Mehrdad Vahdati Articles List

List of Articles Mehrdad Vahdati

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1 - Simulation of Air Gap Thickness on Air Spindle Vibrations in Ultra Precision Machine Tools
Mohammad Akhondzadeh Mehrdad Vahdati

Air spindles are one of the main elements of precise machine tools. Vibration of these spindles is one of the vital issues necessary for investigation. Among parameters which influence air spindle vibrations are rotational speed, compression air method, input nozzle dia More

Air spindles are one of the main elements of precise machine tools. Vibration of these spindles is one of the vital issues necessary for investigation. Among parameters which influence air spindle vibrations are rotational speed, compression air method, input nozzle diameter, air gap pressure. In this study using ANSYS, the effects of air gap thickness on air spindle vibrations have been investigated. In this simulation the air gap is modelled by numbers of linear springs. Then the effect of air gap thickness on air spindle vibrations has been investigated. Rotor externally rotates around stator. Simulation results indicate that for static and transient analysis the values of radial displacements of rotor reduce by decreasing spring length (i.e. rotor and stator gap), and its minimum value are equal to 3.634 µm and 15.6 nm, respectively. Because of constant spring stiffness, in modal and harmonic analysis, results for different spring length haven’t any variation and are equal to 1.053 mm and 23.7 nm, respectively. Manuscript profile
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2 - Simulation of Air Pad Shape on Pressure Distribution in Air Gap of Air Table in Ultra Precision Machine Tools
Mohammad Akhondzadeh Mehrdad Vahdati

Air pads are applicable in ultra precision machines very much. Two main components of these machines, spindle and table, use the advantages of such systems. The performance and efficiency of air pads have big influence on the whole machine quality. Parameters affecting More

Air pads are applicable in ultra precision machines very much. Two main components of these machines, spindle and table, use the advantages of such systems. The performance and efficiency of air pads have big influence on the whole machine quality. Parameters affecting pressure distribution of air tables may be considered as, 1) air compressing method, 2) air nozzle diameter, shape, and size, 3) number of air pads, 4) air gap thickness, etc. In this study, effects of air pad shape on pressure distribution in air gap have been investigated using ANSYS. In this simulation, FOTRAN environment have been employed. Investigated shapes for air pads are triangle, rectangle, pentagon, hexagon, ellipse and circle. Pressure distribution-distance from orifice has been plotted for each air pad shape. The results indicate that the rectangle air pad has best pressure distribution. Manuscript profile
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3 - Measuring Vibration in the Air Slide Tables of Ultra Precision Machines With the Different Number of Air Pockets
Mehrdad Vahdati Sayed AliReza Rasouli

Vibration in the air slide tables of ultra precision machines prevents gaining accuracies within nanometer level. In this work, dissimilar types of internal vibration including small vibrations and pneumatic hammers have been tested and some measures have been offered t More

Vibration in the air slide tables of ultra precision machines prevents gaining accuracies within nanometer level. In this work, dissimilar types of internal vibration including small vibrations and pneumatic hammers have been tested and some measures have been offered to reduce their effects. This paper has also proceeded to the vibration tests on the air slide tables built with different number of air cell (air pocket). Comparison in critical pressures, self-excited vibration analysis, and predicting the behavior of contrastive points of the table (that a tool or a work piece might get installed on it) are the results of experiments by different variations of air pressures. Manuscript profile
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4 - Mold Less Casting, a New Method for Droplet Based Part Manufacturing
Mehrdad Vahdati Hamed Kalami

In the new method of rapid manufacturing, the molten metal is dropped on a substrate, making layers after another. This method has the potentiality to be used for complicated castings which are difficult to make their molds and patterns as usual ways. In droplet-based m More

In the new method of rapid manufacturing, the molten metal is dropped on a substrate, making layers after another. This method has the potentiality to be used for complicated castings which are difficult to make their molds and patterns as usual ways. In droplet-based manufacturing process the castings are constructed by molten metal droplets having proper flow rate, temperature and diameter. In this paper a new system is designed and constructed which makes 3D parts and patterns by depositing molten metal droplets. Raw material wire melts and droplets are generated in droplet generating head. Molten metal Droplets deposit on a high temperature bed making the first layer. Next layers place on the previous ones to shape the final arbitrary part. These droplets are surrounded by natural air. Here tin60%, lead40% alloy wire is used. it is possible to apply other materials or wires having different diameters just with a little change in system. The wire is fed in special speeds which lead to different rates of droplets leaving the nozzle. Droplets have three properties which affect the layers and depositing way. These properties are droplet temperature and volume and their deposition rate. To control them several parameters of the system must be adjusted appropriately. At first it is assumed that these machine parameters are outlet nozzle diameter and feeding wire speed and also droplet temperature which affect droplet volume and deposition rate. Droplet temperature is measured exactly where they leave outlet nozzle. Droplet volume is estimated by several experiments, which lead to learn how different machine parameters create various droplet volumes. By knowing droplet volume and feeding wire speed, droplet rate can be calculated.In this paper the design essence of the constructed droplet based manufacturing machine is told. And dependency of droplet properties to machine adjustments is studied. These studies are done to control droplet properties. By knowing droplet properties, the moving speed of CNC heating table is determined. Manuscript profile
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5 - Evaluation of Parameters Affecting Magnetic Abrasive Finishing (MAF) of Superalloy Inconel 718
Mehrdad Vahdati SeyedAlireza Rasouli

Superalloys generally are among the materials with poor machinability. The removal of metal contaminations, stains, and oxides can positively affect their performance. Magnetic Abrasive Finishing (MAF) is a method which uses a magnetic field to control the material remo More

Superalloys generally are among the materials with poor machinability. The removal of metal contaminations, stains, and oxides can positively affect their performance. Magnetic Abrasive Finishing (MAF) is a method which uses a magnetic field to control the material removal. As another advantage, this method can be used to polish materials such assuperalloys which have high strength and special conditions. In this paper, we investigated the magnetic abrasive finishing of nickel-base superalloy Inconel 718. Since the process is highly influenced by several effective parameters, in this study we evaluated the effects of some of these parameters such as percentage of abrasive particles, gap, rotational speed, feed rate, and the relationship between size of abrasive particles and the reduction of average surface roughness. Using Minitab software package the experiments were designed based on a statistical method. Response surface method was used as the design of the experiment. The regression equation governing the process was extracted through the assessment of effective parameters and analysis of variance. In addition, the optimum conditions of MAF were also extracted. Analysis of the outputs of MAF process experiments on IN718 revealed that gap, weight percent of abrasive particles, feed rate, rotational speed, and size of abrasive particles were the factors that affected the level of changes in surface roughness. The distance between the magnet and the work piece surface, i.e. the gap, is the most important parameter which affects the changes in surface roughness. The surface roughness can decrease up to 62% through setting up the process at its optimum state i.e. in a rotational speed of 1453 rpm, feed rate of 10 mm/min, percentage of abrasive particles equal to 17.87%, size of particles equal to #1200, and gap size of 1 mm. There is a discrepancy of 13% between this prediction and the predicted value by the regression model. With mounting a magnet with a different pole beneath the work piece, magnetic flux density increases up to 35%. Manuscript profile

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List of Articles Mehrdad Vahdati