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WO2020229838A1 - Procédé et appareil d'analyse de poudre métallique - Google Patents

Procédé et appareil d'analyse de poudre métallique Download PDF

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Publication number
WO2020229838A1
WO2020229838A1 PCT/GB2020/051193 GB2020051193W WO2020229838A1 WO 2020229838 A1 WO2020229838 A1 WO 2020229838A1 GB 2020051193 W GB2020051193 W GB 2020051193W WO 2020229838 A1 WO2020229838 A1 WO 2020229838A1
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WO
WIPO (PCT)
Prior art keywords
powder
radiation
region
particles
output
Prior art date
Application number
PCT/GB2020/051193
Other languages
English (en)
Inventor
Ben Robinson
Ben FERRAR
Nicholas Paul WEEKS
Original Assignee
Lpw Technology Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lpw Technology Ltd filed Critical Lpw Technology Ltd
Priority to CA3140502A priority Critical patent/CA3140502A1/fr
Priority to EP20728542.0A priority patent/EP3969211A1/fr
Priority to JP2021568300A priority patent/JP7515519B2/ja
Publication of WO2020229838A1 publication Critical patent/WO2020229838A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/4738—Diffuse reflection, e.g. also for testing fluids, fibrous materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/37—Process control of powder bed aspects, e.g. density
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/90—Means for process control, e.g. cameras or sensors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y30/00—Apparatus for additive manufacturing; Details thereof or accessories therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y40/00—Auxiliary operations or equipment, e.g. for material handling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y50/00—Data acquisition or data processing for additive manufacturing
    • B33Y50/02—Data acquisition or data processing for additive manufacturing for controlling or regulating additive manufacturing processes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/33—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using ultraviolet light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/51—Scattering, i.e. diffuse reflection within a body or fluid inside a container, e.g. in an ampoule
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/85—Investigating moving fluids or granular solids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0091—Powders
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/20—Direct sintering or melting
    • B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/70—Recycling
    • B22F10/73—Recycling of powder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/40—Radiation means
    • B22F12/41—Radiation means characterised by the type, e.g. laser or electron beam
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/06—Investigating concentration of particle suspensions
    • G01N15/075—Investigating concentration of particle suspensions by optical means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N2015/0096—Investigating consistence of powders, dustability, dustiness
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/4738—Diffuse reflection, e.g. also for testing fluids, fibrous materials
    • G01N2021/4764—Special kinds of physical applications
    • G01N2021/4769—Fluid samples, e.g. slurries, granulates; Compressible powdery of fibrous samples
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/85—Investigating moving fluids or granular solids
    • G01N2021/8557—Special shaping of flow, e.g. using a by-pass line, jet flow, curtain flow
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/85—Investigating moving fluids or granular solids
    • G01N2021/8592—Grain or other flowing solid samples
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the present invention relates to a method and apparatus for analysing metal powder, particularly but not exclusively a metal powder used in an additive manufacturing (AM) process.
  • AM additive manufacturing
  • an AM machine produces articles from a powdered metal or alloy.
  • the machine deposits a layer of powder on a build platform and the powder is subsequently selectively fused with a laser or electron beam, to form an article or articles.
  • the process is repeated so that articles are formed layer by layer.
  • unfused powder may be re-used in another build.
  • composition and condition of metal powder used in a build process can have a significant effect of the integrity of an article formed by the process.
  • unfused powder is subject to degradation.
  • a metal powder may gradually oxidise which alters its properties and thus those of an article produced from the powder.
  • the tendency of a powder to oxidise typically increases with temperature, and exposure to temperature may also affect other powder properties. Consequently, the nearer unfused powder is to an article being built, or a heat zone, the more likely it is to suffer degradation.
  • the process may cause some heated particles of powder to be scattered from the powder bed around the manufactured article, degrading the quality of the unfused powder around the article.
  • Powder condition is typically analysed by making a bulk oxygen content measurement.
  • the measurement process involves testing a powder sample, which cannot then be re-used.
  • bulk oxygen content (or other bulk) measurement can give a false impression as to suitability of a powder for re-use, especially where recycled powder is blended with virgin powder to produce a blend with an overall bulk oxygen content below a desired threshold. This is because it is not sensitive to the presence of highly oxidised or otherwise degraded particles which may have a significant deleterious effect on a build even though the bulk oxygen content is below a desired threshold.
  • powder composition and condition can also effect build quality.
  • the presence of contaminant particles can have a similar effect to the presence of highly oxidised particles.
  • Particle size and shape can also effect a build, as can packing density when a layer of powder is formed in an AM machine.
  • a method for analysing a metal powder for use in an additive manufacturing process comprising the steps of: illuminating a region of the powder, without melting the powder, with electromagnetic radiation comprising radiation in the non-visible part of the electromagnetic spectrum;
  • separately detecting the illuminating radiation comprising radiation in the non- visible part of the electromagnetic spectrum, received back from different parts of the illuminated region of the powder, to produce an output which depends on the detected radiation; and processing the output to determine one or more properties of the powder.
  • apparatus for analysing a metal powder for use in an additive manufacturing process comprising:
  • an illumination device for illuminating a region of powder, without melting the powder, with electromagnetic radiation comprising radiation in the non-visible part of the electromagnetic spectrum
  • a detector for separately detecting the illuminating radiation, comprising radiation in the non-visible part of the electromagnetic spectrum, received back from different parts of the illuminated region of the powder and producing an output which depends on the detected radiation;
  • a processor arranged to process the output thereby to determine one or more properties of the powder.
