MATERIALS Essay Example

8Metal Casting

Metal Casting

Metal Casting

Question 1

Metal casting involves pouring the liquid metal into a mold with an aim of achieving the required shape. Almost every metal can be cast with the challenge involved is the production of casts that have the desired compositions, free from any defect, and meet the required strengths, surface finish, and , dimensional accuracy. The process starts with the creation of liquid metal, metal, then the creation of solid shape, casting. Metal casting involves making molten material with ability to flow into very small sections to enable development of intricate shapes. Therefore, it enables modeling of the required shapes and several operations like machining, welding, and forging are minimized. Casting may have a slightly different shape from the pattern used in making the mold (Pearson Education, Inc., 2008). Shrinkage continues after solidification until the casting process cools to the room temperature. Moreover, because of surface tension, the solidifying metal may fail to conform fully to the sharp corners and various intricate features of the surface if the surface tension is high enough. As a result, the cast shape would have a slight difference compared to that of the pattern used (Yadav & Karunakar, 2011, 132). Moreover, the squeeze casting produces some of the parts, which have better physical features such as mechanical properties, dimensional accuracy, and surface finish compared to the expandable mold process.

The squeeze-cutting process involves a combination of both forging and casting. The process involves applying pressure to the molten metal, which keeps the entrapped gases in the solution; therefore, the products lack porosity. Furthermore, the applied transfer of heat results in fine microstructure with proper mechanical features. Depending on the applied pressure and the nature of the die used, the metal, surface finish, and proper dimensional accuracy are found typically within the parts of the squeezed casts. In some cases, metal casting leads to the development of porosity, which has a detrimental effect on the physical properties of the cast (Singh, 2013, 839). In metal casting, pores refer to internal disconnections, which make casts susceptibility to cracking and propagation. This reduces the toughness of the material. Besides, the presence of the pore within materials under tension indicate that material around pore needs to support greater load compared to if there are no pores present; as a result, there is reduction in the strength. Internal defects associated with thermal and electrical features reduce the capability of casts since air is a poor conductor. There are variations in the hardness of materials especially with the changes in the levels of grain fineness numbers, preheating temperatures in the mould, the pouring temperature, and preheating time. Hardness of the casting varies significantly with the changes in various parameters. Hardness of the materials tends to decrease with increase in the grain fineness number and preheating temperatures. Hardness, impact, and tensile strength tend to decline with increased grain fineness number in the material.

Question 2

Sand casting the engine block combines various manufacturing processes: machining, casting, and rapid prototyping. A mold from which the molten metal is poured to make the engine block needs to be made. There are many sand cores and molds used for engine block (New Engineering Practice, 2011). In the engine block, the major tool required is sand casting made from the mold generated through mixing the sand, clay, and water. The main tool essential to procedure the mold is pattern, which is machined through
aluminium and kept on the metal frame before pouring sand mixture and application of vibrations to remove the bubbles. While manufacturing the engine blocks, sand casting is important; however, in some cases the manufacturers prefer die casting since it is more cost effective. The die wear wears out easily because of the high temperatures generated from the molten metal. In addition, the casted engine block is machined to obtain the surface finish and coolant passages. Within the sand casting process, the commonly used in engine block is green sand mould casting which denote the presence of moisture in the sand mold. During the manufacturing process, silica sand, clay, and water are poured into the aluminium block pattern that has a wooden frame. The quality of the sand often affects the surface finish of the engine block, which makes it important to meet the required standards. The strength of the sand needs to be high in a bid to maintain the rigid shape and has to be reusable for formation of the next sand molds. Permeability depends on the size of the sand grains with higher permeability reducing the porosity of the mold.

Prosthetic hips need a proper surface finish considering that they work as integrated body organs. On the other hand, sand casting does not give excellent surface finish and the required metallurgical features. Based on the ABS model of femur, the concept is used as a pattern to prepare the mould for sand casting. During the modeling process, sand is compacted within the pattern, and after removal of the pattern, the mould cavity is left as the shape of the pattern. Moreover, there is preparation of the CO2
mould for provision of strength to the sand and application of alcohol based graphite paint within the mould cavity to acquire the required surface finish (Ruder, Ferni & Kostui, 2012). After cooling the sand cast, a thin layer of prosthetic is finished using abrasive polishing with an aim of removing roughness. Sand casting in manufacturing prosthetic may involve some defects; therefore, to enable defect free casting process, some manufacturers use software. Moreover, sand cast is used outside prosthetic hip to aid in the adhesion. Porous implants structures can be fabricated using different manufacturing routes; however, there is need for standardized format. There are various fabrication methods in the process including ceramic-mold casting, plaster-mold casting, and sand casting. The method used need to ensure that the format is not customized for any particular individual.

Question 3

Aluminium foil is made using aluminium foil that has between 92% and 99% aluminium content. The process commences with rolling the ingot casts acquired through molting the billet aluminium then the product re-rolled on the sheet and foil rolling mills with an aim of achieving the required level of thickness (Madehow, 2011). Moreover, the process requires continuous casting and cold rolling. In most cases, the manufacturers use the beta radiation to ensure that the thickness during production if the foil is maintained. The process involves passing the radiation through the foil to the sensor. Such activity requires greater level of keenness since the intensity of the radiation may be high. In such cases, the rollers are adjusted to increase the level of thickness (Aluminum Foil, 2005). When the level of the intensities become too low, then the foil needs need to be thick while applying more pressure which makes the foil thinner. It is important to note that the continuous casting method in the manufacturing of aluminium foil is much less energy intensive, which makes the method efficient and preferred in most activities. The manufacturers often put two layers together while developing aluminium foils with 0.025mm. This occurs in the final pass and separable afterwards for production of foil that has both bright and matte sides. The matte and exterior sides are bright and in contact with each other for the reduction of tearing, increment in the production rates, controlling the level of thickness, and ensuring smaller diameter roller. However, while rolling, some lubrication is needed to prevent the surface of the foil to be marked with the herringbone pattern (Zendehdel & Hassani, 2012, 15). The commonly used lubricants are kerosene based and sprayed within the surface before the foiled is passed through the mills. Cold rolling and annealed processes are important for hardening of the aluminium.

Manufacturing aluminium foil contributes to grain size effect. When exposed to heated treating, the grains of metals often grow larger. Small grains make metal stronger but less ductile. Manufacturing of the aluminium foil involves annealing which is a softening process in which aluminium is treated. The process hardens the metal. Since the foils are made from aluminium and associated alloys, the composition often remains the same. The main factor that is altered is extreme thickness associated with the foil gauges of the metal (Indra Reddy, 2016, 4). The process involves tempering which is the addition of other elements to strengthen aluminium. Considering that aluminium and some associated alloys are strengthened beyond the basic strength of aluminium through strain hardening which makes the metal non-heat-treatable. Almost all the foils manufactured are non-heat-treatable alloys. During the manufacturing process, aluminium foil is subjected to high temperatures until the required level softness is achieved. While heating, the oil used for lubrication are burned off which leaves the surface dry.


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