The requirements of many part
applications are satisfied in the as-sintered condition. Sintered
properties may be enhanced via various secondary operations. These
operations fulfill different objectives, for example improving the surface
finish or modifying the microstructure. Secondary operations and their uses
are summarized in the following chart (Figure 8).
|
Secondary Operation |
Typical Parts |
Objectives |
|
Repressing |
|
|
|
Coining |
All |
Densification,
modify surface shape (coining), dimensional control |
|
Sizing |
All |
Dimensional control |
|
|
|
|
|
Impregnation |
|
|
|
Oil |
Bearings |
Make bearings
self-lubricating |
|
Resin |
Structural |
Improve
machinability. Prepare surface for plating with other metals. Seal
parts gas or liquid tight. Provide lubrication. |
|
|
|
|
|
Infiltration |
Ferrous |
Improve strength;
seal parts gas or liquid tight. |
|
|
Structural |
Prepare surface for
plating with other metals. Improve ductility and machinability |
|
|
|
|
|
Heat Treating |
|
|
|
Quench and Temper |
Ferrous Structural |
Improve strength and
hardness. |
|
Steam Treat |
Ferrous |
Make surface hard
and wear resistant. Improve corrosion resistance and seal porosity. |
|
|
|
|
|
Machining |
|
|
|
Drill and Tap |
All |
To install set
screws or assembly fasteners. |
|
Turning |
All |
Machine to exact
tolerances. Form undercuts or features not possible with compaction
tooling. |
|
Milling |
All |
Form undercuts or
slots. |
|
Grinding |
All |
Remove stock; make
faces flat and parallel; improve surface finish and dimensional
tolerances. |
|
|
|
|
|
Finishing |
|
|
|
Deburring |
All |
Remove sharp edges
related to punch and die tooling. |
|
Burnishing |
Ferrous Structural
|
Ball size, roller
burnish for size control and surface finish. |
|
Coating Oil Dip |
Ferrous |
Corrosion
resistance. |
|
Copper, Nickel,
Cadmium, Zinc, Chromium Plating |
Ferrous |
Corrosion
resistance; appearance. |
|
Welding |
Ferrous, 6/8 g/cm3
(min.) density
|
Make assemblies from
two or more parts. |
|
Black Oxide |
Ferrous Resin Impregnated
|
Corrosion
resistance, paint base. |
|
Mechanical Surface
Treatments; Glass Beading Wire Brush Sanding, Tumbling/Vibratory
Finishing |
All |
Clean/improve
surfaces. |
|
Shot Peening |
Ferrous Structural Forgings
|
Improve surface
fatigue life. |