Resistance Spot Welding System Research Articles

Derivation of Analytical Expressions for Fast Calculation of Resistance Spot Welding System Currents

Derivation of Analytical Expressions for Fast Calculation of Resistance Spot Welding System Currents

Research on online intelligent welding system based on resistance spot welding of aluminum galvanized steel

The article follows a resistance spot welding system, which integrates a six-axis industrial robot, power supply, pneumatic actuator, welder, cooler, trimmer, software control system, welding analyzer, force feedback sensor and welding fixture to realize monitoring of welding quality and real-time adjustment of welding parameters. Taking the resistance spot welding of 6 series aluminum alloy and DC06 galvanized steel as a study, four groups of electrode combinations, 16-6/16-6, 16-10/16-10, 16-7/16-10, and 16-5/16-16 (steel side/aluminum side), are selected for simulation and analysis, and the electrodes are optimized with the simulation results. By selecting the optimal electrode combination to carry out experiments and analyzing the influence of welding current and welding time on the joint performance, the average pulling shear force of the aluminum alloy steel resistance spot weld head is finally realized to exceed the average pulling shear force of the aluminum alloy aluminum resistance spot weld head, and the fracture is all started from the parent material of the alloy side to achieve the failure of the button, and ultimately a good welding effect is achieved.

Real-Time AI driven Interpretation of Ultrasonic Data from Resistance Spot Weld Process Monitoring For Adaptive Welding

Adaptive resistance spot welding systems typically rely on real-time analysis of dynamic resistance curves and other indirect measurements to estimate weld progress and guide adaptive weld control algorithms. Though efficient, these approaches are not always reliable, and consequently there is a need for improved feedback systems to drive adaptive welding algorithms. As an alternative, an advanced in-line integrated ultrasonic monitoring system is proposed, with real-time weld process characterization driven by artificial intelligence (AI) to create actionable feedback for the weld controller. Such a system would require real-time ultrasonic data interpretation, and for this a solution using deep learning was investigated. The proposed solution monitors the ultrasonic data for key process events and estimates the vertical size of the weld nugget proportional to the stack size throughout the welding process. This study shows that adaptive welding using ultrasonic process monitoring backed by AI-based data interpretation has immense potential. This research highlights the importance of nondestructive evaluation (NDE) in the zero-defect manufacturing paradigm.

Investigation of Inverter Topologies Used in Medium Frequency Direct Current Resistance Spot Welding Systems

Direnç nokta kaynağı (DNK), özellikle otomotiv sanayisinde yaygın bir şekilde kullanılan bir metal birleştirme yöntemidir. Endüstrideki gelişmelere paralel olarak kaynak teknolojileri de gelişmektedir. Geleneksel alternatif akım direnç nokta kaynak sistemleri (AA-DNK), yerini yeni nesil orta frekans doğru akım direnç nokta kaynak (OFDA-DNK) sistemlerine bırakmaktadır. Ayıca, OFDA-DNK, Endüstri 4.0 içerisinde önemli role sahip robotlar ile uyumlu bir şekilde çalışabilecek, enerji verimliliği yüksek yöntemlerden biridir. Bu çalışmada kaynak teknolojisinde önemli yere sahip direnç kaynak yöntemleri sınıflandırılarak yeni nesil OFDA-DNK sistemlerindeki gelişmeler incelenmiştir. İfade edilen kaynak yönteminin avantaj ve dezavantajları, geleneksel AA-DNK sistemleri ile karşılaştırılmıştır. Ayrıca güç elektroniği teknolojisine dayalı OFDA-DNK sistemlerinin evirici topolojisi incelenmiştir.

