Sharif Digital Repository

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... 

The fiber-reinforced composite materials possess advantage for structural purpose in various industries. Delamination is recognized as one of the major causes of damage during drilling of fiber reinforced composites, which not only reduces the structural integrity, but also has the potential for long-term performance deterioration. It is difficult to produce precise quality holes with high efficiency by conventional drilling method. Drilling is frequently applied in production cycle while the anisotropy and nonhomogeneity of composite materials affect the chip deformation and machining behavior during drilling. In this thesis, a new non-traditional drilling technology is presented for solve... 

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... 

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... 

Drilling super alloys with a good hole quality and acceptable surface finish is a constant challenge in modern industries dealing with such materials. Ultrasonic assisted drilling is a modern and nonconventional method of drilling which has attracted many researchers attention recently. In this study deep drilling on Inconel 738 LC is done using ultrasonic assisted drilling technique and the results are compared with those of Electro Discharge Machininng or EDM method. The results show that Ultrasonic Assisted Drilling or UAD is an appropriate alternative for EDM of Inconel. The whole process time is decrease dimensional accuracy is improved and surface roughness is decreased significantly.... 

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... 

Ultrasonic assisted grinding is a novel method for improving the grinding process of difficult-to-cut materials. In the present research a novel set-up has been designed and manufactured for utilizing ultrasonic vibrations in cylindrical grinding. The designed ultrasonic head vibrates a rotating workpiece in axial direction. An alumina-zirconia ceramic (AZ90) has been selected as the workpiece material. Energy aspects and workpiece surface characteristics of ultrasonic assisted cylindrical grinding (UACG) and conventional cylindrical grinding (CG) processes have been analytically modeled and corresponding grinding experiments have been performed. The combined kinematics of the cylindrical... 

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... 

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... 

Machining of Aluminum Metal Matrix Composites faces different problems including adhesive wear, large machining forces, chatter, poor surface quality and therefore low geometric accuracy etc. due to the fact that a ductile matrix is supporting brittle particles. On of the methods used to reduce such difficulties is vibration assisted machining in which a 10 to 20 micron displacement stimulation is applied to the workpiece or tool during machining process. The effect of this method on the milling of the Al/Sic composite is studied through two separate experiments including one and two dimentional vibration assisted milling respectively. Milling forces, tool wear and surface quality are... 

This research studies the feasibility of the BK7 optical glass milling process with ultrasonic vibrations. Due to the fragility of glasses, especially optical glasses, machining is very sensitive and complex. For this reason, it is necessary to think for the glass machiners to minimize the defects and failures of the process. So far, efforts have been made to reduce the defects caused by machining on brittle materials, such as increasing the speed of the period, reducing the feed rate of the tool, changing the geometry and the type of tool, the type of process lubrication, etc. In addition, other operations performed to improve the surface of the glass are of better quality, using hybrid or... 

Nowadays, processes with the ability to machine advanced materials are very much needed by industries. Therefore, compare of a rotary ultrasonic-assisted machining process with a conventional machining process is carried out in this study. In order to evaluate this process, the milling and drilling processes are conducted on the carbon fiber-reinforced polymer composite and titanium materials where cutting forces, surface roughness, and fiber pull-out are selected as critical factors for analysis. As a result, it is seen that rotary ultrasonic-assisted machining has a good performance in the milling and drilling of advanced materials. In particular, it is shown that fiber pull-out is...