Arc Fillet Research Articles

Effect of welding current and speed on solidification cracking susceptibility in gas tungsten arc fillet welding of dissimilar aluminum alloys: Coupling a weld simulation and a cracking criterion

In order to study the effect of welding current and speed on the solidification cracking susceptibility of weld, gas tungsten arc welding of a fillet weld with a cold filler wire was simulated. Simulation was conducted for dissimilar welding of Al–Cu–Mg to Al–Mg–Si aluminum alloys with an Al–Mg filler metal at the welding current range of 145–175 A and welding speed of 18–24 cm/min. The outcomes of simulations, namely temperature gradient, velocity of isotherms, and weld chemical composition obtained for various welding currents and speeds, were used as inputs for a solidification cracking model. The results showed that the dimensions of the weld profile obtained from the simulation exhibited good agreement with experimental results. However, a discrepancy of 10–23% was observed between experimental and simulated results in relation to one dimension of the weld profile, i.e. the distance between the fillet weld corners. This discrepancy was addressed to identify the underlying reasons. According to the model proposed in this study for solidification cracking of aluminum alloys, both higher welding current and higher welding speed led to a higher susceptibility to solidification cracking. This result was justified by considering factors such as secondary arm spacing of dendrites, isotherm velocity, backfill time, and chemical composition and viscosity of the weld pool. Weldability tests were employed to validate the model's performance for predicting the solidification cracking susceptibility. Thus, the optimal welding parameters can be chosen in accordance with these results and production demands.

PRM Path Smoothening by Circular Arc Fillet Method for Mobile Robot Navigation

The problem of motion planning and navigation for mobile robots in complex environments has been a central issue in robotics. Navigating these environments requires sophisticated algorithms that handle obstacles and provide smooth, efficient paths. The Probabilistic Roadmap (PRM) method is a widespread technique in robotics for constructing paths for mobile robot navigation. In this study, we propose a novel path-smoothing method using arc fillets for path planning, building on PRM's foundation in the presence of obstacles. Our method operates in two primary stages to improve path efficiency and quality. The first stage generates the shortest path between the initial and goal states in an obstacle-rich environment using PRM, constructing a straight-line, collision-free route. The second stage smooths corners caused by nodes with arc fillets, ensuring smooth turns and minimizing abrupt changes in direction, resulting in more natural and efficient robot motion. We conducted simulations and tests using various PRM features to evaluate the proposed method. The results indicate that the built route offers a smooth turning motion and quicker, more compact movement while evading obstacles. This study contributes to mobile robot navigation by offering a practical approach to improving pathway quality in challenging environments.

Investigation of fatigue strength of root of lap fillet welds of thin sheet and improvement method

This study investigates the dominant factors of fatigue strength at the root of thin-sheet lap fillet arc welds, which are frequently used in automobile chassis components. A method to improve the root fatigue strength was investigated. The direction of fatigue crack propagation at the root coincided with the direction of maximum circumferential stress range. The circumferential stress was reduced by increasing the distance from the toe to the root (penetration width). Fatigue strength originating from the root was improved in welded joints where the penetration width was increased by adjusting the welding aim point and heat input.

CAF-RRT*: A 2D Path Planning Algorithm Based on Circular Arc Fillet Method

To improve the previous versions of Rapidly-exploring Random Trees (RRT) algorithms, a novel algorithm based on Circular Arc Fillet (CAF-RRT*) for path planning problems in two-dimension workspaces is proposed. Firstly, it is implemented by combining Quick-RRT* with the bidirectional RRT algorithm, which can obtain an initially planned path. Secondly, the cost of the initial planned path cost is reduced by a proposed path optimization strategy based on the triangle rule. Finally, based on the circular arc fillet method, a path smoothing strategy is proposed to process the middle nodes of the path, while further reducing its path cost. The experimental results on MATLAB simulation platform show that compared with other RRT algorithms, the proposed algorithm can reduce the path length by about 2%, ensure the smoothness and security of the path, while increasing the running speed of the algorithm by about 95%, and the experimental results of the robot based on Robot Operating System (ROS) platform also prove the advantages of the algorithm.

