Weld Pitch Research Articles

Optimization of weld pitch on overlay welding using mathematical method

It is important to overlap the even bead continuously to automate the overlay welding process. To obtain the even surface bead on overlay welded product, optimization of pitch distance between the each pass is one of the methods. Therefore, this study determines the optimal second pass pitch distance with respect to welding parameter such as torch position and welding speed. Variety of welding experiments was carried out with different welding parameters using Central Composite Rotatable Design (CCRD) method. Based on the experimental results, empirical models were developed after analyzing correlation between welding parameters and bead height, width and decentration of overlay welding. Finally, optimized empirical models were developed for predicting bead height and width by analyzing the main effect of each factor which affects bead geometry and their influence on interaction. In addition, a mathematical model was developed which determines the bead profile for visualizing the bead shapes using the Matlab curve fitting tool. These two models were combined for one of the overlay bead shape model. Furthermore, the mathematical model is then used to determine the second pass pitch distance, by allowing the same area above and below the point of interaction between two overlay weld pass.

Optimization of Friction Stir Welding Tool Advance Speed via Monte-Carlo Simulation of the Friction Stir Welding Process.

Recognition of the friction stir welding process is growing in the aeronautical and aero-space industries. To make the process more available to the structural fabrication industry (buildings and bridges), being able to model the process to determine the highest speed of advance possible that will not cause unwanted welding defects is desirable. A numerical solution to the transient two-dimensional heat diffusion equation for the friction stir welding process is presented. A non-linear heat generation term based on an arbitrary piecewise linear model of friction as a function of temperature is used. The solution is used to solve for the temperature distribution in the Al 6061-T6 work pieces. The finite difference solution of the non-linear problem is used to perform a Monte-Carlo simulation (MCS). A polynomial response surface (maximum welding temperature as a function of advancing and rotational speed) is constructed from the MCS results. The response surface is used to determine the optimum tool speed of advance and rotational speed. The exterior penalty method is used to find the highest speed of advance and the associated rotational speed of the tool for the FSW process considered. We show that good agreement with experimental optimization work is possible with this simplified model. Using our approach an optimal weld pitch of 0.52 mm/rev is obtained for 3.18 mm thick AA6061-T6 plate. Our method provides an estimate of the optimal welding parameters in less than 30 min of calculation time.

An Experimental Approach to Study the Effect of Welding Parameters on Similar Friction Stir Welded Joints of AZ31B-O Mg Alloy

In this investigation an attempt has been made to study the effect of friction stir welding parameters on mechanical and metallurgical properties of AZ31B-O Mg alloy joints. The selected material was welded using combination of different parameters i.e. tool rotational speed, welding speed and tool shoulder diameter. The effect of weld pitch i.e. ratio of welding speed to tool rotational speed (0.0020mm/rev to 0.05mm/rev) was examined on the mechanical and micro structural properties of friction stir welded joints of AZ31B-O Mg alloy. The linear relationship between tensile strength and weld pitch was observed. The maximum value of tensile strength i.e. 187.8N/mm2 was obtained at weld pitch of 0.05mm/rev using 20mm tool shoulder diameter. Most of the tensile test specimens fractured in the area between Stir Zone (SZ) and Thermo Mechanical Affected Zone (TMAZ) towards the advancing side. The fine and equiaxed grains were observed due to dynamic recrystallization at higher value of weld pitch.

Spot Weld Layout Optimization of Tube Crash Performance With Manufacturing Constraints

Spot weld layout is critical to structural performance of vehicle and its design is also subject to manufacturing constraints. In this study, using thin-walled tube crash as an example, we establish the relation between structural performance and weld layout design with manufacturing constraints from resistance spot welding. First, a straight tube crash performance is evaluated as a function of flange width, weld distance to flange corner, and weld pitch, without consideration of manufacturing constraints. All these parameters exhibit certain influence on the deformation mode and the energy absorption capacity. Then, an S-shaped tube is studied in the design optimization of weld layout by adding manufacturing constraints. The proposed approach can determine optimized results by simultaneously considering crash performance and manufacturing constraints. It is also concluded that weld layout has more significant influence on crash performance in straight tubes than in S-shaped tubes.

