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Total 63 records
, M.Sc. Thesis Sharif University of Technology ; Akbari, Javad (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor)
Abstract
In conventional grinding of hard to cut materials such as Ti6Al4V alloys, surface burning, redeposition and adhesion of chips to wheel and workpeice occur visibly unless it is carried out at low speeds and with high volume of cutting fluid. Ultrasonic assisted grinding (UAG) is an efficient machining process for hard-to-cut materials with poor machinability. UAG improves the machinability of such materials by changing the kinematics of the process. In this research, the effect of imposition of ultrasonic vibration on the grinding of Ti6Al4V is studied. Longitudinal vibration at ultrasonic frequency range (20 kHz) is applied on the workpiece and machining forces and surface roughness are...
Extended Nonlinear Modeling and Stability Analysis of the Peripheral Milling Process
, Ph.D. Dissertation Sharif University of Technology ; Vossoughi, Gholamreza (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor)
Abstract
In this thesis, an extended nonlinear model of peripheral milling process (2D) is presented. For the first time, cutting forces are described through a complete third order polynomial function of the axial depth of cut. Also, cubic nonlinearity is considered for the structural stiffness as a function of tool tip displacement. To complete the model, process damping and tool wear effects are also considered. A set of experiments including modal tests to determine natural frequencies and structural damping ratios; and also cutting force measurements at different feed rates to determine nonlinear cutting force coefficients, are carried out. Also, measurement of critical axial depth of cut at...
Design and Manufacture of Hip Joint Simulator
, M.Sc. Thesis Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Farahmand, Farzam (Co-Advisor)
Abstract
Human joints wear gradually by diseases like arthrosis and will fail. The Pain from joint erode, preventing tracking daily activities, wont disappear by medicines and joint replacement is a common treatment. Hip joint as one of the most important, largest and heaviest joints of the body,is no exception.
Over 600,000 worldwide annual hip replacement surgery is done. The joints are designed in such a way that it can move 15 years without significant wear. Different materials such as ceramics, polymers and metals are used in making it which before in vivo use, itmust succeed many tests like wear test.
Since making artificial joints become increasingly important in recent years and...
Over 600,000 worldwide annual hip replacement surgery is done. The joints are designed in such a way that it can move 15 years without significant wear. Different materials such as ceramics, polymers and metals are used in making it which before in vivo use, itmust succeed many tests like wear test.
Since making artificial joints become increasingly important in recent years and...
Simulation of the Chip Formation and Dynamic Analysis of Micro-Milling Process Considering Size Effects
, Ph.D. Dissertation Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Akbari, Javad (Supervisor)
Abstract
Micromilling is one of the promising micromanufacturing processes used for creating 3D complex micro-scale features such as those used in MEMS devices. The mechanism of chip formation in this technique is different from that in conventional machining, because the size effects due to hardening behavior of microstructures at micro-scales and also the crystallographic orientation of a workpiece texture affects the mechanical behavior where a severe plastic deformation occurs in an induced shear band in front of the tool edge. In the present thesis, micromachining process is investigated by considering these effects. In order to capture the effects of size scale during high speed and large...
Analaysis of Ultrasonic Vibration Assisted Turing of Engineering Ceramics
, M.Sc. Thesis Sharif University of Technology ; Movahhedi, Mohammad Reza (Supervisor) ; Akbari, Javad (Supervisor)
Abstract
Due to high strength, hardness and high resistance to abrasion, ceramics are difficult for machining. Also as the conductivity coefficient of these materials is low, major amount of produced heat during machining process will be absorbed in the cutting tool which causes intensive wear in cutting tool edge. As a result employing traditional machining for these materials because of low machining speed, tool wear, high roughness and large cutting force, has little efficiency in practice. Therefore non-traditional machining method may improve efficacy. In this thesis effect of utilizing ultrasonic vibration in machining process of fused cast silica ceramic has been studied. Aim of this study at...
A Study of the Effects of Ultrasonic Vibration on the Stability of Orthogonal Cutting Process Against Chatter
, M.Sc. Thesis Sharif University of Technology ; Akbari, Javad (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor)
Abstract
Machining chatter is unstable and destructive vibrations that leads to damages to the surface of workpiece and reduces the tool life. These damages have significant effects on surface quality and material removal rate. Many studies have been done on chatter modeling and control in various machining processes. On the other hand, recently, ultrasonic vibrations have been used in many manufacturing processes including cutting to enhance the quality of products. Therefore, it is important to investigate the effect of ultrasonic vibrations on the stability of cutting process. Although a number of advantages such as improved surface roughness of workpiece and reduced machining forces have been...
