Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave, Aug 27, 2022
This is a copy of the published version, or version of record, available on the publisher's websi... more This is a copy of the published version, or version of record, available on the publisher's website. This version does not track changes, errata, or withdrawals on the publisher's site.
On the effect of testing uncertainties in the homologation tests of motorcycle helmets according to ECE 22.05
International Journal of Crashworthiness, Oct 1, 2011
Industrial products designed for a specific task need to prove their capability to fulfil their d... more Industrial products designed for a specific task need to prove their capability to fulfil their design goal through experimental homologation procedures. Homologation standards define the necessary steps for these experimental tests in a very detailed manner but still are not entirely capable of accounting for any imprecisions in the definition of the testing procedure and variability in its carrying out.
Space Telescopes and Instrumentation 2020: Optical, Infrared, and Millimeter Wave, Dec 13, 2020
This is a copy of the published version, or version of record, available on the publisher's websi... more This is a copy of the published version, or version of record, available on the publisher's website. This version does not track changes, errata, or withdrawals on the publisher's site.
In this paper a technique to compute the 3-axis toolpath for a thin-wall component is presented a... more In this paper a technique to compute the 3-axis toolpath for a thin-wall component is presented aiming at maximizing the engagement conditions, keeping the geometry in tolerance. The toolpath generation is based on the static deflection of the component, predicted by coupling a mechanistic model of the cutting forces with a FE model of the workpiece, including, at each machining step, material removal mechanism. The algorithm follows the milling cycle in the reverse order: starts from the finished part, computes the maximum allowable radial depth of cut, and, adding material accordingly, generates the toolpath until the stock is built. The proposed technique has been experimentally validated, proving its effectiveness.
The setup of machining parameters for non-ferric materials such as wood and wood-based materials ... more The setup 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.
The modeling of milling forces is a crucial issue to understand milling processes. In the literat... more The modeling of milling forces is a crucial issue to understand milling processes. In the literature, many force models and experiments to identify force coefficients are found. The objective of this article is to develop a new approach, based on the traditional average force method, able to measure and compute the cutting coefficients for end mills used in plunging operations. This model has been used to evaluate the effect of the radial engagement on the cutting coefficients themselves, proposing a new strategy to update these values for different cutting parameters. This dependency of the cutting coefficient is particularly important for the determination of the stability lobe diagrams, used to predict the chatter conditions. In this article, the method to assess the cutting coefficients, the results of the experimental tests, and the effect of condition-dependent cutting coefficients on process stability are presented.
International Conference on Space Optics — ICSO 2020, Jun 11, 2021
The performance of as-built optical instruments strongly depends on thermal and structural loads,... more The performance of as-built optical instruments strongly depends on thermal and structural loads, since these boundary conditions can affect the geometry of optical surfaces. Variations of temperature influence the volume, and the shape, of the structure proportionally to the coefficient of thermal expansion of the material, while mechanical loads, like gravity, may induce deformations on the optical elements according to the set of applied constraints. Those effects can introduce aberrations that degrade the performance of the optical system. Since software for optical and thermo-structural analysis are usually different, a coupling methodology between these two fields of physics is needed. This is a step-by-step procedure through many platforms. In this work, the procedure devised and used by the authors will be presented. At first, a thermo-mechanical analysis (depending on the loads involved) has to be performed, in order to obtain the final deformed geometry of the optical structure; COMSOL Multiphysics is the finite element solver (FEM) used for these analyses. Then an output data file, containing the coordinates of points belonging to the optical surface, can be generated. The output data are elaborated by a MATLAB routine that allows to convert the set of points into an n-th polynomial expression that best fits the surface data. The fitted polynomial surface is hence imported in ZEMAX ray-tracing software to study the optical performances of the system and the effects of thermo-mechanical loads.
Integrating sensors in machine tools for monitoring purpose entails dealing with different issues... more 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.
Active fixtures represent one of the most industrially relevant alternatives among active chatter... more Active fixtures represent one of the most industrially relevant alternatives among active chatter control techniques in milling, even though control logics and actuation strategies could directly reflect on their effectiveness. Closed-loop controls targeted in the chatter frequency range are commonly adopted for this purpose, but this approach lacks of applicability when chatter frequency exceeds the achievable actuation bandwidth. The purpose of this work is to investigate the effectiveness of potential low-frequency actuation strategies in suppressing chatter vibrations. A dedicated time-domain simulation model, developed and validated by authors, is used to test different actuation strategies in order to highlight the most relevant factors in assessing actuation effectiveness. The simulation results demonstrated that employing actuation frequencies close to the first half-harmonic of the tooth-pass frequency could disrupt the regenerative effect. This allows the mitigation and suppression of chatter phenomenon, increasing the critical axial depth of cut, as discussed in the paper.
International Journal of Machine Tools & Manufacture, Oct 1, 2018
Chatter vibration induces a characteristic pattern on the milled surface, known as chatter marks,... more Chatter vibration induces a characteristic pattern on the milled surface, known as chatter marks, causing a poor surface quality. While several works deal with the prediction of the machined surface in stable condition, surface under chatter vibration has not been extensively studied: it is not clear how vibrations at high chatter frequency return highly spaced chatter marks on the surface. This paper investigates the chatter marks generation mechanisms focusing on this issue, i.e., on the surface spectral proprieties. The generation of the surface profile is regarded as a problem of sampling at the tooth pass frequency (in the time domain) and reconstruction (in the spatial domain) of the cutting tool displacements. Using this analogy, the paper highlights two main effects (aliasing and pseudo moiré), proposing specific formulations. The method is validated by a numerical investigation, based on a surface generation model coupled with a time-domain simulator of the milling process. Finally, an experimental validation is proposed. The formulations presented in this work provide an insight in the relation between chatter frequency and chatter marks pattern. Therefore, if the chatter frequency pattern over the spindle speed is known (e.g., identified via simulations or experiments), the proposed method could support the selection of cutting parameters which results in an acceptable surface, even in highly unstable cutting conditions.
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Papers by Antonio Scippa