Proposition of a new Semantics for Standardized Tolerencing - Principle of its Verification on Coordinate Measuring Machine

6 pagesInternational audienceThe semantics of standardized Dimensioning and Tolerancing D&T), that is to say its meaning by relationship to actual surfaces, on one hand renders difficult the synthesis of a functional D&T and on other hand can not be correctly inspected, in particular with the Coordinate Measuring Machines (CMM). We suggest a new semantics for the tolerancing based on the fitting of an envelope surface on the actual surface. We define the envelope surface, in a unique and general way, as being the theoretical surface in contact with the actual surface on the outside of the material and so that the volume between them is minimal. In others terms, we suggest a unique fitting criterion enabling to define the envelope surface and which we call the criterion of minimal volume. We show the interesting properties of this criterion notably from the point of view of its functional interpretation. We present then a method, for the software of CMMs, enabling the calculation of the envelope surface following the suggested criterion. The performances of this method and the obtained numeric result are compared to the two principals fitting criterions used, the least squares criterion and the minimal form defect criterion (again called minimax or schebyscheff criterion)

Three-dimensional metrology with the virtual fitting gauges

International audienceThe metrology implemented in several classical software equipping the coordinate measuring machines, does not correspond to the standardized tolerancing by zones, virtual conditions and perfect datum features fitted outside the matter. On the basis of these concepts and by generalizing them, a conceptual model of "fitting virtual gauges" is presented. On a part presenting two positional tolerances, the plans of inspection according to the traditional metrology and according to the metrology by fitting gauges, are compared from the point of view of their simplicity and their potential results. A fitting gauges based software is under development. It will make it possible "to save" a certain number of parts declared not conform by traditional threedimensional metrology

The "Gauge model": A New Approach for Coordinate Measurement

6 pagesInternational audienceA new approach for the metrology on Coordinate Measuring Machine (CMM) is presented. It is based on the utilization of virtual gauges. The originality of the presented virtual gauge model is the notion of "fitter gauge" which develops the traditional possibilities of gauges. This model allows the verification of functional specifications of the geometrical tolerancing. An example of inspection of a pattern of hole illustrates the method. The gauge model is based on the TTRS model [1] and its numerical implementation on the small displacement method [2]

Détermination systématique des étapes de contrôle et des cotes de fabrication pour les procédés d'usinage

National audienceThe "academic" method of manufacturing dimensions determination through the decomposition of the manufacturing plan into several steps, each one corresponding to a part holder, is not usable when the part is produced by only one machine, like in the case of screw machining. The transfer of the condition dimensions in manufacturing dimensions is therefore not always direct because the setup operator might also want to control the position of the unfinished surfaces during the adjustment of the machine. This results in introducing intermediate control steps into the manufacturing plan. In this case and for some condition dimensions, several chains of dimensions are possible, thus several manufacturing dimension systems are possible

Towards easier and more functional semantics for geometrical tolerancing

9 pagesInternational audienceGeometrical defects of a manufactured feature are limited by form, size and location tolerances. The standardized semantics of those tolerances, i.e. their interpretation on the manufactured feature, presents a lot of drawbacks. We propose new semantics, based on the fitting of a unique theoretical feature on the manufactured feature. The fitting criterion we propose, named minimum volume criterion, leads to the actual mating envelope of the manufactured feature. For some functional requirements the tolerancing shown to become simpler and more functional

Détection du déréglage le plus probable d'un processus d'usinage par outil coupant

International audienceL'usinage d'une pièce mécanique est caractérisé par le déplacement des outils pour générer les surfaces de la pièce. Ce déplacement répété des outils au contact des pièces successives génère de la variabilité sur les outils qui sont à l'origine des écarts sur les pièces. Il faut donc régulièrement mesurer la (les) dernière(s) pièce(s) produite(nt) et comparer la mesure à la géométrie cible pour corriger ces écarts. Un réglage initial des outils est également nécessaire avant le lancement de la série de pièces. De ce fait, on doit agir sur un certain nombre de paramètres réglables de la machine. Dans le cas d'usinage par machine-outil à commande numérique, on agit principalement sur les correcteurs d'outils. Dans un processus de fabrication, la pièce usinée est soumise à l'action de plusieurs outils de coupe auxquels on associe des correcteurs, pour corriger soit leur position, soit leur forme. Le choix du meilleur réglage possible est trivial si chaque caractéristique n'est impactée que par un seul correcteur. Le problème est différent et plus complexe lorsque chaque caractéristique est impactée par plusieurs correcteurs et qu'il existe par conséquent une structure d'interdépendance entre ces caractéristiques. Cet article présente une stratégie originale consistant à identifier la combinaison de réglage qui compense au mieux le décentrage global de la pièce sur l'ensemble de ses caractéristiques. On fait l'hypothèse que la situation mesurée est la résultante d'un décalage d'un nombre fini d'outils. Si on trouve une combinaison de réglage qui reproduit au mieux l'ensemble des déréglages constatés, il est alors fort probable que ce soit la bonne combinaison de réglages à réalise

Copilot Pro®: A full method for a steering of the machining.

International audienceCopilot Pro® is a method for the initial and regular machine-tools setup, developed by the Symme laboratory of the Savoy University and by the Technical Center of Industries of Screw-machining (Ctdec) in France. Its first step is the organization of the different machining operations, in setup steps, themselves subdivided into measuring steps. The second step consists in determining the manufacturing dimensions to measure at the end of each measuring step. Finally, the third step consists in linking the manufacturing dimensions to both the correctors and the tool-dimensions, in the aim of calculating the corrections that have to be done in function of the deviations measured on the manufacturing dimensions. With this method, the steering of an industrial workpiece is performed with two steering parts instead of ten before

The pilot dimension method: Reconciling Steering and Conformity in Workshops

International audienceIn machining workshops, workpieces are produced according to dimensions known as manufacturing dimensions. For the same workpiece and the same manufacturing plan, several sets of manufacturing dimensions can be used but none satisfy simultaneously the two main missions workshops need to fulfil: (a) Ensuring conformity of products to their design dimension tolerances (also called blueprint tolerances) and (b) steering machines in order to compensate for tool wear. The set of manufacturing dimensions obtained from the design dimensions using the minimal chain of dimensions method is optimal for a conformity check of workpieces but is practically unusable for steering machines because of the complexity of its relationships toward the tool correctors and tools dimensions. The pilot dimensions method consists in, on the one hand, identifying and representing these tool correctors and these tool/program dimensions on the production drawings (besides the manufacturing dimensions) and, on other the other hand, determining their correction values through a mathematical set of relations after having measured the manufacturing dimensions on a workpiece. Doing so will strongly reduce adjustment time, reduce the number of workpieces used for adjustments and greatly enhance the quality of workpiece batches

Multivariate SPC for Total Inertial Tolerancing

This paper presents a joint use of the T² chart and Total Inertial Tolerancing for process control. Here, we will show an application of these approaches in the case of the machining of mechanical workpieces using a cutting tool. When a cutting tool in machining impacts different manufactured dimensions of the workpiece, there is a correlation between these parameters when the cutting tool has maladjustment due to bad settings. Thanks to Total Inertial Steering, the correlation structure is known. This paper shows how T² charts allow one to take this correlation into account when detecting the maladjustment of the cutting tool. Then the Total Inertial Steering approach allows one to calculate the value of tool offsets in order to correct this maladjustment. We will present this approach using a simple theoretical example for ease of explanation