Lap Joint Configuration Research Articles

Metal-cored welding wire for minimizing weld porosity of zinc-coated steel

Metal-cored welding (MCW) wire with an optimal chemical composition was developed to minimize the weld porosity and pits in the cold metal transfer welding of hot-dip galvannealed steel in a lap-joint configuration. The effects of the chemical composition of the welding wire (specifically, the effects of the C, Si, and Mn contents) on the weld porosity formation were investigated through statistical analysis, high-speed imaging of the weld pool behavior, and welding signal analysis. The Si and Mn contents were found to be significant factors in reducing the weld porosity and pits. As the Si and Mn contents decreased, the viscosity of the weld pool decreased and the Zn vapor emission increased. The electrical resistance of the wire also decreased with decreasing Mn content. Although the C content rarely affected the emission of Zn vapor, it affected the hardness of the welds. The response surface model between the wire elements and weld porosity was also estimated, and the chemical composition of the wire was optimized based on this model. The optimal MCW wire with low Si and Mn contents (0.08% C–0.30% Si–0.51% Mn) was fabricated, and its effectiveness in reducing weld porosity was experimentally verified.

Effect of the structural reinforcement of composite adherends on the mechanical strength of adhesive joints

AbstractThis study proposes a novel method to strengthen fiber reinforced plastic (FRP) adherends in a single lap joint (SLJ) by using Kevlar threads. The adherend reinforcement procedure consists of applying a zigzag thread in the fiber glass layers that comprise the adherend in order to subsequently manufacture the adherends using the vacuum infusion method. For this study, three single lap joint configurations were used: Adherends without Kevlar reinforcement (SLJ1), adherends with Kevlar reinforcement with a medium step zigzag (SLJ2) and adherends with Kevlar reinforcement with a small step zigzag (SLJ3). Mechanical tensile tests were carried out to determine the ultimate strength and displacement of the single lap joint configurations studied. Adherends reinforced by Kevlar threads increase the strength and displacement of the single lap joint. However, the influence of the step size of zigzag threads on the adherend does not significantly influence the strength, but significantly affects the maximum displacement of the single lap joint.

Effect of brazing current and speed on the bead characteristics, microstructure, and mechanical properties of the arc brazed galvanized steel sheets

Gas metal arc (GMA) brazing was employed to join hot-dip galvanized steel sheets (GI) in lap joint configuration using CuSi3 filler. The effects of brazing current and speed on the joint characteristics such as bead geometry, microstructure, weldability, microhardness and tensile shear strength were studied. The bead geometry was assessed by examining the bead shape, width, contact angle, penetration width and depth of the fused zone. The microstructural investigations were performed using scanning electron microscopy (SEM), and composition was determined using energy dispersive spectroscopy (EDS). The formation of Fe-Si phases was noticed in the bead which was found to increase with brazing current and brazing speed. The pores were nucleated in GI lap joint at highest current 80A and lower brazing speeds 60–70cm/min. The bead shape and size, joint strength, weldability were found best at a combination of 70A and 80cm/min which could be attributed to a uniform distribution of Fe5Si3(Cu) in the bead. It is suggested that for a pore-free bead structure, the heat input should lie in the range of 58.5–93.6J/mm for the arc brazing of GI sheets.

Remote laser welding of zinc coated steels in a zero-gap lap joint configuration

Zinc coated steels have been increasingly used in the automotive industry due to their excellent corrosion resistance. However, the presence of zinc coating on the steel sheet poses significant challenges in the laser welding process. Zinc has a lower boiling point (906 °C) than the melting point of steel (>1300 °C). When zinc coated steels are laser welded in a zero-gap lap joint configuration, a highly pressurized zinc vapor is readily produced at the faying interface. Without special precaution, a large amount of spatter and blowholes can be produced, which can degrade the weld quality and mechanical performance of the welds. The state-of-the art approach to mitigate the negative impact of zinc vapor is to employ a series of dimples having an approximate height of 0.1–0.2 mm to provide a channel along the faying interface for the resulting zinc vapor to escape. In this study, an innovative remote laser welding process has been developed to directly weld zinc coated steels in a zero-gap lap joint configuration without the use of dimples. Experimental results show that high-integrity welds can be achieved with excellent mechanical performance. The new process can dramatically reduce the cycle time and manufacturing cost by eliminating the dimpling process.

