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Roller burnishing is cold
working the surface of the work piece to improve surface structure. It
produces a fine surface finish by the planetary rotation of harden
rollers over a bored or turned metal surface. The roller burnishing
operation compresses the " projection " (peaks) into the
"indentations" (valleys) thus forming a smooth mirror finished
surface.
In the burnishing process at the point of contact, the
pressure generated by the rollers exceeds. |
the yield point of the piece-part
material, the surface is plastically deformed by cold flowing of
subsurface material. The result is a mirror-like finish and tough,
hardened surface.
The pressure required for roller burnishing depends on various
factors like tensile strength of the material, surface toughness before
and after roller burnishing, ductility, shape of the rolls and
diameters. |
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Roller burnishing tools
generally consists of a series of tapered and highly polished precision
rollers made of high speed steel polished in slots with a retaining
cage. When a tool engages the work piece a hardened mandrel, inversely
to the taper of the rollers. forces them against the surface of the work
piece. |
The tool is constructed
with the rollers axis
parallel to the axis of the mandrel, when a
non-feeding tool is required such as in close
approaches to shoulders or in full bottoming.
Due to this construction the tool depends on the machine feed to advance
along the work piece. |
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In the burnishing process
the pressure is developed when the mandrel tends to overtake the rollers
as the tool feeds along the work piece. This tendency is restricted by a
step on the mandrel. Thus the uniform diameter during the complete pass
is maintained because the tool-mandrel relationship is constant. |
The self-releasing feature
of the tool is provided by the inverse tapers of the rollers and
mandrel. The rollers continue to feed in helical path when the advance
of the tool in to the work piece is stopped. In this process the rollers
move forward on the mandrel to a point where its diameter is smaller and
the burnishing pressure is released. Only a small movement is required
for the tool to release and at that point it can be easily withdrawn
from the work piece.
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