Powder Metallurgy-1

POWDER METALLURGY M. R. Doddamani Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology, Udyambag, Belgaum HISTORY OF POWDER METALLURGY (PM) APPLICATIONS • 3000 B.C. - Egyptians made tools with powder metallurgy • 1839 – Woolaston’s paper described a process for producing compact platinum from platinum sponge powder (first scientific work) • 1900’s tungsten filament for light bulb • 1930’s carbide tool materials • 1960’s automobile parts • 1980’s aircraft engine turbine parts M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum P/M TUNGSTEN LIGHT BULB FILAMENT M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum Molybdenum billet Weight – 1360 kg Diameter – 470 mm Height – 1120 mm M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum WHY PM? • Competitive with processes such as casting, forging, and machining. • Used when • melting point is too high • reaction occurs at melting • too hard to machine • very large quantity • Near 70% of the P/M part production is for automotive applications. • Good dimensional accuracy • Controllable porosity • Size range from tiny balls for ball-point pens to parts weighing 100 lb. Most are around 5 lb. M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum • Can’t do it any other way – Porous bearings and filters – Very high MP metals (W alloys, WC-Co tools) – Very highly alloyed metals • Eliminates other manufacturing operations • High production quantities in highly automated operations WHY PM? M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum • Full-scale Industrialization in past 50 years • >$1.8 Billion per year in North America • Powder metallurgy may be defined as the art of producing metal powders and using them to make serviceable objects. • Powder metallurgy is the name given to the process by which fine powdered materials are blended, pressed into a desired shape, and then heated to bond surfaces • Typically used when large amounts of small, intricate parts with high precision are required • Little material waste and unusual mixtures can be utilized • Used for parts in the automotive industry, household appliances, and recreational equipment INTRODUCTION • Components can be made from pure metals, alloys, or mixture of metallic and non-metallic powders • Commonly used materials are iron, copper, aluminum, nickel, titanium, brass, bronze, steels and refractory metals • Used widely for manufacturing gears, cams, bushings, cutting tools, piston rings, connecting rods, impellers etc. Keep in mind that powder cost more than equivalent cast or wrought material INTRODUCTION M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum GENERAL AND UNIQUE FEATURES • Small size: < 2-3 kg; maximum up to 20 kg • Net shape: 0.127 mm • Very little waste of material (no runner, riser, etc) • Production of porous metal parts: filters, oil- impregnated bearings and gears • Applicability to any type of metals; a unique way for those metals (e.g., Tungsten) which can hardly be handled by other methods CHARACTERIZATION OF POWDERS • Size and distribution • Shape and internal structure • Surface area M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum CHARACTERIZATION OF POWDERS Size and distribution M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum Mixing particles of different sizes allows decreased porosity and a higher packing ratio Micrograph of screened powder particles Characterization of Powders Particle shape and internal structure M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum Atomizing Oxide reduction Electro deposition Particle shapes in metal powders and processes by which they are produced M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum Particle shapes in metal powders and processes by which they are produced CHARACTERIZATION OF POWDERS Inter-particle friction M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum Powder Metallurgy processes Outline of processes and operations involved in making powder metallurgy parts M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum • Liquid metal stream by injecting metal through small orifice • Breaking of stream by jets of inert gas, air or water • Size of particles – temperature of metal, rate of flow, nozzle size and jet characteristics • Most frequently used for metals having low melting point (tin, lead, zinc, cadmium and aluminum) • Principle advantage due to its flexibility POWDER PRODUCTION - Atomization M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum POWDER PRODUCTION - Atomization Melt atomization Rotating consumable electrode M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum POWDER PRODUCTION - Atomization Water Atomization Induction Coil Gas Atomization Gas Atomization - Spherical powder particles - Good "flowability" Water Atomization - Irregular powder particles - Good compactability Gas Atomized Silver Alloy Water Atomized Copper Alloy REDUCTION - reduction of compounds of metals (oxides) - carbon monoxide & hydrogen (reducing agents) - formation of powder - Only available method for refractory