In my previous article ‘The Status Quo of Additive Manufacturing for Heat Exchangers and Where to next?’ I touched on multiple topics that need to be considered when adopting Additive Manufacturing (AM) to produce high performance heat exchangers across a range of market verticals.

In this article I have decided to slightly expand on what I believe to be the hottest topic at Conflux. This being the challenges and opportunities that are associated with the qualification and certification of AM heat exchangers. There is a hive of great discussions going on in the broader metal AM community on qualification and certification.

Qualification and Certification: Is there a difference?

Qualification is effectively the foundation of certification in my opinion. In the AM world this means that the whole AM process flow including the system/platform, process and material need to be qualified to a certain level to produce certified parts that meet standards, design specifications and end use performance targets.

Heat exchangers have been used in engineering systems since the industrial revolution. This means that there is a high level of confidence associated with the performance and reliability of traditionally manufactured heat exchangers. This is naturally driven from the maturity of the manufacturing processes and supporting data that are available in the public domain. In contrast, AM is less mature and there is a lot more qualification data required to support and speed up the certification process.

At Conflux we work across a range of market verticals, some of which are more heavily regulated than others. However, one thing remains constant across all our applications. This being that a single critical defect/pin hole in a single thin wall gas tight structure can be the difference between success or failure.

Above left: Patented Conflux heat exchanger design
Above right: Typical build that is used for characterising thermo mechanical properties.

Important considerations

The finer details and requirements for part certification are often clear as this is driven by industry specific standards that already exist in many instances. In contrast to this, knowledge is still constantly being developed in relation to the qualification of AM in general. Equipment OEM’s have varying approaches to addressing the surrounding topics and it is not uncommon for end users to develop and implement their own qualification processes and standards. This remains true at Conflux as we are one of few companies that are pioneering in the space of AM heat exchangers.

How do we provide our customers with confidence in AM?

Common questions arise from customers in relation to the qualification of the AM process. Having successfully delivered AM heat exchange solutions across both heavily and less regulated industries, we are now in a position where we have answers (but not all of them of course).

Stability and repeatability

We often get asked is AM a stable and repeatable manufacturing method? Yes, with the right approach remains my answer. At Conflux, we have an experienced manufacturing team led by myself, and I have a fair share of AM ‘war stories’ to tell by my own admission!! Our manufacturing philosophy considers AM in a holistic manner. We leave no stone unturned and have our own proof that it is often the small things that make a huge difference to the outcome. We have developed and implemented carefully considered and robust process controls. This when coupled with a geometry specific approach to manufacturing ensures that we always provide our customers with the best chances of success.

To scan or not to scan

Prior to working at Conflux, if asked is CT scanning important to incorporate into your AM process flow? I would have answered: ‘It is a nice to have, but not essential’. Now my opinion is totally the opposite. CT scanning is an essential validation tool that informs and speeds up our development cycles and provides our customers with early confidence that their parts are free of powder and critical defects. The use of CT scanning as a production tool is still questionable due to associated factors such as speed and cost of capital. However, the benefits that we gain at Conflux from CT scanning far outweigh any negatives. Identifying a critical defect in a complex AM heat exchanger can be likened to trying to find a needle in a haystack!!

Above left: Reconstructed CT data showing the as built surface finish of a small tube.
Above right: CT slice image highlighting a critical defect.

CT scanning also enables us to characterise and investigate phenomena that are related to the as built surface finish of AM heat exchange structures. We use reconstructed tomography data to improve the accuracy of our predicted performance and understand the end use implications.

Test, test and test some more

Simulation in the form of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) is a crucial tool for AM heat exchanger development. However, there is no replacement for testing and the importance of empirical data remains critical for the certification of AM heat exchangers. Our in depth and robust development programmes employ a range of physical tests and generally consist of the following:

1. Pressure and leak testing, where parts are subjected to specified proof pressures.

2. Calorimetric testing, to determine performance characteristics such as heat rejection and pressure drop.

3. Durability testing, pressure pulsation, thermal cycling, shock and vibration are performed to investigate durability and gain more statistical confidence.

Above: Test set up for determining the performance characteristics of a Conflux Oil:Water Heat Exchanger.

Material properties

Our core focus at Conflux is centred around developing AM solutions to the thermal and fluid applications. Therefore, we do not class ourselves as a material development company. However, we do fully understand the importance that material properties have in the qualification process for AM technologies. Given this, we perform characterisation work that underpins our realisation of complex geometries. The results from such work enables us to extract the maximum performance from standard AM alloys, feed values into our FEA and CFD for improved simulated accuracy and provide our customers with confidence with regards to the bulk material properties of our products.

Summary

AM is still a nascent technology for heat exchanger production. It is also clear that qualification and certification are two topics that are critical for increasing the adoption and allowing AM heat exchangers to be more mainstream. At Conflux we are enjoying the challenges that we currently face and are looking forward to working with our customers to open up new applications and fully leverage the benefits of AM for providing risk reduced compelling solutions to highly complex thermal management problems.

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