مجله مهندسی ساخت و تولید ایران
سال دوم شماره 4 (زمستان 1394)

Electrical discharge machining (EDM) is a modern machining method which in pace with industrial developments, various studies are aimed at improving this process's parameters including material removal rate. In previous researches, changes in machining tool’s properties and specifications have been investigated as the solution to improve the material removal rate. A novel and efficient process to change material microstructure and properties is equal channel angular pressing (ECAP) that is appropriate method to produce fine grains materials with high strength and adequate properties. In this study, the pure copper material was processed through 4 and 8 passes of ECAP and its effect as a toolfor EDM process, on material removal rate, with different discharge current and pulse ontime was examined. Microstructure of the specimens were analyzed after ECAP operation using electron back scatter diffraction method (EBSD), and the average diameter of grains for specimens were measured using this technique. The results of the experiments indicated that processing the copper tool with ECAP through 4 passes, increases the material removal rate up to 13.2 percent. Moreover, increasing the number of passes of ECAP from 4 to 8 improved the effectiveness of this process on increasing the material removal rate up to 5.5 percent.

In this research, a 3×3 active sonar array consisted of Tonpilz transducers with the common protective coating materials, i.e. polyurethane, corprene, silicone rubber and neoprene has been simulated by COMSOL Multiphysics finite-element software, where the simulation results, including the important characteristics of a sonar array have been analysed and compared. These characteristics include Transmitting Voltage Response (TVR), beam pattern, total radiated power, and Receiving Voltage Sensitivity (RVS). The array coating materials cover major tasks in arrays, one of them is to prevent water and contaminants from entering into the chamber of the array. The performance characteristics of the array with the coating differ significantly with respect to the uncoated one; hence, their investigation and analysis is crucially vital. The simulation results indicated that at the presence of protective coating materials in arrays, the TVR and RVS are reduced in comparison with the uncoated ones while the most reduction in TVR and RVS belongs to neoprene respectively 1.4% and 2.2%. The resonance frequency of the array with the silicone rubber protective layer was measured to be 32 kHz which is the greatest with to the other coating materials. It was also found that the coating materials have no effect on beam width, but increase the band width of the array. Neoprene exhibited the greatest increase in band width as much as 5 kHz.

In this research, a novel severe plastic deformation (SPD) method entitled cyclic flaring and sinking (CFS) is presented for producing of the fine-grained copper tubes. Finite element simulation has determined the influence of design parameters. CFS process includes two different flaring and sinking half-cycles. At flaring half cycle, the flaring punch with two stepped regions is pressed into the tube. Shear and normal tensile strains are applied as a result of the existence of shear zones and increase in the tube diameter. In the second half cycle, the tube is then pressed to sinking die that applies same shear strains and normal compression strain so that the initial diameter of the tube is achieved and high plastic strain is applied. This process can be run periodically on the tube to exert more strain and consequently finer grain size and ultimately achieve better mechanical properties. The true stress-strain curve of pure copper tubes was studied in different cycles. Results show the increasing strength in upper cycles if the yield and ultimate strength were significantly increased to 185 Mpa, and 285 Mpa, respectively from the initial values of 120 Mpa, and 180 Mpa. On the other hand, the elongation to failure was decreased after the process. The average hardness along thickness has reached to 127Hv after eleven cycles from 96 Hv.

One of the most important issues in the manufacturing of composite structures is the ability to connect and assemble them. Design and manufacturing of connections with the appropriate strength is essential. One of the strengthening methods of composite connection is the employment of reinforcing elements in the adhesive layer. The use of additional elements in the adhesive layer leads to uniform stress distribution and consequently improves the joint strength and toughness. In this paper, the idea of using metal wire for enhancing the adhesive joints was developed for the first time. Parameters such as the number of wires, wire diameter and mechanical property of wire were considered as the influencing parameters on the joint strength. Experimental tests were designed in order to evaluate the effect of these parameters and the obtained results were described with the finite element outcomes. It was observed that the joint strength improved more than 90% using 20 wires as reinforcing elements in Araldite 2015 adhesive. It was also found that increasing the number of wires, wire diameter and wire stiffness led to the more uniform stress distribution and increased the joint strength.

