Additive manufacturing apparatus and method

Abstract

A method and an additive manufacturing apparatus, the additive manufacturing apparatus comprising: a device (105) for generating an energy beam (118) for consolidating a build medium (104); the present invention relates to an additive manufacturing device (100) comprising an energy beam (118) and a build chamber (101) comprising a build chamber window (107) through which the energy beam (118) can enter the build chamber (101) and a build region where the build medium (104) can be located to be consolidated by the energy beam (118), where the additive manufacturing device is configured to monitor process emissions from the build region to detect damage to the build chamber window (107).

Description

[0001] The invention of the present application relates to an additive manufacturing apparatus and a method for determining damage to an additive manufacturing apparatus, in particular to a build chamber window of an additive manufacturing apparatus.

[0002] An additive manufacturing method or rapid prototyping method for producing an object involves the layer-by-layer solidification of a material, such as a metal powder material, using an energy beam, such as a laser beam. A layer of powder is deposited on a powder bed in a build chamber, and the laser beam is scanned over a portion of the powder layer corresponding to the cross section of the object being built. The laser beam melts or sinters the powder to form a solidified layer. After the selective solidification of the layer, the powder bed is reduced by the thickness of the newly solidified layer, and another layer of powder is spread on the surface and solidified as needed.

[0003] During the additive manufacturing process, it is known that particulate matter (also commonly referred to as, for example, smoke, black smoke, spatter, or bright sparks) can be generated. This material may adhere to surfaces within the equipment, and in particular may adhere to the build chamber window. Adhesion to the build chamber window can reduce the quality of parts manufactured by the equipment.

[0004] US 2017 / 355147 discloses a machine having a first energy source that delivers an energy beam that can enter the build chamber through a window in the build chamber to consolidate powder that forms part of a powder bed. A second energy source is provided that monitors the reflectivity of the window continuously or at discrete intervals during the build. At least one detector is disposed inside and / or outside the build chamber to detect changes in the energy beam from the second energy source due to changes in the reflectivity of the window. If a change in the reflectivity of the window is detected to be above a threshold, the build is suspended or stopped until the reflectivity is within tolerance, which can be achieved by cleaning the window.

[0005] US 2020 / 114580 discloses an arrangement for determining the degree of contamination of an optical unit (such as a rectangular window). The arrangement comprises a light source arranged in a wall of a processing chamber and adapted to couple radiation into the optical unit toward a center plane of the optical unit, and a determination unit is provided. Residues adhering to the surface of the optical unit may decouple at least a portion of the radiation from the optical unit and be detected by a detector of the determination unit.

[0006] US 2015 / 0165681 discloses providing a laser power meter in a building chamber close to a building surface. The energy source can be controlled based on the power of the energy beam measured in the building chamber.

[0007] US 2022 / 0111599 discloses a method comprising determining anomalies on an optical element using image data from a light sensor that detects reflected portions of an imaging light beam from the optical element.

[0008] US 2018 / 126649 discloses a method for quantifying the effectiveness of a recessed window holder with gas flow purge.

[0009] WO 2019 / 173000 discloses a method in which a change in spot size at a target surface can generate an alarm, a message and / or initiate a purge and / or cleaning cycle.

[0010] According to a first aspect, there is provided a method for detecting damage to a build chamber window of an additive manufacturing apparatus, the additive manufacturing apparatus comprising a build chamber, the build chamber comprising a build chamber window and a build area, an energy beam can enter the build chamber through the build chamber window, a build medium can be located in the build area to be consolidated by the energy beam, the method comprising monitoring the intensity of process emission from the build area.

[0011] Monitoring the intensity of the process emission may include recording the intensity of the process emission. The process emission may be an emission generated by the interaction of the energy beam with the build area and / or the powder bed, for example, monitoring the process emission may include monitoring electromagnetic radiation, for example, from the plasma. Monitoring the intensity of the process emission from the build area may be performed by monitoring a wavelength different from the wavelength of the energy beam. Optionally, a wavelength shorter than the wavelength of the energy beam may be used to monitor the intensity of the process emission. Optionally, a wavelength longer than the wavelength of the energy beam may be used to monitor the intensity of the process emission. Optionally, a first wavelength shorter than the wavelength of the energy beam and a second wavelength longer than the wavelength of the energy beam may be provided for monitoring the intensity of the process emission. Monitoring the intensity of the process emission may be performed by one or more photodiodes (e.g., one or more photodiodes sensitive to a wavelength different from the wavelength of the energy beam). Optionally, a photodiode sensitive to a wavelength shorter than the wavelength of the energy beam may be used to monitor the intensity of the process emission. Optionally, a photodiode sensitive to a wavelength longer than the wavelength of the energy beam may be used to monitor the intensity of the process emission. Optionally, a first photodiode sensitive to a wavelength shorter than the wavelength of the energy beam may be provided and a second photodiode sensitive to a wavelength longer than the wavelength of the energy beam may be provided for monitoring process emissions. The process emissions may include plasma generated by the interaction of the laser beam with the build area. Optionally, monitoring occurs when the energy beam is emitting. Additionally or alternatively, monitoring occurs when the energy beam is not emitting.