  • the method may be performed in any suitable environment.
  • the powder may be a sample of powder fortesting placed in a test container.
  • analysis may take place in an additive manufacturing machine or powder transport apparatus, such as a pipe or conduit.
  • the apparatus may be comprised in testing apparatus, powder transport apparatus or additive manufacturing apparatus.
  • the radiation may be light which includes some non-visible light such as ultra violet and/or infrared light and may additionally include visible light.
  • the illumination device may comprise any suitable illumination device, such as a lamp including an LED, incandescent and/or discharge lamp.
  • a laser such as a laser forming part of an additive manufacturing machine operable to fuse powder in the machine during a build process, could also be used (in a low power mode) to illuminate the powder.
  • the means for illumination may illuminate all of the region of powder simultaneously, or parts of the region separately.
  • the means for illuminating may scan a beam of radiation over the region of powder.
  • one or more illumination devices are provided they are preferably provided in an enclosure into which the metal powder is introduced, or opening on to a barrier through which a sample of powder may be illuminated, and via which illuminating radiation may be received back.
  • the enclosure may prevent or at least restrict ingress of electromagnetic radiation at wavelengths of interest, in order to allow controlled illumination of the metal powder with those wavelengths.
  • the enclosure may be substantially, or capable of being made, substantially light tight.
  • the enclosure may be comprised in an AM machine, or powder transport, manufacturing, processing or handling apparatus.
  • the region of powder may be a surface, particularly a planar surface, of the powder.
  • the method may involve placing the powder into a suitable container, or on a build platform or in a powder recess of an additive manufacturing machine, so that the powder has a substantially planar upper surface, and then illuminating that surface.
  • the method may involve illuminating powder through a suitable transparent barrier forming or forming part of a powder containing structure such as a container or powder manufacture, processing or transport.
  • a suitable transparent barrier forming or forming part of a powder containing structure such as a container or powder manufacture, processing or transport.
  • Such a barrier may be planar, but could be curved such as a wall of or window into a pipe with a generally circular cross-section.
  • the powder may be close packed.
  • the degree to which the powder is close packed may be controlled, such as by tapping the powder in a predetermined way or number of times prior to making a measurement and/or by including a passing the powder through a pre-conditioning funnel prior to measurement.
  • the powder preferably has sufficient depth away from the illuminated surface so that the powder is substantially opaque to the detector.
  • the apparatus may include a barrier, such as a window, transparent or at least partially transparent to wavelengths of radiation of interest, for separating powder to be tested from the illumination device and detector.
  • the apparatus may be arranged so that, in use, powder is supported on or contained by the barrier so that powder in a closed packed form is observable through the barrier.
  • the illumination device may be arranged to illuminate the window
  • the detector is arranged to receive radiation from the window, from a position below the window, or in the case the window is substantially vertical, alongside the window.
  • a barrier is horizontal or substantially horizontal powder can be supported on the barrier in a close packed form.
  • a barrier is not horizontal or substantially horizontal, for example a sidewall of, or window into, a container or pipe an arrangement may be provided to contain powder so that it will stack against the window.
  • this may comprise a valve or flow restrictor in a downstream direction away from the window operable to cause power to stack against the window.
  • the powder may be a sample of powder taken from a batch of powder.
  • the powder may be virgin powder, or recycled powder which has already been used in an additive manufacturing process.
  • Powder may be analysed at different stages in a process, and may be analysed at multiple points in a process.
  • apparatus for analysing powder may be provided at different points on additive manufacturing and powder transport and processing apparatus.
  • powder could be analysed at one or more or any combination of the following stages of a process: as it is transferred into an additive manufacturing machine, in a powder container in the machine, on a platform in the machine, in a powder bed in the machine, in a build container in the machine, as it is transferred out of the machine, after a sieving operation, and after blending with another powder.
  • the detector make take a variety of forms, and may comprise any suitable sensor or sensors.
  • the detector may be positioned to detect radiation at the same side of the region of powder, in particular to the same side of the illuminated surface, as the means for illuminating the powder.
  • the method may involve detecting and the detector may be arranged to detect radiation reflected and/or scattered by the powder.
  • the detector may be arranged to detect illuminating radiation received back from all of the region of powder simultaneously, or from parts of the region separately.
  • the detector may be arranged to scan the region of powder. Relative movement between the detector and powder may be achieved either by moving the detector relative to stationary powder or moving powder past the detector, such as in the case of powder transport apparatus.
  • the detector may include a one or two dimensional array of sensing elements, such as a CCD or CMOS sensor.
  • the detector may include one or more, or an array of photodiodes, spectrometers or spectrophotometers.
  • the detector may include one or more filters for excluding and/or admitting selected wavelengths of electromagnetic radiation.
  • the detector may include one or more focussing elements, such as a lens, for focussing radiation received back from the powder onto one or more sensors.
  • the one or more focussing elements may focus an image of at least part of the region of powder into an image plane, in which may lie one or more sensors.
  • the detector may comprise an image capture device, such as a camera or microscope.
  • the detector may comprise a hyperspectral camera.
  • the apparatus is able to separately detect illuminating radiation received back from different parts of the illuminated region of powder, either because the detector is able to spatially resolve the source of radiation and/or because the detector only detects light reflected from a part of the region at one time and/or because only part of the region is illuminated at one time.