Hot metal gas forming (HMGF) is a process in which the sheet or tube metal is heated to temperatures above half the absolute melting point and then, plastic deformation is placed by applying gas pressure. Due to temperature limitations in hydroforming process, nowadays HMGF process has been of interest to researchers. For this purpose, at first the effect of pressure on the tube bulging of single-layer aluminum tubes was studied. Then two-layer tubes of copper (inside) - Aluminum (outside) were tested. Aluminum tubes from AA6061 and copper tubes from C1220 was selected for study. For comparison the tests were done at two thermal conditions of isothermal and with a temperature gradient, and the rate of expansion and rupture were investigated. The results showed that the maximum bulge to tube bursting in under isothermal condition is better than gradient condition. The highest bulge of about 32.21 percent for single-layer aluminum tubes and about 34.68 percent for two-layer copper-aluminum tubes was obtained under isothermal condition.

Applying ultrasonic phased array transducers has been widely recognized through fault detection and inspection, underwater telecommunications and medical studies due to their uniquely significant properties. One important capability is wave focusing. The main objective in this study is focusing ultrasonic waves using linear phased array transducers. The environment in this research is water. Design and fabrication of these transducers is done in both mechanic and electric sections. First, dimensions of the transducers in terms of their number, size and arrangement elements were determined. The linear arrangement including 8 piezoelectric disks was checked. Based on piezoelectric shape modes, 46 kHz was determined as the appropriate operating frequency for the transducer. Afterwards, the appropriate algorithm for piezoelectric stimulation, backing material and their size in addition to the matching layer were determined; accordingly, simulation and verification of the design and estimation of transducer behavior were applied. Hence, assembly and construction stages of the transducer were done. Electric design includes the design and construction of control and power circuit to stimulate phased array transducers. The constructed transducer’s behavior including acoustic pressure measurement in terms of different height levels of the transducer, piezoelectric stimulation voltage influence and each element influence on acoustic pressure in focused area was experimentally studied. Hydrophone was used to determine the acoustic pressure. Results indicate that one of the most important factors about wave focusing is the number and displacement of the elements. Polyurethane was the most proper choice in phased array transducers due the problems of using PVDF as matching layer. Concerning disk piezoelectric with high diameter proportion rather than high thickness, first radial modes are the proper choice for the transducer’s shape mode. The experimental tests confirm the transducer’s behavior evaluation correctness in terms of the design, extracted algorithm and also the simulation.

In this study the effect of rubber thickness on forming quality of metallic bipolar plates microchannel’s was investigated in rubber pad forming process. ABAQUS/Standard finite element software was used to simulate the process, where the accuracy of the simulation results was evaluated by using experimental results. To perform experimental procedures a die with parallel flow field was used to form SS316 bipolar plate with 0.1 mm thickness. For this purpose the effect of punch load and rubber thickness on channel depth, filling percentage, thickness distribution and thinning percentage of the formed parts were investigated. In this regard, rubber layers thickness of 1 mm to 7.5 mm thickness were tested. First, the effect of punch load and rubber thickness on the microchannels depth of bipolar plates was investigated. The results demonstrate that with increasing punch load and thickness of the rubber layer, leads to increasing the channel depth and filling percentage. Amount of force in forming of four microchannels will decrease from 82.25 kN to 55.15 kN by increasing in thickness of rubber layer from 1.5 to 5.5 mm, that show 31% decrease in forming force to achieve 0.75 mm channel depth; while more increase in rubber layers thickness has no significant effect on forming force. Moreover optimum thickness of rubber layer will decrease from 5.5 mm to 3 mm by decreasing the number of microchannels from 4 to 1. According to the result, increasing the rubber thickness would achieve greater channel depth at equal punch force, which also leads to increase in thinning percentage. Furthermore, increase in the thickness of rubber layer leads to more uniformity of the samples thickness distribution at outer corner radius. Thinning percentage difference at outer corner radius decreases from 3% by using rubber thickness of 1.5 mm to 0.4% by using rubber thickness of 5.5 mm, which indicates considerable improvement in uniformity of thickness distribution.

Abrasive flow machining is one of the modern processes for polishing external surfaces, edges and internal surfaces of industrial parts with close tolerances and superior quality. In this method a viscose fluid which includes abrasive grains, will pass through internal and external features under pressure in a reciprocating motion wherein work piece surface gradually achieves desired surface quality. Low removal rate is one of its restrictions in industrial application. Accordingly, to overcome this drawback, application of centrifugal force is proposed by researches to improve the removal rate. In this research abrasive flow machining assisted with centrifugal force has been simulated by ANSYS CFX. Next, using response surface method, design of experiment is done, and variance analysis method is applied to investigate the effect of rotational velocity parameters of work piece, number of cycles and extrusion pressure and also their interaction effects on material removal rate. According to the results, the rotational velocity of work piece and numbers of cycles has a greater effect on the material removal rate than extrusion pressure. In this process, a regression equation is introduced for predicting the material removal rate.