METHOD FOR THE GENERATIVE PRODUCTION OF A THREE-DIMENSIONAL COMPONENT

Abstract

A method for the generative production of a three-dimensional component in a processing chamber, wherein the steps of providing a metal starting material in the processing chamber and melting the starting material by inputting energy are repeated multiple times, and wherein a process gas is provided in the processing chamber is disclosed. The method provides for the following steps wherein the hydrogen content of the process gases or of a sample of the process gas is determined; the oxygen content of the process gas or of a sample of the process gas is determined by means of an oxygen sensor and/or the dewpoint of the process gases or of a sample of the process gas is determined; and the value determined in step 2 for the oxygen content and/or the dewpoint is/are corrected with the aid of the value for the hydrogen content determined in step 1.

Claims

1. A method for the generative production of a three-dimensional component in a processing chamber, comprising the steps of providing a metal starting material in the processing chamber melting the starting material by inputting energy, repeated multiple times, wherein a process gas is provided in the processing chamber, and wherein the oxygen content of the process gas is determined, characterised in that a first oxygen sensor and a second oxygen sensor are provided, and the oxygen content of the process gas is determined by means of the first oxygen sensor or by means of the second oxygen sensor or both first oxygen sensor and second oxygen sensor depending on the desired quality of the component that is to be produced.

2. The method according to claim 1, characterised in that the first oxygen sensor is a lambda probe.

3. The method according to claim 1, characterised in that the second oxygen sensor determines the oxygen content of the process gas independently of the other constituents of the process gas.

4. The method according to claim 3, characterised in that the second oxygen sensor is a chemical cell.

5. The method according to claim 1, characterised in that the first or second oxygen sensor is arranged inside the processing chamber.

6. The method according to claim 1, characterised in that a portion of the process gas is extracted from the processing chamber and the oxygen content of the portion of process gas extracted from the processing chamber is determined.

7. The method according to claim 6, characterised in that the extracted portion of the process gases is returned to the processing chamber.

8. The method according to claim 1, characterised in that a gas without oxygen is fed into the process gas if the value for the oxygen content determined with the first or second oxygen sensor is greater than a specified comparison value.

9. The method according to claim 1, characterised in that the energy for melting the starting material is supplied with a laser.

10. An apparatus for the generative production of a three-dimensional component, comprising a processing chamber with a structuring platform and an application device for depositing the starting material on the structuring platform, comprising a laser for melting the starting material a process gas feed device for feeding process gas into the processing chamber, characterised in that a first oxygen sensor is provided for determining the oxygen content of the process gas and a second oxygen sensor is provided for determining the oxygen content of the process gas, wherein the second oxygen sensor is designed as a chemical cell and the first oxygen sensor has a faster response time than the second oxygen sensor.

11. The apparatus according to claim 10, characterised in that the first oxygen sensor is designed as a lambda probe.

12. The apparatus according to claim 10, characterised in that the second oxygen sensor operates at a temperature selected from the group consisting of below 500 C., below 300 C., below 100 C., and below 40 C.

13. The apparatus according to claim 10, characterised in that a separate analysis device is provided for each of the first and second oxygen sensors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The invention and further details of the invention will be explained in greater detail in the following text with reference to embodiments thereof represented schematically in the drawing. In the drawing:

[0054] FIG. 1 shows a first apparatus according to the invention for the generative production of a 3-dimensional component and

[0055] FIG. 2 shows an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0056] FIG. 1 is a schematic representation of an apparatus for carrying out the method according to the invention.

[0057] In the following text, an apparatus for generative production of a three-dimensional component is described. As noted earlier, however, the method according to the invention is not limited to the apparatus represented for generative production of three-dimensional components.

[0058] The apparatus is a laser melting apparatus. The laser melting apparatus comprises a processing chamber 1 which serves as the construction space for the three-dimensional component 2.

