Method for the generative manufacture of a 3-dimensional component

Abstract

A method and apparatus for the generative manufacture of a three-dimensional component in a processing chamber, in which the steps “providing a metallic starting material in the processing chamber” and “melting the starting material by means of energy input” are repeated multiple times, wherein a process gas is provided in the processing chamber are disclosed. The method is characterized by the steps: 1) the hydrogen content of the process gas or a sample of the process gas is determined; 2) the oxygen content of the process gas or a sample of the process gas is determined by means of an oxygen sensor and/or the dew point of the process gas or a sample of the process gas is determined; and 3) the values for the oxygen content and/or the dew point determined in step 2 are corrected by means of the value for the hydrogen content determined in step 1.

Claims

1. A method for generative manufacture of a three dimensional component in a processing chamber, wherein the method comprises: repeatedly providing a metallic starting material in the processing chamber multiple times and repeatedly melting the metallic starting material by energy input in the processing chamber multiple times; providing a process gas in the processing chamber; determining an oxygen content of the process gas, wherein the determining of the oxygen content includes: Step 1) initially measuring a hydrogen content of the process gas, Step 2) subsequently measuring the oxygen content of the process gas with an oxygen sensor, and optionally a dew point of the process gas, and Step 3) correcting at least one of values for the oxygen content, and optionally the dew point measured in the Step 2 by a value of the hydrogen content measured in the Step 1; extracting part of the process gas from the processing chamber; further measuring at least one of the oxygen content, and the hydrogen content of the part of the process gas extracted from the processing chamber; and recirculating and returning the part of the process gas into the processing chamber, wherein at least a portion of the part is discarded before the returning and the discarded portion is replaced with inert gas introduced into the processing chamber based upon the further measuring at least one of the oxygen content, and the hydrogen content of the part.

2. The method according to claim 1, characterized in that the oxygen content is measured by a lambda probe.

3. The method according to claim 1, characterized in that the hydrogen content is measured by gas chromatography or optionally by a thermal conductivity detector.

4. The method according to claim 1, wherein the subsequent measuring of the oxygen content of the process gas is by the oxygen sensor and an oxygen analyzer prior to the step 3, wherein a difference between a value measured with the oxygen sensor and a value measured with the oxygen analyzer is correlated with the hydrogen content initially measured, and a resulting correlation is used for correcting the value for the oxygen content in the Step 3.

5. The method according to claim 1, further comprising supplying an oxygen-free gas to the process gas if the correcting value for the oxygen content is higher than a predefined comparative value.

6. The method according to claim 1, characterized in that the energy input for melting the metallic starting material is provided by a laser.

7. The method according to claim 1, characterized in that the process gas comprises the inert gas.

8. The method according to claim 7, characterized in that the inert gas comprises argon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention, as well as further details of the invention, are elucidated below with reference to exemplary embodiments that are schematically illustrated in the drawings. In these drawings:

(2) FIG. 1 shows a first inventive device for the generative manufacture of a 3-dimensional component and

(3) FIG. 2 shows an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) FIG. 1 shows a schematic representation of a device for carrying out the inventive method.

(5) A device for the generative manufacture of a three-dimensional component is described below. As already mentioned above, however, the inventive method is not limited to the illustrated device for the generative manufacture of three-dimensional components.

(6) The device is a laser melting device. The laser melting device comprises a processing chamber 1 that serves as production space for the three-dimensional component 2.

(7) A production platform 3 for accommodating the component 2 to be manufactured is arranged in the processing chamber 1. The production platform 3 features a height adjusting device 4, by means of which the production platform 3 can be adjusted in the vertical direction.

(8) The device 1 also comprises a reservoir 5. The reservoir 5 is designed for accommodating a powdery starting material that can be solidified.

(9) In addition, an application device 6 is provided for applying the starting material onto the production platform 3. Such an application device 6 can be moved in the horizontal direction parallel to the working plane 10.

(10) A laser 7 for generating a laser beam is furthermore provided. A laser beam generated by the laser 7 is deflected by means of a deflection device 8 and focused on a predefined point directly underneath or in the working plane 10 by means of a (not-shown) focusing device. The deflection device 8 makes it possible to change the path of the laser beam in such a way that it melts the locations of the applied layer, which correspond to the cross section of the object 2 to be manufactured.

(11) A process gas supply device 9 is furthermore provided for supplying the processing chamber 1 with a process gas.

(12) The process gas supply device 9 features one or more reservoirs for the process gas or individual components of the process gas, wherein the (not-shown) process gas reservoir is connected to (not-shown) inlets leading into the processing chamber by means of one or more line sections. The inlets for introducing the process gas are realized, e.g., in the form of one or more nozzles and arranged in a lower region of the processing chamber 1. The amount of gas being introduced can be adjusted by means of a control valve 20. It is preferred that at least one nozzle of the process gas supply device is arranged in the region of the bottom of the processing chamber 1 or at a fifth, a quarter, half, two thirds or three quarters of the height between the bottom of the processing chamber 1 and the working plane 10 or approximately at the height of the working plane 10.

(13) The process gas used preferably consists of an inert gas that has a higher density than air at the same temperature, e.g. of argon.

(14) A (not-shown) fan is likewise arranged in a lower region of the processing chamber. Multiple fans may also be provided.

