EP1513670A1 - Laser sintering method with increased process precision, and particles used for the same - Google Patents

Laser sintering method with increased process precision, and particles used for the same

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Publication number
EP1513670A1
EP1513670A1 EP03759859A EP03759859A EP1513670A1 EP 1513670 A1 EP1513670 A1 EP 1513670A1 EP 03759859 A EP03759859 A EP 03759859A EP 03759859 A EP03759859 A EP 03759859A EP 1513670 A1 EP1513670 A1 EP 1513670A1
Authority
EP
European Patent Office
Prior art keywords
particles
particle
coating
temperature
core
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03759859A
Other languages
German (de)
French (fr)
Inventor
Rolf Pfeifer
Jialin Shen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mercedes Benz Group AG
Original Assignee
DaimlerChrysler AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from DE10313452A external-priority patent/DE10313452A1/en
Application filed by DaimlerChrysler AG filed Critical DaimlerChrysler AG
Publication of EP1513670A1 publication Critical patent/EP1513670A1/en
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/632—Organic additives
    • C04B35/634—Polymers
    • C04B35/63404—Polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • C04B35/6342—Polyvinylacetals, e.g. polyvinylbutyral [PVB]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B22F1/102—Metallic powder coated with organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/20—Direct sintering or melting
    • B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/10—Processes of additive manufacturing
    • B29C64/141—Processes of additive manufacturing using only solid materials
    • B29C64/153—Processes of additive manufacturing using only solid materials using layers of powder being selectively joined, e.g. by selective laser sintering or melting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y10/00—Processes of additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y70/00—Materials specially adapted for additive manufacturing
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/63—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B using additives specially adapted for forming the products, e.g.. binder binders
    • C04B35/632—Organic additives
    • C04B35/634—Polymers
    • C04B35/63448—Polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • C04B35/63468—Polyamides
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/64—Burning or sintering processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/36—Process control of energy beam parameters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/10—Auxiliary heating means
    • B22F12/13—Auxiliary heating means to preheat the material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/105—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding
    • B22F2003/1052—Sintering only by using electric current other than for infrared radiant energy, laser radiation or plasma ; by ultrasonic bonding assisted by energy absorption enhanced by the coating or powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
    • B29C64/10—Processes of additive manufacturing
    • B29C64/165—Processes of additive manufacturing using a combination of solid and fluid materials, e.g. a powder selectively bound by a liquid binder, catalyst, inhibitor or energy absorber
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
    • C04B2235/54—Particle size related information
    • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
    • C04B2235/5436—Particle size related information expressed by the size of the particles or aggregates thereof micrometer sized, i.e. from 1 to 100 micron
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
    • C04B2235/66—Specific sintering techniques, e.g. centrifugal sintering
    • C04B2235/665—Local sintering, e.g. laser sintering
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24802—Discontinuous or differential coating, impregnation or bond [e.g., artwork, printing, retouched photograph, etc.]
    • Y10T428/24893—Discontinuous or differential coating, impregnation or bond [e.g., artwork, printing, retouched photograph, etc.] including particulate material
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
    • Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
    • Y10T428/2991—Coated

Definitions

  • the invention relates to a selective laser sintering method according to the preamble of claim 7 and particles for use here according to the preamble of claim 1.
  • Such methods and particles are already known from DE 690 31 061 T2.
  • Selective laser sintering is a rapid prototyping process in which a platform that can be lowered into a construction space (construction space floor) carries a particle layer that is heated by a laser beam in selected areas, so that the particles form a first layer merge. The platform is then lowered by about 20 to 300 ⁇ m (depending on particle size and type) into the installation space and a new particle layer is applied. The laser beam again traces its path and fuses the particles of the second layer with one another and the second with the first layer. This gradually creates a multi-layered particle cake and a component in it, for example an injection mold.
  • SLS Selective laser sintering
  • DE 690 31 061 T2 already suggests preheating the particle layers so that the energy beam only has to introduce a small amount of energy in order to bond the particles. At the same time, this measure has the effect that the temperature differences between irradiated and non-irradiated parts of a layer are reduced - even if this is not disclosed in DE 690 31 061 T2.
  • DE 101 08 612 A1 therefore proposes to replace the usual three-dimensional temperature gradient with an approximately one-dimensional one (in the direction of the installation space floor) by means of a segmented installation space jacket heater.
  • the invention is based on the object of specifying a further method and particles for selective laser sintering, in which the temperature within the piled-up particle cake is as homogeneous as possible.
  • Suitable materials are those that have a softening temperature of less than about 70 ° C.
  • softening temperature is not to be interpreted narrowly, but it is clear to the person skilled in the art that this is to be understood as a temperature at which the particles form a bond with adjacent particles. Partial melting may be necessary for this, but softening (below the glass transition temperature), for example in the case of polymers, may also suffice or it is also conceivable that the activation energy for a chemical bond is exceeded.
  • the object is achieved according to the invention with regard to the particles to be created in that they are suitable for use in selective laser sintering (SLS) (that is to say their diameter is less than approximately 300 ⁇ m) and contain them
  • SLS selective laser sintering
  • a core made of at least a first material
  • an at least partial coating of the core with a second material (further components are optional), the second material having a lower softening temperature than the first material, and the softening temperature of the second material being less than approximately 70 ° C.
  • Suitable second materials can be lower alloys
  • Softening temperature used for example, in fuses (see e.g. JP2001143588A), also saturated linear carboxylic acids with chain length> 16 (e.g. hepta-decanoic acid, melting point 60-63 ° C) or polymers in the broadest sense (see following definition and examples ).
  • the softening temperature of the second material of approximately 70 ° C or less enables laser sintering compared to previously used particles at much lower temperatures and thus also a much lower temperature difference between irradiated particles and the usual room temperature in the order of 20 ° C. Tests show that with the lower maximum temperature difference, the temperature homogeneity of the entire installation space is also improved.
  • the use of particles according to the invention enables a significantly higher process speed.
  • the usual SLS devices can still be used (see, for example, DE 102 31 136 AI), but because of the lower softening temperatures, only a significantly lower energy input is required for sintering. With the same laser power, this can be achieved with a higher travel speed of the laser scanner and thus a higher process speed.
  • the sintered component cools to room temperature much faster.
  • the coating can be produced using the customary coating methods for powder particles. The coating is preferably applied in a fluidized bed reactor or a spray dryer.
