Showing papers on "Butt welding published in 2018"

Microstructure and mechanical properties of friction stir welded and laser welded high entropy alloy CrMnFeCoNi

Abstract: The high entropy alloy CrMnFeCoNi has been shown to have promising structural properties. For a new alloy to be used in a structural application it should be weldable. In the present study, friction stir welding (FSW) and laser welding (LW) techniques were used to butt weld thin plates of CrMnFeCoNi. The microstructure, chemical homogeneity and mechanical behavior of the welds were characterized and compared with the base metal. The tensile stress-strain behavior of the welded specimens were reasonable when compared with that of the base metal. FSW refined the grain size in the weld region by a factor of ∼14 when compared with the base metal. High-angle annular dark field transmission electron microscopy in combination with energy dispersive X-ray spectroscopy showed chemical inhomogeneity between dendritic and interdendritic regions in the fusion zone of LW. Large fluctuations in composition (up to 15 at%) did not change the crystal structure in the fusion zone. Hardness measurements were carried out in the weld cross section and discussed in view of the grain size, low angle grain boundaries and twin boundaries in FSW specimens and the dendritic microstructure in LW specimens.

Butt welding joints recognition and location identification by using local thresholding

Abstract: Manual detection and identification of butt weld joints through welding image in real-time by human observation is subjective in nature, requires experience and can be biased at times. Furthermore, since that most of the welding robots application are programmed by teach and play means that they need to be reprogrammed each time they deal with new task. This is time consuming, plus welding parameters also need to be refined for every new program. Hence, this research aims to tackle the aforementioned issues by suggesting an alternative method that can automatically recognize and locate the butt welding position at starting, middle, auxiliary and end point under three scenarios which are; (1) straight, (2) saw tooth and (3) curve joint. This is done without any prior knowledge of shapes involved. A new approach known as local thresholding is proposed in the segmentation process which consists of image pre-processing, noise reduction and edge region points generation for butt welding joint identification. Region points for butt welding seam path are selected by shape selection generated from contour points according to the three scenarios. Each point is located by 2D coordinates that is usually used by robot controller for path planning. Experimental results showed that the local thresholding approach has managed to fulfill the research objective in detecting, identifying and locating the butt welding joint position in the three different scenarios. When compared with other methods such as background subtraction, local thresholding narrowly loses out in terms of less mismatch error produced. However, it gives the best results in the detection of the butt welding joint edges. Besides having the advantage of the ability to perform identification without prior knowledge from an image, local thresholding also showed that it can work just fine even in the presence of imperfections such as scratches on the surface of mild steel.

Influence of the kissing bond on the mechanical properties and fracture behaviour of AA5083-H112 friction stir welds

Abstract: The kissing bond phenomenon in AA5083-H112 friction stir butt welds was investigated in joints welded using a matrix of welding parameters, with tool rotation speeds of 800, 1000, and 1200 rpm and feed speeds 100, 200, and 300 mm/min. The length of the kissing bond along the cross-section normal to the welding direction was measured to quantify its influence on the mechanical properties. A combination of optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile and fatigue testing were used to elucidate the impact of the kissing bond on the microstructural and mechanical properties development. The fracture type, location, and morphology were studied for the various conditions. The results showed that the welding parameters had a substantial effect on the length of the kissing bond, which was found to decrease with the increase in the welding heat input, as estimated based on the rotation and feed speeds. Moreover, the length and morphology of the kissing bond had a significant influence on the tensile and fatigue fracture type. A shear fracture type was characteristic for welds showing high tensile properties and long fatigue life, whereas fracture along the kissing bond was characteristic for poor tensile properties and short fatigue life.

Experimental study on fatigue performance of high strength steel welded joints

Abstract: The welded joint of steel structure is prone to occur fatigue fracture under dynamic loads. In this paper, an experimental study on the fatigue performance of base material, butt weld, and cross fillet weld of high-strength steels were investigated. The S-N curve was fitted, and the corresponding fatigue life was predicted. Results corroborate that the base material of high-strength steel possess high fatigue resistance. AISC360 and EC3 standard design curves are applicable for the evaluation of the butt weld fatigue performance of Q460D and possess adequate safety margin, but only suitable for low-fatigue life estimation of Q690D butt weld. With respect to cross fillet weld, AISC360 design curve not only is suitable for the fatigue life analysis of Q460D and Q690D but also has enough safety margins, while EC3 and BS7608 codes possess relatively low fatigue limit. In addition, a quantitative analysis on fatigue fracture was conducted on the basis of fatigue damage theory, and the fatigue crack propagation law was disclosed on the basis of fracture morphology. The crack propagation law before instant fracture is consistent with damage development, and the fatigue striation width increases gradually with damage development. The fast crack propagation stage accounts for a small proportion in the fatigue life, thereby indicating that this stage is insufficiently developed.

