Micro-resistance Spot Welding Research Articles

Utilising a novel multi-electrode approach for improving micro-resistance spot welding productivity for electric-mobility battery interconnects

The micro-resistance spot welding is widely used for low-to-medium-volume applications due to its low cost, especially for cylindrical Lithium-ion cell-based modules. Using typical micro-resistance spot welding electrodes in a series configuration, two nuggets/welds are created in a single welding operation. As it is a contact joining process, productivity is limited. This paper developed a novel approach to enhance the productivity of micro-resistance spot welding, where four nuggets were produced instead of two nuggets in a single operation. The critical-to-quality criteria, including joint strength, microstructure, electrical resistance and temperature rise at joints, were demonstrated by comparing the existing and proposed approaches. A reduction in cycle time by up to 57% can be achieved by adopting the proposed approach while maintaining the weld quality.

Micro Resistance Spot Welding Optimization for Ultra-Thin Mo-Re Sheet Used in TWT

<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$30~\mu $ </tex-math></inline-formula> m ultra-thin Mo-Re sheet had been joined by micro resistance spot welding (MRSW) and successfully applied to the low heating power cathode of traveling wave tube (TWT). The effects of different welding parameters, surface state and protection conditions on the joint’s appearance, micro-structure and lap shear strength (LSS) were analyzed in this paper. The results showed that a 63.5 N LSS of the MRSW joint was obtained under the following conditions: electrode force <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$F=9.0$ </tex-math></inline-formula> N, welding current <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I=1000\text{A}$ </tex-math></inline-formula> , ramping time <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{1}=5$ </tex-math></inline-formula> ms, welding time <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$t_{2}=2$ </tex-math></inline-formula> ms and dip in the alcohol for protection. The fracture occurs in the heat affected zone (HAZ). Using metallurgical microscopy observed the nugget, metallurgical fusion could be found, the diameter of nugget was about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi 0.3$ </tex-math></inline-formula> mm, without gas pores. Scanning electron microscopy (SEM) was used to observe the fracture surface. It could be found some “whisker” shape diverged from the joint center to the surroundings in HAZ. The electrode tip was observed by energy dispersive spectroscopy (EDS) and optical profiler. It was found that the tip was uneven and adhered the base metal obviously after spark. Additional work about electrode sticking will be required. The thermal test data showed that the use of ultra-thin Mo-Re sheet can reduce a space TWT cathode heating power (CHP) by 0.57 W, which will effectively save satellite energy and improve the expected working life of vacuum electronic devices.

Heat generation and transfer in micro resistance spot welding of enameled wire to pad

The single-sided micro resistance spot welding (MRSW) of enameled copper wire to pad is widely applied in electronics manufacturing. The welding quality is significantly influenced by the process of heat generation and transfer which are gradually changing and quite uncertain in production. This work is to investigate the thermal process variation under the common influence factors of electrode wear and thermal contact conductance (TCC). Multi signals such as dynamic resistance and electrode temperature were detected to analyze the welding process. A finite element model of electrical-thermal-mechanical coupling was established to simulate the heat generation and transfer in MRSW. The coupled model was validated by comparing the simulated results of temperature and voltage with the experimental measurement. The results show that the electrode wear in single-sided MRSW of enameled wire to pad causes an increase in the resistance and temperature of electrode tip rather than decrease, and it requires reducing the welding parameters instead of increasing. In case of electrode wear, maintaining a consistent temperature rise of electrode tip helps to ensure welding quality. Due to the insulation coating of enameled wire, the normal TCC between electrode tip and workpieces significantly changes in the MRSW process and rapidly rises after the decomposition of insulation coating. TCC needs to be controlled within a reasonable range to prevent insufficient or excessive heat transfer in production.

In-depth evaluation of micro-resistance spot welding for connecting tab to 18,650 Li-ion cells for electric vehicle battery application

In-depth evaluation of micro-resistance spot welding for connecting tab to 18,650 Li-ion cells for electric vehicle battery application

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

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

Quality Monitoring for Micro Resistance Spot Welding with Class-Imbalanced Data Based on Anomaly Detection

Micro resistance spot welding (MRSW) is an important technology widely used in electronics manufacturing for micro component joining. For the joining of micro enameled wire, quality control is heavily dependent on manual inspection till now. In this paper, a quality monitoring approach based on isolation forest (iForest) is proposed to identify abnormal welds and normal welds. Electrode voltage and welding current of over 110,000 spot welds were collected from a production line. The dynamic resistance and heat input were calculated for all welds and used for feature extraction. A class imbalance problem existed in the collected dataset because abnormal welds were far fewer than normal welds. The anomaly detection model based on iForest was established for the imbalanced data classification after comparison with other methods such as one-class (support vector machine) SVM and local outlier factor. Test results show that the similarity of dynamic resistance profile and heat input compared with the previous ten welds are valid features for detecting a part of the abnormal welds. The iForest model is effective for distinguishing incomplete fusion welds from normal welds with high efficiency. It can assist in the on-line quality monitoring of enameled wire welding process in production.

