Electrode Force Research Articles

A novel approach for improving formation of soft zone in 22MnB5 and DP600 materials by resistance spot welding

Abstract In this study, 1.5-mm thick Al-coated hot formed boron alloy 22MnB5 with martensitic structure and Zn-coated DP600 with dual phase structures, which are frequently used together in the automotive industry, were used. Instead of traditional alternating current (AC), a new generation medium–frequency direct current (MFDC) resistance spot welding method was utilized in the joining process. The uniqueness of this work is that it aims to improve the properties of the soft zone formed in the heat effect zone (HAZ) of 22MnB5 materials during resistance spot welding (RSW). For this purpose, a fixture was designed and manufactured for regional rapid cooling (RRC) of the HAZ following the welding process. During RSW, 6.5 kA welding current, 3.6 bar electrode force and 500 ms welding time were used. This RRC method aims to reduce defects in the joint strength caused by hardness changes. Welding processes were carried out in molds designed and produced in accordance with tensile-shear and cross-tension tests. Afterwards, tensile-shear, cross-tension, and fatigue tests were applied to the welded samples. In addition, the effects of the developed system on the weld zones of these samples were examined by microstructure and hardness studies. The tensile-shear and cross-tension results revealed that the regional cooling exhibited approximately 4–6% higher strength, respectively. As a result of the hardness tests, it was observed that the hardness of the tempered soft zone in the 22MnB5 HAZ of the joint increased by 6% with RRC. However, it was determined that through this developed system, RRC in fatigue tests decreased in the fatigue life of the samples at all loads.

Investigating liquid Al electrodes for Ce(III) extraction from LiCl–KCl melts: a kinetic and thermodynamic study

Investigating liquid Al electrodes for Ce(III) extraction from LiCl–KCl melts: a kinetic and thermodynamic study

Resistance spot welding of die-cast and wrought aluminum alloys: Improving weld spot quality through parameter optimization

AbstractWelding aluminum castings is known for a high sensitivity for hydrogen-induced weld porosity. Research has shown that the porosity detected in mixed material resistance spot welds between die-cast and wrought aluminum is predominantly classified as solidification porosity. But, nugget penetration depths into the wrought aluminum alloy are low. In this work, the effect of a forging electrode force during welding current time ti or after the welding current is shut off on weld spot characteristics is investigated, when resistance spot welding (RSW) mixed material joints between EN AC-43500-T6/T7 and EN AW-6082-T6. A current cut-off test based on a welding profile according to VDA 238–401 reveals a welding current time ti between 60 ms ≤ ti ≤ 80 ms as relevant for porosity detection in cross-section analysis. Based on this, different welding profiles are tested, and resulting weld spot characteristics are analyzed when applying chisel tests, cross-section analysis, quasi-static shear tensile tests, and scanning electron microscopy. The application of a forging electrode force reduces weld spot porosity in RSW significantly, while a current downslope leads to an increase. Further, the application of a forging electrode force during welding current time leads to a significant decrease in the standard deviation of s = 1.07 kN to s = 0.08 kN in shear tension force, although the mean shear tension force is increased marginally from 7.07 kN to 7.15 kN. Yet, an increase in weld penetration depth ≥ 20% into EN AW-6082-T6 is only achieved when reducing the initial electrode force to 5 kN and initiating forging electrode force during ti.

Effect of a variable electrode force on the LME crack formation during resistance spot welding of 3G AHSS

AbstractIn the pursuit of lightweight vehicles, third-generation advanced high-strength steels (3G AHSS) with increased mechanical properties are desired to be used for critical components. However, the exposure of these zinc-coated AHSS to the manufacturing conditions during resistance spot welding can trigger liquid metal embrittlement (LME), possibly compromising the mechanical properties. As the reproducibility of LME cracks in resistance spot welding is a challenge, the effect on the static and dynamic mechanical properties of the welds is not yet fully clarified and therefore a distinction between critical and non-critical cracks is not implemented in current standards. To achieve this, it is necessary to provoke LME cracks of a given size, for example by increasing the welding current, reducing the electrode force and hold time, or using manufacturing discontinuities. Due to its significant effect on the heat input and the tensile stresses during the resistance spot welding process, which impacts the LME crack propagation, the focus of this paper is on the electrode force. An expulsion-free decreasing force profile, which consists of a force run-in, force decrease, and force run-out time, has been derived in a two-stage Face-Centered-Central-Composite design of experiment for an electrogalvanized third-generation advanced high-strength steel (3G AHSS) DP1200 HD. The crack location, length, depth, and nugget geometries were investigated for each weld. With the decreasing force profile, it was possible to generate type A, B, and C cracks by parameter adaption, with type B and C cracks being the most dominant. The type C crack formation was investigated by aborting the welding process in defined time steps and the LME cracking mechanism was confirmed by welding dezincified samples. Based on the investigations carried out, the force profile was found suitable for generating different LME crack sizes to further investigate the mechanical joint properties as it was able to reproducibly generate defined cracks without expulsion and excessive electrode indentation while maintaining a minimum nugget diameter.