Effect of SiC and TiC nanoparticle reinforcement on the microstructure, microhardness, and tensile performance of AA6082-T6 friction stir welds

Abstract: During the last decade, friction stir welding has various applications in the automotive, shipbuilding, and aerospace industry due to its versatility. More recently, there have been trials to combine FSW with ceramic nanoparticle reinforcement in order to form MMCs locally on the weld line. This combination could result to potential applications on the above industries. In the present study, optical and electron microscopy, as well as microhardness and tensile testing, were used in order to determine the effect that SiC and TiC nanopowders have on the weld nugget of AA6082-T6 butt welds. It is the first time that such a thorough study via TEM in combination with EDS was conducted for this alloy. Emphasis was given on the distribution of dislocations and on the presence of the intermetallic and reinforcing particles in the weld. It was found that the grain size of all the specimens was dramatically decreased due to the dynamic recrystallization phenomenon. This also provoked the dilution of a lot of the intermetallic particles of the base metal and the multiplication of the dislocations. Between the two reinforced specimens, the SiC presented higher elongation while the TiC presented higher microhardness.

Exploring the hybrid metal extrusion and bonding process for butt welding of Al–Mg–Si alloys

Abstract: The hybrid metal extrusion and bonding (HYB) process is a new solid-state joining technique developed for aluminum alloys. By the use of filler material addition and plastic deformation sound joints can be produced at operating temperatures below 400 °C. The HYB process has the potential to compete with commonplace welding technologies, but its comparative advantages have not yet been fully explored. Here, we present for the first time the results from an exploratory investigation of the mechanical integrity of a 4-mm AA6082-T6 HYB joint, covering both hardness, tensile and Charpy V-notch testing. The joint is found to be free from defects like pores, internal cavities and kissing bonds, yet a soft heat-affected zone (HAZ) is still present. The joint yield strength is 54% of that of the base material, while the corresponding joint efficiency is 66%. The indications are that the HYB process may compete or even outperform conventional welding techniques for aluminum in the future after it has been fully developed and optimized.

Influence of magnetic field orientation on molten pool dynamics during magnet-assisted laser butt welding of thick aluminum alloy plates

Abstract: An externally applied magnetic field has been proved effective in controlling the molten flow behavior during the laser beam welding. This paper reveals how a magnetic field applied in different orientations influences the weld pool dynamics during the full-penetration laser butt welding of thick aluminum alloy plates. A multi-physics coupling model was developed and numerically solved by considering the electromagnetic interaction between static magnetic field and magnetofluid. The dynamic and electromagnetic information within the weld pool were predicted and comparatively analyzed. The results show that Lorentz force and Hartmann effect induced in magnet-assisted weld pool are quite sensitive to magnetic field direction. The horizontally directed magnetic field leads to limited Hartmann effect by inducing additional molten vortexes, while the field aligned vertically to aluminum surface can obviously reduce the molten flow velocity and weaken the Marangoni convection. The work can provide a reference in optimizing the operating parameters when an electromagnetic system is employed to improve the welding quality.

Weld bead recognition using laser vision with model-based classification

Abstract: Weld bead recognition is important for providing information for automatic control of welding process and also for post-weld inspection. Bead geometry profiles can be measured by a laser-line profile sensor projecting a laser line onto the welding surface and receiving the reflection to calculate the height of the surface. As the bead is usually very small, it may be easily covered by the sensor noise or distorted by the bending of the work pieces after welding. In addition, it is difficult to estimate the parameters of bead width and bead height while moving the laser sensor to cover a 3D surface, since the movement may cause unstable measurements. This work investigates using a model-based classification method to automatically segment the bead from the welding surface regardless of the distance and the angle of the scanner to the welding surface. It firstly uses a polynomial model together with the Expectation-Maximisation (EM) algorithm fitting into the distance profiles measured by the laser sensor, and then automatically removes the surface curvature. Consequently the shape of the bead can be easily extracted from the welding surface by applying a small value of threshold depending on the noise level of the data. Experimental results show that the Butt welding bead parameters of bead width and height can be extracted successfully. The method is robust to the bending of the welding surface and the unstable movement of the laser sensor.

