Welding Energy Research Articles

Ultrasonic Welding of Carbon Fiber Reinforced Composite With Variable Blank Holding Force

Energy directors (EDs) have been widely used in ultrasonic welding (UW) of polymers and polymer-based composites. They help concentrate the welding energy and localize the weld at the location where the EDs are present. However, the utilization of EDs increases manufacturing cost and time, especially for complex parts and structures. This paper presents a method for UW of carbon fiber reinforced composite without using EDs. A reusable annular clamp (called a blankholder) is used as part of the weld tool to apply a variable force (called blank holding force) on the composite sheets during the UW. The effect of the blank holding force (BHF) on the weld formation is investigated. The results show that the duration of the BHF had significant impact on the weld formation. There is a critical duration with which a localized weld can form. Suitable durations of BHF at different levels of welding energy are determined by experiments. The main function of the BHF is to create an initial melting area by improving the contact condition. The initial melting area will act as an ED to concentrate the welding energy, and therefore, promotes the formation of a localized weld.

Effect of welding time on microstructure and mechanical properties of Al-Ti ultrasonic spot welds

AA6061 A l alloy and commercial pure Ti sheets were successfully joined by ultrasonic spot welding. The microstructure and mechanical properties of joints under welding time from 0.6 s to 1.4 s were investigated. No intermetallic compounds were founded at the interface of the joints. As the welding time increased, the peak load of the joints firstly increased with the expansion of bond area, then decreased afterwards due to the fatigue crack in Al side. The peak temperature increased with increasing welding time. In the weld region, the aluminum alloy was softened by the weld energy, while the hardness of pure titanium did not change distinctly. All the failure occurred along the interface of the joints with brittle fracture characteristics during tensile shear test.

Induction Pre-Heated Linear Friction Welding

A two-level factorial design of experiments (DOE) approach is used to study the effect of four factors (average rubbing velocity, weld pressure, burn-off distance, and preheat temperature) on two response variables (weld strength and energy input) for the induction heating and linear friction welding of AISI 1020 steel. Weld strength, as analyzed though three-point bending, was insensitive to all four of the design factors. Pressure, upset, and velocity show statistically significant inverse, linear, and linear relationships with energy used, respectively. Pressure has the largest effect on energy used, followed by velocity and upset.

Microstructure and Mechanical Properties of Ultrasonic Spot Welded Mg/Al Alloy Dissimilar Joints

Lightweight structural applications of magnesium and aluminum alloys inevitably necessitate welding and joining, especially dissimilar welding between these alloys. The objective of this study was to examine the feasibility of joining ZEK100 Mg alloy to Al6022 alloy via ultrasonic spot welding, focusing on effects of welding energy. An interface diffusion layer consisting of α-Mg and Al12Mg17 eutectic structure was observed to form, with its thickness increased from ~0.5 µm to ~30 µm with increasing welding energy from 500 J to 2000 J. The tensile lap shear peak load or strength and critical stress intensity of the welded joints first increased and then decreased with increasing welding energy, with their peak values achieved at 750 J. Fatigue life of the joints made at 750 J and 2000 J was equivalent at the lower cyclic loading levels, while it was longer for the joints made at 750 J at the higher cyclic loading levels. Fatigue fracture mode changed from interfacial failure to mainly transverse-through-thickness crack growth with decreasing cyclic loading level, which corresponded well to the bi-linear characteristic of S-N curves. Crack initiation basically occurred at the weld nugget border and at the interface between the two sheets, which can be understood via a theoretical stress analysis.

Investigations on Resistance Behavior at the Interface of Ultrasonically Welded Dissimilar Al/Cu Joints

The key focus of this research study is to analyze the weld joint resistance with microstructural evaluation of ultrasonically welded Al and Cu dissimilar wires. The typical applications of dissimilar wire bonding include automobile parts, electrical safety, and battery terminals. The weldments are further subjected to metallurgical characterization to understand the extent of molecular movements at the interface, uniformity in material diffusibility and the corresponding changes in weld joint resistance due to various ultrasonic welding energies. Ultrasonic welding trials were performed with different levels of process parameters (pressure, weld time, and amplitude) based on design of experiments. Subsequently, the welded specimens were examined through optical microscopy and the corresponding images are captured using image analyzers. Further, SEM images were investigated for understanding the surface morphology and the extent of intermetallic compounds formation and performance. The experimental results show that the increase in welding energy is inversely proportional to the degree of formation of intermetallic compounds/weld joint resistance. Besides, the surface morphology unwinds a uniform weld pattern in most of the samples while there are few voids and non-uniformity for low heat input samples.

