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Caractérisation des usinages robotisés : application aux processus de transformation du matériau bois

Abstract : Nowadays, the robotization of wood machining remains a complicated and uncommon task. This is also due to the significant constraints to which the use of an industrial robot (also known as anthropomorphic or polyarticulated) is subject. These particularly concern operations that require a high degree of precision and agility. Indeed, the forces exerted on the robot's articulations and on the tooling come up against the insufficient natural rigidity of polyarticulated robots. This causes the machine to lose its performance in terms of output and efficiency and degrades the quality of machining. In addition, the variable properties of the wood material do not make the polyarticulated robot the ideal candidate for material removal machining processes. In order to answer this problem, we seek, through this thesis, to improve the machining of robotized wood by taking into account the major technological difficulties: natural rigidity, dimensional quality of machining and cutting forces and interaction between them. Thus the difficulties related to the wood anatomy: Heterogeneity, anisotropy, fibrous texture and singularities. To solve this problem we used a numerically controlled (CNC) machine tool and an anthropomorphic ®Kuka robot equipped with a high-speed machining engine. We instrumented our experimental bench with a force measuring chain and a digital measuring table to quantify the dimensional errors of the machined profiles. Three wood materials are machined: Hardwood (Beech), softwood (Fir) and derived timber (MDF). The results obtained show that there is a direct proportional relationship between cutting forces and degradation of dimensional quality, regardless of the machine used. The higher the forces applied to remove the material, the more the tracking performance of the end effector decreases. In terms of system stability, measurements have shown that the farther the tool works from the robot base, the more the cutting forces fluctuate and the more the dimensional quality deteriorates. This becomes more pronounced when material heterogeneity and density are high. As a result, the robot is less stable and its performance in terms of repeatability in series production degrades. Fluctuations in stress and degradation of dimensional quality are intensified by changing the cutting mode. Cutting forces increase by a factor of 8 when the tool works perpendicular to the wood grain.The case of material-related peculiarities is discussed. Indeed, measurements show a rapid and sudden jump in forces which multiplies by 3 when the cutting edge passes through a knot. This leads to splinters and cracks in the material and degrades the orthogonality of the cut. The variation of the robot feed rates from 4m/min to 9m/min in beech machining resulted in damage to the machined surface in the form of material ripples and splinters due to deviations in the tool path. The same experiments on the variation of the robot feed rates are carried out on other species such as larch (softwood) and oak (hardwood) to study the machining quality. The results found are similar to those obtained previously (material splinters, tool path deviations and cracks).
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https://hal.univ-lorraine.fr/tel-02962837
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Submitted on : Friday, October 9, 2020 - 3:10:49 PM
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  • HAL Id : tel-02962837, version 1

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Oussama Ayari. Caractérisation des usinages robotisés : application aux processus de transformation du matériau bois. Automatique / Robotique. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0080⟩. ⟨tel-02962837⟩

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