Presentation on Powder Methods VIJAY 2008AMD2925

Introduction  Manufacturing process in which fine powder of materials are- Blended or mixed, Compacted (pressed) in to required shape, size and surface finish Sintered (heated) Controlled atmosphere to bond the contacting surfaces of particles and to achieve required properties like strength, density etc.  High quality, complex parts to close tolerances in an economical manner (eliminating additional machining or finishing operations ).  Controlled degree of density, porosity, strength and other properties of material, with minimum waste

Applications ApplicationMetalsUses AbrasiveFe, Sn, ZnCleaning, abrasive wheels AerospaceAl, Be, NbJet engine, heat shield AutomotiveCu, Fe, WValve insert, bushing, gears ElectronicAg, Au, MoDiode heat sink JoiningCu, Fe, SnSolder, electrode MagneticCo, Fe, ZnRelay, magnets ManufacturingCu, Mn, WDies, tools, bearings NuclearBe, Ni, WShielding, filters, reflector Tungsten lamp filaments, oil-less bearings, automotive transmission gears, electrical contacts, nuclear power fuel elements, aircraft brake pads, jet engine components, printed circuit boards, explosives, welding electrodes, rocket fuels, etc [2] Table1:- Application of powder methods [1]

Production of a component 1. Production of powder 2. Preparation of powder including blending and mixing 3. Compacting 4. Sintering 5. Post sintering treatment [3]

Production of Powder 1. Mechanical method (milling)  Ball mills and roller mills  Ferrous and non ferrous materials  Brittle Fig 1:- Ball mill Image courtesy: - Ref. [4]

Production of Powder 2. Electrolytic Deposition Spongy or powdery state of metal Suitable conditions; composition and strength of the electrolyte, temperature, current density, etc Copper, chromium and manganese powders Pure powder Fig 2:- Electrolytic deposition Image courtesy: - Ref. [2]

Production of Powder 3. Reduction of ores  Iron powder 4. Atomisation  Liquid metals – Orifice- Jet stream of gas, water, or steam –Broken into fine particles  To control particle size distribution- Parameters; design and configurations of the jets, pressure and volume of the atomising fluid, thickness of the stream of metal, etc  Production of iron, tool steels, alloy steels, copper, brass, bronze and the low-melting-point metals, such as aluminium, tin, lead, zinc, cadmium powders. [2]

Fig 3:- Vertical gas atomization unitImage courtesy: - Ref. [5]

Preparation of powder  Blending and Mixing To obtain desired properties and characteristics we have to mix Powder of different materials -different grades and sizes- different composition Lubricants and binders. Alloying elements Fig 4:- Powder contents Image Courtesy: - Ref. [2]

 Compacting Loose powder of material is compressed and densified –Green compact- At room temp. Mechanical, hydraulic and pneumatic presses. Fig 5:- Compaction sequence (1)Cycle start (2)Charge die with powder (3)Compaction begin (4) Compaction completed (5) Ejection of part (6) Recharging die Image Courtesy: - Ref.[2]

 Sintering Green compact is heated in a controlled atmosphere Below the melting point but high enough to permit solid state diffusion Held for sufficient time to permit bonding of the particles Sintering temperature range for iron-based alloys is °C and the time varies between 10 and 60 minutes, depending on the application [6] Fig 6:- Sintering processImage Courtesy: - Ref. [7]

Post sintering treatments  Machining  De-burring  Joining  Heat treatment  Double Pressing  Oil Impregnation

Advantages of the powder methods  Complex shapes can be produced.  Close dimensional accuracy with elimination or reduction in machining.  High production rate due to automation.  Wide range of properties like density, porosity and particle size can be obtained.  No waste during fabrication.  Highly skilled labour is not required. [8]

Disadvantages and limitations  Pure metal powders are very expensive.  Size of part produced is limited.  Alloy powders are not easily obtained.  Strength properties are lower than product manufactured by convention way.  Increased tendency to oxidation due t pores.  Poor plastic properties like impact strength, elongation etc.  High pressure and severe abrasion involved in process increase the die cost. [8]

References:- 1. Manufacturing Engineering and Technology by Seropr Kalpakjian and Steven R. Schmid, Chapter 17, Table 17.1 Page Manufacturing Engineering Processes by Leo Alting, Chapter 9, Page tomizer.gif Elements of Workshop Technology by S.K. and A.K. Hajra Choudhury, Chapter 12, Page

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