Longitudinal Bending Distortion Research Articles

Investigation of longitudinal bending distortion of a double-side edge welded fin plate by study of plastic zones

Investigation of longitudinal bending distortion of a double-side edge welded fin plate by study of plastic zones

Control of weld distortion through in-situ preheating of weld filler wire

ABSTRACT The present study deals with a new technique for controlling the weld-induced distortion. This developed technique involves in-situ preheating of welding filler wire before it emerges from the contact tube. Welding filler wire preheating was carried out using an external constant current power source and a specially designed welding torch. Weld beads were deposited on 3.0 mm low carbon steel sheet using a bead on plate technique with different preheat values of welding filler wire by the submerged arc welding process. Electrical signals were recorded to analyze the effect of welding filler wire preheating on arc characteristics. Probability density distribution (PDD) curves from electrical signals indicate that with the rise in preheat value, welding current decreases and results in stable arc characteristics. An increase in preheat value also reduces the longitudinal bending distortion of the sheet. The maximum reduction in the longitudinal bending distortion of the sheet (~53%) was obtained at the maximum preheat value of 200 Ampere.

Optimization of Gas Metal Arc Welding (GMAW) Parameters for Minimum Distortion of T Welded Joints of A36 Mild Steel by Taguchi Method

In this study, the GMAW parameters for welding of A36 mild steel have been investigated to get the minimum of distortion. The type of welded joint used was square groove T-joint fillet weld with filler wire ER70S-6. The welding current and the welding speed were selected as input parameters while the response used was distortion (longitudinal bending distortion and angular distortion). Taguchi method was used to determine optimal welding parameters which the minimum distortion. Design of experiment was set two factors with three level in each factor and three replication, so the L9 Taguchi’s orthogonal array was applied. The minimum conditions were determined using S/N ratio with a quality character of smaller is better (SB). In addition, to determine the significance of the welding parameters used ANOVA. The results show that the welding current of 170 A and the welding speed of 4.0 mm/s were obtained as the minimum of longitudinal bending distortion and angular distortion. Based on analysis of variance, the welding current was a parameter that greatly affects the longitudinal bending distortion with the percentage contribution of 64.36% while angular distortion was strongly influenced by welding speed parameter with the percentage contribution of 53.38%.

Analisis pengaruh arus pengerasan dan kecepatan pengelasan terhadap lebar manik las dan distorsi pada pengelasan gas metal arc welding (GMAW) dengan sambungan tumpul SS 304

Pada kajian ini pengaruh dari arus pengelasan dan kecepatan pengelasan terhadap lebar manik las dan distorsi pada pengelasan gas metal arc welding (GMAW) sambungan tumpul SS 304 telah dilakukan. Bahan yang digunakan dalam kajian ini adalah baja tahan karat tipe 304 (SS 304) dengan konfigurasi sambungan tumpul. Variasi parameter pengelasan GMAW yang digunakan adalah arus pengelasan dan kecepatan pengelasan. Kecepatan pengelasan yang digunakan adalah 115 A, 120 A dan 125 A, sedangkan kecepatan pengelasan yang digunakan adalah 3,6 mm/s, 3,9 mm/s dan 4,2 mm/s. Hasil dari pengelasan akan dianalisis dari lebar manik las dan distorsi yang terjadi. Lebar manik las dan distorsi diukur menggunakan Dino-Lite dan Coordinate Machine Measure (CMM). Metode perpindahan vertikal rata-rata digunakan untuk menghitung distorsi longitudinal bending dan distorsi angular. Hasilnya menunjukkan bahwa menaikan arus pengelasan akan meningkatkan lebar manik las dan distorsi, tetapi jika menaikkan kecepatan pengelasan akan menurunkan lebar manik las dan distorsi. Pada parameter pengelasan 125 A dan 3,6 mm/s menghasilkan lebar manik las atas dan bawah yang terbesar 8,062 mm dan 4,984 mm. Distorsi longitudinal bending dan distorsi angular yang terbesar adalah 1,748 mm dan 4,076 derajat pada parameter pengelasan 125 A dan 3,6 mm/s.

