Papers by Keyword: Aluminium Casting

Abstract: Aluminium is a popular choice for structural applications because of its low weight, large specific strength, excellent heat transmission capabilities, and mostly due to its strength-to-weight ratio being high. Any desired shape or form of aluminium may be manufactured using permanent mould casting operation. However, porosity arises as a typical defect where pores cause an increase in surface roughness, which in turn increases wear and friction of the surface and reduces material strength. A variety of porous characteristics on the surface are formed in the casting process by regulating casting pouring parameters like the temperature and velocity of pouring. The presented research establishes a better knowledge of the relationship between the wear and frictional behaviour with temperature and velocity of pouring. In this context, the casting process has been done by creating a three-dimensional model by Ansys Fluent. Observations reveal that the frictional and wear behaviour of pure aluminium increases with the temperature of pouring and reduces with the velocity of pouring.

Abstract: The foundry casting process is complex and takes various stages to produce the desired component; as a result, simulation is necessary before manufacturing. Hot spots are areas that become thermally isolated and take the longest to cool, resulting in cavities during the solidification of the casting. So it is important to know about the hot spot location and size so that any casting designer can identify the hot spot behaviours before the casting. To predict the initiation of the hot spot, a 3D aluminium permanent mould casting model has been developed by Ansys Fluent. The suitable boundary and initial conditions such as temperature, pressure, convectional heat transfer coefficient, etc. are reasonably established in the simulation of Ansys Fluent. The simulation has been performed for varied pouring parameters i.e. pouring velocity and pouring temperature, to examine the beginning of hot spots. This study can predict the position and approximate size of the hot spots for various pouring conditions and it is found that a hot spot is commonly located below the riser.

Abstract: Aluminium High Pressure Die Castings are economical to produce in high volumes. However, as greater structural demands are placed on such castings, a more detailed understanding is required of the defects which limit their strength. The process is prone to high levels of surface turbulence and fluid break-up, resulting in the entrainment of air into the liquid metal, which may manifest as trapped air porosity or bifilm defects in the finished part. A novel algorithm was developed and integrated into a commercial computational fluid dynamics (CFD) package, to model mould filling, and the formation and transport of such entrainment defects. A commercial High Pressure Die Casting was simulated using this algorithm, to illustrate its application. Castings were also produced, and the results of tensile testing were summarised in the form of Weibull statistics. It was found that where the algorithm predicted a greater quantity of entrained surface film, a reduction in UTS of about 10% was also observed.

Abstract: The combination of Aluminum alloy with lost foam casting (LFC) process is best applied in automotive industry to replace steel components in order to achieve light weight components for reducing fuel consumption and to protect the environment. The LFC process involves process parameters such as the degree of vacuum, foam degradation, expanded polystyrene (EPS) foam density, permeability of foam pattern coatings, pouring temperature, filling velocity, cooling rate, and pressure. The effect of polystyrene foam pattern coating thickness on the porosity and mechanical properties of Aluminum Al-Si LM6 alloy were evaluated experimentally. The coating thickness was controlled by slurry viscosity at range between 18sec to 20sec using Zahn viscosity cup No.5 and the foam pattern was coated up to fifth layer. Aluminum Al-Si (LM6) molten metal was poured into expandable mould and castings were examined to determine porosity distribution, mechanical properties and microscopic observation. Results from X-ray testing reveal the porosity distribution on Aluminum Al-Si LM6 castings is greater at thicker foam pattern coating sample. Meanwhile, the tensile strength of casting decreases when foam pattern coating thickness increases. Microscope observation portray the present of porosity on the casting which shows more gas defects present at thicker foam pattern coating sample. The source of porosity in LFC process is due to air entrainment or the entraining gases from polystyrene foam decomposition during pouring of molten metal. As a conclusion, mechanical strength has inverse relationship with porosity.

Abstract: Research activities on aluminium production technology focus on the successive steps in the production chain of aluminium wrought products. Direct-chill casting of aluminium alloys is a well-developed technology with a long history. But only in the last 20 years, the development of computer modelling offered a means of better understanding of the physical phenomena involved in solidification. The main scientific challenge is to obtain a fundamental insight into the processing of aluminium alloys and to establish quantitative relationships between materials, processes, and performance. A systems approach is employed, covering theoretical and experimental studies on processing into semi-finished products. Special emphasis is placed on experimental verification and industrial applicability with the availability of pilot scale experimental facilities at M2i-TUD. This facilitates the design of process conditions as desired for experimental validation studies. In this paper we will consider main mechanisms of structure and defect formation during solidification of DC cast billets, mostly based in the results obtained in cooperation between Delft University of Technology and Materials Innovation Institute (M2i).

