A High Precision Noncontact Electronic Hole Measurement Gauge for Aerospace Structures0 pages

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A High Precision Noncontact Electronic Hole Measurement Gauge for Aerospace
Structures
Commercial and Military Aircraft, Launch Vehicles and Satellites have a significant
number of fastener holes in their structures. In large aircraft such as the Boeing 747, The
C-17 Military Transport or the new Airbus A380 it is estimated that the number of holes
is well over one million. Some of these fastener holes are more critical than others. In
aircraft, holes that get a high level of attention from QC engineers are those that interface
the connection of the wings of the fuselage (front and back), the vertical stabilizer as well
as fasteners in the engine mounts that keep the engines attached to the wings. In launch
vehicles examples of critical fasteners holes are the ones located where the outside
surface of the launcher is attached to the main structure. As the pressure increases on
aerospace structure manufacturers to develop faster, more efficient and higher quality
methods of assembly they are looking for more modern ways to measure holes.
Traditional hole measurement methods
Today many critical fastener holes are being measured using traditional contact methods
of hole measurement such mechanical bore gauges and go/no go mechanical gauges.
Mechanical bore gauges are made up of a mechanical measurement interface (such as
split ball), which is attached to a standard dimensional measurement instrument such as a
dial indicator. In the case of a split ball device the diameter size changes in relation to the
spreading of the balls. In order to calculate the average diameter of a hole the operator
must make measurements at 0° and 180 degrees at in top middle and bottom of each hole.
This method is typically used where high precision important and the number of holes to
be measured is limit. This method has advantages if the number of holes is limited and
the accuracy level required is low but has distinct disadvantages when companies are
looking to measure a high volume of holes in an accurate and automated method.
In the assembly of aircraft, some fastening applications are more critical than others. In
the most critical applications aircraft manufacturers often use tapered bolts. A good
example of one of the most critical fastener applications where tapered bolts are used is
when aircraft assemblers attach the front and rear wings to the fuselage of the plane.
Accurately measuring the full-length diameter of the boreholes drilled for these bolts
presents a particularly difficult measurement challenge. The traditional method to
measure the fit between the tapered bolt and hole is referred to as the “blue ink” method.
This dated procedure gets it’s name from the way it works. In this case operators start
with a mechanical pin that is the same size as the specified tapered bolt for that hole. The
pin is then painted with blue ink and hammered into the hole. Once removed, the operator
visually inspects how much blue ink remains on the bolt. The less ink remaining, the
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