Sustainability of Welding Process through Bobbin Friction Stir Welding

Welding process is in high demand, which required a competitive technology to be adopted. This is important for sustaining the needs of the joining industries without ignoring the impact of the process to the environment. Friction stir welding (FSW) is stated to be benefitting the environment through low energy consumption, which cannot be achieved through traditional arc welding. However, this is not well documented, especially for bobbin friction stir welding (BFSW). Therefore, an investigation is conducted by measuring current consumption of the machine during the BFSW process. From the measurement, different phases of BFSW welding process and its electrical demand are presented. It is found that in general total energy in BFSW is about 130kW inclusive of all identified process phases. The phase that utilise for joint formation is in weld phase that used the highest total energy of 120kWs. The recorded total energy is still far below the traditional welding technology and the conventional friction stir welding (CFSW) energy demand. This indicates that BFSW technology with its vast benefit able to sustain the joining technology in near future.

Metallurgy and mechanical properties variation with heat input,during dissimilar metal welding between stainless and carbon steel

The present research focus on the metallurgy and mechanical aspect of dissimilar metal welding.One of the common parameters that significantly contribute to the metallurgical aspect on the metal during welding is heat input. Regarding this point, in the present research, voltage, current and the welding speed has been varied in order to observe the effect of heat input on the metallurgical and mechanical aspect of both welded metals. Welding was conducted by Gas Metal Arc Welding (GMAW) on stainless and carbon steel with filler metal of ER 309. After welding, hardness test (micro-Vickers), tensile test, macro and micro-structure characterization and Energy Dispersive Spectroscopy (EDS) characterization were performed. It was observed no brittle martensite observed at HAZ of carbon steel, whereas sensitization was observed at the HAZ of stainless steel for all heat input variation at the present research. Generally, both HAZ at carbon steel and stainless steel did not affect tensile test result, however the formation of chromium carbide at the grain boundary of HAZ structure (sensitization) of stainless steel, indicate that better process and control of welding is required for dissimilar metal welding, especially to overcome this issue.

Influence of MIG/MAG Welding Process on Mechanical and Pitting Corrosion Behaviors on the Super-Duplex Stainless Steel SAF 2507 Welded Joints

The main objective of this research is to better understand the correlation between the constituent phases presented in the super-duplex steel SAF 2507 when it is under welding process by arc shielding gas MIG-MAG (Metal Inert Gas-Metal Active Gas). Conventional short circuit transfer and derivative STT (Surface Tension Transfer) using the 2594 welding wire as a filler metal and the effects on welding power in hardness, toughness and pitting corrosion are considered here. The results showed that the welding energy (Ew) changed the α/γ-phase’s balance and occasionally formed σ-phase in ferrite grain boundaries which led to changes in hardness, toughness and pitting corrosion resistance in molten zone (MZ), heat activated zone (HAZ) and metal base regions (MB). Furthermore, the increased amount of γ-phase improved the pitting corrosion resistance index (PRENγ) mainly in the MZ. This is due to decrease of α-phase fraction and formation of coarser grains, for higher welding energy. The toughness in the MZ decreased with less formation of γ-phase, coalescence of ferritic grains and localized formation of σ-phase, raising the hardness in the HAZ when the welding energy was lower.

Sustainability of manufacturing technology: friction stir welding in focus

The sustainability of quality products is the primary concern of today's manufacturing entrepreneurs. The desire to produce cost effective and competitive products by metal forming or welding process has increased spontaneously. The authors examined the sustainability of friction stir welding (FSW) and evaluated weld joints reliability for health, safety, environment and economic purposes. An interplay between welding speed and tool rotational speed led to the formation of viable structures. The welding energy, materials deformation, emissions and life cycle assessment were analysed in line with the mechanical properties. A bivariate Weibull approximation model was used to predict weld joints reliability. A reliable and sustainable joints were obtained when the Weibull modulus increases as heat input reduces. The authors concluded by linking the tensile property of welded joints, heat input and Weibull modulus to the sustainability of FSW. A closed energy system was recommended for this green technology to be worthwhile.

Effect of Laser-arc Hybrid Welding Energy Parameters on Welding Stability

The high-speed camera was used to collect the droplet transfer pattern and arc pattern of the laser-arc hybrid welding process. Using the methods of image processing and mathematical statistics, the effects of different laser and arc power conditions on the welding stability were studied. The results show that the melting width depends on the welding current, the depth of penetration depends on the laser power, the droplet transition pattern, the actual filament spacing and the arc length determine the welding stability of the laser arc hybrid welding.

