مجله مهندسی ساخت و تولید ایران
سال سوم شماره 1 (بهار 1395)

The increased material removal rate in ultrasonic-assisted wire electrical discharge turning (by∼2 times)was attributed to compressive and rarefying wave front in dielectric and discharge column sliding into plasma channel and molten crater due to applying lateral ultrasonic vibration on the wire. A single discharge was analytically and experimentally studied and the effective forces and factors on plasma channel including Lorentz force¡ increase of pressure and surrounding vapor ionization of plasma channel¡ elongation of molten crater due to lateral displacement of wire and creation of positive and negative pressures of the ultrasonic wave on molten crater were investigated. Experiments were performed in different machining parameters of voltage and power with and without ultrasonic vibrations. By using ultrasonic vibration¡ the plasma density was increased due to decrease of bubble growth. The current density was increased and pressure drop in the end of discharge was increased. As a result¡ a great amount of the material was exploded out of the crater due to bulk boiling. The plasma channel sliding was elongated the molten crater on workpiece surface¡ which leads to material removal increase.

Metallic foams are a new category of metals with a porous structure which possess new mechanical¡ thermal¡ electrical and acoustic properties including low density with simultaneously high stiffness¡ and acoustic and thermal insulation. These materials are utilized as a sandwich core to decrease the structure total weight and also¡ energy absorption and damping. Wide range of metallic foam application makes it necessary to develop a modeling method which can be used in the numerical study of the mechanical behavior of these materials. In this regard¡ a novel geometrical modeling approach is proposed to produce a geometrical model of the foam. This is based on subtracting spherical pores with a random size and random position from the solid sheet which makes a more realistic way of foam sheet modeling. Most of the prior approaches use a repeating unit cell structure. Thus¡ three algorithms¡ including progressive subtraction¡ incremental and random-based subtraction of the pores are presented and developed. The proposed model validation is carried out based on geometrical aspect and with the comparison of four parameters such as relative density¡ cell size ranges¡ distribution of cell sizes in the foam structure and mean cell sizes. Results show a close agreement between modeled foams with real ones. Also¡ geometrical study results that with an increase in the mean cell size¡ relative density first increases and then decreases.

Development of research on aluminum light joints is one of the most effective ways to reduce fuel consumption¡ increase strength and development of aerial structures. In this study¡ the feasibility of Tjoint AA7075 aluminum alloy with using friction stir welding process was studied. For this purpose the AA7075 aluminum joint with different tool offset¡ plunge depth¡ linear and rotational speeds were studied. In order to better understanding the production and distribution of heat¡ welding process was simulated using commercial fluent package software. Depending on the selected parameters in the process¡ the strongest connection was produced in the 1.5mm tool offset on advancing side¡ the 0.4 mm plunge depth¡ 2o tool tilt angle¡ and 1325 rpm rotational speed and 69 mm/min linear velocity¡ respectively. The failure position of all tensile samples was located on the T appendage. Tunnel void was the major defect in the joints which disappeared with increased heat input and cooling rate. The strongest connection which produced in these experiments had 181 MPa strength that nearly 80% of the aluminum base metal. The connection elongation after the tensile test was close to 11 mm.

Phased array transducers because of their unique features¡ are used in many applications. Application of such transducers in non-destructive tests to detect defects such as porosity and crack¡ as well as stress measurement¡ in medicine for medical imaging and treatment of diseases¡ as well as in navigation range finder and acoustic (sonar)¡ are some of the applications of this system. One of the important features of this type of transducer to other transducers¡ is the ability to focus waves at any distance and angle. The main objective of this paper is to study geometric parameters of a linear phased array transducer with 8 piezoelectric elements such as width and thickness¡ the distance between elements as well as excitation frequency and voltage on acoustic pressure at the focal point using numerical methods. First¡ for the purpose of verification¡ the experimental result of an element was compared with the numerical approach. The experimental tests confirm the transducer’s behavior in terms of design¡ extracted algorithm and also the simulation. Acoustic pressure along the crystal axis was measured using both experimental and numerical methods. Experimental tests confirmed the accuracy of the transducer behavior in term of acoustic pressure. Operating frequency and mode shape of piezoelectric element disc shape with 53 mm diameter and thickness of 5 mm¡ was calculated using the finite element method. First radial mode in frequency of 45649 Hz was chosen as suitable frequency and shape mode. Algorithm to obtain the elements time delay to focus the waves was developed in the form of a computer program and its validity was investigated using the finite element method. As expected¡ due to the superposition of acoustic waves in the focal area over a period of time¡ its acoustic pressure is more than the time at which all crystals get excited simultaneously.

