Theta Technologies’ revolutionary non-destructive testing technology offers the perfect quality assurance solution for mass additive manufacture

How nonlinear resonance NDT can help your mass additive manufacturing vision become a reality.

Introduction

You’ve embraced 3D printing as your new metal manufacturing process. Those beautifully intricate metal components have been removed from your printers ready to be subjected to the rigors of post-processing to refine them into the finished article. You’re practically ready to package and ship the parts to your customers, but there’s one final procedure you need to undertake; performing a non-destructive test to assess the part’s suitability for use. You test a relatively small sample of your production. The first one passes, as does the second, and indeed the third, but then you test the fourth and there’s a strong indication of a flaw. The fifth, sixth, and seventh parts you test are also flawed, leading you to question your entire batch. Can you really be confident that the parts you’re sending to your customer are fit for purpose?

 Perhaps you’ve faced this scenario, maybe more than once; but what if there was a way to identify whether those parts were flawed much earlier in the manufacturing process; even before adding unnecessary value and wasting countless hours on post-processing each of the aesthetically pleasing works of art? There is of course a way to prevent this scenario; but before we explain the role that UK-based engineering company, Theta Technologies Limited could play in providing additive manufacturers with that much-needed industry solution, let’s first look at what makes 3D printing such an appealing technology for metal production.

The appeal of 3D printing

Unlike conventional techniques where metals are removed from their cocoon-like castings or bars, the ability of 3D-printing to quite literally create something out of nothing provides both the technology and manufacturers with such overwhelming potential. Already widely adopted for polymers and plastics, additive manufacturing has several key advantages over the more traditional techniques. Shorter production times and less material waste are just two of the notable benefits, but the indisputable appeal of additive manufacturing is the freedom of design. In theory, it is possible to create almost anything with 3D printing, and the possibility of producing more organic, lighter, and complex geometric shapes has almost certainly fuelled the rapid adoption of the technology as a manufacturing technique; but most innovations encounter obstacles in their infancy, and metal additive manufacturing is no different.

Companies seeking to convince their customers of the techniques’ overall effectiveness compared to tried and tested traditional metal manufacturing methods has proved to be one of the most challenging scenarios, and it is in fact 3D printing’s unquestionable versatility that has ultimately proved to be the source of its own difficulties, particularly when it comes to the production of metals. Unfortunately, this issue is not something that can be solved by the manufacturers themselves. The validation of components, regardless of the technique used to create them, can only be accomplished with the implementation of a rigorous quality assurance process, and one that includes effective non-destructive testing. 

For those looking to adopt additive manufacturing for the provision of end-user parts, particularly for demanding and safety-critical applications, the ineffectiveness of existing non-destructive testing options has almost certainly prevented you from realising your vision and unlocking the technologies’ overwhelming potential. Although tried and tested methods in the verification of more traditional materials, NDT techniques such as Visual Inspection, Thermography, Eddy current, and of course, X-ray CT scanning have all seen metaphorical cracks beginning to appear in their own effectiveness when faced with 3D-printed components. Although hugely varied between each technique, limitations in the range of defects identifiable, test penetration depth, and an ability to cope with the surface roughness inherent of additive manufacturing have simply failed to instill confidence in the non-destructive testing processes for additive manufacturers. These concerns have prevented a full adoption of 3D-printed metals for demanding applications in industries such as aerospace, defence, automotive and energy generation. 

The importance of non-destructive testing

Much like traditional metals, there are a number of key defects that can occur during the printing process, and subsequently compromise the integrity of each part; lack of fusion, cracks, and porosity proving to be some of the most common. Regardless of its size, a defect such as a crack could significantly reduce the lifespan of the part. This has numerous cost implications for manufacturers and their customers, but this is far from the worst-case scenario. A defect, of any size within the structure of a metal component could ultimately cause the part to fail when put to use. You only have to imagine the potential consequences of that failure in parts integral to the function of a commercial aircraft or a military submarine to understand how vital it is to implement non-destructive testing as part of your quality assurance process. But fear not! There’s a brand-new NDT solution intent on revolutionising the metal additive manufacturing industry and finally allowing manufacturers to unlock that vast potential. 

Exeter-based, Theta Technologies Limited have recently introduced their unique non-destructive testing technology to the market. Their nonlinear resonance NDT technique, derived from nonlinear acoustics, has been specifically designed to offer a reliable testing solution for metal additive manufacturing and is capable of testing virtually any 3D-printed metal components for those potentially detrimental flaws. This resonance-based method exploits microscopic flaw behaviours within individual samples to help identify signs of these flaws. The entire component is excited into resonance using a variety of signal sources, and a detector system assesses for nonlinearity within the component under test. The signature of the component is closely monitored during the excitation process and defective samples would exhibit an amplitude-dependent frequency response. This allows nonlinear resonance to not only test increasingly complex geometries associated with 3D printing, but it is unaffected by surface roughness and can be performed independently without the need for a ‘known good’ reference sample. 

A new way of working

In 2022, Theta Technologies announced their first commercially available non-destructive testing product, RD1-TT. Utilising nonlinear resonance technology, RD1-TT offers manufacturers a quick-hit solution to identifying flawed components at the earliest possible opportunity; practically eliminating the possibility of continuing to work with parts that are simply not fit for purpose. Just how early are we talking? RD1-TT allows you to perform a non-destructive test of a 3D-printed metal part right out of the build, even while it remains on the print platform. The cost and time-saving benefits of this unique ability alone are truly game-changing. Identifying flaws at such an early stage almost guarantees the prevention of adding value to defective components by giving you the option to remove them from your workflow prior to undertaking those costly post-processing procedures. With cost-saving very much on the agenda of most of us in the current economic climate, what’s not to love about that?

