1 Introduction
1.1 Machine Setup and Cutting Parameters
Levels | Level 1 | Level 2 | Level 3 |
---|---|---|---|
Spindle speed (rpm) | 3000 | 6000 | 9000 |
Feed rate (mm/min) | 300 | 600 | 900 |
1.2 Material Specification
Property | S2-glass fibres | FM94 adhesive system |
---|---|---|
Thickness (μm) | 10 | - |
Strength (MPa) | 4000 | ±50 |
Stiffness (GPa) | 88 | ±1.7 |
Strain failure (%) | 4.45 | 5–10 |
1.3 Hole Quality Analysis
1.3.1 Entrance and Exit Burr Formations
1.3.2 Surface Roughness
1.3.3 Scanning Electron Microscopy (SEM)
1.3.4 Hole Size and Circularity Error
1.3.5 Delamination
2 Experimental Results
2.1 Cutting Forces Analysis
2.2 Hole Quality Analysis
2.2.1 Burr Formations
2.2.2 Hole Size and Error of Circularity
2.2.3 Surface Roughness
2.2.4 Hole Condition Using Optical Microscopy
2.2.5 Delamination Analysis
2.2.6 Scanning Electron Microscopy Analysis
3 FE Model
3.1 Modelling Material Response
3.1.1 Modelling Damage in Al2024-T3 Sheets
Density ρ, (Kg/m3) | Elastic modulus E, GPa | Poisson’s ratio, ν | Melting temperature (C) |
---|---|---|---|
2780 | 73.1 | 0.33 | 502 |
A (MPa) |
B (MPa) | C |
n
|
m
|
d
1
|
d
2
|
d
3
|
d
4
|
d
5
|
---|---|---|---|---|---|---|---|---|---|
265 | 426 | 0.018 | 0.34 | 1 | 0.13 | 0.13 | −1.5 | 0.011 | 0 |
3.1.2 Modelling Damage in Glass Fibre Layers
-
Hashin's fibre tensile failure (σ11 ≥ 0)$$ {\left(\frac{\sigma_{11}}{X_{1t}}\right)}^2+{\left(\frac{\sigma_{12}}{S_{12}}\right)}^2+{\left(\frac{\sigma_{13}}{S_{13}}\right)}^2=1;\kern0.4em {d}_{ft}=1 $$(6)
-
Hashin's compressive tensile failure (σ11 < 0)$$ \frac{\left|{\sigma}_{11}\right|}{X_{1c}}=1;\kern0.4em {d}_{fc}=1 $$(7)
-
Puck 'smatrix tensionand compression failure$$ \begin{array}{l}\left[{\left(\frac{\sigma_{11}}{2{X}_{1t}}\right)}^2+\frac{{\sigma_{22}}^2}{\left|{X}_{2t}.\kern0.5em {X}_{2c}\right|}+{\left(\frac{\sigma_{12}}{S_{12}}\right)}^2\right]+{\sigma_{22}}^2\left[\frac{1}{X_{2t}}+\frac{1}{X_{2c}}\right]=1\\ {}{\sigma}_{22}+{\sigma}_{33}>0;\kern0.4em {d}_{mt}=1\\ {}{\sigma}_{22}+{\sigma}_{33}<0;\kern0.4em {d}_{mc}=1\end{array} $$(8)
Density (Kg/m3) | E11 (GPa) | E22 (GPa) | E33 (GPa) | G12 (GPa) | G13 (GPa) | G23 (GPa) | ν12
| ν13
| ν23
|
---|---|---|---|---|---|---|---|---|---|
1980 | 53.98 | 9.412 | 9.412 | 5.548 | 3 | 5.548 | 0.0575 | 0.0575 | 0.33 |
X1t
(MPa) | X1c
(MPa) | X2t
(MPa) | X2c
(MPa) | X3t
(MPa) | X3c
(MPa) | S12
(MPa) | S13
(MPa) | S23
(MPa) |
---|---|---|---|---|---|---|---|---|
2430 | 2000 | 50 | 150 | 50 | 160 | 76 | 50 | 50 |
3.2 Setup of FE Model
3.2.1 Drill-Workpiece Setup and Boundary Conditions
3.2.2 Mesh Study
3.2.3 Contact, Loading and Boundary Conditions
4 FE Result and Discussion
4.1 Validation of FE Model
4.2 Thrust Force and Torque Results
5 Conclusions
-
The experimental results showed that the thrust force and torque increased with increasing feed rate and decreased with increasing spindle speed, while surface roughness which ranged between 1.5 and 2 μm increased with increasing feed rate and spindle speed.
-
Exit burrs were much prominent than entrance burrs and tended to rise with increasing feed rate. The size of all the drilled holes was greater than the drill nominal diameter of 6 mm and ranged between 1.2 and 16 μm.
-
The maximum entry and exit burr heights were 11.95 and 60 μm, respectively, whereas the maximum entry and exit burr root thickness were around 107 and 372 μm, respectively. Uniform burr without cap was observed at the hole edges after drilling.
-
The optical and SEM microscopy of the hole surfaces showed that good hole quality can be achieved when drilling at feed rates and spindle speeds 3000 rpm and 300 mm/min. CT scans of the drilled holes reflected minor surface delamination in glass fibre layers but no cracks through the laminate thickness. Analysis of SEM images showed that damage in the form of minor delamination, edge chipping/fracture, peel up and fibre spring back following workpiece retractions occurred when drilling at high spindle speeds and feed rates.
-
Under the used spindle speeds and feed rates, no delamination was identified on the internal surfaces of the drilled holes and delamination factors was negligible.
-
To evaluate the efficiency of the numerical model, the collected thrust force and torque data were compared with modelling results for validation. The model provides good estimation of torque (between 0.83 % and 17.9 %) and thrust force (between 3.2 % and 53.2 %) which shows that the FE drilling model is capable of predicting the cutting forces within acceptable levels. Such FE models can be used as a virtual tool to simulate GLARE’s machining response and help making informed decisions on the selection of appropriate cutting parameters. Further improvement on the drilling model will be carried which accounts for the thermo-mechanical coupling effects between the cutting tool and the workpiece.