  • the output may be processed to determine a variety of different properties of powder, including: condition of individual particles of powder; a surface property of the powder and/or individual particles of the powder; a property of the powder or individual particles of powder which affects their interaction with electromagnetic radiation, in particular their ability to reflect and/or scatter particular wavelengths of radiation; the shape of individual particles of powder; surface texture of the powder or individual particles of powder; the presence of contamination; packing density of the powder; and spreadability of powder.
  • the output may comprise values depending on the wavelength or wavelengths or perceived wavelength of radiation received from respective areas of the region of powder.
  • the output may also comprise values depending on the intensity of radiation received back from respective areas of the region of powder.
  • the output may comprise values depending on the intensity of radiation at different wavelengths.
  • the output may comprise values depending on the intensity of radiation over a range of wavelengths, which may be continuous. And/or the values may depend on the intensity of radiation at one or more discrete wavelengths.
  • the output may be a function of the wavelengths detected.
  • the output may comprise a value or values for each of plurality of areas.
  • the areas may be substantially the same size.
  • the areas may be contiguous, or they may be spatially separated.
  • the areas may, together, encompass all or most of the region.
  • each area has an area less than the area of the surface of the powder occupied by a single particle of the powder of average size, and it may be significantly smaller such as 1 ⁇ 4, 1/10 th , l/100 th l/500 th or l/1000 th of that area.
  • each area may be less than 1000 pm 2 or less than 100 pm 2 .
  • at least one and preferably multiple values included in the output are influenced by a single particle of powder.
  • average particle sizes vary between types of powder the optimum size of the area will vary with powder type. This enables the condition of individual particles to be determined.
  • Values obtained from analysing a region of powder may form a data set.
  • the steps of detecting radiation, producing an output and of processing the output may take place at different locations.
  • the data set may effectively comprise an image of all or part of the illuminated region of powder, albeit one which has been, at least in part, taken by recording non- visible wavelengths of radiation.
  • all of the data could not be rendered visible to the human eye without applying false colour to enable features which are in practice only apparent when looking at non-visible wavelengths, to be visible.
  • an image is referred to herein it is to be taken that the image has at least partly been obtained by detecting non-visible electromagnetic radiation, in particular, non-visible light.
  • the image may be a digital image. It may be formed by, or divided into, a plurality of elements such as pixels.
  • the elements may each correspond to an area of the powder from which the detector has separately received radiation, and produced an output.
  • the elements are preferably of substantially the same size.
  • the ratio of elements in the image to the number of particles in the imaged region or surface of the powder is at least of the order of 1 : 1, but preferably higher such as at least 4: 1 or 10: 1 or 100: 1 or 500: 1 or 1000: 1. That way the wavelength or wavelengths of detected radiation represented by that element is likely to be influenced only by properties of a single particle of powder.
  • a data set for processing might typically comprise a value or values for each of 2 to 6 million areas and represent around 5000 particles of size generally in the range 10-110pm or 40-50pm, but the size of a data set may vary significantly depending on application.
  • a data set may comprise data which describes each area of powder, or image element, according to an established colour standard, for example RGB or CIELAB, insofar as the image is formed of visible colours or the standard is capable of describing relevant non-visible electromagnetic radiation of interest, or non-visible wavelengths detected have been represented in a dataset by a false colour.
  • an established colour standard for example RGB or CIELAB
  • regions of the same volume or sample of powder may be analysed.
  • the regions may be adjacent or spaced apart.
  • at least 2, 3, 4, 5, 10, 50, 100 or more regions of the same powder are analysed to form multiple data sets for the powder.
  • the number of data sets will depend on the volume of data required for statistical significance. Analysing multiple regions can help in assessing how well blended the powder is.
  • Data is a set may be processed by comparing a data value or values for one area of the region of powder with those for one or more other areas and/or with reference data.
  • Data in a data set may be removed so that the remaining data represents a chosen sub region of powder, equivalent to cropping of an image. This is useful where the detector includes a focussing element which produces an image in the detector by enabling distortion to be excluded. It also allows for an easier and more reliable comparison between different data sets especially those relating to the same sample.
  • a data set is reduced in size to define 2000 x 2000 contiguous areas of the powder, and so may define an image consisting of 2000 x 2000 image elements.
  • a data set may be processed to determine if its quality is sufficient for further processing and/or to determine if all separately acquired data in a particular set is sufficiently similar. Data that does not meet specified quality criteria may be rejected and not processed further. This may for example involve determining statistics from data and determining if those statistics do, or do not, fall within predetermined ranges, or differ from data set to data set by more than a predetermined threshold.
  • the mean intensity of a particular detected wavelength or range of wavelengths or colour channel used to define detected radiation may be calculated for all areas of the powder from which radiation has been detected, or all areas having greater than a threshold luminance, as well as a deviation from that mean.
  • Data in a data set which relates to space between particles of powder may be identified. This enables that data to be excluded from further processing.
  • Such data may be identified by identifying data which defines areas of the region of powder with a luminous intensity below a predetermined threshold. Space between particles of powder will tend to appear darker, and thus have a lower luminous intensity, than the particles.
  • Such areas of the powder may be regarded as background areas, with the remaining, more luminous, areas being foreground areas.
  • a data set comprises an image this step comprises identifying darker image elements. Darker image elements may be regarded as background elements and lighter elements foreground elements.