Laser dimpling process parameters selection and optimization using surrogate-driven process capability space

Remote laser welding technology offers opportunities for high production throughput at a competitive cost. However, the remote laser welding process of zinc-coated sheet metal parts in lap joint configuration poses a challenge due to the difference between the melting temperature of the steel (∼1500°C) and the vapourizing temperature of the zinc (∼907°C). In fact, the zinc layer at the faying surface is vapourized and the vapour might be trapped within the melting pool leading to weld defects. Various solutions have been proposed to overcome this problem over the years. Among them, laser dimpling has been adopted by manufacturers because of its flexibility and effectiveness along with its cost advantages. In essence, the dimple works as a spacer between the two sheets in lap joint and allows the zinc vapour escape during welding process, thereby preventing weld defects. However, there is a lack of comprehensive characterization of dimpling process for effective implementation in real manufacturing system taking into consideration inherent changes in variability of process parameters. This paper introduces a methodology to develop (i) surrogate model for dimpling process characterization considering multiple–inputs (i.e. key control characteristics) and multiple–outputs (i.e. key performance indicators) system by conducting physical experimentation and using multivariate adaptive regression splines; (ii) process capability space (Cp–Space) based on the developed surrogate model that allows the estimation of a desired process fallout rate in the case of violation of process requirements in the presence of stochastic variation; and, (iii) selection and optimization of the process parameters based on the process capability space. The proposed methodology provides a unique capability to: (i) simulate the effect of process variation as generated by manufacturing process; (ii) model quality requirements with multiple and coupled quality requirements; and (iii) optimize process parameters under competing quality requirements such as maximizing the dimple height while minimizing the dimple lower surface area.

Interface characteristics and performance of magnetic pulse welded copper-Steel tubes

An attempt has been made to join two tubes of pure copper and low carbon steel by magnetic pulse welding in lap joint configuration. Satisfactory welds were obtained with an optimal set of parameters consisting of discharge energy, standoff distance and initial collision angle. The welded interface revealed a wavy morphology with pockets of intermixed metal vortices. High resolution electron microscopy and microanalysis showed the formation of nano-grains along the interface and evidence of short distance interatomic diffusion across the weld joint respectively. The strain hardening effect due to high energy impact led to significantly higher microhardness on the steel side of the interface. Torsion tests confirmed acceptable joint strength as failure took place in the copper base material.

Analytical models for functionally graded adhesive single lap joints: A comparative study

Functionally graded adhesives yielding a varying adhesive Young's modulus along the overlap are increasingly considered in order to allow for a more uniform stress distribution and to reduce the occuring stress concentrations in the adhesive layer of adhesively bonded single lap joints. The present work provides a comparative study of the existing analytical models for planar functionally graded adhesive single lap joints. The respective modelling assumptions as well as the conditions of applicability of the different approaches are examined in detail. In addition, a novel approach and possible extensions of the presented approaches are outlined and discussed. A thorough comparative study comprising various single lap joint configurations and adhesive Young's modulus distributions along the overlap is performed in order to assist the engineer choosing the adequate model for a particular single lap joint design. For an assessment of the accuracy, the calculated adhesive stress fields are compared to numerical results obtained by Finite Element Analyses. In addition, the effects of the adhesive Young's modulus range on the peak adhesive stresses are studied and discussed.