  • the cores are fluidized (swirled) and the second material is supplied by spraying or atomizing a solution (in a suitable solvent), suspension or dispersion.
  • the second material can also be metered in as a solid in the same way as the powder material and agglomerate with the cores.
  • the particles can be coated individually, or can be built up into granules by means of the second material as a binder phase.
  • the layer thickness of the applied coating can be set, for example, via the concentration of the second material in the sprayed solution / suspension / dispersion, the residence time and the temperature in the reactor or spray dryer. Preferred layer thicknesses are between 0.1 and 10 percent of the mean particle radii.
  • the coating contains a polymer, preferably a thermoplastic polymer.
  • the term polymer should again be interpreted broadly. It is not limited to the typical plastics, but also includes polyolefins (waxes), polyacids and bases, organometallic polymers, polymer blends and polymers in the broadest sense, whose softening temperatures do not exceed 70 ° C. It is advantageous if these are in the solid state at room temperature.
  • the group defined in this way is large enough to to be able to select chemically and / or physically adapted coatings for any core materials.
  • the polarity can be specifically selected or the steric polymer structure.
  • the coating can have further components, for example surfactants to improve the flow properties, adhesion promoter to the core, microsinter particles for a second sintering step and other components.
  • the coating contains a polyvinyl acetal, preferably a polyvinyl butyral (PVB).
  • the softening temperature can be specifically selected based on the degree of acetalization (there are a number of unsuitable polyvinyl acetals and butyrals with softening temperatures above 100 ° C, but also a large number of suitable ones with softening temperatures below 70 ° C.
  • the polyvinyl acetals in most are organic Solvents are insoluble and therefore a component connected in this way is generally very durable.
  • it is suitable for investment casting, in particular of cores, since it can be burned out with almost no residual ash. In general, for investment casting of the SLS components, it is advantageous if the coating at least is low in residual ash.
  • poly (alkylene di- or tri-sulfides) are suitable, for example poly (methylene trisulfide) with softening temperatures between 55 and 70 ° C, poly (ethylene glycols) , in particular pol (ethylene glycol) amines or amides with softening temperatures between 50 and 65 ° C, or copolymers of ethylene and linear alkene (di, tri) - oils with chain length> 8 (e.g. poly (ethylene-co-10-undecen- l-ol), melting point about 66 ° C).
  • the coating is not hygroscopic, preferably hydrophobic. This ensures that the particles absorb little or no water and can therefore be stored for a long time without unintentionally clumping.
  • the core contains at least one element from the material group metal, ceramic, polymer.
  • the terms have to be interpreted broadly again.
  • Metal also includes semi-metals, ceramics also sand and the like, and polymer as defined above. Particles with such cores and the coatings described above enable the SLS production of components with practically any physical, in particular mechanical properties.
  • particles with a polymethacrylate core preferably polymethyl methacrylate
  • PMMA polyvinyl acetal, preferably polyvinyl butyral, coating
  • a polyvinyl acetal, preferably polyvinyl butyral, coating are advantageous since such particles can be burned out almost without residual ash.
  • the core contains at least two parts from the material group metal, ceramic, polymer in loose or solid connection.
  • This can be at least two parts of the same group element or different group elements.
  • the parts can be loosely connected (agglomerate) or solid (coating / alloy / chemical compound, etc.). This further increases the selection options with regard to the physical properties of the SLS component to be manufactured.
  • the SLS method to be created the object is achieved according to the invention in that it has the following steps:
  • - Particles are used that contain at least one material whose softening temperature is less than approximately 70 ° C.
  • the injected radiation energy is dimensioned in such a way that it only leads to softening of the coating and thereby to connection of the irradiated particles without melting the core material. It is also advantageous if at least the particle layer to be irradiated is additionally heated, preferably to a temperature level of approximately 2-3 ° C. below the lowest softening temperature of the particle materials used. As a result, temperature inhomogeneities within and from a layer are further reduced. The laser power to be entered is also further reduced.
  • a segmented installation space heater according to DE 101 08 612 AI can also be used for the highest precision requirements.
  • Figure 1 does not show the particles according to the invention according to a first embodiment to scale. These are used in an otherwise customary laser sintering process for the production of objects.
  • the particles have a core 1 made of a PMMA with a softening temperature of approximately 124 ° C. and a coating 2 made of a PVB with a softening temperature of approximately 66 ° C.
  • the laser beam is guided (power »10 watts (less if the strength is low), feed speed» 5 m / s, laser spot diameter «0.4 mm) in such a way that the radiant energy injected to soften the coating 2 and thereby connect the irradiated ones Particles leads without melting the core material.
  • the particles have ben an average diameter of about 35 microns, the coating has a thickness of about 0.3 to 0.7 microns.
  • the particles are only connected via the surface-softened coatings. There are only slight temperature inhomogeneities, which cause low shrinkage and thus high component accuracy. 2, in which the connected particles 1 are shown hatched.
  • the accuracy is further increased if the particle layers are preheated to around 60 ° C, since then the temperature inhomogeneities will decrease significantly further.
  • the laser power and / or feed rate is adjusted accordingly.
  • the preheating is carried out by means of IR radiation on the surface or, in the case of even higher accuracy requirements, by means of the segmented jacket heating according to DE 101 08 612 AI.
  • 1-component particles made of pure PVB with a softening temperature of approximately 66 ° C. and an average diameter of approximately 80 ⁇ m are used. Particles with average diameters of around 50 - 100 ⁇ m are also suitable.
  • the resulting components have lower mechanical resilience and can mainly be used as models or as so-called lost cores, especially in investment casting applications.
  • particles with metallic and / or ceramic cores and preferably also metallic coatings are used.
  • As loading Layers are particularly suitable for all alloys, in particular non-toxic bismuth-lead-indium alloys with a low melting point, which are known to the person skilled in the art, for example, as fuses according to JP2001143588A, or solder alloys such as the bismuth-lead-tin alloy PAD-165-851 the Stan Rubinstein Assoc. , Foxboro, MA 02035 USA (cf.http: // www.sra-solder. Com / pastesp.htm).
  • the mean diameters are preferably 40-150 ⁇ m, for special accuracy requirements also less, for ceramic particles mostly less than 150 ⁇ m, preferably 15 to 40 ⁇ m, for special requirements also up to 5 ⁇ m.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Ceramic Engineering (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Structural Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Optics & Photonics (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Engineering (AREA)
  • Powder Metallurgy (AREA)
  • Glanulating (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)

Abstract

In the rapid prototyping method of selective laser sintering, temperature gradients occur inside and between individual layers, leading to component deformation which is intolerable at least for high-quality components. The aim of the invention is to provide a method for selective laser sintering, whereby the temperature inside the built-up particle cake is as homogeneous as possible. To this end, particles containing at least one material having a maximum softening temperature of approximately 70° C are used.

