Probabilistic-based approach using Kernel Density Estimation for gap modeling in a statistical tolerance analysis

The statistical tolerance analysis has become a key element used in the design stage to reduce the manufacturing cost, the rejection rate and to have high quality products. One of the frequently used methods is the Monte Carlo simulation, employed to compute the non-conformity rate due to its efficiency in handling the tolerance analysis of over-constrained mechanical systems. However, this simulation technique requires excessive numerical efforts. The goal of this paper is to improve this method by proposing a probabilistic model of gaps in fixed and sliding contacts and involved in the tolerance analysis of an assembly. The probabilistic model is carried out on the clearance components of the sliding and fixed contacts for their assembly feasibility considering all the imperfections on the surfaces. The kernel density estimation method is used to deal with the probabilistic model. The proposed method is applied to an over-constrained mechanical system and compared to the classical method regarding their computation time

Geometrical variations management for additive manufactured product

Additive manufacturing (AM) became an advanced research topic due to its ability to manufacture complex shapes. But the ability to achieve predictable and repeatable shapes is critical. Therefore, to optimize the design of an additive manufactured product, tolerancing is a key issue. This paper focuses on geometrical quality assessment of an AM product. It includes a process oriented geometrical model to predict the surface roughness and dimensional deviations, and a geometrical simulation tool to assess the impacts of these deviations on the geometrical behaviour of the joint. An application of the approach is illustrated through a case study

Tolerance analysis — Form defects modeling and simulation by modal decomposition and optimization

Tolerance analysis aims on checking whether specified tolerances enable functional and assembly requirements. The tolerance analysis approaches discussed in literature are generally assumed without the consideration of parts’ form defects. This paper presents a new model to consider the form defects in an assembly simulation. A Metric Modal Decomposition (MMD) method is henceforth, developed to model the form defects of various parts in a mechanism. The assemblies including form defects are further assessed using mathematical optimization. The optimization involves two models of surfaces: real model and difference surface-base method, and introduces the concept of signed distance. The optimization algorithms are then compared in terms of time consumption and accuracy. To illustrate the methods and their respective applications, a simplified over-constrained industrial mechanism in three dimensions is also used as a case study

Tolerance analysis of complex mechanisms - Manufacturing imperfections modeling for a realistic and robust geometrical behavior modeling of the mechanisms

L’analyse des tolérances a pour but de vérifier lors de la phase de conception, l’impact des tolérances individuelles sur l’assemblage et la fonctionnalité d’un système mécanique. Les produits fabriqués possèdent différents types de contacts et sont sujets à des imperfections de fabrication qui sont sources de défaillances d’assemblage et fonctionnelle. Les méthodes généralement proposées pour l’analyse des tolérances ne considèrent pas les défauts de forme. L’objectif des travaux de thèse est de proposer une nouvelle procédure d’analyse des tolérances permettant de prendre en compte les défauts de forme et le comportement géométriques des différents types de contacts. Ainsi, dans un premier temps, une méthode de modélisation des défauts de forme est proposée afin de rendre les simulations plus réalistes. Dans un second temps, ces défauts de forme sont intégrés dans la modélisation du comportement géométrique d’un système mécanique hyperstatique, en considérant les différents types de contacts. En effet, le comportement géométrique des différents types de contacts est différent dès que les défauts de forme sont considérés. La simulation de Monte Carlo associée à une technique d’optimisation est la méthode choisie afin de réaliser l’analyse des tolérances. Cependant, cette méthode est très couteuse en temps de calcul. Pour pallier ce problème, une approche utilisant des modèles probabilistes obtenus grâce à l’estimation par noyaux, est proposée. Cette nouvelle approche permet de réduire les temps de calcul de manière significative.Tolerance analysis aims toward the verification of the impact of individual tolerances on the assembly and functional requirements of a mechanical system. The manufactured products have several types of contacts and their geometry is imperfect, which may lead to non-functioning and non-assembly. Traditional methods for tolerance analysis do not consider the form defects. This thesis aims to propose a new procedure for tolerance analysis which considers the form defects and the different types of contact in its geometrical behavior modeling. A method is firstly proposed to model the form defects to make realistic analysis. Thereafter, form defects are integrated in the geometrical behavior modeling of a mechanical system and by considering also the different types of contacts. Indeed, these different contacts behave differently once the imperfections are considered. The Monte Carlo simulation coupled with an optimization technique is chosen as the method to perform the tolerance analysis. Nonetheless, this method is subject to excessive numerical efforts. To overcome this problem, probabilistic models using the Kernel Density Estimation method are proposed