Parameter optimisation of friction stir welded dissimilar polymers joints

There has been a significant increase in the use of polymeric materials in various areas of industry and engineering, which were previously dominated by metallic components. Recently, the possibility of implementing friction stir welding (FSW) technology for welding polymer-polymer and polymer-metal has come under investigation. Polymeric materials behave differently from metallic ones, and there is still a limited number of research works in the literature concerning this specific topic. In this study, a stationary shoulder made of Teflon was used to weld thin plates of polypropylene and polyethylene together in the lap-joint configuration without external heating. Using a stationary shoulder, the probe generates all the frictional heat and stirs the nearly molten material under an axial force. This article is focused on parameter optimisation for friction stir welded lap joints of dissimilar polymers using a new tool concept. It was concluded that the tool design has the most effective role regarding the lap-shear strength of joints. Welds fabricated with the optimised welding parameters present good surface quality and strength. Moreover, for welding polymeric materials with this method, the main defects have been found on the retreating side of the welds. This behaviour can be explained by insufficient heat generation on the retreating side as well as poor thermal conductivity of polymeric materials.

Fatigue Life Assessment of Friction Stir welded Dissimilar Polymers

In this study, two dissimilar polymers with different thicknesses were welded in the lap joint configuration in order to investigate the fatigue behavior of the obtained welds. A comprehensive study of the fatigue life of friction stir welded dissimilar polypropylene-to-polyethylene in lap shear configuration is presented. There is a lack of research works published on this topic; to the authors knowledge this is the first paper concerning the fatigue behavior of polymeric friction stir welded lap joints. The fatigue life of the strongest welds was compared with the highest performing base material. The FSW joints had good resistance under cyclic loading but in a brittle behavior due to degradation of polymers during this process. The retreating side of the welds suffer from lack of generated heat when compared with the advancing side due to the low thermal conductivity of polymeric materials, leading to crack initiation at the retreating side. However, using high testing frequency, the parent material failed thermally during fatigue tests, while FSW specimens behaved differently.

Microstructure and calorimetric behavior of laser welded open cell foams in CuZnAl shape memory alloy

Cellular shape memory alloys (SMAs) are very promising smart materials able to combine functional properties of the material with lightness, stiffness, and damping capacity of the cellular structure. Their processing with low modification of the material properties remains an open question. In this work, the laser weldability of CuZnAl SMA in the form of open cell foams was studied. The cellular structure was proved to be successfully welded in lap joint configuration by using a thin plate of the same alloy. Softening was seen in the welded bead in all the investigated ranges of process speed as well as a double stage heat affected zone was identified due to different microstructures; the martensitic transformation was shifted to higher temperatures and the corresponding peaks were sharper with respect to the base material due to the rapid solidification of the material. Anyways, no compositional variations were detected in the joints.

Numerical simulation of temperature field, fluid flow and weld bead formation in oscillating single mode laser-GMA hybrid welding

A three dimensional numerical model of oscillating single mode laser-GMA hybrid welding process with lap joint and arc inclination configuration has been developed for the first time. The model is used to investigate the temperature field and fluid flow corresponding to the aforesaid welding process and weld configuration. An asymmetric distribution of arc heat and a cylindrical volumetric distribution of laser heat are established to describe the heat transfer from the combined heat source to the workpieces. The droplet with predefined temperature and velocity is impinged on the weld pool at a given fillet weld angle. Arc pressure, electromagnetic force, Marangoni force and buoyancy are also considered in the model with some modifications with respect to the lap joint and arc inclination configuration. Results show that the droplet impingement process has a significant influence on the weld geometry, temperature field and fluid flow pattern due to the transfer of mass, energy and momentum into the weld pool. These unique temperature fields and flow patterns are characteristic to the lap joint and arc inclination configuration. The proposed model exhibits close correspondence with the experimental results with respect to weld geometry.

