**3. Results and discussion**

18 Tribology in Engineering

Feed Rate **(mm/rev)** 

Microscope (SEM).

**Table 1.** Experimental parameters

**Table 2.** The chemical structure of Al 5005

**Rotation Speed (rev/min)** 

**Figure 1.** The space between the drilling axes (Thickness 10 mm)

**Point Angle (degree)** 

0.1, 0.2, 0.3 400, 800, 1200 90, 118, 130,140 HSS, Ø5, Ø10

% 0.5-1.10 0.3 0.3 0.2 0.20 0.10 0.25 0.15 remainder

N type double-end DIN 338/RN HSS drill bits with 30º helix angle were used in drilling process. Hardness value of these cutting tools was 65 HRc. Each cutting tool was used once in the experiments, and each experiment was repeated three times in accordance with the similar studies [9,11-14,21,22]. The images of BUEs formed on the cutting tool as a result of the drilling processes were taken by means of Leo Evo 40 model Scanning Electron

After combinational drilling processes, the samples were cut with a cutting disc in the middle in parallel with the hole axis in order to measure the roughness of the hole surface. Then, the surface roughnesses were measured with Mitutoyo SJ-201 surface roughness measurement device. In the measurement of the roughness, sampling length and sampling number were chosen by considering the former studies [7,8,16,19,21] as 0.8 mm and 5 (0.8x5), respectively. The other sampling length values of this device were 0.25 mm and 2.5 mm. Generally, the roughness was measured at three different points in parallel with the hole axis in accordance with the studies in literature [7,12,16,18]. But in this study, in order to evaluate the measurements accurately, the measurements were taken from 5 different points, and then Ra values were determined by considering the average of these values.

**Al 5005 Mg Si Fe Cu Mn Cr Zn Other** 

**Drill material and diameter (mm)** 

**elements Al** 

The graphics in Figure 2 were illustrated to enable one a comprehensive assessment of the effects of drilling parameters on the surface roughness in the drilling of Al 5005 without using cooling fluid.

**Figure 2.** The change of the surface roughness with the drilling parameters

As seen from the graphics, the surface roughness decreases with the increase of rotation speed. In former studies [18,23], this case was attributed to the decrease in the cutting and feed force. The most considerable reasons of the decrease in these forces are the decrease in

the contact region between the tool and work piece and the decrease in the shear strength in the cutting region due to the increase in the heat of tool-work piece depending on the cutting speed [18,24].

Also, it was supposed that the influence of BUE on the tool and material increased negatively since the amount of BUE resulting from the adhesive wear increased due to the increase in the feed and cutting forces. As mentioned in the literature, in the machining processes of many alloys including more than one phase in own structures BUE formed due to the adhesion of the chips on the tool surface and cutting edge because of the work hardening [23]. It can be said that BUE especially forming at low cutting speeds affects the surface roughness negatively. since Aluminum and its alloys includes more than one phase. In order to explain this case clearly, BUE formations occurring on the cutting tool edges were also investigated in this study (Figures 3 and 4 a-c). All the images corresponding to the whole cutting parameters were not presented since there were a lot of parameters in the experiment and they were investigated in other sections separately, but the SEM images expressing the mentioned case clearly were presented.

Experimental Investigation of the Effect of Machining Parameters

on the Surface Roughness and the Formation of Built Up Edge (BUE) in the Drilling of Al 5005 21

roughness increased further and a bad surface was formed (Figures 2 a-f). The decrease in BUE due to the increase in cutting speed can be ascribed to the increase in temperature [23,25]. Since high cutting speeds resulted in much more increase in the temperature, BUE on the cutting edge lost its hardness and strength, and in the continuing cutting process it couldn't resist the tensions on itself and it was removed from the cutting edge (Figure 3 and 4 c). Hence, high cutting speeds reduced the tendency to the formation of BUE, and resulted in the decrease in the surface roughness values of the work piece (Figures 2 a-f). Since BUE formed on the cutting edges also spoiled the geometric structure of the cutting tool, the stable and ideal process of the cutting operation was damaged, so the roughness increased (Figure 2 a-f). Also, BUE formed on the cutting edges caused fracturing and abrasion on the cutting edges while it was separating from the cutting edges by the effect of thermal tensions [24]. This case increased the roughness of the hole surface depending on the size of BUE (Figures 4 a-c). The abrasion and fracturing formed on the cutting edge according to

the different machining parameters were presented in Figures 5 and 6, respectively.

