In order to achieve lower CO
2
emissions and lower fuel consumption, modern motor vehicle industries have been reducing automotive weight with an increasing degree in the past years by replacing ...steel structures with brazed and welded components of steel and lightweight metals. In this context, the combination of galvanized steel and aluminum admits considerable application potential. Joints of the two cited different types of materials can be produced by partial brazing, through the Cold Metal Transfer (CMT) process with addition of zinc-based wire alloys. However, stability analysis for this process is still not well understood. Most papers focus on metallurgical characteristics such as intermetallic phase formation and joint strength. In order to assess stability, bead on plate samples made of ZnAl
4
deposits on an automotive DX56D + Z140 galvanized steel was statistically correlated to current and voltage oscillograms as well as high-speed images, after variation of the IBoost parameter from 30 to 150 A. Short-circuit and arc burning times were acquired and used to compute the Vilarinho Regularity Index for Short-Circuit Transfer (IVsc), which is based on variation coefficients. The lower the IVsc, the more stable is the metal transfer. The index was used to assess bead homogeneity. The results pointed that bead homogeneity was found only for IBoost values below 97 A. However, stability was reached for IBoost levels of 97 A (with homogeneous bead) and 150 A (without homogeneous bead). This means that to determine homogeneity, the metal transfer stability, determined through IVsc, is an indicator, but other factors such as current level and its effects over the melt pool must also be considered.
Despite the industrial relevance of LASER welding, determination of sustainable parameterization is still a challenge. Trial and error, or even not totally justified methodologies, are frequently ...applied on LASER welding parametrization. This approach potentially leads to a decrease of the process tolerance and, consequently, increasing the likelihood of imperfections, which means extra operational time and raising of the final cost. The present paper addresses a comparative discussion about five factors experimentally determined and frequently used to predict depth of penetration in LASER welding. The experiments were performed with a 10-kW fiber LASER. In a first batch, power was varied while welding speed was fixed at 1 m/min. In a second batch, welding speed was varied and power was kept at 10 kW. The first demonstrated concern on using these popular factors is the definition and quantification of LASER energy. For evidencing this aspect, two samples were processed with the same welding energy of 120 kJ/m, yet resulting in completely different penetrations. Eventually, an empirical model based on power as a factor allowed a more reliable prediction of the depth of penetration.
To meet the growing demands of various industries for materials that are not only highly resistant but also possess good mechanical properties at a reasonable cost, high strength low alloy steels ...(HSLA) have been developed. However, the low ductility associated with these steels can pose challenges in their application. Moreover, many components undergo gas metal arc welding, further highlighting the importance of ductility in steel conformation. The quest for an optimal heat treatment method capable of adjusting the mechanical properties to meet specific design requirements while enhancing the material’s ductility remains a critical issue. This study presents a comprehensive analysis of the microstructural and mechanical properties of a HSLA steel variant, DOMEX 460MC, subjected to three distinct heat treatment regimes: 400 °C, 580 °C, and 700 °C. Brinell hardness tests and microstructural analyses were conducted for each condition, alongside the evaluation of mechanical behavior through tensile testing following ASTM E8M-04 standards. The findings revealed that heat treatments at 580 °C and 400 °C notably improved ductility, while ductility remained consistent with the original steel at 700 °C. Furthermore, the heat treatment conducted at 580 °C exhibited the highest ultimate strength value among all heat-treated tested conditions.
Over the last years, a profusion of new versions of arc welding processes has overwhelmed the international welding scenario in the industry and academia. Innovations have been made possible not only ...by means of electronics and software developments but also through new concepts in mechanical design and mechanisms. With respect to the tungsten inert gas (TIG) process, low productivity is often a disadvantage, when compared to other arc welding processes. In order to manage this drawback, as well as to better deal with hard wetting materials (Ni-Cr alloys for example), a forward and backward wire oscillation movement has been implemented in TIG systems and finds good acceptability in the industry. However, dedicated wire feed measuring systems for this new operating regime are not available, which limits the process monitoring as a whole and hinders phenomena understanding and parametrization stage. The present paper thus addresses the development of a measuring methodology combined with a transducer, based on an optical encoder, for acquisition of instantaneous angular speed (IAS). The study covers analysis of the performance of previous instrumentation (found unsuitable), description of the dedicated system, and verification methodologies. Results lead to the validation of the system. Therefore, valuable information can now be extracted to provide feedback for this welding process version and avoid instabilities.
