Drilling FRP

A STUDY ON DELAMINATION OF COTTON FIBER REINFORCED PHENOLIC COMPOSITE

MATERIAL DUE TO DRILLING

Sanjay R Patel

Mechanical Engineering DepartmentFaculty of Technology and Engineering

The Maharaja Sayajirao University of Baroda, Vadodara

Apr 13, 2023 Drilling of Hylam 2

Drilling of Fiber Reinforced Plastics

Drilling holes in FRP laminates (or components) is commonly employed machining process for assembly.

It is relatively difficult to achieve desired hole quality in terms of geometry without affecting material properties due to heterogeneity, anisotropy and heat sensitivity.

Geometry is generally affected by the misalignment of the axes and rigidity of machine tool while workpiece material integrity is affected by the action of thrust and the torque of machining.

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Investigations on Drilling of FRPsReports on drilling of various combinations of glass, carbon or aramid fiber reinforced thermosetting or thermoplastics have been readily published. Parameters affecting the hole quality for the investigations are;

Cutting Speeds and Feed ratesDrill BitsLaminate Configuration

Effects of these parameters on cutting torque and thrust induced during drilling have also been studied.

Apr 13, 2023 Drilling of Hylam 4

Drilling of FRP Composites (contd.)

Various drilling induced damages in FRP laminate like cracking, edge chipping, delamination, spalling, fuzzing, fiber debonding and surface roughness are depicted in Fig.1

Therefore conventional drilling process are to be adapted in such a way that minimal mechanical and thermal damage occur.

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Drilling of FRP Composites (contd.)

Fig.1 Drilling Induced Damages in FRPs

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Investigation on Drilling of Hylam

Based on the published literature on drilling characteristic of FRPs a study was made on drilling of Cotton Fibers Reinforced Phenolic Polymer laminate (widely used in industry as Hylam).

Objective of experiment was to understand the effect of drilling parameters on the quality of holes in terms of delamination which is considered very important.

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Material & Means

8 mm thick Laminate as per BS 2572-F3 CNC vertical machining centre

6 mm HSS drill bit

Commercially available material, machining facility and the drill bit were used.

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The Factorial ExperimentA full factorial experiment with two levels of two factors and a level of average value (the ‘center point’ to test linearity of correlation) mentioned in Table 1 were used. A set of 5 holes and its 4 replicates, required 20 holes.

All holes were center drilled first and coolant was used.

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The Drilled HolesArray holes were drilled with proper plan considering identification of factors & levels and randomization. Array and close-up views of the holes are shown below.

Array of drilled holes Close-up view of hole edges

View showing inside surface of holes

Measurements of delamination were made using a microscope with scale.

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The Delamination

Stereo microscope set for 40X magnification

Measurement of Dmax for finding Delamination Factor

Measurements of delamination were made using a microscope with scale.

Delamination was observed more at entry of the hole than at exit.

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Results & Analysis

Values of the table shows FD for high V and low f and the lowest FD for high V and high f .

The centre point values are also in accordance.

The table below presents average delamination factor @ entry for the factors and levels used.

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The graphs of effects indicate;Main effect of V (0.009, the highest) : FD ▲ as V ▲, Main effect of f (-0.002, the lowest): FD ▼ as f ▲, and

Interaction effect (0.006, mid-way) : FD ▲ with V & f ▲

Results & Analysis (contd.)

Main and interaction effects of V & f on FD

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Results & Analysis (contd.)

F > Fα (α = 0.05) for all effects approve significance of none.

Hence establishing correlation was not considered.

Table below presents Analysis of Variance to test the significance of the drilling parameters effects.

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Delamination in Hylam occurs at the hole entry for the selected drilling parameters.

Increase in cutting velocity increases delamination but it decreases with increased feed rate. This could be because of the action of cutting force tend to chip-off more material at higher cutting velocity at cutting edge while at same cutting velocity, higher feed rates reduces the time of interaction.

However the F-test of statistical analysis does not confirm significance of neither main effects nor interaction effect of cutting velocity and feed rate for the chosen levels on the delamination factor.

Conclusion:

Thank You