CH721908A2 - Method for manufacturing an oscillating mass made of heavy metal alloy by additive manufacturing - Google Patents

Abstract

The invention relates to a method for manufacturing an oscillating mass made of a heavy metal alloy by additive manufacturing, said method comprising the following steps: - providing a mixture of a metal powder comprising powder of a heavy metal and powder of a second metallic material, an organic binder and a photopolymerizable polymer to form a photosensitive feedstock; - performing successive passes from a support, each pass comprising the deposition of at least one layer of the feedstock, the deposited feedstock adhering to the feedstock of at least one previously deposited layer, the feedstock deposit at each layer being polymerized at each pass so that the stacking of successive layers forms a green piece of the oscillating mass; - removing the unpolymerized photosensitive polymer; - debinding the green piece; - sintering the debinded piece to obtain a dense roughout of the oscillating mass; - performing a finishing of the dense roughout of the oscillating mass to obtain a decorated oscillating mass.

Description

TECHNICAL FIELD

[0001] The present invention relates to a manufacturing process for obtaining an oscillating mass essentially formed in a heavy metal alloy.

EARLIER ART

[0002] The oscillating weight is a crucial element in automatic watch movements. Watches are known to have a self-winding movement equipped with an oscillating winding weight for winding the movement through the natural movements of the wrist.

[0003] Automatic watches with oscillating weights typically feature a single-piece oscillating weight. However, it is difficult to reconcile a small size with sufficient weight for effective winding. Its design must meet stringent technical requirements to ensure its winding function while also serving as a decorative element. The materials generally used in its construction are gold, platinum, or tungsten.

[0004] To remedy this problem, it is possible to combine materials of different densities as in document EP 3 839 646. However, such a construction is not satisfactory for all types of decoration and requires a number of operations to manufacture and assemble the mass.

[0005] The decoration of its surface allows for artistic executions using numerous techniques, for example crimping, guilloché work, laser engraving or CNC machining, etc...

[0006] In view of the aesthetic trends to obtain increasingly thin or finely decorated pieces, the weight of the metal used is essential and poses many challenges.

[0007] Thus, it is not possible to directly machine a heavy metal such as tungsten to the desired dimensions for an oscillating mass with a fine and complex geometry, particularly in the case of a skeletonized oscillating mass. Indeed, such oscillating masses tend to deform during traditional machining, or they have a complex shape that cannot be achieved by five-axis CNC machining or femtosecond laser ablation.

[0008] Additive manufacturing processes for tungsten parts via laser sintering are also known, but the surface quality and porous appearance of the resulting part are unsatisfactory and do not meet the standards of high-end watchmaking. Furthermore, the alloys used by selective laser sintering (SLS) or selective laser melting (SLM) are not identical to those conventionally used in watchmaking by pressing.

SUMMARY OF THE INVENTION

[0009] The present invention aims to overcome the aforementioned disadvantages by proposing a method for manufacturing an oscillating mass made of a heavy metal alloy such as tungsten, gold or another heavy metal.

[0010] To this end, the present invention relates to a method for manufacturing an oscillating mass made of heavy metal alloy by additive manufacturing in two stages, said method comprising the following stages:

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provision of a mixture of a metallic powder comprising powder of a heavy metal and powder of a second metallic material, an organic binder and a photopolymerizable polymer to form a photosensitive feedstock;

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to perform successive passes from a printing platform, each pass comprising the deposition of at least one layer of the feedstock, the deposited feedstock adhering to the feedstock of at least one previously deposited layer, the feedstock deposit at each layer being selectively polymerized at each pass so that the stacking of successive layers forms a green piece of the oscillating mass;

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remove the unpolymerized photosensitive polymer to free the green piece from the oscillating mass;

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untie the green piece;

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sinter the unbound piece to obtain a dense rough draft of the oscillating mass;

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to perform a finishing of the dense roughing of the oscillating mass to obtain a decorated oscillating mass.

