جستجوی مقالات مرتبط با کلیدواژه "ساخت افزایشی" در نشریات گروه "مکانیک"

Inconel 718 superalloy is widely used in various industries due to its excellent high-temperature properties. The production of components made from Inconel 718 superalloy through the Selective Laser Melting (SLM) method enables the fabrication of parts with complex geometries. Therefore, improving the mechanical properties of parts produced by SLM using secondary strengthening processes is of great importance. This study investigates the effect of cold pre-strain on the tensile and compressive strength of Inconel 718 superalloy samples produced by SLM. The test specimens were produced by the SLM method and subjected to single-stage (5%-15%-30%) and two-stage (4%-12%-16%) loading. To examine the impact of initial loading on mechanical properties, tensile, compression, and hardness tests were performed, and the microstructure behavior was analyzed using an optical microscope. The results indicate that the yield strength and ultimate tensile strength of the Inconel 718 superalloy in the Y-axis (XY plane) increased by 31.8% and 11.6%, respectively, after applying a 30% initial strain along the Z-axis. The compressive yield strength of Inconel 718 superalloy increased by 79.3% in the Z-direction with a 30% pre-strain. In other words, applying pre-strain along the Z-axis affects the compressive strength in the XZ plane as the principal strain and the tensile strength in the XY plane as the shear strain. Increasing pre-strain to 30% has a minimal effect on the hardness properties of Inconel 718 superalloy. The results from the two-stage loading process indicate an enhancement in strength with the increase in the number of loading stages, attributed to the work-hardening phenomenon

Due to the high strength to weight ratio of aluminum and carbon fiber, The use of these two materials and their connection to each other is expanding in the automotive and aerospace industry. The main purpose of this research is to connect three layers of sheets to each other layer by layer, consisting of two layers of aluminum 6061 T6 on both sides with a thickness of 1 mm and a layer of CFRP with a thickness of 0.7 mm in the middle, which was done successfully. 15 pieces of aluminum and CFRP sheets were divided into 25 x 60 mm pieces connected to each other layer by layer using ultrasonic metal welding machine. Finally, with the tensile testing machine, the shear tensile strength of the weld cross-section of all 15 test samples was calculated and measured. The design of the experiment was done with the response surface method, the box behnken type, and three parameters of power, time, and pressure, each at three levels, are considered as variable parameters. In order to design the experiment as well as analyze and check the test data, Design Expert software has been used. In the following, the graphs of the influence of each of the parameters were extracted and the optimal parameters were also obtained. The highest shear tensile strength was obtained with power parameters of 1400 watt, time of 0.4 seconds and pressure of 7 bar equal to about 92 MPa.

With the emergence and expansion of additive manufacturing processes, especially the fused deposition modeling process, extensive research has been conducted on these processes. One important research area is strengthening the printed parts by the fused deposition modeling method. One of the main areas of research is related to the strengthening of printed parts by the fused deposition modeling method. This process enables the production of complex structures and the customization of parts. On the other hand, polylactic acid material is one of the main materials used in this process, which has been noticed over other materials due to its biocompatibility and biodegradability properties. In this research, the effect of annealing heat treatment on the compressive strength and modulus of porous samples has been investigated with the approach of using them in tissue engineering as a scaffold for bone tissue. The samples are 3D printed with wiggle, grid, and honeycomb patterns and with filling percentages of 40, 70, and maximum. In addition, the effect of two parameters, the extrusion width, and the layer height, has also been investigated. To create porous structures with interconnected porosities, the pattern of filling in each layer is rotated to a certain extent, and this causes the introduction of new porous structures that can have wide applications such as being used as scaffolds in tissue engineering. After evaluating the compressive mechanical properties of the samples, the same samples were heat treated, and then their compressive mechanical properties were also evaluated. The obtained results show that the maximum compressive strength and modulus occur in the sample with an extrusion width of 0.6 mm, layer height of 0.25 mm, wiggle filling pattern, and maximum filling percentage. The values ​​of compressive strength and modulus for the non-heat-treated sample are equal to 84.51 MPa and 2.28 GPa respectively and for the heat-treated sample, it is equal to 105.44 MPa and 2.29 GPa respectively.

