mt powder metallurgy
TRANSCRIPT
ME-402 MODULE-3
POWDER METALLURGY PROCESS
BY
RAMESH KUMAR NAYAKASST. PROFESSOR, SME
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ME-402 Manufacturing Technology-I CR-31.Foundry Process: Pattern making, pattern materials, allowances, types of pattern, sand casting types, sand cast,moulding procedure, types of sand, gates and riser (basic design considerations) essential properties of moulding sand,core making, types of cores. Essential qualities, core mixtures and binder sand testing, Mould and core hardness test,fineness test, clay content test, permeability test, moisture content test, sand conditioning. Basic idea about cupolasand other melting furnaces. Melting and pouring procedures for cast Iron, Steel and nonferrous castings. Cleaning ofcasting and defects in casting, die casting. Precision investment casting, shell moulds, centrifugal casting processes,permanent moulds casting, dies casting.2. Metal Working Process: Hot and cold working of Metals: Basic Principles of hot and cold working of metals.Rolling: Types of Rolling, Rolling equipments hot and cold rolling, General deformation pattern, Pressure and forcesin rolling.Forgings: Smith forging, Drop forging, press forging & Machine forging, Description of Presses and hammers,forging defects. Forging die design.Extrusion: Direct, Indirect and impact extrusion and their applications, Extrusion defects.Drawing: Wire and rod drawing, Tube drawing, Process variables in drawing process.
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3. Powder Metallurgy Process: Preparation of powder, properties of powder, fabrication methods & procedure,applications, advantages.
4. Fabrication Processes: Classification, types of welding joints, Gas welding principles, types of flames, equipment,techniques of gas cutting. Electric Arc Welding: Principles of electric welding equipments and electrodes (in brief),principles of Inert Gas Welding. TIG, MIG, sub-merged arc welding. Atomic hydrogen welding, plasma are welding.Resistance Welding: Principle of forge welding, spot-seam, Projection, Upset-butt welding, flash welding. Thermit -welding, electro-slag welding, friction welding Brazing, Soldering.Text Book:1. Manufacturing technology: P.N.Rao (Tata Mc-Graw Hill, Publication. Co.Ltd.)Reference Books:1. Principle of Metal Casting: Hein and Rosenthal.2. Manufacturing Science: A. Ghosh & A.K.Mallick (EWP)3. Principle of Manufacturing Materials and Processes: J.S. Cambell (TMH)4. Welding & Welding Technology - R.Little (TMH)
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Definition of Powder Metallurgy (P/M)
Art and science of producing fine metal powders and semi-
finished or finished components or parts from individual,
mixed or alloyed metal powders with or without the inclusions
of non-metallic constituents
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WHY POWDER METALLURGY ?Feasible when1.The melting point of a metal is too high such as W, Ta, Mo
2. The reaction occurs when melting such as Zr and for super hard tool materials
3. Limitation of solubility of solute in melting/ liquid condition
4. Near-net shape, No waste, controlled porosity, Dimension control better than casting 5
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BASIC STEPS IN POWDER METALLURGY
(P/M)
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1. Powder Manufacture
2. Powder Characterization & Testing
3. Powder Conditioning and Blending/Mixing
4. Powder Compaction
5. Sintering
6. Heat Treatment & Finishing Operations
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INDUSTRIAL PROCESSING STEPS
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POWDER PRODUCTION
Atomization the most common
OthersChemical reduction
of oxidesElectrolytic
deposition Different shapes
producedWill affect
compaction process significantly
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Fig: Methods of mechanical comminution, to obtain fine particles: (a) roll crushing, (b) ball mill, & (c) hammer milling
This method is generally applied for the preparation of powders of brittle materials
(a)
Comminution
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Physico-Chemical Processes
Condensation
•Used for production of zinc and magnesium powders
•Modified distillation technique
•Zinc oxide mixed with charcoal is heated until zinc vapor is formed
by the reaction of zinc oxide and carbon monoxide. Subsequently,
zinc vapor is condensed in the first and second condenser units in
form of fine zinc powder
•Main disadvantage is high oxidation, which is difficult to control
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Thermal Decomposition Gaseous
Pyrolysis Method•Used for production of iron and nickel powders from their carbonyl’s,
which at a certain temperature and pressure decompose to give a gas
and a metal
•Carbonyl’s like Fe(CO)5 and Ni(CO)4 are obtained by passing carbon
monoxide over spongy or powdered metal at suitable temperature (200
– 270 0C) and pressure (70 – 200 atm). At reduced pressure (one atm)
and elevated temperature (150 – 400 0C), both these carbonyl’s
decompose to form carbon monoxide gas and metal powder
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Reduction•Most widely used, oldest, convenient, economical and extremely
flexible method (regarding controlling shape, size and porosity) of
