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

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

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

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

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.

Indirect model based estimation of cutting force and tool tip vibrational behavior in milling machines by sensor fusion

Real time prediction of cutting tool condition and machined surface finish have been attractive research objectives over the last decades. However, providing practical and reliable solutions is still a demanding task for milling machine tools. One of the most challenging literature goals is to obtain a robust estimation of the cutting forces through indirect sensor measurements since many process and tool related quantities are indirectly linked to cutting forces. Another challenging issue in machining process monitoring and control is prediction of surface finish and quality. As the vibration plays a major role in the surface generation, this can be done by accurate prediction of the vibrational displacements at the tool tip during machining operation. In this paper, a novel model based estimation of cutting force and tool tip acceleration is designed and tested based on data fusion of different sensors measurements. In this context, two sensors (piezoelectric accelerometer and eddy-current displacement both mounted inside the spindle structure) have been utilized to acquire the experimental signals over a wide range of frequencies. In order to predict the above mentioned quantities, an optimal state estimator based on Kalman Filter (KF) is used. The models have been obtained by system identification method based on experimental measurements performed on a machine tool. The model based estimator is fed by real data. The results show that the estimation of the impulse force and tool tip acceleration can be achieved accurately in low and high frequency ranges by assigning different weights to the measurement sensors

Energy assessment of different cooling technologies in Ti-6Al-4V milling

Manufacturing craves for more sustainable solutions for machining heat-resistant alloys. In this paper, an assessment of different cooling lubrication approaches for Ti6Al4V milling was carried out. Cryogenic cutting (liquid nitrogen) and conventional cooling (oil-based fluid) were assessed with respect to dry cutting. To study the effects of the main relevant process parameters, proper energy models were developed, validated and then used for comparing the analysed cooling lubrication strategies. The model parameters were identified exploiting data from specifically conceived experiments. The power assessment was carried out considering different perspectives, with a bottom-up approach. Indeed, it was found that cryogenic cooling, thanks to a better tribological behaviour, is less energy demanding (at least 25%) than dry and conventional cutting. If the spindle power is considered, lower saving percentages can be expected. Cryogenic cooling showed its best energy performance (from 3 to 11 times) with respect to conventional cutting if the machine tool perspective is analysed. Considering even the primary energy required for producing the cutting fluids, the assessment showed that cryogenic cooling requires up to 19 times the energy required for conventional cutting

Energy saving opportunities in direct drive machine tool spindles

The aim of the work is to carry out a comprehensive assessment of the energy saving opportunities linked to the introduction of direct drives solutions in machine tool spindle systems. Although there is a clear industrial trend towards the replacement of the traditional motor-transmission based spindle solutions, there is a lack of scientific studies focused on the associated energy-related aspects. For this purpose, two spindle units characterized by similar performances were analyzed from the energy consumption, losses and efficiency perspective. Empirical spindle system energy models were developed exploiting experimental tests performed on a motor test bench used for reproducing different machining conditions. The identified models were used to estimate the energy savings that can be achieved substituting the traditional gearbox-based solution with the novel direct-drive spindle. The analysis was carried out considering a realistic production scenario for the machine equipped with the analyzed spindle. It was demonstrated that about 7% of the energy absorbed by the overall machine can be saved and that this improvement accounts for the 147% of the requested cutting energy. For sake of generality, the analysis was repeated considering different production scenarios and ways of using the machine. It can be concluded that the achievable energy savings are even robust to the change of the executed machining operations

Development of a generalized process-based observer for indirect monitoring of cutting force and tool vibration in milling

In machining processes, cutting forces and vibration measurements are essential to allow cutting process and tool conditions monitoring. Moreover, in order to get 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. Although in the specific literature some cutting force observers, based on Kalman’s filter theory, were developed, a general cutting force observer that is suitable for working in any cutting condition is still missing. Indeed, one of the limitations of the existing approaches is connected to the capability of estimating the cutting forces/vibrations even when the regenerative chatter affects the cutting. This drawback is mainly due to the fact that the model typically used for developing the observer considers only the machine dynamics, but it does not consider the coupling with the cutting process. In order to overcome this shortcoming, in this paper an observer based on a combined machine tool dynamics-cutting process model was conceived. In fact, even the contribution due to the regeneration phenomenon was considered in the observer development. The innovative observer was tested through simulations of stable and unstable cuttings. The estimating properties were compared to the ones achievable using the approach already adopted in the literature. The observed results confirmed the enhancement of the observer monitoring skills in milling operations affected by regenerative chatter