**Figure 5.** SEM images of the abrasion formed on the cutting edges

**Figure 3.** SEM images of BUE formation on the cutting edges. (0.2 mm/dev-118- Ø5 mm)

**Figure 4.** SEM images of BUE formation on the cutting edges. (0.1 mm/rev-118-Ø10 mm)

As seen from the SEM images in Figures 3 and 4 a-c, BUE formation decreased and had a minor effect on the surface roughness because of the increase in the rotation speed, so surface roughness decreased (Figures 4a-f). Since BUE formed on the cutting tool edge during the drilling had an unstable structure, the surface roughness increased. Thus, because of big and unstable BUE due to low cutting speeds (Figures 3, 4 a and b), the surface roughness increased further and a bad surface was formed (Figures 2 a-f). The decrease in BUE due to the increase in cutting speed can be ascribed to the increase in temperature [23,25]. Since high cutting speeds resulted in much more increase in the temperature, BUE on the cutting edge lost its hardness and strength, and in the continuing cutting process it couldn't resist the tensions on itself and it was removed from the cutting edge (Figure 3 and 4 c). Hence, high cutting speeds reduced the tendency to the formation of BUE, and resulted in the decrease in the surface roughness values of the work piece (Figures 2 a-f). Since BUE formed on the cutting edges also spoiled the geometric structure of the cutting tool, the stable and ideal process of the cutting operation was damaged, so the roughness increased (Figure 2 a-f). Also, BUE formed on the cutting edges caused fracturing and abrasion on the cutting edges while it was separating from the cutting edges by the effect of thermal tensions [24]. This case increased the roughness of the hole surface depending on the size of BUE (Figures 4 a-c). The abrasion and fracturing formed on the cutting edge according to the different machining parameters were presented in Figures 5 and 6, respectively.

20 Tribology in Engineering

cutting speed [18,24].

expressing the mentioned case clearly were presented.

**Figure 3.** SEM images of BUE formation on the cutting edges. (0.2 mm/dev-118- Ø5 mm)

**Figure 4.** SEM images of BUE formation on the cutting edges. (0.1 mm/rev-118-Ø10 mm)

As seen from the SEM images in Figures 3 and 4 a-c, BUE formation decreased and had a minor effect on the surface roughness because of the increase in the rotation speed, so surface roughness decreased (Figures 4a-f). Since BUE formed on the cutting tool edge during the drilling had an unstable structure, the surface roughness increased. Thus, because of big and unstable BUE due to low cutting speeds (Figures 3, 4 a and b), the surface

the contact region between the tool and work piece and the decrease in the shear strength in the cutting region due to the increase in the heat of tool-work piece depending on the

Also, it was supposed that the influence of BUE on the tool and material increased negatively since the amount of BUE resulting from the adhesive wear increased due to the increase in the feed and cutting forces. As mentioned in the literature, in the machining processes of many alloys including more than one phase in own structures BUE formed due to the adhesion of the chips on the tool surface and cutting edge because of the work hardening [23]. It can be said that BUE especially forming at low cutting speeds affects the surface roughness negatively. since Aluminum and its alloys includes more than one phase. In order to explain this case clearly, BUE formations occurring on the cutting tool edges were also investigated in this study (Figures 3 and 4 a-c). All the images corresponding to the whole cutting parameters were not presented since there were a lot of parameters in the experiment and they were investigated in other sections separately, but the SEM images

**Figure 5.** SEM images of the abrasion formed on the cutting edges

Experimental Investigation of the Effect of Machining Parameters

on the Surface Roughness and the Formation of Built Up Edge (BUE) in the Drilling of Al 5005 23

chip and cutting edge caused a corruption on the surface quality (Figure 8). This case

resulted in the increase in surface roughness.

**Figure 7.** SEM images of the chips adhering to the helical channels.

**Figure 8.** SEM images of the smearing formed on the cutting tool.

a similar relation emerged in the drilling of Al 5005 (Figure 2 a-f).

rate, *r* is the radius.

In addition, surface roughness changes depending on the feed rate and cutting radius in turning as denoted Ra=0.321(*f*2/*r*) in the Ref. [27]. Where Ra is the roughness, *f* is the feed

Monagham and O'Reily, determined that this relation was valid for the drilling process, and

Similarly, as seen from Figure 2 a-f surface roughness improved with the increase of drill point angle. This case can be explained as follows: The values of plastic deformation region, cutting edge length and chip thickness obtained for the drills having point angles of 118°, 130° and 140° are greater than those obtained for the drill having point angle of 90°.

**Figure 6.** SEM images of the fractures formed on the cutting edges

In a similar manner as BUE formation, the chips adhering to helical channels obstructed the effective removal of the chips by plugging the helical channels partially (Figure 7). This case was more prominent at low rotation speeds, and the roughness increased depending on the this case (Figures 2 a-f).

As seen from the Figure 2 a-f, surface roughness increased with the increase of the feed rate, since the amount of the chips increased due to the increase in the feed rate. Because the increase of the feed rate caused high feed rate, low shear angle and thick chip formation [26]. This case signified that machined surfaces were more influenced from the forces during the cutting process. Likewise, the increase in the feed rate resulted in high friction resistance, pressure and increase in temperature [23,25]. In this case, the chip experienced to shear tensions, and adhered to the cutting tool. The amount of the chip adhesion increased depending on the feed rate, and an unstable structure formed. In order to explain this case better, chip smearing formed on the cutting edge were also investigated (Figure 8). It was supposed that notch effect of these chips on the machined due to the adhesion between the chip and cutting edge caused a corruption on the surface quality (Figure 8). This case resulted in the increase in surface roughness.

