Method and apparatus for producing three-dimensional work pieces

Abstract

A method for producing three-dimensional work pieces comprises the steps of supplying gas to a process chamber accommodating a carrier and a powder application device, applying a layer of raw material powder onto the carrier by means of the powder application device, selectively irradiating electromagnetic or particle radiation onto the raw material powder applied onto the carrier by means of an irradiation device, discharging gas containing particulate impurities from the process chamber, and controlling the operation of the irradiation device by means of a control unit such that a radiation beam emitted by at least one radiation source of the irradiation device is guided over the layer of raw material powder applied onto the carrier according to a radiation pattern containing a plurality of scan vectors.

Claims

1. Method for producing three-dimensional work pieces, the method comprising the following steps: supplying gas to a process chamber accommodating a carrier and a powder application device, applying a layer of raw material powder onto the carrier by the powder application device, selectively irradiating electromagnetic or particle radiation onto the raw material powder applied onto the carrier by an irradiation device, discharging gas containing particulate impurities from the process chamber, filtering the particulate impurities from the discharged gas, and controlling the operation of the irradiation device by a control unit such that a radiation beam emitted by at least one radiation source of the irradiation device is guided over the layer of raw material powder applied onto the carrier according to a radiation pattern containing a plurality of scan vectors; detecting an actual flow rate of a gas stream flowing through the process chamber, comparing the detected actual flow rate with a predetermined set flow rate; and controlling a conveying device which is operated so as to discharge the gas containing particulate impurities from the process chamber in dependence on the result of the comparison between the detected actual flow rate and the predetermined set flow rate such that the detected actual flow rate converges to the predetermined set flow rate, wherein the scan vectors, in at least a section of the radiation pattern, extend substantially parallel to each other, and wherein at least every other scan vector of the substantially parallel scan vectors extends at an angle between 0 and 90 or between 270 and 360 with respect to a direction of flow of a gas stream flowing through the process chamber.

2. Method according to claim 1, wherein adjacent scan vectors, in at least a section of the radiation pattern, are directed in the same direction, or wherein adjacent scan vectors, in at least a section of the radiation pattern, are directed in opposite directions.

3. Method according to claim 1, wherein the radiation pattern is a stripe pattern comprising a plurality of parallel stripes, each stripe being defined by a plurality of scan vectors extending substantially parallel to each other and extending substantially perpendicular to a longitudinal axis of the stripe.

4. Method according to claim 3, wherein the operation of the irradiation device, by the control unit, is controlled such that the radiation beam emitted by the at least one radiation source of the irradiation device is guided over the layer of raw material powder applied onto the carrier such that an advance direction of the radiation beam along the longitudinal axes of the stripes in the stripe pattern extends at an angle between 0 and 90 or between 270 and 360 with respect to the direction of flow of the gas stream flowing through the process chamber.

5. Method according to claim 1, wherein the operation of the irradiation device, by the control unit, is controlled such that the radiation beam emitted by the at least one radiation source of the irradiation device is guided over subsequent layers of raw material powder applied onto the carrier according to radiation patterns which are rotated relative to each other.

6. Method according to claim 1, wherein the actual flow rate of the gas stream flowing through the process chamber is measured by a detection device comprising a gas flow rate sensor disposed in a discharge line via which gas containing particulate impurities is discharged from the process chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention in the following are explained in greater detail with reference to the accompanying schematic drawings, in which:

(2) FIG. 1 shows an apparatus for producing three-dimensional work pieces,

(3) FIG. 2 shows a schematic representation of an exemplary radiation pattern according to which a radiation beam emitted by a radiation source of an irradiation device employed in the apparatus according to FIG. 1 is guided over a layer of raw material powder,

(4) FIG. 3 shows a schematic representation of a further exemplary radiation pattern according to which a radiation beam emitted by a radiation source of an irradiation device employed in the apparatus according to FIG. 1 is guided over a layer of raw material powder, and

(5) FIG. 4 shows a schematic representation of still a further exemplary radiation pattern according to which a radiation beam emitted by a radiation source of an irradiation device employed in the apparatus according to FIG. 1 is guided over a layer of raw material powder.