(15) A recirculation line 14 for part of the process gas is furthermore provided. Part of the process gas can be extracted from the processing chamber 1 through an outlet 15, conveyed through the recirculation line 14 and once again returned into the processing chamber 1 through the inlet 16. The process gas is recirculated, for example, by means of a blower or a compressor 23. A control valve 17 is also provided in the recirculation line 14 in order to adjust the amount of gas being returned into the processing chamber 1. In addition, a line 18 branches off the recirculation line 14 and makes it possible to extract the process gas being conveyed through the recirculation line 14. The line 18 is likewise provided with a control valve 19.

(16) The device furthermore comprises a control unit 11 for controlling the control valve 20 of the process gas supply device 9 and the control valves 17 and 19. The control unit 11 may comprise one or preferably two (not-shown) control devices in a closed control loop. The control devices may also comprise a P-controller, an I-controller, a D-controller or combinations thereof such as a PID-controller.

(17) In addition, a measuring sensor 12 is provided for determining the hydrogen content of the process gas being conveyed through the recirculation line 14 and a lambda probe 13 is provided for determining the oxygen content of the process gas being conveyed through the recirculation line 14. The measuring sensor 12 and the lambda probe 13 are connected to the control unit 11.

(18) An inventive method is described below with reference to an exemplary embodiment.

(19) Argon is introduced into a lower region of the processing chamber 1 as processing gas. Since the process gas supply device 9 introduces the process gas at or below the height of the working plane 10, the processing chamber 1 is filled with the process gas from the bottom toward the top.

(20) In this way, the heavier gaseous argon displaces the lighter air into an upper region of the processing chamber 1, in which a (not-shown) outlet for discharging the air is provided.

(21) If applicable, the process gas located in the processing chamber 1 can be set in turbulence within the processing chamber 1 by means of a fan. Contaminants are removed from the dead spaces of the processing chamber due to these turbulences. In addition, a homogenous gas composition is made available over the entire volume of the processing chamber. Clean process gas can furthermore be supplied to the processing chamber 1 by means of the process gas supply device 9.

(22) A metallic starting material is respectively applied or provided on the production platform 3 in the form of a powder bed by means of the application device 6. The metallic starting material may alternatively also be supplied by means of a powder supply or a wire feed.

(23) The laser 7 subsequently melts the starting material. The two steps “providing starting material on the production platform 3” and “melting the starting material” are repeated multiple times such that the component is produced in layers.

(24) It was determined that the water or water vapor present in the process gas locally breaks down into hydrogen and oxygen due to the energy being input with the laser during the melting process of the starting material.

(25) However, the oxygen content of the process gas should remain below a predefined maximum value during the manufacturing process in order to prevent undesirable oxidations. According to the invention, the oxygen content of the process gas is therefore monitored. For this purpose, a sample of the process gas being conveyed through the recirculation line 14 is fed to the lambda probe 13 and the oxygen content of the sample is determined by means of the lambda probe 13. The thusly determined value for the oxygen content is transmitted to the control unit 11.

(26) The sample is heated in the lambda probe 13 such that hydrogen and oxygen can recombine into water. The value for the oxygen content of the sample determined by the lambda probe 13 is therefore dependent on the hydrogen content of the sample. The higher the hydrogen content of the sample, the lower the value for the oxygen content indicated by the lambda probe 13 because correspondingly more oxygen reacts with the hydrogen and forms water.

(27) This is the reason why the hydrogen content of the process gas or of the process gas being recirculated is determined in addition to the measurement of the oxygen content. For this purpose, a second sample of the process gas is taken and its hydrogen content is determined by means of a measuring sensor 12.

(28) The second sample may be taken upstream or downstream of the location, at which the sample for determining the oxygen content is taken. However, it is also possible to use the same sample for determining the oxygen content and for determining the hydrogen content. In this case, it is advantageous to initially determine the hydrogen content because the measurement by means of the lambda probe 13 also affects the hydrogen content of the sample.

(29) The value for the hydrogen content determined by the measuring sensor 12 is likewise transmitted to the control unit 11. The determined value for the hydrogen content is then used in the control unit 11 for correcting the determined value for the oxygen content. The process gas composition in the processing chamber 1 is then controlled in dependence on the corrected value for the oxygen content. For this purpose, part of the original process gas atmosphere can be discharged through the line 18 and/or the composition and/or amount of the process gas being supplied by the process gas supply device 9 can be changed.

(30) FIG. 2 shows another embodiment of the invention. Identical components are identified by the same reference symbols in both figures.

(31) The embodiment according to FIG. 2 essentially can be distinguished from the embodiment according to FIG. 1 in that an additional sensor 21 is provided for determining the water vapor content or the dew point of the process gas being recirculated. The value for the water vapor content determined with the sensor 21 is likewise transmitted to the control unit 11 and, if applicable, corrected with the aid of the determined hydrogen content in the control unit 11.

(32) Furthermore, individual or all of the parameters oxygen content, hydrogen content and water vapor content, as well as other parameters such as temperature, carbon content, etc., can also be determined directly in the processing chamber 1. This is indicated with an exemplary sensor 22 in FIG. 2. The value or values measured in the process chamber 1 are advantageously also transmitted to the control unit 11 and used for controlling the composition of the process gas atmosphere.

LIST OF REFERENCE SYMBOLS

(33) 1 Processing chamber 2 Component 3 Production platform 4 Height adjusting device 5 Reservoir 6 Application device 7 Laser 8 Deflection device 9 Process gas supply device 10 Working plane 11 Control unit 12 Measuring sensor 13 Lambda probe 14 Recirculation line 15 Outlet 16 Inlet 17 Control valve 18 Line 19 Control valve 20 Control valve 21 Water vapor measurement 22 Sensor 23 Blower