Studying heat-affected zone deformations of electric arc welding

Abstract: The paper studies the influence of the most common defects in permanent electric arc welds made during the welding butt joints in infield oil pipelines, onto the strength characteristics of the welded pipe material around the heat-affected zone. A specimen of a butt weld with an obvious defect was used as a subject of the study. The changes in the geometric parameters of the weld were measured with the standard means; Rockwell hardness in the heat-affected zone was determined in certain areas with justification for the weld process modes. The cause of softening was found to be an increased width of the hot spot on the one side of the weld, where an enlarged crystalline structure appears as a result of the pipe material recrystallization under the influence of heat. Changes in the geometry of the thermal action area are determined by accumulation of molten filler on the one side of the weld when the welding rate is decreased. Some recommendations are given to prevent destruction of the welded structures and appearance of emergencies in infield oil pipelines.

Fatigue crack propagation for Q345qD bridge steel and its butt welds at low temperatures

Abstract: Steel bridges fabricated with Q345qD steels face critical challenges when operating in cold regions with a low ambient temperature. This study aims to investigate, via an experimental program, the low-temperature fatigue crack propagation behavior of Q345qD bridge steel base material and its butt welds. The testing program comprises a series of Charpy impact tests and fatigue crack propagation tests at the room temperature, −20°C and −60°C. The experimental results demonstrate a reduced crack propagation rate in the base material, but an increasing crack propagation rate in the butt welds, with a decreasing ambient temperature. The base material also shows enhanced fatigue crack propagation thresholds with the decreasing temperature. The ductile-to-brittle transition temperature for fatigue is lower than that for fracture in the base material while the weld metal exhibits an opposite trend. Generally, the butt welds present higher resistance against fatigue crack propagation and larger Charpy toughness values than do the base material at all tested temperatures. The Paris-law parameters measured at the room temperature for the base material leads to a conservative assessment of the crack propagation life for a welded joint under a low ambient temperature.

Friction stir butt welding of strain-hardened aluminum alloy with high strength steel

Abstract: Dissimilar metal joining is challenging because of intermetallic compound (IMC) formation. Solid state welding techniques provide an opportunity. 5083-H116 aluminum alloy and HSLA-65 steel sheets were butt welded by friction stir welding. Joint strength and failure position were determined by IMC thickness and stress concentration at welded interface.

Analysis of welding residual stress formation behavior during circumferential TIG welding of a pipe

Abstract: The objective of this study is to analyze the formation behavior of welding residual stresses during the circumferential TIG butt welding of pipes. A three-dimensional thermo-elastic-plastic numerical model has been developed by using MSC-Marc software to predict welding residual stress distributions during single-pass welding of pipes. Using a numerical computational approach, the mechanisms of the changes in stress and strain throughout the pipe welding process is described. Compared with the features of butt welded plate joints, the distribution of welding residual stress in butt welded pipe structures is obviously different. Considering the deformation effect on the plastic strain distribution, the calculation results indicate that the axial and hoop compressive plastic strain at the inner surface of welded pipes is much larger than that at the outer surface. As a result, the tensile axial and hoop residual stress is generated at the inner surface due to the thermal contracting deformation. Consequently, compressive axial residual stress occurs at the outer surface because of the inward contracting deformation and internal stress self-balance. Moreover, it is investigated and explained the phenomenon in which both axial and hoop residual stresses have sharp gradients near the weld stop location at the overlapped weld line of pipe. Because of redistribution of axial residual stresses and hoop plastic flow behaviors, residual stresses near the weld stop location could be changed.

Validation of numerical simulations with X-ray diffraction measurements of residual stress in butt-welded steel plates

Abstract: The present work investigates experimentally and numerically the residual stress induced in the surface of thin steel plates subjected to single pass butt welding. First, the temperature history is...

Data mining in resistance spot welding

Abstract: Resistance spot welding is the dominant process in the present mass production of steel constructions without sealing requirements with single sheet thicknesses up to 3 mm. Two of the main applications of resistance spot welding are the automobile and the railway vehicle manufacturing industry. The majority of these connections has safety-related character and therefore they must not fall below a certain weld diameter. Since resistance spot welding has been established, this weld diameter has been usually used as the gold standard. Despite intensive efforts, there has not been found yet a reliable method to detect this connection quality non-destructively. Considerable amounts of money and steel sheets are wasted on making sure that the process does not result in faulty joints. The indication of the weld diameter by in-process monitoring in a reliable way would allow the quality documentation of joints during the welding process and additionally lead through demand-actuated milling cycles to a substantial decrease of electrode consumption. An annual, estimated reduction in the seven- to nine-figure range could be achieved. It has an important impact, because the economics of the process is essentially characterized by the electrode caps (Klages 24). We propose a simple and straightforward approach using data mining techniques to accurately predict the weld diameter from recorded data during the welding process. In this paper, we describe the methods used during data preprocessing and segmentation, feature extraction and selection, and model creation and validation. We achieve promising results during an analysis of more than 3000 classified welds using a model tree as a predictor with a success rate of 93 %. In the future, we hope to validate our model with unseen welding data and implement it in a real world application.

