WO2020043886A1

WO2020043886A1 - Method for the additive manufacturing of workpieces from a flame-retardant polyamide material, workpieces obtainable thereby, and use of the polyamide material

Info

Publication number: WO2020043886A1
Application number: PCT/EP2019/073230
Authority: WO
Inventors: Jens Klüsener
Original assignee: Airbus Operations Gmbh
Priority date: 2018-08-30
Filing date: 2019-08-30
Publication date: 2020-03-05
Also published as: DE102018121230A1; EP3844210A1

Abstract

The invention relates to a method for the additive manufacturing of flame-retardant workpieces with improved fire behaviour. To this end, polyamide materials are provided which contain a flame retardant, which is selected from one or more of red phosphorus, phosphorus-containing compounds and melamine-based flame retardants. In particular, flame-retardant polyamide materials in powder form which are suitable for selective laser sintering are provided. The workpieces produced by selective laser sintering from these flame-retardant polyamide materials in powder form also have a surprisingly high surface smoothness in addition to the good fire behaviour. A polyamide material consisting of polyamide 6 and red phosphorus is particularly suitable. The workpieces can be used in the interiors of aircraft, in particular in the force-ventilated region.

Description

Process for additive manufacturing of workpieces from a flame-retardant polyamide material, thereby obtainable workpieces and use of the polyamide material

The invention relates to a method for the additive manufacturing of a workpiece from a flame-retardant polyamide material and the workpieces obtainable by this method.

It also relates to a flame-retardant powdered polyamide material and its use in an additive manufacturing process.

Additive manufacturing processes were initially used primarily for the production of individual prototypes (“rapid prototyping”). With the improvement of manufacturing processes, additive manufacturing processes are becoming increasingly important for the production of series products (“rapid manufacturing”).

Selective laser sintering (SLS) is one of the additive manufacturing processes used in industry. An essential application of selective laser sintering is in the production of objects from a thermoplastic. The thermoplastics that can be used in the SLS process are also referred to below as thermoplastic polymer materials or polymer materials for short.

When selecting the polymer materials that can be used in the SLS process, the starting point is the polymer materials which, in isotropic production processes, such as the injection molding of a polymer mass softened in an extruder, lead to products with the desired property profile. These include, for example, good mechanical properties, such as tensile strength, and chemical properties, such as resistance to lubricants and fuels, and good fire protection properties. For fire protection, polymers are usually given flame retardants with flame retardants. In addition, the polymer materials must be suitable for use under the specific process conditions of selective laser sintering. For example, at the high temperature of the powder bed near the melting temperature of the polymer material, the polymer particles must be able to be distributed evenly with a doctor blade to form a thin layer. They are intended to supply a powder bed that is quiet even when a protective gas flows through it. With regard to the end product, it is necessary that products with a suitable porosity are obtained with the powdery polymer material. The porosity of the sintered polymer is decisive for the strength of the finished workpiece. In addition, the powdery polymer material must be constructed in such a way and the selective laser sintering must be carried out in such a way that there is no oversintering.

A variety of polymer materials can be used in selective laser sintering. Polyolefins, polycarbonates, polyamides, polyvinyl chlorides, polybutylene terephthalates, polyacetals, polystyrenes can be used. However, the number of industrially usable polymer materials is rather small for demanding applications in the high-performance sector. Some of the materials available show an inadequate property profile.

Particularly high performance is expected from polymer materials that are used in aircraft construction. For this area of application, polyamide materials show an advantageous property profile. They have high strength and rigidity, good chemical resistance and long-term stability. In addition, they are well suited for selective laser sintering due to their good separation resolution, their level of detail and the post-treatment options.

So that polyamide materials can be used in aircraft construction, they must be equipped with flame retardants. Inorganic-mineral flame retardants, nitrogen-containing flame retardants, phosphorus-containing flame retardants and halogen-containing flame retardants are available for the flame-retardant finishing of polymers. The problem with the introduction of such flame retardants is that they can influence the chemical and physical properties of polyamide materials. The multitude of requirements placed on polymer materials for additive manufacturing processes, in particular selective laser sintering, has led to the development of powdered special products suitable for additive manufacturing. Powdery polymer materials available on the market have therefore been specially optimized for selective laser sintering and are typically not used in injection molding and extrusion processes.

