The Certified Part: Needs in AM Inspection and Certification

2017-12-06

Aya Bentur  

CT at Global Research Inspection and Metrology Lab - GE

Industrial production is required to be a consistent and reliable process. Of course, even machines have glitches, and the most automated process is never error free. To control the outcome of the end product, there is a need for constant inspection. Traditional manufacturing employs inspection processes regarding mainly dimension and form, yet with AM there are more elements to consider. The process of validating AM parts is as complex as the process and build structures, this makes certifying parts a challenge as well. Therefore, here is the next installment in our highlighting the needs series, #AMneeds – Inspection and Certification needs for AM.

A High Priority

New shapes achieved by AM, such as internal lattices or cooling channels, elements that are crucial to the parts’ operational performance, sometimes cannot be examined with traditional inspection techniques. One of the applications of additive manufacturing is specialized parts for aerospace, aviation and automotive. A malfunction or a defect in such a part cannot be acceptable, making accuracy and durability a high priority for the industrialization of additive manufacturing (below powder and finished parts 3D printed in Cameri Italy – GE and Avio Aero).

TiAl Powder and Finished Components 3D printed in Cameri Italy - Image credit - Avio Aero

The Limitations of Conventional Inspection Methods

The need for AM specific inspection methods derives from the difference in the production process between traditional and additive manufacturing. Current inspection methods take into account a series of ‘what can go wrong’ questions, these questions are not the same for AM, making conventional inspection methods limited. One of the first limitations to consider is the material consistency. In CNC for example, the behavior of the material throughout the process is known, it doesn’t change. In metal additive manufacturing the material is transformed in various ways (e.g., from powder to solid) which raises the question: to what extent can the material behavior be predicted? The inspection, in this case, needs to verify how the material is solidified in each layer and location, a need that didn’t exist with previous inspections. Similarly, creating complex inner structures is one of the possibilities opened by AM, the need to examine the inner building of a part is a new need originating with the technology. Technologies such as CT, ultrasound, and X-Ray are currently used for part inspection (below a demonstration of how a component can be checked using X-Ray inspections, up top CT at Global Research Inspection and Metrology Lab – GE).

XRAY Inspection for Industrial Additive Manufacturing
As the build process of AM differs from traditional manufacturing methods so does the surface. The surface is often granulated before reaching post-production, conventional methods find it challenging to inspect rough surfaces, meaning this also requires a new way of approaching the problem.

Inspecting the Production Process as a Whole

Looking at the needs listed above suggests one major change in inspection methods – inspecting the process and not only the final outcome. To reach a valid qualification, taking into account the inner structure and the processed material without destroying the part produced requires an inspection method within the manufacturing process. This approach also has the advantage that it allows correcting “as you go” rather than just scrapping a part at the end – an approach used successfully for electronics such as semiconductor chips and multi-layer printed circuit boards. A team at MTC is also concerned with the lack of defined standards when it comes to industrial additive manufacturing, “An ideal solution might be to inspect products during the manufacturing process and to 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 automatically spot defects, raise the alarm and ultimately adapt or correct the process.” said Dr. Ben Dutton, leading the team. Inspecting each layer as it is built, is just part of it – the additive manufacturing process extends before and after the operation of the machine, meaning so should the inspection. The powder used for example, how many times can the same powder be reused and fed into the powder bed? There is a need to constantly inspect the material prior to its use, or using metallurgical laboratories to verify the integrity of re-used powders. One company tackling this issue is ZEISS which developed scanning electron microscopes capable of testing the morphology of the powders (below). ZEISS is also working on a holistic 3D manufacturing inspection solution for aviation, medical and automotive application, based on its expertise in imaging and measurement technologies. Skipping to the other end of production, post-processing alters the thickness of the walls of the parts, especially when dealing with rough surfaces. Therefore there is a need to set and uphold criteria for post-processing as well as part of the additive production. This leads to another need: looking at the process a whole means the ability to translate the rejects into an improved part and designing or adjusting the part according to the feedback gathered.

Microscopy in ZEISS Additive Manufacturing

AM technology creates an alternative set of needs not just on the production side when compared to traditional manufacturing methods, but also in inspection and certification when compared to the existing inspection methods. In order for AM to truly be an industrial method of manufacturing, inspection and part validation needs to be incorporated as an integral part of the process. A recurrent theme in additive manufacturing is the ‘big picture’, in which the process is seen as a whole. The same manner of thinking can apply to inspection as well, the complexity of the process needs to be answered with systems capable of seeing cause and effect throughout all stages and variables of manufacturing.

What are your thoughts on inspection and certification in AM? Tell us about it or any other #AMneeds you encountered in the comments below. For more inspiration and information follow us on Pinterest or subscribe to our newsletter for weekly updates.

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