مجله مهندسی ساخت و تولید ایران
سال هشتم شماره 10 (دی 1400)

Nano-indentation is a valuable method for determining the mechanical properties of thin films. In this paper, in order to investigate the hardness of different metals, the nano-indentation process on three workpieces with nickel, copper and aluminum is studied by simulating molecular dynamics. According to the force-displacement curves, nickel and aluminum apply the most and the least force to the indenter, respectively. Based on the hardness-displacement curve obtained for the three components, aluminum has the lowest and nickel the highest hardness. The force-displacement curve of aluminum and hardness-displacement curve of nickel was validated by the force-displacement curve of aluminum and hardness-displacement of nickel in the previous study. The results of atomic phase transfer simulation showed that the deformation in nickel is mainly plastic and in aluminum elastic-plastic. Atomic accumulation was validated after the completion of the process on the copper surface with experimental results and simulation of finite element research of the past. By simulating crystal defects in workpieces, it was found that at the same depth and load, the distribution of crystal defects in aluminum, in addition to the depression area, is also present in the surface of the part and the underlying layers, while the dispersion of defects in copper and nickel is less. Dislocation motion was investigated as the main cause of slipping and deformation in workpieces.

This study investigates the effect of using temperature-dependent and constant thermophysical properties on the precision of numerical simulation in the laser welding of titanium Ti60 alloy. A finite element model is made for 3 mm thick Ti60 alloy sheet piece and is affected by the laser beam using a three-dimensional moving heat source. For verification of the finite element model, the numerical results are compared with the results of experimental data. Also, the influence of the number of elements on the results is investigated. The results of the finite element modelling showed that the solidification starts from the bottom of the melt pool and progresses to the top of the sheet and along the weld seam. Also, the best results are obtained with all the thermophysical properties of density, thermal capacity and conductivity were temperature-dependent. The use of constant density reduces the maximum values of the temperature and dimensions of the weld pool, and the use of constant heat capacity increases these values. Still, these changes are such that (less than 2%), constant density and thermal capacity can be used to model the whole laser welding process. However, the use of constant thermal conductivity causes a large error in the maximum values of the temperature (about twice the value of this parameter), and the dimensions of the melt pool, and this parameter cannot be assumed constant in the simulation of laser welding.

One of the problems with laser machining is the heat-affected zone (HAZ) generated due to the intense heat applied to the workpiece. Moreover, in laser micromachining, the imprecise kerf width control reduces precision. A hybrid waterjet–laser (WJL) process without abrasive particles was used to counter these problems. In the hybrid WJL process, water pressure flushes out molten materials from the cut section, thus reducing the kerf width. Waterjet also enhances workpiece cooling compared to dry laser and results in reduced depth of HAZ. In this study, first a waterjet nozzle with a diameter of 0.4 mm was attached to a laser fiber machine featuring a constant wavelength of 1080 nm and power of 1500 W. Then, the interactions of cutting speed, laser power, focal length, and waterjet pressure on the HAZ and kerf width were investigated. CK75 high-carbon steel was used in this study. It was observed that increasing the cutting diameter leads to reduced HAZ depth and kerf width; whereas, increasing the power increases both said parameters. Furthermore, increasing waterjet pressure reduced HAZ depth and kerf width. The minimum HAZ depth and kerf width were obtained at a focal length of 3 mm., whereas the best HAZ depth and kerf width were 57 micrometers and 217 micrometers, respectively.

The Incremental forming is an applied production method in rapid prototyping and manufacturing of sheet products in small batches. Usually this process is performed in environment temperature by a computer numerical control machine or a manipulator. Conducting the process in high temperatures, studying the thickness distribution and improving the forming limit of producing parts are the main research contributions in this field. Also, some efforts have been made to increase the accuracy of manufactured parts and two point incremental forming and using of metallic foams have been proposed. In this research, the usage of polymeric foam as a flexible support is proposed to improve the incremental forming of high density polyethylene sheet with the thickness of 2 mm. Wrinkling and tearing defects for both with and without flexible support processing conditions with different spindle speeds and feed rates were investigated. For this, parts with variable wall angle were used. The results showed, the usage of polymeric foam support improves the forming condition by achieving to the parts with higher wall angle. Also, some samples produced in different working condition were selected and the accuracy of them was investigated using a 3D scanner and the improvement of the accuracy in the condition of using the flexible die support was observed.

Hydroforming is one of the newest sheet metal forming methods that has been widely considered in the industry in the last two decades. In the present research work, the sheet hydroforming process of 2024 aluminum and AZ31B magnesium light-alloys at elevated temperatures has been studied experimentally. In order to evaluate the quality of the produced specimens, the thickness strain created in the cups has been investigated. Then, the relationship between thickness strain distributions with the grain size was discussed using hardness test and microstructure images obtained from scanning electron microscopy (SEM). In order to confirm the gained numerical values, the repeatability of experimental results was performed. The outcomes demonstrated that the suitable temperatures for the hydroforming process of 2024 Al alloy and AZ31B Mg alloy respectively gained to be 250 °C and 200 °C. The maximum amount of elongation and plastic strain (due to simultaneous bending and stretching) occurred in the wall of the cup and despite the friction of contact between the sheet and the matrix in the flange region, the amount of strain in this area increased. According to the results of the current study, the maximum increase in hardness and decrease in grain size were obtained 37% and 20% for AA 2024 and 24% and 42% for AZ31B, respectively, in the wall area in comparison with the bottom of the product.

Surface roughness is one of the most important features in nanoscale machining. Due to the use of nanometer-sized products for use in assemblies that require extremely high accuracy at a fraction of a nanometer, care must be taken in selecting machining parameters that affect the surface roughness. In this study, using molecular dynamics simulations, the machining of a single-crystal copper workpiece by diamond tools with different geometries has been investigated and the final surface roughness has been calculated. The effect of machining parameters such as cutting depth and cutting speed along with parameters related to tool geometry such as rake angle, relief angle and tip radius on surface roughness have been investigated with average roughness (R_a) and root mean square (RMS) measuring instruments. In order to study more precisely the effect of parameters and their interaction with each other, Taguchi method has been used to design experiments. The simulation results show that both the average roughness and root mean square parameters predict the greatest effect on the surface roughness of the workpiece due to the depth of cutting. Based on the presented results, it has been determined that the surface roughness can be improved in different machining conditions based on the selection of parameters, and it is necessary to carefully examine their conditions together before selecting these parameters. Using the Taguchi method, the optimal values of cutting parameters to achieve the best surface roughness in specified dimensions are described as