The Alphacam
project was undertaken for a leading aerospace component manufacturer
and focused on the machining of 2 mm diameter holes at 4 mm nominal
pitch centers around the circumference of liners fitted to turbofan
engines.

The composite liner is mounted on a rotary indexing
table. The angles of the machine’s drill heads are determined using
machined templates that divide the parts into three separate drilling
zones. Typically, components are mounted ‘bell mouth’ down and indexed
in approximately 1/2 degree increments. The comb of drills produce a
series of holes in rings around the part’s circumference. The drill
heads are then stepped in the vertical axis and readjusted to account
for the taper of the components before the process is repeated.

The
accurate positioning and orientation of the drilled holes is
complicated by the non-uniform geometry of the job. The liners are not
true cones. They are not circular in cross section and their profiles
are not completely straight, resulting in complex compound geometry,
which the programming system takes into account.

With a
maximum angular tolerance of +7 degrees on the normality of each hole
to the local surface, it was necessary to calculate the maximum,
average and minimum curvature and slope at each location –and
compensate for the variations accordingly.

In operation, the
customer initially imports CATIA geometry into the programming
application in IGES format. Following specification of the hole
parameters, the system automatically determines the drilling sequence
and generates machine code. It takes around 25 minutes for the system
to create all the geometry for the hole matrices, with a further 35
minutes required to complete the final programming.

Planit Group
www.planit.com