In-process control of distortion in wire and arc additive manufacturing based on a flexible multi-point support fixture

ABSTRACTDistortion induced by non-uniform thermal gradients is one of the major constraints in wire and arc additive manufacturing. A novel flexible multi-point support fixture (FMSF) featured by reconfigured working surface and controllable restraining force is developed as an in-process distortion control technique. FMSF allows the distortion to be suppressed by adjusting the restraining force imposed onto the substrate dynamically as the number of layers increases. Both simulations and experiments are conducted to verify its effectiveness and compare it with other common restraint forms including clamping and pre-springing. The multi-layer deposition results show that a reduction of 96.3% in angular distortion and 86.5% in longitudinal bending distortion are obtained with FMSF, which exhibits great superiority over clamping and pre-springing.

低変態温度溶接材料を用いた溶融金属積層造形材の変形低減法に関する基礎的検討

Current work deals with investigation of the effect of the use of low transformation temperature welding wire (LTT welding wire) on distortion reduction of parts made by wire and arc additive manufacturing technique (WAAM). LTT welding wire and SUS308L wire, which was austenitic stainless steel wire, were used for making WAAM test pieces. Distortion of base plates of test pieces were evaluated by 3D non-contact coordinate measurement system. As a result, longitudinal bending distortion of the base plates of test pieces in which LTT welding wire was partially or fully used was smaller than those of the test piece which was made only by SUS308L wire. Especially, longitudinal bending distortion of the base plates of test pieces which was made only by LTT welding wire was reduced drastically from those of the test piece which was made only by SUS308L wire. However, angular distortion of the base plates were not reduced drastically even if the test piece was made only by LTT welding wire. The difference of the reduction effect of the use of LTT welding wire was discussed by considering the position of neutral plane of each distortion mode.

Transient distortion behavior during TIG welding of thin steel plate

To examine the generation characteristics of excessive distortions involved with the welding-induced buckling of a thin steel plate, the temperature profiles and distortion behaviors of welded plates during tungsten inert gas (TIG) welding were experimentally measured. Large-deformation thermal elastic–plastic analysis based on arc physics-based heat source modeling was utilized to accurately simulate the thermomechanical behavior of the plate during welding. The calculated and measured temperature profiles and distortion behaviors were compared to validate the developed numerical analysis technique. On the basis of the developed analysis technique, the effect of geometric imperfections on the thermomechanical behavior of welded thin steel plates was further investigated. Both angular and longitudinal bending distortions were found to monotonically increase with increasing heat input because of excessive longitudinal bending distortion and the secondary generation of angular distortion during the cooling process when buckling occurred. The through-thickness gradient of the plastic strain that developed with the transient distortion behavior during welding resulted in excessive angular distortion in the welded thin steel plate. It was concluded that the transient distortion behavior during welding should be taken into consideration to accurately predict and control large welding-induced distortions in thin steel plates.

薄板溶接における座屈変形の発生特性に関する実験的研究

In this study, a systematic investigation on the effect of welding conditions on longitudinal bending and angular distortions generated in welded thin plate was experimentally performed with a focus on whether or not the weld buckling distortion occurs. Real-time measurements of temperature profiles and distortion behavior during welding of thin plate were also performed for a more detailed understanding of generation process of weld distortion in thin plate. As the results, longitudinal bending distortion monotonically increases, in which the degree is different depending on the plate thickness, with the weld heat input. Meanwhile, angular distortion does not show a linear increase with the weld heat input and can be arranged coordinately by a curve convex to the parameter of mechanical melting zone, which was proposed based on the theory of inherent strain by authors in previous study, when the weld buckling distortion does not occur. In this regard, however, angular distortion also approximately monotonically increases with either the weld heat input or the parameter of mechanical melting zone, when the weld buckling distortion occurs. This is because the angular distortion-generation process proceeds in the following two stages; angular distortion is primary generated due to inhomogeneous temperature distribution through thickness during welding and secondary in association with buckling behavior during cooling process after welding. This secondary stage results in buckling-induced large angular distortion in welded thin plate. It was thus clarified that it is important to understand the generation characteristics of weld buckling-induced inherent stress and strain especially in the secondary stage for accurate predicting and controlling the weld buckling distortion in thin plate.