An Electrochemiluminescence Device Powered By Streaming Potential for the Detection of Amines

Herein, we report the design, development and optimization of an electrochemiluminescence (ECL) device powered by streaming potential for the detection of amines in flowing solution that can be activated without the need of an electric power supply (Figure 1). The device is based on the concept of streaming potential-driven bipolar electrochemistry [1,2], in which a flow of electrolytic solution passing through a microchannel with charged walls under a pressure gradient causes a streaming potential (E str) as the driving force of bipolar electrodes (BPE). In this study, we explored several experimental parameters to find the optimal operating conditions to drive the coreactant-type ECL reaction of a benzothiadiazole-triphenylamine (BTD-TPA) derivative in our streaming potential-driven device. The ECL emission was successfully detected by a photomultipulier tube (PMT), a digital camera and a spectrometer under the optimized electrolyte conditions including tripropylamine (TPrA) as a coreactant. Finally, we tested the ECL detection of several amines used as coreactants with the device.

Electrode-embedded linear actuating enhanced resistance spot welding of aluminium alloy and dual phase steel

Resistance spot welding (RSW) of aluminium/steel dissimilar materials has important application prospects in industries such as automobiles. However, the relatively poor mechanical properties of the welds due to the issue of brittle intermetallic compounds (IMCs) at the welding interface has been the major concerned by the welding community. A novel modified RSW process that utilizes relatively high-frequency linear actuator embedded in the electrode is proposed and experimentally verified. The linear actuator superimposes a pulsed electrode force to base force which is expected to facilitate the melt flow inside the aluminium nugget and modify the forming process of the IMCs. The experimental results demonstrate that the introduction of linear actuating could significantly increase the area of the aluminium nugget, which means more aluminium was melted. Further, it is observed that the thickness of the IMCs layer was reduced by 81.9 %, with a peak thickness of 1.48 μm. Therefore, 38.5 % improvement in the average peak tensile shear load of the welded joints was achieved. The involved mechanisms were discussed by thermal/force dynamic analysis.

Physical Heat Cycle Measurement of Resistance Spot Welding

Resistance spot welding (RSW) is still the ideal joining method in the automotive industry. Mostly steel sheets are used in the car body, so overlap and layering are required for welding or riveting, as spot welding provides simultaneous clamping force with interfacial welding to ensure the required strength and quality. A fundamental understanding of heating and cooling rates in thermal distributions is essential for predicting microstructure formation in the weld and the heat-affected zones (HAZ) of RSW joints. The ability to measure the heat cycle in the RSW process can be valuable in weld control and welding parameter optimization. RSW parameters can be optimized through tensile shear tests and microscopic investigations. Heat cycle measurement (HCM) demonstrates the welding consequences in terms of the change in mechanical properties and microstructural formations. The accuracy of cooling rate measurements including t8/5 cooling time is very important to predict the microstructural evolution in the HAZ, however, the thermocouple measurement raises numerous challenges due to the high temperature gradient and small weld and HAZ size. During our investigations heat cycle measurement has been conducted experimentally by a K-type thermocouple. The data logger is connected to the output of the thermocouple for recording the voltage to measure the temperature distributions as a function of both time and position during the welding process. Measurement results of 1 mm thick martensitic MS1400 steel overlapped RSW joints are discussed, and the HCM curve of heating and cooling rates of the spot-welding process is presented. The heat cycle during RSW was measured with two different welding parameter combinations. In addition to welding current, welding time, and electrode force, pulsation has shown disparate curves. Numerous experiments have been attempted to measure the heat cycle in HAZ sub-zones due to the difficulty of positioning the thermocouple accurately, uppercritical HAZ, intercritical HAZ, and subcritical HAZ were investigated and measured in both welding parameter combinations. Difficulties were encountered in the experimental work as a result of the instantaneous welding time and the vibration resulting from the passage of alternating electrical current between the two electrodes. A magnetic field is generated that affects the thermocouple measurement and appears as a noisy curve that is filtered out and smoothed. Joule heat, interfacial heat generation, and cooling effects of electrodes are also considered in the experiment.

