Showing 10 results for Laser Welding
Y. Najafi , F. Malekghaini, Y. Palizdar, S. Gholami,
Volume 2, Issue 1 (8-2016)
Abstract
Recent research suggests that extraordinary combinations of strength and ductility can be achieved in the so-called TRIP steels. With the development of these steels, welding with small weld nugget size and acceptable strength are needed. For these reasons present study was carried out to investigate the effect of heat input onweld size, microstructure and the hardness of the welded metal of 0.4%C- 4%Al δ-TRIP steel after continues fiber-laser welding process. To achieve this goal a bead on plate welding with three different values of heat input 28, 60 and 80 J/mm were used.The results of welding process revealed that by increasing the heat input, cooling rate decreased and the volume percent of the δ-ferrite in weld metal increased due to the availability of sufficient time for partitioning of Al in high heat input which leads to the stable δ-ferrite and as a result the difference between the hardness of the weld metal in comparison to the base metal decreased.
M. E. Kazemian, F. Mohsenifar, R. Ghanbarzadeh,
Volume 3, Issue 1 (8-2017)
Abstract
In this paper, laser beam welding of a rectangular piece of steel was simulated using Fluent software. Physical properties of analytical field was constant and its changes with temperature was ignored. In the present work, effect of tool speed and laser power on temperature distribution of workpiece surface and different deeps in the plane of symmetry and also maximum of temperature and depth of penetration were investigated. Using a macro code, geometry generation and meshing of the analytical field by helping required geometric parameters were provided for software. Moreover, laser radiation power was exerted by writing an UDF in the fluent software. In this case, it was assumed that the workpiece is stationary and gaussian thermal source model defined in UDF moves with the intended speed. Results show that at a constant power, maximum temperature of the workpiece decreases with increasing heat source speed, moreover, in this case, gradient of temperature in front of the workpiece and behind of it, increases and decreases respectively. It is found that the temperature in the depth of the workpiece increases with increasing the power.
M.saleh Shaikh Meiabadi, A. Kazerooni, M. Moradi,
Volume 4, Issue 2 (1-2019)
Abstract
Laser welding is a novel method for direct joining of metals and polymers, which leads to a mechanical and chemical bond between metal and polymer. In this study, feasibility of dissimilar joining between St12 and polycarbonate is studied theoretically. Then, the ND: YAG laser is implemented to join St12 and Polycarbonate. Empirical results indicate creation of a joint between St12 and polycarbonate. In order to conduct thermomechanical analysis of the welding process, the finite element model has been developed by Abaqus software. In addition, the cylindrical-involution-normal (CIN) heat source model was used to describe the laser power distribution and FORTRAN software has been used to define the thermal model in welding simulation. Comparison of experimental and simulation results shows that the finite element model is capable of predicting weld width, and therefore the results of the finite element model are verified. Therefore, the finite element model is used to predict residual stresses. The results disclose that dissimilar bonding creates residual tension stresses on the metal surface and compressive residual stresses on the polymer surface.
S. Asadi, T. Saeid, A. Valanezhad, J. Khalil Allafi,
Volume 5, Issue 2 (1-2020)
Abstract
In this research, dissimilar welding of NiTi shape memory alloy to AISI 304 austenitic stainless steel Archwires was investigated. For this purpose, common straight orthodontic archwire with rectangular cross-section and dimensions of (0.635 × 0.432 mm) were selected and the laser welding technique was used to connect the wires. The microstructure, chemical composition and phasesin the weld zone of the joints werestudied with Optical microscopy (OM), Scanning electron microscopy (SEM) equipped with EDS analysis system, focused X-ray diffraction (Micro-XRD).Also, the mechanical properties of the weld zone were investigated by using Vickers microhardness test. Microstructure investigation showed that the obtained microstructure from the laser weld of these alloys has a dendritic and non-homogeneous structure. According to XRD analysis, brittle intermetallic compounds such as Fe2Ti, Cr2Ti, TiNi3, and Ti2Ni wereformed during laser welding in the weld zone. Formation of these brittle intermetallics caused increasing the hardness of the weld zoneabout 800 HV. and decreasing the mechanical properties. Also, Fe2Ti intermetallic particles mainly formed in the weld region near the NiTi fusion zone which results in stress concentration, micro-cracks formation and dropping joints mechanical properties. Therefore, a suitable modification process is required to control the chemical composition of the weld zone and improving the joint properties of dissimilar laser welded archwires of these alloys.
H. Ebrahimzadeh, H. Farhangi,
Volume 6, Issue 2 (12-2020)
Abstract
The non-continuous laser beam in pulsed lasers allows the mechanical peening between two consecutive beams on a still hot weld bead. At a very short time (20, 150 and 300 ms) after laser pulse application, mechanical peening was performed on the welding bead. To achieve these short times, the light sensor detects the nth laser pulse and the mechanical arm starts moving. Upon reaching the tip of the pin near the workpiece, the n + 1th pulse was irradiated to the workpiece surface, and so the pin impact to the weld bead after traveling a short distance. Desirable mechanical properties were obtained at the highest time (300 ms) and highest pressure (6 bars). In this time and pressure the weld beads were not broken due to bending forces of peening.
