Search

Turning slender components is a critical task since workpiece flexibility entails relevant deformations during the process, leading to potential loss of accuracy, lower machining efficiency, and higher manufacturing costs. In this paper, a compensation strategy for diametral error in turning of slender workpieces is presented. The proposed method computes a toolpath that compensate diametral error based on the prediction of such error performed by a finite element-based approach. The developed algorithm automatically generates the compensated toolpath based on few inputs: nominal toolpath, workpiece material, tool geometry, stock dimensions, and fixturing system. First, nominal toolpath is analyzed and discretized, then at each step, workpiece deflection is estimated by coupling the FE model of the workpiece (automatically generated using Timoshenko beam elements) and the cutting forces model. Material removal is considered in the process by updating the geometry of the stock at each step of the machining cycle. Using the predicted deformation of the workpiece the compensated toolpath is generated and the toolpath ISO-standard file is updated. The proposed algorithm was experimentally validated on four case studies: three single diameter bars and a multi-diameter shaft. The results demonstrate the accuracy of the proposed predictive approach, with small deviations in estimating average diametral error (less than 6 μm). Furthermore, it has been demonstrated that the compensated toolpath is successful in reducing the diametral errors by at least 50%, as well as smoothing the error shape, confirming that providing an accurate prediction of the shape error could represent an effective approach for its reduction. The proposed methodology could form the basis of a toolpath simulation and optimization software, useful for machining shops that deals with slender shafts turning. [ABSTRACT FROM AUTHOR]

Among the chatter suppression techniques in milling, active fixtures seem to be the most industrially oriented, mainly because these devices could be directly retrofittable to a variety of machine tools. The actual performances strongly depend on fixture design and the control logic employed. The usual approach in the literature, derived from general active vibration control applications, is based on the employment of adaptive closed-loop controls aimed at mitigating the amplitude of chatter frequencies with targeted counteracting vibrations. Whilst this approach has proven its effectiveness, a general application would demand a wide actuation bandwidth that is practically impeded by inertial forces and actuator-related issues. This paper presents the study of the performance of alternative open-loop actuation strategies in suppressing chatter phenomena, aiming at limiting the required actuation bandwidth. A dedicated time-domain simulation model, integrating fixture dynamics and the features of piezoelectric actuators, is developed and experimentally validated in order to be used as a testing environment to assess the effectiveness of the proposed actuation strategies. An extensive numerical investigation is then carried out to highlight the most influential factors in assessing the capability of suppressing chatter vibrations. The results clearly demonstrated that the regenerative effect could be effectively disrupted by actuation frequencies close to half the tooth-pass frequency, as long as adequate displacement is provided by the actuators. This could sensibly increase the critical axial depth of cut and hence improve the achievable material removal rate, as discussed in the paper. [ABSTRACT FROM AUTHOR]

Integrating sensors in machine tools for monitoring purpose entails dealing with different issues, not only related to accessibility and safety but also to measureable bandwidth and linearity of the sensors. Those factors could be related to the sensor itself but also to sensor–machine interaction that could drastically affect sensor performances and reliability. This paper presents a dedicated experimental investigation of the actual response of microphone transducer inside the machine-tool chamber, highlighting the effects of the machine-tool chamber in altering response linearity. The identified response is then processed with specifically developed equalization filters to correct the measured response and rescale the amplitude of frequency contributions, as required by most chatter detection techniques. The main aspect of both the experimental identification procedure and the development of an effective correction approach are presented and discussed. Finally, the technique is tested in processing signals acquired in experimental chatter tests to estimate the achievable improvements. [ABSTRACT FROM AUTHOR]

Tool-tip frequency response function (FRF) is essential to predict chatter vibration in milling. This key input can be acquired by experimental tests, but a new test has to be performed for every tool clamped on the machine. To avoid such time-consuming procedures, receptance coupling methods have been developed, allowing coupling of the experimental dynamic response of the machine to the numerical model of the tool. Such techniques require joint rotation response, which is hard to experimentally identify. Inversion of receptance coupling technique is usually performed on additional experimental measurements to overcome this issue. This procedure amplifies measurement uncertainties, reducing accuracy of the coupling approach. In this article, a novel receptance coupling technique is presented. Machine and toolkit are connected through two distinct points, eliminating the experimental phase and computation of rotational degrees of freedom (DOFs). Only translation responses are required, acquired by a single test setup. Proposed technique was experimentally validated on different case studies. [ABSTRACT FROM AUTHOR]

• A method to identify depths of cut in 2.5-axis milling is proposed. • Normalized frequency spectrum of total cutting force is exploited. • The method does not require information about cutting direction or force coefficients. • Analytical equations to predict cutting force spectrum are provided. • The method could lay the ground for a force-based cutting parameters monitoring system. This paper presents a novel approach to identify both radial and axial depth of cut in 2.5-axis peripheral milling operations using cutting force signals analysed in the frequency domain (i.e., cutting force spectrum). In detail, the method exploits the normalized cutting force spectrum, which is directly obtained through dedicated analytical formulations, to estimate depths of cut. The proposed approach is promising and differs from previous works since it does require nor the cutting force coefficients or cutting force direction neither a dedicated instrumentation. The developed method was numerically and experimentally validated in different cutting conditions. The results obtained show that depths of cut are identifiable with a maximum absolute error less than 0.4 mm, proving that the proposed approach could be a solid foundation for a force based cutting condition monitoring system in peripheral milling. [ABSTRACT FROM AUTHOR]