Dissimilar joining of aluminum alloy and low-alloy carbon steel by resistance spot welding

In this work, the resistance spot welding (RSW) process was performed to join aluminum alloy and low-alloy carbon steel plates. The macro characteristics including nugget diameters and indentation rates, microstructure and tensile-shear strength of RSW joints were investigated. The results showed that the nugget of the RSW joints comprises a ‘bowl’ shape nugget on the aluminum side and an elliptical shape nugget on the steel side. Also, the intermetallic compound (IMC) layers containing Fe4Al13 and Fe2Al5 were formed around the aluminum/steel interface with the steel side having a tongue-shape and the aluminum side having a needle-shape. According to metallurgical evaluation and temperature distribution of RSW joints analyzed by the finite element method, the nugget on the aluminum side contained the dendritic grains and equiaxed dendritic grains. The nugget on the steel side consisted of a large amount of bainite and a small amount of coarse lath martensite. The nugget diameters and the indentations rates of RSW joints increased when increasing either welding current or welding time, and decreased when increasing the electrode pressure. The maximum values of nugget diameter and indentation rate of RSW joints were 9.076 mm and 4.144% when using the welding current of 16 kA, welding time of 450 ms and electrode force of 3 kN. In tensile-shear tests, the RSW joints showed a shear-off fracture mode. When increasing the welding current, welding time or electrode force, the tensile-shear strength of RSW joints increased first, and then reached a maximum, and finally decreased. The welding current of 16 kA, the welding time of 300 ms, and the electrode pressure of 3 kN were considered as the optimal welding parameters in the present study which resulted in the maximum tensile-shear strength of 2.24 kN. In addition, the IMC layers of the RSW joints exhibited a uniform and continuous appearance with a thickness of approximately 1.9 μm, and the IMC layer in the central area was thicker than that in the edge area.

Effects of ultrasonic vibration on residual stress distribution and local mechanical properties of AA6061/Ti6Al4V dissimilar joints by resistance spot welding

The joining of dissimilar titanium and aluminum alloys has potential applications in railway and aerospace industries, owing to substantial weight reduction and better economic viability. In this study, the residual stress distribution and local mechanical performance of ultrasonic-assisted resistance spot welding (UaRSW) welds were investigated. The welding current, welding time, and electrode force of the RSW process were set as 9.0 kA, 350 ms, and 1.0 kN respectively, and the frequency and power of ultrasonic vibration were 20 kHz and 800 W. The residual stress was evaluated by X-ray diffraction (XRD) method and numerical simulation, and these methods showed a reasonable match. There was tensile residual stress distributed on RSW welds and UaRSW welds, but the value of residual stress was reduced by about 30% at welding nugget and 20% at heat affected zone (HAZ) with the ultrasonic vibration, the reduction of residual stress in UaRSW welds was attributed to the more uniform temperature distribution and lower plastic deformation resistant of AA6061. The welding peak temperature was decreased from 1673.4 °C to 1584.2 °C with the ultrasonic vibration, resulted from the modified Al/Ti contact surface and reduced contact resistance. The miniature tensile test results showed the improvement of mechanical performance by ultrasonic vibration. The maximum load of welding nugget region increased from 19.6 N to 22.3 N, and the elongation obtained 10% increase. This hybrid welding technique shows a potential to improve the quality of welds with ensured efficiency, which is also simple to realize automation in the manufacturing industry.

Microstructure and mechanical properties of similar and dissimilar resistance spot welded DC04 and HRP6222 (DD11) steels

Abstract Low carbon steels are frequently preferred in the automotive industry. The most preferred welding method in vehicle body manufacturing is resistance spot welding (RSW). In this study, RSW joints of DC04 and HRP6222 steels were carried out at two different electrode forces (2.1 kN, 2.4 kN) and three different welding currents (4 kA, 6 kA, 8 kA). The effects of different welding parameters on microstructure, tensile shear force, failure mode and microhardness were investigated. So, the focus was on optimizing the welding parameters. As a result, the RSW process caused the formation of three different regions in the microstructure (the base metal, the heat affected zone and the weld metal). It was observed that the tensile shear force increased as the welding current and electrode force increased. After the tensile shear tests, two different failure modes occurred (interface and pull-out type). Hardness values showed a linear relationship with tensile shear force results. In addition, a significant increase in hardness values was observed from the base metal to the weld metal in all welding parameters.

