Amin Mirahamadi; Nader Sharafi
Volume 2, Issue 2 , March 2009
Abstract
The applications of electrochemical machining are increasing because of increasing requests of industries for materials with high strengh and high hardness. Regular ECM uses a tool with spicified profile shape that is similar to final shape of workpiece. In this reasearch a nozzle that delivers electrolyte ...
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The applications of electrochemical machining are increasing because of increasing requests of industries for materials with high strengh and high hardness. Regular ECM uses a tool with spicified profile shape that is similar to final shape of workpiece. In this reasearch a nozzle that delivers electrolyte to the machining gap is used for machining cylinderical workpieces. By moving the electrochemical jet on the rotating workpiece the desired profile will be shaped on it. Using high voltage and big machining gap is the most important difference between this methode and other conventional ECM mehods.
Mehdi Jafarian; GholamHosein Dehghan; Abbas Vafaeisefat
Volume 2, Issue 2 , March 2009
Abstract
Surface roughness is one of the most important parameters that plays very critical role in determining the quality of engineering components. A good surface quality resulting in improve of fatigue strength, corrosion and wear resistance of the workpiece. On the other hand, increasing cutting speed and ...
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Surface roughness is one of the most important parameters that plays very critical role in determining the quality of engineering components. A good surface quality resulting in improve of fatigue strength, corrosion and wear resistance of the workpiece. On the other hand, increasing cutting speed and decreasing time of machining are desirable for manufacturers in order to reduce costs and increase rate of production. According to importance of above subjects, having high surface with low cost is required to have proper understanding of cutting parameters of WEDM. In this study, the effect of parameters such as Power, Time-off pulse, Open circuit voltage and Servo voltage on Tungsten carbide is investigated.
Zahara Baniamerian; Cirus Aghanajafi
Volume 2, Issue 2 , March 2009
Abstract
Applying two-phase flows improves heat transfer rate which is an important objective in most of applications. Due to environmental concerns and corresponding regulations, carbon dioxide ( ), naturally exists in the atmosphere, has been reintroduced as a possible replacement for the most of commonly used ...
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Applying two-phase flows improves heat transfer rate which is an important objective in most of applications. Due to environmental concerns and corresponding regulations, carbon dioxide ( ), naturally exists in the atmosphere, has been reintroduced as a possible replacement for the most of commonly used refrigerants in air conditioning applications. High pressure working conditions of carbon dioxides had been the only difficulty in applying it in industrial applications for many years. Nowadays, by progressing in manufacturing technologies, the mentioned difficulty can be simply solved and attempts are resumed for replacing HFCs by carbon dioxide. There are limited numbers of experiments applying carbon dioxide as working fluid and due to common laboratories restrictions, that decrease the possibilities of repetition of experiments, there are dominant differences in results of present experiments in the literature. Having specific thermo-physical characteristics, carbon dioxide behaves different from other refrigerants in two-phase conditions. Therefore applying models based on other refrigerants for simulating carbon dioxide behavior results in dominant deviations from reality. In the present article the most recent experiments on carbon dioxide is gathered and investigated from aspect of heat transfer and pressure drop. Most of internal two-phase flows reach the annular flow pattern which has further heat transfer rate in compare with other flow patterns. This issue leads us to select this flow pattern in this article. The most important objective of the present study, apart from having a review on the performed studies, is to compare carbon dioxide efficiency with that of other refrigerants. At last it will appear that applying carbon dioxide as working fluid results in much more heat transfer rate and much less pressure drop level in compare with similar conditions of other refrigerants.
MohamadMehdi Mizanadl; Mohsen Dashti; Mahmoud Khodadad
Volume 2, Issue 2 , March 2009
Abstract
In present paper, the inverse problem of cavity identification, i.e. determining the location and geometric shape of a cavity inside a two dimensional elastic body using temperature measurements obtained by performing a simple heat conduction test is investigated. The Boundary Element Method (BEM) ...
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In present paper, the inverse problem of cavity identification, i.e. determining the location and geometric shape of a cavity inside a two dimensional elastic body using temperature measurements obtained by performing a simple heat conduction test is investigated. The Boundary Element Method (BEM) coupled with Genetic Algorithm (GA) and Conjugate Gradient Method (CGM) is used to solve this inverse problem. A fitness function which is the squared differences between measured temperatures and calculated ones at the same locations on the exterior boundary of a sample containing a cavity is minimized using CGM. Considering that inverse problems are generally ill-posed and local optimization methods require a good initial guess, a mete heuristic model based on GA for determining a good initial guess of the cavity is presented in this study. Then this initial guess is used by CGM to achieve accurate location and geometric shape of cavity. The major cases application of this research is in the casting industry.