[0012] Optionally, the method includes monitoring the entire build area. The energy beam may be a laser beam or an electron beam. Damage may include contamination of the build chamber window, such as material solidified on the chamber side surface of the build chamber window from the manufacturing process. Additionally or alternatively, damage may include fingerprints and / or other contamination of the build chamber window by dirt and / or dust, and / or contamination of other organic or metallic substances. Additionally or alternatively, damage may include one or more cracks and / or one or more scratches and / or other physical flaws and / or defects in the build chamber window itself, other examples of physical defects or defects may include local deformation of the build chamber window, such as expansion and / or any other defect that causes a decrease in light transmittance of the build chamber window and / or changes in energy absorption (e.g., increases the amount of energy absorbed by the build chamber window from the energy beam) and / or changes in the optical properties of the build chamber window. Damage may cause thermal lensing, which may be due to changes in energy absorption of the build chamber window due to damage. Thermal lensing may also result in rapid, erratic changes in the path of the laser beam as it passes through the build chamber window, which may result in rapid changes in the location at which the laser beam contacts the build area (and the area observed by the monitoring system), which may hinder or reduce energy absorption due to movement of the beam (in this case, the intensity of the beam may not change, but a reduction in process emission may be observed due to movement of the beam over the build area (hindering or reducing integration of the beam energy into the surface)).

[0013] Optionally, the build area includes an area where a part can be built. Optionally, the build area includes an area where a powder bed can be formed. Optionally, the additive manufacturing device includes a support for supporting a powder bed. Optionally, the build area includes an area of ​​the support and / or an area within the periphery of the support and an area on a support (e.g., a build plate) for supporting a powder bed. Optionally, the build area includes a surface (optionally the uppermost surface) within the periphery of a support (e.g., a build plate and / or a powder bed). This can allow monitoring of a support for supporting a powder bed or monitoring of anything located on the support, such as a powder bed, or a plate located on the support, or a wiper that can be configured to apply powder to the build area to form a powder bed, or any other device or device configured within the periphery of the support.

[0014] Optionally, the build chamber window has a face exposed to the interior of the build chamber. Optionally, the build chamber window separates one or more components of the energy beam system from the environment within the build chamber. Optionally, the build chamber window is transparent to the energy beam. Optionally, the build region includes a surface (optionally an uppermost surface) within the perimeter of the support and located between the support and the face of the build chamber window exposed to the interior of the build chamber. Optionally, the build region includes a surface (optionally a surface within the build chamber) located on the build chamber side of the face of the build chamber window exposed to the interior of the build chamber. Optionally, the surface does not include the face of the build chamber window exposed to the interior of the build chamber.

[0015] Optionally, the build chamber window forms part of one or more walls forming the build chamber. Optionally, the build chamber window is located entirely within the build chamber and may form part of a module within the build chamber, such as an optical module located within the build chamber. Optionally, the build chamber window is arranged to allow an energy beam to enter the build chamber. Optionally, the build chamber window is formed of a material that allows light to pass therethrough. Optionally, more than one build chamber window is provided.

[0016] Advantageously, it is known to provide an additive manufacturing apparatus having a device for monitoring a build region of the apparatus, which allows the method to be performed without additional parts or assembly complexity when building an additive manufacturing apparatus. The method can advantageously be retrospectively applied to already existing additive manufacturing apparatuses without the need to assemble additional parts. Further advantageously, by using an energy beam for consolidating the build medium, all positions of the build chamber window that the energy beam may pass through when consolidating the build material within the build region can be analyzed.

[0017] Optionally, the energy beam is monitored by a sensor, wherein the optical path of radiation collected by the sensor from the building area at least partially coincides with the path of the energy beam.

[0018] Optionally, the method includes comparing data from the location of the build area to a threshold. The data may be at least one of: (i) a normalized data set, and / or (ii) a spatial extent of the data, and / or (iii) a density of defects. Optionally, the data includes data different from the threshold, optionally below the threshold. Alternatively, the data includes data above the threshold.