DETAILED DESCRIPTION OF DRAWINGS

(6) FIG. 1 shows an apparatus 10 for producing three-dimensional work pieces by selective laser melting (SLM). The apparatus 10 comprises a process chamber 12. A powder application device 14, which is disposed in the process chamber 12, serves to apply a raw material powder onto a carrier 16. The carrier 16 is designed to be displaceable in vertical direction so that, with increasing construction height of a work piece, as it is built up in layers from the raw material powder on the carrier 16, the carrier 16 can be moved downwards in the vertical direction.

(7) The apparatus 10 further comprises an irradiation device 18 for selectively irradiating laser radiation onto the raw material powder applied onto the carrier 16. By means of the irradiation device 18, the raw material powder applied onto the carrier 18 may be subjected to laser radiation in a site-selective manner in dependence on the desired geometry of the work piece that is to be produced. The irradiation device 18 has a hermetically sealable housing 20. A radiation beam 22, in particular a laser beam, provided by a radiation source 24, in particular a laser source which may, for example, comprise a diode pumped Ytterbium fibre laser emitting laser light at a wavelength of approximately 1070 to 1080 nm is directed into the housing 20 via an opening 26.

(8) The irradiation device 18 further comprises an optical unit 28 for guiding and processing the radiation beam 22, the optical unit 28 comprising optical elements such as a beam expander 30 for expanding the radiation beam 22, a focusing lens 32 for focusing the radiation beam 22 at a focus point, a scanner unit 34 and an object lens 36. The scanner unit 34 and the object lens 36 are shown by way of example in the form of a galvanometer scanner and an f-theta object lens. By means of the scanner unit 34, the position of the focus of the radiation beam 22 both in the direction of the beam path and in a plane perpendicular to the beam path can be changed and adapted. The operation of the irradiation device 18 is controlled by means of a control unit 38.

(9) The process chamber 12 is sealable against the ambient atmosphere, i.e. against the environment surrounding the process chamber 12. The process chamber 12 is connected to a gas supply line 39 via which a gas provided by a gas source 40 may be supplied to the process chamber 12. The gas supplied to the process chamber 12 from the gas source 40 may be an inert gas such as, for example, Argon or Nitrogen.

(10) A discharge line 42 serves to discharge gas containing particulate impurities such as, for example, raw material powder particles or welding smoke particles from the process chamber 12 during irradiating electromagnetic or particle radiation onto the raw material powder applied onto the carrier 16 in order to produce a work piece made of said raw material powder by an additive layer construction method. The gas containing particulate impurities is discharged from the process chamber 12 by means of a conveying device 44 such as, for example, a pump. A filter 46 disposed in the discharge line 42 upstream of the conveying device 44 serves to filter the particulate impurities from the gas stream discharged from the process chamber 12.

(11) After passing the filter 46 the gas stream may be recirculated into the process chamber 12 via the gas supply line 39.

(12) By supplying gas from the gas source 40 to the process chamber 12 via the gas supply line 39 and by discharging gas containing particulate impurities from the process chamber 12 via the discharge line 42, a gas flow through the process chamber is induced. Specifically, a gas stream flowing in a direction of flow which is indicated by an arrow F is generated within the process chamber 12. The gas stream carries particulate impurities, such as raw material powder particles, soot or welding smoke particles.

(13) An actual flow rate of the gas stream flowing through the process chamber 12 is detected by means of a detection device 48. The detection device 48 comprises a gas flow rate sensor 50 disposed in the discharge line 42 via which gas containing particulate impurities is discharged from the process chamber 12. The detection device 48 may comprise further gas flow rate sensors which may be disposed within the process chamber 12, but are not shown in FIG. 1. A The further control unit 52, which in the apparatus 10 according to FIG. 1 is formed separate from the control unit 38 for controlling the operation of the irradiation device 18, but may also be formed integral with the control unit 38, serves to control the operation of the conveying device 44 in dependence on the detected actual flow rate of the gas stream flowing through the process chamber 12. Specifically, a comparison device 54 of the further control unit 52 serves to compare the detected actual flow rate with a predetermined set flow rate. The further control unit 52 then controls the conveying device 44 in dependence on the result of the comparison between the detected actual flow rate and the predetermined set flow rate such that the detected actual flow rate converges to the predetermined set flow rate.

