First approach to the analysis of the surface roughness obtained during the dry turning of the UNS A97050-T7 aluminium alloy.

De Agustina, Beatriz ; Marin, Marta ; Rubio, Eva 等

1. INTRODUCTION

The aluminium alloys are considered strategic materials in the aeronautical, motor and aerospace sectors due to their excellent weight to resistance ratio. Specifically, they are employed in the production of different elements that compose aircraft and aerospace vehicles. For such application an improved surface quality for the mechanized parts is required.

In spite of the important role these materials have from a competitive point of view, they can commonly show problems of machinability associated with the heat generated during the machining process. For this reason, although it is possible to evacuate the heat by means of the chip, the tool and the workpiece, cutting fluids are still widely used (Agustina et al., 2008). However, the use of cutting fluids seriously degrades the environment quality and increases the cost of machining. As a result, dry machining has been widely studied in recent years (Nouari et al., 2003).

In this study in order to analyse the evolution of the surface quality of an aluminium UNS A97050-T7 bar with respect to the cutting parameters employed (cutting speed and feed rate) a series of dry turning tests (no longer than 10 seconds) were carried out using tools with coating of TiN.

2. METHODOLOGY

The present work is framed within a serial of studies in which different materials, types of tools and cutting conditions are involved. The main steps of the methodology in which this work was developed are (Agustina et al., 2007):

* Previous activities to the machining operations. These activities consist of the identification of the resources used and the preparation of the protocols both to calculate cutting parameters values and to register data and observations of the machining process.

* Turning tests. In each test a workpiece was mechanized during less than 10 seconds (short tests) under certain conditions of feed, cutting speed and depth of cut using both coated and uncoated cutting tools.

* Monitoring of the process. In order to have graphic documents that can be analysed after the process, all the turning tests described previously were recorded by video and both the chips obtained and the inserts used in each one of them was photographed with a high resolution camera.

* Roughness measurement. In order to systematize test-pieces roughness measurements, firstly, the measurement process has to be defined. This is, basically, to measure the roughness along four lines separated [pi]/2 radians.

* Analysis of tools. From the results obtained, a tool preselection was made. Then, the selected tools were analysed employing both macroscopic and microscopic techniques. The former, using the macrographs taken and a profile projecter that allows measuring the quantity of the adhered material and the latter, by means of techniques of Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS) in order to verify the alterations of the tools geometry.

3. APPLICATIONS

For this study, the workpiece used for the turning tests was a cylindrical bar with a diameter of 54 mm and length of 90 mm of UNS A97050-T7 aluminium alloy.

The cylindrical bar was horizontally dry turned on an EmcoTurn 120 CNC lathe equipped with an EMCO Turn 242 numerical control. The cutting conditions applied were cutting speeds from 40 m/min (0.66m/s) up to 170 m/min (2.83 m/s) and feeds from 0.05 mm/rev up to 0.30 mm/rev. Cutting depth was maintained at 1 mm in all the tests.

TiN coated tools (manufacturer reference SECO DCMT 11T308-F2-TP1000) were employed for the tests.

To observe the machining tests carried out, photographs and videos of the tools and the resulting chips were taken systematically during the tests using a Sony Cybershot DSC-P100 digital camera of high resolution.

To define the surface quality of the workpiece it was selected the parameter Ra (the arithmetical average roughness). The cutoff length was taken as 0.8 mm and the sampling length as 4 mm.

[FIGURE 1 OMITTED]

4. RESULTS

Table 1 represents the values of the rougness (Ra) measured along four lines separated n/2 radians: G1, G2, G3 and G4, for each cutting parameters applied.

To facilitate the analysis of the surface quality obtained on the workpiece under the different combinations of cutting parameters tested, two similar graphics were design to show the evolution of the roughness with respect to the feed (figure 2) and with respect to the cutting speed (figure 3). The values of the roughness Ra represented on both graphics correspond to the arithmetical average of the parameter roughness Ra measured along G1, G2, G3 and G4 for each test.

From figure 2, it can be seen that at cutting speeds of 40, 85 and 170 m/min, the higher the feed, the higher values of roughness was obtained, as was expected (Rubio, et al., 2005), (Kulenovic, et al., 2007).