[0019] The method may include identifying a location where a process emission intensity of a build region is different from a threshold. Optionally, the method includes identifying a location where a process emission intensity of a build region is below a threshold. The method may be performed prior to building a part. The method may include determining a "start / don't start" state for building a part. Advantageously, by determining a "start / don't start" state, the method may save unnecessary waste of build material and / or time because the part build does not meet the required specifications due to a damaged build chamber window. Alternatively, if damage to the build chamber window is identified midway through the build process, the build may have to be terminated, which may mean that build material has been wasted while the part is partially made. Alternatively, if damage to the build chamber window is identified midway through the build, the build chamber window may be (i) replaced or (ii) cleaned without terminating the build, however (i) replacing the build chamber window may mean exposing the interior of the build chamber to potential contamination when the damaged build chamber window is removed in the case of replacing the build chamber window, and (ii) damage to the build chamber window may not be removed by cleaning, for example in the case where the damage to the build chamber window is a crack or the like. Performing this method and generating a "start / no start" signal prior to a build can reduce or even prevent the need to terminate a build part route due to identification of damage to the build chamber window, can save unnecessary waste of build material, and can help the user have confidence that a build will not fail due to damage to the build chamber window.

[0020] The method may rearrange the position of a part to be built within the build area in response to detected damage to the build chamber window. This may allow a build to continue when damage to the build chamber window is identified without having to wait for the build chamber window to be cleaned or replaced. By rearranging the position of a part to be built within the build area, a part may be produced without an energy beam entering the build chamber through a damaged section of the build chamber window.

[0021] Optionally, the method includes monitoring the intensity of process emissions generated by the plurality of energy beams on the build area. The method may include scanning the build area with the plurality of energy beams such that each energy beam irradiates 1 / n of the build area, where n is the number of energy beams, and optionally the build area is scanned at least n times such that each of the n laser beams scans the entire build area. The method may include scanning the entire build area with each of the plurality of energy beams. Optionally, the method includes monitoring the intensity of process emissions generated by two or more energy beams simultaneously on the build area. The method may include monitoring the intensity of process emissions generated by all of the plurality of energy beams simultaneously on the build area. The method may include dividing the build area into a plurality of sections, wherein each discrete section is irradiated by one of the plurality of energy beams, and wherein the number of discrete sections is greater than the number of energy beams. Optionally, adjacent discrete sections are irradiated by different energy beams. Advantageously, this may allow for a distinction between damage to the build chamber window and other factors, such as factors caused by features of the build area. Optionally, the method includes monitoring the intensity of process emissions generated by the multiple energy beams directed to the same portion of the build area, such as sequentially monitoring the intensity of process emissions generated by the multiple energy beams on the same portion of the build area (i.e., monitoring the intensity of process emissions generated by a first energy beam of the multiple energy beams on a portion of the build area, followed by monitoring the intensity of process emissions generated by a second energy beam of the multiple energy beams on the same portion of the build area). By monitoring the intensity of process emissions generated by the multiple energy beams directed to the same portion of the build area, the same portion (or position) of the build area can be irradiated while passing the energy beams through different positions of the build chamber window, which can provide information about whether the detected damage is related to the build chamber window or the build area.

[0022] The method may change the allocated energy beam used to build a part (or part(s)) in response to detected damage to a build chamber window. This may allow a build to continue when damage to the build chamber window is identified without having to wait for the build chamber window to be cleaned or replaced. By changing the energy beam allocation of a part (or part(s) thereof) to be built within the build area, a part may be produced without the energy beam entering the build chamber through a damaged section of the build chamber window.

[0023] Optionally, the energy beam or beams are laser beams. Optionally, the laser beam has an intensity of at least 150W.

[0024] Optionally, the method includes a pre-cleaning step. The pre-cleaning step may include irradiating the build area with an energy beam so as to clean the build area, for example by removing (or burning off) organic or other matter on the build area before damage to the build chamber window is detected. The pre-cleaning step may include irradiating the build area with an energy beam, optionally using less energy than used during the step of monitoring the intensity of process emissions from the build area. Optionally, the method includes a build area homogenization step. The homogenization step may be performed after the step of monitoring the intensity of process emissions from the build area. The homogenization step may include irradiating the build area with an energy beam so as to repair the build area surface and / or reduce the surface texture of the build area so as to improve powder delivery to the build area. Optionally, the method includes scanning the energy beam over the build area in a pattern for causing localized heating of the build chamber window. For example, the scanning pattern includes scanning adjacent rectangular segments of the build chamber window or the build area. Optionally, the rectangular segments have a length in the range of 1 mm to 10 mm (optionally 5 mm). Optionally, the rectangular segments have a length of 10 mm or less. Optionally, the rectangular segment has a width no wider than a width of the laser beam on the build chamber window or build area.

[0025] According to a second aspect of the invention, there is provided a method of manufacturing a product, the method comprising consolidating a build material in a build region within a build chamber layer by layer by an energy beam, the build chamber comprising a build chamber window, the energy beam being able to enter the build chamber through the build chamber window, and a build region, the build medium being able to be located in the build region to be consolidated by the energy beam, the method comprising monitoring process emissions from the build region. Optionally, the method comprises monitoring the intensity of the process emissions.

