مجله مهندسی ساخت و تولید ایران
سال هشتم شماره 5 (امرداد 1400)

In this study, zirconia is joined to S.S310S using a brazing in a furnace under the argon atmosphere. The filler used in this process is a silver-based-alloy which has no active elements in its chemical composition. According to the fact that, unlike S.S310S, oxide ceramics have low wettability compared to alloy fillers, to activate the surface of zirconia with pure Ti-coating. The optimum thickness coating layer was determined to be 200nm. The purpose of surface coating is to reduce the penetration of the Ti-element on the surface of the ceramic sample and to create a TiO2 reaction layer in that area. The samples were joined by a brazing process for one hr. The results obtained from the shear test of brazed specimens showed high strength of specimens with a temperature of 1000˚C at an average of 117 MPa that compared to brazed samples at 1100˚C (96MPa), they had an increase of 21MPa. Then, for microstructural analysis and metallography of the joint area the SEM and OM, were performed. The results of elemental and linear analysis obtained from that area showed the reason for the decrease in strength with increasing temperature is due to excessive penetration of filler components then the formation of non-uniform reaction layer on the zirconia surface. The reaction layers formed in the process include Cu57Zr4 and TiO2(zirconia) and FeAg and FeCrNi (S.S310S) and AgCu phase in braze zone.

Since piezocomposites with 0-3 connectivity are flexible and commonly used in acoustic transducers, we review some of their fabrication methods, which are mainly under the development stage, and evaluate cons and pros of each method. We then suggest a budget type solution casting method to prototype 0-3 piezocomposites which can be used with a wide range of polymeric materials. Using this method, we fabricate PZT/EP and PZT/EP+TPU piezocomposites with PZT weight fractions from 30 to 70 percent. First, PZT powder was mixed with the epoxy resin, and a magnetic stirrer was used to achieve a uniform dispersion of PZT particles in the polymer. After adding the hardener to the solution, a sonicator were used to avoid agglomeration of PZT particles and prepare a uniform solution. The solution was then poured it into a mold and placed in a desiccator container, connected to a vacuum pump, to perform the degassing process. After the polymerization process was completed, samples were dried to complete the curing process. After polishing, the copper electrode plates were placed on both sides of the piezocomposite elements. Finally, the polarization process was performed using the corona discharge method. The results of XRD, FT-IR and SEM analysis depict the uniform dispersion of the PZT particles within the polymer. The prototyped specimens generate electric charge, measured by an oscilloscope, under a dynamic loading.

With the advancement of technology and the great need for thin and light parts with high strength, the need for welding thin sheets has also increased. Nowadays, laser spot welding is used to connect thin sheets of austenitic stainless steel in the production of kitchen wares. The strength and size of the weld nugget are two important parameters in determining the quality of laser spot welding. In this study, thin sheets of stainless steel 316 with a thickness of 0.7 mm were laser spot welded. To perform this welding, a medium power Nd: YAG laser welding machine was used and the effects of effective laser parameters on the strength and size of the weld button were investigated experimentally. Laser frequency at three levels of 5, 7 and 9 Hz, peak laser power at three levels of 1670, 1750 and 1800 W and pulse ON time at three levels of 6, 8 and 10 milliseconds were selected as parameters and test levels. Taguchi L9 method was used to design the experiments. The experimental results show that with increasing laser power, the diameter of the welding button decreases, with increasing the pulse ON time, the diameter of the welding button first increases and then decreases, and with increasing laser frequency, the diameter of the welding button decreases and then increases. In addition, with increasing pulse ON time and laser frequency, the strength of weld nugget increases, and with increasing laser power, the strength of weld button increases firstly and then decreases.

Double action horizontal Neuman Esser reciprocating compressors are utilized during three steps of compressing hydrogen in gasoline production section of many refineries including Esfahan refinery. Since application of any lubricant during compression process are not permitted in these compressors, Teflon ridder rings are placed between piston and cylinders to act as a lubricant and prevent any direct contact between pistons and cylinders. The wearing rate of the ridder rings in these three stages are not equal and consequently the time for their maintenance is not the same. In this research it is intended to increase the life of ridders by reducing the weight of pistons. After studying the effects of replacing the cast iron material of pistons by 7075 aluminum alloy, genetic algorithm is implemented to optimize the design of these pistons. Maximum von-Misses stress and minimum allowable thickness of various sections of piston are the constraints considered during optimization process and Abaqus finite element technique using Python script are utilized during optimization. Replacement of the material reduces the piston weight from 780 kg down to 271 kg and by optimizing the piston design, it was further reduced down to 261 kg which totally could considerably reduce the wearing rate of riders by reducing the total normal force on riders.

Steels with quenching-partitioning (Q-P) heat treatments are the third generation of advanced high strength steels (AHSS) which have been developed due to their interesting combination of mechanical properties including high strength with good flexibility. Partitioning is based on carbon diffusion from martensite (M) to residual austenite (γ_R). In the present investigation, an alloy with a weight composition of % Al 0.054- % Si 1.5 -% Mn 2.2 -% C - 0.21 - Fe containing 0.08% Ti as a micro-alloy was prepared using a vacuum induction melting (VIM) furnace. Purification was performed using an eletro-slag refining (ESR) furnace to reduce sulfur and oxygen and then the molten alloy was cast as an ingot. The ingot was then homogenized at 1200 ° C for 3 hours. The homogenized ingot was then rolled to 1.5 mm thickness sheet by hot and cold rolling processes. After quenching-tempering (Q-T) and quenching-partitioning-tempering (Q-P-T) treatments, the properties of the samples were evaluated by scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), micro-hardness, tensile and Erichsen tests. The Q-P-T samples showed more favorable combination of strength and flexibility in comparison to Q-T samples. The strength and fracture strain of Q-P-T and Q-T samples were 1050 MPa, 24%, and 1185 MPa, 18%, respectively. The Q-P-T samples with remarkably higher strength, showed significantly higher flexibility.

At present, in the processes of manufacturing and assembling multi-layer (sandwich) industrial complexes with different materials, such as mold or fixture production, firstly the parts must be assembled and then drilled simultaneously; otherwise, the desired dimensional or geometrical accuracy will not be achieved. To make these holes, conventional drilling processes are mainly used, which due to the geometric shape and zero cutting speed at the drill tip, cause severe plastic deformation in the cutting zone. The use of conventional drilling process may reduce the dimensional and geometrical accuracy as well as the surface integrity of the inner wall of the holes. To reduce the mentioned problems, one of the relatively new methods proposed for drilling is the helical milling technique. In the present study, in order to compare the capabilities, advantages and disadvantages of these two different drilling methods, a total of 18 drilling tests using conventional drilling and helical milling processes and considering 2 variable parameters of cutting speed and feed rate (each in 3 levels) on metal multi-layer (sandwich) workpiece with 3 different layers of steel including MO40, 304L and CK45 was performed. Based on the obtained results, it can be stated that in order to achieve the desired dimensional (hole diameter) and geometrical (hole roundness) tolerances, the conventional drilling process has a better performance than the helical milling method, but in terms of achieving less surface roughness and better surface integrity (less surface imperfections), helical milling method has better performance than conventional drilling