Weld Length Research Articles

Path planning of spot welding robot based on multi-objective grey wolf algorithm

The path planning of traditional spot welding mostly uses manual teaching method. Here, a new model of path planning is established from two aspects of welding length and welding time. Then a multi-objective grey wolf optimization algorithm with density estimation (DeMOGWO) is proposed to solve multi-object discrete problems. The algorithm improves the coding method and operation rules, and sets the density estimation mechanism in the environment update. By comparing with other five algorithms on the benchmark problem, the simulation results show that DeMOGWO is competitive which takes into account both diversity and convergence. Finally, the DeMOGWO algorithm is used to solve the model established of path planning. The Pareto solution obtained can be used to guide the welding sequence of body-in-white(BIW) workpieces.

Effect of Preheating on Hot Cracking Susceptibility in Pulsed Laser Welding of Invar Alloy

Hot cracking is a serious problem in welding of Invar alloy. The weld hot cracking susceptibility of Invar was evaluated using pulsed laser welding on fish-bone sheet experiment. The pulse wave consisted of preheating pulse and welding pulse. Hot cracks that formed along the grain boundary propagated from the weld upper surface to the inside. The experiments show that adding a preheating pulse can effectively reduce the hot cracking susceptibility of Invar alloy. Finite Element Modeling (FEM) calculations and experimental measurement results show that the welding temperature gradient and cooling rate decrease with increasing preheating pulse duration. However, as the preheating pulse duration increases, the hot cracking susceptibility of the Invar alloy does not decrease all the time, but decreases first and then increases. This is because the increase of heat input leads to the increase of shrinkage plastic strain when the preheating pulse duration increases. The maximum tensile strength of the butt welded joint of the Invar alloy was 467.3 MPa, which is 92.3% of the base metal when the preheating pulse duration is 3 ms. Introduction The Invar alloy is widely applied in precision measurement devices and low temperature resistant structures for its low thermal expansion coefficient, which is less than 1.6 X 10-6 k-1, about 1/10 of low-carbon steel, and it changes very little within large temperature range (Park et al. 2011; Oh et al. 2014; Qiu et al. 2016). With the increase demand for natural gas, liquefied natural gas (LNG) carriers are being built to support long-distance transport. Invar is used for primary and secondary barriers on the containment insulation system of membrane-type LNG carrier. The Invar membranes have thickness of .7 mm are directly in contact the -163°C LNG (American Bureau of Shipping 2006; Bureau Veritas 2011; Zhao et al. 2013; Zhao et al. 2015; Zhao et al. 2019). The total weld length of Invar alloy can reach up to 100 km according to the statistics on a 13 million cubic meter LNG carrier.

Laser micro welding with fiber lasers for battery and fuel cell based electromobility

New challenges are arising within the joining processes in the field of electromobility. Joining highly reflective metals and dissimilar materials such as copper and aluminum – often encountered in battery electrical vehicles – is viewed as a challenging task. Additionally, the use of thin sheets of stainless steel is gaining importance in applications with PEM fuel cells, where the welding length is sometimes up to and even more than five meters long, yet the process speed remains limited.Laser micro welding offers in comparison to conventional joining methods several advantages regarding process speed, parts accessibility, potential of automation, and particularly localized heat input. There are different types of lasers available on the market ranging from the visible to the infrared range, yet choosing the right laser depending on the task can be challenging. Several characteristics are considered when comparing weld quality such as surface finish, reproducibility and mechanical stability. Recently, the possibility of tuning the parameters of a nanosecond pulsed fiber laser to achieve welding is being examined. On another topic, using a novel welding strategy with spatial power modulation – by applying a new geometry – is also being investigated. In this paper, the welding process with the nanosecond pulsed fiber laser is evaluated based on mechanical stability and surface finish, which allows further insight into the suitability of such a method for welding particularly copper and aluminum materials. Additionally, some initial results from the here introduced spatial power modulation technique – used to weld stainless steel sheets – are presented.

