ORIGINAL ARTICLE Development of a stability intelligent control system for turning Gabriel R. Frumusanu & Ionut C. Constantin & Vasile Marinescu & Alexandru Epureanu Received: 25 November 2011 / Accepted: 19 March 2012 / Published online: 5 April 2012 # Springer-Verlag London Limited 2012 Abstract This paper presents a stability control system based on a new strategy, with application in turning. It works by permanent assessment of the system operating point position relative to the stability limit, and process parameter permanent, in-process modification such as this point is always placed in the stable domain zone that gives the highest process perfor- mance. In the case of turning, here approached: (1) this zone is the stability limit proximity; (2) the system operating point position is determined by assessing a cutting force monitored signal feature; and (3) this position is changed by modifying the cutting edge setting angle, the feed rate, and the cutting speed, as it follows: when the risk of overpassing the stability limit is imminent, the setting angle is increased, followed by a feed rate diminishing and then by a worked piece rotation speed reduction, while immediately after surpassing the risk, the three variables modification is reversed, this way the chat- ter onset being permanently avoided and the performance kept in every moment at the highest possible level. The system was experimentally implemented on a transversal lathe. The results of tests on dedicatedly designed specimens are showing a machining productivity significant increase, in conditions of a stable cutting process. The system is simple, and it can be easily added to the existing CNC machine tools, without important modifications. Keywords Stability control system . Stability control strategy . Stability limit proximity . Online monitoring . Cutting force signal featuring . Turning 1 Introduction The machining performance can be characterized by product quality (both dimensional part accuracy and part surface texture), but at the same time by process efficiency. Unfor- tunately, quality and efficiency are going, in principle, one against the other: for example, a cutting regime too intense might damage the quality (e.g., because of vibrations which could appear), while good properties of generated surfaces require (at least at first look) a lower productivity. As it is shown in review papers [1, 2], a wide number of researches were performed during recent years concerning the machining system control, in order to improve the per- formances concerning machining productivity and quality. At the same time, various solutions were imagined to fight against the negative consequences brought by vibrations occurrence, as instability main form of coming to the fore. As regards the chatter control strategies, there are, in principle, two approaches: – Off-line control (chatter prediction), based on stability charts and consisting in choosing the cutting regime such as the system operating point is placed in the stability domain, and – Online control (chatter suppression), based on chatter detection followed by its suppression, either by chang- ing the cutting regime parameters (most often meaning, in fact, their diminution) or by applying other technical solutions—for example cutting speed variation [3–5] or cutting tool oscillation [6]. The strategies in implementing these approaches have the following drawbacks. In case of the first one, the inherent modification of the relative position between the system op- erating point and the stability limit, which might be caused by different factors, cannot be considered. For this reason, the G. R. Frumusanu (*) : I. C. Constantin : V. Marinescu : A. Epureanu Manufacturing Science and Engineering Department, “Dunarea de Jos” University of Galati, Domneasca str.111, 800201 Galati, Romania e-mail: gabriel.frumusanu@ugal.ro Int J Adv Manuf Technol (2013) 64:643–657 DOI 10.1007/s00170-012-4074-7