A flame-retardant polyamide material specially developed for additive manufacturing is commercially available from EOS GmbH under the name PA 2241 FR. This is a polyamide 12 that contains a halogen-containing flame retardant. PA 2241 FR is a white polymer powder and, due to its flame-retardant properties, can be used as a high-performance plastic in the aerospace industry.

Another flame-retardant polyamide material specially developed for additive manufacturing is commercially available from EOS GmbH under the name PA 2210 FR. This is a polyamide 12 that contains a halogen-free flame retardant. PA 2210 FR is a white polymer powder for which aerospace, electrical engineering and electrics are specified as possible areas of application.

It is an object of the present invention to provide an improved method for the additive manufacturing of a workpiece from a flame-retardant polyamide material.

It is a further object of the present invention to provide improved flame-retardant workpieces obtainable by additive manufacturing.

It is a further object of the present invention to provide improved flame-retardant polyamide materials which are suitable for use in an additive manufacturing process. According to a first aspect, the invention relates to a method for additively manufacturing a workpiece from a flame-retardant polyamide material, the flame retardant for the flame-retardant finish of the polyamide material being selected from one or more of red phosphorus, phosphorus-containing compounds and flame retardants based on melamine.

The flame retardant used in the polyamide material may consist of a single one of the above-mentioned materials, such as red phosphorus, or a combination of the above-mentioned materials, such as red phosphorus and a melamine-based flame retardant.

The additive manufacturing process can essentially be a process carried out in a powder bed, such as selective laser sintering (SLS), selective laser melting (SLM) or selective absorbing sintering (SAS). The flame retardant polyamide materials can also be used in fused deposition modeling, fused layer modeling (FLM), mask sintering and polyjet modeling. Here, the flame-retardant polyamide material is processed in the form of a filament or in the form of pellets.

It is preferred that the method comprises the following steps:

a) providing the flame-retardant polyamide material in the form of a powder,

b) applying the powdered, flame-retardant polyamide material to a base to obtain a powder layer;

c) selective irradiation of the areas of the powder layer intended for workpiece formation with radiation, in particular laser radiation, which is suitable for connecting the particles of the powder layer in these areas by sintering or melting and solidifying;

d) repeating steps b) and c) above the respectively last irradiated powder layer as a base until the workpiece is made of flame-retardant polyamide material,

e) separating the workpiece from the powdery, flame-retardant polyamide material which has not been solidified by sintering or melting and solidification. The powdery flame-retardant polyamide material is well suited for processing in a powder bed. It can be spread easily and homogeneously with a doctor blade on the powder bed of the build platform and shows a very good flow behavior in the sintering process and in connection with this an advantageous layer application and particle arrangement.

Furthermore, good material consolidation and shape retention, such as little distortion, is found during laser sintering. The processing window or process window is significantly enlarged. Powdery polyamide material that was not solidified during laser sintering can be reused in the installation space. The refresh rate of the laser sinter powder is high.

The workpiece obtained, based on a polyamide material and at least one flame retardant, such as red phosphorus, shows in the fire test according to AITM- 0002 method B (measurement of the fire length), according to AITM2-0007 (measurement of the flue gas density) and AITM3-0005 (toxicity ) improved fire and toxicity properties.

Another advantage of the method according to the invention is that the workpiece, which is additionally manufactured from a powder, is obtained with a higher surface smoothness after it has been removed from the powder bed.

It is preferred that the polyamide material comprises one or more polyamides or a polymer blend of one or more polyamides with one or more miscible, compatible or immiscible polymers, which are selected in particular from polyolefins, polystyrenes, thermoplastic elastomers and polyacetals, wherein the polyamide content in the polymer blend is at least 30% by weight, preferably at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight.

