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    Chatter Phenomena Prediction in Two-dimensional Milling Process from Chip Formation by Using Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Tavassoli, Meysam (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Chattering in cutting process is one of the destructive phenomena in machining, which results in ripple of workpiece surfaces. In this phenomenon, the displacement of the tool tip moves towards instability and the tool vibration continues. Eventually, the tool jumps or breaks out with relatively large shear forces, which leads to a reduction in the rate of production and machining. Since machining processes are very widespread, phenomenological studies of chatter have progressed in the field of modeling and empirical experiments. Research in the field of modeling is mainly intended to examine the dynamics of the tool in two ways: analytic and finite element. In these methods, there are... 

    Thermo-mechanical Modeling of Angular Contact Ball-Bearings in High Speed Machine Tool Spindles

    , M.Sc. Thesis Sharif University of Technology Zahedi, Ali (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Machining in its general concept forms the major part of manufacturing processes regarding time and cost. Therefore any progress in machining techniques would be well beneficial. High speed machining is one of the recent concepts in machining technology which has attracted much attention and effort. But high speed spindles as the main part of high speed machines, have been notorious for their lack of reliability and sudden failure which originates mostly from thermal problems. In order to ensure reliable operation of spindles it is necessary to predict thermo-mechanical behavior of machine-tool spindles. The major sources of heat in a spindle are angular contact ball bearings (the most... 

    Expansion Modeling of Coronary Stent for Selection of Optimized Stent

    , M.Sc. Thesis Sharif University of Technology Izadi Ramini, Elaheh (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Referring to mortality increasment having sprung from atherosclerosis, work on treatment of coronary heart disease seems to be necessary. Stent implementation is one of stenosis treatment. Stent deployment has been done during past two decades, but clinical evidence showed that because of some weakness in designing and implementing, restenosis occurs again. Material, structure and coating texture of stent are the designing criteria beside stent implementation importance. Thus a lot of activities have been done in this area to improve performance of these applications. Nowadays a lot of companies' researchers try the best to get better their products; consequently there is different types of... 

    Tolerance Analysis and Dimensional Error Propagation in Truss Structures

    , M.Sc. Thesis Sharif University of Technology Aghabeigi, Mostafa (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    An analytical method is developed for description of the assembly process and dimensional error propagation in planar truss structures using two core concepts of “triangular unit cell” and “redundant member”.In order to clarify backbone of the developed method, its connections with other studies in the fields of tolerance analysis, robust design and structural optimization are discussed.Subsequently, triangular unit cell is defined as the basic element of internally determinate trusses and a suitable formulation is derived for calculating its dimensional error propagations characteristics.It is shown that having such a model for a single unit cell is sufficient for tolerance analysis of the... 

    Thermo-elastic Development of Cylindrical and Spherical Superelements and Introduce a New Gigh Speed Angular Contact Bearing Superelement Model

    , M.Sc. Thesis Sharif University of Technology Shamloofard, Mansoor (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Angular contact bearings are utilized in many industrial types of machinery, including machine tools’ spindle. Spindle is one of the most important parts of a machine tool, which has a substantial impact on dynamic properties and stability of machining processes. Spindles’ motion takes place under guidance of bearings, which are mainly angular contact type. Since bearings’ loading under forces that are resulted from angular velocity and temperature increment are intensified, it is required to control the applied forces in operating situation, in order to predict the hardness, accuracy, efficiency, and life time of spindle. Thus, determining the dynamic performance of machine tool’s spindle,... 

    Design and Manufacture of Variable Preload System for High-Speed Spindle Bearings

    , M.Sc. Thesis Sharif University of Technology Razban, Masoud (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Machine tool spindles of late require high stiffness and fast rotation characteristics all at once for high- speed, high-efficient processing, as well as for a wide range of use rotation. Bearing preload is the main reason for Dynamic characteristics of spindle. As such, many studies are being carried out on automatic variable preload control methods that apply a preload to a spindle bearing as an alternative to the existing fixed position preload and constant pressure preload methods. This study introduces a newly design automatic variable preload system. This system can automatically reduced preload with increasing spindle rotational speed through the use of centrifugal force. The system... 

    Migrating From 3D Modelling of the Laser Assisted Machining Process into a Valid 2D Model

    , M.Sc. Thesis Sharif University of Technology Mousavi, Mohammad Amin (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Due to recent advances in laser technology and instruments, laser assisted machining processes has gained extra attention by scientists and industries. Naturally, effective modeling of the process is of great interest for researchers. Machining processes are generally modeled via FE tools and based on the requirements of model, it can be performed either mechanically or thermos-mechanically. About the LAM problems, it is basically meaningless to have a model without considering thermal effects. Hence, modeling is performed in two steps where through the first one, a thermal problem is solved to bring the temperature distribution of the work piece as the initial conditions of the next step.... 

