EP3120954B1 - Method for coating a part - Google Patents

Description

The present invention relates to a device comprising a first part made of a first material and at least one second part made of a second material, the second part being is made of a foam and assembled to the first part.

The technical field of the invention is the field of fine mechanics.

TECHNOLOGICAL BACKGROUND

There are many methods for coating a first part. The known methods generally consist in depositing a layer of the desired material by electrodeposition.

However, this electrodeposition has the disadvantage of only allowing the deposition of thin coatings, which results in low impact resistance.

The shocks applied to said part then lead to marking of the coating, reducing the aesthetic appearance of the part and degrading the performance of the coating.

Another solution consists in using a metal sheet and fixing this metal sheet on the part to be coated acting as a support. Fixing is done by gluing or welding or brazing or force-fitting.

A drawback to this method is that it is not suitable for materials which are brittle of the silicon type.

The document US 2004/035502 A1 describes a method of manufacturing a composite part comprising two parts, where one part is made of at least partially amorphous metal alloy foam.

SUMMARY OF THE INVENTION

The object of the invention is to overcome the drawbacks of the prior art by proposing to provide a process for coating a part in a simple and safe manner without limitation as to the nature of the parts fixed together.

To this end, the invention relates to a manufacturing method according to claim 1.

Preferred embodiments are specified in dependent claims 2-10.

BRIEF DESCRIPTION OF FIGURES

• la figure 1 représente de manière schématique un dispositif qui peut être fabriqué selon un premier mode de réalisation de l'invention;
• les figures 2 à 4 représentent de manière schématique le procédé d'assemblage d'un dispositif selon un premier mode de réalisation de l'invention;
• les figures 5 et 6 représentent de manière schématique une variante du dispositif qui peut être fabriqué selon le premier mode de réalisation de l'invention;
• les figures 7 à 9 représentent de manière schématique une pluralité des dispositifs fabriqués selon des différents modes de réalisation de l'invention.

The aims, advantages and characteristics of the method according to the present invention will appear more clearly in the following detailed description of at least one embodiment of the invention given solely by way of non-limiting example and illustrated by the appended drawings in which:

• the figure 1 schematically represents a device which can be manufactured according to a first embodiment of the invention;
• the figures 2 to 4 schematically represent the method of assembling a device according to a first embodiment of the invention;
• the figures 5 and 6 schematically represent a variant of the device which can be manufactured according to the first embodiment of the invention;
• the figures 7 to 9 schematically represent a plurality of devices manufactured according to different embodiments of the invention.

DETAILED DESCRIPTION

The present invention relates to a method of manufacturing a composite part comprising a first part and at least one second part.

In a first embodiment of the invention visible in figure 1 , the device 10 comprises a first part 11 and a second part 12. The first part 11 is made of a first material while the second part 12 is made of a second material.

According to this first embodiment, the first part or the second part is produced in the form of an at least partially amorphous metallic foam comprising at least one metallic element such as an at least partially amorphous metallic alloy.

This metallic element can be a classic metallic element such as iron, nickel, zirconium, or precious such as gold, platinum, palladium, rhenium, ruthenium, rhodium, silver, iridium or osmium. It will be understood by at least partially amorphous material that the material is able to solidify at least partially in the amorphous phase, that is to say that it is subjected to a temperature rise above its melting point allowing it to locally lose any crystalline structure, said rise being followed by cooling to a temperature below its glass transition temperature allowing it to become at least partially amorphous.

Such foam can be made using different techniques. A first method consists in taking an alloy and heating it until it reaches a liquid state. At this time, gas bubbles are injected into said alloy which is in the liquid state. This injection of gas bubbles occurs before a stage of rapid cooling. This rapid cooling step is carried out to solidify said alloy while trapping the gas bubbles.