In peripheral milling, surface accuracy is crucial for the quality of the machined components, and it is one of the reasons why milling is still essential in the manufacturing field. Nonetheless, both static phenomena, like tool deflections, and dynamic issues such as forced vibrations, impact on the accuracy of the components causing surface errors. In this context, the prediction of surface error is an important tool to guarantee surface accuracy and increase productivity at the same time. This paper presents a novel approach to predict surface location error in 2.5-axis peripheral milling operations considering the stiffness variation along the axial depth of cut. The proposed approach discretizes the endmill in small discs, and it evaluates analytically the cutting force along the cross-feed direction for each disc in the frequency domain. Then, tool dynamic stiffness, which is expressed in terms of frequency response function (FRF), is computed considering the stiffness variation along the tool axis. Finally, the presented approach couples the cutting forces with the tool stiffness, and it evaluates surface error along the tool axis. The method was experimentally tested in different conditions to verify its effectiveness and its limits. The results obtained show how static and dynamic aspects and stiffness variation contribute to surface errors in peripheral milling operations. [Display omitted] • Surface location error along the axial depth of cut in 2.5-axis milling is accurately predicted. • Analytical formulations for cutting forces in frequency domain are proposed. • A RCSA-based approach to predict tool FRF variation along the axial depth of cut is presented. • The proposed approach considers both forced vibrations and variation of the tool dynamic stiffness. • Accuracy of the method is proven by experimental validation on several milling tests. [ABSTRACT FROM AUTHOR]

Electrospinning is a technology used for the production of nanometric fibers starting from a solution of material spun by a needle in an electrostatic field. The jet starts from a needle and its diameter is reduced thanks to the instability of the process that stretch the fiber till nanometric dimension. The productivity of a single needle is very low so multiple needles facing the same collector is the simplest and most used apparatus to achieve an adequate productivity. However jets so produced repel each other making their path diverge from the axis of the needles; this effect can be corrected introducing a system of electrostatic lenses. As soon as the diameter of the filament is commonly tens of nanometers the FE simulation of the process in the work area is nearly impossible due to the very large number of elements required. This paper presents an hybrid approach that couple together an analytical analysis with an FE approach in order to reduce the computational time. The developed model is able to predict the divergence of electrospun multi-jets with and without the corrective effect of an electrostatic lens. The developed approach has been validated thanks to laboratory experimental tests that has proven its accuracy. A simulated test campaign using the Design of Experiment approach has been performed to create a mathematical model to predict the deflection of the filaments with different process parameters. [ABSTRACT FROM AUTHOR]

Chatter vibrations in machining have collected the interest of several research activities in the last decades, mainly due to its detrimental effect on productivity and surface quality. Several approaches and techniques have been developed to mitigate the effect of these unstable vibrations, but the required expertise and setup time usually prevent the widespread industrial application. Retrofittable intelligent active fixtures, capable of monitoring the process in real-time and exert adequate counter-excitations, could allow to overcome some of these limitations. Nevertheless, the use of these devices was always limited to the mitigation of structural chatter vibrations, which are the ones generally fitting in the device bandwidth. This paper deals with the development of an active fixture using an alternative control strategy that exploits low-frequency excitations, with the purpose of mitigating the chatter vibrations at frequencies exceeding the device bandwidth. The paper covers the main aspects of the fixture design and mainly focuses on the theoretical and practical aspects of the followed approach for the control. An experimental tests campaign is finally discussed to show that the proposed approach is actually effective in mitigating chatter vibrations. [ABSTRACT FROM AUTHOR]

The set-up of machining parameters for non-ferric materials such as wood and wood-based materials is not yet defined on a scientific basis. In this paper, a new rapid experimental method to assess the specific cutting coefficients when routing isotropic and orthotropic wood-based materials is presented. The method consists of routing, with different depths of cut, a given material previously machined to a round shape after having it fixed on a dynamometric platform able to measure the cutting forces. The execution of subsequent cuts using different depths of cut allows the calculation of the specific cutting coefficients. With the measurement being done during real routing operations, a method to remove machine vibrations was also developed. The specific cutting coefficients were computed for the whole set of grain orientations for orthotropic materials and as an average for isotropic ones. The aim of this paper is to present and validate the whole method by machining selected materials such as Polytetrafluoroethylene—PTFE (isotropic), Medium Density Fiberboard—MDF (isotropic), beech Laminate Veneer Lumber—LVL (orthotropic) and poplar LVL (orthotropic). The method and the proposed analysis have been shown to work very effectively and could be used for optimization and comparison between materials and processes. [ABSTRACT FROM AUTHOR]