Welding processes are a fundamental part of modern engineering manufacturing. The simulation of materials joining techniques requires the application of thermal models capable of mathematically ...describing the applied heat source distribution. Many different approaches have been developed since the beginning of the CFD revolution. However, one of the most important published works regarding the review and detailing of heat source models was performed almost two decades ago. Hence, the present work was developed specifically focusing on organizing, cataloging, describing, and statistically quantifying the most relevant models already published, with a special focus on the techniques developed in the last twenty years. The reviewed approaches were individually listed concerning their most common applications and limitations. The gathered data includes classified details and condensed information about scientific references, the suitability of each model, and the welding heat source thermal modeling terminology. Additionally, each modeling form was geometrically illustrated in coupling with its equations for an enhanced description and comparison of the geometrical parameters and its expected resultant temperature distributions. The reviewed papers were quantified and statistically enumerated by modeling methodology, welding process type, and number of published works by year. The approaches were also organized chronologically and visually illustrated in a welding heat source modeling timeline. Lastly, the most relevant achievements of the last decades, the research trends, and possibilities for future review works in the field were discussed.
This study aimed to assess and to understand the effect of modulation frequency on weld bead porosity. A fiber laser source with a maximum power of 10 kW was used on SAE 1020 plates. A square wave ...modulation with pulse power at 4 kW and base power at 0 kW was applied, which resulted in a power average of 2 kW. Welding speed was set at 1 m/min, and frequency varied from 20 to 100 Hz. To analyze the pores, longitudinal cross-sections were prepared. The results indicate that the welds produced at low frequencies (20 Hz and 25 Hz) contained a significant amount of large spherical pores. On the other hand, a reduced number of smaller pores were found for high frequencies (50 Hz and 100 Hz). This can be correlated to the penetration depth oscillation, linked to the weld pool fluid flow and the keyhole collapse, which was greater at lower frequencies. In addition, other effects could be noted, such as the widening of the weld bead for low-frequency values, which can be beneficial when the process requires low geometrical tolerances and higher penetration depths for increased degrees of overlap at higher frequencies.
A thermal analysis in laser welding using inverse problems Magalhães, Elisan dos Santos; Paes, Luiz Eduardo dos Santos; Pereira, Milton ...
International communications in heat and mass transfer,
March 2018, 2018-03-00, Letnik:
92
Journal Article
Recenzirano
Odprti dostop
The heat flux inverse analysis is significantly affected by the heat flux distribution in laser welding simulation. This work proposed a different approach for the heat distribution which predicts ...the temperature and the weld bead in laser welding. The influence of the heat flux distribution in an inverse heat conduction problem applied on laser welding simulation is studied by comparing different heat distribution models. An inverse heat conduction algorithm based on the three-dimensional (3D) heat diffusion equation and the enthalpy function to model the phase change problem are used to estimate the heat flux under different heat distributions. The Time Traveling Regularization is applied with the Golden Section method to estimate the heat flux in the studied cases. The proposed cubic root and square root of the volumetric heat distribution presented a good agreement between the weld profile and the experimental temperatures. The heat rate estimation proves to be dependent on the heat distribution. The proposed methodology is an alternative to predict the weld bead profile and the thermal efficiency in low penetration laser welding.
