IRANIAN JOURNAL OF MANUFACTURING ENGINEERING
Year:2016 | Volume:3 | Issue:3 |Papers Count:6

Hot pressing of metal powders is used in production of parts for similar properties to wrought materials. Since residual porosity, inhomogeneous properties, dimensional and geometrical instability and therefore reduction in mechanical strength are the main problems in powder metallurgy components which are due to friction between powder particle interfaces and powder compact and die walls. Because of this, access to parts with high density and homogeneous structure is the great object in powder metallurgy. One of the remedies can be employment of ultrasonic vibrations which is thought to result in increased rates of densification and therefore higher efficiency of the process in increase of part density and strength. To evaluate this solution, this paper deals with the effects of high power longitudinal ultrasonic vibrations on the densification of AA1100 aluminum and Ti-6Al-4V titanium alloy powder under constant applied stress and different temperatures. The effects of powder type and process temperature on the densification behavior and ultrasonic efficiency are discussed. For experimental tests, setup of ultrasonic assisted hot pressing of powders were designed and fabricated. The results show that applying ultrasonic vibrations leads to obtaining higher relative density. In addition, it is found that the effect of ultrasonic vibrations is greater for Ti-6Al-4V powders. However, the temperature has different effects on the ultrasonic vibrations efficiency in two types of powders.

In order to increase the strength of vehicles body as well as reduce the fuel consumption, usage of Advanced High Strength Steels (AHSS) as raw materials for producing car body parts has been increased significantly in the automotive industries during the recent years. From the other aspect, higher strength of these steel types in comparison to common deep drawing steels leads to higher contact pressure on tools faces (dies) and work pieces (steel sheets). This issue has caused lower tool life. Galling, as a state of adhesion corrosion, is one of the main reasons that increases the die maintenance costs and tool scrap rate. In this study, the galling wear of Peugeot 405 door production die has been investigated in which DC04 steel sheets are formed. Considering the international standard tests for galling wear and professional metal forming software, galling resistance of common deep drawing steels are compared with the advanced high strength steels. The effects of different parameters including chemical composition of sheet, heat treatments and rolling process, blank holder pressure, and hardness and roughness of die on galling wear are determined. At last, the proper solutions for decreasing the wear of the die including changing the chemical composition of initial blank, coating the forming tools, and changing blank holder pressure are proposed.

Experimental investigation and numerical modelling of dynamic loading effect on the density, strength and microstructure of the pure and composite parts fabricated from iron powder has been studied in the present paper. Experimental tests have been performed using drop hammer apparatus. Diametral compression test has been used to evaluate the strength of fabricated parts. Also, numerous micrographs have been provided using scanning electron microscopy to investigate the influence of impact loading on the microstructure of compacts. The obtained results show that with increasing compaction energy, density and strength of pure parts increase in three ranges of low, medium and high pressures with different rates. Also, the obtained results by compaction of iron powder with different ceramic powder contents under equal pressure reveal that adding more than 5 percent of ceramic content, sharply decreases the density of composite parts. Examination of graphs taken from the microstructure of compacts reveals that propagation of compressive stress waves through the powder column, causes plastic deformation of particles and forms mechanical inter-locking on a completely uniform structure. Furthermore, a mathematical expression has been presented using dimensional analysis along with genetic algorithm method to predict the values of density of produced pure parts. In this method, after constructing dimensionless numbers based on dimensional analysis approach, these numbers have been used as the inputs of genetic algorithm modelling method. Comparison of the values predicted by this equation with those obtained by experimental values, shows that the results obtained by this model, agree with experimental results surprisingly.

Titanium aluminide intermetallic compounds are a small group of materials that can be used at high temperature structures where the specific strength (strength to density ratio) and specific stiffness (elastic modulus to density ratio) are very important. In this study, some output characteristics of electrical discharge machining (EDM) process; including material removal rate (MRR), surface roughness and topography are investigated for this material. The DOE method of full factorial is used for planning the machining tests that two main input parameters of pulse current and pulse on time are changed in five and four different levels, respectively and other input machining parameters are kept constant during tests. The results show that in lower currents (3 and 6 A), despite the increase in pulse time, there is no significant change in MRR and the MRR for these two currents is negligible, indicating that finishing process of titanium aluminide is difficult and time consuming, but there is no such situation in more currents (12, 24 and 64 A) and the roughing process of this material is optimally carried out. For the currents above the 24 A, the gradient of MRR increase, is decreased because of arc appearance. In the states of higher electrical currents, the lengths of cracks on the machined surface are increased and the widths of cracks are growing. While arc is occurred for the higher electrical discharge energy, the surface roughness and topography are intensively different from the other current and pulse on time conditions.

High pressure torsion is an effective Severe Plastic Deformation method for producing nanostructured bulk materials. In this research, deformation behavior of Aluminum 5452 alloy disks obtained from unconstrained high pressure torsion has been studied. There is a region between adhesive zone and sliding zone defined as critical radius (r*) on vicinity of which, microhardness and effective applied strains (PEEQ) are more than those of other regions. Since Number of Turns and Applied Pressure are the most important parameters of HPT process, for studying their effects on r* of disks, in this research the process was simulated by applying conditions of previous experimental research. For this end, ABAQUS software was used and r* values were calculated and recorded. It was observed that by increasing N and applied P, r* values increase. For better studying the properties of disks obtained from unconstrained HPT process, the process was simulated under applied pressure of 2. 7 GPa and 1, 2, 3 … and 10 turns. Eventually by using PEEQ distribution obtained from software, deformation behavior of disks in higher turns was analyzed, and specially the r* of unconstrained HPT that obtained from experimental tests and simulation, was examined.

Nowadays in different industries, researchers perform many attempts to reduce manpower because it is time consuming and needs high cost, high skill, and involves more human error. For this reason, for eliminating of the manual finishing, this article investigates finishing of special curvature based forging die manufactured by EDM process, the finishing process is performed by abrasive flow machining. These dies usually are finished manually. Abrasive flow machining is used for polishing of points of workpiece, which are in the direction of abrasive flow. This is the reason that, for flow distribution in die curvature an intermediate piece is used in other to provide a passage. Two phase simulation(fluid/solid) of flow in two dimensions shows that the total pressure at each point in complete cycle (piston stroke) is equal to a constant value since a direct relation exists between the amount of material removal in the process and the pressure amount, a uniform polishing could be expected. Performed experiments assert correctness of simulation. Empirical tests showed that the abrasive grain size is larger, the material removal rate is also higher. Also, by increasing the number of courses and concentrations of abrasive, material removal rate is also increasing. Dimensional accuracy has been maintained in this process.