1,721,134 research outputs found
Specificazione e verifica di tolleranze geometriche per superfici libere
No full textLa modellazione di superfici, intese come forme geometriche libere, ha conosciuto ampia diffusione in diversi settori, sia per finalità di stile (industrial design) che per necessità funzionali (aerodinamica, fluidodinamica) e specificità tecnologiche (processi di formatura in generale). L’utilizzo di tali superfici ha però ben presto messo in evidenza le criticità legate alla loro definizione, specificazione e verifica, sia in termini di tolleranze dimensionali che geometriche.
Le tolleranze di profili e di superfici a forma libera sono trattati nella ISO 1101 e nella ISO 1660. La loro duplice classificazione, tra le tolleranze di forma e quelle di posizione, ne rivela la capacità di controllare separatamente ovvero simultaneamente la caratteristica di forma, quella di orientamento e finanche quella di localizzazione della superficie tollerata. Proprio grazie a questa specificità, questo tipo di tolleranza si presta ad un utilizzo estremamente efficace anche in presenza di geometrie regolari a patto di conoscere ed applicare in modo preciso le regole di interpretazione e designazione.
Questo lavoro propone l’analisi degli strumenti normativi suddetti ed in particolare il confronto tra le metodologie di verifica tradizionali, secondo ISO 5460, e quelle supportate dalle moderne apparecchiature di misura a coordinate bi- e tri-dimensionali. In relazione a tale approccio metodologico vengono inoltre proposte le linee di sviluppo di una nuova base normativa specifica per queste tolleranze geometriche, definendo una catena di principi, metodi e strumenti di diretta applicazione nel mondo industriale per la specificazione (designazione e quantificazione) e la verifica delle tolleranze relativamente a profili e superfici free-form
Applicability of Roughness Profile Analysis for Evaluation of Cutting Fluid Efficiency in Reaming Test
No full textA Heuristic Approach for Nesting of 2D Shapes
No full textIn several manufacturing processes, the cutting of 2D parts from sheets is an important task. The arrangement of the parts in the sheets, supported by computers, is called nesting and is addressed to minimize the wasted material. In literature some approaches are proposed, based on genetic or heuristic algorithms which emphasize different characteristics, e. g. the time complexity or the wasted material. In shipbuilding the parts to be arranged have significantly different sizes, which are often difficult to pack in a fast way using the standard methods in literature. In this work an approach is proposed, able to arrange parts with very different dimensions, which is based on the identification of a suitable starting rotation that ensures a solution in a reasonable time. The main steps are: a) importation of the model files of the parts to be packed, b) identification of a preliminary orientation and sorting of the parts (starting position), c) optimization of the position of the parts, ensuring a minimum distance between them. For the starting rotation, three different orientations are considered: i) the original orientation, ii) the x axis coincident with the minimum inertia axis, iii) the x axis aligned with the maximum edge. The orientation is selected in order to obtain the minimum area of the bounding box. The implementaiton of the method has been investigated and the results show the advantages of the approach: reduction of waste material and time for performing the nesting
Conformity Rate Estimation for Shaft-Hole Pattern Fit Not Compliant with the Boundary Condition Design Criterion
Full text linkShaft-hole pattern fits based on the Boundary Condition design criterion allows a 100% acceptability rate, but they may be not economically convenient. If the rejection rate needs to be statistically quantified and the pattern is itself the alignment feature, therefore promoted as datum feature (Intrinsic datum system), there is no trivial solution to create a tolerance stack-up: a unique assembly function cannot be determined. The focus of this contribution is “2x” patterns: different methodologies to create tolerance stack-up assessing assemblability are discussed and verified through Monte Carlo simulation. An equation to transform the variability seen from the Intrinsic datum system to the one seen from an external arbitrary reference system is given. The mutual distance between any two elements of an “nx” pattern is discussed and the implication of multiplicity and datum system is highlighted. A case, derived from an industrial case study, will be discussed by comparing the result from the simulated manual and automated assembly. A path towards “nx” patterns generalization is also presented
Measurement accuracy improvement of laser-based CMM
