.0 µm), concurrently inhibited the formation of interfacial welding defects. Finally, the peak tensile-shear load of aluminum/steel joints is significantly increased under multiple ultrasonic optimization mechanisms.

Electric-thermal-mechanics modeling for in-process phenomena during micro resistance spot welding spark plug of Pt and Inconel600

The spark plug is one of the important components in the gasoline engine's combustion chamber. To reduce vehicle emissions, the platinum spark plug is selected due to its good performance. Due to the high productivity of resistance spot welding (RSW), a micro-scale RSW process is employed to assemble the platinum tip to Inconel600 part in the production of spark plugs. In order to understand the electric-thermal-mechanics phenomena during micro resistance spot welding spark plug for controlling the welding quality and saving electric energy, a three-dimensional simulation model and the in-house finite element program JWRIAN-RSW3D were developed. The potential history and upper electrode displacement results were verified with experiments. Numerical case studies were made to investigate the influence magnitude of welding current on the electric-thermal-mechanics phenomena. The developed model reveals inside phenomena to clearly understand the welding mechanism for potential, current density, temperature, electrode displacement and their distribution/history as well as the molten zone. The comprehensive phenomena of maximum temperature distribution on both base metals and Inconel600 were clarified using a top perspective, revealing differences in distribution on the contact surface between horizontal and vertical sections. To achieve a complete welding joint, the molten zone on the contact area is required carefully in order to facilitate the bonding of both base metals. Based on simulation results for three welding conditions, the alternating current at the magnitude of 1.2 kA with the welding time of 0.1 s is recommended to obtain the welded joint with minimized energy consumption in production.

Metaheuristic optimization and computational investigation of resistance spot welding process parameter employing Jaya, TLBO and Rao-II algorithm

Metaheuristic optimization and computational investigation of resistance spot welding process parameter employing Jaya, TLBO and Rao-II algorithm

Robust Multivariate Functional Control Chart

In modern Industry 4.0 applications, a huge amount of data is acquired during manufacturing processes and is often contaminated with outliers, which can seriously reduce the performance of control charting procedures, especially in complex and high-dimensional settings. In the context of profile monitoring, we propose a new framework that is referred to as robust multivariate functional control chart (RoMFCC) to monitor a multivariate functional quality characteristic while being robust to both functional casewise and componentwise outliers. In the former case, observations of the quality characteristic are contaminated in all functional variables or components, while, in the latter, the contamination affects one or more components independently. The RoMFCC relies on (I) a functional filter to identify componentwise outliers to be replaced by missing components; (II) a robust multivariate functional data imputation method; (III) a casewise robust dimensionality reduction; (IV) a monitoring strategy for the quality characteristic. Through a Monte Carlo simulation study, the RoMFCC is compared with competing schemes that have already appeared in the literature. A case study is finally presented where the proposed framework is used to monitor a resistance spot welding process in the automotive industry. RoMFCC is implemented in the R package funcharts, available online on CRAN.

Development of Q&P steels of third generation under conditions simulating a continuous annealing process, and evaluation of their weldability by the RSW process

Quenching and partitioning, advanced high-strength steels (Q&P-AHSS), are considered as potential candidates to satisfy the current requirements of the automotive industry in terms of passenger safety. Their fabrication at industrial scale has required modifications to well-established processes and thus, obtaining this type of microstructures through easier thermal cycles represents a current challenge for steel manufacturers. Apart from their manufacturing method, their mechanical properties and weldability are equally important. In the present work, Q&P-AHSS were obtained through short-term annealing and isothermal treatments, to further investigate the effects of resistance spot welding (RSW) parameters, on nugget quality and tensile shear strength. Results show that Q&P-AHSS can be welded with success by the RSW process, meeting the required quality specified in the standard AWS D8.9 M-2012.