Mitigation of distortion in large additive manufacturing parts

Distortion mitigation techniques for large parts constructed by additive manufacturing processes are investigated. Unwanted distortion accumulated during deposition is a common problem encountered in additive manufacturing processes. The proposed strategies include depositing equal material on each side of a substrate to balance the bending moment about the neutral axis of the workpiece and applying heat to straighten the substrate. Simple finite element models are used to predict the effectiveness of the mitigation strategies in order to reduce computation time and to avoid costly experiments. The strategy of adding sacrificial material is shown to be most effective and is then applied to the manufacture of a large electron beam deposited part consisting of several thousand deposition passes. The deposition strategy is shown to reduce the maximum longitudinal bending distortion in the large additive manufacturing part by 91%. It is shown that after the distortion mode of concern is identified, simple finite element models can be used to study distortion accumulation trends relevant to the large part. Experimental observations made here, as well as finite element model results, suggest that the order in which the balancing material is added significantly affects the success of the proposed distortion mitigation strategy.

Effect of underfill defects on distortion and tensile properties of Ti-2Al-1.5Mn welded joint by pulsed laser beam welding

Owing to its more precise control of heat input, pulsed laser beam welding is expected to be a choice for welding thin sheets. In this paper, the Ti-2Al-1.5Mn titanium alloy sheets with a thickness of 0.8 mm were welded by a pulsed Nd:YAG laser beam welding system. The underfill defects, welding distortions, microstructures, and tensile properties of the joints were investigated. The results show that the welding defects are strongly influenced by the welding parameters. The residual distortion is related to the specific heat input. Particularly, the maximum angular distortion increases remarkably for the specific heat input higher than 328.5 J/cm. Further investigations reveal that this is mainly due to the formation of underfill defects, while it is not affecting the maximum residual longitudinal bending distortion. In forming underfill defects and changing acicular α′ phase morphology in the fusion zone (FZ) of the welded joint, 328.5 J/cm is a critical specific heat input. Furthermore, tensile test results reveal that the fracture positions are closely related to the underfill rate.

Distortion and residual stress generated by laser beam welding of high strength steel

In order to elucidate distortion and residual stress generated by welding of high strength steel (HT780) by laser beam, a series of experiments and analyses were carried out. The angular distortion generated by bead-on-plate welding was V-shaped and its magnitude was about 2 mm. The longitudinal bending distortion was extremely small. On the surface of the plate, the residual stress component in the welding direction was tensile and it was smaller than the yield stress in the weld metal. The residual stress was almost zero outside the weld metal. The phase transformation range in the cooling stage and the temperature dependency of mechanical properties were obtained. The mechanical properties in the phase transformation range in the cooling stage could not be specified due to transformation expansion. Therefore, they were idealized by considering transformation expansion and transformation superplasticity. The validity of the idealized mechanical properties was verified by simulating the experiment by the thermal elastic–plastic analysis. It was elucidated that the welding out-of-plane distortion and tensile residual stress were largely controlled by phase transformation in the cooling stage, although the bead width of laser beam welding was extremely narrow.

Process–microstructure–property correlations in Al–Li AA2199 friction stir welds

This paper examines the effect of three friction stir welding process parameters on the residual stresses, hardness and distortion for butt welded aluminium–lithium AA2199 alloy, a novel, low density high strength alloy with potential in the aerospace sector. A systematic set of nine trial welds is examined at different tool rotation and traverse speeds as well as tool downforces. The tensile residual stresses (∼50% of parent material yield strength) and the hardness drop in the weld line varied little with any of the friction stir welding process parameters. However, their breadth increased with rotation speed and downforce and decreased with increasing translation speed, which is consistent with increasing heat input. Weld distortion took the form of a saddle with the longitudinal bending distortion correlating strongly with the width of the tensile zone consistent with it being driven by the magnitude of the tensile buckling forces in the weld region.

高張力鋼のレーザ溶接で生じる変形・残留応力

In order to elucidate distortion and residual stress generated by welding of high strength steel (HT780) by laser beam, a series of experiments and analyses were carried out. The angular distortion generated by bead-on-plate welding was V-shape and its magnitude was about 2mm. The longitudinal bending distortion was extremely small. On the surface of plate, the residual stress component in welding direction was tensile and it was smaller than yield stress in the weld metal. The residual stress was almost zero outside the weld metal. The phase transformation range in cooling stage and the temperature dependency of mechanical properties were obtained. The mechanical properties in the phase transformation range in cooling stage could not be specified due to transformation expansion. Therefore, they were idealized by considering transformation expansion and transformation superplasticity. The validity of the idealized mechanical properties was verified by simulating the experiment by the thermal elastic-plastic analysis. It was elucidated that the welding out-of-plane distortion and tensile residual stress were largely controlled by phase transformation in cooling stage although the bead width of laser beam welding was extremely narrow.