[0026] According to a third aspect of the present invention, there is provided an additive manufacturing apparatus, the additive manufacturing apparatus comprising: a device for generating an energy beam for consolidating a build medium; and a build chamber, the build chamber comprising a build chamber window and a build area, the energy beam can enter the build chamber through the build chamber window, the build medium can be located in the build area to be consolidated by the energy beam, wherein the additive manufacturing apparatus is configured to monitor process emissions from the build area to detect damage to the build chamber window. Optionally, the additive manufacturing apparatus comprises a device for monitoring the intensity of the process emissions. The device for monitoring the intensity of the process emissions can be an on-axis monitoring device. Optionally, the energy beam is a laser beam or an electron beam. Optionally, the additive manufacturing apparatus is configured to identify a position where the intensity of the process emissions of the build area is different from a threshold, optionally below a threshold.

[0027] According to a fourth aspect of the present invention, there is provided a method for detecting damage to a build chamber window of an additive manufacturing apparatus, the method comprising indirectly monitoring the intensity of an energy beam. Optionally, the energy beam comprises a laser beam.

[0028] According to a fifth aspect, there is provided a method of detecting damage to a build chamber window of an additive manufacturing apparatus, the method comprising monitoring a build area.

[0029] It will be appreciated that features described with respect to one aspect of the invention may be applied to other aspects of the invention unless incompatible.

[0030] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0031] Figure 1 A schematic diagram of an additive manufacturing apparatus is shown;

[0032] Figure 2 Shows Figure 1 Schematic diagram of the additive manufacturing equipment from the other side;

[0033] Figure 3 a schematic diagram showing a plan view of a build platform within a build area;

[0034] Figure 4 An embodiment of an optical module is shown;

[0035] Figure 5 A flow chart illustrating the method is shown;

[0036] FIG. 6A to FIG. 6D The scanned area groups are shown;

[0037] Figure 7 An example of a cumulative data set is shown;

[0038] Figure 8 The filtered data is shown;

[0039] Fig.9A Clustered data are shown;

[0040] Fig. 9B Noise data are shown;

[0041] Fig.10 A projection showing the location of the laser beam passing through the build chamber window;

[0042] Figure 11 shows data collected at different laser powers;

[0043] Fig.12 Cluster data projected onto the build chamber window is shown;

[0044] as well as

[0045] Fig.13 A comparison between the projection data and the build chamber window is shown.

[0046] refer to Figure 1 and Figure 2 The additive manufacturing apparatus includes a build chamber 101 having partitions 115, 116 therein that define a build area 122 and a surrounding surface 110 on which powder can be deposited. A build platform 102 is disposed within the boundaries of the build area 122 (at Figure 3 104). Build volume 117 is defined by the extent to which platform 102 can be lowered. One or more objects 103 can be built by selective laser melting of powder 104. As successive layers of object 103 are formed, build platform 102 can be lowered within build volume 117 by a drive mechanism (such as motor 113). Figure 3 A plan view of build platform 102 positioned within build area 122 is shown.

[0047] The build is performed by successively depositing layers of powder on the build area 122 to form a powder bed 104 using a dispensing device 108 for dosing powder onto the surface 110 and an elongated wiper 109 for spreading the powder on the build area 122. For example, the dispensing device 108 may be a device as described in WO 2010 / 007396. The wiper 109 moves in a linear direction on the build platform 102.

[0048] Laser module 105 generates laser light for melting powder 104, which is directed as required by optical scanner 106 under the control of computer 130. Laser beam 118 enters chamber 101 through build chamber window 107. In this embodiment, laser module 105 is a fiber laser, such as an nd:YAG fiber laser.

[0049] Figure 4 An example optical module 106 for use in the current embodiment is shown in detail. The optical module comprises: a laser aperture 170 for coupling to the laser module 105; a measurement aperture 171 for coupling to measurement devices 172, 173; and an output aperture 174 through which the laser beam is directed through the build chamber window 107 onto the build area 122 and radiation emitted from the build area 122 is collected.

[0050] The laser beam is steered and focused to a desired location on the powder bed 104 by scanning optics including two tiltable mirrors 175 (only one of which is shown) and focusing lenses 176 , 177 .

[0051] The tiltable mirrors 175 are each mounted to rotate about an axis under the control of an actuator such as a galvanometer. The axes about which the mirrors 175 rotate are substantially vertical, so that one mirror can deflect the laser beam in one direction (the X direction) and the other mirror can deflect the laser beam in a perpendicular direction (the Y direction). However, it should be understood that other arrangements may be used, such as a single mirror rotatable about two axes, and / or the laser beam may be coupled, for example via optical fiber, into a beam guide optical device mounted for linear movement in the X and Y directions. Examples of the latter arrangement are disclosed in US2004 / 0094728 and US2013 / 0112672.

