DE102020000247A1 - Method for additive manufacturing of a three-dimensional body from a metal powder and a body produced in this way - Google Patents

Abstract

The invention relates to a method for producing a three-dimensional body from a noble metal-containing powder, in which a powder layer is applied to a carrier and that area of the applied powder layer which corresponds to the respective layer geometry of the body to be produced is selectively melted by means of a laser, and in which successively further powder layers of the noble metal-containing powder are applied and those areas of the applied powder layer that correspond to the respective layer geometry of the three-dimensional body to be produced are melted. According to the invention, it is provided that for the selective melting of at least one and preferably all powder layers, a laser is used whose laser beam has a wavelength of has less than 600 nm.

Description

The invention relates to a method for additive manufacturing of a three-dimensional body from a precious metal-containing powder, in which the individual particles of this metal powder are fused by a laser beam, the use of a precious metal-containing powder in an additive manufacturing process for the production of a three-dimensional body and one manufactured by an additive manufacturing process three-dimensional body.

Additive manufacturing processes are known. the DE 10 2017 212 182 A1 describes e.g. B. a method for producing a component from a noble metal by selective laser melting, in which a powder layer is applied to a substrate plate and then that area of the applied powder layer that corresponds to the respective layer geometry of the body to be produced is selectively melted by means of a laser. A further powder layer of the noble metal is then applied and that area of the applied powder layer which now corresponds to the layer geometry of the body to be produced is again melted. The aforementioned step is repeated until the three-dimensional body to be produced is produced additively in this way.

Additive manufacturing processes are used, among other things, for the manufacture of luxury goods such as jewelry, watch cases, writing implements or parts thereof made of precious metal or precious metal alloys, to name just a few examples, as they allow the manufacture of precious metal products with a complex geometry in a simple manner allow in that the corresponding component is produced in a manner known per se by applying precious metal-containing particles in layers. Eg describes the EP 1 677 930 B1 a process for the production of jewelry and other precious metal products with complex geometries from a precious metal-containing powder material, wherein the powder metal is subjected to at least one partial melt by exposure to a laser beam, which leads to a bonding of the layer with the immediately preceding layer. The wavelength of the laser used here is 1070 nm. The powder material is an 18-carat gold alloy containing 60-80% by weight gold, 0-15% by weight silver, 5-15% by weight copper, 5-25% by weight Contains wt .-% tin and 0.0-2 wt .-% phosphorus. The porosity of the three-dimensional body produced with it is less than 10% by volume.

The disadvantage of the known method is that the product produced in layers in this way has to be subjected to a mechanical surface treatment such as blasting or polishing in order to adapt this product to the desired aesthetic appearance. the EP 3 142 814 B1 describes the use of gold powder alloys for the production of jewelry by selective laser melting. In the aforementioned publication, a large number of yellow, red or white gold powder alloys are presented which contain 18 carat, 14 carat, 10 carat or 9 carat gold. The power of the laser used here is at least 70 watts and the wavelength is 1070 nm. The pieces of jewelry made from the aforementioned powders have a porosity of less than or equal to 2% by volume.

A decisive quality criterion for pieces of jewelery such as jewelery, watch cases, writing implements or parts thereof is a largely defect-free surface and a flawless shine of the polished areas of the aforementioned articles. An essential prerequisite for achieving this is that the density of the body produced by selective laser melting is greater than or equal to 99.9% by volume and that the maximum defect size is less than or equal to 30 μm. These prerequisites are difficult or impossible to achieve with standard precious metal alloys and the known additive manufacturing processes in which a laser with a wavelength of 1070 nm is used.

It was therefore z. B. in the EP 3 216 545 B1 proposed to add additives to the metal powders used in additive manufacturing in order to improve the energy absorption of the noble metal particles to be fused in the powder bed. Such a measure leads to the fact that the individual powder particles fuse better, which results in a higher density of the three-dimensional body produced from the noble metal-containing powder particles. The disadvantage of this, however, is that the improvement in the material quality leads to color changes.

The color of a three-dimensional body made from precious metal particles is particularly important in the jewelry and watch industry. The manufacturers of such luxury items require the producers of the precious metal powder used in the additive manufacturing of such luxury items that the three-dimensional body made from them has a defined color in accordance with ISO standard 8654 (2018). The above-mentioned addition of additives can disadvantageously lead to the fact that the three-dimensional body produced by laser melting no longer has the desired standard color, but only a similar one. Such a color deviation is generally not accepted, especially in the luxury goods sector.

Another disadvantage of using additives to increase the efficiency of the additive manufacturing process is that the noble metal powder provided with an additive may no longer be hallmarkable, ie does not meet the standards that are e.g. B. a 14-carat, an 18-carat, a 24-carat gold alloy or z. B. a platinum alloy (Pt950) containing at least 95% by weight of platinum. A validation process is therefore required for every alloy provided with such an additive so that it can be hallmarked.