Electrical Parameter Identification of Medium-Frequency DC Resistance Spot Welding System Using Intelligent Algorithm

The three-phase medium-frequency dc resistance spot welding (RSW) system has a complex electrical structure that includes various electrical components. As it is a multiparameter coupled, nonlinear, and time-varying system, it has difficulties in achieving the accurate modeling and analyses when combined with the metal melting process. This study provides a parameter identification method for the electrical structure, which only requires the measurement values of voltages and currents in the input and output terminals of the structure. The method is based on four mathematical equations, according to the electrical and magnetic characteristics of the electrical structure. A particle swarming optimization algorithm was employed to solve the equations. This helped achieve the goal of accurately identifying key parameters, which were difficult to measure directly. Using a model established by MATLAB Simulink, a detailed identification process for seven key parameters of electrical components was properly organized. The corresponding comparisons of two types of currents in terms of measurement and calculated values validated the effectiveness of the proposed method. Two specially designed welding experiments using different metal sheets were conducted to validate the reliability, accuracy, and universality of the results. This article can benefit a comprehensive model establishment as well as system and process optimization for RSW operations.

Intelligent parameters measurement of electrical structure of medium frequency DC resistance spot welding system

Three phase medium frequency direct current (DC) resistance spot welding (RSW) machine has a complex electrical structure. Because the structure included various electrical components, it is hard to establish an accurate and integrated numerical model to simulate the energy delivery and control process. This study employed a particle swarm optimization (PSO) algorithm to conduct an intelligent parameters measurement. The measurement process included three procedures, based on electrical and physical characteristics of the objective electrical system. To verify the accuracy and reliability of the measurement, another numerical model established by MATLAB Simulink was employed. The comparative results showed that the maximum error of all measured parameters was 1%, which meant that the proposed intelligent parameter measurement method was effective, and convinced measurement results can be obtained. This study can benefit to establish a full process numerical calculation or evaluation model of the medium frequency DC RSW system.

Modified Recurrence Plot for Robust Condition Monitoring of Electrode Tips in a Resistance Spot Welding System

Degraded electrodes in a resistance spot welding system should be replaced to ensure that weld quality is maintained. Welding electrodes are subjected to different environmental and operational loading conditions during use. When they are replaced with a fixed interval, replacement may occur too early (raising maintenance costs) or too late (leading to quality issues). This motivates condition monitoring strategies for resistance spot welding electrode tips. Thus, this paper proposes a modified recurrence plot (RP) for robust condition monitoring of welding electrode tips in resistance spot welding systems. The overall procedure for the proposed condition monitoring approach consists of three steps: (1) transformation of a one-dimensional signal to a two-dimensional image, (2) unsupervised feature extraction with LeNet architecture-based convolutional neural networks, and (3) health indicator calculation. RP methods convert dynamic resistance waveforms to RPs. The original RP method provides an image with binary-colored pixels (i.e., black or white) that makes this method insensitive to the change of the waveform signal. The proposed RP method is devised to be sensitive to the change of the waveform signal, while enhancing robustness to external noise. The performance of the proposed RP method is evaluated by examining simulated aperiodic waveform signals with and without external noise. A case study is presented to examine the proposed method’s ability to monitor the condition of resistance spot welding electrodes. The results show that the proposed method outperforms handcrafted, feature-based condition monitoring methods. This study can be used to accurately determine the lifetime of welding electrodes in real time during the spot welding process.

A novel real-time measurement method for dynamic resistance signal in medium-frequency DC resistance spot welding

Resistance spot welding (RSW) is widely used in auto-body manufacturing, and the weld quality is critical to ensure the safety and reliability of an automobile structure. The dynamic resistance (DR) signal is one of the most frequently applied process signals for real-time quality monitoring and control of RSW. However, the accuracy of DR measurement is highly affected by the inductive component of the secondary voltage signal. In a medium-frequency direct-current (MFDC) RSW system, it is proven that traditional DR measurement methods such as the root mean square (RMS) method and average method fail to eliminate the interference of inductance, and barely meet the monitoring requirements. Therefore, a novel real-time DR measurement method based on a forgetting-factor recursive least square algorithm is proposed and tested under simulated and experimental conditions in this paper. Sensitivity analysis is performed to optimize the forgetting factor, which is proven to be the critical parameter of the novel method to balance the convergence speed and oscillation amplitude. With the optimized forgetting factor, the error analysis and comparative study are conducted under different welding modes. The results show that the inductive noise can be effectively eliminated by the new method. The measurement error of the proposed method is limited within ±6 µΩ at a 99.73% confidence level (±3σ) at both constant and time-varying current modes. This study can pave the way for real-time monitoring and control for an MFDC RSW system.