Description

Lasersinterverfahren mit erhöhter Prozessgenauigkeit und Partikel zur Verwendung dabei Laser sintering process with increased process accuracy and particles for use
Die Erfindung betrifft ein Selektives Lasersinterverfahren gemäß dem Oberbegriff des Patentanspruchs 7 und Partikel zur Verwendung dabei gemäß dem Oberbegriff des Patentanspruchs 1. Derartige Verfahren und Partikel sind bereits aus der DE 690 31 061 T2 bekannt.The invention relates to a selective laser sintering method according to the preamble of claim 7 and particles for use here according to the preamble of claim 1. Such methods and particles are already known from DE 690 31 061 T2.
Selektives Lasersintern (SLS, Selective Laser Sintering) ist ein Rapid-Prototyping-Verfahren, bei dem eine in einen Bauraum absenkbare Plattform (Bauraumboden) eine Partikelschicht trägt, die durch einen Laserstrahl in ausgewählten Bereichen erhitzt wird, so dass die Partikeln zu einer ersten Schicht verschmelzen. Anschließend wird die Plattform um etwa 20 bis 300 μm (je nach Partikelgröße und -art) nach unten in den Bauraum gesenkt und eine neue Partikelschicht aufgebracht. Der Laserstrahl zeichnet wieder seine Bahn und verschmilzt die Partikeln der zweiten Schicht miteinander sowie die zweite mit der ersten Schicht. Auf diese Weise entsteht nach und nach ein vielschichtiger Partikelkuchen und in ihm ein Bauteil, zum Beispiel eine Spritzgussform.Selective laser sintering (SLS) is a rapid prototyping process in which a platform that can be lowered into a construction space (construction space floor) carries a particle layer that is heated by a laser beam in selected areas, so that the particles form a first layer merge. The platform is then lowered by about 20 to 300 μm (depending on particle size and type) into the installation space and a new particle layer is applied. The laser beam again traces its path and fuses the particles of the second layer with one another and the second with the first layer. This gradually creates a multi-layered particle cake and a component in it, for example an injection mold.
Innerhalb des Bauraums erfahren bestimmte Bereiche - abhängig von der Geometrie des herzustellenden Bauteils - für einen längeren oder kürzeren Zeitraum eine Erwärmung durch den La- serstrahl während andere gar nicht erwärmt werden. Außerdem wird nur die jeweils oberste Partikelschicht durch den Laser erwärmt, die unteren Schichten geben die aufgenommene Wärme an ihre Umgebung und kühlen ab. Die Folge sind inhomogene Temperaturverteilungen und thermische Spannungen innerhalb des Partikelkuchens, die zu Bauteilverzug führen können.Within the installation space, certain areas - depending on the geometry of the component to be manufactured - are heated by the load for a longer or shorter period of time. jet while others are not heated at all. In addition, only the uppermost particle layer is heated by the laser, the lower layers give the absorbed heat to their surroundings and cool down. The result is inhomogeneous temperature distributions and thermal stresses within the particle cake, which can lead to component distortion.
Bereits in der DE 690 31 061 T2 wird vorgeschlagen, die Partikelschichten vorzuheizen, so dass der Energiestrahl nur noch eine geringe Menge Energie einbringen muss, um die Partikeln zu verbinden. Gleichzeitig bewirkt diese Maßnahme, dass die Temperaturdifferenzen zwischen bestrahlten und nicht bestrahlten Teilen einer Schicht verringert werden - auch wenn dies in der DE 690 31 061 T2 nicht offenbart ist.DE 690 31 061 T2 already suggests preheating the particle layers so that the energy beam only has to introduce a small amount of energy in order to bond the particles. At the same time, this measure has the effect that the temperature differences between irradiated and non-irradiated parts of a layer are reduced - even if this is not disclosed in DE 690 31 061 T2.
Es treten jedoch weiterhin Temperaturgradienten innerhalb und zwischen den einzelnen Schichten auf, wobei insbesondere die erstgenannten zu Bauteilverzug führen, der zumindest bei qualitativ hochwertigen Bauteilen nicht tolerierbar ist.However, temperature gradients continue to occur within and between the individual layers, the former in particular leading to component distortion, which cannot be tolerated, at least in the case of high-quality components.
Als Korrekturmaßnahme wird daher in der DE 101 08 612 AI vorgeschlagen mittels einer segmentierten Bauraummantelheizung den üblichen dreidimensionalen Temperaturgradienten zwangsweise durch einen annähernd eindimensionalen (in Richtung auf den Bauraumboden) zu ersetzen.As a corrective measure, DE 101 08 612 A1 therefore proposes to replace the usual three-dimensional temperature gradient with an approximately one-dimensional one (in the direction of the installation space floor) by means of a segmented installation space jacket heater.
Der Erfindung liegt die Aufgabe zugrunde, ein weiteres Verfahren sowie Partikeln zum selektiven Lasersintern anzugeben, bei welchen die Temperatur innerhalb des aufgeschütteten Par- tikelkuchens möglichst homogen ist.The invention is based on the object of specifying a further method and particles for selective laser sintering, in which the temperature within the piled-up particle cake is as homogeneous as possible.
Diese Aufgabe wird gelöst, in dem die absolute Temperaturdifferenz zwischen den bestrahlten Bereichen und deren Endtemperatur, also der Raumtemperatur, durch die Verwendung geeigne- ter Materialen gesenkt wird. Geeignete Materialen sind solche, die eine Erweichungstemperatur von weniger als circa 70°C aufweisen. Dabei ist der Begriff Erweichungstemperatur nicht eng auszulegen, sondern dem Fachmann ist klar, dass darunter eine Temperatur zu verstehen ist, bei der die Partikeln eine Bindung mit angrenzenden Partikeln eingehen. Dazu kann ein teilweises Schmelzen erforderlich sein, aber z.B. bei Polymeren kann auch ein Erweichen (unterhalb der Glasübergangstemperatur) genügen oder es ist auch denkbar, dass die Aktivierungsenergie für eine chemische Bindung überschritten wird.This object is achieved in that the absolute temperature difference between the irradiated areas and their end temperature, that is to say the room temperature, by using suitable ter materials is reduced. Suitable materials are those that have a softening temperature of less than about 70 ° C. The term softening temperature is not to be interpreted narrowly, but it is clear to the person skilled in the art that this is to be understood as a temperature at which the particles form a bond with adjacent particles. Partial melting may be necessary for this, but softening (below the glass transition temperature), for example in the case of polymers, may also suffice or it is also conceivable that the activation energy for a chemical bond is exceeded.