Prm Path Smoothening by Circular Arc Fillet Method for Mobile Robot Navigation

Prm Path Smoothening by Circular Arc Fillet Method for Mobile Robot Navigation

Rotating squares auxetic metamaterials with improved strain tolerance

Rotating squares auxetic metamaterials have the peculiar feature of a negative Poisson’s ratio. This work proposes and examines how an innovative variable arcs fillet solution, at the interconnection regions between the rotating units, improves the structural response of a titanium alloy-based rotating squares metamaterial. Through a 2D finite element (FE) model of the auxetic structure, we investigated and optimized two fillet configurations: first, a double circular arcs profile; second, a combined elliptical and circular arc fillet. According to the FE results, the optimal configuration of the combined elliptical and circular arc fillet allows an overall 3% elastic strain of the metamaterial, with a Poisson’s ratio (PR) equal to ca. −1. In order to assess the deformation behavior of the proposed metamaterial, we performed a tensile test on a prototype of the optimal solution, 3D printed in Onyx material. The experimental displacement field of the specimen, measured through digital image correlation, exhibited excellent agreement with the FE predictions, with a PR equal to ca. −1 up to a 3% overall strain.

Effect of Ultrasonic Impact Treatment on the Fatigue Performance of Cold Expanded AA6061-T6 Hole

Cold expansion is widely used to improve the fatigue life of fastener holes. However, fatigue crack often initiates at the entrance edge of the hole due to lower compressive or tensile residual stress as a result of cold expansion. In the current study, the entrance edge of the cold expanded hole has been ultrasonically impacted with a specially designed pin, and comparative fatigue tests are performed to evaluate the influence of the ultrasonic impact treatment on the fatigue performance of the cold expanded holes. The findings show that the ultrasonic impact treatment imparted a larger compressive residual stress and created a fillet arc at the entrance edge, which resulted in an obvious reduction in the fatigue crack propagation rate in the earlier stage of the fatigue crack growth and extended the fatigue life of the cold expanded holes further.

Shape optimization of the fillet under a bolt’s head

The stress concentration in the fillet under a bolt’s head is a critical issue for the fatigue life of this component. Remembering the variable notch radius solution observed in many biological structures to lower stress concentrations due to normal loads, this work proposes, examines and optimizes a double circular arc fillet, not re-entering the head. The work implements an ad hoc shape optimization procedure that combines a genetic algorithm (the particle swarm optimization) and a parametric, axisymmetric finite-element model of the bolt: by focusing on an M12 bolt, the analysis focuses on two issues: first, the optimization of the radius of each arc in the fillet; second, the optimization of the bolt’s head height and head’s diameter in combination with the fillet radiuses. By comparing the proposed solution with the fillet geometries for the bolt’s heads from the literature, it appears a noticeable stress reduction, about 14% lower than the standard circular fillet, combined with an easy manufacturing.

An analytical solution for temperature distribution in fillet arc welding based on an adaptive function

This paper presents an analytical solution that can be applied to predict temperature distribution in fillet welds using adaptive function approach developed by authors. The adaptive function method is a general approach to solve the partial differential equation of engineering problem based on developing a flexible function of dimensionless parameters, which circumvent the simplification assumptions required in numerical and analytical solutions proposed so far. This paper intends to develop the adaptive function by manipulating Rosenthal’s equation so that it can be adjusted according to the experimental data, which are the weld pool dimensions and temperature measured at some arbitrary points. To apply the adaptive function in a fillet weld, a new coordinate system is defined in which the x-axis is parallel to the legs of the fillet weld (width direction of the weld plate), the y-axis is parallel to the welding trajectory, and the z-axis is parallel to the penetration of the weld (depth direction of the weld plate). A polar coordinate system is defined for the corner part of the fillet weld. The adaptive function in this part is defined to preserve the consistency of the isotherms. The experimental data were provided by performing GTAW on a stainless steel 316L with various welding current. The results indicate that the novel approach is fast and simple and agrees well with results from experiments.

On the design of fillet welds made of ultra-high-strength steel

Current static design approaches for fillet arc welds made of high- or ultra-high-strength steel (UHSS) do not differ from the design of welds made of conventional steels. However, important issues such as potential softening in heat-affected zone (HAZ), strength at fusion lines, optimal reinforcement geometry, load capacity changes due to local bending moment, and the effect of post-weld treatments on the joint strength require careful consideration in order to ensure optimum performance from these steels. This paper reprises results of previous research works and recent findings and summarizes key aspects of weld design specific to UHSS welds.

A three dimensional finite element analysis of insulated rail joints deterioration

Abstract Railroad corridors include a large number of insulated joints that act as elements of signalling and broken rail detection systems. Unfortunately, insulated joints are provided with a gap to safeguard electrical insulation causing stiffness discontinuity and stress singularity in rail sections in the proximity of insulated joints. Obviously, these problems will have a profound impact on diminishing the service life of insulated joints, and thus on advancing the maintenance costs. This research presents numerical simulations to investigate deterioration (both mechanical and electrical) of insulated joints. A parametric study was performed to quantify the effects of vertical wheel load, friction coefficient, joint inclination, and railhead edge filleting as well as the effect of joint width. The finite element modelling assessed that the joint inclination and arc fillet can effectively prolong the lifetime of joints through mitigations of stresses, strains, and reductions of insulating width. In addition, the friction level is severely affecting the mechanical deterioration at the rail surface in the proximity of rail joints. However, at sub–surface the influence of friction coefficient is relatively small. Finally, the effect of joint width was assessed to be trivial for the studied cases.

