Analysis of the Tool Stick-Out Influence on Machining Chatter

Increased stability in machining processes is highly desired by all machining industries when vibrations and specially chatter occur. This phenomenon is defined as a self-excited vibration that occurs due to the regeneration of waviness of the workpiece surface. In machining industry, the trend is to rely on the trial and error method or mere experience when deciding the machining spindle speeds, depths of cut and tool stick-outs, all of which are parameters directly related to chatter occurrence. Currently, the shortest possible tool stick-out is chosen by default, but literature has proven that longer stick-outs may bring some advantages when it comes to material removal rates. Aiming to prove this theory, this paper will discuss the influence of the tool stick-out on machining chatter occurrence. To that end, the effect of the tool stick-out on the modal parameters of the system, on the Stability Lobe Diagram (SLD) and on productivity will be analysed. Therefore, a number of Tap-Tests to different tool/tool-holder/stick-out combinations have been performed, in order to gather the data (FRFs and SLDs) where the analysis is based on. Last but not least, some machining tests have been conducted aiming to compare the theoretical chatter occurrence conditions, provided by the SLD, with the experimental ones. For that, two Al5083 workpieces have been slot milled under different cutting conditions, facilitating the unexpected results wherein the conclusions have been based upon.

Beat Effect in Machining Chatter: Analysis and Detection

In machining processes, regenerative chatter is an unstable vibration which adversely affects surface finish, cutting tools and spindle bearings. Under some cutting conditions, the beat effect, an interference pattern between two periodical vibrations of slightly different frequencies, has been a common phenomenon where the amplitude of chatter vibration tends to increase and decrease periodically. Until now, few studies have been conducted to analyze the beat effect in machining chatter. On the other hand, researchers have developed various chatter detection methods with the objective to timely avoid detrimental effects induced by chatter. However, none of existing chatter detection methods in the literature has ever considered the beat effect. The neglect of the beat effect will adversely affect the effectiveness of these methods and even result in false alarms. In this paper, the significance level and the mechanism of the beat effect in turning chatter are analyzed by the stability lobe diagram and time domain simulation. Afterward, a multiscale wavelet packet entropy (MWPE) method is proposed to detect machining chatter regardless of the occurrence of the beat effect. The determination strategy of the scale factor in the MWPE is presented based on the beat period, whose relationship with the damping ratio and spindle speed is derived analytically in orthogonal turning scenarios. Finally, machining tests are conducted to verify the feasibility and effectiveness of the proposed chatter detection method with respect to the presence and absence of the beat effect.

Novel Direct Model for Machining Regenerative Chatter

Regenerative machining chatter or resonance in the machining process has traditionally been modeled with the stability lobe approach. This paper presents a new time based direct simulation model and compares it with traditional stability lobe modeling. The direct model has the ability to discriminate directional and time information, resulting in a number of advantages over frequency-based stability lobe analysis.