  • a data set may also be processed to determine, or at least estimate, the number of particles of powder it represents. Where a data set comprises an image this may be achieved by watershed segmentation. This step, where present, is preferably performed after removal of background elements from the image.
  • the number of particles represented by a data set may be estimated by another suitable method not relying on the data set, for example by a knowledge of the size of the area the data set represents, mean size of powder particles and/or packing density of the powder.
  • Data representing foreground areas of the powder represents properties of particles of the powder which affect how the particles interact with the illuminated radiation, including surface properties.
  • the number of particles of powder represented by a data set with a surface property which falls outside a predetermined range may be determined.
  • the proportion of powder with a measured surface property which falls outside a chosen range may be determined.
  • Area selection may be based on a statistical analysis of detected wavelengths. Selected areas may be those for which the detected wavelength(s) defines them as outliers in the wavelength distribution across all the foreground areas. For example, elements may be selected by determining how their wavelength(s) deviate(s) from the mean wavelength(s) of all areas. Preferably the selected areas represent the outlying 5% or less 1% or less, or 0.1% or less of the wavelength distribution of foreground areas.
  • individual particles that have that property can then be identified. To do so groups of connected areas exceeding a predetermined number are identified. The number is chosen to be that which represents the combined area expected to be occupied by a single particle of powder. The identified groups of areas may thus be assumed to represent at least one, but typically one, particle with a property which meets the chosen criteria.
  • this step may be omitted and it assumed that a single image element represents a single particle.
  • Data can then be stored for each identified particle, being the data relating to the area or areas of the powder occupied by the particle.
  • the number of areas in an identified group is indicative of the size of the particle the group represents.
  • the average wavelength(s) of radiation detected from the areas in the group is representative of the colour or other properties of the particle the group represents. This enables the number of identified particles to be determined, as well as properties of the particles and analysis of this data enables various information relating to the powder to be determined or inferred.
  • Particles identified in this way may be further classified by surface property, such as colour, to identify particles having a surface property which falls into a particular range. Other techniques can then be used to select particles of interest from the identified particles.
  • the ratio of background to foreground areas gives an indication of the ratio between particles of powder and space between those particles and thus an indication of the packing density of the particles. Changes in packing density observed in images of a batch of powder taken over time may reveal changes which affect powder flow properties.
  • Determining the overall distribution of wavelengths received from a region of powder, or from all foreground areas of the powder, is indicative of chemical properties of the powder and in particular the degree of oxidation of the powder, since oxidation of metal powders typically affects their interaction with radiation.
  • a knowledge of how oxidation affects the colour of a particular powder type may be used to determine a bulk oxygen content for the powder.
  • the number of particles identified which have returned a wavelength or wavelengths of radiation which falls outside a chosen range can reveal if a powder contains highly oxidised particles or is contaminated, such that it may be desirable that the powder is not used or re-used.
  • the number, together with the calculated or estimated total number of imaged particles may be used to calculate the proportion of particles with a measured property falling outside the chosen range.
  • This information may be used to inform or control subsequent processing of the analysed powder or powder from which the analysed powder was taken.
  • the method may involve the step of indicating that a powder is not suitable for re-use when the number or proportion of particles identified as having a property outside a pre-determined range exceeds a predetermined range.
  • the pre-determined range and the proportion may be established depending on the particular powder being analysed and its intended use.
  • the range is preferably set to encompass values for the measured property indicative of powder that has suffered what may be regarded as normal degradation as a result of being used in a build process, as might typically be caused by exposure to oxygen and low temperatures.
  • those particles having a measured surface property outside of this range are outliers.
  • the method may also involve determining the average measured property of the proportion of measured powder whose measured property falls within the predetermined range. This measure is indicative of the overall average degradation of the powder excluding the outlying significantly degraded particles. This measure therefore gives an indication of the level of degradation resulting from normal degradation.
  • the method may also involve indicating that the tested powder is not suitable for re-use when average measured property of the proportion of powder, and thus approximate proportion of measured particles whose measured surface property falls within the predetermined range is greater (or less) than a predetermined threshold.
  • powder can be indicated as no longer suitable for re-use as a result of the, possibly cumulative, effect of normal degradation.
  • the method may also involve determining the average measured property of all of the powder, and so all measured particles, by processing data for all foreground areas. Such a measure is indicative of the overall average degradation of all the particles, and so may give a similar indication to a bulk oxygen measurement, save that a bulk oxygen measurement will also measure“internal” oxygen of a particle, that being oxygen present inside a particle, as well as oxygen of any oxide outer layer the build-up of which affects a surface property of the particle.
  • the method may also involve indicating that the powder is not suitable for re use when an average measured property of all measured particles, is greater or less than a predetermined threshold.
  • the method may involve controlling apparatus based on a measured property of a powder, such as controlling an AM machine or powder processing, handling or transport apparatus.
  • this may be a mean, and may be obtained by determining the average measured surface property represented by those areas of the region of powder where there are particles of interest.
  • Information relating to a powder analysed by the method may be used to automatically control apparatus including additive manufacturing apparatus and/or powder handling, transport and processing apparatus. Apparatus may for example be caused to discard and/or process powder depending on detected condition of the powder.
  • the processor may be a programmed computer, and may be arranged to cause the apparatus to perform some or all of the method steps discussed above.
  • particles of powder returning radiation comprising a wavelength or wavelengths falling within a particular range may be identified, and this may be used to infer the degree of oxidation of the particles having regard to experimental data relating to the powder type concerned.