It is preferred that the one or more phosphorus-containing compounds be selected from a group comprising: aromatic and aliphatic esters of phosphoric acid, such as resorcinol-bis (diphenylphosphate) (RDP), bisphenol-A- bis (diphenyl phosphate) (BPD) and its oligomers, triphenyl phosphate (TPP), tris (2-ethylhexyl) phosphate (TEHP), tricresyl phosphate (TKP), isopropylated triphenyl phosphate (ITP), ethylenediamine diphosphate, ammonium phosphate, ammonium polyatephosphate, such as Salts of hypophosphorous acid and their derivatives, such as alkyl phosphinate salts, e.g. B. diethylene phosphinate aluminum or diethylene phosphinate zinc or aluminum phosphinate, aluminum phosphite, aluminum phosphonate, phosphonate ester, oligomers and polymeric derivatives of methanephosphonic acid, 9,10-dihydro-9-oxa-10-phosphorylphenanthrene-10-oxide, ammonium polyphosphate, phosphacenes, vi - nylphosphonic acid.

In a preferred embodiment, the flame retardant can consist of red phosphorus or contain red phosphorus.

It is preferred that the one or more melamine-based flame retardants be selected from a group comprising: melamine, melamine derivatives, melamine condensation products, melamine salts, Meier, melam, melon, benzoguanamine, allantoin, polyisocyanurate, melamine cyanurate, melamine phosphate, Dimelamine phosphate, melamine pyrophosphate, melamine polyphosphate, melamine metal phosphates, such as melamine aluminum phosphate, melamine zinc phosphate, melamine magnesium phosphate, the corresponding pyrophosphates and polyphosphates, poly- [2,4- (piperazin-1, 4-yl) -6- (morpholine -4-yl) -1, 3,5-triazine].

It is preferred that the flame retardant is incorporated into the polyamide material in a proportion in the range from 0.1 to 20% by weight, preferably 1 to 15% by weight, based on the total weight of the flame-retardant polyamide material.

It is preferred that the polyamide material contains one or more polyamides selected from the group consisting of polyamide 6, polyamide 11, polyamide 12, polyamide 6.6, polyamide 6.9, polyamide 6.10, polyamide 6.12, polyamide 10.10 and copolyamides thereof, such as polyamide 6/12, PA 6.6 / 6.10, or consists of one or more of these polyamides. It is particularly preferred that the polyamide material consists of polyamide 6 or polyamide 6 in a proportion of at least 30% by weight, preferably at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight contains.

A powdered flame-retardant polyamide material which delivers particularly good results in selective laser sintering comprises polyamide 6 and red phosphorus (hereinafter abbreviated to: PA6-RP), the red phosphorus preferably being present in a proportion of 1 to 15% by weight. The workpiece obtained by selective laser sintering from PA6-RP shows good fire properties, which are also retained in connection with lacquers. With a higher proportion of red phosphorus, such as 14%, V0 can also be achieved in the UL-94 standard. An important fire property is achieved, such as z. B. is required in the railway industry. PA6-RP workpieces show improved properties in fire testing according to AITM-0002 method B (measuring the fire length), according to AITM2-0007 (measuring the smoke density) and AITM3-0005 (toxicity). A heat resistance of at least 85 ° C was determined. Due to this fire behavior, workpieces available from PA6-RP in the additive manufacturing process can be used for the interior of aircraft.

Powdered PA6-RP shows a very good flow behavior in the sintering process with regard to layer application and particle arrangement. The material consolidates well. A high degree of form accuracy (little distortion) is found. The processing window (process window) is significantly enlarged. Powdered PA6-RP that has not solidified can be reused in the installation space. It shows a high refresh rate.

Workpieces manufactured with PA6-RP additively by selective laser sintering show a higher surface smoothness after removal from the powder bed.

It is preferred that the polyamide material contains, in addition to the flame retardant, other auxiliaries, in particular antistatic agents, dyes such as, for example soluble inorganic and / or organic pigments and / or insoluble dyes, fillers, such as, for example, glass fibers, chalk, graphite, carbon black, lubricants, stabilizers and plasticizers.

It is preferred that the powdered, flame-retardant polyamide material has a particle size, in particular in the range from 40 to 110 mΐti.

It is preferred that one, several or all of the following steps are carried out to provide a powdered, flame-retardant polyamide material:

Locating a mixture or compound of the polyamide material and the flame retardant, in particular in the form of a cast block or a granulate or a granular material produced in an extruder,

Comminuting the block or the granulate or the granular material by mechanical processing, preferably grinding, particularly preferably cryogenic grinding, to a powdery material, and

Sieving the powdery material to obtain a sieve fraction of the powdery material with the grain size distribution desired for additive manufacturing.

