Journal of Aerospace Mechanics
Year:2009 | Volume:5 | Issue:3 (17)|Papers Count:7

The laser sheet metal forming process has significant importance in industries such as aerospace, automotive, and ship building, which previously relied on using expensive stamping dies and presses. In this paper, a simplified model has been developed to predict the bending angle. The calculation of bending angle by a simplified model takes less time than three-dimensional finite element simulation, which is used to analyze the process. The effect of process parameters on bending angle and predicting of bending angle by calculating plastic zone have been studied. The tests have shown that the bending angle is directly proportional to the laser power and is in inverse proportion to the path feed-rate and the laser spot beam diameter. The comparison between theoretical and experimental results has shown reasonable agreements.

In Explosive Welding (EXW) process, there is a situation in which high amount of pressure in collision point leads to decrease in impurity of superficial layers and metal gets in contact with another dissimilar metal and Metallurgical bond can be initiated at the interface. In this paper, in addition to introduction of scarf welding, explosive welding of aluminium to copper plate in different conditions of explosive loading performed and shear strength of bond was evaluated through new method. The Relationship between shear strength and explosive loading was demonstrated by establishment of non-linear and logarithmic models through regression method and ANOV A table. Adequacy of the developed models was verified in explosive cladding process. Consequently, explosive loading varieties can be evaluated in one experiment by production of scarf joint between dissimilar metals (according to the computational method employed in this paper) and with development of proper model, the shear strength of cladding metals can be estimated.

It is possible and practicable to make a joint in similar materials, whereas, bonding of dissimilar metals in order to achieve applicable components has been subjected to many investigations. The purpose of this study is to produce scarf joint through explosive welding process (EXW) between chamfered end of aluminium and copper plates. Macroscopic observations and mechanical properties of interface, such as bond shear strength and micro-hardness was carried out on the bond interface. Mathematical models were adopted for the interface properties of the scarf joint to make relationship between the bond shear strength and explosive loading ratio with regression method and variance analysis. These models verify in explosive cladding processes. Consequently, mathematical model which is based on scarf joints in dissimilar metals could predict bond properties of cladding metals under desired explosive loading and flyer plate thickness. This led to establishment of appropriate model to explain shear strength- Explosive loading ratio.

Resin transfer molding, that is a sub-branch of liquid composite molding, is one of the manufacturing methods of polymeric composites. Various modification has been presented to improve this process and enhance the product quality. One of the most important modified suggestions is the vacuum assisted resin transfer molding process with flexible tools. Because of the flexibility of tools, resin flow in the mold compact the fiber preform and consequently the thickness of the preform is varied. This phenomenon will affect all process parameters. In order to achieve more actual results and a proper modeling of the mold filling stage, in this article, the governing equations of the molding of a large part incorporating flexibility of tools, gravitational effects, and also friction losses have been solved analyticaly. Then, numerical results have been compared with other models and existing experimental results. It has been shown that neglecting injection tube in modeling of resin transfer molding process with flexible tools has more errors in comparison with RTM process, using traditional molds.

In recent years, several sheet hydroforming methods have been introduced by researchers. Despite the advantages of these methods, they have some limitations. A new sheet hydro forming process was previously introduced by the authors, where in a polyurethane diaphragm is used to control the blank holder force and to reduce wrinkling in the flange area. In this paper, the effect of significant parameters, including pre-bulging and forming pressure was studied by experimental work and by finite element simulation. It was shown that in forming by the proposed die, a much lower pressure was required compared to those in other sheet hydroformings. Moreover, it was concluded that in the new die, pre-bulging does not considerably affect the sheet thickness distribution. It was also illustrated that by increasing the internal pressure, the critical thickness will be transferred from the punch tip area towards the product wall area. Also, the effect of friction coefficient between the punch and the blank was studied numerically and it was shown that increasing the friction coefficient causes improvement in the thickness distribution.

Forming conical parts is one of the complex and difficult fields in metal forming processes. Because of low contact area of the sheet with punch in the initial stages of forming, high stresses is applied to the sheet that causes tearing. Moreover, since most of the sheet surface in the area between the punch tip and the blank holder is free, when the sheet is drawn, wrinkles are occurred in the wall of the part. Thus, these parts are normally formed by spinning, explosive forming, or multistage deep drawing processes. A few number of research works have been carried out in the area of forming conical parts. In this paper, forming these parts in the hydroforming process is studied, using finite element simulation and experiments. By examining several pressure paths, the effect of pressure path on tearing and thickness distribution of the sheet has been studied. By obtaining the desired pressure path, a conical part with a high depth has been formed.

Using cutting tool vibration equations in x and y directions, the chatter phenomenon in milling process is modeled. To solve these equations, cutting tool structural characteristics, such as natural frequency, damping ratio, and its stiffness in x and y directions must be known. For finding these properties, "Modal Test" is performed and its results are analyzed. The suggested analytical model for chatter phenomenon is tested experimentally in different axial depth of cut and its correctness is proved. The critical depth of cut in slotting Titanium alloy Ti6Al4V with Carbide tool is achieved both experimentally and analytically about 5 mm. After validation the suggested model for predicting chatter, the effect of cutting speed, end mill stiffness, and radial depth of cut on cutting system stability are simulated. Increasing the cutting speed causes system switches between stable and unstable conditions for several times. This is because of the special shape of the Stability Lobe Diagram (SLD). Increasing the end mill stiffness and decreasing the radial depth of the cut or tool work piece engagement make the process more stable.