producing iron, copper, nickel, tungsten, molybdenum and cobalt
powders
•Extremely fine powders with irregular shaped particles are generally
formed
•Metal compounds generally oxides (small quantities of formats,
oxalates and halides) are reduced by the use of reducing agents
(hydrogen, dissociated NH3, CO, coal gas, enriched blast furnace
gas, natural gas, partially combusted hydrocarbons or alkali metal
vapors and carbon) either in solid or gaseous form
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Electro Deposition from Aqueous Solutions &
Fused Salts (Electrolysis Method)•Reversed adaptation of electroplating technique, used for
commercial production of copper, beryllium, iron, zinc, tin, nickel,
cadmium, antimony, silver and lead powders
•Main advantages are economical production, high purity, uniform
shape, size and size distribution
•Main disadvantages are unsuitability for alloy powders, time
consuming method, low productivity and high cost
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Precipitation from Aqueous Solution•Addition of less noble metal higher in the electromotive series
displaces and precipitates the metal from its aqueous solution
•Produces very fine powders with low apparent density
•Used extensively for production of gold and silver powders
Precipitation from Fused Salt•Similar to precipitation from aqueous solution and only difference is
that salts of metal fused with some reactive agents are heated to
high temperature to produce metal powders
•Used for the production of zirconium, beryllium and thorium
powders
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Hydrometallurgical / Gaseous Reduction•Metal powders of nickel, cobalt and copper are produced on
commercial scale
•Involves reduction of aqueous solutions or slurries of salts of
metals with hydrogen under particular combination of high
pressure (400 – 900 psi) and temperature (130 – 210 0C)
•Characterized by use of low grade of ores and production of very
highly pure powders with narrow range of particle size distribution
having spherical shapes and high apparent density
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Oxidation and decarburization
•Used for the production of pure reactive metal powders,
particularly niobium
•Metal carbide and metal oxides are reacted in vacuum at elevated
temperature so that both oxygen and carbon are removed as
carbon monoxide
•Name is given because it removes both oxygen and carbon
simultaneously
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Powder Characterization & Testing
•Economical manufacturing of P/M parts & components
depends upon the physical & chemical characteristics
of the powders, which in turn depend upon the type of
manufacturing method utilized for the production of the
metal powders
•Important to test and verify that powder is suitable for
subsequent processing
•Sampling technique is performed to test the powder
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Powder Conditioning
Metal powders directly after production are generally not suitable
further processing as they does not possess favorable physical or
chemical properties and thus require powder conditioning, which
involves mechanical, thermal (heat treatment) or chemical
treatments or physical alloying (additives as binders) treatments
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Conditioning Methods Used
•Preliminary heat treatment in reducing atmosphere or vacuum like
annealing , which reduces work-hardening, improves apparent
density, decreases oxidation, improves purity, improves pressing
(compressibility & compactability) characteristics
•Blending & mixing (blending is through intermingling of different
powders of same composition and material, whereas mixing is the
intermingling of powders of different materials)
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Characterization Methods
•Chemical composition ( wt analysis or XRD of SEM)•Particle size & their distribution ( Sieve Analysis)•Particle shape ( SEM)•Particle microstructure ( Optical Microscope /SEM)•Apparent density •Tap/ packed density •Flow rate •Compressibility & compact ability •Green density & porosity•Green strength ( Just after compaction before sintering)
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BLENDING OR MIXING
Can use master alloys, (most commonly) or elemental powders that are used to build up the alloys Master alloys are with the normal alloy ingredients
Elemental or pre-alloyed metal powders are first mixed with lubricants or other alloy additions to produce a homogeneous mixture of ingredients
The initial mixing may be done by either the metal powder producer or the P/M parts manufacturer
When the particles are blended: Desire to produce a homogenous blend Over-mixing will work-harden the particles and produce
variability in the sintering process25
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BLENDING POWDERS
Blending powders is the second step in the P/M process
Powders made by different processes have different sizes and shapes and must be well mixed
Powders of different metals can be mixed together
Lubricants can be mixed with the powders to improve their flow characteristics
Fig: Some common equipment geometries for mixing or blending powders. (a) cylindrical, (b) rotating cube, (c) double cone, and (d) twin shell.