A second method for making such a foam consists of using an alloy and heating it until it reaches a liquid state. At this time, chemical agents are injected into said alloy which is in the liquid state. These chemical agents are gas-releasing agents so that the latter, under certain conditions, release gases. These chemical agents or precursors can be, for example, titanium or zirconium hydrides. This release of gas occurs before a rapid cooling step. This rapid cooling step is carried out to solidify said alloy while trapping the gas bubbles.

A variant of this second method consists in providing a material capable of becoming a foam in order to obtain a material which only becomes an amorphous metallic foam when it is shaped. Indeed, the chemical agents used are releasing agents which release gases under certain conditions of temperature and pressure. Thus, by increasing the pressure during cooling, the release of gas is contained. During shaping, the increase in temperature allows the release of the gas and therefore the transformation of the material into foam.

A third method for producing an amorphous metal foam consists of successive deposits of layers of powder, each layer of powder being sintered locally by a laser or electron beam. This local sintering thus makes it possible, at the level of each layer of powder, to create the pores which will make it possible to form the foam.

This advantageously makes it possible to produce coated parts or bi-material parts, the second part 12 is then a coating or an integral part of the first part 11.

In fact, it may be useful, for parts made of fragile materials such as silicon, to have parts coated or made of a more resistant material or having more favorable mechanical properties, or simply to have an entire part of the part is made of another material. This embodiment also makes it possible to simply produce the second part and its assembly with the first part during a single process.

In the case where a part is coated with the amorphous metallic foam, consider the example of a bezel 21 acting as the first part 11, coated with a layer 22 of foam acting as the second part 12 forming a coated part 20 which is the final device 10 as seen in figure 1 . The first material can be a conventionally used material such as steel, brass, aluminum or titanium, but it can also be a so-called fragile material. The term "fragile material" means a material which has no exploitable plastic domain such as for example quartz, ruby, sapphire, glass, silicon, graphite, carbon or a ceramic such as silicon nitride and silicon carbide or a cermet type composite.

The method consists, in a first step, in providing a preform 23 of amorphous metal foam.

A second step consists in taking the part to be coated, here the bezel 21, and placing it in a mold 24 which can be dies 24a, 24b having the negative shape of the coated part as visible at picture 2 . This mold can be formed from two dies. The preform 23 is also placed in the mold.

For example, if you want to coat the entire surface of a bezel or a cog with a 0.1 millimeter layer of amorphous metallic foam, the mold will have the shape of the cog or bezel and dimensions equal to the dimensions of the cog to which are added the 0.1 millimeter of the layer. There is therefore a space 25 to be filled.

In a third step, a heating step is carried out. This heating step consists in heating the assembly to a temperature between the glass transition temperature Tg and the crystallization temperature Tx of the preform. At this temperature, the amorphous metals have a viscosity which decreases sharply, the decrease in viscosity being dependent on the temperature: the higher the temperature, the more the viscosity decreases. This viscosity allows the amorphous metal, when subjected to stress, to fit into every corner of a mold.

This rise in temperature also makes it possible to heat the gas bubbles present in the foam preform. However, a heated gas expands so that it will occupy a larger volume. Since the amorphous metal of the foam is in a so-called viscous state, this expansion of the gas causes the foam preform to expand, this preform begins to swell as visible to the picture 3 . Consequently, the volume taken up by the preform increases. This increase in the volume of the preform associated with the shaping characteristics of amorphous metals results in the filling of the mold as visible at the figure 4 .

To allow the expansion of the amorphous metal foam preform, it is necessary that the pressure in the negative is lower than the pressure of the gas inside the preform otherwise there can be no expansion. In the case of a sealed mould, provision is made to place the cavity formed by the two dies under vacuum. In the case where the two dies form a non-sealed mould, provision will be made for the enclosure in which the mold is located to be placed under vacuum or at a pressure sufficiently lower than the pressure of the gas.

Similarly, to prevent the stress exerted by the expansion of the preform from leading to separation of the two dies from the mould, these two dies can be fixed together via fixing means such as screws or simply by exerting a force on them. pressure.

