Prediction of welding distortion during assembly process of thin plate structures

Ships and automobiles are fabricated front thin plates. To assemble parts, welding is commonly employed. However, welding distortion in large thin-plate panel structure is usually cased by buckling due to the residual stress. In this study, an elastic finite element method for predicting the welding distortion of three-dimensional thin-plate structures with considering welding sequence was proposed. In this method, the inherent strain was employed to model the local shrinkage due to welding itself, and the interface element was introduced to simulate the assembly process. The proposed method was applied to study the influence of welding sequence on the buckling distortion of the large thin-plate panel structure during assembly.

Numerical simulation and control of welding distortion for double floor structure of high speed train

The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code.Then,the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner software.The effects of welding sequence,clamping configuration and reverse deformation on welding distortion of floor structure were examined numerically.The results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor structure.Compared with the welding sequence,the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor structure.In the case of30 mm reverse deformation,the maximum deformation can be reduced about 70%in comparison to an actual welding process.

Finite element analysis of welding distortion control by trailing intense cooling

A new moving or dynamic thermal tensioning technique-welding with trailing intense cooling was numerically simulated by finite element method(FEM)and experimentally investigated.The simulation results indicate that trailing intense cooling can increase significantly the longitudinal tensile plastic strain within the weld and its adjacent zone during cooling stage,which can partially or completely counterbalance the longitudinal compressive plastic strain formed in the heating stage and the solidification shrinkage formed in the cooling stage.Therefore the longitudinal shrinkage remaining in the weld and the adjacent zone is greatly reduced,which means that the residual stresses in the weldments are kept in a lower value and the residual distortion can be mitigated effectively.Meanwhile a series of parametric studies were conducted to demonstrate the influences of several key parameters such as cooling distance, cooling power and cooling width on the effectiveness of distortion control.Experimental results also verify the effectiveness of this distortion control technique and the reliability of the numerical simulation.

SOLID-STATE PHASE TRANSFORMATION OF WELDED METAL IN CONTROL OF WELDING DISTORTION PROCESS

Based on the tests of a build-up welding at plate edge (BWPE) and amulti-layer build-up welding on plate (MBWP), the article studies on the solid-state phasetransformations which affect welding distortion process and on the influence rule of transformationstarting temperature (TST) of welded metal to the welding residual distortion. The weldingdistortion can be decreased or controlled by the transformation volume expansion caused bysolid-state phase transformation of welded metal during the cooling. The test results of BWPE showthat when TST is at about 190 deg C, the bending distortion of welded specimen is the smallest, andits displacements at free end are decreased to 58 percent and 67 percent compared with those ofconventional welding electrodes A102 and E5015, which TST are less than room temperature and equalto 758 deg C respectively. The test results of MBWP show that when TST were at 100 approx 250 deg C.the welded specimen would appear reversible bending distortion compared with those of A102 andE5015. The maximum deflection value of reversible bending distortion in 8 mm thick plate is -2.94 mmat about 170 deg C of TST. The test results provide a valuable method to decrease or to controlwelding residual distortion.

Knowledge modeling based on interval-valued fuzzy rough set and similarity inference: prediction of welding distortion

Knowledge-based modeling is a trend in complex system modeling technology. To extract the process knowledge from an information system, an approach of knowledge modeling based on interval-valued fuzzy rough set is presented in this paper, in which attribute reduction is a key to obtain the simplified knowledge model. Through defining dependency and inclusion functions, algorithms for attribute reduction and rule extraction are obtained. The approximation inference plays an important role in the development of the fuzzy system. To improve the inference mechanism, we provide a method of similaritybased inference in an interval-valued fuzzy environment. Combining the conventional compositional rule of inference with similarity based approximate reasoning, an inference result is deduced via rule translation, similarity matching, relation modification, and projection operation. This approach is applied to the problem of predicting welding distortion in marine structures, and the experimental results validate the effectiveness of the proposed methods of knowledge modeling and similarity-based inference.

Low stress no distortion welding for aerospace shell structures

To fit in with the strict geometrical integrity and ensure dimensionally consistent fabrication of the welded aerospace structures. the low stress no distortion(LSND)welding, a technique for thin materials, was poineered and developed to provide an ininprocess active control of welding distortion. Satisfactory distortion free results were achieved in both welding of jet engine cases of heat-resistance alloys and rocket fuel tanks of aluminuim alloys, and there need no. reworking operations for post-weld distortion correction. Based on the 'static' method a newly developed method for dvnamic in-process control is also discussed in this paper. Both methods provide quanutiative in-process control of incompatible strains in weld zone and low stress no distortion welding results.

New development in welding thin-shell aluminum alloy structures with high strength

From the viewpoint of welding mechanics, two new welding methods-welding with trailing peening and welding with trailing impactive rolling were introduced. For aluminum alloy thin-shell structures with high strength, welding will lead to hot cracking, poor joint and distortion. In order to solve them, trailing impactive device was used behind welding torch to impact the different positions of welded joints, thus realizing the welding with free-hot cracking, low distortion and joint strengthening. By use of impactive rolling wheels instead of peening heads, the outlook of welded specimen can be improved and stress concentration at weld toes can be reduced. Equipment of this technology is simple and portable. It can used to weld sheets, longitudinal and ring-like beams of tube-like structures, as well as the thin-shell structures with closed welds such as flanges and hatches. So the technology has the wide application foreground in the fields of aviation and aerospace.