A Comparative Study of Single-Phase AC and Medium Frequency DC Resistance Spot Welding Using Finite Element Modeling

This work deeply explored differences between single-phase AC resistance spot welding (RSW) and three phase medium frequency DC RSW systems. The main difference between the two types of RSW systems was that they used different electrical structures, which led to different energy delivery modes. The RSW operation with former type had a simple but low cost structure, while the latter type had opposite features in these two aspects. In this work, a two-dimensional (2D) finite element (FE) model, which combined characteristics of thermal, electrical, and mechanical fields, was established, and then three modes of input welding currents, which were DC input mode, standard sinusoidal input mode and standard single-phase AC RSW input mode, were delivered into the welding system in the FE model. The three modes of welding currents had strictly the same effective values, and effected the same welding time. By means of iterative calculations between thermal-electrical and mechanical fields, the information of temperature increasing trend, dynamic resistance and electrode displacement under the three input modes were obtained. Some important characteristics about the energy delivery and absorptions, and mechanical properties variations under different welding current input modes which cannot be accurately obtained by actual welding operations had been obtained in this work. Also, other analyses about actual data processing and applications, and mechanical variations of the facilities during the welding process were provided. The work can supple valuable references for actual welding applications.

Impact of the Winding Arrangement on Efficiency of the Resistance Spot Welding Transformer

In this paper, the impact of the winding arrangement on the efficiency of the resistance spot welding (RSW) transformer is presented. First, the design and operation of the transformer inside a high power RSW system are analyzed. Based on the presented analysis, the generation of imbalanced excitation of the magnetic core is presented, which leads to unfavorable leakage magnetic fluxes inside the transformer. Such fluxes are linked to the dynamic power loss components that significantly decrease the efficiency of the transformer. Based on the presented analysis, design guidelines to reduce the unwanted leakage fluxes are pointed out. The presented theoretical analysis is confirmed by measurements using a laboratory experimental system. The presented experimental results confirm that the proposed improved winding arrangement increased the efficiency of the transformer in average for 6.27%.

Adaptive Resistance Spot Welding Process that Reduces the Shunting Effect for Automotive High-Strength Steels

Although short-pitch resistance spot welding (RSW) significantly increases vehicle body strength, its application has been limited because of the associated shunting effect. In this study, a reference-based adaptive RSW process intended to minimize the shunting effect was proposed, and a related RSW system that controls welding current and power was developed to implement the adaptive method. The proposed RSW method compensates for the heat input loss caused by the shunting effect based on the estimated weld pitch and reference data obtained under suitable welding conditions. An exponential model was developed using a unique indicator (i.e., the ratio of the adaptive welding heat input to the reference welding heat input until the reference welding power curve peak) to estimate the weld pitch. A logistic growth model was next developed based on the relationship of the nugget diameter, heat input, and weld pitch to estimate the heat input compensation. A unique strategy using power control with a modified reference power curve was applied to supply the calculated heat input compensation. The experimental results intended to validate the proposed adaptive RSW process indicated that the proposed process effectively reduced the shunting effect and produced an improved nugget shape relative to the conventional RSW process.

Impact of the Switching Frequency on the Welding Current of a Spot-Welding System

This paper deals with an analysis of a middle-frequency resistance spot-welding (RSW) system with a dc welding current controlled by a pulsewidth modulated inverter, which supplies a welding transformer with a full-wave rectifier mounted at the secondary. Welding transformers in the automotive industry are usually mounted on the arm of a moving robot, so the weight is important. To achieve the same welding power with a large welding current, the transformer's weight can be reduced with a higher PWM switching frequency. This higher frequency allows a reduction in the transformer's iron-core cross section with shorter primary and secondary windings. Unfortunately, the leakage inductances prevent the RSW system from achieving the same nominal welding current at higher frequencies. The frequency-dependent maximum welding current is a characteristic behavior of the RSW system, which can be determined by sophisticated and time-consuming simulations or with the expensive measurements. The third option presented in this paper is determination of an analytical solution, which allows calculation of the maximum welding current as function of frequency or any parameter of the RSW system circuit model. The analytically calculated frequency-dependent function of the maximum welding current was completely confirmed by measurements on an industrial RSW system and by numerical simulations.