Gap tolerance allowance and robotic operational window for friction stir butt welding of AA6061

In this work, it was determined that with increasing weld pitch, the occurrence of a “lazy S” defect in the weld nugget of friction stir welded (FSWed) AA6061 became increasingly pronounced, though its impact on the bend performance of the weld was negligible. For a fixed weld pitch of 0.48, the effect of gap, i.e. the spacing between two sheets at the butt joint interface, on the joint quality of AA6061 was evaluated in terms of the welding defects, microstructure, hardness and bend performance. Fully penetrated welds without metallurgical defects such as wormholes were obtained up to a joint gap of 0.5mm. Though the overall microhardness and bend performance of the welds remained unaffected until a joint gap of 0.8mm, the decrease in the forge force during FSW beyond a joint gap value of 0.5mm may represent a more critical limit in regards to the industrial application of the process; this is especially important when applying force control during processing to ensure a constant shoulder penetration in the material for addressing practical considerations, such as thickness variations in the assembly, clamping distortions and tool wear. Based on these results and using force amplitudes recorded during the welding experiments, a robotic scenario was synthesized with an appropriate operational window for continuous-path friction stir butt welding (FSBW) of 3.18-mm-thick sheets clamped to a 1m×1m horizontal welding table. An appropriate industrial robot model was selected and the associated geometric workcell layout was developed for this application. This scenario was implemented in a physical prototype and used to successfully produce 1-m-long FSWed assemblies that exhibited good tensile mechanical performance.

Computational Analysis of Material Flow During Friction Stir Welding of AA5059 Aluminum Alloys

Workpiece material flow and stirring/mixing during the friction stir welding (FSW) process are investigated computationally. Within the numerical model of the FSW process, the FSW tool is treated as a Lagrangian component while the workpiece material is treated as an Eulerian component. The employed coupled Eulerian/Lagrangian computational analysis of the welding process was of a two-way thermo-mechanical character (i.e., frictional-sliding/plastic-work dissipation is taken to act as a heat source in the thermal-energy balance equation) while temperature is allowed to affect mechanical aspects of the model through temperature-dependent material properties. The workpiece material (AA5059, solid-solution strengthened and strain-hardened aluminum alloy) is represented using a modified version of the classical Johnson-Cook model (within which the strain-hardening term is augmented to take into account for the effect of dynamic recrystallization) while the FSW tool material (AISI H13 tool steel) is modeled as an isotropic linear-elastic material. Within the analysis, the effects of some of the FSW key process parameters are investigated (e.g., weld pitch, tool tilt-angle, and the tool pin-size). The results pertaining to the material flow during FSW are compared with their experimental counterparts. It is found that, for the most part, experimentally observed material-flow characteristics are reproduced within the current FSW-process model.

Effect of tool geometry on mechanical and microstructural behaviours in dissimilar friction stir welding of AA 5086–AA 6061

The aim of this investigation is to study the effect of geometric tool parameters on mechanical and microstructural behaviours during dissimilar friction stir welding of 5 mm thick plates of AA 5086-O and AA 6061-T6. Three tool geometries were used, including a tool with a concave shoulder and a conical probe with three grooves, flat shoulder and threadless cylindrical probe, and a tool with a flat shoulder and a threaded cylindrical probe. It was found that the tool with a concave shoulder and a conical probe with three grooves produces higher heat input and temperatures that provides more homogeneous stir zones than the other tools. In addition, the grain sizes of the stir zone in the AA 6061 side of all the welds are finer than those produced in the AA 5086 side, and decreasing the weld pitch, i.e. a ratio of welding to rotational speed, results in coarser grain structures in the stir zone.

KS5J32 Al합금 마찰교반접합부의 인장성질에 미치는 접합조건의 영향

The effect of welding condition on tensile properties of KS5J32 Al Alloy was investigated under various welding conditions. The 1.6 mm thick KS5J32 alloy sheets were joined by friction stir welding (FSW) technique with butt joint. The tool rotation speeds were 1000, 1250 and 1500 rpm, and the welding speeds were varied within the range from 100 to 600 mm/min. Voids mainly occurred at the advancing side of the tool probe, when the tool rotation speed was low, due to insufficient materials flow. When the weld pitch exceeded 0.4 mm/rev, voids were observed under all welding conditions and the area of voids increased with increasing weld pitch. For void-free specimens, fracture always occurred at base materials. However voids affected the location of fractures, base metal or welded zone, when the voids existed within the welds.

Investigation on Joining Method Replacement for Vehicle Body’s Assembly

Various joining methods (i.e., spot welding, arc welding, laser beam welding) have been used for vehicle body assembly. However it is unclear for the equivalent conversion of various joints which has the equivalent joint strength for the vehicle body, such as weld-bonded joint, SPR joint, which have been considered likely to replace RSW in the area of high strength steel’s joining. In order for the flexible design in the auto line of vehicles body’s joining, the equivalent (strength) weld pitch design method for various joints, including the joining of similar and dissimilar materials, is presented in this work. And some primary simulating results are presented and discussed. It is shown that the conversion method for various joints can be established based on the joint’s shear failure criteria. And the conversion results can be influenced by the sheet gage obviously. The failure criteria of various joint still need further investigation based on the simulating and experimental results.

