Showing papers on "Butt welding published in 2015"

Effect of backing plate material in friction stir butt and lap welding of 6063-T4 aluminium alloy

Abstract: 6063-T4 aluminum alloy plates were friction stir butt and lap welded using three different backing plate materials: mild steel, stainless steel, and asbestos. Effects of backing plate material on macrostructure, peak mid-section temperatures in heat affected and weld nugget zones, and weld mechanical properties were obtained for each of the cases. Effect of backing plate material was seen to be more significant in lap than butt welding. While lap welds obtained even at a low welding speed, for mild steel and stainless steel backing plates, contained multiple weld defects leading to failure in lap shear tests from weld nugget zone, corresponding welds obtained with asbestos backing plate were defect free resulting in failure from base metal region. In butt as well as lap configuration, asbestos backing plate which had the lowest thermal diffusivity was observed to provide the largest process window within which defect free welds could be obtained.

Numerical and parametric modeling and analysis of weld-induced residual stresses

Abstract: A three-dimensional thermo-elasto-plastic finite element analysis is used to determine the residual stress distribution and the distortion field in butt and fillet plates. The employed finite element model is first verified against existing experimental results of thermal distortion and then is used for analyzing 12 case studies accounting for various plate thicknesses and welding sequences. Weld induced residual stress distributions have been estimated and discussed. The effects of thickness, welding sequences and finite element size have been investigated. A two-dimensional parametric relationship of residual stresses has been developed.

Material processing with ultra-short pulse lasers working in 2μm wavelength range

Abstract: New wavelengths of laser radiation are of interest for material processing. Results of application of the all-fiber ultrashort pulsed laser emitting in 2 µm range, manufactured by Novae, are presented. Average output power was 4.35 W in a single-spatial-mode beam centered at the 1950 nm wavelength. Pulses duration was 40 ps, and laser operated at 4.2 MHz pulse repetition rate. This performance corresponded to 25 kW of pulse peak power and almost 1 µJ in pulse energy. Material processing was performed using three different focusing lenses (100, 30 and 18 mm) and mechanical stages for the workpiece translation. 2 µm laser radiation is strongly absorbed by some polymers. Swelling of PMMA surface was observed for scanning speed above 5 mm/s using the average power of 3.45 W focused with the 30 mm lens. When scanning speed was reduced below 4 mm/s, ablation of PMMA took place. The swelling of PMMA is a consequence of its melting due to absorbed laser power. Therefore, experiments on butt welding of PMMA and overlapping welding of PMMA with other polymers were performed. Stable joint was achieved for the butt welding of two PMMA blocks with thickness of 5 mm. The laser was used to cut a Kapton film on a paper carrier with the same set-up as previous. The cut width depended on the cutting speed and focusing optics. A perfect cut with a width of 11 µm was achieved at the translation speed of 60 mm/s.

Process modeling and parameter optimization using radial basis function neural network and genetic algorithm for laser welding of dissimilar materials

Abstract: The welded joints of dissimilar materials have been widely used in automotive, ship and space industries. The joint quality is often evaluated by weld seam geometry, microstructures and mechanical properties. To obtain the desired weld seam geometry and improve the quality of welded joints, this paper proposes a process modeling and parameter optimization method to obtain the weld seam with minimum width and desired depth of penetration for laser butt welding of dissimilar materials. During the process, Taguchi experiments are conducted on the laser welding of the low carbon steel (Q235) and stainless steel (SUS301L-HT). The experimental results are used to develop the radial basis function neural network model, and the process parameters are optimized by genetic algorithm. The proposed method is validated by a confirmation experiment. Simultaneously, the microstructures and mechanical properties of the weld seam generated from optimal process parameters are further studied by optical microscopy and tensile strength test. Compared with the unoptimized weld seam, the welding defects are eliminated in the optimized weld seam and the mechanical properties are improved. The results show that the proposed method is effective and reliable for improving the quality of welded joints in practical production.

Finite Element Analysis of Residual Stress in Butt Welding of Two Similar Plates

Abstract: In this paper, Manual Metal Arc Welding of carbon steel plates was studied. The finite element analysis of residual stresses in butt welding of two similar plates is performed with the ANSYS software. This analysis includes a finite element model for the thermal and mechanical welding simulation. It also includes a moving heat source, material deposit, temperature dependent material properties, metal plasticity and elasticity, transient heat transfer and mechanical analysis. The welding simulation was considered as a sequential coupled thermo-mechanical analysis and the element birth and death technique was employed for the simulation of filler metal deposition. The residual stress distribution and magnitude in the axial direction is to be obtained. A good agreement between the computation and experimental results is to be obtained.