Constructive and technological method of increasing durability of “choke connections”

Welded circular seams of “choke joints”, as a rule, have deviations from the specified diameter. This leads to uneven deformation, and sometimes to the absence of deformations in some areas of the seam. With repeated static loads, destruction arises in these places. To connect to the maintenance system of connections with the base metal, used as a guide, surface plastic deformation of the zone zone is carried out. A technology and equipment have been developed that allow plastically deforming the area of transition from the weld to the base metal along the entire length of the circular weld. As a result of plastic deformation along the technological groove, the characteristics of low-cycle fatigue of welded joints are obtained, which are not inferior to the base metal. To reduce stresses in the zone of transition from the weld to the base metal, it is proposed, first, to perform a circular groove on the base metal by machining, as close as possible to the specified zone. To assess the influence of the shape and size of the groove on the stress-strain state of the zone of conjugation of the weld metal with the base metal, FEM calculations were carried out

A systematic study on the effect of coating type and surface preparation on the wettability of Si-Bronze brazing filler material on GI and GA-coated DP600

Zn-coated advanced high strength steels are popular in the automotive industry due to their excellent combination of mechanical strength and ductility as well as superior corrosion resistance provided by the Zn-coating – with hot-dip galvanized and galvannealed coatings being the most popular. Gas metal arc brazing technology is a non-fusion joining method, proposed as an alternative to the gas metal arc welding process due to several advantages: The arc-brazing process delivers significantly lower heat input to the substrate, which minimizes the Zn-coating burn-off leading to higher corrosion protection for the joined parts, and reduces the HAZ softening phenomenon which affects the mechanical integrity of the substrate, while at the same time reduces welding defects such as porosity and blowholes. The strength of an arc-brazed joint depends on the spreading of the molten filler material over the joint to create a bond between the parts as the molten braze solidifies. Existing literature on the subject suggests that heat input is the main driving factor controlling the wettability of the molten braze material with the type of shielding gas used also having an effect. However, the influence of different types of Zn-coatings and their respective surface condition (i.e., clean, or unclean) on the wettability of Cu-based molten braze materials during arc-brazing has not been investigated. The present work investigates the effect of surface morphology of galvanized and galvannealed DP600 steel in the as-received and plasma cleaned conditions on the wettability of molten Si-Bronze (CuSi3Mn1) brazing filler material in the bead-on-plate configuration. The findings of this work clearly demonstrate that the type of coating and its surface condition has a significant effect on the spreading of the molten filler material and on the growth of the intermetallic compound layer at the joint interface and therefore, should be taken into consideration as a factor that can impact the efficacy of an arc-brazed joint. • Evaluating surface morphology of different Zn-coatings to calculate their surface free energy. • Establishing a clear link between the surface roughness of Zn-coated steels on the wettability of molten Si-Bronze filler material. • The study shows that the wettability of the molten filler material is also affected by the presence of organic contaminants on the coating surface. • This work shows the relevance of surface morphology in controlling the wetting length of weld brazed joints. • The thickness of the intermetallic compound layer at the braze interface can be controlled by using oxygen plasma cleaning.

Assessing profile damage of uncoated and AlTiN coated FSW tools after successive travel on AA6061-T6 plate

The quantitative assessment of profile damage of square (SQ) and threaded with three intermittent flat faces (TIF) tool pin was appraised and presented for both uncoated and AlTiN coated tools during friction stir passes on AA6061-T6 plates successively after different travel lengths. Significantly lower profile damage with small amount of profile twisting was noted for TIF tool pin as compared to the SQ tool pin owing to lower force and torque, as predicted by finite element (FE) results. For AlTiN coated tools, the pin profile damage reduced significantly due to high wear resistance, hardness and good adhesion of coating with the tool substrate. Significantly lower temperature rise was noted in the AlTiN coated tool compared to the uncoated tool. A mathematical approach to predict the heat generation was presented and predicted temperatures were found in good agreement with FE results. Plastic deformation of sharp corners, adhesion and abrasion wear of flat faces, and initiation of crack near tool pin-shoulder interface was noted in uncoated tools however, they got reduced in the AlTiN coated tool. The delamination of coating near the tool pin edge, flat surfaces and near the tool pin-shoulder interface was noted due to dislodging of adhered work material. Fairly uniform tensile strength and flexural load were obtained after different weld lengths for AA6061-T6 FSW joints prepared with the AlTiN coated TIF tool pin.

Determination of LME sensitivity of zinc-coated steels based on the programmable deformation cracking test

The current work presents a new test method to evaluate liquid metal embrittlement (LME) susceptibility of zinc-coated steels in arc processes under application-oriented conditions. The procedure is based on the programmable deformation cracking test (PVR test). The PVR test is a variation of a controlled tensile test for hot cracking investigations in arc welding processes. Two dual-phase steels (DP600, DP980) and five transformation-induced plasticity steels (TRIP690, TRIP700, TRIP700, TRIP1100, TRIP1200) were used. The investigations showed that comparable thermo-mechanical loading conditions can be guaranteed for materials of different sheet thicknesses in the PVR test through a targeted adjustment of the heat input per unit length of weld. Furthermore, it was shown that the critical deformation rate {v}_{cr} (used for assessing hot cracking susceptibility) may also be used to assess the LME susceptibility of a particular steel. Furthermore, another LME susceptibility parameter, the relative reduction in load-bearing ability DeltaSigma could be derived, which may be used to understand how LME cracking affects materials’ mechanical and fracture properties.