Computationally efficient welding distortion simulation techniques

The study's aim is to improve the applicability of finite element analysis to the prediction of welding distortions, with particular emphasis on out-of-plane deformations. Robust simulation strategies are established which take account of material properties and joint configurations, but are at the same time computationally efficient. This is achieved by reducing the full transient thermo-elastoplastic analysis to variants of an uncoupled thermal, elasto-plastic and structural treatment. A two-dimensional cross-section thermal model was used to establish thermal transients. The maximum temperatures, experienced at each node during the welding cycle, were then used to link the thermal welding strains to the elasto-plastic and structural response of the welded structures. Three efficient models have been identified that reduce the transient analysis to a simple multi-load-step analysis and these were applied to sample butt-welded plates. The simulation techniques are supported by full-scale welding tests on steel plates. The evolution of angular distortion can be treated simply through non-linear, stepwise, static analyses. This captures important effects of restraint and material properties. The longitudinal bending distortion can then be established via simple elastic-perfectly plastic algorithms, through a fictitious elastic thermal load analysis.

すみ肉溶接で生じる面外変形の高精度予測

In order to predict the distortion generated by welding with high accuracy, distortion with fillet welding was measured by three-dimensional photographic measurement. Then, the experiment was simulated by three-dimensional thermal elastic-plastic analysis by FEM. The important matters that should be noted on predicting the distortion with high accuracy were shown by comparing with the results of the experiment and those of the analysis.The results of measuring temperature could be accurately simulated by non-steady state thermal conduction analysis based on FEM. In carrying out the elastic-plastic analysis, four conditions (equilibrium equation, constitutive equation, condition of compatibility and yield condition) should be satisfied. In welding, the temperature largely changed from a melting temperature to a room temperature. So, yield stress of materials largely changed, too. In particular, yield stress becomes about zero above 700°C. The analysis should be carried out under the yield condition that equivalent stress generated in temperature increment ΔT did not exceed yield stress of materials at high temperature above 700°C. It should be sufficiently recognized that the obtained results were not reliable if the yield condition was not satisfied. Angular distortion generated in fillet welding could be accurately predicted by regarding the weld metal as a deposited metal not assuming that a deposited metal zone was a simple triangle. Specifying an influence factor on longitudinal bending distortion was difficult because the absolute value was small. However, it was indicated that the reasonable result could be obtained by regarding the weld metal as a deposited metal because the absolute value of longitudinal bending distortion at pass (2) (the second pass) of which restraint was severer became smaller than that at pass (1) (the first pass).

すみ肉Ｔ継手に生じる縦収縮・縦曲り変形に関する研究

This paper deals with experimental data and a predictive method of longitudinal shrinkage and bending distortion which are important in the development of the high accuracy production system of the large welding structures. The longitudinal shrinkage and bending distortion can be calculated from the inherent force, namely Tendon Force, which is related to the total of the inherent strain. First the experimental values of the longitudinal shrinkage, longitudinal bending distortion and the inherent strain were obtained under various welding conditions. Next, the theoretical equation was proposed to calculate the longitudinal shrinkage and bending distortion from the inherent strain. As the results, the validity of the theoretical equation on the longitudinal shrinkage and bending distortion is shown by the comparison between values predicted from inherent force and experimental values.

Recent M.I.T. Research on Residual Stresses and Distortion in Welded Structures

This paper presents a summary of recent efforts by the Welding Research Group at the Department of Ocean Engineering, M.l.T. The major thrust of the efforts has been to develop technologies of reducing residual stresses and distortion through in-process control. Part 1 discusses reduction of longitudinal bending distortion of built-up beams, reduction of radial distortion and residual stresses in girth- welded pipes, reduction of forces acting on tack welds during butt welding, and reduction of residual stresses and distortion in high-strength steel weldments. Part 2 presents a brief summary of other research studies, including the forming of steel plates by line heating with a high-power laser beam, an intelligent system for flame straightening of panel structures, and the development of a knowledge- based system for minimizing out-of-plane distortion of welded structures.