Mechanical performance and electrical resistance of ultrasonic welded multiple Cu-Al layers

The mechanical performance and electrical resistance of dissimilar and multi-layered Cu-Al sheets, which represent the battery electrodes and tabs, were evaluated by ultrasonic welding (UW). Different possibilities of lap-joining configurations using sheets of Cu and Al were considered. The weld strength at each weld interface of the multi-layered joint was evaluated by 90° peel test and by heat input measured by an infrared imager (IR). The strength of each weld interface of UW joined multiple Cu-Al layers were found to be strong enough to produce a through-thickness tearing. A typical weld criterion for producing a developed nugget was achieved. Weld quality at interfaces was assessed by cross-sectioning the UW joint parts. Depending on the lap-joint configuration, weld interfaces were characterized by bonded and unbonded interfaces. Measuring the electrical resistance passing through the joints demonstrated that the unbonded weld interface produced an increase in the joint electrical resistance. The joint electrical resistance measurement is shown to be used as a criterion to validate the quality of Cu-Al battery cell joints.

Laser spot welding of laser textured steel to aluminium

Laser welding of dissimilar metals (steel and aluminium) was investigated with the aim to increase the maximum tensile shear load of the Fe-Al joints. The increase was achieved by texturing the surface of steel prior to the laser spot welding process which was performed in a lap-joint configuration with the steel positioned on top of the aluminium and with a texture faced down to the aluminium surface. This configuration enabled an increase of the bonding area of the joints, because the molten aluminium filled in the gaps of the texture, without the need of increasing the process energy which typically leads to the growth of the intermetallic compounds. Different textures (containing hexagonally arranged craters, parallel lines, grid and spiral patterns) were tested with different laser welding parameters. The Fe-Al joints obtained with the textured steel were found to have up to 25% higher maximum tensile-shear load than the joints obtained with the untextured steel.

Dissimilar Materials Laser Welding between Stainless Steel 304 and Thermoplastics

Nowadays, dissimilar materials welding, especially between metal to plastics, has been become the hottest issue. The objective of the study is to investigate the effects of physical properties of plastics on the weldability and the quality of the dissimilar materials welding between SUS304 stainless steel and plastics. In experiment, the lap joint configuration with SUS304 put on the top was applied. The welding speed, focal position, and keeping period of weld after welding were varied. The results indicated that the decomposition temperature of plastics affected both weldability and quality of joint after welding. Moreover, crazing was a prominent property to be considered for long-term use of the dissimilar materials welding as the specimen could fracture by itself after a period of time without any application of the external load.

Corrosion Behavior of MIG Brazed and MIG Welded Joints of Automotive DP600-GI Steel Sheet

Galvanized dual-phase steel sheets are extensively used by the auto industry for their corrosion resistance property. Welding by the metal inert gas (MIG) process causes degradation of the steel in the vicinity of the joint due to excessive zinc evaporation. In order to minimize Zn loss, the MIG brazing process has been tried out in lap joint configuration over a heat input range of 136–204 J mm−1. The amount of zinc loss, intermetallic formation and corrosion properties in the joint area has been evaluated for both MIG brazing and MIG welding. Corrosion rate of 21 mm year−1 has been reduced to 2 mm year−1 by adopting MIGB in place MIGW. Impedance study has shown that the corrosion mechanism in base metal, MIG brazed and MIG welded joints is dominated by charge transfer, diffusion and mixed mode control processes, respectively.

The stresses in single lap joints with a functionally graded adhesive bondline: an efficient modelling approach

AbstractIn this work, an efficient analytical model for the stress analysis of single lap joints with a functionally graded adhesive bondline is proposed which considers peel as well as shear stresses in the adhesive. The model takes into account the nonlinear geometric characteristics of a single lap joint under tensile loading and allows for the analysis of various adhesive Young's modulus variations. The obtained stress distributions are compared to results of detailed Finite Element analyses and show a good agreement for several single lap joint configurations. In addition, different adhesive Young's modulus distributions and their effect on the peel and shear stresses are studied and discussed in detail. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