Inconel 718 is used in a wide range of industries such as oil and gas, nuclear, aviation, and etc. due to its excellent mechanical properties. The use of additive manufacturing (AM) to manufacture parts is increasing rapidly Due to the dimensional limitations in the manufacturing of parts using the additive manufacturing methods, these parts must be connected to other parts in different applications with the help of conventional methods such as welding. In this research, the thermal analysis of plasma welding of an Inconel 718 sheet made by SLM method using ABAQUS software is discussed. Input heat with Gaussian distribution was entered into the model by DFLUX subprogram with FORTRAN program language. In order to validate the thermal model, the temperature was measured during the welding process using a thermocouple. A relatively good match is observed between the numerical and experimental thermal analysis results. The microstructure of the welded samples was examined with an optical microscope and the microstructure of base metal, fusion zone, and heat affected zone were investigated. The dendritic structure in the welding area and the occurrence of recrystallization in the heat-affected area was evident. The tensile test results showed that the sample without welding has a higher yield and ductility.

It is not possible to fabricate the complex geometry of coherent cooling channels with conventional machining methods, so channels can be created in the mold using additive manufacturing processes such as selective laser melting. Parts created by selective laser melting always have porosity, and the amount of porosity depends on process parameters. On the other hand, the ability to make porous materials with a selective laser melting process has made these materials with features such as lower density and better heat transfer in the aerospace industry, automobile, medical uses and heat exchangers to be the attention of researchers and according to Porosity Percentage, in addition to directly affecting mechanical properties, also affects heat transfer. In this research, the effect of porosity on heat transfer in the mold was investigated. First, the model and mold were designed, in order to investigate the effect of porosity, four simulation models with volume porosity percentage of 0, 10, 20 and 30% were performed and analyzed in the software. The analysis of the results shows that the increase in the percentage of porosity in the mold causes a faster increase in temperature in the mold, also with the increase in the percentage of porosity in the mold, the speed of temperature decrease in the mold increases. And the cooling of the part happens faster. Examining the results of the maximum thermal gradient of the non-porous material compared to the material with 30% porosity shows a 21% increase in the thermal gradient in the porous material

With the introduction of additive manufacturing processes and 3D printers, a lot of research has been done and is being done in this field. Methods based on polymer extrusion, known as fused deposition modeling, are one of the most widely used additive manufacturing methods. Most of the research done in the fused deposition modeling method is related to increasing the mechanical properties of the printed samples. Optimization of process parameters, addition of metal and non-metal filler particles, use of post-processing operations (types of heat treatment, use of ultrasonic waves, etc.), and use of continuous fibers are the main methods used. The most effective method for increasing mechanical properties, especially tensile mechanical properties, is the use of continuous fibers with high strength such as carbon, glass, and aramid. Of course, the use of continuous natural fibers such as linen, hemp, etc. has also been considered. This research aims to investigate the compressive properties of 3D-printed samples using the fused deposition modeling method. In this regard, the compressive strength of polymer samples made of neat polylactic acid and composite samples of polylactic acid/continuous glass fiber is investigated. It is clear that if the continuous fibers are placed in the direction of applying the compressive load, they are not able to withstand the compressive load. Therefore, in this research, by placing the fibers in the direction perpendicular to the direction of the load and considering the phenomenon of transverse strain, the fibers are subjected to tension, and the compressive strength of the composite sample increases by 10% compared to the pure polymer sample.

In recent years, additive manufacturing has gained significant importance in the field of production. Most of the additive manufacturing technologies for metals involve melting and solidification processes, leading to metallurgical challenges. The friction stir additive manufacturing process is a novel solid-state method that does not face the common metallurgical challenges associated with the traditional melting methods. This process can be used for the production of aluminum-silicon carbide nanocomposites that find many applications in industries such as military, aerospace, automotive, etc. The primary objective of this research is to experimentally analyze the effect of tool rotational speed, tool traverse speed, and number of passes in friction stir additive manufacturing on the microhardness and wear amount of aluminum-silicon carbide nanocomposite manufactured by this method. To this end, the response surface method and Minitab software were used for experimental design, statistical analysis, and optimization of the parameters. Multi-objective optimization settings were selected to increase microhardness and reduce wear. The combinations of optimal values of the parameters were determined to achieve the optimization goals, and the results were validated. The optimization result with 0.87 desirability is obtained with a tool rotational speed of 1000 rpm, a tool traverse speed of 50 mm/min, and one pass. The predicted optimal responses of 104 Vickers for microhardness and 0.013 gr for wear had a small percentage of error compared to the experimental results.

