Advanced Materials Research Vol. 445

Abstract: The bicycle is not only a pollution-free method of transportation, but also has sport and recreation functions. Therefore, the bicycle attracted attention in now society gradually. This study uses the rigid-plastic finite element (FE) DEFORM^TM software to investigate the plastic deformation behavior of a 7075 aluminum alloy workpiece as it is formed through a ring rolling die. This study systematically investigates the relative influences of ring rolling velocity, entering velocity, and workpiece temperature under various ring rolling forming conditions. The effective strain, effective stress, and workpiece damage distribution in the ring rolling process are also investigated. Results confirm the suitability of the proposed design process, which allows a ring rolling manufacturer to achieve a perfect design during finite element analysis.

Abstract: In order to study the effect of deformation extent on microstructure and mechanical properties of as-cast AZ91D magnesium alloy, experiments of direct extrusion were performed at temperature of 420 and different extrusion ratios. The microstructure and mechanical properties of billets and extrudates were measured. Experimental results show that the grain size of as-cast AZ91D magnesium alloy can be dramatically refined by extrusion. Direct extrusion can obviously improve the mechanical properties of as-cast AZ91D magnesium Alloy, comparing with the pre-extruded billet, the tensile strength, yield strength and elongation of extrudate can be improved by at least 83%, 154% and 150% respectively. As the extrusion ratio increases, the tensile strength and yield strength of extrudate will increase at first and then fall.

Abstract: Flexible forming technology provides significant application potential in the manufacturing of complex shaped components even at miniaturized levels. The most attractive characteristic of this technology is simplicity, and its feasibility for prototype processes and low-volume production. The main purpose of this study is to clarify the decisive characteristics of micro deep drawing of metallic foils by using flexible forming technology. In this work a new technique is adopted using rigid punch, rigid holder and rubber pad, so that a particular gap is allocated between the blank holder and a fixed plate to allow the rubber pad to expand through it. The key process parameters studied here are rubber hardness, rubber-pad dimensions, drawing velocity, and initial gap value. Stainless steel 304 foils are used with thickness of 0.1mm. To investigate the effect of soft material properties, urethane rubber with hardness of 20, 40 and 60 shore A is utilized. Also, the punch diameter used in this study is 4mm. Moreover, many drawing experiments are conducted with punch velocities range of (0.1mm/s-100mm/s) to show the effect of process velocity. FEA using the commercial software ABAQUS/Standard is used to simulate the drawing process at micro scale. A hyperelastic material model is adopted to define the flexible pad and an elastic-plastic model is defined for the blanks.

Abstract: In this paper, the finite element method is used to investigate the effect of preform shapes on the strain hardening distribution in the wall of the extruded cup of backward extrusion. A series of simulations on the backward extrusion with three different preform shapes (flat, concave and convex) and without preform using the FEM program DEFORM 2D was carried out, respectively. The influence of preform shapes on the effective strain distribution in the extruded wall was examined. A hardness vs. effective strain curve for an annealed AL6061 Aluminum was first obtained using a simple forging test in conjunction with FE simulations, then the curve was used to convert the effective strain distribution into the hardness distribution in the extruded wall. The results of FEM calculations reveal that the concave shape preform has the best effect on the hardness strengthening at the extruded wall of backward extrusion.

Abstract: In this paper, the finite element method is employed in conjunction with the abductive network to predict the optimum blank contour of an inner elliptic flange with unevenness in the flanging process. Different flange heights combined with various aspect ratios of the inner elliptic flange are taken into account as the process parameters in this study. A finite element-based code is utilized to investigate the material flow characteristics under different process parameters, and the abductive network is then employed to synthesize the data sets obtained from numerical simulations, thus establishing a predictive model. From this model, an optimal blank contour for producing an elliptic inner flange with unevenness can be found.

