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Chiappini E.,Laboratorio MUSP | Tirelli S.,Laboratorio MUSP | Albertelli P.,Polytechnic of Milan | Strano M.,Polytechnic of Milan | Monno M.,Polytechnic of Milan
International Journal of Machine Tools and Manufacture | Year: 2014

Titanium alloys are hard-to-cut materials and need to be machined at relatively low cutting speeds with obvious negative consequences on the profitability of machining. In order to enhance material removal rate (MRR), a strategy that relies on higher depths of cut could be chosen if vibrational issues due to regenerative chatter did not occur. A lot of research was done to suppress regenerative chatter without detrimental effects on productivity. One of the most interesting chatter suppression methods, mainly due to its flexibility and relative ease of implementation, is spindle speed variation (SSV), which consists in a continuous modulation of the nominal cutting speed. Sinusoidal spindle speed variation (SSSV) is a specific technique that exploits a sinusoidal law to modulate the cutting speed. The vast scientific literature on SSV was mainly focused on cutting process stability issues fully neglecting the study of the mechanics of chip formation in SSV machining. The aim of this work is to fill this gap: thus, finite element method (FEM) models of Ti-6Al-4V turning were setup to simulate both SSSV and constant speed machining (CSM). The models consider both the micro-geometry of the insert and the coating. Numerical results were experimentally validated on dry turning tests of titanium tubes exploiting the experimental assessment of cutting forces, cutting temperatures and chip morphology. Tool-chip contact pressure, tool engagement mechanism and the thermal distribution in the insert are some of the analysed numerical outputs because they cannot be easily assessed by experimental procedures. These quantities were useful to compare thermo-mechanical loads of the insert both in CSM and SSSV machining: it was observed that the loads significantly differ. Compared to CSM, the modulation of the cutting speed involves a higher tool-chip contact pressure peak, a higher maximum temperature and higher temperature gradients that could foster the main tool wear mechanisms. © 2013 Elsevier Ltd.

Grasso M.,Polytechnic of Milan | Goletti M.,Laboratorio MUSP | Annoni M.,Polytechnic of Milan | Colosimo B.M.,Polytechnic of Milan
International Journal of Abrasive Technology | Year: 2013

In waterjet/abrasive waterjet (WJ/AWJ) cutting systems, the components of both the ultra high-pressure (UHP) intensifier and the cutting head are subject to faults and performance degradation. Abrasive particles are responsible for focusing tube wear and orifice breakage, whereas challenging pressure conditions are responsible for the wear and cracks of UHP pump components. The impact of these factors on quality and productivity leads to the need for reliable condition-monitoring systems in WJ/AWJ shop floors. This paper investigates a new approach for the online health condition assessment of both UHP pump and cutting head components by using a single type of information source, i.e., the plunger displacement signal. A multivariate analysis of variance (MANOVA) was performed to study the effects of actual faulty components on the acquired signals during AWJ cutting. The results demonstrate that plunger displacement signals are suitable for detecting and identifying critical faults in WJ/AWJ cutting systems. Copyright © 2013 Inderscience Enterprises Ltd.

Albertelli P.,Polytechnic of Milan | Goletti M.,Laboratorio MUSP | Monno M.,Polytechnic of Milan
Procedia CIRP | Year: 2013

This paper presents a new Receptance Coupling Substructure Analysis (RCSA) approach. The technique represents a valid instrument to predict Frequency Response Function, and consequently chatter free cutting conditions, of a not previously tested mill. The proposed RCSA methodology exploits experimental dynamic compliance measurements and the Finite Element (FE) model of a tool to estimate, through a new defined formulation, both the matrices of receptances of the spindle-tool holder assembly and the tool-tool holder connection stiffness. These data, together with the FE model of any new desired mill, can be used to estimate the relative tool tip dynamic compliance. The suggested formulation basically overcomes the drawbacks in the estimation of "rotation/ torque" receptances that often limits the accuracy of the classical RCSA. The proposed innovative approach was experimentally tested and validated.