Determination of Strain and Stress Fields in Welded Joints of S960-QC Steel

Abstract The paper presents the results of two butt welded joints by conventional method. The welding process was performed using a variety of linear welding energy. The studies included experimental and computational part. In experimental studies determined the distribution of hardness and mechanical properties of the individual analyzed sections of welded joints. The data obtained were intended to determine the extent of zones in the welded joints that have certain strength characteristics. Also conducted uniaxial tensile tests of welded joints with the registration of displacement fields on the surface of specimens by means of Aramis video-system what the final result are images of strain fields map on the surface of welded joints. The resulting strain values were compared with the results of numerical computations FEM.

Optimization and metallurgical studies of CO2 laser welding on austenitic stainless steel to carbon steel joint

ABSTRACTIn the present work, the 4 kW CO2 laser welding process has been optimized for austenitic stainless steel (AISI 316)/ low carbon steel (AISI 1018) joint by using Taguchi based grey relational analysis. The experimental results make clear that the AISI 316/AISI 1018 laser welded joints are effectively enhanced by optimizing the input parameters. The metallurgical studies have been carried out for the optimum welded samples using an optical microscope to observe weld appearance and energy dispersive X-Ray analysis carried out to measure the nature of the matrix and chemical element distribution in the weld interface.

The Analysis of Welding Conditions Under the Flux of Double-Sides Joints Without Edge Preparation

This paper represents the results of analysis for automatic welding conditions under the flux of double-sides butt joint without edge preparation. As the process characteristics, a specific energy of welding, joint formation rate, average weld width, fusion rate of base metal and other parameters were used. It is determined an optimal joint rate of about 1 cm2/s, that can be used to calculate welding conditions. The paper founds the use of linear dependence between specific energy of welding and cross-section area of base metal’s fusion.

Performance Prediction for Ultrasonic Spot Welds of Short Carbon Fiber-Reinforced Composites Under Shear Loading

Ultrasonic welding is a well-known technique for joining thermoplastics and has recently been introduced to joining carbon fiber-reinforced composites (CFRC). However, suitable models for predicting joint performance have not yet been established. At present, most failure models for bonded composites are built based on uniform adhesive joints, which assume constant joint properties. Nevertheless, the joint properties of ultrasonic spot welds for CFRC are variable, which depend on the input welding parameters. In this paper, the effect of welding energy, which is the most important welding parameter, on the joint properties is investigated. Then, a surface-based cohesive performance model based on mode-II (in-plane) shear loading is developed to predict the joint performance, wherein the critical fracture parameters in the model are described via the functions of welding energy. After comparing the simulated results with experiments, the model is proven feasible in predicting the joint properties of the ultrasonic spot welds under shear loading condition, and hence, a mix-mode cohesive-zone model is practical to predict the joint performance under any loading conditions with the predicted fracture parameters.

Combined effects of MIG and TIG arcs on weld appearance and interface properties in Al/steel double-sided butt welding-brazing

AA5052 aluminum alloy and Q235 low-carbon steel of 3.0mm thickness were butt joined without groove. The combined effects of the MIG-TIG double-sided arc on the weld appearance and interface properties were investigated in three aspects: weld appearance, interfacial properties and joint tensile strength. Form efficiency was defined to evaluate the quality of the weld appearance. The strength of the whole joint and the brazed interface were examined in the tensile tests of joints with and without excess weld metal, respectively. The weld appearance can be well characterized by the form efficiency. The form efficiency is found to be most sensitive to TIG current. Sensibility of the form efficiency to MIG voltage and welding speed is relatively low, indicating that the TIG arc at the back of the weld is the key factor for the double-sided weld appearance. Double-sided weld appearance can be achieved at a maximum welding speed of 2.2cm/s because a part of welding energy is input by TIG arc directly to the back weld. The interfacial properties of the joints are closely tied to the heat input ratio of MIG and TIG. Proper input ratio (1.35–1.64) leads to uniform deformation of the base metals and suppresses the initiation of the cracks in interfacial IMC layer. The differences between the interfacial strength and the whole joint strength indicate that the optimum weld appearance with desirable excess weld metal provides extra 20MPa strength for the whole joint. Benefitting from combined effects of the best weld appearance and toughest interfacial IMC layer, the highest tensile strength of the joint exceeds 70% the tensile strength of 5052 alloy.

Studies on Electro Mechanical Aspects in Ultrasonically Welded Al/Cu Joints

Ultrasonic welding has been widely used to bond dissimilar conductive wires, battery cell terminals in relay applications. In this paper, dissimilar metals, Al/Cu were joined using ultrasonic welding for conductive applications. Welding trials were carried out by varying three control parameters: (1) vibrational amplitude (40, 60, and 80 µm), (2) clamping pressure (1, 1.2, and 1.4 bar), (3) weld time (0.1, 0.2, and 0.3 s). Experimental trails were designed based on L9 Taguchi method. Interpretation of tensile strength and microhardness results revealed that the satisfactory weldments were obtained for higher welding energies when compared to low welding energies. From the microstructural analysis, the bond formation of metals and failure modes were studied. SEM and XRD images revealed the four major intermetallic compounds at the interface of joint; AlCu, Al2Cu, Al3Cu4, and Al4Cu9 with resistivity values of 11.415, 8.027, 10.612, and 14.243 Ω-cm respectively. The resistivity values of intermetallic compounds observed in the joint was almost 5–6 times higher than the Al.

