1. Processing of Powder Metals, Ceramics, Glass & Superconductors

2. Powder Metals Commonly used metals in P/M
Iron,Tin, Copper, Aluminum, and Nickel
It is a completive process with forging and machining
Parts can weigh as much as little as 2.5Kg or up to 50Kg

3. Powder Metallurgy c a b
Fig: (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 production
Blending
Compaction
Sintering
Finishing operations

5. Particle Size, Distribution, and shape
Particle size is measured by screening
In addition to screen analysis one can use:
Sedimentation – measuring the rate that particles settle in a fluid
Microscopic analysis – using a
scanning electron microscope
Light scattering
Optical – particles blocking a beam of light that is sensed by a photocell
Suspending particles in a liquid & detecting particle size and
distribution
Fig: Particle shapes in metal powders,and the processes by which they are produced.Iron powders are produced by many of these processes

6. Powder Particles
Fig : (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 milling
Fig : Methods of metal-powder production by atomization;(a) melt atomization; (b) atomization with a rotating consumable electrode

8. 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.

9. 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
Fig: 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 part
Fig: A7.3 MN (825 ton) mechanical press for compacting metal powder.

11. 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.

12. 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 casting
Fig: 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 metal
Tungsten-carbide dies are used
Punches are generally made of the similar materials
Dimensions are watched very close

14. Metal Injection Molding
MIM uses very fine metal powders blended with a polymer
The molded greens are then placed in a furnace to burn off the plastics
Advantages of injection molding
Produces complex shapes
Mechanical 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 metal
Extrusion – has improved properties and parts my be forged in a closed die to get final shape
Pressureless compaction – gravity filled die and used to make porous parts
Ceramic molds – molds are made by made by investment casting and the powder is compressed by hot isostatic pressing
Spray deposition – shape-generation process
An example of powder rolling

16. Sintering
Sintering - Green compacts are heated in a furnace to a temperature below melting point
Improves the strength of the material
Proper furnace control is important for optimum properties
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

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 phase
Mechanical Properties

19. 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
Parts may be impregnated with
a fluid to reduce the porosity
Fig: 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 part
Other finishing operations
Heat treating
Machining
Grinding
Plating

21. 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

22. Process Capabilities
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

23. Process Capabilities Limitations High cost
Tooling cost for short production runs
Limitations on part size and shape
Mechanical properties of the part
Strength
Ductility

24. Economics of Powder Metallurgy
Competitive with casting and forging
High initial cost
Economical for quantities over 10,000 pieces
Reduces or eliminates scraps

25. Shaping Ceramics Processing ceramics
Crushing or grinding the raw materials in to very fine particles
Mixing with additives
Shaping, drying , and firing the material

26. SLIP CASTING

27. Processing steps involved in making ceramic parts