Numerical analysis of weld pool for galvanized steel with lap joint in GTAW

Galvanized steel is widely used and its demand is growing in automotive industry due to high quality requirement for corrosion resistance. Although there are a lot of demands on using galvanized steel as automotive parts especially for outer body, it has a grave flaw in its welding process. The difficulty is low weldability due to various defects such as porosities and blow holes in weldment, which occurred during welding. A solution to prevent these defects is using hybrid welding process, with two more welding processes. One of the hybrid solutions is using Gas tungsten arc welding (GTAW) as leading position in order to remove the zinc (Zn) coating on the surface before the followed practical fusion welding process. In this research, a numerical analysis model which can predict the eliminated Zn coated layers and the area of Fusion zone (FZ). Developed numerical analysis model was validated through comparing experiment to simulation. Basically, arc heat flux, arc pressure, electromagnetic force and Marangoni flow were employed as the boundary conditions and body force terms. Governing equations such as the continuity, momentum, Volume of fluid (VOF) and energy equations were adopted as usual. In addition to previous model, concentrated arc heat flux and contact thermal conductance models are newly suggested and showed successful result. They are adopted to realize edge concentrated arc and interfacial thermal conductance in lap joint fillet arc welding. Developed numerical analysis model successfully simulated the weld pool and temperature profile therefore the predicted Zn removed area considerably coincided with experimental result.

Fatigue Life Prediction Method for Arc Welded Structure(Applying Nominal Structural Stress to Double Fillet Arc Welded Lap Joint)

Fatigue Life Prediction Method for Arc Welded Structure(Applying Nominal Structural Stress to Double Fillet Arc Welded Lap Joint)

Fatigue design of lattice materials via computational mechanics: Application to lattices with smooth transitions in cell geometry

A numerical method based on asymptotic homogenization theory is presented for the design of lattice materials against fatigue failure. The method is applied to study the effect of unit cell shape on the fatigue strength of hexagonal and square lattices. Cell shapes with regular and optimized geometry are examined. A unit cell is considered to possess a regular shape if the geometric primitives defining its inner boundaries are joined with an arc fillet, whose radius is 1% of the cell length. An optimized cell shape, on the other hand, is obtained by minimizing the curvature of its interior borders, which are conceived as continuous in curvature to smooth stress localization.For a given multi-axial cyclic loading, failure surfaces of metallic hexagonal and square lattices are provided along with their modified Goodman diagrams to assess the effect of mean and alternating stresses on the fatigue strength. In good agreement with the experimental data available in literature, the numerical results show that the shape of the unit cell has a major impact on the fatigue performance of the lattice material. For example under fully reversible tension, the fatigue strength of optimized square lattices of 10% relative density is shown to be 54% higher than that of their conventional counterparts with regular cell geometry.

A control system for uniform bead in fillet arc welding on tack welds

Positioning a workpiece accurately and preventing weld distortion, tack welding is often adopted before main welding in the construction of welded structures. However, this tack weld deteriorates the final weld bead profile, so that the grinding process is usually performed for a uniform weld bead profile. In this study, a control system for uniform weld bead is proposed for the fillet arc welding on tack welds. The system consists of GMA welding machine, torch manipulator, laser vision sensor for measuring the tack weld size and the database for optimal welding conditions. Experiments have been performed for constructing the database and for evaluating the control capability of the system. It has been shown that the system has the capability to smooth the bead at the high level of quality.

Neural network model of heat and fluid flow in gas metal arc fillet welding based on genetic algorithm and conjugate gradient optimisation

Although numerical calculations of heat transfer and fluid flow can provide detailed insights into welding processes and welded materials, these calculations are complex and unsuitable in situations where rapid calculations are needed. A recourse is to train and validate a neural network, using results from a well tested heat and fluid flow model to significantly expedite calculations and ensure that the computed results conform to the basic laws of conservation of mass, momentum and energy. Seven feedforward neural networks were developed for gas metal arc (GMA) fillet welding, one each for predicting penetration, leg length, throat, weld pool length, cooling time between 800°C and 500°C, maximum velocity and peak temperature in the weld pool. Each model considered 22 inputs that included all the welding variables, such as current, voltage, welding speed, wire radius, wire feed rate, arc efficiency, arc radius, power distribution, and material properties such as thermal conductivity, specific heat and temperature coefficient of surface tension. The weights in the neural network models were calculated using the conjugate gradient (CG) method and by a hybrid optimisation scheme involving the CG method and a genetic algorithm (GA). The neural network produced by the hybrid optimisation model produced better results than the networks based on the CG method with various sets of randomised initial weights. The CG method alone was unable to find the best optimal weights for achieving low errors. The hybrid optimisation scheme helped in finding optimal weights through a global search, as evidenced by good agreement between all the outputs from the neural networks and the corresponding results from the heat and fluid flow model.