  • Embodiments of aspects of the invention provide a non-destructive method and apparatus for determining powder condition and deciding whether or not a powder sample is suitable for re-use in a particular build operation. Where the determination is made by looking at the proportion of outlier particles this provides a new and useful measure of powder condition which enables improved decision making, and therefore powder use, over current measurements of bulk powder properties.
  • the method and apparatus is also useful for identifying the presence of contaminant particles where those particles a surface property which differs to the same property of particles of interest.
  • a method for analysing a metal powder for use in an additive manufacturing process comprising the steps of: providing the powder in a close packed state adjacent a barrier; illuminating a region of the powder through the barrier; separately detecting the illuminating radiation received back from different parts of the illuminated region of the powder through the barrier, to produce an output which depends on the detected radiation; and processing the output to determine one or more properties of the powder.
  • apparatus for analysing a metal powder for use in an additive manufacturing process comprising: a container or conduit for metal powder comprising a barrier which, in use, contains powder to be analysed in a close packed state; an illumination device for illuminating a region of powder with electromagnetic radiation though the barrier; a detector for separately detecting the illuminating radiation received back from different parts of the illuminated region of the powder through the barrier and producing an output which depends on the detected radiation; and a processor arranged to process the output thereby to determine one or more properties of the powder.
  • the barrier may be a wall of a container or conduit.
  • the barrier may be a window in the wall or a container or conduit, the window being at least partially transparent to electromagnetic radiation of interest.
  • the electromagnetic radiation may be light including infra-red, visible and ultra violet light.
  • the third and fourth aspects of the invention may include any or all features of the first and second aspect of the invention as desired, or as appropriate save that, for the third and fourth aspects, it is not necessary that the powder is illuminated with non-visible electromagnetic radiation or that non-visible radiation is detected.
  • Figures 1 to 3 are schematic views of embodiments of apparatus for analysing powder condition
  • Figure 4 to 6 are schematic views of embodiments of powder processing and transport apparatus including apparatus for analysing powder condition
  • Figure 7 is a schematic side view of an additive manufacturing machine including various apparatus for analysing powder condition
  • Figure 8 is a schematic plan view of the apparatus of figure 7;
  • Figure 9 is a flowchart showing steps involved in processing an image of powder
  • Figure 10 is a graph showing number of particles against wavelength.
  • figure 1 shows a first apparatus for analysing metal powder. It comprises an openable substantially light tight enclosure 1.
  • the enclosure houses a container 2 for powder 3 which may take the form of a dish or slide, or any other suitable form.
  • the container is open to the top and has a substantially square opening with a side of about 10mm, giving it a cross-sectional area of about 100mm 2 . It has a depth of at least 2mm.
  • the illustrated container is shallow, but it could be significantly deeper so that the container is elongate. The container may be removed from the enclosure.
  • the enclosure also houses a lens (or microscope) 4 which is mounted to (or comprised in) a digital camera 5 sensitive to ultraviolet and infra-red, in addition to visible, light, and lamps 6 emitting ultraviolet, infra-red and visible light.
  • the camera 4 comprises a substantially square sensor, such as a CCD sensor, with approximately six mega pixels (twelve mega pixels in another embodiment) and is connected to a computer 7 which comprises a keyboard and mouse or other user interface and is connect to a display 8 and/or other output device.
  • the lamps are arranged to provide a diffuse light. They are shown as dome or flat dome lamps. In an alternative arrangement (and in other embodiments) a ring light could be used.
  • a sample of powder 3 taken from a batch of powder to be analysed is introduced into the container 2, either with the container in or out of the enclosure 1.
  • the powder is introduced in sufficient quantity to form a close packed depth of powder which entirely obscures the bottom of the container 2 when viewed from above. So the depth of powder typically comprises at least two, and preferably more than two, layers of particles.
  • the powder is levelled in the container, such as by tapping the container, so that it has a substantially flat upper, planar surface. If powder has been introduced into the container whilst outside the enclosure the container is then positioned in the enclosure beneath the microscope and the enclosure closed.
  • the lamps 6 are then activated.
  • the lamps may be controlled by the computer 7.
  • the lamps are arranged to illuminate the upper surface of the powder 3 in the container 2. Illuminating the powder with lamps in a substantially light tight enclosure enables powder to be analysed in controllable and repeatable light conditions. Note that in this and other described embodiments the lamps may be positioned differently and may be positioned in front of the camera and/or lens.
  • the camera 5 is then caused to take a digital image of the illuminated surface of the powder in the container and to transmit it to the computer 7.
  • the digital image comprises information relating to all wavelengths of light detected by the camera.
  • the camera and microscope are arranged to take an image of about 12mm 2 of the surface of the powder in the container. Multiple images of the surface of the powder are taken until substantially all of the surface of the powder has been imaged.
  • the camera and lens may have a different field of view. The surface of the powder could thus be captured in a single image.
  • Metal powders used in AM processes typically have an average diameter of the order of tens of microns.
  • the number of particles visible to the surface of the powder imaged by the camera will be of the order of thousands and so about three orders of magnitude less than the number of pixels of the sensor.
  • the camera is thus able to produce a digital image of the surface of powder in which there about 1000 times as many pixels as the number of particles of powder shown in the image.
  • the image taken by the camera is then transmitted to the computer 7 for processing.
  • Figure 2 shows a second apparatus for analysing metal powder.
