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Renishaw Ti6Al4V metal powder re-use study

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There are various issues and concerns surrounding the re-use of metal powders through metal powder bed processes. This presentation discusses some of these issues and presents the latest results of a powder re-use study, in which a single batch of Ti6Al4V alloy powder was used over 38 routine builds. Chemistry and physical properties of the powder were assessed over the period of the study as well as tensile properties of built test bars.

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Renishaw Ti6Al4V metal powder re-use study

  1. 1. Investigating the effects of multiple powder re-use cycles in AM Lucy Grainger Product Marketing Engineer, Renishaw
  2. 2. Why even investigate powder re-use in AM?
  3. 3. • Feedstock should be reliable for process repeatability and predictability • Powder properties and machine parameters are closely related • Reduce potential waste Why even investigate powder re-use in AM?
  4. 4. Why is titanium so special?
  5. 5. Why titanium? Ti-6Al-4V alloy High strength to weight ratio High corrosion resistance 45 % lighter than steel $$$$$
  6. 6. Why use additive manufacturing? SubtractiveAdditive Billet CNC machining Component + waste – high buy-to-fly Powder Powder bed fusion Near net shape + little waste – low buy-to-fly
  7. 7. What steps contribute to a re-use cycle?
  8. 8. Re-use cycle Metal powder bed fusion Routine build + test samples Remove build plate Sieving Remaining un-melted powder Re-use Return sieved powder to silo repeat
  9. 9. AM250 system AM250 Max build volume 250 mm x 250 mm x 300 mm Build rate* 5 cm³ to 20 cm³ per hour Layer thickness 20 to 100 µm Laser beam diameter 70 µm at powder surface Laser options 200 W Power supply 230 V 1PH 16 A Power consumption 1.6 kWh Gas consumption < 30 l/hr * Build rate is dependent on material, density & geometry, not all materials build at the highest build rate.
  10. 10. Minimising possible contamination Renishaw AM machines are unique in the way the inert atmosphere in the build chamber is created. 1. A vacuum is created, 35-50mbar: • This removes air and any humidity from the entire system 2. The chamber is filled with ~600 litre of high purity argon. 3. The atmosphere is maintained at below 1000ppm (0.1%) oxygen and can be set to run below 100ppm (0.01%) for titanium (Ti6Al4v) and other alloys. Key Benefit: Gas consumption is typically <30 L/hr and laser melting commences approx. 10 minutes after the process cycle starts. All Renishaw systems are suitable for building reactive materials.
  11. 11. Both chemistry and physical properties of the powder are essential to the quality of the end product!
  12. 12. Powder chemistry – Titanium alloy grades Element % Ti6Al4V Grade 5 Ti4Al4V (ELI) Oxygen 0.20 0.13 Nitrogen 0.05 0.05* Carbon 0.08 0.08 Hydrogen 0.0125 0.0125 Aluminium 5.5-6.75 5.5-6.50 Vanadium 3.5-4.5 3.5-4.5 Interstitial Alloying *Some grades quote 0.03% max
  13. 13. Physical characteristics of powder Flow PSD – Particle size distributionShape/morphology Density/Packing Flowability is important for consistent layers, it is directly influenced by PSD, packing and particle shape. x
  14. 14. Test samples for analysis Tensile test bars: 3 x as built 3 x as machined Density block Powder capsule 60 g of powder approximately
  15. 15. Results - Chemistry
  16. 16. Chemistry - Oxygen 0 500 1000 1500 2000 0 5 10 15 20 25 30 35 40 Oxygen/ppm No. of builds 1300 ppm Ti6Al4V ELI max. 2000 ppm Ti6Al4V grade 5 max. • Initial study over 20 builds • Second study over 38 builds
  17. 17. Chemistry - Nitrogen 0 100 200 300 400 500 0 5 10 15 20 25 30 35 40 Nitrogen/ppm No. of builds N ppm max N ppm alternative max • Initial study over 20 builds • Second study over 38 builds
  18. 18. Experimental results - Physical
  19. 19. Powder morphology Virgin powder Build number 3 Virgin powder
  20. 20. Powder morphology Virgin powder Build no. 18 Build no. 38
  21. 21. Powder morphology Build number 38
  22. 22. Particle size distribution and flow Volumedensity/% Size Classes / µm Little change in particle size distribution over 38 builds
  23. 23. Particle size distribution and flow 0.00 10.00 20.00 30.00 40.00 50.00 60.00 0 5 10 15 20 25 30 35 40 Particlesize/µm No. of builds D90 D50 D10
  24. 24. Particle size distribution and flow 0.00 10.00 20.00 30.00 40.00 50.00 60.00 0 5 10 15 20 25 30 35 40 Particlesize/µm No. of builds D90 D50 D10 Agglomerate Small particle sintered to larger particle
  25. 25. Particle size distribution and flow 0 5 10 15 20 25 30 35 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 5 10 15 20 25 30 35 40 Flow/sg-1 D50/µm Builds Flow D50
  26. 26. Tensile properties 600 700 800 900 1000 1100 1200 0 5 10 15 20 25 30 35 40 UTS/MPa Build Machined As built
  27. 27. • Density – previous study showed consistently dense components • Fractography of tensile test bars • Repeat but over normal running conditions with new powder additions Further work
  28. 28. • Re-use doesn’t seem to affect the AM process • General but not significant changes to the powder both chemically and physically • This is an extreme look at how powder is affected by being used in an AM process, regular topping up of the silo with virgin powder will most likely dampen the effect of the chemical and physical changed to the powder • There doesn’t seem to be any requirement to dispose of powder - this obviously depends on the requirements of the component. Conclusions
  29. 29. Email: lucy.grainger@renishaw.com

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