LEC 7

• continuous improvement of process quality & product quality

• Preprocess QA:

  • detemination of boundary conditions, & material requirements

• In-Process QA:

  • monitoring of layer-by-layer building process

• Post-Process QA

  • material tests

  • non-destructive component tests

    
    

• condition:

  • machine status

    • position of all axes (coater, build platform)

    • Cooling systems (flow rates, temperatures)

    • PBF/ DED:

      • laser status (power, temperature)

    • PBF:

      • build platform temperature

    • PBF-EB/M: vacuum chambe -> monitoring of pressure

• Meltpool:

  • temperature intensity: one measurement point

  • size, shape, temperature profil: multiple measurement points

• powder bed

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• build space

• device that measures the energy of thermal (electromagnetic) radiation

• exact emissivity is unknown during the process

• standard pyrometers only deliver qualitative trend

• Pyrometer principle (2 photodiodes) directly intigrated into beam path using mirrors

• measures emitted process light

• fast processing of the signal

• Deviation expected values and total values indicate errors

  • not every process irregulaty leads to component defects

Imganing method:

• camera integrated into the beam path

• observes the processing zone, even when laser is moving

  • melt pool:

    • stability, dimensions and behavour determines quality and stabiltiy of process

• integrated camera takes picture after each printed layer (coating, Exposure)

• light source from different directions for better picture quality

• Image processing detects:

  • incomplete coating

  • grooves (Rillen)

  • cavities (Hohlräume)

• device creates image of infrared radiation

  • λ = 1-14 μm

• Emissivity during process must be knwon but isnt, that why only qulitative trends

• Temperature distrubition of the part

  • no direct information about component quality

• irregularities of the powder bed

• Overheating

• relationship between defects and process parameters is complex

• Sensors need high resolution & fast detection

• Process parameters must be adjusted quickly

• real time data processing requires high computational power