an abrasive machining operation which utilizes
a rough chemical-mechanical-polishing (CMP)
process, where a sample (such as a metal,
ceramic, plastic, glass, or silicon substrate)
is machined, smoothed, and planarized to
a high degree of refinement or accuracy
using a rotating, serrated, cast-iron-alloy
circular plate and an abrasive slurry grit
in water suspension applied to the plate
in a controlled fashion.. Typically, a soft
material - called a lap - is charged with
an abrasive. The lap is then used to cut
a harder material - the workpiece. The abrasive
embeds within the softer material which
then acts as a holder for the abrasive and
permits it to score across and cut the harder
Accuracy and Surface Roughness -
Lapping can be used to obtain
a specific surface roughness; it is also
used to obtain very accurate surfaces, usually
very flat surfaces. Surface roughness and
surface flatness are two quite different
concepts. Unfortunately, they are concepts
that are often confused by the novice.
A typical range of surface
roughness that can be obtained without resort
to special equipment would fall in the range
of 1 to 30 Ra.
Surface accuracy or flatness
is usually measured in Helium Light Bands,
one HLB measuring about 0.000011 inches
(11 millionths of an inch). Again, without
resort to special equipment accuracies of
1 to 3 HLB are typical. Though flatness
is the most common goal of lapping, the
process is also used to obtain other configurations
such as a concave or convex surface.
Speed Lapping -
High-speed lapping, also
known as fine grinding or flat honing, was
actually introduced to the United States
in the 1990s, awareness of the process remains
surprisingly low and is mostly limited to
large manufacturers with in-house component
Traditional lapping is a painstaking process
using a wet abrasive slurry to slowly finish
parts to precise flatness, parallelism and
surface finish. The abrasive slurry requires
extensive, time-consuming cleaning of both
parts and equipment. Even with the cleaning,
abrasive particle are often ground into
the part itself causing "grit impregnation"
that can hurt the part's performance-particularly
in fluid sealing applications.
In contrast, high-speed lapping uses a fixed
abrasive wheel in place of the wet slurry.
This dramatically reduces the lengthy cleaning
process and eliminates grit impregnation.
Advanced machine controls combine the rapid
stock removal rate of traditional grinding
with the precision finishing of traditional
flat lapping. Automated systems to load
and unload part further speed up the process.
The results are impressive.
High-speed lapping can finish parts up to
20 times faster than traditional flat lapping.
This yields significant cost savings, often
up to 40 percent versus traditional lapping.
In fact, high-speed lapping can even cost
less than traditionally low-cost grinding
methods, since simple inexpensive parts
carriers replace costly fixtures.
High-speed lapping is ideal for all types
of metals, including steel, brass, aluminum,
phosphorus bronze, tungsten carbide, cast
iron, and powder metals. The process is
also used for plastic, ceramic, glass, carbon,
and other materials.
The high-speed lapping process
is well-suited for parts with either a regular
or irregular shape and a wide range of sizes.
Some very thin parts may be difficult to
finish due to limitations of the carriers
that hold the parts in place during the
process. Flatness and parallelism can be
maintained within single digit micron tolerances.
Surface finishes of 1 Ra micrometers can
be routinely achieved.
A key commercial consideration
is the number of parts to be finished. The
process is generally used for parts with
annual volumes of one million or more. Companies
with sufficient demand can purchase the
equipment or contract with outside companies
that specialize in high speed lapping.