Development of Situation Awareness Model in Robotic Spot-welding (RSW) System based on Sensor Data Visualization

The advancement of prognostics and health management (PHM) using the industrial internet of things (IIoT) and artificial intelligence (AI) has enabled stable mass production with assured quality. However, the manufacturing industry often faces variable conditions like design and material changes. Before applying PHM systems, it is crucial to design a system that recognizes these changes. This study developed a robust situation awareness model for a robotic spot-welding (RSW) system, resilient to reduced training data, using sensor data visualization and convolutional neural networks (CNN). Four variable situations were established based on thickness and material changes: GI steel 0.6 t, GI steel 1.0 t, mild steel 0.8 t, and GA steel 0.8 t, with GI steel 0.8 t as the reference. Data were collected using process parameters (welding current and electrode force) for each situation. A fuzzy-based energy pattern image (FEPI) visualization technique was applied to visualize energy differences in the spot-welding process from four sensors (current, voltage, electrode force, displacement). Using these techniques, thickness and material variation awareness models were constructed. The classification accuracy of CNN models trained on time-series data was evaluated to verify the effectiveness under reduced training data conditions.

Micro-resistance welding of NiTi shape memory alloy wire and MP35N wire

The micro-resistance welding between NiTi shape memory alloy and Co-35Ni-20Cr-10Mo alloy (MP35N) wires was investigated to gage the feasibility of their future applications. Welding current and electrode force significantly affected the joint breaking force. The highest joint breaking force (0.99 kgf) at the optimized welding parameter (0.51 kA, 7.500 kg) was accomplished by maximizing the solid-state bonded area and minimizing the heat-affected zone (HAZ). This highest joint breaking force was higher than that of the micro-resistance welded NiTi wire joint reported in previous studies. Furthermore, the cyclic tensile test revealed that the accumulated residual strain of NiTi wire was reduced after welding. This could be attributed to the reduction in the dislocation density through grain growth in the HAZ of NiTi wire during the welding process.

Optimization and Simulation Parameters of the Resistance Spot Welding for Commercial Aluminium (AA1050) at Low Power Welding Machine

This study aims to find the best conditions of resistance spot welding in commercial Aluminium AA1050 to obtain the maximum tensile shear strength of the joint using a low-power supply welding machine. The chosen parameters for this study were welding current, welding time, and electrode force using a 90 kVA welding machine. The investigation used the DoE method with Taguchi’s technique to reduce the number of experiments where two sheet thicknesses (1 mm and 2 mm) were used in this work. The software program Minitab 18 analyzed the results using the main effects plots and the interaction plots to identify the most significant parameters and their effect on the joint strength. The best conditions for maximum tensile shear force were 14.85 kA welding current and 0.79 kN electrode force for both thicknesses and two cycles and 12 cycles welding time for 1 mm and 2 mm sheet thickness, respectively. The maximum tensile strength obtained was 250 N and 225 N for 1mm and 2mm sheet thickness, respectively. A mathematical equation was developed to predict the shear force with 19.9 % and 17.9 % error for 1 mm and 2 mm thicknesses, respectively. The best conditions were applied in ANSYS 2022R1 multi-physics to obtain the temperature distribution with time history, where the result shows the nugget size according to the molten temperature. The percentage of discrepancy between actual and numerical nugget size was 8 %.