Effect of groove depth and plunge depth on microstructure and mechanical properties of friction stir butt welded AA6061-T6

Abstract: In the present study, a backing plate that characterized by an arc groove was employed in the friction stir butt welding of AA6061-T6 aluminum alloy in order to eliminate root flaws. The effect of ...

Butt Welding of Round Drive Belts

Abstract: Abstract The on-going rapid development of industry encourages development of new production technologies and designing of machines that use inventive mechanical engineering solutions, a big demand for parts of such machines being a natural consequence. Polymeric power transmission belts are a good example of that. This paper proposes an improvement in the process of production of such belting. Their production includes cutting to length and splicing of elastic round belts to obtain endless belts of the specified length. This is the key phase of the whole production process. A number of splicing methods are available using different physical phenomena. One of them is butt welding technique. In this process heat is applied on the material through an additional heating element called the heat platen. The effect depends on several factors, including preparation of the work pieces. Due to its characteristics the process is often carried out by hand. The need for automated manufacturing was created by important factors associated with manufacturing on an industrial scale: cost, time and quality. The proposed butt welding machine, complete with a control system is an answer to this need. The practical benefits include improved repeatability of splices, time savings and less work load for the operator.

Dissimilar Friction Stir Butt Welding of Aluminum and Copper with Cross-Section Adjustment for Current-Carrying Components

Abstract: Manufacturing dissimilar joints of aluminum and copper is a challenging task. However, friction stir welding (FSW) was found to be a suitable technique to produce aluminum–copper joints. Due to different electrical conductivities between aluminum and copper, an adjustment of the cross-section is required to realize electrical conductors free of resistive losses. Taking this into account, this paper presents initial results on the mechanical and electrical properties of friction stir butt welded aluminum and copper blanks having thicknesses of 4.7 mm and 3 mm, respectively. Three different approaches were investigated with the aim to produce sound welds with properties similar to those of the used base materials. Friction stir welding has been conducted at a welding speed of 450 mm/min. Subsequently, the welded specimens were subjected to metallographic analysis, tensile testing, and measurements of the electrical conductivity. The ultimate tensile force of the best joints was about 10 kN, which corresponds to joint efficiencies of approximately 72% of the aluminum base material. The analysis of electrical joint properties led to very promising results, so that the potential of FSW of Al–Cu butt joints with sheets having different thicknesses could be confirmed by the investigations carried out.

Evaluation of multi-pass welding-induced residual stress using numerical and experimental approaches

Abstract: In the present work the welding-induced residual stresses in steel plates, due to multi-pass welding are investigated numerically and experimentally. The transient finite element model is developed...

Magnetic pulse welding: machine optimisation for aluminium tubular joints production

Abstract: Magnetic pulse welding (MPW) has recently been increasingly investigated for specific dissimilar material joining applications since this is a solid state clean process, with good energy efficiency...

Thermal Analysis Simulation for Laser Butt Welding of Inconel625 Using FEA

Abstract: Laser welding process is employed in the manufacturing of critical components where the final assembly units necessitate strict tolerances like low distortions and residual stresses. Laser beam welding offers several advantages like low heat input, very narrow heat affected zone, low residual stresses, low distortions and good mechanical joint properties in the weld joints when compared to the conventional techniques like Tungsten Inert Gas Arc welding processes. However, the implementation of laser beam welding holds certain challenges like process parameters optimization, experimental set-up and handling and expensive costs. In order to minimize the complex experimental process, simulation techniques using Finite Element Methods (FEM) are employed in order to estimate the heat input and weld process optimization prior to the experiments. This greatly helps in the optimization and estimation of the incurred stresses and distortions with the adapted weld process with known input weld process parameters. The present work reports the Gaussian heat source model for the laser welding of Inconel 625 Alloy plates. The developed moving heat source model is presented and demonstrated with the thermal profiles in terms of the thermal histogram, temperature profiles in the joint cross sections through welded region, interface across the joints.