SECONDARY OPS

Secondary Operation Typical Parts Objectives
RE-PRESSING    
Coining All Densification, dimensional control
Sizing All Dimensional control
IMPREGNATION    
Oil Bearings Self Lubrication
Resin Structural Improve maching properties.
Prepare surface for plating with
other metals. Seals parts gas or
liquids tight.
INFILTRATION    
  Ferrous Improve strength. Seals parts gas or
liquids tight.
  Structural Improve machining properties.
Improve ductility. Prepare surface
for plating with other metals.
HEAT TREATING    
Quench & Treat Ferrous Structural Improve Strength and hardness
Steam Treat Ferrous Surface hardening to improve wear
resistance. Corrosion resistance
and porosity sealing.
MACHINING    
Drill & Tap All To install set or assembly screws
Turning All Machine to exact tolerances and form undercuts.
Milling All Form Under cuts or slots
Grinding All Remove excess stock; make faces
parallel and improve surface finish and tolerances.
FINISHING    
De-burring All Remove sharp edges related to
punch and die tooling.
Burnishing Ferrous Ball size, roller burnishing for size
control and surface finish.
Coating, Oil Dip Ferrous Corrosion resistance.
Copper, Nickel,
Cadmium, Zinc,
and Chromium plating.		 Ferrous Corrosion resistance and apint base
Welding Ferrous:
6.8g/cm3 min.
density		 Assembly from two or more parts
Mechanical Surface All Clean/Improve surface

Treatments: Glass Beading, Wire Brush, Sanding, Tumbling/Vibratory Finish, Shot Peening

ADDITIONAL INFORMATION

The controlled porosity in P/M parts permits their impregnation with oil or a resin. Also, with suitable compaction techniques, porosity can vary in different areas of the P/M part.

Oil-impregnated P/M bearings have been used in automobiles since the late 1920's. Conventional P/M bearings can absorb from 10 to 30% by volume of, generally, additive-free, non-automotive engine oils.
Impregnation is achieved by soaking the parts in heated oil, or by vacuum techniques. When friction heats the part, the oil expands and flows to the bearing surface. On cooling, the oil returns into the metal's pores by capillary action.

The same porosity which is so beneficial for oil impregnation can be quite detrimental to a part undergoing some secondary operations. Molten salts, cutting fluids, cleaning and plating solutions can be trapped in the pores, thereby leading to later corrosion, or unsightly "bleed-out". Parts are typically pre-impregnated with a resin prior to any such exposure to fluids or solutions, and immersion in molten salts is discouraged altogether.

Burr relief slots are practical modifications to inside diameters of parts with hubs being drilled and tapped to receive set screws.
Use of such a slot or recess provides room for the machining burr while still keeping it away from the shaft on which the part is mounted.