Farhad Talebi; Sayed Mehdi Sayed Nasrollah; Fatemeh Yousefi
Volume 2, Issue 2 , March 2009
Abstract
Present paper is a result of consideration in reducing steady-state time of heating systems. For this purpose one should study boundary condition of the system until steady state condition. In the research, a laboratory heating system was considered using numerical simulation and the numerical results ...
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Present paper is a result of consideration in reducing steady-state time of heating systems. For this purpose one should study boundary condition of the system until steady state condition. In the research, a laboratory heating system was considered using numerical simulation and the numerical results were compared with several experimental tests. Studies shows that the steady-state time reduces significantly via two major methods called "Initial Heat Method" and "Initial Velocity Method". These two methods can apply in experimental tests planning and also in numerical simulation programs. Complete results for the experiments of both methods were presented in previous papers, and a little survey of them with some physical analysis from similar heating systems was explained in this research. Furthermore two correlation equations were presented for dimensionless time vs. dimensionless initial heat and dimensionless initial velocity using statistical methods.
MohamadReza Elhami; Mojtaba Heydari
Volume 2, Issue 2 , March 2009
Abstract
One of the main factors in poor performance of machine tools is undesirable vibrations. Unbalancing in rotary elements of machine tools cause induced vibration in machine head that influences on precision of processing material. The work presented in this paper is intended to resolve this problem. In ...
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One of the main factors in poor performance of machine tools is undesirable vibrations. Unbalancing in rotary elements of machine tools cause induced vibration in machine head that influences on precision of processing material. The work presented in this paper is intended to resolve this problem. In this paper, a 3- DOF system has been modeled with design parameters in a machine tool. Based on technical specification of material used in this milling machine real amount of parameters were calculated. The equations solved and the amplitude movement of machine head in a crucial condition of vibration obtained. The main aim of optimization in this work is to reduce this amplitude by considerable amount. For this purpose, two approaches have been suggested. The first approach is solving the dynamic equations of 3-DOF model and changing stiffness and damping property of machine body material so that reduce the head movement to the desired level. It was found that such an especial material is not easy available and in case of finding, is not economical. Therefore, the second approach was suggested, i.e. adding a dynamic absorber to the drilling machine in three different positions to improve the situation. In this approach, only one DOF is added to the model and solve four differential equations with unknowns of mass (MD) and stiffness constant of spring (KD) for dynamic absorber. The mechanical impedance was used for these equations and the results obtained in complex coordination. In MATLAB, a procedure for optimization of MD and KD of dynamic absorber has been developed. Finally, the range of available MD and KD in industrial market was defined. The results have shown that adding dynamic absorber both more effective and more economical than changing material. The final achievement is though, the place of installing dynamic absorber. If the dynamic absorber install on the machine head is much more effective than putting in the base of machine tools, as a regular practice. Finally, a design criteria has been suggested for mass and stiffness of the dynamic absorber.
Navid Negahbani; Mostafa Ghayour
Volume 2, Issue 2 , March 2009
Abstract
In this paper a modular wheel less snake-like robot by considering viscous friction is modeled. The motion equations of the robot are derived. Then by imitating a real snake motion, the robot is controlled on the way that tracks the predefined trajectory. The controller controls the center of mass and ...
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In this paper a modular wheel less snake-like robot by considering viscous friction is modeled. The motion equations of the robot are derived. Then by imitating a real snake motion, the robot is controlled on the way that tracks the predefined trajectory. The controller controls the center of mass and global orientation. The motion of the robot is simulated for tracking a line and a sine curve. It is shown that the robot tracks the trajectories smoothly.
Ebrahim Harirbafan; MOhsen Mohseni Shakib; AliAkbar Karimi; Mojtaba Heydari
Volume 2, Issue 2 , March 2009
Abstract
Flexible joint has the most critical role in Thrust Vector Control (TVC) solid fuel rockets. In this paper, a new analytic method for calculation of stiffness of spherical Elastomer-Metal joint by the theory of linear elasticity and Velasof Kantorowicz analytic method is developed. Velasof Kantorowicz ...
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Flexible joint has the most critical role in Thrust Vector Control (TVC) solid fuel rockets. In this paper, a new analytic method for calculation of stiffness of spherical Elastomer-Metal joint by the theory of linear elasticity and Velasof Kantorowicz analytic method is developed. Velasof Kantorowicz analytic method is based on cross displacement which is driven from bending equation. Then flexible joint is simulated by ABAQUS code under bending load when thrust vector angle is critical (i.e. 15 degrees). Seven different configurations of metal and rubber layers are considered. In each configuration, required bending is determined when thrust vector is 15 degrees and maximum stress is calculated. Based on these results best selection of elastomer material and stiffness is proposed. Finally, the results of analytical and those of simulation are compared which show good agreement. This comparison shows that the derived formula predicts stresses precisely.