Gianni Campatelli

A heuristic approach to meet geometric tolerance in High Pressure Die Casting

Abstract In High Pressure Die Casting (HPDC), geometrical distortions usually happen during the cooling phase, due to the reduced cooling time and the high thermal gradient inside the product itself. This phenomenon affects most the thin walled products. The usual die design practice considers only the linear shrinking of the product during the cooling as a consequence of the difficult to take in account also the geometrical deformations. In this essay a simple finite element design strategy that allows the designer to improve the die shape is presented. The proposed approach uses an automatic iterative optimization technique based on a heuristic algorithm, which could be easily applied to most of the Finite Element (FE) commercial software: the basic concept of the method is simply to move the nodes defining the die surface in the opposite direction to the error due to the cooling phenomena. An automotive component has been selected as a case study: the aim was to improve the planarity tolerance of a planar surface of the casted product. Results show the efficiency of the proposed method that, despite its simplicity, is able to provide an optimal solution with a small number of iterations.

Real time detection and tracking of Gauzes by RFID UWB technique

The paper presents the implementation of the GUID (Gauzes UWB Identifier) system to control the path of gauzes and other medical instruments during surgical operations. The system allows tracking of these devices during the entire surgery, with particular reference to real-time localization of gauzes within the patients body. A precise localization of gauzes, available to the surgeon, permits an easy removal of these devices, which are sometimes difficult to identify by visual perception. The final objectives are the improvement of the patient safety, of surgeon working procedures, and the reduction of stress conditions of the surgical staff. The GUID prototype is based on RFID Ultra Wide Band(UWB) technology and the experimental phases were carried out in laboratory using the tags both in air and in biological tissue. The results show the performance of a correct identification of the tags and the accuracy of the calculated position with respect to the real position of the tags.

Numerical investigation of chatter suppression in milling using active fixtures in open-loop control

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.

Solutions and Business Models for Wireless Charging of Electric Vehicles

This article describes possible scenarios for wireless charged electric vehicles, as they are discussed within the UNPLUGGED project. It gives a brief introduction into wireless technology and explains the three possible implementation steps for charging electric vehicles: stationary, static en-route and dynamic en-route. Based on these scenarios the impact of wireless charging on future mobility, especially in urban environments is discussed.

Effects of cutting conditions on forces and force coefficients in plunge milling operations

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.

Investigation and Correction of Actual Microphone Response for Chatter Detection in Milling Operations

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.

Two-points-based receptance coupling method for tool-tip dynamics prediction

ABSTRACT 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.

Introducing wireless charging facilities for electric vehicles: the case study of Firenze

In a World with an increasing population and related mobility needs, a traditional internal combustion engine based mobility paradigm cannot be considered the only possible solution. This is particularly true for cities full of masterpieces and historical buildings as Firenze, used as case study. Specifically it combines very high mobility needs for tourists and inhabitants with a very high sensitivity to air pollution problems for its artistic heritage. However, the autonomy of the available vehicles is still an issue to be exceeded for a large electric mobility implementation. Within this paper, a structured method to implement static and dynamic wireless charging systems in urban mobility will be presented. The parametric nature of the model is a fundamental feature of the methodology, because makes it easy to be used as a framework for feasibility analysis: the developed analysis could be easily applied also to other cities because the required input are quite easy to be obtained.

Geometric Tolerance Evaluation Using Combined Vision – Contact Techniques and Other Data Fusion Approaches

The development of ever-pressing requirements for geometric tolerances has produced two main measuring needs: to obtain the geometric values of industrial products with higher precision and to obtain these values in a reduced time span. In order to accomplish these objectives, one of the most investigated and applied approaches is the use of multiple sensors on a traditional coordinate measuring machine (CMM). The resulting machine is usually referred to as a hybrid CMM and it is able to combine the data from optical and contact sensors in order to produce the measurement of a specific object with higher precision and in less time with respect to the traditional CMM approach. This chapter briefly explains the hybrid CMM characteristics and the working principles of the most used sensors. Then the method for the treatment of the data acquired by the multiple sensors is presented, starting from the basic problem of data registration to the algorithm to integrate and fuse the optical and touch probe data.

Analytical – FE simulation of a multi-jet electrospinning process to predict material flow

Abstract 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.