Lap Joint Configuration Research Articles

Friction Melt Bonding: An innovative process for aluminium-steel lap joints

A new process based on Friction Stir Welding has been developed to weld dissimilar metals, particularly steel and aluminum, in a lap-joint configuration. In this Friction Melt Bonding process, frictional heat generated by the rotating and translating tool brings about local and transient melting (Figure 1). Welding then occurs owing to controlled reactivity and solidification at the interface between the two plates. With an adequate choice of the welding parameters, low alloy steel and aluminium alloys have been successfully welded. Characterisation of the microstructure was systematically performed to highlight the influence of the process parameters, particularly the temperature cycle, on the steel-Al interface. The thickness of the intermetallic layer varies from a couple of micrometers to tens of micrometers depending on the advancing speed of the tool (Fig. 2). The lap shear properties of the joints were also investigated and analysed based on the morphology of the intermetallic layer.

镀锌钢板零间隙光纤激光搭接焊接的研究

镀锌钢板零间隙光纤激光搭接焊接的研究

镀锌钢板零间隙光纤激光搭接焊接的研究

镀锌钢板零间隙光纤激光搭接焊接的研究

Parameter Optimization in Al6061/HIF GA Steel Friction Stir Lap Welds

Friction Stir welding has been attempted to study the feasibility of FSW between aluminium sheet (AA 6061) of 2 mm thick and Zinc coated steel (HIF-GA) sheet of 1 mm thick in lap joint configuration. The interfacial area of dissimilar welds has been analyzed by XRD, EPMA,TEM with EDS and nano indentation technique to identify the IMC distribution pattern depending on the combined effect of rotational speed and travel speed as well as the effect of energy and thermal cycle. The average joint strength is significantly influenced by the thermal cycle, respective torque and combined effect of rotational speed and travel speed as well as energy input. Improved joint strength between Al and coated steel could be obtained within a combination of rotational speed and travel speed as well as energy input. Force and torque response during FSW have been analyzed in terms of parameter optimization and joint performance.

Two-pass laser welding of galvanized high-strength dual-phase steel for a zero-gap lap joint configuration

A welding procedure based on using two-pass laser scans is introduced for joining overlapped galvanized high-strength steel sheets. The first pass is based on a defocused laser spot that scans across the top of the overlapped sheets and heats the zinc coating at the faying surface to be melted and vaporized, while the second pass is executed with a focused laser spot in order to perform the welding. Completely defect-free welds were obtained by using this two-pass laser welding procedure. An on-line machine vision system and a spectrometer were applied to analyze the stability of the laser welding process. An energy-dispersive X-ray spectroscopy (EDS) was carried out to determine the atomic percent of zinc and iron of the DP980 coupons. Mechanical testing was conducted to evaluate the mechanical properties of the welds. The experimental results show that the weld joints obtained by the two-pass laser welding approach have a higher failure value than those obtained by a single pass laser welding of galvanized steel with mechanically removed zinc at the faying surface under the same welding speed and laser power.

On laser welding of thin steel sheets

This paper presents a process–structure–property relationship study of laser welds as a continuous consolidation method for joining thin monophased steel foils, thereby providing a more effective, less costly method to construct automotive catalytic converters. A body centred cubic (bcc) iron–chromium–aluminium alloy doped with Mischmetal was utilised in this study. Both pulsed and continuous wave modes were used to establish the limit welding diagrams for lap joint configuration. Actual laser welding parameters were selected using several testing conditions. The laser welds behaved substantially different from the base material under creep and high temperature oxidation. The difference was mainly attributed to the changes in grain morphology, precipitation of aluminium nitrides and carbides, and relocalisation of the reactive elements during liquid metal flow upon keyhole formation, solidification and cooling.

Optimization of laser welding thin-gage galvanized steel via response surface methodology

The increasing demand of light weight and durability makes thin-gage galvanized steels (<0.6mm) attractive for future automotive applications. Laser welding, well known for its deep penetration, high speed and small heat affected zone, provides a potential solution for welding thin-gage galvanized steels in automotive industry. In this study, the effect of the laser welding parameters (i.e. laser power, welding speed, gap and focal position) on the weld bead geometry (i.e. weld depth, weld width and surface concave) of 0.4mm-thick galvanized SAE1004 steel in a lap joint configuration has been investigated by experiments. The process windows of the concerned process parameters were therefore determined. Then, response surface methodology (RSM) was used to develop models to predict the relationship between the processing parameters and the laser weld bead profile and identify the correct and optimal combination of the laser welding input variables to obtain superior weld joint. Under the optimal welding parameters, defect-free weld were produced, and the average aspect ratio increased about 30%, from 0.62 to 0.83.