Once the preform has expanded, a cooling step is performed. This cooling step is done to freeze the amorphous metal foam preform and form the intermediate piece. The device is then separated from the dies to obtain the device of the figure 1 .

In the case where a part is bi-material, it will be understood that the final part is composed of a first part 11 in any material and a second part 12 in amorphous metal foam. The method consists, in a first step, in providing an amorphous metal foam preform. For example, it may be a bi-material bezel consisting of a base 31 acting as a first part 11 on a second part 12 made of a second material. This second part 12 then forms an outer shell 32 of the bezel as seen on the figure 5 .

In another example, the final part 10 may be an axle 41 whose studs 42 are made of a second material as seen in figure 6 .

These two examples highlight the advantage of a bi-material part, which is to be able to select the material according to the use made of it.

A second step consists in obtaining the first part 11 of the bi-material part and placing it in a mold having the shape and dimensions of the final part.

In this second step, the preform is also placed in the mould. The preform has a shape similar to that of the second part.

In a third step, a heating step is carried out. This heating step consists of heating the assembly to a temperature between the glass transition temperature Tg and the crystallization temperature Tx of the preform. At this temperature, the amorphous metals have a viscosity which decreases sharply, the decrease in viscosity being dependent on the temperature: the higher the temperature, the more the viscosity decreases. This viscosity allows the amorphous metal to fit into every corner of a mould. This rise in temperature also makes it possible to heat the gas bubbles present in the foam preform.

However, a heated gas expands so that it will occupy a larger volume. Since the amorphous metal of the foam is in a so-called viscous state, this expansion of the gas causes the foam preform to expand, this preform begins to swell. Consequently, the volume taken up by the preform increases. This increase in the volume of the preform associated with the shaping characteristics of amorphous metals leads to the filling of the mold, ie the filling of the space dedicated to the second part of the final part.

Once the preform has expanded, a cooling step is performed. This cooling step is done to freeze the amorphous metal foam preform and form the intermediate piece.

In a variant of this first embodiment visible in figure 7 , it is possible that the first part 11 of the final part is provided with a cavity 13. This cavity 13 is used to improve the connection between the first part 31 and the second part 32 in cases where the second part 32 is a coating or is used to form a bi-material part. The production of a cavity 13 allows, during manufacture, the amorphous metal foam to extend therein to reinforce the connection between the first part and the second part.

This cavity can be fitted with or be replaced, depending on the case, by structuring 14 which increases the roughness and therefore grips it as visible on the figure 8 .

In an alternative of the first variant of the first embodiment, the cavity is arranged to have a shape such that its surface is not constant. This means that the cavity does not present a constant profile as a function of depth. Ideally, it will be expected that the profile of the cavity widens according to the depth so as to create a natural restraint.

This possibility makes it possible to have a method in which the step of transforming the preform into foam and the step of expanding said foam take place at the same time. This is made possible because the release of gas by the precursor chemicals and the expansion of the foam occur when the material is heated.

Consequently, the method consists in obtaining the preform which is not in the form of a foam and placing it in the mold. The whole is then heated to a temperature allowing the precursor chemical agents to release gas, this temperature also allowing the gases to expand and cause the material to expand.

In the different embodiments, the control of the expansion of the amorphous metal foam preform can be done in several ways.

A first solution consists in modifying the density of the gas bubbles during the manufacture of the foam. One method of making amorphous metal foam is to inject gas bubbles into the molten metal and cool it to trap those bubbles. The injection of gas bubbles can be controlled so that they are distributed more or less homogeneously and more or less densely. It will then be understood that the greater the density of the gas bubbles, the greater the volume of gas enclosed in the foam. However, the greater the volume of gas enclosed, the greater the expansion will be due to the expansion of the gas during the heating step.

