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108 Part II: Metrology
• Inspection to ensure that Teflon coating is properly applied to medical
inhalant canisters.
6. COORDINATE MEASURING MACHINE (CMM)
Part II.E.6
Explain the basic operation of a CMM,
including use of the x, y, and z axes, and the
limitations of locating functional datums,
target points, and target areas. (Application)
Body of Knowledge II.E.6
The coordinate measuring machine (CMM) is a flexible measuring device capable of
providing highly accurate dimensional position information along three mutually
perpendicular axes. This instrument is widely used in manufacturing industries
for the post-process inspection of a large variety of products and their components.
It is also very effectively used to check dimensions on a variety of process
tooling, including mold cavities, die assemblies, assembly fixtures, and other
work holding or tool positioning devices.
Over the last decade, coordinate measuring machines have become a primary
means of dimensional quality control for manufactured parts of complex form,
where the volume of production does not warrant the development of functional
gauging. The advent of increasingly inexpensive computing power and more
fully integrated manufacturing systems will continue to expand the use of these
machines into an even larger role in the overall quality assurance of manufactured
parts.
Coordinate measuring machines can most easily be defined as physical representations
of a three-dimensional rectilinear coordinate system. Coordinate measuring
machines now represent a significant fraction of the measuring equipment
used for defining the geometry of different-shaped workpieces. Most dimensional
characteristics of many parts can be measured within minutes with these
machines. Similar measurements would take hours using older measuring equipment
and procedures.
Besides flexibility and speed, coordinate measuring machines have several
additional advantages:
1. Different features of a part can be measured in one setup. This
eliminates errors introduced due to setup changes.
2. All CMM measurements are taken from one geometrically fixed
measuring system, eliminating the accumulation of errors resulting
from using functional gauging and transfer techniques.
3. The use of digital readouts eliminates the necessity for the interpretation
of readings, such as with dial or vernier-type measuring scales.