EFFECTS OF DRILLING PARAMETERS ON HOLE INTEGRITY WHEN DRILLING HYBRID FIBER COMPOSITE HALF CYLINDERS

Hybrid composites consist of two or more types of reinforcing fibers in one or
more types of matrices in its construction. This material is being widely used in
applications such as aerospace, aeronautical and oil and gas. In conventional
machining, drilling is the most applied method accounting for as much as 40% for
all material removal process. Drilling of fiber reinforced polymer composite is
substantially different from the metallic materials due to different mechanical
properties. The drilling of this material may generate delamination of drilled
holes on the hybrid composite. This problem has adverse effect on the
performance of the structure developed from fiber composites and also their
mechanical properties and reliability of produced parts. Machining problems
occur mainly due to the diverse fiber and matrix properties, fiber orientation, and
inhomogeneity of the material. This study is focused on the investigation of the
damage occurred, internal surface roughness and microstructure of the drilled
holes in a HFRE composite half cylinders. The parameters studied are narrowed
to focus on the effects of the drilling parameters which are feed rate and spindle
speed of 40% fiber volume fraction of woven glass and carbon fibers. Carbon and
glass fiber reinforced epoxy half cylinders were fabricated using Hand Lay Up
Technique. CNC Milling Machine was used to drill holes on the sample at
different feed rate (mm/rev) and spindle speeds (rpm). The drilled samples were
analyzed in terms of Average Surface Roughness (Ra) using Mitutoyo Surface
Roughness Tester SV300, Damage Factor (Fo) using Mitutoyo 3-D Non-Contact
Measuring System and Microstructural Analysis using Field Emission Scanning
Electron Microscope (FESEM). Best results of Damage Factor (Fo) was obtained
from sample A3 [lowest feed rate, 0.05 (mm/rev) and highest spindle speed 3000
(rpm)] with a damage factor of 0.96346 and minimized splintering problem. The
Fd was analyzed in terms of splintering problems as there is no hole surface
delamination identified from 3-D Non-Contact Measuring System. Best results of
Average Surface Roughness (Ra) obtained is 1.343 (J.Lm) of hole 2 from Sample
A3. The micrograph observation shows no distinct relationship of the drilling parameters with the results. The best result obtained from the FESEM is from
sample C3 (3000rpm, 0.2mm/rev) with no know damages identified.