Nonlinear Resonance NDT: Unlocking the design potential of metal additive manufacturing

Puntozero is an innovative start-up with the goal of creating specific design methodologies for additive manufacturing (AM). The company seeks to move away from traditional design constraints and fully realise the potential of AM by exploiting the concepts of generative design, topology optimisation, implicit modelling and lattice structures.

Co-founder of Puntozero, Francesco Leonardi states that, “Behind every shape, there is a function, and we often tend to connect them in a reciprocal and direct link, but it is extremely clear in this component how the shapes must evolve according to materials, technologies and printing parameters.”

Puntozero’s recent work with m4p material solutions Gmbh on the production of valves provided an ideal opportunity to put Theta Technologies' nonlinear resonance technology to the test. The metal powder manufacturer prides itself on the development, manufacturing, refining and selling of metal powders for an array of 3D printing processes.

It provides a connection between powder metallurgy and AM with a key focus on customer requirements. The valves, designed by Puntozero that were to be the subject of the non-destructive test were printed using m4p material solutions’ in-house printers and featured multiple complex design features; something that a nonlinear resonance test is unaffected by. 

The selection of the appropriate material for 3D printed parts is a key factor in the overall success of a component. Development Engineer at m4p material solutions, Bastian Kallenbach realises the significance in learning about each part and understanding its intended use in order to select the most appropriate material for the job.

“Due to the specific requirements for fluid-conveying material, the highly corrosion-resistant Superduplex-alloy m4pTM Type10-SDX was selected as a suitable enabler. Its characteristics profile also matches a reasonable level of wear resistance as well as an adaptable process-ability, which makes it possible to control residual stress-prone geometries and thus print them reliably and reproducibly,” said Kallenbach.

A successful test of the 3D printed valves would therefore not only confirm Theta’s credentials in the non-destructive testing of complex 3D printed components, but also validate m4p material solutions’ meticulous attention to detail towards metal powder production.

As part of the process, Theta Technologies was provided with two 3D printed metal valves, both of which had previously been tested using dye penetrant and visual inspection non-destructive testing methods. Both samples were tested using Theta Technologies' RD1-TT; a machine that can not only cope with the complex design geometries associated with 3D printed materials but can also conduct an entire test of a single component in under one minute.

This makes RD1-TT a good fit for rapid triaging or for those looking to utilise AM for mass manufacturing. A nonlinear resonance test is undertaken by exciting a component in order to generate a linear response. If a part is flaw free, there will be no change in the response received by the detector once the excitation of the part is increased. If a part is flawed however, there will be clear signs of nonlinearity when that same signal is increased. After the rapid tests of the valves were performed, it was immediately apparent that one of the parts was flawed due to a significant differentiation in response. Using a nonlinear damage metric, there were clear discriminations between the two components across all six batches of reproducibility testing.

D1-TT is Theta Technologies’ first commercially available non-destructive testing product that is capable of a rapid pass/fail testing process for 3D printed metals, conventional metals and composite parts.

“These latest results are yet more evidence for the effectiveness of our nonlinear resonance NDT technique," Professor James Watts, Chief Technical officer at Theta Technologies commented. "Once again our RD1-TT product has detected flaws that, because of the complex shape of these parts, would be invisible to conventional techniques. It is great to see creative designs like this realised in practice, and our technique should help AM manufacturers deliver the benefits of AM even for demanding applications.”

The overall test process validates what Theta Technologies has long believed - that increasingly complex AM metal parts can now subject to a rapid and more importantly accurate non-destructive test process. When used in a production environment, RD1-TT can be used to test 3D printed metal components immediately after printing. This offers manufacturers an instant understanding of the integrity of a part, which if flawed, can be removed from the workflow prior to adding unnecessary value through additional steps such as post-processing. The design limitations of 3D printed metals that were effectively imposed on designers through a lack of effective non-destructive testing methods with the ability to cope with complex parts look set to become a thing of the past. This will be welcome news for the AM designers and manufacturers who seek to push the boundaries of design and adopt metal 3D printing as a genuine option for mass manufacture.

Key facts about the RD1-TT

• It leverages Theta Technologies unique nonlinear resonance non-destructive testing technique
• The first NDT technology capable of testing AM parts in under one minute.
• RD1-TT can test parts with complex geometries and varying surface finish.
• It allows immediate post-printing inspection allows manufacturing scalability.
• Simple pass/fail test results do not require highly-trained operators.