Decomposition of ultrasonically welded carbon fiber/polyamide 66 and its effect on weld quality

Ultrasonic welding of 4 mm thick carbon fiber/polyamide 66 (Cf/PA 66) composite samples in a lap configuration was completed to characterize the effect of weld energy on weld strength. In general, it was seen that weld strength was proportional to weld energy; however, with excessive energy, the weld strength decreased. Weld indentation had little influence on joint strength, whereas thermal decomposition of Cf/PA 66 composite was the main reason for the low joint strength. Higher weld energy caused thermal decomposition of Cf/PA 66 composite and degradation of tensile strength of welded workpieces. A decomposition index of the joint was proposed and calculated to predict weld quality. When the decomposition index was small, joint strength increased with the weld area while high decomposition index of polyamide 66 (i.e. >30.5%) led to the decrease in joint strength based on the experimental data. The optimal decomposition index was found in the range of 12–30.5% depending on joint strength.

Hybrid ultrasonic spot welding of aluminum to carbon fiber reinforced epoxy composites

Ultrasonic metal welding has been applied for joining aluminum AA5754 sheets to a thermoset matrix composite consisting in a carbon fiber reinforced epoxy resin (CF/epoxy). To overcome the limitations of thermosetting resins, that, unlike thermoplastic polymers, cannot melt due to their chemical structure, a thermoplastic film of Polyamide 6 (PA6) has been used as a surface layer of the CF/epoxy stack before curing. The functional surface created on the thermoset matrix composite enables a fast welding with a metallic sheet. By a proper selection of welding energy and force, an average adhesion strength of 34.8MPa has been obtained on CF/epoxy-PA6-AA5754 ultrasonically welded joints.The morphological characterization has revealed that the aluminum-composite interface is characterized by carbon fibers in a direct contact or even embedded in aluminum, whose surface presents pores and crevices due to the pronounced plastic deformation of the Al interfacial area.

Efficiency of the Inertia Friction Welding Process and Its Dependence on Process Parameters

It has been widely assumed, but never proven, that the efficiency of the inertia friction welding (IFW) process is independent of process parameters and is relatively high, i.e., ~70 to 95 pct. In the present work, the effect of IFW parameters on process efficiency was established. For this purpose, a series of IFW trials was conducted for the solid-state joining of two dissimilar nickel-base superalloys (LSHR and Mar-M247) using various combinations of initial kinetic energy (i.e., the total weld energy, E o), initial flywheel angular velocity (ω o), flywheel moment of inertia (I), and axial compression force (P). The kinetics of the conversion of the welding energy to heating of the faying sample surfaces (i.e., the sample energy) vs parasitic losses to the welding machine itself were determined by measuring the friction torque on the sample surfaces (M S) and in the machine bearings (M M). It was found that the rotating parts of the welding machine can consume a significant fraction of the total energy. Specifically, the parasitic losses ranged from 28 to 80 pct of the total weld energy. The losses increased (and the corresponding IFW process efficiency decreased) as P increased (at constant I and E o), I decreased (at constant P and E o), and E o (or ω o) increased (at constant P and I). The results of this work thus provide guidelines for selecting process parameters which minimize energy losses and increase process efficiency during IFW.

Influence of welding parameters on intermetallic compounds formation in dissimilar steel/aluminum friction stir welds

It is difficult to obtain a quality joining of steels to aluminum alloys by fusion welding processes due to the large difference between melting temperatures and the formation of thick brittle Al/Fe intermetallic compounds at the joint interface. In this study, lap welds between Al 1100 and St37 steel were performed by solid-state friction stir welding with different tool rotation and welding speeds. FeAl and Fe3Al with thicknesses of up to 93 μm were the intermetallic compound layers formed at the joint interfaces. Shear tensile test and Scanning Electron Microscopy results showed that Fe-rich intermetallic compounds are not detrimental to joint strength and some defects, like voids, are responsible for the deteriorated weld strength. The welding parameters determine bond properties by controlling the distribution of welding energy as heat or mechanical work. At low welding speeds, mechanical work is the dominant factor. The optimum tensile strength is achieved at low welding speeds and high rotation speeds, where both factors of heat input and mechanical work are in equilibrium.