Study of Ultrasonic Vibration Assisted Grinding of Fused Silica Ceramic
, M.Sc. Thesis Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Akbari, Javad (Supervisor)
Abstract
Fused silica is an important industrial ceramics with low machinability due to high brittleness, low hardness and high chemical reactivity. Traditional machining of this ceramic is very inefficient. Ultrasonic vibrations assisted grinding of this ceramic could create pieces with high accuracy and good surface quality. The main objective of this thesis is to investigative Ultrasonic vibrations assisted grinding of fused silica. Ultrasonic vibrations with a frequency of 20 kHz and amplitude in the range of 10-40 micron is applied to workpiece during grinding process. It is shown that in the ultrasonic assisted grinding, machining forces decreases by up to 45% and surface roughness reduces by...
Investigation of Wear Properties of Nanocrystalline through Multiscale Modeling of Nanoindentation and Nanoscratch Test
, Ph.D. Dissertation Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor)
Abstract
Nanocrystalline materials have received increasing attention during the last decades. Polycrystalline structures with grain sizes less than 100 nm are referred as nanocrystalline (NC). Their mechanical properties differ significantly from polycrystalline structures. As an example, hardness and wear resistance of nanocrystalline structures are higher than those of polycrystalline structures. With the reduction of grain size, hardness increases based on the Hall–Petch relation. However, at the very small grain sizes the Hall–Petch relation breaks down and a fundamental shift takes place in hardening mechanism. Molecular dynamics (MD) simulation offers a powerful method for the investigation of...
Optimization of Scan Algorithms in Selective Laser Sintering
, M.Sc. Thesis Sharif University of Technology ; Movahhedi, Mohammad Reza (Supervisor) ; Khodaygan, Saeed (Supervisor)
Abstract
One of the most important manufacturing methods using technologies AM, is the SLS method. This method because it would significantly reduce the construction time is the ability to build a variety of materials, is pervasive. The SLS devices input is part CAD file which is then part layered, a layer of powder is poured on the bed. Each layer is defined contour on the part and then scanned by laser inner layer is hatched by laser. Scanning algorithms and hatching in the SLS is an important part of building that has an impact on properties part and a lot of research has been done about it. synthetic scan algorithms presented in this study. The purpose of this algorithm is that part warpage and...
Dynamic Stability of Parallel Kinematic Machine Tools
, M.Sc. Thesis Sharif University of Technology ; Zohoor, Hassan (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor)
Abstract
Parallel kinematics machine tools (PKMs) are being received in recent years and their capability for machining has been widely studied. One of the disadvantages of these kinds of machine tools is dependency of their structural properties on their configuration. In this thesis, the effect of this dependency on machine stability for the case of a hexapod and a hexaglide machine tool is studied. The process of modeling and analysis are implemented for the hexaglide and hexapod machine tools. In the modeling, the legs are modeled using rod and beam elements whereas platform is assumed to be rigid. Both experimental and analytical analysis show that dominant frequencies of PKMs at tool tip are in...
Optimal Design of the High Speed Spindle Bearings to Reduce Non Repeatable Run Out
, M.Sc. Thesis Sharif University of Technology ; Khodaygan, Saeed (Supervisor) ; Movahhedy, Mohammad Reza (Co-Advisor)
Abstract
Creating synchronous conditions of precision and speed in rotating systems is a requirement for the design of these systems. The requirement to create these conditions is essential in various applications, such as machine tools and computer equipment. One of the main sources of error in the motion of the high speed spindles is the occurrence of non-repetitive runouts. The presence of non-repetitive runouts at high speeds greatly affects the accuracy of the rotating motion of rotating systems and reducing its effects is always considered in the design of high speed rotary systems. Usually, one of the most important factors in the occurrence of non-repetitive runouts is related to spindle...
Feasibility of Fabrication of Functionally Graded Titanium Dental Implants Using SLS Technique
, M.Sc. Thesis Sharif University of Technology ; Farahmand, Farzam (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor)
Abstract
Dental implants should be biocompatible. This ability cause bone growth beside implant and increases stability of implant. Manufactoring method and materials used in implants are main parameters affectig biocompatibility of implants. Fabrication of functionally graded structures is a novel method to increase biocompatibility. Stress shielding is one of the main causes of failures in current dental implants. This phenomenon takes place due to different young modulus of dental implants and host bone. Pouros structures remedial this problem and implant’s young modulus comes closer to host bone. The aim of this project is to study feasibily of fabrication of functionally graded titanium dental...
Molecular Dynamics Simulation of Nano-Diamond Synthesis by Shock Wave
, Ph.D. Dissertation Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Movahhedy, Mohammad Reza (Co-Advisor)
Abstract
In the field of high-pressure material science, diverse carbon systems under pressure have been intensively studied with interest in synthesizing new phases. A variety of these synthetic phases which have met various applications in today technology are called the amorphous diamond. The pressure-induced structural transition of carbonaceous material to amorphous diamond is realized by shock compression and rapid quenching. The shock compression and rapid quenching generate the high pressure (several GPa) and the temperature (several hundred K) in a fraction of a microsecond.Since the mechanical and electrical properties of the synthetic diamond are severely sensitive to the atomic structure,...