[0052] In order to ensure that the focus of the laser beam remains in the same plane when the deflection angle of the laser beam changes, it is known to provide an f-θ lens after the tiltable mirror. However, in this embodiment, a pair of movable lenses 176, 177 are provided before the tiltable mirror 175 (relative to the direction of travel of the laser beam) for focusing the laser beam when the deflection angle changes. The movement of the focusing lenses 176, 177 is controlled synchronously with the movement of the tiltable mirror 175. The focusing lenses 176, 177 can be movable toward and away from each other in a linear direction by an actuator such as a voice coil 184.

[0053] The tiltable mirror 175 and focusing lenses 176, 177 are appropriately selected to transmit both the laser wavelength and the wavelength of the collected radiation, which may contain characteristic spectral peaks of the material being processed.

[0054] The beam splitter 178 is disposed between the focusing lenses 176, 177 and the laser 105 and the measuring device 172, 173. The beam splitter 178 is a notch filter that reflects light having the laser wavelength but allows light having other wavelengths to pass therethrough. The laser light is reflected toward the focusing lenses 176, 177, and light not having the laser wavelength collected by the scanning optics is transmitted to the measuring aperture 171.

[0055] The optical module 106 further includes a heat sink 181 for capturing laser light transmitted through the beam splitter 178 .

[0056] Various measuring devices may be connected to the measuring aperture 171. In this embodiment, a camera 173 and a photodiode measuring arrangement 172 are provided for measuring the radiation collected by the optical scanner. The photodiode measuring arrangement 172 comprises a first photodiode 172A and a second photodiode 172B which are configured in this embodiment to detect different wavelengths. Another beam splitter 185 decomposes the radiation reflected to the aperture 171 so as to direct part of the radiation to the photodiode measuring arrangement 172 and part to the camera 173.

[0057] Photodiode measurement arrangement 172 provides a measurement of the light emitted from build area 122 exposed to the laser beam, and camera 180 captures an image of this area.

[0058] In use, computer 130 controls laser 105 and optical module 106 to scan a laser beam over build area 122 during object formation based on geometric data stored on computer 130 so as to solidify selected areas of a powder layer forming part of powder bed 104 .

[0059] In a first embodiment, the entire build area 122 is scanned with a laser beam, and a photodiode measurement arrangement 172 can be used to record the interaction of the laser with the build area 122. In this embodiment, the laser wavelength is about 1080 nm, the first photodiode 172A is configured to detect wavelengths in the range of 700 nm to 1050 nm, and the second photodiode is configured to detect wavelengths in the range of 1100 nm to 2000 nm. In the current embodiment, only the first photodiode 172A is needed to record the optical process emissions from the bed generated by the interaction of the laser with the bed. The optical process emissions in the current embodiment have a wavelength shorter than the laser wavelength. Therefore, in this embodiment, the first photodiode 172A indirectly monitors the intensity of the laser on the build area 122. By scanning the entire build area 122 with a laser (the laser passes through the build chamber window 107 into the build chamber 101), all locations of the build chamber window can be assessed for damage. The data recorded during this process can be filtered to obtain areas that produce low intensity readings of laser interaction with build area 122, which can be used to assess damage to build chamber window 107, as will be explained in more detail below with respect to the second embodiment.

[0060] In a second embodiment, the invention is described with respect to a multi-laser machine, in particular an additive manufacturing apparatus comprising four lasers.

[0061] In this embodiment, four lasers may enter the build chamber through a single build chamber window 107, it being understood that in other embodiments, the laser beams may enter through multiple windows in the build chamber. Each laser may be directed by optical module 106 toward build region 122 to consolidate the build material within build region 122 during fabrication of object 103, and the interaction of each laser with build region 122 may be monitored by coaxial photodiode measurement arrangement 172 and / or camera 173.

[0062] Now refer to Figure 5 A method 200 of determining damage to a build chamber window 107 is described.

[0063] In a first step 210, the building area 122 is divided into a plurality of groups of scanning zones. The plurality of groups of scanning zones in combination cover the entire building area. In this embodiment, the building area 122 is divided into the same number of groups of scanning zones as there are lasers in the additive manufacturing device, that is, into four groups of scanning zones. Fig. 6A A first set of scan areas 302 is shown, Figure 6B A second set of scan areas 304 is shown, Figure 6C A third set of scan zones 306 is shown, and Fig.6D A fourth group of scan areas 308 is shown. Each group of scan areas 302, 304, 306, 308 represents one quarter of the total build area. Within each group of scan areas 302, 304, 306, 308, no two scan areas share a common edge, e.g. Fig. 6A As can be seen in FIG. 1 , scan area 302A shares no common edges with any of scan areas 302B, 302C, or 302D, scan area 302B shares no common edges with any of scan areas 302C or 302D, and scan areas 302C and 302D share no common edges.

[0064] In a second step 220, each laser scans build area 122, and the results are recorded using photodiode measurement arrangement 172. To efficiently perform step 220, in the current embodiment, all four lasers are used simultaneously. During each scan of build area 122 (each laser scans a quarter of build area 122), build area 122 is scanned four times.

