 What is powder metallurgy? Powder metallurgy is a branch of metallurgy dealing with the metal and non-metal powders and then using them for economical manufacturing of high-precision components. Powder metallurgy consists of the following six basic steps, namely A. Powder production, B. Powder conditioning, C. Powder compacting or pressing, D. Sintering, E. Sizing or impregnation, and F. Testing and inspection. First comes powder production in which the metal or non-metal undergoes various mechanical processes like machining, crushing, milling, shorting, graining and atomization to produce powder in the form of small chips, fillings, break-offs, etc. For the volatile metals and carbonyls, physical processes like condensation and thermal decomposition are used to carry out powder production. The powder produced through these processes are mainly spherical in shape. These processes are usually carried out in closed containers to avoid formation of metal oxides. For metals in their oxide-oxalate format or halide states, reduction principle is used where reducing agents like carbon, hydrogen, ammonia and carbon monoxide are used for economical and flexible powder production of irregular shape. For metals in their active solution or few salts, electrochemical processes are used. They ensure perfect control of powder size and type by varying parameters like high current, low metal ion concentration, low temperature and thus can obtain highly pure crystalline shape. Second comes powder conditioning which makes use of heat treatment, sieving and blending to reduce impurities and oxide content, obtain desired powder size and obtain a homogeneous mixture of powders. Third comes powder compacting which is a process of pressing and imparting shape to the powder mix using a dye and punch arrangement. The powder mix is fed in through a vibrating hopper and feeder which allows smooth flow of powder and dye. Pressure is then applied on the powder mix through the upper punch. After sufficient time and pressure application, the upper punch is lifted and the compact powder mix, called as green compact, is ejected out with the help of bottom punch. The density of this compact depends on pressure applied. Next comes centering process which makes use of heat and soaking to help the compact crystal undergo neck formation, neck growth and pore rounding resulting in increased strength and hardness of compact. Next comes sizing or impregnation which is a process of rectifying the centered compact to the final required dimensions. Sizing is done by placing the compact in a master dye and applying pressure. Last comes testing and inspection which tests the components after centering and sizing for compressive strength, tensile strength, porosity, density, hardness, microstructure etc. Processes of powder metallurgical components depend largely on the properties of loose metals from which they are made. They are hence tested under three main groups. First are basic properties which test the chemical composition, shape, size, porosity and specific surface of the material. Second comes compacting properties like apparent density defined as the mass per unit volume of loose and packed powder, compressibility defined as the ability of the powder to undergo compression under applied pressure, green strength defined as the mechanical strength of a green compact and green spring defined as the expansion of compact under ejection. Last comes centering properties which consists of dimensional changes during centering calculated by the ratio of change in the length to centred length. Centering density calculated again as the ratio of density of solid material to that of the censored component and microstructure examination which is usually done by etching the sample followed by visual observation through microscope. Advantages of powder metallurgy include special characteristics due to mixing of both metallic and non-metallic powders and high purity components with a drawback of high equipment cost, limited size of production and storage issues. Applications of powder metallurgy, first self lubricating bearings. These are the bearings which do not require any external lubrication during its function working. Small amount of graphite is used for increasing porosity in which oil is impregnated with the help of high pressure or vacuum. These bearings work due to the temperature rise caused by friction from rotating shaft inducing a reduction in the viscosity of oil here by increasing its flow rate. Hence the oil is pulled out from the pores and starts to circulate rapidly. Second, cermets. Cermet is a combination of two words sir from ceramics and metes from metals. Ceramics have high temperature strength and hardness whereas metal powders have good shock resisting ability and cermets have both these properties and are combined using approximately 20 to 40 percent ratio of metallic binders. Cermets are used in flame holders and nozzles of jet propulsion. Third comes center metal friction materials. These materials are used in clutches, brakes and places where controlled friction are necessary. Fourth, production of refactory materials. Used in filament of electric bulbs, electrical contacts, high temperature furnaces and rocket nozzles, these materials during casting or forging react with the environment and hence powder metallurgy is used in their production. Hence comes the end of the quick revision of joining process. Finally, it's time for this episode's question. What is atomization? Also, it's time to answer our last episode's question. What do you mean by coalescence? In engineering, coalescence means to bond pieces of metal into a continuous hole by liquefying parts of each piece, bringing the liquids into contact and then allowing the combined liquid to solidify. So like, subscribe and comment with your feedback to help us make better videos. Thanks for watching. In the next episode of Mechanical Engineering Insiders, find out how molding of polymers is done.