فصلنامه مکانیک هوافضا
سال سیزدهم شماره 3 (پیاپی 49، پاییز 1396)

Electromagnetic forming is a high energy rate forming process which is applied for manufacturing and assembly of many parts that are used in automobile and aerospace industries. In this process¡ the electromagnetic body forces (Lorentz forces) are used to produce metallic parts. In this article¡ the influence of important process parameters such as discharge voltage¡ friction coefficient¡ clearance between the tube and die¡ wall thickness and length of tube¡ on the radial displacement and workpiece thinning were investigated. The output of governing equations in the form of pressure applied on the part via a subroutine in a Fortran Program. A dynamic analysis using two dimensional axisymmetric models were performed and Johnson-Cook theory was applied to represent the effect of strain rate sensitivity and show the plastic behavior in the deformation process. Finally¡ the numerical results were compared with the results reported by other researchers and found a good agreement between them.

In this paper¡ the effect of the primary cavity depth in different input parameters (pulse duration and spark current)¡ in the Electrical Discharge Machining(EDM) on surface integrity(white layer thickness¡ HAZ¡ micro hardness and micro crack density) of DIN 1.2379 cold work tool steel has been studied. According to the obtained results¡ increasing the initial depth of hole¡ decreased the white layer thickness¡ micro crack density on the Machined surface and HAZ. The results of the micro hardness also¡ indicate growth the value of hardness in the layers close to the machined surface along the depth and after passing through a specified depth from machined surface¡ this process stopped and then¡ the machined surface micro hardness reduced.

Present study describes approach of applying RSM with a Pareto-based multi-objective GA to optimize the deep drawing process. Previous studies¡ integrated the FEA and optimization technique to find the optimal parameters by transforming multi objective-problem into a single-objective problem. This paper aims to minimize the functions of fracture and wrinkle. Design variables are blank-holding-force and draw-beads geometry. RSM has been used for design of experiment and finding relationships between variables and functions. Proposed approach has been investigated on a fuel-tank drawing part and it has been observed that it is more effective and accurate than traditional ‘trial and error’ procedure.

One of the main goals of researchers in metal powders laser sintering¡ is optimization of process parameters in order to close out the main properties of the raw materials have been produced to the piece. For this purpose¡ many experiments have been carried and parameters such as density¡ hardness¡ micro hardness¡ strength¡ surface finish¡ appearance¡ and residual stress have been studied. In this paper the influence of parameters such as laser power¡ scanning speed¡ and powder material and etc. on output parameters such as penetration depth¡ strength¡ balling phenomenon is investigated. In order to produce a multi-layer fully dense parts by the process of pulsed laser¡ to optimize the performance of the laser and material parameters at first¡ it is necessary to single layers is investigated. Experiments carry out on free powder bed depth is 5 mm. Each piece of a single layer on the substrate with once laser scanning powder is produced. Movement of the laser beam on the surface produce a washer with 20mm diameter.

In this paper try with use of cryogenic cooling by liquid nitrogen damage such as surface roughness¡ micro cracks¡ surface oxidation and burns¡ as well as control the grinding force in grinding titanium alloy to get their minimum. In addition to the latest statistical techniques appropriate to the nature and effect of each of the grinding parameters (cutting speed¡ work speed and depth of cut) and the interaction effect of surface roughness on the output power of vertical and tangential force put to their optimal levels has identified. This paper demonstrates the use of liquid nitrogen as a coolant has a positive effect on reducing surface roughness and grinding forces¡ the surface also reduces the damages of the work piece and the titanium alloy surface oxidation during grinding to prevent. In addition¡ each of the parameters including¡ cutting speed¡ work speed and depth of the outputs of the paper¡ to be effective¡ for example by increasing shear rate increases the surface roughness and grinding forces are reduced¡ as well as increased depth of cut increases the surface roughness and forces.

In this research casted Aluminum alloy A356 and Al2O3 powder were used as matrix and reinforcement¡ respectively. 5wt. % of Al2O3 with Al powder in the ratio of Al/Al2O3=1 for increasing the wettability were milled and injected to melt. Three different argon flow gas rate (2.5¡ 5¡ 10 liter/min) were selected for injection Al2O3(p) within molten Al and investigated the effects of that on microstructure and mechanical properties. Results showed¡ with increasing powder gas flow rate from 2.5 to 5 liter/min¡ mechanical properties such as hardness and compression strength are enhanced from 62.28 HB and 230.2 MPa to 78.7 HB and 539.1 MPa¡ respectively. While wear test represents decreasing of around 26 percent in coefficient of friction. But¡ with further enhancement in gas flow rate to 10 liter/min due to porosity increasing and agglomeration of Al2O3 particles¡ hardness and compression strength in comparison of composite with 5 liter/min flow rate reduced 21 and 37 percent¡ respectively. In this way¡ coefficient of moderate friction increased from 0.42 in composite with 5 liter/min flow rate to 0.56 in metal matrix composite with 10 liter/min flow rate.

Thixoforging is known as a modern process for the production of parts in semi-solid state that has been developed in recent years. Thixoforging involves forging of nondendritic structure ingots in the temperature range of liquid and solid phases. The purpose of this study was to investigate the effect of primary microstructure¡ Hydraulic Ram speed and heat treatment on metallurgical and mechanical properties of parte in thixoforging process. Microstructural study has been investigated by using optical microscopy¡ scanning electron and image analysis software. Results show that the increase of forming speed from 1 to 5 mm/s cause the decrease of grain size from 85 to 73 micrometer in which case the final compressive strength equal 433 MPa were measured. Also¡ accomplishment of T6 heat treatment causes formation of globular Si eutectic phase and precipitation of Mg2Si hard particles in matrix phase that lead to increasing the compressive strength from 433 to 522MPa and hardness increase from 79 to 88 HV.

Because of high strength to weight ratio¡ 6061 aluminum has many applications in different industries like automotive and aerospace industries and can help to reduction of fuel consumption. Forming limit diagram (FLD) is a useful method for sheet metal formability identification. Whereas calculation of forming limit diagram by experimental tests is expensive and time consumption¡ in the present research two numerical criteria is presented for forming limit diagram calculation of 6061 aluminum. Numerical simulation is done by Abaqus software. Numerical criteria of FLD prediction are imported to the Abaqus software to predict the forming limit diagram of 6061 aluminum. Bragard method was used for calculation of experimental forming limit diagram. This method is more accurate than other methods which read forming limit strains from the elements which are near the fracture zoon. Numerical criteria are ductile fracture and FLD criteria which their prediction was compared with experimental forming limit diagram. Results show that ductile fracture criterion has more accuracy for forming limit diagram prediction of 6061 aluminum. Moreover¡ numerical results of punch’s force-displacement were compared with experimental results. Results show that numerical results have a good agreement with experiment.