[0065] In the first scan of the build area 122, the first laser scans the first group of scan areas 302, the second laser scans the second group of scan areas 304, the third laser scans the third group of scan areas 306, and the fourth laser scans the fourth group of scan areas 308. In the second scan of the build area 122, the second laser scans the first group of scan areas 302, the third laser scans the second group of scan areas 304, the fourth laser scans the third group of scan areas 306, and the first laser scans the fourth group of scan areas 308. In the third scan of the build area 122, the third laser scans the first group of scan areas 302, the fourth laser scans the second group of scan areas 304, the first laser scans the third group of scan areas 306, and the second laser scans the fourth group of scan areas 308. In the fourth scan of the build area 122, the fourth laser scans the first group of scan areas 302, the first laser scans the second group of scan areas 304, the second laser scans the third group of scan areas 306, and the third laser scans the fourth group of scan areas 308. Once all four scans of the build area 122 are completed, each of the first laser, the second laser, the third laser, and the fourth laser has scanned the entire bed, and the photodiode measurement arrangement 172 has obtained a record of each of the first laser beam, the second laser beam, the third laser beam, and the fourth laser beam interacting with the entire bed.

[0066] When the laser beam enters the build chamber 101 through the build chamber window 107, if there is damage to the build chamber window 107 (e.g., contamination of the build chamber window 107 or a crack or other defect in the build chamber window 107), the build chamber window 107 may absorb more laser energy than an undamaged window. The additional energy absorbed by the build chamber window 107 may cause local deformation of the window, such as local expansion of the build chamber window 107, which may cause the laser beam to defocus and / or cause the path of the laser beam to change (thermal lensing). This may cause the energy density of the laser beam on the build area 112 to drop. The drop in the laser beam energy density on the build area 112 may cause a drop in the amount of plasma or other process emissions generated by the interaction of the laser beam with the material in the build area. Therefore, due to the reduction in the amount of process emissions generated in the area monitored by the photodiode measurement arrangement 172, the photodiode measurement arrangement 172 will record a lower intensity signal. As part of the method, it may be advantageous to use small stripes in close proximity to each other to scan the laser beam over the build area 112 so as to cause local heating of the build chamber window 107 near the defect. In the present embodiment, this can be achieved by raster scanning the laser beam over each scanning area, e.g. Fig.6D Scan area 308C is shown as being scanned (in a raster fashion) starting in one corner of the rectangular scan area with stripes parallel to the short sides of the rectangular scan area. In a third step 230, data associated with low intensity signals are identified.

[0067] In this embodiment, the raw data obtained by the process monitoring device includes photodiode and power value signals. Laser performance may vary from laser to laser, for example due to performance tolerances, in other words, it may be indicated that each laser operates at the same power throughout the method, but variations in power may be achieved between lasers. In addition, each laser is associated with a photodiode measurement arrangement 172, and each photodiode measurement arrangement 172 may have a slightly different response to the same stimulus, which may be due at least in part to each photodiode having a unique gain value. It may be useful to normalize the photodiode signal to a power value to allow direct comparison between data points in the data set.

[0068] Figures 7 to 13 The data shown in demonstrates the method of the present embodiment and was generated using a titanium plate located on platform 102. Raster scanning of the scan area was performed by multiple laser beams as described above. The scanning parameters were: point distance = 75 μm, exposure time = 50 μs, scanning speed = 1.25 m / s, batch spacing 65 μm. The data was collected using a first photodiode 172A (monitoring the process emission generated by the interaction of the laser beam with the titanium plate).

[0069] In this embodiment, data is collected at a 100 kHz native capture rate and includes data relating to x-position, y-position, focus, and photodiode readings synchronized with the laser energy.

[0070] The intensity data for each laser beam was normalized by calculating its z-score to give a mean value of zero, and the data was measured in the number of standard deviations from the mean.

[0071] The equation used to calculate the z-score is:

[0072]

[0073] Here, x is the intensity value of the pixel, μ is the overall mean intensity and σ is the standard deviation.

[0074] Performing z-scoring on the photodiode data allows direct comparison between photodiode signals. Figure 7 An example of z-score data for a fourth set of scan areas 308 for a particular layer is shown (ie, all scan areas 308A, 308B, 308C, 308D were scanned by the same laser).

[0075] After the raw data has been normalized, it is computationally beneficial to reduce the data set by accumulating or smoothing the data. The data is divided into a two-dimensional pixel grid, for example, each pixel can be a square with a side length of 200 μm. As will be understood, each 200 μm pixel will contain multiple data points from multiple shadow lines of the scan. For each pixel, the average of all intensity values ​​of the data points belonging to it is calculated (in other embodiments, the sum or maximum value or another value can be used). In other words, the values ​​are accumulated by spatial division. Figure 7 An example of a cumulative data set for a fourth set of scan zones 308 for a particular layer is shown (ie, all scan zones 308A, 308B, 308C, 308D were scanned by the same laser).