Dr Homam Naffakh-Moosavy, Eng. Ali Rasouli,
Volume 7, Issue 2 (1-2022)
Abstract
In this research similar joining of NiTi shape memory alloy was studied. For this purpose, NiTi alloy in the form of wires with circular cross section possessing martensitic phase structure at room temperature was used. By utilizing Nd:YAG pulsed laser welding method followed by optimizing its technical parameters, a defectless joint in terms of appearance and metallurgical properties was obtained. In the next step, the effect of various pulsed laser duration time on properties of the obtained similar joint of NiTi was investigated. Moreover, the resultant microstructures were studied using optical microscope (OP) and Scanning Electron Microscope (SEM) equipped with chemical analysis of EDS. Furthermore, the samples prepared under different pulsed laser duration time conditions were characterized by using tensile and micro-hardness tests. Investigating the results of the performed evaluations revealed that higher levels of heat input has resulted in grain growth, dissolution of precipitations as well as reduction in hardness and ultimate tensile strength of the samples in the joint zone.
M. Foumani, H. Naffakh-Moosavy, A. Rasouli, H. Aliyari,
Volume 8, Issue 1 (8-2022)
Abstract
Surface roughness in the welding processes is one of the important parameters in the laser welded metal connections which affects laser beam absorption directly. When the laser beam is irradiated to the surface of the base metal, the surface roughness plays an important role in the amount of beam absorption and the amount of melting achieved and directly affects the penetration depth. The main purpose of this study is to investigate the effect of roughness mentioned above in the equal parameter for this widely used aluminum alloy. Microstructural Surveys were performed on three different roughness levels of the sample and the results obtained from the analysis of samples by optical microscope (OM), atomic force microscope (AFM) and Scanning electron microscopy (SEM) analysis showed that, increasing the surface roughness up to Ra = 0.16 micrometer, caused the greater degree of beam engagement by the surface grooves, hence more concentration of the beam photons and more melting obtained, so the depth of penetration increases by consuming a lower amount of energy.
H. Gorji, Dr. S. M. Barakat, S. R. Shoja Razavi, S. S. Babaie Sangetabi, M. Erfanmanesh,
Volume 8, Issue 1 (8-2022)
Abstract
The aim of the present study is to investigate the mechanical and microstructural properties of 1.7225 steel in laser welding process using Nd:YAG pulsed laser device and then to determine the optimal focal length relative to the part in the welding area. After welding, microstructural characterization, microhardness and tensile tests were performed. Evaluations showed that the optimal focal length for welding of steel sheet 1.7225 with a thickness of 1 mm, it was about 9 mm and the focus was 1 mm below the surface of the part. Due to the high thermal concentration and cooling rate in laser welding, a completely martensitic microstructure has been observed in the molten and heat-affected regions of all specimens. In this alloy, the hardness of the base metal is 310±10 HV. After welding, the hardness of the sample with the optimal focal length has reached 625±10 HV in the heat affected zone and 730±10 HV in the melting zone. Also, the results of tensile test showed that the tensile properties of the sample with the optimal focal length were almost similar to the base steel and fracture was observed in the base steel region.
R. Mahdizade, S. A.asghar Akbari Mousavi, S. Mehdipour,
Volume 9, Issue 2 (1-2024)
Abstract
In this study, non-homogenous welding of nimonic 75 superalloy to Monel 400 with 1 mm thickness was investigated with pulsed Nd:YAG laser welding. The mechanical properties of the joint were analyzed with optical and scanning electron microscope, X-ray diffraction, micro-hardness test and tensile test. In the case of non-homogeneous welding of Nimoinc 75 superalloy to Monel 400, defects such as liquation cracks and porosity in the welded samples were observed. these defects were removed with increasing the preheating temperature and decreasing the heat input. The results showed the voltage, pulse width, pulse frequency and welding speed should be selected as 500 volts, 9 milliseconds, 3 Hz and 0.9 mm/s respectively to reach the proper penetration depth. Also, the investigations show that the welding structure is composed of austenitic matrix containing columnar dendrites and some cellular areas. The mechanical properties of the weld metal were reduced after joining and segregation causes a change in the amount of elements and the appearance of intermetallic compounds in the spaces between dendrites and cells. All non-homogeneous samples broke during the tensile test from the weld metal area.
R. Abbasi, S. A.a. Akbari Mousavi, Y. Vahidshad,
Volume 10, Issue 1 (6-2024)
Abstract
The present study focuses on optimizing the mechanical properties and microstructure of laser welding in Haynes 25 (L-605) cobalt-based superalloy. Initially, the influence of laser welding variables such as laser power, pulse frequency, welding speed, and pulse width on the mechanical and metallurgical properties of the weld joints is investigated. By examining the welding variables, the values of G (thermal gradient) and R (cooling rate) are calculated, and their ratio (G/R) and cooling rate (G×R), which predominantly affect the solidification microstructure, are determined. The structural correlation with the mechanical properties resulting from welding is examined. In this research, it is considered to obtain the welding variables to create a high percentage of the structure in the form of equiaxed dendrite. Microstructural analysis reveals the growth of equiaxed grains and dendritic structures in the weld zone. The high cooling rate in the weld pool leads to dendritic solidification starting from columnar dendrites at the weld walls and ending in equiaxed dendrites at the center of the weld. The microhardness value in the weld zone is HV 328, which is very close to the microhardness of the base material. The tensile strength of the weld samples reaches about 93% to 94% of the base metal tensile strength. Tensile testing of the weld samples indicates a ductile-brittle fracture. Examination of the scanning electron microscope confirms the presence of dimples, intergranular cracks, and microvoids in the fracture zone.