If necessary, the angular surface of the particles of the powdery material obtained after grinding can be rounded before or after sieving.

It is preferred that in step c) the powder layer is irradiated with laser radiation with a wavelength that lies within the absorption band of the flame retardant, in particular of red phosphorus. In this case, the absorption by the flame retardant contributes to the required heating of the sintered powder.

It is alternatively preferred that in step c) the powder layer is irradiated with laser radiation with a wavelength that lies outside the absorption band of the flame retardant, in particular of red phosphorus, which is in particular on the long-wave side of visible light or more precisely in the range the infrared radiation is above 3000 nm. When the powder layers are exposed outside the absorption band of the flame retardant, in particular of red phosphorus, the required heating of the sintered powder advantageously takes place predominantly through absorption of the polyamide material.

It is also preferred that in step c) the laser radiation is emitted by an infrared laser, such as a CO2 laser, an Nd: YAG laser or a fiber laser.

It is preferred that the laser energy radiated in step c) is in the range from approximately 0.10 to 0.30 J / mm ³ , preferably approximately 0.15 to 0.25 J / mm ² , in particular approximately 0.2 J / mm ² mm ³ lies. The procedure for determining the optimally radiated energy is described in connection with the exemplary embodiment.

According to a further aspect, the invention relates to a flame-retardant workpiece that can be obtained by an additive manufacturing process as described above.

According to a further aspect, the invention relates to the use of a flame-retardant polyamide material, which is as defined above and in particular is in powder form, for additive manufacturing, in particular by means of selective laser sintering or selective laser melting, of a flame-retardant workpiece , in particular a flame-retardant workpiece with a high surface smoothness.

According to a further aspect, the invention relates to a flame-retardant polyamide material, as defined above and in particular in powder form, for the additive manufacturing of a flame-retardant workpiece, in particular by selective laser sintering or selective laser melting.

It is preferred that the flame-retardant powdered polyamide material is obtainable from

Production of a mixture or compound or blend from the polyamide material and the flame retardant, in particular in the form of a cast block or a granulate or a granular material produced in an extruder, Comminuting the block or the granulate or the granular material by mechanical processing, in particular grinding, preferably cryogenic grinding, to a powdery material, and

Before or after sieving, the angular surface of the particles obtained from the pulverulent material can be rounded off.

The additive manufacturing method according to the invention, in particular selective laser sintering, can be used for the manufacture of various workpieces, in particular components for interior applications in aircraft, such as interior fittings, for example system installations. Molded edge protectors can be manufactured to protect sandwich components in the aircraft interior, such as corner connector butt strips. The improved flame retardant properties by combining a polyamide material with a flame retardant as defined above, such as in particular red phosphorus, is particularly important for the pressurized area of the aircraft.

The invention is described below on the basis of an exemplary embodiment with reference to FIGS. 1 to 5, in which:

1 graphical representations of the results of the measurement of the avalanche angle and the avalanche energy of the examined polyamide powder in a revolution powder analyzer,

2 graphical representations of the results of the measurement of the surface fractal and the surface linearity of the examined polyamide powder in a revolution powder analyzer;

Fig. 3 shows the photographic representation of the flow behavior of in the drum of

Revolution Powder Analyzers rotating powdered polyamide materials; 4 shows a system for carrying out the additive manufacturing of workpieces according to the invention and workpieces used for comparison;

5 shows a diagram in which the component density is plotted as a function of the volume energy density.

Three powdery polyamide materials are characterized with regard to their powder properties. A flame-retardant polyamide material according to the invention, which comprises polyamide 6 as the polymer base and red phosphorus as the flame retardant (hereinafter referred to as PA6-RP), a polyamide material made of polyamide 6 without flame retardant (hereinafter referred to as PA6) and a polyamide material made from polyamide are examined 12 with proven suitability for selective laser sintering as a second comparison (hereinafter referred to as PA12).

The powdered PA6-RP and the powdered PA6 are processed into test specimens by selective laser sintering.

The proportion of red phosphorus in the PA6-RP can advantageously be 1 to 15%. The PA6-PR used in the following experiments contains 3 to 6% red phosphorus.