An efficient analysis model for functionally graded adhesive single lap joints

Employing a functionally graded adhesive the efficiency of adhesively bonded lap joints can be improved significantly. However, up to now, analysis approaches for planar functionally graded adhesive joints are still not addressed well. With this work, an efficient model for the stress analysis of functionally graded adhesive single lap joints which considers peel as well as shear stresses in the adhesive is proposed. Two differential equations of the displacements are derived for the case of an axially loaded adhesive single lap joint. The differential equations are solved using a power series approach. The model incorporates the nonlinear geometric characteristics of a single lap joint under tensile loading and allows for the analysis of various adhesive Young׳s modulus variations. The obtained stress distributions are compared to results of detailed Finite Element analyses and show a good agreement for several single lap joint configurations. In addition, different adhesive Young׳s modulus distributions and their impact on the peel and shear stresses as well as the influence of the adhesive thickness are studied and discussed in detail.

Analysis of composite bolted joints by a macro-modelling approach

Purpose – The purpose of this paper is the development and the assessment of detailed and macro-modelling methodology approaches, suitable for the analysis of composite material bolted joints. Design/methodology/approach – A benchmark single-lap, single-bolt composite joint configuration is investigated, in order to demonstrate the different joint analysis approaches which are applicable in advanced riveted/bolted parts of aeronautical structures. In particular, several joint macro-models, i.e. numerical and analytical ones, as well as a detailed three-dimensional FE solid joint representation, were developed and compared in terms of stiffness prediction, while they were validated using respective experimental results. In addition, the numerical macro-model is implemented in a full scale, multi-bolt fuselage panel in order to demonstrate its capability to efficiently predict the panel’s response under compressive loads. Findings – Good correlation was observed between the majority of the models’ predictions and the relative experimental data regarding the lap joint configuration, while the simplified numerical macro-model showed some discrepancies due to the contact instabilities, which, however, may be accepted taking into account the remarkable solution time reductions. In the same manner, the FE macro-model illustrates sufficient accuracy in the prediction of the panel’s response, while, simultaneously, it maintains a low CPU time. Originality/value – The present study is part of Nikolaos Perogamvros’ doctoral thesis, an original research work. There are very limited literature papers which include the development and the assessment of different efficient and detailed composite joint analysis approaches, regarding their accuracy and efficiency in the stiffness prediction of a composite bolted joint configuration, as well as on the prediction of a multi-bolt panel’s response.

Numerical modelling of gas metal arc joining of aluminium alloy and galvanised steels in lap joint configuration

Advanced pulsed current gas metal arc based processes are increasingly attempted for the joining of aluminium alloys and galvanised steel sheets. The bead profile and the thickness of the interfacial Fe–Al intermetallic (IMC) layer significantly influence the failure strength of these joints. Although several experimental studies have examined the nature and extent of the IMC phases and consequent joint strength, quantitative efforts to estimate bead profile and the IMC layer thickness as function of process conditions and resulting heat input are scarce. We present here for the first time a coupled theoretical and experimental study to estimate the bead profile and Fe–Al IMC layer thickness for joining of galvannealed steel and aluminium alloy sheets in a typical lap joint configuration. The computed values of bead profile and IMC layer thicknesses are validated with the corresponding experimental results.

Microstructure and mechanical properties of pulsed laser welded Al/steel dissimilar joint

Pulsed laser welding was used in joining pure aluminum to stainless steel in a lap joint configuration. It is found that the mechanical properties of the laser joints were closely correlated with the bead geometry, i.e., penetration depth. In order to study the correlation, two typical laser welds with different penetration depths were analyzed. In high penetration depth (354 μm) joint, Al-rich Fe–Al IMCs with microcracks were formed at the Al/fusion zone (FZ) interface. The joint strength was found to be (27.2±1.7) N/mm and three failure modes were observed near the Al/FZ interface. In low penetration depth (108 μm) joint, Fe-rich Fe–Al IMCs without any defect were formed at the Al/FZ interface. The joint strength was found to be (46.2±1.9) N/mm and one failure mode was observed across the FZ.