Testing for external defects in components

If a new customer started a discussion with you, saying that they had a component that needed testing for external defects, such as wrapping at a macro level and balling at the meso level, would you feel confident in what was being discussed? If they then proceeded to discuss layer macro defects such as warping and crossover defects, and then discussed meso defects such as swelling and delamination, would you be aware of the manufacturing processes associated with these defect types?

Just as a reminder, a couple of definitions are included here: meso is the scale of features with linear dimensions from submillimetre to several millimetres and micro is a scale of features with linear dimensions less than one millimetre.

To help you further, the causes of the defects can include factors such as the material type, as some are more susceptible to specific defects due to the properties of the material, for example titanium and oxidation, aluminium with porosity and bimetallic materials, leading to deformation and cracks. Feed material contamination can be an issue, along with process control and parameters, plus ontamination including foreign material in the melt pool.

For those of you who have not already guessed the manufacturing process, it is one of the seven main additive manufacturing (AM) processes called directed energy deposition (DED). This process focuses a thermal energy source to both melt and fuse the deposited materials.

There is a free issued standard available, titled: ‘PAS 6011:2020 – Additive manufacturing – Non-destructive testing for use in directed energy deposition – Guide’, which covers much more than this brief text. There are also sketches and explanations covering the DED process, along with a couple of sections mentioning NDT: 6. Prerequisites, design considerations and processes for NDT; and 9. NDT summary of methods. Optical methods are covered in section 9.5, 9.6 covers electromagnetic methods, 9.7 covers ultrasound methods, 9.8 covers radiographic methods, 9.9 covers thermographic methods and 9.10 covers mechanical methods.

Further along in the standard there are more sections relating to NDT, including ‘10.3 NDT techniques selection by capability and applicability’, which has a subsection ‘10.3.5 Measurement capability’ and other good paragraphs that are valuable considerations when writing procedures and, to an extent, instructions.Remembering it is a free standard, there is a good amount of information relating to product technology and NDT and I think many NDT testers would gain something from having a read of it. It can be found at: https://knowledge.bsigroup.com/products/additive-manufacturing-non-destructive-testing-for-use-in-directed-energy-deposition-guide/standard

Within BINDT, there is a Terahertz User Group and this is becoming a strong positive group looking at promoting this newer technology and what it can possibly be used for. BINDT will be helping to promote this group via Branch meetings, online and through short articles in NDT News. Further information about the Terahertz User Group and a leaflet describing the capabilities and application of terahertz technologies can be found at: www.bindt.org/branches-and-committees/User-Groups/terahertz-user-group

If you are a PCN certificate holder, you can gain points towards the renewal and recertification of existing certificates and the Branch meetings are a free way of doing so, plus you may also learn something that is useful for your work. It also provides for Engineering Council continuing professional development (CPD) points. Many of the Branch activities are available online and can be accessed via a mobile phone or preferably a laptop; typically, BINDT will issue a certificate of attendance for your records, again at no cost.

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