  • a light tight enclosure 1 is provided underneath a container 2 for containing powder 3.
  • the enclosure houses an upwardly directed camera 5 and lens 4 and lamps 6, similar to those of the embodiment of figure 1.
  • the base of the container is transparent or at least partially transparent to the wavelengths of light produces by the lamps and to which the camera is sensitive. The camera is thus able to take an image or images of the surface of powder 3 in the container 2 through the base of the container.
  • the top surface of the base of the container, on which powder is supported, is substantially planar, so that camera is inherently presented with a flat surface of powder to image.
  • the bottom surface of the base of the container is substantially parallel to its top surface.
  • Figure 3 shows another apparatus for analysing powder 3.
  • This comprises an elongate tube 2, with one closed end, for containing powder.
  • the tube 2 has one flat side wall 2a.
  • the tube is of square or rectangular cross-section, both other cross-sections are possible, such as a D-shaped cross section.
  • a camera 5 and lens 4 assembly is provided in a substantially light enclosure 1 together with lamps 6 in the manner of the apparatus of figures 1 and 2.
  • the camera is directed towards the flat side wall of the container.
  • This side wall is at least partially transparent to the wavelengths of light produced by the lamps and to which the camera is sensitive, and, similar to the base of the container 2 of figure 2 it has two substantially parallel, opposite, planar sides.
  • the camera is arranged to image close packed powder contained in the container through the side wall.
  • the container is mounted for movement relative to the enclosure and camera allowing the camera to image different parts of the surface of a sample of powder contained in the container.
  • FIG. 4 shows powder transport apparatus comprising pipes 10 leading into and out of a powder sieve, and into a powder blending device.
  • Each pipe 10 includes a planar or substantially planar transparent window 11 over which is fitted a light tight enclosure 1 which houses a digital camera 5 fitted with an appropriate lens 4 for taking an image of powder in the pipe 10 through the window 11.
  • a lamp or lamps 6 is/are provided in the enclosure around the lens 4 to illuminate the powder through the window 11.
  • the camera outputs its image, comprising information relating to all wavelengths of light detected by the camera to a computer 7 with output device 8. Alternatively or additionally the output may be sent to a computer or processor controlling the powder transport apparatus or associated equipment.
  • a valve 12 (such as a butterfly valve) is provided in the pipe 10 downstream of the blending device for permitting and preventing the flow of powder through the pipe. This enables the pipes to be filled with powder so that close packed powder is presented to the windows 11 in the pipe, which are transparent to the wavelengths of light produced by the lamps and to which the cameras are sensitive.
  • the digital camera 5 has a sensor with about 1000 times the number pixels than the expected number of powder particles visible in the area of the window 11 imaged by the camera when the pipe is full of close packed powder to be analysed.
  • the lamp or lamps 6 emit and the camera 4 is sensitive to a broad spectrum of light including ultra violet, visible and infra-red light.
  • the window 11 is substantially transparent to this broad spectrum of light.
  • a window 11 and associated enclosure 12 with camera 5 is provided in both of the pipes 10 leading to and from the sieve enabling the condition of powder to be analysed before and after sieving. Cameras also enable the condition of powder entering both inlets to the powder blending device to be analysed.
  • Windows could be provided into powder transport conduits or powder storage containers of other types of apparatus, such as for example an additive manufacturing machine.
  • Figure 5 shows a powder storage apparatus comprising a hopper with a lower frustro conical wall and a cylindrical sidewall.
  • An upright pipe 10 is connected to an inlet at the top of the hopper, via a valve 12 for permitting and preventing the flow of powder through the pipe 10 into the hopper.
  • An outlet is provided at the bottom of the hopper, also fitted with a valve 12 for permitting and preventing the flow of powder out of the hopper.
  • the hopper is for storing metal powder, and could be used together with or form a part of an atomiser used to produce metal powder.
  • Two windows 11 are provided in the frustro conical base of the hopper, each of which is fitted an enclosure housing a lamp 6 and camera 5 with lens 4 (of the type shown in figure 4) for imaging powder in the hopper which is close packed against the window.
  • the window is transparent to the wavelengths of light produces by the lamps and to which the camera is sensitive, and has opposed substantially parallel planer surfaces.
  • the pipe 10 leading into the hopper 12a is provided with five pairs of windows evenly spaced along a section of the pipe above the valve at the inlet to the hopper. Each window is fitted with a respective enclosure 1 housing a camera 5 with lens 4 and lamps 6 in the manner of the enclosures 1 under the hopper 12a. These cameras enable close packed metal powder in the pipe to be imaged at various positions along the length of the pipe. This is useful, for example, in being able to determine if a powder being received into the pipe 10 has changed over time, for example during a production run.
  • Each of the camera provides an output to a computer or processor 7, which in turn provides an output to a user via a suitable user interface 8 or equipment controlled by the output.
  • a single camera may be moveably mounted relative to the pipe and arranged to image powder at different positions along the length of the pipe.
  • the valve 12 at the inlet to the hopper can be closed to cause powder to fill the pipe in a close packed fashion for imaging.
  • FIG. 6 shows a part of a pipe for transporting powder.
  • the pipe is fitted with a bypass conduit 10a, provided with valves 12 which enable the flow of powder to be controlled into and out of the bypass.
  • a further valve 12 is disposed in the pipe between the connections to the conduit.