Effect of Pin Length and Rotation Rate on the Tensile Strength of a Friction Stir Spot-Welded Al Alloy: A Contribution to Automated Production

Friction stir spot welding (FSSW) is performed on thin plates of an aluminum alloy in a lap joint configuration with tools of different pin lengths and various rotation rates. The effects these process parameters have on the joint properties of the welds are investigated. The tensile strength of the welds decreased when the rotation rate was increased. The tensile strength of welds made with a pinless tool is on average 90% the strength of the full penetration spot welds. Intermediate pin lengths were tested between these two extremes. It was found that the tensile strength decreases as the pin length increases from pinless to 10% bottom plate penetration. Three distinct failure modes were identified when the welds were placed under tensile loading: shear mode, mixed mode, and nugget-pullout mode. The dependence of static joint strength on these process parameters is discussed.

Real-time monitoring of laser welding of galvanized high strength steel in lap joint configuration

Two different cases regarding the zinc coating at the lap joint faying surface are selected for studying the influence of zinc vapor on the keyhole dynamics of the weld pool and the final welding quality. One case has the zinc coating fully removed at the faying surface; while the other case retains the zinc coating on the faying surface. It is found that removal of the zinc coating at the faying surface produces a significantly better weld quality as exemplified by a lack of spatters whereas intense spatters are present when the zinc coating is present at the faying surface. Spectroscopy is used to detect the optical spectra emitted from a laser generated plasma plume during the laser welding of galvanized high strength DP980 steel in a lap-joint configuration. A correlation between the electron temperature and defects within the weld bead is identified by using the Boltzmann plot method. The laser weld pool keyhole dynamic behavior affected by a high-pressure zinc vapor generated at the faying surface of galvanized steel lap-joint is monitored in real-time by a high speed charge-coupled device (CCD) camera assisted with a green laser as an illumination source.

Laser Beam Weldability of High-Manganese Austenitic and Duplex Stainless Steel Sheets

Manganese alloyed stainless steels represent a cost-effective alternative to conventional CrNi- stainless steels due to strong fluctuations of the market prices for nickel seen during the last years. In CrMnNi steels, nickel is partially replaced by lower-cost manganese and small amounts of nitrogen for stabilization of the austenitic phase. This also brings benefits regarding the mechanical properties, as it results in an increased material strength. Laser beam welding of such materials was investigated for direct comparison with standard CrNi steels. Main emphasis was laid on finding adequate process parameters to achieve a stable welding process and obtain a good weld quality. Two different laser sources, a 4.4 kW Nd:YAG and a 5 kW CO2 laser, were used to weld 1.5 mm stainless steel sheets in continuous wave mode. A high-Mn austenitic (1.4376) and a lean duplex (1.4162) steel, as well as the standard austenitic (1.4301) and duplex (1.4362) grades were selected as test materials. Both butt and lap joint configurations were studied. Experiments were carried out systematically, varying the welding speed, laser power and focal point position in order to determine adequate process windows. The influence of the shielding gas type and flow rate on the process stability and the weld quality were investigated. The effects of weld edge preparation on the weld appearance and quality levels attained were also examined. The obtained welded joints were subjected to radiographic tests for detection of internal imperfections. Also a metallurgical characterization of the samples regarding the resulting phase composition or balance and hardness depending on the welding process parameters was conducted. Furthermore, tensile and potentiodynamic tests were performed to evaluate the mechanical and corrosion properties, respectively. The results provide an insight into the advantages and limitations of the laser beam welding process for joining high-manganese alloyed stainless steels. Conditions for the production of defect-free and corrosion-resistant welds having good mechanical properties could be determined.

Finite-element thermal analysis of laser welding of galvanized high-strength steel in a zero-gap lap joint configuration and its experimental verification

A three-dimensional (3D) finite element (FE) model is applied to predict the temperature evolution in the laser welding of galvanized high-strength steels in a zero-gap lap joint configuration. A rotary Gaussian volumetric heat source model is introduced to simulate the laser energy input. The temperature data measured by thermocouples are used to verify the boundary conditions of the thermal model. The experimentally verified finite element model is then used to predict the weld pool size and the area of vaporized zinc at the faying surface. A feature parameter that represent the ratio of the zinc coated vaporized area to the area of molten pool at the faying surface has been established. The acquired values of the feature parameters could be used to numerically estimate the weld quality with respect to the different laser welding parameters. A series of tensile shear tests for the lap-jointed DP980 steel coupons has been performed correspondingly. The experimental results show that failure load of lap joint of galvanized DP980 steel increases with a lower welding speed or higher laser power. It is found that there is a potential relationship between the area of vaporized zinc at the faying surface of lap joint of galvanized steel and the final weld quality, and a decrease in the welding speed or increase in laser power mitigates to a certain extent the defects caused by zinc vapor in the weld bead.