Die Erfindung ist in Bezug auf die zu verwendenden Partikeln und das zu schaffende Verfahren durch die Merkmale der Pa- tentansprüche 1 und 7 wiedergegeben. Die weiteren Ansprüche enthalten vorteilhafte Ausgestaltungen und Weiterbildungen.With regard to the particles to be used and the method to be created, the invention is represented by the features of patent claims 1 and 7. The further claims contain advantageous refinements and developments.
Die Aufgabe wird bezüglich der zu schaffenden Partikeln erfindungsgemäß dadurch gelöst, dass sie zur Verwendung beim Selektiven Laser Sintern (SLS) geeignet sind (also ihr Durchmesser kleiner als circa 300μm ist) und sie enthaltenThe object is achieved according to the invention with regard to the particles to be created in that they are suitable for use in selective laser sintering (SLS) (that is to say their diameter is less than approximately 300 μm) and contain them
- einen Kern aus mindestens einem ersten Material- A core made of at least a first material
- eine mindestens teilweise Beschichtung des Kerns mit einem zweiten Material, (weitere Komponenten sind optional) wobei das zweite Material eine niedrigere Erweichungstemperatur aufweist als das erste Material, und die Erweichungstemperatur des zweiten Materials weniger als circa 70° C beträgt.an at least partial coating of the core with a second material (further components are optional), the second material having a lower softening temperature than the first material, and the softening temperature of the second material being less than approximately 70 ° C.
Geeignete zweite Materialien können Legierungen mit niedrigerSuitable second materials can be lower alloys
Erweichungstemperatur sein, die z.B. in Schmelzsicherungen (vgl. z.B. JP2001143588A) verwendet werden, außerdem gesättigte lineare Carbonsäuren mit Kettenlänge > 16 (z.B. Hepta- decansäure, Schmelzpunkt 60-63 °C) oder auch Polymere im weitesten Sinne (vgl. nachfolgende Definition und Beispiele) . Die Erweichungstemperatur des zweiten Materials von circa 70° C oder weniger ermöglicht im Vergleich zu bisher verwendeten Partikeln das Lasersintern bereits bei wesentlich niedrigeren Temperaturen und somit auch eine wesentlich niedrigere Temperaturdifferenz zwischen bestrahlten Partikeln und der üblichen Raumtemperatur in der Größenordnung von 20° C. Versuche zeigen, dass mit der niedrigeren maximalen Temperaturdifferenz auch die Temperaturhomogenität des gesamten Bauraums verbessert wird.Softening temperature used, for example, in fuses (see e.g. JP2001143588A), also saturated linear carboxylic acids with chain length> 16 (e.g. hepta-decanoic acid, melting point 60-63 ° C) or polymers in the broadest sense (see following definition and examples ). The softening temperature of the second material of approximately 70 ° C or less enables laser sintering compared to previously used particles at much lower temperatures and thus also a much lower temperature difference between irradiated particles and the usual room temperature in the order of 20 ° C. Tests show that with the lower maximum temperature difference, the temperature homogeneity of the entire installation space is also improved.
Materialien mit wesentlich höheren Erweichungstemperaturen bedingen größere Temperaturinhomogenitäten und somit geringere Bauteilgenauigkeit, die für Präzisionsanwendungen nicht mehr ausreicht. Materialien mit wesentlich niedrigeren Erwei- chungstemperaturen können nur vergleichsweise aufwendig über längere Zeit gelagert werden, da sichergestellt werden muss, dass sie sich nicht unbeabsichtigt verbinden. Im Sommer sind jedoch Temperaturen von über 30 °C im Schatten und von über 50 °C in der Sonne auch in Deutschland erreichbar und deshalb könnte es zu unbeabsichtigten Materialerweichungen und -Verbindungen kommen. Daher ist es vorteilhaft zweite Materialien mit Erweichungstemperaturen > 30 °C, vorzugsweise größer 50 °C, zu verwenden.Materials with significantly higher softening temperatures require greater temperature inhomogeneities and therefore lower component accuracy, which is no longer sufficient for precision applications. Materials with significantly lower softening temperatures can only be stored for a relatively long time, since it must be ensured that they do not unintentionally bond. In summer, however, temperatures of over 30 ° C in the shade and over 50 ° C in the sun can also be reached in Germany, and this could lead to unintentional material softening and connections. It is therefore advantageous to use second materials with softening temperatures> 30 ° C, preferably greater than 50 ° C.
Als weiteren Vorteil ermöglicht die Verwendung erfindungsgemäßer Partikeln eine wesentlich größere Prozessgeschwindigkeit. Die üblichen SLS-Vorrichtungen sind weiter verwendbar (vgl. z.B. DE 102 31 136 AI) aber aufgrund der niedrigeren Erweichungstemperaturen ist zum Sintern nur ein wesentlich niedrigerer Energieeintrag erforderlich. Dieser ist bei gleicher Laserleistung mit höherer Verfahrgeschwindigkeit des Laserscanners und somit höherer Prozessgeschwindigkeit erzielbar. Außerdem kühlt das gesinterte Bauteil wesentlich schneller auf Raumtemperatur ab. Die Herstellung der Beschichtung kann nach den üblichen Be- schichtungsverfahren für Pulverpartikel erfolgen. Bevorzugt wird die Beschichtung in einem Wirbelschichtreaktor oder einem Sprühtrockner aufgebracht.As a further advantage, the use of particles according to the invention enables a significantly higher process speed. The usual SLS devices can still be used (see, for example, DE 102 31 136 AI), but because of the lower softening temperatures, only a significantly lower energy input is required for sintering. With the same laser power, this can be achieved with a higher travel speed of the laser scanner and thus a higher process speed. In addition, the sintered component cools to room temperature much faster. The coating can be produced using the customary coating methods for powder particles. The coating is preferably applied in a fluidized bed reactor or a spray dryer.
