The purpose of this work is to study the behavior of the acoustic emission (AE) signal as the cutting tool wears up to the end of its life, aiming the automatic definition of the moment to change the tool. Several turning experiments were carried out in both, finish and rough conditions, using coated carbide tools. The AE signal was acquired during the experiments and, after suitable conditioning, was stored in the computer. A discussion about the use of the mean RMS acoustic emission signal as a parameter in the evaluation of the tool condition was also done. The results were graphically plotted and analyzed. It was concluded that the AE signal is strongly influenced by the tool wear and that the cutting conditions are very important, since the signal shows a very different behavior between finish and rough turning. The main conclusion of this work is that AE monitoring is a very good way to establish the moment to change the tool, since the mean RMS of the signal shows a sharp increase close to the end of tool life in finish turning and a decrease, also close to the end of tool life, in rough turning operations. So, a criterion to the determination of the moment to change the cutting tool was established, based on the change of the AE curve slope during the tool life.183227238Agostinho, O.L., Rodrigues, A.C.S., Lirani, S., (1977) Tolerâncias, Ajustes, Desvios e Análise de Dimensões, pp. 213-215. , Ed. Edgard Blücher LtdaBlum, T., Inasaki, I., A Study on Acoustic Emission from the Orthogonal Cutting Process (1990) Journal of Engineering for Industry, 112, pp. 203-211Bonifácio, M.E.R., (1993) Monitoramento do Processo de Torneamento de Acabamento Via Sinais de Vibração, , Dissertação de Mestrado, Universidade Estadual de Campinas, Campinas-SP, BrasilDan, L., Mathew, J., Tool Wear and Failure Monitoring Techniques for Turning - A Review (1990) International Journal of Machine Tools and Manufacture, 30, pp. 579-598Diniz, A.E., (1989) A Rugosidade Superficial da Peça em Processus de Tomeamento: Critério de Fim de Vida e Fatores de Influência, , Tese de Doutorado, Universidade Estadual de Campinas, Campinas-SP, Brasil(1992) Tool Monitoring System, , Catálogo de Produto, Stuttgart, AlemanhaHanchi, J., Klamecki, B.E., Acoustic Emission Monitoring of the Wear Process (1991) Wear, 145, pp. 1-27König, W., Ketteler, G., Dornfeld, D.A., Aktueller Stand von Werkzeug - Und Prozebüberwachung bei der Zerspanung (1993) VDI Berichte NR. 988, pp. 363-376Lan, M.S., Dornfeld, D.A., Experimental Studies of Tool Wear via Acoustic Emission (1982) Proceedings of the 10th NAMRC, pp. 305-311. , Hamilton, CanadaLiang, S.Y., Dornfeld, D.A., Detection of Cutting Tool Wear Using Adaptive Time Series Modeling fo Acoustic Emission Signal (1987) ASME Winter Annual Meeting, , BostonLiu, J.J., (1991) Monitoring the Precision Machining Process: Sensor, Signal Processing and Information Analysis, , Doctoral Thesis, University of California at Berkeley, USAMoriwaki, T., Tobito, M., A New Approach to Automatic Detection of Life of Coated Tool Based on Acoustic Emission Measurement (1990) Journal of Engineering for Industry, 112, pp. 212-218Naerheim, Y., Lan, M.S., Acoustic Emission Reveals Information about the Metal Cutting Process and Tool Wear (1988) Proceedings of 16th NAMRC, pp. 240-244Vilella, R.C., Diniz, A.E., Cupini, N.L., Rodrigues, A.C.S., Otimização das Condições de Usinagem em Células de Fabricação (1989) Revista Máquinas e Metais, (281), pp. 48-54Willians, R.V., (1968) Acoustic Emission, p. 5. , British Steel Corporation Ltd., Adam Hilger Ltd