Design and Fabricating of a High Speed Micro Spindle
, M.Sc. Thesis Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Akbari, Javad (Supervisor)
Abstract
According to development of industry in every field such as nanotechnology and micro electro mechanical system (MEM) fabricating of high speed machining with micro dimension has been expanded. Micro spindles are such a device which is useful in many industries such as air space and electronic field. These machines can work in high speed and production rate with vast variety of features. Their dimensions are in millimeter range. So they can manufacture miniature features. Fabricating and technical science production of a high speed micro spindle with speed of more than 100000 RPM (micro macro milling) is purpose of this project. After to literature review according to science of micro...
Numerical Simulation of Laser Assisted Machining of Hard-to-Machine Alloys
,
M.Sc. Thesis
Sharif University of Technology
;
Movahhedy, Mohammad Reza
(Supervisor)
;
Akbari, Javad
(Supervisor)
Abstract
Laser Assisted Machining is a novel type of machining in which laser beam warms up the workpiece locally. Using laser beam in machining leads to a reduction in machining forces, an increase in tool life and an improvement in surface quality. This study introduces the process, reviews literatures related to it and then, simulates the process thermo-mechanically. A process in which a Gaussian pulsed ND-YAG laser beam of 700w power is used for machining of AISI 52100 is simulated, considering sufficient properties of material. Simulations are done using Abaqus®/Standard and Abaqus®/Explicit softwares. Also, Abaqus®/CAE visual interface, Intel® Visual Fortran compiler alongside with Microsoft...
Ultrasonic Assisted Machining of Metal Matrix Composites
,
M.Sc. Thesis
Sharif University of Technology
;
Movahhedy, Mohammad Reza
(Supervisor)
;
Akbari, Javad
(Supervisor)
Abstract
In metal matrix composites, the metal is reinforced with ceramic particles to get appropriate properties for hardness, resistance to fatigue, wear resistance and strength. Aluminum matrix composites have lower density than steels. These kinds of materials are used in military, automotive and aerospace industries due to their high strength to weight ratio and resistance to corrosion and wear. Application development of these materials are limited due to high machining and production costs. High ductility and strength of these materials and also hardness of ceramic particles cause rapid wear of tools and higher roughness of the surface. In this project the effect of ultrasonic vibration of a...
Robust Control of Self-Excited Vibration in Machining Arm
, M.Sc. Thesis Sharif University of Technology ; Moradi, Hamed (Supervisor) ; Movahhedi, Mohammad Reza (Supervisor)
Abstract
Nowadays, applications of industrial robots are significantly increasing due to their flexibility, programmable, accuracy, rapidity and etc. Among these, machining robots play an important role at manufacturing industries. One of the main concerns of the researchers, is the tip vibrations of robot arms. In most times, these vibrations are self-excited, unpredictable and intolerable. Thus, finding a method for reducing vibration should be investigated. The purpose of vibration control is vibration suppression to enhance the reliability of the system. The aim of this project is the modeling of the machining robot arm in turning process and then application of robust control to reduce...
, M.Sc. Thesis Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Akbari, Javad (Supervisor)
Abstract
In Ultrasonic Assisted Machining (UAM) a mechanical vibration is added to the relative motion of the tool and workpiece. The frequency of vibration is typically from 20kHz to 100kHz and the amplitude is in the range of 10 to 20 microns. Experiments show that using this method improves the machining performance. Reduction in machining forces and tool wear and improving the cooling condition are some of the advantages of UAM. In this work, the forces of ultrasonic assisted milling are investigated. Applying thin shear plane theorem provides an acceptable theoretical base with minimum dependence on experimental data to analyze machining forces. To evaluate the model and find the effect of...
Chatter Detection in Machining Using Time-frequency Signal Analysis Methods
, M.Sc. Thesis Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Akbari, Javad (Supervisor)
Abstract
Regenerative chatter is a self-exited vibration that causes poor surface finish, tool wear and breakage and excessive noise. It is, therefore, essential to avoid chatter occurrence passively by selecting cutting conditions that guarantee the stability of the process, or detect and suppress chatter at its onset during the process. The latter has become more important due to the complex and nonlinear dynamics of metal removal and the rising interest in automated systems. Wavelet and Hilbert-Huang transforms are used to detect chatter in machining processes including milling and surface grinding, in this thesis. In the first part of the thesis, chatter detection in milling is studied. The...
Finite Element Simulation of Machining Chatter in Turning and Milling with Orthogonal Geometry, Taking into Account of Two-Dimensional Machine Tool Dynamics
, M.Sc. Thesis Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor) ; Khodaygan, Saeed (Co-Advisor)
Abstract
Chatter vibration is a major obstacle in high quality machining. This undesirable vibration decreases the production rate, surface quality, tool life and machine tool life. In the last few decades, a lot of models have been presented to predict chatter. Most of the models, whether linear or nonlinear, have focused on modeling of machine tool dynamics and either disregard the effective parameters of chip formation process or apply some of these parameters through simplified equations. In this research, a finite element simulation of chip formation is combined with the dynamics of machine tool to investigate chatter and its effective factors. The proposed approach, unlike common mathematical...