It is also known to subject the three-dimensional bodies produced by additive manufacturing to what is known as hot isostatic pressing. Such a process can lead to a density of almost 100% by volume. Such a pressing is a complex process, which has a negative impact on the efficiency of the additive manufacturing process. However, the aforementioned heat treatment also has the disadvantage that the metal structure becomes coarser, which is accompanied by a reduction in the hardness of the material and the ability to be polished of the three-dimensional body produced by laser melting from precious metal particles.

It is therefore the object of the present invention to improve a method for additive manufacturing of a three-dimensional body from a noble metal-containing powder in such a way that an improved density and a reduced defect size of the three-dimensional body produced by the method according to the invention is achieved, as well as the use of such a powder. In addition, a three-dimensional body made from noble metal particles is to be proposed.

The method according to the invention provides that the wavelength of the laser used in laser melting is less than or equal to 600 nm, preferably in a range between 300 nm to 600 nm, more preferably in a range between 500 nm to 600 nm, more preferably in a range between 520 and 550 nm and the laser beam in particular has a wavelength of 535 nm.

The three-dimensional body according to the invention, in particular an item of jewelry such as a piece of jewelry, a watch or a writing instrument or parts thereof, is characterized in that an additive manufacturing process is used to manufacture it from a powder containing precious metals, which uses a laser with a wavelength of less than or equal to 600 nm and in particular of 535 nm are used.

The measures according to the invention have the advantage that with standard noble metal powders, i.e. with noble metal powders that do not have any additives that improve the absorption of the laser beam, three-dimensional bodies can be produced by selective laser melting, which are characterized in that they have a density greater than or equal to 99 , 9% by volume. Such a high density of the three-dimensional body produced with the method according to the invention brings with it in an advantageous manner that even high requirements, such as those demanded by manufacturers of luxury items such as watches, jewelry and writing implements - as explained at the beginning - are met. In an advantageous manner, no post-processing such as hot isostatic pressing is therefore generally required in the case of a body produced in this way. Since, as already stated, the measures according to the invention make it possible to use noble metal-containing powders to which no additives are added to increase energy absorption, the three-dimensional bodies produced with the method according to the invention not only have a high surface quality, there is also a change in color that occurs or can occur in the known processes due to the addition of additives. An additional validation effort, which - as already explained above - occurs when standard alloys are changed by adding additives, is also not necessary. The measures according to the invention therefore advantageously allow an efficient production of three-dimensional bodies from standard noble metal powder by means of an additive manufacturing process.

Advantageous further developments of the invention are the subject of the subclaims.

Further details and advantages of the invention can be found in the exemplary embodiments which are described below. The content of precious metals in the alloys described below corresponds to the ISO 9202 standard.

The first exemplary embodiment of an additive method for producing a three-dimensional body by means of selective laser melting of a powder containing noble metals is based on a gold alloy. In the exemplary embodiment described here, this has 75% by weight of gold and copper and silver in a total proportion of 25% by weight. So it is an 18-carat gold alloy. In the case of such a gold alloy, a gold content of 75% by weight is prescribed in order to be hallmarkable. The proportion of copper and silver is selected depending on the desired color of the material. A representative of such a gold alloy is e.g. B. a gold alloy, which has 75 wt .-%, 20 wt .-% copper and 5 wt .-% silver. Such an alloy corresponds to a 5N alloy according to the aforementioned ISO 8654.

The gold alloy of the first exemplary embodiment used in the additive manufacturing process has a powder particle size distribution that is between d ₁₀ = 10 μm and d ₉₀ = 50 μm. The additive process was carried out on a TruPrint 1000 machine from the manufacturer Trumpf.

A test body, which was produced in a known manner by additive laser melting of the powder particles of the gold alloy described using a laser with a wavelength of 1070 mn, has a material density of 99.50-99.90% by volume, the Production was carried out with a maximum laser energy of 150 W and a resulting volume energy of 325 J / mm ³ .

A test body that was produced under comparable process conditions, but with a laser that uses a wavelength of 535 nm, has a material density of 99.97 +/- 0.02% by volume. The use of laser radiation with a wavelength of 535 nm thus leads to a significant increase in the density of the test body produced by the additive manufacturing process, the maximum defect size being less than or equal to 30 μm.

Comparable values are obtained with a gold alloy, which has 75 wt .-% gold, 5-12.5 wt .-% silver and 12.5-20 wt .-% copper, as well as with a gold alloy that has 75 wt .-% Gold, 13-15 wt% palladium and 10-12 wt% other metals. Even with a 14-carat gold alloy, which has 58.5% by weight gold, 10-34.5% by weight silver and 7-40.5% by weight copper, the density of the aforementioned is significantly improved Alloys made solid body given.

The method described can be used not only with 14- or 18-carat gold alloys, but also, for example, with 8- to 22-carat gold alloys. Even with gold alloys of a different composition, there is an increased density of the body made from the corresponding alloy by means of an additive laser melting process.

