The technology of producing threads, especially in materials that are difficult to cut, is a rare subject of research and scientific publications. The requirements for the production of these elements apply not only to the geometry, but also to the quality of the surface obtained. This is particularly important in the aviation industry, where the durability of the threaded connection affects passenger safety. Due to the design of the thread, the quality of its surface is assessed visually in industrial practice. The authors of this study decided to examine the surface topography of external threads made by turning on Inconel 718 shafts in order to confirm the visual evaluation, as well as to investigate the influence of such factors as cutting speed, turning direction and type of profile. Three types of contours were cut for the research: triangular, trapezoidal symmetrical and trapezoidal asymmetrical. Turning of each was carried out twice at cutting speeds v_c = 17 m/min and v_c = 30 m/min. On each of the threads, the side surface of the profile made in the direction of the insert feed and the opposite surface were examined. The surface texture parameters Sa, Sq, Sp, Sv, Sz, Ssk and Sku were determined and compared. It was noticed that the thread surfaces show a tendency to irregular roughness, which was confirmed by the analysis of the Sku and Ssk coefficients. The sides of the contours made in the direction of the insert feed are characterized by a higher roughness in relation to the opposite sides, which may result from high cutting forces and difficulties with chip evacuation. With the cutting speed being considered, lower values of Sa and Sq were obtained for v_c = 17 m/min, which differed from the visual assessment, proving its high subjectivity.

This piece of work deals with the influence assessment of the kind of coating of the cutting inserts and their wear on the dimensional accuracy and the top layer microstructure and roughness of the surface machined with constant cutting parameters v_c = 85 m/min, f = 0.14 mm/obr and a_p = 0.2 mm. The tests were performed on shafts made of Inconel 718 material under the conditions of finish turning, requiring a tool life of more than 20 min. The cutting inserts of identical geometry made of fine-grained carbide covered with coatings were applied by the PVD and CVD method. The values of the obtained diameter dimensions were assessed in reference to the assumed ones, as well as the values of the surface roughness and stereometry and the microstructure of the top layer. The nature and mechanisms of edge wear and its value expressed by the VB_C parameter were also assessed. It was determined in the tests that the machined surface quality defined by the Ra and Sa roughness parameters and the dimensional accuracy were influenced not only by the coating microhardness but also by the method of applying the given coating. The lowest values of the tested roughness parameters were observed for the surface machined with an edge, with the S205 coating applied by the CVD method, which was characterized by the lowest microhardness. The edge with this coating also showed the lowest wear, defined by the VB_C parameter, which translated into dimensional accuracy. Furthermore, the edge with the S205 coating also provided the best results with regard to the surface layer microstructure. The least favorable results, both in terms of dimensional accuracy and surface roughness, were obtained for the surface machined with a 1115-PVD-coated edge. The highest wear value was also recorded for this edge.

This paper presents a comparison of surface morphology obtained after machining Inconel 718 by the conventional insert, by Wiper insert and by using the cutting insert made by Spark Plasma Sintering (SPS). The shape of the special insert was obtained by employing Wire Electrical Discharge Machining (WEDM). The paper focuses on the description of surface topography after turning in dry and wet conditions. The performed investigation included longitudinal turning tests of Inconel 718 performed in a range of variable feeds. Surface topography measurements have been performed with the application of Nanoscan 855. The performed analysis includes a parametric evaluation of the obtained surfaces. With the Wiper insert, the Sa surface roughness parameter was obtained below 0.6 µm in the whole range of used feed rates. The surface roughness parameter Sa measured on the surface after machining by special insert depends on the cutting conditions (wet and dry machining). After, the dry machining parameter Sa, similar to the Wiper insert, was below 0.6 µm in the whole range of used feed rates. Unfortunately, cutting Inconel 718 using special insert with feed rate f = 0.25 mm/rev and cooling generated a surface with Sa parameter over 2 times higher than for the same feed rate without cooling, while this parameter, after turning by conventional insert, increases over 4 times using feed rate f = 0.25 mm/rev compared to feed rate f = 0.05 mm/rev during machining with cooling. This ratio is lower for conventional insert in dry machining because of sticking, which arises at the smallest feed rate according to previous research.

This paper presents the results of investigation that was performed on shafts composed of Inconel 718. Tests were performed in dry and wet conditions. Cutting parameters, such as feed and depth of cut, were constant. The cutting speed was changed. The investigation was performed for various shaft shapes: cylindrical, taper 30°, taper 45°, and sphere. For that reason, the value of the angle between the machined surface and the cutting edge changed. The lowest values of the roughness parameters, Ra and Rz, were obtained for a larger value of the angle between the machined surface and cutting edge. The investigation showed that cutting speed, machining conditions (dry and wet machining), and the variable angle between the machined surface and the cutting edge influenced the surface roughness. Application of a higher cutting speed resulted in lower roughness values. Lower values of roughness parameters were obtained by wet machining.

Nowadays, great emphasis is placed on increasing the efficiency of machining processes. However, this cannot be done at the expense of quality worsening of the machined surface. In this paper the influence of Wiper geometry on Ra and Rz surface roughness parameters is described when finishing turning of materials used in the aviation industry: austcnitic stainless steel XCrNiNb18-9, low alloy steel 14NiCr14 and aluminum alloy A356, as well as the chips generated in the cutting process in terms of shape were assessed. It was found that for the lowest tested feed rate during turning with a Wiper insert, the values of Ra and Rz parameters do not differ significantly from the roughness parameters obtained during machining with a conventional insert. The beneficial effect of feed rate on surface roughness for the Wiper insert is clearly visible above f >= 0.12 mm/rev. The biggest difference in roughness parameters was recorded for the highest value of the applied feed f = 0.28 min/rev. Using conventional insert, Ra and Rz values are almost three times bigger than for Wiper insert. The influence of the cutting speed on the Ra and Rz parameters depends on the type of material being processed. Increasing cutting speed from v(c) =120 in/min to v(c) = 200 m/min for stainless steel. Ra and Rz values decrease about 35%. Similar situation noticed for aluminum alloy, but increasing cutting speed decrease Ra and Rz values only about 18%. The situation is different for low alloy steel. Increasing the cutting speed increases the Ra and Rz parameters by about 37%. Rz/Ra ratio shows that for feed rate f <= 0.12 min/rev. cutting process is unstable. because the values are between 5.5-7.5, but should oscillate around 4. Increasing feed rate value to f= 0.2 min/rev allows to stabilize the process and the ratio value is close to 4. Wiper insert create the same form chips as a conventional insert, using the same value of feed rate.

Cutting inserts made of ceramic materials are used in rough machining processes of Inconel 718. This article compares sintered carbide S205 inserts with 6160 ceramic inserts after finish turning of Inconel 718 with a hardness of 45 HRC. The evaluation focused on insert wear, surface topography and changes in cutting edge radius. The results show differences in the wear of S205 and 6160 inserts. S205 inserts characterize the formation of buildup on the rake face, while 6160 inserts tend to form buildup on the flank face. Furthermore, ceramic 6160 inserts are more prone to notch wear. Surface topography analysis revealed the formation of individual high peaks on surfaces machined with ceramic inserts. The Sa parameter for all cutting conditions studied did not exceed 0.45 µm.