Aerospace firms should consider inspections when using 3D printing

Rolls-Royce Trent 700 Engine
Rolls-Royce Trent 700 reportedly delivers optimised fuel burn, emissions and noise performance.

Aerospace manufacturers need to consider ease of inspection when deciding to use 3D printing, according to a non-destructive testing (NDT) expert who is developing best practice guidelines for the industry.

Dr Ben Dutton from the Manufacturing Technology Centre (MTC) in Coventry said there was a real concern about the lack of inspection standards at a time when the use of 3D printing, or additive manufacturing (AM), is on the increase.

He commented: “The advantage of AM is that it offers total freedom in designing the part, but unfortunately that makes it hard to inspect.

Dr Ben Dutton will be speaking about the topic at a free seminar at the Materials Testing 2015 exhibition in Telford on Tuesday September 8.

“The more complex the component is internally, the more difficult it is for NDT. Another problem is that the surface finish is typically rougher than conventional manufacturing processes so inspection methods such as ultrasound, which require a finer surface finish, are less suitable.”

Dutton is leading the drive to develop NDT best practice guidelines on behalf of ISO through BSI and is involved in a similar initiative with ASTM.

The NDT Specialist said trials are being carried out to determine the best way to examine components produced by AM, focusing on defects that are unique to AM, and ways to optimise analysis, where a number of NDT methods are being considered.

The guidelines are expected to be published next year.

He noted that X-ray computer tomography is emerging as the most promising inspection technology, but it has its limitations and there is room for improvement to adapt it better to AM, with research in this area currently be undertaken.

While computer radiography is sometimes used, detecting flaws accurately depends on selecting the correct settings, such as enough projections to cover the part thoroughly.

He recommended companies use only experienced practitioners, carry out visual inspection as an initial step, and when in doubt use double testing – where the product is inspected twice by different inspectors.

He added: “The ideal solution would be to inspect products during the manufacturing process and take a snapshot of every layer.

“Some machines already have the capability to do this, but the next step would be to develop systems which could spot the defects themselves and raise the alarm.

“Another solution might be to inspect after machining. The smoother surface would potentially allow the use of other inspection methods, although this would add further to the manufacturing cost if the part is found to be defective after machining.

“Another post-process is hot isostatic pressing, which has shown to reduce the size of internal defects in the parts.

Dutton concluded: “Internationally, a lot of effort is going into creating inspection standards and some companies are developing their own procedures. There is a real sense of urgency, particularly in aerospace.

“For now, manufacturers need to consider how critical the part is in safety terms and the requirements for inspection when making the decision to use additive manufacturing.”