A comparative study on resistance spot and laser beam spot welding of ultra-high strength steel for automotive applications

In this study, the effect of resistance spot welding (RSW) and laser beam spot welding (LBSW) processes on evolution of microstructure, load endurance capabilities, heat affected zone (HAZ) softening, and corrosion resistance of ultra-high-strength (UHSS) steel joints welded in lap joint design is investigated. The UHSS sheets of dual phase 1000 grade (UHSDP1000) having 1.20 mm thickness were joined using the RSW and LBSW parameters optimized by response surface methodology (RSM). The microstructural features of welding regions of RSW and LBSW joints were studied using optical microscopy (OM). The load endurance capabilities of RSW and LBSW joints were assessed using the tensile shear failure load (TSFL) and cross-tensile failure load (CTFL) tests. The ruptured surfaces of TSFL and CTFL tested samples were examined utilizing scanning electron microscopy (SEM). The microhardness distribution of divergent regions of RSW and LBSW joints was evaluated and imputed to the TSFL and CTFL failure of joints. The corrosion resistance of RSW and LBSW joints was analyzed using potentiodynamic corrosion and immersion corrosion tests. The RSW joints showed 183% and 62.79% greater TSFL and CTFL endurance capabilities than LBSW joints. The TSFL and CTFL endurance capabilities of LBSW joints are inferior to RSW joints due to the smaller load bearing area. It causes the stress concentration in FZ and HAZ of LBSW joints. The RSW joints and LBSW joints disclosed TSFL and CTFL failure in button pull out rupture mode with tearing of HAZ. The failure of RSW and LBSW joints in HAZ is due to the softening caused by martensitic tempering and coarsening of grains. The LBSW joints disclosed inferior resistance to corrosion than RSW joints due to the higher martensite content which contributes to greater fraction of favorable pitting sites and decreased corrosion resistance.

Experimental research on mechanical, material, and metallurgical properties of Inconel 600: Application in elevated temperature environment

Experimental research on mechanical, material, and metallurgical properties of Inconel 600: Application in elevated temperature environment

Quality monitoring for a resistance spot weld process of galvanized dual-phase steel based on the electrode displacement

AbstractIn previous works, it has been found out that the electrode displacement in resistance spot welding has a high potential to be used as a measurement factor to monitor joint quality and to subsequently optimize the welding parameters. By extracting characteristic points in the displacement curve, it is possible to create and evaluate different parameter sets and to predict the formation of expulsion. These characteristic points include for example the maximum displacement of the electrodes, the time of the maximum displacement, the indentation displacement in the weld and hold time, or the velocity of the electrodes. In previous work, it was already shown that the indentation displacement showed satisfying results in predicting the nugget diameter for a press hardened 22MnB5 + AS150 under laboratory conditions. Based on that, a newly derived methodology for using the electrode displacement in monitoring a resistance spot weld process is shown for a galvanized dual-phase steel CR440Y780T-DP GI50/50-U. This methodology combines the knowledge of previous research and is split into three steps: the detection of manufacturing discontinuities, the evaluation of expulsion, and the monitoring of the nugget diameter. For this, the electrode velocity at the beginning of the process and the indentation displacements in the weld and hold time are being used to evaluate the resistance spot welding process.

Online estimation and characteristic analysis of double nugget diameters during aluminum/steel resistance spot welding process

Online estimation and characteristic analysis of double nugget diameters during aluminum/steel resistance spot welding process

Half-sectioned spot weld parameter optimisation for liquid metal embrittlement analysis in advanced high-strength steels

Half-section welding has been proposed as a method to observe nugget growth throughout the resistance spot welding process. Some past studies used this technique as an in-situ monitoring approach to analyse the cracking behaviour during welding. However, there is a lack of understanding regarding the half-sectioned welding parameters, which critically impacts the liquid metal embrittlement cracking index. This study optimised half-sectioned welding parameters for liquid metal embrittlement crack analysis by developing process maps that compare the half-sectioned and full-section processes. It was found that the liquid metal embrittlement crack located at the weld shoulder can correlate to the temperature gradient in the heat-affected zone. This study proposes half-sectioned welding as a viable technique for liquid metal embrittlement analysis.