A. Production and characterization of the powders for selective laser sintering A1. production method

A cast PA6-RP block or a coarse-grained granulate is used as the starting material for the production of the PA6-RP sinter powder. The block or granulate is cryogenically ground with a mill to a fine, powdery material. By sieving the powdery material, a sieve fraction with a grain size distribution desired for additive manufacturing is obtained. After cryogenic grinding, the particles have, for example, a particle size in the range from 40 to 110 mΐti and in particular an angular, irregular surface.

The comparative powdered PA6 without flame retardant is produced using the same process. A2. Characterization of the powdered Polvamid materials in a Revolution Powder Analyzer

Powdered PA6-RP, PA6 and PA12 are analyzed in a Revolution Powder Analyzer (RPA). In this way, the flow behavior, the fluidizability and the granulation of the powdery materials can be measured and the suitability for selective laser sintering can be estimated.

1 shows the avalanche angle and the avalanche energy of powdered PA6-RP, PA6 and PA12.

2 shows the surface fractal or the surface roughness and the surface linearity of the three powders.

3 shows three photos which show the flow behavior of powdered PA6-RP and powdered PA6 at a rotation speed of 10 min ^-1 in the Revolution Powder Analyzer. Recording conditions: 10 frames / second (FPS).

(I) standard measurement of PA6-RP at room temperature;

(II) standard measurement of PA6 at room temperature;

(III) Temperature-controlled measurement of PA6 at 100 ° C.

B. Selective laser sintering of powdered PA6-RP and PA6

The powdered PA6-RP and PA6 obtained in this way are placed in the powder storage container 118 of the manufacturing device 100 according to FIG. 4. The optimal laser energy is first determined in laser sintering experiments. Subsequently, test specimens are produced for further investigations by selective laser sintering.

B1. Implementation device

The preliminary tests for determining the density of the workpieces as a function of the exposure parameters and the production of test specimens are carried out in a conventional laser sintering system, the structure of which corresponds to the manufacturing device 100 shown schematically in FIG. 4. The manufacturing device 100 has a CO2 laser 104, a system for guiding the laser beam 106, a powder bed 108 with a vertically movable construction platform 110, in which the workpiece 102 is produced, a powder storage container 118, a powder collecting container 124 and a powder application device 112 with a Squeegee 120 on. Furthermore, a control device 114 is provided for controlling the manufacturing process. In particular, the control device 114 controls the laser beam steering device 106 and thus the speed of the focused laser in the building plane, the laser power, the vertical movement of the building platform 110 and the horizontal movement of the powder application device 112. The laser sintering system furthermore has one or more heating devices for heating the powdery polyamide material or material powder 116 in the powder bed to a temperature above the glass transition temperature and below the melting temperature of the powdery polyamide material (heating devices not shown).

The sintered powders 116 made of PA6-RP or PA6 produced under A. are shaped into the workpiece 102 in the laser beam powder bed manufacturing device 100.

The CO2 laser 104 generates a high-energy laser beam at a wavelength of 10.6 mΐti, with which the powdered PA6-RP and the powdered PA6 are shaped into test specimens.

For the layer-by-layer production of the workpiece 102, the powdered PA6-RP 116 from the powder reservoir 118 with the doctor blade 120 is distributed uniformly and repeatedly in thin powder layers on the building platform 110. On the opposite side of the building platform 110, a powder collecting container 124 is provided, which holds excess powdered PA6-RP or PA6.

Data on the shape of the workpiece 102, for example in the form of CAD data, are stored in the control device 114. The control device 114 then directs the laser beam 122 by means of the laser beam steering device 106 such that the entire cross section of the workpiece 102 is consolidated at the level of this layer. The control device 114 then moves the building platform 110 downward by a certain amount in order to apply the next layer of powder and to solidify the cross section again. B2. Definition of the parameters for PA6-RP

Selective laser sintering produces porous workpieces, with the porosity and density of the material depending on the exposure parameters, such as beam diameter and beam power and the speed at which the laser beam moves across the powder layer. These physical parameters determine the amount of energy introduced into a certain volume of the powder layer (measured quantity here is J / mm3). Since the porosity and density of the sintered workpiece are decisive for the material properties, such as workpiece strength, the best exposure conditions for PA6-RP are determined in preliminary tests. Table 1 shows the results for 19 tests with different parameters, Table 2 the results of the density measurement and the evaluation. The evaluation is made with: +++ (particularly well suited), ++ (well suited) to + (usable).