Analyse des tolérances des systèmes complexes – Modélisation des imperfections de fabrication pour une analyse réaliste et robuste du comportement des systèmes

Tolerance analysis aims toward the verification of the impact of individual tolerances on the assembly and functional requirements of a mechanical system. The manufactured products have several types of contacts and their geometry is imperfect, which may lead to non-functioning and non-assembly. Traditional methods for tolerance analysis do not consider the form defects. This thesis aims to propose a new procedure for tolerance analysis which considers the form defects and the different types of contact in its geometrical behavior modeling. A method is firstly proposed to model the form defects to make realistic analysis. Thereafter, form defects are integrated in the geometrical behavior modeling of a mechanical system and by considering also the different types of contacts. Indeed, these different contacts behave differently once the imperfections are considered. The Monte Carlo simulation coupled with an optimization technique is chosen as the method to perform the tolerance analysis. Nonetheless, this method is subject to excessive numerical efforts. To overcome this problem, probabilistic models using the Kernel Density Estimation method are proposed.L’analyse des tolérances a pour but de vérifier lors de la phase de conception, l’impact des tolérances individuelles sur l’assemblage et la fonctionnalité d’un système mécanique. Les produits fabriqués possèdent différents types de contacts et sont sujets à des imperfections de fabrication qui sont sources de défaillances d’assemblage et fonctionnelle. Les méthodes généralement proposées pour l’analyse des tolérances ne considèrent pas les défauts de forme. L’objectif des travaux de thèse est de proposer une nouvelle procédure d’analyse des tolérances permettant de prendre en compte les défauts de forme et le comportement géométriques des différents types de contacts. Ainsi, dans un premier temps, une méthode de modélisation des défauts de forme est proposée afin de rendre les simulations plus réalistes. Dans un second temps, ces défauts de forme sont intégrés dans la modélisation du comportement géométrique d’un système mécanique hyperstatique, en considérant les différents types de contacts. En effet, le comportement géométrique des différents types de contacts est différent dès que les défauts de forme sont considérés. La simulation de Monte Carlo associée à une technique d’optimisation est la méthode choisie afin de réaliser l’analyse des tolérances. Cependant, cette méthode est très couteuse en temps de calcul. Pour pallier ce problème, une approche utilisant des modèles probabilistes obtenus grâce à l’estimation par noyaux, est proposée. Cette nouvelle approche permet de réduire les temps de calcul de manière significative

Evolutionary Cost-Tolerance Optimization for Complex Assembly Mechanisms Via Simulation and Surrogate Modeling Approaches: Application on Micro Gears

With the introduction of new technologies, the scope of miniaturization has broadened. The conditions under which complicated products are designed, manufactured, and assembled ultimately influence how well they perform. The intricacy and crucial functionality of products are frequently only fulfilled through the use of high-precision components such as micro gears. In power transmission systems, gears are used in a variety of industries. Micro gears or gears with micro features, with tolerances of less than 5 m, are pushing manufacturing processes to their technological limits. Monte-Carlo simulation methods enable an accurate forecast of inaccuracies in compliance. The complexity of the micro gear's design, on the other hand, increases the simulation computation and runtime. An alternative method for simulation is to create a surrogate model to predict the behavior. This paper proposes a statistical surrogate model to predict the conformity of a pair of micro gears. Afterward, the advantage of the surrogate model enables the optimal tolerances assignment while taking gear functionality, and production cost into account

Patient characteristics and laboratory data at baseline.

<p>Values reported as median (minimum-maximum) and comparisons made using Wilcoxon sign rank test. Antibody levels are expressed as mean fluorescence intensity (MFI). #ICAM-1 levels were statistically significantly higher in CM than in UM (p = 0.0037).</p><p>Anti-VSA (CD36-binding) levels were statistically significantly higher in CM than in UM (p = 0.048).</p