[0076] A filter -tσ is applied to the z-score data of the cumulative data set so that only data below a tolerance t multiple of the negative standard deviation is retained. The lower limit filter parameter t is an input parameter and can be user defined. In the current embodiment, a value of 2 is used for t. The value of t can be set by the user. The value of t can vary between different materials because the process emission (such as plasma) generated by the interaction of the laser beam and the build area varies between different materials, and therefore the value of t may need to be adjusted accordingly.

[0077] Figure 8 shows the filter applied to Figure 7 The data remaining after applying the filter represents the locations of the build area 122 where the lowest intensities were recorded by the measuring devices 172 , 173 . Figure 8 The remaining data shown in 404 may be grouped into data islands, including 402, 404, 406. However, not all of the remaining data may indicate damage to build chamber window 107, and the remaining data may be cleaned up until the noise is removed.

[0078] The Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm is applied to the remaining data in order to isolate dense defect areas in the remaining data from the background noise. The DBSCAN method finds clusters in the data by looking at the number of neighbors within a defined neighborhood of each data point. The clustering results depend on two input parameters: ε, the radius to search around each point; and minpts, the minimum number of points within this radius to start identifying a cluster.

[0079] Each data point is labeled as one of three types of points:

[0080] ●Core points, at least the minpts number of points within ε of the data point

[0081] ●Border points, which are reachable from a core point but have fewer than minpts within its radius

[0082] ●Outliers, which are not core points and cannot be reached from any core point

[0083] The DBSCAN algorithm can include the following steps:

[0084] ●For each point in the dataset, find all its neighbors within ε

[0085] ●If the number of neighbors:

[0086] ○Less than minpts, identify the point as an outlier

[0087] ○More than minpts, identify the point as a core point

[0088] ■If the point is within ε of the core point:

[0089] ● Already marked as an outlier, re-mark as part of the cluster

[0090] ● If it is not defined, it is marked as part of the cluster. If it is also a core point, its neighbors are added to the cluster.

[0091] ●Continue to the next undefined point

[0092] In other words, the DBSCAN algorithm used in this embodiment performs a depth-first search from a core point.

[0093] After performing the DBSCAN algorithm on the filtered data, two clusters are found in this example that are distinguishable from the background noise. Fig.9A Data that the algorithm has grouped into clusters (including clusters 402 , 404 ) is shown. Fig. 9B Data that has been determined to be noise by the algorithm by applying a threshold is shown, including data islands 406, which are based on the spatial extent of the cluster(s). The threshold is proportional to the beam diameter on the window, e.g., in the current embodiment, data islands having a spatial extent less than the laser beam diameter on the build chamber window are considered noise.

[0094] In a fourth step 240 of the method, the location(s) where the laser light passes through build chamber window 107 that are associated with clusters of low intensity signals are identified. Fig.10A projection of the position of a laser beam passing through build chamber window 107 in order to reach clusters 402, 404 on build area 122 is shown. In this figure, laser position 575 is shown, which is related to the position where the laser beam is directed toward build area 122, and in this embodiment, laser position 575 is considered to be the center point of a tiltable mirror used to project the laser beam through an exit aperture in the optical module (e.g., the center of tiltable mirror 175 used to project the laser beam through aperture 174 of optical module 106). By knowing the laser beam position (approximately the center of the beam guide optics, which in this embodiment is the center of the tiltable mirror) and the distance relative to build area 122, the path taken by the laser from the optical module to build area 122 can be calculated. The position on build chamber window 107 that the laser passes through when build area 122 corresponds to clusters 402, 404 can be calculated because the relative positions of build area 122, build chamber window 107, and optical module are known. Fig.10 In the example shown, the laser passes through build chamber window 107 at 504 when illuminating a portion of build area 122 corresponding to cluster 402 , and the laser passes through build chamber window 107 at 504 when illuminating a portion of build area 122 corresponding to cluster 404 .

[0095] Although Figure 7 Figure 11 shows data collected for three different laser powers, Fig.11A shows the data collected when a 300W laser beam was used, Fig. 11B shows the data collected when a 200W laser beam was used, and Fig. 11C The data collected when using a 150W laser beam is shown. Figure 11 also shows clusters of data identified on build area 122 using the above method. As can be seen from Figure 11, all three laser powers (300W, 200W and 150W) generate data that allow the same cluster of points on build area 122 to be identified.