A new method for welding aluminum alloy LY12CZ sheet with high strength

From the viewpoint of welding mechanics, a new welding technology—trailing peening was applied firstly to weld aluminum alloy LY12CZ sheet with high susceptibility to hot cracking. Trailing peening can exert a transverse extrusion strain on the metal in brittle temperature region (BTR) which can compensate for the tensioning strain during the cooling procedure post welding. So, welding hot cracking of LY12CZ sheet can be controlled effectively on the special jig for hot cracking experiment, and the phenomenon of hot cracking can’t be found in specimens with large dimensions finally. At the same time, welding with trailing peening can decrease welding distortion caused by longitudinal and transverse shrinkage of weld obviously. Due to strengthening the poor position-weld toe during the process of welding, the residual stress distribution of welded joint is more reasonable. Contrast with conventional welding, mechanical properties such as tensile strength, prolongation ratio and cold-bending angle of welded joint with trailing peening can be improved obviously, and rupture position of welded joint transits from weld toe at conventional welding to weld metal at trailing peening. So, welding with trailing peening can be regarded as a dynamic welding method with low stress, little distortion and hot cracking-free really. As far as theoretical analysis is concerned, the technology of trailing peening can be used to weld the materials with high susceptibility to hot cracking such as LY12CZ and LD10, and solve the welding distortion of thin plate-shell welded structures which contain closed welds such as flange. In addition, the technology of trailing peening has many advantages: simple device, high efficiency, low cost and flexible application which make the welding method have widely applied foreground in the field of aeronautics and aerospace.

The mechanical measuring method of welding heat source efficiency

Based on the principle of residual deformation induced by superposition of the welding residual stress and working stress, the welding heat source efficiency has been determined by measuring displacement changes of specimens under loading and unloading in tensile tests, and combining with calculating welding parameters. Meanwhile, the welding heat source eficiencies obtained are compared with those of the measuring-calculating method. The research results show that the welding heat source efficiencies are almost the same as those obtained by the measuring-calculating method. Therefore, the welding heat source efficiency can be determined accurately by this method, and a new determining method of the heat source efficiency for the welding heat process calculating has been provided.

Predictive analysis of buckling distortion of thin-plate welded structures

The welding buckling distortions of thin plated structures were investigated based on finite element methods.An engineering treatment method for predicationg the buckling distortion was proposed.The equivalent applied thermal load was used to simulate the welding residual stress,thus the calculation of complex welding distortion can be transformed into 3D elastic structural applied load analyses,which can reduce the quantities of calculating work effectively.The validation of the method was verified by comparison of the numerical calculation with experimental results.The prediction of buckling distortion for side walled structures of passenger train was performed and the calculation was in agreement with measuring results in general.It is shown that the main factors for producing the buckling are the intermittent fillet and plug weld during welding the stiffened beams and columns to the panel.

Mechanism of biaxial pre-stress method on welding residual stress and hot cracks controlling

Based on the conventional uniaxial pre-tensile stress method during welding, this study presents a new method of welding with biaxial pre-stress. With the help of numerical simulation, experiments were carried out on the self-designed device. Except for the control on residual stress and distortion us-welded, the experimental results also show its effect on the prevention of hot cracks, thus this method can make up for the disadvantage of the conventional pre-stress method. Hot cracks disappear when the value of pre-stress surpasses 0. 2 σs（yield limit）. Welded thin plates with low-level residual stress, little distortion and no hot cracks are obtained with longitudinal pre-tensile stress level between 0. 6σsand 0. 7σs and precompressive stress between 0. 2 σs and 0. 3 σs in transverse direction.

Numerical Analysis of Welding Residual Stress and Distortion in Laser+GMAW Hybrid Welding of Aluminum Alloy T-Joint

A 3-D finite element model is developed to predict the temperature field and thermally induced residual stress and distortion in laser＋GMAW hybrid welding of 6061-T6 aluminum alloy T-joint. And the characteristics of residual stress distribution and deformation are numerically investigated. In the simulation, the heat source model takes into account the effect of joint geometric shape and welding torch slant on the heat flux distribution and a sequentially coupled thermo-mechanical method is used. The calculated results show that higher residual stress is distributed in and surround the weld zone. Its peak value is very close to the yield strength of base metal. Besides, a large deformation appears in the middle and rear part of the weldment.

STUDY ON THE PREDICTIVE METHOD OF BUCKLING DEFORMATIONS OF THIN-PLATE WELDED STRUCTURES

The buckling formation and influence factors during welding thin - plated structures were investigated based on finite element methods, An engineering treatment method for prdicating the buckling distor- tion was proposed in here. It was used the equivalent applied thermal - load to simulate the welding residual stress,therefore the calculation of complex welding distoriton can be transformed into 3D elas- tic structural applied- load analyses, which can reduce the quantities of calculating works effectively. The validation of the method was verified by comparison of the numerical simulation and experimental results. The simulation of buckling distorition for side - walled structrues of paseenger train was per- formed and the calculation was in agreement with measuring results in general. It was shown that the main factors for producing the buckling were the intermittent fillet and ping the during welding the stiffened beams and columns to the panel.The existence of the free edge of panels would reduce the crit- ical buckling stress and enlarge the deflection obviously,but the continuous weld in closed frames didn' t degrade the buckling situation.