PROCESS FOR PRODUCING A SHAPED BODY BY LAYERWISE BUILDUP FROM MATERIAL POWDER

• US 20140332507A1
• Filed: 11/29/2012
• Published: 11/13/2014
• Est. Priority Date: 11/29/2011
• Status: Active Grant

• Current Assignee: ReaLizer GmbH (Dmg Mori Co., Ltd.)
• Original Assignee: ReaLizer GmbH (Dmg Mori Co., Ltd.)
• Inventors: Fockele, Matthias
• Granted Patent: US 9,713,856 B2
• Time in Patent Office: Days
• US Class Current: 219/121.61
• CPC Class Codes: B22F 10/28 Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
• CPC Class Codes: B22F 10/32 of the atmosphere, e.g. composition or pressure in a building chamber
• CPC Class Codes: B22F 10/36 of energy beam parameters
• CPC Class Codes: B22F 10/362 for preheating
• CPC Class Codes: B22F 12/30 Platforms or substrates
• CPC Class Codes: B22F 12/38 Housings, e.g. machine housings
• CPC Class Codes: B23K 26/32 taking account of the properties of the material involved
• CPC Class Codes: B23K 26/342 Build-up welding
• CPC Class Codes: B29C 64/153 using layers of powder being selectively joined, e.g. by selective laser sintering or melting
• CPC Class Codes: Y02P 10/25 Process efficiency

Abstract

The invention relates to a method for producing a moulded body by building up layers of powdered material, comprising the steps of:

• a) preparing a layer of powdered material,
• b) heating the layer using controlled radiation by irradiating selected points of the layer according to a cross-sectional pattern of the moulded body assigned to said layer according to the geometry description data of the moulded body, so that the powdered material is solidified by melting to form connecting regions according to the cross-sectional pattern of the moulded body,
• c) preparing a next layer of powdered material on the layer irradiated most recently and
• d) heating the most recently prepared layer using controlled radiation by radiating selective points of the layer according to a cross-sectional pattern of the moulded body assigned to said layer, so that the powdered material is solidified by melting to form connecting regions according to said cross-sectional pattern of the moulded body,
• and
• e) repeating steps c) and d) multiple times at least until the build-up of the moulded body is complete, wherein the energy application to selected points in radiation steps d) can be varied per unit of time by performing the radiation according to the respective radiation point on the powdered layer.

Claims

1. Method for producing a moulded body by building up layers of powdered material, comprising the steps of:

a) preparing a layer (34) of powdered material,

b) heating the layer (34) using controlled radiation by irradiating selected points of the layer (34) according to a cross-sectional pattern of the moulded body (2) assigned to said layer (34) according to the geometry description data of the moulded body (2), so that the powdered material is solidified by melting to form connecting regions according to the cross-sectional pattern of the moulded body (2),

c) preparing a next layer of powdered material (34) on the layer irradiated most recently and

d) heating the most recently prepared layer (34) using controlled radiation by irradiating selective points of the layer (34) according to a cross-sectional pattern of the moulded body assigned to said layer, so that the powdered material is solidified by melting to form connecting regions according to said cross-sectional pattern of the moulded body (2),

and

e) repeating steps c) and d) multiple times at least until the build-up of the moulded body (2) is complete, wherein the energy application to selected points by means of irradiation in irradiation steps d) can be varied per unit of time by means of radiation according to the respective irradiation point on the powdered layer (34),

characterised in that

in radiation steps d) the application of energy to selected points per

unit of time to a respective irradiation point (I, II, III, IV) on the respective layer (34) is selected as a function of the thermal conductivity of a respective defined, immediate, three-dimensional surrounding region (38) of the irradiation point (I-IV) and is modulated automatically accordingly by setting irradiation parameters, such as the energy density of the radiation at the irradiation point and/or the duration of the irradiation at the irradiation point, wherein as a measure of the thermal conductivity of the defined, immediate, three-dimensional surrounding region of the respective irradiation point the volume already solidified by melting powdered material within said surrounding region is determined from geometry description data of the moulded body, and wherein the application of energy to selected points per unit of time to the irradiation point is selected to be greater within specific tolerances, the higher the thermal conductivity of its surrounding region (38).