Improving reliability of modelling heat and fluid flow in complex gas metal arc fillet welds—part II: application to welding of steel

In order to improve the reliability of numerical calculations of heat and fluid flow in fusion welding, a model was proposed in part I of this paper to determine the uncertain welding input parameters from a limited volume of experimental data. The application of the model for the complex gas metal arc (GMA) fillet welding of mild steel is reported in this part of the paper. The values of the arc efficiency, effective thermal conductivity and effective viscosity were evaluated as a function of the heat input. A vorticity-based mixing-length hypothesis was also used to independently calculate the values of the effective viscosity and effective thermal conductivity. Good agreement was obtained between the values of these parameters calculated using the two techniques, indicating the effectiveness of the proposed model in improving the reliability of heat and fluid flow calculations in fusion welding. The shape and size of the fusion zone, finger penetration characteristic of the GMA welds and solidified free surface profile computed using the optimized values of the uncertain welding parameters were in fair agreement with the corresponding experimental results for various welding conditions. In particular, the computed values of the leg length, the penetration depth and the actual throat agreed well with those measured experimentally for various heat inputs.

Improving reliability of modelling heat and fluid flow in complex gas metal arc fillet welds—part I: an engineering physics model

Although numerical heat transfer and fluid flow models have provided significant insight about fusion welding processes and welded materials in recent years, several model input parameters cannot be easily prescribed from fundamental principles. As a result, the model predictions do not always agree with the experimental results. In order to address this problem, the approach adopted here is to develop and test a model that embodies a heat transfer and fluid flow sub-model and an algorithm for optimizing and learning the values of uncertain process variables from a limited volume of experimental data. The heat transfer and fluid flow sub-model numerically calculates three-dimensional temperature and velocity fields, the weld geometry and the shape of the solidified weld reinforcement surface during gas metal arc (GMA) welding of fillet joints. Apart from the transport of heat from the welding arc, additional heat from the metal droplets is also considered in the model. Alternative algorithms for optimization of uncertain welding variables are examined. The overall model is capable of estimating uncertain parameters such as the arc efficiency, effective thermal conductivity and effective viscosity from a limited number of data on weld geometry. Part I of this paper is focused on the details of the numerical model, optimization technique used and an examination of the important features of the model. In an accompanying article (part II), the application of the model to GMA fillet welding of mild steel is described.

Heat and fluid flow in complex joints during gas metal arc welding—Part II: Application to fillet welding of mild steel

A numerical model described in part I [W. Zhang, C.-H. Kim, and T. DebRoy, J. Appl. Phys. 95, 5210 (2004)] was used to investigate the heat transfer and free surface flow during gas metal arc fillet welding of mild steel. Dimensional analysis was used to understand the importance of heat transfer by conduction and convection and the role of various driving forces on convection in the liquid weld pool. The calculated shape and size, finger penetration characteristic and solidified surface profile of the fillet welds were in fair agreement with the experimental results for various welding conditions. The calculated cooling rates were also in good agreement with independent experimental data. The effect of welding parameters on important weld bead characteristics was quantitatively studied using the numerical model. The results reported here indicate a significant promise for understanding and control of gas metal arc fillet welding processes based on fundamental principles of transport phenomena.

Modeling of temperature field and solidified surface profile during gas–metal arc fillet welding

The temperature profiles, weld pool shape and size, and the nature of the solidified weld pool reinforcement surface during gas–metal arc (GMA) welding of fillet joints were studied using a three-dimensional numerical heat transfer model. The model solves the energy conservation equation using a boundary fitted coordinate system. The weld pool surface profile was calculated by minimizing the total surface energy. Apart from the direct transport of heat from the welding arc, additional heat from the metal droplets was modeled considering a volumetric heat source. The calculated shape and size of the fusion zone, finger penetration characteristic of the GMA welds, and the solidified free surface profile were in fair agreement with the experimental results for various welding conditions. In particular, the computed values of important geometric parameters of fillet welds, i.e., the leg length, the penetration depth, and the actual throat, agreed well with those measured experimentally for various heat inputs. The weld thermal cycles and the cooling rates were also in good agreement with independent experimental data.