The fused deposition modeling process is an advanced manufacturing technique that builds parts layer_by_layer. Due to the layered construction, printed parts with this process have low surface quality and poor dimensional accuracy. high surface roughness limits the use of these parts in many fields of application such as aerospace and medicine, which require high precision and quality. Laser polishing is an emerging industrial process that can improve surface quality. correct selection of laser parameters greatly reduces the cost and time of surface treatment of additive manufacturing parts. In this research, the effect of 3D printer parameters and surface angle of the produced samples on the surface roughness of the parts was studied separately. The effect of each printing parameters is explained by drawing a thermal map and layering thickness is introduced as the most important parameter affecting the surface roughness. Also, the process of roughness changes is evaluated based on the angle of the printed surface in the form of a diagram. Then, the relationship between printing parameters and the geometric shape of printed parts with selected laser parameters was presented to achieve the best surface quality.

In this study, samples reinforced with continuous metal wire as both a reinforcing component and a shape memory actuator were printed via the Fused Deposition Modeling (FDM) additive manufacturing method. Shape memory materials are a significant subset of smart materials that can recover their original shape in response to a specific stimulus such as heat, magnetism, electricity, moisture, etc. The stimuli for shape memory materials are generally classified into two main categories: direct and indirect. In some cases, direct stimulation may not be possible for shape recovery, and introducing solutions for adding indirect stimulation capability to these materials can expand their application range. In this study, the chromium-nickel metal wire was used as a reinforcing agent to improve the mechanical properties and introduce indirect stimulation capability to the materials by applying voltage simultaneously using the in-situ impregnation method in the FDM process. Adding continuous fibers through the in-situ impregnation method during the printing of parts significantly enhances the mechanical properties of polymeric samples. According to the obtained results for a 0.15 mm diameter metal wire, the increase in tensile strength for 5% and 10% reinforced samples was 63% and 134%, respectively. The increase in flexural strength for samples reinforced with 5% and 10% metal wire was 10% and 105%, respectively.

The development of reliable numerical tools for predicting the integrity of machined surfaces is significant. This paper introduces a new customized FE model to predict the deformation during turning of electron beam fused (EBM) Ti6Al4V alloy under dry cutting. The needle microstructure and exotic nano-hardness types of materials are modeled and implemented using a user subroutine in the FE model. The developed FE model provides the possibility of predicting the microstructure (thickness of alpha lamella), the changes in nano-hardness caused by machining operations in dry conditions.

Titanium and its alloys, especially the Ti6Al4V alloy, have many uses in the aerospace and medical industries due to their unique properties. The production of Ti6Al4V alloy by additive method has been very much considered due to the characteristic of this method. But due to the fact that these parts also require final machining. As a result, it is very important to achieve optimal parameters from a faster and more economical method. In this article, simulation of cryogenic machining of EBM Ti6Al4V alloy in order to study microstructural changes. done. It was validated by comparing the experimental results and simulation of the material model. Then, using the validated FE model, the effects of shear speed on forces, thermal loads and microhardness were discussed.

In the first part of this study, the mechanical properties of the uniform auxetic unit cell (negative Poisson’s ratio) have been investigated for application in the hip implant. We used auxetic cells to increase the contact surface between implant and bone under tensile loads. The elastic modulus of the uniform auxetic structure have been obtained by numerical, analytical and experimental methods in y direction. Comparing the elastic modulus in y direction of the analytical and numerical simulation with experimental tests showed there are a good agreement between the results. In the second part, the gradient structure has been used in order to reduce the stress shielding on the contact surface of the bone and implant, increase the efficiency of implant replacement and reduce infection. In the gradient structure, the elastic modulus in the contact surfaces is considered close to the elastic modulus of the bone, and gradually increases in the next layers. The elastic modulus of the gradient structure was calculated by two numerical and analytical methods. In the numerical method, the elastic modulus was obtained from Abaqus software and coding on MATLAB. The difference of the elastic modulus in these two methods was 4.8%, which shows that there is an acceptable agreement between the results.

