Influence of the coating tool on the morphology of the chips obtained during the dry turning of UNS A97050-T7 aluminium alloys.

De Agustina, Beatriz ; Rubio, Eva Maria ; Marcos, Mariano 等

1. INTRODUCTION

The aluminium alloys are widely used in the aeronautical, aerospace and automotive industries. This is due to the excellent weight to resistance ratio of these types of alloys. Nevertheless, in spite of the important role these materials have from the competitive point of view, they can commonly show problems of machinability associated with the tool wear (Nouari et al., 2005; Xie et al., 2003; Sebastian et al., 2003). That has made that traditionally cutting fluids had been used in machining processes. However, they are pollutants and increase the total cost of the process considerably. Therefore, researches have been focused on the development of cleaner production technologies applications as dry machining.

In this study, series of tests have been carried out with a workpiece of aluminium UNS A97050-T7 by dry machining. The chips obtained under different cutting conditions (cutting speed and feed rate), using tools with different coatings were designated according to their morphology. Also, a classification of the chips as favourable or unfavourable was made taking into account the security of the machining process, the integrity of the tool and the surface quality of the workpiece.

2. METHODOLOGY

The main steps of the methodology are (Agustina et al, 2007; Agustina et al., 2008; Rubio et al., 2005):

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

* Turning tests. In each test a workpiece is mechanized 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 before have been recorded by video and both the chips obtained and the inserts used in each one of them have been photographed with a camera of high resolution.

* Collection of the chips. Chip or chips obtained in each test are collected, identified and saved so they are perfectly identified and accessible for any later confirmation to the realization of the tests.

* Designation of the chips. The different types of chips obtained during the cutting tests have been designated according to their morphology, based on the ISO 3685 standards (ISO 3685, 1993).

* Classification of the chips. Once the chips have been grouped according to their basic form and type they have been classified as favourable or unfavourable from the point of view of the security of the process, the tool integrity and surface finish. That is, a chip will be considered as favourable with regard to: the security of the process, when it does not imply a danger for its continuity; the tool integrity, whether it does not produce or can produce the failure/wear of the tool; the surface finish, whether or not it causes an important deterioration of the workpiece surface.

3. APPLICATIONS

In this study series of tests were carried out on a cylindrical bar with a diameter of 70.0 mm and length of 90.0 mm of aluminium UNS A97050-T7. The cylindrical bar was horizontally dry turned on an EmcoTurn 120 CNC lathe equipped with an EMCO Turn 242 numerical control by using two types of cutting tools with identical geometry and base of WCCo from SECO manufacturer: TiN coated tool (DCMT11T308-F2TP100) and uncoated tools (DCMT11T308-F2-HX). Table 1 shows the different cutting parameters employed during the tests.

4. RESULTS

The chips obtained at most of the cutting condition parameters were continuous for both uncoated and coated tools employed. These types of chips have been classified, on one hand, according to the morphology based on the standard classification ISO 3685, as snarled chips. On the other hand, as unfavourable chips, from all the points of view considered: the security of the machining process, the integrity of the tool and the surface quality of the workpiece. The continuous knocking of these chips deteriorates the surface quality of the workpiece and after a time of machining it would be necessary to stop the process and manually disentangle the spindle. As example of these types of chips, figure 1 shows the chips obtained at 200 m/min y 0.05 mm/rev with the coated (TP1000) and uncoated (HX) tools.

[FIGURE 1 OMITTED]

Solely favourable chips, at least from some of the points of view studied, were obtained for the uncoated chips at feed of 0.25 mm/rev with cutting speeds of 125 and 200 m/min (figure 2) and for the coated tools at 0.25 mm/rev and 50 mm/rev (figure 3). However, under such cutting paramaters (higher feeds) the roughness surface obtaining during machining is greater.

[FIGURE 2 OMITTED]

The long tubular chips obtained (figure 2a) have been classified as favourable only from the point of view of the security procees as these chips break off before they could tangle around the spindle lathe. Nevertheless, they could deteriorate the surface quality.

[FIGURE 3 OMITTED]

Summarizing, in this study, at the higher feeds applied, the chips obtained were more suitable for the machining process than ones obtained at lower feeds. Thus, the uncoated tools performed more improved behaviour than the coated tools. This result was expected as the tools with the TiN coating such as the TP1000 tools, according to the previous research (Mabrouki et al., 2008) lead to generate high magnitude of cutting forces and roughness during the machining. Nevertheless, these tools were considered in this study due to the fact that, in some cases, the aluminium alloys take part of hybrid components that require be mechanized all together.

5. CONCLUSIONS

The main conclusions of this study are presented in the following points:

--A larger quantity of favourable chips are obtained at the higher feeds for both coated and uncoated tools used during the dry turning of the UNS A97050-T7 alloys.

--Tools with TiN coating lead to obtain a larger quantity of unfavourable chips than KX tools.

--It is proposed to carried out other tests such as the measurement of hardness, width and micro-structural composition of the chips and new turning tests using other types of tools with different geometry and materials and applying other cutting parameters to complete the study.

6. ACKNOWLEDGMENTS

Funding for this work was provided in part by the Spanish Ministry of Science and Innovation (Directorate general of research), Project DPI2008-06771-C04-02.

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-CISF'2007, ISBN: 978-84-611-8001-1, July 2007, Madrid

Agustina, B.; Marin, M. & Rubio, E.M. (2008). First approach to the analysis of the surface roughness obtained during the dry turning of the UNS A97050-T7 aluminium alloy, Annals of DAAAM for 2008, 215-216, ISSN: 1726-9679

Mabrouki, T., Girardin, F., Asad, M. & Rigal, J., (2008). Numerical and experimental study of dry cutting for an aeronautic aluminium alloy (A2024-T351), International Journal of Machine Tools & Manufacture, Vol. 48, No. 11, (September 2008), 1187-1197, ISSN: 0890-6955

Nouari, M.; List, G.; Girot, F. & Coupard, D. (2003). Experimental analysis and optimisation of tool wear in dry machining of aluminium alloys. Wear, Vol. 255, No. 7-12, (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. Journal of Materials Processing and Technology, Vol. 162-163 (May 2005), 682-689, ISSN: 0924-0136

Sebastian, M.A.; Sanchez, J.M.; Rubio, E.M.; Carrilero, M.S.; Diaz, J.E. & Marcos, M. (2003). BUE and BUL formation mechanisms in dry cutting of AA7050 alloy, Proceedings of the 14th International DAAAM Symposium, "Intelligent Manufacturing & Automation: Focus on Reconstruction and Development". Katalinic, B. (Ed.),pp. 125-126, October 2003, Viena

Xie, X.; Yan X.; Ding, F.; Zhang, S.; Chen, M.G. & Chang, Y.A. (2003). A study of microstructure and microsegregation of aluminium 7050 alloy. Materials Science and Engineering Vol.355, No. 1-2 (August 2003), 144-153, ISSN: 0921-5093

*** ISO 3685:1993, Tool-life testing with single-point turning tools, 1993

Tab.1. Cutting parameters applied

Feed (f mm/rev) 0.05 0.15 0.25

Cutting speed (v, mm/min) 50 125 200
Depth of cut (d, mm) 0.5 0.5 0.5