Micro-resistance spot welding of cylindrical battery packets in FEM calculations

Due to the increasing demand for connecting cells in packets to power electric tools, bicycles and electric cars, the issue of the quality of battery cells with busbars joints with the use of external heat electrodes is particularly important. The paper presents the conditions of the joining process and modelling results using the DC source. Modelling was performed using commercially available Sorpas 3D software. It included checking the influence of the busbar shape, clamping force, electrode material, the shape of electrode face, the length of the tungsten inserts in the welding electrodes on the amount of heat and the diameter of the connections. Modelling results revealed in particular increased heat generation and connection diameters for electrodes with a smaller work surface, however, industrial practice shows that the electrode face diameter durability is limited and that the electrodes flatten - the electrode face diameter increases.

Mechanical Properties and Microstructures on Dissimilar Metal Joints of Stainless Steel 301 and Aluminum Alloy 1100 by Micro-Resistance Spot Welding

Aluminum and stainless steel are metals that have some mechanical property advantages. Welding technology has been developed to join both different and dissimilar metals applied in a construction. The property advantages have been used to improve the performance of a construction. However, welding performance still creates a problem as a result of properties’ differences in metals. This study investigated the mechanical properties of a steel-aluminum joint with the thickness of less than 1 mm, welded by resistance spot welding (RSW); it is called a micro-RSW. Mechanical properties of the joint were analyzed by tensile test and were measured at the fracture area on the tensile test specimen. Moreover, it also analyzed intermetallic microstructure in the nugget or welding joint. Welding time of 8 CT was an optimum parameter on a welding process to get the maximum load. The fractographic structure of a stainless steel-aluminum joint showed a brittle nugget. Moreover, the fracture area on the aluminum side was larger than that of the stainless steel. Intermetallic compound (IMC) was created by melting and joining it through the heat input in the welding process. IMC in SS301-AA1100 nugget affected a brittle joint.

Optimization of a dissimilar platinum to niobium microresistance weld: a structure–processing–property study

Dissimilar metal resistance spot welds, critical to the manufacture of medical devices, typically form brittle intermetallic compounds that are prone to failure. Here, a case study of biocompatible metals platinum and niobium using advanced analytical techniques is presented. It describes the variation of properties and microstructure using microresistance spot welding under four conditions, including a legacy process and processing conditions optimized by design of experiments. Adjustments to the electrode force, welding current, surface roughness, and pulse duration and exchanging the platinum anode contact for a cathode result in a joint with less porosity and greater uniformity in the thickness, chemistry, and microstructure of the fusion zone. The optimized microstructure contains fewer defects, with increased plasticity under deformation and a more uniform microstructure reducing the propensity for failure and variability between welds. Extensive analysis with optical, scanning electron, transmission electron microscopy coupled with nano- and micromechanical testing (such as micropillar compression) was used to characterize the weld zone.

Microstructure and mechanical properties of micro-resistance spot welding between stainless steel 316L and Ti-6Al-4V

In this study, austenitic stainless steel 316L and titanium alloy (ASTM grade 5) were welded together by micro-resistance spot welding at different combinations of welding parameters and by using specifically designed electrode geometry. The welded joints were subjected to tensile shear strength test in order to determine the strength of the welded zones. In addition, micro-hardness and microstructural examinations of the fracture mode (failure analysis) were carried out in order to examine the influence of welding parameters on the welded joints. The results showed that using a combination of 2.0 kN welding current, 100 ms welding time, and 241 N welding force yield the highest load value, 378.25 N by using full factorial design of experiment (DOE). Welding current is the most significant parameter which is obtained through analysis of variance (ANOVA). However, the increase in welding current should be controlled to avoid weld metal expulsion. The microstructure of these resistance-welded metals are detailed and investigated by using SEM and EDS mapping analysis. Based on the SEM observations, columnar dendritic structures can be seen at the fusion zone (FZ) of the welded nugget.