materials (W - hydrogen, Mo) ELECTROLYTIC DEPOSITION - Electrolysis of acidified solution (anode & cathode) - Deposit of metal powder on cathode - Periodic removal of powder followed by subsequent treatment - Powder with dendritic structure (interlocking) POWDER PRODUCTION - Method is mainly used for the production of Copper and iron powder CARBONYLS - Formation of metal carbonyls - Reaction of iron & carbon with carbon monoxide - Decomposition of reaction products into iron & nickel - Powder of small, dense, uniformly spherical particles of high purity COMMUNICATION - Crushing into small particles mechanically - Usage of roll, ball and hammer mills - Brittle & ductile materials (angular & flaky particles) POWDER PRODUCTION POWDER PRODUCTION Mechanical Communication methods Ball milling Roll crushing Hammer milling M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum • To obtain uniformity • Mixing of powder – air, inert atmosphere, in liquids • Mixing time – few minutes to several days • Addition of lubricants (reduced friction, greater flowability) • Stearic acid or zinc stearate in proportion of 0.25 % to 5 % by weight (typical lubricants) • Mixing must be carried out under controlled conditions to avoid deterioration (excessive mixing – alteration of particle shape, work hardening, difficulty in compaction) • Usage of blending equipments BLENDING or MIXING BLENDING or MIXING Cylindrical Double cone Twin shell Rotating cube M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum • Most important operation • Most compacting is done cold, there are some applications for which compacts are hot pressed • Purpose – consolidation of the powder into the desired shape • Two types - pressure techniques - pressureless techniques COMPACTION M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum • Increased compaction pressure – Provides better packing of particles and leads to ↓ porosity – ↑ localized deformation allowing new contacts to be formed between particles M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum • At higher pressures, the green density approaches density of the bulk metal • Pressed density greater than 90% of the bulk density is difficult to obtain • Compaction pressure used depends on desired density • Smaller particles provide greater strength mainly due to reduction in porosity • Size distribution of particles is very important. For same size particles minimum porosity of 24% will always be there – Box filled with tennis balls will always have open space between balls – Introduction of finer particles will fill voids and result in↑ density COMPACTION (a) Compaction of metal powder to form a bushing. The pressed powder part is called green compact. (b) Typical tool and die set for compacting a spur gear. Single action Double action Punch Punch Die Part M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum Additional Considerations During Compacting • When the pressure is applied by only one punch, the maximum density occurs right below the punch surface and decreases away from the punch • For complex shapes, multiple punches should be used Compaction with a single moving punch, showing the resultant nonuniform density (shaded), highest where particle movement is the greatest. Density distribution obtained with a double-acting press and two moving punches. Note the increased uniformity compared to above Figure. Thicker parts can be effectively compacted. Density Variation Density variation in compacting metal powders in different dies: (a) and (c) single-action press (b) and (d) double-action press. Note in (d) the greater uniformity of density in pressing with two punches with separate movements as compared with (c). Generally, uniformity of density is preferred, although there are situations in which density variation, and hence variation of properties, within a apart may be desirable. COMPACTION - Pressure Die Compaction DIE COMPACTION - Die & two punches (upper and lower) - Powder compaction between two punches - Processing steps 1. Filling die cavity with properly weighed amount of powder (geometry dependant) 2. Application of pressure by movement of the upper & lower punches towards each other 3. Ejection of green compact by lower punch - Pressure range from 19 to 50 tons/sq. in. - Pressure application through mechanical (10 – 50 tons, 6 – 150 strokes/min) or hydraulic (upto 5000 tons, speed less than 20 strokes/min) COMPACTION - Pressure M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum ISOSTATIC PRESSING • Application of hydrostatic pressure • Pressure is applied simultaneously and in all directions • Two types - Cold Isostatic pressing (CIP) - Hot Isostatic Pressing (HIP) COMPACTION - Pressure M. R. Doddamani, Faculty, Dept. of Mechanical Engg., Gogte Institute of Technology,Udyambag, Belgaum HISTORY OF POWDER �METALLURGY (PM) APPLICATIONS P/M TUNGSTEN LIGHT BULB FILAMENT WHY PM? GENERAL AND UNIQUE FEATURES CHARACTERIZATION OF POWDERS POWDER PRODUCTION - Atomization Additional Considerations During Compacting Density Variation