Tensile properties of a friction stir welded magnesium alloy: Effect of pin tool thread orientation and weld pitch

Microstructures, tensile properties and strain hardening behavior of a friction stir welded (FSWed) AZ31B-H24 magnesium alloy were studied at varying welding speeds, rotational rates and pin tool thread orientations. After friction stir welding (FSW) both yield strength (YS) and ultimate tensile strength (UTS) were observed to be lower but strain hardening exponent became much higher due to the presence of recrystallized grains in the stirred zone (SZ) and thermomechanically affected zone (TMAZ). The left-hand thread pin tool rotating clockwise generated good FSWed joints and mechanical properties due to the downward material flow close to the pin surface, while the right-hand thread pin tool turning clockwise caused an upward material flow and resulted in inferior joints. The YS and UTS increased and strain hardening exponent decreased with increasing welding speed. The YS as a function of grain sizes obeyed the Hall-Petch relationship well, and it also increased with decreasing rotational rate. Both YS and UTS were observed to increase linearly with increasing weld pitch (a ratio of welding speed to rotational rate). A significantly higher YS of ∼170 MPa was achieved at a high weld pitch of 1.2 mm/rev, in comparison with that (∼110 MPa) using a weld pitch ranging from 0.0039 to 0.24 mm/rev. All the FSWed AZ31B-H24 joints failed in-between the SZ and TMAZ. Dimple-like ductile fracture characteristics appeared in the base metal, while some cleavage-like flat facets together with dimples and river marking were observed in the FSWed samples.

Observations on the design and modelling of some joined thin-walled structural sections

In a recent experimental and analytical study for the axial progressive collapse of some thin-walled structural sections, no consistent reliability could be obtained for the prediction of crush parameters for different geometries and materials with an analytical approach that relied on a yield hinge model. Square and spot-welded top-hat sections were compared. This situation occurs because the assumed equivalence between the top-hat and square sections according to the yield hinge model of the folding structures, does not appear valid for the actual structures. Some of the dependences between the actual structure and the model are discussed, particularly for the top-hat geometry. Observations on a beneficial positioning of the spot-welds in a top-hat section are reported, and common recommendations for an optimum weld pitch are critically examined. Modes 1 and 2 deformations are identified for the well-known quasi-inextensional, regular (asymmetric) progressive folding of thin-walled sections having a rectangular (core) cross-section, such as square and top-hat sections. The deformation modes are characterized by different proportions of inward and outward movements of the material during folding. Possible implications for the stability of collapse and for the analytical formulae are indicated.

Experimental defect analysis and force prediction simulation of high weld pitch friction stir welding

Experimental data for AA 6061-T6 friction stir welded at rotational and travel speeds ranging from 1000 to 5000 rev min−1 and from 290 to 1600 mm min−1 (11–63 ipm) are presented. The present paper examines the forces and torques during friction stir welding (FSW) with respect to mechanistic defect development owing to process parameter variation. Two types of defects are observed: wormholes and weld deformation in the form of significant excess flash material. A 3D numerical model, implemented using the computational fluids dynamics package Fluent, is used to simulate and investigate the parametric relationship of the forces and torques during FSW. In order to establish a mechanistic quantification of the FSW process, two mechanical models, the Couette and the viscoplastic fluid flow models, were simulated and compared with experimental data for AA 6061-T6.

Dependence of the breaking force of non-woven fabrics on weld pitch in ultrasound welding

Dependence of the breaking force of non-woven fabrics on weld pitch in ultrasound welding

Material flow patterns and cavity model in friction-stir welding of aluminum alloys

Friction-stir welding (FSW) of 3-mm-thick plates of 6061 Al and LF6 Al was conducted and the materials’ flow patterns in the weld nugget along three perpendicular planes were analyzed. The onion structure viewed on any cross section normal to the travel direction is independent of weld position. The weld morphology was examined along its length by considering planes of different depths parallel to the surface. These showed semicircle streaks whose shapes depended on the depth of the observation plane. It is determined that the weld nugget is composed of a series of identical half ellipsoid regions. A tentative simplified cavity model is presented to explain the mass flow pattern and formation of defects in the weld nugget. This model is based on the assumption that only the metal between the pin surface and the last maximum circle created by the pin rotation is in a plasticized state. From this model, it is shown that the location and size of the cavity formed during the rotation of the pin changes cyclically and it is related to the position of the pin’s center. The holes or slots left in the weld nugget center or near the advancing side are directly related to the size of the cavity. The welding parameters or weld pitch affects the volume of the cavity, and consequently influence the weld defects. A large weld pitch will cause holes to be formed in the weld nugget because of the large cavity. The flow patterns, which show that the plasticized material flows from both advancing and retreating sides to the weld center behind the pin, can be easily explained with this cavity model.