A second solution consists in controlling the expansion of the amorphous metal foam by modifying the temperature of the heating step. Indeed, when a gas is subjected to heating, the momentum of the particles that compose it increases. At constant volume, this results in an increase in pressure, because the number of collisions between particles per unit area increases. If the pressure should remain constant, then the volume of the gas should increase, according to the ideal gas law. Consequently, by increasing or decreasing the heating temperature during the heating step, the volume of the gas enclosed in the amorphous metal foam is varied and its expansion is therefore modified.

In a third solution, the control of the expansion of the amorphous metal foam is done by controlling the atmosphere in the heating enclosure of the second embodiment or in the cavity of the mold in the first embodiment. This solution assumes that expansion is possible from the moment the pressure of the gas enclosed in the amorphous metallic foam is greater than that of the atmosphere outside the foam. The ideal is for the outside atmosphere to be close to a vacuum so as to favor the expansion of the foam as much as possible. Therefore, by adjusting the external pressure, the amplitude of the expansion of said foam is adjusted knowing that the greater the pressure of the external atmosphere, the less the expansion will be.

It will be understood that various modifications and/or improvements and/or combinations obvious to those skilled in the art can be made to the various embodiments of the invention described above without departing from the scope of the invention defined by the appended claims.

Of course, it is conceivable that the cavities can be replaced or supplemented with protuberances 15 as visible at figure 9 . These protuberances are the negatives of the cavities and have the same function. By this is meant that the amorphous metal foam is shaped so as to be able to envelop this or these protrusions and improve the connection between the first part and the second part.

Claims (10)

1. A method of manufacturing a part (10) consisting of a first portion (11) made of a first material and a second portion (12) made of a second material, said method further comprising the following steps:

   - procuring a preform made of the second material, said second material being an at least partially amorphous metal adapted to increase in volume subject to temperature and pressure conditions;

   - procuring said first portion and a mould comprising two dies forming a cavity, and placing said first portion and the preform between the two dies having the negative shape of the part to be manufactured;

   - heating the combination to a temperature between the glass transition temperature Tg and the crystallisation temperature Tx of the preform in order, at the latest during this step, to enable the preform to form a foam and to enable expansion of said preform in order to fill the negative shape of the part and form said part;

   - cooling the combination to solidify the preform and separate the part from the dies, and in that the expansion of the amorphous metal foam preform is achieved when the pressure between the two dies is less than the gas pressure inside the preform, and:

   - in the case of a sealed mould, placing the cavity under vacuum to allow the expansion of the amorphous metal foam preform, or

   - in the case of an unsealed mould, placing the mould in an enclosure and placing the enclosure under vacuum or at a pressure sufficiently less than the gas pressure to allow the expansion of the amorphous metal foam preform.
2. The method of manufacture as claimed in claim 1, characterised in that the expansion of the preform is used to form a coated part.
3. The method of manufacture as claimed in claim 1, characterised in that the expansion of the preform is used to form a bimaterial part.
4. The method of manufacture as claimed in any one of claims 1 to 3, characterised in that the first portion is provided with at least one cavity (13) into which the amorphous metal foam forming the second part extends.
5. The method of manufacture as claimed in any one of claims 1 to 4, characterised in that the first portion is provided with at least one protuberance (15) around which the amorphous metal foam forming the second part extends.
6. The method of manufacture as claimed in any one of claims 1 to 5, characterised in that the first portion is provided with structures (14) enabling better attachment of the second portion.
7. The method of manufacture as claimed in any one of the preceding claims, characterised in that it includes a preliminary step of fabrication of an at least partially amorphous metal alloy foam preform.
8. The method of manufacture as claimed in any one of the preceding claims, characterised in that the expansion of the foam is controlled by temperature, the higher the temperature the greater the expansion.
9. The method of manufacture as claimed in any one of the preceding claims, characterised in that the expansion of the foam depends on the gas density in the foam, the greater the trapped gas volume the greater the expansion.
10. The method of manufacture as claimed in any one of the preceding claims, characterised in that the expansion is produced by making the pressure in the foam greater than the ambient pressure.

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