[0059] A structuring platform 3 for supporting the component 2 to be produced is arranged inside processing chamber 1. Structuring platform 3 is equipped with a height adjustment device 4, by means of which the height of structuring platform 3 may be adjusted vertically.

[0060] Apparatus 1 further comprises a reservoir 5. Reservoir 5 is designed to hold a powder starting material which can be solidified.

[0061] Additionally, an application device 6 is provided for depositing the starting material on structuring platform 3. Such an application device 6 is movable horizontally, parallel to work level 10.

[0062] A laser 7 for generating a laser beam is also provided. A laser beam generated by laser 7 is deflected via a deflection mechanism 8 and focused on a predetermined point below or in work level 10 through a focusing device (not shown). The path of the laser beam may be altered by deflecting mechanism 8 in such manner that it melts the locations of the deposited layer that correspond to the cross section of the object 2 that is to be produced.

[0063] A process gas feed device 9 is also provided, by means of which processing chamber 1 may be charged with a process gas.

[0064] Process gas feed device 9 is equipped with one or more reservoirs for the process gas or individual constituents of the process gas, wherein the process gas reservoir (not shown) is connected via one or more line segments to outlets (not shown) which open into the processing chamber. The inlets, e.g., one or more nozzles for introducing process gas are arranged in an lower region of processing chamber 1. The quantity of gas that is introduced is adjustable by means of a control valve 20.

[0065] At least one nozzle of the process gas feed device is preferably arranged in the bottom region of processing chamber 1 at a height equivalent to one fifth, one quarter, one half, two thirds or three quarters of the height between the bottom of processing chamber 1 and work level 10 or approximately level with work level 10.

[0066] An inert gas such as argon having greater density than air at the same temperature is preferably provided as the process gas.

[0067] A fan device (not shown) is also arranged in a bottom region of the processing chamber. Multiple fan devices may also be provided.

[0068] A circulating line 14 for a portion of the process gas is also provided. A portion of the process gas may be extracted from processing chamber 1 through an outlet 15, forwarded through circulating line 14 and returned to processing chamber 1 again through inlet 16. The circulation of the process gas is effected for example by means of a blower or compressor 23. A control valve 17 is also provided inside circulating line 14, by means of which the quantity of gas that is returned to processing chamber 1 is controllable. A line 18 is also provided which branches off from circulating line 14 and which makes it possible to draw off the process gas which is transported through circulating line 14. Line 18 is also fitted with a control valve 19.

[0069] The apparatus further comprises a controller 11 for controlling control valve 20 of process gas feed device 9 and control valves 17 and 19. Controller 11 may comprise one or preferably two regulating devices (not shown) with a closed control circuit. The regulating devices may also comprise a P-regulator, an I-regulator, a D-regulator and combinations thereof, such as a PID-regulator. I

[0070] A second oxygen sensor 12 for determining the oxygen content of the process gas circulating through circulating line 14 and a lambda probe 13 for determining the oxygen content of the process gas circulating through circulating line 14 are also provided. The second oxygen sensor 12 and lambda probe 13 are connected to controller 11.

[0071] The following text describes a method according to the invention with reference to an embodiment thereof.

[0072] Argon is fed into a a bottom region of processing chamber 1 as the process gas. Since process gas feed device 9 introduces the process gas that the height of work level 10 or lower, processing chamber 1 is filled with the process gas from the bottom up.

[0073] Consequently, the heavier gaseous argon forces the lighter air into the top region of processing chamber 1, in which an outlet (not shown) is provided to allow the air to escape.

[0074] The process gas in processing chamber 1 may optionally be agitated by means of a fan device inside processing chamber 1. The turbulence has the effect of removing impurities from dead spaces in the processing chamber. It also creates a homogeneous gas composition throughout the entire volume of the processing chamber. Clean process gas may also be introduced into processing chamber 1 via process gas feed device 9.

[0075] A metal starting material is deposited or provided on structuring platform 3 in the form of a powder bed by application device 6. Alternatively, the metallic starting material may also be introduced via a power feed or a wire feed.