Automotive box section design under torsion Part 2: Behaviour and implications on weight reduction

A well-calibrated and validated finite element procedure, described in companion paper 1, was used in producing data on the stiffnesses, elastic limits and strengths of automotive box sections under torsion. The modelling procedure was first used in analysing all the experimental geometries, and these preliminary analyses helped to define the scope of further numerical work. This work, which consisted of 76 analyses, investigated the main effects identified—section thickness, cross-sectional area, model length and section design—and their interactions. Particular emphasis was given to quantifying the implications of the various effects on weight reduction by replacing spot welding with adhesive bonding as the fabrication technique. Further tests and analyses were also conducted to investigate the effects of weld pitch on torsional stiffness and to compare the properties of adhesively bonded, laser-welded and spot-welded sections.

Studies on a computational model and the stress field characteristics of weld-bonded joints for a car body steel sheet

Based on analyses of the local structure and hardness distribution of weld-bonded joints, a computational model composed of the base metal, the HAZ, the nugget and the adhesive layer is established. Both indentation and the inhomogeneity of the mechanical properties in joints are considered, an annular bonded surface area and a damaged adhesive zone also being taken into account. At the same time, discussions are made on a typical load–displacement curve of weld-bonded joints by the tensile shear test. Using the model established, stress fields of resistance spot welded joints and two types of weld-bonded joints which are made by adhesives with different elastic modulus have been given by the finite element method. In addition, the effect of the weld pitch on the stress and strain fields of two weld-bonded joints are investigated.

Studies on Transient Stresses and Deformation Behavior of Groove due to Butt-Welds of Thin Mild Steel Plates (3rd Report)

In the previous reports, it has been shown that transverse forces acting on tack welds and deformation behavior of groove during butt-welding varied with sizes of welded plates and welding conditions significantly. The purpose of this report is to clarify effects of plate width, length of weld, tack weld pitch and welding condition on the maximum tensile force acting on a finishing end tack weld and to propose a suitable method to predict the maximum tensile force which is a primary factor of end cracking of butt-welding joints.A series of numerical calculations is performed based on unsteady heat conduction analysis and uncoupled elasto-plastic thermal stress analysis by use of the finite element method. Effect of mesh subdivision on accuracy of calculated results is carefully examined. It is suggested that use of a small time increment and a mesh size proportionate to weld heat input is necessary to acquire satisfactory results.An approximate formula to estimate the maximum tensile force acting on a finishing end tack weld is proposed. It is shown that the estimated values are fairly in good agreements with the calculated and/or measured values obtained hitherto, and that if we consider the optimum average width of fused zone for a welded joint with a given size, the maximum tensile force is specified only by welding speeds and becomes maximum for a specific welding speed.

平板の突合せ溶接進行中の拘束材・仮付け溶接に作用する引裂力について

This paper deals with the effect of welding conditions on separating forces produced in restraints like strong backs or tack welds during butt welding.The calculations have been carried out on variations of separating forces during welding under various conditions of heat input, plate length and restraint or tack weld pitch, using the finite element method explained previously. It is assumed that the rigidity of restraints and tack welds is infinite.The main conclusions obtained in the study are summarized as follows:The larger the effective molten pool length on the mechanical point of view (lM) is, the larger is the difference of separating forces between restraints and tack welds. The result depends on the type of restraint: in case of restraint like strong back, the restraint acts as a restraint after heat source passed through it, but in case of tack weld, the tack weld melts and cannot act as a restraint after heat source passed through it.The maximum separating force produced in an end restraint or an end tack weld ((Fy/h)emax) can be characterized as follows.(Fy/h)emax in the end tack weld is smaller than in the end restraint under the following conditions:lp=1200mm 416≤lM≤1663 (mm) 6000≤q/υh≤24000 (cal/cm2)where lp is a restraint or tack weld pitch, lM is an effective molten pool length on the mechanical point of view and q/υh is heat input per unit thickness and unit weld length.(Fy/h)emax increases as the heat input (q/υh) increases under consta-nt lM and decreases as the effective molten pool length (lM) increases under constant q/υh.Effect of plate length (L) on (Fy/h)emax depends on the welding conditions (q/υh, lM) and plate length (L).A restraint pitch has larger effects on (Fy/h)emax than a tack weld pitch.These results can be applied to tow electrodes submerged arc welding under the conditions that distance between leading electrode and trailing electrode (lLT) is small compared to lM.