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The largest facility to date has a volume of 27 m3, adequate to accommodate all work-pieces, welding equipment and even a programmable robotic system. By purging the enclosure with inert gas an operating oxygen content is low enough to prevent oxidation during welding and cooling.
Monitoring the Oxygen Content
Control and real-time monitoring of the oxygen content of the purge gas is crucial if discolouration and loss of corrosion are to be avoided.
Techniques for measuring oxygen content have been available for decades but only recently have instruments been developed speci cally for welding applications. Users increasingly demand complete absence from discolouration and no loss of corrosion resistance and this implies purge gas oxygen content to be as low as 20 ppm (0.002%). Very few oxygen purge monitors are capable of meeting this sensitiv- ity but the PurgEye [Figure 7] instruments cover all requirements.
CONCLUSION
A crucial bene t of 3-D printing is that it opens up possibilities for the production of complex designs that otherwise might not be practical or economic.
In terms of applications for WAAM and DMLS/DMEBS the welding version is most suitable for heavier and larger products whilst the powder alternative is best applied where smaller, delicate objects are required. In other words, welding is essentially a bulk depo- sition technique and powder is a precise and highly controlled process.
Many alloys need to be protected from contamina- tion during the welding operation. The formation of metallic oxides can reduce corrosion resistance and affect mechanical properties. The use of an effective oxygen-free inert gas environment is essential.
REFERENCES
1. Cancer patient receives rst 3D printed sternum and rib cage. Orthopaedics and Spine, July 2017.
2. Direct metal laser sintering, Bertol et al, Mate- rials & Design, 2010.
3. Laser-Based Additive Manufacturing Processes. Woodhead Publishing, 2018.
4. World’s rst class approved 3D printed propeller. International Institute of Marine Surveying, May 2017.
5. Design for Wire and Arc Additive Layer Manufac- ture. Mehnen et al. 20th CIRP Design Conference, Nantes April 2010.
6. Wire & Arc Additive Manufacturing. Williams et al, Materials Science & Technology 2016 Vol 32
7. Williams S. WAAM Current and Future Develop- ments. Additive Manufacturing for Aerospace, Defence and Space conference. London, March 2016.
8. Damen shipyards release further details about world’s rst 3D printed propeller. 3D Printing Industry. September 2017.
9. Wire+arc additive manufacturing vs. traditional machining from solid: a cost comparison. Martina F.
10. Huntingdon Fusion Techniques Ltd, UK
Acknowledgements
Fig 1: Figs 2, 3: Fig 4:
Fig 5: Figs 6, 7:
www.researchgate.net
FIT Prototyping GmbH Germany Cran eld and WAAM3D ltd waam3d.com Damen Shipyards, Netherlands Huntingdon Fusion Techniques Ltd, UK
About the author
Dr M J Fletcher is a quali- ed metallurgist with exten- sive experience in welding and non-destructive testing. He works as an independent con- sultant, providing support to a wide range of manufacturing industry on a global basis
Technical Papers
Huntingdon Fusion Techniques
Stukeley Meadow SA16 0BU Carms UK
Tel: +44 1 554 836 836 Fax: +44 1 554 836 837
hft@huntingdonfusion.com www.huntingdonfusion.com
ITAtube Journal No2/May 2019
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