Effects of welding parameters on electrode element diffusion during micro-resistance spot welding

Copper electrodes are commonly employed in micro-resistance spot welding (MRSW), a dominant process used to join ultra-thin metallic sheets. During welding, some copper from the electrodes inevitably diffuses into the spot welds, changing the chemical compositions and properties of the resulting welded joints. In this study, 0.05-mm-thick Ti alloy metallic sheets were welded via MRSW under various combinations of welding parameters (ramping time, welding time, holding time, welding current, and electrode force). The effects of these welding parameters on electrode elemental diffusion were investigated via elemental analysis. Elemental composition of welded joints was measured via energy-dispersive spectrometry after tensile-shear tests. No copper was detected in the heat-affected zone or base material, but the amount of copper in the welding nuggets varied significantly with the welding parameters. Moreover, comparing copper element and hardness maps in weld nugget, the welding nugget hardness increased when more copper diffused into it.

Extremely fast formation of Cu[sbnd]Sn intermetallic compounds in Cu/Sn/Cu system via a micro-resistance spot welding process

High-temperature-stable circuit interconnects are highly desirable for the wide band-gap semiconductor devices to operate in harsh environment (>200 °C). In this study, a full Cu3Sn interconnect with the melting point of 679 °C was fabricated by using a micro-resistance spot welding process in an extremely short time of 200 ms and under a low pressure of 0.08 MPa at ambient temperature in Cu/Sn (30 μm)/Cu interconnection system. The microstructure evolution of CuSn intermetallic compounds indicated that the joule heat-induced temperature coupled with the passage of electric current significantly enhanced the interfacial reaction at the liquid Sn/solid Cu metallization interface. Accompanying with the speedy electromigration of Cu atoms in the molten Sn solder, the columnar dendritic Cu6Sn5 compounds were formed due to constitutional supercooling and then were totally transformed into Cu3Sn compounds. The resulted Cu3Sn interconnect exhibited a higher mechanical strength than Sn-based interconnects, offering this type of interconnect a promising application in high-temperature power electronics.

Effect of Welding Current and Welding Time for Micro Resistance Spot Welding on Dissimilar Thin Thickness Materials of Al 1100 and KS 5 Spring Steel

In the dissimilar materials and dissimilar thin thickness sheets joining, welding current and welding time parameters of resistance spot welding (RSW) effect weld ability. RSW used for joining thin plate less than 1000 μm is called micro-resistance spot welding (μRSW). The objective of this article is to study the effect of welding current and welding time to the joining dissimilar thin thickness materials and the microstructure of a weld joint. The thickness of Al 1100 is 400 μm, and KS 5 Spring Steel is 200 μm. Welding parameters are Cycle Time 0.5, 1, 1.5, Welding Current 1kA and 2 kA, and holding time 10 second. Welding current 1kA, Cycle time of 0.5 produce maximum shear load of 227.4 N and fracture area of 6.644 mm2. Welding current 2 kA, cycle time of 1.5 affect maximum load of 222.7 N and fracture area of 10.559 mm2. Welding parameters lead to the majority fracture on aluminum material. The welding current and cycle time do not significantly affect maximum shear load and fracture area.

Micro-Resistance Spot Welding of Nickel Free Austenitic Stainless Steel

Micro-resistance spot weldability of nickel free stainless steel sheet was studied to fabricate medical implants. Weld lobe was established and the effect of welding parameters on joint strength was investigated. Weld nugget represented a rapidly quenched austenitic cellular structure whose cell size is several μm with a little ferrite. The amount of δ-ferrite in weld nugget is smaller than that predicted by some Schaefller diagrams due to rapid solidification during micro-resistance spot welding.

Microresistance spot welding of Kovar, steel, and nickel

Microresistance spot welding of 0.2–0.5 mm thickness Kovar, steel, and nickel using different types of power supply was investigated. The effects of process parameters (welding current/pulse energy, electrode force, and welding time/pulse width) on joint strength and nugget diameter were studied. The maximum values of welding current and nugget diameter that did not result in weld metal expulsion and/or electrode–sheet sticking were determined. The difference between micro- and ‘large scale’ resistance spot welding was also considered. It was noted that the difference between micro- and large scale resistance spot welding is due not only to the difference in the scale of the joints, but also to the fundamental difference in the electrode forces (pressures) used. Based on the results of the present work, nominal process parameters are recommended for microresistance spot welding of Kovar, steel, and nickel when using different power supplies.