**2. Experimental method**

16 Tribology in Engineering

In former studies on hole surface quality, Nouari and his colleagues subjected Al 2024-T3 to dry drilling process, and did some optimizations and analysis experimentally for both the dimensional accuracy of the machined surface and longevity of cutting tools [9]. In their study, they used sintered tungsten carbide (STC) cutting tools and high speed stell (HSS) cutting tools, and set the feed rate to 0,04 mm/rev and cutting speed to 25, 65, 165 m/min. They concluded from the experiments that STC cutting tools are more convenient in comparison with HSS cutting tools from the points of tool life, deviation in hole diameter and surface roughness. Lin investigated tool life, surface roughness, tool abrasion and burr formation for the process of the high speed machining of stainless steel material with TiN coated carbide tool [10]. As a result of his researches, he determined that the abrasions in shear edge result from the high feed rate in low cutting speed, and optimum cutting speed for desired burr height and surface roughness was 75 m/min. In addition, he determined that in high speed machining of stainless steels the tool life increased considerably in case of adjusting the feed rate to the values lower than 0,05 mm/rev. Lin and Syhu, studied on the treatment of the tool life and burr formation in the drilling of stainless steel with the drill bits coated by different materials [11]. Kurt et al., investigated the effect of cutting parameters on the drilling temperature, cutting force and surface roughness in the drilling of Al 2024 alloy with DLC coated drill. In their study, they determined that the most effective factors influencing the hole surface quality are feed rate and drill diameter [12]. They observed that the change in feed rate and diameter at high cutting speeds affects the average surface roughness considerably. Dudzinski et al., determined that the tool life was very short in the drilling of Inconel 718; therefore the surface quality gets worse [13]. They determined that the main wear mechanism seen in the cutting tools used was abrasion. In addition, they observed that the chips resulted in the formation of built-up-edge (BUE) by adhering on the cutting tool, and the removal of BUE from the cutting tool repeatedly caused notches. Klçkap investigated the roughness of hole surface and the height of the burrs formed at the hole exit in the drilling of Al 7075 material [14]. Also in another research, Klçkap, experimentally studied on the effects of cutting speed, feed rate and different cooling techniques on the temperature and the roughness of hole surface in the drilling of Al 7075 [15]. In their study, they observed that the most appropriate cooling technique was oil cooling from the point of good surface roughness. Also, they determined that the roughness increased with the increase of the feed rate, while it decreased with the increase of rotation speed. Hanyu et al. investigated the effects of finely crystallized diamond coating method, which was developed by themselves, on the surface roughness in the dry and semi-dry drilling of Al 7075 alloy [16]. They demonstrated experimentally that finely crystallized diamond coating method yields four times better results in comparison with the conventional diamond coating method. Konig and Grass investigated the effects of cutting parameters on the roughness of hole surface and surface tissue in the drilling of fiber reinforced thermosets [17]. They denoted that the surface roughness increases with increase of the feed rate. In his study, Tosun, optimized the drilling parameters affecting the burr height and surface roughness of DIN 42CrMo4 steel material by considering different drill materials, cutting speeds, drill point angles and feed rates with the help of Grey Relational Analysis (GRA) [18]. Sur et al. studied on the effects of Ti alloy on the surface roughness in

In this study, Al 5005 was drilled by considering various drilling parameters such as diameter, point angle, feed rate and rotation speed. CNC milling machine (Taksan, TMC 700V) with vertical machining centre was used in the experiments. The spindle power of the machine, rotation speed and feed rate values were taken as 5.5 kW, 50-8000 rev/min and maximum 0.6 mm/rev, respectively. Maximum feed rate values of the work table on X, Y and Z axes were 500, 600 and 450 mm, respectively. Factorial design, in which the effects of mostly different and unrelated factors on a definite characteristic are investigated, was taken into consideration in design process of the experiment. In factorial design, the experimental design is established by processing the variable parameters (or their levels) crossingly [21]. In this study, the experiments were conducted in accordance with 72 different combinations (21.32.41) by using 2 levels for the drill diameter, 4 levels for the point angle, 3 levels for the rotation speed and the feed rate. The values of variable parameters in conducted experiment were selected in compliance with the similar studies as shown in Table 1 [9,10,14,18].

In this study, the cutting fluid was not used in order to observe the effect of drill parameters on the roughness of the hole surface [22]. Al 5005 material used in the experiments was in the dimension of 10mmx70mmx400mm, and its chemical properties were given in Table 2. In the drilling process, the space between the axes of each hole on the sample was adjusted to be 20 mm (Figure 1).


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 19

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

**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

**3. Results and discussion** 

using cooling fluid.

**Table 1.** Experimental parameters


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

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

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 Microscope (SEM).

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.
