Sharif Digital Repository

In present research, a cohesive based finite element model has been introduced to estimate median crack depth during mechanical machining on optical glasses. Development of the machining numerical model has been initiated by investigating the indentation process. Experimental results of this step have been calibrated primary numerical model which has been used in the scratch process. Due to differences between the scratch mechanism and indentation one, mathematical bases fracture formulas and cohesive relations have been developed. After extracting primary result, using them in the scratch model and developing the primary model, ultimately numerical model has been evolved to an abstract... 

Lameness in dairy cattle is a crucial welfare issue in dairy industry, and over the years scientists are attempting to present a detection method. In recent years it is attracting more attention to make the identification and discrimination of sounds and lames systematic and automatic. Right now, the most hopeful results have been obtained through the measurement of Ground Reaction Forces (GRF) of hooves, and analysis of load distribution between four legs, which seems applicable for wide use in dairy industry. However, the accuracy, validity, and reliability of discrimination is still far from an acceptable point, that is because of a great lack in understanding quantitative effects of the... 

Technology, especially in recent centuries, has changed human form of life. Case studies show that there is a mutual relationship between human being and technology; Human is a technological being and technology is also a social entity. Therefore, trying to develop a conceptual framework to describe the important role of technical artifacts in our life can be regarded as a legitimate philosophical concern. Peter Paul Verbeek is one of the contemporary philosophers who take this concern seriously. He, by using the doctrines of The Empirical Turn in the philosophy of technology, has developed a lexical system, called post-phenomenology, to describe the role of Technology in human’s perception... 

All the main knowledge currents —from the humanities to the experimental sciences— consider themselves explicitly or implicitly indebted to Neo-Kantianism, an approach that, by removing the sensory-material component from the production of reality, prevented the entry of all accidental and unexpected elements into the various fields of human knowledge and gave a not very productive peace to the European world: the peace that came to Europe not only in experimental sciences but also in politics and economy, but it made the existence of Europe weak and sterile. This is the judgment that I have tried to make as far as I can to show what fate the acceptance of Neo-Kantianism brings to man. The... 

In the proccess of making key slots in lock parts, broaching is necessary. The only procedure or at least the best procedure for making the slots is broaching. High speed and precision, surface quality and the ability to create complicated surfaces in one step are the advantages that make broaching suitable for this product. The cost of tool maintainance and replacement is very important to make this process efficient economically, therefore, determining the factors affecting tool life are important for industries. The purpose of this study is to increase the life of narrow broaching tools. In other words, in this study, the purpose is to design and manufacture the tool in such a way that... 

Thin films of materials, in order to have magnificent structure and properties, can use in complicated technology such as; electronic, optic and magnetic systems. Printed interconnects can be made by the deposition of suspensions of metal nanoparticles (e.g., silver and gold) followed by thermal sintering. The nanoparticle sintering process involves atomic diffusion resulting in shrinkage. As a result, the interconnects are prone to residual stresses generated during the thermal sintering process. The residual stress can cause cracks and delamination in the thin films and can cause permanent geometrical changes in the underlying substrates which may affect the functionality of the... 

Foil gas bearings are compliant surface, self-acting hydrodynamic bearings that use ambient gas as their working fluid. They do not require external pressurization and are typically constructed from several layers of sheet metal foils. In high-speed, high-temperature applications the GFB’s have the advantage of developing higher load capacities than with fixed geometry gas bearings. Since GFB’s have a complex structure consisting of a spring-like substructure with an overlying flexible surface, there exists a great variety of permutations on any given design. At current work presents a 1D model for GFB with couple solving Reynolds and Euler-Bernoulli beam equation. This mean top foil assume to... 

Improvements in the technology of manufacturing mechanical parts in recent years, has enabled the manufacturers to produce machine tools in small sizes (installable on a desk) which look like conventional counterparts and are called desk-top size machine tools. One important aspect of machine tools operation is the machined surface integrity. Thus, it is necessary to compare desk-top size machines with their conventional counterparts from this point of view. This comparison is the purpose of this thesis in which “surface error” and “surface roughness” of milling machines as a kind of machine tools are compared between conventional and miniaturized machines. To compare the surface errors,... 