Abstract: In the machining of Aluminum alloys used in lightweight structural application in automotive, shipbuilding and aerospace industries the consumption of cooling lubricant during the machining operations is very important. Among these, non-heat treatable aluminum alloy 5083 because of its reasonable strength, better corrosion resistance, weldability and ability to take surface finishes is better than the others. The associated costs of coolant acquisition, use, disposal and washing the machined components are significant, up to four times the cost of consumable tooling used in the cutting operations. To reduce the costs of production and to make the processes environmentally safe, the goal of the aeronautical manufacturers is to move toward dry cutting by eliminating or minimizing cutting fluids. This goal can be achieved by using coated carbide tools at high cutting speeds. To achieve this goal, different cutting conditions were tested in dry conditions. The elementary orthogonal cutting process was chosen, the cutting and feed cutting forces components were measured by using Kistler force dynamometer.

Abstract: Extrusion is a metal forming process which involves plastic deformations. Economic significance of extrusion is due to its material efficiency, labor costs reduction, elimination of intermediate treatments, better output quality, and high production rates. Bearing length is one of the important features in extrusion dies. The aim is to make all the material points in outgoing profile have the same flow velocity, so in an effective design the flow velocity of thick features is controlled to be same as for thinner features. AA2024 alloy is widely used in military and aerospace industries. It has a high heat treatment capacity and strength to weight ratio. Other characteristics include excellent toughness, fatigue behavior, crack growth resistance, and machinability. However it is difficult to extrude. The purpose of this paper is to determine a strategy for designing bearings in direct extrusion dies which are used in production of parts from AA2024 aluminum alloy. Proper design of bearings is among factors of controlling material flow in this process and has an important role in scrap rate reduction. Using ABAQUS finite element software package, direct extrusion process is simulated. Results are explored and investigated for different conditions and finally, an efficient bearing configuration is introduced. Finally, it is shown that using uniform bearing for complicated sections is not possible. Optimum design is also presented using finite element analysis.

Abstract: The present study examines deformation textures in low-carbon steel with microstructural heterogeneity. EBSD and XRD have been used in order to follow the evolution of the texture in relation with deformation evolution. The non-deformed material shows a {111} fibre texture (γ-fibre), with a main component {111} <112>. The deformation aptitude may be related for bcc metals to the evolution of this fibre texture component. To follow the evolution of the deformation textures, tensile tests were performed from 5% up to failure. During deformation, the {111} <110> deformation component sharpens. In the presence of this component in the non-deformed sheet, plastic flow is easy, while the grain reorientation from the initial orientation {111} <112> towards the bcc deformation orientation {111}<110> implies an important micro-constraint state, which is able to initiate cracking in the studied sheet during drawing. Heterogeneous structure that develops during deformation induces heterogeneous mechanical behaviour; noted this evolution is not predictable using global characterization techniques. The morphological analysis shows the micro-band presence. In a heterogeneous structure the risk of cracking seems to increase in the presence of small grains {111} <112 > clusters. The EBSD technique showed the adjustment of the grain orientation from the component {111} <112> towards the global deformation orientation {111} <110>. This process can explain the possibility of crack propagation in a globally ductile material characterized by a main component {111} <110>.

Abstract: In this study a number of thermal treatment schemes over a wide range of temperatures between 120˚ to 350˚ C and times (30 120 minutes) have been experimented in an effort to understand the effect of thermal treatment on tensile properties of vacuum die cast modified aluminum alloy A356. The results show that, the morphology of eutectic silicon has a sound effect on the tensile properties of the tested alloy. The content of magnesium-based intermetallic phases, their morphology and distribution throughout the matrix affect the mechanical properties of the aged alloy as well. The reduction in the strengths of the alloy treated at 350°C for two hours should be at least attributed partly to the absence of the magnesium-based intermetallic phase. However the presence of sufficient amount of magnesium intermetallic phase had played important role in strengthening the alloy thermally treated at 200°C for 90 minutes.

Abstract: Gravity die casting (GDC) and low pressure die casting (LPDC) methods were used to compare the mechanical properties and porosity distribution in a 5-step mould design. Commercially available A356 alloy was used for the experiments. Ar and Ar+H₂ mixture were used to achieve two different hydrogen levels, i.e. 0,1 and 0,2 ml/100g Al, respectively. Although the porosity level was lower in LPDC, the tensile properties were lower than GDC due to the fact that LPDC melt had 50 mm bifilm index, whereas GDC melt had 20 mm. This investigation has shown that the metal quality has a larger effect over the mechanical properties than the porosity content.