Sharif Digital Repository

During the turning operation, the interaction of the metal cutting process and machine tool causes a dynamic instability called self-excited vibration or chatter. Limited productivity rate, decrease in tool life, poor surface quality and noisy workplace are some adverse effects of the chatter vibration. Chatter suppression in machining processes results in more material removal rate, high precision and surface quality. In this thesis, two control strategies are developed to suppress chatter vibration in turning process including a worn tool. A single degree of freedom model of the turning process including tool wear is briefly described. In the first stage, a sinusoidal spindle speed... 

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... 

Designing a part of an on site repair system for refurbishing steam turbine high pressure control valve has been done in this project. The main role of this control valve is to control the input flow to the turbine in different working condition . However, due to high temperature and pressure, the seat is exposed to erosion. R epairing this part in workshop requires great amount of time and cost, because the valve is a part of the turbine body and must be cut and rewelded to the turbine body. S o using an on-site repair method is highly needed. In addition, due to the limited visibility and access to the valve seat, and accurate... 

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... 

One of the most important processes in the manufacture of mechanical parts in the industry is the machining process. High-speed milling is growing in aerospace, automotive, and many other industries due to advantages such as high material removal rates and better surface finish. However, the instability caused by self-excited vibration (chatter) is not only one of the main limitations for the productivity and quality of the workpiece but also reduces the life of machines and tools. In this research, after introducing the matter of milling flexible parts, the basic concepts of machining are first described, and common terms in machining are explained. Then, a review of past research has been...