On the other hand, analysing the evolution of the roughness with the cutting speed, in figure 3, it can be observed that the tendency of the values of the roughness measured was the opposite as it was with respect to the feed, though less accentuated, specially at 0.30 mm/rev for the higher cutting speeds applied 85, 125 and 170 m/min. Under such cutting conditions the values of roughness hardly varied.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

5. CONCLUSIONS

The surface quality of the aluminium UNS A97050-T7 bar which is obtained during dry turning short tests (no longer than 10 seconds) improves with the descent of the feed and with the increase of the cutting speed. From these two parameters, the feed is the parameter more influencial in the surface roughness.

Taking into account these results, it would be convenient to carry out new tests using values of the nearer feed to the values that have lead to obtain the best surface quality in this study as well as other values of the cutting depths in order to complete the work.

6. ACKNOWLEDGMENTS

Funding for this work was provided in part by the Spanish Ministry of Education and Science (Directorate General of Research), Project DPI2005-09325-C02-02.

7. REFERENCES

Agustina, B.; Rubio, E.M.; Sanz, A., Domingo R. (2007). A classification of the UNS A97050-T7 aluminium alloy chips in short duration tests under dry cutting conditions, Proceedings of the MESIC-CISIF'2007, Sebastian Perez, M.A. (Ed), pp 1-8, ISBN: ISBN(CD): 978-84-611-8001-1, July 2007, Madrid.

Agustina, B.; Rubio, E.M.; Marin, M.M.; Sebastian, M.A. (2008). Analysis of the material adhered on inserts with and without TiN coating during the dry turning of the aluminium alloy UNS A97050-T7, Proceeding of the CIRP ICME'08, Roberto Teti, R. (Ed), pp 1-6, July 2008, Naples.

Agustina, B.; Rubio E.M.; Marcos, M. (2007). Study of the adhered material to the cutting tools on dry turning of aluminium alloys, Proceedings of the 18th International DAAAM Symposium, DAAAM International, Katalinic, B. (Ed), pp 215-216, October 2007, Zadar.

Kulenovic, M.; Begic,; Cekic, A. (2007) Experimental Investigation of Carbon Steel in High Speed Cutting, Proceedings of the 18th International DAAAM Symposium, DAAAM International, Katalinic, B. (Ed), pp 411-412, October 2007, Zadar.

Nouari, M.; List, G.; Girot, F.; Coupard, D. (2003). Experimental analysis and optimisation of tool wear in dry machining of aluminium alloys. Wear 255 (7-12) August-September 2003, 1359-1368, ISSN: 0043-1648.

Rubio, E.M.; Camacho A.M.; Sanchez-Sola, J.M.; Marcos, M. (2005) Surface roughness of AA7050 alloy turned bars. Analysis of the influence of the length of machining, J. Mater. Process. Technol. 162-163C, May 2005, 682-689, ISSN: 0924-0136.

DE AGUSTINA, B[eatriz]; MARIN, M[arta] & RUBIO, E[va] *

* Supervisor, Mentor

Tab. 1. Ra ([micro]m) measured under the different cutting
parameters applied.

 Ra ([micro]m)

v(m/min), G1 G2 G3 G4
f(min/rev)

170,0.30 2.796 3.689 2.875 3.616
170,0.20 1.569 1.537 1.522 1.537
170,0.10 0.592 0.576 0.593 0.578
170,0.05 0.316 0.403 0.396 0.424

125,0.30 3.386 3.326 3.313 3.313
125,0.10 0.488 1.383 0.564 1.780
125,0.05 0.482 0.537 0.458 0.627

85,0.30 3.351 3.496 3.398 3.215
85,0.20 1.556 1.633 1.651 1.823
85,0.10 0.812 1.011 1.025 1.058
85,0.05 0.881 0.799 0.905 1.082

65,0.30 3.754 3.669 3.780 3.624
65,0.10 1.385 1.573 1,690 1.730
65,0.05 1.135 1.369 1.127 1.507

40,0.30 4.310 3.935 4.509 4.617
40,0.20 3.225 3.799 2.929 3.628
40,0.10 1.603 1.814 1.583 2.115
40,0.05 1.900 2.215 1.785 2.579