  • the bypass conduit comprises a substantially planar window 11 to which is fitted an enclosure 1 housing a camera with lens and lamp in the manner of the enclosures of figures 4 and 5.
  • the output of the camera is connected to a computer or processor 7 and a display or other output or apparatus to be controlled depending on the output of the camera 8.
  • the bypass conduit is formed by a pipe with a smaller cross-section than pipe 10.
  • the valves may be controlled to allow powder travelling in the pipe 10 to flow into and fill the conduit, enabling the camera 4 in the enclosure 1 to image the powder in a close packed fashion. Effectively the bypass enables a sample to be taken from powder flowing in the conduit for analysis, enabling close packed powder to be imaged even if powder is not moving through the pipe in a closed packed state.
  • Figures 7 and 8 show an additive manufacturing machine 13.
  • the machine comprises an enclosure 1 which is or can be made substantially light tight.
  • the enclosure houses a powder delivery container 14 with a powder delivery piston 15, a build container 14a with a build platform 16, and a wiper blade 17 mounted to a moveable support for transferring powder from the powder delivery container to the build container.
  • the enclosure also houses output optics 18 of a laser for selectively melting powder on the build platform 16.
  • the enclosure 1 additionally houses two cameras 5 with appropriate lenses 4 for taking an image of an area of the top surface of powder in the powder delivery and build containers, and lamps 6 disposed around each camera.
  • An imaging sensor 19 and lamp 20 is also mounted to the moveable support for the wiper blade 17 and arranged to scan an image of the surface of powder in the powder supply or build containers as the wiper blade travels to and fro across the containers.
  • the lamps 6, 20 emit, and the cameras 5 and sensor 19 are sensitive to, a broad spectrum of light including ultra violet, visible and infra-red light.
  • a camera 5 with lens 4 and associated lamps 6 are also mounted in enclosures 1 positioned behind windows through the sidewall of the powder and build containers 14, 14a, through which they are able to image close packed powder in those containers.
  • a further camera 5 with lens 5 and associated lamps 6 is mounted in an enclosure 1 positioned beneath a window formed in the platform extending between the powder and build containers, and thus able to image powder on that platform.
  • the three windows are all transparent to the wavelengths of light produces by the lamps and to which the camera is sensitive.
  • the window in the platform has opposed substantially parallel opposed planar surfaces.
  • the windows into the powder and build containers may also have such surfaces, or be shaped to conform to the shape of the internal wall of the container where this is not flat.
  • the cameras 5 and sensor 19 are arranged to output an image to a connected computer or processor 7 with an output device 8, or arranged to control the additive manufacturing machine in dependence on the output.
  • the digital camera 5 and sensor 19 are arranged to produce an image of powder with about 1000 times the number pixels than the number of particles shown in the imaged area of powder.
  • each embodiment of the apparatus produces a digital image of the surface of powder in the apparatus.
  • the digital image comprises a set of data defining properties of image elements comprising information relating to all wavelengths of light detected by the camera, and thus the wavelength or wavelengths of light received by the camera from each area of the surface of the powder corresponding to an element of the image.
  • the ratio of image elements to the number of particles of powder shown in the image is about 1000.
  • the image data is transmitted to the computer where it is stored in a manner where the wavelength or combination of wavelengths of light, or perceived wavelength represented by and the luminous intensity of each element of the image is defined - such as in the CIELAB colour space by variables L, a and b.
  • the computer is arranged to process the image data in order to determine information relating to the condition of the powder shown in the image by performing at least some of the steps shown by figure 4.
  • the image may be cropped to a predetermined size, excluding elements outside a boundary (or some other chosen region) of the original image.
  • This optional step allows distorted areas of an image to be excluded as well as enabling images taken by different cameras or sensors to be reduced to represent the same area and/or to have the same number of pixels.
  • the remaining image data, or remaining image data may then be tested 22 to ensure that it is of sufficient quality for further processing. If not, it is rejected at 23 and a new image is obtained.
  • the computer identifies elements with a luminance below a predetermined threshold and removes these from the image data at 24, with the aim of removing elements which represent space between particles of powder (or other background material) in the image.
  • the actual threshold will depend upon characteristics of the particular apparatus being used and type of powder being tested. With the elements of the image removed which lie outside the threshold the remaining image elements are taken to represent particles of powder in the foreground of the image.
  • the data for the remaining image elements may then be processed at 25 to estimate the number of particles they represent using a suitable technique, such as watershed segmentation.
  • the total number of particles represented can also be estimated in other ways. For a given powder and apparatus the number of particles expected to be visible in an area of the surface of the powder corresponding to that represented by the image data can be calculated with a knowledge of the expected particle size and expected packing density of the powder.
  • the data for the remaining image elements is then statistically analysed at 26 to determine how the wavelength(s) or perceived wavelength represented by each image element is distributed about the corresponding mean value for all remaining elements to detect outlier elements representing a wavelength(s) or perceived wavelength that places them outside a threshold proportion of the entire population of elements. This may be performed using a Chi-squared test for outlier detection. Other approaches may be used, including the use of machine learning.
  • the relevant proportion of the population may be selected according to the type of powder being analysed, but a typical proportion is 0.1%, that is to say that the elements of interest, the outlier population, make up 0.1% of the entire population of elements.
  • FIG. 5 which plots the number of image elements on the vertical axis against a measure of perceived wavelength (or colour) on the horizontal axis.
