The turning tests were performed using cutting conditions recommended by the cutting tool manufacturer for this particular cast iron grade and hard...

The turning tests were performed using cutting conditions recommended by the cutting tool manufacturer for this particular cast iron grade and hardness. The results and corresponding discussions concerned with the components of the turning force, tool life/wear, and surface roughness are presented below. 3.1 Turning force components. Figure 5 shows the minimum, average, and maximum values of the turning force components obtained during the tests with and without the application of minimal quantity lubrication. The cutting force presented the highest amplitude values (Fig. 5a), followed by feed and passive forces (Fig. 5b and c, respectively). For the same type of texture, MQL led to lower values of turning forces, probably due to the reduction of friction associated with the lubricant effect. However, a reduction of approximately 9% for the average values was noticed, thus indicating that the application of cutting fluid did not contribute to a dramatic reduction in the force components. Moreover, a larger scatter in the force values was observed when turning with MQL in comparison with dry cutting, regardless of the texture type. This may have occurred due to the non-uniform distribution of the fluid between workpiece-tool and chip-tool interfaces. Trent and Wright [16] state that in metal cutting, chip flows under conditions of seizure and sliding. In the former, observed near the cutting edge, relative movement between the chip and tool is not expected to take place due to the high compressive stress. As a result, the surfaces are bonded and the force required to overcome bonding is higher than that required to shear the work material. Under sliding, however, the compressive stress is much lower and relative movement between chip and tool is observed. Therefore, the presence of dimples where cutting fluid can be stored is likely to affect turning forces under sliding only, but is sufficient to decrease the friction coefficient between chip and tool and promote a slight reduction in all the components of the turning force, as can be seen in Fig. 5. No clear trend can be observed with the increase of the step value (distance between two adjacent rows of dimples); nevertheless, Fig. 5 shows that the lowest average values were obtained for the tool with step 100 and application of MQL. This indicates a greater potential of such texture in relation to the others. Short step values can damage the chamfer surface due to the presence of a heat-affected zone and resolidified material. In contrast, an excessive increase of the step reduces the quantity of cavities per unit area and the force behaviour should tend to be similar to that observed for the non-textured tool. One must bear in mind that a smooth surface is subjected to less wear than a rough one due to friction between surfaces. However, according to [17], liquid lubricants can improve the performance of a rough surface better than of a smooth surface. This phenomenon occurs because small amounts of coolant/lubricant are generally stored in valleys, thus reducing the cutting temperature and, in some circumstances, of maximum flankwear during dry (a) and MQL (b) turning