Table 1: Definition of the laser parameters for the selective laser sintering of PA6-RP and PA6

Table 2: Density measurement and evaluation

The preliminary tests and their evaluation according to Tables 1 and 2 to determine the density as a function of the exposure parameters are summarized in FIG. 5. Then a maximum component density with a volume energy density (J / mm ³ ) of 0.197 J / mm ³ and with a volume energy density of 0.328 J / mm ³ .

For the volume energy density of approximately 0.2 J / mm ³ , an even better sintering result is found compared to approximately 0.33 J / mm ³ . The greatest component density with the best sintering result is thus obtained with a volume energy density of approximately 0.2 J / cm ³ .

B3. Production of test specimens for the analysis of fire behavior

After determination of the advantageous volume energy density workpiece 102 made of PA6-RP and PA6 in the form of test specimens for the investigation of the fire behavior are produced in the setting device 100. After complete additive manufacturing, the test specimens are pulled out of the powder bed. Loose sinter powder adhering to the test specimens can be easily removed. The surface of the test specimen is smooth.

The fire tests are carried out according to the standards AITM2-0002 (flammability), procedure B, AITM-0007 (smoke test) and AITM3-0005 (toxicity). The following results are obtained:

With these fire properties, PA6-RP is suitable for the production of components for the interior of aircraft, such as the pressurized area. Reference symbol list:

100 laser beam powder bed manufacturing device 102 workpiece

104 CO2 laser

106 laser beam steering device

108 powder bed

110 construction platform

112 powder application device

114 control device

116 material powder

118 powder storage containers

120 squeegees

122 laser beam

124 powder collection container

Claims

Expectations

1. A method for additively manufacturing a workpiece from a flame-retardant polyamide material, the flame retardant for the flame-retardant finishing of the polyamide material being selected from one or more of red phosphorus, phosphorus-containing compounds and flame retardants based on melamine.

2. The method of claim 1, comprising the steps of:

a) providing the flame-retardant polyamide material in the form of a powder,

c) selective irradiation of the areas of the powder layer which are provided for the workpiece formation with radiation which is suitable for connecting the particles of the powder layer in these areas to one another by sintering or melting and solidification;

e) separating the workpiece from the powdered, flame-retardant polyamide material which has not been solidified by sintering or melting and solidification.

3. The method according to claim 1 or 2, characterized in that

- The polyamide material comprises one or more polyamides or a polymer blend of one or more polyamides with one or more miscible, compatible or immiscible polymers, which are selected in particular from polyolefins, polystyrenes, thermoplastic elastomers and polyacetals, the polyamide content in Polymer- blend is at least 30% by weight, preferably at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight, and / or

- The one or more phosphorus-containing compounds from one

A group can be selected that includes: aromatic and aliphatic esters of phosphoric acid, such as resorcinol bis (diphenyl phosphate), bisphenol A bis (diphenyl phosphate) and their oligomers, triphenyl phosphate, tris (2-ethylhexyl) phosphate, tricresyl phosphate , isopropylated triphenyl phosphate, ethylenediamine diphosphate, ammonium phosphate, ammonium polyphosphate, phosphinates, such as salts of hypophosphorous acid and their derivatives, such as alkylphosphinate salts, e.g. B. diethylene phosphinate aluminum or diethylene phosphinate zinc or aluminum phosphinate, aluminum phosphite, aluminum phosphate, phosphonate esters, oligomers and polymeric derivatives of methanephosphonic acid, 9,10-dihydro-9-oxa-10-phosphorylphenanthrene-10-oxide , Ammonium poly-phosphate, phosphacenes, vinylphosphonic acid, and / or

the one or more flame retardants based on melamine are selected from a group which comprises: melamine, melamine derivatives, melamine condensation products, melamine salts, Meiern, melam, melon, bentuanuanamine, allantoin, polyisocyanurates, melamine cyanurate, melamine phosphate, dimelamine phosphate, Melamine pyrophosphate, melamine polyphosphate, melamine metal phosphates, such as melamine aluminum phosphate, melamine zinc phosphate, melamine magnesium phosphate, the corresponding pyrophosphates and polyphosphates, poly- [2,4- (piperazin-1, 4-yl) -6- (morpholin-4 -yl) -1,3,5-triazine]