Im Wirbelschichtreaktor werden die Kerne fluidisiert (verwirbelt) und es erfolgt eine Zufuhr des zweiten Materials durch Einsprühen oder Verdüsen einer Lösung (in einem geeigneten Lösungsmittel) , Suspension oder Dispersion. Ebenso kann das zweite Material aber auch als Feststoff in gleicher Weise wie das Pulvermaterial zudosiert werden und mit den Kernen agglomerieren.In the fluidized bed reactor, the cores are fluidized (swirled) and the second material is supplied by spraying or atomizing a solution (in a suitable solvent), suspension or dispersion. Likewise, the second material can also be metered in as a solid in the same way as the powder material and agglomerate with the cores.
Je nach Verweilzeit des Partikelmaterials in der Beschich- tungsvorrichtung können die Partikeln (eines einzelnen erstem Materials oder eines Materialgemisches) einzeln beschichtet werden, oder mittels des zweiten Materials als Binderphase zu Granulaten aufgebaut werden. Die Schichtdicke der aufgetragenen Beschichtung lässt sich beispielsweise über die Konzent- ration des zweiten Materials in der eingesprühten Lösung /Suspension/Dispersion, die Verweilzeit und die Temperatur im Reaktor, beziehungsweise Sprühtrockner einstellen. Bevorzugte Schichtdicken liegen zwischen 0,1 und 10 Prozent der mittleren Partikelradien.Depending on the dwell time of the particle material in the coating device, the particles (of a single first material or a material mixture) can be coated individually, or can be built up into granules by means of the second material as a binder phase. The layer thickness of the applied coating can be set, for example, via the concentration of the second material in the sprayed solution / suspension / dispersion, the residence time and the temperature in the reactor or spray dryer. Preferred layer thicknesses are between 0.1 and 10 percent of the mean particle radii.
In einer vorteilhaften Ausführungsform des erfindungsgemäßen Partikels enthält die Beschichtung ein Polymer, vorzugsweise ein thermoplastisches Polymer. Dabei ist der Begriff Polymer wieder weit auszulegen. Er beschränkt sich nicht nur auf die typischen Kunststoffe, sondern umfasst auch Polyolefine (Wachse) , Polysäuren und -Basen, metallorganische Polymere, Polymerblends und Polymere im weitesten Sinne, deren Erweichungstemperaturen nicht über 70 °C liegen. Vorteilhaft ist es, wenn diese bei Raumtemperatur im festen Aggregatzustand vorliegen. Die so definierte Gruppe ist ausreichend groß, um für beliebige Kernmaterialien chemisch und/oder physikalisch angepasste Beschichtungen auswählen zu können. So kann beispielweise die Polarität gezielt ausgewählt werden oder auch die sterische Polymerstruktur. Für spezielle Anforderungen kann die Beschichtung jedoch weitere Komponenten aufweisen, z.B. Tenside zur Verbesserung der Fließeigenschaften, Haftvermittler zum Kern, Mikrosinterpartikeln für einen zweiten Sinterschritt und weitere Bestandteile.In an advantageous embodiment of the particle according to the invention, the coating contains a polymer, preferably a thermoplastic polymer. The term polymer should again be interpreted broadly. It is not limited to the typical plastics, but also includes polyolefins (waxes), polyacids and bases, organometallic polymers, polymer blends and polymers in the broadest sense, whose softening temperatures do not exceed 70 ° C. It is advantageous if these are in the solid state at room temperature. The group defined in this way is large enough to to be able to select chemically and / or physically adapted coatings for any core materials. For example, the polarity can be specifically selected or the steric polymer structure. For special requirements, however, the coating can have further components, for example surfactants to improve the flow properties, adhesion promoter to the core, microsinter particles for a second sintering step and other components.
In einer besonders vorteilhaften Ausführungsform des erfindungsgemäßen Partikels enthält die Beschichtung ein Polyviny- lacetal, vorzugsweise ein Polyvinylbutyral (PVB) . Einerseits kann anhand des Acetalisierungsgrades die Erweichungstemperatur gezielt ausgewählt werden (Es gibt eine Reihe ungeeigne- ter Polyvinylacetale und -butyrale mit Erweichungstemperaturen über 100 °C, aber auch eine große Zahl geeigneter mit Erweichungstemperaturen unter 70 °C. Andererseits sind die Polyvinylacetale in den meisten organischen Lösungsmitteln unlöslich und somit ist ein so verbundenes Bauteil grundsätzlich sehr haltbar. Andererseits ist es für den Feinguß, insbesondere von Kernen, geeignet, da es nahezu ohne Restasche ausbrennbar ist. Generell ist es für eine Feingußanwendung der SLS-Bauteile vorteilhaft, wenn die Beschichtung zumindest restaschearm ist.In a particularly advantageous embodiment of the particle according to the invention, the coating contains a polyvinyl acetal, preferably a polyvinyl butyral (PVB). On the one hand, the softening temperature can be specifically selected based on the degree of acetalization (there are a number of unsuitable polyvinyl acetals and butyrals with softening temperatures above 100 ° C, but also a large number of suitable ones with softening temperatures below 70 ° C. On the other hand, the polyvinyl acetals in most are organic Solvents are insoluble and therefore a component connected in this way is generally very durable. On the other hand, it is suitable for investment casting, in particular of cores, since it can be burned out with almost no residual ash. In general, for investment casting of the SLS components, it is advantageous if the coating at least is low in residual ash.
Weitere geeignete Beschichtungsmaterialen sind in geeigneten Datenbanken wie BEILSTEIN oder GMELIN zu finden: So eignen sich Poly (alkylen-di- oder -tri-sulfide) , z.B. Poly (methylen- trisulfide) mit Erweichungstemperaturen zwischen 55 und 70°C, Poly (ethylenglykole) , insbesondere Pol (ethylenglykol) amine oder -amide mit Erweichungstemperaturen zwischen 50 und 65 °C, oder auch Copolymere aus Ethylen und linearen Alken (di, tri) - ölen mit Kettenlänge > 8 (z.B. Poly (ethylen-co-10-undecen-l- ol) , Schmelzpunkt circa 66°C) . Bei einer weiteren vorteilhaften Ausführungsform des erfindungsgemäßen Partikels ist die Beschichtung nicht hygroskopisch, vorzugsweise hydrophob. Dies gewährleistet, dass die Partikeln nur wenig oder gar kein Wasser aufnehmen und somit über lange Zeit lagerfähig sind ohne unbeabsichtigt zu ver- klumpen .Other suitable coating materials can be found in suitable databases such as BEILSTEIN or GMELIN: For example, poly (alkylene di- or tri-sulfides) are suitable, for example poly (methylene trisulfide) with softening temperatures between 55 and 70 ° C, poly (ethylene glycols) , in particular pol (ethylene glycol) amines or amides with softening temperatures between 50 and 65 ° C, or copolymers of ethylene and linear alkene (di, tri) - oils with chain length> 8 (e.g. poly (ethylene-co-10-undecen- l-ol), melting point about 66 ° C). In a further advantageous embodiment of the particle according to the invention, the coating is not hygroscopic, preferably hydrophobic. This ensures that the particles absorb little or no water and can therefore be stored for a long time without unintentionally clumping.