Swinging laser and hot wire welding method for implementing butt welding on narrow gap of thick plate

Abstract: The invention relates to a swinging laser and hot wire welding method for implementing butt welding on a narrow gap of a thick plate. The method comprises the steps of design of a conducting nozzle (4), welding of back welding beads (6), multiple superposed welding of filling welding beads (7) and welding of capping welding beads, wherein the effective length L of the conducting nozzle is equal to [H/cos(theta)]+5 mm, the effective extending-out length of a filler wire (5) is K, a groove gap (2) of a workpiece (3) to be welded is controlled in a range D being 6 to 10mm, during the back welding bead welding, an included angle between a laser beam (1) and the welding direction is controlled to be 80 to 85 degrees, in addition, the focal point of the laser beam is a negative value, during the filling welding bead welding, the included angle between the laser beam (1) and the welding direction is controlled to be 85 to 90 degrees, in addition, the focal point of the laser beam is a positive value, the inclined angle theta between the filler wire and the back welding beads is controlled to be 20 to 60 degrees, after each pass of filling welding bead welding, the welding seam surface is cleaned, in addition, welding slag generated on the side wall of the workpiece to be welded is cleared away, finally, the welding of the capping welding beads is completed, and the incomplete fusion is eliminated.

Microstructure and fracture behaviour of flash butt welds between dissimilar steels

Abstract: Flash butt welds between high carbon steel and chrome–nickel steel were studied in this article. Light and electron microscopic studies have shown that the welded joints have a complex structure consisting of several phases. In addition to pearlite colonies, austenite microvolumes and regions of high strength martensite, the welds contain brittle inclusions of titanium sulphide and carbide particles. The mechanical behaviour of the welded joints is negatively influenced by the dramatic change in hardness in the weld zone. Fractographic analysis of dynamically fractured welds between carbon steel and stainless steels has shown that the fracture in the weld samples occurs in both steels. This behaviour of the material is caused by the non-uniform distribution of martensitic regions within the weld. The formation of martensitic regions in the structure of the material is a major cause of the reduction in the fatigue crack resistance of the welded joints.

Modulated fiber laser welding of high reflective AZ31

Abstract: Power sine modulation fiber laser welding (FLW) of AZ31 magnesium alloy was conducted. When the diameter of transmission fiber and focal spot was 400 μm and 0.4 mm, respectively, the average laser powers for penetrating a 2.7-mm-thick AZ31 plate at a welding speed of 5 m/min were reduced by about 33 % by using modulated FLW. The relationship between modulation parameters (i.e., amplitude, frequency, and average laser power) and weld depth which was closely related to the transfer efficiency of laser energy was studied through partial penetration laser welding test on 8-mm-thick AZ31 plate based on quadratic regression orthogonal design. It was found that influence of power modulation on laser welding of AZ31 alloy was highly dependent on laser power density. In the low power density range, laser energy coupling efficiency could be significantly improved by combining low amplitude with high frequency or high amplitude with low frequency. With the increasing of laser power density, the optimum frequency corresponding to maximum weld depth decreased, and the positive effect of the favorable combination of high amplitude and low frequency on laser energy coupling continuously weakened. When laser power density was high enough, power modulation had hardly positive effect on weld depth and energy coupling efficiency. It was argued that improvement of energy coupling efficiency in laser welding of AZ31 by using power modulation was due to the reduction in the portion of energy lost into surroundings. Finally, laser butt welding was conducted on 2.7-mm-thick AZ31 under the condition of high beam quality and the tensile strength of both butt-welded joint and base metal that was tested.

Ultrasonic welding of dissimilar materials: A review

Abstract: During the last few years ultrasonic welding has become significant attention regarding its suitable applications in comparison to traditional welding techniques. Bonding of dissimilar materials has always been a challenging task due to poor control on grain size and sensitive mechanical properties that could have been made by joining with traditional welding techniques. Moreover, joining dissimilar materials such as Aluminum/steel, metal/glass, Aluminum/copper had not been achieved without the usage of ultrasonic welding technique. This work presents a review of literature regarding the usage of ultrasonic welding technique in many applications. Additionally, this paper provides different examples and applications of ultrasonic welding technique and its application. Main advantages of this technique are, clean and undamaged exterior parts of weld, power savings, stable and strong bond, time efficiency.

Numerical and experimental study on butt weld with dissimilar thickness of thin stainless steel plate

Abstract: Systematic numerical investigation is performed to study the effects of different case studies on butt welding of dissimilar thicknesses plates which is a normal type of welding geometry in shipyards. To start with, the numerical study of thermo-mechanical analysis is verified by experimental test results reported in this paper. In the experiment, two stainless steel plates with 2.5 and 4 mm thicknesses are welded with single-pass butt welding with GMAW. The numerical investigation is conducted with eight different case studies, belonging to three different groups to evaluate the effects of each case on the structural response. These eight cases are grouped according to the heat input position, welding parameters, and different ratios between thicknesses. It is concluded from the results that the changing ratio between thicknesses has a significant effect on the structural response.

Material flow during friction stir spot welding of dissimilar Al2024/Al materials

Abstract: In the present paper, the material flow and intermixing during friction stir spot welding of dissimilar Al2024/Al materials were investigated. The dissimilar materials had quite different strength. The microstructural evolutions taking place during a series of lap and butt welds were observed. The effect of penetration depths, dwell time, rotational speed and tool geometry were systematically investigated. The material flow and formation of the intermixed region were explained by a modified model.