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Usually gravity filled cavity at room temperature
Pressed at 60-100 ksi
Produces a “Green” compact Size and shape of finished
part (almost) Not as strong as finished
part – handling concern
Friction between particles is a major factor
COMPACTION
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COMPACTION OF METAL POWDERS
Blended powders are pressed together
The powder must flow easily into the die
Size distribution is an important fact They should not be all the same size Should be a mixture of large and small particles
The higher the density the higher the strength 28
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COMPACTION TOOLING
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COMPACTION CYCLE
1. Cycle Start2. Charge die
w/powder3. Compaction
begins4. Compaction
complete5. Ejection of
compaction6. Recharging of die
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ISOSTATIC PRESSING
• Because of friction between particles
• Apply pressure uniformly from all directions
• Wet bag (left)
• Dry bag (right)
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ISOSTATIC PRESSING
Cold isostatic Pressing (CIP)Metal powder is
placed in a flexible rubber mold
Pressurized hydrostatically
Uses pressures up to 150 KSI
Typical application is automotive
cylinder liners Fig: 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.
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HOT ISOSTATIC PRESSING Hot Isostatic
pressing Container is
made of high-melting-point sheet metal
Uses a inert gas as the pressurizing medium
Common conditions for HIP are 15KSI at 2000F
Mainly used for super alloy components
Fig: Schematic illustration of hot isostatic pressing.The pressure and temperature variation vs.time are shown in the diagram
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Increased compaction pressure Provides better packing of particles and leads to ↓
porosity ↑ localized deformation allowing new contacts to be
formed between particles36
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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
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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
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IMPORTANCE OF PUNCH AND DIE MATERIALS
Depends on the abrasiveness of the powder metal
Tungsten-carbide dies are used
Punches are generally made of the similar materials
Dimensions are watched very closly
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OTHER SHAPING PROCESSES
Rolling – powder is fed though the roll gap and is used to make coins and sheet metal
Extrusion – has improved properties and parts my be forged in a closed die to get final shape
Pressure less compaction – gravity filled die and used to make porous parts ( Filters)
Ceramic molds – molds are made by investment casting and the powder is compressed by hot isostatic pressing
An example of powder rolling
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SINTERING Parts are heated to 80% of melting temperature Transforms compacted mechanical bonds to
much stronger metal bonds Many parts are done at this stage. Some will
require additional processing
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Green Compact Product
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Stages in Sintering Process
(a)Adhesion without shrinkage
(diffusion of particles and formation of grain
boundaries)
(b)Densification and grain growth stage
(c)Formation of closed pores space
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Mechanism of Sintering Process
(a). Adhesion Mechanism
(b). Material Transport Mechanism
(i). Recovery & recrystallization
(ii). Plastic flow
(iii). Evaporation & condensation
(iv). Volume diffusion
(v). Surface diffusion
(vi). Grain boundary diffusion
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SINTERING
44 Fig: 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
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SINTERING
Final part properties drastically affected
Fully sintered is not always the goal Example- Self lubricated bushings
Dimensions of part are affected45
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Sintering Ctd.
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Liquid Phase Sintering
During sintering a liquid phase, from the lower MP
component, may exist
Alloying may take place at the particle-particle interface
Molten component may surround the particle that has not
melted
High compact density can be quickly attained
Important variables:
Nature of alloy, molten component/particle wetting,
capillary action of the liquid 50
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SINTERING CTD.
Gases commonly used for sintering: H2, N2, inert gases or vacuum
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EXAMPLE
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MECHANICAL PROPERTIES ( Steel Alloys)R
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SECONDARY & FINISHING OPERATIONS
To improve the properties of sintered P/M products several additional operations may be used:Coining and sizing – compaction operations Impact forging – cold or hot forging may be
used
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Infiltration – metal infiltrates the pores of a sintered part to produce a stronger part and produces a pore free part
Other finishing operationsHeat treatingMachiningGrindingPlating
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Examples of P/M Parts, Showing Poor Designs and Good ones.