Joining aluminum die castings and wrought aluminum by resistance spot welding

Resistance spot welding (RSW) is an economic, robust welding process, which is easy to automate and widely used in automotive industry. In this work, the resistance spot weldability of die-cast aluminum alloys EN AC-AlSi7MnMg, EN AC-AlSi9Mn and EN AC-AlSi10MnMg-T6/T7 to wrought aluminum alloy EN AW-AlSi1MnMg-T6 is investigated when applying the standard welding profile as recommended in VDA 238-401 considering main challenges in welding aluminum die castings, for example, porosity and inhomogenities. Weldability is best for EN AC-AlSi10MnMg-T6/T7, but the results show limited applicability of VDA 238-401 in general, especially for high total sheet thicknesses, because of invalid electrode force favouring spatter formation and weld spot irregularites. Still, all spot welds between die castings and 2 mm wrought aluminum sheets reach the recommended shear tension forces for spot diameter dw of 5·√t (2 mm: 5.95 kN; 3 mm: 8.96 kN; according to DIN EN ISO 18595), although being afflicted with solidification porosity and liquation cracking. Gas porosity is not observed and solidification porosity is only found to be significant for weld spot failure when being located close to the joining level, which is observed at welding depths of approximately 50% into the wrought aluminum sheet. Here, a failure path across the nugget is found. Weld porosity apart from the joining level is less significant and failure path is found along the fusion line between nugget and wrought aluminum. Instead, hardness difference between nugget and HAZ is the main reason for weld spot failure. Although the applied welding current profile is not suited best for RSW of mixed joints between aluminium die castings and wrought aluminium alloys, the results confirm its potential, for example, a significantly reduced gas porosity compared to applied fusion welding processes.

Machine learning tool for the prediction of electrode wear effect on the quality of resistance spot welds

The quality of resistance spot welding (RSW) joints is strongly affected by the condition of the electrodes. This work develops a machine learning-based tool to automatically assess the influence of electrode wear on the quality of RSW welds. Two different experimental campaigns were performed to evaluate the effect of electrode wear on the mechanical strength of spot welds. The resulting failure load of the joints has been used to define the weld quality classes of the machine learning tool, while data from electrode displacement and electrode force sensors, embedded in the welding machine, have been processed to identify the predictors of the tool. Some machine learning algorithms have been tested. The most performing algorithm, i.e., the neural network, achieved an accuracy of 90%. This work provides important theoretical and practical contributions. First, the decreasing thermal expansion of the weld nugget as the electrode degradation advances results in a strong correlation between the difference of the maximum displacement value and the last value recorded during the welding and the relative failure load. Then, this work offers a practical decision support tool for manufacturers. In fact, the automatic detection of low-quality welds allows to reduce or eliminate unnecessary redundant welds, which are performed to compensate for the uncertainty of electrode wear. This leads to savings in time, energy, and resources for manufacturers. Finally, general recommendations for the timing of redressing or replacing the electrode are provided in the manuscript based on the company willingness to accept some non-compliant welds or not.

Optimization of resistance spot welding with surface roughness dissimilar mild steel with stainless steel

Resistance spot welding plays a critical role in the manufacture dissimilar material industry. However, there are differences in mechanical properties between mild steel and satinless steel so as to reduce the quality of welded joints. In order for differences in mechanical properties to be corrected, surface roughness was treated. The aim of this study was to optimize the welding parameters of DRSW with surface roughness by analysis using the Taguchi and Anova Methods. In this study discusses about investigates the Resistance spot welding parameters on weld geometry, mechanical properties, and SEM EDS on dissimilar materials of mild steel and stainless steel. The material thickness of the mild steel and stainless steel are 1 mm, respectively. The process parameters of the resistance spot welding joint used, example; surface roughness, current, welding time, and electrode force. Quality welding joint test results include weld geometry, mechanical properties, and SEM EDS. Weld geometry testing to determine the weld nugget profile. The mechanical properties test was shear tensile test, while the SEM EDS included macrostruture and microstructure observations. The results showed the highest nugget diameter 6.65 mm highest shear tensile strength 7.66 kN. The most influential parameter is current by 75.08 %, then surface roughness by 12.35 %. The highest tensile strength has fewer defects. Surface roughness treatment before welding is very good to make welding quality joints between mild steel and quality stainless steel increase. Surface roughness treatment was very good to be included when making welding procedures for welding engineers for welding processes resistance spot welding dissimilar mild steel with stainless steel.

Increase of electrode life in resistance spot welding of aluminum alloys by the combination of surface patterning and thin-film diffusion barriers

