Analysis of selected surface roughness parameters the AW 6082 T 6 aluminum alloy after turning process

The paper presents selected research results concerning the surface roughness analysis of 2D and 3D after the turning process AW 6082 T6 aluminum alloy. The conical and spherical surfaces were analyzed. Samples made of aluminum alloy were made on a DMG MORI CTX450 numerically controlled lathe equipped with the Sinumerik 840D control system. The Hommel-Etamic T8000 RC-12-40 measuring device with a measuring radius of 2 μm was used to measure the selected surface roughness parameters. The Keyence VHX-5000 microscope was also used in the study to visualize the resulting surfaces.

In selecting the technological parameters of turning machining, it is important to choose the feed speed correctly because it affects the time of the machining.This parameter is directly influenced by the obtained surface roughness parameters, which is important especially when the turning is the final machining [2-4, 6, 7].The technologist, striving to obtain satisfactory machining time and the required surface quality, most often has to decide whether to increase the cutting speed at a low depth or to increase the depth of cut while maintaining the cutting speed at a reduced level [8,9].Together with the improvement of machining efficiency and the development of highperformance cutting methods, the requirements for modern cutting tools are increasing.The basic determinant of the suitability of the machining tool is to ensure an adequate quality of the surface layer after processing.
This article analyzes the influence of feed speed on the obtained values of selected surface roughness parameters after the AW 6082 T6 aluminum alloy turning processa material important for the industrial sector.

Research methodology
The tests used semi-finished products made of aluminum alloy AW 6082 T6 in the shape of rollers with a diameter of 80 mm.The samples were made in two variants: with conical surfaces and with spherical surfaces.
The dimensions of conical samples are: the height of the truncated cone L = 30 mm, the diameters of the cone bases D1 = 30 mm and D2 = 50 mm.
Samples with spherical geometry had a radius of R = 30 mm.Their dimensions are shown in fig. 1.The turning process was carried out using a cooling liquid.
In tab.I, the technology of sample preparation is presented.During the research a Sandvik folding knife was used (holder DCLNL2525M and plate CNMG120408-PM4225).The machining process was carried out on a numerically controlled CTX450 lathe from DMG. Selected surface roughness parameters were measured using a Hommel-Etamic T8000 RC-12-40 device for measuring contour, roughness and topography, with a measuring tip of 2 μm radius.The measurement of 2D parameters was carried out perpendicular to the traces created after machining.For each of the variants, a minimum of 10 repetitions were performed.
3D topography was made on the surface 1.6 × 1.6 mm with 160 rows.TURBO WAVE software was used for analysis.The elementary segment was selected on the basis of literature [1,5,10,11].The Keyence VHX-5000 microscope was used to visualize the surface after treatment.

Results
The analysis of selected surface roughness parameters 2D and 3D after the aluminum alloy turning process.From the group of 2D parameters the parameters Ra (arithmetic mean of ordinates roughness) and Rz (maximum height profile roughness) were analyzed, while from the group 3D-Sa parameters (arithmetic mean deviation of the surface unevenness from the reference plane), Sz (maximum height of the 3D profile), St (deviation of the main texture direction of the surface from the axis of 90°, perpendicular to the direction of data collection), and Sku (the coefficient of concentration of the topography height distribution (ordinates)).
Tab. II presents isometric views of conical surfaces after the aluminum alloy turning process and obtained values of 3D roughness parameters.
Based on the tests carried out and the analysis of the results, the selected 3D roughness parameters (Sa, Sz, St) were found along with the increase of the feed rate in the whole range of feed speed values used.The parameter of the surface roughness of 3D Sku in all cases remained at the same level.
Tab. III presents the isometric views of spherical surfaces after the aluminum alloy turning process and obtained values of 3D roughness parameters.Similarly as in the case of conical surfaces, also for the spherical surfaces an increase in selected surface roughness parameters was observed along with the increase of the feed speed.It was also noted that with the same feed rate values, Sa, Sz and St parameters are higher for spherical surfaces than for conical surfaces.
The surface topography mapsboth conical and sphericalshow the traces of surface formation typical of machining, constituting a kinematic-geometric representation of the tool.
Tab. IV presents the photographs of conical and spherical surfaces obtained after the treatment of the aluminum alloy AW 6082 T6, with a magnification of ×300.By analyzing the posted photographs of the surface after the rolling process with different feed speeds, it can be seen that as the feed rate increases, the surface furrows become deeper and deeper.It was found that all surfaces are characterized by parallel traces of the blade.On the surface of the samples, you can also see the loss of material, which is the result of chipping.Fig. 2 shows the influence of the feed speed value on the Ra parameter value of the conical and spherical surface after the aluminum alloy turning process.On the basis of the conical and spherical surface tests, the surface roughness parameter Ra was increased along with the increase of the feed speed.Noteworthy is the large concentration of results around the average value.For a feed rate of 0.15 mm/rev, the roughness parameter Ra was approx. 1 mm.With the increase of the feed value, the difference between the Ra parameter for conical and spherical surfaces is increasingwith a feed rate of 0.35 mm/rev, it is 35%.Fig. 3 shows the values of the Rz parameter of the 2D surface roughness depending on the value of the feed speed.

TABLE IV. Photographs of conical and spherical surfaces created after machining of an aluminum alloy
For a conical surface, a four-fold increase in the surface roughness parameter Rz parameter for a feed rate of 0.35 mm/rev was observed in relation to the value of the feed rate of 0.15 mm/rev.

Conclusions
On the basis of the analyzes and experimental studies carried out, the following general conclusions were formulated:  In the whole range of applied feed speed, an increase in surface roughness parameters was observedboth 2D (Ra, Rz) and 3D (Sa, Sz, St). For conical surfaces, a larger spread of the obtained results was observedstandard deviation (fig. 2 and fig.3). In surface photographs after the turning process with different feed rates, it can be seen that as the feed rate increases, the surface furrows become deeper.All surfaces are characterized by parallel traces of the tool edge.
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