Mt Powder Metallurgy 5l4e56

ME-402 MODULE-3

POWDER METALLURGY PROCESS

RAMESH KUMAR NAYAK ASST. PROFESSOR, SME

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Ramesh K Nayak, SME, KIIT University

BY

Ramesh K Nayak, SME, KIIT University

ME-402 Manufacturing Technology-I CR-3 1. 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 cupolas and other melting furnaces. Melting and pouring procedures for cast Iron, Steel and nonferrous castings. Cleaning of casting 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 forces in 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. 2

3. Powder Metallurgy Process: Preparation of powder, properties of powder, fabrication methods & procedure,applications, advantages.

Ramesh K Nayak, SME, KIIT University

4. Fabrication Processes: Classification, types of welding ts, 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, Upsetbutt 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) 3

Definition of Powder Metallurgy (P/M) Art and science of producing fine metal powders and semiRamesh K Nayak, SME, KIIT University

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 when Ramesh K Nayak, SME, KIIT University

1. 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

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BASIC STEPS IN POWDER METALLURGY (P/M) Ramesh K Nayak, SME, KIIT University

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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Ramesh K Nayak, SME, KIIT University

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INDUSTRIAL PROCESSING STEPS

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POWDER PRODUCTION  Atomization

the most

 

Ramesh K Nayak, SME, KIIT University

common  Others Chemical reduction of oxides Electrolytic deposition

 Different

shapes produced 

Will affect compaction process significantly 9

Ramesh K Nayak, SME, KIIT University

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Comminution (a)

Ramesh K Nayak, SME, KIIT University

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

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Physico-Chemical Processes Condensation • Used for production of zinc and magnesium powders

• Modified distillation technique Ramesh K Nayak, SME, KIIT University

• 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

to give a gas and a metal • Carbonyl’s like Fe(CO)5 and Ni(CO)4 are obtained by ing 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

Ramesh K Nayak, SME, KIIT University

carbonyl’s, which at a certain temperature and pressure decompose

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Reduction • Most widely used, oldest, convenient, economical and extremely flexible method (regarding controlling shape, size and porosity) of 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

Ramesh K Nayak, SME, KIIT University

producing iron, copper, nickel, tungsten, molybdenum and cobalt

vapors and carbon) either in solid or gaseous form 15

Electro Deposition from Aqueous Solutions & Fused Salts (Electrolysis Method) Ramesh K Nayak, SME, KIIT University

• Reversed adaptation of electroplating technique, used for commercial production of copper, beryllium, iron, zinc, tin, nickel, cium, 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 Ramesh K Nayak, SME, KIIT University

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 pressure (400 – 900 psi) and temperature (130 – 210 0C)

Ramesh K Nayak, SME, KIIT University

metals with hydrogen under particular combination of high • 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, Ramesh K Nayak, SME, KIIT University

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 19

Ramesh K Nayak, SME, KIIT University

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Powder Characterization & Testing • Economical

manufacturing

of

P/M

parts

&

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 that powder is suitable for subsequent processing

Ramesh K Nayak, SME, KIIT University

components depends upon the physical & chemical

• Sampling technique is performed to test the powder 21

Powder Conditioning Metal powders directly after production are generally not suitable further processing as they does not possess favorable physical or Ramesh K Nayak, SME, KIIT University

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 Ramesh K Nayak, SME, KIIT University

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

Ramesh K Nayak, SME, KIIT University

•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) 24

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 process

Ramesh K Nayak, SME, KIIT University



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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.

Ramesh K Nayak, SME, KIIT University



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COMPACTION 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

Ramesh K Nayak, SME, KIIT University



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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

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

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COMPACTION TOOLING

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COMPACTION CYCLE 1. 2.

4.

5.

6.

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3.

Cycle Start Charge die w/powder Compaction begins Compaction complete Ejection of compaction Recharging of die

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ISOSTATIC PRESSING • Because of friction between particles

• Wet bag (left) • Dry bag (right)

Ramesh K Nayak, SME, KIIT University

• Apply pressure uniformly from all directions

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ISOSTATIC PRESSING 

Ramesh K Nayak, SME, KIIT University

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 33 high-pressure chamber.

