Why are the parts manufactured using powder metallurgy of near net shape? For mixtures of dissimilar...

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Mechanical Engineering

Why are the parts manufactured using powder metallurgy of nearnet shape? For mixtures of dissimilar metal powders, explain how(a) blending/mixing, and (b) compaction are carried out beforesintering. Explain how (i) blending/mixing and (ii) compactionsteps influence the (a) sintering step and (b) porosity developmentin the processed part.

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A Powder mixing and compaction Blending refers to mixing of same kind of metal powders whereas mixing refers to the uniform mixing of powders of different kind Mixing or blending of elementary powders is carried out in mixers or ball mills or attritor mills under inert or controlled atmospheres Oxidation and explosion of powders should be prevented during mixing by ensuring inert atmosphere in the mixer Powder size could be controlled using high speed ball milling of the powders Compaction of metal powders is the process of pressing green powders inside closed diepunch assembly Powders are compacted by applying suitable pressure through punches Lubrication is necessary to reduce interparticle friction and particledie wall friction Lubricants such as graphite powder zinc stearate powders are usually blended with metal powders before compaction Density of compacts is important from the point of view of handling the green compacts In compaction the particles come closer and establish contact A heterogeneous mix of particle shape and size will promote uniform density of compacts Softer powders promote higher green density Similarly higher compaction pressure leads to higher density of the compact Admixed lubricant also promotes higher green density The density of the compact is not uniform along the compact height due to nonuniform transfer of compact pressure from the punch to the compact Compaction die and See Answer

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