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Transcript of Powder Metallurgy
Producing Metal Powders
Traditionally achieved by a mechanical press, which allows high production. Hydraulic presses can exert much higher forces (5,000 tons compared to 60) but have low productivity
Cold Isostatic Pressing
- the product is forced into a sizing die of the correct shape by a sizing punch
Powder Metallurgy: What is it?
- taking loose powder or a blend of different powders, placing them in a die, and squeezing them between punches to make a
briquette (green compact)
- heating the briquette enough so that the particles are joined by diffusion, but not melted together
- since sintering slightly deforms and shrinks the briquette, sizing, machining, heat treating or impregnating may be required to complete the product
A stream of molten metal is transformed into a spray of droplets that solidify into metal powder
Inert gas, air or water can be used to break up the stream and create the metal particles
Hot Isostatic Pressing
Other processes include
chemical reduction- reduction (removal of oxygen) of metal oxide gasses, bringing them back to their metallic state. Produces spongy and pourous particles
Metal Powder Injection molding
Powder is loaded into molds made of rubber or other lastomeric material and subjected to high pressures at room temperature. Pressure is transmitted by water or oil
Same as cold isostatic pressing, but an inert gas like argon or helium is used in a pressure chamber to provide the squeeze. It provides more density and achieves a finer microstructure than the cold process
Powders are preformed to an oversized shape and temperatures get as high as 2000 degrees F and with pressures as high as 15,000 psi.
Injects powder into molds much like plastic
injection molding process. Though, the particle
size of the powder much be much finer than
It is then combined with a thermoplastic binder
After compaction the briquette is sintered after the binder is removed.
This process allows thin walls, high densities unsymmetrical shapes and accurate dimensions
The briquette or "green compact" is made in a conventional press and then sintered. Followed by a restrike or forge that brings the part to a final and increased density
Mechanical properties can exceed those of wrought metals.
High fatigue and impact strength compared to other P/M methods
Used to create dimensional accuracy
- oil or other liquid is placed within the pores of the P/M product.
Used for prelubricated bearings.
When temp increases, the oil from the pores flows to the surface.
When temperature decreases, oil flows back into the pores through capillary action
What other secondary processes might be used on P/M parts?
Drilling and threading
Not all designs are easily
- the filling of a metal's pores with another metal of lower melting point than the base material.
The infiltration metal is heated to a temperature above its melting point but below that of the porous metal part. Liquid metal is allowed to enter into the porous network and solidifies, filling the pores with solid metal and increasing the density of the part.
Produces "net shape" parts.
Meaning the parts need no or
very little secondary processing
Rotating Consumable Electrode
More rapid cooling
Higher production rates
More Spherical Particles