In this study the initial critical load in yoke plates is found by experimental testes. The finite element analysis is carried out in both linear and nonlinear buckling cases in ansys software. Analytical solution for buckling in case of rectangular plate is investigated and compared with finite element simulation and experimental tests. For accuracy in results¡ the simple tension test is carried out for plate for both the longitudinal and transverse tensile test specimens and full stress-strain curve of steel st52 that is obtained from experimental testes import to software for simulation. The agreement between numerical¡ analytical and experimental results is very good.

In this paper¡ a new approach for calculation of the cutting force coefficients which are the most important and significant factor in prediction of machining forces¡ is presented for flat end mills. The proposed methodology models a practical mechanism for collecting and analyzing experimental data. The surface error is the measured parameter used for defining the cutting-force coefficients. Neglecting the effects of other factors that cause to deflect cutting tools¡ in cutting process¡ the machining forces imposed on flat end mills are considered as the most important factor in deflection of machining tool that leading surface error. In this research¡ The Ving-Lee model which is an appropriate force model with a good ability on milling process mechanical modeling is used. In proposed method¡ the related cutting force coefficients of the force model are calculated by measuring the surface error on a profile of the machined surface along End Mill that caused by tool deflection under machining forces¡ and by correlate error along this profile to tool deflection and use of equation between tool deflection and cutting force. The resulted forces and surface error¡ when applying the new cutting force coefficients show a good agreement between the predicted and measured.

Drilling machining processes is one of the most widespread applications in manufacturing of various mechanical parts and equipment. One of the interesting technologies in drilling¡ micro drilling process that is critical in industries such as precision manufacturing nozzle for refueling vehicles¡ parts and camera clock is used. The drilling operations of metals¡ for having holes with desired quality and accuracy¡ it is required that various factors such as spindle rotation speed¡ feed rate and drill diameter evaluated. In drilling¡ increase the speed of spindle rotation speed machining and material removal rate is also increasing¡ and the other side is the erodes faster tool. Therefore¡ careful selection of various parameters in the drilling operation is necessary. In this paper¡ by doing experiments¡ a linear regression model to predict the rate of material removal rate during the second drilling operation based brass spindle rotation speed¡ feed rate¡ tool diameter and effective interactions are presented. Then¡ using statistical sensitivity analysis Sobol¡ the impact of parameters on material removal rate is obtained. The results of the sensitivity analysis show that the rate of material removal rate has the greatest impact on advancing the tool diameter is the least effect on the rate of material removal.

The electrical resistance between the different components of fuel cell¡ related to the compressive stress between the various components is the fuel cell. In this study¡ two important goals pursued: first obtain the least stress on the gaskets for leakage will not happen and additional investigated the effect of stress distribution on gas diffusion layer on the amount of electrical resistance. To reach this goal¡ first designed experimental setup and achieved 2MPa minimum compressive stress on the gasket to prevent leakage. Then by another experimental setup effect of compressive stress on resistance value between the different parts have been investigated. Then according to experimental data¡ effect of clamping force on electrical resistance in simulation was investigated. Moreover effective parameters on pressure distribution on gas diffusion layer and electrical resistance was investigated. It was observed that the electrical resistance decreases by increasing clamping force. also observed pressure distribution in 4 bolt not uniform. By increasing bolt up to 8 the pressure uniformity was better than 4 bolt. But by increasing the number of bolt 8 to 12 significant changes not occurred.