A novel traction–separation law for the prediction of the mixed mode response of ductile adhesive joints

A new traction–separation law that represents the constitutive relation of a ductile adhesive material in Mode I and Mode II is developed and introduced in interface elements for the finite element analysis of adhesive joints, within the framework of Cohesive Zone Modeling (CZM) techniques. The proposed law is based on the embedded process zone approach and is formulated to address the mixed-mode loading and fracture of adhesively bonded joints. This law is first used for the description of the pure Mode I (opening) and pure Mode II (sliding) loading and fracture and then it is integrated into a developed mixed-mode model in order to account for the dependence of the separate pure mode laws. The traction increasing part of the law is described by an exponential function, whereas the softening part is described by a linear decrease. Prediction of damage initiation is established through the nominal quadratic stress criterion, whereas the damage propagation is established through the linear energetic criterion. Experimental results from steel-to-steel single lap and Double Strap Joint configurations have been utilized for the validation of the proposed law and mixed-mode model. Comparisons are also provided from finite element analyses with the already known trapezoidal law and with the PRP (Park–Paulino–Roesler) model. The proposed law adequately captures the elastoplastic behaviour of the tested adhesive joints, in terms of their global response. Additionally, the strength of the tested joints is predicted with great accuracy.

Validation of an Hcr-based fracture initiation criterion for adhesively bonded joints

The singular stress fields that develop around wedges found in adhesively bonded scarf and double lap joint configurations are fully determined by employing Williams’ eigenfunction expansion method in combination with a path independent contour integral method. The intensities of the near-tip stress fields (H) are then used as fracture initiation parameters in order to predict the strengths of these joints. The predicted strengths are compared to experimental results found in literature and the conditions for the validity of the proposed Hcr-based fracture initiation criterion are examined.

Using standard adhesion tests to characterize performance of material system options for insulated rail joints

Insulated joints (IJs) are often required every few kilometres along railway tracks for signal blocks and rail break detection; practical experience has shown that their life is often a fraction of the life of other track elements on some rail lines subjected to high tonnage freight. This article reports findings from a project conducted to study different bond systems consisting of various combinations of adhesives, fibrous insulators, and rail surface treatments that were of potential interest for increasing the service life of IJs for rail applications. The study was performed in parallel with a finite-element analysis and did not focus on testing real IJs but rather on common adhesion test specimens such as the single lap joint and double cantilever beam configurations. The aim of using these specimens was to simulate potential load and environmental conditions on standard test specimens that were less expensive and easier to construct, test, and analyse. The main goal of the project was to compare a number of combinations of potential IJ components through an extensive test programme. The results highlighted several possible combinations that may warrant further study as actual IJ prototypes. In particular, several material combinations involving materials not currently used by IJ vendors had higher overall performances when compared to currently used combinations, although the extension of improved test specimen performance to actual IJ configurations and service conditions may not follow.

Optimal process parameters for thermoplastic polyetheretherketone joints fabricated using transmission laser welding and Lumogen® IR absorptive pigment

This study investigates the effects of the process parameters (laser power and irradiation time) on the bond quality of transmission laser welded polyetheretherketone. Commercially available Lumogen® IR pigment was added to the bulk of the polymer for laser absorption. Quasisimultaneous beam configuration was used to weld injection molded samples of 0.7 mm thickness in a lap joint configuration. Combinations of laser power (40–80 W) and irradiation times (10–50 s) were investigated. The laser power was found to have the most effect on weld strength, while irradiation time did not have a marked effect on weld strength. At optimal process conditions, the weld strength ranged from 20 to 45 MPa. High variability in weld strength was seen within groups with identical process parameters and was attributed to the variability in material morphology as a result of injection molding. X-ray tomography was utilized to view intact weld interfaces. A significant finding was the presence of voids (up to 0.5 mm diameter) at the weld interface.

Magnetic Properties Improvement of Amorphous Cores Using Newly Developed Step-Lap Joints

This paper focuses on the study of lap joints for amorphous cores, where the magnetic loss and noise related to lap-joint configurations are considered. Both the conventional step-lap (CSL) and a newly developed step-lap (NSL) are addressed, in which special emphasis is put on the underlying physical mechanisms in the step-lap number and overlap. The NSL core exhibits unique distribution of step-lap numbers and overlap alignment that will reduce the core sensitivity subject to the variations of magnetostriction. Finally, to investigate the performance of magnetic properties, a three-phase wound amorphous-cored transformer with capacity 1850 kVA is constructed. Experimental results illustrate that the proposed NSL core can provide better performance of lower core loss, exciting power, and noise than the conventional counterparts.