HOT ISOSTATIC PRESSING 

Fig: Schematic illustration of hot isostatic pressing.The pressure and temperature variation vs.time are shown in the diagram

Ramesh K Nayak, SME, KIIT University

Hot Isostatic pressing  Container is made of high-meltingpoint sheet metal  Uses a inert gas as the pressurizing medium  Common conditions for HIP are 15KSI at 2000F  Mainly used for super alloy components

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compaction pressure

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 Increased

Provides better packing of particles and leads to ↓ porosity  ↑ localized deformation allowing new s to be formed between particles 

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Ramesh K Nayak, SME, KIIT University

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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 

Box filled with tennis balls will always have open space between balls Introduction of finer particles will fill voids and result in↑ density

Ramesh K Nayak, SME, KIIT University

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 

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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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

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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

Ramesh K Nayak, SME, KIIT University

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 

Ramesh K Nayak, SME, KIIT University

Green Compact Product

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Stages in Sintering Process (a)Adhesion without shrinkage

of

particles

and

formation

boundaries) (b)Densification and grain growth stage (c)Formation of closed pores space

of

grain

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(diffusion

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Mechanism of Sintering Process

(b). Material Transport Mechanism

(i). Recovery & recrystallization (ii). Plastic flow (iii). Evaporation & condensation

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(a). Adhesion Mechanism

(iv). Volume diffusion (v). Surface diffusion (vi). Grain boundary diffusion

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SINTERING

Ramesh K Nayak, SME, KIIT University

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

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

Dimensions of part are affected 45

Sintering Ctd.

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Liquid Phase Sintering 

During sintering a liquid phase, from the lower MP component, may exist Ramesh K Nayak, SME, KIIT University



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

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SINTERING CTD.

EXAMPLE

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Gases commonly used for sintering:  H2, N2, inert gases or vacuum

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MECHANICAL PROPERTIES ( Steel Alloys)

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SECONDARY & FINISHING OPERATIONS 

– metal infiltrates the pores of a sintered part to produce a stronger part and produces a pore free part  Other finishing operations  Infiltration

Heat treating  Machining  Grinding  Plating

Ramesh K Nayak, SME, KIIT University

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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Examples of P/M Parts, Showing Poor Designs and Good ones. Ramesh K Nayak, SME, KIIT University

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DEFECTS IN PM PRODUCTS

• Improper bonding (after compacting & sintering – presence of foreign materials) • Inhomogeneous properties (improper lubrication)

Ramesh K Nayak, SME, KIIT University

• Improper density (green compact)

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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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

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PROCESS CAPABILITIES Limitations Ramesh K Nayak, SME, KIIT University

High cost  Tooling cost for short production runs  Limitations on part size and shape  Mechanical properties of the part Strength Ductility 

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ECONOMICS OF POWDER METALLURGY  Competitive

initial cost

 Economical  Reduces

for quantities over 10,000 pieces

or eliminates scraps

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 High

with casting and forging

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DIE DESIGN FOR P/M Thin walls and projections create fragile tooling.



Holes in pressing direction can be round, square, Dshaped or any straight-through shape.



Draft is generally not required.



Generous radii and fillets are desirable to extend tool life.

Ramesh K Nayak, SME, KIIT University

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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

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

Very good material utilization

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

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

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)

Ramesh K Nayak, SME, KIIT University

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APPLICATIONS OF PM 1.Cemented carbide cutting tools

3.Magnetic cores for transformers 4.Antifriction bearings 5.Bulb filaments

Ramesh K Nayak, SME, KIIT University

2.Heavy duty brake pads

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EXAMPLE PARTS

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Powder Metallurgy: Porous Metals Oil-impregnated Porous Bronze Bearings nic.sav.sk

Ramesh K Nayak, SME, KIIT University

Filters

www.ondrives.com

66 www.hd-bearing.com

Powder Metallurgy: Connecting Rods

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www.dps-performance.com

Forged on left; P/M on right

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Powdered Metal Transmission Gear

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• 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

2. saddles of inlet and exhaust valves 3. valve spring plate

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1. connected rod with big end cap

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

•P/M products can be designed to provide the targeted

properties •Variations in product size, production rate, quantity, mechanical properties, and cost

Ramesh K Nayak, SME, KIIT University

materials that are otherwise very difficult to manufacture

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ADVANTAGES AND DISADVANTAGES OF POWDER METALLURGY

Advantages

–High production rates

–Wide variations in compositions –Wide property variations –Scrap is eliminated or reduced

–Inferior strength properties –High tooling costs –High material cost –Size and shape limitations –Dimensional changes during sintering

–Density variations

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–Elimination or reduction of machining

Disadvantages

–Health and safety hazards 72

CONCLUSIONS 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

Ramesh K Nayak, SME, KIIT University

•P/M

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Ramesh K Nayak, SME, KIIT University

THANK YOU FOR YOUR ATTENTION……

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