22 Tribology in Engineering

**Figure 6.** SEM images of the fractures formed on the cutting edges

this case (Figures 2 a-f).

In a similar manner as BUE formation, the chips adhering to helical channels obstructed the effective removal of the chips by plugging the helical channels partially (Figure 7). This case was more prominent at low rotation speeds, and the roughness increased depending on the

As seen from the Figure 2 a-f, surface roughness increased with the increase of the feed rate, since the amount of the chips increased due to the increase in the feed rate. Because the increase of the feed rate caused high feed rate, low shear angle and thick chip formation [26]. This case signified that machined surfaces were more influenced from the forces during the cutting process. Likewise, the increase in the feed rate resulted in high friction resistance, pressure and increase in temperature [23,25]. In this case, the chip experienced to shear tensions, and adhered to the cutting tool. The amount of the chip adhesion increased depending on the feed rate, and an unstable structure formed. In order to explain this case better, chip smearing formed on the cutting edge were also investigated (Figure 8). It was supposed that notch effect of these chips on the machined due to the adhesion between the

**Figure 7.** SEM images of the chips adhering to the helical channels.

**Figure 8.** SEM images of the smearing formed on the cutting tool.

In addition, surface roughness changes depending on the feed rate and cutting radius in turning as denoted Ra=0.321(*f*2/*r*) in the Ref. [27]. Where Ra is the roughness, *f* is the feed rate, *r* is the radius.

Monagham and O'Reily, determined that this relation was valid for the drilling process, and a similar relation emerged in the drilling of Al 5005 (Figure 2 a-f).

Similarly, as seen from Figure 2 a-f surface roughness improved with the increase of drill point angle. This case can be explained as follows: The values of plastic deformation region, cutting edge length and chip thickness obtained for the drills having point angles of 118°, 130° and 140° are greater than those obtained for the drill having point angle of 90°.

Furthermore, since the cutting tool was worn away faster due to the expansion of the friction surface of the cutting edge with the decrease of the point angle [28] the stability of the cutting process was influenced negatively, therefore the roughness increased as seen from the Figure 2 a-f. Also, the pressure applied on the hole surface was decreased owing to the decrease in radial force with the increase of the point angle. Hence, the roughness arisen on the surface was less in comparison with the drills having small point angles.

On the other hand, it was supposed that surface roughness was also influenced by BUE arisen on the cutting edge. The change in BUE on the cutting tool depending on the different point angles was illustrated in Figure 9. As seen, as the point angle decreased, BUE influenced the form of the cutting tool more negatively. Therefore, this case affected the stability of the cutting tool during the cutting process, and caused an increase in surface roughness (Figure 2 a-f).

Experimental Investigation of the Effect of Machining Parameters

on the Surface Roughness and the Formation of Built Up Edge (BUE) in the Drilling of Al 5005 25

In addition, it was seen in the drilling process that the roughness values obtained for a drill with a diameter of Ø10 mm was bigger than those obtained for a drill with a diameter of Ø5 mm (Figure 2 a-f). This case was attributed to the increase of the forces due to the increase of the length of the cutting edge [23,28]. Also, as seen from Figure 10, it was supposed that the expansion of the deformation area due to the increase of drill diameter resulted in a rise in

**Figure 10.** SEM images of BUE formation on the cutting edges at different drill diameters. (800 rev/min-

In this study, BUEs arisen on the cutting edges and the effect of drilling parameters (rotation speed, feed rate, drill diameter and point angle) on the surface roughness of the work piece were investigated experimentally in the drilling process of Al 5005 alloy on CNC milling

i. The surface roughness decreased with the increase of the rotation speed and point angle, while it increased with the increase of the feed rate and drill diameter. ii. It was observed that BUE arisen on the cutting edges caused fractures and wears on the

iii. BUE formation decreased with the increase of the rotation speed, therefore the value of

iv. BUE plugged the helical channels partially by adhering on them, and obstructed the

v. BUE spoiled the form of the cutting tool more as the drill point angle decreased, and

machine. The inferences achieved were presented as follows:

cutting edges during the removal from the cutting edges.

this case resulted in an increase in the surface roughness.

surface roughness decreased.

effective removal of the chips.

0.2 mm/rev-118)

**4. Conclusion** 

BUE formation which caused an increase in the roughness (Figure 2 a-f).

**Figure 9.** SEM images of BUE formation on the cutting edges at different point angles (1200 rev/min-0.1 mm/rev)

In addition, it was seen in the drilling process that the roughness values obtained for a drill with a diameter of Ø10 mm was bigger than those obtained for a drill with a diameter of Ø5 mm (Figure 2 a-f). This case was attributed to the increase of the forces due to the increase of the length of the cutting edge [23,28]. Also, as seen from Figure 10, it was supposed that the expansion of the deformation area due to the increase of drill diameter resulted in a rise in BUE formation which caused an increase in the roughness (Figure 2 a-f).

**Figure 10.** SEM images of BUE formation on the cutting edges at different drill diameters. (800 rev/min-0.2 mm/rev-118)