Development of fuzzy controller for inverter DC resistance spot welding using system identification

Adaptive Resistance spot welding (RSW) technologies have been developed and applied within the automotive industry to improve the weldability of automotive steels, including conventional and high strength steels. Almost all adaptive RSW systems require an inverter DC RSW system as a platform because such a system can generate various types of current waveforms effectively with higher control frequency than an AC RSW system. In this work, a fuzzy controller for an inverter DC RSW system that can control constant current and more complex current waveforms was developed as a platform for adaptive control of RSW. This study used System identification (SI) to model the inverter DC welding system effectively. To optimize the fuzzy controller for the SI model, fuzzy scaling factors were optimized using a genetic algorithm. To apply the scaling factor of the fuzzy controller with the SI model to a real system, the scaling factors were adjusted using response surface methodology.

Analysis of Proportional Integral and Optimized Proportional Integral Controllers for Resistance Spot Welding System (RSWS) – A Performance Perspective

ABSTRACTThis paper is an attempt to accomplish a performance analysis of the different control techniques on spikes reduction method applied on the medium frequency transformer based DC spot welding system. Spike reduction is an important factor to be considered while spot welding systems are concerned. During normal RSWS operation welding transformer’s magnetic core can become saturated due to the unbalanced resistances of both transformer secondary windings and different characteristics of output rectifier diodes, which causes current spikes and over-current protection switch-off of the entire system. The current control technique is a piecewise linear control technique that is inspired from the DC-DC converter control algorithms to register a novel spike reduction method in the MFDC spot welding applications. Two controllers that were used for the spike reduction portion of the overall applications involve the traditional PI controller and Optimized PI controller. Care is taken such that the current control technique would maintain a reduced spikes in the primary current of the transformer while it reduces the Total Harmonic Distortion. The performance parameter that is involved in the spikes reduction technique is the THD, Percentage of current spike reduction for both techniques. Matlab/SimulinkTM based simulation is carried out for the MFDC RSWS with KW and results are tabulated for the PI and Optimized PI controllers and a tradeoff analysis is carried out.

Eliminating short switching cycles when using hysteresis control of resistance spot welding systems

PurposeThis paper aims to present two hysteresis-control algorithms designed for medium-frequency, direct-current, resistance-spot-welding (MFDC RSW) systems. The first proposed control algorithm (MSCHC) eliminates the short switching cycles that can occur when using the existing hysteresis-control algorithms. This control minimises the number of switching cycles that are needed to generate the selected welding current. The welding-current ripple can be high when using this control algorithm. Therefore, a second algorithm (HCRR) is presented that reduces the welding-current ripple by half.Design/methodology/approachThe proposed hysteresis controllers consist of the transformer’s magnetic-flux-density hysteresis regulator and a welding-current hysteresis regulator. Therefore, the welding current must be measured and the saturation of the iron core must be detected. The proposed hysteresis controller supplies the inverter with the signals needed to generate the supply voltage for the RSW transformer, which then generates the selected welding current.FindingsThe proposed MSCHC algorithm produces the smallest possible number of switching cycles needed to generate the selected welding current. The high welding-current ripple can be reduced if the number of switching cycles is increased. The observed number of switching cycles and the welding-current ripple change if the welding resistance and/or inductance change.Originality/valueThe number of switching cycles can be minimised when using the first proposed control algorithm (MSCHC), and so the switching power losses can be minimised. If the welding-current ripple produced by the first control algorithm is unacceptable, the second control algorithm (HCRR) can reduce it by increasing the number of switching cycles.

Review of Application of the Electrical Structure in Resistance Spot Welding

Resistance spot welding (RSW) is frequently employed in current industrial occasions. This paper reviewed recent advances of the electrical structure of the RSW system. Two types of electrical structures are used in RSW machines. Single-phase ac power source has a simple structure but low control frequency and power factor, and the measurement and control for the machine have some special operations. While three-phase medium frequency dc power source has a complex structure and high control frequency but high cost, and frequently switching the direction of the output welding current may induce many negative phenomena in the welding transformer. The characteristics of the two structures are presented in detail in this paper. Corresponding measures have been taken to deal with the phenomena during the process, respectively, for the two types of electrical structures, according to the previous works. Though many significant achievements have been gained in previous works, it is expected to be more improvements required in the future. This paper can provide references and enlightens for academic researches or actual production in RSW operations.