The root pass represents a challenge for welders. Being the first pass of the joint, it requires full penetration and is more prone to metallurgical defects. There needs to be a balance between the ...forces acting on the molten pool to avoid incomplete penetration or burnthrough. Additionally, the hardness in the heat affected zone (HAZ) should not exceed 350 HV, beyond which there is susceptibility to cold cracking. When different thicknesses are present in the joints, it is often thought that greater thicknesses require higher welding energy (the ratio between power and welding speed). This has also been verified in the literature. The present work aims to test if it be possible to weld the root pass of four plates of different thicknesses (7 mm, 10 mm, 12.7 mm, and 25.4 mm) considering a similar welding energy. This would make the parameterization robust, as the welder would not need to change the welding energy to perform the process under different conditions. An experimental evaluation was conducted on shipbuilding steel ASTM A131 DH36 using the GMAW process, evaluating both the geometric characteristics of the weld bead and the microstructure at different thicknesses. Cooling rates were predicted based on an in-house finite volume method (FVM) computational code. The results indicated that although all welds met the main requirement of full penetration, the metallurgical requirement of a maximum hardness of 350 HV in the HAZ was only achieved at thicknesses of 7 mm and 10 mm. This occurred because, in greater thicknesses (12.7 mm and 25.4 mm), the cooling rate was elevated due to the thickness itself and the use of a higher feed rate. Consequently, in the coarse grain heat affected zone (CGHAZ), there was a shift from the ferritic field to the bainitic field. To meet the requirements, it is advisable to adjust parameters, such as increasing weld energy or applying preheat treatment. Another alternative involves planning subsequent passes to induce a tempering effect on the root. In summary, for geometrical purposes, a constant energy can be used, whereas metallurgical objectives might necessitate greater energy input with increasing thickness.
TIG welding process with dynamic feeding: a characterization approach e Silva, Régis Henrique Gonçalves; dos Santos Paes, Luiz Eduardo; Okuyama, Marcelo Pompermaier ...
International journal of advanced manufacturing technology,
06/2018, Letnik:
96, Številka:
9-12
Journal Article
Recenzirano
Wire forward and backward oscillation in automatic feeding tungsten inert gas (TIG) process have been pointed as a simple technique to achieve high productivity levels and process stability for a ...wider operation range, compared to the conventional version. However, in this case, physical aspects related to the involved phenomena are still not fully understood. Based on that, the present paper addresses a characterization analysis of low frequency dynamic wire feeding process, in order to yield some contribution to the knowledge gain of these phenomena. Both conventional automatic feeding and autogenous process were taken as a reference. The study covers system description as well as metal transfer modes, welding pool temperature gradient, and respective weld geometry. Bead on plate welding was performed and monitored with high-speed and thermographic cameras. Dynamic oscillation showed good stability and proved to be more flexible among other versions, as feeding speed and power do not need to be correlated. In order to enable proper wire dynamic movement monitoring, a special motion measuring system was developed.
The use of remelting as heat treatment for metallic components has grown on an industrial scale, particularly in sectors where surface hardness is a requirement. Using a conventional Tungsten Inert ...Gas (TIG) welding torch, it is possible to induce desirable microstructures, promote grain refinement, and as a result, increase hardness. However, one of the main challenges concerns understanding the effects of remelting strategies based on the torch/tool path planning. It is possible to draw different conclusions under the same processing parameters depending on the tool's trajectory. Therefore, the present study aims to assess the influence of remelting path strategies on the AISI 1045 steel hardness, correlating its microstructure with thermal variables obtained from an in-house Finite Volume numerical model. Two different approaches are analyzed, namely Strategy 1 and Strategy 2.The former was characterized as a single direction movement with 77 s average time between beads, while Strategy 2 was chosen as double direction movement (zigzag) without interbead time. In both cases, TIG remelting was applied autogenously with 120A Direct Current Electrode Negative (DC-), at 15 cm/min, with a 30% overlap ratio for five parallel beads, and with Argon as shielding gas. The results pointed out that both strategies promoted a hardness increase relative to the base metal, 23% for Strategy 1 and 9% for Strategy 2. This factor was attributed to grain refining. The simulation revealed that Strategy 1 is more suitable than Strategy 2 to boost the hardness is related to the higher solidification cooling rate (166 °C/s versus 137 °C/s, respectively) and lower time above 900 °C (7 s versus 12 s, respectively).
Display omitted
•This study assessed the influence of two TIG remelting strategies on hardness.•Strategy 1 consisted of a single direction and Strategy 2 of a double direction.•Both strategies presented a hardness increase relative to the base metal.•Grain refining is related to the hardness increase and was evident in Strategy 1.•Strategy 1showed a higher solidification cooling rate and a lower time above 900 °C.
