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on the surface roughness, while level 4 (10000mm/min) of feed rate was significantly different than the remaining levels (Table 5). The highest surface roughness value was obtained with feed rate of 10000 mm/min ( R a = 6,057 μm), while the lowest surface roughness value was obtained with feed rate of 2500 mm/min ( R a = 5,486 μm). The effects of the machining parameters on the mean surface roughness values are shown in Fig. 4. The surface roughness value increased with increasing feed rate and tool diameter and with decreasing spindle speed. The effect of the depth of cut parameter on the surface roughness value was negligible because of the same density in the profile area. Although the surface roughness decreased with increasing feed rate, the illustration shows that the average R a value decreased slightly at 7500 mm /min of feed rate. This can be explained by the interaction effect of the tool diameter-feed rate. The interaction effects of machining parameters on the surface roughness are presented in Fig. 5. The interaction effect of spindle speed-feed rate, tool diameter-feed rate, and spindle speed-tool diameter feed influenced the surface roughness. However, the interaction effect of machining parameters was not significant. From the effect of dual interactions graph of spindle speed- feed rate, the surface roughness is found to be minimal at high spindle speed (24000 rpm) with low feed rate (2500 mm/min). In addition, the friction, machining force, and contact area between the cutting tool and the workpiece increases with the increased feed rate. Further, higher spindle speed means higher tooth passing frequencies and provides shorter plane area/reduction in chip thickness and hence the machining force and surface roughness decreases ( Sarıkaya and Güllü 2014). The surface roughness is found to be minimal at high cutting speed with low feed rate. According to tool diameter- feed rate interaction, the high surface roughness occurred with an increase in tool diameter and feed rate. The reason for the high roughness can be explained with the increasing feed rate and tool diameter, causing vibration and a temperature rise between the work piece and the cutting tool (Suresh et al. 2012). The surface roughness values of the machined samples with 4 mm of tool diameter and 7500 mm /min of feed rate were observed, according to the processing conditions of 4 mm tool diameter and 5000 mm /min feed rate. However, with the increase in tool diameter (6 mm), the 5000 mm/min of feed rate provided a smoother surface quality than 7500 mm /min of feed rate. The effect of dual interaction graph of spindle speed-tool diameter shows that the surface roughness decreased with increasing spindle speed and decreasing tool diameter. Also, the best surface roughness was observed at a small tool diameter (4 mm) and a high spindle speed (24000 rpm). Compared to the surface roughness values with different spindle speeds (18000 rpm and 24000 rpm) at 4 and 6 mm of depth of cut, the lowest roughness value was provided at 2400 rpm of spindle speed and 4 mm of depth of cut. Table 5. Results of the Duncan Test for Feed Rate Levels Feed_rate (mm/min) N Mean HG 2500 80 5.486 a 7500 80 5.550 a 5000 80 5.676 a 10000 80 6.057 b* HG: Homogenous group *: The highest surface roughness value
İşleyen & Karamanoğlu (2019). “ Roughness of MDF ,” B io R esources 14(2), 3266-3277. 3272
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