Patent ID: 12246384

DETAILED DESCRIPTION OF THE INVENTION

As explained hereinabove, the invention relates to a support frame for a part intended to undergo a sintering step of a method for producing a part, in particular for watchmaking. The sintering step consists of sintering a green body having an initial shape. During sintering, the body shrinks to give it a final shape with a shrinkage coefficient relative to the initial shape. Generally, the initial shape has proportions that correspond to the desired shape of the part to be obtained after the sintering step.

In order to preserve this shape, a support frame is used, which has at least one face which supports the body during the sintering step, the geometry of the supporting face being in relief. The relief is configured to support the body in its initial shape and in its final shape, such that the body maintains its proportions with a shrinkage coefficient. The relief of the support frame guides the shrinking of the body throughout the sintering step in order to maintain the shape of the body as it shrinks, regardless of the material that is chosen.

The support frame is preferably made in one piece and comprises, for example, Al2O3, preferably exclusively. The green body is, for example made of ceramic or metal.

The supporting face comprises a sliding part, over which the body can move as it shrinks. For this purpose, the supporting face has a roughness index Ra greater than 1, preferably greater than 3, or even greater than 4.

Alternatively, a powder spray is applied to the supporting face to allow the body to slide during shrinkage.

Preferably, the supporting face is determined such that it is arranged relative to the gravitational axis to avoid the risk of gravity-induced deformation.

The supporting face comprises at least two parts, each arranged at two different levels, each part being in contact with the body during sintering. Different levels is understood to mean that one part is higher or lower than the other in the relief of the supporting face.

According to an alternative embodiment, one of the parts is intended to be in contact with the body in its final shape and not in its initial shape. Alternatively, the two parts are intended to be in contact with the body in its initial shape and in its final shape.

The figures hereinbelow show different embodiments of the support frame.

The supporting face of the support frame inFIG.1comprises a central part3and two side parts4,5. The side parts preferably have a roughness index that allows for sliding. Preferably, the central part also has such a roughness. The central part3is substantially horizontal and is raised relative to the side parts4,5, which slope gently down from the central part3. The junctions of the central part3and of the side parts4,5form a step. The central and side parts are sized so as to allow the body to shrink, regardless of the material that is selected.

The green body is intended, for example, to form a component of a buckle of a bracelet, and comprises a thick portion6in the centre and two thin portions7,8on either side to form a one-piece body. The thin portions7,8are curved downwards and extend to below the level of the central portion6. The green body is disposed on the support frame such that the thick portion6rests on the central part3of the supporting face, and such that the thin portions7,8each rest on a side part4,5of the supporting face.

During the sintering step, the body shrinks to its final shape, which is shown inFIG.2. The volume of the final body is less than the volume of the initial green body due to shrinkage, but the proportions and shape of the body2are substantially preserved. The ends of the thin portions7,8of the body2are closer to the central part3than to the side parts4,5.

Thanks to the support frame, the body does not become deformed during sintering. The relief of the supporting face counteracts the deformation of the body caused by gravity. For this purpose, the support frame is configured such that the supporting face is oriented perpendicular to the direction of gravity.

The second embodiment of the support frame inFIGS.3and4shows a support frame10for sintering a buckle placed the other way around relative to the support frame1inFIG.1or2.

The support frame10comprises a supporting face provided with a central part13forming a bottom and two raised side parts14,15. The green body2is identical to that in the first embodiment, but is lying upside down on the support frame. Thus, the ends of the thin portions7,8are higher than the thick portion6.

The side parts14,15are intended to be in contact with the body in its initial shape and in its final shape. Thus, the body2is supported by the thin portions7,8in contact with the side parts14,15of the supporting face. The thick portion6is suspended in the initial shape of the body.

After the sintering step, shown inFIG.4, the shrunken body2has a reduced volume. Thus, the thick portion6rests on the central part13of the supporting face. In this embodiment, the central part13is intended to be in contact with the body2in its final shape and not in its initial shape.

The relief of the supporting face is configured to correspond at least in part to the final shape of the underside of the body2. Each side part14,15forms an oblique angle with the central part, the angle corresponding to the angle formed by a thin portion7,8with the thick portion6of the shape of the body2.

FIG.5shows a third embodiment of a support frame20with a domed or convex central part23, on which rests a body12in its final shape. The body12is a bracelet part16provided with a buckle17and a thick end18, which is in its final shrunken shape as shown inFIG.5. The support frame20comprises a first raised side part14for retaining the buckle17in the initial shape of the body12. The support frame20comprises a second side part25stepped downwards from the central part23. The thick end18of the bracelet rests on this second side part25in its initial shape and in its final shape. After shrinking into its final shape, the thick end18touches the step defined by the stepping between the central part23and the second side part25.

In the fourth embodiment shown inFIG.7, the support frame30is configured to allow for the formation of straight elongated wires22, shown inFIG.6. The initial green body has an elongated wire shape, which is to be preserved after sintering, and which is very difficult to preserve without a support frame.

The support frame inFIG.7comprises a plurality of grooves31for holding the wires22during sintering, each groove being intended to hold one wire. The wire-shaped green bodies are disposed in the grooves31to prevent the deformation thereof during sintering.

Each groove is provided with a central part forming the bottom of the groove and two raised side parts forming the edges of the groove. The side parts extend away from the central part.

FIGS.8and9show a first groove profile according to a first alternative embodiment, with the body22in its initial shape inFIG.8and in its final shape inFIG.9. InFIG.8, the wire22rests on the two side parts34,35before the sintering step. Thus, the wire does not rest on the central part33of the supporting face in its initial shape. The width of the wire22is greater than the width of the central part33.

During sintering, the body22shrinks to a final body shape, in this case to the shape of an elongated wire. After the wire has shrunk, its width is smaller than the distance between the two side parts, such that it slides into the groove until it makes contact with the central part33of the supporting face, as shown inFIG.9.

Thanks to the relief of the supporting face of each groove in the support frame, the wire remains straight and does not become deformed.

FIGS.10and11show alternative embodiments of the grooves41,51in the support frames40,50, with the grooves41,51having different profiles.

The grooves41inFIG.10have a flared shape, for example with an angle of at least 80° or even at least 100°, and a rounded bottom43. In its initial shape, the cylindrical body32rests on the side parts44,45, and in its final shape, the body32rests on the rounded bottom43. The cylindrical shape of the wire is thus preserved during the sintering step.

In the alternative embodiment shown inFIG.11, the grooves51have a shape with a sloping bottom.

The invention further relates to a method for sintering a green body, in particular for watchmaking, the green body having an initial shape.

The method comprises a first step wherein the green body is disposed on a support frame provided with a supporting face in relief according to the invention, such that the green body is at least partially in contact with a first part of the supporting face of the support frame.

The invention comprises a second step wherein the green body is sintered on the support frame such that it shrinks from its initial shape to a final shape. In its final shape, the body is at least partially in contact with a second part of the supporting face of the support frame, the second part being different from the first.

The first and second parts can be oriented differently from one another, in particular relative to gravity.

Preferably, the body slides along the support frame from its initial shape into its final shape during the second step.