The second exemplary embodiment for producing a three-dimensional body by means of an additive manufacturing process is based on a powder of a platinum alloy which has 95% by weight of platinum and 5% by weight of copper. A conventional laser melting process was carried out with the aforementioned machine. Bodies which were produced with a wavelength of the laser beam used of 1070 nm had material densities of 99.7-99.95% by volume. In contrast, test bodies that were produced under otherwise identical process conditions with a laser wavelength of 535 nm, material densities of 99.94 +/- 0.03 vol 600 mm / s, which results in an introduced volume energy of up to 170 J / mm ^3.

Similar values result when using powder particles made of an alloy containing 95% by weight of platinum and 5% by weight of ruthenium or 95% by weight of platinum and 5% by weight of cobalt or 95% by weight of platinum, 3 Wt .-% gallium and 2 wt .-% copper or 95 wt .-% platinum, 2 wt .-% gold and the remainder consisting of other metals as well as 95 wt .-% platinum, 1.5 wt .-% gold, 1% by weight ruthenium and the remainder other metals.

However, the method described is not limited to an alloy with 95% by weight of platinum; B. an alloy with 85 wt .-% platinum, can be used in the additive manufacturing process described.

The same applies to the other platinum group metals, in particular to palladium, rhodium, ruthenium or iridium and to a mixture of the aforementioned metals of the platinum group.

A third exemplary embodiment for producing a three-dimensional body by means of an additive manufacturing process is based on a powder of a silver alloy. In the exemplary embodiment described here, a silver alloy is used which contains between 92.5-93.5% by weight silver and the remainder copper. The advantages described in the above exemplary embodiments also result here. The method described is therefore also suitable for the additive manufacturing of a three-dimensional body from powders containing silver.

The three exemplary embodiments described above have in common that a laser with a wavelength of 535 nm was used in each case. However, the method described is not restricted to this wavelength. This is advantageous, but not mandatory. Possible laser wavelengths that can be used in the described method for additive manufacturing are in a range of less than or equal to 600 nm, preferably in a range between 300 nm and 600 nm, more preferably in a range between 500 nm and 600 nm, more preferably in a range between 520 nm and 550 nm.

In summary, it should be noted that the method described and the use of gold- or silver-containing powders or powders that contain one or more platinum group metals are advantageous three-dimensional bodies, in particular with a complex geometry, can be produced which are characterized by a high density of greater than or equal to 99.9% by volume of the solid body, the maximum defect size preferably being less than or equal to 30 μm. Since the measures according to the invention make it possible to dispense with the use of additives to improve energy absorption, there are no color deviations from the underlying standard alloy and a validation of the powders used is also not necessary. Another advantage of the measures according to the invention is that no complex post-processing is required. The method according to the invention thus advantageously allows an efficient production of three-dimensional bodies from powders containing noble metals. This is particularly advantageous in the jewelry and watch industry and in the manufacture of high-quality writing implements.

The method described can not only be used in the jewelry and watch industry and in general in the luxury goods industry, but is also suitable for technical applications, in particular in the field of dental technology, measurement technology or medicine, to name just a few examples of such technical fields of application .

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102017212182 A1 [0002]
• EP 1677930 B1 [0003]
• EP 3142814 B1 [0004]
• EP 3216545 B1 [0006]

Claims (8)

Method for producing a three-dimensional body from a powder containing precious metals, in which a powder layer is applied to a carrier and that area of the applied powder layer that corresponds to the respective layer geometry of the body to be produced is selectively melted by means of a laser, and in which further powder layers of the precious metal-containing powder are successively melted Powder applied and those areas of the applied powder layer which correspond to the respective layer geometry of the three-dimensional body to be produced are melted, characterized in that a laser is used for the selective melting of at least one and preferably all powder layers, the laser beam of which has a wavelength of less than 600 nm . Procedure according to Claim 1 , characterized in that the wavelength of the laser beam used is in the range between 300 nm and 600 nm, preferably in the range between 500 nm and 600 nm, in particular in the range between 520 nm and 550 nm and is preferably 535 nm. Method according to one of the preceding claims, characterized in that the powder layer contains a powder made of a silver-containing metal or a gold-containing metal. Method according to one of the preceding claims, characterized in that the powder layer has a powder which contains palladium, platinum, rhodium, ruthenium and / or iridium. Use of a noble metal-containing powder for the production of a three-dimensional body by means of an additive manufacturing process according to one of the preceding claims, characterized in that the powder contains gold, silver, platinum, palladium, rhodium, ruthenium and / or iridium. Use of a noble metal-containing powder according to the preceding claim, characterized in that gold in a proportion of 75% by weight or 58% by weight or platinum or at least one platinum group metal in a proportion of 85% by weight or 95% by weight or silver is contained in a proportion of 92.5 to 93.5% by weight. Three-dimensional body, which is made from a noble metal-containing powder, characterized in that a method according to one of the to manufacture the body Claims 1 until 4th is used. Three-dimensional body according to Claim 7 , characterized in that the density of the body is greater than 99.9% by volume.