Albertelli P.,Polytechnic of Milan | Goletti M.,Laboratorio MUSP | Monno M.,Polytechnic of Milan
International Journal of Machine Tools and Manufacture | Year: 2013

The cutting process stability depends on machine tool dynamics that is strongly influenced by the tool. Receptance coupling substructure analysis (RCSA) can be used to estimate the tool tip dynamic compliance and consequently the chatter free cutting conditions when the machine is equipped with a tool that has not been previously tested. This methodology can be particularly useful on real shop-floors where a lot of different tool-tool holder configurations are generally used. RCSA typically combines experimental dynamic compliance measurements performed on a machine equipped with a selected tool and the finite element (FE) models of both the already tested tool and the new ones. This paper presents a new receptance coupling substructure analysis (RCSA) approach that overcomes the drawbacks in the estimation of the receptances that contain rotational and moment contributes. This indeed often limits the accuracy of the RCSA techniques presented in other scientific works. The proposed formulation allows to better estimate both the matrices of receptances of the spindle-tool holder assembly and the tool-tool holder connection stiffness. Those quantities are used, together with the FE model of the new tool, to predict the unknown tool tip dynamic compliance. Some useful guidelines to implement the proposed RCSA are also defined: they allow to manage the procedure accuracy considering the experimental methodology typically used to measure dynamic compliances. The proposed innovative RCSA is experimentally tested and validated. © 2013 Elsevier Ltd.

Di Mauro M.,Polytechnic of Milan | Maggioni M.F.,Polytechnic of Milan | Grasso M.,Polytechnic of Milan | Grasso M.,Laboratorio MUSP | Colosimo B.M.,Polytechnic of Milan
Procedia CIRP | Year: 2016

In industrial applications, the continuously growing development of multi-sensor approaches, together with the trend of creating data-rich environments, are straining the effectiveness of the traditional Statistical Process Control (SPC) tools. Industrial data streams frequently violate the statistical assumptions on which SPC tools are based, presenting non-normal or even mixture distributions, strong autocorrelation and complex noise patterns. To tackle these challenges, novel nonparametric approaches are required. Machine learning techniques are suitable to deal with distributional assumption violations and to cope with complex data patterns. Recent studies showed that those methods can be used in quality control problems by exploiting only in-control data for training (such a learning paradigm is also known as "one-class-classification"). In recent studies, the use of distribution-free multivariate SPC methods was proposed, based on unsupervised statistical learning tools, pointing out the difficulty of defining suitable control regions for non-normal data. In this paper, a Self-Organizing Map (SOM) based monitoring approach is presented. The SOM is an automatic data-analysis method, widely applied in recent works to clustering and data exploration problems. A very interesting feature of this method consists of its capability of providing a computationally efficient way to estimate a data-adaptive control region, even in the presence of high dimensional problems. Nevertheless, very few authors adopted the SOM in an SPC monitoring strategy. The aim of this work is to exploit the SOM network architecture, and proposing a network design approach that suites the SPC needs. A comparison study is presented, in which the process monitoring performances are compared against literature benchmark methods. The comparison framework is based on both simulated data and real data from a roll grinding application. © 2016 The Authors.

Carroccia A.,Polytechnic of Milan | Grasso M.,Polytechnic of Milan | Grasso M.,Laboratorio MUSP | Maggioni M.,Polytechnic of Milan | Colosimo B.M.,Polytechnic of Milan
Procedia CIRP | Year: 2016

The machine tool industry is facing the need to increase the sensorization of production systems to meet evolving market demands. This leads to the increasing interest for in-process monitoring tools that allow a fast detection of faults and unnatural process behaviours during the process itself. Nevertheless, the analysis of sensor signals implies several challenges. One major challenge consists of the complexity of signal patterns, which often exhibit a multiscale content, i.e.; a superimposition of both stationary and non-stationary fluctuations on different time-frequency levels. Among time-frequency techniques, Empirical Mode Decomposition (EMD) is a powerful method to decompose any signal into its embedded oscillatory modes in a fully data-driven way, without any ex-ante basis selection. Because of this, it might be used effectively for automated monitoring and diagnosis of manufacturing processes. Unfortunately, it usually yields an over-decomposition, with single oscillation modes that can be split into more than one scale (this effect is also known as "mode mixing"). The literature lacks effective strategies to automatically synthetize the decomposition into a minimal number of physically relevant and interpretable components. This paper proposes a novel approach to achieve a synthetic decomposition of complex signals through the EMD procedure. A new criterion is proposed to group together multiple components associated to a common time-frequency pattern, aimed at summarizing the information content into a minimal number of modes, which may be easier to interpret. A real case study in waterjet cutting is presented, to demonstrate the benefits and the critical issues of the proposed approach. © 2016 The Authors.

