Journal of Aerospace Mechanics
Year:2013 | Volume:9 | Issue:3 (33) (MANUFACTURING AND PRODUCTION)|Papers Count:9

This paper compares the shrinkage of the components manufactured by injection molding, using inserts made of epoxy resin and metal alloys with low melting point (LMPA). For this purpose, in first stage, two cube molds (inserts) manufactured by epoxy resin and a low melting point alloy (150MCP). At the using an injection machine, two types of polymers, (polyethylene and polystyrene) were injected into the inserts. Then exact dimensions of the injected components, plus shrinkage caused by inserts materials, (epoxy resin and metal alloys with low melting point) were measured. Also, the effect of injection parameters on shrinkage of the components, investigated, these parameters include injection pressure, holding time and temperature of the polymer melt. The results indicate a reduction in shrinkage in components of polyethylene, which is made in LMPA insert. Reduction in length and width and height are 62.0, 46.0 and 75.0 respectively. Polystyrene components made by both inserts, have about the same percentage of the shrinkage. Increasing the injection pressure and holding time, significantly reduced the shrinkage of components in both inserts.

In recent years, demand for increasing quality and tool life and for decreasing machining force has led to the use of vibratory tool instead of fixed one in the conventional cutting. Tool wear as one of the most important economical parameters, must be considered. As will be shown in the present paper, heat as the most important parameter can decrease tool life significantly. Thermal analysis of tool tip temperature in ultrasonic assisted turning (UAT) is very complex because of the high frequency fluctuations in the nature of this process. In this paper, ABAQUS finite element software has been used for the thermal analysis of orthogonal turning of Al7075-T6 to study the effect of machining parameters (cutting speed and feed rate) and vibration parameters (amplitude and frequency) on the tool tip temperature in UAT. A comparison has also been made with the conventional turning (CT) temperature. It has been shown that, when the tool engages with the work piece, the cutting tool temperature increases. This increase in UAT is more obvious than the temperature decrease occurring when the cutting tool separates from the work piece. Moreover, with increasing vibration amplitude, the maximum tool temperature also increases. In constant vibration speed, low amplitude and high frequency should be used to achieve minimum temperature.

Multi-layered tube hydro-forming is suitable to produce multi-layered joints to be used in special application in the industries. In this paper, for first time, three-layered tube (inner layer of copper, middle layer of aluminum foam and outer layer of brass) hydro-forming processes was numerically simulated using finite element method by ABAQUS/Explicit 6.10. One of the effective methods in improving the tube hydro-forming is by using the pulsating internal pressure. It was shown that pulsating pressure improves the formability in hydro-forming of three-layered tubes. Since three-layered sandwich tubes hydro-forming has not been reported in the literature, the middle layer thickness was gradually decreased and approaching to zero. The present results are compared with experimental results of bi-layered tube in hydro-forming process. Comparison of numerical and experimental results have shown good agreements

Use of Tailor-Welded Blanks (TWBs) in production has significant advantages such as weight and cost reduction. These benefits cause TWBs to be considered in aerospace and automotive industry. However, their application requires processes that increase their poor formability in comparison with base materials. One of these procedures is the use of fluid pressure in sheet metal forming. In this paper hydro-mechanical deep drawing process of tailor-welded low carbon steel blanks with different thicknesses is studied using FEM and verified experimentally and effect of friction between blank and tooling elements on weld-line movement and thickness distribution is investigated. Results of FEM are in good agreement with experiments. Results show that it is possible to control thickness distribution and weld-line movement by proper design of friction condition inasmuch as elimination of weld-line movement in bottom of the produced cup.

Cone spinning, is a complicated plastic forming process under multi-factor effects. Processes variable in this research are: mandrel angular speed, roller feed rate and clearance. Influence of these parameters are: analyzed on forming forces and flange state. In order to perform process experimental, a test rig is used which is composed of a manual lathe, a geared stepper motor, a linear encoder, a 3-axis KISTLER dynamometer, a high speed motion control card and a high resolution data acquisition card. The software used for simulation is ABAQUS 6.9 which its advantage is using explicit dynamics FE formulation method. The results from the FE model are compared with experimental results obtained from NC spinning machine. The used material is commercially aluminum (1050 series). The results show the following: (1) with the growing of the roller feed rate, all components force of spinning force and Wrinkling increase. (2) With the growing of the mandrel angular speed, all components force of spinning force and Wrinkling decreases. (3) Maximum affect on response variables is by clearance and minimum influence is by mandrel angular speed.

The cooling slope (CS) method is one of the semi-solid methods that the molten alloy with a suitable amount of superheat is poured on a cooling slope for achieving fine and non-dendritic structure. This paper discusses the effect of temperature on the final microstructure of A356 aluminum alloy. These temperatures are casting temperature, mold temperature and CS plate temperature. The dendritic primary phase in the conventionally cast A356 alloy has transformed into a nondendritic one in cast ingots on a cooling plate at 5 different casting temperature, 3 different mold temperature and also two conditions of using a cooling system or without it. It was found that the microstructure gets finer decreasing casting temperature to 6250C. The CS used in this study, which also controls the surface temperature, has a significant effect on the microstructure. This effect is 22% decrease on average grain diameter and 8.5% increase on the shape factor at the weakest case. Also increasing the mold temperature up to 2000C causes globularity and appropriate distribution of a-Al particles.

In machine dynamics, the tool point frequency response functions (FRFs) are employed to predict the stable machining conditions. A combined analytical-experimental substructuring procedure is proposed to determine the tool point FRFs usable for different holder-tool configurations. Contact interface of holder-spindle and tool-holder is modeled using translational and rotational springs and dampers spread in the length of contact surface. These joint parameters are defined using finite element method. This enables the analyst to introduce the contact stiffness and damping in more detail taking into account variations of normal pressure in the tool-holder and holder-spindle joints. The dynamic analysis of the holder is done using Timoshenko beam theory by chebyshev method. The tool dynamics is modeled by Euler-Bernoulli beam theory using the method of equivalent diameter. For the purpose of shifting the tool stability lobes to a higher level, tool damping parameter is modified by internal frictional damper and the effect is analyzed by analytical methods and experimental study. New method for continuous dynamic coupling is presented. The method employs the measured spindle-machine FRFs and analytical models of the tool and holder to predict the tool tip FRFs. An experimental case study is provided to demonstrate the applicability of the proposed method.

Nowadays, material removal is one of the most important processes in industries. In this research, some important parameters in turning process such as; machining forces, stresses and heat flux on tool/workpiece contact area against variations of machining parameters are simulated via ABAQUS 6.9. Then, machining forces in two directions are measured by experimental techniques. Experimental values are compared with simulated results. This comparison shows a very good agreement.