2. Method according to claim 1, characterised in that the selective irradiation of points by means of the controlled scanning of the respective powdered layer (34) is performed by a bundled laser beam (24), whereby as a function of the thermal conductivity of the defined immediate environment of the respective current irradiation point (I-IV) the radiation power and/or the extent of the point of impact of the laser beam on the powdered layer (34) and/or the beam scanning speed at the irradiation point (I-IV) is adjusted.

3. Method according to either claim 1, characterised in that the measurement determined from the geometry description data of the moulded body for the thermal conductivity of the defined, immediate, three-dimensional surrounding region of the respective irradiation point is used for automatically controlling the irradiation parameter to be modulated by means of a control apparatus (28) controlling the irradiation process.

4. Method according to claim 3, characterised in that the determined values of the measurement for thermal conductivity or values derived therefrom are saved in association with respective geometry description data of the relevant irradiation points (I-IV), so that they can be read and processed by the control apparatus (28) in order to control the irradiation processes during the building process.

5. Method according to claim 1, characterised in that to determine the measurement for the respective thermal conductivity of the immediate surrounding regions of the considered irradiation points (I-IV) a theoretical model of the moulded body (2) or a region thereof is divided into individual layers according to the data, preferably according to the individual built-up layers (34), and said layers (34) are divided into a plurality of volume elements (40) with a volume element height corresponding to the layer thickness (d), wherein the volume elements (40) are assigned to irradiation points and are representative thereof, in that for each volume element (40) which is representative of a relevant irradiation point a respective three-dimensional, immediate surrounding region (38) is defined, and in that as a measurement for determining the thermal conductivity of the defined immediate surrounding region (38) of a relevant irradiation point (I-IV) the number of volume elements in the surrounding region (38) of the part of the moulded body already solidified by remelting is taken into account during irradiation of the relevant irradiation point (I-IV).

6. Method according to claim 5, characterised in that in the respective defined, three-dimensional immediate surrounding region (38) of a relevant irradiation point the number of volume elements (40) of the part of the moulded body (2) already solidified by remelting is taken into consideration, which volume elements are in layers below the layer (34) of the considered irradiation point.

7. Method according to claim 6, characterised in that the number of volume elements in the surrounding region (38) of the part of the moulded body already solidified by remelting is also taken into consideration, which volume elements are in the layer of the currently considered irradiation point (I-IV).

8. Method according to claim 1, characterised in that irradiation parameter sets with irradiation parameters, which depend on the respective thermal conductivity of the defined immediate surrounding regions of the irradiation points considered, are saved in association with geometry description data of said irradiation points, so that they can be read and processed by the control apparatus (28) in order to control the irradiation processes.

9. Method according to claim 1, characterised in that the sequencing of the irradiation points during the irradiation of a respective layer (34) is selected taking into consideration the measurement determined from the geometry description data for the thermal conductivity of the defined, three-dimensional, immediate surrounding regions of the irradiation points.

10. Device, which is set up for performing the method according to claim 1, comprising a processing chamber housing (8) with a support platform (14) for supporting the moulded body to be produced, a layer preparation apparatus (16) for preparing respective powdered layers on the support platform (14), an irradiation apparatus (18) for irradiating the powdered layer prepared most recently on the support platform (14) according to the geometry description data of the moulded body to be produced and a control apparatus (28) for controlling the irradiation apparatus (18),

characterised in that

the control apparatus is set up and programmed to control the irradiation apparatus so that the application of energy to selective points per unit of time is performed on a respective irradiation point (I-IV) on the respective layer (34) as a function of the thermal conductivity of a respective defined, three-dimensional, immediate surrounding region (38) of the irradiation point (I-IV), which thermal conductivity is determined on the basis of geometry description data of the moulded body to be produced, by setting suitable irradiation parameters, such as the energy density of the radiation at the irradiation point, and/or the duration of the irradiation of the irradiation point.

11. Device according to claim 10, characterised in that the irradiation apparatus (18) comprises a laser (20) and beam deflecting unit (22) for controlling the deflection of the laser beam (24) emitted by the laser.