Joining thin galvanized low carbon steel sheet to AA6056-T4 by resistance spot welding and adhesive weld bounding

Multimaterial assemblies made by resistance spot welding (RSW) process offer a cost-efficient lightweight solution for automotive body-in-white production. However, joining different materials, such as steel (Fe) and aluminum (Al), brings issues due to their different physical properties and low weldability. The present work investigated the evolution of the weld between a thin galvanized low carbon steel sheet and an AA6056-T4 aluminum alloy from macroscopic observations to the evolution of the intermetallic compound layer (IMC) during RSW. Comparisons between homogeneous Al-Al RSW, Fe-Al RSW and Fe-Al adhesive weld bonding for different mechanical solicitations were also realized. Observations showed that the interface for short welding periods is composed of a thin and discontinuous IMC layer. The interface also presents defects that facilitate crack initiation and propagation, leading to an interfacial fracture mode. The different mechanical tests carried out demonstrated that the Al-Al and Fe-Al welds reached a similar maximum tensile load under the shear–tensile test. However, Fe-Al assemblies under cross-tensile test showed poor mechanical properties. The use of an adhesive layer with an Fe-Al spot weld seems to be a potential solution, as it is easily implementable on production lines and improves the mechanical properties of Fe-Al assemblies.

Numerical modeling of liquid metal embrittlement initiation during resistance spot welding of third generation advanced high strength steel – Effect of welding schedule and electrode alignment

Third generation (GEN3) advanced high-strength steels are increasingly used to reduce vehicle body structure weight for improved fuel economy. Zinc-induced liquid metal embrittlement (LME) has become a prevalent challenge when these steels are welded by resistance spot welding (RSW). In the literature, various numerical models have been developed to study LME during RSW of GEN3 steels. Those models tend to have a limited utility in predicting how various factors such as RSW parameters affect LME cracking. In this study, a novel LME calculation method has been developed by integrating an electro-thermo-mechanical finite element model of RSW process with an LME ratio for crack initiation established from hot tensile testing data. The onset of different types of LME cracking is tracked throughout the weld region over the entire course of RSW including the final cooling stage after electrode retraction. The model is validated using an existing set of literature data that involves different welding schedules, electrode geometries and electrode misalignments. The local temperature and stress conditions during RSW are calculated and used to understand how different welding parameters affect the severity of LME cracking. It is found that electrode misalignment exacerbates crack initiation on outer surfaces of the spot weld due to the tensile stress arisen from the off-centered squeeze force as well as the reduced surface cooling to electrodes. Initiation of cracks between the steel sheets, taking place mainly after electrode retraction, is not significantly affected by the welding schedule and the electrode tip diameter.

Advanced process characterization and machine learning-based correlations between interdiffusion layer and expulsion in spot welding

Over the past decades, substantial endeavors have been dedicated to unraveling the intricacies inherent to Resistance Spot Welding (RSW). However, a comprehensive and consensual understanding of the RSW process physics is still lacking, including the exact number of physical phases behind the RSW process. For example, a widely accepted model indicates that metal only starts melting after the peak of dynamic resistance, while the latest research on welding uncoated materials challenges this by suggesting that melting begins around the resistance peak. Furthermore, most of existing physical models only consider welding materials without coatings in a controlled lab setting, whereas coated sheet metal is the norm in real production. Addressing these challenges, this paper introduces an enhanced model for RSW that considers the melting phase of the coating's InterDiffusion Layer (IDL) in Press Hardening Steels (PHS). This phase is believed to influence both welding quality and the occurrence of expulsions. Additionally, the timing at which each phase starts has been determined by analyzing real-time, multi-variable sensing data from various welding scenarios, and a signal processing technique has been devised to automatically identify when these phases begin. Leveraging this refined process understanding and characterization, meaningful explainable features are extracted, and a data-driven multilayer perceptron model is constructed for 1) predicting IDL thickness and 2) detecting expulsions upon predicted IDL thickness. The experimental results validate that the proposed IDL-inclusive model advances existing physical models for RSW and the IDL prediction improves the RSW defect detection and process monitoring.