    Study of the Effects of Powder Dispensing Mechanism on Selective Laser Sintering Process

    , M.Sc. Thesis Sharif University of Technology Mahmoodi, Amir Hossein (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Additive manufacturing (Simply called A.M.) is a group of manufacturing technologies that is developing rapidly and is being used widely in some industries like car manufacturing, Aerospace and producing Biomedical devices, In a way that some researchers believe that A.M. methods will change the future of manufacturing. One of the most important A.M. techniques is the Selective Laser Sintering (SLS) method that is mostly used in industrial applications. A SLS machine has a lot of sub systems and mechanisms that have key role in the Laser Sintering process. One of the mechanisms of SLS machine is the Powder Dispensing mechanism that produce layers of unsintered powder as thin as 100 microns... 

    The Effect of Different SLS Parameters on the Density of Polymer-Metal Parts

    , M.Sc. Thesis Sharif University of Technology Montazeri, Ali (Author) ; Movahhedi, Mohammad Reza (Supervisor)
    Selective Laser Sintering (SLS) is one of the powder-based Additive Manufacturing (AM) technology in which parts built by CO2 laser. In this research work, Titanium-PMMA-Stearic Acid powders are mixed together to produce parts by Indirect Metal Laser Sintering (IMLS) method. The optimum process parameters such as energy density, Percentage composition of Titanium-PMMA and Scan Sintering are obtained by adopting the Taguchi method for getting the maximum density and minimum porosity. Experiments are planned by Taguchi’s Mix-L8 orthogonal array. According to the results obtained from this study, the percentage of combination Ti-PMMA and Energy density, respectively, are a major parameters that... 

    Design and Prototyping of an Ultra High Speed Air Micro Spindle

    , M.Sc. Thesis Sharif University of Technology Ghasemian, Behnam (Author) ; Movahhedi, Mohammad Reza (Supervisor)
    Today, the need for high-speed machine tools, in areas such as defense, medical and electronic for producing parts with millimeter dimensions, and with features smaller than the millimeter, increased. To meet this need, the machine tool can be used with smaller dimensions and with high speed. These machines are able to produce these parts with high production rates.The project aims to improve technical design and construction of a micro spindle to achieve sustained speed about one hundred thousand RPM. In this project, the first step in understanding the fundamentals of the theory and the system components, and the whole operation was performed. The design is based on studies carried out in... 

    Prediction of Machining Chatter Based on 2 Dimensional FE Dynamic Modeling of Chip Formation

    , M.Sc. Thesis Sharif University of Technology Haj Mohammadi, Mohammad Saleh (Author) ; Movahhedi, Mohammad Reza (Supervisor)
    In machining processes, chip formation is one of the most important methods to obtain the final shape of a work-piece. Improving the machining processes leads to the increase in the material removal rate (MRR) and reduction of high economical costs. Vibration is an undesirable phenomenon in machining processes because it results in reduction of material removal rate (MRR), poor surface finish and increased tool wear. Among various types of vibration, self-excited vibration or chatter is the most important one. It is obvious from previous investigations that for prediction of machine tools vibration, many simplifications were assumed while the linear and non-linear effects are not considered... 

    Simulation of Chip Segmentation in Metal Cutting Using ALE Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Rakhshan Haghighifard, Pedram (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Since it is important to obtain the suitable cutting conditions for machining and investigate the effect of various parameters on this process, the simulation of this process has been developed extensively by using the finite element method in recent years. Due to very large plastic deformation and also continuous chip flow, one of the most appropriate techniques in modeling chip formation is the arbitrary Lagrangian-Eulerian (ALE) finite element method which has been used in several papers using some traditional codes like ABAQUS or personal codes in recent years. However, one of the limitations in this method is the use of a continuous mesh retains with no change in connectivities which is... 

    Analytical and Experimental Modeling and Predicting Chatter Occurrence during Thin-walled Parts Milling

    , M.Sc. Thesis Sharif University of Technology Sotoudeh, Mahsa (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Milling of thin-walled parts is a widely used process in aeronautical and automotive industries. Along the milling of these low rigidity parts, large quantities of material are removed using high removal rate conditions with the risk of the instability of the process as the result of chatter vibration. Self-excited chatter vibration is an undesirable phenomenon in all machining processes and many efforts have been made in order to understand its mechanism and deal with its destructive effects. Studying chatter in machining processes with variable dynamics, which this thesis represents an instance of it, has been taken into consideration in the recent years. Most of researches done in this... 

