Method of optimizing the joints between layers in modelling or prototyping involving layer decomposition, and the parts obtained

#The present invention relates to a method for optimizing the joints between layers along portions of the layers which are flush with the surface of a part obtained by computer-aided modeling or prototyping involving layer decomposition, as well as the elementary layers obtained by the method, and the parts resulting from their assembly.

#Rapid prototyping methods are themselves known. For example, European Patent No. 0 585 502-B1 discloses a prototype part which is produced using software for decomposing the part to be produced into elementary layers. The layers are assembled together, and the final assembly is then externally reworked, in particular, to remove any roughnesses or imperfections resulting from assembly.

#FIGS. 3 and 4 schematically show an assembly of layers which illustrate the problem encountered. In the illustrated assembly of two layers (1, 2), a portion of the joint (3) becomes externally flush, at (4). It will be understood that the zone (5) of the layer (1) comprises little material at this location, which, by machining and polishing, can result in the removal of material from the zone (5) of the joint (3), as is schematically shown in FIG. 4, at (6). This results in an imperfect part, with an irregular surface, which is unsatisfactory for certain applications.

#FIG. 1A is a CAD representation of a part that is complicated to produce, with several possible alternative situations.

#FIG. 1B is a CAD representation of a layer obtained with the method of the present invention, illustrating the layer in three dimensions.

#FIGS. 2A and 2B represent a layer obtained in accordance with the present invention, seen from above in FIG. 2A, and in section in FIG. 2B.

#Referring first to FIG. 5 of the drawings, the essential parameters of a joint obtained in accordance with the method of the present invention include an angle (α) between the tangent and the plane of a layer, a length (a) of a portion (7) of the joint (3′) (corresponding to portions of the joint (3) between the adjacent layers shown in FIG. 3) which forms a profile connecting the two adjacent layers, an offset (b) of the plane of the layer, and a normal ({right arrow over (n)}) at the junction point (4′). In accordance with the present invention, the joint portion (7) is normal to the tangential plane (T) over a length (a). Note that if (a) is constant, (b) is f(α), and if α=π/2, b=0.

#The above-discussed problems associated with a joint of this type are solved as a result; however, the layers obtained through such a calculation will be of variable thickness. In addition, the profile of the layer can vary all along the periphery, and the line of the joint (portions of which are formed at an incline in FIG. 5) is not necessarily in one and the same plane. For angles (α) close to π/2, it will also be necessary to suitably position the layers relative to one another, as explained below.

#Referring to FIG. 6, and with all other things being equal for the embodiment of FIG. 5, the following are carried out. The amount of material at the joint is controlled (the objective sought). The position of the layer (in X,Y) is controlled by a centering insert (8). The position of the layer (in Z) is controlled by a positioning profile (8′). This also results in control and reinforcement of the assembly and of its mechanical strength.