Improving Weldability of Press Hardened Steel Through Combining Stepped Current Pulse and Magnetically Assisted Resistance Spot Welding Process

Abstract Press-hardened steel (PHS), characterized by its extremely high strength, has wide applications in vehicle body manufacturing as an innovative lightweight material. Nevertheless, the poor weldability of PHS results in poor weld toughness and a high risk of interfacial fracture (IF), posing challenges to the resistance spot welding (RSW) process. Introducing an external magnetic field in the welding process to perform electromagnetic stirring (EMS), the magnetically assisted RSW (MA-RSW) process has been proven an effective method to improve the weld toughness of high-strength steel, but it may increase the risk of expulsion. In response to these challenges, this study introduces a new process called SPMA-RSW to improve the weldability of PHS by combining MA-RSW and the stepped-current pulses (SP) technique, which can enlarge the weld lobe. Nugget appearance, microstructure, microhardness, and mechanical properties were systematically investigated by comparing traditional RSW, MA-RSW, SP-RSW, and SPMA-RSW. The result showed that the SPMA-RSW process would significantly increase the nugget size, inhibit the shrinkage voids, finer the grain size of PHS welds, and harden the nugget region. This increased the lap-shear strength and changed the fracture mode from brittle IF mode to ductile plug fracture (PF) mode at the same heat input. Specifically, the peak load and energy absorption were increased by 32.3% and 84.2%, respectively. Then, an analytical model was developed to reveal the mechanism of the effect of EMS on the fracture mode transition and was verified by experiment. This work can help improve the weld quality and thermal efficiency of the RSW process for PHS.

Joining performance and thermal mechanism of stainless steel/GFRP bonding joints via single-side resistance spot welding process

Joining performance and thermal mechanism of stainless steel/GFRP bonding joints via single-side resistance spot welding process

Examination on joining of 2 mm thick dissimilar stainless steel plates using resistance spot welding

In the present study, dissimilar metals such as austenitic stainless steel (ASS) and duplex stainless steel (DSS) with a thickness of 2 mm are joined by resistance spot welding process to investigate the welding metallurgy and failure behavior under different heat inputs. Non-uniform electrode impressions are observed on ASS and DSS sides due to their different thermal conductivity and electrical resistivity. The microstructure of the Fusion Zone (FZ) shows that higher heat input accelerates the growth of Intra Granular Austenite (IGA) due to faster cooling. Scanning electron microscopy (SEM) - Energy Dispersive x-ray (EDX) investigation at FZ showed that Chromium & Molybdenum decrease with increasing heat input due to a decrease in ferrite content. X-ray diffraction analysis confirmed that ferrite formation is limited at higher heat input. Microhardness study revealed that the higher hardness is in the middle of the weld nugget, which is due to the presence of equiaxed grains and IGA. The lowest hardness on the ASS side of Heat Affected Zone (HAZ) is due to the phenomenon of grain growth, and the HAZ DSS side has a higher hardness than DSS Base Metal (BM) due to the mechanism of solid solution strengthening. The tensile shear test showed that the tensile shear strength increases with the addition of heat. SEM Examination of the fracture surface revealed the presence of an equiaxed dimple structure on the ASS side, confirming ductile fracture, and torn bonds on the DSS side, confirming quasi-gap fracture due to the work-hardening ability of both plates. This study is carried out to understand the relationship between mechanical, metallurgical, and failure behaviours, because, researches on joining of dissimilar (AISI 316 L and DSS 2205) stainless steel sheets using Resistance Spot Welding process is very limited and need to be studied in detail.