When resistance spot welding aluminum alloys, high electrode forces are required to reduce the electrical contact resistances between the electrodes and the sheet metals. The high contact resistances and the resulting thermal load cause extensive degradation of the electrode working faces. Weld spatter occurs after only a few weld cycles, significantly reducing the quality of the weld. Conventional resistance welding machines are limited in terms of maximum electrode force and weld current. As a result, weld quality and electrode life are inadequate. The aim is to increase the achievable electrode life by surface patterning the electrode working faces and creating thin-film diffusion barriers by physical vapor deposition (PVD). Patterning is intended to penetrate the oxide layers of the aluminum sheets and increase the proportion of electrically conductive contact areas. The different influences of patterning by particle blasting and contour turning will be investigated. As a further approach, thin-film diffusion barriers of up to 3 μm are deposited on the electrodes to prevent direct Al-Cu contact. Therefore, metallic coating materials (Ni and W) and an electrically highly conductive ceramic coating material (TiB2) are investigated. The combination of electrode patterning and thin-film diffusion barriers is tested in electrode life studies. It is shown that these modified electrode working faces can limit degradation effects and contribute to an increase in electrode life. In addition, the weld quality can be improved compared to the reference condition.

On the Optimization of Resistance Projection Welding Process

The resistance projection welding process for weld nuts has several parameters to reach good joint quality. In this study, three welding parameters were chosen, such as electrode force, welding period and welding current to examine the process. Design of experiments was prepared to optimize the conditions. The three above mentioned parameters were changed systematically with Response Surface Method, where the linear and the quadratic effects of the parameters can be estimated. During the experiments three output parameters, such as ultimate torque, weld spatter and inspection of screw were determined, and optimization were performed for the resistance projection welding process of the weld nut

Modeling of Resistance Spot Welding Using FEM

The resistance spot welding process is significant for joining materials in the automotive industry because it offers high speed and can be easily automated. Recently, there has been a demand in the automotive industry to reduce vehicle weight to improve fuel efficiency. Aluminium alloys are considered a viable alternative for auto-body materials to meet this requirement. It not only helps enhance fuel efficiency but also addresses the issue of vehicle corrosion. However, joining aluminium through resistance spot welding presents serious challenges compared to steel. One significant difficulty arises from the faster deterioration of electrodes. Aluminium alloys possess high electrical and thermal conductivity, significant shrinkage during solidification, and a natural oxide coating. These features make the spot welding process for aluminium alloys notably distinct. When exposed to high temperatures, aluminium undergoes a chemical reaction with the copper alloy found in the electrode material. This results in the unpredictable removal of material from the electrode surfaces, causing wear and significantly reducing the lifespan of the electrode during spot welding of aluminium alloys. This decrease in electrode tip longevity poses a significant drawback in weldability, as the durability of the electrode tip significantly affects its suitability for automotive applications. Due to the rapid nature of the process, obtaining crucial information, such as the transient distribution of current density and temperature through experimental methods, becomes challenging. Therefore, this study aims to develop an integrated computer simulation model using the finite element method to analyze the resistance spot welding process of aluminium alloys. Multiple calculations were performed considering different welding currents, weld times, electrode forces, and various surface conditions of the aluminium sheets. The simulation considers the nonlinear, temperature-dependent, thermo-physical properties of the materials. Interestingly, it was observed that in most cases, the nugget diameter is formed within a short time frame of 0.02 to 0.04 seconds, and further application of welding current primarily increases the heating of the electrode face. Moreover, the aluminium sheets’ initial surface condition significantly influences the nugget’s formation. Several other conclusions have been drawn as a result of this study.

Investigation Parameters of Resistance Spot Welding For AA1050 Aluminum Alloy Sheets

The parameters of resistance spot welding (RSW) performed on low strength commercial aluminum sheets are investigated experimentally, the performance requirements and weldability issues were driven the choice of a specific aluminum alloy that was AA1050. RSW aluminum alloys has a major problem of inconsistent quality from weld to weld comparing with welding steel alloys sheet, due to the higher thermal conductivity, higher thermal expansion, narrow plastic temperature range, and lower electrical resistivity. Much effort has been devoted to the study of describing the relation between the parameters of the process (welding current, welding time, and electrode force) and weld strength. Shear-tensile strength tests were performed to indicate the weld quality. A weld lobe diagrams were constructed to evaluate the weldability of three sheet thicknesses of this alloy. Most appropriate welding time and electrode force are 5 cycles and 1.75- 2.25 kN respectively. The ranges of the weldability are 14-28, 18-30, and 22-32 kA for 0.6, 1.0, and 1.5 mm sheet thicknesses respectively. A statistical regression analysis was used to demonstrate the relationship of the process parameters and the strength of the weldments. Two empirical equations for each thickness were proposed to estimate the shear tensile strength of the weldments, one for quadratic and the other linear relationship between the process parameters and the strength. There are no significant differences between the equations when applied to the available data.