Presentation on theme: "Processing of Powder Metals, Ceramics, Glass & Superconductors"— Presentation transcript:
1 Processing of Powder Metals, Ceramics, Glass & Superconductors
2 Powder Metals Commonly used metals in P/M Iron,Tin, Copper, Aluminum, and NickelIt is a completive process with forging and machiningParts can weigh as much as little as 2.5Kg or up to 50Kg
3 Powder MetallurgycabFig: (a)Examples of typical parts made by powder-metallurgy processes. (b) Upper trip lever for a commercial irrigation sprinkler, made by P/M. This part is made of unleaded brass alloy; it replaces a die-cast part, with a 60% savings. (c) Main-bearing powder metal caps for 3.8 and 3.1 liter General Motors automotive engines.
4 Production of Metal Powders Powder productionBlendingCompactionSinteringFinishing operations
5 Particle Size, Distribution, and shape Particle size is measured by screeningIn addition to screen analysis one can use:Sedimentation – measuring the rate that particles settle in a fluidMicroscopic analysis – using ascanning electron microscopeLight scatteringOptical – particles blocking a beam of light that is sensed by a photocellSuspending particles in a liquid & detecting particle size anddistributionFig: Particle shapes in metal powders,and the processes by which they are produced.Iron powders are produced by many of these processes
6 Powder ParticlesFig : (a) Scanning electron-microscopy photograph of iron-powder particles made by atomization. (b) Nickel-based superalloy powder particles made by the rotating electrode process.
7 Methods of Powder Production Fig: Methods of mechanical communication, to obtain fine particles: (a) roll crushing, (b) ball mill, & (c) hammer millingFig : Methods of metal-powder production by atomization;(a) melt atomization; (b) atomization with a rotating consumable electrode
8 Blending PowdersBlending powders is the second step in the P/M processPowders made by different processes have different sizes and shapes and must be well mixedPowders of different metals can be mixed togetherLubricants can be mixed with thepowders to improve their flowcharacteristicsFig: Some common equipment geometries for mixing or blending powders. (a) cylindrical, (b) rotating cube, (c) double cone, and (d) twin shell.
9 Compaction of Metal Powders Blended powders are pressed togetherThe powder must flow easily into the dieSize distribution is an important factThey should not be all the same sizeShould be a mixture of large and smallparticlesThe higher the density the higherthe strengthFig: 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
10 Equipment Uses 100-300 ton press Selection of the press depends on the part and the configuration of the partFig: A7.3 MN (825 ton) mechanical press for compacting metal powder.
11 Isostatic Pressing Cold isostatic Pressing (CIP) Metal powder is placed in a flexiblerubber moldPressurized hydrostaticallyUses pressures up to 150 KSITypical application is automotivecylinder linersFig: Schematic diagram, of cold isostatic, as applied to forming a tube.The powder is enclosed in a flexible container around a solid core rod.Pressure is applied iso-statically to the assembly inside a high-pressure chamber.
12 Isostatic Pressing Hot Isostatic pressing Container is made of high-melting-point sheet metalUses a inert gas as the pressurizing mediumCommon conditions for HIP are 15KSI at 2000FMainly used for super alloy castingFig: Schematic illustration of hot isostatic pressing.The pressure and temperature variation vs.time are shown in the diagram
13 Punch and Die Materials Depends on the abrasiveness of the powder metalTungsten-carbide dies are usedPunches are generally made of the similar materialsDimensions are watched very close
14 Metal Injection Molding MIM uses very fine metal powders blended with a polymerThe molded greens are then placed in a furnace to burn off the plasticsAdvantages of injection moldingProduces complex shapesMechanical properties are nearly equal to those of wrought products
15 Other Shaping Processes Rolling – powder is fed though the roll gap and is used to make coins and sheet metalExtrusion – has improved properties and parts my be forged in a closed die to get final shapePressureless compaction – gravity filled die and used to make porous partsCeramic molds – molds are made by made by investment casting and the powder is compressed by hot isostatic pressingSpray deposition – shape-generation processAn example of powder rolling
16 SinteringSintering - Green compacts are heated in a furnace to a temperature below melting pointImproves the strength of the materialProper furnace control is important for optimum propertiesFig: Schematic illustration of two mechanism for sintering metal powders: (a) solid-state material transport; (b) liquid-phase material transport.R= particle radius, r=neck radius, and p=neck profile radius
17 Sintering Particles start forming a bond by diffusion Vapor-phase transport – heated very close to melting temperature allows metal atoms to release to the vapor phaseMechanical Properties
19 Secondary & Finishing Operations To improve the properties ofsintered P/M products severaladditional operations may beused:Coining and sizing – compaction operationsImpact forging – cold or hotforging may be usedParts may be impregnated witha fluid to reduce the porosityFig: Examples of P/M parts,showing poor designs and good ones.Notes that sharp radii and re entry corners should be avoided and that threads and transverse holes have to be produced separately by additional machining operations.
20 Secondary & Finishing Operations Infiltration – metal infiltrates the pores of a sintered part to produce a stronger part and produces a pore free partOther finishing operationsHeat treatingMachiningGrindingPlating
21 Design Considerations for P/M Design principles to considerShape of the compact must be simple and uniformProvision must be made for the ejection of the partWide tolerances should be used when ever possible
22 Process CapabilitiesIt is a technique for making parts from high melting point refractory metalsHigh production ratesGood dimensional controlWide range of compositions for obtaining special mechanical and physical properties
23 Process Capabilities Limitations High cost Tooling cost for short production runsLimitations on part size and shapeMechanical properties of the partStrengthDuctility
24 Economics of Powder Metallurgy Competitive with casting and forgingHigh initial costEconomical for quantities over 10,000 piecesReduces or eliminates scraps
25 Shaping Ceramics Processing ceramics Crushing or grinding the raw materials in to very fine particlesMixing with additivesShaping, drying , and firing the material