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Tolerance Analysis by Adaptative Polyhedra – AToPAd

Tolerancing by adaptative polyedra

Simulation of the geometric variabilities of over constrained mechanical systems.<br />Integration of dimensional and geometric specifications (form, orientation and position).<br />Taking local deformations into account: coupling into purely geometric and mechanical constitutive laws.<br />Development of the digital twin of mechanical assemblies

Obtaining a realistic simulations of the behavior of the assemblies

At the part level, integration of the representative geometric details of the production processes, •<br />At the mechanism level, integration of a contact architecture coupled with a behavior representative of the functioning of a mechanical system. At the part scale, the integration of shape defects drastically increases the complexity of contact modeling. This leads tolerance analysis tools to make assumptions that limit the type of part variations while specializing the types of architecture (isostatic or hyperstatic), integrating (or not) the mobility of the mechanism, addressing (or not) local deformations of contact surfaces and part stiffness. Due to the complexity of the physical phenomena to address, it is necessary to rethink and develop an adaptive acuity of the system modeling in relation to the functional requirements to be met.

Characterization of the geometric variability throughout the product life cycle.
Simulation of the realistic behavior of mechanism and to develop new theoretical basis for multi-physical tolerance. The theoretical developments and digital tools implemented in the AToPAd project will systematically validate on laboratory examples, on first, and then applied on industrial mechanism proposed by industrial partners. One of the major originality of this project is that the developed tools will be shared in open source format. In addition, a CAD library of studied systems will be freely available. Finally, guidelines will be defined concerning the acuity level to be met and the associated modeling to develop according to the functional requirement and expected behavior of the system.

First publication in June 2022 of the first release of the SkinModel component insise the release 2.0.2 of the PolitoCAT application.

Creation of a users community dedicated to the open source platform of the AToPAd project.
Creation of a open database of examples.

An integrated open source CAT based on Skin Model Shapes by Restrepo at al. presented at the 17th CIRP Conference on Computer Aided Tolerancing.
PolitoCAT v2.0.2 for Windows64, a free software under the GNU LGPL license, with a kernel based on politopix and a graphical interface. This is the first contribution to the AToPAd project.

The development of innovative manufacturing processes leads to design innovative and optimized products with both complex architecture and original geometries. These technological breakthroughs forced the engineers to rethink the way we design and integrate these new functionalities.
The control of the geometric variability of mechanical systems is based on the modeling of tolerances and the main objective is to qualify the conformity of a mechanical system with respect to functional requirements (clearance, flush, alignment, etc.) according to the geometric variations of the parts.
Actually, we are facing to a significant disrupting between the continuous increasing functionalities and capacities of production and metrology equipment, while tolerance simulation tools have serious limitations, mainly due to the complexity of the mathematical tools to be implemented. Closing these critical gaps to obtain realistic simulations of the behavior of the assemblies requires major developments at two different scales:
• At the part level, to integrate representative geometric details of the production processes,
• At the mechanism level, to integrate a contact architecture coupled with a behavior representative of the functioning of a mechanical system.

At the part scale, the integration of shape defects drastically increases the complexity of contact modeling. This leads tolerance analysis tools to make assumptions that limit the type of part variations while specializing the types of architecture (isostatic or hyperstatic), integrating (or not) the mobility of the mechanism, addressing (or not) local deformations of contact surfaces and part stiffness.
Due to the complexity of the physical phenomena to address, it is necessary to rethink and develop an adaptive acuity of the system modeling in relation to the functional requirements to be met.
The AToPAd project aims to overcome these scientific bottlenecks, in particular by developing realistic tools for characterizing shape defects at the part scale. The integration of these defects must be combined with the deformation of the contact surfaces. Simulation of these defects and deformations at the mechanism scale will ensure continuity between these different scales and validate their overall performance.

To this end, a further study of research works in geometric for a multi-physical tolerancing approach is proposed, considering a discrete and realistic representation of shapes (Skin Model Shapes) developed by LURPA coupled with tolerance analysis methods based on polyhedra models carried out in I2M. Through this innovative coupling, the project will contribute:
• To characterize the geometric variability throughout the product life cycle,
• To simulate the realistic behavior of mechanism and to develop new theoretical basis for multi-physical tolerance.
The theoretical developments and digital tools implemented in the AToPAd project will systematically validate on laboratory examples, on first, and then applied on industrial mechanism proposed by industrial partners. One of the major originality of this project is that the developed tools will be shared in open source format. In addition, a CAD library of studied systems will be freely available. Finally, guidelines will be defined concerning the acuity level to be met and the associated modeling to develop according to the functional requirement and expected behavior of the system.

Project coordination

Denis Teissandier (INSTITUT DE MECANIQUE ET D'INGENIERIE DE BORDEAUX)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LURPA LABORATOIRE UNIVERSITAIRE DE RECHERCHE EN PRODUCTION AUTOMATISEE
I2M INSTITUT DE MECANIQUE ET D'INGENIERIE DE BORDEAUX

Help of the ANR 269,352 euros
Beginning and duration of the scientific project: November 2019 - 42 Months

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