    Predicting Stability in Low Depth Milling

    , M.Sc. Thesis Sharif University of Technology Mozaffari, Hojjatollah (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Chatter in milling causes problems like damage to the device, losing precision or sleekness, increase in cannibalization, damage to the spindle, higher level of noise, and problem in thin objects. Current theories in regenerative chatter in filing, has a high relation with a work time (ρ~1), but in less deep filing (ρ≪1), these theories have errors (ρ is time per rotation period). Some of the usages of less deep filing are: 1- surfaces that are hard to file 2- creating curve surfaces 3- sleeking surfaces.Formulating these chatters and solving them using nonlinear methods help using the correct filing depth to reduce them. Goal of this project is to solve chatter equations in low depth filing... 

    Parametric Tolerance Analysis of Rigid Assemblies

    , M.Sc. Thesis Sharif University of Technology Salehvesal, Amir Hossein (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    In a mechanical system, dimensional and geometrical tolerances of components propagate kinematically through assembly and accumulate in a way that alters the critical dimensions of the assembly. Analysis of the accumulation of components tolerances and their influences on the critical dimensions of the assembly (design requirements) and also understanding the behavior of the entire system according to these effects is called tolerance analysis. Tolerance analysis is a key tool in quality improvement, cost reduction and profit growth, and it plays an important role in industrial productions. The Majority of mechanical systems are 3-Dimentional in nature, and approximating them as... 

    Fabrication of Micro-Strain Gauge Using Electrohydrodynamic 3D Printing Technique

    , M.Sc. Thesis Sharif University of Technology Aerafi Firozabadi, Ali (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    A significant number of small-scale sensor sales have been reported in recent years. Strain gauges are one of the most common tools for measuring the length change of a part. Nowadays, 3D printing technology can be used in the fabrication of small-scale sensitive sensors, and metal nanoparticles printing are especially suitable for the production of flexible electronic sensors. Electro-hydrodynamic printer, with micro-scale printing capabilities, can be used as a new invention in fabrication of sensors. This type of printer uses the inkjet printing method and the basis of this type of printer is to apply an electric field to shrink the fluid jet. In the present study, pure ethanol was first... 

    Multiphysics Modeling and Magnetic Control of Powder Deposition Process in DMD Method of Additive Manufacturing Technology

    , M.Sc. Thesis Sharif University of Technology Nejati Eghteda, Sina (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Direct Metal Deposition is one of the methods of Additive manufacturing that has seen the most spread in recent years. In this method metal powder is directed towards the free surface of the workpiece through a nuzzle, and is simultaneously heated to become molten in a melting pool by a laser beam and begins the deposition process. One of the parts that make up a DMD system is powder feeding nuzzle. These nuzzles usually encounter a similar fundamental problem: that the effect of gravity on the stream of metal powder and the carrier fluid causes this stream to deviate from its intended position. To prevent this, nuzzles are usually designed with a fixed downward angle and the angle of the... 

    Study of Chatter Stability in Boring Using Operating Deflection Shape

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Zohreh (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Chatter in machining systems is a limiting factor of workpiece surface, tool and machine life and material removal rate. Because of this, studying and modeling of vibrations is very important in the machining. This study is much importer in the boring operation because boring bar's length to diameter ratio is very high and so it is very sensitive to vibrations. As we know, vibration characteristics of a machine change between its operating condition and its resting mode. Because of this it's better to study machine's vibrations when it's working. This study requires some methods that can find operating parameters of machine. The aim of this work is to find these parameters. For finding these... 

    Design and Prototyping of a Continuous Coaxial Nozzle for Uniforml Metal Powder Deposition at Various Angles

    , Ph.D. Dissertation Sharif University of Technology Nasiri Khansari, Mohammad Taghi (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Direct metal deposition (DMD) process is an additive manufacturing technology that is rapidly gaining laser importance due to its various capabilities in applications such as coating, repairing high-value damaged parts, rapid prototyping and even production in small quantities. Among the equipment needed for this process, nozzle is perhaps the most important component because its performance affect the efficiency of powders trapped in the molten pool, and is crucial to the quality of the deposited layer. The existing nozzle designs can be categorized in two groups; lateral and coaxial nozzles; and the coaxial ones are divided into continuous and discontinuous types. Coaxial nozzles have... 

    Hip Joint Preforms Designing Steps With Inverse Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Nejati, Masoud (Author) ; Movahhedi, Mohammad Reza (Supervisor) ; Akbari, Javad (Co-Advisor)
    Forging process is recognized as the high speed method, economical and with ability to produce high strength parts between metal forming processes. Preform design is the most important step in forging process. In the past this work was done based on experiences. In the complex parts because of error in design there was probability of diverse dies, so that method needed to spent so many times and costs. However recently with progress in computer programming we don’t need to produce diverse dies but spend many times. In this field many investigations are done to dispose designers skills, so forging preform design based on inverse finite elements method is denoted for this gold. In this thesis...