Methods for increasing the productivity of polymer films ultrasonic welding

ABSTRACT Determined that with increasing length of contact butt welding of the waveguide linearly increases the speed and performance of seam welding. The use of low-power piezoelectric transducers for ultrasonic welding of polymer films with bilateral extraction of energy from the transducer improves the performance and efficiency of the welding process.

A Study on the Shear Lag Effects in Longitudinally Welded Connections Subject to Eccentricity

AbstractIn United States design specifications, shear lag in longitudinally welded connections is accounted for by means of a tabulated factor, which until 2010 was only applicable to plate‐type members having equal length welds on each side, subject to the further constraint of having a minimum weld length equal to the distance between the welds. This created the paradox that connections with longitudinal welds shorter than the distance between the welds were considered by the Specification to have no capacity at all. Research in extant literature based on historical experimental data developed alternative factors that augmented and replaced the previous approaches, making them applicable to longitudinally welded plates, angles, channels, tees, and wide‐flange shapes having equal or unequal weld lengths, and without any weld length‐to‐connection width limitation. This paper presents the results of an experimental study of shear lag effects in longitudinally welded tension members under both in‐plane and out‐of‐plane eccentricity. Forty specimens were tested representing twenty configurations and the experimental results were compared to three theoretical values – (a) the shear lag factor from the 2016 American Institute of Steel Construction (AISC) Specification, (b) the shear lag factor based on a bi‐planar model found in literature, and (c) the shear lag factor from the 2010 AISC Specification. It is concluded that the shear lag factor provided in the 2016 AISC Specification offers the best prediction of the capacity of longitudinally loaded welded connections subject to both in‐plane and out‐of‐plane eccentricity.

A Cooks Distance Approach to Control the Haz and Arc Length of Tig Mild Steel Weld

The heat affected zone and arc length parameters have a vital role to play in determining the integrity of a weld structure. The cooks distance is a statistical diagnostic employed in this study to select the best optimum combination of welding process parameters. Mild steel plate was the choice material used to produce the weld specimen, which was welded with the Tungsten inert gas method. The RSM model was used to develop an optimal solution that can explain the behavior of the welded joint with respect to the heat affected zone and arc length, different diagnostic techniques were employed which includes the normal probability plot and cooks distance plot. The model developed has sufficient merit as the results obtained shows that the cooks distance values is within the range of 0 and 1 indicating the absence of outlier in the data making the optimal solution highly acceptable.

A Cooks Distance Approach to Control the Haz and Arc Length of Tig Mild Steel Weld

The heat affected zone and arc length parameters have a vital role to play in determining the integrity of a weld structure. The cooks distance is a statistical diagnostic employed in this study to select the best optimum combination of welding process parameters. Mild steel plate was the choice material used to produce the weld specimen, which was welded with the Tungsten inert gas method. The RSM model was used to develop an optimal solution that can explain the behavior of the welded joint with respect to the heat affected zone and arc length, different diagnostic techniques were employed which includes the normal probability plot and cooks distance plot. The model developed has sufficient merit as the results obtained shows that the cooks distance values is within the range of 0 and 1 indicating the absence of outlier in the data making the optimal solution highly acceptable.

Effect of filler wire strength on high strength low alloy steels

Fusion welding of Ti-Nb microalloyed steels often leads to softening in the heat affected zone (HAZ) due to weld thermal cycles. Apart from heat input and width of HAZ, selection of filler wire also plays an important role, to achieve the minimum strength requirement of the parent material. Steel plates with 800 MPa ultimate tensile strength were butt welded using pulsed gas metal arc welding (P-GMAW) process, with undermatching, matching and overmatching strength filler wires. Welding parameters were selected in such a way that the heat input per unit weld length is almost constant. In all the samples, microstructural features were similar in the HAZ region. Static tensile tests indicated that failure in the samples welded using undermatching filler occurred at welded region, whereas the samples welded with matching and overmatching fillers failed at HAZ region. Further fracture studies indicated that, in case of under matching filler wire samples, crack propagates along the Widmanstatten ferrite present in the weld zone, whereas in other two samples, crack initiated at coarse TiN – matrix interface in the HAZ region. This study shows that overmatching fillers are recommended to overcome strength loss due to HAZ softening.