In einer vorteilhaften Ausführungsform des erfindungsgemäßen Partikels enthält der Kern mindestens ein Element aus der Materialgruppe Metall, Keramik, Polymer. Dabei sind die Begriffe wieder weit auszulegen. Metall umfasst auch Halbmetalle, Keramik auch Sand und Ähnliches, und Polymer gemäß der vorherstehenden Definition. Partikeln mit derartigen Kernen und vorstehend beschriebenen Beschichtungen ermöglichen die SLS- Herstellung von Bauteilen mit praktisch beliebigen physikalischen, insbesondere mechanischen Eigenschaften.In an advantageous embodiment of the particle according to the invention, the core contains at least one element from the material group metal, ceramic, polymer. The terms have to be interpreted broadly again. Metal also includes semi-metals, ceramics also sand and the like, and polymer as defined above. Particles with such cores and the coatings described above enable the SLS production of components with practically any physical, in particular mechanical properties.
Für Feingußanwendungen sind insbesondere Partikeln mit einem Polymethacrylat-Kern, vorzugsweise Polymethylmethacrylat-For investment casting applications, in particular particles with a polymethacrylate core, preferably polymethyl methacrylate
(PMMA) -Kern, und einer Polyvinylacetal-, vorzugsweise Polyvi- nylbutyral-, Beschichtung vorteilhaft, da derartige Partikeln nahezu restaschefrei ausbrennbar sind.(PMMA) core, and a polyvinyl acetal, preferably polyvinyl butyral, coating are advantageous since such particles can be burned out almost without residual ash.
Vorteilhaft ist es auch, wenn der Kern mindestens zwei Teile aus der Materialgruppe Metall, Keramik, Polymer in loser oder fester Verbindung enthält. Dabei kann es sich um mindestens zwei Teile desselben Gruppenelementes oder verschiedener Gruppenelemente handeln. Die Teile können lose verbunden sein (Agglomerat) oder fest (Beschichtung/Legierung/Chemische Verbindung, etc.). Dadurch werden die Auswahlmöglichkeiten hinsichtlich physikalischer Eigenschaften des herzustellenden SLS-Bauteils weiter erhöht. Die Aufgabe wird bezüglich des zu schaffenden SLS-Verfahrens erfindungsgemäß dadurch gelöst, dass es folgende Schritte aufweist :It is also advantageous if the core contains at least two parts from the material group metal, ceramic, polymer in loose or solid connection. This can be at least two parts of the same group element or different group elements. The parts can be loosely connected (agglomerate) or solid (coating / alloy / chemical compound, etc.). This further increases the selection options with regard to the physical properties of the SLS component to be manufactured. With regard to the SLS method to be created, the object is achieved according to the invention in that it has the following steps:
- Auftragen einer Schicht aus Partikeln auf eine Ziel- fläche,- applying a layer of particles on a target surface,
- Bestrahlen eines ausgewählten Teils der Schicht, entsprechend einem Querschnitt des Gegenstandes, mit einem Energiestrahl, so dass die Partikel im ausgewählten Teil verbunden werden,Irradiating a selected part of the layer, corresponding to a cross section of the object, with an energy beam, so that the particles in the selected part are connected,
- Wiederhohlen der Schritte des Auftragens und des Bestrahlens für eine Mehrzahl von Schichten, so dass die verbunden Teile der benachbarten Schichten sich verbinden, um den Gegenstand zu bilden, wobei- repeating the steps of applying and irradiating for a plurality of layers so that the joined parts of the adjacent layers join to form the article, wherein
- Partikeln verwendet werden, die mindestens ein Material enthalten, dessen Erweichungstemperatur weniger als circa 70° C beträgt .- Particles are used that contain at least one material whose softening temperature is less than approximately 70 ° C.
Dadurch werden die vorstehend genannten Vorteile hinsichtlich der Homogenität des Temperaturgradienten und der daraus resultierenden Bauteilqualität sowie der Prozeßgeschwindigkeit erzielt. Diese Vorteile treten nicht nur bei erfindungsgemä- ßen Partikeln auf, sondern auch bei Partikeln, die nur aus einem einzigen Material bestehen oder homogen zusammengesetzt sind, solange sie nur mindestens ein Material enthalten, dessen Erweichungstemperatur weniger als circa 70° C beträgt.This achieves the advantages mentioned above with regard to the homogeneity of the temperature gradient and the resulting component quality and the process speed. These advantages occur not only in the case of particles according to the invention, but also in the case of particles which consist only of a single material or are composed homogeneously, as long as they contain only at least one material whose softening temperature is less than approximately 70 ° C.
Bei erfindungsgemäßen Partikeln ist es insbesondere in Hinsicht auf die Bauteilgenauigkeit vorteilhaft, wenn die eingekoppelte Strahlungsenergie derart bemessen ist, dass sie nur zur Erweichung der Beschichtung und dadurch zur Verbindung der bestrahlten Partikeln führt, ohne dabei das Kernmaterial aufzuschmelzen. Vorteilhaft ist es auch, wenn zumindest die jeweils zu bestrahlende Partikelschicht zusätzlich beheizt wird, vorzugsweise auf ein Temperaturniveau von circa 2-3°C unter der niedrigsten Erweichungstemperatur der verwendeten Partikel- materialien. Dadurch werden Temperaturinhomogenitäten innerhalb einer Schicht und von dieser ausgehend weiter reduziert. Ebenso wird die einzutragende Laserleistung weiter reduziert.In the case of particles according to the invention, it is particularly advantageous with regard to component accuracy if the injected radiation energy is dimensioned in such a way that it only leads to softening of the coating and thereby to connection of the irradiated particles without melting the core material. It is also advantageous if at least the particle layer to be irradiated is additionally heated, preferably to a temperature level of approximately 2-3 ° C. below the lowest softening temperature of the particle materials used. As a result, temperature inhomogeneities within and from a layer are further reduced. The laser power to be entered is also further reduced.