[0011] In accordance with other advantageous variants of the invention:

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the metal powder mixture comprises at least 90% of its mass of heavy metal powder;

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The heavy metal is chosen from: tungsten, gold, platinum, rhenium;

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the second metallic material is chosen from: copper, nickel, manganese-nickel, nickel-copper alloy, nickel-cobalt alloy; nickel-iron alloy, copper-cobalt alloy, nickel-copper-manganese alloy;

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Optionally, the mixture includes an additive chosen from: chromium, molybdenum, tantalum, boron, carbon;

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Additive manufacturing is a two-step metal additive manufacturing process based on the photopolymerization of a feedstock to obtain a green part;

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each layer has a thickness between 5 µm and 100 µm; and preferably between 15 µm and 75 µm;

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the sintering stage is carried out at a temperature between 1200°C and 1800°C for a time between 15 minutes and 40 hours;

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the sintering step is carried out in a neutral or reducing environment;

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the finest or most complex structure of the oscillating mass has a thickness of between 0.1 mm and 0.5 mm after the sintering step, for the thinnest parts of the oscillating mass.

[0012] The invention also relates to an oscillating mass essentially made of heavy metal alloy obtained via the process according to the invention.

[0013] Other features and advantages of the present invention will become apparent in the following description of a preferred embodiment, presented by way of non-limiting example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 represents a schematic view of the manufacturing process according to the invention.

Figure 2 illustrates a perspective view of an oscillating mass obtained via the manufacturing process according to the invention.

DETAILED DESCRIPTION

[0015] The present invention relates to a method for manufacturing an oscillating mass essentially made of heavy metal.

[0016] The invention described below aims to address the problems listed above in relation to the prior art that has been presented.

[0017] In particular, one objective is to produce oscillating masses essentially made of heavy metal alloy such as tungsten, a material of particular interest for its density and hardness.

[0018] Thus, the invention relates to a manufacturing process enabling the obtaining of an oscillating mass essentially formed of heavy metal alloy, and an oscillating mass obtained by the implementation of such a manufacturing process.

[0019] The additive manufacturing process for an oscillating mass made of heavy metal alloy comprises the following steps:

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E0: provision of a mixture comprising powder of a heavy metal, powder of a second metallic material, tungsten powder and powder of the second material forming a metallic powder, an organic binder and a photoinitiator polymer to form a photosensitive feedstock;

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E1: perform successive passes from a printing platform, each pass comprising the deposition of at least one layer of the feedstock, the deposited feedstock adhering to the feedstock of at least one previously deposited layer, the deposit of the feedstock at each layer being locally polymerized at each pass so that the stacking of successive layers forms a green piece of the oscillating mass;

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E2: separate the unpolymerized polymer from the polymerized feedstock to free the green part from the oscillating mass;

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E3: perform a debinding to remove the organic binder from the green piece and form a porous structure;

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E4: sinter the unbound part to obtain the oscillating mass, the porous structure closing during the sintering phase;

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E5: Perform a finishing of the dense roughing of the oscillating mass to obtain a decorated oscillating mass.

[0020] According to the invention, the manufacturing process comprises a main step E1 consisting of a successive-pass additive manufacturing method from a support platform, each pass comprising the deposition of at least one layer of the feedstock, the feedstock deposited at the time of the deposition of a given layer adhering to the feedstock of at least one previously deposited layer. The deposition of the feedstock at each layer is controlled at each pass so that the stacking of the feedstock deposited during the successive passes forms a rough outline of the oscillating mass.

[0021] One of the main difficulties is to find suitable parameters for the additive method to obtain a thin oscillating mass to limit the bulk while preserving the solidity of the oscillating mass with an elaborate/openwork/skeletonized structure without the material forming the oscillating mass deforming under its own weight.

[0022] According to one embodiment of the invention, each layer of mixture has a thickness between 5µm and 100µm.

[0023] According to an advantageous embodiment, each pass includes a step of depositing at least one layer of mixture followed by a step of selective polymerization of the mixture previously deposited under the action of a UV lamp for example.

[0024] This three-dimensional printing solution by depositing successive layers followed by selective photopolymerization is known under the technology called "SLA" or DLP.

[0025] According to the invention, the metal powder comprises at least 90% of its mass of heavy metal. The heavy metal is chosen from: tungsten, gold, platinum or rhenium.

[0026] The second metallic material is chosen from: copper, nickel, manganese-nickel, nickel-copper alloy, nickel-cobalt alloy; nickel-iron alloy, copper-cobalt alloy, nickel-copper-manganese alloy.

[0027] According to an optional embodiment of the invention, the metal powder comprises an additive selected from: chromium, molybdenum, tantalum, boron, carbon.