Feasibility of slotted end connections improved with thicker sections in tension: Experimental and numerical investigation

Gusset plate slotted end connections are effective and convenient techniques for connecting tubular members in building structures. A net section crack is the dominant failure mode found in conventional slotted end connections unless strengthening measures are adopted. The improved connection involves a thick-walled circular hollow section (CHS) set at both ends of the member to increase the area of the net section. A series of laboratory tests and associated numerical models were conducted to investigate the mechanical performance of the improved slotted end connection under axial tensile loading. The load-displacement relationship, stress distribution characteristics, and typical failure modes are all incorporated and discussed. Different from tear-out failure or net section crack failure in a conventional connection, the improved connection shows gross section cracks after experiencing extensive gross section yielding. The improved connection enables the length of the fillet weld (LW) to be greatly reduced without causing a reduction in the load-bearing capacity. With the gradual increase in the length of the fillet weld (LW = 60, 90, and 120 mm), the axial load-bearing capacity of the improved connection is approximately 34.6%, 15.8%, and 4.9% higher than that of the conventional connection, respectively. From the validated FE analysis, the local stress concentration near the slot end can be reduced by approximately 50%, and the shear lag has little effect on the strength of the net section. The load-bearing capacity, ductility, and failure modes of the improved connection show better performance than those of the conventional connection.

A study of the mechanical behavior of rectangular steel tubular column strengthened using intermittent welding angle steel

From the perspective of the development of steel structures in China, the existing steel structure had experienced decades of service. However, due to the change of its functionality, and the erosion caused due to the surrounding environment, reinforcement of steel has become necessary. Thus, the research on reinforcement theory and methods of the existing steel structures has become an important measure in the “reinforcement period”. Steel angle welding on the surface of steel columns is a common method used in practical engineering. However, the traditional continuous welding angle steel reinforcement of rectangular steel pipe columns leads to a large amount of welding work on the construction site, thus prolonging the construction time and increase the project cost. Moreover, the quality of welding also cannot be guaranteed. Therefore, in order to reduce the cost of field welding and reinforcement of the construction project, intermittent welding is proposed in this work. In this paper, the finite element analysis of rectangular steel tube column models that were strengthened using different intermittent welded angle steel under axial and eccentric compression is discussed out and the results are compared with the experimental results for validation. Further, a large number of numerical models with different parameters are analyzed. From the analysis, the ultimate bearing capacity and the load transfer mechanism of the rectangular steel tube columns that were strengthened using intermittent angle steel under eccentric and axial compression are studied, and the optimal weld spacing and weld length are obtained. The results provide a theoretical base for future practical engineering applications.

A study on simulation analysis for laser-welded I-core sandwich plate with different material properties and T-joint weld characteristic

Stiffness and strength of sandwich plate vary depending on similar (SI) or dissimilar (DSI) material element (faceplate or core) and laser weld geometry. The issues of I-core sandwich plate characteristics are essential to attain practical sandwich plate application. Hence, research on different material properties and T-joint weld characteristics of I-core sandwich steel plate presents a positive understanding of various character factors that affect sandwich plate bending performance. In this paper, the I-core sandwich steel plate characteristic was investigated using finite element analysis (FEA). The 3-point bending with a fine meshing, interaction of elements, and load applied was kept constant. The partition size at the laser weld geometry is smaller, and the partition size continuously grows when further away from the weld geometry. The result shows that a combination of weak and strong material on either element will reduce I-core sandwich's stiffness and strength unless strong material is assigned at the faceplate and core. Moreover, there is a significant change when rootgap is present. This influencing the centric and eccentric of the weld. The weld width produces a perfect bending as wholesome T-joint, yet to achieve such traits is impossible in reality but possible when the weld length is closer to the length of the core. The exploration of these characteristics in response to I-core sandwich steel plate holds a good response in engaging for the multiple variables that affect the plate's stiffness and strength.

Influence of Copper Interlayers on the Magnetic Pulse Welding Process between Aluminum and Steel

Magnetic pulse welding (MPW) is a promising joining technology for the large-scale production of dissimilar metallic joints. Although the heat input is comparatively low, the temporary occurrence of high temperatures in the joining gap was found to play an important role during the joint formation. It is possible that the melting or even the boiling temperature of the involved materials will be exceeded, and fusion welding will occur. The purpose of this study is to investigate the influence of target materials with different thermal properties on the joint formation and weld seam characteristic. Therefore, MPW between steel targets and aluminum flyers was performed with and without copper coatings on steel. The lower melting temperature of copper compared to steel had no significant effect on the appearance of the mixed zones in the interface and the amount of molten target material or aluminum, respectively. Nevertheless, the comparison of the higher impact energies showed, that the copper interlayer can lead to a decrease in the weld length or a degradation of the weld quality due to an extended intermetallic phase formation or cracks. This result is important for the parameter adjustment of magnetic pulse welding processes.