Abstract: A comprehensive numerical model has been developed for the calculation of the final microstructure and mechanical properties of aluminium casting alloys after heat treatment. The calculation is chained in such a way that the resultant microstructure of the previous processing step, such as casting, is used as the initial condition of the following step. In this paper an A357 alloy is chosen to study the microstructure and the evolution of the mechanical properties through the process from casting to heat treatment. The microstructure and mechanical properties are predicted and compared with experimental measurements.

Abstract: The ability of Al-Si alloys to be cast into complex shapes, coupled with a favourable strength-to-weight ratio, has given them an advantage in the automotive industry. To further improve casting quality, many have turned to semi-solids, where alloys exhibit flow properties that stem from the material's dual liquid-solid nature and globular microstructure. The SEED (Swirled Enthalpy Equilibration Device) process is a novel rheocasting technology yielding a semi-solid slurry from the mechanical agitation (swirling) and cooling of molten aluminum. In the current work, a SEED processed 357-T6 alloy displayed typical yield and ultimate tensile strength values of 210-250 and 300-320 MPa, respectively. Furthermore, the average elongation observed was 12-17%.

Abstract: Web gate system of aluminum castings in permanent molds is investigated in order to improve the quality of aluminum castings produced in permanent molds. The metal flow in the mold were observed and conducted using graphite molds and real time X-ray radiography recorded at a rate of 30 images per second through those molds. The affects of web thickness on flow patterns, gas entrapment, jetting possibility are studied and discussed. Flow and solidification simulation programs were employed to predict the flow behavior under the different conditions that can prevail in permanent mold gating. The study highlights the characteristic features of web gate system used in permanent mold aluminum foundries and recommends gating procedures designed to avoid common defects, and provides direct evidence on the filling pattern and heat flow behavior in permanent mold castings.

Abstract: Since the early 1960s hot isostatic pressing (HIP) was used to improve the quality of castings made of various alloys. The closure of pores, originating from the casting process, is considered as the main source of these improvements. For the aluminium alloy Al-9Si-3Cu specimens for tensile testing were machined from castings either squeeze casted and heat treated to T4 and T6 conditions or investment casted. The effect of HIP on density, roughness and mechanical properties was investigated. The density and roughness of the squeeze casted specimens did not change remarkably and their tensile strength became worse, because the initial heat-treatment-state was destroyed by HIP. The investment casted specimens became denser and roughness became worse due to closure of pores near the surface. Although roughness after HIP was higher than in the initial state, tensile strength was improved significantly by HIP, because of closure of the pores in the specimen.

Abstract: A new technology has been developed for making refractory products based on the naturally occurring wollastonite (calcium metasilicate) intended for the aluminum industry. The application of natural wollastonite requires no hydrothermal treatment in an autoclave, which considerably simplifies the manufacturing process and reduces its cost. A qualitative comparative analysis of natural wollastonite from different mineral deposits was made to choose an optimal modification with consideration for its availability. The articles were made by using steel-mold pressing, slip casting and vacuum forming methods. For the development of technology for manufacturing large-sized complex-shaped products the slip casting method was used and the slip basic composition was determined comprising 80% of wollastonite as a basic solid phase and 20% of plasticizers. The improvement in the thermal resistance of wollastonite-based ceramics is assured by applying special techniques, namely by addition of course-grained fillers. Thus, addition of about 15% of a course-grained fraction into the fine wollastonite-based slip improves the thermal resistance of ceramics and affords 2-3 times increase in their service life. The efficient way to increase the wollastonite-based ceramics thermal resistance is addition of inorganic fibers. With the use of an inorganic fiber, the materials have been produced with an apparent density ranging from 0.5 to 1.5 g/cm3 and an ultimate compressive strength of 0.5 to 10 MPa. The study has been made into ceramics structure comprising inorganic fibers. The developed materials are chemically inert to aluminum melt. They show no sticking, no mechanical erosion and they are thermal-resistant. With the above methods, the following products are being made on the basis of the naturally occurring wollastonite: spouts, lining plates, heat nozzles, stopper-rod devices, pipes and other articles that have been operating successfully in the aluminum industry of Russia.