Mixing or Blending of Metallic Powders: Compacting of Powder, Sintering


Mixing or Blending of Metallic Powders

After the formation of metallic
powders, proper mixing or blending of powders is
the first step in the forming of powder metal parts. The mixing
is being carried out either
wetย ย ย  or
dry using an efficient mixer to produce
a homogeneous mixture.


Compacting of Powder

Compacting is the technique of
converting loose powder in to compact accurately defined shape and size. This
is carried out at room temperature in a die on press machine. The press used
for compacting may be either mechanically or hydraulically operated. The die
consists
ย  of a cavity of the shape of the
desired part. Metal powder is poured in the die cavity
and pressure is applied using punches, which usually work from
the top and bottom of the die as shown in Fig. Dies are usually made of
high grade steel, but sometimes carbide dies
are
used for long production runs. In compacting process, the pressure
applied should be uniform and applied simultaneously from above and
below. The pressure applied should be high
enough to produce cold welding of the
powder.
Cold welding imparts a green strength, which
holds the parts
together and allows
them to be handled.


The metal parts obtained after
compacting are not strong and dense. To improve these properties, the parts
should be sintered.

Sintering

Sintering is the process of
heating of compacted products in a furnace to below the melting point of at
least one of the major constituents under a controlled atmosphere. The
sintering temperature and time vary with the following factors-
1.Type of metal powder
2.ย Compressive load used, and
3.ย Strength requirements of the finished parts.



Powder metallurgy die setup
Powder metallurgy die
setup


In the sintering furnace,
the metal parts
are gradually heated
and soaked at the required temperature. During this
gradually heating process, powders bond themselves into coherent bodies.
Sintering results in strengthening of fragile green compacts produced by the
pressing operation. It also increases electrical
conductivity, density and ductility of the powder metal parts.


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