Aerospace manufacturers need to consider the lack of standardized and precise inspection when deciding to use 3D printing, according to non-destructive testing (NDT) expert Dr. Ben Dutton from the Manufacturing Technology Centre in Coventry. Dutton recently spoke about the topic at a seminar at the Materials Testing 2015 exhibition in Telfor, UK in September and is developing best practice guidelines for the industry.
He says there is a real concern about the lack of inspection standards at a time when the use of 3D printing, also known as additive manufacturing (AM) is on the rise. The technique is applicable to metal parts as well as plastic components, and its use is slated to increase over time.
“The advantage of AM is that it offers total freedom in designing the part, but unfortunately that makes it hard to inspect,” he said. “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.”
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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. He says trials are being carried out to determine the best way to examine components produced by AM, focusing on defects that are unique to AM, as well as ways to optimise analysis, where a number of NDT methods are being considered. The guidelines are expected to be published next year.
According to Dutton, X-ray computer tomography is emerging as the most promising inspection technology, and much research is taking place in this area, but it has its limitations and there is room for improvement to adapt it better to AM. While computer radiography is sometimes used, detecting flaws accurately depends on selecting the correct settings, such as using enough projections to cover the part thoroughly.
Dutton recommends that 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. “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.”
For metal parts, another approach 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,” says Dutton. “Another post-process is hot isostatic pressing, which has shown to reduce the size of internal defects in the parts.”
Internationally, a lot of effort is going into creating inspection standards. There is a real sense of urgency, particularly in aerospace, and some companies are developing their own procedures. But 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.
Elsewhere, Texan aviation services company M7 Aerospace is offering a new service to create precise, three-dimensional portraits of entire planes, down to one-thousandth of an inch. To execute the job, M7 purchased a Z Corporation ZScanner 700 PX, claimed to be the world’s only handheld laser scanner that precision-scans large objects such as aircraft and automobiles – items that previously have been too big to capture by hand.
Older but still viable aircraft are sometimes called upon to perform more modern roles and require modification such as ballistic blankets, avionics upgrades, and external sensor installations for missile defense systems.
These modifications can be time-consuming and expensive without precise data, which is often lacking due to the absence of original paper design documents or because of variations in a given craft. Variations in an aircraft can result from manufacturing conditions, modification, and wear and tear.
“There’s an increasing demand for large-scale scanning capability in aviation, as well as other industries that engage in reverse engineering, inspection, 3D archiving, measurement, damage assessment and similar uses,” said Richard Honey, president of AGS 3D. “There’s a growing need for both our government and commercial customers to keep their older aircraft flying and productive.”
M7 recently used the ZScanner to precisely capture the entire surface of a Fairchild Metroliner in a resolution of 0.1mm in just three days. The Fairchild Metroliner is a 19-seat commuter class turboprop aircraft with a 57-foot wingspan. The same job would have taken months, or years, if attempted at all, with other scanning technology.
“This new scanning capability from Z Corporation helps us do that. By automatically capturing deep engineering data, we can more quickly and efficiently reverse-engineer aircraft and components that were originally designed in the 2D era – before 3D computer-aided design was readily available,” says Joe Furnish, M7 Aerospace vice president of engineering services.
While most scanning technology requires jigs, fixtures, tripods or mechanical arms, the 3D ZScanner is self-referencing – it automatically determines its location in space without the need for external orienting devices. The user simply sweeps the scanner over the target surface and “paints” it with complete freedom of movement around aircraft, automobiles, boats, or other large objects. As the user paints with the scanner, the digitized object appears on a laptop screen, eliminating costly and time-consuming post-processing.
The ZScanner 700 PX’s breakthrough in scale stems from built-in photogrammetric software, previously available only in fixed-position 3D scanners that lack the mobility, speed and convenience of a handheld device. This capability, with laser scanning for fine data capture at high resolution, is combined in the ZScanner 700 PX and provides high accuracy on very large objects.
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