مجله مهندسی ساخت و تولید ایران
سال نهم شماره 3 (خرداد 1401)

In this paper, a six-axis force/torque sensor is designed and fabricated using strain gauge. The characteristic of minimal mechanical coupling or independent output voltages is very important in designing this type of sensors. For this purpose, an arrangement consisting of 24 strain-gauges is used so that the output voltages of the six Wheatstone bridges corresponding to the loading components are independent of each other. Sensor is subjected to single and combined loads, the output of the Wheatstone bridges is measured and coupling error is calculated. An average of 7.3% of coupling error indicates the independence of the outputs from each other. The calibration process was performed according to the ANSI1979 and the sensor specifications were calculated. The minimum accuracy and maximum nonlinearity error are related to Fx loading and equal to 14.78%Fs and 6.42%Fs respectively and the maximum repeatability error related to the Mz loading is equal to 9.63%Fs. In order to reduce hysteresis losses, loading is applied directly to flexible structure for the Fz. As a result, the accuracy has increased significantly to 3.99%Fs and the errors of nonlinearity and repeatability have decreased to 0.52%Fs and 2.60%Fs.

Ore sorting proposed as an important step in the ore dressing of chromite processing and limited results have been reported in this field. By using this method, which is included in the classification of physical separations, significant energy savings and increased production are made. In this project, the separation of chromite has been accomplished by designing and building an ore sorting device. For this purpose, minerals are first imaged by a 3D scanner, and after creating a cloud of points, the volume of the corresponding stone piece is obtained, and based on that, the equivalent diameter of the stone piece is determined. Then ores placed on the device’s conveyor and the mass of each pieces are measured by load cell sensor and the density of minerals determined. Finally, according to the size and specified conditions of each fraction, the grade of stone pieces determined and based on the specified limit for grade, it is directed to the concentrate section (valuable part) or tailings (non-valuable part). The obtained results illustrated that the Sabzevar chromite with a grade of 26.16 percent with gaunge minerals after ore sorting, produces an initial concentrate with 33.11 and 83.92 percent of the grade and recovery respectively.

In this paper, nondestructive measurement of residual stress in welded steel parts joint using digital image correlation method has been investigated. For this purpose, samples of A36 sheet were prepared and arc welding with shielding gas (GMAW) was performed on them. In order to measure nondestructive residual stress in all parts, digital image correlation method has been used. Base and welded samples with and without heat treatment have been evaluated with this method. The heat treatment of the samples is of the tempering type, which is performed in order to reduce the residual stress of the welded samples. In order to measure non-destructive residual stress, a new relationship has been introduced which is based on Hooke's law. Residual stress values are calculated by measuring the displacement and strain of the samples and placing their values in the given new relation. Examining the results, it has been found that the heat treatment performed on the samples has reduced the residual stress values by approximately 33% and the digital image correlation method has sufficient and appropriate accuracy for measuring nondestructive residual stresses.

In addition to non-destructive testing, the weld joints in large structures must also be confirmed by mechanical destructive testing (such as tensile and impact tests). Drop weight tear test (DWTT) is a reliable test to evaluate ductile fracture and crack arrestability of pipelines. Previous research has focused on measuring and comparing the base metal fracture energy from DWTT using finite element and experimental methods. However, in the present research, the spirally welded seam of API X65 steel specimens were machined from an actual pipe and tested using DWTT. The load-displacement curves obtained from both numerical and experimental methods have been evaluated and compared regarding correction factors. Using the obtained correction factors (from important characteristics of the load-displacement curve such as total absorbed energy, crack initiation and propagation energy are used), the load-displacement curve of simulation can be relied upon with acceptable accuracy. Real curves can be obtained with a relatively large amount of time and money. For the steel used in the present study, the correction factor for base and weld metal is 1.8. The use of this value will also be acceptable for steels of the same grade. The weld metal correction factor using the simulation (based on Gurson-Tvergaard-needleman method) was 1.7, which was slightly different from the experimental value.

The swirler of the gas turbine combustion chamber is usually designed from nickel-based superalloys and produced by the conventional precision casting method under vacuum. The production of such parts is associated with high waste due to geometrical complexity, high dimensional accuracy and also the use of ceramic cores. In recent decades, the use of the additive manufacturing process as a new and alternative method has been growing for the production of complex metal parts in the power plant industry. In this research, a gas turbine Swirler and several Inconel 625 samples were fabricated by SLM in optimal conditions of the main variables of the manufacturing process such as laser power, scanning speed and the thickness of the melted layer. Microstructural studies were performed by optical Microscope on samples and some structural defects such as incomplete local melting, porosity, non-metallic oxide phases and Microcracks were identified. The printed swirler was compared with the computer model in all important and final Surfaces by non-contact dimensioning method. The surface quality and dimensional accuracy of the part were acceptable and it was evaluated within the tolerance range of the casting part. Also, hardness and tensile tests at ambient temperature were performed on the heat treated samples. The results showed that the values of the tensile properties of the printed samples were higher in the parameters of yield strength and ultimate strength, but lower in the parameter of relative elongation and the hardness was also the same.

The main purpose of this study is experimental and numerical investigation on failure of friction stir welded AA6061-T6 joint under tensile-shear test using damage model. In the past, due to the problem of development in high-strength welds, fatigue and corrosion resistance in aluminum, the use of welding in these industries was limited. However, with the advent of the friction stir welding process, aluminum alloys has been considered and their welding has become possible. The use of lightweight materials, especially aluminum alloys in the automotive, shipbuilding and aerospace industries is increasing rapidly and the operation of these alloys requires the development of joining and welding methods. Therefore, the study and analysis of friction stir welding is substantial. In this study Gurson-Tevergaard- Needleman (GTN) model is utilized to study the failure of welded joint. A finite element (FE) model is developed to simulate failure of the welded joint under tensile-shear test. To validate the model, 8 samples including 4 samples of friction stir welds with conventional tool and 4 samples with bobbin tool are welded with different welding parameters to obtain failure. The comparison between experimental and FE model results shows that the GTN model has a good reliability to predict the failure force. In addition, the results show that the FE model can predict truly the starting of failure in the welded joint.