4. The method according to any one of the preceding claims, characterized in that the polyamide material contains one or more polyamides selected from the group consisting of polyamide 6, polyamide 11, polyamide 12, polyamide 6.6, polyamide 6.9, polyamide 6.10 , Polyamide 6.12, polyamide 10.10 and copolyamides thereof, such as polyamide 6/12, PA 6.6 / 6.10, or consists of one or more of these polyamides.

5. The method according to any one of the preceding claims, characterized in that the polyamide material consists of polyamide 6 or polyamide 6 in a proportion of at least 30 wt .-%, preferably at least 50 wt .-%, preferably at least 70 wt. -%, more preferably at least 90 wt .-% contains.

6. The method according to any one of the preceding claims, characterized in that the polyamide material contains, in addition to the flame retardant, other auxiliaries, in particular antistatic agents, dyes, such as soluble inorganic and / or organic pigments and / or insoluble dyes, fillers , such as glass fibers, chalk, graphite, carbon black, lubricants, stabilizers and plasticizers.

7. The method according to any one of the preceding claims, characterized in that the flame retardant in a proportion in the range of 0.1 to 20 wt .-%, preferably 1 to 15 wt .-%, based on the total weight of the flame retardant polyamide material , is introduced into the polyamide material.

8. The method according to any one of the preceding claims, characterized in that the powdery, flame-retardant polyamide material has a particle size in particular in the range from 40 to 110 mΐti.

9. The method according to any one of the preceding claims, characterized in that one, several or all of the following steps are carried out for the provision of a powdery, flame-retardant polyamide material:

Preparation of a mixture or compound of the polyamide material and the flame retardant, in particular in the form of a cast block or a granulate or a granular material produced in an extruder,

Comminution of the block or of the granulate or of the granular material by mechanical processing, preferably grinding, particularly preferably cryogenic grinding, to a powdery material, and - sieving the pulverulent material to obtain a sieve fraction of the pulverulent material with the grain size distribution desired for additive manufacturing, and

- if necessary, before or after the rounding off of the angular surface of the particles obtained after grinding from the powdery material.

10. The method according to any one of the preceding claims, characterized in that in step c) the radiation is a laser radiation whose wavelength

- lies within the absorption band of the flame retardant, or

- is outside the absorption band of the flame retardant, or

- is on the long-wave side of visible light, or

- is in the range of infrared radiation, or

- is above 3000 nm, or

- is emitted by an infrared laser, such as a CO2 laser, an Nd: YAG laser or a fiber laser.

11. The method according to any one of the preceding claims, characterized in that the laser energy radiated in step c) in the range from about 0.10 to 0.30 J / mm ³ , preferably about 0.15 to 0.25 J / mm ³ , in particular about 0.2 J / mm ³ .

12. Flame-retardant workpiece, which is obtainable by an additive manufacturing method according to one of claims 1 to 11.

13. Use of a flame-retardant polyamide material, which is defined as in one of the preceding claims and in particular in powder form, for additive manufacturing, in particular by selective laser sintering or selective laser melting, of a flame-retardant workpiece, in particular a flame-retardant Work piece with a high surface smoothness.

14. Flame retardant polyamide material, which is as defined in one of the preceding claims and in particular is in powder form, for the additive manufacturing of a flame-retardant workpiece, in particular through selective laser sintering or selective laser melting.

15. A flame-retardant polyamide material according to claim 14, which is in powder form and is obtainable by:

Preparation of a mixture or compound or blend of the polyamide material and the flame retardant, in particular in the form of a cast block or a granulate or a granular material produced in an extruder,

Comminution of the block or of the granulate or of the granular material by mechanical processing, in particular grinding, preferably cryogenic grinding, to a powdery material, and

- sieving the powdery material to obtain a sieve fraction of the powdery material with the grain size distribution desired for additive manufacturing, and