Novel Manufacturing Technique of Metal Foams by Mechanical Processing of Hollow Spheres
Uma Shankar, C
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Aluminium foams have high specific strength and higher stiffness than other contemporary packaging materials. They have important application as packaging material for critical applications that needs highest safety standards. Commercially, established processes for manufacturing of metal foam include Hydro/Alcan Process, Alporas Process, Gasar/Lotus process, Alulight/Foaminal process, Formgrip Process, ALUHAB and Powder Metallurgy route. In the above methods, control of the shape and size of pores is difficult. In these techniques significant changes in the chemistry of the melt is carried out to foam the metals. The Gap area of the above commercial processes is minimised by “Hollow sphere technique”. This process overcomes the limitations in achieving the cell wall thickness, shape of the pores, non-uniformity of pore size and its distribution in comparison to existing commercial established process. Moreover, it is easy to fabricate foams, with desired/tunable mechanical properties. This thesis discusses, the fabrication technique of hollow spheres using a special die by successive pressing of hollow tube through a series of ten die cavities. The fabricated hollow spheres are cured in the required shape using suitable bonding material (resin based or metal binder). The advantage of this process being, any asymmetrical shape is easier to fabricate and mechanical properties can be controlled by using spheres with different diameters and varying wall thickness. This process does not require any additional alloy nor does it require huge experimental facilities for fabrication. This mechanical processing method of hollow sphere technique can fabricate different diameter spheres with varying wall thickness. By arranging spheres in desired pattern, “graded foams” which is a new concept exhibiting peculiar properties is introduced. This work includes assessment of mechanical properties and its comparison with respect to commercially available foams. The main properties under consideration were yield strength, Young’s modulus, plateau stress, densification strain and energy absorption evaluation. This thesis also, discusses practical application of developed product in the field of engineering as base isolators, which is novel. The thesis concludes by highlighting advantages of this technique over the other existing commercially established fabrication routes: • Desired/tunable Mechanical properties can be achieved on case-to-case basis with ease and can be supported by impact simulations using finite element analysis. • It is the fastest and easiest way for production of High purity aluminium foam and in achieving any asymmetrical shapes. • Relative Densities of the order of 10%, 20%, 30%, 40%, 50 % and higher can be achieved by varying only the hollow sphere diameter or wall thickness of the sphere. • Cost effective and Environment/Eco-friendly and Recyclable This route of hollow spheres fabrication and the final product is different from the prevalent commercially established routes of metal foam fabrication using hollow sphere technique.