Tensile shear load in resistance spot welding of dissimilar metals: An optimization study using response surface methodology

Resistance spot welding (RSW) is being applied extensively in different industries, specifically the automotive sector. Therefore, this study was conducted to optimize the tensile strength load (TSL) in RSW by investigating the application of dissimilar materials as input parameters. The optimization process involved the combination of different galvanized and non-galvanized steel materials. The production of car bodies using galvanized steel with approximately 13.0 microns thick zinc (Zn) coating was found to be a standard practice, but this zinc layer usually presents challenges due to the poor weldability. This study prepared 27 units of TSL samples using a spot-welding machine and a pressure force system (PFS) for the electrode tip. The aim was to determine the optimal TSL through the exploration of specified RSW parameters. The process focused on using the response surface methodology (RSM) to achieve the desired outcome while the Box-Behnken design was applied to determine the input parameters. The optimal TSL obtained was 5265.15 N by setting the squeeze time to 21.0 cycles at a welding current of 24.5 kA, a welding time of 0.5 s, and a holding time of 15.0 cycles. The highest TSL value recorded was 5937.94 N at 21.0 cycles, 27.0 kA, 0.6 s, and 15.0 cycles respectively. These findings were considered significant to the enhancement of productivity across industries, specifically in the RSW process. However, further study was required to investigate additional response variables such as the changes in hardness and microstructure.

Towards region-based robotic machining system from perspective of intelligent manufacturing: A technology framework with case study

The region-based robotic machining system is mainly used for repair and remanufacturing of the complex components with local defects. Taking the automotive body manufacturing as an example, the resistance spot welding process is highly prone to randomly distributed and tiny-sized welding slag splashes, which poses a great challenge to the locally automated removal of the welding slag defects. In this paper, we construct a region-based robotic machining system that integrates the processes of defect detection, defect region division and positioning, and machining path decision-making, aiming to enhance the automation of locally grinding of automotive body welding slags. Both the framework of the system and the implementation process are proposed. In the framework, the improved YOLO v3 algorithm is put forward to accurately detect the automotive body welding slags by virtue of the machine vision and deep learning. Based on this, the K-means algorithm is used to divide the welding slags into the regions, so that the problem of positioning individual welding slag is transformed into the problem of positioning the boundary points of welding slag region. The binocular image-based region boundary points matching is then presented to accurately locate the welding slag regions accordingly. The Dijkstra algorithm is finally employed to make an autonomous decision on the pre-planned grinding path of automotive body welding slags based on the positioning results. The experiments on a case of locally robotic grinding of the welding slags on an automotive door frame are implemented to verify the effectiveness and practicality of the system. This study provides a valuable reference for the locally automated repair of automotive body welding slag defects, putty defects, paint defects, etc.

Prediction of the fatigue curve of high-strength steel resistance spot welding joints by finite element analysis and machine learning

The process of resistance spot welding is extensively utilized in automotive assembly. Analyzing the fatigue strength of resistance spot welded (RSW) joints of thin plate high-strength steel holds significant importance in reducing production costs and enhancing vehicle safety during operation. By combining finite element analysis (FEA) and machine learning (ML), a novel method has been developed to predict fatigue curves of RSW joints with high-strength steels of different thicknesses, widths, and nugget diameters. In this study, the impact of various experimental conditions, such as the thickness and width of the sheet material, and the diameter of the nugget, on the fatigue test results, has been quantified. Moreover, the model established through this research enables accurate prediction of the F-N fatigue curves of RSW joints without the need for fatigue testing, thereby saving costs and time required for experimentation. The average error is approximately 8% of the experimental results.

Effect of post-welding sensitisation on the degree of sensitisation of the welding zones of AISI 304 resistance spot welding joints studied by using an electrochemical minicell

ABSTRACT In resistance spot welding (RSW) joints of austenitic stainless steel (ASS), a small-scale electrochemical cell (minicell) was used for assessing individually, on each of the three welding zones, of size less than 1000 µm (fusion zone (FZ), heat affected zone (HAZ) and base metal (BM)), the combined effect of a RSW process and post-welding sensitisation on the degree of sensitisation (DOS). The results show that the three welding zones have different microstructures that make each of them respond differently to post-welding sensitisation. The DOS varies with post-welding sensitisation time in all three welding zones, but it varies at a different rate in each welding zone (the highest rate in the FZ). This variation is due to the fact that when the DOS reaches a certain level, which is observed when plotting the reactivation charge (Qr) versus the post-welding sensitisation time, a microstructural regeneration occurs.