Für höchste Präzisionsanforderungen kann zusätzlich eine seg- mentierte Bauraumheizung gemäß der DE 101 08 612 AI eingesetzt werden.A segmented installation space heater according to DE 101 08 612 AI can also be used for the highest precision requirements.
Mit verbundenen erfindungsgemäßen Partikeln und/oder nach dem erfindungsgemäßen Verfahren hergestellte Gegenstände weisen in Ihrer Ist-Geometrie nur minimale schwindungsbedingte Abweichungen gegenüber ihrer vorgegebenen Soll-Geometrie auf.With connected particles according to the invention and / or objects manufactured according to the method according to the invention, their actual geometry shows only minimal deviations due to shrinkage compared to their specified target geometry.
Nachfolgend werden anhand der Figuren 1 und 2 sowie mehrerer Ausführungsbeispiele das erfindungsgemäße Partikel und das erfindungsgemäße Verfahren näher erläutert:The particle according to the invention and the method according to the invention are explained in more detail below with reference to FIGS. 1 and 2 and several exemplary embodiments:
Figur 1 zeigt nicht maßstabsgerecht die erfindungsgemäßen Partikeln gemäß einem ersten Ausführungsbeispiel. Diese wer- den in einem ansonsten üblichen Lasersinter-Verfahren zur Herstellung von Gegenständen verwendet. Die Partikeln weisen einen Kern 1 aus einem PMMA mit einer Erweichungstemperatur von circa 124 °C und eine Beschichtung 2 aus einem PVB mit einer Erweichungstemperatur von circa 66°C aufweisen. Der La- serstrahl wird so geführt (Leistung » 10 Watt (bei geringen Festigkeitsanforderungen auch weniger) , Vorschubgeschwindigkeit » 5 m/s, Laserspotdurchmesser « 0,4 mm), dass die eingekoppelte Strahlungsenergie zur Erweichung der Beschichtung 2 und dadurch zur Verbindung der bestrahlten Partikeln führt, ohne dabei das Kernmaterial aufzuschmelzen. Die Partikeln ha- ben einen mittleren Durchmesser von circa 35 μm, wobei die Beschichtung eine Dicke von circa 0,3 bis 0,7 μm aufweist.Figure 1 does not show the particles according to the invention according to a first embodiment to scale. These are used in an otherwise customary laser sintering process for the production of objects. The particles have a core 1 made of a PMMA with a softening temperature of approximately 124 ° C. and a coating 2 made of a PVB with a softening temperature of approximately 66 ° C. The laser beam is guided (power »10 watts (less if the strength is low), feed speed» 5 m / s, laser spot diameter «0.4 mm) in such a way that the radiant energy injected to soften the coating 2 and thereby connect the irradiated ones Particles leads without melting the core material. The particles have ben an average diameter of about 35 microns, the coating has a thickness of about 0.3 to 0.7 microns.
Bei einem derartigen Verfahren unter Verwendung dieser Parti- kein erfolgt die Verbindung der Partikeln nur über die oberflächlich erweichten Beschichtungen. Es treten nur geringe Temperaturinhomogenitäten auf, die eine geringe Schwindung und somit hohe Bauteilgenauigkeit bewirken. Vgl. Fig. 2, in welcher die verbundenen Partikeln 1 schraffiert dargestellt sind. Die aus Gründen der besseren Darstellbarkeit verdickten, nicht maßstabsgerechten Beschichtungen wurden in den Verbindungsbereichen gerade soweit oberflächlich erweicht, dass eine Verbindung der Partikeln erfolgte.In such a method using these particles, the particles are only connected via the surface-softened coatings. There are only slight temperature inhomogeneities, which cause low shrinkage and thus high component accuracy. 2, in which the connected particles 1 are shown hatched. The coatings, which were thickened for the sake of better representability, were not softened to the surface in the connection areas to such an extent that the particles were connected.
Die Genauigkeit wird noch weiter erhöht, wenn die Partikelschichten auf circa 60 °C vorgewärmt werden, da sich dann die Temperaturinhomogenitäten noch deutlich weiter verringern. Die Laserleistung und/oder Vorschubgeschwindigkeit wird entsprechend angepasst. Die Vorwärmung erfolgt mittels einer IR- Bestrahlung der Oberfläche oder bei noch höheren Genauigkeitsanforderungen mittels der segmentierten Mantelheizung gemäß der DE 101 08 612 AI.The accuracy is further increased if the particle layers are preheated to around 60 ° C, since then the temperature inhomogeneities will decrease significantly further. The laser power and / or feed rate is adjusted accordingly. The preheating is carried out by means of IR radiation on the surface or, in the case of even higher accuracy requirements, by means of the segmented jacket heating according to DE 101 08 612 AI.
Gemäß einem weiteren Ausführungsbeispiel werden 1-kompo- nentige Partikeln aus reinem PVB mit einer Erweichungstemperatur von circa 66°C und einem mittleren Durchmesser von circa 80 μm verwendet. Partikeln mit mittleren Durchmessern von circa 50 - 100 μm sind ebenfalls geeignet. Die dabei entstehenden Bauteile weisen geringere mechanische Belastbarkeit auf und sind vorwiegend als Modelle oder auch als sog. verlorene Kerne insbesondere bei Feingussanwendungen einsetzbar.According to a further exemplary embodiment, 1-component particles made of pure PVB with a softening temperature of approximately 66 ° C. and an average diameter of approximately 80 μm are used. Particles with average diameters of around 50 - 100 μm are also suitable. The resulting components have lower mechanical resilience and can mainly be used as models or as so-called lost cores, especially in investment casting applications.