[0096] In particular, FIG. 11 shows data from scan area 308D, which includes data collected with cluster 402 ( Fig.9A ) related to lower intensity data. As shown in Figure 11 (e.g. Fig. 11B), the lower intensity data associated with cluster 402 is confined to scan zone 308D, i.e., the lower intensity data associated with cluster 402 does not continue across the boundary between scan zones 308D and 306D. A discontinuity at the boundary between scan zones indicates damage to build chamber window 107 because the laser that scanned scan zone 308D and the laser that scanned scan zone 306D passed through build chamber window 107 at different locations on build chamber window 107, and thus localized damage to build chamber window 107 may not exist at the two points of laser entry through build chamber window 107. However, if the low intensity data does continue across the boundary between two adjacent scan zones, this may indicate a problem with build area 122 rather than build chamber window 107. By increasing the number of scan zones, such that adjacent scan zones that share a common edge are processed by different lasers (e.g., having more scan zones than the number of lasers), the likelihood of observing a discontinuity of low intensity regions at the boundaries between scan zones may be increased if there is damage to the build chamber window, and thus, the confidence with which the low intensity data can be assigned to damage to build chamber window 107 may be increased. Defects on the build region other than build chamber window 107 may also be identified by comparing two sets of data for the same scan zone but that have been generated using different laser beams. If both sets of data contain the same (or similar) defect, this indicates that the defect is related to the build region.

[0097] Fig.12 The cluster of Figure 11 is shown projected onto the build chamber window 107. The results of the above analysis can be examined to check for damage to the build chamber window. Fig.12 The image can be printed at proper scale and compared directly to the build chamber window. Fig.13 Shows Fig.12 This comparison with the build chamber window. Fig.13 As can be seen in FIG. 6 , crack 602 is present in build chamber window 107 and is well aligned with the projection of cluster 402 on build chamber window 107 .

[0098] In the above described embodiment, the data collected was using a titanium build plate positioned on build platform 102. However, this need not be the case, and in other embodiments, build platform 102 may be scanned directly, or in still other embodiments, a scan of each layer may be performed on the topmost layer of powder on powder bed 104, e.g., a separate powder layer for each scanned layer.

[0099] While the embodiments described above have used an on-axis monitoring system including at least one photodiode to monitor laser interaction with the build area, in other embodiments this need not be the case and a monitoring system located off-axis may be used, such as a camera located within the build chamber. Other embodiments may not use the DBSCAN algorithm, but may use other clustering algorithms known to the skilled person. Still other embodiments may address the use of a clustering algorithm.

Claims

1. A method for detecting damage to a build chamber window of an additive manufacturing device, the additive manufacturing device comprising a build chamber, the build chamber comprising a build chamber window and a build area, an energy beam can enter the build chamber through the build chamber window, a build medium can be located in the build area to be consolidated by the energy beam, the method comprising monitoring the intensity of process emissions from the build area.

2. The method according to claim 1, wherein: The process emissions are monitored by a sensor, wherein an optical path of radiation collected by the sensor from the build area at least partially coincides with a path of the energy beam.

3. The method according to claim 2, comprising: Data collected by the sensor from locations in the build area is compared to a threshold value.

4. The method according to claim 3, wherein: The data is at least one of: (i) a normalized data set, and / or (ii) a spatial extent of the data, and / or (iii) a density of defects.

5. A method according to any preceding claim, wherein: The method is performed prior to building a part and optionally includes determining a "start / no start" state for building the part.

6. A method according to any preceding claim, comprising: Parts to be built are repositioned within the build area in response to detected damage to the build chamber window.

7. A method according to any preceding claim, comprising: Intensities of process emissions produced by the plurality of energy beams at the build area are monitored.

8. The method according to claim 7, comprising: The distributed energy beam used to build a part or a section of a part is altered in response to the detected damage to the build chamber window.

9. The method according to claim 7 or claim 8, comprising: The intensity of process emissions produced by multiple energy beams directed to the same portion of the build area is monitored.

10. The method according to any one of claims 2 to 9, comprising: The energy beam is scanned over the build area in a pattern for causing localized heating of a build chamber window.

11. A method for manufacturing a product, the method comprising consolidating a build material in a build area located in a build chamber layer by layer by an energy beam, the build chamber comprising a build chamber window and a build area, the energy beam being able to enter the build chamber through the build chamber window, a build medium being able to be located in the build area to be consolidated by the energy beam, the method comprising monitoring process emissions from the build area.

12. An additive manufacturing device, comprising: means for generating an energy beam for consolidating a build medium; and a build chamber comprising a build chamber window and a build area, the energy beam being capable of entering the build chamber through the build chamber window, the build medium being capable of being located in the build area to be consolidated by the energy beam, wherein the additive manufacturing apparatus is configured to monitor process emissions from the build area to detect damage to the build chamber window.

13. The additive manufacturing apparatus according to claim 12, wherein: The additive manufacturing apparatus comprises means for monitoring the intensity of the process emissions.

14. The additive manufacturing apparatus of claim 13, configured to identify locations of the build region where an intensity of the process emission is below a threshold.

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