No full textIn the last years, a wide attention to the methodologies for the reverse engineering (RE) has been given, as an answer to the increased interest in the industrial and scientific fields. The reverse engineering is always envisaged as a technology focused on the selection of the digitalization equipment and on the software tools for the manipulation of the data and the reconstruction of the surface: the technological aspects are not considered therefore of it the demands work them relating the object. At the Dipartimento di Architettura Urbanistica e Rilevamento of the University of Padova, it is in course the "project Functional Integrated Reverse Engineering", finalized to the realization of a new technological workplace for the reverse engineering of prototypes and industrial products. This ambient consists of hardware technologies, based on a CMM Laser, and of software technologies. A critical aspect, in the phase of reconstruction of geometric feature, is the accuracy of the acquisition system that can be obtained with the precision of the workings and the methods of assemblage. Its however possible to increase the precision of the acquired data by means of the modeling of the geometric errors of the system, and numerous are the relevant scientific contributions. This job describes the application and the elaboration of a mathematical model based on the cinematic of the rigid bodies, for the correction of the geometric errors of the machine of measure to scansion laser used for the acquisition of small archaeological biomedicali and mechanical manufacts.. The model of compensation of the geometric errors is realized with the direct method, measuring the motion of the movement guides using an external device. Every error has been acquired experimentally using a commercial CMM which metrological reference. The proposed model is therefore an elaboration of the direct mapping of the positions assumed from the system in its movements to the inside of the working volume. In the following pages they introduce the mathematical model, the process of acquisition of the experimental data and the analysis of the characteristics of the CMM Laser. Finally they are introduced the results of the validation of the system using a calibrated artefact, specifically realized
Application of reverse engineering techniques for the analysis of orthodontic models
No full textIl settore bio-medicale è un campo in cui l’utilizzo di tecniche di Reverse Engineering porta molteplici vantaggi. In questo lavoro si presenta un’applicazione del RE in ambito ortodontico, finalizzato all’analisi della morfologia del palato. Principale problema in questa tipologia di analisi è la definizione di una procedura ripetibile per la ricostruzione del modello matematico e per l’ottenimento di parametri significativi al variare della morfologia dovuta alla crescita del soggetto. Lo studio è rivolto in particolare all’analisi del volume e dei parametri della superficie delimitata dal colletto. Si illustra inoltre l’ottimizzazione della procedura finalizzata alla riduzione delle esigenze hardware e software necessarie senza penalizzare la precisione dei risultati finali. Il metodo proposto è stato utilizzato nell’analisi delle variazioni morfologiche del palato di pazienti affetti da Palatoschisi, curati mediante l’utilizzo della tecnica del disgiuntore rapido, e nello studio degli effetti a lungo termine dell’intubazione neo natale. Per entrambi i casi si riportano i risultati geometrici principali
Enhancing tolerance stack-up analysis with variable-dependent admissible limits
Full text linkThis work introduces the concept of variable-dependent admissible limits for tolerance stack-up analysis, where limits adapt based on geometrical and non-geometrical variables. Unlike traditional methods that assume fixed limits, the proposed approach integrates these dependencies into both variational and Monte Carlo analyses, enabling broader tolerances while maintaining functionality. A case study from the automotive sector demonstrates the methodology's effectiveness. This innovation shifts tolerance analysis from a purely geometrical to a functional domain, improving accuracy, reducing costs, and supporting compact and safe designs in industrial applications
A surface roughness predictive model in deterministic polishing of ground glass moulds
No full textThe introduction of deterministic NC grinding and polishing operations, in the manufacturing of free-
form glass components for precision optics, requires the characterization of surface topography
evolution as a function of process parameters. In this work, a model based on Reye’s wear hypothesis is
proposed for the assessment of surface roughness prediction as a function of operating parameters, in
the deterministic polishing process of glass moulds. Accordingto Reye’s hypothesis, the removed
material per unit area is proportional to the work due to the friction force: the removed material per
unit area can be computed by adequately integrating the areal material ratio function (Abbott–Firestone
curve) of the surface and can be associated with the amplitude roughness parameter; the work due to
the friction force per unit area is proportional to the integral of the product of pressure and velocity in
the time interval and can be derived from the process parameters by means of the Hertz theory. The
model assessment was performed on ground glass flat samples polished with different operating
parameters, mapping the surface roughness using an atomic force microscope (AFM). The developed
model shows a satisfactory estimate of surface roughness evolution during the polishing process and
confirms the experimental results found in the literature for the Preston coefficient
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