Finite element analysis of stress and distortion for welding reinforced structure of angular steel

A 3-D finite element model of residual stress and distortion in welded structure with square section for angle steel is developed based on thermal-elastic-plastic theory. The residual stress and deformation for welded structure under different conditions are calculated and their distribution characteristics are comparatively analyzed. Results show that, relatively larger stress is generated in and near the weld zone for the welded joint. With an increase in weld length, both equivalent stress and residual distortion increase accordingly, but the effect of weld length on welding residual stress is limited. Under the conditions of 20 mm, 50 mm and 100 mm long welds, the deformations of the three reinforced structures caused by 15000 Pa external load are 4.80mm, 4.79mm and 4.78mm respectively, indicating they have the similar bearing capacity.

Fatigue fracture assessment of 10CrNi3MoV welded load‐carrying cruciform joints considering mismatch effect

AbstractFatigue experiments and numerical simulations based on the linear elastic fracture mechanics (LEFM) theory were conducted on the evenmatched (EM) and undermatched (UM) 10CrNi3MoV load‐carrying cruciform welded joints (LCWJs). The study firstly experimentally investigated the fatigue crack growth rate (FCGR) of base metal, EM, and UM weldments. The corresponding Paris parameters as essential input data are provided to assess the fatigue crack propagation behavior for weld toe and weld root failure caused by notch stress concentration variations. On the one hand, the stress intensity factors (SIFs) at weld toe and weld root were calculated considering the effects of LCWJ specimen geometries, initial crack types, and sizes. The comparisons between simulated results and standards analytical solutions were executed, which exhibit good accordance. It proved that the fatigue fracture simulation procedure based on LEFM is appropriate for the fatigue assessment of LCWJs. Eventually, it conducted the parametric analysis by predicted S–N curves, which included in the weld length, initial crack shape, initial crack size, penetration length, and materials fracture parameter, to explore some safety assessment reference lines for both failure modes of LCWJ.

Comparison of tool wear during friction stir welding of Al alloy and Al-SiC metal matrix composite

Aluminum matrix composites have received considerable attention due to their high specific strength and specific stiffness, high hardness, and wear resistance along with being light in weight. These composites are preferably joined using friction stir welding process. The major concern in friction stir welding is the wear of the welding tool pin which is the backbone of the process. The wear is due to the prolonged contact between the tool and the harder reinforcements in the composite materials. The present work deals with the study of tool wear and its surface roughness with respect to different selected friction stir welding parameters such as rotational speed, transverse speed, length of weld, and different composition of Aluminum composite. It was found that the total amount of material removed from the tool and the surface roughness of the tool is in direct proportion to the rotational speed of the tool and the length of the weld but inversely proportional to the transverse rate. The increase in wt.% of SiC reinforcement leads to the higher tool wear but reduces the surface roughness of the tool.

Fatigue life evaluation of deck to U-rib welds in orthotropic steel deck integrating weldment size effects on welding residual stress

Fatigue of orthotropic steel decks (OSDs) has significantly limited the service life of such structures, and the welding residual stress (WRS) has been reported as a prominent factor that should be considered in their fatigue life evaluations. However, the weldment size effect on WRSs is often neglected in the conventional evaluation. This paper performed fatigue life evaluations of deck to U-rib welds in an OSD integrating the weldment size effects. First, the concept and hypotheses of the weldment size effect on WRSs were outlined in detail. Second, the sequential coupling method was selected for the WRS simulation, which was then experimentally verified using the blind hole method. Third, the influences of longitudinal and transverse weldment sizes on WRSs were analyzed by comparing the simulated WRS results corresponding to welding structures with different longitudinal sizes and U-rib numbers, respectively. Finally, fatigue life evaluation of the welds was conducted based on a modified S-N curve. The results show that (1) the WRSs at the welds can be accurately simulated through the adopted thermal-structural sequential coupling method; (2) the weldment size has a definite influence on the local distribution of WRSs: the WRS decreases exponentially with the increase of the longitudinal welding length; (3) the proposed method, which integrates the size effect on WRSs with the life evaluation, provides a relatively reasonable fatigue life for the deck to U-rib welds. In summary, the findings of this study enhance our understanding of the distribution laws of WRSs in OSDs, and suggest that it is vital to integrate the weldment size effects on WRSs in the process of accurately predicting fatigue life.