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... 

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... 

High speed machining is becoming a progressive trend in machining processes. The main part of a high speed machine tool is its spindle. The purpose of this thesis is to design and manufcture a high speed spindle for milling machine that can rotate at speed of 16000 rpm. This spindle can be used as a test bed for experimental parametric study on the effects of spindle design parameters on the performance of spindle bearings. Various components of the spindle is studied and designed. High speed angular contact bearings and roller bearings are used in the spindle to provide high precision as well as good thermal performance. The spindle is built and tested for high precision machining with... 

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... 

Gantry milling machines are one of the types of machine tools that have vast application in various industries. Considering requirements such as quality and roughness of work pieces which are becoming restricted day after day, it is necessary that various parts of this machine have sufficient functionality and precision so that it can fulfill the quality requirements; and production of these expensive machines be cost-effective. One of the most important parts of a gantry milling machines is its crossbeam that undergoes deflections when exposed to applied forces during work conditions and can have undesirable effect on work piece precision. Therefore, the goal of this research is to design... 

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... 

In this work, a virtualized ball-end milling model is presented in Unity game engine environment, in which the machining process is simulated by proposing a new geometric approach. The model calculates and illustrates cutter-workpiece engagement area and cutting forces in a real-time manner. To calculate cutter-workpiece engagement, the workpiece’s top surface is considered a set of nodes. Then, using a new geometric method, the engagement area is calculated at any node on the engaging surface. Utilizing the calculated engagement area and adopting mechanistic force model, the cutting forces applied from each node on the workpiece surface to the tool’s cutting edge are calculated. The cutting... 

Nowadays, microgyroscopes are among the most important products of MEMS. The production of small, precise and inexpensive gyroscopes has become possible as the result of recent developments in fabrication technology. In this thesis it is intended to introduce a new method for manufacturing more precise microgyroscopes regarding manufacture facilities. Using this new method, sensitivity and resistance of microgyroscopes are increased against noises which are primarily caused by vibration and rotation about undesirable axes. The rotational movement imposed on the gyro is detected through fluid flow within its torus channel. This transformation facilitates the measurement of the initial motion.... 

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... 

Superalloys are widely used in aerospace and power industries due to the good performance at high temperatures for examples gas turbines, steam turbines and aircraft components. In addition to the turbines cobalt-base superalloys are used in medical implants such as knee and hip joints. The main strengths of the superalloys are heat-resistant, retaining their high mechanical and chemical properties at high temperatures, high melting temperatures, high corrosion resistance, resistance to thermal fatigue, thermal shock, creep, and erosion. Because of difficult to machine properties of superalloys, grinding is one of the effective methods for machining superalloys. The surface integrity of the... 

U-shaped assembly lines usually are more effective than straight lines. Therefore special attention has been paid to u-shaped line balancing problem in recent years. On the other hand most articles on the line balancing problems are investigated for the first time. However, within the lifetime of an ALB, the balancing problems do not occur only once prior to its construction, but rather continuously as rebalancing. For example whenever the demand structure or production technology changes or producing seasonal products, the ALB needs to be reconfigured. So many balancing issues in the real world are related to re-balancing of production lines.
Therefore in this study, U-shaped assembly... 

Delamination is a major problem in drilling of fiber-reinforced composite materials. Thrust force is an important factor leading to propagation of delamination during drilling process. One of effective methods to reduce machining forces is application of ultrasonic vibrations. In this study ultrasonic assisted drilling is applied to reduce thrust force in drilling of GFRP laminates. In order to conduct experiments a setup is designed and fabricated to apply both vibrations and rotation to drill bits. Using Taguchi method, a set of experiments is conducted with feed rate, spindle speed, point angle and ultrasonic vibration amplitude as control factors. The results show that applying...