Development of single-side resistance spot welding technology applying in-process welding current and electrode force controls

An indirect resistance spot welding process with single-side electrode access was developed for automotive applications. The variable controls of electrode force and welding current during welding were studied in order to achieve the promotion of weld nugget formation and the suppression of expulsion without sacrificing the productivity and design flexibility of automobiles. The welding experiments were performed on lapped test coupons of 0.7-mm-thick cold-rolled sheet with tensile strength of 270 N/mm2 and 1.6-mm-thick cold-rolled sheet with tensile strength of 980 N/mm2 using a resistance spot welding system consisting a servo-motor-controlled welding gun and an inverter DC power supply. Welding experiments verified that the occurrence of expulsion and formation of molten nugget were significantly influenced by the heat generation and melting process at an initial period during welding and manageable by applying the variable patterns of electrode force and welding current. When welding was performed under the large shunting condition simply with the constant force and current pattern of 400 N in electrode force, the appropriate current range was less than 1 kA. On the other hand, it extended to 2.6 kA when performed with the variable force and current pattern of 800 N in force and 4 kA in current at the first stage and 400 N in force at the second stage, confirming the fact that the variable pattern successfully suppressed the expulsion and promoted the nugget formation. Numerical simulations were conducted to compare the difference in welding phenomena between the constant force and current pattern and the variable force and current pattern and clarified that the effect of variable force and current pattern on the promotion of nugget formation and the suppression of expulsion.

Optimization of Resistance Spot Welding Transformer Windings Using Analytical Successive Approximation and Differential Evolution

A welding transformer represents a vital part of a resistance spot welding (RSW) system. Therefore, it is essential to ensure minimum copper loss in the windings. This paper describes a single-objective optimization procedure, which includes searching for the minimum copper loss in RSW transformer windings in regard to the dimensions of the primary and secondary windings. Copper loss in windings is obtained using an improved analytical method of successive approximation, which enables the calculation of current density distribution in coils with rectangular conductors. Finally, the calculated optimum windings' dimensions are further used in a parametric numerical model with the finite element method to confirm the reduction of copper loss.

Usage of a Simplified and Jiles–Atherton Model When Accounting for the Hysteresis Losses Within a Welding Transformer

The proposed paper deals with a nonlinear dynamic model of a welding transformer, where the effects of hysteresis losses are accounted for by the simplified method and by the inverse form of the Jiles-Atherton hysteresis model. Both models have been modified in such a way that they can be used when the magnetically nonlinear characteristic of the entire device is determined experimentally. The aforementioned characteristics are given in the form of approximation polynomials. For defining magnetically nonlinear characteristic and both the Jiles-Atherton hysteresis model and the simplified model, an optimization procedure based on the differential evolution is applied for obtaining the parameters of applied approximation polynomials. The main goal of this paper is to evaluate both discussed models regarding their suitability to be included into dynamic model of a welding transformer used in the optimization of the entire resistance spot welding system. The evaluation focuses on achieved accuracy and computational effort required to implement the discussed models.

Study of safety operation of AC resistance spot welding system

This study deals with the safety operation of AC resistance spot welding (RSW) system. The input of the RSW system is the firing angle of the silicon-controlled rectifier (SCR) during each control cycle. Wrongly choosing a firing angle may induce disastrous consequence. The range of firing angle depends on the system's power factor angle; the relation between the firing angle, power factor angle and conduction angle is highly non-linear. After comparing three methods, a simple mathematical model is proposed in this study to facilitate the online calculation of the power factor angle and selection of the proper firing angle, so that the safety operation of RSW system can be guaranteed. In this condition, the RSW machine can work at the machine's the most capacity, the calculated value of power factor angle should be the lowest limit for actual selected firing angle of SCR. Finally, experimental results confirmed the effectiveness of the proposed mathematical model.