[0076] Then, the starting material is melted by means of laser 7. The two steps providing a metal starting material on structuring platform and melting the starting material are repeated multiple times so that the component is constructed layer by layer.

[0077] However, the oxygen content of the process gas should not exceed a predetermined maximum value through the manufacturing process in order to avoid undesirable oxidation reactions. According to the invention, the oxygen content of the process gas must therefore be monitored. For this, a sample of the of process gas circulating through circulating line 14 is passed to lambda probe 13, and the oxygen content of the sample is determined by lambda probe 13. The oxygen content value obtained thereby is transmitted to controller 11.

[0078] In the lambda probe 13, the sample is heated, in which case it is possible for hydrogen and oxygen to recombine to form water. The value calculated by lambda probe 13 for the oxygen content in the sample is therefore not exactly equal to the actual oxygen content of the process gas. For many applications, in which exact reproducibility is not of paramount importance, this inaccuracy is acceptable.

[0079] However, if components are to be manufactured with reproducible properties, such as safety-critical components or components which must possess specific minimum mechanical properties for example, even minor variations in the oxygen content are not permissible.

[0080] For this reason, in addition to or alternatively to the measurement by the first oxygen sensor, the oxygen content in the process gas or in the process gas that is transported in the circuit may also be determined by means of the second oxygen sensor. For this purpose, a second sample is taken from the process gas and the oxygen content thereof is determined by means of the second oxygen sensor 12. A measuring apparatus or measuring element that functions without any interaction with the other constituents of the process gas is used as the second oxygen sensor 12. In particular, the value measured for the oxygen content is not distorted by the measurement itself.

[0081] The value for the hydrogen content calculated by measuring sensor 12 is also transmitted to controller 11. The composition of the process gas in processing chamber 1 is then regulated on the basis of the value calculated for the oxygen content. For this purpose, a portion of the original process gas atmosphere may be diverted via line 18 and/or the composition and/or quantity of process gas fed in through process gas feed device 9 may be adjusted.

[0082] FIG. 2 shows another embodiment of the invention. Identical components are identified with the same reference signs in the two figures.

[0083] The design according to FIG. 2 differs from the one in FIG. 1 essentially in that a separate extraction unit 30 is provided for extracting process gas from processing chamber 1 and transporting it to an analysis device 31. Extraction unit 30 is positioned in the immediate vicinity of the processing location where the powder is melted by laser 7, and within the circulating stream that propels the process gas through processing chamber 1 and circulating line 14. A part of the process gas is forwarded to the first and/or second oxygen sensor 12, 13 via extraction unit 30.

[0084] The design according to FIG. 2 also enables existing plants to be upgraded easily for generative production. All that has to be done is to route extraction line 30 into the inside of processing chamber 1. No other direct modifications to the plant are necessary. An external analysis device 31 with first and second oxygen sensors 12, 13 is attached to extraction unit 30 and connected to controller 11 of the existing plant or an external controller. Analysis device 31 switches to oxygen measurement by means of first oxygen sensor 12 or by means of second oxygen sensor 13 depending on the quality standards required.

LIST OF REFERENCE SIGNS

[0085] 1 Processing chamber

[0086] 2 Component

[0087] 3 Structuring platform

[0088] 4 Height adjustment device

[0089] 5 Reservoir

[0090] 6 Application device

[0091] 7 Laser

[0092] 8 Deflecting mechanism

[0093] 9 Process gas feed device

[0094] 10 Work level

[0095] 11 Controller

[0096] 12 Measuring sensor

[0097] 13 Lambda probe

[0098] 14 Circulating line

[0099] 15 Outlet

[0100] 16 Inlet

[0101] 17 Control valve

[0102] 18 Line

[0103] 19 Control valve

[0104] 20 Control valve

[0105] 21 Water vapour measurement

[0106] 22 Sensor

[0107] 23 Blower

[0108] 30 Extraction line

[0109] 31 Analysis device