The use of additive manufacturing provides the opportunity to create complex geometries at a low cost. This paper introduces a novel nature-inspired additive manufactured graded lattice structure based on an elliptic unit cell. Altering the unit cells' dimensions by the dimension ratios in each repetition results in a graded layer. Linear tessellated layers provide a highly porous, graded structure whose specific properties can be customized at any spatial location. Geometric features were calculated with high accuracy using analytical analysis. Abaqus simulations were utilized to determine the mechanical properties of unit cells, layers, and lattices. A compression test was conducted on a polymer specimen made by the DLP technique to validate the results. For a conformal model, the elastic modulus along the latitude axis is five times bigger than the value along the longitude axis. An 8.8-fold increase in the elastic modulus is achievable by decreasing the longitude ratio from 1 to 0.75. A reduction of 0.3% in porosity by setting the longitude ratio to 0.75 and a decrease of 2% in porosity by lessening the latitude ratio to 0.75 results in increases of 2.6 and 2.77 folds in the elastic modulus along two directions, respectively. It is possible to tailor geometrical and mechanical properties to meet any design preference by selecting the proper dimension ratios, which can be utilized for medical implant design.

The additive manufacturing method, as the newest way of producing parts in medicinal and industrial fields, has made significant advancements in recent years. Among the existing methods, digital light processing (DLP) using flexible membranes is one of the most extensively utilized polymer-based approaches. Dimensional accuracy along the vertical and plane axis of the printed parts is one of the key issues in manufacturing polymer parts, both layer by layer and layerless. In this article, utilizing the system designed and manufactured in this faculty's laboratory, as well as three flexible fluorinated ethylene propylene membranes of varying thicknesses and Provision and Anycubic resins, the influence of the calibration technique and initial distance on the dimensional accuracy of printed parts in the DLP method have been investigated experimentally. By assessing the compressive forces caused by the initial distance, it was discovered that the compressive force increases when the initial distance was determined in membranes with thicknesses of 100, 150, and 200 microns in both resins, resulting in a 17.5% - 34.1% decrease of the part's thickness is caused by the fact that by positioning it at the appropriate initial distance, the resulting error can be greatly reduced. Furthermore, for both of the resins stated, reducing the thickness of the flexible membrane has a direct link with increasing the dimensional accuracy in the printed parts.

The additive manufacturing system using the continuous liquid interface production (CLIP) method, which was designed and constructed by the researchers of this article, was utilized in this research to examine the impacts of the oxygen control area's thickness on the speed of producing parts. The main goal of this research is to produce porous parts 10 times faster compared to the digital light processing (DLP) method. However, it's crucial to look at the printing height, the part failure rate, as well as the part curing depth in order to achieve this speed increase. One of the most crucial factors affecting the aforementioned circumstances is undoubtedly the oxygen control zone. Therefore, two window-shaped (island and microchannel) special gas-permeable membranes were utilized as the bed of the liquid resin container to generate this zone. Furthermore, employing each of the aforementioned windows, parts with a porous and complex structure were manufactured and evaluated. The usage of an island-like container increased the duration of continuous printing by 107% before the separation force begins, reduced maximum separation force by 4.7 times, and increased the height of the printed component by 30%, according to the study's findings. It also improved the part's visual quality.

The use of Additive Manufacturing (AM) techniques in medical science has resulted in a great change in this field, especially in bone tissue engineering. One of these techniques is the Fused Deposition Modeling (FDM) which is used to make bone scaffolds. From view point of bone tissue engineering, bone scaffolds must have acceptable mechanical properties in addition to the required biological properties. In this study, at first the printing parameters including layer height, printing speed and number of filaments in each row were determined and bone scaffolds were made with two different materials polylactic acid (PLA) and polycaprolactone (PCL) and were subjected to the compression tests. The results of Young’s modulus and yield stress analyzed in Design Expert software showed that increasing the layer height reduces the mechanical properties. Also, increasing the number of filaments in each row increases the elastic modulus of the scaffold. For example, for scaffolds made of PLA, the maximum modulus of elasticity belongs to 12 filament scaffolds with a layer height of 0.1, which is equal to 319 MPa, and the minimum elastic modulus belongs to 8 filament scaffolds with a layer height of 0.3, which is equal to 143 MPa. Printing speed for scaffolds made of PLA does not have a significant effect on the Young’s modulus and yield stress. But for scaffolds made of PCL, increasing the printing speed reduces the modulus of elasticity but it doesn’t have a significant effect on yield stress.