(14) The operation of the irradiation device 18, by means of the control unit 38, is controlled such that the radiation beam 22 emitted by the radiation source 24 of the irradiation device 18 is guided over the layer of raw material powder applied onto the carrier 16 by means of the powder application device 14 according to a radiation pattern 56, 56, 56 as depicted in any one of FIGS. 2 to 4. The radiation pattern 56 shown in FIG. 2 is a stripe pattern comprising a plurality of parallel stripes S. Each stripe S of the stripe pattern is defined by a plurality of scan vectors V extending substantially parallel to each other and substantially perpendicular to a longitudinal axis L of the stripe S. Within each stripe S of the stripe pattern, adjacent scan vectors V are directed in opposite directions. As becomes apparent from FIG. 2, the scan vectors V of the radiation pattern 56 are oriented relative to the direction of flow F of the gas stream flowing through the process chamber 12, such that the scan vectors V extend at an angle of approximately 315 and approximately 135 with respect to the direction of flow F of the gas stream flowing through the process chamber 12.

(15) Further, the operation of the irradiation device 18, by means of the control unit 38, is controlled such that the radiation beam 22 emitted by the radiation source 24 of the irradiation device 18 is guided over the layer of raw material powder applied onto the carrier 16 such that an advance direction A of the radiation beam 22 along the longitudinal axes L of the stripes S in the stripe pattern extends at an angle of approximately 45 with respect to the direction of flow F of the gas stream flowing through the process chamber 12. By orienting the scan vectors V in the radiation pattern 56 and the advance direction A of the radiation beam 22 along the longitudinal axes L of the stripes S in the stripe pattern in dependence on the direction of flow F of the gas stream flowing through the process chamber 12, the absorption of radiation energy and/or shielding of the radiation beam 22 emitted by the radiation source 24 of the irradiation device 18 may be reduced.

(16) Finally, the operation of the irradiation device 18, by means of the control unit 38, is controlled such that the radiation beam 22 emitted by the radiation source 24 of the irradiation device 18 is guided over subsequent layers of raw material powder applied onto the carrier 16 according to radiation patterns which are rotated relative to each other. Specifically, the radiation pattern 56 which is depicted in FIG. 2 and which is used for irradiating a first layer of raw material powder is rotated about approximately 90 so as to form the radiation pattern 56 depicted in FIG. 3. Upon irradiating a second layer of raw material powder which is applied onto the first (already irradiated) layer of raw material powder, the radiation beam 22 emitted by the radiation source 24 of the irradiation device 18 is guided according to the radiation pattern 56.

(17) Like the radiation pattern 56, the radiation pattern 56 also is a stripe pattern comprising a plurality of parallel stripes S, wherein each stripe S is defined by a plurality of scan vectors V extending substantially parallel to each other and substantially perpendicular to a longitudinal axis L of the stripe S. Within each stripe S, adjacent scan vectors V are directed in opposite directions. The scan vectors V of the radiation pattern 56 are oriented relative to the direction of flow F of the gas stream flowing through the process chamber 12, such that the scan vectors V extend at an angle of approximately 45 and approximately 225 with respect to the direction of flow F of the gas stream flowing through the process chamber 12.

(18) An advance direction A of the radiation beam 22 along the longitudinal axes L of the stripes S in the stripe pattern extends at an angle of approximately 315 with respect to the direction of flow F of the gas stream flowing through the process chamber 12. By rotating the radiation pattern 56, 56 upon irradiating subsequent layers of raw material powder, excessive shrinkage and residual stresses in the generated work pieces may be minimized.

(19) A further exemplary radiation pattern 56 is depicted in FIG. 4. Like the radiation patterns 56, 56 the radiation pattern 56 also is a stripe pattern comprising a plurality of parallel stripes S, wherein each stripe S is defined by a plurality of scan vectors V extending substantially parallel to each other and substantially perpendicular to a longitudinal axis L of the stripe S. Within each stripe S, adjacent scan vectors V are directed in the same direction. The scan vectors V of the radiation pattern 56 are oriented relative to the direction of flow F of the gas stream flowing through the process chamber 12, such that the scan vectors V extend at an angle of approximately 0 with respect to the direction of flow F of the gas stream flowing through the process chamber 12.

(20) An advance direction A of the radiation beam 22 along the longitudinal axes L of the stripes S in the stripe pattern extends at an angle of approximately 90 with respect to the direction of flow F of the gas stream flowing through the process chamber 12.