Load Ratio Effect on the Fatigue Behaviour of Adhesively Bonded Joints: An Enhanced Damage Model

Structural adhesives are used widely in aerospace and automotive applications. However, fatigue damage in these adhesives is an important factor to be considered in the design of adhesively bonded structural members that are subjected to cyclic loading conditions during their service life. Fatigue life of adhesively bonded joints depends mainly on the fatigue load and the load ratio. A fatigue damage model is presented in this paper to include the effect of fatigue mean stresses on the failure behaviour of adhesively bonded joints. The fatigue damage model is developed using an effective strain-based approach. The model is implemented on a tapered single lap joint configuration and is validated by experimental test results. The adhesive layer in the tapered single lap joint is modelled by using a cohesive zone with a bi-linear traction-separation response. The adverse effect of increasing fatigue mean stresses on the failure behaviour of adhesively bonded joints is successfully predicted.

Study of friction stir joining of thin aluminium sheets in lap joint configuration

Thinning in friction stir lap joints and its relation with the process variables was investigated. Friction stir welds were made on 1 mm thick AA6111 aluminium alloy sheets in order to study the effects of rotation rate, traverse speed, plunge depth, tilt angle and pin height on faying surface defects. Sheet thinning on the advancing and retreating sides was quantified and the lap shear strength of the joints was evaluated. A decrease in the pitch of the runs at constant rotation rate increased the sheet thinning and reduced the joint strength in a linear manner. Process pitch and pin height were found to be the most critical factors in determining the faying surface lift up. A pin of the same height as the sheet thickness resulted in maximum lap shear strength. Tool tilt did not show a significant effect on the sheet thinning.

Laser welding of galvanized DP980 steel assisted by the GTAW preheating in a gap-free lap joint configuration

With the increasing need for reducing the vehicle’s weight, improving fuel efficiency and safety, as well as the corrosion resistance, more and more galvanized high-strength steels have been used in the automotive industry. However, the successful laser welding of galvanized steels in gap-free lap joint configuration is still a big challenge. The high-pressurized zinc vapor is readily developed at the interface of the two metal sheets due to the lower boiling point of zinc (around 906 °C) than the melting point of steel (over 1300 °C). The failure of mitigating the high-pressurized zinc vapor at the interface leads to the formation of different weld defects such as the spatters and blowholes, which not only damage the weld surface quality but also deteriorate the mechanical properties of welds. Until now, there is no open literature on successfully obtained the defect-free welds of galvanized high-strength steels by using only laser welding. In this paper, a new welding procedure based on using GTAW as an auxiliary preheating source with a fiber laser as a main heat source is introduced. The controlled heat management during the preheating by GTAW will transform the zinc coating at the top surface of galvanized DP 980 steel metal sheet into the zinc oxides, which will dramatically improve the coupling of the laser power to the welded material. By the formation of the zinc oxides generated by the preheating of GTAW, the keyhole is readily formed, which provides the weld with a full penetration and allows the high-pressurized zinc vapor at the interface to be vented out through the keyhole. The completely defect-free laser welds have been obtained by using this welding method. Furthermore, a charge-coupled device video camera with the frame rate of 30 frames per second is used to on-line monitor the molten pool. By the analysis of the molten pool images, it is revealed that when the welding process is stable, the keyhole is kept open. However, the keyhole is readily collapsed when the welding process is unstable. In addition, the microhardness and tensile shear tests are carried out to evaluate the mechanical properties of laser welded joints. It is demonstrated that the welds of high strength are obtained in the laser welds.

Non-Linear Analysis of a Ductile Adhesive in the Single Lap Joint Under Tensile Loading

In this article, potential use of ductile adhesives in structural applications is taken into consideration and their possible advantages over traditional structural adhesives are discussed. For this purpose, the performance of a very ductile adhesive with high strain to failure was investigated in the single lap joint (SLJ) configuration in tensile loading, and the joint was modeled using the finite element method (FEM) to analyze its non-linear solutions. In analyzing the joint, consideration is given to the stress distributions in the adhesive layer and the load to failure was predicted. The predicted values were well in agreement with the previous experimental results, and the stress distributions of the ductile adhesive differed in many respects from traditional structural adhesives. In order to see the differences, a structural modern epoxy has also been analyzed.