The 3D printing technology allows the production of parts with complex geometry quickly. However, the printed parts have poor mechanical properties due to the nature of their layers and the presence of defects such as cavities and poor adhesion between the layers. This paper investigates the use of ultrasonic vibrations to improve the mechanical properties of acrylonitrile-butadiene-styrene printed components. Samples were fabricated with standard geometry of tensile test using a desktop 3D FDM printer. Process parameters are layer thickness and infill. Also, the time of ultrasonic imposing was selected as a variable parameter. The thickness of the print layers are 0.15, 0.2, and 0.30 mm, and the infill is 60, 80, and 100%. The design of the experiment was performed by the response level method. Then the uniaxial tensile test was performed on the samples, and the data were analyzed by analysis of variance (ANOVA). The results showed that the application of ultrasonic vibrations significantly improves the tensile strength of printed parts, which is greater in lower thickness. Also, with increasing the infill, the effect of ultrasonic vibrations increases, which can be due to better bonding of the print layers due to ultrasonic vibrations and reducing the number of pores in the low infill values. Therefore, it is found that by applying ultrasonic vibrations to the 3D printed samples, their mechanical properties were improved and could be used in performance evaluation.

In recent years, considerable efforts have been deducted to evaluate the quality of various products. In this regard, quality control of products fabricated by the additive manufacturing methods has become a new interest. In the 3D printing industry, Defect detection could have a vital role in the final evaluation of products. In this study, artificial defects are located in PLA samples printed with different infills via the Fused Deposition Modeling (FDM) method. In order to detection of the mentioned defects in these parts, the Active IR Thermography was employed. Thermal stimulation was selected as excitation method. Two different excitation formation including transmission and reflection mode are used. In order to validate the results, the temperature-pixel diagram for each sample were illustrated. The effect of Gaussian filter on thermal images was also investigated to facilitate the identification of the obtained images. The experimental results indicated the capability of thermally stimulated thermographic inspection in detection of defects in FDM printed parts.

Selective laser sintering is one of the methods of additive manufacturing based on powder bed which is widely used in various industries today. In this process, the amount of laminated mass has a high impact on reducing the porosity and quality of the final parts produced. For this purpose, in this study, a mechanism was designed and developed to investigate and achieve the maximum amount of laminated mass in a laminating process. The optimal state was obtained using the central composite design method. The results show that the parameters of blade velocity, angle under blade, and excess powder percentage have a greater effect on the amount of laminated mass, respectively. The optimized laminated mass was predicted by the experimental model to be 0.811 g, in which case the velocity is 2.78 cm / s, the blade angle is 3.1 ° and the initial powder content is 159%. To validate the model, the experimental experiment was performed based on the parameters of the optimal state, in which the laminated mass was measured 0.83 g, which shows that the error of the obtained model is 2.2%.

The upcoming article investigates the mechanical properties of FDM printed composite material with continuous glass fibers and ABS matrix. The printer designed to produce this composite uses ABS polymer filament and ABS/GF pre-impregnated composite filament. Pre-impregnated filament is designed and produced by a filament production line. In order to build a 3D printer with composite printing capability, a normal FDM printer was subjected to modifications in the structure and nozzle. Finally, after building a 3D printer with composite printing capability, tensile and bending samples were printed and the mechanical properties were tested according to standard instructions. The obtained properties were also compared with the printed pure ABS sample. The modulus of elasticity and tensile strength of the ABS/GF sample has increased by 540% and 260%, respectively, compared to the printed pure ABS sample. Based on the three-point bending test, the modulus and flexural strength of the printed composite have increased by 140% and 100%, respectively, compared to the pure polymer sample. The duration of making composite by FDM printer is not much different compared to polymer printing, but due to the presence of continuous glass fibers or other reinforcing fibers it greatly improves the mechanical properties of the manufactured sample, that's why the use of this method can be justified compared to FDM printing with pure polymer method.