IRANIAN JOURNAL OF MANUFACTURING ENGINEERING
Year:2019 | Volume:6 | Issue:5 |Papers Count:6

In current research, in order to manufacture reinforced polypropylene composite with carbon fibers and CaCO3 nano-particles, polypropylene granules were fed to an extruder with specific percentages of maleic anhydride compatibilizer and calcium carbonate nano-particles and then extruded compound granules were hot-pressed inside a mold. After generating resin sheets from these granules, they were sandwiched between carbon fiber plain fabrics and heat-pressed, consequently samples of nano-composite are prepared. Standard mechanical tests of tensile, bending and impact were performed on prepared samples of both types of reinforced polypropylene composite with carbon fibers containing nano-particles and without nano-particles. Results showed that composite specimens containing calcium carbonate nano-particles endure 87% more tensile strength, 26% more bending strength and 40% more impact strength than specimens without nanoparticles. The maleic anhydride compatibilizer, due to formation of polypropylene-calcium carbonate copolymer, improves the uniformity of the compound and increases adhesion between polypropylene and calcium carbonate phases. Because of higher elasticity modulus of nano-particle compared to the polypropylene matrix as well as the possible nucleation of nano-particles in the polymer matrix, the overall strength of the nano-composite sample has increased. Also due to the symmetric shape of the quasi-spherical calcium carbonate nano-particles, these particles have isotropic properties in different directions and lead to an increase in the level of crystallinity in the polymeric matrix and the strength of the nano-composite. The dispersion of nano-particles in the polypropylene base causes the impact energy to be spread across the whole cross-section and thus the energy absorption capacity increases before fracture.

In this research, four titanium diboride based ultra-high temperature ceramics: monolithic TiB2 (additive free), TiB2-5 wt% Si3N4, TiB2-20 vol% SiC and TiB2-20 vol% SiC-5 wt% Si3N4 samples were fabricated by spark plasma sintering process at 1900 ° C for 7 min under 40 MPa. The microstructures of TiB2-based composites were affected by the introduction of SiC and Si3N4 additives as the relative densities and sinterability of the samples significantly improved. The XRD, SEM and EDS analyses as well as density measurements were employed as the characterization methods. Based on these analyses, the in-situ formation of TiN, SiO2 and BN nano-platelets in the TiB2-Si3N4 and TiB2-SiC-Si3N4 samples, due to the chemical reaction of SiC and Si3N4 with the surface oxide impurities of TiB2 particles (TiO2 and B2O3) was verified. The elimination of such harmful oxide films and the in-situ formation of several secondary phases led to the prevention of fanatic grain growth of TiB2 matrix and microstructural development and phase evolution of TiB2-based ceramics. In addition, the sinterability of samples increased via liquid phase sintering mechanism as a result of formation of molten SiO2 during the sintering process.

Explosive forming is one of the novel sheet metal forming processes in which released energy of explosion is reason of forming. Explosive forming using gas mixture is one of the explosive forming processes. In this process, after getting desired pressure in the mixture of two gases, required energy for forming is obtained by combustion in the chamber. In this research, a new method for forming of aluminum tubes by exploding gas mixture (33% oxygen-68% hydrogen) has been investigated. In order to make plastic deformation in AA6063 aluminum tubes under energy of explosion shock, an experimental setup has been designed and fabricated. Using this setup, aluminum tubes have been formed under different loading conditions and the effect of initial gas pressure and location of ignition on forming and suitable production of part in accordance with die configuration have been investigated. Experimental results show that the initial gas pressure of 12bar with mixing ratio of 32%oxygn-68%hydrogen can cause complete forming of tube in accordance with the die configuration. More initial gas pressure leads to bursting of tube before contact die wall. Also middle of tube is best location of ignition to obtain complete forming of tube.

Milling is an important and conventional method of metal Cutting, in which many studies have been fulfilled so far. Study of machining the nickel-based superalloys is felt to be essential due to their high strength and various applications in the power plants, aerospace industries etc. Cutting force and surface roughness are two of the important factors in machinability that due to the high importance of it, has been studied. In this article, the influence of four parameters of machining nickel-based superalloys, namely, cutting speed, feed rate, depth of cut and presence or absence of cooling as research inputs on the milling of Inconel 738 were investigated. In total, 64 experiments have been completed as full factorial design. By measuring cutting forces and surface roughness of the samples after the milling process, the obtained models were utilized to predict the effect of various above parameters, to optimize the milling parameters and to obtain the desired surface finish. In addition, the artificial intelligence techniques such as neural network and genetic algorithm were employed to predict the output parameter and to find the optimum milling parameters. The comparison of the experimental and predicted results shows the success of the modeling with 97 percent accuracy and a precise optimization.

The warpage which has been occurred in the injected molded parts has always been a problem, as it may affect the function of the part and make it unusable. The main factors which has some effects on warpage of parts are the differential cooling, differential shrinkage, orientation effects and corner effects. According to the part each one of these effects may has the most impact on the warpage of the part. The most important reason which creates shrinkage in the parts is the difference between the temperatures of two sides of the molds (core side and cavity side), it is possible to minimize this shrinkage by decreasing this differential temperature. After a couple of analysis in Moldflow software it’ s been shown that the differential cooling has the most influence on warpage of the part. It is possible to control the differential cooling with the coolant temperature which inters to the cooling channels of the mold. In order to find the optimized coolant temperature for both sides of the mold to decrease warpage of the part, a DOE analysis has been prepared. It’ s been shown that the difference between the temperatures of the sides of the mold has much more influence than the average temperature of these sides on the warpage of the parts.

Porous materials are a special class of engineering materials which have received increasing interest for technical and medicinal applications within the last decade. However, one of the main challenges in the cutting of porous structure is the microfractures occurred around pores having a profound impact on the final surface quality. In this study, the effect of tool geometry on the magnitude of microfractures around pores of porous silicon has been investigated. The results reveal that as rake angle decreases, microfractures around pore edges increase influencing the cutting pressure. The calculated pressure in the contact area shows a decrease as the rake angle decreases. Increase in microfractures can be explained based on a large tensile stress area formed beneath the tool cutting edge as tool tip feeds toward pore. The simulation results agree well with the experimental results. The findings also reveal that by choosing the optimal tool rake angle in the cutting process, a nanometric surface flatness (25 nanometer) can be achieved on porous silicon.