Für Anwendungen, die höheren physikalischen, insbesondere mechanischen Anforderungen entsprechen müssen, werden Partikeln mit metallischen und/oder keramischen Kernen und vorzugsweise ebenfalls metallischen Beschichtungen eingesetzt. Als Be- Schichtungen eignen sich dabei vor allen Legierungen, insbesondere ungiftige Wismut-Blei-Indium-Legierungen mit niedrigem Schmelzpunkt, die dem Fachmann z.B. als Schmelzsicherungen gemäß der JP2001143588A bekannt sind oder Löt-Legierungen wie beispielsweise die Wismut-Blei-Zinn Legierung PAD-165-851 der Stan Rubinstein Assoc . , Foxboro, MA 02035 USA (vgl. http: //www. sra-solder. com/pastesp.htm) .For applications that have to meet higher physical, in particular mechanical requirements, particles with metallic and / or ceramic cores and preferably also metallic coatings are used. As loading Layers are particularly suitable for all alloys, in particular non-toxic bismuth-lead-indium alloys with a low melting point, which are known to the person skilled in the art, for example, as fuses according to JP2001143588A, or solder alloys such as the bismuth-lead-tin alloy PAD-165-851 the Stan Rubinstein Assoc. , Foxboro, MA 02035 USA (cf.http: // www.sra-solder. Com / pastesp.htm).
Bei metallischen Partikeln liegen die mittleren Durchmesser vorzugsweise bei 40-150 μm, für besondere Genauigkeitsanforderungen auch darunter, bei keramischen Partikeln meist unter 150 μm, vorzugsweise bei 15 bis 40 μm, für besondere Anforderungen auch bis zu 5 μm. In the case of metallic particles, the mean diameters are preferably 40-150 μm, for special accuracy requirements also less, for ceramic particles mostly less than 150 μm, preferably 15 to 40 μm, for special requirements also up to 5 μm.

Claims

Patentansprücheclaims
1. Partikel zur Verwendung beim Selektiven Laser Sintern (SLS) enthaltend - einen Kern 1 aus mindestens einem ersten Material1. Containing particles for use in selective laser sintering (SLS) - a core 1 made of at least one first material
- eine mindestens teilweise Beschichtung 2 des Kerns 1 mit einem zweiten Material, wobei das zweite Material eine niedrigere Erweichungstemperatur aufweist als das erste Material, d a d u r c h g e k e n n z e i c h n e t , dass die Erweichungstemperatur des zweiten Materials weniger als circa 70° C beträgt.- An at least partial coating 2 of the core 1 with a second material, the second material having a lower softening temperature than the first material, so that the softening temperature of the second material is less than approximately 70 ° C.
2. Partikel nach Anspruch 1 d a d u r c h g e k e n n z e i c h n e t , dass die Beschichtung 2 ein Polymer, vorzugsweise ein thermoplastisches Polymer, enthält.2. Particles according to claim 1 that the coating 2 contains a polymer, preferably a thermoplastic polymer.
3. Partikel nach Anspruch 2 d a d u r c h g e k e n n z e i c h n e t , dass die Beschichtung 2 ein Polyvinylacetal, vorzugsweise ein Polyvinylbutyral, enthält.3. Particle according to claim 2, that the coating 2 contains a polyvinyl acetal, preferably a polyvinyl butyral.
4. Partikel nach einem der vorhergehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t , dass die Beschichtung 2 nicht hygroskopisch, vorzugsweise hydrophob ist. 4. Particle according to one of the preceding claims, characterized in that the coating 2 is not hygroscopic, preferably hydrophobic.
5. Partikel nach einem der vorhergehenden Ansprüche, d a d u r c h g e k e n n z e i c h n e t , dass der Kern 1 mindestens ein Element aus der Materialgruppe Metall, Keramik, Polymer enthält.5. Particle according to one of the preceding claims, that the core 1 contains at least one element from the metal, ceramic, polymer material group.
6. Partikel nach Anspruch 5, d a d u r c h g e k e n n z e i c h n e t , dass der Kern 1 mindestens zwei Teile aus der Materialgruppe Metall, Keramik, Polymer in loser oder fester Verbindung enthält.6. Particle according to claim 5, so that the core 1 contains at least two parts from the material group metal, ceramic, polymer in loose or solid connection.
7. Verfahren zur Herstellung eines dreidimensionalen Gegenstandes mittels SLS aufweisend folgende Schritte:7. A method for producing a three-dimensional object by means of SLS comprising the following steps:
- Auftragen einer Schicht aus Partikeln auf eine Ziel- fläche,- applying a layer of particles on a target surface,
- Bestrahlen eines ausgewählten Teils der Schicht, entsprechend einem Querschnitt des Gegenstandes, mit einem Energiestrahl, so dass die Partikel im ausgewählten Teil verbunden werden,Irradiating a selected part of the layer, corresponding to a cross section of the object, with an energy beam, so that the particles in the selected part are connected,
- Wiederhohlen der Schritte des Auftragens und des Bestrahlens für eine Mehrzahl von Schichten, so dass die verbunden Teile der benachbarten Schichten sich verbinden, um den Gegenstand zu bilden, d a d u r c h g e k e n n z e i c h n e t ,Repeating the steps of applying and irradiating for a plurality of layers so that the joined parts of the adjacent layers join to form the object, so that the object is made,
- dass Partikeln verwendet werden, die mindestens ein Material enthalten, dessen Erweichungstemperatur weniger als circa 70° C beträgt .- that particles are used that contain at least one material whose softening temperature is less than approximately 70 ° C.
Verfahren nach Anspruch 7, d a d u r c h g e k e n n z e i c h n e t , daß Partikeln nach einem der Ansprüche 1 bis 6 verwendet werden. Method according to claim 7, characterized in that particles according to one of claims 1 to 6 are used.
9. Verfahren nach einem der Ansprüche 7 oder 8, d a d u r c h g e k e n n z e i c h n e t , dass zumindest die jeweils zu bestrahlende Partikel- schicht zusätzlich beheizt wird, vorzugsweise auf ein9. The method according to claim 7, wherein the at least the particle layer to be irradiated in each case is additionally heated, preferably to one
Temperaturniveau von circa 2-3° C unter der niedrigsten Erweichungstemperatur der verwendeten Partikelmaterialien.Temperature level of about 2-3 ° C below the lowest softening temperature of the particle materials used.
10. Gegenstand aus miteinander verbundenen Partikeln, dadurch gekennzeichnet, dass er aus Partikeln nach einem der Ansprüche 1 bis 6 hergestellt wurde und/oder dass er mittels eines Verfahrens nach einem der Ansprüche 7 bis 9 hergestellt wurde. 10. Object made of interconnected particles, characterized in that it was produced from particles according to one of claims 1 to 6 and / or that it was produced by a method according to one of claims 7 to 9.
EP03759859A 2002-06-18 2003-06-16 Laser sintering method with increased process precision, and particles used for the same Withdrawn EP1513670A1 (en)

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