Of course, if saving time and money wasn’t enough to intrigue you then don’t worry; we’ve only just scratched the surface of the benefits that this technology offers additive manufacturers. RD1-TT has been developed to provide manufacturers with a rapid go/no-go in-house test system; and when we say rapid, we mean rapid. Less than a minute after initiating the test of your 3D-printed part, you will know whether the component is defective with a simple pass or fail test result presented on the integrated touchscreen display. Where the more traditional NDT techniques are limiting additive manufacturers to testing smaller samples of their production due to the far from time-efficient nature of their test processes, this rapid detection system offers the first realistic option of performing a cost-effective, non-destructive test in a mass production environment.

Can nonlinear resonance compete with X-ray CT?

So where does this new technology stack up against one of the leading non-destructive testing technologies on the market, X-ray CT scanning? For decades, X-ray CT has been the go-to non-destructive testing solution for metal manufacturers despite some key drawbacks; lengthy test times (hours in most cases), and eye-watering costs to name just two. The radiographic technique uses X-rays to penetrate an object and present reconstructed images of the component under test. Although like most technology these are improving all the time, the resolution of the resulting images is one of the key contributors to the ineffectiveness when testing the more intricate geometries of 3D-printed parts and as a result, it simply cannot detect the same level of tiny flaws that nonlinear resonance can. The complexity of the procedure and associated radiographic safety implications have also been a well-documented consideration for anyone intending to utilise this technology for in-house non-destructive tests. Each test requires the presence of a highly trained operative to perform the procedure safely and interpret the results. In comparison, RD1-TT helps to eliminate these additional costs by offering a standalone unit and simplified test procedure that almost any member of your team could perform once the initial training and setup have been undertaken. 

Of course, your non-destructive testing procedures will ultimately be dictated by the type of data you require, and existing technologies do happen to assume one advantage over nonlinear resonance at present. Unlike x-ray CT scanning or thermography NDT techniques, nonlinear resonance is not intended to provide you with a detailed indication of exactly where the flaw sits within a component; but does that really matter? 

For most manufacturers, simply knowing whether a part is flawed is the only information they need to make an informed decision about the part’s continued existence in their production workflow, but should you categorically need to identify the defect’s location, to assess any underlying issues with the design, RD1-TT, and X-ray CT could in fact form a perfectly harmonious relationship. Identifying flawed components quickly and earlier in the process with RD1-TT means that you are only subjecting flawed parts to additional X-ray CT tests to identify the flaw’s location rather than working with perfectly viable components to identify whether the part is indeed defective. In fact, utilising both techniques as part of your manufacturing process in this way could actually help deliver a return on your investment much quicker.  

Does new mean better?

When it comes to embracing new technology, there is quite often entirely justifiable scepticism when something enters the market claiming to be the ‘next big thing’. Theta Technologies have been well aware of this for some time and have been working closely with customers looking to adopt additive manufacturing processes for a number of years with the goal of offering them a much-needed solution to the quality assurance challenges they face to enable the production of viable and more complex products. Notoriously complex heat exchangers, 3D-printed metal valves and aircraft turbine blades are just some of the components that have been subjected to nonlinear resonance feasibility tests, and the technology has continued to ascertain its ability to deliver reliable non-destructive test results. This has led to increasing intrigue within the additive manufacturing community and has recently peaked the interest of some major organisations, perhaps none more notable than BAE Systems.

In late 2022, Theta Technologies announced a major project collaboration with aerospace and defence giants, BAE Systems and the Additive Manufacturing Research Centre (AMRC) North West. The project has seen RD1-TT put through its paces on-site at the AMRC in Preston, UK, to test a plethora of both metal 3D-printed and composite components for BAE systems. The aerospace and defence manufacturers were seeking a new non-destructive testing solution that would not only allow them to simplify the testing process but help prevent them from working with flawed components over longer periods of time. BAE Systems believe that nonlinear resonance is going to be key to developing rapid, whole-item testing that can support the in-process assessment of parts. The project is a significant step, not only for the continued validation and development of nonlinear resonance NDT technology but for the additive manufacturing industry as a whole. 

Changing the process

So, let’s revisit the scenario you were prompted with at the very start. You’ve embraced 3D printing as your new metal manufacturing process. Those beautifully intricate metal components have been removed from the printers ready to be put through the rigours of post-processing in order to refine them into the finished article. Here is where it all changes… 

You need to establish whether your 3D-printed parts are suitable for their intended purpose. Immediately after the build, you place the part inside RD1-TT to perform a nonlinear resonance non-destructive test. You hit the test button and less than a minute later the RD1-TT display presents the result; the part is flawed. You know this flaw means the part could fail when put to use, and potentially risk compromising your manufacturing reputation with your customers, so you remove it from your production and move on.

If, like so many others have been looking to implement AM into your manufacturing processes but haven’t yet found the confidence to commit to putting it into production due to a lack of suitable non-destructive testing options, your wait could very well be over. Theta Technologies’ revolutionary nonlinear resonance NDT technology is already starting to offer metal additive manufacturers that highly sought-after confidence in the integrity of the parts that they are supplying to their customers. But it doesn’t stop there. RD1-TT, truly promises to be the first non-destructive testing solution that is truly capable of unlocking metal 3D-printings’ overwhelming potential, and ultimately speed up the acceptance of additively manufactured parts to wider industries.

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