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DEFECTS IN PM PRODUCTS
• Improper density (green compact)
• Improper bonding
(after compacting & sintering – presence of foreign materials)
• Inhomogeneous properties (improper lubrication)
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DESIGN CONSIDERATIONS FOR P/M
Design principles to consider
Shape of the compact must be simple and uniform
Provision must be made for the ejection of the part
Wide tolerances should be used when ever possible
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P/M PROCESS CAPABILITIES
Advantages It is a technique for making parts from high melting point
refractory metals
High production rates
Good dimensional control
Wide range of compositions for obtaining special mechanical and physical properties
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PROCESS CAPABILITIES
Limitations
High costTooling cost for short production runsLimitations on part size and shapeMechanical properties of the part
Strength Ductility
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ECONOMICS OF POWDER METALLURGY
Competitive with casting and forging
High initial cost
Economical for quantities over 10,000 pieces
Reduces or eliminates scraps
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DIE DESIGN FOR P/M Thin walls and projections create fragile tooling.
Holes in pressing direction can be round, square, D-shaped or any straight-through shape.
Draft is generally not required.
Generous radii and fillets are desirable to extend tool life.
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ADVANTAGES OF P/M Virtually unlimited choice of alloys, composites,
and associated properties Refractory materials are popular by this
process
Controlled porosity for self lubrication or filtration uses
Can be very economical at large run sizes (100,000 parts)
Long term reliability through close control of dimensions and physical properties
Wide latitude of shape and design
Very good material utilization
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DISADVANTAGES OF P/M
Limited in size capability due to large forces
Specialty machines
Need to control the environment – corrosion
concern
Will not typically produce part as strong as
wrought product. (Can repress items to overcome
that)
Cost of die – typical to that of forging, except that
design can be more – specialty
Less well known process
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FINANCIAL CONSIDERATIONS
Die design – must withstand 100 ksi, requiring specialty designs
Can be very automated 1500 parts per hour not uncommon for average
size part 60,000 parts per hour achievable for small, low
complexity parts in a rolling press Typical size part for automation is 1” cube
Larger parts may require special machines (larger surface area, same pressure equals larger forces involved)
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1.Cemented carbide cutting tools
2.Heavy duty brake pads
3.Magnetic cores for transformers
4.Antifriction bearings
5.Bulb filaments
APPLICATIONS OF PMR
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EXAMPLE PARTS
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Powder Metallurgy: Porous Metals
Oil-impregnated Porous Bronze Bearingsnic.sav.sk
www.hd-bearing.com
www.ondrives.com
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Filters
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Forged on left; P/M on right
Powder Metallurgy: Connecting Rods
www.dps-performance.com 67
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Powdered Metal Transmission Gear
• Warm compaction method with 1650-ton press• Teeth are molded net shape: No machining• UTS = 155,000 psi• 30% cost savings over the original forged part
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AUTOMOTIVE COMPONENTS
1. connected rod with big end cap
2. saddles of inlet and exhaust valves
3. valve spring plate
4. distribution shaft driving pulley
5. strap tension gear roller
6. screw nut
7. fuel pump filter
8. embedding filter
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SUMMARY
•Powder metallurgy can produce products out of
materials that are otherwise very difficult to manufacture
•P/M products can be designed to provide the targeted
properties
•Variations in product size, production rate, quantity,
mechanical properties, and cost
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Advantages
–Elimination or reduction of machining
–High production rates
–Wide variations in compositions
–Wide property variations
–Scrap is eliminated or reduced
Disadvantages
–Inferior strength properties
–High tooling costs
–High material cost
–Size and shape limitations
–Dimensional changes during sintering
–Density variations
–Health and safety hazards
ADVANTAGES AND DISADVANTAGES OF POWDER METALLURGY
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CONCLUSIONS
•P/M is a proven technology dating back centuries.
•By utilizing 97% original material, cost and energy are
minimized
•Properties and dimensions are easily controlled.
•Wide variety of P/M applications which are still increasing
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THANK YOU FOR YOUR
ATTENTION……
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