Double pulse laser welding of 6082 aluminium alloys

Abstract: Double pulse laser welding is investigated to reduce hot cracking in 6082 aluminium alloy welds. Therefore, Nd:YAG and diode laser pulses are superimposed and synchronised with a specific delay. The diode laser heats the parent metal and weld metal during weld spot solidification to compensate for solidification shrinkage and thermal contraction. The results of conventional pulsed laser welding prove that hot cracking is strongly dependent on the pulse peak power of the Nd:YAG laser, which constrains the crack free penetration depth. Adding the diode laser pulse at a defined time during weld spot solidification eliminated hot cracking. The double pulse welding method allowed the butt welding of 0·5 mm thick 6082 aluminium alloys without the formation of hot cracking.

Super-thick steel plate welding method

Abstract: The invention relates to a super-thick steel plate welding method. According to the method, the fabrication weldability of super-thick steel can be effectively improved, and the construction efficiency and the weld inspection first-pass yield can be improved. The method comprises the following steps of 1, processing a welding groove; 2, preparing before welding; 3, preheating before welding; 4, welding. The method is simple; the improved design of the welding groove is reasonable and reliable, and the method is suitable for common domestic single wire submerged arc welding machines and is high in practicability; a combined welding process of taking super low hydrogen electrode arc welding as backing weld and adopting submerged arc welding for filling and cosmetic welding is adopted, and the welding advantages of the two processes are integrated; the fabrication weldability of the super-thick steel plate is greatly improved, the welding quality of the super-thick steel plate is controlled, the first-pass yield of super-thick steel plate butt weld inspection is improved, and the method can be widely applied to welding construction of low-alloy high-strength structural steel super-thick steel plates which are 60-300mm in thickness and has good technical, economic and social benefits.

Investigation on Tensile Strength of Friction Stir Welded Joints in PP/EPDM/Clay Nanocomposites

Abstract: Polymer-based nanocomposites due to their advantages such as corrosion resistance,adequate mechanical properties and low cost are widely used in modern technologies. The increasing application of these nanocomposites, and hence their welding seems unavoidable. In this paper, a novel hottool in friction stir welding process is used for butt welding nanocomposite plates of 5 mm thick containing polypropylene , ethylene-propylene diene monomerand Cloisite 15A. Response surface method is used to design experiments and determine the effect of process parameters such as tool rotational speed, welding speed, tool shoulder temperature and clay content on weld tensile strength. The results show that although increasing clay content in the base material increases its tensile strength but decreases the weld tensile strength; such that in the specimens with 0, 3 and 6% clay content, the weld tensile strength equals to 94, 80 and 61 percent of the respective base materials.

Dissimilar Metal Active Gas Welding of TWIP and DP Steel Sheets

Abstract: In the last years, TWIP steels have been proposed for the fabrication of car-body components, due to their excellent combination of strength and toughness. However, a widespread usage of these steels for such applications is conditional on the employment of dissimilar welding with other automotive high-strength steel grades. In this study, dissimilar butt weld seams of TWIP and Dual Phase steel sheets fabricated by metal active gas welding are examined. The microstructural and mechanical characterization of the welded joints were carried out by optical metallography, microhardness, tensile testing, and fractographic examination. The heat affected zone on the TWIP side was fully austenitic and the only detectable effect was grain coarsening; on the dual phase side new martensite formed close to the fusion zone, while ferrite, and tempered martensite occurred away from the fusion zone. The welded tensile specimens exhibit a plastic behavior influenced by the TWIP steel, even though with more limited tensile strengths and elongation at fractures. The tensile specimens predominantly broke within the weld seams, with the fractures surfaces being ductile.

Optimization of welding thickness on casting-steel surface for production of forging die

Abstract: There are many drawbacks of traditional mold manufacturing technology, especially for dies used on large-scale hydraulic press, such as poor forging penetration, high difficulty of open die-forging process of modules, inferior hardness after heat treatment, high cost, massive waste of invalid forging dies, and so on. Therefore, a new method of mold making is put forward in this paper, which is to do surface welding on casting-steel. The FEM simulation experiments were done to establish a simplified finite element model of the surface welding mold based on JXZG casting-steel. Then, the thermal cycle curve method was used to simulate the surface welding and tempering process. Meanwhile, the temperature field and residual stress field under different welding thickness were analyzed. The finite element modal of landing gear used in a large civil aircraft was established, and then elastic-plastic finite element method was utilized to simulate the forming process of billet and to analyze the temperature field and residual stress distribution of different time. The results demonstrated that FEM could simulate the actual process of surface welding on casting-steel effectively. The equivalent stress close to welding line decreased when the welding thickness inclined, and then it leveled out when the welding thickness was 15 mm; on contrary, the equivalent stress far from welding line increased when the welding thickness declined and the impact of weld pass on casting-steel matrix enlarged which increased the possibility of defects when the casting-steel was used. In sum, when the impact of welding thickness and the cost of mold making are taken into consideration, 16 mm was chosen as the optimal surface welding thickness under given working conditions of landing gear.