  • This shows a generally bell-shaped curve of distribution about a mean value at 27, and lower 28 and upper 29 thresholds which identify the outlying 0.1% of the population represented by the area under the curve outside the thresholds.
  • the outlier elements are then subjected to a connected component filter at 30 to determine if they are spatially connected in the image they define. Any group of connected image elements which exceeds a predetermined number of elements is considered to represent a single particle.
  • the data representing each such identified group is associated with a unique particle identifier with the first identifier identifying the largest group of connected elements, the second identifier identifying the next largest group of connected elements, and so on.
  • the computer has produced sets of image data which define the size and surface property of individual particles affecting how they interact with the different wavelengths of light with which they have been illuminated that causes them to represent statistical outliers within the powder.
  • That surface property includes colour insofar as visible light is concerned but is broader in that it includes properties that alter interaction with ultraviolet and infrared light. Inclusion of these non-visible wavelengths increases the range of particle properties, especially relating to particle composition, which can be detected by the apparatus.
  • This data is then analysed at 31 to extract useful data relating to the condition of the analysed powder, including:
  • the first measure above will, assuming that the batch of powder from which the sample is taken is well mixed or the imaged area of a powder is representative of the constitution of the powder as a whole, generally mirror the proportion of significantly degraded particles throughout the sample and throughout the, or batch of, powder tested. Multiple samples may be taken from a given batch and analysed separately, or multiple tests performed on a batch of powder in order to improve accuracy such as by taking multiple images of a surface of the powder. And/or a particular sample could be analysed, mixed, and then reanalysed. An appropriate wavelength range and threshold minimum proportion outside that range can be determined for a given powder and build and where the proportion of particles outside the threshold exceeds the chosen limit the batch of powder is deemed unsuitable for re-use, at least for the build in question.
  • this measure enables powder condition to be determined independent of a bulk quantity.
  • the second measure provides an indication of the average degradation of the remaining powder when the particles lying outside the threshold have been discounted. Such a measure is more akin to the result of a conventional bulk oxygen measurement, but obtained in a more convenient and non-destructive way, save that it excludes the influence of significantly degraded particles (or any internal oxygen). Powder may be deemed unsuitable for re-use where the average wavelength received from the remaining particles, when the particles lying outside the predetermined range have been discounted, lies outside another predetermined range.
  • the third measure is similar to the second measure, but takes account of the significantly degraded particles. Powder may be deemed unsuitable for re-use where the average wavelength of light received from particles lies outside another predetermined range.
  • a decision whether or not to re-use powder can be based on one or more of the three measures described above. Typically a powder would not be re-used if any measure determines that the powder should not be re-used. In one embodiment the first and second measures are calculated and powder deemed unsuitable for re-use if either measure indicates this.
  • Non-powder artefacts may be detected in the powder.
  • Anomalous powder particles may also be detected, for example particles made of different material to that intended, where the anomalous particles may be identified by an observable property.
  • An estimate of total incident energy received by the powder may be made.
  • Images taken form powder processed by different machines, such as AM machines, may be used to compare machine performance and/or determine machine health. Images taken a different time periods and/or different positions in apparatus can help to track transit of powder through the apparatus.
  • the output of test results may automatically cause the apparatus to perform a certain function. For example, powder may be rejected for further use, or combined with other powder to refresh it before further use.
  • An additive manufacturing machine may be stopped or a wiper blade caused to remove a layer of powder and replace it before any powder is fused.
  • Data relating to analysis of powder may be stored so as to validate a build using the powder. In particular, analysis of at least part of the surface of layers of powder deposited during a build process may be stored to provide evidence of the consistency or otherwise of the powder used throughout a build process. Also, time stamped data can be compared from multiple images of powder taken at different points throughout a powder transport system to audit the performance of that system, e.g to show how effectively oxidised or contaminated powder moves through it.
  • the computer is provided with suitable software to cause the camera to take an image, to process the image to determine colour distribution amongst image elements, to enable a user to input ranges, proportions or other values, to calculate one or more of the three measures, to determine if a particular sample may or may not be re-used having regard to the range(s) and proportion specified by a user and to output this result to a user via the display 8 or otherwise.

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Abstract

Le procédé et l'appareil d'analyse d'une poudre métallique destinée à être utilisée dans un procédé de fabrication additive selon la présente invention consistent : à éclairer une région de la poudre, sans faire fondre la poudre, à un rayonnement électromagnétique comprenant un rayonnement dans la partie non visible du spectre électromagnétique ; à détecter séparément le rayonnement éclairant, comprenant un rayonnement dans la partie non visible du spectre électromagnétique, renvoyé par différentes parties de la région éclairée de la poudre, pour produire une sortie qui dépend du rayonnement détecté ; et à traiter la sortie pour déterminer une ou plusieurs propriétés de la poudre. La poudre peut être éclairée par une lumière comprenant un rayonnement ultraviolet et/ou infrarouge et le rayonnement ultraviolet et/ou infrarouge renvoyé détecté.
PCT/GB2020/051193 2019-05-15 2020-05-15 Procédé et appareil d'analyse de poudre métallique WO2020229838A1 (fr)

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EP3872481A1 (fr) * 2020-02-28 2021-09-01 The Boeing Company Procédés et systèmes de détection d'impuretés dans un matériau pour fabrication additive
WO2024149879A1 (fr) 2023-01-12 2024-07-18 Universität Stuttgart Appareil et procédé de classification d'une poudre métallique

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