20-11-2012, 03:14 PM
Powder Metallurgy
Powder-Metallurgy-ISE.ppt (Size: 4.35 MB / Downloads: 131)
Process Capabilities
A technique for making parts from high-melting-point refractory metals which may be difficult or uneconomical to produce by other methods.
Offer high production rates on relatively complex parts, by the use of automated equipment requiring little labor.
Production of sintered parts
The general sequence of operations involved in the powder metallurgy process is shown schematically in figure above.
The component powders are mixed, together with lubricant, until a homogeneous mix is obtained.
The mix is then loaded into a die and compacted under pressure, after which the compact is sintered.
Mixing
The object of mixing is to provide a homogeneous mixture and to incorporate the lubricant.
Popular lubricants are stearic acid, stearin, metallic stearates, especially zinc stearate, and increasingly, other organic compounds of a waxy nature.
Additionally, over-mixing usually further reduces the green strength of the subsequent compacts probably by component coating the whole surface of the particles, thereby reducing the area of metal contact on which the green strength depends. The flow properties also are impaired good flow is essential for the next step i.e. loading the powder into the die.
Sintering
Sintering is a key part of the operation.
The compact acquires the strength needed to fulfill the intended role as an engineering component.
In general , sintering requires heat.
Suffice to say that atomic diffusion takes place and the welded areas formed during compaction grow until eventually may be lost completely.