Albertelli P.,Polytechnic of Milan | Mussi V.,Laboratorio MUSP | Monno M.,Polytechnic of Milan
International Journal of Advanced Manufacturing Technology | Year: 2014

Regenerative chatter vibrations generally limit the achievable material removal rate in machining. The diffusion of spindle speed variation (SSV) as a chatter suppression strategy is mainly restricted to academy and research centers. A lack of knowledge concerning the effects of non-stationary machining is still limiting its use in real shop floors. This research is focused on the effects of spindle speed variation technique on tool duration and on wear mechanisms. No previous researches have been performed on this specific topic. Tool wear tests in turning were carried out following a factorial design: cutting speed and cutting speed modulation were the investigated factors. The carbide life was the observed process response. A statistical approach was used to analyze the effects of the factors on the tool life. Moreover, the analysis was extended to the wear mechanisms involved during both constant speed machining and SSV. The worn-out carbide surfaces were examined under a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. Significant differences were appreciated. It was observed that SSV tends to detach the coatings of the inserts, entailing a mechanism that is quite unusual in wet steel turning and thus fostering the wear of the tool. The performed analysis allowed to deduce that the intensified tool wear (in SSV cutting) is mainly due to thermo-mechanical fatigue. © 2014 Springer-Verlag London.

Goletti M.,Laboratorio MUSP | Grasso M.,Laboratorio MUSP | Annoni M.,Polytechnic of Milan
Procedia CIRP | Year: 2013

The most important advantages of water jet are the capability to cut nearly every material, the low cutting temperature and the negligible cutting forces. When end users are interviewed, most of them point out that the most critical problem of water jet machines is the reliability of the system components, together with the difficulty in estimating their life time. As far as the UHP (Ultra High Pressure) intensifier is concerned, there are several components that work under extreme fatigue conditions, as the pressure inside the cylinders can reach 400 or even 600 MPa. Nearly every critical component is located into the UHP intensifier, but different failure scenarios can be envisaged, leading to different pattern deviations from nominal behavior conditions. In this paper a correlation analysis on multiple signal features with the health status of the machine is presented. Then a multi-sensor based monitoring approach is discussed and tested on a real case study: it is based on the usage of control charts for in-control region definition and possible detection of faults.

Strano M.,Polytechnic of Milan | Mussi V.,Laboratorio MUSP | Monno M.,Polytechnic of Milan
International Journal of Material Forming | Year: 2010

Design and manufacturing issues are here studied about the production of hollow structures made of an outer high resistance skin and a metal foam filler. These structures can be very useful as reinforcements against lateral impacts of vehicles. In car bodies, at the waistline or door height, the available space is very limited. Compact bars with light weight, high energy absorption efficiency and limited maximum deflection (i. e. high maximum load) are required. The skin of the proposed structure provides strength and stiffness and can be assembled to the vehicle body. The foam core provides energy absorption properties. The combination of non conventional technologies (hydroforming and metal foams) allows for the production of lightweight, high performance components, particularly suited for flexural resistance in terms of amount of energy absorbed for a given maximum load. A performance indicator y is proposed with the aim of comparing the performance of side impact absorbers with different cross sections and made of different materials. The tube hydroforming process is investigated as a suitable way for performance improvement of metal foam filled structures in side impacts, particularly for non-constant section bars. © 2010 Springer-Verlag France.

Albertelli P.,Polytechnic of Milan | Mussi V.,Laboratorio MUSP | Ravasio C.,University of Bergamo | Monno M.,Polytechnic of Milan
Procedia CIRP | Year: 2012

Spindle Speed Variation (SSV) is a well known technique to suppress regenerative chatter vibration both in turning and milling operations but a lack of knowledge regarding the effects of non stationary cutting conditions is still limiting its diffusion in the industrial scenario. In this paper an experimental study regarding the effects of Spindle Speed Variation technique on tool wear in steel turning is presented. The experimental tool wear tests were arranged and performed following a full factorial design: the cutting speed and the cutting speed modulation were the main investigated factors. The flank wear width was the main considered process response and it was monitored continuously during wear tests up to the end of the tool life. The effects of the factors were analyzed through the Analysis of Variance (ANOVA) approach. © 2012 The Authors.

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