The analysis of tool life and wear mechanisms in spindle speed variation machining

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

A simulation approach for predicting energy use during general milling operations

Manufacturing processes have a high impact on global energy consumption. Machine tool’s environmental impact is typically dominated by the energy absorbed during the use phase. Energy efficiency is progressively considered as an additional performance index in comparing alternative machines, process planning, and machining strategies. For this purpose, this paper proposes a simulation approach that estimates the energy used by a machine tool in producing a generic workpiece by general milling operations. The developed tool simulates the execution of a standard ISO part program, basing on an explicit geometric and mechanistic representation of the cutting process, coupled with an energy model of the machine tool reproducing the power consumption of spindle, axes, and auxiliary units. Energy models were identified by an experimental characterization procedure that can be easily adopted in industrial contexts. The simulator was validated comparing the estimated energy with measurements performed on different cutting tests, evaluating also its computational effort. Moreover, the simulator performances were compared to alternative energy evaluation methods proposed in the literature

Model-based broadband estimation of cutting forces and tool vibration in milling through in-process indirect multiple-sensors measurements

In machining processes, cutting forces measurement is essential to allow cutting process and tool conditions monitoring. Moreover, in order to have information about the quality of the milled part, the amplitude of the tool tip vibration would be very useful. Since both the measurements are extremely complicated especially in an industrial scenario, in this study, an in-process model-based estimator of cutting forces and tool tip vibration was designed and properly tested. The developed estimator relies on both a machine dynamic model and on indirect measurements coming from multiple sensors placed in the machine. The machine dynamic model was obtained through an experimental modal analysis session. The estimator was developed according to the Kalman filter approach. The fusion of multiple sensors data allowed the compensation of machine tool dynamics over an extended frequency range. The accuracy of the observer estimations was checked performing two different experimental sessions in which both the force applied to the tool and the tool tip vibration amplitude were measured. In the first session, the tool was excited with different sensorized hammers in order to appreciate the broad bandwidth of the performed estimations. In the second one, real cutting tests (steel milling) were done and the cutting forces were measured through a dynamometer; tool tip vibrations were measured as well. The experimental results showed that the indirect estimation of cutting forces and tool tip vibrations exhibit a good agreement with respect to the corresponding measured quantities in low and high frequency ranges. The contribution of this research is twofold. Firstly, the conceived observer allows estimating the tool tip vibrations that is a useful information strictly connected to the surfaces quality of the processed workpiece. Secondly, thanks to a multi-sensors approach, the frequency bandwidth is extended especially in the low frequency range

Experimental investigation of energy saving opportunities in tube bending machines

In the scenario of containing the global warming, devising energy savings strategies in industry has become a proper and urgent matter. Since manufacturing is one of the most energy demanding sectors, research and the linked industries started tackling this issue proposing new eco solutions. In this paper, an experimental investigation of the energy saving opportunities in tube bending machines is performed and critically discussed. The analysis is carried out comparing an electrical tube bender and a hydraulic machine of comparable size. The experimental measured are also used to fit energy models that are used to extend the comparison considering different working conditions of the tube- bending machines. The results show that relevant energy savings can be achieved introducing the electrical drives

Object-oriented modelling of a flexible beam including geometric nonlinearities

In this paper, an efficient approach for the modelling and simulation of slender beams subject to heavy inertial loads is presented. The limitations imposed by a linear formulation of elasticity are overcome by a second order expansion of the displacement field, based on a geometrical exact beam model. In light of this, the nonlinearities of the elastic terms are shifted as inertial contributions, which yields an expression of the equations of motion in closed form. Thanks to the formulation in closed form, the proposed model is implemented in Modelica, with particular care to the suitability of the model with respect to the Modelica Multibody library. After describing the model formulation and implementation, the paper presents some simulation results, in order to validate the model with respect to benchmarks, widely adopted in literature

Adult GH deficiency - the value of IGF-I estimation

In patients with growth hormone (GH) deficiency (GHD) the diagnostic value of IGF-I levels has been recently revisited. A normal IGF-I value does not exclude GHD, because its secretion is complex and depends by several factors other than GH, such as age, nutritional status, obesity, as well as catabolic illness. Due to the complexity and costs of GH stimulation tests, several authors have analyzed the predictive and diagnostic value of the concentration of plasma IGF-I in patients suspected for GHD. The evaluation of IGF-I is also determinant to individualized dose-titration strategies, able to avoid the common adult side effects of substitutive therapy with recombinant GH. Current recommendations in clinical practice for GH replacement therapy, in GHD adults, agree on GH dosing regimens to be individualized independently of body weight using IGF-I levels as a biomarker of the treatment. For these reasons, in a clinical setting, appropriate normative values in different age groups in a large healthy population must be established in single laboratories, while, considering the relatively small sex difference, a different reference range for sex seems not necessary. This review discusses the more recent debated issues in the literature on the role of IGF-I, as well as other IGF system components, in the management of adult patients with GHD

On the mechanics of chip formation in Ti-6Al-4V turning with spindle speed variation

"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. (C) 2013 Elsevier Ltd. All rights reserved.

The use of nematodes in assessing ecological conditions in shallow waters surrounding a Mediterranean harbour facility

The spatial distribution and structure of nematode assemblages in the area surrounding the harbour of Vado Ligure (Savona, NW Mediterranean) were studied in relation to the influence of natural and anthropogenic environmental factors. Stations were selected following an “anthropogenic gradient” from sites located near the city centre and its harbour to more pristine and distant sites. Sediment quality was determined by considering both sediment granulometric and chemical parameters (hydrocarbons, heavy metals, total organic matter, proteins, carbohydrates) as well as nematode abundance, diversity, life strategies, trophic structure and assemblage composition. A high correlation between environmental characteristics and the nematode response was found. On the basis of the comparison of these results, which identified three distinct sub-areas associated with different levels of environmental quality, a set of nematode indicator genera was selected for the future evaluation of quality status

RODIN project, Topology Optimization 2.0?

RODIN project is an attempt to propose a new kind of topology optimization tools. It has been motivated by the combination of two events: (1) the industrials demands for getting past serious limits identified in the available tools, (2) the advent of a new mathematical approach in the mid 2000's presenting very interesting properties. This project has been launched in July 2012 and is supported by French public funding. It is a collaborative project that gathers ten partners (ranging from academics to software editors and industrials end-users) and firmly aims at overcoming technical and scientific locks in the area of topology optimization. RODIN is therefore an ambitious and risky project that will possibly mark the birth of a new numerical tool