[0028] The binder is present at a level of 40% to 50% by mass in the feedstock to obtain a fluid feedstock that is easy to implement during additive manufacturing.

[0029] The E0 step of preparing the mixture may include a preliminary preparation step in which the heavy metal powder particles are coated with a thin layer of Al2O3 by ALD, PVD, CVD, or fluidized bed deposition to make the powder more optically suitable. Alternatively, the heavy metal powder may be coated with the second metallic material to homogenize the alloy beforehand. The powder is then ready to be mixed with the organic binder and the photoinitiator polymer to form a photopolymerizable feedstock.

[0030] The size of the particles forming the metal powder is between 5 µm and 15 µm to obtain a good particle density within the feedstock.

[0031] More generally, the oscillating mass 1 obtained has a general shape of a skeletonized, openwork, and/or decorated half-disc, the thinnest parts 10, 11, 12, 13 of the oscillating mass having a thickness between 0.2mm and 0.5mm.

[0032] During the debinding step E3, the organic binder present in the part is dissolved or burned to form a porous structure (also called a brown part). This porous structure will disappear during the subsequent sintering step E4, as the part shrinks during sintering. Therefore, the oscillating mass must be oversized when printed in step E1.

[0033] Preferably, the temperature is increased to the desired sintering temperature. Once sintering is complete, the temperature is gradually lowered.

[0034] Sintering is carried out in a neutral or reducing environment. Sintering can, for example, be carried out under an inert atmosphere using Argon.

[0035] Depending on the needs of a person skilled in the art, several sinterings may be carried out to achieve the desired result.

[0036] The process may include a finishing step traditionally used for oscillating masses, which may include precision machining, sandblasting, crimping, laser ablation, etc.

[0037] Such a process thus makes it possible to obtain an oscillating mass which has a complex shape and which is not achievable by conventional machining methods such as five-axis CNC machining or femto laser ablation.

Claims (10)

1. A method for manufacturing an oscillating mass (1) made of a heavy metal alloy by additive manufacturing, said method comprising the following steps: - providing a mixture of a metal powder comprising powder of a heavy metal and powder of a second metallic material, an organic binder, and a photopolymerizable polymer to form a photosensitive feedstock mixture; - making successive passes from a substrate, each pass comprising the deposition of at least one layer of the feedstock, the deposited feedstock adhering to the feedstock of at least one previously deposited layer, the feedstock deposit at each layer being polymerized in each pass so that the stacking of successive layers forms a green part of the oscillating mass; - removing the unpolymerized photosensitive feedstock to release the green part of the oscillating mass; - debinding the green part; - sintering the debinded part to obtain a dense blank of the oscillating mass; – to perform a finishing of the dense roughing of the oscillating mass (1) to obtain a decorated oscillating mass (1). 2. A manufacturing process according to claim 1, characterized in that the metal powder comprises at least 90% of its mass of heavy metal. 3. Manufacturing process according to claim 1 or 2, characterized in that the heavy metal is selected from: tungsten, gold, platinum, rhenium. 4. A manufacturing process according to any one of the preceding claims, characterized in that the second metallic material is selected from: copper, nickel, manganese-nickel, nickel-copper alloy, nickel-cobalt alloy; nickel-iron alloy, copper-cobalt alloy, nickel-copper-manganese alloy. 5. A process according to any one of the preceding claims, characterized in that the metal powder comprises an optional additive selected from: chromium, molybdenum, tantalum, boron, carbon. 6. A process according to claim one of the preceding claims, characterized in that the additive manufacturing is a two-step metal additive manufacturing, based on the photopolymerization of a feedstock to obtain a green part. 7. A method according to any one of the preceding claims, characterized in that each layer has a thickness between 5 µm and 100 µm, and preferably between 15 µm and 75 µm. 8. A process according to any one of the preceding claims, characterized in that the sintering step is carried out at a temperature between 1200°C and 1800°C for a time between 15 minutes and 40 hours. 9. A process according to any one of the preceding claims, characterized in that the sintering step is carried out in a neutral or reducing environment. 10. A method according to any one of the preceding claims, characterized in that the oscillating mass (1) has a thickness of between 0.1mm and 0.5mm after the sintering step, for the thinnest parts (10, 11, 12, 13) of the oscillating mass (1).