PAS 6011:2019 NDT of DED additive manufacturing

I was attending a meeting at the BINDT headquarters in Northampton and, during a break, one of the attendees asked me where I get my ideas from for the topics for this column. If you have read these articles in the past you will have noticed that the subject matter has no specific focus other than non-destructive testing (NDT), condition monitoring (CM) and structural health monitoring (SHM) in general. Topics can relate to historical applications or, as in this memorandum, a very current subject matter.

What has taken my interest this month is a draft document, ‘PAS 6011:2019 Non-destructive testing of directed energy deposition (DED) additive manufacturing – Guide’. A publicly available specification (PAS) document is a guide and, as such, takes the form of guidance and recommendations; it is not to be regarded as a British Standard, but can lead to the development of 

To understand what is being discussed, the following text is provided: ‘Direct energy deposition (DED) is an additive manufacturing (AM) process, which focuses a thermal energy source to melt and fuse deposited materials. It is one of the seven main AM methods (ISO/ASTM 52900) and represents with powder bed fusion (PBF) one of the two main commercial processes for metal additive manufacture (MAM)’. DED has been in use since the 1960s with three-dimensional welding and became an accepted AM process in the 1990s but, due to its association with military equipment, it received little 

Within the introduction the document states that: ‘In the short to medium term, NDT has been repeatedly identified as critical to the success of AM by providing a means of validating the quality of the build and gathering data to increase knowledge and understanding’, which is a noble aim and understanding of how valuable NDT can be when applied correctly. Further in the introduction there is a paragraph that states: ‘This PAS focuses on the determination of the part’s quality through the use of NDT. It examines traditional, new and emerging techniques, identifying their suitability for use with DED’. Within the introduction, a cautionary comment is given: ‘There is a lack of in-situ monitoring capability. Current in-situ methods are only suitable for part surface defects, while real-time monitoring has not been adequately demonstrated for DED’. Within the text it explains possible applications: ‘These points in the process have been identified as optimal for use of NDT, including between the deposition of layers (intra-layer), after the build process (post build) and, if necessary, in post-processing (finished/post process)’.

The potential flaws will be in the micro-, meso- and macro-millimetre ranges, so can be very small. The PAS does not specify which NDT methods are to be used or how to apply them, neither does it specify acceptance/rejection levels, but it does offer guidance on the factors that should be considered when developing procedures. Some of the flaws include layer defects, such as cross-over defects, delamination, warping, start-stop defects and swelling.

So, for all you good people out there, are you ready for AM NDT requirements?

In conclusion, I find inspiration in a wide range of sources and have a natural interest in engineering. I avoid politics, if possible, and try to offer an honest opinion based on what I hope may be of interest to you, the reader.

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