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2 Journal of Machine Engineering

2 2009

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A new strategy of tool path planning based on hydrodynamic data to machine marine propeller

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Breteau T. , Damay T. , Duc E. , Hascoët J.-Y.

Journal of Machine Engineering

2009

tom Vol. 9, No. 1

29--40

Marine propellers are complex surfaces that are usually machined with a perfect roughness in order not to disturb the theoretical flow. Because this requirement is penalizing from a manufacturing point of view, the global objective of the study is to propose an approach in which the machining parameters are linked to functional properties of the blade in order to remove the polishing phase. To reach this objective, hydrodynamic data are used: streak lines, that are computed during the propeller design phase, characterize the fluid behavior at the close vicinity of the blade. Those lines, which are theoretically continuous at the leading edge, turn out to be discontinuous, due to the computing method. To be consistent with the fluid behavior as much as possible, the idea presented in the paper is to compose a continuous trajectory, especially at the leading edge, to mill the surface. Thus, an algorithm is developed to plan tool paths which are smoothed at leading edge using Bezier curves. Moreover, this algorithm allows to quantify the cusp height at the leading edge to avoid a drop in performance using criteria linked to the dynamical behavior of a five axis machine tool. In this work, a strategy is developed and enables multiaxial milling of a blade surface by using geometric and hydrodynamic data and by respecting the associated constraints.

A new multidisciplinary approach for three-dimensional foil machining

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Jaouen R. , Martineau J. P. , Hascoet J.-Y. , Damay T.

Journal of Machine Engineering

2009

tom Vol. 9, No. 1

5--17

The context of this paper implies disciplines of mechanical design, machining and hydrodynamics behaviours applied to propellers. Performances of propellers are linked with their shape and their surface texture. To optimise hydrodynamics behaviours, it is demonstrated in this paper that required polishing operation is not essential. To study the influence of an predefined surface texture on the performances of a three-dimensional foil, a comparative analysis is conducted. The presented methodology allows the definition of tool paths, according to the desired surface texture and upstream flow. Three foils are machined, and their performances are compared to each other: the first, considered as the reference, has a surface roughness like mirror, the second features machined peaks parallel to the upstream flow and the third has machined peaks following streamlines obtained by Computational Fluid Dynamics for operating conditions. The validation of this method is experimental: on the one hand by the manufacturing of foils following pre-established trajectories, and on the other hand by the functional test in hydrodynamic tunnel. This paper presents the methodology steps, and the hydrodynamic behaviours that the three different foils show. In a first approach, the different surface textures do not influence the lift coefficient but strongly influence the drag coefficient of a foil. Furthermore several hypotheses educed from the observed tendencies are discussed.